CA1157612A - Heat shrinkable film and process for preparing the same - Google Patents
Heat shrinkable film and process for preparing the sameInfo
- Publication number
- CA1157612A CA1157612A CA000357481A CA357481A CA1157612A CA 1157612 A CA1157612 A CA 1157612A CA 000357481 A CA000357481 A CA 000357481A CA 357481 A CA357481 A CA 357481A CA 1157612 A CA1157612 A CA 1157612A
- Authority
- CA
- Canada
- Prior art keywords
- film
- temperature
- ethylene polymer
- ethylene
- stretching
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
- B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
- B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
- B29C55/16—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial simultaneously
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C61/00—Shaping by liberation of internal stresses; Making preforms having internal stresses; Apparatus therefor
- B29C61/003—Shaping by liberation of internal stresses; Making preforms having internal stresses; Apparatus therefor characterised by the choice of material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C61/00—Shaping by liberation of internal stresses; Making preforms having internal stresses; Apparatus therefor
- B29C61/06—Making preforms having internal stresses, e.g. plastic memory
- B29C61/08—Making preforms having internal stresses, e.g. plastic memory by stretching tubes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
- B29K2023/04—Polymers of ethylene
- B29K2023/06—PE, i.e. polyethylene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2323/04—Homopolymers or copolymers of ethene
Abstract
ABSTRACT A process for simultaneously, biaxially orienting tubular ethylene polymer film by expansion and extension of the tube under particular conditions for heating the expanding tube, to give a heat shrinkable film. The heat shrinkable film has excellent heat shrinkability, shrinkage stress, transparency, heat sealability and impact resistance, and is very suited for use in shrink packaging.
Description
BACKGR~UND OF THE INVENTION
-The present invention relates to a heat shrinXable film prepared by a tubular process from an ethylene polymer and a process for preparing the same.
Hitherto~ a polyviIIyl chloride film, a polypropylene film and a polyethylene film are known as heat shrinkable films.
A heat shrinkable poly~inyl chloride film has an excellent characteristic such that it shows a good shrinkability at a relatively low temperature, e.g. in the vicinity of 100C,, but has the disadvantages that an additive such as a plasticizer or a heat stabilizer added to the resin may cause a hygienic problem and also that the film generates hydrogen chloride upon the lS destruction treatment by fire of the used film.
A heat shrinkable polyp~opylene film has a good heat shrinkability because of being subjected to biaxial stretching, but has the disadvantages that it reveals only at a relatively high temperature of 100 to 140C. and also that the heat seal strength is not so large.
On the other hand, a heat shrinkable film made of ethylene polymers such as a polyethylene shrinkable ;
film has been widely employed in shrink packaging, since it is inexpensi~e and has a large heat seal strength.
The heat shrinkable polyethylene film has been prepared by a so-called inflation process which is one of tubular processes and in which a molten tube extruded from a die is blown-up as it is by the pressure of an internal gas.
In such a conventional process, an effective molecular orientation does not take place and, therefore, a known heat shrinkable film of ethylene polymers has not always satisfactory characteristics. For instance, the film strength is small and the elongation is large. Also, the film shows a high heat shrinkage percent at a temperature near the melting point of the polymer, but the heat shrinkable temperature range is narrow, and also the close adhesion of the film to articles to be wrapped is no~ sufficlent due to small shrinkage stress.
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Although it is theoretically clear that the mechanical properties of the ilm are improved by stretching the film, it has been considered to be difficult to highly stretch a film of ethylene polymers by conventional processes so as to impart the heat shrinkability to the film.
In order to eliminate the disadvantages of heat shrinkable polyethylene films, there are proposed a process as disclosed in Japanese Patent Publication Nos.
18893/1962 and 9086/1964 in which a polyethylene film is irradiated with ionizing radiation so as to cause intermol0cular crosslinklng and then stretched with heat, and a process as disclosed in Japanese Patent Publication No. 20432/1973 in which a resin irradiated with radiation or a mixture of resins containing the irradiated resin is subjected to the formation of film followed by stretching. However, these processes have the disadvantages that the radiation treatment increases the cost, and that the heat sealability of the film is bad, and that it is impossible to recover the waste film. Also, a low density polyethylene shrinkable film is poor in transparency, Accordingly, it is an object of the present invention to provide a heat shrinkable film of ethylene polymers which can reveal an excellent heat shrinkability and a large shrinkage stress.
A further object of the i~vention is to provide a heat shrinkable film suited for use in shrink wrapping, which can closely adhere to articles to be wrapped and which has excellent transparency, heat sealability and impact resistance.
Another object of the invention is to provide a process for preparing a heat shrinkable ethylene polymer film havlng excellent heat shrinkability and shrinkage 35 stress by means of blaxial stretching. ;
These and other ojbects of the present invention will become apparent from the description hereinafter, .. . . ........... .
..
-. -.
~ L5761Z
BRIEF DESC~IPTION OF THE DRAWINGS
Figs. 1 and 2 are illustrative section views showing an embodiment of practicing the process of the present invention SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a process for preparing a heat shrinkable ethylene polymer fllm which comprises the steps of ~1) introducing a non-stretched tubular film of an ethylene polymer having a density of 0.91 to 0.93 g.tcm3 at 25C. into a tubular biaxial stretching apparatus, a film obtained by melt-extruding said ethylene polymer and cooling the extrudate to solidify without stretching it showing a tensile strength at 300 % elongation of not less than 15 kg./cm.2 at a temperature ~.
of 15C. below the melting point of said ethylene polymer,
-The present invention relates to a heat shrinXable film prepared by a tubular process from an ethylene polymer and a process for preparing the same.
Hitherto~ a polyviIIyl chloride film, a polypropylene film and a polyethylene film are known as heat shrinkable films.
A heat shrinkable poly~inyl chloride film has an excellent characteristic such that it shows a good shrinkability at a relatively low temperature, e.g. in the vicinity of 100C,, but has the disadvantages that an additive such as a plasticizer or a heat stabilizer added to the resin may cause a hygienic problem and also that the film generates hydrogen chloride upon the lS destruction treatment by fire of the used film.
A heat shrinkable polyp~opylene film has a good heat shrinkability because of being subjected to biaxial stretching, but has the disadvantages that it reveals only at a relatively high temperature of 100 to 140C. and also that the heat seal strength is not so large.
On the other hand, a heat shrinkable film made of ethylene polymers such as a polyethylene shrinkable ;
film has been widely employed in shrink packaging, since it is inexpensi~e and has a large heat seal strength.
The heat shrinkable polyethylene film has been prepared by a so-called inflation process which is one of tubular processes and in which a molten tube extruded from a die is blown-up as it is by the pressure of an internal gas.
In such a conventional process, an effective molecular orientation does not take place and, therefore, a known heat shrinkable film of ethylene polymers has not always satisfactory characteristics. For instance, the film strength is small and the elongation is large. Also, the film shows a high heat shrinkage percent at a temperature near the melting point of the polymer, but the heat shrinkable temperature range is narrow, and also the close adhesion of the film to articles to be wrapped is no~ sufficlent due to small shrinkage stress.
.
.. - ., .
:
11576iZ
Although it is theoretically clear that the mechanical properties of the ilm are improved by stretching the film, it has been considered to be difficult to highly stretch a film of ethylene polymers by conventional processes so as to impart the heat shrinkability to the film.
In order to eliminate the disadvantages of heat shrinkable polyethylene films, there are proposed a process as disclosed in Japanese Patent Publication Nos.
18893/1962 and 9086/1964 in which a polyethylene film is irradiated with ionizing radiation so as to cause intermol0cular crosslinklng and then stretched with heat, and a process as disclosed in Japanese Patent Publication No. 20432/1973 in which a resin irradiated with radiation or a mixture of resins containing the irradiated resin is subjected to the formation of film followed by stretching. However, these processes have the disadvantages that the radiation treatment increases the cost, and that the heat sealability of the film is bad, and that it is impossible to recover the waste film. Also, a low density polyethylene shrinkable film is poor in transparency, Accordingly, it is an object of the present invention to provide a heat shrinkable film of ethylene polymers which can reveal an excellent heat shrinkability and a large shrinkage stress.
A further object of the i~vention is to provide a heat shrinkable film suited for use in shrink wrapping, which can closely adhere to articles to be wrapped and which has excellent transparency, heat sealability and impact resistance.
Another object of the invention is to provide a process for preparing a heat shrinkable ethylene polymer film havlng excellent heat shrinkability and shrinkage 35 stress by means of blaxial stretching. ;
These and other ojbects of the present invention will become apparent from the description hereinafter, .. . . ........... .
..
-. -.
~ L5761Z
BRIEF DESC~IPTION OF THE DRAWINGS
Figs. 1 and 2 are illustrative section views showing an embodiment of practicing the process of the present invention SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a process for preparing a heat shrinkable ethylene polymer fllm which comprises the steps of ~1) introducing a non-stretched tubular film of an ethylene polymer having a density of 0.91 to 0.93 g.tcm3 at 25C. into a tubular biaxial stretching apparatus, a film obtained by melt-extruding said ethylene polymer and cooling the extrudate to solidify without stretching it showing a tensile strength at 300 % elongation of not less than 15 kg./cm.2 at a temperature ~.
of 15C. below the melting point of said ethylene polymer,
(2) biaxially stretching said non-stretched :
tubular film to give a biaxially oriented film by means of an internal gas pressure at a temperature within the orientable temperature range under the following conditions:
(a) the surface temperature of the film at a starting point of expansion being within the range of 15 to 25C. below the melting point of the polymer, (b) the film in a stretching zone extending from the starting point to a finishing point of expansion having a temperature gradient such that the surface temperature of the film at a position of 1/4 to 1~3 the length of the stretching zone from the starting point is maximum, and the difference between the maximum surface temperature and the surface temperatu~e of the film at the starting point being nat more than 5C., (c) the temperature drop of the film from the maxlmum temperature position ~o the finishing point being within the range of 15 to 20C , and (d) the film being cooled while traveling from the finishing point to a distance of 1.0 to 1.5 times . .
- : :
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~57612 the vertical distance of the s~retching zone so that the surface temperature of the film drops by 30 to 40C,, and
tubular film to give a biaxially oriented film by means of an internal gas pressure at a temperature within the orientable temperature range under the following conditions:
(a) the surface temperature of the film at a starting point of expansion being within the range of 15 to 25C. below the melting point of the polymer, (b) the film in a stretching zone extending from the starting point to a finishing point of expansion having a temperature gradient such that the surface temperature of the film at a position of 1/4 to 1~3 the length of the stretching zone from the starting point is maximum, and the difference between the maximum surface temperature and the surface temperatu~e of the film at the starting point being nat more than 5C., (c) the temperature drop of the film from the maxlmum temperature position ~o the finishing point being within the range of 15 to 20C , and (d) the film being cooled while traveling from the finishing point to a distance of 1.0 to 1.5 times . .
- : :
-. . : .
, , .
-. , ; ~........ - . .
~57612 the vertical distance of the s~retching zone so that the surface temperature of the film drops by 30 to 40C,, and
(3) recovering the resulting biaxially oriented film, The biax~ally oriented ethylene polymer film so obtained has an excellent heat shrinkability and a large shrinkage stress, and is very suitable for use in shrink wrapping, Thus, the present invention also provide a heat shrinkable ethylene polymer film having a heat shrinkage percent of not less than 25 % and a heat shrinkage stress of not less than 12 kg,/cm2, respectively at a temperature of 15C. below the melting point of the ethylene polymer, DETAILED DESCRIPTION
A polyethylene film is essentially superior in characteristics such as heat sealability and impact j~ -resistance to a polypropylene film and a polyvinyl chloride film. Particularly, the strength of a heat sealed portion of the polyethylene film after wrapping is large, and this is very useful for shrink packaging of heavy articles, It is very significant that the defect of a conventional heat shrinkable polyethylene film, i,e, poor heat shrinkability, has been improved by the invention without losing the above advantageous characteristics. The heat shrinkable ethylene polymer film of the invention has also the feature that the transparency is superior to that of a conventional polyethylene film, An ethylene polymer employed in the present invention as a raw material o non-stretched tubular film is a low density polymer having a density of 0,91 to 0.93 g.lcm3 at 25C, The ethylene polymer is selected from homopolymers of ethylene ~the ethylene homopolymer being hereinafter referred ~o as "polyethylene") such as low density polyethylene and linear low density polyethylene and copolymers of ethylene as a main component ,, . .
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and an a-olefinically unsaturated monomer. In case of the copolymers, there are preferred copolymers containing not more than 25 % by weight of an a-olefin having 3 to 12 carbon atoms, particularly not more than 15 % by weight of an ~-olefin having 4 to 6 carbon atoms. The reason that these copolymers are preferred is that the copolymers provide a non-stretched film which is more suited for use in the process of the present invention as compared with polyethylene and also provide a stretched film excellent particularly in impact strength, impact strength of beads sealed portion, bar heat seal strength and impact strength of bar heat sealed portion. It is essential that a non-stretched tubular film obtained by melt-extruding an ethylene polymer and cooling the extrudate to solidify it without stretching, that is, a film obtained by melt-blending an ethylene polymer at a temperature of 200 to ~50C., extruding downward the molten mass through a circular die having a slit of 75 mm. in diameter maintained at 250C. and cooling the outside of the tube with water to give a tubular film of 66 mm. in diameter and 190 ~m.
in thickness, shows a tensile strength at 300 % elongation of not less than 15 kg./cm2 at a temperature of 15C.
below the melting point of the ethylene polymer. Any ethylene polymers having the above characteristics are usable as a raw material of the non-stretched tubular film to be oriented biaxially according to the process of the present invention.
One of the reasons that biaxial stretching of polyethylene has been considered to be difficult is generally that the tensile strength of the film in the stretching zone is weak and the stable stretching cannot be made. The present inventors have overcome difficulties involved in conventional processes and succeeded in conducting the stable stretching by combination of use of the above-mentioned particular ethylene polymer as a raw material with particular stretching conditions mentioned below. When polymers other than the above-mentioned partlcular ethylene polymers are employed as , ~
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raw materials, stable stretching is impossible even by conducting according to the process of the present invention and no desired heat shrinkable film is obtained.
According to the process of the presen~
invention, ethylene polymer films showing a high shrinkage percent and a large shrinkage stress at a relati~ely low temperarure can be prepared by simultaneous expansion and extension of a tube in the orientation temperature range capable o~ cau~lng an effective high orientation of the film by means of a tubular process so as to simultaneousl~, biaxially orient the film.
Non-stretched tubular ethylene polymer films prepared by melt-extruding in tubular form and cooling the tubular film to solidify it according to known processes are employed as starting ethylene polymer films in the present invention. (I`
The orientable temperature range of the , ethylene polymer changes depending on its melting point.
Therefore, effective orientation and progress of uniform ¦
and stable stretching cannot be desired, if the temperature of the film at a starting point of expansion and the temperature gradient of the film in a stretching zone are not exactly set upon expansion and extension of the tube.
In the process of the invention, it is the most preferable that the film temperature at the starting point of expansion falls within the range of 15 to l 25C. below the melting point of the ethylene polymer. , When the film temperature at the starting point is higher than the above range, the strength of the film in the neighborhood of the starting point of expansion is weak, and not only the bubble becomes eas~ to rupture at that portion, but also it brings about lowering of the internal p~essure of the bubble and in its turn lowering of the stretching tension, and as a result, the effects produced by stretching and the strength and shrinkage percent of ¦
the stretched film are decreased. On the other hand, when the film temperature at the starting point of li ' - ' '' '' ' ; '''. ' ' ~ , , - ~ , ~` :,. , '' ~ 15761Z
expansion is lower than the above range, the internal pressure of the bubble and in its turn the stretching tenslon become too large, and there is increased the frequency of the break of the film, i e. the puncture of the bubble. Even if the film is not broken, it becomes in the state of the so-called neck stretching and the surface of the film roughens, resulting in the increase of unevenness in fllm thickness and the decrease of the transparency.
The present inventors have also found that it is optimum to carry out the expansion and extension of the tubular film with a temperature gradient such that the film in a stretching zone extending from the starting point of expansion to a fi~ishing point of expansion reaches the maximum temperature at the position of 1/4 to 1/3 the length of the stretching zone from the starting point, the difference between the maximum temperature and the temperature of the film at the starting point is not more than 5C., and the tempelature drop of the film from the maximum temperature position to the finishing point is in the range of 15 to 20C. Thus, in the present invention a strict temperature control of the film is necessary. The temperature gradient in the stretching zone has a great influence on the stretching stability and the physical properties of the stretched film.
When the temperature gadient during tra~elling of the film from the starting point of expansion to the position of lt4 to 1/3 the length of the stretching zone is a downward gradient, the stability of the expanding bubble is increased, but well-balanced stretching in the machine and trans~erse directions cannot be conducted.
This not only results in unevenness in thickness, but also is eas~ to cause a great unbalance in shrinkability of the stretched film, and also the transparency is lowered.
Also, when the temperature gradient during this period is more than 5C., the temperature of the ..
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g film approaches to the melting point of ethylene polymer, and as a result, the tensile strength and elongation of the film become small and the transverse sway of the bubble and in its turn rupture of the bubble are increased.
The bubble can be prevented from becoming unstable by suddenly dropping the temperature of the film by 15 to 20C. below the maximum temperature while the film travels from the maximum temperature position to the finishing point of expansion. The lack of the temperature drop during this period causes not only instabillty and frequent rupture of the bubble and unevenness in film thickness, but also lowering of the heat shrinkability and shrinkage stress of the stretched film. On the other hand, when the temperature drop is lS more than the above range, the internal pressure of the bubble abnormally increases and the stability in the neighborhood of the strating point of expansion is broken, so the upper portion of the bubble sways and the rupture of the bubble increases in the upper portion.
It has also been found that the stretching can be the most stably conducted when the temperature gradient of the film is further maintained so that while the film travels from the finishing point of expansion to a distance of 1.0 to 1.5 times the vertical distance of the stretching zone, the temperature of the film drops within 30 to 40C. of the temperature of the finishing point of expansion at which the film reaches its maximum diameter, in addition to the above-mentioned temperature gradient of the film in the stretching zone. The temperature gradient during this period is also important for the stability of stretching as well as the temperature gradient in the stretching zone. When the temperature drop is insufficient, the sway of the whole bubble occurs and the unevenness in thickness of the stretched ¦
film becomes large, and in extreme case, the rupture of the bubble may take place. Also, when the temperature drop is too steep, the stabillty in the neighborhood of the starting point of expansion becomes poor and the .; . . ............ . . . .
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~L157612 upper portion of the bubble transversely sways.
By maintaining strictly the temperature gradient as mentioned above, it has now become possible to conduct stable stretching of ethylene polymers which has not been able to be attained by conventional processes, and also the obtained film has a good transparency and uniform thickness The biaxially stretched film drwan out of a stretching apparatus may be annealed, as occasion demands.
A proper annealing temperature is from 55 to 85C.
- - It is not necessary to stretch the film in the same ratio in both the machine and transverse directions.
However, in order to obtain the film having good physical properties, it is desirable to stretch the film in a stretching ratio of at least 2.5 in each of the machine and transverse directions.
The heat shrinkable film of the present invention has improved heat shrinkability and heat shrinkage stress as compared with blown films of a polymer of the same kind. Conventional heat shrinkable films of ethylene polymers require a particular heating condition in heat shrinking, since they must be heated to near the melting point. However, the heat shrinkable film of the invention can be very easily applied to shrink wrapping by employing a generally used oven for heat shrinkable polypropylene film such as a tunnel oven. Also, the film of the invention is usable at wrapping temperatures of wide range because of having a high heat shrinkage percent at relatively low temperatures, and accordingly is of very wide application.
The heat shrinkable film of the invention also has an improved transparency. While the haze of conventional shrinkable films of low density polyethylene are more than 10 %, the ha7e of the film of the invention is less than about 8 % and in a preferable embodiment is at most about 5 %. The breaking strength of the film of the invention is improved to more than 2 times that of conventional shrinkable films, and also the film of the invention has improved impact strength, heat seal strength .
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1157612 1.
and impact strength of sealed portion. Therefore, half thickness is sufficient as compared with conventional ~
shrinkable films in case of using with the same object, and ;
accordingly the present invention has a large effect on saving resources. Also, the resistance to film breaking by an external force after wrapping can be remarkably increased.
The heat shrinkable film of the present invention is suitably employed for shrink packaging, and is 10 particularly suita~le for assembly packaging of angular, !
heavy or beautiful articles such as bottle, can, welding rod, sash, tool, parts, toy, stationery, book, magazine, drapery and plywood~
The present invention is more specifically lS described and explained by means of the following Examples, in which data are those measured according to the following methods.
1. Heat shrinkage percent A film having a size of 10 cm. X 10 cm. is 20 immersed in glycerin at a prescribed temperature for 10 l seconds, the length (A cm.) of a side is measured after 1 immersion and the heat shrinkage percent is calculated l according to the following equation. I
Heat shrinkage percent = 10 A X 100 i 2. Heat shrinkage stress ~
The shrinkage stress is measured accodring to ¦1 ASTM 2838-6~ ¦
3~ Tensile strength at 300 % elongation ¦i 3Q By employing Tensilon tensile strength tester equipped with an oven made by Toyo-Baldwin Co., a film sample is placed in the oven for five minutes and is then elongated at a rate of 300 mm./min., and the tensile strength is measurcd when the elongation reaches 300 %.
A polyethylene film is essentially superior in characteristics such as heat sealability and impact j~ -resistance to a polypropylene film and a polyvinyl chloride film. Particularly, the strength of a heat sealed portion of the polyethylene film after wrapping is large, and this is very useful for shrink packaging of heavy articles, It is very significant that the defect of a conventional heat shrinkable polyethylene film, i,e, poor heat shrinkability, has been improved by the invention without losing the above advantageous characteristics. The heat shrinkable ethylene polymer film of the invention has also the feature that the transparency is superior to that of a conventional polyethylene film, An ethylene polymer employed in the present invention as a raw material o non-stretched tubular film is a low density polymer having a density of 0,91 to 0.93 g.lcm3 at 25C, The ethylene polymer is selected from homopolymers of ethylene ~the ethylene homopolymer being hereinafter referred ~o as "polyethylene") such as low density polyethylene and linear low density polyethylene and copolymers of ethylene as a main component ,, . .
~, .
- ;.
I
~lLS761Z
and an a-olefinically unsaturated monomer. In case of the copolymers, there are preferred copolymers containing not more than 25 % by weight of an a-olefin having 3 to 12 carbon atoms, particularly not more than 15 % by weight of an ~-olefin having 4 to 6 carbon atoms. The reason that these copolymers are preferred is that the copolymers provide a non-stretched film which is more suited for use in the process of the present invention as compared with polyethylene and also provide a stretched film excellent particularly in impact strength, impact strength of beads sealed portion, bar heat seal strength and impact strength of bar heat sealed portion. It is essential that a non-stretched tubular film obtained by melt-extruding an ethylene polymer and cooling the extrudate to solidify it without stretching, that is, a film obtained by melt-blending an ethylene polymer at a temperature of 200 to ~50C., extruding downward the molten mass through a circular die having a slit of 75 mm. in diameter maintained at 250C. and cooling the outside of the tube with water to give a tubular film of 66 mm. in diameter and 190 ~m.
in thickness, shows a tensile strength at 300 % elongation of not less than 15 kg./cm2 at a temperature of 15C.
below the melting point of the ethylene polymer. Any ethylene polymers having the above characteristics are usable as a raw material of the non-stretched tubular film to be oriented biaxially according to the process of the present invention.
One of the reasons that biaxial stretching of polyethylene has been considered to be difficult is generally that the tensile strength of the film in the stretching zone is weak and the stable stretching cannot be made. The present inventors have overcome difficulties involved in conventional processes and succeeded in conducting the stable stretching by combination of use of the above-mentioned particular ethylene polymer as a raw material with particular stretching conditions mentioned below. When polymers other than the above-mentioned partlcular ethylene polymers are employed as , ~
;. . .
, ~, :
:, ~ 15761Z
raw materials, stable stretching is impossible even by conducting according to the process of the present invention and no desired heat shrinkable film is obtained.
According to the process of the presen~
invention, ethylene polymer films showing a high shrinkage percent and a large shrinkage stress at a relati~ely low temperarure can be prepared by simultaneous expansion and extension of a tube in the orientation temperature range capable o~ cau~lng an effective high orientation of the film by means of a tubular process so as to simultaneousl~, biaxially orient the film.
Non-stretched tubular ethylene polymer films prepared by melt-extruding in tubular form and cooling the tubular film to solidify it according to known processes are employed as starting ethylene polymer films in the present invention. (I`
The orientable temperature range of the , ethylene polymer changes depending on its melting point.
Therefore, effective orientation and progress of uniform ¦
and stable stretching cannot be desired, if the temperature of the film at a starting point of expansion and the temperature gradient of the film in a stretching zone are not exactly set upon expansion and extension of the tube.
In the process of the invention, it is the most preferable that the film temperature at the starting point of expansion falls within the range of 15 to l 25C. below the melting point of the ethylene polymer. , When the film temperature at the starting point is higher than the above range, the strength of the film in the neighborhood of the starting point of expansion is weak, and not only the bubble becomes eas~ to rupture at that portion, but also it brings about lowering of the internal p~essure of the bubble and in its turn lowering of the stretching tension, and as a result, the effects produced by stretching and the strength and shrinkage percent of ¦
the stretched film are decreased. On the other hand, when the film temperature at the starting point of li ' - ' '' '' ' ; '''. ' ' ~ , , - ~ , ~` :,. , '' ~ 15761Z
expansion is lower than the above range, the internal pressure of the bubble and in its turn the stretching tenslon become too large, and there is increased the frequency of the break of the film, i e. the puncture of the bubble. Even if the film is not broken, it becomes in the state of the so-called neck stretching and the surface of the film roughens, resulting in the increase of unevenness in fllm thickness and the decrease of the transparency.
The present inventors have also found that it is optimum to carry out the expansion and extension of the tubular film with a temperature gradient such that the film in a stretching zone extending from the starting point of expansion to a fi~ishing point of expansion reaches the maximum temperature at the position of 1/4 to 1/3 the length of the stretching zone from the starting point, the difference between the maximum temperature and the temperature of the film at the starting point is not more than 5C., and the tempelature drop of the film from the maximum temperature position to the finishing point is in the range of 15 to 20C. Thus, in the present invention a strict temperature control of the film is necessary. The temperature gradient in the stretching zone has a great influence on the stretching stability and the physical properties of the stretched film.
When the temperature gadient during tra~elling of the film from the starting point of expansion to the position of lt4 to 1/3 the length of the stretching zone is a downward gradient, the stability of the expanding bubble is increased, but well-balanced stretching in the machine and trans~erse directions cannot be conducted.
This not only results in unevenness in thickness, but also is eas~ to cause a great unbalance in shrinkability of the stretched film, and also the transparency is lowered.
Also, when the temperature gradient during this period is more than 5C., the temperature of the ..
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g film approaches to the melting point of ethylene polymer, and as a result, the tensile strength and elongation of the film become small and the transverse sway of the bubble and in its turn rupture of the bubble are increased.
The bubble can be prevented from becoming unstable by suddenly dropping the temperature of the film by 15 to 20C. below the maximum temperature while the film travels from the maximum temperature position to the finishing point of expansion. The lack of the temperature drop during this period causes not only instabillty and frequent rupture of the bubble and unevenness in film thickness, but also lowering of the heat shrinkability and shrinkage stress of the stretched film. On the other hand, when the temperature drop is lS more than the above range, the internal pressure of the bubble abnormally increases and the stability in the neighborhood of the strating point of expansion is broken, so the upper portion of the bubble sways and the rupture of the bubble increases in the upper portion.
It has also been found that the stretching can be the most stably conducted when the temperature gradient of the film is further maintained so that while the film travels from the finishing point of expansion to a distance of 1.0 to 1.5 times the vertical distance of the stretching zone, the temperature of the film drops within 30 to 40C. of the temperature of the finishing point of expansion at which the film reaches its maximum diameter, in addition to the above-mentioned temperature gradient of the film in the stretching zone. The temperature gradient during this period is also important for the stability of stretching as well as the temperature gradient in the stretching zone. When the temperature drop is insufficient, the sway of the whole bubble occurs and the unevenness in thickness of the stretched ¦
film becomes large, and in extreme case, the rupture of the bubble may take place. Also, when the temperature drop is too steep, the stabillty in the neighborhood of the starting point of expansion becomes poor and the .; . . ............ . . . .
. , .
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~L157612 upper portion of the bubble transversely sways.
By maintaining strictly the temperature gradient as mentioned above, it has now become possible to conduct stable stretching of ethylene polymers which has not been able to be attained by conventional processes, and also the obtained film has a good transparency and uniform thickness The biaxially stretched film drwan out of a stretching apparatus may be annealed, as occasion demands.
A proper annealing temperature is from 55 to 85C.
- - It is not necessary to stretch the film in the same ratio in both the machine and transverse directions.
However, in order to obtain the film having good physical properties, it is desirable to stretch the film in a stretching ratio of at least 2.5 in each of the machine and transverse directions.
The heat shrinkable film of the present invention has improved heat shrinkability and heat shrinkage stress as compared with blown films of a polymer of the same kind. Conventional heat shrinkable films of ethylene polymers require a particular heating condition in heat shrinking, since they must be heated to near the melting point. However, the heat shrinkable film of the invention can be very easily applied to shrink wrapping by employing a generally used oven for heat shrinkable polypropylene film such as a tunnel oven. Also, the film of the invention is usable at wrapping temperatures of wide range because of having a high heat shrinkage percent at relatively low temperatures, and accordingly is of very wide application.
The heat shrinkable film of the invention also has an improved transparency. While the haze of conventional shrinkable films of low density polyethylene are more than 10 %, the ha7e of the film of the invention is less than about 8 % and in a preferable embodiment is at most about 5 %. The breaking strength of the film of the invention is improved to more than 2 times that of conventional shrinkable films, and also the film of the invention has improved impact strength, heat seal strength .
- , , . .:
.
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1157612 1.
and impact strength of sealed portion. Therefore, half thickness is sufficient as compared with conventional ~
shrinkable films in case of using with the same object, and ;
accordingly the present invention has a large effect on saving resources. Also, the resistance to film breaking by an external force after wrapping can be remarkably increased.
The heat shrinkable film of the present invention is suitably employed for shrink packaging, and is 10 particularly suita~le for assembly packaging of angular, !
heavy or beautiful articles such as bottle, can, welding rod, sash, tool, parts, toy, stationery, book, magazine, drapery and plywood~
The present invention is more specifically lS described and explained by means of the following Examples, in which data are those measured according to the following methods.
1. Heat shrinkage percent A film having a size of 10 cm. X 10 cm. is 20 immersed in glycerin at a prescribed temperature for 10 l seconds, the length (A cm.) of a side is measured after 1 immersion and the heat shrinkage percent is calculated l according to the following equation. I
Heat shrinkage percent = 10 A X 100 i 2. Heat shrinkage stress ~
The shrinkage stress is measured accodring to ¦1 ASTM 2838-6~ ¦
3~ Tensile strength at 300 % elongation ¦i 3Q By employing Tensilon tensile strength tester equipped with an oven made by Toyo-Baldwin Co., a film sample is placed in the oven for five minutes and is then elongated at a rate of 300 mm./min., and the tensile strength is measurcd when the elongation reaches 300 %.
4. Melting point By employing a micro melting point apparatus ¦
(No. 2544 type made by ShLmadzu Corporation), a film I
sample ha~;ng z sizc of 2 mm. X 2 mm. and a thickness of .. , , .. . ~
~, . ' !
'. ' .
' ' " ' -~ ' ' . ' ' ' ' ' . . : ' . : ' ' ~
, . , ' ' . ~
- 12 - ~ 7 ~ l 2 about 0.2 mm. is heated at a rate of 2C./min. and the melting point is measured by determining a point at which the transparency of the sample changes suddenly.
(No. 2544 type made by ShLmadzu Corporation), a film I
sample ha~;ng z sizc of 2 mm. X 2 mm. and a thickness of .. , , .. . ~
~, . ' !
'. ' .
' ' " ' -~ ' ' . ' ' ' ' ' . . : ' . : ' ' ~
, . , ' ' . ~
- 12 - ~ 7 ~ l 2 about 0.2 mm. is heated at a rate of 2C./min. and the melting point is measured by determining a point at which the transparency of the sample changes suddenly.
5 Surface temperature of film S By employing a surface thermometer to which a chromel-constantan thermocouple (4.5 ohms) having a diameter of about 1 mm. and a length of exposed portion of aboùt 15 mm. is attached, the nose of the thermocouple is contacted with the surface of a film, and the value after 30 seconds is regasded as the surface temperature.
In case that the radiant heat of a heat source is strong, one side of the thermocouple which does not contact with the film is covered with an aluminum foil to prevent its influence.
EXample 1 A low density polyethylene having a melting point of 111.5C. and a density at 25C. of-0.920 g./cm3 (commercial name "UBE Polyethylene HF 019" made by Ube Industries Ltd.) was melt-blended at a temperature of 200 to 250C. and extruded downward through a circular die maintained at 250C. The diameter of a slit of the circular die was 75 mm. and the slit gap was 0.8 mm. The extruded molten tubular film was cooled to room temperature by slidingly contacting the inside surface of the film with the outside surface of a cylindr-ical mandrel haYing an outer diameter of 66 mm. in which a cooling water of 20C.
was circulated and which was positioned just below the die, while passing the outside surface of the film through a water bath. The thus formed tu~ular non-stretched film had a diameter of about 66 mm. and a thickness of 190 ~m. The tensile strength at 3Q~ ~ elongation at 96 5C. (i.e. at a temperature of 15C. below the melting point of the polyethylene~ of the non-stretched film was 21 kg./cm2 As shown in Fig. 1, the non-stretched film so obtained was employed as a starting material 1, and was led to a biaxIal stretching apparatus A to conduct expansion and extension.
* Trade Mark .
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I''' The temperature of the film at an outlet of a preheater 4 was maintained at 65C. by adjusting the ~oltage and current of a circular infrared heater of the preheater.
S Eight circular infrared heaters of a main heater S were fallen into four divisions, and the voltage and current of each diYision were adjusted. The film was biaxially stretched 3 times in both the machine and transverse directions by the air pressure of a pressurized air admitted into the tuhular film between low-speed nip rolls 2 and high-speed nip-rolls 3 and the relative peripheral speeds of the low-speed and high-speed nip rolls 2 and 3 in an air stream flowing along the tube from a cooling air ring 6 positioned below the main heater 5.
By the adjustment of thé voltage and current of the di~ided circular infrared heaters of the main heater 5 and t~e adjust~ent of the flo~ rate and temperature of the air stream, the temperature of the film at each of positions as shown in Fig 2 was maintained so that the temperature at a starting point of expansion 101 was 88C., I
the temperature at a position 102 of about 1/3~5 the ?
vertical distance L of a streching zone C from the starting point lal was 90C. which was maximum temperature, the temperature at a finishing point of expansion 103 was 75C. ~ ;
and the temperature at a position 104 located at a distance of 1.2 times the vertical distance L of the stretching zone from the finishing point 103 was 4~C. The vertical distance L of the stretching zone C extending from the i starti~g point 101 to the finishing point 103 was about 210 mm., and the dia~eter of the bubble at the finishing point was 195 mm.
The thus stretched tubular film was then collapsed through collapser rolls 7 and the nip rolls 3 and drawn out of the stretching apparatus, and was then introduced into an annealing apparatus B through nip rolls 8. The flattend film was inflated again with air to the original tube state along rolls 9, and was annealed foT 10 seconds by blowing a hot air of 75C~ to the tube from slits 1 1 , , ,j .
.
.... ..
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, ., ~, , , ,.,," .. . , j~ . . ... .
- 14 ~ lZ
11 of a heating cylinder 10 and was cooled to room temperature by a cooling cylinder 12. The cooled tube was collapsed again through collapser rolls 13, drawn out of nip rolls 14 and wound up. During the above contir,uous operation, the bubble scarcely swayed and was stable without rupture of the bubble.
The obtained film had a thickness of 21 ~m., thrinkage percents at 96.5C. of 26 ~ in the machine direction and 28 % in the transverse direction, and shrinkage stresses at 96.5C. of 15 kg./cm2 in the machine direction and 15 kg.~cm2 in the transverse direction.
Fifty polystyrene vessels having a height of 75 mm. and a maximum diameter of 40 mm. charged with a lactic acid beverage were arranged in ten rows and pre-wrapped in a lot with the film, and passed for 8 seconds through a commercially available tunnel oven with blowing a hot air of 105C. The film adhered closely to the vesels without wrinkle despite of uneven shape, and showed a good transparency such that the prints and content of the vessels were clearly visible through the film. Also, the wrapping film was not torn from the sealed and other portions, even if one end of the film was grabbed up, and showed a sufficient strength for practical use.
Example 2 A non-stretched tubular film having a diameter of 66 mm and a thickness of 190 ~m. was prepared from a -low density ethylene polymer having a melting point of 124C. and a density at 25C. of 0.923 g./cm3 (commercial name "Ultzex 2020L" made by Mitsui Petrochemical Industries, Ltd ) in the same manner as in Example 1 except that the inside of the extruded tubular film was cooled with air and the outside was cooled with water. The tensile strength at - 300 ~ elongation at la9C. of the non-stretched film was 16 kg./cm2 The non-stretched film was biaxially stretched in the same manner as in Example 1 except that the temperature of the film at the outlet of the preheater 4 was 70C., ,~ * Trade Mark - .' .
, 15 ~157612 the temperature at the starting point 101 was 100C., the temperature at a distance 102 of 1/4 the length L of the stretchin~ zcne from the starting point 1~1 was 132C.
(maximum temperature), the temperature at the finishing S point 103 was 87C., and the temperature at a distance 104 of 1.3 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 210 mm., and the maximum diameter of the bubble at the finishing point of expansion was 185 mm.
The operation was continued for 5 hours, but there was little sway of the bubble during the operation.
The bubble was stable and did not rupture.
The stretched film was then annealed for 10 seconds by blowing a hot air of 70C. in the same manner as in Example 1. The stretched film so obtained had a thickness of 21 ~m~, shrinkage percents at 109C. of S0 % in the machine direction and 45 ~ in the transverse direction, and shrinkage stresses at 1~9C. of 22 kg.lcm2 in the machine direction and 2Q kg./cm2 in the transverse direction.
Five pieces of a round iron bar having a diameter of 12 mm. and a length of 20 cm. (total weight:
about 1 kg~) were arranged in a row and pre-wrapped with;
the stretched film, and passed for about 8 seconds through a commercially available tunnel oven with blowing a hot air of 105C. The wrapping film adhered closely to the round bars and there was no wrinkle.
The fragility was observed by repeatedly dropping the packages to a floor from a height of 1 m. Among 10 , packages, 3 packages were broken in the second dropping, and other 3 packages, 2 packages and the residual 2 packages were broken in the third, fourth and fifth droppings, respectively.
The same dropping test was carried out by employîng the packages with a c-ommercially available shrinkable polyethylene film (made by Okura Kogyo Co.) l having a thickness of 4Q ~m~ Among 10 packages, 7 packages , i were broken in the first dropping and the residual 3 1.
7filZ
, packages were broken in the second dropping.
Example 3 A non-stretched tubular film having a diameter of 66 mm. and a thickness of 190 ~m. was prepared from a low density polyethylene having a melting point of 123C. and a density at 25C. of 0.923 g./cm3 (commercial name "Neozex 2006H" made by Mitsui Petrochemical Industries, Ltd.) in the same manner as in Example 1. The tensile strength at 300 ~ elongation at 108C. of the non-stretched film was 17 kg./cm2 The non-stretched film was biaxially stretched in the same manner as in Example l except that the temperature of the film at the outlet of the preheater 4 was 65C., the temperature at the starting poing 101 was 100C., the temperature at the position 102 of 1/4 the length L of the stretching zone from the starting point 101 was 104C., the temperature at the finishing point 103 was 86C. and the temperature at the position 104 of 1.2 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 230 mm., and the maximum diameter of the bubble at the finishing point of expansion was 210 mm.
There was little sway of the bubble during the stretching operation for 5 hours. The bubble was stable and did not rupture.
The stretched film was then annealed for 10 seconds by blowing a hot air of 80C. in the same manner 3a as in Example 1. The stretched film so obtained had a thickness of 19.8 ~m., heat shrinkage percents at 108C.
of io ~ in the machine direction and 46 % in the transverse direction, and shrinkage stresses at 108C. of 19 kg./cm2 in the machine direction and 17 kg./cm2 in the transverse direction.
Three orange juice aluminum cans were arranged in a row and pre-wrapped with the stretched film, and passed for 12 seconds through a commercially available e~, * Trade Mark :
~iS7612 tunnel oven with blowing a hot air of 110C. The wrapping ;
film adhered closely to the cans. The wrapping film was not torn from the sealed and other portions, even if one l end of the package was grabbed up, and showed a sufficient S strength for practical use.
Ex'amp'l'e 4 ;
A non-stretched tubular film having a diameter of ' 66 mm. and a thickness of 540 ~m. was prepared from a copolymer of ethylene and 8.5 % by weight of 4-methyl-1-pentene having a melting point of 123C. and a density at 25C. of 0.923 g./cm.3 in the same manner as in Example 1.
The tensile strength at 300 % elongation at 108C. of the non-stretched film was 18 kg./cm.
The non-stretched film was biaxially stretched in the same manner as in Example 1 except that the temperature of the film at the outlet of tne preheater 4 was 80C., the temperature at the starting point 101 was 103C., the temperature at the position 102 of 1/4 the length L of the stretching zone from the starting point 101 , was 106C., the temperature at the finishing point 103 was 87C., and the temperature at the position 104 of 1.2 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 240 mm., and the maximum diameter of the bubble at the finishing point of expansion was 23~ mm.
There was little sway of the bubble during the stretching operation for 5 hours., and the stretching ¦, operation was continued stably.
3Q The stretched film was then annealed for 10 seconds by blowing a hot air of 70C. in the same manner as in Example 1. The stretched film so obtained had a thickness of 35 ~m., heat shrinkage percents at 108C. of 48 ~ in the machine direction and 45 ~ in the transverse direction, and shrinkage stresses at 108C. of 20 kg./cm.2 in the machine direction and 25 kg./cm,2 in the transverse direction.
A set of aluminum sash members consisting of 4 I' '.
.~,.......... . . . .
, ' ` ' , - 18 - llS7612 members of 17 mm in thickness, 25 mm. in width and 550 mm.
in length and 4 members of 17 mm. in thickness, 35 mm. in width and 430 mm. in length were arranged in three rows in three layers and pre-wrapped with the stretched film, and passed for about 5 seconds through a commercially available tunnel oven with blowing a hot air of 130C. Despite of the irre~ularity of the sash members to be wrapped due to the difference in length, the film adhered closely to the sash members and the sash members were tightly bound together.
Example 5 A non-stretched tubular film having a diameter of 66 mm. and a thickness of 400 ~m. was prepared from a copolymer of ethylene and 6.2 % by weight of l-butene having a density at 25C. of 0.924 g./cm3. and a melting point of 122C. in the same manner as in Example 1. The tensile strength at 300 % elongation at 107C. of the non-stretched film was 22 kg./cm.2 The non-stretched film was biaxially stretched in the same manner as in Example 1 except that the temperature of the film at the outlet of the preheater 4 was 75C., the temperature at the starting poing 101 was 101C., the temperature at the position 102 of 1/4 the length L of the stretching zone from the starting point 101 was 105C., the temperature at the finishing point 103 was 86C., and the temperature at the position 104 of 1.2 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 230 mm., and the maximum diameter of the bubble at the finishing point 103 was 235 mm. The stretching was stably continued for about 3 hours.
The stretched film was annealed for 10 seconds by blowing a hot air of 70C. in the same manner as in Example 1. The stretched film so obtained had a thickness of 25 ~m., heat shrinkage percents at 107C. of 44 ~ in the machine direction and 48 ~ in the transverse direction and shrinkage stresses at 107C. of 20 kg./cm.2 in the machine . , ,; .
`' ; ' ~lS7612 - 19 - :
direction and 22 kg./cm2 in the transverse direction.
Twenty copies of a B5 size notebook of 30 sheets were piled up and pre-wrapped with the stretched film, and passed for about 8 seconds through a commercially available tunnel oven with blowing a hot air of 120C. The film adhered closely to the notebooks without protrusion at sealed corner portions. Even if one end of the upper portion of the package was pushed lightly, the piled and packaged notebooks did not slip. The notebooks were tightly bound together and the package was in good packaging state suited for transportation.
The physical properties of the stretched films obtained in Examples 1 to 5 are shown in the following Table together with those of a commercially available low density polyethylene shrinkable film (made by Okura Kogyo Co.) (Comparative Example 1) and a film formed and stretched by means of a conventional blow-up process employing the same ethylene polymer as used in Example 2 (Comparative Example 2).
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As is clear from comparison of Example 1 with Comparative Example 1 and comparison of Example 2 with Comparative Example 2, the heat shrinkable film of the present invention has larger film strength, seal strength, impact strength and impact strength of sealed portion than the blown up, shrinkable films of polymers of the same kind, despite of being thin. The excellent properties coupled with the improvement in transparency and heat shrinka~ility show that the film of the present invention has a large practical value.
.
In case that the radiant heat of a heat source is strong, one side of the thermocouple which does not contact with the film is covered with an aluminum foil to prevent its influence.
EXample 1 A low density polyethylene having a melting point of 111.5C. and a density at 25C. of-0.920 g./cm3 (commercial name "UBE Polyethylene HF 019" made by Ube Industries Ltd.) was melt-blended at a temperature of 200 to 250C. and extruded downward through a circular die maintained at 250C. The diameter of a slit of the circular die was 75 mm. and the slit gap was 0.8 mm. The extruded molten tubular film was cooled to room temperature by slidingly contacting the inside surface of the film with the outside surface of a cylindr-ical mandrel haYing an outer diameter of 66 mm. in which a cooling water of 20C.
was circulated and which was positioned just below the die, while passing the outside surface of the film through a water bath. The thus formed tu~ular non-stretched film had a diameter of about 66 mm. and a thickness of 190 ~m. The tensile strength at 3Q~ ~ elongation at 96 5C. (i.e. at a temperature of 15C. below the melting point of the polyethylene~ of the non-stretched film was 21 kg./cm2 As shown in Fig. 1, the non-stretched film so obtained was employed as a starting material 1, and was led to a biaxIal stretching apparatus A to conduct expansion and extension.
* Trade Mark .
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I''' The temperature of the film at an outlet of a preheater 4 was maintained at 65C. by adjusting the ~oltage and current of a circular infrared heater of the preheater.
S Eight circular infrared heaters of a main heater S were fallen into four divisions, and the voltage and current of each diYision were adjusted. The film was biaxially stretched 3 times in both the machine and transverse directions by the air pressure of a pressurized air admitted into the tuhular film between low-speed nip rolls 2 and high-speed nip-rolls 3 and the relative peripheral speeds of the low-speed and high-speed nip rolls 2 and 3 in an air stream flowing along the tube from a cooling air ring 6 positioned below the main heater 5.
By the adjustment of thé voltage and current of the di~ided circular infrared heaters of the main heater 5 and t~e adjust~ent of the flo~ rate and temperature of the air stream, the temperature of the film at each of positions as shown in Fig 2 was maintained so that the temperature at a starting point of expansion 101 was 88C., I
the temperature at a position 102 of about 1/3~5 the ?
vertical distance L of a streching zone C from the starting point lal was 90C. which was maximum temperature, the temperature at a finishing point of expansion 103 was 75C. ~ ;
and the temperature at a position 104 located at a distance of 1.2 times the vertical distance L of the stretching zone from the finishing point 103 was 4~C. The vertical distance L of the stretching zone C extending from the i starti~g point 101 to the finishing point 103 was about 210 mm., and the dia~eter of the bubble at the finishing point was 195 mm.
The thus stretched tubular film was then collapsed through collapser rolls 7 and the nip rolls 3 and drawn out of the stretching apparatus, and was then introduced into an annealing apparatus B through nip rolls 8. The flattend film was inflated again with air to the original tube state along rolls 9, and was annealed foT 10 seconds by blowing a hot air of 75C~ to the tube from slits 1 1 , , ,j .
.
.... ..
~ '' '' ' ' .
, ., ~, , , ,.,," .. . , j~ . . ... .
- 14 ~ lZ
11 of a heating cylinder 10 and was cooled to room temperature by a cooling cylinder 12. The cooled tube was collapsed again through collapser rolls 13, drawn out of nip rolls 14 and wound up. During the above contir,uous operation, the bubble scarcely swayed and was stable without rupture of the bubble.
The obtained film had a thickness of 21 ~m., thrinkage percents at 96.5C. of 26 ~ in the machine direction and 28 % in the transverse direction, and shrinkage stresses at 96.5C. of 15 kg./cm2 in the machine direction and 15 kg.~cm2 in the transverse direction.
Fifty polystyrene vessels having a height of 75 mm. and a maximum diameter of 40 mm. charged with a lactic acid beverage were arranged in ten rows and pre-wrapped in a lot with the film, and passed for 8 seconds through a commercially available tunnel oven with blowing a hot air of 105C. The film adhered closely to the vesels without wrinkle despite of uneven shape, and showed a good transparency such that the prints and content of the vessels were clearly visible through the film. Also, the wrapping film was not torn from the sealed and other portions, even if one end of the film was grabbed up, and showed a sufficient strength for practical use.
Example 2 A non-stretched tubular film having a diameter of 66 mm and a thickness of 190 ~m. was prepared from a -low density ethylene polymer having a melting point of 124C. and a density at 25C. of 0.923 g./cm3 (commercial name "Ultzex 2020L" made by Mitsui Petrochemical Industries, Ltd ) in the same manner as in Example 1 except that the inside of the extruded tubular film was cooled with air and the outside was cooled with water. The tensile strength at - 300 ~ elongation at la9C. of the non-stretched film was 16 kg./cm2 The non-stretched film was biaxially stretched in the same manner as in Example 1 except that the temperature of the film at the outlet of the preheater 4 was 70C., ,~ * Trade Mark - .' .
, 15 ~157612 the temperature at the starting point 101 was 100C., the temperature at a distance 102 of 1/4 the length L of the stretchin~ zcne from the starting point 1~1 was 132C.
(maximum temperature), the temperature at the finishing S point 103 was 87C., and the temperature at a distance 104 of 1.3 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 210 mm., and the maximum diameter of the bubble at the finishing point of expansion was 185 mm.
The operation was continued for 5 hours, but there was little sway of the bubble during the operation.
The bubble was stable and did not rupture.
The stretched film was then annealed for 10 seconds by blowing a hot air of 70C. in the same manner as in Example 1. The stretched film so obtained had a thickness of 21 ~m~, shrinkage percents at 109C. of S0 % in the machine direction and 45 ~ in the transverse direction, and shrinkage stresses at 1~9C. of 22 kg.lcm2 in the machine direction and 2Q kg./cm2 in the transverse direction.
Five pieces of a round iron bar having a diameter of 12 mm. and a length of 20 cm. (total weight:
about 1 kg~) were arranged in a row and pre-wrapped with;
the stretched film, and passed for about 8 seconds through a commercially available tunnel oven with blowing a hot air of 105C. The wrapping film adhered closely to the round bars and there was no wrinkle.
The fragility was observed by repeatedly dropping the packages to a floor from a height of 1 m. Among 10 , packages, 3 packages were broken in the second dropping, and other 3 packages, 2 packages and the residual 2 packages were broken in the third, fourth and fifth droppings, respectively.
The same dropping test was carried out by employîng the packages with a c-ommercially available shrinkable polyethylene film (made by Okura Kogyo Co.) l having a thickness of 4Q ~m~ Among 10 packages, 7 packages , i were broken in the first dropping and the residual 3 1.
7filZ
, packages were broken in the second dropping.
Example 3 A non-stretched tubular film having a diameter of 66 mm. and a thickness of 190 ~m. was prepared from a low density polyethylene having a melting point of 123C. and a density at 25C. of 0.923 g./cm3 (commercial name "Neozex 2006H" made by Mitsui Petrochemical Industries, Ltd.) in the same manner as in Example 1. The tensile strength at 300 ~ elongation at 108C. of the non-stretched film was 17 kg./cm2 The non-stretched film was biaxially stretched in the same manner as in Example l except that the temperature of the film at the outlet of the preheater 4 was 65C., the temperature at the starting poing 101 was 100C., the temperature at the position 102 of 1/4 the length L of the stretching zone from the starting point 101 was 104C., the temperature at the finishing point 103 was 86C. and the temperature at the position 104 of 1.2 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 230 mm., and the maximum diameter of the bubble at the finishing point of expansion was 210 mm.
There was little sway of the bubble during the stretching operation for 5 hours. The bubble was stable and did not rupture.
The stretched film was then annealed for 10 seconds by blowing a hot air of 80C. in the same manner 3a as in Example 1. The stretched film so obtained had a thickness of 19.8 ~m., heat shrinkage percents at 108C.
of io ~ in the machine direction and 46 % in the transverse direction, and shrinkage stresses at 108C. of 19 kg./cm2 in the machine direction and 17 kg./cm2 in the transverse direction.
Three orange juice aluminum cans were arranged in a row and pre-wrapped with the stretched film, and passed for 12 seconds through a commercially available e~, * Trade Mark :
~iS7612 tunnel oven with blowing a hot air of 110C. The wrapping ;
film adhered closely to the cans. The wrapping film was not torn from the sealed and other portions, even if one l end of the package was grabbed up, and showed a sufficient S strength for practical use.
Ex'amp'l'e 4 ;
A non-stretched tubular film having a diameter of ' 66 mm. and a thickness of 540 ~m. was prepared from a copolymer of ethylene and 8.5 % by weight of 4-methyl-1-pentene having a melting point of 123C. and a density at 25C. of 0.923 g./cm.3 in the same manner as in Example 1.
The tensile strength at 300 % elongation at 108C. of the non-stretched film was 18 kg./cm.
The non-stretched film was biaxially stretched in the same manner as in Example 1 except that the temperature of the film at the outlet of tne preheater 4 was 80C., the temperature at the starting point 101 was 103C., the temperature at the position 102 of 1/4 the length L of the stretching zone from the starting point 101 , was 106C., the temperature at the finishing point 103 was 87C., and the temperature at the position 104 of 1.2 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 240 mm., and the maximum diameter of the bubble at the finishing point of expansion was 23~ mm.
There was little sway of the bubble during the stretching operation for 5 hours., and the stretching ¦, operation was continued stably.
3Q The stretched film was then annealed for 10 seconds by blowing a hot air of 70C. in the same manner as in Example 1. The stretched film so obtained had a thickness of 35 ~m., heat shrinkage percents at 108C. of 48 ~ in the machine direction and 45 ~ in the transverse direction, and shrinkage stresses at 108C. of 20 kg./cm.2 in the machine direction and 25 kg./cm,2 in the transverse direction.
A set of aluminum sash members consisting of 4 I' '.
.~,.......... . . . .
, ' ` ' , - 18 - llS7612 members of 17 mm in thickness, 25 mm. in width and 550 mm.
in length and 4 members of 17 mm. in thickness, 35 mm. in width and 430 mm. in length were arranged in three rows in three layers and pre-wrapped with the stretched film, and passed for about 5 seconds through a commercially available tunnel oven with blowing a hot air of 130C. Despite of the irre~ularity of the sash members to be wrapped due to the difference in length, the film adhered closely to the sash members and the sash members were tightly bound together.
Example 5 A non-stretched tubular film having a diameter of 66 mm. and a thickness of 400 ~m. was prepared from a copolymer of ethylene and 6.2 % by weight of l-butene having a density at 25C. of 0.924 g./cm3. and a melting point of 122C. in the same manner as in Example 1. The tensile strength at 300 % elongation at 107C. of the non-stretched film was 22 kg./cm.2 The non-stretched film was biaxially stretched in the same manner as in Example 1 except that the temperature of the film at the outlet of the preheater 4 was 75C., the temperature at the starting poing 101 was 101C., the temperature at the position 102 of 1/4 the length L of the stretching zone from the starting point 101 was 105C., the temperature at the finishing point 103 was 86C., and the temperature at the position 104 of 1.2 times the length L of the stretching zone from the finishing point 103 was 48C. The vertical length L of the stretching zone was about 230 mm., and the maximum diameter of the bubble at the finishing point 103 was 235 mm. The stretching was stably continued for about 3 hours.
The stretched film was annealed for 10 seconds by blowing a hot air of 70C. in the same manner as in Example 1. The stretched film so obtained had a thickness of 25 ~m., heat shrinkage percents at 107C. of 44 ~ in the machine direction and 48 ~ in the transverse direction and shrinkage stresses at 107C. of 20 kg./cm.2 in the machine . , ,; .
`' ; ' ~lS7612 - 19 - :
direction and 22 kg./cm2 in the transverse direction.
Twenty copies of a B5 size notebook of 30 sheets were piled up and pre-wrapped with the stretched film, and passed for about 8 seconds through a commercially available tunnel oven with blowing a hot air of 120C. The film adhered closely to the notebooks without protrusion at sealed corner portions. Even if one end of the upper portion of the package was pushed lightly, the piled and packaged notebooks did not slip. The notebooks were tightly bound together and the package was in good packaging state suited for transportation.
The physical properties of the stretched films obtained in Examples 1 to 5 are shown in the following Table together with those of a commercially available low density polyethylene shrinkable film (made by Okura Kogyo Co.) (Comparative Example 1) and a film formed and stretched by means of a conventional blow-up process employing the same ethylene polymer as used in Example 2 (Comparative Example 2).
: :
.
~ 57f~12 .~ o o o ~ o U~ o o o o U~ o ~ I , O X ~ o oo ~ `D O
~) ~ ~ ~ ~ ~ oo o o . . . . a~
o X o ~ o o o o ~ o ~ o X
e~ .,~
. ~
J
. 1~ O O O O OD O Il~
X ~ oo ,-1 `D O 11~ ~
o ~ C~l ~ O
. U~ U~O O O O L~ O G~ O U~
X 1~ o o ~ ~ t~ O _1 O ~
~ CO ~
. O~ COO O O O U7 o L~ o ,~
X ~1 0 ~ ~ ) O O _I
CJI ~
C`l O ~ O ~, :
. ~ ~ O O O O ~ 0 00 0 C:
oX ~ O O t`~ Ln O ~1 ~1 ~ oo 00 ~ ~ CO _1 ~1 ~ , , ~ 00 ~ 00 . _~ ~10 0 0 0 ~ O ~ 0 00 X t`l O U'l 1~ o ~ IJ~
~Ll IJ~ .
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, , . . . ~ ' . . _ . . , , . , ~ , , ~_I , . . ~ . . . ~
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.In . ~ h ~ Ei b O ~n Ei b O
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. O CO U~ O ~ O O L~ ~ _I i ' X ~ I ~ ~ ~ ~ I
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_ p, .. ... p, .. .. .,~
d~ ~ t)4 ~ h bO ,!4 bO ~ I~
. . . a~ `~ L
~r~ . . .~ . . . ~ h .,~ ~, V ~1 ~ r~ a h ~3 h ~ ' V
O ~ . . . 1::
O O ~ 1 ~
a~ .. .. ~,, .. .. ~ ,.
a~ . - . - - ~o a.~ - ~ ~ ~ ~.
td .0 ,~ . . . . . .!4 ~ -~1) ~ S ~ ....
:~ .r~ C~) . O ~ O ~ ~ .
~: ~ O ~ O ~ ~ h O ~ O ~ E~ .
~1 ~ U~ ~ .
U~ . L ~, ~ ~ V~ ~ ~ ~ _, ~ ~ _ O +~
O 0 ¢ ¢ ~ ¢ ¢ Z i _, I .
!
~' :
. : , , :
11~7G~Z
As is clear from comparison of Example 1 with Comparative Example 1 and comparison of Example 2 with Comparative Example 2, the heat shrinkable film of the present invention has larger film strength, seal strength, impact strength and impact strength of sealed portion than the blown up, shrinkable films of polymers of the same kind, despite of being thin. The excellent properties coupled with the improvement in transparency and heat shrinka~ility show that the film of the present invention has a large practical value.
.
Claims (11)
1. A process for preparing a heat shrinkable ethylene polymer film which comprises the steps of (1) introducing a non-stretched tubular film of an ethylene polymer having a density of 0.91 to 0.93 g./cm3 at 25°C. into a tubular biaxial stretching apparatus, a film obtained by melt-extruding said ethylene polymer and cooling the extrudate to solidify without stretching it showing a tensile strength at 300 % elongation of not less than 15 kg./cm.2 at a temperature of 15°C. below the melting point of said ethylene polymer, (2) biaxially stretching said non-stretched tubular film to give a biaxially oriented film by means of an internal gas pressure at a temperature within the orientable temperature range under the following conditions:
(a) the surface temperature of the film at a starting point of expansion being within the range of 15°
to 25°C. below the melting point of said polymer, (b) the film in a stretching zone extending from the starting point to a finishing point of expansion having a temperature gradient such that the surface temperature of the film at a positon of 114 to 1/3 the length of the stretching zone from the starting point is maximum, and the difference between the maximum surface temperature and the surface temperature of the film at the starting point being not more than 5°C., (c) the temperature drop of the film from the maximum temperature position to the finishing point being within the range of 15° to 20°C., and (d) the film being cooled while traveling from the finishing point to a distance of 1.0 to 1.5 times the vertical distance of the stretching zone so that the surface temperature of the film drops by 30° to 40°C., and (3) recovering the resulting biaxially oriented film.
(a) the surface temperature of the film at a starting point of expansion being within the range of 15°
to 25°C. below the melting point of said polymer, (b) the film in a stretching zone extending from the starting point to a finishing point of expansion having a temperature gradient such that the surface temperature of the film at a positon of 114 to 1/3 the length of the stretching zone from the starting point is maximum, and the difference between the maximum surface temperature and the surface temperature of the film at the starting point being not more than 5°C., (c) the temperature drop of the film from the maximum temperature position to the finishing point being within the range of 15° to 20°C., and (d) the film being cooled while traveling from the finishing point to a distance of 1.0 to 1.5 times the vertical distance of the stretching zone so that the surface temperature of the film drops by 30° to 40°C., and (3) recovering the resulting biaxially oriented film.
2. The process of Claim 1, wherein the film for measurement of tensile strength obtained by melt-extruding the ethylene polymer and cooling the extrudate to solidify without stretching it is one taken from a tubular film having a diameter of 66 m. and a thickness of 190 µm.
obtained by melt-blending the ethylene polymer at a temperature of 200° to 250°C., extruding downward the molten mass through a circular die having a slit of 75 mm.
in diameter maintained at 250°C. and cooling the outside of the tube with water
obtained by melt-blending the ethylene polymer at a temperature of 200° to 250°C., extruding downward the molten mass through a circular die having a slit of 75 mm.
in diameter maintained at 250°C. and cooling the outside of the tube with water
3. The process of Claim 1, wherein the non-stretched tubular film is stretched at least 2.5 times in each of the machine and transverse directions.
4. The process of Claim 1, wherein said ethylene polymer is a homopolymer of ethylene.
5. The process of Claim 1, wherein said ethylene polymer is a copolymer of ethylene and not more than 25 by weight of an a-olefin having 3 to 12 carbon atoms.
6. The process of Claim 1, wherein said ethylene polymer is a copolymer of ethylene and not more than 15 %
by weight of an .alpha.-olefin having 4 to 6 carbon atoms.
by weight of an .alpha.-olefin having 4 to 6 carbon atoms.
7. A heat shrinkable film of ethylene polymer having a heat shrinkage percent of not less than 25 % and a heat shrinkage stress of not less than 12 kg./cm2, respectively at a temperature of 15°C. below the melting point of the polyethylene.
8. The heat shrinkable film of Claim 7, which is a stretched film of an ethylene polymer having a density of 0,91 to 0.93 g./cm.3 at 25°C., a non-stretched film made of said ethylene polymer having a tensile strength at 300 elongation of not less than 15 kg./cm2 at a temperature of 15°C. below the melting point of said ethylene polymer.
9. The heat shrinkable film of Claim 7, wherein said ethylene polymer is a homopolymer of ethylene.
10. The heat shrinkable film of Claim 7, wherein said ethylene polymer is a copolymer of ethylene and not more than 25 % by weight of an .alpha.-olefin having 3 to 12 carbon atoms.
11. The heat shrinkable film of Claim 7, wherein said ethylene polymer is a copolymer of ethylene and not more than 15 % by weight of an .alpha.-olefin having 4 to 6 carbon atoms.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP105067/1979 | 1979-08-20 | ||
| JP10506779A JPS5628826A (en) | 1979-08-20 | 1979-08-20 | Thermoshrinking film and manufacturing thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1157612A true CA1157612A (en) | 1983-11-29 |
Family
ID=14397605
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000357481A Expired CA1157612A (en) | 1979-08-20 | 1980-08-01 | Heat shrinkable film and process for preparing the same |
Country Status (3)
| Country | Link |
|---|---|
| US (2) | US4354997A (en) |
| JP (1) | JPS5628826A (en) |
| CA (1) | CA1157612A (en) |
Families Citing this family (43)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4532189A (en) * | 1982-02-19 | 1985-07-30 | W. R. Grace & Co., Cryovac Div. | Linear polyethylene shrink films |
| US4536365A (en) * | 1983-12-22 | 1985-08-20 | American Cyanamid Company | Process for the manufacture of equally biaxially oriented film |
| US4617241A (en) * | 1984-01-23 | 1986-10-14 | W. R. Grace & Co., Cryovac Div. | Linear polyethylene stretch/shrink films |
| US4590124A (en) * | 1984-05-10 | 1986-05-20 | W. R. Grace & Co., Cryovac Div. | Storm window film |
| US4551380A (en) * | 1984-05-10 | 1985-11-05 | W. R. Grace & Co., Cryovac Div. | Oriented heat-sealable multilayer packaging film |
| US4514465A (en) * | 1984-05-30 | 1985-04-30 | W. R. Grace & Co., Cryovac Div. | Storm window film comprising at least five layers |
| US5059481A (en) * | 1985-06-17 | 1991-10-22 | Viskase Corporation | Biaxially stretched, heat shrinkable VLDPE film |
| US4976898A (en) * | 1985-06-17 | 1990-12-11 | Viskase Corporation | Process for making puncture resistant, heat-shrinkable films containing very low density polyethylene |
| CA1340037C (en) * | 1985-06-17 | 1998-09-08 | Stanley Lustig | Puncture resistant, heat-shrinkable films containing very low density polyethylene copolymer |
| US5256351A (en) * | 1985-06-17 | 1993-10-26 | Viskase Corporation | Process for making biaxially stretched, heat shrinkable VLDPE films |
| US4853602A (en) * | 1985-12-24 | 1989-08-01 | E. I. Dupont De Nemours And Company | System for using synchronous secondaries of a linear motor to biaxially draw plastic films |
| CA1297651C (en) * | 1986-03-03 | 1992-03-24 | Tomoji Mizutani | Heat shrinkable film |
| BR8707774A (en) * | 1987-06-17 | 1989-10-03 | Du Pont | SYSTEM FOR THE USE OF SYNCHRONIC SECONDARIES OF A LINEAR MOTOR IN BIAXIAL DRAWING OF PLASTIC FILMS |
| EP0299750B1 (en) * | 1987-07-13 | 1994-09-28 | Mitsubishi Kasei Corporation | Linear polyethylene film and process for producing the same |
| JPH0729378B2 (en) * | 1987-08-14 | 1995-04-05 | 株式会社興人 | Method for producing polyethylene heat-shrinkable film |
| JPH0825670B2 (en) * | 1987-08-19 | 1996-03-13 | キヤノン株式会社 | Paper skew feeding device |
| US4814135A (en) * | 1987-12-22 | 1989-03-21 | Union Carbide Corporation | Process for extrusion |
| CA1294101C (en) * | 1988-09-21 | 1992-01-14 | Hideo Isozaki | Process for preparing heat shrinkable polyethylene film |
| DK399489D0 (en) * | 1989-04-10 | 1989-08-14 | Kohjin Co | IRRICULATED AND HEATABLE POLYAETHYLENE FILM |
| US5298202A (en) * | 1989-07-28 | 1994-03-29 | W. R. Grace & Co.-Conn. | Double bubble process for making strong, thin film |
| US6025448A (en) * | 1989-08-31 | 2000-02-15 | The Dow Chemical Company | Gas phase polymerization of olefins |
| US5158836A (en) * | 1991-02-21 | 1992-10-27 | W. R. Grace & Co.-Conn. | Oriented film of high clarity and gloss |
| US5219666A (en) * | 1990-03-23 | 1993-06-15 | W.R. Grace & Co.-Conn. | Oriented film of high clarity and gloss |
| US5216800A (en) * | 1990-04-28 | 1993-06-08 | Mazda Motor Corporation | Method and apparatus for attaching a lid member of automobile |
| US6538080B1 (en) | 1990-07-03 | 2003-03-25 | Bp Chemicals Limited | Gas phase polymerization of olefins |
| CA2048296C (en) * | 1990-08-13 | 2002-09-24 | Henry G. Schirmer | Blends of polypropylene and ethylene copolymer and films made from the blend |
| US5165965A (en) * | 1990-12-28 | 1992-11-24 | Reynolds Metals Company | Method for providing predistored images on shrinkable film |
| US5278272A (en) | 1991-10-15 | 1994-01-11 | The Dow Chemical Company | Elastic substantialy linear olefin polymers |
| US5582923A (en) * | 1991-10-15 | 1996-12-10 | The Dow Chemical Company | Extrusion compositions having high drawdown and substantially reduced neck-in |
| US5674342A (en) * | 1991-10-15 | 1997-10-07 | The Dow Chemical Company | High drawdown extrusion composition and process |
| US5395471A (en) * | 1991-10-15 | 1995-03-07 | The Dow Chemical Company | High drawdown extrusion process with greater resistance to draw resonance |
| US5525695A (en) * | 1991-10-15 | 1996-06-11 | The Dow Chemical Company | Elastic linear interpolymers |
| US5783638A (en) * | 1991-10-15 | 1998-07-21 | The Dow Chemical Company | Elastic substantially linear ethylene polymers |
| JPH0664039A (en) * | 1992-08-20 | 1994-03-08 | Mitsui Petrochem Ind Ltd | Method and apparatus for production of biaxially oriented film and shrink film |
| DE4313153C1 (en) * | 1993-04-22 | 1994-05-05 | Stewing Nachrichtentechnik | Increasing tear resistance in heat shrinkable plastic film - extruding strip, partially cross-linking, stretching at temp. below crystalline m.pt. and finally cross-linking during shrinkage. |
| US6322883B1 (en) | 1994-07-15 | 2001-11-27 | Exxonmobil Oil Corporation | Uniaxially shrinkable biaxially oriented polypropylene film with HDPE skin |
| US5792534A (en) * | 1994-10-21 | 1998-08-11 | The Dow Chemical Company | Polyolefin film exhibiting heat resistivity, low hexane extractives and controlled modulus |
| US6685871B2 (en) * | 2001-05-15 | 2004-02-03 | Honeywell International Inc. | Toughened biaxially oriented film |
| US7147930B2 (en) | 2003-12-16 | 2006-12-12 | Curwood, Inc. | Heat-shrinkable packaging films with improved sealing properties and articles made thereof |
| DE102005014474A1 (en) * | 2005-03-27 | 2006-10-05 | Huhtamaki Forchheim Zweigniederlassung Der Huhtamaki Deutschland Gmbh & Co. Kg | Process for producing a stretched plastic film |
| CN101117036A (en) * | 2006-07-31 | 2008-02-06 | 陶氏全球科技股份有限公司 | Layered film combination, packaging made by the layered film combination and use method thereof |
| US10363700B2 (en) | 2011-08-26 | 2019-07-30 | Dow Global Technologies Llc | Bioriented polyethylene film |
| US9902102B2 (en) * | 2013-08-30 | 2018-02-27 | Berry Plastics Corporation | Process for forming film |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3022543A (en) * | 1958-02-07 | 1962-02-27 | Grace W R & Co | Method of producing film having improved shrink energy |
| GB938766A (en) * | 1961-01-30 | 1963-10-09 | Grace W R & Co | Transparent polyethylene film |
| DE1504458C3 (en) * | 1963-12-19 | 1975-10-02 | Hoechst Ag, 6000 Frankfurt | Biaxially stretched high pressure polyethylene flat sheet and process for its production |
| US3299194A (en) * | 1964-03-09 | 1967-01-17 | Du Pont | Oriented films of ethylene polymers |
| US3509116A (en) * | 1966-04-13 | 1970-04-28 | Grace W R & Co | Ethylene-butene copolymer |
| US3465072A (en) * | 1966-10-20 | 1969-09-02 | Grace W R & Co | Method for forming biaxially oriented film |
| GB1189999A (en) * | 1966-11-30 | 1970-04-29 | Grace W R & Co | Production of Biaxially Oriented Films |
| US3891737A (en) * | 1973-11-21 | 1975-06-24 | Reynolds Metals Co | Method of making a heat shrinkable film of polyethylene copolymers thereof and article produced therefrom |
| JPS5952643B2 (en) * | 1977-01-27 | 1984-12-20 | 三井化学株式会社 | ethylene copolymer |
| US4192935A (en) * | 1978-01-06 | 1980-03-11 | DuPont of Canada Limited | Ethylene polymers of high melt index |
| DE2801541A1 (en) * | 1978-01-14 | 1979-07-19 | Hoechst Ag | AETHYLENE COPOLYMERS AND THEIR USE FOR THE PRODUCTION OF FILMS |
| AU523866B2 (en) * | 1978-04-18 | 1982-08-19 | Du Pont Canada Inc. | Manufacture of film |
| US4258166A (en) * | 1979-06-08 | 1981-03-24 | Mobil Oil Corporation | Low density polyethylene film |
-
1979
- 1979-08-20 JP JP10506779A patent/JPS5628826A/en active Granted
-
1980
- 1980-08-01 CA CA000357481A patent/CA1157612A/en not_active Expired
- 1980-08-11 US US06/177,185 patent/US4354997A/en not_active Expired - Lifetime
-
1982
- 1982-02-19 US US06/350,376 patent/US4463153A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| US4463153A (en) | 1984-07-31 |
| US4354997A (en) | 1982-10-19 |
| JPS5628826A (en) | 1981-03-23 |
| JPS5736142B2 (en) | 1982-08-02 |
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