CA1143522A

CA1143522A - Method for producing polyester container

Info

Publication number: CA1143522A
Application number: CA000324263A
Authority: CA
Inventors: Akiho Ota; Fumio Negishi
Original assignee: Yoshino Kogyosho Co Ltd
Current assignee: Yoshino Kogyosho Co Ltd
Priority date: 1978-06-29
Filing date: 1979-03-27
Publication date: 1983-03-29
Also published as: FR2491873A1; US4375442A; AU4548279A; FR2429660A1; FR2491873B1; US4572811A; IT1164039B; GB2024087B; DE2911149C2; NL8105759A; CH636556A5; NL7902235A; US4590021A; IT7948837A0; FR2429660B1; DE2911149A1; AU520521B2; US4379099A; GB2024087A

Abstract

ABSTRACT OF THE DISCLOSURE
Spherulites grow in such sections as neck, neck and, bottom center or bottom periphery of a hollow bottle-shaped container of biaxially orientation-blow molded polyethylene terephthalate where the the resin is not substantially subjected to orientation, thereby to improve the thermal resistance, stiffness and content resistance of such sections to almost the same extent as the biaxially oriented sections of the container such as shoulder and cylindrical sections thereof. The aforesaid sections of the preformed piece before being blow-molded or of the blow-molded container where the resin is not substantially subjected to orientation are first heated at 120 - 180°C for 3 - 8 minutes and, then, annealed at room temperatures, with a result that such sections have a suphrulite texture of an increased density and are opacified in white or milky white.

Description

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1,' 1 jl ~ACKGROS~ND OF THE INVENTION

2 ~` The present invention relates to a hollow blow-molded

3 ~I container of a biaxially oriented polyester resin and, more

4 ll specifically, to a process for manufacturing such a container

5 1l of hollow bottle shape free from crazing regardless of the

6 1,l type of its contents, in which such sections as neck, neck

7 ill end or bottom section thereof where the resin is not substantiall Y

8 ll subjected to orientation are protected against thermal

9 lll deformation.
ll Polyethylene terephthalate has a wide range of 11 ll applications in the field of containers for foodstuffs, 12 l~ flavoring materials, cosmetics and so on, because it can 13 'll be molded, by orientation-blowing, into transparent thin-walled 14 ~ containers having a high stiffness, impact strength and 15 '1l improved hygienic qualities with a higher molding accuracy.
16 II In ordinary direct blow molding processes in which the top 17 ll and bottom parts of an extruded parison are held by a mol~
18 1 and compressed air i5 blown into the thus held parison to 19 1 expand the same into a container shape, resultant containers 1 may often be unsatisfiable in respect of strength and 21 1 transparency because the parison is oriented only monoaxially.
22 j! Therefore, in blow molding, there prevails a so-called ~ ll biaxially-orienting blow-molding process in which the parison 24 ll is oriented not only laterally but also longitudinally in 'j a temperature range suitable for such orientation, and 26 1¦ biaxially~oriented blow-molded containers show increased 27 I~ stiffness and strength as well as improved gas barrier r' 28 1l properties and transparency. However, even in such a biaxially-29 II orienting blow-molding process, such sections as neck, neck 30 ~ end and bottom section of the resultant conta~ners cannot Il ~1 . I

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I ~' enjcy an lmprovement 1n physical properties and are ' susceptible to thermal deformatlon, because such sections 3 ~I are not subjected to orientation, that is to say, molecular 4 1l orientation never or hardly occurs and the bond between l, the mol~cular chains constituting polymer crystals is not 6 11l strong in these sections.
As is well-known, those contalners which are used 8 11 for storing volatile liquids require very tight sealing.
9 1I Therefore~ the neck ends of such containers are usually ~l sealed with a crown cap caulked thereon or a cap placed 11 ,I thereon with interposition of a packing.
1~ I However, if the neck section is deformed by some external 13 i factors such as heat, the aforementioned sealing effect 14 ~ of the sealing means is diminished. While, if the polyester , containers are used to store highly-concentrated alcohol, 16 I ester, or cosmetics or solvents containing these, the afore-17 l mentioned non-oriented sections may be permeated by the 18 ~I content to be crazed and, eventually, the liquid content 19 I may leak from the neck end. Also, if such containers are I filled with carbonated beverages, their bottoms may be 'l bulged out due to an increase in internal pressure and 22 ¦I crazing to such an extent to debase their standing stability and, ultimately, the contalners may be bursted.

24 1 On the other hand, such containers are used to store such 1 liquids as juice or sauce that are filled therein under 26 I heat-sterilization, their neck end portlons may be deformed, 27 1l due to the filling temperature, to such an extent that the 1 28 ,11 containers cannot be sealed completely even with a cap 29 1I having an inner sealing seat.
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11~35~2 SUMM~RY OF TIIE INVENTION
2 I The present lnvention provides an improved method 3 ll for producing a polyester container, especially, biaxially-4 ll oriented blow-molded polyester resin container, in which ~l only those portions of the container such as neck and bottom 6 l, sections which are not substantially subjected to orientation 7 ll are first heated and then annealed so as to increase the 8 I density of supherulite texture in such portions and, thereby, 9 I to improve their thermal reslstance, stiffness and content il resistance to the same extent as those of the cylindrical sections of the container. The cylindrical section has 12 1I molecules therein orientated by biaxial or$entation and 13 I its physical properties, especially transparency and mechanical 14 l~ strength, are improved. While, as a result of t~e aforementione~
Il heat treatment, since the neck and bottom sections are 16 l' blushed by spherulite texture grown therein and their content 17 I resistance is further improved. Namely, these sections 18 1I will not be crazed by penetration of the content such as ¦ alcohol, ester, surfactant or the like. Also, since the 19 ~1 1~ neck section becomes more tough, a cap or like capping 21 1l means can be caulked or attached thereonto more stably.
22 1I Further, since their thermal reslstance is improved by the 23 ~¦ aforesaid heat treatment, hotter contents can be filled in 24 1l the container.
lli Accordingly, an object of the present invention is 26 I to provide a bottle-shaped container of biaxially orientation 27 I blow-molded polyester resin, in which those portions where 28 ~, the resin is not substantially subjected to orientation are 29 I blushed and crystallized by growth of spherulite structure.
Another object of the present inven-tion is to provide ., I

~ _ 4 _ 1 11 a bottle-shaped container of biaxially orlentation-blow 2 1I molcled polyester resln, in which the density of spherulite 3 j~ texture in such sectlons of the container as neck, neck end, 4 1~ bottom center and perphery where the resin is not substantially 5 ll subjected to orientation is increased to prevent th~se 6 l¦ sections from being deformed by heat and crazed by the content.

7 ¦¦ Yet another object of the present invention is to 8 ll produce a container in a simplified manner, in which those 9 Il~ sections of a preformed piece which are not subjected to 1 biaxial orientation in the succeeding blow molding process 11 j are subjected to heating and subsequent annealing in advance 12 ll to improve the thermal resistance and content resistance 13 of these sections.
14 ' Still another object of the present invention is to I produce a container, in which those sections of the container 16 I which are not substantially oriented in the preceding 17 l~ biaxial orientation-blow molding process are subjected to 18 ¦I heating and subsequent annealing, after said blow molding l9 process, to improve the strength and content resistance 20 ¦ of these sections to almost the same level as those of the 21 1I cylindrical section of the container.
22 D~TAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
~ l These and other object and features of the present 24 1! invention will become apparent from the following description 25 l¦ of the preferred embodiments of the present invention when 26 I read with reference to the accompanying drwings, in which:
27 1I Fig. 1 is a front view of a container according to 28 I the present invention, showing its neck section in a partially 29 jl broken form;

1I Fig. 2 is a sectional view of an equipment of 1l - 5 -35'~Z
1 jl a preferred embodiment of the present invention used for 2 ~I heating the neck section of the container;
3 I' Fig. 3 is a paxtially broken section of an equipment 4 ll of another preferred embodiment of the present invention ll used for heating the neck section of the container;
,1 6 ~I Fig. 4 is a partially broken section of the container 7 'l according to the present invention having upper end portion 8 ll of its neck section blushed and crystallized;
g ~I Fig. 5 is a front view of an equipment for heating ' only the upper end portion of the neck section of the 11 i container;
12 ; Fig. ~ is a partially broken section of a preformed 13 piece having its bottom center blushed and crystallized, 14 I and Fig. 6B is a partially broken section of a con-tainer 15 ! obtained by biaxially orientation-blow molding the preformed 16 I piece of Fig. 6A;
17 ll Fig. 7Ais a partially broken section of a preformed 18 ' piece having its bottom periphery blushed and crystallized, 19 ~I, and Fig. 7B is a partially broken section of a container il obtained by biaxially orientation-blow molding the preformed 21 ' piece of Fig. 7A; and 22 ~I Fig. 8A is a partially broken section of a preformed ~ I piece which is blushed and crystallized wholly from the 24 l, periphery to center of its bottom, and Fig. 8B is a partially ~1 broken section obtained by biaxlally orientation-blow 26 molding the preformed piece of Fig. 8A.
27 ll, Referring now to the drawings, especially to Fig. 1, 28 1I the reference numeral 10 is a hollow bottle-shaped container 29 I having a threaded neck section 11, cylindrical section 12 30 ¦¦ and bottom section 13.
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1 i! The container 10 is obtained by heating a preformed piece 2 ¦¦ of polyethylene terephthalate and, in a mold, orienting the 3 1I same first in the longitudinal directlon and, then, blowing 4 ll air therainto to orient the same in the lateral direction.
l, Those shoulder, cylindrical and bottom sections of the 6 l¦ container 10 which are biaxially oriented are transparent, 7 1~ but the neck section 11 having a higher density o~ spherulite 8 I texture show a milky white color. Such a higher denslty 9 li of spherulite texture is attained by subjecting the container , as blow-molded to heating and subsequent annealing.
ll ll In the meantime, containers of biaxially orientain-blow 12 '! molded polyethylene terephthalate resin are sometimes 13 i heat-set at a temperature somewhat above the softening 14 ~l point of the resin to improve thelr thermal resistance.
l In such a heat-setting process, the container body is 16 I appropriately held by a mold or like means to prevent 17 1I thermal deformation. However, even with this, the neck 18 lll section may often be deformed by heat to go out of diminsional 19 ll accuracy. Therefore, the neck section is blushed and 'i crystallized prior to heat-setting to obtain polyethylene 21 ll terephthalate resin containers having an improved dimensional 22 il stability as well as dimensional stability of their neck ~ ll sections.
24 ~ Various means may be devlsed for blushing and 1 crystallizing the neck section 11 of the container 10, 26 1 as ememplified by the preferred embodiment according to 27 ~11 the present invention shown in Fig. 2.
28 ~ In the preferred embodiment shown in Fig. 2, the 29 l~ container 10 is placed on a base rest 21, and a hold 22 is 1ll inserted in its neck section 11 for preventing inward _ j _ l l, deformation of the latter. Around the neck section 11, 2 1I provided is a heatex 23 comprising an electromaynetic 3 ll inductor which heats by radiation and then anneals the 4 ~l neck section l 1 to blush and crystalize the same.
5 ll A shielding plate 24 provided directly beneath the heater 23 6 , functions to prevent the influence of the radiant heat from 7 ll reaching those portions of the bottle 10 under the neck 8 l~ section 11. The base rest 21 or hold 22 may be turned to 9 j¦ rotate the container 10 relatively to the heater 23 so that ll the incident radiant heat is evenly distributed around the ll I neck section 11.
12 il Alternatively, in the foregoing preferred embodiment, I
13 1, instead of the hold 22, a metal cap 25 (for example, split- ¦
14 Il, cavity mold shape cap) may be placed on the neck section 11 lS I to heat the same by applying the radiant heat onto the 16 metal cap 25.
17 l¦ Further, as shown in Fig. 3, the neck section 11 may 18 ¦¦ be heated through the metal cap 25 which is fitted onto the 19 1~ neck section 25 and induction-heated by electrodes 26 provided 20 1l externally of the metal cap 25. Thereafter, the neck 21 ll section 11 is annealed to be blushed and crystallized.
22 ¦ll The metal cap 25 is removed after this processing.
23 ll In the latter case, the base rest 21 and, thus, 24 ~I the container 10 is not required to be rotated relatively 25 ll to the heater. Also, since only the neck section 11 is 26 ' subjected to heating, the shielding plate 24 is not necessary.
27 ~11 Especially, in the preferred embodiment using the cap 25, 28 ! only the neck section 11 can be heated positively without 29 ¦ being deformed.
30 1 Theoretically, the minimum temperature at which the Il .
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~ resin material, namely, po]yethylene terephthalate, of the 2 1I neck section 11 is crystallized is its glass transltion 3 ll point (70C) and the shortest heating time required to 4 Ij crystallize the same is the time that elapses before crystal I¦ nuclei begin to be formed. Namely, it must be a-t least 6 Ij about 2 minutes and 30 seconds. Therefore, heat treatment 7 I for about 2 minutes and 30 seconds at about 70C is sufficient 8 ! to crystallize the resin material of the neck section 11.
9 1 However, as a matter of course, since the productivity I must be increased, without causing a thermal deformation due to overheating, under such condtions that the neck 12 section 11 has a substantial thickness and the resin material 13 I does not have a high thermal conductivity, certain limitations 14 1l are naturally imposed on the heating time and temperature.
lS As a result of a series of experimations, the inven-tors 16 ,j have found that the temperature at which the neck section 11 17 1l is crystallized as shown in Fig. 1 without causing a thermal 18 1I deformation ranges from 120C to 180C and, preferably, 19 ll from 140C to 170C, and it is appropriate that, in the 1I foregoing temperature range, the neck section 11 is heated 21 ll for a time that is required for the entire polyethylene 22 i terephthalate resin material thereof crystallized, preferably, 23 1 for 3 - 8 minutes and, more preferably, for 3 - 5 minutes, 24 Il although the heating time varies substantially significantly 1I depending upon the thickness of the neck section 11 and 26 l its ambient temperature.
27 li The neck section 11 crystallized under the aforementioned 28 I heating conditions appear, in section, as shown in Fig. 2.
29 l~ This particular example shown in Fig. 3 was heated at 155 C
1~ for 4 minutes and 30 seconds. I

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35'~2 ,1 ~ After being heated as mentioned herein-above, 2 l¦ the neck section 11 is annealed at room temperatures at 3 ll least 30 seconds to have its density of spherulite texture 4 ~ increased over the entirety thereo~ and to be blushed and 5 l¦ crystallized into mikly white color.
6 I As a result of this processing, since not only the ? I! crazing resistance of the neck section 11 but also its 8 1I mechanical properties such as stiffness, impact resistance, 9 ll abrasion resistance and external pressure resistance are o l! considerably improved~ any screwed cap or caulkable cap ll ll such as a crown cap that is fitted onto the neck section 11 12 ,j having the thus improved mechanical strength can maintain 13 I the content of the container 10 in a hermetically sealed 14 'I state over a longer period. ¦
1 Also, in the container thus heat-relnforced by the 16 ~¦ method according to the present invention, since its neck 17 lll section 11 is blushed, lt is identlfied at a glance and 18 ll the extent of its heat reinforcement can be easily determined 19 l! depending upon the degree of blushing. I
,¦ Fig. 4 shows a container having only its neck end 11a 21 , blushed and crystalllzed. In generall, if the neck end is 22 deformed or damaged by stress cracking in fitting thereinto 23 ~11 an inner sealing seat 14 or if it is crazed by the content, 24 l, the latter may leak out of the neck end. While, if the neck i end 11a has its density of spherulite texture increased to 26 'l be blushed and crystallized, the inner sealing seat 14 can 27 ,I be held in place and securely prevent the leakage of the 28 ' content.
29 1l If a heater is placed directly above the container 10 I to heat the neck end 11a, its upper end face is heated must I~ - 10 -lij I
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I ~I strongly, but it must be hea~ed circumfÆrentially evenly.
2 ll, For this purpose, the container 10 may be held on a rotatable 3 ~ ig 28 as shown in Fig. S.
4 'll The preferred embodiment of the heating equipment of jl Fig. 5 uses a far infrared ray bar heater 27 as its heating 6 illl element. The heater 27 is disposed slightly spaced above 7 1l apart from the upper end of the container 10, and the container 1~ is placed on the base jig 28 fixed onto the upper end of 9 ~¦ a rotatable shaft 29 which is rotated at a constant speed.
lll Thus, since the container 10 is rotated relatively to the heater 27 at a constant speed, the neck end 11a is heated ¦
12 '1 evenly in the circumferential direction of the neck section 11.
13 ll Thus, the heat distribution around the neck end 11a is well 14 1 improved.
1S l! The following table compares the densities of the 16 ,I sections of polyethylene terephthalate containers obtained 17 1~ in the aforemetioned manner.
19 1~ Table Density g/cm ' I _ l Container #l Container #2 21 1 _ _ __ 22 ¦1 Neck end 1.3640 1.3582 l (blushed) _ _ 24 ,j Neck 1.3436 1.3441 l section 'I
26 ,l Cylindrical 1.3556 1~3555 27 ll section I _ _ _ i 28 1l 29 ~ Due to increased density of spherulite texture, 30 l the neck end has a larger density than those of neck and ll l ;' 5'~:2 1 ll cylindrical sections. The density of the neck end could be 2 ¦ increased up to 1.37.
I Althoug~ in -the aforementioned preferred embodiment, 4 ll the neck end is subjected to heat treatment after the 1~ blow-molding of the container, the neck end oE a preformed 6 l¦ piece constituting the primary molding of the container 7 I may be first subjected to heat treatment to be blushed and I crystallized before being subjected to a biaxial orientation-9 ~ blow molding.
ll Figs. 6A through 8B show modified preferred embodiments of the containers according to the present invention, in which 12 I the bottom section of a preformed piece is subjected to 13 , heat treatment to blush and crystallize, in advance, those 14 I sections of the container which are not biaxially oriented in the succeeding process.
16 ,l The preformed piece 15 obtained by injection or 17 ll extrusion moldlng has ~ thlck-walled and bottomed hollow 18 1¦ with a prefinished threaded neck 11. As shown in Fig. 6A, 19 ll the piece 15 has its bottom center 16 heated and annealed `I in a manner as mentioned previously and the bottom center 21 'I 16 is blushed with its partially increased density of 22 1l spherulite texture. The thus treated piece is then heated 23 ''I uniformely at 140C - 220C before being biaxially orientation- j 24 I blow molded in a mold into a hollow container.
,~ As shown in Fig. 6B, the grown spherulite texture at its 26 bottom center 13a is maintained as it was and, thus, the 27 l, bottom center can have a sufficient strength against crazing 28 ~l, and thermal deformation.
29 '~ In the preferred embodiment shown in Fig. 7A, , the cylindrical section of a preformed piece near its bottom ~ - 12 - ;

1 ll has its periphery l7 heated and annealed, and the periphery ~ 1, 17 is blushed and crystallized with an increased density 3 l~ of spheruli~e texture, Likewise~ the thus treated piece 4 i, is then biaxially orientation-blow molded into a container 1 as shown in Fig. 7B. As a result of this treatment, 6 1 a spherulite texture develops in and along the bottom 7 !I periphery 13b of the container 10 to increase its thermal 8 ~ resistance and function to prevent deformation. In Fig. 8A, 9 ll the preformed piece 15 has its section 18 from the bottom ¦ center to periphery heated and annealed so that -the section 18 11 ll is blushed. Then, the thus treated piece is biaxially 12 ll orientation-blow molded into a container 10 as shown in Fig.
13 1 8B having a developed spherulite texture in and over its 14 I entire bottom section 19 ranging from the center to the i neightboring periphery.
16 l According to the present invention, as fully described 17 I hereinbefore, those sections of a biaxially orientation-blow 18 ' molded polyester resin container such as its neck, neck end 19 li and bottom section which are not substantially oriented !l are subjected to heat treatment for improving the density 21 , of spherulite texture in such sections, so that these æ ¦I sections are protected against deformation and crazing.
23 1l Also, since the aforesaid sections having a spherulite 24 'I texture presents a milky white color which aggreably l contrasts with the transparent cylindrical section the 26 l, container may obtain a good-looking pattern according to 27 I the present invention.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for producing a hollow bottle-shaped con-tainer of biaxially oriented polyester resin comprising the steps of:
heating sections of said container, which are not sub-stantially oriented by a biaxial orientation-blow molding process, at 120 - 180°C for a period of at least 2 1/2 minutes by suitable heating means; and annealing the thus heated sections at room temperatures so as to increase the density of spherulite texture of the polymer material in said sections until such section appears milky white in color.

2. The method for producing a hollow bottle-shaped container of biaxially orientation-blow molded polyester resin according to claim 1, wherein said polyester resin comprises a polyethylene terephthalate.

3. The method according to claim 1, wherein said sections which are not substantially oriented comprise the neck section, neck end and bottom section of said container.

4. The method according to claim 1, wherein during said heating step said container is placed on a rotary jig and said neck section is subjected to heat from said heating means.

5. The method according to claim 1, wherein said heating means comprises an infrared ray bar heater.

6. A method for producing a container of biaxially oriented polyester resin comprising the steps of:
preforming the polyester resin material into a hollow thick-walled and bottomed piece;

heating the bottom section of said preformed piece at 120°C - 180°C for a period of 2 1/2 to 5 minutes by suitable heating means;
annealing the heated section at room temperatures until a spherulite structure develops in the resin material of the thus heated bottom section and appears milky white in color;
evenly preheating the entirety of said preformed piece at 140°C - 220°C;
biaxially orienting the thus preheated piece in a mold;
and releasing the thus biaxially oriented container from the mold.

7. A method for producing a container of biaxially oriented polyester resin comprising the steps of:
preforming the polyester resin material into a hollow thick-walled and bottomed piece;
evenly preheating the thus preformed piece at 140°C -220°C and then transferring the preheated preformed piece into a mold and biaxially orienting the same therein into a hollow bottle-shaped container;
heating the neck section of said hollow bottle-shaped piece at 120°C - 180°C for a period of 2 1/2 to 8 minutes by subjecting said neck section to suitable heating means; and annealing said neck section at room temperature until a spherulite texture develops in the resin material of the thus heated bottom section and appears milky white in color.

8. The method according to claim 7, wherein said container has the neck section preformed and threaded.

9. The method according to claim 7, wherein said heating means comprises an electromagnetic induction heating device, and a metal ring is fitted onto the outside of said section of the container as a heating medium.

10. The method according to claim 7, wherein said container has a shoulder section and which is covered with a shielding plate so as to minimize a thermal influence thereon from said heating means.

11. A hollow blow-molded container of biaxially oriented polyethylene telephthalate resin wherein at least one of the neck portion and bottom portion of said container is crystallized to exhibit a white color.

12. A hollow blow-molded container of biaxially oriented polyethylene telephtalate resin wherein at least one of the neck portion and bottom portion of said container is crystallized to exhibit a white color and wherein the body of the container is heat-set.