WO1996007699A1

WO1996007699A1 - High shrinkage copolymer film

Info

Publication number: WO1996007699A1
Application number: PCT/US1995/011041
Authority: WO
Inventors: Edward K. Bullock
Original assignee: Applied Extrusion Technologies, Inc.
Priority date: 1994-09-07
Filing date: 1995-08-29
Publication date: 1996-03-14
Also published as: AU3462195A; CA2199465A1; BR9508998A; EP0779911A1; MX9701781A; NZ292443A

Abstract

A biaxially oriented polymer shrink film having a machine direction (MD) shrinkage of greater than a transverse direction (TD) shrinkage such that TD is less than or equal to MD/2 in the range of 100 °C to 140 °C. The film comprises at least one of the following: (a) a polyolefin copolymer; (b) a polyolefin terpolymer; (c) blends of polyolefin copolymers and homopolymers; (d) blends of polyelefin copolymers and terpolymers; (e) blends of polyolefin terpolymers and homopolymers; and (f) blends of polyolefin copolymers, homopolymers and terpolymers; wherein the copolymer comprises a first and second monomer. The first monomer is selected from the group consisting of ethylene, propylene, butylene and mixtures thereof; and the second monomer is selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof. The first monomer is present in the range of 99.5 % to 75 % by weight and the second monomer is present in the range of 0.5 % to 25 % by weight. The terpolymer comprises: (i) a primary monomer of ethylene, propylene, butylene and mixtures thereof; (ii) a secondary monomer of alpha olefin monomers having two to ten carbon atoms and mixtures thereof; and (iii) a tertiary monomer of alpha olefin monomers having two to ten carbon atoms and mixtures thereof, wherein the primary monomer is present in the range of 50 % to 99 % by weight and the secondary and tertiary monomers are present in the range of 0.5 % to 49.5 % by weight. The homopolymer is polyethylene, polypropylene and polybutylene.

Description

HIGH SHRINKAGE COPOLYMER FILM

SPECIFICATION BACKGROUND OF THE INVENTION

The present invention is directed to shrink films having high unidirectional shrinkage in the machine direction (MD) compared to the transverse direction (TD) . The invention is also directed to processes for producing such shrink films, processes for using shrink films to produce laminates and resultant laminates of such shrink films. The invention also includes processes for using such shrink films and laminates to package and/or label articles, and resultant articles to which such shrink film or laminates of such shrink film are applied. More specifically the present invention is directed to the previously mentioned embodiments with respect to utilizing oriented polymer films, i.e., oriented polypropylene (OPP) films, having a varying polymer content, to produce polyolefin shrink films and laminates having high unidirectional shrinkage, which is particularly advantageous in labeling articles, such as beverage containers, which may have an irregular shape.

A unique feature of a shrink film is its capacity, upon exposure to heat, to shrink or, if restrained, to create shrink tension within the film. When such a shrink film is used in a process to label or wrap a container, and then it is subjected to a heat history, this process causes the film to shrink around the product, producing a tight, transparent or opaque, wrapping that conforms to the contour of the article and provides useful functions required of label or packaging materials.

The ability of a film to shrink upon exposure to some level of heat arises from the orientation of the film during manufacture. During film manufacture, the films are usually heated to their orientation temperature range, which varies with the different polymers used for the films, but is usually above room temperature and below the melting temperature of the polymer. The film is then stretched in the cross or transverse direction (TD) and in the longitudinal or machine direction (MD) to orient it. After being stretched, the film is rapidly cooled to quench it, thus freezing the film in its oriented state. Upon heating, the orientation stresses are relaxed and the film will begin to shrink back to its original, unoriented dimension.

The polyvinyl chloride (PVC) , polystyrene, polyester, and polyolefin families of shrink films provide a wide range of physical and performance film characteristics. Film characteristics play an important role in the selection of a particular film and may differ for each type of packaging or labeling applications.

Polyolefins have been most successful with applications where moderate to high shrink forces are preferred. Polyolefin films are also used on automatic, high speed shrink wrapping equipment where shrink and sealing temperature ranges are more clearly controlled. Polyolefin films are particularly suitable for those types of applications because polyolefin films tend to be cleaner, leaving fewer deposits and less residue, which extend the life of the equipment, as well as reducing equipment maintenance. The PVC films generally have lower shrink forces, and will seal and shrink over much broader temperature ranges than the polyolefins. A drawback to PVC films however, is their tendency to emit noxious gases upon heat sealing and upon combusting during incineration, resulting in corroded machinery, as well as a health hazard.

Currently, polyolefin shrinkable films are produced in accordance with the present invention by a secondary MD orientation of a biaxially oriented film to increase the MD shrinkage. The amount of MD shrinkage is defined by the extent of MD orientation.

Polyolefin shrink films having a higher shrinkage in the machine direction than in the transverse direction are disclosed or suggested in the prior art.

In Peiffer et al.. United States Patent No. 5,292,561, both single and multiple layer plastic films are disclosed, which have a higher shrinkage capacity in the machine direction than in the transverse direction. In the single layer product, the film is 60-95% polypropylene, with the remainder being a hydrogenated hydrocarbon. In the multilayer form of the product, the core is of the same composition as the single layer product; namely, 60-95% polypropylene, with the remainder being hydrogenated hydrocarbon. Also, in the multilayer form of the invention, the outer laverfs) can be an ethylene-propylene copolymer with a preferred ethylene content in the range of 2% to 10% by weight, and most preferably about 3% to about 6% by weight. There is absolutely no disclosure of forming the core layer of the multilayer film or the single layer in the single layer film of the aforementioned ethylene-propylene copolymer.

Japanese Kokoku No. 63[1988]-62,390 discloses a shrinkable film wherein the core is a physical blend of a propylene-ethylene copolymer (ethylene content 4.5% by weight) and a butene-ethylene copolymer (ethylene content 3% by weight) . This polymer blend constitutes the core layer disclosed in Example 1 of the Japanese publication. It should be noted that although the publication generally states that the shrinkage in either the MD or TD direction can be the greatest, there is neither a specific disclosure of any biaxially oriented film having a higher orientation (i.e., greater shrinkage) in the MD direction than in the TD direction, nor is there any method disclosed for forming such a product. Thus, the sole teaching in the Japanese '390 publication is with respect to the formation of conventional prior art shrinkable films having a higher TD shrinkage capacity than MD shrinkage capacity.

Japanese Publication No. 89005545, like the aforementioned Japanese '390 publication, only generally states that the heat shrink capacity in the transverse or longitudinal direction is more than twice that of the other direction. However, the only specific teaching in the '545 publication is with respect to the formation of conventional biaxially oriented film having a higher TD shrinkage than MD shrinkage.

European Publication No. 0 498 249, which was published on August 12, 1992, corresponding to United States Application Serial No. 08/144,629, the entire disclosure of which is incorporated by reference herein, and which is assigned to the same assignee as the present invention, generally describes a single or multilayer biaxially oriented polyolefin film with the predominant orientation in the MD direction and having an MD shrinkage capacity of 4% to 40% in the temperature range of 100*C to 140'C, and a TD shrinkage capacity in the range of -15% to 15% between 100*C and 140*C. In accordance with this publication, the most preferred film is formed of a polypropylene homopoly er. Although the European ^,249 publication does generally state that copolymers of polypropylene with minor amounts of ethylene or an alpha olefin and the respective blends can also be used, there is no disclosure of specific copolymer compositions with percentage ranges of the components thereof.

The European '249 publication also discloses various processes for making biaxially oriented polymer shrink films. These processes involve subjecting a biaxially oriented polymer film to processing conditions and temperatures effective to produce biaxially oriented polymer shrink films having thermal shrink properties including shrinkage in the machine direction of the film and transverse direction of the film, as a function of the MD reorientation mechanical MD/TD draw ratio. The invention disclosed in the European '249 publication also is directed to processes for making biaxially oriented polymer shrink films which involve subjecting a biaxially oriented polymer film to processing conditions and temperatures effective to produce biaxially oriented polymer shrink films having thermal shrink properties including shrinkage in the machine direction of the film and transverse direction of the film as a function of temperature.

It is important that shrink film must manifest a resistance to MD directional alteration in dimension during typical label preparation and application to maintain uniform repeat length and registration as imparted by applied heat/or tension history.

The film must also be resistant to MD and/or TD directional label curl to maintain uniform label flatness in such applications. The film should maintain overall web flatness, as exhibited by typical oriented polyolefin films, as well as single web or lamination stiffness as required for conventional printing, laminating, and labeling operations. Heretofore, these features having been lacking in prior art films.

The invention of the European '249 publication is based on the discovery of temperature, machine draw parameters and film parameters that allow for control of resultant shrink of a polymer film. More particularly, by achieving a balance of temperature, draw ratio, line speed and oriented film properties, the process of that invention is able to produce enhanced machine direction (MD) shrinkage with a very low degree of transverse direction (TD) shrinkage. That balancing of MD and TD shrinkage, particularly in oriented polypropylene (OPP) films, imparts unique shrink label and packaging characteristics of that invention.

Hercules, Incorporated, prior to the invention described and claimed herein, did sell opaque, biaxially oriented polyolefin films having a higher MD shrinkage capacity than TD shrinkage capacity. These films were sold under the designations VISION* 370W and VISION* 370HW, respectively. Both of these latter products included multilayers, with the core layer including a polypropylene homopoly er and a propylene- ethylene copolymer (ethylene content 2.2%) . Again, prior to the instant invention, the composition of the core of each of these products was changed to a 100% propylene-ethylene copolymer (ethylene content 0.6%). Although this product has achieved some commercial success, it has been determined that the transverse direction expansion is more than is desirable for the primary intended application of the film, i.e., for use in forming labels on metal cans and other containers.

It is highly desirable however, to be able to achieve better control over the transverse direction shrinkage characteristics by the selection of the components of the film, rather than by manipulation of the manufacturing process discussed previously in connection with the European '249 publication. These results are achieved by the present invention. OBJECTS OF THE INVENTION

Accordingly, it is a general object of this invention to provide a high shrinkage film and method of producing the film which overcome the disadvantages of the prior art.

It is a further object of this invention to provide a film and method of producing the film which is a polyolefinic copolymer with variable ethylene content or a blend of polyolefinic homopolymers and/or copolymers and/or terpolymers to produce a film with higher shrinkage with lower levels of MD orientation.

It is yet another object of this invention to provide a film and method of producing the film at lower mechanical MD orientation to provide for higher shrinkages with better web flatness.

SUMMARY OF THE INVENTION

These and other objects of this invention are achieved by providing shrink films that are biaxially oriented single layer or multiple layer polymer films having a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2, most preferably in the temperature range of 100*C to 140^*C. The film consists of single layer films or multilayer films. The multilayer films include a core layer and one or more outer layers. The single layer of the single layer film and the core layer of the multilayer film comprise a polymer composition comprised of at least one of the following:

(a) a polyolefin copolymer;

(b) a polyolefin terpolymer;

(c) physical blends of polyolefin copolymers and polyolefin homopolymers;

(d) physical blends of polyolefin copolymers and polyolefin terpolymers;

(e) physical blends of polyolefin terpolymers and polyolefin homopolymers; and

(f) physical blends of polyolefin copolymers, polyolefin homopolymers and polyolefin terpolymers; wherein the copolymer is comprised of a first and second monomer:

(i) the first monomer being selected from the group consisting of ethylene, propylene, butylene and mixtures thereof; and

(ii) the second monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof; wherein the first monomer is present in the copolymer in an amount in the range of 99.5% to 75% by weight and the second monomer is present in the copolymer in an amount in the range of 0.5% to 25% by weight in either a random or non-random sequence within the copolymer; wherein the terpolymer is comprised of a primary, secondary and tertiary monomer:

(i) the primary monomer being selected from the group consisting of ethylene, propylene, butylene and mixtures thereof;

(ii) the secondary monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof; and

(iii) the tertiary monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof, wherein the primary monomer is present in the terpolymer in an amount in the range of 50% to 99% by weight and the secondary and tertiary monomers are present in the terpolymer in an amount in the range of 0.5% to 49.5% by weight; wherein the homopolymer is selected from the group consisting of polyethylene, polypropylene and polybutylene; and wherein the MD and TD shrinkage capacities are as follows:

MD TD

TEMP. SHRINKAGE CAPACITY SHRINKAGE CAPACITY

100'C > 5% > -10%

120^*C > 10% > -12%

140"C > 15% > -10%. In another embodiment of the invention, the defined shrinkage capacity occurs within the range of 100^*C to 120^*C. In yet another embodiment of the invention, the defined shrinkage capacity occurs at 120"C.

In the preferred embodiment of this invention the polyolefin copolymers are from the group consisting of linear low density polyethylene copolymers including a monomer from the class consisting of butylene, hexene and octane, said monomer being present in an amount from between 0.5% and 49.5%; propylene/ ethylene copolymers; propylene/butylene; and butylene/ethylene copolymers.

In the preferred embodiment of this invention the polyolefin homopolymers are selected from the group consisting of low density polyethylene having a density in the range of 0.910 to 0.930 gms/cm³ (measured at 23°C according to ASTM D1505, as are all density measurements discussed herein), high density polyethylene having a density in the range of 0.931 to 0.960 gms/cm³, isotactic polypropylenes with heptane insolubles greater than 90% and greater than 0.5 g/10 min. MFR (MFR = melt flow rate, according to ASTM D1238 at 230*C and 2.16 kilograms) , and poly-1-butene.

In the preferred embodiment of this invention the polymer composition comprises a primary polymer from the group consisting of:

(a) polyolefin copolymers; and

(b) physical blends of polyolefin copolymers and polyolefin homopolymers; and wherein the polyolefin copolymers are propylene copolymers with a co-monomer selected from the group consisting of alpha olefins with two to ten carbon atoms, said co-monomer being present in the range of 0.5% to 25% by weight; and wherein the homopolymers are selected from the group consisting of polyethylene, polypropylene, and polybutylene homopolymers.

Most preferably the polymer composition utilized in this invention comprises primarily polyolefin copolymers selected from the group consisting of: (a) propylene copolymers having a co-monomer selected from the group consisting of alpha olefins with two to ten carbon atoms, said co-monomer being present in the range of 0.5% to 25% by weight; and (b) a blend of polypropylene and a propylene/ethylene copolymer in which the ethylene is present in the range of 0.5% to 25% by weight.

In accordance with the invention described and claimed herein reference to "polyolefin homopolymers", in addition to including polyolefin polymers of a single monomer only, also includes polyolefin copolymers with less than 0.5% of a co- monomer therein.

DESCRIPTION OF THE DRAWINGS

Other objects and many attendant features of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 shows a schematic illustration showing a sequential blown film process for making shrink film;

Fig. 2 shows a schematic illustration showing a sequential tenter film process for making shrink film;

Fig. 3 is a schematic illustration showing an out-of- line process for making shrink film; and

Fig. 4 is a schematic illustration showing a process for making shrink film laminates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The basic processes for producing polymer films for use in accordance with the present invention to make the novel polymer shrink films may be selected from the group of conventional processes such as the tubular and tenter techniques as described in ASN 08/144,629, the entire disclosure of which is incorporated by reference herein.

MD re-orientation involves placing a conventional biaxially oriented polymer film on a series of heated rolls or in an oven, and by keeping the temperature of the heated rolls or oven below the melting temperature of the film, the stress necessary to orient the film is reduced. For example, polypropylene begins to shrink near 100° Centigrade (C) and shrinkage continues to increase until melting at greater than about 160'C. The MD re-orientation can take place after the biaxially oriented film is produced, or in some cases, the MD re-orientation can take place in a continuous process, while the biaxially oriented film is produced. Most polymer films respond to this MD orientation with an enhanced high temperature shrinkage. The majority of the films' response is in the direction of the imposed strain.

The basic processes for producing polymer films for use in accordance with the present invention to make the novel polymer shrink films may be selected from the group of conventional processes for producing biaxially oriented polymer films, such as the tubular and tenter techniques.

In general, in the tubular or bubble process, molten polymer is extruded from an annular die and then quenched to form a tube. The wall thickness of the tube is controlled partly by the annular die gap and partly by the relative speeds of extrusion and haul-off. The tube passes through slow running nip rolls and is then re-heated to a uniform temperature. Transverse drawing is achieved by increasing the air pressure in the tube, the draw ratio, and/or by adjustments to the volume of entrapped air. The air is trapped by pinch rolls at the end of the bubble remote from the extruder and these are generally run at a faster speed than the first pair, thus causing drawing of the film in the machine direction. The tubular process thus obtains simultaneous transverse (TD) and machine direction (MD) orientation.

In the tenter process, the polymer is extruded through a slot die and quenched. The extruded sheet is normally oriented in two sequential steps. The first step is usually longitudinal or MD orientation between rolls running at different speeds. In the second stage, the film enters a tenter frame, which it is stretched laterally or TD by means of diverging chains of clips. Whereas the bubble process operates at constant pressure, the tenter frame process operates at constant rate of elongation. Somewhat higher stretching forces are required in the second stage which may be carried out at slightly higher temperatures. This is mainly due to crystallization of the film during the first stretching operation. The tenter frame process can also be carried out as a simultaneous operation in which an extruded sheet with beaded edges is biaxially oriented in a tenter frame equipped with a wide diverging roller grips for holding and stretching the film.

The tenter operation has the advantage of considerable versatility, producing films with a wide range of shrink properties.

After stretching, polymer orientation is locked into the film by cooling. When the oriented film is subsequently heated up to temperatures in the vicinity of the stretching temperature, the frσzen-in stresses become active and the film shrinks. Strains and stresses which are related to the degree of orientation and the forces which are applied during stretching are thereby recovered.

For purposes of the present invention, the biaxially oriented polyolefin MD shrink films may be a clear, opaque or metalized film.

The biaxially oriented polyolefin MD shrink films may be monolayer films, multilayer films, coextruded films, extrusion coated films or coated films.

The biaxially oriented polyolefin MD shrink films may also contain additives or coatings which reduce the coefficient of friction between two films surfaces or between the film surface and another object such as might be a part of packaging or labeling equipment or may be a part of a container handling line with containers labeled with films of this invention.

The biaxially oriented polyolefin MD shrink films may consist of outer layers which allow the ability to be heat sealed to form an adhesive bond to a second heat sealable film or to be heat sealed to another surface such as a container. The outer heat seal layers may be an inherent part of the film such as achieved by co-extrusion or may be an added layer after the initial film forming processing such as can be achieved by extrusion coating or other standard solution coating techniques standard the film industry. The biaxially oriented polyolefin MD shrink films may contain other oriented film additives such as anti-blocking agents, lubricants, anti-stats, antioxidants, and antacids, and opacifiers, whiteners, and colorants.

The biaxially oriented polyolefin shrink films may be treated by corona, flame or other surface treatment techniques well known to the oriented film industry and contain additives or coatings or coextruded layers to increase the surface functionality which will improve the surface adhesion to other requirements of the film surface such as printing, lamination adhesion, label adhesion, and metalization.

The biaxially oriented polyolefin MD shrink films should preferably have a total thickness between 40 to 250 gauge, and more preferably in the range between 70 to 140 gauge.

The biaxially oriented polyolefin MD shrink films may be used as labels or other forms of packaging. They may be used as single layers of film or may be used as lamination of films with two or more shrink films or with at least one shrink film and one or more non-shrink films. Polymer Description

For purposes of the present invention, the polymer composition or the core layer composition, of multilayer films, of the biaxially oriented MD shrink films consists primarily of polyolefin copolymers, terpolymers or physical blends of polyolefin copolymers and/or terpolymers, or physical blends of polyolefin copolymers or terpolymers with polyolefin homopolymers. For purposes of the present invention, a physical blend of polymers does not require a chemical reaction between the polymers, but is achieved by mechanical mixing.

The polyolefin copolymers of this invention may be selected from copolymers which are composed of ethylene, propylene, or butylene as the primary component and are composed of other alpha olefin monomers with two to ten carbon atoms. The co-monomer alpha olefin may be present in a range of 0.5% to 25% by weight and may exist in a random or non-random sequence within the copolymer composition. These include, but are not limited to, linear low density polyethylene copolymers which are typically composed of ethylene with lesser amounts of butylene, hexene, or octane as the co-monomer; propylene/ethylene copolymers; propylene/butylene copolymers; and butylene/ethylene copolymers. For purposes of the present invention, polyolefin copolymers with less than 0.5% by weight of a co-monomer are classified as a homopolymer of the predominant component.

The polyolefin terpolymers of this invention can be selected from terpolymers which are composed of ethylene, propylene, or butylene, as the primary component and may be composed of secondary and tertiary monomers of other alpha olefins with two to ten carbon atoms. The composition of the primary monomer may be from 50% to 99% by weight with the composition of the secondary and tertiary monomers between 0.5% to 49.5% by weight.

The homopolymers of this invention can be selected from polyethylene, polypropylene, or polybutylene polymers. Polyethylene homopolymers which generally are designated as low density polyethylenes (density = 0.910 to 0.930), and high density polyethylenes. Polypropylenes are generally from the group of isotactic polypropylenes with heptane insoluble content of greater than 90% and greater than 0.5 g/10 min. MFR. The polybutylene homopolymer is generally poly-1-butene. Polyolefin copolymers with less than 0.5% of a co-monomer, for purposes of this invention, are considered homopolymers, and are classified as a homopolymer of the predominant component. Polymer Description

The preferred polymer composition of this invention is composed primarily of polyolefin copolymers or blends of polyolefin copolymers and homopolymers where the copolymers are selected from the group of propylene copolymers with the co- monomer selected from the group of alpha olefins with two to ten carbon atoms, where the co-monomer is present at a composition of 0.5% to 25% by weight and the homopolymers are selected from polyethylene, polypropylene, or polybutylene homopolymers.

The most preferred polymer composition of this invention is composed primarily of polyolefin copolymers where the copolymers are selected from the group of propylene copolymers with the co-monomer selected from the group of alpha olefins with two to ten carbon atoms, where the co-monomer is present at a composition of 0.5% to 25% or is composed primarily of a blend of polypropylene and a propylene/ethylene copolymer where the ethylene is present at a composition of 0.5% to 25%.

Shrink Rang?

The MD and TD shrinkage capacities of the films of the present invention are as follows:

TEMp M£ IE

100*C: > 5% > -10%

120*C: > 10% > -12%

140'C: > 15% > -10%

The films of the present that are biaxially oriented single layer or multiple layer polymer films having a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 at 120*C.

In a more preferable embodiment, the film of the present invention has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 throughout the temperature range of 100"C to 120"C.

In the most preferable embodiment, the film of the present invention has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 throughout the temperature range of 100^βC to 140*C.

The shrink films of this invention can also exhibit a variety of surface behavior or characteristics common to typical biaxially oriented packaging films as is known to the art.

The character of a polymer surface can be changed in several ways. One method is to expose the surface to an energy source, such as a corona discharge, flame, plasma, or an x-ray or electron bombardment. This can be done over a broad temperature range in an inert atmosphere or reactive atmosphere. Depending on the temperature, intensity, rate of application and frequency of the energy and the nature and concentration of the chemical medium in contact with the surface before, during, and/or after energy application, a wide range of physical and/or chemical modifications of the film surface can be effected.

A second way to change a polymer surface is to cause an internal chemical additive to bloom to the surface by the application or removal of heat from the film. Alternatively, a substance on the surface of the film can be made to migrate inside of the film and away from the surface by the application or removal of heat from the film. The chemical nature of the substance or additive and the time/temperature history to which it is exposed can lead to a wide range of possible surface modifications.

A third way to change a polymer surface is to cause a change in surface morphology by the application of heat and/or pressure to the film. The physical and topological nature of the surface can be altered, for example, by annealing a film and changing the crystalline structure present on the film surface.

The MD re-orientation of biaxially oriented polymer films is more complex than for conventional films due at least in part to initial residual stresses placed on the film.

In prior art procedures, polymer strapping, fibers and film can be drawn or tensilized to re-orient the structure to produce properties different from the original product.

Measurement of Unrestrained Linear Shrinkage

In the present invention, the following procedure, derived from ASTM method D2732-83, which is designed to measure unrestrained linear shrinkage in both the machine and transverse directions, was used for measuring unrestrained linear thermal film shrinkage in a single direction at a time.

A polydimethylsiloxane fluid (0.5 cs) bath is first preheated to desired temperatures within the range of about 100'C to 140'C.

Film samples are precut to 0.5 inches by 22 centimeters (cm) and a 20 cm span is marked in the sample center. Ends are left on a sample so that the sample can be anchored for immersion. One end of at least three films of each sample is placed in an immersion rack. A 1.2 gram metal alligator clip is attached to the free long end of each film strip to keep the film from floating in the bath. The machine direction and the transverse direction are tested for each film. The heater/stirrer is then turned off and the samples on the rack are immersed into the proper temperature bath for five seconds prior to being removed from the liquid. The samples are measured and their percent shrinkage calculated. For example, with a 20 centimeter sample length, a shrinkage of 1 millimeter equals 0.5% shrinkage. The average percent shrinkage of all the samples run in one direction (MD or TD) is then recorded for a particular film sample. If there is an elongation rather than a shrinkage, a negative value is reported.

The unique thermal shrink properties, combined with the orientation/tensile properties of the novel polymer shrink films of the present invention allow for the useful practice of using conventional labeling equipment of the novel films of the present invention.

The tensile strength, elongation and modulus were measured using the ASTM D882 test procedure.

The processes of the present invention for producing shrink film and resultant shrink film layers and laminates, as described herein, are polymer-based polyolefin films. In this regard, the polyolefin character of the film is preferably a copolymer of propylene with ethylene or other alpha olefin co- monomers. Ethylene or butene copolymers, with an alpha olefin co-mononer from C₂ to C₁₀ or propylene, ethylene or butene copolymers as blends with other polyolefin homopolymers or copolymers, can be used.

Typical commercially available film-forming propylene homopolymers are crystalline or isotactic in their molecular structure and normally have a melt flow rate of about 0.5 to 10 dg/min. Conventionally, the polyolefins are compounded with conventional additives such as anti-oxidants, light stabilizers, inorganic antacids, such as calcium oxide or magnesium aluminum hydroxide carbonate hydrate in addition to fatty acid amide slip agents and antiblock particulates common to packaging film technology.

In accordance with the present invention, the novel polymer shrink films of the present invention can be used as a single web or formed into a laminate, with use as a laminate being particularly beneficial.

For purposes of the present invention, any conventional lamination process may be used inasmuch as the novel polymer shrink film of the present invention has been observed to be capable of being suitably laminated using known technology, e.g., selected from the group consisting of wet bonding, dry bonding, hot melt or wax laminating, extrusion lamination, and thermal or heat laminating; however, dry bonding and thermal or heat laminating are preferred.

Dry bonding involves applying adhesive to one of the films or webs. The solvent is evaporated from the adhesive and the adhesive-coated web is combined with the other web material by heat and pressure or by pressure only.

Thermal laminating brings together coated substrates under heat and pressure. Typically, the webs are heated to the softening point of the coating; however, improved results, e.g., in clarity are obtained when using preheat rolls and a steam box.

Related to this, labels are normally printed and the printing is expected to be permanent. If the exposed printed surface is abraded, then the printing can be removed or scuffed. If, however, the printing is on the inside surface of a clear film and this clear film is laminated to another film, the printing is protected by the clear film. Alternatively, the printing can be on the inside surface of the clear or opaque web which is then laminated to the clear protective overweb. In addition, the outermost surface of the laminate can be made matte, glossy, of low coefficient of friction, different in surface functionality or composition, independent from the nature of the surface required to accept inks. Printing can also be applied to a clear film layer and either a clear or opaque film, or a metallized version of either type of film, can be laminated to the printed web.

For purposes of the present invention, the novel polymer shrink films may be printed using conventional printing techniques including flexographic printing and rotogravure printing.

Flexographic printing procedures typically employ presses selected from the group consisting of stack, central- impression, and in-line presses. Flexographic printing which employs a central impression or common impression plate is preferred.

The process of using the novel polymer shrink films of the present invention to produce laminates which are applied to an article in accordance with the present invention has been discovered to overcome the previously mentioned disadvantages. Also, shrinkable films with different shrinkage properties can be laminated to a common printed shrinkable film to give laminates with different shrinkage properties tailored to the particular container or the requirements of the application. In addition, shrinkable films of different shrinkage properties can also be laminated together to give a laminate whose shrinkage properties might be difficult to achieve using only a single film.

Related to the embodiment of the present invention which can employ film laminates, the heat shrinkable laminations may be composed of two or more polymer shrink films or heat shrinkable films. Each polymer shrink film or web may function on its own as a heat shrinkable label or each film may be clear or opaque, metallized or non-metallized, have similar or dissimilar surface character and shrinkage properties.

The process according to the present invention may be further appreciated by reference to the following examples, which are of course, only representative of the present invention and in no way are meant to limit the present invention in any way to the particulars which are disclosed. Thus, the following are given merely as non-limiting examples to further explain the present invention. Sequential Blown Film Process

The manufacturing apparatus used in the sequential blown film process as shown in Fig. 1 consists of an extruding system 1, a tubular die 2, a water bath quench system 3, a nip roll assembly 4, reheating oven 5, a single stage bubble blowing section 6 (where MD and TD draw occur) , a convergence section 7, including convergence rolls 7a, 7b and 7c, and draw rolls 8, a heating oven 9 for altering shrinkage properties, draw rolls 10 and a mill roll winder 11.

The extrusion system 1 consists of an extruder with output capabilities of 400 lb/hr. The terminal end of the extruder has an annular die 2 which forms the melted polymer into a hollow polymer tube (six inches in diameter) .

After the polymer tube has been extruded, it is quenched in a temperature controlled water bath 3. The tube continues through a nip 4 and into ovens 5 where the polymer tube is reheated. At this point, the tube is blown into a thin- walled bubble 5. The controlled internal pressure in the polymer tube causes the hot tube to expand, drawing the film in the TD direction. A fast nip (with speed SI) draw rolls 8, located after a multi-roll 7 v-shaped convergence section 7, causes the bubble to be drawn in the MD simultaneous with TD draw. The drawn film of width (Wl) passes through a heating oven 9. The width is allowed to contract at the end of the oven (to W2) , resulting in altered TD shrink properties. The film is pulled through the heating oven by a nip of draw rolls 10, located at the end of the oven. The speed at which the nip pulls the film through the oven is represented by S2. By controlling speeds SI and S2, the MD shrinkage properties are altered. S2 speed can be greater than, equal to, or less than SI depending upon the final shrink properties desired. The film is then wound onto a roll using a mill roll winder 11. In the present invention, the standard tubular process would not be necessary but may be used. In addition, in the present invention, the heatsetting step in the starting tower film is not necessary, but may be utilized. Sequential Tenter Film Process

The manufacturing apparatus used for purposes of the present invention is illustrated schematically in Fig. 2. It is composed of four extruders in an extruder and die section 21, a one/two stage MD draw section 22, a tenter oven 23, a post MD stretch unit 24 and a mill roll winder 25.

The extrusion system 21 is composed of one main extruder (60 kg/hr maximum output) and three satellite extruders (two with 12 kg/hr maximum output and one with a 6 kg/hr maximum output) (not shown) .

The casting unit of one of the one/two stage MD draw section 22 is composed of an air knife (not shown) , a chrome casting roll 26, a water bath (not shown) , and a dewatering air knife (not shown) . The melt is laid on a chill roll (not shown) , which brings one side of the casting into contact with a cold mirror chrome surface. Seconds later, the other side of the casting is introduced to the water bath. The casting drum or roll 26 is oil heated and cooled, allowing for rapid temperature change.

The forward draw unit 27 of the MD draw section 22 allows the film to travel around a dancer roll (not shown) , six preheated rolls (not shown) , around six draw rolls (not shown) , four anneal (fast) rolls (not shown) , and an exit dancer roll (not shown) . By using circulating oil, all of the rolls are capable of heating and cooling.

The tenter oven 23 consists of six sections (not shown) . Each section has a separate temperature control (not shown) and a fan (not shown) for air flow control. The oven has electrically heated air with a variable temperature range of 50*C to 250*C in any section. The maximum draw for any single section using a standard uniax width is seven times. By using two orientation sections, the tenter is capable of a ten times maximum TD draw. The oven is equipped with clip cooling, that enables draw at temperatures of over 200'C.

The tensilizer is an in-line post MD draw unit 24, which takes film directly from the tenter oven. The MD tensilizer consists of nine mirror chrome preheat rolls (not shown) , one or two stage draw (not shown) , and four chrome fast (anneal) rolls (not shown) . The unit uses 180 degree wraps on the nine preheat rolls (not shown) to reduce slippage. The rolls are mounted alternately on two separate frames. The preheat rolls temperature is controlled in adjoining pairs. Infrared heating is an option at the point of draw.

Out Of Line Process

The manufacturing apparatus shown in Fig. 3 consists of an unwind stand 31, 15 driven film rolls 32 (each with a variable speed and heating control) , including a driven chill roll, and a winding stand 33. Biaxially oriented film to be converted into shrinkable film is loaded into the unwind stand 31. This film can be produced by any process; however, biaxially oriented films made by a tentering or a bubble process are generally used. This film can be clear or opaque and single layer or multilayer. The film is usually in the thickness range of 50 to 200 gauge, most preferably 60 to 140 nominal gauge.

After unwinding, the film passes from a feed section (three powered rollers - i.e., nos. 1-3), into a preheat section. This section of three powered rollers, i.e., nos. 4-6, contains two large diameter preheated rolls with a 180 degree wrap of film, to raise the incoming film to proper operating temperature. The film is then passed through a draw zone of five driven rolls, i.e., nos. 7-11, followed by a corona treatment zone with two drive ceramic rolls, i.e., nos. 12 and 13, then over a large diameter chill roll no. 14 which reduces the film temperature before windup, and finally, through an output nip (no. 15) before windup.

Driven roll speeds are increased from unwind to windup enabling the film to be drawn or tensilized in the machine or longitudinal direction. The roll speed of roll no. 1 at the entrance to the feed zone is nominally 800 feet/minute. Roll speed at the chill roll no. 14 varies from 100 to 1500 feet/minute, depending on the amount of draw desired to be imparted to the film. The mean operating temperature of the process is usually between 90*C to 150"C with the chill roll temperature ranging from 60*F to 90*F. As used herein, "roll speeds" are the machine speeds that are measured using a tachometer, wherein "SI" is input roll speed measured in feet/minute; and "S2" is output roll speed measured in feet/minute.

"Film speeds" are the actual surface film speeds as measured by a tachometer, wherein "Fl" is the input film speed measured in feet/minute; and "F2" is the output film speed measured in feet/minute. "Tl" is defined as input film thickness and "Wl" is input film width. "T2" is output film thickness and "W2" is output film width.

As used herein:

Run Speed Ratio is RS = S2/S1

Film Draw Ratio is RD = Tl x Wl/(T2 x W2)

MD Mechanical Draw is the ratio of output roll speed to input roll speed.

For purposes of the present invention, the input roll speed (SI) has a preferred range of 200 to 1500 ft./min. with a more preferred range of 750 to 850 ft./min. with a most preferred range of 800 ft./min.

The output roll speed (S2) has a preferred range of 201 to 1501 ft./min. with a more preferred range of 1050 to 1400 ft./min. and with a most preferred range of 1100 to 1300 ft./min. RD is calculated at a preferred range of 1.01 to 1.5 with a more preferred range of 1.1 to 1.34 and a most preferred range of 1.25 to 1.4. The preferred temperature range for imparting the desired shrink properties is 70*C to 160*C with a more preferred range of 90"C to 130"C and a most preferred range of 100'C to 120'C.

The preferred method of and means for heating the film may be by use of heated rolls, a hot air oven or an infrared oven. The more preferred method of heating the film is by the use of heated rolls and infrared ovens, with the most preferred method being heated rolls. The preferred number of draw gaps is between 1 and 12 with the more preferred number being between 1 and 6.

The film thickness at SI has a preferred range of 40 to 200 gauge with a more preferred gauge in clear film within the range of 60 to 110 gauge and in opaque film within the range of 90 to 140 gauge. The most preferred gauge in clear film is within the range of 70 to 90 gauge and within the range of 120 to 140 gauge in opaque film.

The type of film anchorage during draw includes electrostatic pinning and nip rolls with both types being preferred. The film tension during draw has a preferred range of 2000 psi to 10,000 psi.

Laminations Of Shrink Label Films

Fig. 4 schematically illustrates a film lamination process wherein a film lamination is prepared by coating one side of one roll of film 31 with an adhesive solution 42, evaporating the solvent in an oven 43, then bringing the coated side into contact with another roll of film 44 in a combining nip 45. The resulting roll of shrinkable label film lamination 46 is then wound up.

A 20 inch wide roll 41 of film is mounted in the primary unwind stand of a Faustel printer-coater-laminator. This film can be either clear or opaque shrink film.

A thermosetting urethane adhesive, Morton Adcoat 333, is diluted with methyl ethyl ketone until a #2 Zahn cup viscosity of 17.5 is achieved. This adhesive solution 42 is placed into a reservoir 47 in contact with a 130 quad pattern gravure cylinder 48, chosen to deliver an adhesive coating weight of 0.7 to 1.5 lb/ream to the film at 2000 ft/. in.

One side of the shrinkable label film is coated with the adhesive by direct gravure coating. If the film is caused to be opaque by containing voids, it is preferred that the side to be coated with adhesive consist of a thin, non-voided skin.

Solvent is evaporated from the film coated with adhesive in a drying tunnel 43 maintained at 170"C to 180*C during a 3.5 second residence period. The tension in this film web is maintained at 0.75 lb/linear inch.

A second roll 44 of 20 inch wide shrinkable label film is mounted in a secondary unwind stand. It can be either a clear or opaque, coated or metallized shrinkable label film. The tension of this film web is maintained at from about 1 to 1.25 lb./linear inch.

The coated surface of the primary film is then brought in contact with one side of the second shrinkable label film roll under pressure in a combining nip 45. If the second film is caused to be opaque by containing voids, it is preferred that the side to be brought in contact with the adhesive coated side consist of a thin, non-voided skin. The resulting laminated roll 46 is wound up on a winding stand.

The novel shrink films of the preset invention have been discovered to be particularly advantageous in labeling articles having irregular shapes. For purposes of the present invention, the article may be straight-walled or contoured aluminum, steel, metal, plastic, glass, composite, or a tubular or spiral wound cardboard container (especially a can or tin) for beverages, especially soda and beer, foods or aerosols.

Either a single layer or laminate layers of novel polymer shrink films in accordance with the present invention are capable of being heat shrunk onto an article, such as a beverage can, the upper and bottom parts of which are tapered inwardly. The novel shrink films and laminates of novel shrink films of the present invention are particularly advantageous in labeling more modern beverage cans which taper inwardly at the upper and lower extremities so that a label must either avoid extending to these extremities or must conform closely to the shapes thereof; for example, in accordance with the procedures disclosed in U.S. Patent No. 4,844,957, the entire disclosure of which is incorporated by reference herein.

For purposes of this particularly described embodiment of the present invention, incoming packages are spaced by an infeed worm and transferred, via the infeed star, to a central rotary carousel. Here, firmly located between a base platform and overhead centering bell, they are caused to rotate about their own axis. As the film label is withdrawn laterally from the magazine, it receives hot melt adhesives to provide the overlap bond, although other previously described methods of adhesion may also be utilized in accordance with the present invention, e.g., providing a heat seal layer. Continued rotation of the package past a short brushing section ensures a positive overlap seal. The fully labelled packages are then transferred, via the discharge star-wheel, to the down-stream conveyor.

The labeller is particularly useful for applying wrap¬ around film labels made from shrinkable plastic film in which case, the overlap bond is achieved by the previously mentioned hot melt adhesive technique. The adhesive used is dependent upon the type of plastic film used. The plastic film label is applied in the previously described otherwise conventional way by the labeller using the hot melt adhesive, and the size of the film label is such that it extends (top and bottom) beyond the cylindrical portion of the bottle or can. After labelling, bottles or cans are passed through a heating section to ensure the upper and lower film label areas shrink tightly and uniformly to the bottle contours. For purposes of the present invention, it has been discovered that hot air preferably be directed towards the top and bottom of the film label or other specific area of the labelled container where a non-uniform contour is located to allow preferential shrinkage of the heat shrink film labels in these areas.

In contrast to the present invention, none of the conventional non-shrink film labels have been observed to be as suitable for labeling of irregularly shaped beverage containers, and other irregularly shaped articles, as contemplated in accordance with the present invention. For example, conventional non-shrink film labels have been observed to distort during the process of applying the same to irregular shaped articles, for example by heat shrinking. More particularly, however, such conventional non-shrink film labels, and particularly laminated non-shrink film labels, do not readily conform to the irregular shape of the article, for example, especially at the tapered extremes of beverage containers such as cans.

Thus, in accordance with the present invention, an irregularly shaped article, such as a beverage container, which includes a cylindrical wall of metal, glass or plastic, and a top and a bottom on the wall, wherein the wall tapers inwardly adjacent to the top/bottom to form top and bottom tapered portion(s) is provided with a heat shrinkable film, or lamination of novel shrink films produced in accordance with the present invention, to encircle the wall and conform to the tapered portions, for example, as disclosed in U.S. Patent Nos. 4,704,172 and 4,844,957, the disclosures of which are incorporated by reference herein. Preferably, the shrink film label comprises first and second films as a lamination.

Examples

In the present invention, the polymers which may be used to produce this new MD shrink film include:

(a) a polyolefin copolymer;

(b) a polyolefin terpolymer;

(c) physical blends of polyolefin copolymers and polyolefin homopolymers;

(d) physical blends of polyolefin copolymers and polyolefin terpolymers;

(e) physical blends of polyolefin terpolymers and polyolefin homopolymers; and

(i) the first monomer being selected from the group consisting of ethylene, propylene, butylene and mixtures thereof; and (ii) the second monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof; wherein the first monomer is present in the copolymer in an amount in the range of 99.5% to 75% by weight and the second monomer is present in the copolymer in an amount in the range of 0.5% to 25% by weight in either a random or non-random sequence within the copolymer; wherein the terpolymer is comprised of a primary, secondary and tertiary monomer: (i) the primary monomer being selected from the group consisting of ethylene, propylene, butylene and mixtures thereof; (ii) the secondary monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof; and (iii) the tertiary monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof, wherein the primary monomer is present in the terpolymer in an amount in the range of 50% to 99% by weight and the secondary and tertiary monomers are present in the terpolymer in an amount in the range of 0.5% to 49.5% by weight;

wherein the homopolymer is selected from the group consisting of polyethylene, polypropylene and polybutylene; and wherein the MD and TD shrinkage capacities are as follows:

MD TD

TEMP, SHRI KAGE CAPACITY SHRINKAGE CAPACITY

100'C > 5% > -10%

120'C > 10% > -12%

140^*C > 15% > -10%.

The examples of this invention are presented as a demonstration of the object of this invention where the level of MD shrinkage is a function of the composition of the polymer employed when prepared under similar MD orientation process conditions. Of course, MD orientation conditions, primarily the degree of MD orientation, and to a lesser degree the temperature of MD orientation, also have a significant relation to the level of MD shrinkage in the resultant MD shrink films.

Examples are listed using polyolefin polymer compositions including polypropylene, polypropylene with a seven (7) percent hydrogenated hydrocarbon resin additive, propylene/ethylene copolymers at about 1.4%, about 2.2%, and about 4.5% ethylene, a blend of polypropylene and an approximately 2.2% propylene/ethylene copolymer, and an approximately 8% propylene/butylene copolymer.

These polymer compositions were processed at three levels of MD orientation by an out of line MD orientation process, as described in the detailed description.

As detailed in Table I, it is shown that the level of MD shrinkage, especially at higher temperatures up to 140"C, is a function of the polymer composition. The standard polypropylene polymer composition of example 1, results in the lowest level of MD shrinkage at 140*C. The level of MD shrinkage can be increased by other polymer additives, such as a hydrogenated hydrocarbon resin as detailed in example 2, but the object of this invention is to achieve this improved MD shrink performance by modification of the base polymer by the addition of a co-monomer or co-monomers to the polyolefin polymer. This results in a reduction in melting point and overall crystallinity and under equivalent MD shrink films processing conditions, as described in this invention, a higher level of MD shrinkage, especially at higher temperatures up to 140^CC.

These new polymer shrink films are advantageous over the prior art as they achieve a higher level of maximum MD shrinkage and achieve a given level of MD shrinkage at a lower temperature. These aspects are useful in achieving a MD shrink film which has a higher level of MD shrinkage, which is useful in shrinking to the non-uniform contour of an articles or container with a higher percentage of dimensional change. These aspects are also useful in achieving a MD shrink film which has a given MD shrinkage at a lower temperature which is advantageous for certain labeling or packaging processes or is beneficial to minimize the temperature exposure of the labeled or package article or container.

The approach of this invention, by modifying the polyolefin polymer composition to achieve higher levels of MD shrinkage, is preferred over other approaches as described in the prior art such as employing a higher level of MD orientation in the manufacturing process, which results in increased manufacturing difficulties, or by adding non-polyolefin polymer additives to the polymer composition, such as a hydrogenated hydrocarbon resin, which is typically more complex, more expensive and may have other detrimental side effects as a consequence of the non-polyolefin additives such as plate out on production, labeling or packaging equipment.

These examples are meant only as a demonstration of this invention and are not meant to be inclusive or limiting in any manner. Examples - Process

An out of line MD orientation process was used to prepare polyolefin shrink films. This process is similar to the out of line process described in the detailed description. All samples were first prepared as biaxially oriented films by a standard tubular polypropylene oriented film forming process. Overall biaxial film orientation was approximately 7 times in the MD and TD direction.

The out of line process is approximately described as in Fig. 3, and consists of an unwind stand, a series of fifteen driven and heated rolls (variable speed and temperature) , a chill roll, a treatment section, and a winding or take-up section.

Three MD orientation process conditions were used to prepare polyolefin shrink films. These process conditions varied primarily in the degree of MD orientation. This is achieved by changing the ratio of maximum to minimum roll speed. An increase in roll speed ratio results in an increase in MD film orientation and consequently, MD shrinkage. Process 1

The minimum roll speed for the out of line MD orientation process was 1000 ft/ in. and this was the first roll after the unwind section. The maximum roll speed was 1050 ft./min. and this was the tenth roll in this series of rolls. The roll surface temperatures varied from 100*C to 125'C. Prpcess 2

The minimum roll speed for the out of line MD orientation process was 1000 ft./min. and this was the first roll after the unwind section. The maximum roll speed was 1234 ft./min. and this was the tenth roll in this series of rolls. The roll surface temperatures varied from 100"C to 125*C. Process 3

The minimum roll speed for the out of line MD orientation process was 1000 ft./min. and this was the first roll after the unwind section. The maximum roll speed was 1300 ft./min. and this was the tenth roll in this series of rolls. The roll surface temperatures varied from 100"C to 125*C. Example 1

The polymer composition of example 1 consists of a polypropylene polymer sold by the EXXON Corporation under the designation Exxon Escorene PD 4222 El, MFR = 4 g/10 min. and about 94% heptane insolubles. This sample also contains minor amounts of other additives such as an amide slip agent (0.25 weight percent Kemamide B, from the Witco Chemical Company) and a clay antiblock (0.20 weight percent Kaophile* 2, from Georgia Kaoline) . Example 2

The polymer composition of example 2 consists of isotactic polypropylene sold under the designation Himont Profax* 6501, MFR = 4 g/10 min. and a 7 weight percent of a hydrogenated hydrocarbon resin sold by Hercules Incorporated (under the designation Hercules Regalrez* 1128) . This example also contains minor amounts of other additives such as an amide slip agent (0.12 eight percent Kemamide B, Witco Chemical), clay antiblock (0.36 weight percent of equal parts of Kaophile 2, Georgia Kaolin and Kaopolite SFO, from Antor, Inc.), and an antioxidant (0.10 weight percent Ethanox 330, Ethyl Chemical) and an antacid (0.10 weight percent calcium stearate) . Example 3

The polymer composition of example 3 is a propylene/ethylene copolymer, Exxon Escorene PP 9122 (about 2.2 percent ethylene) . Example 4

The polymer composition of example 4 is a propylene/ethylene copolymer, Exxon Escorene PLTD 994 (about 1.4 percent ethylene) . Example 5

The polymer composition of example 5 is a propylene/ethylene copolymer Fina 8573 (about 4.5 percent ethylene) . Example 6

The polymer composition of example 6 is a 50/50 blend of a polypropylene, Exxon Escorene PD 4222 El and a propylene/ethylene copolymer, Exxon Escorene PP 9122 (about 2.2 percent ethylene) . Example 7

The polymer composition of example 7 is a propylene/butylene copolymer, Shell Cefor SRD4-12 (about 8 percent butylene) .

Without further elaboration the foregoing will so fully illustrate my invention that others may, by applying current or future knowledge, adapt the same for use under various conditions of service.

Claims

CL IMSI claim:

1. A biaxially oriented shrink film comprising a biaxially oriented single layer or biaxially oriented multiple layers having a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 within the temperature range of 100*C to 140"C, wherein the film is selected from the group consisting of single layer films and multilayer films, said multilayer films including a core layer and one or more outer layers, characterised in that said single layer of the single layer film and the core layer of the multilayer film comprises a polymer composition comprised of at least one of the following:

(a) a first polyolefin copolymer;

(b) a second polyolefin copolymer;

(c) physical blends of the first polyolefin copolymer and second polyolefin homopolymers;

(d) physical blends of the first polyolefin copolymer and second polyolefin copolymer;

(e) physical blends of the second polyolefin copolymer and polyolefin homopolymers; and

(f) physical blends of the first polyolefin copolymer, polyolefin homopolymers and the second polyolefin copolymers; wherein the first polyolefin copolymer is comprised of a first and second monomer:

(ii) the second monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof; wherein the first monomer is present in the copolymer in an amount in the range of 99.5% to 75% by weight and the second monomer is present in the copolymer in an amount in the range of 0.5% to 25% by weight in either a random or non-random sequence within the copolymer; wherein the second polyolefin copolymer is comprised of a primary, secondary and tertiary monomer:

(iii) the tertiary monomer being selected from the group consisting of alpha olefin monomers having two to ten carbon atoms and mixtures thereof, wherein the primary monomer is present in the second polyolefin copolymer in an amount in the range of 50% to 99% by weight and the secondary and tertiary monomers are present in the second polyolefin copolymer in an amount in the range of

0.5% to 49.5% by weight; wherein the homopolymer is selected from the group consisting of polyethylene, polypropylene and polybutylene; and wherein the MD and TD shrinkage capacities are as follows:

MD TD

TEMP. SHRINKAGE CAPACITY SHRINKAGE CAPACITY

100'C > 5% > -10%

120*C > 10% > -12%

140*C > 15% > -10%

2. The film of Claim 1, characterised in that the first polyolefin copolymer is selected from the group consisting ofpropylene/ethylenecopolymers; propylene/butylenecopolymers; butylene/ethylene copolymers and linear low density polyethylene copolymers which include a monomer selected from the group consisting of butylene, hexene and octane, said monomer being present in an amount from between 0.5% and 49.5% by weight.

3. The film of Claim 1, characterised in that the polyolefin homopolymers are selected from the group consisting of low density polyethylene having a density in the range of 0.910 to 0.930 grams/cubic centimeter, high density polyethylene having a density in the range of 0.931 to 0.960 grams/cubic centimeter, isotactic polypropylenes with heptane insolubles greater than 90% and greater than 0.5 grams/10 minutes MFR, and poly-1-butene.

4. The film of Claim 2, characterised in that the polyolefin homopolymers are selected from the group consisting of low density polyethylene having a density in the range of 0.910 to 0.930 grams/cubic centimeter, high density polyethylene having a density in the range of 0.931 to 0.960 grams/cubic centimeter, isotactic polypropylenes with heptane insolubles greater than 90% and greater than 0.5 grams/10 minutes MFR, and poly-l-butene.

5. A process for making a biaxially oriented polymer MD tensilized shrink film, the film having a machine direction (MD) shrinkage of greater than a transverse direction (TD) shrinkage such that TD is less than or equal to MD/2 at temperatures in the range of 100°C to 140*C, characterised in that the method comprises the steps of:

(a) selecting a biaxially oriented film according to claim 1; and

(b) subjecting the biaxially oriented polymer film to an additional MD orientation at a temperature effective to produce biaxially oriented polymer shrink films having the shrinkage characteristics as defined in claim 1.

6. In combination, an article to be packaged as a shrink film characterised in that it comprises a film as set forth in claim 1.

7. The film of Claim 1 characterised in that the polymer composition comprises a primary polymer from the group consisting of:

(a) polyolefin copolymers; and

8. The film of claim 1 charcterised in that the polymer composition comprises primarily polyolefin copolymers selected from the group consisting of: (a) propylene copolymers having a co-monomer selected from the group consisting of alpha olefins with two to ten carbon atoms, said co-monomer being present in the range of 0.5% to 25% by weight; and (b) a blend of polypropylene and a propylene/ethylene copolymer in which the ethylene is present in the range of 0.5% to 25% by weight.

9. The film of claim 1 charcterised in that the biaxially oriented shrink film is a multilayer film.

10. The film of claim 1 charcterised in that the biaxially oriented shrink film is a clear film.

11. The film of claim 1 charcterised in that the biaxially oriented shrink film is an opaque film.

12. The film of claim 1 further characterised by one or more of a lubricant, a slip agent, an antiblock agent, an antioxidant, an antacid, an anti-stat agent, an opacifier, a whitener, a colorant, or combinations thereof.

13. The film of claim 1 charcterised in that the biaxially oriented shrink film comprises a heat seal layer.

14. The film of claim 1 charcterised in that the biaxially oriented shrink film comprises a multilayer film is a coextruded film extrusion coated film, laminated film or coated film.

15. The film of claim 1 charcterised in that the biaxially oriented shrink film comprises a metalized film.

16. The film of claim 1 charcterised in that the film has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 at the temperature of 120^*C.

17. The film of claim 16 charcterised in that the first polyolefin copolymer is selected from the group consisting of propylene/ ethylene copolymers; propylene/butylene copolymers; butylene/ ethylene copolymers and linear low density polyethylene copolymers which include a monomer selected from the group consisting of butylene, hexedene and octane, said monomer being present in an amount from between 0.5% and 49.5% by weight.

18. The film of claim 16 charcterised in that the polyolefin homopolymers are selected from the group consisting of low density polyethylene having a density in the range of 0.910 to 0.930 grams/cubic centimeter, high density polyethylene having a density in the range of 0.931 to 0.960 grams/cubic centimeter, isotactic polypropylenes with heptane insolubles greater than 90% and greater than 0.5 grams/10 minutes MFR, and poly-1-butene.

19. The process of claim 5 charcterised in that the film has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 within the temperature range of 100'C to 120*C.

20. The process of claim 5 charcterised in that the film has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 at the temperature of 120 'C.

21. The combination of claim 6 charcterised in that the film has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less than or equal to MD/2 within the temperature range of 100"C to 120*C.

22. The process of claim 5 charcterised in that the film has a machine direction (MD) shrinkage capacity of greater than a transverse direction (TD) shrinkage capacity such that TD is less tan or equal to MD/2 at the temperature of 120*.