JPH0626881B2 - Linear polyethylene shrink film - Google Patents

Description

Detailed Description of the Invention

The present invention relates to a heat-shrinkable and thermoplastic packaging film. In particular, the present invention relates to a multilayer film core and / or
Alternatively, it relates to a shrink film which uses a linear low-density polyethylene or a linear intermediate-density polyethylene resin to form the intermediate layer.

The present invention relates to novel and useful heat-shrinkable film compositions. One of the distinguishing characteristics of shrinkable films is the ability of the film to generate shrink tension within the film when the film shrinks when heated to a certain temperature and the shrinkage is constrained.

The manufacture of shrinkable films, as is known in the art, involves heating a generally resinous material to its flow or melting temperature which is then extruded from a die for extrusion into a cylindrical or flat form. This is achieved by extrusion. After extrusion,
After quenching and cooling, the extrudate is reheated to its orientation temperature. The orientation temperature range for a given film is
The resinous polymers that make up the film and their formulations change with different ones. However, the orientation temperature range is generally said to be room temperature or higher and lower than the film melting point.

As used herein, the term "oriented" or "orientation" refers to stretching a film heated to an orientation temperature range and then immediately quenching it to physically align the molecules and modify the molecular alignment of the material. However, it is intended to mean a process for improving the physical properties of the film, such as shrink tension and orientation relaxation stress, or a product obtained thereby. These two properties are in accordance with ASTM D2839-69 (1975
It can be measured by annual revision). When the stretching method is applied in one direction, a uniaxial orientation is obtained. When the stretching force is applied in two directions, a biaxial orientation is obtained. The term orientation is also used herein interchangeably with heat shrinkability. The term heat-shrinkable is used to indicate a heat-set material by stretching and cooling in its stretched dimension. Oriented, or heat-shrinkable materials, when heated to a suitable temperature below their melting range,
It tends to return to its original unstretched dimensions.

Returning to the basic process of making the above films, it can be seen that the once extruded and quenched film is then reheated to its orientation temperature for orientation. To stretch and orient, there are many dimensions, such as the "blown bubble method."
Alternatively, the “tenter frame method” can be used. These terms are known to those skilled in the art and are referred to as the orienting process. In this case, the material is stretched in the transverse direction (TD) and in the machine or machine direction (MD). After stretching, the film is rapidly quenched to fix the oriented molecular morphology.

After fixing the morphology of the oriented molecules, the film can be stored as rolls and used for the purpose of tightly packing various articles. In this regard, the product to be packaged is wrapped in a heat-shrinkable material by first heat sealing the shrink film to itself, if necessary.
The wrapped product can then be heated to an elevated temperature, for example by passing it through hot air or a hot water bath. This causes the film to shrink around the product, resulting in a rigid package that closely conforms to the contour of the product. The above general overview of film production is not exhaustive as the method is known in the art. For example, U.S. Pat. Nos. 4,274,900; 4,229,241, 4,194,039, 4,1.
88,443, 4,048,428, 3,821,
See 182 and 3,022,543.

For those skilled in the art, many variations can be made to the above general method depending on the end use of the film and the desired properties to impart to the film. For example, film molecules are cross-linked during the process,
The use properties and other properties of the film can be improved. Cross-linking and methods of doing it are well known in the art. Cross-linking can be accomplished chemically by irradiating the film or, alternatively, using peroxide. Another possible variant is to coat a fine mist of silicone spray onto the interior of the newly extruded material to improve the subsequent processability of the material. A method of providing such an internal coating is described in US Pat.
No. 9,018.

Shrink films of polyolefins, especially polyethylenes, have a contraction force (the force per unit area exerted by the film on its cross section during shrinkage), a degree of free shrinkage (when heated to a high temperature without restraint, the material exhibits a certain Degree of reduction in linear dimension), tensile strength (maximum force that can be applied to a unit area film before the film is torn), sealability,
Shrink temperature curve (shrink vs. temperature curve), tear initiation point and tear resistance (force to initiate and continue to tear film), optical properties (material gloss, haze, clarity) and It provides a wide range of physical and use properties such as dimensional stability (the ability of the film to retain its original dimensions under different types of storage conditions).
The characteristics of the film play an important role in choosing a particular film and are different for each packaging application and each package. Product size, weight, shape, rigidity, number of product components, other packaging materials used with the film, and available packaging materials must be considered.

In view of the above physical properties of polyethylene films, as well as the many applications already in use for these films, and the many possible uses for these films, any of the above physical properties of these films will be considered. There is a great need to improve everything, or, of course, it's easy to see what needs to be done.

It is therefore a general object of the present invention to provide an improved heat shrinkable polyolefin film over the films used in the prior art.

Another object of the present invention is to provide a polyolefin film having improved shrink tension.

Yet another object of the present invention is to provide a polyolefin shrink film having improved optical properties.

Yet another object of the present invention is to provide a polyolefin shrink film having a wide shrink temperature range.

Yet another object of the present invention is to provide a polyolefin shrink film having improved sealing properties.

Yet another object of the present invention is to provide a polyolefin shrink film having improved tear propagation resistance.

Yet another object of the present invention is to provide a polyolefin shrink film having improved machinability.

Yet another object of the present invention is to provide an improved polyethylene shrink film in which a linear low density polyethylene or linear intermediate density polyethylene resin is used to construct the core and / or intermediate layer of a multilayer film. That is.

The above and other objects are achieved by providing a polyolefin shrink film as described herein.

Unless otherwise stated, defined or limited in the following description, the term polymer or polymer resin as used herein refers to homopolymers, copolymers, terpolymers, block polymers, Includes graft polymers, disordered polymers, and alternating polymers.

As used herein, the term "melt flow", or "melt flow coefficient", as described in ASTM D 1238, refers to the amount of thermoplastic resin (in grams) that can be extruded from an orifice at a given pressure and temperature. ).

The term "core" or "core layer" as used herein means a layer in a multi-layer film surrounded on both sides by another layer.

The "skin" or "skin layer" described in the present specification
The term means the outer (or surface) layer of a multi-layer film.

"Intermediate" or "intermediate layer" described in this specification
The term means a layer of a multilayer film that is neither a core layer nor a skin layer.

"Low density polyethylene" described in the present specification
The term (LDPE) means a homopolymer of ethylene with a density of 0.910 to 0.925.

As used herein, the term "linear low density polyethylene" (LLDPE) has a density of 0.910-0.
At 925 is meant a copolymer of ethylene and up to 8% butene, octene, or hexene with little or no branching or cross-linking along the polymer chain.

As used herein, the term "linear medium density polyethylene" (LMDPE) has a density of 0.926-0.
At 940 is meant a copolymer of ethylene with up to 8% butene, octene, or hexene with little or no branching or cross-linking along the polymer chain.

The term "ethylene vinyl acetate copolymer" (EVA) described in the present specification means that ethylene and vinyl acetate have a large amount of units derived from ethylene and a small amount of units derived from vinyl acetate. Means a copolymer made from

The term "ethylene-propylene copolymer" (EPC) described in the present specification means that a unit derived from propylene is present as a main component, and a unit derived from ethylene is a minor component. It means a copolymer made from a polymer and a propylene monomer.

"Propylene homopolymer" described in the present specification
The term (PP) means a thermoplastic resin having a density of about 0.90 and obtained by polymerizing propylene by a method known in the art using a suitable catalyst.

In the present invention, flexible, heat-shrinkable packaging with a combination of desired physical properties such as shrink tension, optical properties, severability, hermeticity, shrink temperature range, and tear resistance. It has been found that a thermoplastic film for use is obtained by the multilayered flexible thermoplastic packaging film of the present invention. This multi-layer film has a core layer containing a linear low density polyethylene resin. It is believed that linear medium density polyethylene resin can be used in place of linear low density polyethylene resin. In a preferred three-layer embodiment, in addition to the core layer described above, two skin layers are included, each containing a propylene homopolymer and an ethylene / propylene copolymer blend. Preferably, the multilayer film is oriented to be heat shrinkable in at least one direction.

The multilayer film can be combined with other polymeric materials in specific applications. For example, a relatively thin layer can be added to one or both sides of the substrate of a suitable three-layer structure to improve seal strength or reduce gas and moisture permeability.

In another embodiment of the invention, a five layer film structure is realized. A suitable five-layer structure is
It has the same core layer and skin layer as the above three-layer structure, and two intermediate layers each containing a mixture of an ethylene / vinyl acetate copolymer and an ionomer resin or a linear density polyethylene. Contains. It is currently believed that linear intermediate density polyethylene can be used in place of the intermediate layer linear density polyethylene.

Referring to FIG. 1, which shows a cross section of a preferred three-layer embodiment of the present invention, this embodiment comprises a core layer 2 and skin layers 1 and 3. In Figure 1,
The preferred thickness ratio of the three layers is illustrated to be 1/3/1. The preferred core layer 2 construction comprises a linear medium density polyethylene polymer. However, even if a linear intermediate density polyethylene polymer is used as the constituent of the core layer,
The properties of the final film product are believed to be substantially unchanged. The core layer 2 is made of low density polyethylene (or linear medium density polyethylene) of the product, or linear low density polyethylene (or linear medium density polyethylene) (a) ethylene-propylene copolymer, or (b ) Ethylene / vinyl acetate copolymer, or (c) ethylene /
It may consist of a blend of vinyl acetate copolymer and ionomer resin, or (d) a blend of low density polyethylene. Therefore, according to the present invention, various compounding compositions for the core layer 2 can be selected from the following group:

(1) 10 to 100% LLDPE and 0 to 90% E
Blend with PC (2) 10-100% LMDPE and 0-90% E
Blend with PC (3) 10-80% LLDPE and 20-90% E
Blend with VA (4) 10-80% LMDPE and 20-90% E
Blend with VA (5) 10-80% LLDPE and 10-80% E
Blend with VA and 10-80% ionomer resin (6) 10-80% LMDPE and 10-80% E
Blend with VA and 10-80% ionomer resin (7) 10-80% LLDPE and 20-90% L
Blend with DPE (8) 10-80% LMDPE and 20-90% L
Blends with DPE where LLDPE is an abbreviation for linear low density polyethylene as defined above. LMDPE is an abbreviation for linear medium density polyethylene as defined above. EPC is an abbreviation for the ethylene-propylene copolymer defined above. EVA is an abbreviation for the ethylene-vinyl acetate copolymer defined above. The term ionomer resin is intended to broadly encompass the group of ionomer resins. One of the most well-known ionomer resins is Dulyn under the trade name of Surlyn.
ont). Tests have shown that the most preferred core layer composition consists essentially of linear low density polyethylene. This material is Dow Chemical
Dowlex from Chemical
x) marketed under the trade name of 2045.

Returning to FIG. 1, and in particular skin layers 1 and 3, suitable skin layer compositions are selected from the following group:

(1) EPC (2) Blend of 70-90% EPC and 10-30% PP (3) 70-90% EPC and 10-30% LLD
Blend with PE (4) 70-90% EPC and 10-30% LMD
Formulation with PE All abbreviations are the same as previously described for the composition of the core layer. In addition, PP is an abbreviation for the propylene homopolymer defined above. Also, experience has shown that a particularly suitable skin layer composition consists essentially of a blend of 20% PP and 80% EPC.

A propylene homopolymer is commercially available under the tradename PD 064 from Hercules Chemical Company. Ethylene / propylene copolymer is a Soltex chemical (Solt
42X01 from ex Chemical, or Solvay Chemical
commercially available under the trade name KS400.

Throughout the specification and claims, all percentages are by weight and densities are in g / cc.

Summarizing the experience to date, a particularly preferred embodiment of the present invention shows that the core layer consists essentially of linear low density polyethylene and the skin layer comprises essentially 20% propylene homogenous weight. It consists of a blend of 80% ethylene / propylene copolymer.

The above-mentioned three-layer composition is generally preferable from the viewpoint of manufacturing economical efficiency over the structure having four or more layers, but various five-layer compositions which are satisfactory from the viewpoint of physical properties. I also made things. However, the manufacturing cost of a five-layer film is generally higher than that of a three-layer film. Referring to FIG. 2, which is a cross-sectional view of a preferred five-layer film of the present invention, a preferred five-layer thickness ratio of 2/2/1/2/2 is shown. The core layer 6 can comprise any of the core layer compositions described above for the three-layer embodiment core layer. The core layer is essentially (1) an ethylene / propylene copolymer (EP
C) or (2) ethylene-vinyl acetate copolymer (EV
It can consist of A).

The skin layers 4 and 8 of the five-layer embodiment are shown in FIG.
Can comprise any of the same skin layer compositions as previously described for the skin layers 1 and 3 of the three-layer embodiment.

In the embodiment of the five layers of FIG.
And 7 are included. It may comprise any of the compositions described above for core layer 2 of these intermediate layer embodiments. The composition of the intermediate layers 5 and 7 can be selected from the following group.

(1) EVA (2) Blend of 20-80% LLDPE and 20-80% ionomer resin (3) Blend of 20-80% LMDPE and 20-80% ionomer resin Experience In accordance with US Pat. No. 5,968,962, a particularly preferred five-layer structure is skin layers 4 and 8 consisting essentially of ethylene-propylene copolymer (EPC), essentially ethylene-vinyl acetate copolymer 90%.
And intermediate layers 5 and 7 consisting of a blend of 10% and an ionomer resin, and a core layer 6 consisting essentially of linear low density polyethylene. EPC is 42X0 from Soltex Chemical
It is marketed under the trade name of 1. EVA is commercially available from du Pont Chemical Company under the trade name Alathon 3137. The ionomer resin is Surly
n) and Surlyn 1601 are commercially available from du Pont Chemical Company. LLDPE is Dow Chemical
chemical) to Dowlex
It is commercially available under the trade name of 2045.

As will be readily apparent to those skilled in the art, all of the above percentages by weight can vary slightly. Further, these ratios are based on additives such as the above-mentioned silicone mist and slip agent (Slip ag).
ents) or antiblocking agents can be added and coated as a result of slight variations. A preferred detackifying agent is silica commercially available from Johns Manville under the trade name White Mist. Suitable slip agents are erucamide (commercially available under the trade name Kemamide E from Humko Chemical), stearamide (commercially available under the trade name Chemamide S from Fumco Chemical), and N, N-di. Oleoyl ethylenediamine (Glyco Chemical
1) marketed by the company under the trade name of Acrawax C). A suitable silicone propellant is General Electric
c) a liquid polyorganosiloxane commercially available from General Electric Company as SF18 polydimethylsiloxane.

The general range of addition of these additives is as follows.

(1) Silica: 250 to 3000 ppm (2) Akrawax C: 200 to 4000 ppm (3) Erucamide: 200 to 5000 ppm (4) Stearamide: 250 to 5000 ppm (5) Silicone spraying agent: 0.5 mg / square foot or more Throughout the specification and claims the word "consisting essentially of" is not meant to exclude slight variations in the percentage by weight or additives of this type.

Additional layers and / or small amounts of additives of the type described above may optionally be added to the three-layer or five-layer construction of the present invention, although the desired shrink tension, shrinkage of the multilayer film of the present invention is desirable. Care must be taken not to adversely affect the properties, optical properties and other properties.

In a preferred method of making the other multi-layer linear low density polyethylene or linear intermediate density polyethylene shrink film of the present invention, the basic steps are to compound the various other polymers used and coextrude the layers. Is a step of producing a multi-layered film by means of stretching and then orienting the film biaxially. These steps and any additional desired steps will now be described in detail.

The method of the present invention begins by first blending the raw materials (ie, polymeric resin) in the desired proportions and ranges described above. The resin is usually purchased from the manufacturer in the form of pellets and can be compounded on one of the many commercially available compounders known in the art. During the compounding process, the additives and / or reagents desired to be used can be purchased.

The compounded resin and additives and / or reagents are then fed into the hopper of the extruder and then simultaneously into the die for extrusion. For a three-layer film, if a different composition is used for each layer, it is necessary to use at least three extruders. Two extruders are fed with the desired material for the inner and outer skin layers, and the other extruder is fed with an example of a linear low density or linear medium density polyethylene material desired to be used for the core layer. Other extruders can be used if necessary. Preferably, the racking ratio
And co-extruding the material as a tube with a diameter depending on the desired final diameter. This coextruded tube is relatively thin and is referred to as tape. Circular coextrusion die molds are known in the art and can be purchased from many manufacturers. In addition to performing tubular coextrusion, slotted die dies can be used to extrude the material in planar form. If desired, known single-layer or multilayer extrusion coating methods can be used.

Another additional step that can be used is to irradiate the tape or unexpanded tube or sheet with high energy electrons from an accelerator to crosslink the tape material. When the film material is composed predominantly of ethylene, such as polyethylene or ethylene vinyl acetate copolymer, the cross-linking significantly increases the structural strength of the film, i.e., the ability to stretch the material before it is torn. Irradiation also improves the optical properties of the film and changes the film properties at elevated temperatures. When using the irradiation process, a suitable irradiation amount is 0.5 MR to 12.0.
It is MR. MR is the abbreviation for Megarad, where Megarad is 1 × 10 ⁶ rads, where 1 rad is the amount of ionizing irradiation that results from the absorption of 100 ergs of energy per gram of irradiated material, regardless of the irradiation source. In some cases, the multilayer film is first stretched and then irradiated, or when sequentially coated, after irradiation of one or a group of layers before the final stretching and orienting step. Layers can be added.

As mentioned above, an additional step that may be performed at any time is to spray finely powdered silicone inside the newly extruded tape. Details of this process are 198.
It is described in U.S. Pat. No. 289,018 dated July 31, 1st.

Coextrusion followed by quenching and cooling, irradiation if necessary, reheating of the extruded tape, continuous expansion by application of internal air pressure, to obtain a narrow tape with thick walls as desired. Change the film to a wide film with a thin wall. This process is often oriented by the "trapped bubble method"
Or it is called "Racking". After stretching, the air bubbles are deflated and the film is wound on a semi-finished roll called "mill roll". The laking process orients the film laterally and to some extent longitudinally to rearrange the molecules, thereby imparting shrinkage to the film and organizing the physical properties of the film. The additional longitudinal or machine direction stretch serves to collapse the blown bubbles at a faster rate than the rolls which serve to transfer the reheated "tape" to the area of racking or blown bubbles. Can be achieved by rotating the shrink roll. All these orientation methods are known in the art. The following examples are provided in order to clearly explain the scope of the invention to those skilled in the art.

[0054]

Example 1 A five-layer structure with a layer thickness ratio of 2/2/1/2/2 was extruded with four extruders. 9 in extruder No. 1 with die-type orifices for both interlayers
0% ethylene-vinyl acetate copolymer (vinyl acetate 12
%) [Arason 3137 (melting coefficient 0.5)] and 1
0% ionomer resin [Sarlin 1601 (density 0.9
40, melt coefficient 1.4)]. This formulation also contains 1100 ppm of erucamide [Chemamide E].
And 1100 ppm of stearamide [Chemamide S]
Was included. A No. 2 extruder with a die-type orifice for the core layer was fed with 100% linear bottom density polyethylene [Dowrex 2045 (density 0.920, melting coefficient 1.0)]. Both No. 3 and No. 4 extruders with die-type orifices for the skin layer are 11
100% ethylene-propylene copolymer (3.5% ethylene) mixed with 00 ppm erucamide [Chemamide E], 1100 ppm stearamide [Chemamide S] and 1100 ppm silica [White Mist] [Solutex 42X01 (melt flow 4.5)] was supplied. Extruder No. 1 was maintained in the temperature range of 390-425 ° F. Extruder No. 2 was maintained in the temperature range of 410-470 ° F. Extruder No. 3 was maintained in the temperature range of 350-370 ° F. Extruder No. 4 was maintained in the temperature range of 345-365 ° F. The circular die mold was kept in the temperature range of 390-435 ° F.

After extruding the layers through a 10 inch circular die orifice, a cylindrical extrudate having a tape thickness of about 15 mils and a tube width of about 95/8 inch is chilled at a rate of about 37 feet / minute. It was quenched and cooled by passing it through. The tube was then reheated and oriented by passing it through a heating zone or oven at a rate of 38 feet / minute. The furnace was heated by horizontal, vertical, and steam heating elements. In this example, steam heating, where the horizontal heating element was kept at 200 ° F and the vertical heating element was kept at 300 ° F, to provide heat by passing it through a pipe or can placed inside the furnace. The element was supplied with 2 psi of steam.

After heating as described above, the tubular extrudate is expanded, about 4.8 to 1 times in the transverse direction and about 4.3 in the longitudinal direction.
Stretched ~ 1x. Thereafter, the film was cooled by quenching with water to fix the oriented structure. The final film
The gauge was about 75 gauge.

Experimental data obtained for this film composition are given in Table 1 together with the data of the other examples.

[0058]

Example 2 A five-layer structure with a layer thickness of about 2/2/1/2/2 was extruded with four extruders. No. 1 extruder with die-type orifices for both intermediate layers 11
50% ethylene-vinyl acetate copolymer containing 00 ppm erucamide [Chemamide E] (12% vinyl acetate)
A blend of [Arason 3137 (melting coefficient 0.5)] and 50% linear low density polyethylene [Dowrex 2045 (density 0.920, melting coefficient 1.0)] was supplied.
A No. 2 extruder with a die-type orifice for the core layer was fed with 100% linear low density polyethylene [Dowrex 2045 (density 0.920, melting coefficient 1.0)]. The No. 3 and No. 4 extruders each having a die-type orifice for the skin layer were both mixed with 1100 ppm of erucamide [chemamide E] and 1100 ppm of silicone [white mist], and 100% ethylene-propylene Polymer (2.7% ethylene) [ARCO K-193 (melt flow 2.3)] was fed.

Extruder No. 1 was maintained in the temperature range of 405-415 ° F. Extruder No. 2 was maintained in the temperature range of 400-475 ° F. Extruder No. 3 was maintained in the temperature range of 355-435 ° F. Extruder No. 4 is 355-410 ° F
Circular die type kept in the temperature range of 390 to 425 °
The temperature range of F was maintained.

After the layers have been extruded through a 10 inch circular die orifice, a cylindrical extrudate of tape thickness of about 17 mils and width of about 83/4 inches is passed through cold water at a rate of about 39 feet per minute. It was cooled by quenching. The tubular extrudate was then reheated and oriented by passing it through a heating zone or oven at a rate of 38 feet / minute. The furnace was heated by horizontal, vertical, and steam heating elements. In this example, the horizontal heating element was kept at 212 ° F. The vertical heating element was maintained at 343 ° F and the steam heating element, which supplies heat by passing through a pipe or can placed inside the furnace, was supplied with 7 psi of steam.

After heating as described above, the tubular extrudate was expanded to about 4.8 to 1 times in the transverse direction and about 4.5 in the longitudinal direction.
Stretched ~ 1x. Then, it was cooled by quenching with water to fix the alignment structure. The final film thickness is about 7
It was 5 gauge.

The data obtained for this film composition are listed in Table 1.

[0063]

Example 3 A three-layer structure with a layer thickness ratio of about 1/3/1 was extruded with four extruders. 33 for extruders No. 1 and 2 with die-type orifices for core layer
100% containing 00ppm erucamide [Chemamide E]
Of linear low density polyethylene [Dowrex 2045 (density 0.920, melting coefficient 1.0)] was supplied. No.3 and No.4 with dice type orifice for the epidermis
Both extruders were blended with 3300 ppm erucamide [Chemamide E] and 1100 ppm silica [White Mist], and 1650 ppm Akrawax C 80% ethylene-propylene copolymer (3.5%).
Ethylene) [Solutex 42X01 (melt flow 4.
5)] and 20% of a propylene homopolymer [Hercules PD064 (density 0.906, melting coefficient 3.5)].

Extruder No. 1 was maintained in the temperature range of 395-485 ° F. Extruder No. 2 was maintained in the temperature range of 425-470 ° F. Extruder No. 3 was maintained in the temperature range of 370-375 ° F. Extruder No. 4 is 370-375 ° F
Kept in the temperature range of. The circular die mold was kept in the 385 ° F temperature range. For this example, the actual temperature at which the extruder and die mold were held was not stated.

After extruding the layer through a 10 inch circular die orifice, the tubular extrudate was quenched by passing it through cold water at a rate of about 39.5 feet / minute.
When the tape was extruded, the inside of the extruded cylinder was coated with a fine mist of fine silicone at a rate of 5 to 7 mg · square foot. The cooled tubular extrudate was then reheated and oriented by passing it through a heating zone or oven at a rate of about 37.7 ft / min. The furnace was heated by horizontal, vertical, and steam heating elements. In this example, the horizontal heating element was kept at 200 ° F. 305 ° vertical heating element
3.5 psi for steam heating elements that are kept at F and supply heat by passing through pipes or cans placed inside the furnace
Was supplied.

After heating as described above, the tubular extrudate was stretched approximately 4.8 to 1 times in the transverse direction and approximately 4.5 to 1 times in the longitudinal direction. Thereafter, the film was cooled by quenching with water to fix the oriented structure. The final film gauge was about 75 gauge.

The data obtained for this film composition are listed in Table 1.

[0068]

[Table 1] Table 1 Example I II III Layer ratio 2/2/1/2/2 2/2/1/2/2 1/3/1 Tensile strength × 100 (psi) (Note 1) MD 97.1 125.2 124.6 TD 110.5 105.1 130.7 Elongation (%) (Note 2) MD 86 98 98 113 TD 65 107 107 102 Modulus x 100 (psi) (Note 3) MD 90.3 98.3 96.5 TD 101.4 99.4 97.6 Tear propagation (g) (Note 4) MD 4.10 4.33 9.60 TD 4.01 5.53 9.83 Tear resistance (pound) (Note 5) MD 0.70 0.61 0.60 TD 0.90 0.83 0.67 Shrinkage at 200 ° F Free shrinkage (%) (Note 6) MD 16 14 12 TD 18 20 17 Shrinkage tension ( psi) (Note 7) MD 239 304 288 TD 327 457 509 260 Shrinkability at 260 ° F Free shrinkage (%) (Note 6) MD 52 49 48 TD 57 57 57 54 Shrinkage tension (psi) (Note 7) MD 220 345 434 TD 365 422 538 280 ° F shrinkage Free tension (psi) (Note 6) MD 71 66 66 62 TD 67 67 68 64 Shrinkage tension (psi) ( Note 7) MD 237 348 432 TD 304 304 362 584 Optical properties (Note 8) Haze (%) 2.5 2.1 2.0 Gloss (45 °) 94 88 88 Total transmittance 92.5 92.2 92. 2 (Note) (1) ASTM D 882 (2) ASTM D 882 (3) ASTM D 882 (4) ASTM D 1938 (5) ASTM D 1004 (6) ASTM D 2732 (7) ASTM D 2838 (8) ASTM D 1003 All data in Table 1 above are average values obtained by the ASTM standard method. It will be apparent to those skilled in the art from the foregoing description and examples that many changes and modifications can be made within the spirit and scope of the present invention. Therefore, the above detailed description and the preferred embodiments of the present invention can be carried out. It should be understood that the particular examples provided are examples only.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a preferred three-layer embodiment of the present invention.

FIG. 2 is a cross-sectional view of a preferred five-layer embodiment of the present invention.

Claims (7)

[Claims] 1. A core layer, further comprising two skin layers.
And the core layer contains linear medium density polyethylene
And the skin layer is a. Ethylene / propylene copolymer; b. 70-90 wt% ethylene / propylene copolymer
And 10 to 30% by weight of propylene homopolymer
Thing; c. 70-90 wt% ethylene / propylene copolymer
And 10 to 30% by weight of linear low density polyethylene
Thing; d. 70-90 wt% ethylene / propylene copolymer
And 10 to 30% by weight of linear intermediate density polyethylene.
Multilayer Poriore containing composition selected from the group consisting of; compound
Film film. 2. From linear intermediate density polyethylene essentially
A multilayer polyolefin according to claim 1 containing a core layer comprising
Film. 3. From linear intermediate density polyethylene essentially
Consisting of a core layer and an ethylene / propylene copolymer weight of 80% by weight
Is it a blend of 20% by weight homopolymer of propylene
3. The method according to claim 1, containing two skin layers consisting essentially of
Multi-layer polyolefin film. 4. From linear medium density polyethylene essentially
Core layer consisting of: 90% by weight ethylene-vinyl acetate copolymer
Essential from a blend of body and 10% by weight ionomer resin
Of two intermediate layers; and ethylene / propylene co-weight
The skin layer according to claim 1, which comprises a skin layer essentially consisting of coalescence.
Multi-layer polyolefin film. 5. Further comprising at least two intermediate layers,
The outer intermediate layer contains linear low density polyethylene.
The described multilayer polyolefin film. 6. The core layer comprises: a. 10 to 100% by weight of linear intermediate density polyethylene
0 to 90% by weight of ethylene / propylene copolymer
Compound; b. 10-80% by weight of linear medium density polyethylene and 2
Combination with 0-90% by weight ethylene-vinyl acetate copolymer
Compound; c. 10-80% by weight of linear intermediate density polyethylene, 1
0-80% by weight ethylene-vinyl acetate copolymer, and
And 10-80% by weight of an ionomer resin; d. 10-80% by weight of linear medium density polyethylene and 2
A blend with 0 to 90 wt% low density polyethylene; a copolymer blend selected from the group consisting of:
Item 1. The multilayer polyolefin film according to item 1. 7. An intermediate layer further comprising : a. 10 to 100 wt% linear low density polyethylene and 0
~ 90 wt% ethylene / propylene copolymer blend
Thing; b. 10 to 100% by weight of linear intermediate density polyethylene
0 to 90% by weight of ethylene / propylene copolymer
Compound; c. 10 to 80% by weight of linear low density polyethylene and 20
Polymerization with ethylene-vinyl acetate copolymer up to 90% by weight
Blending with the body; d. 10-80% by weight of linear medium density polyethylene and 2
Combination with 0-90% by weight ethylene-vinyl acetate copolymer
Compound; e. 10-80% wt% linear low density polyethylene, 1
0-80% by weight ethylene-vinyl acetate copolymer, and
And 10-80% by weight of an ionomer resin; f. 10-80% by weight of linear intermediate density polyethylene, 1
0-80% by weight ethylene-vinyl acetate copolymer, and
And 10-80% by weight of an ionomer resin; g. 10 to 80% by weight of linear low density polyethylene and 20
~ 90 wt% low density polyethylene blends; h. 10-80% by weight of linear medium density polyethylene and 2
Blends with 0-90% by weight low density polyethylene; i. Ethylene-vinyl acetate copolymer; j. 20-80% by weight of linear low density polyethylene and 20
-80% by weight formulation with ionomer resin; k. 20-80 wt% linear medium density polyethylene and 2
A blend with 0 to 80% by weight of an ionomer resin; according to claim 1 having a composition selected from the group consisting of:
Multi-layer polyolefin film.