JPH0342180B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-shrinkable, thermoplastic packaging film. In particular, the present invention relates to a shrink film that uses linear low density polyethylene or linear intermediate density polyethylene resin to constitute the core and/or intermediate layer of the multilayer film. The present invention relates to a new and useful heat-shrinkable film composition. One of the distinguishing features of a shrinkable film is the film's ability to contract when heated to a certain temperature, and when that contraction is restrained, to generate shrinkage tension within the film. Shrink film production, as is known in the art, generally involves heating a resinous material to its flow or melting temperature and extruding it through an extrusion die in a cylindrical or flat shape. This is achieved by After extrusion and cooling, the extrudate is reheated to its orientation temperature. The orientation temperature range for a given film will vary with different resinous polymers and formulations from which the film is made. However, the orientation temperature range is generally said to be above room temperature and below the melting point of the film. In this specification, the term ``oriented'' or ``orientated'' refers to a film that is heated to an orientation temperature range, stretched, and then immediately rapidly cooled to physically align the molecules to modify the molecular arrangement of the material. shall mean a process, or a product obtained thereby, that improves the physical properties of, for example, contraction tension and oriented relaxation stress. These two properties are
It can be measured according to ASTM D2839-69 (revised in 1975). When the stretch is applied in one direction, a uniaxial orientation is obtained. Biaxial orientation is obtained when stretching forces are applied in two directions. As used herein, the term orientation is also used interchangeably with heat shrinkability. The term heat-shrinkable is used to describe a material that is heat-set by stretching and cooling in its stretched dimension. Oriented or heat-shrinkable materials tend to return to their original unstretched dimensions when heated to a suitable temperature below their melting point range. Returning to the basic process of manufacturing the film described above, it can be seen that the film, once extruded and quenched, is then reheated to its orientation temperature to orient it. Stretching and orientation can be achieved in many dimensions, for example by the ``blown bubble method'' or the ``tenter frame method.'' These terms are known to those skilled in the art and are referred to as orientation steps. In this case, the material is stretched in the transverse direction (TD) and in the longitudinal or machine direction (MD). After stretching, the film is rapidly quenched to fix the oriented molecular morphology. After fixing the oriented molecular morphology, the film can be stored in rolls and used for tight packaging of various articles. In this regard, the product to be packaged is first encapsulated within the heat-shrinkable material by optionally heat-sealing the shrink film to itself. Thereafter, the wrapped product can be heated to a high temperature, for example by passing it through hot air or a hot water bath. This causes the film to contract around the product, creating a rigid package that closely conforms to the contours of the product. The above general overview of film production is not exhaustive as this method is well known in the art. For example, U.S. Patent No. 4274900;
No. 4188443, No. 4048428, No. 3821182 and No.
See No. 3022543. For those skilled in the art, many variations can be made to the general method described above, depending on the end use of the film and the desired properties to be imparted to the film. For example, the molecules of the film can be cross-linked during the process to improve the use properties and other properties of the film. Cross-linking and methods for performing it are known in the art. Cross-linking can be accomplished chemically by irradiating the film or alternatively using peroxide. Another possible modification method is to coat the interior of the newly extruded material with a fine mist of silicone spray to improve the subsequent processability of the material. A method for making such an internal coating is described in U.S. Patent Application No. 289,018, filed July 31, 1981. Shrink films of polyolefins, especially polyethylenes, have shrinkage force (the force per unit area that the film exerts on its cross section during shrinkage), degree of free shrinkage (a certain linear direction that the material exhibits when heated to high temperature without restraint). degree of reduction in dimension), tensile strength (the highest force that can be applied to a unit area of film before the film is torn), sealability, shrinkage temperature curve (the curve that shows the relationship between shrinkage and temperature), tear initiation point, and Tear resistance (the force at which the film begins to tear and the force at which it continues to tear), optical properties (gloss, haze, clarity of the material) and dimensional stability (the ability of the film to maintain its original dimensions under different types of storage conditions) provides a wide range of physical and usage properties such as the ability to hold Film properties play an important role in the selection of a particular film and vary depending on each packaging application and each packaged product. Consideration must be given to the size, weight, shape, stiffness of the product, number of product components, other packaging materials used with the film, and available packaging materials. Considering the above-mentioned physical properties of polyethylene films, as well as the many applications that have already been used for these films, and the many applications that may yet be envisaged, any of the above-mentioned physical properties of these films, or Everything is in great need of improvement, and it will be easy to see what must be done from now on. It is therefore a general object of the present invention to provide a heat-shrinkable polyolefin film that is improved over films used in prior art methods. Another object of the present invention is to provide a polyolefin film with improved shrinkage tension. Yet another object of the present invention is to provide a polyolefin shrink film with 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 with improved sealing properties. Yet another object of the present invention is to provide a polyolefin shrink film with improved tear propagation resistance. Yet another object of the present invention is to provide a polyolefin shrink film with improved machinability. Yet another object of the present invention is to provide an improved polyethylene shrink film in which linear low density polyethylene or linear intermediate density polyethylene resin is used to constitute the core and/or intermediate layer of the multilayer film. . These and other objects are achieved by providing the polyolefin shrink films described herein. Unless otherwise stated, defined, or limited in the following description, the term polymer or polymer resin as used herein refers to homopolymer, copolymer, terpolymer, block polymer, graft polymer. , disordered polymers, and alternating polymers. The term "melt flow" or "melt flow coefficient" as used herein is the amount (in grams) of thermoplastic resin that can be extruded from a given orifice at a given pressure and temperature, as described in ASTM D1238. . As used herein, the term "core" or "core layer" refers to a layer in a multilayer film that is surrounded on both sides by another layer. As used herein, the term "skin" or "skin layer" refers to the outer (or surface) layer of a multilayer film. As used herein, the term "intermediate" or "interlayer" refers to a layer of a multilayer film that is neither a core layer nor a skin layer. "Low density polyethylene" described herein
The term (LDPE) means a homogeneous polymer of ethylene with a density of 0.910 to 0.925. "Linear low density polyethylene" described herein
The term (LLDPE) refers to ethylene and less than 8% butene, with a density of 0.910 to 0.925 and with little or no branching or cross-linking along the polymer chain.
It means a copolymer with octene or hexene. "Linear intermediate density polyethylene" described herein
The term (LMDPE) refers to ethylene and less than 8% butene, with a density of 0.926 to 0.940 and a molecule with little or no branching or cross-linking along the polymer chain.
It means a copolymer with octene or hexene. The term "ethylene vinyl acetate copolymer" (EVA) as used herein refers to a compound made from ethylene and vinyl acetate, in which a large amount of units derived from ethylene is present, and only a small amount of units derived from vinyl acetate are present. means a copolymer. The term "ethylene propylene copolymer" (EPC) as used herein refers to units derived from propylene present as the main component, and units derived from ethylene present as minor components of ethylene monomer and propylene. A copolymer made from monomers. "Propylene homogeneous polymer" described herein
The term (PP) refers to a thermoplastic resin having a density of approximately 0.90 and obtained by polymerizing propylene using suitable catalysts by methods known in the art. In the present invention, a flexible, heat-shrinkable packaging thermoplastic with a desired combination of physical properties such as shrink tension, optical properties, cuttability, sealability, shrink temperature range, and tear resistance is used. It has been found that films can be obtained with the multilayered flexible thermoplastic packaging film of the present invention. This multilayer film has a core layer containing a linear low density polyethylene resin. It is believed that linear intermediate density polyethylene resins can be used in place of linear low density polyethylene resins. A preferred three-layer embodiment includes, in addition to the core layer described above, two skin layers each comprising a propylene homopolymer and an ethylene-propylene copolymer blend. Preferably, the multilayer film is oriented to be heat shrinkable in at least one direction. This multilayer film can be combined with other polymeric materials in specific applications. For example, relatively thin layers can be added to one or both sides of the matrix of a suitable three-layer structure to improve seal strength or reduce gas and moisture permeability. In other embodiments of the invention, a five layer film structure is implemented. A preferred five-layer structure has the same core and skin layers as the three-layer structure described above, with the addition of an ethylene-vinyl acetate copolymer and an ionomer resin or linear low-density polyethylene, respectively. Contains two intermediate layers containing the formulation. It is currently believed that linear intermediate density polyethylene can be used in place of linear low density polyethylene in the intermediate layer. Referring to FIG. 1, which shows a cross section of a preferred three layer embodiment of the invention, this embodiment consists of a core layer 2 and skin layers 1 and 3.
In Figure 1, the preferred thickness ratio of the three layers is 1/3/1
It is exemplified that A preferred core layer 2 composition consists of a linear medium density polyethylene polymer. However, it is believed that the use of a linear intermediate density polyethylene polymer as a constituent of the core layer does not substantially alter the properties of the final film product. The core layer 2 consists of linear low-density polyethylene (or linear intermediate-density polyethylene), or linear low-density polyethylene (or linear intermediate-density polyethylene) and (a) an ethylene-propylene copolymer, or (b) ) Ethylene/vinyl acetate copolymer,
Alternatively, it may consist of (c) a blend of an ethylene/vinyl acetate copolymer and an ionomer resin, or (d) a copolymer blend of low density polyethylene. According to the invention, various formulation compositions for the layer 2 of the core can therefore be chosen from the following groups: (1) Blends of 10-100% LLDPE and 0-90% EPC (2) Blends of 10-100% LMDPE and 0-90% EPC (3) Blends of 10-80% LLDPE and Blends with 20-90% EVA (4) Blends with 10-80% LMDPE and 20-90% EVA (5) Blends with 10-80% LLDPE and 10-80% EVA and
Blends with 10-80% ionomer resins (6) Blends with 10-80% LMDPE with 10-80% EVA and 10-80% ionomer resins (7) Blends with 10-80% LLDPE and 20 Blends with ~90% LDPE (8) Blends with 10-80% LMDPE and 20-90% LDPE Here, 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 ethylene-propylene copolymer as defined above. EVA is an abbreviation for ethylene-vinyl acetate copolymer as defined above. The term ionomer resin is intended to broadly encompass the group of ionomer resins. One of the most prominent ionomer resins is commercially available from du Pont under the trade name Surlyn. Testing has shown that the most preferred core layer composition consists essentially of linear low density polyethylene.
This material is commercially available from Dow Chemical Company under the trade name Dowlex 2045. Returning to FIG. 1, particularly epidermal layers 1 and 3, suitable epidermal layer compositions are selected from the following group: (1) EPC (2) Blends of 70-90% EPC and 10-30% PP (3) Blends of 70-90% EPC and 10-30% LLDPE (4) 70-90 % EPC and 10-30% LMDPE. All abbreviations are the same as mentioned above for the core layer composition. Additionally, PP is an abbreviation for propylene homopolymer as defined above. Experience has also shown that a particularly suitable skin layer composition is 20% PP.
and consists essentially of a blend of 80% EPC. Propylene homopolymer is commercially available from Hercules Chemical Company under the trade name PD064. Ethylene Propylene Copolymer 1 Soltex Chemical
Chemical under the trade name 42X01, or Solvay Chemi-cal.
It is commercially available under the product name KS400 from the company. Throughout the specification and claims, all percentages are by weight and densities are in g/cc. To summarize previous experience, a particularly preferred embodiment of the present invention is such that the core layer consists of essentially linear low density polyethylene and the skin layer consists of essentially 20% propylene homopolymer and 80% propylene homopolymer. % of ethylene-propylene copolymer. Although the three-layer compositions described above are generally preferred over structures of four or more layers from a manufacturing economic standpoint, various five-layer compositions are also produced which are satisfactory from a physical property standpoint. Ivy. However, manufacturing costs for five-layer films are generally higher than for three-layer films. 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 are shown. Core layer 6 may be comprised of any of the core layer compositions previously described for the core layer of the three layer embodiment. The core layer can also consist essentially of (1) ethylene propylene copolymer (EPC) or (2) ethylene vinyl acetate copolymer (EVA). Skin layers 4 and 8 of the five layer embodiment can be comprised of any of the same skin layer compositions as previously described for skin layers 1 and 3 of the three layer embodiment of FIG. The five layer embodiment of FIG. 2 also includes intermediate layers 5 and 7. The core layer 2 of these intermediate layer embodiments may consist of any of the compositions previously mentioned. The compositions of the intermediate layers 5 and 7 can also be selected from the following group: (1) EVA (2) Blends of 20-80% LLDPE and 20-80% ionomer resins (3) Blends of 20-80% LMDPE and 20-80% ionomer resins According to experience A particularly preferred five-layer structure is skin layers 4 and 8 consisting essentially of ethylene-propylene copolymer (EPC), a blend of essentially 90% ethylene-vinyl acetate copolymer and 10% ionomer resin. and a core layer 6 consisting essentially of linear low density polyethylene. EPC is Soltex Chemical (So-
It is commercially available from Ltex Chemical under the trade name 42X01. EVA is Ala-thon
Du Pont Chemical under the trade name 3137.
Chemical). Ionomer resins are Surlyn and Surlyn 1601
du Pont Chemical under the trade name
Chemical). LLDPE is commercially available from Dow Chemical Company under the trade name Dowlex 2045. As will be readily apparent to those skilled in the art, all of the above weight percentages may vary slightly. These proportions can also be varied slightly as a result of adding or coating additives, such as the silicone mist mentioned above, and slip agents or antiblocking agents.
A preferred antiblocking agent is silica available from Johns Manville under the trade name White Mist. A suitable slip agent is Erucamide (Humko Ch.
-emical) Kemamide E
Stearamide (commercially available under the trade name Chemamide S from Humco Chemical Company), and N,N-dioleoylethylenediamine (commercially available under the trade name Acrawax C from Glyco Chemical Company) commercially available). A preferred silicone propellant is a liquid polyorganosiloxane commercially available from General Electric Company as General Electric SF18 polydimethylsiloxane. The general range of addition of these additives is as follows. (1) Silica: 250-3000ppm (2) Aklawax C: 200-4000ppm (3) Erucamide: 200-5000ppm (4) Stearamide: 200-5000ppm (5) Silicone spray: 0.5mg/square foot or more This specification and Throughout the claims, the word ``consisting essentially'' means that it does not exclude slight variations in the proportions by weight or of such additives. Further layers and/or small amounts of additives of the type described above may be added to the three- or five-layer structures of the present invention, as desired, depending on the desired shrinkage tension, shrinkage properties, and optical properties of the multilayer film of the present invention. Care must be taken not to adversely affect the characteristics and other properties. In the preferred method for manufacturing multilayer linear low density polyethylene or linear intermediate density polyethylene shrink films of the present invention, the basic steps are compounding the polymers used in the various layers and coextruding the layers to create the multilayer film. Then, the film is stretched and oriented biaxially. These steps and additional desirable steps are described in detail below. The process of the present invention begins by blending the raw materials (i.e., polymeric resins) in the desired proportions and ranges described above. Resins are usually purchased in pellet form from manufacturers and can be compounded in one of the many commercially available compounders known in the art. During the compounding process, additives and/or reagents that are desired to be used can be incorporated. The formulated resin and additives and/or reagents are then fed to the hopper of the extruder and then to the coextrusion die. For three layer films, at least three extruders should be used if different compositions are used in each layer. Two extruders are fed with the material desired for the inner and outer skin layers, and the other extruder is fed with the example linear low density or linear medium density polyethylene material desired for use in the core layer. Other extruders can be used as needed. Preferably, the materials are coextruded as a tube with a diameter depending on the racking ratio and the desired final diameter. This coextruded tube is relatively thin and is referred to as tape. Circular coextrusion dies are known to those skilled in the art and can be purchased from many manufacturers. In addition to performing tubular coextrusion, slotted dies can be used to extrude the material in planar form. Known single layer or multilayer extrusion coating methods can be used if desired. Other additional processes that may be used include bombarding the tape, or unexpanded tube, or sheet with high energy electrons generated from an accelerator to cross-link the tape material. When the film material consists primarily of ethylene, such as polyethylene or ethylene-vinyl acetate copolymers, cross-linking significantly increases the structural strength of the film, ie, the force with which the material can be stretched before tearing. Irradiation also improves the optical properties of the film and changes the properties of the film at elevated temperatures.
When using the irradiation process, the suitable irradiation dose is 0.5MR ~
It is 12.0MR. MR is an abbreviation for Megarad.
The megarad is 1 x <sup>106</sup> rad, and 1 rad is 1 rad per gram of irradiated material, regardless of the irradiation source.
It is the amount of ionizing radiation resulting from the absorption of 100 ergs of energy. In some cases, the multilayer film may be first stretched and then irradiated, or in sequential coatings, one or a group of layers may be irradiated and then subjected to other steps before the final stretching or orientation step. You can add layers. As previously mentioned, an optional additional step is to spray finely powdered silicone onto the interior of the newly extruded tape. Details of this process are described in US patent application Ser. No. 289,018, filed July 31, 1981. Co-extrusion is followed by quenching, irradiation if necessary, reheating of the extruded tape, and continuous expansion using internal air pressure to produce a thick-walled, narrow tape to the desired film thickness. Change it to a thin, wide film with a thin wall. This process is often referred to as the "trapped bubble method" or "racking" of orientation. After stretching, the air bubbles are deflated and the film is rolled onto semi-finished rolls called ``mill rolls''. The racking step orients the film laterally and to some extent longitudinally and rearranges the molecules, thereby imparting shrinkage ability to the film and modifying its physical properties. The additional longitudinal or machine direction stretch serves to collapse the blown bubbles at a faster rate than the rolls, which serve to transport the reheated ``tape'' to the area of lacing or blown bubbles. This can be achieved by rotating a shrink roll. All these orientation methods are known in the art. The following examples are included to clearly convey the scope of this invention to those skilled in the art. Example 1 A five-layer structure with a layer thickness ratio of approximately 2/2/1/2/2 was extruded using four extruders. 90% ethylene-vinyl acetate copolymer (vinyl acetate 12%) [Arason 3137 (melting coefficient 0.5)] and 10% ionomer resin [12% vinyl acetate] were added to a No. 1 extruder with die-type orifices for both intermediate layers. Surlyn 1601 (density
0.940, melting coefficient 1.4)]. The formulation also contained 1100 ppm erucamide (Chemamide E) and 1100 ppm stearamide (Chemamide S). The No. 2 extruder, which has a die-shaped orifice for the core layer, is made of 100% linear low-density polyethylene [Dowlex 2045 (density
0.920, melting coefficient 1.0)]. No. 3 and No. 3 with a die-shaped orifice for the epidermal layer.
Both extruders in No. 4 contained 100% ethylene-propylene copolymer (3.5% ethylene) [Soltex] mixed with 1100 ppm erucamide [Chemamide E], 1100 ppm stearamide [Chemamide S], and 1100 ppm silica [White Mist]. 42X01
(melt flow rate 4.5)] was supplied. Extruder No. 1 was maintained at a temperature range of 390-425°.
Extruder No. 2 was maintained at a temperature range of 410-470°C. Extruder No. 3 was maintained at a temperature range of 350-370°. Extruder No. 4 was maintained at a temperature range of 345-365°. The circular die mold was kept at a temperature range of 390-435㎓. After extruding the layers through a 10-inch circular die-type orifice, approximately 37 feet/37 feet of tubular extrudate with a tape thickness of approximately 15 mils and a tube width of approximately 9 5/8 inches are produced.
Quench cooling was achieved by passing through cold water at a rate of 10 min.
The tube was then reheated and oriented by passing it through a heating zone or furnace at a rate of 38 feet/minute.
The furnace was heated by horizontal, vertical, and steam heating elements. In this example, a horizontal heating element is
I kept it at 200〓. The vertical heating element is kept at 300〓,
Steam at 2 psi was supplied to a steam heating element that provided heat by passing it through a vip or can placed inside the furnace. After heating as above, the cylindrical extrudate is expanded by approximately 4.8 to 1 times in the transverse direction and approximately 4.3 to 1 times in the longitudinal direction.
Stretched 1x. Thereafter, the film was cooled by quenching with water to fix the blended structure. The final film gauge was approximately 75 gauge. The experimental data obtained for this film composition are listed in Table 1 along with data for other examples. Example 2 A five-layer structure with layer thicknesses of approximately 2/2/1/2/2 was extruded using four extruders. No. 1 extruder with die orifices for both intermediate layers contains 1100 ppm Erucamide [Chemamide E]
Blend of 50% ethylene-vinyl acetate copolymer (vinyl acetate 12%) [Arason 3137 (melting coefficient 0.5)] with 50% linear low density polyethylene [Dowlex 2045 (density 0.920, melting coefficient 1.0)] was supplied.
No. 2 with a die-shaped orifice for the core layer
The extruder uses 100% linear low-density polyethylene [Gurex 2045 (density 0.920, melting coefficient 1.0)]
was supplied. Both No. 3 and No. 4 extruders each have a die-type orifice for the skin layer.
1100ppm of erucamide [chemamide E] and
A 100% ethylene propylene copolymer (2.7% ethylene) (ARCO K-193 (melt flow 2.3)) mixed with 1100 ppm silicone (white mist) was fed. Extruder No. 1 was maintained at a temperature range of 405-415°.
Extruder No. 2 was maintained at a temperature range of 400-475°. Extruder No. 3 was maintained at a temperature range of 355-435°. Extruder No. 4 was maintained at a temperature range of 355-410°C. The circular die mold was kept at a temperature range of 390-425㎓. After extruding the layers through a 10 inch circular die orifice, the tape is approximately 17 mils thick and approximately 8 mm wide.
The 3/4 inch cylindrical extrudate was quench cooled by passing it through cold water at a rate of about 39 feet/minute. The tubular extrudate was then reheated and oriented by passing it through a heating zone or furnace at a rate of about 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°. Vertical heating elements are kept at 343〓 and steam heating elements, which supply heat by passing through pipes or cans placed inside the furnace, are
7 psi water vapor was supplied. After heating as above, the cylindrical extrudate is expanded by approximately 4.8 to 1 times in the transverse direction and approximately 4.5 to 1 times in the longitudinal direction.
Stretched 1x. Thereafter, the oriented molecular structure was fixed by quenching with water. The final film thickness was approximately 75 gauge. The data obtained for this film composition are listed in Table 1. Example 3 A three-layer structure with a layer thickness ratio of approximately 1/3/1 was extruded using four extruders. Extruders No. 1 and 2 with die orifices for the core layer contained 3300 ppm erucamide [Chemamide E].
100% linear low density polyethylene [Dowrex
2045 (density 0.920, melting coefficient 1.0)] was supplied. No. 3 with a die-shaped orifice for the epidermal layer
and No. 4 extruder both contain 80% ethylene-propylene copolymer (3.5% ethylene) mixed with 3300 ppm erucamide [Chemamide E], 1100 ppm silica [White Mist], and 1650 ppm Akrawax C. A blend of Soltex 42X01 (melting coefficient 4.5) and 20% propylene homopolymer (Hercules PD064 (density 0.906, melting coefficient 3.5)) was provided. Extruder No. 1 was maintained at a temperature range of 395-485°.
Extruder No. 2 was maintained at a temperature range of 425-470°. Extruder No. 3 was maintained at a temperature range of 370-375°. Extruder No. 4 was maintained at a temperature range of 370-375°. The circular die was kept at a temperature of 385°C. For this example, the actual temperatures at which the extruder and die were held were not listed. After extruding the layer through a 10 inch circular die orifice, it was quenched by passing cold water through the cylindrical extruder at a rate of about 39.5 feet/minute. During extrusion of the tape, the inside of the extruded tube was coated with a fine mist of silicone at a rate of 5-7 mg/ft². The cooled cylindrical extrudate was then reheated and oriented by passing it through a heating zone or furnace at a rate of about 37.7 feet/minute. The furnace was heated by horizontal, vertical, and steam heating elements. In this example, a horizontal heating element is
I kept it at 200〓. The vertical heating element is kept at 305〓,
3.5 psi for steam heating elements that provide heat by passing through pipes or cans placed inside the furnace
of water vapor was supplied. After heating as described above, the cylindrical extrudate was stretched about 4.8-1 times in the transverse direction and about 4.5-1 times in the longitudinal direction. Thereafter, the film was quenched with water to fix the orientation structure. final film
The gauge was approximately 75 gauge. The data obtained for this film composition are listed in Table 1.

【table】

[Table] All data in Table 1 above are average values obtained using ASTM standard methods. It will be apparent to those skilled in the art that from the foregoing description and examples, many modifications and variations can be made within the spirit and scope of the invention; It is to be understood that the specific examples shown are for illustration purposes only.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a preferred three-layer embodiment of the invention, and FIG. 2 is a cross-sectional view of a preferred five-layer embodiment of the invention.

Claims (1)

[Claims] 1. Contains a core layer and further contains two skin layers, the core layer containing linear low density polyethylene, and the skin layer comprising: a. ethylene-propylene copolymer. b. A blend of 70-90% by weight of ethylene-propylene copolymer and 10-30% by weight of propylene homopolymer; c. A blend of 70-90% by weight of ethylene-propylene copolymer and 10-30% by weight of A composition selected from the group consisting of a blend with linear low density polyethylene; Contains multilayer polyolefin film. 2. A multilayer polyolefin-in-film according to claim 1, comprising a core layer consisting essentially of linear low density polyethylene. 3 A core layer consisting essentially of linear low density polyethylene and two skin layers consisting essentially of a blend of 80% by weight ethylene-propylene copolymer and 20% by weight propylene homopolymer. A multilayer polyolefin film according to claim 1 containing: 4 a core layer consisting essentially of linear low density polyethylene; two intermediate layers consisting essentially of a blend of 90% by weight ethylene-vinyl acetate copolymer and 10% by weight ionomer resin; and ethylene. - A multilayer polyolefin film according to claim 1, containing a skin layer consisting essentially of a propylene copolymer. 5. The multilayer polyolefin in-film according to claim 1, further comprising at least two intermediate layers, the intermediate layer containing linear low density polyethylene. 6 The core layer is made of a blend of 10-100% by weight of linear low-density polyethylene and 0-90% by weight of ethylene-propylene copolymer; b 10-80% by weight of linear low-density polyethylene; 20
Blends with ~90% by weight of ethylene-vinyl acetate copolymer; c 10-80% by weight of linear low density polyethylene, 10
~80% by weight ethylene-vinyl acetate copolymer,
and 10-80% by weight of ionomer resin; d 10-80% by weight of linear low density polyethylene and 20
A multilayer polyolefin film according to claim 1, comprising a copolymer blend selected from the group consisting of: -90% by weight of low density polyethylene; 7 further comprising an intermediate layer, a blend of 10-100% by weight of linear low-density polyethylene and 0-90% by weight of ethylene-propylene copolymer; b 10-100% by weight of ethylene-propylene copolymer; Blend of linear medium density polyethylene and 0 to 90% by weight ethylene/propylene copolymer; c 10 to 80% by weight linear low density polyethylene and 20% by weight
Blends with ~90% by weight of ethylene-vinyl acetate copolymer; d with 10-80% by weight of linear medium density polyethylene;
Blends with 20-90% by weight of ethylene-vinyl acetate copolymer; e 10-80% by weight of linear low-density polyethylene, 10
~80% by weight ethylene-vinyl acetate copolymer,
and blends with 10-80% by weight of ionomer resin; f 10-80% by weight of linear medium density polyethylene;
Blends with 10-80% by weight of ethylene-vinyl acetate copolymer and 10-80% by weight of ionomer resin; g 10-80% by weight of linear low density polyethylene and 20
Blends with ~90% by weight of low density polyethylene; h with 10-80% by weight of linear medium density polyethylene
Blends with 20-90% by weight of low-density polyethylene; i ethylene-vinyl acetate copolymer; j 20-80% by weight of linear low-density polyethylene;
Blends with ~80% by weight ionomer resin; k with 20-80% by weight linear medium density polyethylene
A multilayer polyolefin film according to claim 1 having a composition selected from the group consisting of: 20-80% by weight of an ionomer resin;