HK1056703A - Die-cuttable biaxially oriented films - Google Patents

Description

Die-cuttable biaxially oriented film

Technical Field

The present invention relates to conformable and die-cuttable biaxially oriented films and label stock, and more particularly to biaxially stretch oriented monolayer and multilayer films and label stock.

Background

The manufacture and cutting of pressure sensitive adhesive materials for labels has long been known and consists of a face or facestock material for labels or signs, a layer of pressure sensitive adhesive applied to the back side thereof and a release liner or carrier covering the adhesive. The release liner or carrier serves to protect the adhesive during shipping and storage, to facilitate smooth transfer of a row of individual labels after they have been die cut, and to enable the carrier to be peeled off smoothly from the face stock layer in a labeling line to the point where the individual labels are sequentially dispensed. The release liner or carrier remains uncut from die cutting to dispensing and can be wound and unwound to facilitate storage, movement and use of the row of individual labels carried on the liner.

In general, the feature that the label is not reliably dispensed means that the label is not dispensed as the carrier moves along the peel plate, i.e. does not "leave" the carrier and adhere to the object being dispensed. This failure to dispense is believed to be related to an excessive peel value between the label facestock and the release liner. Dispensability also depends on the stiffness of the facing material. Failure to dispense is also characterized by the label becoming crumpled at the dispensing speed of transfer from the carrier to the object due to insufficient stiffness of the label. Another particular requirement in various label application applications is the ability to apply polymer film labels at high production speeds, as increasing production speeds has significant cost savings advantages.

In various label applications, it is desirable that the facestock be a polymeric film having properties lacking from paper, such as clarity, durability, strength, water resistance, abrasion resistance, gloss, and other properties. Historically, polymeric facestock materials have been used at thicknesses greater than about 3 mils (75 microns) to ensure dispensability on automatic labeling machines. For example, in label applications, plasticized polyvinyl chloride films having a thickness of about 3.5 to 4.0 mils (87.5 to 100 microns) have been used because of the flexibility required. However, it has been recognized that migration of plasticizers added to PVC films to convert rigid films to flexible films is a major cause of a reduction in the desired properties of such films (e.g., adhesion, colorability, shrinkage, and flexibility). Eventually, plasticizer migration can cause wrinkling, cracking, and visible damage to the face layer and/or label. It is also desirable to reduce the thickness or thickness of the facing material to save material costs. The reduction in thickness of the face stock often results in a reduction in stiffness and thus the ability to die cut and dispense labels in a reliable, industry accepted manner using automated machinery. The labels are also made from polymeric facestock materials in place of polyvinyl chloride for environmental protection.

The polymeric materials used in the prior art for making labels include biaxially oriented polypropylene ("BOPP") having a thickness of as low as about 2.0 mils (50 microns). These materials are cost effective due to their low cost and have sufficient stiffness to permit good dispensing. However, these materials have high tensile modulus in both the Machine Direction (MD) and the Cross Direction (CD), and the resulting labels are poorly adaptable.

For rigid surfaces such as glass, adaptability problems have been encountered, for example, when biaxially oriented films are applied to rigid objects such as glass bottles, the application process cannot be successfully completed. Higher stiffness labels tend to bridge the surface depressions and molded seams formed during bottle formation, thus creating an undesirable surface appearance on the applied label like trapped air bubbles. This problem has somewhat hindered the replacement of prior art glass bottle labeling techniques with pressure sensitive adhesive labels, such as the direct adhesion of enamel to the bottle surface during the glass bottle manufacturing process, but this appearance is perceived by consumers as unattractive. This enamel technology is not environmentally acceptable due to the hazardous ink components and contamination of the ink during the recycling of the broken glass bottles. The test with the relatively stiff oriented polypropylene film has also not been entirely successful for soft objects such as plastic bottles because such labels do not have the flexibility required to conform to soft plastic containers. Oriented polypropylene films are also more difficult to print than PVC or polyethylene films.

Other materials that may be used are low cost, conformable unoriented polyethylene and polypropylene films. However, when both films are thin, both are difficult to die cut and cannot be dispensed. In europe, an unoriented thicker polyethylene capstock material has been successfully used to make labels. The facing material is die-cuttable and can be dispensed on an automated dispensing device operating at high speeds. A conventional thickness for such european "standard" polyethylene capstock material is about 4.0 mils (100 microns). The tests for reducing the thickness of the polyethylene facestock material to reduce cost have not been made because the thinner polyethylene facestock is not easily die cut, die marks are left on the liner after die cutting, and cut lines are left on the die cut labels. In addition, thinner facing materials are difficult to dispense at higher running speeds along the stripper plate due to their lower stiffness.

Summary of The Invention

One embodiment of the present invention is a die-cuttable biaxially oriented monolayer film comprising polyethylene, propylene polymer or copolymer, or mixtures thereof, having a density of about 0.940 g/cc or less, wherein the film has a tensile modulus in the machine direction greater than the tensile modulus in the transverse direction of about 150000 psi or less, and is free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters. In one embodiment, the biaxially oriented monolayer film has been biaxially stretch oriented and heat set.

In another embodiment, the present invention is directed to a die-cuttable, stretch-oriented multilayer film comprising:

(A) a substrate layer having an upper surface and a lower surface, the substrate layer comprising polyethylene having a density of about 0.940 g/cc or less, propylene homopolymer or copolymer, or mixtures thereof, the substrate layer being free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters, and

(B) a thermoplastic polymer first skin layer adhered to the upper surface of the substrate layer, wherein the multilayer film has a tensile modulus in the machine direction that is greater than the tensile modulus in the cross direction, and a tensile modulus in the cross direction of about 150000 psi or less. The biaxially oriented multilayer film is particularly useful in the manufacture of facestock materials for adhesive labels that contain an adhesive.

In yet another embodiment, the present invention is directed to a die-cuttable biaxially stretched, oriented monolayer film comprising at least one polyolefin wherein the film has been stretch oriented at a machine direction stretch ratio of from about 9: 1 to about 10: 1 and a transverse direction stretch ratio of from greater than 1: 1 to about 3: 1.

Description of the preferred embodiments

In one embodiment, the present invention relates to the manufacture of biaxially stretch oriented monolayer and multilayer films wherein the films are characterized by good conformability, die-cuttability and/or dispensability. In some embodiments, high clarity films can be made. Although conformable films are generally less die-cuttable, the present invention provides conformable films having desirable die-cuttability, and thus, may be used in label applications for bottles, tubes, or other applications where transparent and conformable labels are desired. Multilayer film structures comprising skin layers for providing printability, or skin layers for providing other desirable properties such as stiffness, which can reduce film thickness, or both, can be made according to the process of the present invention.

In one embodiment, the biaxially stretched, oriented monolayer film of the present invention comprises polyethylene, a propylene polymer or copolymer, or mixtures thereof, having a density of about 0.940 g/cc or less, wherein the film has a machine direction tensile modulus greater than the transverse direction tensile modulus of about 150000 psi or less, and is free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters.

Suitable ethylene homopolymers include polyethylene having a density of about 0.940 or less. Polyethylene having a density of about 0.850 to about 0.925 grams per cubic centimeter is commonly referred to as low density polyethylene, while polyethylene having a density between about 0.925 and about 0.940 grams per cubic centimeter is technically referred to as medium density polyethylene. The low and medium density polyethylenes can also be characterized by a melt index (as determined by ASTM test method D1238, condition E) of from 0.5 to about 25. In addition to the above densities and melt indices, low density polyethylene can be characterized by a tensile strength of between about 2200 and about 3200 psi (typically about 2700 psi), while medium density polyethylene can be characterized by a tensile strength of between about 3000 and about 4000 psi (typically about 3400 psi).

The low and medium density polyethylenes suitable for use as the first skin layer of the facing material of the present invention are commercially available from a variety of sources. Examples of suitable polyethylenes are summarized in table 1 below.

TABLE 1

Commercial polyethylene

Trade purchased product brand	Manufacturing company	Melt flow index (g/10 min)	Density (g/cm)3)
				Rexene1017	Rexene	2.0	0.920
Rexene1058	Rexene	5.5	0.922
				Rexene1080	Rexene	2.0	0.930
Rexene2030	Rexene	5.0	0.919
				Rexene2034	Rexene	7.5	0.925
Rexene2038	Rexene	9.0	0.917
				Rexene2040	Rexene	12.0	0.917
Rexene2049	Rexene	20.0	0.917
				NA-334	Equistar	6.0	0.918
NA-217	Equistar	5.5	0.923
				NA285-003	Equistar	6.2	0.930
Exact3027	Exxon	3.5	0.900
				Exact3022	Exxon	9.0	0.905
Exact3139	Exxon	7.5	0.900
				SLP9053	Exxon	7.5	0.900
AffinityPF1140	Dow Chemical	1.6	0.895
				Sclair11G1	Nova	0.72	0.920
Dowlex2027	Dow Chemical	4.0	0.941

The monolayer film may comprise a propylene homopolymer or copolymer, or a blend of a propylene homopolymer and at least one propylene copolymer. When a blend of homopolymer and copolymer is used to make a film, the blend may comprise from about 5% to about 95% by weight of homopolymer and from about 95% to about 5% by weight of copolymer. Propylene homopolymers that may be used alone or in admixture with the propylene copolymer as described above include various propylene homopolymers such as those having a Melt Flow Rate (MFR) of from about 1 to about 20 (as determined by ASTM test method D1238, condition L). Propylene homopolymers having a melt flow rate of at least about 4 (preferably at least about 8) are particularly useful and impart good die-cutting properties to the film. Suitable propylene homopolymers can also be characterized as having a density of from about 0.88 to about 0.92 grams per cubic centimeter.

For many suitable propylene homopolymers, a variety of sources are commercially available. Some suitable homopolymers are summarized in table II below.

TABLE 2

Commercially available propylene homopolymer

Trade purchased product brand	Manufacturing company	Melt flow index (g/10 min)	Density (g/cm)3)
				WRD5-1057	Union Carbide	12.0	0.90
DX5E66	Union Carbide	8.8	0.90
				5A97	Union Carbide	3.9	0.90
5E98	Union Carbide	3.2	0.90
				Z9470	Fina	5.0	0.89
Z9470HB	Fina	5.0	0.89
				Z9550	Fina	10.0	0.89
6671XBB	Fina	11.0	0.89
				3576X	Fina	9.0	0.89
3272	Fina	1.8	0.89
				SF6100	Montell	11.0	0.90

The propylene copolymers which may be employed generally include copolymers of propylene with up to about 40 weight percent of at least one alpha-olefin selected from the group consisting of ethylene and alpha-olefins having from 4 to about 8 carbon atoms. Examples of suitable alpha-olefins include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Propylene copolymers generally useful in the present invention include copolymers of propylene with ethylene, 1-butene or 1-octene. Propylene alpha-olefin copolymers suitable for use in the present invention include random copolymers and block copolymers, although random copolymers are generally preferred. Blends of the copolymers, as well as blends of the copolymers with propylene homopolymers, may be used as components of the substrate layer. In a preferred embodiment, the propylene copolymer is a propylene-ethylene copolymer having an ethylene content of from about 0.2% to about 10% by weight. Preferably, the ethylene content is from about 3% to about 10% by weight, and more preferably from about 3% to about 6% by weight. For propylene-1-butene copolymers, a 1-butene content of up to about 15% by weight is suitable. In one embodiment, the 1-butene content is generally in the range of about 3 weight percent up to about 15 weight percent, and in other embodiments, the content may range from about 5 weight percent to about 15 weight percent. Propylene-1-octene copolymers suitable for use in the present invention may contain up to about 40% by weight of 1-octene. Generally, the propylene-1-octene copolymer may contain up to about 20% by weight of 1-octene.

Propylene copolymers suitable for use in the present invention can be prepared by techniques known to the skilled person and many such copolymers are commercially available. For example, copolymers suitable for use in the present invention may be prepared by copolymerizing propylene with an alpha-olefin, such as ethylene or 1-butene, in the presence of a single site metallocene catalyst. Some suitable commercially available propylene copolymers are listed in table III below. Propylene copolymers suitable for use in the present invention have an MFR of from about 1 to about 20, preferably from about 1 to about 12.

TABLE 3

Commercially available propylene homopolymer

Commercial product name	Manufacturer(s)	% ethylene	% 1-butene	Melt flow Rate (g/10 min)	Density (g/cm)3)
						DS4D05	Union Carbide	-	14	6.5	0.890
DS6D20	Union Carbide	3.2	-	1.9	0.890
						DS6D81	Union Carbide	5.5	-	5.0	0.900
SRD4-127	Union Carbide	-	8	8.0	NA
						SRD4-104	Union Carbide	-	11	5.0	NA
SRD4-105	Union Carbide	-	14	5.0	NA

The monolayer films of the invention described above are also characterized by being free of copolymers of vinyl monomers and ethylenically unsaturated carboxylic acid or ester comonomers. Such copolymers are considered to be absent from the film when the amount of such copolymers in the film is less than about 0.1% by weight. Specific examples of copolymers that are outside the contemplated scope of the films of the present embodiments are copolymers of Ethylene Vinyl Acetate (EVA), Ethylene Methyl Acrylate (EMA) and ethylene n-butyl acrylate (EnBA).

While the films of the present invention may contain other polymers and copolymers, the level of incompatible polymers and copolymers should be minimized or substantially avoided when it is desired to obtain a clear (low haze) film. The level of incompatible polymer that can be included depends on the particular polymer (e.g., degree of incompatibility) and the degree of haze permitted.

The monolayer films of the present invention may incorporate various nucleating agents and particulate fillers. The nucleating agent should be added in an amount sufficient to provide the desired modification of the crystalline structure without adversely affecting the desired film properties. It is generally desirable to utilize nucleating agents to improve the crystalline structure and provide a large number of relatively small crystals or spherulites to improve the clarity, stiffness and die-cutting properties of the film. It is clear that the amount of nucleating agent added to the film formulation should not adversely affect the transparency of the film. Nucleating agents that have been used so far for polymer thin films include inorganic nucleating agents and organic nucleating agents. Examples of inorganic nucleating agents include carbon black, silica, kaolin, and talc. Organic nucleating agents that have been proposed for use in polyolefin films include salts of aliphatic mono-or dibasic acids or arylalkyl acids such as sodium succinate, sodium glutarate, sodium caprate, sodium 4-methylpentanoate, aluminum phenylacetate and sodium cinnamate. Alkali metal and aluminum salts of aromatic and cycloaliphatic carboxylic acids, such as aluminum, sodium or potassium benzoate, sodium beta-napthalate, lithium benzoate, and aluminum tert-butylbenzoate are suitable organic nucleating agents. Substituted sorbitol derivatives such as bis (benzylidene) sorbitol and bis (alkylbenzylidene) sorbitol, wherein the alkyl group contains from about 2 to about 18 carbon atoms, and the like, are also suitable nucleating agents. More specifically, such as 1, 3, 2, 4-dibenzylidene sorbitol; sorbitol derivatives such as 1, 3, 2, 4-di-p-methylbenzylidenesorbitol and 1, 3, 2, 4-di-p-methylbenzylidenesorbitol are suitable nucleating agents for polypropylene. For suitable nucleating agents, a variety of sources are commercially available. Millad 8C-41-10 is a masterbatch of 10% Millad3988 (sorbitol nucleating agent) and 90% polypropylene, available from Milliken Chemical Co.

When the granulating agent is incorporated into a film, the amount of granulating agent incorporated into the film formulation of the present invention is generally quite low, ranging from about 100 to about 2000 or 4000ppm of the film. The preferred amount of nucleating agent should not exceed 2000ppm, and in one embodiment the optimum concentration is about 300 and 500 ppm.

The film may contain other additives and particulate fillers to improve the properties of the film. For example, the film may contain a colorant such as TiO₂、CaCO₃And the like. E.g. small amounts of TiO₂The presence of (b) will result in a white face. The substrate layer may also contain an antiblocking agent. AB-5 is an antiblock masterbatch comprising 5% solid state synthetic amorphous silica and 95% low density polyethylene available from Schulman inc. (3550West Market Street, Akron, Ohio 44333). ABPP05SC is a propylene copolymer antiblock masterbatch containing 5% synthetic amorphous silica available from Schulman. The antiblock agent (silica) can be used in the substrate layer in an amount of about 500 to about 5000ppm, with about 1000ppm being preferred.

In some embodiments, particularly where it is desired that the film be transparent, although the film does not contain inert particulate filler, a very small amount of particulate filler may still be present in the film due to impurities and the like. The term "free" means that the particulate filler content of the film is less than about 0.1% by weight. Films that do not contain particulate fillers are particularly useful where it is desired to produce transparent films that can be characterized by low haze, e.g., less than 10% or less than 6% haze, and in some cases less than about 2%. Haze or clarity is measured with a BYK-Garderer haze-gloss meter known in the art. It has been observed that the biaxially oriented film of the present invention which is free of filler particles has high transparency and in some cases, the film is clear and transparent. As noted above, when a transparent film is desired, the film should contain no or only a small amount of incompatible polymers and copolymers.

The monolayer films of the present invention can be formed by a variety of techniques known to the skilled artisan, including blown or cast extrusion, extrusion coating, or a combination of such techniques. As noted above, the films of the present invention are biaxially stretch oriented. Simultaneous biaxial orientation or sequential biaxial orientation may be employed in the preparation of the films of the present invention. One preferred method of making a monolayer film is a simultaneous biaxial orientation process.

While the die-cuttable biaxially stretch-oriented monolayer films claimed in this invention may be produced by a stretching process in which the Machine Direction (MD) stretch is equal to or greater than the Cross Direction (CD) stretch, in one embodiment it is preferred that the MD stretch orientation be at least about 10%, or even 20%, greater than the CD stretch orientation. The MD oriented stretch ratio may be from about 3: 1 to about 10: 1 or more, although typically the MD stretch ratio is from about 5: 1 to about 10: 1. In other embodiments, the MD stretch ratio may be from about 9: 1 to about 10: 1 or more. As noted above, CD stretch ratio is often lower than MD stretch ratio. Thus, the CD stretch ratio may be from greater than 1: 1 to about 5: 1, or from greater than 1: 1 to about 3: 1 or from greater than 1: 1 to about 2: 1. In a specific example of the latter embodiment, a stretch oriented polyolefin monolayer film having an MD stretch ratio of from 9: 1 to 10: 1 is CD stretch oriented at a stretch ratio of greater than 1: 1 to about 2: 1 or 3: 1 or 4: 1. Polyolefins useful in this embodiment include polyethylene, polypropylene, copolymers of propylene and up to about 40 weight percent of at least one alpha-olefin selected from ethylene and alpha-olefins having from 4 to about 8 carbon atoms as described above, and mixtures thereof. Thus, in this particular embodiment, the polyolefins include low density polyethylene, medium density polyethylene, and high density polyethylene, although low and medium density polyethylene is more commonly used. High density polyethylene refers to polyethylene having a density of greater than about 0.940 to about 0.965 grams per cubic centimeter.

The monolayer film of the present invention is formed biaxially oriented by hot stretching at or above the softening temperature of the film. The temperature employed in the hot-stretching step depends inter alia on the composition of the film and on the presence or absence of nucleating agents. When sequential orientation is employed, the MD stretching temperature may be different than the CD stretching temperature. Generally, MD orientation is performed at a temperature lower than the CD orientation temperature. For example, for a propylene homopolymer, the temperature at which MD orientation is performed may be about 140 ℃ and the temperature at which CD orientation is performed may be about 180 ℃.

In one embodiment of the invention, the single-layer film, which is stretch-oriented to the desired draw ratio under heated conditions, is then passed through an annealing roller to perform an annealing or heat-setting operation. After the heat-setting or annealing operation, the film is passed through cooling rolls to complete the heat-stretching and heat-setting operation. In another embodiment, the heat-stretched film is relaxed in the MD and CD to about 5% to about 25%, typically about 10% to about 20%, prior to the annealing or heat-setting step. The temperature at which the hot stretching step and heat setting step are carried out will depend on the particular polymer used to form the monolayer film and may range from about 110 c to about 180 c. The temperature at which the hot stretching and heat setting steps are carried out may be the same, although in some cases the temperature at which the heat setting step is carried out is slightly higher than the temperature at which the hot stretching step is carried out. Thus, the heat-setting step may be carried out at up to about 180 ℃. When the hot-stretched film of the present invention is subjected to a heat-setting or annealing step, the film is typically heat-set or annealed for about 5 to about 25 seconds, more typically about 10 to about 20 seconds. The heat-set or annealed stretch-oriented monolayer film of the present invention has substantially no "memory" effect that returns to its previous configuration under the influence of heat. That is, the heat-set and annealed films of the present invention will not shrink or deform when subsequently subjected to high temperatures.

The thickness of the monolayer film described above may depend on the intended use of the film and may range from about 0.5 mils (12.5 microns) to about 6 mils (150 microns). In general, however, the biaxially stretch oriented monolayer films of the present invention will have a thickness of from about 1 mil to about 3.5 or 4 mils. In one embodiment, the film thickness is from about 2 to about 2.5 mils.

The biaxially stretch oriented monolayer film of the present invention described above has stiffness characteristics that allow the film to be used in applications such as a die-cuttable label stock. Thus, the biaxially stretch oriented monolayer film of the present invention may have a Gurley stiffness in the machine direction of from about 3 to about 50, typically from about 5 or 10 up to about 50. The transverse Gurley stiffness of the monolayer film of the present invention is generally lower than the machine direction Gurley stiffness. The Gurley stiffness of the monolayer film of the present invention is determined according to TAPPI Gurley stiffness test T543 pm.

As noted above, the films of the present invention may also comprise a stretch-cuttable, oriented, multilayer film comprising:

(A) a substrate layer having an upper surface and a lower surface, the substrate layer comprising polyethylene having a density of about 0.940 g/cc or less, propylene homopolymer or copolymer, or mixtures thereof, the substrate layer being free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters, and

(B) a thermoplastic polymer first skin layer adhered to the upper surface of the substrate layer, wherein the multilayer film has a tensile modulus in the machine direction that is greater than the tensile modulus in the cross direction, and a tensile modulus in the cross direction of about 150000 psi or less.

Any of the monolayer films described above may be used as the substrate layer of the multilayer film prior to orientation. That is, the substrate layer of the multilayer film of the present invention can comprise any of the polyethylenes described above, any of the propylene homopolymers or copolymers, or mixtures thereof, wherein the substrate layer is free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters. The substrate layer may also contain any of the ingredients such as fillers, colorants, nucleating agents, antiblocking agents, and the like, as optional in the monolayer film described above. If it is desired to obtain a transparent multilayer film, the substrate layer should be free of inert particulate filler. If it is desired to obtain opaque multilayer films, the substrate layer may contain the particulate fillers described above.

The first skin layer may comprise any of a variety of other thermoplastic polymers. Examples of thermoplastic polymers and copolymers suitable for use as the first skin layer of the multilayer film of the present invention include polyolefins, polyamides, polystyrenes, polystyrene-butadienes, polyesters, polyester copolymers, polyurethanes, polysulfones, polyvinylidene chlorides, styrene-maleic anhydride copolymers, styrene-acrylonitrile copolymers, ethylene methacrylic acid sodium or zinc salt based ionomers, polymethyl methacrylates, celluloses, fluoroplastics, acrylic polymers and copolymers, polycarbonates, polyacrylonitriles, ethylene-vinyl acetate copolymers, and mixtures thereof. The choice of the composition of the first skin layer is a function of the desired properties of the first skin layer (e.g., cost, weatherability, printability, etc.).

The first skin layer may, indeed often contains, a mixture of a polyolefin, such as polyethylene, propylene polymers and copolymers, and a copolymer of ethylene and a comonomer of an ethylenically unsaturated carboxylic acid or ester, such as EVA. For example, one suitable skin composition comprises a 50: 50 ratio blend of polypropylene and EVA.

The first skin layer may also contain other additives such as particulate fillers, antiblocking agents, nucleating agents, and the like, as described above. When it is desired to obtain a transparent multilayer film, the first skin layer (and substrate layer) is generally free of particulate filler. If it is desired to obtain an opaque film, the skin (and/or substrate) may contain particulate fillers. Thus, the opaque to transparent multilayer films of the present invention can be made, and the transparent films can be characterized by a haze of less than 10%, or less than 6%, or even less than about 2%.

In yet another embodiment of the present invention, a multilayer film comprising a substrate layer having an upper surface and a lower surface and a first skin layer of a thermoplastic polymer adhered to the upper surface of the substrate layer may also comprise a second skin layer adhered to the lower surface of the substrate layer, the second skin layer may comprise any of the thermoplastic polymers described above as suitable for the first skin layer, and the composition of the second skin layer may or may not be the same as the first skin layer. In general, the two skin layers are not identical due to the different performance requirements for the two skin layers. The first surface layer is required to have printability, weather resistance and the like, and the second surface layer is required to have good adhesion properties to the adhesive layer.

The multilayer films of the present invention can be made by a variety of techniques known to the skilled artisan, including blown or cast extrusion or extrusion coating or a combination of these techniques. U.S. Pat. No. 5186782(Freedman) and U.S. Pat. Nos. 5242650(Rackovan et al) and 5435963(Rackovan et al) disclose methods suitable for making multilayer films. These patents are incorporated herein by reference. The multilayer film can be formed by simultaneous extrusion using a coextrusion die of a known type, and then the layers are bonded to each other to form a permanent composite, thereby forming an integral coextruded body. Alternatively, the substrate layer is extruded onto the substrate to form the substrate layer, and then the first skin layer (and optionally the second skin layer) is formed on the substrate layer by extrusion coating techniques to form a two or three layer structure in which the layers are bonded to each other to form a permanent composite. Yet another embodiment is made by separately forming two or three films by extrusion techniques and then laminating them together by applying heat and pressure.

Generally, the substrate layer is thicker than the first skin layer and the second skin layer. In another, although generally not preferred, embodiment, the first skin layer may be thicker than the substrate layer. Thus, the thickness ratio of the three-layer film may be about 90: 5 to 5: 90. However, preferred thickness ratios of the three-layer film (substrate layer: first skin layer: second skin layer) include 90: 5, 80: 10, 70: 15, 85: 5: 10 and 80: 5: 15.

As noted above, the multilayer film of the present invention is biaxially stretch oriented. Either simultaneous biaxial orientation or sequential biaxial orientation techniques may be used to prepare the multilayer films of the present invention. In one embodiment of the present invention, the preferred method of making the multilayer film of the present invention is a simultaneous biaxial orientation technique.

In some examples, the die-cuttable biaxially stretch-oriented multilayer films of the present invention described above can be made by Machine Direction (MD) stretching and Cross Direction (CD) stretching of the film, wherein the amount of machine direction stretching is equal to or greater than the amount of cross direction stretching, and the MD stretch orientation is often at least about 10%, or even 20%, greater than the CD stretch orientation. The MD oriented stretch ratio may be from about 3: 1 to about 10: 1 or more, but a preferred MD stretch ratio is from about 5: 1 to about 10: 1. In other embodiments, the MD stretch ratio is from about 9: 1 to about 10: 1 or more. As noted above, the CD stretch ratio is typically lower than the MD stretch ratio. Thus, the CD stretch ratio is from greater than 1: 1 to about 5: 1, or from greater than 1: 1 to about 3: 1 or from greater than 1: 1 to about 2: 1.

The thickness of the multilayer film described above is from about 0.5 mil (12.5 microns) to about 6 mils (150 microns), depending on the intended use of the film. In general, however, the multilayer films of the present invention can have a thickness of from about 1 to about 3.5 or 4 mils, or from about 2 to about 3 mils. This thickness is particularly suitable for the manufacture of labels to be applied to rigid and flexible objects. As previously mentioned, the multilayer film facestock material of the present invention is particularly characterized as being capable of being formed into very thin films (i.e., 1-3 mils) suitable for use in label applications.

The selection of the particular polymer used as the second skin layer depends on the properties and characteristics desired for the second skin layer. The polymer used as the second skin layer should be compatible with the substrate layer polymer to ensure adequate adhesion to the substrate layer. For example, if the substrate layer comprises a propylene polymer, a second skin layer comprising at least some propylene polymer will adhere to the substrate layer without forming an intermediate transition layer. It has been found that if the second skin layer is of a different composition than the first skin layer, the facing materials have a reduced tendency to stick to each other when wound.

In one embodiment, it is preferred that the second skin layer comprises a polymer which is softer than the propylene polymer or copolymer, or blend of propylene polymer and copolymer, used to make the substrate layer, especially when the second skin layer is bonded to the release liner by means of an adhesive, in particular it is preferred that the tensile modulus of the material of the second skin layer is lower than the tensile modulus of the material constituting the substrate layer. The use of a lower tensile modulus second skin layer results in a better die-cutting of the facing material when compared to a facing material having a higher tensile modulus for the second skin layer material than for the base material layer material.

The stiffness of the multilayer film of the present invention is important for timely dispensing of labels along a peel plate at higher line speeds. Biaxial orientation of the multilayer film increases the machine direction tensile modulus and the transverse direction tensile modulus. The increase in the longitudinal tensile modulus helps to achieve dimensional stability and good printing register properties.

The stiffness of the machine direction oriented multilayer film should generally be at least about 2 or 3 and can be as high as 50 or 60 Gurley. Generally, the stiffness of the machine direction oriented multilayer film ranges from about 5 or 10, up to about 25 or 35Gurley (as measured by TAPPI Gurley stiff Test T543 pm). The transverse Gurley stiffness is generally in the same range as the machine direction, but the CD stiffness is lower than the MD stiffness.

The biaxially stretch oriented monolayer and multilayer films of the present invention described above are further characterized by a transverse direction tensile modulus of about 150000 psi or less. The Tensile modulus of the film can be determined according to ASTM test D882 entitled "tension Properties of Thin Plastic Sheeting". In one embodiment of the invention, the film of the invention has a tensile modulus in the transverse direction which is lower than the tensile modulus in the machine direction. Labels made from such films have better flexibility. Thus, in one embodiment, the machine direction stretch film of the inventive film may be up to 200000 or even up to 250000 psi with a cross direction tensile modulus of 150000 psi or less. In other embodiments, the tensile modulus in the machine direction is 150000 or less, even 125000 or less, and the tensile modulus in the transverse direction is less than 100000 psi.

The following examples, which are summarized in Table IV, illustrate monolayer films of the present invention. In the following examples and throughout the specification and claims, all parts and percentages are by weight, temperatures are in degrees celsius, and pressures are at or near atmospheric, unless otherwise indicated.

The films listed in Table IV were prepared from molten material passing through an extrusion die and then cast onto a chill roll. The extrudate was cut into 10X 10 square centimeter pieces and then biaxially heat stretched on a laboratory film stretcher at a stretch rate of 400%/second at the stretch ratios specified in Table IV. The drawing machine was a KARO type IV drawing machine (manufactured by Br * ckner Maschinenbau). The oriented film was relaxed and annealed (heat set) as shown in table IV. Some properties of the monolayer films of examples 1-11 are set forth in Table V.

TABLE IV

Biaxially oriented single-layer film

Examples	Film composition	Draw ratio		Orientation temperature (. degree.C.)	(ii) slack%1	Annealing time (seconds)2	Thickness (mil)
								MD	CD
		1	11G1							7∶1	5∶1	122	10	20	2.26
2	11G1			8∶1	5∶1	118	10	20	1.82
		3	11G1							8∶1	5∶1	122	10	20	1.40
4	6D81			5∶1	5∶1	122	10	20	3.28
		5	6D81							8∶1	4∶1	130	10	20	2.58
6	6D81			9∶1	4∶1	130	10	20	2.30
		7	DS4D05							8∶1	4∶1	130	10	20	2.46
8	DS4D05			10∶1	2.5∶1	130	10	20	3.24
		9	DS4D05							10∶1	4∶1	130	10	20	2.16
10	5E98+2％NA3			10∶1	2.5∶1	160	10	10	2.86
		11	DS5E98							10∶1	2.5∶1	160	10	10	2.07

¹Percent reduction in MD and CD stretch ratios

²The annealing temperature is the same as the orientation temperature³Millad 8C41-10

TABLE V

Properties of biaxially oriented monolayer film

Examples	Thickness (mil)	Gurley stiffness		2% secant modulus (psi)		Haze (%)
							MD	CD	MD	CD
		1	2.26	7.0	5.8						63,600	33,100	1.7
2	1.82					3.9	3.4	42,200	28,500	2.1
		3	1.40	1.7	1.6						42,200	32,700	4.6
4	3.28					28.3	27.2	73,300	72,800	1.1
		5	2.58	15.2	10.1						80,000	74,700	1.3
6	2.30					11.8	7.2	89,100	67,800	1.3
		7	2.46	16.6	12.6						113,300	87,800	0.9
8	3.24					43.6	29.6	152,000	93,300	0.9
		9	2.16	12.8	7.2						134,500	99,800	0.7
10	2.86					51.9	32.4	234,300	149,400	4.9
		11	2.07	18.6	11.3						235,600	145,500	5.2

The following examples 12-14 illustrate multilayer films of the present invention. The multilayer film is manufactured by coextrusion techniques as described above. The film was biaxially oriented at the temperature and draw ratio shown in Table VI. The drawing speed was 400%/second. Some properties of the films of examples 12-14 are set forth in Table VII.

TABLE VI

Biaxially oriented multilayer film

Examples	Substrate layer	Surface layer	Total thickness (mils)	Draw ratio		Orientation temperature (. degree.C.)	(iv) relaxation (%)1	Annealing time (seconds)2
									MD	CD
				12	11G1						2027	2.14	7∶1	5∶1	118	10	20
13	11G1	2027	2.52			8∶1	4∶1	130	10	20
				14	6D81						50％5E98 50％EVA*	2.76	8∶1	4∶1	130	10	20

^*Equistar UESP 242F; EVA containing 18% VA¹Percent reduction in MD and CD stretch ratios²The annealing temperature is the same as the orientation temperature

TABLE VII

Properties of biaxially oriented multilayer film

Examples	Total thickness (mils)	Gurley stiffness		2% secant modulus (psi)		Haze (%)
							MD	CD	MD	CD
		12	2.14	4.8	4.4						43,700	33,600	2.6
13	2.52					17.4	11.3	86,900	71,100	5.6
		14	2.76	16.8	12.2						73,000	63,000	71.1

The die-cuttability of the biaxially oriented films of examples 1 to 14 was evaluated in the following manner: the film was die cut into shaped sections and the frictional energy required to separate the matrix from the die cut sections was measured. A low value of friction energy (e.g., about 150 g-cm or less) indicates that the film has good die-cutting properties. Values of friction energy below 120, even below 100, are particularly desirable. Details of this assay are disclosed In U.S. Pat. No. 5961766 entitled "Method For Selecting A substrate For Use In A cutting Operation," which is incorporated herein by reference.

Each test sheet of film and paper liner having a size of 7 × 10 inches (17.8 × 25.4 cm) was passed through a die cutter to cut the film into 10 pieces without cutting the paper liner. The die cutter has a cylindrical profile. The die cutting roll had a 3 inch (76.2 mm) diameter with one transverse cavity and ten surrounding cavities. Each die cavity was 6 inches (152.4 mm) long (or transverse), 15/16 inches (22.25 mm) wide (or deep) and had a radius of 3/32 inches (2.38 mm) in diameter. The spacing between adjacent cavities was 1/8 inches (3.175 mm). The anvil roll diameter was 5 inches (127 mm). The gap between the anvil roll and the die tip was 2.2 mils (0.0559 mm). The die press was 300 psi (208500 kg/m) and the die travel speed was 15 m/min.

Each test piece is die cut to a depth sufficient to penetrate the film but not the liner. The resulting slices were rectangular in shape and arranged side by side in 10 slices in the transverse direction and the longitudinal direction of each slice on the test piece. The long side of each slice is parallel to the long side of the next adjacent slice. The slices were 7/8 × 6 inches (22.25 mm × 152.4 mm) in size and were arranged equidistant from each other. The spacing between each section was 1/8 inches (3.175 mm). During the die cutting process, a portion of the facing material (matrix) to be discarded is created around the cut sheet.

The test specimens are cut by cutting the die-cut test sheet along the long side centerline of one slice and then along the long side centerline of the next adjacent slice. The cuts are parallel to each other. Each test sample consists of one half of one slice, one half of the next adjacent slice, and a portion of the matrix surrounding the slice.

The frictional energy required to separate the matrix from the die-cut sections in each sample was determined using a modified TA-XT2 Fabric Analyzer (Stable Micro System, Unit105, Black Down Rural Industries, Hase Hill, Haslemere, SurreyGU273AY, England). The TA-XT2 fabric analyzer is a tensile testing apparatus. The tester is modified as follows: the clamp on the upper beam is folded and removed, and is replaced by an upper L-shaped fixing clamp, one arm of the upper L-shaped fixing clamp is connected with the upper frame, and the platform mounted on the base is folded and removed, and is replaced by a lower L-shaped fixing clamp. The procedure for each test sample was as follows: the matrix edge of the test specimen is attached to the upper L-shaped holder and the edge of each slice portion adjacent to the attached matrix edge is attached to the lower L-shaped holder. The fabric analyzer was started to separate the substrate from the sliced sections at a speed of 5 mm/sec.

The force exerted by the separation matrix during separation and the displacement of the test sample along the length of the force exerted by the separation matrix are plotted using software provided by a TA-XT2 fabric analyzer. The area under the curve was determined using the software of a TA-XT2 fabric analyzer. The area under the curve is in grams-seconds. The measurements were multiplied by the peel speed (5 mm/sec) and the units (i.e., mm to cm) were appropriately corrected to express the calculated friction energy in grams-centimeters (g-cm). The friction energy of the sample is higher, which indicates that the cutting performance of the facing material is poor or the adhesive reflows poorly. The test results for the films of examples 1-14 are summarized in Table VIII. For each film, approximately seven test specimens were tested and the average of the test results for these specimens is shown in Table VIII.

TABLE VIII

Results of friction energy test

Example films	Friction energy (g-cm)
		1	68
2	93
		3	109
4	54
		5	51
6	41
		7	74
8	85
		9	43
10	40
		11	65
12	57
		13	54
14	36

In another embodiment of the present invention, the biaxially oriented monolayer or multilayer film of the present invention may be used to make label stock for adhesive labels. The label material comprises the above single-layer film or multi-layer film and an adhesive layer adhesively bonded to one surface of the film.

In one embodiment, an adhesive-containing label material for adhesive labels comprises:

(A) a die-cuttable biaxially oriented multilayer film comprising:

(A-1) a substrate layer having an upper surface and a lower surface, the substrate layer comprising polyethylene having a density of about 0.940 g/cc or less, a propylene polymer or copolymer, or mixtures thereof, the substrate layer being free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters, and

(A-2) a first skin layer of a thermoplastic polymer adhered to the upper surface of the base material layer, wherein the multilayer film has a tensile modulus in the machine direction higher than that in the transverse direction and a tensile modulus in the transverse direction of 150000 psi or less, and

(B) an adhesive layer having an upper surface and a lower surface, wherein the upper surface of the adhesive layer is adhered to the lower surface of the substrate layer.

Multilayer films suitable for use as such label materials have been described in detail above. The adhesive layer in this embodiment is adhered to the lower surface of the base material layer. In addition, the biaxially oriented multilayer film (a) may further comprise a second skin layer (a-3) adhered to the lower surface of the base material layer, in which case the second skin layer is located between the base material layer and the adhesive layer. A second skin layer as described above may be employed.

The adhesive layer may be applied directly to the lower surface of the substrate layer or, in the case of a second skin layer, to the second skin layer, or the adhesive layer may be transferred from a liner compounded with the multilayer film. Generally, the bond coat has a thickness of about 0.1 to about 2 mils (2.5 to 50 microns). Adhesives suitable for use in the label stock of the present invention are commercially available in the art. Typically, these adhesives include pressure sensitive adhesives, heat activated adhesives, hot melt adhesives, and the like. Pressure sensitive adhesives are particularly preferred. These adhesives include acrylic adhesives as well as other elastomers such as natural rubber or synthetic rubbers containing polymers or copolymers of styrene, butadiene, acrylonitrile, isoprene, and isobutylene. Pressure sensitive adhesives are well known in the art and any of the known adhesives may be used in the facing materials of the present invention. In a preferred embodiment, the major component of the pressure sensitive adhesive is a copolymer of an acrylate, such as 2-ethylhexyl acrylate, and a polar comonomer, such as acrylic acid.

In the manufacture of label materials from the single and multilayer films according to the invention described above, a liner or carrier material may be added. The liner or support may comprise a multi-layer liner made by the process disclosed in U.S. patent 4713273, the disclosure of which is incorporated herein by reference, or may be a conventional liner or support composed of a single layer of paper or film that may be supplied in roll-to-roll form. If the liner or carrier does not previously have a release coating, nor itself contains components that inherently produce a release surface on the surface in contact with the adhesive, the liner or carrier can be coated with a release coating (e.g., silicone). If a release coating is used, it is dried or cured by an appropriate method after coating.

The release surface of the release liner or carrier may be coated with a layer of pressure sensitive adhesive that is subsequently transferred to the label material to which the release liner or carrier is to be adhered. The adhesive adheres to the biaxially oriented film when the label material is compounded with a liner or carrier. Thereafter, the liner or carrier is removed to expose the adhesive, which remains permanently adhered to the biaxially oriented film.

In some applications, the adhesive layer may be a heat activated adhesive or a hot melt adhesive, which, unlike pressure sensitive adhesives, may be used in-mold label applications. If the adhesive is a heat activated adhesive or a hot melt adhesive, a release liner having inherent release properties as is required with pressure sensitive adhesives is not required.

The method of producing a pressure-sensitive adhesive label material from the above biaxially oriented film according to the present invention is explained as follows: the liner or carrier material may comprise a multi-layer liner or a conventional liner or carrier consisting of a single layer of paper or film with a release coating, which paper or film may be supplied in roll form. The release surface of the release liner or carrier may be coated with a layer of pressure sensitive adhesive that is subsequently transferred to an oriented film to which the release liner or carrier is to be adhered. The adhesive will adhere to the film when the film is composited with a liner or carrier. Thereafter, the liner or carrier is removed to expose the adhesive, which remains permanently adhered to the biaxially oriented film.

The biaxially oriented film may be printed prior to die cutting into individual labels. The printing step may be performed before or after the liner is combined with the oriented film, but before the label material is die cut into individual labels. In order to obtain high quality images or text, the film must be held in precise registration between the printing steps (e.g., between successive prints of different colors), and in order for the images and text to be accurately located on the label, the film must be accurately registered between the printing and the subsequent die cutting steps. The film is subjected to tension during printing, which may cause some temperature increase, for example when the UV ink is cured, and therefore it is necessary to maintain the stability of the longitudinal dimension of the film.

As noted above, the biaxially oriented film of the present invention is die-cuttable and the label material carried on the liner is die-cuttable into an array of spaced pressure sensitive labels carried on a release liner or carrier. The die-cutting step may be carried out in a well-known manner by means of a die-cutting die, for example a rotary die-cutting die, which also involves peeling off of the ladder-shaped film, i.e. the trimmings around the labels formed, which should be discarded after the die-cutting (the "rungs" of the ladder represent the spaces between successive labels). After peeling, the label remains on the liner at regular intervals. One failure mode during this operation relates to poor die cutting of the labels, which remain on the substrate when the carrier is peeled off. With such failure modes, poor die cutting is more likely to cause label retention and adhesion to the substrate material when peeling the substrate and separating the labels due to the reduced degree of peeling. Another failure mode is the die cutting through the adhesive and portions of the liner leaving a cut in the liner. Yet another failure mode is caused by insufficient strength of the film being die-cut, and due to the lower strength of the matrix material, the matrix material around the die-cut label tends to tear when peeled from the liner. The film of the invention has enough strength, and can avoid or reduce the phenomenon of cracking during peeling.

Die cut labels on liners or carriers can be dispensed and adhered to a variety of objects by techniques known to the skilled artisan. For example, the labels are dispensed and applied to passing workpieces by stripping the liner or carrier in a progressive manner with a reverse peel edge to expose the adhesive side of the label and projecting the label into contact with the passing workpiece. In the context of the present invention, the workpiece may be an object to be affixed, such as a glass bottle or other rigid article, which often has an irregular surface, and thus requires a label that is soft and can be closely affixed (conformed) to its surface without localized surface depressions caused by bridging. The adhered object may be a flexible plastic container.

While the invention has been described with reference to a preferred embodiment, it is understood that various changes will become apparent to those skilled in the art upon reading the specification. Accordingly, the inventive concepts disclosed herein encompass such modifications as fall within the scope of the appended claims.

Claims (75)

1. A die-cuttable biaxially stretched, oriented monolayer film comprising polyethylene, a propylene polymer or copolymer, or mixtures thereof, having a density of about 0.940 g/cc or less, wherein the film has a machine direction tensile modulus greater than the cross direction tensile modulus, the film has a cross direction tensile modulus of about 150000 psi or less, and the film is free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters.

2. The film of claim 1 comprising a propylene copolymer.

3. The film of claim 2 wherein the propylene copolymer is a copolymer of propylene and up to about 40 weight percent of at least one α -olefin selected from the group consisting of ethylene and α -olefins having from 4 to about 8 carbon atoms.

4. The film of claim 3 wherein the α -olefin is ethylene or 1-butene.

5. The film of claim 1 comprising polyethylene having a density of about 0.890 to about 0.925 grams per cubic centimeter.

6. The film of claim 1 which is free of inert particulate filler.

7. The film of claim 1 which contains an inert particulate filler.

8. The film of claim 1 having a haze of less than about 10%.

9. The film of claim 1 having a haze of less than about 6%.

10. The film of claim 1 having a haze of less than about 2%.

11. The film of claim 1 wherein the machine direction stretch orientation is at least about 10% greater than the cross direction orientation.

12. The film of claim 11 wherein the film is machine direction oriented and has a draw ratio of from about 5: 1 to about 10: 1.

13. The film of claim 1, wherein the film comprises at least one nucleating agent.

14. The film of claim 1 having a Gurley stiffness in the machine direction of from about 10 to about 50.

15. The film of claim 1 having a thickness of about 3.5 mils or less.

16. The film of claim 1 having a thickness of from about 2 to about 2.5 mils.

17. The film of claim 1, wherein the film has been biaxially stretch oriented and heat set.

18. The film of claim 1 wherein the film comprises polyethylene having a density of from about 0.890 to about 0.925 grams per cubic centimeter.

19. The film of claim 1 wherein the film has been oriented at a machine direction stretch ratio of from about 9: 1 to about 10: 1 and a transverse direction stretch ratio of greater than 1: 1 to about 3: 1.

20. The film of claim 19 wherein the transverse draw ratio is less than about 2: 1.

21. The film of claim 1 having a friction energy of less than about 120 g-cm.

22. A die-cuttable biaxially stretch oriented monolayer film comprising polyethylene, propylene polymer or copolymer, or mixtures thereof, having a density of 0.940 g/cc or less, wherein the film has a machine direction stretch orientation at least 10% greater than the cross direction stretch orientation, and a cross direction stretch modulus of 150000 psi or less, and wherein the film is free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters.

23. The film of claim 22 wherein the machine direction stretch orientation is at least about 20% greater than the transverse direction stretch orientation.

24. The film of claim 22 wherein the film has been machine direction oriented at a stretch ratio of from about 5: 1 to about 10: 1.

25. The film of claim 22 comprising polyethylene having a density of from about 0.890 to about 0.925 grams per cubic centimeter.

26. The film of claim 22 comprising a copolymer of propylene and up to about 40% by weight of at least one olefin selected from the group consisting of ethylene and α -olefins having from 4 to about 8 carbon atoms.

27. The film of claim 22 wherein the film has been stretch oriented, has a machine direction stretch ratio of from about 9: 1 to about 10: 1, and a transverse direction stretch ratio of greater than 1: 1 to about 3: 1.

28. A die-cuttable stretch-oriented multilayer film comprising

(A) A substrate layer having an upper surface and a lower surface, the substrate layer comprising polyethylene having a density of about 0.940 g/cc or less, propylene homopolymer or copolymer, or mixtures thereof, the substrate layer being free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters, and

(B) a thermoplastic polymer first skin layer adhered to the upper surface of the substrate layer, wherein the multilayer film has a tensile modulus in the machine direction that is greater than the tensile modulus in the cross direction, and a tensile modulus in the cross direction of about 150000 psi or less.

29. The film of claim 28 wherein the substrate layer is free of inert particulate filler.

30. The multilayer film of claim 28, wherein the substrate layer comprises a propylene copolymer.

31. The multilayer film of claim 28 wherein the substrate layer comprises a copolymer of propylene with up to about 40% by weight of at least one α -olefin selected from the group consisting of ethylene and α -olefins having from 4 to about 8 carbon atoms.

32. The film of claim 31 wherein the α -olefin is ethylene or 1-butene.

33. The multilayer film of claim 28 wherein the substrate layer comprises polyethylene having a density of from about 0.890 to about 0.925 grams per cubic centimeter.

34. The multilayer film of claim 28 wherein the first skin layer (B) contains an inert particulate filler.

35. The multilayer film of claim 28 wherein the first skin layer (B) is free of inert particulate filler.

36. The multilayer film of claim 28 having a haze of less than 10%.

37. The multilayer film of claim 28 having a haze of less than 6%.

38. The multilayer film of claim 28, wherein the first skin layer comprises at least one polyolefin, polyamide, polystyrene-butadiene, polyester copolymers, polyurethane, polysulfone, polyvinylidene chloride, styrene-maleic anhydride copolymers, styrene acrylonitrile copolymers, ionomers of ethylene methacrylic acid sodium or zinc salts, polymethyl methacrylate, cellulose, fluoroplastics, acrylic polymers and copolymers, polycarbonate, polyacrylonitrile, ethylene-vinyl acetate copolymers, and mixtures thereof.

39. The multilayer film of claim 28 wherein the substrate layer and the first skin layer are formed by a coextrusion process.

40. The multilayer film of claim 28, wherein the machine direction stretch orientation is at least 10% greater than the cross direction orientation.

41. The multilayer film of claim 28, which has been machine direction oriented at a stretch ratio of from about 5: 1 to about 10: 1.

42. The multilayer film of claim 28, wherein the substrate layer or the first skin layer or both contain a nucleating agent.

43. The multilayer film of claim 28 comprising a second skin layer adhered to the lower surface of the substrate layer.

44. The multilayer film of claim 43, wherein the second skin layer has a different composition than the first skin layer.

45. The multilayer film of claim 28, having a Gurley stiffness in the machine direction of from about 10 to about 50.

46. The multilayer film of claim 28 having a total thickness of from about 2 to about 3 mils.

47. The multilayer film of claim 28, wherein the film has been biaxially stretch oriented and heat set.

48. The multilayer film of claim 28, wherein the multilayer film has been stretch oriented at a machine direction stretch ratio of from about 9: 1 to about 10: 1 and a transverse direction stretch ratio of greater than 1: 1 to about 3: 1.

49. The multilayer film of claim 28 having a friction energy of less than 120.

50. The multilayer film of claim 28 having a friction energy of less than 80.

51. A die-cuttable biaxially stretch oriented multilayer film comprising:

(A) a substrate layer having an upper surface and a lower surface, the substrate layer comprising polyethylene having a density of about 0.940 g/cc or less, a propylene polymer or copolymer, or mixtures thereof, the substrate layer being free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters, and

(B) a first skin layer of a thermoplastic polymer adhered to the upper surface of the substrate layer, wherein the multilayer film has a machine direction stretch orientation at least 10% greater than a cross direction stretch orientation, and a cross direction tensile modulus of 150000 psi or less.

52. The film of claim 51 wherein the machine direction stretch orientation is at least about 20% greater than the transverse direction stretch orientation.

53. The film of claim 51 wherein the film has been stretched in the machine direction at a stretch ratio of from about 5: 1 to about 10: 1.

54. The film of claim 51 wherein the substrate layer comprises a copolymer of propylene and up to about 40% by weight of at least one α -olefin selected from the group consisting of ethylene and α -olefins having from 4 to about 8 carbon atoms.

55. The film of claim 51 wherein the substrate layer comprises polyethylene having a density of about 0.890 to about 0.925 grams per cubic centimeter.

56. A label material for adhesive labels comprising an adhesive, the material comprising:

(A) a die-cuttable biaxially oriented multilayer film comprising:

(A-1) a substrate layer having an upper surface and a lower surface, the substrate layer comprising polyethylene having a density of about 0.940 g/cc or less, a propylene polymer or copolymer, or mixtures thereof, the substrate layer being free of copolymers of ethylene and ethylenically unsaturated carboxylic acids or esters, and

(A-2) a first skin layer of a thermoplastic polymer adhered to the upper surface of the base material layer, wherein the multilayer film has a tensile modulus in the machine direction higher than that in the transverse direction and a tensile modulus in the transverse direction of 150000 psi or less, and

(B) an adhesive layer having an upper surface and a lower surface, wherein the upper surface of the adhesive layer is adhered to the lower surface of the substrate layer.

57. The label material of claim 56, wherein the substrate layer comprises a propylene copolymer.

58. The label material of claim 56 wherein the substrate layer comprises a copolymer of propylene with up to about 40% by weight of at least one α -olefin selected from the group consisting of ethylene and α -olefins having from 4 to about 8 carbon atoms.

59. The label stock of claim 58, wherein the alpha-olefin is ethylene or 1-butene.

60. The label material of claim 56 in which the substrate layer is free of inert particulate filler.

61. The label material of claim 56, wherein the substrate layer comprises polyethylene having a density of from about 0.890 to about 0.925 grams per cubic centimeter.

62. The label stock of claim 56 in which the multilayer film (A) has been biaxially oriented and heat set.

63. The label material of claim 56 wherein the multilayer film (A) has a Gurley stiffness in the machine direction of from about 10 to about 50.

64. The labelstock of claim 56 wherein the multilayer film (A) has a machine direction stretch orientation at least about 20 percent greater than a cross direction stretch orientation.

65. The labelstock of claim 56 wherein the multilayer film (A) has been stretched in the machine direction at a stretch ratio of from about 5: 1 to about 10: 1.

66. The label material of claim 56, wherein the adhesive layer is a pressure sensitive adhesive layer.

67. The labelstock of claim 56 wherein the multilayer film (A) has been stretch oriented at a stretch ratio in the machine direction of from about 9: 1 to about 10: 1 and a stretch ratio in the transverse direction of greater than 1: 1 up to about 3: 1.

68. The label material of claim 67, wherein the cross-directional stretch ratio is less than 2: 1.

69. A pressure sensitive adhesive label die-cut from the labelstock of claim 56.

70. A die-cuttable biaxially stretched, oriented monolayer film comprising at least one polyolefin wherein the film has been stretch oriented, the machine direction stretch ratio being from about 9: 1 to about 10: 1 and the transverse direction stretch ratio being greater than 1: 1 to about 3: 1.

71. The film of claim 70 wherein the draw ratio in the transverse direction is less than 2: 1.

72. The film of claim 70, wherein the film comprises polyethylene, propylene polymers or copolymers, or mixtures thereof.

73. The film of claim 70 wherein the film comprises a copolymer of propylene and ethylene or at least one α -olefin having from 4 to about 8 carbon atoms.

74. A die-cuttable, stretch-oriented multilayer film, comprising:

(A) a substrate layer having an upper surface and a lower surface and comprising at least one polyhydrocarbon,

(B) a first surface of a thermoplastic polymer adhered to the upper surface of the substrate layer, wherein the multilayer film has been stretch oriented at a stretch ratio in the machine direction of from 9: 1 to about 10: 1 and a stretch ratio in the transverse direction of from greater than 1: 1 to about 3: 1.

75. The multilayer film of claim 71, wherein the multilayer film has been transversely stretch oriented at a stretch ratio of less than 2: 1.