WO1998041590A1

WO1998041590A1 - Adhesive article with a polystyrene/styrene elastomer film

Info

Publication number: WO1998041590A1
Application number: PCT/US1998/002867
Authority: WO
Inventors: Joseph T. Bartusiak
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1997-03-14
Filing date: 1998-02-12
Publication date: 1998-09-24

Abstract

The present invention provides an adhesive article including a nonoriented backing film including a polystyrene resin and a styrenic thermoplastic elastomer, wherein the backing film exhibits substantially complete severability upon application of a force of about 11 Newtons or less; and an adhesive coated on a major surface of the nonoriented backing film. The nonoriented backing film has strength and provides controlled severability in the desired direction without significant stress whitening or cloudiness. Also provided is a method for making such an adhesive article.

Description

ADHESIVE ARTICLE WITH A POLYSTYRENE/STYRENE ELASTOMER FILM

Field of the Invention

The present invention relates to a film and an adhesive article. More particularly, it pertains to a film backing with excellent dispensing properties comprising a blend of polystyrene material and styrenic elastomer material and a adhesive article comprising the same. Also included is a method for making a adhesive article comprising a film backing with excellent dispensing properties.

Background of the Invention Polypropylene film has been recognized as a generally low cost backing for adhesive-coated tapes. Conventional adhesive-coated tapes made with such film backings, however, have not been easy to cut transversely by manually pulling them against teeth in the type of dispensing blades normally provided on tabletop dispensers of the type found in homes, offices, or factories. This is particularly true after the teeth on such a dispensing blade have become dulled because of use or damage.

Instead, tapes having backings made of unplasticized polyvinylchloride, cellophane, or cellulose acetate are in general use, which are available from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, USA, under the trade identifiers Nσs. 600, 610 and 810 respectively. These are typically used because of the ease and precision with which they can be manually cut by the dispensing blade on such a tabletop dispenser. Because such backings are not significantly stretched over the dispensing blade, the teeth on the dispensing blade produces a serrated cut edge in the backing closely corresponding to the shape of the cutting blade teeth. A force of under about 11 Newtons is required to cut the tape via the dispensing blade when the tape is cut in a manner emulating the cutting test described herein. Such tapes are typically relatively costly, however. Thus, a search for a low cost dispensable tape has been ongoing for years.

Attempts to solve the problem of manually cutting or dispensing adhesive tapes made with low cost copolymer backings have involved backings made from a polystyrene and styrene elastomer blend, which are described in Japanese Patent Document Nos. 56,027,326 (Mitsubishi); 58,189,282 (Asahi Dow); and 53,113,845 (Toyo Kagaku). Generally these attempts involve orienting or combining orienting and laminating the films to acquire certain properties. The process of orienting requires additional equipment and adds to the cost of the tape backing, however.

Summary of the Invention

The present invention provides a dispensable (i.e., severable) film useful as the backing of an adhesive article, such as a tape, a label and the like. One embodiment of the present invention is an adhesive article including: a nonoriented backing film including a polystyrene resin and a styrenic thermoplastic elastomer, wherein the backing film exhibits substantially complete severability upon application of a force of about 11 Newtons or less; and an adhesive coated on a major surface of the nonoriented backing film. The adhesive article can further include additional layers. In one alternative embodiment, a release layer is coated on a major surface of the nonoriented backing film; a tie layer is coated on an opposite major surface of the nonoriented backing film between the pressure sensitive adhesive and the nonoriented backing film. In another alternative embodiment, a tie layer is between the release layer and the nonoriented backing film and the adhesive is coated on the opposite surface of the nonoriented backing film.

In a further embodiment of the present invention is an adhesive article including a nonoriented backing film comprising: about 35 wt-% to about 70 wt-% of a polystyrene resin having a melt flow index of about 1 -50 grams per 10 minutes; and about 30 wt-% to about 65 wt-% of a styrenic thermoplastic elastomer having a melt flow index of about 3-20 grams per 10 minutes; and an adhesive coated on a surface of the nonoriented backing film.

Useful adhesives in the invention include those derived from acrylics, olefins, natural rubbers, synthetic rubbers such as polyisoprene, polyisobutylene and blends thereof. Preferably, useful adhesive materials are those categorized as pressure sensitive adhesives (PSA) which is understood to mean that a bond is formed with a surface of a wide variety of substrates (e.g., paper) after briefly applying light pressure. The elastomer composition referred to above preferably includes a polystyrene resin having a melt flow index of about 1-50 grams per 10 minutes and a styrenic thermoplastic elastomer having a melt flow index of about 3-20 grams per 10 minutes. More preferably, the styrenic thermoplastic elastomer is selected from the group of branched S-B(styrene-butadiene) block copolymers or linear S-B-S (poly(styrene-b-butadiene-b-styrene)) triblock copolymers, linear S- I-S (poly(styrene-b-isoprene-b-styrene)) and linear S-EB-S (poly(styrene-b- ethylene-butylene-b-styrene)) triblock copolymers, each containing polystyrene terminal segments and elastomer segments. Most preferably, the styrenic thermoplastic elastomer is selected from the group of styrene/butadiene (S-B) block copolymer, linear S-I-S (poly(styrene-b-isoprene-b-styrene)), and mixtures thereof. Where the styrenic thermoplastic elastomer is a styrene/butadiene block copolymer, it is preferred that butadiene is in an amount of about 7.5 wt-% to about 16.25 wt-%) .

Another embodiment of the present invention is a method for making a nonoriented film including the steps of: providing an elastomer composition including: (a) a polystyrene resin; and (b) a styrenic thermoplastic elastomer; processing and forming the elastomer composition at a temperature sufficient to produce a film that exhibits substantially no stress whitening or cloudiness and exhibits substantially complete severability upon application of a force of about 11 Newtons or less. Preferably, the elastomer composition is processed at a temperature sufficient to produce the backing film having a break stress of about 35 x 10³ kPa or more and a break elongation of about 20% to about 150%). Most preferably, the temperature is about 177°C to about 199°C. Preferably, the step of processing and forming the elastomer composition includes extruding the elastomer composition through a die manifold and passing the extruded elastomer composition between nip rollers to form a film.

Yet another embodiment of the invention is a method for making an adhesive article comprising the steps of: providing a nonoriented film made by the method comprising the steps of: providing an elastomer composition comprising: (a) a polystyrene resin; and (b) a styrenic thermoplastic elastomer; processing and forming the elastomer composition at a processing temperature sufficient to produce a film that exhibits substantially complete severability upon application of a force of about 11 Newtons or less; and coating an adhesive on a first major surface of the nonoriented film. The method for making an adhesive article can also include the step of coating a release coat material on a second major surface of the nonoriented film. Preferably, the steps of forming and forming the elastomer composition into a film, coating the adhesive and coating the release coat material occur substantially simultaneously to form the adhesive article.

Brief Description of the Drawings Fig. 1 is an enlarged perspective view of a length of an adhesive article of the invention.

Fig. 2 is a enlarged perspective view of a coextruded adhesive article, or tape, in accordance with the invention.

Fig. 3 an enlarged perspective view of a cutting blade used in the test to determine severability. Detailed Description of the Invention

The present invention describes an adhesive article, such as a tape, having a backing film including polystyrene and styrenic thermoplastic elastomer having excellent dispensing properties. Although films of polystyrene materials and films of styrenic thermoplastic elastomer materials are known, neither material by itself provides a film having the handling, dispensability or mechanical properties of the film of the present invention. General purpose polystyrene films tend to chip, fracture, and break irregularly and unpredictably when severed. Also, the brittleness of polystyrene films will not allow it to be processed by conventional film extrusion techniques. Styrenic thermoplastic elastomer films, on the other hand, are very flexible, however, their toughness makes trimming difficult. The films tend to stretch, string out, and stress whiten when severed. The present invention surprisingly provides a nonoriented film that severs substantially cleanly and exhibits few, if any, of these disadvantages. The nonoriented film of the invention requires no additional manipulation for orientation either in an uniaxial or biaxial direction. Preferably, the nonoriented film is also not laminated. Although tape backings made from blends of polystyrene and styrene elastomer are known, these are oriented or oriented and laminated, which adds additional cost. It will be readily recognized that although adhesive articles other than tapes can be made using the nonoriented films of the invention, tapes are primarily discussed in the following description and examples which are illustrative of the advantages of the film of the present invention.

A tape for use in home or office should maintain a certain strength for specific applications such as, mending, holding, and wrapping. It should possess the strength necessary to withstand force acting on it in the plane of the film while being readily severable when subjected to forces applied in a direction normal to the plane of the film. This provides a controlled severability which enables the tape to sever cleanly and in the desired direction. It should also not turn significantly cloudy or white under stress, as during dispensing. For purposes of this invention, the terms "dispensable," "severable" and "complete severability" are used interchangeably. They refer to the ability of the tape to be easily and precisely cut in a straight line and exhibit little, if any, stress cracking, whitening or cloudiness, visible elongation, visible tailing, visible deformation, or the like, along the severed edge. A variety of devices and techniques can be used to sever the tapes of the invention. Useful devices include the dispensing blades used in commercially available table top tape dispensers such as, for example, the dispensing blades found on the SCOTCH Brand Model C-40 or C-15 Tabletop Dispenser available from Minnesota Mining and Manufacturing Company of St. Paul, Minnesota. Other useful devices include slitting knives, die cutting devices, rotary cutting devices and the like. The preferred tape of the invention may also be readily severed or torn to the desired length using one's hands, i.e., the tape is hand tearable.

To provide such desirable characteristics in a tape, the backing film preferably has a break stress (i.e., break strength) of about 35 x 10³ kilopascals or more, performed according to ASTM No. D3759-88 and a break elongation of about 20%) to about 150%>. The tape backing as performed according to ASTM No. D3759-88 should also preferably dispense via a controlled ductile puncture and tearing mechanism having a cutting force of about 11 Newtons or less in which the serrated edge of the tape backing shows complete severability or, in other words, a regular, uniform pattern of teeth with substantially no evidence of ruffling, "dog earing," or stress whitening.

Referring to Fig. 1, there is shown a length of one preferred embodiment of an adhesive article according to the present invention, generally designated by the reference numeral 10. Tape 10 is intended to be cut in its transverse direction parallel to edges 13 on the types of cutting blades typically used in tabletop dispensers. Tape 10 includes a nonoriented polystyrene/styrenic elastomer backing film 12. As used herein, "nonoriented" refers to a flat film extruded through a T-shaped die followed by chilling the film by contacting it to a water-cooled roll, generally at a temperature of about 100°F ( about 37.8°C), or less. The film of the present invention may undergo a very small amount of orientation which may occur as a result of contacting the extruded flat film with the water-cooled roll, i.e., the film of the present invention may be "oriented" to the very small extent that such orientation is inherent in forming the film. However, the film of the present invention is not additionally manipulated to orient the film in any direction. Coated on one side (or optionally both sides) of nonoriented backing film 12 is a layer 14 of adhesive, which may be any of a number of known adhesives.

The nonoriented polystyrene/styrenic elastomer backing film 12 of tape 10 typically has a thickness in a range of about 0.0013 cm to about 0.005 cm. Generally, the tape backing is sufficiently thick such that tape made from the backing does not become too flimsy and hard to handle, and sufficiently thin such that tape made from the backing does not become too rigid and hard to manually dispense. Tape backings within a thickness range of about 0.0025 cm to about 0.0041 cm are preferred for desired feel, flexibility, strength, and dispensing characteristics of the tape.

An adhesive is typically applied to the backing film 12 using conventional coating weights (e.g., about 0.0017-0.0034 grams per square centimeter) such that the adhesive layer 14 of tape 10 has a thickness in a range of about 0.0013 cm to about 0.004 cm. The use of exceptionally high coating thicknesses of adhesive on the polystyrene/styrenic elastomer backing (e.g., over about 0.004 cm) to form a tape can adversely effect the cut-off properties of that tape compared to a tape with the same backing and a lower coating thickness of the same adhesive. The adhesive coated on the film of the present invention to form the tape may be activated by pressure, heat, or both.

Suitable adhesives for coating on the film of the present invention include pressure sensitive adhesives (PSA) and non-pressure sensitive adhesives. A pressure sensitive adhesive is conventionally understood to refer to an adhesive that can form a bond to a surface of a wide variety of substrates after briefly applying light pressure. An accepted quantitative description of a PSA is given by the Dahlquist criterion line, which indicates that materials having a storage modulus (G') of less than about 3 x 10⁵ Pascals (measured at 10 radians/second at room temperature, about 20°C to 22°C) have pressure sensitive adhesive properties while materials having a G' in excess of this value do not. Thus, more specifically, a non-PSA refers to a material that has a storage modulus at least above the Dahlquist criterion line, and more preferably, a storage modulus above 1 x 10⁶ Pascals. Useful materials for the adhesive layer in the invention include those derived from silicone, acrylics, olefins, synthetic rubbers such as polyisoprene and polyisobutylene, and blends thereof. Preferably, the adhesive layer includes an acrylic pressure sensitive adhesive, such as the type described in U.S. Patent Nos. 2,884,126 and Re 24,906. Typically, however, the adhesive is one that does not include organic solvents. The nonoriented backing film 12 may optionally have a release layer (or low adhesion backsize (LAB)) coated on its surface 15 opposite the adhesive. The polystyrene/styrenic elastomer backing film may, optionally be treated with a conventional primer or tie layer, or by flame, or corona discharge, or other surface treatments, to enhance the adhesion of the adhesive to the backing film, or the release (LAB) layer to the backing film, not shown in Fig. 1. Typically, however, the primer or tie layer is one that does not include organic solvents. Referring now to Figure 2, there is shown a tape wound as a coil, generally designated by the reference numeral 16. Tape 16 includes a nonoriented polystyrene/styrenic elastomer backing film 17, a layer 18 of adhesive. Also shown is a release layer 19 (or low adhesion backsize ("LAB") layer), which typically has a thickness in the range of about 0.0001 cm to about 0.002 cm. Such release or LAB layers are optional and restrict adhesion of the adhesive to the surface of the backing opposite the adhesive layer (surface 15 in Fig. 1) when the tape is wound in a coil. Such materials useful for release layers are well known in the adhesive coated tape-making art.

A number of materials are useful as the tie layer. They include, but are not limited to, ethylene/vinyl acetate copolymer, carboxylated ethylene/vinyl acetate copolymer such as that commercially available under the trade designation CXA 3101 from DuPont (Wilmington, DE), copolymers of ethyl ene and methyl acrylate such as that commercially available under the trade designation POLY-ETH 2205 EMA from Gulf Oil and Chemicals Co. (Atlanta, GA), ethylene/acrylic acid copolymer such as that commercially available from Dow Chemical Co. (Midland, MI), a copolymer of ethylene with a metal acrylate such as that commercially available under the trade designation SURLYN from DuPont, maleic anhydride modified polyolefins and copolymers of polyolefins such as that commercially available under the trade designation MODIC from Mitsubishi Chemical Co. (Chesapeake, VA), polyolefins containing homogeneously dispersed vinyl polymers such as that commercially available under the trade designation VMX from Mitsubishi Chemical Co., a polyolefin grafted with polar functional groups such as that commercially available under the trade designations POLYBOND from Reichold Chemicals Inc. (Pensacola, FL), and PLEXAR from Chemplex Company (Tuckahoe, NY), a copolymer of ethylene and acrylic acid such as that commercially available under the trade designation PRIMACOR from Dow Chemical Co., and a copolymer of ethylene and methacrylic acid such as that commercially available under the trade designation NUCREL from DuPont. The optional tie layer 20, as described above, typically has a thickness in the range of about 0.0001 cm to about 0.002 cm. Thus, the backing film is optionally capable of being coated with a variety of substances, depending upon the end use and consumer demands.

An adhesive article may also optionally be passed into a nip form and drawn to the desired caliper by adjusting the take away rate when, for example, the component films of the adhesive article are simultaneously coextruded. The nonoriented backing film includes polystyrene and a styrenic thermoplastic elastomer. It is expected that various fillers and/or additives known in the art could also be added to the backing film for various purposes such as to provide color, antioxidants, etc. The polystyrene used in the present invention preferably has a melt flow index (MFI) (ASTM D1238, 5 kg, 200°C) of about 1-50 grams per 10 minutes, and has a weight average molecular weight of about 100,000 to about 600,000. Suitable polystyrenes include those available under the trade designations STYRON 666D from Dow Chemical (Midland, MI), NOVACORE 777 from NOVACORE Chemicals, Inc. (Leominster, MA), HUNTSMAN 208 from Huntsman Chemical Co. (Salt Lake City, UT), and Amoco G102 from Amoco Chemical Co. (Chicago, IL).

The styrenic thermoplastic elastomer is preferably selected from the group of branched S-B(styrene-butadiene) block copolymers or linear S-B-S (poly(styrene-b-butadiene-b-styrene)) triblock copolymers, linear S-I-S (poly(styrene-b-isoprene-b-styrene)) and linear S-EB-S (poly(styrene-b-ethylene- butylene-b-styrene)) triblock copolymers, each containing polystyrene terminal segments and elastomer segments. Most preferably, the styrenic thermoplastic elastomer is selected from the group of styrene/butadiene (S-B) block copolymer, linear S-I-S (poly(styrene-b-isoprene-b-styrene)), and mixtures thereof. A preferred S-B block copolymer is composed of about 20%) to about 90%> by weight of the styrene units and about 80%> to about 10% by weight of the butadiene units. Preferably the S-B block copolymer has a melt flow index (MFI) (Condition G, ASTM D1238) of about 3-20 grams per 10 minutes.

Suitable S-B thermoplastic elastomers include those available under the trade designations K-RESIN, from Phillips Petroleum Co. (Pasadena, TX), FINAPRENE from Fina Chemical Co. (Dallas, TX), and STEREON from Firestone Tire and Rubber Co. (Akron, OH). The type and amount of both the polystyrene and the styrenic thermoplastic elastomer used in the present invention are chosen such that the desired strength, ease of dispensing, and absence of stress whitening in the tape backing is obtained. With these desired properties in mind, polystyrene is in an amount of preferably about 15 wt-%, more preferably about 20 wt-%>, most preferably about 35 wt-%> to preferably about 85 wt-%>, more preferably about 80 wt-%), most preferably about 70 wt-%>. The styrenic thermoplastic elastomer is in an amount of preferably about 15 wt-%, more preferably about 25 wt-%, most preferably about 30 wt-% to preferably about 85 wt-%, more preferably about 75 wt-%), most preferably about 65 wt-%>. Additionally, such polystyrene/styrenic thermoplastic elastomer compositions preferably include about 7.5 wt-%> to about 16.25 wt-%) rubber (typically butadiene rubber). Generally, below about 7.5 weight percent (wt-%) butadiene rubber, the film tends to split easily and is difficult to fabricate into tape; on the other hand, at above about 16.25 weight percent, the film becomes ductile and the dispensed piece of tape will have distorted end portions adjacent to its newly cut end.

The adhesive articles including the backing film of the present invention are typically made using conventional extrusion processing methods and conventional coating methods, wherein the polystyrene/styrenic elastomer backing is made by using the process described above. The tie layer, release material and adhesive are applied offline in separate steps to form the finished adhesive article, such as a tape. A tape produced by an offline method might have a layered configuration of release layer - polystyrene/styrenic elastomer film - tie layer - adhesive. Another method of making the finished tape is to use the coextrusion processing method, wherein the polystyrene/styrenic elastomer backing, tie layer, release material and adhesive are simultaneously coextruded through a coextrusion die to form a finished tape. A tape produced by a coextrusion method can have a layered configuration of release layer - tie layer - polystyrene/styrenic elastomer film - adhesive.

The temperatures used in the preparation of the backing film affects the mechanical properties of the film and the stress whitening phenomenon. For example, the processing temperature (e.g., the extruder and die temperature) can effect the desired strength, ease of dispensing, and absence of stress whitening in the backing. Preferably, the processing temperature is maintained such that a nonoriented backing is produced which exhibits substantially complete severability upon application of a force of about 11 Newtons or less on the backing. More preferably, the processing temperature is maintained such that a nonoriented backing having a break stress of about 35 x 10³ kPa or more and a break elongation of about 20%) to about 150%> is produced. Most preferably, the processing temperature is maintained at about 177°C to about 199°C. Generally, as the processing temperature is increased above about 199°C, the film strength decreases, the break elongation decreases, and the film tends to stress whiten in the machine direction. This yields an undesirable backing film for tape constructions.

Referring again to Fig. 1, backing film 12 has a longitudinal (i.e., machine direction) break strength (i.e., break stress) parallel to the edges 11 of at least about 35 x 10³ kilopascals, more preferably about 55 x 10³ kilopascals, will break before it is longitudinally stretched by about 80% (at most by about 150%), and has sufficient integrity in its transverse direction (i.e., cross direction) parallel to the edges 13 such that there is little, or no, fibrillation (i.e., separation into separate strands) in its longitudinal direction.

A severability test, which demonstrates the severability of the film, is described in detail below with reference to Fig. 3. This test further shows that a force of only 11 Newtons (N), preferably 10 N, or less, is needed to sever the film cleanly. Fig. 3 illustrates the cutting portion of a device 40 for testing the ease and precision with which a film 41 can be cut on or dispensed over a cutting blade 42 of the type presently used on the SCOTCH Brand Model C-40 or C-15 Tabletop Dispenser available from Minnesota Mining and Manufacturing Company of St. Paul, Minnesota. A pressure sensitive adhesive (about 0.002 gm/cm²) is applied to one surface of the film to facilitate testing. The blade 42, which is formed of about 0.05 cm thick nickel plated steel, includes a rectangular land portion 43 at least as wide as the film 41 and about 0.4 cm long in the direction corresponding to the longitudinal direction of the film 41 where it extends across the blade 42. The land portion 43 defines a generally planar upper land surface 44 to which the adhesive coating of the film 41 can be temporarily adhered. The blade 42 also includes a support portion 46 at one edge of and disposed at a right angle to the land portion 43, which support portion 46 is held to the frame 47 via screw 49. A scribe line 45 is used to ensure exact positioning of the blade with respect to support 46. The blade 42 still further includes a generally U-shaped portion 48 at the edge of the land portion 43 opposite the support portion 46. A row of teeth 50 is located along the distal edge of U-shaped portion 48. Each tooth 50 is generally triangular, has a tip in or slightly higher than the plane of the land surface 44 and spaced from the tips of adjacent teeth 50 by about 0.1 cm, is defined by the intersection of distal surfaces 51 of the U-shaped portion 48 (which surfaces 51 are disposed at right angles to the land surface 44) and has a distal tip angle measured in the plane of the land surface 44 of about 90°.

The land surface 44 is adapted to have the adhesive coating of the film 41 temporarily adhered thereto to restrain forward motion of the adhered portion of the film 41 during severing of the film 41 by the teeth 50. The blade 42 is positioned over the upper edge surface of support 47 and fixed so that the plane defined by the tips of the teeth 50 and the land surface 44 is disposed at about 10° with respect to the horizontal.

The means for pulling the film 41 at a predetermined angle and rate to sever it against the teeth 50, and for recording the force required to sever the film 41 include a storage oscilloscope and a model 1122 Instron tensile tester. The path of movement for the crosshead is at an angle of about 30° with respect to the plane defined by the frame 47.

To test the force required to cut a particular film 41, a length of the film 41 is obtained, adhered to the planar land surface 44, positioned around the blade 42, and secured in the upper jaw of the Instron. The film extends around and is lightly tensioned against the teeth 50 on the blade 42. The drive mechanism of the Instron is then activated to move the test blade from its initial position at a rate of 25 cm/minute, which movement, because of the angle at which the teeth 50 are tilted, causes tension to be applied to the film 41 extending over the teeth 50 between the land surface 44 and the upper Instron jaw beginning at one outer edge so that the film 41 is progressively transversely severed by the teeth 50.

The distance of the upper crosshead jaw from the dispensing teeth is 5 cm. The combination of the rate of movement of the jaw and the jaw separation from the dispensing teeth provides a strain rate of 500%) per minute.

The force required to sever the film 41 along the teeth 50 is recorded on a Model 2090 Nicolet storage oscilloscope. The highest force reading is then determined. This is normally the initial puncture force. The sweep rate is adjusted so that the complete dispensing force versus time graph is completely displayed on the screen.

Because the angle has a large influence on the dispense values, it is important that the apparatus utilized to secure the blade be rigid, not interfere with the film whose dispensing force is being measured and securely hold the blade so angles are maintained and the tips of the blade lie in the same plane as the upper jaw faces. It is further desirable to mark the blade and the upper jaw so when the sample is positioned it is vertical between these two marks. This further ensures consistent measurements by maintaining angles precisely. At least 10 and preferably 20 measurements are made and the average force reported. Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated. Additionally, unless otherwise indicated, an adhesive was applied to the backing film in Examples 1-17 solely for the purpose of affixing the backing film for testing and that the results are shown for the backing film itself. Examples 1-5 Preparation of Polystyrene/Styrenic Thermoplastic Elastomer Films

The following examples illustrate the dispensibility characteristics and the stress whitening phenomena of the present invention. Polystyrene/styrenic elastomeric polymer blend films according to the invention were prepared first by batch blending a general purpose polystyrene resin and a styrenic thermoplastic elastomer material in a tumbler until thoroughly mixed. The mixed materials were fed into a feed hopper of a 4.45 cm single screw extruder available from Prodex (Fords, NJ). The extruder having an extruder barrel temperature adjusted to produce a stable homogenous melt was used to supply the materials to a 35.6 cm wide single manifold die.

The polystyrene/styrenic elastomer melt was extruded through the single manifold die so as to obtain a flat film. The film was then passed into a nip formed by two water cooled steel rolls which had 10/C water circulating through them, one of which had a rubber outer sleeve. The melt drawn to the desired caliper of about 0.0041 cm by adjusting the take away rate. Alternatively, the film could be cast onto either one of the steel rolls without nipping and then drawn to the desired caliper.

The general purpose polystyrene resin material comprised STYRON 666D polystyrene having a melt flow rate of 7.5 g/10 minutes under ASTM D- 1238, specific gravity of 1.04, vicat softening point of 212°F (100°C), and tensile at break of 37 x 10³ kilopascals, available from Dow Plastics, the Dow Chemical Company, Midland, MI. The styrenic thermoplastic elastomer material comprised K-RESLN KR05 having a MFI of 8.0 g/10 minutes under ASTM D- 1238 condition G, density of 1.01 , vicat softening point of 87°C, and a tensile yield strength of 28 kilopascals, available from Phillips 66 Chemical Company, Pasadena, TX. Examples 1-5 were made using 55%> polystyrene + 45%> styrenic elastomer by weight. The feed rate of the blend material was maintained at 26 revolutions per minute (rpm) while the processing temperature varied from 177°C to 221°C at 11°C increments. The film thickness was 0.04 mm.

The films were slit to a 15.2 cm width and then laminated by hand with an acrylic pressure sensitive adhesive having an adhesive thickness of about 0.02 mm. The adhesive was solely for the purpose of holding the test samples on the land area of the test apparatus and was of the type described in U.S. Patent No. Re 24,906.

The resultant samples were then tested to determine dispensing force, break stress and break elongation values of the film. Break stress and break elongation were determined by ASTM D3759-88 and slightly modified in the following manner: strips (2.54 cm wide by 12.7 cm) were cut from the longitudinal or machine direction of the film samples using sharp razor blades and an undamaged (i.e., scratch free and dent free, etc.) resilient surface. Samples were taken from the middle and both sides of the film web. A Mitutoyo caliper gauge, model IDC-112E, was used to determine the thickness of the top, middle and bottom of each sample. The thickness reported was the average of these values. Two sections of nylon reinforced strapping tape were applied across the test samples to provide a 5.1 cm spacing between each section. The strapping tape protected the samples from damage by the jaws of the test device. A model 1122 Instron tensile tester was used to measure the break stress and break elongation of the samples. A 5.1 cm jaw separation and a speed of 25.4 cm/minutes were used for measuring break stress and break elongation. Sintec Software, a Division of MTS System Corporation, was used for materials testing in conjunction with the Instron tensile tester.

The results are reported in Table 1. It was observed that the serrated edge of the film of Examples 1-5 displayed a regular, uniform pattern of teeth with no evidence of ruffling or stress whitening except for Examples 4 and 5, which showed stress whitening upon dispensing and break stress and elongation testing. This is believed to be due to the higher processing temperatures. Thus, the film's strength versus processing temperature can be seen from the data in Table 1.

Table 1

Examples 6-17

Preparation of Polystyrene/Styrenic Thermoplastic Elastomer Films

Having Varied Elastomer Content

The following examples illustrate the physical properties and the dispensibility characteristics of the present invention by varying the relative weight percent of the polystyrene and the styrenic thermoplastic elastomer.

General purpose polystyrene when made by casting into a thin film results in a very stiff, crinkling film that splits easily. By blending styrenic elastomer with the pure polystyrene, such as clear high-impact polystyrenes under the trade designation K-RESIN (Phillips Petroleum Co., styrene/rubber ratio of 75/25), for example, the film becomes less stiff and crinkly and more acceptable to the customer as a pliable tape. For the styrene-butadiene-styrene (SBS) block copolymers and styrene-butadiene (SB) branched copolymers, the butadiene content is determined by the relationship: (butadiene content in SB(S)) x SB(S parts by weight x 100

PS parts by weight + SB(S) parts by weight

Polystyrene/styrenic elastomeric polymer films (0.04 mm thick) were prepared according to Examples 1-5 except as follows: the processing temperature of the extruder and die were maintained consistently at 188°C. The water cooled steel rolls had 38°C water circulating through them. The compositions and thicknesses of the resulting films are given in Table 2. The films were slit, laminated with pressure sensitive adhesive, and tested for dispensability. Break stress and break elongation were tested as described in Examples 1-5. The results of these tests are also given in Table 2.

The films of Examples 6-15 dispensed easily and maintained a serrated edge, which showed a regular, uniform pattern of teeth with no evidence of ruffling or stress whitening. Examples 16-17 showed evidence of distortion and ruffling of the dispensed edge. Film strength was adequate for Examples 6-15.

Examples 16-17 are weaker and tend to stretch easily. Examples 6 and 7 were found to split easily while handling and while going through coating and slitting machinery. Examples 8-17 handled adequately and could be run through tape manufacturing equipment without splitting or breaking.

Table 2

Thus, the films of Examples 8-15 could be useable as backing films in adhesive articles. The polystyrene is in an amount of about 70 wt-%> to about 35 wt-%) and the styrenic elastomer is in an amount of about 30 wt-%> to about 65 wt-%), wherein the elastomeric composition contains about 7.5 wt-%> to about 16.25 wt-%) butadiene rubber. Below 7.5 weight percent butadiene rubber, the film tends to split easily and is difficult to fabricate into tape; on the other hand, at above 16.25 weight percent butadiene rubber, the film becomes ductile and the dispensed piece of tape will have distorted end portions adjacent to its newly cut end. They all had the necessary strength. They did not stretch too much and dispensed easily. There was no stress whitening. They were easily processed and handled well on equipment. They did not fibrillate or dog ear when dispensed.

Examples 18-22 Preparation of an Adhesive Article

A finished tape product containing a pressure sensitive adhesive (PSA), backing film, and release layer (i.e., Low Adhesion Backsize (LAB's)) was made by a process known as the multilayer process. The tape product was prepared using three extruders to supply the three components to a three layer feedblock affixed on top of a single manifold die. The three layer feedblock is available from the Cloeren Company and contained a selector plug structure giving an A/B/C layering sequence. The 45.7 cm wide single manifold die is available from Extrusion Dies Inc. (EDI).

A hot melt PSA material comprising a composition as the type described in U.S. Pat. Nos. 2,884,126 and Re 24,906, was fed into a 34 mm (3.4 cm) diameter co-rotating twin screw extruder available from Leistritz, and transferred via heated transfer piping to the "A" port location in the Cloeren feedblock. The PSA material was fed to the die so that it constituted an outer layer of the finished tape product. A blend of general purpose polystyrene resin material comprised STYRON 666D polystyrene having a MFI of 7.5 g/10 minutes, obtained from Dow Plastics and styrenic thermoplastic elastomer material comprised K-RESIN KR10 having a MFI of 8.0 g/10 minutes, obtained from Phillips 66 Chemical Company was prepared according to the procedures and materials described in Example 5 (elastomer content examples). The blend of polystyrene and styrenic elastomer materials consisted of 60% STYRON 666D + 40% KR10, respectively.

This blend was fed into a 51mm (5.1 cm) diameter single screw extruder available from The Berlyn Corporation, and transferred via heated transfer piping to the "B" port location in the Cloeren feedblock. The backing material was fed to the die so that it constituted the middle layer of the finished tape product.

A low adhesion backsize (LAB) material comprised a fluorochemical graft copolymer as the type described in U.S. Pat. No. 5,336,717 was fed into a 32 mm (3.2 cm) diameter single screw extruder available from Killion Extruders, Inc., and transferred via heated transfer piping to the "C" port location in the

Cloeren feedblock. The LAB material was fed to the die so that it constituted an outer layer.

The adjustable vanes on the Cloeren feedblock were positioned in the flow channels to match the material velocities at the point of flow convergence in the flow channel. Distribution Pins were positioned in the feedblock so that the tip of the vane formed a gap between the vane and the distribution pin. The gap was varied to achieve velocity changes of the materials coming off the tip of the vane. The distribution pins were used to correct for non-uniformity in the individual layers in the transverse direction (TD). The product exiting the Cloeren feedblock into the EDI die was generally rectangular in cross section and comprised a layering sequence of PSA/ polystyrene and styrenic elastomer blend/LAB. The rectangular product was comparatively smoothly compressed along its Y axis (i.e., its height) while at the same time being comparatively smoothly expanded along its X axis (i.e., width) direction. The now wide, relatively thin product was passed through adjustable lips in the die so as to obtain a flat product. The product was then passed into a nip formed by two water cooled steel rolls, one of which had a rubber outer sleeve, and drawn to the desired caliper by adjusting the take away rate. Alternatively, the tape product could be cast onto either one of the steel rolls without nipping and then drawn to the desired caliper.

The feed rates of each material were adjusted so as to give the thicknesses and compositions identified in Table 3. The PSA material was processed at a machine temperature of about 165°C. The polystyrene and styrenic elastomer blends were processed at a machine temperature of about 193°C. The LAB material was processed at a machine temperature of about 165°C. The casting roll temperature was maintained at about 10°C.

Testing of Examples 18-22 were performed in a similar manner as to that described in Examples 1-5. The dispensability, break elongation, and break stress results are listed in Table 4. Examples 18 and 22 maintained a serrated edge which showed a regular, uniform pattern of teeth with no evidence of ruffling or stress whitening.

Table 3

Table 4

Examples 23-26 Preparation of an Adhesive Article Having Tie Layer

An adhesive article, or tape product, may incorporate a tie layer if so desired. Tapes were prepared according to the procedures and materials described in Examples 18-22 except as follows. The film in Example 23 contains 2 layers (1 layer of polystyrene and styrenic elastomer blend, and 1 LAB layer). The films in Examples 24-26 contain 3 layers (1 layer of the polystyrene and styrenic elastomer blend, 1 layer of an intermediate tie layer and 1 LAB layer). The intermediate tie layer material which was fed into a 32 mm (3.2 cm) diameter single screw extruder available from Killion Extruders to the Cloeren feedblock such that it employed an intermediate middle layer between the LAB layer and the polystyrene and styrenic elastomer blend layer. Example 24 employed BYNEL CXA 3101 (believed to be a carboxylated ethylene/vinyl acetate, available from DuPont and having a melt flow index of 3.5 g/10 minutes and a DSC melting point of 74.5°C) as the intermediate layer. Example 25 employed ELVAX450 ethylene/vinyl acetate copolymer (82%o ethylene/18%) vinyl acetate, available from Dupont and having a melt flow index of 8 g/10 minutes and a vicat softening point of 61°C) as the intermediate layer.

Example 26 employed MODIC E 300K (believed to be a maleic anhydride modified ethylene/vinyl acetate graft copolymer, available from Mitsubishi Petro Chemical Company and having a melt flow index of 3.5 g/10 minutes and a DSC melting point of 92°C) as the intermediate layer.

For Examples 23-26 the PSA may be coated at the same time using a Cloeren feedback set up or similar or may be adhesive coated in a separate operation to form a finished tape product. In Examples 23-26, a PSA was coated off-line on each of the layered configurations above using a conventional water- based acrylic adhesive.

The thickness of each of the layers in these adhesive articles, or tapes, are provided in Table 5. The dispensibility, break elongation and break stress results are provided in Table 6.

Table 5

Table 6

Example 27 Preparation of an Adhesive Article Having a Tie Layer and LAB

An adhesive article, or tape product, was prepared according to the procedures and materials described in Examples 18-22 except as follows. The film in Example 27 contains 4 layers (1 layer of PSA, 1 layer of the polystyrene and styrenic elastomer blend, 1 layer of an intermediate tie layer, and 1 LAB layer). The tape product was prepared using four extruders to supply four components to a 5 layer feedblock, available from Cloeren Company and containing a selector plug structure BEDCA layering sequence. The Cloeren feedblock was affixed to a 25.4 cm wide single manifold die available from Extrusion Dies Inc. The PSA material was fed from the Leistritz twin screw extruder to the

"B" and "E" port locations in the Cloeren feedblock by splitting the PSA material into two heat transfer piping using a T-connector. The styrene/styrenic thermoplastic elastomer blend was fed from the Berlyn single screw extruder to the "D" port location in the Cloeren feedblock. The intermediate tie layer was fed from the Killion single screw extruder to the "C" port location in the Cloeren feedblock. The LAB material was fed from a second 32 mm (3.2 cm) diameter single screw extruder available from Killion Extruders Inc. to the "A" port location in the Cloeren feedblock.

The PSA material is similar to that described for Examples listed in Table 3. The polystyrene/styrenic elastomer blend is similar to that described in the Examples of Table 3. The intermediate tie layer material is similar to that described in Example 24, Table 5. The LAB material is similar to that described in the Examples listed in Table 3.

The thickness of each of the layers in the tape product of Example 27 is provided in Table 7. The dispensibility, break elongation, and break stress results are provided in Table 8.

Table 7

Example PSA Backing Tie Layer LAB Total

Thickness Thickness Thickness Thickness Thickness

(mm) (mm) (mm) (mm) (mm)

27 0.033 0.038 0.006 0.006 0.083

Table 8

Example Break Break Dispense

Stress Elongation Force

(xlO³ KPa) (%) (Newtons)

27 53.5 58 7.3

Comparative Examples

The force required to provide acceptable dispensing of a number of backings of commercially available pressure sensitive adhesive tapes was determined and compared to the dispensing force of the film of the invention, where films from Examples 1 -27 were compared with currently commercially available tapes. The data is shown in Table 9.

No. 810 tape, No. 600 and No. 610 tapes are available from the Minnesota Mining and Manufacturing Company. The 810 tape employs a cellulose acetate film backing. The 600 tape employs an oriented unplasticized poly vinyl chloride film backing. The 610 tape employs a cellophane film backing.

Table 9

The data show that dispensability of films of the invention is generally equivalent to that of the No. 810 tape product, the No. 600 tape product and No. 610 tape products currently available.

The complete disclosures of all patents, patent applications, and publications are incorporated herein by reference as if individually incorporated. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims

WHAT IS CLAIMED IS:

1. An adhesive article comprising : a nonoriented backing film comprising a polystyrene resin and a styrenic thermoplastic elastomer, wherein the backing film exhibits substantially complete severability upon application of a force of about 11 Newtons or less; and an adhesive coated on a major surface of the nonoriented backing film.

2. The adhesive article of claim 1 further comprising a release layer coated on an opposite major surface of the nonoriented backing film.

3. The adhesive article of claim 2 further comprising a tie layer between the backing film and the adhesive.

4. The adhesive article of claim 1 further comprising a tie layer and a release layer, wherein the tie layer is between the backing film and the release layer.

5. The adhesive article of claim 1 wherein the polystyrene has a melt flow index of about 1-50 grams per 10 minutes.

6. The adhesive article of claim 1 wherein the styrenic thermoplastic elastomer has a melt flow index of about 3-20 grams per 10 minutes.

7. The adhesive article of claim 1 wherein the styrenic thermoplastic elastomer is selected from the group of branched S-B(styrene-butadiene) block copolymers or linear S-B-S (poly(styrene-b-butadiene-b-styrene)) triblock copolymers, linear S-I-S (poly(styrene-b-isoprene-b-styrene)) and linear S-EB-S (poly(styrene-b-ethylene-butylene-b-styrene)) triblock copolymers, each copolymer containing polystyrene terminal segments and elastomer segments, and mixtures thereof.

8. The adhesive article of claim 1 wherein the styrenic thermoplastic elastomer is selected from the group of a styrene/butadiene block copolymer, a linear (poly(styrene-b-isoprene-b-styrene)), and mixtures thereof.

9. The adhesive article of claim 8 wherein the styrene/butadiene block copolymer comprises about 20%> to about 90% styrene units and about 80% to about 10%) butadiene units.

10. The adhesive article of claim 1 wherein the backing film comprises about 35 wt-%) to about 70 wt-%> of the polystyrene and about 30 wt-%_> to about 65 wt-%) of the styrenic thermoplastic elastomer.

11. The adhesive article of claim 1 wherein the styrenic thermoplastic elastomer comprises a styrene/butadiene block copolymer having butadiene in an amount of about 7.5 wt-% to about 16.25 wt-%.

12. The adhesive article of claim 1 wherein the film backing has a break stress of about 35 x 10³ kPa or greater.

13. The adhesive article of claim 1 wherein the backing film has a break elongation of about 20%) to about 150%).

14. The adhesive article of claim 1 wherein the adhesive contains substantially no organic solvents.

15. The adhesive article of claim 2 wherein the release layer contains substantially no organic solvents.

16. An adhesive article comprising : a nonoriented backing film comprising: about 35 wt-%) to about 70 wt-% of a polystyrene resin having a melt flow index of about 1-50 grams per 10 minutes; and about 30 wt-%) to about 65 wt-%> of a styrenic thermoplastic elastomer having a melt flow index of about 3-20 grams per 10 minutes ; and a pressure sensitive adhesive coated on a surface of the nonoriented backing film.

17. The adhesive article of claim 16 wherein the styrenic thermoplastic elastomer is selected from the group of branched S-B(styrene-butadiene) block copolymers or linear S-B-S (poly(styrene-b-butadiene-b-styrene)) triblock copolymers, linear S-I-S (poly(styrene-b-isoprene-b-styrene)) and linear S-EB-S (poly(styrene-b-ethylene-butylene-b-styrene)) triblock copolymers, each copolymer containing polystyrene terminal segments and elastomer segments, and mixtures thereof.

18. The adhesive article of claim 17 wherein the styrenic thermoplastic elastomer comprises a styrene/butadiene block copolymer having about 20%) to about 90%) styrene units and about 80% to about 10% butadiene units.

19. The adhesive article of claim 18 wherein butadiene is in an amount of about 7.5 wt-%) to about 16.25 wt-%> of the backing film.

20. The adhesive article of claim 16 wherein the backing film has a break stress of about 35 x 10³ kPa or greater.

21. The adhesive article of claim 16 wherein the backing film has a break elongation of about 20% to about 150%.

22. A method for making a nonoriented film comprising the steps of: providing an elastomer composition comprising:

(a) a polystyrene resin; and

(b) a styrenic thermoplastic elastomer; processing and forming the elastomer composition at a processing temperature sufficient to produce a film that exhibits substantially complete severability upon application of a force of about 11 Newtons or less.

23. The method for making a nonoriented film of claim 22 wherein the predetermined processing temperature is about 177┬░C to about 199┬░C.

24. The method for making the nonoriented film from claim 22, wherein the step of providing an elastomer composition comprises the styrenic thermoplastic elastomer selected from the group of branched S-B(styrene- butadiene) block copolymers or linear S-B-S (poly(styrene-b-butadiene-b- styrene)) triblock copolymers, linear S-I-S (poly(styrene-b-isoprene-b-styrene)) and linear S-EB-S (poly(styrene-b-ethylene-butylene-b-styrene)) triblock copolymers, each copolymer containing polystyrene terminal segments and elastomer segments, and mixtures thereof.

25. The method for making the nonoriented film from claim 22, wherein the step of providing an elastomer composition comprises the styrenic thermoplastic elastomer comprising a styrene/butadiene block copolymer wherein butadiene is in an amount of about 7.5 wt-%> to about 16.25 wt-% of the elastomer composition.

26. The method for making the nonoriented film from claim 25 wherein the polystyrene has a melt flow index of about 1-50 grams per 10 minutes.

27. A method for making an adhesive article comprising the steps of: providing a nonoriented film made by the method comprising the steps of: providing an elastomer composition comprising: (a) a polystyrene resin; and (b) a styrenic thermoplastic elastomer; processing and forming the elastomer composition at a processing temperature sufficient to produce a film that exhibits substantially complete severability upon application of a force of about 11 Newtons or less; and coating an adhesive on a first major surface of the nonoriented film.

28. The method for making an adhesive article from claim 27 further comprising the step of coating a release coat material on a second major surface of the nonoriented film.

29. The method for making an adhesive article from claim 28 wherein the steps of forming and forming the elastomer composition into a film, coating the adhesive and coating the release coat material occur substantially simultaneously to form the adhesive article.