Field

The present invention relates to adhesive tapes and methods for making such tapes, in particular adhesive tapes with improved unwind and tear properties.

Background

Numerous varieties of adhesive tapes comprising a backing sheet or film with an adhesive layer are known. Various embodiments adapted for specialty use, ease of application, strength, tear propagation, and other performance attributes have been disclosed. In many embodiments, adhesive tapes are wound into roll form.

In many instances, many adhesive tapes are dispensed and applied by hand. That is, the end of the tape is grasped by hand, force is applied manually to remove a desired length or "piece" of tape from the roll, and then the "piece" of tape is separate from the main body of tape on the roll. While the separation can be carried out by cutting with a tool (e.g., with scissors or knife), it is typically preferable that the tape be such that the separation can be carried out by tearing by hand without using a cutting device. In order to be amenable to such manual manipulation, a tape should exhibit several characteristics. The tape should exhibit a sufficiently low removal or "unwind" force that it is capable of being unrolled with unaided hand strength. If the necessary peel force is too high, the tape cannot be removed from roll by hand; and if the tape exhibits an unduly low peel force the roll may be unstable and subject to telescoping and other defects. In addition, the tape should exhibit a sufficiently low tear initiation force and tear propagation to permit hand tearing. Moreover, the tear propagation characteristics should typically be such that the resultant tear is relatively straight and true in the desired direction so as to yield a straight resultant edge rather than a ragged, uneven terminus.

In order to attain desired unwind performance with the backing and the adhesive selected for a specific application, tapes typically incorporate additional components such as release coatings (sometimes referred to as a low adhesion backsize or "LAB") on the front surfaces of backings, and liners between the adhesive and backing of successive portions or plies of tape to obtain satisfactory release properties such that the tape can be unwound from roll form (or removed from a stack) and used. Use of release coatings increases complexity and cost of product manufacture, necessitating use of additional processing steps (e.g., application of priming layer, application of release agent, oven drying, etc.) and materials; potentially leads to undesired release of volatile organic compounds ("VOCs") into the environment; and increases the potential risk of quality control failure, contamination of adherends, etc. Similarly, incorporation of a release liner entails greater complexity, cost, and other challenges.

In order to achieve desired tear initiation and propagation properties with polymeric film tape backings, it has been known to form perforations in the film. For instance, US Patent Nos. 6,635,334 (Jackson et al.) and 7,138, 169 (Shiota et al.) discloses polymeric films and adhesive tapes having a plurality of perforations therein to modify resultant tear properties. US Patent No. 7,037, 100 (Strobel et al.) discloses apparatus and methods for flame-perforating films to form such perforations.

The need exists for additional embodiments of adhesive tapes and methods for making them, particularly simplified constructions that can be made without using release coatings, drying ovens for solvents, or radiation curing processes.

Summary

The present invention provides novel adhesive tapes and methods for making such tapes. The tapes can be simply made, eliminating the need for incorporation of a release coating, and can provide surprising combinations of tensile strength, conformability, and hand tear performance.

Briefly summarizing, tapes of the invention comprise, and in some instances consist essentially of:

(A) a backing member having opposing front and rear major faces and comprising a principal film that: (a) comprises one or more orientable polymers; and (b) has: (1) first and second major faces; (2) a land portion wherein the principal film is capable of temperature-induced elastic recovery; and (3) one or more modification zones, each modification zone comprising a rim portion protruding from the first major surface of the principal film and surrounding a central opening extending through the principal film and opening on both the first and second major faces thereof, wherein the average thickness of each rim portion is greater than the average thickness of the land portion surrounding the modification zone; and

(B) an adhesive layer comprising normally tacky, pressure sensitive adhesive on the rear major face of the backing member;

wherein the first major surface of the principal film is the front major surface of the backing member.

In brief summary, the method of the invention for making adhesive tape comprises:

(A) providing a precursor film that: (a) is capable of thermally-induced elastic recovery; and (b) has first and second major sides;

(B) differentially heating at least one target zone of the precursor film above its relaxation temperature (T _r ) while maintaining the temperature of the portion of the precursor film surrounding the target zone at a temperature below its T _r so as to cause dimensional modification of the precursor film within the modification zone such that a portion of film material in the precursor film in the target zone undergoes thermally-induced elastic recovery (i.e., moves relative to other portions of the film material) and forms a modification zone comprising a central portion surrounded by a rim portion wherein maximum thickness of the rim portion becomes relatively greater and the relative thickness of the central portion decreases until an opening extending between the first and second major sides of the precursor member is formed;

(C) cooling the modification zone to below T _r thereby yielding a principal film having: (1) first and second major faces; (2) a land portion wherein the principal film is capable of thermally- induced elastic recovery; and (3) one or more modification zones, each modification zone comprising a rim portion protruding from the first major face of the principal film and surrounding a central opening extending through the principal film and opening on both the first and second major faces of the principal film; and.

(D) applying normally tacky, pressure sensitive adhesive disposed to the second side of the principal film, thereby yielding adhesive tape. Typically, one or more segments of the adhesive tape will then be wound upon itself into roll form or a plurality of segments of the adhesive tape will arranged in stack form.

Typically the tape is in the form of one or more sheets wound into roll form or two or more sheets arranged in a stack. When in roll or stack form, the adhesive on an overlying sheet or portion of tape is in contact with the first side of the tape backing of an underlying sheet or portion of tape. In accordance with the invention, the first side of the tape backing is free of release coating. Contrary to general teachings in the flame perforation and flame treatment art, in the invention the modification zones of tapes of the invention are formed using fuel-rich flame impingement conditions.

We have surprisingly found that good performance can be achieved with a simplified tape construction that does not use a release coating or LAB. It has been discovered that desired unwind and peel force properties can be achieved via the interaction of the rim portion of each modification zone (which is perforated) and the overlying adhesive layer, instead of using incorporation of release agent(s) on the surface of the backing film as is conventional. The invention provides tapes that exhibit desirable performance and properties including good tear strength and easy straight-line hand tearing. Tapes of the invention can be easily produced via simple manufacturing operations without the need for a release coating, thereby enabling high speed, cost effective production. The invention can be used to provide tapes for a variety of applications, including, e.g., packaging tape, masking tape, duct tape, hand-tearable masking sheets, release liners, medical tape, and other utility tapes. Tapes of the invention can be readily torn by hand in straight or substantially straight lines, yet provide effective tensile strength to be used in a variety of adhesive tape applications. Tapes of the invention can be readily optimized as desired for a variety of specific performance

applications. Tapes of the invention can be made with surprisingly good unwind properties. In some embodiments, tapes of the invention can provide surprisingly good performance as masking tapes to which deposited paint will adhere with minimal or no paint penetration, even despite having the backing having central openings passing therethrough. These and other advantageous embodiments can be made utilizing the discovery that flame-formed modification zones with central opening can be formed using fuel-rich conditions.

The invention makes possible construction of masking tapes using polymer films rather than paper backings, thereby also providing water resistant properties in addition to desirable hand tear and conformability properties. The resultant combination of crease, fold, and tear properties of tapes of the invention enable numerous advantages in painting applications including attaining sharp paint lines as well as soft paint edges as desired. Many paper-backed masking tapes are subject to slivering or shredding, particularly in water or wet environments; masking tapes of the invention provide surprising advances in performance thereover.

Tapes of the invention can also be made with high breathability and conformability properties. Such embodiments can be well suited for many medical applications. Tapes of the invention can be made that provide secure box and container sealing; tapes of the invention can be made that exhibit good foldability that enables secure attachment to box corners and edges without flagging or lifting while being readily opened by hand without the necessity of cutting tool such as knife or scissors

The invention is described herein with reference to tapes. It will be understood, however, that the invention also encompasses adhesive-coated backing members with modification zones, and methods for making same, that are in other configurations (e.g., large width sheets or blankets, etc.) as well as the ribbon-like relatively long, relatively thin configuration commonly referred to as "tape".

Brief Description of Drawing

The invention is further explained with reference to the drawing wherein:

Fig. 1 is a perspective view of an illustrative roll of tape of the invention;

Fig. 2 is a cross-sectional view of a portion of a backing member of an illustrative embodiment of tape of the invention showing a modification zone;

Fig. 3 is a cross-sectional view of a portion of a tape of an illustrative embodiment of the invention; and Fig. 4 is a photograph of a portion of the first major face of the backing member of an illustrative embodiment of tape of the invention.

These figures are not to scale and are intended to be merely illustrative and not limiting. Key and Glossary

For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification.

The term "orientable" means that the polymer material, if heated above a certain temperature (T ₀ or orientation temperature) and drawn, will undergo shifting and orientation of polymer segments therein, and then if cooled below T ₀ , will retain some of the imparted orientation when released. The temperature at which a specific polymer film may be oriented will depend in part upon the distribution of segments of polymer materials within the film. T ₀ is typically above the melt temperature of the lower melting fraction of polymer segments within the film but below the melt temperature of the higher melting fractions of polymer segments within the film.

The term "polymer" will be understood to include polymers, oligomers, copolymers (e.g., polymers formed using two or more different monomers), and combinations thereof, as well as polymers, oligomers, or copolymers that can be formed in a miscible blend by, for example, coextrusion or reaction, including transesterification. Both block and random copolymers are included, unless indicated otherwise.

The term "thermally-induced elastic recovery" refers to the action or response whereby a member or body of material, upon being heated to a threshold temperature (referred to herein as T _r or relaxation temperature), spontaneously changes its shape or configuration, without application of external mechanical form-changing forces (e.g., gravity, embossing, molding, etc.) or without undergoing material removal effects (e.g., mechanical etching, ablation such as by laser, combustion, evaporation, etc.).

Flame properties are commonly correlated with the molar ratio of oxidizer to fuel. The exact ratio of oxidizer to fuel needed for complete combustion is known as the stoichiometric ratio. The equivalence ratio is defined as the stoichiometric oxidizer: fuel ratio divided by the actual oxidizer:fuel ratio. For "fuel-lean", or oxidizing, flames there is more than the stoichiometric amount of oxidizer and so the flame equivalence ratio is less than one. For "fuel-rich" flames, there is less than the stoichiometric oxidizer present in the combustible mixture and thus the equivalence ratio is greater than one.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviations found in their respective testing measurements.

Weight percent, percent by weight, % by weight, and the like are synonyms that refer to the concentration of a substance as the weight of that substance divided by the weight of the composition and multiplied by 100.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes a mixture of two or more compounds. As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

For purposes of clarity and without intending to be unduly limited thereby, the tape sheets or strips in a group of any two sequentially stacked sheets or strips are referenced as an overlying tape sheet and an underlying tape sheet with the adhesive layer of the overlying tape sheet adhered to the front or first face of the backing of the underlying tape sheet.

Detailed Description of Illustrative Embodiments

Fig. 1 shows an illustrative roll of tape of the invention. Roll 10 comprises tape 12 wound upon itself into roll form on optional core 14. Tape 12 comprises backing member 16 and adhesive layer 18.

As shown in Figs. 2 and 3, tape 12 comprises a backing member 16 having a front major face and rear major face. The backing member comprises, and in this instance consists essentially of principal film 19 having a plurality of modification zones 20 each comprising rim portion 22 surrounding central opening or perforation 24. The rim portions 22 protrude from first major face 26 and central opening 24 extends through principal film 19 from the first major face 26 to the second major face 28 thereof. Modification zone 20 is surrounded by land portion 30. The thickness of rim portion 22, indicated as dimension B, is greater than the thickness of the surrounding land portion 30, indicated as dimension A. Backing Member

Backing members in tapes of the invention may be single layer (i.e., consist of the principal film) or multilayer (i.e., comprise the principal film and one or more secondary layers), wherein the principal film comprises an oriented polymeric film. The backing member is selected in part for the its flexibility and strength properties such that the resultant tape can be fabricated, handled, and applied as desired as well as provide desired performance.

The principal film typically has a thickness from about 12 to about 75 microns, though it will be understood that principal films having thickness outside this range may be used in accordance with the invention if desired.

Backing members used herein comprise and may consist essentially of oriented polymeric materials, including thermoplastic compositions. The film is typically a thermoplastic, especially a polyolefin, including polypropylene in specific embodiments. Other polymers may be

advantageously employed, especially those polymers which are commonly used for making biaxially oriented films, such as poly(ethylene terephthalate) (PET) and other polyesters. For the purposes of the present invention, the term "polypropylene" is meant to include copolymers comprising at least about 90% propylene monomer units by weight. "Polypropylene" is also meant to include polymer mixtures comprising at least about 75% polypropylene, by weight. Illustrative examples of suitable films for use herein include mono-oriented polypropylene (MOPP), sequentially and simultaneously biaxially-oriented polypropylene ("BOPP" and "sBOPP", respectively), blown films, e.g., made by any known process including, for example, tenter stretching, single bubble, double bubble, and triple bubble processes, multilayer films, and combinations thereof. The polypropylene used herein is typically preferably predominantly isotactic, and thus has a chain isotacticity index of at least about 80%, an n-heptane soluble content of less than about 15% by weight, and a density between about 0.86 and about 0.92 grams/cm ³ measured according to ASTM D 1505-96 ("Density of Plastics by the Density-Gradient

Technique"). Suitable additional polymers in such mixtures include, but are not limited to, propylene copolymers, polyethylenes, polyolefins comprising monomers having from four to eight carbon atoms, and other polypropylene resins.

Further, the polypropylenes useful in this invention may be copolymers, terpolymers, quaterpolymers, etc., having ethylene monomer units and/or alpha-olefin monomer units with 4-8 carbon atoms. Other suitable co-monomers include, but are not limited to, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbomene, and 5-methylnorbomene. Said co-monomer(s) may be present in an amount so as not to adversely affect the desired properties and characteristics of the films, and tapes described herein, typically their content being less than 10 percent by weight. One suitable polypropylene resin is an isotactic polypropylene

homopolymer resin having a melt flow index of about 2.5 g/10 minutes, available under the product designation 3374 from Total Petrochemicals Inc. (formerly FINA Oil and Chemical Co.), Dallas, Tex.

Polypropylene for use in the present invention may optionally include, in an amount so as not to adversely affect the desired characteristics and properties described herein, typically between about 1 and about 40% by weight of a resin, of synthetic or natural origin, having a molecular weight between about 300 and about 8000, and having a softening point between about 60°C and about 180°C. Such resin can be chosen from petroleum resins, styrene resins, cyclopentadiene resins, and terpene resins. Petroleum resins typically have, as monomeric constituents, styrene, methylstyrene, vinyltoluene, indene, methylindene, butadiene, isoprene, piperylene, and/or pentylene. Styrene resins typically have, as monomeric constituents, styrene, methylstyrene, vinyltoluene, and/or butadiene. Cyclopentadiene resins typically have, as monomeric constituents, cyclopentadiene and optionally other monomers. Terpene resins typically have, as monomeric constituents, pinene, alpha-pinene, dipentene, limonene, myrcene, and camphene. These resins may be partially or fully hydrogenated.

Many materials suitable for use in the backing of a tape of the invention are readily available commercially. For instance, numerous biaxially oriented polypropylene ("BOPP") films are available commercially. Illustrative examples of suitable biaxially oriented polypropylene films for use in the invention include:

1. BOPP TT 30, TT35, or TT 40 gauge non-heat sealable film; BOPP BA 30, BA35, or BA 40 gauge heat sealable film; IM-BOPP or CI-BOPP, metalized film with optional heat sealable layers; PL or PCS BOPP, white cavitated film with optional metalized layer and optional heat sealable layers; all from AmTopp Division of Interplast Group, Livingston NJ.

2. 2578 BOPP, YT62 BOPP, YM17S BOPP and 2500H BOPP films, from Toray Plastics America, North Kingstown RI.

3. PROPAFILM™ MVU 15 and PROPAFILM™ RB35 white coextruded film, from Innovia Films Inc, Atlanta GA.

4. OPT Film grade BOPP, from YemChio Co. Ltd., Tapei, Taiwan.

Backing members of tapes of the present invention may optionally include additives and other components as is known in the art. For example, the backing member or component members thereof may contain fillers, pigments and other colorants, antiblocking agents, lubricants, plasticizers, processing aids, antistatic agents, nucleating agents, antioxidants and heat stabilizing agents, ultraviolet-light stabilizing agents, and other property modifiers. Fillers and other additives are preferably added in an amount selected so as not to adversely affect the properties attained by the preferred embodiments described herein.

Illustrative examples of organic fillers include organic dyes and resins, as well as organic fibers such as nylon and polyimide fibers, and inclusions of other, optionally crosslinked, polymers such as polyethylene, polyesters, polycarbonates, polystyrenes, polyamides, halogenated polymers, polymethyl methacrylate, cyclo-olefin polymers, and the like. Illustrative examples of inorganic fillers include pigments, fumed silica and other forms of silicon dioxide, silicates such as aluminum silicate or magnesium silicate, kaolin, talc, sodium aluminum silicate, potassium aluminum silicate, calcium carbonate, magnesium carbonate, diatomaceous earth, gypsum, aluminum sulfate, barium sulfate, calcium phosphate, aluminum oxide, titanium dioxide, magnesium oxide, iron oxides, carbon fibers, carbon black, graphite, glass beads, glass bubbles, mineral fibers, clay particles, metal particles, and the like.

In some applications it may be advantageous for voids to form around the filler particles during an orientation process, or use entrained blowing agents to form voids. Organic and inorganic fillers may also be used effectively as antiblocking agents. Alternatively, or in addition, lubricants such as polydimethyl siloxane oils, metal soaps, waxes, higher aliphatic esters, and higher aliphatic acid amides (such as erucamide, oleamide, stearamide, and behenamide) may be employed.

The backing member may contain antistatic agents, including aliphatic tertiary amines, glycerol monostearates, alkali metal alkanesulfonates, ethoxylated or propoxylated

polydiorganosiloxanes, polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, ethanol amides, mono- and diglycerides, and ethoxylated fatty amines. Organic or inorganic nucleating agents may also be incorporated, such as dibenzylsorbitol or its derivatives, quinacridone and its derivatives, metal salts of benzoic acid such as sodium benzoate, sodium bis(4-tert-butyl-phenyl)phosphate, silica, talc, and bentonite.

Antioxidants and heat stabilizers can further be incorporated, including phenolic types (such as pentaerythrityl tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 1,3,5- trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benze ne), and alkali and alkaline earth metal stearates and carbonates. Other additives such as flame retardants, ultraviolet-light stabilizers, compatibilizers, antimicrobial agents (e.g., zinc oxide), electrical conductors, and thermal conductors (e.g., aluminum oxide, boron nitride, aluminum nitride, and nickel particles) may also be blended into the polymers used to form the tape backing member. In some embodiments it is preferred that backing member be treated (e.g., flame treated, corona treated, etc.) on its second or rear major face to improve subsequent adhesive coating and anchorage. Flame treatment can be performed as described in US Patent No. 7,635,264 (Strobel et al.) or in Journal of Adhesion Science and Technology 15 (1), 1-21 (2001). For the improvement in adhesion of all types of materials, the optimal flame equivalence ratio is typically about 0.96, which generates a fuel-lean flame. The resulting flame treated PP surface typically have an ASTM D2578-09 test value of about 50 to about 70 mJ/m ² . Although flame treatment of the surface to be adhesive coated is preferable, for some tape constructions, it may not be necessary to perform a flame treatment. In some instances, it may be possible to achieve adequate adhesive anchorage using only a standard corona discharge treatment applied during film manufacture as is widely practiced in the plastics industry.

Modification Zones with Rims and Perforations In Principal Layer

The principal layers of backing members of tapes of the invention have modification zones with rims surrounding central openings or perforations extending from the first face thereof toward the second face thereof. Adhesive is coated on the second major face while the rims that provide desired release properties from overlying adhesive protrude from the front or first major face. Use of backing members with perforations has been known in the art to impart desired resultant tensile and tear strength and tear properties to such tapes. We have surprisingly discovered that imparting modification zones with rims as described herein can function as release agents, eliminating the necessity for separate release coatings and liners which would be conventionally employed.

Surprising aspects of the present invention are more easily appreciated with an understanding of the effective equivalence ratio used in flame impingement processes.

In a fuel-rich flame, the overall environment in which the film is exposed is primarily reducing in nature because of the high concentration of hydrogen atoms, carbon monoxide, and hydrocarbon free radicals, yet some oxidation of the film occurs because there are some oxidizing species still present in the flame product gases. In contrast, in a fuel-lean flame such as is taught in the art for the surface treatment of polymers to impart higher adhesion properties thereto, the overall environment is highly oxidizing because of the high concentrations of oxygen molecules and hydroxyl radicals.

Flame impingement to carry out differential heating and modification of the principal film in accordance with the invention requires relatively high flame powers to effectively form desired modifications in the polymer film at reasonable film speeds. For example, flame powers of at least about 15,000 Btu/hr per inch of cross-web burner length (1730 Watts/cm) are desirable to enable flame impingement at speeds of from about 20 to over 100 meters/min. When using the fuel-lean flames that are taught in the art as optimal for the flame processing of polymers, such conditions of high flame power and relatively low film speed cause significant oxidation of the polymer surface. When a surface is highly oxidized, adhesion to that surface is typically high. Thus, if a fuel-lean flame is used for flame impingement, the resulting rims are oxidized to such an extent that the pressure-sensitive adhesives tend to adhere more strongly to the rims, thereby interfering with and in some instances preventing unwind of the tape. We have found that undesired oxidation of the polymer rim surface can be limited by using low-power fuel-lean flames (for example, at powers of less than about 3000 Btu/hr-in.). However, when using such low-power flames, it is either not possible to effectively modify the film at commercially viable film speeds.

It is surprising that fuel-rich flames can be used at sufficiently high powers to enable desired modification at film speeds of more than about 20 meters/min, but without causing the excessive oxidation of the rims that would prevent the smooth and easy unwinding of the finished tape.

It has been unexpectedly found that backing members having modifications as described herein (i.e., raised rims protruding from the first major face of the backing surrounding central openings) can enable release from the adhesive of overlying tape portions or sheets from underlying portions without use of a release coating on the first side of the backing or an intervening removable release liner. Such rims are of sufficient height to enable the finished tape to be unwound without excessive force, tearing of the backing, or cohesive failure of the adhesive.

By eliminating the need for such coatings or liners, the present invention enables significant simplification of tape manufacture and use because no coating steps, drying ovens, solvent recovery systems, or radiation curing processes, as are typically involved with use of release coatings, are necessary. Elimination of solvents eliminates volatile organic compounds, and also eliminates the energy to run ovens such that the overall tape manufacturing process is more efficient. The absence of oven drying causes less thermal damage to oriented film substrates, simplifies web handling operations, and enables use of a much smaller space for manufacturing operation.

The rims of melted polymer on the first major face of the principal film enable the smooth and easy unwind of tapes made therefrom in accordance with the invention. It is thought that the maximum height of the rims is a critical parameter enabling adhesive release and subsequent unwind because the highest points on the rim are the locations that hold the pressure sensitive adhesive farthest from the primary surface of the principal film, i.e., the portion of the first face or side between central openings and their surrounding rims. Adhesion between the highest points of the rim produced with a fuel-rich flame and the adhesive will be limited because the small area of contact between the rim and the adhesive and the low extent of oxidation of the rim.

Fig. 4 is a photograph of a portion of the first or front major face of a backing member comprising principal film 19 having an array of modification zones 20 each comprising rims portions 22 surrounding of central opening or perforation 24, the modification zones 20 being surrounded by land portion 30.

The configuration and arrangement of the modification zones provide a principal film that can be readily torn in straight or substantially straight lines, yet has a sufficient tensile strength to be used as a backing member in adhesive tape s. Tear initiation and propagation parameters of tapes can be controlled as desired by controlling the arrangement and geometry of the modification zones.

The principal film is typically tearable by hand in at least one direction, and can be formed such that it is hand tearable in two perpendicular directions. The principal films of the invention can have relatively low tear initiation energy and relatively high tear propagation energy as compared to similar polymeric films that are not modified to possess modification zones in accordance with the invention. In addition, the modification zones of principal films of the invention allow tearing of the films in substantially straight lines compared to similar polymeric films that have not been modified in accordance with the invention. The modification zones allow such improved tear properties without excessively weakening the tensile strength of the film, and additionally provide a desirable reduction in the tensile elongation-to-break of the film.

In many embodiments where improved tear properties are desired, the modification zones in the polymeric film are typically preferably non-circular and have a length at least 1.25 times their width, and typically at least 2 times their width. Although different individual modification zones across the principal film may exhibit variation, with their respective central portions or perforations and surrounding rim portions varying somewhat in size, they typically each have a major axis and a minor axis. The major axis is a line along the length of the modification zone, and the minor axis is a line along the width of the modification zone. In one implementation, a line projected along the major axis of each modification zone passes through an adjacent second modification zone. In specific implementations a line projected along the major axis of each modification zone passes through an adjacent modification zone along or parallel to the minor axis of the adjacent modification zone.

The modification zone are arranged in a fashion such that they promote easy tearing of the film in the down-web or machine direction (MD) and in the cross-web or transverse direction (TD). The modification zones sufficiently preserve the tensile strength of the film while allowing straight line tearing of the film such that the film is suitable as a tape backing. The central openings or perforations and complementary surrounding rim portions are typically elongate ovals, rectangles, or other non-circular shapes arranged in a fashion such that the major axis of each modification zone intersects adjacent modification zones or passes near adjacent modification.

A feature of tapes of the invention is the perforations in the backing each have a raised ridge or rim formed during flame impingement. This raised ridge consists of polymer material from the interior of the modification zone that has elastically recovered from the orientation imposed on the precursor film. Previously, this rim has been observed to provide enhanced tear properties of the perforated film and to also impart slight textures that cause the film to more closely resemble a conformable material. As discussed above, such raised ridges or rims have been surprisingly found to eliminate the need for use of a release coating or liner in an adhesive tape construction.

As discussed in US Patent No. 7,037,100 with reference to Fig. 4 therein,

"The perforation pattern formed in polymeric film 14 has a strong influence on the tear and tensile properties of the cloth-like films and tape backings of the invention. In reference now to FIG. 4, a portion of an enlarged layout of a typical perforation pattern 28 is shown, with the machine direction oriented up and down, and the transverse direction oriented left to right. Depicted perforation pattern 28 comprises a series of rows of perforations, identified as a first row having perforations la, lb, and lc; a second row having perforations 2a, 2b, and 2c; a third row having perforations 3a, 3b, and 3c; a fourth row having perforations 4a, 4b, and 4c; and a fifth row having perorations 5a, 5b, and 5c. Typically the perforations form a pattern extending along most or all of the surface of a film, and thus the pattern shown in FIG. 4 is just a portion of one such pattern."

US Patent Nos. 6,635,334 (Jackson et al.) and 7,138,169 (Shiota et al.) disclose a number of patterns that might be used in for modification zones in a principal film accordance with the present invention to attain desired resultant tear, crease, folding, and other physical properties of the resultant tape.

Without wishing to be bound by any theory, it is believed that the density of the modification zone pattern contributes to both the conformability and fold-ability of the films and tapes of this invention and the tear and tensile properties, and that lowering the density or changing its distribution in such a way as to provide channels, along either the machine direction (MD) or the cross-web or transverse direction (TD) or both, in which a propagating tear might encounter no modification zones, results in decreased conformability, and less desirable tear and tensile properties along the direction of such a modification- free channel, compared to the most preferred pattern. Tapes of this invention conform to substrates such as boxes, containers, skin, automotive parts and panels, and other materials thereby enabling the intimate contact of the pressure sensitive adhesive with the part or substrate and thus increasing the adhesion between the tape and the substrate. In addition, adhesive tapes of present invention can be folded so as to produce a soft paint edge when used in a typical paint spraying operation, as is well known for comparable paperbacked masking tapes.

Also, it is believed that the raised rim portion around each central opening serves to blunt propagation of the tear, resulting in better control of the tear by hand, and increase in tear propagation force (relative to that of original film). The tear initiation force, however, is reduced, relative to that of original film, especially for the most preferred pattern, because the modification zone density guarantees that the edge of any film or tape so constructed will have modification zones including central openings either at or extremely near the edge. Therefore, for the purposes of tear initiation, the inventive films and tapes behave similarly to notched films but without the occurrence of significant slivering, which is a problem for paper-backed masking tapes especially when utilized in a wet environment.

Modification Methods

Principal films of the present invention can be manufactured using various film forming, orientation, and flame impingement techniques that provide modification zones with rims surrounding central openings as described herein.

Formation of modification zones (i.e., raised rim surrounding a central opening or perforation) in films in accordance with the invention to yield a principal film is carried out by

(A) providing a precursor film that: (a) is capable of thermally-induced elastic recovery; and (b) has first and second major faces;

(B) differentially heating at least one target zone of the precursor film above its relaxation temperature (T _r ) while maintaining the temperature of the portion of the precursor film

surrounding the target zone at a temperature below its T _r so as to cause dimensional modification of the precursor film within the target zone such that a portion of film material in the target zone undergoes thermally- induced elastic recovery and forms a modification zone comprising a central portion surrounded by a rim portion wherein maximum thickness of the rim portion becomes relatively greater and the relative thickness of the central portion decreases until an opening extending between the first and second major faces of the precursor member is formed; and then

(C) cooling the modification zone to below T _r thereby yielding a principal film having: (1) first and second major faces; (2) a land portion wherein the principal film is capable of thermally- induced elastic recovery; and (3) one or more modification zones, each modification zone comprising a rim portion protruding from the first major face of the principal film and surrounding a central opening extending through the principal film and opening on both the first and second major faces of the principal film An adhesive tape of the invention is then made by applying normally tacky, pressure sensitive adhesive disposed to the second major face of the principal film (i.e., when the backing member consists essentially of the principal film) or to the second major surface of the backing member (i.e., when the backing member comprises the principal layer and an optional secondary layer bonded to the second major face of the principal film (e.g., by extrusion)).

It is not necessary for each of the modification zones to be wholly identical to the others or absolutely precise in shape, size, or openness. Many techniques and apparatus known in the art for flame impingement can be employed in the present invention. As they do when used for conventional flame impingement, when used to form modification zones in accordance with the invention, such techniques and apparatus will yield principal films having modification zones that vary somewhat in size and perfection of shape. This does not have a significant deleterious effect on the current invention.

The method and process conditions used to carry out formation of modification zones are selected in part based upon the desired modification zones and nature of the films. It is typically preferred that the process be carried out so as to minimize the degree of thermal damage the film undergoes aside from formation of the desired modification zones.

Passing the web through the flame impingement station at higher speed results in formation of relatively smaller modification zones. As will be understood by those skilled in the art, other flame impingement conditions used (such as the flame power, the burner-to-film separation, or backing roll patterns) can be adjusted to attain similar modification zone sizes and spacing or any desired array of modification zones.

The pattern of depressions in the backing roll that are used to achieve the desired differential heating determines in part the arrangement and dimensions of the resultant modification zones with each modification zone corresponding to a dimple or depression in the backing roll. In some instances, the modification zones are arranged in an ordered array. In some instances, the modification zones are arranged in a random manner. If desired, the modification zones may have substantially similar individual configuration (i.e., from using backing rolls with depressions that are substantially in shape and dimension), of the modification zones may have varied individual configuration (i.e., from using backing rolls having depressions that vary accordingly in shape, dimension, or both).

If desired, a tape may be made wherein the principal film has first segment having a first array of a plurality of modification zones and a second segment having a second array of a plurality of modification zones wherein the first array differs from the second array in one or more characteristics. This can be achieved by using a backing roll having corresponding arrays of depressions to form the multiple segments simultaneously or forming the respective segments of modification zones sequentially.

As desired, the respective arrays of modification zones may be formed that include differences in one or more of the characteristics selected from the group consisting of: (1) average distance between adjacent modification zones, (2) shape of modification zones, (3) dimension of modification zones, and (4) average thickness of rim portions.

Flame impingement can be performed by, for example, the process specification given for Example 1 of US Patent No. 7,037, 100. Such apparatus ordinarily employs premixed laminar flames in which the fuel and the oxidizer are thoroughly mixed prior to combustion. However, in contrast to the process described in US Patent No. 7,037, 100, for this invention a fuel-rich flame is used. The side of the film that is exposed to the flame during formation of the modification zones develops the rims of elastically recovered polymer material that surround the central opening. It has been surprisingly found that these rims can effectively act as the release surface for the adhesive subsequently applied by minimizing the contact between the backing member and the adhesive when wound into the common roll form of tape. Because the rim surface needs to exhibit release properties, it is critical that the process for formation of modification zones be performed by using flame conditions that do not overly oxidize the first major surface of the film in either the raised rims or surrounding land portion; that is, by using flame conditions that minimize the adhesion-promoting characteristics of the surface oxidation typically caused by exposure to a flame. While flame-induced surface oxidation cannot be totally eliminated, oxidation is maximized at a flame equivalence ratio of 0.92 to 0.96, but minimized at flame equivalence ratios of at least about 1.05, which are fuel-rich flames [See C. Stroud et ah, Progress in Energy and Combustion Science, 34 (6), 696-713 (2008)]. It is therefore necessary to conduct the flame impingement process using a fuel-rich flame, preferably with an equivalence ratio of about 1 and preferably at least about 1.05. Use of fuel-rich flames for flame impingement of polymer films is contrary to essentially all recommendations in the art of flame treating. The advantages obtained from using such backing members (e.g., improvement in unwind in the tape roll form is good, resistance to paint penetration, etc.) are surprising outcomes from this processing choice.

Secondary Layer

Optionally, backing members of tapes of the invention may comprise a secondary layer on the second major face of the principal layer to impart desired properties to the resultant tape.

The secondary layer may be single layer or multilayer. The secondary layer may be permeable or impermeable. After formation of the modification zones in the principal film, the secondary layer may be bonded to the second major face thereof by lamination, by extrusion of the secondary layer onto the principal film, etc.

Those skilled in the art will be able to readily select suitable material(s) for use in the secondary layer, dependent in part upon the nature of the principal film, desired application of the tape, etc. In many illustrative embodiments, the optional secondary layer comprises one or more polyolefin polymers.

Adhesive

The adhesive coated as the second major face of the backing member may be any suitable adhesive as is known in the art. Preferred adhesives are normally tacky, pressure sensitive adhesives. Selection of adhesive will be dependent in large part upon the intended use of the resultant tape. Illustrative examples of suitable adhesives include those based on acrylates, rubber resin such as natural rubber, butyl rubber, styrene copolymers, etc., silicones, and combinations thereof. The adhesive may be applied by solution, water-based or hot-melt coating methods. The adhesive can include hot melt-coated formulations, transfer-coated formulations, solvent-coated formulations, and latex formulations, as well as laminating, thermally-activated, and water- activated adhesives and are not limited except so as to provide a desirable balance of tape roll unwind and adhesion properties.

Those skilled in the art will be able to select suitable adhesives for use in the invention, dependent in large part upon the desired application.

Illustrative examples of tackified rubber hot melt adhesives that are suitable for use in tapes ofthe invention are disclosed in US Patent Nos. 4,125,665, 4, 152,231, and 4,756,337.

Illustrative examples of acrylic hot melt adhesives that are suitable for use in tapes of the invention are disclosed in US Patent Nos. 4,656,213 and 5,804,610.

Those skilled in the art will be able to readily select rotary rod or other suitable coating techniques for applying adhesive for use in articles of the invention. Selection of the coating method will be dependent in part upon the flow characteristics of the adhesive, desired penetration of adhesive into central openings, etc. Those skilled in the art will be able to readily select suitable methods for applying or coating adhesive on the sheet. Illustrative examples include rotary rod die coating, knife coating, drop die coating, etc. Illustrative examples of rotary rod coating methods that may be used to make tapes of the invention are disclosed in US Patent Nos. 4,167,914, 4,465,015, and 4,757,782. To enhance adhesion between the backing member and the adhesive, adhesion promoting treatment(s) may be applied to the second major face of the backing member, e.g., flame treatment under fuel-lean conditions, exposure to corona, chemical primers, etc.

Pressure sensitive adhesives are well known to possess aggressive and permanent tack, adherence with no more than finger pressure, and sufficient ability to hold onto an adherend.

Additionally, the adhesives can contain additives such as tackifiers, plasticizers, fillers, antioxidants, stabilizers, pigments, diffusing materials, curatives, fibers, filaments, and solvents.

In some embodiments, the adhesive optionally can be cured by any suitable method to modify the properties thereof including rendering it less likely to flow. In particular the crosslinking level can be chosen so as to provide a balance of good tape roll unwind and finished adhesive properties. Typical crosslinking can be provided by well known methods such as radiation-induced crosslinking (for example, UV or e-beam); thermally induced crosslinking, chemically reactive crosslinking or combinations thereof.

The adhesive may be applied in any desired amount, and typically is applied to provide a conventional dry coating weight between about 5 to about 100 g/m ² . Thicker adhesive coatings tend to increase probability of causing undesirable increases in unwind force. Too thin coatings are not functional or tend to wet substrate surfaces poorly.

A general description of useful pressure sensitive adhesives may be found in the

Encyclopedia of Polymer Science and Engineering, Vol. 13, Wiley-Interscience Publishers (New York, 1988). Additional description of useful pressure sensitive adhesives may be found in

Encyclopedia of Polymer Science and Technology, Vol. 1, Interscience Publishers (New York, 1964).

Following application of adhesive to the backing member, tape of the invention may be converted to desired configurations using known approaches, e.g., slitting, rolling, etc. Sheets of tape of the invention may be wound into roll form (e.g., one or more sheets of the tape wound upon itself about an optional core), or stacked in sheet form. In accordance with the invention, surprising advantages provided by such tape assemblies include easy unwind as the interface between the adhesive layer of overlying plies and first major face with raised rims of the principal film of underlying plies separate easily, as well as good hand tear, conformability, and other tape properties.

Applications

The invention can be used to manufacture tapes or sheets for many applications including packaging tapes, paint masking tapes, general utility or "duct" tapes, medical tapes, masking films, liners, as well as laminates with one or more additional layers including nonwovens, foams, etc. Those with skill in the art will be able to readily select suitable backing and adhesive materials to make tapes of the invention well suited for a specific application.

Examples

The invention will be further understood with reference to the following illustrative examples and comparative examples.

Several abbreviations and units are used in the description of the Examples including the following:

Precursor Films

Four precursor input films were prepared as described below using one or more of the following polymers:

Table 1 : Polymer Identification

¹ Reported in g/10 min as determined by ASTM D1238-95: MFR at 230°C, 2.16 kg condition. The MFR and % ethylene values were provided by the manufacturers.

² Total Chemicals, Inc., Houston, Texas

³ Exxon Mobil Corporation, Irving, Texas

Film 1 : 0.04 mm-thick (1.6 mil) single-layer BOPP film comprising Polymer C was oriented 5.4: 1 in the length (machine or MD) direction and 8.5: 1 in the cross-web (transverse or TD) direction, corona treated on one side and had an estimated wetting tension = 40 to 44 mil m ² (ASTM D2578-9). Film 1 was prepared using a conventional sequential stretching process. A general description of sequentially stretched BOPP via a tentered process is described in

"Polypropylene: The Definitive User's Guide and Databook", C. Maier and T. Calafut, Plastics Design Library, 13 Eaton Ave., Norwich, NY, 1998.

Film 2: A three-layer 0.038 mm thick (1.6 mil) biaxially oriented (sBOPP) film consisting of one LLDPE (polymer B) surface or skin layer co-extruded with polypropylene in the core layer and in the other skin layer. This film was oriented 6.5: 1 in the MD and 7.3: 1 in the TD. The polypropylene side was corona treated and had an estimated wetting tension of about 37 mJ/m ² (ASTM D2578-9). Polymer A was used for the polypropylene layers. Film 2 was prepared using a linear-motor-based simultaneous-stretching process as described in US Patent Nos. 4,675,582; 4,825, 1 11 ; 4,853,602; 5,036,262; 5,051,225; and 5,072,493.

Film 3 : 0.04 mm thick (1.6 mil) three-layer BOPP film oriented 5.4: 1 in the length (machine or MD) direction and 8.5: 1 in the cross-web (transverse or TD) direction, flame treated on one side with an estimated wetting tension of 44 to 50 mJ/m ² (ASTM D2578-9). Polymer A was used for all three layers. Film 3 was prepared using a linear-motor-based simultaneous- stretching process as described in US Patent Nos. 4,675,582; 4,825,1 1 1 ; 4,853,602; 5,036,262; 5,051,225; and 5,072,493. Film 4: 0.03 mm thick (1.2 mil) three-layer BOPP film oriented 5.4: 1 in the length (machine or MD) direction and 8.5: 1 in the cross-web (transverse or TD) direction, flame treated on one side with an estimated wetting tension of 44 to 50 mJ/m ² (ASTM D2578-9). Polymer A was used for all three layers. Film 4 was prepared using a linear-motor-based simultaneous- stretching process as described in US Patent Nos. 4,675,582; 4,825,1 1 1 ; 4,853,602; 5,036,262; 5,051,225; and 5,072,493.

The precursor films were corona treated on one side during film manufacture. Each precursor film was slit into approximately 33 cm wide sample widths using a razor blade cutter equipped with fresh blades.

The precursor films were then flame treated on the previously corona-treated side to further improve subsequent adhesive coating and anchorage. The flame treatment was performed using the burner described in US Patent No. 7,635,264 facing a smooth water-cooled backing roll held at 80°F. The flame treatment conditions were: a flame power of 6000 Btu/hr-in. of burner cross-web dimension, a flame equivalence ratio of 0.96 (which corresponds to an air-to-natural gas ratio of 10.0: 1), a burner-to-film separation of 9 mm, and a film speed of 120 m/min. Note that a flame equivalence ratio of 0.96 generates a fuel-lean flame. The resulting flame treated PP surface had an ASTM D2578-09 test value of 70 mJ/m ² .

Each precursor film was then flame impinged (i.e., differentially heated and then cooled), largely in accordance with the process specification given for Example 1 of US Patent No.

7,037, 100, forming the distinctive modification zones of the invention. The pattern etched into the backing roll was similar to that shown in Fig. 4. The pattern consisted of ovals arranged in a cross-hatched array with an oval major dimension of 0.025 in. and a minor dimension of 0.020 in., with the ends of each oval having a full radius to provide an overall length of about 0.045 in.

In contrast to the process described in US Patent No. 7,037,100, for this invention a fuel- rich flame was used. The flame impingement process was conducted using a flame equivalence ratio of 1.07 (which corresponds to an air/fuel ratio of about 9.0: 1).

Other conditions were: a flame power of 15000 Btu/hr-in. of burner cross-web dimension (1730 W/cm), a burner-to-film separation of 12 mm, and a backing roll temperature of 50°F. To vary the extent (dimensions) of the modification zones including the height of the rims formed around the central opening, the film speed during flame impingement was varied from 20 to 80 m/min.

After flame impingement to form modification zones, some of the resulting principal films were then coated with hot-melt adhesive on the second major face of the backing member that had been previously corona-and-flame treated; that is, the adhesive was coated onto the side of the film opposite that of the elevated rims. Table 2 lists the resultant principal film identification, precursor film identification, and film speed during differential heating.

Table 2: Principal Film Identification

Principal Precursor Flame Speed

Film Film (m/min)

F-28 #3 80

F-29 #4 45

F-30 #4 50

Samples of Film #1 (BOPP) that were flame impinged at speeds of 45 m/min and 60 m/min were coated with a hot-melt acrylate PSA. The adhesive was applied using a rotary-rod die with a die gear pump speed of 1 1 RPM. A coat weight of about 21 g/m ² was applied at a speed of 31.5 ft/min and the extruder, hose, and die temperatures were set to 325°F. It is important to note that the adhesive was coated on the second major face of the principal layer so that in a roll of tape, the adhesive surface would be wound into direct contact with the first major surface or flame impinged surface bearing the rims.

After coating onto the flame impinged BOPP backing, the adhesive was partially cross- linked by exposure to UV-C at a dosage of 20 mJ/cm ² . Partial cross-linking of the hot-melt acrylate adhesive is beneficial for maintaining a low unwind force after aging of the finished tape. Cross-linking of the adhesive helps to prevent the adhesive from gradually flowing off of the elevated rims onto the remainder of the polymer backing, which would tend to increase the unwind force of the tape if such flow were to occur. After coating, the resulting tape was slit into rolls of 19 mm (0.75 inch) and 38 mm (1.5 inch) widths for properties testing. It is believed that greater thicknesses of adhesive coating may provide improved resistance of the tape to paint penetration.

Films from Table 2 films listed as F-4, F-6, F-8, F-22, F-30, and F-31 were coated with a hot-melt tackified rubber PSA. The coater consisted of a COPERION™ ZSK-30 twin screw extruder with four heating and melting zones in line with a Zenith melt pump to deliver consistent coat weights. Two die set-ups were used. One set up used a 4-inch slotted drop die deckled to deliver a PSA melt onto film passing at approximately 3 to 6 meters per minute. The coated film was nipped between rubber and silicone covered rollers. The second set-up used a slotted contact die which contacted the passing film similar to a rotary rod die to deposit a layer of adhesive onto the passing film. This set-up produced a tape that did not have desirable properties and was used primarily to demonstrate the difference with the drop die coating. In each case, the resultant coated film was razor slit to 50 mm width and wound directly to 14 to 18 meter sample rolls to generate examples of tapes of the invention. These rolls were then tested for various tape properties normally used to evaluate packaging tape. A tackified synthetic rubber adhesive was used to create proto-type packaging tape rolls for evaluation. In these examples, the rubber was an SIS (styrene- isoprene-styrene) block copolymer and the tackifier was an aromatically modified C5 hydrocarbon resin. The rubber/ tackifier ratios were typical for packaging tape applications - between about 42 % rubber to about 52 % rubber. Low levels of phenolic and thioester stabilizers were also used to help stabilize these adhesives in the hot melt coating of the flame impinged films.

Most of the examples were made using a "drop" die, which "drops" a melt onto the film between two rolls, a rubber roll and a silicone roll. The rolls are aligned and trammed so that the adhesive layer is essentially compressed onto the film. A second method using a "contact' die was also used. This mimics a rod die coating process, in which rod pressure applies the adhesive directly to the film. Unexpectedly, the pressure rod application may force adhesive into the central openings of the Example films, leaving voids where fluid or spray may penetrate. In addition, release properties of principal films coated by the drop (non-contact) die method appear to be superior to those found using the pressure rod die.

Three methods were used to apply hot melt adhesive in accordance with the invention, fist, drop die, allows molten adhesive to drop from die lips to film passing beneath; second, contact die, allows die to directly contact surface of film to be coated results in more penetration of adhesive into and through central openings; and, third, rotary rod as described in US Patent No. 4, 167,914 (Mldota) rolling bank of adhesive polymer is applied to web and distributed by means of rotary rod.

Table 3 : Coated Ta e Exam les

Tape Principal Coat Coat Wt

Adhesive Comment

Example Film Method (g/m ² )

E-l l F-22 Rubber Drop Die 21.7 Good

E-12 F-22 Rubber Drop Die 21.7 Good

E-13 F-31 Rubber Drop Die 16.7 Good

E- 14 F-9 Acrylic Rotary Rod 20.9 Good

E- 15 F-6 Acrylic Rotary Rod 20.9 Paint penetration resistance low

Test Methods and Results

Rim Height: The height of rim above the surface of the 40 micron thick unmodified polypropylene film was determined with optical interferometry using a Wyko NT9800 interferometer. This technique measures the profile of an object using interferometry. Vertical- scanning interferometry (VSI) uses multiple wavelengths of light and measures tall features by scanning the microscope head downwards and measuring the light intensity of each pixel. The Wyko settings used to generate the topographical map of the modification zones were as follows: VSI mode, lOx objective, l .Ox field-of-view, full resolution, 2% modulation threshold, "stitching enabled" to generate a 3 x 3 mm or 5 x 5 mm topographical maps. Prior to calculating the rim heights, a terms removal function (tilt) in the Vision 3.44 software was applied to the images to remove sample tilt. At least eight measurements were performed on each sample. The rims tend to be of greatest height along the long side of the oval-shaped modification zone. The maximum rim height detected by interferometry for each sample is given in the Table 4 below.

Adhesion to Backing (ASTM D3300 Method B). Adhesion-to-backing tests were conducted on the principal film samples to evaluate the unwind properties of the film. Two commercially available tapes (3M® 3750 Packaging Tape and 3M® 6200 Highland™ Matte Office Tape) were used for the testing. The 3750 Packaging Tape comprises a synthetic hot melt rubber resin adhesive coated onto a clear BOPP backing. The 6200 Highland™ Matte Office Tape comprises an acrylic adhesive coated onto a matte plastic film backing.

Test specimens 0.75 inches width (19 mm) were laminated to Example principal films and peeled at a speed of 230 cm/minute.

Testing was conducted on samples with no aging, on samples aged for one week in a

90°F/90% humidity chamber, and on samples aged for one week in a 120°F chamber.

Table 5: Adhesion to Backing

The data in Table 4 shows that adequate adhesive release from flame-impinged films is possible without any release coating. In addition, the adhesive unwind from the principal films is strongly dependent upon the flame impingement process conditions; lower speeds or equivalently longer dwell times in the thermal zones creates larger modification zones with larger central openings and thicker rims, thereby giving lower adhesion values. As the modification zones become less distinct (i.e., higher line speed or decreased thermal exposure) the adhesion to backing values approach the un-flame impinged control films (compare films F-l 1 and F-12). Effect of Fuel Mixture

The fuel/air mixture in the flame system used to carry out modification in accordance with the invention has an unexpectedly distinct effect on adhesion to backing or adhesive release value. Two flame equivalence ratios, i.e., 0.93 (fuel-lean) and 1.06 (fuel-rich) were utilized in this test. The results of equivalence ratio and perforation process condition on adhesion to backing tests using two acrylic adhesive coated tapes, 3M® 6200 Highland Matte Office Tape and 3M® 3650 Mailing Tape are shown in Table 6:

Table 6: Flame Equivalence Ratio Effect on Adhesion to Backing (ASTM D3300 Method

B)

For both adhesive tapes tested, the effect of both resultant rim structure and air/fuel ratio of the flame impingement conditions are shown. The F-6 films exhibited significantly larger rims, which act to limit adhesive contact, hence results in very low adhesion to backing values. For these very structured films there is only a small effect of equivalence ratio shown. Conversely, for the F-12 flat control films, there is no structural effect so any difference in adhesion to backing values results from the different equivalence ratios employed; fuel-rich (that is equivalence ratio of 1.06) samples exhibit lower values for all samples tested. Unexpectedly, the combined effects of thermally-induced elastic recovery and equivalence ratio favoring a fuel rich flame (that is equivalence ratio of about 1.0 or more) is significant. These tape samples in roll form exhibit good unwind or adhesive release. Tear (initiation and propagation)

Mechanical properties of the film samples were tested to evaluate the tear performance of the films with respect to degree of modification. Film samples were tested using ASTM D 1938-08 "Tear Propagation Resistance (Trouser Tear) of Plastic Film and Thin Sheeting by a Single-Tear Method." Results are shown below in Table 7.

Table 7: Tear Propagation Resistance

In Table 7 the data indicates that lower flame impingement speeds give increased tear propagation resistance. Lower speeds yield larger amounts of rim material, which may serve as "crack stopping" structures in the film to unexpectedly yield improved tear propagation resistance compared to the control F- 12.

Tear initiation of samples were measured as follows. A test adhesive coated tape strip is mounted along the axis of a tensile testing machine using a rounded sample grip assembly referred to as a quarter-round, that is, a one-quarter section cut of an input cylindrical steel rod. The specimen is mounted so that tensile loading is along one edge only, due to the mounted quarter round fixtures. The test strip is progressively stretched along the length or axial direction, subjecting the tape edge to progressively increased loading until a tear or rupture initiates along that edge. The load force and extent of elongation at this point are reported as the tear initiation force and tear elongation value, respectively. Maximum tear and break by elongation were evaluated using a tensile test with the tape sample mounted on "quarter rounds" on one side of a piece of tape to force the stretched tape to tear preferentially on one side of the tape. This mimics and thus measures the force necessary to initiate a tear from one side of the tape typical of a finger or hand tear operation. Table 8: Tear Initiation Properties

Tear initiation values less than about 65 N are considered "hand tearable." The data in Tape 8 shows that tear initiation unexpectedly increases with increasing extent of perforation, that is, lower process speeds and subsequently larger melted rim extent. The same mechanism of crack stopping may apply in this test as well. The data follow the same trend for multilayer Film #2 as well. Larger, thicker rims may reinforce the material so that the force and elongation to break are increased. By comparison, a commercial hand-tearable BOPP tape (3M® Cat. No. 3842) exhibits tear initiation values equivalent to the inventive cases. Also by comparison, an un-modified BOPP adhesive tape (F- 12) cannot be torn by hand.

Pinch Tear Test

Various uncoated precursor films were tested for TD and MD tear by a method similar to the "Pinch Tear" test described in col. 15 of US Patent No. 7,138,169 (Shiota et al.).

Approximately fifty 8 cm x 30 cm portions of modified principal film samples were cut so that the 30-cm dimension was oriented in either the TD (transverse or cross-web direction) or MD (machine or down-web direction), for testing TD tear or MD tear, respectively. Several small 1 cm long slits were then made with a razor blade along the 8 cm edge of the samples to be tested. These slits provided a site for tear initiation. The samples were then torn in accordance with the Pinch Tear test. Samples were judged to "fail" the tear test if the number of adjacent rows of modification zones across which the tear propagates is greater than two. The results of the tear tests are reported as "percent failure." Lower failures indicate straight tear along the lines of the modification zones. The results are shown below in Table 9. Table 9: Pinch Tear Test

Paint penetration test

Samples of principal film, which were 1.5 inches (40 mm) in width and 9.5 inches (241 mm) in length, were taped to a black-painted test panel. The front surfaces of each tape sample were then painted using the following conditions, equipment, and materials:

Spray Gun - ANEST-IWATA™ (IWA5669), 1.3 Tip Basecoat Gun

Spray conditions - 70°F

Waterborne Basecoat - PPG™ ENVIROBASE™ (T400 White reduced 10% with T494 Thinner)

Solvent Basecoat - PPG™ DBC (DELTRON™ Base Coat) (Code 040 White reduced 100% with DT870)

After baking dry, the painted test sample strips were peeled back to reveal the extent, if any, of paint bleed-through the central openings.

A semi-quantitative imaging method was used to determine the extent of paint penetration as a function of process conditions. The equipment used to capture and analyze images of the portions of the painted panels masked by the principal film samples are as follows:

A NIKON® D70s digital SLR camera was fitted with an AF-S DX Zoom NIKKOR®

Lens (18-70 mm). The camera was set with f/3.5-4.5 GIF-ED, a focal length of 70 mm and using automated exposure setting. The digital images were processed using NIKON® Camera Control

Pro 2.7.1 software.

The lighting arms were located on both sides of the camera and set at a 45° angle and the bulbs elevated 15° relative to the arm angle. Four 150 W incandescent flood bulbs were used to light the stage and a light diffusing box was placed around the stage. The camera lens was placed 41 mm from the stage platform and the images obtained were 30008 x 2000 pixels.

The photographic files were subjected to grayscale analysis using ImageJ (www.

rsb.info.nih.gov/ij/) public domain software covering approximately 760,000 pixels centered over the area of interest to eliminate edge effects. White paint that penetrated through the backing film exhibits a high grayscale (lighter) value than the black background, and hence can be

quantitatively determined by grayscale analysis.

Interpretation of the grayscale image analysis is as follows. The grayscale distribution is calculated over the analysis area as a histogram count vs. gray value. The mean peak grayscale value calculated from this histogram is a measure of 'blackness.' The blacker the panel (that is, the lower the grayscale mean value), the lower the amount of white paint bleeding through.

Additionally, because the grayscale values range from 0 (blackest) to 255 (whitest), the high value 'tail' from grayscale values of 100 to 255 was calculated as a summation. The lower this value, the less white paint bleed through and the blacker the panel. Ideally for use in a tape masking situation, desirable attributes include adequate rim formation via thermally- induced elastic recovery to permit both tape roll unwind as well as facile hand tear in multiple directions while simultaneously reducing or eliminating the potential for paint bleed through through the central openings. Thus, comparing the image analysis data with both film tear and unwind data can indicate preferred embodiments. Results are shown in Table 10.

Table 10: Paint Penetration Resistance Test

The data in Table 10 indicate that lower flame impingement speeds, which create larger central openings, also allow more paint to penetrate as evidenced by the higher grayscale mean value. At higher speeds, as for example F- 1 1, the extent of paint penetration is much reduced. Unexpectedly, adhesive coated construction E- 14 also prevents paint penetration. It is believed that the adhesive coating layer acts to prevent paint from penetrating through the construction.

It was observed that the flame impingement process unexpectedly provides excellent paint anchorage as well as adhesive release, that is, tape unwind. Since adhesive release or tape unwind is usually provided by a release coating, which often results in poor paint anchorage, the data suggests this process yields a superior tape backing having a desirable combination of adhesive release and paint anchorage, without the need for an additional coating operation, thereby saving materials cost and process time and cost as well.

Table 1 1 describes several illustrative embodiments with tackified rubber pressure and the properties thereof.

Table 1 1 : Tackified Rubber PSA Coated Ta e Exam les

Notes: All samples except # 2C coated with a drop die, example 2C was coated with a contact die

It has been unexpectedly found that rolls of tape made with tackified rubber PSA, applied with a slotted drop die, can be produced without the use of a release coating layer when using suitably principal films of the invention as backing members. Tackified rubber PSAs are preferred for strong adhesion and holding power in box and carton sealing applications, but typically suffer from unacceptably high unwind forces (> 40 oz/in width) without using a release layer. It is more surprising that such constructions, produced using a flame impingement process that exposes the 'unwind' surface to flame exposure, still exhibit good unwind properties yet the adhesive retains very good tack and adhesion properties.

It is believed that the rims formed via thermally-induced elastic recovery during the flame impingement process not only promote the lower unwind force, they also serve to provide tear initiation points which allow the ability to hand tear tapes made using such films as backing members - without the need to score, serrate or otherwise roughly slit the edges. Examples, made with certain degrees of flame impingement coupled with certain coating conditions and formulations, produced novel tapes that both unwind and have practical tack values that seal boxes and mend a variety of items. Moreover, these example tapes tear straight in both the downweb and cross directions and do not require a dispenser.

Most surprisingly, the example tapes show that the combination of usable unwind and acceptable tack was maintained even after a two week aging process at elevated temperature (i.e., 120°F). In typical embodiments, usable and unacceptable combination to be unwind is less than about 15 oz/in and rolling wheel less than about 100 mm. In some cases, the tack was even improved, as exhibited by lower rolling wheel values on aged rolls. This, plus the aforementioned conformability, appears to promote adhesion to typical cardboard boxes. Further, the modification zones allow securely sealed boxes to be opened as desired without the need for cutting devices. Blunt items facilitate downweb tear and simple hand strength is sufficient to cleanly open box flaps. The combination of all the features, including a low cost processing method without drying ovens, appears to be unique and novel.

As the data demonstrates we have discovered a novel film-backed construction for potentially very low cost tape that still provides desirable combinations of attributes. The novel tape backing comprises a low cost biaxially oriented polypropylene (BOPP) film which may be either tenter stretched or may comprise blown film, and may in addition comprise more than one film layer.

Unexpectedly there exists a process condition window which yields a film having improved hand tearability in both directions, good mechanical unwind when formed into an adhesive coated roll of tape, excellent paint anchorage and little or no bleed-through of paint or other liquids. For greater extents of modification, the film is more difficult to tear and exhibits poor paint penetration resistance. For lesser extents of flame impingement the film is too difficult to tear by hand and provides too little surface roughness to allow easy mechanical separation of adjacent wound adhesive coated layers. Also unexpectedly, modification as provided herein also provides for improved conformance of an adhesive coated tape to irregular or fibrous substrate surfaces such as boxes and cartons. Tapes made with such flame impinged backing member do not behave like flat film backed tapes but more like creped paper tapes, yet the formation of modification zones in oriented films as described herein enables the formation of tapes exhibiting improved tensile strength while being hand tearable.

The complete disclosure of all patents, patent documents, and publications cited herein are incorporated by reference. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for variations obvious to one skilled in the art will be included within the invention defined by the claims.