Stress-whitening embossable film

Abstract: An embossable sheet, having at least one stress-whitening layer comprising a blend of: a) at least one heat-stable polymer selected from the group consisting of polypropylene and a polymethyl alkene, said alkene having from 3 to 7 carbon atoms, b) at least one other polymeric material immiscible therewith, and c) an effective amount of an antioxidant, said sheet exhibiting stress-whitening which is stable at 136°C for at least 7 days.

Description: Background of the Invention Field of the Invention The invention relates to embossable films which stress whiten or craze when pressure is applied thereto. The films are especially useful for wire identification. Description of the Related Art A wide variety of materials and methods have been used to produce identification means, e.g., tags, labels and the like, for a range of applications. One type of identification device known in the art involves film or sheet material, usually in tape form, which may be imprinted using an embossing device. One embodiment is an embossable label material which changes color during embossing. This results in improved contrast of the image symbols, which are usually white, compared to the background color. Formation of this white color by embossing is typically referred to as stress-whitening. Embossed labels of this type are disclosed in U.S. Patent Nos. 2,925,625; 2,996,822; 3,036,945; 3,650,059; 3,887,734 and 3,542,630. Material disclosed in these patents, when provided in tape form, are useful for producing labels using an embossing labeler. Labels obtained by prior art methods exhibited good contrast between image symbols and label background. The majority of these plastic labels require polyvinyl chloride or copolymers of polyvinyl chloride. Polypropylene or polymethylmethacrylate may be incorporated therein. All of these compositions have one distinct drawback. If the label is subjected to sufficient heat, the plastic will anneal, and the stresses caused by embossing will be released. The image thus disappears and identification is lost. It has now been discovered that compositions of the present invention, comprising blended polymer sheets or tapes, overcome this problem and exhibit image retention at temperatures significantly higher than prior art compositions. Summary of the Invention The invention provides a sheet or tape material which may be used for making signs or identification labels which possesses the property of stress-whitening. Identification marks or sign legends are produced by the exertion of pressure by a suitable embossing tool or labeler. The functional material may be provided in single sheet form or it may be a multilayer structure. Specifically, the invention provides an embossable sheet, having at least one stress-whitening layer comprising a blend of: a) at least one heat-stable polymer selected from the group consisting of polypropylene and a polymethylalkene, said alkene having from 4 to 7 carbon atoms, b) at least one other polymeric material immiscible therewith, selected from the group consisting of acrylonitrile-butadiene-styrene copolymers, polymethylmethacrylate, polystyrene, polycarbonate, and styrene-acrylonitrile, and c) an effective amount of an antioxidant, said sheet exhibiting stress-whitening which is stable at 136°C for at least 7 days. Embossable sheets of the invention may comprise a single layer or may be multilayer sheets comprised of 2 or more layers, each of which may contain blends of olefins, ABS, and ionomers. The sheet exhibits stress whitening upon the application of pressure, which is stable to 136°C for at least 7 days, preferably to about 150°C for at least 7 days. The additional layers may be included for purposes such as providing color to the sheet or tape, adding adhesive for attachment of the sign or label to other surfaces or substrates or protecting the embossed surface. Multilayer embossable sheet according to the invention comprises at least one layer containing a blend as described herein above and at least one other layer. Preferably, the other layer is a pigmented layer over which is placed a layer as described herein above containing the blend as described herein above. Preferably, the embossable sheet comprises a transparent top layer. According to the invention the embossable tape is capable of being applied by an embossing tool, comprising an embossable sheet containing a stress-whitening layer as disclosed herein above having a layer over adhesive affixed thereto. A preferred tape according to the invention shows an embossable sheet comprising a clear layer of said stress-whitening layer, and a colored layer under said stress-whitening layer. Preferably, the stress-whitening layer comprises a polymer blend comprising polypropylene and acrylonitrile-butadiene styrene. Preferred embossable sheets according to the invention comprise at least one stress-whitening layer comprising a major proportion of the heat-stable polymer and a minor proportion of an immiscible polymeric material selected from acrylonitrile-butadiene styrene (ABS) copolymers, polycarbonates, polymethylmethacrylates, polystyrenes, and styrene-acrylonitrile copolymers. According to the invention it is preferred that the heat-stable polymer is polypropylene and wherein said blend comprises acrylonitrile-butadiene styrene. In one preferred embodiment, the embossable sheets comprise from 50% to 95% polypropylene, and correspondingly, from 50 to 5% of an acrylonitrile-butadiene-styrene copolymer, wherein said sheets exhibit stress whitening upon the application of pressure, said whitening being stable to 150°C for at least 7 days. In another preferred embodiment the embossable sheets comprise from 50% to 95% polymethyl pentene (PMP), and correspondingly, from 50% to 5% of an acrylonitrile-butadiene-styrene copolymer wherein said sheets exhibit stress whitening upon the application of pressure, said whitening being stable to 150°C for at least 7 days. When the sheet is prepared and used according the invention, an embossed image is formed with white embossed symbols against a transparent, neutral, opaque or colored background. The images formed by embossing are unusually stable, particularly when exposed to elevated temperatures. Thus, articles of the invention remain unchanged at temperatures which destroy images produced with previously disclosed stress-whitening sheets or tape. Detailed Description of the Invention Articles of the present invention may be provided in sheet or tape form. These materials are capable, under suitable circumstances, of forming clearly visible images wherein the image symbols are relatively sharply defined against a selected background. The background may be clear, colorless, tinted or opaque with color provided by the addition of suitable pigments. The background selection affects the acuity of the image which is usually white in color. The image is formed during the application of pressure to the sheet or tape products. A suitable means of applying pressure is the use of a means of embossing such as a device used to make embossed labels. The sheet or tape material is subjected to stresses during the embossing process which causes the sheet to deform. At the points of greatest deformation crazes or voids form in the material. This change modifies the passage of light through the sheet by scattering light from the sheet. The result of light scattering from these crazes or voids is the formation of white symbols which become visible against the background of the original color of the unstressed sheet. This type of color formation is generally referred to as stress whitening. Sheet or tape products suitable for the present invention have a thickness in the range of from 25 micrometers (1 mil) to 1 millimeter (40 mils), with from 150 micrometers to 300 micrometers (7-12 mils) being preferred. The same materials may be used in the production of both sheet and tape formats. Suitable materials for sheet formation are usually derived from polymeric compositions which are described as rigid or semi-rigid. Rigid or semi-rigid materials are characterized by certain physical properties. They normally exhibit tensile values in the region of 264 kg/cm 2 (3,750 psi) to 369 kg/cm 2 (5,250 psi). Elongation values will typically range from 250% to 350%. Stress-whitening characteristics are provided in both single and multilayer sheets of the invention. It is possible, for instance, to apply embossing pressure to single layer structures and observe whitening and image formation in the stressed areas. These images tend to display good contrast between image and background areas. However, image edges may be fuzzy and lacking in crisp definition. Improvements in image appearance are possible using multilayer structures and processing techniques. Two layer and three layer structures have been studied; image improvement is most noticeable with three layer sheets. Whether single or multilayer sheets are provided, the function of stress-whitening occurs within a single layer of material. This layer comprises a blend of immiscible polymers which separate into domains. The size of the domains influences the appearance of the final sheet. Appearance of this single layer after embossing varies from somewhat transparent to translucent. The stress-whitening layer comprises a polymer blend. A major proportion of the blend is derived from a heat-stable polymer selected from polypropylene and a polymethylalkene wherein the alkene has from 4 to 7 carbons in the alkyl chain. These polymers exhibit some tendency to stress-whiten alone, this property is significantly improved by blending polymers such as acrylonitrile-butadiene-styrene copolymers, polymethylmethacrylate, polystyrene, polycarbonate, and styrene-acrylonitrile with the heat-stable polymers. However, the ratios in the blend must be carefully controlled. Contrast between image and background is reduced as the concentration of the second polymer is increased; it is preferable that the majority of the polymer blend comprise the heat-stable polymer. Preferred embodiments of the invention contain from 50% to 90% of a heat-stable polymer selected from the group consisting of polypropylene and polymethylpentene, correspondingly from 45% to 5% of acrylonitrile-butadiene styrene, polymethylmethacrylate, polystyrene, polycarbonate, or styrene-acrylonitrile, and from 0.05% to 2% of an antioxidant. In addition to the blend of two polymers, it is preferred to add an antiaging agent to the stress-whitening layer in order to further improve the aging characteristics of the polymer blend. Useful antiaging agents include UV stabilizers, heat stabilizers and antioxidants. These agents reduce the tendency for the sheet to discolor and become brittle with age and/or heat. Useful materials include hindered amines, nickel complexes, benzophenones, and benzotriazolers, including the antioxidants available under the trade name Irganox™, from Ciba Geigy. The antiaging agent may be present in amounts up to 5%, preferably from 0.5% to 2%. Single layer sheets, comprising blended polymers, of the type described above, may be further enhanced by the addition of color. It is important to maintain maximum contrast between the white image and the background color. For this reason the enhancing color is usually in the form of a colorant which is soluble in the polymer blend. The embossable sheet then becomes either translucent or opaque in appearance. It is also possible to add pigmented colorants. This is, however, less desirable since the pigments tend to interfere with the image contrast. Other optional ingredients may also be present in the stress-whitening layer including elastomers, lubricants and antistatic polymers. A preferred embodiment exhibiting improved image contrast is obtained by placing an intense pigmented layer behind the stress-whitening layer. This yields a bi-layer structure. In this embodiment, the image forming, stress-whitening layer is attached to a backing layer which comprises a pigmented polymer, typically such polymer is also blended with a polyolefin to improve cohesion of the layers. This pigmented layer preferably contains a substantial proportion of polypropylene to which is added a precompounded colored pigment concentrate. Other polyolefins may also be used in the pigmented layer; very low density polyethylene (VLDPE) may be added to the pigment layer in proportions ranging from 0 to 60 weight percent, preferably up to 40%; however, layers with no VLDPE are most preferred. Other ingredients may also be present in the colored layer. A small amount of Surlyn™ ionomer may be used as a nucleating agent; antioxidant may also be added to this layer. When present, Surlyn™ is added in the range of from 0 to 10%, preferably from 3% to 5%. Using a colored backing sheet of suitable color strength provides a sharper contrast between the white image and the background than that seen in a single layer embodiment. There is also some improvement in image definition. The preferred levels of pigmentation for optimum image appearance are from 10% to 100%. Further improvements in image contrast are possible by placing a transparent layer or "clear coat" over the stress-whitening layer. This three layer embodiment contains the imaging, stress-whitening layer sandwiched between the transparent layer and a pigmented underlayer. The transparent top layer may comprise any transparent film-forming polymer. Preferred embodiments comprise a very low density polyethylene (VLDPE)/polypropylene blend, having a majority of polypropylene. VLDPE materials are selected from such as ethylene α-olefin copolymers containing from 5 to 15 mole percent of an α-olefin, preferably a butene, hexene, or octene. Molecular weights of these materials range from 135,000 to 266,000 with polydispersities ranging from 3.72 to 5.98. Small amounts of antiaging agents, such as UV stabilizers and antioxidants may also be added to the top layer. When used, the amounts range up to 2%, preferably 0.5%. As well as improving the appearance of imaged sheets of the invention, the multilayer sheets are less susceptible to premature stress-whitening than single layer sheets. Single layer sheets must be carefully handled as they will readily whiten under the relatively low forces encountered when the sheet is flexed or bent. This problem is substantially reduced with the two layer structure and is completely avoided with three layer structures. Placing the stress-whitening layer in the center (neutral) plane of a three layer sheet structure minimizes accidental stress-whitening of the film during processing and casual handling. A higher percentage of heat-stable polymers may be used in the polymer blend of the stress-whitening layer without fear of significant accidental whitening. The use of this higher level of heat-stable polymer yields an embossing sheet with improved contrast. Stress-whitening sheets, single and multilayer, of the invention are made by mixing the heat-stable polymer and the other ingredients together and coating by known techniques such as extrusion or calendaring. A number of stress-whitening compositions are known in the art. These compositions provide acceptable contrast between image and background and have proved to be satisfactory for many applications such as sign production and identification labels. However, products which have been disclosed previously suffer from a significant disadvantage in heat stability. If such a sign or label is subjected to elevated temperatures, the image disappears. This occurs when the polymer, usually vinyl chloride or a copolymer of vinyl chloride, is raised to a temperature slightly above the annealing point. Compositions of the present invention have been shown to survive temperatures which destroy images of earlier embossable image forming products. For instance the embossed white image formed with a commercial tape product available from ROTEX™ was destroyed within 15 seconds when exposed to a temperature of 136°C. A similar product using compositions of the present invention survived the same temperature substantially unchanged for the duration of a seven day aging experiment. The samples also survived for seven days with only minor changes at 150°C. Sheets of the invention are useful as signs, labels, packaging, decoration and identification. The instant sheets are particularly useful in such as the electrical industry where they can be used as wire identification even in areas where the wires are exposed to prolonged periods of elevated temperatures. In a preferred embodiment for this use, the embossed sheet is provided with prepunched holes preferably horseshoe shaped, oval, round, or teardrop shaped, to provide individual tags for surrounding a continuous, elongate object such as a wire or pipe. Sheets of the invention are used with commercially available embossing machines such as the Dymo Mite Tapewriter™, available from Dymo Industries, Inc. Test Methods Initial White Contrast Evaluation The film run number was embossed on a 9,5mm (3/8") wide strip of film with a Scotch™ EA-450 label maker, available from Minnesota Mining and Manufacturing Company, (3M), for identification and evaluation purposes. A whiteness contrast scale from 0-4 was chosen for consistency with the current rating methods in the art. A value of 4 is given to the highest white contrast and is equivalent to PVC-based Scotch™ #760 label tape, also available from 3M. A classification of 0 means that the sheet has no white contrast. The contrast (WC) measurement is further described in United States patents US 4,082,711 and US 4,463,119. Aging/Image Stability Test For these studies, exposure to a temperature of 136°C for 7 days was chosen to qualify films for a desired 105°C rating. The film run number and the word "aged" were embossed on a 0.95 cm wide strip of each film under study, with a Scotch™ EA-450 brand label maker. Control samples, embossed with the run number and the letters "BBB", were kept at room temperature as an image and film stability reference. After exposure of the embossed film for 168 hours at 136°C, the aged samples were removed, visually inspected and compared to the control sample films for such characteristics as yellowing, white contrast retention and embrittlement. Delamination Method The embossed films were observed for delamination before and after embossing as well as before and after aging. Delamination of a film is noted if a layer peels away from the base film without assistance. Examples Example 1 A Killion 1.25 inch (31mm) single screw extruder with an L/D ratio of 24/1 was used to compound a stress-whitening polymer blend composition using the following temperature profile: zone 1, 176°C; zone 2, 193°C; zone 3, 226°C; end cap, 226°C, and neck tube, 220°C. The stress-whitening polymer blend contained 40% acrylonitrile butadiene styrene (ABS) terpolymer, "CYCOLAC DFA-1000R", available from General Electric, 59% polypropylene, "PP1024", available from Exxon, and 1% anti-oxidant, Irganox™ 1076, available from Ciba-Geigy. Using a second 1.25 inch (31mm) Brabender single screw extruder, a colored polymer blend composition was compounded using the following temperature profile: zone 1, 164°C; zone 2, 193°C; zone 3, 216°C; zone 4, 221°C; end cap, 221°C, and neck tube, 221°C. The colored polymer blend contained 89% polypropylene (PP1024), 10% carbon black concentrate, CBE 102P, available from Charles B. Edwards and Company, and 1% anti-oxidant, (Irganox™ 1076). The extrudate from both extruders was fed into a 10 inch (25,4 cm) EDI (Extrusion Dies Inc.) multilayer extrusion die and processed using the following temperature profile: Die Temp, 221°C; Feed block, 221°C; Cast roll Temp, 32°C. The line speed was 4.2 meters per minute. The EDI die used was designed to produce a single film 1 mil (25 micrometers) to 40 mils (1 mm) thick. A three layer feedblock in combination with the die allows for the multi layer film extrusion. The upper layer of the film was the stress-whitening polymer blend. Disposed below this layer was the carbon-black filled polymer. The carbon black in this layer provided good contrast between an embossed image, which appeared white, and the general background of the film. After extrusion, the film was cooled so that it could be wound into a non-blocking jumbo roll. This roll was then converted into sheet or tape form. Sheets of the extruded bi-layer film were tested for image contrast (white contrast ranges from 0 for poor to 4 which represents maximum contrast) as described above. The product was also tested for delamination and image stability, and the results are reported in Table 1. Comparative Example C2 The example was made according to example 1 except the stress-whitening polymer blend contained no polypropylene. It contained 99% ABS and anti-oxidant, (1% Irganox™ 1076). The product also tested for delamination and image stability, and the results are reported in Table 1. Comparative Example 3 The example was made according to example 1 except the colored polymer blend contained 29% polypropylene (PP1024), 60% very low density polyethylene, "Flexomer" DFDA-1138 available from Union Carbide, 10% carbon black concentrate (CBE 102P) and 1% anti-oxidant, (Irganox™ 1076). Test results are shown in Table 1. Example 4 The example was made according to example 3 except the stress-whitening blend contained 40% ABS (CYCOLAC DFA-1000R), 59% polypropylene (PP1024) and 1% anti-oxidant, (Irganox™ 1076). Test results are shown in Table 1. Example 5 The example was made according to example 4 except the stress-whitening polymer blend contained 40% PMMA VM100, "VM100" available from Rohm-Haas, 59% polypropylene (PP1024) and 1% anti-oxidant, (Irganox™ 1076). Test results are shown in Table 1. Comparative Example C6 The example was made according to example 5 except the stress-whitening polymer contained no polypropylene. The polymer contained 99% PMMA (VM100), and 1% anti-oxidant, (Irganox™ 1076). Test results are shown in Table 1. Comparative Example C7 The example was made according to example 5 except the stress-whitening polymer was not a blend and the backing contained no flexomer. It contained 89% polypropylene (PP1024), 10% carbon black concentrate (CBE 102P), and 1% anti-oxidant (Irganox 1076). Test results are shown in Table 1. Example 8 The example was made according to example 7 except the stress-whitening polymer blend contained 40% PMMA VM100 (Polymethyl Methacrylate # VM100 by Rohm-Haas), 59% polypropylene (PP1024), and 1% anti-oxidant, (Irganox 1076). Test results are shown in Table 1. Bilayer Examples EX No. WC Layer B (Stress-whitening) Layer C (Colored Layer) Delam. of layers Image Stability 1 4.0 B = 40% Cycolac ABS + 59% PP 1024 + 1% Irganox 1076 no slight decrease C = 89% PP 1024 + 10% black + 1% Irganox 1076 C2 4.0 B = 99% Cycolac ABS + 1% Irganox 1076 yes Shrinks yellows C = 89% PP 1024 + 10% black + 1% Irganox 1076 C3 4.0 B = 99% Cycolac ABS + 1% Irganox 1076 yes Shrinks yellows C = 29% PP 1024 + 60% DFDA-1138 (flexomer)+ 10% black + 1% Irganox 1076 4 4.0 B = 40% Cycolac ABS + 59% PP 1024 + 1% Irganox 1076 no slight decrease C = 29% PP 1024 + 60% DFDA-1138 (flexomer)+ 10% black + 1% Irganox 1076 5 3.5 B = 40% PMMA VM100+ 59% PP 1024 + 1% Irganox 1076 no slight decrease C = 29% PP 1024+ 60% DFDA-1138 (flexomer)+ 10% black + 1% Irganox 1076 C6 0 B = 99% PMMA VM100+ 1% Irganox 1076 partial none C = 29% PP 1024+ 60% DFDA-1138 (flexomer)+ 10% black + 1% Irganox 1076 C7 0 B = 99% PMMA VM100+ 1% Irganox 1076 yes none C = 89% PP 1024+ 10% black + 1% Irganox 1076 8 4.0 B = 40% PMMA VM100+ 59% PP 1024 + 1% Irganox 1076 partial decrease WC C = 89% PP 1024+ 10% black + 1% Irganox 1076 Example 9 A 1.25 inch Brabender single screw extruder was used to compound a stress-whitening polymer blend composition containing 20% "Polystyrene 666" available from Dow and 80% polypropylene "PP3014", available from Exxon. After extrusion, the film was cooled so that it may be wound into a non-blocking jumbo roll. This roll was then converted into sheet or tape form. Sheets of the extruded single layer film were tested for image contrast delamination and image stability as noted in example 1, and the results are shown in Table 2. Example 10 This example was conducted under the same processing conditions as example 9. The single layer stress-whitening blend contained 80% polypropylene (PP3014) and 20% ABS. Example 11 This example was conducted as described in Example 9, except that the single layer stress-whitening blend contained 80% polypropylene (PP3014), 10% ABS (CYCOLAC DFA 1000-R), and 10% polystyrene 666 (PS 666). Example 12 This example was conducted according to Example 9. The single layer stress-whitening blend contained 80% polypropylene (PP3014), and 20% ABS (CYCOLAC DFA 1000-R), and one part anti-oxidant (Irganox 1076). Comparative Example C13 This example was conducted according to example 9. The single layer non stress-whitening blend contained 80% ethylene (Linear Low Density Polyethylene, LLDPE # 6806 available from Dow) and 20% polystyrene (PS 666). Comparative Example C14 The sample was made according to example 13. The single layer non stress-whitening blend contained 80% ethylene (LLDPE 6806) and 20% ABS (CYCOLAC DFA 1000-R). Comparative Example C15 The sample was made according to example 9. The single layer stress-whitening blend contained 80% ethylene, (low density polyethylene, LDPE 1550P available from Eastman Kodak) and 20% polystyrene (PS 666). Comparative Example C16 The sample was made according to example 15. The single layer stress-whitening blend contained 80% ethylene (LDPE 1550P) and 20% ABS (CYCOLAC DFA 1000-R). Comparative Example C17 The sample was made according to Example 15. The single layer stress-whitening blend contained 80% ethylene (LDPE 1550P) and 10% ABS (CYCOLAC DFA 1000-R), and 10% polystyrene (PS 666). Comparative Example C18 The sample was made according to example 15. The single layer stress-whitening blend contained 80% ethylene (Low Density Polyethylene, LDPE 4012, available from Dow) and 20% ABS (CYCOLAC DFA 1000-R). Comparative Example C19 The sample was made according to example 15. The single layer stress-whitening blend contained 80% ethylene (High Density Polyethylene, HDPE 3150B, available from Amoco) and 20% ABS (CYCOLAC DFA 1000-R). Example 20 The sample was made according to example 9. The single layer stress-whitening blend contained 59% polypropylene (PP3014), 20% ABS (CYCOLAC DFA 1000-R), 10% ethylene vinyl acetate compound (Elvax 350 available from Dupont), 10% ethylene (HDPE 3150B), and 1% antioxidant (Irganox 1076). Example 21 The example was made according to example 20 except that the ethylene component was LDPE 1550P. Example 22 The sample was made according to example 20. The single layer stress-whitening colored blend contained 74% polypropylene (PP3014), 20% ABS (CYCOLAC DFA 1000-R), 1 % anti-oxidant (Irganox 1076), and 5% pink concentrate (specially compounded in polystyrene from Charles B. Edwards and Co.). Example 23 The sample was made according to example 9 except that the Head PSI was 9645 kPa (1400 PSI) and the torque was 95N/m (70 ft/pd). The blend composition was the same as example 22 except 69 % polypropylene (PP3014) and 10% pink concentrate. Example 24 The example was made according to example 23 except that the blend composition contained 64% polypropylene (PP3014) and 15% pink concentrate. Example 25 The example was made according to example 23 except that the blend composition contained 74 % polypropylene (PP3014) and 5% blue concentrate (CBE 22452-S, blue compounded in polystyrene available from C.B. Edwards and Co.). Example 26 The example was made according to example 25 except that the blend composition contained 69% polypropylene (PP3014) and 10% blue concentrate (CBE 22452-S). Example 27 The example was made according to example 26 except that the blend composition contained 2.5% Blue concentrate and 2.5% pink concentrate. Example 28 The example was made according to example 27 except that the blend composition contained 64% polypropylene (PP3014), 5% blue concentrate (CBE 22452-S) and 5% pink concentrate. Example 29 The example was made according to example 28 except that the blend composition contained 74% polypropylene (PP3014) and 5% black concentrate (CBE 102 P). Example 30 A 34 mm co-rotating intermeshing Leistritz twin screw extruder with an L/D ratio of 42:1 was used to compound a polymer blend composition. The single layer stress-whitening colored blend contained 79% polypropylene (PP1024), 5% ABS (CYCOLAC DFA 1000-R), 15% polystyrene (PS666), and 1% anti-oxidant (Irganox 1076). Example 31 The example was made according to example 30 except that the stress-whitening colored blend contained 10% ABS (CYCOLAC DFA 1000-R) and 10% polystyrene (PS666). Example 32 The example was made according to example 30 except that the stress-whitening colored blend contained 74% polypropylene (PP1024), 15% ABS (CYCOLAC DFA 1000-R), and 5% polystyrene (PS666). Example 33 The example was made according to example 30 except that the stress-whitening colored blend contained 77% polypropylene (PP1024), 5% ABS (CYCOLAC DFA 1000-R), 15% polystyrene (PS666) and 3% anti-oxidant (Irganox 1076). Example 34 The example was made according to example 30 except that the stress-whitening colored blend contained 74% polypropylene (PP1024), 20% ABS (CYCOLAC DFA 1000-R), 2.5% blue concentrate (CBE 22452-S), 2.5% pink concentrate, and 1% anti-oxidant, (Irganox 1076). Example C35 A Killion single screw extruder was used to compound a clear polymer blend composition for the top layer which contained 50% very low density polyethylene (Flexomer DFDA-1137, available from Union Carbide), and 50 % polypropylene (Polypropylene 3014 available as PP 3014 from Exxon). A second single screw extruder (1 inch screw with L/D ratio of 19:1) was used to compound a stress-whitening polymer blend composition which contained 20% ABS (CYCOLAC DFA 1000-R), 55% polypropylene (PP3014 ) and 25% polybutylene (PB0400 available from Shell Chemical). Using a third single screw extruder (Brabender 1 inch screw with L/D ratio of 30:1) a colored polymer blend composition was compounded which contained 89% polypropylene (PP3014), 10% carbon black concentrate (CBE 102P with a carbon black let down ratio of 1:100 available from Charles B. Edwards & Company) and 25% butylene (Polybutylene PB0400 available from Shell). The extrudate from all three extruders was fed into a multilayer coextrusion feedblock atop an EDI (Extrusion Dies Incorporated) extrusion die. This feedblock/die combination was designed to produce a multilayer film 25 µ (1 mil) to 1 millimeter (40 mils) thick. The top layer of the film was produced as a clear polymer blend to enhance clarity and reduce excessive stress-whitening. The stress-whitening layer was placed in the center on a neutral plane to protect it from handling problems. The bottom layer contained a colored polymer blend. The color in this layer provided good contrast between the embossed image, which appeared white, and the general background of the film. Disposed between the clear top coat and the colored layer was the stress-whitening layer. The same after-extrusion processing and evaluations apply as in example 1. Examples C35-C39 show that when a multilayer embossing tape is made without antioxidant, the image stability is adversely affected; yellowing is seen as well as loss of white contrast and brittleness. Example C36 The example was made according to example C35 except the stress-whitening center layer contained 20% ABS (CYCOLAC DFA 1000-R) and 80% polypropylene (PP3014). The colored polymer blend contained 20% ABS (CYCOLAC DFA 1000-R), 10% black concentrate (CBE 102P), and 70% polypropylene (PP3014). Example C37 The example was made according to example C36 except the top clear layer polymer blend contained 40% very low density polyethylene (Flexomer DFDA-1137), and 60% polypropylene (PP3014). Example C38 The example was made according to example C37 except the stress-whitening polymer blend contained 40% ABS (CYCOLAC DFA 1000-R) and 60% polypropylene (PP3014). Example C39 The example was made according to example C38 except the top clear layer polymer blend contained 20% very low density polyethylene (Flexomer DFDA-1137), and 80% polypropylene (PP3014). Example 40 The example was made according to example 35 except that the top clear layer was compounded in a single screw extruder with a 1 inch screw and L/D ratio of 19:1. The top layer contained 40% very low density polyethylene/(Flexomer DFDA-1138, available from Union Carbide), 58% polypropylene (PP 3014) and 2% anti-oxidant (Irganox 1076). A second single screw extruder (Brabender extruder, 1.25 inch screw with L/D ratio of 30:1) was used to compound a stress-whitening polymer blend composition which contained 20% acrylonitrile butadiene styrene (ABS) terpolymer e.g. (Lustran ABS available from Monsanto), 58% polypropylene (PP1024 ) and 2% anti-oxidant (Irganox 1076). A third single screw Killion extruder was used to extrude the third layer which contained 100% polypropylene (PP1024). The extrudate from all three extruders was fed into a multilayer coextrusion feedblock atop an extrusion die. This feedblock/die combination was designed to produce a multilayer film from 25 µ to 1 millimeter in thickness. Example 41 The example was made according to example 40 except that the bottom layer contained a colored polymer blend of 89% polypropylene (PP1024), 10% black concentrate (CBE 102 P) and 1% anti-oxidant (Irganox 1076). Example 42 The example was made according to example 41 except that the colored polymer blend contained 88% polypropylene (PP1024), 10% pink concentrate (specially compounded in polystyrene from Charles B. Edwards), and 2% anti-oxidant (Irganox 1076). Example 43 The example was made according to example 42 except that the colored polymer blend contained 68% polypropylene (PP1024), 30% blue concentrate (CBE 22452-S), and 2% anti-oxidant (Irganox 1076). Example 44 The example was made according to example 43 except that the colored polymer blend contained 88% polypropylene (PP1024), 10% black concentrate (CBE 102 P), and 2% anti-oxidant (Irganox 1076). Example 45 The example was made according to example 44 except that the clear top layer contained 40% very low density polyethylene (Flexomer DFDA-1138 available from Union Carbide), 59% polypropylene (PP 1024), and 1% anti-oxidant (Irganox 1076). The center stress-whitening layer contained 40% ABS (Lustran available from Monsanto) and 1% anti-oxidant (Irganox 1076). The bottom layer contained 99% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 46 The example was made according to example 45 except that the bottom layer contained a polymer blend of 59% polypropylene (PP1024), 40% very low density polyethylene (Flexomer DFDA-1138), and 1% anti-oxidant (Irganox 1076). Example 47 The example was made according to example 46 except that the bottom layer contained a polymer blend of 39% polypropylene (PP1024), 60% very low density polyethylene (Flexomer DFDA-1138), and 1% anti-oxidant (Irganox 1076). Example 48 The example was made according to example 47 except that the bottom layer colored polymer blend contained 29% polypropylene (PP1024), 60% very low density polyethylene (Flexomer DFDA-1138), 10% black concentrate (CBE 102P) and 1% anti-oxidant (Irganox 1076). Example 49 The example was made according to example 48 except that the stress-whitening polymer blend contained 40% ABS (Magnum 9010 available from Dow), 59% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 50 The example was made according to example 49 except that the stress-whitening polymer blend contained a different type of ABS, i.e., Magnum 941 available from Dow . Example 51 The example was made according to example 50 except the stress-whitening polymer blend contained a different type of ABS, i.e., Magnum 343 available from Dow. Example 52 The example was made according to example 51 except the stress-whitening polymer blend contained a different type of ABS, i.e., Cycolac DFA-1000R available from General Electric. Example 53 The example was made according to example 52 except that the stress-whitening polymer blend contained 40% polymethyl methacrylate (PMMA VM100 available from Rohm and Haas), 59% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 54 The example was made according to example 53 except that the stress-whitening polymer blend contained 99% polymethyl methacrylate (PMMA VM100 available from Rohm and Haas) and 1% anti-oxidant (Irganox 1076). Example 55 The example was made according to example 52 except that the stress-whitening polymer blend contained 40% styrene (polystyrene, PS 685 available from Dow), 59% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 56 The example was made according to example 55 except that the stress-whitening polymer blend contained 99% styrene (polystyrene, PS 685) and 1% anti-oxidant (Irganox 1076). Example 57 The example was made according to example 56. The stress-whitening polymer blend contained 40% polycarbonate (polycarbonate "Makrolon" 2600 available from Mobay), 59% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 58 The example was made according to example 57 except that the extruders were set at: top clear layer 10RPM, center stress-whitening layer, 35RPM and bottom colored polymer blend, 15RPM. The stress-whitening polymer blend contained 5% polycarbonate (polycarbonate "Makrolon" 2600 available from Mobay), 94% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 59 The example was made according to example 56 except that the stress-whitening polymer blend contained 40% styrene-acrylonitrile copolymer (SAN "Tyril" available from Dow), 59% polypropylene (PP1024) and 1% anti-oxidant (Irganox 1076). Example 60 The example was made according to example 59 except the stress-whitening polymer blend contained 99% styrene-acrylonitrile (SAN "Tyril" available from Dow) and 1% anti-oxidant (Irganox 1076). Example 61 The example was made according to example 53 except that the colored polymer blend contained 89% polypropylene (PP1024), 10% black concentrate (CBE 102P) and 1% anti-oxidant (Irganox 1076). Example 62 The example was made according to example 61 except that the stress-whitening polymer blend contained 99% polymethyl Methacrylate (PMMA VM100 available from Rohm and Haas) and 1% anti-oxidant (Irganox 1076). Example 63 The example was made according to example 62 except that the stress-whitening polymer blend contained 40% ABS (Cycolac DFA-1000R), 59% polypropylene (PP1024), and 1% anti-oxidant (Irganox 1076). The colored polymer blend contained 89% polypropylene (polypropylene, PP4092 available from Exxon), 10% black concentrate (CBE 102 P) and 1% anti-oxidant (Irganox 1076). Example 64 Examples 64 through 66 demonstrate a variety of pigments types and amounts in the backing layer of the multilayer embossed tape of the invention. Example 64 was made according to exam le 63 except that the clear top layer extruder head PSI was 1,378 x 10 8 Pa (2000 PSI) and the amps were set at 3 amps. The center stress-whitening layer extruder Head PSI was 1,306 x 10 8 Pa (1750 PSI) and the torque was 140 N/m (104 ft/pds). The bottom colored polymer blend extruder temperature profile was zone 1 at 160°C, zone 2 at 186°C, zone 3 at 221°C, head PSI at 1,378 x 10 8 Pa (2000 PSI), and the screw RPM at 25 RPM. The feedblock used was a 5 layer feedblock manufactured by Peter Cloeren and Co. Two vanes were pinched off to produce the three layer film. The colored polymer blend layer contained 89% polypropylene (polypropylene, PP1024 available from Exxon), 10% blue concentrate (blue concentrate compounded in polypropylene, CBE 22087 P, available from C.B. Edwards and Co.), and 1% anti-oxidant (Irganox 1076). Example 65 The example was made according to example 64 except that the colored polymer blend contains blue concentrate compounded in polystyrene (CBE 22452-S, available from C.B. Edwards and Co.. Example 66 The example was made according to example 65 except the center stress-whitening layer extruder Head PSI was 2120 and the torque was 173 N/m (128 ft/pds). The bottom colored polymer blend extruder temperature profile was set for zone 1 at 150°C, zone 2 at 177°C, head PSI at 27580 kPa (4000 PSI), and the screw RPM at 60 RPM. The top clear polymer blend contained 40% Ultra Low Density Polyethylene (Flexomer DFDA-1138 from Union Carbide), 59.5 % polypropylene (PP1024), and 0.5% anti-oxidant (Irganox 1076). The stress-whitening polymer blend contained 40% ABS (Cycolac DFA-1000R), 59.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). The colored polymer blend contained 89.5% polypropylene (polypropylene, PP1024 available from Exxon), 10% black (CBE 102 P) and 0.5% anti-oxidant (Irganox 1076). Example 67 The example was made according to example 66 except that the colored polymer blend contained a polypropylene homopolymer compounded with 89.5% polypropylene/polyethylene co-polymer (PP 7C50 available from Shell Chemical Co.). Example 68 The example was made according to example 67 except that the clear top layer polymer blend contained 59.5% polypropylene (PP1024), 30% very low density polyethylene (Flexomer DFDA-1138), 10% Ionomer (Surlyn 1702 available from Dupont) and 0.5% anti-oxidant (Irganox 1076). Example 69 Examples 69-72 vary the type of flexomer and the type of ABS resin used. As can be seen, flexomer DFDA-9063 has a negative effect on yellowing of the white contrast, and so is not preferred. Example 69 was made according to example 61 except that the top clear polymer blend contained 20% very low density polyethylene (Flexomer DFDA-9063 from Union Carbide), 79.5% polypropylene (PP1024), and 0.5% anti-oxidant (Irganox 1076). The stress-whitening polymer blend contained 40% ABS (Cycolac GSE available from General Electric), 59.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). The colored polymer blend comprised 86.5% polypropylene (polypropylene, PP1024 available from Exxon), 10% black (CBE 102 P), 3% Ionomer (Surlyn 1702 available from Dupont), and 0.5% anti-oxidant (Irganox 1076). Example 70 The example was made according to example 69 except that the stress-whitening center layer contained ABS (Cycolac DFA-1000R available from General Electric). Example 71 The example was made according to example 70 except that the top clear polymer blend comprised 20% very low density polyethylene (Flexomer DFDA-1138 from Union Carbide), 79.5% polypropylene (PP1024), and 0.5% anti-oxidant (Irganox 1076). Example 72 The example was made according to example 71 except that the stress-whitening center layer contained ABS (Cycolac GSE, available from General Electric). Example 73 Examples 73-80 demonstrate the ability to increase the nonpolypropylene polymer content in the stress-whitening layer of the embossing tape of the invention. Example 73 was made according to example 72 except that the stress-whitening center layer comprised 100% polypropylene (polypropylene, PP1024). Example 74 The example was made according to example 73 except that the stress-whitening polymer blend contained 5% ABS (Cycolac DFA-1000R, available from General Electric), 94.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 75 The example was made according to example 74 except the stress-whitening polymer blend contained 10% ABS (Cycolac DFA-1000R, available from General Electric), 89.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 76 The example was made according to example 75 except the stress-whitening polymer blend contained 15% ABS (Cycolac DFA-1000R), 84.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 77 The example was made according to example 76 except the stress-whitening polymer blend contained 20% ABS (Cycolac DFA-1000R), 79.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 78 The example was made according to example 77 except the stress-whitening polymer blend contained 25% ABS (Cycolac DFA-1000R), 74.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 79 The example was made according to example 78 except the stress-whitening polymer blend contained 30% ABS (Cycolac DFA-1000R), 69.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 80 The example was made according to example 79 except the stress-whitening polymer blend contained 35% ABS (Cycolac DFA-1000R), 64.5% polypropylene (PP1024) and 0.5% anti-oxidant (Irganox 1076). Example 81 The example was made according to example 79 except the cast roll was set at 10°C. The top clear polymer blend contained 10% very low density polyethylene (Flexomer DFDA-1138 from Union Carbide), 89.75% polypropylene (PP1024), and 0.25% anti-oxidant (Irganox 1076). The stress-whitening polymer blend contained 30% ABS (Cycolac DFA-1000R), 69.75% polypropylene (PP1024) and 0.25% anti-oxidant (Irganox 1076). The bottom colored polymer blend comprised 86.75% polypropylene (PP1024), 10% black (CBE 102 P), 3% Ionomer (Surlyn 1702 available from Dupont), and 0.25% anti-oxidant (Irganox 1076). Example 82 A single screw Killion extruder was used to compound a clear polymer blend composition for the top layer which contained 99.25% polypropylene (PP 1024), 0.25% nucleating agent/clarifying agent (MILLAD 3905 available from Milliken Chemical) and 0.5% anti-oxidant (Irganox 1076). A second single screw extruder (Berlyn 5,1 cm (2 inch) extruder with an L/D ratio of 32:1) was used to compound a stress-whitening polymer blend composition which contained 30% ABS (Cycolac DFA-1000R), 69.25% polypropylene (PP1024), 0.25% nucleating agent (MILLAD 3905), and 0.5% anti-oxidant (Irganox 1076). A 34 mm co-rotating intermeshing Leistritz twin screw extruder with an L/D ratio of 42:1 was used to compound a colored polymer blend composition comprising 89.25% polypropylene (PP1024), 10% carbon black (CBE 102P), 0.25% nucleating agent (MILLAD 3905), and 0.5% anti-oxidant (Irganox 1076). The extrudate from all three extruders was fed into a multilayer coextrusion feedblock atop an extrusion die as outlined in example 35. Example 83 The example was made according to example 82 except that the clear top polymer blend contained 20% ultra low density polyethylene (Flexomer DFDA-1138), 69.25% polypropylene (PP1024), 0.25% nucleating agent (MILLAD 3905), and 0.5% anti-oxidant (Irganox 1076). Example 84 The example was made according to example 35 except that a single screw 2,5 cm (1") screw with L/D ratio of 19:1) extruder was used to compound the clear polymer blend composition. The top layer contained 20% very low density polyethylene (Flexomer DFDA-1138), and 79.5% polypropylene (PP1024 from Exxon) and 0.5% anti-oxidant (Irganox 1076). A second single screw Killion extruder was used to compound a stress-whitening polymer blend composition which comprised 30% ABS (Cycolac DFA-1000R), 69.5% polypropylene (PP1024), and 0.5% anti-oxidant (Irganox 1076) and was coated with a third single screw Killion extruder. The colored polymer blend contained 86.5% polypropylene (PP1024), 10% carbon black (CBE 102P), 3% Ionomer (Surlyn 1702), and 0.5% anti-oxidant (Irganox 1076). Example 85 This example was made according to example 84 except that the top layer contained 17% very low density polyethylene (Flexomer DFDA-1138), and 79.5% polypropylene (PP1024 from Exxon), 3% Ionomer (Surlyn™ 1702), and 0.5% anti-oxidant (Irganox™ 1076). Example 86 A Killion 2.54 cm single screw extruder with an L/D ratio of 42/1 was used to compound a stress-whitening polymer blend composition comprising 69.5 % polymethylpentene (TPX MX007, available from Mitsui Chemical), 30% acrylonitrile-butadiene-styrene terpolymer and 0.5% antioxidant (Irganox™ 1076). A second Killion 2.54 cm single screw extruder with an L/D ratio of 42/1 was used to compound a second polymer blend contained 69.5% polymethylpentene (TPX MX007, available from Mitsui Chemical), 30% acrylonitrile-butadiene-styrene terpolymer and 0.5% antioxidant (Irganox™ 1076). The extrudate from both extruders was fed into a multilayer extrusion die and process for a three layer film extrusion. The outer layers, i.e., the top and bottom layers were composed of the second polymer blend. The stress-whitening layer was the center layer. Example C87 This Example was made according to example 86, except that the stress-whitening layer comprised 99.5% ABS, and 0.5% antioxidant (Irganox™ 1076).

Claims: An embossable sheet comprising at least one stress-whitening layer comprising a blend of: a) at least one heat-stable polymer selected from the group consisting of polypropylene and a polymethylalkene, said alkene having from 4 to 7 carbon atoms, b) at least one additional polymeric material immiscible therewith selected from the group consisting of acrylonitrile-butadiene-styrene copolymers, polymethylmethacrylate, polystyrene, polycarbonate, and styrene-acrylonitrile, and c) an effective amount of an antioxidant, said sheet exhibiting stress-whitening which is stable at 136°C for at least 7 days. An embossable sheet according to claim 1 wherein said heat-stable polymer is polypropylene, and wherein said blend comprises of polypropylene and of acrylonitrile-butadiene-styrene copolymer. A multilayer embossable sheet comprising at least one layer containing a blend according to claim 1 and at least one other layer. A multilayer embossable sheet according to claim 3 wherein said other layer is a pigmented layer over which is placed said layer containing said blend. An embossable sheet according to claim 3 further comprising a transparent top layer. An embossable tape capable of being applied by an embossing tool, comprising an embossable sheet containing a stress-whitening layer according to claim 1 having a layer of adhesive affixed thereto. An embossable tape according to claim 6 wherein said embossable sheet comprises a clear layer over said stress-whitening layer, and a colored layer under said stress-whitening layer. An embossable tape according to claim 7 wherein said stress-whitening layer comprises a polymer blend comprising of polypropylene and of acrylonitrile-butadiene styrene copolymer. A wire-identification label capable of being applied by an embossing tool, comprising a sheet according to claim 1, said sheet having at least one teardrop shaped or horseshoe shaped hole punched therein.

Inventors: KRUEGER DENNIS L, LOCKRIDGE ROCHELLE L, MARTIN PHILIP G, SCHLAEGER GARY W, KRUEGER, DENNIS L., LOCKRIDGE, ROCHELLE L., MARTIN, PHILIP G., SCHLAEGER, GARY W., KRUEGER, DENNIS L., MINNESOTA M,. AND MAN.COM., LOCKRIDGE, ROCHELLE L., MINNESOTA M,. AND MAN.COM., MARTIN, PHILIP G., MINNESOTA M,. AND MAN.COM., SCHLAEGER, GARY W., MINNESOTA M,. AND MAN.COM.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1993
Main classification: C08L23
IPC codes: B32B27, B44C1, C08L23, G09F3