Printable heat transfer material

Abstract: Described is a printable heat transfer material having cold release properties, which material includes a flexible first layer having first and second surfaces. The first layer typically will be a film or a cellulosic nonwoven web. A second layer overlays the first surface of the first layer and includes a thermoplastic polymer, such as a hard acrylic polymer or a poly(vinyl acetate). A third layer overlays the second layer and includes a thermoplastic polymer which melts in a range of from about 65°C to about 180°C. The first layer may be a cellulosic nonwoven web, such as a latex-impregnated paper. The thermoplastic polymer of which the second layer is composed may have a glass transition temperature of at least about 25°C. The second layer also may include an effective amount of a release-enhancing additive, such as a divalent metal ion salt of a fatty acid, a polyethylene glycol, or a mixture thereof. The third layer may include a film-forming binder, which binder may include a powdered thermoplastic polymer. For an ink jet printable heat transfer material, a fourth layer may overlay the third layer, which fourth layer includes a film-forming binder and a powdered thermoplastic polymer. If desired, a fifth layer may overlay the second layer, thereby being located between the second layer and the third layer. The fifth layer may include a film-forming binder which melts in a range of from about 65°C to about 180°C.

Description: The present invention relates to a heat transfer material, such as a heat transfer paper. In recent years, a significant industry has developed which involves the application of customer-selected designs, messages, illustrations, and the like (referred to collectively hereinafter as "customer-selected graphics") on articles of clothing, such as T-shirts, sweat shirts, and the like. These customer-selected graphics typically are commercially available products tailored for that specific end-use and are printed on a release or transfer paper. They are applied to the article of clothing by means of heat and pressure, after which the release or transfer paper is removed. Some effort has been directed to allowing customers the opportunity to prepare their own graphics for application to an article of clothing. The preparation of such graphics may involve the use of colored crayons made from a heat-transferable material. Such crayons have been made available in kit form, which also includes an unspecified heat transfer sheet having an outlined pattern thereon. In a variation of the kit, the transferable pattern is created from a manifold of a heat transfer sheet and a reverse or lift-type copy sheet having a pressure transferable coating of heat transferable material thereon. By generating the pattern or artwork on the obverse face of the transfer sheet with the pressure of a drafting instrument, a heat transferable mirror image pattern is created on the rear surface of the transfer sheet by pressure transfer from the copy sheet. The heat transferable mirror image then can be applied to a T-shirt or other article by heat transfer. The creation of personalized, creative designs or images on a fabric such as a T-shirt or the like through the use of a personal computer system has been described in document WO 90/00 473. The method involves electronically generating an image, electronically transferring the image to a printer, printing the image with the aid of the printer on an obverse surface of a transfer sheet which has a final or top coating consisting essentially of Singapore Dammar Resin, positioning the obverse face of the transfer sheet against the fabric, and applying energy to the rear of the transfer sheet to transfer the image to the fabric. The transfer sheet can be any commercially available transfer sheet, the heat-transferable coating of which has been coated with an overcoating of Singapore Dammar Resin. The use of abrasive particles in the Singapore Dammar Resin coating also has been described. The abrasive particles serve to enhance the receptivity of the transfer sheet to various inks and wax-based crayons. WO 91/06433 discloses a heat transfer sheet comprising a flexible support, a transferable thermoplastic layer receptive to printing and/or writing agents and capable of adhering to the materials making up the surface of the item and a release component incorporated in the flexible support or in the form of an intermediate layer placed between the support and transferable layer. WO 95/08419 discloses a heat activated applique with an upper thermoplastic elastomer layer bonded to a cloth substrate by a thermoplastic adhesive. Improved heat transfer papers having an enhanced receptivity for images made by wax-based crayons, thermal printer ribbons, and impact ribbon or dot-matrix printers have been disclosed. For example. a cellulosic base sheet has an image-receptive coating containing from 15 to 80 percent of a film-forming binder and from 85 to 20 percent by weight of a powdered polymer consisting of particles having diameters from 2 to 50 µm (micrometers). The binder typically is a latex. Alternatively, a cellulosic base sheet has an image-receptive coating which typically is formed by melt extrusion or by laminating a film to the base sheet. The surface of the coating or film then is roughened by, for example, passing the coated base sheet through an embossing roll. GB-A-2243332 discloses a method for printing an image on an image receiving member comprising the steps of transferring an image onto a transfer sheet comprising a hot-melting type adhesive layer to provide a print sheet and retransfering the ink image and the hot-melting type adhesive onto the image receiving member by heatedly pressing the transfer sheet to thereby provide a final print on the receiving member. Some effort also has been directed at generally improving the transfer of an image-bearing laminate to a substrate. For example, an improved release has been described, in which upon transfer the release splits from a carrier and forms a protective coating over the transferred image. The release is applied as a solution and contains a montan wax, a rosin ester or hydrocarbon resin, a solvent, and an ethylene-vinyl acetate copolymer having a low vinyl acetate content. Additional effort has been directed to improving the adhesion of the transferred laminate to porous, semi-porous, or non-porous materials, and the development of a conformable transfer layer which enables the melt transfer web to be used to transfer images to uneven surfaces. US-A-4322467 discloses a decalcomania comprising a backing layer a release layer deposited thereon and at least one layer formed of heat processable melted themoplastic ink deposited over said release layer, said thermoplastic ink being heat processed from a molten condition to at least a partially solidified condition prior to deposition on said release layer and exhibiting pressure sensitivity at a temperature below that where said ink becomes heat processable. Finally, it may be noted that there are a large number of references which relate to thermal transfer papers. Most of them relate to materials containing or otherwise involving a dye and/or a dye transfer layer, a technology which is quite different from that of the present invention. In spite of the improvements in heat transfer papers, they all require removal of the carrier or base sheet from the material to which an image has been transferred while the carrier or base sheet still is warm. This requirement causes unique problems when transfer is attempted with a hand-held iron because of both uneven heating which is characteristic of hand ironing and cooling of previously ironed portions of the transfer material. Consequently, there is an opportunity for an improved heat transfer paper which will permit removal of the carrier or base sheet after it has cooled, i.e., a printable heat transfer paper having cold release properties. There also is a need for such a paper which is ink jet printable. The present invention intends to overcome the problems discussed above. This object is solved by the printable heat transfer material according to independent claims 1 and 5. Further advantageous features, aspects and details of the invention are evident from the dependent claims and the description. The claims are intended to be understood as a first, non-limiting approach to defining the invention in general terms. The present invention addresses some of the difficulties and problems discussed above by providing a printable heat transfer material having cold release properties, which material includes a flexible first layer having first and second surfaces. The first layer typically will be a film or a cellulosic nonwoven web. A second layer overlays the first surface of the first layer and is composed of a thermoplastic polymer having essentially no tack at transfer temperatures (e.g., 177 degrees Celsius or °C), a solubility parameter of at least 19 (Mpa) ½ , and a glass transition temperature or T g of at least 0°C. The second layer further comprises an effective amount of a release-enhancing additive wherein said release enhancing additive is a divalent metal ion salt of a fatty acid. The thermoplastic polymer of which the second layer is composed may be a hard acrylic polymer or poly(vinyl acetate). A third layer overlays the second layer and includes a thermoplastic polymer which melts in a range of from 65°C to 180°C. By way of example, the first layer may be a cellulosic nonwoven web. For example, the cellulosic nonwoven web may be a latex-impregnated paper. As another example, the thermoplastic polymer included in the second layer may have a glass transition temperature of at least 25°C. As a further example, the third layer may include a film-forming binder, which binder may include a powdered thermoplastic polymer. The second layer also includes an effective amount of a release-enhancing additive, such as a divalent metal ion salt of a fatty acid or a mixture thereof with a polyethylene glycol. For example, the release-enhancing additive may be calcium stearate or a mixture thereof with a polyethylene glycol having a molecular weight of from 2,000 to 100,000. If desired, a fourth layer may overlay the third layer in order to provide an ink jet printable heat transfer material. The fourth layer typically includes a film-forming binder and a powdered thermoplastic polymer, each of which melts in a range of from 65°C to 180°C. Optionally, a fifth layer may overlay the second layer, in which case the third layer will overlay the fifth layer, rather than the second layer. The fifth layer includes a film-forming binder which melts in a range of from 65°C to 180°C as described above. The resulting ink jet printable heat transfer material possess cold release properties. As used herein, the term "printable" is meant to include the placement of an image on a material by any means, such as by direct and offset gravure printers, silk-screening, typewriters, laser printers, dot-matrix printers, and ink jet printers, by way of illustration. Moreover, the image composition may be any of the inks or other compositions typically used in printing processes. The term "ink jet printable" refers to the formation of an image on a material, e.g., paper, by means of an ink jet printer. In an ink jet printer, ink is forced through a tiny nozzle (or a series of nozzles) to form droplets. The droplets may be electrostatically charged and attracted to an oppositely charged platen behind the paper. By means of electrically controlled deflection plates, the trajectories of the droplets can be controlled to hit the desired spot on the paper. Unused droplets are deflected away from the paper into a reservoir for recycling. In another method, the droplets are ejected on demand from tiny ink reservoirs by heating to form bubbles as the print head scans the paper. The term "molecular weight" generally refers to a weight-average molecular weight unless another meaning is clear from the context or the term does not refer to a polymer. It long has been understood and accepted that the unit for molecular weight is the atomic mass unit, sometimes referred to as the "dalton". Consequently, units rarely are given in current literature. In keeping with that practice, therefore, no units are expressed herein for molecular weights. As used herein, the term "cellulosic nonwoven web" is meant to include any web or sheet-like material which contains at least 50 percent by weight of cellulosic fibers. In addition to cellulosic fibers, the web may contain other natural fibers, synthetic fibers, or mixtures thereof. Cellulosic nonwoven webs may be prepared by air laying or wet laying relatively short fibers to form a web or sheet. Thus, the term includes nonwoven webs prepared from a papermaking furnish. Such furnish may include only cellulose fibers or a mixture of cellulose fibers with other natural fibers and/or synthetic fibers. The furnish also may contain additives and other materials, such as fillers, e.g., clay and titanium dioxide, surfactants, antifoaming agents, and the like, as is well known in the papermaking art. The term "hard acrylic polymer" as used herein is intended to mean any acrylic polymer which typically has a T g of at least 0°C. For example, the T g may be at least 25°C. As another example, the T g may be in a range of from 25°C to 100°C. A hard acrylic polymer typically will be a polymer formed by the addition polymerization of a mixture of acrylate or methacrylate esters, or both. The ester portion of these monomers may be C 1 -C 6 alkyl groups, such as, for example, methyl, ethyl, and butyl groups. Methyl esters typically impart "hard" properties, while other esters typically impart "soft" properties. The terms "hard" and "soft" are used qualitatively to refer to room-temperature hardness and low-temperature flexibility, respectively. Soft latex polymers generally have glass transition temperatures below 0°C. These polymers flow too readily and tend to bond to the fabric when heat and pressure are used to effect transfer. The less hard, more easily deformed hard polymers generally require fillers to sufficiently harden the coating. Thus, the glass transition temperature correlates fairly well with polymer hardness. As used herein, the term "cold release properties" means that once an image has been transferred to a substrate, such as cloth, the backing or carrier sheet (the first layer in the present invention) may be easily and cleanly removed from the substrate after the heat transfer material has cooled to ambient temperature. That is, after cooling, the backing or carrier sheet may be peeled away from the substrate to which an image has been transferred without resisting removal, leaving portions of the image on the carrier sheet, or causing imperfections in the transferred image coating. As stated earlier, the present invention provides a printable heat transfer material having cold release properties. The printable heat transfer material includes a flexible first layer having first and second surfaces. The flexible first layer serves as a base sheet or backing. The flexible first layer typically will be a film or a cellulosic nonwoven web. In addition to flexibility, the first layer also should have sufficient strength for handling, coating, sheeting, and other operations associated with its manufacture, and for removal after transferring an image. By way of example, the first layer may be a paper such as is commonly used in the manufacture of heat transfer papers. In some embodiments, the first layer will be a latex-impregnated paper. By way of illustration only, the latex-impregnated paper may be a water leaf sheet of wood pulp fibers or alpha pulp fibers impregnated with a reactive acrylic polymer latex such as Rhoplex® B-15 (Rohm and Haas Company, Philadelphia, Pennsylvania). However, any of a number of other latices can be used, if desired, some examples of which are summarized in Table A, below. The impregnating dispersion typically will contain clay and an opacifier such as titanium dioxide. Exemplary amounts of these two materials are 16 parts and 4 parts, respectively, per 100 parts of polymer on a dry weight basis. By way of example only, the first layer may have a basis weight of 50 g/m 2 (13.3 lbs/1300 ft 2 ) before impregnation. The impregnated paper generally may contain impregnant in a range of from 5 to 50 percent by weight, on a dry weight basis, although in some cases higher levels of impregnant in the paper may be suitable. As an illustration, the paper may contain 18 parts impregnating solids per 100 parts fiber by weight, and may have a basis weight of 58 g/m 2 (15.6 lbs/1300 ft 2 ), both on a dry weight basis. A suitable caliper is 97 ± 8 µm (micrometers) (3.8 ± 0.3 mil). In addition to the paper being impregnated with polymer dispersions as described above, it also may be impregnated with a solution or dispersion of polymers which are wholly or partially soluble in, for example, hot water. For example, the paper may be impregnated with a pigment-containing poly(vinyl alcohol) solution. Other soluble polymers include, by way of illustration only, styrene-maleic anhydride copolymers (base soluble), starch, polyvinylpyrrolidone, and carboxyethyl cellulose. The first layer is readily prepared by methods which are well known to those having ordinary skill in the art. In addition, paper-impregnating techniques also are well known to those having ordinary skill in the art. Typically, a paper is exposed to an excess of impregnating dispersion, run through a nip, anddried. A second, or release, layer overlays the first surface of the first layer. The second layer is composed of a thermoplastic polymer having essentially no tack at transfer temperatures (e.g., 177°C), a solubility parameter of at least 19 (Mpa) ½ , and a glass transition temperature of at least 0°C. As used herein, the phrase "having essentially no tack at transfer temperatures" means that the second layer does not stick to the third layer (or fifth layer, if present) to an extent sufficient to adversely affect the quality of the transferred image. By way of illustration, the thermoplastic polymer may be a hard acrylic polymer or poly(vinyl acetate). For example, the thermoplastic polymer may have a glass transition temperature (T g ) of at least 25°C. As another example, the T g may be in a range of from 25°C to 100°C. Examples of suitable polymers include those listed in Table A which have suitable glass transition temperatures. The second layer also includes an effective amount of a release-enhancing additive, such as a divalent metal ion salt of a fatty acid or a mixture thereof with a polyethylene glycol. For example, the release-enhancing additive may be calcium stearate or a mixture thereof with a polyethylene glycol having a molecular weight of from 2,000 to 100,000. A third layer overlays the second layer and includes a thermoplastic polymer which melts in a range of from 65°C to 180°C. The third layer functions as a transfer coating to improve the adhesion of subsequent layers in order to prevent premature delamination of the heat transfer material. The layer may be formed by applying a coating of a film-forming binder over the second layer. The binder may include a powdered thermoplastic polymer, in which case the third layer will include from 15 to 80 percent by weight of a film-forming binder and from 85 to 20 percent by weight of the powdered thermoplastic polymer. In general, each of the film-forming binder and the powdered thermoplastic polymer will melt in a range of from 65°C to 180°C. For example, each of the film-forming binder and powdered thermoplastic polymer may melt in a range of from 80°C to 120°C. In addition, the powdered thermoplastic polymer will consist of particles which are from 2 to 50 µm (micrometers) in diameter. Desirably, the thickness of the third layer will be from 12 to 80 µm (micrometers). In general, any film-forming binder may be employed which meets the criteria specified herein. As a practical matter, water-dispersible ethylene-acrylic acid copolymers have been found to be especially effective film-forming binders. Similarly, the powdered thermoplastic polymer may be any thermoplastic polymer which meets the criteria set forth herein. For example, the powdered thermoplastic polymer may be a polyolefin, polyester, ethylene-vinyl acetate copolymer, or polyolefin. The term "melts" and variations thereof are used herein only in a qualitative sense and are not meant to refer to any particular test procedure. Reference herein to a melting temperature or range is meant only to indicate an approximate temperature or range at which the film-forming binder and/or powdered thermoplastic polymer melt and flow under the conditions of the melt-transfer process to result in a substantially smooth film. In so doing, such materials, and especially the powdered thermoplastic polymer, may flow partially into the fiber matrix of the fabric to which an image is being transferred. Manufacturers' published data regarding the melt behavior of film-forming binders or powdered thermoplastic polymers correlate with the melting requirements described herein. It should be noted, however, that either a true melting point or a softening point may be given, depending on the nature of the material. For example, materials such a polyolefins and waxes, being composed mainly of linear polymeric molecules, generally melt over a relatively narrow temperature range since they are somewhat crystalline below the melting point. Melting points, if not provided by the manufacturer, are readily determined by known methods such as differential scanning calorimetry. Many polymers, and especially copolymers, are amorphous because of branching in the polymer chains or the side-chain constituents. These materials begin to soften and flow more gradually as the temperature is increased. It is believed that the ring and ball softening point of such materials, as determined by ASTM Test Method E-28, is useful in predicting their behavior in the present invention. Moreover, the melting points or softening points described are better indicators of performance in this invention than the chemical nature of the polymer. Alternatively, the third layer may be a melt-extruded film. The criteria for a melt-extruded film which forms the third layer are generally the same as those described above for the third layer. The polymer of which a melt-extruded third layer is composed typically will melt in a range of from 80°C to 130°C. The polymer should have a melt index, as determined in accordance with ASTM Test Method D-1238, of at least 25 g/10 minutes. The chemical nature of the polymer is not known to be climacteric. Polymer types which satisfy these criteria and are commercially available include, by way of illustration only, copolymers of ethylene and acrylic acid, methacrylic acid, vinyl acetate, ethyl acetate, or butyl acrylate. Other polymers which may be employed include polyesters, polyamides, and polyurethanes. Waxes, plasticizers, rheology modifiers, antioxidants, antistats, antiblocking agents, and other additives may be included as either desired or necessary. The melt-extruded third layer may be applied with an extrusion coater which extrudes the molten polymer through a screw into a slot die. The film exits the slot die and flows by gravity onto the first layer. The resulting coated first layer is passed through a nip to chill the second layer and bond it to the first layer. For less viscous polymers, the molten polymer may not form a self-supporting film. In these cases, the first layer may be coated by directing it into contact with the slot die or by using rolls to transfer the molten polymer from a bath to the first layer. Because the inks employed in ink jet printers are aqueous based, a fourth layer is useful for a printable heat transfer material on which an image is to be placed by an ink jet printer. The fourth layer prevents or minimizes feathering of the printed image and bleeding or loss of the image when the transferred image is exposed to water. Thus, the fourth layer is an ink jet print layer or coating. The fourth layer may be, for example, the second or print layer described in U.S. Patent No. 5,501,902 to Kronzer, which patent is incorporated herein by reference. Thus, the fourth layer may include particles of a thermoplastic polymer having largest dimensions of less than 50 µm (micrometers). Desirably, the particles will have largest dimensions of less than 20 µm (micrometers). In general, the thermoplastic polymer may be any thermoplastic polymer which meets the criteria set forth herein. Desirably, the powdered thermoplastic polymer will be selected from the group consisting of polyolefins, polyesters, polyamides, and ethylene-vinyl acetate copolymers. The fourth layer also includes from 10 to 50 weight percent of a film-forming binder, based on the weight of the thermoplastic polymer. Desirably, the amount of binder will be from 10 to 30 weight percent. In general, any film-forming binder may be employed which meets the criteria set forth herein. When the fourth layer includes a cationic polymer as described below, a nonionic orcationic dispersion or solution may be employed as the binder. Suitable binders include polyacrylates, polyethylenes, and ethylene-vinyl acetate copolymers. The latter are particularly desired because of their stability in the presence of cationic polymers. The binder desirably will be heat softenable at temperatures of about 120°C or lower. The basis weight of the fourth layer may vary from 5 to 30 g/m 2 . Desirably, the basis weight will be from 10 to 20 g/m 2 . The fourth layer may be applied to the third layer by means well known to those having ordinary skill in the art, as already described. The fourth layer typically will have a melting point of from 65°C to 180°C. Moreover, the fourth layer may contain from 2 to 20 weight percent of a cationic polymer, based on the weight of the thermoplastic polymer. The cationic polymer may be, for example, an amide-epichlorohydrin polymer, polyacrylamides with cationic functional groups, polyethyleneimines, polydiallylamines, and the like. When a cationic polymer is present, a compatible binder should be selected, such as a nonionic or cationic dispersion or solution. As is well known in the paper coating art, many commercially available binders have anionically charged particles or polymer molecules. These materials are generally not compatible with the cationic polymer which may be used in the fourth layer. One or more other components may be used in the fourth layer. For example, this layer may contain from 1 to 20 weight percent of a humectant, based on the weight of the thermoplastic polymer. Desirably, the humectant will be selected from the group consisting of ethylene glycol and poly(ethylene glycol). The poly(ethylene glycol) typically will have a weight-average molecular weight of from 100 to 40,000. A poly(ethylene glycol) having a weight-average molecular weight of from 200 to 800 is particularly useful. The fourth layer also may contain from 0.2 to 10 weight percent of an ink viscosity modifier, based on the weight of the thermoplastic polymer. The viscosity modifier desirably will be a poly(ethylene glycol) having a weight-average molecular weight of from 100,000 to 2,000,000. The poly(ethylene glycol) desirably will have a weight-average molecular weight of from 100,000 to 600,000. Other components which may be present in the fourth layer include from 0.1 to 5 weight percent of a weak acid and from 0.5 to 5 weight percent of a surfactant, both based on the weight of the thermoplastic polymer. A particularly useful weak acid is citric acid. The term "weak acid" is used herein to mean an acid having a dissociation constant less than one (or a negative log of the dissociation constant greater than 1). The surfactant may be an anionic, a nonionic, or a cationic surfactant. When a cationic polymer is present in the fourth layer, the surfactant should not be an anionic surfactant. Desirably, the surfactant will be a nonionic or cationic surfactant. However, in the absence of the cationic polymer, an anionic surfactant may be used, if desired. Examples of anionic surfactants include, among others, linear and branched-chain sodium alkylbenzenesulfonates, linear and branched-chain alkyl sulfates, and linear and branched-chain alkyl ethoxy sulfates. Cationic surfactants include, by way of illustration, tallow trimethylammonium chloride. Examples of nonionic surfactants, include, again by way of illustration only, alkyl polyethoxylates, polyethoxylated alkylphenols, fatty acid ethanol amides, complex polymers of ethylene oxide, propylene oxide, and alcohols, and polysiloxane polyethers. More desirably, the surfactant will be a nonionic surfactant. Finally, a fifth or intermediate layer may overlay the second layer and underlay the third layer, thereby being located between the second layer and the third layer. In general, the fifth layer is not helpful when the third layer is formed from a film-forming binder. When the third layer is a melt-extruded film, however, the third layer may have poor adhesion to the second layer. Poor adhesion may result in delamination in a printer, especially in laser printers, of the third layer from the second layer. To prevent delamination in such cases, the fifth layer is necessary. In general, the fifth layer may include a film-forming binder which melts in a range of from 65°C to 180°C as described for the third layer. Moreover, the fifth layer also may include a powdered thermoplastic polymer as described for the third layer. If desired, any of the foregoing film layers may contain other materials, such as processing aids, release agents, pigments, deglossing agents, antifoam agents, and the like. The use of these and similar materials is well known to those having ordinary skill in the art. The layers which are based on a film-forming binder may be formed on a given layer by known coating techniques, such as by roll, blade, and air-knife coating procedures. The resulting heat transfer material then may be dried by means of, for example, steam-heated drums, air impingement, radiant heating, or some combination thereof. The present invention is further described by the examples which follow. Whenever possible, units of measurement also will be expressed as SI units (International System of Units), whether Basic or Derived. Unless indicated otherwise, all parts are parts by weight and all basis weights are on a dry-weight basis. When the drying of a coating is specified in an example, a Model 28 Precision Scientific Electric Drying Oven was used. Images were transferred to Haynes® Brand 100 percent cotton T-shirts or their equivalent. Washing tests were carried out in a standard home washing machine and dried in a standard home drier. Image transfer involved the use of either a Proctor Silex® brand non-steam home hand iron set at 163°-177°C and/or a cotton setting or a Model S-600 heat transfer press (Hix Corporation, Pittsburgh, Kansas). Examples In the following Examples only those embodiments form part of the invention in which the second layer includes a release enhancing additive comprising a divalent metal ion salt of a fatty acid. Because of the large amount of experimental data and the complexity of the products being tested, a coding system is used to present the data. First layers (or base papers) are identified as IA, IB, etc. The second layers are identified as IIA, IIB, etc.; third layers as IIIA, etc.; fourth layers as IVA, etc.; and fifth layers as VA, VB, etc. Accordingly, Tables I-V are presented below. In these and all subsequent tables, the letter "I" has been skipped to avoid confusing an identifying designation as a Roman numeral from which the letter portion had been omitted. Unless otherwise stated, the second layers were applied as dispersions in water with a meyer rod and dried in a forced air oven. The dried coating weight was between 9 and 17 g/m 2 (between 2.5 and 4.5 lb/1300 ft 2 ) unless otherwise stated. Initial screening experiments were designed to determine if the concept of a "cold peelable" ink jet heat transfer material was feasible. These experiments are summarized in Table VI, below. Samples (identified in the "ID" column) in Table VI (and subsequent tables) are numbered with the table number and a letter (A to Z); for example. "VIA" would be the first sample in Table VI. The screening technique employed involved placing a paper towel on a T-shirt press (Hix Model S-600, Hix Corp., Pittsburgh, Pennsylvania). A film of the third layer was placed on the paper towel, and the coated experimental sample was placed on the film. The resulting "sandwich" then was heat pressed for 30 seconds at 185°C (365°F). After pressing, about one third of the paper was removed immediately while the sandwich was still hot, about one third after 30 seconds, and the remaining one third after cooling to ambient temperature. The ease of peeling then was rated subjectively as excellent, good, fair or poor (the poor samples usually could not be removed at all). The design parameters of one of the most interesting samples, VIP, were then incorporated into an ink jet printable, cold peelable heat transfer paper, VIQ, by laminating a film of Nucrel® 599 (layer IVA) to the second layer-coated paper in a heat press at 100°C for 30 seconds, then coating this sample with the type IVA coating. The sample was then printed with a test pattern and transferred to T-shirt material (100% cotton). The image transferred well after pressing for 30 seconds at 191°C (375°F) and cooling. The image transferred completely and was smoother and more glossy than "hot peeled" transfers using type C-90642 paper (a hot peel heat transfer paper commercially available from Kimberly-Clark Corporation). In the first set of experiments, the third layer was always an extruded film. The next set of experiments, summarized in Table VII, below, were done to try all water-based coatings. Combinations of Microthene® FE532 and Michem® 58035 proved to work fairly well with several second layers - especially Rhoplex® HA16 and clay. The transferred polymer still had a glossy surface. Also, wash tests of T-shirt materials with transfers from these samples didn't retain color as well as controls made with the C-90642 hot peel paper (images were transferred after heat pressing 30 seconds at 182°C or 360°F). Using the third layers IIIB or IIIC, and BP101 (first layer IB), and a new second layer, IIH, seemed to solve the gloss problem. Second layer IIH had a matte, "micro-rough" surface from the Celite® 263 filler which is a diatomaceous earth. These results are summarized in Table VIII, below. Heat pressing conditions were the same as in Table VII. The IIID base coat - using Micropowders MPP635VF in place of the ethylene-vinyl acetate copolymer Microthene® FE532 was tried to see if the washability could be improved. It didn't release from the IIH second layer, however. The next set of experimental samples involved the preparation of a series of second layer-coated samples, followed by coating them with the Nucrel® 599 film (IIIA third layer) by taping the samples to a paper web being coated. The coated samples which showed sufficient adhesion of the base coat were coated with a fourth layer, IVA, printed with a test pattern and transferred to 100% cotton T-shirt material using a hand iron. The iron was set at the #6 setting (cottons) and pre-heated. The paper was ironed with two passes using quite a bit of pressure; i.e., one pass down the length of each side of a 21.6 cm x 27.9 cm (8 1/2" x 11") sheet, overlapping in the middle. Then, 10 rapid trips over the paper, each covering the entire surface, were made using moderate pressure. The paper was removed after cooling for one minute. The results are summarized in Table IX. Samples IXB and IXC were duplicated in trial runs TR-A and TR-B, respectively. However, when the precursor rolls were coated with the IIIA third layer, adhesion was poor and no usable material was obtained. This led to the modification of the second layer again, i.e., reducing the amount of Carbowax® PEG 20M to 10 parts (IIN second layer). Trials TR-C and TR-D made with this release coat were more successful, but the extrusion coating step (application of the IIIA third layer) had to be run very slowly (60 fpm) in order to prevent film delamination from occurring in processing. It was observed that there were several disadvantages with samples from TR-C and TR-D. Transfers made with TR-D, which had an additional polymer layer transferred to the fabric (fifth layer), tended to develop cracks in the polymer layer after several washings. A similar but less severe problem was seen with sample TR-C. This was probably partly because, in hot peeling the paper, some polymer is left on the paper while in the cold peel designs it is all transferred. Another factor is that people probably will tend to use less heat and pressure when ironing the cold peel design, since it always will transfer the entire polymer layer even though the penetration into the fabric isn't as complete as it could be. Still another problem was the expected high cost of the multiple coatings for this design, especially since one of the coatings was done on an extruder at a very slow speed. It seemed possible that all these problems could be solved if all the coating could be done with water-based polymers, so new water-based alternatives were sought. Results of the next set of experiments with all water-based coatings are summarized in Table X. These were evaluated using the hand ironing technique already described. Some of the samples, especially XE which has no fifth layer, looked very promising. The elimination of the fifth layer seemed to give less image cracking. This was thought to be due to using lower molecular weight polymers (IIIE), which should flow more into the fabric when the image was transferred. However, since neither of these components would release from the IIN second layer, alternative second layers were sought. The results are summarized in Table XI. Several conclusions were drawn from the data in Table XI. Again, the ironing technique described earlier was used. The second layers were the first to give good release of the micropowders-Michem® Prime coatings, giving a product which seemed nearly acceptable. One attempt to soften the polymer mass being transferred (sample XIC) was in the right direction. This sample employed a lower molecular weight ethylene-acrylic acid binder than Michem® Prime 4983. The Unimoll® 66 and Tones 0201 were added to see if the Orgasol®, which is a polyamide, could be softened. The Tones 0201 did soften it considerably, but gave more ink bleeding on printing and poor washability. Following these promising results, it was discovered that the Carboset® 760 tends to yellow when heated. Sample XIG was made to see if an unsaturated bond paper could be used for the first layer (or base paper) of this design, e.g., to eliminate odors from the saturant as well as formaldehyde. Unfortunately, it tended to delaminate too easily, leaving a possibility of ironing failures. Therefore, in the next set of experiments, some formaldehyde free, low odor latices from B. F. Goodrich were evaluated as both the saturants and second layers. B. F. Goodrich provided two formaldehyde-free versions of Hycar 26172, namely, a formaldehyde-free Hycar® 26106 and a formaldehyde-free Hycar® 26084. The 26172 and 26106 are hard acrylics, while 26084 is softer and has a slight acrylate odor. First layer or base paper IF, an eucalyptus-hardwood blend base paper at a basis weight of 62 g/m 2 (16.5 lb per 1300 sq. ft.), was saturated with formulations containing each latex combined with 25 dry parts of Titanium Dioxide dispersion (PD 14). The saturant pickup was 40±4%. After drying, each sample was heated for 30 seconds at 191°C (375°F) in a heat press and also ironed on the hottest hand iron setting over a piece of T-shirt material. Neither of the samples having the Hycar® 26172 variants yellowed on heat pressing. They yellowed slightly when ironed. The samples having Hycar® 26084 and 26106 variants yellowed more. The four latices were also evaluated as second layers, each having 20 dry parts Carbowax® PEG 20M. The third layer used for these tests was IIIF, and the fourth layer was IVB. After these coatings were applied to the second layers, the samples were ironed onto T-shirt material, cooled, and peeled off. The data are summarized in Table XII. Unfortunately, the "least yellowing" latex samples did not provide release like the modified 26106 or 26172. This was thought to be due to differences in surfactants, since some surfactants can provide release by concentrating at the coating surface. Indeed, when calcium stearate was added, release became excellent. Several additional attempts to soften the transferred image (polymer) on the T-shirt material are summarized in Table XIII. Again, the ironing technique described earlier was employed. From this work it was learned that lower third layer basis weights (sample XIIIC) made the cracking worse. Lower molecular weight waxes or polymers (sample XIIIB) eliminated the cracking but washability was worse, namely, more loss of color on washing. igher molecular weight polymers, such as Microthene® FE 532 and Orgasol® 3501, added to the third layer gave more cracking. The data summarized in Table XIII confirmed the difficulty in making the transferred polymer image softer while eliminating the cracking and retaining good washability. The only clue to solving this problem was that the cracking became worse when the coating weight was reduced (sample XIIIC). This is opposite to what one might expect, since the cracking always appeared to come from excess polymer on the fabric surface. Accordingly, higher third layer basis weights were investigated. The results of these investigations are summarized in Table XIV; again, ironing was carried out as described earlier. The data in Table XIV confirmed the need for a heavy third layer to eliminate the cracking problem. It now is known that the cracks in the polymer on the fabric develop when the entire polymer mass being transferred is too hard or if the molecular weights of the materials are too high. The fourth layer polymer mass in itself has a high molecular weight and this cannot be modified without creating printability or washability problems. The third layer can be much lower in molecular weight or much softer, but it becomes effective only if its mass is much greater than the fourth layer mass. However, too low a molecular weight gives poor washability. All the third layer modifications done thus far have been ineffective in providing the needed effect at the 2.7 kg (6 lb) per ream coating weight. Samples in Table XIV which gave the softest touch after transferring to the T-shirt material showed no cracking, but generally lost more color on washing. In these samples, many of the materials which gave the softening effect were more effective in the fourth layer than in the third layer. It is thought that the calcium stearate in the third layer had a hardening effect, while the ammonium stearate gives a soft tactile impression since it loses ammonia on drying to become stearic acid. The Carbowax® PEG 20M is a very soft, waxy material which gave the desired softening affect but seemed to make the image more water sensitive. (Of course, PEG is water soluble.) Surprisingly, the PEG 200 seemed to have a softening affect without negatively affecting washability. One theory for this is that it may soften the Orgasol® polyamide at high temperatures, when the transfer is being carried out, but may become incompatible again after cooling. Then, it simply washes out of the polymer mass when the fabric is washed. More work has to be done before the ideal PEG level and molecular weight are determined. PEG 200 may be too volatile and the vapor could be irritating, while Carbowax® PEG 20M gives poor washability. Some in-between molecular weight may be ideal. Five separate preparations of Sample XIVJ have given acceptable results. In each attempts the printed sample was ironed onto a 100% cotton T-shirt material using the previously described procedure. The T-shirt material was washed five times in a home laundry with the machine set on the warm/cold cycle. There was no cracking of the image. Comparing the XIVJ sample and a control, the XIVJ sample gave a more glossy image area if cold peeled, but not if hot peeled, from the fabric. The control was "hot peel" type C-90642.

Claims: A printable heat transfer material comprising: a flexible first layer having first and second surfaces and selected from the group consisting of films and cellulosic nonwoven webs; a second layer overlaying the first surface of the first layer, which second layer comprises a thermoplastic polymer having essentially no tack at transfer temperatures, selected from the group consisting of hard acrylic polymers and polyvinylacetate and having a glass transition temperature of at least 0° C; and wherein the second layer further comprises an effective amount of a release-enhancing additive wherein said release enhancing additive is a divalent metal ion salt of a fatty acid, a third layer overlaying the second layer, which third layer comprises a thermoplastic polymer selected from the group of polyolefins, polyesters and ethylene (vinylacetate) wherein said thermoplastic polymer melts in the range of 60° C to 180° C; whereby the second and third layers are adapted such that after the transfer of an image onto a substrate the first layer may be easily and cleanly removed from said substrate after the heat transfer material has been cooled to ambient temperature. The printable heat transfer material of claim 1, in which the third layer comprises a film-forming binder. The printable heat transfer material of one of claims 1 or 2 in which the third layer comprises a powdered thermoplastic polymer and a film-forming binder. The heat transfer material according to one of claims 1 to 4 further comprising: a fourth ink jet print layer overlying the third layer, which fourth layer comprises a film-forming binder selected from the group of polyacrylates, polyethylenes, and ethylene-vinyl acetate copolymers and a powdered thermoplastic polymer selected from the group of polyacrylates, polyethylenes, and ethylene-vinyl acetate copolymers, in which each of the film-forming binder and the powder thermoplastic polymer melts in a range of from 65°C to 180°C. A printable heat transfer material comprising: a flexible first layer having first and second surfaces and selected from the group consisting of films and cellulosic nonwoven webs; a second layer overlaying the first surface of the first layer, which second layer comprises a thermoplastic polymer having essentially no tack at transfer temperatures, selected from the group consisting of hard acrylic polymers and polyvinylacetate and having a glass transition temperature of at least 0°C; and wherein the second layer further comprises an effective amount of a release-enhancing additive, wherein said release enhancing additive is a divalent metal ion salt of a fatty acid, a fifth layer overlaying the second layer, which fifth layer comprises a film-forming binder selected from the group of polyolefins, polyesters and ethylene (vinylacetate) and which melts in the range of from 65°C to 180°C; and a third layer overlaying the second layer, which third layer comprises a thermoplastic polymer film selected from the group of polyolefins, polyesters and ethylene (vinylacetate) and wherein said thermoplastic polymer film melts in the rage of 65°C to 180°C; whereby the second and fifth layer are adapted such that after the transfer of an image onto a substrate the first layer may be easily and cleanly removed from said substrate after the heat transfer material has been cooled to ambient temperature. The printable heat transfer material according to claim 5 further comprising: a fourth ink jet print layer overlaying the third layer, which fourth layer comprises a film-forming binder selected from the group of polyacrylates, polyethylenes, and ethylene-vinyl acetate copolymers, and a powdered thermoplastic polymer selected from the group of polyacrylates, polyethylenes, and ethylene-vinyl acetate copolymers, and a powdered thermoplastic polymer, in which each of the film-forming binder and the powder thermoplastic polymer melts in a range of from 65°C to 180 °C; and wherein the thermoplastic polymer film comprised in the third layer is a melt-extruded polymer film. The printable heat transfer material of any one of the preceding claims, in which the first layer is a cellulosic nonwoven web. The printable heat transfer material of claim 7, in which the cellulosic nonwoven web is a latex-impregnated paper. The printable heat transfer material of any one of the preceding claims, in which the thermoplastic polymer comprising the second layer has a glass transition temperature of at least 25°C. The printable heat transfer material of any one of the preceding claims, in which the third layer and/or the fifth layer has a solubility parameter less than 19 (Mpa) ½ . The printable heat transfer material of any of the preceding claims, in which the release-enhancing additive is calcium stearate. The printable heat transfer material of any of the preceding claims wherein the release-enhancing agent further comprises a polyethylene glycol. The printable heat transfer material according to claim 12 wherein polyethylene glycol has a molecular weight of from 2,000 to 100,000.

Inventors: KRONZER FRANCIS JOSEPH, KRONZER, FRANCIS JOSEPH
Applicants: KIMBERLY CLARK CO, KIMBERLY-CLARK WORLDWIDE, INC.
Application year: 1997
Main classification: B41M5
IPC codes: B41M5, B41M7, B32B7, B44C1