METHOD OF PROVIDING IMAGES ON AN IMAGE RECEPTOR MEDIUM

Abstract: A method of providing an image on an image receptor medium is disclosed that involves forming an image on an image transfer medium and transferring the image to an image receptor medium. Using hot roll lamination as the transfer method, acceptable image transfer quality can be achieved at transfer rates in the range from 0.3 to 3.0 m/min, and more advantageously, 0.3 to 4.6 m/min. The image receptor medium includes an image reception layer comprising a polymeric component including one or more polymers, each polymer having a Vicat softening point and a melting point sufficiently higher than room temperature to avoid tackiness and handling difficulties. The image receptor medium can optionally include a substrate layer to enhance properties such as durability and weather resistance, a prime layer, and an adhesive layer.

Description: Method of Providing Images on an Image Receptor Medium Field of the Invention This invention relates to films useful as image receptor media such as those used in advertising and promotional displays, and more particularly to a method of providing images on such media. Background of the Invention Advertising and promotional displays often include graphic images appearing on structural surfaces such as truck sides and awnings, or free-hanging as banners. To prepare the display, an image may be formed on an adhesive-backed image receptor medium, sometimes referred to as a graphic marking film, which is then adhered to the desired substrate. Alternatively, the image may be formed first on an image transfer medium, and transferred to the image receptor medium. The image receptor medium usually includes a base material with an additional receptor layer overlying it. The base material is typically a plasticized vinyl film, although paper may also be used. Although the graphic display may be intended for a long term installation of 5 years or more, it is often a relatively short term (3 months to I year) outdoor installation. In the case of a short term display, the image receptor medium is desirably a low cost, weather resistant, durable graphic marking film having good printability and adhesion of inks and/or toners that is easily applied to and removed from a surface. The polyvinylchloride (PVC) base films currently used in graphic marking films are generally too costly for a short term application, and present problems with plasticizer migration, plasticizer staining and adhesive anchorage. In addition, the the vinyl composition itself may present problems. For instance, the chlorinated composition of vinyl may lead to environmental difficulties related to vinyl disposal and use in applications having a risk of fire, and the cadmium found in stabilizers used in most vinyl formulations is restricted or prohibited in many countries. Paper-based media are not sufficiently durable or weather resistant and tear easily when removed. Polyolefin base films are low cost and contain no plasticizer but do not provide good ink/toner adhesion. The application of the receptor layer over the base film usually requires an additional process step, thus adding cost to the manufacturing process. Electrography is a well known method for creating images. Electrography involves passing a substrate, normally a dielectric material, through an electrographic printing device, one type of which is an electrostatic printer. In the printer, the substrate is addressed with static electric charges (e.g., as from a stylus) to form a latent image which is then developed with suitable toners. This technique is especially suitable for producing large scale images for use on posters and signs. At the conclusion of the electrographic process where the toned image has been developed on the dielectric substrate, the printed substrate can be enclosed between two layers of clear vinyl plastic film and used directly in an outdoor application, such as a sign. Because the typical dielectric substrates are paper-based, however, they frequently lack the weather resistance required for outdoor signs. More durable substrates such as polyvinylchloride (PVC) and polyvinylacetate (PVA) films are difficult to image directly because of their electrical and mechanical properties. To produce large signs that are suitable for outdoor display, the toned image electrographically deposited on a dielectric substrate can be transferred to a more weather resistant image receptor medium. The dielectric substrate is then known as a carrier or an image transfer medium. This technique is discussed in U.S. Patent No. 5,262,259. Transfer of the toned image from an image transfer medium to an image receptor medium typically requires the application of pressure and heat through, for example, lamination in a heated pressure roll system (hot roll lamination). This type of image transfer technique is described in U.S. Patent No. 5, 1 14,520. Though the hot roll lamination system is effective, the transfer rates have been considered slow (generally between 0.5 and 1.0 meters per minute). Summary of the Invention There is a need for a method of transferring images via hot roll lamination to a low-cost, durable, weather resistant image receptor medium at faster transfer rates than are currently possible. The invention solves the problems in the art by disclosing a method of providing an image on an image receptor medium in which transfer rates can be significantly faster than current methods while retaining excellent quality of the transferred image. The method involves first forming an image on an image transfer medium and then transferring the image to an image reception surface of an image receptor medium. The image receptor medium comprises an image reception layer having two opposing major surfaces, one of which is a surface for receiving images. The image reception layer comprises one or more polymers, each polymer having a Vicat softening point and a melting point sufficiently higher than room temperature to avoid tackiness and handling difficulties Preferably, each polymer is characterized by a Vicat softening point of less than about 100 °C and a melting point of less than about 150 °C. More preferably, the Vicat softening pointe is less than about 93 °C and the melting point is less than about 121 °C. The image reception layer provides properties of image receptivity to the image receptor medium. "Image receptivity" means that an image formed on or applied to the image receptor medium adheres completely or nearly completely after being subjected to a tape snap test in which 3M SCOTCH Tape No. 610 (commercially available from 3M Company, St. Paul, MN, USA) is firmly applied to the image and then removed with a rapid snapping motion Suitable polymers for the image reception layer can be selected from ethylene vinyl acetate, acid-modified ethylene vinyl acetate, acid/acrylate-modified ethylene vinyl acetate, anhydride- modified ethylene vinyl acetate, acid-modified ethylene acrylate, anhydride-modified ethylene acrylate, ethylene ethyl acrylate, ethylene methyl acrylate, ethylene acrylic acid, ionomer, polyester, and combinations thereof. The image receptor medium may further comprise an optional polymer substrate layer on a second major surface of the image reception layer opposite the image reception surface. Examples of suitable polymers for the substrate layer include nonplasticized polymers such as low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, polyester, polyamide, polycarbonate, polyurethane, polystyrene, and acrylic. The substrate layer can also comprise polyvinyl chloride. The image is preferably formed by electrography, which includes electrostatic or electrophotography. Image transfer is preferably accomplished by hot roll lamination, as described in U.S. Patent No. 5, 1 14,520. Using these techniques in the method of this invention, acceptable image transfer quality may be achieved at transfer rates in the range from 0.3 to 3.0 meters per minute (m/min) and more advantageously 0.3 to 4.6 m/min. These transfer rates are faster than those possible using currently available image receptor media, which could lead to increased productivity and cost savings in the printing process. The image receptor medium can advantageously comprise only a single layer and thus may be manufactured by a relatively simple and inexpensive process. In the case where the image receptor medium includes a substrate layer in addition to the image reception layer, the medium can combine the best properties of several resins in the various layers. For example, the substrate layer can be made with resins of generally low cost that also provide specific physical properties for the intended application. These properties may include dimensional stability, conformability, elastomeric properties, die cuttability, stiffness and flexibility. The image receptor medium need not contain plasticizers in any of its layers, thereby avoiding problems associated with plasticizer migration and plasticizer staining. In addition, the polymers included in the image receptor medium can be nonhalogenated. Thus, certain regulatory limitations (pertaining for example to polyvinyl chloride (PVC)) can be avoided in the disposal of waste materials. In another aspect, the invention provides the above-described image receptor medium. Brief Description of Drawings Figure 1 is a schematic representation of one type of printing station used to form the image in the method of this invention. Figure 2 is a schematic representation of a method of transferring an image from an image transfer medium to an image receptor medium according to this invention. Figure 3 is a schematic cross-sectional view illustrating the image receptor medium used in the method of this invention, including an optional substrate layer. Figure 4 is a schematic cross-sectional view illustrating the image receptor medium used in the method of this invention, including an optional substrate layer and optional prime layer. Embodiments of the Invention One method of forming images on an image transfer medium is an electrographic method as shown in Figure 1 , in the form of electrostatic printing. In Fig. 1, an image transfer medium 1 comprises a conductive paper substrate 2 having a first dielectric layer 4 and then a release coating 6 on at least one surface. The image transfer medium can optionally also include conductive layers (not shown) either between the dielectric layer 4 and the substrate 2, or on the substrate surface opposite the release coating 6, or both. The surface of the image transfer medium 1 having the release coating 6 passes through the station in a direction 8 so that the coated surface of the paper first passes a stylus writing head 10 which deposits a charge 12 leaving spaces 14 on the surface which are uncharged. After passing by the writing head 10, the image transfer medium 1 then passes a toning station comprising a toner applicator 16 which contacts a liquid toner bath 18 in a container 20. The liquid toner 22 is carried on the toner applicator 16 and is deposited over the entire surface of the image transfer medium 1 and then removed from the noncharged areas with a vacuum channel 28, providing toned areas 24 and untoned areas 26. Each of a series of these printer stations deposits a separate image, commonly in one of the four different colors: black, cyan, magenta, and yellow. The completed color image, referred to as the toned image, is displayed on the release surface of the image transfer medium. This technique is described in U.S. Patent No. 5,262,259. Such electrostatic printers are known in the art and are commercially available from, for example, 3M, Xerox Engineering Systems, Raster Graphics, Inc. and Nippon Steel Corporation. After the image is formed on the image transfer medium, the method of this invention then involves transferring the image to the image reception surface of an image receptor medium. The transfer can be accomplished in many ways known in the art such as passing the sheets together through heated nip rolls in a method known as hot roll lamination, or placing the sheets together on a heated platen in a vacuum drawdown frame. If the final image on the image receptor medium is to be of high quality and have good color fidelity the transfer should be largely complete (meaning little or no ink or toner remains behind on the image transfer medium) and without distortion. Under the conditions of the transfer process the image must therefore release easily from the image transfer medium surface and adhere well to the image reception surface of the image receptor medium. Figure 2 shows a schematic illustration of a preferred image transfer apparatus 31. A supply roll 33 is arranged to continuously feed an image receptor medium web 37 having an image reception surface 38 around a series of cylindrical idler rolls 41, 43, 45, and 47. Cylindrical pressure roll 49 is supported at its ends by movable supports (not shown) capable of urging the roll toward backup roll 51 with sufficient pressure to form a nip area 53 and engage and compress web materials fed into the nip area 53. At least one of rolls 49 and 51 is driven by a drive means, such as a variable speed electric motor or the like (not shown), to cause rolls 49 and 51 to counter-rotate at the desired speed and draw the web through the nip at the desired rate, referred to as the transfer rate. The transfer rate is preferably as fast as possible to maximize productivity, while not so fast as to unacceptably degrade the quality of the transferred image. Roll 35 is arranged to continuously feed a previously imaged image transfer medium 39 into contact with the image receptor medium 37 such that the image comes into contact with the image reception surface 38 of the image receptor medium. When the webs 37 and 39 reach the nip area 53 they are drawn between rolls 49 and 51 and pressed together so that the images carried on web 39 are brought into intimate contact with web 37 and pressed against the image reception surface 38. In addition, at least the roll 49 contacting web 39 from which the images are to be released must be heated to raise the temperature of the web materials as they pass through the nip area. Alternatively, both rolls 49 and 51 can be heated. Nip pressure between rolls 49 and 51 is controlled typically by air or hydraulic cylinders impinging on the ends of the axle of roll 49. Useful nip pressures are typically between 45 and 100 pounds per square inch (psi), or 3-7 kg/cm 2 , depending on the imaging materials being transferred. Upon exiting the nip area 53 the webs are fed onto support table 59 for cooling. Webs 37 and 39 are then separated with the image now transferred to web 37. This image transfer technique, known as "hot roll lamination", is described in detail in U.S. Patent No. 5,1 14,520 (Wang et al.), and forms a part of the Scotchprint™ Electronic Graphics System commercially available from 3M's Commercial Graphics Division. The choice of image transfer medium, imaging materials, and image receptor medium is important to ensure that full transfer of the image is achieved without damaging the image. A description of image transfer media and liquid toners useful in electrostatic printing is found in U.S. Patent Nos. 5, 1 14,520 and 5,262,259. The image receptor medium is generally a flexible sheet that has properties of image receptivity as previously defined. The medium should have chemical and physical properties that render it suitable for its intended use. For example, if the intended use is an outdoor advertising display, the image receptor medium should have good weathering properties and sufficient integrity to withstand handling in the application and removal process. In order to achieve the rapid transfer rates contemplated by this invention, the image receptor medium 60 shown in Figure 3 comprises an image reception layer 64 and an optional substrate layer 68 overlying and in contact with one surface of the image reception layer. Image reception layer 64 has an outer surface 66 for receiving images. Image Reception Layer Image reception layer 64 comprises a polymeric component of one or more polymers suitable for providing receptivity to inks and toners used in the printing process described above and good image transfer quality properties at the desired rate of image transfer using hot roll lamination. Good image transfer quality is indicated by a fully transferred, high quality image having no significant pinholes, defects or distortion. Moreover, the image reception layer preferably remains whole and shows minimal tendency to adhere to non-imaged portions of the image transfer medium. The polymeric component for the image reception layer preferably comprises one or more resins capable of being extruded or coextruded into a substantially two-dimensional sheet. These resins are capable of bonding without delamination to an adjacent optional substrate layer if the layers are coextruded or laminated. Alternatively, the polymeric component may be in the form of a polymer dispersion capable of being coated onto a substrate layer by a method such as roll coating. The polymer or polymers of the image reception layer can be characterized by a Vicat softening point (American Society for Testing Materials method ASTM D-1525) and a melting point as determined by differential scanning calorimetry (DSC) according to ASTM D-3418. In general, these temperatures should be sufficiently higher than room temperature to avoid tackiness and handling difficulties while being low enough to provide acceptable image receptivity properties. Preferably, each polymer in the the image reception layer has a Vicat softening point of less than about 100 °C and a melting point of less than about 150 °C. More preferably, the Vicat softening point is less than about 93 °C and the melting point is less than about 121 °C. Suitable polymers are chosen from the following: ethylene vinyl acetate (EVA) such as resins commercially available under the tradename EL VAX from E.I. Du Pont de Nemours and Co. ("Du Pont"); acid-, anhydride- or acid/acrylate-modified EVA copolymers such as selected resins commercially available under the tradename BYNEL from Du Pont; acid- or anhydride-modified ethylene acrylate copolymers including selected BYNEL resins from Du Pont; ethylene-ethyl acrylate (EEA) copolymer such as DPDA resin from Union Carbide Chemicals and Plastics Company, Inc.; ethylene methyl acrylate (EMA) such as OPTEMA TC-120 resin from Exxon Chemical Co.; ethylene acrylic acid (EAA) such as PRIMACOR resin from Dow Chemical Co. or ADCOTE aqueous dispersion from Morton International; ionomer such as SURLYN ethylene methacrylic acid copolymer resin from Du Pont; polyester such as BOSTIK resin from Bostik, Inc.; and blends of the above-mentioned materials. Modified EVA resins from the BYNEL CXA Series 3000 from Du Pont are one preferred polymeric component for the image reception layer. Resins in this series contain an EVA base resin blended with polymers having acid and acrylate functionalities. The added chemical functionality of this series of BYNEL resins contributes to their excellent printability and ink adhesion characteristics. These resins are typically used in coextrusion processes as relatively thin adhesive tie layers sandwiched between thicker functional layers. Another preferred polymeric component for the image reception layer is the SURLYN series of ethylene methacrylic acid copolymer ionomer resins from Du Pont. The polymeric component can comprise 100% by weight of the image reception layer, or it can comprise some smaller amount. The quantity of polymeric component in the image reception layer is preferably maximized within the limits of performance requirements of the image receptor medium for the intended application. Routine efforts could be needed to optimize this quantity. The optimum quantity will depend upon the desired application, and the performance of the polymeric component could be affected by other additives in the image reception layer such as those described below. The image reception layer can contain other components such as pigments, fillers, ultraviolet (UV) absorbing agents and stabilizers, slip agents, antistatic agents and carrier resins for additive such as pigments, all of which are familiar to those skilled in the art. If image reception layer 64 is used with a substrate layer 68, image reception layer 64 is relatively thin as compared to substrate layer 68, and preferably has a thickness in the range from about 2.5 to about 127 microns (0.1 to 5 mils). If image reception layer 64 is not associated with a substrate layer 68, then image reception layer 64 may need to be thicker than the above-described range to provide the required durability and dimensional stability for the intended application. Optional Substrate Layer A substrate layer 68 can be included in the image receptor medium construction if, for example, an additional layer is required to provide sufficient durability and dimensional stability. The substrate layer is most commonly white and opaque for graphic display applications, but could also be transparent, colored opaque, or translucent. The substrate layer can comprise any polymeric material having desirable physical properties for the intended application. Properties of flexibility (or stiffness), durability, tear resistance, heat resistance, conformability to non-uniform surfaces, die cuttability, weatherability and elasticity are examples. For example, a graphic marking film used in short term outdoor promotional displays typically can withstand outdoor conditions for a period in the range from about 3 months to about one year and can exhibit tear resistance and durability for easy application and removal. The material for the substrate layer is preferably a resin capable of being extruded or coextruded into a substantially two-dimensional film. Examples of suitable materials include polyester, polyolefin, polyamide, polycarbonate, polystyrene, acrylic, polyurethane, and polyvinyl chloride. Preferably, the substrate layer comprises a nonplasticized polymer to avoid difficulties with plasticizer migration and staining. The substrate layer can also contain other components such as pigments, fillers, ultraviolet absorbing agents, slip agents, antiblock agents, antistatic agents, and processing aids familiar to those skilled in the art. A typical thickness of the substrate layer 10 is in the range from about 12.7 to about 254 μm (0.5 to 10 mils). However, the thickness can be outside this range so long as the resulting image receptor medium is not too thick to be fed into the image transfer device of choice. A useful thickness is generally determined based on the requirements of the intended application. Optional Prime Layer As illustrated in Figure 4, image receptor medium 70 includes an optional prime layer 69 located on the surface of the substrate layer 68 opposite the image reception layer 64. The prime layer serves to increase the bond strength between the substrate layer and an adhesive layer (not shown) if the bond is not sufficiently strong without the prime layer. The presence of an adhesive layer makes the image receptor medium useful as a graphic marking film. Although it is preferable to use a pressure sensitive adhesive, any adhesive that is particularly suited to the substrate layer and to the selected application can be used. Such adhesives are those known in the art and may include aggressively tacky adhesives, pressure sensitive adhesives, repositionable or positionable adhesives, hot melt adhesives, and the like. Such adhesives are commercially available from 3M. The adhesive layer is preferably covered with a release liner (not shown) that provides protection to the adhesive until the image receptor medium is ready to be applied to a surface. Prime layer 69 may also by itself serve as an adhesive layer in some applications. The prime layer preferably comprises an ethylene vinyl acetate resin containing from about 5 weight percent to about 28 weight percent vinyl acetate and a filler such as talc to provide a degree of surface roughness to the prime layer, helping to prevent blocking and promote adhesion of the adhesive. The filler is generally present in an amount in the range from about 2% to about 10% by weight. It is within the scope of this invention to include other layers in addition to the image reception layer 64, the optional substrate layer 68, and the optional prime layer 69. Additional layers can be useful for adding color, enhancing dimensional stability, promoting adhesion between dissimilar polymers in the above- described layers, and the like. After an image has been transferred to the image receptor medium, an optional protective overiaminate layer (not shown) can be adhered to the imaged surface. The overiaminate layer can protect the image receptor medium from the effects of ambient humidity and direct sunlight, as well as protecting the image from nicks, scratches, and splashes. In addition, the overiaminate layer can impart a desired finish to the image, such as high gloss or matte. Suitable overiaminate layers include any suitable transparent plastic sheet material bearing an adhesive on one surface. Use of such overiaminate layers is, for example, described in U.S. Patent No. 4,966,804. Image receptor media 60 and 70 can be made by a number of methods. Layer 64 and optional layers 68 and 69 can be simultaneously extruded using any suitable type of extrusion or coextrusion die and any suitable method of film making such as blown film extrusion or cast film extrusion. An adhesive layer can be coextruded with the other layers, transferred to the image receptor medium from a liner, or directly coated onto the image receptor medium in an additional process step. For the best performance in coextrusion, the polymeric materials for each layer are chosen to have similar properties such as melt viscosity. Techniques of coextrusion are found in many polymer processing references, including Progelhof, R.C., and J.L. Throne, "Polymer Engineering Principles", Hanser/Gardner Publications, Inc., Cincinnati, OH, 1993 Alternatively, one or more of the layers can be extruded as a separate sheet and the sheets laminated together to form the image receptor medium One or more of the layers can also be formed by coating an aqueous or solvent-based dispersion onto one or more previously extruded layers. This method is less desirable because of the extra process steps and the additional waste involved The finished image receptor medium can be subjected to a surface treatment method such as corona treatment to improve the ink and toner receptivity of the image reception layer for certain applications. The invention is further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. Example 1. Four samples of image receptor media each comprising a substrate layer and an image reception layer according to this invention were made as follows: For each of two samples, film was produced using a cast extrusion process. Resin pellets were fed to a 4.45 cm (1.75 in) Prodex single screw extruder with a temperature profile from 171 °C (340 °F) to 232 °C (450°F) with a melt temperature of 207 °C (405 °F). A drop die was used to cast the extrudate onto a polyethylene terephthalate (PET) base film approximately 30 cm (12 inches) wide and 0.05 mm (0.002 in) thick. The resulting film construction was run between a steel chill roll and a rubber backup roll to solidify the molten resin into a layer having a thickness of approximately 0.05 mm (0.002 in). Sample 1 A made by this method contained BYNEL CXA 3101 acid/acrylate-modified EVA resin from Du Pont with no further additives, while Sample IB contained only BYNEL CXA 1 123 acid-modified EVA resin, also from Du Pont. Both samples were corona treated using a handheld corona treating device Model #BD-20C manufactured by Electro- Technic Products, Inc. of Chicago, IL, USA. The final two samples (samples 1 C and ID), along with a comparative film sample (sample C-l), were made using a conventional blown film coextrusion process. Each of three extruders A, B, and C supplied a melt formulation to an annular die where the melts were combined to form a single molten stream consisting of three distinct layers in a sleeve shape. For each sample, the melt of extruder A formed the image reception layer, the melt of extruder B formed the substrate layer, and the melt of extruder C formed the prime layer. For comparative sample C-l , each layer comprised only LLDPE or a combination of LDPE and LLDPE as the polymeric components . The molten polymer sleeve was then blown to its final diameter and thickness by introducing air into the sleeve and trapping it between the die and nip rolls at the top of the blown film tower. The film sleeve was then slit into two flat film webs, each of which was corona treated on the image reception layer side and wound onto a core. The resulting samples each had a thickness of about 0.1 mm (0.004 in), although layer thickness distribution varied. The layer formulations and thicknesses are shown in the tables below. Layer Formulations AMPACET 10407 UV inhibitor 5 5 5 concentrate (Ampacet Corp., Tarrytown, NJ) AMPACET 19270 black color 5 3 concentrate (Ampacet Corp., Tarrytown, NJ) AMPACET 11976 Ti0 2 color 25 concentrate (Ampacet Corp., Tarrytown, NJ) " Layer Thicknesses Layer Sample IC Sample ID Sample C-l [% of total film [% of total film [% of total film thickness] thickness] thickness] Image reception layer 40 40 30 Substrate layer 45 45 40 Prime layer 15 15 30 All of the samples were evaluated for image transfer quality. To accomplish this a multicolored weather bar graphic was imaged on SCOTCHPRINT™ 8601 Transfer Media available from 3M in a SCOTCHPRINT™ 9512 electrostatic printer. The toned image on the transfer medium was then placed in contact with the image reception layer of the multilayered film and the two sheets were passed through a Pro-Tech Model EGS-692 hot roll laminator set at 96 °C (205 °F) and 441 kPa (64 psi). For each sample, the transfer rate was gradually increased until transfer quality became poor. The quality of the transferred image was visually rated as "poor", "fair", "good", or "excellent". Results are found in the table below. Sample aage Maximum . .. ra&sffer acceptable < aKty image transfer -rate [xn/mm ffltoDl 1A Good 3.7 (12) IB Good 3.7 (12) IC Good 2.6 (8.5) ID Good 3.1 (10) C-l Fair-Good 0 5 (1.5) Comparative sample C-l only exhibited acceptable image transfer quality at very low rates of transfer. It is important to note that Sample 1 D which contained not only BYNEL CXA 3101 modified EVA resin but about 13 % by weight of LDPE in the form of carrier resin provided good ink adhesion and image transfer quality This result is somewhat surprising because LDPE and LLDPE (exemplified by Sample C- 1 ) are poor ink receptors Example 2. Twelve samples of image receptor media were provided with an image according to this invention and evaluated for image transfer quality Each of the samples was a film between 25 and 254 microns thick made by standard extrusion methods and comprising a single image reception layer Evaluated for comparison were a film of LDPE and a commercially available image receptor film (SCOTCHPRINT™ CONTROLTAC™ marking film 8620 from 3M) Images were generated on SCOTCHPRINT™ 8601 transfer media in a SCOTCHPRINT™ 9512 electrostatic printer using standard SCOTCHPRINT™ toners All of these products are commercially available from 3M A toned image was then transferred to each film sample using a Pro-Tech Model EGS-692 hot roll laminator set at 96 °C (205 °F) and 441 kPa (64 psi) Transfers were run at rates of 0 6 and 3 1 meters per minute (m/min) (2 and 10 feet per minute (fpm)) The samples were evaluated for image transfer quality at both low and high transfer speeds using a visual standard method rating system (VSM). This method involves inspection of the transfer medium after transfer for remaining toner and inspection of the receptor medium for transfer image quality, uniformity of color and presence of defects. The media are compared to standard samples and given a number rating. A minimum rating of 8.5 is required for acceptable transfer, while a rating of 10.0 is considered perfect toner transfer. The lowest rating is 4.0. The polymers and corresponding results are summarized in the table below: All of the samples exhibited excellent transfer quality at 0.6 m/min, except comparison sample C-3 (LDPE). All samples except sample 2K showed significantly better transfer quality than comparison samples C-2 and C-3 at 3.1 m/min. Example 3. Two samples of image receptor media were evaluated for image transfer quality using the hot roll lamination technique with respect to lamination temperature, lamination pressure, transfer speed and image transfer media. The first sample was Sample ID film described in Example 1. The image reception layer comprised BYNEL CXA 3101 acid/acrylate-modified EVA resin from Du Pont and titanium dioxide (TiO 2 )-based white color concentrate containing 50% LDPE as a carrier resin to make the layer appear white. The prime layer comprised EL VAX 3135B EVA resin from Du Pont and a black color concentrate to make the layer appear black. A second film was made by extruding a 102 micron (4 mil) thick layer comprising SURLYN 1705 ethylene acid copolymer ionomer resin from Du Pont. The film was pigmented white with about 20 % by weight of a TiO - based color concentrate containing 8.55% by weight LDPE and contained an ultraviolet radiation stabilizer package similar to that recommended by the resin manufacturer and comprising a pair of ultraviolet radiation absorbers, a hindered amine light stabilizer, and an antioxidant. The film was corona discharge treated on one side. A 25.4 μ (1 mil) thick acrylic pressure sensitive adhesive layer was laminated to the corona treated surface using a pair of heated nip rolls, and a release liner was added to protect the adhesive layer. This film was designated as sample 3 A. Weather bar graphic images were formed in the same manner as described in Example 1 on SCOTCHPRINT™ 8601 and SCOTCHPRINT™ 8603 transfer media, both available from 3M. The images were transferred to samples ID and 3 A, along with a comparison sample of SCOTCHPRINT™ CONTROLTAC™ marking film 8620, using a hot roll laminator at combinations of high and low lamination temperatures (96 °C and 88 °C), high and low lamination pressures (441 kPa and 276 kPa) and high and low transfer speeds (1.5 m/min and 0.5 m/min). Image transfer quality was evaluated using the visual standard method rating system (VSM) of Example 2. Results are summarized in the table below. Sample Image l-amination Laminatio Transfer Transfer Tr nsfer Temperature Pressure Speed Quality Me ia [MPa(p*J)J (m/min fVSM] <foita)l Scotchprint™ Scotchprint™ 96 (205) 441 (64) 0.5 (1.5) 10 0 8620 8601 3A Scotchprint™ 96 (205) 441 (64) 1.5 (5.0) 10.0 8601 ID Scotchprint™ 96 (205) 441 (64) 1.5 (5 0) 9.5* 8601 ID Scotchprint™ 96 (205) 276 (40) 1.5 (5.0) 9.0* 8601 ID Scotchprint™ 88 (190) 441 (64) 1 5 (5.0) 8.5* 8601 ID Scotchprint™ 88 (190) 276 (40) 1.5 (5.0) 6 5* 8601 ID Scotchprint™ 96 (205) 441 (64) 0 5 (1 5) 30 0 8603 ID Scotchprint™ 96 (205) 441 (64) 1 5 (5.0) 7 0 8603 ID Scotchprint™ 96 (205) 276 (40) 1 5 (5 0) 6 5 8603 ID Scotchprint™ 88 (190) 441 (64) 1.5 (5.0) 7 0 8603 ID Scotchprint™ 88 (190) 276 (40) 1 5 (5 0) 8603 6 0 * Portions of image reception layer stuck to white, non-imaged areas of image transfer media Both samples ID and 3 A exhibited good transfer quality at the higher transfer speed when SCOTCHPRINT™ 8601 transfer media was used However, Sample ID (containing the BYNEL modified EVA resin) stuck to the white nontoned areas of the transfer media This result was surprising since sample 2E of Example 2 comprising a film of 100% BYNEL modified EVA resin received an image from SCOTCHPRINT™ 8601 transfer media without sticking It is thought that corona treatment of sample ID may have caused the sticking Example 4 Four samples of image receptor media were prepared by coating aqueous polymer dispersions on polymeric films to form an image reception layer. Each coating solution was prepared by adding butyl carbitol coating agent and two types of ultraviolet (UV) stabilizing agent to the aqueous polymer dispersion with stirring. Formulations are shown in the table below. Ingredient Solution #1 Solution #2 quantity [g] quantity [g] SURLYN ionomer dispersion 56220, 200 31% solids (Du Pont) ADCOTE 50T4983 ethylene acrylic acid 200 dispersion, 25% solids (Morton International) Butyl carbitol coating agent 10.7 10.65 TINUVIN 1 130 UV stabilizing agent 1.62 1.3 (Ciba-Geigy Corp.) TINUVIN 123 UV stabilizing agent 1.1 0.89 (Ciba Geigy Corp.) Each solution was coated onto a polyester substrate and a vinyl substrate using a knife bar coating method with the wet gap set at 3.0 mils. The coatings were each dried for 4 minutes at 93 °C (200 °F) to produce an image receptor medium comprising an image reception layer and a substrate layer. The samples were designated as 4 A - 4D. Each sample was provided with an image and evaluated for image transfer quality on SCOTCHPRINT™ 8601 transfer media as described in Example 1, with lamination speeds of 1.2, 2.1, 3.1, and 3.8 m/min. Results are summarized in the table below. Sample Image Sutøtrate Image nsf r quality at transfer speeds reception layer layer polymer 1.2 m/min 2.1 m/min 3.1 m/min 3.8 m/min (4 fpm) (7 fpm) (10 fpm) (12.5 fpm) 4A Ionomer polyester 9.5 7.0 6.0 4B EAA polyester 9.5* 9.0* 8.0* — 4C Ionomer vinyl ~ 9.5 9.0 8.0 4D EAA vinyl ~ 9.5* 9 0* 8.5* * Portions of image reception layer stuck to white, non-toned areas of transfer media All samples exhibited good transfer quality, especially on the softer vinyl substrate. Samples 4B and 4D (containing EAA) did stick to the white non-toned areas of the image transfer media It is important to note that both samples 4 A and 4B (having the harder polyester substrate) exhibited good toner receptivity at transfer rates of up to 2.1 m/min, even though it has been previously believed that a soft conformable film was needed to receive toned images Comparative Example 5. For comparison to the above examples, samples of commercially available multilayered coextruded adhesive-backed label films were evaluated for ink adhesion and image transfer quality. The samples included FASCLEAR and PRIMAX label films from Avery International Corporation of Pasadena, CA. Pieces of each film were mounted onto 30 cm x 30 cm sheets of 3M SCOTCHCAL™ 180- 10 graphic marking film for evaluation. Each of the label film samples was evaluated for image transfer quality. Multicolored weather bar graphics were printed on SCOTCHPRINT™ 8601 transfer media from 3M in a SCOTCHPRINT™ 9512 electrostatic printer. The toned images were then transferred to the sample films using a Pro-Tech Model EGS-692 hot roll laminator set at 96° C and 441 kPa (64 psi) An image was transferred to each sample at both 0.5 m/min (1.5 fpm) and 1.2 m/min (4 fpm). The imaged samples were examined for image transfer quality using visual standard method (VSM) ratings. All of the samples were then evaluated using a Crosshatch adhesion test as follows. Each sample was scribed with ten parallel lines spaced about 1.6 mm (1/16 in) apart using the corner of a sharp razor blade. The scribed lines cut through the toner layer only and not the base film. Another set of similar lines was scribed through the toner at right angles to the first set resulting in a Crosshatch pattern. A 2.5 cm x 10.2 cm (1 in x 4 in) piece of 3M SCOTCH tape #610 was then applied over the Crosshatch pattern and wiped with two firm application strokes using a 3M PA-1 applicator squeegee. The tape was pulled off using a sharp jerk and the crosshatched sample was observed for toner removal. Results are shown below. Test PRIMAX FASCLEAR label film label Ωlm Image transfer quality at 0.5 m/min < 4.0 9.5 Image transfer quality at 1.2 m/min < 4.0 < 4.0 Toner adhesion at 0.5 m/min no removal no removal Toner adhesion at 1.2 m/min some removal no removal The PRIMAX film showed poor image transfer quality at both speeds (worse than the lowest possible rating). The FASCLEAR film showed good image transfer quality at the slower transfer rate, but poor image transfer quality at the faster transfer rate. By comparison, films described in the previous examples exhibited acceptable image transfer quality at transfer rates of up to 3.8 m/min (12.5 fpm). The invention is not limited by the embodiments just described. The claims follow.

Claims: Claims 1. A method of providing an image on an image receptor medium, comprising the steps of: (a) forming an image on an image transfer medium; (b) transferring the image of step (a) on to an image receptor medium, the image receptor medium comprising an image reception layer having two opposing major surfaces, wherein a first major surface is a surface for receiving images, said image reception layer comprising a polymeric component including one or more polymers, each polymer having a Vicat softening point and a melting point sufficiently higher than room temperature to avoid tackiness and handling difficulties. 2. The method of claim 1, wherein each polymer in the image reception layer has a Vicat softening point of less than about 100 °C and a melting point of less than about 150 °C. 3. The method of either of claims 1 or 2, wherein the polymeric component of the image reception layer is selected from the group consisting of ethylene vinyl acetate, acid-modified ethylene vinyl acetate, acid/acrylate-modified ethylene vinyl acetate, anhydride-modified ethylene vinyl acetate, acid-modified ethylene acrylate, anhydride-modified ethylene acrylate, ethylene ethyl acrylate, ethylene methyl acrylate, ethylene acrylic acid, ionomer, polyester, and combinations thereof. 4. The method of any of claims 1-3, wherein the polymeric component of the image reception layer is acid/acrylate-modified ethylene vinyl acetate or ethylene methacrylic acid copolymer ionomer. 5. The method of any of claims 1-4, wherein the image receptor medium further comprises a polymer substrate layer on a second major surface of the image reception layer opposite the image reception surface, the substrate layer having an outer surface. 6. The method of claim 5, wherein the image receptor medium further comprises a prime layer on the outer surface of the substrate layer, the prime layer having an outer surface. 7. The method of claim 6, wherein the image receptor medium further comprises an adhesive layer on the outer surface of the prime layer. 8. An image receptor medium obtainable from the method of any of claims 1-7.

Inventors: ADEN STEPHEN J, AUSTIN STEVEN R, EMSLANDER JEFFREY O, ADEN, STEPHEN, J., AUSTIN, STEVEN, R., EMSLANDER, JEFFREY, O.
Applicants: MINNESOTA MINING AND MAUFACTUR, MINNESOTA MINING AND MAUFACTURING COMPANY
Application year: 1996
Main classification: G03G7
IPC codes: B41M5, B44C1, G03G7