Latent image receiving sheet and microcapsules for use therein

Abstract: A latent image receiving sheet comprises a substrate bearing microcapsules having walls of a nonmeltable polymer which is a thermosetting aminoplast resin. The walls of the microcapsules have an elongation less than 1%, and the image receiving sheet and microcapsules are resistant to heat. Surprisingly, the latent image receiving sheet capsules nonetheless rupture upon application to the record material of a point source energy input or pulse comprising a ΔT of at least 115°C per one millisecond. The latent image receiving sheet may be an ink transfer sheet or print plate, a gravure sheet, a cryptic message receiving sheet or an imageable sheet.

Description: This invention relates to record material in the form of a latent image receiving sheet. Record material systems are well known in the art and are described in many patents, for example, U.S. Patent Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748; 4,181,771; 4,246,318; and 4,470,057 to which reference can be made for detailed information. In thermally responsive systems, basic chromogenic material and acidic color developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a colored mark. U.S. Patent No. 4,529,681 discloses a light- and heat-sensitive record material relying on use of permeable capsules relying on heat to effect coloring component permeation through the thermoplastic capsule wall. US-A-4873168 discloses heat treatment of an imaging sheet carrying a coating of microcapsules containing a radiation curable composition and an associated image-forming agent. Imaging is accomplished not by heating but by subjecting the microcapsules to a uniform rupturing force after they have been image-wise exposed to actinic radiation. US-A-4682194 discloses a heat-sensitive recording material incorporating microcapsules having a glass transition point of from 60 to 200°C. It is an object of the present invention to provide a novel latent image receiving sheet utilizing non-meltable microcapsules. According to the present invention, there is provided a latent image receiving sheet, comprising a substrate carrying microcapsules containing a core material, characterized in that: (a) the microcapsule walls are of a nonmeltable polymer having an elongation of not more than 1% and are produced by in situ polymerization in an aqueous manufacturing vehicle of resins selected from melamine and formaldehyde, methylol melamine, or methylated methylol melamine, wherein the polymerization is conducted at a temperature of at least 65°C, preferably about 75°C; (b) said microcapsules are resistant to heat as measured by not becoming substantially permeable when placed in a 150°C oven for one minute; (c) said microcapsules are however rupturable upon application thereto of a point source energy input comprising ΔT of at least 115°C per one millisecond, preferably at least 145°C per one millisecond; with the proviso that the latent image receiving sheet does not carry complementary mutually reactive imaging reagents on the same surface of the sheet. The invention also extends to the use of the latent image receiving sheet in a thermal imaging process, and to the latent imaging process itself. The latent image receiving sheet can take the form of a variety of useful products including: a) an ink transfer sheet or print plate. In this embodiment, the microcapsules contain a dye, ink, pigment, or dye precursor. The latent image is recorded by means of application of a point source energy input or pulse comprising a ΔT of at least 115°C per one millisecond. The sheet is then pressed against a second sheet resulting in transfer of a visible image corresponding to the capsules on the latent image sheet which had been ruptured by the point source energy pulse. Sublimable dyes can be used in a variation and the latent image transferred after capsule rupture by heating the latent image sheet to effect transfer of dyes to a second sheet. b) a low cost gravure type of sheet. In this embodiment, the microcapsules contain a low boiling or a high vapor pressure solvent, or a gas. The latent image receiving sheet when exposed to a point source energy input or pulse comprising a ΔT of a least 115°C per one millisecond results in a sheet with a selected field of ruptured capsules. The ruptured capsules define the latent image. Over time the contents of the ruptured capsules evaporate, leaving a low cost gravure type of sheet. An ink can be squeegeed over the sheet to fill the voids created by the ruptured capsules. A second sheet can then be pressed against the latent image receiving sheet to effect transfer of an image corresponding to the ruptured capsules. c) a cryptic message receiving sheet. In this embodiment, the microcapsules, similar to b) above, contain a low boiling or high vapor pressure solvent, or a gas. The latent image receiving sheet when exposed to a point source energy input or pulse comprising a ΔT of at least 115°C per one millisecond results in a sheet with a selected field of ruptured capsules. As in b) above, this selected field constitutes a latent image in that selection can be in a predetermined pattern. The image can be developed by application of tone fine particles, such as xerographic toners, onto the sheet. These will preferentially adhere to the ruptured capsule sites. d) an imageable sheet. In this embodiment, the microcapsules contain one of either a chromogen or developer. The latent image receiving sheet when exposed to a point source energy input or pulse comprising ΔT of at least 115°C per one millisecond results in a sheet with a selected field or pattern of ruptured capsules. The ruptured capsules define a latent image. The image can be made visible by application to the latent image receiving sheet of a solvent or dispersion containing the second component of chromogen or developer, whichever was omitted from the capsule contents. The invention will now be more fully described with a particular focus on the capsules used. The latent image receiving sheet of the invention comprises a substrate bearing microcapsules having walls selected from non-meltable or thermoset resin. The walls of the microcapsules are selected to have an elongation not more than 1%. Surprisingly, the non-meltable walls of the microcapsules rupture upon application thereto of a point source energy input comprising a ΔT of at least 115°C per one millisecond. The latent image receiving sheet has adhered microcapsules having walls of thermosetting or non-meltable resin with critically an elongation of not more than 1%. The thermosetting resin is selected from methylated methylol melamine, or selected from combinations of melamine and formaldehyde, or methylol melamine polymerized at a temperature of at least 65°C, preferably about 75°C. The microcapsule walls are non-meltable. Exposure of the latent image receiving sheet to a point source energy input comprising a ΔT ("change in temperature") of at least 115°C per one millisecond ruptures the capsules and this is theorized to occur due to induced or produced stresses. The microcapsules can contain any core material conventionally used in microencapsulation. These can include various combinations of a solvent, a hydrophobic or hydrophillic material, liquid preferably hydrophobic liquid, gas, developer or chromogen, inks, dyes, toners, or pigments. The novel sheet with microcapsules of the invention has a variety of new uses. Upon exposure of the sheet with microcapsules to a point source energy input comprising a ΔT ("change in temperature") of at least 115°C per one millisecond, the microcapsules rupture. Though the microcapsule and sheet material characteristics are described in terms of a point source energy input such as a thermal print head, it is readily apparent and understood that such record material or image receiving sheet can be imaged with a larger input device such as a rapidly heating block or multiplicity of thermal print heads assembled as a larger unit. Point sources for purposes of the invention can take the form of a thermal print head, laser, focussed hot jets, heated stylus and the like. The ability to effect a change in temperature of at least 115°C per one millisecond at the receiving sheet's surface is needed to effect the unusual shattering of the non-meltable capsules of the invention. Shattering is believed attributable to induced or produced thermal stresses though the invention disclosed herein should not be construed as limited to this one underlying theory, as other mechanisms may also be operating. Upon application of the appropriate ΔT to the sheet in a selective pattern, a latent image is recorded on the sheet by virtue of rupture of the microcapsules, which one can think of in terms of an assembly of sealed bottles, some of which, however, are selectively shattered so that they have open tops, thus becoming open containers. An appropriate developer material can be applied across the surface of the sheet by conventional applicator means such as sponging, spraying, cotton swab or other applicator to develop the image. Alternatively, if a hydrophobic material is placed in the capsule, a hydrophobic ink or dye applied across the surface of the sheet will, preferentially, adhere to the hydrophobic material resulting in an image. The capsules of the latent image receiving sheet, unlike the prior art, do not melt or become porous, but rather fracture from the rapid change in temperature or energy input. If the microcapsules are constructed such as to encapsulate a hydrophobic material, then after recording a latent image on the receiving sheet with a thermal print head, a hydrophobic ink can be applied across the surface of the sheet, and it will preferentially occupy the capsules with shattered tops exposing hydrophobic material when the freely applied hydrophobic ink is squeegeed or wiped away from the surface of the sheet. Conversely, hydrophillic materials can be encapsulated for use with hydrophillic inks. The result is a low-cost gravure type of print plate or transfer sheet. Alternatively, ink or dye can be encapsulated in the capsules to also create a similar transfer sheet. If use as a print plate is contemplated, then the substrate is typically selected of more rigid stock or even synthetic material for better durability. The latent image receiving sheet can be used as optical recording medium, such as for recording of digitized information by laser or thermal print head. The latent image receiving sheet also finds use for transfer of information in latent form. Being created by a thermal print head, transmission of cryptic messages is made possible. The latent image can be subsequently developed as herein earlier described. The capsules of the receiving sheet, unlike the prior art, do not melt or become porous upon energy input, but rather fracture from the rapid change in temperature or energy input such as an energy pulse. Exposure of the receiving sheet to an energy input, such as with a thermal print head, or other source capable of generating the appropriate ΔT shatters the microcapsules and encodes the latent image. The capsules of the latent image receiving sheet, unlike the prior art, do not melt upon energy input, but rather appear to rupture from rapid change in temperature or energy input. Significantly this gives rise to a novel material which is heat resistant. Surprisingly the latent image receiving sheet of the invention can be placed in a hot oven (150°C) for substantial time periods such as one minute and the capsules do not become permeable. Conventional thermal paper by contrast images in an oven almost instantaneously. The insulating characteristics of the wall material and the absence of heat dissipation via phase change appears to lead to a high concentration of energy at the contact area between the point source and the capsule. The elongation value for the wall material of the microcapsules can be taken from tables for various resins. The published values correlated well with the observed phenomena and provide a convenient means to select appropriate resins. Resins having elongation values of not more than 1% selected to be used as wall material result in microcapsules with nonmeltable polymeric shells or wall material displaying the unusual characteristics of shattering attributable to induced thermal stresses. Table 1 summarizes elongation values for a variety of resin materials. Resin Elongation (%) acetal 60-75 acrylic 20-50 cellulose 5-100 fluorcarb 80-400 ionomers 100-600 polyamides 25-300 polycarbonates 60-100 polyethylenes 5-900 polypropylenes 3-700 polystyrenes 1-140 vinyls 2-400 epoxies 1-70 phenolics 1-2 phenol formaldehyde 0.4-2 melamine formaldehyde 0.6-1.0 polyester 40-300 polyester alkyd 0.5-2 silicone 100 urea formaldehyde 0.5 urethane 300-1000 nylon 300 The elongation of the polymeric shells or wall is determined for purposes of the invention, from the elongation (%) value of the bulk resins when polymerized and using standards tests such as ASTM test method D638. More conveniently, tables of elongation (%) values for a variety of resins are available from a variety of sources including pages 532 to 537 of Principles of Polymer Systems , 2nd Edition by Ferdinand Rodriguez of Cornell University, published by Hemisphere Publishing Corporation (1970). The elongation values for the bulk material correlated well as a surprising predictor of resins functional in the invention. Instead of melting, becoming plasticized with other melted materials, or increasing in permeability due to a phase transformation, the wall of the capsules of the invention appears to rupture. Failure of the capsule wall appears attributed to a high temperature gradient and nonsteady state of heat transfer. Such conditions create localized thermal stresses. The magnitude of the stress depends on the properties of the material. A brittle wall can sustain less strain and thus ruptures. Elongation properties appear to correlate well with wall brittleness and facilitate selection of resin. The capsules of the invention surprisingly fracture upon application of a point source energy input comprising a change in temperature (ΔT) of at least 115°C per one millisecond. ΔT can be calculated according to the formula S = E α (T- To) S refers to stress E is modulus of elasticity α is coefficient of linear thermal expansion ΔT is T-To in the above formula. S which is stress ranges for melamine formaldehyde polymers from 5x10 3 psi to 13x10 3 psi and for phenol formaldehyde polymers ranges from about 5x10 3 psi to about 9x10 3 psi. To calculate the lower practical point source energy input S is taken as (5x10 3 ) psi. The modulus of elasticity ranges from about (11x10 5 ) to (14x10 5 ) psi. On the lower range thus, E is taken as 11x10 5 . The coefficient of linear thermal expansion is (4x10 -5 )°C. Therefore, 5x10 3 = (11x10 5 ) (4x10 -5 ) (T-To) (T-To) = ΔT = 113.6° or about 115°C per one millisecond. By this method the calculated threshold ΔT is about 115°C. A second method of arriving at ΔT is by way of the data derived from Example 1. Example 1 demonstrates that the temperature at the record system surface when using a conventional fax such as a Canon Fax 230 is greater than 170°C. This is the temperature that the surface of the paper or media sees. The temperature of the thermal print head is higher, but the temperature observed at the surface of the media is alone relevant as regards the thermal stresses to which the capsules on the surface of the paper are subjected. Room temperature is approximately 25°C and thus should be substracted from the temperature measured, 170°C - 25°C = 145°C. Based on the quantity of dye present, ΔT to effect fracture was calculated as approximately at least 115°C per one millisecond but preferably 145°C per one millisecond. Since the capsules are nonmeltable or thermoset in character, there is no latent heat capacity and substantially no phase change. In the examples, the latent image receiving sheet when subjected to a thermal print head, resulted in ruptured capsules observed with a scanning electon microscope. The capsule core material can include inks, dyes, toners, chromogens, solvents, gases, liquids, and pigments. The capsule core material is relatively independently selected. The core can be any material which is substantially water insoluble. Extensive lists of other core materials are listed in U.S. Patent 4,001,140. The core material can be any material dispersible in water and wrappable by the wall material. This can include air. As a more specific description of a useful core material, an imaging material such as chromogen, dye, toner, or pigment and the like can be prepositioned in the microcapsules as the core material. The core can be selected to be colorless electron donating compounds, dye precursor or chromogens which form color by reacting with a developer material. Representative examples of such compounds include substantially colorless compounds having a lactone, a lactam, a sulfone, a spiropyran, an ester or an amido structure in their partial skeleton such as triarylmethane compounds, bisphenylmethane compounds, xanthene compounds, fluorans, thiazine compounds, spiropyran compounds and the like. Eligible electron donating dye precursors which are chromogenic compounds, such as the phthalide, leucauramine and fluoran compounds, for use in the color-forming system are well known. Examples of the chromogens include Crystal Violet Lactone (3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide. U.S. Patent No. Re. 23,024); phenyl-, indol-, pyrrol-, and carbazol-substituted phthalides (for example, in U.S. Patent Nos. 3,491,111: 3,491,112; 3,491,116; 3,509,174); nitro-, amino-, amido-, sulfon amido-, aminobenzylidene-, halo-, anilino-substituted fluorans (for example, in U.S. Patent Nos. 3,624,107, 3,627,787, 3,641,011; 3,642,828; 3,681,390); spiro- dipyrans (U.S. Patent No. 3,971,808); and pyridine and pyrazine compounds (for example, in U.S. Patent Nos. 3,775,424 3,971,808); and pyridine and pyrazine compounds (for example, in U.S. Patent Nos. 3,775,424 and 3,853,869). Other specifically eligible chromogenic compounds, not limiting the invention in any way, are: 3-diethylamino-6-methyl-7-anilino-fluoran (U.S. Patent No. 3,681,390); 2-anilino-3-methyl-6-dibutylamino-fluoran (U.S. Patent 4,510,513) also known as 3-dibutylamino-6-methyl-7-anilino-fluoran; 3-dibutylamino-7-(2-chloroanilino) fluoran; 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-3-5'6-tris(di-methylamino)spiro[9H-fluorene-9'1(3'H)-isobenzofuran]-3'-one; 7-(1-ethyl-2-methylindol-3-yl)-7-(4-diethylamino-2-ethoxyphenyl)-5,7-dihydrofuro[3,4-b]pyridin-5-one(U.S. Patent No. 4,246,318); 3-diethylamino-7-(2-chloroanilino)fluoran (U.S. Patent No. 3,920,510); 3-(N-methylcyclohexylamino)-6-methyl-7-anilino-fluoran (U.S. Patent No. 3,959,571); 7-(1-octyl-2-methylindol-3-yl)-7-(4-diethylamino-2-ethoxyphenyl) -5,7-dihydrofuro[3,4-b] pyridin-5-one; 3-diethylamino-7, 8-benzofluoran; 3, 3-bis(1-ethyl-2-methylindol-3-yl) phthalide; 3-diethylamino-7-anilinofluoran; 3-diethylamino-7-benzylamino-fluoran; 3'-phenyl-7-dibenzylamino-2,2'-spiro-di-[2H-1-benzo-pyran] and mixtures of any of the following. Solvents such as the following can optionally be included in the microcapsules: 1. Dialkyl phthalates in which the alkyl groups thereof have from 4 to 13 carbon atoms, e.g., dibutyl phthalate, dioctylphthalate, dinonyl phthalate and ditridecyl phthalate 2. 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (U.S. Patent No. 4,027,065) 3. ethyldiphenylmethane (U.S. Patent No. 3,996,405) 4. alkyl biphenyls such as monoisopropylbiphenyl (U.S. Patent No. 3,627,581) 5. C 10 -C 14 alkyl benzenes such as dodecyl benzene 6. diaryl ethers, di(aralkyl)ethers and aryl aralkyl ethers, ethers such as diphenyl ether, dibenzyl ether and phenyl benzyl ether 7. liquid higher dialkyl ethers (having at least 8 carbon atoms) 8. liquid higher alkyl ketones (having at least 9 carbon atoms) 9. alkyl or aralkyl benzoates, e.g., benzyl benzoate 10. alkylated naphthalenes 11. partially hydrogenated terphenyls The solvent, if included, can be selected to facilitate dissolving the dye mixture, if included. If the capsules include chromogens, the latent image of the receiving sheet can be made visible by various conventional acidic developer materials preferably as dispersions or solutions applied to the latent image receiving sheet following application of the latent image. Other variations can include prepositioning the acidic developer material in substantially contiguous relationship to the chromogen material. Developer can be positioned in the capsules and chromogen applied following rupture, or alternatively, chromogen can be positioned in the capsules. Examples of eligible acidic developer material include: clays, treated clays (U.S. Patent Nos. 3,622,364 and 3,753,761); aromatic carboxylic acids such as salicylic acid; derivatives of aromatic carboxylic acids and metal salts thereof (U.S. Patent No, 4,022,936); phenolic developers (U.S. Patent Nos. 3,244,550 and 4,573,063); acidic polymeric material such as phenol-formaldehyde polymers, etc. (U.S. Patent Nos. 3,455,721 and 3,672,935); and metal-modified phenolic resins (U.S. Patent Nos. 3,732,120; 3,737,410; 4,165,102; 4,165,103; 4,166,644 and 4,188,456). Processes of microencapsulation are now well known in the art. U.S. Patent No. 4,100,103 describes a method for capsule formation involving reaction between melamine and formaldehyde; British Patent No. 2,062,750 describing a process for producing microcapsules having walls produced by polymerization of melamine and formaldehyde in the presence of a styrenesulfonic acid. The process of U.S. Patent No 4,552,811 is preferred. Reference can be made to these patents for further details. The latent image receiving sheet includes a substrate or support material which is in sheet form. For purposes of this invention, sheets can be referred to as support members and are understood to also mean webs, rolls, ribbons, tapes, belts, films, cards and the like. Sheets denote articles having two large surface dimensions and a comparatively small thickness dimension. The substrate or support material can be opaque, transparent or translucent and could, itself, be colored or not. The material can be fibrous including, for example, paper and filamentous synthetic materials. It can be a film including, for example, cellophane and synthetic polymeric sheets cast, extruded or otherwise formed. Binder material can be included to assist adherence of the capsules to the substrate and can include materials such as polyvinyl alcohol, hydroxy ethylcellulose, methylcellulose, methyl-hydroxypropylcellulose, starch, modified starches, gelatin and the like. Latex such as polyacrylate, styrene-butadiene, rubber latex, polyvinylacetate and polystyrene can also be advantageously used. The examples which follow are given to illustrate the invention and should not be considered as limiting. In the examples all parts or proportions are by weight and all measurements are in the metric system, unless otherwise stated. EXAMPLE 1 Ascertaining Media Surface Temperature Using Fax Machine Coatings of color former dispersion were prepared on a thin translucent paper substrate. Segments of the coatings were taped to a sheet of bond paper and used as the copy sheet in a Canon Fax-230. Melting was readily evident as clear (amorphous) characters on a relatively opaque background. Using this technique, the temperature at the surface of the media or sample was determined to be at least above 170°C with a Canon Fax-230. Color Former Melting Temp. Melt in Fax? diButyl N102 ∼ 170°C Yes PSD-150 ∼ 200°C No Green 118 ∼ 230°C No EXAMPLE 2 Microcapsule Preparation Internal Phase (IP) 20 g N102 180 g Trimethylolpropane triacrylate (TMPTA) monomer 2 g 2-Isopropyl Thioxanthone Photo Initiator 2 g Ethyl-4-Dimethylamino benzoate Photo Initiator 24 g 2,2-Dimethoxy-2-phenyl acetophenone Photo Initiator Combine the first two components and dissolve with heat, then dissolve the photo initiators. External Phase (EP) 25 g Colloid 351 (∼25% solids) acrylate) Acrylic polymer, Rhone-Poulenc (butyl 198 g Water Adjust pH to 5.0 using 20% NaOH. Emulsification Place 170 g of EP in blender and with mild agitation add the IP solution. Increase the blender speed to achieve desired drop size (eg., 50% of volume approximately 4.0µ) measured by Microtrac particle size analyzer from Leeds and Northrup Instruments, North Wales, PA 19454. Encapsulation Combine the following: 25 g Colloid 351 (∼25% Solids) 42 g Water pH adjusted to 4.8 with 20% NaOH 30 g Cymel 385 (∼80% solids) Add 70 g of the above to the emulsion and transfer to a vessel in a water bath. With stirring, heat the emulsion to 65°C and allow to process several hours for encapsulation to occur. Coating Combine equal weight parts of: 1. Finished capsule dispersion 2. 10% aqueous solution of Airvol 103 This mixture is applied to paper or other desired substrate using, for example, a fixed gap applicator set at 2.54 x 10 -5 m (0.001 inch). The resultant dried coating can be used to make a latent copy in a thermal printer such as a commercial facsimile machine. The latent image copy can be developed by contacting with or applying on an appropriate developer for the N102 color former. A typical example would be a 20% solution of Durez #27691 (p-phenylphenol formaldehyde resin) in xylene. The resin can also be applied in aqueous dispersion or emulsion form and then heated to promote the development of the black copy. If desired, the resultant copy may be "fixed" or deactivated to thermal and/or pressure response by exposing to U.V. to polymerize the components. Approximately 5 second exposure to 15 Watt GE Bulbs (F15T8-BLB) is sufficient to "fix" the copy. After fixing, the sheet is resistant to scuff or abrasive induced markings. Because of the reactive nature of the coating prior to fixing, the coating can suffer handling damage. This damage can be reduced by applying an overcoat that does not interfere with the thermal imaging nor with the subsequent fixing exposure. A typical overcoat would be the application of a 10% aqueous solution of Airvol 540 using a #3 wire wound rod. The photoinitiators can be omitted in the capsules of the latent image receiving sheet. Chromogen can be optionally included or excluded as desired. EXAMPLE 3 DRY DEVELOPMENT a. Two sheets were prepared: microcapsule formulation of Example 2 was coated on one sheet color developer formulation was coated on another. b. The capsule containing sheet was imaged with a thermal print head. c. The imaged capsule sheet was coupled face-to-face with a color developer sheet. The developer sheet is a sheet coated with a phenolic resin dispersion Durez 32421 phenolic resin dispersion (∼ 50% solids) benzoic acid, 2-hydroxy polymer, with formaldehyde, nonylphenol and zinc oxide. Both sheets coupled together were sent between two fusing rolls heated to 110°C. d. The substrate of the color developer sheet was peeled off. It revealed a fully developed image remaining on the imaging sheet. EXAMPLE 4 INTERNAL PHASE (IP) 160 g TMPTA 40 g Durez 27691 (p-phenylphenol formaldehyde resin) 12 g 2,2-dimethoxy-2-phenylacetophenone (photoinitiator) With heating, dissolve the resin in the TMPTA, then add the photoinitiator and dissolve. This IP was encapsulated as in Example 2 and resultant capsule dispersion coated and top coated. The coated media was run through a commercial facsimile to produce an image. This image was developed by application of a commercial toner such as Minolta MT Toner II. The black toner particles selectively adhere to the image-wise broken capsules. Toner in the background was removed by gentle brushing, etc. The toner is fused by heating in an oven or on a heated drum or the like. EXAMPLE 5 Same as Example 4, but imaging with FAX and toner application steps were repeated to add second color. Multicolor images can be obtained using repetition of the process. EXAMPLE 6 PLAIN PAPER/TRANSFER IMAGE a. Plastic sheet imaged with toner (as in Example 3 or 4) was coupled with bond paper, and both sheets were sent together between two fusing rolls heated to 90°C. b. Plastic sheet was removed. c. Transfer image was obtained on plain paper. EXAMPLE 7 IMAGING WITH TONERS a. Melamine formaldehyde (MF) microcapsules containing sec-butyl biphenyl solvent (SureSol 290) only were prepared according to the invention. b. Imaging sheet was made by coating microcapsules on a plastic sheet and applying PVA overcoat. c. Latent image was produced using Canon 230 FAX machine in a copy mode. d. Portion of the sample was placed into a container with a commercial toner (electrostatic copier toner). e. The container was tightly closed and shaked to deposit toner on the sample surface. f. After excess toner was removed from sample using brush, red image on white background was obtained. EXAMPLE 8 IMAGING WITH THERMAL TRANSFER RIBBON a. Microcapsule latent imaging sheet, which did not contain dye, or color developer was used. b. A latent image was recorded onto the sheet using a Canon 230 facsimile machine. c. The imaged sheet with selectively broken capsules or latent image was brought into the contact with the coated side of a thermal transfer ribbon and sent through heated fusing rolls. d. When plastic of thermal transfer ribbon was removed, a colored image on the microcapsule imaging sheet was obtained. EXAMPLE 9 TRANSFER SHEETS a. A latent image was recorded onto a sheet containing empty or solvent - only microcapsules using a Canon 230 facsimile machine. b. Blue color ink was evenly distributed on the surface of the above sheet. c. The excess ink was removed by pressing inked imaging sheet against smooth clay coated paper. d. Inked surface of above sheet was positioned on top of plain paper sheet and sent through a steel pressure rolls nip. (Applied pressure = 170 pli). Blue high contrast print was obtained on paper. pli = pounds per lineal inch. e. In a variation, black commercial printing press ink was used. Excess ink was removed from the sample using blade-like tool. After the transfer to paper, black print on clean white background was obtained. EXAMPLE 10 TRANSFER SHEET Internal Phase (IP) 180 g trimethylolpropanetriacrylate (TMPTA) monomer 20 g 1,3,3-trimethylindolino-6'chloro-8'methoxybenzopyrylospiran 12 g 2,2-dimethoxy-2-phenylacetophenone (photoinitiator) Combine components and dissolve with heat. This IP was encapsulated as in Example 1 and resultant capsule dispersion applied to suitable substrate using a #12 wire wound rod. The coating was dried and top coated with a 10% aqueous solution of Airvol 540 using a #3 wire wound rod. The coated media was run through a commercial facsimile to produce a master image. When the master image was heated in contact with a developer sheet, a copy was obtained due to sublimation of the spiran from the image-wise broken capsules. The imaged master could be used multiple times to make additional copies. Imaged copies are obtained on a commercially available carbonless CF sheet such as comprised of a p-phenylphenol formaldehyde type resin.

Claims: A latent image receiving sheet, comprising a substrate carrying microcapsules containing a core material, characterized in that: (a) the microcapsule walls are of a nonmeltable polymer having an elongation of not more than 1% and are produced by in situ polymerization in an aqueous manufacturing vehicle of resins selected from melamine and formaldehyde, methylol melamine, or methylated methylol melamine, wherein the polymerization is conducted at a temperature of at least 65°C, preferably about 75°C; (b) said microcapsules are resistant to heat as measured by not becoming substantially permeable when placed in a 150°C oven for one minute; (c) said microcapsules are however rupturable upon application thereto of a point source energy input comprising ΔT of at least 115°C per one millisecond, preferably at least 145°C per one millisecond; with the proviso that the latent image receiving sheet does not carry complementary mutually reactive imaging reagents on the same surface of the sheet. A latent image receiving sheet according to claim 1, wherein the core material comprises an ink, dye, toner, chromogen, solvent, gas, hydrophobic liquid or pigment. A latent image receiving sheet according to claim 1 or claim 2, wherein the sheet is an ink transfer sheet or print plate. A latent image receiving sheet according to claim 1 or claim 2 wherein the sheet is a gravure sheet. A latent image receiving sheet according to claim 1 or claim 2 wherein the sheet is a cryptic message-receiving sheet. A latent image receiving sheet according to claim 1 or claim 2 wherein the sheet is an imageable sheet. A process for producing a latent image on a latent image receiving sheet according to any preceding claim, comprising the step of selectively applying a point source energy input comprising ΔT of at least 115°C per one millisecond to the sheet, preferably at least 145°C per one millisecond. Use of a latent image receiving sheet according to claim 1 in a thermal imaging process in which a latent image is produced by selective application of a point source energy input comprising ΔT of at least 115°C per one millisecond to the sheet, preferably at least 145°C per one millisecond.

Inventors: BROWN ROBERT W, FELDMAN LUCY, MILLER ROBERT E, SCHLEICHER LOWELL, BROWN, ROBERT W., FELDMAN, LUCY, MILLER, ROBERT E., SCHLEICHER, LOWELL
Applicants: APPLETON PAPER INC, APPLETON PAPERS INC.
Application year: 1993
Main classification: B41M5
IPC codes: B41M5, B01J13, B41C1, G03F7, B41M1