Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/41—Base layers supports or substrates

Definitions

• the present invention relates to heat-sensitive recording paper, in particular, one having fast thermal response and which will cause reduced transfer of tailings to the thermal head.
• heat-sensitive recording paper Because of simplicity in the mechanism of color image formation by heating and the relative compactness of the recording apparatus with which it is used, heat-sensitive recording paper has been used extensively in various applications. As the use of heat-sensitive recording paper is expanding, the demand for reduced transfer of tailings to the thermal head and for higher sensitivity is also becoming more strict.
• Conventional heat-sensitive recording paper has clay, talc and calcium carbonate incorporated in substrate paper.
• the substrate paper is weak in its ability to absorb the components of the heat-sensitive layer that melt upon heating and its capability of suppressing the transfer of tailings to the thermal head is almost nil.
• pigments capable of absorbing high oil contents have so far been incorporated in either the heat-sensitive color-forming layer or the undercoat layer or the substrate paper itself.
• Japanese Patent Publication No. 61-56118 and Japanese Patent Public Disclosure No. 59-155097 have proposed that pigments of high oil absorption be contained in the undercoat layer.
• An object, therefore, of the present invention is to provide heat-sensitive recording paper that has fast thermal response, that produces high color density and that causes reduced transfer of tailings to the thermal head.
• the present inventors found that it would be more effective to provide a small amount of pigment between the substrate paper and a leuco dye containing color-forming layer rather than providing an undercoat layer on the substrate paper, e.g. as disclosed in EP-A-190875 which discloses a heat sensitive paper with the heat sensitive layer on a paper substrate, the substrate paper being impregnated with a surface size. More specifically, the present inventors found that with the same pigment used in the undercoat layer of heat-sensitive recording paper, the transfer of tailings to the thermal head would decrease as the air permeability of the undercoat layer decreased.
• the air permeability of paper is an index of the ease with which air can pass through the paper and is proportional to the void volume of the paper. Thus, it is considered to be related to the absorbability of fusible components in the heat-sensitive color-forming layer.
• the overall air permeability will unavoidably decrease compared to the substrate paper per se.
• the transfer of tailings to the thermal head will also increase because the paper fibers have low affinity for the fusible components in the heat-sensitive color-forming layer.
• the present inventors conducted various studies in order to realize substrate paper (support) that had an air permeability close to that of substrate paper and which had high affinity for the fusible components in the heat-sensitive color-forming layer.
• the present inventors found that when the surface of substrate paper was impregnated with a pigment in a dry weight of at least 1 g/m2, the air permeability of the substrate paper decreased to increase the transfer of tailings to the thermal head but that when the pigment content was less than 1 g/m2, the decrease in the air permeability of substrate paper could be sufficiently prevented to decrease the possible transfer of tailings to the thermal head.
• the particles of pigment to be used should not be so large as to file up voids in the substrate paper and their size is preferably in the range of 0.1 - 2 ⁇ m.
• it preferably has an oil absorption of at least 120 ml/100 g as measured in accordance with JIS K 5101.
• Specific examples of pigments that have this level of oil absorbing capability include calcium carbonate, barium sulfate, titanium oxide, talc, pyrophyllite, kaolin, calcined kaolin, aluminum hydroxide, aluminum oxide, magnesium silicate, calcium silicate, white carbon, urea-formaldehyde resin powder, polyethylene resin powder, etc. These pigments may be used either on their own or as admixtures.
• pigments having an oil absorption of less than 120 mg/100 g may be incorporated in amounts which are usually less than 50 wt%.
• pigments should be impregnated only into the surface of substrate paper. If they are impregnated in the entire bulk of substrate paper, its void volume will decrease to result in lower sensitivity.
• the depth of impregnation is usually no more than a third of the thickness of substrate paper but this is not the requirement that must be satisfied in a strict way.
• the degree of pigment impregnation is preferably less than about 1 g/m2.
• conventional coating machines may be used to have pigment particles disposed between fibers on the surface of substrate paper, but more preferably, the pigment particles are loaded by spraying over wire parts or by means of a size press during the making of substrate paper.
• any conventional adhesives may be used in incorporating the pigments in substrate paper and specific examples include: polyvinyl alcohols of various molecular weights; starch and its derivatives; cellulose derivatives such as methoxy cellulose, carboxymethyl cellulose, methyl cellulose and ethyl cellulose; water-soluble polymers such as poly(sodium acrylate), poly(vinylpyrrolidone), acrylamide/acrylate ester copolymer, acrylamide/acrylate ester/methacrylic acid terpolymer, alkali salts of styrene/maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin and casein; and latices of polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/vinyl acetate copolymer
• the substrate paper to be used in the present invention may be made from either hardwood pulp or softwood pulp. If necessary, glass fibers and various kinds of synthetic pulp may be mixed to make the substrate paper.
• the substrate paper permits easy entrance of pigments between fibers on the paper surface, so it is preferred to select substrate paper having a water absorption of no more than 30 g/m2 as measured by the Cobb test (JIS P-8140). However, if the degree of sizing is too high, it becomes difficult to impregnate the substrate paper with pigments. Therefore, the water absorption should be at least 20 g/m2 as measured by the Cobb test. Common sizes such as rosins, alkenyl succinates, alkylketene dimers, etc. may be used as internal sizes. These sizes may be fixed with such compounds as aluminum sulfate and cationic starch.
• the substrate paper may have incorporated therein the known pigments described above.
• the sensitivity of heat-sensitive recording paper is determined by the efficiency with which the heat from the thermal head can be utilized by the heat-sensitive color-forming layer.
• the present inventors noting the heat insulating property of substrate paper itself, studied the relation between the thickness of the substrate paper and its sensitivity. As a result, they found that the sensitivity of substrate paper wound increase with increasing thickness. In practical applications, however, the thickness of substrate paper is limited by its compatibility with printing apparatus.
• Substrate paper that is impregnated with a pigment in an amount of less than 1 g/m2 on a dry weight basis in accordance with the present invention has substantially the same thickness as the substrate paper.
• the thickness of the substrate paper can be increased by 7 - 10 ⁇ m which corresponds to the thickness of an undercoat and this contributes improved sensitivity. If the thickness of substrate paper is less than 60 ⁇ m, satisfactory sensitivity will not be attained. If the substrate paper is thicker than 70 ⁇ m, the paper roll diameter will be so much increased as to cause difficulty in setting the paper on the printing apparatus.
• colorless or pale colored color-forming lactone compounds that can be used in the color-forming layer:
• Color developers made of phenols or organic acids may also be selected from along those known in the art and may be illustrated by the following: bisphenol A; benzyl p-hydroxybenzoate; n-butyl di(4-hydroxyphenyl)acetate; bisphenol S; 4-hydroxy-4′-isopropyloxydiphenylsulfone; 1,1-di(4-hydroxyphenyl)dichlorohexane; 1,7-di(hydroxyphenylthio)-3,5-dioxaheptane.
• Heat-fusible organic compounds having melting points of 50 - 150°C may be used as sensitizers. They may also be selected from among known compounds as exemplified below: phenyl p-hydroxynaphthoate; p-benzylbiphenyl; benzylnaphthyl ether; dibenzyl terephthalate; benzyl p-benzyloxybenzoate; diphenyl carbonate; ditolyl carbonate.
• the organic or inorganic pigments to be used in the color-forming layer are not limited in terms of oil absorption or in any other particular way and may be exemplified by the following: calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, surface-treated fine particles of inorganic materials such as calcium carbonate and silica, and fine particles of organic materials such as urea-formaldehyde resin, styrene/methacrylic acid copolymer and polystyrene resin.
• the heat-sensitive color-forming layer may also contain various waxes as required and they may be selected from among known examples such as paraffin, amide-based wax, bisimide-based wax and metal salts of higher aliphatic acids.
• Adhesives that can be used include: polyvinyl alcohols having various molecular weights; starch and its derivatives; cellulose derivatives such as methoxy cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose; water-soluble polymers such as poly(sodium acrylate), poly(vinylpyrrolidone), acrylamide/acrylate ester copolymer, acrylamide/acrylate ester/methacrylic acid terpolymer, alkali salts of styrene/maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin and casein; and latices of polyvinyl acetate, polyurethane, styrene/butadiene copolymer, poly
• composition having this recipe was pulverized with a sand grinder to an average particle size of 1.5 ⁇ m.
• composition having this recipe was pulverized with a sand grinder to an average particle size of 2 ⁇ m.
• Dispersion A 75 parts
• dispersion B 125 parts
• calcium carbonate 30 parts
• 10% polyvinyl alcohol 200 parts
• 30% paraffin dispersion 17 parts
• 30% zinc stearate dispersion 17.1%
• the solution was applied to the undercoated paper in a deposit of 4.5 g/m2 on a dry basis and dried to prepare heat-sensitive recording paper.
• Fine paper (air permeability, 35 seconds; thickness, 65 ⁇ m) of the same type as used in Example 1 was directly treated as in Example 1 to form a heat-sensitive color-forming layer, thereby making heat-sensitive recording paper.
• Fine paper air permeability, 35 seconds; thickness, 55 ⁇ m was directly treated as in Example 1 to form a heat-sensitive color-forming layer, thereby making heat-sensitive recording paper.
• the testing machine used was adapted from a commercial thermal facsimile. Under the conditions of 10 msec for the recording time per line and 8 x 8 dots/mm for the scanning density, pulse width was modulated so that 0.50 mJ of energy would be applied per dot. The number of lines printed was 64. The resulting color density was measured with a Macbeth densitometer Model RD-514 and used as a representative value of recording sensitivity.
• Tailings that were transferred to the thermal head were inspected visually and evaluated by the following criteria: O, tailings were negligible and acceptable for practical purposes; ⁇ , some tailings were transferred but they caused little problem in practice; X, extensive tailings made the operation inpracticable.
• the present invention provides heat-sensitive recording paper that has fast thermal response and which shows high sensitivity without causing any undesired transfer of tailings to the thermal head.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Heat Sensitive Colour Forming Recording (AREA)

Applications Claiming Priority (2)

Publications (3)

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• 1988
  • 1988-11-24 JP JP63297015A patent/JPH02143896A/ja active Pending
• 1989
  • 1989-11-22 DE DE1989617565 patent/DE68917565T2/de not_active Expired - Fee Related
  • 1989-11-22 EP EP19890312104 patent/EP0370782B1/en not_active Expired - Lifetime

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