JPS60193693A - Heat-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To improve a fading or a disapperance of color property which generates during the preservation of a picture by applying a surface protective layer composed mainly of casein, a copolymer of acrylamide and acrylnitryl and a cross-linking agent on a thermosensitive color-forming layer. CONSTITUTION:In heat-sensitive recording sheets consisting of a thermosensitive color-forming layer containing an electron donor achromatic dye and an electron acceptor compound as main components on a support element, casein and a copolymer of acrylamide and/or methacrylamide and acrylnitryl and/or methacrylnitryl are mixed as main components of a protective layer. In addition, a compound containing the methyrol group is used as a cross-linking agent. Under the above-mentioned formulation, a protective layer having satisfactory plastic and oil resistance and sufficient water-proofness and without losing a whiteness of heat-sensitive recording paper.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a heat-sensitive recording sheet. More specifically, the present invention relates to a heat-sensitive recording sheet that improves fading or erasing of color that occurs during storage of heat-sensitive recorded images, and color development.

(Prior Art) A thermosensitive recording sheet is known as a recording material in which paper, synthetic paper, film, or the like is used as a support, and a thermosensitive coloring layer that develops color when heated is formed on the support. A heat-sensitive recording sheet is a sheet that records images by utilizing physical and chemical changes in substances caused by thermal energy, and many processes are being studied.

A heat-sensitive recording sheet that utilizes the physical change of a substance due to heat is a heat-sensitive recording sheet in which a coating layer made of metal stearate, gallic acid, etc. is provided on a support.

In addition, various coloring mechanisms have been proposed that utilize chemical changes caused by heat, and among these, a so-called two-component coloring type thermosensitive recording sheet is representative.

Two-component color-forming heat-sensitive recording sheets are made by dispersing an acid color-forming colorless leuco dye and a solid acid component such as bisphenol A (BPA) (7) in the form of fine particles, and then mixing the paint with pigments, adhesives, etc. It is coated on a support, and records are obtained by utilizing the coloring reaction that occurs when one or both of a color-forming substance and/or a color-developing substance melt and come into contact with each other when heated.

Such heat-sensitive recording sheets are already used in calculators, medical measuring equipment,
It is widely used for recording purposes in paperbacks, automatic ticket vending machines, etc.

However, conventional heat-sensitive recording sheets of this type have the disadvantage that both colored and non-colored areas lack storage and stability.

In other words, when a plastic such as polyvinyl chloride or polyvinylidene chloride comes into contact with the surface of the heat-sensitive layer, the colored part may fade or disappear due to the plasticizers, stabilizers, additives, etc. contained in the plastic. or

For example, if a thermosensitive recording sheet on which recording or printing has been performed is stored in direct contact with a polyvinyl chloride wrap film or bag for a long period of time, the colored portion will disappear.

Uncolored areas are easily colored by organic solvents such as alcohol, toluene, and ethyl acetate, so if organic solvent is accidentally dropped during storage or if exposed to organic solvent vapor, uncolored areas may become colored. The image becomes indistinguishable from the recorded image. The use of adhesives containing organic solvents also has the disadvantage that uncolored areas develop color, so their use must be avoided.

(Object of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks and provide a heat-sensitive recording sheet having improved water resistance, plasticizer resistance, solvent resistance, and oil resistance and long-term storage stability.

(Structure of the Invention) The present invention provides a heat-sensitive recording sheet in which a heat-sensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound as main components is provided on a support.
acrylamide and/or methacrylamide;
This is a heat-sensitive recording sheet characterized by providing a surface protective layer containing as main components a copolymer of acrylonitrile and/or methacrylonitrile and a crosslinking agent.

(Detailed Description of the Invention) The polymeric substance used for the surface protective layer must have excellent film-forming performance and the film must not be dissolved by organic solvents, plasticizers, etc. Furthermore, since thermosensitive recording sheets cannot be exposed to high temperatures during coating and drying of the protective layer due to their basic property of developing color due to heat, they must have sufficient film-forming performance even when drying at low temperatures.

In addition, in order to minimize the decrease in print density due to the influence of the protective layer, the amount of coating must be small, and even if the protective layer is thin, it will have good water resistance, t = J plasticity resistance, solvent resistance, etc. It must satisfy the required performance.

Using casein as the main component of the material constituting the surface protective layer has been proposed in Japanese Patent Application Laid-Open No. 57-29491, but this proposal does not take water resistance into consideration. In addition, the film formed after casein is assimilated and dried is brittle, prone to minute cracks, and plasticizers and oils tend to seep through the cracks, reducing its function as a protective layer. do. Commonly used crosslinking agents such as glyoxal, polyaldehyde, and epoxy are effective in imparting water resistance to casein, but these agents cause yellowing due to reaction with casein, making the recording paper white. Good results are not necessarily obtained because the heat-sensitive layer may significantly reduce the heat resistance or develop color in the heat-sensitive layer when the protective layer is coated and dried.

Therefore, as a result of various studies, the present inventors mixed a copolymer consisting of casein, acrylamide and/or methacrylamide, and acrylonitrile and/or methacrylonitrile (hereinafter referred to as an acrylamide-acrylonitrile copolymer). When used as the main component of the protective layer and a compound containing a methylol group is used as the crosslinking agent, it has good plasticizer resistance and oil resistance.
It has been found that a protective layer that has sufficient water resistance and does not impair the whiteness of thermal recording paper can be obtained. At the same time, the coating properties of this paint were also good when applied using a coating machine such as a Meyer bar, air knife, or blade.

In the present invention, the acrylamide/acrylonitrile copolymer is a copolymer (aqueous solution) of 50 to 95% by weight of acrylamide and/or methacrylamide and 5 to 50% by weight of acrylonitrile and/or methacrylonitrile.

Examples of compounds containing a methylol group suitable for the present invention include dimethylol urea, dimethylol methylene, dimethylol melamine, dimethylol ethylene, dimethylol acetamide, dimethylol triazone, and polymethylol urea.

In the present invention, the mixing ratio of casein and acrylamide/acrylamide is 1:9 to 9:1.
When these are 100 parts, the amount of the compound containing a methylol group added is from 5 parts to 100 parts, preferably from 40 to 100 parts.

Regarding the mixing ratio of casein and acrylamide/acrylonitrile copolymer, if the mixing ratio of casein is greater than the above range, the coating film will become hard, break, or crack. Furthermore, when this recording paper is used in applications where printing is performed with ultraviolet curable printing ink, a phenomenon occurs in which the adhesiveness of the ink is significantly impaired. On the other hand, if the mixing ratio of casein is less than the above range, plasticizer resistance and oil resistance will decrease. If the amount of the compound containing a methylol group exceeds the above range, the oil resistance will decrease and the object of the present invention will not be achieved.

In the present invention, a protective layer mainly composed of casein, an acrylamide/acrylonitrile copolymer, and a compound containing a methylol group is provided on the heat-sensitive layer, but pigments and waxes are also added to improve compatibility with the thermal head. Other adhesives may be used in combination, or in order to improve marking performance and adhesion to printing ink. Pigments used for this purpose include inorganic pigments such as calcium carbonate, clay, talc, titanium oxide, magnesium carbonate, aluminum silicate, and organic pigments such as polystyrene particles. Waxes include fatty acids such as oleic acid, fatty acid salts such as zinc stearate, polyolefins such as paraffin wax, and other silicone oils.
Oils such as whale oil can also be used.

Examples of the adhesive include starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol, and polyurethane. In addition, monosaccharides such as sorbitol are also used. Further, an antifoaming agent, a partitioning agent, a leveling agent, etc. may be used as necessary. However, the present invention is not limited to these components.

The coating amount of the protective layer is 0.21! /rr1'~9I/
rr1' is preferably 2g/rr1' to 5p/rn'. If the amount is less than this range, coating properties will be poor and there will be problems in developing solvent resistance, and if it is more than this range, heat transfer of the thermal head will be insufficient and print density will decrease.

Coating the protective layer in two layers is effective in developing solvent resistance, and using this method is also effective.

Typical examples of the colorless or light-colored color-forming substance (electron-donating colorless dye) used in the heat-sensitive layer of the present invention are as follows, but the present invention is not limited to these typical examples.

Crystal violet lactone, malachite green lactone, 3,3-bis(valadimethylaminophenyl)4,5,6,7tetra-rolfthalide, benzo-β-naphthospiropyran. 3-Methyl-di-βnaphthospiropyran, 1,3,3-trimethyl-6'-chloro-8'-
Methoxyindolinopage spirobilane, N-phenyl rotamyl lactam, 3-ethylamino-6-chlorofluoran, 3-morpholino-5,6-benzofluorane, 3-diethylamino-6-methyl-7-chlorofluoran , 3-diethylamino-6,7-dimethylfluorane, 3-diethylamino 7,8-benzofluorane, 3
-diethylamino-6-medoxyfluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-5,6-pendi-tupendylaminofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-N ethyl tolylamino-6-methyl-7
-anilinofluorane, 3-diethylamino-7-(N
-3-)lifluoromethylphenyl)aminofluorane.

The color-developing substance (electron-accepting compound) used in the present invention is the following substance, which liquefies or vaporizes at room temperature or higher, preferably 70°C or higher, and reacts with the color-forming substance to release it. 4.4'-isopropylidene diphenol, 4゜4'-
Impropylidene bis(2-chlorophenol), 4.
4'-Impropylidene bis(2-tert-butylphenol), 4.4'-Secondaryphthylidene diphenol, 4.4'-Cyclohexylidene diphenol, 4-phenylphenol, 4-hydroxydiphenoxide, Methyl-4 -Hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxyacetophenone, salicylic acid anilide, novolac type phenolic resin, halogenated novolac type phenolic resin, α-
Naphthol, β-naphthol, 2,2-bis-(4-hydroxyphenyl)-n-hebutane, 4,4'-thiobis-(6-t-butyl-3-methylphenol), 4,4'-butylidenebis Examples include phenolic substances such as -(6-t-butyl-3-methylphenol) and 4゜4'-dihydroxydiphenylsulfone, among which phenolic substances generally have two or more hydroxyl groups in one molecule. Phenolic substances exhibit particularly excellent effects. In addition, benzoic acid esters such as butyl paraoxybenzoate and benzyl paraoxybenzoate can be used or used in combination. In the present invention, a color-forming substance and a color-developing substance are dispersed in a binder. In this case, it is desirable to disperse the dispersed particles using a dispersing machine such as a sand grinder until the particles are as small as possible, specifically, particles of 5 μm or less. As a dispersion aid, a surfactant such as a dispersant or antifoaming agent may be used if necessary. Also, to further prevent the coating material from adhering to the thickening agent or the thermal head,
Fillers such as talc, clay, calcium carbonate, titanium oxide, starch, etc. can also be added. Antifoaming agents to suppress foaming during coating and surfactants to improve coating properties can also be added. Further, in order to improve color development, waxes can be pulverized or used in the form of an emulsion.

As a binder, a natural polymer such as starch or a synthetic polymer such as polyvinyl alcohol is used.As for the 2゜coating method, both the heat-sensitive layer and the protective layer are coated with a coater such as an air knife, bar, roll, or plaid. , drying is done at a relatively low temperature.

If smoothing treatment is performed using a supercalender or the like after applying the heat-sensitive layer and/or after applying the protective layer, good results can be obtained in terms of color density and uniformity of the color image.

By providing a solvent-resistant layer on the back side of the support or as an undercoat layer for the heat-sensitive layer, it is possible to suppress the penetration of organic solvents from the back side, and it is also possible to obtain products with improved storage stability. can.

The present invention will be explained in more detail below using examples. Parts in each example indicate parts by weight.

Example 1 (1) Preparation of Solution A 3-(N-Methyl-N-cyclohexylamino)-6-methyl-7-anilinofluorane 4.0 parts 3-diethylamino-7-orthochloroanilinofluorane 1. 0 parts 5% aqueous hydroxyethyl cellulose 20.0 parts The composition in this ratio is ground to an average particle size of 2 microns using a sand grinder.

(2) Preparation of Solution B 4.4'-isopropylidene diphenol (bisphenol A) 25.0 parts Stearic acid amide 15.0 parts Hydroxyethyl cellulose 5% aqueous solution 140.0 parts Average particle size 2
Grind down to microns.

(3) Formation of coloring layer 70 parts of Tal 250% aqueous dispersion, 25 parts of liquid A, 180 parts of liquid B
and 240 parts of a 5% aqueous solution of hydroxyethyl cellulose as a binder to prepare a coating liquid.

This coating solution was coated on a 59 g/f+1' high-quality paper using a Mayer bar so that the coating weight after drying was 7 g/rn' to obtain a heat-sensitive recording sheet before coating with a protective layer.

(4) Formation of a protective layer As a protective layer, 30 parts of ammonium aqueous solution of casein, 40 parts of acrylamide/acrylonitrile copolymer (vapilol C-1013G, Showa Denko Department), 25 parts of dimethylol urea (J-001, Showa Denko Department) The coating amount was 3117 rr with a coating solution consisting of 5 parts of calcium stearate and 5 parts of calcium stearate.
+' coating to obtain a heat-sensitive recording sheet according to the present invention.

Example 2 On the heat-sensitive recording sheet used in Example 1 before coating the protective layer, 10 parts of ammonium aqueous solution of casein, acrylamide-acrylonitrile copolymer (Vapyrol C-101)
3G) 50 parts, dimethylolurea (J-001) 25
A coating amount of 4 parts of a coating solution consisting of 5 parts of zinc stearate and 5 parts of zinc stearate was applied.
A heat-sensitive recording sheet according to the present invention was obtained by coating the film to a thickness of 17 m''.

Example 3 On the heat-sensitive recording sheet used in Example 1 before coating the protective layer, 20 parts of ammonium aqueous solution of casein and acrylamide/acrylonitrile copolymer (Vapyrol C-10) were added.
13G), 40 parts of polyurethane emulsion, and 10 parts of zinc stearate at a coating weight of 41/
A heat-sensitive recording sheet according to the present invention was obtained by applying the coating so as to obtain rrf.

Comparative Example 1 A coating solution consisting of 95 parts of casein ammonium solution and 5 parts of calcium stearate was applied on the heat-sensitive recording sheet used in Example 1 before the protective layer was applied at a coating amount of 3 y/m. It was applied like this.

Comparative Example 2 A coating liquid consisting of 95 parts of acrylic 7mide/acrylonitrile copolymer (Bavilol C-1013G) and 5 parts of calcium stearate was applied onto the heat-sensitive recording sheet used in Example 1 before the protective bird coating. It was applied so that the coating amount was 39/rrl.

Comparative Example 3 On the heat-sensitive recording sheet used in Example 1 before coating the protective layer, 30 parts of caseinate ammonium solution and acrylamide
Acrylonitrile copolymer (Bavilol C-1013G
) 40 parts, glyoxal 25 parts, zinc stearate 5 parts
Next, apply the coating liquid to each part so that the coating amount is 4 g/rr1'.

〔Test method〕

Water resistant commercially available barcode printer (Tokyo Electric HP-9
After printing a sample using 303), it was immersed in water at 20° C. for 24 hours, left to dry indoors, and then the degree of decolorization of the print was sensory evaluated in comparison with the initial print.

Plasticizer resistance: PVC rubber (Mitsui Toatsu) was placed on the sample printed with the above commercially available barcode printer,
The degree of decolorization of the print was sensory evaluated after being left for 40'024 hours under a load of 30011/ca.

Oil Resistance 2 Cottonseed oil was applied to a sample printed using the above-mentioned commercially available barcode printer, and the degree of decolorization of the print was sensory evaluated after being left at 40° C. for 24 hours.

Print density: After printing with a Hiroshi Ishida label printer JP-N, it was measured with a Bretag densitometer.

The bend should be 5 cm x 20 cm (
A test piece cut to a length (width/length) was stretched 10 times under a load of 100 g, and the water resistance, oil resistance, and plasticizer resistance of that part were measured and compared with a blank.

Note that the coating amount is the coating amount when completely dry. Table 1 summarizes the results for each side.

As is clear from these results, the heat-sensitive recording sheet according to the present invention is significantly superior in water resistance, oil resistance, plasticizer resistance, and print density compared to the comparative example. In addition, since the protective layer coating film is softer than that of the comparative example, the area where the recording sheet is folded has excellent barrier properties against oil and plasticizer.

Patent Applicant Oji Paper Co., Ltd. Procedural Amendment (Voluntary) Showa J. 4” Date of Case Indication of Showa J. 1999 Patent Application μ Tata No. 21 No. 2 Title of Invention Thermal Recording Sheet 3, Comparison with the Amendment Person Case Related Patent Applicant Name Name Oji Paper Co., Ltd. Agent Address No. 7-j, Ginza 3-chome, Chuo-ku, Tokyo Mr. Oji Sales Company-wide Column C, Contents of Amendment (1) Specification O/J Pages O/L ``30 parts of ammonium aqueous solution'' in the /- line ~ /j line is ``Ammo'
“10 parts of ammonium aqueous solution” on page 16 of the specification, line O≠
is corrected to "47 parts of ammonium-13 aqueous solution."

□31 Correct "20 parts of ammonium aqueous solution" in lines 12 and 13 of 1JA booklet O/A page O to "33 parts of ammonium ljti aqueous solution."

4) On page 16 of the specification, line O, "1 part of ammonium solution" is corrected to "633 parts of ammonium-13 aqueous solution."

5) Page 17 of the specification, O// line [30 parts of casein ammonium solution] was changed to "casein ammonium/1% aqueous solution 2
00 copies,” he corrected.

Claims (1)

[Scope of Claims] (1') In a heat-sensitive recording sheet in which a heat-sensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound as main components is provided on a support, casein and 1. A heat-sensitive recording sheet, characterized in that it is provided with a surface protection layer containing as main components a copolymer of acrylamide and/or methacrylamide, acrylonitrile and/or methacrylonitrile, and a crosslinking agent. (2) The heat-sensitive recording sheet according to claim (1), wherein the crosslinking agent contains a compound having a methylol group as a main component. (3) The heat-sensitive recording sheet according to claim (1), wherein the surface protection layer further contains inorganic and/or organic pigment fine particles and waxes.