JPH0425877B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention comprises a normally colorless or slightly pale color-forming dye, a color developer comprising an organic acid or a phenolic substance that causes the color-forming dye to develop color by heating,
The present invention relates to a heat-sensitive recording material having a heat-sensitive coloring layer containing a binder. More specifically, this heat-sensitive recording material has long shelf life,
In particular, the water resistance of the paint film, the water resistance of the colored part, the discoloration that occurs when it comes into close contact with a plastic film that contains a lot of plasticity (hereinafter referred to as plasticizer resistance), and the discoloration that occurs when oil such as meat or edible oil is attached. The present invention relates to a heat-sensitive recording material with improved oil resistance (hereinafter referred to as oil resistance). (Prior Art) Conventionally, there are various known heat-sensitive recording sheets in which a paint obtained by dispersing a lactone compound such as crystal violet lactone and a phenol compound such as bisphenol A in a binder such as polyvinyl alcohol solution is coated on a support. Special Public Service 1977-
14039). (Problems to be Solved by the Invention) When this type of heat-sensitive recording sheet receives heat, the color-forming lactone compound and the organic acid or phenol compound chemically react to develop color. In this case, the basic properties required of a heat-sensitive recording sheet are that it has good color development, is as white as possible in appearance and has the appearance of natural paper, and has long shelf life.In addition, particularly important properties include: It is required to have (a) high sensitivity, (b) no staining (sticking), and (c) no lees adhering to the thermal head, and good compatibility with the thermal head. ing. In this way, heat-sensitive recording materials are desired to have the above-mentioned properties depending on their use, but these dye-type color-forming materials are unstable to light, water, temperature, plasticizers, oil, etc. Therefore, changes over time during storage are always a problem. Therefore, when desired printing is performed on such a recording sheet, the recording color development is extremely clear, but if the coloring area is made of plastic film containing a large amount of plasticizer (for example, a soft vinyl chloride film) ), or if it is stored with oil or fat attached, the adhesive part will fade in color. Also, when the colored part is in contact with water for a long period of time, significant discoloration usually occurs. These discolorations are particularly noticeable in color-forming type heat-sensitive recording materials that use dyes mainly composed of colorless or light-colored lactone compounds, and this discoloration depends on the chemical structure of the color-forming lactone compound used. It is presumed that the above-mentioned inconvenience occurs because plasticizers and oils, especially organic acids and phenolic compounds, dissolve in oil without contacting the heat-sensitive recording material, and this is a common problem that occurs when the heat-sensitive recording material comes into contact with oil or plasticizers. As such, there has been a strong demand for its elimination. The present invention aims to solve these problems and provide a heat-sensitive recording material having improved water resistance, plasticizer resistance and oil resistance, and long-term storage stability. (Means for Solving the Problems) The present inventors obtained a coloring layer by copolymerizing a monomer having an acetoacetate group, acrylamide, and polyvinyl alcohol on a heat-sensitive coloring layer provided on a support. A protective layer mainly composed of 100% by weight of a water-soluble polymer compound and 5 to 100% by weight of a crosslinking agent is provided, and the protective layer has an oil absorption of 100ml/100g or more and an apparent specific volume of 3ml as a filler. /g or more,
By containing ultrafine silicic acid powder with an average particle size of 1.5μ or less, it prevents plasticizers, oils, etc. from penetrating the heat-sensitive coloring layer, and prevents discoloration when it comes into close contact with a soft polyvinyl chloride film or when oil is attached. showing excellent effects on and states king,
It has been found that head compatibility with head lees becomes good, there is no deterioration of the above-mentioned plasticizer resistance, oil resistance, water resistance, etc., and clear images with high density can be recorded even with minute thermal energy. For example, when the surface of a heat-sensitive recording material is simply coated with cottonseed oil, a conventional heat-sensitive recording material without a protective layer, or simply a water-soluble polymer compound with barrier properties such as ordinary saponified PVA, casein, etc., and a crosslinking agent. When a heat-sensitive recording material provided with a protective layer containing . On the other hand, in the heat-sensitive recording material containing the water-soluble polymer compound containing the acetoacetate group of the present invention, the colored portion hardly disappears even after 24 hours or more. The protective layer of the heat-sensitive recording material of the present invention contains a crosslinking agent, a lubricant, and/or a pigment in addition to the above-mentioned water-soluble polymer compound containing an acetoacetate group, thereby imparting water resistance to the coating film. It is possible to further prevent discoloration when immersed in water, and it is also possible to prevent staking of the thermal head to the film surface and adhesion of scum to the thermal head when recording on the coating surface. . Therefore, the present invention can be used, for example, as a thermal recording ticket for automatic ticket vending machines, as well as for coupon tickets and commuter passes that require long shelf life, as well as for POS.
Not only is it suitable for use as label paper for sticking to the packaging surface of fresh foods and oily meats packaged with vinyl chloride film using a barcode pricing system, but it is also a facsimile paper for long-term storage. It can also be used as printer paper. The materials used in the heat-sensitive recording material of the present invention will be explained in detail below. (1) 3-diethylamino-
6-Methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-(N-methyl-N- cyclohexylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-chloroanilinofluorane, 3-[N-ethyl-N-
(p-methylphenyl)amino]-6-methyl-
Fluorane series such as 7-anilinofluorane, 3-diethylamino-7-(metatrifluoromethyl)anilinofluorane, 3,3-bis-
(p-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone), 3,3-bis-(p-dibutylaminophenyl) phthalide, 3,3-bis-(p-dimethylaminophthalide) enyl) phthalide, triphenylmethane series such as 4-hydroxy-4'-dimethylaminotriphenylmethane lactone, 3-methyl-di-β-naphtosvirorane, 1,3,3-
Spirolane series such as trimethyl-6'-chloro-8'-methoxyindolinobenzospirolane, as well as auramine series, rhodamine lactam series,
Leuco dyes such as phenothiazines are also used. However, the present invention is not limited to these representative examples. (2) Color-developing substances that cause color-forming dyes to develop color when heated include inorganic solid acidic substances such as acid clay, zeolite, and silicon oxide, and organic acids such as oxalic acid, maleic acid, gallic acid, and benzoic acid, and their derivatives. Although phenolic compounds and metal salts are also used, it is preferable to use phenolic compounds with low water solubility, and among them, phenolic compounds having two or more hydroxyl groups in the molecule are preferable. For example, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-
Isopropylidene (2-methylphenol),
4,4'-isopropylidene bis(2,1-tert
-butylphenol), 4,4'-sec-butylidene diphenol, 4,4'-cyclohexylidene diphenol, 4-tert-butylphenol,
4,4'-cyclohexylidene diphenol, 4
-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, naphthol, β-naphthol, methyl-4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, 4-hydroxyacetophenone, p-
Examples include oxybenzoic acid esters, novolak type phenolic resins, and halogenated novolak type phenolic resins, and one or more of them can be used arbitrarily. However, it is not limited to these. (3) The binder for the heat-sensitive coloring layer is not particularly limited, and all known binders can be used. It is preferable that the liquid does not develop color, aggregate, or become highly viscous when mixed with the liquid. In addition, characteristics such as not inhibiting color development and strong film formation are required, but there are particular requirements regarding compatibility with the thermal head, such as staking, dust adhesion, and abrasion in order to provide a protective layer. For example, polyvinyl alcohol, starch, hydroxyethyl cellulose,
Gum arabic, polyvinylpyrrolidone, alkali salts of acrylic acid (or methacrylic acid) ester copolymers, alkali salts of styrene/maleic anhydride copolymers, alkali salts of isobutylene/maleic anhydride copolymers, acrylamide copolymers, etc. water-soluble polymer compounds and styrene/butadiene copolymers, polyvinyl acetate,
Examples include polymer latexes such as acrylic acid ester copolymers, emulsions, and the like. Furthermore, in addition to the above-mentioned color-forming dye, color-developing substance, binder, etc., various substances shown below can be added to the heat-sensitive color-forming layer according to the present invention, if necessary. For example, inorganic pigments and other fillers may be added to improve coating fluid suitability and whiteness.
Various waxes such as higher fatty acid amides, higher fatty acid metal salts, dibenzyl terephthalate, and other thermofusible substances and melting point depressing substances can be added to improve color development sensitivity, and are compatible with other waxes to improve dispersibility and coating suitability. Certain defoamers, dispersants, wetting agents, etc. can be used. In the present invention, as the material for the protective layer formed on the surface of the thermosensitive coloring layer, a water-soluble polymer compound containing an acetoacetate group is used as a protective layer forming agent, and a crosslinking agent, a pigment, a lubricant, etc. are used in combination as necessary. The monomer having an acetoacetate group used in the copolymerization of the water-soluble polymer compound having an acetoacetate group of the present invention is an alcohol having a double bond, such as allyl alcohol, croton alcohol, butenyl alcohol, isopropenyl It is a reaction product of alcohol etc. and diketene, and when allyl alcohol and diketene are reacted, allyl acetoacetate is obtained. The chemical reaction formula in this case is It can be shown as The average degree of polymerization of polyvinyl alcohol (PVA) used in the copolymerization is usually selected from the range of 300 to 2000, and the average degree of saponification is preferably 70 to 100 mol%. If the average degree of polymerization is less than 300, the adhesive strength will be insufficient, and if it is more than 2000, the viscosity of the binder itself will become too high, making it inconvenient to use. If the average degree of saponification is less than 70 mol%, it becomes difficult to dissolve in water, which is not preferable. As mentioned above, the water-soluble polymer compound containing an acetoacetate group used in the present invention is a copolymer of a monomer having an acetoacetate group, acrylamide, and polyvinyl alcohol. For example, a copolymer using allyl acetoacetate as a monomer having an acetoacetate group can have the following structure. These copolymerizations are carried out by adding a mixture of acrylamide and the above monomers having an acetoacetate group to the above PVA aqueous solution, and using a peroxide (ammonium persulfate, hydrogen peroxide, etc.) as a polymerization initiator using a normal solution polymerization method. The usual method is to polymerize at 80° to 100°C for grafting onto PVA, but another method is to graft a copolymer of acrylamide and the above-mentioned monomer having an acetoacetate group onto PVA. Another method is polymerization. The content of the acetoacetate group can be 0.05 mol% or more based on the water-soluble polymer compound, up to the maximum within the range of water solubility, but it is usually 0.1
~20 mol%, especially from 0.5 to 10 mol%. If the content of acetoacetate groups is too small, it is difficult to obtain the effects of the present invention.
On the other hand, even if the amount is more than necessary, the expected effect cannot be obtained considering the amount used. In addition to the water-soluble polymer compound containing an acetoacetate group, other water-soluble polymers can also be used as the protective layer forming agent. The water-soluble polymers include polyvinyl alcohol, casein,
Starches, hydroxyethyl cellulose, gum arabic, polyvinylpyrrolidone, alkali salts of acrylic acid (or methacrylic acid) ester copolymers, alkali salts of styrene/maleic anhydride copolymers, alkali salts of isobutylene/maleic anhydride copolymers , alkali salts of diisobutylene/maleic anhydride copolymers, acrylamide (or methacrylamide)/acrylic acid (or methacrylic acid) ester copolymers, water-soluble polymer compounds and emulsions such as vinyl acetate, or
An example is SBR latex. The requirements for a protective layer forming agent are that it has excellent film-forming performance and that the resulting film does not dissolve in plasticizers, oils, organic solvents, etc., and at the same time, it must be able to form a heat-sensitive coloring layer during coating. To prevent color development
The water-soluble polymer compound must have sufficient film-forming performance even under relatively low-temperature drying conditions of 100°C or lower. Examples of crosslinking agents include dialdehydes such as glyoxal and polyaldehyde, polyamines such as polyethyleneimine, epoxy polyamide resins, diglycidyls such as glycerin diglycidyl ether, dimethylol urea, ammonium persulfate, ferric chloride, etc. Metal salts such as magnesium chloride and known compounds such as ammonium chloride are used. Water resistance using these crosslinking agents requires treatment at a considerably high temperature for some water-soluble polymer compounds that do not contain acetoacetate groups, whereas the water-soluble polymer compounds that have acetoacetate groups according to the present invention Because molecular compounds have significant reactivity,
It has the great advantage of being able to exhibit practical water resistance at low temperatures that are at the level of drying. As fillers, kaolin, clay, talc,
Examples include calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, silica, synthetic aluminum silicate, synthetic magnesium silicate, aluminum oxide, polystyrene fine particles, urea-formalin resin fine particles, and the like. In the present invention, ultrafine powdered silicic acid having an oil absorption of 100 ml/100 g or more, an apparent specific volume of 3 ml/g or more, and an average particle size of 1.5 μ or less has good compatibility with the protective layer forming agent of the present invention, satisfies the above requirements, and It has been found that it is an optimal filler that can also provide compatibility and printability. In addition, as lubricants, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, paraffin wax,
Microcrystalline wax or the like can be used. Therefore, the amount of the protective layer forming agent and crosslinking agent must be at least 50% by weight of the total components of the protective layer; if it is less than this, the properties of plasticizer resistance and oil resistance will deteriorate, making it unsuitable. be. Water-soluble polymer compound
The amount of crosslinking agent relative to 100% by weight is from 5 to 100% by weight, preferably from 10 to 80% by weight. In this case, if the amount of crosslinking agent is less than 5% by weight, crosslinking will not proceed sufficiently, and therefore, not only will sufficient water resistance and compatibility with the thermal head not be obtained, but the molecular structure due to crosslinking will be Because we can't keep it secret,
This results in a decrease in plasticizer resistance and oil resistance, making it impossible to obtain the desired effect. The coating amount of the protective layer is adjusted as appropriate to the extent that heat conduction from the thermal head to the coloring layer is not inhibited, and is usually 1 to 10 g/m2, preferably ² to 10 g/m2.
It is preferable to set it to 7 g/m ² . In this way, desired effects can be obtained without reducing thermal sensitivity. Supports used in the present invention include high quality paper,
Papers such as medium-quality paper, art paper, coated paper, cast coated paper, paperboard, and tissue paper are generally used, but plastic film, synthetic paper, laminated paper, aluminum foil, etc. can also be used. (Examples) 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 liquid A 3-(N-methyl-N-cyclohexylamino)
-6-Methyl-7-anilinofluorane 6 parts 5% hydroxyethyl cellulose aqueous solution 24 parts (2) Solution B preparation 4,4'-isopropylidene diphenol 25 parts Stearamide 16 parts 5% hydroxyethyl cellulose aqueous solution 140 parts Above Part A and Part B are separately ground and dispersed in a sand mill to an average particle size of 3 μm or less. (3) Preparation of liquid C 10% (allyl acetoacetate-acrylamide-
PVA copolymer composition ratio: 2/3/5) 60 parts (PVA: degree of saponification 88%, degree of polymerization 1100) 60% kaolin dispersion 4 parts 30% zinc stearate 2 parts 30% polyaldehyde solution 3 parts ( 4) Formation of coloring layer 40 parts of 60% aqueous dispersion of ultrafine silicic acid with oil absorption 200ml/100g, apparent specific volume 3ml/g, average particle size 1.3μ, A
Mix 30 parts of liquid, 200 parts of liquid B, and 100 parts of a 10% polyvinyl alcohol aqueous solution as a binder to prepare a coating liquid. This coating solution was coated onto a base paper of 50 g/m ² to a dry weight of 7 g/m ² , and then calendered to provide a heat-sensitive coloring layer with a base smoothness of 250 seconds. (5) Formation of protective layer A protective layer was formed by coating liquid C on the coloring layer to a dry weight of 3 g/m ² to obtain a heat-sensitive recording material having a two-layer structure. Comparative Example 1 In place of the acetoacetate group-containing copolymer, which is a water-soluble polymer compound of liquid C (protective layer paint) used in Example 1, a saponification degree of 98 mol% and a polymerization degree of 98 mol% were used.
A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1 except that 1100 saponified PVA was used. Comparative Example 2 In place of the acetoacetate group-containing copolymer, which is a water-soluble polymer compound of liquid C (protective layer paint) used in Example 1, a saponification degree of 88% mol% and a polymerization degree were used.
A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1 except that 1100 saponified PVA was used. Comparative Example 3 Liquid C (protective layer paint) used in Example 1 contains acetoacetate group, which is a water-soluble polymer compound
Ammonium solution of casein (10
A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1, except that % aqueous solution) was used. After each heat-sensitive recording material of the above Examples and Comparative Examples was left at room temperature for 3 days, it was colored with a solid black record using Copix 7100 (trade name, manufactured by Toshiba Electric Corporation). A clear black color image was obtained at a high density of 1.2 or higher. Next, a predetermined test piece was prepared from this material by a conventional method, and the water resistance, vinyl chloride film resistance, and oil resistance of the colored portion were measured by the following tests. The results are shown in the table. As is clear from this table, in each of the Examples, satisfactory results were obtained, but in the Comparative Examples, appropriate results were not obtained in some respects. (1) Water resistance test: A test piece is immersed in water for 24 hours (at room temperature) and then taken out, and evaluated based on the elution state of the protective layer and the residual concentration after drying. (2) PVC film resistance test: A soft polyvinyl chloride film was superimposed on the specimen and heated at 20°C and 300°C.
The concentration is measured when both are brought into contact for 24 hours under a load of g/m ² . (3) Oil resistance test: Apply cottonseed oil to a test piece using a conventional method, leave it at 20°C and 40°C for 24 hours, and then evaluate the residual concentration.

[Table] The symbols in the table are the results of evaluating various physical properties in the order of ◎○○△△×. ◎ is extremely excellent;
× means extremely poor quality. As is clear from the table above, Example 1 is the same as Comparative Examples 1 to 3.
It is known that PVC film resistance and oil resistance are improved compared to . (Effects of the Invention) According to the present invention, it is possible to obtain a heat-sensitive recording material that has excellent water resistance, plasticizer resistance, and oil resistance. It is also extremely useful as printer paper.

Claims (1)

[Claims] 1. 100% by weight of a water-soluble polymer compound obtained by copolymerizing a monomer having an acetoacetate group, acrylamide, and polyvinyl alcohol on a thermosensitive coloring layer provided on a support;
A protective layer containing 5 to 100% by weight of a crosslinking agent as a main component is provided, and the protective layer is made of ultrafine silicic acid having an oil absorption of 100 ml/100 g or more, an apparent specific volume of 3 ml/g or more, and an average particle size of 1.5 μ or less. A heat-sensitive recording material comprising: