JPH0558042A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve solvent resistance, plasticizer resistance, oil resistance, water resistance and sticking resistance of a thermal recording material obtained by forming a thermal color forming layer containing a leuco dye, a developer and a binder on a support. CONSTITUTION:A ternary copolymer consisting of an isobutylene unit, a maleic anhydride unit and an n-butyl acrylate unit is used at least as a part of a binder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material comprising a support and a heat-sensitive color forming layer containing a developer such as a leuco dye, an organic acid and a binder. The present invention relates to a heat-sensitive recording material characterized by using, as at least a part of the binder, a terpolymer containing an isobutylene unit, a maleic anhydride unit and an n-butyl acrylate unit.

[0002]

2. Description of the Related Art Recording materials in which a thermosensitive coloring layer that develops color by heating is provided on a support have been widely put into practical use.

A color image can be recorded by heating the surface of such a recording material with a thermal head or a thermal pen, and a facsimile, a computer output, a printer such as a calculator, an automatic ticket vending machine, a POS label, etc. Widely used in the field.

Generally, in such a heat-sensitive recording material, a leuco dye and a color developing agent such as a phenolic substance are individually dispersed in the form of fine particles, and then both are mixed, and a binder, a sensitizer, a filler, It is manufactured by applying a coating liquid with a lubricant etc. to the surface of paper or plastic film and drying it, and one or both of the leuco dye and the color developer are melt-adhered by heating to obtain color development records. It is a thing.

The properties generally required for a thermal recording paper are as follows: (1) Color is developed by a short time contact with a thermal head,
High print density, (2) No sticking between the thermal head and recording material, no dust adhered to the thermal head, (3) Water resistance, no discoloration of colored print due to contact with water, (4) It has oil resistance, solvent resistance, plasticizer resistance, and there is no discoloration of color printing due to contact with organic solvent, oil, plasticizer, and the like.

[0006]

On the other hand, conventional binders for heat-sensitive recording materials include polyvinyl alcohol, methyl cellulose, hydrocyloethyl cellulose, starch, oxidized starch, alkyd resin, petroleum resin, maleic acid resin, epoxy resin, polyester. Resins, acrylic acid ester copolymers, gelatin, polystyrene and the like are used.

However, in these conventional binders,
It is difficult to satisfy all the required properties of the above-mentioned various thermal recording papers, and particularly in the fields of POS labels and automatic ticket vending machines, there has been a strong demand for a binder excellent in water resistance and plasticizer resistance.

[0008]

DISCLOSURE OF THE INVENTION As a result of intensive studies conducted by the present inventors to overcome the above-mentioned drawbacks of conventional thermal recording materials, as a part of at least a part of the binder for the color forming layer, an isobutylene unit, It has been found that the use of a terpolymer containing maleic anhydride units and n-butyl acrylate units can improve the color development, water resistance, plasticizer resistance and coating film strength of thermal recording paper. The invention was completed.

The terpolymer used in the present invention can be produced by a conventional method using isobutylene, maleic anhydride and n-butyl acrylate as raw material monomers. For example, it can be produced by charging these raw material monomers into a reaction vessel and copolymerizing them with a radical polymerization initiator by a solution polymerization method or a precipitation polymerization method.

The radical polymerization initiator can be appropriately selected and used from those conventionally used. For example, di (dodecanoyl) peroxide,
Organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, 2,2'-azobisisobutyronitrile, 2,2 '
-Azobis (2-methylbutyronitrile), dimethyl-
2,2'-azobisisobutyrate, α, α'-azo-
Azo compounds such as α-ethylbutyronitrile can be used. The amount of the radical polymerization initiator used is generally about 0.05 to 5.0 with respect to 100 parts by weight of the monomer.
The range is parts by weight.

As the solvent used in the polymerization reaction, various solvents which do not inhibit radical polymerization can be used. For example, ketones such as acetone and methyl ethyl ketone, aliphatic hydrocarbons such as n-hexane and n-octane, aromatic hydrocarbons such as benzene and toluene,
Fatty acid esters such as ethyl acetate and isopropyl acetate,
Ethers such as diisopropyl ether, dioxane, and tetrahydrofuran can be used, and chlorinated hydrocarbons such as methylene chloride and chloroform can be used. These solvents may be used alone or as a mixture.

The polymerization temperature varies depending on the solvent used, the radical polymerization initiator and the like, but is generally in the range of 0 to 200 ° C, preferably 30 to 150 ° C. The polymerization time also varies depending on the solvent used, the radical polymerization initiator, the polymerization temperature, etc., but is generally in the range of 1 to 50 hours, preferably 2 to 20 hours. Also, the polymerization can generally be carried out under atmospheric pressure or higher pressure.

Separation and recovery of the produced terpolymer from the liquid after completion of the polymerization is carried out by drying the precipitated polymer by filtration after removing the liquid by filtration when the precipitation polymerization method is adopted, and by using a solvent when the solution polymerization method is adopted. It is carried out by ejecting and drying.

When the raw material monomers are charged, the copolymer having a uniform composition can be obtained by considering the difference in the polymerization reactivity of the raw material monomers. For example, n-butyl acrylate having a slightly low reactivity is charged so that the concentration in the reaction system becomes high in the initial stage of the polymerization reaction, while maleic anhydride has a constant concentration in the reaction system during the polymerization reaction. It is preferable to charge so that.

If the molecular weight of the terpolymer used in the present invention is too low, the coating strength of the obtained heat-sensitive color forming layer will be low, and the sticking resistance will be low. 10,000-400,000 because it causes difficulties in handling during processing (the viscosity of the aqueous solution becomes high, etc.)
It is preferably in the range of. The composition molar ratio of the isobutylene unit, the maleic anhydride unit and the n-butyl acrylate unit in the terpolymer is such that when the ratio of the maleic anhydride unit is too small and the n-butyl acrylate unit is excessive. The alkaline water solubility of
Not only does this cause inconvenience, but the solvent resistance and plasticizer resistance of the resulting heat-sensitive color forming layer decrease, which is not preferable.
If the butyl acrylate units are too small and the proportion of maleic anhydride units is too large, not only the obtained thermosensitive coloring layer tends to be hard and brittle, but also the water resistance is deteriorated.
It is desirable to be in the range of 0.8 to 1.2: 0.2 to 2.

The terpolymer used in the present invention is insoluble in ordinary water, but since it has a maleic anhydride group in the molecule, it reacts with an alkaline substance such as NaOH or NH _3. It becomes Na salt, NH ₄ salt, etc., and is used after being made water-soluble. The amount of alkali necessary for water solubilization varies depending on the compositional molar ratio of structural units of the copolymer and the type of alkali, but is usually 0.2 to 1 times equivalent to the acid value of the copolymer.

The heat-sensitive recording material of the present invention is prepared by dissolving or dispersing a conventional leuco dye, a color developer and a terpolymer and, if necessary, auxiliary additives in a suitable solvent to form a heat-sensitive color forming layer forming liquid. It can be produced by preparing it, coating it on the surface of a support such as paper, synthetic paper, or plastic film, and drying it at a low temperature of 80 ° C. or lower to prevent color development. As the leuco dye, a conventional non-coloring leuco dye, for example, a colorless or pale leuco dye having a lactone ring, a lactam ring or a spirolane ring is preferably used.
An organic acidic substance is used as the developer, and examples thereof include various organic acids and various phenols. This organic acidic substance reacts with the leuco dye under heating to develop the leuco dye.

Specific examples of the leuco dye include the following.

Crystal violet, malachite green lactone, 3,3-bis (paradimethylaminophenyl) -6-aminophthalide, 3,3-bis (paradimethylaminophenyl) -6-paratoluenesulfonamide, 3-diethylamino-7. -Dibenzylaminofluorane, 3-diethylamino-7- (N-methylanilino) fluorane, 3-diethylamino-7- (N-methylparatoluidino) fluorane, 3-diethylamino-
6-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7
-Phenylaminofluorane, 3-diethylamino-7
-Phenylfluorane, 3-morpholino-5,6-benzofluorane.

Examples of the color developer include the following. Aromatic carboxylic acids such as phthalic anhydride, gallic acid and salicylic acid, and 4,4'-isopropylidenediphenol, 4,4'-isopropylidenebis (2
-Chlorophenol), 4,4'-isopropylidene bis (2-t-butylphenol), 4,4'-s-butylidene diphenol, 4,4 '-(1-methyl-n-hexylidene) diphenol, 4 -Phenylphenol,
4-hydroxydiphenoxide, methyl-4-hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxyacetophenone, anilide salicylate, novolac type phenol resin, halogenated novolac type phenol resin, α-naphthol, β-naphthol, etc. Phenolic compound.

In the present invention, auxiliary components which can be optionally used are talc, clay, calcium carbonate,
Fillers such as titanium dioxide and starch particles, waxes as pressure-color-developing inhibitors, surfactants and whitening agents for dispersion and defoaming, and the like.

In addition to the terpolymer as a binder,
Various conventional binders can be appropriately used in combination, for example, polyvinyl alcohol, starch, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, and other cellulose derivatives; sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide- Acrylic ester copolymer,
Acrylic amide-acrylic acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer alkali salt, isobutylene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, etc. Molecules: Polyvinyl acetate, polyurethane, styrene-butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, styrene-butadiene copolymer It can be used in latex such as coalesced.

In the present invention, the terpolymer is 0.2 to 1.0 times equivalent of alkali, that is, ammonia, NaOH, KOH, M with respect to the acid value (derived from maleic anhydride group) of the resin.
It is used after being solubilized by heating it with water such as g (OH) ₂ . This copolymer is used in a proportion of 0.1 to 20 parts by weight, preferably 1 to 5 parts by weight, based on 1 part by weight of the leuco dye, and if necessary, it is a conventional compound unless the object of the present invention is particularly hindered. Can be used in combination with other binders as indicated above. in this case,
The total amount of the binder is 0.2 to 80% by weight, preferably 5 to 30% by weight in the thermosensitive coloring layer.

The heat-sensitive recording material of the present invention is produced by the following method using the above-mentioned materials.

According to a conventional method, a color-forming compound (leuco dye) and a color-developing agent (organic acidic substance) are separately added to water or other additives as necessary, a protective colloid agent such as polyvinyl alcohol, a dispersant and an interface. It is pulverized with a disperser such as a ball mill, an attritor or a sand mill together with an activator to obtain a dispersion liquid. Next, the pulverized dispersion liquid of the color forming compound and the color developer is mixed with an aqueous alkaline salt solution of a terpolymer and a cross-linking waterproofing agent such as a water-soluble epoxy compound to prepare a coating liquid. The heat-sensitive recording material of the present invention is obtained by applying the composition onto a support such as a sheet or synthetic paper using a bar coater or the like so that the application amount is 5 to 50 g / m ^2, and drying at a low temperature of 80 ° C. or lower.

Between the thermosensitive coloring layer and the support or on the thermosensitive coloring layer, polyvinyl alcohol, an alkali salt of a terpolymer, an alkali salt of an isobutylene-maleic anhydride-N-phenylmaleimide copolymer, if necessary. Isobutylene-
You may provide the protective layer with the alkali salt etc. of the amidation modification product of a maleic anhydride-N-phenyl maleimide copolymer.

According to the present invention, when an isobutylene-maleic anhydride-N-phenylmaleimide copolymer is used as a binder, the color development with time of the coating liquid slurry and the background color formation after drying after coating are often observed. It is possible to obtain a heat-sensitive recording material excellent in color development by a thermal head, sticking resistance, durability, oil resistance and plasticizer resistance.

The terpolymer used in the present invention can be effectively used not only as an ordinary thermal head type heat-sensitive recording material but also as a binder for an electric heat-sensitive recording material, a magnetic heat-sensitive recording material and the like.

[0029]

EXAMPLES The present invention will now be described in more detail with reference to examples. In addition, "part" in an Example shows a weight part.

(1) Formation of Coloring Layer The following composition liquid was prepared in order to produce a heat sensitive layer composition.

(Production of Terpolymer) (A) In a 1 liter autoclave equipped with a stirrer, 250 g of acetone, 9.8 g of maleic anhydride (0.1 mol) and 25.6 g of n-butyl acrylate (0) (1.2 mol) was charged, and the mixture was stirred for 30 minutes to be dissolved by mixing, nitrogen substitution was carried out, and then 67.3 g (1.2 mol) of isobutene was charged and the temperature was raised to 65 ° C.

Subsequently, separately prepared 2,2'-azobisisobutyronitrile 1.64 g (0.01 mol), maleic anhydride 88.3 g (0.9 mol), and n-butyl acrylate 38.5 g. (0.3 mol) and acetone 100
g of the mixed solution was continuously charged over 5 hours, and further 3
The polymerization reaction was carried out at 65 ° C. for an hour. After completion of the polymerization, the solution in the autoclave was taken out, air-dried overnight and then vacuum dried at 80 ° C. to obtain 214.0 g of a polymer.

The average molecular weight of this polymer measured by GPC was 96,80 in terms of polystyrene.
0, number average molecular weight 37,200, acid value 520mg
It was KOH / g. The infrared absorption spectrum of the polymer was measured to find that the absorption derived from the isobutylene unit was 1,390.
cm ^-1, confirming the 1,370Cm ^-1, absorption 1,850Cm ^-1 derived from maleic anhydride units, the 1,770Cm ^-1, absorption derived from n- butyl acrylate units in 1,730Cm ^-1 The composition molar ratio of the isobutylene unit, the maleic anhydride unit and the n-butyl acrylate unit calculated based on the ¹ H-NMR measurement value was 1: 1.0: 0.4.
It was 8.

(B) In a 1 liter autoclave equipped with a stirrer, 180 g of acetone and 3.9 g of maleic anhydride.
(0.04 mol) and n-butyl acrylate 38.5
3 g of isobutene after charging g (0.3 mol), stirring for 30 minutes and dissolving by mixing to perform nitrogen substitution.
(0.6 mol) was charged and the temperature was raised to 75 ° C.

Subsequently, 1.64 g (0.01 mol) of 2,2'-azobisisobutyronitrile separately prepared, 35.3 g (0.36 mol) of maleic anhydride, and 38.5 g of n-butyl acrylate. (0.3 mol) and acetone 70
g of the mixed solution was continuously charged over 5 hours, and further 3
The polymerization reaction was carried out at 75 ° C. for an hour. After completion of the polymerization, the solution in the autoclave was taken out, air-dried overnight, and vacuum dried at 80 ° C. to obtain 135.2 g of a polymer.

The average molecular weight of this polymer as measured by GPC was 62,30 in terms of polystyrene.
0, number average molecular weight 24,600, acid value 332 mg
It was KOH / g. The composition molar ratio of isobutylene unit, maleic anhydride unit and n-butyl acrylate unit calculated based on the ¹ H-NMR measurement value of the polymer was 1:
It was 1.03: 1.45.

Example 1 In order to prepare a thermosensitive color forming layer-forming liquid, a mixture having the following composition was mixed and ground using a sand grinder to prepare liquids A, B and C.

Liquid A: 3-diethylamino-6-methyl-7-40 parts N-phenylfluorane (leuco dye) 10% aqueous polyvinyl alcohol solution 50 parts water 150 parts Solution B: water 100 parts Bisphenol A (developing agent) 100 parts 10% polyvinyl alcohol aqueous solution 100 parts C liquid: calcium carbonate 50 parts 30% polyacrylic acid 10 parts ammonium aqueous solution (dispersant) water 100 parts The A, B and C solutions prepared as described above are mixed and further (A A 15% aqueous solution of the terpolymer obtained in () was mixed (neutralization degree with ammonium: 60%) to prepare a thermosensitive color forming layer forming liquid.

This coating solution was applied to a high-quality paper weighing 50 g / m ² using a bar coater so that the solution amount was 30 g / m ² and then dried at 50 ° C. to obtain a thermosensitive recording paper of the present invention.

Example 2 Except that 200 g of a 20% aqueous solution of the terpolymer obtained in (B) above (neutralization degree with ammonia: 80%), 200 g, was used instead of the aqueous solution of the terpolymer of Example 1. In the same manner as in Example 1, a thermal recording material of the present invention was obtained.

Comparative Example A thermal recording material for comparison was obtained in the same manner as in Example 1 except that an aqueous solution of a terpolymer was not used.

The results of measuring the performance of the thermal recording materials obtained in Examples 1 and 2 and Comparative Example are shown in Table 1.

[0043]

[Table 1] (1) Water resistance: After dipping the test piece in water at 20 ° C. and 40 ° C. for 24 hours, the coated surface was strongly rubbed and the separation of the compounded silica was visually determined.

(2) Water resistance fading: A test piece developed by a heat gradient printer at 110 ° C. and 100 ° C. for 5 seconds was immersed in water at 20 ° C. and 40 ° C. for 24 hours, and the color density before and after immersion was measured by reflection type color density. The degree of fading was measured by measuring with Macbeth RD-514.

(3) Sticking: After printing with a thermal printer MTP-201 (manufactured by Seiko Denshi), the printed surface was observed and judged with a scanning electron microscope.

(4) Print Density: A sample developed with a heat gradient printer at 110 ° C. for 5 seconds was measured with a color densitometer.

(5) Solvent resistance: Methyl ethyl ketone and ethyl alcohol were instilled on a sample piece which had been developed by a heat gradient printer at 110 ° C. for 5 seconds, and the discoloration of the instilled portion was visually judged.

(6) Plasticizer: A sample piece colored by a heat gradient printer at 110 ° C. for 5 seconds was sandwiched between thick vinyl chloride sheets and left at room temperature under a load of 300 g / cm ² , and the degree of fading was visually observed. It was judged by.

(7) Whiteness: Murakami type GLOSS METE
It was measured by RGM-3M.

(8) Pot life of coating liquid for protective layer: Judgment was made by the change in viscosity of the coating liquid which was allowed to stand at room temperature. It is preferable that the viscosity increase is small.

[0051]

The present invention provides a heat-sensitive recording sheet having not only improved solvent resistance, plasticizer resistance and oil resistance, but also significantly improved water resistance, and further improved sticking resistance.

Claims (1)

[Claims] 1. A thermosensitive recording material comprising a support and a thermosensitive coloring layer containing a leuco dye, a color developer and a binder, wherein an isobutylene unit and maleic anhydride are used as at least a part of the binder. A thermosensitive recording material comprising a terpolymer comprising an acid unit and an n-butyl acrylate unit.