JP2721505B2 - Thermal recording sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermosensitive recording sheet in which a protective layer made of a specific resin component is provided on a thermosensitive coloring layer provided on a support.

(Prior Art) Conventionally, it is known to produce a thermosensitive recording sheet by applying a colorless lactone compound such as crystal violet lactone and an acidic compound such as a phenol compound on a support together with a water-soluble binder. It is. The thermal recording sheet thus obtained is widely used for recording in facsimile machines, automatic ticket vending machines, calculators, medical measuring instruments and the like. However, in the heat-sensitive recording sheet manufactured using the water-soluble binder in this way, the resulting color image is unstable with respect to moisture or organic solvents, and may come into contact with water or the plastic sheet in the PVC sheet. There was a drawback in that the color-developed part was easily discolored and decolored when it came into contact with the agent zone. In addition, the accumulation of scum of the heat-sensitive layer in the thermal head due to sticking is attracting attention as a factor inhibiting the speeding up of a thermal printer which requires high applied energy. Various methods have been proposed as methods for overcoming such disadvantages, such as a method of using a water-resistant agent in combination with a water-soluble binder, a method of improving a binder resin, and a method of providing a protective layer.

(Problems to be Solved by the Invention) Properties required for the protective layer include the following.

1. The color-forming layer on the thermal recording sheet must be completely protected from moisture by a protective layer (water resistance).

2. Sticking does not occur during heating printing, sticking residue does not adhere to the thermal head, and the thermal head does not wear (sticking resistance).

3. The decrease in print density due to the influence of the protective layer is small, and there is no decrease in whiteness as a heat-sensitive recording sheet (color developability).

4. It can prevent the decoloring and fading substances such as organic solvents, oils and plasticizers from penetrating into the coloring layer (solvent resistance, oil resistance, plasticizer resistance).

Many conventional resin compositions have been proposed as protective layer forming resins for the purpose of satisfying the above-mentioned required properties.
At present, a heat-sensitive recording sheet that is practically satisfactory has not been obtained.

The present invention provides a thermal head having improved solvent resistance, plasticizer resistance and oil resistance, significantly improved water resistance, and further improved sticking resistance by improving a protective layer provided on a heat-sensitive coloring layer on a support. The purpose of the present invention is to provide a heat-sensitive recording sheet with improved runnability.

(Means for Solving the Problems) According to the present invention, an object of the present invention is to provide a thermosensitive recording sheet having a thermosensitive coloring layer provided on a support, wherein (a) α-olefin, (B) It has been found that this is achieved by a heat-sensitive recording sheet characterized in that a protective layer comprising a copolymer of maleic anhydride and (c) maleic imide or an N-substituted derivative thereof is provided. .

The α-olefin used in the present invention means a linear or branched olefin having a carbon-carbon unsaturated double bond at the α-position, particularly an olefin having 2 to 12 carbon atoms, particularly 2 to 8 carbon atoms. . Representative examples are ethylene, propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene, 1-hexene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl -1-
Penten, 2-ethyl-1-butene, 2,4,4-trimethyl-1-pentene and the like can be mentioned. Of these, isobutylene is particularly preferred. Here, isobutylene also includes a return BB containing isobutylene. These α-
The olefins may be used alone or in combination of two or more.

The maleimide or N-substituted derivative thereof used in the present invention includes maleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, Nn-butylmaleimide, Nt-butylmaleimide. , N-alkylmaleimides such as N-cyclohexylmaleimide, N-alkylphenylmaleimides such as N-phenylmaleimide, N-methylphenylmaleimide, N-ethylphenylmaleimide, or N-methoxyphenylmaleimide, N Preferred examples include N-alkoxyphenylmaleimides such as -ethoxyphenylmaleimide, and halides thereof (eg, N-chlorophenylmaleimide). Among these, maleimides having a phenyl group at the N-position, especially N-phenylmaleimide, are preferred.

Composition ratio of (a) α-olefin and (b) maleic anhydride and (c) maleic imide or its N-substituted derivative constituting the copolymer [(a) / ((b) +
(C))] is preferably in the range of 1/1 to 3/1 in molar ratio, and the composition ratio of (ii) maleic anhydride and (iii) maleic imide or N-substituted derivative (( B) /
(C)) is preferably in a molar ratio of 95/5 to 30/70. The copolymer is 0.2 to 1.0 with respect to maleic anhydride.
Double equivalents of alkali, i.e., ammonia, NaOH, KOH, Mg
(OH) _{2 and the} like are heated in water to make them water-soluble and used.

Polyvinyl alcohol, starch, hydroxyethylcellulose, methylcellulose, styrene-maleic anhydride copolymer and the like conventionally used as a resin component for constituting the protective layer may be used in combination with the above copolymer, and in particular, The use of polyvinyl alcohol in combination with the above copolymer is effective in improving the physical properties of the protective layer. In this case, the polyvinyl alcohol and the copolymer are 95: 5 to 20:80, preferably 95: 5 to 50:50
The weight ratio is preferably used. The polyvinyl alcohol is used by crosslinking with a polyhydric aldehyde such as glyoxal, and the copolymer is used by crosslinking with a polyfunctional epoxy compound such as glycerin diglycidyl ether, whereby the water resistance of the protective layer is increased. Can be more complete.

In the present invention, typical examples of the heat-sensitive color-forming component constituting the heat-sensitive color-forming layer include two components of a color-forming substance and a color-developing substance that reacts with the color-forming substance to form a color when heated. A typical example of the color-forming substance is a color-forming lactone compound. The color-forming lactone compound may be any as long as it reacts with the acidic compound upon heating to form a color.
For example, various leuco compounds such as triphenylmethane type, triphenylmethanephthalide type, fluoran type, leuco auramine type, spiropyran type and the like can be mentioned. Examples of color-developing substances include, for example, 4-phenylphenol, 4-hydroxyacetophenone, 2,2'-diacetoxyphenol, 2,2'-methylenebis (4-chlorophenol), and 2,2'-methylenebis ( 4-methyl-6-t-butylphenol, 4,4'-isopropylidenediphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4'-isopropylidenebis (2-methylphenol ), 4,4'-sec-butylidenephenol,
4'-ethylenediphenol, 4,4'-ethylenebis (2
Phenolic compounds such as -methylphenol).

Examples of the support used in the thermal recording sheet of the present invention include paper, synthetic paper, film, and woven sheet.

In the present invention, in order to bond and support the thermosensitive coloring layer on the support, various conventional binders can be appropriately used, for example, polyvinyl alcohol, starch, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, Cellulose derivatives such as ethyl cellulose; sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylate copolymer, acrylamide-acrylate-methacrylic acid terpolymer, styrene-maleic anhydride copolymer alkali Salts, isobutylene-maleic anhydride copolymer alkali salts, water-soluble polymers such as polyacrylamide, sodium alginate, gelatin, casein; polyvinyl acetate, polyurethane, styrene-butadiene copolymer, polyacryl , Polyacrylic acid ester, vinyl chloride - vinyl acetate copolymer, polybutyl methacrylate, ethylene - vinyl acetate copolymer, styrene - butadiene - can be exemplified latexes such as the acrylic copolymer.

In the present invention, if necessary, auxiliary additives commonly used in this type of heat-sensitive recording material, such as fillers, surfactants, and heat-fusible substances, can be used in combination. In this case, as the filler, for example, other than inorganic fine powder such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, surface-treated calcium and silica, Organic fine powders such as urea-formalin resin, styrene-methacrylic acid copolymer, and polystyrene resin can be mentioned. Examples of the heat-fusible substance include higher fatty acids and their esters, amides, and metal salts, as well as various types. Waxes, condensates of aromatic carboxylic acids and amines, phenyl benzoate, higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalate, higher ketones, dibenzyl terephthalate, hydroxy naphthoate esters, α -Naphthohydroquinone diether and the like.

 Hereinafter, the present invention will be described more specifically with reference to examples.

(1) Formation of thermosensitive coloring layer The following composition liquid was prepared.

Each liquid was dispersed in a ball mill for 24 hours and mixed well to obtain a thermosensitive coloring layer forming liquid. The coating amount of this fine paper of 65 g / m ² is
Apply one side using a bar coater so that it becomes 7 g / m ² ,
The sheet was dried to form a thermosensitive coloring layer.

(2) Formation of a protective layer A 10% aqueous solution of a copolymer of isobutylene, maleic anhydride, and N-phenylmaleimide having a molar composition ratio of 50:27:23 (a degree of neutralization of maleic anhydride with ammonia of 60%) was used. I
Liquid, 10% polyvinyl alcohol (Kuraray Povar PVA-1
05) Make the aqueous solution II, mix these with the following formula,
This was used as a protective layer forming liquid.

This was applied to the sheet having the heat-sensitive layer formed thereon obtained in the above (1) so as to have a coating amount of 4 g / m ² to obtain a heat-sensitive recording sheet.

Comparative Example 1 On the upper surface of the thermosensitive coloring layer-formed sheet obtained in (1) of Example 1, A thermosensitive recording sheet was obtained by applying such a coating solution so that the coating amount was 4 g / m ² .

Example 2 A 10% aqueous solution of a copolymer having a molar ratio of isobutylene, maleic anhydride and N-phenylmaleimide of 50:35:15 (a degree of neutralization of maleic anhydride with ammonia of 50%) was added to I.
Liquid, 10% polyvinyl alcohol (Kuraray Povar PVA-1
05) Formulation below, using aqueous solution as liquid II The heat-sensitive recording sheet was obtained by applying a coating solution comprising the same to the heat-sensitive coloring layer-formed sheet obtained in Example 1 (1) so that the coating amount was 4 g / m ² .

Each of the thus obtained heat-sensitive recording sheets was dried in a 50 ° C hot air drier for 5 minutes, and then roll temperature was 45 ° C and nipple pressure was 75kg / c.
The coated surface was smoothed by passing through a calender with m ² and a roll speed of 10 m / min three times. After that, each thermosensitive recording sheet has a temperature of 20 ° C.
The curing was performed for 6 days in a 60% RH environment.

The physical properties of the heat-sensitive recording sheet and the pot life of the protective layer forming coating liquid used in Examples 1, 2 and Comparative Example 1 were examined. The results are shown in the table.

(1) Water resistance (wet rub): The test piece was immersed in water at 20 ° C. and 40 ° C. for 24 hours, and then the coated surface was strongly rubbed to visually determine the presence or absence of separation of the compounded silica. The lower the separation of the compounded silica, the better the water resistance.

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

(3) Anti-sticking: Thermal printer MTP-201
After printing by (Seiko Electronics Co., Ltd.), the printed surface was observed and judged with a scanning electron microscope. The smaller the change of the coated polymer due to heat, the better the sticking resistance.

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

(5) Solvent resistance: Methyl ethyl ketone and ethyl alcohol were instilled on a sample piece that had developed color at 110 ° C. for 5 seconds using a heat gradient printer, and the fading of the instilled portion was visually determined. The smaller the degree of fading, the better the solvent resistance.

(6) Plasticizer resistance: A sample piece that had been colored at 110 ° C. for 5 seconds by a heat gradient printer was sandwiched with an agricultural vinyl chloride sheet and left at room temperature under a load of 300 g / cm ² to visually check the degree of fading. Judged. The smaller the degree of fading, the better the plasticizer resistance.

(7) Whiteness: measured by Murakami's GLOSS METER GM-3M.

(8) Pot life of coating liquid for protective layer: Determined by a change in viscosity of the coating liquid left at room temperature. Those having a small increase in viscosity are preferred.

(Effects of the Invention) The present invention provides a heat-sensitive recording sheet in which the solvent resistance, the plasticizer resistance and the oil resistance are improved, the water resistance is remarkably improved, and the sticking resistance is further improved.

Claims (1)

(57) [Claims] 1. A thermosensitive recording sheet having a thermosensitive coloring layer provided on a support, wherein (a) α-olefin, (b) maleic anhydride and (c) maleic imide or A heat-sensitive recording sheet provided with a protective layer containing a copolymer of the N-substituted derivative as a component.