JP2777226B2 - 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.

[Conventional technology]

2. Description of the Related Art It is conventionally 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 together with a water-soluble binder onto a support. 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 is a drawback in that the color-developed portion is easily discolored and decolored when contacted with an agent or the like. 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. As methods for overcoming such disadvantages, various methods have been proposed, such as a method of using a water-proofing agent in combination with an aqueous solution binder, a method of improving a binder resin, and a method of providing a protective film.

[Problems to be solved by the invention]

The characteristics required for the protective film include the following.

1. The coloring layer on the thermal recording sheet is 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 friction of the thermal head does not occur (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).

Conventionally, many resin compositions have been proposed for forming a protective layer for the purpose of satisfying the above-mentioned required characteristics. However, 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 problem]

According to the present invention, the object is to provide a thermosensitive recording sheet in which a thermosensitive coloring layer is provided on a support, wherein α-
Olefin-maleic anhydride copolymer and general formula RO (AO) _n H (I) (wherein R is an alkyl group having 1 to 10 carbon atoms, and A is a carbon number which may be substituted by a phenyl group) 2 to 4 vic-alkylene groups, wherein A in each () may be the same or different, and when different, the same A and different A are O
May be connected in blocks or may be connected randomly, and n is an integer of 1 to 20). The thermoplastic aqueous solution obtained by subjecting the polyoxyalkylene glycol monoether represented by The problem is solved by a heat-sensitive recording sheet characterized in that a protective layer containing a conductive resin as a main component is provided.

The α-olefin-maleic anhydride copolymer used in the present invention is an α-olefin and maleic anhydride,
Or a chain reaction through a carbon-carbon double bond of an α-olefin, maleic anhydride and another type of monomer containing a carbon-carbon double bond copolymerizable with an α-olefin, maleic anhydride. Means a polymer.

The α-olefin referred to herein means a linear or branched olefin having a double bond at the 1-position, such as ethylene, propylene, 1-butene, isobutylene, and 1-olefin.
Pentene, 2-methyl-1-butene, 1-hexene, 2
-Methyl-1-pentene, 3-methyl-1-pentene,
Carbon number 2 such as 2-ethyl-1-butene and diisobutylene
-12, preferably 2-8 alpha-olefins are included. These α-olefins are used alone or in combination of two or more. The thermoplastic water-soluble resin of the present invention obtained by modifying the isobutylene-maleic anhydride copolymer has high heat distortion temperature, high thermal decomposition temperature, and excellent strength, so that isobutylene is used as the α-olefin. Is particularly preferred.

Maleic anhydride used includes maleic acid, monoalkyl maleate, dialkyl maleate,
Some maleic acid derivatives such as chlormaleic acid and citraconic acid may be contained. The content of these derivatives is not particularly limited, but is usually up to 80% (w / w).

Other types of monomers containing a carbon-carbon double bond copolymerizable with α-olefin and maleic anhydride used herein include styrene, alkyl-substituted styrene, vinyl ether, vinyl ester, vinyl halide, and allyl ether. And vinyl compounds such as allyl alcohol, allyl ester, acrylonitrile, acrylate, methacrylate, acrylamide, and methacrylate, diene such as isoprene and butadiene, maleimide, and N-substituted maleimide.
These monomers can be used alone or in combination of two or more.

The copolymer molar ratio of the α-olefin-maleic anhydride copolymer used in the present invention is suitably from 1 to 5 mol of α-olefin to 1 mol of maleic anhydride (when maleic acid derivative is contained as a whole). is there. If the amount of the α-olefin is less than 1 mol per 1 mol of maleic anhydride, the thermoplasticity of the copolymer will be poor, and if it is more than 5 mol, the water solubility of the copolymer will decrease. When a mixture of an α-olefin and another type of monomer is used, the sum of these may be used so as to fall within the above range.

Although the molecular weight of the α-olefin-maleic anhydride copolymer is not particularly limited, physical properties such as thermoformability of the thermoplastic water-soluble resin used in the present invention, strength and flexibility of the molded product are appropriate. 1,000 to 1,000,0
00 is preferred.

The α-olefin-maleic anhydride copolymer used in the present invention is partially known, and may be prepared by a known method (for example, Japanese Patent Publication No. 53-38095). -Obtained by copolymerizing olefins, maleic anhydride and other types of monomers using a radical catalyst. In brief, the radical polymerization catalyst used in the copolymerization includes organic peroxides such as cumene hydroperoxide, t-butyl hydroperoxide, and benzoyl peroxide; and α, α'-azobisisobutyro. Nitrile,
α, α'-azo-α-ethylbutyronitrile, α, α '
Azo compounds such as -azo-α-methylvaleronitrile. Polymerization is carried out by a solution polymerization or precipitation polymerization method using a solvent that does not inhibit radical polymerization, for example, ascent, methyl ethyl kent, benzene, toluene, ethyl acetate, isopropyl acetate, dioxane, tetrahydrofuran, chloroform and the like. It is also possible to carry out by bulk polymerization without using a solvent. The polymerization temperature is not particularly limited, but is usually in the range of 0 to 200 ° C,
The polymerization time is also usually in the range of 1 to 50 hours. Separation of the formed α-olefin-maleic anhydride copolymer from the polymerization-terminated liquid is carried out by removing the precipitated polymer by filtration and dewatering in the case of precipitation polymerization, and by drying out the solvent in the case of solution polymerization. Done.

The polyoxyalkylene glycol monoether of the general formula (I), which is another raw material of the present invention, has 1 to 1 carbon atoms.
The alkanol of 10 may be substituted with a phenyl group in the presence of a base catalyst such as potassium hydroxide, sodium hydroxide, pyridine, picoline, 2-methylimidazole or an acid catalyst such as boron trifluoride or tin tetrachloride. Good carbon number 2
~ 10 vic-alkylene oxides can be obtained by addition reaction.

Examples of the alkanol having 1 to 10 carbon atoms used in the present invention include methanol, ethanol, propanol, butanol, heptanol, nonanol, decanol, and the like, and further, a phenyl group may have 2 to 10 carbon atoms which may be substituted. As the vic-alkylene oxide, for example,
Examples include ethylene oxide, propylene oxide, 1,2-epoxybutane, 1,2-epoxypentas, and styrene oxide.

The addition reaction of the alkylene oxide to the alkanol proceeds almost stoichiometrically, and a polyoxyalkylene glycol monoether having an average molar number of the added alkylene oxide to the alkanol is obtained.
If the average addition mole number of the alkylene oxide is too large, the addition reaction of the alkylene oxide takes time, and the esterification reaction between the obtained polyoxyalkylene glycol monoether and α-olefin-maleic anhydride copolymer is also slow. Therefore, it is appropriate to be in the range of 1 to 20.

The amount of catalyst used is 0.1 to 5% by weight based on alkanol.
Is appropriate. The solvent is usually unnecessary, but may be diluted with no active hydrogen, for example, acetone, tetrahydrofuran, dioxane or the like.

The reaction is usually suitably carried out at 30 to 150 ° C. for 1 to 30 hours.

If no unreacted alkylene oxide remains in the reaction solution after the reaction, the reaction solution containing the polyoxyalkylene glycol monoether may be used as it is for the esterification reaction with the α-olefin-maleic anhydride copolymer. If unreacted alkylene oxide remains in the reaction solution, it is preferable to remove the alkylene oxide by distillation and then use it in an esterification reaction with an α-olefin-maleic anhydride copolymer.

The thermoplastic water-soluble resin used in the present invention is obtained by adding a polyoxyalkylene glycol monoether of the general formula (I) to an α-olefin-maleic anhydride copolymer by an esterification reaction. As a condition of the esterification, a method in which an α-olefin-maleic anhydride copolymer and an esterification catalyst are charged into a polyoxyalkylene glycol monoether diluted with an organic solvent, if necessary, and heated and stirred is preferable.

 The above esterification is a half esterification.

As the esterification catalyst, an acid catalyst such as formic acid or p-toluenesulfonic acid, or a basic catalyst of a tertiary amine, pyridine, or an imidazole compound is suitable. The amount of the esterification catalyst used is suitably from 0.1 to 3% by weight in the case of an acid catalyst and from 0.1 to 5% by weight in the case of a basic catalyst, based on the α-olefin-maleic anhydride copolymer. As a solvent to be used, a solvent that dissolves both the starting compound and the resulting compound, for example, dimethylformamide, ascent, tetrahydrofuran and the like are suitable.

If the degree of esterification is too small, the thermoplasticity of the resulting thermoplastic resin will be insufficient, so that at least 5%, especially at least 8%, of the maleic anhydride groups in the α-olefin-maleic anhydride copolymer will be esterified. Is appropriate.

The reaction temperature varies depending on the type of the α-olefin-maleic anhydride copolymer or polyoxyalkylene glycol monoether used, but generally 50 to 200 ° C. is preferable. The reaction time is suitably from 1 to 30 hours.

After completion of the esterification reaction, unreacted polyoxyalkylene glycol monoether and a solvent used are removed by distillation to obtain a thermoplastic water-soluble resin as a residue.

The thermoplastic water-soluble resin used in the present invention has various physical properties (softening point, melt viscosity, film strength, etc.) depending on the type of α-olefin-maleic anhydride copolymer or polyoxyalkylene glycol monoether, the difference in esterification rate, and the like. (A degree of water solubility) can be obtained, but generally it can be melt-molded and has excellent film properties.

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, 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 triphenyl metal type, triphenyl metal phthalate 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-methylphenol). -6-t-butylphenol), 4,4'-isopropylidenepyridene diphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4'-isopropylidenebis (2
-Methylphenol), 4,4'-sec-butylidenephenol, 4,4'-ethylenediphenol, and 4,4'-ethylenebis (2-methylphenol).

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, Waxes, condensates of aromatic carboxylic acids and amines, phenyl benzoate, higher linear glycols, dialkyl 3,4-epoxy-hexofudophthalate, higher ketones, dibenzyl terephthalate, hydroxynaphthoic esters, α-naphthohydroquinone Diether and the like.

In the present invention, the thermoplastic water-soluble resin is prepared by adding 0.2 to 1.0 equivalents of an alkali immediate ammonia, NaOH, KOH, Mg (OH) _2, etc., in water with an acid value (derived from maleic anhydride group) of the resin. It is used under water by heating.

Further, the thermoplastic water-soluble resin may be used in combination with polyvinyl alcohol, starch, hydroxyethylcellulose, methylcellulose, styrene-maleic anhydride copolymer or the like conventionally used as a resin component for constituting the protective layer. In particular, the use in combination with polyvinyl alcohol is effective in improving the physical properties of the protective layer. In this case, the polyvinyl alcohol and the thermoplastic water-soluble resin are 95: 5 to 20:80, preferably 95: 5
It may be used in a weight ratio of ~ 50: 50. Incidentally, the polyvinyl alcohol is used by crosslinking with a polyvalent aldedo such as glyoxal, and the thermoplastic water-soluble resin is used by crosslinking with a polyfunctional epoxy compound such as glycerin diglycidyl ether to form a protective layer. Water resistance can be made more complete.

〔Example〕

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

Reference Example 1 (Formation of Thermosensitive Coloring Layer) The following composition was prepared to produce a thermosensitive layer composition.

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
Using a bar coater to apply 7 g / m ² on one side,
After drying, a heat-sensitive recording sheet was obtained.

Reference Example 2 (Production of Thermoplastic Water-Soluble Resin) (A) 32 g of methanol and 0.32 g of 2-methylimidazole were charged into a 1-liter autoclave, and after addition of nitrogen, 264 g of ethylene oxide was gradually injected at 60 to 80 ° C. to perform an addition reaction. ,
Polyoxyethylene glycol monomethyl ether having an average addition mole number of ethylene oxide of 6 (a mixture of addition mole numbers of n = 4 to 8 centered on n = 6 according to GPC analysis) was obtained. Then, 17.8 g of the obtained polyoxyethylene glycol monomethyl ether, an isobutylene-maleic anhydride copolymer having a weight average molecular weight of 50,000 (Isoban 04,
(Recla Co., Ltd.) (copolymer composition molar ratio, isobutylene:
Maleic anhydride = 1: 1) 30.8 g, 2-methylimidazole
0.50 g and 100 g of DMF were charged into a three-necked flask equipped with a reflux condenser, and the mixture was stirred and heated at 80 to 90 ° C. for 5 hours under a stream of N ₂ gas to carry out an esterification reaction.

When unreacted polyoxyethylene glycol monomethyl ether in the reaction completed solution was quantified by GPC using polypropylene glycol as an internal standard substance, the average conversion of polyoxyethylene glycol monomethyl ether was 50%.

The reaction-terminated liquid was dried at 120 ° C. under reduced pressure, DMF and unreacted polyoxyethylene glycol monomethyl ether were distilled off, and 39.5 g of a partially esterified product of isobutylene-maleic anhydride copolymer with polyoxyethylene glycol monomethyl ether was removed. Obtained.

(B) A 1 l autoclave was charged with 46.1 g of ethanol and 0.5 g of 2-methylimidazole, and after addition of nitrogen, 264 g of ethylene oxide was gradually injected at 70 to 90 ° C to perform an addition reaction.
Polyoxyethylene glycol monomethyl ether having an average number of added moles of ethylene oxide of 6 (a mixture of n = 4 to 8 according to GPC analysis) was obtained. Next, an isobrylene-maleic anhydride-N-phenylmaleimide copolymer (isobutylene: maleic anhydride: N-phenylmaleimide copolymer composition) having 29.2 g of polyoxyethylene glycol monomethyl ether and a weight average molecular weight of 35,000 thus obtained was obtained. Molar ratio = 0.50: 0.35: 0.15) 30.8 g, 2-
0.50 g of methyl imidazole and 150 g of ascent are charged to a three-necked flask equipped with a reflux condenser, and heated to 80 to 100 ° C. with N _2.
For 5 hours to carry out an esterification reaction.

The analysis of the reaction-terminated liquid showed that the conversion of polyoxyethylene glycol monomethyl ether was 45%.

The reaction-terminated liquid was dried at 120 ° C. under reduced pressure, and ascent and unreacted polyoxyethylene glycol monomethyl ether were distilled off. Esterified product 43.8g
I got

Example 1 A 10% aqueous solution of a partially esterified product of isobutylene-maleic anhydride copolymer obtained in (A) of Reference Example 2 and polyoxyethylene glycol monomethyl ether (thermoplastic water-soluble resin) (degree of neutralization with ammonia) 60%)
Liquid, 10% polyvinyl alcohol (Kuraray Povar PVA 10
5) The aqueous solution was used as liquid II, and these were mixed according to the following formulation to obtain a protective layer forming liquid.

This was applied to the sheet on which the heat-sensitive layer had been formed obtained in Reference Example 1 so as to have a coating amount of 7 g / m ² (solid content) to obtain a desired heat-sensitive sheet.

Example 2 A 10% aqueous solution of a partially esterified product (thermoplastic water-soluble resin) of the isobutylene-maleic anhydride-N-phenylmaleimide copolymer obtained in Reference Example 2 (B) with polyoxyethylene glycol monomethyl ether. (Protection layer forming liquid) was prepared by mixing the same formulation as in Example 1 except that (the degree of neutralization with ammonia 60%) was changed to Liquid I. This was applied to the heat-sensitive layer-formed sheet obtained in Reference Example 1 at a coating amount of 4 g / m ^2.
(Solid content) to obtain a desired heat-sensitive sheet.

Comparative Example 1 On the upper surface of the heat-sensitive layer-formed sheet obtained in Reference Example 1. The coating liquid was applied so that the coating amount was 4 g / m ² (solid content) to obtain a thermosensitive recording sheet.

Each heat-sensitive sheet thus obtained is dried in a hot air dryer at 50 ° C for 5 minutes.
After drying for minutes, the coated surface was smoothed by passing through a calender at a roll temperature of 45 ° C., a nipple pressure of 75 kg / cm ² and a roll speed of 10 m / min three times. Thereafter, the heat-sensitive sheet was cured in an environment of a temperature of 20 ° C. and a humidity of 60% for 6 days. The performance of the heat-sensitive recording sheet and the pot life of the protective layer forming coating liquid were examined. The results are shown in the table.

(1) Water resistance: After immersing the test piece in water of 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 that developed color at 110 ° C and 100 ° C for 5 seconds by a heat gradient printer was immersed in water at 20 ° C and 40 ° C for 24 hours, and the color density before and after immersion was measured using a Macbeth RD reflective color densitometer. Measured at -514 and compared the degree of fading.

(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.

(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 was added to a sample piece that had been colored at 110 ° C. for 5 seconds with a heat gradient printer.
Ethyl alcohol was instilled, and the fading of the instilled portion was visually judged.

(6) Plasticizer resistance: A sample piece that had developed color at 110 ° C. for 5 seconds with a heat gradient printer was sandwiched with a thick vinyl chloride sheet, left at room temperature under a load of 300 g / cm ² , and the degree of fading was visually observed. Judged.

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

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

〔The invention's effect〕

According to the present invention, there is provided a heat-sensitive recording sheet having significantly improved water resistance as well as improved solvent resistance, plasticity resistance and oil resistance, and further improved sticking resistance.

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Claims (1)

(57) [Claims] 1. A thermosensitive recording sheet having a thermosensitive coloring layer provided on a support, wherein an α-olefin-
Maleic anhydride copolymer and general formula RO (AO) _n H ( _where R is an alkyl group having 1 to 10 carbon atoms, and A is vic having 2 to 4 carbon atoms which may be substituted by a phenyl group) -An alkylene group, A in each () may be the same or different, and if different, the same A and a different A are connected at random even if connected in a block via O And n is an integer of 1 to 20). A protective layer mainly composed of a thermoplastic water-soluble resin obtained by an esterification reaction with a polyoxyalkylene glycol monoether represented by the following formula: A heat-sensitive recording sheet characterized by the following.