JPH06183149A - Thermal recording layer protective coating agent - Google Patents

Abstract

PURPOSE:To provide the title coating agent capable of forming a protective layer excellent in printing preservability such as water resistance or solvent resistance and background color development preventing properties on the thermal recording layer of a thermal recording material. CONSTITUTION:A thermal recording layer protective coating agent is used in order to form a protective layer on the upper surface of the thermal recording layer consisting of a leuco dye, a developer reacting with the leuco dye by heating to develop a color and a binder formed on a support and contains a carboxyl group-containing aqueous polymer (A) and an oxazoline group- containing aqueous polymer (B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel heat-sensitive recording layer protective coating agent, and more specifically, it can improve the storage stability of prints such as water resistance and plasticizer resistance and can prevent fog (ground coloration). Therefore, the present invention relates to a heat-sensitive recording layer protective coating agent suitable for manufacturing heat-sensitive recording paper such as labels and printer paper.

[0002]

2. Description of the Related Art In recent years, a thermosensitive recording paper having a dye-based thermosensitive recording layer formed by combining a leuco dye and a phenolic acidic substance has been widely used in the fields of printers, labels, etc. The demands for quality improvement are also diversified and sophisticated. Along with this, attempts have been made to improve the storability of printing such as water resistance and plasticizer resistance.

As one of those techniques, an attempt has been made to provide a transparent protective layer on the heat-sensitive recording layer.
For example, Japanese Patent Publication No. 2-9953 discloses a protective layer containing polyvinyl alcohol as a main component and an epoxy compound containing two or more epoxy groups or an ethyleneimine compound containing two or more ethyleneimine groups. , JP
JP-A 2-190388 discloses a protective layer containing a water-soluble resin or an aqueous emulsion resin, an aqueous ammonia solution of zinc oxide, and an aziridine compound.

[0004]

In these methods, since the component added to the protective layer is a low molecular weight compound, water resistance,
The storability of printing such as plasticizer resistance and the effect of preventing background color development are not sufficient.

The present invention is a heat-sensitive recording layer protective coating capable of forming a protective layer capable of preventing fog (background color development) on the heat-sensitive recording layer while improving the storage stability of printing such as water resistance and plasticizer resistance. It is an object to provide an agent.

[0006]

In order to solve the above problems, the present invention provides a leuco dye formed on a support,
A heat-sensitive recording layer protective coating agent for forming a protective layer on the upper surface of a heat-sensitive recording layer composed of a developer and a binder which react with the leuco dye to develop a color when heated, and which comprises a carboxyl group-containing aqueous polymer (A ) And an aqueous oxazoline group-containing aqueous polymer (B) are provided.

The carboxyl group-containing aqueous polymer (A), which is one of the coating agent components used in the present invention, is not particularly limited, but generally, carboxyl group-modified polyvinyl alcohol, carboxyl group-containing acrylic emulsion, carboxyl group-containing styrene- Butadiene latex is often used. Among these, the strength of the coating film,
From the viewpoint of durability, carboxyl group-modified polyvinyl alcohol is particularly preferable.

The carboxyl group-modified polyvinyl alcohol (A) means that the carboxyl group-containing polymerizable monomer such as acrylic acid, methacrylic acid or itaconic acid is copolymerized with vinyl acetate and then partially or completely suspended. The commercially available products are K polymers KL-118, KL-318, and KL-50 manufactured by Kuraray Co., Ltd.
6, KM-118, etc.

The other oxazoline group-containing aqueous polymer (B) of the coating agent component used in the present invention is
It is obtained by polymerizing an addition-polymerizable oxazoline (a) and optionally at least one other monomer (b).

In the present invention, the addition-polymerizable oxazoline (a) is represented by the following general formula 1.

[0011]

[Chemical 1]

[In the formula 1, R 1, R 2, R 3 and R 4 each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, a phenyl group or a substituted phenyl group, and R 5
Represents an acyclic organic group having an addition-polymerizable unsaturated bond. ]
Specific examples include 2-vinyl-2-oxazoline, 2-
Vinyl-4-methyl-2-oxazoline, 2-vinyl-
5-methyl-2-oxazoline, 2-isopropenyl-
2-oxazoline, 2-isopropenyl-4-methyl-
2-oxazoline, 2-isopropenyl-5-ethyl-
2-oxazoline can be mentioned, and one kind or a mixture of two or more kinds selected from these groups can be used. Among them, 2-isopropenyl-2-oxazoline is industrially easily available and suitable.

The amount of the addition-polymerizable oxazoline (a) used is not particularly limited, but is preferably 5% by weight or more in the polymer (B). If the amount is less than 5% by weight, the degree of curing will be insufficient and the durability and water resistance of the protective layer will tend to be impaired.

In the present invention, the other monomer (b) means
There is no particular limitation as long as it is a monomer that does not react with the oxazoline group and is copolymerizable with the addition-polymerizable oxazoline (a),
For example, methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
(Meth) acrylic acid esters such as methoxypolyethylene glycol (meth) acrylate; sodium (meth) acrylate, potassium (meth) acrylate, (meth)
(Meth) acrylates such as ammonium acrylate;
Unsaturated nitriles such as (meth) acrylonitrile; unsaturated amides such as (meth) acrylamide and N-methylol (meth) acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; methyl vinyl ether,
Vinyl ethers such as ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α, β-unsaturated monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride; α such as styrene and α-methylstyrene ，
The β-unsaturated aromatic monomers may be mentioned, and one kind or a mixture of two or more kinds thereof may be used.

The oxazoline group-containing aqueous polymer (B) is
The addition-polymerizable oxazoline (a) and optionally at least one other monomer (b) can be produced by solution polymerization or emulsion polymerization in an aqueous medium by a conventionally known polymerization method. The aqueous medium that can be used is not particularly limited as long as it can be mixed with water, but, for example, water, methanol, ethanol, propanol, isopropanol, butanol, tertiary butanol, ethylene glycol, ethylene glycol monomethyl ether, ethylene. Examples thereof include glycol monobutyl ether, diethylene glycol, acetone and methyl ethyl ketone.

In the present invention, the carboxyl group-containing aqueous polymer (A) and the oxazoline group-containing aqueous polymer (B)
The blending ratio with is not particularly limited, but the polymer (B) is 1 to 1 with respect to 100 parts by weight of the aqueous polymer (A).
A range of 00 parts by weight is preferred. If the amount is less than 1 part by weight, the degree of curing will be insufficient, and the durability and water resistance of the protective layer will be impaired. If the amount is more than 100 parts by weight, the thermal sensitivity of the protective layer formed by the protective coating agent will be low. Adhesion to the recording layer tends to be impaired.

If desired, conventional additives such as sensitizers, fillers, surfactants and heat-fusible substances may be used in combination with the above-mentioned heat-sensitive recording layer protective coating agent. In this case, as the filler, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powder such as surface-treated calcium or silica, and the like, Examples thereof include organic fine powders of urea-formalin resin, styrene / methacrylic acid copolymer, polystyrene resin, and the like. Examples of the heat-fusible substance include higher fatty acids or their esters, amides or metal salts. , Various waxes,
A mixture of aromatic carboxylic acid and amine, benzoic acid phenyl ester, higher linear glycol, 3,4-epoxy-
Examples thereof include dialkyl hexahydrophthalate, higher ketones, and other heat-fusible organic compounds having a melting point of about 50 to 200 ° C.

The protective layer of the heat-sensitive recording layer can be obtained by applying the protective coating agent of the present invention onto the heat-sensitive recording layer formed on a sheet-shaped support such as paper, synthetic paper or plastic film and drying it.

For the heat-sensitive recording layer, a known leuco dye, a color developer, and various additives and, if necessary, various additives and auxiliaries are dispersed in a binder component to form a heat-sensitive recording layer forming material on paper, synthetic paper,
It is obtained by coating and drying a sheet-shaped support such as a plastic film.

As the binder, known binders can be used, for example, polyvinyl alcohol, starch or modified products and derivatives thereof, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, gelatin, casein, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid. Examples thereof include salts, styrene / maleic anhydride copolymers, isobutylene / maleic anhydride copolymers, styrene / butadiene copolymers, polyvinyl acetate, polyacrylic acid esters and the like. Further, the carboxyl group-containing aqueous polymer (A) and the oxazoline group-containing aqueous polymer (B) used in the heat-sensitive recording layer protective coating agent of the present invention can also be used as a binder for the heat-sensitive recording layer-forming material. .

As the leuco dye, known leuco compounds such as triphenylmethane dyes, fluoran dyes, phenothiazine dyes, auramine dyes, spiropyran dyes and indolinophtalide dyes can be used. Specific examples of such leuco dyes include 3,3-bis (p-dimethylaminophenyl) phthalide and 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone). 3,3-bis (p-dimethylaminophenyl) -5-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide , 3-cyclohexylamino-6-chlorofluorane, 3-dimethylamino-5,
7-Dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7,8-benzfluorane, 3-diethylamino-6-methyl-7-chlorofluor Oran, 3- (Np-tolyl-N-ethylamino)-
6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3- (N-
(3'-Trifluoromethylphenyl) amino) -6-
Diethylaminofluorane, 2- (3,6-bis (diethylamino) -9- (o-chloroanilino) xanthyl benzoate lactam), 3-diethylamino-6-methyl-7- (m-trichloromethylanilino) fluorane,
3-dimethylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-N-methyl-N-amylamino-
6-methyl-7-anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-
Anilinofluorane, 3-diethylamino-5-methyl-7-dibenzylaminofluorane, benzoylleucomethylene blue, 6'-chloro-4'-methoxy-benzoindolino-pyrrilospirane, 5'-bromo-3'-
Methoxy-benzoindolino-pyrrilospirane, 3-
(2'-hydroxy-4'-dimethylaminophenyl)
-3- (2'-methoxy-5'-chlorophenyl) phthalide, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-nitrophenyl) phthalide, 3- (2'-Hydroxy-4'-diethylaminophenyl) -3- (2'-methoxy-5'-
Methylphenyl) phthalide, 3- (2'-hydroxy-
4'-dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-methylphenyl) phthalide, 3-morpholino-7- (N-propyl-trifluoromethylanilino) fluorane, 3- Pyrrolidino-7-
Trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7- (N-benzyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7-
(Di-p-chlorophenyl) methylaminofluorane,
3-diethylamino-5-chloro-7- (α-phenylethylamino) fluorane, 3- (N-ethyl-p-toluidino) -7- (α-phenylethylamino) fluorane, 3-diethylamino-7- (α -Methoxycarbonylphenylamino) fluorane, 3-diethylamino-5-methyl-7- (α-phenylethylamino) fluorane, 3-diethylamino-7-piperidinofluorane, 2-chloro-3- (N-methyltoluidino) -7-
(Pn-butylanilino) fluorane, 3- (N-benzyl-N-cyclohexylamino) -5,6-benzo-7-α-naphthylamino-4′-bromofluorane,
3-diethylamino-6-methyl-7-mesitidino-
4 ', 5'-benzofluorane etc. can be mentioned.

The color developer is a compound that reacts with the leuco dye when heated to develop a color, and a phenolic substance, an organic or inorganic acid compound, or an ester or salt thereof can be used. For example, gallic acid Acid, salicylic acid, 3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid,
3,5-di-α-methylbenzyl salicylic acid, 4,4 ′
-Isopropylidene bisphenol, 4,4'-isopropylidene bis (2-chlorophenol), 4,4'-
Isopropylidene bis (2,6-dibromophenol), 4,4'-isopropylidene bis (2,6-dichlorophenol), 4,4'-isopropylidene bis (2-methylphenol), 4,4'-isopropylidene Redenebis (2,6-dimethylphenol), 4,4′-isopropylidenebis (2-tert-butylphenol),
4,4'-sec-butylidene bisphenol, 4,4 '
-Cyclohexylidene bisphenol, 4,4'-cyclohexylidene bis (2-methylphenol), 4-te
rt-Butylphenol, 4-phenylphenol, 4-
Hydroxydiphenoxide, α-naphthol, β-naphthol, 3,5-xylenol, thymol, methyl-4
-Hydroxybenzoate, 4-hydroxyacetophenone, novolac-type phenol resin, 2,2'-thiobis (4,6-dichlorophenol), catechol, resorcin, hydroquinone, pyrogallol, phloroglysin, phloglycin carboxylic acid, 4-tert-octyl Catechol, 2,2'-methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-te)
rt-butylphenol), 2,2′-dihydroxydiphenyl, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate,
Benzyl p-hydroxybenzoate, p-hydroxybenzoic acid-p-chlorobenzyl, p-hydroxybenzoic acid-
o-chlorobenzyl, p-hydroxybenzoic acid-p-methylbenzyl, p-hydroxybenzoic acid-n-octyl, benzoic acid, zinc salicylate, 1-hydroxy-2-
Naphthoic acid, 2-hydroxy-5-naphthoic acid, zinc 2-hydroxy-6-naphthoate, 4-hydroxydiphenyl sulfone, 4-hydroxy-4'-chlorodiphenyl sulfone, bis (4-hydroxyphenyl) sulfide, 2- Hydroxy-p-toluic acid, 3,5-di-te
rt-Butyl salicylate zinc, 3,5-di-tert-butyl salicylate tin, tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid, stearic acid, 4-hydroxyphthalic acid, boric acid, thiourea derivative, etc. be able to.

[0023]

The thermal recording layer protective coating agent of the present invention comprises:
Since it contains the carboxyl group-containing aqueous polymer (A) and the oxazoline group-containing aqueous polymer (B), the protective layer becomes strong due to the reaction of forming an ionic interaction or a covalent bond between the carboxyl group and the oxazoline group. As a result, it is possible to form a heat-sensitive recording material which is excellent in print storage stability such as water resistance and plasticizer resistance. Further, fogging of the heat-sensitive recording layer can be prevented by the oxazoline group trapping an acidic component that causes background color formation.

[0024]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to the following examples.
In the following, "%" means "% by weight" and "part" means "part by weight" unless otherwise specified.

-Production Example 1 (Production Example of Polymer (B))-116 parts of deionized water and V-50 (Wako Pure Chemical Industries, Ltd.) were placed in a flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube and a thermometer. Polymerization initiator (2,2′-azobis (2-amidinopropane) dihydrochloride) (4 parts) manufactured by a corporation was charged and heated to 70 ° C. while gently flowing nitrogen gas. A monomer composed of 48 parts of methoxypolyethylene glycol acrylate (ethylene glycol is an average 9-mer, NK ester AM-90G manufactured by Shin-Nakamura Chemical Co., Ltd.) and 32 parts of 2-isopropenyl-2-oxazoline, which had been adjusted in advance. The mixture was added dropwise from the dropping funnel in 1 hour. Nitrogen gas was kept flowing during the reaction to keep the temperature in the flask at 70 ± 1 ° C. After completion of the dropping, the mixture was kept at the same temperature for 6 hours and then cooled to obtain an oxazoline group-containing polymer aqueous solution (1) having a nonvolatile content of 41.5%, pH 7.0 and a viscosity of 290 centipoise.

-Production Example 2 (Production Example of Polymer (B))-In a flask similar to that used in Production Example 1, 782.4 parts of deionized water and Hitenol N-08 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) 128 parts of a 15% aqueous solution of oxyethylene nonylphenyl ether sulfate ammonium salt) was charged, the pH was adjusted to 9.0 with an appropriate amount of aqueous ammonia (28%), and the mixture was heated to 70 ° C. while gently flowing nitrogen gas. 64 parts of a 5% aqueous solution of potassium persulfate was injected thereinto, and subsequently 288 parts of butyl acrylate and styrene 2 which had been prepared in advance.
88 parts and 2-isopropenyl-2-oxazoline 64
The monomer mixture consisting of parts was added dropwise over 3 hours.
Nitrogen gas was kept flowing during the reaction to keep the temperature in the flask at 70
The temperature was kept at ± 1 ° C. After maintaining the same temperature for 2 hours after completion of dropping, the internal temperature was raised to 80 ° C. and stirring was continued for 1 hour to complete the reaction. Then, it is cooled and the nonvolatile content is 39.8%, p
An aqueous dispersion of an oxazoline group-containing polymer (2) having H8.0 and a viscosity of 25 centipoise was obtained.

-Examples 1 to 4 and Comparative Examples 1 to 3 Liquids A and B having the formulations shown in Table 1 were mixed for 48 hours using a ball mill to prepare dispersions A and B.
A mixture of liquid A and liquid B is a high-quality paper (basis weight 50 g /
m ² ) was coated on one side and dried at room temperature for 2 days to form a thermosensitive recording layer having a coating amount of 7 g / m ² . Further, on this heat-sensitive recording layer, a heat-sensitive recording layer protective coating agent (liquid C) having the composition shown in Table 1 was applied and dried at room temperature for 2 days to form a protective layer having a coating amount of 2 g / m ² . A thermosensitive recording paper was obtained.

[0028]

[Table 1]

[0029] For the back surface of the recording sheet, the pressure-sensitive adhesive layer which is provided an acrylic pressure-sensitive adhesive layer so that the coating amount 20 g / m ² silicone resin surface of a release paper coated with silicone resin And then cut out into an appropriate size to obtain a heat-sensitive adhesive label.

Next, a sample of the heat-sensitive adhesive label obtained as described above was printed with a label printer, and a color development test, a sticking test and various storability tests were conducted. The results are shown in Table 2. The method of each test is as follows.

Color density: Color was printed with a label printer, and the color developed portion was measured with a Macbeth densitometer.

Background density: The non-printed portion was measured with a Macbeth densitometer.

Plasticizer resistance: The color was printed with a label printer, the sample was coated with a polyvinyl chloride sheet, and the densities after 72 hours at room temperature before and after coating were compared.

Water resistance: Print color was developed with a label printer, the sample was immersed in normal temperature water, and the densities were compared before and after 24 hours from the immersion.

Oil resistance: The color was printed with a label printer, sesame oil was applied to the sample, and the densities before application and after 24 hours from application were compared.

Sticking: Sticking sound at the time of printing, printing failure, etc. were tested.

[0037]

[Table 2]

As is clear from Table 2, the heat-sensitive recording layer protective coating agent of the present invention can form a heat-sensitive recording material which is excellent in preservability of printing such as water resistance and plasticizer resistance and anti-grounding property. It is a thing.

[0039]

EFFECT OF THE INVENTION Since the heat-sensitive recording layer protective coating agent of the present invention contains the carboxyl group-containing aqueous polymer (A) and the oxazoline group-containing aqueous polymer (B), the ionic mutual reaction between the carboxyl group and the oxazoline group is caused. A strong protective layer can be formed on the heat-sensitive recording layer by the action or reaction to form a covalent bond, and thus a heat-sensitive recording material excellent in print storage stability such as water resistance and plasticizer resistance can be produced. Further, fogging can be prevented by the oxazoline group trapping an acidic component that causes background color formation. Therefore, it is useful for manufacturing thermal recording paper such as labels and printer paper.

Claims (2)

[Claims] 1. A heat-sensitive recording for forming a protective layer on the upper surface of a heat-sensitive recording layer comprising a leuco dye formed on a support, a developer which reacts with the leuco dye by heating to develop a color, and a binder. A layer protective coating,
A heat-sensitive recording layer protective coating agent comprising a carboxyl group-containing aqueous polymer (A) and an oxazoline group-containing aqueous polymer (B). 2. The heat-sensitive recording layer protective coating agent according to claim 1, wherein the carboxyl group-containing aqueous polymer (A) is a carboxyl group-modified polyvinyl alcohol.