JPH028084A - Coating composition for thermal recording paper - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coating composition for heat-sensitive recording paper that is excellent in color development and running properties on a thermal head.

(Prior art) Thermal recording paper (1) does not require development, (2) has a paper quality similar to that of regular paper, (3) is easy to handle, (4) has high color density, and (5) is difficult to use during recording. Due to its advantages such as no noise, it has become rapidly popular in the field of facsimiles and printers in recent years.

Thermosensitive recording paper is usually prepared by coating a colorless or pale color-forming colorless dye and a developer in a separated state together with a binder and other additives on the surface of a base paper. In the recording apparatus, when a heat-generating element such as a thermal head or a thermal pen comes into contact with this thermal recording paper, the dye and the color developer react to develop color, and a recorded image is formed on the thermal recording paper.

Usually, colorless color-forming dyes include leucolactone compounds,
A leuco dye such as a spirolan compound is used, and a phenol compound or an organic acid is used as a color developer.

Recently, with the spread of thermal recording methods, recording devices have become more diverse and sophisticated, and the quality required for thermal recording paper has also become more sophisticated. In particular, as the speed of thermal heads increases, thermal recording paper that can record high-density and clear images even with a small amount of thermal energy, does not cause sticking or head slag, has good color development, and has good head running properties is being developed. It has been demanded.

The binder contained in the coating composition for thermal recording paper adheres and fixes colorless color-forming dyes, color developers, pigments, and various other additives to the base paper, and also has excellent color development and head running properties. , and should not cause problems with recording paper quality such as background fogging.

Examples of binders for thermal recording paper include polyvinyl alcohol, starch, casein, gelatin, gum arabic,
Methyl cellulose, ethyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose, polyacrylamide, copolymer of acryl amide or methacrylic amide and N-methylolacryl amide, acryl amide or methacrylic amide and N - Water-soluble polymers such as terpolymers of methylolacrylic acid amide and acrylonitrile or methacrylonitrile, styrene-butadiene copolymers, methyl methacrylate-butadiene copolymers,
Polymer latexes such as acrylonitrile-butadiene copolymers, vinyl acetate copolymers, acrylic acid ester copolymers, and carboxy-modified copolymers of these copolymers are known. One type or a combination of two or more types selected from these can be used as a binder (see, for example, JP-A-62-42884).

In particular, when a polymer latex is used as a binder, a paint with higher concentration and lower viscosity can be obtained compared to when only a water-soluble polymer is used as a binder, so the coating speed can be increased. This has great advantages, such as making it possible to reduce the drying load, improve the productivity of coating heat-sensitive recording paper, and reduce energy costs. However, conventional polymer latexes have drawbacks such as problems with recording quality such as inhibiting color development and background fog, and problems with head running such as thermal fusion in the thermal head. However, it was not sufficient for practical use.

(Problems to be Solved by the Invention) In view of this background, the present inventors have conducted repeated research in order to develop a polymer latex for use as a binder for thermal recording paper that has improved color development and thermal head running properties. As a result, they discovered that by using a latex with an increased content of ethylenically unsaturated acid in the copolymer as a binder, a thermal recording paper with extremely excellent color development and head running properties could be obtained, and the present invention was completed. I ended up doing it.

(Means for solving the problem) Thus, according to the present invention, the ethylenically unsaturated acid monomer 5
~30% by weight as a copolymer component, and MFT
A coating composition for heat-sensitive recording paper is provided, which contains a copolymer latex having a (minimum film-forming temperature) of 50° C. or lower as a binder.

The copolymer latex used in the present invention will be explained below.

Ethylenically unsaturated acid monomers include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, butenetricarboxylic acid; itaconic acid monoethyl ester, fumaric acid, etc. Monoalkyl esters of unsaturated dicarboxylic acids such as acid monobutyl ester and maleic acid monobutyl ester; unsaturated sulfonic acids or their alkali salts such as sulfonityl acrylate Na salt, sulfopropyl methacrylate Na salt, acrylamide propane sulfonic acid, etc. is exemplified. The content of the ethylenically unsaturated acid monomer in the copolymer is from 5 to 30% by weight, and if it is less than 5% by weight, the coloring properties are poor and thermal fusion to the thermal head is likely to occur.

Moreover, if it exceeds 30% by weight, the viscosity of the copolymer latex and the viscosity of the coating material will increase, making it impractical. Preferably it is 10 to 25% by weight.

Monomers to be copolymerized with the ethylenically unsaturated carboxylic acid include fats such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and halogen-substituted butadiene. Group conjugated diolefin;
Styrene, α-methylstyrene, monochlorostyrene,
Aromatic vinyl compounds such as vinyl toluene; alkyl esters of acrylic acid and methacrylic acid such as methyl acrylate, methyl methacrylate, ethyl acrylate, and butyl acrylate; ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; Furthermore, β-hydroxyethyl acrylate, acrylamide, methacrylamide, N-methylol acrylamide,
Diacetone acrylamide and the like can be used.

The copolymer latex of the present invention is a latex with an MFT (minimum film forming temperature) of 50°C or less; if the temperature exceeds 50°C, the copolymer latex's binding strength decreases and it no longer functions as a binder. Put it away. Preferably MFT
is a copolymer latex with a temperature of 40°C to -20°C. Midfielder
T can be varied in various ways by changing the constituent monomer composition of the copolymer latex. In the copolymer latex of the present invention as a binder, if the copolymer contains the unsaturated acid monomer and the MFT is within the above temperature range, the copolymer components other than the unsaturated acid monomer ( There are no particular restrictions on the type and amount of monomers. A particularly preferred combination of monomers constituting the copolymer is one or more monomers selected from unsaturated acid monomers/aliphatic conjugated dienes/aromatic vinyl compounds, ethylenically unsaturated nitriles, and methacrylic acid esters. monomers/a small amount of monomers other than the above as necessary, and one or more monomers selected from unsaturated acid monomers/acrylic esters/aromatic vinyl compounds, ethylenically unsaturated nitriles, and methacrylic esters. /A small amount of monomers other than those listed above, if necessary.

In the present invention, the method for producing the copolymer latex itself is not particularly limited, and for example, known emulsion polymerization methods such as batch emulsion polymerization and continuous emulsion polymerization can be employed. Various additives used in general emulsion polymerization, such as, molecular weight regulators, chelating agents, and electrolytes, can be used, and the polymerization temperature can be selected from either high or low temperatures. Furthermore, after the completion of polymerization, the copolymer latex has a known pH of 1i! Conditioners, dispersants, preservatives, etc. may also be added.

Next, the coating composition for heat-sensitive recording paper (hereinafter sometimes referred to as heat-sensitive coating liquid) used in the present invention will be described.

Generally, a heat-sensitive coating liquid is prepared by separately dispersing a color former and a color developer in a water-soluble polymer solution using means such as a ball mill or a sand mill.

The resulting dispersion of color former and color developer is mixed with inorganic pigments, waxes, higher fatty acid amides, metal soaps, and if necessary, ultraviolet absorbers, antioxidants, antifoaming agents, fluorescent dyes, and colorants. Add dye, binder, etc. to make a coating liquid. These additives may be added at the time of dispersion. As the binder, the copolymer latex of the present invention can be used alone or in combination with a water-soluble binder such as polyvinyl alcohol or starch.

The coating liquid is generally applied onto the support such that the coating amount of the color former is 0.2 g/m to 1.0 g/m''.

The color forming agent used in the present invention is not particularly limited as long as it is used in general pressure-sensitive recording paper, heat-sensitive recording paper, etc. To give a specific example, (1) triarylmethane compounds such as 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone L3-(p-dimethylaminophenyl) phenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)3-(2-phenylindol-3-yl)phthalide, 3,3-bis-(p -ethylcarbazol-3-yl)-3-dimethylaminophthalide, 3゜3-bis-(
(2-phenylindol-3-yl)-5-dimethylaminophthalide, etc.; (2) diphenylmethane compounds,
For example, 4,4-bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl leuco auramine, N-2,4,5-)lichlorophenyl leuco auramine, etc.; (3) Xanthine compounds, such as rhodamine B-anilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-butylaminofluorane, 3-diethylamino-7(2-
chloroanilino)fluoran, 3-diethylamino-6
-Methyl-7-ayurinofluorane, 3-piperidino-
6-Methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-anilinofluorane, 3
-cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-
7-(β-ethoxyethyl)aminofluorane, 3-diethylamino-6-chloro-7-(T-chloropropyl)aminofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-N -cyclohexyl-
N-methylamino-6-methyl-7-anilinofluorane, -3-diethylamino-7-phenylfluoran, etc.; (4) Thiazine compounds, such as benzoylleucomethylene blue, p-nitrobenzoylleucomethylene blue, etc.; ( 5) Spiro compounds, such as 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3
-Methylnaphtho-(3-methoxy-benzo)-spiropyran, etc., or a mixture thereof can be mentioned. These are determined by the application and desired properties.

The color developer used in the present invention includes phenol derivatives,
Aromatic carboxylic acid derivatives are preferred, and bisphenols are particularly preferred. Specifically, as phenols, p
-Octylphenol, pter t-butylphenol, P-phenylphenol, 2.2-bis(p-hydroxyphenyl)propane, 1.1-bis(p-hydroxyphenyl)pentane, 1.1-bis(p-hydroxyphenyl) Hexane, 2.2-bis(p-hydroxyphenyl)hexane, 1.1-bis(p-hydroxyphenyl)2-ethyl-hexane, 2.2-bis(4-hydroxy-3,5-dichlorophenyl)propane, etc. can be given.

Aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate,
Examples of 3.5-di-α-methylbenzylsalicylic acid and carboxylic acid include polyvalent metal salts thereof.

These color developers may be added as a eutectic with a thermofusible substance with a low melting point in order to melt at a desired temperature and cause a color reaction, or the low melting point compound may be added to the surface of the color developer particles. It is preferable to add it in a fused state.

Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylene bisstearamide, and higher fatty acid esters.

Examples of the metal soap include polyvalent metal salts of higher fatty acids, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

Inorganic pigments include kaolin, calcined kaolin, talc,
Examples include waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, titanium oxide, and barium carbonate.

Methods for applying the coating liquid onto the support include blade coating method, air knife coating method, gravure coating method, roll coating coating method, spray coating method, tip coating method, bar coating method, Kokyu strusion coating method, etc. Conventionally known coating methods can be used.

Thus, a thermosensitive recording paper using the copolymer latex of the present invention, which has good color development and good head running properties, is provided.

The present invention will be specifically explained below with reference to Examples. Note that parts and percentages in Examples and Comparative Examples are based on weight unless otherwise specified.

Examples 1-5. Comparative Examples 1 to 5 (Creation of copolymer latex) Water, emulsifier, inorganic salt,
The monomers and molecular weight regulators shown in Tables 1 and 2 were added together with the chelating agent and polymerization initiator, and polymerization was carried out at 60° C. for 15 hours with rotational mixing. The conversion rate is 9 in both cases.
It reached over 5%.

The obtained copolymer latex (present invention example latex A-
E, Comparative Example Latex a-e) was cooled with water, unreacted monomers were removed, and the pH of the latex was adjusted with sodium hydroxide.
was adjusted to 7, and the solid content concentration was adjusted to 45%.

(Measurement of latex viscosity) The viscosity of latex prepared with a pI of 7 and a solid content concentration of 45% was measured in an environment of 25°C ± 1°C using a B-type viscometer (Tokyo Keiki model, BL model). .The results are shown in Tables 1 and 2.
Also listed in the table.

(Measurement of MFT of latex) MFT of the prepared latex was measured as follows. A latex liquid film is formed to a constant thickness on a stainless steel plate with a temperature gradient. When the water evaporates and a latex film is formed, due to the temperature gradient, the latex film is divided into parts where a transparent latex film is formed and parts where whitening or cracks are formed. The boundary of this discontinuous point is visually determined, and the temperature at this point is defined as MFT. The obtained results are also listed in Tables 1 and 2.

(Preparation of heat-sensitive coating liquid) 20g each of crystal violet lactone, stearamide, and 2,2-bis(p-hydroxyphenyl)propane were added to 5% polyvinyl alcohol (Kuraray PVA).
105) Dispersion was carried out with an aqueous solution IQOg in a ball mill overnight. Further, 100 g of light calcium carbonate was dispersed in 200 g of a 0.5% aqueous solution of sodium hexametaphosphate using a Coles mixer (manufactured by Shimazaki Seisakusho). These and an emulsion of zinc stearate were mixed so that the ratio of active ingredients was as follows.

Crystal violet lactone: Stearamide: 2.2-bis(p-hydroxyphenyl)propane:
Light calcium carbonate: zinc stearate = 1:'2:3
:6:0.5 In addition to the above formulation, polyvinyl alcohol (Kuraray P
VA 117) and the active ingredients of the copolymer latex were added at the above ratio of 1:1, and the solid content concentration was adjusted to 20%.

(Coating) The obtained heat-sensitive coating liquid was applied to high-quality paper with a basis weight of 60 g/m2 using a wire bar so that the dry coating amount was 5 g/m2, and after drying in a hot air oven at 50°C, linear pressure was applied. 100k
g/cm supercalender twice at room temperature to obtain thermal recording paper.

(Thermal recording paper evaluation) The following tests were conducted on the obtained thermal paper.

(1) Solid printing was performed in a 6 cm square area using a head-running thermal paper printer (manufactured by Fujitsu ■). Sensory evaluation was performed on the movement of the thermal head.

○: Runs smoothly.

Δ: Some catching occurs due to fusion to the thermal head.

×: Significant catching due to fusion to the thermal head occurs.

(2) Color development The color density of the 6 cm square solid printed area obtained in (1) was measured using a Hunter whiteness meter. The smaller the number, the better.

(3) Water-resistant adhesiveness The coated surface was rubbed 10 times with a cotton swab soaked in water, and the degree of peeling of the coated layer was visually evaluated.

○: Not peeled off at all.

Δ: Peeled off, but the coating layer remains.

×: Most of the coating layer peels off.

The above results are shown in Table 3.

Comparative Example 6 Acrylic acid amide 77 g 5 N-methylol methacrylic acid amide 1 1 in a three-bottle flask equipped with a thermometer and a nitrogen inlet tube
0g of diethylene glycol, 5g of methacrylic acid monoester of diethylene glycol, 8g of methyl methacrylate, and 400g of water, and nitrogen was blown there for 30 minutes. Set the liquid temperature to 20℃
8 g of triethanolamine and 0.8 g of ammonium persulfate were each added as an aqueous solution to initiate polymerization. The reaction was carried out for 3 hours to obtain an aqueous copolymer solution.

Evaluation was conducted using the same amount of this copolymer aqueous solution in place of the copolymer latex of the example in terms of solid content. The results are also listed in Table 3.

From the above results, it can be seen that thermal recording paper having excellent color development and head running properties can be obtained from the coating composition for thermal recording paper containing the copolymer latex of the present invention as a binder.

The use of copolymer latex a and b improves head running properties,
Although the color development was relatively good, the water-resistant adhesion was poor and it hardly functioned as a binder.

Procedural amendment (spontaneous) 3 years and 72 months in the Showa era

Claims (1)

[Claims] A thermosensitive material comprising, as a binder, a copolymer latex containing 5 to 30% by weight of an ethylenically unsaturated acid monomer as a copolymerization component and having an MFT (minimum film forming temperature) of 50°C or less. Coating composition for recording paper.