JPH04110188A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material having an overcoat layer having no gloss, like plain paper and strong against wearing contamination and excellent in sealing fixability and printability by constituting the overcoat layer of a mixed composition of polyvinyl alcohol and starch. CONSTITUTION:In a thermal recording material wherein a thermal recording layer containing at least a color former and a developer developing the color former at the time of heating and an overcoat layer are provided on a support, the overcoat layer is constituted of a mixed composition of polyvinyl alcohol and starch. The mixing ratio of starch to polyvinyl alcohol is 5-300 pts.wt., pref., 10-200 pts.wt. per 100 pts.wt. of polyvinyl alcohol. The coating amount of the coating solution forming the overcoat layer is not especially limited but generally set to 0.1-20g/m<2>, pref., set to about 0.5-10g/m<2> on a dry wt. basis.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal recording medium, which is non-glossy, resistant to abrasion and dirt, and has the performance of plain paper with excellent imprint fixing properties and printability. It is related to.

[Prior Art] Heat-sensitive recording materials capable of developing color using thermal energy from a heat-sensitive head are well known. Such thermal recording media are relatively inexpensive, and the recording devices are compact and relatively easy to maintain, so they are used not only as recording media for facsimiles and various calculators, but also in a wide range of fields, such as thermal recording media. . However, it has problems in fingerprint resistance and solvent resistance, and has the disadvantage that, for example, when the recording layer comes into contact with human sebum or solvent, the recording density decreases and unnecessary coloration called background fog occurs.

As a method to overcome these drawbacks, a method is proposed in which an aqueous emulsion of a resin having film-forming ability and chemical resistance is coated on the heat-sensitive recording layer (Japanese Patent Laid-Open No. 12834/1983).
7), a method of applying a water-soluble polymer compound such as polyvinyl alcohol (Utility Model Application Publication No. 56-i25354), etc. have been proposed. However, the current situation is that improvements come with new drawbacks, and that satisfactory results are not necessarily obtained.

For example, when applying a water-based resin coating on a heat-sensitive recording layer, it is necessary to limit the drying temperature to avoid coloring of the recording layer due to high-temperature drying, which inevitably results in insufficient curing of the resin layer and A so-called sticking phenomenon, in which the recording head and the resin layer stick together, is likely to occur.

Therefore, attempts have been made to improve the recording running properties by incorporating pigments, lubricants, curing agents, etc. into the overcoat layer. Further, when such an overcoat layer is provided, there is a drawback that the fixing property during stamping is poor and the stamp is easily wiped off. Furthermore, it was glossy and had properties far different from that of plain paper.

On the other hand, with the diversification of uses for thermosensitive recording paper, in recent years it has become popular to print by trapping, gravure, off-line, etc., and excellent performance in printability is also required.

(Problems to be Solved by the Invention) It is an object of the present invention to provide a heat-sensitive recording material having an overcoat layer that is non-glossy, similar to plain paper, resistant to abrasion and dirt, and excellent in imprint fixability and printability. This is the purpose.

[Means for Solving the Problems] The present invention provides a heat-sensitive recording material comprising, on a support, a heat-sensitive recording layer and an overcoat layer containing at least a color former and a color former that causes the color former to develop color when heated. , a heat-sensitive recording material characterized in that the overcoat layer is composed of a mixed composition of polyvinyl alcohol and starch.

[Effect]

In the present invention, the material constituting the heat-sensitive recording layer is not particularly limited, and may be heat-sensitive.

Any combination of materials that can cause a coloring reaction due to the thermal energy generated by the metal can be used, such as a combination of a colorless or light-colored basic dye and an inorganic or organic acidic substance, ferric stearate, etc. Examples thereof include a combination of a higher fatty acid metal salt and a phenol such as gallic acid, a diazonium compound, a coupler compound, and a so-called photofixable heat-sensitive recording material containing a compound that exhibits a basic atmosphere when thermally melted.

However, the specific overcoat layer of the present invention provided on the recording layer has extremely excellent recording properties, especially when applied to a combination of a basic dye and an acidic substance, and is therefore particularly preferred. Various types of colorless to light-colored basic dyes are known, and examples include the following.

3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3.3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2- Dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3
-(2-methylindol-3-yl)phthalide, 3,
3-bis(1,2-dimethylindol-3-yl)-
5-dimethylaminophthalide, 3.3-bis(1゜2-
dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazole-3
-yl)-6-dimethylaminophthalide, 3.3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3
-(1-Methylvirol-3-yl)-6-dimethylaminophthalide and other triallylmethane dyes, 4.4'-
Bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2,4,
Diphenylmethane dyes such as 5-MJ chlorophenyl leuco auramine, hendiyl leucomethylene blue, p
- Thiazine dyes such as nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6 '-methoxybenzo)spiropyran, 3-propyl-spirodibenzopyran and other spiro dyes, rhodamine B-anilinolactam, rhodamine (p-nitroanilino)lactam, rhodamine (
Lactam dyes such as 0-chloroanilino)lactam, 3
-dimethylamino-7-medoxyfluoran, 3-diethylamino-6-medoxyfluoran, 3-diethylamino-7-medoxyfluoran, 3-diethylamino-
7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,
7-dimethylfluorane, 3-(N-ethyl-p-toluidino)-7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-
diethylamino-7-N-methylaminofluorane, 3
-diethylamino-7-dibenzylaminofluorane,
3-diethylamino-'1-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3-(N −
Ethyl T)-)luidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-P-toluidino)-6-methyl-7-(p-)luidino)fluorane,
3-diethylamino-6-methyl-7phenylaminofluorane, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran, 3-(N-ethyl-N-iso-amylamino)-6-methyl- 7-tunylaminofluorane, 3-(N-cyclohexyl-N
-methylamino)-6-methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6methyl-7-phenylaminofluorane, 3-diethylamino- 6-Methyl-7-xylidinofluorane, 3-diethylamino-7-(0-chlorophenylamino)fluoran, 3-
Fluoran dyes such as dibutylamino-7-(o-chlorophenylamino)fluoran and 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluoran.

Various types of inorganic or organic acidic substances are also known that develop color upon contact with basic colorless dyes, such as activated clay, acid clay, attapulgite, bentonite, colloidal silica, aluminum silicate, etc. 4
-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol, 2゜2'-dihydroxydiphenol, 2,
2'-methylenebis(4-methyl-6-tert-isobutylphenol), 4.4'-isopropylidenebis(2-tert-butylphenol), 4.4'-5
ec butylidene diphenol, 4-phenylphenol, 4,4'-isopropylidene diphenol (bisphenol A), 2,2'-methylenebis (4-chlorophenol), hydroquinone, 4°4'-cyclohexylidene diphenol, benzyl 4-hydroxybenzoate,
Phenolic compounds such as dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolac type phenolic resin, phenol polymer, benzoic acid, p-
tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3
, 5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methyl Aromatic carboxylic acids such as benzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, Examples include organic acidic substances such as these phenolic compounds and salts of aromatic carboxylic acids and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel.

In the heat-sensitive recording material of the present invention, the ratio of the color former and color former in the recording layer is appropriately selected depending on the type of color former and color former used, and is not particularly limited. For example, when using a basic colorless dye and an acidic substance,
In general, 1 to 50 parts by weight, preferably 1 to 10 parts by weight, of acidic substances are used per part by weight of basic colorless dye.

To prepare a coating solution containing these substances, the coloring agent and the coloring agent are generally dispersed together or separately using water as a dispersion medium using a stirring/pulverizing machine such as a ball mill or an attritor sand grinder. It is prepared as

This coating liquid contains starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, and adhesives.
Polyvinyl alcohol, diisobutylene/maleic anhydride copolymer salt, styrene/maleic anhydride copolymer salt,
Ethylene/acrylic acid copolymer salt, styrene/acrylic acid copolymer salt, styrene/butadiene copolymer emulsion, etc. accounts for 10 to 40% by weight of the total solids, preferably 15% by weight.
It is used in an amount of about 30% by weight.

Furthermore, various auxiliary agents can be added to the coating liquid.
For example, dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginates, fatty acid metal salts, ultraviolet absorbers such as hensifenones and triazoles, and other antifoaming agents. , fluorescent dyes, colored dyes, and the like.

In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, kaolin,
Inorganic pigments such as clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay, stearamide, methylene bisamide stearate, oleic acid amide, palmitic acid amide,
Sensitizers such as matcha oleic acid amide and coconut fatty acid amide can also be added.

In the heat-sensitive recording material of the present invention, paper, plastic film, synthetic paper, etc. are used as the support. The coating method for the recording layer is not particularly limited, and it can be formed according to conventionally well-known and commonly used techniques, such as bar coating, air knife coating, rondo blade coating, pure blade coating, short dwell coating, etc. It is formed by coating and drying. In addition, when a plastic film is used as a support, the coating efficiency can be improved by subjecting the surface to a treatment such as corona discharge or electron beam irradiation. The amount of coating liquid to be applied is not particularly limited, but it is usually 2 to 12 g/n (dry weight).
Preferably it is in the range of about 3 to 1 Og/bo.

In the heat-sensitive recording material of the present invention, an overcoat layer is formed on the thus obtained heat-sensitive recording layer, and the feature of the present invention is that the materials constituting the overcoat layer include polyvinyl alcohol and starch. It consists in using a mixed composition.

An aqueous solution of polyvinyl alcohol and an aqueous starch solution have a characteristic of poor compatibility with each other, and as a result, a dried film of a mixed composition of a rainwater solution tends to be non-uniform and micro-cracked.

The present invention skillfully utilizes this characteristic as an advantage, and by forming an overcoat layer of a microcracked dry film of a thermosensitive material on the heat-sensitive recording layer, it is matte and resistant to scratches and stains. The present invention was completed by confirming that the fixation of the stamp and printability were improved.

The polyvinyl alcohol that forms such an overcoat layer includes fully saponified or partially saponified polyvinyl alcohol, polyvinyl alcohols modified with various functional groups such as the following (acetoacetyl-modified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, sulfonic acid). Modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silico-modified polyvinyl alcohol), and the like.

The starch forming the overcoat layer includes oxidized starch,
Examples include starches such as etherified starch, dialdehyde starch, and esterified starch.

The mixing ratio of polyvinyl alcohol and starch is 5 to 300 parts by weight, preferably 10 to 200 parts by weight, per 100 parts by weight of polyvinyl alcohol.

Incidentally, if the amount is less than 5 parts by weight or more than 300 parts by weight, it will not be possible to form an overcoat layer with non-uniform micro-cracks in the dried film, and therefore the desired effect of the present invention will not be obtained. I can't.

The overcoat layer consisting of both of the above substances contains inorganic substances such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, aluminum hydroxide, diatoms, fine particulate anhydrous silica, and activated clay. Pigments and organic pigments such as urea resins can also be added.

Further, in order to further improve the water resistance and plasticizer resistance of the overcoat layer, a curing agent may be added to the coating liquid forming the overcoat layer. Examples of the curing agent for crosslinking include glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, alum, ammonium chloride, and the like.

The coating liquid for forming the overcoat layer is generally prepared as an aqueous coating liquid, and after being thoroughly mixed and dispersed using a mixing/stirring machine such as a mixer, attritor, ball mill, or roll mill as necessary, various publicly known coating liquids are prepared. It is applied onto the heat-sensitive recording layer using a coating device and dried.

The coating liquid may contain lubricants such as zinc stearate, calcium stearate, stearic acid amide, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium dioctyl sulfosuccinate, and dodecylhenzensulfone, as necessary. Surfactants such as sodium acid, lauryl alcohol sulfate/sodium salt, alginates, fatty acid metal salts, ultraviolet absorbers such as benzphenone and triazole, antifoaming agents, fluorescent dyes, and coloring dyes. It can also be added as appropriate.

The coating amount of the coating liquid forming the overcoat layer is not particularly limited, but is generally 0.1 to 2 by dry weight.
It is prepared in a range of about 0 g/rrf, preferably about 0.5 to 10 g/rrf.

By the way, 0.1g/rr? If it is less than 20 g/lri, the desired effect of the present invention cannot be sufficiently obtained, and if it exceeds 20 g/lri, there is a risk that the recording sensitivity of the heat-sensitive recording medium will be significantly lowered.

Incidentally, after forming the overcoat layer, a supercalender treatment can be performed as necessary to further improve image quality and image density.

Furthermore, when base paper is used as a support, an undercoat layer consisting of an adhesive and a white pigment is provided, and a heat-sensitive recording layer and an overcoat layer are provided thereon to improve recording density, sensitivity, and storage stability. In particular, in order to eliminate the influence of oil, plasticizer, etc. from the back side, a back barrier layer made of an adhesive and a white pigment can be provided on the back side of the recording medium to improve storage stability. As the adhesive used for these undercoat layer and back barrier layer, those used for the above-mentioned heat-sensitive layer can be used.

Further, as the white pigment, those that can be contained in the above-mentioned overcoat layer can be used.

Further, various known techniques in the field of heat-sensitive recording material manufacturing may be added as necessary, such as applying an adhesive treatment to the back surface of the recording material and processing it into an adhesive label.

〔Example〕

The present invention will be described in more detail with reference to Examples below, but it is of course not limited thereto.

Further, unless otherwise specified, parts and percentages in the layers indicate parts by weight and percentages by weight, respectively.

Example 1 ■ Preparation of liquid A 3-(N-cyclohexyl-N-methylamino)-6-
Methyl-7-phenylaminofluorane 10 parts Methylcellulose 5% aqueous solution 5 parts Water
30 parts of this composition was ground with a sand grinder until the average particle size was 3 μm.

■Preparation of Solution B Benzyl 4-hydroxybenzoate 20 parts Methylcellulose 5% aqueous solution 5 parts Water
55 parts of this composition was ground with a sand grinder until the average particle size was 3 μm.

(2) Formation of Recording Layer 45 parts of liquid A, 80 parts of liquid B, 50 parts of a 20% oxidized starch aqueous solution, and 10 parts of water were mixed and stirred to prepare a coating liquid.

The obtained coating liquid was applied to synthetic paper (trade name: FPG-80, manufactured by Tamago Yuka Co., Ltd.) so that the coating amount after drying was 6 g/rrf, and dried to obtain a heat-sensitive recording material.

■ Formation of overcoat layer On the heat-sensitive recording layer of the above-mentioned heat-sensitive recording material, apply a coating liquid having the following composition so that the coating amount after drying is 2 g/n.
It was dried and further smoothed using a super calender to obtain a heat-sensitive recording material having an overcoat layer.

10% aqueous solution of completely saponified polyvinyl algol 25
parts (PVA117, manufactured by Kuraray) 10% aqueous solution of etherified starch 20 parts (Aberefkus 2530, Aberefkus l) Calcium carbonate 5 parts (Softon 1500,
30% dispersion of zinc stearate (manufactured by Shiraishi Kogyo Co., Ltd.)
1.7 parts wetting agent 0.
1 part Example 2 A thermosensitive recording material was obtained in the same manner as in Example 1, except that a coating liquid having the following composition was applied as an overcoat layer and dried.

7% aqueous solution of completely saponified polyvinyl alcohol 36
(PVA117, manufactured by Kuraray Co., Ltd.) 10% aqueous solution of oxidized starch 20 parts (Ace A, manufactured by Tamago Cornstarch Co., Ltd.) Calcium carbonate
5 parts (Softon 1500, manufactured by Shiraishi Kogyo Co., Ltd.) 30% dispersion of zinc stearate 1.7 parts Wetting agent 0.1 part Example 3 As an overcoat layer, a coating liquid having the following composition was applied and dried. A thermosensitive recording material was obtained in the same manner as in Example 1.

Completely saponified polyvinyl alcohol in 7% water solution
36 parts (PVA124, manufactured by Kuraray Co., Ltd.) 10% aqueous solution of dialdehyde starch 20 parts (Chikara J Sidas C5S, manufactured by Nippon Carlift Co., Ltd.) Calcium carbonate 5 parts (So7 tons 1500
, Shiraishi Kogyo Co., Ltd.) 30% dispersion of zinc stearate
1.7 parts wetting agent 0
．． 1 part Example 4 A thermosensitive recording material was obtained in the same manner as in Example 1, except that a coating liquid having the following composition was applied as an overcoat layer and dried.

10% aqueous solution of silyl-modified polyvinyl alcohol 25
parts (R-110, manufactured by Kuraray Co., Ltd.) 20 parts of a 10% aqueous solution of etherified starch (Abe ν
Fuchs 2530, manufactured by Aberefkus) 5 parts of calcium carbonate (Softon 150)
0, Shiraishi Kogyo Co., Ltd.) 30% dispersion of zinc stearate 1.7 parts wetting agent
0.1 part Comparative Example 1 A thermosensitive recording material was obtained in the same manner as in Example 1 except that no overcoat layer was provided.

Comparative Example 2 A heat-sensitive recording material was obtained in the same manner as in Example 1, except that a coating liquid having the following composition was applied as an overcoat layer and tested.

7% water soluble fi of fully saponified polyvinyl alcohol
25 parts (PVA117, manufactured by Kuraray Co., Ltd.) 5 parts of calcium carbonate (Softon 1500, manufactured by Shiroishi Kogyo Co., Ltd.) 30 parts of zinc stearate
% dispersion 1.7 parts wetting agent
0.1 part Comparative Example 3 A thermosensitive recording material was obtained in the same manner as in Example 1, except that a coating liquid having the following composition was applied as an overcoat layer and dried.

20 parts of 10% aqueous solution of etherified starch (7 Berefuks 2530, manufactured by 7 Berefuks) 5 parts of calcium carbonate (Softon 1500)
, Shiraishi Kogyo Co., Ltd.) 30% dispersion of zinc stearate
1.7 parts wetting agent 0
．． Using one part of the seven types of heat-sensitive recording materials thus obtained, P
Image recording was obtained using ANAFAX UF-5E, and the following evaluations were performed and the results are shown in Table 1.

[Stamping suitability]

A seal was stamped with a Shachihata name, and one minute later, it was wiped with gauze to determine the suitability of the stamp.

[Recording density]

The maximum density of the obtained recorded image was measured using a Machhes densitometer (manufactured by Machhes, model RD-100R).

[Printability] Using UV ink, ink fixability was evaluated using an off-line printing machine.

[Scratch aptitude]

The back of the fingernail was rubbed on the thermal paper, and judgment was made based on the degree of color staining.

[Fingerprint resistance]

A fingerprint was pressed onto the recorded image, and judgment was made based on the degree of color reduction one day later.

[Glossiness] Measurements were made with a variable angle photometer at an angle of incidence of 75°.

The evaluation criteria for sealability, printability, scratchability, and fingerprintability were as follows.

"Evaluation Criteria" ○...Excellent ×...Poor [Results] As is clear from Table 1, the present invention in which the overcoat layer was composed of a mixed composition of polyvinyl alcohol and starch The heat-sensitive recording material has no gloss, is resistant to abrasion and dirt, and has excellent imprint fixation and printability.

Claims (1)

[Claims] (1) In a heat-sensitive recording material in which a recording layer and an overcoat layer containing at least a color former and a color former that causes the color former to develop color when heated are provided on a support, the overcoat layer is made of polyvinyl alcohol and starch. A heat-sensitive recording material comprising a mixed composition of.