JPH0768932A - Heat-sensitive recording paper - Google Patents

Abstract

PURPOSE:To obtain a heat-sensitive recording paper with no fog of the skin and no decrease in coloring ability by a method wherein a substrate of the heat-sensitive recording paper is made of a neutral paper and a sizing agent to be used is an alkylketene dimer and the m.p. of the synthesized sizing agent is set at a specified temp. or higher. CONSTITUTION:A heat-sensitive recording paper is provided with a heat-sensitive coloring layer contg. a colorless or lightcolored leuco dye and a color developer developing a color by being brought into contact with this on the upper face of a substrate. In this case, the substrate is made of a neutral paper and a sizing agent to be used is an alkylketene dimer and the m.p. of the synthesized sizing agent is set at 50 deg.C or higher. Namely, the alkylketene dimer with a specified m.p. exhibits good sizing generating properties and there exists no possibility of decrease in coloring ability. It is possible thereby to obtain a heat-sensitive recording paper with no fog of the skin and no decrease in coloring ability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium, and more particularly to an improvement of a thermosensitive recording paper provided with a thermosensitive coloring layer containing a colorless or slightly pale leuco dye and a color developing agent for coloring under heat. is there.

[0002]

2. Description of the Related Art A heat-sensitive recording system using a normally colorless or slightly pale leuco dye and a color developer that develops the color of the leuco dye when heated does not require a developing step and is easy to maintain hardware. Since it has such features, it is widely used for recording in various printers, facsimiles and measuring instruments.

Conventionally, high-quality paper is generally used as a support for thermal paper. In acidic papermaking, rosin-based sizing agents and fillers such as clay and talc are added internally to make paper.
A sulfuric acid band is usually used as a fixing agent for this rosin-based sizing agent, and the pH of the paper surface is on the acidic side due to the sulfate radicals remaining in the paper, and the color-forming substances that make up the thermal paper are the surface of the paper. In the above, it reacts with acidic ions, and it becomes easy to cause background covering during a long-term storage period.

As an improvement, JP-A-55-15608
It has been proposed in No. 7 to use neutral paper as a support for thermal paper, and for neutral paper to further improve the surface property of the support, a Yankee machine is used to improve the surface property of the support. To improve the recording sharpness is disclosed in JP-A-62-58.
No. 80 is disclosed.

[0005]

By the way, as the sizer used for the neutral papermaking, there are generally petroleum-based resins, styrene-based resins, higher alcohols, alkenylsuccinic anhydrides, alkylketene dimers and the like. However, among them, alkylketene dimer has the best size expression and is used as a general printing paper or writing paper.
It has been found that when a base paper for a heat-sensitive paper containing a leuco dye and an acidic substance as the main components as in the present invention is used, a problem that the color-forming ability described below is deteriorated occurs.

As a result of various studies on the cause of this problem, the inventors of the present application have found that an alkylketene dimer having a specific melting point has good size expression and does not cause a decrease in coloring ability.

Particularly when neutral paper is used as a support for thermal recording paper, when printed thermal paper is stored for a long period of time,
Prints are faint, blurry, or barely visible in some cases. When the thermal paper is stored for a long time in this way, there is a phenomenon that the sensitivity and the saturation density at the time of production are lowered. Hereinafter, this phenomenon is referred to as a decrease in coloring ability. If the coloring ability is lowered, the print density is lowered, making it difficult to read, and there is a problem that the original function as recording paper is lost.

In the case of neutral paper making, a synthetic sizing agent is used as the sizing agent, and as the representative sizing agent, an alkyl ketene dimer emulsion type and an alkenyl succinic acid type emulsion type are used. The structure of the alkylketene dimer is shown below.

[0009]

[Chemical 1]

The melting point of the above alkyl ketene dimer is
Depends on the alkyl group. When an alkylketene dimer having a melting point of less than 50 ° C. is used, the alkylketene dimer reacts with the color developing agent, and as a result, the color developing agent that develops the leuco dye is lost and the color developing ability is reduced. It is expected to decrease.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thermal paper which is a feature of the neutral paper itself and which is free from the background fog and the deterioration of the coloring ability for a long period of time.

[0012]

DISCLOSURE OF THE INVENTION The present invention provides a thermosensitive recording comprising a support and a thermosensitive coloring layer containing a colorless or slightly light-colored leuco dye and a color developer which develops a color when contacted with the leuco dye. In the paper, the heat-sensitive recording paper is characterized in that the support is neutral papermaking, an alkylketene dimer is used as a sizing agent to be used, and the synthetic sizing agent has a melting point of 50 ° C. or higher.

[0013]

[Function] In a heat-sensitive recording paper containing a leuco dye and an acidic substance as main components, by using as a base paper a neutral paper having an alkylketene dimer having a melting point of 50 ° C. or more as a sizing agent, the background covering is reduced, Moreover, it is possible to obtain an excellent thermosensitive recording paper that does not cause a decrease in color forming ability.

[0014]

EXAMPLE The present invention has a melting point of 5 as a sizing agent for neutral paper.
This is achieved by using an alkyl ketene dimer at 0 ° C or higher.

The leuco compound used in the thermal recording paper of the present invention includes 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3,3-bis (p-dimethylaminophenyl) phthalide. , 3- (p-
Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindole-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-ethylcarbazol-3-yl) -6-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -6-dimethylamino Examples thereof include triallylmethane dyes such as phthalide and 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6-dimethylaminophthalide.

Further, diphenylmethane dyes such as 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, and benzoyl leuco methylene blue. , Thiazine dyes such as p-nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spirodinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-
Spiro dyes such as benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6′-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, Examples include lactam dyes such as rhodamine (o-chloroanilino) lactam.

Further, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 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-7-
N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3- (N-ethyl-p-toluidino) )
-6-Methyl-7-phenylaminofluorane, 3-
(N-ethyl-p-toluidino) -6-methyl-7-
(P-Toluidino) fluorane, 3-diethylamino-
7- (2-carbomethoxy-phenylamino) fluorane, 3- (N-cyclohexyl-N-methylamino)-
6-methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane,
3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 3-diethylamino-7- (o-chlorophenylamino) fluorane, 3-dibutylamino-
7- (o-chlorophenylamino) fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6- Methyl-
Examples thereof include fluoran dyes such as 7-anilinofluorane and 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane. The proportion of the leuco compound in the total solid content of the coating liquid forming the heat-sensitive recording layer is 1 to 30% by weight, preferably 5 to 20% by weight.

Various types of color developing agents are known which develop a color of a leuco compound when it is heated, for example, 4-te.
rt-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-butylphenyl), 4,4'- sec-butylidene diphenol, 4-phenylphenol, 4,4′-isopropylidene diphenol (bisphenol A), 2,2 ′
-Methylenebis (4-chlorophenol), hydroquinone, 4,4'-cyclohexylidene diphenol, 4
-Benzyl hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolac type phenol resin, phenolic compounds such as 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-methylbenzyl) salicylic acid, 3,5
-Di-tert-butylsalicylic acid, 3-phenyl-5-
Aromatic carboxylic acids such as (α, α-dimethylbenzyl) salicylic acid and 3,5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic dicarboxylic acids and, for example, zinc, magnesium, aluminum, calcium, titanium, Examples thereof include organic acids such as salts with polyvalent metals such as manganese, tin and nickel.

The proportion of the developer is 1 to 50% by weight based on the total solid content of the coating liquid for forming the thermosensitive recording layer.

Similarly, in the paint for forming the thermosensitive coloring layer, the polymers used as the binder include starch and its derivatives, hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose and other cellulose derivatives, polyvinyl and the like. Alcohol, sodium polyacrylate, polyvinylpyrrolidone, acrylamide
Acrylic ester copolymer, acrylamide / acrylic ester / methacrylic acid copolymer, styrene / maleic anhydride copolymer, alkali salt, polyacrylamide, sodium alginate, gelatin, water-soluble polymer such as casein, polyvinyl acetate ． Polyurethane, polyacrylic acid ester, polymethacrylic acid ester, vinyl chloride, vinyl acetate copolymer, aqueous emulsion of ethylene / vinyl acetate copolymer, styrene / butadiene copolymer, styrene / butadiene / acryl copolymer Latex etc. are used.

In the paint for forming the heat-sensitive color-developing layer, usual auxiliary additives such as pigments, heat-soluble substances, lubricants, surfactants, fluorescent dyes, storage stabilizers, etc. may be added as required. It goes without saying that they can be used in combination, for example, calcium carbonate, silica, zinc oxide, titanium oxide,
Inorganic fine powder such as aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, surface-treated calcium and silica, organic fine powder such as urea-formalin resin, styrene-methacryl copolymer, polystyrene resin , Stearic acid, fatty acids such as behenic acid, stearic acid amide, p-benzylbiphenyl, terphenyl, triphenylmethane, benzyl p-benzyloxybenzoate, β-benzyloxynaphthalene, β
-Naphthoic acid phenyl ester, 1-hydroxy-2-
Naphthoic acid phenyl ester, 1-hydroxy-2-naphthoic acid methyl ester, diphenyl carbonate, terephthalic acid dibenzyl ester, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dibenzyloxoinaphthalene, 1,2-bis (phenoxy) ethane, 1,2- (3-methylphenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane,
1,4-bis (phenoxy) butane, 1,4-bis (phenoxy) -2-butene, dibenzoylmethane, 1,4
-Bis (phenylthio) butane, 1,4-bis (phenylthio) -2-butene, 1,3-bis (2-vinyloxyethoxy) benzene, 1,4-bis (2-vinyloxyethoxy) benzene, p- (2-vinyloxyethoxy) biphenyl, p-aryloxybiphenyl, p-
Propagyloxybiphenyl, dibenzoyloxymethane, 1,3-dibenzoyloxypropane, dibenzyl disulfide, 1,1-diphenylethane, 1,1-diphenylpropanol, p- (benzyloxy) benzyl alcohol, 1,3- A heat-fusible substance such as diphenoxy-2-propanol, N-octadecylcarbonyl-p-methoxycarbonylbenzene, N-octadecylcarbamoylbenzene is used.

In addition to calcium carbonate, various fillers and fixing agents of various sizes can be used for the support. Further, in order to improve the dot reproducibility of the thermal recording paper, a large amount of filler is added or the oil absorption Larger fillers can also be used.

Further, in the heat-sensitive recording paper of the present invention, if necessary, an inorganic pigment and a binder as a main component or an intermediate layer containing a binder as a main component is provided between the support and the heat-sensitive color forming layer. An overcoat layer can be provided on the recording layer.

Next, the color-forming ability test method will be described. Originally, the color-developing ability test method is to store the obtained thermal recording paper under normal environmental conditions (for example, 20 ° C.-65% RH) for 1 to 2 years, perform a printing test after storage, and print density before storage. And it is necessary to compare the print density after storage. However, since the test itself requires a long period of time, the inventors of the present application diligently pursued a test method for color developing ability, and as a result, 40 ° C-
By storing for 10 days under environmental conditions under 90% RH, an accelerated test method corresponding to about 1 year of storage under normal storage conditions was found.

The present invention will be described in more detail below with reference to specific examples. Preparation of heat-sensitive paint Liquid A: 3-butylamino-6-methyl-7-anilinofluorane 9 parts by weight Polyvinyl alcohol: 12% aqueous solution 15 parts by weight Ammonium polystyrene acrylate: 12% aqueous solution 0.7 parts by weight Water 30 parts by weight Part liquid B: 2,2-bis (4-hydroxyphenyl) propane 20 parts by weight m-terphenyl 20 parts by weight polyvinyl alcohol: 12% aqueous solution 50 parts by weight ammonium polystyrene acrylate: 12% aqueous solution 3 parts by weight water 62. 3 parts by weight The respective liquids of the above composition were separately dispersed by a sand grinder until the average particle diameter became 1 μm or less. Solution C: Light calcium carbonate 20 parts by weight Water 80 parts by weight Solution C was dispersed for 15 minutes using a homomixer.

Solution A prepared above: 54.7 parts by weight, B
Liquid: 155.3 parts by weight and Liquid C: 100 parts by weight, and this mixture was mixed with zinc stearate (30% dispersion liquid) 3
3.3 parts by weight, 100 parts by weight of polyvinyl alcohol (12% aqueous solution), and 80 parts by weight of water were added to obtain a heat-sensitive paint.

Example 1 Using 70 parts of bleached hardwood kraft pulp and 30 parts of bleached softwood kraft pulp beaten to 350 ml of CF with a Rabus type beater, the melting point of alkylketene dimer as a neutral sizing agent was 50 ° C. [trade name: Size Pine K 287; manufactured by Arakawa Chemical Industry Co., Ltd.] was added to the pulp at 1%, and precipitated calcium carbonate white luster flower PC: Shiraishi Industry Co., Ltd.
Manufactured] is added, and hand-papermaking is performed with a TAPPI type sheet machine,
After pressing, it was air-dried to obtain 50 g of tsubo and 25% ash neutral paper.

The heat-sensitive paint was applied on the support obtained above so that the coating amount after air drying was 4 g / m ² , and further gloss treatment was performed to obtain a surface smoothness of about 500 seconds. To obtain a heat-sensitive recording paper.

Example 2 A thermosensitive recording paper was prepared in the same manner as in Example 1 except that the melting point of the alkylketene dimer was 52 to 58 ° C. (trade name: Hacon 603; manufactured by Dick Hercules). Obtained.

Comparative Example 1 In the same manner as in Example 1 except that the melting point of the alkylketene dimer was 38 ° C. (trade name: Size Pine K-902; manufactured by Arakawa Chemical Industry Co., Ltd.). A thermosensitive recording paper was obtained.

Comparative Example 2 In the same manner as in Example 1 except that the melting point of the alkylketene dimer used in Example 1 was 38 ° C. [trade name: Size Pine K-903; manufactured by Arakawa Chemical Industry Co., Ltd.]. A thermosensitive recording paper was obtained.

Comparative Example 3 A thermosensitive recording paper was prepared in the same manner as in Example 1 except that the melting point of the alkylketene dimer was 42 to 48 ° C. (trade name: Hacon 601; manufactured by Dick Hercules). Obtained.

Comparative Example 4 A thermosensitive recording paper was prepared in the same manner as in Example 1 except that the melting point of the alkylketene dimer was 42 to 48 ° C. (trade name: Hercon 701; manufactured by Dick Hercules). Obtained.

The thermosensitive recording paper obtained above was subjected to the color development test described above. 40 for color development test
℃ -90% RH storage for 10 days, then 20
An accelerated test method was used in which temperature and humidity were controlled at -65% RH, printing was performed, and comparison was made with the print density of the thermal recording paper before storage. The test results are shown in the following table.

[0035]

[Table 1]

In the above table, ○ indicates that the print density after storage is the same as that before storage, Δ indicates that the print density after storage is slightly lower than that before storage, and × indicates print after storage. The density is clearly inferior to that before storage, and the mark XX shows almost no print even after printing after storage.

As shown in the evaluation results of the above table, in Examples 1 and 2 of the present invention, the melting point of the alkyl ketene dimer as the neutral sizing agent is 50 ° C. or higher,
The print density after storage is the same as the print density before storage, and the thermal recording paper has excellent long-term storage properties. Further, in all of Comparative Examples 1 to 4 outside the above conditions, the print density after storage was slightly lower than the print density before storage, or was clearly inferior, and almost no print was visible even after printing after storage. There was no color, and there was a problem with the coloring ability.

[0038]

As described above, the heat-sensitive recording paper of the present invention is a heat-sensitive recording paper containing a leuco dye and an acidic substance as main components, and the base paper thereof is an alkylketene dimer having a melting point of 50 ° C. or more as a sizing agent. The present invention is characterized by using the above-mentioned neutral paper, and it is a thermal recording paper with little background covering and no problem of color forming ability.

Claims (1)

[Claims] 1. A thermosensitive recording paper comprising a support and a thermosensitive coloring layer containing a colorless or slightly pale leuco dye and a developer which develops a color when contacted with the leuco dye. A heat-sensitive recording paper, characterized in that a synthetic sizing agent has a melting point of 50 ° C. or higher, using an alkyl ketene dimer as a sizing agent used in functional papermaking.