JP2597422B2 - Thermal recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermosensitive recording material in which a protective layer is provided on a thermosensitive coloring layer. More specifically, the present invention relates to a heat-sensitive recording material having good color-forming sensitivity and sufficiently exhibiting oil resistance as a function of a protective layer.

[Prior Art] A thermosensitive recording material is known in which a thermosensitive coloring layer which develops color when heated is formed using paper, synthetic paper, film or the like as a support.

The heat-sensitive recording material is usually a color-forming substance such as a colorless or light-colored leuco dye and a color-developing substance that causes the color-forming substance to develop color when heated, for example, boric acid, oxalic acid, an acidic substance such as tartaric acid, or naphthol, A phenolic substance such as 2-bis (p-hydroxyphenyl) propane, catechol, resorcin and the like may be suitably added together with an adhesive and, if necessary, additives such as pigments such as calcium carbonate and clay, waxes and defoamers. A thermosensitive coloring layer forming solution is prepared by using a solvent, the solution is coated on a support such as paper, and dried to produce a liquid.

The heat-sensitive recording material thus obtained is widely used for recording in calculators, medical measuring instruments, facsimile machines, automatic ticket vending machines, CD / ATMs, and the like.

However, conventionally, this type of heat-sensitive recording material has a drawback in storage stability in both a colored portion and a non-colored portion. That is, when a plastic such as polyvinyl chloride or polyvinylidene chloride comes into contact with the surface of the heat-sensitive coloring layer, the color-developed portion is discolored by a plasticizer, a stabilizer, an additive, or the like contained in the plastic, or the uncolored portion is It does not develop color.

For example, if a plastic eraser is left on the surface of the heat-sensitive layer for several hours, or if the heat-sensitive recording material is stored in a polyvinyl chloride bag and kept in direct contact with the bag for a long period of time, the color image disappears. In addition, there are inconveniences such as decoloring by fingerprints and decoloring by a fluorescent pen.

In addition, since the uncolored portion is easily colored by an organic solvent such as alcohol, toluene, and ethyl acetate, the uncolored portion may be accidentally dropped during storage or exposed to the vapor of the organic solvent when exposed to the vapor of the organic solvent. It develops color and cannot be distinguished from the recorded image. Use of an adhesive containing an organic solvent is also inconvenient because it is necessary to avoid the use of an uncolored portion because coloration occurs.

Providing a protective layer on the surface of the heat-sensitive recording layer to improve the storage stability of the heat-sensitive recording material is disclosed in, for example, JP-A-56-126193.
Numerous proposals have been made in Japanese Patent Application Laid-Open No. 59-232893 and Japanese Patent Application Laid-Open No. 60-99696.

Such a protective layer is extremely effective, for example, when it comes into direct contact with a polyvinyl chloride film, in order to prevent the plasticizer contained in the film from penetrating into the thermosensitive coloring layer, and to prevent the colored portion from erasing. It is. In addition, penetration of oil such as salad oil can be suppressed by the protective layer, and discoloration due to oil can be prevented.

Many of the proposals made so far involve basic properties required for the protective layer, such as (1) organic solvents, plasticizers, oils, and the like, which tend to color uncolored areas or cause fading of colored areas. Prevent the penetration of such substances into the heat-sensitive layer (hereinafter, this property is referred to as oil resistance).

(2) Even if water adheres, dissolution of the protective layer film does not occur, and problems such as blocking by water do not occur (hereinafter, this property is referred to as water resistance).

(3) The print density should not decrease much due to the influence of the protective layer.

(4) Sticking to the thermal head, adhesion of scum, and wear of the head do not occur during heating printing.

As disclosed in Japanese Patent Publication No. 2-2439, attempts have been made to balance such properties by dividing the protective layer into two or more layers.

The protective layer provided on such a heat-sensitive recording material is an adhesive for imparting oil resistance and bonding other materials, and a cross-link for expressing water resistance by further polymerizing the adhesive. In addition to waxes and pigments that are added to prevent sticking to the thermal head, etc., as well as antifoaming agents and viscosity modifiers to improve the coating properties of the protective layer there were.

However, when the above-mentioned protective layer is provided on a normal thermosensitive coloring layer, it has been difficult to efficiently satisfy both oil resistance and coloring sensitivity.

[Problems to be Solved by the Invention] An object of the present invention is to provide a heat-sensitive material that sufficiently exhibits oil resistance as a function of the protective layer even when the amount of the protective layer applied is small, and the protective layer has a very small decrease in color-forming sensitivity. To provide a recording material.

[Means for Solving the Problems] The present inventors have come to the attention that the relationship between the thermosensitive coloring layer and the protective layer is important in order to solve the above problems,
As a result of continuing extensive research, the heat-sensitive coloring layer has a Beck smoothness of 60 seconds or more and a cobb absorption of 35%.
g / m ² or less is important, and a protective layer mainly composed of a water-soluble polymer substance is further provided thereon with a dry weight of 0.5 g / m ^2.
It is necessary to form the coating so as to be not less than 5 g / m ² or less, thereby finding that it is possible to obtain a heat-sensitive recording material having excellent oil resistance and high color sensitivity, and completed the present invention. .

According to the study of the present inventors, the smoothness of the heat-sensitive coloring layer and the water absorption are related to the state of formation of the protective layer film, and the smoothness of the heat-sensitive coloring layer is high, and the heat-sensitive coloring layer having a reduced water absorption is more effective. ,
The film forming property of the protective layer can be improved, and the oil resistance at the same coating amount of the protective layer becomes excellent.

The protective layer of the thermosensitive coloring layer having low smoothness has poor oil resistance. The reason is that the unevenness is remarkable, and even if a protective layer is provided on it, the unevenness cannot be covered sufficiently. This is probably due to a decrease in sex.

In the present invention, the Bekk smoothness of the thermosensitive coloring layer is 60 seconds or more,
More preferably, it is set to 100 seconds or more. In this case, the Beck smoothness is usually measured according to the standard specified in JIS-P8119. Any method may be used as a means for improving smoothness. For example, it is preferable to use fine particles of 2 μm or less as particles of a dye, a developer, a sensitizer, a pigment, and the like to be used in the thermosensitive coloring layer, and the coating method is bar coating or air knife coating. More blade coating gives more favorable results. If the heat-sensitive coloring layer before applying the protective layer is subjected to a smoothing treatment using a super calender or the like, desired smoothness can be more easily obtained.

The oil resistance of the protective layer is worse for the heat-sensitive coloring layer having greater water absorption, and does not exhibit sufficient oil resistance. This is because, during the coating of the protective layer, the water-soluble polymer substance for imparting oil resistance penetrates into the thermosensitive coloring layer having a large water absorption, and as a result, the film forming property of the protective layer is deteriorated. It is considered to be. In the present invention, the bump absorbency of the protective layer is 35 g / m ² or less, more preferably 30 g / m ² or less. Cobb water absorption is JIS-P8140
It is common to measure with. In order to obtain such a Cobb water absorption degree, for example, a pigment having a low water absorption is selected as a pigment used in the thermosensitive coloring layer, and a hydrophilic adhesive such as starch or polyvinyl alcohol is used as an adhesive instead of a hydrophilic adhesive.
It is effective to use SBR latex or the like. It is also effective to use a crosslinking agent in the thermosensitive coloring layer.

In the present invention, in order to set the Bekk smoothness of the heat-sensitive coloring layer to 60 seconds or more and the Cobb water absorption to 35 g / m ² or less, the above-described means may be appropriately used within a range that does not impair other quality or operability. , May be used in combination. If the value is in such a range, the object can be sufficiently achieved, but if it is out of this range, an appropriate result cannot be obtained.

Next, a protective layer mainly composed of a water-soluble polymer substance is formed on the thermosensitive coloring layer. This protective layer must have a coating amount of 0.5 g / m ² or more and 5 g / m ² or less on a dry weight basis. Preferably, it is 1 g / m ² or more and 4 g / m ² or less. 0.5g / m
^{When the} coating amount is less than ² , oil resistance is not sufficiently developed and 5 g / m ²
When the coating amount is larger, the color sensitivity due to the protective layer is greatly reduced, which is not practical.

Preferred examples of the water-soluble polymer material used for the protective layer include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetaldehyde-modified polyvinyl alcohol, modified polyvinyl alcohol such as epoxy-modified polyvinyl alcohol, starch, modified starch, casein, gelatin, glue, Examples include chitosan, polyamide, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, alkali salts of styrene-maleic anhydride copolymers and esters thereof, and diisobutylene-maleic anhydride copolymer salts. It is possible to use an emulsion-type adhesive in addition to such a water-soluble polymer substance.

In addition, as a material for forming the protective layer, a pigment or a wax mainly intended to prevent sticking to the thermal head, a crosslinking agent for improving water resistance by crosslinking with a water-soluble polymer substance, and the like. Other, wetting agent,
Viscosity modifiers, defoamers and the like may be added.

As pigments, calcium carbonate, clay, talc, titanium oxide, magnesium carbonate, zinc oxide, aluminum silicate, silica, inorganic pigments such as aluminum hydroxide,
Organic synthetic pigments such as starch granules, flour, silicone resin, urea-formalin resin, phenolic resin, melamine-formalin resin, epoxy resin, guanamine-formalin resin, polystyrene resin and the like can be used.

Examples of the crosslinking agent used together with the adhesive for improving the water resistance include melamine, epoxy compounds, glyoxal, dimethylol urea, polyaldehyde, zirconium salts and the like.

Examples of waxes include higher fatty acids such as stearic acid, higher fatty acid metal salts such as zinc stearate, calcium stearate, zinc behenate, and aluminum stearate, stearic acid amide, oleic acid amide, erucic acid amide, and behenic acid amide. Higher fatty acid amides and methylolated products thereof, polyethylene wax, paraffin wax, carnauba wax, microcrystalline wax and the like can be used.

In the present invention, any other conventionally used components of the heat-sensitive recording material may be used.

Basic dyes containing a thermosensitive coloring layer include 3,3-
Triallylmethane dyes such as bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-6-methyl-7-phenylaminofluoran, 3-dibutylamino-6-methyl-7-phenyl Aminofluoran, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-phenylaminofluoran, 3-dibutylamino-7- (o-chlorophenylamino) fluoran, 3- (N-ethyl- (N-isoamyl) amino-6-methyl-7-phenylaminofluoran and the like.

Any color developer may be used as long as it has a property of liquefying or dissolving with an increase in temperature and a property of being colored by contact with the basic dye.

Representative examples include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxy-diphenylmethane, 4,4'-isopropylidene diphenol, hydroquinone, 4,4'-cyclohexylidene diphenol, 4,4'-dihydroxydiphenyl sulfide, 4,
4'-thiobis (6-tert-butyl-3-methylphenol), 4,4'-dihydroxydiphenylsulfone,
4-hydroxy-4'-isopropoxydiphenyl sulfone, bis- (3-allyl-4-hydroxyphenyl)
Sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, 4-hydroxybenzoic acid Phenyl, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, 4
Phenolic compounds such as chlorophenyl hydroxybenzoate, 4,4'-dihydroxydiphenyl ether,
Benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid,
Aromatic carboxylic acids such as 3,5-di-tert-butylsalicylic acid, and organic acids such as salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, and calcium. Is mentioned.

In the heat-sensitive recording material of the present invention, the support material on which the heat-sensitive coloring layer is formed is not particularly limited. For example, paper, pigment coated paper, synthetic fiber paper, synthetic resin film, and the like can be appropriately used. Generally, paper is preferred.

In preparing the thermosensitive coloring layer-forming coating liquid, water is used as a dispersion medium, and a dye and a coloring agent are dispersed by a pulverizer such as a ball mill, an attritor, and a side grinder to form a coating liquid.

In such a coating liquid, starch, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / butadiene copolymer emulsion and the like are used as binders. 2 to 40% by weight of total solids, preferably 5 to 25%
Used by weight.

Various auxiliaries may be added to the coating liquid as needed. For example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium salt of lauryl alcohol sulfate, metal salts of fatty acids, and the like, other antifoaming agents, fluorescent dyes, coloring dyes, and the like can be added.

A pigment may be used in combination to make the heat-sensitive coloring layer whiter. Examples of pigments include clay, talc, heavy calcium carbonate, light calcium carbonate, silica, calcium silicate, aluminum silicate, diatomaceous earth, aluminum oxide, titanium dioxide, inorganic pigments such as zinc oxide, urea-formalin, phenol, Organic pigments using epoxy, melamine, guanamine / formalin resins, and the like can be used.

In order to prevent fading after coloring, a preservability improver may be added. As such a storage improver, a phenol compound is effective. For example, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5
-Cyclohexylphenyl) butane, 1,1-bis (2-
Methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4 '-(1-phenylethylidene) bisphenol, 4,4'-[1,4-phenylenedis (1-methylethylidene)] bisphenol, 4 And 4 '-[1,3-phenylenebis (1-methylethylidene)] bisphenol.

Examples of waxes include higher fatty acids such as stearic acid, higher fatty acid metal salts such as zinc stearate, calcium stearate, zinc behenate, and aluminum stearate, stearic acid amide, oleic acid amide, erucic acid amide, and behenic acid amide. Examples include higher fatty acid amides, methylolated fatty acid amides, polyethylene wax, paraffin wax, carnauba wax, and microcrystalline wax.

Examples of sensitizers for improving the sensitivity of the heat-sensitive recording material include parabenzyl biphenyl, dibenzyl terephthalate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, di-o-chlorobenzyl adipate, and the like.
It is possible to use 1,2-di (3-methylphenoxy) ethane, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, 1,2-bis (3,4-dimethylphenyl) ethane and the like. it can.

In the heat-sensitive recording material of the present invention, the method for forming the heat-sensitive coloring layer and the protective layer is not particularly limited. For example, as a method of applying the coating liquid, an appropriate coating device such as an air knife coater or a blade coater can be used.

The heat-sensitive coloring layer is generally formed so as to have a dry weight in the range of ² to 12 g / m ² .

Oil or solvent from the back surface, or suppress the penetration of plasticizer, it is also possible to provide a suitable back layer for curl control, in this case, from the back surface by having the same properties as the protective layer of the present invention Oil permeation can be suppressed.

Further, various known means such as providing an undercoat layer below the heat-sensitive coloring layer as necessary may be used.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

Formation of heat-sensitive coloring layer Preparation of basic dye dispersion A 3-Di-n-butylamino-6-methyl-7-phenylaminofluoran 40 parts by weight Polyvinyl alcohol 10% solution 20 parts by weight Water 40 parts by weight Developer Preparation of Dispersion B 4,4'-isopropylidene diphenol 40 parts by weight Polyvinyl alcohol 10% solution 20 parts by weight Water 40 parts by weight Preparation of sensitizer dispersion C Di-p-methylbenzyl oxalate 40 parts by weight Polyvinyl alcohol 20% by weight of 10% liquid 40 parts by weight of water The compositions for preparing the above liquids A to C were separately pulverized with a sand grinder to an average particle size of 0.5 µm.

Preparation of Pigment Dispersion D 40 parts by weight of light calcium carbonate (Brilliant 15, Shiraishi Industry Co., Ltd.) 60 parts by weight of 0.7% sodium hexamethanoate solution This composition was dispersed with a Cowles dispersing machine.

 Preparation of Pigment Dispersion E Silica (Mizukasil P527, Mizusawa Optical Co., Ltd.) 30 parts by weight Water 70 parts by weight This composition was dispersed with a Cowles dispersing machine.

Further, 20% zinc stearate dispersion and 20% stearamide dispersion were prepared as dispersions F and G, and SBR latex (trade name: PT-1015, manufactured by Nippon Zeon Co., Ltd.) and 10% An aqueous solution of polyvinyl alcohol (NL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) (hereinafter abbreviated as PVA) was used.

A coating liquid was prepared by changing the mixing ratio of these A to G liquids, latex and PVA, and this coating liquid was applied to 50 g / m ² base paper so that the coating amount was 7 g / m ² after drying, By drying, a thermosensitive coloring layer was formed on the base paper support. By changing the pressure conditions, a super calendar treatment was performed to change the smoothness.

Absolute dry blending ratio of the thermosensitive coloring layer before applying these protective layers,
Table 1 shows the results of measurement of Beck smoothness and Cobb water absorption. Beck smoothness was measured according to JIS-P8119, and Cobb water absorption was measured according to JIS-P8140.

Formation of protective layer Polyvinyl alcohol (NH
-18, saponification degree 98.0-99.0, polymerization degree 1800, Nippon Synthetic Chemical Industry Co., Ltd.), and the following protective layer coating liquid A was prepared.

Dry weight blending ratio Polyvinyl alcohol 10% solution 50 Kaolinite clay 60% dispersion (UW-90, manufactured by EMC) 30
Zinc stearate 20% dispersion 10 Dimethylol urea 5 Glyoxal 5 For comparison, use the same procedure except that SBR latex (trade name: PT-1015, manufactured by Zeon Corporation) was used instead of the 10% polyvinyl alcohol solution. , Protective layer coating solution B
It was created.

These two types of protective layer coating liquids were applied onto the previously prepared thermosensitive coloring layer at a coating concentration of 10% using a Meyer bar while changing the coating layer, followed by drying. Then Beck smoothness is 1100
I did a super calendar so that it became seconds.

The oil resistance and color sensitivity of the nine heat-sensitive recording materials thus obtained were measured.

The oil resistance was determined by heating and coloring a heat-sensitive recording paper, applying a commercially available salad oil, and evaluating the decoloring condition after one day. ○ indicates a level at which there is little decoloration and can be determined to be acceptable, Δ indicates a level at which some decolorization is observed but is not practically problematic, and × indicates that the decolorization is severe and not practical. Each level is shown.

The color sensitivity was measured using a commercially available thermosensitive facsimile modified for testing. Under the conditions of one line recording time of 10 msec, main scanning density of 8 dots / mm and sub-scanning density of 8 lines / mm,
The applied energy per dot was 0.39 mJ, and printing was performed on 128 lines. Macbeth densitometer
It was measured by RD-914 to determine the color sensitivity of the heat-sensitive recording material.

A density of 1.2 or more is sufficient color development sensitivity, and 1.0 to 1.2 is a little low but does not cause any practical problem, and 1.0 or less represents low color development sensitivity and a practically hindered level.

 Table 1 shows the results.

[Effects of the Invention] According to the present invention, it was possible to provide a heat-sensitive recording material in which the protective layer has extremely excellent oil resistance and the decrease in color-forming sensitivity is extremely small.

Claims (1)

(57) [Claims] 1. A thermosensitive layer comprising a protective layer provided on a thermosensitive coloring layer containing at least one basic dye formed on a support and a color developer capable of forming a color upon contact with the basic dye. In the recording material, the Cobb water absorption of the heat-sensitive coloring layer is 35 g / m ² or less, the Beck smoothness is 60 seconds or more, and the protective layer mainly composed of a water-soluble polymer substance is 0.5 g / m ^{2 in} dry weight. A heat-sensitive recording material provided so as to be at least 5 g / m ² or less.