JPH06278363A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material superior in color forming sensitivity and recording image shelf stability by providing a color-forming substance, a color-developer for coloring this substance an alkyl vinyl ether copolymer-modified polyvinyl alcohol resin of a specific average molecular weight, and a condensation naphthalene sulfonate on a substrate. CONSTITUTION:This is formed by providing a thermal color-forming layer containing a color-forming substance, a color-developer for said substance, an alkyl vinyl ether copolymer-modified polyvinyl alcohol resin (AVE modified PVA) of having an average molecular weight of 3000-25000, and a condensation naphthalene sulfonate on a substrate. If the AVE modified PVA in use has an average molecular weight less than 3000, a dispersion performance is deteriorated, and the thermal color-forming layer is also deteriorated in strength and binding power to the substrate. If more than 25000, a dispersion performance is deteriorated. The condensation naphthalene sulfonate typified by a compound shown by a formula improves a color forming sensitivity without impairing a shelf stability when being used in combination with the AVE modified PVA. In the formula, Z represents monovalent alkali metal atom or anmonium group, and (n) represents a repeat number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material excellent in color developing sensitivity and storability of recorded images.

[0002]

2. Description of the Related Art A thermosensitive recording material is a recording material in which a thermosensitive coloring layer capable of recording a colored image by heating is provided on a substrate such as paper, plastic film, metal vapor-deposited paper, etc. A color image can be obtained by heating with a built-in thermal printer, laser printer, or the like. A color image can be obtained by simply heating the thermosensitive recording material, so it is not only for copying books, documents, etc., but it is also an output record of electronic calculators, facsimile machines, various calculators, and ID cards, commuter passes, and boarding tickets. Widely used for writing various labels and the like.

The heat-sensitive color forming layer of the above heat-sensitive recording material usually contains a color-forming substance, a developer and a binder which develop the color of the color-forming substance by heating, and the heat-sensitive color forming layer has a high concentration when heated for a short time. It is required to have an excellent color-developing sensitivity of developing color.

The thermosensitive color-developing layer contains a color-forming substance obtained by dispersing the color-forming substance in the form of fine particles in a water-based medium containing a binder using a dispersing machine such as a ball mill or a sand grinder. It is provided by mixing a dispersion liquid and a dispersion liquid containing a color developer, which is separately obtained in the same manner as this dispersion liquid, and coating the mixture liquid on a substrate and drying.

The color-developing sensitivity of the thermosensitive color-developing layer thus obtained is higher as the dispersed particle size of each of the color-developing substance and the color developer dispersed in each dispersion prepared in the above dispersion step is smaller. The dispersion performance of the binder used has a great influence on the dispersed particle size.

Conventionally, polyvinyl alcohol, starch and its derivatives, cellulose derivatives, casein, gelatin, gum arabic, polyvinylpyrrolidone, as binders,
It is known to use polyacrylamide, salts of copolymers containing styrene and maleic anhydride as constitutional units, synthetic resin emulsions such as polyvinyl acetate and poly (meth) alkyl acrylate, and styrene-butadiene copolymer latex. ing.

However, the conventional binders do not have sufficient dispersibility, and even if it is attempted to make up for this lack of dispersibility by a strong mechanical stirring operation, it is difficult to carry out industrially. In addition, it has been attempted to use a surfactant together to make up for the lack of dispersibility of the conventional binder, but the image recorded in the thermosensitive coloring layer of the resulting thermosensitive recording material is discolored or decolored over time. As a result, the problem that image storability is low occurs.

Further, in order to solve the above problems, it is preferable to use a vinyl acetate resin containing a sulfonic acid group as a binder having both binding performance and dispersion performance.
It is disclosed in Japanese Patent Publication No. 9691.

However, a thermal recording material provided with a thermosensitive coloring layer having satisfactory coloring sensitivity and storability of recorded images has not been obtained by the above technique.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the prior art, and an object of the present invention is to provide a heat-sensitive recording material excellent in color developing sensitivity and storability of recorded images.

[0011]

As a result of various studies, the inventor of the present invention uses a specific copolymerized modified polyvinyl alcohol resin having excellent dispersion performance as a binder, and uses this resin in combination with a specific compound. The inventors have completed the present invention, knowing that the object can be achieved by.

That is, the present invention comprises: (A) a color-developing substance, (B) a color developer that develops a color by heating the color-developing substance, and (C) an alkyl vinyl ether copolymer-modified polyvinyl alcohol resin having an average molecular weight of 3000 to 25000. And (D) a heat-sensitive recording material comprising a heat-sensitive color-forming layer containing a condensed naphthalene sulfonate on a substrate.

The present invention will be described in detail below.

The heat-sensitive recording material of the present invention comprises (A) a color-developing substance, (B) a color developer which develops a color of the color-developing substance by heating,
(C) alkyl vinyl ether copolymer modified polyvinyl alcohol resin having an average molecular weight of 3000 to 25000 (hereinafter referred to as AVE modified PVA) and (D) condensed naphthalene sulfonate,
Further, an aqueous dispersion containing various additives used as desired
(Y) can be obtained by coating one side or both sides of a base material and drying.

The (A) color-forming substance used in the present invention is
For example, there are leuco compounds such as triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, and spiropyran-based dyes, and specifically, 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-bis (p -Dimethylaminophenyl) -6-dimethylaminophthalide, 3,
3-bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3- (Np-tolyl-N-ethylamino) -6 -Methyl-7- (N-phenylamino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-
6-chlorofluorane, 3-diethylamino-7- (3
-Fluoromethyl) phenylaminofluorane, benzoyl leuco methylene blue, 6-chloro-8-methoxy-benzoindolinopyrilospirane, 6-bromo-8-
Methoxy-benzoindolinopyrilospirane and the like can be mentioned.

Further, as the developer (B) which is heated with the color-forming substance to develop the color of the color-forming substance, for example, phenol, p-methylphenol, α-naphthol, β-
Naphthol, 2,2-bis (p-hydroxyphenyl)
Propane [also known as bisphenol A], 2,2-bis (p
-Hydroxyphenyl) butane, 4,4-cyclohexylidene diphenol, benzoic acid, salicylic acid, tartaric acid and the like can be mentioned.

Neither the (A) color-forming substance nor the (B) developer is limited to the above substances.

Used as a binder for a thermosensitive coloring layer (C)
AVE-modified PVA has not only excellent binding performance but also excellent dispersion performance, and it is possible to use vinyl ester and alkyl vinyl ether by solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization, or a combination of these methods. The resin obtained by polymerization is usually obtained by a method such as partial or complete saponification in a medium in the presence of an alkali or an acid, and the average molecular weight, constitutional units and proportions thereof are different.
It is also possible to use two or more types of modified PVA in combination.

Examples of the above vinyl ester include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl formate, vinyl pivalate and the like, with vinyl acetate being preferred. The vinyl ester may be used in combination of two or more upon copolymerization.

As the above-mentioned alkyl vinyl ether, any of linear or branched, saturated or unsaturated alkyl groups can be used, and the alkyl group of the alkyl vinyl ether has a carbon number of 8 or more, which is a color-forming substance or a color developer. It is preferable because it has excellent performance of dispersing additives and the like, and dispersed particles having a small particle size are easily obtained. In addition, since an AVE-modified PVA obtained by using one having a large number of carbon atoms tends to have a high aqueous solution viscosity and a low water solubility, the number of carbon atoms of the alkyl group is usually preferably 18 or less. The alkyl vinyl ether does not necessarily have a single carbon number in the alkyl group, and is represented by the carbon number of the alkyl group of the main component.

Examples of the alkyl vinyl ether include 2-ethylhexyl vinyl ether, lauryl vinyl ether, stearyl vinyl ether and the like, and the alkyl vinyl ethers may be used in combination of two or more in the copolymerization. Among the alkyl vinyl ethers, lauryl vinyl ether is preferable.

The AVE-modified PVA used in the present invention usually comprises an alkyl vinyl ether unit, a vinyl alcohol unit and a vinyl ester unit. The vinyl ester units are saponified and converted into vinyl alcohol units. It does not have to exist.

The amount of vinyl ether units in the AVE-modified PVA is 0, based on the total number M of alkyl vinyl ether units, vinyl alcohol units and vinyl ester units.
02 to 3 mol% is preferable, and 0.1 to 1 mol% is more preferable. If this amount is less than 0.02 mol%, the dispersion performance of AVE-modified PVA may not be sufficient, and if it exceeds 3 mol%, AV
The water solubility of E-modified PVA tends to decrease, and the viscosity of aqueous solutions tends to increase.

The amount of vinyl alcohol units in the AVE-modified PVA is preferably 60 to 99.98 mol% and more preferably 80 to 99.98 mol% based on the same total number M of moles as in the case of the alkyl vinyl ether units. If this amount is less than 60 mol%, the dispersion performance of the AVE-modified PVA may be insufficient and the water solubility will be low.

The vinyl ester unit in the AVE-modified PVA is a copolymerized unit left unsaponified in the PVA due to the vinyl ester used as a part of the raw material of the AVE-modified PVA. It depends on the degree of saponification of PVA,
When fully saponified, there are zero vinyl ester units. The amount of vinyl ester units in the AVE-modified PVA used in the present invention is preferably 0 to 39.98 with respect to the same total number M of moles as in the case of the alkyl vinyl ether units.
Mol%, and more preferably 19.98 mol% or less. If this amount greatly exceeds 39.98 mol%, AVE modification
The heat softening temperature, oil resistance, and plasticizer resistance of PVA are low, and the heat-sensitive coloring layer tends to have insufficient heat resistance, oil resistance, plasticizer resistance, and water solubility.

The AVE-modified PVA used in the present invention is soluble in water and usually has an alkyl vinyl ether unit, a vinyl alcohol unit and a vinyl ester unit. In addition to these units, vinyl ester and alkyl units are also included as constitutional units. The unit of the other monomer (X) copolymerizable with vinyl ether may be contained in an amount of 5 mol% or less based on the total number M of moles.

Examples of the above-mentioned monomer (X) include allyl glycidyl ether, glycidyl (meth) acrylate, 1-allyloxy-3,4-epoxybutane, 1-
Epoxy group-containing monomers such as (3-butenyloxy) -2,3-epoxypropane, monomers having a carboxyl group such as (meth) acrylic acid, (iso) crotonic acid, itaconic acid, fumaric acid and the like And olefins such as (meth) acrylamide, ethylene and propylene. Of these, acrylamide is preferable. The carboxyl group of the above monomer unit having a carboxyl group may be in the form of a monovalent alkali metal salt in AVE-modified PVA.

The average molecular weight (by GPC method) of the AVE-modified PVA used in the present invention is 3000 to 25000, preferably 5000 to 25.
It is 000. If the average molecular weight is less than 3000, the dispersibility is low, the strength of the resulting thermosensitive color developing layer and the binding force to the substrate are low, and if it exceeds 25,000, the dispersibility is low, both of which are not preferable.

The AVE-modified PVA used in the present invention includes the AVE-modified PV obtained by saponifying a resin obtained by a copolymerization reaction.
Not only A, but also the AVE-modified PVA obtained by post-treating the obtained AVE-modified PVA to adjust its average molecular weight to 3000 to 25000 is included.

The above-mentioned post-treatment method has, for example, a cleavage agent for cleaving the main chain of polyvinyl alcohol (for example, hydrogen peroxide, periodic acid and its salt, etc.) as a copolymerized unit of vinyl ester and alkyl vinyl ether. There is a method of coexisting in a saponification reaction system of a vinyl ester copolymer resin or adding to a slurry or an aqueous solution of AVE-modified PVA.

The condensed naphthalene sulfonate as the component (D) used in the present invention is typically a compound represented by the following general formula (I), and the storage stability is lowered by using it in combination with AVE-modified PVA. It is intended to improve the color development sensitivity without causing it.

[0032]

[Chemical 1] However, in the formula, Z represents a monovalent alkali metal atom or an ammonium group, and n represents a repeating number.

The compound represented by the above general formula (I) is a substance obtained by sulfonation of naphthalene with sulfuric acid, then formalin is added thereto for condensation and neutralization, and a commercially available product can be used. it can. The aldehyde used for the condensation may be an aldehyde other than formaldehyde, but formaldehyde is preferred.

The number of repetitions n in the general formula (I) of the above (D) is 1-8, more preferably 4-6. Further, the component (D) to be used does not necessarily have to be a single n, and is represented by the number of n which is the main component. When n is less than 1, the dispersibility may not be improved even when combined with AVE-modified PVA, and when n is more than 8, it may be difficult to use due to low water solubility.

The amount of component (D) used is 1 with respect to component (C).
-20% by weight is preferred. If less than 1% by weight, AVE modified PVA
Even if it is combined with
Even if it is used in excess of weight%, the dispersibility is not improved so much, and if it is used in a large amount, the storage stability may be deteriorated.

The composition of the heat-sensitive color forming layer of the heat-sensitive recording material of the present invention is arbitrarily selected according to the desired performance of the material, but usually (A), (B), (C) and (D) The total weight of the components in the thermosensitive coloring layer is 10% by weight or more, more preferably 30 to 80% by weight, and the total weight of the component (A) is 30 to 80% by weight,
30 to 80% by weight of component (B), 2 to 39.98% by weight of component (C)
It is preferable that the component (D) is about 0.02 to 9.99% by weight.

The thermosensitive coloring layer of the thermosensitive recording material of the present invention comprises
If desired, various additives can be contained within the range not impeding the present invention.

Examples of the above-mentioned various additives include pigments such as calcium carbonate, satin white, titanium dioxide, talc, kaolin and clay, sensitizers such as stearic acid amide and zinc stearate, and water-soluble or water-dispersible additives. Polymeric substances,
Examples include water resistant agents such as glyoxal and urea resins, defoaming agents, and lubricants.

Examples of the above water-soluble or water-dispersible polymer substances include polyvinyl alcohol resins, starch and its modified products and their derivatives, methyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, polyacrylamide, poly (meth) acryl. Acid salts, water-soluble polymeric substances such as salts of maleic anhydride copolymer resins, polystyrene-based, polyvinyl acetate-based, vinyl acetate-ethylene-based,
There are aqueous emulsions and latexes of polyvinyl chloride-based, SBR-based, poly (meth) alkyl acrylate-based, polyvinyl chloride-based resins, etc., and water-soluble or water-dispersible polymer substances are non-volatile with respect to component (C). The amount of 30% by weight or less in terms of minutes can be used together.

The base material of the heat-sensitive recording material of the present invention is not limited to a shape, and the material is, for example, paper, paperboard or a material obtained by sizing them with a surface sizing agent, a plastic film or sheet, or a surface coating of these. ,
There are metal vapor-deposited paper, synthetic paper containing plastic and a filler, or those coated on the surface thereof. Among them, papers such as paper and paperboard are preferable.

The above-mentioned dispersion liquid (Y) is a liquid in which the component (A) is dispersed and contained in an aqueous medium containing the components (C) and (D), and the component (B) is dispersed and contained in the same manner. It is preferable to obtain each of these solutions separately and then mix these solutions in order to avoid troubles such as color development due to the reaction of both components (A) and (B) due to heat generation during dispersion.

Moreover, (C) and (C) used for dispersion of the component (A)
The components (C) and (D) used for dispersion of the component (D) and the component (B) do not necessarily have the same properties. The components (C) and (D) used above do not necessarily have to be dissolved in the aqueous medium in which the components (A) or (B) are dispersed before the start of dispersion, (A) or (B) Since the components are dissolved during dispersion, the components (C) and (D) are in the form of powder or liquid.
It may be added to the aqueous medium together with the component (A) or the component (B).

The above-mentioned various additives may be added before the dispersion of the component (A) or (B) is started, during the dispersion, or after the dispersion is completed, but those which are unstable during strong dispersion mixing, such as emulsions and latexes. Is preferably added to and mixed with the liquid after the dispersion or the dispersion (Y) to be applied to the substrate. Further, various additives can be contained in either the liquid containing the component (A), the liquid containing the component (B), or both of these liquids.

In order to disperse the component (A) or (B), in any case, for example, a dispersion mixer which is usually used for producing paints can be used, and specific examples thereof include a sand grinder and a ball mill. To be The two liquids obtained were mixed at a temperature below the temperature at which they did not develop color when mixed, and then dispersed.
Get (Y).

In order to form the thermosensitive color developing layer by coating the dispersion (Y) containing the components (A), (B), (C) and (D) on a substrate, any coater such as, for example, A roll coater, air doctor, blade coater, gravure coater, etc. can be used, and the coating amount (after drying) is usually 1 to 20 g /
It is about m ² , more preferably 3 to 10 g / m ² . The application is
It may be performed twice or more if desired.

The solid content concentration of the dispersion liquid (Y) to be applied is arbitrarily selected according to the desired coating amount and the like, but is preferably 10 to 40% by weight in consideration of workability and drying property. It is a range. The dispersion (Y) coated on the substrate can be dried by any method, but when it is dried by heating, it is performed at a temperature not higher than the temperature at which the coating layer develops color.

The surface of the heat-sensitive recording layer of the heat-sensitive recording material of the present invention is coated with PVA, modified PVA, AVE modified PVA, CMC, MC.
The thermal recording layer can be protected from oils and plasticizers by overcoating with an aqueous solution of starch, etc. Epoxy group modified PVA (Japanese Patent Publication No. 3-62157)
The use of the material described in Japanese Patent Laid-Open Publication No. 1993-242242 makes it possible to particularly strongly protect the heat-sensitive recording layer.

[0048]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Unless otherwise specified, “part” means part by weight.

Example 1 Preparation of solution (i) 35 parts of crystal violet lactone, AVE modified PVA-
A ball mill was charged with 30 parts of a 10% by weight aqueous solution of I, 0.4 parts of formalin-condensed naphthalenesulfonic acid ammonium salt (n = 5, non-volatile content 40% by weight) and 35 parts of water, and then the ball mill was operated for 2 hours for grinding.・ Dispersing liquid
got (i).

The AVE-modified PVA-I used above is an AVE-modified PVA obtained by saponifying a copolymer resin obtained by solution polymerization of vinyl acetate and lauryl vinyl ether in methanol with methanol using caustic soda. is there. Its composition (NMR
Is 0.5 mol% of lauryl vinyl ether unit, 87.6 mol% of vinyl alcohol unit and 11.9 mol% of vinyl acetate unit, and its number average molecular weight (solvent:
0.1 molar NaCl aqueous solution, polyethylene glycol equivalent GPC
By law) is 15000.

Preparation of liquid (ii) and liquid (iii) 35 parts of bisphenol A, 70 parts of a 10 wt% aqueous solution of AVE-modified PVA-I, formalin-condensed naphthalenesulfonic acid ammonium salt (n = 5, nonvolatile content 40 wt) %) And 150 parts of water were charged into a ball mill, and this ball mill was operated for 2 hours for pulverization and dispersion to obtain a liquid (ii).

Next, to the ball mill containing the above liquid (ii), 30 parts of calcium carbonate (fine particle type of 0.02 to 0.08 μm) is added.
And 15 parts of stearic acid amide were added, and a ball mill was further operated for 2 hours to carry out pulverization and dispersion to obtain a liquid (iii).

Liquid (i) and liquid (iii) at 30 ° C. respectively obtained above
The above liquids were mixed at a ratio of 300 parts of the liquid (iii) to 100 parts of the liquid (i) so that the liquid temperature did not rise, to obtain an aqueous dispersion liquid composition. Then, the composition, as the coating amount relative to one side of the paper having a basis weight of 50 g / m ² (dry weight) is 5 g / m ^2, it was coated with a coating rod and dried at 60 ° C. Thermal I got the recording paper.

The average particle size of the particles dispersed in each of the liquid (i) and the liquid (ii) collected in a small amount during the preparation of the liquid (iii), the color density of the thermosensitive recording paper and the storability of the recorded image The measurement test was conducted by the following method, and the results are shown in Table 4.

Further, even if a part of the heat-sensitive recording paper obtained above is cut and strongly folded twice so that the fold lines intersect at approximately 90 °, cracking of the heat-sensitive color developing layer, generation of powder, No abnormalities such as peeling were observed.

Measurement Test Method 1. Measurement of Average Particle Diameter of Particles in Dispersion The average particle diameter (μm) of particles in liquid (i) and liquid (ii) was measured by a particle size distribution measuring device (manufactured by Seishin Co., SKA -5000).

2. Measurement of Coloring Density of Thermosensitive Recording Paper The thermosensitive recording paper was conditioned under an atmosphere of 20 ° C. × 65% RH for 24 hours to prepare a sample. An image is color-recorded on the thermosensitive recording layer of the sample using a thermosensitive facsimile receiver (built-in thin film thermal head), and the recording density of the image is immediately measured with a Macbeth densitometer (Macbeth RD-918 type), The value was defined as the color density (DA).

3. Measurement of storability The heat-sensitive recording paper on which the image was color-recorded and the color density was measured in the above 2 was stored at 20 ° C. × 65% RH for 30 days, and the recording density (DB) was measured again as Macbeth density. It was measured using a meter (RD-918). The storability (%) was calculated by the following formula using each value of this DB and DA measured in the above 2. The higher the storability value, the less the fading of the recorded image over time, and the more excellent the storability is. Storability (%) = (DB / DA) x 100

Examples 2 to 14 Instead of the AVE-modified PVA-I used in Example 1, polyvinyl alcohol resins having the properties shown in Table 1 (Examples 2 to 9) and Table 2 (Examples 10 to 14) were used. A thermal recording paper was obtained in the same manner as in Example 1 except that it was used. The color density and storability of this thermosensitive recording paper and the average particle size of the particles of liquid (i) and liquid (ii) were measured. The measurement results are shown in Table 4. Further, the folding test of the thermal recording paper was conducted in the same manner as in Example 1,
No abnormality was found in any of them. Incidentally, Examples 2 and 4
The polyvinyl alcohol-based resin used in 1 was a 10% by weight aqueous solution prepared by adding hydrogen peroxide to an aqueous solution of lauryl vinyl ether copolymer-modified PVA to adjust the average molecular weight of the PVA.

Examples 15 to 18 Formalin-condensed naphthalene sulfonate (n = 5, z =
The same procedure as in Example 1 was carried out except that a formalin-condensed naphthalenesulfonate having the properties shown in Table 2 was used instead of the ammonium group). The amount of the formalin-condensed naphthalene sulfonate used in Examples 15 to 18 is the same as that of Example 1 in terms of nonvolatile content. The measurement results are shown in Tables 4 and 5.

Examples 19 to 22 Same as Example 1 except that the amounts of AVE-modified PVA-I, formalin-condensed naphthalene sulfonate (n = 5, z = ammonium group) and water used were as follows. I did.
The measurement results are shown in Table 5. A folding test was conducted in the same manner as in Example 1, but no abnormality was observed.

Example No. Liquid (i) (part) Liquid (iii) (part) (a) (b) Water (a) (b) Water 19 30 1.8 1.8 35 70 4.2 4.2 150 20 30 0.09 35 70 0.21 150 21 90 0.4 75 75 210 0.92 310 22 9 0.4 36 21 0.92 139 (Note) (a) 10% by weight aqueous solution of AVE modified PVA-I (b) Formalin condensed naphthalene Sulfonate (n =
5, z = ammonium group, nonvolatile content 40% by weight)

Example 23 1/5 of each weight of the 10% aqueous solution of AVE-modified PVA-I used to obtain each of the liquid (i) and the liquid (iii) in Example 1 was mixed with polyvinyl alcohol (average molecular weight). A thermosensitive recording paper was obtained in the same manner as in Example 1 except that a 10% aqueous solution having a viscosity of 24500 and a saponification degree of 88 mol% was used instead. The color density and storability of this thermosensitive recording paper and the average particle size of the particles dispersed in each of the liquid (i) and the liquid (ii) were measured. The measurement results are shown in Table 5.

Comparative Examples 1 to 4 The procedure of Example 1 was repeated except that the polyvinyl alcohol resin and the formalin-condensed naphthalene sulfonate having the properties shown in Table 3 were used. The measurement results are shown in Table 5. When a folding test was conducted in the same manner as in Example 1,
No abnormality was observed in Comparative Example 3 except that fine cracking occurred.

In Comparative Example 1, formalin-condensed naphthalene sulfonate was not used, and as the polyvinyl alcohol resin used in Comparative Example 3, hydrogen peroxide was used similarly to those used in Examples 2 and 4. A 10% aqueous solution was used although the average molecular weight was adjusted.

Comparative Example 5 Instead of the AVE-modified PVA-I used in Example 1, vinyl acetate and a sodium allylsulfonate copolymer saponified product having the properties shown in Table 3 were used, and a formalin-condensed naphthalenesulfonate salt was used. A thermal recording paper was obtained in the same manner as in Example 1 except that it was not used. The color density and storability of this thermosensitive recording paper and the average particle size of the particles of liquid (i) and liquid (ii) were measured. The measurement results are shown in Table 5.

Comparative Examples 6 and 7 In place of the formalin-condensed naphthalene sulfonic acid ammonium salt used in Example 1, in Comparative Example 6, the same weight as the formalin-condensed naphthalene sulfonic acid ammonium salt used in Example 1 was calculated. Example 1 was repeated except that sodium diisopropylnaphthalene monosulfonate was used, and in Comparative Example 7, the same weight of polyoxyethylene nonylphenyl ether as the nonvolatile content was used with the formalin-condensed naphthalenesulfonic acid ammonium salt used in Example 1, respectively.
A thermosensitive recording paper was obtained in the same manner as in (1). The color density, storability and average particle size of the particles dispersed in each of the liquid (i) and the liquid (ii) were measured. The measurement results are shown in Table 5.

[0068]

[Table 1]

[0069]

[Table 2]

[0070]

[Table 3]

[0071]

[Table 4]

[0072]

[Table 5]

[0073]

The heat-sensitive recording material of the present invention has the effect of being excellent in color development sensitivity and storability of recorded images.

Claims (6)

[Claims] 1. The following (A) component, (B) component, (C) on a substrate:
A heat-sensitive recording material comprising a heat-sensitive coloring layer containing the component and the component (D). Component (A): Color-forming substance (B) Component: Developer that develops the above (A) color-forming substance by heating (C) Component: Alkyl vinyl ether copolymerized modified polyvinyl alcohol resin (D) with an average molecular weight of 3000 to 25000 ) Component: Condensed naphthalene sulfonate 2. The amount of the alkyl vinyl ether unit of the component (C) is 0.02 to the total number of moles of the vinyl alcohol unit, the vinyl ester unit and the alkyl vinyl ether unit.
The thermal recording material according to claim 1, which is 3 mol%. 3. The heat-sensitive recording material according to claim 1, wherein the alkyl vinyl ether as the component (C) has an alkyl group having 8 to 18 carbon atoms. 4. The heat-sensitive recording material according to claim 1, wherein the alkyl vinyl ether as the component (C) is lauryl vinyl ether. 5. The heat-sensitive recording material according to claim 1, wherein the component (D) is an ammonium salt or sodium salt of formalin-condensed naphthalenesulfonic acid. 6. The content of component (D) in the thermosensitive coloring layer is
The heat-sensitive recording material according to claim 1, which is 1 to 20% by weight based on the component (C).