JP3329930B2 - Thermal recording sheet - Google Patents

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 sheet having excellent water resistance, solvent resistance and color development.

[0002]

2. Description of the Related Art A thermosensitive coloring component layer comprising a colorless or pale-colored lactone compound (color-forming substance) and an acidic compound such as an organic acid or a phenol compound (a color-developing substance) is provided on a support. Sheets are widely used for recording sheets such as facsimile machines, computer terminals, printers for calculators and medical measuring instruments, POS labels, barcode labels, etc. because they develop color when heat is applied.

[0003] As binders for the heat-sensitive coloring component in the heat-sensitive recording sheet, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, starch, gelatin, casein, gum arabic, isobutylene-maleic anhydride copolymer salt, styrene Water-soluble polymers such as maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt and aqueous emulsions such as styrene-butadiene copolymer emulsion are used ( JP-A-54-128347).

[0004] Among the above water-soluble polymers, polyvinyl alcohol (hereinafter abbreviated as PVA) in particular has excellent adhesive properties, and is widely used because a relatively small amount thereof exhibits high binder power. However, when a water-soluble polymer such as PVA is used, there is a problem that when the solid content concentration in the coating liquid is increased, the coating liquid viscosity increases, and coating unevenness occurs, and color unevenness occurs. On the other hand, when the solid content concentration is reduced, drying for a long time is required, and there is a problem that drying unevenness occurs and color developability is reduced. Also,
When a water-soluble polymer is used as the binder, the color image formed by the compatibility and reaction between the color-forming lactone compound and the acidic compound is unstable with moisture or an organic solvent. Due to the contact or the contact with the plasticizer in the vinyl chloride resin film, there is a disadvantage that the color-developed portion is easily discolored or disappears. In order to cope with such drawbacks, a method is known in which a water-resistant polymer such as formalin, glyoxal, dialdehyde starch, glutaraldehyde, aldehyde acrylamide, or an alkali metal tetraborate is used in combination with a water-soluble polymer (particularly). Kaisho 56
155790, JP-A-61-162383, etc.). Further, it is known that the water resistance is improved by imparting crosslinking properties to PVA itself (Japanese Patent Application Laid-Open No. 58-1983).
193189). However, the above-mentioned water resistance method requires a heat treatment at a high temperature of 100 ° C. or more, and thus has a problem that the heat-sensitive recording sheet develops color during the heat treatment.

[0005] On the other hand, when an aqueous emulsion such as a styrene-butadiene copolymer emulsion is used, a low viscosity is maintained even when the solid content concentration in the coating liquid is increased. And can be dried for a short time. However, the conventional styrene-butadiene copolymer emulsion uses a low-molecular surfactant at the time of its production, so that the color-forming lactone compound forms a color (hereinafter, referred to as spontaneous color) without applying heat. There was a problem.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording sheet which has no spontaneous coloring, has good coloring properties, and is excellent in water resistance and solvent resistance.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that a mercapto group is present in the molecule.
Polyvinyl Alcohol-Based Polymer Having Dispersion as Dispersion Stabilizer
Mel the thermal recording sheet, and the molecule having a water-insoluble polymer polyvinyl alcohol polymer grafted produced by emulsion polymerization using a heat-sensitive color-forming component layer
Disperse polyvinyl alcohol polymer having capto group
A thermosensitive recording sheet having a film made of a water-insoluble polymer grafted with a polyvinyl alcohol-based polymer produced by emulsion polymerization used as a stabilizer on a thermosensitive coloring component layer was found, and the present invention was completed. .

Hereinafter, the present invention will be described in detail. The water-insoluble polymer grafted with the polyvinyl alcohol-based polymer in the present invention has a mercapto group in the molecule
Milk using polyvinyl alcohol polymer as dispersion stabilizer
Reduction is produced by polymerization, polyvinyl alcohol polymer is an aqueous emulsion as a raw material to a water-insoluble polymer grafted dispersoid. Examples of the water-insoluble polymer that is a dispersoid include a water-insoluble synthetic polymer and a natural polymer. Among them, a synthetic polymer is preferable. As the synthetic polymer, a homopolymer or copolymer of an ethylenically unsaturated monomer and / or a diene monomer is preferable. The glass transition temperature of the water-insoluble polymer is -60 ° C to 30 ° C.
C is preferable, and -40 C to 20 C is more preferable.

The ethylenically unsaturated monomers include (meth) acrylate monomers, vinyl ester monomers, styrene monomers, halogenated unsaturated monomers, and olefin monomers. And the like. As the (meth) acrylate-based monomer, a monomer having an alkyl group having 1 to 12 carbon atoms is preferable. For example, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid Propyl, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, dimethylaminoethyl (meth) acrylate and their quaternaries, (meth) acrylamide, N,
N-dimethyl (meth) acrylamide, (meth) acrylamide-2-methylpropanesulfonic acid and its sodium salt, hydroxyethyl (meth) acrylate, caprolactone-modified (meth) acrylate, N-methylol (meth) acrylamide N-alkylolamides of α, β-ethylenically unsaturated carboxylic acids, such as
Examples include ethylene glycol di (meth) acrylate. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, and vinyl pivalate. Styrene-based monomers include styrene, α-methylstyrene, o
-Methylstyrene, p -methylstyrene, p -styrenesulfonic acid and alkali metal salts thereof (sodium salt,
Potassium salt) and the like. Examples of halogenated unsaturated monomers include vinyl chloride, vinyl fluoride, vinyl bromide,
Examples include vinylidene chloride, vinylidene fluoride, and vinylidene bromide. Examples of the olefin-based monomer include ethylene, propylene, and isobutylene. Unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, fumaric acid, and maleic acid, and salts thereof can also be copolymerized. Examples of the diene-based monomer include butadiene, isoprene, chloroprene, and neoprene.

The PVA polymer grafted on the water-insoluble polymer in the present invention has a mercapto group in the molecule.
Produced by emulsion polymerization using PVA-based polymer as dispersion stabilizer
Built . As the PVA-based polymer having a mercapto group, a PVA-based polymer having a mercapto group only at the terminal is preferable because it is easy to handle without fear of insolubilization, and a PVA-based polymer having a mercapto group only at one end is preferable. More preferred. In the case of using a PVA-based polymer having a mercapto group in the main chain, care must be taken because there is a possibility that the PVA itself may form a disulfide bond due to oxidation of the PVA itself and become insoluble. In addition, the PVA-based polymer having a mercapto group at the terminal is, in addition to the mercapto group at the terminal,
The VA-based polymer may have various functional groups such as anionic, cationic or nonionic in the main chain or side chain. PVA-based polymers having a mercapto group at only one end are, for example, usually polyvinyl ester-based polymers obtained by polymerizing vinyl monomers mainly composed of vinyl ester-based monomers in the presence of thiolic acid. It can be prepared by saponification by a method.

The degree of polymerization of the PVA polymer used in the present invention is not particularly limited, but is preferably 3500 or less, more preferably 1500 or less. Further, the degree of saponification of the PVA-based polymer varies depending on the type of other modifying groups,
Although not specifically defined, 70 mol% or more is preferable from the viewpoint of water solubility. The aqueous emulsion to be used in the present invention, substantially from the PVA polymer grafted to the water-insoluble polymer is a dispersoid exhibit the function as a dispersant, PVA polymer having a mercapto group at the terminal only preferably made of tone with the dispersed agent. However, a conventionally known PVA-based polymer can be used as long as performance such as emulsion polymerization stability is not impaired, or an emulsion stabilizer can be used in combination without spontaneous coloration. The PVA-based polymer having a mercapto group at the terminal can chemically bond (graft bond) with the water-insoluble polymer constituting the dispersoid to give an extremely stable aqueous emulsion. The graft ratio of the PVA-based polymer to the water-insoluble polymer in the aqueous emulsion is preferably 30% or more, and more preferably 50% or more.

Method for producing an aqueous emulsion in the [0012] present invention are emulsion polymerization using a PVA-based polymer having a mercapto group in the molecule in the dispersion stabilizer, the method has good grafting efficiency with respect to various monomers An aqueous emulsion that is stable on an industrial scale can be provided .

The average particle size of the dispersoid of the aqueous emulsion of the present invention is not particularly limited, but is preferably from 0.05 to 2.0 μm, more preferably from 0.1 to 1.5 μm. further,
The concentration of the dispersoid in this aqueous emulsion may be appropriately selected depending on various situations, but is preferably 20 to 70% by weight, and more preferably 30 to 60% by weight. Also, P
The amount of the VA polymer used is not particularly limited, either.
0.1 parts by weight based on 100 parts by weight of the water-insoluble polymer as the dispersoid
It is preferably 5 to 100 parts by weight, more preferably 1 to 50 parts by weight. Among them, when the binder power is particularly required, the amount of the PVA-based polymer is preferably 4 to 50 parts by weight, and when the water resistance is particularly required, the amount of the PVA-based polymer is preferably 2-30 parts by weight are preferred.

As the heat-sensitive coloring component in the heat-sensitive recording sheet of the present invention, two components of a color-forming substance and a color-developing substance which reacts with the color-forming substance to form a color when heated are listed as typical examples. A typical example of the color-forming substance is a color-forming lactone compound. The color-forming lactone compound may be any compound that can form a color by reacting with an acidic compound when heated, and examples thereof include various compounds such as triphenylmethane, triphenylmethanephthalide, fluoran, leuco auramine, and subiropyran compounds. Leuco compounds. The color-developing substance may be an acidic compound having a property of being liquefied or vaporized at 70 ° C. or higher and reacting with the leuco compound to form a color.
Phenylphenol, 4-hydroxyacetophenone,
2,2'-diacetoxyphenyl, 2,2'-methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,
4'-isopropylidene diphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4 '
-Isopropylidenebis (2-methylphenol),
4,4'-sec-butylidenephenol, 4,4'-
Ethylenediphenol, 4,4'-ethylenebis (2-
Phenolic compounds such as methylphenol).

The support substrate used in the heat-sensitive recording sheet of the present invention includes paper such as high quality paper, medium quality paper, coated paper, plastic film, film laminated paper, woven sheet and the like.

Next, a specific method for producing the heat-sensitive recording sheet of the present invention using a color-forming lactone compound and a phenol compound will be described. The color-forming lactone compound and the phenol compound are separately pulverized into fine particles by grinding, and if necessary, fillers such as clay, talc, calcium carbonate, waxes, surfactants, etc. are added, and the mercury is further incorporated into the molecule.
Disperse polyvinyl alcohol-based polymer with
A water-insoluble polymer PVA based polymer produced grafted by emulsion polymerization using the Jozai added an aqueous emulsion of a dispersoid, the heat-sensitive coating solution was made of tone, and applying it onto a supporting substrate, After drying to form a thermosensitive coloring component layer, the thermosensitive recording sheet of the present invention can be obtained. If necessary, add mercapto on the thermosensitive coloring component layer.
Polyvinyl alcohol-based polymer having a group as a dispersion stabilizer
An aqueous emulsion containing a water-insoluble polymer grafted with a PVA-based polymer produced by the emulsion polymerization used as a dispersoid is applied and dried to form a film. As a coating method, a roll coating method is preferable. The drying temperature is preferably 30 ° C to 90 ° C.
It is preferred to lower the drying temperature to 0 ° C to 60 ° C. In this case, it is also effective to apply the above-mentioned aqueous emulsion of the present invention on a supporting substrate in advance and form a layer composed of the aqueous emulsion, and then apply the heat-sensitive coating liquid of the present invention. Moreover, not containing the aqueous emulsion of the present invention comprising an aqueous binder thermosensitive coating solution <br/> to, prepare, which was coated on a support base, to form a heat-sensitive color-forming component layer, the heat-sensitive color-forming component layer A film obtained by forming the above-mentioned aqueous emulsion of the present invention into a film can also be formed thereon. Further, the aqueous emulsion of the present invention, be used in combination a small amount of an aqueous binder comprising a conventional water-soluble resin or water dispersible resin may also heat-sensitive recording sheet obtained by the production method of the present invention A conventionally known overcoat layer may be further provided.

When the above-mentioned aqueous emulsion is used as a thermosensitive coloring component binder in the present invention, the amount used in terms of solid content is 0.1 to 100 parts by weight of the thermosensitive coloring component.
The amount is preferably 5 to 500 parts by weight, more preferably 1 to 200 parts by weight. The amount of the aqueous emulsion used in the present invention in the case of forming a film as an overcoat layer on the thermosensitive coloring component layer is such that the coating amount in terms of solid content is 0.1%.
2-5 g / m ² is preferred. When forming the overcoat layer, the concentration of the coating solution composed of the aqueous emulsion is
It is preferably from 0.5 to 30% by weight, more preferably from 1 to 20% by weight.

The heat-sensitive recording sheet of the present invention has remarkably excellent water resistance and solvent resistance, and also has good coloring. The reason for this is unknown, but is presumed as follows. That is, in the molecule used in the present invention
Polyvinyl Alcohol Polymer Having Mercapto Group
Produced by emulsion polymerization using as a dispersion stabilizer
An aqueous emulsion having a water-insoluble polymer grafted with a system polymer as a dispersoid, when dried to form a film,
This is probably because the PVA-based polymer and the dispersoid composed of the water-insoluble polymer form separate layers (sea-island structure). Therefore, it is presumed that high binder power (adhesive strength) and solvent resistance, which are characteristics of the PVA-based polymer, are exhibited, and water resistance, which is a characteristic of the water-insoluble polymer, is simultaneously exhibited.

[0019]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following examples, "%" and "parts" are by weight unless otherwise specified. The graft ratio of PVA to the dispersoid in the aqueous emulsion is as follows:
The film obtained by forming an aqueous emulsion was immersed in water at 40 ° C. for one week, and the weight loss of the film was measured.

Example 1 (Preparation of emulsion) In a pressure-resistant autoclave equipped with a nitrogen inlet and a thermometer, a P having a mercapto group at one end was prepared.
4% aqueous solution 1 of VA (degree of polymerization 300, degree of saponification 92.0 mol%, mercapto group content 6.5 × 10 ⁻⁵ eq / g)
Were charged 00 parts, after 4.0 two adjust the pH with sulfuric acid, were charged 60 parts of styrene. Next, 40 parts of butadiene was press-fitted from a pressure-resistant meter and heated to 70 ° C., and then 25 parts of a 2% aqueous potassium persulfate solution was press-fitted to start polymerization. The internal pressure decreased from 4.6 kg / cm ^{2 as the} polymerization progressed,
After a lapse of time, it was 0.4 kg / cm ² , and the polymerization rate was 99.0%. The resulting styrene - butadiene copolymer emulsion had a solid content concentration of 45.5 percent, a viscosity 140 m Pa · s, an average particle diameter of 0.4 .mu.m, a glass transition temperature of 10 ° C. of the dispersoid, graft ratio to the dispersoid of PVA It was 85% stable.

(Preparation of heat-sensitive coating solution) Crystal violet lactone 8 parts, talc 25 parts, stearamide 1
A 30% solution was prepared by adding 5 parts and a small amount of a dispersant and water, and this was designated as solution A. In addition, bisphenol A2
5 parts, 25 parts of talc and a small amount of dispersant and water
A 0% solution is prepared and used as solution B. The solution A and the solution B were separately placed in a paint shaker, crushed and dispersed using 5 mmφ glass beads, and then mixed with 30 parts of the solution A and 30 parts of the solution B, and then mixed with the styrene-butadiene copolymer emulsion. 10 parts and 20 parts of water were added to prepare a heat-sensitive coating solution.

(Preparation method of heat-sensitive recording sheet) The coating amount after drying the above-mentioned heat-sensitive coating liquid on high-quality paper of 50 g / m ² is 7 g / m ^2.
Is applied using a wire bar and dried at 50 ° C., then at 50 ° C., 50 kg / cm ² , 10 m / mi.
The sheet was passed through a calender roll three times under the condition of n to prepare a heat-sensitive recording sheet.

(Evaluation method) (1) Stability of leaving the heat-sensitive coating liquid The state of the coating liquid when the heat-sensitive coating liquid was left at 40 ° C. for 30 days was evaluated by a five-point scale. 5: Extremely good (no change in state) 4: Good (slightly thickening less than 2 times) 3: Normal (2 times or more thickening occurred) 2: Poor (gelling, bumping occurred) 1: extremely Poor (gelling) (2) Water resistance After the heat-sensitive recording sheet was immersed in water at 20 ° C. or 40 ° C. for one day and night, the degree of elution by rubbing the coated surface with a finger was evaluated in five steps. 5: Extremely good (no elution) 4: Good (almost no elution) 3: Normal (slight elution) 2: Poor (very high elution) 1: Extremely poor (very high elution) (3) Color density Thermal recording The sheet for heating was colored and measured with a Macbeth densitometer. The measured value of the Macbeth densitometer is adjusted so that the perfect black is 1.82 and the perfect white is 0.00. (4) Solvent Resistance After the heat-sensitive recording sheet was heated and colored, a commercially available soft vinyl chloride resin film was brought into contact with the colored surface, and a load was applied to the sheet, and the sheet was allowed to stand at 45 ° C. for 2 days. The coloring density was measured with a Macbeth densitometer, and the discoloration due to the plasticizer was compared.

Comparative Example 1 In the aqueous emulsion used in Example 1,
Instead of PVA having a mercapto group at one end, an anionic emulsifier (trade name: Sandet BL, Sanyo Chemical Co., Ltd.)
Except for using Ltd.) 4 parts, in the same manner as in Example 1 Styrene - obtain a butadiene copolymer emulsion (solid content of 45%, a viscosity of 90m Pa · s). Evaluation was performed in the same manner as in Example 1 using this emulsion.

Comparative Example 2 The procedure of Example 1 was repeated, except that 30 parts of a 15% aqueous solution of unmodified PVA (polymerization degree 1750, saponification degree 98.5 mol%) was used instead of the styrene-butadiene copolymer emulsion. Evaluation was performed in the same manner as in Example 1.

Comparative Example 3 In place of the styrene-butadiene copolymer emulsion in Example 1, an acetoacetyl group-modified PVA obtained by reacting PVA with diketene (polymerization degree 1500, saponification degree 99 mol%, acetoacetyl group modification) (Amount of 5 mol%) was evaluated in the same manner as in Example 1 except that 30 parts of a 15% aqueous solution was used.

Example 2 In the styrene-butadiene copolymer emulsion of Example 1, a PVA having a mercapto group at the terminal and a carboxyl group-modified PVA having a mercapto group at the terminal (polymerization degree 350, saponification degree Styrene-butadiene in the same manner as in Example 1 except that 100 parts of a 4% aqueous solution of 96 mol%, a mercapto group content of 4.9 × 10 ⁻⁵ eq / g, and 2 mol% of itaconic acid were copolymerized. A copolymer emulsion was obtained (solids concentration 44.9%,
Viscosity 150 meters Pa · s, an average particle diameter of 0.3 [mu] m, a glass transition temperature of 10 ° C. of the dispersoid, a graft ratio of 75% to dispersoids PVA).

Example 3 PVA having a mercapto group at a terminal (polymerization degree 300, saponification degree 88.2 mol%, mercapto group) was placed in a glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer and a nitrogen inlet. 5 parts of content 6 × 10 ⁻⁵ eq / g) and 125 parts of ion-exchanged water were added and completely dissolved at 95 ° C. Then, after adjusting the pH to 3.0 with sulfuric acid, methyl methacrylate 1
0 parts and 10 parts of n-butyl acrylate were added, and after purging with nitrogen, the temperature was raised to 65 ° C., and 2.5 parts of 2% potassium bromate was added to start polymerization, and methyl methacrylate was further added for 2 hours. 40 parts and 40 parts of n-butyl acrylate were continuously added. The polymerization was completed in 3 hours, the solid content concentration 46.8%, viscosity of 160 m Pa · s, an average particle diameter of 0.
A stable methyl methacrylate-n-butyl acrylate copolymer emulsion having a particle size of 4 μm, a glass transition temperature of the dispersoid of 10 ° C., and a graft ratio of PVA to the dispersoid of 83% was obtained. Evaluation was performed in the same manner as in Example 1 using this emulsion.

Table 1 shows the evaluation results of Examples 1 to 3 and Comparative Examples 1 to 3.

[0030]

[Table 1]

[0031]

The heat-sensitive recording sheet of the present invention has a high water resistance, a high barrier property against organic solvents, a good coloring property, and an excellent preservability of a colored image.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuya Katayama 1621 Sazu, Kurashiki City, Okayama Prefecture Inside Kuraray Co., Ltd. (72) Inventor Daisuke Miyake 1-12-39 Umeda, Kita-ku, Osaka Examination in Kuraray Co., Ltd. Hiromi Ito (56) References JP-A-4-208489 (JP, A) JP-A-2-72993 (JP, A) JP-A-1-230681 (JP, A) JP-A-1-171882 (JP, A A) JP-A-5-331214 (JP, A) JP-A-5-59106 (JP, A) JP-A-5-112605 (JP, A) JP-A-60-197229 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) B41M 5/28-5/34 C08F 2/24

Claims (4)

(57) [Claims] 1. Polyvinyl resin having a mercapto group in a molecule.
Emulsion polymerization using alcohol-based polymer as dispersion stabilizer
A thermosensitive recording sheet having a water-insoluble polymer grafted with a polyvinyl alcohol-based polymer produced in the thermosensitive coloring component layer. 2. Polyvinyl resin having a mercapto group in the molecule.
Emulsion polymerization using alcohol-based polymer as dispersion stabilizer
A heat-sensitive recording sheet having a film made of a water-insoluble polymer grafted with a polyvinyl alcohol-based polymer produced on the heat-sensitive coloring component layer. 3. A color-forming substance, a color-developing substance and a molecule.
Polyvinyl alcohol polymer having mercapto group
Applying a heat-sensitive coating solution comprising an aqueous dispersion having a water-insoluble polymer to which a polyvinyl alcohol-based polymer produced by emulsion polymerization using a dispersion stabilizer is grafted on a support substrate, A method for producing a thermosensitive recording sheet, characterized by drying. 4. The chromogenic material, coating the heat-sensitive coating solution comprising Akirairosei material and an aqueous binder on the support substrate, after forming the heat-sensitive color forming component layer by drying, Mel in the molecule
Disperse polyvinyl alcohol polymer having capto group
Applying a water-based emulsion having a water-insoluble polymer to which a polyvinyl alcohol-based polymer produced by emulsion polymerization used as a stabilizer is dispersed as a dispersoid on the thermosensitive coloring component layer, and drying. A method for manufacturing a recording sheet.