JPH0247088A - Thermal sensitive recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal sensitive recording material which can correspond to high speed, and has high sensitivity to gain high density and clear image by providing a primary layer containing fine aggregate emulsion particles between a base material and a coloring layer. CONSTITUTION:A primary layer containing fine particle aggregate emulsion particles is provided between a base material and a coloring layer. The used particles contains 0.5-90pts.wt. of copolymer made of 1-50pts.wt. of unsaturated carboxylic acid and 90-50pts.wt. of vinyl monomer copolymerizable with the acid, and 99.5-10pts.wt. of different type of polymer formed by polymerizing with vinyl monomer of different composition from the copolymer are mixed in such a manner that the diameter of the copolymer is 0.05-0.5mum and the diameter of the aggregate particles is 0.2-3.0mum as fine particle aggregate emulsion. The using amount is 10-60pts.wt. of dry weight ratio to the binder, and the thickness of the primary layer is 5-15mum of dry film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-sensitive recording material used in information equipment, such as facsimiles, printers, data communications, combiator terminals, and the like. More specifically, the present invention relates to a heat-sensitive recording material with excellent color development sensitivity as information devices such as facsimiles become faster.

[Conventional technology]

The heat-sensitive recording material is obtained by dispersing, for example, a colorless or light-colored leuco dye as a coloring agent and a phenolic compound such as bisphenol A as a color developer in a binder, applying the mixture to a substrate such as paper, and drying. The heat-sensitive recording material obtained in this way develops color when heated with a thermal head or a thermal pen, and images can be easily recorded. It is used in a wide range of fields, including tickets, commuter passes, etc.

In particular, as the speed of information equipment continues to increase, it is desired that the heat-sensitive materials used be compatible with high-speed recording.

One way to increase the speed is to increase the temperature of the heat head to improve color development, but as the temperature of the heat head increases, problems such as adhesion of residue and sticking tend to occur. In addition, the snow cap on the heat head becomes shorter, making it impractical.

When paper is used as a base material, when the thermosensitive coloring layer forming liquid is applied directly to the paper, the liquid penetrates into the paper, and therefore the amount of thermosensitive coloring component present on the surface of the paper is small (and the color formation a
The disadvantage is that the change is low. Japanese Patent Publication No. 55-8678
In order to prevent this, No. 9 discloses a method of forming an intermediate layer containing fine particles of synthetic resin between the base material and the heat-sensitive coloring layer to obtain a high-density and clear image. However, with wooden swords and methods, it is difficult to obtain sufficient sensitivity to withstand the required high-speed recording performance.

[Problem to be solved by the invention]

An object of the present invention is to provide a highly sensitive heat-sensitive recording material capable of producing high-density and clear images in the field of heat-sensitive recording, which is compatible with increasing speeds of information equipment.

[Means to solve the problem]

In order to solve the above problem, an undercoat layer is provided between the base material and the heat-sensitive recording layer, and the undercoat layer has heat insulating properties to prevent the heat from the thermal head from escaping toward the base material. It is thought that if this can be prevented, color development sensitivity can be increased and high-speed recording performance can be imparted. The inventor of the present invention believed that in order to achieve this, it would be sufficient to make the coating layer porous, and as one method to do so, the inventor investigated various forms of fine particles as a filler, and found that an emulsion of fine particle aggregates having porous properties It was found that the color development sensitivity was significantly improved when particles were used, and the present invention was completed.

That is, the present invention provides a heat-sensitive recording material having a color forming layer containing a base material, a color forming agent, and a color developing agent that develops a color when in contact with the color forming layer, in which fine particle aggregate emulsion particles are provided between the base material and the color forming layer. The object of the present invention is to provide a heat-sensitive recording material characterized by having an undercoat layer containing.

The fine particle aggregate emulsion particles used in the present invention are a copolymer (a) consisting of 1 to 5 parts by weight of an unsaturated carboxylic acid and 99 to 50 parts by weight of a vinyl monomer copolymerizable therewith.
Fine particle aggregate emulsion particles consisting of a mixture of 5 to 90 parts by weight and 99.5 to 10 parts by weight of a heteropolymer (b) formed by polymerizing a vinyl monomer with a composition different from this, The heavy body (b) exists as particles with a diameter of 0.05 to 0.5μ, and the particle diameter of the aggregate particles is 0.2 to 3.0μ.
This is a fine particle aggregate emulsion with a particle diameter of 0μ.

Emulsion particles having such a structure are produced by emulsion polymerization of 1 to 50 parts by weight of an unsaturated carboxylic acid and 99 to 50 parts by weight of a vinyl monomer copolymerizable with the unsaturated carboxylic acid in the first step, and then this copolymerization. The carboxylic acid in the polymer emulsion is neutralized with an alkaline substance in an amount of 0.3 to 3.0 molar equivalents, and in the second step, using the neutralized emulsion as seed particles, a copolymer (a) with a composition different from that of copolymer (a) is prepared. 9 parts of vinyl monomer per 0.5 to 90 parts by weight of the solid content of the neutralized emulsion.
It is obtained by adding 9.5 to 10 parts by weight and carrying out emulsion polymerization.

During this neutralization, it is necessary for the unsaturated carboxylic acid copolymer to be swollen with an alkali, and under the swelling of R, a vinyl monomer different from (a) containing a crosslinking monomer as necessary is added. The particles are added and subjected to emulsion polymerization to obtain particles, which are aggregates of fine particles.

The unsaturated carboxylic acids used in the present invention include, for example, unsaturated basic acids such as acrylic acid, methacrylic acid, and crotonic acid, unsaturated dibasic acids such as itaconic acid, fumaric acid, and maleic acid, or monoesters thereof. Among the selected one or more, acrylic acid and methacrylic acid are particularly preferred.

The amount of these unsaturated carboxylic acids used is 1 to 50 parts by weight, preferably 2 to 20 parts by weight based on the total monomer components in the copolymer (a).
Parts by weight, more preferably 5 to 15 parts by weight. If it is less than 1 part by weight, the swelling of the emulsion particles due to alkali G will be small and particles that are aggregates of fine particles will not be obtained, and if it exceeds 50 parts by weight, water resistance will be poor.

Examples of vinyl monomers copolymerizable with unsaturated carboxylic acids that constitute the polymer composition of copolymer (a) include styrene, α
- Aromatic vinyl compounds such as methylstyrene and vinyltoluene, (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate, vinyl acetate, vinyl propionate, etc. Vinyl esters such as (meth)acrylonitrile, vinyl cyanide compounds such as (meth)acrylonitrile, vinyl chloride, vinyl halides such as vinylidene chloride, and the like are used. In addition, as a functional monomer, in addition to unsaturated carboxylic acid, (meth)acrylamide, N-methylol (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, etc. are used as necessary. be done.

Further, in order to adjust the degree of swelling of the emulsion particles by alkali neutralization, a crosslinkable monomer, which will be described later, can be copolymerized if necessary. The amount of this crosslinking monomer used is 20 parts by weight or less, preferably 10 parts by weight or less, and the appropriate amount to be used depends on the type and amount of unsaturated carboxylic acid used, the type of vinyl monomer, etc. different.

Types of alkaline substances used to swell emulsion particles include inorganic alkaline substances such as potassium hydroxide, sodium, calcium, and sodium silicate, volatile alkaline substances such as ammonia, dimethylethanolamine, triethylamine, and triethanolamine. ,
Organic alkaline substances such as morpholine can be used.

The copolymer (a) serving as the seed particles is prepared by a conventional emulsion polymerization method. As the surfactant used, anionic surfactants and nonionic surfactants may be used alone or in combination.

The amount of surfactant used is not particularly limited, but is usually 0.1 to 10 parts by weight based on 100 parts by weight of the total weight.

In producing seed particles, polymerization is carried out by dropping various monomers all at once, in portions, or continuously in the presence of a polymerization initiator and a surfactant. The interstitial polymerization is usually carried out at a polymerization temperature of 20 to 90°C under a nitrogen purge.

The copolymer emulsion obtained in this way is neutralized with the above-mentioned alkaline substance, and in the second step, the neutralized emulsion is used as seed particles to add a crosslinking monomer depending on the need for a composition different from that of the copolymer (a). By adding the vinyl monomers contained therein and carrying out emulsion polymerization, an aggregate emulsion in which different types of polymer (b) particles are aggregated in one particle is obtained. At this time, the amount of vinyl monomers including crosslinking monomers may be 10 to 90 parts by weight based on 0.5 to 90 parts by weight of the solid content of the neutralized emulsion.
99.5 weight 1 part.

Crosslinkable monomers used as necessary include monomers having two or more polymerizable unsaturated bonds in one molecule, such as divinylbenzene, ethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate. , ethylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, diallyl phthalate, and the like.

When using the above crosslinking monomer, vinyl monomer 1
00 parts by weight or less, preferably 111 parts by weight or less
below.

Vinyl monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, methyl (meth)acrylate, ethyl (meth)acrylate, (
(meth)acrylic acid esters such as butyl meth)acrylate, vinyl esters such as vinyl acetate and vinyl propionate, vinyl cyanide compounds such as (meth)acrylonitrile, vinyl halides such as vinyl chloride and vinylidene chloride, butadiene and other conjugated diene compounds.

In addition, copolymers (a
) In addition to the unsaturated carboxylic acid used in ), (meth)acrylamide, N-methylol (meth)acrylamide, 2
Hydroxyethyl (meth)acrylate, glycidyl (
Functional monomers commonly used in emulsion polymerization, such as meth)acrylate, may be used alone or in combination.

Heterogeneous polymers obtained by combining the above monomers (
The glass transition point of b) is preferably 50°C or higher, more preferably 70°C or higher. Glass transition point is 50°C
In the following, styrene, methyl methacrylate, methyl methacrylate,
It is preferable to use acrylonitrile alone or in combination with other monomers.

The composition of the copolymer (a) obtained by copolymerizing unsaturated carboxylic acid and the heteropolymer (b) containing a crosslinkable monomer if necessary need to be different compositions. If the composition is the same, the desired porous particle structure cannot be obtained, resulting in single, uniform particles, making it impossible to obtain a highly sensitive recording material and resulting in insufficient color density. As a preferable composition, unsaturated carboxylic acid copolymer (a)
It is preferable that the compatibility of the heterogeneous polymer (b) containing a crosslinking monomer (b) if necessary is poor and that phase separation is easy to occur.

The particulate polymer thus obtained consists of a copolymer (a) consisting of an unsaturated carboxylic acid and a vinyl monomer copolymerizable therewith, and a crosslinking monomer (a) if necessary to have a different composition. consisting of a heterogeneous polymer (b) containing (a), (b)
) are present unevenly in one particle, the particle size of the particles in which (a) and (b) are mixed is 0.2 to 3.0μ, and the particle size of the heterogeneous polymer (b) in the particle is It is an aggregate of fine particles of 0.05 to 0.5μ. The particle size of the different polymer (b) is 0.
If it is less than 0.05 μm, the porosity is insufficient and a good highly sensitive heat-sensitive recording material cannot be obtained. Moreover, if it exceeds 0.5μ, a stable aggregate of fine particles cannot be obtained.

The microparticle aggregate emulsion particles obtained in this way are different from the conventional method for producing gold-rice shield-shaped particles by phase separation (for example, Kobunshi Ronshu, 33, 575 (1976)), and the emulsion particles in the National Sugar Emulsion Particles is polymerized on or near the surface of the particle to form golden rice sugar, which is significantly different from that in which the entire particle is an aggregate of fine particles.

Therefore, the fine particle aggregate emulsion particles are themselves porous due to their morphology.

This confirmation can be made by adding carbon oil having the same refractive index as the particle composition to the fine particle powder and observing it with an optical microscope. In the case of homogeneous single particles that are not porous, the particle interface cannot be seen and the presence of particles cannot be confirmed, but the particles of the present invention are clearly porous since the presence of particles can be confirmed. The porosity of the particles themselves and the presence of irregularities on the surface of the particles give the undercoat layer of the heat-sensitive recording material porosity, and the coloring layer is used to transfer thermal energy from the thermal head to the substrate. It is thought that thermal energy is accumulated in the film and the coloring sensitivity is improved.

On the other hand, with the uniform emulsion technique of all-American sugar particles, the coloring density is not sufficient, and there is a big difference from the emulsion of porous fine particle aggregates.

A heat-sensitive recording material using the present fine particle aggregate emulsion particles is produced as follows.

The composition forming the undercoat layer is mixed with the fine particle aggregate using an organic polymer compound as a binder, applied onto the substrate, and dried.

The base material may be paper, plastic sheet, etc., but paper is usually used.

Examples of the organic polymer compound used include water-soluble polymers such as polyvinyl alcohol, oxidized starch, and hydroxyethyl cellulose, and emulsion latexes such as styrene-butadiene latex and acrylic emulsion.

The amount of the fine particle aggregate emulsion used is usually 10 to 60 parts by weight based on the binder on a dry weight basis. Further, if necessary, inorganic pigments such as calcium carbonate, magnesium carbonate, talc, kaolin, etc. can be mixed and used.

The thickness of the undercoat layer is usually 5 to 15 microns in dry film thickness.

Basic colorless dyes such as fluoran colorless dyes, triallylmethane dyes, and phenothian dyes are used as color formers in the thermophilic recording layer mixture coated on the undercoat layer. is a phenolic compound,
Aromatic carboxylic acids and the like are used. The ratio of color former to color developer in the heat-sensitive recording layer is usually 1 to 1 part by weight of color former.
30 parts by weight of color developer are used. The total amount of the color forming agent and color developer is usually 100 parts by weight based on 30 parts by weight of the binder.

As the binder, organic polymer compounds such as water-soluble polymers such as polyvinyl alcohol, oxidized starch, and hydroxydiethyl cellulose, styrene, butadiene-based synthetic rubber latex, and acrylic emulsions are used as binders for heat-sensitive recording materials. things are available.

The color former and color developer used in the heat-sensitive recording layer of the present invention are separately wet-pulverized and dispersed in the presence of a dispersion stabilizer using a ball mill, etc. After dispersion, the color former and color developer are combined with the above. In addition to the agent, if necessary, inorganic pigments such as calcium carbonate, magnum carbonate, talc, and kaolin, ultraviolet absorbers such as benzophenone and triazole, wax, and thickeners such as fatty acid amide are thoroughly mixed and stirred. ,
A formulation of a heat-sensitive recording layer is obtained.

The liquid mixture for the heat-sensitive recording layer is applied onto the undercoat layer to a thickness of about 2 to 10 μm after drying, and dried.

[Examples] All parts or percentages in the examples shown below represent parts by weight or percentages by weight.

Polymerization Example 1 In the first step, 100 parts of water and 0.05 parts of sodium lauryl sulfate are charged into a separable flask equipped with a stirrer, a thermometer, and a reflux condenser, and the temperature is raised to 70° C. while stirring and purging with nitrogen. Keep the internal temperature at 70°C, add 0.8 parts of potassium persulfate as a polymerization initiator, confirm that it has dissolved, and mix the monomer mixture of 4 parts of methyl methacrylate, 4 parts of butyl acrylate, and 2 parts of methacrylic acid. was added and allowed to react for 2 hours.

After the reaction is completed, 1.6 parts (about 1.1 molar equivalent) of 28% aqueous ammonia is added to the obtained copolymer emulsion, and the mixture is thoroughly stirred to neutralize and swell to form seed particles.

Separately, add 85 parts of styrene and 5 parts of divinylhenzene to 50 parts of water and 0.5 parts of sodium lauryl sulfate and stir well to prepare a second-stage monomer emulsion. This vinyl monomer emulsion is continuously injected into the neutralized and swollen seed particles over a period of 4 hours to cause a reaction, and after the injection, aging is carried out for 3 hours.

The resulting emulsion had a solid content of approximately 40% and a viscosity of 65 cp.
s (BM type viscometer rotor N (Ll, rotation speed 6 Orpm
.

The temperature was 25"C), and the pH was 8.5. The particle size was measured using an electron microscope, and the average particle size was 0.9μ, and the particle size of component (b) of the fine particle aggregate was 0.1 to 0.3μ. Met.

When this fine particle aggregate emulsion was dried, carbon oil was added, and it was observed under an optical microscope, the presence of particles was confirmed, and it was confirmed that it was a porous material.

Polymerization Examples 2 to 5 Amount of surfactant, degree of neutralization, difference in alkaline substance, copolymer (a)/heterogeneous polymer (b) ratio, monomer composition, crosslinkable monomer, functional group monomer Polymerization was carried out by the method of Polymerization Example 1 with the composition shown in Table 1, and a fine particle aggregate emulsion was obtained.

Polymerization Example 6 In the first step, polymerization was carried out using exactly the same vinyl monomer composition as shown in Polymerization Example 1 to obtain a copolymer emulsion.

The unneutralized particles, which are not subjected to neutralization and swelling with an alkaline substance, are used as seed particles as they are, and the monomer composition of the second stage is exactly the same as that of Polymerization Example 1, which is added in the same manner. Polymerization was performed.

The obtained emulsion has p! (is 2.2, solid commitment 4
0%, the viscosity was 10 cps, and the average particle diameter was 0.9 μ, but it was not an aggregate of birch-like fine particles as seen in Example 1,
They were sugar-like particles with uneven surfaces.

Polymerization Examples 7 to 8 Polymerization Example 7 is a reaction in which the unsaturated carboxylic acid monomer in the first stage reaction of Polymerization Example 1 is replaced with MMA and no unsaturated carboxylic acid is used, and the first stage reaction of Polymerization Example 1 is Polymerization example 8 is a product obtained by replacing the raw monomer in the reaction with styrene.
shall be.

In both Polymerization Examples 7 and 8, fine particle aggregate emulsion particles were not obtained, and the particles were uniform.

The composition and properties of the above emulsion are summarized in Table 1.

Example 1) Preparation of undercoat formulation Using the fine particle emulsion of the above polymerization example, the following composition was sufficiently stirred and mixed to produce an undercoat formulation for heat-sensitive recording materials.

Fine particle emulsion Solid content 40% 25 parts by weight Ponlon S-1120 Solid content 45% 70 parts by weight (acrylic emulsion manufactured by Mitsui Toatsu) Carbital 90
Solid content 73% 5 parts by weight (calcium carbonate dispersion manufactured by Japan IPC) 11) Preparation of heat-sensitive recording layer formulation
A blend is prepared by separately dispersing the color developer dispersion) using a sand mill.

A & 3-diethylamino-6-methyl-7anilinofluorane 20% hydroxyethyl cellulose aqueous solution 5 parts by weight Water 75 parts by weight B
Liquid Bisphenol A 20% N part 20%
Hydroxyethyl cellulose 5 parts by weight Petrolite R-50C microcrystalline wax (manufactured by Hariko) 5 parts by weight Water
After thoroughly dispersing 70 parts by weight in a sand mill, l! 15
parts by weight, 40 parts by weight of liquid B, 20 parts by weight of calcium carbonate,
25 parts by weight of a 20% polyvinyl alcohol aqueous solution (K-117 Kuraray IJ) was taken and sufficiently stirred and mixed to obtain a composition for a heat-sensitive coloring layer.

The above-mentioned undercoat composition was applied to a commercially available high-quality paper (basis weight: 50 g/rr) using a bar coater so that the coating amount after drying was 15 g/rd, and dried. Then, the heat-sensitive recording layer composition was applied after drying. It was coated using a bar coater in an amount of 15 g/bore and dried to obtain a heat-sensitive recording material.

For comparison, we also applied a mixture in which the entire amount of fine-particle emulsicone in the undercoat formulation was replaced with calcium carbonate.
A thermosensitive recording material was obtained.

Color development is done using a thermal facsimile [■Toshiba COPIX650]
03 was used to develop a printed color, and the density was measured using a Maches densitometer.

Shown below.

Table 2 The results are shown in Table 2. [Effects of the invention] As shown in Table 2, the heat-sensitive recording material using the fine particle aggregate emulsion as a filler is made of sugar-like particles or
It was found that uniform particle emulsions can provide superior print density compared to inorganic calcium carbonate.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (2)

[Claims] (1) A heat-sensitive recording material having a base material and a coloring layer containing a coloring agent and a coloring agent that develops a color when in contact with the coloring layer, containing fine particle aggregate emulsion particles between the base material and the coloring layer. A heat-sensitive recording material characterized by having an undercoat layer. (2) Fine particle aggregate emulsion particles consist of 0.5 to 90 parts of copolymer (a) consisting of 1 to 50 parts by weight of an unsaturated carboxylic acid and 99 to 50 parts by weight of a vinyl monomer copolymerizable therewith.
A fine particle aggregate consisting of 99.5 to 10 parts by weight of a heteropolymer (b) obtained by polymerizing a vinyl monomer having a composition different from this, and the copolymer (b) 2. The heat-sensitive recording material according to claim 1, which is a fine particle aggregate which exists as particles having a diameter of 0.05 to 0.5 μm and has a particle diameter of 0.2 to 3.0 μm.