JP3415232B2 - Thermal recording material - 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 material, and more specifically, it has good printing suitability without running obstacles such as sticking and dust sticking to a thermal head, and has high density even at low energy. The present invention relates to a heat-sensitive recording material which produces a clear image and has excellent color development sensitivity and dot reproducibility.

[0002]

2. Description of the Related Art With the diversification of information equipment, a variety of performances are required for heat-sensitive recording materials to be used. Especially, high color-developing sensitivity capable of coping with high-speed recording and low energy of thermal head and thermal pen. In addition, dot reproducibility and high oil absorption, which is excellent in running performance of thermal heads and thermal pens, are required. As a method for improving the color development sensitivity of the thermosensitive recording material, 1) the surface smoothness is improved to improve the matching property with the thermal head, and 2) the intermediate between the base material and the thermosensitive coloring layer has a high heat insulating property. Although it is considered to provide layers, the latter method, which is particularly effective, is being actively studied.

JP-A-59-5093 and JP-A-59-171685
JP-A-59-225987, and further JP-A-60-2
Japanese Patent No. 48390 discloses a method in which heat-expandable resin particles are introduced into an intermediate layer and subjected to heat treatment to be foamed to provide heat insulation. However, such a method is not practical because it is difficult to always adjust to a constant and uniform foaming state, and further the smoothness of the surface is greatly impaired. Japanese Unexamined Patent Publication (Kokai) No. 62-117787 discloses a method of further providing a second intermediate layer after the foaming treatment for the purpose of improving the smoothness at the time of foaming, but the problem has not been solved yet. .

JP-A-62-5886, JP-A-62-138286
JP, JP-A-63-281886, and JP-A-3-14
Japanese Patent No. 7888 discloses a method of containing hollow emulsion particles having voids inside the particles in an intermediate layer during drying. Although this method is improved in smoothness as described above, the color development sensitivity is lower than that in the case of using heat-foamable particles. Further, in the heat-sensitive recording material containing the above-mentioned various particles in the intermediate layer, since the particles themselves do not have oil absorbability, there is no problem about running obstacles such as adhesion of the hot melt to the head, that is, residue adhesion. Not resolved. As described above, according to the conventional technology, there is no running obstacle such as adhesion of dust to the head, and a heat-sensitive recording material excellent in color developing sensitivity has not been obtained.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a heat-sensitive recording material which is free from running obstacles such as dust deposits on the head, has a high density and a clear image even at low energy and is excellent in color development sensitivity and dot reproducibility. To provide.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the coating solution for forming an intermediate layer between the base material and the thermosensitive color developing layer is treated with water. When the crosslinked hydrophilic particles in a swollen state, that is, "hydrogel particles" are contained, "open voids" are uniformly generated in the intermediate layer after drying, and the layer itself is made porous. Heading, it came to complete the present invention. That is, the present invention is a thermosensitive recording material having a base material and a thermosensitive color developing layer containing a color former and a color developing agent which develops color when contacted with the base material. It is a cross-linked hydrophilic particle in a swollen state and has a particle size of 0.1 to 2 in a water-containing state.
The hydrogel particles are 0μm have a middle layer which uniformly made porous after dried with hydrous state, the hydrogel
The particle has at least 2 polymerizable unsaturated bonds in the molecule.
Water-soluble unsaturated monomer (b)
Particles obtained by precipitation polymerization of the monomer (a) in an organic solvent
Is a material which is separated from an organic solvent and is swollen by absorbing water .

The hydrogel particles used in the present invention are
The particle size in the water-containing state is 0.1 to 20 µ, preferably 0.15 to 10 µ, and more preferably 0.2 to 5 µ. Here, if the particle size is less than 0.1 μm, its preparation is difficult, and even if it can be prepared, the effect of adding the hydrogel particles is significantly reduced. The particle size is 2
When it exceeds 0 μ, the smoothness of the intermediate layer is deteriorated and the desired high color development sensitivity cannot be obtained.

The above-mentioned hydrogel particles are produced by a method of precipitating and polymerizing a water-soluble unsaturated monomer containing a cross-linking agent in an organic solvent, and drying and absorbing and swelling with water.
It was the one .

Of the above methods, the precipitation polymerization method is particularly preferable in view of the particle size range of the hydrogel particles of the present invention. The precipitation polymerization method includes (meth) acrylamide, methylol (meth) acrylamide, acrylic acid,
Methacrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, N, N
-Dimethylaminoethyl (meth) acrylate or its quaternary compound, N, N-diethylaminoethyl (meth) acrylate or its quaternary compound, N, N-dimethylaminopropylacrylamide or its quaternary compound, etc. At least one water-soluble unsaturated monomer (a)
, And a crosslinkable water-soluble monomer (b) having at least two polymerizable unsaturated bonds in the molecule such as methylenebisacrylamide and bisacrylamidoacetic acid, but the polymer is insoluble. An example is a method of polymerizing in a certain organic solvent using an initiator that is soluble in the solvent, separating the precipitated particles from the solvent, and swelling with water.

In this polymerization, if necessary,
It is also possible to use water-insoluble unsaturated monomers such as styrene and methyl methacrylate, and crosslinkable water-insoluble monomers such as divinylbenzene and mono / polyethylene glycol (meth) acrylate. For the purpose of improving the particle size and controlling the particle size, a polymer or a surfactant that is soluble in the solvent may be added as a dispersion stabilizer. Here, the organic solvent used in the polymerization is not particularly limited as long as it satisfies the above conditions, and may be a single solvent or a mixture.

The thermosensitive recording material provided with the intermediate layer containing the hydrogel fine particles of the present invention is manufactured as follows. The compound forming the intermediate layer is prepared by mixing the above-mentioned hydrogel fine particles with a binder composed of an organic polymer compound, inorganic pigments such as calcium carbonate, clay, silica and talc, and plastic pigments such as polystyrene particles. Examples of the base material include paper and plastic sheets. The binder used is, for example, styrene-butadiene latex,
It is selected from an aqueous dispersion system such as an acrylic emulsion, an aqueous system of polyvinyl alcohol, starch, hydroxyethyl cellulose, and a mixture thereof. The amount of hydrogel particles used in the intermediate layer is 0.5 on a dry weight basis.
-30% by weight, preferably 0.5-15% by weight.

If the amount of the hydrogel fine particles used is less than 0.5% by weight, the effect of adding the hydrogel fine particles is not recognized.
The desired high color development sensitivity cannot be obtained. On the other hand, if the amount used exceeds 30% by weight, the viscosity of the composition will increase too much, making it difficult to apply the composition onto a substrate. The thus-prepared composition is applied onto a base material, which is usually applied so as to have a dry weight of 5 to 15 g / m ² . Examples of the color-developing agent in the thermosensitive color-developing layer applied on the intermediate layer include:
Basic colorless dyes such as fluoran colorless dyes, triallylmethane dyes and phenothiazine dyes are used, and phenol compounds and aromatic carboxylic acids are used as color developers.

The ratio of the color former to the developer in the thermosensitive color developing layer is
Usually, 1 to 30 parts by weight of the color developer is used with respect to 1 part by weight of the color former. In addition, the binder is usually used in an amount of about 30 parts by weight based on 100 parts by weight of the color former and the developer. As the binder, those similar to those exemplified in the section of the intermediate layer are used. The color-developing agent and the color-developing agent used in the thermosensitive color-developing layer of the present invention are wet-ground and dispersed in the presence of a dispersion stabilizer by a ball mill or the like. After dispersion, in addition to color formers and developers, the above binders and, if necessary, inorganic pigments such as calcium carbonate, talc and kaolin, UV absorbers such as benzophenone and triazole, sensitizing wax and fatty acid amide. The agents are thoroughly mixed and stirred to obtain a thermosensitive coloring layer formulation. The thermosensitive color-forming layer is usually mixed on the intermediate layer in a dry weight of 2 times.
It is applied and dried so that the amount becomes about 10 g / m ² .

[0014]

[Examples] Specific examples of the present study will be described below, but the present invention is not limited thereto. The following parts and% all indicate parts by weight and% by weight. [I] Preparation of Hydrogel Particles Preparation Example 1 A separable flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 700 parts of isopropyl alcohol, 70 parts of acrylamide, 15 parts of methylenebisacrylamide, and 15 parts of methacrylic acid, and nitrogen was stirred with stirring. 70 while replacing
Raise the temperature to ℃. The internal temperature was kept at 70 ° C., 0.5 part of azobisisobutyronitrile was added as a polymerization initiator, and stirring was continued for 8 hours. Isopropyl alcohol was removed from the obtained particle dispersion by an evaporator and dried to obtain particle powder, which was added again to water to prepare a 10% dispersion. The particle size of the obtained hydrogel particles was 0.7 μm by the laser scattering method.

Preparation Examples 2 to 5 In Preparation Example 1, the type of unsaturated monomer used was changed, and the same polymerization, solvent separation and water addition were carried out to prepare an aqueous dispersion of hydrogel particles. Incidentally, Preparation Examples 3 and 4
At the time of polymerization, polyvinylpyrrolidone was added as a dispersion stabilizer.

Comparative Preparation Example 1 A device similar to Preparation Example 1 was charged with 900 parts of water, 70 parts of acrylamide, 15 parts of methylenebisacrylamide and 15 parts of methacrylic acid, and 30 ° C. while stirring and substituting nitrogen.
Up to. The internal temperature was kept at 30 ° C., 1 part of ammonium persulfate and 1 part of ferric ammonium sulfate were added as a polymerization initiator, stirring was stopped after 5 minutes, and the mixture was allowed to stand for 8 hours to obtain a hydrogel. The obtained hydrogel was pulverized with a pulverizer to obtain hydrogel particles having an average particle diameter of 70μ. The results are summarized in Table-1.

[0017]

[Table 1]

Examples 1 to 5 and Comparative Examples 1 to 3 [II] Preparation of Thermosensitive Recording Material i) Preparation of Formulation for Intermediate Layer Hydrogel particles and commercially available hollow emulsion particles are shown in Table 2. The components blended in a ratio were thoroughly mixed with stirring to prepare a formulation for the intermediate layer. ii) Preparation of Thermosensitive Coloring Layer Formulation Solution A (color former dispersion) and solution B (developing agent dispersion) having the following compositions were separately dispersed in a sand mill, and then 15 parts of solution A and solution B were used. 40 parts, calcium carbonate 20
Parts, 10% polyvinyl alcohol aqueous solution (Kuraray, 1
17) 50 parts was taken and sufficiently stirred and mixed to prepare a formulation for the thermosensitive color developing layer. ──────────────────────────────────── 3-Dimethylamino-6-methyl-7-anilinoflu Oran 20 parts (Solution A) 15% hydroxyethyl cellulose aqueous solution 7 parts Water 73 parts ────────────────────────────────── ─── Bisphenol A 20 parts (B solution) 15% hydroxyethyl cellulose aqueous solution 7 parts Petrolite R-50 5 parts (Hariko's microcrystalline wax) ────────────────── ─────────────────── The above-mentioned compound for the intermediate layer is commercially available high-quality paper (basis weight: about 50 g / m
² ) was coated with a bar coater to a dry coating amount of 15 g / m ² and dried. Subsequently, the thermosensitive coloring layer composition was applied by a bar coater so that the dry coating amount was 10 g / m ^2, and dried to obtain a thermosensitive recording material.

The color is developed by a thermal paper printer (TH
-PMD) was used to print color with a printing voltage of 24 V and an applied energy of 0.34 mJ / dot, and the density was measured using a Macbeth densitometer. Furthermore, by directly observing the sticking property and the adhesion of dust to the thermal head when the printing color is developed with the printing voltage of 27 V and the applied energy of 0.73 mJ / dot, the printing suitability is ◎; best, ○; good, △; normal, X: evaluated in four stages of poor. The results are shown in Table-2.

[0020]

[Table 2]

[0021]

INDUSTRIAL APPLICABILITY In the heat-sensitive recording material of the present invention having a heat-sensitive color-forming layer containing a base material and a color-developing agent and a color-developing agent which develops a color in contact with the color-developing agent, between the base material and the heat-sensitive color-developing layer. The heat-sensitive recording material containing hydrogel particles in the intermediate layer provided has good printing suitability without running obstacles such as sticking and sticking of dust to the head, and high density and clear images can be obtained even at low energy. Excellent color development sensitivity and dot reproducibility.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-37467 (JP, A) JP-A-5-222108 (JP, A) JP-A-2-47088 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (3)

(57) [Claims] 1. A heat-sensitive recording material having a base material and a thermosensitive color-forming layer containing a color-developing agent and a color-developing agent which develops a color by contacting with the color-developing agent, wherein the base material and the thermosensitive color-developing layer swell with water. The cross-linked hydrophilic particles in a water-containing state, the hydrogel particles having a particle size of 0.1 to 20 μm in a water-containing state are used in a water-containing state, and have an intermediate layer uniformly made porous after drying.
The hydrogel particles have less polymerizable unsaturated bonds.
With at least two crosslinkable water-soluble monomers in the molecule (b),
Precipitation polymerization of water-soluble unsaturated monomer (a) in an organic solvent
The resulting particles were separated from the organic solvent and swollen with water.
Heat-sensitive recording material which is characterized in that those allowed. 2. The heat-sensitive recording material according to claim 1, wherein the intermediate layer contains hydrogel particles in an amount of 0.5 to 30% by weight on a dry weight basis. 3. The hydrogel particles are obtained by polymerizing the unsaturated monomer in an organic solvent in which the unsaturated monomer is dissolved but the polymer is insoluble, and the precipitated particles are removed from the solvent. The heat-sensitive recording material according to claim 1, which is prepared by separating and swelling with water.