JPS5911291A - Heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To provide a heat-sensitive recording material substantially free from ground color development and excellent in developed color density, wherein anionic group containing PVA is incorporated as a binder in a heat-sensitive layer together with a color former based on a metallic salt of an organic acid and a phenol base color developer. CONSTITUTION:When dispersing a color former based on a metallic salt of an organic acid (e.g., ferric stearate) and a phenol base color developer (e.g., gallic acid) into a binder, anionic group containing PVA [preferably acid-modified PVA obtained by treating PVA with acetic acid (salt)] is used as a binder. A dispersed composition thus obtained is applied as a heat-sensitive coating liquid onto a base such as a recording paper to obtain the objective recording material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material, and more specifically, a heat-sensitive layer is formed from a heat-sensitive composition using polyvinyl alcohol containing anionic groups as a binder, and if necessary, the surface of this heat-sensitive layer is further coated. This invention relates to a heat-sensitive recording material with almost no background coloration obtained by coating with polyvinyl alcohol.

Conventionally, a heat-sensitive composition containing an organic acid metal salt coloring agent such as ferric myristate or ferric stearate, and a phenolic coloring agent such as tannin or gallic acid is applied to a support such as recording paper. It is known that heat-sensitive recording materials can be obtained by

Only 1. This heat-sensitive composition is unstable, and in particular, when this composition is dispersed in a medium containing a binder and applied to a support such as recording paper, it is said that the composition gradually develops color over time. There are drawbacks.

This coloring phenomenon is generally referred to as background coloring, and various efforts have been made to prevent this background coloring.

For example, as shown in U.S. Pat. No. 2,663,654, etc., - the color former and the phenolic color developer are solvent coated using polyvinyl butyral as a binder, or the color former and the color developer are applied separately. Methods have been proposed in which the material is applied individually and in layers.

However, these methods are not only unable to sufficiently prevent background discoloration, but also require complicated coating liquid preparation and coating operations, making them unsuitable for practical use.

Therefore, the inventors of the present invention have conducted intensive research in order to overcome the drawbacks of the above-mentioned conventional techniques and to obtain a heat-sensitive recording material with almost no ground coloring through simple operations. As a result, they found that the objective could be achieved by using anionic group-containing polyvinyl alcohol as a binder in the heat-sensitive composition. It has been found that IF can be more effectively prevented from forming background color by coating with alcohol.The present invention was completed based on these findings.

That is, the present invention provides a heat-sensitive recording material having a heat-sensitive layer formed of a composition in which an organic acid metal salt color former and a phenolic color developer are dispersed in a binder, which contains an anionic group as the binder. Provided is a heat-sensitive recording material characterized in that polyvinyl alcohol is used, and the surface of a heat-sensitive layer formed using polyvinyl alcohol containing anionic groups as a binder is coated with polyvinyl alcohol. It provides recording materials.

In the heat-sensitive recording material of the present invention, the heat-sensitive layer formed on the support is basically composed of a composition in which an organic acid metal salt color former and a phenol color developer are dispersed in a binder. . This heat-sensitizing agent composition has been widely used in the past, and various types can be used in the present invention without any particular limitations. Therefore, there are various organic acid metal salt coloring agents that can be used here, and they may be selected as appropriate depending on the purpose of use. Specifically, ferric stearate, ferric myristate, nickel palmitate,
Preferred examples include, but are not limited to, higher fatty acid metal salts such as tin stearate, silver behenate, silver stearate, and ferric pelargonate.

On the other hand, various phenolic color developers can be used, and there are no particular limitations, and they may be appropriately selected depending on the type of the organic acid metal salt color developer described in 1) and 2 above. Specifically, tannins, gallic acid, methyl gallate,
Ethyl gallate, propyl gallate, lauryl gallate, pyrogallol.

Suitable examples include diphenylcarbazide, but the present invention is not limited thereto.

In the present invention, it is necessary to use polyvinyl alcohol containing anionic groups as a binder for dispersing the above-mentioned color former and color developer. Polyvinyl alcohol containing this anion group can be obtained by subjecting polyvinyl alcohol to various treatments, for example, by treating it with a weak acid such as acetic acid or acetate, and further with a strong acid such as sulfuric acid. Acid-modified polyvinyl alcohol obtained by treatment with an acetate is preferred.

As described above, when polyvinyl alcohol containing anionic groups such as acid-modified polyvinyl alcohol is used as a binder, the following effects 0) to (4) can be achieved.

fil When the above-mentioned color former and color developer are dispersed into fine particles, they can be easily dispersed without causing aggregation.

(2) When the respective dispersions of the above-mentioned color forming agent and color developer are mixed, there is no fear that the liquid will develop color or have a high viscosity.

[3)! Even if a coating liquid of the thermal composition is applied to a support such as recording paper for a long period of time, there is no risk of background color development, discoloration of printed areas, or smearing.

(4) When printing is performed on the resulting thermal recording paper using a thermal printer or the like, the coloring sensitivity is good.

Such an effect cannot be obtained using other binders such as hydroxyethyl cellulose, starch or unmodified polyvinyl alcohol.

In the present invention, the heat-sensitive agent composition constituting the heat-sensitive layer can be obtained by dispersing the above-mentioned organic acid metal salt color former and phenol color developer in anionic group-containing polyvinyl alcohol as a binder. In this case, it is preferable that the dispersed particles be crushed using a crusher such as a ball mill until the particles are as small as possible, specifically, a particle size of several microns or less. In addition, activators such as dispersants and antifoaming agents can be used as grinding aids, if desired, and brighteners, wax, talc, clay, starch, etc. can also be added.

In the present invention, when coating the above-mentioned composition on a support to form a heat-sensitive layer, the above-mentioned components are dispersed in water to form a heat-sensitive agent coating solution, and this is applied or impregnated. The support to which the above composition is applied is generally paper, but synthetic resin films, woven fabric sheets, etc. can also be used.

The thus obtained heat-sensitive recording material of the present invention exhibits almost no ground coloring even after long-term storage, and has very good coloring sensitivity when printed with a thermal printer or the like.

In the present invention, in order to more effectively prevent background discoloration, K,
The surface of the heat-sensitive layer formed on the support as described above can be coated with polyvinyl alcohol. There are various types of polyvinyl alcohol used here, but those with a valence of 70 mol% or more are usually preferred.Specifically, unmodified polyvinyl alcohol, acid-modified polyvinyl alcohol, etc. I/7/L/: 2-l, Various modified polyvinyl alcohols including nitrogen-modified polyvinyl alcohol can be mentioned. In order to coat the surface of the heat-sensitive layer with polyvinyl alcohol, it is sufficient to apply a heat-sensitive agent coating liquid onto the support, thoroughly dry the formed heat-sensitive layer, and then coat an aqueous solution of polyvinyl alcohol over it. .

The heat-sensitive recording material of the present invention obtained in this manner has almost no background coloration and has good color development sensitivity during printing, so it is widely used as paper for heat-sensitive recorders, heat-sensitive facsimiles, heat-sensitive copying machines, etc. and can be used effectively.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 First, 20 g of ferric stearate, anion group-containing polyvinyl alcohol (manufactured by Nippon Gosei Kagaku Co., Ltd.).

A solution consisting of 20 g of a 10% aqueous solution of T-330H), 0.02 g of an anionic surfactant (sodium lauryl sulfate) and 409 g of water, and 10 g of gallic acid.

Anionic group-containing polyvinyl alcohol (Nippon Gosei Chemical Co., Ltd.)
A solution B consisting of 10 g of a 10% aqueous solution of T-330H (manufactured by Co., Ltd., T-330H) and 20 g of water, and a solution C consisting of 50 g of a polyethylene wax emulsion with a concentration of 30% were prepared.

Next, the above-mentioned liquids A and B were separately ground for 2 days using a ball mill (to ensure sufficient dispersion, and then
Liquid, B liquid and C liquid were mixed to obtain a heat-sensitive coating liquid.

Subsequently, this heat-sensitive coating liquid was allowed to stand for about 1 hour, and then coated on patterned paper so that the coated area of the heat-sensitive layer after drying was about 5 g/♂ to obtain heat-sensitive recording paper. The background color density of this thermal recording paper was measured using a Macbeth densitometer. The results are shown in Table 1.

Comparative Example 1 The same operation as in Example 1 was performed except that hydroxyethylcellulose was used instead of the anionic group-containing polyvinyl alcohol in Liquids A and B. Table 1 shows the results of the ground color test.

Comparative Example 2 The same operation as in Example 1 was performed except that polyvinyl alcohol was used instead of the anionic group-containing polyvinyl alcohol in Liquids A and B. Table 1 shows the results of the ground color test.

Comparative Example 3 The same operation as in Example 1 was performed except that oxidized starch was used instead of the anion group-containing polyvinyl alcohol in Liquids A and B. Table 1 shows the results of the ground color test.

Comparative Example 4 The same operation as in Example 1 was performed except that bF)Vc SBR latex was used instead of the anionic group-containing polyvinyl alcohol in Liquids A and B. Table 1 shows the results of the ground color test.

Table 1 *1 ◎Very good, ○Good, △Slightly poor, X poor*2
Stored in an atmosphere with a temperature of 30°C and relative humidity of 90%.

Example 2 After thoroughly drying the heat-sensitive recording paper obtained in Example 1, a 10% aqueous solution of polyvinyl alcohol (M, Gozenol NH-18, manufactured by Nippon Gosei Kagaku Co., Ltd.) was added to the top of the heat-sensitive layer of the recording paper. It was coated so that the coating amount after drying was 4 g/7712.

Regarding the thermal recording paper obtained in this way, that is, the thermal recording paper whose thermal layer is coated with polyvinyl alcohol,
A background color test was conducted using a Macbeth densitometer. The results are shown in Table 2.

Example 3 The same operation as in Example 2 was carried out except that the coating lid after polyvinyl alcohol was dried was changed from 4/η12 to 89/m,''.Results of ground coloring test are shown in Table 2.

Stored in an atmosphere with a temperature of 30℃ and relative humidity of 90%.

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Claims (1)

[Scope of Claims] 0) A heat-sensitive recording material having a heat-sensitive layer formed of a composition in which an organic acid metal salt color former and a phenol color developer are dispersed in a binder, wherein an anion is used as the binder. A heat-sensitive recording material characterized by using polyvinyl alcohol containing a group. (2) The heat-sensitive recording material according to claim 1, wherein the anionic group-containing polyvinyl alcohol is acid-modified polyvinyl alcohol modified with acetic acid or an acetate. (3) In a heat-sensitive recording material having a heat-sensitive layer formed from a composition in which an organic acid metal salt color former and a phenol color developer are dispersed in a binder, polyvinyl alcohol containing an anionic group is used as the binder. A heat-sensitive recording material characterized in that the surface of the heat-sensitive layer is coated with polyvinyl alcohol. (4) Polyvinyl alcohol containing anionic groups is
The heat-sensitive recording material according to claim 3, which is acid-modified polyvinyl alcohol modified with acetic acid or acetate. (5) The polyvinyl alcohol covering the surface of the heat-sensitive layer is
The heat-sensitive recording material according to claim 3, which contains unmodified polyvinyl alcohol or modified polyvinyl alcohol having a Ken scale of 70 mol % or more.