JPS59214691A - Thermal recording paper - Google Patents

Abstract

PURPOSE:To provide a thermal recording paper which is free from background fogging and can be coated at a high speed at a high temp., by dispersing two components of a dye precursor and a coupler for forming a color through the reaction with said precursor under heating in a aliphatic hydrocarbon and microencapsulating both or one of them. CONSTITUTION:In a thermal recording paper containing two components of a usually colorless or light-colored dye precursor, e.g., 3-diethylamino-6-methyl-7- anilinofluoran, and a coupler, e.g., 4,4'-isopropylidenediphenol, as main components, both or either one of said two components is dispersed in an org. solvent comprising aliphatic or alicyclic hydrocarbons, e.g., cyclohexane, inert to said two components and microencapsulated to prepare a coating liquid, which is then applied to a base paper and dried to obtain the objective thermal recording paper.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording paper, and more particularly to a thermal recording paper in which a dye precursor and/or a color developer are microencapsulated. To provide a heat-sensitive recording paper that can be coated and dried at high speed and high temperature and has no background fog.

Recently, thermal recording methods have many advantages such as non-impact, no noise during recording, no need for developing and fixing, and easy maintenance management of equipment. It has been used in a wide range of fields, including recorders for medical measurement, low- and high-speed facsimiles, automatic ticket vending machines, and thermal copying.

In the past, there have been many examples of using microcapsules in thermal recording paper. For example, Tokko Sho 4゛9-
Publication No. 70 describes a method for producing multicolor thermosensitive recording paper. Here, two or more basic coloring substances (dye precursors) and electron-accepting substances (developer) having different coloring reaction temperatures, and a water-insoluble substance (in the case of a liquid, A multicolor thermosensitive recording paper is described in which a mixture of microencapsulated (microencapsulated) materials is coated on the paper surface.

Japanese Patent Publication No. 49-15227 describes a method for producing heat-sensitive recording paper. Here, we describe capsules containing an electron-donating substance (dye precursor), capsules containing an ion-reactive coloring agent, and thermal recording paper coated with wax dispersed in the electron-donating substance (developer). ing.

JP-A-57-12695 discloses a [thermal recording method]. Here, a color former (dye precursor), a color former (color developer), and a heat-sensitive microcapsule that is compatible with at least one of the above two components and whose core material is a sublimable thermofusible substance is used. It describes a heat-sensitive recording paper that performs thermal recording after being pressurized with a recording paper (destroying the microcapsules) and imparts fixability to the recorded image.

However, in these three publications, the substance that dissolves the dye precursor or color developer is microencapsulated, and the microcapsules are destroyed by pressure, like in so-called pressure-sensitive copying paper, which contaminates the coated surface. It has a disadvantage in terms of storage stability.

On the other hand, Japanese Unexamined Patent Publication No. 145046/1983 discloses a "method for producing heat-sensitive recording material." Here, it consists of a two-component system of a color-forming substance (dye precursor) and an electron-accepting substance (color developer), and either or both of them are microencapsulated in fine powder form. This paper describes a heat-sensitive recording paper manufactured by a composite coacervation method using a polyanion.

However, the method disclosed in the above-mentioned publication is a microencapsulation method limited to a complex coacervation method using phytic acid or its metal salt, and is not versatile. Furthermore, it is a well-known fact to those skilled in the art that even if heat is directly recorded on thermosensitive recording paper until the state 1, which does not destroy the microcapsules, the microcapsules cannot be destroyed, and almost no color reaction occurs. The disadvantage is that there is no

On the other hand, as thermal recording paper has been widely used in many fields, there has been a trend toward higher sensitivity and mass production. However, higher sensitivity and mass production are contradictory issues for mass production, where higher sensitivity requires coating at higher speeds and higher temperatures. The higher the sensitivity, the more carefully the coating must be performed at a low speed and low temperature to prevent background fogging, and mass production is hampered by the need for high-speed coating at high temperatures.

As a result of studies to solve the above-mentioned drawbacks, the present inventors found that
The problem could be solved by using microcapsules for both or one of the two components on the coated surface of the heat-sensitive recording paper.

That is, in thermal recording paper that contains two main components: a normally colorless or light-colored dye precursor and a color developer that reacts with the dye precursor when heated and causes the dye precursor to develop color, the paper is inert to the two components. The present invention provides a heat-sensitive recording paper in which both or one of the two components dispersed in an organic solvent consisting of aliphatic hydrocarbons and alicyclic hydrocarbons is microencapsulated.

The heat-sensitive recording paper of the present invention has the advantage that it can be coated in large quantities at high temperatures and high speeds, and can be obtained without background fog.

Moreover, the higher the sensitivity of the thermal recording paper, the more effective it is that it can be applied at high speeds from low-temperature drying to high-temperature drying.

If the dye is dispersed in an organic solvent that is inert to the main body and the color developer, no color reaction will occur even if the two components come into contact as long as the solvent is present. By microcapsulating both or one of the two components, the two components are brought into a non-contact state, making it possible to produce thermal recording paper without background fog even during high-temperature, high-speed coating.

In the heat-sensitive recording paper used in the present invention, it is necessary to destroy the microcapsules on the coated surface and volatilize the organic solvent immediately after coating or immediately before printing.

After the organic solvent is volatilized, the two components on the coated surface are in a fine solid state and are not in contact with each other, so that no background fogging occurs.

Next, each component used in the thermal recording paper of the present invention will be specifically illustrated below.

Examples of organic solvents of aliphatic hydrocarbons or alicyclic hydrocarbons that are inert to the dye precursor and color developer used in the present invention are given below. Examples of aliphatic hydrocarbons include ligroin, keron, mineral spirits, and petroleum.

Examples of alicyclic hydrocarbons include cyclopentane, methylcyclopentane, 1- or 1,3-dimethylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, and 1,2,4-trimethylcyclohexane. I can do it. However, if the boiling point of the above-mentioned solvent is too low, it will evaporate during the microencapsulation process, which is not preferable. Furthermore, if the boiling point is too high, it is not desirable because it may remain on the coated surface. Therefore, the boiling point is 50°C to 300°C, preferably 70°C.
~200°C.

As for the dye precursor, dye precursors generally used for thermal recording paper can be used, such as crystal violet lactone, 3-diethylamino-7-methylfluoran, 3-diethylamine-6-chloro-7-methylfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-anilinofluorane, 3-diethylamine-7-(2'-chloroanilino)fluoran, 3-dibutylamino-7-(2'- chloroanilino)fluoran, 3-diethylamine-7-(
3'-chloroanilino)fluoran, 3-diethylamine-6-methyl-7-anilinofluoran, 3-(N-
Ethyl-p-1luidino)-6-methyl-7-anilinofluorane, 3-(N-methylcyclohexylamino)
Examples include -3-methyl-7-anilinofluorane and 3-piperidino-3-methyl-7-anilinofluorane.

As for the color developer, acidic substances generally used in thermal recording paper can be used, such as phenol, p-tert-
p-phenylphenonope p-phenylphenonope α-
Naphthol, p-hydroxyacetophenol, 2.2
'-dihydroxydiphenol 4.4'-ingropylidene bis(2-tert-butylphenol), 4-.
4'-isopropylidene diphenol, 4.4'-cyclohexylidene diphenol, novolac type phenol resin, benzoic acid, pLert-butylbenzoic acid, p-oxybenzoic acid, p-oxybenzoic acid benzyl ester,
p-oxybenzoic i? 2 Methyl ester, 3-benzyl-4-hydroxybenzoic acid, β-naphthoic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-methyl-
Examples include 5-tert-butylsalicylic acid, stearic acid, oxalic acid, and maleic acid.

In the present invention, in addition to the above-mentioned main components, a binder, a pigment, and various additives can be added as necessary.

Regarding the quantitative relationship between the dye precursor and color developer of the present invention and the organic solvent, the proportion of this component in 10% of the mixture with the solvent is
-60 weight percent, preferably 20-50 weight percent, more preferably 30-40 weight percent.

This is because if the ratio is low, it is difficult to volatilize the solvent, and if the ratio is high, it is difficult to disperse the component and it is difficult to microencapsulate uniform particles.

In the present invention, the microcapsules can be destroyed using a device such as a supercalender.

Next, the microencapsulation method used in the present invention may be any method known in the art. For example, a phase separation method, an interfacial polymerization method, an in-situ method, a spray drying method, etc. can be used, but the method is not limited to these.

Examples of the coating method include coating the entire surface of the support using an air knife coater, gravure coater, etc., or coating a portion of the support using a flexible printing machine, gravure printing machine, etc.

Examples of the support include paper, various nonwoven fabrics, synthetic paper, metal foil, plastic film, etc., or a composite sheet made of a combination of these.

Hereinafter, the present invention will be specifically explained with reference to Examples. Note that "parts" indicate parts by weight.

Example (1) Preparation of a microcapsule dispersion containing the skeleton before dyeing A styrene-maleic anhydride copolymer heated to 60°C was dissolved with a small amount of sodium hydroxide at pH 4.
A dye dispersion prepared by dispersing 30 parts of 3-diethylamino-6-methyl-7-anilinofluorane in 70 parts of cyclohexane in 100 parts of a 5% aqueous solution of
80 parts (pulverized and dispersed for 8 hours) were dispersed and emulsified to prepare an emulsion with emulsified particles of approximately 4 to 5 microns. Separately, 10 parts of melamine,
When 25 parts of a 37% formaldehyde aqueous solution, 65 parts of water and a small amount of sodium hydroxide were added and heated to 60°C,
It became transparent in 15 minutes to obtain a melamine-formalin initial condensate. This initial condensate was added to the emulsion, and the liquid temperature was 60°C.
Continue stirring for an hour to complete the microencapsulation.

(2) Preparation of color developer dispersion 4.40 parts of 4'-isopropylidene diphenol was added to Maron M'S-25 (Daido Kogyo ■ 25% aqueous solution of sodium salt of styrene-maleic anhydride copolymer) 4.8 1 part and 88.5 parts of water and dispersed in a ball mill for 48 hours.

(3) Preparation of sensitizer dispersion p-benzoyloxybenzoic acid benzyl ester (m
150 parts of styrene-maleic anhydride copolymer ammonium salt (75 parts of a 10% aqueous solution of ammonium salt of styrene-maleic anhydride copolymer) and 2 parts of water
The mixture was dispersed in 75 parts and dispersed in a ball mill for 72 hours.

A heat-sensitive coating liquid having a concentration of 25% was prepared as follows using the dispersions (1) to (3) above. Note that each dispersion part is the dry solid content.

Charcoal 5.0 parts (1) dye-containing capsules 8.5 parts (2) color developer dispersion 5.0 parts (3) sensitizer dispersion 3.0 parts 10% polyvinyl alcohol aqueous solution 5. 5 parts The heat-sensitive coating liquid containing the dye-containing microcapsules prepared here was dried on base paper with a basis weight of 501/m' using a Mayer bar at a drying temperature of 100°C, so that the coated amount was 5.6 f'/n? It was coated so that The obtained coated paper had a white background with no background fog.

The microcapsules on the coated surface of this coated paper were destroyed using a super calender controlled at 10 Ky/ca, and the cyclohexane contained therein was volatilized. This coated paper that had been passed through the supercalender had high smoothness and had no background fog, which was similar to the background after coating. Furthermore, when a printing test was carried out using a facsimile tester manufactured by Matsushita Electronic Components, a clear black printed image with an optical density of 1.15 could be obtained.

Incidentally, when a printing test was conducted without applying pressure to the coated paper, no printing image was formed on the coated surface.

Comparative Example (1) Preparation of Dye Dispersion 3-Diethylamino-6-methyl-7-anilinofluoran xso part t Dispersed in 18 parts of Maron MS-25 and 332 parts of water, and pulverized and dispersed in a ball mill for 48 hours.

(2) Preparation of developer dispersion liquid This is the same as (2) in the embodiment.

(3) Preparation of sensitizer dispersion Same as (3) in Example.

A heat-sensitive coating liquid with a concentration of 25% was prepared as follows using the dispersions (1) to (3) above. Note that each dispersion part is the dry solid content.

Charcoal 5.0 parts (1) Dye dispersion 2.0 parts (2) Color developer dispersion 5.0 parts (3) Sensitizer dispersion 3.0 parts 10% polyvinyl alcohol aqueous solution 3. When 8 parts of the prepared heat-sensitive coating liquid was dried and coated at 100° C. in the same manner as in the examples, the resulting coated paper had background fog. When the coated surface of the coated paper in which this texture blistering occurred was measured with an optical densitometer, it showed a value of 0.30, which was not usable.

Claims (1)

[Claims] (1) A thermosensitive recording paper containing two main components: a normally colorless or light-colored dye precursor and a color developer that reacts with the dye precursor to develop color when heated, and is inert to the two components. A thermal recording paper characterized in that both or one of the two components dispersed in an organic solvent consisting of certain aliphatic hydrocarbons and alicyclic hydrocarbons is microencapsulated.