JPH0259072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermal recording paper, and more specifically, it comprises two components: a normally colorless or light-colored dye precursor and a color developer that reacts with the dye precursor when heated to develop a color. In thermal recording paper containing as main components, a small amount of the two components is dispersed in an aliphatic hydrocarbon or an organic solvent consisting of aliphatic hydrocarbons that is inert to the two components and does not dissolve the two components. The present invention relates to a thermal recording paper characterized in that one component is microencapsulated, and provides a thermal recording paper that can be coated and dried at high speed and high temperature and is free from background fog.

Recently, thermal recording methods have been widely used in printers such as computer output and calculators because they have many advantages such as non-impact, no noise during recording, no need for developing and fixing, and easy equipment maintenance. , medical measurement recorder field,
It has been used in a wide range of applications, including low- and high-speed facsimile fields, automatic ticket vending machines, and thermal copying fields.

Conventionally, there have been many examples of using microcapsules in thermal recording paper. For example,
Publication No. 70 has 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, Multicolor thermosensitive recording paper is used to record multicolor thermal recording paper, which is coated with a mixture of microencapsulated (microencapsulated) substances on the paper surface.

Japanese Patent Publication No. 49-15227 describes a method for producing heat-sensitive recording paper. Here, we introduce a capsule containing an electron-donating substance (dye precursor), a capsule containing an ion-reactive color former, and an electron-accepting substance (color developer).
It describes heat-sensitive recording paper coated with wax dispersed therein.

Special Publication No. 57-12695 describes ``thermal recording method''
There is. Here, from microcapsules whose core material is a color former (dye precursor), a color former (color developer), and a sublimable thermofusible substance that is compatible with at least one of the above two components. After heating (destroying the microcapsules), thermal recording is performed using a thermal recording paper that fixes the recorded image.

However, in these three types of publications, substances that dissolve dye precursors or color developers are microencapsulated, and the microcapsules are destroyed by pressure, as in so-called pressure-sensitive copying paper, resulting in contamination of the coated surface. It has disadvantages in terms of gender.

On the other hand, Japanese Patent Publication No. 52-145046 discloses a method for producing heat-sensitive recording materials. Here, two types of substances are used: a color-forming substance (dye precursor) and an electron-accepting substance (color developer).
Describes a heat-sensitive recording paper made of a composite coacervation method using a polyanion made of phytic acid or a metal salt thereof, in which either or both of the components are microencapsulated in fine powder form. ing.

However, the method disclosed in the above publication is a microencapsulation method limited to a complex coacervation method using phytic acid or its metal salt, and is not widely used. Furthermore, as is well known to those skilled in the art, even if the microcapsules are directly heat-recorded on thermal recording paper without being destroyed, 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 requires high-speed coating at high temperatures.

As a result of studies to solve the above-mentioned drawbacks, the present inventors found that at least one component of the dye precursor and color developer in the heat-sensitive recording layer of heat-sensitive recording paper is an aliphatic hydrocarbon or a color developer that does not dissolve the two components. If the problem could be solved by using microcapsules dispersed in an organic solvent consisting of alicyclic hydrocarbons, the present invention would solve the problem by using a normally colorless or light-colored dye precursor and reacting with the dye precursor upon heating. Color developer that colors the body 2
In a thermal recording paper containing the two components as main components, the two components are dispersed in an organic solvent consisting of an aliphatic hydrocarbon or alicyclic hydrocarbon that is inert to the two components and does not dissolve the two components. at least 1 of
The present invention provides a thermal recording paper characterized in that components are 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.

Inert to dye precursors and color developers;
For those dispersed in an organic solvent that does not dissolve the components, the dye precursor and color developer are dispersed in an organic solvent consisting of aliphatic hydrocarbons or alicyclic hydrocarbons that do not dissolve the two components. Even if the dispersion liquid of the two components comes into contact, the two components are
The components are in a non-contact state, and no color reaction occurs even when applied and dried at high temperatures and high speeds. Therefore, even if heat-sensitive recording paper is manufactured by coating and drying at high temperatures and high speeds, background fogging does not occur. After that, even if the microcapsules are destroyed during thermal recording, the dye precursor and color developer are similarly dispersed in an organic solvent consisting of aliphatic hydrocarbons or alicyclic hydrocarbons that does not dissolve these two components. , the two components are in a non-contact state,
Does not cause background fog.

Immediately after coating, the thermal recording paper used in the present invention
Alternatively, it is necessary to destroy the microcapsules on the coated surface and volatilize the organic solvent 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 and do not dissolve these two components are given below. Examples of aliphatic hydrocarbons include ligroin, kerosene, mineral spirits, and petroleum. In addition, examples of alicyclic hydrocarbons include cyclopentane, methylcyclopentane,
Examples include 1,1- or 1,3-dimethylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, and 1,2,4-trimethylcyclohexane. However, if the boiling point of the above solvent is too low, it will evaporate during the microencapsulation process, which is not preferable. Also, if the boiling point is too high, it will remain on the coated surface, which is not preferable. Therefore, the boiling point
The temperature is 50°C to 300°C, preferably 70°C to 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-methylfluorane, 3-diethylamino-6
-Chloro-7-methylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3
-diethylamino-7-anilinofluorane, 3
-diethylamino-7-(2'-chloroanilino)
Fluoran, 3-dibutylamino-7-(2'-chloroanilino)fluoran, 3-diethylamino-7-(3'-chloroanilino)fluoran, 3-
Diethylamino-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-6
-Methyl-7-anilinofluorane, 3-(N-
Methylcyclohexylamino)-3-methyl-7
-anilinofluorane, 3-piperidino-3-methyl-7-anilinofluorane, and the like.

As for the color developer, acidic substances generally used in thermal recording paper can be used, such as phenol,
p-tert-butylphenol, p-phenylphenol, a-naphthol, p-hydroxyacetophenol, 2,2'-dihydroxyphenol,
4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'-isopropylidene diphenol, 4,4'-cyclohexylidene diphenol, novolac type phenolic resin, benzoic acid,
p-tert-butylbenzoic acid, p-oxybenzoic acid, p-oxybenzoic acid benzyl ester, p-
Oxybenzoic acid methyl ester, 3-benzyl-
Examples include 4-hydroxybenzoic acid, β-naphthoic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-methyl-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 amount of this component is 10 to 60% by weight, preferably 20% by weight of the mixture with the solvent.
~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,
Phase separation method, interfacial polymerization method, in-situ method, spray drying method, etc. can be used.
There is no limitation 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 flexo printing machine, gravure printing machine, etc.

Examples of the support include paper, various nonwoven fabrics, synthetic paper, metal foil, plastic film, and composite sheets 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) Creation of a microcapsule dispersion containing a dye precursor A styrene-maleic anhydride copolymer heated to 60°C was dissolved in 100 parts of a 5% aqueous solution with a pH of 4.0 with a small amount of sodium hydroxide. , 3-diethylamino-6-methyl-7 in 70 parts of cyclohexane
- 80 parts of a dye dispersion containing 30 parts of anilinofluorane (pulverized and dispersed in advance in a ball mill for 48 hours) was dispersed and emulsified to prepare an emulsion with emulsified particles of about 4 to 5 microns. Separately, 10 parts of melamine, 25 parts of 37% formaldehyde aqueous solution, 65 parts of water, and a small amount of sodium hydroxide were added and heated to 60°C.
The mixture became transparent within minutes to obtain a melamine-formalin initial condensate. This initial condensate was added to the emulsion, and stirring was continued for 3 hours at a liquid temperature of 60°C to complete microencapsulation.

(2) Preparation of color developer dispersion 40 parts of 4,4'-isopropylidene diphenol and 4.8 parts of Maron MS-25 (Daido Kogyo Co., Ltd., 25% aqueous solution of sodium salt of styrene-maleic anhydride copolymer) and dispersed in 88.5 parts of water and 48% in a ball mill.
Distribute time.

(3) Preparation of sensitizer dispersion Disperse 150 parts of p-benzoyloxybenzoic acid benzyl ester (mp 91 to 93°C) in 75 parts of a 10% aqueous solution of ammonium salt of styrene-maleic anhydride copolymer and 275 parts of water. Disperse in a ball mill for 72 hours.

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-encapsulated 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 Dye-encapsulated microcapsules prepared here The coating weight after drying at 100℃ using a Mayer bar on base paper with a basis weight of 50g/ ^m2 was 5.6g/m2.
It was coated so that it was ^m2 . 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 calendar controlled at 10 kg/cm ² and the cyclohexane contained therein was volatilized. Through supercalendering, this coated paper had high smoothness and was similar to the background after coating, with no background fog. Furthermore, when a printing test was performed using a facsimile tester manufactured by Matsushita Electronic Components, the optical density was 1.15.
A clear black printed image could be obtained.

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

Comparative Example (1) Preparation of dye dispersion 150 parts of 3-diethylamino-6-methyl-7-anilinofluorane was dispersed in 18 parts of Maron MS-25 and 332 parts of water, and the mixture was ground and dispersed in a ball mill for 48 hours.

(2) Preparation of developer dispersion liquid Same as (2) in Example.

(3) Adjustment 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 3.8 parts The heat-sensitive coating liquid prepared here. 100 as in the example
When dry coating was carried out at ℃, the obtained coated paper showed fogging on the background. When the coated surface of the coated paper with this background fog was measured with an optical densitometer, it showed a value of 0.03, which was not usable.

Claims (1)

[Claims] 1. A normally colorless or light-colored dye precursor and 2. a color developer that reacts with the dye precursor when heated to develop a color.
In a thermal recording paper containing the two components as main components, the two components are dispersed in an organic solvent consisting of an aliphatic hydrocarbon or alicyclic hydrocarbon that is inert to the two components and does not dissolve the two components. at least 1 of
A thermal recording paper characterized by microencapsulated components.