JPS63252783A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material enhanced in transparency as compared conventional ones, by limiting the ratio of the refractive index of a component contained in microcapsules to the refractive index of an oil phase component of an emulsified dispersion. CONSTITUTION:It is considered that an interface having a great effect on light transmittance is the inner interface of microcapsule walls and the outer interface of the microcapsule walls making contact with an oil phase component of an emulsified dispersion. Therefore, as the refractive index of a component contained in microcapsules approaches the refractive index of the oil phase component of the emulsified dispersion, light is transmitted through a thermal recording layer more easily, and the transmittance becomes higher. Accordingly, by setting the ratio of the referactive indices in the range of 0.97-1.30, it is possible to cause the haze of the thermal recording layer to be not more than about 30%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) The thermal recording method (1) does not require development, (2) when the support is paper, the paper quality is similar to ordinary paper, and (3) is easy to handle. (4) High color density, (5) Simple and inexpensive recording device, and (6) No noise during recording. , the use of thermal recording is also expanding.

Against this background, in recent years, in order to adapt to multicolor, overhead projectors (
It has become desirable to develop a transparent heat-sensitive recording material that can be directly recorded with a thermal head for use in OHP.

However, with conventional transparent heat-sensitive recording materials, when the image area of the original is brought into close contact with the original and irradiated with light, the image area of the original absorbs infrared rays, raising the temperature of the image area, which causes the thermal recording film to develop color. Tokoro i! It is a transparent heat-sensitive film and does not have the thermal sensitivity to allow direct thermal recording with a thermal head used in facsimiles and the like.

Furthermore, the heat-sensitive layer of a heat-sensitive recording material that can be thermally recorded with a thermal head is devitrified, and it has not been possible to achieve the desired transparency even if the material is simply coated on a transparent support.

The present inventors have conducted extensive research into heat-sensitive recording materials, and have adopted a combination of a colorless or light-colored basic dye precursor and a color developer as a color-forming system, contained the former in microcapsules, and added a certain amount of the latter to a color-forming system. It was discovered that when the two were emulsified and dispersed under different conditions and then mixed and coated on a support, the resulting heat-sensitive layer became transparent, and a heat-sensitive recording material with excellent transparency was provided. No. 121875).

(Problems to be Solved by the Invention) As mentioned above, such a heat-sensitive recording material with excellent transparency is particularly useful for multicolor printing and OHP applications, but it is difficult to use when projecting with some types of OHP devices. In the case where the heat-sensitive layer is multilayered for multicolor, even better transparency may be required.

As a result of further various studies on improving the transparency, the present inventors found that, among the various components constituting the heat-sensitive layer, one of the combinations of a basic colorless dye precursor and a color developer as a color former was selected. The heat-sensitive The inventors have discovered that the transparency of the layer is significantly improved and have arrived at the present invention.

Accordingly, an object of the present invention is to provide a heat-sensitive recording material with improved transparency compared to conventional materials.

(Means for Solving the Problems) The above object of the present invention is to prepare microcapsules containing one component of a colorless or light-colored basic dye precursor and a color developer, and to mix the other component with water. In a heat-sensitive recording material in which a coating liquid containing an emulsified dispersion that is dissolved in a sparingly soluble or insoluble organic solvent and then emulsified and dispersed is coated on a support, the refractive index of the component inside the microcapsule and the emulsified dispersion are determined. This was achieved by a heat-sensitive recording material characterized in that the ratio of the refractive index of the oil phase components is 0.97 to 1.03.

(Function) Generally, when light passes through an interface, the transmittance is:
It is known that the closer the refractive indexes of the materials before and after the interface become, the higher they become. However, it is a surprising discovery that when various components coexist, such as in a heat-sensitive layer, the ratio of the refractive index of the components inside the microcapsules to the refractive index of the oil phase component of the emulsified dispersion becomes particularly important. be. This discovery was made by chance because the refractive index of both of the above components could be changed more easily and over a wider range than other components contained in the heat-sensitive layer, but based on this fact, the following It is possible to infer as follows. In other words, if we look in more detail at the case where light passes through the heat-sensitive layer, the light passes through the binder containing additives, the microcapsule wall, the components inside the microcapsules, and the oil phase component of the emulsion powder. You can think of the left. In this case, both the binder and the microcapsule wall are polymer compounds, and their refractive indexes are considered to be approximately equal. Therefore, the interfaces that greatly affect the light transmittance are considered to be the inner interface of the microcapsule wall and the outer interface of the microcapsule wall that is in contact with the oil phase component of the emulsion dispersion. The closer the refractive index of the component in the capsule is to the refractive index of the oil phase component corresponding to the number of emulsions, the easier it is for light to pass through the heat-sensitive layer, and the transmittance increases.

In the present invention, the ratio of their refractive indexes is set to 0. 97-1
．． 03, the haze of the heat-sensitive layer can be reduced to about 30% or less, and in particular, the ratio of the refractive indexes of the two can be set to 0.99 to 0.99.
By setting it to 1.01, the haze can be reduced to about 20% or less.

The basic dye precursor used in the heat-sensitive layer of the present invention includes:
A colorless or light-colored compound is appropriately selected from known compounds that develop color by donating electrons or accepting protons such as acids. Such compounds have partial skeletons such as lactones, lactams, sultones, spiropyrans, esters, and amides, and these partial skeletons are ring-opened or cleaved upon contact with a color developer. Preferred compounds include Examples include triarylmethane compounds, diphenylmethane compounds, xanthine compounds, thiazine compounds, and spiropyran compounds.

A particularly preferred compound is a compound represented by the following general formula.

In the formula, R1 is an alkyl group having 1 to 8 carbon atoms, R2 is an alkyl group having 4 to 18 carbon atoms, an alkoxyalkyl group, or a tetrahydrofurfuryl group, and R3 is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms. Alternatively, the halogen atom and R4 represent a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

As the substituent for R4, an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogenated alkyl group, and a halogen atom are preferable.

As a color developer that causes a color-forming reaction when thermally melted with the basic colorless dye used in the present invention, any known color developer can be used as appropriate6.For example, as a color developer for leuco dyes, phenolic compounds, Examples include triphenylmethane compounds, sulfur-containing phenolic compounds, carboxylic acid compounds, sulfone compounds, urea or thiourea compounds, etc. For details, see, for example, Paper Valve Technology Times (1985) 49-54. and pages 65-70. Among these, especially those with a melting point of 50℃~2
50°C is preferable, and 60°C to 200°C, water-soluble phenols and organic acids are especially desirable. It is preferable to use two or more color developers in combination because the solubility increases.

In the present invention, by encapsulating the above-mentioned basic dye precursor or color developer in microcapsules, it is possible to prevent fogging during the production of heat-sensitive materials, and at the same time, to improve the shelf life and archival stability of heat-sensitive materials. can be taken as a thing. In this case, by selecting the wall material and manufacturing method of the microcapsules, it is possible to increase the image density during recording.

In particular, the amount of basic dye precursor or color developer used is 0°05
It is preferable that it is 5.0 g/rrr.

Examples of the wall material of the microcapsule include polyurethane, polyurea, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, styrene-acrylate copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, etc. . In the present invention, two or more of these polymeric substances can also be used in combination.

In the present invention, among the above-mentioned polymeric substances, polyurethane, polyurea, polyamide, polyester, polycarbonate, etc. are preferable, and polyurethane and polyurea are particularly preferable.

The microcapsules used in the present invention are preferably microencapsulated by emulsifying a core material and then forming a wall of a polymer material around the oil droplets. In this case, a polymer material is formed or an actant is formed. Add to the inside of the oil droplet and/or to the outside of the oil droplet.

Details of microcapsules that can be preferably used in the present invention, such as a preferred method for producing microcapsules, are described in, for example, JP-A-59-222716.

Here, the organic solvent for forming oil droplets can be appropriately selected from those commonly used as pressure-sensitive oils. Among these, preferred oils include compounds represented by the following general formulas (V) to (■), triallylmethane (e.g., tritolylmethane, tolyldiphenylmethane), terphenyl compounds (e.g., terphenyl), and alkylated oils. In addition to diphenyl ether (for example, propyl diphenyl ether), hydrogenated terphenyl (for example, hexahydroterphenyl), diphenyl ether, esters such as maleic ester represented by the general formula (■) can be mentioned.

(V) In the formula, R1 is hydrogen or an alkyl group having 1 to 18 carbon atoms,
R2 represents an alkyl group having 1 to 18 carbon atoms. pl, q
l represents an integer of 1 to 4, and the total number of alkyl groups is 4
Must be within fII.

In addition, the alkyl group of R1 and R2 is preferably an alkyl group having 1 to 8 carbon atoms.

(Vl) In the formula, R3 is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R4 is an alkyl group having 1 to 12 carbon atoms.

n represents 1 or 2.

R2 and q2 represent integers of 1 to 4. When n=1, the total number of alkyl groups is 4 or less, and when n=2, the total number of alkyl groups is 6 or less.

(■) In the formula, R5 and R6 represent a hydrogen atom or the same or different alkyl groups having 1 to 18 carbon atoms.

m represents an integer from 1 to 13. R3 and q3 represent an integer of 1 to 3, and the total number of alkyl groups is 3 or less.

In addition, the alkyl group of R5 and R6 is particularly preferably an alkyl group having 2 to 4 carbon atoms.

Examples of the compound represented by formula (V) include dimethylnaphthalene, diethylnaphthalene, and diisopropylnaphthalene.

Examples of the compound represented by formula (Vl) include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, and diisobutylbiphenyl.

Examples of compounds represented by formula (■) include 1-methyl-
1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, 1-
Propyl-1-dimethylphenyl-1-phenylmethane is mentioned.

In the formula, R is an alkyl group of 01 to C18, but especially 01 to
C5 alkyl groups are preferred.

It is also possible to use the above oils together or with other oils.

In the present invention, an auxiliary solvent may be added to the above-mentioned organic solvent as a low-boiling-point solubilizing agent. Particularly preferred examples of such co-solvents include ethyl acetate, isopropyl acetate, butyl acetate and methylene chloride.

In the present invention, the size of the microcapsules is preferably 4μ or less, particularly preferably 2.5μ or less, as measured by the measurement method described in JP-A No. 60-214990. .

The preferred microcapsules produced as described above are not ruptured by heat or pressure as used in conventional recording materials, and the reactive substances contained in the core and outside of the microcapsules are It can penetrate through the capsule wall and react.

In the present invention, the wall material of the microcapsule is selected,
If necessary, a glass transition point adjusting agent (for example, Japanese patent application 1986-
119862) to prepare microcapsules consisting of walls with different glass transition points, and by selecting combinations of basic colorless dye precursors with different hues and their color developers. It is possible to achieve intermediate colors. Therefore, the present invention is not limited to monochrome thermal paper, but can also be applied to two-color or multi-color thermal paper and thermal paper suitable for recording images with gradation.

The emulsified dispersion of a basic dye precursor or color developer in the present invention is obtained by dissolving the basic dye precursor or color developer in an organic solvent that is sparingly soluble or insoluble in water, and then dissolving the basic dye precursor or color developer in an organic solvent containing a surfactant. It is used in the form of an emulsified dispersion by mixing it with an aqueous phase containing a water-soluble polymer as a protective colloid.

As the organic solvent that is sparingly soluble or insoluble in water, the same ones as in the case of the microcapsules described above can be used.

The water-soluble polymer to be included as a protective colloid in the aqueous phase mixed with the oil phase in which the basic dye precursor or color developer is dissolved is selected from known anionic polymers, nonionic polymers, and amphoteric polymers. Although it can be selected as appropriate, polyvinyl alcohol, gelatin, cellulose derivatives, etc. are preferred.

Further, as the surfactant to be contained in the aqueous phase, one can be appropriately selected from anionic or nonionic surfactants that do not cause precipitation or aggregation by interacting with the above-mentioned protective colloid. .

Preferred surfactants include sodium alkylbenzenesulfonate (eg, sodium lauryl sulfate), dioctyl sodium sulfosuccinate, polyalkylene glycol (eg, polyoxyethylene nonylphenyl ether), and the like.

An emulsified dispersion can be easily obtained by mixing and dispersing an oil phase and an aqueous phase containing a protective colloid and a surfactant using means commonly used for fine particle emulsification, such as high-speed stirring and ultrasonic dispersion. .

An agent for lowering the melting point of the color developer may be appropriately added to the emulsified dispersion of the color developer or the microcapsules of the color developer. Some of these melting point depressants also have the function of controlling the glass transition point of the capsule wall. Examples of such compounds include hydroxy compounds, carbamate ester compounds, sulfonamide compounds, and aromatic methoxy compounds, the details of which are described in, for example, Japanese Patent Application No. 59-244190.

These melting point depressants can be used in an amount of 0.1 to 2 parts by weight, preferably 0.5 to 1 part by weight, per 1 part by weight of the color developer that lowers the melting point. It is preferable that the color developer and the color developer whose melting point is lowered thereby are used at the same location. When adding to different locations, it is preferable to add 1 to 3 times the above amount.

The heat-sensitive recording material of the present invention can be coated using a suitable binder.

Binders include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, gum arabic, gelatin, polyvinylpyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene-vinyl acetate, etc. Various emulsions such as polymers can be used. The amount used is 0.2 to 5 g1rd as solid content.

The heat-sensitive recording material of the present invention is produced by preparing a coating liquid containing microcapsules encapsulating a color former and a dispersion in which at least a color developer is emulsified and dispersed, and other additives such as a binder. It is coated on a support such as a resin film by a coating method such as bar coating, blade coating, air knife coating, gravure coating, roll coating, spray coating, dip coating, etc. and dried to a solid content of 2.5 to
The heat-sensitive layer of the heat-sensitive material thus produced has very good transparency.

In the present invention, not only known transparent supports such as polymer films, but also opaque supports such as paper, or those coated with an undercoat can be used. .

When the heat-sensitive recording material of the present invention is used for OH and P, the transparent support is preferably polyethylene terephthalate film (PET) or cellulose triacetate film (TAC) from the viewpoints of dimensional stability, cost, strength, etc.

The paper used for the support is heat extracted pH 6 sized with a neutral sizing agent such as an alkyl ketene dimer.
~9 Neutral paper (described in JP-A-55-14281)
The use of is advantageous in terms of storage stability over time.

In order to prevent the coating liquid from penetrating into the paper and to improve the contact between the thermal recording head and the thermal recording layer, Japanese Patent Application Laid-Open No. 57-1166
The paper described in No. 87 and having a Bekk smoothness of 90 seconds or more is advantageous.

Also, paper having an optical surface roughness of 8μ or less and a thickness of 40 to 75μ, described in JP-A-58-136492, JP-A-58-136492.
Paper with a density of 0.9 g/cm 3 or less and an optical contact ratio of 15% or more as described in JP-A-69097,
Canadian Standard Freeness (JIS) as described in No.-69097
Paper made from pulp beaten to 400 cc or more with P8121) to prevent penetration of coating liquid, JP-A-5
No. 8-65695, the glossy side of base paper made by a Yankee machine is used as the coating surface to improve color density and resolution, and JP-A-59-35985 discloses corona discharge treatment on base paper. Papers and the like which have been coated to improve their coatability may also be used in the present invention with good results. In addition to these, any support commonly used in the field of heat-sensitive recording paper can be used as the support of the present invention.

On the heat-sensitive layer, there are anti-sticking, anti-scratch,
It is desirable to provide one or more protective layers for the purpose of imparting water resistance, flatness, antistatic properties, etc.

Examples of binders used in the protective layer include methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, starches, gelatin, gum arabic,
Casein, styrene-maleic anhydride copolymer hydrolyzate, styrene-maleic anhydride copolymer hydrolyzate, isobutylene-maleic anhydride copolymer hydrolyzate, polyvinyl alcohol, silica-modified polyvinyl alcohol, carboxy-modified polyvinyl pyrrolidone,
There are water-soluble polymers such as sodium polystyrene sulfonate and sodium alginate, and water-insoluble polymers such as styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, and polyvinyl acetate emulsion. In particular, silica-modified polyvinyl alcohol is preferred.

These may be used alone or in combination of two or more.

When used together, silica-modified polyvinyl alcohol 1
It is preferable that the amount of other polymers is 0.01 to 0.5 parts by weight based on the weight part.

Pigments, metal soaps, wax, crosslinking agents, etc. are added to the protective layer for the purpose of improving matching with the thermal head during printing and improving the water resistance of the protective layer.

Pigments include zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, Rouseki, kaolin, aluminum hydroxide, colloidal silica, amorphous silica, etc., and the amount of these added is 0% of the total weight of the polymer. .05~2
The amount is particularly preferably 0.1 to 0.5 times. If the amount is below the lower limit of the above range, it is ineffective in improving head matching properties, and if the amount is above the upper limit, the transparency and sensitivity of the heat-sensitive recording material will be significantly reduced, impairing its commercial value.

Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, calcium stearate, and aluminum stearate, and the amount thereof is 0.5 to 20% by weight, preferably 1 to 10% by weight of the total weight of the protective layer. It is added in Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylolstearamide, and polyethylene wax, and the amount is 0.5 to 40% by weight, preferably 1% by weight of the total weight of the protective layer.
It is added in a proportion of ~20% by weight.

Further, when forming a protective layer on the heat-sensitive layer, a surfactant is added to the coating solution for forming the protective layer in order to form a uniform coating layer. Surfactants include sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, etc. Specifically, di(2-ethylhexyl)sulfosuccinic acid, di(n-
Examples include sodium salts or ammonium salts of sulfosuccinic acid (hexyl)sulfosuccinic acid, etc.

Furthermore, a surfactant, a polymer electrolyte, or the like may be added to the protective layer to prevent charging of the heat-sensitive recording material. The solid content coating amount of the protective layer is usually preferably 0.2 to 5 g, more preferably 1 g to 3 g/m2.

(Effects of the Invention) Since the heat-sensitive recording material of the present invention has significantly improved transparency, its performance as an OHP is equivalent to that of a conventional transparent heat-sensitive film, and its color reproduction when producing multiple colors is also extremely good.

In addition, the transparency can be easily adjusted by adjusting the refractive index of the components within the microcapsules and the oil phase components of the emulsified dispersion, making it possible to produce thermosensitive films with a certain degree of transparency with good reproducibility. can.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

[Preparation of capsule liquid]

Compounds of OA in Table 1 and Takene 1-D-11ON (
20 g of capsule wall material (manufactured by Narita Pharmaceutical Co., Ltd.) was added to a mixed solvent containing 25 g of methylene chloride and dissolved. This leuco dye solution was mixed with an 8% polyvinyl alcohol aqueous solution of 50%
g, mixed with an aqueous solution of 15 g of water and 0.2 g of 2% sodium salt of dioctyl sulfosuccinate (dispersant), and mixed with an Ace Hosogenizer manufactured by Nippon Seiki ■ to 10.00 Orp.
The mixture was emulsified at m for 5 minutes, 150 g of water was added, and the mixture was reacted at 40° C. for 3 hours to produce a capsule liquid with a capsule size of 0.7 μm.

[Preparation of emulsified dispersion]

The compound OB in Table 1 was dissolved in 10 g of ethyl acetate.

The obtained developer solution was mixed with an aqueous solution of 50 g of 8% polyvinyl alcohol aqueous solution, 50 g of water, and 0.5 g of sodium dodecylbenzenesulfonate, and was heated to 10,000 γpm using an Ace homogenizer manufactured by Nippon Seiki ■. Emulsification was carried out for 5 minutes at room temperature to obtain an emulsified dispersion with a particle size of 0.5μ.

[Preparation of heat-sensitive material] 5.0 g of the above capsule liquid, 10.0 g of the emulsified dispersion, and 5.0 g of water were stirred and mixed, and the solid content was 15 μm on a transparent polyethylene terephthalate (PET) support with a thickness of 70 μm.
glrd and dried, and then a 2 μm protective layer having the following composition was provided to prepare a transparent thermosensitive film.

Silica-modified polyvinyl alcohol (PVA R2105 manufactured by Kuraray H) 1 part by weight (solid content)
Colloidal silica (Nissan Chemical ■Snowtex 30) 1.5 parts by weight (solid content)
Zinc stearate (Hydrin Z-7 manufactured by Tokyo Yushi Corporation) 0.02 parts by weight (solid content) Paraffin wax (Hydrin P-7 manufactured by Middle East Yushi Corporation) 0.01 parts by weight (solid content) Each of the substances shown in Table 1 For each sample made using the material,
The results of measuring the refractive index of the components within the microcapsules, the refractive index of the oil phase of the emulsified dispersion, and their ratios are shown in Table 2 as values representing transparency, along with the degree of haze measured with an integrating sphere haze meter.

The results in Table 2 demonstrate that the heat-sensitive recording material of the present invention has a low haze degree and extremely excellent transparency.

Claims (1)

[Claims] Microcapsules containing one component of a colorless or light-colored basic dye precursor and a color developer, and an emulsion dispersion obtained by dissolving the other component in an organic solvent that is sparingly soluble or insoluble in water and then emulsifying and dispersing it. In a heat-sensitive recording material in which a coating liquid containing a substance is coated on a support, the ratio of the refractive index of the component inside the microcapsules to the refractive index of the oil phase component of the emulsified dispersion is 0.97 to 1. .03.