JPH0422685A - Binder for thermal transfer layer and sublimation thermal transfer ink ribbon - Google Patents

Abstract

PURPOSE:To enhance preservability and recording density by containing a carboxy modified polyvinyl acetoacetal resin and/or a carboxy modified acetoacetal/butyl acetal mixed polyvinyl acetal resin. CONSTITUTION:The content of the carboxyl group contained in a carboxy modified polyvinyl acetoacetal resin (A) and/or a carboxy modified acetoacetal/ butyl acetal mixed polyvinyl acetal resin is shown as the wt. percentage of the carboxyl group in the acetal resin or (B) and as the value of the carboxyl group in the mixture of the acetal resins (A), (B). The content of the carboxyl group in the acetal resin (A) and/or (B) is usually 0.5-9wt.%, pref., 0.57wt.%, further pref., 2-5wt.% and, when the content is below 0.5wt.%, sufficient preservability and recording density are not obtained and, even when the content exceeds 9 wt.%, preservability and recording density are not enhanced to a large extent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a binder for a thermal transfer layer and a sublimation thermal transfer ink ribbon using the binder.

[Prior Art] Conventionally, image recording by the sublimation thermal transfer method has been carried out using an ink ribbon and recording paper, but specifically, a thermal transfer layer containing a sublimable dye, a binder, etc. In a state where the thermal transfer layer surface of the ink ribbon formed by the ink ribbon and the receiving layer surface of the recording paper having the dye receiving layer on the base sheet are brought into contact with each other, the temperature etc. are controlled based on the image signal. This is carried out by applying thermal energy to the ink ribbon using a thermal head or laser to sublimate the dye in the thermal transfer layer, and then transferring the sublimated dye from the thermal transfer layer to the receiving layer of the recording paper.

In this sublimation thermal transfer method, the amount of thermal energy applied to the thermal transfer layer of the ink ribbon is changed according to changes in image signals obtained from a television, CRT color display, color facsimile, magnetic camera, etc. By varying the amount of dye sublimated and transferred, it is possible to obtain an image record with good gradation on the receiving layer of recording paper. In addition, when performing thermal transfer, if three types of ink ribbon containing dyes of one of the three primary colors of yellow, magenta, and cyan are used in the thermal transfer layer, and each color is transferred onto the same receiving layer surface of the recording paper in a layered manner, a full-color image can be obtained. Image recording can also be performed.

[Problems to be Solved by the Invention] However, many of the thermal transfer layers of ink ribbons used in conventional sublimation thermal transfer methods have problems with storage stability and recording density. In other words, conventional ink ribbons have poor storage stability because dyes contained in the thermal transfer layer tend to bleed out and crystallize, which can reduce recording density and cause uneven recording density. It had become. In order to prevent such leaching and crystallization of dyes, attempts have been made to use ester resins or amide resins that are highly compatible with dyes as binders in the thermal transfer layer (Japanese Patent Laid-Open No. 63-34191). This method improves storage stability, but on the other hand, when the thermal transfer layer is heated, it is difficult for the dye to sublime and evaporate, making it difficult to obtain sufficient recording density. The problem is that there is no.

Recently, a method of using polyvinyl acetoacetal resin as a binder for the thermal transfer layer has been proposed (Japanese Patent Application Laid-open No. 151484/1984), but even with this method, it is not always possible to improve the storage stability and recording density of the ink ribbon. It wasn't enough.

As a result of various studies to solve these problems, the present inventors have found that by using a specific polyvinyl acetal resin having a carboxyl group as a side chain as a binder for a thermal transfer layer, a sublimation method with excellent storage stability and recording density has been developed. It was discovered that a thermal transfer ink ribbon can be obtained, and the present invention was completed.

[Means for Solving the Problems] That is, the first invention of the present invention is to contain a carboxy-modified polyvinyl acetoacetal resin (A) and/or a carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B). A sublimation thermal transfer ink ribbon comprising: a binder for a thermal transfer layer, and a thermal transfer layer containing a sublimable dye and the binder for a thermal transfer layer on a base material.

Moreover, the second invention of the present invention is characterized in that a carboxy-modified polyvinyl acetoacetal resin (A) and/or a carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B) and a polyvinyl acetal resin having no carboxyl group ( A binder for a thermal transfer layer characterized by containing C), and on a base material,
This is a sublimation thermal transfer ink ribbon characterized by having a thermal transfer layer containing a sublimable dye and the above-mentioned binder for a thermal transfer layer.

The present invention will be explained in more detail below.

First, the binder for a thermal transfer layer according to the first aspect of the present invention will be explained.

The binder resin used in the binder for the thermal transfer layer of the present invention is a polyvinyl acetal (hereinafter referred to as carboxy-modified polyvinyl acetal) resin having a carboxyl group as a side chain, and more specifically, a carboxy-modified polyvinyl acetoacetal resin ( A) (hereinafter referred to as acetal resin (A)), carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B) (hereinafter referred to as acetal resin (B)), or these acetal resins (A) and acetal resin
(B). These acetal resins (A) and acetal resins (B) are known per se (for example, JP-A-58-191701, JP-A-60-226508, JP-A-58-9).
8306 and JP-A-58-98307)
It is.

The present invention is characterized in that these acetal resins (A) and (B) are used alone, or a mixture of acetal resin (A) and acetal resin (B) is used as a binder resin for a thermal transfer layer of a sublimation thermal transfer ink ribbon. That is.

The acetal resins (A) and (B) used in the present invention are:
All of them have a unit to which at least one carboxyl group is bonded as a side chain (hereinafter referred to as a carboxyl unit) as a unit constituting the resin, and in addition to the carboxyl unit, as a unit constituting the resin, The acetal resin (A) has an acetoacetal unit, and the acetal resin (B) has both an acetoacetal unit and a butyl acetal unit. The mixed polyvinyl acetal resin in the present invention refers to a polyvinyl acetal resin having two or more different acetal units.

Contained in the carboxy-modified polyvinyl acetoacetal resin (A) and/or the carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B) (hereinafter referred to as acetal resin (A) and/or (B)) used in the present invention. The content of carboxyl groups in the acetal resin (A) or (B) is expressed as the weight percentage occupied by carboxyl groups (in terms of C0OH), and in the case of a mixture of the acetal resins (A) and (B), the content of the carboxyl groups in the acetal resin (A) or (B) Shows the value of carboxyl group in

The content of carboxyl groups in the acetal resin (A) and/or (B) is usually in the range of 0.5 to 9% by weight, preferably 0.5 to 7% by weight, more preferably 2 to 5% by weight. Desirably, if it is less than 0.5% by weight, sufficient preservability,
Recording density cannot be obtained, and even if it exceeds 9% by weight, storage stability
There is no significant improvement in recording density.

The content of carboxyl groups in the acetal resin (A) and/or (B) is determined by converting the carboxyl group into a sodium salt and quantifying the sodium using an atomic absorption spectrophotometer into carboxyl groups. It is shown as a value.

In addition, some or all of the carboxyl groups in the acetal resin (A) and/or (B) are acidic (-COO
H) form, salt form (sodium, potassium.

It may be in the form of lithium, ammonia, amines, etc.), lower alkyl (methyl, ethyl, propyl, butyl, etc.), ester, or a combination of these forms, but especially when the carboxyl group is in the acid form. for,
It has excellent dye dispersibility in organic solvents when obtaining a dye composition in which the dye and binder used to form the thermal transfer layer are uniformly mixed in an organic solvent, and the adhesion of the thermal transfer layer to the substrate. From this point of view, it is preferable that a small number of carboxyl groups (or some of them be in the acid form).

Next, the content of acetal units in the acetal resin (A) and/or (B) used in the present invention is usually 65% by weight or more, preferably in the range of 70 to 85% by weight, and the content of acetal units is 65% by weight or more, preferably in the range of 70 to 85% by weight. If it is less than this, the resin may become difficult to dissolve in the organic solvent, and the recorded density of the image may decrease.

In addition, when the acetal units in the acetal resin (A) and/or (B) consist of two types, acetoacetal units and butyl acetal units, in addition to the content ratio of the acetal units, butyl acetal units/acetoacetal The weight ratio of the units is preferably 2.3 or less, particularly preferably 1.5 or less. If the weight ratio exceeds 2.3, the resin may become difficult to dissolve in organic solvents or the recorded density of the image may deteriorate. may decrease.

In addition, the weight ratio of the butyl acetal unit and the acetoacetal unit in the acetal resin (A) and/or CB) was determined using an infrared spectrophotometer. - Measure the characteristic absorption of 10000I11-1 due to the dioxane ring, and the characteristic absorption of 945 cl' due to the 1,3-dioxane ring to which CH2 is bonded to the acetoacecool unit, and calculate the value calculated from the absorbance ratio of the two. show.

Acetal resin (A) and/or (
There is no problem even if B) contains about 20% by weight or less of non-acetalized vinyl alcohol units.

In addition, the acetal resin (A) and/or (B) contains 3 weight fatty acid vinyl ester units derived from polyvinyl alcohol polymer (hereinafter referred to as PVA) used as a type of raw material to obtain the resin. There is no problem even if it is present in a small amount of about % or less. The content of fatty acid vinyl ester units can be determined by adding an aqueous solution of caustic soda to the resin dissolved in ethyl alcohol, heating it, and hydrolyzing the ester portion to generate fatty acid soda (the remaining caustic soda is neutralized with sulfuric acid). Next, an internal standard substance (propionic acid is used in the case of vinyl acetate) and phosphoric acid are added, and the fatty acid produced by the decomposition of the fatty acid soda is quantified using a gas chromatograph, and the amount of fatty acid can be calculated by converting the amount.

In the present invention, when acetal resin (A) and acetal resin (B) are used together, acetal resin (A) and (B)
There is no particular restriction on the mixing ratio of the acetal resin (B) to 80 to 40 parts by weight of the acetal resin (A), although there is no particular restriction on the mixing ratio.

Acetal resin (A) and/or (
The average degree of polymerization of B) is not particularly limited, but is usually 200.
A range of ˜4000, particularly 300-3000 is preferred.

If the average degree of polymerization is less than 200, the ability to retain the shape of the thermal transfer layer and fix the thermal transfer layer to the ink ribbon base material is weak, and if it exceeds 4,000, the solubility in organic solvents may decrease, or the strength during the acetalization reaction may decrease. Since the viscosity of the reaction solution increases, it is necessary to take measures such as lowering the concentration of the reaction system, which may reduce the productivity of the resin. In addition, the average degree of polymerization when consisting of a mixture of acetal resin (A) and acetal resin (B) is expressed by the value of the average degree of polymerization shown by the mixture.

Next, a method for producing the acetal resin (A) and/or (B) used in the present invention will be explained.

The acetal resins (A) and (B) used in the present invention include PVA having a carboxyl group as a side chain (including PVA having a side chain that converts into a carboxyl group by reacting with a strong acid used as a catalyst in the acetalization reaction). ) as a raw material and acetalize this PVA with acetaldehyde to produce acetal resin (A),
Further, by acetalizing two types of aldehydes, acetaldehyde and butyraldehyde, in combination, acetal resin CB) can be obtained.

Polyvinyl alcohol having a carboxyl group as a side chain (hereinafter referred to as carboxy-modified PVA) can be prepared using known methods such as Japanese Patent Publication No. 46-7605 and Japanese Patent Application Laid-open No. 1987-57.
It can be obtained by the method described in Publication No. 94002 and the like. Specifically, fatty acid vinyl esters (vinyl acetate,
vinyl propionate, vinyl formate, etc.), unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, crotonic acid, etc.), ethylenically unsaturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.), ethylenically unsaturated dicarboxylic acids. Acid anhydride (maleic anhydride), (meth)acrylic acid alkyl ester [methyl (meth)acrylate, (meth)
One or two of ethyl acrylate, butyl (meth)acrylate, ethylhexyl (meth)acrylate, etc.], (meth)acrylonitrile, (meth)acrylamide, etc.
It can be obtained by saponifying a copolymer with more than one species.

Furthermore, fatty acid vinyl esters and monomers having a side chain that reacts with a strong acid used as a catalyst in the acetalization reaction to convert into a carboxyl group [e.g., acrylamide (described in Japanese Patent Publication No. 7605/1983), meth Carboxy-modified PVA can also be obtained by saponifying or alcohololyzing a copolymer with one or more types of acrylamide.

The carboxyl group in the carboxy-modified PVA may be in the form of an acid, a salt, an acid amide, an alkyl ester, or a combination thereof. In addition, carboxy-modified P
Two or more VAs having different carboxyl group content, carboxyl unit structure, carboxyl group shape, average polymerization degree, or saponification degree can also be used in combination.

By acetalizing the carboxy-modified PVA thus obtained, the carboxy-modified polyvinyl acetal resin used in the present invention can be obtained. There are no special restrictions on the conditions at that time, and known methods and conditions can be employed. For example, organic solvents such as methanol, aldehyde [acetaldehyde alone is used to obtain acetal resin (A),
When obtaining acetal resin (B), use a combination of acetaldehyde and butyraldehyde] and a strong inorganic acid as a catalyst to perform an acetalization reaction by suspending the carboxy-modified PVA, and add water to the resulting polyvinyl acetal solution. A method of adding carboxy-modified polyvinyl acetal to precipitate carboxy-modified polyvinyl acetal, or adding carboxy-modified P
A method is used in which the above-mentioned aldehyde and a strong inorganic acid catalyst are added to an aqueous solution of VA to cause an acetalization reaction, and as the reaction progresses, carboxy-modified polyvinyl acetal is precipitated in the aqueous reaction system. Furthermore, in these methods, instead of carboxy-modified PVA, the PVA
The resin used in the present invention can also be obtained by carrying out a saponification reaction using a strong acid catalyst and an acetalization reaction in parallel using the aforementioned fatty acid vinyl ester copolymers used to obtain VA.

The carboxy-modified polyvinyl acetal resin thus obtained can be neutralized before or after precipitation, if necessary, and then washed with water, filtered, dried, etc., and can be obtained in the form of powder.

Incidentally, as the reaction apparatus used for the above reaction, those used in the production of known polyvinyl acetal resins can be used as they are.

Moreover, additives and the like can be added to the binder for a thermal transfer layer of the present invention as necessary.

Next, the binder for a thermal transfer layer according to the second aspect of the present invention will be explained.

The binder for a thermal transfer layer of the second invention includes a polyvinyl acetal resin (C) having no carboxyl group in the acetal resin (A) and/or (B).
It consists of a resin composition that is used in combination with.

As the polyvinyl acetal resin (C) that does not have a carboxyl group, P that does not have a carboxyl group
Known polyvinyl acetal resins obtained by acetalizing VA, such as polyvinyl acetoacetal, acetoacetal/butyl acetal mixed polyvinyl acetal, formacecool/acetoacetal/butyl acetal mixed polyvinyl acetal, polyvinyl butyl acetal, etc., or combinations thereof. You can use something like this.

Methods for using acetal resin (A) and/or (B) and polyvinyl acetal resin (C) in combination include mixing them in powder or solution form, or adding carboxy-modified PVA (acetalization PV with side chains that convert into carboxyl groups during reaction
A mixture can also be obtained by a method of causing an acetalization reaction by coexisting PVA (containing A) and PVA having no carboxyl group.

The amount of the above polyvinyl acetal resin (C) used is:
lO to 1.500 parts by weight, preferably 20 to 1.500 parts by weight per 100 parts by weight of acetal resin (A) and/or (B)
A range of 500 parts by weight is desirable; if it exceeds 1,500 parts by weight, the proportion of carboxyl groups will be low and sufficient storage stability and recording density will not be obtained, so it is not preferable.

In addition, the content of carboxyl groups in the resin composition in which polyvinyl acetal resin (C) is blended with acetal resin (A> and/or (B)) is usually 0.5 to 9% by weight.
, preferably 0.5 to 7% by weight, more preferably 2 to 7% by weight
A range of 5% by weight is desirable; if it is less than 0.5% by weight, sufficient storage stability and recording density cannot be obtained, and even if it exceeds 9% by weight, there is no significant improvement in storage stability or recording density.

Further, the content of acetal units in the resin composition in which polyvinyl acetal resin (C) is blended with acetal resin (A) and/or (B) is usually 65% by weight or more, preferably in the range of 70 to 85% by weight. If the acetal unit content is less than 65% by weight, the resin may become difficult to dissolve in organic solvents or the recorded density of images may decrease.

Furthermore, when the acetal units in the resin composition are composed of two types, acetoacetal units and butyl acetal units, in addition to the content ratio of the acetal units, the weight ratio of butyl acetal units/acetoacetal units is preferably It is desirable that the weight ratio be 2.3 or less, particularly 1.5 or less; if the weight ratio exceeds 2.3, the resin may become difficult to dissolve in organic solvents (or the recorded density of the image may decrease). There is.

Acetal resin (A) and/or (
The average degree of polymerization of the resin composition in which B) is blended with polyvinyl acetal resin (C) is not particularly limited, but is usually 2.
A range of 00 to 4,000, particularly 300 to 3,000 is preferred. When the average degree of polymerization is less than 200, the ability to retain the shape of the thermal transfer layer and fix the thermal transfer layer to the base material of the ink ribbon is weak;
If it exceeds 4,000, the solubility in organic solvents may decrease, and the viscosity of the reaction solution during the acetalization reaction may become high (thus, it is necessary to take measures such as lowering the concentration of the reaction system, which reduces the productivity of the resin. Sometimes.

Moreover, additives and the like can be added to the resin composition containing the above-mentioned polyvinyl acetal resin (C), if necessary.

Next, a binder containing the acetal resin (A) and/or (B) of the first invention, or a binder containing the acetal resin (A) and/or (B) of the second invention and a polyvinyl acetal resin (C ) A method of forming a thermal transfer layer on a base material using a binder containing the following will be described to produce a sublimation thermal transfer ink ribbon.

The thermal transfer layer containing the binder described above can be formed by applying a dye composition in which a sublimable dye, a binder, and various additives are dissolved and dispersed in an organic solvent onto a substrate and drying the composition.

The binder resin used to obtain the dye composition includes the resin containing the acetal resin (A) and/or (B) of the first invention, or the acetal resin (A) and the second invention. A resin composition containing (B) and a polyvinyl acetal resin (C) is used.

As the sublimable dye, a wide range of dyes can be used without particular limitation, and examples thereof include anthraquinone dyes, azo dyes, and methine dyes. In addition, as necessary, various additives may be used, such as mold release agents such as silicone-based, fluorine-based, or amide-based compounds, dispersants such as various surfactants, drying accelerators such as cellulose derivatives, and various extinguishers. Examples include foaming agents.

As the organic solvent, lower alcohols, esters, ketones, aromatics, aliphatic hydrocarbons, or a mixed solvent of two or more of these can be used.

Although a wide range of materials can be used as the base material without particular limitation, for example, a film of polyester, polyamide, polyimide, triacetate, etc. having a thickness of about 3 to 20 gm is suitably used.

A sublimation thermal transfer ink ribbon can be obtained by applying the above-described dye composition onto a substrate using known methods and devices such as printing and coating, and drying to form a thermal transfer layer.

The resulting thermal transfer layer preferably has a thickness of about 0.5 to 5 pm. Further, the proportion of the binder contained in the thermal transfer layer is 3 to 80% by weight, preferably 20% by weight based on the thermal transfer layer.
~50% by weight, and approximately 3~20% by weight relative to the dye.
It is about 0% by weight, preferably about 50 to 150% by weight.

[Examples] The present invention will be described below based on Examples, Comparative Examples, and Manufacturing Examples. In addition, unless otherwise specified below, "department" and "department"
%" represents parts by weight and % by weight, respectively.

Production example 1 of polyvinyl acetal 400 parts of methanol and 35% methanol in a reaction vessel equipped with a stirrer
Add 5 parts of hydrochloric acid, then add acrylamide-modified PVA
82 parts (weight part 1730, residual acetic acid groups 4.5%, acrylamide content 13.2%) were added and dispersed in the methanol containing the above hydrochloric acid while stirring. Further, 60 parts of acetaldehyde was added to this system, and an acetoacetalization reaction was carried out at a liquid temperature of 60° C. for 6 hours to obtain a viscous methanol solution of polyvinyl acetoacetal. After cooling and neutralizing this solution, water was added to this solution while stirring to perform a precipitation operation, followed by washing with water, filtration, and drying to obtain a carboxy-modified polyvinyl acetoacetal resin in the form of white powder. The properties of this resin are shown in Table 1.

Production Examples 2 to 5 and 7 to 10 Carboxy-modified polyvinyl acetoacetal resins having properties shown in Table 1 were obtained in the same manner as in Example 1 except that the production conditions were changed as shown in Table 1. In addition, Production Examples 3 and 4 are both examples using two types of carboxy-modified PVA,
Production Example 5 is an example in which acrylamide-modified PVA and non-carboxy-modified PVA were allowed to coexist in the acetalization reaction system to obtain a mixture of acetoacetal resins of these two types of PVA.

Production Example 6 A reaction was carried out in the same manner as in Production Example 1 under the production conditions shown in Table 1 to obtain a methanol solution of polyvinyl acetoacetal. Next, after cooling and neutralizing this solution, a caustic soda aqueous solution was added, and the temperature was kept at 20 to 30°C for 5 minutes.
Stirring was continued for an hour.

Thereafter, the same procedure as in Production Example 1 was performed to precipitate, wash with water, and dry to obtain a carboxy-modified polyvinyl acetoacetal resin in which the carboxyl group was in the form of a sodium salt. Its properties are shown in Table 1.

Production Example 11 400 parts of methanol and 35% methanol in a reaction vessel equipped with a stirrer
Add 5 parts of hydrochloric acid, then add acrylamide-modified PVA
82 parts (degree of polymerization: 1730, residual acetic acid groups: 4.5%, acrylamide content: 13.2%) were added and dispersed in the above-mentioned methanol containing hydrochloric acid under stirring. 30 parts of acetaldehyde and 28 parts of butyraldehyde were added to this system, and the liquid temperature was 6.
A mixed acetalization reaction using acetaldehyde and butyraldehyde was carried out at 0° C. for 6 hours to obtain a viscous acetoacetal/butyl acetal mixed polyvinyl acetoacetal resin. The properties of this resin are shown in Table 1.

Production Examples 12 to 16 Production Example 11 except that the production conditions were changed as shown in Table 1.
In the same manner as above, a carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin having the properties shown in Table 1 was obtained. In addition, Production Example 13 is an example using two types of carboxy-modified PVA, and Production Example 14 is an example using carboxy-modified PV.
This is an example in which A and non-carboxy-modified PVA were made to coexist in an acetalization reaction system to obtain a mixture of acetoacetal/butyl acetal mixed polyvinyl acetal resin of these two types of PVA.

Production Examples 17 to 19 Non-carboxy-modified polyvinyl acetal resins having the properties shown in Table 1 were obtained in the same manner as Production Example 1 except that the production conditions were changed as shown in Table 1. In addition, Production Examples 17 and 18 both use one type of PVA, and the former is an example in which a mixed acetal resin is obtained by reaction with two types of aldehydes, and the latter is an example in which an acetal resin is obtained using one type of aldehyde. be. In addition, in Production Example 19, two types of P
This is an example in which an acetal resin was obtained by reacting VA with one type of aldehyde.

Production Example 20 A carboxy-modified polyvinyl acetoacetal resin having the properties shown in Table 1 was obtained in the same manner as in Example 1 except that the production conditions were changed as shown in Table 1.

The amount of cetal units in the obtained polyvinyl acetal resin was measured in accordance with JIS K672g.

Examples 1 to 30 and Comparative Examples 1 and 2 Various polyvinyl acetal resins obtained in the ink ribbon prerecording production examples were used singly or in combination as binder wood pieces in the dye compositions below. A dye composition having the following composition was obtained. The binder resins used are shown in Table 2.

Mixture composition of dye composition Binder resin 3 parts Sublimation dye 5 parts (Sumiplus Red FB) Methyl ethyl ketone 62 parts Toluene 30 parts This dye composition was applied to one side of a 6 pm thick polyester film so that the film thickness after drying was Igm. The ink ribbon was coated by wire bar coating and dried to produce an ink ribbon.

Belly! In order to evaluate the performance of the ink ribbon obtained as described above by performing thermal transfer onto a recording paper, a recording paper having a dye-receiving layer on the surface was obtained as follows. That is, a composition for forming a dye-receiving layer having the following formulation was applied to polypropylene synthetic paper (manufactured by Tamako Yuka Co., Ltd., Yubo FPG 15) as a base sheet.
A recording paper was prepared by coating and drying a receptor layer on one side of 0) by wire bar coating so that the coated layer thickness after drying was 150 μm.

Composition of dye-receiving layer forming composition Toluene Methyl ethyl ketone Cyclohexanone 70 parts 10 parts 20 parts Ink ribbon (1) Preservability The ink ribbon obtained as described above was left in an environment at a temperature of 40" C1 and a relative humidity of 80%. The surface of the ink ribbon was then observed to determine the number of days until crystallization of the sublimable dye in the thermal transfer layer was observed.The results are shown in Table 2.

(2) Recording density Using the ink ribbon and recording paper obtained as described above,
The thermal transfer layer of the ink ribbon and the image receiving layer of the recording paper are stacked so that they are in contact with each other, and a thermal head (manufactured by Kyocera ■) [MT
Thermal transfer was performed under the following conditions using a thermal transfer printer equipped with a -85-6MPD2 (partially glazed thin film head).

Immediately after thermal transfer, the density of the image transferred and formed on the recording paper was measured using a reflection densitometer (
Macbeth Densitometer RD-918). The results are shown in Table 2.

Thermal transfer conditions: Head applied voltage: 11.2V Pulse width: 1.0-16.0m5ec Printing speed:
33.3m5ec/1ine density
= 6 pieces 7mm Platen hardness Near 0'' Platen diameter: 25mm Linear pressure: 4 kg/10cm Feeding speed: 5.0mm 7 seconds Comparative Example 3 In the blending of the dye composition used in the production of the ink ribbon in Example 1, the binder Instead of 3 parts of resin, use polyester resin (SF Primer No. 750).
, manufactured by Dainippon Ink ■, an ink ribbon was produced in the same manner as in Example 1, except that 10 parts of active ingredient 30%) and 0.5 parts of incyanate curing agent (active ingredient 20%) were used. Its storage stability and recording density were measured. The results are shown in Table 2.

Comparative Example 4 In the formulation of the dye composition used for producing the ink ribbon in Example 1, 3 parts of polyamide resin (Milpex 1000, manufactured by Henkel Hakusui, softening temperature 130 to 150°C) was used instead of 3 parts of binder resin. An ink ribbon was manufactured in the same manner as in Example 1, except that the ink ribbon was used, and its storage stability and recording density were measured. The results are shown in Table 2.

As mentioned above, as is clear from the results shown in Table 2, the ink ribbons of each example obtained using the binder for thermal transfer layer of the present invention have excellent storage stability and recording density compared to the comparative example. Recognized as excellent.

Furthermore, in each Example, the dye composition had good dispersibility, and the thermal transfer layer formed on the base material had excellent shape retention and fixing properties.

[Effects of the Invention] As explained above, the acetal resin (A) and/or (B) of the present invention, or the acetal resin (A) and/or
Alternatively, an ink ribbon for sublimation thermal transfer using a binder for a thermal transfer layer containing (B) and a polyvinyl acetal resin (C) is free from dyes in the thermal transfer layer leaching to the surface or crystallizing during storage. It has excellent storage stability, does not inhibit sublimation and diffusion of the dye when heated by a thermal head, etc., and can realize image recording with excellent recording density.

Furthermore, when obtaining a dye composition, it has the advantage of increasing the dispersibility of the dye and improving the shape retention and fixing properties of the thermal transfer layer.

Claims (6)

[Claims] (1) Carboxy-modified polyvinyl acetoacetal resin (A) and/or carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B)
) A binder for a thermal transfer layer, comprising: (2) Carboxy-modified polyvinyl acetoacetal resin (A) and/or carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B)
2. The binder for a thermal transfer layer according to claim 1, wherein the content of carboxyl groups in ) is 0.5 to 9% by weight. (3) Carboxy-modified polyvinyl acetoacetal resin (A) and/or carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B)
3. The binder for a thermal transfer layer according to claim 1, wherein the content of acetal units in ) is 65% by weight or more, and the weight ratio of butyl acetal units/acetoacetal units is 2.3 or less. (4) A sublimation thermal transfer ink ribbon comprising, on a base material, a thermal transfer layer containing a sublimable dye and the binder for a thermal transfer layer according to claim 1. (5) Carboxy-modified polyvinyl acetoacetal resin (A) and/or carboxy-modified acetoacetal/butyl acetal mixed polyvinyl acetal resin (B)
) and a polyvinyl acetal resin (C) having no carboxyl group. (6) A sublimation thermal transfer ink ribbon comprising, on a base material, a thermal transfer layer containing a sublimable dye and the binder for a thermal transfer layer according to claim 5.