JP2008285513A - Method for producing polyvinyl acetoacetal, polyvinyl acetoacetal produced by using the method, heat transfer layer binder using the polyvinyl acetoacetal and heat transfer ink ribbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for producing polyvinyl acetoacetal. <P>SOLUTION: The method for producing a polyvinyl acetoacetal, in which the weight ratio of a cis type vinyl acetoacetal part/a trans type vinyl acetoacetal part in the acetoacetal part of a polyvinyl acetoacetal is 1-4, comprises an acetalization reaction process of effecting an acetalization reaction between a polyvinyl alcohol and acetaldehyde in a water solvent in a reactor, a reaction product discharge process of discharging a reaction product from the reactor after the attainment of the acetoacetalization degree of the formed polyvinyl acetoacetal to at least 11 wt.% and an aging reaction process of subjecting the discharged reaction product to an aging reaction in a reactor different from the above reactor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing polyvinyl acetoacetal. More specifically, a polyvinyl acetoacetal production method in which the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part in the acetoacetal part of polyvinyl acetoacetal is 1 to 4, and polyvinyl aceto produced using the method The present invention relates to an acetal, a thermal transfer layer binder using the polyvinyl acetoacetal, and a thermal transfer ink ribbon.

  Polyvinyl acetoacetal is produced by acetalizing polyvinyl alcohol with acetaldehyde in the presence of an acidic catalyst. As a method for acetalizing polyvinyl alcohol, there are mainly methods such as a water medium method, a solvent method, and a homogenization method.

  The “aqueous medium method” refers to, for example, dissolving polyvinyl alcohol in hot water, keeping the obtained aqueous solution at a relatively low temperature of 20 ° C. or less, and adding an acid catalyst and an aldehyde to the acetalization reaction. In this method, the reaction temperature is increased and the reaction temperature is raised and ripened at a high temperature of 40 ° C. or higher to complete the reaction, and then neutralization, washing with water, dehydration and drying are performed.

  The “solvent method” refers to, for example, suspending a polyvinyl alcohol powder in a solvent such as methanol, adding an aldehyde in the presence of an acid catalyst, and dissolving the reaction product in the solvent as the acetalization proceeds. This is a method in which the reaction is carried out in the system, neutralized after the completion of the reaction, water is added and precipitated, and finally, washing, dehydration and drying are performed.

  “Homogenization method” refers to, for example, adding an aldehyde to a polyvinyl alcohol aqueous solution in the presence of a catalyst to start an acetalization reaction, and adding a water-compatible polyvinyl acetal resin solvent before precipitation. In this method, the reaction is carried out in a homogeneous system from beginning to end while preventing precipitation, and after the completion of the reaction, neutralization is performed, water is added to cause precipitation, and finally, washing, dehydration and drying are performed.

  The polyvinyl acetoacetal obtained by the method as described above is used for a wide range of applications such as paints, adhesives, binders, formed bodies, etc., but in accordance with each application, polyvinyl acetoacetal having physical properties as required should be used. Is desirable. As an example, the polyvinyl acetoacetal used for a binder is demonstrated below.

  The binder refers to a kind of binder and has various uses. For example, it is used for a thermal transfer ink ribbon. The thermal transfer ink ribbon is used for image recording by a sublimation thermal transfer method. Image recording by the sublimation thermal transfer system is a recording paper having a thermal transfer layer surface of a thermal transfer ink ribbon having a thermal transfer layer containing a sublimable dye, a binder, etc. on a substrate, and a dye receiving layer on a substrate sheet. In the state where the receiving layer surfaces are in contact with each other, the thermal transfer ink ribbon is sublimated by applying thermal energy to the thermal transfer ink ribbon by a thermal head or laser whose temperature is controlled based on the image signal. This is done by transferring the dye sublimated from the thermal transfer layer to the receiving layer of the recording paper.

  In this sublimation thermal transfer system, the amount of thermal energy applied to the thermal transfer layer of the thermal transfer ink ribbon is changed according to the change of the image signal by a TV, CRT color display, color facsimile, magnetic camera, digital camera, etc. By changing the amount of dye sublimated and transferred from the toner, it is possible to obtain an image record having good gradation on the receiving layer of the recording paper. In addition, in the case of thermal transfer, if each color is transferred onto the same receiving layer surface of the recording paper using three types of thermal transfer ink ribbons each containing one of the three primary colors of yellow, magenta, and cyan in the thermal transfer layer, a full color Image recording can also be performed.

  However, many thermal transfer layers of thermal transfer ink ribbons used in conventional sublimation thermal transfer methods have problems with storage stability and recording density. For example, conventional thermal transfer ink ribbons are prone to erosion and crystallization of dyes contained in the thermal transfer layer, and thus have low storage stability. In addition, the tendency of dye leaching and crystallization to occur causes the recording density to decrease and the recording density spots to occur.

  In order to solve such problems, Patent Document 1 discloses that the thermal transfer layer binder has a specific structure of acetoacetal degree of 87% by weight or more and cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal in the acetoacetal part. A technique for including polyvinyl acetoacetal having a weight ratio of 1 to 4 is proposed.

  Although the storage stability has been improved by using this polyvinyl acetoacetal as a binder for the thermal transfer layer, since this polyvinyl acetoacetal is produced using a solvent method, a large amount of organic solvent is required for the production of polyvinyl acetoacetal. Therefore, further development has been expected for the manufacturing method, such as the need for a recovery step of the organic solvent and the odor caused by the organic solvent.

  As a technique relating to a method for producing polyvinyl acetoacetal, for example, Patent Document 2 discloses a polyvinyl acetal resin that is excellent in washing and removing metal components remaining in a resin and has little adhesion to production equipment over a long period of time. A method for stable production is disclosed.

  Patent Document 3 discloses a method for producing a polyvinyl acetal-based resin in which the produced particles hardly aggregate, and Patent Document 4 discloses a method for producing a polyvinyl acetal resin having excellent adhesion used for an interlayer film for laminated glass. Reference 5 discloses a method for producing a polyvinyl acetal resin having a high degree of acetalization of about 80 mol% or more.

Japanese Patent No. 3065111. Japanese Patent Application Laid-Open No. 2004-217764. Japanese Patent Application Laid-Open No. 2002-069127. JP 2000-001514 A. JP-A-6-228227.

  The main object of the present invention is to provide a novel production method capable of obtaining a polyvinyl acetoacetal that can be suitably used for a thermal transfer layer binder without using an organic solvent.

  As a result of intensive studies on a method for producing polyvinyl acetoacetal using a water medium method, the present inventors can obtain polyvinyl acetoacetal that can be suitably used for a thermal transfer layer binder without using an organic solvent. A new manufacturing method has been found.

  In the present invention, first, an acetalization reaction step of advancing the acetalization reaction of polyvinyl alcohol and acetaldehyde in an aqueous solvent in a reactor, and after the degree of acetoacetalization of the produced polyvinyl acetoacetal reaches at least 11% by weight By passing at least a reactant discharge step of discharging the reactant from the reactor and an aging reaction step of aging the discharged reactant in a reactor different from the reactor, the polyvinyl acetoacetal Provided is a method for producing polyvinyl acetoacetal in which the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part in the acetoacetal part is 1 to 4.

  In the present invention, in addition to the control of the weight ratio of the cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part described above, at least the acetalization reaction step, the reactant discharge step, and the aging reaction step are passed. Provides a method for producing polyvinyl acetoacetal that can increase the degree of acetoacetalization of polyvinyl acetoacetal to 87 wt% or more.

  The polyvinyl acetoacetal produced by using the production method according to the present invention can be used for a wide variety of applications. For example, it can be suitably used as a thermal transfer layer binder.

  The thermal transfer layer binder can be suitably used for a thermal transfer ink ribbon. Specifically, a thermal transfer ink ribbon having a substrate and a thermal transfer layer laminated on at least one surface of the substrate, the sublimation dye and the thermal transfer layer binder being included in the thermal transfer layer. Can do.

  The polyvinyl acetoacetal production method according to the present invention can obtain polyvinyl acetoacetal that can be suitably used as a thermal transfer layer binder, although no organic solvent is used. Moreover, since the polyvinyl acetoacetal manufacturing method which concerns on this invention does not use an organic solvent, the process of collect | recovering the used organic solvent is unnecessary, and can reduce a effort and cost.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments for carrying out the invention will be described with reference to the drawings. In addition, embodiment described below shows an example of typical embodiment of this invention, and, thereby, the range of this invention is not interpreted narrowly.

<About the production method of polyvinyl acetoacetal>
The method for producing polyvinyl acetoacetal according to the present invention will be described with reference to FIG. FIG. 1 is a flowchart of the method for producing polyvinyl acetoacetal according to the present invention.

  The method for producing polyvinyl acetoacetal according to the present invention is roughly divided into an acetalization reaction step (I), a reactant discharge step (II), and an aging reaction step (III). Hereinafter, each process will be described in detail.

(I) Acetalization reaction step In the acetalization reaction step (I), polyvinyl alcohol and acetaldehyde are acetalized in a reactor. At this time, it is one of the features of the present invention that the acetal reaction proceeds in an aqueous solvent. As described above, in the method for producing polyvinyl acetoacetal according to the present invention, since no organic solvent is used, a step of recovering the used organic solvent is unnecessary, and labor and cost can be reduced.

  In the solvent method, the aldehyde is concentrated and reduced in a solvent such as methanol, and due to the quality variation of the solvent, the precipitation is unstable and the particle shape varies. In the present invention, the aldehyde is consumed in the reaction. Therefore, purification after the reaction is easy, the reaction system is stable, and a stable fine powder having a small primary particle shape can be produced.

  By generating a stable fine powder having a small primary particle shape, the porosity of the finally obtained polyvinyl acetoacetal can be increased. That is, porous polyvinyl acetoacetal can be produced. Porous polyvinyl acetoacetal has an advantage of excellent detergency such that, for example, impurities such as salts taken into the resin during polymerization can be easily washed.

  In the acetalization reaction step (I), the type of the raw material polyvinyl alcohol is not particularly limited, and a wide range of materials can be used. Examples thereof include those obtained by completely or partially saponifying one or two or more polymers of fatty acid vinyl esters such as vinyl acetate, vinyl formate, and vinyl propionate.

  Further, a saponified product of a copolymer obtained by copolymerizing a fatty acid vinyl ester and another monomer copolymerizable with the fatty acid vinyl ester within a range not hindering the present invention, or polyvinyl alcohol is post-modified. The post-modified product obtained in this way can be used as the raw material polyvinyl alcohol.

  Furthermore, the raw material polyvinyl alcohol used in the present invention can be used in combination by a method in which two or more kinds of polyvinyl alcohols having different average polymerization degree, saponification degree, or structural unit are allowed to coexist in the acetoacetalization reaction system. From the economical aspect, polyvinyl alcohol obtained by saponifying a vinyl acetate polymer is more preferable.

  In the acetalization reaction step (I), the type of raw material acetaldehyde is not particularly limited, and ordinary ones can be used. The quality is not particularly limited, and an industrial product is sufficient.

  The amount of acetaldehyde used is preferably 42 to 100 parts by weight, more preferably 50 to 90 parts by weight with respect to 100 parts by weight of polyvinyl alcohol.

  When the amount exceeds 100 parts by weight, the reaction rate is greatly increased, and it is difficult to control the weight ratio of cis-type vinyl acetoacetal / trans-type vinyl acetoacetal and the degree of acetoacetalization, making it difficult to obtain polyvinyl acetoacetal having the desired properties. In addition, since a large amount of unreacted acetaldehyde remains, there is a concern about the influence on the product odor. Conversely, at 42 parts by weight or less, since the amount of acetaldehyde is small, it is difficult to increase the degree of acetoacetalization.

  The acetalization reaction step (I) is preferably performed in the presence of an acid catalyst as necessary. In the acetalization reaction step (I) of the present invention, the type of acid catalyst suitable for use is not particularly limited. For example, hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, citric acid, paratoluenesulfonic acid, etc. can be used alone or in combination of two or more. These acid catalysts are preferably added in an appropriate amount so that the pH of the reaction solution is generally 0.3 to 2.0.

  Each raw material in the acetalization reaction step (I) and the method for supplying the acid catalyst are not particularly limited. For example, (1) a method of supplying three types from separate supply ports, (2) a method of previously mixing an aqueous polyvinyl alcohol solution and an acid catalyst, and supplying this mixed solution and acetaldehyde from separate supply ports, (3) A method of previously mixing an aqueous polyvinyl alcohol solution and acetaldehyde and supplying the mixed solution and the acid catalyst from separate supply ports can be employed. Among these methods, the methods (1) and (2) are preferable from the viewpoint of reaction efficiency.

Although the form of the reactor for carrying out the acetalization reaction step (I) is not particularly limited, a tank reactor such as a tank reactor or a tube reactor is preferable. In order to react each raw material and the acid catalyst in a uniform field, the reactor is preferably provided with a stirring blade. In this case, the stirring conditions are preferably such that the stirring power per unit volume is 0.4 kw / m ³ or more. It is for expressing sufficient mixing and stirring.

  Any known stirring blade can be used as the stirring blade. For example, three retreat wings, paddle wings, anchor wings, max blend wings, full zone wings, and the like can be used. From the viewpoint of sufficiently achieving mixing, it is particularly preferable to use so-called large wings such as Max Blend wings and full zone wings.

  When the acetalization reaction step (I) is performed, if there are voids in the reactor, the precipitation of polyvinyl acetoacetal formed by the reaction at the interface between the voids and the liquid surface may occur. Then, the precipitation of polyvinyl acetoacetal causes problems such as clogging the discharge port of the reactor or increasing dirt in the reactor. In order to prevent such harmful effects, the reactor is preferably filled with water in advance. By adopting a method of supplying each raw material and the acid catalyst in a state where water is filled, generation of voids in the reactor can be prevented. In order to prevent the generation of voids, it is more preferable to use a full liquid reactor as the reactor.

  The reaction temperature in the acetalization reaction step (I) is preferably 20 to 50 ° C, more preferably 30 to 50 ° C. If the reaction temperature is less than 20 ° C., the progress of the reaction is considered to be relatively slow. On the contrary, when the reaction temperature is high, it is considered that polymer adhesion tends to occur in the tank reactor.

(II) Reactant discharge step Reactant discharge step of discharging the reactant from the reactor after the acetoacetal degree of the polyvinyl acetoacetal produced in the acetalization reaction step (I) reaches at least 11% by weight (II )I do. In the reactant discharge step (II), the reason for discharging the reactant after the degree of acetoacetalization reaches at least 11% by weight is to obtain porous polyvinyl acetoacetal. Porous polyvinyl acetoacetal has an advantage of excellent detergency such that, for example, impurities such as salts taken into the resin during polymerization can be easily washed.

  In the reactant discharge process (II), the surface of the pipe and the welded part of the reactor and the inner wall of the pipe are smooth so that the reactant does not stagnate locally or macroscopically in the vicinity of the reactor outlet or in the pipe. It is preferable to use what carried out.

  Both the acetalization reaction step (I) and the reactant discharge step (II) are preferably performed continuously. This is because the reactor is always filled with the reaction solution. The following specific method can be given as an example for smoothly proceeding with both steps. For example, (1) a method in which raw material is introduced from the upper part of the reactor and continuously discharged from the lower part of the reactor, and (2) a raw material is supplied from the upper part of the reactor to the lower lower layer of the reactor using an insertion tube. A suitable method is a method of continuously discharging from the upper part, (3) a method of supplying raw materials from the lower part of the reactor, and continuously discharging from the upper part of the reactor.

(III) Aging reaction step The reaction product discharged from the reactor in the discharging step (II) is transferred to another reactor to perform an aging reaction. The aging reaction temperature is in the range of room temperature to 60 ° C., preferably 40 to 60 ° C., and the reaction time is set so as to reach and complete the desired degree of acetoacetalization. Usually, it is set within a range of 1 to 12 hours, preferably 1 to 10 hours.

  The aging step (III) is performed in a reactor different from the reaction step (I). This is because the degree of acetalization of the resulting polyvinyl acetoacetal can be increased by carrying out the aging reaction in a separate vessel compared to the case where the acetalization reaction is advanced in a single-stage reactor (Comparative Example described later). 2). Thus, in the present invention, in the ripening step (III), the final polyvinyl acetoacetal can be increased to the target degree of acetalization (for example, 87% by weight or more).

  The aging reaction product obtained through the aging reaction step (III) is acidic due to the acid catalyst. In order to neutralize this reaction product, an alkali neutralizing agent such as sodium hydroxide or sodium bicarbonate is added. Usually, the pH is adjusted to 7-11.

  Then, the neutralized reaction product is dehydrated, washed with water and dried to obtain the intended polyvinyl acetoacetal. The dehydration method, the water washing method, and the drying method are not particularly limited, and can be performed by a general method.

<About polyvinyl acetoacetal>
The polyvinyl acetoacetal produced using the method for producing polyvinyl acetoacetal according to the present invention can obtain a polyvinyl acetoacetal that can be suitably used for a thermal transfer layer binder, although no organic solvent is used. .

  The acetoacetalized portion of the polyvinyl acetoacetal according to the present invention is composed of an acetoacetalized portion having two stereoisomeric structures, that is, a cis-type vinyl acetoacetal portion and a trans-type vinyl acetoacetalized portion, In order to use it suitably for the thermal transfer layer binder, in the present invention, the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part is set to 1 to 4. It is because heat resistance will fall when a weight ratio exceeds four. A more preferred weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part is 1 to 3.

  The measurement of the weight ratio of the cis-type vinyl acetoacetal moiety and the trans-type vinyl acetoacetalized moiety can be performed by nuclear magnetic resonance (NMR) spectrum. For example, the CH group signal contained in the cis-type vinyl acetoacetal moiety is detected near 98 ppm on the 13C-NMR measurement spectrum, and the CH group signal of the trans-type vinyl acetoacetal moiety is detected around 92 ppm. Since the difference in each signal is the difference in CH group content, the weight ratio of the cis-acetoacetalized portion to the cis-type vinylacetoacetal portion and trans-type vinylacetoacetal portion is the signal ratio on the 13C-NMR measurement spectrum, That is, it is represented by an area ratio.

  A specific method for calculating the weight ratio will be described with reference to FIGS. FIG. 2 is a partially enlarged view of the 13C-NMR spectrum of polyvinyl acetoacetal of Example 1 described later, and FIG. 3 is an explanatory diagram for calculating the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part. It is.

  The weight ratio of the cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part is expressed by the area ratio of the cis-type signal and the trans-type signal. Specifically, as shown in FIG. 3, assuming that each signal is a triangle, the height of the signal is H, and the length of the base is L, the cis-type signal area Ac is 1/2 × Hc × Lc, The trans-type signal area At is ½ × Ht × Lt. The weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part can be obtained from Ac / At, that is, Hc · Lc / Ht · Lt.

  One of the characteristics of the polyvinyl acetoacetal produced using the method for producing polyvinyl acetoacetal according to the present invention is that it has a high degree of acetoacetalization in addition to the above physical properties, even though no organic solvent is used. . The degree of acetoacetalization is not particularly limited, but the degree of acetoacetal is preferably 87% by weight or more in order to be suitably used for a thermal transfer ink ribbon described later. This is to improve the storage stability and recording density of the thermal transfer ink ribbon.

  Moreover, since the polyvinyl acetoacetal which concerns on this invention does not use the organic solvent in the process of the manufacture, there is no generation | occurrence | production of the odor resulting from a residual solvent, and it is advantageous also in an environmental aspect.

Furthermore, since the polyvinyl acetoacetal which concerns on this invention uses the manufacturing method mentioned above, the particle shape is a fine powder shape (average particle diameter of 0.5-2.5 micrometers), and porosity (porosity, porosity, porosity) ) Is also expensive. That is, since it is porous (specific surface area 1.5 to 3.5 m ² / g), it is excellent in washing and removing salts and the like, and has a low residual salt concentration.

  Here, the portions other than the acetalized portion of the polyvinyl acetoacetal according to the present invention are a vinyl alcohol unit derived from a raw material polyvinyl alcohol, a fatty acid vinyl ester unit, or the like. In addition, when the raw material polyvinyl alcohol is a saponified product of a copolymer with a fatty acid vinyl ester, or a post-modified product of polyvinyl alcohol, it is copolymerized in addition to the above two units. It also encompasses units derived from other monomers or post-modifications.

  The part of the vinyl alcohol unit in the polyvinyl acetoacetal according to the present invention is 12% by weight or less, preferably 5 to 12% by weight. This is because if the number of vinyl alcohol units in the polyvinyl acetoacetal is large, the properties of the ink ribbon are adversely affected, for example, the storage stability of the resulting ink ribbon is poor.

  Further, the fatty acid vinyl ester unit portion may be present in an amount of about 3% by weight or less. Further, the portion of the unit derived from the copolymer and post-modification is 8% by weight or less, preferably 5% by weight or less. This is because if the number of fatty acid vinyl ester units in the polyvinyl acetoacetal is large, the properties of the ink ribbon are adversely affected, such as poor storage stability of the ink ribbon obtained.

  The average degree of polymerization of the polyvinyl acetoacetal according to the present invention is not particularly limited, but is usually in the range of 200 to 4000, particularly 300 to 3000. If the average degree of polymerization is less than 200, the shape of a thermal transfer layer, which will be described later, is retained, and the force for fixing the thermal transfer layer to the base material of the ink ribbon becomes weak. Conversely, when the average degree of polymerization exceeds 4000, the solubility in organic solvents decreases.

<About thermal transfer layer binder>
The polyvinyl acetoacetal manufactured using the manufacturing method according to the present invention can be suitably used for a thermal transfer layer binder.

  Various additives and the like can be added to the thermal transfer layer binder of the present invention as necessary. Also, known polyvinyl acetals (for example, acetacetal / butyl acetal mixed polyvinyl acetal, form acetal / acetoacetal / butyl acetal mixed polyvinyl acetal, polyvinyl butyl acetal, etc.) or a combination resin thereof can be added as a binder resin. . The amount of these resins added is preferably 30% by weight or less, more preferably 15% by weight or less. This is because when the amount of the binder resin added is large, the viscosity becomes high, which causes a problem such as poor handling.

  The polyvinyl acetoacetal used for the thermal transfer layer binder according to the present invention is characterized by a high degree of acetoacetal. In particular, it is preferably 87% by weight or more. This is because the higher the degree of acetoacetation, the lower the hydrophilicity and the better the solubility in a solvent. In addition, the higher the degree of acetoacetalization, the better the compatibility with the solvent, and the merit of improving the storage stability and recording density of the thermal transfer ink ribbon described later is also produced.

  Moreover, the polyvinyl acetoacetal used for the thermal transfer layer binder according to the present invention is porous. Porous polyvinyl acetoacetal has good organic solvent absorbability, and can improve the solubility and mixing at the time of producing the thermal transfer layer binder. Further, with the improvement in solubility, there is a merit that the dissolution time is shortened.

<Thermal transfer ink ribbon>
The thermal transfer layer binder can be suitably used for a thermal transfer ink ribbon. Specifically, the sublimation dye and the thermal transfer layer binder can be contained in the thermal transfer layer of the thermal transfer ink ribbon having a base material and a thermal transfer layer laminated on at least one surface of the base material.

  The thermal transfer ink ribbon according to the present invention is a method for printing a dye composition in which a sublimable dye, a thermal transfer layer binder, and various additives are dispersed in an organic solvent using a known method and apparatus such as printing and coating. It can be formed by coating and drying to form a thermal transfer layer.

  The sublimable dye is not particularly limited, and a wide range of dyes can be used. For example, anthraquinone series, azo series, methine series dyes and the like can be mentioned. Moreover, the various additives used as needed are not particularly limited. For example, mold release agents such as silicon-based, fluorine-based, and amide-based compounds, dispersants such as various surfactants, drying accelerators such as cellulose derivatives, and various antifoaming agents.

  The organic solvent is not particularly limited. For example, lower alcohols, esters, ketones, aromatics, aliphatic hydrocarbons, or a mixed solvent of two or more of these can be used.

  The substrate is not particularly limited, and a wide range of substrates can be used. For example, a film of polyester, polyamide, polyimide, triacetate or the like having a thickness of about 3 to 20 microns can be suitably used.

  The thermal transfer layer forming the thermal transfer ink ribbon according to the present invention preferably has a thickness of about 0.5 to 5 microns. This is because if the thermal transfer layer is too thin, the print becomes thin, and if it is too thick, a clear print cannot be obtained.

  The ratio of the thermal transfer layer binder contained in the thermal transfer layer is about 3 to 80% by weight, preferably about 20 to 50% by weight, based on the thermal transfer layer. Furthermore, the ratio to the dye is about 3 to 200% by weight, preferably about 50 to 150% by weight. This is for obtaining good printability.

  Since the thermal transfer ink ribbon according to the present invention contains the thermal transfer layer binder using the polyvinyl acetoacetal according to the present invention, the dye in the thermal transfer layer is stored without being eroded or crystallized on the surface during storage. Excellent in properties. In addition, it is possible to realize image recording with an excellent recording density without inhibiting dye sublimation and divergence when heated by a thermal head or the like. Furthermore, when obtaining a dye composition, it has the advantage of improving the dispersibility of the dye and improving the shape retention and fixing properties of the thermal transfer layer.

  Hereinafter, typical examples according to the present invention will be described with reference to comparative examples.

<Production of polyvinyl acetoacetal>
The polyvinyl acetoacetal of Examples 1-5 and Comparative Examples 1-4 was manufactured with the method described below.

Example 1
First, 900 g of pure water, 100 g of polyvinyl alcohol having an average polymerization degree of 2410, and a saponification degree of 98 mol% were put into a 3 L dissolution tank equipped with a stirrer and heated to obtain a polyvinyl alcohol aqueous solution.

  Next, a cylindrical glass container having a capacity of 200 ml having three supply ports at the bottom and one discharge port at the top was prepared. The cylindrical glass container was filled with pure water, and the internal temperature was maintained at 40 ° C. while stirring at 400 rpm with an anchor blade.

  While continuing stirring with an anchor blade at an internal temperature of 40 ° C., the 10 wt% polyvinyl alcohol aqueous solution prepared above, 35 wt% hydrochloric acid and acetaldehyde as the acid catalyst, and the polyvinyl alcohol aqueous solution feed rate at 60 g / hr, hydrochloric acid It introduced from the lower part of the cylindrical glass container so that it might become 30 weight part and 70 weight part of acetaldehyde, and the acetalization reaction was performed in the cylindrical glass container.

  After the degree of acetoacetalization of the produced polyvinyl acetoacetal has reached at least 11% by weight, while introducing an aqueous polyvinyl alcohol solution, hydrochloric acid, and acetaldehyde from the bottom of the cylindrical glass container, in parallel, from the top of the cylindrical glass container The reaction solution was drained. When the liquid discharged from the cylindrical glass container was collected and measured, the degree of acetoacetalization at the outlet of the cylindrical glass container was 40% by weight.

  The discharged reaction solution was sent to a 2 L aging tank having a stirring blade with three receding blades (transfer amount: 1 L), and 140 parts of 35 wt% hydrochloric acid was added. Thereafter, an aging reaction was carried out in the aging tank at 60 ° C. and a rotational speed of 250 rpm for 8 hours to increase the degree of acetoacetalization to 87.8% by weight.

  Thereafter, an aqueous sodium hydroxide solution was added to the reaction solution after aging, and the pH was adjusted to 7.5 to stop the acetoacetalization reaction. After the neutralized reaction solution was cooled to room temperature, it was dehydrated to a water content of 45% by weight with a centrifuge. Thereafter, 10 times the amount of pure water was added to the resin to dilute, and the mixture was stirred at room temperature for 30 minutes and washed with water.

  This dehydration and water washing operations were repeated twice, and then again dehydrated and dried to obtain a white powder of polyvinyl acetoacetal.

(Example 2)
Polyvinyl acetoacetal was obtained using the same method as in Example 1 except that the reaction temperature in the cylindrical glass container was 50 ° C. and the aging reaction temperature was 55 ° C.

(Example 3)
A polyvinyl acetoacetal was obtained in the same manner as in Example 1 except that polyvinyl alcohol having an average polymerization degree of 1700 and a saponification degree of 98.4 mol% was used as the raw material polyvinyl alcohol.

Example 4
A polyvinyl acetoacetal was obtained in the same manner as in Example 1 except that polyvinyl alcohol having an average polymerization degree of 600 and a saponification degree of 98.2 mol% was used as the raw material polyvinyl alcohol.

(Example 5)
Polyvinyl acetoacetal was obtained in the same manner as in Example 1 except that the reaction temperature in the cylindrical glass container was 10 ° C.

(Comparative Example 1)
A reactor equipped with a stirrer and a reflux condenser was charged with 520 parts of methanol and 15 parts of 35% hydrochloric acid, and 100 parts of polyvinyl alcohol having an average polymerization degree of 2430 and a saponification degree of 98 mol% were added with stirring. Next, 125 parts of acetaldehyde was added thereto and reacted at a temperature of 60 ° C. for 6 hours to obtain a methanol solution of polyvinyl acetoacetal.

  After cooling the obtained methanol solution and neutralizing with ethylene oxide, water was added with stirring to perform the precipitation operation, washing with water and drying to obtain a white powdery polyvinyl acetoacetal.

(Comparative Example 2)
1200 parts of pure water was put in the reactor, and 100 parts of polyvinyl alcohol used in Example 1 was added thereto and dissolved by heating. After dissolution, the internal temperature of the reactor was maintained at 30 ° C., and 30 parts by weight of 35% by weight hydrochloric acid and 70 parts of acetaldehyde were gradually added to carry out an acetoacetalization reaction to precipitate a white powder of polyvinyl acetoacetal. . Thereafter, 140 parts by weight of 35% by weight hydrochloric acid was added to the same reactor, and the aging reaction was carried out for 8 hours at a reactor internal temperature of 60 ° C. After the aging reaction, filtration, washing and drying were performed in the same manner as in Example 1 to obtain polyvinyl acetoacetal.

(Comparative Example 3)
In a reactor equipped with a stirrer and a reflux condenser, 520 parts of methanol and 2 parts of 35% hydrochloric acid were charged, and 100 parts of polyvinyl alcohol having an average polymerization degree of 2430 and a saponification degree of 98 mol% were added with stirring. Next, 225 parts of acetaldehyde was added thereto and reacted at a temperature of 60 ° C. for 6 hours to obtain a methanol solution of polyvinyl acetoacetal. After cooling this solution and neutralizing with ethylene oxide, water was added with stirring to perform the precipitation operation, followed by washing with water and drying to obtain a white powdery polyvinyl acetoacetal.

(Comparative Example 4)
A reactor equipped with a stirrer and a reflux condenser was charged with 520 parts of methanol and 15 parts of 35% hydrochloric acid, and 100 parts of polyvinyl alcohol having an average polymerization degree of 2430 and a saponification degree of 98 mol% were added with stirring. Next, 300 parts of acetaldehyde was added thereto and reacted at a temperature of 60 ° C. for 1 hour to obtain a methanol solution of polyvinyl acetoacetal. After cooling this solution and neutralizing with ethylene oxide, water was added with stirring to perform the precipitation operation, followed by washing with water and drying to obtain a white powdery polyvinyl acetoacetal.

<Measurement of weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part of acetoacetal part>
The 13C-NMR spectra of the polyvinyl acetoacetal obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were measured, and the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part was calculated.

The 13C-NMR measurement was performed under the conditions shown in Table 1 below.

  Each measured value is shown in FIG. As shown in FIG. 4, the weight ratio of the cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part of the acetoacetal part of the polyvinyl acetoacetal part produced using the method for producing polyvinyl acetoacetal according to the present invention is 1 to It was confirmed that it was within the range of 4.

<Measurement of degree of acetoacetalization>
The measurement of the degree of acetoacetalization of the polyvinyl acetoacetal obtained in Examples 1 to 5 and Comparative Examples 1 to 4 was performed according to the following procedure.

Ｓ：ポリビニルアセトアセタールの質量（ｇ）
Ｐ：純分（％）
Ｆ：０．１水酸化ナトリウム溶液の力価 About 0.4 g of each polyvinyl acetoacetal obtained in Examples 1 to 5 and Comparative Examples 1 to 4 was weighed into a conical triangular flask, and 10 mL of butyl alcohol was added and dissolved. 10 mL of 1N hydroxylamine hydrochloride solution was added with shaking, and a condenser was attached and heated on a water bath for 60 minutes. Thereafter, the mixture was sufficiently cooled, 10 mL of methyl alcohol was added with shaking, and the liberated hydrochloric acid was titrated with 0.1N sodium hydroxide solution using bromophenol blue as an indicator, and the titration amount was set to a mL. Separately, a blank test was performed. The titration amount of the 0.1N sodium hydroxide solution required for the blank test was set to b mL, and the degree of acetoacetalization (% by weight) was calculated by the following formula 1.

S: Mass of polyvinyl acetoacetal (g)
P: Pure (%)
F: Potency of 0.1 sodium hydroxide solution

  Each measured value is shown in FIG. As shown in FIG. 4, it was confirmed that all the acetoacetalization degrees of the polyvinyl acetoacetal produced using the method for producing polyvinyl acetoacetal according to the present invention showed a high acetoacetalization degree of 85% by weight or more. This is a value equivalent to the polyvinyl acetoacetal of Comparative Example 1 produced using an organic solvent.

<Manufacture of ink ribbons>
A dye composition was obtained using the polyvinyl acetoacetals of Examples 1 to 5 and Comparative Examples 1 to 4 obtained above as binders in the dye compositions shown in Table 2 below.

  The obtained dye composition was applied to one side of a 6 micron thick polyester film by wire bar coating so that the thickness after drying was 1 micron and dried to obtain an ink ribbon.

<Preparation of recording paper>
In order to evaluate the performance of the ink ribbon obtained above by performing thermal transfer on the recording paper, a recording paper having a dye receiving layer on the surface was prepared. The composition for forming a dye-receiving layer having the composition shown in Table 3 is applied to one side of a polypropylene synthetic paper (FPG 150 manufactured by YUPO CORPORATION) as a base sheet so that the coating layer thickness after drying is 150 microns. Then, a receiving layer was formed by applying and drying by wire bar coating to prepare a recording paper.

<Evaluation of ink ribbon>
As the evaluation of the ink ribbon, the following (1) storage stability and (2) recording density were examined. Each evaluation method will be described.

(1) Preservability The ink ribbon obtained above was left in an environment at a temperature of 40 ° C. and a relative humidity of 80%, and the surface of the ink ribbon was observed. Then, the number of days until crystallization of the sublimation dye in the thermal transfer layer was observed was examined. The results are shown in FIG.

(2) Recording density Using the ink ribbon and the recording paper obtained above, the thermal transfer layer of the ink ribbon and the receiving layer of the recording paper are stacked so as to contact each other, and a thermal transfer printer equipped with a thermal head is used. Thermal transfer was performed under the conditions described above.

  Immediately after the thermal transfer, the density of a portion corresponding to an energization pulse width of 14 msec of the image transferred and formed on the recording paper was measured using a reflection densitometer. The results are shown in FIG.

  As shown in FIG. 4, the ink ribbons (Examples 1 to 5) using polyvinyl acetoacetal having a cis / trans weight ratio of 1 to 4 in the acetoacetal portion have an cis / trans weight ratio of 5.7. It was confirmed that both the storage stability and the recording density were superior to the ink ribbons using the polyvinyl acetoacetal of Examples 3 and 4.

  Further, as shown in FIG. 4, the ink ribbons (Examples 1 to 4) using polyvinyl acetoacetal having an acetoacetal degree of 87% by weight or more use the polyvinyl acetoacetal of Comparative Examples 2 to 4 of 87% by weight or less. It was confirmed that both the storage stability and the recording density were superior to the ink ribbon.

  Furthermore, referring to the results of Comparative Example 1, the production method according to the present invention was performed even though the cis / trans ratio was in the range of 1 to 4 and the degree of acetoacetalization was 87% by weight or more. It can be confirmed that both the storage stability and the recording density are inferior to those of the ink ribbon using the polyvinyl acetoacetal produced by using the same. This is thought to be because, in the production method of Comparative Example 1, an organic solvent is used at the time of polymerization, so that the porosity of the resin obtained is smaller than that in the production method using the aqueous solvent according to the present invention. . That is, if the porosity of the resin is small, the unreacted aldehyde remaining in the resin cannot be sufficiently washed, so that the residual aldehyde is considered to adversely affect the storage stability and recording density of the ink ribbon.

  On the other hand, in the production method according to the present invention, a water-based solvent is used in place of the organic solvent, and the method of increasing the porosity such as performing the reactant discharge step is performed, so that porous polyvinyl acetoacetal can be obtained. it can. Therefore, since the unreacted aldehyde can be sufficiently removed by washing the unreacted aldehyde remaining in the resin, it is possible to prevent the storage stability and recording density of the ink ribbon from being lowered by the remaining aldehyde.

  From the above, the thermal transfer ink ribbon having the polyvinyl acetoacetal manufactured by the manufacturing method according to the present invention has excellent storage stability without causing the dye in the thermal transfer layer to penetrate or crystallize during storage. It has been found that image recording with excellent recording density can be realized without hindering dye sublimation and divergence when heated by a thermal head or the like.

  In each of Examples 1 to 5, the dye dispersibility was good when obtaining the dye composition, and the thermal transfer layer formed on the substrate was excellent in shape retention and fixing properties.

  As described above, the method for producing polyvinyl acetoacetal according to the present invention can control the cis / trans weight ratio in the acetoacetal part of polyvinyl acetoacetal to 1 to 4 in spite of not using an organic solvent. it can. Therefore, the polyvinyl acetoacetal manufactured using the manufacturing method which concerns on this invention can be used suitably for a thermal transfer layer binder.

  Moreover, although the polyvinyl acetoacetal manufacturing method which concerns on this invention does not use the organic solvent, it can raise the acetoacetalization degree to a high value. Therefore, the polyvinyl acetoacetal manufactured using the manufacturing method according to the present invention, particularly the polyvinyl acetoacetal whose degree of acetoacetalization is increased to 87% by weight or more can be suitably used for the thermal transfer layer binder.

  Furthermore, the polyvinyl acetoacetal produced using the production method according to the present invention has the advantages of improving the dispersibility of the dye and improving the shape retention and fixing properties of the thermal transfer layer when obtaining a dye composition.

  The method for producing polyvinyl acetoacetal according to the present invention can control the physical properties of polyvinyl acetoacetal to the physical properties that can be suitably used for the thermal transfer layer binder, although no organic solvent is used. In addition, since the polyvinyl acetoacetal production method according to the present invention does not use an organic solvent, it is excellent in utility costs such as steam and power, and a process for recovering the used organic solvent is unnecessary, reducing labor and cost. can do. Furthermore, since there is no odor due to the organic solvent, there is little adverse effect on the environment.

  Since the polyvinyl acetoacetal obtained by the method for producing polyvinyl acetoacetal according to the present invention is a physical property that can be suitably used as a thermal transfer layer binder, the thermal transfer binder containing the polyvinyl acetoacetal according to the present invention is used as a thermal transfer ink ribbon. If used, it is possible to provide a thermal transfer ink ribbon having excellent storage stability and recording density.

It is a flowchart of the polyvinyl acetoacetal manufacturing method which concerns on this invention. 2 is a partially enlarged view of 13C-NMR spectrum of polyvinyl acetoacetal of Example 1. FIG. It is explanatory drawing which calculates the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part. It is a figure which shows the evaluation about the property of Examples 1-5 and Comparative Examples 1 and 2, and the preservability and recording density of the ink ribbon using the polyvinyl acetoacetal of Examples 1-5 and Comparative Examples 1 and 2.

Claims (5)

An acetalization reaction step of advancing the acetalization reaction of polyvinyl alcohol and acetaldehyde in an aqueous solvent in a reactor;
A reactant discharge step of discharging the reactant from the reactor after the degree of acetoacetalization of the produced polyvinyl acetoacetal reaches at least 11% by weight;
A maturing reaction step of maturing the discharged reactants in a reactor separate from the reactor;
At least through
A method for producing polyvinyl acetoacetal, wherein the weight ratio of cis-type vinyl acetoacetal part / trans-type vinyl acetoacetal part in the acetoacetal part of polyvinyl acetoacetal is 1 to 4. Through at least the acetalization reaction step, the reactant discharge step, and the aging reaction step,
The method for producing polyvinyl acetoacetal according to claim 1, wherein the degree of acetoacetalization of the polyvinyl acetoacetal is 87% by weight or more.   The polyvinyl acetoacetal manufactured by the manufacturing method of the polyvinyl acetoacetal of Claim 1 or 2.   A thermal transfer layer binder using the polyvinyl acetoacetal according to claim 3. A substrate;
A thermal transfer layer laminated on at least one surface of the substrate;
A thermal transfer ink ribbon having
The thermal transfer ink ribbon, wherein the thermal transfer layer contains a sublimable dye and the thermal transfer layer binder according to claim 4.

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