JP2928575B2 - Binder for thermal transfer recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a binder for a thermal transfer recording medium having improved printability.

[Prior art] In recent years, the development of thermal facsimile, thermal printer, etc. has been remarkable, and as a recording method used there,
A thermal transfer recording type is often used. This thermal transfer recording method generally uses a thermal transfer tape in which a thermal transfer layer mainly composed of a heat-fusible substance as a binder and a colorant is formed on a tape-like support, and is printed by a heating element such as a thermal head. The layer is melt-transferred onto a piece of paper in the form of a print image to form a predetermined print image.

As a heat-fusible substance that is a main component of the binder,
Conventionally, a wax such as carnauba wax or paraffin wax is mainly used, and a thermoplastic resin such as an ethylene-vinyl acetate copolymer is used in combination.

[Problems to be Solved by the Invention] However, such a thermal transfer layer containing wax as a main component is excellent in sensitivity to printing by a thermal head and can be melt-transferred quickly. Since it is required to further improve the friction resistance so that the image and the obtained printed image are not rubbed or stained with other objects, it is necessary to improve the adhesive strength and cohesion of the transfer composition to the subject. The fact is that it is required to measure.

[Means for Solving the Problems] Accordingly, the present inventors have conducted intensive studies on such a binder for a thermal transfer recording medium, and as a result, have found that such a purpose can be achieved by using a specific crystalline polyester resin. Thus, the present invention has been completed.

That is, the present invention relates to a method for producing a polymer, comprising: (A) at least 50 mol% of the diol component has the formula HOCH _{2 n}
(B) 50% by mole or more of the acid component is terephthalic acid and isophthalic acid, of which at least half is terephthalic acid. A binder for a thermal transfer recording medium, comprising a crystalline polyester resin having a heat of crystal fusion of 1 J / g or more, an average molecular weight of 800 to 8,000 and an acid value of 5 KOH mg / g or less. ".

A feature of the present invention is that a specific crystalline polyester resin is used as a binder for a thermal transfer recording medium as described above. By using such a resin, the adhesive strength and cohesive strength of the transfer composition to the copy body can be improved, a clear printed image can be obtained, and the friction resistance can be improved.

The (A) diol component of the polyester resin of the present invention comprises:
At least 50 mol%, preferably at least 70 mol% of the components have the formula
It must be a glycol represented by HOCH _{2 n} OH (where n = 3 to 7), and the (B) acid component is at least 50 mol%, preferably at least 60 mol%, of terephthalic acid and isophthalic acid. Yes, it is necessary that at least half of this is terephthalic acid, and if it is out of these ranges, the adhesive strength and cohesive strength of the transfer composition to the subject will decrease, which is not practical.

Examples of the glycol represented by the formula HOCH _{2 n} OH (where n = 3 to 7) of the present invention include 1,3-propanediol and 1,4-propanediol.
Butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, preferably 1,4-
Butanediol and 1,6-hexanediol. Other diols that can be used in combination include 1,2-ethanediol, 1,4-cyclohexanedimethanol, 2,2-dimethyl-1,3-propanediol, 1,2-propanediol, and 1,3-butane. Diol, 1,2-butanediol, diethylene glycol, triethylene glycol and the like can be mentioned.

Examples of acid components that can be used in combination other than terephthalic acid and isophthalic acid include malonic acid, succinic acid, adipic acid, phthalic anhydride, phthalic acid, sebacic acid, and azelaic acid.

The crystalline polyester of the present invention further has a heat of crystal fusion.
1 J / g, preferably 3 J / g or more, average molecular weight of 800 to 8000,
Preferably it is 3000-7000. When the heat of crystal fusion is less than 1 J / g, the resin itself may be sticky and stick to each other. On the other hand, when the molecular weight is less than 800, the cohesive force is reduced and the printed image becomes unclear.

The heat of crystal fusion of the present invention is determined by a specific heat curve (preferably 30
Is a value calculated using a straight line obtained by directly extrapolating the specific heat curve shown at a temperature of not less than 150 ° C. to the low temperature side as a base line.
The measurement is performed from 0 ° C to 150 ° C at a heating rate of ° C / min.

The average molecular weight of the present invention is a number average molecular weight determined by a so-called end group method, and is calculated by the following formula after measuring the acid value and hydroxyl value of a polyester resin sample.

Also, the acid value must be 5 KOHmg / g or less,
If it exceeds mg / g, the dispersibility of the pigment becomes too good, and the abrasion resistance (retention rate) of the print deteriorates, which is inappropriate. In forming a thermal transfer layer on a support using the crystalline polyester resin of the present invention as a binder, it is possible to perform hot melt coating, but it is preferable to perform solution coating by dispersing or dissolving the resin in a solvent. .
Solvents that can be used in this solvent system include organic solvents such as toluene, methyl ethyl ketone, cyclohexane, butyl acetate, and dioxane. The thermal transfer layer obtained in this manner retains a good dispersion state even when a large amount of a coloring agent is contained as compared with the conventional thermal transfer layer using a hot-melt type wax. Can be reduced, and the resulting printed image has extremely excellent sharpness.

As the colorant used together with the binder of the present invention, any of pigments and dyes such as inorganic pigments and organic pigments conventionally used in thermal transfer recording media are suitably employed.

Examples of inorganic pigments include titanium dioxide, carbon black, zinc oxide, Prussian blue, cadmium sulfide and iron oxide, and chromates of lead, zinc, barium and calcium. Further, by appropriately adding an extender such as silicic acid powder, calcium carbonate, magnesium carbonate, diatomaceous earth, kaolin, white carbon, talc, etc., the melt transferability can be improved and the sharpness of the print can be improved.

Examples of organic pigments include azo-based, thioindigo-based, anthraquinone-based, anthranthrone-based, and triphenedioxazine-based pigments, vat dye pigments, phthalocyanine pigments, metal (eg, copper) phthalocyanine and its derivatives, and quinacridone pigments.

Examples of organic dyes include acid dyes, direct dyes, disperse dyes, oil-soluble dyes, and metal-containing oil-soluble dyes.

The ratio between the polyester resin and the colorant is usually 5 to 20.
% By weight.

In forming the thermal transfer layer, a plasticizer or a wax may be added, if necessary, in addition to the crystalline polyester resin and the colorant of the present invention. Examples of the wax include carnauba wax, montan wax, paraffin wax, microcrystalline wax and the like, and examples of the plasticizer include dioctyl phthalate,
Examples thereof include tricresyl phosphate and dibutyl phthalate, which are blended at a ratio of 10% or less based on the total amount of the thermal transfer layer. Such plasticizers or waxes improve heat sensitivity.

As the support on which the thermal transfer layer is formed, for example,
Polyester film, polypropylene film, nylon film, polycarbonate film, cellulose triacetate film, polyimide film, glassine paper, condenser paper and the like having a size of about 20 μm.

[Function] When the crystalline polyester resin of the present invention is used as a binder in a thermal transfer recording medium, the adhesive force to a subject and the cohesive force of a transfer layer are remarkably improved as compared with a conventional wax-based resin, and clear printing is achieved. Is obtained.

EXAMPLES Next, the present invention will be described in detail with reference to examples.

Production example of polyester resin 0.6 mol of terephthalic acid, 0.4 mol of isophthalic acid, 1,6-
1.1 mol of hexanediol and 200 ppm of dibutyltin oxide as a catalyst were charged into a four-necked two-volume flask equipped with a stirrer, a thermometer, and a packed tower.
The reaction is continued until the water stops flowing, and then the pressure is reduced to 500 mmHg for 30 minutes at this temperature, and a crystalline polyester resin having a molecular weight of 3760 (acid value 3.4 KOHmg / g) and a heat of crystal fusion of 30 J / g by the end group method. (A) was obtained.

Thereafter, polyester resins (B) to (D) having compositions and physical properties as shown in Table 1 were obtained in the same manner. Further, for comparison, resins (E) to (G) having the compositions shown in the same table were produced in the same manner.

Examples 1 to 4 Four types of thermal transfer compositions were prepared using each of the obtained polyester resins (A) to (D). The ratio of each sequence is as follows.

(Components) (parts by weight) ○ Polyester resins (A) to (D) 15 ○ Cyanine blue (CI74160) 2 ○ Wax (microcrystalline wax, melting point about 80 ° C, manufactured by Toyo Petrolite Co., Ltd.) 1 ○ Talc ( Talc SM, manufactured by Nippon Talc Co., Ltd. 1.8 ○ Colloidal silica (Aerosil # 300, manufactured by Nippon Aerosil Co., Ltd.) 0.2 ○ Toluene 60 ○ Methyl ethyl ketone 20 After kneading and dispersing each component uniformly with a ball mill, polyester film ( It was applied to a thickness of 5 μm) using a bar coater so that the film thickness after drying became 4 μm, and dried to obtain a thermal transfer layer.

When the obtained thermal transfer medium was mounted on a thermal printer (word processor SANWORD MINI SWP-310 manufactured by Sanyo Electric Co., Ltd.) and printed on high quality paper, clear print images were obtained with any of the resins. The printed image was rubbed with an eraser (S-50 manufactured by Seed Rubber Co., Ltd.) until the density became as low as possible, and measured with a Macbeth densitometer (RD914), and the retention was calculated from the ratio to the initial density. Was.

Example 1 (Resin A), Example 2 (Resin B), Example 3
(Resin C) and Example 4 (Resin D)
85%, 90%, 88% and 85%.

Comparative Example 1 Using a polyester resin (E), the following proportions of a mixture were melt-kneaded in a kneader, and hot-melt-coated on a polyester film (5 μm thick) so that the dry film thickness was 4 μm. Was manufactured. Other than that, the experiment was performed in the same manner as in Example 1.

(Ingredients) (parts by weight) ○ Polyester resin (E) 15 ○ Cyanine blue (before) 2 ○ Wax (before) 1 ○ Talc (before) 1.8 ○ Colloidal silica (before) 0.2 The printed image was not as sharp as in the example. The retention was 80%.

Comparative Examples 2 and 3 Example 1 was conducted using polyester resins (F) and (G).
A thermal transfer medium was manufactured in the same manner as described above, but the resin (F),
(G) The resulting thermal transfer layer was also sticky because it itself was sticky, and printing could not be performed.

Comparative Example 5 A polyester film (thickness: 5 μm) was melt-kneaded with a compound in the following ratio by a kneader, and hot melt-coated to a dry film thickness of 4 μm. The retention of a printed image using the obtained thermal transfer medium was 30%.

(Components) (parts by weight) ○ Carnauba wax (from Brazil) 15 ○ Paraffin wax (melting point 70 ° C) 64 ○ Ethylene-vinyl acetate copolymer 15 (Soarex R-CH) ○ Cyanine blue 6 [Effect] The present invention A thermal transfer medium using the crystalline polyester resin of (1) as a binder gives a clear printed image and significantly improves the abrasion resistance of the printed image, and is therefore extremely useful in industry.

Claims (1)

(57) [Claims] (1) at least 50 mol% of the diol component is represented by the formula
(B) 50 mol% or more of the acid component is terephthalic acid and isophthalic acid, and more than half of these are HO- (CH ₂ ) _n -OH (where n = 3 to 7). Is a terephthalic acid resin composition, and comprises a crystalline polyester resin having a heat of crystal fusion of 1 J / g or more, an average molecular weight of 800 to 8000, and an acid value of 5 KOHmg / g or less.