JPH0367695A - thermal transfer sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a thermal transfer sheet, and more specifically, it is useful for a thermal transfer method using a sublimable dye (thermally transferable dye), and is useful for peeling off a dye layer during thermal transfer. The purpose of the present invention is to provide a thermal transfer sheet that has excellent prevention properties and can provide excellent image density.

(Prior art) Inkjet methods, thermal transfer methods, etc. have been developed as methods for providing excellent monochrome or full-color images easily and at high speed in place of conventional general printing methods. The most excellent method is the so-called sublimation thermal transfer method, which uses sublimable dyes, as it has excellent continuous gradation properties and provides full-color images comparable to color photographs.

The thermal transfer sheet used in the above-mentioned sublimation type thermal transfer method has a dye layer containing a sublimable dye formed on one side of a base film such as a polyester film, and a dye layer containing a sublimable dye on one side of the base film to prevent the thermal head from sticking. A heat-resistant layer provided on the other side is generally used.

The dye layer surface of such a thermal transfer sheet is placed on a transfer material having an image-receiving layer made of polyester resin, etc., and the dye in the dye layer is transferred to the transfer material by heating it in an imagewise manner from the back side of the thermal transfer sheet with a thermal head. The desired image is formed.

(Problems to be Solved by the Invention) The thermal transfer method described above has the excellent advantage of being able to create different shades of image depending on the temperature of the thermal head. If the temperature of the thermal head is increased, the binder forming the dye layer will soften and adhere to the transfer material, causing the inconvenience that the thermal transfer sheet and the transfer material will adhere. A problem arises in that the dye layer peels off during peeling and transfers directly to the surface of the transfer material.

Also, as a method of increasing the image density, there is a method of increasing the dye concentration of the dye layer, but in this case, the ratio of the binder to the dye in the dye layer becomes small, and as a result, the same problem as above occurs. occurs.

A method to solve this problem is to add a material such as polyurethane or polyester between the base film and the dye layer.
A method of providing an adhesive layer made of an adhesive resin has been proposed. A common method for forming such an adhesive layer is to apply a coating liquid in which an adhesive resin is dissolved or dispersed in a solvent onto the surface of a base film and dry it.

However, the following problems arise with this method of providing an adhesive layer.

(1) In order to maintain good sensitivity of the resulting thermal transfer sheet, it is desirable that both the base film and the adhesive layer be as thin as possible, but if the base film is as thin as, for example, several μm, However, there is a problem in that it is not easy to apply the adhesive layer coating liquid to this surface, and uneven coating tends to occur.

(2) Also, the thinner the adhesive layer is, the more desirable it is, and it is necessary to use a coating liquid with a low solid content to form a thin adhesive layer. There is a problem in that a large amount of organic solvent is consumed in the formation of . Further, even with such a method, it is very difficult to form a uniform adhesive layer with a thickness of 1 μm or less.

Therefore, in the conventional method, when the adhesive layer is thin, peeling of the dye layer cannot be sufficiently prevented, while when it is thick, the problem of decreased sensitivity cannot be avoided.

Therefore, an object of the present invention is to provide a thermal transfer sheet that does not cause peeling of the dye layer during transfer, has good thermal efficiency, and can provide high image density.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides a thermal transfer sheet comprising a dye layer formed on a base film, in which the base film is a polyethylene terephthalate film or a polyethylene naphide film having an easy-to-adhesion layer that is stretched and heat-treated at the same time as the base film. This is a thermal transfer sheet characterized by being a phthalate film.

(Function) By forming an easily adhesive layer on the surface of the base film after or at the same time as forming the film, and simultaneously stretching the base film and the easily adhesive layer to a predetermined thickness, Even with a base film of μm thickness, a very thin and uniform adhesive layer can be formed on its surface. By using this as a base film for a thermal transfer sheet, it is possible to form a dye layer on the surface during transfer. It is possible to provide a thermal transfer sheet that does not cause peeling, has good thermal efficiency, and can provide high image density.

Therefore, it is possible to prevent peeling even if the dye concentration of the dye layer is significantly increased, and as a result, the thermal efficiency and print density of the thermal head are significantly improved without causing peeling of the dye layer.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments of the present invention.

As the base film of the thermal transfer sheet of the present invention, a polyethylene terephthalate film or a polyethylene naphthalate film (preferably a polyethylene-2,6-naphthalate film) is used. The thickness of the above-mentioned base film after the stretching treatment is, for example, 0.5 to 50
μm, preferably about 3 to 10 μm.

The easily adhesive layer formed on the surface of the base film has good adhesion to both the base film and the dye layer,
In addition, it is preferable to use a resin that does not dissolve in the organic solvent used when forming the dye layer, and furthermore, the dye is less likely to transfer when heated during thermal transfer.

As the resin capable of forming such an easily adhesive layer, various resins that are conventionally widely used as adhesives can be used, but particularly preferably water-based acrylic resin, water-based polyurethane resin, water-based polyester resin, water-based polyamide resin,
Examples include aqueous polybutadiene resins, and these resins can be used alone or in combination with other resins.

These water-based resins are water-soluble resins or water-soluble resins obtained by making each resin hydrophilic to the extent that it does not become water-soluble and dispersing or emulsifying it in water. Therefore, even if the easy-adhesive layer made of these water-based resins is a very thin layer, it has good adhesion to both the base film and the dye layer, and the dye in the dye layer does not migrate during thermal transfer. Less is.

Of course.

The present invention is not limited to the above water-based resins.

The easy-adhesion layer made of the adhesive resin as described above is formed by applying the resin to the adhesive layer when forming the base film by a known method such as an inflation method or an extrusion method, or after film formation and before stretching. Alternatively, it can be formed by laminating a film made of adhesive resin, followed by cold stretching treatment or hot stretching treatment, and more preferably heat treatment.

By adopting such a method, it is possible to form a relatively thick and uniform adhesive layer before the stretching process, and even if the base film after the stretching process is a very thin film, the surface of the base film can be easily bonded. It becomes possible to form a very uniform and thin easy-to-adhesion layer of less than Ium.

In addition, if the easy-adhesive layer formed is too thick, the sensitivity of the resulting thermal transfer sheet will be reduced and the amount of dye in the dye layer transferred to the easy-adhesive layer will be large; Therefore, the preferred thickness range is 1 μm or less,
More preferably, it is 0.005 to 1 μm.

In addition, when forming an easily adhesive layer, it is preferable to include fine particles such as calcium carbonate, barium sulfate, silica, talc, clay, etc. in the coating liquid used, and the easily adhesive film obtained in this way. This is preferable because it suppresses blocking properties and improves handling workability.

The sublimable (thermally transferable) dye layer formed on the base film as described above is a layer in which a dye is supported by an arbitrary binder resin.

As the dye to be used, any dye used in conventionally known thermal transfer sheets can be effectively used in the present invention.
Not particularly limited. For example, some preferred dyes include MS Red G, Macr
olex Red Violet R, Ceres R
ed7B, Samaron Red HBSL, Re
Examples of yellow dyes include Holon Brilliant Yellow 6GL,
PTY-52, Macrolex Yellow 6G, etc., and as a blue dye, Kaya Set Blue 14
．． Examples include Vaxolin Blue AP-FW, Holon Brilliant Blue SR, MS Blue 100, and the like.

As the binder resin for supporting the heat-transferable dye as described above, any conventionally known binder resin can be used, and preferred examples include ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxy cellulose, hydroxybrobyl cellulose, methyl cellulose, Cellulose resins such as cellulose triacetate and cellulose acetate butyrate,
Examples include vinyl resins such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinylpyrrolidone, and polyacrylamide, and polyester. Among these, cellulose,
Acetal-based, butyral-based, and polyester-based resins are preferred. In particular, as binders, polyvinyl acetoacetal resins and triacetate cellulose resins have excellent compatibility with dyes, and the dye/binder weight ratio of the dye layer to be formed is 0. 5 or more, preferably 1 or more, and more preferably 2 to 5, there is little tendency for the dye to precipitate or form crystal grains within the dye layer. This is preferable because the sensitivity and density of the transferred image are increased.

The dye layer of the thermal transfer sheet of the present invention is basically formed from the above-mentioned materials, but may also contain various conventionally known additives as required.

Preferably, such a dye layer is prepared by adding the above-mentioned sublimable dye, binder resin, and other optional components in a suitable solvent, dissolving or dispersing each component, and preparing a paint or ink for forming the dye layer, which is then added to the above-mentioned solvent. It is formed by coating and drying on the easy adhesion layer or stable adhesion layer.

The dye layer formed in this way has a thickness of about 0.2 to 5.0 μm, preferably about 0.4 to 2.0 μm, and the sublimable dye in the dye layer has a thickness of about 5 to 5.0 μm. ~90% by weight
, preferably in an amount of 10 to 70% by weight.

The adhesive strength between the easily adhesive layer and the dye layer formed thereon is 10 gf/T-peel strength at 20°C.
cm or more, more preferably 20 gf/cm
or more, and 20 gf/c+s at 100°C
It is preferably at least 50 gf/ca+, and more preferably at least 50 gf/ca+. Such adhesive strength can be easily achieved by considering the combination of the resin forming the easy-adhesion layer and the binder forming the dye layer. T-peel strength less than 10 gf/am at 20°C or 100°C
If it is less than 20 gf/cm, when the dye layer and the material to be transferred are fused during thermal transfer, the dye layer may be carried to the material to be transferred, which is not preferable.

The thermal transfer sheet of the present invention as described above exhibits sufficient performance as it is, but it may be further provided with an anti-adhesive layer, that is, a release layer, on the surface of the dye layer. A heat-resistant layer may be provided on the back surface of the sheet in order to prevent adverse effects caused by the heat of the thermal head.

The transfer material used to form an image using the thermal transfer sheet as described above may be any material as long as its recording surface has dye receptivity to the above-mentioned dyes. If the material is paper, metal, glass, synthetic resin, etc. that does not have any properties, a dye-receiving layer may be formed on at least one surface thereof.

Examples of transfer materials that do not require the formation of a dye-receiving layer include polyolefin resins such as polypropylene, halogenated polymers such as polyvinyl chloride and polyvinylidene chloride, vinyl polymers such as polyvinyl acetate and polyacrylic ester, Polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polystyrene resins, polyamide resins, copolymer resins of olefins such as ethylene and propylene and other vinyl monomers,
Examples include fibers, woven fabrics, films, sheets, and molded products made of ionomers, cellulose resins such as cellulose diacetate, and polycarbonates. Particularly preferred are sheets or films made of polyester, or processed paper provided with a polyester layer.

In addition, in the present invention, even if the transfer material is non-dyeable such as paper, metal, glass, etc., a solution or dispersion of the dyeable resin as described above is coated on the recording surface and dried, or By laminating these resin films, it can be used as a transfer material. Furthermore, even if the transfer material has the dyeability described above, a dye-receiving layer may be formed on the surface thereof from a resin having better dyeability, as in the case of the paper described above.

The dye-receiving layer formed in this manner may be formed from a single material or from a plurality of materials, and may also contain various additives within the range that does not impede the purpose of the present invention. Of course.

Such a dye-receiving layer may be of any thickness, but is generally between 5 and 50 .mu.m thick. Although such a dye-receiving layer is preferably a continuous coating, it may also be formed as a discontinuous coating using a resin emulsion or resin dispersion.

The means for applying thermal energy used when performing thermal transfer using the above-mentioned thermal transfer sheet and the above-mentioned recording material are as follows:
Any conventionally known application means can be used. For example, by controlling the recording time with a recording device such as a thermal printer (for example, Video Printer VY-100 manufactured by Hitachi), heat of about 5 to 100 mJ/mnf can be applied. By applying energy, a desired image is formed.

(Example) Next, the present invention will be explained in more detail by giving examples and comparative examples. In the text, parts or percentages are based on weight unless otherwise specified.

Example 1 Polyethylene terephthalate with an intrinsic viscosity of 0.64 was
An unstretched film having a thickness of looILm was obtained by melt extrusion onto a cooling drum at a temperature of 0 to 300°C. This film was stretched 4 times in the machine axis direction at 80° C., and then coated with an easily adhesive shoe coating liquid (1) shown in Table 1 below. Subsequently, the film was stretched 4 times in the transverse direction at 110° C., and further heat-treated at 210° C. to obtain a biaxially stretched polyester film having an easily adhesive layer thickness of 0.1 μm and a total film thickness of 6 μm.

After forming a heat-resistant layer on the back of the base film, apply coating liquid A for dye layer shown in Table 2 below to the surface of the easy-adhesion layer until the dry thickness is 1.
．． The thermal transfer sheet of the present invention was obtained by coating and drying to a weight of 2 g/rrf. Incidentally, Tables 1 and 2 also list each coating liquid used in the following Examples and Comparative Examples.

[1 wheat A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1.

The coating liquids in Table 3 are those listed in Tables 1 and 2 above.

Examples 2 to 10 The materials shown in Table 3 below were used in place of the coating liquid for easy adhesion and the coating liquid for dye layer in Example 1, and other Example 11 Polyethylene-2,6-naphthalate film 28
An unstretched film with a thickness of 1100 u was obtained by melt extrusion onto a cooling drum at a temperature of 0 to 320°C. This film 1
After stretching 4 times in the machine axis direction at 10° C., the coating liquid (1) for easy adhesion shown in Table 1 was applied. Subsequently, it was stretched 4 times in the transverse direction at 140°C, and further heat-treated at 240°C to give an easily adhesive layer thickness of 0. A biaxially oriented polyethylene naphthalate film having a thickness of 1 μm and a total film thickness of 6 μm was obtained.

After forming a heat-resistant layer on the back surface of the base film, coating solution A for dye layer formation shown in Table 2 was applied to the surface of the easy-adhesion layer so that the dry thickness was 1.2 g/rrr, and then dried. A thermal transfer sheet of the present invention was obtained.

Examples 12 to 17 The materials shown in Table 4 below were used in place of the coating solution for easy adhesion and the coating solution for dye layer in Example 11.

A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except for the above.

Comparative Example 1 The coating liquid (1) for easy adhesion shown in Table 1 was applied to 6 μm polyethylene terephthalate with a heat-resistant layer formed on the back surface, and dried at 100'C for 10 minutes. Thereafter, in the same manner as in Example 1, coating liquid A for dye layer shown in Table 2 was applied to obtain a thermal transfer sheet of a comparative example.

Comparative Examples 2 to 10 Thermal transfer sheets of comparative examples were prepared in the same manner as in comparative example 1, except that the materials in Table 5 below were used in place of the coating liquid for easy adhesion and the coating liquid for dye layer in comparative example 1. I got it.

(Hereinafter, blank space) 1ijLj A thermal transfer sheet of a comparative example was obtained in the same manner as in Comparative Example 11 except for the lid and the like.

Comparative Example 11 6μm polyethylene-2,6 with heat-resistant layer formed on the back side
- The naphthalate film was coated with the coating solution (1) for easy adhesion of footwear shown in Table 1 and dried at 100°C for 10 minutes. Thereafter, in the same manner as in Example 1, coating liquid A for dye layer shown in Table 2 was applied to obtain a thermal transfer sheet of a comparative example.

Comparative Examples 12 to 16 The materials shown in Table 6 below were used in place of the easy-adhesion shoe coating solution and the dye layer coating solution in Comparative Example 11, and the dye layer surfaces of the thermal transfer sheets of the above Examples and Comparative Examples were coated. The dye layers were made to face each other, and a pressure of 5 Kgf/crrr was applied from the heat-resistant layer side at 150° C. for 5 seconds to completely fuse the dye layers together. Thereafter, it was cut into strips with a width of 25 mm, and the T-peel strength was measured at 20° C. and 100° C., and the results shown in Table 7 below were obtained. Adhesion was judged according to the following criteria (T-type peel strength is JIS K 68
54).

0: 50 gf/c+a or more, or fracture of the base material or cohesive failure of the dye layer occurred.

○: 20 gf/cm or more, less than 50 gf/cmΔ
: 10 gf/cm or more, less than 20 gf/cm
: The thermal transfer sheets of the above examples and comparative examples and the transfer material having a dye receiving layer made of polyester resin are superimposed with the dye layer and the dye receiving layer facing each other, Head applied voltage from the back of the thermal transfer sheet: 12, OV, printing time: 16.0
m5ec, /1ine, traveling speed 33.3m5ec, /
Thermal head recording was performed under 1ine conditions and the following 7th
Obtained the results in the table. The recorded images were visually evaluated according to the following criteria.

○: There was no peeling of the dye layer, and clear color development was observed.

Δ: Less than 10% of the dye layer was peeled off and transferred to the transfer material, resulting in a partially unclear image.

×: 10% or more of the dye layer was peeled off and transferred to the transfer material, resulting in a partially unclear image.

Negative 15-1 Mugi (Effect) According to the present invention as described above, an easily adhesive layer is formed on the surface of the base film after or simultaneously with the film formation, and the base film and the easily adhesive layer are simultaneously formed. By stretching the film to a predetermined thickness, even if the base film is several micrometers thick, a very thin and uniform adhesive layer can be formed on the surface of the base film, which can be used as a thermal transfer sheet. By using it as a base film, it is possible to provide a thermal transfer sheet that does not cause peeling of the dye layer during transfer, has good thermal efficiency, and can provide high image density.

Therefore, it is possible to prevent peeling even if the dye concentration of the dye layer is significantly increased, and as a result, the thermal efficiency and print density of the thermal head are significantly improved without causing peeling of the dye layer.

Claims (5)

[Claims] (1) In a thermal transfer sheet formed by forming a dye layer on a base film, the base film is a polyethylene terephthalate film or a polyethylene naphthalate film having an easily bonded layer that is stretched and heat treated at the same time as the base film. A thermal transfer sheet characterized by: (2) The thermal transfer sheet according to claim 1, wherein the T-peel strength between the dye layer and the adhesive layer is 10 gf/cm or more at 20°C and 20 gf/cm or more at 100°C. (3) The thermal transfer sheet according to claim 1, wherein the T-peel strength between the dye layer and the adhesive layer is 20 gf/cm or more at 20°C and 50 gf/cm or more at 100°C. (4) The thermal transfer sheet according to claim 1, wherein the thickness of the easily adhesive layer is in the range of 0.005 to 1 μm. (5) The thermal transfer sheet according to claim 1, wherein the binder of the dye layer is a polyvinyl acetal resin or a cellulose resin.