JPS63290785A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To provide both lubricity and adhesiveness, which are generally contradictory properties, and obtain a feed-improving layer with a favorable film-forming property, by causing the feed-improving layer to comprise a graft copolymer having a polymer excellent in release properties and lubricity as a side chain and a polymer excellent in adhesiveness and film-forming properties as a backbone chain. CONSTITUTION:A feed-improving layer provided on the upper side of a base film comprises a graft copolymer having a polymer excellent in release properties and lubricity as a side chain and a polymer excellent in adhesiveness and film-forming properties as a backbone chain. The polymer excellent in release properties and lubricity is preferably a polymer having a critical surface tension of not more than 22 dyne/cm and a frictional coefficient of not more than 0.3. The polymer excellent in adhesiveness and film-forming properties is preferably a polymer having a critical surface tension of not less than 37 dyne/cm. In order that the backbone chain moiety, e.g., an acrylic polymer moiety and the side chain moiety, e.g., a silicone polymer moiety display the respective characteristics thereof, they are preferably used in a weight ratio of 2:0.5-1:3.5. The thickness of the feed-improving layer is preferably 0.1-1.5 mum. By this, release properties and lubricity are developed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal transfer recording medium used in a thermal transfer printer.

BACKGROUND OF THE INVENTION PET (polyethylene terephthalate), ie, polyester, films are commonly used as substrates for thermal transfer recording media.

However, the surface temperature of the thermal head during printing instantaneously increases to 3.
As temperatures reach over 00℃, some of the PET film melts,
There is a problem that the film tends to stick to the thermal head, resulting in poor film transport, adversely affecting printing, and even more likely to cause the so-called stick phenomenon, in which film transport completely stops and printing becomes impossible.

For this reason, attempts have been made to improve film transportability by applying various coatings such as silicone, epoxy, and fluorine coatings to the top surface of the film.

Problems to be Solved by the Invention However, in all of these cases, the stick prevention effect is insufficient, or it is necessary to cure the film after film formation in order to obtain heat resistance and film strength, and the curing reaction is accelerated. However, there were problems such as requiring heat treatment at a high temperature for a long time, and the workability was extremely poor, making it impossible to put it into practical use. Furthermore, even if the stick prevention effect is sufficient, the adhesion to the PET surface is poor, so it may fall off due to friction with the thermal head.
Some of them were deposited on the thermal head and caused printing defects.

An object of the present invention is to provide a new thermal transfer recording medium that does not have these drawbacks.

Means for Achieving the Invention The inventors of the present invention have conducted various studies in order to achieve both the contradictory properties of mold releasability, lubricity, and adhesion, and to obtain a transport-improving layer with good film-forming properties. It was discovered that a suitable transport-improving layer could be obtained by employing a graft copolymer with a polymer with excellent adhesiveness and film-forming properties as a side chain and a polymer with excellent adhesiveness and film-forming properties as a main chain, and the present invention was made based on the findings. has been achieved.

According to the present invention, in a thermal transfer recording medium in which a heat-melting ink layer is provided on the lower surface of a base film and a transport improving layer is provided on the upper surface, the transport improving layer is made of a polymer having excellent mold releasability and lubricity. A novel thermal transfer recording medium is provided, which is characterized by being made of a graft copolymer whose main chain is a polymer having excellent adhesiveness and film-forming properties as a side chain.

As a guideline for selecting a polymer having excellent mold releasability and lubricity, it is desirable to have a critical surface tension of 22 dyne/cm or less and a friction coefficient of 0.3 or less. As such a polymer, fluorine-based, silicon-based, etc. can be used, but polydimethylsiloxane (critical surface tension: 21 dyn) is preferably used.
e/cm, friction coefficient 0.1) can be used. In addition, the critical surface tension of the polymer used for the side chain is 22 dyne/c.
If the coefficient of friction is 0.3 or more, the mold releasability will be insufficient, and if the coefficient of friction is 0.3 or more, the slippage with the thermal head will be poor, and in either case, sticking will occur.

In addition, as a guideline for polymers with excellent adhesiveness and film-forming properties, critical surface tension is 37 dyne/cm or more, and tensile strength is 60.
kg/- or more is desirable. As such a polymer, epoxy, polyamide, acrylic, polyester, polyvinyl acetate, etc. can be used, and polymethyl methacrylate (critical surface tension: 39 dyne/cm, tensile strength: 400 kg/- or more) is preferably used. The critical surface tension of the polymer used for the main chain is 37 dyne/c.
If the tensile strength is less than 60 kg/-, sufficient adhesive force cannot be obtained to the PET base, and if the tensile strength is less than 60 kg/-, sufficient strength to withstand friction with the thermal head cannot be obtained.

In order for the main chain portion, such as a portion of an acrylic polymer, and the side chain portion, such as a portion of a silicone polymer, to exhibit their respective characteristics, it is desirable that the weight ratio be in the range of 270.5 to 1:3.5.

In addition, it is preferable that the thickness of the transport improvement layer is 0.1 to 1.5 μm.

By coating the graft copolymer polymerized with this combination on the PET base, the main chain with high critical surface tension acts effectively for adhesion at the interface with the base PET.
On the other hand, by arranging side chains with low critical surface tension and low coefficient of friction on the surface side, mold release properties and lubricity are exhibited. In addition, the strength of the coating film as a whole is maintained by the main chain, which simultaneously possesses contradictory properties such as mold releasability, lubricity, and adhesion, and provides sufficient film strength and productivity without post-curing. This has led to the achievement of a transport-improving layer with unprecedented properties that are excellent in both properties. In other words, in the case of the graft copolymer, the acrylic main chain effectively works for adhesion at the interface with the base PET, while the silicone side chains are arranged on the surface side, thereby exhibiting mold releasability and lubricity. Furthermore, the strength of the coating film as a whole is maintained by the acrylic main chain.

Taking the case of a combination of a silicone polymer and an acrylic polymer as an example, the performance of a product obtained by graft polymerization of these polymers is completely different from a mere blend of silicone and acrylic or a silicone-acrylic random copolymer. In other words, a simple blend or copolymer has physical properties intermediate between silicone and acrylic, such as heat resistance, lubricity,
Mold releasability, adhesiveness, film-forming property, toughness, high reactivity, etc. are all intermediate properties between the two, and are half-hearted and insufficient.

In contrast, graft copolymers have properties that combine the characteristics of both silicone and acrylic.

In other words, as mentioned above, it has the heat resistance, mold releasability, and lubricity of silicone, and the adhesion, toughness, film-forming property, and high reactivity of acrylic without reducing each, and has sufficient anti-stick performance. Good productivity can be obtained at the same time. Incidentally, silicone-acrylic block copolymers also have this tendency, but it is less pronounced than graft copolymers.

As the base film used in the present invention, commonly used films such as polyethylene tereftate can be used.

Further, as the heat-melting ink layer, those generally used in heat-sensitive transfer recording media can be used.

The thermal transfer recording medium of the present invention is prepared by applying a solution of a graft copolymer obtained by a conventional method and diluting it with an appropriate solvent onto a base film using a champion coater, drying it, and then applying the same to the opposite side by a conventional method. It can be manufactured by applying a layer of hot-melt ink.

Effects of the Invention According to the present invention, it is possible to completely prevent the occurrence of stickiness, and it also has excellent film-forming properties and adhesion to PET, so it does not fall off at the thermal head and there is no need for a curing process at high temperatures. Therefore, it has excellent workability and can provide an improved conveyance layer with excellent performance and productivity.

In addition, if heat resistance is particularly required, curing can be performed by post-treatment, but in the case of the present invention, it is possible to select a highly reactive polymer for the main chain, so it is possible to cure at room temperature, etc., slowly and with high productivity. It has the advantage of being able to set good conditions for

EXAMPLES Next, Examples and Comparative Examples will be shown, but the scope of the present invention is of course not limited to these.

Example 1. Methyltrimethoxysilane was added to a polymethyl methacrylate solution together with a polymerization initiator at a weight ratio of 1:1 to polymethyl methacrylate, and addition polymerization was carried out to form silicone.
Obtain an acrylic graft copolymer. After the obtained polymer is purified, it is diluted with a MEK/MIBK mixed solvent to have a solid content of 5%. The obtained solution is applied to a 6 μm thick PET film using a champion coater so that the dry coating thickness is 0.2 μm. Next, a thermal transfer ink consisting of 30 parts of carnauba, 30 parts of paraffin wax, 20 parts of carbon black, and 20 parts of a dispersant and the like is applied to the opposite side of the PET film to a thickness of 3.5 μm.

The heat-sensitive transfer ribbon obtained in this way has a width of 2601 cm,
As a result of finishing the roll with a length of 250m and running test with a thermal transfer line printer, the environmental temperature was 5℃.
No sticking phenomenon occurred in the entire temperature range of ~40°C, and good printing was obtained. The same thing happened when I increased the power of the printer excessively. Also, throughout the test, no deposits were observed on the thermal head, and no deposits were observed from the PET base.

Example 2゜Example 1. A similar test was conducted using tetrafluoroethylene in place of methyltrimethoxysilane, and the same good results as in Habo were obtained.

Example 3゜Aron US-31001 (manufactured by Bunyasei Kagaku Kogyo ■) 100
part, dibutyltin dilaure as curing catalyst) 0
．． Part 005, Coronate EH (Japan Polyurethane Industries ■
0.3μ when dried on the PET surface.
It is coated so that

In contrast, Example 1. As a result of applying heat-sensitive transfer ink in the same manner as above and performing the same test, good results similar to those of Habo were obtained.

Comparative example 1゜100 parts of polydimethylsiloxane and 10 parts of acrylic resin
Dry 0 parts of the blend mixture onto 6μ thick PET.
．． A thermal transfer ribbon was obtained by applying the same thermal transfer ink as in Example 1 to the opposite side. Example 1 using the thermal transfer ribbon obtained in this way. A similar print test was conducted.

As a result, even at room temperature, in the case of printed items with a large print area, a sticking phenomenon occurred, resulting in poor printing, and deposits were observed on the thermal head, which caused missing prints. Adhesion to the PET base was also insufficient (it easily peeled off from the base when rubbed strongly by hand).

Procedural amendment July 27, 1986

Claims (1)

[Claims] 1. A heat-melting ink layer is provided on the lower surface of the base film,
In a thermal transfer recording medium provided with a transport improving layer on the upper surface, the transport improving layer is a grafted material having a polymer having excellent mold release properties and lubricity as a side chain and a polymer having excellent adhesive properties and film forming properties as a main chain. A thermal transfer recording medium characterized by being made of a copolymer. 2. Provide a heat-melting ink layer on the bottom surface of the base film,
In a thermal transfer recording medium provided with a transport improving layer on the upper surface, when the transport improving layer is used alone, the critical surface tension is 2.
The branches are polymers with a friction coefficient of 2 dyne/cm or less and a friction coefficient of 0.3 or less, and also have a critical surface tension of 37 dyne.
2. The thermal transfer recording medium according to claim 1, wherein the thermal transfer recording medium is made of a graft copolymer having a polymer having a molecular weight of 1/cm or more. 3. The thermal transfer recording medium according to claim 2, wherein the graft copolymer has a silicone polymer or a fluorine polymer as a branch and an acrylic polymer as a trunk. 4. The thermal transfer recording medium according to claim 3, wherein the silicone polymer is polydimethylsiloxane. 5. Weight ratio of acrylic part and silicone part is 2:0.5
to 1:3.5 and the thickness is 0.1 to 1
．． Claim 3 or 4 characterized in that it is 5μ
Thermal transfer recording medium described in .