JPH0257390A - Heat transfer sheet - Google Patents

Abstract

PURPOSE:To improve the sensitivity of a heat transfer sheet and to reduce the wear of a thermal head with conductive carbon by forming a back layer of specific substance and binder as main agents, and specifying its surface resistance to a specific range. CONSTITUTION:A back layer is formed of polyisocyanate and binder as main agents with the rich polyisocyanate thereby to form the layer of very reduced thickness. Accordingly, a heat transfer sheet having high sensitivity is provided. Even if the quantity of the contained carbon is 10% or less, a surface resistance of a range of 10<6> to 10<12>OMEGA/square is provided. Accordingly, even if the carbon to be contained is relatively small in amount, sufficient charge preventing property is imparted. Therefore, a problem of the wear of a thermal head with the carbon can be solved. The polyisocyanate compound is used in amount of 20wt.% or more of the sum of polyisocyanate and the binder to generate a coating film remarkably adapted for the back layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a thermal transfer sheet, and more particularly to a novel thermal transfer sheet having an excellent antistatic and heat-resistant slip layer (back layer) made of a specific material.

(Prior Art) Conventionally, when printing output prints from computers or word processors by a thermal transfer method, a thermal transfer sheet having a heat-melting ink layer provided on one side of a base film has been used.

This conventional thermal transfer sheet has a thickness of 1 mm as a base film.
Using paper such as capacitor paper or paraffin paper with a thickness of 0 to 20 μm, or a plastic film such as polyester or cellophane with a thickness of 3 to 20 μm, a layer of heat-melting ink made by mixing coloring agents such as pigments and dyes with wax is applied. It is manufactured by coating.

In addition, when using heat-resistant materials such as plastic films as the base film, the thermal head may stick during printing, impairing the peeling and slipping properties of the thermal head, or tearing the base film. To avoid this problem, we form a heat-resistant layer made of silicone resin, etc.
In addition, the slip properties are improved by incorporating a lubricant or the like into the layers. Further, in order to prevent charging during printing or other handling, conductive carbon is included to impart antistatic properties.

(Problems to be Solved by the Invention) G. The back layer in conventional thermal transfer sheets needs to be formed relatively thick in order to prevent the base film from tearing, which reduces the sensitivity of the heat transfer sheet. It has the following drawbacks.

In addition, in the manufacturing process, when silicone oil or silicone resin is used, there is a lot of repellency of the T agent for forming the back layer against the base film, making it difficult to form an even coating film.

Furthermore, conductive carbon is added to these back layers as part of static prevention 11, but in order to provide sufficient conductivity, the binder that forms the heat-resistant layer and the conductive carbon must be added. The problem is that more than about 10% of the total hl of conductive carbon is required, resulting in slow wear of the thermal head due to the conductive carbon.

Therefore, one object of the present invention is to provide a thermal transfer sheet that solves the disadvantages such as climate.

(1 step to solve the problem) The above objects are achieved by the present invention as described below.

That is, the present invention provides a thermal transfer sheet that has a transfer layer that melts when heated on one side of the base film, and a back layer on the other side of the base film that is in contact with the thermal head. , the back layer is formed of polyisocyanate and a binder as a single agent, and has a surface resistance value in the range of 10 6 to 10 12 Ω/□.

(Function) By forming the back layer using polyisocyanate and a binder as two agents and enriching the polyisocyanate, a very thin back layer is formed, making it possible to create a highly sensitive heat transfer 7J sheet. provided.

In particular, in the present invention, even if the amount of conductive carbon is relatively small (A), sufficient antistatic properties are imparted, so that the problem of wear of the thermal head due to the conductive carphone is sufficiently solved.

(Preferred Embodiments) Next, the present invention will be explained in more detail with reference to preferred embodiments.

As the base film used in the present invention, the same base film used in conventional thermal transfer sheets can be used as is, and other films can also be used, and there are no particular limitations.

Examples of preferred base films include polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride,
Polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber,
Papers such as plus deck such as ionomer, condenser paper and paraffin paper, non-woven fabrics, etc. may be used, and base films made of composite materials such as stiff straw may also be used.

The J7 thickness of this base film can be changed as appropriate depending on the material so that its strength and thermal conductivity are appropriate, but its thickness is preferably, for example, 2 to 7 25μ.
It is m.

The back layer, which mainly characterizes the present invention, is provided on one side of the above-mentioned ↓ (material film). It is valid.

In the present invention, the above-mentioned back layer is formed from polyisocyanate and a binder as main ingredients, and is characterized by (1) incorporating conductive carbon.

Conventionally, it has been known to use polyurethane made of polyol and polyisocyanate to form various paints, coating agents, or back layers, or to use polyisocyanate as a crosslinking agent in other resin liquids to form crosslinked resin layers. However, in these known methods, the polyisocyanate is used in a very small amount relative to the resin to be crosslinked, so-called simply as a crosslinking agent.

In the present invention, unlike these conventional examples, by using a polyisocyanate compound as the main ingredient of the back layer, that is, in an amount accounting for 20% or more of the total of the polyisocyanate and the binder, it is very suitable for the back layer. It was found that a coating film was formed.

As the polyisocyanate used in the present invention, general polyisocyanates can be used, but preferred are polyurethane polyisocyanates having a relatively high molecular weight and reacted with polyisocyanate dimers, trimers, or polyol compounds. Specifically, for example, a cyclic trimer of 2,4-tolylene diisocyanate, a cyclic trimer of 2,6-tolylene diisocyanate, a trimer of diphenylmethane-4,4'-diisocyanate, 3 mol reaction product of diphenylmethane-4,4'-diisocyanate and 1 mol of trimethylolpropane, reaction product of 3 mol of 2,4-tolylene diisocyanate and 1 mol of trimethylolpropane, 3 mol of 2.
6-Reaction product of 1-lylene diisocyanate and 1 mol of trimethylolpropane, 3 mol of 2,4-tolylene diisocyanate and 1 mol of trimethylolethane, 3 mol of 2,6-tri reaction product of diisocyanate and 1 mole of trimethylolethane,
A reaction product of a mixture of 3 moles of 2,4- and 2,6-tolylene diisocyanate and 1 mole of trimethylolpropane, a cyclic trimer of a mixture of 2,4- and 2,6-tolylene diisocyanate, etc. Stabilized polyisocyanates blocked with phenol or cresol can be mentioned.

These polyisocyanates are, for example, bamboonate (
(manufactured by Trial Chemical), Parnock (manufactured by Dainippon Ink Chemical), Coronate (manufactured by Nippon Polyurethane), Duranate (manufactured by Asahi Kasei Industries), Dismodur (manufactured by Bayer), Polyisocyanate (manufactured by Dainichiseika Kogyo Co., Ltd.), etc., and can be used in the present invention by hand.

In the present invention, the polyisocyanate described above is preferably used in combination with a binder.

Examples of these binders include ethyl cellulose, droxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose resins such as nitrified surfaces, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral. , vinyl resins such as polyvinyl acetal, polyvinylpyrrolidone, and polyacrylamide, polyester resins, and polyurethane resins such as silicone or fluorine-modified polyurethane resins. Among these, cellulose-based, acetal-based, butyral-based, Those having some reactive groups 1, for example, hydroxyl groups therein, such as polyester and polyurethane, are preferred.

ff1ffl of the above binder and polyisocyanate
The ratio is such that the polyisocyanate accounts for 20% or more of the total of both, preferably 50 to 95% by weight. If the amount of polyisocyanate used is less than 20% by weight, the heat resistance of the back layer will be insufficient, while if no binder is used, the film will become brittle.

In addition, in the present invention, when forming the back layer from the above-mentioned materials, heat release agents and lubricants such as wax, higher fatty acid amide, ester, and surfactant, or fluororesin are added in order to improve the slip properties of the back layer. Organic powders such as, inorganic particles such as silica, clay, talc, calcium carbonate, etc. can be included. In addition, in order to improve the heat resistance of the back layer, hydrotalcite DHT-4A (Kyowa Chemical Industry Source), Talc Micro Ace Shi-1 (Nippon Talc), and Teflon Leburon L-4 (Daikin T Co., Ltd.) were used as heat resistant agents. manufactured by),
Graphite fluoride 5CP-10 (manufactured by Nisei Kagaku Kogyo), graphite AT40S (manufactured by Oriental Sangyo) or silica, calcium carbonate, precipitated barium, urea crosslinked powder, acrylic crosslinked powder, silicone powder, wood powder, molybdenum disulfide, boron nitride It is possible to include fine particles such as -f-.

Another feature of the present invention is that in forming the back layer from the materials described above, a relatively small amount of conductive carbon is incorporated therein to impart sufficient antistatic properties to the back layer.

According to research conducted by the present inventors, in order to impart satisfactory antistatic properties to the back layer, conductive carbon of more than 10% by weight and q% is included in the back layer, and its surface resistance value is increased to approximately 1012Ω.
/□ or less, but the back layer containing such an amount of conductive carbon has a significant abrasiveness on the thermal head, and reducing the IA of the conductive carbon will result in antistatic properties of 1 minute. The problem of not having one has been resolved.

As described above, the inventor of the present invention has determined that when forming a film enriched with polyisocyanate-1 and incorporating conductive carbon therein, the surface resistance value of the back layer can be increased by selecting the film formation conditions. Change 17: It has been found that even a relatively small amount of conductive carbon can provide sufficient antistatic properties.

That is, when applying the ink for the back layer, the higher the solid content (see Example 2), the faster the coating speed (see Example 3), the higher the drying temperature (see Example 1), It has been found that the surface resistance value decreases significantly even at the same conductive carbon concentration when the aging conditions after drying are at a high temperature and for a long time (see Example 4).

Therefore, according to the present invention, by selecting manufacturing conditions such as 5 to 10, 10 layers can be produced! 9 of less than 1% conductive carbon
However, a thermal transfer sheet having a surface resistance value of 10 12 Ω/□ or less, preferably 10 6 to 10 9 Ω/□ is provided.

As the conductive carbon used in the present invention, any conductive carbon conventionally used for conductive plastics or for preventing static electricity on plastics can be used. Preferred specific examples include those available on the market under the names of Ketchen Black EC and Ketchen Black EC600JD.

In the present invention, the conductive carbon described above preferably accounts for 10% by weight or less of the back layer, more preferably 1 to 10 f.
l [used in the amount of bond%.

If the amount of the conductive carphone used exceeds the above range, the antistatic property will be sufficient, but the problem of wear of the thermal head will occur, while if it is too small, satisfactory antistatic property will not be obtained.

For the back layer, prepare a coating solution by dissolving or dispersing the above materials in a suitable solvent such as acetone, methyl ethyl ketone, toluene, xylene, etc., and apply this coating solution using a gravure coater, roll coater, wire bar, etc. It is formed by coating and drying using a conventional coating method, and at that time, as described above, the ink concentration, coating conditions, drying conditions, aging conditions, etc. are appropriately selected.

The thickness of the coating], that is, the thickness of the back layer is also important, and in the present invention, a thickness of 0.5 g/rn' or more, preferably 0.1 to 10.5 g/m'' based on solid content, provides sufficient performance. It is possible to form a back layer having the following properties.

It is also effective to form a brimer layer made of polyurethane resin or the like before forming the two back layers.

In the present invention, in addition to the base film described in (1) above, a heat-melting ink layer is formed from an ink blended with necessary materials.

The ink for forming the hot-melt ink layer used in the present invention comprises a colorant and a vehicle, and may further contain various additives as necessary.

The coloring agent is preferably an organic or inorganic pigment or dye that has good properties as a recording material, for example, one that has sufficient color density and does not discolor or fade due to light, heat, temperature, etc.

Further, it may be a substance that is colorless when not heated but develops color when heated, or a substance that develops color when it comes into contact with something coated on the transfer target. In addition to the colorants forming cyan, magenta, yellow, and black, colorants of various other colors can also be used.

The vehicle used includes wax as a main component, and mixtures of wax with drying oil, resin, mineral oil, cellulose, rubber derivatives, and the like.

Representative examples of wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. Furthermore, various waxes are used, such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolatum, assorted waxes, fatty acid esters, and fatty acid amides. It will be done.

Furthermore, a thermally conductive substance can be blended into the hot-melt ink in order to provide the hot-melt ink layer with good thermal conductivity and melt transferability. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum disulfide.

In addition to hot melt coating, methods for forming a hot melt ink layer directly or indirectly on a base film include:
Examples include hot lacquer coating, gravure coating, gravure reverse coating, roll coating, and many other methods of applying the ink. The thickness of the ink layer formed should be determined to balance the required concentration and thermal sensitivity and is in the range of 0.1 to 30 μm, preferably in the range of 1 to 20 μm.

In the present invention, a surface layer can be further formed on the ink layer. The surface layer forms a part of the transfer film, forms the surface in contact with the transfer paper, seals the printed area of the transfer paper during transfer, prevents scumming, and prevents the ink layer from being covered. It has the function of improving adhesion to transfer paper.

The wax used to form the surface layer is the same substance as the wax used in the hot-melt ink layer described above.

The surface layer made of the wax is formed by coating and cooling a wax melt, coating and drying an organic solvent solution containing the wax, coating and drying an aqueous dispersion containing particles of the wax, and the like.

The coating of the surface layer, as well as the formation of the ink layer, can also be done by various techniques. In the present invention, the thickness of this layer is preferably 0.5 mm to prevent insufficient sensitivity even when printing energy is low as in high-speed printers.
It is 1 μm or more and less than 5 μm.

It is recommended that an appropriate amount of extender pigment be added to the surface layer. This is because bleeding and trailing of printed characters can be better prevented.

Thermal transfer images generally have glossy and beautiful prints, but the documents may become difficult to read, so matte prints are sometimes desirable. In such a case, for example, as proposed by the applicant (Japanese Patent Application No. 58-208306),
A thermal transfer sheet is formed by coating a base film with an inorganic pigment such as silica, calcium carbonate, etc. dispersed in an appropriate solvent to provide a matte layer, and then coating a heat-melting ink layer. good. Alternatively, the base film itself may be matted and used (this is also the technique of Japanese Patent Application No. 1983-208307 proposed by the applicant).

Since it goes without saying that the present invention can be applied to thermal transfer sheets for color printing, multicolor thermal transfer sheets are also included within the scope of the present invention.

(Effects) According to the present invention as described above, by forming the back layer using polyisocyanate and a binder as main ingredients and enriching the polyisocyanate, a very thin back layer is formed, which improves sensitivity. A thermal transfer sheet with a high temperature is provided.

In particular, in the present invention, by selecting the manufacturing conditions of the thermal transfer sheet, sufficient antistatic properties can be imparted even with a relatively small amount of conductive carbon, so that the problem of thermal head wear due to conductive carbon can be sufficiently prevented. Resolved.

(Example) Hereinafter, 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 Back layer" 1.2 Earthen construction polyvinyl butyral resin (S-LEC BX1, manufactured by Tsukiki Kagaku ■) 4.35 parts polyvinyl butyral resin (S-LEC 131°S, manufactured by M-Sui Kagaku ■)
3.35 parts conductive carbon (Ketchen Black ECD, +600, manufactured by Lion@)
1.30 parts methyl ethyl ketone 65.
7 parts Toluene 25.3 parts Polyisocyanate XDT (XEL curing agent (D),
7.83 parts polyisocyanate TDI (curing agent for IIR-430,
7.83 parts of multi-layer ink (liquid preparation) were mixed.

The ink composition for the back layer was prepared by thoroughly kneading the clay composition, and a 6.0 μm thick polyester film (trade name:
After coating the surface of Lumirror (manufactured by Higashi [) ■) using the gravure coating method to a coating amount of 0.5 g/m'' (solid content), it was dried with warm air. At this time, the film was transported The speed was 150rn/rnin, and the temperature of the drying oven was (1).
50 to 70°C, (2) 90 to 100°C, and (3) 1
The drying temperature was set at 20-7Ii130°C to examine the influence of the drying temperature. The obtained film was further cured by heating in an oven at 60° C. for 5 hours to form a back layer.

The ratio of polyisocyanate to binder NC01011 in the ink composition for the back layer is 1.8, and the ratio of carbon in the back layer is 5.3.
%.

Separately, transfer the transfer ink composition with the following composition into a blade kneader.
The mixture was kneaded for 6 hours while heating to 90°C.

Paraffin wax 10 parts Carnauba wax 10 parts Polybutene (VH-1
00, manufactured by Nippon Oil ■) 1 part carbon black (Geest 3, manufactured by Tokai Electrode ■)
2 parts The above ink composition was heated at a temperature of 100°C, and coated on the other surface of the base film described in 1- by a hot-melt roll coating method to a coating amount of about 5.5 parts. A thermal transfer ink layer was formed by coating the ink to give a thermal transfer sheet of the present invention.

Surface resistance value of the back layer of the thermal transfer sheet obtained in Section 1-
Ω/□) using Atopan Test's surface resistance meter TR-860.
1, measured at 24°C and R880%,
It was as follows.

(1) 0.5X109 (2) 1.8X106 (:I)2. lXl0' Example 2 The amount of solvent in the ink composition of Example 1 was changed as follows,
The temperature during drying was 100°C, and the film transport speed was 1.
A thermal transfer sheet of the present invention was formed in the same manner as in Example 1, and the surface resistance was measured in the same manner.

(1) Methyl ethyl ketone 171.0 parts Toluene 665 parts (solid content 4%) (
2,lXl0') (2) Methyl ethyl ketone
68.4 parts toluene 26.6
parts (solid content 10%) (1,9 x 106) (3) Methyl ethyl ketone 45.6 parts Toluene
17.7 parts (solid 15%) (2.9X
106) Example 3 In Example 1, the coating speed of the ink for the back layer was changed as follows, the temperature during drying was 100° C., and the film conveyance speed was set to 150 m/min.
A thermal transfer sheet of the present invention was formed in the same manner as described above.

(1) 50tn/min, (15XtO') (2
) 10 parts m/min, (3,5X106) (3) 15
0m/min, (0,5X106) (4) 200m/r
nin, (1,8X108) Example 4 In Example 1, the drying temperature was set to 100°C, the film transport speed was set to 150 m/min, and the aging conditions were changed as shown below. A thermal transfer sheet of the present invention was formed in the same manner.

(1) 50℃, 3 days (1, tXto8) (2)
50℃, 7 days (2,3X106) (3) 10
0℃, 3 days (0.9X IO') (4) 10
0° C., 7 days (106 or less) (The surface resistance value before aging treatment was 2.0×106.

Furthermore, the heat-resistant sheet according to the present invention obtained as described above can be coated with a back layer ink composition necessary to enable smooth conveyance without wrinkles when printing under the above-mentioned printing conditions. As a result of examining the amount, it was found that 0.2 g/m'' was sufficient. Ink composition (m, p, 69°C)
If the coating amount of the back layer is 5.0 g/m'', a printing energy of 1.0 mJ/dot is required to obtain sufficient print density with the navigation transfer ink layer, but if the coating amount of the back layer is 0. .2
g/rn', 0.7 mJ/Ft is sufficient and printing energy can be reduced by about 30%.

Claims (4)

[Claims] (1) A thermal transfer sheet comprising a transfer ink layer that melts when heated on one side of a base film and a back layer on the other side of the base film that contacts the thermal head, where the back layer is made of polyisocyanate. and a binder as main ingredients, and its surface resistance value is 10^6 to 1.
A thermal transfer sheet characterized by having a resistance of 0^1^2Ω/□. (2) The thermal transfer sheet according to claim 1, wherein the polyisocyanate forming the back layer accounts for 20% or more by weight of the total of the polyisocyanate and the binder. (3) The amount of conductive carbon is 1 to 10% by weight of the back layer
The thermal transfer sheet according to claim 1, wherein the thermal transfer sheet occupies . (4) The thermal transfer sheet according to claim 1, wherein the thickness of the back layer is 0.5 μm or less.