JPH03248886A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To reduce the effect receiving from the surface of paper to be transferred and to perform transfer of high image quality by adding a polyurethane resin having a bisphenol skeletal and a colorant to heat-meltable ink as main components. CONSTITUTION:The polyurethane resin having a bisphenol skeletal being the essential component of a thermal transfer recording medium is generally characterized in that a number average MW as polystyrene measured by a gel permeation chromatography (GPC) method is about 20000 or less and a glass transition point (Tg) measured by a differential thermobalance (DSC) method is about 40 deg.C or higher. When Tg is within this range and the MW of the polyurethane resin is high, sensitivity lowers and this lowering is estimated to be caused by the intermolecular flocculation force based on the entanglement of a molecular chain and, when the number average MW is about 20000 or less, especially, 10000 or less, good transfer and fixing properties can be obtained and, further, the effect due to the surface properties of paper to be transferred is not received. As a colorant, black type dye or pigment such as carbon black, oil black or graphite can be used.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a thermal transfer recording medium used in thermal transfer recording devices such as printers and facsimiles, and more specifically, to a thermal transfer recording medium that can be used in thermal transfer recording devices such as printers and facsimiles. The present invention relates to a thermal transfer recording medium that enables high-quality transfer recording.

[Conventional technology]

Thermal transfer recording method uses a thermal transfer recording medium made by coating at least one layer of heat-melting ink on a sheet-like base material, and stacks this heat-melting recording medium so that the heat-melting ink layer is in contact with the transfer paper. In addition, this is a recording method in which an ink layer is heated and melted by a heating head from the base material side of a thermal transfer recording medium to obtain a transferred image on a transfer paper. According to this method,
It has been widely used in recent years because the device used has low noise, is easy to operate and maintain, and plain paper can be used as the transfer paper.

[Problem to be solved by the invention]

However, conventional hot-melt inks such as those mentioned above
The binder material is mainly composed of wax, and when the wax softens, the hot melted ink is transferred to the surface of the transfer paper, so there is a problem that it is easily affected by the surface of the transfer paper. there were. In other words, the wax has a large viscosity drop due to heat and a very low melt viscosity, so if the surface of the transfer paper is uneven, the contact area of the ink to the depressions during melting is small, for example, the surface of the transfer paper is rough. When the solid smoothness is less than 30 to 40 seconds, ink application becomes uneven, which causes image quality deterioration.

Therefore, by increasing the thickness of the ink so that more ink is transferred to one point, the ink will reliably cover the surface of the transfer paper, eliminating the problems of decreased recording density and blur due to poor ink transfer. However, on the other hand, the blurring becomes larger and the size of one dot becomes larger, which deteriorates the resolution and causes deterioration of image quality.

In addition, as for the use of resin as a binder material for heat-melting ink,
No. 4-163044, No. 56-98269, No. 621
No. 30887 is known, but it cannot be said that it is sufficient in terms of performance.

Therefore, an object of the present invention is to provide a thermal transfer recording medium that is less affected by the surface of the paper to which the image is to be transferred and is capable of high-quality image transfer. Another object of the present invention is to provide a thermal transfer recording medium with good resolution.

[Means to solve the problem]

As a result of intensive research, the present inventors confirmed that the above objective could be achieved by changing the binder material of heat-melting ink from the conventional wax-based binder material to a polyurethane resin having a bisphenol skeleton. Furthermore, they have discovered that by providing a release layer between a base material and a heat-melt ink layer using the polyurethane resin as a binder material, a transferred image with higher sensitivity and higher quality can be obtained,
The present invention has now been completed.

That is, the present invention provides a thermal transfer recording medium formed by coating a heat-melting ink on a base material, wherein the heat-melting ink contains a polyurethane resin having a bisphenol skeleton and a colorant as main components. It provides a recording medium.

Waxes conventionally used as binder materials for hot-melt inks include paraffin wax, carnauba wax, montan wax, beeswax, wood wax, candelilla wax, low molecular weight polyethylene, α-olefin oligomers, and modified products thereof. If necessary, mineral oil such as spindle oil, vegetable oil such as linseed oil, tung oil, etc.
By mixing and dispersing plasticizers such as dioctyl phthalate and dibutyl phthalate, higher fatty acids such as oleic acid and stearic acid, their metal salts, amides, and other derivatives with dyes and pigments, and coating them on a thin layer of plastic film or condenser paper. It was considered a thermal transfer recording medium.

Waxes, which are conventional binder materials, have a relatively clear melting point in the temperature range of about 50°C to about 150"C because they are crystalline, and when heated above the melting point, they rapidly change from the solid phase. Changes to liquid phase.And 30"C below the melting point.
At moderately high temperatures, it becomes a low viscosity liquid with a viscosity of about 10-2 to 10 poise.

On the other hand, many resins essentially do not have a melting point, and gradually change from a solid phase to a liquid phase after reaching the glass transition point (Tg). The viscosity change during this period is at most 103 to 105 po even at a temperature about 50"C higher than Tg.
It usually decreases only to the level of ISE. In the case of thermal transfer recording, the transfer and fixing sensitivity is basically controlled by the melt viscosity and melt viscoelasticity of the binder material, so using resins as the binder material for heat-melt ink is clearly a sensitive issue. It is disadvantageous. However, the present inventors have discovered that by using a specific polyurethane resin binder material, high resolution can be achieved without sacrificing sensitivity, and high-quality transfer recording can be performed without being affected by the surface of the transfer paper. I found out. The details of the thermal transfer recording medium of the present invention will be explained below.

As the base material of the thermal transfer recording medium of the present invention, there are used papers such as capacitor paper and glassine paper, thin sheets and films of plastics such as polyester, polyimide, polycarbonate, polyamide, polyethylene, and polypropylene. The thickness of the base material is preferably in the range of about 2 to 20 mm. In addition, when recording using a thermal head, etc., in order to improve heat resistance, runnability, etc. on the side of the base material that comes into contact with the thermal head, silicone-based, fluorine thread compounds, resin layers, crosslinked polymer layers, metal A layer etc. may be provided.

The polyurethane resin having a bisphenol skeleton, which is an essential component of the thermal transfer recording medium of the present invention, generally has a number average molecular weight of about 20,000 or less in terms of polystyrene measured by gel permeation chromatography (GPC) method.
Glass transition point (Tg) measured by differential calorimetry (DSC) method
) is about 40°C or more, more preferably a number average molecular weight of about 1oooo or less, and a Tg of about 55°C to 90°C.
Use one within the range. When Tg is less than 55°C, particularly less than 40°C, blocking of the hot-melt ink tends to occur, resulting in a lack of stability during storage and use. Moreover, when Tg exceeds 90° C., although the thermal stability is good, the sensitivity is lowered, resulting in a lack of practicality, and there is a possibility that the application may be limited.

It has been experimentally found that even if Tg is within the above range, sensitivity decreases when the molecular weight of the polyurethane resin is high. This is presumed to be due to the cohesive force between molecules based on the entanglement of molecular chains, and the number average molecular weight is approximately 200.
Good transfer and fixing properties were obtained when it was 00 or less, especially 1oooo or less. Furthermore, it has been found that this method is not affected by the surface properties of the receiving paper. The setting of the weight average molecular weight may vary depending on the use of the thermal transfer recording medium. When it is desired to obtain a binary transferred image as with conventional wax-based inks, the weight average molecular weight is also about 20,000 or less, more preferably about 100.
It is desirable to make the softening characteristics of the resin more sensitive by setting the molecular weight distribution to 00 or less and narrowing the molecular weight distribution. on the other hand,
If you want to obtain density gradation or multilevel transferred images, or if you want to use it repeatedly many times, it is desirable to melt and transfer a resin that exhibits gradual softening characteristics according to the applied energy. It does not necessarily have to be small, and may be set to about 20,000 or more. Of course, even in this case, a binary transfer image can also be obtained satisfactorily.

Furthermore, the shape of the molecular weight distribution does not necessarily have to be a shape having a single molecular weight peak, but may be a distribution shape having a plurality of molecular weight peaks, or a crosslinked or branched polymer component may be used in combination. However, the weight average molecular weight is 100
If it is set to 00 or more, especially 40,000 or more, it is disadvantageous in terms of sensitivity.

The polyurethane resin having a bisphenol skeleton used in the present invention has the following formula: (In the formula, R+ and R2 are hydrogen atoms, alkyl groups, or phenyl groups. or a halogen group.) 2) Diols such as bisphenol compounds and their propion oxide adducts and ethylene oxide adducts, and aliphatic isocyanate compounds and alicyclic isocyanate compounds having two isocyanate groups in the molecule; It is a polyurethane resin obtained by addition polymerization with an aromatic isocyanate compound, such as toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate, etc., and further contains an isocyanate group in the molecule. A branched or crosslinked polyurethane resin may be obtained by using an isocyanate compound having three or more isocyanate compounds.

Although the binder material of the present invention can sufficiently achieve its purpose even if it is composed of only one or more of the above polyurethane resins, other polymers and additives may be added and mixed as necessary.

For example, styrene, vinyltoluene, α-methylstyrene, 2-methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, aminostyrene and other styrene and its derivatives, homopolymers and copolymers of substituted products, Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, acrylic acid esters such as methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hyacrylic acid, butadiene, isoprene, etc. Dienes, acrylonitrile, vinyl ethers, maleic acid and maleic esters, maleic anhydride,
Vinyl monomers such as cinnamic acid and vinyl chloride can be used alone or in copolymers with other monomers. Of course, the vinyl resin may also be used as a crosslinked polymer using a polyfunctional monomer such as divinylbenzene.

Furthermore, polycarbonate, polyamide, polyester, silicone resin, fluorine resin, epoxy resin,
Phenol resins, terpene resins, petroleum resins, hydrogenated petroleum resins, alkyd resins, ketone resins, cellulose derivatives, etc. may be used.

When these polymers or oligomers are used in the form of copolymers, the copolymers include random copolymers,
Copolymerization modes such as alternating copolymers, graft copolymers, block copolymers, and interpenetrating copolymers can be appropriately selected and used depending on the required use. In addition, when using a mixture of two or more types of polymers or oligomers, in addition to mechanical mixing such as melt mixing, solution mixing, or emulsion mixing, they may be mixed by coexistence polymerization, multistage polymerization, etc. during polymerization of the polymer or oligomer components. It's okay.

Furthermore, if necessary, waxes, oils, and liquid plasticizers such as those used in conventional hot-melt inks may be added and mixed. However, in terms of image quality, it is preferable that the polyurethane resin component generally accounts for 30% or more, preferably 70% or more by volume of all binder material components.

1 Colorants include black dyes and pigments such as carbon black, oil black, and graphite; C, 1, PigmentYel
low l, same 3. Same 74. 97. Acetoacetate arylamide monoazo yellow pigment (Fast Yellow) such as 98;
12+ A7toacetic acid arylamide bisazo yellow pigment such as 13 and 14;
oiv19+ Same 77, Same 79, C, 1, Disper
Yellow dyes such as Se Yellow 164; C, I.

Pigment Red 48+ 49:1. Same 5
3:1. 57:1. 81, 122. Red or pink pigment of the same grade 5; C, I.

5olvent Red 52+ Same 58. Red dye of grade 8; c.

1. Blue light dyes and pigments such as copper phthalocyanine and its derivatives and modified products such as Pigment B1ue15:3 can be used, and dyes and pigments well known for conventional printing inks and other coloring applications such as colored or colorless sublimable dyes can be used. can be used.

These dyes and pigments may be used alone or in combination of two or more. Of course, the color tone may be adjusted by mixing with an extender pigment or a white pigment. Furthermore, in order to improve the dispersibility of the binder material components, the surface of the colorant may be treated with a surfactant, a coupling agent such as a silane coupling agent, or a polymeric material, or a polymeric dye or polymeric graft may be added to the surface of the colorant. Pigments may also be used.

The thermal transfer recording medium of the present invention is formed by placing a heat-melting ink, which is a mixture of the polyurethane resin, a colorant, and, if necessary, the various additives described above, on a base material. Furthermore, if a release layer is provided between the base material and the heat-melting ink layer, a thermal transfer recording medium with higher sensitivity can be obtained.

The release layer contains silicone resins, higher fatty acids, higher fatty acid metal salts, fatty acid derivatives, higher alcohols,
Alternatively, waxes or the like may be used. Waxes are particularly preferably used, such as paraffin wax, montan wax, carnauba wax, beeswax, wood wax, candelilla wax, low molecular weight polyethylene, α-olefin oligomers, and modified products thereof as binders for heat-melting inks. Known waxes that have been conventionally used as materials include4. The above waxes may be used alone or in combination of two or more. In addition to waxes, resins such as ethylene vinyl acetate copolymer, ethylene-acrylic acid copolymer, polyethylene, petroleum resin, etc. may be added in order to improve the strength of the coating film.

The heat-melting ink of the present invention is produced by forming a solution or dispersing emulsion in a solvent or dispersion medium that can dissolve or stably disperse the binder material, and mixing and dispersing it using a ball mill, sand mill, attritor, basket mill, three-roll mill, etc. It can be prepared by machine. Alternatively, the mixture may be melt-mixed using a heating type Miki roll, a heating type kneader-1 heating type sand mill, a heating type attritor, etc., without using any particular solvent or the like. Furthermore, a polyurethane resin as the main binder material may be prepared by synthesis in the presence of colorants, additives, etc., and may be used as a heat-melting ink.

The heat-melting ink thus prepared is coated and printed on a substrate by a solution or melt coating method using a gravure coater, a wire bar, or the like.

Alternatively, the hot-melt ink may be pulverized by a spray drying method, a pulverization method, etc., and then powder coated onto a base material by an electrostatic coating method or the like. In this case, after powder coating, heating, pressurization, solvent treatment, etc. may be further performed as necessary to fix the heat-melting ink onto the base material.

〔Example〕

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

In addition, in the following examples, parts represent parts by weight unless otherwise specified.

Example 1 <Synthesis of polyurethane resin A> 350 g of G1652 (2 mol adduct of bisphenol A with propylene oxide, manufactured by Kao ■) was placed in a separable flask No. 11, heated and kept at 110°C, and subjected to MDI.
(manufactured by Nippon Polyurethane ■) was added little by little to obtain polyurethane resin A.

<Preparation of heat-melt ink> Heat-melt ink components having the following composition were kneaded in a ball mill at room temperature for 24 hours to prepare heat-melt ink.

・Ethylene-vinyl acetate copolymer 2 parts ・Carbon black 4 parts ・Toluene
40 parts methyl ethyl ketone
40 parts of the hot-melt ink liquid obtained above was added to a thickness of 4-4.
It is applied onto the polyimide film using a wire bar,
It was dried at 60°C to provide a 2.5 jrm thick hot melt ink layer.

Example 2 A thermofusible ink having the following composition was kneaded in a ball mill at room temperature for 24 hours to prepare a thermofusible ink.

・Polyurethane resin 8 12 parts ・Ethylene-vinyl acetate copolymer 3 parts ・Carbon black
Part 5/Toluene
40 parts/Methyl ethyl ketone 40 parts The hot-melt ink liquid obtained above was applied onto a 4-thick polyester film using a wire bar, dried at 60°C, and a 2.5-thick hot-melt ink was applied onto the polyester film. An ink layer was provided.

Example 3 A thermofusible ink having the following composition was kneaded in a ball mill at room temperature for 24 hours to prepare a thermofusible ink.

・Polyurethane resin B 13 parts 8 ・Ethylene-vinyl acetate copolymer 3 parts ・Carbon black 4 parts ・Toluene
40 parts methyl ethyl ketone
40 parts of the hot-melt ink liquid obtained above was applied onto a 4p thick polyester film using a wire bar,
It was dried at 60''C to form a heat-melting ink layer with a thickness of 2.5 tiles.

Example 4 The following layers were formed on a 6-thick polyester film to form an ink sheet as a thermal transfer recording medium.

■Release layer Microcrystalline wax (melting point = 75℃) 10
A release layer was provided by applying the film to a thickness of 1.5 μm using a wire bar in a 0°C constant temperature bath.

(2) Heat-melt ink layer The heat-melt ink liquid of Example 1 was coated onto the release layer using a wire bar so that the heat-melt ink layer had a thickness of 3 μm to obtain a heat transfer ink sheet.

Example 5 The following layers were formed on a 4 μm thick polyester film to form an ink sheet as a thermal transfer recording medium.

■Release layer Oxidized paraffin wax (melting point -85°C) at 100°C
A release layer was provided by coating 1.5 parts and 1 m thick using a wire bar in a constant temperature bath.

(2) Heat-melt ink layer The heat-melt ink liquid of Example 2 was coated onto the release layer using a wire bar so that the heat-melt ink layer had a thickness of 31M to obtain a heat transfer ink sheet.

Example 6 The following layers were formed on a polyester film having a thickness of 4p to form an ink sheet as a thermal transfer recording medium.

(2) Release layer A release layer was provided by applying carnauba wax (melting point -82°C) to a thickness of 1.51M using a wire bar in a 100°C constant temperature bath.

■ Heat-melt ink layer The heat-melt ink liquid of Example 3 was coated on the release layer using a wire bar so that the heat-melt ink layer had a thickness of 3 parts and 1 m to form a heat transfer ink sheet. did.

Comparative Example 1 A heat-fusible ink having the following composition was melt-mixed at loO'c and kneaded using three rolls to prepare a heat-fusible ink.

・Paraffin wax (melting point = 72°c) 50 parts・
20 parts of carnauba wax, 1 part of ethylene-vinyl acetate copolymer, 20 parts of carbon black The hot-melt ink obtained above was placed on a 41M thick polyester film on a hot plate heated to 110'C. The heat-melting ink layer was applied with a wire bar to a thickness of 3 μm to obtain a heat transfer ink sheet.

10 Comparative Example 2 A thermofusible ink having the following composition was kneaded in a ball mill at room temperature for 24 hours to prepare a thermofusible ink.

・Ethylene-vinyl acetate copolymer 3 parts ・Carbon black 5 parts ・Toluene
40 parts methyl ethyl ketone
40 parts of the hot-melt ink liquid obtained above was applied onto a 4-tone thick polyester film using a wire bar,
It was dried at 60° C. to form a 2.5-thick heat-melt ink layer.

Comparative Example 3 The following layers were formed on a polyester film having a thickness of 611 m to form an ink sheet as a thermal transfer recording medium.

■Release layer Microcrystalline wax (melting point -75°C) 1
A mold release layer was provided by coating to a thickness of 1.5 mm using a wire bar in a constant temperature bath at 00°C.

■Thermofusible ink layer - Paraffin wax (melting point = 72°C) 12 parts - Carnauba wax 2 parts - Ethylene-vinyl acetate copolymer 2 parts - Carbon black
Part 4/Toluene
40 parts methyl ethyl ketone 40
The heat-melt ink liquid obtained by kneading the above composition at 40°C for 24 hours in a ball mill was placed on the release layer with a wire bar so that the heat-melt ink layer was 3 mm thick. A thermal transfer ink sheet was prepared.

Comparative Example 4 The following layers were formed on a 4-thick polyester film to form an ink sheet as a thermal transfer recording medium.

(2) Release layer A release layer was provided by applying carnauba wax (melting point -82°C) to a thickness of 1.5 cm using a wire bar in a 100°C constant temperature bath.

■ Heat-melt ink layer The heat-melt ink liquid of Comparative Example 2 was applied onto the release layer using a wire bar so that the heat-melt ink layer had a thickness of 3 parts m, and a heat-melt ink sheet was formed. did.

Using the ink sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 4 above, a serial printer PC-P manufactured by NEC Corporation was used.
Printing was performed using R150V, and the print density, recording sensitivity, and resolution of the transferred image were tested.

The results are shown in Table-1.

3 Table The evaluation method for the recording characteristics shown in Table 1 above is as follows.

Print density: Continuous printing was measured using a Macbeth reflection densitometer.

The surface quality of the transfer paper is different from thermal transfer paper. Beck smoothness 200 seconds, bond paper 155 4 Seconds.

Recording sensitivity: Thermal head heating element size (1/12
Evaluation was made based on the energy (E) applied to the thermal head required to record transfer dots corresponding to 1.2 mm (mm-83-) on thermal transfer paper at a print density of 1.2.

Evaluation criteria ○; E <0.08mJ/dat Δ; 0.013mJ/dot≦E≦0.11mJ/d
otX; 0.11 mJ/dot<E or resolution that does not reach print density 1.2: Evaluated based on legibility of kanji (especially those with a large number of strokes).

Evaluation criteria: O: Good legibility Δ: Normal
A supplementary explanation is given below.

Comparative Example 1, which uses wax as a binder, shows relatively good printing results on thermal transfer paper, but on bond paper with uneven surfaces, the print density is low, and when there are kanji characters with a large number of strokes, the characters are distorted. may be difficult to read. On the other hand, Example 1 showed very good printing results and showed high printing density even on bond paper. Ta.

Comparative Example 3.4 showed the effect of providing a release layer containing wax as a main component between the base material and the heat-melting ink layer. However, although this result shows an improvement in printing quality compared to Comparative Example 1゜2, Example 1, which does not have a release layer,
- Inferior to heat-melting ink sheets of No. 3.

Examples 4 to 6 also showed the effect of providing a release layer containing wax as a main component between the base material and the hot-melt ink layer, and the print quality was further improved compared to Examples 1 to 3.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a thermal transfer recording medium that is less affected by the unevenness of the surface of the transfer paper and can provide a high-quality transferred image. Furthermore, the thermal transfer recording medium of the present invention can provide a transfer image with even higher sensitivity by providing a release layer containing wax as a main component between the base material and the heat-melting ink layer. is obtained.

Claims (1)

[Claims] 1. A thermal transfer recording medium formed by coating a heat-melt ink on a substrate, characterized in that the heat-melt ink contains a polyurethane resin having a bisphenol skeleton and a colorant as main components. thermal transfer recording media. 2. The thermal transfer recording medium according to claim 1, further comprising a release layer between the base material and the heat-melting ink layer.