JP2786503B2 - Thermal transfer recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermal transfer recording medium used in a thermal transfer recording apparatus such as a printer, a facsimile, etc.
The present invention relates to a thermal transfer recording medium capable of performing high-quality transfer recording without being affected by the surface of a receiving paper.

[Conventional technology]

The thermal transfer recording method uses a thermal transfer recording medium obtained by applying at least one layer of a thermal fusible ink on a sheet-like substrate, and superimposes the thermal transfer recording medium such that the thermal fusible ink layer is in contact with the transfer target paper. In addition, this is a recording method in which the ink layer is heated and melted by a heating head from the substrate side of the thermal transfer recording medium to obtain a transfer image on the transfer receiving paper. According to this method, the apparatus to be used has been widely used in recent years because the apparatus to be used is low noise, has excellent operability and maintainability, and can use plain paper as a transfer paper.

[Problems to be solved by the invention]

However, the conventional hot-melt ink as described above, the binder material is the main component of the wax, because the wax is softened to transfer the hot-melted ink to the surface of the receiving paper, There has been a problem that the transfer paper is easily affected by the surface. That is, since the wax has a large decrease in viscosity due to heat and a very low melt viscosity, if there is unevenness on the surface of the receiving paper, the contact area of the ink to the concave portion at the time of melting is small. When the Beck smoothness is less than 30 to 40 seconds, the ink ride becomes uniform, which is a cause of image quality deterioration.

If the thickness of the ink is increased so that a large amount of ink is transferred to one point, the ink surely covers the surface of the paper to be transferred, so that there is no problem of a decrease in recording density or blur due to poor transfer of the ink. However, on the other hand, the bleeding becomes large, the size of one dot becomes large, and the resolution becomes poor, which causes deterioration in image quality.

Further, as those using a resin as a binder material of the hot-melt ink, JP-A-54-87234 and JP-A-54-16304
No. 4, No. 56-98269, No. 62-130887, etc. are known, but it is hard to say that performance is sufficient.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thermal transfer recording medium which is less affected by the surface of a sheet to be transferred and can perform high-quality transfer. Another object of the present invention is to provide a thermal transfer recording medium having good resolution.

[Means for solving the problem]

The present inventors have conducted intensive studies and confirmed that the above object can be achieved by changing the binder material of the hot-melt ink from a conventional wax-based binder to a polyurethane resin having a bisphenol skeleton. Further, by providing a release layer between the substrate and the hot-melt ink layer using the polyurethane resin as a binder material,
It has been found that a transfer image with higher sensitivity and higher image quality can be obtained, and the present invention has been completed.

That is, the present invention provides a thermal transfer recording medium obtained by applying a hot-melt ink onto a substrate, wherein the hot-melt ink contains a polyurethane resin having a bisphenol skeleton and a coloring agent as main components. A recording medium is provided.

Conventionally, waxes 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 oils such as spindle oil and linseed oil, vegetable oils such as tung oil, plasticizers such as dioctyl phthalate and dibutyl phthalate, higher fatty acids such as oleic acid and stearic acid, metal salts thereof, amide and other Derivatives are mixed and dispersed together with dyes and pigments and applied to a thin plastic film or condenser paper to form a thermal transfer recording medium.

Such conventional waxes as binder materials have a relatively clear melting point in a temperature range of about 50 ° C. to about 150 ° C. because of their crystalline nature, and when heated above the melting point, the solid phase rapidly changes from a solid phase to a liquid phase. Changes to At a temperature about 30 ° C. higher than the melting point, the liquid becomes a low-viscosity liquid having a viscosity of about 10 ^{−2 to} 10 poise.

On the other hand, many resins have essentially no melting point, and gradually change from a solid phase to a liquid phase at the glass transition point (Tg). The change in viscosity during this period usually decreases to at most about 10 ³ to 10 ⁵ poise even at a temperature about 50 ° C. higher than Tg. In the case of thermal transfer recording, the transfer and fixing sensitivity is basically governed by the melt viscosity and melt viscoelasticity of the binder material. Disadvantageous. However, when the present inventors use a specific polyurethane resin-based binder material, the resolution can be increased without sacrificing sensitivity, and further, high-quality transfer recording can be performed without being affected by the surface of the receiving paper. Was found. Hereinafter, the details of the thermal transfer recording medium of the present invention will be described.

As the base material of the thermal transfer recording medium of the present invention, condenser paper, papers such as glassine paper, polyester, polyimide,
Thin-film sheets and films of plastics such as polycarbonate, polyamide, polyethylene, and polypropylene are used. The thickness of the substrate is preferably in the range of about 2 to 20 μm. When recording is performed using a thermal head or the like, a silicon-based or fluorine-based compound, a resin layer or a crosslinked polymer layer, a metal A layer or the like 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 polystyrene-equivalent number average molecular weight of about 20,000 or less as measured by gel permeation chromatography (GPC) and a differential thermal balance (DSC) method. The measured glass transition point (Tg) is about 40 ° C
More preferably, those having a number average molecular weight of about 10,000 or less and a Tg in the range of about 55 ° C to 90 ° C are used.
When the Tg is less than 55 ° C., particularly less than 40 ° C., the blocking of the hot-melt ink tends to occur, and the stability during storage and use is lacking. When the Tg exceeds 90 ° C., the thermal stability is good, but the sensitivity is reduced, and thus the practicality is lacking, and the use may be limited.

It has been experimentally confirmed that the sensitivity is lowered when the molecular weight of the polyurethane resin is high even when the Tg is within the above range. This is presumed to be due to cohesion between molecules based on entanglement of molecular chains, etc., and the number average molecular weight is about 20,000
Below, good transfer and fixing properties were obtained especially when the value was 10,000 or less. Furthermore, they also found that they were not affected by the surface properties of the receiving paper. The measurement of the weight average molecular weight may vary depending on the use of the thermal transfer recording medium. When a binary transfer image is desired to be obtained in the same manner as a conventional wax-based ink, the weight average molecular weight is about 20,000 or less, more preferably about 10,000 or less, and the molecular weight distribution is narrowed to make the softening characteristics of the resin more sharp. It is desirable. On the other hand, when it is desired to obtain a density gradation property or a multi-value transfer image, or to use repeatedly many times, it is desirable to melt-transfer a resin exhibiting a gradual softening characteristic in accordance with the applied energy. It is not necessary to reduce the average molecular weight,
It may be set to 0 or more. Of course, even in this case, a binary transfer image can be obtained well. Furthermore, the shape of the molecular weight distribution does not necessarily need 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, when the weight average molecular weight is set to 10,000 or more, particularly 40,000 or more, it is disadvantageous in sensitivity.

The polyurethane resin having a bisphenol skeleton used in the present invention has the following formula: (In the formula, R ¹ and R ² are a hydrogen atom, an alkyl group or a phenyl group. R ³ , R ⁴ , R ⁵ and R ⁶ are a hydrogen atom, an alkyl group or a halogen group.) And diols such as propion oxide adducts and ethylene oxide adducts thereof and aliphatic isocyanate compounds having two isocyanate groups in the molecule, alicyclic isocyanate compounds, aromatic isocyanate compounds such as toluene diisocyanate TDI), a polyurethane resin obtained by addition polymerization with 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate, etc., and further using an isocyanate compound having three or more isocyanate groups in the molecule to form a branched or branched resin. It may be a crosslinked polyurethane resin.

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

For example, styrene and vinyl toluene, α-methylstyrene, 2-methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, styrene such as aminostyrene and derivatives thereof, homopolymers and copolymers of substituted products, Methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid esters such as hydroxyethyl methacrylate and methacrylic acid,
Acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate, and acrylic acids, butenes such as butadiene and isoprene, acrylonitrile, vinyl ethers,
Maleic acid and maleic acid esters, maleic anhydride, cinnamic acid, vinyl chloride and other vinyl monomers alone or copolymers with other monomers can be used.
Needless to say, the vinyl resin may be used as a crosslinked polymer using a polyfunctional monomer such as divinylbenzene.

Furthermore, polycarbonate, polyamide, polyester, silicone resin, fluorine resin, epoxy resin, phenol resin, terpene resin, petroleum resin, hydrogenated petroleum resin, alkyd resin, ketone resin, cellulose derivative and the like may be used. . When these polymers or oligomers are used in the form of a copolymer, the copolymer may be a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, A copolymerization mode such as a penetration copolymer can be appropriately selected and used. When two or more kinds of polymers and oligomers are mixed and used, in addition to mechanical mixing such as melt mixing, solution mixing, and emulsion mixing, polymer and oligomer components are mixed by coexistence polymerization, multistage polymerization, or the like. You may.

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

Colorants include carbon black, oil black,
Black dyes such as graphite; CI Pigment Yellow 1, 3, and 74,
97, 98 etc. acetoacetate arylamide monoazo yellow pigments (fast yellow); CI Pigment Yellow 12, 1
3, acetoacetate arylamide-based bisazo yellow pigment such as 14; CISolvent Yellow 19, 77, 79, CI Disperse Ye
yellow dyes such as llow164; CI Pigment Red 48, 49: 1, 53:
1, 57: 1, 81, 122, 5 etc. red or red pigment; CIS
red pigments such as olvent Red 52, 58 and 8; CI Pigment Bl
Blue dyes and pigments such as copper phthalocyanine and derivatives thereof such as ue15: 3 can be used, and dyes and pigments known in conventional printing inks and other coloring applications such as colored or colorless sublimable dyes 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 or a white pigment. Furthermore, the surface of the colorant is treated with a surfactant, a coupling agent such as a silane coupling agent, a polymer material, or a polymer dye or a polymer graft pigment to improve the dispersibility of the binder component. May be used.

The thermal transfer recording medium of the present invention is formed by disposing a heat-meltable ink obtained by mixing the polyurethane resin, the colorant and, if necessary, the various additives described above on a substrate.
Further, when a release layer is provided between the base material and the heat-meltable ink layer, a thermal transfer recording medium with higher sensitivity can be obtained.

For the release layer, silicone resins, higher fatty acids, higher fatty acid metal salts, fatty acid derivatives, higher alcohols, waxes and the like are used. Particularly preferably, waxes are used, for example, paraffin wax,
Montan wax, carnauba wax, beeswax, wood wax, candelilla wax and low molecular weight polyethylene, α
-Known waxes conventionally used as binder materials for hot-melt inks such as olefin oligomers and modified products thereof. The above waxes may be used alone or in combination of two or more. In addition to waxes, ethylene-
Vinyl acetate copolymer, ethylene-acrylic acid copolymer,
Resins such as polyethylene and petroleum resin may be added.

Production of the hot melt ink of the present invention, in a solvent or dispersion medium capable of dissolving or stably dispersing the binder material,
It can be prepared as a solution or a dispersion emulsion by using a mixing and dispersing machine such as a ball mill, a sand mill, an attritor, a basket mill, and a three-roll mill. Further, the solvent may be melt-mixed with a heated three-roll mill, a heated kneader, a heated sand mill, a heated attritor, or the like without particular use of a solvent. Furthermore, a polyurethane resin as a main binder material may be prepared by synthesis in the presence of a coloring agent, an additive, and the like, to obtain a hot-melt ink.

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

Alternatively, the heat-meltable ink may be pulverized by a spray drying method, a pulverizing method, or the like, and then powder-coated on the substrate by an electrostatic coating method or the like. In this case, after the powder coating, if necessary, heating, pressurizing, solvent treatment, or the like may be performed to fix the hot-melt ink on the base material before use.

〔Example〕

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

In the following examples, parts are by weight unless otherwise specified.

Example 1 <Synthesis of polyurethane resin A> G1652 (Propylene oxide 2 of bisphenol A)
350 g of a mole adduct (Kao Corporation) was placed in a separable flask, heated and kept at 110 ° C., and 170 g of MDI (Nippon Polyurethane Corporation) was added little by little to obtain a polyurethane resin A.

<Preparation of hot melt ink> A hot melt ink component having the following plasticity was kneaded in a ball mill at room temperature for 24 hours to prepare a hot melt ink.

・ Polyurethane resin A 14 parts ・ Ethylene-vinyl acetate copolymer 2 parts ・ Garbon black 4 parts ・ Toluene 40 parts ・ Methyl ethyl ketone 40 parts The hot-melt ink liquid obtained above was applied to a 4 μm-thick polyimide film by a wire bar, 60 ℃
To provide a hot-melt ink layer having a thickness of 2.5 μm.

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

・ 12 parts of polyurethane resin B ・ Ethylene-vinyl acetate copolymer 3 parts ・ Carbon black 5 parts ・ Toluene 40 parts ・ Methyl ethyl ketone 40 parts The hot-melt ink liquid obtained above was applied to a 4 μm-thick polyester film by a wire bar, and
It dried at ℃ and provided the 2.5-micrometer-thick hot-melt ink layer.

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

・ 13 parts of polyurethane resin B ・ Ethylene-vinyl acetate copolymer 3 parts ・ Carbon black 4 parts ・ Toluene 40 parts ・ Methyl ethyl ketone 40 parts The hot-melt ink liquid obtained above was applied on a 4 μm-thick polyester film with a wire bar,
It dried at ℃ and provided the 2.5-micrometer-thick hot-melt ink layer.

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

Release layer 100 microcrystalline wax (melting point = 75 ° C)
The coating was applied to a thickness of 1.5 μm with a wire bar in a constant temperature bath at 0 ° C. to provide a release layer.

Heat-meltable ink layer The heat-meltable ink liquid of Example 1 was applied on the release layer with a wire bar so that the heat-meltable ink layer had a thickness of 3 µm, to obtain a thermal 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 An oxidized paraffin wax (melting point = 85 ° C.) was applied to a thickness of 1.5 μm with a wire bar in a constant temperature bath at 100 ° C. to provide a release bath.

Heat-meltable ink layer The heat-meltable ink liquid of Example 2 was applied onto the release layer with a wire bar so that the heat-meltable ink layer had a thickness of 3 μm to obtain a thermal transfer ink sheet.

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

Release Layer Carnauba wax (melting point = 82 ° C.) was applied with a wire bar to a thickness of 1.5 μm in a thermostat at 100 ° C. to form a release layer.

Heat-meltable ink layer The heat-meltable ink liquid of Example 3 was applied onto the release layer with a wire bar so that the heat-meltable ink layer had a thickness of 3 µm, to obtain a thermal transfer ink sheet.

Comparative Example 1 A hot-melt ink having the following composition was melt-mixed at 100 ° C. and kneaded with a three-roll mill to prepare a hot-melt ink.

・ 50 parts of paraffin wax (melting point = 72 ° C.) ・ 20 parts of carnauba wax ・ 10 parts of ethylene-vinyl acetate copolymer ・ 20 parts of carbon black The hot-melt ink obtained above was heated on a hot plate heated to 110 ° C. It was applied on a 4 μm thick polyester film with a wire bar so that the thickness of the hot-melt ink layer was 3 μm to obtain a thermal transfer ink sheet.

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

・ 12 parts of unsaturated polyester resin ・ Ethylene-vinyl acetate copolymer 3 parts ・ Carbon black 5 parts ・ Toluene 40 parts ・ Methyl ethyl ketone 40 parts The hot-melt ink liquid obtained above was applied to a 4 μm-thick polyester film by a wire bar, and
It dried at ° C, and provided the 25-micrometer-thick hot-melt ink layer.

Comparative Example 3 The following layers were formed on a 6 μm-thick polyester film to form an ink sheet as a thermal transfer recording medium.

Release layer 100 microcrystalline wax (melting point = 75 ° C)
The coating was applied to a thickness of 1.5 μm with a wire bar in a constant temperature bath at 0 ° C. to provide a release layer.

Hot-melt ink layer ・ Paraffin wax (melting point = 72 ° C) 12 parts ・ Carnauba wax 2 parts ・ Ethylene-vinyl acetate copolymer 2 parts ・ Carbon black 4 parts ・ Toluene 40 parts ・ Methyl ethyl ketone 40 parts The above composition is used in a ball mill. The heat-meltable ink liquid obtained by kneading at 40 ° C. for 24 hours is coated on the release layer with a wire bar so that the heat-meltable ink layer has a thickness of 3 μm. And

Comparative Example 4 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 Carnauba wax (melting point = 82 ° C.) was applied with a wire bar to a thickness of 1.5 μm in a thermostat at 100 ° C. to form a release layer.

Heat-meltable ink layer The heat-meltable ink liquid of Comparative Example 2 was applied on the release layer with a wire bar so that the heat-meltable ink layer had a thickness of 3 μm, to obtain a thermal transfer ink sheet.

A serial printer PC manufactured by NEC Corporation using the ink sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 4.
Printing was performed using -PR150V, and the print density, recording sensitivity, and resolution of the transferred image were tested.

 Table 1 shows the results.

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

Printing density: Continuous printing was measured with a Macbeth reflection densitometer.

Thermal transfer paper has a Beck smoothness of 200
Seconds, bond paper is 15 seconds.

Recording sensitivity: Thermal head heating element size (1 / 12mm = 83
μm) on a thermal transfer paper with a print density of 1.
The evaluation was made based on the thermal head applied energy (E) required for recording in 2.

Evaluation criteria ○; E <0.08mJ / dot △; 0.08mJ / dot ≦ E ≦ 0.11mJ / dot ×; 0.11mJ / dot <E or print density does not reach 1.2 Resolution: legibility of kanji (especially with many strokes) ).

Evaluation Criteria 良好: Good readability △: Normal ×: Difficult to read The evaluation results of each heat-fusible ink shown in Table 1 are supplementarily described below.

Comparative Example 1 using wax as a binder material shows relatively good printing results on thermal transfer paper, but has low print density on bond paper having irregularities on the surface of the receiving paper, and character crushing on kanji with many strokes. And may be difficult to read. On the other hand, in Example 1, a very good print result was shown, and a high print density was shown even with the bond paper.

Comparative Examples 3 and 4 showed the effect of providing a release layer containing a wax as a main component between the base material and the hot-melt ink layer. However, although the results show that the print quality is improved as compared with Comparative Examples 1 and 2, Examples 1 to 3 in which the release layer was not provided.
3 is inferior to the hot-melt ink sheet.

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

〔The invention's effect〕

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

Continuation of front page (56) References JP-A-2-158388 (JP, A) JP-A-62-144996 (JP, A) JP-A-64-47588 (JP, A) JP-A-62-152795 (JP) JP-A-62-13383 (JP, A) JP-A-2-131989 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41M 5/38-5/40

Claims (2)

(57) [Claims] 1. A thermal transfer recording medium comprising a base material coated with a heat-fusible ink, wherein the heat-fusible ink contains a polyurethane resin having a bisphenol skeleton and a coloring agent as main components. recoding media. 2. The thermal transfer recording medium according to claim 1, further comprising a release layer between the substrate and the heat-fusible ink layer.