JPH0710631B2 - Transfer type thermal recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention has a thermal transferable ink layer having a laminated structure of two or more layers and enables clear recording even on recording paper having a poor surface smoothness. Regarding the medium.

2. Description of the Related Art The transfer-type thermal recording method is widely used as a plain paper recording method with a simple device, but the printing quality is easily influenced by the smoothness of the surface of the recording paper, and it is suitable for recording paper with poor surface smoothness. It was difficult to make clear prints.

In order to improve such a defect, heat treatment after printing is conventionally performed (JP-A-58-76276), magnetic force after transfer and (JP-A-52-9).
6549), electrostatic force (Japanese Patent Laid-Open No. 55-65590), or a large amount of an oily substance to reduce the viscosity of the ink during recording (Japanese Patent Laid-Open No. 60-25762), thermal decomposition ( JP-A-60-82389) and a method of thermally sensitizing or thermally expanding an ink with a heat-expandable substance (JP-A-60-25762) have been proposed. A technique for improving print quality by forming a multi-layered heat-meltable ink layer has been conventionally known. A heat-meltable ink layer having a slightly different melting point is laminated, and a pigment is added to either or both. (JP-A-59-224392), techniques such as providing a heat-fusible layer containing no color material on the ink layer (JP-A-60-97888) have been proposed.

However, in the method in which the ink which is melted and becomes liquid is transferred and recorded as described above, the smoothness of the recording paper surface is improved, although the relationship of the print quality is improved. When the recording paper was inferior, the printing quality was different, and by comparison, the relationship that the printing quality was poor when the smoothness was inferior could not be fundamentally improved.

On the other hand, when heat energy is applied, it shows tackiness but does not melt to a low-viscosity liquid, has some mechanical strength, and sticks to the convex part of the recording paper to cover the concave part. There is a proposal (Japanese Patent Laid-Open No. 54-87234) that suggests that if a transfer ink is used, it is possible to print with high print quality even on recording paper having a poor surface smoothness. Since it contains an inferior resin as a main component, it has a drawback that a large amount of heat energy and pressure are required at the time of recording, and there are problems such as the life of the heat resistant thermal head of the support and heat storage during recording. As a method of sensitizing such a resin ink, there is a peeling layer which has been used for a long time in transfer printing technology, and a wax peeling layer is used even in the millisecond-class pulse recording currently used in transfer-type thermal recording. There is also a suggestion that it is effective (JP-A-47-11215). However, the wax alone or the heat-fusible resin added to the wax is an easily meltable release layer, which is storable before recording, is recorded at high temperature, and is recorded continuously when the thermal head heats up. Mainly due to the meltability of wax and the fact that it becomes a low-viscosity liquid when melted, the release layer is absorbed by the ink layer and loses its effect, the release layer collapses before recording, and even to the non-printed area. In addition to having the drawback of melting and causing stains and crushed characters, there were also relatively large restrictions in production.

OBJECT The object of the present invention is to provide a transfer type thermal recording medium which is capable of clear printing even on recording paper having a poor surface smoothness, is easy to manufacture, and has excellent recording stability and reliability. .

Structure The present invention provides a transfer type thermal recording medium comprising a heat-resistant support and a thermal transferable ink layer, wherein the ink layer has a laminated structure of two or more layers, and the first layer on the support side has a heat melting property. 80 pigments and waxes with a heat of fusion of 30 cal / g or more in the substance
% Or more, the thermal transfer material of the uppermost layer has a tensile strength of 20 kg / cm ² or more at 20 ° C and an elongation at 20 ° C.
It is a transfer type thermal recording medium characterized by containing 80% or more of resin of 200% or more.

The melting point of the wax of the first layer has a peak value in the suggested thermal analysis.
Those below 100 ° C are desirable. Examples of such waxes include natural waxes such as beeswax, whale wax, candelilla wax, rice wax, carnauba wax, montan wax, and ozokerite, and petroleum waxes such as paraffin wax and microcrystalline wax. However, various modified waxes, hydrogenated waxes, long-chain fatty acids and their derivatives and salts thereof, etc. may be mentioned.

The other component of the heat-fusible substance of the first layer is a binder resin, and polyethylene, polypropylene, ethylene vinyl acetate copolymer or the like can be used, but it is not always an essential component.

However, the pigment is an essential component. The term "pigment" as used herein means a component that disperses in the wax component but does not dissolve, and also includes a coloring pigment as a coloring material. When the pigment is contained, the layer can be prevented from collapsing and peeling off due to an increase in ambient temperature, and if the pigment is a colored pigment, the printed characters after recording become clear.

Unlike the first layer, the top layer is a resin that does not undergo a clear phase change from solid to liquid, and whose viscosity continuously changes with increasing temperature. Its tensile strength and elongation are JIS K 676.
It is the value measured from 0 to 1966.

Examples of such resins include polyesters, polyamides, ethylene-vinyl acetate copolymers, styrene-butadiene copolymers, and the like, and among these, selected in consideration of pigment separability, thermal characteristics, and the like. To be done.

In addition to the above, it is possible to add a tackifier such as a terpene resin or a rosin derivative or a wax as the heat-meltable component of the uppermost layer, but it is desirable that the total amount thereof does not exceed 20%. It is more desirable to include a pigment. The amount of the pigment added is determined by the sensitivity during recording, the high temperature storability and the like. Excessive addition of pigment deteriorates the printing characteristics during recording, which is not desirable.
% Or less is desirable. Further, if no pigment is added at all, blocking tends to occur due to storage at high temperature, and the running property of the recording medium during recording may deteriorate.

In order to manufacture the transfer type thermal recording medium in which the first layer and the uppermost layer are laminated as described above, a usual coating means can be used. That is, the first layer can be easily manufactured industrially by a hot melt coating method and the uppermost layer can be easily manufactured by a solvent dispersion coating method.

In the transfer mechanism at the time of recording of the transfer type thermal recording medium of the present invention, first, the uppermost layer whose viscosity is reduced by a heat signal to generate an adhesive force adheres to the surface of the recording paper and separates the recording paper and the recording medium. As a result, the melted first layer is peeled off in the layer, and the ink is transferred to the recording paper. At this time, the non-printed portion of the first layer does not soften or melt due to the cohesive force due to containing the pigment and the buffer effect due to the heat of fusion of the wax, and maintains a strong adhesive force with the support. .

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 As the first layer, candelilla wax (heat of fusion 40 cal / g) 89 parts by weight Ethylene vinyl acetate copolymer (ethylene content 85%) 3 parts by weight Carbon black (average particle size 28 μm) 8 parts by weight 1st dispersed for 5 hours in a thermal attritor at ℃
A recording medium 1 was obtained by coating a biaxially stretched polyester film having a thickness of 6 μm with a layer ink liquid to a thickness of 3 μm by a hot melt method.

As the top layer, ethylene vinyl acetate copolymer (ethylene content 82%) Tensile strength 32 kg, spreading rate 600% 18.4 parts by weight Carbon black (average particle size 28 μm) 1.6 parts by weight MEK 48 parts by weight Ethanol 32 parts by weight at 40 ° C The liquid dispersed for 24 hours in a ball mill kept warm was coated on the first layer of the recording medium 1 by a coater so that the thickness of the uppermost layer after drying would be 2 μm, and heated with hot air at 50 ° C. Recording medium 2 was obtained after drying for 3 minutes.

Example 2 As the first layer, paraffin wax 155 ° F (heat of fusion 48 cal / g) 85 parts by weight lecithin 3 parts by weight 12 parts by weight of carbon black (average particle size 32 μm) were dispersed in a thermal attritor at 120 ° C. for 10 hours. A recording medium 3 was obtained by coating a biaxially stretched polyester film having a thickness of 6 μm with the ink liquid for one layer to a thickness of 3.5 μm by a hot melt method.

For top layer Polyamide (average molecular weight 4000) Tensile strength 25 kg, elongation 250% 16 parts by weight Carbon black (average particle size 32 mm) 4 parts by weight 80 parts by weight of isopropyl alcohol dispersed in a ball mill at room temperature for 48 hours at blade coater Was coated on the first layer of the recording medium 3 so that the thickness of the uppermost layer after drying was 3 μm, and dried with warm air of 50 ° C. for 3 minutes to obtain a recording medium 4.

Comparative Example 1 A recording medium 5 prepared in exactly the same manner as in Example 1 was used except that carbon black was omitted from the first layer of Example 1. Comparative Example 2 The resin of the uppermost layer of Example 1 was terpene resin (YS The recording medium 6 was changed to Polystar T-100 manufactured by Arakawa Chemical Co., Ltd.

A recording test was performed using each of the above recording media. Record 8d
Using ot / mm serial head, recording speed is 50 characters / sec. Head pressing pressure is 5kg / cm ² , recording energy is 0.4.
The pulse width was set to 2 msec and 3 msec with W / dot. The recording paper used was Gilbert Bond paper under the trade name Oken type smoothness of 12 seconds. The results are shown in Tables 1 and 2.

As shown in Table 1, the recording medium having only the first layer cannot be recorded with a satisfactory print quality because the recording medium having a poor surface smoothness is scratched.

Further, as shown in Table 2, in the recording medium 5 not containing the pigment in the first layer, the phenomenon in which the non-printed portion is transferred to the printed portion frequently occurs at high temperature and during continuous recording. In addition, the uppermost resin is tensile strength,
When a terpene resin having a small elongation is used, recording blur occurs and the function of the uppermost layer is not exhibited.

Effect The present invention is to laminate a first layer containing a pigment-containing wax as a main component, and preferably a pigment-containing uppermost layer containing a resin having a tensile strength of 20 kg / cm ² or more and an elongation of 200% or more as a main component. Thus, it is possible to perform clear printing on a recording paper having a poor surface smoothness.

Claims (3)

[Claims] 1. A transfer-type thermal recording medium comprising a heat-resistant support and a heat-transferable ink layer provided thereon, wherein the ink layer has a laminated structure of two or more layers, and the first layer on the support side has a heat-melting property. 8 pigments and waxes with a heat of fusion of 30 cal / g or more in the substance
It is characterized in that it contains 0% or more, and the thermal transfer material of the uppermost layer contains 80% or more of resin having a tensile strength of 20 kg / cm ² or more at 20 ° C and an elongation of 200% or more at 20 ° C. Transfer type thermal recording medium. 2. The layered structure according to claim 1, wherein the first layer has a thickness of 3 to 8 μm and the uppermost layer has a thickness of 0.5 to 4 μm.
The transfer type heat-sensitive recording medium according to the item. 3. The transfer type thermal recording medium according to claim 1, wherein the layer closest to the support contains 50% or more of the amount of pigment in the entire thermal transfer ink layer.