JPS61132386A - Thermal transfer material - Google Patents

Abstract

PURPOSE:To print sharp images with high density even on a recording medium poor in surface smoothness, by using a heat-transferrable ink layer of two-layer composite structure in which the upper layer is in a corrugated form. CONSTITUTION:The thermal transfer material 11 comprises the heat- transferrable ink layer 13 on an ordinarily sheet form base 12. The ink layer 13 has a two-layer composite structure comprising the first ink layer 13a and the second ink layer 13b provided in this order from the base side. The first ink layer is provided by using a crystalline heat-fusible binder, while the second ink layer 13b provided on the layer 13a is heated and cooled, whereby the rugged pattern of the surface of the first ink layer appears at the surface of the second ink layer. The binder used for providing the second ink layer must have cohesive force higher than that in the first ink layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal transfer material capable of producing thermally recorded images of good print quality even on recording media with poor surface smoothness.

Should I use thermal transfer recording method? In addition to the general characteristics of thermal transfer recording methods, such as being lightweight, compact, noise-free, and easy to operate and maintain, it also eliminates the need for colored processed paper and provides excellent durability of recorded images. It has these characteristics and has recently begun to be widely used.

This thermal transfer recording method generally uses a thermal transfer material formed by coating a sheet-like support with a thermal transfer material ink made of a heat-melting binder and a colorant dispersed therein. The thermal transferable ink layer is superimposed on the recording medium so as to be in contact with the recording medium, and heat is supplied from the support side of the thermal transfer material by a thermal head to transfer the melted ink layer onto the recording medium, thereby transferring heat onto the recording medium. A transferred image is formed according to the supplied shape.

However, in conventional thermal transfer recording methods, the transfer recording performance, that is, the print quality, is greatly affected by the surface smoothness of the recording medium. In the case of media, there is a problem in that print quality is significantly degraded. For this reason, paper with high surface smoothness is generally used as a recording medium, but paper with high smoothness is rather special, and ordinary paper has various degrees of unevenness due to the entanglement of fibers. Therefore, in the case of paper with large surface irregularities, the hot melted ink cannot penetrate into the fibers of the paper during printing and only adheres to the convexities on the surface or the vicinity thereof, resulting in sharp edges of the printed image. Otherwise, part of the image may be missing, resulting in a decrease in print quality.

Conventionally, for recording media with poor surface smoothness,
In order to obtain a recorded image with good print quality, for example, a hot-melt binder with a low melt viscosity should be used at least in the surface layer.

Alternatively, a method has been adopted based on the idea that by increasing the layer thickness of the thermally transferable ink layer, molten ink is faithfully adhered to or penetrated into the fine uneven structure of a recording medium such as paper. However, when a binder with a low melt viscosity is used, the ink layer becomes sticky even at relatively low temperatures, resulting in problems such as decreased storage stability and staining of non-printed areas of the recording medium, and also causes problems such as bleeding of transferred images. arise. Furthermore, when the thickness of the transferable ink layer is increased, bleeding increases and the amount of heat supplied from the thermal head also needs to be increased, resulting in a decrease in printing speed.

The main purpose of the present invention is to eliminate the drawbacks of the conventional thermal transfer recording method described above, maintain various thermal transfer performances, and provide a recording medium with good surface smoothness. It is an object of the present invention to provide a thermal transfer material capable of giving high density and sharp prints even to poor recording media.

As a result of research for the above-mentioned purpose, the present inventors have found that, in order to achieve high-quality printing on recording media with poor surface smoothness, the present inventors have found that, as a result of the above-mentioned conventional thinking, molten ink is applied to fine irregularities on recording media. We have reached the conclusion that there are limits to the idea of faithfully adhering or penetrating the structure, as described below.

Figure 1 shows an example of a cross-sectional curve measured using a stylus needle on pound paper with relatively poor smoothness (smoothness 12 seconds by Beck smoothness meter). The distance from the upper end of the protrusion to the lower end of the recess (that is, the depth of the valley) often exceeds 10 mm, and the width of the recess sometimes exceeds 10 mm (note that the vertical and horizontal scales in Figure 1 are is not uniform). Therefore, Fig. 2 is a cross-sectional view of a typical thermal transfer material and thermal head during recording, superimposed on this cross-sectional curve, with the vertical and horizontal scales being approximately the same (in the figure, 1 is the thermal transfer material). , which is formed by providing a thermally transferable ink layer 3 on one surface of a support 2.

Further, as can be seen from 4 (representing the recording medium and 5 representing the thermal head), it is impossible to completely fill large surface recesses with molten ink. Also,
When printing on a recording medium with poor surface smoothness, in reality, as shown in Figure 3, which is an enlarged cross-sectional view of the contact area between the thermal transfer material and the recording medium immediately after thermal transfer, the thermal melting The transfer of ink is incomplete, and only a part of the heated part adheres to the convex part of the recording medium or its vicinity, and in addition to the non-heated part a, part C of the heated part corresponding to the concave part of the recording medium
remains without being transferred, and as a result, the print turbidity may be insufficient or a part of the image (section 08 in the figure) may be missing.
It was found that the print quality was degraded.

The present inventors have investigated the cause of such incomplete transcription.
As a result of further detailed investigation, it was found that it was impossible to sufficiently prevent incomplete transfer to uneven recording media with a single layer of thermally transferable ink, and that a thermally transferable ink layer with a multilayer structure of at least two layers was used. It has been found that it is extremely effective to use an ink layer and to form the upper layer 1 in a concavo-convex shape in order to actively cause separation between the heated portion and the non-heated portion.

The thermal transfer material of the present invention is based on such knowledge, and more specifically, a first ink layer and a second ink layer are provided on a support in order from the support side, and both of the ink layers are heated. a meltable binder, and the first
The ink layer has crystallinity, and further, after coating the second ink layer, the surface of the second ink layer is made to have an uneven structure by heating above the melting point of the first ink layer and cooling. It is something.

Furthermore, the thermal transfer material of the present invention comprises a first ink layer and a second ink layer provided on the support in order from the support side,
The ink layer ii is composed of a heat-melting ink layer having crystallinity, and the second ink layer is composed of a copolymer of terpenes and phenols, and further, after coating the second ink layer, a first ink layer is formed. The surface of the second ink layer is formed into an uneven structure by heating the ink layer to a temperature higher than the melting point of the ink layer and cooling the ink layer.

In other words, in the case of a conventional single layer, if a sufficient amount of heat is applied that the ink is easily peeled off from the support, the ink's permeability into the paper becomes too good, and it adheres only to the convex parts of the paper, resulting in the ink not being able to be applied to highly uneven paper. On the other hand, only unclear prints were obtained. Also, during transfer, if the ink layer does not penetrate the paper and is unevenly distributed around the convex parts, forming a bridge between the convex parts and hiding the concave parts of the paper, it may peel off from the support. However, according to the present invention, when heating conditions are such that the first ink layer is likely to peel off, the second ink layer does not penetrate into the paper very much, and the convex portions bridge together, forming concave portions. Since the second ink layer is a concave and convex layer, the print is sharp and good print quality can be obtained even on highly uneven paper.

It has also been proposed to divide the thermal transferable ink layer into two layers and make the upper layer uneven or dotted (Japanese Patent Application Laid-open No. 57-56295), but this does not give rise to tonality in the recorded image. However, the ideal balance of forces for layer transfer described above cannot be obtained.

Hereinafter, the present invention will be described in further detail with reference to the drawings as necessary. In the following descriptions, "%" is used to express quantitative ratio.
” and “parts” are based on weight unless otherwise specified.

FIG. 4 is a schematic cross-sectional view in the thickness direction of a thermal transfer material in the most basic embodiment of the present invention.

That is, the thermal transfer material 11 is usually a sheet-like support 1.
A thermally transferable ink layer 13 is formed on 2. Further, the thermal transferable ink layer 13 itself has a multilayer structure,
A first ink layer 13a and a second ink layer provided in order from the support side.
It consists of an ink layer 13b.

As the support 12, conventionally known films and papers can be used as they are; for example, films of relatively heat-resistant plastics such as polyester, polycarbonate, triacetylcellulose, nylon, polyimide, cellophane or parchment paper, Condenser paper or the like can be suitably used. The thickness of the support is preferably about 2 to 15 microns when considering a thermal head as a heat source for thermal transfer, but it is preferable to use a heat source such as a laser beam that can selectively heat the thermal transfer ink layer. There are no particular restrictions on its use. In addition, when using a thermal head, a heat-resistant protective layer made of silicone/resin, fluororesin, polyimide resin, epoxy resin, phenol resin, melamine resin, nidomi cellulose, etc. is applied to the surface of the support that comes into contact with the thermal head. By providing this, it is possible to improve the thermal properties of the support, or it is also possible to use a support material that could not be used conventionally.

The first ink layer 13a is for smooth transfer of the entire thermal transferable ink layer including the second ink layer 13b, and when the thermal transfer material is peeled off from the recording medium during transfer recording, it is necessary to transfer the thermal transfer material to the support or the second ink layer. It peels off from the interface with the ink layer or causes cohesive failure and peels off within the first ink layer, effectively causing transfer. In order to act in this manner, the cohesive force of $11 INOG must be as small as 2 to 50 kg/cm' at 20°C. 1. Melt viscosity (rotational viscometer) at 50°C is 0.5 cps to 500 cps, especially 2
It is preferable that it exhibits ~200 cps. 15
If the melt viscosity at 0° C. is less than 0.5 cps, the recorded image is likely to be smudged, and if it exceeds 500 cps, it becomes difficult to peel off.

The heat-melting binder constituting the first ink layer is as follows:
Use one that has crystallinity.

For example, natural waxes such as spermaceti wax, beeswax, lanolin, carnauba wax, candelilla wax, montan wax, ceresin wax, paraffin wax,
Petroleum wax such as microblisterine wax, oxidized wax, ester wax, low molecular weight polyethylene, synthetic wax such as Fischer-Tropsch wax, higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, stearyl alcohol, Higher alcohols such as behenyl alcohol, esters such as fatty acid esters of sucrose and fatty acid esters of sorbitan, amides such as oleylamide, polyolefin resins such as polyethylene and polypropylene, voivinyl alcohol resins, isotactic polystyrene resins Polymers with crystallinity such as polyoxymethylene, polyethylene oxide, polyamide resin, polyester resin, and cellulose resin can be used.
They are used alone or in combination so that the melt viscosity and cohesive force are controlled to be within the above range, and the layer thickness is 0.1 to iopm.

The second ink layer 13b is formed into an uneven shape by providing the second ink layer on the crystalline first inog layer 13a that satisfies the above conditions, heating it above the melting point of the first ink layer, and further cooling it. is necessary, and the heating temperature, heating time, and number of cycles of heating φ and cooling are not particularly limited. In this manner, by heating and cooling after providing the second ink layer, the irregularities on the surface of the crystalline first ink layer appear on the surface of the second ink layer.

The second ink layer is peeled off from the support when the first ink layer is peeled off, so the cohesive force may be large; rather, after being transferred to the recording medium, the second ink layer is peeled off from the support. If excessive penetration occurs, the density of the printed surface will vary, making it impossible to print clearly, so the cohesive force must be greater than that of the first ink layer. In order to achieve clear printing, it is preferable that the second ink layer does not penetrate excessively onto the recording medium and adheres to the recording medium while maintaining its layer state. From this point of view, the larger the cohesive force, the better. suitable. Since the cohesive force during heating is approximately proportional to the cohesive force at room temperature, it can be indirectly determined based on the cohesive force at room temperature.

The cohesive force of the first ink layer and the second ink layer is determined by a relative relationship, and the cohesive force of the second ink layer is higher than the cohesive force of the first ink layer, and is 30 to 300 kg/
A range of cr rn' is preferred.

The melt viscosity of the second ink layer at 150°C is 200c.
ps~L, 000.0OOcps, especially 500~20
The melt viscosity is preferably in the range of 0.0OOcps, preferably higher than the melt viscosity of the first ink layer. 2OOcp
If it is less than s, the ink will permeate from the place where it comes into contact with the convex part of the recording member, and the ink will be easily cut off at that part, or the ink will be trapped and solidified in the capillary tubes around the convex part, which will cause the ink to penetrate into the concave part of the recording medium. will run out of ink. Also 1,
If it exceeds 000,000 cps, melting of the convex portions is difficult to occur, so that adhesive force to the recording medium cannot be obtained and transfer failure occurs.

The function of this second ink calendar is that when heat is applied and the ink contacts the paper, it does not penetrate too deeply into the paper and uses the small contact points on the paper as a foothold to form a film on the entire dot or in the connection between dots. The method is to form a pattern and transfer it onto the uneven paper in a shape similar to that of a lid.

The heat-melting binder constituting the second ink layer includes polyamide resin, polyester resin, epoxy resin, polyurethane resin, acrylic resin, vinyl chloride resin, cellulose resin, polyvinyl alcohol resin, and ethylene-acetic acid. Polyolefin resins such as vinyl copolymers, phenolic resins, styrene resins, natural rubber, styrene-butadiene rubber, imprene rubber, gloloprene rubber, and other noelastomers are used as the main component, singly or in combination, and the viscosity above is used as necessary. The cohesive force is within the range not exempted from tax, the main component of the first layer, a plasticizer such as tricresyl phosphate, dibutyl phthalate, mineral oil,
A suitable mixture of vegetable oil and the like may be used.The second ink layer may also be configured as follows in addition to the above. That is, a copolymer of terpenes, including monoterpenes such as limonene and pinene, and phenols, such as phenol, cresol, and bisphenol A, can also be used as the second ink layer.

When the second ink layer is made of a copolymer of terpenes and phenols, the second ink layer has a melt viscosity of 200 to 200 at 150°C.

The melt viscosity is desirably in the range of 000 CPS and needs to be higher than the melt viscosity of the first ink layer.

If it is less than 200 CPS, the ink will permeate from the place where it comes into contact with the convex part of the recording medium, and the ink will easily run out at that part, or the ink will be trapped and solidified in the capillary tubes around the convex part, which will cause the ink to penetrate into the concave part of the recording medium. The state is "out of ink". Furthermore, if it exceeds 200°000CP5, melting of the convex portions is difficult to occur, and therefore adhesive strength to the recording medium cannot be obtained, resulting in poor transfer.

The thickness of the second ink layer is preferably in the range of 0.01gm or more and topm or less, and furthermore, O.1gm or more L07 layer m
The following is desirable. If the layer thickness of the second ink layer is less than 0.01 gm, the second ink layer will be too thin and the effect of the second ink layer described above will not be expressed, and if it exceeds 1071 m, the second ink layer will become too thin. Although the role of the ink layer is fulfilled, the sharpness of the print tends to be lacking.

At least one of the ink layers 1.2 contains a colorant. It is desirable that both layers contain a colorant, but either one may be used depending on the layer thickness.Also, the melting temperature and melt viscosity conditions mentioned above naturally apply to the colorant or addition if necessary. This is a state in which other additive machining is mixed in.

As the coloring agent, various dyes and pigments widely used in the field of printing and recording are used.

The colorant content is 80% for each of the ink layers 1.2.
% or less, and a range of 1 to 80% is suitable for the entire thermal transferable ink layer. Further, each ink layer 1.2 may further contain additives such as a dispersant or a filler made of fine metal powder, fine inorganic powder, metal oxide, etc., if necessary.

The thermal transfer material of the present invention is in a state as shown in FIG. 5 before transfer, but during transfer, it is heated and pressed in contact with the recording medium 4 between the head 6 and the platen 5 as shown in FIG. Heat softens by heating.

The dot portion is pressed against the recording medium 4 and flattened.

At this time, the second ink layer adheres to the convex portion of the recording medium 4, and
Generates adhesive force with the recording medium. After the transfer, when the recording medium 4 and the transfer material 11 are subjected to tIIIa as shown in FIG.
Because it cuts at the concave position, a sharp image can be obtained.

In order to obtain the thermal transfer material of the present invention, the above-described heat-melting paint, colorant, and additives for each of the ink layers 1.2 are melt-kneaded using a dispersion device such as a 7 tritor, or an appropriate The ink is kneaded with a solvent to obtain a hot-melt or solution or dispersion ink, and these inks are sequentially applied on a support to form the first. After forming the second ink layer, it may be heated to a temperature higher than the melting point of the first ink layer and further cooled to form an uneven layer, and the temperature range varies depending on the material forming the first ink layer.

The planar shape of the thermal transfer material of the present invention is not particularly limited, but it is generally used in the form of a typewriter ribbon or a wide tape used in line printers.

Further, for color recording, it is also possible to use a heat-sensitive transfer material in which heat-melting ink of several tones is applied separately in stripes or blocks.

Although the thermal transfer recording method using the above-mentioned thermal transfer material is not particularly different from a normal thermal transfer recording method, the case where the most typical thermal head is used as the heat source will be described for the sake of caution.

FIG. 8 is a schematic cross-sectional view of the thickness and direction of the thermal transfer material showing its outline. That is, the recording medium 4 is brought into close contact with the heat-melting ink layer 13 of the heat-sensitive transfer material 1, and if necessary, the recording medium is further supported from the back side by the platen 5 and a ripening pulse is applied by the hardening head 6 to coat the ink layer 13. is heated locally according to the desired printing or transfer pattern. The temperature of the heated portion of the ink layer 13 rises, and the first ink layer in particular rapidly melts or softens, and is transferred to the recording medium together with the melted and softened second ink layer, leaving a recorded image 13c. Its more microscopic state is as explained in FIGS. 5 to 7.

Although an example in which a thermal head is used as a heat source for thermal transfer recording has been described above, it is easy to understand that the present invention can be implemented similarly when using other heat sources such as laser light.

The present invention will be explained in more detail with reference to Examples below.

1 mouth 11 Carbon black 10 parts Montan wax 20 parts Low molecular weight oxidized polyethylene 10 parts Paraffin wax 60
Ink A for the first ink layer was prepared by adding 30 molecules of each component in the above formulation to 1JIW in a sand mill while heating to 100° C., and adding carbon black to the mixture.

Solid polyamide resin 6.5 parts Phenol resin 3.5 parts Oil-soluble black dye
1 part isopropyl alcohol
81 parts Each component of the above formulation was stirred in a homomixer to obtain a second ink layer coating liquid B. A first ink layer having a thickness of 3 m was obtained by hot melt coating Ink A on a 6 g, m polyethylene terephthalate film using a Meyer par.

Coating liquid B was applied on the gPJi ink layer to an average thickness of about 2 JL using a mailer bar. After removing the elm solvent, the thermal transfer material was heated to 80° C. for 5 minutes and cooled to room temperature to obtain a thermal transfer material. Ta.

The melting temperature of ink A is 70°C (DSC method), and 15
The melt viscosity at 0°C was 10Cp3. Polyamide resin forming the second ink layer.

The melt viscosity of the mixture of phenolic resin and oil-soluble blank dye was 14.000 cps.

Gold was deposited on the surface of the heat-sensitive transfer material thus obtained to a thickness of 10 mm, and using a scanning electron microscope, the sample surface was
'When it was tilted and observed at 2,500x magnification, it was observed that it had an uneven shape.

An applied voltage of 7.5 V was applied using this thermal transfer material.

When printing was carried out on pound paper (Beck smoothness: 12 seconds) with a pulse width of 4 ms, very clear and high quality printing was obtained.

Comparative Example Ink A and Ink B were prepared in the same manner as in Example 6.
A first ink layer with a thickness of 3 pm was obtained by hot-melt coating ink A onto polyethylene terephthalate using a roller, and then coating liquid B was coated onto the first ink layer using a roller. It was coated to a uniform thickness of about 2 tiles, and the solvent was removed to obtain a heat-sensitive transfer material. The heat-sensitive transfer material was not subjected to any heat treatment compared to the heat-sensitive transfer material of the example, and the surface condition was observed using the same method as in the example, and it was confirmed that there was no unevenness. The heat-sensitive transfer material thus obtained exhibited almost the same function as the example in terms of covering the paper surface, but the printing edge was poor and lacked sharpness.

Next, an example will be shown in which the second ink layer is made of a copolymer of terpenes and phenols.

Carbon black 10 parts Montan wax 20 parts Molecular weight polyethylene oxide 10 parts Paraffin wax 60
By mixing each component of the above formulation in a sand mill for 30 minutes while heating to 100°C, carbon black is dispersed and the first ink layer ink At-a! I arranged it.

Five types of terpenes - Phenol resin 1O part Yasushi Oil Industry - YS Polystater - 80 oil-soluble black dye
2 parts Methyl ethyl ketone 88 parts Each component of the above recipe was stirred in a homomixer to obtain a second ink layer coating liquid C. Ink A was hot-melt coated onto a 6-layer polyethylene terephthalate film using a coater to obtain a first ink layer having a thickness of 3 JLm.

Coating liquid C was applied onto the first ink layer to an average thickness of about 21 L using a mailer bar. After removing the elm solvent, the thermal transfer material was heated for 80"05 minutes, and cooled to room temperature to form a thermal transfer material. Obtained.

The melting temperature of ink A is 70°C (DSC method), and 15
The melt viscosity at 150°C of the mixture of terpene-phenol resin and oil-soluble black dye forming the second ink layer was 2800 cpu.
Met.

Gold was deposited on the surface of the heat-sensitive transfer material obtained in this way to a thickness of 10 mm, and using a scanning electron microscope, the sample surface was
Tilt it 2500 times! ! Upon inspection, it was found that the surface was uneven.

An applied voltage of 7.5 V was applied using this thermal transfer material.

When printing was carried out on pound paper (Beck smoothness: 12 seconds) with a pulse width of 4 ms, very clear and high quality printing was obtained.

Comparative Example Prescription Polyamide resin (A) 10 parts Isopropyl alcohol 90 parts A second ink layer made of the above formulation was applied as a uniform coating layer on the first ink layer made of recipe A of the example to a thickness of 2 μm by thermal transfer. I barreled the wood.

The melt viscosity of this polyamide resin at 150°C is 2500
cps. The heat-sensitive transfer material thus obtained exhibited almost the same function as the example in terms of covering the paper surface, but the edges of the printed image were not sharp and lacked sharpness.

[Brief explanation of the drawing]

Figure 1 shows the cross-sectional curve of pound paper (smoothness 12 seconds according to Beck's smoothness clock) using a stylus meter. , ink layer thickness 5 layers) and thermal head (dot side length 120 g)
FIG. 3 is a schematic cross-sectional view of the thermal transfer material and recording medium after thermal transfer, FIG. 4 is a schematic cross-sectional view in the thickness direction of an embodiment of the thermal transfer material of the present invention, and FIG. Figure 7 is the fourth
FIG. 8 is a schematic sectional view for explaining the overall embodiment of the thermal transfer recording method using the thermal transfer material of the present invention. 1, LL----1 thermal transfer material 2.12----1 support 3.13----1 thermal transferable ink layer L 3 a-----1st ink layer 13 b---- -@2 ink layer 13c --
-1--Transferred image 4-----1~--Recording medium 5--------Platen 6--------Thermal head-- Figure 3 Urizuki 4 Senman 5 Figure 7 Mouth Δ

Claims (6)

[Claims] (1) A first ink layer and a second ink layer are provided on a support in order from the support side, both of the ink layers have a heat-melting binder, and the first ink layer has crystallinity. Further, after coating the second ink layer, the first ink layer is applied.
A thermal transfer material, characterized in that the surface of the second ink layer is made to have an uneven structure by heating to a temperature higher than the melting point of the ink layer and cooling. (2) The thermal transfer material according to claim 1, wherein the cohesive force of the second ink layer is higher than the cohesive force of the first ink layer. (3) The melt viscosity of the second ink layer at 150°C is higher than the melt viscosity of the first ink layer, and the melt viscosity of the second ink layer at 150°C is 200 to 1,000°C.
0,000 cps, and the first ink layer has a melt viscosity of 0.5 to 500 cps at 150°C. (4) The thermal transfer material according to claim 1, wherein at least one of the first ink layer and the second ink layer contains a colorant. (5) A first ink layer and a second ink layer are provided on the support in order from the support side, the second ink layer being a heat-melting ink layer having crystallinity, and the second
The ink layer is made of a copolymer of terpenes and phenols, and after coating the second ink layer, the surface of the second ink layer is heated to a temperature higher than the melting point of the first ink layer and then cooled, thereby forming an uneven structure on the surface of the second ink layer. A heat-sensitive transfer material characterized by: (6) The thermal transfer material according to claim 5, wherein at least one of the first ink layer and the second ink layer contains a colorant.