JPH03120081A - Thermal transfer method - Google Patents

Abstract

PURPOSE:To prevent texture staining of a material to be transferred, tailing of printing, etc., due to rubbing with an ink layer by a method wherein a surface resin layer which is not perforated under an ordinary state and is perforated by heat of a thermal head is formed on the surface of the ink layer of a thermal transfer sheet. CONSTITUTION:A thermal transfer sheet wherein a transfer ink layer which melts by heating is formed on one side surface of a substrate film and a surface resin layer which is perforated by heat of a thermal head is formed on the surface thereof, is superimposed on a material to be transferred and carrying speed of the thermal transfer sheet is made comparatively high compared with the carrying speed of a material to be transferred. Therefore, though a state of a film can be maintained as a whole by the heat of the thermal head, a film having many fine pores can be formed. Thereby, texture staining of the material to be transferred, tailing of printing, etc., due to rubbing with the ink layer can be thoroughly prevented. Further, since a thin film has a property wherein many fine pores are generated based on the quantity of heat to be applied from the thermal head, a quantity of ink corresponding to the quantity of heat of the thermal head is transferred to the material to be transferred, and various density printing from light colour to thick colour comes capable of being performed.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a thermal transfer sheet, and more specifically to a thermal transfer method (hereinafter simply referred to as N-time mode) in which the conveyance speed of the transfer material is higher than the conveyance speed of the thermal transfer sheet. law).

(Prior art and its problems) Conventionally, when printing output prints from computers or word processors using a thermal transfer method, a thermal transfer sheet with a heat-melting ink layer provided on one side of a base film has been used. .

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

One problem with the thermal transfer method using the above thermal transfer sheet is that
This is an economic problem because printing can be performed only once at the same location, and therefore a thermal transfer sheet with the same width as the printing is consumed.

A known method to solve this problem is to use a thermal transfer sheet for multiple printing that can be printed multiple times at the same location, but with this method, the printing rate decreases depending on the number of times it is used. There is a problem in that printing with uniform density is difficult.

Another method is an N-times mode method in which the conveying speed of the transfer material is relatively higher than the conveying speed of the thermal transfer sheet (both conveying methods may be in the same direction or in opposite directions). In this method, if the conveyance speed of the transfer material is N, the conveyance speed of the thermal transfer sheet is N゛, and N>N', the printing distance is N, but the consumption amount of the thermal transfer sheet is N. For example, N =5 and N' =1, the amount of thermal transfer sheet consumed is 115, which is very economical.

However, in this method, the transfer material and the thermal transfer sheet move while being subjected to relative friction, which causes background smudges and trailing of the print on the transfer material, making it difficult to print with clear and high resolution. There's a problem.

One way to solve the problem of background smearing is to form a colorless wax store on the surface of the ink layer, but this surface resin layer is easily removed by friction and is not a sufficient solution. On the other hand, as a way to solve tailing,
There is a method of forming an ink layer using a wax with a relatively high melt viscosity, but with this method, the ink layer has poor wettability to the transfer material, and voids (white spots) may occur when the transfer material has a rough surface such as paper. This makes it difficult to print with high density and high resolution.

Therefore, an object of the present invention is to solve the above-mentioned 9-bit drawbacks, and to provide an N-time mode thermal transfer method that is free from scumming, trailing, etc. during printing, and has improved printing density, resolution, etc. That's true.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, in the present invention, a thermal transfer sheet, which has a transfer ink layer that melts when heated on one side of a base film and a surface resin layer that opens holes on the surface thereof by the heat of a thermal head, is placed on a transfer material, and thermal transfer is performed. This is a thermal transfer method characterized by making the conveyance speed of the sheet relatively high compared to the conveyance speed of the transfer material.

(Function) By forming a surface resin layer on the surface of the ink layer of the thermal transfer sheet that does not form holes under normal conditions, but which opens due to the heat I of the thermal head, even in the N-fold mode method, the ink layer and Problems such as background smudges on the transfer material and trailing of printed characters due to rubbing are completely prevented.

In addition, since the thin film described above has the property of producing many fine holes in response to the amount of heat applied from the thermal head, the amount of ink corresponding to the amount of heat from the thermal head is transferred to the transferred material, resulting in various colors ranging from light colors to one color. This makes it possible to print at a density of , and it is possible to form full-color images with particularly excellent gradation.

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

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

Specific examples of preferred base films include polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride,
There are plastic films such as polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, and ionomers, papers such as condenser paper and paraffin paper, nonwoven fabrics, and base films that are composites of these. There may be.

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

In the present invention, a heat-melting ink layer is formed on the surface of the base film, preferably via an ink retaining layer, from an ink containing necessary materials.

The ink retaining layer has the effect of preventing the ink layer from peeling off from the base film all at once, and is made of a thermoplastic resin that has good adhesion to the ink layer, such as a thermoplastic resin that has been widely used for adhesive purposes. It is made of adhesive resin.

The thickness of the ink retaining layer is not particularly limited, but is preferably 5 μm or less in order not to reduce thermal sensitivity during thermal transfer.

Of course, this ink retaining layer may be omitted.

The ink layer provided on the base film or the ink retaining layer comprises a colorant and a vehicle, and may further contain various additives as required. The above-mentioned coloring agent is an organic or inorganic pigment or dye that has good properties as a recording material, for example, one that has sufficient color density and does not turn brown due to light, heat, temperature, etc. Preferably, of course, colorants of various colors such as cyan, magenta, and yellow can be used in addition to black.In the present invention, in order to perform N times printing with a relatively small area of ink layer, The coloring agent (needs to be set at a relatively high concentration; it depends on the thickness of the ink layer, but when the ink layer is preferably in the range of 3 to 20 μm, the preferred concentration is 20 to 70% by weight, more preferably is in the range of 30 to 50% by weight, and if the concentration is too low, the printing density will be insufficient, and if it is too high, the ink will not wet the paper easily and voids will easily occur, which is not preferable.

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

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

Representative examples of wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. In addition, various waxes such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolactam, assorted waxes, fatty acid esters, fatty acid amides, etc. used.

The ink consisting of the above colorant and vehicle is preferably blended so that the melt viscosity at 100°C is 300 cps or more, and wax alone has a melt viscosity of 300 cps or more.
If it is not possible to make the melt viscosity higher than ps, it is possible to use various thermoplastic resins such as vinyl resins in combination to increase the cohesive force and improve the melt viscosity. Usually, the melt viscosity can be increased to 300% by using vinyl resin in an amount of 7% or more by weight of the wax.
cps or higher. The preferred melt viscosity is 1
It is 300 to 1,000 cps at 00°C.

Methods for forming the ink layer on the base film include hot melt coating, hot lacquer coating, gravure coating, gravure reverse coating, roll coating, and many other methods of applying the respective coating liquids. can be mentioned.

In the present invention, a thermally porous surface resin layer is further formed to improve the ink.

The above-mentioned surface resin layer is a uniform film with no openings in a normal state, that is, a state where it is not locally heated by a thermal head, and even if something touches the surface, it will not contaminate the object. However, when the base film is heated from the back side with a thermal head, a large number of micropores are formed only in the heated portion and in accordance with the amount of heat applied. .

It has been found that a coating having the properties described above can be formed from a resin (or a mixture) having contradictory properties at the same time. In other words, a resin containing a resin component that undergoes physical changes such as shrinkage, melting, or cracking due to the heat applied from the thermal head, and a resin component that does not cause physical changes such as shrinkage, melting, or cracking due to the heat. By using a thermal head, the entire film can maintain its state due to the heat of the thermal head, but it is possible to form a film with many fine pores.

Resins (mixtures) having such characteristics include mixtures of hydrophilic resins and hydrophobic resins, mixtures of low melting point (or low crystallinity) resins and high melting point (or high crystallinity) resins, and low melting point (or A block or graft copolymer consisting of a low crystallinity) resin segment (soft segment) and a high melting point (or high crystallinity) resin segment (hard segment), a block or graft copolymer consisting of a hydrophilic segment and a hydrophobic segment Examples include merging.

Examples of hydrophilic resins include polyethylene glycol, partially saponified or fully saponified polyvinyl alcohol, poly(meth)acrylamide, its N-substituted derivatives, poly(meth)acrylic acid, water-soluble esters thereof or salts thereof, polyvinylpyrrolidone, Conventionally known synthetic or natural hydrophilic resins such as water-soluble polyurethane resins, hydroxyethyl cellulose, and carboxymethyl cellulose can be mentioned.

In addition, examples of hydrophobic resins include ethyl cellulose,
Cellulose resins such as hydroxypropyl cellulose, methyl cellulose, cellulose acetate, cellulose acetate butyrate, and nitrified cotton; polyether resins such as polypropylene glycol and polytetramethylene glycol; vinyl resins such as polyvinyl acetate, polyvinyl butyral, and polyvinyl acetal; Examples include polyurethane resins such as polyester resins, silicone, and fluorine-modified polyurethane resins.

Also preferably used are block or graft copolymers of a hydrophilic resin segment as described above and a hydrophobic resin segment as described above. Particularly preferred copolymers are copolymers of polyethylene oxide and other polyalkylene oxides, polyurene resins obtained by using polyethylene gelcol and other hydrophobic polyalkylene glycols, polyester polyols, etc. as polyol components. be.

Also, a mixture of a low melting point (or low crystallinity) resin and a high melting point (or high crystallinity) resin, a low melting point (or low crystallinity) resin segment (soft segment) and a high melting point (or high crystallinity) resin segment ( As a block or graph graft copolymer consisting of a hard segment), a low melting point resin (segment) such as aliphatic polyether, aliphatic polyester, aliphatic polyamide, polybutadiene, polychloroprene, polyisoprene, polysiloxane, etc. Examples include mixtures or block or kraft copolymers with high melting point resins (segments) such as polystyrene, aromatic polyether, aromatic polyester, aromatic polyamide, and polyurethane resins.

From the viewpoint of the porosity of the surface resin layer formed and the strength of the coating, the mixing or copolymerization ratio of the amphoteric components is preferably in the range of 10:90 to 90:10 by weight.

If one portion is too small, the porosity will be insufficient, and if the other portion is too small, the physical properties such as coating strength will be insufficient.

In the present invention, the above resin can be used alone, but it is also preferable to use it in combination with a crosslinking agent or curing agent such as polyisocyanate to form a crosslinked structure. Such crosslinking further improves the strength of the surface resin layer. However, if the crosslinking density is too high, the porosity will decrease, so the crosslinking should be done to an extent that does not impair the porosity.

Further, as long as the above-mentioned characteristics of the surface resin layer are not lost, fillers such as fine lubricant powder and fine single fibers can be added to improve the integrity, film strength, mold releasability, etc. of the surface resin layer.

In addition, the heat-opening resin film has a heat deformation temperature of less than 100°C, preferably 50 to 80°C, and has low adhesion to the transfer material (and does not release well from the ink layer). It can be formed from a moldable thermoplastic resin.

Examples of resins that can form a surface resin layer having such characteristics include silicone wax, silicone resin, silicone-modified polyurethane resin, polyester resin, polyvinyl 1 sealant, polyether resin, and silicone-modified resin such as acrylic resin. Preferably, other polyester resins, polyamide resins, polystyrene resins, acrylic resins, petroleum resins, cellulose resins,
Epoxy resins, phenolic resins, polyurethane resins, ethylene/vinyl acetate resins, vinyl chloride/vinyl acetate resins, polybutyral resins, pinene resins, coumaron indene resins, and the like can also be used alone or as a mixture.

When the resin has a thermal deformation temperature of 100° C. or higher, the heat from the thermal head may not form fine pores or form coarse pores in the surface layer, which is not preferable. Furthermore, if the heat deformation temperature is less than 50° C., handling of the thermal transfer sheet becomes difficult, and the porosity depending on the amount of heat decreases, which is not preferable. Further, in the case of a resin that has high adhesiveness to the transfer material, that is, a resin with low mold releasability, the surface layer is also transferred to the transfer material during thermal transfer, which is undesirable because the surface layer is destroyed.

Although the reason for the above-mentioned thin film made of resin is not clear,
When locally heated, many fine pores or cracks on the order of several to tens of microns are generated, and the number of these fine pores increases or the pore area increases depending on the thermal energy applied. there were. These pores are thought to be due to differences in the physical properties of the constituent resins (segments) due to heat.

Formation of the surface resin layer can be performed by various techniques similar to the formation of the ink layer. In the present invention, the thickness of the surface resin layer is preferably 0.1 μm or more and 5 μm or less in order to avoid insufficient sensitivity even when the printing energy is low (such as in a high-speed printer). The strength is insufficient, and on the other hand, if it is too thick, the porosity is insufficient.

When the thermal transfer sheet having the surface resin layer formed as described above is heated by a thermal head from the back side of the base film, many micropores or cracks on the order of several to tens of microns are formed in the heated area. The molten ink oozes out through these holes and is transferred to the transfer material.
Since the amount of transfer ink changes depending on the amount of heat, it is possible to print with any density from one color to one color.

However, if the amount of heat is large or the surface resin layer has a heat deformation temperature of 1
When forming from a thermoplastic resin with a temperature of 00°C or less, there is a risk that the surface resin layer itself may be transferred to the transfer material, so silicone oil or silicone is added to the surface resin layer to prevent adhesion to the transfer material. It is also preferable to include a mold release agent such as wax or various lubricants, or to form a thin layer of the mold release agent and/or lubricant on the surface resin layer.

It goes without saying that a layer for preventing sticking of the thermal head may be provided on the back surface of the thermal transfer sheet of the present invention.

The method of the present invention includes an N-times mode method in which the conveyance speed of the transfer material is relatively higher than the conveyance speed of the thermal transfer sheet (the conveyance directions of both may be the same or opposite).
It is characterized in that the thermal transfer sheet detailed above is used as the thermal transfer sheet.

The N-fold mode method itself is well known, and the method of the present invention may be any of these known N-fold mode methods. In addition, the transfer material used is conventional paper, plastic film, synthetic paper, etc.
Not particularly limited.

In the method of the present invention, if the conveying speed of the transfer material is N, and the conveying speed of the thermal transfer sheet is No, and N>N', the printing distance is N, but the consumption amount of the thermal transfer sheet is No, for example, N. =5 and N' =1, the amount of thermal transfer sheet consumed is 115, which is the conventional value, which is very economical, and furthermore, background smearing and trailing of prints, which were problems of the conventional method, do not occur.

In the method of the present invention, color printing is naturally possible, and in this case, a multicolor thermal transfer sheet prepared as described above may be used.

(Effects) According to the present invention as described above, by forming a surface resin layer that does not form holes in the surface of the ink layer of the thermal transfer sheet under normal conditions, but which opens due to the heat of the thermal head, the ink layer and Problems such as background stains on the transfer material and trailing of printed characters due to rubbing are completely prevented.

In addition, the thin film described above has the property of producing many fine holes in response to the amount of heat applied from the thermal head, so the amount of ink corresponding to the amount of heat from the thermal head is transferred to the transferred material, resulting in various colors ranging from light to dark colors. This makes it possible to print at a density of , and it is possible to form full-color images with particularly excellent gradation.

(Example) Hereinafter, the present invention will be explained in more detail by giving Examples and Comparative Examples. In the text, parts or percentages are based on weight unless otherwise specified.

Example 1 A transfer ink composition having the following composition was kneaded using a blade kneader for 6 hours while heating to 90°C.

Ink Ink ester wax 10 parts Oxidized wax 10 parts Paraffin wax
60 parts carbon black
12 parts The above ink composition was heated at a temperature of 100°C, and a slip layer was formed on the back side by hot-melt roll coating on the surface of a 6.0 μm thick polyester film (trade name "Lumirror" manufactured by Toshi). The amount of application is about 7
A thermal transfer ink layer was formed by applying the ink to give a ratio of g/d.

Next, as polyol components, polyethylene glycol (molecular weight 2,000) and polyethylene adipate diol (
A 20% solution of block polyurethane resin (molecular weight 2,000) in l:1 in methyl ethyl ketone (contains a small amount of polyisocyanate crosslinking agent) was applied at a rate of 0.7 g/rrf based on solid content using a bar coater. This was dried to form a surface resin layer, and silicone oil was further applied to the surface at a rate of about 0.2 g/rd to obtain a thermal transfer sheet of the present invention.

Examples 2 to 7 Thermal transfer sheets of the present invention were obtained in the same manner as in Example 1 except that a surface resin layer made of the following composition was formed in place of the surface resin layer of Example 1.

A 25% toluene/methyl ethyl ketone solution of a 1:1 weight ratio mixture of hydrophobic polyester polyurethane resin and water-soluble polyether polyurethane resin (film thickness 0.5μ)
m).

30% methyl ethyl ketone/isopropyl alcohol solution (film thickness 1.5 μm) of a mixture of polymethacrylamide and polyethyl acrylate in a weight ratio of 1:2.

Futanitis A 25% toluene solution of a 2:1 weight ratio mixture of vinyl acetate/ethylene copolymer resin and water-soluble polyether polyurethane resin (film thickness 2.0 μm).

A 20% solution of a 1=1 block copolymer of polybutadiene and polystyrene in toluene (film thickness: 1.5 μm).

30% polysiloxane polyol as a polyol component
% polyurethane resin in 20% methyl ethyl ketone solution (film thickness 1.0 μm).

A 20% toluene solution of a l=1 mixture of polyethylene adipate and polystyrene (film thickness 1 μm).

Example 8 The ink composition used in Example 1 was heated at a temperature of 100°C, and a slip layer was formed on the back side using a hot-melt roll coating method to form a polyester film with a thickness of 6.0 μm (trade name: Lumirror). A thermal transfer ink layer was formed by applying the ink to a coating amount of approximately 7 g/d on the surface of a paper (manufactured by Shimizu Corporation).

Next, apply the following coating solution for forming a surface resin layer to 1.0% based on solid content.
A hot porous resin layer was formed by coating and drying at a rate of 0.4 oz/m.

Surface 1 ■ Koko liquid plate vinyl chloride/vinyl acetate copolymer (heat distortion temperature 74℃)
20 parts silicone resin
20 parts melamine resin slippery particles
5 parts toluene 100
Furthermore, the following coating solution was applied to the surface of the porous resin layer at a rate of 0.5 g/rrr based on solid content and dried to form a surface smooth layer to obtain a thermal transfer sheet of the present invention. .

' Ink Seri Carnauba wax 10 parts Polyethylene wax (mp=140℃) 20 parts Nonionic surfactant 1 part Isopropanol
100 parts water
30 parts Comparative Example 1 A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the surface resin layer was not formed in Example 1.

Use Example 1 The thermal transfer sheets of the above Example and Comparative Example were printed and compared using an N-time mode printing evaluation machine (N=6), and the results are shown in Table 1 below. Note that TRWl (manufactured by Jujo Paper Industries) was used as the recording paper.

○: Good Rapid I”-jku △: Slightly poor ×: Bad

Claims (1)

[Scope of Claims] (1) A thermal transfer sheet with a transfer ink layer that melts when heated on one side of a base film and a surface resin layer that opens holes on the surface by the heat of a thermal head is used as a transfer material. A thermal transfer method characterized in that the conveying speed of the thermal transfer sheets is relatively high compared to the conveying speed of the transfer material. (2) The thermal transfer method according to claim 1, wherein the thickness of the surface resin layer is in the range of 0.2 to 5 μm. (3) The thermal transfer method according to claim 1, wherein the thickness of the ink layer is in the range of 3 to 20 μm. (4) The thermal transfer method according to claim 1, wherein an ink retaining layer is formed between the base film and the ink layer. (5) The thermal transfer method according to claim 1, wherein a mold release agent and/or a lubricant is provided in or on the surface of the surface resin layer.