JPH07102743B2 - Thermal transfer film - Google Patents

Description

The present invention relates to a novel thermal transfer film used in thermal transfer recording type printers and facsimiles.

[Conventional technology]

There is a thermal transfer recording system as one of recording systems for printers and facsimiles. This is because a heat transfer film having a heat fusible ink layer on a base film is overlaid on a transfer paper such as plain paper, heat from a thermal head is applied from the back of the heat transfer film, and the heat fusible ink (hereinafter abbreviated as ink). ) Is transferred to the transfer paper and recording is performed.

Such a conventional thermal transfer film has the following drawbacks because it has only an ink layer made of a binder and a colorant provided on a flat base film. Ie 1
It is a so-called one-time product in which the ink layer in the recording area is completely transferred to the base film after printing twice and cannot be used more than once, so the recording cost is high and the number of heat transfer film replacements is high. There are drawbacks such as additional labor.

[Problems to be solved by the invention]

The present invention has been made in view of the above circumstances, and an object thereof is to provide a thermal transfer film that can be used many times.

[Means for solving problems]

Therefore, as a result of intensive studies by the present inventors, in a heat transfer film in which a heat fusible ink layer is provided on a base film, the heat fusible ink layer has a high cohesive force on the base film side, and the transfer paper We found a new fact that a thermal transfer film that gives a gradient of cohesive force in the ink thickness direction so that the cohesive force becomes low on the side can print many times,
The present invention has been completed.

As a method of imparting a gradient of cohesive force in the ink thickness direction, other additives such as a low melting point resin, a colorant, a softening agent, a petroleum resin, a surfactant, a lubricant, and the like to be added to the ink component may be used. A cohesive force gradient can be provided in the ink layer by adding an electron beam reactive component to the ink and irradiating an electron beam from the back surface of the base film opposite to the ink application surface to cause a crosslinking reaction of the electron beam reactive component. .

As shown in FIG. 1, the thermal transfer film of the present invention has a base film 1 and an ink layer 2 as a basic structure, and the ink layer is an ink component 21 composed of a low melting point resin, a colorant, and additives to be blended if necessary. And a portion (hereinafter referred to as a polymer) 22 cross-linked and polymerized by irradiation with an electron beam. At the time of printing, as shown in FIG. 2, the ink 2 melted by the heat applied from the thermal head 3 is transferred onto the transfer paper 4 and then peeled off as shown in FIG. Part of the ink layer on the paper (hereinafter referred to as paper) side is transferred,
Since a part of the ink having a high cohesive force remains on the base film without being transferred, it can be used for printing many times.

There are various cross-linking methods for improving the cohesive force of the ink layer, and when classified by the energy source, there are heating, ultraviolet irradiation, electron beam irradiation and the like.

The method using internal heating is the most general method, but the degree of crosslinking is almost determined by the composition, so it is extremely difficult to impart a gradient of cohesive force in the thickness direction of a thin coating layer like ink. When ultraviolet rays have a strong black color in the colored layer or have a strong hiding property like ink, the transmittance in the coating layer is rapidly attenuated, and it is difficult to give a cohesive force gradient. On the other hand, the electron beam is preferable because the transmission distance can be arbitrarily adjusted depending on the irradiation conditions regardless of the blackness, and a cohesive force gradient can be imparted.

For example, when the acceleration voltage of the electron beam is 150 kV, the transmission power is about 160 g / m ^2, the change in transmittance occurs between 40~160g / m ^2. Therefore, if the object to be irradiated with the electron beam is contained within this range, it is possible to control the layered change of the amount of the cross-linking polymerization reaction inside the object and to give the gradient of the cohesive force.

The substrate film used in the present invention may be a heat-resistant film, and examples thereof include plastic films such as stretched polyester, polyamideimide, and polyimide, and paper such as condenser paper and glassine paper.
The thickness can be applied in the range of 1.0 to 20 μm.

If the thickness is thin, it is easy to tear, and if it is more than 20 μm, the printing energy becomes large and it is not practical.

As the low melting point resin used for the ink layer, paraffin wax, microcrystalline wax, carnauba wax, ceresin wax, oxidation wax, ester wax, polyethylene wax, other natural wax,
A synthetic wax or the like is used, and carbon black, an organic pigment, an inorganic pigment, a dye or the like is used as a colorant.

Further, as the additives to be blended as necessary, appropriate ones can be selected and used from the following.

That is, as a softening agent, an organic acid ester such as a phthalic acid ester-based or adipic acid ester-based or a phosphoric acid ester-based softener,
Epoxy-based other plasticizers, oily substances such as mineral oil, vegetable oil, animal oil, castor oil, liquid rubber and vaseline and other liquid or semi-solid substances at room temperature are used.

As the petroleum resin, an aliphatic, alicyclic, or aromatic homopolymer or copolymer is used.

The surfactant is selected from anionic type, cationic type, nonionic type and amphoteric type.

As the lubricant, polyhydric alcohol ester, higher alcohol, higher fatty acid, fluorocarbon, fatty acid amide type, ester type and the like are used.

Further, other polymers can be added, but as such a polymer, an ethylene-ethyl acrylate copolymer,
Ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-unsaturated acid copolymer, ethylene-vinyl acetate copolymer saponification product, ethylene-acrylic acid copolymer, polyisobutylene, butyl rubber, polybutadiene, polybutene, polyisoprene, It is selected from natural rubber and the like. In the present invention, an electron beam reactive component is required, and as such a component, an acryloyl group, a methacryloyl group as a reactive group,
A compound having a group selected from a vinyl group and the like is preferable, but a polymer of the ethylene-ethyl acrylate copolymer or lower also undergoes a crosslinking reaction by an electron beam and contributes to improvement of cohesive force.

As a compound having an acryloyl group, a methacryloyl group, a vinyl group or the like as an electron beam reactive group, a monofunctional compound having one such reactive group in the molecule and a polyfunctional compound having two or more such reactive groups in the molecule There is. As the monofunctional compound, a compound having a simple structure compound and a functional group (eg, hydroxyl group, carboxyl group, amino group, etc.) other than the electron beam reactive group in the molecule, and as the polyfunctional compound, a polyol polyacrylate, an epoxide-modified compound Polyacrylates such as polyol polyacrylate, lactone-modified polyol polyacrylate, polyester acrylate, epoxy acrylate, urethane acrylate, polybutadiene skeleton polyacrylate, isocyanuric acid skeleton polyacrylate, or polymethacrylate and polyallyl ether corresponding to each are used. .

More specific examples of such monofunctional compounds include 2-ethylhexyl acrylate, isodecyl acrylate, 2-hydroxyethyl acrylate, cyclohexyl acrylate, carbitol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, 3-butoxy-. There are 2-hydroxypropyl acrylate, alkylphenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, ω-hydroxyhexanoyloxyethyl acrylate, acryloyloxyethyl succinate, acryloyloxyethyl phthalate and the like. Also, multifunctional 1,4-butanediol diacrylate as a compound, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, polyethylene glycol diacrylate _{(CH 2 = CH-COOC 2} H 4 O n OC-CH = CH
_2; n = _1~200) polypropylene glycol diacrylate _{(CH 2 = CH-COOO 3} H 6 O n OC-CH = CH 2; n = 2~20
0), pentaerythritol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallyl cyanurate, trimethylolpropane triallyl ether, pentaerythritol tetraacrylate, dipentaerythritol polyacrylate, propylene oxide-modified trimethylolpropane polyacrylate , Ε-caprolactone modified dipentaerythritol polyacrylate, ethylene oxide modified bisphenol A polyacrylate, ethylene oxide modified bisphenol S polyacrylate,
α, ω-diacryloyl- (bisalkylene glycol) phthalate, α, ω-tetraacryloyl- (bistrimethylolpropane) -tetrahydrophthalate,
α, ω-hexaacryloyl- (bispentaerythritol) -adipate, bisphenol A type epoxy acrylate, novolac type epoxy acrylate, polyhydric alcohol type epoxy acrylate, polybutadiene type epoxy acrylate, polyisocyanate / 2-hydroxyethyl acrylate reaction product, poly Ether polyol / diisocyanate / 2-hydroxyethyl acrylate reaction product, polyester polyol / diisocyanate / 2
-Hydroxyethyl acrylate reaction product, isocyanuric acid / 2-hydroxyethyl acrylate reaction product, melamine / 2-hydroxyethyl acrylate reaction product, acrylic modified-1,2-polybutadiene, acrylic modified-1,4-polybutadiene modified acrylic Examples include polyacrylic acid alkyl ester. Further, a methacrylate corresponding to the above acrylate can be used.

The molecular weight of the electron beam reactive component is preferably in the range of 100 to 20,000, and is not limited to the above compound examples as long as it is in this range. If it has a molecular weight of 100 or less, it has a drawback that it is highly volatile and has poor workability, and that even if a small amount of unreacted material causes a bad odor. On the other hand, when the molecular weight is 20,000 or more, the viscosity increases and the coatability decreases.

Further, the electron beam reactive component can be used not only alone but also in combination of two or more kinds, and the addition amount in the ink is lower than the low melting point resin, the colorant, and the additive to be blended as necessary. It is necessary that the amount is 2-45 parts by weight with respect to 100 parts by weight of the ink component. If the amount is less than 2 parts by weight, it is impossible to print many times. On the contrary, if the amount is more than 45 parts by weight, the ink coatability is deteriorated and excessive printing energy is required.

As a method for coating an ink comprising such a low melting point resin, a colorant, an electron beam reactive component, and additives to be blended as necessary on a substrate film, either a solution method or a hot melt method may be used. You can do it.

The thickness of the ink layer to be coated is preferably in the range of 5 to 20 μm, and when it is 5 μm or less, the printing density after the second printing decreases, and when it is 20 μm or more, a large amount of ink printing energy is required. Ink layer is insufficiently melted,
It may not be possible to print satisfactorily, and high-speed printing may not be possible.

Irradiation with an electron beam is performed from the back surface of the substrate film after coating.
Irradiation can be done in air, but can also be done by reducing the oxygen concentration in an inert gas. In addition, another film may be brought into contact with the ink surface to reduce the oxygen concentration.

The dose when irradiating with such an electron beam is preferably in the range of 1 to 50 Mrad, and if it is 1 Mrad or less, the reaction of the ink is insufficient, or the cohesive force gradient in the ink layer is difficult to be imparted, and multiple printing is possible. It is impossible, and on the contrary, the reaction is completed at 50 Mrad or more, the effect of printing many times is saturated, and it is unnecessary for more than this.

Next, the gradient of cohesive force in the ink layer will be described.

Since it is difficult to directly measure the gradient of cohesive force in the ink layer, the indirect method is adopted. That is, at the time of electron beam irradiation, a 10 μm thick high-density polyethylene film (density: 0.97 g / cm ³ ) (denoted as (a)) and the same polyethylene film (denoted as (b)) on the ink surface were irradiated. Then, the cohesive force gradient was determined by measuring the gel fraction of the films (a) and (b) after irradiation with electron beams from the side of the substrate film.

The conditions under which the gel fractions of the films (a) and (b) obtained by this method give a cohesive force gradient are as follows.

That is, (a): gel fraction: 10 to 50 wt% (b): gel fraction: 0 to 40 wt% (a)-(b) ≧ 10 wt%.

If the gel fraction of (a) is 50 wt% (hereinafter abbreviated as%) or more, the energy required for printing after a large number of times is large and the printing density is reduced. The gel fraction of (a) is 10% or less,
When the lower gel fractions of (a) and (b) are within 10%, the cohesive force gradient is almost the same and the number of printings is reduced.

[Action]

The reason why the thermal transfer film of the present invention enables printing many times is presumed to be as follows.

That is, the electron beam reactive component is uniformly present in the ink layer immediately after coating, but the electron beam absorbed dose of the ink decreases with the ink thickness by irradiating the electron beam from the back surface of the base film. In addition, as shown in FIG. 1, the electron beam-reactive component has a higher cross-linking reaction on the side of the substrate film, the content of the polymer is large, and the polymers are entangled with each other to increase the cohesive force of the ink. On the contrary, on the paper side in the ink layer, the content of the polymer is low or there is no polymer, so that the cohesive force remains low.

2 to 3 show the printing process when the printing frequency is small.

If the polymer is uniformly present in the ink layer and is entangled with each other, the ink must be sufficiently adhered to the paper in order to unentangle the polymer during printing. However, when the ink thickness is large, the ink does not flow sufficiently due to the heat from the thermal head, and therefore the adhesion is not sufficient and printing is not performed. Conversely, when the heat is sufficiently transferred and the adhesion is sufficient, once The amount of ink transferred by printing is large and the number of times of printing is small.

However, in the printing shown in FIGS. 2 to 3, the portion of the ink layer in contact with the paper, which has a low cohesive force, has a high fluidity of the ink, and easily adheres to the paper. Even if the polymer is not entangled with each other, destruction occurs from a portion having a low cohesive force, and printing is performed, and at the same time, the ink sufficiently remains on the base film.

As the number of times of printing increases, the portion with low cohesive force disappears in the ink layer, and the cohesive force of the paper side portion gradually increases.
However, since the ink thickness is reduced, the flow and adhesion of the ink to the paper due to the heat from the heat sensitive head is also sufficient, and the condition that the entanglement of the polymer can be released is obtained.

Further, FIGS. 4 to 5 show a printing process in a place where the number of printing is large. In this process, the portion of the ink layer having low cohesive force disappears, but since the ink thickness is thin, the ink is sufficiently adhered to the paper and the entanglement of the polymer is in a state of being fully decomposed.

It is considered that the thermal transfer film according to the present invention can be printed many times as described above.

〔Example〕

Next, the present invention will be described with reference to examples. All parts are parts by weight and% are parts by weight.
Is.

Examples 1-3 After coating the hot-melt ink containing the above components on a polyester film having a thickness of 6 μm with an ink thickness of 15 μm,
High density polyethylene film (density: 0.97g) with a thickness of 115μm on the back surface of the polyester film to give a cohesive force gradient in the thickness direction so that the cohesive force is high on the substrate film side in the ink layer and low on the paper side. / cm ³ ), and an electron beam with an accelerating voltage of 150 kV was irradiated on the polyethylene film at a dose of 20 Mrad to prepare a thermal transfer film.

The portion of the polyethylene film which comes into contact with the polyester film is a film (a) having a thickness of 10 μm, and the film (b) is also placed on the ink side, and (a) and (b)
The gel fraction after electron beam irradiation was measured.

The results under the conditions of Examples 1 to 3 were as follows regardless of the amount of the electron beam reactive component.

(A) Gel fraction: 15% (b) 〃: 2% Due to this fact, the ink layer is crosslinked, that is, the gradient of cohesive force is higher on the substrate film side and lower on the paper side. .

Example 4 The same heat-fusible ink as in Example 2 (electron beam reactive component: 10 parts) was applied to a polyester film having a thickness of 6 μm to give an ink thickness of 10 μm, and then the back surface of the polyester film was subjected to Examples 1 to 3. 120 μm including film (a) similar to
A high-density polyethylene film having a thickness of 2 mm was placed, and at the same time, the film (b) was placed on the ink side, and an electron beam with an acceleration voltage of 150 kV was irradiated from the back side of the polyester film at a dose of 40 Mrad to produce a thermal transfer film.

The results showing the cohesive force gradient in this example were as follows.

(A) Gel fraction: 21% (b) 〃: 4% Example 5 After applying a heat-meltable ink comprising the above ink components on a polyester film having a thickness of 6 μm to an ink thickness of 15 μm, a high-density polyethylene film having a thickness of 115 μm similar to that of Examples 1 to 3 is placed on the back surface of the polyester film,
An electron beam with an accelerating voltage of 150 kV was irradiated onto the polyethylene film at a dose of 20 Mrad to produce a thermal transfer film.

The gel fractions of the films (a) and (b) in this example were as follows.

(A) Gel fraction: 15% (b) 〃: 2% Comparative Example 1 The same heat-melting ink as in Example 4 was applied on a polyester film having a thickness of 6 μm to an ink thickness of 15 μm, and then applied to the back surface of the polyester film. Place only the film (a),
At the same time, the film (b) was placed on the ink side, and irradiation was performed from the back side of the polyester film with an electron beam having an acceleration voltage of 150 kV as 2 Mrad to produce a thermal transfer film.

The gel fractions of the films (a) and (b) were as follows.

(A) Gel fraction: 2% (b) 〃: 2% As described above, in the thermal transfer film of this example, no gradient of cohesive force is provided in the ink layer.

Comparative Example 2 Irradiation with an electron beam of 10 Mrad was performed in Comparative Example 1 to produce a thermal transfer film.

The gel fractions of the films (a) and (b) were as follows.

(A) Gel fraction: 20% (b) 〃: 20% Also in this example, no gradient of cohesive force is provided in the ink layer.

Example 6 2 Ethylhexyl acrylate 40 parts Ethyl acrylate 40 parts Methyl methacrylate 15 parts Glycidyl methacrylate part The above acrylate-based monomer was dissolved in ethyl acetate, and 1 part of benzoyl peroxide was added and heated and weighted,
After hexane is added dropwise to remove the precipitated high molecular weight substance, hexane is additionally added dropwise to the supernatant liquid, the precipitate is collected, the low molecular weight substance dissolved in the supernatant liquid is removed, and toluene is added. Then add 2 hydroxyethyl acrylate,
Using hexamethylenetetramine as a catalyst, a reaction between a glycidyl group and a hydroxyl group was performed to obtain an acrylic resin having a molecular weight of about 10,000 and having an acryloyl group in the molecule.

The acrylic resin was used as an electron beam reactive component to prepare the following heat-meltable ink.

A high-density polyethylene film having a thickness of 90 μm including the same film (a) as in Examples 1 to 3 on the back surface of the polyester film after coating the hot-melt ink on a polyester film having a thickness of 6 μm to an ink thickness of 10 μm At the same time as placing the film, the film (b) was placed on the ink surface, and an electron beam with an acceleration voltage of 150 kV was irradiated from the back side of the polyester film at a dose of 20 Mrad to produce a thermal transfer film.

The results showing the cohesive force gradient in this example were as follows.

(A) Gel fraction: 35% (b) 〃: 15% Further, the thermal transfer films obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were mounted on a thermal printer, and plain paper was used as a transfer target paper many times. I tried printing. The results are shown in Table 1.

The results shown in Table 1 show the print density in terms of reflection density (OD), and the larger this value is, the more appropriate the printing is. The value is 0.6 or more in the visually readable range. preferable.

As shown in the examples of Table 1, the product of the present invention can be printed many times. As is clear from the comparison with the comparative example, the cohesive force of the ink is increased in the thickness direction of the ink so that the cohesive force on the base film side is high and the cohesive force on the paper side is low in the heat-meltable ink layer. It has become possible.

The present invention is not limited to these embodiments, and various modifications can be made without departing from the technical idea of the present invention.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to provide a thermal transfer film capable of printing many times, and its industrial value is great.

[Brief description of drawings]

The drawings all show embodiments of the present invention. FIG. 1 is a sectional view of a thermal transfer film, and FIGS. 2 to 5 are schematic sectional views showing a usage state. Explanation of symbols 1 .... Base film, 2 .... Ink layer 3 .... Thermal head, 4. Transfer paper 21 .... Ink component, 22 .. Polymer

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-60-183192 (JP, A) JP-A-56-127492 (JP, A) JP-A-59-222387 (JP, A) JP-A-61- 100495 (JP, A) JP 61-291185 (JP, A)

Claims (2)

[Claims] 1. A thermal transfer film comprising a base film and a heat-meltable ink layer formed thereon, wherein the heat-meltable ink layer has a high cohesive force on the base film side and a low cohesive force on the opposite side. A thermal transfer film, characterized in that a cohesive force gradient is provided in the layer thickness direction. 2. The ink layer contains an electron beam-reactive component, and the electron beam-reactive component is cross-linked by irradiating the electron beam from the back surface of the substrate film to cause a cohesive force gradient in the thickness direction of the ink layer. Claim 1 which is provided with Claim 1
The thermal transfer film according to the item.