JPH0513072B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an image recording material that performs thermal transfer recording by heating the recording material in response to an applied signal using a thermal head, laser, flash light, or direct application of an electric signal. . [Prior Art] Many thermal recording methods have been proposed since ancient times that utilize changes in the physical properties and chemical reactivity of materials in response to the application of thermal energy.
Among them, dye coloring reactions between colorless dyes such as crystal violet lactone, fluoran series, and spiropyran series and phenolic compounds such as bisphenol A, other organic acids, and inorganic acids, and organic reducing agents such as organic acid metal salts and phenols. , a thermosensitive color recording method that utilizes thermal reactions with metal sulfides, organic chelating agents, and organic sulfur compounds, and changes in thermophysical properties such as heat melting and heat sublimation properties to coat inks and coloring materials on paper, etc. The thermal transfer recording method for transferring information onto a recording medium has been actively researched and efforts have been made to improve it in recent years. In particular, the latter thermal transfer recording method is capable of recording on plain paper, has good light resistance, stability, and storage stability of recorded images, and has a simple recording mechanism, so it is highly reliable. Because it has the advantages of
It is applied to printers, facsimile machines, copiers, etc. However, in the case of the method of thermally sublimating the dye, it has the advantage of being able to reproduce continuous gradation of density, but on the other hand, it has poor recording sensitivity, storage stability of the recording medium, fixing stability of the recorded image, and light fastness. etc. There is a problem. In addition, in the case of a method of thermally melting the ink and transferring and recording the ink corresponding to the applied signal onto paper etc., the above problem is reduced, but usually a crystalline wax with a low melting point is used as a binder for the heat-sensitive ink layer. Therefore, there are problems such as a decrease in resolution and weak strength of transferred and fixed images due to thermal diffusion in the recording medium. Further, crystalline waxes have the disadvantage that it is difficult to obtain clear images due to light scattering of the crystalline phase. In other words, in order to obtain clear color images, especially pictorial full-color reproduction images, by overlapping recording of ink materials several times, magenta, yellow, and cyan ink materials are usually used. secondary color and even 3
The next color is obtained. For example, when a secondary color is obtained by superimposing two types of ink materials, the color difference between the actually obtained secondary color and the intended secondary color is determined by the transparency of the ink materials. When overlapping recording is performed, at least if the transparency of the ink material overlaid on the upper layer, or more precisely, the transparency of the ink material binding layer, is good, the reflected light from the overlapping ink layers will be reflected from the pigment itself. Due to the characteristics, the secondary color reflected light becomes closer to that of the reflected light, and the color reproducibility becomes better accordingly. Conventionally, examples of using resin as a binding component of a heat-sensitive ink layer include JP-A-54-87234 and JP-A-56-
No. 98269, etc. are known, but all of these are aimed at improving the fixation and durability of prints for thermal ink materials that use the wax as a binder, and they are used as a binder for the purpose of color reproduction. There is no technical disclosure focusing on the transparency of ingredients. [Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a thermal transfer recording material that enables clear color reproduction. Another object of the present invention is to provide a heat-sensitive transfer recording material with good resolution. Still another object of the present invention is to provide a thermal transfer recording material with good recording sensitivity, transfer and fixing properties. [Means and effects for solving the problem] As a result of intensive studies, the present inventors have changed the binder of the thermal ink material from a conventional one mainly composed of crystalline waxes to a substantially amorphous one. The present invention was completed based on the discovery that the object of the present invention can be achieved by changing to a transparent polymer material and adding a small amount of a releasing substance. That is, the present invention provides a recording material in which a heat-melting thermal ink material layer is provided on a support, wherein the thermal ink material contains a colorant and a glass transition temperature of 40.
A transparent polymer having a number average molecular weight of 10,000 or less at temperatures above ℃ to 60℃ and showing no clear melting point;
The main component is a release material having a melting point or softening point of 50°C or more and less than 80°C, the polymer is selected from at least styrene-acrylic resin, epoxy resin, and petroleum resin, and the non-volatile material of the heat-sensitive ink material This heat-sensitive recording material contains 65% by weight or more of the polymer and the releasing substance in a weight ratio of 70:30 to 99:1. The polymer used as a binder resin in the ink material of the present invention (hereinafter referred to as the polymer of the present invention) is:
It is an amorphous polymer and is different from crystalline polymers (such as polyethylene terephthalate) that are conventionally used as base materials for thermal transfer materials. The polymer of the present invention has a glass transition temperature of 40°C or more and 60°C or less and a number average molecular weight of 10,000 or less,
The polymer is a transparent polymer having no definite melting point and selected from at least styrene-acrylic resin, epoxy resin, and petroleum resin. Waxes conventionally used as binding materials for thermal ink materials include paraffin wax, carnauba wax, montan wax, beeswax, wood wax, candelilla wax, low molecular weight polyethylene, α-olefin oligomer, and these waxes. If necessary, mineral oil such as spindle oil, vegetable oil such as linseed oil and tung oil, plasticizers such as dioctyl phthalate and diptylphthalate, oleic acid, stearic acid, etc. A thermal transfer recording material was produced by mixing and dispersing higher fatty acids, their metal salts, amides, and other derivatives together with dyes and pigments, and coating the mixture on a thin layer of plastic film or capacitor paper. Waxes, which are conventional binding materials, have a relatively clear melting point in the temperature range of about 50℃ to about 150℃ because they are crystalline, and when heated above the melting point, they rapidly change from a solid phase to a liquid phase. change into phases. and about 10 ^-2 to about 10 poise at a temperature about 30℃ higher than the melting point.
It becomes a low viscosity liquid. On the other hand, in the case of amorphous polymers such as the polymer of the present invention, there is essentially no melting point, and the solid phase gradually changes to the liquid phase after reaching the glass transition temperature (Tg). , does not show a clear melting point above the glass transition temperature. The viscosity change during this period basically follows the WLF equation or Andrade equation, and is usually 10 ³ even at a temperature 50°C higher than Tg.
Holds a viscosity of ~10 ⁵ poise. In the case of thermal transfer recording, the transfer and fixing sensitivity is basically controlled by the melt viscosity and melt viscoelasticity of the binding material, so using an amorphous polymer as a binding material for thermal ink is This is obviously disadvantageous in terms of sensitivity. However, the present inventors have found that using the polymer of the present invention having a specific molecular weight and Tg as a binding material and further adding a release material improves image quality and image stability without sacrificing sensitivity. We found that it could be significantly improved. That is, in the heat-sensitive recording material of the present invention, at least 65% of the specific polymer of the present invention is contained in the non-volatile components of the heat-sensitive ink layer as a binder component of the heat-sensitive ink layer.
By using % by weight, the scattering of transmitted light that conventionally occurs due to crystals in the crystalline polymer binding layer completely disappears, resulting in clear images in color reproduction, especially in color reproduction by overlapping recording of ink materials. It is possible to maintain the transparency of the binder layer, which is essential for obtaining the desired results. Generally, using a polymeric material as a binder is considered to be disadvantageous in terms of recording sensitivity, but in the present invention, two factors, the number average molecular weight and the glass transition temperature of the polymer of the present invention, are controlled. By utilizing the low energy effect of the release material at the interface of the support, it is possible to maintain the same recording sensitivity as conventional wax-based heat-sensitive recording materials while creating a binding layer similar to that seen in wax-based materials. In addition to obtaining excellent resolution by preventing heat diffusion during printing, the polymer's unique flexibility and abrasion resistance properties make it possible to print with excellent fixation. The heat-sensitive recording material of the present invention will be explained in detail below.
The heat-sensitive recording material of the present invention has a polystyrene-equivalent number average molecular weight of about 1000 or less as measured by gel permeation chromatography (GPC), and a glass transition temperature (Tg) measured by differential scanning calorimetry (DSC). About 40℃ or more and 60℃ or less, more preferably a number average molecular weight of about 5000 or less, and a Tg of about 50℃ or less
The polymer of the present invention in the range of 60°C is used as a binder at least substantially in the non-volatile components of the thermal ink material.
Use it so that it contains 65% or more by weight. That is, when the content of the polymer of the present invention in the non-volatile components of the thermal ink material is less than 65% by weight, the transparency of the thermal ink material deteriorates significantly and good color reproducibility cannot be obtained. For,
When the content of the polymer of the present invention is 65% by weight or more, particularly 70% by weight or more, very good transparency is exhibited, and excellent effects can be obtained particularly in color reproduction by overlapping ink materials. This is due to an increase or decrease in the crystalline component that occupies the total thermal ink material component.As the crystalline component occupies the thermal ink material component increases, the degree of light scattering by the crystals increases. This is thought to be due to the deterioration of transparency. Further, when the Tg of the polymer of the present invention is less than 50°C, particularly less than 40°C, blocking of the thermal ink material tends to occur, resulting in a lack of stability during storage and use. If the Tg exceeds 80°C, the thermal stability is good, but the sensitivity is lowered, so it is impractical and cannot be used for anything other than special purposes. It has been experimentally confirmed that even if the Tg is within the above range, the sensitivity decreases when the molecular weight of the polymer of the present invention is high. This is presumed to be due to the cohesive force between molecules based on entanglement of molecular chains, etc., and good transfer and fixing properties were obtained when the number average molecular weight was about 10,000 or less, particularly 5,000 or less. The setting of the weight average molecular weight may vary depending on the use of the thermal transfer recording material. When it is desired to obtain a binary transfer image as with conventional wax-based inks, the weight average molecular weight should also be about 40,000 or less, more preferably about 10,000 or less,
It is desirable to make the softening properties of amorphous polymers more sensitive by narrowing the molecular weight distribution.
On the other hand, if you want to obtain density gradation or multilevel transfer images, or if you want to use it repeatedly many times, it is desirable to melt-transfer an amorphous polymer that exhibits gradual softening characteristics depending on the applied energy. The weight average molecular weight does not necessarily have to be small, and may be set to about 40,000 or more. Of course, even in this case, a binary transfer image can also be obtained satisfactorily. Furthermore, the shape of the molecular weight distribution does not necessarily have to be a shape having a single molecular weight peak, but may be a shape having a plurality of molecular weight peaks, or a crosslinked or branched polymer component may be used in combination. However, when the weight average molecular weight is set to about 10,000 or more, particularly 40,000 or more, it is disadvantageous in terms of sensitivity. The polymers of the invention can be selected from styrene-acrylic resins, epoxy resins and petroleum resins. Styrene-acrylic resins include styrene, vinyltoluene, α-methylstyrene,
2-methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, aminostyrene and its derivatives, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, and methacrylic acid, methyl acrylate, ethyl acrylate Acrylic acid esters such as , butyl acrylate, α-ethylhexyl acrylate, and copolymers with acrylic acid can be used. Alternatively, a crosslinked polymer may be formed using a polyfunctional monomer such as divinylbenzene. Furthermore, epoxy resin and petroleum resin can be used. When these polymers of the present invention are used in the form of a copolymer, the copolymer may be not only a random copolymer but also an alternating copolymer, a graft copolymer, and a block copolymer depending on the required use. , interpenetrating copolymers, and the like can be appropriately selected and used. In addition, when two or more types of polymers of the present invention are mixed and used, in addition to mechanical mixing such as melt mixing, solution mixing, and emulsion mixing, co-polymerization and multistage polymerization methods are used during polymerization of the polymer components of the present invention. You can also mix it with etc. The releasing substance added as a binding material component together with the polymer of the present invention can be used by differential scanning calorimetry (DSC).
It is an organic substance or an organic/inorganic low molecular weight polymer that is solid at room temperature with a melting point measured by the ring and ball method or a softening point measured by the ring and ball method of 50°C or higher and 80°C or lower, and which rapidly becomes a low-viscosity liquid when the melting point or softening point is exceeded. Refers to substances with relatively low surface energy. Melting point/
If the softening point is below 50°C, it will lack stability during storage and use, and if the melting point is above 200°C, the additive will have little effect on the thermal energy applied in normal thermal recording methods. do not have. In the temperature range of 100 to 180℃, the melt viscosity is approximately
Low viscosity and/or critical surface tension that rapidly decreases to 10 poise or less, more preferably about 1 poise or less, about 40 dyn/cm or less, more preferably about
A substance having a low surface energy of 30 dyn/cm or less acts effectively as a releasing substance. Specifically, higher fatty acids such as palmitic acid and stearic acid, fatty acid metal salts such as zinc stearate, fatty acid esters or partially saponified products thereof, fatty acid derivatives such as fatty acid amides, higher alcohols, and polyhydric alcohols. derivatives such as esters, waxes such as paraffin wax, carnauba wax, montan wax, beeswax, wood wax, candelilla wax, low molecular weight polyethylene with a viscosity average molecular weight of about 1000 to about 10000, polypropylene, polybutylene, etc. polyolefins, or olefins, low molecular weight copolymers of α-olefins and organic acids such as maleic anhydride, acrylic acid, methacrylic acid, vinyl acetate, etc., low molecular weight oxidized polyolefins, halogenated polyolefins, lauryl methacrylate, Stearyl methacrylate, etc. Methacrylic esters with long alkyl side chains, acrylic esters or acrylic esters with perfluoro groups, methacrylic esters alone or copolymers with vinyl monomers such as styrenes, polydimethyl Low molecular weight silicone resins and silicone-modified organic substances such as siloxane and polydiphenylsiloxane, as well as cationic surfactants such as ammonium salts and pyridinium salts having long-chain aliphatic groups,
Alternatively, anionic, nonionic surfactants, perfluorinated surfactants, etc. that similarly have long-chain aliphatic groups,
One or more types can be selected and used. These releasable substances melt when heated, and due to their low cohesive force and/or low surface energy effect, they melt between the molecules of the polymer of the present invention, which is the main binding material, at the interface between the thermal ink material and the support. Alternatively, since excessive cohesive force or adhesive force at the interface between the polymer of the present invention and the support is reduced, it becomes possible to apply energy with lower energy, thereby improving recording sensitivity, image quality, and especially resolution. Most of the releasing substances are crystalline materials, so if they are added in excess, the crystals will cause light scattering, deteriorating transparency and, in particular, color reproducibility, so they should not be added in excess of what is necessary. Furthermore, because of the low viscosity and/or low surface energy, the ink may have poor fixability to a recording medium such as paper, or the image may be spread and the resolution may be reduced. On the other hand, if the amount added is small, it cannot effectively perform its function. Therefore, the weight ratio of the polymer of the present invention to the release agent in the thermal ink binding material is about 70:30 to about 70:30.
When used in a ratio of 99:1, particularly preferably in the range of about 80:20 to about 95:5, the thermal ink material of the present invention can most effectively achieve its objectives, particularly without deteriorating color reproduction. Of course, even if the amount of the polymer of the present invention is reduced to less than 65% by weight in the binder material, it can be put to practical use as a thermal ink, but as described above, the image quality tends to deteriorate significantly. Note that the releasing substance and other ink materials such as the polymer of the present invention may form a chemical bond when mixed.
In particular, in order to improve the dispersion of the releasing substance, the reaction and interaction between the active groups in the polymer of the present invention and the active groups of the releasing substance can be utilized to stabilize the dispersion. It is also effective to graft or uniformly disperse the polymer of the present invention and the release material by polymerizing or condensation polymerizing the polymer monomer of the invention in the presence of the release material. In addition to this, the heat-sensitive recording material of the present invention further includes a charge control and/or inhibitor, a conductive agent, an antioxidant,
Thermal conductivity improvers, magnetic materials, ferroelectric materials, preservatives, fragrances, anti-blocking agents, reinforcing fillers, mold release agents,
A foaming agent, a sublimating substance, an infrared absorbing agent, etc. may be added inside or outside the heat-sensitive ink material. However, as mentioned above, the weight concentration of the polymer component of the present invention in the non-volatile components of the total thermal ink material is
It is necessary to account for 65% or more, particularly preferably 70% or more. Colorants include black dyes and pigments such as carbon black, oil black, and graphite; CIPigment.
Acetoacetate arylamide monoazo yellow pigments (Fast Yellow series) such as Yellow 1, 3, 74, 97, and 98; acetoacetate arylamide disazo yellow pigments such as CIPigment Yellow 12, 13, and 14;
CISolvent Yellow19, 77, 79, CI
Yellow dye such as Disperse Yellow 164; CIPigment
Red48, 49:1, 53:1, 57:1, 81,
122, 5 grade red or red pigment; CISolvent
Red dyes such as Red52, Red58, Red8; CIPigment
Blue15: tertiary copper phthalocyanine and its derivatives,
Dyes and pigments conventionally known for printing inks and other coloring applications can be used, such as modified blue dyes and pigments, colored or colorless sublimable dyes, and the like. These dyes and pigments may be used alone or in combination of two or more. Of course, it can be mixed with extender pigments and white pigments,
You may also adjust the color tone. Furthermore, in order to improve the dispersibility of the binder component, the surface of the colorant may be treated with a surfactant, a coupling agent such as a silane coupling agent, or a polymer material, or a polymer dye or polymer graft pigment may be used. It's okay. The thermal transfer recording material of the present invention is formed by placing on a support a thermal ink material containing a mixture of the polymer of the present invention, a releasing substance, a colorant, and, if necessary, the various additives mentioned above. Ru. The thermal ink materials are mixed into a solution and/or dispersed emulsion in a solvent and/or dispersion medium that can dissolve and/or stably disperse the binder material, and mixed and dispersed using a ball mill, sand mill, attritor, three-roll mill, etc. It can be prepared in a machine. Alternatively, the mixture may be melt-mixed using a heated triple roll, heated pressure kneader, Banbury mixer, etc., without using any solvent or the like. Furthermore, the polymer of the present invention, which is the main binding material, may be prepared by polymerization in the presence of colorants, additives, release substances, etc., and used as a heat-sensitive ink material. The heat-sensitive ink material thus prepared is coated and printed on a support by a solution and/or melt coating method using a gravure coater, a wire bar, or the like. Alternatively, the heat-sensitive ink material may be pulverized by a spray drying method, a pulverization method, or the like, and then powder-coated onto a support by an electrostatic coating method or the like. In this case, after powder coating, heating, pressurization, solvent treatment, etc. may be further performed as necessary to fix the heat-sensitive powder ink on the support before use. Furthermore, when preparing such a heat-sensitive powder ink, the polymer of the present invention, which is the main binding material, is subjected to suspension polymerization or dispersion polymerization in the presence of colorants, additives, release substances, etc. A powder ink may be prepared by direct polymerization, such as by a direct polymerization method. As the support, polyesters such as polyethylene terephthalate, polyimides and imide copolymers, fluorine polymers, plastic films such as polypropylene, thin sheets such as capacitor paper, and films are conveniently used. These sheets, films, or rolls are used with the addition of thermal property modifiers, mold release agents, antistatic agents, conductive agents, and reinforcing agents to improve thermal conductivity, thermal stability, etc. It's okay. In addition, when recording is performed using a thermal head, etc., silicone-based, fluorine-based compounds, resin layers, or crosslinked polymer layers are added to the side of the support that comes into contact with the thermal head in order to improve heat resistance, runnability, etc. , a metal layer, a ceramic layer, etc. may be provided. Furthermore, the above-mentioned film internal additives may be added to the outer layer. The surface of these supports may be smooth, or may have irregularities, grooves, etc., or may be porous. Alternatively, an electrothermal conversion element or a photothermal conversion element having a structure similar to that of a thermal head may be directly used as the support, and a heat-sensitive ink layer may be provided thereon. The thickness of the support film or sheet and the thickness of the heat-sensitive ink layer may be appropriately selected depending on the application, but in general, it is easy to use a support with a thickness of about 1 μm to about 200 μm. In order to improve resolution, a range of about 1 μm to about 10 μm is preferred. Thermal ink layer is 0.5μm
It is easy to use if it is set in the range of about 1 μm to about 20 μm, depending on the purpose, up to about 50 μm. An intermediate layer for controlling adhesion may be disposed between the thermal ink layer and the support, or the thermal ink layer itself may be a multilayer coating layer of multiple types of thermal ink materials with different physical properties, or multiple types of thermal ink materials with different physical properties may be coated within a plane. The ink material may be divided and coated. The heat-sensitive recording material formed in this way is heated in response to an applied signal by means such as a thermal head, laser, flash light, or direct electrical signal, and is brought into contact with a recording medium such as paper or film. The heat-sensitive ink material is transferred and recorded by being ejected in a non-contact state or in a non-contact state. In addition to mechanical forces such as pressurization and foaming, in order to improve recording performance,
It is also possible to use electric fields, magnetic fields, ultrasonic waves, solvents, etc. in combination. [Examples] The present invention will be explained below with reference to Examples, but the present invention is of course not limited to these Examples. In addition, in the following examples, parts represent parts by weight unless otherwise specified. Example 1 Seven types of thermal ink materials having the following compositions were kneaded in a ball mill for 40 hours. Thermal ink (composition is shown in the table below) 25 parts Toluene 75 parts

[Table] Thermal ink material obtained (Ink No.
1 to 7) were applied onto a polyester film with a thickness of 6 μm by wire bar coating and dried to prepare a heat-sensitive recording material with a heat-sensitive ink thickness of 3 μm. Typical recording properties of these thermal recording materials were evaluated using an FXP-6 thermal transfer printer manufactured by Fuji Xerox Co., Ltd. The results are shown in the table below.

〔Effect of the invention〕

The heat-sensitive recording material of the present invention is particularly excellent in color image reproducibility, recording sensitivity, transferability, fixing performance, and resolution on a transfer material. The amorphous polymer used in the present invention is different from crystalline wax, which is a binder used in conventional heat-sensitive recording materials, by using the polymer of the present invention as a binder. Since the light scattering that occurs when using the heat-sensitive recording material of the present invention is completely eliminated or can be controlled to a substantially problem-free level, the binding layer of the heat-sensitive recording material of the present invention exhibits extremely good transparency. In particular, for the purpose of obtaining clear color images, especially pictorial full-color reproduction images, by overlapping recording of ink materials several times, for example, magenta, yellow, and cyan ink materials are overlaid to produce secondary or tertiary colors. When obtaining a thermal ink layer of the present invention, the heat-sensitive ink material of the present invention is layered as at least the upper layer ink material, and since its transparency is good, the reflected light from the lower layer ink layer is also reduced due to the characteristics of the pigment itself. It is possible to obtain a color with no color difference from the desired secondary or tertiary color. Furthermore, conventionally, using a polymeric material as a binder instead of a wax-based binder is considered to be disadvantageous in terms of recording sensitivity, but in the present invention, by using a specific amorphous polymer, a wax-based binder can be used. It is possible to obtain the same recording sensitivity as when using a binder, and by taking advantage of the properties of the polymer material, that is, its slow melting properties, it eliminates the thermal diffusion of the applied energy in the ink material and achieves excellent resolution. Obtainable. Furthermore, since a polymer is used as a binder, it is flexible and durable against friction, etc., and can also improve the poor fixing properties, which was a drawback of conventional wax-based heat-sensitive recording materials.

Claims (1)

[Claims] 1. In a recording material in which a heat-melting thermal ink material layer is provided on a support, the thermal ink material contains a colorant, a glass transition temperature of 40°C or more and 60°C or less, and a number average molecular weight of 10,000 or less, and The main components are a transparent polymer that does not show a clear melting point and a mold-releasing substance with a melting point or softening point of 50°C or more and less than 80°C, and the polymer is made of styrene-acrylic resin, epoxy resin, and petroleum resin. at least 65% selected and in the non-volatile components of said thermal ink material.
1. A heat-sensitive recording material, characterized in that the weight ratio of the polymer to the releasing substance is from 70:30 to 99:1.