JPH0544355B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an image recording material in which thermal transfer recording is performed by heating the recording material in response to an applied signal using a thermal head, laser, flash light, or means for directly applying an electric signal. [Description of the Prior Art] Many methods have been proposed for a long time regarding thermal recording methods 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 in recent years, and efforts are being made to improve it. 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 to paper etc., the above problem is reduced, but usually low melting point crystalline wax is used as a binder for the heat-sensitive ink layer. In order to use
There are problems such as a decrease in resolution due to thermal diffusion in the recording medium and weak strength of transferred and fixed images. 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, by overlapping ink materials several times, magenta, yellow, and cyan ink materials are usually used, and these ink materials are overlaid. secondary colors and even tertiary colors are obtained. For example, when a secondary color is obtained by overlapping 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 intended to improve the fixation and durability of printing with respect to the wax and the thermal ink material used as a binder, and they are used as a binder for the purpose of recoloring. 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] In the course of intensive studies, the present inventors have determined that the binder of the thermal ink material is based on conventional crystalline waxes, which have a substantially clear melting point. The present invention was completed by confirming that the object of the present invention can be achieved by changing to a transparent polymer that does not exhibit . 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 has a glass transition temperature of 40°C or more and 80°C.
The main component is a transparent polymer (excluding polyester resin) with a number average molecular weight of 10,000 or less that does not show a clear melting point, and the polymer is present in the non-volatile components of the thermal ink material at approximately 90% by weight. % or more of the heat-sensitive recording material. The transparent polymer used in the present invention, which does not have a clear melting point, basically has a clear melting point, unlike crystalline polymers (such as polyethylene terephthalate) that are conventionally used as base materials for thermal transfer materials. It is a substantially amorphous transparent polymer with a glass transition temperature of 40°C or higher and a number average molecular weight of 10,000 or lower. 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 dibutyl phthalate, and higher grades such as oleic acid and stearic acid are added. By mixing and dispersing fatty acids, their metal salts, amides, and other derivatives with dyes and pigments, and coating them on a thin layer of plastic film or capacitor paper,
It was considered a thermal transfer recording material. 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 at a temperature about 30℃ higher than the melting point, about 10 ^-2 to about
It becomes a low viscosity liquid of 10 poise. On the other hand, in the case of transparent polymers that do not exhibit a clear melting point, there is essentially no melting point, and the polymer gradually changes from a solid phase to a liquid phase after reaching the glass transition temperature (Tg). The viscosity change during this period basically follows the WLF equation or Andrade equation, and the viscosity is maintained at approximately 10 ³ to 10 ⁵ piose even at a temperature about 50°C higher than Tg. 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, we found that using a transparent polymer with a specific molecular weight and Tg without a clear melting point as a binding material, without sacrificing sensitivity.
It has been found that image quality and image stability can be significantly improved. That is, in the heat-sensitive recording material of the present invention, at least 50% by weight of a transparent polymer that does not exhibit a specific clear melting point is used in the non-volatile components of the heat-sensitive ink layer as a binder component of the heat-sensitive ink layer. ,
The scattering of transmitted light that conventionally occurred due to the crystals in the crystalline polymer binding layer completely disappears, improving color reproduction,
In particular, it is possible to maintain the transparency of the binder layer, which is essential for obtaining clear images when reproducing colors by overlapping recording of ink materials. 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 are considered: the number average molecular weight and glass transition temperature of a transparent polymer that does not have a clear melting point. By controlling this, we can maintain recording sensitivity equivalent to that of conventional wax-based heat-sensitive recording materials, prevent heat diffusion in the binding layer that occurs with wax-based materials, and obtain excellent resolution. By taking advantage of its flexibility and abrasion resistance, it is possible to print with excellent fixation properties. Hereinafter, the heat-sensitive recording material of the present invention will be explained in detail. The heat-sensitive recording material of the present invention has a polystyrene-equivalent number average molecular weight of about 10,000 or less as measured by gel permeation chromatography (GPC), and a glass transition temperature (Tg) measured by differential scanning calorimetry (DSC). It is more preferable that the number average molecular weight is about 5000 or less and the Tg is about 50 to 80 °C.
A transparent polymer or oligomer having no distinct melting point within the range of 90% by weight or more of the non-volatile components of the thermal ink material is used as a binder material. In other words, if the content of the transparent polymer that does not exhibit a clear melting point is less than 50% by weight based on the non-volatile components of the thermal ink material, the transparency of the thermal ink material will deteriorate significantly and good color reproducibility will be impaired. On the other hand, when the content of a transparent polymer that does not have a clear melting point is approximately 90% by weight or more, it exhibits very good transparency, and has an excellent effect on color reproduction by layering ink materials. Obtainable. This is due to the increase or decrease of the crystalline component in the total heat-sensitive ink material component, and as the amorphous component in the heat-sensitive ink material component increases, the degree of light scattering by the crystals increases. This is thought to be due to the deterioration of transparency. It is also a transparent polymer that does not have a clear melting point.
When Tg is less than 50°C, especially less than 40°C, blocking of the thermal ink material tends to occur, resulting in a lack of stability during storage and use. If 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 also decreases when the molecular weight of a transparent polymer that does not exhibit a clear melting point 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 in the same way 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, and by narrowing the molecular weight distribution, a clear melting point can be achieved. It is desirable to make the softening properties of transparent polymers more sensitive.
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, you can melt and transfer a transparent polymer that exhibits gradual softening properties and does not have a clear melting point depending on the applied energy. It is desirable to have a weight average molecular weight of 40,000 or more, and it is not necessary to reduce the weight average molecular weight. Of course, even in this case, a binary transfer image can also be obtained satisfactorily. Furthermore, the shape of the molecular weight distribution is
It does not necessarily have to have a shape having a single molecular weight peak, but may have a distribution 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 chemical composition and structure of the transparent polymer, which does not exhibit a distinct melting point, of course affects the properties of the thermal ink material, but the effect is not as great as the molecular weight and Tg mentioned above. If the molecular weight and Tg values are within the specified ranges, it can basically be used as the thermal ink material of the present invention. For example, styrene, vinyltoluene, α-methylstyrene, 2-methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, aminostyrene and other styrene and its derivatives, homopolymers and copolymers of substituted products, methyl methacrylate , methacrylic acid esters such as ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, and methacrylic acid,
Acrylic acid esters and acrylic acid such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, dienes such as butadiene and isoprene, acrylonitrile, vinyl ethers, maleic acid and maleic esters, maleic anhydride, cinnamic acid Vinyl monomers such as vinyl chloride, vinyl acetate, etc. can be used alone or in copolymers with other monomers. Of course, the vinyl resin may also be used as a crosslinked polymer using a polyfunctional monomer such as divinylbenzene. Furthermore, polycarbonate, polyamide, epoxy resin, polyurethane, silicone resin, fluorine resin, phenol resin, terpene resin, petroleum resin, hydrogenated petroleum resin, alkyd resin, ketone resin, cellulose derivative, etc. may be used. When these transparent polymers or oligomers that do not have a clear melting point are used in the form of a copolymer, the copolymer may be a random copolymer, an alternating copolymer, a graft copolymer, etc. depending on the required use. Copolymerization modes such as coalescence, block copolymers, and interpenetrating copolymers can be appropriately selected and used. In addition, when using a mixture of two or more types of polymers or oligomers, in addition to mechanical mixing such as melt mixing, solution mixing, or emulsion mixing, they may be mixed by coexistence polymerization, multistage polymerization, etc. during polymerization of the polymer or oligomer components. It's okay. The thermal ink material of the present invention can sufficiently achieve its purpose by using only these transparent polymers and oligomers that do not have a clear melting point as its binder. Oils and liquid plasticizers such as those used in materials may be added and mixed. In addition, olefin-based single or copolymers such as ethylene and propylene, organic acid-grafted olefin-based copolymers, chlorinated paraffins, low-molecular urethane compounds, plasticizers that are solid at room temperature, surfactants, etc. can be used for charge control and /or inhibitor, conductive agent,
Add antioxidants, thermal conductivity improvers, magnetic substances, ferroelectric substances, preservatives, fragrances, antiblocking agents, reinforcing fillers, foaming agents, sublimation substances, infrared absorbers, etc. inside or outside of the thermal ink material. It may be used by adding it. However, as mentioned above, the transparent polymer component that does not exhibit a clear melting point accounts for 50% or more by weight, particularly preferably 70%, of the total non-volatile components of the thermal ink material.
It is necessary to occupy at least the following. 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, CIPigment 3, CIPigment 74, CIPigment 97, and CIPigment 98;
CISolvent Yellow19, 77, 79, CI
Yellow dye such as Diaperse 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 well known for conventional 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, the color tone may be adjusted by mixing with an extender pigment or a white pigment. 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 heat-sensitive transfer recording material of the present invention can be produced by placing a heat-sensitive ink material, which is a mixture of a transparent polymer or oligomer that does not have a clear melting point, a colorant, and, if necessary, the various additives mentioned above, on a support. It is formed. The thermal ink materials are mixed by forming a solution and/or dispersion emulsion in a solvent and/or dispersion medium that can dissolve and/or stably disperse the binder material, and mixing and dispersing 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 a solvent or the like. Furthermore, in the presence of colorants, additives, etc., a transparent polymer that does not exhibit a clear melting point, which is the main binding material,
Oligomers may be prepared by polymerization and used as thermal ink materials. 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 powdered 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, melting 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, an amorphous polymer, which is the main binding material, is directly processed by suspension polymerization method, dispersion polymerization method, etc. in the presence of colorants, additives, etc. A powder ink may also be prepared by polymerizing using a 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 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 a 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, a support with a thickness of about 1 μm to about 200 μm is easy to use. Approximately 1μm to improve resolution
A thickness of about 10 μm is preferred. The thermal ink layer is
From about 0.5μm to about 50μm depending on the application.
Usually, it is easy to use if it is set in the range of about 1 μm to about 20 μm. Between the thermal ink layer and the support,
By arranging an intermediate layer to control adhesion, by making the thermal ink layer itself a multilayer coating layer of multiple types of thermal ink materials with different physical properties, or by separately coating multiple types of ink materials with different physical properties within a plane. good. The heat-sensitive recording material thus formed is heated in accordance with the applied signal by means such as a thermal head, laser, flash light, or direct electrical signal, and is heated to a recording medium such as paper or film. The heat-sensitive ink material is transferred and recorded by being ejected in a contact state or in a non-contact state. In order to improve recording properties, it is possible to use not only mechanical forces such as pressurization and foaming, but also electric fields, magnetic fields, ultrasonic waves, solvents, etc. [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 Heat-sensitive ink material having the following composition was coated with a thickness of 6 μm.
A heat-sensitive recording material was prepared by coating the heat-sensitive ink layer on a polyester film such that the thickness of the heat-sensitive ink layer after cooling or drying was 3 μm. Thermal ink material A paraffin wax (melting point = 69℃) Softening agent (lubricating oil) Blue pigment (CIPigment Blue 15:3) 85 parts 5 parts 10 parts After melt-mixing the above composition at 100℃, 3 bottles Knead with a roll mill to make a thermal ink material,
This was applied with a wire bar to a polyester film on a hot plate heated to 110°C to obtain a heat-sensitive recording material.

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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 comprises a colorant and an amorphous polymer having a glass transition temperature of 40° C. or more and 80° C. or less and a number average molecular weight of 10,000 or less. (however,
(excluding amorphous polyester resin), and the amorphous polymer is contained in a non-volatile component of the heat-sensitive ink material in an amount of approximately 90% by weight or more.