JPS61244591A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enable clear color reproduction, by using a substantially amorphous transparent high molecular weight material in place of a conventional binder comprising a crystalline wax as a main constituent, as a binder for a thermal recording ink material. CONSTITUTION:In a recording material comprising a heat-fusible thermal recording ink material layer on a base, the ink material comprises an amorphous polymer and a coloring agent as main constituents, the polymer being used in an amount of at least 50wt% in non-volatile components of the ink material. The amorphous polymer means a substantially amorphous transparent polymer primarily showing no clear melting point.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is a thermal transfer method in which a recording material is heated in response to an applied signal using a thermal head, a laser, a flash light, or a means for directly energizing an electric signal. The present invention relates to image recording materials for recording.

[Description of prior art]

A number of methods have been proposed since ancient times, including the use of crystal violet lactone and fluoran. Dye coloring reactions between colorless dyes such as spiropyran series and phenolic compounds such as bisphenol A, other organic acids, and inorganic acids, organic acid metal salts and organic reducing agents such as phenols, metal sulfides, organic chelating agents, A thermosensitive color recording method that utilizes a thermal reaction with an organic sulfur compound, and a thermosensitive transfer recording that transfers ink or coloring material to a recording medium such as paper using changes in thermophysical properties such as heat bath melting properties and heat sublimation properties. The law has been actively researched in recent years, and efforts are being made to improve it.

In particular, the latter thermal transfer recording method is highly reliable because it can record on plain paper, the recorded image has good light resistance, stability, and storage stability, and the recording mechanism is simple. Printers, facsimiles,
It is applied to copying machines, etc.

In the case of a method in which the dye is thermally sublimated while the pressure is 1,
Although it has the advantage of being able to reproduce continuous gradation of density, it has problems with recording sensitivity, storage stability of the recording medium, fixing stability of recorded images, light resistance, etc. In addition, in the case of a method in which the ink is transferred and recorded by thermally melting the ink in response to the applied signal, the above problem is reduced, but usually a crystalline wax with a low melting point is used to bind the heat-sensitive ink layer. Since it is used as an agent, it has problems such as a decrease in resolution due to thermal diffusion in the recording medium and weak strength of transferred and fixed images.Also,
Crystalline waxes have the disadvantage that the light scattering of the crystalline phase makes it difficult to obtain clearer images.

In other words, in order to obtain clear color images, especially Victorian full-color reproduction images, by repeatedly recording ink materials, magenta, yellow, and cyan ink materials are usually used. The materials are superimposed to produce secondary and even tertiary colors. For example 2
When a secondary color is obtained by superimposing different types of ink materials, the color difference between the obtained secondary color and the desired secondary color is determined by the transparency of the ink material. When overlapping recording is performed, a small amount of reflected light (from the overlaid ink layer 7+, 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) is closer to the secondary color reflected light (due to the characteristics of the pigment itself), and the color reproducibility becomes better.

Conventionally, examples of using a resin as a binding component of a heat-sensitive ink layer include JP-A-54-87234 and JP-A-56-982.
No. 69, etc. are known, but all of these are aimed at improving the fixation and durability of prints for thermal ink materials that use wax as a binder, and are used as a binder for the purpose of color reproduction. There is no technical disclosure focusing on the transparency of ingredients.

[Problem that the invention seeks to solve]

Therefore, an object of the present invention is to provide a heat-sensitive transfer recording material that enables clear color reproduction.

13= Another object of the present invention is to provide a thermal transfer recording material with good resolution.

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 found that the binder for thermal ink materials has changed from the conventional binder mainly composed of crystalline waxes to substantially amorphous binders. It was confirmed that the object of the present invention could be achieved by changing to a transparent polymer material of high quality, and the present invention was completed.

That is, the present invention provides a recording material in which a heat-melting heat-sensitive ink material layer is provided on a support, wherein the heat-sensitive ink material contains an amorphous polymer and a colorant as main components, and the amorphous polymer is a heat-sensitive ink material. In the non-volatile components of
This is a heat-sensitive recording material characterized in that it contains 0% by weight.

The amorphous polymer used in the present invention is a substantially non-crystalline polymer that basically does not have a clear melting point, unlike crystalline polymers (such as polyethylene terephthalate) conventionally used as base materials for thermal transfer materials. A crystalline transparent polymer having a glass transition temperature of 40"C or higher and a number average molecular weight of 10,000 or lower is preferable.

Conventionally, waxes 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 oligomers, and copolymers and modified products thereof. Oil, vegetable oil such as tung oil, plasticizers such as dioctyl phthalate and diptylphthalate, higher fatty acids such as oleic acid and stearic acid, their metal salts, amides and other derivatives are mixed and dispersed in dyes and pigments, etc. to form a thin layer. It was used as a thermal transfer recording material by coating it on a plastic film or capacitor paper.

Since waxes, which are conventional binding materials, are crystalline, they have a relatively clear melting point in the temperature range of about 50°C to about 150°C, and when heated above the melting point, It suddenly changes from solid phase force to liquid phase.

At a temperature about 30° C. higher than the melting point, it becomes a low viscosity liquid of about 10 −2 to about 10 poise. On the other hand, in the case of an amorphous polymer, there is no essential melting point, and the polymer gradually changes from a solid phase to a liquid phase at the glass transition temperature (Tg). The viscosity change during this period basically follows the WLF formula or Andrade formula, and is approximately 50°C below Tg.
Even at high temperatures, the viscosity usually does not decrease, up to about 103 to 10' poise at most. In the case of thermal transfer recording, the transfer and fixing sensitivity is basically controlled by the melt viscosity and melt viscoelasticity of the binder material, so using an amorphous polymer as a binder for thermal ink has a This is clearly disadvantageous. shi71) Shi while.

The inventors have discovered that using an amorphous polymer with a specific molecular weight and Tg as a binding material can significantly improve image quality and image stability without sacrificing sensitivity.

That is, in the heat-sensitive recording material of the present invention, a specific amorphous polymer is used as a binder component in the heat-sensitive ink layer in a small amount (both 50% by weight) in the non-volatile component of the heat-sensitive ink material.
As a result, the scattering of transmitted light that conventionally occurred due to the crystals of the crystalline polymer binding layer is completely eliminated, and in order to obtain clear images in color reproduction, especially in color reproduction due to overlapping recording of ink materials, The transparency of the essential binder layer can be maintained.

Generally, using a polymeric material as a binder is considered to be disadvantageous in terms of recording sensitivity, but in the present invention, it is possible to control two factors, the weight average molecular weight and the glass transition temperature IW of the amorphous polymer. By using this technology, it is possible to maintain recording sensitivity equivalent to that of conventional wax-based heat-sensitive recording materials, while preventing heat diffusion in the binding layer E, which occurs with wax-based materials, and obtaining excellent resolution. The main characteristics are flexibility and abrasion resistance), and printing with excellent fixing properties is possible.

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 10,000 or less measured by gel permeation chromatography (GPC), and a glass transition temperature (Tg) measured by differential scanning calorimetry (DSC). ) is about 40”0 or more, more preferably the number average molecular weight is about 5.0
An amorphous polymer or oligomer having a Tg in the range of about 50° C. to 80° C. is used as a binder in an amount of at least 50% by weight of the non-volatile components of the thermal ink material.

That is, if the nonvolatile polymer content is less than 50% by weight based on the nonvolatile components of the thermal ink material,
The transparency of thermal ink materials deteriorates significantly and good color reproducibility cannot be obtained, whereas
When the amount is 0% by weight or more, especially 70% by weight or more, very good transparency is exhibited, and excellent color reproduction can be obtained by superimposing the ink materials on (a). this is,
Increase/decrease f in crystalline component that accounts for I in all thermal ink material components
This is thought to be due to the fact that as the amount of amorphous components in the thermal ink material increases, the degree of light scattering due to crystals increases and the transparency deteriorates. Also, the Tg of the amorphous polymer is 50'
If the temperature is less than O, especially less than 40℃, blocking of the thermal ink material is likely to occur (lack of stability during storage or use.If Tg exceeds 80℃, thermal stability is good. However, since the sensitivity decreases, it is impractical and cannot be used except for special purposes.Experiments have shown that even if the Tg is within the above range, if the molecular weight of the amorphous polymer is high, the sensitivity decreases. This was confirmed based on the entanglement of molecular chains (η), etc. (presumed to be due to the cohesive force between molecules). Good transfer and fixing properties were obtained in both cases.The setting of the weight semiuniform molecular weight varies depending on the application 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 is also about 40,000 or less, more preferably about 10,000 or less, and the molecular weight distribution is narrowed.
Therefore, it is desirable to improve the softening properties of amorphous polymers. On the other hand, if you want to obtain uneven 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. For this purpose, it is not necessarily necessary to reduce the weight average molecular weight (it may be set to about 40,000 or more. Of course, even in this case, a binary transfer image can 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 distribution shape having a plurality of molecular weight peaks, or a crosslinked or branched polymer component may be used in combination.

However, when the weighted 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 amorphous polymer naturally affect the properties of the thermal ink material, but the effect is not as great as the molecular weight and Tg mentioned above. , basically the thermal ink of the present invention, nk, t,
It is possible to apply it.

Examples include styrene, vinyltoluene, α-methylstyrene, 2-methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, aminostyrene, and other homopolymers and copolymers of styrene and its derivatives and substituted products. , methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, and acrylic esters such as methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and acrylic acid, butadiene, isoprene dienes such as acrylonitrile, vinyl ethers, maleic acid and maleic esters, maleic anhydride,
Vinyl monomers such as cinnamic acid, vinyl chloride, and vinyl acetate may be used alone or in copolymers with other monomers.

In addition, condensation resins include phthalic acid, phthalic anhydride, in-7thalic acid, terephthalic acid, hexahydrophthalic anhydride,
Saturated dibasic acids such as malonic acid, cono-phosphoric acid, daltaric acid, adipic acid, and sebacic acid; unsaturated dibasic acids such as maleic anhydride, fumaric acid, itaconic acid, and tetrahydrophthalic anhydride; and ethylene glycol; 1. 2-propylene glycol, 1,6-hexanediol, bisphenol A
Polyester resins obtained by polycondensation with diols such as 1-bisphenol A propylene oxide adduct and bisphenol A ethylene oxide adduct may also be used. In this case, a trifunctional compound such as trimellitic acid, glycerin, or trimethylolpropane may be further used to form a branched or crosslinked polyester. 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 amorphous polymers or oligomers are used in the form of a copolymer, the copolymer may be a random copolymer, an alternating copolymer, a draft copolymer, or a block copolymer depending on the required use. , interpenetrating copolymers, and the like 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, and emulsion mixing, mixing may be performed by co-polymerization, multistage polymerization, etc. during polymerization of polymer and oligomer components.

Although the heat-sensitive ink material of the present invention can sufficiently achieve its purpose by using only these amorphous polymers and oligomers as its binder, it is possible to achieve the purpose by using only these amorphous polymers and oligomers as binders. Various waxes, oils, and liquid plasticizers 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 anti-+H agent, conductive agent, antioxidant, thermal conductivity improver, magnetic material, ferroelectric material, preservative, fragrance, anti-blocking agent,
A reinforcing filler, a mold release agent, a foaming agent, a sublimable substance, an infrared absorber, and the like may be added inside or outside the heat-sensitive ink structure 1.

However, as mentioned above, in the total heat-sensitive ink material non-volatile components,
It is necessary that the amorphous polymer component accounts for 50% or more in terms of weight concentration, particularly preferably 70% or more.

Colorants include carbon black, oil black,
Black dye and pigment such as graphite: C, 1, Pigma-nt
Acetoacetate arylamide monoazo yellow pigments (fast yellow series) such as Yellow 1, 3, 74, 97, and 98: C, 1, Pigment Yellow
Acetoacetate arylamide disazo yellow pigment such as w12, w13, w14; C,1,5olvent Yel
low19, 77, 79, C, 1, Dispers
e Yellow dye such as Yellow 164; C, 1, Pi
gment Red 48, 49:1, 53:1,
Red or red pigments such as 57:1, 81, 122, 5; C,1,5olvent Red52, 58
, 8th grade red dye: C, 1, Pigment Bl
Colorful dyes and pigments such as copper phthalocyanine such as 15:3 copper phthalocyanine and derivatives and modified products thereof, conventional printing inks such as colored or colorless sublimable dyes, and dyes and pigments well known for other coloring purposes can be used.

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 it 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 polymeric material, or a polymeric dye or polymer grafting agent may be used. Pigments may also be used.

The thermal transfer recording material of the present invention is formed by placing a thermal ink material, which is a mixture of an amorphous polymer or oligomer, a colorant, and, if necessary, the various additives described above, on a support. The heat-sensitive ink materials are mixed into a bath solution and/or a dispersed emulsion in a solvent and/or dispersion medium that can dissolve and/or stably disperse the binder material, and are prepared using a ball mill, sand mill, attritor, three-roll mill, etc. It can be prepared using a mixing/dispersing machine.

Also, without using any solvent etc. (heated 3-roll,
Bath melt mixing may be performed using a heating and pressure kneader, a Bamba IJ mixer, or the like.

Furthermore, a thermal ink material may be prepared by polymerizing an amorphous polymer or oligomer as the main binding material in the presence of a colorant, additive, etc.

The heat-sensitive ink material prepared in this way is coated with a bath liquid and/or coated on the support using a gravure coater, a wire bar, etc.
Alternatively, it can be applied and printed using a melt coating method.

' Alternatively, the thermal ink material may be powdered by a spray drying method, a pulverization method, etc., and then powder coated onto a support by an electrostatic coating method or the like. In this case, after powder coating,
Furthermore, heat-sensitive powder ink may be fixed on a support by heating, pressurizing, solvent treatment, etc. as necessary.Furthermore, when preparing such a heat-sensitive powder ink, A powder ink may be prepared by polymerizing an amorphous polymer, which is the main binding material, in the presence of a colorant, an additive, etc., by a direct polymerization method such as a suspension polymerization method or a dispersion polymerization method.

Convenient supports include polyesters such as polyethylene terephthalate, polyimides and imide copolymers, fluorine polymers, plastic films such as polypropylene, thin sheets and films such as capacitor paper (
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. When recording using a thermal head, etc., the side of the support in contact with the thermal head must be coated with silicone-based, fluorine-based compounds, resin layers, or cross-linked polymers to improve heat resistance, runnability, etc. One layer, 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 uneven portions, 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 thermal 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, support thicknesses of about 1 μm to about 200 μm are easily used. In order to improve the resolution, the thickness is preferably about 1 μm to about 10 μm. The heat-sensitive ink layer is convenient to use if it is set in a range of about 0.5 μm to about 50 μm depending on the intended use, usually about 1 μm to about 20 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 the thermal ink layer itself may be a multilayer coating layer of multiple types of thermal ink materials with different physical properties. The initial injection of multiple types of ink may be divided into 1-L.

The heat-sensitive recording material thus formed has a thermal head,
It is heated in response to the applied signal by means such as a laser, a flash source, or by directly transmitting an electric signal, and is made to fly in contact with or without contact with a broken recording material such as paper or film. This causes the thermal ink material to be transferred and recorded. In order to improve recording properties, it is also possible to use not only mechanical forces such as pressurization and foaming, but also electric fields, magnetic fields, ultrasonic waves, solvents, etc.

〔Example〕

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 the following examples, parts represent parts by weight unless otherwise specified.

Example 1 A heat-sensitive recording material was prepared by applying a heat-sensitive ink material having the following composition onto a polyester film having a thickness of 6 μm so that the thickness of the heat-sensitive ink layer after cooling or drying was 3 μm.

Thermal ink material After melt-mixing the above composition at 100°C, cross-mixing was carried out in a three-roll mill to obtain a thermal ink material.
"C" was applied onto a heated polyester film on a hot plate using a wire bar to obtain a heat-sensitive recording material.

The above composition was mixed in a ball mill at room temperature for 40 hours to obtain a heat-sensitive ink material, which was coated on a polyester film with a wire bar and dried to obtain a heat-sensitive recording material.

Note that the following thermal ink material C-Hζ was also prepared in the same manner as above to create a thermal recording material.

The table below shows the results of evaluation of typical recording properties of the thermal recording materials having the thermal ink materials of A-H using a Fuji Xerox FX P-6 thermal transfer printer.

The method for evaluating the recording characteristics shown in the above table ζ is as follows.

Recording sensitivity: Thermal head heating element size (1/8 m
m = 125 μm) The energy applied to the thermal head (E) required to record a transfer dot corresponding to f (E < 0.9 mJ/dot Δ; 0.9 mJ/dot <;, E < 1.2
mT/dot x; 1.2 mJ/dot E Resolution: How kanji are distorted (especially those with a large number of strokes) Transparency: The degree of color turbidity and fixation when OHP sheet 2 transfer recording is projected onto a screen : Occurrence of peeling of ink and staining around the transferred image when rubbed with fingers or eraser f As shown above, the conventional type (A
) has slightly better recording sensitivity, but kanji with a large number of strokes may be blurred and difficult to read.
Furthermore, when the transferred image was rubbed with a finger, stains were generated around the transferred image.

On the other hand, the thermal recording material (B) according to the present invention has almost the same recording sensitivity as the wax type (A), and furthermore, clear prints without crushing can be obtained, and even if the transferred image is rubbed, the ink does not peel off or stain. Also, in terms of transparency, the wax type (A) had a clear dark blue color (
In contrast, a bright blue projected image with no turbidity was obtained.

Further, it was confirmed that the relationship between C and E shows the contribution of number average molecular weight control to the improvement of recording sensitivity, and the relationship between DH and D shows the contribution of glass transition temperature control.

Example 2 A thermal ink material having the following composition was prepared in the same manner as B in Example 1, and the thermal ink layer thickness after drying was 2.5 μm.
A heat-sensitive recording material was prepared by applying the following coating.

The obtained heat-sensitive recording material was evaluated in the same manner as in Example 1 except for its transparency at °C, and it was found that the same size of the material could be heated with approximately 1.4 times the applied energy (E: 0.85 mJ/'eito) as that of the wax mold. It was possible to record transfer dots, and strong prints with clear edges and no peeling of the ink even when rubbed with a finger were obtained.

Example 3 A heat-sensitive ink material having the following composition was prepared in the same manner as in Example 2, and a heat-sensitive recording material was prepared and evaluated.

The recording sensitivity was approximately 1.1 times as much applied energy as that of the wax type (E = 0.7 mJ/dot), and printing was obtained that was equivalent to Example 2 in terms of resolution and degree of fixation.

Example 4 A heat-sensitive ink material having the following composition was prepared in the same manner as B in Example 1, and a heat-sensitive recording material was prepared and evaluated.

The recording sensitivity was determined by the applied energy (approximately 80% of B in Example 1).
E: 0.7 mJ/dot), and clear prints with sufficient fixing strength were obtained.

Example 5 A heat-sensitive ink material having the following composition was prepared in the same manner as B of Example 1 to produce a heat-sensitive recording material.

The recording sensitivity is approximately 1.3 times the applied energy of the wax type (
E'::0.8 mJ/dot), and prints with sufficient resolution and fixation IW were obtained.

〔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 disassembly property on a transfer material.

The amorphous polymer used in the present invention is different from the crystalline wax used as a binder in conventional heat-sensitive recording materials. The binding layer of the heat-sensitive recording material of the present invention exhibits extremely good transparency because the light scattering that occurs when using the heat-sensitive recording material can be completely or substantially controlled to such an extent that this problem does not occur.

In particular, ink materials of magenta, yellow, and cyan colors are overlaid for the purpose of obtaining clear color images, especially Victorian full-color reproduction images, by overlapping and recording ink materials several times. Alternatively, when obtaining a tertiary color, if a small amount of the thermal ink material of the present invention is used as an upper layer ink material, its transparency is good, so that the reflected light from the lower ink layer is also absorbed by the pigment. The light is close to reflected light due to its own characteristics, and 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 is used. It is possible to obtain the same recording sensitivity as when using a binder, and by taking advantage of the characteristics of the polymer material, that is, the gentle bath melting characteristics, thermal diffusion of the applied energy in the ink material is eliminated, resulting in an excellent You can get better resolution. Furthermore, since it uses a polymer as a binder, it is flexible and durable against friction, etc., and can also improve the poor fixability, which was a drawback of conventional wax-based heat-sensitive recording materials. .

Claims (1)

[Scope of Claims] 1. A recording material in which a heat-melting heat-sensitive ink material layer is provided on a support, wherein the heat-sensitive ink material contains an amorphous polymer and a colorant as main components, and the amorphous polymer is heat-sensitive. A heat-sensitive recording material, characterized in that the ink material contains at least 50% by weight of non-volatile components. 2. The glass transition temperature of the amorphous polymer is 40°C or higher,
The heat-sensitive recording material according to claim 1, which has a number average molecular weight of 10,000 or less.