JP2006082382A - Thermal transfer receiving sheet and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal transfer receiving sheet suitable for a dye thermal transfer printer and provided with a low density layer containing hollow particles, and has a print density equivalent to that of synthetic paper or foam film without using expensive synthetic paper or foam film. In addition, the present invention provides a thermal transfer receiving sheet having a small print density, a change in print density, a white spot in print, and a small change in thickness before and after printing, and an extremely low unevenness after printing.
The present invention relates to a thermal transfer receiving sheet in which a low-density layer and an image-receiving layer are sequentially laminated on at least one surface of a sheet-like support mainly composed of cellulose pulp, and at least the low-density layer is bound. Resin and pre-expanded hollow particles, and the particle size distribution of the hollow particles is 10% or less of particles of 10 μm or more. TAPPI-No. The thermal transfer receiving sheet is characterized in that the Oken smoothness based on 5 is 5000 seconds or more.
[Selection figure] None

Description

  The present invention is a thermal transfer receiving sheet used in a printer which forms an image by superimposing a thermal transfer dye sheet (hereinafter simply referred to as “ink ribbon”) and thermally transferring the colorant of the thermal transfer sheet using a thermal head as a device. It is about. More specifically, the present invention is suitable for thermal printers, particularly dye thermal transfer printers, is low cost, has a high density similar to a silver salt photograph, and can obtain an image with excellent uniformity (hereinafter simply referred to as a thermal transfer receiving sheet). This may be referred to as “receiving sheet”).

  In recent years, thermal printers have attracted attention, and dye thermal transfer printers that can print clear full-color images have attracted attention. The dye thermal transfer printer superimposes a dye layer containing a dye on an ink ribbon and an image receiving layer containing a dye-stainable resin on a receiving sheet (hereinafter sometimes simply referred to as “receiving layer”). The image is formed by transferring the dye at a required portion of the dye layer to the receiving layer by a predetermined concentration by heat supplied from the above. The ink ribbon is composed of dye layers of three colors of yellow, magenta and cyan, or four colors obtained by adding black to this. A full-color image is obtained by repeatedly transferring each color dye on the ink ribbon to the receiving sheet in order. In such a dye thermal transfer type printer, the receiving sheet is generally supplied in a sheet state.

In recent years, with the development of thermal printers and the development of digital image processing technology using computers, the images obtained have improved dramatically, and the thermal transfer system has expanded its market. With the improvement of thermal head technology and the development of temperature control technology, there is an increasing demand for high speed and high sensitivity printing systems. Therefore, how to efficiently use the amount of heat generated by a heating device such as a thermal head for image formation is an important technical issue. In addition, in order to reduce the price of the printer and simplify the structure, there is a technical challenge to reduce the pressure in printing with a thermal head and to further extend the life of the head.
Currently, printers that can print one A6 size sheet in 30 seconds or less are on the market, and it is expected that the demand for higher printing speed will increase in the future.

  In order to efficiently form a high-quality and high-density image on a receiving sheet, a receiving layer mainly composed of a dye-dyeable resin is provided on the support, but a film is used as the supporting substrate of the receiving sheet. If used, the heat from the thermal head escapes to the substrate due to excellent smoothness, resulting in insufficient sensitivity, and the film does not have cushioning properties. May occur. In order to solve this problem, as a support, a support in which a foam film is bonded to a core material layer such as paper (see, for example, Patent Document 1), a thermoplastic resin such as a polyolefin resin as a main component, a void (void) ) A support in which a biaxially stretched film (so-called synthetic paper) including a structure is bonded to a core material layer such as paper has been proposed (see, for example, Patent Document 2). Receptor sheets using these supports are excellent in heat insulation and smoothness, but have drawbacks such as no paper texture and high cost.

  When paper is used as the support substrate of the receiving sheet, the sensitivity is insufficient as in the case of the film, and the paper has a slightly better cushioning property than the film, but the ink ribbon and the receiving layer are caused by uneven density of paper fibers. There is a drawback that unevenness of printing occurs due to the unevenness of adhesion. In order to solve this problem, by providing an intermediate layer containing hollow particles between a sheet-like support such as paper and the receiving layer, the intermediate layer has a heat insulation effect, and is effective in improving the transfer density. (For example, refer to Patent Documents 3 and 4). The sensitivity of this receptor sheet is improved by the heat storage effect due to the heat insulation of the air in the hollow particles contained in the intermediate layer and the effect of improving the adhesion between the ink ribbon and the receptor sheet due to the cushioning property, but the hollow particles are intermediate. Since it is exposed on the surface of the layer, there are irregularities due to the hollow particles, and the surface smoothness is poor. Therefore, the uneven adhesion between the ink ribbon and the receiving sheet has been dealt with to some extent by the pressing force between the thermal head and the platen roll during printing and the deformation due to the cushioning property of the intermediate layer. However, there is a drawback that sufficient image quality cannot be obtained by printing with the printer of the above.

  In order to solve this problem, by setting the mass average particle diameter of the hollow particles contained in the intermediate layer to 2 to 7 μm, and setting 50% by mass or more thereof in the particle diameter range of 2 to 6 μm, the surface unevenness is improved, There is a description that an intermediate layer excellent in cushioning property, heat insulating property, and smoothness can be formed to obtain a receiving sheet having excellent image quality, sensitivity, glossiness, and texture similar to paper (for example, patent document) 5). However, even if 50% by mass or more of the hollow particles are in the range of 2 to 6 μm in size, if coarse particles are present, large irregularities are generated partially by using the single particles or the coarse particles as a core, and printing. In a recorded product, uneven density and white spots occur, resulting in a defect that the uniformity of the image is insufficient.

  In order to obtain good cushioning properties, it is an effective means to increase the volume hollow ratio of the hollow particles, but there is a drawback that the sheet surface is easily damaged when the volume hollow ratio is increased. That is, there is a problem that when a printed product is handled, scratches occur on the surface of the sheet such as a nail or a pen tip, and the commercial value is remarkably lowered. Furthermore, by adjusting the viscosity of the paint containing the hollow particles, the dispersibility of the foam particles for forming the intermediate layer is improved, the workability is improved, and the heat density and smoothness of the intermediate layer are excellent. There is a proposal to obtain a high receiving sheet (Patent Document 6). However, only by means for improving the dispersibility of foamed particles and improving workability by adjusting the viscosity of the paint, the foamed particles in the paint cannot be agglomerated, and the agglomerates remain in the intermediate layer. As a result, the heat insulation by the air in the aggregate is added to the heat insulation derived from the expanded particles, and the print density is increased, but the aggregate is not uniformly crushed, the print density is uneven, the print defect, There is a problem that dents on the surface after printing occur and the commercial value is remarkably lowered.

  In addition, for thermal transfer image receivers provided with an intermediate layer containing expanded particles, a hollow particle intermediate layer having the same sensitivity and uniformity as synthetic paper and expanded film is provided to improve defects such as density unevenness and white spots. A proposal has been made to reduce the hollow particle diameter to 35 μm or less (see, for example, Patent Document 7). However, the hollow particles constituting the low density layer contain aggregates in the coating, and if the hollow particles or the aggregates of the hollow particles are 35 μm or less, problems such as uneven density and white spots are improved. However, the voids in the agglomerates remain even after the low density layer is formed. In this case, since the voids themselves also exert a heat insulating effect, the heat insulating property of the low density layer is higher than that expected for the volumetric hollowness of the original hollow particles, and the print density and hue are not stable. , The commercial value is lost.

  That is, in the thermal transfer printing method and / or the sublimation thermal transfer method, the ribbon dye is fixed to the receiving layer by sublimation / diffusion in the order of yellow, magenta, and cyan by the heat of the printer, so that such aggregates remain in the low density layer. In this case, the first color yellow has a higher print density due to the effect of heat insulation utilizing the voids in the aggregate and the volumetric hollowness of the hollow particles. However, the voids in the aggregates of the hollow particles in the low-density layer are crushed by the heat and printing pressure during the first color printing, and only the heat insulating effect due to the volumetric hollow ratio of the hollow particles can be expected. The print density for the second and subsequent colors decreases. Such a phenomenon becomes more prominent, for example, when printing under high humidity conditions. The reason is that the binder resin used for the low density layer is softened by the effect of moisture plasticization by moisture absorption. In addition, the crushing of the hollow particles in the low density layer due to the aggregates not only destabilizes the printing density and hue, but also prints compared to the thermal transfer transfer receiving sheet using synthetic paper or foam film. It promotes the deterioration of the feeling of unevenness later, and significantly reduces the commercial value.

JP 61-197282 A (first page) JP-A-62-198497 (first page) Japanese Patent Laid-Open No. 1-27996 (first page) JP 63-87286 A (first page) JP-A-9-99651 (2nd page) JP 2000-158831 A (page 2-3) Japanese Patent No. 2001-39043 (2nd page)

  The present invention has been made in view of the above circumstances, and solves the above-described problems of conventional dye thermal transfer receiving sheets, and is particularly suitable for a dye thermal transfer printer, and is provided with a low density layer containing hollow particles. In the same way as expensive synthetic paper and foamed film, the change in printing density due to the environment is extremely small, the unevenness after printing is good, and low-cost, high-sensitivity, high-quality thermal transfer receiving paper is provided. It is something to try.

The present invention includes the following aspects. That is,
[1] In a thermal transfer receiving sheet in which a low density layer and an image receiving layer are sequentially laminated on at least one side of a sheet-like support mainly composed of cellulose pulp, the low density layer includes at least a binder resin and a foamed hollow Particles having a particle size distribution of 10 μm or more and 10% or less as the particle size distribution of the hollow particles. TAPPI-No. 5. A thermal transfer receiving sheet, wherein the Oken smoothness based on 5 is 5000 seconds or more.
[2] The thermal transfer receiving sheet according to [1], wherein the low density layer is formed from a low density layer paint having a density ratio of low density layer paint density / low density layer paint calculated density = 0.7 to 1.2. .
[3] The thermal transfer receiving sheet according to [1] or [2], wherein the hollow particles have an average particle diameter of 0.5 to 10 μm.
[4] The thermal transfer acceptance according to any one of [1] to [3], wherein the particle size distribution of the hollow particles is obtained by dispersing the hollow particles using a sand mill, cowless and / or ball mill. Sheet.
[5] The thermal transfer receiving sheet according to any one of [1] to [4], wherein the binder resin contained in the low density layer is a water-soluble and / or water-dispersible resin.
[6] The thermal transfer receiving sheet according to any one of [1] to [5], wherein the hollow particles contained in the low-density layer have a volume hollowness of 75 to 95%.
[7] The thermal transfer receiving sheet according to any one of [1] to [6], wherein the low density layer has a thickness of 10 to 110 μm.
[8] The thermal transfer receiving sheet according to any one of [1] to [7], wherein the mass ratio of the hollow particles to the total solid mass of the low-density layer coating is 30 to 75%.
[9] The thermal transfer receiving sheet according to any one of [1] to [8], which has a barrier layer laminated between the low density layer and the image receiving layer.
[10] The thermal transfer receiving according to any one of [1] to [9], having a back layer containing at least a binder resin and an inorganic and / or organic pigment on the side of the substrate on which the image receiving layer is not provided. Sheet.

  The hollow particles contained in the low density layer are (a) foamed hollow particles produced by heating and foaming a thermoplastic polymer material containing a thermally expandable substance, and (b) forming a shell from the polymer-forming material. A microcapsule-like hollow particle obtained by volatilizing and escaping the pore-forming material from a microcapsule produced by a microcapsule polymerization method using a volatile liquid as a pore-forming material. It is preferable to consist of at least one selected from

  The receiving sheet of the present invention is suitable for a high-sensitivity and high-quality receiving sheet because the change in printing density due to the environment and unevenness after printing are improved.

  In the receiving sheet having a low density layer containing hollow particles, if the aggregate of hollow particles is present in the low density layer, the smoothness of the receiving layer is lowered and a uniform image is difficult to obtain, but Since the air gap has a heat insulating property, a highly sensitive thermal transfer receiving paper can be obtained. However, when printing with the thermal transfer method or sublimation thermal transfer method, such as thermal transfer method or sublimation thermal transfer method, which prints continuously with yellow, magenta, cyan, the aggregates in the low density layer are Due to the pressure of the platen roll, the first color is crushed during yellow printing, and after the second color, the heat insulation effect due to the voids inside the aggregate cannot be effectively used, and the dye transfer from the second color onward is not performed sufficiently. Further, since the aggregates are crushed, a uniform image cannot be obtained, the heights of the high density printed portion and the low density portion after printing are generated, and the commercial value is remarkably lowered. In addition, since the binder resin used for the low density layer is softened under high humidity conditions, the aggregates are crushed significantly, and extremely deteriorated such as a decrease in printing density and a feeling of unevenness after printing.

  According to the present invention, the Oken-type smoothness of the receiving layer of the receiving sheet obtained by setting the particle size distribution of the hollow particles forming the low density layer to “10% or less of particles of 10 μm or more” is 5000 seconds or more. Therefore, the image uniformity is excellent and the aggregate of hollow particles is extremely small, so there is almost no crushing during the yellow printing of the first color due to the heat of the thermal head during printing or the pressure of the thermal head and the platen roll. The dye transfer for the second and subsequent colors is sufficiently performed, and a receiving sheet having an excellent performance that printing density and unevenness after printing are hardly generated even in printing under high humidity conditions can be easily obtained. As the particle size distribution of the hollow particles of the low density layer, it is important that the particle size of 10 μm or more is 10% or less, preferably 5% or less. In order to obtain a desired particle size distribution, a sand mill (also referred to as “sand grinder”), a cowless, a ball mill, or the like can be used for dispersing the hollow particles. In general, a sand mill used for dispersion of inorganic pigments and organic pigments is preferably used, and it has been found that the aggregates of the hollow particles are efficiently and uniformly dispersed under the condition that the hollow particles are not crushed.

  For example, in the case of a sand mill, preferable grinding conditions include clearance: 300 μm to 1 mm, rotation speed: 500 to 3000 rpm, bead material: glass, size: φ1 to 3 mm, filling amount: 40 to 70%, flow rate: 0.5 to Distributed processing is performed at about 51 / min. If the clearance is less than 300 μm, clogging of the dispersion occurs. If the clearance exceeds 1 mm, the beads may break and be mixed into the dispersion. If the rotational speed is less than 500 rpm, the dispersibility may be poor, and if it exceeds 3000 rpm, the viscosity of the dispersion may increase rapidly and the fluidity of the dispersion may be impaired. If the bead filling amount is less than 40%, the shaft of the sand mill may be shaken and good dispersion may not be achieved. If the filling amount exceeds 70%, the hollow particles may be crushed.

  At the time of dispersion, known additives such as sodium alkylsulfosuccinate, sodium dialkylsulfosuccinate, sodium acrylate, sodium polyphosphate, sodium hexametaphosphate, etc., and hydrophilic such as polyvinyl alcohol resin, cellulose resin and derivatives thereof, casein, starch derivatives, etc. It is also possible to contain and disperse a functional polymer resin, (meth) acrylic acid ester resin, styrene-butadiene copolymer resin, urethane resin, polyester resin, ethylene-vinyl acetate copolymer resin, or the like. The low-density layer paint prepared by using the hollow particle dispersion obtained in this manner has good workability regardless of the paint viscosity.

Regarding the dispersion state of the paint forming the low density layer, the density ratio of the low density layer paint (low density layer paint density / low density layer paint calculated density) is 0.7 to 1.2. Preferably, it is formed, more preferably the density ratio is 0.8 to 1.1.
When the density ratio of the low-density layer coating material is less than 0.7, a large amount of foam is contained in the coating material. For example, a small amount of fine voids are contained in a low-density layer obtained by applying a paint on a sheet-like support and drying it with hot air or the like. The printing density of the receiving sheet formed in this way combines the heat insulation effect of the hollow particles and the heat insulation effect due to the fine voids in the coating layer, so the heat insulation is extremely high, but the heat during printing is high. The coating layer is greatly crushed, which significantly impairs the product value, and if printing is performed under high humidity conditions, the coating layer due to moisture is plasticized, so that the coating layer is significantly crushed during printing, and the printing density decreases. End up. On the other hand, when the density ratio of the low density layer coating is higher than 1.2, it means that the hollow particles are crushed at the time of dispersion, and the effects, cushioning properties, and heat insulating properties expected of the hollow particles cannot be obtained, and the print density And the image quality is significantly reduced.

  The layer structure of the receiving sheet of the present invention basically comprises a sheet-like support, a low density layer, and a receiving layer, and these layers will be described in detail below.

(Sheet support)
As the sheet-like support of the receiving sheet of the present invention (hereinafter sometimes simply referred to as “support”),
(1) High-quality paper, coated paper, art paper, cast coated paper, laminated paper provided with at least one thermoplastic resin layer such as polyolefin resin, synthetic resin impregnated paper, emulsion impregnated paper, synthetic rubber latex impregnated paper, synthetic Papers mainly composed of cellulose pulp, such as resin-added paper, foamed paper containing thermally expandable particles, and paperboard;
(2) Plastic films mainly composed of thermoplastic resins such as polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyamides, polyvinyl chloride and polystyrene;
Etc. are preferred. Among the above-mentioned various sheet-like supports, papers mainly composed of cellulose pulp have low heat shrinkability, good heat insulation, good texture as a receiving paper, and low price. Preferably used.

  The sheet-like support of the present invention may have a structure in which a first base material layer on which a receiving layer is formed, an adhesive layer, a release agent layer, and a second base material layer are sequentially laminated. Of course, supports having a type of structure can also be used.

  The sheet-like support used in the present invention preferably has a thickness of 100 to 300 μm. Incidentally, if the thickness is less than 100 μm, the mechanical strength thereof is insufficient, the rigidity of the receiving sheet obtained therefrom is small and the repulsive force against deformation is insufficient, and the receiving sheet curl generated at the time of printing is sufficient. May not be prevented. On the other hand, if the thickness exceeds 300 μm, the thickness of the receiving sheet to be obtained becomes excessive, which may lead to a decrease in the number of receiving sheets stored in the printer. In some cases, this causes an increase and makes it difficult to make the printer compact.

(Low density layer)
In the present invention, a low density layer is formed on at least one side of a paper base material mainly composed of cellulose pulp as a support. The low-density layer consists of binder resin and hollow particles as the main components, and since this low-density layer has a porous structure and high cushioning properties, it is highly sensitive even when paper is used as the substrate. A sheet is obtained.

The dispersion distribution of the hollow particles in the low-density layer gives the receiving sheet an appropriate degree of deformation freedom, and improves the followability and adhesion of the receiving sheet to the printer head shape and the ink ribbon shape. The thermal efficiency of the printer head can be improved, and the print density of the printed image can be increased to improve the image quality. Also, in the high energy application operation of the high-speed printer, it is possible to prevent printing defects due to ribbon wrinkles generated on the ink ribbon at the same time.
By dispersing and distributing the hollow particles in the low density layer, the heat insulating property of the receiving sheet is improved, thereby improving the thermal efficiency of the thermal head with respect to the receiving layer, so that the print density is increased and the image quality is also improved.
Even if the receiving sheet is subjected to high pressure by the thermal head and the conveying roll of the printer, this stress can be absorbed inside the receiving sheet. Resistance to formation is improved.

The hollow particles used in the low density layer of the present invention are composed of a shell formed of a polymer material and one or more hollow parts surrounded by the shell, and the maximum particle size of the hollow particles is It is preferably 25 μm or less, more preferably 20 μm or less. The average particle size of the hollow particles is preferably 0.5 to 10 μm, more preferably 0.8 to 8 μm.
Although there is no special restriction | limiting about the manufacturing method of a hollow particle, It can select from what was manufactured as follows.
(A) Expanded hollow particles produced by heating and foaming a thermoplastic polymer material containing a thermally expandable substance.
(B) The pore-forming material is volatilized and escaped from the microcapsules produced by the microcapsule polymerization method using the polymer-forming material as the shell-forming material and the volatile liquid as the pore-forming material. Microcapsule-like hollow particles obtained by the above process.

  Forming foamed hollow particles by using, as hollow particles, particles made of a thermoplastic material containing a thermally expansible material in an unfoamed state and foaming by heat in a heating process or a drying process at the time of manufacturing a receiving sheet Is also possible. However, as described above, if a thermoplastic material containing a thermally expandable material is foamed by heating during the manufacturing process of the receiving sheet, it is difficult to foam to a uniform particle size, and the particle size after thermal expansion is strictly limited. Since it cannot be managed, the surface of the low-density layer becomes a surface with large unevenness, and the smoothness may be inferior. Since the receiving sheet having the low density layer as described above has large irregularities on the surface of the receiving layer, the uniformity of the heat-transferred image may be lowered and the image quality may be inferior. Therefore, in the present invention, hollow foamed particles produced by thermally expanding particles made of a thermoplastic material containing a thermally expandable material in advance are preferably used.

  The foamed hollow particles produced by thermally expanding a thermoplastic material-containing thermoplastic material are, for example, a volatile material such as n-butane, i-butane, pentane, and / or neopentane as a thermally expandable core material. Encapsulating low-boiling hydrocarbons in a thermoplastic material, and using a homopolymer or copolymer of vinylidene chloride, acrylonitrile, styrene, (meth) acrylic acid ester, etc. as the capsule shell (wall) material By subjecting the obtained particles to a treatment such as heating in advance, the particles are thermally expanded to a predetermined particle diameter to form hollow particles in an already foamed state.

  In addition, hollow particles in the already foamed state produced by thermally expanding the thermoplastic material-containing thermoplastic material as described above generally have a small specific gravity, so that the handling workability and dispersibility are further improved. Foamed composite hollow particles in which an inorganic powder such as calcium carbonate, talc, titanium dioxide or the like is attached to the surface of the foamed hollow particles by heat fusion and the surface is coated with the inorganic powder can also be used in the present invention.

The maximum particle diameter of the secondary particles of the foamed hollow particles used in the present invention is preferably 25 μm or less, more preferably 20 μm or less. If the maximum particle size including the secondary particles of the foamed hollow particles exceeds 25 μm, the thermal transfer image may be uneven in density and white spots due to coarse particles, resulting in poor image quality.
The average particle diameter is preferably 0.5 to 10 μm, more preferably 0.8 to 8 μm. Foamed hollow particles produced by thermally expanding a thermoplastic material-containing thermoplastic material have a higher cushioning property and higher flexibility than the above-mentioned microcapsule-like hollow particles, and therefore have an average particle diameter of 10 μm or less. Can be used in the present invention.
When the average particle diameter of the foamed hollow particles is less than 0.5 μm, the volumetric hollow ratio of the obtained hollow particles is lowered, the heat insulating property and the cushioning property are generally lowered, and the sensitivity and the image quality improvement effect are sufficiently obtained. It may not be possible. On the other hand, when the average particle diameter exceeds 10 μm, the smoothness of the resulting low density layer surface is lowered, the unevenness of the surface of the receiving sheet becomes excessive, the uniformity of the thermal transfer image becomes insufficient, and the image quality is inferior, which is not preferable. .

  The microcapsule-like hollow particles used in the present invention contain a polymer material, for example, a styrene-acrylic copolymer or a hard resin such as a melamine resin as a shell, and a volatile liquid such as water in the core. The microcapsule is dried, and water is volatilized and escaped to form a hollow core part. This microcapsule is obtained from a polymer-forming material (shell-forming material) and a volatile liquid (pore-forming material) by a microcapsule-forming polymerization method.

The maximum particle size of the microcapsule-like hollow particles used in the present invention is preferably 25 μm or less, more preferably 20 μm or less. When the maximum particle diameter of the microcapsule-like hollow particles exceeds 25 μm, the thermal transfer image may cause unevenness in density of prints and white spots due to coarse particles, resulting in poor image quality. The average particle size of the microcapsule-like hollow particles is preferably 0.7 to 8 μm, more preferably 0.8 to 7 μm. When the average particle diameter of the microcapsule-like hollow particles is less than 0.7 μm, the volumetric hollow ratio of the hollow particles is lowered, and the heat insulating property and cushioning property are generally lowered, and the effect of improving sensitivity and image quality is sufficiently obtained. It may not be possible. On the other hand, when the average particle diameter exceeds 8 μm, the smoothness of the resulting low density layer surface is lowered, the unevenness of the receiving sheet surface becomes excessive, the uniformity of the thermal transfer image becomes insufficient, and the image quality is inferior, which is not preferable. .
The average particle size of the hollow particles can be measured using a known particle size measuring device, and can be measured using, for example, a laser diffraction type particle size distribution analyzer (trade name: SALD2000, manufactured by Shimadzu Corporation). it can.

  The volume hollowness of the hollow particles used in the present invention is preferably 75 to 95%. If the volume hollowness is less than 75%, the image quality may be deteriorated, which is not preferable. On the other hand, when the volume hollowness exceeds 95%, the strength of the coating layer is inferior, the hollow particles are destroyed during coating drying, and the surface smoothness may be lowered, which is not preferable.

  The volume hollowness of the hollow particles indicates the ratio of the volume of the hollow portion to the volume of the particles. Specifically, the specific gravity of the hollow particle dispersion composed of the hollow particles and the poor solvent, the hollow particles in the dispersion The specific gravity of the polymer resin forming the shell (partition) of the hollow particles and the specific gravity of the poor solvent can be obtained. The poor solvent is a solvent that does not dissolve and / or swell the polymer resin that forms the partition walls of the hollow particles, and examples thereof include water and isopropyl alcohol. The volume hollowness of the hollow particles can also be determined from a cross-sectional photograph of the intermediate layer using, for example, a small-angle X-ray scattering measurement device (trade name: RU-200, manufactured by Rigaku Corporation).

  The blending amount of the hollow particles in the low density layer is preferably in the range of 30 to 75%, more preferably in the range of 35 to 70% in terms of the ratio of the hollow particle mass to the total solid mass of the low density layer. . When the mass ratio of the hollow particles to the total mass of the low density layer is less than 30%, the heat insulation and cushioning properties of the low density layer are insufficient, and the sensitivity and image quality improvement effect may not be sufficiently obtained. On the other hand, if the mass ratio of the hollow particles exceeds 75%, the coating property of the resulting low density layer coating material is deteriorated, the coating film strength is lowered, and the desired effect may not be obtained.

The thickness of the low density layer for the low density layer to exhibit desired performance such as heat insulation and cushioning is preferably 10 to 110 μm, more preferably 20 to 90 μm, and particularly preferably 25 to 85 μm. If the film thickness of the low density layer is less than 10 μm, the heat insulation and cushioning properties may be insufficient, and the sensitivity and image quality improvement effect may be insufficient. On the other hand, if the film thickness exceeds 110 μm, the effects of heat insulation and cushioning are saturated, which is economically disadvantageous. The density of the low density layer is determined approximately by the volumetric hollow ratio of the hollow particles, the blending amount of the hollow particles, and the like, and is preferably about 0.2 to 0.5 g / cm ³ .

The low density layer of the present invention contains hollow particles and a binder resin. The coating material for a low density layer of the present invention is preferably an aqueous coating material considering the solvent resistance of the hollow particles. Accordingly, the binder resin can be either water-based or organic solvent-based, but is preferably an aqueous resin.
The binder resin to be used is not particularly limited. For example, hydrophilic polymer resins such as polyvinyl alcohol resins, cellulose resins and derivatives thereof, casein, and starch derivatives are film forming properties, heat resistance, and flexibility. Are preferably used. Also, emulsions of various resins such as (meth) acrylic acid ester resins, styrene-butadiene copolymer resins, urethane resins, polyester resins, ethylene-vinyl acetate copolymer resins are used as low-viscosity and high-solids aqueous resins. . In view of coating strength, adhesion, and coatability of the low density layer, the binder resin used for the low density layer is preferably a combination of the hydrophilic polymer resin and an emulsion of various resins.

  For the low density layer, various additives such as antistatic agents, inorganic pigments, organic pigments, resin crosslinking agents, antifoaming agents, dispersing agents, colored dyes, mold release agents, lubricants, etc. You may use suitably selecting a seed | species or 2 or more types.

  The low density layer of the present invention comprises a coating solution for a low density layer containing at least hollow particles and a required component of a binder resin, a bar coater, a gravure coater, a comma coater, a blade coater, an air knife coater, a gate roll coater, a die coater. Using a known coater such as a coater, curtain coater, lip coater, and slide bead coater, it can be coated on a sheet-like support and dried to form.

  When the low density layer is applied, a molding surface may be used, or a metal plate, a metal drum, a plastic film, or the like having good dimensional stability and a highly smooth surface may be used. Moreover, in order to make it easy to peel the low-density layer from the molding surface, if necessary, a higher fatty acid release agent such as calcium stearate and zinc stearate, a polyethylene release agent such as polyethylene emulsion, and wax on the molding surface. In addition, a release agent such as silicone may be applied.

  In the present invention, calendering after coating of the low density layer, barrier layer, and receiving layer is effective in reducing unevenness on the surface of the receiving sheet and smoothing, especially calendering after coating of the low density layer. More preferably. There are no particular limitations on the calendar device used for the calendar process, the nip pressure, the number of nips, the surface temperature of the metal roll, and the like. Preferred pressure conditions for performing the calendar process are, for example, 0.5 to 150 mPa, preferably Is 1 to 100 mPa. As the temperature condition, the hollow particles are not destroyed from room temperature, and the Tg temperature of the binder resin for the low density layer is preferable, for example, 20 to 150 ° C, more preferably 30 to 120 ° C. As the calendar device, for example, a calendar device generally used in the paper industry such as a super calendar, a soft calendar, and a gloss calendar can be appropriately used.

(Barrier layer)
In the present invention, a barrier layer is preferably provided on the low-density layer, and a receiving layer is provided on the barrier layer. In this barrier layer, the solvent of the coating material for the receiving layer is generally an organic solvent such as toluene or methyl ethyl ketone, and is effective as a barrier for preventing the swelling and dissolution of the hollow particles of the low-density layer due to permeation of the organic solvent.
In addition, since the surface of the low density layer has irregularities due to the hollow particles of the low density layer, the receiving layer provided on the surface may have irregularities on the surface. In many cases, there are problems with image uniformity and resolution. In order to improve this problem, it is effective to improve the image quality to provide a barrier layer containing a flexible and elastic binder resin.

As the binder resin used for this barrier layer, a resin having excellent film forming ability, preventing penetration of an organic solvent, and having elasticity and flexibility is used. Specifically, it is formed from a hydrophilic polymer such as polyvinyl alcohol, starch, modified starch, casein, urethane resin, vinyl acetate resin, polyester resin, acrylic resin and copolymer thereof, or a resin using them in combination.
In addition, in the low density layer and the barrier layer, in order to improve concealability and whiteness, and improve the texture of the receiving sheet, as an inorganic pigment, calcium carbonate, titanium dioxide, zinc oxide, aluminum hydroxide, barium sulfate, White inorganic pigments such as silicon dioxide, aluminum oxide, talc, kaolin, diatomaceous earth, and satin white, and fluorescent dyes may be included.

The solid content coating amount of the barrier layer is preferably in the range of 0.5 to 10 g / m ² , more preferably in the range of 1 to 8 g / m ² . Incidentally, when the barrier layer solid content coating amount is less than 0.5 g / m ² , the barrier layer may not completely cover the surface of the low density layer, and the organic solvent permeation preventing effect may be insufficient. On the other hand, when the coating amount of the barrier layer solid content exceeds 10 g / m ² , not only is the coating effect saturated and uneconomical, but also the heat insulation effect of the low density layer due to the excessive thickness of the barrier layer, The cushioning property is not sufficiently exhibited, and the image density may be lowered, which is not preferable.

(Receptive layer)
In the receiving sheet of the present invention, a receiving layer is provided on the low density layer or the barrier layer. The receiving layer itself may be a known dye thermal transfer receiving layer. As the resin for forming the receiving layer, a resin having a high affinity for the dye transferred from the ink ribbon and having a good dyeing property is used. Examples of such dye-dyeable resins include polyester resins, polycarbonate resins, polyvinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, polyvinyl acetal resins, polyvinyl butyral resins, polystyrene resins, polyacrylate resins, and cellulose. Examples thereof include cellulose derivative resins such as acetate butyrate, thermoplastic resins such as polyamide resin, and active energy ray curable resins. These resins preferably have a functional group reactive with the crosslinking agent used (for example, a functional group such as a hydroxyl group, an amino group, a carboxyl group, or an epoxy group).

In order to prevent the receiving layer and the ink ribbon from being fused by heating with a thermal head during printing, one or more of a crosslinking agent, a release agent, a slipping agent, etc. are added to the receiving layer. It is preferable that it is blended as an agent.
Moreover, you may add 1 or more types, such as fluorescent dye, a plasticizer, antioxidant, a pigment, a filler, an ultraviolet absorber, antistatic agent, etc. in said receiving layer as needed. These additives may be mixed with the component for forming the receiving layer before coating, or may be coated on and / or under the receiving layer as a coating layer different from the receiving layer.

The solid coating amount of the receiving layer is in the range of 1 to 12 g / m ² , more preferably 3 to 10 g / m ² . Incidentally, if the solid coating amount of the receiving layer is less than 1 g / m ² , the receiving layer may not completely cover the surface of the low density layer or the barrier layer. There may be a fusing problem that the receiving layer and the ink ribbon adhere to each other. On the other hand, if the solid content coating amount exceeds 12 g / m ² , not only is the coating effect saturated and uneconomical, but also the coating strength of the receiving layer is insufficient or the coating thickness is excessive. Therefore, the heat insulating effect of the sheet-like support is not sufficiently exhibited, and the image density may be lowered.

  The receiving layer is a coating for the receiving layer comprising a solution obtained by adding a necessary additive such as a mold release agent to the dye-dyeable resin as described above, or a dispersion in which it is dissolved in an appropriate organic solvent. Using a known coater such as a bar coater, a gravure coater, a comma coater, a blade coater, an air knife coater, a gate roll coater, a die coater, a curtain coater, a lip coater, and a slide bead coater, It can be formed by coating on a support, drying and then heat-curing as necessary.

(Back layer)
In the receiving sheet of the present invention, a back layer may be provided on the back side of the sheet-like support (the side opposite to the side on which the receiving layer is provided). The back layer is mainly composed of a resin effective as an adhesive, and may contain a crosslinking agent, a conductive agent, an anti-fusing agent, an inorganic and / or organic pigment, and the like.

  For the back layer of the present invention, a back layer forming resin effective as a binder resin is used as necessary. This resin is effective in improving the adhesive strength between the back surface layer and the support, print transportability of the receiving sheet, preventing scratches on the receiving layer surface, and preventing dye transfer to the back layer contacting the receiving layer surface. As such a resin, an acrylic resin, an epoxy resin, a polyester resin, a phenol resin, an alkyd resin, a urethane resin, a melamine resin, a polyvinyl acetal resin, and a reaction cured product of these resins can be used.

  In the back layer of the present invention, a cross-linking agent such as a polyisocyanate compound or an epoxy compound may be appropriately added to the back layer coating material in order to improve the adhesion between the sheet-like support and the back layer. As a compounding ratio, generally about 1-30 mass% is preferable with respect to the back layer total solid content.

A conductive agent such as a conductive polymer or a conductive inorganic pigment may be added to the back layer of the present invention in order to improve print transportability and prevent static electricity. Examples of the conductive polymer include cationic, anionic and nonionic conductive polymer compounds. Examples of the cationic polymer compound include polyethyleneimine, acrylic polymers containing cationic monomers, and cation-modified acrylamide polymers. And cationic starch. Examples of the anionic polymer compound include polyacrylate, polystyrene sulfonate, and styrene maleic acid copolymer. Generally, the blending ratio of the conductive agent is preferably about 5 to 50% by mass with respect to the total solid content of the back surface layer.
Examples of conductive inorganic pigments include compound semiconductor pigments such as oxides and / or sulfides, and inorganic pigments coated with the compound semiconductor pigments. Examples of the compound semiconductor include copper (I) oxide, zinc oxide, zinc sulfide, and silicon carbide. Examples of inorganic pigments coated with a compound semiconductor include titanium oxide and potassium titanate coated with semiconductor tin oxide, and acicular and spherical conductive inorganic pigments are commercially available.

  If necessary, an organic or inorganic filler can be blended in the back layer of the present invention as a friction coefficient adjusting agent. As the organic filler, nylon filler, cellulose filler, urea resin filler, styrene resin filler, acrylic resin filler, and the like can be used. As the inorganic filler, silica, barium sulfate, kaolin, clay, talc, heavy calcium carbonate, light calcium carbonate, titanium oxide, zinc oxide and the like can be used. For example, in the case of nylon powder, the average particle size is preferably about 1 to 15 μm, and the blending amount is preferably about 2 to 30% by mass based on the total solid content of the back surface layer, although it depends on the particle size.

  If necessary, the back surface layer can contain an anti-fusing agent such as a lubricant and a release agent. Examples of the anti-fusing agent include non-modified and modified silicone oils, silicone block copolymers, silicone compounds such as silicone rubber, phosphate ester compounds, fatty acid ester compounds, fluorine compounds, and the like. Further, conventionally known antifoaming agents, dispersants, colored pigments, fluorescent dyes, fluorescent pigments, ultraviolet absorbers and the like may be appropriately selected and used.

The solid content coating amount of the back layer is preferably in the range of 0.3 to 10 g / m ² . More preferably, it is 1-8 g / m < ² >. When the back layer solid content coating amount is less than 0.3 g / m ² , the scratch resistance when the receiving sheet is rubbed is not sufficiently exhibited, coating defects occur, and the surface electrical resistance value increases. There is a case. On the other hand, when the solid content coating amount exceeds 10 g / m ² , the effect is saturated, which is uneconomical.

  The present invention will be described in detail by the following examples, but the scope of the present invention is not limited thereto. In Examples, “%” and “parts” indicate “% by mass” and “parts by mass” unless otherwise specified.

Example 1
"Formation of back layer"
As a sheet-like support, art paper (trade name: OK Kanto N, 174.4 g / m ² , manufactured by Oji Paper Co., Ltd.) having a thickness of 150 μm is used, and coating liquid 1 for the back layer having the following composition is applied on one side thereof. The back layer was formed by coating and drying so that the film thickness after drying was 3 g / m ² .
Back layer coating solution-1
Polyvinyl acetal resin (trade name: ESREC KX-1, manufactured by Sekisui Chemical Co., Ltd.) 40 parts polyacrylic acid ester resin (trade name: Julimer AT613, manufactured by Nippon Pure Chemical) 20 parts nylon resin particles (trade name: MW330, manufactured by Shinto Fine) ) 10 parts zinc stearate (trade name: Z-7-30, manufactured by Chukyo Yushi) 10 parts cationic conductive resin (trade name: Chemistat 9800, manufactured by Sanyo Chemical) 20 parts water / isopropyl alcohol = 2/3 (mass) Ratio) 400 parts of liquid mixture

"Formation of low density layer"
The hollow particle dispersion was dispersed by cowless with the following composition to obtain a dispersion in which the hollow particles having a particle size distribution of 10 μm or more were 5% or less (average particle diameter: 5.0 μm).
Hollow particle dispersion-1
Polyacrylonitrile-based expanded particles 50 parts Sodium acrylate 0.1 parts Polyvinyl alcohol (trade name: PVA205, manufactured by Kuraray, degree of polymerization 500) 5 parts Water 200 parts

Next, on the surface opposite to the side on which the back layer of the sheet-like support is provided, a coating solution for low density layer-1 having the following composition (low density layer coating density / low density layer coating calculated density = 0.8) The coating was dried so that the film thickness after drying was 43 μm to form a low density layer.
Coating solution for low density layer-1
Hollow particle dispersion-1 250 parts polyvinyl alcohol (trade name: PVA205, manufactured by Kuraray, degree of polymerization 500) 5 parts styrene-butadiene latex (trade name: PT1004, manufactured by Asahi Kasei) 40 parts

"Formation of receiving sheet"
Further, a barrier layer coating liquid-1 having the following composition is applied and dried on the low density layer so that the solid content coating amount is 2 g / m ² , and a barrier layer is formed. The receiving layer coating solution-1 having the following composition was applied and dried so that the solid content coating amount was 5 g / m ² , and then cured at 50 ° C. for 48 hours to form a receiving layer to obtain a receiving sheet. It was.
Coating liquid for barrier layer-1
Polyvinyl alcohol (trade name: PVA105, manufactured by Kuraray, polymerization degree 500) 100 parts Water 1000 parts
Receiving layer coating solution-1
Polyester resin (trade name: Byron 200, manufactured by Toyobo) 100 parts silicone oil (trade name: KF393, manufactured by Shin-Etsu Chemical Co., Ltd.) 3 parts polyisocyanate (trade name: Takenate D-140N, manufactured by Takeda Pharmaceutical Co., Ltd.) 5 parts Toluene / Methyl ethyl ketone = 1/1 (mass ratio) mixture 400 parts

Example 2
In the dispersion of hollow particles of Example 1, the dispersion method was dispersed by cowless and further dispersed by a sand mill, and the particle size distribution of the hollow particles contained in the dispersion was 3% or less (average particle size 4.3 μm). A receiving sheet was obtained in the same manner as in Example 1 except that the low-density layer paint density of the low-density layer paint-1 of Example 1 / the calculated density of the low-density layer paint = 1.0.

Example 3
In the dispersion of hollow particles of Example 1, the dispersion method was dispersed with cowless and then further dispersed with a sand mill, and the particle size distribution of the hollow particles contained in the dispersion was 1% or less (average particle size 2.5 μm). A receiving sheet was obtained in the same manner as in Example 1 except that the low-density layer paint density of the low-density layer paint-1 of Example 1 / the calculated density of the low-density layer paint = 1.1.

Example 4
A receiving sheet was obtained in the same manner as in Example 2 except that the hollow ratio of the hollow particles in Example 2 was 75.5% (average particle diameter 4.2 μm).

Example 5
A receiving sheet was obtained in the same manner as in Example 2 except that the hollow ratio of the hollow particles in Example 2 was 89.0% (average particle diameter: 4.5 μm).

Example 6
A receiving sheet was obtained in the same manner as in Example 4 except that the low-density layer of Example 4 was 32 μm.

Example 7
A receiving sheet was obtained in the same manner as in Example 4 except that the low-density layer of Example 4 was 100 μm.

Example 8
A receiving sheet was obtained in the same manner as in Example 2 except that the mass ratio of the hollow particles in the low-density layer of Example 2 was 30%.

Example 9
A receiving sheet was obtained in the same manner as in Example 2 except that the mass ratio of the hollow particles in the low-density layer of Example 2 was 70%.

Example 10
A receiving sheet was obtained in the same manner as in Example 2, except that the thickness of the barrier layer in Example 2 was 1 μm.

Example 11
A receiving sheet was obtained in the same manner as in Example 2 except that the thickness of the barrier layer in Example 2 was 5 μm.

Comparative Example 1
Except that the hollow particles having a particle diameter of 10 μm or more in the hollow particle dispersion of Example 1 is 12% (average particle diameter is 7.0 μm), and the density ratio of the low-density layer coating amount is 0.6. A receiving sheet was obtained in the same manner as in Example 1.

Comparative Example 2
Except that the hollow particles having a particle diameter of 10 μm or more in the hollow particle dispersion of Example 1 are 15% (average particle diameter 8.0 μm), and the density ratio of the low-density layer coating amount is 0.4. A receiving sheet was obtained in the same manner as in Example 1.

Evaluation The receiving sheets obtained in each of the above examples and comparative examples were evaluated by the following methods, and the results obtained are shown in Table 1.

(Measurement of particle size of hollow particles)
The particle size distribution was measured using a Shimadzu SALD2000J.

(Receptive layer surface smoothness)
The receiving layer surface of the receiving sheet obtained in each of the above Examples and Comparative Examples is referred to as “J. TAPPI-No. Evaluation was performed with a Oken type smoothness meter based on No. 5.

[Print density and change in print density]
Using the commercially available thermal transfer video printer (trade name: UP-DR100, manufactured by Sony Corporation) on the receiving sheets obtained in the above Examples and Comparative Examples, yellow, magenta, Using an ink ribbon provided with an ink layer containing sublimable dyes for each of the three cyan colors together with a binder, the surface of the ink layer of each color is brought into contact with the surface of the test receiving sheet in sequence, and heating is controlled stepwise by a thermal head. As a result, a predetermined image was thermally transferred to the receiving sheet, and halftone single-color and overlaid images of each color were printed.
With respect to the recorded images for each applied energy transferred onto each receiving sheet, the reflection density was measured using a Macbeth reflection densitometer (trade name: RD-914, manufactured by Kollmorgen). The density of the high gradation portion corresponding to the 16th step from the lowest applied energy is displayed in Table 1 as the print density.

Furthermore, the change in the print density is the same as that of the above-mentioned Examples and Comparative Examples in which the humidity was adjusted for 8 hours or more in an environment of 20 ° C. and 50% RH and 20 ° C. and 90% RH. Printing was performed under each environment, the reflection density of the printed material was measured, and calculated according to the following formula.
Change in print density = (20 ° C., 90% RH print reflection density) − (20 ° C., 50% RH print reflection density)

[Print white spot]
For the printed matter of each Example and Comparative Example obtained by the above-mentioned print density evaluation, the recording of the gradation portion corresponding to the optical density (black) of 0.3 for the recording image for each applied energy transferred onto the receiving sheet. The uniformity of the image was visually evaluated for the presence or absence of printed white spots. Good evaluation results were indicated by ◯, normal results by △, and marked defects by ×.

[Change in thickness of receiving sheet before and after printing]
The thickness change was performed by printing the receiving sheets obtained in each of the above Examples and Comparative Examples, which were conditioned for 8 hours or more in an environment of 20 ° C. and 90% RH, under each environment. The paper thickness before and after printing at the step portion was measured and calculated by the following formula.
Change in thickness = (thickness before printing at 20 ° C. and 90% RH) − (thickness after printing at 20 ° C. and 90% RH)

[Unevenness after printing of receiving sheet]
About the printed matter of each Example and Comparative Example obtained by the above-mentioned print density evaluation, the unevenness on the surface of the receiving layer was visually evaluated. The case where there was almost no unevenness and the appearance was excellent was indicated by ○, the case where the unevenness was slightly, Δ, and the case where the unevenness was conspicuous and the appearance was poor was indicated by ×.

From the results of Examples 1 to 11 in Table 1, the thermal transfer receiving sheet of the present invention has a high printing density, a sufficiently small change in printing density due to the environment, no white spots in printing, and a small change in thickness before and after printing. And it became clear that it is a receiving sheet with very little unevenness after printing.
On the other hand, in Comparative Examples 1 and 2, since the conditions of the receiving sheet of the present invention are not satisfied at the same time, a good receiving sheet with small print density, change in print density, white spot in print, and thickness change before and after printing is obtained. I couldn't.

  The receiving sheet of the present invention is suitable for dye thermal transfer printers, and is a receiving sheet provided with a low-density layer containing hollow particles, which is equivalent to an expensive synthetic paper or foam film, and changes in printing density or printing depending on the environment. The thickness change before and after is small, the unevenness after printing is improved, and it is a high-sensitivity, high-quality receiving sheet that greatly contributes to the industry.

Claims (10)

  In a thermal transfer receiving sheet in which a low-density layer and an image-receiving layer are sequentially laminated on at least one surface of a sheet-like support mainly composed of cellulose pulp, the low-density layer includes at least a binder resin and pre-expanded hollow particles. And the particle size distribution of the hollow particles is 10% or less of particles of 10 μm or more. TAPPI-No. 5. A thermal transfer receiving sheet, wherein the Oken smoothness based on 5 is 5000 seconds or more.   The thermal transfer receiving sheet according to claim 1, wherein the low density layer is formed from a low density layer paint having a density ratio of low density layer paint density / low density layer paint calculated density = 0.7 to 1.2.   The thermal transfer receiving sheet according to claim 1 or 2, wherein the hollow particles have an average particle diameter of 0.5 to 10 µm.   The thermal transfer receiving sheet according to any one of claims 1 to 3, wherein the particle size distribution of the hollow particles is obtained by dispersing the hollow particles using a sand mill, cowless and / or ball mill. .   The thermal transfer receiving sheet according to any one of claims 1 to 4, wherein the binder resin contained in the low density layer is a water-soluble and / or water-dispersible resin.   The thermal transfer receiving sheet according to any one of claims 1 to 5, wherein a volumetric hollow ratio of the hollow particles contained in the low density layer is 75 to 95%.   The thermal transfer receiving sheet according to claim 1, wherein the low density layer has a thickness of 10 to 110 μm.   The thermal transfer receiving sheet according to any one of claims 1 to 7, wherein the mass ratio of the hollow particles to the total solid mass of the low-density layer coating is 30 to 75%.   The thermal transfer receiving sheet according to any one of claims 1 to 8, further comprising a barrier layer laminated between the low density layer and the image receiving layer.   The thermal transfer receiving sheet according to any one of claims 1 to 9, further comprising a back layer containing at least a binder resin and an inorganic and / or organic pigment on a side of the substrate on which the image receiving layer is not provided. .