JPH06336090A - Melt transfer type ink image receiving sheet - Google Patents

Abstract

PURPOSE:To provide the title image receiving sheet good in the reproducibility of a dot and obtaining high recording density. CONSTITUTION:A melt transfer type ink image receiving sheet having a sheet like support based on cellulose pulp, the resin coating layer formed on one surface of the support and containing a thermoplastic resin as a main component and the image receiving layer formed on the resin coating layer and based on a resin and pigment is characterized by that the elastic modulus in the thickness direction of the sheet is 10kg/cm<2> or less and the average height of the surface unevenness of the ink image receiving layer at a wavelength of 1-10mm is 2mum or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melt transfer type ink image receiving sheet. More specifically,
TECHNICAL FIELD The present invention relates to a melt transfer type ink image-receiving sheet which, when used in a melt transfer type heat transfer printer using a thermal head, has excellent dot reproducibility and can obtain an excellent print ink image having a high recording density.

[0002]

2. Description of the Related Art A thermal fusion transfer recording system utilizing a thermal transfer ink sheet and a thermal head is widely used in printers such as word processors and facsimiles because of its simple mechanism and easy maintenance. High quality paper has been used as the image receiving sheet. However, in recent years, due to full-color thermal transfer recording, in order to obtain higher gradation reproducibility than before, in printers, the size of each dot is changed from the method of acquiring gradation without changing the size of one dot. In the ink image receiving sheet (hereinafter abbreviated as image receiving sheet), the dot shape of the melt-transferred ink is faithfully reproduced in full color recording from low applied energy to high applied energy. It is important to have dot reproducibility, to transfer a sufficient amount of ink, and to have a high recording density.

The characteristics of the image receiving sheet are required to correspond to full-color thermal transfer images as described above. That is, when a plain paper for ordinary printing is used as the image receiving sheet, a phenomenon that a part of the ink is not transferred due to the surface being too rough, i.e., missing or conversely, the surface is too smooth and the anchoring effect of the ink is generated. The ink does not work and the transferred ink is reversely transferred to the ink ribbon, so that missing is likely to occur. All of these cause poor dot reproducibility. In addition to the decrease in recording density due to the poor dot reproducibility as described above, the decrease in recording density due to the low ink absorbability of the ink image receiving layer (hereinafter abbreviated as image receiving layer) may occur. is there.

In order to improve the transferability of ink in the image receiving layer, it is known that the Beck smoothness of the transfer sheet is set to 200 seconds or more (JP-A-59-187892). Further, the unevenness on the surface of the image receiving layer is within 3 μm or 1
There is also a proposal that it is necessary to make the waviness within 10 μm per mm (Japanese Patent Laid-Open No. 59-85792). Separately, an image receiving layer having a Beck's smoothness of 300 seconds or less and a print surface roughness of 0.6 μm or more and 5 μm or less has been reported (Japanese Patent Laid-Open No. 60-110488).
Further, there is known an image receiving sheet in which the height of the protrusions of the image receiving layer is 1 to 5 μm and the center line average roughness of the surface of the image receiving layer is in the range of 0.3 to 1.5 μm (JP-A-62-62). -288
085). These image-receiving sheets merely define a static surface shape, and good recording may be obtained in the case of binary monochromatic recording. However, in multi-valued recording that requires full color and gradation, the conventional image receiving sheet as described above has insufficient dot reproducibility, and satisfactory recording quality cannot be obtained.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional melt transfer type ink image-receiving sheet, has good dot reproducibility when used in a thermal transfer color printer, and is a good ink having a high recording density. An object of the present invention is to provide a melt transfer type ink image-receiving sheet capable of obtaining image recording.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that a sheet-shaped support containing cellulose pulp as a main component and a support formed on one surface of this support, And a resin coating layer containing a thermoplastic resin as a main component, and a sheet having an ink image receiving layer formed on the resin coating layer and containing a resin and a pigment as a main component, and the sheet has the following conditions, (1) Elasticity modulus in the thickness direction is 10 kg / cm ² or less, and (2) Average height of surface irregularities of the ink image receiving layer having a wavelength of 1 to 10 mm is 2 μm or less. The inventors have found that the sheet solves the above-mentioned problems, and completed the present invention.

[0007]

The reason why the dot reproducibility of the recorded image is good and the color density is high by using the image receiving sheet using the base paper having the above-mentioned constitution is presumed as follows. In the melt transfer printer, the image receiving sheet is conveyed while being sandwiched between the recording head and the platen roll together with the ink ribbon and pressed to heat and transfer the ink image. At this time, the higher the adhesion between the recording head and the ink ribbon or the ink ribbon and the image receiving layer of the image receiving sheet, the better the dot reproducibility and the higher the recording density. In order to achieve good adhesion between the ink ribbon and the image receiving layer, in addition to the small surface roughness represented by the average height, the ink ribbon and the image receiving layer deform due to deformation under the pressing condition of the platen roll. It is desired to have a function that improves the property. The deformability of the image receiving sheet is better when the elastic modulus is lower.

As a result of extensive studies based on the above viewpoint,
(1) The elastic modulus in the thickness direction is 10 kg / cm ² or less,
(2) Use of a melt transfer type ink image-receiving sheet having an average height of surface irregularities of 2 to 10 mm with a wavelength of 1 to 10 mm in the ink image-receiving layer results in good dot reproducibility of recorded images and high color density. Was found to be obtained.

The base paper used as the support of the present invention is
Contains cellulose pulp as a main component. The type of pulp used is not particularly limited, but for example, wood pulp such as chemical and mechanical pulp of hardwood and conifer, waste paper pulp, non-wood natural pulp such as hemp and cotton, polyethylene and polypropylene as raw materials. Examples thereof include synthetic pulp and the like, and these may be used in combination. The base paper forming the support of the present invention, in addition to the above cellulose pulp, acrylic fibers and rayon fibers, phenolic fibers, polyamide fibers, organic fibers such as polyester fibers,
Inorganic fiber such as glass fiber, carbon fiber, alumina fiber, etc.
Various fibers may be mixed and made. From the viewpoint of mixability, it is preferable to add 50% by weight or more of cellulose pulp.

Various kinds of anionic, nonionic, cationic, or amphoteric retention aids, paper strengthening agents, sizing agents and fillers can be appropriately selected and used in the step of making pulp into paper. Additives for papermaking, such as dyes, pH adjusters, slime control agents, antifoaming agents, etc., can also be used according to the application. Further, by using a coating method such as a size press, a gate roll, a blade coater or an air knife coater, starch, polyvinyl alcohol, a surface sizing agent, a pigment or the like can be coated on the surface of the raw paper. In the papermaking of the base paper, pulp having a freeness of 450 cc or more is used as a main raw material and formed into a sheet by an ordinary papermaking machine. First, it is formed into a sheet by the wire part in the papermaking process, and then dehydrated by the press part. Then, it is dehydrated in a dryer part.

The resin coating layer in the present invention is preferably formed of an extrusion coatable polyolefin resin. For example, homopolymers of low density polyethylene, high density polyethylene, polypropylene, polybutene, polypentene, etc., or copolymers of two or more olefins such as ethylene-polypropylene copolymers, or ethylene and α-olefins. The linear low-density polyethylene, which is a copolymer of, and a mixture of two or more thereof can be used, and those having various densities and melt indexes can be used alone or in a mixture thereof.

A white pigment may be added to the resin coating layer of the present invention in order to improve the whiteness of the image receiving sheet. White pigments include titanium oxide, zinc oxide, talc,
And calcium carbonate can be used. Further, in the present invention, a resin metal salt such as stearic acid amide or zinc stearate, an antioxidant such as hindered phenol, or a pigment or dye such as cobalt blue or ultramarine may be added to the resin coating layer. The coating amount of the resin coating layer is preferably 10 to 40 g / m ² . If the coating amount of the resin coating layer is less than 10 g / m ² , dot reproducibility is poor, which is not preferable. When the coating amount of the resin coating layer exceeds 40 g / m ² , the recording density decreases, which is not preferable. In order to prevent curling of the image receiving sheet, a resin coating layer may be provided on both sides of the support.

The image-receiving layer of the present invention includes EVA, wax,
In addition to the rosin compound, a known resin may be mixed and used as a binder resin. As these resins,
Water-soluble resins such as polyvinyl alcohol, oxidized starch, etherified starch, methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, casein, gelatin, soybean protein, polyvinylpyrrolidone, polyacrylamide and polyacrylic acid, and vinyl chloride resin, chloride Vinyl-vinyl acetate copolymer resin, vinylidene chloride resin, vinyl chloride-vinylidene chloride copolymer resin, acrylic ester copolymer resin, methacrylic ester copolymer resin, butyral resin, silicone resin, polyester resin, vinylidene fluoride resin, Water-insoluble resins such as nitrocellulose resin, styrene resin, styrene-acrylic copolymer resin, styrene-butadiene copolymer, etc. are used. When forming the coating layer, the above resin is used as a solution, emulsion, or latex. These resins can be used alone or in combination of two or more.

Examples of the pigment used together with the resin for forming the image receiving layer of the present invention include zinc oxide, titanium oxide, calcium carbonate, silicic acid, silicates, clay, talc, mica,
Calcined clay, aluminum hydroxide, barium sulfate, lithopone,
Titanium dioxide, zinc oxide, and other inorganic pigments, polystyrene, polyethylene, polypropylene, epoxy resins, melamine resins, phenol resins, polystyrene acrylic copolymer powders and beads, starch powders, cellulose powders,
There are microspheres, hollow particles and the like, and these can be used alone or in combination of two or more kinds.

The total amount of the resin used in the image-receiving layer of the present invention is preferably in the range of 20 to 100% by weight, and the total amount of the pigment is in the range of 80 to 0% by weight. Preferably there is. When the amount of all the resins used is less than 20% by weight, the ink transfer property of the obtained image receiving layer may be insufficient, and the dot reproducibility and the recording density may be insufficiently increased.

EVA, wax, rosin compound, other binder resin and pigment of the image receiving layer can be dispersed into a paint by a method which has already been industrialized.
That is, a solution in which EVA, a wax, a rosin compound, and other binder resin are liquefied is mixed with a pigment or a pigment dispersion at a predetermined ratio, and a stirrer, a sand grinder, etc. may be mixed with a dispersion medium in some cases. The concentration and liquid state can be adjusted by mixing and dispersing using a suitable disperser. To form the image-receiving layer on the resin coating layer, a normal coating method, that is, a Mayer bar method, a gravure roll method, a reverse roll method, a blade method, a knife method, an air knife method, a slit die method or the like coating step, And a dry solidification step may be used.

Generally, in order to make the function of the image receiving layer sufficient,
The coating amount of the image receiving layer coating after drying and solidification is preferably 4 to ²⁰ g / m ² . An overcoat layer may be provided on the image-receiving layer in order to further provide writability, matteness and naturalness. As the binder resin for the overcoat layer, the same resins as those usable for the image receiving layer may be used alone or in combination of two or more. As the pigment used together with the resin for forming the overcoat layer, the same pigments that can be used for the image receiving layer can be used, but they are also used for the overcoat layer in order to improve the smoothness of the overcoat layer and prevent transfer defects. The average particle diameter of the pigment to be used is preferably 5 μm or less.

The total resin used in the overcoat layer of the present invention is used in the range of 15 to 80% by weight of the total coating solids, and the pigment is preferably used in the range of 85 to 20% by weight. If the amount of the resin used is less than 15% by weight, the strength of the coating film becomes weak and the image receiving layer may be peeled off from the ink ribbon, which may cause recording failure, which is not preferable. If the amount of the resin used is more than 80% by weight, the surface of the overcoat layer becomes too smooth, the anchoring effect of the ink does not work, and bleeding is likely to occur, which is not preferable.

The resin and pigment used in the overcoat layer of the present invention can be dispersed and made into a paint by the same method as the resin and pigment used in the image receiving layer. The method of forming the overcoat layer on the image receiving layer of the present invention may be the same as the method of forming the image receiving layer on the resin coating layer. Since the overcoat layer is inferior in ink absorbability to the image receiving layer, the thickness of the overcoat layer is made as thin as possible within the range where the strength of the coating film can be maintained, and the transferred ink is moved to the image receiving layer promptly. The recording density is improved when the layer absorbs ink. Therefore, the coating amount of the overcoat layer is 2 to 10 g / m.
² is preferred.

When the image-receiving sheet of the present invention is run in a printer, an antistatic agent may be applied to at least one surface of the image-receiving sheet in order to prevent static electricity and running troubles. Alternatively, it may be added in the image receiving layer and / or the overcoat layer, or may be applied as a back coat. A cationic hydrophilic polymer is effectively used as the antistatic agent.

In order to adjust the elastic modulus in the thickness direction of the image-receiving sheet, with respect to the support, the freeness of the cellulose pulp, the blending of the softening agent, the adjustment by the pressure of the wet press in the paper making process, etc., and the resin coating layer, The type of laminate resin, adjustment with additives, and the image-receiving layer and overcoat layer can be adjusted by compounding, curing conditions, addition of a plasticizer and the like. Among them, the method of controlling the elastic modulus in the thickness direction of the support containing cellulose pulp as the main component is the simplest. The elastic modulus in the thickness direction of the support substantially correlates with the density of the base paper. Therefore, the elastic modulus in the thickness direction can also be adjusted by adjusting the density of the support by the wet press pressure in the paper making step, the machine calender after paper making, and the super calender treatment. An image-receiving sheet satisfying the above conditions can be recorded by a thermal color printer,
The dot reproducibility of an image is better and the recording density is higher than that of a known thermal transfer image-receiving sheet composed only of a resin and a pigment.

[0022]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. All "parts" in Examples and Comparative Examples are "parts by weight". Examples 1 to 6 Using the cellulose pulp raw materials, various types of wet press pressures shown in Table 1 were used to obtain 6 types of supports with different elastic moduli in the support thickness direction by handmaking. Further, the surface height of each support was changed by a machine calendar or a super calendar. Then, a polyethylene resin containing 13% of titanium dioxide was laminated on the surface of the support at a coating amount of 20 g / m ² to form a resin coating layer. Further, a polyethylene resin containing no titanium dioxide was laminated on the back side of the base paper so that the coating amount was 20 g / m ² . Furthermore, after the corona treatment was applied to the surface of the resin coating layer, the mixture having the composition shown below was mixed by a stirrer to obtain an image receiving layer coating material having a coating amount after drying of 8 g / m ² . So that it has a modulus of elasticity in the thickness direction of 10 kg.
/ Cm ² or less, and the average height of surface irregularities was 2 μm or less to prepare a melt transfer type ink image-receiving sheet.

Image Receiving Layer Coating Composition Weight Part EVA Emulsion (Polysol EVA AD-2, Showa High Polymer, solid content 55%) 291 Stabilized rosin ester emulsion (Super Ester E-720, Arakawa Chemical Industry, solid content 50) %) 80

Comparative Examples 1 to 8 Melt transfer type ink image receiving sheets were prepared under the conditions shown in Table 1 in the same manner as in Examples. However, the elastic modulus in the thickness direction of the image receiving sheet was set to be larger than 10 kg / cm ² , or the average height of the surface irregularities was set to be larger than 2 μm. Test The image-receiving sheets of the above-mentioned Examples and Comparative Examples were subjected to 20 ° C. and 65% R
After controlling the humidity for 2 hours in an environment of H, the elastic modulus in the thickness direction and the height of the surface unevenness of the ink image receiving layer having a wavelength of 1 to 10 mm were measured, and a commercially available thermal transfer color printer (CHC-445,
Table 1 shows the results of melt transfer recording of ink images by Shinko Electric Co., Ltd.).

Evaluation (1) Elastic Modulus in Thickness Direction The image-receiving sheet is compressed with Tensilon at a speed of 2 mm / min and a maximum load of 100 kg. The thickness of the image receiving sheet at the time of compression and the pressure per unit area are measured to obtain a stress-strain curve. The elastic modulus in the thickness direction is defined as the inclination of the straight line portion having a thickness change of 2% or more. (2) Concavo-convex height of wavelength 1 to 10 mm Using a surface roughness meter (Surfcoder, manufactured by Kosaka Laboratory), the concavo-convex (roughness) of the image receiving layer surface of the image receiving sheet is measured, and a voltage signal corresponding to the surface irregularity Frequency analyzer (CF-9
40, manufactured by Ono Sokki Co., Ltd.) and frequency analysis is performed by the fast Fourier transform method to obtain a power spectrum. This value corresponds to the average height of the unevenness, but since the unit is voltage, it is converted to the length unit. For conversion, it is calculated from a standard plate (accessory of the surface roughness meter) with a known average height of irregularities and the corresponding voltage. (3) Dot Reproducibility The dots of the ink transferred from the ink ribbon to the image receiving layer were satisfactorily reproduced.

[0026]

[Table 1]

[0027]

According to the present invention, it becomes possible to put into practical use a melt transfer type ink image-receiving sheet which has good dot reproducibility of a melt heat transfer ink image and can obtain a high recording density, which greatly contributes to the industrial world. .

Claims (1)

[Claims] 1. A sheet-shaped support containing cellulose pulp as a main component, a resin coating layer formed on one surface of the support and containing a thermoplastic resin as a main component, and formed on the resin coating layer. And an ink image receiving layer containing a resin and a pigment as main components, the sheet having the following conditions: (1) Elastic modulus in the thickness direction of 10 kg / cm ² or less; (2) Ink image receiving layer The average height of surface irregularities having a wavelength of 1 to 10 mm is 2 μm or less, the melt transfer type ink image receiving sheet.