JP2575340B2 - Laminated resin sheet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated resin sheet having excellent anti-curl properties, and in particular, does not curl even when heat is applied during printing, playing cards, art paper. , Printing paper such as poster paper, computer foam paper, electrostatic plotter paper,
The present invention relates to a laminated resin sheet that can be used as information paper such as a base sheet of an image receiving sheet for thermal transfer recording.

The laminated resin sheet of the present invention is, in particular, a support for an image receiving sheet for thermal transfer recording, particularly after thermal transfer for color copying used in a video printer or the like for forming a character or image on a receptor by an electrical signal such as a thermal head. It is useful as a support in which curling is prevented.

[Prior art] Conventionally, in an image receiving sheet for thermal transfer recording, a transfer sheet having a transfer layer containing a sublimable or vaporizable dye and a receiving sheet are superimposed, and the transfer sheet is heated during printing. Then, the dye contained in the transfer layer is sublimated or vaporized to be dyed on a receiving sheet, and a dye image is formed on the receiving sheet to perform thermal transfer.

Specifically, in a transfer type thermal recording system using a heat source controlled by an electric signal such as a thermal head, a transfer body 2 having a color material layer 22 and a base 21 as shown in FIG. A color copy is obtained by sandwiching a receiving sheet 1 having a support 12 and a drum 3 between a drum 3 and a heat source 4 and heating the color material of a layer 22 in accordance with an electric signal to transfer the color material onto an image receiving layer 11. Printing.

The image receiving layer 11, the material used depends on the content of the coloring material used, in the case of a hot-melt type coloring material containing a pigment, the support 12 itself may be used, but a sublimable basic dye type In the case of a coloring material, an activated clay (active clay) layer is used, and in the case of a sublimable disperse dye type coloring material, a polymer material coat layer of polyester or the like is used.

However, in the conventional receiving sheet, the thickness of the support is uneven or the surface is uneven, so that the surface of the image receiving layer 11 itself has unevenness of 5 to 15 μm, or undulation of 10 to 20 μm per 1 mm. there were. Although such irregularities and undulations can be somewhat improved by the surface treatment using a super calender, there is naturally a limit. For this reason, the color material transferred from the color material layer 22 has a surface irregularity of 3 to 5 μm or more or an undulation of 1 m for the image receiving layer 11.
In the case of 10 μm or more per m, not only the heat-melting color material but also the sublimable color material are not accurately transferred in accordance with the image signal, causing image quality disorder such as missing dots or missing dots in the image, and rough tones in the intermediate color. (JP-A-59-214696)
issue).

Further, as the support 12, paper or inorganic fine powder is 40 to 50.
A synthetic paper consisting of a stretched film of a thermoplastic resin containing 5% by weight (Japanese Patent Publication No. 46-40794), or a transparent polyethylene terephthalate film or a transparent film coated with an inorganic compound such as silica or calcium carbonate together with a binder to give a white color. Coated synthetic paper with improved degree and dyeability is used.

However, considering the after-use (copying, pencil writing, preservation, etc.) of the heat-transferred receiving sheet, the image receiving sheet for thermal transfer recording has strength, dimensional stability,
From the viewpoint of adhesion to the print head, it is preferable to use a synthetic paper having a large number of microvoids inside obtained by stretching a polyolefin resin film containing an inorganic fine powder (Japanese Patent Laid-Open Nos. 60-245593 and 61-245593). No. 112693, Japanese Patent Application No. 62-
25080).

[Problems to be Solved by the Invention] Such a polyolefin resin-based synthetic paper has an opacity and a soft feeling, and in order to improve the adhesiveness with a print head and the paper supply / discharge property, it is necessary to use a material. The film is stretched at a temperature lower than the melting point of the polyolefin resin to form microvoids inside.

However, the melting point of the polyolefin resin is as low as 167 ° C. or less as compared with polyethylene terephthalate or polyamide (240 to 255 ° C.), and the temperature of the surface of the receiving sheet at the time of printing by the print head is short. Since the melting point is 190 to 200 ° C., which is higher than the above melting point, it has been pointed out that a problem occurs in that the synthetic paper shrinks due to heat during printing, and the heat-transferred receiving sheet is curled on the printed, printed inner surface. (JP-A-60-245593 and JP-A-61-283595).

On the other hand, in order to reduce such heat shrinkage and prevent curling, lamination can be performed with the stretching temperature set near the melting point of the base resin. In this case, however, the opacity and softness of the base resin can be reduced. This causes a problem such as a decrease in

[Means for Solving the Problems] The present invention has been made in view of the above problems, and has a biaxially stretched film as a base layer, and the front and back surfaces thereof are sandwiched by a uniaxially stretched film. In a laminated resin sheet having a three-layer structure of at least a surface layer, a base material layer, and a back surface layer, the thickness and the filler content of the front surface layer are maximized, and the thickness and the filler content are sequentially increased as the base material layer and the back surface layer progress. Is a laminated resin sheet characterized by having a smaller size.

In the present invention, the thickness of the surface layer of the uniaxially stretched film of the laminated resin sheet on the side where the image receiving layer is provided is determined by the thickness of the base layer of the biaxially stretched film which is easily contracted by receiving heat conduction from the thermal head. By making it thicker, the influence of the heat conduction on the substrate layer is reduced (shrinkage of the substrate layer is reduced) to prevent curling. This means that the base layer of commercially available synthetic paper YUPO FPG (trade name of Oji Yuka Synthetic Paper Co., Ltd.) occupies about 1/2 of the total thickness, and the thickness of the surface layer and the thickness of the back surface layer are each synthetic paper. It is clearly different from what accounts for about 1/4 of the total.

Further, in order to prevent curling, it is necessary to use a film having a small heat shrinkage. Therefore, the stretching temperature and the annealing temperature during the production of the laminated resin sheet are set to be high.

In addition, in order to impart opacity and softness to the surface layer, in the present invention, the content of the inorganic fine powder in the surface layer is made larger than that of the base material layer to increase the generation of microvoids, and the thermal head Good adhesion with
The transferred image was made good.

In the uniaxially stretched film of the back layer, the content of the inorganic fine powder is made smaller than that of the base material layer to reduce the number of microvoids generated by stretching,
The thermal head gives the surface layer rigidity to overcome the heat shrinkage force generated on the surface layer by touching the surface layer, and by making the thickness of the back layer thinner than the surface layer, the back layer has a tendency to curl in a concave shape. This counteracts the convex curl property of the laminated resin sheet, thereby improving the curl properties of the entire laminated resin sheet.

The laminated resin sheet of the present invention is basically a surface layer, a base material layer,
It is composed of at least three back layers.

(Base Material Layer) The base material layer (B) contains inorganic fine powder having a specific surface area of 10,000 cm ² / g or more in an amount of 10 to 45% by weight, preferably 15 to 35% by weight, and has microvoids formed by biaxial stretching. A biaxially stretched polyolefin resin film containing a large number of
Its thickness accounts for 20 to 40% of the total thickness of the laminated resin sheet.
The base material layer having a thickness of 45 to 180 μm, preferably 50 to 100 μm is used. A polyolefin resin film containing 0 to 25% by weight of inorganic fine powder on both surfaces of such a base material layer is used as a surface adhesive layer (E). ) And a back adhesive layer (F) made of a polyolefin resin film containing 0 to 25% by weight of an inorganic fine powder. These adhesive layers (E, F)
Is sufficient to be 0.5 to 10 μm.

When the thickness of the base material layer is less than 20% of the total thickness, the rigidity (stiffness) of the laminated resin sheet is reduced, and the practical use as a base material for heat transfer receiving paper or various printing papers is lacking. 48 thick
%, The thickness of the surface layer becomes thin, so that the temperature rise of the base material layer due to the heating of the thermal head or the like increases, the amount of shrinkage increases, and the curl prevention effect decreases.

(Surface layer) The surface layer (A) of the stretched multilayer polyolefin resin film on the ink receiving layer side contains inorganic fine powder having a specific surface area of 10,000 cm ² / g or more in an amount of 30 to less than 80% by weight, preferably 40 to 65% by weight. It is a polyolefin resin film having a thickness of 50 to 200 μm, preferably 60 to 120 μm, which is uniaxially stretched.

The uniaxially stretched film of this surface layer and the back layer described below is
Each may be a single layer or a uniaxially stretched film of a multilayer structure.

The sum of the thicknesses of the front surface layer and the back surface layer is 52 to 80% of the total thickness of the laminated resin sheet.

(Back Layer) A back layer (C) laminated on the side opposite to the ink receiving layer.
Is an inorganic fine powder having a specific surface area of 10,000 cm ² / g or more
The uniaxially stretched resin film having a thickness of less than 0% by weight, preferably 10 to 25% by weight and having a thickness of 30 to 100 μm, preferably 20 to 80 μm, including the backside layer,
Fine long voids (voids) with inorganic fine powder as the core
And many fine cracks on its surface.

(Constituent Materials) Examples of the polyolefin resin constituting the surface layer, the base material layer and the back surface layer include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and poly (4-methylpentene-1). ), Among which polypropylene is heat-resistant,
It is preferable in terms of solvent resistance and cost.

Polystyrene, polyamide, polyethylene terephthalate, partial hydrolyzate of ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer and salts thereof, vinylidene chloride copolymer such as vinyl chloride / vinylidene chloride copolymer And the like.

Examples of the inorganic fine powder include calcium carbonate, calcined clay, diatomaceous earth, talc, titanium oxide, barium sulfate, aluminum sulfate, and silica.

(Other Layers) In the stretched multilayer polyolefin resin film, other layers can be laminated in addition to the surface layer, the base material layer, and the back surface layer for other purposes. For example, 8-60% by weight, preferably 40-55% by weight of inorganic fine powder having a specific surface area of 10,000 cm ² / g or more outside the surface layer and / or outside the back layer.
The uniaxially stretched polyolefin resin film to be contained can be laminated (D, G) to impart writability.

(Production of Laminated Resin Sheet) The production of the laminated resin sheet of the present invention will be specifically described. First, the following compositions (A), (B) and (C) are prepared.

(A) Composition for forming surface layer (a) 20 to 70% by weight of polypropylene (b) Resin selected from polystyrene, high density polyethylene, medium density polyethylene, low density polyethylene, ethylene / vinyl acetate copolymer 0 to 20 (C) inorganic fine powder 30 to 80% by weight (B) base layer forming composition (a) polypropylene 35 to 95% by weight (b) high density polyethylene, medium density polyethylene, low density polyethylene, ethylene / acetic acid Resin selected from vinyl copolymer 0 to 20% by weight (c) Fine inorganic powder 10 to 45% by weight (C) Composition for forming back layer (a) 70 to 95% by weight of polypropylene (b) Polystyrene, high density Polyethylene, medium-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer 0 to 20% by weight (c) inorganic fine powder 5 to 30% by weight The composition for forming a base material layer (B) ) A resin sheet of the composition (A) for forming a surface layer is melt-laminated on one side of a uniaxially stretched film sheet, and 10 to 30% by weight of an inorganic fine powder is coated on the other side.
A resin sheet of the resin composition (C) for forming a back layer is melt-laminated, and once cooled, the multilayer sheet is heated again and stretched in the direction perpendicular to the uniaxial stretching direction of the sheet (B). Obtained by heat treatment.

By this stretching, the sheet of the composition (B) is biaxially stretched, and a number of voids (microvoids) are formed therein. On the other hand, the surface layer (A) and the back layer (C) become a film stretched only in a uniaxial direction by the stretching,
Fine irregularities occur on the surface, surface smoothness (Beck index)
Is about 300 to 3,000 seconds.

The thickness of each of the surface layer, the back surface layer and the base material layer is 1.1 or more, preferably 1.15, with the thickness of the base material layer as 1.
~ 1.30, the thickness of the back layer is 0.9 or less, preferably 0.70 ~ 0.8
Assume 5.

If the thickness of the surface layer is smaller than the above range, the curl property is deteriorated, and if the thickness of the back layer is larger than the above range, the curl property is deteriorated.

Specifically, the thickness of each layer of the surface layer, the base material layer, and the back surface layer is such that the total thickness of the surface layer and the back surface layer is in the range of 52 to 80% of the total thickness of the laminated resin sheet, and Base material layer thickness is 20 ~
Preferably it is 40%. The outermost layer (D, G) preferably has a thickness of 0 to 50% of the thickness of the surface layer (A). The outermost layers (D, G) are important for arbitrarily controlling the surface properties (for example, surface smoothness, glossiness, pencil writing properties and slip properties) of the laminated resin sheet, and are optimal for each purpose. The setting of blending and wall thickness is performed. For example,
It has the following composition:

a) Polypropylene 20 to 70% by weight b) Resin selected from polystyrene, high density polyethylene, medium density polyethylene, low density polyethylene, ethylene / vinyl acetate copolymer 0 to 20% by weight c) Inorganic fine powder 30 to 80% by weight % When the thickness of the base material layer exceeds 40% of the total thickness, the heat shrinkage of the base material layer due to heating from the surface layer increases, and the effect of improving curl is reduced. Conversely, the thickness of the base material layer is 20% of the total thickness
Below this, the rigidity of the laminated resin sheet is reduced, and the resin sheet lacks suitability as a substrate for thermal transfer receiving paper or various printing papers.

Thus, in the laminated resin sheet of the present invention, the base material layer (B)
Compared with the uniaxially stretched film layer or the non-axially stretched film layer, is strong against tensile force, but easily shrinks due to heat and is weak in curl prevention. Therefore, the opacity is improved by increasing the thickness of the surface layer (A), increasing the filler content, and stretching to increase the number of voids in the surface layer (A).

Further, in the back layer (C), in order to impart rigidity, the amount of filler is reduced, and the amount of voids due to stretching is reduced.

Therefore, it is important that the surface layer contains a large amount of the inorganic fine powder, and the content and the thickness of the inorganic fine powder are sequentially reduced in the order of the base layer and the back layer. The content of the inorganic fine powder in the surface layer is preferably selected so that the surface smoothness (Beck index) measured by JIS P-8120 is about 500 to 3,000 seconds.

The inorganic fine powder to be mixed with the surface layer is selected so as not to form as large a convex portion as possible on the surface layer, and preferably has a residual 325 mesh of 10 ppm or less. The particle size is preferably 3 μm or less.

The backside layer (C) on the opposite side of the surface transfer image receiving layer contains inorganic fine powder in an amount of 5 to 30% by weight, preferably 5 to 30% by weight, in order to impart slipperiness with a roll during transfer and writeability to the backside layer after transfer. Is preferably contained so that the surface smoothness (Beck index) measured by JIS P-8120 is 50 to 2,000 seconds.

The thickness of the entire laminated resin sheet is generally 30 to 500 μm,
Preferably it is 100 to 300 μm. The laminated resin sheet preferably has a Young's modulus of 9,000 to 26,000 kg / cm ² .

(Effect) The laminated resin sheet is stretched in the softening point temperature range near the melting point by making the surface layer (A) thicker than the base material layer (B) and containing a large amount of inorganic fine powder. Even under the annealing temperature condition, the transfer image obtained is sharp because it has a moderate microvoid inside and improves the adhesion to the thermal head when used as a substrate for thermal transfer receiving paper.

When the surface layer (A), which is a uniaxially stretched film layer, is stretched under the same stretching conditions as the substrate layer, which is a biaxially stretched film layer, the heat shrinkage in both the longitudinal and transverse directions is small. Therefore, in order to prevent curling caused by one-sided heating from the surface layer (A), the surface layer (A) having a small heat shrinkage is made as thick as possible so that the base layer (B) having a large heat shrinkage is obtained. The curl is prevented by lowering the heat transfer (temperature) to shrinkage.

Since the back surface layer (C) does not receive heat like the surface layer (A), the generation of microvoids can be reduced by reducing the content of the inorganic fine powder as much as possible than the base material layer (B). Rigidity is given to the back surface to prevent curling. Further, by making the thickness of the back surface layer (C) thinner than that of the front surface layer (A), it is possible to have a slight curl (to the extent that there is no practical problem) in the back surface direction. To prevent curling.

In the case where it is necessary to provide the back surface with a writing property using a pencil or the like or a slipperiness with a roll at the time of thermal transfer, the surface layer composition (G) is added to the outermost layer of the back surface layer (C). A layer having a thickness not exceeding 20% of the thickness of C) may be provided. However, if the thickness exceeds 20% of the thickness of the back layer (C), the rigidity is improved and the back curl effect is reduced by the back layer (C).

(Thermal Transfer Image Receiving Sheet) A thermal transfer image receiving sheet is obtained by applying a coating liquid for forming an image receiving layer on the surface of the laminated resin sheet of the present invention, drying the solvent, and scattering the solvent.

The thickness of this image receiving sheet is 80 to 280 μm,
Those having a Taber stiffness of 3 to 15 g-cm measured at 8125 are preferred in terms of curling prevention and paper supply / discharge properties.

(Image receiving layer) As the resin forming the image receiving layer, oligoester acrylate resin, saturated polyester resin, vinyl chloride / vinyl acetate copolymer, acrylic ester / styrene copolymer, epoxy acrylate resin and the like are used. Is dissolved in toluene, xylene, methyl ethyl ketone, cyclohexanone and the like, and used as a coating liquid.

This coating liquid may contain an ultraviolet absorber and / or a light stabilizer to enhance light resistance.

Examples of the ultraviolet absorber include 2- (2'-hydroxy-3,3'-di-t-butylphenyl) -5-chlorobenzotriazole and 2- (2-hydroxy-3,5-t-
Amylphenyl) -2H-benzotriazole, 2- (2 '
-Hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-t-butylphenyl) -benzotriazole, 2- (2 '-Hydroxy-3', 5'-di-
(t-amylphenyl) benzotriazole and the like.

Examples of the light stabilizer include distearyl pentaerythritol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite,
Dinonylphenylpentaerythritol diphosphite, cyclic neopentanetetraylbis (octadecylphosphite), tris (nonylphenyl) phosphite, 1- {2- [3- (3,5-di-t-butyl-4) -4 -Hydroxyphenyl) propionyloxy] ethyl} -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like. .

The amount of these UV absorbers and light stabilizers added depends on the image receiving layer 3
Is preferably 0.05 to 10 parts by weight, preferably 0.1 to 2 parts by weight, and 0.5 to 3 parts by weight, and more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the resin.

Further, a release agent can be contained in the image receiving layer in order to improve releasability from the thermal transfer sheet. Polyethylene wax, amide wax,
Solid waxes such as Teflon powder; fluorine-based and phosphoric acid ester-based surfactants;

As the silicone oil, an oily one can be used, but a hardening type is preferred.

Furthermore, the image receiving layer is further improved in the whiteness of the image receiving layer to further enhance the sharpness of the transferred image, and at the same time, imparts writability to the surface of the sheet to be heat-transferred, and prevents the transferred image from being retransferred. Can be added with a white pigment. As the white pigment, titanium oxide, zinc oxide, kaolin clay and the like are used, and these can be used as a mixture of two or more kinds. As the titanium oxide, anatase-type titanium oxide and rutile-type titanium oxide can be used. Examples of the anatase-type titanium oxide include KA-10, KA-20, and KA-.
15, KA-30, KA-35, KA-60, KA-80, and KA-90 (all manufactured by Titanium Industry Co., Ltd.). Rutile-type titanium oxides include KR-310, KR-380, KR-460 and KR-480 (both manufactured by Titanium Industry Co., Ltd.). The addition amount of the white pigment is preferably 5 to 50 parts by weight based on 100 parts by weight of the resin constituting the image receiving layer.

 The thickness of the image receiving layer 11 is generally 0.2 to 20 μm.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

The methods for evaluating the curl height, heat shrinkage, image evaluation, and opacity quality in the examples are based on the following measurement methods.

Curl height The laminated resin sheet to be measured and the image receiving sheet transferred by Hitachi Color Video Printer VD-50 (trade name) are 200 mm in MD (machine direction) direction.
It is cut into a rectangle 120mm wide in the width and TD (traverse direction) direction, and the floating height (mm) when this is placed on a flat surface for 24 hours at a temperature of 23 ° C and a humidity of 50% is measured. .

Heat shrinkage The laminated resin sheet was placed on a flat surface without fixing, and the dimensions (l) of the laminated resin sheet when left at a temperature of 120 ° C for 30 minutes were measured, and the difference between the original length (l _O ) and this l was measured. And the heat shrinkage was determined by the following equation.

Opacity Determined according to JIS P-8138.

Image evaluation An image receiving sheet and a transfer film "TTF Cyan" (trade name) manufactured by Mitsubishi Paper Mills Co., Ltd., coated and dried with a sublimable dye, are overlaid, and a thermal gradient tester (Toyo Seiki Type-HG-100) is used. , Heat the hot plate by 5 points at 10 ° C intervals from 120 ° C,
Heating was performed at a pressure of Kg / cm ² for 2 seconds to obtain a transferred image.

Measure the density of the resulting transferred image with a Macbeth densitometer,
The following five levels were used for evaluation.

5: Very good.

4: Good.

3: There is no problem in practical use.

2: There is a problem in practice.

1: Not practical.

Production Example of Laminated Resin Sheet Example 1 (1) Polypropylene 7 having a melt index (MI) of 0.8
5% by weight, 25% by weight of calcium carbonate with an average particle size of 1.5 μm
After mixing (B) and kneading with an extruder set at 270 ° C,
It was extruded into a sheet and cooled by a cooling device to obtain a non-stretched sheet. After heating this sheet to 150 ° C., it was stretched 5 times in the machine direction.

(2) Polypropylene 45% by weight of MI 4.0 has an average particle size of 1.5
The composition (A) for the surface layer mixed with 55% by weight of calcium carbonate of 55 μm was melt-kneaded by an extruder, and the extruded sheet was laminated on one surface of the 5-fold stretched sheet of (1). 85% by weight of MI 4.0 polypropylene on the other side of the double-stretched sheet
A composition (C) for a back layer obtained by mixing 15% by weight of calcium carbonate having an average particle size of 1.5 μm with another extruder is melt-kneaded,
Extruded and laminated, then cooled to 60 ° C, then 165 ° C
And stretch in the transverse direction by 7.5 times with a tenter, 167 ° C
And cooled to 60 ° C., and the ears were slit to obtain a laminated resin sheet having a three-layer (A / B / C: wall thickness of 65/55/45 μm) structure.

The opacity of this laminated resin sheet was 95%, and the thermal shrinkage of this sheet was 1.0% in the MD direction and 0.2% in the TD direction.

Comparative Example 1 (1) Polypropylene 7 having a melt index (MI) of 0.8
5% by weight, 25% by weight of calcium carbonate with an average particle size of 1.5 μm
After mixing (B) and kneading with an extruder set at 270 ° C,
It was extruded into a sheet and cooled by a cooling device to obtain a non-stretched sheet. After heating this sheet to 150 ° C., it was stretched 5 times in the machine direction.

(2) Polypropylene 45% by weight of MI 4.0 has an average particle size of 1.5
The composition (A) for the surface layer mixed with 55% by weight of calcium carbonate of 55 μm was melt-kneaded by an extruder, and the extruded sheet was laminated on one surface of the 5-fold stretched sheet of (1). On the other side of the double-stretched sheet, a composition (C) for the back layer, in which 15% by weight of calcium carbonate having an average particle size of 1.5 μm is mixed with polypropylene by weight of MI 4.0 and melt-kneaded by another extruder, is extruded and laminated. Then, after cooling to 60 ° C., it is heated to 160 ° C., stretched in a transverse direction by 7.5 times with a tenter, annealed at 163 ° C., cooled to 60 ° C., slit the ears, and cuts three layers (A / B / C: 65/45/55 μm).

The opacity of this laminated resin sheet is 97% and the heat shrinkage is MD
2.5% in the direction and 1.6% in the TD direction.

Comparative Example 2 A stretched laminated resin sheet having a three-layer structure with a thickness of A / B / C: 45/55/60 μm was produced in the same manner as in Example 1 except that the width of the slit of the die was changed.

Comparative Example 3 A laminated resin sheet having a three-layer structure having a thickness of A / B / C: 40/80/40 μm was produced in the same manner as in Example 1 except that the slit width of the die was changed.

Comparative Example 4 (1) Polypropylene 8 having a melt index (MI) of 0.8
5% by weight, 15% by weight of calcium carbonate with an average particle size of 1.5μm
After mixing (B) and kneading with an extruder set at 270 ° C,
It was extruded into a sheet and cooled by a cooling device to obtain a non-stretched sheet. After heating this sheet to 150 ° C., it was stretched 5 times in the machine direction.

(2) An average particle size of 1.5 in 55% by weight of polypropylene with MI 4.0
The composition (A) for the surface layer mixed with 45% by weight of calcium carbonate of 45 μm was melt-kneaded with an extruder, and the extruded sheet was laminated on one surface of the 5-fold stretched sheet of (1). 85% by weight of MI 4.0 polypropylene on the other side of the double-stretched sheet
A composition (C) for a back layer obtained by mixing 15% by weight of calcium carbonate having an average particle size of 1.5 μm with another extruder is melt-kneaded,
Extrusion lamination, then cooled to 60 ° C, heated to 165 ° C, stretched in a transverse direction by 7.5 times with a tenter, annealed at 167 ° C, cooled to 60 ° C, and slit the ears. A laminated resin sheet having a layer (A / B / C: thickness 40/80/40 μm) structure was obtained.

Comparative Example 5 (1) Polypropylene 7 having a melt index (MI) of 0.8
5% by weight, 25% by weight of calcium carbonate with an average particle size of 1.5 μm
After mixing (B) and kneading with an extruder set at 270 ° C,
It was extruded into a sheet and cooled by a cooling device to obtain a non-stretched sheet. After heating this sheet to 150 ° C., it was stretched 5 times in the machine direction.

(2) Polypropylene 85% by weight of MI 4.0 has an average particle size of 1.5
The composition (A) for the surface layer mixed with 15% by weight of calcium carbonate of 15 μm was melt-kneaded with an extruder, and the extruded sheet was laminated on one surface of the 5-fold stretched sheet of (1). 45% by weight of MI 4.0 polypropylene on the other side of double-stretched sheet
A composition (C) for a back layer obtained by mixing 55% by weight of calcium carbonate having an average particle size of 1.5 μm with another extruder is melt-kneaded.
Extruded and laminated, then cooled to 60 ° C, then 165 ° C
And stretch in the transverse direction by 7.5 times with a tenter, 167 ° C
And cooled to 60 ° C., and the ears were slit to obtain a laminated resin sheet having a three-layer (A / B / C: wall thickness of 65/55/45 μm) structure.

Example 2 (1) Polypropylene 7 having a melt index (MI) of 0.8
5% by weight, 25% by weight of calcium carbonate with an average particle size of 1.5 μm
After mixing (B) and kneading with an extruder set at 270 ° C,
It was extruded into a sheet and cooled by a cooling device to obtain a non-stretched sheet. After heating this sheet to 150 ° C., it was stretched 5 times in the machine direction.

(2) An average particle size of 1.5 in 55% by weight of polypropylene with MI 4.0
Formulation containing 45% by weight of calcium carbonate (D)
And 45% by weight of MI 4.0 polypropylene with an average particle size of 1.5μ
The mixture (A) containing 55% by weight of calcium carbonate is melt-kneaded in separate extruders, laminated in a die, co-extruded into a sheet form, and the surface of a 5-fold stretched sheet (D) of (1). Is laminated on the other side, while calcium carbonate 1 having an average particle size of 1.5 μm is added to 85% by weight of polypropylene of MI 4.0 on the other side.
The composition (C) containing 5% by weight was melt-kneaded in another extruder, extruded and laminated, then cooled to 60 ° C.
° C, stretched 7.5 times in the transverse direction with a tenter,
Annealed at 60 ° C, cooled to 60 ° C, and slit the ears to obtain a laminated resin sheet having a three-layer (D / A / B / C: thickness 3/57/55/45 µm) structure.

Example 3 (1) Melt index (MI) 0.8, melting point 165-167 ° C
3% by weight of high-density polyethylene and 25% by weight of calcium carbonate having an average particle size of 1.5 μm were mixed (B) with 72% by weight of polypropylene and kneaded with an extruder set at 270 ° C. Composition containing 99.7% by weight of polypropylene and 0.3% by weight of calcium carbonate (E,
F) was kneaded at 270 ° C. using another extruder, and then supplied to one coextrusion die, extruded into a sheet, and cooled by a cooling device to obtain a three-layer unstretched sheet. After heating this sheet to 140 ° C., it was stretched 5 times in the machine direction.

(2) Polypropylene 45% by weight of MI 4.0 has an average particle size of 1.5
The composition (A) for the surface layer mixed with 55% by weight of calcium carbonate of 55 μm was melt-kneaded by an extruder, and the extruded sheet was laminated on one surface of the 5-fold stretched sheet of (1). 85% by weight of MI 4.0 polypropylene on the other side of the double-stretched sheet
A composition (C) for a back layer obtained by mixing 15% by weight of calcium carbonate having an average particle size of 1.5 μm with another extruder is melt-kneaded,
Extruded and laminated.

Then, after cooling to 60 ° C., it is heated to 165 ° C., stretched in a transverse direction by 7.5 times with a tenter, annealed at 165 ° C., cooled to 60 ° C., and the ears are slit and shown in FIG. A laminated resin sheet having a five-layer structure (A / E / B / F / C: thickness 70/2/50/2/40 μm) was obtained.

The density of the laminated resin sheet was as shown in Table 1, and the opacity was 85% and the curl height was 5 mm.

Example 4 At the time of laminating (2) of Example 3, the surface layer (A) was
The composition (D) for the outermost surface layer obtained by mixing 45% by weight of calcium carbonate having an average particle size of 1.5 μm with 55% by weight of polypropylene of MI 4 was melt-kneaded by another extruder and laminated. At the same time, a polypropylene 58 of MI 4 is placed under the back layer (C).
The composition (G) for the outermost backside layer, in which 42% by weight of calcium carbonate having an average particle size of 1.5 μm was mixed with the same by weight, was melt-kneaded by another extruder and laminated.

The stretching conditions were the same as in Example 3, and the stretching was performed for 7 layers (D / A / E /
B / F / C / G: A laminated resin sheet having a structure with a thickness of 8/62/2/50/2/35/5 μm) was obtained.

Production of Image Receiving Sheet for Thermal Transfer Recording On the surface layer (A) of the laminated resin sheet having a 3 to 7 layer structure produced in the above Examples and Comparative Examples, an image receiving forming composition having the following composition was dried by a wire bar coating. The resulting coating was dried to a thickness of 4 μm and dried to obtain an image receiving sheet for thermal transfer recording.

Saturated polyester (Toyobo Byron 200 Tg67 ° C) 5.3 parts by weight (Toyobo Byron 290 Tg77 ° C) 5.3 parts by weight Vinylite VYHH (Union carbide vinyl chloride / vinyl acetate copolymer) 4.5 parts by weight Titanium oxide (Titanium Industries KA- 10) 1.5 parts by weight Amino-modified silicone oil (Shin-Etsu Silicon KF-393) 1.1 parts by weight Epoxy-modified silicone oil (Shin-Etsu Silicon X-22-343) 1.1 parts by weight Toluene 30 parts by weight Methyl ethyl ketone 30 parts by weight Cyclohexane 22 parts by weight The results of the heat shrinkage, opacity and curl height of the laminated resin sheet are shown in Table 1. Table 2 shows the curl height and image results after thermal transfer of the image transfer sheet for thermal transfer recording.

[Brief description of the drawings]

FIG. 1 is a sectional view of a laminated resin sheet according to an embodiment of the present invention, and FIG. 2 is a plan view of a transfer thermosensitive recording apparatus. DESCRIPTION OF SYMBOLS 1 ... Image transfer sheet for thermal transfer recording, 11 ... Image receiving layer, 12 ... Support, 2 ... Transfer, 14 ... Protrusion, A ...
... surface layer, B ... base material layer, C ... back surface layer, E ... surface adhesive layer, F ... back surface adhesive layer.

Claims (3)

(57) [Claims] 1. A laminated resin sheet having a three-layer structure of a biaxially stretched film as a base material layer and at least a surface layer, a base material layer, and a back surface layer sandwiched by a monoaxially stretched film on the front and back surfaces, A laminated resin sheet wherein the thickness and the filler content of the front surface layer are the largest, and the thickness and the filler content are sequentially reduced as the base layer and the back surface layer are formed. 2. The filler content of the surface layer is 30-80% by weight, the filler content of the base layer is 10-45% by weight, and the filler content of the back layer is 5-30% by weight. 2. The laminated resin sheet according to item 1 above. 3. The method according to claim 1, wherein when the thickness of the base material is 1, the thickness of the surface layer is 1.1 or more, and the thickness of the back surface layer is 0.9 or less. The laminated sheet according to the above.