JP2003211610A - White laminated polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white laminated polyester film excellent in whiteness, bending wrinkle resistance, and printability. <P>SOLUTION: The white laminated polyester film is obtained by laminating white polyester layers (A) containing fine inorganic particles on both surfaces of a white polyester layer (B) containing fine air bubbles and characterized in that the total thickness of the film is 25-50 μm, and that the thickness of each of the white polyester layers (A) is 2-5 μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a white laminated polyester film. More specifically, the present invention relates to a white laminated polyester film which is excellent in whiteness, crease resistance and printability and is suitable as a receiving sheet base material for thermal transfer recording.

[0002]

2. Description of the Related Art As one of recording methods in hard copy technology, heat-sensitive transfer recording, which has features such as non-impact, easy operation / maintenance, low cost, and miniaturization, is drawing attention. The thermal transfer recording method is a transfer sheet (ink ribbon) having an ink layer which is a color material-containing layer and a receiving sheet are superposed and melted or sublimated and transferred according to heating of the thermal head from the ink ribbon side. A component containing a coloring material or a coloring material is transferred onto a receiving sheet in the form of fine dots and printed.

As a receiving sheet base material for such thermal transfer recording, titanium oxide has been conventionally used in polyester.
A white polyester film containing an inorganic fine particle such as calcium carbonate or barium sulfate or a resin incompatible with polyester is used. Furthermore, generally, a receiving layer for enhancing the printing function is provided on these films,
It is used as a receiving sheet for thermal transfer recording.

Further, there is a demand for a white polyester film having a high whiteness which improves the printing and recording accuracy, enhances the sharpness of a printed image, and gives a more luxurious appearance. In order to meet such requirements, it is known that a plurality of kinds of the above-mentioned inorganic fine particles are added together, a mixture of the inorganic fine particles and an incompatible resin is added together, and the like. As such a white polyester film, for example, JP-A-4-153232 and JP-A-6-322153 are disclosed.

In recent years, thermal transfer recording has been made finer and faster, and in the thermal transfer recording receiving sheet using the above-mentioned white polyester film, the printing dots constituting the printed image are not sufficiently transferred. Or, the print density was low, and as a result, the printed image was unclear and the printability was poor.

As a method for improving the above problems, there is known a method in which a white polyester layer containing bubbles is laminated with a polyester-based layer or a polyester layer containing inorganic fine particles to make the surface highly smooth. Examples of such white polyester film include Japanese Patent Publication No. 7-37
No. 098, Japanese Patent Application Laid-Open No. 5-329969, Japanese Patent Application Laid-Open No. 6-238787 and the like are disclosed.

[0007]

[Problems to be Solved by the Invention] However, Japanese Patent Publication No. 7-3
The white polyester films disclosed in JP-A-7098, JP-A-5-329969, JP-A-6-238787 and the like can improve printability, but have fine wrinkles, so-called folds, on the surface of the film during handling and bending. There was a practical problem that wrinkles tended to occur.

In view of the above problems, the present invention provides a white laminated polyester film which is excellent in whiteness, crease resistance and printability and is suitable for use as a receiving sheet base material for thermal transfer recording. To aim.

[0009]

In order to achieve the above-mentioned object, the present invention has the following constitution. That is, the white polyester layer (A) containing inorganic fine particles is laminated on both sides of the white polyester layer (B) containing fine bubbles,
The total film thickness is 25 μm or more and 50 μm or less, and the white polyester layer (A) containing inorganic fine particles is 2 μm or more 5
It is a white laminated polyester film having a thickness of not more than μm.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The white laminated polyester film of the present invention is mainly composed of polyester. Here, the main component is a polyester component of 50% by weight or more, preferably 60% by weight or more.

The polyester used in the present invention is a polymer obtained by condensation polymerization from a diol component and a dicarboxylic acid component. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid and adipic acid. , Sebacic acid and the like, and the diol is, for example, ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like.

As the polyester used in the present invention,
Specifically, for example, polyethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate (polyethylene naphthalate) and the like can be used. .

These polyesters may be homopolyesters or copolyesters, and as a copolymerization component, for example, a diol component such as diethylene glycol, neopentyl glycol, polyalkylene glycol, phthalic acid, isophthalic acid, It is also possible to use a dicarboxylic acid component such as 2,6-naphthalenedicarboxylic acid and 5-sodium sulfoisophthalic acid.

As the polyester used in the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferable because they are excellent in strength, heat resistance, water resistance, chemical resistance and the like.

Further, among the polyesters used in the present invention, if necessary, resins other than polyesters, additives such as ultraviolet absorbers, ultraviolet stabilizers, and heat-resistant stabilizers may be used as long as the effects of the present invention are not impaired. Agents, anti-oxidation stabilizers, organic lubricants, organic fine particles, fillers, nucleating agents, dyes, dispersants,
A coupling agent or the like may be added.

In the present invention, it is necessary to incorporate inorganic fine particles in the white polyester layer (A).
By adding the inorganic fine particles, the whiteness and the transportability can be improved.

The inorganic fine particles may or may not have a bubble-forming property. The inorganic fine particles include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, silica, alumina, mica, titanium mica, talc, clay, kaolin, fluorine. Lithium fluoride, calcium fluoride or the like can be used.

The bubble-forming property of the inorganic fine particles depends not only on the difference in surface tension with the polyester but also on the average particle size and cohesiveness. Typical examples of the inorganic fine particles having a bubble-forming property are calcium carbonate, barium sulfate, magnesium carbonate and the like.

On the other hand, the inorganic fine particles having no bubble-forming property mainly whiten the film due to the difference in refractive index with polyester, and typical examples thereof include titanium oxide, zinc oxide, cerium oxide and mica. For example, titanium.

These inorganic fine particles may be used alone or in combination of two or more kinds. Further, the inorganic fine particles may be in a form such as porous or hollow porous, and further, in order not to impair the effects of the present invention, surface treatment is performed in order to improve dispersibility in the resin. May be.

The average particle size of the inorganic fine particles in the present invention in the polyester is preferably 0.05 to 3 μm, more preferably 0.07 to 1 μm. If the average particle diameter is out of the above range, the inorganic fine particles may have poor uniform dispersion due to aggregation or the like, or the particles themselves may reduce the gloss or smoothness of the film surface.

The amount of the inorganic fine particles added to the white polyester layer (A) is not particularly limited, but is preferably 1 to 30% by weight, more preferably 2 to 25% by weight, and further 3 to.
A range of 20% by weight is particularly preferable. If the added amount is less than the above range, it may be difficult to improve the properties such as whiteness and hiding property (optical density) of the film, while if it is more than the above range, the gloss or smoothness of the film surface Not only tends to decrease, but also causes problems such as film breakage during stretching and powder generation during post-processing.

In the white laminated polyester film of the present invention, the white polyester layer (A) is laminated on both sides of the white polyester layer (B). The white polyester layer (B)
Needs to be a layer containing fine bubbles. That is, by containing fine air bubbles inside the polyester layer (B), an adiabatic effect against the heating of the thermal head during thermal transfer recording can be obtained, and heat can be efficiently transferred to the printed portion. Further, the cushioning property enhances the adhesion between the thermal head and the printing surface, so that the heat transfer to the printed portion becomes more uniform and more efficient.

The method of containing fine bubbles is not particularly limited. For example, a method of forming a bubble by containing a foaming agent, foaming by heating during extrusion or film formation or foaming by chemical decomposition, or gas during extrusion. Alternatively, a method of adding a vaporizable substance, a method of adding a thermoplastic resin (incompatible resin) incompatible with polyester, and uniaxially or biaxially stretching it to generate fine bubbles,
A method of adding a large amount of bubble-forming inorganic fine particles instead of the incompatible resin is generally used. Any method may be used as long as it is within the scope of the present invention, but film-forming property, easiness of adjusting the amount of bubbles contained therein, and formation of finer and more uniform-sized bubbles. It is particularly preferable to use an incompatible resin from the viewpoints of easiness and lightness.

The fine air bubbles in the present invention are those in which the film itself is provided with heat insulating properties and cushioning properties in order to improve printability. Specifically, as described above, it is contained in the white polyester layer (B). Bubbles generated by using the incompatible resin as a core are preferable.

As for the size of the bubbles, the cross section (thickness direction) of the white polyester layer (B) is measured by a scanning electron microscope (SE).
M) or a transmission electron microscope (TEM) or the like, the average value of the cross-sectional area of the bubble portion (however, excluding the incompatible resin portion which becomes the nucleus of bubble generation) is 1 to 25 μm.
² is preferable, and more preferably 1.5 to 20.
Those in the range of ² μm ² and more preferably ² to 15 μm ² are particularly preferable.

The incompatible resin referred to in the present invention is a thermoplastic resin other than polyester and is a thermoplastic resin which is incompatible with the polyester, and is dispersed in the polyester in the form of particles, The stretching has a great effect of forming bubbles in the film. More specifically, the incompatible resin referred to in the present invention is a system in which the polyester and the incompatible resin are melted by measurement by a known method using a differential scanning calorimeter (DSC) or the like, It is a thermoplastic resin in which a Tg corresponding to the incompatible resin is observed in addition to the glass transition temperature corresponding to polyester (hereinafter abbreviated as Tg). The Tg of the incompatible resin is preferably below the melting point of the polyester. The melting point of the incompatible resin is preferably lower than the melting point of polyester and higher than the temperature (heat treatment temperature) at which the film is heat-fixed and oriented during film formation.

From this point of view, examples of the incompatible resin include olefin resins such as polyethylene, polypropylene, polybutene and polymethylpentene, styrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins and fluorine resins. Resin or the like is preferably used. These may be homopolymers or copolymers, and two or more incompatible resins may be used in combination. Of these, polyolefins such as polypropylene and polymethylpentene having a small critical surface tension are preferable, and polymethylpentene is particularly preferably used.

Since polymethylpentene has a relatively large difference in surface tension with polyester and has a high melting point, it is characterized by a large effect of forming bubbles per addition amount.
It is particularly preferable as an incompatible resin.

When the white polyester layer (B) contains an incompatible resin, the content thereof is not particularly limited, but is 1 to 3.
It is preferably 5% by weight, and more preferably in the range of 3 to 20% by weight. When the addition amount is less than 1% by weight, it may be difficult to improve the whiteness and hiding property of the film, and when the addition amount is more than 35% by weight, the film tends to be broken during stretching. , Productivity may decrease.

Further, by adding a dispersant in addition to the incompatible resin to the white polyester layer (B) of the present invention, the dispersed diameter of the incompatible resin becomes small, so that the bubbles generated by stretching are made finer. This is more preferable because it is possible to improve the whiteness and film-forming property of the film as a result. As the dispersant exhibiting the above effects, an olefin-based polymer or copolymer having a polar group such as a carboxyl group or an epoxy group or a functional group reactive with polyester,
Polyalkylene glycol, a surfactant, a heat adhesive resin, etc. can be used. These may be used alone or in combination of two or more. As a method of adding these dispersants, blending with mixing with polyester, copolymerization such as random copolymerization, block copolymerization, and the like can be adopted. It may also be a partial copolymerization which is an intermediate state between the two.

The amount of the dispersant added is preferably 0.05 to 10% by weight, more preferably 0.1 to 7% by weight, and particularly preferably 0.2, in the white polyester layer (B).
~ 5% by weight. When the addition amount is less than 0.05% by weight, the effect of making bubbles finer tends to be small. On the other hand, if the amount is more than 10% by weight, the effect of adding the incompatible resin becomes small, and problems such as a decrease in whiteness and an increase in cost are likely to occur.

In the present invention, the white polyester layer (A) and / or the white polyester layer (B) is used in order to give the white laminated polyester film a higher whiteness.
It is desirable to include an optical brightener in the. A fluorescent whitening agent absorbs ultraviolet rays in sunlight or artificial light, retains the function of radiating them by converting them into visible light of purple to blue, and lowering the brightness of polymer substances by its fluorescent action. It is a compound that promotes whiteness.

The fluorescent whitening agent is not particularly limited, and for example, trade names "Ubitech" (Ciba Geigy), "OB-1" (Eastman), "TBO".
(Sumitomo Seika Co., Ltd.), “K-Call” (Nippon Soda Co., Ltd.), “Kayalite” (Nippon Kayaku Co., Ltd.), “Leukopoor” EGM (Client Japan Co., Ltd.) and the like can be used. The optical brightener may be used alone or in combination of two or more kinds in some cases. In the present invention, it is excellent in heat resistance, has good compatibility with the above-mentioned polyester, can be uniformly dispersed, and has little coloring and does not adversely affect the resin (for example, trade name "OB-1" (Eastman Co.)). Particularly preferred.

The content of the fluorescent whitening agent in the white polyester layer (A) or (B) is preferably 0.01 to 1.5% by weight, more preferably 0.03 to 1% by weight, and further 0. Those in the range of 0.05 to 0.5% by weight are particularly preferable. When the content is less than 0.01% by weight, it is difficult to obtain a sufficient whitening effect, and when the content exceeds 1.5% by weight, whiteness and light resistance are deteriorated due to deterioration of uniform dispersibility and coloring of the fluorescent whitening agent itself. Problems such as easy deterioration may occur.

The white laminated polyester film of the present invention needs to have a laminated constitution having the white polyester layer (A) on both sides of the white polyester layer (B).

In addition, the white laminated polyester film of the present invention, in which the white polyester layer (A) is laminated on both sides of the white polyester (B) to form a three-layer laminated structure, the film-forming property is further improved, It is preferable because the practicality such as the property can be improved.

In the present invention, the type of polyester used in each layer of the white polyester layer (A) and the white polyester (B) may be the same or different. For example, it is preferable that the polyester used for the white polyester layer (A) is polyethylene naphthalate and the polyester used for the white polyester layer (B) is polyethylene terephthalate, because effects such as light resistance and rigidity can be improved. In addition, it is preferable that the polyester used for the white polyester (A) is a copolyester and the polyester used for the white polyester layer (B) is a homopolyester, since the effect of improving the adhesion can be obtained.

In the present invention, the method for laminating the white polyester layer (A) and the white polyester layer (B) may be a method of forming a composite by coextrusion during melt film formation, or a method of forming the respective films separately, Any of the laminating methods may be used, but the former method is more preferable in terms of cost and the like.

When the white laminated polyester film of the present invention is used as a receiving sheet substrate for thermal transfer recording,
It may be used alone or in combination with other materials.
Examples of other materials include plain paper, high-quality paper, medium-quality paper, coated paper, art paper, cast-coated paper, resin-impregnated paper, glassine paper, laminated paper, synthetic paper, non-woven fabric, or other types. Films and the like can be used.
When the film of the present invention is attached to another material, it is preferable to attach another material to the surface opposite to the surface on which the receiving layer is provided.

The total thickness of the white laminated polyester film of the present invention is required to be in the range of 25 to 50 μm in view of whiteness and practical characteristics. In addition, when laminated with other materials, the lower limit of the thickness of the white laminated polyester film of the present invention is 25 μm from the viewpoint of handleability.
And preferably 30 μm. On the other hand, when the total film thickness exceeds 50 μm, the flexibility tends to be poor, and troubles such as paper jam in the printing machine are likely to occur. When the total film thickness exceeds 50 μm,
Since the strength is too high, the printability tends to be inferior because it is likely to be broken or wrinkled.

In the white laminated polyester film of the present invention, the total thickness of the film is in the range of 25 to 50 μm, and the white polyester layer (A) containing the inorganic fine particles is satisfied in the range of 2 μm to 5 μm. The white polyester layer (A), which is necessary and contains inorganic fine particles, preferably has a thickness of 2.5 to 4.5 μm. By satisfying the respective thicknesses of the white polyester layer within the above ranges, a white laminated polyester film having excellent whiteness, crease resistance, and printability, which is optimal for use as a receiving sheet base material for thermal transfer recording, can be obtained. Obtainable.

White polyester layer (A) containing inorganic fine particles even when the total film thickness is in the range of 25 to 50 μm.
When the thickness is less than 2 μm, the strength of the film decreases, and it becomes difficult to obtain sufficient strength as a receiving sheet. on the other hand,
When it is thicker than 5 μm, the flexibility of the film is lowered, so that the surface of the film is likely to be bent or wrinkled, and the heat insulating property is insufficient so that the printability may be lowered.

In the present invention, the difference between the white polyester layers (A) on both sides is preferably 0.5 μm or less, more preferably 0.3 μm or less, and further preferably 0.2 μm or less. The smaller the difference in thickness between the two surfaces, the more evenly the stress at the time of bending and bending can be received, and more crease resistance can be imparted.

As for the whiteness of the white laminated polyester film of the present invention, the whiteness measured from the white polyester layer (A) side is preferably 70% or more, more preferably 80% or more, further 90% or more. Is particularly preferable. When the whiteness is less than 70%, the printed image may give a dark impression.

Further, the color tone b value measured from the white polyester layer (A) side is preferably 2 or less, more preferably 1 or less, and further preferably 0 or less. When the color tone b value is larger than 2, the printed image may give an old impression. In the present invention, the optical density is preferably 0.5 or more, more preferably 0.6 or more, from the viewpoint of hiding property.

The white laminated polyester film of the present invention preferably has a glossiness of 70% or more, more preferably 75% or more, and particularly preferably 80% or more. By setting the glossiness to 70% or more, it is possible to suppress unevenness or chipping of the printed image.

In the present invention, one or both surfaces of the white polyester layer (A) may be appropriately coated.

The specific gravity of the white laminated polyester film of the present invention is preferably 0.6 or more and less than 1.2, more preferably 0.7 or more and less than 1.1. Specific gravity is 0.
If it is less than 6, a large amount of air bubbles must be included in order to reduce the specific gravity, and as a result, the film strength may decrease and film breakage may easily occur during film formation, resulting in reduced productivity. There is. Further, when the specific gravity is 1.2 or more, the cushioning property and the heat insulating property may be deteriorated to deteriorate the printability, or the whiteness of the film may be insufficient and the printed image may have a dark impression. .

The breaking strength of the white laminated polyester film of the present invention is preferably 60 MPa or more and less than 150 MPa, more preferably 90 MPa or more and 120 M or more.
It is less than Pa. If the breaking strength is less than 60 MPa, the printability may be deteriorated due to breakage or wrinkles that are likely to occur during transport in the printing machine, and film breakage may easily occur during film formation, resulting in reduced productivity. There is a nature. Further, when the breaking strength is 150 MPa or more, the flexibility is impaired, the cushioning property and the heat insulating property are deteriorated, the printability is deteriorated, and the paper jam may be caused by the folding in the printing machine.

Next, the method for producing the white laminated polyester film of the present invention will be described, but the present invention is not limited to such examples.

In a composite film forming apparatus having an extruder (a) and an extruder (a), in order to form a white polyester layer (B), dried polyester chips and, if necessary, dried incompatible resin are used. 1 to 3 incompatible resin
The mixture of 5% by weight is supplied to the extruder (a) heated to 260 to 300 ° C., melted and introduced into the T-die composite die. A dispersant may be added to this raw material in an amount of 0.05 to 10% by weight, if necessary. In addition, the incompatible resin may be added by drying a master chip beforehand.

On the other hand, as the resin used for the white polyester layer (A), polyester chips, a master chip of inorganic fine particles and a master chip of a light-proofing agent are mixed so that the amount of the inorganic fine particles is 1 to 30% by weight. , Fully vacuum dry. If necessary, an optical brightener may be added to this raw material in an amount of 0.01 to 1.5% by weight. Next, this dry raw material was heated at 260 to 300 ° C. in an extruder (a).
The polymer of the extruder (a) is laminated so that the polymer of the extruder (a) is on both surface layers (both sides) of the polymer of the extruder (a) described above. Extrusion molding is performed to obtain a molten laminated sheet.

This melt-laminated sheet was subjected to a surface temperature of 10-6.
On a drum cooled to 0 ° C., static electricity is adhered and cooled to be solidified to produce an unstretched laminated film. The unstretched laminated film is guided to a roll group heated to 70 to 120 ° C., and 2 to 5 in the longitudinal direction (longitudinal direction, that is, film advancing direction).
Double stretching and cooling with a roll group of 20 to 30 ° C.

Subsequently, the white polyester layer (A) side of the film stretched in the longitudinal direction was subjected to corona discharge treatment,
A coating liquid for forming an antistatic layer is applied to the treated surface. Hold both ends of this film with clips and guide it to the tenter 90
Stretching is performed 2 to 5 times in a direction (transverse direction) perpendicular to the longitudinal direction in an atmosphere heated to 150 ° C.

The stretching area ratio (longitudinal stretching ratio × horizontal stretching ratio) is preferably 6 to 20 times. Area magnification is 6
If it is less than twice, the whiteness and film strength of the obtained film tend to be insufficient, and conversely, if it exceeds 20 times, tearing tends to occur during stretching.

The biaxially stretched laminated film thus obtained is subjected to a heat treatment at 150 to 240 ° C. for 1 to 30 seconds in a tenter in order to complete the crystal orientation and impart flatness and dimensional stability. The white laminated polyester film of the present invention can be obtained by slowly cooling to room temperature, and then cooling to room temperature and winding.

In the heat treatment step, a relaxation treatment of 3 to 12% may be performed in the lateral direction or the longitudinal direction, if necessary.

The biaxial stretching may be either sequential stretching or simultaneous biaxial stretching, and the biaxial stretching may be followed by re-stretching in either longitudinal or transverse directions, or in both directions.

The stretching temperature and the stretching ratio can be appropriately selected according to the lamination ratio of the white polyester layer (A) and the white polyester layer (B) or the addition amount of the inorganic fine particles added to the polyester (A). preferable.

The white laminated polyester film of the present invention thus obtained is excellent in whiteness and crease resistance. A receiving sheet for heat-sensitive transfer recording using the film as a substrate has excellent printability and crease resistance. Therefore, the white polyester film of the present invention is a film having properties suitable as a receiving sheet base material for thermal transfer recording.

[Characteristic Measuring Method and Evaluation Method] The characteristic value of the present invention is based on the following evaluation method and evaluation criteria.

(1) Film Thickness The cross section of the white laminated polyester film of the present invention is a scanning electron microscope S-2100A type (manufactured by Hitachi, Ltd.).
The length of each white polyester layer in the thickness direction was measured from a cross-sectional photograph taken by magnifying and observing at 500 to 5,000 times, and the thickness of each layer was obtained by back-calculating from the magnification.
In obtaining the thickness of each layer, sectional photographs of a total of 5 locations arbitrarily selected from mutually different measurement fields of view were used, and the average value was used as the thickness of the white polyester layer.

In particular, for the white polyester layer (A), the thickness of each of the two surfaces was obtained at a total of 5 places, and the total average was calculated to obtain the thickness. Further, at that time, the difference between the laminated thicknesses of both surfaces of the white polyester layer (A) in each visual field was calculated, and the average was taken as the laminated thickness difference.

(2) Crease resistance On the surface of the white laminated polyester film of the present invention opposite to the surface on which the receiving layer is formed, a paper sheet with a pressure-sensitive adhesive having a thickness of 65 μm (label sheet for KOKUYO word processor Thailand-2110-W ) Were evenly adhered to each other to prepare a receiving sheet for evaluation of creases. The receiving sheet is cut into a length of 200 mm and a width of 20 mm, one end of which is fixed with tape, and 100 is attached to both sides of the circular core.
18 g of a receiving sheet for crease evaluation with a film surface facing inward with an iron circular core of 6 mm in diameter attached with a weight of g
After folding back at 0 degree and pulling the receiving sheet for crease evaluation at the other end at a speed of 20 mm / sec, the generation state of wrinkles on the film surface was visually observed and judged as follows. ⊚: No wrinkles, or no wrinkles with a length of 2 mm or more and wrinkles with a length of 2 mm or less within 3 pieces / cm ² . ○: no more wrinkle length 2mm, less wrinkles length 2mm are three / more than cm ² 10 pieces / cm ² within ones. X: Wrinkles with a length of 2 mm or more, or wrinkles with a length of 2 mm or less 10 pieces / cm ² or more. ⊚ and ∘ are practical.

(3) Specific gravity The white laminated polyester film of the present invention is 50 mm × 6.
The sample obtained by cutting to a size of 0 mm was measured using a high-precision electronic hydrometer SD-120L (manufactured by Mirage Trading Co., Ltd.) according to the method A (underwater substitution method) of JIS K-7112. The measurement was performed at a temperature of 23 ° C. and a relative humidity of 65.
% Conditions.

(4) Whiteness From the white polyester layer (A) side of the white laminated polyester film of the present invention, using a spectroscopic color difference meter SE-2000 type (manufactured by Nippon Denshoku Industries Co., Ltd.), JIS Z-8722 is obtained. Under the following optical conditions, the tristimulus values of color, X value, Y value,
The Z value was measured, and the whiteness was calculated by the following formula: whiteness (%) = 4 × 0.847 × Z value−3 × Y value.

(5) Hiding power The optical density (OD) was determined, and the optical density was measured using an optical densitometer TR927 (manufactured by Macbeth). The larger the measured value, the higher the hiding power.

(6) Breaking strength Ten strip-shaped samples, each having a length of 18 cm and a width of 1 cm, were taken in the lengthwise and widthwise directions of the white laminated polyester film of the present invention. Tensilon tensile tester AMF / RTA100 manufactured by Toyo Sokki Co., Ltd.
Then, the test piece is gripped at a test length of 10 cm and pulled at a speed of 30 cm / min, and the load-elongation relationship is recorded. The value of the strength at the time of sample breakage was obtained from the recording, and was expressed as the average of 10 samples in each direction.

(7) Transportability A coating solution for forming a receiving layer described below was coated on the white laminated polyester film of the present invention by a gravure coater, and then 120 ° C.
After drying for 1 minute, a receiving sheet for thermal transfer recording having a receiving layer thickness of 0.1 μm was obtained.

Next, a color printer Professional Col
or Point 2 (manufactured by Seiko Denshi Kogyo Co., Ltd.) and a dedicated CH705 (Yellow, Magenta, Cyan: manufactured by Seiko Eye Supply Co., Ltd.) is used as an ink ribbon to print a test pattern. The transportability of the receiving sheet was evaluated according to the following four grades. ○ The above was judged to be good. ⊚: Can be transported without problems and has no wrinkles. ◯: Paper that could be conveyed, but had small wrinkles of less than 1 mm on the receiving paper. Δ: The paper which can be conveyed but has large wrinkles of 1 mm or more, or small wrinkles of less than 1 mm are conspicuous. X: A piece that could be conveyed but was broken, or one that could not be conveyed and was jammed.

(8) Printability The following receiving layer-forming coating liquid was applied to the white laminated polyester film of the present invention by a gravure coater, and then 120
After drying at 0 ° C. for 1 minute, a receptive sheet for thermal transfer recording having a receptive layer thickness of 0.1 μm was obtained.

Receptor layer forming coating liquid: Urethane-modified polyethylene water dispersion (urethane modification ratio = 20% by weight, emulsified by heating in aqueous ammonia solution to obtain water dispersion) was diluted with water to obtain a solid content. The concentration is 3%.

Next, as a color printer, Profession
Using al Color Point 2 (manufactured by Seiko Denshi Kogyo Co., Ltd.), a dedicated CH705 (yellow,
Magenta, Cyan: Seiko Eye Supply Co., Ltd.
Test pattern of 8 gradations was printed on the receiving layer forming surface of the receiving sheet. Next, the printed test pattern was evaluated for print density, print dot shape, and image sharpness by the following methods to determine printability.
The print density was obtained from the optical density (reflection density) in the reflection method. That is, the optical densitometer TR for the magenta part
The reflection density was measured using 927 (manufactured by Macbeth) and 5
The following four-level evaluation was performed from the average value of the reflection density measured twice. ○ The above was judged to be good. ⊚: 0.13 ≦ ODmin and 0.85 ≦ ODmax ◯: 0.1 ≦ ODmin <0.13 and 0.7 ≦ ODmax <0.85 Δ: 0.07 ≦ ODmin <0.1, And 0.5 ≦ ODmax <0.7 ×: ODmin <0.07, and ODmax <0.5, where ODmin and ODmax respectively represent the reflection density of the printed portion of the lowest gradation and the highest gradation. .

The dot shape is yellow on the printing surface,
The magenta and cyan portions of each of the three colors were magnified 100 to 300 times and observed using a reflection optical microscope, and the following four-stage evaluation was performed on the shape of the printed dots. ○ The above was judged to be good. ⊚: All three colors have a clean circular shape and are extremely good. ◯: Good although there was a slight “chip”. Δ: “Chipped” and “crushed” are seen. Or the dots are small. X: "Chipped" and "crushed" are remarkable. Or the dots are extremely small.

[0076]

EXAMPLES The present invention will be described with reference to the following examples and comparative examples, but the present invention is not limited thereto.

Example 1 In a composite film-forming apparatus having an extruder (a) and an extruder (a), polyethylene terephthalate (hereinafter referred to as PET) chips were averaged to form a white polyester layer (A). A raw material containing 7% by weight of anatase-type titanium oxide fine particles having a particle diameter of 0.2 μm and 0.2% by weight of a fluorescent whitening agent was dried at 180 ° C. for 3 hours, and then supplied to the extruder (A) side, and 285 It was melted at ℃ and introduced into a T-die composite die.

On the other hand, in order to form the white polyester layer (B), 10.5% by weight of polymethylpentene (hereinafter referred to as PMP) was added to the PET chip, and polyethylene glycol having a molecular weight of 4000 (hereinafter referred to as a dispersant) was used. , PEG) of 1.2% by weight was dried at 180 ° C. for 3 hours, then supplied to the extruder (a) side, melted at 285 ° C., and introduced into a T-die composite die.

Then, the white polyester layer (A) was merged in the die so as to be laminated on both surface layers of the white polyester layer (B), and then coextruded into a sheet to obtain a melt-laminated sheet. The molten laminated sheet was contact-cooled and solidified by an electrostatic charge method on a cooling drum whose surface temperature was kept at 25 ° C. to obtain an unstretched laminated film. Then, the unstretched laminated film was stretched 2.9 times in the longitudinal direction (longitudinal direction) using a roll group heated to 95 ° C. according to a conventional method, and cooled with a roll group at 25 ° C. to obtain a uniaxially stretched film. did.

Further, the uniaxially stretched film was subjected to corona discharge treatment in air, and the treated surface was coated with the following antistatic layer-forming coating liquid by a bar coating method using a metering bar. While guiding both ends of the coated uniaxially stretched film with clips, the uniaxially stretched film is guided to a preheating zone in the tenter.
After preheating and drying at 0 ° C., the film was continuously stretched 3.4 times in a heating zone at 125 ° C. in a direction perpendicular to the longitudinal direction (width direction).

Further, in the heat treatment zone in the tenter, 21
A polyester having a thickness of 31 μm in which a white polyester layer (A) has a thickness of 2.5 μm on one side and a white polyester layer (B) has a thickness of 26 μm. A white laminated polyester film in which an antistatic layer having a thickness of 0.11 μm was provided on the film was obtained.

The characteristics of the white laminated polyester film thus obtained are as shown in Table 1, and it is understood that the whiteness is excellent. In addition, the printability and the crease resistance are at a high level, and it can be seen that it is excellent as a receiving sheet base material for thermal transfer recording.

Example 2 The film thickness of Example 1 was 2.5 μm on one side for the white polyester layer (A) and 34 μm for the white polyester layer (B).
A white laminated polyester film was obtained in the same manner as in Example 1 except that the thickness was 39 μm. The properties of this film are as shown in Table 1, and were excellent in each property, and particularly excellent in transportability.

Example 3 The film thickness of Example 1 was changed to 3.4 μm on one side for the white polyester layer (A) and 33.2 for the white polyester layer (B).
Example 1 except that a thickness of 40 μm was used.
A white laminated polyester film was obtained by the same method as described above.
The properties of this film are as shown in Table 1 and were excellent in each property, particularly in transportability and printability.

Example 4 The film thickness of Example 1 was set such that the white polyester layer (A) was 4.0 μm on one side and the white polyester layer (B) was 34 μm.
A white laminated polyester film was obtained in the same manner as in Example 1 except that the thickness was 42 μm. The properties of this film are as shown in Table 1 and were excellent in each property.

Example 5 The film thickness of Example 1 was 3.8 μm on one side for the white polyester layer (A) and 40.4 for the white polyester layer (B).
Example 1 except that a thickness of 48 μm was adopted.
A white laminated polyester film was obtained by the same method as described above.
The properties of this film are as shown in Table 1, and were excellent in each property, and particularly excellent in transportability and crease resistance.

Comparative Example 1 The film thickness of Example 1 was 1.7 μm on one side for the white polyester layer (A) and 37.6 for the white polyester layer (B).
Example 1 except that a thickness of 41 μm was used.
A white laminated polyester film was obtained by the same method as described above.
The properties were inferior in crease resistance and whiteness as shown in Table 1.

Comparative Example 2 The same method as in Example 1 except that the film thickness of Example 1 was 43 μm in which the white polyester layer (A) was 6 μm on one side and the white polyester layer (B) was 31 μm. Thus, a white laminated polyester film was obtained. The characteristics of this film are as shown in Table 1, and the crease resistance was relatively poor and the printability was particularly poor.

Comparative Example 3 The film thickness of Example 1 was 2.9 μm on one side for the white polyester layer (A) and 17.2 for the white polyester layer (B).
Example 1 except that the thickness was set to 23 μm.
A white laminated polyester film was obtained by the same method as described above.
The properties of this film are as shown in Table 1, the whiteness was poor, and the other properties were relatively low.

Comparative Example 4 The same method as in Example 1 except that the film thickness of Example 1 was 59 μm in which the white polyester layer (A) was 3 μm on one side and the white polyester layer (B) was 53 μm. Thus, a white laminated polyester film was obtained. The characteristics of this film are as shown in Table 1, and the crease resistance and the printability were relatively low, and the transportability was poor.

Comparative Example 5 The white polyester layer (A) had a film thickness of 1.5 μm on one side and the white polyester layer (B) had a film thickness of 58 μm.
A white laminated polyester film was obtained in the same manner as in Example 1 except that the thickness was 61 μm. The characteristics of this film are as shown in Table 1, and the whiteness and printability were relatively low, and the transportability and crease resistance were poor.

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[Table 1]

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The white laminated polyester film of the present invention is a film excellent in whiteness, crease resistance and printability, and can be suitably used particularly as a receiving sheet base material for thermal transfer recording. .

Continued front page    F-term (reference) 2H111 AA01 AA05 AA26 AA27 CA25                 4F074 AA16 AA66 CA03 CA04 CC02Y                       CC04Y CC05Z DA20 DA23                       DA52                 4F100 AA00B AA00H AA21B AA21H                       AK01A AK03A AK41A AK41B                       AK42B AL05A BA03 BA06                       BA10B BA16 DE01B DE01H                       DJ00A DJ06A GB90 HB00A                       HB00B JA20 JA20B JB16A                       JL05 JL10A JL10B JN21                       JN30 YY00 YY00B

Claims (6)

[Claims] 1. A white polyester layer (A) containing inorganic fine particles is laminated on both sides of a white polyester layer (B) containing fine bubbles, and the total film thickness is 25 μm or more and 50 μm or less and contains inorganic fine particles. A white laminated polyester film having a white polyester layer (A) of 2 μm or more and 5 μm or less. 2. The white laminated polyester film according to claim 1, wherein the white polyester layers (A) on both sides have a thickness difference of 0.5 μm or less. 3. The white laminated polyester film according to claim 1, which has a whiteness of 70% or more, an optical density of 0.5 or more, and a glossiness of 70% or more. . 4. The white polyester layer (A) contains inorganic fine particles in an amount of 1 to 30% by weight.
The white laminated polyester film according to claim 3. 5. The white laminated polyester film according to claim 1, wherein the white polyester layer (B) contains a thermoplastic resin which is incompatible with the polyester. 6. The white laminated polyester film according to claim 5, wherein the thermoplastic resin incompatible with the polyester is polyolefin.