JPH1160766A - Fine foam-containing polyester film and release paper for seal print - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film for simultaneously satisfying adhesiveness to a coated layer such as a silicon-coated layer, etc., and transporting properties during paper feed, comprising two kinds of films having glossiness on the surface in specific ranges, respectively. SOLUTION: A polyester composition containing 8.0-25 wt.%, preferably 10-20 wt.% of a thermoplastic resin such as a polypropylene, etc., incompatible with a polyester (one obtained from an aromatic dicarboxylic acid or its ester and a glycol as main starting raw materials, for example, comprising >=80% repeating structural unit composed of ethylene terephthalate unit or ethylene-2,6- naphthalate unit) is drawn in at least one direction to give the objective fine foam-containing polyester film having >=33% glossiness GC on the surface of one film and 25±7% glossiness GA on the surface of the other film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microbubble-containing polyester film and a release paper for seal printing comprising the film.

[0002]

2. Description of the Related Art Biaxially oriented polyester films are widely used as industrial materials because they have various properties in a highly balanced manner and are excellent in cost performance. Among the polyester films, the polyester film containing incompatible thermoplastic resin is made into a polyester film, and the fine bubble-containing polyester film is a white opaque film that is lightweight and has cushioning properties. It is used for applications such as synthetic paper such as release paper for printing, and magnetic cards. In particular, the demand for release paper for sticker printing is increasing, but the sheet of the seal print, in which the image receiving paper and release paper are integrated, is not conveyed as a single sheet when fed to the printer, but is multi-fed. There is a problem of being done. Further, the fine bubble-containing polyester film is inferior in adhesiveness to a silicon coat, and therefore, improvement is required.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester film containing fine bubbles, which simultaneously satisfies the adhesiveness with a coating layer such as a silicon coat and the transportability during paper feeding. It is.

[0004]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by adopting a specific configuration, and have completed the present invention. Was. That is, the gist of the present invention is:
Gloss G _C of one film surface is 33% or more,
It consists in fine-bubble-containing polyester film and the sticker for release paper comprising the same, wherein the gloss G _A of the other film surface is 25 ± 7%.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The polyester constituting the film of the present invention is, for example, a polyester obtained by using an aromatic dicarboxylic acid or an ester thereof and a glycol as a main starting material, and 80% or more of the repeating structural units are ethylene terephthalate units or ethylene-2, Refers to a polyester having 6-naphthalate units. Then, other conditions may be contained as long as the conditions do not deviate from the above range.

As the aromatic dicarboxylic acid component, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid,
For example, one or two or more of isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid, etc.) can be used. As the glycol component, in addition to ethylene glycol, for example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like can be used.

In producing the polyester film containing fine bubbles of the present invention, a method of stretching a polyester containing an incompatible thermoplastic resin in at least a uniaxial direction is preferably used. In this case, the content An of the thermoplastic resin incompatible with the polyester is usually 8.0 to 25 as a ratio to the total amount with the polyester.
%, Preferably in the range of 10 to 20% by weight.
When An is less than 8.0% by weight, the amount of air bubbles formed in the film is too small, so that it is not possible to impart sufficient lightness and cushioning properties, which are features of the polyester film containing fine cells. And it tends to be difficult to adjust the glossiness of both sides of the film to a desired range. On the other hand, when An exceeds 25% by weight, the mechanical strength and thermal stability of the film tend to be poor, and the roughness of the film surface may be too large. Similarly, it tends to be difficult to adjust the film gloss to a desired range. Such a film may be unsuitable for applications such as release paper which require a high texture and a high adhesiveness of a coating agent such as a silicone coat.
If An exceeds 25% by weight, productivity problems such as frequent film breakage during stretching may occur.

Specific examples of thermoplastic resins incompatible with polyester include polyolefins such as polyethylene, polypropylene, polymethylpentene, and polymethylbutene, as well as polystyrene, polycarbonate, polyphenylene sulfide, and liquid crystal polyester.
Among these, polypropylene, polymethylpentene, and polystyrene are preferable from the viewpoint of cost and productivity,
More preferably, it is polypropylene. In the following description, a thermoplastic resin incompatible with polyester is represented by polypropylene.

The above-mentioned polypropylene is usually 95
Crystalline polypropylene homopolymers having at least mol%, preferably at least 98 mol%, of propylene units are preferred. In the case of amorphous polypropylene, the polypropylene may bleed out on the surface of the unoriented polyester sheet in the film production process, and the surfaces of the cooling drum, the stretching roll, and the like may be contaminated. In addition, when polypropylene other than propylene units, for example, a polypropylene copolymerized with more than 5 mol% of ethylene units is used, the generation of fine bubbles tends to be insufficient.

The above polypropylene usually has a melt flow index (MFI) of 0.5 to 30 g / 10 min.
Preferably it is selected from the range of 1.0 to 15 g / 10 minutes. When the MFI is less than 0.5 g / 10 min, the generated bubbles tend to be too large, and breakage tends to occur during stretching. When the MFI exceeds 30 g / 10 min, the uniformity of the film density over time And the productivity may deteriorate in the production line.

The glossiness of the polyester film containing fine bubbles of the present invention can be represented by the method 3 (60 ° glossiness) of JIS Z 8741-1983, and the glossiness G _C of one film surface is 33% or more. There, it is necessary that the gloss G _a of the other film surface is 25 ± 7%. If G _C is less than 33%, the adhesion between the film substrate and the coating layer becomes insufficient when a coating layer such as a silicon coat is provided. A preferred range of G _C is 40 ± 7%
And more preferably 40 ± 5%.

[0012] When G _A is less than 18%, it unduly the roughness of the film surface, thereby impairing the feel when used as a product such as a sticker. Meanwhile G _A 32%
Is exceeded, when printed sheets such as sticker prints (integrated with image receiving paper and release paper) are formed due to their smoothness, the problem of so-called double feed, in which single sheets are not fed, is likely to occur. The preferred range of G _A is 25 ± 5%, even more preferably 25 ± 3%.

For the above reasons, when the fine bubble-containing polyester film of the present invention is used as a release paper for a seal print, its high gloss surface is coated with a silicone coat (release layer).
It is preferred that the low glossy surface be the back surface of the integrated sheet. A print coat, a back coat (back coating layer), or the like can be applied to the low gloss surface as needed.

The inherent viscosity I of the polyester film constituting the fine-bubble-containing polyester film of the present invention at the film stage I
VA is preferably in the range of 0.45 to 0.70. When the intrinsic viscosity is less than 0.45, the film tends to be easily broken at the time of film formation, and the size of the bubbles becomes non-uniform, and it becomes difficult to control the density. . On the other hand, when the intrinsic viscosity is 0.7
If it exceeds 0, the generation of fine bubbles tends to decrease.

The density of the film of the present invention is usually 0.70
~ 1.25g / cm^Three , Preferably 0.80 to 1.20
g / cm^Three , More preferably 0.90 to 1.15 g /
cm ^Three Range. 1.30g / cm film density
^Three Is greater than one of the characteristics of the film of the present invention.
Cushioning properties tend to be impaired. Meanwhile, Phil
0.70g / cm^Three If less than the film
It tends to have poor mechanical strength and thermal stability,
The continuity of production may be adversely affected.

The surface roughness Ra of the film of the present invention is usually 0.05 μm or more, preferably 0.08 to 0.4.
0 μm, and more preferably 0.10 to 0.30 μm. When Ra is smaller than 0.05 μm, the properties are different from the paper-like texture unique to the fine bubble-containing film. The film of the present invention is preferably white and has a high degree of concealment from the viewpoint of imparting a high-grade feel to the product, particularly when used as a release paper for seal printing or an image receiving paper.

The film of the present invention may contain titanium dioxide, barium sulfate, and other white pigments for imparting whiteness and hiding properties. In order to further increase the whiteness, it is effective to add a fluorescent whitening agent.
Two or more kinds of white pigments can be contained, but in that case, it is preferable to contain at least titanium dioxide or barium sulfate.

The content of the white pigment in the total raw material is 0.5 to
20% by weight, preferably in the range of 1.0 to 15% by weight. Examples of fluorescent brighteners that can be suitably used include "Ubitek" manufactured by Ciba-Geigy and "OB1" manufactured by Eastman. The preferred content of the optical brightener in the total raw materials is in the range of 0 to 0.30% by weight.

The hiding degree of the film of the present invention is usually 0.3
Or more, preferably 0.5 or more. If the degree of concealment is less than 0.3, the light-shielding property of the film is insufficient, and the value as release paper for seal print or image receiving paper is reduced.
The whiteness of the film of the present invention is determined according to JIS L101.
It can be represented by a W value according to the C method of 5-1981. The film W value is usually 70 or more, preferably 80 or more. If the W value is smaller than 70, color modulation tends to impair the high-grade appearance of the release paper for seal printing or the image receiving paper.

In the present invention, in addition to the white pigment and the fluorescent whitening agent in the polyester and / or polypropylene, if necessary, a known antioxidant,
Additives such as heat stabilizers, antistatic agents, dyes, pigments, and surfactants can be added. On both sides of the film of the present invention, a silicon coat (release layer), a back coat (back coating layer) and the like can be applied. In order to enhance the adhesion between the film and the coat layer, various primer coating layers are provided. be able to. The primer layer may be applied during the film manufacturing process, or may be applied after the film is manufactured.

Examples of the water-soluble or water-dispersible polyester resin used for the primer layer include JP-B-47-40.
873, JP-A-50-83497, JP-A-50-121336, JP-A-52-155640
The polyesters known in Japanese Patent Application Laid-Open Publication No. H10-163, etc. can be used. Here, the dicarboxylic acid component of the polyester includes, as examples of aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 2,5-naphthalenedicarboxylic acid and ester-forming derivatives thereof, and the like.As examples of aliphatic dicarboxylic acids, Oxybenzoic acid and its ester-forming derivatives are exemplified.

As the glycol component of the ester, aliphatic, alicyclic, aromatic diols and the like can be used. Examples thereof include ethylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, 1,4- Cyclohexane dimethanol, p-xylene diol and the like, and poly (oxyalkylene)
Examples of glycols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like.

As the polyester, not only the saturated linear polyester comprising the above-mentioned ester-forming component but also 3
A polyester comprising a compound having an ester-forming component of a valency or lower or a polyester having a reactive unsaturated group can also be used. Examples of the water-soluble or water-dispersible polyurethane resin used for the primer layer include JP-B-42-24194, JP-B-46-7720, JP-B-46-10193, and JP-B-49-37.
839, JP-A-50-123197, JP-A-53-126058, JP-A-54-13809
For example, a polyurethane-based resin described in Japanese Patent Publication No. 8 or the like can be used. The main components of the polyurethane-forming component are a polyisocyanate, a polyol, a chain extender, a crosslinking agent and the like.

Examples of polyisocyanates include tolylene diisocyanate, phenylene diisocyanate,
4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate and the like. Examples of polyols include polyoxyethylene glycol, polyoxypropylene glycol, polyethers such as polyoxytetramethylene glycol, polyethylene adipate, polyethylene-butylene adipate, polyesters such as polycaprolactone, acrylic polyols, castor oil, and the like. There is.

Examples of the chain extender or crosslinking agent include ethylene glycol, propylene glycol, butanediol, diethylene glycol, trimethylolpropane, hydrazine, ethylenediamine, diethylenetriamine, 4,4'-diaminodiphenylmethane,
4'-diaminodicyclohexylmethane, water and the like. As the polyurethane resin, a molecular weight of 300 to 2
Preferred is a resin comprising a compound having at least one 0000 polyol, polyisocyanate, a chain extender having a reactive hydrogen atom, a group that reacts with an isocyanate group, and at least one anionic group.

The anionic group in the polyurethane resin is
It is used as a lithium salt, sodium salt, potassium salt, or magnesium salt such as -SO ₃ H, -OSO ₃ H, and -COOH. Of these, sulfonate groups are particularly preferred. Examples of the melamine-based cross-linking agent used in the primer layer include methoxymethylated melamine, butoxymethylated melamine and the like, which are alkylol- or alkoxyrolled melamine-based compounds. Can be used. The epoxy crosslinking agent used in the present invention may be water-soluble or 50% water-soluble.
Any compound having the above epoxy group may be used.

The addition of the crosslinking agent improves the fixation, water resistance, solvent resistance and mechanical strength of the coating layer. As a result, after the application of the overcoat layer, the adhesion to the overcoat layer is improved. In particular, the melamine-based crosslinking agent has a high curing rate, and is more effective when used together with a curing catalyst such as a protonic acid or its ammonium salt. The amount of the curing agent used is preferably from 0.1 to 60% by weight based on the dry solid content of the coating film.

As a method of applying the coating agent to be used as the primer layer to the polyester film containing fine bubbles, any known coating method can be applied. For example, the rod coat method,
A roll coating method, a gravure coating method, a roll brushing method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method, or the like can be applied alone or in combination.

The coating may be performed on one side or both sides. In the case of double-sided coating, for example, a silicon coat (release layer)
It is preferable that two layers such as a back coat (back coating layer) can be easily provided on the opposite surface. In the step of applying the primer layer, it is preferable to apply the polyester layer to the microbubble-containing polyester film before the completion of the crystal orientation. The fine-bubble-containing polyester film before the completion of the crystal orientation is defined as an unstretched film that has been extruded in the form of a sheet from a die of a melt extruder onto a rotary cooling drum and cooled and solidified, and the unstretched film is stretched in the longitudinal or transverse direction. And a biaxially stretched film that has been stretched in a direction perpendicular to the stretching direction of the uniaxially stretched film and has not yet undergone orientation crystallization by heat setting. Among them, a method of applying a coating solution to a uniaxially stretched film and drying the coating solution while the polyester film containing fine bubbles is laterally stretched and heat-set by a tenter is preferable.

The solid content concentration of the above coating agent is usually 30% by weight or less, preferably 15% by weight or less. The coating amount is preferably 0.5 to 20 g / m ² , more preferably 1 to 10 g / m ² . The coating agent for the primer layer of the microbubble-containing polyester film of the present invention may include, if necessary, a coating improver, a thickener, a lubricant, polymer particles, inorganic particles, pigments, dyes, antioxidants, and ultraviolet absorbers. Agent, infrared absorber,
An antistatic agent, an antifoaming agent, a foaming agent and the like can be contained. Further, since the coating liquid uses water as a medium, an emulsion such as a water-soluble resin such as gelatin or polyvinyl alcohol, or an emulsion such as a vinyl resin or an epoxy resin can be added to the coating liquid as needed.

In the production of the film of the present invention, a method in which a polymer compounded in a predetermined manner is melted and extruded, and then stretched in at least one axial direction according to a roll stretching method, a tenter method or the like is preferably used. However, a biaxial stretching method and a heat treatment method are usually used in combination in order to form fine bubbles well and appropriately satisfy film strength and dimensional stability.

Hereinafter, in the production of the film of the present invention,
An example in which biaxial stretching is used will be described in detail. The film can be composed of a single raw material (single-layer film) or composed of multiple layers (laminated film)
May be. First, the raw material of the compound for each layer is supplied to an extruder corresponding to each layer, melt-kneaded for each extruder line, and extruded from a die as a molten sheet. When forming a laminated sheet, the polymer of each layer is guided to a die usually through a multi-manifold or a feed block.

Next, the molten sheet extruded from the die is rapidly cooled and solidified on a rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature, to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness and cooling effect of the sheet, it is necessary to increase the adhesion between the sheet and the rotary cooling drum, and in the present invention, the electrostatic application adhesion method is preferably employed.

Next, the obtained sheet is biaxially stretched to form a film. Microbubbles in the polyester film containing the incompatible thermoplastic resin are generated by such stretching. First, a stretching temperature of usually 70 to 150 ° C, preferably 75 to 130 ° C, usually 2.5 to 6.0 times,
Preferably, the unstretched sheet is stretched in one direction (longitudinal direction) under a stretch ratio of preferably 3.0 to 5.0 times. For this stretching, a roll and tenter type stretching machine can be used. Then usually 75 to 150 ° C, preferably 8
Under the conditions of a stretching temperature of 0 to 140 ° C. and a stretching ratio of usually 2.5 to 6.0 times, preferably 3.0 to 5.0 times, the film is stretched in a direction (horizontal direction) orthogonal to the first stage. Obtain an axially oriented film. For such stretching, a tenter-type stretching machine can be used.

A method in which the above-described unidirectional stretching is performed in two or more stages can be adopted, but also in this case, it is preferable that the final stretching ratio falls within the above range. The unstretched sheet can be simultaneously biaxially stretched so that the area magnification becomes 6.25 to 36 times. Heat treatment is 15
Perform at 0 to 250 ° C. for 1 second to 5 minutes under 30% elongation, limited shrinkage or constant length. After biaxial stretching, 110 ° C
After performing re-stretching by 1.05 to 2.0 times in the longitudinal direction at a temperature of about 180 ° C., a heat treatment may be employed. At this time, it is also possible to appropriately employ a technique such as heat setting before re-longitudinal stretching, longitudinal relaxation after re-longitudinal stretching, or micro-magnification longitudinal stretching before or after re-longitudinal stretching. In addition, re-stretching may be similarly performed in the lateral direction. Further, various surface treatments or the like may be performed in the film forming process as needed.

For example, by employing the method described above,
Although the film of the present invention can be produced, the thickness of the film is usually 20 to 250 μm, preferably 40 to 250 μm.
２００200 μm. In addition, taking advantage of its features, release paper for sticker printing, image receiving paper for printers, labels,
It is suitably used for recording paper, posters, planographic printing plates, packaging materials, sticky notes, and the like.

[0037]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In addition, the evaluation method in an Example and a comparative example is as showing below. Also,
In the Examples and Comparative Examples, all “parts” in the component ratios mean “parts by weight”, and the silicone-based surfactant is “SH193” manufactured by Toray Silicone Co., Ltd. (1) Intrinsic viscosity of polyester [η] (dl / g) Phenol / tetrachloroethane: 50/50 (weight ratio) is mixed with 1 g of polyester from which other polymer components incompatible with polyester and white pigment have been removed. The solvent was added and dissolved at a ratio of 100 ml, and measured at 30 ° C. (2) Melt flow index MFI
(G / 10 min) Measured according to JIS K-6758-1981. The higher this value, the lower the melt viscosity of the polymer. (3) Average particle size of white pigment Centrifugal sedimentation type particle size distribution analyzer (SA-CP manufactured by Shimadzu Corporation)
Integrated volume fraction 5 in equivalent spherical distribution measured by type 3)
The particle size of 0% was defined as the average particle size. (4) Glossiness Method 3 according to JIS Z-8741-1983 using a variable-angle gloss meter VGS-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.
(60 ° gloss), the light incidence was measured in the MD direction. The average value was calculated assuming that the number of measurements on each surface was 3, and the result was defined as the glossiness. (5) Film density (g / cm ³ ) A 10 cm × 10 cm square sample was cut out from an arbitrary portion of the film, and the weight was measured. Next, the thickness was measured at any nine locations using a micrometer, and the weight per unit volume was calculated from the average value and the weight. The number of measurements was 5, and the average value was taken as the film density. (6) Center line average surface roughness Ra Measured using a universal surface profile measuring instrument SE-3F manufactured by Kosaka Laboratory. One side (cast side) of sample under the following conditions
Was measured 12 times, and the average value of 10 points excluding the upper and lower two points was taken.

・ Diameter of stylus tip: 2 μm ・ Measurement force: 0.03 gf ・ Measuring length: 2.5 mm ・ Cutoff value: 0.08 mm (7) Occlusion degree Visual light using Macbeth densitometer TD-904 Was measured. The number of measurement points was 5. The larger the value, the lower the light transmittance. (8) Whiteness (W value) The whiteness (W value) was measured by a method C of JISL1015-1981 using a colorimeter 300A type (C light source: 2 ° visual field) manufactured by Nippon Denshoku Industries Co., Ltd. The number of measurements was set to 5, and the average value on both sides of the film was defined as whiteness. (9) Evaluation of suitability for feeding to printing machine The film was cut into A4 size sheets, 30 of which were stacked and mounted on the manual feed port of Ricoh's Imagio DA355 copier. It was confirmed.

○: 30 sheets are fed, and no double feed has been performed. (Good transportability) Δ: 30 sheets were fed once or twice. X: 30 sheets were fed three times or more. (Poor transportability) (10) Adhesion evaluation of silicon coat (high gloss surface of film) Curable silicone resin (KS-77 manufactured by Shin-Etsu Chemical Co., Ltd.)
9) 100 parts by weight, curing agent (CAT manufactured by Shin-Etsu Chemical Co., Ltd.)
PL-8) A coating liquid comprising 1 part by weight and 2,200 parts by weight of a mixed solvent of methyl ethyl ketone / toluene was prepared. This coating solution was applied off-line to the high gloss side of the film by a roll coating method so as to have a coating thickness of 0.1 μm after curing to form a cured silicone resin film. After leaving this sample in a room at 23 ° C./50% RH for 30 days,
The coated surface was rubbed with a fingertip several times, and the degree of detachment of the cured silicone film was judged according to the following evaluation criteria, and used as a measure of adhesion.

：: No drop-off (good adhesion) ×: Drop-off (poor adhesion) (11) Evaluation of tactile sensation of the film × ○ indicates that the release paper for seal printing is considered to be a suitable product.

The method for producing the raw material polyester used in the examples is as follows. <Production of polyester resin> 33.7 parts of dimethyl terephthalate, 20.0 parts of dimethyl isophthalate, 3-
A mixture of 9.1 parts of sodiosulfodimethylisophthalate, 40 parts of ethylene glycol, 10 parts of diethylene glycol, and 0.047 parts of calcium acetate monohydrate was mixed with 200 to 2 parts.
The transesterification was carried out at 30 ° C. until the theoretical amount of methanol had distilled off.

Next, 0.09 parts of orthophosphoric acid and 0.025 parts of antimony trioxide were further added, and polymerization was carried out at 280 ° C. under reduced pressure. The specific viscosity of the polymer thus obtained is
1.53. <Production of Polyurethane Resin> Polyether containing sulfonate group obtained by sulfonating polyether of ethylene oxide extracted from allyl alcohol with sodium metabisulfite (SO ₃ content: 8.3% by weight, polyethylene oxide content: 83% by weight) 192 parts, 1013 parts of polytetramethylene adipate (molecular weight: 2250), and 248 parts of polypropylene oxide polyether (molecular weight: 550) started with bisphenol A were mixed under vacuum,
Dehydrate at ℃. The mixture was heated to 70 ° C., and 178 parts of isophorone diisocyanate and hexamethylene-1,
A mixture with 244 parts of 6-diisocyanate is added, and the resulting mixture is then stirred at a temperature in the range from 80 ° C. to 90 ° C. until the isocyanate content is 5.6% by weight.

The prepolymer is cooled to 60 ° C., and 56 parts of biuret polyisocyanate obtained from 3 moles of hexamethylene diisocyanate and 1 mole of water, and 175 parts of bisketimine obtained from isophoronediamine and acetone are sequentially added. Water preheated to 50 ° C., in which 15 parts of hydrazine hydrate are dissolved, is added to this mixture with vigorous stirring. Thus, an aqueous polyurethane dispersion was obtained. <Adjustment of coating agent for primer layer> 25 parts of the polyester resin, 65 parts of the polyurethane resin, and 10 parts of methoxymethylated melamine were weighed, and an aqueous dispersion having a total solid content of 10% by weight was prepared. did.

Example 1 13% by weight of a crystalline polypropylene chip having an MFI of 10 g / 10 minutes based on a polyethylene terephthalate chip having an intrinsic viscosity of 0.69, and 2.5% by weight of titanium oxide having an average particle diameter of 0.3 μm %, Optical brightener OB1 0.05% by weight
After blending with 0.1% by weight of a silicone-based surfactant, the mixture was uniformly blended to prepare a polyester raw material X.

After the above raw material X was charged into an extruder,
The obtained melt was guided to a T-die, extruded in a slit shape, and cooled on a cast roll at 30 ° C. to obtain an unoriented sheet. And the film flow direction (vertical direction)
The film was roll-stretched 3.82 times at 82 ° C., and a primer layer coating agent was applied to both sides of the obtained uniaxially stretched film to a thickness of 5 μm. Next, the film was stretched 3.8 times in the transverse direction at 125 ° C., and further heat-treated at 230 ° C. for 5 seconds in a tenter stretching machine to finally obtain a biaxially oriented film having a thickness of 100 μm and containing fine bubbles.

The obtained film had excellent silicone coat adhesion and good paper feeding (conveyance) to a copying machine. Example 2 A biaxially oriented film containing fine bubbles was obtained in the same manner as in Example 1 except that the coating was not performed on both surfaces of the film.

Comparative Example 1 A biaxially oriented film containing fine bubbles was obtained in the same manner as in Example 1 except that the amount of the crystalline polypropylene chips was changed to 7.8% by weight. Comparative Example 2 In Example 1, a biaxially oriented film containing fine bubbles was obtained in the same manner as in Example 1 except that the amount of the crystalline polypropylene chips was changed to 7.8% by weight and coating was not performed on both surfaces of the film. .

Comparative Example 3 A biaxially oriented film containing fine bubbles was obtained in the same manner as in Example 1 except that the amount of the crystalline polypropylene chips was changed to 26% by weight. The results obtained above are shown in Table 1 below.

[0049]

[Table 1]

[0050]

According to the present invention, it is possible to provide a fine-bubble-containing polyester film that simultaneously satisfies the adhesiveness with a coating layer such as a silicon coat and the transportability during paper feeding. And the industrial value of the present invention is very high

Claims (3)

[Claims] The glossiness G _C of one of the film surfaces is 33.
Not less than%, fine-bubble-containing polyester film, wherein the gloss G _A of the other film surface is 25 ± 7%. 2. The fine-bubble-containing polyester film according to claim 1, which has a primer coating layer on both sides. 3. A release paper for a seal print, comprising the polyester film containing fine bubbles according to claim 1.