JPS62241928A - White polyester film - Google Patents

Abstract

PURPOSE:To obtain the titled light-screening biaxially oriented film having an excellent whiteness and a nonglaring gloss, by melt-kneading a polyester containing TiO2, SiO2 and an optical brightener, forming the mixture into a film and orienting this film. CONSTITUTION:A polyester such as polyethylene terephthalate is mixed with 8-20wt% TiO2 of an average particle diameter <=0.5mu, which is purified and, if necessary, surface-treated with an oxide of Al, Si or the like, 0.5-5wt% SiO2 of an average particle diameter of 1-10mu and 10-1,000ppm of an optical brightener having a fluorescence peak at a wavelength of 400-500nm, and the mixture is melt-kneaded and melt-extruded at 280-300 deg.C into a sheet. The obtained sheet is solidified by quenching into an amorphous sheet, which is biaxially oriented in the lengthwise and crosswise directions and heat-set at a predetermined temperature to obtain the titled film having a shrinkage <=1.5% after heat treatment at about 150 deg.C for about 30min and a surface roughness of 0.1-0.5mu. If necessary, an easily printable thin-film layer comprising, e.g., a water-dispersible polyester composition is applied to at least either surface of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a white polyester film, and more particularly to a biaxially oriented white polyester film having excellent whiteness and non-glossy gloss.

Polyester in general, and polyethylene terephthalate in particular, is widely used as a film because of its excellent mechanical and chemical properties.

Recently, with the advancement of information and recording fields, polyester films have come to be used for magnetic recording cards such as telephone cards, writing materials such as electronic whiteboards, and the like. Polyester films used in these applications are generally required to have light-shielding properties that do not allow light to pass through from the back side.

A method for imparting light-shielding properties to a film includes a method of incorporating inert inorganic particles into a polyester film, for example, as described in Japanese Patent Publication No. 44-26752.

It has been proposed in JP-A No. 57-205824 and the like to contain a relatively large amount of titanium dioxide in a polyester film.

However, when titanium dioxide is contained in polyester in an amount of about 5% by weight or more, the resulting film becomes yellowish due to the decomposition of polyester due to titanium dioxide during polyester production or due to the hue of titanium dioxide itself. . For example, in telephone cards based on such films, the white background on the printed surface appears yellowed, and electronic whiteboards also appear yellowed.

Therefore, in order to use the film for these purposes, it is necessary to print or coat the film with a white paint, which is disadvantageous in terms of productivity and economy.

In addition, titanium dioxide is an excellent substance in terms of providing light-shielding properties to films, but because the particle size is small, the surface of the film obtained is relatively flat even if a large amount of titanium dioxide is contained in polyester. , the film becomes glossy. Phone cards, electronic whiteboards, and the like that use such films as they are tend to reflect light from lighting, etc., resulting in problems such as a lack of quality and difficulty in reading characters.

In order to overcome this drawback, it is generally considered that the film surface is subjected to post-processing such as alkali treatment or sandblasting to make the surface rough, but this method is not sufficient in terms of performance and is not economical. There are more disadvantages. In addition, in order to eliminate this drawback, it is possible to incorporate particles with a large particle size into polyester to impart light-shielding properties to the film and to roughen the film surface, but according to the research results of the present inventors, In order for a film to have light-shielding properties, it is necessary to contain a large amount of these particles, and the number of coarse particles mixed in the particles increases dramatically compared to fine particles, so Filter clogging and film tearing were likely to occur, and the resulting film had many fisheyes.

In view of the above-mentioned circumstances, the inventors of the present invention have arrived at the present invention as a result of intensive research into a light-shielding white polyester film that has excellent whiteness and a non-glossy luster.

Accordingly, an object of the present invention is to provide a light-shielding white polyester film having excellent whiteness and non-glossy gloss. Another object of the present invention is to provide a light-shielding white polyester film with excellent whiteness, non-glare gloss, and easy printability, which is particularly useful as a base film for magnetic recording cards and writing materials. It's about doing.

Structure/Effect of the Invention This object of the present invention is that, according to the present invention, the average particle size is 0.
8-20% by weight of titanium dioxide less than 5μ.

It is made of polyester containing 0.5 to 5% by weight of silica with an average particle size of 1 to 10 μm and a fluorescent whitening agent having a fluorescent peak at a wavelength of 400 to 5000 nm, and if desired, easily printable sS is applied to at least one side of the film. This is accomplished by layered biaxially oriented polyester films.

The unique point of the present invention is that titanium dioxide and silica of a specific particle size are contained in a polyester under specific conditions, and furthermore, a specific amount of a fluorescent brightener is contained in the polyester. As a result, the biaxially oriented polyester film has properties such as excellent whiteness, light shielding properties, and matte gloss, and if necessary, a thin coating layer of adhesive can be formed on the surface of the film to improve printability or adhesion of the magnetic layer. It can also improve your sexuality.

The polyester used in the present invention may be any material as long as it can be formed into a film, such as polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1
, 4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, and the like. Of course, these polyesters may be homopolyesters or copolyesters, and examples of copolymerization components include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, and adipic acid.

Dicarboxylic acid components such as sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, and 5-sodium sulfoisophthalic acid; trimellitic acid in an amount range such that the polymer remains substantially linear.

Examples include polyfunctional carboxylic acid components such as pyromellitic acid.

In the present invention, the titanium dioxide contained in the polyester has anatase crystal form.

Any multi-type one may be used. Further, for the purpose of improving the dispersion of titanium dioxide into polyether, titanium dioxide whose surface is treated with oxides such as aluminum, silicon, zinc, or various organic substances can also be used.

The average particle size of titanium dioxide is 0.5 μm or less, preferably 0.05 to 0.4 μm. Here, the average particle size means the "equivalent spherical diameter" of particles at 50% by weight of all particles measured. Furthermore, the term "equivalent spherical diameter" refers to an imaginary sphere having the same volume as the particle, and can be calculated from measurements using a conventional sedimentation method. If the average particle size of titanium dioxide is larger than 0.5 μm, there will generally be many coarse particles and the light-shielding property will be poor, which is not preferable.

The added content of titanium dioxide polyester is 8-20% by weight, preferably 12-11% by weight. If the content of titanium dioxide is less than 8% by weight, the light-shielding property of the film will not be sufficient, while if it exceeds 20% by weight, the light-blocking property will be saturated, so no improvement in the effect will be seen, and on the contrary, the film will be less effective during stretching. A problem also arises in that the film is more likely to break.

The silica used in combination with titanium dioxide in the present invention may be either crystalline silica or amorphous silica in terms of crystal form, and its production method may be either a dry method or a wet method. In addition to pure silica, silica contains metals such as aluminum and magnesium, and has a silicon content of 80%.
It is also possible to use the above materials, or those whose silica surface has been surface-treated with various metals or organic compounds.

The average particle size of silica is 1 to 10 μm, preferably 2 μm.
~8 μm. The average particle size is defined in the same manner as for titanium dioxide described above. When the average particle size is less than 1 μm, the surface of the obtained film is flat and glossy. Moreover, if it exceeds 10 μm, the film surface will become too rough,
When used in magnetic cards, there are problems such as poor magnetic recording conversion characteristics, and poor filterability during film production. Added silica content is 0.5
-5% by weight, preferably 2-4% by weight. If the amount of silica added is less than 0.5% by weight, the film surface will be glossy, and if it exceeds 511% by weight, the magnetic recording conversion characteristics will deteriorate and the film will often break during film stretching. Also occurs.

Further, in the present invention, the fluorescent whitening agent to be contained in the polyester may be of any type as long as it has a fluorescent peak at a wavelength of 400 to 500 ngc, but a suitable one is Uvitex 08 (trade name, manufactured by Ciba Kaigy). , 08-1
Examples include those commercially available from Eastman Co., Ltd.

The added content of polyester in the fluorescent whitening agent is preferably 10 to 1000pp, more preferably 50 to 600pp.
E) DI.

It is preferable that titanium dioxide and silica in the present invention be subjected to a purification process to adjust particle size and remove coarse particles before incorporating them into polyester. As industrial means for the purification process, examples of crushing means include jet mills and ball mills, and examples of classification means include dry or wet centrifuges. Of course, two or more of these methods may be used in combination for stepwise purification.

Various methods can be used to incorporate titanium dioxide, silica, and fluorescent brightener into polyester. The following methods can be cited as representative methods.

(a) A method of adding it before the end of the transesterification or esterification reaction during polyester synthesis, or adding it before the polycondensation reaction.

(a) A method of adding it to polyester and melting it.

(1) In the methods of (a) and (b) above, a masterbatch is produced by adding a large amount of additives, or a masterbatch is prepared by adding a large amount of titanium dioxide, silica, or a fluorescent brightener. A method of producing a batch, intermixing it with a polyester that does not contain particles, and containing a predetermined amount of additives.

In addition, when using the method (a) of adding additives during polyester synthesis, it is preferable to add the additives to the reaction system as a slurry dispersed in glycol.

The polyester film forming conditions are known methods, for example, usually 280
A method of melting and extruding into a sheet at ~300°C, rapidly solidifying it to form an amorphous sheet, and then biaxially stretching it vertically and horizontally, or sequentially biaxially in the order of vertically, horizontally, and vertically, a method of simultaneously biaxially stretching vertically and horizontally, etc. can be adopted.

The biaxially stretched film is preferably heat-set at a predetermined temperature to improve dimensional stability. In particular, when post-processing such as printing or coating with a magnetic layer is applied, 150
The shrinkage rate of the film after heat treatment at ℃ for 30 minutes is preferably 2% or less, more preferably 1% or less, and the post-processability and quality of the obtained product are good.
preferable.

The biaxially oriented polyester film of the present invention preferably has a surface roughness Ra of 0.1 to 0.5 μm. If the surface roughness is less than 0.1 μm, gloss will occur, and if it exceeds 0.5 μm, the surface will become too rough.
Magnetic cards and the like have poor electromagnetic conversion characteristics and are not preferred.

Such surface roughness is basically the average particle size of titanium dioxide and silica.

It can be adjusted by changing the amount added, and can also be slightly adjusted by changing the stretching conditions.

In the present invention, the biaxially oriented polyester film is preferably provided with an easily printable 11I layer on at least one surface thereof. The format of the easy-to-print U layer can be formed by any method. For example, there is a method of forming the film during the production of a biaxially oriented film and a method of forming it after the production of the biaxially oriented film.A specific example of the former is, for example, applying a ms film forming solution to the surface of an unstretched film and then stretching it in the biaxial direction. ,
Alternatively, a method may be mentioned in which a thin film forming liquid is applied to the surface of a uniaxially stretched film and then further stretched in the perpendicular direction.A specific example of the latter is a method in which an M film forming liquid is applied to the surface of a biaxially stretched film. It will be done.

Of these, the former is preferably applied in-line. A normal coating method can be used as the coating method.

The easily printable thin film forming agent improves the adhesion between printing inks such as water-soluble inks, U-curing inks, urethane, vinyl chloride, vinyl acetate, etc., and magnetic recording compositions containing iron oxide, etc. There is no particular limitation as long as it is. Preferred examples of specific thin film forming agents include water-soluble polyester compositions, water-dispersible polyester compositions, water-dispersible polyurethane compositions, and water-dispersible polyacrylic acid compositions. Among these, polyester-based compositions, especially water-dispersed polyester-based compositions, are difficult to discolor due to the decomposition of the thin film forming agent when using polymer recovered products (reclaim polymers) such as film edges generated during film production9. Therefore, it is preferable.

The biaxially oriented white polyester film of the present invention can be used in all applications requiring light-shielding properties and opacity, but is particularly preferably used as a base film for photographic paper for writing materials such as magnetic recording cards and N-child whiteboards.

Example The present invention will be further explained below with reference to Examples.

Note that various physical property values and characteristics in the present invention were measured as follows.

(1) Film surface roughness (Ra) JIS B
Measured according to 0601. Using a stylus type surface roughness meter (SURFCOM3B) manufactured by Tokyo Seimitsu Co., Ltd., the radius of the needle is 2.
A chart (film surface roughness curve) was drawn under the conditions of μ and load of 0.079. A part of the measurement length is extracted from the film surface roughness curve in the direction of its center line, and the roughness curve is expressed as Y-f(X ), the value (Ra:μ7FL) given by the following formula is defined as the film surface roughness.

Ra −1/Lj', If (x) ldx
In the present invention, Ra is expressed as the average value of 5 measurements after 8 measurements were made with the reference length set at 0.25mm, and 3 of the largest values were removed.

(The number of protrusions determined from the 21 protrusion distribution. Using a three-dimensional roughness meter (SE-3GK) manufactured by Kosaka Laboratory, the needle diameter was 3 μ7 FL.
R, stylus force 30q1 measurement length 1w1s sampling pitch 2
The protrusion profile on the film surface is imaged three-dimensionally (stereoscopically) under the following conditions: μm1 cutoff 0.25 rm, vertical magnification 20,000 times, lateral magnification 200 times, number of scans 150.

When the profile is cut in a plane perpendicular to the thickness direction of the film, the plane where the total cross-sectional area of the profile of each protrusion is 70% of the area of the measurement area of the film is defined as the reference level (0 level). , let y be the number of protrusions that are cut when cutting with a plane that is parallel to the plane of the reference level and separated by a distance X in the height direction of the protrusions.

A protrusion distribution curve can be drawn by sequentially increasing or decreasing X, reading the number of y at that time, and plotting it on a graph. The value of y when this distance X is 1 μm is expressed as the "number of protrusions."

(3) Color machine CM-20 model ・(
(manufactured by Color Machine Co., Ltd.) and obtained LliIi.

Judgment was made using a value and b value. The color tone of a film judged to have excellent whiteness is one having the following values.

88≦L value -2≦a value≦1 -5≦b value≦2 (4) Light shielding property Total transmittance (Tt) measured with 5EP-HUP (Boitzk integrating sphere type) manufactured by Nippon Seimitsu Kogaku Co., Ltd. It was judged.

The total transmittance (Tt”) is preferably 10% or less, especially 5%.
% or less is preferable.

(5) Synthesis of printable and easily printable thin film layer material> Dimethyl terephthalate 159 parts by weight (0.82 mol)
, 29 parts by weight (0.15 mol) of dimethyl isophthalate
, 9 parts by weight (0.03 mol) of 5-sodium isophthalate, 135 parts by weight (1,50 mol) of 1.4-butanediol, and 202 parts by weight of 2,2-bis[4-(2human Ooxyethoxy)phenyl]propane. (0,50 mol) and 0.34 parts by weight (o, oos mol) of tetrabutoxytitanium
was charged into a reaction vessel, and a transesterification reaction was carried out at 150°C to 170°C. Next, while increasing the temperature from 170°C to 250°C, the pressure was gradually reduced, and a polycondensation reaction was further carried out under high vacuum. The reduced viscosity (ηsp/c) of the resulting copolymerized polyester measured using a phenol/tetrachloroethane (6/4) mixed solution was 0.70 dl/9.

20 parts by weight of this copolyester was dissolved in 80 parts by weight of dioxane, and 180 parts by weight of water was added dropwise to the resulting solution under high-speed stirring at 100 revolutions/minute to obtain a bluish milky white dispersion. This dispersion was then mixed with 20Mlf-1
Dioxane was distilled off under reduced pressure. In this way, a polyester aqueous dispersion having a solid content concentration of 1 wt% was obtained.

Furthermore, a double portion of a nonionic surfactant: polyoxyethylene nonylphenyl ether (HL B-12,8) was added to 180 parts by weight of the polyester aqueous dispersion, and further 618 parts by weight of water was added to prepare a coating liquid. did.

Preparation of gravure printing ink> Commercially available gravure ink for cellophane printing containing nitrocellulose and O-gin oil as the main binder: CLS-
2 parts by weight of a stock solution of 709 White (manufactured by Dainippon Ink ■) was diluted with 1 part by weight of a mixed solvent of toluene/ethyl acetate/methyl ethyl ketone-1/1/1 to prepare a paint for evaluation.

<Evaluation of printability> After coating a gravure ink having the above composition on a polyester film on which an easily printable thin film was formed using the above easily printable thin film layer forming coating liquid, Scotch tape No.
600 (manufactured by Three M Company) Width 19.4all.

Glue length 81 so that there are no air bubbles, and then apply J on top of this.
The 51 questions of the laminated parts were smoothed and pasted using a manual load roll as described in IS C2701 (1975) using a Tensilon UM- manufactured by Toyo Baldwin Co., Ltd. at a head speed of 300 awg/
This sample is peeled off by one character in minutes, the peel strength at this time is determined, and this is divided by the tape width to determine g/α. Note 1
In the case of peeling, the laminate is taken with the tape side facing down and the distance between the chucks is 51.

Examples 1 to 4 and Comparative Examples 1 to 9 Polyethylene terephthalate pellets (PET) with an intrinsic viscosity of 0.65 and additives were mixed in the proportions shown in the table, and then melted and mixed in a twin-screw extruder. Then, it was extruded onto a cooling drum to obtain an unstretched sheet. followed by 90
℃ and a longitudinal stretching ratio of 3.3 times.

After stretching at a transverse stretching ratio of 3.5 times, heat treatment was performed at 210° C. for 4 seconds to obtain a stretched film with a thickness of 75 μm.

The quality of the obtained film is shown in Table-1. Example 1~
Sample No. 4 had good white discoloration, anti-glossy properties, and light-shielding properties. On the other hand, all of Comparative Examples 1 to 9, which did not satisfy the requirements of the present invention, had some kind of drawback.

Examples 5 to 8 In Examples 1 to 4, the unstretched sheets were stretched at 90°C to a longitudinal stretching ratio of 3.3 times, and then the coating solution of the easily printable thin film layer material was coated on a uniaxially stretched film by the kiss coating method. A film on which an easily printable film layer was formed was obtained in the same manner as in Examples 1 to 4, except that the film was coated on one side of the film and then further stretched at a transverse stretching ratio of 3.5 times.

The surface roughness, number of protrusions (1), and transmittance of this film were the same as those of Examples 1 to 4.

The printability of the obtained film was evaluated by the method described in (4) above. The peel strength is shown below.

Claims (1)

[Claims] 1. 8-20% by weight of titanium dioxide with an average particle size of 0.5 μm or less, 0.5-5% by weight of silica with an average particle size of 1-10 μm.
and a biaxially oriented white polyester film having non-glossy luster, which is made of a polyester containing a fluorescent whitening agent having a fluorescent peak at a wavelength of 400 to 500 nm. 2. The white polyester film according to claim 1, wherein the content of the fluorescent whitening agent is 10 to 1000 ppm. 3. The white polyester film according to claim 1, wherein the polyester film has a shrinkage rate of 1.5% or less when heat treated at 150° C. for 30 minutes. 4. The surface roughness (Ra) of the polyester film is 0.1
The white polyester film according to claim 1, which has a thickness of 0.5 μm. 5. The white polyester film according to any one of claims 1 to 4, wherein an easily printable thin film layer is provided on at least one side of the polyester film. 6. The white polyester film according to claim 5, wherein the easily printable thin film layer is made of water-dispersible polyester. 7. The white polyester film according to any one of claims 1 to 5, wherein the polyester film is a base film for a magnetic recording card or a writing material.