JPH0430975B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a white polyester film, and more particularly to a biaxially oriented white polyester film having excellent whiteness and non-matte gloss. BACKGROUND OF THE INVENTION Polyester in general, and polyethylene terephthalate in particular, has excellent mechanical and chemical properties and is therefore widely used as a film. 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, Japanese Patent Publication No. 44-26752,
It has been proposed in JP-A-57-205824 and the like to incorporate a relatively large amount of titanium dioxide into a polyester film. However, when titanium dioxide is contained in polyester in an amount of about 5% by weight or more, the resulting film has a yellowish tinge due to the decomposition and coloring of the polyester by titanium dioxide during polyester production, or due to the hue of titanium dioxide itself. becomes. For example, the white background of the printed surface of a telephone card based on such a film appears yellowed, and also appears yellowed on an electronic whiteboard.
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,
Although 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 surface of the film, according to the research results of the present inventors, in order to impart light-shielding properties to the film, must contain a large amount of these particles, and since the amount of coarse particles mixed in the particles increases dramatically compared to fine particles, filter clogging and film tearing are likely to occur during film production. Moreover, the obtained film had many defects. Purpose of the Invention In view of the above-mentioned circumstances, the present inventors 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. SUMMARY OF THE INVENTION 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 that has excellent whiteness, non-glossy gloss, and is easy to print, which is particularly useful as a base film for magnetic recording cards and writing materials. It's about doing. Structure/Effects of the Invention According to the present invention, 8 to 20% by weight of titanium dioxide having an average particle size of 0.5 μm or less,
It is made of a 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 fluorescence peak at a wavelength of 400 to 5000 nm, and whose main acid component is terephthalic acid. This is achieved by a biaxially oriented polyester film provided with an easily printable thin film layer on at least one side. The unique feature 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.If necessary, a thin coating layer of adhesive can be formed on the surface of the film to improve printability or magnetic properties. It is also possible to improve layer adhesion. The polyester used in the present invention is a polyester whose main acid component is terephthalic acid, and can be formed into a film. Although the glycol component constituting the polyester is not particularly controlled,
Preferred examples include ethylene glycol, tetramethylene glycol, and 1,4-cyclohexanedimethanol. Specific examples of polyester include polyethylene terephthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, and the like.
These polymers may be homopolymers or copolymers, and the copolymer components include diethylene glycol, neopentyl glycol,
Diol components such as polyalkylene glycol, dicarboxylic acid components such as adipic acid, sepacic acid, phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, and 5-sodium sulfoisophthalate; the polymer maintains substantially linear shape. Examples include polyfunctional carboxylic acid components such as trimellitic acid and pyromellitic acid in a range of amounts. The proportion of the copolymerized acid component is preferably 15 mol% or less, more preferably 10 mol% or less. In the present invention, the titanium dioxide contained in the polyester may be either anatase type or ruti type in crystal form. Furthermore, for the purpose of improving the dispersion of titanium dioxide into polyester, 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 it is 0.05 to 0.4 μm. Here, the average particle size means the "equivalent spherical diameter" of particles at 50% by weight of all measured particles. Furthermore, the term "equivalent spherical diameter" refers to an imaginary sphere having the same volume as the particle, and can be calculated from measurement 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 12-17% 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, and no improvement in the effect will be seen, and on the contrary, the film will suffer during stretching. Another problem arises in that the number of film breaks increases. 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 that contains metals such as aluminum and magnesium and has a silicon content of 80% or more, or silica that has been surface-treated with various metals or organic compounds can also be used. The average particle size of silica is 1 to 10 μm, preferably 2 to 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. Also, if it exceeds 10μm,
There are problems in that the surface of the film is too rough, resulting in problems such as poor magnetic recording conversion characteristics when used in magnetic cards, 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 surface of the film will be glossy, and if it exceeds 5% by weight, there will be problems such as deterioration of magnetic recording conversion characteristics and increased film breakage during film stretching. 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 nm, but preferable ones include Ubitex OB (trade name, Ciba Kaigy Co., Ltd.); Examples include those commercially available as OB-1 (Eastman Co.). The added content of polyester in the fluorescent whitening agent is preferably 10 to 1000 ppm, more preferably 50 to 1000 ppm.
It is 600ppm. 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 in which it is added before the completion of the transesterification or esterification reaction during polyester synthesis, or a method in which it is added before the polycondensation reaction. (a) A method of adding it to polyester and melting and kneading it. (c) In the methods of (a) and (b) above, a master polymer is produced by adding a large amount of additives, or a master is prepared by adding a large amount of titanium dioxide, silica, or a fluorescent brightener. A method of producing a polymer, kneading 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 a known method, for example, usually by melt extrusion into a sheet at 280 to 300°C, rapidly cooling and solidifying it to form an amorphous sheet, and then sequentially biaxially stretching vertically and horizontally, or vertically, horizontally, and vertically in this order. For example, a method of simultaneous biaxial stretching in the longitudinal and transverse directions 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 magnetic layer coating is applied, the shrinkage rate of the film after heat treatment at 150°C for 30 minutes is preferably 2% or less, more preferably 1% or less. Processability and the quality of the obtained product are good, which is 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 and the electromagnetic conversion characteristics will be poor in magnetic cards, etc., which is not preferable. The surface roughness can basically be adjusted by adjusting the average particle diameter and the amount of titanium dioxide and silica added, and can also be adjusted to a certain extent by changing the stretching conditions. In the present invention, the biaxially oriented polyester film is preferably provided with an easily printable thin film layer on at least one of its surfaces. The easily printable thin film layer can be formed in any manner. For example, there are two methods: one is formed during the production of a biaxially oriented film, and the other is formed after the biaxially oriented film is produced. A specific example of the former is, for example, a method in which a thin film forming liquid is applied to the surface of an unstretched film and then stretched 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, and a specific example of the latter is a method in which a thin film forming liquid is applied to the surface of a biaxially stretched film. . 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 and UV-curable inks, urethane, vinyl chloride, vinyl acetate, etc., and magnetic recording compositions containing iron oxide, etc. It is not particularly limited 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 compositions, especially water-dispersed polyester compositions, are
This is preferable because when using recovered polymers (reclaim polymers) such as film edges generated during film production, the thin film forming agent is less likely to generate foreign matter or discolor due to decomposition or the like. 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 electronic whiteboards. Examples Hereinafter, the present invention will be further explained 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) Measured according to JIS B 0601. Tokyo Precision Co., Ltd.
A chart (film surface roughness curve) was drawn using a stylus type surface roughness meter (SURFCOM 3B) manufactured by Co., Ltd. under the conditions of a needle radius of 2 μm and a load of 0.07 g.
A part of measurement length L is extracted from the film surface roughness curve in the direction of its center line, the center line of this extracted part is taken as the X axis, the direction of longitudinal magnification is taken as the Y axis, and the roughness curve is expressed as ), when expressed as
The value (Ra: μm) given by the following formula is defined as the film surface roughness. Ra=1/L∫ ^L ₀ |f(x)|dx In the present invention, eight measurements are taken with a reference length of 0.25 mm, and Ra is expressed as the average value of five measurements, excluding three from the largest value. (2) Number of protrusions determined from protrusion distribution Using a three-dimensional roughness meter (SE-3CK) manufactured by Koita Research Institute, the needle diameter was 3 μmR, the needle pressure was 30 mg, the measurement length was 1 mm,
Sampling pitch 2μm, cutoff 0.25mm,
20,000x vertical magnification, 200x horizontal magnification,
The profile of protrusions on the film surface is imaged three-dimensionally (three-dimensionally) under the condition of 150 scans. When the profile is cut in a plane perpendicular to the film thickness direction, the plane where the total new area of the profile of each protrusion is 70% of the area of the film measurement area is set to the reference level (0
level), and let y be the number of protrusions that are cut when the protrusions are cut at a plane parallel to the plane of the reference level and separated by a distance x in the height direction. Increase or decrease x sequentially, then y
By reading the number of and plotting it on a graph, a protrusion distribution curve can be drawn. The value of y when this distance x is 1 μm is shown as the "number of protrusions." (3) Color tone The surface color of the film was measured using Color Machine CM-20 model (manufactured by Color Machine Co., Ltd.), and the obtained L value,
Judgment was made using a value and b value. The color tones of films judged to have excellent whiteness are those having the following values. 88≦L value -2≦a value≦1 -5≦b value≦2 (4) Light blocking property Total transmittance (Tt) measured with SEP-HUP (Poitzk integrating sphere type) manufactured by Nippon Seimitsu Kogaku Co., Ltd. It was measured with The total transmittance (Tt) is preferably 10% or less, particularly preferably 5% or less. (5) Printing name <Synthesis of easily printable thin film layer material> Dimethyl terephthalate 159 parts by weight (0.82 mol), dimethyl isophthalate 29 parts by weight (0.15
9 parts by weight (0.03 mol) of 5-sodium isophthalate, 135 parts by weight (1.50 mol) 1,4-butanediol, 202 parts by weight (0.50 mol) 2,2-bis[4-(2hydroxyethoxy)phenyl]propane mole) and tetrabutoxytitanium 0.34
Pour part by weight (0.0005 mol) into the reaction vessel, and add 150
The transesterification reaction was carried out at a temperature of 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 obtained copolymerized polyester measured using a phenol/tetrachloroethane (6/4) mixed solution was 0.70 dl/
It was hot at g. 20 parts by weight of this copolymerized polyester 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 10,000 revolutions per minute to obtain a bluish, milky white dispersion. This dispersion was then distilled under reduced pressure of 20 mmHg to remove dioxane. Thus, the solid content concentration is 10wt%
An aqueous polyester dispersion was obtained. Further, 2 parts by weight of a nonionic surfactant: polyoxyethylene nonyl phenyl ether (HLB=12.8) was added to 180 parts by weight of the aqueous polyester dispersion, and 618 parts by weight of water was further added to prepare a coating liquid. <Preparation of gravure printing ink> Commercially available gravure ink for cellophane printing whose main binders are nitrocellulose and rosin oil: CLS-709 white (manufactured by Dainippon Ink Co., Ltd.)
2 parts by weight of the stock solution 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 (Three M Co., Ltd.) was applied. (manufactured) width
19.4 mm long and 8 cm long without bubbles, smoothed the adhesive layer with a manual load roll as described in JIS C2701 (1975), and used Tensilon UM- manufactured by Toyo Baldwin Co., Ltd. The sample is then peeled in a T-shape at a head speed of 300 mm/min, the peel strength at this time is determined, and this is divided by the tape width to determine g/cm. In addition, in T-peeling, the laminate was placed with the tape side facing down, and the distance between the take-off chucks was 5 cm. 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 listed in Table 1, and then melted and mixed in a twin-screw extruder. It was extruded onto a cooling drum to obtain an unstretched sheet. Subsequently, the film was stretched at 90° C. at a longitudinal stretching ratio of 3.3 times and a transverse stretching ratio of 3.5 times, followed by heat treatment 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. Examples 1 to 4 had good whiteness, gloss prevention, and light shielding properties. On the other hand, Comparative Examples 1 to 9, which did not satisfy the requirements of the present invention, all had some drawbacks.

[Table] Examples 5 to 8 After stretching the unstretched sheets in Examples 1 to 4 to a longitudinal stretching ratio of 3.3 times at 90°C, the above-mentioned coating solution of the easily printable thin film layer material was uniaxially coated by the kiss coating method. Examples 1 to 4 except that the stretched film was coated on one side and then further stretched at a transverse stretching ratio of 3.5 times.
In the same manner as above, a film on which an easily printable thin film layer was formed was obtained. The surface roughness, number of protrusions, hue, and transmittance of this film showed the same values as Examples 1 to 4. The printability of the obtained film was evaluated by the method (5) above. The peel strength is shown below.

【table】

Claims (1)

[Claims] 1. 8 to 20 titanium dioxide particles with an average particle size of 0.5 μm or less
A glossy product made of a 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 fluorescence peak at a wavelength of 400 to 500 nm, and whose main acid component is terephthalic acid. Biaxially oriented white polyester film with non-glare luster. 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, which has a shrinkage rate of 2% or less when heat treated at 150° C. for 30 minutes. 4 The surface roughness (Ra) of the polyester film is
The white polyester film according to claim 1, which has a thickness of 0.1 to 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.