JPS626975B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyester (hereinafter simply referred to as polyethylene terephthalate) film whose main unit is stretched ethylene terephthalate, and in particular, in order to provide a film with excellent transparency and ease of slipping, a melt-extruded raw film is rolled-stretched. The present invention relates to improvement in stretchability when uniaxially stretching in the longitudinal direction of melt extrusion using a machine. Polyethylene terephthalate film is known to have excellent properties such as mechanical properties, heat resistance, and chemical resistance, and therefore polyethylene terephthalate film is widely used for various purposes. Normally, polyethylene terephthalate film is required to be easily slippery from the viewpoint of ease of handling, both in the manufacturing process and in post-processing and use in various applications. Transparency is generally required. On the other hand, the general method for manufacturing stretched polyethylene terephthalate film is to melt-extrude sufficiently dried polyethylene terephthalate resin into a sheet using a melt extruder, cool it with a cooling roll, and then roll the resulting melt-extruded original film into a heated roll. A method of obtaining a uniaxially stretched film by preheating using a tenter and then stretching uniaxially in the direction of melt extrusion with a stretching roll, and further stretching the uniaxially stretched film in the width direction of the uniaxially stretched film using a tenter, and further heat setting. There is a sequential biaxial stretching method.
Metals, especially iron, are generally used as materials for heating rolls and stretching rolls due to their good thermal conductivity, ease of processing, and durability.The surfaces are mirror-finished to achieve good adhesion to the film and a beautiful film surface. Many of them have been polished to a perfect condition. However, as the surface temperature of the roll increases, the coefficient of friction between the film and the roll rapidly increases due to the thermal softening properties of the plastic, and eventually the film becomes sticky. In the case of polyethylene terephthalate, a roll with hard chrome plating on the surface and amorphous polyethylene terephthalate partially stick together at around 80°C, and completely stick together at around 90°C. Under such conditions, if the film and roll are bonded continuously, so-called stick slips will occur.
The surface of the film not only becomes very ugly due to irregular and discontinuous adhesion marks with the roll, but also causes visible scratches, impairing the stretchability and quality of the finished film. In order to prevent such adhesion, methods such as roughening the surface of the roll have been taken, but heating with a roll with a roughened surface in this way has poor adhesion, and the rough surface of the roll is attached to the film surface. is transferred and spoils the beauty of the resulting film.
Another method is to coat the roll surface with a non-adhesive substance, such as a fluorine-containing polymer, but this makes the film slippery on the roll surface, which may scratch the coating layer on the roll surface, or cause the coating layer to separate from the roll. This may cause the roll to peel off, significantly shortening the roll's service life. Such stick and slip properties are closely related to the lubricant normally contained in polyester resin for film, and the fewer the irregularities formed on the surface of the melt-extruded raw fabric by the lubricant, the better the stick and slip properties will be. Significant. Therefore, if the lubricant content is reduced in order to increase the transparency of the film, the productivity and quality of the film will be impaired. An object of the present invention is to provide a stretched film mainly composed of ethylene terephthalate, which does not impair transparency or appearance and has excellent slip properties. The objective is to improve the stretchability when uniaxially stretching. Stretchability here means the stick-slip property described above. In order to increase the slipperiness of the unstretched original fabric and film, unevenness is formed on the surface of the undrawn original fabric and film to improve the smoothness between the metal and the film.
A common method is to reduce the coefficient of friction between films, and methods include forming polyethylene terephthalate-insoluble fine particles within polyethylene terephthalate during the polycondensation process of polyethylene terephthalate (internal particle method), titanium oxide, calcium carbonate, silicon dioxide, talc,
A method of adding inert inorganic fine particles such as kaolin, alumina, aminosilicate, clay, etc. (external particle method)
and so on. As an internal particle slip agent, for example, a method is known in which a calcium compound used as a transesterification catalyst is precipitated into a polymer as an insoluble precipitate, and this precipitate reduces the coefficient of friction on the film surface. There is. However, such precipitates do not necessarily precipitate quantitatively during polycondensation, and the amount that naturally precipitates during polycondensation does not provide sufficient results in both slipperiness and transparency. do not have. In addition, the polyethylene terephthalate insoluble compound produced in the polymer is
It is relatively easily destroyed during the stretching process after melt extrusion,
When the film is collected and reused, there is a drawback that the slipperiness is reduced. On the other hand, in the case of an inorganic particulate slip agent, even in a catalyst system that does not form a polyethylene terephthalate insoluble compound in the polymer, slip properties can be imparted by uniformly dispersing it. In this case, the larger the diameter of the particles and the higher the content, the better the lubricity will be, but on the other hand, the transparency of the film will be impaired, making it very difficult to achieve a good balance between lubricity and transparency. Have difficulty. Among inorganic fine particles, silicon dioxide has a refractive index close to that of polyethylene terephthalate, and has very good light transmittance. Although it is effective in imparting elasticity, it is still insufficient for improving the slipperiness of highly transparent films, especially for improving the uniaxial stretchability of unstretched films. The inventors of the present invention conducted extensive studies on various inorganic fine particles, and as a result, they arrived at the present invention, which has remarkable effects. That is, the present invention is a polyester composition containing 0.01 to 3% by weight of the total resin composition of finely powdered silica coated with a polyolefin wax and having a particle size of 0.01 to 10μ in a polyester containing ethylene terephthalate as a main unit. This is a method for producing a stretched polyester film, which is characterized by melt-extruding the extruded sheet and then uniaxially stretching the extruded sheet in the longitudinal direction using a roll stretching machine. Eye stretching may be performed. The present invention will be explained in more detail. In the present invention, the polyester with ethylene terephthalate as the main unit refers to polyethylene terephthalate alone, polyester with a copolymer component present to the extent that the main properties of polyethylene terephthalate are not impaired, and polyester with other polyesters, or other polyesters that can be mixed. Specifically, it is a polyester containing 80% by weight or more, preferably 90% by weight or more of ethylene terephthalate units. Here, the glycol component for copolymerization is propylene glycol,
Diethylene glycol, trimethylene glycol, butanediol, hexamethylene glycol, neopentyl glycol, cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, etc., and acid components include adipic acid, sebacic acid, isophthalic acid, naphthalene dicarboxylic acid, P -β-oxyethoxybenzoic acid, diphenyl ether-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, etc. Of course, polyamide, polyolefin, etc.
They may be mixed in amounts not exceeding 20% by weight. Preferred conditions for producing the polyethylene terephthalate film of the present invention are that the fine particles are added to polyethylene terephthalate, the resulting polyester composition is then melt-extruded into a sheet, and then a stretching roll is used to extend the film in the longitudinal direction of the melt-extruded
Uniaxial stretching is carried out at ~140°C by at least 2 times, preferably at least 2.5 times. In order to obtain a biaxially stretched film, the above-mentioned uniaxially stretched film is then subjected to second-axis stretching in the width direction at 80 to 140° C. by at least 2 times, preferably 2.5 times or more, using a tenter. The stretched film obtained by the method of the present invention has a thickness of 10 to 2000 .mu.m, although the thickness thereof is not limited, and a thickness of a biaxially stretched film of 4 to 500 .mu.m, preferably 12 .mu.m or more. As for the method of adding the fine particles, for example, it is most preferable to disperse them in the form of a slurry in ethylene glycol and add them during the polycondensation process. It may be dispersed by Furthermore, during the production of the polyethylene terephthalate, there is no problem in adding other known stabilizers, toners, pigments, etc. The finely powdered silica used together with the polyethylene terephthalate in the present invention has a particle size of 0.01 to 10 microns, preferably 0.1 to 5 microns, and is amorphous silicon dioxide whose surface has been treated with polyolefin wax. If the particle size is less than 0.01μ, it is insufficient to impart slipperiness, and if the particle size is more than 10μ, there will be a foreign body feeling that can be seen with the naked eye when made into a film, which will impair the aesthetic appearance of the film and cause problems in the extruder. This is not desirable as it may clog the filter. The amount of finely divided unsilica used in the present invention to be added to the polyester needs to be 0.01 to 3% by weight (based on the total resin composition), preferably 0.025 to 0.5% by weight. If it is less than 0.01% by weight, the slip properties will be insufficient, and if it exceeds 3% by weight, the transparency will be markedly reduced, which is not preferable. Polyolefin waxes have various chemical structures, and although not particularly specified, polyethylene waxes and polypropylene waxes are preferred. If no surface treatment is applied, secondary aggregation of silica particles tends to occur during polymerization or in an extruder due to hydrogen bonds between silanol groups present on the silica surface, but this can be prevented by applying polyolefin wax treatment. Secondary aggregation like this is difficult to occur,
Appropriately dispersed irregularities are formed on the surfaces of the unstretched original fabric and the biaxially stretched film, and the slipperiness is improved. The present invention will be described below with reference to Examples, but of course the present invention is not limited to the following Examples. In addition, each measurement value described in the examples was measured by the following method. Friction coefficient (film-film) Using a slip tester, ASTMD-1894B
Measured according to the law. Friction coefficient (undrawn original fabric - metal) Using a slip tester described in ASTMD-1894B, a hard chrome-plated iron plate was placed on the support base, an undrawn original fabric was attached to the back side of the weight, and the measurement was carried out in a heated tensilon. . The measurement method followed the ASTMD-1894B method. Haze of film Diffuse transmittance (Td) and total transmittance (Tt) of the film were measured using a model S-3 haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd., and calculated from the following formula. Haze (%)=Td/Tt×100 Intrinsic viscosity of polymer Measured at 30°C in phenol/1,1,2,2-tetrachloroethane=60/40 (weight ratio). Example 1 An esterification reaction was carried out at room temperature from 100 parts of terephthalic acid and 1.25 moles of ethylene glycol to obtain bis-(β-hydroxyethyl terephthalate). Next, finely powdered silica with an average particle size of 3 μm whose surface was treated with polyethylene wax was added to ethylene glycol, and the resulting slurry was uniformly dispersed by high-speed rotation at room temperature and 0.0438 part of antimony trioxide was added to the bis-(β-) produced above. After adding the polymer to hydroxyethyl terephthalate), the temperature was gradually raised and the pressure was reduced, and finally polymerization was carried out at 275° C. under a reduced pressure of 0.1 mmHg to obtain master pellets with a silica concentration in the polymer of 0.2% by weight and an intrinsic viscosity of 0.62. The master pellets thus obtained and a silica-free polymer with an intrinsic viscosity of 0.62 obtained by polymerization in the same manner were sufficiently mixed and dried at a predetermined ratio, and then formed into a sheet at 290°C by a conventional method. The film was stretched at 930° C. with a longitudinal stretch ratio of 3.2 times and at 110° C. with a transverse stretch ratio of 3.0 times using a carbon roll stretching machine, and then heat treated at 200° C. to obtain a film with a thickness of 25 μm. The friction coefficient at 93°C between the unstretched original film and the hard chrome-plated metal plate and the occurrence of scratches during longitudinal stretching are shown in Table 1, and the friction coefficient and haze between the films are shown in Table 2. Both the stretchability of the original fabric and the slipperiness of the film were excellent. Example 2 The same procedure as in Example 1 was carried out except that fine powder silica having an average particle size of 1 μm and whose surface was treated with polyethylene wax was used. The friction coefficient at 93°C between the unstretched original film and the hard chrome-plated metal plate and the occurrence of scratches during longitudinal stretching are shown in Table 1, and the friction coefficient and haze between the films are shown in Table 2. The stretchability of the unstretched original film and the slipperiness and transparency of the film were both excellent. Comparative Example 1 The same procedure as in Example 1 was carried out except that fine powder silica having an average particle size of 3 μm and whose surface was not treated with polyethylene wax was used. The friction coefficient at 93°C between the unstretched original film and the hard chrome-plated metal plate and the occurrence of scratches during longitudinal stretching are shown in Table 1, and the friction coefficient and haze between films are shown in Table 2. It can be seen that the stretchability of the unstretched original fabric, the slipperiness of the film, and the transparency are inferior to those obtained when finely powdered silica treated with Tux is used. Example 2 The same procedure as Example 1 was carried out except that talc having an average particle size of 3 μm and not surface treated was used. The unstretched original fabric and the hard chrome-plated metal plate
The friction coefficient at 93°C and the occurrence of scratches during longitudinal stretching are shown in Table 1, and the film-to-film friction coefficient and haze are shown in Table 2. In comparison, it can be seen that the stretchability of the unstretched original film and the slipperiness and transparency of the film are inferior. Comparative Example 3 The same procedure as in Example 1 was carried out except that kaolin having an average particle size of 1 μm and not surface-treated was used. The friction coefficient at 93°C between the unstretched original film and the hard chrome-plated metal plate and the occurrence of scratches during longitudinal stretching are shown in Table 1, and the friction coefficient and haze between the films are shown in Table 2. It can be seen that the stretchability of the unstretched original fabric, the slipperiness of the film, and the transparency are inferior to those obtained when wax-treated finely powdered silica is used. Comparative Example 4 The same procedure as in Example 1 was carried out except that calcium carbonate having an average particle size of 1 μm and not surface-treated was used. The friction coefficient at 93°C between the unstretched original film and the hard chrome-plated metal plate and the occurrence of scratches during longitudinal stretching are shown in Table 1, and the friction coefficient and haze between the films are shown in Table 2. Compared to the case of using wax-treated fine powder silica, the stretchability of the unstretched original fabric, the slipperiness of the film, and the transparency were inferior.

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Claims (1)

[Claims] 1 A polyester composition containing 0.01 to 3% by weight of the total resin composition of finely powdered silica coated with polyolefin wax and having a particle size of 0.01 to 10μ is melt-extruded into a sheet in a polyester containing ethylene terephthalate as a main unit. . Thereafter, the extruded sheet is uniaxially stretched in the longitudinal direction using a roll stretching machine.