JPH0458812B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a biaxially oriented polyester film that is smooth and highly improved in slipperiness and abrasion resistance. <Conventional technology and problems to be solved> Polyester represented by polyethylene terephthalate has excellent mechanical properties, electrical properties,
Due to its chemical resistance and dimensional stability, it is used as a base material in many fields such as magnetic recording, capacitors, packaging, plate making, electrical disconnection, and photographic film. When polyester film is used in these applications, the required properties differ depending on the application, but the universally required property is workability when handling the film, and in order to improve this, the slipperiness of the film, It is necessary to reduce the coefficient of friction. In addition, when a magnetic layer is coated on the surface of a film used as a base film for audio, video, and computer applications, which have been growing rapidly in recent years, and used as a magnetic recording medium, poor slipperiness and abrasion resistance may cause problems when coating the magnetic layer. Friction and abrasion between the coating roll and the film surface are severe, and scratches are likely to occur on the film surface. Furthermore, even after the film coated with the magnetic layer is processed into products such as audio, video, and computer tapes, many guide parts, recording/playback heads, etc. are Significant friction and wear occur between the two, and a white powdery substance is generated due to scratches on the surface of the polyester film, which is often a major cause of missing magnetic recording signals, that is, dropouts. In order to improve these properties required of polyester films, the most commonly employed method is to add inactive fine particles to polyester in order to impart irregularities to the film surface. This method can be broadly divided into two. One of them is the precipitation method, in which one or more metal compounds soluble in ethylene glycol, such as calcium compounds and lithium compounds, are added before and after the transesterification reaction or esterification reaction, and the polyester manufacturing process, especially the polymerization process, is carried out. This is a method in which these are precipitated as fine particles insoluble in polyester during the process. Another method that is compared to the precipitation method is the addition method, in which calcium carbonate, calcium sulfate, kaolin, silica, titanium dioxide, etc. are added as they are or after being made into fine particles during polyester synthesis or molding. Generally speaking, the larger the particle size of the particles in polyester, the greater the effect of improving slipperiness, but for precision applications such as magnetic tape, especially video, the particles themselves are large, causing dropouts and other problems. Therefore, the particles contained in polyester need to be as fine as possible. However, at present, it is extremely difficult to simultaneously satisfy these contradictory characteristics. <Means for Solving the Problems> The present inventors have discovered that in recent years, the precision of magnetic recording tapes has been further promoted, and there is a growing demand for improvements in the slipperiness and abrasion resistance of films for magnetic tapes. In view of the above, we have discovered a film for magnetic tape that has a smooth film surface, excellent slipperiness and abrasion resistance, and is less prone to defects such as dropouts, and has arrived at the present invention. That is, the gist of the present invention is that the average particle diameter is 0.01 to
A biaxially oriented polyester film characterized by containing 0.01 to 1.0% by weight of rutile titanium dioxide having an average particle size of 0.30 μm and 0.002 to 0.5% by weight of anatase titanium dioxide having an average particle size of 0.31 to 1.0 μm. The present invention will be explained in more detail below. The polyester referred to in the present invention refers to aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid, or esters thereof, and glycols such as ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, etc. It is a polyester that can be obtained by polycondensing. This polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or by polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol.
Alternatively, it can also be obtained by a method such as polycondensation of diesters of aromatic dicarboxylic acids. Typical examples of such polymers include polyethylene terephthalate and polyethylene-2,6-
Examples include naphthalate. This polymer may be a homopolymer or may be a copolymer of a third component. In any case, in the present invention, ethylene terephthalate units and/or
80 mol% ethylene-2,6-naphthalate units
Polyesters having the above properties are preferred. A feature of the present invention is that two types of titanium dioxide having different Mohs hardness, which is a measure of particle hardness, and average particle diameter are added in specific amounts. To explain further, titanium dioxide, which has a high Mohs hardness, has a great property of having better slipperiness than titanium dioxide, which has a low Mohs hardness.
Due to the high Mohs hardness, the particles have a high hardness during the magnetic tape manufacturing process and when used as a magnetic tape, so they have the disadvantage that scratches are likely to occur on the film surface, guide pins, etc. In addition, titanium dioxide, which has a low Mohs hardness, has inferior slipperiness compared to titanium dioxide, which has a high Mohs hardness, but when used in the magnetic tape manufacturing process and as a magnetic tape, the small hardness of the particles makes it difficult to use on film surfaces, guide pins, etc. It has the characteristic that it is advantageous in terms of the occurrence of scratches. As described above, the greatest feature of the present invention is that by combining two types of titanium dioxide with different Mohs hardnesses, only the good characteristics of both can be utilized to the maximum extent. The average particle size of rutile titanium dioxide is small and has a high Mohs hardness of 6.0 to 7.0.The average particle size is 0.01 to 7.0.
It must be 0.30μm, and the average particle size must be 0.05~
Preferably, it is 0.27 μm. Average particle size 001μm
If it is less than this, the effect of improving slipperiness will be insufficient, so it is not preferable. On the other hand, if the average particle diameter exceeds 0.30 .mu.m, the smoothness of the film surface decreases and the number of large particles that cause dropouts increases, which is not preferable. Also, the amount added to the polyester is
It is necessary to set the amount to 0.01 to 1.0% by weight, and more preferably the amount added is 0.1 to 0.7% by weight. The amount added
If it is less than 0.01% by weight, the effect of improving slipperiness and abrasion resistance will be insufficient, which is not preferable. On the other hand, if the amount added exceeds 1.0% by weight, the smoothness of the film surface decreases and the amount of coarse particles that cause dropouts increases, which is not preferable. The average particle size of anatase titanium dioxide is large and has a small Mohs hardness of 5.5 to 6.0.
A range of 0.31 to 1.0 μm is required, and the average particle size is more preferably 0.40 to 0.70 μm. Average particle size
If it is less than 0.31 μm, the effect of improving wear resistance will be insufficient, so it is not preferable. On the other hand, if the average particle diameter exceeds 1.0 .mu.m, the smoothness of the film decreases and the number of large particles, which causes dropouts, increases, which is not preferable. Also, the amount added to the polyester
Must be 0.002 to 0.5% by weight, and even 0.005
~0.3% by weight is more preferred. If the amount added is less than 0.002% by weight, the effect of improving wear resistance will be insufficient, which is not preferable. On the other hand, if the amount added exceeds 0.5% by weight, the smoothness of the film surface decreases and the amount of coarse particles that cause dropouts increases, which is not preferable. In order to improve slipperiness and wear resistance, the difference in average particle size between small particles of rutile-type titanium dioxide and large particles of anatase-type titanium dioxide must be at least
It is preferably 0.05 μm or more. The titanium dioxide used in the present invention is not limited in any way, including its manufacturing method, as long as it satisfies the conditions specified above. Further, a material without surface treatment may be used, or a material with surface treatment may be used. The value of the volume shape factor is 0.10 to π/6
It is preferable to use one within this range. [However, the volumetric shape factor F is expressed by the following equation. F=V/D In ^the formula, V is the particle volume (μm ³ ), and D is the maximum diameter (μm) of the particle in the projection plane. ] The volume shape factor is expressed in terms of the degree of sphericity of particles, and the closer to π/6, the closer to spherical the particle becomes. The average particle diameter used here is the value of 50% of the cumulative (weight basis) in the equivalent spherical diameter distribution measured with a centrifugal sedimentation type particle size distribution measuring device manufactured by Shimadzu Corporation. The titanium dioxide used in the present invention can be added to the polyester at any stage in the polyester manufacturing process, but it is preferably added after the transesterification or esterification reaction and before the polycondensation. In addition, the particles may be added to the polyester manufacturing process in either a slurry or powder form, but usually when adding particles to the polyester manufacturing process, automation, ease of metering, Particles are generally added as an ethylene glycol slurry from the viewpoint of improving dispersibility and simplifying the recovery system. When dispersing particles into a slurry, it is necessary to disperse them into a state of primary particles with as little agglomeration as possible. In order to uniformly disperse the particles to the state of primary particles, any method such as dispersion, crushing, pulverization, classification, and sieving can be employed as necessary. In order to obtain particles with a predetermined average particle size, methods such as pulverization, classification, and overtreatment of commercially available particles may be employed. When adding the particles as an ethylene glycol slurry, adding the particles so that the proportion of coarse particles of 2 μm or more in the slurry is 0.5% by weight or less based on the total particles reduces coarse protrusions on the surface of the film when it is made into a polyester film. It is particularly preferable for this purpose. In the present invention, if necessary, inert particles may be used in addition to titanium dioxide as long as the average particle size and content are such that they do not increase the number of coarse particles and do not adversely affect the smoothness of the film surface. It's okay.
In addition to the above-mentioned inert particles, fine particles precipitated by a reaction between a catalyst residue and a phosphorus compound in the reaction system can be used in combination. In the present invention, known methods can be employed for polymerizing polyester containing titanium dioxide. For example, as a catalyst for the polycondensation reaction, one or more of antimony compounds, germanium compounds, titanium compounds, etc. are used, heated to about 230 to 300°C, and the reaction is allowed to proceed by distilling off ethylene glycol under reduced pressure. In addition, when making a film, a known film forming method is used, for example, polyester chips are melt-extruded into a film at 270 to 300°C, then cooled and solidified at 40 to 70°C to form an amorphous sheet, and then sequentially biaxially in the vertical and horizontal directions. A method such as stretching or simultaneous biaxial stretching and heat treatment at 160 to 240° C. (for example, the method described in Japanese Patent Publication No. 30-5639) can be employed. <Examples> The present invention will be explained in more detail by Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In addition, various physical properties and characteristics were measured or defined as follows. In the examples, "parts" and "%" mean "parts by weight" and "% by weight," respectively. (1) Average particle size Centrifugal sedimentation type particle size distribution measuring device manufactured by Shimadzu Corporation
Use the cumulative value (weight basis) of 50% in the equivalent sphere diameter distribution measured by the SA-CP3 type. (2) Surface smoothness of film The method described in JIS B0601-1976 was used. The measurement was performed using a surface roughness measuring machine model SE-3F (manufactured by Koita Research Institute). Stylus diameter 2μ, stylus diameter 30mg,
The cutoff value was 0.05 mm, and the measurement length was 25 mm.
Measurements were made at 12 points, the maximum and minimum values were cut out, and the average value of the 10 points was shown. (3) Sliding property Represented by the friction coefficient, which is ASTM D-
1894, using a method modified to allow measurement using tape-shaped samples. The sample at the time of measurement had a width of 15 mm and a length of 150 mm, and the tensile speed was 20 mm/min. The measurements were carried out in an atmosphere with a temperature of 21±2° C. and a humidity of 65±5%. (4) Evaluation of scratches on the film surface The degree of scratches was evaluated by shining light on the film surface in a dark room. There are almost no scratches on the film surface ○ There are scratches on a part of the film surface △ There are scratches that can be visually observed on the entire surface of the film × (5) Abrasion resistance (evaluation of white powder) Figure 1 The film was run over a length of 500 m using the running system shown in Figure 2, and the amount of wear on the hard chrome fixing pin of 6 mm diameter, indicated by I, was visually evaluated. It doesn't stick at all. ○ Slight adhesion. △ The amount of adhesion is large. × (6) Number of coarse protrusions Aluminum was deposited on the surface of the film and measured by the two-light velocity method using an interference microscope. Calculate the number of protrusions that exhibit interference fringes of 4th or higher order at a measurement wavelength of 0.5μ.
The figures are calculated per ^25cm3 . Example 1 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and 0.09 parts of magnesium acetate tetrahydrate were placed in a reactor, heated to raise the temperature, and methanol was distilled off to perform a transesterification reaction, which took 4 hours from the start of the reaction. The transesterification reaction was substantially completed. Next, small particles of rutile titanium dioxide with an average particle size of 0.25 μm were dispersed in ethylene glycol, classified and overtreated, and 0.3% by weight was added.
and 0.1% by weight of large-particle anatase-type titanium dioxide with an average particle size of 0.50 μm previously dispersed in ethylene glycol, classified and overtreated, and mixed thoroughly.
After adding ethyl acid phosphate
0.04 part of antimony trioxide and 0.035 part of antimony trioxide were added and polycondensation was carried out for 4 hours to obtain a polyethylene terephthalate resin having an intrinsic viscosity of 066. After drying the polymer under vacuum, it is passed through an extruder to a thickness of
A 160 μm thick amorphous original film was prepared, then stretched 4 times in the machine direction and 3.9 times in the cross direction, and heat treated at 230° C. to obtain a biaxially stretched polyethylene terephthalate film with a thickness of 10 μm. The properties of the obtained polyester film are shown in Table 1. As shown in Table 1, the surface smoothness, slipperiness, occurrence of scratches, abrasion resistance, and number of coarse protrusions of the obtained film were very good, and were at extremely satisfactory levels as a film for magnetic tape. Example 2 The same method as in Example 1 was used except that the average particle diameter of the small-particle rutile titanium dioxide used in Example 1 was 0.15 μm instead of 0.25 μm, and the amount added was 0.5%. A biaxially stretched polyester film was obtained. The properties of the obtained polyester film were determined first.
Shown in the table. As shown in Table 1, the properties of the obtained film were the same as those of Example 1, and were at an extremely satisfactory level as a film for magnetic tape. Comparative Example 1 A biaxially stretched polyester film was produced in the same manner as in Example 1, except that 0.3% of rutile titanium dioxide having an average particle size of 0.25 μm was dispersed in ethylene glycol and subjected to classification and overtreatment. Obtained. The properties of the obtained polyester film are shown in Table 1. As shown in Table 1, the obtained film was poor in scratch resistance and abrasion resistance, and had insufficient properties as a magnetic tape. Comparative Example 2 Anatase-type titanium dioxide with an average particle size of 0.45 μm was dispersed in ethylene glycol in advance, classified,
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that 0.07% of the overtreated film was added alone. The properties of the obtained polyester film are shown in Table 1. As shown in Table 1, the obtained film had poor slip properties and abrasion resistance, and was insufficient as a magnetic tape characteristic. Comparative Example 3 Small particle rutile titanium dioxide with an average particle size of 0.25 μm was dispersed in ethylene glycol in advance, classified,
The same method as in Example 1 was carried out, except that 0.3% of the overtreated material and 0.07% of the classified and passed rutile titanium dioxide were dispersed in advance in ethylene glycol and large-particle rutile titanium dioxide with an average particle size of 0.45 μm were thoroughly mixed. A biaxially stretched polyester film was obtained. The properties of the obtained polyester film are shown in Table 1. As shown in Table 1, although the obtained film has satisfactory properties in terms of slipperiness and abrasion resistance, it is inferior in terms of the occurrence of scratches and is insufficient for use in magnetic tapes. Comparative Example 4 Small particle rutile titanium dioxide with an average particle size of 0.25 μm was dispersed in ethylene glycol in advance, classified,
Large-particle anatase titanium dioxide with an average particle size of 0.45 μm and 1.5% of the over-treated product is pre-dispersed in ethylene glycol, then classified and over-treated.
A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that 0.07% was thoroughly mixed and added. The properties of the obtained polyester film were determined first.
Shown in the table. As shown in Table 1, the obtained film has satisfactory properties in terms of slipperiness and abrasion resistance, but is inferior in terms of the number of coarse protrusions and is insufficient for use in magnetic tapes. Comparative Example 5 Small particle rutile titanium dioxide with an average particle size of 0.25 μm was dispersed in ethylene glycol in advance, classified,
0.3% of the over-treated material and 0.7% of the large-particle anatase-type titanium dioxide with an average particle size of 0.45 μm pre-dispersed in ethylene glycol, classified and filtered.
A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the ingredients were thoroughly mixed and added. The properties of the obtained polyester film are shown in Table 1. As shown in Table 1, the obtained film has satisfactory properties in terms of slipperiness and abrasion resistance, but is inferior in terms of the number of coarse protrusions and is insufficient for use in magnetic tapes.

[Table] <Effects of the Invention> As detailed above, the film of the present invention is a film containing specific amounts of small-particle rutile titanium dioxide with a specific particle size and large-particle anatase titanium dioxide with a specific particle size. It has excellent surface smoothness, slipperiness, and abrasion resistance required for polyester films for magnetic tapes, and is resistant to scratches and white powder that occur when running on metal roll surfaces during magnetic tape manufacturing and use. It has the characteristic that the amount generated is extremely small. In addition, when used for video tapes, it has a characteristic of significantly fewer large protrusions that can cause dropouts, so it can be used in a wide range of applications such as magnetic tapes, vapor deposition, capacitors, and packaging. Can be done.

[Brief explanation of the drawing]

Figure 1 shows the running system for evaluating wear resistance.
is a 6mmφ hard chrome fixing pin, and is a tension meter, and θ is 130°.

Claims (1)

[Claims] 1 0.01 to 1.0% by weight of rutile titanium dioxide with an average particle size of 0.01 to 0.30 μm and an average particle size of 0.31 to 0.30 μm
0.002~0.5 of 1.0μm anatase titanium dioxide
A biaxially oriented polyester film characterized by containing % by weight.