JPH025175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium that is suitable for video magnetic tapes, magnetic video disks, etc. and is capable of high-density recording and has excellent running properties. Generally, electroplating, electroless plating, vacuum deposition,
Magnetic tape, which is obtained by forming a ferromagnetic metal thin film on a plastic film substrate using methods such as sputtering or ion brating, has no binder resin or the like that exists between the magnetic materials, compared to conventional coated tapes. Therefore, it is suitable for high-density recording. As the film substrate, a biaxially stretched polyethylene terephthalate film (hereinafter referred to as polyester film) is usually used. Polyester film has good heat resistance, excellent mechanical strength, and the adhesion strength of vacuum-deposited films is relatively high, so it is often used with thin films of ferromagnetic metals such as iron, nickel, and cobalt. A magnetic recording medium is obtained by forming it on the surface. However, in video magnetic tapes in which a ferromagnetic metal thin film is directly applied to a polyester film, the thickness of the magnetic layer is extremely thick, which affects thickness loss, which reduces video output, compared to conventional coated tapes. It is thin, about 0.5μ at most. Therefore, the roughness on the surface of the base film becomes the roughness on the surface of the magnetic layer. Therefore, the presence of coarse protrusions on the film surface immediately causes dropouts. Furthermore, when recording short wavelengths, for example, 1 μm, the distance between the magnetic head and the tape should be approximately 200 mm in order to reduce the distance loss between the magnetic head and the magnetic layer to 1 dB or less.
It is reported that Å. From this point of view as well, a base film with a flat surface is desired. In this way, the surface roughness of the base film is
It directly affects the characteristics such as the size of the video output, the temporal variation of the output, and the dropout of the video signal. Therefore, it is desirable that the film surface be as flat as possible. However, on the other hand, polyester film is rolled into a long length and subjected to processes such as vapor deposition and coating. Therefore, the film surface has no irregularities at all.
If the film is extremely flat, scratches may occur during the film manufacturing process due to contact between the film and the metal roll. Furthermore, when the film is rolled up into a roll, surface defects such as wrinkles and lumps may occur, or in severe cases, blocking may occur, which significantly impairs the rewinding process and the passability of post-processing processes.
Such scratches, creases, bump-like surface defects, etc. are not good when a magnetic thin film is provided and the characteristics of a magnetic tape, especially a video tape, are evaluated because they cause deterioration of the characteristics, especially frequent dropouts. Moreover, using a completely flat film with no unevenness on the surface,
When a magnetic tape is made of a magnetic metal thin film, it has extremely poor sliding properties with the head and cannot run smoothly. Since a completely flat film causes various problems as mentioned above, it is necessary to form some unevenness on the film surface. As a method to improve slipperiness by imparting irregularities to the film surface, inert fine particles based on the residue of the catalyst used during polyester production are precipitated into the polymer, or inert inorganic particles such as silica, kaolin, calcium carbonate, etc. A method of roughening the surface of a film by adding particles of a compound is known. However, such a surface roughening method is difficult for magnetic tapes having a magnetic metal thin film layer provided on the surface of the film, especially for video tapes. For example, in the method of adding inorganic particles, extremely fine particles are required, which requires pulverization and classification. However, the particles obtained in this way always have a particle size distribution, and the presence of coarse particles is unavoidable.To completely remove coarse particles, it takes a large amount of time and cost, and it is difficult to use industrially. disadvantageous to Furthermore, even if non-metallic coarse particles are obtained in this way, dispersion in the polymer becomes a problem and often causes agglomeration. On the other hand, in the precipitation method based on catalyst residue, it is difficult to completely prevent the agglomeration and coarsening of precipitated particles during the polymerization reaction and form particles with a constant particle size in the polymer with good reproducibility. Therefore, the present inventors conducted intensive studies to obtain a polyester film for magnetic tape provided with a magnetic metal thin film that does not impair video characteristics and has good running properties, and as a result, the present invention was completed. That is, the present invention is a polyester film containing 0.2 to 10% by weight of a polyoxyalkylene glycol component, and the surface roughness of the film is 0.003 to 0.06μ at the maximum height. It resides in a magnetic recording medium on which a magnetic metal thin film layer is formed. The present invention will be explained in more detail. The polyester referred to in the present invention refers to a polyester obtained using terephthalic acid or its alkyl ester and ethylene glycol as main starting materials, but other third components may be used as part of the raw materials. The third component includes one or more aromatic dicarboxylic acid components such as isophthalic acid, naphthalene dicarboxylic acid, or alkyl esters thereof, and one or more glycol components such as propylene glycol and tetramethylene glycol. Can be used. In any case, the polyester of the present invention is
A polyester in which at least 80% of the repeating structural units are ethylene terephthalate units. The polyester film used in the present invention must have a surface roughness of 0.003 to 0.06 μ at the highest height. (The highest value of this height is JIS-
In order to form such a film (measured by the method defined in B0601), it is necessary to include a polyoxyalkylene glycol component in the film. Examples of specific compounds of this polyoxyalkylene glycol include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, copolymers of ethylene oxide and propylene oxide, and copolymers of ethylene oxide and tetrahydrofuran. Examples include. The molecular weight of polyoxyalkylene glycol is
400 to 200,000, preferably 500 to 100,000 in terms of thermal dimensional stability and ease of handling in the film forming process
The one is good. To give a preferred specific example, polyoxyalkylene glycol has a molecular weight of 3,000 to 100,000,
Polyoxytetramethylene glycol is 500~
5000. The content of polyoxyalkylene glycol in the film is 0.2 to 10% by weight, and even 0.5 to 8% by weight.
It is preferable to select within the range of . The content of polyoxyalkylene glycol is
If the amount is less than 0.2% by weight, the surface roughening of the polyester film will not be sufficient, while if it is more than 10% by weight, the surface of the film will tend to become too rough and should not be used for this purpose. Can not. The polyoxyalkylene glycol contained in the polyester film may be in the form of a bond with polyester, or may be in the form of just mixed with polyester. The case where polyoxyalkylene glycol is contained in a form bonded to polyester means, for example, when polyoxyalkylene glycol is contained in polyester production, at any time from the beginning of esterification or transesterification to the completion of polycondensation. A method of adding polyoxyalkylene glycol as a glycol component to obtain a polyester containing polyoxyalkylene glycol as a glycol component and forming a film using this alone, or blending the copolymer thus obtained with another polyester and then There is a method of forming a film containing a predetermined amount of polyoxyalkylene glycol. In the latter case, the copolymer containing polyoxyalkylene glycol does not necessarily need to have polyethylene phthalate as its main component;
In addition to terephthalic acid, isophthalic acid,
It may contain other dicarboxylic acids, and glycol components such as 1,4-butanediol, 1,
Glycols such as 3-propanediol and hexamethylene glycol may be used.
In this case, the content of polyoxyalkylene glycol in the copolymer is suitably 5 to 50% by weight. The latter method is preferred in order not to damage the original properties such as mechanical properties of the polyester film. When polyoxyalkylene glycol is mixed with polyester, there are methods such as mixing in a guide tank after the completion of the polyester polymerization reaction, or mixing at the time of coating. The thus obtained polyester containing polyoxyalkylene glycol is melt extruded and
An unstretched film is obtained, further biaxially stretched sequentially or simultaneously, and then heat-set to obtain a biaxially stretched oriented polyester film. In the present invention, it is particularly preferable to stretch at a temperature of 95°C, preferably 100°C or higher in order to develop fine and uniform roughness on the surface. The thickness of the biaxially stretched polyester film used in the present invention is preferably 6 to 15 μm for this purpose, but is not limited thereto. In the present invention, the magnetic metal thin film can be formed by the various methods described above, but among them, methods such as vacuum evaporation, sputtering, and ion plating are preferred. Further, as the ferromagnetic metal material, iron, cobalt, nickel, or an alloy thereof is preferably used. Hereinafter, the present invention will be explained by giving specific examples. In addition, in the following examples, "part" or "%" is
Each refers to parts by weight or % by weight. A method for evaluating characteristic values in the present invention will be described below. 1 Surface roughness Using an ET-10 type thin film step measuring instrument manufactured by Kosaka Institute Co., Ltd., a cross-sectional curve was drawn at a vertical magnification of 500,000 times and a horizontal magnification of 200 times, as defined by JIS-B0601 (stylus force of 50 mg or less). The maximum height (Rmax) was shown using the method. 2 Measurement of friction coefficient The film was brought into contact with a metal pin with a diameter of 4 mm and a surface finish of 0.2S made of SUS420 at an angle of 135° (θ), and a load of 22.3 g (W) was applied to one end.
It was run at a speed of 880 mm/min, the resistance force (F)g at the other end was measured, and the coefficient of friction was determined using the following formula. μ = 1/θln (F/W) = 0.424ln (F/22.3) 3 Relative viscosity (ηrel.) Dissolve 1g of polymer in 100ml of mixed solvent of phenol/tetrachloroethane 50/50 (weight ratio)30
Measured at °C. Example 1 90 parts of dimethyl terephthalate, average molecular weight 8500
10 parts of polyoxyethylene glycol, 60 parts of ethylene glycol and 0.09 parts of magnesium acetate tetrahydrate
A portion of the mixture was placed in a reactor and a transesterification reaction was carried out.
The reaction starts when the internal temperature reaches 160℃.2
After an hour, the temperature was raised to 200°C, and after another 2 hours, the temperature was raised to 230°C. After the transesterification reaction was completed, 0.046 part of triester phosphate and 0.04 part of antimony trioxide were added, and a polycondensation reaction was carried out according to a conventional method. That is, the reaction temperature was gradually increased from 230° C. at the start of the reaction, and finally reached 280° C., while the pressure was gradually decreased to finally reach 0.5 mmHg. After 3 hours, the reaction was stopped,
The pressure inside the system was restored and the polymer was extracted to obtain a polyester copolymer containing 10% polyoxyethylene glycol. The ηrel. of this polymer was 1.90. Next, 30 parts of the copolymerized polyester and 70 parts of a polyoxyalkylene glycol-free polyethylene terephthalate resin separately produced by a conventional method were dry blended, dried under vacuum at 160°C for 6 hours, melted at 290°C, and dried in a T-die. After extrusion and quenching, the film was stretched 4 times in the longitudinal direction at 95℃, 3.5 times in the transverse direction at 105℃, and heat-set at 230℃ to increase the thickness.
A 12μ biaxially stretched oriented film was obtained. The surface roughness, friction coefficient, etc. of the obtained film were evaluated. Furthermore, the thickness is increased by vacuum deposition on the surface of this film.
A 0.2μ cobalt ferromagnetic thin film was formed and the output at 4MHz was evaluated as a videotape. The results are shown in Table 1. Example 2 97 parts of dimethyl terephthalate, average molecular weight
3 parts of polyoxyethylene glycol 20,000, 65 parts of ethylene glycol, and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor in the same manner as in Example 1.
A transesterification reaction and a subsequent polycondensation reaction were performed to obtain a polyester resin in which 3% polyoxyethylene glycol was copolymerized. The ηrel. of this copolymer was 1.84. Next, the copolymerized polyester was vacuum-dried at 160°C for 6 hours and melt-extruded at 290°C to obtain a biaxially stretched oriented polyester film having a thickness of 12μ in the same manner as in Example 1. To the polyester film,
A ferromagnetic thin film of cobalt with a thickness of approximately 0.2μ was deposited by vacuum evaporation, and video evaluation was performed. The results are shown in Table 1. Example 3 52.9 parts of dimethyl terephthalate, 29.5 parts of 1,4-butanediol, 40 parts of polyoxytetramethylene glycol with a molecular weight of 1000, and 0.01 part of tetra-n-butyl titanate were placed in a reactor, and a transesterification reaction was carried out under heating and stirring. Summer. In other words, the internal temperature
The reaction was started at 160°C, and after 2 hours the temperature was raised to 200°C.
After another 2 hours, the temperature was increased to 220°C. After the transesterification reaction was completed, 0.01 part of tetra-n-butyl titanate was further added to carry out a polycondensation reaction. That is, the reaction temperature was gradually increased from 220° C. at the start of the reaction and finally reached 245° C., while the pressure was gradually decreased from normal pressure to finally reach 0.5 mmHg. After 2.5 hours, the reaction was stopped, the pressure inside the system was restored, and the polymer was extracted to obtain a polybutylene terephthalate-polytetramethylene glycol copolymer. ηrel. of the copolymer is 3.7
It was hot. 37.5 parts of this copolymer and 96.25 parts of polyethylene terephthalate resin that does not contain polyoxyalkylene glycol are dry blended,
After drying under vacuum at 160°C for 6 hours, melting at 285°C, extruding from the lower die, quenching, stretching 4 times in the machine direction with rolls at 95°C, then stretching 3.5 times in the transverse direction with a tenter at 100°C. Heat set at 220℃, thickness 12μ
A biaxially stretched oriented polyester film was obtained. A ferromagnetic metal thin film layer was formed by vapor depositing cobalt to a thickness of 0.2μ on this polyester film to create a magnetic tape, and the video output was evaluated. The results are shown in Table 1. Example 4 A masterbatch resin containing 10% polyoxyethylene glycol was prepared by melt-mixing 10 parts of polyoxyethylene glycol with an average molecular weight of 6000 in an extruder to 90 parts of polyethylene terephthalate containing no polyoxyethylene glycol. It was created. 20 parts of this masterbatch resin and 80 parts of polyethylene terephthalate resin not containing polyoxyethylene glycol were dry blended, vacuum dried at 160°C for 6 hours, then melt extruded at 290°C, and the same procedure as in Example 1 was carried out. After obtaining a biaxially stretched oriented film with a thickness of 12μ, a magnetic tape with a cobalt ferromagnetic thin film of a thickness of 0.2μ was further prepared, and video evaluation was attempted. The results are shown in Table 1. Comparative Example 1 A polyethylene terephthalate resin containing fine particles based on catalyst residue was produced as follows. That is, 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.08 parts of calcium acetate hydrate.
1 part and 0.018 part of lithium acetate dihydrate are placed in a reactor, heated and raised in temperature, methanol is distilled off, and transesterification is carried out.
The temperature was raised to 230°C over a period of time, and the transesterification reaction was substantially completed. Next, 0.05 part of phosphoric acid, 0.19 part of triethyl phosphate, and 0.04 part of antimony trioxide were added to the product after the transesterification reaction, and then a polycondensation reaction was carried out according to a conventional method. 3.5
After a period of time, the reaction was stopped and the pressure in the system was restored to obtain a polyethylene terephthalate resin with ηrel.=1.72. This polyester contained many fine particles. Then, a film was formed in the same manner as in Example 1 to a thickness of 12 μm.
After obtaining the biaxially stretched oriented polyester film,
Subsequently, a cobalt ferromagnetic thin film layer with a thickness of 0.2 μm was formed by vapor deposition, and video evaluation was performed, but no output was obtained and the film was unsuitable for high-density recording. The evaluation results are shown in Table 1. Comparative Example 2 An ethylene glycol slurry of terephthalic acid with a molar ratio of ethylene glycol to terephthalic acid of 1.30 was charged into the esterification reaction product with an esterification reaction rate of 97%, which had been left in the reaction tank in advance, and the slurry was batch-treated. The esterification reaction was carried out by the method. The esterification reaction rate at the end of the reaction is 97
% and number average degree of polymerization was 4.9. Approximately 1/2 of the resulting reaction product was subjected to the subsequent polycondensation reaction, and the remainder was used again for the next batch of esterification reaction. To 106 parts of the esterification reaction product (equivalent to 100 parts of ethylene terephthalate units) transferred to the polycondensation reaction tank, 0.01 part of phosphoric acid and antimony trioxide were added.
Add 0.04 parts and carry out a polycondensation reaction,
A polyethylene terephthalate resin with ηrel.1.75 was obtained. The resin has excellent transparency, and almost no particles based on catalyst residue are formed. Next, using the resin, melt extrusion and stretching orientation were performed in the same manner as in Example 1 to obtain a biaxially oriented polyethylene terephthalate film. The film had poor slipperiness and the coefficient of friction could not be measured. Also, during vapor deposition, there were many problems due to poor film slippage. The evaluation results are shown in Table 1. 【table】

Claims (1)

[Claims] 1 0.2 polyoxyalkylene glycol component
A polyester film containing ~10% by weight, and the surface roughness of the film is at the highest value of height.
A magnetic recording medium in which a magnetic metal thin film layer is formed on a biaxially stretched polyester film having a thickness of 0.003 to 0.06μ.