KR100200428B1 - Manufacturing method of biaxially oriented ployester film for high density magnetic recording medium - Google Patents

Abstract

The present invention relates to a polyester film which is widely used as an industrial base material due to its excellent physical and chemical properties. In particular, the present invention relates to a high density magnetic recording medium having excellent running characteristics of the film and excellent physical properties such as wear resistance and mechanical strength. It is an object of the present invention to provide a suitable biaxially oriented polyester film.

The present invention specifically biaxially stretches and thermosets an unstretched film in which a polyethylene naphthalate resin containing aluminum silicate particles having a specific particle size and a polyethylene naphthalate resin containing hexahedral calcium carbonate particles having a calsite structure of a specific particle size are laminated. A method of manufacturing a biaxially oriented polyester film characterized in that the manufacturing method, the film produced as described above is excellent in smoothness and biactivity at the same time excellent film running resistance when applied for high-density magnetic recording media, friction resistance, mechanical properties, etc. This shows excellent performance.

Description

Manufacturing method of biaxially oriented polyester film for high density magnetic recording medium

The present invention relates to a polyester film having high mechanical strength and good dimensional stability, and having an extremely smooth film surface, which exhibits excellent electron conversion characteristics when made of magnetic tape, and which has excellent abrasion resistance and runability. The present invention relates to a method for producing a biaxially oriented polyester film for a high-density magnetic recording medium having excellent properties, extremely low abrasion and scratches when rubbing with a film or metal roll, and having a thin thickness and excellent mechanical strength.

Polyester films are widely used as industrial base materials because of their excellent physical and chemical properties. In particular, biaxially stretched polyethylene terephthalate films have superior planarity, dimensional stability, and mechanical strength compared to other films, such as base films for video and audio magnetic recording media, films for condensing and electrical insulation, packaging and graphics, etc. It is widely used as an industrial film.

The magnetic recording medium is obtained by forming a magnetic layer on the surface layer of the base film using magnetic particles together with a binder, or by coating the surface of the base film with magnetic metal by vacuum deposition, sputtering or plating. However, in recent years, as the demand for high-density recording on magnetic recording media increases, the emphasis has been on improving heat resistance and physical properties. Polyethylene terephthalate films have long been used as magnetic recording films, and much effort has been made to improve these films in order to meet the demands of high density magnetic recording media. However, polyethylene terephthalate does not have sufficient heat resistance, so the dimensional stability of the film is poor, and its mechanical strength is difficult to increase beyond a certain degree. Therefore, there is a demand for the development of a film that satisfies all the properties required for a high density magnetic recording medium.

On the other hand, polyethylene naphthalate having a naphthalene ring in the molecular chain has a rigid molecular structure, so films made of this material are known to be excellent in heat resistance, mechanical strength and dimensional stability, specifically, Japanese Patent Publication No. 48-29514 Japanese Patent Laid-Open No. 50-45877, Japanese Patent Laid-Open No. 56-19012, and the like disclose magnetic recording tapes employing polyethylene naphthalate films as base films and methods for producing the same. However, the conventional manufacturing methods do not fully utilize the advantages of polyethylene naphthalate only because the polyethylene naphthalate film is manufactured by simply manufacturing the polyethylene terephthalate film, and the productivity is low, so it is not satisfactory for commercial use.

On the other hand, in recent years, the improvement of the magnetic recording medium has been rapidly made, which naturally requires the improvement of the quality of the base film. For example, high density recording is required to be used for magnetic tape such as video tape, and a base film having a high smooth surface is required. However, in order to improve the process runability, diactivity, and abrasion resistance of the film, external particles such as calcium carbonate, silica, alumina, zirconia, titanium dioxide, crosslinked polymer particles are added to the film, and by any catalyst precipitation in the film. Internal particle methods in which particles are produced are already known. For this reason, the surface roughness of the film due to the particles used should be maintained at an appropriate level. At this time, if the surface roughness of the film is lowered to an appropriate level by using particles of too small particle size, the electron conversion characteristics of the tape can be improved when used as a magnetic tape, but the running performance in the film manufacturing process is poor and the film is used when used with the film. Although the running property of the film may be improved, the giant protrusions generated by the large particles in the film may increase the surface roughness of the film, thereby deteriorating the electron conversion characteristics such as dropout of the magnetic tape.

In order to improve the electron conversion characteristics, smoothness is required on the surface of the nonmagnetic support, and appropriate roughness is required in order to improve handing and running characteristics. There is a need for a film that can satisfy these two opposing properties simultaneously.

As a specific polyester film production method that can satisfy the two properties described above, a method of forming a discontinuous coating structure by applying a specific coating on the film surface (Japanese Patent Laid-Open No. 3-80410, Japanese Patent Laid-Open No. 60) -180837, SO 60-180838, SO 56-16937, SO 58-68223), when the polyester film is used as a magnetic tape, the surface of the film surface on which the magnetic material is applied or deposited and the opposite surface thereof is different from that of the magnetic tape. A method of forming a laminated polyester film having improved electron conversion characteristics and runability in a film manufacturing process when produced (Japanese Patent Application Laid-Open No. Hei 1-26337, Hei 1-26338, Japanese Laid-Open Patent Publication No. 57-36340, Small 57- 36341, small 57-36342, small 57-36343, flat 2-269048, flat 2-214657, flat 3-187741, flat 3-325674).

However, due to the extremely low surface roughness of the film surface on which the magnetic material is applied or deposited, such a film may cause blocking, abrasion and scratches due to friction with metal rolls in the film manufacturing process. In spite of the low surface roughness of the film, when made of magnetic tape, the electronic conversion characteristics of magnetic tape such as dropout may be deteriorated. Conventionally, in order to improve wear resistance of a film, a method of adding high-hardness microparticles such as alumina oxide to the front surface of a film (Japanese Patent Laid-Open Publication No. Hei 2-24823, Hei 2-129230, Hei 3-169932, Hei 5-16224 ) And a method of forming a discontinuous coating by applying a coating containing high hardness microparticles (Japanese Patent Laid-Open Nos. Hei 6-64034, Hei 6-143409, Hei 6-179762, Hei 6-200064) and the like are known.

However, the polyester film obtained by the conventional technique as described above has good elasticity, heat resistance, mechanical strength, and chemical properties, has sufficient surface smoothness for high density magnetic recording, and is difficult to satisfy all physical properties such as running and abrasion resistance. to be. It is an object of the present invention to provide a biaxially oriented polyester film for a high density magnetic recording medium capable of satisfying not only excellent elastic modulus, heat resistance, mechanical strength and chemical properties but also excellent surface smoothness, running property and wear resistance at the same time. .

That is, the present invention uses a certain amount of particles having a specific particle diameter in the film composed of polyethylenetaphthalate resin having an intrinsic viscosity of 0.45 or more and 0.70 or less, thereby adjusting the centerline average roughness of the film to satisfy a specific range of conditions. At the same time, the present invention provides a method for producing a polyester film which is excellent, has high mechanical strength and good dimensional stability by stretching under specific film forming conditions, and has excellent physical properties with little dropout.

The present invention specifically relates to polyethylenenaphthalate resins having an intrinsic viscosity of 0.45 to 0.70 and containing an aluminum silicate particle having an average particle diameter of 0.01 to 0.1 µm and a hexahedral structure of a calsite structure having an average particle diameter of 0.5 to 1.5 µm. A high-density magnetic recording medium characterized in that it is prepared by stretching and thermal curing after making an unstretched film loaded with polyethylene naphthalate resin having an intrinsic viscosity of 0.45 to 0.70% by weight containing calcium carbonate particles. It relates to a method for producing a biaxially oriented polyester film.

Hereinafter, the present invention will be described in detail.

The polyethylene naphthalate used in the present invention means a polymer containing 90 mol% or more of polyethylene-2,6-naphthalate, and a mixture of polyester and polyethylene naphthalate in a range that does not significantly impair the properties of polyethylene naphthalate or As the main structural unit, a copolymer including ethylene naphthalate unit may be used. Polyethylenenaphthalate may include stabilizers such as phosphoric acid, phosphorous acid and esters thereof. The intrinsic viscosity of such polyethylene naphthalate is preferably in the range of 0.45 to 0.70 (more preferably 0.50-0.65).

The average particle diameter of the aluminum silicate microparticles used in the polyester film (I) is 0.01-0.1 µm, the least occurrence of wear and scratches and excellent wear resistance. When the thickness exceeds 0.1 µm, the mean square surface roughness of the film is 0.01 µm or more. As a result, the electronic conversion characteristics of the tape may deteriorate when the magnetic particles are made of magnetic tape. When the thickness is less than 0.01 μm, the mean square surface roughness of the film becomes 0.01 μm or less, and the difference between the maximum height Rp and the maximum depth Rv is 0.03 μm or less at the surface center line, thereby exhibiting sufficient electron conversion characteristics. If the amount is more than 0.5% by weight, the surface roughness is increased, the electron conversion characteristics are lowered, and when the amount is less than 0.05% by weight, the wear resistance of the film cannot be sufficiently exhibited.

When the average particle diameter of the calcite-shaped calcium carbonate particles having a calcitic structure used in the polyester film (II) is 0.5 to 1.5 µm (more preferably, 0.5 to 1.0 µm), the process running property of the film is the best, and it is less than 0.5 µm. When the particles are used, the running performance deteriorates, and when the particle size is larger than 1.5 mu m, a large protrusion is formed in the film, thereby showing high surface roughness. This is a factor that worsens the electron conversion characteristics when the magnetic material is transferred to the film (I) surface on which the film is applied or deposited on the film roll to increase the surface roughness, and when manufactured with the magnetic tape. In addition, when the added amount of particles is 0.1 to 5.0% by weight (more preferably, 0.5 to 2.0% by weight), the number of surface protrusions having a uniform size in the film increases and the density increases, so that the centerline average surface roughness (Ra) is 0.01-. It is lowered to 0.015 µm, and the process running property of the film is excellent. When the added amount is more than 5.0% by weight, the process runability of the film becomes good, but the surface roughness is increased, and the coarse particles increase due to the agglomeration of particles, which is transferred to the film (I) surface on which the magnetic material is applied or deposited on the film roll to increase the surface roughness. When manufactured with magnetic tape, it becomes a factor to deteriorate the electron conversion characteristics, and when used at less than 0.1% by weight, wear resistance cannot be sufficiently exhibited.

The biaxially oriented polyester film made of polyethylene naphthalate can be obtained by the following method.

A polyethylene naphthalate polymer containing particles is produced by a conventional method, and then made into chips and dried. This polymer is loaded through a coextruder and cooled to cure on a cooling drum. The unstretched film was stretched 2.0 to 5.0 times in the longitudinal direction at 110 ° C. to 160 ° C., then stretched 2.0 to 5.0 times in the transverse direction at 130 ° C. to 180 ° C., and heated at 200 ° C. to 250 ° C. for 1 second to 10 minutes. Harden.

The biaxially stretched polyester film according to the present invention has a tensile stress (F-5 value) of 15 kg / mm 2 or more in the longitudinal and lateral directions, a heat shrinkage of 2% or less in the longitudinal and lateral directions, and a crystallinity of 40 or less. It is desirable to manufacture so that the physical properties.

As described above, the present invention provides an unstretched film made of polyethylenenaphthalate resin having an extreme viscosity suitable for producing a polyester film, and controls drawing conditions within a specific range during the film forming process, and controls a particle source having a specific particle size in an appropriate range. By adjusting so as to satisfy the conditions, it is possible to economically obtain a film having physical properties suitable for high density magnetic recording media.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, and the evaluation of the overall physical properties measured herein was measured by the following method.

(1) F-5 value

The F-5 value represents the tensile stress measured when the film sample of 10 mm width was stretched 5% with a tensile tester at a temperature of 25 ° C., a distance of 100 mm between chucks, and a tensile speed of 20 mm / min.

(2) YOUNG'S MODULUS

The Young's modulus was shown as the initial Young's modulus at the time of tension when the film sample of 10 mm width was extended | stretched at the temperature of 25 degreeC, the distance of 100 mm between chucks, and the tensile speed of 20 mm / min.

(3) heat shrinkage

Heat shrinkage was measured after the film specimens were left in an oven at 150 ° C. for 30 minutes.

(4) Film centerline roughness (SRa) and centerline maximum roughness (SPmax)

SRa and SRmax were measured using a three-dimensional surface roughness meter manufactured by KOSAKA of Japan.

(5) crystallinity

It was measured using the density gradient tube method.

(6) oligomer amount

The film specimen was immersed in chloroform for 5 minutes and the amount of oligomer extracted in chloroform was analyzed by U.V. to the size of the peak measured at 245 mm of WAVELENGTH.

(7) active activity

The polyester film was made of a roll tape of a predetermined width, and then driven while contacting with a metal guide roll fixedly for a long time, the degree of scratching on the surface of the film was observed under a microscope, and the amount of powder generated on the guide roll was visually observed to determine as follows.

Class A: Almost no scratch on film surface after friction with guide roll.

Class B: Small scratches on the film surface after friction with the guide roll.

Class C: Scratches on the film surface after friction with the guide roll.

Level 1: Almost no powder occurs.

Level 2: Small amount of powder occurs.

Level 3: A large amount of powder occurs.

(8) dropout

Using a conventional method, the magnetic layer is coated on the surface of a biaxially oriented polyester film with a thickness of 4 μm to produce a video tape, and then the optimal current is recorded on the video tape by a five-step disparity signal. It was regarded as dropout that the duration time was 15 µsec or more, the measurement was continued for 30 minutes, and then averaged per minute and calculated.

Example 1

A mixture of 100 parts by weight of 2,6-dimethylnaphthalate, 70 parts by weight of ethylene glycol, 0.07 parts by weight of magnesium acetate tetrahydrate, 0.03 parts by weight of antimony trioxide and germanium dioxide was heated in a reactor to release methanol, and transesterification was carried out. Was carried out. The reaction mixture was completed transesterification over 4 hours. To the reaction mixture, 0.03 parts by weight of trimethyl phosphate and 1.0 parts by weight of aluminum silicate particles having a mean particle size of 0.05 占 퐉 (Japanese catalyst) were subjected to a polycondensation reaction for 4 hours to obtain polyester (I). The reaction was carried out in the same manner as the polyester (I), and polycondensation reaction was carried out by adding hexahedral calcium carbonate particles of calsite structure having an average particle diameter of 1.0 µm in place of aluminum silicate to carry out the polycondensation reaction. ) 15% of the polyester (I) synthesized above and 85% of the particleless polyester polymer were mixed and fed to the extruder 1, 15% of the polyester (I), 50% of the polyester (II) and 35% of the particleless polyester Was fed to extruder 2 and applied at 290 ° C. to extrude through a feed block to join the polymers. The resultant was cooled and solidified in a casting drum at 30 ° C. using an electrostatic casting method to produce an amorphous non-stretched two-layer film. . The unstretched film was stretched 4.0 times in the longitudinal direction at 130 ° C., 3.5 times in the transverse direction at 140 ° C., and then thermally cured at 230 ° C. for 40 seconds to obtain a film having a thickness of 8 μm. Thereafter, a magnetic tape was prepared by applying an iron oxide magnetic material to the obtained polyester film, and the physical properties were evaluated and shown in Tables 1 and 2.

Example 2

The film was obtained by the same method as Example 1 except that the longitudinal draw ratio was 4.5 times and the lateral draw ratio was 4.0 times, and the film properties are shown in Tables 1 and 2.

Example 3

Except for changing the particle addition amount and size was carried out in the same manner as in Example 1 to obtain a film, the film properties are shown in Table 1 and 2.

[Comparative Examples 1,2,3]

Under the conditions shown in Table 2 was carried out in the same manner as in Example 1 to obtain a film, the film properties are shown in Table 2.

TABLE 1

TABLE 2

As can be seen from the above examples and comparative examples, the biaxially oriented polyester film prepared with polyethylene naphthalate as the main component according to the present invention has excellent smoothness and biactivity at the same time, so that the film runs when applied for high density magnetic recording media. It has excellent properties, extremely low wear and scratches when friction with metal rolls, and mechanical properties.

Claims (4)

Polyhedral calcium carbonate with a calcined structure of polyethylenenaphthalate resin having an intrinsic viscosity of 0., 45-0.70 containing 0.05-0.5% by weight of aluminum silicate particles having an average particle diameter of 0.01-0.1 µm Preparation of biaxially oriented polyester film for high-density magnetic recording media, characterized by biaxially stretching and thermosetting a non-stretched film having a polyvinyl naphthalate resin having an extreme viscosity of 0.45 to 0.70 containing 0.1 to 5.0% by weight of particles Way. The method for producing a biaxially oriented polyester film for a high density magnetic recording medium according to claim 1, wherein the polyester resin contains 90 mol% or more of ethylene naphthalate units. 2. A method for producing a biaxially oriented polyester film for a high density magnetic recording medium according to claim 1, wherein the biaxial stretching is performed by stretching 2.0-5.0 times in the longitudinal direction and 2.0-5.0 times in the transverse direction. The method for producing a biaxially oriented polyester film for a high density magnetic recording medium according to claim 1, wherein the thermal curing is performed at 200-250 ° C for 1 second to 30 minutes.