KR0175548B1 - Biaxially Oriented Polyester Film for High Density Magnetic Recording Media - Google Patents

Abstract

The present invention relates to a biaxially oriented polyester film for high density magnetic recording media composed of polyethylene naphthalate having a smooth surface, good mechanical strength, and excellent dimensional stability. The purpose of this invention is to obtain a biaxially oriented polyester film useful as a base film for high density magnetic recording media which has no defects such as drop-out, and its technical configuration is 0.01 to 1.0% by weight of inert particles having an average particle diameter of 0.01 to 2.0 µm. A biaxially stretched unstretched film composed of polyethylene naphthalate resin having an intrinsic viscosity of 0.45 to 0.70 is biaxially stretched in the longitudinal and transverse directions, respectively, so that the tensile stress of the film is not less than 15 kg / mm2 in the transverse longitudinal direction and the heat shrinkage is bidirectional air 2 % Or less, crystallinity is 40% or less in both directions, Young's modulus is 600kg / mm2 or more in both directions, oligomer A biaxially oriented polyester film useful for high-density magnetic recording media, characterized in that the amount is 5 mg / m 2 or less, the center line average roughness SRa is 0.005 to 0.015 mu m and the center line maximum roughness SPmax is 0.05 to 0.3 mu m.

Description

Biaxially Oriented Polyester Film for High Density Magnetic Recording Media

The present invention relates to a biaxially oriented polyester film for high density magnetic recording media composed of polyethylene naphthalate having a smooth surface, good mechanical strength, and excellent dimensional stability. The present invention relates to a biaxially oriented polyester film useful as a base film for a high density magnetic recording medium having excellent mechanical strength and no defects such as output fluctuation or drop-out during reproduction.

In general, polyesters, especially polyethylene terephthalate, have excellent mechanical and chemical properties, and thus are widely used in medical and industrial textiles. Especially, biaxially stretched polyester films have flatness, dimensional stability, and mechanical strength. It is excellently used as a base film for magnetic recording media such as video and audio, capacitors and films for electrical insulation, and industrial films such as packaging or graphics.

In particular, the magnetic recording medium is obtained by forming a magnetic layer using a magnetic component or magnetic metal on the surface of the film together with a binder or by depositing it on a base film by vacuum deposition or sputter plating. As the demand for high-density recording of the medium has recently increased, the quality improvement for the base film has been rapidly progressed.

In general, polyethylene terephthalate does not have sufficient heat resistance, so the dimensional stability of the film is poor and it is difficult to increase the mechanical strength beyond a certain limit. Therefore, there has been a great demand for the development of a film having all the characteristics 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, and thus a base film for a high density magnetic recording medium made of polyethylene naphthalate has been developed. In other words, Japanese Patent Laid-Open Publication No. 48-29541, Japanese Patent Laid-Open No. 56-19012, Japanese Patent Laid-Open No. 50-45877 and the like propose a magnetic recording tape to which a polyethylene naphthalate film is applied as a base film.

However, all of these methods produce a polyethylene naphthalate film by a method of manufacturing a conventional polyethylene terephthalate film, and thus do not fully utilize the advantages of polyethylene naphthalate and are not satisfactory for commercial use due to low productivity.

Therefore, the inventors of the present invention provide a biaxially oriented polyester film for a high-density magnetic recording medium having excellent heat resistance and dimensional stability, excellent smoothness, high activity, thin thickness, and excellent mechanical strength by using a rigid molecular structure of polyethylene naphthalate. As a result, it was possible to obtain desired smoothness and diactivity by adjusting the average roughness of the centerline of the film by using inert particles having a constant particle diameter in the film composed of polyethylene naphthalate resin having an intrinsic viscosity of 0.45 or more and 0.75 or less. The present invention can be improved by improving the production yield of a polyester film for high density magnetic recording media having excellent mechanical strength and good dimensional stability and having excellent physical properties without causing dropout. will be.

The present invention makes an unstretched film of polyethylene naphthalate resin having an intrinsic viscosity of 0.45 to 0.70 containing 0.01 to 1.0 wt% of inert particles having an average particle diameter of 0.01 to 2.0 µm in polyester, which is longitudinally at 110 to 160 ° C. After stretching at 2.0 to 5.0 times, stretching at 2.0 to 5.0 times at 130 to 180 ° C. in the lateral direction, and thermal curing at 200 to 250 ° C. for 1 second to 10 minutes, the biaxially oriented polyester film for high density magnetic recording medium. At 5% elongation, tensile stress is 15kg / mm2 or more in the longitudinal and lateral directions, Young's modulus is 600kg / mm2 or more in the longitudinal and transverse directions, thermal shrinkage is 2% or less in the longitudinal and transverse directions, crystallinity is 40% or less, A biaxially oriented polyester for a high density magnetic recording medium characterized by satisfying that the oligomer amount is 5 mg / m 2 or less, center line average roughness SRa is 0.005 to 0.015 mu m and center line maximum roughness S Rmax is 0.05 to 0.3 mu m. It relates to the name.

Hereinafter, the present invention will be described in detail.

The polyethylene naphthalate used in the present invention is a polymer containing polyethylene 2.6-naphthalate of 90 mol% or more, and a mixture or main structural unit of other polyester and polyethylene naphthalate in a range that does not significantly impair the properties of polyethylene naphthalate. Copolymers containing ethylene naphthalate units can also be used. Polyethylene naphthalate may also include stabilizers such as phosphoric acid, phosphorous acid and esters thereof. The intrinsic viscosity of polyethylene naphthalate (measured in a mixed solvent of phenol and 1,1,2,2-tetrachloroethane at 30 ° C) is preferably 0.45 or more and 0.70 or less, and more preferably 0.50 to 0.65.

The present invention provides a polyester film having improved productivity while having advantages of excellent heat resistance, mechanical strength, and dimensional stability of polyethylene naphthalate. In particular, the amount of oligomers generated on the surface of the film is reduced, so that the dropout occurs less when used as a magnetic recording medium and the electron conversion characteristics are excellent.

The average particle diameter of the inert particles used in the present invention is 0.01 to 2.0 mu m, preferably 0.05 to 1.5 mu m. This average particle diameter can be obtained from the scanning electron micrograph of the particle or the transmission electron micrograph of the particle in the film by the following equation, and the particle shape is easily observed.

Average particle diameter (X) = Xi /

(Xi: particle diameter of the measured particle, n: total number of measured particles)

If the particle size exceeds 2.0㎛, the surface roughness is increased and coarse particles are generated so that many defects such as drop out occur when using magnetic tape. In addition, when the particle size is smaller than 0.01 占 퐉, it is difficult to impart surface projections to the film, resulting in poor activity and runability.

The total amount of particles added is 0.01 to 1.0 wt% with respect to the resulting polymer, preferably 0.05 to 0.9 wt%. If it is less than 0.01wt%, the activity and runability are poor, and if it exceeds 1.0wt%, the centerline average roughness will be high and the coarse particle generation by particle aggregation will increase, so the maximum centerline roughness value will be raised.

Therefore, many dropouts occur. The input form of the particles may be either a form dispersed in water, a form dispersed in ethylene glycol, or a form dispersed in a mixture of water and ethylene glycol. The inert particles to be added may be at least one selected from the group consisting of silica, kaolin, calcium carbonate, titanium dioxide, alumina, feldspar, talc, or two or more selected from the group. These inert particles may have a spherical, swollen or flake shape, and there are no particular restrictions on the hardness, specific gravity, color, etc. of these particles. The biaxially oriented polyester film consisting of polyethylene naphthalate can be obtained by the following method. Polyethylene naphthalate polymers containing particles are prepared by conventional methods, then made into chips and then dried. The polymer was extruded through an extruder and cured on a cooling drum to obtain an unstretched film, which was then stretched 2.0 to 5.0 times in the longitudinal direction at 110 to 160 ° C., and then from 2.0 to 5.0 at 130 to 180 ° in the transverse direction. The film was stretched 5.0 times, and preferably thermally cured at 200 to 250 ° C. for 1 second to 10 minutes while relaxing to 1% to 30% in the transverse direction.

The biaxially stretched polyester film according to the present invention, obtained in the above method, has a tensile stress (hereinafter referred to as F-5 value) at 5% elongation of 15 kg / mm 2 or more in the longitudinal direction and transverse direction, and a Young's modulus of 600 kg in the longitudinal direction transversely. / Mm2 or more, thermal shrinkage is 2% or less in both longitudinal and lateral directions, crystallinity is 40% or less, oligomer amount is 5 mg / m2 or less, center line average roughness (SRa) is between 0.005 μm and 0.015 μm, and the maximum center line roughness ( S Rmax) is between 0.05 μm and 0.3 μm.

Films with an F-5 value of less than 15 kg / mm 2 can easily be obtained even in polyethylene terephthalate films and do not have the advantage of using expensive polyethylene naphthalate. Films with a Young's modulus of less than 600 kg / mm 2 have insufficient dimensional stability with respect to external forces, and such films can also produce polyethylene terephthalate, making use of expensive polyethylene naphthalate useless. If the thermal contraction rate is 2.0% or more at 150 ° C, it is not suitable as a base film for high density magnetic recording media. The crystallinity of the film is preferably 40% or less, and when it is 40% or more, productivity is reduced due to the difficulty of the process in the heat setting step.

The centerline average roughness of the film according to the invention is preferably in the range of 0.005 to 0.015 µm, more preferably in the range of 0.007 to 0.013 µm. When the average roughness is less than 0.005㎛, the coefficient of friction of the film becomes high, and the running characteristics are poor when used as a magnetic recording tape.When the average roughness exceeds 0.015㎛, when the surface roughness of the film is deteriorated, it is used as a magnetic recording medium. Drop out occurs more often. For the same reason, the centerline maximum roughness is preferably in the range of 0.05 to 0.3 µm. On the other hand, if the amount of oligomer exceeds 5mg / ㎡ occurs a lot of defects during magnetic coating.

As described above, the present invention provides a particle source having an unstretched film of resin with an extreme viscosity polyethylene naphthalate suitable for producing a polyester film, controlling the stretching conditions within a specific range during the film forming process, and having a specific particle size. It is possible to economically advantageously obtain a film having suitable physical properties for the high density magnetic recording medium by overcoming the conventional limitation by adjusting to satisfy the appropriate range condition.

In the present invention, the measurement of each property and physical properties was measured by the following method.

(1) F-5 value

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

(2) YOUNG'S MODULUS

Young's modulus is represented by the initial Young's modulus at the time of tension | tensile_strength measured when the film sample of 10 mmmm is extended | stretched at the temperature of 25 degreeC, the distance of 100 mm between chucks, and the tension rate 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.

The heat export rate is calculated as [(ℓ _O / ℓ) / ℓ _O ] × 100 (%), where ℓ _O is the original length and ℓ is the length measured after the heat treatment.

(4) Centerline average roughness (SRa) and centerline maximum roughness (SRmax) of film:

The average roughness (SRa) and the maximum roughness (SRmax) were measured using the 3-dimensional surface roughness meter made from Kosaka made in Japan, respectively.

(5) crystallinity

It was measured using the density gradient tube method.

(6) oligomer amount

After immersing the film specimen in chloroform for 5 minutes, the amount of oligomer extracted in chloroform is analyzed by the size of the peak measured at wavelength 245nm using U.V.

(7) active activity

The polyester film was made of a roll tape of a predetermined width, and then fixed to a metal guide roll and run while contacting for a long time. Then, the degree of scratching on the surface of the film was observed under a microscope, and the percentage of the guide roll was visually observed to determine as follows. .

Level 1: Almost no scratch on film surface after friction with guide roll

Level 2: Small scratches on the film surface after friction with the guide roll

Level 3: Scratches on the film surface after friction with the guide roll

(8) drop out

The biaxially oriented polyester film was coated with a magnetic layer having a thickness of 4 μm using a conventional method to produce a video tape, and then the optimum current was recorded on the video tape as a five-step disparity signal, and the attenuation of the video head output was 20 dB, A duration of 15 µsec or more was regarded as a dropout, measured continuously for 30 minutes, and averaged per minute, divided into grades A to D for evaluation.

A: less than 10 / min

B: 10 or more / min-less than 30 / min

C: 30 or more / min-less than 50 / min

D: 50 or more per minute

Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1

A mixture of 100 parts of 2,6-dimethylnaphthalate, 70 parts of ethylene glycol, 0.07 parts of magnesium acetate tetrahydrate, 0.03 parts of antimony trioxide, and germanium dioxide was heated in a reactor to carry out a methanol exchange and transesterification. The reaction mixture was completed transesterification over 4 hours. After adding 0.03 part of trimethyl phosphate and the particle | grains of Table 1 to this reaction mixture, the polycondensation reaction was performed for 4 hours, and the polyester chip was obtained. After drying, the resultant was extruded through an extruder to obtain an unstretched film. The stretched film was stretched 4.0 times in a longitudinal direction at 130 ° C., stretched 3.5 times in a transverse direction at 140 ° C., and thermally cured at 230 ° C. for 40 seconds to obtain a thickness 8. A μm film was obtained. As a result of evaluating the physical properties of this oriented film, as shown in Table 1, the physical properties such as mechanical strength, dimensional stability, oligomer amount, diactivation, and drop out were excellent.

Example 2

A 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 Table 1.

Example 3

A film was obtained by the same method as Example 1 except that the film was stretched 3.7 times in the longitudinal direction at 120 ° C. and 3.5 times in the transverse direction at 130 ° C. to obtain a film.

Comparative Example 1

A film was obtained by the same method as Example 1 except for using particles having an average particle diameter of 2.1 μm, and the physical properties of the film are shown in Table 1.

Comparative Example 2

A film was obtained by the same method as Example 1 except for using particles having an average particle diameter of 9 nm, and the physical properties of the film are shown in Table 1.

Comparative Example 3

Except that the addition amount of particles was 1.1wt% Example 3 light was carried out in the same manner to obtain a film and the physical properties of the film are shown in Table 1.

Claims (5)

A biaxially stretched unstretched film composed of polyethylene naphthalate resin having an intrinsic viscosity of 0.45 to 0.70 containing inert particles having an average particle diameter of 0.01 to 2.0 µm in 0.01 to 1/0% by weight was biaxially stretched in the longitudinal and transverse directions, respectively. A biaxially oriented polyester film for high density magnetic recording media, characterized by being satisfied. F-5 value in MD direction ≥ 15 kg / mm2 TD direction F-5 value ≥ 15 kg / mm2 MD direction Young's modulus ≥ 600 kg / mm2 TD direction Young's modulus ≥ 600 kg / mm2 150 ° C Heat shrinkage MD direction ≤ 2% 150 ° C Heat shrinkage TD direction ≤ 2% crystallinity ≤ 40% oligomer amount ≤ 5 mg / m 2 0.005 ≤ SRa ≤ 0.015 0.05 ≤ SRmax ≤ 0.3 Μm)] The biaxially oriented polyester film of claim 1, wherein the polyethylene naphthalate contains at least 90 mole percent polyethylene-2,6-naphthalate. The biaxially oriented polyester film according to claim 1, wherein the inert particles are mixed with at least one selected from the group consisting of silica, kaolin, calcium carbonate, titanium dioxide, alumina, feldspar, talc and the like. The unstretched film made of polyethylene naphthalate resin according to claim 1 is stretched 2.0 to 5.0 times in the longitudinal direction at 110 to 160 ° C, then stretched 2.0 to 5.0 times at 130 to 180 ° in the transverse direction and 200 to 250 Biaxially oriented polyester film, characterized in that the thermal curing at 1 ℃ to 10 minutes. The biaxially oriented polyester film according to claim 1, wherein the final film has a thickness of 10 µm or less.