JP2520415B2 - Polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film, and more particularly to a biaxially oriented polyester film which is excellent in abrasion resistance and is suitable as a base film for a magnetic tape.

[Prior Art] Conventionally, as a biaxially oriented polyester film, a polyester film having a surface hardness within a certain range (for example, JP-A-53-112952) is known.

[Problems to be Solved by the Invention] However, the abrasion resistance required for a base film for a magnetic tape is becoming more and more severe as the recording density becomes higher. The quality of the product was not sufficient because it dropped out.

An object of the present invention is to solve the above problems and provide a base film for a magnetic tape having excellent wear resistance.

[Means for Solving Problems] In the present invention, the average surface roughness Ra of the film is 0.0015 to 0.03.
5 μm, surface projection volume parameter φ is 0.5 × 10 ^{3 to} 3.0 × 10
^The present invention relates to a polyester film having a surface hardness of ⁶ and a surface hardness of 8 to 50 gf / μm ² .

The polyester of the present invention is not particularly limited, but usually polyethylene terephthalate, polyethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, polyethylene 2,6 naphthalate, polybutylene terephthalate, etc. are used. To be Among them, polyethylene terephthalate is preferable.

The average surface roughness Ra of the film of the present invention is 0.0015 ~ 0.035μ
m, preferably 0.0025 to 0.030 μm, and more preferably 0.0045 to 0.025 μm. If the average surface roughness Ra of the film is smaller than the above range, the running property when used as a magnetic tape is poor, and if it is larger than the above range, recording dropouts (dropout) when used as a magnetic tape increases, which is not preferable.

Further, the surface protrusion volume parameter φ of the film of the present invention
Is 0.5 × 10 ^{3 to} 3.0 × 10 ⁶ , preferably 1.0 × 10 ^{3 to} 1.0 × 1.
0 ⁶

When the surface projection volume parameter φ is smaller than the above range, the winding appearance during film winding becomes poor and the running property when used as a magnetic tape becomes poor, which is not preferable. If φ is larger than the above range, the number of dropouts in a magnetic tape increases, which is not preferable.

The surface hardness of the film of the present invention is 8 to 50 gf / μm ² ,
It is preferably in the range of 12-40 gf / μm ² . If the surface hardness is smaller than the above range, the running property and dropout of a magnetic tape will be poor, which is not preferable. Also,
When the surface hardness is larger than the above range, the number of dropouts when the magnetic tape is formed is large, which is not preferable.

Further, the static friction coefficient of the film of the present invention is not particularly limited, but it is preferable that the static friction coefficient of at least one surface is in the range of 0.2 to 3.0 because the running property and dropout when used as a magnetic tape are good.

Next, the method for producing the film of the present invention will be described by taking polyethylene terephthalate as an example.

Manganese acetate is added as a catalyst to dimethyl terephthalate and ethylene glycol, and an ester exchange reaction is carried out while distilling off methanol by a conventional method. Then, methylene glycol, a polymerization catalyst and the like are added, and polycondensation is performed while heating under vacuum to obtain a pelletized polymer. In this case, it is preferable that the polymer contains a lubricant such as internally precipitated particles and inorganic particles from the viewpoint of running property when used as a magnetic tape, but the average surface roughness Ra and surface protrusion volume parameter of the film. In order to make φ within the range of the present invention, it is preferable that the inorganic particles are sufficiently dispersed and overtreated. Among them, in order to bring the surface hardness within the range of the present invention, it is particularly effective to contain inorganic particles having a small crystallization acceleration effect coefficient (10 or less). The average diameter of the particles contained is in the range of 0.05 to 2.0 μm, and it is preferable that the particle size distribution be as close to monodisperse as possible in order to obtain good running properties and dropout when used as a magnetic tape. Moreover, the particle type and particle size of the particles contained may be two or more.

Further, when the intrinsic viscosity of the polymer is in the range of 0.5 to 0.9, particularly 0.65 to 0.9, it is extremely effective in setting the surface hardness within the range of the present invention.

Next, this pellet-shaped polymer was sufficiently vacuum dried at 170 to 200 ° C., then this was supplied to an extruder and melt-extruded at 280 to 290 ° C., after suppressing a flow rate fluctuation through a gear pump,
After passing through a filter capable of capturing 99% or more of solids of 3 μm or more, it is led to a T-shaped mouthpiece and discharged from this mouthpiece as a sheet-like melt.

This sheet-shaped melt is wound around a cooling drum, closely adhered thereto, and then cooled and solidified to form an unstretched film.

Next, this unstretched film is biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but the sequential biaxial stretching method is particularly preferable. The stretching conditions in this case are 3.0 in the longitudinal direction.
A method is suitable in which the film is stretched by 4.0 to 4.0 times, preferably 3.0 to 3.6 times, and then stretched in the width direction by 3.2 to 4.5 times, preferably 3.3 to 4.0 times. The stretching speed is preferably in the range of 10 ³ to 10 ⁷ % / min. The stretching temperature in the longitudinal direction is in the range of the glass transition point of the polymer or higher and the cold crystallization temperature or lower, and in the width direction in the range of the cold crystallization temperature of the polymer or higher and the melting point or lower. It is effective in obtaining a range of surface hardness.

Further, this stretched film may be further stretched in at least one direction.

The biaxially stretched film thus obtained is heat-treated. Normally 180 to 230 while holding both edges of the film with clips
Pass through a tenter heated to ℃, preferably 180 to 205 ℃.
At this time, the relative humidity in the tenter is 50 to 95%, preferably
The range of 65 to 90% is particularly suitable for keeping the surface hardness within the range of the present invention. The time is preferably in the range of 0.5 to 30 seconds.

Further, the biaxially stretched film may be subjected to calender treatment using a heating calender device after cutting the edge portion. At this time, calendering at a temperature of 40 to 90 ° C. and a linear pressure of 10 to 200 kg / cm is suitable for keeping the surface hardness of the film within the range of the present invention.

EFFECTS OF THE INVENTION The present invention has an average surface roughness and a surface protrusion volume parameter in specific ranges, and the surface hardness of the outermost surface layer by the measuring method of the present invention is in a specific range. As a result of being able to soften the impact force applied to the protrusions, the following effects were obtained.

(1) A magnetic tape having excellent wear resistance and less dropout can be obtained.

(2) Excellent running property when used as a magnetic tape.

(3) The winding appearance when winding the film is good.

[Measurement Method of Characteristic] The characteristic value of the present invention is based on the following measuring method and evaluation criteria.

(1) Average surface roughness (Ra), maximum surface roughness (Rt) In accordance with JIS-B-0601, a stylus-type surface roughness meter (Kosaka Laboratory High-precision thin-film level difference measuring machine ET-10, stylus) Tip radius 0.5μ
m) was used, and the cutoff was 0.08 mm and the measurement length was 4 mm.

(2) Surface projection volume parameter φ Using Kosaka Laboratory's high-precision thin film step measuring device ET-10, stylus tip radius 0.5 μm, cutoff 0.08 mm, measurement length 1.0 mm, vertical magnification 200,000 times, horizontal magnification 2000 times At, the surface roughness curve of the film is measured. A peak count level is provided every 0.005 μm in parallel above the average line (center line) of this curve, and the point where the above-mentioned peak count level is crossed at least once between two points where the curve crosses the average line. When there is, this is regarded as one peak, and the number of this peak is determined during the measurement length. For each peak count level, the number of peaks is determined, and the number of peaks determined for the n-th peak count level from the average line is defined as PC (n). When the peak count level at which the number of peaks starts to become zero during the measurement length is the 1st position from the average line, the surface protrusion volume parameter φ
Is It is expressed by and uses the average value taken 50 times at different places.

(3) Surface hardness Dynamic ultra micro hardness tester (DUH-50 manufactured by Shimadzu Corporation)
Type), measuring load 0.1gf, loading speed 0.0056gf / s,
The dynamic indentation hardness was measured from the indentation depth under the condition of holding time of 15 seconds. A triangular indenter with an opposite angle of 115 ° was used as the indenter.
At the time of measurement, the film thickness was set to 15 μm, and the film was attached to a 1 mm-thick stainless steel plate and measured. The measurement was repeated 50 times, and the average was taken as the surface hardness.

(4) After thoroughly kneading the magnetic coating liquid consisting of γ-Fe ₂ O ₃ containing dropout Co, polyester urethane, poly (vinyl chloride-vinyl acetate) copolymer, butyl acetate and methyl isobutyl ketone, triisocyanate was further added. In addition, it is further dispersed to make a magnetic coating liquid. This magnetic coating liquid is applied on a thermoplastic resin film to a thickness of 5 μm and dried. After that, it is calendered, slit into 1/2 inch width, and assembled into a video cassette. Signals were input and played using a VCR, and the number of dropouts in which a -16dB condition lasted for 5 μsec was counted using a dropout counter (TG-7 / 1 manufactured by Shibasoku). The measurement was performed for 60 minutes, and the 1/60 was defined as the number of dropouts. This dropout number is 0
Dropouts in the range of 5 / min: Good, 5.1
Dropout when the number of pieces / minute or more was determined to be defective.

(5) Runnability Using the tape runnability tester TBT-300 type manufactured by Yokohama System Laboratory Co., Ltd., the video tape made in the same manner as above was run in an atmosphere of 20 ° C and 60% RH, and the initial ΜK was calculated from the following formula.

μK = 0.733 log (T ₁ / T ₀ ) where T ₀ is the entrance tension and T ₁ is the exit tension. The guide diameter is 6mmφ, the guide material is SUS27 (surface roughness 0.2S),
The winding angle is 180 ° and the running speed is 3.3cm / sec.

When the above μK was in the range of 0.15 to 0.35, the runnability was good.

(6) Crystallization acceleration coefficient The difference between the cold crystallization temperature Tcc of the polymer and the glass transition point Tg (Tcc-Tg) measured using a Perkin Elmer DSC (differential scanning calorimeter) II type is defined as ΔTcg. ΔTcg (I) of polyester containing 1% by weight of inert inorganic particles,
ΔTcg (II) and ΔTcg (II) and ΔTcg (II) of polyester that does not contain inert inorganic particles of the same viscosity as this were measured.
The difference [ΔTcg (II) -ΔTcg (I)] of (I) was taken as the crystallization promoting coefficient of the inert inorganic particles.

The measurement conditions of DSC are as follows. That is,
10 mg of a sample is set in a DSC apparatus, melted at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. This quenched sample is 10 ℃
The temperature is raised at 1 / min, and the glass transition point Tg is detected. The temperature was further raised and the crystallization exothermic peak temperature from the glass state was set as the cold crystallization temperature Vcc.

(7) Intrinsic viscosity Measured at 25 ° C using O-chlorophenol.

[Examples] The present invention will be described based on examples.

Examples 1 to 3 and Comparative Examples 1 to 3 100 parts by weight of terephthalic acid and 43 parts by weight of ethylene glycol were kneaded to prepare a slurry. 50 parts by weight of terephthalic acid and ethylene glycol 21.5 stored at 245 ° C in the reactor
The slurry was continuously added to a part by weight of the reaction product at a constant rate, an esterification reaction was performed at 245 ° C. under normal pressure, and water produced was continuously distilled out of the rectification column. The feeding time of the slurry was completed in 3 hours and 30 minutes, and the esterification reaction was completed in 4 hours. Terephthalic acid 10
The esterification reaction product corresponding to 0 parts by weight was transferred to a polymerization device, and 0.045 parts by weight of phosphoric acid, 0.023 parts by weight of antimony trioxide, and synthetic calcium carbonate fine particles having a sharp particle size distribution, and triethylammonium phosphate (vs. Particle 5
(Wt%) is added to ethylene glycol and dispersed well,
Add the over-treated ethylene glycol slurry,
The polycondensation reaction was carried out according to a conventional method. No internal particles were present in the obtained polymer, and a polyester containing 1% by weight of synthetic calcium carbonate was obtained (Polyester A). The intrinsic viscosity of this polyester was 0.830, and the crystallization acceleration coefficient was 3.5.

Next, a polyester containing no particles (polyester B) was obtained by the same production method as above.

Pellets obtained by mixing the above polyester A and polyester B with synthetic calcium carbonate fine particles at various ratios were used.
It was dried under reduced pressure (3 Torr) at 0 ° C. for 3 hours. The pellets were supplied to an extruder, melt-extruded at 300 ° C., wrapped around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and cooled and solidified to form an unstretched film having a thickness of about 170 μm. This unstretched film was stretched at
It was stretched twice. This stretching was performed with two sets of roll peripheral speed difference, and the stretching speed was 10,000% / min. This uniaxial film was stretched 3.6 times in the width direction at 100 ° C at a stretching rate of 2000% / min using a stenter, and then heat treated for 5 seconds in a tenter at a temperature of 200 ° C and a humidity of 90% RH while holding both ends with clips. After that, the edge portion was cut to obtain a film having a thickness of 14 μm.

The average surface roughness Ra, the surface projection volume parameter φ, and the surface hardness of this film are as shown in Table 1.

Next, Table 1 also shows the results of measuring dropout and runnability using this film as a magnetic tape.

By using a film having a specific average surface roughness, a specific surface protrusion volume parameter, and a specific surface hardness, it is possible to satisfy both the running property and the dropout when the magnetic tape is used.

Comparative Example 4 100 parts by weight of dimethyl terephthalate, 62 parts by weight of ethylene glycol, and 0.06 part by weight of calcium acetate as a catalyst were subjected to a transesterification reaction by a conventional method. The product was 0.04 part by weight of antimony trioxide, 0.07 part by weight of lithium acetate and 0.04 parts by weight of calcium acetate was added, followed by phosphorous acid.
After adding 0.02 part by weight and 0.10 part by weight of trimethyl phosphate, polycondensation was carried out to obtain an intrinsic viscosity of 0.469 and an internal particle amount of 0.35.
A polymer containing 100 parts by weight (based on 100 parts by weight of polyester) was obtained. The internal particles contained 1.2% by weight of calcium element, 1.9% by weight of lithium element and 4.9% by weight of phosphorus element. The intrinsic viscosity was 0.440. 180 ℃ for the above pellets
It was dried under reduced pressure (3 Torr) for 3 hours. The pellets were supplied to an extruder, melt-extruded at 300 ° C., wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic cast method, cooled and solidified to form an unstretched film having a thickness of about 210 μm. This unstretched film was stretched 4.0 times in the longitudinal direction at 95 ° C. and then stretched 4.3 times in the width direction to obtain a biaxially stretched film. Further, with the width of this film fixed, a heat treatment was carried out with a tenter at 212 ° C and a humidity of 10%. The thickness of the obtained film was 12 μm, and the average surface roughness Pa was 0.
The surface projection volume parameter φ was 1.2 × 10 ⁵ . However, the surface hardness of this film was 55 gf / μm ² . The crystallinity of this film was 39%.

Next, when this film was used as a magnetic tape and the number of dropouts was measured, it was 45 pieces / minute, which was unsatisfactory. The runnability was also poor with μK of 0.36 (Table 1).

As described above, when the surface hardness of the film was not within the range of the present invention, the film did not satisfy both the dropout characteristics and the running property when used as a magnetic tape.

Example 4, Comparative Examples 5 to 6 Instead of the synthetic calcium carbonate fine particles added in Example 1, various inorganic fine particles having the same average particle diameter were used to prepare a biaxially oriented polyester film in the same manner as in Example 1. Had made. The amount of the inorganic fine particles contained in this film is the same as in Example 1.

The average surface roughness Ra, surface projection volume parameter φ, and surface hardness of this film are as shown in Table 2.

Next, Table 2 also shows the results of measuring dropout and runnability using this film as a magnetic tape.

As can be seen from Table 2, only the biaxially oriented polyester film having the average surface roughness Ra, the surface protrusion volume parameter φ, and the surface hardness within the scope of the present invention has a running property when used as a magnetic tape. You can be satisfied with the dropout together.

Example 5, Comparative Examples 7 to 8 The pellets obtained by mixing the polyester A and the polyester B used in Example 1 so that the synthetic calcium carbonate content was 0.20% were extruded in the same manner as in Example 1. More melt extrusion was performed to obtain an unstretched film. Powder only stretched Various conditions for biaxially stretching the film, average surface roughness
Biaxially stretched films having different Ra, surface protrusion volume parameter φ, and φ were obtained (Table 2).

Table 2 also shows the results of measuring dropout and runnability using this film as a magnetic tape.

As can be seen from Table 2, the biaxially oriented polyester film in which any one of the average surface roughness Ra, the surface protrusion volume parameter φ, and the surface hardness is out of the range of the present invention has a running property when used as a magnetic tape. And dropout cannot both be satisfied.

Claims (1)

(57) [Claims] 1. The average surface roughness Ra of the film is 0.0015 to 0.03.
5 μm, surface projection volume parameter φ is 0.5 × 10 ^{3 to} 3.0 × 10
A polyester film having a surface hardness of ⁶ and a surface hardness of 8 to 50 gf / μm ² .