JPH0768369B2 - Biaxially oriented polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is suitable as a biaxially oriented polyester film, and more particularly, as a base film for packaging and magnetic recording media, which is excellent in scratch resistance and abrasion resistance. The present invention relates to a biaxially oriented polyester film.

[Prior Art] As the biaxially oriented polyester film, a film in which spherical silica and inert inorganic particles are contained in polyester (for example, JP-A-63-235337), rutile titanium dioxide and anatase titanium dioxide are used. Films containing them (for example, JP-A-62-205134) are known.

[Problems to be Solved by the Invention] However, the conventional biaxially oriented polyester film is
With the increase in process speed of film processing process, magnetic layer coating and calendering process for magnetic media applications in recent years,
Defects such as (1) the film surface is easily scratched by contacting rolls, and (2) powder is deposited on the roll due to the film surface being scraped, resulting in problems in the processing process and product performance. Has become a particular problem these days.

The present invention has such problems, that is, (1) a film surface is easily scratched by a contact roll or the like due to an increase in process speed, and (2) a film surface is scraped so that powder adheres to the roll. It is an object of the present invention to provide a film having excellent surface scratch resistance and abrasion resistance.

[Means for Solving the Problems] In the present invention, the average particle diameter d ₁ is 0.005 to ₁ μm, and the shape factor is
The rutile type titanium dioxide particles of 0.6 to 1 are contained in an amount of 0.2 to 3% by weight, and the average particle diameter d ₂ (where d ₁ <d ₂ ) is 0.3 to
Inert particles with a diameter of 2 μm and a shape factor of 0.8-1 are 0.01-
0.2% by weight, the crystallization promoting coefficient of the inert particles is 20
The present invention relates to a biaxially oriented polyester characterized by having a temperature of not higher than ° C.

The polyester in the present invention mainly comprises at least one structural unit selected from ethylene terephthalate, ethylene α / β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate and ethylene 2,6-naphthalate units. As a constituent. However, other components may be copolymerized within a range not hindering the present invention, preferably within 15 mol%.

Further, in the case of polyester containing ethylene terephthalate as a main constituent, scratch resistance and abrasion resistance are further improved, which is particularly desirable.

The titanium dioxide particles in the present invention need to be rutile type. The anatase type is not preferable because it cannot satisfy the high level of abrasion resistance which is the object of the present invention.

The average particle size of the titanium dioxide particles in the present invention is 0.005
˜1 μm, preferably 0.01 to 0.5 μm. If the average particle size is smaller than the above range, the scratch resistance of the film becomes poor, which is not preferable. If the average particle size is larger than the above range, the abrasion resistance becomes poor, which is not preferable.

The shape factor of the titanium dioxide particles in the present invention is 0.6 to 1
It is necessary to be. If the shape factor is smaller than the above range, scratch resistance is poor, which is not preferable.

The content of titanium dioxide particles in the present invention is 0.2 to 3
%, Preferably 0.3-2% by weight. If the content is less than the above range, the scratch resistance of the film becomes poor, which is not preferable. On the contrary, if the content is more than the above range, the abrasion resistance of the film becomes poor, which is not preferable.

The average particle size of the inert particles in the present invention is 0.3 to 2 μm.
m, preferably 0.4 to 1.5 μm. If the average particle size is smaller than the above range, the scratch resistance of the film becomes poor, which is not preferable. If the average particle size is larger than the above range, the abrasion resistance becomes poor, which is not preferable.

In order to improve both scratch resistance and abrasion resistance, the average particle diameter (d ₁ ) of the rutile titanium dioxide particles is required.
And the average particle diameter (d ₂ ) of the inactive particles must be d ₁ <d ₂ . When d ₁ ≧ d ₂ , abrasion resistance is poor, which is not preferable.

The shape factor of the inert particles in the present invention needs to be 0.8 to 1. If the shape factor is smaller than the above range, scratch resistance becomes poor, which is not preferable.

The content of the inert particles in the present invention is 0.01 to 0.2% by weight, preferably 0.03 to 0.15% by weight. If the content is less than the above range, the scratch resistance of the film becomes poor, which is not preferable. On the contrary, if the content is more than the above range, the film has poor abrasion resistance, which is not preferable.

The crystallization acceleration coefficient of the inert particles in the present invention needs to be 20 ° C or lower, preferably 15 ° C or lower. If the crystallization acceleration coefficient is larger than the above range, scratch resistance,
It is not preferable because the abrasion resistance is poor. The lower limit of the crystallization promoting coefficient is not particularly limited, but about 0 ° C. is the manufacturing limit.

The type of the inert particles in the present invention is not particularly limited, but in the case of substantially spherical silica particles, calcium carbonate, and organic fine particles (for example, crosslinked polystyrene particles) derived from corodile silica, the crystallization acceleration coefficient is set to the present invention. The effect is particularly large when the range is set, and scratch resistance and abrasion resistance are further improved, which is particularly desirable.

It is desirable that the corodile silica referred to here is particles produced by using sodium silicate as a main raw material and removing alkali components.

The surface projection flatness of the film of the present invention is preferably 7 to 16 because scratch resistance and abrasion resistance are improved.

In the present invention, the above composition is the main component, but other polymers may be blended within a range not impairing the object of the present invention, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, etc. Inorganic or organic additives may be added to the extent that they are usually added.

The film of the present invention is a film in which the above composition is biaxially oriented. The unstretched film and the uniaxially oriented film are not preferable because they have poor scratch resistance and abrasion resistance.

Further, the plane orientation index showing the degree of the biaxial orientation is not particularly limited, but is preferably in the range of 0.935 to 0.975, particularly 0.940 to 0.970 because scratch resistance and abrasion resistance are further improved.

When the density index of the film of the present invention is in the range of 0.02 to 0.05, scratch resistance and abrasion resistance are further improved, which is particularly desirable.

Further, the film of the present invention, the surface average roughness Ra in the width direction is 0.
The range of 005 to 0.030 μm, especially 0.007 to 0.025 μm is particularly preferable because scratch resistance becomes further excellent.

When the coefficient of friction μK of the film of the present invention is in the range of 0.20 to 0.35, scratch resistance is further improved, which is particularly desirable.

Further, in the present invention, when the surface resistivity of the film is 1 × 10 ¹⁵ Ω or less, scratch resistance and abrasion resistance are further improved, which is particularly desirable.

When silica is used as the inert particles of the film of the present invention, the surface particle concentration of the silica is not particularly limited,
When the surface layer particle concentration is in the range of 0.05 to 0.15, scratch resistance and abrasion resistance are further improved, which is particularly desirable.

Next, a method for producing the film of the present invention will be described.

First, as a method of incorporating rutile type titanium dioxide into a predetermined polyester, it may be added before polymerization, during polymerization, or after polymerization, but it is mixed with ethylene glycol which is a diol component of polyester in the form of a slurry. The method of adding them after dispersion is effective. As a method of adjusting the content of particles, a method of diluting a high-concentration master pellet during film formation is effective. Using rutile titanium dioxide, the melt viscosity of the master pellet at a high concentration, preferably 1 to 5% by weight, and the copolymerization component are adjusted,
Difference between glass transition point Tg and cold crystallization temperature Tcc (Tcc-Tg)
It is extremely effective to keep the temperature at 65 to 110 ° C, especially 75 to 100 ° C.

Next, it is effective that the inert particles are added to the slurry dispersed in ethylene glycol before or during the polymerization reaction to obtain the average particle diameter within the range of the present invention. Here, the following method is effective for obtaining the crystallization promoting coefficient of the present invention.

(1) Inactive particles consist of elements VI A, VII A, II B, I of the Periodic Table of the Elements
When containing any element of Group II B or IV B: 20% ethylene glycol sol (slurry) with 1 g of particle solid content in water
After adjusting the ethylene glycol sol so that the PH value when mixed with 100 cc is in the range of 7 to 12, preferably in the range of 9 to 11, and the sodium content is 0.15 to 0.6% by weight based on the particle solid content. Then, polycondensation with a predetermined dicarboxylic acid (or ester thereof) is performed to obtain a polyester containing inert particles.

(2) When the inert particles contain any one of the elements of Group IV A and VA of the periodic table of the elements: Before the inert particles are dispersed in ethylene glycol, they are washed with a polar solvent such as methanol or ethanol and dispersed. Ammonium phosphate salt as an auxiliary agent is added to the particles in an amount of 0.1 to 5% by weight and dispersed in ethylene glycol. After dispersing fine glass beads etc. as a medium, the medium is further dispersed by removing the medium such as glass beads. Proceed. Polyethylene containing a slurry of the thus obtained particles of ethylene glycol and a predetermined dicarboxylic acid (or ester thereof) is polycondensed to obtain a polyester containing inert particles.

(3) When the inert particles are organic fine particles: The inert particles are mixed and dispersed in ethylene glycol in the form of a slurry. A slurry of the thus obtained particles of ethylene glycol and a predetermined dicarboxylic acid (or ester thereof) are polycondensed to obtain a polyester containing inert particles.

In the present invention, it is also preferable to separately produce polyesters containing inert particles and knead them in a melting step, or to mix polyesters of high concentration master containing a large amount of inert particles in an appropriate amount. Has been adopted.

Most preferable is a method in which a polyester containing substantially no internal particles and a high concentration of inert particles is diluted with a particle-free polyester containing no particles.

Thus, after sufficiently drying the polyester pellets containing a predetermined amount of inert particles, it is supplied to a known melt extruder, extruded into a sheet form from a slit die at 270 ° C to 330 ° C, and cooled on a casting roll. An unstretched film is made by solidifying. When making this unstretched film, the draft ratio (slit width of the die / thickness of the unstretched film) during casting is preferably a high value of 16 times or more. When the shape factor is within the range of the present invention, since a peculiar phenomenon that particles concentrate in the surface layer portion occurs when performing high draft casting, it is particularly effective in the present invention to perform such high draft casting. .

Next, this unstretched film is biaxially stretched and biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. In the case of the sequential biaxial stretching method, it is general to stretch in the longitudinal direction and then in the width direction, but this sequence may be reversed. The biaxial stretching conditions are not necessarily constant depending on the stretching method, the type of polymer, etc., but usually in the longitudinal direction and the width direction in the range of 80 to 160 ° C., preferably 90 to 150 ° C., and the stretching ratio is 3.0 to 5.0, respectively.
Fold, preferably in the range of 3.2 to 4.5 times, and the stretching speed is 10
A range of 00 to 70,000% / min is suitable.

Next, this stretched film is heat-treated. The heat treatment conditions are a constant length and a relaxation of 1 to 15% in the width direction, preferably 2 to 10%, and 1.01 to 1.2 times in the width direction, preferably 1.05 to
1.15 times fine stretching, 150-230 ℃, preferably 170-220 ℃
The range of 0.5 to 60 seconds is preferable.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Content of particles (% by weight) 100 g of polyester is added to a solvent that dissolves polyester and does not dissolve particles and heated to completely dissolve the polyester, and then ultracentrifuge 55P manufactured by Hitachi Koki Co., Ltd. Using -72, stretching separation is performed at 30,000 rpm for 40 minutes, and the obtained particles are vacuum dried at 100 ° C. When a dissolution peak corresponding to a polymer is observed when the particles are measured with a scanning differential calorimeter, a solvent is added again to the particles, and the particles are heated and cooled, and then stretched and separated. The particles are weighed when no dissolution peak is observed. This weight is divided by 100 g, and the content is expressed as a percentage. In addition, if necessary, it is quantified by utilizing pyrolysis gas chromitography, infrared absorption, Raman scattering, SEM-XMA and the like.

(2) Average particle size of particles (μm) Thickness of a film containing particles perpendicular to the film plane
An ultrathin section of 1000Å was taken, the particles were observed using a transmission electron microscope (for example, JEM-1200EX manufactured by JEOL Ltd.), and the value averaged over 100 visual fields was taken as the average particle diameter. However, here, the average particle diameter is the average particle diameter of the primary particles, and is obtained from the effective diameter of each primary particle even when the particles are in an agglomerated state.

(3) Shape factor of particles Thickness of a film containing particles perpendicular to the plane of the film
An ultrathin section of 1000 Å was taken, and the rectangular and long diameters of the particles were observed using a transmission electron microscope (for example, JEM-1200EX manufactured by JEOL Ltd.) and averaged over 100 fields of view. The average value of this rectangle and the major axis was used as the shape factor of the particles.

(4) Surface protrusion flatness 2 A scanning electron microscope with a detection method [ESM-3200, manufactured by Elionix Co., Ltd.] and a cross-section measuring device [PMS-1, manufactured by Elionix Co., Ltd.] were used to measure the smoothness of the film surface. Image processing device [IBAS2000, Carl Zeiss Co., Ltd.]
Manufactured] and reconstruct the film surface projection image on IBAS2000 based on this gray value. Next, in this surface protrusion image, 10
A circle-equivalent diameter was calculated from the area of each protrusion obtained by binarizing a gradation or more, and this was used as the surface protrusion diameter. Next, the highest value among the individual protrusions measured in the same manner was taken as the height. This measurement was carried out for 1 mm ² , and the average values were taken as the surface projection diameter d and the surface height h, and the surface projection diameter d and the surface projection height h obtained by the above method were used.
The d / h was defined as the surface protrusion flatness.

The magnification of the scanning electron microscope is usually 3000 times, but an optimum magnification can be selected in the range of 2000 to 5000 times depending on the size of the protrusion.

(5) Plane orientation index Using an Abbe refractometer with sodium D line (wavelength 589 nm) as a light source, the biaxially oriented film has a refractive index (A) in the thickness direction and is rapidly cooled into water at 10 ° C. after melt pressing. The refractive index (denoted as B) in the thickness direction of the non-oriented (amorphous) film thus prepared was measured, and A / B was taken as the plane orientation index. Use methylene iodide as the mounting solution at 25 ° C and 65
It was measured at% RH.

(6) Glass transition point Tg, cold crystallization temperature Tcc It was measured using a Perkin-Elmer DSC (differential scanning calorimeter) type II. The conditions for 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
The temperature is raised at 10 ° C / 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 Tcc. Here, the difference between Tcc and Tg (Tcc-Tg) is defined as ΔTcg.

(7) Crystallization acceleration coefficient By the above method, ΔTcg (A) of the polyester containing 1% by weight of the inert particles and ΔTcg (B) of the polyester containing no inert particles of the same viscosity as the polyester were measured, ΔT
Difference between cg (B) and ΔTcg (A) [ΔTcg (B) -ΔTcg
(A)] was used as the crystallization acceleration coefficient of the inert particles.

(8) Density index The density of the film measured using a density gradient tube consisting of n-heptane / carbon tetrachloride was d ₁ (g / cm ³ ), and this film was melt-pressed and then rapidly cooled in water at 10 ° C. Difference from the density d _{2 of} the non-oriented (amorphous) film made by (d ₁ −d ₂ )
Was defined as the density index.

(9) Friction coefficient μK Using tape running tester TBT-300 period [manufactured by Yokohama System Laboratory Co., Ltd.], the tape was run in an atmosphere of 20 ° C. and 60% RH, and the initial μK (friction coefficient) was as follows. Calculated from the formula.

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

(10) Surface resistivity Measured using a super-insulator [Kawaguchi Electric Co., Ltd.] VE-40 type.

(11) Surface layer particle concentration Using a secondary ion mass spectrometer (SIMS), the concentration ratio of the metal element contained in the inert particles and the carbon element of polyester is defined as the particle concentration, and the film surface to depth obtained by the measurement
100 Å density average value C ^s and depth 5000 to 10000 Å density average value
The ratio C ^S / C ^B and C ^B was surface particle concentration. The measuring device and conditions are as follows.

Measurement conditions Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany Measurement conditions Primary ion species: O ₂ ⁺ Primary ion acceleration voltage: 12KV Primary ion current: 200nA Raster area: 400μm □ Analysis area: Gate 30% Measurement vacuum degree: 6.0 × 10 ^-9 Torr E-GUN: 0.5KV-3.0A (12) Scratch resistance Tape running tester TBT300D / H type [Yokohama System Research Co., Ltd.] Is slit into a tape with a width of 1/2 inch, and the tension is 30 g and the running speed is 250 m / min. Then, on the tape guide pin of the video cassette (stainless steel guide pin having a surface roughness of about 2500 nm at Rt). After traveling for 60 m at a wrapping angle of 60 °, the amount of scratches produced at that time was visually judged according to the following criteria.

No scratch at all ... 5 points Shallow scratch ... 3 points Deep scratch ... 1 point Also, between 5 points and 3 points 2 points between 4 points, 3 points and 1 point
It was a point. At this time, 3 points or more are good scratch resistance, 3
Below the point, scratch resistance was determined to be poor.

A film having less than 3 points as judged at this time causes the film surface to be worn and deep scratches during processing of the film or during traveling as a product, resulting in a marked deterioration in product quality.

(13) Scratch resistance A film is slit into a width of 1/2 inch and a single blade is pressed vertically against it, and it is run for 20 cm while it is pushed 0.5 mm (running tension: 500 g, running speed: 6.7 cm /
Seconds). At this time, the height of the shavings on the surface of the film attached to the tip of the single-edged blade was read with a microscope and used as the shaving amount (unit: μ
m). When the average value of the abrasion amount on both sides is 5 μm or less, the abrasion resistance is very good: when it is 5 to 7 μm, the abrasion resistance is:
Good, and when it exceeds 7 μm, abrasion resistance was judged to be poor. The value of 7 μm is a critical point for rigorously determining whether or not a film surface is scraped in a working process such as a printing process or a calendering process, resulting in a process-related product performance problem.

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

Examples 1 to 5 and Comparative Examples 1 to 6 Rutile type titanium dioxides having different average particle diameters were uniformly dispersed in ethylene glycol, heat-treated at 195 ° C. for 2 hours, and then polycondensed with dimethyl terephthalate after an ester exchange reaction. A polyester containing 2% by weight of rutile type titanium dioxide particles was obtained (Polyester A).

Next, colodyl silicas having different average particle diameters were uniformly dispersed in ethylene glycol, transesterified with dimethyl terephthalate, and then polycondensed to obtain a polyester containing 1% by weight of silica particles derived from corodyl silica. (Polyester B). In this case, by changing the PH value and the sodium content when adjusting the ethylene glycol slurry of silica particles, polyesters having different crystallization promoting coefficients were produced.

The above-mentioned polyester A, polyester B, and polyester not containing particles were mixed in such a manner that the respective contents became predetermined amounts, and the pellets were dried at 180 ° C. for 3 hours under reduced pressure (3 Torr). Feed the pellets into the extruder at 290 ° C
Melt extruded at a surface temperature of 30 using the electrostatic cast method.
It was wound around a casting drum at ℃ and solidified by cooling to make an unstretched film having a thickness of about 180 μm. The draft ratio at this time was 22.

This unstretched film was stretched 3.4 times in the longitudinal direction at 90 ° C. 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 at a stretching rate of 3000% / min at 100 ° C in a width direction using a stenter to give a width of 3.6%.
The film was double-stretched and slightly stretched 1.05 times in the width direction, and then heat-treated at 210 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of 15 μm. As shown in Table 1, the performance of these films is such that when the average particle diameter, content, particle shape factor and crystallization promoting coefficient of the inert particles are within the range of the present invention, both scratch resistance and abrasion resistance are obtained. Excellent films were obtained (Examples 1-
5) When the requirements of the present invention were not satisfied, films having both scratch resistance and abrasion resistance could not be obtained (Comparative Examples 1 to 6). The polyester was polyethylene terephthalate in both the examples and comparative examples.

Examples 6 to 8 and Comparative Examples 7 to 11 Instead of the silica of the polyester B of Example 1, polyesters containing 1% by weight of inactive particles other than silica were obtained. In this case, those having different PH values and sodium contents at the time of preparing an ethylene glycol slurry depending on the kind of particles, and those having different crystallization promoting coefficients depending on the presence or absence of a dispersant were manufactured. A film having a thickness of 15 μm was obtained in the same manner as in Example 1 by using pellets in which these polyesters were mixed in the same manner as in Example 1 so that the respective contents became a predetermined amount. As shown in Table 2, the performance of these films is such that when the average particle diameter, content, shape factor and crystallization promoting coefficient of the inert particles are within the range of the present invention, both scratch resistance and abrasion resistance are Although excellent films were obtained (Examples 6 to 8), when the requirements of the present invention were not satisfied, films having both scratch resistance and abrasion resistance were not obtained (Comparative Examples 7 to 11). The polyester was polyethylene terephthalate in both the examples and comparative examples.

[Advantages of the Invention] The present invention provides a rutile titanium dioxide having an average particle size, content, and shape coefficient in a specific range, an average particle size, content, and
Since it is a biaxially oriented polyester film that also contains inert particles with a shape factor within a specific range, it has excellent scratch resistance and abrasion resistance that can withstand recent severe operating conditions while maintaining slipperiness. The obtained film is obtained.

The use of the film of the present invention is not particularly limited, but the film is particularly useful as a base film for a magnetic recording medium, which has a great influence on product performance due to scratches on the film surface during processing and scraping of the film surface.

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Claims (2)

[Claims] 1. Rutile titanium dioxide particles having an average particle diameter d ₁ of 0.005 to ₁ μm and a shape factor of 0.6 to ₁ are contained in an amount of 0.2 to 3% by weight, and an average particle diameter d ₂ (where d ₁ <d ₂ ) Is 0.3
~ 2μm, 0.01 in the form factor of 0.8-1 inert particles
~ 0.2 wt%, the crystallization promoting coefficient of the inert particles is 2
A biaxially oriented polyester film having a temperature of 0 ° C. or lower. 2. The biaxially oriented polyester film according to claim 1, wherein the surface projection flatness of the film is 7 to 16.