JP2525449B2 - Biaxially oriented polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film suitable as a base film for magnetic tapes and the like.

[Prior Art] Conventionally, a means for containing an inactive substance such as titanium oxide, silica, calcium carbonate, etc. in a biaxially oriented polyester film in order to have handleability and bone easiness (for example, JP-A- 59-178224, etc.) is known.

[Problems to be Solved by the Invention] However, the conventional polyester film has a film processing step, for example, a printing step in packaging applications,
With the increase in the process speed such as the magnetic layer coating / calendering process for magnetic media applications, the abrasion resistance required for the film is becoming more and more severe. Recently, the problem that the surface of the shavings causes a trouble in the processing process and product performance has become a problem.

In addition, magnetic tapes, especially video tapes, require a smooth base film for higher output, but in recent years, the cost of video tapes has been further reduced, so that even with no back coat, even better running performance is provided. Base film is required. However, it is difficult for the conventional polyester film to satisfy these properties at the same time.

An object of the present invention is to solve the above problems and to provide a polyester film having excellent wear resistance and running property even though it is smooth.

[Means for Solving the Problems] In the present invention, in a biaxially oriented polyester film containing inert particles, among projections having a height of 20 nm or more, half or more of the projections have a projection height h (unit: μm). And the radius of curvature β of the projection tip (unit: μm) satisfy the following expression: a biaxially oriented polyester film.

0.1 × h ^−0.3 <β <1.0 × h ^−0.9 The polyester of the present invention is not particularly limited, but is usually polyethylene terephthalate, polyethylene α, β-bis (2-chlorophenoxy) ethane 4,4′-dicarboxylate, poly Butylene terephthalate or the like is used. Among them, polyethylene terephthalate is preferable.

The polyester film of the present invention must contain inert particles. When the inert particles are not contained, the running property becomes poor, which is not preferable.

Examples of the types of inert particles contained in the polyester film of the present invention include calcium carbonate, silica, titanium oxide, and alumina. Among them, silica is preferable. In particular, colloidal silica is effective in keeping the relationship between the height of the protrusion and the radius of curvature of the protrusion tip within the scope of the present invention.

The crystallization promoting coefficient of the inert particles contained in the polyester film of the present invention is not particularly limited, but is 3 to 18 ° C.
In the case of the above range, it is effective to set the relationship between the height of the protrusion and the radius of curvature of the protrusion tip within the range of the present invention.

The particle diameter of the inert particles contained in the polyester film of the present invention is preferably 0.08 to 1.5 μm, and more preferably 0.10 to 1.2 μm. , Which is extremely effective within the scope of the present invention.

Furthermore, when the particle size variation coefficient of the inert particles is preferably 1.0 or less, more preferably 0.6 or less, the relationship between the projection height and the projection tip radius of curvature is extremely effective in keeping the scope of the present invention. .

When the content of the inert particles contained in the polyester film of the present invention is preferably 0.01 to 2% by weight, more preferably 0.05 to 1% by weight, the abrasion resistance and the running property are better. It is desirable because it becomes even better.

In addition, internal particles may be contained within a range that does not impair the object of the present invention.

In the polyester film of the present invention, among the protrusions on the film surface, the number of protrusions having a height of 20 nm or more is
The range of 10,000 to 80,000 pieces / mm ² is preferable because the running property and the wear resistance are further improved.

Further, in the polyester film of the present invention, among projections having a height of 20 nm or more on the surface of the film, half or more thereof, preferably 70% or more, more preferably 80%
Regarding the above protrusion, the relation between the protrusion height h (unit: μm) and the protrusion tip curvature radius β (unit: μm) satisfies the following formula (1), more preferably the following formula (2), and particularly preferably the following formula. Need to be

0.1 × h ^−0.3 <β <1.0 × h ^−0.9 …… (1) 0.1 × h ^−0.3 <β <0.8 × h ^−0.8 …… (2) 0.1 × h ^−0.3 <β <0.6 × h ^−0.7 … (3) Of the protrusions with a protrusion height of 20 nm or more, if the radius of curvature β of the protrusion tip is too large for more than half of the protrusions,
It is not preferable because the running property becomes poor. On the other hand, if the radius of curvature β of the tip of the projection is too small, the abrasion resistance becomes poor, which is not preferable.

Further, the average surface roughness of the film of the present invention is not particularly limited, the average surface roughness of at least one surface 0.0030 ~ 0.06
The range of 0 μm is desirable because both the running property and the wear resistance are further improved.

The coefficient of static friction of the film of the present invention is not particularly limited, but it is desirable that the coefficient of static friction of at least one surface is in the range of 0.2 to 3.0 because the running property and abrasion resistance are further improved.

Further, in the polyester film of the present invention, the standard deviation of surface protrusion height is preferably 2 μm or less, more preferably 1 μm.
When it is in the range of m or less, abrasion resistance is further improved, which is desirable.

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

First, inert particles are added to polyester. The time of addition may be before polymerization, during polymerization, or after polymerization,
It is preferable to use a method of mixing and dispersing in the form of a slurry into ethylene glycol, which is a diol component of polyester, or the like, and the effect of the present invention is further enhanced. Further, at this time, it is preferable to disperse fine glass beads or the like as a medium and then highly disperse the particles by a medium dispersion method of removing the glass beads or the like, since the effect of the present invention is further enhanced. Further, heat-treating the particles in the stage of slurry is suitable for keeping the relationship between the height of the protrusion and the radius of curvature of the protrusion tip within the range of the present invention.

Next, after fully drying this polyester, it is supplied to an extruder, filtered with high precision, melt-extruded from a slit-shaped die, and cooled and solidified to form an unstretched film.

Further, the draft ratio (slit width of the die / thickness of the unstretched film) at the time of casting is a high value of about 3 to 10 times, which makes the relationship between the projection height and the projection tip curvature radius within the scope of the present invention. Suitable for

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. However, it is preferable to use the sequential biaxial stretching method in which stretching is first performed in the longitudinal direction and then in the width direction so that the relationship between the protrusion height and the radius of curvature of the protrusion tip is within the range of the present invention. The stretching temperature and the stretching ratio are not particularly limited, but the stretching height and the projection tip radius of curvature are within the scope of the present invention when the stretching is performed 3 to 5 times at a temperature of 70 to 120 ° C. in both the longitudinal and width directions. It is suitable for

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

If necessary, the stretched film can be heat-treated. The heat treatment conditions in this case are:
It is preferably carried out at a temperature of 150 to 220 ° C, preferably 170 to 210 ° C for 0.5 to 30 seconds.

Further, calendering this film is effective in keeping the relationship between the height of the projection and the radius of curvature of the projection tip within the range of the present invention. The calender conditions are not particularly limited, but a temperature of 30 to 90 ° C. and a linear pressure of 30 to 250 kg / cm are preferable. The calender treatment may be performed after the heat treatment, or may be performed before the heat treatment.

[Operation] In the film of the present invention, the height of the surface protrusion and the shape of the tip of the protrusion have a specific relationship, so that the contact state with the mating member becomes a unique state, the friction on the surface is reduced, and the protrusion is removed. Is estimated to disappear.

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

Average particle size Particles are uniformly dispersed in ethylene glycol to form a slurry, which is diluted to a concentration suitable for measurement, and measured with a centrifugal sedimentation particle size measuring device (SA-CP2 type manufactured by Shimadzu Corporation).
The obtained particle size distribution was plotted on a logarithmic probability paper, and the median diameter at the point where the cumulative passage percentage became 50% was defined as the average particle size d of the particles.

Particle size variation coefficient The particle size distribution obtained in the same manner as the measurement of the average particle size,
Approximate the normal distribution by the method of least squares to obtain the standard deviation σ.
A value obtained by dividing the standard deviation σ by the average particle diameter d, that is, σ / d was used as the particle diameter variation coefficient.

Particle content Measured amount of precipitated particles: 100 g of polyester is added to a solvent which dissolves polyester and does not dissolve inert particles, and heated to completely dissolve polyester. This solution was used as a 300 centrifuge using Hitachi Koki Co., Ltd. ultracentrifuge 55P-72.
Centrifuge at 00 rpm for 40 minutes and vacuum-dry the resulting particles. When the particles are measured with a scanning differential calorimeter,
When a melting peak corresponding to polyester is observed, the solvent is added again to the particles, and the particles are heated and dissolved, and then centrifuged. When the melting peak is no longer observed, the particles are regarded as precipitated particles and the weight is measured. This weight was divided by 100 grams, and the content in percentage was taken as the content.

 Usually, about three centrifugation operations are sufficient.

In addition, if necessary, quantification using fluorescent X-ray or the like is performed.

Crystallization acceleration coefficient The difference (Tcc-Tg) between the cold crystallization temperature Tcc of the polymer and the glass transition point Tg measured using a DSC (Differential Scanning Calorimeter) II type manufactured by Perkin Elmer Co. was defined as ΔTcg, and 1 The ΔTcg (I) of the polyester containing wt% of the inactive particles and the ΔTcg (II) of the polyester containing no inactive particles of the same viscosity as this were measured to obtain ΔTcg (II) and ΔTcg (I). ) Difference [ΔTcg (II) -ΔTcg (I)] was taken as the crystallization promoting coefficient of the inactive 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 Tcc.

Number of protrusions, standard deviation of protrusion height 2 Detector type scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] and cross-section measurement device [PMS-1, manufactured by Elionix Co., Ltd.] The measured height of the protrusion when scanning with the height set to 0 is sent to the ideal value [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] (512 x 512 pixels), and the image on the film surface is reproduced on the image processor. To construct. The highest value among the measured individual protrusions is taken as the height of the protrusion, and the protrusion height is obtained for each protrusion. Repeat this measurement 500 times at different locations.
At this time, count the number of protrusions whose protrusion height is 20 nm or more,
The number of protrusions was converted to 1 mm ² .

Further, the heights of all the above-mentioned projections were applied to a normal distribution centered on the projection height 0, and the standard deviation at this time was defined as the surface projection height standard deviation.

The magnification of the scanning electron microscope is usually 3000 times, but the optimum magnification can be selected in the range of 2000 to 5000 times according to the size of the protrusion. Similar to when measuring the height standard deviation and the number of protrusions, the height information from the scanning electron microscope and cross-section measuring device is sent to the image processing device (512 x 512 pixels) and reconstructed as a film surface protrusion image. Then, the protrusion tip curvature radius β was calculated based on the following definition for each of the measured protrusions having a protrusion height of 20 nm or more.

On an image processing device (512 × 512 pixels), a cross-sectional curve (y = f) of a projection passing through the apex of the projection of the film surface projection image
In (x)), the value of the projection height corresponding to the portion of 9 pixels in total including the apex of the projection as the center is given by the following formula (4)
By interpolating the function represented by (1) with the least squares method, the radius of curvature β _{MD in the} longitudinal direction and the radius of curvature β _TD in the width direction were calculated according to the following equation (5). Next, the radius of curvature β of the projection tip was calculated from this value by the following equation (6).

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

y = ax ² + bx + c (4) β ^{MD, TD} = 1 / | y ″ | (5) β = 2 β _MD β _TD / (β _MD + β _TD ) …… (6) Runability Film 1 / Slit to 2 inches, tape running tester TBT-300 type (manufactured by Yokohama System Laboratory Co., Ltd.) was used, run at 20 ° C., 60% RH atmosphere, and the initial μK was calculated from the following formula. .

μK = 0.733 log (T ₁ / T ₂ ) where T ₂ is the input tension and T ₁ is the output 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.

Those having μK of 0.35 or less were regarded as having good running properties.
The value of μK of 0.35 is a critical value for determining whether the running property during film processing or when a product is extremely deteriorated.

Abrasion resistance A film is slit into a tape with a width of 1/2 inch, a single blade is pressed vertically, and the product is run for 20 cm while being pushed 0.5 mm (running tension: 500 g, running speed: 6.7 cm /
Seconds). At this time, the height of the scraped material on the surface of the film attached to the tip of the single-edged blade was read with a microscope and used as the wear amount (unit: μ
m). When this wear amount was 8 μm or less, wear resistance was determined to be good, and when it exceeded 8 μm, wear resistance was determined to be poor.
This value of 8 μm is a critical value as to whether or not abrasion powder generated by abrasion of the film surface during film processing or running as a product affects product quality.

[Example] Next, an embodiment of the present invention will be described based on an example.

Example 1 Colloidal silica particles having a crystallization acceleration coefficient of 5.0 ° C., an average particle size of 0.3 μm and a particle size variation coefficient of 0.21 were uniformly dispersed in ethylene glycol, and heat-treated at 197 ° C. for 1 hour and 30 minutes, and then dimethyl terephthalate was added. Polymerization gave polyethylene terephthalate pellets A. The content of particles with respect to the polymer was 1.0% by weight.

Similarly, crystallization acceleration factor 8.0 ℃, average particle size 0.6μ
m, a colloidal silica particle having a particle size variation coefficient of 0.28 was uniformly dispersed in ethylene glycol, heated at 196 ° C. for 1 hour and 42 minutes, and then polymerized with dimethyl terephthalate to obtain a polyethylene terephthalate pellet B.
The content of particles with respect to the polymer was 1.0% by weight.

50 parts by weight of the above pellets A, 0.5 parts by weight of pellets B, and 49.5 parts by weight of pellets C of polyester containing no particles are mixed and dried under reduced pressure at 180 ° C. for 3 hours (3
Torr), then fed to the extruder and melt-extruded at 290 ° C.
After carrying out high precision filtration, it was wound around a casting drum having a surface temperature of 30 ° C. by an electrostatically applied casting method and cooled and solidified to prepare an unstretched film having a thickness of about 150 μm. still,
The draft ratio at this time was 5.8.

This unstretched film was stretched 3.4 times in the longitudinal direction at 90 ° C. This drawing was carried out at a peripheral speed difference between the two sets of rolls, and the drawing speed was 12000% / min.

Stretching speed of this uniaxial film using a stenter 2500%
Stretched 3.6 times in the width direction at 100 ° C / min.
Calendered at ℃ and linear pressure of 100kg / cm under constant length
The film was heat treated at 210 ° C. for 5 seconds to obtain a film having a thickness of 12 μm.

The number of projections of 20 nm or more of this film was 71200 / mm ² , and the relationship between the projection height h and the projection tip curvature radius β was 98% within the range shown by the equation (1).

The standard deviation of surface protrusion height of this polyester film is
It was 0.095 μm.

 The surface roughness of this film was 12.0 nm.

Next, the abrasion resistance of this polyester film was measured and found to be good at 4 μm. The running property was also good at 0.21 (Table 2).

Thus, it can be seen that when the relationship between the protrusion height and the radius of curvature of the protrusion tip is in a specific range, the film can have good wear resistance and running properties even though the surface is smooth. .

Examples 2 to 3 and Comparative Examples 1 to 3 Biaxially oriented polyester films are produced by variously changing the type of particles contained, the crystallization promoting coefficient, the particle size, the particle size variation coefficient, the content, the film forming conditions and the like. (Table 1).

When the relationship between the height of the protrusion and the radius of curvature of the tip of the protrusion was within the range of the present invention, both the running property and the wear resistance were good even though the surface was smooth. However, when the relationship between the height of the protrusion and the radius of curvature of the protrusion tip is out of the range of the present invention, both the running property and the wear resistance could not be satisfied (Table 2).

EFFECTS OF THE INVENTION Since the present invention is a biaxially oriented polyester film in which the height of the surface protrusion and the shape of the tip of the protrusion have a specific relationship, the contact state with the mating member becomes a peculiar state. It has an excellent effect.

In the film processing step, since the film surface is not scraped even if the processing speed is increased, troubles due to scrapes are eliminated.

Despite its smooth surface, it has good running properties, so there is no need for a back coat when used as a magnetic tape.
Moreover, high output can be obtained.

Claims (1)

(57) [Claims] 1. A biaxially oriented polyester film containing inert particles, wherein among projections having a height of 20 nm or more, more than half of the projections have a projection height h (unit: μm) and a projection tip curvature radius β (unit: The biaxially oriented polyester film is characterized by satisfying the following expression. 0.1 × h ^−0.3 <β <1.0 × h ^−0.9