JPH02214733A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To provide the subject film containing specific amounts of two specific kinds of inert particles, having excellent scratch resistance and abrasion resistance and suitable as a base film for magnetic tape, packaging film and film for various industrial materials. CONSTITUTION:The objective film contains two kinds of inert particles A and B each having Mohs hardness of >=6. The particle A has an average particle diameter d1 of 10-500nm and its content in the film is 0.2-2.0wt.%. The particle B has an average particle diameter d2 of 300-1,500nm and larger than the average diameter d1 of the particle A and its content in the film is 0.005-0.15wt.%. The difference of Mohs hardness of the particle A and that of the particle B is preferably >1. The standard deviation of the height distribution of the surface protrusions of the film is preferably <250nm. The surface resistivity of the film is preferably <1X10<15>OMEGA.cm.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a biaxially oriented polyester film, which has excellent scratch resistance and abrasion resistance, and is particularly suitable as a base film for magnetic tapes, packaging, and films for various industrial materials. A biaxially oriented polyester film with excellent properties.

[Prior Art] The present applicant previously proposed a base film for packaging, capacitors, or magnetic tapes with an average particle size of 0.05 to
A biaxially oriented polyester film containing particles with a diameter of 2.0 μm and a Mohs hardness of 7 or more has been proposed (Japanese Patent Laid-Open No. 6
3-230741@publication).

In this film, by incorporating hard particles, the abrasion resistance of the film surface is improved, and by making the particle size of the particles relatively large, the film has good properties during film processing and when used as a product. This ensures smoothness and running properties.

[Problems to be Solved by the Invention] However, polyester films, particularly biaxially oriented polyester films used as base films for magnetic tapes and packaging films that require high mechanical properties, have higher abrasion resistance, Even better scratch resistance has been required, and
The film proposed in Publication No. 1 is no longer sufficient.

For example, as the speed of various processes increases, there is a growing demand for high scratch resistance that does not damage the film surface even when it comes into contact with various high-speed rolls in the process, but the above proposed film is simply a comparison. If only hard particles with a large target particle size are included, the hardness and abrasion resistance will be improved in the areas where the particles protrude like projections on the film surface. Since the surface part itself is not reinforced, there is a risk of scratches on this skin part.

In addition, as a result of not reinforcing the background part, the retention force of the particles on the film surface part, which are used to improve wear resistance, is not sufficient, and there is a risk that the particulate parts will be scraped off as film powder by external forces received from contacting rolls, etc. When this scraping occurs, it adheres to the roll surface, etc., and the film surface is further damaged by the deposits, and the film powder that falls off becomes foreign matter, which may cause disturbances in various processing steps or damage the product itself. There is a risk that performance may deteriorate.

The present invention has focused on the above-mentioned problems, and aims to further improve the surface scratch resistance and abrasion resistance against abrasion and the like of a biaxially oriented polyester film.

[Means for Solving the Problems] The biaxially oriented polyester film of the present invention that meets this objective contains inert particles A and B, both of which have a Mohs hardness of 6 or more, and the particles A have an average particle diameter d1 of 10. ~500nII1
1 content is 0.2~2゜0% by weight, particle B has an average particle size d
2 is 300 to 1500 nm and larger than the average particle diameter d1 of the particles A, and the content is o, oos ~ 0.15%
consists of something that is.

The polyester in the present invention includes ethylene terephthalate, ethylene α/β-bis(2-chlorophenoxy)ethane-4,4-dicarboxylate, ethylene 2,6
- Contains at least one structural unit selected from naphthalate units as a main constituent. However, other components may be copolymerized within a range that does not impede the present invention, preferably within 15 mol%.

Further, polyester containing ethylene terephthalate as a main component is particularly desirable because it has better scratch resistance.

The film of the present invention contains two types of inert particles A and B.

Both particles A and B have a Mohs hardness of 6 or more.

Particles A are particles with a relatively small average particle size, and mainly reinforce the background portion of the film, but if the Mohs hardness is less than 6, this reinforcing effect becomes small, and the desired effect of improving scratch resistance cannot be obtained. In addition, if this background reinforcing effect is small, the bonding force between the particles B or the protrusions on the film surface formed by the particles B will be reduced and the bonding force with the background will be reduced, making it easy to be scraped off. Therefore, it is necessary to sufficiently reinforce the film background. It is desirable that the Mohs hardness of the particles A is 6 or more from this point of view as well. Since particles B have a larger average particle size than particles A, the film surface protrusions formed by particles B are higher on average than the film surface protrusions formed by particles A. The formed film surface protrusions mainly come into contact with the roll and the like. Therefore, if the film surface protrusions formed by the particles B are too soft, the film surface will be easily scraped and the wear resistance will decrease. Therefore, in order to obtain the desired wear resistance, the Mohs hardness of the particles B should be 6 or more. be done.

Particles A are relatively small particles with an average particle diameter d1 of 10 to 500. If the average particle size is smaller than this range, the effect of improving the hardness and reinforcing the film background will be weakened, and the scratch resistance will be poor, which is not preferable. In addition, if the average particle size is larger than the above range, the particle distribution becomes too coarse, the film background reinforcing effect is weakened, the strength to hold the particles B or the film surface protrusions formed by the particles B is reduced, and the particle B Alternatively, the protrusions on the film surface are likely to be scraped due to this. Furthermore, the chances of the protrusions on the film surface themselves being scraped by the particles A increase, which is not preferable.

In addition, the content of U in the particles is in the range of 0.2 to 2.0% by weight.
4 will be made. If the amount is less than this range, the effect of reinforcing the film background due to the inclusion of Particle A will be weakened, and desired scratch resistance will not be obtained. If the amount is more than this range, the content may become too large and the structure may become brittle, and the film itself may be easily scraped off or the contained particles may easily fall off, which is not preferable.

The particles B are relatively large particles with an average particle diameter d2 of 300 to 1500, and the average particle diameter d2 is set larger than the average particle diameter d1 of the particles A (d2>dl).

Since the particles B are relatively large particles, the height of the film surface protrusions formed by the particles can be made higher than that by the particles A, and the surface roughness of the portions can be made rougher. If it becomes coarse, the coefficient of friction can be reduced and the scratch resistance of the film surface will improve as a result, but the effect of roughening the average grains will be reduced and the weight scratch resistance will deteriorate, which is not preferable. On the other hand, if it is larger than the above range, the particles B themselves or the surface protrusions formed by the particles B are likely to be scraped off, which is not preferable.

The content of particles B is adjusted to a range of o, oos to 0.15% by weight. If the amount is less than this range, the effect of reducing the coefficient of friction due to the inclusion of particles B will be weakened, making it impossible to obtain desired scratch resistance. On the other hand, if the amount exceeds the above range, the number of particles B or protrusions on the film surface caused by particles B will be too large, making it easy to be scraped off, which is not preferable.

In the relationship between particles A and B, the average particle diameters d1 and d2
Regarding any size relationship, d2>dl as described above. If d1≧d2, the functions of reinforcing the film surface by the particles A and lowering the film surface friction coefficient by the particles B are reversed, but in this case, the above-mentioned content causes problems as described above.

In other words, in the present invention, although the possible ranges of d113 and d2 overlap, it is possible to set d1 to d2 on the premise that the content m of particle A and the content of particle B are respectively within predetermined ranges. is necessary.

Further, regarding the Mohs hardness, it is preferable that the Mohs hardness of particle A - Mohs hardness of particle B>1, and it is more preferable that the difference is 2 or more. By increasing this difference, the particles A tend to become harder, so that the film background reinforcing effect is improved. As for particles B, as long as they have a Mohs hardness of 6 or more, the necessary abrasion resistance of the film surface is ensured.

In the film of the present invention, it is desirable that the standard deviation σ of the height distribution of surface protrusions is smaller than 250 nm. Tall surface protrusions are formed by particles B having a large average particle diameter, but the more tall protrusions there are, the more likely they are to be scraped off. The method for measuring σ will be described later, but in actual measurements it is difficult to determine whether a protrusion is formed by particles A or B, so the standard deviation of the distribution measured for all protrusions on a certain surface area is It is effective to define σ<250 nm, and desired wear resistance can be obtained.

The specific material of the inert particles A and B is not particularly limited as long as it satisfies the above-mentioned requirements, but it is preferably a material that has an affinity with polyester. When the affinity is good, the contained particles are difficult to aggregate and are easily dispersed uniformly, and
Since the bonding force with the film base material can be maintained high, particles or protrusions on the film surface formed by the particles are difficult to be scraped off. As such an inert particle, particle A
For example, zirconia, titanium nitride,
Examples include α-alumina, γ-alumina, and δ-alumina, and examples of the material of particle B include silica, α-alumina, and rutile titanium dioxide.

The present invention uses the above-mentioned composition as a main component, but other types of polymers may be blended within a range that does not impede the purpose of the present invention, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, etc. may be blended. Inorganic or organic additives may be added to the extent that they are normally added.

The film of the present invention is a film in which the above composition is biaxially oriented. An unstretched film or a -axially oriented film is undesirable because it has poor scratch resistance and particles or film surface protrusions formed by particles tend to fall off.

In addition, the plane orientation index representing the degree of biaxial orientation is not particularly limited, but scratch resistance and wear resistance are better when it is in the range of o, 935 to 0.975, particularly 0°940 to 0.970. This is desirable since it will be even better. Also,
It is particularly desirable for the density index of the film of the present invention to be in the range of 0.02 to 0.05, since this provides even better scratch resistance and abrasion resistance.

Further, the film of the present invention has an average surface roughness Ra in the width direction of 0.005 to 0.030 μm, particularly 0.007 to 0.00 μm.
A thickness in the range of 0.025 μm is particularly desirable because the scratch resistance becomes even better.

The friction coefficient μK of the film in the present invention is 0.20 to 0.
．． A value in the range of 35 is particularly desirable because the scratch resistance becomes even better.

Moreover, the surface resistivity of the film of the present invention is 1×1015
It is particularly desirable that the value is smaller than Ω·α because scratch resistance and abrasion resistance will be even better. If the film powder exceeds this value, it is not preferable because if the film powder is scraped off, the film powder tends to become agglomerated due to static electricity, etc., and the agglomerated film powder tends to damage the film surface.

Next, a method for manufacturing the film of the present invention will be explained.

Ru.

First, as a method for incorporating inert particles A and B into a given polyester, they may be added before, during, or after polymerization, but they can be added to ethylene glycol, which is the diol component of the polyester, in the form of a slurry. An effective method is to mix, disperse, and add. Moreover, as a method for adjusting the content of particles, a method of diluting a high-molecular-weight master pellet during film formation is effective. Using particles A and B, the melt viscosity and copolymerization components of the master pellet are adjusted to a high concentration, preferably 1 to 5% by weight, and the glass transition point T is adjusted.
It is very effective to keep the difference between g and the cold crystallization temperature TCC (TCC-To) between 65 and 110°C, particularly between 75 and 100°C.

Furthermore, it is effective to add a slurry of inert particles A and B dispersed in ethylene glycol before or during the polymerization reaction to obtain an average particle size within the range of the present invention.

In the present invention, a high concentration master polyester containing inert particles A1B separately may be produced, but particles A and B may be mixed at a high concentration in advance at a predetermined mixing ratio during polymerization or master pellet production. The most preferable method is to keep the prepared master pellet in the film and dilute it with other chips or pellets at the film manufacturing stage to reach a predetermined concentration.

After sufficiently drying the polyester pellet containing a predetermined amount of inert particles A and B, it is supplied to a known melt extruder, extruded at 270°C to 330°C into a sheet with a slit-like die, and then passed through a casting roll. The film is then cooled and solidified to form an unstretched film. When producing this unstretched film, the draft ratio (slit width of die/thickness of unstretched film) during casting is preferably a high value of 16 times or more. When high draft casting is performed, a peculiar phenomenon occurs in which particles concentrate on the surface layer, and particles A
, B can easily exhibit their intended functions, so performing such high draft casting is particularly effective in the present invention.

Next, this unstretched film is subjected to two-wheel stretching to achieve biaxial orientation. As the stretching method, a sequential two-wheel stretching method or a simultaneous two-wheel stretching method can be used. In the case of the sequential two-wheel stretching method, it is common to stretch in the longitudinal direction and then in the width direction.
This order may be reversed and stretched. The conditions for two-wheel stretching are not necessarily constant depending on the stretching method, type of polymer, etc., but are usually in the range of 80 to 160°C, preferably 90 to 150°C in both the longitudinal and width directions, and the stretching ratio is 3° to 5°C, respectively. 0 times, preferably in the range of 3.2 to 4.5 times, and the stretching speed is preferably in the range of 1000 to 70.000%/min.

Next, this stretched film is heat treated. The heat treatment conditions are 1 to 15%, preferably 2 to 10% in the constant length and width direction.
under relaxation of
0°C, preferably 0.5 to 6 in the range of 170 to 220°C
0 seconds is suitable.

[Function] In the biaxially oriented polynisdel film of the present invention as described above, the grain 8 has a small average grain size d1, a high Mohs hardness of 6 or more, and a large content, so that the surface of the film is sufficiently formed. It has a large average grain size d2, a Mohs hardness of 6 or more, and has significantly improved scratch resistance.
In addition, the surface of the film is roughened by the small content of particles B, which lowers the coefficient of friction and further improves scratch resistance, and the protrusions formed on the surface of the film by particles B are kept sufficiently hard, improving wear resistance. is improved. Furthermore, as the film surface is reinforced by the particles A, the holding power of the particles B or the film surface protrusions formed by the particles B is also increased, so that they are less likely to be scraped off, and the abrasion resistance is further improved.

[Method of Measuring Physical Properties and Evaluating Effects] The methods of measuring the characteristic values and evaluating the effects of the present invention are as follows.

(1) Particle content (wt%) 1 g of polyester is incinerated with a plasma device, and the amount of each element in the polyester is determined using an atomic absorption spectrometer (for example, AA-680 model manufactured by Shimadzu Corporation). The performance of the particles consisting of the element is calculated from the molecular weight of the particles and determined as weight %. Note that the chemical composition of the particles can be determined by methods such as X-ray diffraction.

In addition, if necessary, it can also be quantitatively determined using fluorescent X-ray analysis, pyrolysis gas chromatography, infrared absorption, Raman scattering, or the like.

(2) Average particle size (nm) The film containing the particles was cut into ultrathin sections perpendicular to the plane of the film to a thickness of 1000 mm, and sliced using a transmission electron microscope (for example, JEH-1200EX, etc.). The particles were observed and the average value over 100 visual fields was defined as the average particle diameter. However, the average particle size herein refers to the average particle size of primary particles, and is determined from the effective diameter of each primary particle even when the particles are in an agglomerated state.

(3) Measuring a test piece with the same composition and structure as the particles added to the Mohs hardness film, or using a mineral before being crushed into particles as a test piece, and scratching each other with a standard mineral for Mohs hardness measurement,
The hardness number is measured to the nearest 0.1 depending on whether scratching occurs.

(4) Standard deviation of height distribution of surface protrusions Two-detector scanning electron microscope [ESM-3200,
manufactured by Elionix Co., Ltd.] and a cross-sectional measuring device [PMS-1,
Elionix Co., Ltd.! The measured height of the protrusion when scanning Ill with the height of the flat surface of the film as O was measured using an image processing device [IBAS2000, Carl's? chair(
Co., Ltd.], and an image of the protrusions on the film surface is reconstructed on an image processing device. Next, a circular equivalent diameter is determined from the area of each protrusion obtained by binarizing the protrusion portion using this surface protrusion image, and this is taken as the average diameter of the protrusion. Furthermore, the highest value among the binarized individual protrusion portions is determined as the height of the protrusion, and this value is determined for each protrusion.

This measurement is repeated 500 times at different locations, and the height distribution of the measured protrusions is assumed to be a normal distribution (normal distribution centered at the point of height O) and approximated by the least squares method to calculate the height distribution. The standard deviation was calculated. Moreover, the magnification of the scanning electron microscope is selected between 1000 and 8000 times.

(5) Planar orientation index Using an Atsube refractometer with sodium D11 (wavelength 589nffl) as a light source, the refractive index in the thickness direction of the biaxially oriented film (denoted as A) was determined, and after melt pressing, the temperature was rapidly cooled in water at 10°C. The refractive index (referred to as B) in the thickness direction of the non-oriented (amorphous) film produced was measured, and A/B was taken as the plane orientation index. Methylene iodide was used as the mounting solution, and the measurement was performed at 25° C. and 65% RH.

(6) Glass transition point Tg, cold crystallization temperature Tcc Measured using a PerkinElmer DSC (differential scanning calorimeter) type II. The conditions for DSC are as follows. That is,
Sample 10TrLg is set in a DSC device, melted at a temperature of 300° C. for 5 minutes, and then cooled in liquid nitrogen. This rapidly cooled sample is heated at a rate of 10° C./min, and the glass transition point TO is detected. The temperature was continued to be gradually raised, and the exothermic peak temperature of crystallization from the glass state was defined as the cold crystallization temperature Tcc. Here, the difference between TCC and TO (Tcc-Tg> is defined as ΔTca.

(7) Density index The density of the film measured using a density gradient tube made of n-hebutane/carbon tetrachloride was set to ρ1 (g/CI), and after melt pressing, the film was rapidly cooled in water at 10°C. The difference between the density ρ2 of the non-oriented (amorphous) film made (
ρ1−ρ2) was taken as the density index.

(8) The friction coefficient μ was measured using a tape runability tester model TBT-300 [manufactured by Yokohama System Research Institute Co., Ltd.] at 20°C and 60% RH.
The vehicle was run in an atmosphere, and the initial μk (friction coefficient) was determined from the following formula.

-0,733log(71/To) to μ, where 1"
0 is the inlet tension, and T1 is the outlet tension. Guide diameter is 6M
The guide material is 5US27 (surface roughness 0.
23), the wrapping angle is 180°, the traveling speed is 3.3QI/
Seconds.

(9) Surface specific resistance super insulation test [manufactured by Kawaguchi Electric Seisakusho Co., Ltd.] Measured using VE-40 model.

(10) Scratch resistance tape running tester TBT300 D/H type [Using Yokohama System Research Institute 1, the film was slit into tapes with a width of 1/2 inch, tension was 30 g, and running speed was 25
The tape was run for 60 m at a wrapping angle of 60° over a video cassette tape guide pin (a stainless steel guide pin with a surface roughness of about 2500 nm at Rt) at 0 TrL/min, and the scratches formed during that time were measured. Judgment was made visually according to the following criteria.

Items with no scratches at all...5 points Items with shallow scratches...3 points Items with deep scratches...・・・・・・・・・1 point and 5
The middle point between points and three points was set as 4 points, and the middle point between 3 points and 1 point was set as 2 points. At this time, a score of 3 or more was considered good scratch resistance, and a score of less than 3 was considered poor scratch resistance.

If the film scores less than 3 points at this time, the quality of the product will be significantly poor because the surface of the film will be abraded and deep scratches will occur during processing or during running when the film is made into a product.

(11) Press one blade perpendicularly against a tape-like slit of abrasion-resistant film 1/2 inch wide, roughly press O, Sa, 20 crb og, running speed: 6.7 CIl! /second). At this time, the height of the scraped material on the surface of the film attached to the tip of the single blade is read with a microscope, and the amount of chipping is measured in μm.) If the average value of both sides of this chipping is 5 μm or less, the chipping resistance is very good. ,
When it was 5 to 7 μm, it was determined that the abrasion resistance was good, and when it was more than 7 μm, it was determined that the abrasion resistance was poor. This value of 7 .mu.m is a critical point for strictly determining whether or not trouble in the process and product performance will occur due to scraping of the film surface during processing steps such as printing and calendering.

[Example] The present invention will be explained based on examples.

Examples 1 to 15 Inert particles A include zirconia, titanium nitride, α-alumina, γ-alumina, and δ, each having a different average particle diameter d1 but within the range of the present invention, and a Mohs hardness within the range of the present invention. - Select alumina particles, and as particle B, select silica, α-alumina, and rutile titanium dioxide particles, each having a different average particle diameter d2 but within the range of the present invention, and a Mohs hardness within the range of the present invention; , uniformly dispersed in ethylene glycol, heat-treated at 195°C for 2 hours, and polycondensed after transesterification with dimethyl terephthalate to obtain a polyester containing each particle at a considerably higher concentration than the range specified in the present invention. created and made it into a master pellet.

Each master pellet and polyester pellets containing no particles are mixed so that the content of particles A and B falls within the content range of the present invention, and the mixed pellets are mixed with polyester pellets containing no particles.
It was dried under reduced pressure (3 Torr) at 0° C. for 3 hours. The pellets were fed into an extruder, melt-extruded at 290°C, and cast using an electrostatic casting method at a surface temperature of 30°C.
It was wound around a drum and cooled and solidified to produce an unstretched film with a thickness of about 180 μm. The draft ratio at this time was 22.

This unstretched film was stretched 3 to 4 times in the longitudinal direction at 90°C. This stretching was carried out with a difference in the circumferential speed of two sets of rolls, and the stretching speed was 10,000%/min. This -axis film was stretched to 100% using a stenter at a stretching speed of 3000%/min.
℃ to 3.6 times in the width direction, and while slightly stretching 1.05 times in the width direction, heat treated at 210℃ for 5 seconds to a thickness of 15 μm.
The performance of these films is shown in Table 1.
Since the average particle diameter, Mohs hardness, and content of B were within the range of the present invention, a film excellent in both scratch resistance and abrasion resistance was obtained.

Comparative Examples 1 to 10 The average particle diameter of inert particles A and B is outside the scope of the present invention, the content is outside the scope of the present invention, and
Regarding the Mohs hardness that falls outside the scope of the present invention, the thickness was 15μ by the same manufacturing method as in the above example.
A biaxially oriented polyester film of m was obtained. As shown in Table 2, the performance of these films is that even if the average particle diameter, Mohs hardness, or m content of particles A and B are out of the range of the present invention, they achieve both scratch resistance and abrasion resistance. No acceptable film was obtained. In addition, the polyester in both Examples and Comparative Examples was polyethylene terephthalate.

[Effects of the Invention] As explained above, according to the present invention, a biaxially oriented polyester film containing two types of inert particles A and B having an average particle diameter, Mohs hardness, and content ω in a specific range. Therefore, a film with excellent scratch resistance and abrasion resistance (abrasion resistance) that can withstand today's harsh conditions of use can be obtained.

Claims (1)

[Claims] 1. Two types of inert particles A, both of which have a Mohs hardness of 6 or more;
Particles A have an average particle diameter d_1 of 10 to 500.
nm, the content is 0.2 to 2.0% by weight, the particle B has an average particle diameter d_2 of 300 to 1500 nm and is larger than the average particle diameter d_1 of the particle A, and the content is 0.005 to 0.15.
% by weight. 2. The biaxially oriented polyester film according to claim 1, wherein the difference between the Mohs hardness of the particles A and the Mohs hardness of the particles B is greater than 1. 3. The biaxially oriented polyester film according to claim 1 or 2, wherein the standard deviation of the height distribution of the surface protrusions is smaller than 250 nm. 4. The biaxially oriented polyester film according to any one of claims 1, 2 and 3, which has a surface resistivity smaller than 1 x 10^1^5 Ωcm.