JP2621461B2 - Biaxially oriented polyester film - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a biaxially oriented polyester film, which is particularly suitable as a base film for magnetic tape, a film for packaging and a film for various industrial materials, and has scratch resistance and abrasion resistance. The present invention relates to a biaxially oriented polyester film having excellent properties.

[Prior art] The applicant has previously reported an average particle size of 0.05 to 2. as a base film for packaging, for a capacitor, or for a magnetic tape.
A biaxially oriented polyester film containing particles of 0 μm and Mohs hardness of 7 or more has been proposed (JP-A-63-23).
No. 0741). In this film, by containing hard particles, while improving the abrasion resistance of the film surface, by making the particle diameter of the particles relatively large, good film processing and when the product Slipperiness,
The runnability is ensured.

[Problems to be Solved by the Invention] However, a polyester film, particularly a biaxially oriented polyester film used as a base film for a magnetic tape or a packaging film requiring high mechanical properties, has higher abrasion resistance, Excellent scratch resistance has been demanded, and the film proposed in Japanese Patent Application Laid-Open No. 63-230741 is no longer sufficient.

For example, with the increase in the speed of various processes, a high scratch resistance that does not damage the film surface even when it comes into contact with various high-speed rolls in the process is being demanded,
By simply including one kind of hard particles having a relatively large particle size as in the above proposed film, the hardness of the portion protruding in a projecting manner on the film surface is increased by the particles, but the wear resistance is improved. Since the background of the film (the surface portion other than the protruding portion) itself is not reinforced, there is a possibility that the background portion may be scratched.

In addition, as a result of the fact that the ground portion is not reinforced, the particle holding force on the film surface portion for improving abrasion resistance cannot be said to be sufficient, and the particle portion may be shaved as film powder by an external force received from a contacting roll or the like. When the scraping occurs, the scraping adheres to the roll surface and the like, and furthermore, the film surface is further damaged by the deposit, and the falling film powder becomes a foreign substance, which may be a disturbance in various processing steps, or the product itself may be damaged. Performance may be reduced.

The present invention pays attention to the above-mentioned problems, and aims to further improve the scratch resistance and the wear resistance against abrasion and the like of the surface of the biaxially oriented polyester film.

[Means for Solving the Problems] The biaxially oriented polyester film of the present invention for this purpose contains two kinds of particles A and B, and the particles A are composed of α-alumina, γ-alumina, δ-alumina, Consisting of one kind of particles selected from zirconia, titanium nitride and organic polymer, the average particle size is 5 to 400 nm, and the content is 0.1 to 2% by weight.
The particles B are composed of one kind of particles selected from silica, calcium carbonate, alumina, rutile-type titanium oxide and an organic polymer, and have an average particle diameter of 400 to 1500 nm and a content of 0.01 to 0.4% by weight. And the standard deviation of the height distribution of the projections formed on the film surface is smaller than 250 nm.

The polyester in the present invention is ethylene terephthalate, ethylene α · β-bis (2-chlorophenoxy)
Ethane-4,4'-dicarboxylate, ethylene 2,6
-At least one structural unit selected from naphthalate units is used as a main component. However, other components may be copolymerized within a range that does not impair the present invention, preferably within 15 mol%.

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

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

Particle A is a particle having a relatively small average particle size and mainly reinforces the background portion of the film. In order to enhance the background reinforcing effect, particles having high hardness or particles having good affinity with the film are selected. You. As particles having high hardness, particles composed of α-alumina, γ-alumina, δ-alumina, zirconia, and titanium nitride are preferable, and as particles having good affinity, organic polymer particles, for example, crosslinked polystyrene particles, silicon particles And tetrafluoroethylene particles.

The organic polymer particles in the present invention have a scratch resistance and a dubbing resistance more preferably when the temperature at the time of 10% weight loss in the heating weight loss curve is 360 ° C., preferably 380 ° C., and more preferably 400 ° C. or more. Is particularly desirable.

The particles A are relatively small particles having an average particle diameter d1 of ₅ to 400 nm. If the average particle size is smaller than this range,
This is not preferred because the reinforcing effect of the film background is weakened and the scratch resistance becomes poor. On the other hand, if the average particle size is larger than the above range, the distribution of the particles becomes too coarse, the effect of reinforcing the film background is weakened, the strength of retaining the particle B or the film surface projections formed by the particles B decreases, and the particle B Alternatively, film surface protrusions due to this are likely to be scraped. Further, it is not preferable because the chances of shaving the film surface projections themselves due to the particles A increase. A more preferred range of the average particle diameter d ₁ is 10 to 200 nm.

Organic polymer particles in the present invention, the temperature at the time of 10% weight loss in the heating weight loss curve is 360 ℃, preferably 380 ℃,
More preferably, the temperature is 400 ° C. or more, since the scratch resistance and the dubbing resistance are further improved.

The content of the particles A is adjusted to a range of 0.1 to 2.0% by weight. If the amount is less than this range, the effect of reinforcing the film background due to the inclusion of the particles A is weakened, and a desirable scratch resistance cannot be obtained. If the content is larger than this range, the content becomes too large, and there is a possibility that the film becomes brittle structurally, and the film itself is easily scraped off or the contained particles are easily dropped off, which is not preferable. A more preferred content is 0.3 to 1.0% by weight.

Particle B is a particle having a larger average particle diameter than Particle A, and increases the roughness of the film surface due to the film surface protrusions formed by Particle B and reduces the coefficient of friction of the surface, thereby improving the scratch resistance. In addition, it aims at reducing the resistance when the film comes into contact with another surface such as a roll during processing or the like, so that the film surface is hardly scraped off. Examples of the material of the particles B capable of achieving these are silica, calcium carbonate, alumina, rutile-type titanium oxide, and an organic polymer. As the organic polymer particles, the same material as the particles A described above can be used.

Further, the particles B, and the average particle size d ₂ are relatively large particles of 400～1500Nm, it is set larger than the average particle size d ₁ of particle A. 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 of the particles A, and the surface roughness of that portion can be made rough. When the roughness is rough, the coefficient of friction can be reduced, and as a result, the scratch resistance of the film surface is improved.However, when the average particle diameter d ₂ is smaller than the above range, the effect of roughening the film surface is reduced, and the resistance to the film is reduced accordingly. It is not preferable because the scratching property is deteriorated. On the other hand, if it is larger than the above range, the particles B themselves or the surface projections formed by the particles B are easily scraped off, which is not preferable.

The content of the particles B is adjusted in the range of 0.01 to 0.4% by weight. If it is less than this range, the effect of reducing the friction coefficient due to the inclusion of the particles B is weakened, so that desirable scratch resistance cannot be obtained. Conversely, if the amount is larger than the above range, the particles B or the film surface projections due to the particles B, which are borne by the film ground portion reinforced by the particles A, become too large, so that it is not easy to scrape off. A more preferred content is 0.01 to 0.1% by weight.

In the film of the present invention, the standard deviation σ of the height distribution of the surface projections needs to be smaller than 250 nm. The surface protrusions having a high height are formed by particles B having a large average particle diameter. However, if the number of the protrusions is large, the surface protrusions are easily removed. Although the method of measuring σ will be described later, it is difficult to determine whether the projections are formed by particles A or B in the actual measurement, so the standard deviation of the distribution measured for all the projections for a certain surface portion Is effective, and by setting σ <250 nm, desirable wear resistance can be obtained. Such a standard deviation of the height distribution of the protrusions can be achieved, for example, by optimizing the draft ratio in the casting step of the melt film formation.

In the film of the present invention, the difference between the cold crystallization temperature and the glass transition point of the polyester containing particles A and the difference between the cold crystallization temperature and the glass transition point of the polyester not containing particles A is 8 ° C. , Preferably less than 5 ° C. The method of measuring this difference will be described later,
If this difference is small, the affinity of the particles for the film can be improved. By increasing the affinity of the particles A having a large content, both the abrasion resistance and the scratch resistance are further improved.

The present invention is based on the above composition, but may be blended with other polymers within a range that does not impair the object of the present invention, and may also be used as an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber, 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. For unstretched film and uniaxially oriented film,
It is not preferable because the scratch resistance becomes poor and the particles or the film surface projections formed by the particles easily fall off.

The plane orientation index indicating the degree of the biaxial orientation is not particularly limited, but is preferably in the range of 0.935 to 0.975, and particularly preferably in the range of 0.940 to 0.970, because the scratch resistance and the wear resistance are further improved. Further, when the density index of the film of the present invention is in the range of 0.02 to 0.05, scratch resistance,
This is particularly desirable because the abrasion resistance is further improved.

Further, the film of the present invention has a surface average roughness Ra in the width direction.
It is particularly desirable that the scratch resistance be in the range of 0.005 to 0.030 μm, particularly 0.007 to 0.025 μm, because the scratch resistance will be further improved.

The coefficient of friction μk of the film in the present invention is 0.20 to 0.35
It is particularly preferable that the ratio is within the range, since the scratch resistance is further improved.

The surface specific resistance of the film of the present invention is 1 × 10 ¹⁵ Ω · cm
It is particularly desirable that the ratio be smaller than the above, since the scratch resistance and the wear resistance are further improved. Above this value, if the film powder is scraped off, the film powder is likely to be clumped due to static electricity or the like, and the clumped film powder is likely to damage the film surface, which is not preferable.

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

First, as a method for incorporating particles A and B into a predetermined polyester, the particles may be added before, during, or after the polymerization, but they are mixed in a slurry form with ethylene glycol, which is a diol component of the polyester. It is effective to disperse and add. As a method of adjusting the content of particles, a method of diluting a high-concentration master pellet at the time of film formation is effective. Using particles A and B,
The melt viscosity of the master pellet at a high concentration, preferably 1 to 5% by weight, the copolymerization component is adjusted, and the difference between the glass transition point Tg and the cooling crystallization temperature Tcc (Tcc−Tg) is 65 to 110 ° C. It is extremely effective to keep the temperature at 75 to 100 ° C.

The addition of the particles A and B to the slurry dispersed in ethylene glycol before or during the polymerization reaction is effective for obtaining the average particle size within the range of the present invention.

In the present invention, a high-concentration master polyester containing the particles A and B separately may be produced. However, the particles A and B may be produced at a high mixing concentration in advance at the time of polymerization or production of a master pellet. The most preferred method is to put the prepared master pellet into a predetermined concentration by diluting the prepared master pellet with other chips and pellets in the film production stage.

Thus, after sufficiently drying the polyester pellets containing a predetermined amount of particles A and B, it is supplied to a known melt extruder, extruded at 270 ° C. to 330 ° C. from a slit die into a sheet, and is cast on a casting roll. Cool and solidify to make an unstretched film. When making this unstretched film,
The draft ratio at the time of casting (slit width of die / thickness of unstretched film) 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 portion, and it becomes easy for particles A and B to exert their intended functions. Further, since the standard deviation of the projection height on the film surface becomes smaller due to the concentration of the particles on the surface layer, such a high draft casting is particularly effective in the present invention.

Next, the unstretched film is biaxially stretched and biaxially oriented. As the 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, the stretching is generally performed in the order of the longitudinal direction and the width direction, but the stretching may be performed in the reverse order. The biaxial stretching conditions are not necessarily constant depending on the stretching method, the type of polymer, etc., but are usually in the longitudinal direction and the width direction at 80 to 160 ° C., preferably in the range of 90 to 150 ° C., and the stretching ratio is 3.0 to
The range is 5.0 times, preferably 3.2 to 4.5 times, and the stretching speed is suitably in the range of 1000 to 70,000% / min.

Next, this stretched film is heat-treated. The heat treatment conditions are under a fixed length and under a relaxation of 1 to 15%, preferably 2 to 10% in the width direction, and 1.01 to 1.2 times, preferably 1.0 to 1.0 times in the width direction.
Under 5 to 1.15 times fine stretching, 150 to 230 ° C, preferably 170 to 22
0.5 to 60 seconds in the range of 0 ° C is preferred.

[Method for Measuring Physical Properties and Method for Evaluating Effect] The method for measuring characteristic values and the method for evaluating effect according to the present invention are as follows.

(1) Particle content (% by weight) 1 g of polyester was incinerated with a plasma device, and the amount of each element in the polyester was quantified using an atomic absorption spectrometer (for example, AA-680 type manufactured by Shimadzu Corporation). The amount of the particles made of the element is converted from the molecular weight of the particles, and is calculated as% by weight. The chemical composition of the particles can be known by a method such as X-ray diffraction.

Further, if necessary, the quantification can be performed using X-ray fluorescence analysis, pyrolysis gas chromatography, infrared absorption, Raman scattering, or the like.

(2) Average particle size (nm) The film containing the particles is made into an ultra-thin section perpendicular to the film plane with a thickness of 1000 mm, and the particles are obtained using a transmission electron microscope (for example, JEM-1200EX manufactured by JEOL Ltd.). Observe 100
The value averaged over the visual field was defined as the average particle size. Here, the average particle size is the average particle size of the primary particles, and is determined from the effective diameter of each primary particle even when the particles are in an aggregated state.

(3) Standard deviation of height distribution of surface protrusions Film surface in a two-detector scanning electron microscope [ESM-3200, manufactured by Elionix Inc.] and a cross-section measuring device [PMS-1, manufactured by Elionix Inc.] The measured value of the height of the projection when scanning is performed with the height of the flat surface set to 0 is sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.], and the image of the film surface projection is reconstructed on the image processing apparatus. Next, a circle-equivalent diameter is determined from the area of each projection obtained by binarizing the projection portion on the surface projection image, and this is defined as the average diameter of the projection. The highest value among the binarized individual projections is defined as the height of the projection, and this is determined for each individual projection. This measurement is repeated 500 times in different places, and the height distribution of the measured protrusions is regarded as a normal distribution (normal distribution centered on a point having a height of 0), and the minimum is 2
The standard deviation of the height distribution was determined by multiplication. The magnification of the scanning electron microscope is selected between 1000 and 8000 times.

(4) Plane orientation index Using an Abbe refractometer as a light source for sodium D line (wavelength 589 nm), the refractive index (A) in the thickness direction of the biaxially oriented film and quenching into water at 10 ° C after melt pressing. The refractive index (referred to as B) in the thickness direction of the non-oriented (amorphous) film thus produced was measured, and A / B was defined as a plane orientation index. Use methylene iodide as the mounting solution, 25 ° C, 65
It was measured at% RH.

(5) Glass transition point Tg, cold crystallization temperature Tcc Measured using a DSC (differential scanning calorimeter) type II manufactured by PerkinElmer. The conditions of DSC are as follows. That is, 10 mg of a sample is set in a DSC device, and 5
After melting for a minute, cool in liquid nitrogen. The quenched sample is heated at a rate of 10 ° C./min, and the glass transition point Tg is detected. The temperature was further increased, and the crystallization exothermic peak temperature from the glassy state was defined as the cold crystallization temperature Tcc. Here, the difference between Tcc and Tg (Tcc−Tg) is defined as ΔTc g.

(6) Density Index The density of the film measured using a density gradient tube composed of n-heptane / carbon tetrachloride is defined as ρ ₁ (g / cm ³ ). After melt-pressing the film, the film is rapidly cooled into 10 ° C. water. Difference (ρ) from the density ρ _{2 of} the non-oriented (amorphous) film
₁₋ ρ ₂ ) was used as the density index.

(7) Coefficient of friction μk Using a tape running property tester TBT-300 type [manufactured by Yokohama System Laboratory Co., Ltd.], run at 20 ° C and 60% RH atmosphere, and the initial μk (coefficient of friction) is expressed by the following formula. I asked more.

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, and the guide material is SUS27 (surface roughness 0.2
S), the winding angle is 180 °, and the running speed is 3.3cm / sec.

(8) Surface specific resistance Measured using a super insulation meter [Kawaguchi Electric Mfg. Co., Ltd.] VE-40.

(9) Scratch resistance Using a tape running tester TBT300D / H type [Yokohama System Laboratory Co., Ltd.], slit the film into a 1/2 inch wide tape, tension 30g, running speed 250m / min. Winding angle on tape guide pin of video cassette (stainless steel guide pin with surface roughness of about 2500nm with Rt surface roughness)
The vehicle was run for 60 m at 60 °, and the amount of scratches formed at that time was visually determined according to the following criteria.

No scratches at all ... 5 points Shallow scratches ... 3 points Deep scratches ... 1 point Also, 4 points at the middle of 5 points and 3 points, 3 points and 1 point The middle was given two points. At this time, three or more points have good scratch resistance,
Less than 3 points were regarded as poor scratch resistance.

A film having less than 3 points determined at this time has a severely damaged surface due to abrasion of the film surface during processing of the film or running as a product, so that the quality of the product is significantly deteriorated.

(10) Abrasion resistance A piece of film is slit into a tape with a width of 1/2 inch, and one piece is pressed vertically, and the film is further pushed in by 0.5 mm and run for 20 cm (running tension: 500 g, running speed: 6.7 cm) /
Seconds). At this time, the height of the shavings on the film surface attached to the tip of the single blade was read with a microscope and the shaving amount (unit: μ)
m) When the average value of the abrasion amount on both sides was 12 μm or less, the abrasion resistance: good, and when it exceeded 12 μm, the abrasion resistance: poor. The above boundary values are obtained by processing the film surface in processing steps such as printing and calendaring.
This is a critical point for determining whether or not a trouble in product performance occurs in the process.

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

Examples 1 to 8 As particles A, α-alumina, γ-alumina, δ-alumina, zirconia, titanium nitride, and organic polymer particles having different average particle diameters d ₁ but within the scope of the present invention were selected. As B, silica, calcium carbonate, alumina, each having a different average particle diameter d ₂ but within the scope of the present invention,
Rutile-type titanium oxide and organic polymer particles were selected, uniformly dispersed in ethylene glycol, respectively, and heat-treated at 195 ° C. for 2 hours. After transesterification with dimethyl terephthalate, polycondensation was performed. Create a polyester containing a considerably higher concentration than the specified range,
It was made into a master pellet.

Each master pellet and a polyester pellet containing no particles were mixed so that the particles A and the particles B were within the range of the content of the present invention, and the mixed pellets were mixed.
It was dried under reduced pressure (3 Torr) at 0 ° C. for 3 hours. The pellets were supplied to an extruder, melt-extruded at 290 ° C., wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method, cooled and solidified to form 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 differences, and the stretching speed was 10,000% / min. This uniaxial film is stretched in the width direction at 100 ° C at a stretching speed of 3000% / min using a stenter.
The film was heat-treated at 210 ° C. for 5 seconds while being stretched 3.6 times and slightly stretched 1.05 times in the width direction to obtain a biaxially oriented polyester film having a thickness of 15 μm. As shown in Table 1, the performance of these films is such that the materials of the particles A and B are specified in the present invention, and the average particle size and the content are within the range of the present invention. A film excellent in both properties was obtained.

Comparative Examples 1 to 10 Particles A and B having a mean particle size outside the range of the present invention, a content outside the range of the present invention, and a combination of particles other than those specified in the present invention regarding the material of the particles In each case, a biaxially oriented polyester film having a thickness of 15 μm was obtained in the same manner as in the above examples. The performances of these films were as shown in Table 2, as shown in Particle A,
Even if any of the material, average particle size, and content of B deviated from the range of the present invention, a film capable of achieving both scratch resistance and abrasion resistance was not obtained. Note that the embodiment,
In both comparative examples, the polyester was polyethylene terephthalate.

[Effects of the Invention] As described above, according to the present invention, two types of particles A and B selected from a specific material and having a specific range of an average particle size, a content, and a projection height distribution are used. Since the biaxially oriented polyester film is contained, a film having excellent scratch resistance and abrasion resistance (abrasion resistance) that can withstand recent severe use conditions can be obtained.

────────────────────────────────────────────────── (5) Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 7:00 (56) References JP-A 1-311131 (JP, A) JP-A 63- 278939 (JP, A) JP-A-2-129230 (JP, A)

Claims (2)

(57) [Claims] (1) It contains two kinds of particles A and B, and the particle A has α
-Alumina, γ-alumina, δ-alumina, zirconia, composed of one kind of particles selected from titanium nitride and an organic polymer, the average particle size is 5 to 400 nm, the content is 0.1 to
2% by weight, and particles B are silica, calcium carbonate,
Alumina, composed of a kind of particles selected from rutile type titanium oxide and organic polymer, the average particle size is 400 ~ 1500n
m, a biaxially oriented polyester film having a content of 0.01 to 0.4% by weight and a standard deviation of a height distribution of protrusions formed on the film surface being smaller than 250 nm. 2. The biaxially oriented polyester film according to claim 1, having a surface resistivity of less than 1 × 10 ¹⁵ Ω · cm.