JPH07304095A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To provide a biaxially oriented polyester film in which powder is prevented from being generated in a high-speed traveling and coefficient of friction is small by specifying both the uniformity index of a surface projection measured in the width direction and a projection interval. CONSTITUTION:In at least one side of a biaxially oriented polyester film, the uniformity index of a surface projection measured in the width direction is regulated to 0.35-2.0 and a projection interval is regulated to 1-20mum. Therefore, high speed crystallization polyester composition is used in which crystallization speed is rapid and crystallization index is 10-60 deg.C. The surface temperature of at least one side of a melt extruded film containing such polyester as a main component is held for 0.5-20 seconds at least at the temperature above the temperature lower than the lowered crystallization temperature of polyester by 70 deg.C, and also at most below the lowered crystallization temperature. Then, an least one side of the melt extruded film is cooled at glass transition temperature or below. Thereafter an unstretched film is biaxially stretched. Thereby a desired surface projection is formed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biaxially oriented polyester film.

[0002]

2. Description of the Related Art As a biaxially oriented polyester film, a film having surface projections formed by a particle addition method (for example, JP-A-59-171623) or polyester crystals (for example, JP-A-5-131600).
It has been known.

[0003]

In recent years, the processing speed of films has become faster and faster in various applications of films, for example, magnetic layer coating / calendering processes for magnetic media applications and printing processes for packaging applications. There is. Conventionally, as a method of lowering the friction coefficient of the film surface, particles are usually added to the film to form surface protrusions, but the problem of powder being generated at high speed due to falling off of the particles, and polyester With the protrusions formed by the crystals, the problem that the effect of reducing the friction coefficient during high-speed running is insufficient is becoming apparent.

The present invention solves the above problems, no powder is generated even when traveling at high speed (hereinafter referred to as "good powder generation"), and high speed running friction is small (hereinafter referred to as "good friction coefficient").
The challenge is to provide a film.

[0005]

A biaxially oriented polyester film having a surface protrusion uniformity index measured in the width direction of 0.35 to 2.0 and a protrusion interval of 1 to 20 μm on at least one surface of the film. It was done.

The polyester constituting the present invention is not particularly limited, but ethylene terephthalate, ethylene 2,6-naphthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate When at least one structural unit selected from the group consisting of ethylene terephthalate is used as a main constituent, ethylene terephthalate is used as a repeating unit.
In the case of polyester containing 5 mol% or more, powder generation and friction coefficient are further improved, which is desirable. Also, 15
Copolymer components of less than mol%, such as polyethylene glycol, diethylene glycol, cyclohexanedimethanol, isophthalic acid, dimer acid, etc., especially 0.00
Coexistence of 1 mol% or more of polyethylene glycol is desirable because it has a further effect on powder generation and friction coefficient.

In order to obtain the surface morphology of the film of the present invention, it is effective to use a high-speed crystallization polyester composition having a high crystallization rate, but its crystallization index is 10 to 60 ° C.
Preferably 15-55 ° C, more preferably 20-50
When the temperature is in the range of ° C, powder generation is further improved, which is particularly desirable. Also, the crystallization temperature Tc of the polyester composition
When c is 90 to 150 ° C., powder generation is further improved, which is desirable.

Further, the polyester used in the present invention can be rapidly treated by the presence of magnesium acetate, a phenyl ring-containing phosphorus compound, or antimony oxide (or germanium oxide) as a catalyst / heat stabilizer during transesterification or polymerization. It is desirable because a crystallized polyester is easily obtained and the surface morphology of the present invention is easily obtained.

The film of the present invention contains the above-mentioned composition as a main component, but may be blended with other polymers within a range not impairing the object of the present invention, and may also contain an antioxidant, a heat stabilizer, a lubricant, Additives such as an ultraviolet absorber and an antistatic agent may be added.

The film of the present invention is a film obtained by biaxially orienting the above composition, but a uniaxial or non-orientated film is not preferred because it causes powder generation and a poor friction coefficient.
The degree of this orientation is not particularly limited, but when the Young's modulus, which is a measure of the degree of molecular orientation of the polymer, is 400 kg / mm ² or more in both the longitudinal direction and the width direction, the powder generation and the friction coefficient are further improved. So highly desirable. Also,
The upper limit of the Young's modulus, which is a measure of the degree of molecular orientation, is not particularly limited, but normally about 1500 kg / mm ² is a manufacturing limit. Further, the film of the present invention has a Young's modulus in the transverse direction of the film larger than that in the longitudinal direction, preferably 50 to 1
000kg / mm ^{2 By} increasing, powder generation,
It is desirable because the coefficient of friction can be further improved.

The film of the present invention may be a monolayer film of the above polyester, but in order to more stably enable biaxial stretching, the above high speed crystallized polyester composition is
A polyester composition having a larger crystallization index, preferably a crystallization index of 10 ° C. or more, is used as a base layer portion.
On at least one side thereof, a thickness of 0.03-3 μm, in particular,
A film having a laminated structure in the range of 0.05 to 2 μm, more preferably 0.1 to 1.5 μm is desirable.

The film of the present invention has a surface protrusion uniformity index of 0.3 measured in the width direction on at least one surface thereof.
It should be in the range of 5 to 2.0, preferably 0.4 to 1.8, and more preferably 0.45 to 1.7.
If the surface protrusion uniformity index is larger than the above range or smaller than the above range, both powder generation and the friction coefficient become poor, which is not preferable.

Further, the protrusion interval measured in the width direction is 1 to
It should be in the range of 20 μm, preferably 1 to 15 μm, and more preferably 1 to 10 μm. If the interval between the protrusions is larger than the above range, powder is generated and the friction coefficient becomes poor, which is not preferable. The manufacturing lower limit of the protrusion spacing is about 1 μm.

The film of the present invention may or may not contain particles, but when the content of particles in the film is 0.5% by weight or less, especially 0.0
When the amount is 1 to 0.3% by weight, the friction coefficient is further improved, which is desirable. When the average diameter of the particles is 0.01 to 2 μm, powder generation and the coefficient of friction are further improved, which is desirable.

The film of the present invention has powder generation and friction when the order of molecules existing near the surface protrusion is higher than the order of molecules existing near the protrusion on at least one surface of the film. It is desirable because the coefficient becomes even better. Although the details are not always clear, it is considered that the crystallinity of the part near the surface protrusion becomes higher than that of the other part due to the growth of spherulites, and therefore the powder generation and the friction coefficient are improved. . The degree of ordering of molecules existing near the surface protrusions and the degree of ordering of molecules existing outside the protrusions are compared, for example, by comparing the diffraction images by low-temperature electron diffraction at each position of the film cross section. It can be determined by doing.

Further, the film of the present invention is transparent when the average surface roughness of one surface of the film is larger than that of the other surface by 2 to 50 nm, particularly 5 to 40 nm, while maintaining the powder generation and the friction coefficient. It is desirable because it is easy to obtain an excellent film.

Next, a method for producing the film of the present invention will be described. First, it is effective to allow lithium acetate, magnesium acetate, potassium acetate, phosphorous acid, phosphonic acid, phosphinic acid or their derivatives, antimony oxide, or germanium oxide to be present during transesterification or polymerization. A particularly desirable combination is magnesium acetate and phosphonic acid (or a derivative thereof) and antimony oxide, and desirable examples of the phosphonic acid (or a derivative thereof) include phenylphosphonic acid, dimethylphenylphosphonate and the like.

This polyester is extruded into a sheet form from a slit-shaped die by a known melt extruder and cooled by a casting roll to prepare an unstretched film.

In the present invention, in the process of cooling the melt-extruded film containing polyester as the main component on the surface of the cooling roll, the temperature (Tm + 1) higher than the glass transition temperature Tg of polyester A and 100 ° C. higher than the melting temperature Tm is used.
It is preferable that the desired surface projections are formed by heat-treating the unstretched film from the opposite surface in contact with the cooling roll at a temperature of not more than 00 ° C.) and thereafter biaxially stretching the unstretched film. The temperature is more preferably 20 ° C. higher than Tg (Tg + 20 ° C.) or higher and 80 ° C. higher than Tm (Tm + 80 ° C.) or lower, further preferably 40 ° C. higher than Tg (Tg + 40 ° C.) or higher and Tm or lower. As a method of heat-treating the unstretched film from the surface opposite to the one in contact with the cooling roll, hot air or radiant heat from an infrared heater can be used, but it is not limited to this method.

The surface roughness of the cooling roll surface is 0.2.
When it is S or more and 10 S or less, the crystallinity of the film surface before stretching can be increased to a desired crystallinity, which is preferable. More preferably, the surface roughness of the surface of the cooling roll is 0.3 S or more and 8 S or less. When the surface roughness of the roll surface is less than 0.2 S, the unstretched film adheres to the cooling roll, which is not preferable. Further, if the surface roughness exceeds 10 S, desired surface protrusions may not be formed, or the film may slip on the cooling roll, which is not preferable.

In the present invention, when heat-treating an unstretched film that has been cooled and solidified, the temperature (Tcc-20 ° C.) of at least one surface (or surface layer) thereof is 20 ° C. lower than the cold crystallization temperature Tcc of polyester A. Above, the temperature (Tmc +
40 ° C.) or less so as to be kept for 0.5 to 100 seconds, and then biaxially stretched at a temperature of Tg or more and a temperature 20 ° C. higher than Tcc (Tcc + 20 ° C.) or less, whereby a desired surface protrusion is obtained. It is preferable because it is formed. More preferably, it is 0.5 to 50 at Tcc or more and Tmc or less.
The heat treatment is such that it is maintained for 0.5 to 20 seconds at Tcc or more and more preferably Tcc or less.

In the present invention, the unstretched film is finely stretched in the uniaxial direction to give birefringence of 0.5 × 10 ⁻³ to 50 × 10 ^−3.
Then, the surface (or surface layer) temperature of at least one side of the slightly stretched film is at least 20 ° C. lower than the cold crystallization temperature Tcc of polyester A (Tcc−20 ° C.), and 40 ° C. below the lowered crystallization temperature Tmc. High temperature (Tmc +
40 ° C.) or less so as to be maintained for 0.3 to 50 seconds, and then biaxially stretched at a temperature of Tg or more and 20 ° C. higher than Tcc (Tcc + 20 ° C.) or less,
It is preferable because a desired surface protrusion is formed. More preferably, Tcc or more and Tmc or less, 0.5 to 20
Seconds, and more preferably at a temperature 10 ° C above Tcc (T
cc + 10 ° C.) or higher and a temperature 20 ° C. lower than Tmc (Tmc-20 ° C.) or lower, and is a heat treatment for 0.5 to 15 seconds.

The heat treatment method includes a method of heat treatment by winding on a heating roll, a method of hot air treatment from the opposite surface of the roll which is in contact with the roll, or a surface of the opposite surface which is in contact with the roll when wound on the roll. There is a method of heat treatment with an infrared heater, a method of heat treatment with an infrared heater between rolls, a method of heating with a stenter, etc., but the method is not particularly limited to these.

In the present invention, the temperature of at least one surface (or surface layer) of the melt-extruded film containing polyester as a main component is set to the temperature-lowering crystallization temperature Tm of polyester A.
When the temperature is 70 ° C. lower than Tc (Tmc-70 ° C.) or higher and the temperature-lowering crystallization temperature of the polyester A is Tmc or lower, 0.5 to
It is preferable to hold for 20 seconds, then cool to a glass transition temperature Tg or lower, and then biaxially stretch the unstretched film to form a desired surface protrusion.

As described above, the treatment method is a method in which a film having a high temperature immediately after extrusion is gradually cooled to crystallize it, or a film which has been once cooled and solidified is reheated to be crystallized, or There is a method of heat treatment in a state of being slightly stretched in the uniaxial direction, and one of these methods can be carried out in the film forming process of the film to obtain a target surface morphology. Two or more of the above may be used in combination in the film forming process of the film.

Next, in the case of obtaining the film of the present invention in a laminated constitution, pellets of the high-speed crystallized polyester A are dried and then fed to a known melt extruder 1, which has a crystallization index of 10 ° C. or more. The large polyester B is fed to the extruder 2, and the polyester A is laminated on at least one side of the polyester B using a manifold or a merging block having two or more layers, and two or more layers are formed from a slit-shaped die. The sheet is extruded and cooled on a casting roll to make an unstretched film. In this case, a method of stacking by using a merging block having a rectangular merging cross section is effective for stably obtaining the surface morphology of the present invention. This is extruded into a sheet from a slit-shaped die and cooled with a casting roll to prepare an unstretched film. The subsequent manufacturing method is the same as that described above.

The use of the film of the present invention is not particularly limited, but the use in which powder generation has a great influence on product performance, for example, for magnetic materials, for thermal transfer of ink ribbons, OH, etc.
It is ideal for graphics such as P and for packaging.

[0028]

[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) Surface protrusion uniformity index, protrusion interval Using a high precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory, average surface roughness Ra, maximum height Rt (peak to valley), center line maximum. The height Rp and the protrusion spacing Sm were measured.
The conditions are as follows, and the average value of 20 measurements was used as the value. The surface protrusion uniformity index was defined by the following formula from the measured maximum height Rt (peak to valley) and the centerline maximum height Rp.

・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measuring length: 1 mm ・ Cutoff value: 0.08 mm ・ Protrusion uniformity index: (Rt-Rp) / Rp Incidentally, Ra, Sm, Rt , Rp, etc. are defined, for example, in Jiro Nara “Measurement / Evaluation Method of Surface Roughness” (General Technology Center, 1983). (2) Particle content A solvent in which the polyester is dissolved and the particles are not dissolved is selected, and the particles are centrifuged from the polyester to determine the weight percentage of the particles.

(3) Thickness of Laminated Portion Using a secondary ion mass spectrometer (SIMS), the element and the polyester derived from the highest concentration of particles in the film in the depth range of 3000 nm from the surface layer The concentration ratio (M ⁺ / C ⁺ ) of the carbon element is used as the particle concentration, and analysis is performed in the thickness direction from the surface to a depth of 3000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration once reaching the maximum value starts to decrease again. Based on this concentration distribution curve, the depth at which the surface layer particle concentration becomes 1/2 of the maximum value of (the depth is deeper than the maximum value) was determined, and this was taken as the laminated thickness. The conditions are as follows.

(1) Measuring device Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany (2) Measuring condition Primary ion species: O ₂ ⁺ primary ion accelerating voltage: 12 KV Primary ion current: 200 nA Raster area: 400 μm □ Analysis area: Gate 30% Measurement vacuum degree: 5.0 × 10 ^-9 Torr E-GUN: 0.5 KV-3.0 A In the case of crosslinked polymer particles, SIMS can be used for measurement. Since it is difficult, the depth profile similar to the above may be measured by XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy) or the like while etching from the surface to obtain the laminated thickness.

The most general method for obtaining the laminated thickness is by observing with an electron microscope such as a transmission electron microscope.
This is a method of recognizing the interface from the change state of the particle concentration and the difference in contrast by observing the cross section of the film by (transmission) to obtain the laminated thickness. Alternatively, the layer thickness may be determined by recognizing the interface by XPS (X-ray photoelectron spectroscopy) or infrared spectroscopy while etching from the surface, or after peeling the layered portion,
It is also possible to determine the stack thickness using a thin film step measuring machine.

(4) Average particle size The cross section of the film is measured with a transmission electron microscope to 3000-1.
Observe at 00000 magnification. The thickness of the slice was set to about 100 nm, the measurement was performed at different places, the number of particles was 5000, and the volume average diameter d was obtained from the following formula from the particle diameter and its volume fraction. Here, di is the particle size and NVi is the logarithmic integration rate.

D = Σdi · NVi If the image is difficult to observe with a transmission electron microscope like organic particles, staining may be appropriately performed, or a field emission scanning electron microscope may be used instead of the transmission electron microscope. There is also a method of using. Furthermore, instead of observing the cross section, a method of removing the polyester from the surface by plasma etching and observing the exposed particles may be used.

(5) Young's modulus According to the method specified in JIS-Z-1702,
25 using an Instron type tensile tester
It was measured at 65 ° C. and 65% RH.

(6) Low Temperature Electron Diffraction The cross section of the ultrathin section was observed with a transmission electron microscope, and the black lizard portion under the protrusion was observed by JEM2000F manufactured by JEOL.
Using X-2, acceleration voltage 100-200kV, temperature -1
A low temperature electron diffraction image was observed at 10 ° C.

(7) Powder Generation The film was slit to 10 mm, and a contact length of 10000 m was run on a metal guide post (SUS304, surface finish 2S, diameter 6 mm) at a wrapping angle of 180 degrees at a speed of 1500 m / min. Then, the powder adhering to the guide post is observed. The traveling tension entering the guide post was 90 grams, and the atmosphere was 25 ° C. and 60% RH. The state of the adhered powder was ranked in the following 5 levels, and 4 to 5 points were evaluated as good, 3 points as unsatisfactory, and 1 to 2 as defective. This corresponds to the quality of powder generation in the actual film processing process.

5: No powder adhered at all 4: Slight powder adhered (1/10 of the tape contact area)
Less than 3: 3: Powder adheres (1/4 to 1/10 of the same) 2: Powder considerably adheres (1/2 to 1/4 of the same) 1: A large amount of powder adheres (1/2 or more of the same) (8) Friction coefficient during high-speed running In the evaluation of (7) above, the tension of the guide post output during running was measured, and the friction coefficient was determined by the Euler equation. A friction coefficient of 0.3 or less was judged to be good, and a friction coefficient of more than 0.3 was judged to be bad. This reflects practical workability.

(9) Crystallization temperature, melting temperature, falling temperature Crystallization temperature, crystallization index, measured using a Perkin Elmer DSC (differential scanning calorimeter) type II. The measurement conditions of DSC are as follows. That is, 10 mg of the sample was set in the DSC device, and 3
After melting for 5 minutes at a temperature of 00 ° C., it is quenched in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected. Further, the temperature is further raised, and the crystallization exothermic peak temperature from the glass state is the crystallization temperature Tcc, the endothermic peak temperature due to the crystal melting is the melting temperature Tm, and the crystallization exothermic peak temperature at the time of the temperature lowering is also the crystallization. Temperature Tm
c. The difference between Tcc and Tg (Tcc-Tg) is defined as the crystallization index.

(10) Birefringence: The refractive index nMD in the longitudinal direction and the refractive index nTD in the width direction of the uniaxially oriented film were measured using an Abbe refractometer, and defined by the difference between these values, that is, | nMD-nTD | . The light source was sodium D line (wavelength: 589 nm), and the mount solution was methylene iodide at 25 ° C. and 65% RH.

(11) Film temperature A radiation thermometer, a contact type surface thermometer, or a thermolabel was attached to the film for measurement. The temperature of the film in the molten state was measured by inserting a thermocouple into the radiation thermometer or the film in the molten state.

[0043]

EXAMPLES The present invention will be described based on examples.

Examples 1-5, Comparative Examples 1-2 Transesterification catalyst 0.1 wt% magnesium acetate, polymerization catalyst antimony trioxide 0.03 wt%, heat stabilizer dimethyl phenyl phosphonate 0.35 wt% As the above, polyethylene terephthalate (PET) having a crystallization index of 45 ° C. and polyethylene-2,6 naphthalate (PEN) having a crystallization index of 55 ° C. were manufactured substantially as no particles.
The intrinsic viscosity was 0.65. Also, particles obtained by adding particles to these polymers with a biaxial kneader were prepared. These chips were dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours, then melted at 290 ° C. in an extruder, extruded into a sheet, and cooled on one side on a casting roll with a surface temperature of 20 ° C., while hot air was blown on one side. It was sprayed and heated at different temperatures and times.

This film was stretched 4.0 times in two steps in the longitudinal direction at a temperature of 80 ° C. This stretching was performed with the difference in peripheral speed between the two sets of rolls. This uniaxially stretched film was stretched 4.5 times in the width direction at 100 ° C. at a stretching speed of 5000% / min using a stenter, and heat-treated at 200 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film having a thickness of 12 μm. A polyester film was obtained.

The parameters of the invention for these films,
The performance is as shown in Table 1, and it can be seen that when the parameters of the present invention are within the range, the film is excellent in powder generation and friction coefficient, but when it is not, the purpose cannot be achieved.

Examples 6 to 11, Comparative Examples 3 to 4 Transesterification catalyst was 0.1% by weight of magnesium acetate, polymerization catalyst was 0.03% by weight of antimony trioxide, and heat stabilizer was 0.35% by weight of dimethylphenylphosphonate. As the above, polyethylene terephthalate (PET) having a crystallization index of 45 ° C. and polyethylene-2,6 naphthalate (PEN) having a crystallization index of 65 ° C. were manufactured substantially as no particles.
The intrinsic viscosity was 0.65. Further, by a known method, PET having an intrinsic viscosity of 0.65 and a crystallization index of 75 ° C. and a crystallization index of 1
PEN was prepared at 10 ° C., and these chips were appropriately mixed to adjust the crystallization index. These polymers were used for the laminated portion (polyester A) and the base layer portion (polyester B), and dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours, respectively.
Each of them was fed to two extruders and melted at 290 ° C., and these polymers were combined and laminated in a rectangular confluent block (feed block) for 2 or 3 layers, and then sheet-shaped using an electrostatically applied casting method. Then, it was extruded and cooled and solidified on a casting roll having a surface temperature of 20 ° C. to prepare an unstretched film having a two- to three-layer structure.

These unstretched films were placed on a non-adhesive silicone roll at a temperature of 30 ° C. while cooling one side,
Hot air was blown on the non-contact surface of the roll to change the temperature and the time of heating. Further, a non-adhesive silicone roll was heat-treated while changing the surface temperature and treatment time, and a non-adhesive silicone roll was also heat-treated with hot air on a casting roll in the same manner as in Example 1 without using the silicone roll. This film was heated at a temperature of 80 ° C. to 4.0 in two steps in the longitudinal direction.
It was stretched twice. This stretching was performed with the difference in peripheral speed between the two sets of rolls. This uniaxially stretched film was stretched 3 to 6 times in the width direction at 100 ° C. at a stretching speed of 5000% / min using a stenter,
Heat treatment was performed at 200 ° C. for 5 seconds under a constant length to obtain a biaxially oriented polyester film having a thickness of 9 μm.

The parameters of the invention of these films,
The performance is as shown in Tables 2 and 3, and it is understood that when the parameter of the present invention is within the range, the film is excellent in powder generation, but when it is not, the purpose cannot be achieved.

[0050]

[Table 1]

[Table 2]

[Table 3]

[0051]

INDUSTRIAL APPLICABILITY According to the present invention, the biaxially oriented polyester film has a surface morphology which cannot be achieved by a usual method, so that the biaxially oriented polyester film is excellent in powder generation and friction coefficient at high speed running. The film was completed.

Claims (6)

[Claims] 1. A surface protrusion uniformity index measured in the width direction of at least one surface of the film is 0.35 to 2.
0, a biaxially oriented polyester film having a protrusion interval of 1 to 20 μm. 2. The biaxially oriented polyester film according to claim 1, wherein the content of particles in the film is 0.5% by weight or less. 3. The order of molecules existing in a portion near the surface protrusion is higher than that of a molecule existing in a portion other than the protrusion on at least one surface of the film. The biaxially oriented polyester film described. 4. The biaxially oriented polyester film according to claim 1, wherein the average surface roughness Ra of one surface of the film is 2 to 50 nm larger than that of the other surface. 5. A polyester containing 85 mol% or more of ethylene terephthalate in a repeating unit.
The biaxially oriented polyester film according to item 4. 6. The polyester film according to claim 1, wherein the Young's modulus in the transverse direction of the film is 50 to 1000 kg / mm ² larger than the Young's modulus in the longitudinal direction.