JPH11170358A - Biaxially oriented polyester film and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive to uniformize the widthwise physical properties without lowering the lengthwise Young's modulus of a film by a method wherein the lengthwise Young's modulus of the film is ensured to be more than a specified value and the widthwise difference among the lengthwise thermal shrinkage factor is set to be a specified value or less. SOLUTION: A lengthwise Young's modulus at the manufacturing of a biaxially oriented polyester film through the lengthwise and the crosswise stretchings of an unoriented polyester film is set to be 600 kg/mm<2> or more. The widthwise difference among the lengthwise thermal shrinkage factor at the predetermined temperature is set to be 0.2%/m or less. In this case, when the lengthwise Young's modulus is set to be 700 kg/mm<2> or more and the lengthwise thermal shrinkage factor over the whole width of the film is set to be about 1.5% or less, more favorable results can be obtained. As a means for lowering the crosswise stretching stress for obtaining the biaxially oriented polyester, a higher crosswise stretching temperature method, a lower crosswise stretching rate method, a lower pre-heating temperature method and the like are put into consideration. However, as a method for lowering a stretching stress without exerting bad influence on the physical properties of the film, a higher crosswise stretching temperature method is the best.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film having uniform physical properties in the film width direction and high longitudinal strength and a method for producing the same.

[0002]

2. Description of the Related Art A biaxially oriented polyester film having a high strength in the longitudinal direction is usually a film having a high heat shrinkage (heat yield) in the longitudinal direction, because the film is stretched in the longitudinal direction at a high draw ratio. For this reason, the film shrinks in the vertical direction in the horizontal stretching zone and heat fixing zone compared to the type in which the strength of the biaxial orientation is balanced (balance type) and the horizontal-stretched film in which the horizontal strength is greater than the vertical direction. A phenomenon (hereinafter, sometimes referred to as bowing) in which the vertical length of the center portion in the horizontal direction (width direction) differs from that of the edge portion in the vertical direction (hereinafter sometimes referred to as bowing) is likely to occur. Due to this bowing, the physical properties in the width direction become non-uniform, and the heat collection and the mechanical characteristics in the center portion and the edge portion in the width direction are greatly different, causing various adverse effects.

As a specific example of the adverse effect, for example, in the case of a magnetic recording medium, film properties are different depending on the position of the base film in the width direction of the raw film.
The skew caused by touching the magnetic head and heat collection is different, and when coating the magnetic paint through the drying process, it runs curvedly due to the difference in expansion and contraction in the film width direction, affecting the productivity. ing.

In order to make the physical properties uniform in the film width direction, it is effective to reduce bowing. As the method, JP-A-57-57629 and JP-A-5-57629
Japanese Patent Application Laid-Open No. 8-24418 proposes a method of performing fine stretching in a heat setting zone. However, according to the inventor's knowledge,
When this method is applied to the verticalizing type,
The heat yield in the vertical and horizontal directions increases, which is particularly bad for magnetic recording applications.

In Japanese Patent Application Laid-Open No. 9-57845,
A method has been proposed in which fine stretching is performed a number of times in the transverse direction.
No mention is made of a film of the longitudinal tension type with g / mm ² or more.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to remedy the above-mentioned drawbacks and to provide a film having a Young's modulus in the machine direction of 600 k.
g / mm ² or more, and to provide a biaxially oriented polyester film in which the difference (distribution) in the width direction of the heat absorption in the longitudinal direction at 105 ° C. is uniformized to 0.2% / m or less over the entire width. It is in.

[0007]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, the present invention has been described.
By stretching at a magnification of 0 or more and reducing the stress in the transverse stretching, it is possible to achieve uniform physical properties in the width direction without lowering the Young's modulus in the longitudinal direction, and characteristics after commercialization. The present inventors have found that a biaxially oriented polyester film having no influence on film formation can be formed, and have reached the present invention.

That is, the present invention provides: The film has a Young's modulus in the machine direction of 600 kg / mm ² or more, and the difference in the heat shrinkage in the machine direction in the width direction is 0.
1. a biaxially oriented polyester film characterized by being 2% / m or less, and 2. When the unstretched polyester film is stretched in the machine direction and then stretched in the transverse direction to produce a biaxially oriented polyester film, it is stretched in the machine direction so that the Young's modulus in the machine direction is 600 kg / mm ² or more. 5 to 5.0 kg
The film is stretched in the transverse direction with a stress of / mm ² , the longitudinal Young's modulus is 600 kg / mm ² or more, and the difference in the longitudinal heat shrinkage at 105 ° C. in the width direction is 0.2% / m or less. This is a method for producing a biaxially oriented polyester film, characterized in that the film is a biaxially oriented film.

[0009] The biaxially oriented polyester film in the present invention is a vertical warp type having high strength in the longitudinal direction.
In addition, the film has a uniform physical property distribution in the width direction.

The biaxially oriented polyester film has a Young's modulus in the longitudinal direction of at least 600 kg / mm ² , preferably at least 700 kg / mm ² . In order to obtain this Young's modulus, the stretching ratio in the machine direction is set to 4.0.
It is preferably at least twice, and more preferably at least 4.3 times.
At this time, the stretching method may be one-stage stretching or two or more stages of longitudinal multi-stage stretching. The longitudinal strength of this film is
13. F-5 value of 14.0 kg / mm ² or more;
It is preferably at least 5 kg / mm ² .

In the biaxially oriented polyester film, the difference in the heat shrinkage in the longitudinal direction at 105 ° C. in the width direction is 0.2% / m or less. And this vertical heat yield is preferably 3% or less over the entire width, and more preferably 1.5% or less. It is conceivable to increase the heat setting temperature in order to reduce the heat yield. However, if the heat setting temperature is increased, the heat yield in the stenter increases and the bowing increases, which is not preferable.

[0012] The biaxially oriented polyester film has a thickness of 1000 g / m2 at a temperature of 100 ° C.
of the elongation of the film in the machine direction when a load of m ² is applied,
It is preferable that the difference in the width direction is 0.1% / m or less.

In order to obtain such a biaxially oriented polyester film, it is necessary to set the clip stress in the transverse stretching (lateral stretching) to 3.5 to 5.0 kg / mm ² . Means for reducing the transverse stretching stress include a method of increasing the transverse stretching temperature, a method of decreasing the transverse stretching ratio, a method of decreasing the preheating temperature, and a method of decreasing the birefringence after uniaxial stretching. As a method of lowering the stretching stress without exerting the effect, a method of increasing the transverse stretching temperature is more preferable. However, the transverse stretching temperature depends on the longitudinal stretching (longitudinal stretching) magnification, but if it is excessively increased, the thickness unevenness becomes extremely poor, and it takes a long time to adjust the thickness unevenness, lowering the productivity and adjusting the die adjusting bolt. Since it is difficult to adjust the interval, periodic unevenness occurs at the pitch.
It is preferable to adjust the longitudinal stretching ratio and the transverse stretching ratio so that the transverse stretching stress has an appropriate value so as not to increase too much. And
It is preferable that the dependency of the Young's modulus in the longitudinal direction on the transverse stretching stress is 10 kg / mm ² or less per 1.0 kg / mm ^{2 of the} transverse stretching stress.

The polyester in the present invention is a linear polyester comprising a dicarboxylic acid component and a glycol component.

Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, and the like. Of these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferred. As the glycol component, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol,
Examples thereof include diethylene glycol and neopentyl glycol. Among these, ethylene glycol,
1,4-butanediol is preferred, and ethylene glycol is particularly preferred.

Among such polyesters, polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate or polybutylene terephthalate is
In particular, polyethylene terephthalate, polyethylene-2,
6-Naphthalenedicarboxylate is preferred because it has excellent mechanical properties and thermal properties.

The polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate or polybutylene terephthalate may be a polyester obtained by copolymerizing a dicarboxylic acid component or a glycol component at a ratio of, for example, 10 mol% or less. It may be a polyester obtained by copolymerizing a small amount of a polyvalent compound having a functionality or higher in a range where the polyester becomes substantially linear (for example, 5 mol% or less).

When the copolymer component is polyethylene terephthalate, the acid component is isophthalic acid,
Examples thereof include 6-naphthalenedicarboxylic acid and 4,4′-diphenyldicarboxylic acid, and examples of the glycol component include propylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, and neopentyl glycol.

Examples of the copolymer components of polyethylene-2,6-naphthalenedicarboxylate include terephthalic acid, isophthalic acid, and 4,4'-diphenyldicarboxylic acid as acid components, and 1,4 and 4'-diphenyldicarboxylic acid as glycol components. -Butanediol, 1,6-hexanediol,
Propylene glycol, 1,5-pentanediol,
Examples thereof include 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol and the like.

Examples of the copolymer component of polybutylene terephthalate include isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyldicarboxylic acid as an acid component, and ethylene glycol, 1, and Examples thereof include 6-hexanediol, propylene glycol, 1,5-pentanediol, 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol and the like.

As the copolymerization component of polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate and polybutylene terephthalate, in addition to the above components, for example, hexahydroterephthalic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, etc. And a glycol component such as 1,3-propanediol, polyethylene glycol, polytetramethylene glycol, dipropylene glycol, triethylene glycol, and an alkylene oxide adduct of bisphenol A. As the above polyester, a homopolymer or a copolymer can be used, and a blend of these polyesters can also be used.

The above polyester has a melting point (Tm) of 15 or more.
The volume resistance in the molten state at a high temperature is 50H
0.5 × 10 ⁹ Ω · cm under the measurement condition of AC voltage of z
The following is preferred. Polyester having such a volume resistivity can be obtained, for example, by incorporating a compound having an alkali metal salt, or by copolymerizing a quaternary phosphonium salt of sulfonic acid. Adhesion can be obtained.

Further, in order to improve the winding property of the polyester film and to provide the surface properties required for each application, organic or inorganic fine particles having an average particle size of about 0.001 to 5.0 μm are used. For example, it is preferable to mix and contain at a rate of 0.01 to 2.0 wt%. Such fine particles include, for example, dry silica, wet silica, zeolite,
Inorganic fine particles such as calcium carbonate, calcium phosphate, kaolin, kaolinite, clay, talc, titanium oxide, alumina, zirconia, aluminum hydroxide, calcium oxide, graphite, carbon black, zinc oxide, silicon carbide, silver oxide, and crosslinked acrylic resin particles And organic particles such as crosslinked polystyrene resin particles, melamine resin particles, and crosslinked silicone resin particles.

If necessary, a lubricant, an antioxidant,
Antistatic agents, colorants, pigments, tendency brighteners, plasticizers, ultraviolet absorbers, other resins, and the like can be added.

In the production of the biaxially oriented polyester film according to the present invention, first, a molten polyester is extruded onto a rotary cooling drum, brought into close contact with the rotary cooling drum, and cooled to obtain an unstretched film. At that time, an electrostatic charge is applied in a non-contact manner to the air side (opposite to the cooling drum) surface of the extruded molten film near the rotating cooling drum in the vicinity thereof. For example, the polyester is supplied to an extruder, melted at a temperature from the melting point of the polymer to 350 ° C., the molten polymer is discharged from a die, and an electrostatic charge is further applied to the discharge film so as to adhere to the cooling drum. An unstretched film can be manufactured by cooling and solidifying. In addition, it is preferable to dry a polyester raw material before supplying to an extruder. The unstretched film is further stretched in the machine direction, and then stretched in the transverse direction to form a biaxially stretched film. In order to obtain such a biaxially stretched film, a temperature at which the unstretched film can be stretched (for example, Tg (glass transition temperature) of polyester −10 ° C.)
(Tg + 80 ° C. or less) and stretched in the biaxial direction. Further, the stretching ratio is preferably set at 4 times or more and 6 times or less in the longitudinal direction, and more preferably 4.3 times or more and 5 times or less. The transverse stretching is preferably performed at a magnification of 3.0 to 4.0 times in the transverse direction of the film and stretching at a temperature equal to or higher than the longitudinal stretching temperature. The area magnification is preferably 8 to 24 times. Biaxially stretched film, for example, stretch the unstretched film in the longitudinal direction, and then stretch in the transverse direction,
It can be produced by a so-called longitudinal-horizontal stretching method, or a longitudinal multi-stage stretching method in which the machine is stretched in several times in the machine direction and then stretched in the machine direction. The biaxially stretched film may be further stretched in the longitudinal direction or the uniaxial direction in the transverse direction, or in the biaxial direction in the longitudinal direction and the transverse direction to form a biaxially stretched film. The biaxially stretched film further has a temperature lower than the melting point (Tm) of the polyester, preferably Tm to (Tm).
(m-220) ° C. and then cooled to room temperature. The biaxially stretched film thus obtained is provided on its surface with a surface activation treatment (for example, a plasma treatment, an amine treatment, Corona treatment, etc.).

The polyester film of the present invention preferably has a thickness of 0.5 to 20 μm, depending on the use. This polyester film has as few surface defects as possible such as a capacitor film (for example, a film having a thickness of 3 μm or less), a film for a printer ribbon (for example, a film having a thickness of about 5 μm), a heat-sensitive stencil printing, a magnetic recording, particularly a base film for QIC. Is more useful for preferred applications. In particular, according to the knowledge of the present inventor, in a magnetic recording medium, the thermal expansion and contraction property (TMA) under constant load becomes important,
It is important that the stretching property in the width direction under heating is uniform, but the polyester film of the present invention satisfies these properties, and the film is not suitable for the manufacturing process such as running curve in the drying process after magnetic coating. It can prevent troubles in the heating step and is useful as a base film for magnetic recording, especially for QIC.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value was measured by the following method.

1. Lateral stretching stress A strain gauge is attached to the clip of the tenter, the tension is analyzed by wireless communication, and the transverse stretching stress is measured using the uniaxial thickness.

2. Young's Modulus From a biaxially oriented polyester film, five pieces of film having a width of 10 mm and a length of 100 mm were cut out from the biaxially oriented polyester film as long sides, and these films were cut at a rate of 10 mm / min using a tensile tester manufactured by Toyo Seiki. The Young's modulus is calculated from the slope of the rise of the tensile / stress-strain curve.

3. Heat shrinkage Specimens having a width of 10 mm and a length of 300 mm or more are cut out in the longitudinal direction and the width direction, and a rating of 300 mm is given in the longitudinal direction of these test pieces.
It is put in a hot air circulation oven at 05 ° C., taken out after 30 minutes, and left to cool for 10 minutes. The distance between the scores of this test piece is measured by n = 5, and the average value of (the score interval before the heat treatment-the score interval after the heat treatment) × 100 / the score interval [%] before the heat treatment is defined as the heat shrinkage.

4. Thickness unevenness A piece of film of 2 m is cut out from the biaxially oriented polyester film in the longitudinal direction and measured with an electronic micrometer manufactured by Anritsu. The percentage obtained by dividing the difference between the maximum thickness and the minimum thickness by the average thickness is defined as the thickness unevenness.

5. TMA elongation and difference in width direction From biaxially oriented polyester film, 10m in longitudinal direction
m, a plurality of sample films of 5 mm in width direction are cut out in the width direction of the film, and these are TM-3000 manufactured by Vacuum Riko.
To give a tension of 1000 g / mm ² , and heated at 10 ° C./min in a nitrogen atmosphere to measure the longitudinal stretching property.
The elongation at the temperature of 0 ° C. is divided by the sample length to obtain the elongation. Then, the difference between the maximum value and the minimum value of the elongation in the width direction is determined.

6. Cutting In the production of biaxially oriented polyester films in Examples and Comparative Examples, the presence or absence of film cutting is evaluated according to the following evaluation criteria. ○: No cutting for 10 hours △: Cutting once every 10 hours ×: Cutting twice or more every 10 hours

Example 1 Polyethylene terephthalate having an intrinsic viscosity of 0.60 (Tm = 2) was prepared by mixing silica particles having an average particle diameter of 0.6 μm with polyester in an amount of 0.05 wt% with respect to polyester.
56 ° C., Tg = 69 ° C.)
After drying at 0 ° C. for 3 hours, the mixture was fed to an extruder, melt-extruded at 280 ° C., and cooled on a metal roll at 30 ° C. to obtain an unstretched film.

Next, this unstretched multilayer film was heated to 80 ° C. by heating with an infrared heater, stretched 4.5 times in the longitudinal direction (longitudinal direction), and immediately cooled to 20 ° C. Subsequently, the film was stretched 3.7 times at 95 ° C. using a tenter transverse stretching machine in the horizontal direction, heat-fixed at 220 ° C., wound up after 2% toe-in in the heat-fixing zone, and wound up.

The obtained biaxially oriented polyethylene terephthalate film has a Young's modulus of 730 kg / mm ² ,
The heat shrinkage in the vertical direction at 5 ° C. is 1.2%, the horizontal heat recovery is almost 0%, and the uniformity of the vertical heat recovery in the width direction is 0.2% / max.
m, the maximum difference in elongation at 100 ° C. by TMA is 0.0
At 8% / m, all the characteristics were good. The transverse stretching stress at this time was 0.25 kg / mm ² .

When this polyethylene terephthalate film was used for a long-play magnetic recording tape, the running in a drying oven in the tape manufacturing process was satisfactory without any bending.

[Examples 2 to 7] When the film was formed under the conditions of Example 1 except for the conditions shown in Table 1, good results were obtained. However, in Example 7, the stretching in the longitudinal direction was performed by multi-stage stretching, and 1
The second stage stretching is 2.5 times at 110 ° C. and the second stage stretching is 90 times.
Performed 1.9 times at ° C. Table 1 shows the results.

[Comparative Example 1] As shown in Table 2, the same procedure as in Example 1 was carried out except that the longitudinal stretching ratio was 4.7 times and the transverse stretching temperature was 90 ° C. The difference was as high as 0.3%, and the running of the inside of the drying oven was curved during the tape manufacturing process, and good results were not obtained. Table 2 shows the results.
Shown in

[Comparative Examples 2 to 5] When the film was formed under the conditions of Example 1 except for the conditions shown in Table 2, as shown in Table 2, the results were insufficient.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

According to the present invention, by appropriately setting the transverse stretching stress, it is possible to obtain a longitudinal-tensilized type film having uniform physical properties in the width direction and having appropriately small longitudinal and lateral heat yields. As a result, when used as a film for a thermal transfer printer ribbon or a film for magnetic recording, it is possible to obtain a film having good skew, good productivity and good quality for magnetic recording when running as a result of thermal expansion and contraction in the manufacturing process. Can be.

Claims (6)

[Claims] 1. The film has a Young's modulus in the machine direction of 600 kg.
/ Mm ² or more, and the difference in the heat shrinkage in the longitudinal direction in the width direction is 0.2% / m or less. 2. At a temperature of 100 ° C., 10
2. The biaxially oriented polyester film according to claim 1, wherein a difference in an elongation percentage in a width direction of the film in a width direction when a load of 00 g / mm ² is applied is 0.1% / m or less. 3. When the unstretched polyester film is stretched in the machine direction and then stretched in the transverse direction to produce a biaxially oriented polyester film, the Young's modulus in the machine direction is 600 kg /
stretched in a longitudinal direction so as to be mm ² or more, then 3.5
The film is stretched in the transverse direction with a stress of 5.0 kg / mm ² , has a Young's modulus in the machine direction of 600 kg / mm ² or more, and has a difference of 0.2% / m in the machine direction in the machine direction at 105 ° C. in the machine direction. A method for producing a biaxially oriented polyester film, comprising: 4. The difference in elongation percentage in the width direction of the biaxially oriented polyester film in the width direction when a load of 1000 g / mm ² is applied in the film length direction at a temperature of 100 ° C. is 0.1%. / M or less, the method for producing a biaxially oriented polyester film according to claim 3. 5. The method for producing a biaxially oriented polyester film according to claim 3, wherein the stretching ratio in the machine direction is 4 times or more. 6. The dependence of the Young's modulus in the transverse direction on the transverse stretching stress is 10 kg / mm ² per 1.0 kg / mm ^{2 of} transverse stretching stress.
method for producing a biaxially oriented polyester film according to claim 3, wherein at mm ² or less.