JPS60203422A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain the titled film whose wet expansion coefficient is low, in- plane direction difference of a thermal expansion coefficient is small and tearing strength is high, by constituting the film with a mixture of poly-1,4-cyclohexylene dimethylane terephthalate and polyethylene terephthalate. CONSTITUTION:The titled film is a biaxially oriented film consisting of a mixture of 95-70wt% poly-1,4-cyclohexylene dimethylane terephthalate whose more than 90mol% of an ingredient of glycol is 1,4-cyclohexane dimethanol and more than 80mol% of an ingredient of acid is terephthalic acid and 5-30wt% polyethylene terephthalate whose more than 90mol% of the of ingredient the glycol is ethylene glycol and more than 80mol% of the ingredient of the acid is the terephthalic acid, and this is the film whose inner face refractive index including a longitudinal and lateral directions is 1.580-1.640, density is 1.200-1.280(g/cm<2>), thermal expansion coefficient is 10-30(X10<-6>/ deg.C), wet expansion coefficient is 3-8(X10<-6>/%RH), in-plane direction difference of the thermal expansion coefficient is within 6X10<-6>/ deg.C and the in-plane direction difference of the wet expansion coefficient is within 4X10<-6>/%RH.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film containing 95 to 70% by weight of poly-1,4-cyclohexylene dimethylene terephthalate and 5 to 30% by weight of polyethylene terephthalate. The present invention relates to a biaxially oriented polyester film which is made of a mixed polyester of 50% and has a low humidity expansion coefficient, a small in-plane difference in thermal expansion coefficient, and high tear strength.

BACKGROUND ART Conventionally, a biaxially oriented film of polyethylene terephthalate I has been known as a general-purpose biaxially oriented low humidity expansion film. This film has well-balanced properties and is widely used as an excellent industrial material. However, it is still insufficient for applications where dimensional changes due to humidity are particularly important, such as flexible magnetic disks.

11. The objective of the present invention is to provide a film that has properties equivalent to those of polyethylene terephthalate mono-biaxially oriented films, but has improved long-term thermal deterioration resistance, humidity expansion coefficient, etc. An object of the present invention is to provide a film suitable as a base for a flexible magnetic disk, which has a small in-plane direction difference in index and has high tear strength.

Structure of the Invention As a result of intensive research into the physical properties of various polymers, the present inventor has discovered that
The inventors have discovered that a film obtained by mixing two kinds of polyesters having a specific composition and biaxially oriented to have specific in-plane properties can satisfy the above-mentioned objectives, and have thus arrived at the present invention.

Specifically, the present invention is directed to poly-1,4-cyclohexylene dimethylene terephthalate 95, in which 90 mol% or more of the glycol component is 1,4-cyclohexane dimetatool and 80 mol% or more of the acid component is terephthalic acid. ~70% by weight,
A biaxially oriented film made of a mixture of 5 to 30% by weight of polyethylene terephthalate, in which 90 mol% or more of the glycol component is ethylene glycol and 80 mol% or more of the acid component is terephthalic acid, including the longitudinal and lateral directions. In-plane refractive index 1.580-1,640. Density 1,210~
1.280 (!?/cm).

Temperature expansion coefficient 10 to 30 (X10-'/℃), humidity expansion rate 3 to 8 (X10''/%RH), in-plane direction difference in temperature expansion coefficient within 6 x 10+/℃, humidity expansion rate in-plane This is a biaxially oriented polyester film characterized in that the direction difference is within 4×10″G/%RH.

The 1,4-cyclohexane dimetatool in the present invention can be produced, for example, by catalytic reduction of dimethyl terephthalate or terephthalic acid, but it may be produced by any method.

The ratio of cis to trans isomers of 1.4-cyclohexane dimetatool is not particularly limited, but is preferably in the range of cis to trans isomers -4/6 to O/10.

Poly-1,4-cyclohexylene dimethylene terephthalate in the present invention can be produced by conventional polyester production methods. For example, by direct esterification of terephthalic acid and 1,4-cyclohexane dimetatool or with dimethyl terephthalate.
It can be produced by transesterification of 1.4-cyclohexane dimetatool.

The poly-1,4-cyclohexylene dimethylene terephthalate thus produced may be copolymerized with a third component in a small proportion.

The third component includes alkylene glycols such as ethylene glycol, ramethylene glycol, hexamethylene glycol, etc.; isophthalic acid, oxybenzoic acid, naphthalene dicarboxylic acid.

Examples include aromatic dibasic acids such as diphenyldicarboxylic acid; aliphatic dibasic acids such as adipic acid, sebacic acid, and ε-caprolactone. In addition, such poly-1,4
- In cyclohexylene dimethylene terephthalate,
For example, phosphoric acid and phosphorous acid.

and stabilizers such as esters thereof, titanium dioxide,
It may contain matting agents, lubricants, etc. such as particulate silica, kaolin, calcium carbonate, calcium phosphate, etc.

Furthermore, the polyethylene terephthalate in the present invention can be produced by conventional polyester production methods. For example, it can be produced by direct esterification of terephthalic acid and ethylene glycol or by transesterification of dimethyl terephthalate and ethylene glycol.

The polyethylene terephthalate thus produced may be copolymerized with a third component in a small proportion. As this third component, alkylene glycols such as tetramethylene glycol, hexamethylene glycol, etc.; 1,4-
Alicyclic glycols such as cyclohexane dimetatool;
Isophthalic acid.

Examples include aromatic dibasic MMs such as oxybenzoic acid, naphthalene dicarboxylic acid, and diphenyldicarboxylic acid; and aliphatic dibasic acids such as adipic acid, sebacic acid, and ε-caprolactone. Such polyethylene terephthalate also contains stabilizers such as phosphoric acid, phosphorous acid and their esters, titanium dioxide, finely divided silica,
Power A Lin.

Matting agents, lubricants, etc. such as calcium carbonate, calcium phosphate, etc. may also be included.

In the present invention, the mixing ratio of poly-1,4-cyclohexylene dimethylene terephthalate and polyethylene terephthalate is 95:5 to 70:30 (wt%)
, preferably 93 to 85:15 (wt%). If the proportion of polyethylene terephthalate is less than 5% by weight, problems arise such as the tear strength of the biaxially oriented film being low and, for example, easily tearing during film formation. Furthermore, if the proportion of polyethylene terephthalate 1 is greater than 30% by weight, the humidity expansion coefficient of the biaxially oriented film becomes large, which is not preferable.

The biaxially oriented film of the present invention comprises poly-1,4-cyclohexylene dimethylene ethylene terephthalate-1.95-705-7.
0 polyethylene terephtacy and 1-5 to 30% by weight, it can basically be produced by conventional methods for producing accumulated IC biaxially oriented polyester films. For example, it can be produced by extruding dry polyester through a die using a melt-extrusion machine, rapidly cooling it to obtain an unstretched film, and then sequentially or simultaneously biaxially stretching the unstretched film and heat-setting it. Furthermore, film forming conditions will be explained. It is appropriate to dry the polymer chips at 110° C. for about 3 hours, but the drying time is not limited thereto. Although an ordinary extruder may be used, it is particularly preferable to use measures to improve the extrusion precision, such as the use of a metering pump, pressure control, and the like. Since the melting temperature of the polymer changes depending on the polymer composition, it is preferable to select the melting temperature accordingly. For the above polymer compositions, a temperature range of 295-315°C is usually chosen.

The appropriate temperature of the casting drum is 10 to 60°C, but the lower the polyethylene terephthalate content, the more preferable it is to rapidly cool the drum, and in that case, a surface temperature of 20 to 40°C is appropriate. The stretching temperature is usually 80 to 14
The temperature is 0° C., and cutting at a temperature lower than this causes uneven stretching, while at a temperature higher than this, the stretching effect tends to be reduced.

More preferably, a temperature range of 100 to 120° C. is selected, whereby the above-mentioned physical property values can be easily obtained. The stretching ratio in the longitudinal direction is 3.0 to 5.0 times, preferably 3.3 to 4 times.
．． 3 times, 3.0 to 5.0 times laterally, preferably 3.5
Select ~4.5x.

If the stretching ratio is less than this range, the refractive index will be smaller than the above value, and if the stretching ratio exceeds this range, not only will the film be cut frequently during film production, which is undesirable, but even if the film is obtained, humidity will be low. The expansion rate is extremely high and good results cannot be obtained.

The stretching method may be a known method. For example, longitudinal stretching can be performed by heating between two rolls with different circumferential speeds, and horizontal stretching can be performed by gripping both ends of the film with clips and holding the film in a row of clips while heating. It is possible to stretch by increasing the row spacing. The obtained biaxially oriented film was heated at 130 to 220°C.
Preferably, the refractive index, density, temperature/humidity/expansion coefficient of the present invention can be obtained by heat setting at 160 to 200°C for 1 to 100 seconds.

Regarding the in-plane difference in temperature/humidity expansion coefficient, when a film is formed by a normal longitudinal and lateral stretching method, the area near the center in the width direction of the film is included in the scope of the present invention. However, the quantitative percentage included varies depending on the film forming conditions and polymer composition. Typically, 10 to 70% of the total width is within the scope of the present invention. On the other hand, in the portions near both ends of the film in the width direction, the in-plane difference in temperature-humidity expansion coefficient is large, and this generally falls outside the scope of the present invention. The reason for this is the bowing phenomenon that occurs during heat-setting in a tenter. However, by including polyethylene terephthalate, this bowing phenomenon can be reduced.
Portions near both ends of the film in the width direction can also be included within the scope of the present invention.

Since the optimum range changes depending on the polymer composition, it is necessary to select conditions appropriately. For example, 87 mol% of terephthalic acid and 13 mol% of isophthalic acid are used as acid components,
In the case of a polymer consisting of a mixture of 1 to 85% by weight of poly-1,4-cyclohexylene dimethylene lentil clay and 15% by weight of polyethylene terephthalate, the glycol component is 100% 1,4-cyclohexane dimetatool.
The heat setting conditions are preferably 160 to 200°C and 20 to 40 seconds.

By appropriately selecting the above-mentioned film forming conditions, the resulting biaxially oriented film has a refractive index of 1.580 to 1 in each direction of the film surface.
．． 640. Preferably 1.585 to 1,630. Density 1
, 200 to 1.280 (g/c), preferably 1.2
10-1.270 (g/CT11'), thermal expansion coefficient 10-30 (X 10-67°C), preferably 15
~27 (X10-'/'C), humidity expansion coefficient 3-8 (xl
O-6/%RH), preferably 4 to 8 (xlO'/%
RH), the in-plane direction difference in thermal expansion coefficient is 6×10″G/℃
, preferably within 4 x 10'/℃, and the in-plane direction difference in humidity expansion coefficient is 4 x 10'/%RH1, preferably 3 x 1
0″G/%R1-1 or less.

If the in-plane refractive index of the film is less than 1.580, the orientation of the molecular chains is insufficient, and the strength of the film, especially the A7 index, is insufficient for engineering purposes.

On the other hand, when the in-plane refractive index is larger than 1.64, the refractive index in the 90' direction becomes 1.58 or less, and the orientation of the molecular chains becomes larger. The purpose of the present invention is to provide a film with good orientation balance that is useful as a film for flexible disks, and the bias in the orientation of molecular chains as described above is not preferable. More preferably 1.585 to 1
, 630, which further improves the alignment balance. Also, the density is 1.200 to 1.2809
/cm, and if it is lower than 1.200, crystallization will be insufficient and the desired humidity expansion coefficient cannot be obtained. The coefficient of thermal expansion is 10 to 30 (x10''G/°C), more preferably 15 to 27 (x10'/°C).The coefficient of thermal expansion is
In general, the smaller the better, but for the base of a flexible magnetic disk, it is preferable that the thermal expansion coefficient be close to that of the disk drive device, since off-track between the magnetic disk and the head will be reduced.

The temperature expansion coefficient of the disk drive device can be easily set to around 20 x 10'G/°C, so it is preferably 20 x 10'/°C.
However, it is difficult to obtain a value close to 20×10-6/°C. Generally, the lower the humidity expansion coefficient is, the better for any purpose, but the inherent hygroscopic expansion of the material cannot be avoided, and it is difficult to reduce it to 3 x 10'/%Rl-1 or less. However, if the RH is lower than 8 x 10''6/%Rl-1, the improvement effect will clearly appear and it will be useful compared to the conventionally used polyethylene terephthalate 11 x 10'/%Rl-1.The in-plane direction difference in thermal expansion coefficient is , in order to reduce the off-track, it should be 5x10'/'C or less, preferably 4x10'/'C or less.FiI F9
The difference in i Pa elongation in the plane direction is also preferably smaller in order to reduce off-track, and is preferably 4 x 10'/%RH or less, preferably 3 x 10''G/%RH or less.

The biaxially oriented film of the present invention can have an appropriate thickness depending on its use, but the thickness is usually 12 to 12 μm.
5μm, 50 for flexible disk base applications
˜100 μm rL is chosen.

The method for measuring characteristic values in J3 according to the present invention is as follows.

(1) Refractive index: Based on Atsube's refraction 54.

(2) Density: by normal hebutane-tetrachlorine carbon density gradient tube.

(3) Temperature expansion coefficient 2 A constant load elongation tester ('1-TL 2 type) manufactured by Nippon Automatic Control Co., Ltd. is placed in a constant temperature and humidity chamber to measure it. Measurement samples were prepared in advance under predetermined conditions (e.g. 70°C).
, 30 minutes), and then the sample was attached to a testing machine and heated at 20°C and 60% relative humidity, and at 40°C and 60% relative humidity.
Measure the thermal expansion coefficient by reading the dimensional change between %RH and %RH. The original sample length at this time is 505
#ffl, sample width is 1/4 inch. The load applied during measurement was constant at 5 g/l/4 inch width. If a long sample cannot be obtained, measurement can be performed using a thermomechanical analyzer TM-3000 manufactured by Shinku Riko Co., Ltd. When determining the difference between the maximum value and the minimum value of the coefficient of thermal expansion, 1-M-3000 is used. - The dimensions of the rimpu are 15 mm in length and 5 mm in width, and the temperature is 10°C and the humidity is O.
It is determined by reading %RH and the dimensional change at a temperature of 40°C and a humidity of 0%RH.

(4) Humidity expansion coefficient: In the same way as when calculating the temperature expansion coefficient, use a constant load elongation tester manufactured by Nippon Jidosha Control Co., Ltd.
℃, humidity 90% RH conditions, take a sample that has been treated in advance, temperature 20 ℃, humidity 30% RH)-1 and 20.
Measure the dimensional changes that occur between ℃ and 70% RH.

If the sample cannot be taken for a long time, place the thermomechanical analyzer manufactured by Shinku Riko Co., Ltd. in a constant temperature and humidity environment, as in the case of measuring the thermal expansion coefficient.
Measure under the above conditions.

(5) In-plane directional difference in temperature/humidity expansion coefficient: above [3), f
41, measure the values in each direction every 15 degrees or 30 degrees, and calculate (maximum value - minimum value).

(6) Tensile strength: According to ASTM D 1922-67,
The tensile strength of the film in the flow direction (MD) and the direction perpendicular to the flow direction (TD>) is measured using a Toyo Seiki eave load tensile tester.

Example Next, the present invention will be specifically explained with reference to Examples.

Example 85 mol% of terephthalic acid as a basic acid component.

15 mol% of isophthalic acid and 1.
Using 100% 4-cyclobekyl nondimethazole, 0.05 mol% titanium oxide (based on the acid component) as a catalyst,
0.5% by weight of kaolin clay with an average particle size of 0.6 microns was added as a lubricant, placed in an autoclave, heated under stirring to transesterify, and then polycondensed to poly-1,
4-cyclohexylene dimethylene terephthalate was obtained.

Next, 85% by weight of the poly-1,4-cyclohexylene dimethylene terephthalate and 15% by weight of polyethylene terephthalate separately produced by a conventional method are mixed,
Dry.

This polyester was melt extruded at 300°C and cooled on a quenching drum maintained at 40°C to obtain an unstretched film of 1000 microns. This unstretched film was brought into contact with a metal roll adjusted to 90°C and preheated, and then stretched 3°6 times in the longitudinal direction between rolls having different circumferential speeds while being irradiated with an infrared heater (surface temperature 1000°C).

Next, the longitudinally stretched film was heated to 115°C with a tenter at 3.7°C.
It was laterally stretched twice. While holding both ends of the obtained biaxially stretched film with clips, it was heat-set at 200°C and rolled up.
The product had a thickness of 75 microns. The physical property values are shown in Table 1.

Example 2 In Example 1, the dibasic acid component was 100 mol% of terephthalic acid, and the content of polynyletine terephthalate was 30% by mole.
Weight% binding, melting temperature 310℃, quenching drum temperature 2
A biaxially oriented film of 75 microns was obtained in the same manner as in Example 1, except that the temperature was 0°C, the preheating temperature was 80°C, and the heat setting temperature was 180°C. The physical property values are shown in Table 1.

Example 3 Content M of polyethylene terephthalate in Example 1
was set at 5% by weight, heat setting was carried out at 160° C., and a biaxially oriented film of 75 microns [1 inch] was obtained. Other conditions are the same as in Example 1. Table 1 shows the physical properties of this film.

Comparative Example 1 Polyethylene terephthalate was polymerized by a conventional method. The film forming conditions of Example 1 were a melting temperature of 290°C, a quenching drum temperature of 20°C, a longitudinal stretching preheating temperature of 80°C, and a transverse stretching temperature of 10°C.
A 75 micron biaxially oriented film was obtained in the same manner as in Example 1 except that the heat setting temperature was 5°C and the heat setting temperature was 225°C. The physical properties of this film are shown in Table 1.

Comparative Example 2 A 75 micron 2@oriented film was obtained in exactly the same manner as in Example 2, except that the heat setting temperature was 230°C. Table 1 shows the physical properties of this film.

Comparative Example 3 Example 1 except that the dibasic acid component in Example 1 was 100 mol% of terephthalic acid, the polyethylene terephthalate containing ■ was 0% by weight, and the heat setting temperature was 230°C.
A 75 micron biaxially oriented film was obtained in the same manner as above.

The physical properties of this film are shown in Table-1.

(Left below) One side (DII) The biaxially oriented film of the present invention is suitable as a base for flexible magnetic disks.The reason for this is that the 11 degree expansion coefficient is smaller than that of polyethylene terephthalate film, which allows the magnetic track and head to The off-track of the disk is small and high recording density can be obtained.Although the coefficient of thermal expansion is relatively large, this is within the range in which the thermal expansion coefficient of the drive device does not match that of the disk. "This is not a disadvantage. Also, since the in-plane direction difference in the temperature-humidity expansion coefficient is small, it can easily be used to reduce off-track by a tracking servo mechanism, which is advantageous.On the other hand, the in-plane direction difference in refractive index It is also suitable for transparent conductive films for liquid crystal display devices and protective covers.It also has strong tear resistance, so the film does not tear during film production.
This improves the stability of the process.

Claims (1)

[Claims] 95 to 70% by weight of poly-1,4-cyclohexylene dimethylene terephthalate, in which 90 mol% or more of the glycol component is 1,4-cyclohexane dimetatool, and 80 mol% or more of the acid component is brephthalic acid; A biaxially oriented film made of a mixture of 5 to 30% by weight of polyethylene terephthalate, in which 90 mol% or more is ethylene glycol and 80 mol% or more of the acid component is terephthalic acid, and has an internal refractive index including the longitudinal and lateral directions. 1,5
80-1,640. Density 1.200~1.280 (9
/cm), thermal expansion coefficient 10-30 (Xio4/c>
, humidity expansion coefficient 3 to 8 (x10'/%RH), in-plane direction difference in temperature expansion coefficient within 6 x 10''1'/℃, in-plane direction difference in humidity expansion coefficient within 4 x 10'/%RH A biaxially oriented polyester film characterized by: