JPS63197630A - Production of biaxially stretched polyester film - Google Patents

Abstract

PURPOSE:To produce a film excellent in easy adhesiveness, by a method wherein a polyester pellet is melted in gas containing at least 1 vol.% of carbon dioxide to be formed into a film by extrusion and the extruded film is stretched 2.0- below 4.5 times in the longitudinal direction and subsequently stretched in the lateral direction to be subjected to heat treatment. CONSTITUTION:A polyester pellet is supplied to an extruder under an atmosphere containing at least 1 vol.% or more of CO2 and melted. The molten polyester sent out from the extruder passes through a filter and is quantitatively supplied by a gear pump to be guided to a molding die and emitted from a die slit to form a molten sheet which is, in turn, brought into close contact with a casting drum for cooling and solidifying said sheet to obtain a molded sheet. There is no special limit in a stretching system and a no-nip system or the like can be arbitrarily selected. The stretching magnification in the longitudinal direction is set to a range of 2.0- below 4.5 times. When the stretching magnification is too high, a polyester film excellent in adhesiveness and dielectric breakdown is not obtained. Stretching temp. is set to the glass transition temp. of the polyester pellet or more. Next, the stretching in the lateral direction and heat treatment are performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a polyester film, and more particularly to a method for producing a film with excellent adhesive properties.

[Prior Art] There have been many attempts to improve the adhesion between polyester films and other objects or themselves. How to combine (for example,
JP-A No. 46-1123, etc.), a method of adding a resin with excellent adhesiveness to the polyester (e.g., JP-A No. 5B-Sho.
No. 25331, etc.), and a method of corona discharge treatment of the surface of the polyester film (for example, Japanese Patent Publication No. 53-3).
1509, etc.), and plasma processing methods (for example, Japanese Patent Publication No. 59-7725, etc.).

[Problems to be Solved by the Invention] However, the above method deteriorates film properties such as transparency, mechanical strength, thermal dimensional stability, slipperiness, and ease of taking out the film. Not only does this have to be done frequently, but it also has the disadvantage of being extremely expensive to manufacture.

The object of the present invention is to produce a polyester film with excellent adhesive properties without using the above raw materials, production processes, or additional equipment.

[Means for Solving the Problems] The present invention involves melting a polyester pellet in a gas containing at least 1% by volume of carbon dioxide, and extruding the polyester film from a molding die into a polyester film in the longitudinal direction.
．． The present invention relates to a method for producing a biaxially stretched polyester film, which comprises stretching the film by 0 times or more and less than 4.5 times, followed by stretching and heat treatment in the width direction.

Polyester is a polymer having ester bonds in its main chain, and typical examples include polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphthalate, polyethylene α, β-bis(2
-chlorophenoxy)ethane 4,4'-dicarboxylate, poly(1°4-cyclohexylene dimethylene naphthalate), copolymers thereof, and blends with others. Such polyester is
The intrinsic viscosity (measured in orthochlorophenol at 35°C) is preferably 0.5 or more.

Of course, the polyester may contain additives known for use in polymers, such as stabilizers, viscosity modifiers, antioxidants, fillers, slip agents, antiblocking agents, and the like.

The thickness of the polyester film of the present invention is not particularly limited, but is 500 μm or less, preferably 125 μm.
Hereinafter, the effect is particularly remarkable in the case of a thin film, preferably 25 μm or less.

Melt-extruding polyester pellets in a gas containing carbon dioxide (hereinafter referred to as CO2) means that the atmospheric gas in contact with the polyester pellets supplied to the extruder is
O2 at least 1% by volume or more, preferably 20% by volume
It is to be supplied to an extruder under an atmosphere containing the above. Of course, the effects of the present invention will be more pronounced if the atmospheric gas through which the molten polymer is discharged from the nozzle contains at least 1% by volume of CO2.

If the CO2 gas content is less than 1% by volume, not only will it not be possible to provide easy adhesion, especially easy adhesion to the A1 vapor deposited film, which is the objective of the present invention, but also the surface roughness (Ra) will be 100%.
It is difficult to obtain a smooth film with a diameter of mμ or less, and furthermore, it is difficult to obtain a film with a high dielectric breakdown voltage (BDV).

Furthermore, in the case of the present invention, gases other than CO2 include various carbon oxides, various nitrogen oxides, various sulfur oxides,
Nitrogen, argon, helium, oxygen, etc. are preferable, and the mixing ratio of CO2 and nitrogen is preferably 1/99 to 10010. Preferably, the range of 20/80 to 80/20 makes the effects of the present invention significant. In the case of the present invention, CO2 should be supplied at the stage of unmelted polyester pellets,
By the method of blowing CO2 into a molten polymer as disclosed in Japanese Patent Publication No. 50-6026, it is impossible to obtain a high-strength stretched film with a smooth surface and no defects as in the present invention.

Further, the pressure of the CO2 gas in contact with the polyester pellets is not particularly limited and can be arbitrarily selected from a reduced pressure of about 400 mmHg to an increased pressure of up to 10 atm, but in the case of the present invention, it is 1.5 to 3 atm. The effect is more pronounced on the pressurized side.

Further, a filter may be attached after melting and before extrusion from the die, and the effect of the present invention becomes more significant as a finer filter with a nominal cut of 1 to 5 μm is used.

Furthermore, the pressure applied in the step of melting, compressing and defoaming the polyester pellets is 10 to 500 kO/ci.

Preferably 20 to 300 kg/cJ, more preferably 8
A range of 0 to 250 kg/ri is preferred in the present invention.

The melt extrusion temperature is at least the melting point Tll1 and Tm
The temperature range is below +150° C., and the temperature is as low as possible, and the residence time of the molten polymer is also short, preferably less than 30 minutes, more preferably less than 10 minutes.
This is preferable not only from the viewpoint of preventing thermal decomposition but also because it makes the effects of the present invention more noticeable.

The molten pomer thus sent out from the extruder passes through a filter, is fed in a fixed amount by a gear pump, and is guided to a molding nozzle.The molten sheet is discharged from the nozzle slit, and is brought into close contact with the casting drum where it is cooled and solidified, and then molded. Get a sheet. As a method for bringing it into close contact with the casting drum, a known electrostatic application method, air knife method, press roll method, or the like can be used. The crystallinity of the obtained cast film can be achieved by adjusting the temperature of the casting drum, and in the case of the present invention, the effect of crystallinity is not significant, but the density method (proportional ratio between crystal density and amorphous density) (obtained by distribution) is preferably less than 20%, more preferably less than 10%.

Of course, the crystallinity may be 20% or more.

Next, the surface material of the roll stretched in the longitudinal direction can be arbitrarily selected depending on the purpose of use, such as a metal roll, a ceramic roll, a rubber roll, or a roll coated with an organic surface layer. Furthermore, there are no particular limitations on the stretching method;
You can arbitrarily select a no-nip type, a nip type, a multi-idler set, etc.

The stretching ratio in the longitudinal direction is 2.0 times or more and less than 4.5 times, preferably 2.2 to 4.2 times.

If the stretching ratio is too large, the polyester film will not have excellent adhesion, especially adhesion to the AI deposited film, and high dielectric breakdown properties. On the other hand, if the stretching ratio is too small, the adhesiveness and film thickness tend to be uneven, and the surface smoothness is deteriorated, which is not preferable.

The stretching temperature is higher than the glass transition temperature To of the polyester pellet for better adhesion and surface smoothness. On the other hand, stretching at a temperature lower than Tg is advantageous for improving dielectric breakdown voltage.

Next, the stretching ratio in the width direction is suitable for the purpose of the present invention in a range of 1.5 to 4.5 times, and the product of the stretching ratio in the longitudinal direction and the width direction is preferably about 6 to 16 times. . The heat treatment temperature, time, relaxation rate, etc. can be freely used depending on the application, and a temperature of 150 to 190°C is preferable.

Of course, any process in the production of biaxially oriented films can include corona discharge treatment in air or specific gases such as nitrogen and carbon dioxide, plasma treatment, flame treatment, and radiation such as ultraviolet rays, gamma rays, and electron beams. Treatments such as coating, embossing, etc. may be used to enhance the effects of the present invention.

[Measurement method and evaluation method] (1) Surface roughness Ra is JIS 80601-1
Centerline average roughness measured according to 976 with a cutoff of 0.25 mm.

(2) Dielectric breakdown voltage (BDV) is ASTM-D1
49 at 100 V/sec at 25°C.

(3) Adhesion was determined by depositing aluminum to a thickness of 200 at a vacuum level of 10''' Torr, and applying an adhesive mixture of Atocoat 503-3E-5D and Atocoat FJ to a thickness of 1 μm on the aluminum vapor-deposited surface. On top of that, as a sealant, a 30 μm thick film of "Trefan'No" (manufactured by Toshiku Co., Ltd.) P-3401 was pressed onto the treated surface at 80°C, and aged at 40°C for 2 days. Then, measure the 90 degree peel force between the base film and the sealant.

It was divided into 5 levels depending on the peeling force.

Peeling force (g/cm) 5 200 or more 4 160 to less than 200 3 120 to less than 160 2　　　80～less than 120 1 ~ less than 80 [Example] The present invention will be explained based on examples.

Examples 1-5. Comparative Examples 1-2 Polyethylene terephthalate (0-
Using pellets (having an intrinsic viscosity of 0.58 in chlorophenol and a glass transition temperature of 70°C and containing 0.3% by weight of silicon oxide with an average particle size of 200 mμ as an additive),
After drying at 180° C. for 8 hours under a vacuum of m + nHg, the pressure was released to 1 atm with a gas mixture of 25% carbon dioxide and 75% nitrogen by volume, and the pellet was filled with the above mixed gas without exposing it to the atmosphere. The melt was fed into the hopper of a melt extruder. The pellets supplied to the extruder are melted at 285°C, passed through a filter that cuts nominally 8 μm or more, extruded into a sheet from a nozzle, and then chromium plated at 60°C while applying an electrostatic charge. Roll (0,18
surface finish) to create a cast film of poor quality. The sheet was stretched at various stretching ratios at 65°C using a longitudinal stretching device, then stretched 3°5 times in the width direction at 75°C, and then heat-treated at 175°C for 5 seconds at a constant width. A biaxially stretched film with a thickness of 12 μm was obtained.

As shown in Table 1, the adhesion and surface smoothness of the A1 deposited film vary greatly depending on the stretching ratio, and the stretching ratio is 4.5.
It can be seen that those with a ratio of less than 2 times, preferably in the range of 2.2 to 4.2 times, are excellent in various properties such as adhesiveness.

Comparative Example 3 After drying the pellets used in Examples 1 to 5 and without using the carbon dioxide gas used for extrusion, using oxygen gas instead, biaxial stretching and heat treatment were performed in the same manner as in Example 3, A film with a thickness of 12 μm was obtained. When the adhesiveness was evaluated in the same manner as in the examples, the evaluation was 1, indicating that the adhesiveness was poor.

Table 1 [Effects of the Invention] Since the present invention uses a cast sheet obtained by melt-extruding polyester pellets in an atmosphere containing carbon dioxide, the obtained biaxially oriented polyester film exhibits the following excellent properties. be.

■ A film with no surface defects can be obtained.

■ A high-strength film with a high Young's modulus can be obtained.

■ It becomes a film with excellent adhesion and slipping properties.

■ Creates a film with low molecular weight such as oligomers that is difficult to bleed out.

■ Creates a film with excellent barrier properties against gases such as oxygen and water vapor.

■ The film has excellent thermal dimensional stability and low thermal skew.

■ It becomes a film with high dielectric breakdown voltage.

■ Slitting property, that is, the film is free from chips and hairs on the slit end surface.

■ It becomes a film with almost no change in physical properties after oral administration.

[Co., Ltd.] Even if a roll made of a material that easily sticks, such as a metal roll, is used, it does not stick even at high temperatures, and a film with a smooth surface can be obtained.

Claims (1)

[Claims] Polyester pellets are melted in a gas containing at least 1% by volume of carbon dioxide, and a polyester film extruded from a molding die is stretched 2.0 times or more and less than 4.5 times in the longitudinal direction, and then stretched in the width direction. A method for producing a biaxially stretched polyester film, which comprises stretching and heat treatment.