JPH02235615A - Manufacture of polyester film - Google Patents

Abstract

PURPOSE:To enable a film with small unevenness in its thickness and smooth in its surface to be obtained by close-cooling solidifying a molten polyester sheet on the surface of a cooled body having a liquid film of water, after that, drawing it 4.5 times or more at the total drawing magnification by multistage in a longitudinal direction. CONSTITUTION:A molten polyester sheet is close-cooling solidified on the surface of a cooled body having a liquid film of water, and then, drawn 4.5 times or more at the total drawing magnification by multistage in a longitudinal direction. As methods in making a liquid film interposed onto the surface of the cooled body there is a method (bedewing method) that an air contained with moisture is sprayed, and then bedewed, on the surface of the cooled body being kept at the dew point of lower, a method of applying by effusion rollers or transferring rollers, and a method of spraying water vapor with an electrostatic charge, however, it is preferable to adapt a bedewing method which is superior to be thin of 3mum or below in the average thickness (d) of the liquid film of water. And, if the cool-solidification is carried out while applying an electrostatic charge during the casting period, it becomes effective much more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a polyester film.

[Prior Art] A method of casting a polyester sheet on the surface of a cooling body with a liquid film such as water interposed therein is described in BP 1140175.
, is known from Japanese Patent Publication No. 5G-35133.

In addition, the stretching of polyester in the longitudinal direction at a high magnification in two or more stages is disclosed in Japanese Patent Publication No. 52-1090.
This method is known from Japanese Patent Publication No. 9, Japanese Patent Publication No. 52-33666, and the like.

[Problems to be Solved by the Invention] However, each of the above manufacturing methods has the following drawbacks.

(1) In order to obtain a high stretching ratio in the longitudinal direction, the stretching temperature is increased and the stretching is performed in multiple stages (high-temperature high-magnification stretching). For this reason, the thickness of the obtained film increases, and the surface becomes rough and easily abraded.

■ Because stretching is carried out at high temperature and high magnification, the stretching rolls are easily soiled and the resulting film is more likely to develop surface defects.
Productivity is hindered by cleaning and replacing rolls.

(3) When a liquid film is present, the molten sheet easily slides on the surface of the cooling body.

[Means for Solving the Problems] An object of the present invention is to provide a high-magnification stretching method that improves the above-mentioned drawbacks. That is, after the molten polyester sheet 1 is tightly cooled and solidified on the surface of the cooling body having a liquid film of water, the total stretching ratio is 4 in multiple steps in the longitudinal direction.
．． Bolier characterized by being stretched 5 times or more. The present invention relates to a method for producing stell film.

The polyester of the present invention is a general term for polymers having ester bonds in the main chain obtained by condensation polymerization of glycol and dicarboxylic acid. Typical glycols include ethylene glycol, butanediol, hexylene glycol, and cyclohexane. Dimethanol, neopentyl glycol, etc. Typical dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, dimer acids, eicoic acids, etc. Typical polyesters include polyethylene terephthalate, butylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene 12 nophthalate, etc., and particularly preferred in the present invention are polyethylene terephthalate 1, -.

Of course, the above polymer may contain known additives such as stabilizers, viscosity modifiers, antioxidants, fillers, slip agents, antistatic agents, antiblocking agents, mold release agents, and the like.

Methods for interposing a liquid film on the surface of the cooling body include a method of blowing humid air onto the surface of the cooling body kept below its dew point to cause condensation (condensation method), and a method using a seepage roller or transfer method. There are methods such as coating with a roller and spraying water vapor with an electrostatic charge, but in the case of the present invention, where the thinner average film thickness d of the water film is 3 μm or less, the better, the condensation method is used. is preferred. The average film thickness d of this water liquid is calculated from the weight of water using an infrared absorption method.

The measurement directly determines the thickness of the liquid film on the surface of the cooling body. If necessary, it is also possible to measure the thickness of the liquid film interposed between the molten sheet and the surface of the cooling body from the top of the molten sheet onto the surface of the cooling body. Although the expression "liquid film" is used, the liquid does not necessarily have to form a uniform continuous film, and may be a collection of discontinuous droplets such as those obtained by a dew condensation method.

Further, it is preferable that the height h of the meniscus formed at the position where the molten sheet contacts the surface of the cooling body is larger than the average film thickness d of the water film.

The height h of this meniscus varies depending on various factors, such as the surface tension of the polymer, the surface roughness of the molten sheet, the roughness and surface tension of the cooling body surface, the auxiliary adhesion force by other adhesion methods such as electrostatic application, and the discharge It depends on the distance from the die to the surface of the cooling body, the angle at which the molten sheet comes into close contact with the drum, the density of droplets on the surface of the cooling body, the size of the droplets, etc. That is, the height h of the meniscus can be changed by appropriately combining these parameters. The height of the meniscus refers to the height in the vertical direction from the crescent-shaped cooling body surface, which is caused by the surface tension of the liquid created near the contact point between the molten body and the cooling body surface. Measuring h requires precision, so it is best to take a photo with a fiberscope and then analyze it. The value of h is 1 to 20 μmSd and is 3 μIn or less and 0. 1 μm or more, and h
>d, preferably h>2d, since a stable cast sheet can be obtained.

In addition, as a method of casting while applying an electrostatic charge, a method known in Japanese Patent Publication No. 37-6142 and the like can be used in combination.

As a method of stretching at a high magnification in the longitudinal direction,
As is known from Japanese Patent Application No. 3666, a multi-stage stretching method is known which includes a step of stretching at a high temperature and a step of stretching at a low temperature. By stretching in multiple stages in this way, the stretching ratio in the longitudinal direction can be increased to 5.
Since the speed can be approximately 9 times higher, high-speed film formation of 200 m/min or more is possible. It is true that the multi-step stretching method is a preferable method for cost reduction processes, but the resulting film has large thickness irregularities, a rough film surface, and even a film surface with poor abrasion resistance. Not only are there problems in terms of quality, but the stretching rolls tend to become dirty in a short period of time, resulting in defects on the film surface. In other words, the total stretching ratio in the longitudinal direction is 4.5.
If it were made to be more than twice as high, it would have the fatal disadvantage of causing problems in terms of quality and production.

However, it was discovered that if such a cast sheet, which is stretched at a total stretching ratio of 4.5 times or more, is formed into a film under specific conditions, the above-mentioned drawbacks will not occur, resulting in the present invention. It is. That is, the above-mentioned drawbacks can be overcome by using a polyester sheet that is cooled and solidified in close contact with the surface of a cooling body having a liquid film of water as the cast sheet. At this time, the effect will be even greater if the material is cooled and solidified while applying an electrostatic charge during casting.

The stretching method in the longitudinal direction includes multi-stage stretching below the yield point, followed by almost normal stretching, and a method of stretching approximately 2 times at a high temperature and low stretching speed, followed by approximately normal stretching 2.5 to 3 times.
There are methods of stretching 5 times and stretching 4.5 to 7 times in total, but all of them require stretching at a higher temperature than the normal stretching temperature in the longitudinal direction. The effect of the present invention is remarkable when the stretching ratio is 4.5 times or more, preferably 5 times to 9 times. When stretching at high temperature, the stretching speed is
As slow a speed as possible, for example 10000%/
It is preferable to carry out the reaction in minutes or less, but the time is not limited thereto.

It is clear that the longitudinally stretched film thus obtained may be stretched in the width direction or heat treated as required. Particularly in the case of the present invention, the effect becomes remarkable by biaxial stretching.

[Measurement method] A method for measuring words used in the present invention will be described.

(1) Thickness unevenness Sample a film sample in a predetermined direction with a length of 10 m in the longitudinal direction and the maximum length in the width direction, measure the thickness continuously with a strain gauge, and calculate the thickness between the maximum thickness and the minimum thickness. The value obtained by dividing the difference Δd by the average thickness d, expressed as a percentage.

2 Surface roughness R, cutoff 0, 2 according to JIS-80601-1976
Maximum roughness measured at 5mm R. It is.

(3) External Haze The value obtained by subtracting the internal haze measured in the tetralin solution from the total haze measured according to JIS-K6714 is defined as the external haze.

[Effects of the Invention] The following effects are produced by using a sheet using a specific casting method for high-temperature, high-magnification stretching.

(1) Even though the stretching ratio in the longitudinal direction is as high as 4.5 times or more, a film with small thickness unevenness and a smooth surface can be obtained.

■ The obtained film has excellent abrasion resistance.
Furthermore, the film has high strength in the longitudinal direction and has properties suitable for a base film for magnetic tape.

(3) It becomes a stable film in which oligomers and additives do not easily bleed onto the film surface, making it excellent for applications such as electrical insulation films.

(4) A film with excellent electrical insulation properties can be obtained as a capacitor film.

(5) A film with excellent adhesion properties such as printability and metal deposition properties can be obtained.

(6) It is a stretching process in which the stretching rolls are less likely to get dirty, requiring less cleaning and replacement of the rolls, and is a highly productive process.

■ The same orientation can be obtained by stretching at a lower temperature than with ordinary cast films, and stable stretching with less tearing is possible.

[Example] Next, in order to make it easier to understand the effects of the present invention, an example will be described.

Example 1 Polyethylene terephthalate (intrinsic viscosity [η] in 0-chlorophenol 0.65, average particle size 3 as an additive)
T i 02 of 00 mμ is 0. After drying under vacuum at 180°C using a conventional method, the mixture was fed to an extruder, melted at 285°C, quantitatively measured using a gear pump, and melted to a constant thickness from a T-die nozzle. The sheet was discharged. A mirror-finished drum (surface roughness R. 0.1 μm) at 50 m/min while applying an electrostatic charge throughout the sheet.
It was cooled and solidified in close contact with the top. At this time, on the mirror drum,
Air containing saturated water vapor at 80° C. is blown onto a drum maintained at 25° C., and water droplets are uniformly deposited on the drum so that the average water film thickness d is 1 μm.

In addition, the height h of the water meniscus formed between the electrostatically charged molten sheet and the cooling drum was maintained at 2.5 μm.

The cast film thus obtained was stretched 1.8 times in the longitudinal direction on rolls heated to 100°C, and then stretched 3.6 times on rolls heated to 90°C to give a total length of 6.5 times in the longitudinal direction. Stretched twice. Next, it was stretched 4 times in the width direction in a tenter heated to 95°C, and heat treated at 210°C for 7 seconds while relaxing 5% in the width direction to a thickness of 1.
A 2 μm biaxially stretched polyester film was obtained.

The stretching temperature in the longitudinal direction was relatively low, allowing for high-magnification stretching, and stable stretching was possible with no deposits or other stains on the rolls even after prolonged stretching. Table 1 shows the properties of the film thus obtained.

When a film with the above characteristics is used as a base film for magnetic tape, it has excellent running and slipping properties.
Furthermore, a magnetic tape with excellent wear resistance can be obtained.

Comparative Example 1 The casting method with a water film intervening used in Example 1 was changed to the normal electrostatic application casting method without intervening a water film, and the other conditions were completely the same as in Example 1, and biaxial stretching heat treatment was performed. did.

As a result, due to strong orientation during stretching in the longitudinal direction, the film frequently broke during stretching in the width direction, making stable stretching impossible. However, the results of measuring the quality of the biaxially stretched film are shown in Table 2. Ta.

Table 1 As described above, unless the casting method is specified, not only stable stretching cannot be performed, but also a film of excellent quality cannot be obtained.

Claims (2)

[Claims] (1) A polyester characterized in that a molten polyester sheet is cooled and solidified in close contact on the surface of a cooling body having a liquid film of water, and then stretched in multiple steps in the longitudinal direction at a total stretching ratio of 4.5 times or more. Film manufacturing method. (2) The method for producing a polyester film according to claim (1), wherein the polyester film is cooled and solidified in close contact with the surface of the cooling body while applying an electrostatic charge.