JP2570304B2 - Method for producing polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a polyester film having no surface defects and excellent running properties.

[Prior Art] As a polyester film having excellent running properties, it is possible to add a polyalkylene glycol to polyester as disclosed in JP-A-56-90423, JP-A-58-177522, and JP-A-59-227421. And JP-A-62-96530.

[Problems to be Solved by the Invention] However, the above-mentioned film has the following problems.

(1) In the case of a thick film of 150 μm or more, the inclusion of polyalkylene glycol results in a film with few surface defects, but in the case of a thin film of 100 μm or less, the effect of improving the surface defect is almost recognized. I can't.

(2) When the humidity is low, the coefficient of friction between films or between films and metals, ceramics, etc. is small.
Although it has excellent running properties, when the humidity is as high as 70% or more, the coefficient of friction increases, resulting in poor running properties.

(3) When a film to which polyalkylene glycol is added is used as a base film for a magnetic tape, raw film alone is excellent in slipperiness, but when used as a magnetic tape, it is inferior in slipperiness. And the transfer of the so-called lubricant deteriorates.

[Means for Solving the Problems] The present invention relates to a method of stretching a polyester film containing 0.01 to 1.8% by weight of a polyalkylene glycol by using a roll, wherein the E value is 10 to 60 before the roll stretching.
And a method for producing a polyester film characterized by performing a corona discharge treatment.

The polyester of the present invention is a polymer having a polyester bond in its main chain by polycondensation from a dicarboxylic acid and a diol, and terephthalic acid,
Isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,
4'-diphenylenedicarboxylic acid, diphenylether-4,4'-dicarboxylic acid, diphenylethane-4,4'-
Examples include dicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, and modified products thereof such as alkyl, alkoxy, and halogen. Examples of the diol include ethylene glycol, diethylene glycol, cyclohexanedimethanol, cyclohexanediol, butanediol, neopentyl glycol, hydroquinone, resorcinol, 4,4'-dioxydiphenyl, naphthalenediol, and 4,4'-dioxydiolefin. Enyl ethers and modified products thereof. Of course, it may be a polyester derived from an oxycarboxylic acid such as hydroxybenzoic acid or hydroxynaphthoic acid or a derivative thereof. Preferred polyesters of the present invention include polyethylene terephthalate, polyethylene naphthalate, polycyclo-xan dimethanol terephthalate, polybutylene terephthalate, and poly (ethylene-1,2-bis-diphenoxyethane-p, p'-diorboxoxy). Rate) and its derivatives. The intrinsic viscosity of the polyester film is 0.4 to 1.2, preferably 0.5 to 0.8.
Are preferred. Of course, an optional additive can be contained as needed.

Polyalkylene glycols include polyethylene glycol, polytetramethylene glycol, polyhexamethylene glycol, ethylene oxide / propylene oxide copolymer, ethylene oxide / tetramethylene oxide copolymer, polyethylene glycol dilaurate, polyethylene glycol distearate, and polypropylene glycol distearate. And their derivatives.

In the present invention, the content of the polyalkylene glycol in the polyester film is in the range of 0.01 to 1.8% by weight, preferably 0.03 to 1.0% by weight. Content is 0.01% by weight
If it is less than 1, even if the corona discharge treatment is performed, the effect of the present invention on no defect on the surface and improvement in running performance is not recognized. Conversely, if the content exceeds 1.8% by weight, regardless of the presence or absence of the corona discharge treatment, the surface defects will increase as compared with those without the corona discharge treatment, and the running property will further deteriorate. Further, the melt extrusion stability also decreases. It should be noted that even if the content of the polyalkylene glycol is in the range of 0.01 to 1.8% by weight, it becomes worse than the non-added / untreated one without the corona discharge treatment of the present invention. is there.

The molecular weight of the polyalkylene glycol is 500 to 5,000,000
And more preferably in the range of 1000 to 500,000. If the molecular weight is less than 500, the effect of the present invention is weak,
If it exceeds 000000, the dispersibility in the polyester film is poor, and coarse projections are likely to be formed on the film surface.

The method of blending the polyalkylene glycol with the polyester is not particularly limited, but a masterbatch method is preferably employed because the blending amount is small. For example, a masterbatch containing about 1 to 20% by weight of a polyalkylene glycol is prepared and blended with a polyester so that the amount of the polyalkylene glycol is within the scope of the present invention. Of course, it is a matter of course that the polyester containing the polyalkylene glycol may be directly formed into a film.

Corona discharge treatment means that when a strong electric field is localized, such as when a high voltage is applied to an electric wire, a local discharge limited to that region occurs.This is called corona discharge, Surface treatment with a film under discharge. As the corona discharge, an alternating current is usually used, but a positive or negative corona may be used as necessary. In the case of AC, a frequency in the range of 10 to 200 kHz is often used. The strength at the time of corona discharge treatment is represented by E value, and E value = W / (D ·
V), W is the processing intensity (W), D is the processing width (m), and V is the film speed (m / min). Therefore, E
Values are given in units of W · min / m ² . This E value is 10-6
0, preferably in the range of 25-50. When the E value is less than 10, the effect of the present invention is not obtained. Conversely, if it exceeds 60, the surface defects will increase more than the untreated one, and the running property will deteriorate. Of course, corona treatment of a polyester containing no polyalkylene glycol has the opposite effect. The oxygen concentration of the atmosphere in which the corona discharge treatment is performed is preferably 1% by volume or less in order to make the effect of the present invention remarkable. It is more preferably at most 0.1% by volume. The temperature of the untreated film is preferably near the glass transition temperature of the polyester film. The polyester film surface layer thus obtained seems to have a very slight crosslinked structure. The treated film was immersed in a phenol / ethane tetrachloride = 3/2 (weight ratio) mixed solution,
After heating for a minute, the weight of the residue was measured to be 10-100p
It can be seen from the fact that there are about pm.

In the present invention, a polyester containing a specific amount of the polyalkylene glycol is melted at a temperature of 260 to 330 ° C. by a conventional method, then a fixed amount is measured by a gear pump, and discharged from a molding die having a fixed gap slit. Then, while applying an electrostatic charge, it is brought into close contact with a casting drum cooled to 60 to 15 ° C., and solidified by cooling to obtain a cast sheet. The cast sheet was subjected to a corona discharge treatment with an E value of 10 to 60 (W · min / m ² ) in air, and then preheated on a chrome plating roll heated to 80 to 110 ° C. Immediately after stretching 2.5 to 4.5 times in the direction, it is rapidly cooled to 60 ° C or less. Subsequently, after heating to 90 to 120 ° C with a tenter, the film is stretched in the width direction by 2.5 to 5 times, and immediately at 150 to 250 ° C for 0.5 times.
Heat treatment is performed for 15 seconds to obtain a polyester film having a thickness of 1 to 350 μm. Needless to say, coating or compounding, surface treatment such as embossing, heat treatment, or the like may be performed in any step in the present manufacturing process.

[Action] The present invention is intended to form a non-adhesive hard thin film on the surface layer of the polyester film by adding a polyalkylene glycol to the polyester and subjecting the surface to a specific corona discharge treatment. It is thought that as a result, not only was there no flaw or adhesion of the sticky substance on the polyester film surface, but also the running property was improved by forming a hard thin film.

[Effect of the Invention] The surface of the polyester film thus obtained has no defects, and of course, has no stain on the stretching roll for film formation, and is excellent in slipperiness and easy adhesion without long-term surface defects. Can be formed stably. Furthermore, when the obtained film is used as a magnetic tape, it has excellent running characteristics with a magnetic head, and has the disadvantages of generating wear powder and increasing running torque, unlike conventional products. The film of the present invention is useful as a film for a magnetic recording medium, in which the surface smoothness is particularly important because of the characteristics such as no film.

[Measurement methods for physical properties] (1) Surface defects are indicated by x when the surface defects are visible under polarized light on the biaxially stretched film, and are not visible under polarized light, but those that can be observed with a 250-fold optical microscope are denoted Those that cannot be observed even with a microscope and have a uniform surface are indicated by a circle.

(2) The coefficient of dynamic friction μk with the metal head is determined by contacting a fixed hard chrome-plated 6 mmφ fixing pin with a winding angle of 135 ° (θ), applying a load of 53 g (T ₂ ) to one end, This is run at a speed of one minute, the resistance (T ₁ (g)) at the other end is measured, and μk is determined by the following equation.

_{μk = 0.424n (T 1/53} ) (3) running property is to the polyester film of the present invention,
A commercially available standard video tape (film width 1/2 inch, HS-T120 manufactured by TDK Corporation) is superimposed and wound with a tension of 100 g, left at 40 ° C and 65% RH for 2 days, and then only the film of the present invention is taken out. , Dynamic friction coefficient μk at 25 ℃ 65RH%
Ask for. If the value of μk exceeds 1.0, ×, 1.0 to 0.5
△, 0.5-0.3 〜, less than 0.3 ◎
Indicated by

Examples Example 1 Polyethylene terephthalate containing 7% by weight of polyethylene glycol having a molecular weight of 4000 as polyalkylene glycol (intrinsic viscosity at 25 ° C. of o-chlorophenol)
0.68, dimethyl silicone oil 100ppm as an additive) as a master polymer, polyethylene terephthalate (o-chlorophenol at an intrinsic viscosity of 25 ° C 0.63,
As an additive, silicon dioxide having an average particle size of 300 mμ was added to 0.25% by weight), and when the polyester film was formed, it was blended so that the polyethylene glycol component was 0.5% by weight.

The blend is melted at 280 ° C. by a conventional method, and the melt is discharged from a molding die while applying an electrostatic charge.
The resin was cooled, solidified and adhered to a casting drum maintained at 30 ° C. The cast sheet is heated to 70 ° C., on both sides of the surface of which the E value is 30 (W min / m ² ) and the oxygen concentration is less than 1%,
After performing corona discharge treatment in argon, use a roll
After stretching 3.8 times in the longitudinal direction at 100 ° C. and 4.2 times in the tenter at 105 ° C., heat-treating at 150 ° C. for 5 seconds, and then using a roll, stretching 1.2 times in the longitudinal direction at 175 ° C.
Heat treatment was performed at 8 ° C. for 8 seconds to obtain a 9 μm thick repolyester film. The running property of the film thus obtained is
The film was very excellent (）), had no surface defects (○), and had no adhesion of stretch roll stains, and stable stretching was possible.

The high voltage generator used for corona discharge treatment
An HS-2001 type manufactured by Kasuga Electric Co., Ltd. was used, and an AC power supply of 30 kHz was used.

Comparative Examples 1 to 3 As shown in Table 1, the presence or absence of corona discharge treatment and polyalkylene glycol used in Example 1 were examined.

As described above, when only the polyalkylene glycol is added or only the corona discharge treatment is performed, the running property is worse than that of the blank. It can be seen that the effect of the present invention is exhibited by the synergistic effect of the polyalkylene glycol content and the corona discharge treatment.

Examples 2 to 4 and Comparative Example 4 The procedure was the same as in Example 1 except that the amount of polyethylene glycol used in Example 1 was changed.

As described above, the content of the polyalkylene glycol is in the range of 0.01 to 1.8 wt%, preferably 0.03 to 1.0 wt%.

5 Examples 5 to 7, Comparative Example 5 A biaxially stretched film was produced in the same manner as in Example 1 except that the E value used in Example 1 was changed, and the same evaluation was performed. The corona discharge treatment was performed in the atmosphere.

Thus, it can be seen that the E value must be in the range of 10-60.

Claims (1)

(57) [Claims] In a method of stretching a polyester film containing 0.01 to 1.8% by weight of a polyalkylene glycol using a roll, an E value of 10 to 60 is used before stretching the roll.
A method for producing a polyester film, comprising subjecting a polyester film to a corona discharge treatment.