JPH10258458A - Biaxially oriented polyester film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To neatly take up a broad film after being made into the film and further realize the favorable planeness of a product by a method wherein the thickness of the film is set to be more than a specified thickness and the ratio between the surface roughnesses of the front and of the surfaces of the film is set to be a specified value or less. SOLUTION: The thickness of a biaxially oriented polyester film is limited to be 50μm or more, preferably to 70μm or more and more preferably to 100μm or more. The ratio between the surface roughness Ra of the front and of the rear surfaces of the film must be 1.3 or less, preferably 1.255 or less and more preferably 1.2 or less. When the ratio between the surface roughnesses of the front and of the rear surfaces of the film goes wide of the above-mentioned range, unpreferably poor conveyability at the process of the film and poor taken-up state at the cutting of a product. Polyester, which is enough dried, is fed to various extruders and passed through a filter, which is selected in response to necessity, and melt-extruded through a mouthpiece slit into a shape of a film. The filmy polyester is quenched and solidified into an amorphous state by being cast on a casting film, the temperature of which is controlled to be 20-60 deg.C.

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 effectively used for various applications such as graphics, plate making, magnetic recording media, and electric insulating materials.

[0002]

2. Description of the Related Art Biaxially oriented polyester films have many advantages over other materials in terms of their good film-forming properties, cost, etc., and have been used for graphics, plate making, magnetic recording media, electrical insulating materials, packaging, etc. Widely used in the field.

[0003]

In recent years, the film forming speed of polyester films has tended to increase in order to improve the production capacity and reduce costs. The temperature rise state of the film is different between the front and back, and the characteristics of the front and back of the product film differ according to it, and when cutting a wide film after forming into a narrow width, it can not be wound up neatly, processing into the final product At the time, when the film is heated, the shrinkage behavior on the front and back sides of the film is different, so that there are problems such as meandering and poor flatness of the product.

An object of the present invention is to solve a problem which is difficult to solve by the conventional techniques as described above.

[0005]

According to the present invention, there is provided a biaxially oriented polyester film characterized in that the thickness of the film is 50 μm or more and the ratio of the surface roughness Ra of the front and back surfaces of the film is 1.3 or less. Is what you do.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As the polyester in the present invention, polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polyethylene-α, β-bis (2-chlorophenoxy) ethane-4,4 '-Dicarboxylate and the like are used, among which polyethylene terephthalate, polyethylene-2,6-naphthalate, polyethylene-α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate are preferable, and particularly Polyethylene terephthalate, polyethylene-2,6-
Naphthalate is preferred. The polyester of the present invention may be one of the above-mentioned polymers alone, a copolymer of two or more polyesters, or a mixture of two or more polyesters. Various additives may be added as long as the effects of the present invention are not impaired.

Although not particularly limited, the biaxially oriented polyester film of the present invention more preferably contains inert particles such as inorganic particles and organic particles. Silicon dioxide, calcium carbonate, and aluminum oxide are used as the inorganic particles, and ethylvinylbenzene-divinylbenzene copolymer, polymethyl methacrylate, and the like are used as the organic particles. These inert particles can be used alone or in combination of two or more kinds having different types or particle diameters. By containing these inert particles, the slipperiness of the film is improved, and the handleability and transportability in the film forming and processing steps are improved.

The thickness of the biaxially oriented polyester film of the present invention is limited to 50 μm or more, preferably 70 μm or more, more preferably 100 μm or more.

Further, the surface roughness Ra of the film of the present invention must be 1.3 or less, preferably 1.25 or less, more preferably 1.2 or less. If the ratio of the surface roughness to the front and back is out of the above range, it is not preferable because the transportability at the time of film processing and the winding state at the time of cutting the product are poor.

Although not particularly limited, the ratio of the refractive index between the front and back of the film is preferably 1.01 or less, more preferably 1.008 or less, and even more preferably 1.006 or less. This is preferable because meandering or the like does not occur during film processing.

Next, a method for producing the film of the present invention will be described.

As the polyester of the present invention, those obtained by various methods can be used. After the polyester is sufficiently dried, it is supplied to various extruders, passed through a filter selected as required, and then melt-extruded into a film through a die slit. This film-like polyester is rapidly cooled and solidified on a casting drum controlled at a temperature of 20 to 60 ° C. to be in an amorphous state. At this time, it is more preferable to improve the adhesion between the drum and the polyester film by using various kinds of electrostatic application devices.

The obtained amorphous polyester is first stretched and oriented in the longitudinal direction. In the longitudinal stretching, after passing through a sufficiently heated roll and preheating, the polyester is used to have a glass transition point (Tg) or higher and a cold crystallization temperature (Tc).
c) Using the difference in peripheral speed of the roll at the following temperature. When a thick film is to be formed, the amount of heat is insufficient only by heating with rolls.Therefore, there is a method in which an infrared radiation type heater is installed between rolls with different peripheral speeds, and stretching is performed while heating the film with this heater. Used. When an infrared radiation type heater is used, the heater may be provided on only one side of the film, or may be provided on both sides. However, it is particularly desirable to provide the heater on both sides to obtain the film of the present invention. There is no particular limitation on the infrared radiation type heater, but in the case of a condensing type or a diffuse type heater in which a bar-shaped quartz infrared lamp is covered with a semi-elliptical reflecting shade with a mirror surface, the film can be efficiently heated, It is particularly preferable because the heater body is compact and can be installed in a narrow space when installed in a vertical stretching machine.

The temperature difference between the front and back of the film during longitudinal stretching is not particularly limited, but is preferably 10 ° C. or less, preferably 7 ° C. or less, more preferably 5 ° C. or less, in order to obtain the effects of the present invention.

Although not limited, the stretching section during longitudinal stretching (the distance between the center of the roll at which stretching starts and the center of the roll at which stretching ends) is 400 mm or less, preferably 350 mm or less, and more preferably 300 mm or less. Stretching is desirable for obtaining the effects of the present invention.

Next, stretching orientation is performed in the transverse direction. The stretching in the transverse direction is carried out by various types of stenters using the T
The stretching is performed about 2 to 5 times at a temperature of not less than g and not more than Tcc.

Next, heat treatment is performed. The heat treatment is performed in a temperature range from Tcc to the melting point (Tm) of the biaxially stretched film. The heat treatment may be carried out under tension or under relaxation of several percent.

[0018]

[Methods for measuring physical properties and evaluating effects]

(1) Film surface roughness Ra, ratio of front and back The following conditions were obtained by ET-30HK manufactured by Kosaka Laboratory Co., Ltd.
Randomly select a measurement point, measure five times, and average the average Ra
And

Vertical magnification: 20,000 times Horizontal magnification: 200 times Cut-off: 0.25 mm Measurement length: 0.5 mm Feed pitch: 5 μm Stylus curvature radius: 2 μm Stylus speed: 100 μm / sec Number of measurement units: 80 films The measurement was performed for the front and back sides, and the ratio was calculated using the smaller value as the denominator.

(2) Refractive index of film, ratio of front and back Abbe refractometer (Abego refractometer type 4 manufactured by Atago Co., Ltd.)
T), the sodium D line (wavelength 589 nm)
And using methylene iodide as an intermediate liquid and a refractive index of 1.7
Using the test piece No. 2, the refractive index in the longitudinal direction was measured using the prism surface side as a measurement surface. The film was measured on the front and back, and the ratio was calculated using the smaller of the two values as the denominator.

(3) Film Temperature During Stretching The film was measured at an emissivity of 0.95 using a radiation type non-contact thermometer (for example, non-contact thermometer type 505 manufactured by Minolta Co., Ltd.).

(4) Winding The film is cut into a width of 500 mm, and the winding speed is 200 m /
The film roll is left for 24 hours at a tension of 25 kg / m. The film roll is left standing for 24 hours, and the appearance is visually observed. If any wrinkles are found at 3 or more places or 2 mm or more of the end face is defective, the wrinkles are 3 places. Less and the end face deviation is 2mm
Less than good.

(5) Curl Ratio The film was sampled to a size of 210 mm in the longitudinal direction and 50 mm in the lateral direction, and one end of the sample was attached to a string having a 10 g weight suspended as shown in FIG. And measure the amount of curl. The curl rate is calculated by dividing the curl amount (mm) by the film thickness (mm).

When the curl rate was less than 100, ○ The curl rate was 100 or more and less than 150. Δ The curl rate was 150 or more.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments.

Example 1 (Tables 1 and 2) Polyethylene terephthalate (PET) pellets obtained by various methods were dried in a vacuum at 180 ° C. for 4 hours, fed to an extruder and melted at a temperature of 280 ° C. After passing through a filter, the mixture was extruded from a die and cooled and solidified on a casting drum having a surface temperature of 25 ° C. by using an electrostatic application method to obtain an amorphous unstretched PET film. The unstretched film is heated up and down by a vertical stretching machine in which a diffused infrared radiation heater with a reflector is installed vertically.
stretching section 270 while heating both sides of the film at kW / m
It was stretched 3.3 times in the longitudinal direction in mm. At this time, the temperature on the front surface of the film was 98 ° C., the temperature on the back surface of the film was 97 ° C., and the difference was 1 ° C. Successively, 105 ° C with a stenter
And then heat-treated at 225 ° C. for 3 seconds. The thickness of the obtained film is 100 μm,
The ratio of the surface roughness Ra of the front and back of the film was 1.05, and the ratio of the refractive index of the front and back of the film was 1.002. When the figure winding and curl rate of this film were measured,
Good with no wrinkles or end face deviations, with a curl rate of 20
Was very good.

Examples 2 to 4, Comparative Examples 1 to 3 (Tables 1 and 2) Using the same pellets as in Example 1, using the same extruder and stretching apparatus as in Example 1, the transverse stretching conditions were In the same manner as in Example 1, stretching was performed biaxially in the vertical and horizontal directions. Table 1 shows the longitudinal stretching conditions.
In addition, the properties of the obtained film were as described in Table 2. When the ratio of Ra on the front and back of the film is within the range of the present invention, the rolled form and the flatness were both good, but when the ratio of Ra was out of the range of the present invention, the rolled form and / or the flatness were both good. Was bad.

[0028]

[Table 1]

[Table 2]

[0029]

According to the present invention, the ratio of the surface roughness Ra of the front and back surfaces of a biaxially oriented polyester film having a thickness of 50 μm or more is set to 1.3 or less, thereby improving the winding shape and flatness after cutting the film. It is intended to improve the workability and the quality of the final product when used in various applications such as graphic, plate making, magnetic recording media, packaging and the like.

The biaxially oriented polyester film of the present invention can be widely and effectively used in various applications other than the above applications.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a method for measuring a curl rate for evaluating the effect of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67:00

Claims (4)

[Claims] 1. A film having a thickness of 50 μm or more,
A biaxially oriented polyester film, wherein the ratio of surface roughness Ra on the front and back of the film is 1.3 or less. 2. The biaxially oriented polyester film according to claim 1, wherein the refractive index ratio between the front and back surfaces of the film is 1.01 or less. 3. The method for producing a biaxially oriented polyester film according to claim 1, wherein the temperature difference between the front and back of the unoriented film in the longitudinal direction is 10 ° C. or less. . 4. The method according to claim 1, wherein, when the unoriented film is stretched in the longitudinal direction, the stretching is performed while heating by a heater of an infrared radiation type in a stretching section of 400 mm or less, and on both sides of the film. Item 4. The method for producing a biaxially oriented polyester film according to any one of Items 3.