JPS60228123A - Manufacture of biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain economically the high-quality titled film which is flat and superior in lubricity and adhesive properties, by a method wherein an amorphous state film made of polyethylene terephthalate is oriented in a longitudinal direction in a plurality of times and then the film is oriented in a lateral direction. CONSTITUTION:Super-draw orientation of an amorphous state film having polyethylene terephthalate for its main ingredient is performed desirably at magnification of more than 1.9 times at the temperature of 100-150 deg.C so that an index of birefringence becomes 0.001-0.020 in a longitudinal direction, to begin with, and then the same is oriented into 1.3-3.5 times at the temperature of 80-120 deg.C so that the index of birefringence becomes 0.015-0.055 in the longitudinal direction. Then after the film has been oriented into 1.1-2.0 times at the temperature of 85-120 deg.C and longitudinal orientation magnification of the same has been made more than 4.0 so that the index of birefringence becomes 0.040-0.080 in the longitudinal direction further, the film is oriented in a lateral direction at orientation magnification of 2.5-5.0 at the temperature of 90-140 deg.C and an aimed product is obtained by fixing the same thermally at the temperature of 150-250 deg.C further.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a biaxially oriented polyester film. For more details, please refer to the following for more details. However, it is an extremely useful film, especially as a base film for magnetic tapes.

In particular, with the rapid spread of video, there is a demand for high quality and inexpensive video magnetic tapes. In order to meet these demands, the biggest challenge has become how to reduce costs while maintaining the high quality of the base film.

Up until now, improvements in the quality of base films for magnetic tapes have been
This goal has been achieved using a wide variety of methods, but in particular, films that increase the longitudinal stretching temperature and lower the longitudinal stretching ratio compared to the commonly used one-step stretching method improve the flatness and smoothness of the film, as well as the adhesion with the magnetic layer. It is known to be extremely superior in

(JP 7-66936.37-/l'9122, r
r-J-? 3.2 J, 31-! 317/5',
! I-2/1722, jr-717, 29 and 61-
760123, etc.).

[Problem that the invention seeks to solve]

Although high quality is being realized by the above-mentioned method, the film obtained by the above-mentioned method is...

Since the film has a low orientation in the longitudinal direction and the degree of plane orientation after biaxial stretching and fixation is as low as possible, it has the disadvantage that the longitudinal stretching ratio must be lower and lighter than normal stretching formulations. Were present. However, the productivity during polyester film production strongly depends on the winding speed and the overall stretching ratio in the longitudinal direction.
This comes at the expense of productivity.

Therefore, in order to eliminate the above-mentioned drawbacks, the present inventors filed a patent application
-/6194, etc., we have proposed a method of increasing the stretching ratio while maintaining product quality.

However, since this stretching method performs longitudinal stretching in two stages, the longitudinal stretching ratio before the transverse stretching is about ≠, θ times, which is approximately the same as the conventionally known normal stretching ratio. Currently, as long as ln after longitudinal stretching is set to o, oro or more, even if the method of the above application is followed, other stretching methods (
Tokukai 60-7! , 10-/34361. Oh Lbij#
- J'47.2, etc.), a stretching ratio of more than 100% has been achieved. However, as in the previous proposal, if the longitudinal stretching ratio before the lateral stretching was at most ti, o times, it was impossible to reduce the cost even if it was possible to maintain the current level. Therefore, while maintaining high quality,
In order to reduce costs, it is strongly required to further increase the longitudinal stretching ratio before transverse stretching while keeping the birefringence after longitudinal stretching as low as possible.

[Means for solving problems]

The present inventors aimed to answer such a request.

After careful consideration, we decided to increase the number of stretching stages in the longitudinal direction to three or more stages.
Moreover, by incorporating so-called super draw stretching in which no orientation occurs during the initial longitudinal stretching, and by keeping the birefringence low after longitudinal stretching, we have achieved flatness, easy slipping, and a magnetic layer. We have discovered a method that maintains high quality of the magnetic tape, such as adhesive properties, and allows stretching at a high magnification without worsening thickness unevenness.

That is, the gist of the present invention is as follows: (1) First, a substantially amorphous film containing polyethylene terephthalate as a main component is heated in the longitudinal direction so that the birefringence (Δn+) is o, ooi −o, O
.
〜0.061 (at least one step and second step stretching), then the birefringence (Δna) in the vertical direction on the page
Stretch in at least one stage (third stage stretching) so that O2θgo-o, oro, and stretch longitudinally and then transversely so that the longitudinal stretching ratio before transverse stretching is ψ, 0 times or more. This is a method for producing a biaxially stretched polyester film.

The polyester used in the present invention is a polyester containing 10% by weight or more of ethylene terephthalate units,
The remaining 20% by weight or less.

It may also be a copolymerized polyester or other polymer. The polyester may contain stabilizers such as phosphoric acid, phosphorous acid and esters thereof, additives such as titanium dioxide, particulate silica and kaolin, and lubricants.

In the present invention, an unstretched polyester film is first stretched in at least one step in the longitudinal direction so that ln is 0.00/-0,020. The purpose of the longitudinal stretching at this stage is to suppress the crystallization and orientation of the film as much as possible and stretch the film at an open rate. Therefore, if the stretching ratio is low,
It does not contribute to increasing the speed of stretching. A preferable stretching ratio in the first stage is 8 times or more. On the other hand, in the first stage, high magnification stretching is performed,
Moreover, it is virtually impossible to suppress crystallization and reduce Δnl to below o, ooi. On the other hand, if the stretching ratio is increased to make Δn1 more than o, o, 2o, the stretching ratio in the second and subsequent stages will not become high, and the overall longitudinal stretching ratio cannot be increased, which is not preferable. In order to stretch at a high draw ratio and make Δn1 in the range of 0.00/-0,0,20, it is necessary to apply so-called super draw stretching, and it is necessary to draw at a temperature higher than or equal to ioo°C and lower than or equal to izo°C. is preferred. At temperatures below 100° C., orientation progresses too much, which is undesirable. On the other hand, at temperatures above Izo° C., crystallization progresses too much, which is undesirable. It is preferable to cool the film obtained by K in this way (hereinafter referred to as "rB-0 film") to a temperature below the stretching wave glass transition temperature because the thickness becomes uniform.

The lower the orientation of the B-0 film, the better the stretchability of the film in the next step, so it is also possible to perform heat treatment to relax the orientation, if necessary. At that time, the heat treatment step for relaxing the orientation is such that the surface of the film after the first stretching is brought into contact with a roll Ic controlled at 100~/jO℃ for less than 3 seconds/03 times or more. It is something. When such orientation relaxation treatment is included, Δn7 of the film after orientation relaxation (hereinafter referred to as "B-l film") is o, ooi -o, o, y,
Must be within the range o. In the above-mentioned relaxation step, if the roll surface temperature is less than 100° C., the orientation relaxing effect will not be exhibited, and if it is 710° C. or more, the thickness uniformity will deteriorate.

In addition.

If the orientation is relaxed for a long time, crystallization may proceed too much, which may deteriorate the lateral stretchability. The preferable range of Δn1 of the film after the first stage stretching is from o, ooi to 0.0.
/ Less than 2.

The thus obtained B-0 or B-1 film in which Δn1 is in the range of o, ooi to 0.020 is then preferably heated to a temperature of 20° C. to 1, 3 to 7
Birefringence (Δn2) is 0.0/j −0 at a stretching ratio of
, Ojj in the longitudinal direction of the device.

If the Δn2 of the film after the first-stage stretching is lower than 0.01j, it is not preferable to reduce the ΔnH to θ, oro or less in the third-stage stretching because the thickness unevenness in the longitudinal direction will be extremely worsened.

On the other hand, if in2 is set to more than o, ozs in the first stage stretching,
This is not preferable because the thickness unevenness after the second stage stretching becomes worse at Kt to such an extent that it cannot be corrected in the final stage process. However, according to the method of the present invention, Δn2 after the second stage stretching is o, oiz ~
o, osj range, the thickness unevenness after the second stage stretching cannot be said to be extremely good, but surprisingly, the thickness unevenness can be rapidly corrected in the next final stage stretching step. . Note that Δn2 is o, ois without third-stage stretching.
It is not preferable to simply carry out transverse stretching after finishing the longitudinal stretching while keeping the film in the range of -o, orz, since the thickness unevenness in the film will deteriorate and the mechanical properties in the longitudinal direction will be insufficient. on the other hand,
In order to compensate for uneven thickness and lack of mechanical strength, a method is known in which a film having Δn2 in the range of o, otz to o, oss after the second stage stretching is horizontally stretched, and then longitudinally stretched again. (% Kaisho TR-IIR 2 Co. No. 0, etc.) However, this method requires a re-stretching machine for the balance film for re-stretching, which naturally increases the equipment cost. In addition, Δnz after the second stage stretching in the method of the present invention
it, preferably in the range of o, o-o-o, o-da-j, more preferably in the range of 0.02j to o, oIIz.

Thus, in order to obtain a film that is excellent in both flatness and slipperiness and uneven thickness, it is essential to perform longitudinal stretching and then proceed to the transverse stretching step according to the method of the present invention.

If the temperature of the second stage stretching is below rθ°C, the film becomes thick and thin due to necking stretching, which is not preferable. On the other hand, 120
If the temperature is higher than 0.degree. C., the degree of crystallinity after longitudinal stretching becomes too high, making transverse stretching difficult.

In addition, since the lower the temperature, the better the stretchability is, more preferably Ioz
below ℃. From B-〇 or B-l film with Δnl of 0.0-〇 or less, Δn2 is 0.0/jt~0.0! r
The number of stretching stages in the second stage of stretching to produce the film after the Jo λ stage stretching is 7 to 3 stages. t, bΔn2=0.0/! It is also possible to stretch multiple times between t and o, o t t. However, it is preferable that '' be drawn in one stage. Further, if the stretching ratio in this process is /,3 or less, there is little contribution to improving the stretching ratio and it is unsuitable for this purpose. On the other hand, 3. In order to stretch the film at a high draw ratio of more than double, it is necessary to stretch at a high temperature, but as a result, the degree of crystallinity after longitudinal stretching is too high, making transverse stretching difficult. . Naturally, it is preferable to apply an orientation relaxation process in this process. The film thus obtained is hereinafter referred to as "B-λ
”.

Then, as the third stage of stretching, the birefringence (
The film is stretched in the longitudinal direction so that Δn3) does not exceed o or oro. The stretching temperature in the final stage stretching process in the longitudinal direction is
If it is too low, the thickness unevenness of the biaxially stretched film will not be improved even if Δn3 is less than o or oro, and if it is higher than 120°C, the transverse stretchability will be deteriorated. Therefore, in order to improve thickness unevenness, the temperature is preferably 0°C or higher. More preferably,
℃ or higher. Furthermore, in the third stage stretching, Δn3 is 0.
．． 0IO to o, o r o, preferably o, ozz to 0.07, more preferably o, o 6° to 0.07
It is advantageous for K to be stretched so as not to exceed 0 in order to facilitate flatness and prevent breakage during lateral stretching. The third stage stretching is
It is usually carried out as the final step of the longitudinal stretching process, and is preferably carried out in one step in a short period of time.

The surface of the rolls used in the longitudinal stretching process described above is made of ceramic or entomer (e.g., a copolymer mainly composed of propylene hexafluoride and vinylidene fluoride, silicone resin, ethylene propylene copolymer, chlorosulfonated polyethylene, etc.) or fluororesins such as tetrafluoroethylene/perfluoropropyl vinyl ether copolymer, tetrafluoroethylene, or tetrafluoroethylene filled with polyimide, etc. Preferably, it is coated.

Note that materials other than those mentioned above may be used as long as they have a large heat transfer coefficient and are not prone to adhesion. Note that the heating in the longitudinal stretching step may be performed in combination with a method other than the above-described heat transfer from the rolls (for example, using a radiation heater, hot air, in a heat medium), etc.

The longitudinally stretched film obtained by the method described above is
Although it can be used at
-/(stretched in the transverse direction at 40°C, stretching ratio j to j, 0 times, and further heat-set at /j O-210°C to obtain a film with excellent dimensional stability.Furthermore, re-stretched. It is also possible to make a tensa film in the longitudinal direction, a tensa film in the transverse direction, and a tensa film in the longitudinal and lateral directions.
After stretching i, i to 3.0 times at 0-170°C using wide rolls in the longitudinal direction, //5O
Heat treatment at -230°C is recommended.

According to the method of the present invention, the longitudinal stretching step before the transverse stretching is performed in three or more stages, and the longitudinal stretching ratio before the transverse stretching is μ, θ times or more, preferably μ, 1 times or more.

〔Effect of the invention〕

According to the method of the present invention, without amplifying thickness unevenness,
Moreover, it maintains the flatness and smoothness and excellent adhesion properties suitable for magnetic tape, especially as a base film for video.
Since the longitudinal stretching magnification before lateral stretching can be made extremely high, manufacturing costs can be reduced.

〔Example〕

The present invention will be explained below with reference to Examples, and the method for measuring the properties of the film is as follows.

(1) Thickness Using a continuous film thickness measuring device manufactured by Madara Anki Denki Co., Ltd., the thickness was measured along the longitudinal direction at the horizontal center of the biaxially stretched film, and the thickness was calculated according to the following formula.

(2) Coefficient of dynamic friction (μd) Fixed hard chrome-plated metal roll (diameter A was
), the film is brought into contact with the wrapping angle /310 (so
j,? Apply a load of f (T2) to one end / m /
By running this at a speed of m, the resistance force at the other end (T+ (f
) ) was measured, and the coefficient of friction during running was calculated using the following formula.

(3) Center line average surface roughness (Ra) Measured as follows using a surface roughness measuring instrument (SFi-JFK) manufactured by Koita Research Institute. The tip radius of the stylus was 2 μm, and the load was 30η. A part with a reference length L (, 2, 7wn) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve is created by taking the center line of this extracted part as the lx axis and the vertical magnification direction as the y axis. y = f (When expressed as xi, the value given by the following formula is expressed in μm. However, the cutoff value is I Opm. Ra is 5 points in the vertical direction and 5 points in the horizontal direction.
The average value of a total of 10 points was calculated.

one! jJJf: l f(x) f ax (4) Intrinsic viscosity ([da]) Sample 200■ is phenol/tetrachloroethane = rO
The mixture was added to 20 yd of a mixed solution of /10 and dissolved by heating at about /10°C for 1 hour, and then measured at 30°C.

(5) Birefringence The retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and the birefringence (Δn) was calculated using the following formula.

Δn=− where R; retardation d; film thickness 6) Film temperature The temperature of the film at the stretched portion was measured using an infrared radiation thermometer manufactured by Burns.

Example 1 (Manufacturing method of polyester) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.10 part of calcium acetate hydrate, and 0.1 part of thiium dihydrate in vinegar. /7 parts was charged into a reactor, heated to raise the temperature, and methanol was distilled off to perform a transesterification reaction.After the start of the reaction, it took some time to reach 230T, and the transesterification was substantially completed. .

Next, 0.0% triethyl phosphate was added to the reaction product. ．． 3
! After addition of o and or parts of antimony trioxide as a polycondensation catalyst, polymerization was carried out according to a conventional method to obtain a polyester. The polyester has a particle size of approximately 0.
A large number of uniform and fine precipitated particles containing calcium, lithium, and phosphorus elements of about 3-/μ were interspersed. The polyester A had [η) = o, b s.

Separately, polyester B ([η”J=0.61) containing almost no such internal precipitated particles was produced and mixed with the above polyester at a ratio of A/B = i/l (weight ratio). It was used as a raw material for membranes.

(Film Forming Method) The unstretched polyethylene terephthalate film was formed into a biaxially stretched film using a longitudinal stretching device and a tenter (lateral stretching and heat setting device). The details of the film forming method are described below.

First, after drying the raw material polyester, it is melt extruded to a thickness of 1A.
An unstretched film ([η]=0.62) of O-200μ was obtained. Next, the film was passed through a longitudinal stretching device, and after being preheated to rj°C with the first few rolls, the film was stretched to 2.0°C at a roll temperature of 30°C due to the difference in circumferential speed between the low speed roll and the high speed roll.
The film was stretched 3 times in the first stage to obtain a film with Δfll = 0.006. Subsequently, the second stage stretching is carried out by 2.0 times at a roll temperature of rz°C using the peripheral speed difference between the first stage low speed roll and the high speed roll, and Δn2 = 0. A film of OFO was obtained. Furthermore.

The same film was passed through the third stage of stretching rolls to a temperature of J℃.
The third stage of stretching was carried out at a stretching ratio of 8 to 8 to give Δna=0. OA
A film of j was obtained. In addition, between the stretching rolls in the first-stage stretching and the third-stage stretching, an infrared heater is used in combination to heat the rolls, and an infrared radiation thermometer is used to measure the first-stage stretching and the The film temperatures in the three-stage stretching section were measured to be 1.20°C and 103°C, respectively. The thus obtained longitudinally stretched film was stretched in the transverse direction by a factor of 3.1 at 1tIo°C using a tenter.
A biaxially stretched film having a thickness of /jμ was obtained by heat setting with zirc.

Example K The λ-th stage stretching temperature was set from rr°C to 102°C, and the stretching ratio was 1. The thickness trμ was made in the same manner as in Example 1 except that it was multiplied by j.
A biaxially stretched film was obtained.

Comparative Example 1 Child heating was carried out in the same manner as in Example/, and as the first stage stretching, the stretching roll temperature/30°C stretching ratio was 3. After performing the first stage stretching at q times to obtain a film with Δn=o, oao, the second stage stretching was performed at a roll temperature of 5°C between the second stage stretching rolls, and 21 times stretching, Δn=0.063. A longitudinally stretched film was obtained.

After the lateral stretching, the same treatment as in Example 1 was performed, and the thickness/j
A biaxially stretched film of μ was obtained. Infrared heater heating was used in both the first and second stage stretching.

Comparative Example λ Child heating was performed in the same manner as in Example 1, and infrared heater heating was also used on the first drawing roll, and the transverse drawing temperature was set at /1 with the roll.
After transverse stretching at 0° C. and a transverse stretching ratio of 3.2 times, the film was heat-set at 2/j° C. to obtain a biaxially stretched film having a thickness of ljμ.

Table 1 shows the properties of each of the above films.

As is clear from Table 1, by lowering Δn after longitudinal stretching, the flatness and smoothness are good, and by performing three-step stretching, the stretching ratio is extremely high despite the low Δn after longitudinal stretching. In addition, a film suitable for magnetic tape with small thickness unevenness can be obtained.

Table l

Claims (1)

[Claims]
+) is 0.00I No. 020 (first stage stretching), and then the birefringence index (Δzu) in the longitudinal direction is 0.0/j to 0.011. Stretching is performed in at least one stage (second stage stretching), and then stretched in at least one stage (third stage stretching) so that the birefringence index (Δns) becomes o, oao-o, oro in the longitudinal direction of the page. stretching),
A method for producing a biaxially stretched polyester film, which comprises longitudinally stretching the film so that the longitudinal stretching ratio before the transverse stretching is 1.1.0 times or more, and then transversely stretching the film. (2) The first stage stretching is carried out at a temperature of 0°C or more and 10°C or less, and the 3rd stage drawing is carried out at a temperature of 0°C or more and 0°C or less.
98. The method for producing a biaxially stretched polyester film according to claim 97, wherein the stretching is carried out at a temperature of 1.20° C. or higher and 1.20° C. or lower. (3) The method for producing a biaxially stretched polyester film according to claim 1 or 2, wherein the first stage stretching ratio is at least 100%.