JPS5936851B2 - Manufacturing method of polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a film with excellent slipperiness from a substantially amorphous film containing polyethylene terephthalate (hereinafter abbreviated as PET) as a main component; Specifically, the present invention relates to a method of stretching a rapidly cooled PET film in three stages in the longitudinal direction to change the state of particles appearing on the surface of the film to further impart slipperiness.

Conventionally, the method of stretching a film in two or more stages is
Various methods are known, but these known methods do not significantly improve slipperiness compared to the conventional one-step stretching.

In particular, when a film stretched in the longitudinal direction by the above-mentioned known method is further stretched in the perpendicular direction to form a biaxially stretched film, the smoothness is better than that obtained by horizontally stretching a conventional single-stage longitudinally stretched film. You can only get practically the same thing. That is, even if various conditions are changed in the known multi-stage stretching method, the slipperiness not only is not improved but is even worsened, and thickness uniformity, film haze, etc. are worse than in the conventional one-stage stretching method. In particular, the reality is that it is hardly used in the production of PET films. The inventors have l
We have diligently studied a multistage stretching method that takes advantage of the uniformity of thickness, haze, and stable productivity during horizontal stretching, which are the characteristics of longitudinal stretching, and have developed a multistage stretching method to produce a film with excellent slipperiness. It was reached.

That is, the gist of the present invention is to obtain amorphous PE obtained by a conventional method.
After stretching the T film in the longitudinal direction (first step) so that the birefringence becomes 1.0 to 12 x 10-0, the surface temperature becomes 100-
While in contact with a roll at 150°C for 0.5 seconds or more, stretching is carried out by 1.03 times or more in the longitudinal direction (second stage), and further 8
The purpose is to stretch the film by 2.5 to 4.5 times in the longitudinal direction at a temperature of 0 to 1.20°C (third stage).

By further stretching the l-axis stretched film thus obtained in the transverse direction by 2.5 times or more using a conventional method and heat-treating it, the thickness uniformity, haze, etc. are the same as those of the one-step longitudinal stretching method, and the film is easy to slip. An unprecedented biaxially stretched film with improved properties can be obtained.

Aspects of the present invention will be explained in detail below.

The polyethylene terephthalate in the present invention has 80% or more of terephthalic acid as the acid component, and the glycol component consists of 80% or more of ethylene glycol, and may also be a copolymer or blend of other components with different amounts and types. good.

In addition, the polymer used may contain phosphoric acid and its esters or inorganic particles (silica, kaolin, calcium carbonate, calcium phosphate, etc.) during the polymerization step, or inorganic particles may be blended with the polymer after polymerization. Good too.

After sufficiently drying the polymer obtained in this way, the
The mixture is melt-molded through an extruder controlled at 0°C, a filter, and a die, and cast onto a rotating drum to obtain a rapidly solidified film.

This rapidly cooled film is substantially in an amorphous state (hereinafter referred to as A film). Next, the amorphous film is stretched in the longitudinal direction at a temperature higher than the glass transition temperature, and the birefringence (hereinafter referred to as Δn) is
The film is 1.0 to 12% 10-3 (hereinafter referred to as B-1 film). The birefringence index is determined by the following method. That is, the birefringence is determined by determining the retardation value using a polarizing microscope and a Bereck compensator, and calculating the birefringence (Δn) from the following equation.

If the Δn of the B-1 film is less than 1.0×10-3, the slipperiness will not improve even if the subsequent steps are optimized;
If it is 0-3 or higher, crystallization will progress significantly in the subsequent steps, and even if the longitudinal stretching conditions in the second and subsequent stages are optimized within the scope of the present invention, especially when subjecting to biaxial stretching, the film cannot be held with clips during transverse stretching. This is not preferable because it causes frequent breaks in the vicinity of the surface, making it difficult to obtain stable manufacturing conditions. It is preferable for the B-1 film to be cooled to below the glass transition temperature after stretching in terms of thickness uniformity. Next, the B-1 film was brought into contact with a roll whose surface was controlled at 100 to 150°C for 065 seconds or more, and 1.
A B-2 film is obtained by stretching 03 times or more. In the main stretching step, if the roll surface temperature is less than 100°C, no slipperiness will be imparted, and if it is 150°C or higher, the thickness uniformity will deteriorate. When producing a biaxially stretched film using this film, it is necessary to suppress the thermal crystallization of the B2 film as low as possible, and in the case of PET, the average crystallinity of the entire B-2 film in the thickness direction is 8% or less. preferable. However, crystallinity C
is a perfect crystal. These values were determined by assuming a density of 1.45t/C77i and a completely amorphous density of 1.33y/d.

In other words, in the case of biaxial stretching, the increase in crystallization in the second stage of stretching should be limited to the surface layer of the film at most, and the formation of microcrystals should be suppressed as much as possible in the film thickness direction as a whole. becomes the point.

Therefore, the roll surface temperature during the second stage stretching was 150℃.
Even in this case, it is preferable to keep the film temperature at most 135° C. or lower. If the contact time to the roll is less than 0.5 seconds, slipperiness will not be imparted. Although the necessary contact time depends on the degree of request for imparting slipperiness, a condition of 1.5 seconds or more is usually preferably used. When producing a biaxially stretched film using this film, this process should be completed within 10 seconds at most in order to obtain stable production. Stretching ratio is 1.0
If it is less than 3 times, the thickness uniformity deteriorates and the slipperiness effect decreases, which is not preferable. The maximum magnification in this step depends on the surface temperature of the rolls being brought into contact, but should be kept to 1.30 times or less. If it exceeds 1.30 times, the slipperiness will improve, but the haze of the film will also increase, and the crystallinity will also increase to 15% or more, making it impossible to biaxially stretch the film, so it is preferable. do not have.

The roll surface materials used in this process include ceramics, elastomers (Viton (a copolymer mainly composed of propylene hexafluoride and vinylidene fluoride, a trade name manufactured by DuPont), silicone, EPT (ethylene propylene copolymer), Hypalon (chlorosulfonated polyethylene), etc., or fluorine resins such as polyfluorinated ethylene, etc.
Although it is preferable that the roll be coated, other materials than the above may be used as long as the heat transfer coefficient is smaller than that of the chrome-plated roll and the material does not cause significant adhesion. Note that the effects described in the present invention will not be achieved if the heating for stretching in this step is performed by a method other than heat transfer from the rolls as described above (for example, using a radiator heater, hot air, or in a heat medium). The effects of the present invention can be obtained by optimizing the conditions for the combination of heating by rolls and other heating means. It is preferable that the roll at the end of stretching of the B-2 film is driven as necessary and has a structure in which the film can be nipped with non-adhesive rolls. Next, it is longitudinally stretched 2.5 to 4.5 times at a temperature of 80 to 120°C (
B-3 film) process begins. If the stretching temperature is less than 80° C., the orientation after stretching becomes high, the boards near the particles in the film become large, and the haze becomes high.

In particular, biaxial stretching is undesirable because the film tends to tear easily due to the preceding and following reasons, and only a film with high haze can be obtained. If the temperature exceeds 120°C, it is difficult to stably obtain a film with an appropriate degree of orientation, so especially when used for biaxial stretching, the film tends to break easily and the strength in the biaxial direction is insufficient. This is not preferable because it causes a mixture of the above and the like, and also worsens the thickness unevenness in the width direction.

In this step, any one of a method of drawing using rolls, a method of drawing with a flip pass with radiation provided between the rolls, a method of using hot air as a heating source, or a combination thereof may be used.

The stretching temperature here refers to the temperature of the film at the start of stretching, and when controlling the temperature with a group of rolls, if a sufficient number of rolls are installed, the temperature of the roll surface can be approximately ±
The film temperature is within 2℃. If the stretching ratio in this step is less than 2.5 times, the thickness uniformity will deteriorate, which is undesirable.
．． When the temperature exceeds 5 times, thermal crystallization is significantly promoted, especially for B.
-3 When a biaxially stretched film is produced by stretching a film in the transverse direction, it is difficult to obtain stable manufacturing conditions because the film frequently breaks near the clips gripped during the transverse stretching. In addition, if the roll material etc. are optimized, the second stage stretching and the third stage stretching are
Since stretching can be performed at almost the same temperature, by placing a single-drive nip roll between the second and third stages, it is possible to directly stretch the film in the third stage without preheating. be. The film obtained by the above method can be used as it is, with high strength in the longitudinal direction, excellent slipperiness, and a uniform thickness. Stretching temperature 90 to 1 by conventional method in direction
Biaxially stretched 2.5 to 4.0 times at 40°C, 150 to 24
A film with excellent dimensional stability can be obtained by heat setting at 0°C, and in the case of longitudinal re-stretching, the transverse stretching can be carried out at 80°C.
~130℃, 2.5~4.0 times, stretched 1.3~3.0 times at 90~170℃ using wide rolls in the machine direction, and then heat treated at 160~240℃. A film with sufficient strength and slipperiness can be obtained.

Next, the drawings will be explained.

FIG. 1 is a diagram showing an example of a one-stage stretching apparatus for longitudinal film stretching of the present invention.

In the figure, rolls 1 and 8 are chrome-plated drive cooling rolls, roll v is a rubber-lined nip roll,
Rolls 2 to 7 are floating heating rolls made of Viton A (a copolymer of propylene hexafluoride and vinylidene fluoride, trade name of DuPont Co., Ltd., wall thickness: 2 m77!). FIG. 2 is a diagram showing an example of a two-stage stretching apparatus for longitudinal film stretching of the present invention. In the figure, rolls 9 and 15 are chrome-plated driving cooling rolls, rolls 10 to 14 are Viton A
(Same as above: wall thickness 3 mu) floating heating roll. Roll 15' is a rubber-lined nip roll. The gap between each roll is 2m77 to prevent slipping on the roll as much as possible! Also, the torque on the roll surface is 120V for rolls 2 to 4, and 120V for rolls 5 and 4.
6 is adjusted to become 507. FIG. 3 is a diagram showing an example of a three-stage stretching apparatus for longitudinal film stretching of the present invention. In the figure, rolls 15, 21, and 22 are chrome-plated driving cooling rolls, and rolls 16 to 20 are floating heating rolls made of Hypalon 40 (trade name of DuPont, wall thickness: 2 mm). FIG. 4 is a diagram showing an apparatus in which the first-stage stretching zone (1), the second-stage stretching zone 01), and the third-stage stretching zone (E) of the film longitudinal stretching apparatus of the present invention are connected.

Each port is the same as shown in FIGS. 1 to 3 above. Example 1 Polyethylene terephthalate with an intrinsic viscosity of 0.60 (0.1% carrion with an average particle size of 2.3μ) polymerized by a conventional method
(added during polymerization) was dried at 170°C for 3 hours, extruded at 285°C, brought into contact with a rotating drum maintained at 30°C in sheet form from a T-die, and rapidly solidified to form a sheet with a width of 300 mm and a thickness of 20 mm.
An unstretched film of 0μ was obtained.

Note that a known electrostatic casting method was used to bring the molten polymer into close contact with the rotating drum. Next, longitudinal stretching was performed using the apparatus shown in FIG. 4 under the following conditions.

At this time, stretching was substantially performed between rolls 5 and 7 in the first stage, between rolls 10 and 14 in the second stage, and between rolls 18 and 20 in the third stage.

The temperature of the film on roll 18 was measured with an infrared non-contact thermometer and was found to be about 105°C. Next, horizontally 3
．． After stretching the film 6 times at 110°C, it was heat-treated at 220°C to obtain a biaxially stretched film with a thickness of 11μ. The winding speed after biaxial stretching is about 90 m/min, and the heat treatment time is 4 seconds.

Comparative Example 1 The same unstretched polyethylene terephthalate film as in Example 1 (thickness: 130 μm, width: 30011 mm) was stretched in one stage through the first and second stages of the apparatus shown in FIG. 4, starting from roll 15 and thereafter.

The stretching conditions were 110°C and 3.5 times. In addition, in this comparative example, stretching was substantially performed between rolls 19 and 20, and the film temperature on roll 19 was measured in the same manner as in the example and was 90°C, Δn=8.6×10 -2
It was hot. This film was laterally stretched and heat treated under the same conditions as in Example 1. Comparative Example 2 An unstretched film under the same conditions as Example 1 was longitudinally stretched under the following conditions.

The third stage of stretching is substantially carried out between rolls 19 and 20 in FIG. 4, and the film temperature on roll 19 is 10.
It was 9℃.

This film was laterally stretched and heat-set under the same conditions as in Example 1 to obtain a biaxially stretched film of 11μ. Example 2 Biaxial stretching was carried out under the same conditions as in Example 1 except that the temperature of rolls 10 and 11 was lowered to 60°C.

/''Comparative Example 3 A biaxially stretched film was obtained under exactly the same conditions as in Example 2 except that the second stage stretching ratio was lowered to 1.01.

Example 3 In Example 1, the surface temperature of rolls 16 to 20 was set to 20
Longitudinal and horizontal stretching were carried out under exactly the same conditions except that the temperature was lowered to ℃.
A biaxially stretched film was obtained.

In this example, the third stage of longitudinal stretching is substantially carried out by rolls 15 and 1.
The temperature of the film immediately after coming out from the roll 15 was 108°C. Examples 1-3, Comparative Examples 1-
The properties of the film obtained in step 3 are shown in the following table.

These results can be summarized as follows.

(1) A comparison between Example 1 and Comparative Example 1 (one-stage stretching) shows that according to the present invention, the friction coefficient decreases with the same haze and thickness unevenness. (2) Example 2 is a condition in which the contact time with the heating roll in the second drawing step is shorter than that in Example 1, but it can be seen that even under these conditions, the coefficient of friction is more advantageous than in Comparative Example 1. .

(3) Comparative Example 3 is a condition in which the second stage stretching ratio is outside the range of the present invention, and it can be seen that the haze and thickness unevenness are significantly deteriorated.

(4) In Comparative Example 2, both the second-stage stretching temperature and the stretching ratio were outside the range of the present invention, and it can be seen that the haze and friction coefficient were deteriorated.

(5) In Example 3, the second and third stages were essentially directly connected by sandwiching the Nipro rolls, and it was found that the friction coefficient and thickness unevenness were improved compared to Comparative Example 1. Understood 5/
0 Furthermore, according to the present invention, the overall longitudinal stretching ratio can be increased by the amount of the first stage magnification x the second stage magnification, that is, about 1.55 times, while maintaining the film quality at the same or higher level. If the speed of the unstretched film remains the same, the productivity, that is, the manufacturing speed, can be increased by as much as 55%.

For example, if the upper limit of the production speed when obtaining a biaxially stretched film by ordinary one-stage longitudinal stretching is Vlm/Mm, the upper limit speed V2 according to the present invention can be obtained.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 are views of the first, second, and third stage stretching apparatus, respectively, for carrying out the method of the present invention. FIG. 4 shows an example of a film longitudinal stretching apparatus for carrying out the method of the present invention. Roll 1, 8, 9, 21
, 22: Cooling drive roll (chrome plating), roll 1
', 15', 22': Nituprol (Gum Lycong)
, Rolls 2-7, 10-14: floating heating rolls (Viton A), Rolls 15-20: floating heating rolls (Hypalon 40).

Claims (1)

[Claims] 1 A substantially amorphous film containing polyethylene terephthalate as a main component has a birefringence index (Δn) of 1 in the longitudinal direction.
．． After stretching it to 0 to 12 x 10^-^3, it is brought into contact with a roll having a surface temperature of 100 to 150 °C for at least 0.5 seconds at a stretching ratio of at least 1.03 times, and then stretched to 80 to 150 °C. A method for producing a polyester film, characterized by further stretching in the machine direction by 2.5 to 4.5 times at a temperature of 120°C.