JPS6392434A - Manufacture of thin biaxially stretched film - Google Patents

Abstract

PURPOSE:To make it possible to reduce the incidence of breakage of a film during lateral stretching and the amount of loss at the edge part of the film by a method wherein the thickness of the film at the position 10mm inward from the grasping part of the clip of a tenter is kept within the specified range. CONSTITUTION:During the manufacture of a biaxially stretched film, which is made of thermoplastic resin and the thickness of which is 5mum or less, with a tenter, the resin is stretched with the tenter in such a manner that the thickness H, mu, of the film at the position lying toward the middle of the film by 10mm from the grasping part of the clip of the tenter is kept within the range represented by a formula. In the formula, (t) denotes the thickness at the middle part of the film at the outlet of the tenter, mu; Z is lateral draw ratio; sigmaE represents the stress at yield of a film, which is in the state after unidirectional stretching and before the following unidirectional stretching, at the temperature of the clip of the tenter, kg/mm<2>; and sigmaC is the stress at yield in lateral stretching of a film under the longitudinally stretched state at the drawing temperature of the tenter, kg/mm<2>. Thus, during the manufacture of a stretched film having the thickness of 5mum or less, the frequency of the breakage of the film near an edge during the lateral stretching of the tenter is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing a biaxially stretched film of thermoplastic resin having a diameter of 5 μm or less by a tenter method.

More specifically, when stretching a thermoplastic polymer film in the width direction, it stabilizes operability by reducing accidents of film breakage within the stenter, and reduces loss of edge portions that do not become products. The present invention relates to a method for stably producing a biaxially stretched film of thermoplastic resin.

[Prior art and its problems] When stretching a film in the width direction, film breakage often occurs near the film edges for extremely thin films.
This breakage significantly reduces operability. In addition, when film breaks occur, the production stoppage time is short, in some cases for a few minutes, due to disposal of broken debris and re-inspection of equipment.
If it is long, it may take several tens of minutes, and extrusion from the die may continue, resulting in a loss of resin. Also, the work during this time will have a significant negative 1FU. The thinner the film, the more breakage accidents occur during the manufacturing process, especially 5.
The frequency of this phenomenon increases significantly in film forming and stretching of micrometers or less.

One of the reasons why the film tends to break when stretched in the width direction is presumed to be due to insufficient cooling of the tenter clip as described below. In a tenter, the side edges of the film are held with clips and stretched in the width direction, and the film is heat treated at a high temperature while the side edges of the film are held with the clips. The clip, together with the film, is exposed to high temperatures during heat treatment. When the film is taken out from the tenter, the clips are separated from the film and returned to the tenter, and the process of gripping the film again and stretching it in the width direction is repeated. By the way, the clip is not cooled down to the stretching temperature at the position where it is gripped for stretching the film, and is not sufficiently cooled from the state where it was heated during the heat treatment. At this time, if the temperature of the clip is higher than the stretching temperature, the film of the clip gripping portion is locally heated by the high temperature clip. In the stretching zone of the tenter, the film near the edges is at a higher temperature than the center and is more easily stretched.

Therefore, the area near the edge is locally stretched to a high magnification, and that area often becomes young, leading to breakage of the film.

This type of breakage occurs more frequently as the film thickness decreases, and to prevent this, preliminary measures such as thickening the film near the edges are taken, but the thickness of the film near the edges simply changes. However, if the film is too thick beyond the limit, stress concentration tends to occur near the clip gripping part (= J), and the clip and film get caught or become loose, making it more likely to break. .

Furthermore, if the end portions of the film are made thicker than necessary, the loss will naturally increase, which will be disadvantageous in terms of performance.

[Object of the Invention] The present invention has been devised by taking into account the problems of the prior art and examining various conditions for stable and less likely to break. In other words, when producing biaxially stretched thermoplastic resin films of 5 μm or less using the tenter method, it is possible to reduce the incidence of film breakage during stretching in the width direction of the film, and to reduce the loss of edge portions that do not become products. It is an object of the present invention to provide a method for producing a thin biaxially stretched thermoplastic resin film that can reduce the amount of water used.

[Configuration 1 of the Invention] The present invention provides a method for manufacturing a biaxially stretched thermoplastic resin film of 5 μm or less by a tenter method, in order to prevent the film from breaking, the thickness of the film is 1° C. at a position 10 mm from the tenter clip gripping portion. −1 (μm), σC /
, / is the transverse stretching ratio, σF is the clip temperature of the tenter d
σC is the yield point stress (kMm...2) of the stretched film after being uniaxially stretched at 3 times, and σC is the yield point stress (kMm...2) of the film stretched longitudinally at the stretching temperature of the tenter in the transverse direction. 2. A method for producing an axially stretched film.

According to the method of the present invention, when producing a stretched film of 5 μm or less, the frequency of film breakage near the edges during horizontal stretching in a tenter is reduced.

The cause of film breakage is that the clip that grips the film edge is in the tenter's lateral stretching process (heat setting zone).
When the heated clip is heated to a high temperature and is not cooled down sufficiently, it returns to the tenter, grips the film in the tenter, and advances to the stretching zone. When the film near the clip reaches a higher temperature than the central part and is laterally stretched in the stretching zone, the high-temperature end parts of the film are more easily stretched than the central part, and the film This is because the thickness becomes extremely thin and eventually breaks. The optimal thickness of the film V-J at or near the clip gripping portion varies depending on the stretching ratio at one denter portion, the clip temperature, and the stress at yield point of the film at the stretching zone temperature, as described above. If the film thickness is thinner than the above lower limit condition, the area near the edge will be stretched locally and the film thickness will become thinner in that area, causing operational troubles such as tearing of the film edge. If the thickness in the vicinity is thicker than the above upper limit condition, stress concentration tends to occur in the vicinity of the clip gripping portion, making it easy to warp and break. Needless to say, too much resin usage (loss) is generated at the discarded end portion of the film.

Film materials to which the production method of the present invention can be applied include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalene dipropoxylate,
Examples include thermoplastic resins such as high-density polyethylene, polypropylene, nylon 6, and nylon 66.

The present invention will be explained below with reference to Examples.

Example ■ and Comparative Example ■ (Experiment No. 1 to 17) Intrinsic viscosity 0
．． 60 [orthochlorophenol, 25°C] polyethylene terephthalate resin was melted at 280'C. It is cast onto a cooling roll at 40°C using a T-die and immediately cooled to produce an unstretched film. At this time, the film thickness at the ends and center of the unstretched film was adjusted and varied using a die thickness adjustment bolt.

This unstretched film was stretched in the longitudinal direction at a stretching ratio of 3.6 times, then widthwise (horizontally) stretched using a tenter, and further heat-set at 200°C to 230'C.

Table 1 shows the results. From the results in Table 1, 1 from the clip
It has been found that if the film thickness inside 0 mm does not satisfy σC Z X t X −<H≦zxtx5σF, problems such as frequent film breakage occur during stretching.

Example ■ When producing a 1.5 μm thick biaxially stretched film of polyethylene-2,6-naphthalene dicarpoxylate with an intrinsic viscosity of 0.7, the first stage stretching was carried out at 105°C for 30 minutes.
．． It was applied at a stretching ratio of 9 times, and then 122° in the second axis direction.
The film was stretched 4.1 times at C, further heat treated at 235°C, and rolled up at 110 m/min. At this time, the thickness of the ear end is 35
When the thickness was .mu.m or more, film breakage problems occurred due to stress concentration. Also, attach the tenter clip to 160'
It was also found that if the thickness of the edge portion was 12 μm, breakage was likely to occur unless the sample was cooled to below C.

[Effects of the Invention] According to the present invention, an extremely thin two-wheel stretched film of 5 μm or less can be produced under stable operating conditions. In addition, for bulky film, it is important to make the side edges of the film gripped with tenter clips about 2 to 5 times thicker than the center of the film to prevent breakage due to stress concentration, incorrect gripping of the clips, and excessive curling. This can avoid film breakage caused by this, and furthermore, the amount of edge loss can be minimized.

Claims (1)

[Claims] When producing a biaxially stretched film made of thermoplastic resin with a thickness of 5 μm or less using a tenter, the film thickness H (μm) at a position 10 mm closer to the center of the film than the gripping part of the tenter clip. , Z×t×σC/σE
<H≦5×Z×t A method for producing a thin biaxially stretched film comprising stretching with a tenter. [However, t is the thickness of the central part of the film at the exit of the tenter (μ
m), Z is the stretching ratio in the transverse (width) direction, and σC is the yield stress of the stretched film at the stretching temperature of the tenter (k
g/mm^2), σE is the yield stress of the stretched film at the tenter clip temperature (kg/mm^2)
.