JP2618463B2 - Stretched film manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a direction (TD) perpendicular to a flow direction (MD).
And a method for producing a porous stretched film which is further stretched in the machine direction (MD).

[Conventional technology]

When manufacturing a porous stretched film, in the stretched film manufacturing method performed in the MD stretching step after the TD stretching step, MD
When the film is weakly stretched during stretching, uneven stretching occurs, and when the film is strongly stretched, troubles such as breakage of the film easily occur, and it is difficult to perform stable continuous stretching.

MD stretching after TD stretching in stable state without trouble
In order to improve the draw ratio of the stretched film to produce a biaxially stretched film having an excellent balance of physical properties, the conventional method for producing a stretched film had to be reviewed.

[Problems to be solved by the invention]

The object of the present invention is that there is no trouble such as uneven stretching and stretching breakage, and furthermore, the physical properties of TD and MD are excellent, and furthermore, it is possible to carry out MD stretching stably while performing MD stretching at a high magnification after TD stretching. It is to provide a method for producing a stretched film.

[Means for solving the problem]

The present inventors have diligently studied to achieve the above object,
Finally, the present invention has been reached.

That is, in a method for producing a porous stretched film in which the film is stretched in a direction perpendicular to the flow direction and further stretched in the flow direction, the film stretched at least two times in the direction perpendicular to the flow direction is formed. This is a method for producing a stretched film, wherein the film is contracted by 10% to 50% in a direction perpendicular to the film and then stretched in a flow direction.

In the method for producing a porous stretched film of the present invention, the unstretched film is forcibly heat-shrinked from the outlet of the TD stretcher to the entrance of the MD stretcher after TD stretching. Heat shrinkage is above TD stretching temperature,
It is performed in the range of 10% to 50% to TD at a resin melting temperature of -5 ° C or less. Preferably it is 20% to 35%.

When the temperature is lower than the TD stretching temperature, the film is unlikely to be thermally shrunk, and when the temperature exceeds the resin melting temperature of −5 ° C., it is difficult to obtain porosity of the film. If the heat shrinkage is less than 10%, unevenness or stretching breakage occurs during MD stretching, and if it exceeds 50%, it becomes difficult to balance physical properties.

After the forced heat shrinkage as described above, if the MD stretching is performed by heating sufficiently at an appropriate temperature, the occurrence of uneven stretching and stretch breakage can be suppressed, and continuous production of the film at a high MD stretching ratio becomes possible. .

Examples of the unstretched film applicable to the present invention include a film formed by blending an inorganic filler and an additive to be blended as needed with a thermoplastic resin.

〔Example〕

 Hereinafter, embodiments will be described.

Examples 1 to 5 and Comparative Examples 1 to 2 100 parts by weight of polyethylene (LLDPE manufactured by Mitsubishi Yuka Co.) were mixed with 150 parts by weight of barium sulfate powder and 1.25 calcium stearate.
The mixture containing the parts by weight was formed into a film using a known extruder to obtain a film having a thickness of 300 μm and a width of 250 m / m.

After heating this film to 95 ° C using a known tenter
After stretching 5 times to TD, it was forcibly shrunk to the temperature shown in Table 1 with a heating roll, and further MD stretched under a stretching condition shown in Table 1 using a known roll stretching machine to obtain a porous stretched film. Obtained. The results are shown in Table 1.

Examples 6 to 10, Comparative Examples 3 to 4 100 parts by weight of polypropylene (manufactured by Mitsui Toatsu Chemicals), 177 parts by weight of barium sulfate powder and 1.2 parts by weight of calcium stearate
The mixture containing 5 parts by weight was formed into a film using a known extruder to obtain a film having a thickness of 300 μm and a width of 250 m / m.

This film was heated to 120 ° C. using a known tenter and stretched 5 times to TD. Then, the film was forcibly shrunk to the temperature shown in Table 1 with a heating roll, and further reduced to Table 1 using a known roll stretching machine. MD stretching was performed under the following stretching conditions to obtain a porous stretched film. The results are shown in Table 1.

(Effects of the Invention) The present invention improves the drawbacks of conventional techniques, such as stretch breakage and stretching unevenness occurring in MD stretching after TD stretching, and improves the drawbacks after TD stretching.
This is a method for producing a porous stretched film that can perform stable stretching even in TD stretching at a high magnification while being MD stretching.

Claims (1)

(57) [Claims] 1. A method for producing a porous stretched film in which a film is stretched in a direction perpendicular to the flow direction and further stretched in the flow direction, wherein the film is stretched at least two times in a direction perpendicular to the flow direction. After shrinking by 10% to 50% in a direction perpendicular to the flow direction, and then stretching the film in the flow direction.