JPS58198536A - Production of porous film having excellent air permeability - Google Patents

Abstract

PURPOSE:To obtain a porous film having excellent air permeability and various uses as permeable packaging materials, separating-filtering membranes, etc., by melt-kneading two kinds of thermoplastic resins having different melting points and poor compatibility with each other, molding the mixture into a film followed by stretching. CONSTITUTION:A thermoplastic resin A such as polypropylene having a m.p. of 160 deg.C is melt-kneaded with a thermoplastic resin B having poor compatibility with a resin A and a m.p. which is at least 20 deg.C higher than that of the resin A, such as a polycarbonate having a m.p. of 245 deg.C. The mixture is molded to a temp. higher than the m.p. of the resin A but lower than the m.p. of the resin B into a sheet which is then stretched at least monoaxially to obtain the titled porous film.

Description

[Detailed Description of the Invention] The present invention is a porous film with excellent air permeability!・Relates to the manufacturing method.

Conventionally, as a method for obtaining a porous film by a stretching method, for example, a method in which an inorganic powder is added to a polyolefin resin and then stretched; Many methods have been proposed in which two or more types of thermoplastic resins are melt-kneaded, molded, and stretched into a belt-like material. However, in the latter method, it is necessary to obtain a porous film with excellent ventilation, for example, a method of further adding powder of an inorganic substance, a method of adding a scarlet substance so as not to melt it, a method of adding Air permeability can be improved by methods such as extracting the material η before or after drawing it, or creating cracks or voids by mechanically deforming the arc-stretched sheet at low temperatures and creating cracks or voids. A method of improvement was being taken.

Nine porous films produced by these conventional methods are
The presence of additives such as inorganic fillers causes problems in chemical resistance, electrical properties, etc., and otherwise the manufacturing process requires 411 complicated steps.

The present invention provides a method for producing a porous film with excellent air permeability without using papermaking using an additive substance of an inorganic filler or complicated processes as in the above-mentioned conventional method. The gist is that a mixture of thermoplastic resin A and thermoplastic resin B, which has poor compatibility with resin AK and whose melting point is at least 20 T higher than the melting point of resin B, is The resin is melt-kneaded and formed into a sheet at a temperature higher than the melting point of Resin A and lower than the melting point of Resin B, and then stretched in at least one direction at a temperature lower than the melting point of Resin B. A method for producing a porous film with excellent air permeability.

In the present invention, thermoplastic resin A is mixed with thermoplastic resin B, which has poor compatibility with resin AK and whose melting point is at least 20°C higher than resin A, as the raw material resin for rounding in porous film production. It is used as In this way, the first resin A and resin B used in the present invention are required to have a relationship of poor compatibility, and
The quality of the resin can be determined by various conventional methods, but an example of a method preferably used in the present invention is 2. Prepare a sheet with a thickness of about 100 microns by mixing the two resins at a temperature higher than the melting point of the resin with the higher melting point, and bend the sheet at a 90° angle 9 times at room temperature. When you look at it, if the bent part is whiter than the surrounding area,
A method for determining poor compatibility may be presented.

Examples of combinations of thermoplastic resins that have poor compatibility and a melting point difference of at least 20°C and are suitable for use in the present invention include polyolefin resins, styrene resins, polyvinyl chloride resins, and polyamide resins. Combinations having a melting point of 20 and selected from resins, polyacrylate resins, polyester resins, polycarbonate resins, thermoplastic polyflex resins, and fluororesins may be mentioned. Preferred specific examples include polypropylene/polycarbonate, polypropylene and ethylene-tetrafluoroethylene copolymer, polyolefin resin and boria, thermoplastic polyurethane resin and fluorine resin, and polychloride. Examples include a combination of vinyl resin and fluorine resin.

Further, the melting point of resin A is at least 20°C lower than that of resin A.
Due to the high resin B usage WkK, if too much F11 resin A is used, the degree of porosity of the final film tends to decrease. When stretching the film, the tendency to break and make it difficult to stretch the film increases. Therefore, with respect to the total IK of resins A and B, resin A should be 70 to 95% by weight, and resin B should be 30 to 1% by weight.
KFi for producing porous films according to the invention, preferably used in a proportion of 5 coulometric
First, resins A and B are melted and kneaded at a temperature higher than the melting point of resin B, thereby creating a homogeneous mixture as a whole. Mixing roll for this round, Banbury Miki? -1 extrusion machine etc. may be used, and the kneaded product as described above is usually preferably formed into pellets.

Next, it is molded into a sheet, and the molding temperature at this time is higher than the melting point of the resin AO and lower than the melting point of the resin B. When molded under such temperature conditions, the resin B remains in a solid phase and is uniformly dispersed throughout the sheet in very fine particles.

If this sheet is formed at a temperature higher than the melting point of resin B, even if it is stretched in the subsequent process, it will be highly porous and only have poor air permeability. I can't do it.

Note that a calender roll or various extruder machines for forming the resin kneaded material into a sheet shape may be employed.

Next, the sheet-like material obtained as described above is stretched in at least one direction using a roll stretching machine, a tenter stretching machine, etc., and the temperature conditions at this time are such that when the melting point of the resin A is exceeded, it becomes porous. Therefore, the temperature is preferably 410°C or higher than the melting point of Resin A, rather than warm temperatures where the melting point of Resin A is lower.
A lower temperature is used.

In addition, during the stretching in the present invention, it may break during stretching,
Needless to say, conditions such as low degree of II where stretching is not possible are never adopted.

By stretching under the temperature conditions of the present invention, boundary 11iiK displacement or peeling between resin A and resin B occurs not only inside but also on the surface, and fine communication holes are formed, allowing ventilation. A porous film with excellent properties can be obtained. Although the stretching direction may be one direction, it is preferable to stretch the film in two directions, vertically and horizontally, to obtain a porous film with high air permeability at a relatively low stretching ratio.

Further, the stretching ratio in the present invention is preferably 2 times or more, and by adjusting the stretching ratio, it is possible to obtain a material with good air permeability.

The method for producing the porous film of the present invention is the method described above, in particular, a thermoplastic resin A and a thermoplastic resin B having poor compatibility with the resin A and having a melting point of at least 20°C. melt-kneading the mixture at a temperature higher than the melting point of Resin B, molding it into a sheet at a temperature higher than the melting point of Resin A and lower than the melting point of Resin B; Since this method requires stretching in at least one direction at a temperature lower than the melting point, unlike conventional methods, it is necessary to add additives such as inorganic fillers or
A porous film with excellent air permeability can be produced without requiring complicated processes.

Therefore, according to the present invention, a porous film that does not contain any additives other than the thermoplastic resin, or even if it does contain them, has a small amount and is excellent in chemical resistance, electrical properties, etc., and also has excellent KA air permeability. It can be manufactured without requiring complicated processes.

Furthermore, according to the present invention, by appropriately selecting the types of resins to be combined, mixing ratio, stretching conditions, etc., the Kjt+, porosity, air permeability, strength, heat resistance, chemical resistance, electrical properties, texture, etc. can be improved. It is possible to adjust various physical properties so that they fall within desired ranges. The porous film produced according to the present invention can be used as a breathable packaging material, sterilized paper, battery separator, separation material, etc.
It can be suitably used in a wide range of applications, such as membranes, electrical cables, contans, etc., bird-performance insulation shavers such as transformers, synthetic paper applications, building materials, wallpaper, leather substitutes, and clothing materials.

The present invention will be illustrated below with examples.

Example 1 Polypropylene (melting point, 160°C) and polycarbonate (melting point, 245°C) were mixed into the first J! l! Mix in the proportions shown in and knead with a twin-screw kneader as shown in No. tlQ.
The mixture was kneaded to form -H pellets, which were put into a center-screw extruder and molded to a thickness of about 400 mm at the m degree shown in Table 1. Next, a stretched film was obtained by stretching in one direction or two directions using a roll stretching machine or a tenter stretching machine under the stretching temperature conditions and stretching ratio shown in Table 1. Table 1 shows the measurement results of the air permeability of the obtained film.

Example 2 15 weight of ethylene-7-tetrafluoroethylene copolymer (melting point: 267°C) was added to polypropylene (melting point: 160°C) and the mixture was set at a temperature of 285°C. Mixing was performed using a twin-screw extrusion kneader to temporarily create pellets. Next, the pellets were put into a single screw extruder set at a temperature of 220°C to form a sheet with a thickness of 400°C, and the temperature was set at 140°C.
The film was stretched 4 times in the machine direction using a roll stretching machine set at a temperature of 180 degrees, to obtain a stretched film with a thickness of 180 degrees. The air permeability of the obtained film was 1600//m--atm.
The obtained film was impregnated with dogsilbenzene oil, and the dielectric constant and dielectric loss tangent were measured at 20° C. and 50° C. As a result, the dielectric constant and dielectric loss tangent were 2.2 and 0.02−.

The film can be suitably used as a voltage insulating material for power cables, capacitors, transformers, etc.

Example 3 15 weight of 6-nylon resin (melting point: 224°C) was added to high-density polyethylene (melting point: 125°C), and the mixture was mixed in a twin-screw extrusion kneader set at a temperature of 250°C. Once the pellets are created, Next, add 20 crested berets.
Pour into a single-screw extruder set at 0°C and 1m degree to a thickness of 40°.
A sheet with a thickness of 150 mm was formed and stretched 6 times in the machine direction using a 1+ roll stretching machine set at a temperature of 120'C to obtain a stretched film with a thickness of 150 mm. The air permeability of the obtained film was 3100
It was 17m1-m atm. l Also, set the above pellet to a temperature of 250°C1. The film was molded into a sheet using a Shizuku extruder K and stretched in the same manner as above (also, the air permeability of the stretched film was H751/d-am/atm).

%8゛fapplicant Sekisui Chemical Co., Ltd. Representative Fuji Numa Motoi 11th

Claims (1)

[Scope of Claims] L A mixture of thermoplastic resin A and thermoplastic resin B which has poor phase droplet properties and a melting point which is at least 20°C higher than that of resin B, is prepared by adding a mixture of thermoplastic resin A and thermoplastic resin B, which has a melting point of at least 20° C. Melt and knead,
The resin is molded into a sheet at a temperature higher than the melting point of Resin A and lower than the melting point of Resin B, and then molded into a sheet at a temperature lower than the melting point of Resin AO in at least one direction. A method for producing porous films. 2. Resin A is polypropylene, resin B is eddy//-
A method for controlling a porous film with excellent air permeability according to item 1m, which is a tetra-70 ethylene copolymer. 3. Is it possible to achieve the breathability described in item 1, where resin A is polypropylene and resin B is polycarbonate? Also, a method for producing a porous film. 4s, the porous material with excellent air permeability according to item 1, item 2, or item 3, wherein the amount of resin A in the compound is 70 to 95% by weight, and the amount of resin B is 30 to 5% by weight. The manufacturing method of Quality Filno. 5 Paragraph 1, Paragraph 2, Paragraph 1, or Paragraph 4f, in which the temperature during stretching is 11 degrees lower than the melting temperature of resin A by 10 °C or more.
Manufacturing capacity of porous film described in R? ).