JPS63162734A - Production of porous film - Google Patents

Abstract

PURPOSE:To obtain a porous film having sufficient openability, good water vapor permeability and gas permeability and an excellent balance among physical properties and tensile strength, by stretching crosswise a film comprising a polyolefin resin and an inorganic filler and stretching lengthwise thin film. CONSTITUTION:A resin composition comprising 100pts.wt. polyolefin resin and 50-500pts.wt. inorganic filler is melt-molded into a film. This film is stretched crosswise at a stretch ratio of 3-10 and further stretched lengthwise at a stretch ratio of 1.1-5 to obtain the purpose porous film. When the amount of the inorganic filler is below 50pts.wt. the gas permeability is not sufficient, while when this amount is above 500pts.wt., the film cannot be satisfactorily stretched due to increased rigity, and the gas permeability is decreased. When the stretch ratio is below 3, the gas permeability is not sufficient, when it is above 10, break during stretch occurs and the film cannot stably obtained. When it is below 1.1, the effect of molecular orientation is inappreciable, while when it is greater than 5, a problem of break during stretch occurs.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a film that has sufficient openness, good moisture permeability and air permeability, a very good balance of physical properties, and excellent tear strength. It is.

[Prior Art] Conventionally, a porous film has been obtained by forming a film from a resin composition in which a polyolefin resin is filled with various incompatible substances and then stretching the film (Japanese Patent Publication No. 53-12542,
JP-A-56-99242, JP-A-57-59727, JP-A-60-129240, etc.).

However, the film obtained by Kowara's method is longitudinal (the running direction of the film, hereinafter referred to as f&MD).
and the lateral direction (direction perpendicular to the longitudinal direction, hereinafter referred to as 1fiTD), the physical properties such as tensile strength are poorly balanced
Moreover, it has the disadvantage that tear strength is weak compared to MD.

Although the method of JP-A-60-129240, in which a film containing a polyolefin resin and barium sulfate as an essential component as an incompatible substance is stretched in at least one direction, has been greatly improved, it is still not satisfactory.

In general, as a method for stretching a film to improve the physical property balance between MD and TD, a biaxial stretching method has traditionally been used in which longitudinal stretching is followed by transverse stretching (for example,
No. 5639).

In the case of a porous film using an inorganic filler, it is impossible to obtain a film with excellent physical property balance between MD and TD and tear strength even if the biaxial stretching method is used.

That is, in a method in which longitudinal stretching is performed first, no matter how the longitudinal stretching ratio and longitudinal stretching temperature are adjusted,
It is impossible to form a film that is stable during transverse stretching, has a sufficient amount of air permeability upon completion, and has an excellent balance of physical properties and tear strength.

This is because, in a temperature range that causes necking during transverse stretching, film tearing or tearing due to film shrinkage in the MD direction occurs, making molding impossible.

On the other hand, although forming is possible in a temperature range where necking stretching of the film does not occur, the stretched portion of the film after transverse stretching is only near the stretching start point, and even if the stretching ratio is increased, the stretching region near the stretching start point will be further stretched. This is because it has the disadvantage that the air flow does not propagate in the lateral direction, so it is impossible to obtain a sufficient amount of ventilation uniformly over the entire width, and the balance of physical properties becomes poor.

[Pi point to be solved by the invention] The purpose of the present invention is to
An object of the present invention is to provide a method for producing a porous film having an excellent balance of physical properties between TD and TD and tear strength.

[Means for Solving the Problems] The present inventors have made extensive studies to achieve the above object, and have finally completed the present invention.

That is, in the present invention, a resin composition consisting of 100 parts by weight of a polyolefin resin and 50 to 500 parts by weight of an inorganic filler is melt-formed into a film, and then the film is
This method of producing a porous film is characterized by horizontally stretching the film by a factor of 10 to 10, and then longitudinally stretching the film by a factor of 1.1 to 5.

The present invention will be explained in detail below.

In the present invention, polyolefins and if-resins include polypropylene, low density polyethylene, linear low density polyethylene, homopolymers such as homobutylene, ethylene-propylene polymers, ethylene-butene copolymers, and ethylene-vinyl acetate copolymers. These are copolymers such as or blends thereof.

As the inorganic filler in the present invention, one or more of barium sulfate, calcium carbonate, talc, kaolin, calcium chloride, silicon, etc. can be used, and barium sulfate and calcium carbonate are particularly preferably used.

The amount of inorganic filler used is 100ffi of polyolefin resin.
50 to 500 parts by weight per part ffi, preferably 10 (1 to 400 parts ffffi).

If the amount used is less than 50 parts by weight, sufficient air permeability cannot be obtained, and if it is used in excess of 5 (1 (l) fig parts, the film becomes stiffer and cannot be stretched properly, resulting in a decrease in air permeability. .

Next, the method for producing the porous film of the present invention will be explained.

After adding other additives to the polyolefin resin and inorganic filler as necessary, they are mixed using a Henshol mixer, a Spur mixer, or a tumbler type mixer, and then a conventional single or twin screw extruder. The mixture is kneaded and made into pellets. Next, these pellets are formed into a film using an inflation molding machine or a T-die molding machine. At this time, it is also possible to directly form a film using an extruder without pelletizing.

Next, the film formed by an extruder is heated 3 times to 10 times at a temperature between the glass transition point and melting point of the film, preferably between 40°C and 150°C, preferably between 60°C and 120°C. Stretch in the horizontal direction. in this case,
If the temperature is less than 40°C, the film will crack before the elongation reaches the yield point, making it difficult to stretch the film properly. If the temperature exceeds the melting point, the flow of molecular chains will cause the film to become unsatisfactory during transverse stretching. It is not possible to obtain adequate ventilation. Also,
If the stretching ratio is less than 3 times, a sufficient amount of ventilation cannot be obtained. Alternatively, stretching unevenness occurs and the stretching unevenness remains even after longitudinal stretching, reducing the commercial value. Further, if the stretching is increased by 10 times, stretching breakage occurs and a stable film cannot be obtained.

The transversely stretched film is then heated within the range of the glass transition temperature to the melting point of the resin composition, preferably from room temperature to the melting point (-2
The film is stretched 1.1 to 5 times in the machine direction at a temperature of 0°C.

If it is less than 1.1 times, no molecular orientation effect is observed, and 5
If it is larger than that, a problem of stretch cut will occur.

During longitudinal stretching, if the temperature is lower than the glass transition temperature of the resin composition, stretching is impossible due to freezing of the micro-Brownian motion of the molecular chains. Furthermore, at temperatures higher than the melting point, the film becomes extremely sticky to the roll and cannot be stretched.

The tear strength exhibited by the film of the present invention cannot be obtained with films produced by conventional methods in which longitudinal stretching is followed by transverse stretching.

[Examples] Examples 1 to 18 Comparative Examples 1 to 5 The resins and inorganic fillers shown in Table 1 were mixed in the proportions shown in Table 1 using a Henschel mixer, and then uniformly mixed using a twin screw kneader. The mixture was kneaded to produce pellets. This was melted into a film using a T-die extruder. Thereafter, the film was stretched in the TD and then in the MD under the stretching conditions shown in Table 1 to obtain a film having the physical properties shown in Table 1.

Comparative Examples 6 to 11 A film produced in the same manner as in Example 1 was stretched in the machine direction under the stretching conditions shown in Table 1, and then stretched in the transverse direction to obtain a film having the physical properties shown in Table 1.

Comparative Example 12 A film produced in the same manner as in Example 1 was stretched only in the longitudinal direction under the stretching conditions shown in Table 1 to obtain a film with the physical properties shown in Table 1.

Comparative example! 3 A film produced in the same manner as in Example 1 was stretched only in the transverse direction under the stretching conditions shown in Table 1 to obtain a film with the physical properties shown in Table 1.

In addition, the physical property evaluation method is as follows.

(1) Strength; 25[01!1 (width) xloo+n
A piece of film of m (length) is bowed with a bow length speed of 20
Measurement is performed using a tension tensile tester at 0 mm /min. The intensity at the time of negotiation is measured for MD and TD respectively.

(2) Moisture permeability, according to ASTM E96-66(D). Moisture loss (3) Elongation measured by cup method at 32°C under 50% RH atmosphere, in accordance with JIS 6732.

Test piece 25mm (width) xloomm (length)
(4) Tear strength: According to JIS L 1085,
Test piece width 10a+m, length 100mtn, cut 50
Let it be mm.

Further, the average value of the minimum load and maximum load shown when tearing at a tensile strength of 200 mm/min is taken.

[Effects of the Invention] As is clear from the Examples, the porous film produced by the production method of the present invention has a very good physical property balance between MD and TD and excellent tear strength. Furthermore, in the manufacturing method of the present invention, the defective width of the edge portion is extremely smaller than in the method of stretching in the MD and then in the TD, and the yield based on the raw material is improved.

Conventional porous films have the disadvantages of being easily torn in one direction, easily stretching in one direction, and having low strength, so they cannot be used alone, and even if they are used in exposed areas, they require no reinforcing agents. It was necessary to use it. However, in the case of the porous film manufactured by the manufacturing method of the present invention, there is no need for reinforcing materials even if it is used not only as a single unit but also in the exposed part of the surface, which makes it cost-effective and expands the range of uses. It becomes possible.

For example, with conventional disposable diapers, it was necessary to provide a protective release tape in addition to the adhesive tape when putting on and taking off diapers, but when using the film according to the present invention, the protective release tape can be removed because the TD elongation is small and the strength is high. Doesn't require tape. This leads to significant cost reduction.

In addition, since it has an excellent texture, it is also effective to use it for waterproof items that come into direct contact with the skin, and from this point of view as well, the range of uses can be expanded.

Although the film according to the present invention has the above-mentioned advantages, its greatest feature is that its physical property balance can be set to the most useful balance according to the application by adjusting the stretching ratio. Another major feature is that the amount of ventilation can be freely selected depending on the purpose of use.

Claims (1)

[Claims] 1) 100 parts by weight of polyolefin resin and 5 parts by weight of inorganic filler
A resin composition comprising 0 to 500 parts by weight is melt-formed to form a film, and then the film is horizontally stretched 3 to 10 times, and further longitudinally stretched 1.1 to 5 times. Method of manufacturing porous film.