JPH0684452B2 - Method for producing porous film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a film having sufficient opening properties, good moisture permeability and breathability, an excellent balance of physical properties, and excellent tear strength. Is.

[Prior Art] Conventionally, a porous resin is obtained by forming 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, films obtained by these methods have physical properties in the longitudinal direction (the running direction of the film, hereinafter referred to as MD) and the transverse direction (direction perpendicular to the longitudinal direction, hereinafter referred to as TD), such as tensile strength. However, it has the disadvantage that the tear strength is weak against MD.

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

Generally, as a method of stretching the film to improve the physical property balance between the MD and TD, a biaxial stretching method in which the longitudinal stretching and the transverse stretching are performed has been conventionally performed (for example, JP-B-30-5639).
issue).

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

That is, in the method of performing the longitudinal stretching first, no matter how the longitudinal stretching ratio and the longitudinal stretching temperature are adjusted,
It is impossible to form a film that has stretching stability during transverse stretching, has a sufficient air flow rate at the time of completion, and has excellent physical property balance and tear strength.

This is because in the temperature range where necking occurs during transverse stretching, film tearing or tearing due to MD direction film shrinkage occurs and molding becomes impossible.

On the other hand, although the film can be molded in a temperature range where necking stretching of the film does not occur, the stretched part of the film after transverse stretching is only near the stretching start point, and even if the stretching ratio is increased, the stretching vicinity is further stretched near the stretching start point. This is because it is not possible to obtain a sufficient amount of ventilation evenly over the entire width and the physical property balance and the like are deteriorated because the portion has the drawback that it does not propagate laterally.

[Problems to be Solved by the Invention] An object of the present invention is to provide MD and
An object of the present invention is to provide a method for producing a porous film which is excellent in balance of physical properties of TD and tear strength.

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

That is, the present invention is 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 melted to form a film, and then the film is transversely stretched 3 to 10 times, Further, the method is a method for producing a porous film, which is characterized by longitudinally stretching 1.1 to 5 times.

Hereinafter, the present invention will be described in detail.

The polyolefin resin in the present invention, polypropylene, low density polyethylene, linear low density polyethylene,
It is a homopolymer such as polybutylene, a copolymer such as an ethylene-propylene polymer, an ethylene-butene copolymer, an ethylene-vinyl acetate copolymer, or a blend thereof.

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

The amount of the inorganic filler used is 50 to 500 parts by weight, preferably 100 to 400 parts by weight, based on 100 parts by weight of the polyolefin resin.

If the amount used is less than 50 parts by weight, sufficient ventilation cannot be obtained,
When it is used in excess of 500 parts by weight, the rigidity of the film is increased, the stretching cannot be performed well, and the air flow rate is reduced.

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

After adding other additives to the polyolefin resin or the inorganic filler as needed, a Henshol mixer,
Mix using a spur mixer, tumbler type mixer,
Then, the mixture is kneaded by a usual single-screw or twin-screw extruder and pelletized. These pellets are paired to form 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 with an extruder without pelletizing.

Next, the film formed by an extruder is heated to a temperature not lower than the glass transition point and not higher than the melting point of the film, preferably from 40 ° C.
3 at temperatures of 150 ° C, preferably between 60 ° C and 120 ° C
Stretch 10 to 10 times in the transverse direction. In this case, when the temperature is lower than 40 ° C, the film is torn before the elongation exceeds the yield point and the stretching cannot be performed well. Sometimes it is not possible to get a satisfactory air flow rate. Further, if the draw ratio is less than 3 times, a sufficient ventilation amount cannot be obtained. Alternatively, stretching unevenness occurs, and stretching unevenness remains even after longitudinal stretching, which lowers the commercial value. On the other hand, if it exceeds 10 times, stretching may occur and a stable film may not be obtained.

The transversely stretched film is then in the range of the glass transition temperature to the melting point of the resin composition, preferably from room temperature to the melting point (-20
(Stretching) 1.1 to 5 times in the machine direction.

If it is less than 1.1 times, the effect of molecular orientation is not observed, and if it is more than 5 times, the problem of stretch breakage occurs.

In the longitudinal stretching, if the temperature is lower than the glass transition temperature of the resin composition, the stretching cannot be performed due to the freezing of the Micro Brownian motion of the molecular chain. Further, at a temperature 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 by a film produced by a conventional method in which transverse stretching is performed after longitudinal stretching.

[Examples] Examples 1 to 18 Comparative Examples 1 to 5 Resins shown in Table 1 and inorganic fillers were mixed in a ratio shown in Table 1 using a Henschel mixer, and then uniformly mixed with a twin screw type kneader. The mixture was kneaded to prepare pellets. This was melt-cast into a film using a T-die extruder. Then, the film was stretched in TD and then in 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 The film formed in the same manner as in Example 1 was stretched in the machine direction under the stretching conditions shown in Table 1 and then in the transverse direction to obtain a film having the physical properties shown in Table 1.

Comparative Example 12 The film formed in the same manner as in Example 1 was stretched only in the machine direction under the stretching conditions shown in Table 1 to obtain a film having the physical properties shown in Table 1.

Comparative Example 13 The film formed 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 having the physical properties shown in Table 1.

The methods for evaluating physical properties are as follows.

(1) Strength: A 25 mm (width) x 100 mm (length) film piece is measured with a tension tensile tester at a pulling speed of 200 mm / min. The strength at break is measured for MD and TD respectively.

(2) Water vapor transmission rate: According to ASTM E96-66 (D). Decrease in water content at 32 ℃, 50% RH by cup method (3) Elongation; conform to JIS K 6732.

Test piece 25mm (width) x 100mm (length) (4) Tear strength; JIS L 1085 conforming, but test piece width 10m
m, length 100 mm, cut 50 mm. Also, tensile strength 200 mm /
Take the average value of the minimum load and maximum load shown when tearing as min.

[Effects of the Invention] As is apparent from the examples, the porous film produced by the production method of the present invention is very excellent in the physical property balance between MD and TD and in tear strength. Furthermore, the manufacturing method of the present invention is
As compared with the method of stretching to TD after stretching, the defective width of the ear portion is extremely reduced, and the yield with respect to the raw material is improved.

The conventional porous film cannot be used as a simple substance because it has a drawback that it is easy to tear in one direction and can be easily stretched in one direction and its strength is small, and a reinforcing agent is used even if it is used in a part exposed on the surface. There was a need. However, in the case of the porous film produced by the production method of the present invention, it is not only required to be used as a single body but also to be used in a portion exposed on the surface, a reinforcing material is not required, which is advantageous in terms of cost and can be expanded in use. Becomes

For example, conventionally, in a disposable diaper, etc., it was necessary to provide a protective peeling tape separately from the adhesive tape at the time of attachment / detachment, but when the film according to the present invention is used, the protective peeling tape has a small TD elongation and high strength. Does not need This leads to a great cost reduction.

Moreover, since it is excellent in the feel of the skin, it is also effective to use it for a waterproof product that comes into direct contact with the skin, and the application can be expanded from this point as well.

The film according to the present invention has the above-mentioned advantages, but the greatest feature is that the physical property film can be set to the most useful one according to the application by adjusting the stretching ratio. Another major feature is that the air flow rate can be freely selected according to the purpose of use.

Claims (1)

[Claims] 1. A resin composition comprising 100 parts by weight of a polyolefin resin and 50 to 500 parts by weight of an inorganic filler is melted to form a film, and then the film is transversely stretched 3 to 10 times, and further, A method for producing a porous film, which comprises longitudinally stretching 1.1 to 5 times.