JPH02289631A - Porous film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to porous films. Specifically, when used as a breathable sheet for clothing, medical use, filtration materials, etc., it is a porous film made of a silk composition containing a filler and a polyolefin resin suitable for use.

(Prior Art) Many attempts have been made heretofore to uniaxially stretch a film or sheet obtained by blending a filler into a polyolefin resin and melt-molding it as a means of producing a porous film. However, these films still have problems with the anisotropy of film properties, particularly the balance between the tensile strength in the machine direction (stretching direction) and the transverse direction, and the surface strength.

One way to improve the anisotropy and surface strength of the film is to stretch the film at as low a ratio as possible to make it porous, but satisfactory results have not yet been obtained. Another possibility is to biaxially stretch the original fabric, but there are problems in that the equipment cost is high and the range of stretching conditions is narrow, making operational management difficult. (Problems to be Solved by the Invention) The present invention improves the drawbacks of porous films produced by conventional methods, and has a good balance of physical properties between tensile strength and moisture permeability in uniaxial stretching, and high surface strength. The purpose of this invention is to provide a porous film that can be made thinner than the above film.

(Means for Solving the Problems) As a result of intensive studies to achieve the above-mentioned object, the present inventors have determined that a composition made of polyethylene with specific physical properties as a resin material is molded by a specific method and uniaxially stretched. The present invention was achieved by confirming that the porous film with specific physical properties obtained by this method was compatible with the above purpose. That is, the gist of the present invention is that (a) the density is 0.9 - 0.965 g/cm3;
Melt index is 2g/10min or less, flow ratio is 50
~120 linear polyethylene 100 to 50 parts by weight, (
(1) 0 to 50 parts by weight of branched low-density polyethylene with a melt index of 2 g/10 minutes or less and a flow ratio of 70 or less, and a total of IIkIOO of the linear polyethylene in (a) above and the branched low-density polyethylene in (1). 1 part by weight
A mixture of 00 to 400 parts by weight of a filler is inflation-molded with a blow-up ratio of 2 to 8 and a frost line height of 2 to 50 times the diameter of the annular slit of the die. It is a porous film with a thickness of 90μ or less obtained by uniaxially stretching the film in the drawing direction at a stretching ratio of 1.2 to 8 times. are both 50
Below arm, moisture permeability is 1500 g/m2・24h
``The present invention resides in a porous film having the above characteristics and having a surface strength satisfying the following formula: surface strength [kgl≧35×film thickness].

The present invention will be explained in detail below.

The resin component in the present invention consists of (a) a specific linear polyethylene alone, or a mixture of this linear polyethylene and (a) a specific branched low-density polyethylene.

(A) The linear polyethylene has a density of 0.91 to
Examples include linear low-density polyethylene with a density of 0.95 g/cm3 and high-density polyethylene with a density of 0.965 g/cm3 or less.

The above linear low density polyethylene is composed of ethylene and other α-
It is a copolymer with olefin, and is different from branched low-density polyethylene produced by conventional high-pressure methods. Linear low density polyethylene is, for example, ethylene and its 4 to 1
About 7% by weight, preferably about 5 to 15% by weight of butene, hexene, octene, decene, 4-methylpentene-
It is produced by copolymerizing other α-olefins such as No. 1 with a Ziegler-type catalyst or a Phillips-type catalyst used in the production of high-density polyethylene by a medium-low pressure process.

This material is made by converting conventional high-density polyethylene into a short branched structure using a copolymer component, and using this short chain branching to appropriately reduce the density to 0. Old ~0.95 g,/c
It is a polyethylene with a structure of about m3, which has a more linear structure than conventional branched low-density polyethylene, and more branching than high-density polyethylene. This linear low-density polyethylene has higher tensile strength than high-pressure low-density polyethylene, which is produced by radical polymerization at high temperature and pressure.
Strength properties such as impact strength and rigidity, environmental stress cracking resistance (ES
It has excellent properties such as CR), heat resistance, and heat sealability, and has been used in various fields in recent years. Particularly in the field of films, high-pressure low-density polyethylene is rapidly being replaced by linear low-density polyethylene due to its superior physical properties.

In addition to the linear low-density polyethylene described above, linear high-density polyethylene can also be used as the linear polyethylene (a) in the present invention, and its density is 0.965 g/c.
It must be less than m3.

That is, the density of the linear polyethylene in (a) above is 0.9
It is necessary to be in the range of 1 to 0.965 3/cm3, preferably in the range of 0.1 to 0.95 g/cm3, and more preferably in the range of 0.915 to 0.940 3/ca3. If the density is higher than the above range, the impact resistance and flexibility will be significantly reduced, while if the density is lower than the above range, the porosity and tensile strength will be reduced. In addition, the melt index of these linear polyethylenes is 2 g/10 minutes or less,
It is preferably in the range of 0.1 to Ig/10 minutes; if the melt index is higher than the above, the tensile strength and surface strength will decrease, which is not preferred.

Furthermore, as linear polyethylene, its fluidity ratio is 50 to 1.
20, preferably one with a relatively wide molecular weight distribution in the range of 60 to 90 is used. If the fluidity ratio is higher than the above range, the surface strength will decrease, and if it is lower than the above range, the moldability will decrease, which is not preferable.

To produce linear polyethylene with such a fluidity ratio,
According to a well-known method, for example, a method is employed in which polymers having different molecular weights are sequentially polymerized using two or more polymerization tanks to produce a blend.

Note that the melt index in the present invention is based on JIS
This value was measured in accordance with Condition 4 of Table 1 of JIS K 7210, which is a reference standard for K 6760. In addition, the fluidity ratio is measured by using the above melt index measuring device and applying a shear force of 1
The extrusion rate (g/
10 minutes), which is calculated as . Furthermore, the density is JI
This is a value measured in accordance with Sκ6760.

The fluidity ratio is a measure of the molecular weight distribution of the resin used; a small fluidity ratio value indicates a narrow molecular weight distribution, and a high fluidity ratio value indicates a wide molecular weight distribution. In the present invention, only the linear polyethylene described in (a) above may be used as the resin component, but if linear polyethylene is used as the main component and a specific amount of branched low-density polyethylene described above is blended therein, This is desirable because it improves film formability and stretchability.

Branched low density polyethylene includes ethylene homopolymers and copolymers of ethylene and other copolymer components.

Copolymerization components include vinyl acetate, ethyl acrylate,
Vinyl compounds such as methyl acrylate, brobylene, 4
-Olefins having 3 or more carbon atoms such as 1-methylpentene, hexene, and octene. The copolymerization amount of the copolymerization component is 0.5 to 18% by weight, preferably 2 to 1% by weight.
It is about 0% by weight. These branched low density polyethylene
According to 2), it is preferably obtained by radical polymerization using a radical generator such as oxygen or an organic peroxide.

Branched low density polyethylene has a melt index of 2g
/10 minutes or less, preferably 0
．． It is in the range of 1 to Ig/10 minutes. Also, the flow ratio is 7
It needs to be 0 or less, preferably 30 to 7.
It is in the range of 0. If the melt index and fluidity ratio are higher than the above, the surface strength of the film decreases, which is not preferable.

Furthermore, the density of branched low density polyethylene is 0.91 to 0.
．． 94 g/cm3, preferably 0.91-0.930
y,/cm3, particularly preferably 0.915 to 0.
A range of 925 g/cm3 is preferable from the viewpoint of improving surface strength.

The blending ratio of linear polyethylene in (a) and branched low-density polyethylene in (x) is 100 to 100%
50 parts by weight, preferably 95 to 80 parts by weight, and 0 to 50 parts by weight, preferably 5 to 50 parts by weight of branched low density polyethylene.
It is 20 parts by weight.

Next, the fillers used in the present invention include well-known inorganic and organic fillers. Inorganic fillers include calcium carbonate, talc, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, aluminum hydroxide, zinc oxide, magnesium hydroxide, calcium oxide,
Magnesium oxide, titanium oxide, alumina, miyuki, asbestos powder, glass powder, shirasu balloon, zeolite,
Examples include silicate clay, especially calcium carbonate, talc,
Clay, silica, diatomaceous earth, barium sulfate, etc. are suitable. Examples of the organic filler include cellulose powders such as wood flour and pulp, which may be used alone or in combination. The filler preferably has an average particle size of 30μ or less, more preferably 10μ, and most preferably 0.8 to 5μ.

If the particle size is too large, the density of the pores in the stretched film will be poor, and if the particle size is too small, the dispersibility in the resin will be poor and the moldability will be poor. Note that it is desirable to surface-treat the filler with a fatty acid or a metal salt thereof in terms of dispersibility in the resin and stretchability of the film.

The blending ratio of the filler is particularly preferably selected from the range of 100 to 400 parts by weight of the filler to 100 parts by weight of the linear polyethylene (a) and the branched low-density polyethylene (a). The blending ratio is 120 to 300 parts by weight. When the amount is less than the above range, sufficient pores will not be formed in the resulting stretched film, resulting in a low degree of porosity.

On the other hand, if the blending amount of the filler is greater than the above range, the kneading properties, dispersibility and film formability will be poor, and the surface strength of the stretched film will also be reduced. In addition to the above-mentioned ingredients, well-known antioxidants, lubricants, heat and ultraviolet stabilizers, pigments, antistatic agents, fluorescent agents, etc. can be added as desired.

To produce the porous film of the present invention, first, the above-mentioned linear polyethylene, branched low-density polyethylene, and filler are mixed in the above-mentioned proportions, then kneaded to form pellets, and then inflation-molded into an unstretched film. shall be.

Drums, tumbler type mixers, ribbon blenders, Henschel mixers, super mixers, etc. are used to mix linear polyethylene, branched low-density polyethylene, and fillers, but high-speed stirring type mixing such as Henschel mixers is used. machine is preferable. Polyethylene is usually lO~15
It is used as a powder of 0 mesh, but from the viewpoint of uniformity and handling, powder of 20 to 60 mesh is more preferable. Next, the mixture obtained above is kneaded using a well-known kneading device such as a screw extruder, twin-screw extruder, mixing bowl, Banbury mixer, or two-wheeled kneading reed.

In the present invention, an unstretched film is formed from the blend obtained above by an inflation method, and then this unstretched film is subjected to a stretching treatment.

Inflation molding is carried out under the conditions of a blow-up ratio of 2 to 6, preferably 3 to 6, and a frost line height of 2 to 50 times, preferably 5 to 20 times, the diameter of the annular slit of the die. If the blow-up ratio is lower than the above range, the tensile strength and impact strength of the film will decrease, and if it is higher than the above range, the stability of bubble molding will decrease, which is not preferable. Also, if the height of the frost line is lower than the above range, the tensile strength of the film will decrease,
On the other hand, if it is higher than the above range, the molding stability of the bubble will decrease, which is not preferable.

The unstretched film formed by the inflation method is then uniaxially stretched in the longitudinal direction (the direction in which the film is taken off). For uniaxial stretching, a roll stretching method is usually adopted, but a tubular stretching method may be used in which the uniaxial direction (take-off direction) is emphasized. Further, the stretching treatment may be carried out in one stage or in multiple stages of two or more stages.

The stretching treatment is usually carried out at a temperature ranging from 100°C lower than the melting point of the resin composition to 20°C lower than the melting point, particularly at a temperature ranging from 90°C lower than the melting point of the resin composition to 50°C lower than the melting point. is preferable; at a temperature lower than this range, stretching unevenness tends to occur in the film, and at a temperature higher than this range, the porosity of the film tends to decrease.

The stretching ratio needs to be 1.2 to 8 times, preferably 1.5 to 4 times. If the stretching ratio is less than 1.2 times, the effect of stretching is insufficient, and the porosity and tensile strength of the film are insufficient. If the stretching ratio exceeds 8 times, the film will have excessive molecular orientation in the longitudinal direction, which is undesirable because the surface strength of the film will decrease. Note that heat treatment after uniaxial stretching can stabilize the dimensional accuracy of the film, and known surface treatments such as corona treatment and flame treatment can also be applied.

The film of the present invention is a porous film obtained by the above method, and has a thickness of 90 μm or less, and has a bending resistance in both the longitudinal and transverse directions of 50 mm or less, Moisture permeability is 1500 g/yx
2-24 hr or more, and surface strength [kg]≧3
5 x film thickness [++ usl. Furthermore, this film contains micropores with an average pore diameter of 0.05 to 5μ.
Unit volume - 0.1 cc as pore volume per cm3
The above has been formed.

(Examples) The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

Example 1 A solid catalyst obtained by reacting 5 g of magnesium ethylate and 50 cc of titanium tetrachloride at 130°C was used to copolymerize ethylene and butene-1, resulting in a melt with a butene-1 content of 4.5% by weight. Linear polyethylene with an index (Ml) of 200 g/10 min and linear polyethylene with a butene-1 content of 4.5% by weight and an Ml of 0.055 g/10 min were prepared. The two types of linear polyethylene obtained above were mixed in equal amounts, and the former: 0.3
g/10 minutes, flow ratio: 701 density: 0,930 g/
cm'' of linear polyethylene was obtained. To 100 parts by weight of this linear polyethylene was added calcium carbonate (average particle size: 1.2 cm).
2μ, fatty acid treatment), 0.05 parts by weight of 2.6-ditertiary petitlouva cresol (antioxidant), and 0.05 parts by weight of calcium stearate (lubricant) were mixed with stirring in a Henschel mixer. The resulting mixture (melting point 120°C) was passed through a twin screw mixer II machine DSM-65 (
The mixture was kneaded and granulated using a Double Screw Mixer (manufactured by Japan Steel Works, Ltd.).

This granulated product was inflation-molded using a 40 + wmφ extruder under the following conditions to form a film with a thickness of 65 μm.

[Extrusion conditions] Cylinder temperature: 170- 190- 210-
230°C head, die temperature = 200°C Diameter of die annular slit (D): 100 IIlm Take-up speed: 8 n+/min. Blow ratio (BU
R): 3.0 Frost line height (FLH): 700 mm Folding diameter: 471no+ The film obtained by the above method was slit in the take-up direction, and then uniaxially stretched using a roll stretching machine under the following conditions.

[Stretching conditions] Stretching temperature: 50°C Stretching ratio: 2.5 times Stretching speed: 11.0 w/win
．． The stretched film had a thickness of 45 μm, was porous and sufficiently whitened, had no stretching unevenness, and was a porous film with a beautiful surface. The performance of this film is shown in Table 1 below.

The method for measuring the performance evaluation items in Table 1 is as follows.

(a) Tensile strength and elongation: According to ASTM 8B2-647. 2O nun width x 501lll+1 length, pulling speed: 50 1in/fflIn. (b) Moisture permeability: ASTM E26-66(E)
According to.

(c) Flexibility: Judgment was made based on the feel of the hand according to the following criteria.

◎: Extremely soft.

O: Soft.

△: Slightly hard.

X: Hard.

(d) Film puncture strength (area strength): A test film is obtained by cutting the film into a square of 100 mm x 100 mm, and this film is fixed from above and below with a holding ring with an inner diameter of 80 mm.

A round bar-shaped plunger with a diameter of 20 n+aφ and a hemispherical tip with a radius of 10 mm was attached to the tensile testing machine, and this was pressed against the test film fixed as above at a crosshead speed of 500 mm/min. The magnitude of surface strength is determined by the tensile strength at that time. The tensile strength indicates the maximum strength, and the elongation at break is expressed by the distance traveled by the plunger after it hits the film.

(e) Rigidity/softness (mm): JIS LI018
- Measured using the 45° force angle lever method in 1977. Measurements were performed at a temperature of 20° C. and a relative humidity of 65%.

Example 2 80 parts by weight of linear polyethylene of old: 0.3 g/10 min, flow ratio = 70, density: 0.930 g/cra3 used in Example 1, and MI: 0.4 g/10 min , a mixture with 20 parts by weight of branched low-density polyethylene (40 mesh) having a fluidity ratio of 4o and a density of 0.922 g/cm3 was used as the resin component, and the other conditions were exactly the same as in Example 1. Films were manufactured and their performance evaluated. The results are shown in Table 1.

Comparative Examples 1 to 6 Porous films were produced in the same manner as in Example 1, except that the composition of the resin component, inflation molding conditions, and stretching conditions in Example 1 were changed as shown in Table 1. However, in the case of Comparative Example 1, the thickness of the original film was 150 μm.
As a result of stretching the film under the conditions shown in Table 1, the thickness of the film after stretching was 30 μm.

Table 1 shows the performance evaluation results of the obtained porous film.

(Effects of the Invention) The porous film of the present invention has the following advantages.

l) Film physical properties: The anisotropy of the film after uniaxial stretching is
This is a significant improvement over conventional uniaxially stretched films, resulting in improved vertical and horizontal balance.

In particular, the tensile strength in the transverse direction (direction perpendicular to the stretching direction) is increased.

2) Porosity: Because it has less bi-stretching unevenness and uniform continuous pores, it has much better moisture permeability and gas permeability than conventional uniaxially stretched films. It also has good water resistance.

3) Workability: Heat sealing strength is improved.

4) Economic efficiency: By reducing the amount of liquid or waxy hydrocarbon polymer and making it possible to make the wall thinner, it is possible to significantly reduce costs.

5) Incinurability: It is easily incinerated and does not generate harmful gases.

Based on the properties listed above, the porous film of the present invention can be used, for example, for clothing that takes advantage of moisture permeability (waterproof products, rain gear, etc.), for battery separators, for filtration materials (air dust removal, mist removal, industrial wastewater), Suitable for use in medical and other applications.

Claims (1)

[Claims] (B) Density is 0.91 to 0.965 g/cm^3, melt index is 2 g/10 minutes or less, and flow ratio is 50 to 1.
100 to 50 parts by weight of linear polyethylene of No. 20, and (b)
Melt index is 2g/10min or less, flow ratio is 70
0 to 50 parts by weight of the following branched low-density polyethylene and 100 to 4 parts by weight of the total amount of the linear polyethylene in (a) and the branched low-density polyethylene in (b) above.
00 parts by weight of filler was inflation-molded with a blow-up ratio of 2 to 8 and a frost line height of 2 to 50 times the diameter of the annular slit of the die. A porous film with a thickness of 90μ or less obtained by uniaxially stretching the film in the drawing direction at a stretching ratio of 1.2 to 8 times, the film having a bending resistance in the longitudinal and transverse directions. A porous film having a thickness of 50 mm or less, a moisture permeability of 1500 g/m^2.24 hr or more, and a surface strength satisfying the following formula: surface strength [kg] ≧ 35 x film thickness [mm]. .