JP2859346B2 - Porous film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a porous film. For details, for clothing,
The present invention relates to a porous film using a composition obtained by mixing a filler with a polyolefin resin, which is suitable for use as a breathable sheet for medical use, filtration material, and the like.

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

One method for improving the anisotropy and surface strength of the film is to draw at a draw ratio as low as possible to realize porosity. However, satisfactory results have not yet been obtained. In addition, it is conceivable that the raw material is biaxially stretched, but there is a problem that equipment cost is high and the operation management is severe because the range of stretching conditions is narrow.

(Problems to be Solved by the Invention) The present invention has improved the drawbacks of such a conventional porous film, and has a good balance between the tensile strength and the moisture permeability in uniaxial stretching and a large surface strength. It is an object of the present invention to provide a porous film that can be made thinner than the above film.

(Means for Solving the Problems) The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, formed and uniaxially stretched a composition using polyethylene having specific physical properties as a resin material by a specific method. As a result, it has been confirmed that the porous film having specific properties obtained thereby conforms to the above object, and the present invention has been accomplished. That is, the gist of the present invention is (a) a linear polyethylene having a density of 0.91 to 0.965 g / cm ³ , a melt index of 20 g / 10 min or less, and a flow ratio of 70 or less.
100 to 50 parts by weight, (b) a branched low-density polyethylene having a melt index of 20 g / 10 min or less and a flow ratio of 70 or less.
50 parts by weight, based on 100 parts by weight of the total amount of the linear polyethylene of (A) and the branched low-density polyethylene of (B),
0.0001-0.1 parts by weight of radical generator and 100-400 of filler
A blow-up ratio of 2 was used after the crosslinking reaction was performed or while the crosslinking reaction was being performed, using a composition prepared by blending parts by weight.
~ 8, inflation molding with the height of the frost line being 2 to 50 times the diameter of the annular slit of the die, and stretching the obtained film in the drawing direction of the film at a stretching ratio of 1.2 ~
A porous film having a thickness of 90 μ or less obtained by uniaxially stretching the film by 8 times, and both the longitudinal and lateral flexibility of the film are 50 mm or less, and the moisture permeability is 1500 g / m ^2.
-A porous film characterized by having a surface strength of 24 hours or more and a surface strength satisfying the following formula: surface strength [kg] ≥ 35 x film thickness [mm].

 Hereinafter, the present invention will be described in detail.

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

The linear polyethylene of the above (a) has a density of 0.91
Linear low density polyethylene and a density of ~0.95g / cm ³ is 0.965
g / cm ³ or less high-density polyethylene.

Linear low-density polyethylene is a copolymer of ethylene and another α-olefin, and is different from a branched low-density polyethylene produced by a conventional high-pressure method. The linear low-density polyethylene is, for example, ethylene and about 4 to 17% by weight, preferably about 5 to 15% by weight of other α-olefin such as butene, hexene, octene, decene, and 4-methylpentene-1. Is produced using a Ziegler-type catalyst or a Phillips-type catalyst used in the production of high-density polyethylene at a medium-to-low pressure. This compound, a conventional high-density polyethylene and short branched structure by the copolymerization component, density obtained by the 0.91~0.95g / cm ³ approximately lowers suitably utilizing Re this short chain branching Yes,
It is more linear than conventional branched low-density polyethylene,
Polyethylene having a structure with more branches than high-density polyethylene. This linear low-density polyethylene has strength properties such as tensile strength, impact strength and rigidity, environmental stress cracking resistance (ESCR), and heat resistance compared to high-pressure low-density polyethylene produced by radical polymerization under high temperature and high pressure. And has excellent properties such as heat sealability, and has been used in various fields in recent years. Particularly in the field of film, the substitution of high-pressure low-density polyethylene with linear low-density polyethylene is rapidly progressing due to its superiority in physical properties.

As the linear polyethylene (a) in the present invention, in addition to the linear low-density polyethylene, a linear high-density polyethylene can be used, but the density must be 0.965 g / cm ³ or less.

That is, the density of the linear polyethylene of the above (a) is 0.91
It is preferably in the range of 0 to 0.965 g / cm ³ , especially 0.915 to 0.930 g / cm ³ . When the density is higher than the above range, the impact resistance and the flexibility are reduced. On the other hand, when the density is lower than the above range, the flexibility, the porosity, the dimensional stability and the tensile strength are lowered, although the flexibility is excellent. Further, the melt index of these linear polyethylenes is 20 g / 10 min or less, preferably 10 g / 10 min or less, more preferably in the range of 0.1 to 5 g / 10 min, and the flow ratio of the linear polyethylene is 70 or less, especially Those having a range of 10 to 50 are preferably used. If the melt index is higher than the above, the tensile strength and the surface strength are undesirably reduced.
On the other hand, if the flow ratio is higher than the above, the surface strength decreases, which is not preferable.

The melt index in the present invention is JIS K
It is a value measured in accordance with Condition 4 of Table 1 of JIS K 7210 which is a cited standard of 6760. Also the flow ratio with the melt index instrument shear 10 ⁶ dynes / cm ³ (load 11
131 g) and 10 ⁵ extrusion rate of dynes / cm ³ (load 1113 g) (g / 10
Min), and Is calculated. Further, the density is a value measured according to JIS K 6760.

The flow ratio is a measure of the molecular weight distribution of the resin used,
If the value of the flow ratio is small, the molecular weight distribution is narrow, and if the value of the flow ratio is large, the molecular weight distribution is wide.

In the present invention, only the linear polyethylene of the above (A) may be used as a resin component, but when the linear polyethylene is a main component and the branched low density polyethylene of the above (B) is blended in a specific amount, This is desirable because film formability and stretchability are improved.

Branched low density polyethylene includes ethylene homopolymers and copolymers of ethylene with other copolymerization components. Examples of the copolymerization component include vinyl compounds such as vinyl acetate, ethyl acrylate and methyl acrylate, and olefins having 3 or more carbon atoms such as propylene, 4-methylpentene-1, hexene and octene. The copolymerization amount of the copolymer component is 0.5 to 18% by weight, preferably 2 to 1%.
It is about 0% by weight. These branched low-density polyethylenes are prepared by the usual high pressure method (1000-3000 kg / cm ² )
Desirably, it is obtained by radical polymerization using a radical generator such as an organic peroxide.

Branched low density polyethylene has a melt index of 20
g / 10 minutes or less, preferably in the range of 10 to 1 g / 10 minutes, and those having a flow ratio of 70 or less, particularly in the range of 30 to 70 are suitably used. If the melt index and the flow ratio are higher than those described above, the surface strength of the film is undesirably reduced. Further, the density of the branched low-density polyethylene is preferably 0.930 g / cm ³ or less, particularly preferably in the range of 0.915 to 0.925 g / cm ³ from the viewpoint of improving the surface strength.

The mixing ratio of the linear polyethylene (a) and the branched low-density polyethylene (b) is 100 to 5 linear polyethylene.
The amount is 0 to 50 parts by weight, preferably 5 to 20 parts by weight, based on 0 parts by weight, preferably 95 to 80 parts by weight.

As the radical generator used in the present invention, those having a decomposition temperature in which the half-life is 1 minute and in the range of 130 to 300 ° C. are preferable. For example, dicumyl peroxide, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-
3, α, α'-bis (t-butylperoxyisopropyl) benzene, dibenzoyl peroxide, di-t-
Butyl peroxide and the like. The amounts of the radical generators are the same as those of the above-mentioned (a) linear polyethylene and (b)
Is selected from the range of 0.0001 to 0.1 part by weight with respect to 100 parts by weight of the total amount of the branched low-density polyethylene, and if less than this range, the surface strength of the obtained film is almost the same as that of the case of no addition. On the other hand, if it is larger than this range, the melt index becomes too low, so that the film is apt to be cut off during film formation and the surface of the film becomes rough, which is not preferable.

Next, well-known inorganic and organic fillers are used as the filler used in the present invention. As inorganic fillers, 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, Examples include titanium oxide, alumina, mica, asbestos powder, glass powder, shirasu balloon, zeolite, silicate clay, and the like. Particularly preferred are calcium carbonate, talc, clay, silica, diatomaceous earth, and barium sulfate. Examples of the organic filler include cellulosic powders such as wood flour and pulp, which are used alone or in combination.
The filler preferably has an average particle size of 30 μm or less, particularly 10 μm, and most preferably has an average particle size of 0.8 to 5 μm. If the particle size is too large, the denseness of the pores of the stretched film will be poor, and if the particle size is too small, the dispersibility in the resin will be poor,
Moldability is also poor. The surface treatment of the filler with a fatty acid or a metal salt thereof is desirable in terms of dispersibility in a resin and stretchability of a film. The compounding amount of the filler is selected from the range of 100 to 400 parts by weight based on 100 parts by weight of the total amount of the linear polyethylene (a) and the branched low-density polyethylene (b). 120 to 300 parts by weight. When the amount is less than the above range, the resulting stretched film has insufficient pores to be formed, resulting in low porosity. On the other hand, when the compounding amount of the filler is larger than the above range, kneadability,
Dispersibility and film formability are poor, and the surface strength of the stretched film is further reduced. In addition, in addition to the above components, if necessary, well-known antioxidants, heat and ultraviolet stabilizers, lubricants, pigments, antistatic agents, fluorescent agents, and the like can be added.

In the present invention, a linear polyethylene, a branched low-density polyethylene, a radical generator and a filler are mixed in the above-mentioned ratio by the method of the following A or B, and then kneaded into a pellet, followed by inflation molding. To make an unstretched film.

A: A linear polyethylene, a branched low-density polyethylene, a radical generator and a filler are mixed, kneaded using a kneading machine such as an extruder or a Banbury mixer, and then pelletized, and the pellets are used for inflation molding.

B: A mixture of linear polyethylene and branched low-density polyethylene with a large amount of radical generator (about 5000 to 10,000 ppm)
At a temperature at which the radical generator hardly reacts with the polyethylene, and at a temperature higher than the melting point of the polyethylene, a melt-kneaded pellet is prepared in advance to prepare a masterbatch. It is mixed with a branched low-density polyethylene and a filler, kneaded, and then pelletized, and the pellets are used for inflation molding.

According to the method described in the above A or B, when linear polyethylene and branched low-density polyethylene are kneaded with a radical generator, a crosslinking reaction by the radical generator occurs, polyethylene is molecular-coupled, and a high molecular weight component is increased. In addition, a modified polymer having a reduced melt index can be obtained. This modified polymer is more likely to be oriented in the transverse direction at the time of inflation molding than the polymer before modification, and the film thus obtained has a remarkably improved tensile strength and impact strength when stretched. .

In this case, the melt index (Ml ₂ ) of the modified polymer at 190 ° C. is 2 g / 10 min or less, preferably in the range of 0.1 to 1 g / 10 min, and the ratio (Ml ₁ ) of the polymer before modification to the melt index (Ml ₁ ) Ml ₂ / Ml ₁ ) is 0.1 to 0.9, especially 0.1 to 0.
It is desirable to adjust so as to fall within the range of 8 from the viewpoint of film forming processability and stretchability. Furthermore, the flow ratio (FR ₂ ) of the modified polymer is 50 or more, preferably in the range of 50 to 120, and the ratio (FR ₂ ) to the flow ratio (FR ₁ ) of the polymer before modification is
/ FR ₁ ) is desirably adjusted so as to be 1.1 or more, particularly in the range of 1.1 to 10, from the viewpoint of film formability and stretchability.

Drums, tumbler-type mixers, ribbon blenders, Henschel mixers, supermixers, etc. are used to mix linear polyethylene, branched low-density polyethylene, radical generators and fillers. A stirrer-type mixer is desirable, and the polyethylene is preferably supplied in the form of a powder of usually 10 to 150 mesh, especially 20 to 60 mesh. The kneading of the obtained mixture is carried out using a well-known kneading device such as a screw extruder, a twin-screw extruder, a mixing roll, a Banbury mixer, a twin-screw kneader and the like.

In the present invention, an unstretched film is formed from the composition obtained above by an inflation method, and then the unstretched film is stretched.

Inflation molding, blow-up ratio is 2-8,
Preferably, the frost line height is 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 decrease, and if it is higher than the above range, the molding stability of the bubble decreases, which is not preferable. Also, if the height of the frost line is lower than the above range, the tensile strength of the film decreases,
If it is higher than the above range, the molding stability of the bubble is undesirably reduced.

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). The uniaxial stretching is usually performed by a roll stretching method, but may be a tubular stretching method in which the uniaxial direction (drawing direction) is emphasized. The stretching may be performed in one stage or in two or more stages.

The stretching treatment is preferably performed at a temperature in the range of 100 ° C. lower than the melting point of the resin composition to 20 ° C. lower than the melting point, particularly in the range of 90 ° C. lower than the melting point of the resin composition to 50 ° C. lower than the melting point, If the temperature is lower than this range, stretching unevenness occurs in the film, and if the temperature is higher than this range, the porosity of the film tends to decrease.

The stretching ratio needs to be 1.2 to 8 times, and if it is less than this range, the porosity and tensile strength of the stretched film are insufficient. On the other hand, when the stretching ratio exceeds 8 times, the film has an excessively high molecular orientation in the longitudinal direction, and the surface strength of the film is undesirably reduced. If the film is heat-treated after uniaxial stretching, the dimensional accuracy of the film can be stabilized, and a known surface treatment such as corona treatment or frame treatment can be performed.

Film of the present invention, which is obtained by the above method, moreover thickness is less porous film 90Myu, moisture permeability is not less 1500g / m ² · 24hr or more, longitudinal and transverse direction of the film Are 50 mm or less in hardness and have a surface strength of surface strength [kg] ≧ 35 × film thickness [mm].

(Effect of the Invention) Based on the above properties, the porous film of the present invention has sufficient surface strength in spite of being a thin film, has high moisture permeability, has good water vapor film permeability, and has no fear of stuffiness. . Furthermore, since the bending resistance in the vertical direction and the horizontal direction is small, the film is soft and the texture is good. Therefore, for clothing,
It is suitable for use in medical applications, filtration materials, battery separators and the like.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples unless it exceeds the gist.

Example 1 Density: 0.921 g / cm ³ , Melt Index (Ml): 1.0 g / 1
0 minutes, flow ratio: 19, copolymer component: 10% by weight of butene-1,
90 parts by weight of linear low-density polyethylene powder (40 mesh) having a melting point of 120 ° C, density: 0.924 g / cm ³ , Ml: 2.0 g / 10 min, flow ratio: 35 ) 10 parts by weight, 0.05 parts by weight of 2,6-di-tert-butylparacresol (antioxidant) and 0.05 parts by weight of calcium stearate (lubricant) were mixed with stirring in a Henschel mixer, and then 0.02 parts by weight was added thereto. 2,5-dimethyl-
2,5-di (t-butylperoxy) hexyne-3 and 200
Parts by weight of calcium carbonate (average particle size 1.2 μm, treated with fatty acid) were mixed and stirred. The resulting mixture is twin-screw kneader
Use DSM-65 (Double Screw Mixer manufactured by Japan Steel Works, Ltd.)
The mixture was kneaded at 0 ° C. to perform a crosslinking reaction with a radical generator, and then granulated. The Ml of the granulated product was 0.2 g / 10 min, and the flow ratio was 55.

The granulated product was blown by a 40 mmφ extruder under the following conditions to form a film having a thickness of 65 μm.

[Extrusion conditions] Cylinder temperature: 170-190-210-230 ° C Head and die temperature: 200 ° C Die annular slit diameter (D): 100mm Take-up speed: 8m / min. Blow ratio: 3.0 Frost line height (FLH ): 700 mm Folding diameter: 471 mm The film obtained by the above method was slit in the take-off direction and uniaxially stretched by a roll stretching machine under the following conditions.

[Stretching conditions] Stretching temperature: 50 ° C Stretching ratio: 2.5 times Stretching speed: 11.0 m / min. The film thus obtained is porous and sufficiently whitened, has no stretching unevenness, and has a beautiful surface. It was a porous film. Table 2 below shows the performance of this film.
It was shown to.

The measuring method of the performance evaluation items in Table 2 is as follows.

(A) Stretchability: A: No cutting, uniform stretching, no stretching unevenness.

：: No cutting, almost no stretching unevenness.

Δ: No cutting, slightly uneven stretching.

×: Large cutting or stretching unevenness.

(B) Tensile strength: According to ASTM 882-64T.

20mm width x 50mm length, pulling speed: 50mm / min. (C) Moisture permeability: according to ASTM E26-66 (E).

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

A: Extremely soft.

：: Soft.

Δ: slightly hard.

X: Hard.

(E) Film puncture strength (surface strength): The film is cut into a square of 100 mm x 100 mm to obtain a test film, and this film is fixed from above and below with a holding ring having an inner diameter of 80 mm.

Attach a hemispherical plunger with a round bar shape with a diameter of 20 mm and a tip of a radius of 10 mm to the tensile tester, and press it against the test film fixed as above at a crosshead speed of 500 mm / min. Is used to determine the magnitude of the surface strength. The tensile strength was the value at the time when the maximum strength was shown.

(F) Bending resistance (mm): Measured by the 45 ° cantilever method of JIS L1018-1977. The measurement was performed at a temperature of 20 ° C. and a relative humidity of 65%.

Examples 2 to 5 A porous film was produced in the same manner as in Example 1 except that the stretching temperature and the stretching ratio were changed as shown in Table 1, and the performance was evaluated. Table 2 shows the results.

Examples 6 to 7, Comparative Example 1 and Comparative Example 4 A porous film was produced in the same manner as in Example 1 except that the mixing ratio of the filler was changed as shown in Table 1, and the performance was evaluated. evaluated. Table 2 shows the results. In Examples 6 and 7, the Ml of the modified polymer obtained by kneading the raw material mixture and performing a cross-linking reaction with a radical generator was 0.2 g / 10 min, and the flow ratio of the modified polymer was 60 g, respectively. And 55.

Comparative Examples 2-3 In Example 1, the inflation molding conditions are shown in Table 1.
A porous film was produced and the performance was evaluated exactly in the same manner as in Example 1 except that the film was changed as described above. Table 2 shows the results.

Comparative Example 5 In Example 1, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 which is a radical generator was used.
When a porous film was produced in exactly the same manner as in Example 1 except that No. was added and the stretching ratio was changed as shown in Table 1, a film having performance that was highly satisfactory in stretching unevenness was not obtained. . Table 2 shows the results.

Comparative Example 6 The same linear low-density polyethylene powder, branched low-density polyethylene powder and filler as used in Example 1 were used in the amounts shown in Table 1 and mixed under stirring in a Henschel mixer, and then stirred. Meanwhile, 15 parts by weight of dipentaerythritol octanoate (plasticizer) was added thereto and mixed. Using this mixture, a porous film was produced in the same manner as in Example 1 except that the film was treated under the molding conditions and stretching conditions shown in Table 1, and the performance was evaluated. Table 2 shows the results.

Comparative Example 7 The same linear low-density polyethylene powder, branched low-density polyethylene powder and filler as used in Example 1 were used in the amounts shown in Table 1 and mixed under stirring in a Henschel mixer, and then stirred. 20 parts by weight of a polyhydroxy saturated hydrocarbon (plasticizer produced by the method of Reference Example 1 in JP-A-59-136334) was added and mixed with the mixture. Using this mixture, a porous film was produced in the same manner as in Example 1 except that the film was treated under the molding conditions and stretching conditions shown in Table 1, and the performance was evaluated. Table 2 shows the results.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-63-161037 (JP, A) JP-A-64-18625 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 9/00-9/14 B29C 55/00-55/30 C08L 23/00-23/36

Claims (1)

(57) [Claims] (1) 100 to 50 parts by weight of linear polyethylene having a density of 0.91 to 0.965 g / cm ³ , a melt index of 20 g / 10 min or less, a flow ratio of 70 or less, and (b) a melt index of 2
0 g / 10 min or less, 0 to 50 parts by weight of branched low-density polyethylene having a flow ratio of 70 or less, based on 100 parts by weight of the total amount of the linear polyethylene of (a) and the branched low-density polyethylene of (b). Using a composition comprising 0.0001 to 0.1 parts by weight of a radical generator and 100 to 400 parts by weight of a filler, after performing a crosslinking reaction or while performing the crosslinking reaction, a blow-up ratio of 2 to 8, a frost line Inflation molding with a height of 2 to 50 times the diameter of the annular slit of the die, and a thickness of 90 μm or less obtained by uniaxially stretching the obtained film with a stretching ratio of 1.2 to 8 times in the film take-off direction. The film has a hardness of 50 mm or less in both longitudinal and lateral directions, a moisture permeability of 1500 g / m ² · 24 hr or more, and a surface strength of the following formula: Surface strength [kg] Satisfies ≧ 35 × film thickness [mm] The porous film characterized by and.