JPH0853561A - Method for producing finely porous elastomer film - Google Patents

Abstract

PURPOSE:To obtain a finely porous film capable of being stretched in a stretching process without causing the breakage of the film and without lowering the generation efficiency of voids due to the stretchability of the film, and good in the balance between water vapor permeability and water resistance and in the balance between the physical properties of the film in the MD and TD directions. CONSTITUTION:The method for producing the finely porous elastomer film comprises forming a film from a thermoplastic elastomer composition produced by adding 90-120 pts.wt. of a surfacetreated inorganic filler having an average particle diameter of 1.8-3.0mum to 100 pts.wt. of a resin composition comprising 20-50wt.% of an ethylene-propylene-diene copolymer and 80-50wt.% of an ethylene-vinyl acetate copolymer, biaxially stretching the formed film preferably into the lengths of 2-3.5 times in the longitudinal and lateral directions, respectively, and subsequently annealing the biaxially stretched film under smaller stretching times than those in the biaxial stretching process preferably under the stretching of 1.5-2.5 times (smaller than those in the biaxial stretching process) in the longitudinal and lateral directions, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a microporous elastomer film, and in particular, it is useful in the fields of clothing, hygiene products, medical products, surgical-related products, etc., which are required to have moisture permeability. The present invention relates to a technique effective for obtaining a hydrophilic elastomer film.

[0002]

2. Description of the Related Art Generally, as a technique for making a polymer film microporous, there is a method in which a polymer composition containing a fine powdery inorganic filler is formed into a sheet and then stretched. According to this method, a method has been proposed in which a sheet is made from a thermoplastic elastomer composition and stretched to produce a porous sheet having a pore size of 10 μm or less (JP-A-60-166436).
Issue). On the other hand, using a thermoplastic elastomer composition obtained by blending an ethylene-propylene-diene copolymer rubber, an ethylene-vinyl acetate copolymer and an inorganic filler,
A method of uniaxially stretching to produce a thin microporous elastomer film has also been proposed (Japanese Patent Laid-Open No. 5-50522).

[0003]

However, in the former method, since blocking occurs when the film is thinned, only a thick sheet-like product having a film thickness of 0.15 to 0.16 mm can be obtained. Further, in the latter method, a thin microporous film can be obtained, but even if micropores (voids) are formed at the interface between the polymer and the inorganic filler by stretching, the film has stretchability. Due to the relationship, the void shrinks, and there is still room for improvement in terms of moisture permeability. By the way, for the thin microporous film by the stretching, it is necessary to balance the degree of moisture permeability and the degree of water resistance, for example, if the moisture permeability is high and the pore size of the void is too large, the water resistance is high. Will fall. In addition, it is necessary to balance the physical properties of the film in the longitudinal / transverse (MD / TD) directions.

In view of the above-mentioned prior art, the present invention provides a thin microporous film by stretching, obtains a thin microporous film without reducing the void generation efficiency due to the stretchability of the film, and To provide a microporous film having a well-balanced humidity and water resistance, to obtain a microporous film having a well-balanced physical property in the MD / TD direction of the film, and to provide a production method without film breakage during stretching. Especially. Further, other objects and novel features of the present invention will be apparent from the following description.

[0005]

The present invention is based on 100 parts by weight of a resin composition comprising 20 to 50% by weight of an ethylene-propylene-propylene copolymer rubber and 80 to 50% by weight of an ethylene-vinyl acetate copolymer. And the average particle size is 1.8-
After biaxially stretching a film formed from a thermoplastic elastomer composition containing 90 to 120 parts by weight of a 3.0 μm surface-treated inorganic filler, under a draw ratio smaller than the draw ratio during the biaxial stretching. The present invention relates to a method for producing a microporous elastomer film, which comprises subjecting the biaxially stretched film to an annealing treatment. As a preferred embodiment, the stretching ratio during biaxial stretching is 2 to 2 in the machine direction and the transverse direction. It is 3.5 times, and the draw ratio during annealing is 1.5 to 2.5 times in the machine direction and the transverse direction (provided that it is smaller than the draw ratio during biaxial drawing). .

The ethylene-propylene-diene copolymer rubber (hereinafter sometimes referred to as EPDM) used in the present invention is a copolymer containing ethylene, propylene and a diene compound. As the diene compound,
Examples include ethylidene norbornene, 1,4-hexadiene, dicyclopentadiene and the like. The EPDM preferably has a propylene content of 10 to 80% by weight, more preferably 15 to 70% by weight.

The EPDM has a number average molecular weight of 400,000 to 6
It is preferably 0,000, and the density is preferably 0.87 g / cm ³ or less. In addition, the melt index of EPDM (190
C, 2.16 kg load), 0.1-5.0 g /
It is preferably within 10 minutes, more preferably 0.1 to 10.
It is 1.0 g / 10 minutes.

The EPDM basically consists of the above-mentioned components, but within a range that does not impair the characteristics of the copolymer, for example, α-such as butene-1 or 4-methylpentene-1. It may contain an olefin.

The ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as EVA) used in the present invention has a vinyl acetate content of 5 to 30% by weight and a melt index (190 ° C., 2. 16 kg load) is 0.2-2
A 5 g / 10 min copolymer is preferred. When the content of vinyl acetate is less than 5% by weight, rubber elasticity is poor, while 3
If it exceeds 0% by weight, the film will be blocked and it will be difficult to form a film. The preferred vinyl acetate content is 15-30.
% By weight. For melt index,
If it is less than 0.2 g / 10 minutes, the film forming processability is poor, and 25
If it exceeds g / 10 minutes, film formation by the air-cooled inflation method becomes difficult. The preferred melt index is 15-
It is 25 g / 10 minutes.

The blending ratio of EPDM in the resin composition comprising the EPDM and EVA is based on the resin component (100
% By weight) is 20 to 50% by weight. This EPD
When the compounding ratio of M is lower than 20% by weight, the elasticity of the obtained elastomer film is lowered and the tensile stress becomes large, while when it is higher than 50% by weight, the thin film formability of the elastomer film is increased. Lower.

On the other hand, the blending ratio of EVA is 80 to 50% by weight based on the resin component (100% by weight).
Is. The reason for limiting the blending ratio of the EVA is that if it is higher than 80% by weight, the elongation of the elastomer film becomes insufficient, and if it is lower than 50% by weight, the thin-film moldability deteriorates.

The inorganic fillers used in the present invention include talc, calcium carbonate, gypsum, carbon black, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate and sulfuric acid. Use calcium, calcium phosphate, aluminum hydroxide, zinc oxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, silas balun, zeolite, silicate clay, cement, silica fume, mica powder, etc. However, talc, titanium oxide, calcium carbonate, silica and the like are particularly preferable. These inorganic fillers can be used alone or in combination. As the inorganic filler, it is preferable to use one whose surface is treated with a surface treatment agent such as stearic acid or a silane coupling agent, and the untreated one causes a decrease in affinity, which may cause powder falling or film breakage during stretching. Is not preferable. The degree of surface treatment is
It is preferably about 0.5 to 1.5 PHF (parts by weight of surface treatment agent to 100 parts by weight of inorganic filler). As the inorganic filler, it is preferable to add a powdery inorganic filler having an average particle diameter of 1.8 to 3.0 μm. If the average particle size of the inorganic filler is less than 1.8 μm, it becomes difficult to generate fine pores, and moisture permeability cannot be efficiently imparted. On the other hand, when the average particle diameter exceeds 3.0 μm, the water vapor transmission rate becomes high but the void diameter becomes large, so that the water resistance and the film strength decrease, which is not preferable. The total amount of the inorganic filler added is 90 to 120 parts by weight based on the weight of EPDM + EVA (100 parts by weight). If it is less than 90 weight, the water vapor permeability is insufficient,
If it exceeds the weight part, the void generation efficiency is too high,
It is not preferable because the pore size becomes large and the water resistance and the film strength decrease.

Polyolefin may be further added to the thermoplastic elastomer composition of the present invention. As the polyolefin, polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene is preferable. The amount of the polyolefin added is preferably 1 to 10 parts by weight based on the weight of EPDM + EVA (100 parts by weight).

Various additives such as a heat stabilizer, a UV absorber, an antistatic agent, an antioxidant, and a coloring agent may be appropriately blended in the thermoplastic elastomer composition of the present invention.

The pre-stretched film made of the above-mentioned thermoplastic elastomer composition can be formed into a film by the T-die method, but an inflation film formed by the air-cooled inflation method is preferable in terms of MD / TD balance and thinning. . The inflation film is obtained, for example, by kneading the composition at a temperature of 160 ° C. or lower and forming the film by an air-cooling inflation method with a blow-up ratio of 2.0 to 5.0. The matters disclosed in JP-A-3-128945 can be applied to the method for producing such a film.

The thickness of the above-mentioned film is appropriately selected depending on the application, but for example, the film thickness after stretching is 30 to 50 μm.
When it is m, it is preferably about 80 to 120 μm.

After the biaxial stretching, the film is annealed at a stretching ratio smaller than the stretching ratio during the biaxial stretching. The annealing treatment (annealing) refers to heating and heat-setting (heat treatment) while holding both ends of the stretched film with, for example, tenter, and the annealing is performed at a temperature of 30 to 60 ° C. for 30 seconds to 10 seconds. It can be done in an air bath for a minute. According to the earnest studies by the present inventors, the film is biaxially stretched preferably in the MD and TD directions by a factor of 2 to 3.5, and the film is annealed under a stretching ratio at that time, From the relationship with the stretchability of the film, it was found that the residual stress was too large and the film ruptured. Also, when the film after biaxial stretching is immediately released from the stretched state,
It was also found that due to the stretchability of the film, the film shrinks and only a film with a considerably lower draw ratio than the set draw ratio can be obtained. Therefore, it is smaller than the stretching ratio during the biaxial stretching, and preferably 1.5 to 1.5 in the MD and TD directions.
The film is broken at the time of stretching by returning the film to 2.5 times (however, it must be smaller than the ratio at the time of biaxial stretching) and annealing the film under the ratio at which the residual stress after stretching is reduced. There is no, it is possible to obtain a thin microporous film by stretching without reducing the void generation efficiency due to the stretchability of the film, and, in combination with the thermoplastic elastomer composition, the balance between moisture permeability and water resistance. By the biaxial stretching, the film M
A microporous film having a well-balanced physical property in the D / TD direction could be obtained. If the annealing condition is less than the above lower limit, there is no annealing effect and
On the other hand, when the content exceeds the upper limit, the water rupture and the pore size become large and the water resistance becomes poor.

By the above method of the present invention, a microporous elastomer film thinned to a considerable thickness can be obtained at a predetermined stretching ratio. The thickness of the elastomer film is appropriately selected depending on the application, but is, for example, 30 to 5
A thickness of about 0 μm can be obtained.

[0019]

EXAMPLES Next, examples of the present invention will be shown. The test methods in Examples and Comparative Examples are as follows. (1) Water vapor transmission rate; conforms to JIS Z0208. (2) Water resistance: According to JIS L1092. (3) Breaking strength; conforms to JIS L1096. (4) Breaking elongation: According to JIS L1092. (5) 50% 2-cycle strain; conforming to JIS L1096. However, the measured values of the breaking strength, the breaking elongation, and the 50% 2-cycle strain are MD / TD values.

Example 1. Ethylene-propylene-diene copolymer (number average molecular weight 450,000, density 0.87 g / cm
³ , MI = 0.1 g / 10 min, propylene content 27% by weight) 40% by weight, ethylene-vinyl acetate copolymer (vinyl acetate content 28% by weight, MI = 20 g / 10
Min) 60 parts by weight of a resin composition consisting of 60 parts by weight, and 100 parts by weight of stearic acid-treated calcium carbonate (average particle size: 2 μm, stearic acid: 1.0 PHF) are added to the composition at 160 ° C. The raw film having a thickness of 80 μm was formed into a film by the air-cooled inflation method under the following conditions. Die diameter ・ ・ ・ 150mm, Blow ratio ・ ・ ・ 3.5, Extruder cylinder temperature ・ ・ ・ 160 ° C Resin temperature at die outlet ・ ・ ・ 170 ° C, Resin pressure at die outlet ・ ・ ・ 350kg / cm ² , extrusion rate ... 100 kg / hr, take-up speed ... 10 m / min,

Next, the original film obtained above is
In a biaxial stretching machine, under the following conditions, and as shown in Table 1, initially, after stretching at a draw ratio (MDxTD = 2.5x2.5), the draw ratio is MDxTD = 1.5x1.5. After returning, the original film was annealed under the draw ratio. Stretching method: Simultaneous biaxial stretching, Stretching speed: 10 m / min, Preheating temperature / hour: 45 ° C./90 seconds, Annealing temperature / hour: 40 ° C./60 seconds (air bath),

Regarding the obtained elastomer film,
The moisture vapor transmission rate, water resistance, breaking strength, breaking elongation, and 50% 2-cycle strain were measured. The results are shown in Table 1.

Example 2. In Example 1, the original film was initially stretched by a biaxial stretching machine (MDxTD =
3.5x3.5), and then draw at MDxTD
= 2.5 × 2.5 and the original film was annealed under the stretching ratio, in the same manner as in Example 1 except that an elastomer film having a thickness of 32 μm was obtained. Physical properties of the obtained elastomer film were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 In Example 2, the original film was stretched by a biaxial stretching machine (MDxTD = 3.5x).
After stretching in 3.5), the original film was annealed under the same stretching ratio without returning the stretching ratio, and the film was broken during the annealing.

Comparative Example 2 In Example 1, the original film was stretched by a biaxial stretching machine (MDxTD = 2.5x).
After stretching in 2.5), the original film was annealed under the same stretching ratio (MDxTD = 2.5x2.5) without returning the stretching ratio.

Comparative Example 3 In Example 1, the original film was stretched at a stretching ratio MDxTD = 2.5 × 2.5, but was left as it was and was not annealed. The stretching ratio of the stretched film was MDxTD = 1.
It has fallen to 7x1.7.

Comparative Example 4 In Example 2, the original film was stretched at a stretching ratio MDxTD = 3.5 × 3.5, but was left as it was and was not subjected to annealing treatment. The stretching ratio of the stretched film was MDxTD = 2.
It has dropped to 6x2.6.

Physical properties of the films obtained in Comparative Examples 1 to 4 were measured in the same manner as in Example 1 except for Comparative Example 1. These results are shown in Table 1 together with the results shown in Comparative Example 1.

Comparative Example 5. An elastomer film was obtained in the same manner as in Example 1 except that the stearic acid-treated calcium carbonate was replaced with one having an average particle size of 1.5 μm. Physical properties of the obtained elastomer film were measured in the same manner as in Example 1. The results are shown in Table 1.
Shown in

Comparative Example 6. An elastomer film was obtained in the same manner as in Example 1, except that the stearic acid-treated calcium carbonate was replaced with one having an average particle size of 4.0 μm. Physical properties of the obtained elastomer film were measured in the same manner as in Example 1. The results are shown in Table 1.
Shown in

Comparative Example 7. An elastomer film was obtained in the same manner as in Example 1, except that the amount of stearic acid-treated calcium carbonate was changed to 60 parts by weight. About the obtained elastomer film, Example 1
The physical properties were measured in the same manner as in. The results are shown in Table 1.

Comparative Example 8. An elastomer film was obtained in the same manner as in Example 1 except that the amount of stearic acid-treated calcium carbonate was changed to 150 parts by weight. About the obtained elastomer film, Example 1
The physical properties were measured in the same manner as in. The results are shown in Table 1.

Comparative Example 9. The elastomer film was stretched in the same manner as in Example 1 except that calcium carbonate that had not been treated with stearic acid was used. However, the film was ruptured during stretching. Moreover, when the surface of the film was touched, the powder of calcium carbonate had a large tendency to fall off to the extent that it adhered to the hand. The results are shown in Table 1.
In Table 1, the vertical and horizontal magnifications are the same.
Some of them are shown in magnification only in one direction (for example, 2.5 means 2.5 × 2.5 times).

[0034]

[Table 1]

The following can be seen from the results shown in Table 1 above. Relationship between Draw Ratio and Annealing As shown in Table 1, the draw ratio during biaxial stretching is preferably M.
Less than 2 to 3.5 times in the D direction and the TD direction, preferably 1.5 to 2.5 times in the MD direction and the TD direction (provided that it is smaller than the magnification at the time of biaxial stretching), By annealing the film under a ratio that reduces the residual stress after stretching, it has fine pores of an appropriate size, excellent moisture permeability and water resistance, and is relatively M
It can be seen that a stretchable film having a good physical property balance in the D / TD direction can be obtained. (Examples 1 and 2). Stretching ratio,
When the same magnification is used during annealing [3.5 x 3.5
Double] (Comparative Example 1), the micropores generated by stretching are expanded and broken due to the residual stress applied to the film. If the draw ratio is 2.5 × 2.5 (Comparative Example 2), the drawing is possible, but for the same reason, the micropores are enlarged, and the water resistance is extremely lowered. When the post-stretching annealing step was not performed (Comparative Examples 3 and 4), the film removed from the chuck of the biaxial stretching machine after stretching rapidly contracted. By performing annealing after stretching as shown in Examples 1 and 2, the rapid shrinkage after removal from the biaxial stretching machine disappeared. Moreover, by performing the annealing as shown in Examples 1 and 2, the moisture permeability could be efficiently imparted for the first time. Relationship between Average Particle Size of Calcium Carbonate and Addition Amount As shown in Table 1, when the average particle size of calcium carbonate (CaCO ₃ ) is small (Comparative Example 6), micropores are less likely to be formed, and the transparent particles are efficiently transmitted. Wetness cannot be imparted. With a commercially available calcium carbonate-filled polyethylene film, a film having sufficient moisture permeability at such a particle size can be obtained, but since the film obtained in the present invention has elasticity, it is formed once. Also, the fine holes contracted, and voids could not be efficiently generated unless the average particle size was made larger than this. When the average particle diameter becomes large (Comparative Example 6), the water vapor permeability becomes high, but the pore diameter of the void becomes large, so that the water resistance decreases. On the other hand, when the particle size was appropriate, an elastomer film having a good balance of physical properties such as moisture permeability and water resistance was obtained. When the amount of calcium carbonate added is small, the moisture vapor transmission rate is insufficient (Comparative Example 7), and when the amount added is too large, the void generation efficiency is too high, resulting in an increase in the pore size and deterioration in water resistance and film physical properties. (Comparative example 8).

[0036]

As described above, according to the present invention, there is no film breakage during stretching, and a thin microporous film can be obtained by stretching without lowering the void generation efficiency due to the stretchability of the film. It was possible to obtain a microporous film in which the moisture permeability and the water resistance were well balanced and the physical properties of the film in the MD / TD direction were well balanced.

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Claims (2)

[Claims] 1. An ethylene-propylene-propylene copolymer rubber 20 to 50% by weight and an ethylene-vinyl acetate copolymer 8
From a thermoplastic elastomer composition obtained by blending 90 to 120 parts by weight of a surface-treated inorganic filler having an average particle size of 1.8 to 3.0 μm with 100 parts by weight of a resin composition consisting of 0 to 50% by weight. A method for producing a microporous elastomer film, comprising biaxially stretching a formed film, and then annealing the biaxially stretched film under a stretching ratio smaller than the stretching ratio at the time of the biaxial stretching. 2. The stretching ratio during biaxial stretching is 2 to 3.5 times in the longitudinal and transverse directions, and the stretching ratio during annealing is 1.5 to 2.5 times in the longitudinal and transverse directions. , Which is smaller than the magnification at the time of biaxial stretching).
The method for producing the microporous elastomer film according to claim 1.