JP2005263862A - Porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film having both high transparency and moisture permeability and excellent strength.
SOLUTION: A linear low density polyethylene resin composition comprising 30 to 50% by weight of linear low density polyethylene and 70 to 50% by weight of an inorganic filler is stretched 1.1 to 1.6 times in at least one axial direction. A porous film to be obtained, in which the linear low density polyethylene has a melt index of 0.5 g / 10 min or more and a linear low density polyethylene of less than 3 g / 10 min of 30 to 70% by weight and a melt index of 3 g / 10 min or more, 20 g / It is a porous film which consists of 70-30 weight% of linear low density polyethylene of 10 minutes or less, and the difference of the melt index of the said linear low density polyethylene is 3 or more.
[Selection figure] None

Description

  The present invention relates to a novel porous film containing linear low density polyethylene and an inorganic filler. Specifically, the present invention provides a porous film having both high transparency and moisture permeability and excellent strength.

  Conventionally, a porous film is a method in which a resin composition obtained by adding an inorganic filler to a thermoplastic resin is melted and formed into a sheet shape, and then the interface between the thermoplastic resin and the inorganic filler is removed by stretching or the like. Manufactured by. These porous films have waterproof and moisture permeability that allows gas such as air and water vapor to pass through and blocks water droplets and so on. Widely used as a sheet.

  However, these porous films are opaque due to irregular reflection of light because there are many fine voids formed by interfacial peeling between the thermoplastic resin and the inorganic filler. Therefore, when constructing as a moisture permeable waterproof sheet on the roof or wall of a building, specifically when tucking the moisture permeable waterproof sheet on a support such as a pillar, the support behind the mark is seen through Because it was not possible, there were problems such as that it took time for construction work and required skill for the workers.

  The porous film that solves the above-mentioned transparency is a porous film in which a predetermined amount of an inorganic filler is added to a polyolefin resin having a specific melt index to form an unstretched sheet, and the stretched film is stretched at a predetermined stretch ratio. A film has been proposed (see Patent Document 1).

JP 2001-270954 A

  However, since the porous film is manufactured at a low stretch ratio, it has excellent transparency, but when used as a moisture-permeable waterproof sheet for building materials, the porous film has moisture permeability at a specified low stretch ratio. It is insufficient, and it is not possible to sufficiently prevent condensation caused by the temperature difference between indoor and outdoor. Further, in order to impart high moisture permeability, it has been studied to increase the draw ratio and to increase the melt index of the polyolefin resin, but the former decreases transparency and the latter decreases film strength. There was a problem, and there was room for improvement in terms of achieving both high transparent moisture permeability and strength.

  Accordingly, an object of the present invention is to provide a porous film having both high transparency and moisture permeability and excellent strength.

  The present inventors have conducted intensive research on the development of a porous film to solve the above problems. As a result, a predetermined amount of inorganic filler is added to a linear low density polyethylene resin mixture composed of two component linear low density polyethylenes having different melt indexes to form an unstretched sheet, which is stretched at a predetermined low magnification. As a result, the inventors have found that the porous film obtained by doing so has both high transparency and moisture permeability and is excellent in strength, and have completed the present invention.

  That is, the present invention provides a linear low density polyethylene resin composition comprising 30 to 50% by weight of linear low density polyethylene and 70 to 50% by weight of an inorganic filler, at least uniaxially at an area magnification of 1.1 to 1.6 times. A porous film obtained by stretching in a direction, wherein the linear low density polyethylene has a melt index of 0.5 g / 10 min or more and less than 3 g / 10 min. A porous film comprising 70-30% by weight of linear low density polyethylene of 10 min or more and 20 g / 10 min or less, wherein the difference in melt index of the linear low density polyethylene is 3 or more.

The porous film of the present invention has an extremely high moisture permeability that has never been achieved while having excellent transparency, and also has a sufficient film strength. Specifically, a moisture permeability of 5000 g / m ² or more and a total light transmittance of 60% or more can be achieved while having a sufficient film strength.

  From this, the porous film and laminated sheet of the present invention can be suitably used as a moisture permeable waterproof sheet for building materials with added visibility, agricultural applications such as multi-sheets, and hygiene materials such as disposable diapers and sanitary napkins. It can also be suitably used for medical applications such as surgical clothes, clothing applications such as disposable rain feathers, and waste disposal applications.

  The present invention is described in detail below.

  The porous film of the present invention forms an unstretched sheet by adding a predetermined amount of an inorganic filler to a linear low-density polyethylene resin mixture composed of two-component linear low-density polyethylene having different melt indexes, It can obtain by extending | stretching by low magnification.

  The linear low density polyethylene used in the present invention is not particularly limited, and is an α-olefin having 4 to 8 carbon atoms such as ethylene and 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like. And a copolymer thereof can be used. Further, the density of the linear low density polyethylene can be used without any particular limitation, but if it is in the range of 0.90 to 0.94, a porous film excellent in flexibility can be obtained. preferable.

  The porous film of the present invention has two components having different melt indexes as the above-mentioned linear low density polyethylene for the purpose of expressing high moisture permeability at a low draw ratio and maintaining the strength of the obtained porous film. It is important to mix a certain amount of the linear low density polyethylene. Specifically, the linear low density polyethylene has a melt index of 0.5 g / 10 min or more and a linear low density polyethylene (hereinafter abbreviated as “low MI linear low density polyethylene”) having a melt index of 0.5 g / 10 min or more and less than 3 g / 10 min. It is composed of 70 to 30% by weight of a linear low density polyethylene (hereinafter abbreviated as high MI linear low density polyethylene) having an index of 3 g / 10 min or more and 20 g / 10 min or less, and the difference in melt index between the linear low density polyethylene is It is essential that the number is 3 or more.

  First, the low MI linear low density polyethylene mainly contributes to maintaining the strength of the obtained film. That is, when the linear low density polyethylene having a melt index of 3 g / 10 min or more is used, it is difficult to maintain the strength of the obtained film. In addition, it is difficult to impart flexibility to the obtained film.

  Next, the high MI linear low density polyethylene is blended mainly for the purpose of expressing moisture permeability at a low draw ratio specified in the present invention. When the linear low density polyethylene has a melt index of less than 3 g / 10 min, it is difficult to impart sufficient moisture permeability at the low draw ratio specified in the present invention. Film breakage or the like occurs during film formation, resulting in poor film formation stability, and the strength of the obtained porous film is lowered.

  Further, the mixing ratio of the two-component linear low-density polyethylene having different melt indexes described above affects the balance between the transparent moisture permeability and strength of the obtained porous film. That is, when the proportion of the low MI linear low density polyethylene exceeds 70% by weight and the proportion of the high MI linear low density polyethylene is less than 30% by weight, the film strength is sufficient, but the low The stretch ratio is not preferable because moisture permeability is not sufficiently exhibited. When the proportion of the low MI linear low density polyethylene is less than 30% by weight and the proportion of the high MI linear low density polyethylene exceeds 70% by weight, high transparency and moisture permeability can be expected. This is not preferable because the strength is greatly reduced.

  Furthermore, when the difference in melt index between the above-described two-component linear low density polyethylene is less than 3, it is difficult to balance the above-described film strength retention and moisture permeability development at a low draw ratio, more preferably. Is 3 or more and less than 15.

  For this reason, the porous film of the present invention comprises 30 to 70% by weight of low MI linear low density polyethylene and 70 to 30% by weight of high MI linear low density polyethylene, and the melt index of the above linear low density polyethylene. By blending a linear low density polyethylene having a difference of 3 or more, high transparency and moisture permeability can be exhibited at a low draw ratio specified in the present invention, and the strength of the obtained film can be maintained.

  Each component of the two-component linear low density polyethylene may be constituted by a kind of linear low density polyethylene, or may be constituted by two or more kinds of linear low density polyethylene. good. When constituted by two or more types of linear low density polyethylene, the melt index is an average value thereof.

  The inorganic filler used in the present invention is not particularly limited, and inorganic salts such as calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide and aluminum hydroxide, and inorganic such as zinc oxide, magnesium oxide and silica Silicates such as oxides, mica, vermiculite, talc, and organometallic salts can be used. These can be used alone or in combination. Among these, calcium carbonate is particularly preferable in consideration of cost performance and releasability from the resin.

  Here, as calcium carbonate, heavy calcium carbonate produced by mechanically pulverizing and classifying calcite-type crystalline limestone with good purity, carbon dioxide compounding method, calcium chloride soda method, lime soda, etc. Particles such as light calcium carbonate produced by a wet chemical reaction can be used without limitation.

  The average particle diameter of the inorganic filler described above is preferably 0.1 to 10 μm. When the average particle size of the inorganic filler is in the above range, the dispersibility is good, the formation of communication holes during stretching is easy, and the film is not easily broken during film formation and can be manufactured with high productivity. .

  Furthermore, it is particularly preferable that the inorganic filler is calcium carbonate satisfying the average particle diameter.

  In the present invention, the blending ratio of the linear low density polyethylene and the inorganic filler is 30 to 50% by weight of the linear low density polyethylene and 70 to 50% by weight of the inorganic filler. When the blending ratio of the inorganic filler is less than 50% by weight, the film may be difficult to be porous when stretched, and the moisture permeability may not be sufficiently expressed. When the blending ratio of the inorganic filler exceeds 70% by weight, the film It is not preferable because tearing or the like is likely to occur at the time of molding, and the productivity is lowered and the strength of the obtained film is also lowered.

  The porous film of the present invention is a range that does not impair the object of the present invention, further linear low density polyethylene and other polyolefin resins, other thermoplastic resins such as petroleum resins, pigments, stabilizers, surfactants, Plasticizers, oils, and other additives can be added as needed. Of these, low density polyethylene is preferably blended for the purpose of imparting high-speed film forming properties. 1-10 weight part is preferable with respect to 100 weight part of linear low density polyethylene resin compositions, and, as for the compounding quantity, 2-7 weight% is more preferable.

  Moreover, it is preferable to mix | blend a hindered phenol-type heat stabilizer and a phosphorus-type heat stabilizer as a heat stabilizer at the time of extrusion molding.

  Examples of the hindered phenol heat stabilizer include 2,6-di-t-butyl-4-methylphenol and tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate]. Methane, 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) trione, 3, 3′3 ″, 5,5′5 ″ -hexa-t-butyl-a, a′a ″-(mesitylene-2,4,6-triyl) tri-p-cresol, octadecyl-3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate, 2,6-di-t-butyl-4- (4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, Tris (3,4-di-t-bu Le-4-hydroxybenzyl) isocyanurate and the like, it is preferable to blend 0.01 to 2 parts by weight with respect to the linear low-density polyethylene 100 parts by weight of the resin composition of the present invention.

  Examples of phosphorus-based heat stabilizers include tris (2,4-di-t-butylphenyl) phosphite and bis [2,4-bis (1,1-dimethylethyl) -6-methylphenyl] ethyl phosphite. Phosphite series, tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrakis (2,4-di-tert-butylphenyl) -4 Phosphonites such as 4,4'-biphenylene phosphonite are mentioned, and it is preferable to blend 0.01 to 2 parts by weight with respect to 100 parts by weight of the linear low density polyethylene resin composition of the present invention.

  Furthermore, for example, when used for outdoor use such as a moisture-permeable waterproof sheet for building materials, in addition to the above-mentioned hindered phenol-based antioxidant and phosphorus-based heat stabilizer, hindered amine-based light having a molecular weight of 1500 to 4500. It is preferable to add a stabilizer.

  Examples of hindered amine light stabilizers include N, N ′, N ″, N ′ ″-tetrakis- (4,6-bis- (butyl- (N-methyl-2,2,6,6-tetramethylpiperidine). -4-yl) amino) -triazin-2-yl) -4,7-diazadecane-1,10-diamine, 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6- Condensates of pentamethyl-4-piperidinol and β, β, β ′, β ′, tetramethyl-3,9- (2,4,8,10-tetraoxaspiro [5,5] undecane) diethanol, etc. Examples include a polymer of dimethyl acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol. Moreover, these can be used individually or in mixture of 2 or more types. In particular, A) N, N ′, N ″, N ′ ″-tetrakis- (4,6-bis- (butyl- (N-methyl-2,2,6,6-tetramethylpiperidin-4-yl) Polymerization of a) amino) -triazin-2-yl) -4,7-diazadecane-1,10-diamine and B) dimethyl succinate with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol A mixture of materials is preferable because a high weather resistance improving effect can be obtained. In this case, the combined ratio of both hindered amine light stabilizers is preferably about 2/8 to 8/2 in weight ratio (A / B).

  A general method for producing the porous film of the present invention will be described.

  The mixing and granulation method of each component constituting the resin composition of the present invention and additives to be blended as necessary is not particularly limited, and a known method can be adopted. For example, after mixing with ordinary Henschel mixer, super mixer, tumbler mixer, etc., generally kneading and pelletizing with high kneading type twin screw extruder, tandem kneading machine etc. by methods such as strand cut, hot cut, underwater cut etc. To do.

  The pelletized composition is formed into a film shape with a circular die or a T die attached to the tip of an extruder, and is made into a porous film by a known method such as uniaxial or biaxial stretching. The cooling method when using the T-die method is not particularly limited, and a known method such as a nip roll method, an air knife method, or an air chamber method can be employed.

  The above-mentioned film-formed sheet is at least at a magnification of 1.1 to 1.6 times in the temperature range of normal temperature or more and less than the softening point of the resin by a known method such as a roll stretching method or a tenter stretching method. By stretching in a uniaxial direction, the porous film of the present invention can be obtained. Further, the stretching may be single-stage stretching or multi-stage stretching, and if necessary, heat treatment may be performed after stretching.

  The porous film of the present invention is obtained by stretching at least one axial direction at a low magnification of 1.1 to 1.6 times the area magnification for the purpose of imparting high transparency. When the draw ratio is less than 1.1, high transparency is maintained, but a peeling void between the resin and the inorganic filler is not sufficiently formed, which is not preferable because moisture permeability decreases. On the other hand, when the draw ratio exceeds 1.6 times, high moisture permeability is exhibited, but light is irregularly reflected by the formed voids, which is not preferable because the transparency is significantly lowered. For this reason, the draw ratio is preferably 1.1 to 1.6 times, and more preferably 1.2 to 1.4 times in terms of achieving both high transparency, moisture permeability, and strength.

  The thickness of the porous film is preferably 10 to 50 μm and more preferably 20 to 40 μm in order to achieve both high transparency, moisture permeability and strength.

  The porous film of the present invention is laminated with a breathable reinforcing material, so that it can be used for building materials such as house wrap and roofing, agricultural applications such as multi-sheets, hygiene materials such as disposable diapers and sanitary napkins, and medical clothing such as surgical clothes. It can be suitably used for applications, apparel applications such as disposable rain wings, and waste disposal applications.

The breathable reinforcing material is not particularly limited, and for example, a nonwoven fabric, a woven fabric, a split fabric, a mesh, a net, a filter, paper, a fabric, or the like can be used. At this time, a breathable reinforcing material that easily inhibits the moisture permeability of the porous film, such as a woven fabric, preferably has an opening ratio of 30% or more, and more preferably 50% or more. On the other hand, it inhibits the transparency of the porous film tends to gas-permeable reinforcing element as non-woven fabric is preferably those having a basis weight 30 g / m ² or less thin, more preferably not more than 20 g / m ² or less. The material of the breathable reinforcing material is not particularly limited, and polyolefin, polyester, nylon, or the like can be used.

  The production method of the laminated sheet is not particularly limited, and a known method can be used, and the laminated sheet can be obtained by bonding by a method such as thermal lamination, hot melt lamination, dry lamination, or wet lamination.

  Examples and Comparative Examples are shown below, but the present invention is not limited to these Examples.

  Table 1 shows linear low density polyethylene used in Examples and Comparative Examples.

尚、実施例及び比較例に記載した物性値は以下に示す方法によって測定したものである。

In addition, the physical-property value described in the Example and the comparative example was measured by the method shown below.

1) Thickness Measured with a dial gauge according to JIS K 6734.

2) Air permeability It measured with the Oken type air permeability meter according to JISP8117.

3) Moisture permeability Measured according to JIS L 1099. The 1Hr measurement value was converted to 24Hr under the conditions of a measurement temperature of 40 ° C. and a humidity of 90%.

4) Total light transmittance It measured according to JISK7105 using the direct reading haze computer HGM-2DP by Suga Test Instruments.

5) Tensile strength Measured under conditions of a test piece width of 25 mm, a tensile speed of 200 mm / min, and a distance between chucks of 50 mm.

Example 1
Linear low-density polyethylene (trade name: IDEMISUSU LL 0234CL density = 0.919 g / cm ³ MI = 2.1 g / 10 min manufactured by Idemitsu Petrochemical Co., Ltd.), linear low-density polyethylene (trade name: MORETEC 1018CN) Density = 0.910 g / cm ³ MI = 8.0 g / 10 min Idemitsu Petrochemical Co., Ltd. 20 parts by weight, as an inorganic filler, calcium carbonate (trade name: LAC2000, Dowa Calfine Co., Ltd. average particle size = 2.0 μm) 100 parts by weight of a resin composition consisting of 60 parts by weight, 0.5 parts by weight of a hindered amine light stabilizer (manufactured by Ciba Specialty Chemicals, trade name: Tinuvin 622LD), and a hindered phenol as a heat stabilizer Thermal Stabilizer (Ciba Specialty Chemicals, trade name: IRGA OX3114) 0.2 parts by weight of phosphorus-based heat stabilizer (Ciba Specialty Chemicals, trade name: IRGAFOS 168) in addition to formulation and 0.3 parts by weight, was performed granulation, the film-forming.

  For granulation, a twin screw extruder with a vent was used to extrude into a strand at a cylinder temperature of 180 ° C., cooled in a water bath, cut to about 5 mm and dried to form pellets. Next, the pellet was film-formed with a T-die film forming machine. At this time, the lip clearance was 1.2 mm, the die temperature was 230 ° C., and the cast roll temperature was 20 ° C. Further, the film was uniaxially stretched 1.3 times with a roll stretching machine set at 60 ° C., and then in-line annealed with a heat setting roll set at 80 ° C. to obtain a porous film.

Table 2 shows the evaluation results of the thickness, air permeability, moisture permeability, total light transmittance, and tensile strength of the porous film. The obtained porous film had a high transparent moisture permeability with a moisture permeability of 6900 g / m ² and a total light transmittance of 66%. Moreover, the tensile strength in the film MD direction was 9.8 N / 25 mm, and sufficient strength was maintained.

Examples 2-5
A porous film was obtained in the same manner as in Example 1 except that the type and blending ratio of the linear low density polyethylene were changed to the blending shown in Table 2. The results are shown in Table 2. All of the obtained porous films had high transparent moisture permeability with a moisture permeability of 6500 g / m ² or more and a total light transmittance of 65% or more. Moreover, the tensile strength in the film MD direction also maintained sufficient strength.

Examples 6-7
A porous film was obtained in the same manner as in Example 1 except that the stretching ratio was changed to the ratio shown in Table 2. The results are shown in Table 2. Each of the obtained porous films had a high transparent moisture permeability with a moisture permeability of 5000 g / m ² or more and a total light transmittance of 60% or more, and maintained sufficient strength.

Examples 8-9
A porous film was obtained in the same manner as in Example 1 except that the thickness of the film was changed to the thickness shown in Table 2. The results are shown in Table 2. Each of the obtained porous films had a high transparent moisture permeability with a moisture permeability of 5000 g / m ² or more and a total light transmittance of 60% or more, and maintained sufficient strength.

Examples 10-11
A porous film was obtained in the same manner as in Example 1 except that the blending ratio and stretching ratio of the linear low density polyethylene and the inorganic filler were changed to the blending and stretching ratio shown in Table 2. The results are shown in Table 2. Each of the obtained porous films had a high transparent moisture permeability with a moisture permeability of 5000 g / m ² or more and a total light transmittance of 60% or more, and maintained sufficient strength.

Example 12
The blending ratio is 20 parts by weight of linear low density polyethylene (trade name: IDEMISUSU LL 0234CL density = 0.919 g / cm ³ MI = 2.1 g / 10 min, manufactured by Idemitsu Petrochemical Co., Ltd.), linear low density polyethylene (trade name) : MORETEC 1018CN Density = 0.910 g / cm ³ MI = 8.0 g / 10 min Idemitsu Petrochemical Co., Ltd. 20 parts by weight, calcium carbonate (trade name: LAC2000, Dowa Calfine Co., Ltd.) as an inorganic filler 100 parts by weight of a resin composition comprising 60 parts by weight of a particle diameter = 2.0 μm) and low density polyethylene (trade name: Mirason 16P density = 0.923 g / cm ³ MI = 3 with respect to 100 parts by weight of the resin composition .7 g / 10 min (Mitsui Petrochemical Co., Ltd.) The same as in Example 1 except that the composition was changed to 4 parts by weight. Thus, a porous film was obtained. The results are shown in Table 2. The obtained porous film had a moisture permeability of 6100 g / m ² , a high transparent moisture permeability with a total light transmittance of 65%, and maintained sufficient strength. Moreover, the casting speed at the time of film forming improved to 35 m / min.

比較例１〜２
線状低密度ポリエチレンの配合比を表３に示す配合に変更した以外は、実施例１と同様にして多孔質フィルムを得た。結果を表３に示した。比較例１で得られた多孔質フィルムは、強度は保持しているものの、低延伸倍率では十分な透湿性が発現せず、透湿度が大きく低下した。また、全光線透過率も低下した。一方、比較例２で得られた多孔質フィルムは、高い透明透湿性を有していたが、強度が著しく低下した。

Comparative Examples 1-2
A porous film was obtained in the same manner as in Example 1 except that the blending ratio of the linear low density polyethylene was changed to the blending shown in Table 3. The results are shown in Table 3. Although the porous film obtained in Comparative Example 1 maintained strength, sufficient moisture permeability was not exhibited at a low draw ratio, and the moisture permeability was greatly reduced. Moreover, the total light transmittance also decreased. On the other hand, the porous film obtained in Comparative Example 2 had high transparent moisture permeability, but the strength was significantly reduced.

Comparative Example 3
A porous film was obtained in the same manner as in Example 1 except that the type and blending ratio of the linear low density polyethylene were changed to the blending shown in Table 3. The results are shown in Table 3. The obtained porous film maintained strength, but did not exhibit sufficient moisture permeability at a low draw ratio, and the moisture permeability was greatly reduced. Moreover, the total light transmittance also decreased.

Comparative Examples 4-6
A porous film was obtained in the same manner as in Example 1 except that the type and blending ratio of the linear low density polyethylene were changed to the blending shown in Table 3. The results are shown in Table 3. Each of the obtained porous films had high transparent moisture permeability with a moisture permeability of 5000 g / m ² or more and a total light transmittance of 60% or more, but the strength was remarkably lowered.

Comparative Example 7
A porous film was molded in the same manner as in Example 1 except that the type and blending ratio of the linear low density polyethylene were changed to the blending shown in Table 3. However, film breakage occurred in the stretching process, and a porous film could not be stably formed.

Comparative Example 8
A porous film was obtained in the same manner as in Example 1 except that the type and blending ratio of the linear low density polyethylene were changed to the blending shown in Table 3. The results are shown in Table 3. The obtained porous film maintained strength, but did not exhibit sufficient moisture permeability at a low draw ratio, and the moisture permeability was greatly reduced. Moreover, the total light transmittance also decreased.

Comparative Example 9
A porous film was molded in the same manner as in Example 1 except that the type of linear low density polyethylene was changed to that shown in Table 3. However, flum tears frequently occurred in the stretching process, and a porous film could not be formed.

Comparative Examples 10-11
A porous film was obtained in the same manner as in Example 1 except that the stretching ratio was changed to the ratio shown in Table 3. The results are shown in Table 3. The porous film obtained in Comparative Example 10 had a significantly reduced moisture permeability, and the porous film obtained in Comparative Example 11 exhibited sufficient moisture permeability, but the total light transmittance was significantly reduced.

Comparative Examples 12-13
A porous film was obtained in the same manner as in Example 1 except that the blending ratio and stretching ratio of the linear low density polyethylene and the inorganic filler were changed to the blending and stretching ratios shown in Table 3. The results are shown in Table 3. The porous film obtained in Comparative Example 12 did not exhibit sufficient moisture permeability at a low stretch ratio, and the moisture permeability was significantly reduced.

  On the other hand, the porous film obtained in Comparative Example 13 could not stably form a film before stretching, and could not form a porous film.

Claims (1)

  A linear low density polyethylene resin composition comprising 30 to 50% by weight of linear low density polyethylene and 70 to 50% by weight of an inorganic filler is obtained by stretching at least uniaxially at an area magnification of 1.1 to 1.6 times. 30 to 70% by weight of a linear low density polyethylene having a melt index of 0.5 g / 10 min or more and less than 3 g / 10 min and a melt index of 3 g / 10 min or more and 20 g / 10 min. A porous film comprising 70-30% by weight of the following linear low density polyethylene, wherein the difference in melt index of the linear low density polyethylene is 3 or more.