JP2006274014A - Method for manufacturing polyethylene-based porous film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyethylene-based porous film which has both the excellent water proofness and moisture permeability and the high weather resistance and light resistance. <P>SOLUTION: The method for manufacturing a polyethylene-based porous film, comprising pore-forming by orientating a film consisting of 100 parts by mass of a polyethylene-based resin, 50-100 parts by mass of an inorganic filler, 0.5-20 parts by mass of titanium oxide and 0.2-5 parts by mass of a hindered amine-based light stabilizer, is characterized in that the above film is orientated biaxially and thus an areal draw ratio at the time of the orientating is from more than 2 times to not more than 3.5 times. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel method for producing a polyethylene-based porous film. More specifically, the present invention relates to a method for producing a porous film that can be used outdoors such as for building materials, agriculture, and waste disposal, and further relates to a method for producing a polyethylene-based porous film with improved weather resistance and light resistance.

  Conventionally, porous films that have both gas permeability (moisture permeability) such as water vapor and liquid leak-proof properties include sanitary materials such as paper diapers and sanitary napkins, functional packaging materials such as desiccants and disposable warmers, and disposables. It is widely used for simple clothing such as gloves and rain feathers, waterproof building materials such as house wrap, agricultural applications such as multi-agricultural sheets, and waste disposal applications such as compost-coated sheets. In particular, various methods of use have been developed for waterproof building materials, agricultural applications, and waste disposal applications as the usefulness of the waterproof and moisture-permeable performance of porous films is recognized.

  The most general method for producing such a porous film is to form a film by thermally melting a resin composition filled with a filler with an extruder, and causing interfacial peeling between the filler and the resin by uniaxial stretching or biaxial stretching. It is a method to make it. This method is widely used because a porous film having both gas permeability and liquid leakage prevention properties can be obtained at low cost. Furthermore, when a polyethylene resin is selected as the resin, it is particularly excellent in molding stability in the stretching process and exhibits good gas permeability. Therefore, a polyethylene resin is often used for the porous film.

  Even when trying to give the porous film the weather resistance and light resistance required for outdoor applications such as waterproof building materials, agricultural applications, waste treatment applications, etc., the porous film has a large contact surface area with oxygen due to the porous nature. However, due to the fact that the stabilizer tends to bleed out and the interaction between the stabilizer and the inorganic filler, it was not possible to achieve a sufficient effect with a normal stabilizer formulation.

  For these reasons, several studies have been made on the weather resistance imparting of porous films. The present inventors have already proposed a polyethylene-based porous film having excellent weather resistance containing titanium oxide and a specific hindered amine light stabilizer (see Patent Document 1). This polyethylene-based porous film is a film excellent in weather resistance having a tensile elongation of 100% or more after the accelerated test even when irradiated with an ultraviolet ray equivalent to exposure for one year outdoors in the accelerated weather resistance test.

JP 2004-131590 A

  In recent years, the porous film used in the above-mentioned outdoor use is disposed of when the weather resistance deteriorates and deteriorates. Therefore, it is desired to develop a film that has higher weather resistance and can be used outdoors for a longer period of time. ing.

  Japanese Patent Application Laid-Open No. 2004-131590, which is a prior art, provides a porous film in which gas permeability (moisture permeability) and mechanical properties are balanced when the draw ratio of the film is 1.1 to 2.0 times. The examples show a porous film stretched 1.6 times in the film flow direction.

  However, when high weather resistance is to be imparted to a film comprising a blending ratio of polyethylene resin, inorganic filler, titanium oxide and hindered amine light stabilizer described in JP-A-2004-131590, for example, weather resistance When an attempt is made to produce a porous film in which the tensile elongation after irradiation is maintained at 70% or more of the tensile elongation before irradiation when irradiated with an ultraviolet ray equivalent to exposure for one year outdoors in the accelerated test. When stretched within the range of the stretch ratio, moisture permeability tends to decrease, and there is room for improvement.

  Accordingly, an object of the present invention is to provide a method for producing a polyethylene-based porous film having excellent moisture permeability and higher weather resistance than before.

  As a result of intensive studies on the development of a polyethylene-based porous film having excellent moisture permeability and high weather resistance and light resistance, the present inventors have found that a polyethylene-based resin, an inorganic filler, titanium oxide, and a hindered amine-based light stability It has been found that the above problems can be solved by biaxially stretching a film containing an agent at a specific area stretching ratio, and the present invention has been completed.

  That is, the present invention stretches a film containing 100 parts by mass of a polyethylene resin, 50 to 100 parts by mass of an inorganic filler, 0.5 to 20 parts by mass of titanium oxide, and 0.2 to 5 parts by mass of a hindered amine light stabilizer. A porous film which is made porous, characterized in that the film is stretched biaxially and the area stretch ratio during stretching is more than 2.0 times and 3.5 times or less. This is a method for producing a polyethylene-based porous film.

  The porous film obtained by the production method of the present invention has higher weather resistance than before. Accordingly, such a porous film can be suitably used particularly for outdoor applications such as manure sediment-coated sheets, agricultural multi-sheets, house wraps, roof base materials, vegetable-coated sheets, and wood-coated sheets.

  The present invention is described in detail below.

  In the production method of the present invention, a film obtained by blending a polyethylene resin with an inorganic filler, titanium oxide, and a hindered amine light stabilizer is biaxially stretched, and the area ratio at the time of stretching exceeds 2.0 and 3.5 times. In the following, a polyethylene-based porous film (hereinafter sometimes simply referred to as a porous film) is produced.

In the present invention, the index of weather resistance and light resistance of the obtained porous film is a glazing resistance accelerated test in which 264 MJ / m ² of ultraviolet rays (300 to 400 nm) is irradiated with a sunshine carbon arc lamp, and the porous film after the test It was evaluated by the tensile elongation.

  In general, moisture-permeable materials used outdoors such as building materials, agricultural applications, and waste disposal applications are directly exposed to sunlight, and thus are required to have weather resistance and light resistance. The required level of weather resistance and light resistance depends on each application and usage environment, but it is a porous film used for house wrap for building materials, multi-sheets for agricultural applications, compost-coated sheets for waste disposal applications, etc. Therefore, it is desired that it can be used for at least 2 months or more and for one year or more depending on the application.

Therefore, the weather resistance and light resistance level of the porous film applicable to this application was set to one year of outdoor use, and 264 MJ / m ² of ultraviolet rays corresponding to the average solar ultraviolet ray amount for one year was irradiated. At this time, the weather resistance and light resistance were evaluated by the tensile elongation retention in MD (film flow direction) of the porous film after the wrinkle resistance acceleration test. The tensile elongation retention rate is an index indicating how much the tensile elongation after the accelerated test is retained with respect to the tensile elongation before the weather resistance accelerated test, and is obtained by the following formula.

  Tensile elongation retention (%) = (tensile elongation after accelerated test / tensile elongation before accelerated test) × 100

  The porous film obtained by the production method of the present invention preferably has a tensile elongation retention of 70% or more, and more preferably 75% or more. In the porous film described in the examples of JP-A-2004-131590, the tensile elongation of the porous film after the weather resistance acceleration test is 100% or more. At this time, the tensile elongation retention is 41 ~ 66%. When the porous film is used outdoors, depending on the application, if the tensile elongation is lowered, the porous film may be broken at the time of operation. Therefore, the weather resistance and light resistance of the porous film obtained by the production method of the present invention were evaluated by having a tensile elongation retention of 70% or more. That is, the object of the present invention is to produce a highly weatherable porous film that is less susceptible to deterioration and has little change in tensile elongation in a weathering acceleration test.

Of course, the porous film obtained by the production method of the present invention has the same tensile elongation retention as that of the porous film described in Examples of JP-A-2004-131590. Requires an irradiation amount of ultraviolet rays exceeding 264 MJ / m ² and can be used outdoors for a longer period of time.

  As the polyethylene-based resin used in the method for producing a porous film of the present invention, known resins can be used without any particular limitation, but representative examples thereof include branched low density polyethylene, medium density polyethylene, and high density. Polyethylene, linear low density polyethylene (ethylene-α-olefin copolymer), a copolymer of ethylene and vinyl alcohol fatty acid ester, a copolymer of ethylene and vinyl alcohol, ethylene and a vinyl group-containing fatty acid alkyl ester Copolymers and mixtures of these polymers can be used. Examples of the linear low density polyethylene include copolymers of ethylene and α-olefins having 4 to 8 carbon atoms such as 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. It is done. Moreover, as long as the effect of the present invention is not impaired, a polyolefin resin other than the polyethylene resin may be added as necessary.

  Among these, low-density polyethylene, medium-density polyethylene, high-density polyethylene and linear low-density polyethylene that are excellent in cost performance and releasability from filler are preferable, but linear low-density polyethylene is particularly preferable for film formation stability, strength, Since a porous film with good balance such as flexibility can be obtained, it is more preferable.

In addition, when the density of the polyethylene resin (mixture in the case of a mixture) is 0.910 to 0.935 g / cm ³ and the melt index is 0.5 to 15 g / 10 minutes, particularly the molding stability and A porous film having a good balance between mechanical strength and moisture permeability is obtained, which is preferable.

  In the method for producing a porous film of the present invention, it is important that the blending ratio of the inorganic filler is 50 parts by mass to 100 parts by mass with respect to 100 parts by mass of the polyethylene resin. When the blending ratio of the inorganic filler is less than 50 parts by mass, it is not preferable because the film is not sufficiently porous when stretched and moisture permeability is not sufficiently exhibited. Moreover, since the weather resistance and light resistance of the porous film obtained will fall when the addition amount of an inorganic filler exceeds 100 mass parts, it is unpreferable. In the production method of the present invention, a porous film having an excellent moisture permeability, weather resistance, and light resistance can be obtained by employing the blending ratio within the above range and the stretching method and stretch ratio described later. Can be manufactured. In consideration of moisture permeability, weather resistance and light resistance of the resulting porous film, the blending ratio of the inorganic filler is preferably 60 to 100 parts by mass, and more preferably 60 to 90 parts by mass with respect to 100 parts by mass of the polyethylene resin. Part is preferred.

  In the present invention, the inorganic filler does not include separately added titanium oxide, but other inorganic fillers are not particularly limited, and known inorganic fillers for porous films can be used. Specifically, inorganic salts such as calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide and aluminum hydroxide, inorganic oxides such as zinc oxide, magnesium oxide and silica, silica such as mica, vermiculite and talc. Acid salts 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, and the formation of communication holes at the time of stretching is easy, and the film is not easily broken at the time of molding and can be produced with high productivity.

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

  In the method for producing a porous film of the present invention, in order to improve the weather resistance and light resistance of the resulting porous film, titanium oxide and a hindered amine light stabilizer are blended in the film.

  As is generally known, titanium oxide reflects and reduces light that induces radical reactions. Since it does not interact with the filler or move through the resin unlike the organic light absorber of the same light-proofing agent, it is optimal as the light-proofing agent for the porous film. The hindered amine light stabilizer combined with this quenches the radical reaction caused by the reduced light and the oxidation reaction caused by oxygen. Here, the hindered amine light stabilizer is a tertiary amine whose piperidine ring is a tertiary amine that is less deactivated by an acid such as a decomposition product of a phosphorus stabilizer or a fatty acid for surface treatment of an inorganic filler, A high-molecular-weight amine that is difficult to out is preferable in the present invention because it exhibits excellent weather resistance and light resistance. In the present invention, the blending ratio of the inorganic filler in the above range, using this titanium oxide and a hindered amine light stabilizer, and further employing a stretching method and a stretching ratio described later, moisture permeability, weather resistance Porous film excellent in heat resistance and light resistance can be produced.

  In this invention, the compounding ratio of a titanium oxide is 0.5-20 mass parts with respect to 100 mass parts of polyethylene-type resin, Preferably it is 1-5 mass parts. If the blending ratio is less than 0.5 parts by mass, the resulting film has insufficient light hiding and ultraviolet absorbing properties, and the effect of improving weather resistance and light resistance cannot be obtained. On the other hand, when the amount is more than 20 parts by mass, the effect of improving the weather resistance and light resistance of the resulting porous film is in an equilibrium state, and the cost performance is lowered, and the productivity and strength of the film are lowered.

  As the titanium oxide used in the present invention, titanium oxide having a rutile type or anatase type crystal structure can be used without limitation. Among these, those having an average particle diameter of 0.01 to 0.5 μm having a rutile-type crystal structure are suitable for reasons such as light shielding and ultraviolet absorption of the resulting porous film.

  The titanium oxide used in the present invention is preferably titanium oxide surface-treated with silica and / or alumina. Titanium oxide surface-treated with silica and / or alumina does not deteriorate the polyethylene resin in contact with the photoexcitation, and can further improve the weather resistance and light resistance of the porous film of the present invention. The surface-treated titanium oxide is 2 to 20 parts by mass, preferably 4 to 20 parts by mass with respect to 100 parts by mass of titanium oxide for reasons such as dispersibility in the obtained porous film and stability of titanium oxide. Those coated with a portion of silica and / or alumina are preferred. In particular, when rutile type titanium oxide coated with 4 to 10 parts by mass of silica and alumina is used, the effect of improving weather resistance and light resistance is most obtained. Such surface-treated titanium oxide is already commercially available from, for example, Taioxide Corporation.

  Furthermore, the titanium oxide used in the present invention can be surface-treated by adding a higher fatty acid and / or a higher fatty acid metal salt for the purpose of improving dispersibility in a polyethylene resin during film forming. What coat | covered the surface of this titanium oxide by the compounding ratio of a higher fatty acid and / or a higher fatty acid metal salt 2-20 mass parts with respect to 100 mass parts of titanium oxides, Preferably 4-20 mass parts is suitable. When the blending ratio is in the above range, good dispersibility is exhibited.

  In this invention, the mixture ratio of a hindered amine light stabilizer is 0.2-5 mass parts with respect to 100 mass parts of polyethylene-type resin, Preferably it is 1-3 mass parts. When the blending ratio is less than 0.2 parts by mass, the effect of improving weather resistance and light resistance cannot be obtained, and when it is more than 5 parts by mass, the effect of improving weather resistance and light resistance is in an equilibrium state and the cost is increased. It is not preferable for practical use.

  The hindered amine light stabilizer used in the present invention preferably has a molecular weight of 1500 to 4500, and the piperidine ring is preferably a tertiary amine. When the molecular weight is 1500 or more, bleedout to the film surface after forming the porous film is reduced, so that the long-term weather resistance and light resistance of the obtained porous film are guaranteed. In addition, it is difficult to obtain a product having a molecular weight exceeding 4500.

  Furthermore, when the piperidine ring is a secondary amine, the interaction with the acidic substance contained in the raw material composition, such as a hydrolyzate of a phosphorus-based antioxidant or a fatty acid, is unavoidable. The film discolors over time and the commercial value decreases. For this reason, in order to satisfy long-term weather resistance, light resistance, and discoloration resistance, the hindered amine light stabilizer preferably has a molecular weight of 1500 to 4500 and the piperidine ring is a tertiary amine. .

  As the hindered amine light stabilizer used in the present invention, amines such as N-Me type and N-R type can be used. N-Me type includes 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-pentamethyl Examples include condensates of -4-piperidinol and β, β, β ′, β ′, tetramethyl-3,9- (2,4,8,10-tetraoxaspiro [5,5] undecane) diethanol, and the like. The N—R type includes a polymer of dimethyl succinate 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 Mixtures of products are preferred because high weather resistance and light resistance improvement effects 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).

  In the present invention, the obtained porous film further contains other thermoplastic resins such as petroleum resins, pigments, stabilizers, surfactants, plasticizers, oils, and other additives within the range not impairing the object of the present invention. It can be added in a timely manner as required. Among these, as a heat stabilizer at the time of extrusion molding, a blend of a hindered phenol heat stabilizer and a phosphorus heat stabilizer is suitable.

  Examples of hindered phenol heat stabilizers include 2,6-di-t-butyl-4-methylphenol, 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-butyl 4-hydroxybenzyl) isocyanurate and the like, it is preferable to blend 0.01 to 2 parts by weight per 100 parts by weight polyethylene resin 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 , 4'-biphenylene phosphonite and the like, and 0.01 to 2 parts by mass is preferably blended with 100 parts by mass of the polyethylene resin of the present invention.

  Next, a description will be given of a method for producing a porous film by forming a film containing the above-described structure, that is, a polyethylene resin, an inorganic filler, titanium oxide, and a hindered amine stabilizer, and stretching the film.

  The mixing and granulating method of each component constituting the film 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 an ordinary Henschel mixer, super mixer, tumbler mixer, etc., generally kneading and pelletizing with a high kneading type twin screw extruder, tandem kneading machine, etc. by methods such as strand cutting, hot cutting, underwater cutting, etc. To do.

  Next, the above pelletized composition is formed into a film with a circular die or a T die attached to the tip of the extruder. Among them, it is preferable to form a film by an inflation method using a circular die because the molding stability can be improved.

  The greatest feature of the present invention is that a film having the above structure, particularly a film in which the amount of the inorganic filler is adjusted to the above range, is stretched in the biaxial direction, and the area stretch ratio during stretching is 2.0 times. Over 3.5 times or less.

  In the present invention, the method for stretching a film containing a polyethylene resin, an inorganic filler, titanium oxide, and a hindered amine stabilizer in the biaxial direction is not particularly limited, and is not lower than the normal temperature and lower than the softening point of the resin. Known methods such as a roll stretching method, a tenter stretching method, and a mandrel stretching method can be employed within the temperature range. Moreover, it can also heat-process as needed after extending | stretching.

  In the present invention, the film must be stretched biaxially. By stretching in the biaxial direction, it is possible to achieve more efficient porosity. In this stretching, the area stretch ratio must be more than 2.0 times and 3.5 times or less. The area stretch ratio is the ratio of the area of the film before stretching and the area of the film after stretching in the biaxial direction. An area magnification of 2.0 times or less is not preferable because moisture permeability cannot be sufficiently exhibited. On the other hand, if it exceeds 3.5 times, the weather resistance is lowered, which is not preferable. In consideration of moisture permeability and weather resistance of the resulting porous film, the area stretch ratio is preferably 2.1 to 3.2.

  Further, when the film is stretched in the biaxial direction and the area stretch ratio at that time is more than 2.0 times and 3.5 times or less, the film flow direction (hereinafter referred to as MD) is perpendicular to MD. Each stretching ratio in the direction (hereinafter referred to as TD) is not particularly limited, but may be stretched 1.5 to 3.0 times in MD and 1.1 to 2.0 times in TD. It is preferable because the film formation stability is excellent and the strength balance of the obtained film is good. The area stretch ratio can be calculated by multiplying the MD stretch ratio and the TD stretch ratio.

  In the present invention, the film must be stretched in the biaxial direction, and the area stretch ratio must be more than 2.0 times and 3.5 times or less. Even if it is stretched at a draw ratio of more than 2.0 times and 3.5 times or less in only one direction of MD or TD, the object of the present invention cannot be achieved. When the film is stretched only in the uniaxial direction, the porous film is easily broken during production, and the production becomes difficult. In addition, even if a porous film is obtained, the moisture permeability decreases, and further, the film physical properties in the MD and TD of the porous film are greatly different, and the film physical properties in the direction perpendicular to the stretched direction are decreased. This is not preferable.

  The present invention is a film containing a polyethylene resin, an inorganic filler, titanium oxide, and a hindered amine stabilizer, and 50 parts by mass to 100 parts by mass of the inorganic filler with respect to 100 parts by mass of the polyethylene resin. In addition, the film is stretched in the biaxial direction, and the area stretch ratio at the time of stretching is more than 2.0 times and 3.5 times or less, so that it has excellent moisture permeability and higher weather resistance. It is the method of manufacturing the porous film which has. That is, the present invention is achieved by combining an optimum blending ratio, particularly a blending ratio of the inorganic filler, a stretching method, and a stretching ratio.

  In the porous film obtained by the production method of the present invention, the weather resistance and light resistance largely depend on the thickness, and the thicker the thickness, the better the weather resistance, but according to the production method of the present invention, the inorganic filler By adjusting the amount, adding titanium oxide and a hindered amine light stabilizer, and further adopting the above-mentioned stretching method and stretching ratio, it efficiently suppresses resin degradation factors such as heat and ultraviolet rays over a long period of time. Therefore, the weather resistance and light resistance of the resulting porous film can be maintained. In particular, when the thickness of the obtained porous film is 10 to 100 μm, not only the effect of improving the weather resistance and light resistance due to the thickness is great, but also a porous film excellent in cost performance and excellent in tear strength of the film is obtained. This is preferable. More preferably, the above balance is excellent when the thickness is 20 to 50 μm.

The porous film obtained by the production method of the present invention is not particularly limited, but preferably has a porosity of 10 to 30%. When the porosity is in the above range, the film has excellent moisture permeability. Further, the moisture permeability of the porous film is not particularly limited, but is 3000 g / m ² · 24 hr or more when used for an application that is more functional and requires more moisture permeability. Is preferred.

  The porous film obtained by the production method of the present invention can be laminated with a breathable reinforcing material to form a moisture-permeable waterproof sheet that requires weather resistance and light resistance for building materials, agricultural applications, waste disposal applications, etc. It can be used suitably.

  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. In addition, the material of the breathable reinforcing material is not particularly limited, and polyolefin-based, polyester-based, and nylon-based materials can be used, but when laminated with the porous film of the present invention, a heat-sealing method is used. In consideration of easy lamination, the surface layer preferably contains a polyethylene resin having a melting point peak of 130 ° C. or lower.

  The method for laminating the porous film and the breathable reinforcing material is not particularly limited, and a known method can be used. Specifically, methods such as thermal lamination, dry lamination, and wet lamination can be employed. Either method can provide good interlayer adhesion strength. Among these, in consideration of workability and economy, the method of bonding the porous film of the present invention and the breathable reinforcing material by heat fusion is preferable. In the heat fusion method, a porous film and a breathable reinforcing material are unwound from an unwinder, and are laminated between the drum roll and silicon rubber roll heated by electric heating, dielectric heating, heating medium circulation heating, etc. In general, a method of nip and heat-sealing and winding is used. The heat fusion temperature is preferably less than the melting point of the raw material composition.

  In addition, in order to provide long-term weather resistance and light resistance with the laminated sheet, an appropriate amount of a hindered amine light stabilizer, an ultraviolet absorber, or a mixture of both is added to the breathable reinforcing material to provide weather resistance and light resistance. Is more preferable.

  Furthermore, the breathable reinforcing material may be waterproof (water repellant), and as a waterproofing agent (water repellant) that can be used for waterproofing, insoluble aluminum soap, paraffin, wax, methyl hydrogen poly In addition to siloxane and terminal hydroxyl group-containing dimethylpolysiloxane, polymer compounds having trifluoromethyl at the end of the pendant chain with respect to the polymer chain, surfactants having fluoromethyl as a hydrophobic group, and the like can be mentioned. These may be used alone or as a mixture of two or more.

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

  Table 1 shows polyethylene resins, inorganic fillers, titanium oxide, hindered amine light stabilizers, and ultraviolet absorbers used in Examples and Comparative Examples.

  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) Water vapor permeability Measured according to JIS Z 0208.

  Measurement was performed under conditions of a measurement temperature of 40 ° C. and a humidity of 90%.

4) Tensile elongation According to JIS K 7127, measurement was performed under the conditions of a test piece width of 25 mm and a tensile speed of 200 mm / min.

5) Weather resistance and light resistance Evaluation of weather resistance and light resistance is based on the value of tensile elongation in the MD direction of the porous film after a weather resistance accelerated test in which an ultraviolet ray equivalent to 1 year outdoor exposure is applied. did.

First, a weather resistance test was performed in accordance with JIS A 1415. A sunshine weather meter (model name S80 Suga Test Instruments Co., Ltd. irradiance 255 W / m ² <300 to 700 nm>) using a sunshine carbon arc lamp as a weather resistance promoting device was used. The weather resistance test was performed by irradiating the ultraviolet light so that the total irradiation intensity of the ultraviolet part (300 to 400 nm) was 264 MJ / m ² under the conditions of water spraying at a black panel temperature of 63 ° C. for 18/120 minutes using the weather resistance promoting device. I went there.

  After performing the weather resistance acceleration test, the tensile elongation in the MD direction of the porous film after the weather resistance acceleration test was measured in accordance with JIS K 7127 under the conditions of a test piece width of 25 mm and a tensile speed of 200 mm / min. The tensile elongation was measured at n = 5, and if the tensile elongation retention calculated from the average value was 70% or more, it was evaluated that the weather resistance and light resistance were good.

6) Calculated by a porosity specific gravity measurement method.
Porosity = (d ₀ −d ₁ ) / d ₀
d ₀ : Specific gravity of the film before porosity.
d ₁ : Specific gravity of the film after being made porous.

Example 1
As shown in Table 1, 80 parts by mass of calcium carbonate (product of Calfine, product name: LAC2000), titanium oxide (product of Tyoxide) with respect to 100 parts by mass of linear low density polyethylene (product of Idemitsu Petrochemical, product name: LLDPE0234CL) , Trade name: R-TC30) 3.0 parts by weight, hindered amine light stabilizer (manufactured by Ciba Specialty Chemicals, trade name: Tinuvin 622LD) 1.5 parts by weight, mixed and granulated, Film forming was performed.

  For granulation, a φ30 mm 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 is melt-formed at an extrusion temperature of 180 ° C. with an inflation film forming machine, then stretched to MD at a stretch ratio of 2.4 times between rolls heated to 60 ° C., and further heated to 200 ° C. The resulting mandrel stretching machine was stretched to TD at a stretch ratio of 1.3 times to obtain a polyethylene-based porous film.

  The physical properties measured for the porous film thus obtained are shown in Table 2. The obtained porous film had good moisture permeability, and also had a high retention rate of 70% or more after the tensile elongation retention rate after the weather resistance acceleration test.

Examples 2-3
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 physical properties measured for the porous film thus obtained are shown in Table 2. The obtained porous film had good moisture permeability, and also had a high retention rate of 70% or more after the tensile elongation retention rate after the weather resistance acceleration test.

Example 4
A porous film was obtained in the same manner as in Example 1 except that the blending ratio and the draw ratio of the inorganic filler were changed to the ratios and ratios shown in Table 2. The physical properties measured for the porous film thus obtained are shown in Table 2. The obtained porous film had good moisture permeability, and also had a high retention rate of 70% or more after the tensile elongation retention rate after the weather resistance acceleration test.

Comparative Example 1
Except for changing the draw ratio to the ratio shown in Table 3, production of a porous film was attempted in the same manner as in Example 1, but film breakage occurred during TD stretching, and a porous film could be produced. could not.

Comparative Examples 2-3
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 physical properties measured for the porous film thus obtained are shown in Table 3. The porous films obtained in Comparative Examples 2 and 3 had excellent weather resistance, but the moisture permeability was greatly reduced.

Comparative Example 4
Except for changing the stretching ratio to the ratio shown in Table 3, production of a porous film was attempted in the same manner as in Example 1, but film breakage occurred during stretching in the MD direction to produce a porous film. I could not.

Comparative Examples 5-6
A porous film was obtained in the same manner as in Example 1 except that the blending ratio and the stretching ratio of the inorganic filler were changed to the ratios and ratios shown in Table 3. The physical properties measured for the porous film thus obtained are shown in Table 3. Although the porous film obtained in Comparative Example 5 had excellent weather resistance, the moisture permeability was remarkably lowered, and the effect could not be expected as an outdoor waterproof moisture-permeable material. Although the porous film obtained in Comparative Example 6 had excellent moisture permeability, the tensile elongation retention after the weather resistance acceleration test was less than 70%.

Claims (1)

A film comprising 100 parts by weight of a polyethylene resin, 50 to 100 parts by weight of an inorganic filler, 0.5 to 20 parts by weight of titanium oxide, and 0.2 to 5 parts by weight of a hindered amine light stabilizer is stretched to make it porous. A method for producing a porous film, wherein the film is stretched in the biaxial direction, and the area stretch ratio at the time of stretching is more than 2.0 times and 3.5 times or less. Quality film manufacturing method.