JP2007161787A - Polyethylene porous film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyethylene based porous film which further improves weatherability and light resistance. <P>SOLUTION: The porous film is obtained by stretching a film comprising 100 pts.mass polyethylene based resin and 50-200 pts.mass inorganic filler at least in the film flowing direction to render the film porous, and the polyethylene based resin has a Z-average molecular weight (Mz) of not less than 300,000 and comprises a linear low density polyethylene composed of a copolymer of ethylene and a ≥6C α-olefin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, porous films that have both gas permeability (moisture permeability) such as water vapor and liquid leakage prevention (water resistance) are sanitary materials such as disposable diapers and sanitary napkins, and functional packaging such as desiccants and disposable warmers. It is widely used for materials, simple clothing such as disposable gloves and rain feathers, waterproof building materials such as house wrap, agricultural applications such as multi-agricultural sheeting, and waste disposal applications such as manure deposit coating sheets and capping sheets. In particular, various usage methods have been developed for waterproof building material use, agricultural use, and waste treatment use as the excellent waterproofness and moisture permeability of porous films are recognized.

  The most common 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 then interfacially peeling the filler and the resin by uniaxial stretching or biaxial stretching. This is a method of making it porous. This method is widely used because a porous film having both moisture permeability and waterproofness can be obtained at low cost.

  Furthermore, when a polyethylene resin is selected as the resin, the polyethylene film is widely used for the porous film because it is particularly excellent in molding stability in the stretching process and exhibits good moisture permeability.

  However, even if it is intended to provide the porous film with the weather resistance and light resistance required for the above-mentioned waterproof building material use, agricultural use, and waste treatment use, the normal stabilizer formulation is porous and oxygen. It is difficult to achieve a sufficient effect due to the large contact area with the filler, the tendency of the stabilizer to bleed out, the interaction between the stabilizer and the inorganic filler, and the like.

  For these reasons, several studies have been made on imparting weather resistance to 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-based 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 ultraviolet rays equivalent to exposure for one year outdoors in the weathered accelerated test.

JP 2004-131590 A

  In recent years, for porous films used for outdoor applications, development of films that have higher weather resistance and can be used outdoors for a longer period of time is desired due to the prolonged product life and disposal problems after use. It is rare. That is, a porous film having a weather resistance higher than that of the polyethylene-based porous film described in Patent Document 1 is being demanded.

  Accordingly, an object of the present invention is to provide a polyethylene-based porous film that is excellent in moisture permeability and waterproofness and has higher weather resistance than before.

  The present inventors diligently investigated the development of a polyethylene-based porous film having excellent moisture permeability and waterproofness, and having high weather resistance and light resistance. As a result, it has been found that the above-mentioned problems can be solved by using a specific linear low density polyethylene for the porous film, and the present invention has been completed.

  That is, the present invention is a porous film obtained by stretching a film containing 50 to 200 parts by mass of an inorganic filler with respect to 100 parts by mass of a polyethylene resin at least in the flow direction of the film, The polyethylene resin comprises a linear low-density polyethylene having a Z average molecular weight (Mz) of 300,000 or more and made of a copolymer of ethylene and an α-olefin having 6 or more carbon atoms. This is a polyethylene-based porous film.

  The polyethylene-based porous film of the present invention has higher weather resistance and light resistance than before. Accordingly, such a porous film is particularly suitable for outdoor use such as house wrap, roof base material, agricultural multi-sheet, manure deposit covering sheet, waste capping sheet, vegetable protection sheet, wood protection sheet and the like. be able to.

  The present invention is described in detail below.

  The polyethylene porous film of the present invention (hereinafter sometimes referred to simply as “porous film”) is a porous film in which a polyethylene resin and an inorganic filler are made porous by stretching the film at least in the film flow direction. The polyethylene-based resin is a film excellent in weather resistance and light resistance, characterized by comprising a specific linear low density polyethylene and having a specific average molecular weight.

In the present invention, the index of weather resistance and light resistance of the obtained porous film is a weather resistance acceleration test in which 528 MJ / m ² of ultraviolet light (300 to 400 nm) is irradiated with a sunshine carbon arc lamp. It was evaluated by the tensile elongation.

  In general, waterproof and moisture-permeable sheets used outdoors such as for building materials, agriculture, and waste disposal 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 varies depending on each application and usage environment, but in general, it is a porous film used for house wrap for building materials, multi-sheets for agriculture, manure deposit covering sheets for waste treatment, etc. Therefore, it has been required that it can be used for at least two months or more and for one year or more depending on the application. Furthermore, in recent years, the movement of the above-mentioned outdoor waterproof / breathable sheet for long-term product life and reduction of waste has been activated, and not only the product but also each component constituting the product has high weather resistance and light resistance. Is required. Among them, the porous film is a central member responsible for waterproof and moisture permeability, and further improvement in weather resistance and light resistance is strongly desired.

Therefore, in the present invention, the weather resistance and light resistance level of the porous film that can be suitably used for these outdoor applications are set to 2 years of outdoor use, and an ultraviolet ray of 528 MJ / m ² corresponding to the ultraviolet ray amount of sunlight for 2 years. It was decided to irradiate. At this time, the weather resistance and light resistance of the porous film were evaluated based on the fact that the tensile elongation in MD (film flow direction) of the porous film after the weather resistance acceleration test was 100% or more. Tensile elongation is one index for judging the degree of molecular weight reduction due to UV degradation from the viewpoint of physical properties. If it is maintained at 100%, it can be said to be sufficiently satisfactory in recent years. In particular, in order to obtain a material that more satisfies weather resistance and light resistance, after irradiating with 528 MJ / m ² of ultraviolet rays corresponding to the amount of ultraviolet rays for two years of sunlight, the tensile elongation is 150% or more. It is preferable that it is 200% or more. As a matter of course, the longer the tensile elongation of the porous film after the ultraviolet irradiation, the longer it can be used.

  The polyethylene-based resin used in the porous film of the present invention is a linear low density polyethylene made of an α-olefin copolymer having an average molecular weight (Mz) of 300,000 or more and ethylene and 6 or more carbon atoms. It is characterized by comprising.

  In the present invention, the Z average molecular weight (Mz) can be determined by measuring the molecular weight of a polyethylene resin by gel permeation chromatography (GPC) as described in detail later. In the case of a porous film containing an inorganic filler, a polyethylene resin is extracted with a solvent, and the molecular weight of the obtained polyethylene resin is measured by GPC, or the inorganic filler is dissolved with an acid / alkali. The molecular weight of the obtained polyethylene resin can be determined by measuring with GPC. In the present invention, when the polyethylene resin is a mixture of ethylene and a linear low density polyethylene made of an α-olefin copolymer having 6 or more carbon atoms and another ethylene resin, What is necessary is just to obtain | require Z average molecular weight (Mz) by measuring a mixture by GPC. Naturally, when the polyethylene-based resin is a linear low-density polyethylene consisting of ethylene and an α-olefin copolymer having 6 or more carbon atoms, the linear low-density polyethylene is measured by GPC. Thus, the Z average molecular weight (Mz) may be obtained.

  In the present invention, the polyethylene resin must have a Z average molecular weight (Mz) of 300,000 or more. When the Z average molecular weight (Mz) is less than 300,000, it is not preferable because the weather resistance and light resistance of the resulting porous film are lowered. Furthermore, when the weather resistance and light resistance of the obtained porous film are taken into consideration, the Z average molecular weight (Mz) is preferably 330,000 or more. On the other hand, the upper limit value of the Z average molecular weight (Mz) is not particularly limited, but is preferably 500,000 or less in view of film formability and industrial production of polyethylene resin.

  In the present invention, the polyethylene-based resin comprises linear low-density polyethylene made of an α-olefin copolymer having a Z-average molecular weight (Mz) satisfying the above range and having 6 or more carbon atoms. Is. In particular, linear low density polyethylene made of a copolymer of ethylene and 1-octene having 8 carbon atoms is preferably included. Further, in the linear low density polyethylene, the content of the α-olefin having 6 or more carbon atoms is not particularly limited, but in consideration of the balance between the flexibility of the film and the weather resistance and light resistance, it is 0. It is preferable that it is 0.5 mol%-5.0 mol%.

  In the present invention, the polyethylene resin may be one type of polyethylene resin or a mixture of a plurality of polyethylene resins as long as the Z average molecular weight (Mz) satisfies the above range. However, it must necessarily contain linear low density polyethylene made of ethylene and an α-olefin copolymer having 6 or more carbon atoms. When the polyethylene-based resin contains linear low-density polyethylene composed of ethylene and an α-olefin copolymer having 6 or more carbon atoms, the weather resistance and light resistance of the resulting porous film can be further improved. it can.

  In the present invention, the polyethylene resin includes linear low density polyethylene composed of ethylene and an α-olefin copolymer having 6 or more carbon atoms, and known ethylene resins such as branched low density polyethylene and high density polyethylene. Alternatively, it may be a mixture of ethylene and a linear low density polyethylene composed of an α-olefin having less than 6 carbon atoms. In the case of these mixtures, in order to improve the weather resistance and light resistance of the resulting porous film, a linear low-residue composed of ethylene and an α-olefin copolymer having 6 or more carbon atoms in a polyethylene resin. It is preferable that 50 mass% or more of density polyethylene is contained. When such a mixture is used, the weather resistance and light resistance of the film specified in the present invention are satisfied, and the texture and film-forming property of the film can also be improved.

  As a matter of course, the polyethylene-based resin is a single linear low-density polyethylene composed of ethylene having a Z average molecular weight (Mz) of 300,000 or more and an α-olefin copolymer having 6 or more carbon atoms. In this case, a porous film with improved weather resistance and light resistance can be obtained.

In the present invention, the polyethylene-based resin is not particularly limited with respect to other physical properties, but those having a normal film-forming range can be used, and a melt flow rate (MFR) of 0.5 can be used. 10 to 10 g / 10 min and a density of 0.900 to 0.960 g / cm ³ can be used. In particular, when a film is formed by an inflation film forming method, the melt flow rate (MFR) of the polyethylene resin is preferably 0.5 to 5.0 g / 10 minutes. Moreover, when the balance of the softness | flexibility of a film, a weather resistance, and light resistance is considered, it is preferable that a density is 0.910-0.940g / cm < ³ >. In addition, when the said polyethylene-type resin is a mixture, the melt flow rate and density of a mixture should just satisfy the said range. When the polyethylene-based resin is composed only of linear low density polyethylene made of ethylene and an α-olefin copolymer having 6 or more carbon atoms, the melt flow rate and density of the linear low density polyethylene are It only has to satisfy the range.

  In the present invention, the reason why the weather resistance and light resistance of the resulting porous film are dramatically improved by using the polyethylene resin is not clear, but is estimated as follows. In general, it is considered that the weather resistance of a resin is better as the average molecular weight is higher, that is, the melt flow rate is lower. However, when the polyethylene-based resin used as a film is considered to have a film-forming property, the film-forming process is difficult unless it has a melt flow rate in the above range. In particular, when the melt flow rate is low, high weather resistance and light resistance can be expected, but a load is applied to the machine during film formation, resulting in a significant reduction in productivity. Therefore, the melt flow rate satisfies the above range, and by using a polyethylene resin having a Z average molecular weight of 300,000 or more, the film forming property of the film is maintained, and the high molecular weight effective for improving the weather resistance. Since many components can be present, it is considered that a porous film having improved weather resistance and light resistance can be obtained.

  Further, when the polyethylene resin comprises a linear low density polyethylene composed of ethylene and an α-olefin copolymer having 6 or more carbon atoms, for example, when considering a polyethylene resin of the same density, It is considered that a porous film having improved weather resistance and light resistance can be obtained because the amount of tertiary carbon that easily deteriorates in the polyethylene resin is reduced.

  In the porous film of the present invention, a polyethylene-based resin that satisfies only the requirement of Z average molecular weight (Mz), or linear low-density polyethylene made of ethylene and an α-olefin copolymer having 6 or more carbon atoms is used. When compared with those that only satisfy the requirements for inclusion, the weather resistance and light resistance are remarkably improved. This is a synergy between the effect of defining the Z-average molecular weight (Mz) of the polyethylene resin and the effect of including a linear low-density polyethylene composed of ethylene and an α-olefin copolymer having 6 or more carbon atoms. It is considered that a porous film exhibiting effects and other effects and having improved weather resistance and light resistance can be obtained.

  In the porous film of the present invention, the blending ratio of the polyethylene resin and the inorganic filler is 50 to 200 parts by mass of the inorganic filler with respect to 100 parts by mass of the polyethylene resin. When the blending amount 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. On the other hand, when the blending ratio of the inorganic filler exceeds 200 parts by mass, tearing or the like is likely to occur during film formation and productivity is lowered, and the strength of the obtained porous film is also not preferred.

  The inorganic filler used in the present invention is not particularly limited, and a known inorganic filler 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. Moreover, these can also be used individually or in mixture of multiple types. Among these, calcium carbonate is particularly preferable in consideration of cost performance and peelability from the polyethylene 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 porous film of the present invention, in order to improve the weather resistance and light resistance, it is preferable to blend titanium oxide and a hindered amine light stabilizer into the porous film. These titanium oxide, hindered amine light stabilizer, and other additives can be the same as those described in JP-A No. 2004-131590.

  Among these, it is preferable to mix 0.5 to 10 parts by mass of titanium oxide surface-treated with silica and alumina as the titanium oxide with respect to 100 parts by mass of the polyethylene resin. Further, as the hindered amine light stabilizer, A) N, N ′, N ″, N ′ ″-tetrakis- (4,6-bis- (butyl- (N-methyl-2,2,6,6) -Tetramethylpiperidin-4-yl) amino) -triazin-2-yl) -4,7-diazadecane-1,10-diamine, B) dimethyl succinate and 4-hydroxy-2,2,6,6- It is possible to blend 1 to 5 parts by mass of a polymer mixture of tetramethyl-1-piperidineethanol (weight ratio A / B: 2/8 to 8/2) with respect to 100 parts by mass of polyethylene resin. Since the weather resistance and light resistance of a quality film can be further improved, it is more preferable. Such surface-treated titanium oxide is already commercially available from, for example, Tyoxide Co., Ltd., and hindered amine light stabilizers are already commercially available from, for example, Ciba Specialty Chemicals.

  Next, a general method for producing the polyethylene-based porous film of the present invention will be described.

  First, the method for mixing and granulating the polyethylene-based resin and the inorganic filler, and if necessary, titanium oxide, a stabilizer, an additive and the like are not particularly limited, and a known method can be adopted. For example, after mixing with a normal 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 To do. A master batch of inorganic filler can also be used.

  Next, in the present invention, the pelletized product is formed into a film shape with a circular die or a T die attached to the tip of the extruder, and the porous film is formed by a known method such as a uniaxial or biaxial stretching method. To do. In the present invention, film formation by inflation film formation using a circular die suitable for film formation of a resin having a particularly low melt flow rate is preferred.

  The film-formed sheet is a porous material defined by stretching in at least a uniaxial direction at a temperature range not lower than normal temperature and lower than the softening point of the resin by a known method such as a roll stretching method or a tenter stretching method. A film can be obtained. The draw ratio is not particularly limited, but when the area draw ratio is 1.1 to 3.5 times, a porous film in which gas permeability and mechanical properties are balanced 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. Considering the productivity when laminating the porous film and the breathable reinforcing material by heat fusion, it is preferable to reduce the heat shrinkage rate of the film by heat treatment.

  In the present invention, the weather resistance and light resistance of the porous film largely depends on its thickness, and the thicker the thickness, the better the weather resistance, but the polyethylene resin used satisfies a specific Z average molecular weight (Mz), Moreover, the weather resistance and light resistance of the resulting porous film can be maintained by comprising linear low density polyethylene made of ethylene and an α-olefin copolymer having 6 or more carbon atoms. In particular, when the thickness is 10 to 200 μm, not only the effect of improving the weather resistance and light resistance due to the thickness is great, but also a porous film having excellent cost performance and excellent film tear strength can be obtained. More preferably, the above balance is excellent when the thickness is 20 to 120 μm.

In addition, the porous film of the present invention has a weather resistance of 528 MJ / m ² , which corresponds to the amount of ultraviolet light for two years of sunlight, in order to satisfy the high weather resistance and light resistance recently required for outdoor use. It is preferable that the tensile elongation in MD after the acceleration test is 100% or more, preferably 150% or more, and more preferably 200% or more. Moreover, in order to satisfy the high weather resistance and light resistance required for outdoor applications in recent years, the above-described tensile elongation is further satisfied, and the tensile elongation retention rate (tensile elongation retention rate (%) = (accelerated) The tensile elongation after the test / tensile elongation before the acceleration test) × 100) is preferably 50% or more.

Furthermore, in the porous film of the present invention, the water pressure resistance after irradiation with 528 MJ / m ² of ultraviolet rays corresponding to the amount of ultraviolet rays for two years of sunlight is preferably maintained at 10 kPa or more, preferably 50 kPa or more. Further, the moisture permeability after irradiation with 528 MJ / m ² of ultraviolet light corresponding to the amount of ultraviolet light for two years of sunlight is preferably 1000 g / m ² 24 Hr or more, preferably 3000 g / m ² 24 Hr or more. .

  In addition, the porous film of the present invention is suitably used for waterproof and moisture-permeable sheets that require weather resistance and light resistance, such as building material use, agricultural use, and waste treatment use, by laminating with a breathable reinforcing material. it can. As the kind of the breathable reinforcing material and the lamination method, those described in JP-A-2004-131590 can be employed.

  Further, the porous film of the present invention and the laminated sheet thereof are not particularly limited, for example, heat processing or sealing processing such as in-between processing through an adhesive layer, or imparting heat shielding properties by aluminum deposition. For the purpose of imparting conductivity by coating with conductive materials, processing for the purpose of imparting functionality such as anti-slip properties and water repellency by coating other materials, coating, etc., or for providing design properties such as printing and embossing Secondary processing such as processing described above can also be performed.

  Examples and Comparative Examples are shown below, but the present invention is not limited to these Examples. In addition, the physical-property value described in the Example and the comparative example was measured by the method shown below.

1) Measurement of gel permeation chromatography (GPC) Using a high-temperature GPC apparatus manufactured by Senshu Kagaku Co., Ltd., the molecular weight of the polyethylene resin was measured under the following conditions, and the Z-average molecular weight (Mz) was measured.
Solvent: orthodichlorobenzene, flow rate: 1.0 ml / min, column temperature: 145 ° C., detector: high temperature differential refraction detector, column: SHODEX UT807 (1), 806M (2), 802.5 (1 Main), sample concentration: 0.1% by weight, injection amount: 0.50 ml.

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

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

4) 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%.

5) Tensile elongation According to JIS K 7127, the tensile strength was measured under the conditions of a specimen width of 25 mm and a tensile speed of 200 mm / min.

6) Weather resistance and light resistance Evaluation of weather resistance and light resistance is based on the tensile elongation value in the MD direction of the porous film after performing a weather resistance accelerated test that irradiates an ultraviolet ray equivalent to exposure for two years outdoors. 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 ray portion (300 to 400 nm) would be 528 MJ / m ² under the conditions of water spray at a black panel temperature of 63 ° C. for 18/120 minutes. 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 average value was 100% or more, it was evaluated that the weather resistance and light resistance were good.

Example 1
As shown in Table 1, with respect to 100 parts by mass of linear low density polyethylene (manufactured by prime polymer, trade name: MORETEC0138N), 120 parts by mass of calcium carbonate (product of Calfine, trade name: LAC2000), titanium oxide (manufactured by Tyoxide, Product name: R-TC30) 4.0 parts by mass, hindered amine light stabilizer (manufactured by Ciba Specialty Chemicals, product name: Tinuvin 111 FLD) 2.0 parts by mass, mixed granulation, film Molding 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 draw ratio of 2.0 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 elongation of 200% or more after the weather resistance acceleration test.

Examples 2-4
A porous film was obtained in the same manner as in Example 1 except that the linear low density polyethylene was changed to the type shown in Table 2. The results are shown in Table 2. The obtained porous film had good moisture permeability, and had a high elongation of 150% or more after the tensile resistance acceleration test.

Comparative Examples 1-3
A porous film was obtained in the same manner as in Example 1 except that the linear low density polyethylene was changed to the type shown in Table 3. The results are shown in Table 3. The obtained porous film had good moisture permeability, but the tensile elongation after the weather resistance acceleration test was 100% or less, and the weather resistance was remarkably lowered.

Claims (1)

A porous film obtained by stretching a film comprising 50 to 200 parts by mass of an inorganic filler with respect to 100 parts by mass of a polyethylene resin at least in the flow direction of the film, and the polyethylene resin is A polyethylene-based porous film comprising a linear low-density polyethylene having a Z average molecular weight (Mz) of 300,000 or more and comprising a copolymer of ethylene and an α-olefin having 6 or more carbon atoms. .