Polyolefin microporous membrane

Abstract

To provide a polyolefin microporous membrane that achieves improved balance of water resistance, moisture permeability, and flexibility, when applied as moisture-permeable waterproof membranes for garments.SOLUTION: Provided is a polyolefin microporous membrane having a film thickness of 1 μm or more and 30 μm or less, a puncture strength of 0.5 N or more and 1.1 N or less, a moisture permeability of 9500 (g / (m2 day)) or more, and a bubble point pressure of 0.3 MPa or more and 1.0 MPa or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a microporous polyolefin membrane that is widely used for filters and clothing applications. [Background technology]

[0002] Polyolefin microporous membranes are used as moisture-permeable waterproof membranes for filters and clothing because they have excellent pressure resistance, moisture permeability, and flexibility.

[0003] In addition, clothing using breathable waterproof membranes is used in outdoor and sports equipment, so it is expected to be used in harsh outdoor environments. Therefore, there is a growing demand for breathable waterproof membranes to withstand high water pressure. However, in order to improve water pressure resistance, membranes are generally designed to be thicker and stronger, which can result in poor breathability and flexibility. As described above, moisture-permeable waterproof membranes are required to achieve a high level of compatibility between the conflicting properties of water pressure resistance, moisture permeability, and flexibility. For example, Patent Document 1 discloses a moisture-permeable waterproof membrane that has high moisture permeability and is water-resistant even when thin. Patent Document 2 discloses a porous film that is breathable, water-resistant, and flexible. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6117503 [Patent Document 2] JP 2023-14022 A Summary of the Invention [Problem to be solved by the invention]

[0005] When attempting to apply the moisture-permeable waterproof film described in Patent Document 1 to clothing, there is a problem that the balance between water pressure resistance and moisture permeability is insufficient. In addition, the technology in Patent Document 2 has excellent flexibility due to the use of an elastomeric resin, but the water pressure resistance is insufficient, and there is a problem that the balance between water pressure resistance and flexibility is insufficient.

[0006] As described above, the present invention provides a polyolefin microporous membrane which, when used as a moisture-permeable waterproof membrane, has a better balance of water resistance, moisture permeability, and flexibility than conventional techniques. [Means for solving the problem]

[0007] In order to solve the above problems and achieve the object, the present invention has the following configuration. In the following description, a numerical range expressed using "~" means a range including the numerical values ​​before and after "~" as the lower and upper limits. [1] The film thickness is 1 μm or more and 30 μm or less, the puncture strength is 0.5 N or more and 1.1 N or less, and the moisture permeability is 9500 (g / (m 2 3. A microporous polyolefin membrane having a bubble point pressure of 0.3 MPa or more and 1.0 MPa or less. [2] The polyolefin microporous film according to [1], having a tensile breaking strength of 40 MPa or more and 100 MPa or less in at least one of the longitudinal direction (MD) and the transverse direction (TD). [3] The polyolefin microporous film according to [1] or [2], having a tensile modulus of 400 MPa or less in at least one of the longitudinal direction (MD) and the transverse direction (TD). [4] The polyolefin microporous film according to any one of [1] to [2], having a porosity of 50% or more and 75% or less. [5] Air permeability is 30sec / 100cm 3 The polyolefin microporous membrane according to any one of [1] to [4], which is: [6] The microporous polyolefin membrane according to any one of [1] to [5], having an average pore size of 60 nm or more. [7] Weight average molecular weight measured by gel permeation chromatography (GPC) is 7.0 × 105 The microporous polyolefin membrane according to any one of [1] to [6] above. [8] The polyolefin microporous membrane according to any one of [1] to [7], having a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) measured by gel permeation chromatography (GPC) method of 1.0 or more and 5.0 or less. [9] The polyolefin microporous membrane according to any one of [1] to [8], which is used for a filter.

[10] A filter comprising the polyolefin microporous membrane according to any one of [1] to [8].

[11] The polyolefin microporous film according to any one of [1] to [8], which is used for clothing.

[12] Clothing comprising the polyolefin microporous membrane according to any one of [1] to [8]. Effect of the Invention

[0008] According to the present invention, when used as a moisture-permeable waterproof membrane, it is possible to provide a polyolefin microporous membrane which has a better balance of water resistance, moisture permeability, and flexibility than conventional techniques. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[0010] [Polyolefin microporous membrane] The polyolefin microporous membrane according to the embodiment of the present invention has a thickness of 1 μm or more and 30 μm or less. It is preferably 1 μm or more and 20 μm or less, more preferably 1 μm or more and 15 μm or less, even more preferably 1 μm or more and 10 μm or less, particularly preferably 1 μm or more and 7 μm or less, and most preferably 3 μm or more and 7 μm or less. By setting the membrane thickness within the above range, a polyolefin microporous membrane having an excellent balance between water resistance and flexibility can be obtained. If the membrane thickness is less than the above range, sufficient mechanical strength cannot be obtained, and handling during membrane production and processing is deteriorated. In addition, if the membrane thickness exceeds the above range, the polyolefin microporous membrane becomes hard and flexibility is deteriorated. The membrane thickness can be set within the above range by adjusting the discharge amount of the polyolefin resin, the stretching ratio, and the porosity of the polyolefin microporous membrane.

[0011] The polyolefin microporous membrane according to the embodiment of the present invention has a pin puncture strength of 0.5N or more and 1.1N or less. It is preferably 0.5N or more and 1.0N or less, more preferably 0.5N or more and 0.9N or less, particularly preferably 0.5N or more and 0.8N or less, and most preferably 0.5N or more and 0.7N or less. By setting the pin puncture strength within the above range, a polyolefin microporous membrane with an excellent balance between water resistance and flexibility can be obtained. If the pin puncture strength is less than the above range, sufficient water pressure resistance cannot be obtained, and water resistance is deteriorated. If the pin puncture strength exceeds the above range, the polymer chains are too oriented, so that the polyolefin microporous membrane becomes hard and the flexibility is deteriorated. The method of controlling the pin puncture strength is not particularly limited. For example, the pin puncture strength tends to decrease when the membrane thickness decreases. In addition, if the temperature condition of the first stretching step is increased, orientation in the stretching step becomes difficult, and the pin puncture strength tends to decrease. In addition, when the condition of the magnification ratio in the first stretching step is increased, the orientation in the stretching step progresses, so the pin puncture strength tends to increase. In addition, by lowering the temperature in the second stretching step, recrystallization can be suppressed, so the pin puncture strength tends to decrease. In addition, when the draft ratio during gel-like sheet formation is increased, the melt-oriented structure formed between the die and the cooling roll is easily formed. Furthermore, when the cooling rate is increased during gel-like sheet formation, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be able to be stretched at a higher temperature in the first stretching step. In addition, when the conditions of the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane are made higher molecular weight and narrower molecular weight distribution, the melt viscosity increases, so that the shape retention at high temperatures of the gel-like sheet increases even if it is a thin film, and it tends to be possible to stretch the gel-like sheet at a higher temperature in the above-mentioned first stretching step. The pin puncture strength can be controlled within a desired range by appropriately controlling the membrane thickness, the temperature in the first stretching step, the temperature in the second stretching step, the draft ratio during formation of the gel-like sheet, and the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane.

[0012] The polyolefin microporous membrane according to the embodiment of the present invention preferably has a thickness-equivalent pin puncture strength of 0.05 N / μm or more. More preferably, it is 0.06 N / μm or more, even more preferably, it is 0.07 N / μm or more, and particularly preferably, it is 0.08 N / μm or more. By setting the thickness-equivalent pin puncture strength within the above range, it can withstand deformation due to pressure even when a high pressure is applied as a filter. The upper limit of the thickness-equivalent pin puncture strength is preferably 0.25 N / μm or less, since it is easy to achieve compatibility with pressure loss, more preferably 0.20 N / μm or less, even more preferably 0.15 N / μm or less, and most preferably 0.12 N / μm or less. The method of controlling the thickness-equivalent pin puncture strength is not particularly limited. For example, if the temperature condition of the first stretching step is increased, orientation in the stretching step becomes difficult, and the thickness-equivalent pin puncture strength tends to decrease. In addition, if the magnification condition of the first stretching step is increased, orientation in the stretching step progresses, and the thickness-equivalent pin puncture strength tends to increase. In addition, by lowering the temperature in the second stretching step, recrystallization can be suppressed, so that the thickness-equivalent pin puncture strength tends to decrease. In addition, when the draft ratio during gel-like sheet formation is increased, the melt-oriented structure formed between the die and the cooling roll is easily formed. Furthermore, when the cooling rate is increased during gel-like sheet formation, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be stretched at a higher temperature in the first stretching step. In addition, when the weight-average molecular weight and molecular weight distribution conditions of the polyolefin microporous membrane are made higher molecular weight and narrower molecular weight distribution, the melt viscosity increases, so that the shape retention at high temperatures increases even if the gel-like sheet is thin, and the above-mentioned first stretching step tends to be able to stretch at a higher temperature. By appropriately controlling the membrane thickness, the temperature in the first stretching step, the temperature in the second stretching step, the draft ratio during gel-like sheet formation, and the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane, the thickness-equivalent pin puncture strength can be controlled within the desired range.

[0013] The polyolefin microporous membrane according to the embodiment of the present invention has a moisture permeability of 9500 (g / (m 2 ·day)) or more. Preferably, it is 9750 (g / (m2 ·day)) or more, and more preferably 10,000 (g / (m 2 ·day)) or more, and more preferably 10250 (g / (m 2 ·day)) or more. Particularly preferably, it is 10500 (g / (m 2 By setting the moisture permeability in the above range, the membrane has sufficient moisture permeability as a water-permeable waterproof membrane. The upper limit of the moisture permeability is not particularly limited, but is preferably 25,000 (g / (m 2 ·day)) or less, and 2 ·day)) or less, and more preferably 15,000 (g / (m 2 ·day) or less is more preferable. The method of controlling the moisture permeability is not particularly limited. For example, when the temperature condition of the first stretching step is increased, the subdivision (refining of the pore structure) of the polyolefin resin in the stretching step can be suppressed, so the moisture permeability tends to increase. In addition, when the magnification condition of the first stretching step is increased, the subdivision (refining of the pore structure) of the polyolefin resin in the stretching step progresses, so the moisture permeability tends to decrease. In addition, when the magnification of the second stretching step is increased, the pore structure formed in the first stretching step and the washing step is coarsened, so the moisture permeability tends to increase. In addition, when the draft ratio during the formation of the gel-like sheet is increased, it becomes easier to form a melt-oriented structure formed between the die and the cooling roll. Furthermore, when the cooling rate is increased during the formation of the gel-like sheet, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be able to be stretched at a higher temperature in the first stretching step. Furthermore, when the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane are increased and the molecular weight distribution is narrowed, the melt viscosity increases, so that the shape retention of the gel-like sheet at high temperatures increases even if the sheet is thin, and it tends to be possible to stretch the sheet at a higher temperature in the first stretching step. By appropriately controlling the temperature and stretching ratio in the first stretching step, the stretching ratio in the second stretching step, the draft ratio in forming the gel-like sheet, and the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane, the moisture permeability can be controlled within a desired range.

[0014] The polyolefin microporous membrane according to the embodiment of the present invention has a bubble point pressure of 0.3 MPa or more and 1.0 MPa or less. It is preferably 0.3 MPa or more and 0.9 MPa or less, more preferably 0.3 MPa or more and 0.8 MPa or less, even more preferably 0.3 MPa or more and 0.7 MPa or less, and particularly preferably 0.3 MPa or more and 0.6 MPa or less. By setting the bubble point pressure within the above range, a polyolefin microporous membrane excellent in water resistance and moisture permeability can be obtained. When the bubble point pressure exceeds the above range, the pore size becomes small, so the moisture permeability deteriorates. Also, when the bubble point pressure is less than the above range, the moisture permeability is excellent due to the coarse pore structure, but in the evaluation of water resistance, the coarse pore part becomes a weak point and sufficient water pressure resistance cannot be obtained. The method of controlling the bubble point pressure is not particularly limited. For example, if the temperature condition of the first stretching step is increased, the subdivision of the polyolefin resin in the stretching step (refining of the pore structure) can be suppressed, so the bubble point pressure tends to decrease. In addition, when the condition of the ratio in the first stretching step is increased, the polyolefin resin is fragmented (pore structure is refined) in the stretching step, so the bubble point pressure tends to increase. In addition, when the ratio in the second stretching step is increased, the pore structure formed in the first stretching step and the washing step is coarsened, so the bubble point pressure tends to decrease. In addition, when the draft ratio is increased during the formation of the gel-like sheet, the melt-oriented structure formed between the die and the cooling roll is easily formed. Furthermore, when the cooling rate is increased during the formation of the gel-like sheet, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be able to be stretched at a higher temperature in the first stretching step. In addition, when the conditions of the weight average molecular weight and molecular weight distribution of the polyolefin microporous film are made high molecular weight and narrow molecular weight distribution, the melt viscosity increases, so that the gel-like sheet has an increased shape retention at high temperatures even if it is a thin film, and it tends to be able to be stretched at a higher temperature in the above-mentioned first stretching step. The bubble point pressure can be controlled within a desired range by appropriately controlling the temperature and stretching ratio in the first stretching step, the stretching ratio in the second stretching step, the draft ratio in forming the gel-like sheet, and the weight average molecular weight and molecular weight distribution of the polyolefin microporous membrane.

[0015] The polyolefin microporous membrane according to the embodiment of the present invention preferably has a tensile breaking strength of 40 MPa or more and 100 MPa or less in at least one of the longitudinal direction (MD) and the transverse direction (TD). It is preferably 40 MPa or more and 90 MPa or less, more preferably 40 MPa or more and 80 MPa or less, even more preferably 40 MPa or more and 70 MPa or less, and particularly preferably 40 MPa or more and 60 MPa or less. By setting the tensile breaking strength within the above range, a polyolefin microporous membrane having an excellent balance between water resistance and flexibility can be obtained. By setting the tensile breaking strength to the above lower limit or more, sufficient water pressure resistance can be obtained, and water resistance can be improved. Furthermore, the handling properties during film formation and processing can be improved. In addition, by setting the tensile breaking strength to the above upper limit or less, it is possible to prevent the polymer chains from being excessively oriented, and to prevent the polyolefin microporous membrane from becoming hard and losing flexibility. The method of controlling the tensile breaking strength is not particularly limited. For example, if the temperature condition of the first stretching step is increased, orientation in the stretching step becomes difficult, and the tensile breaking strength tends to decrease. In addition, when the condition of the ratio in the first stretching step is increased, the orientation in the stretching step proceeds, so the tensile breaking strength tends to increase. In addition, by lowering the temperature in the second stretching step, recrystallization can be suppressed, so the tensile breaking strength tends to decrease. In addition, when the draft ratio during the formation of the gel-like sheet is increased, the melt-oriented structure formed between the die and the cooling roll is easily formed. Furthermore, when the cooling rate is increased during the formation of the gel-like sheet, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be able to be stretched at a higher temperature in the first stretching step. In addition, when the conditions of the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane are made higher molecular weight and narrower molecular weight distribution, the melt viscosity increases, so that the gel-like sheet tends to have higher shape retention at high temperatures even if it is a thin film, and to be able to be stretched at a higher temperature in the above-mentioned first stretching step. The tensile strength at break can be controlled within a desired range by appropriately controlling the temperature in the first stretching step, the temperature in the second stretching step, the draft ratio in forming the gel-like sheet, and the weight average molecular weight and molecular weight distribution of the polyolefin microporous membrane.

[0016] The polyolefin microporous membrane according to the embodiment of the present invention preferably has an average tensile breaking strength in the machine direction (MD) and the transverse direction (TD) of 40 MPa or more and 100 MPa or less. It is preferably 40 MPa or more and 90 MPa or less, more preferably 40 MPa or more and 80 MPa or less, even more preferably 40 MPa or more and 70 MPa or less, and particularly preferably 40 MPa or more and 60 MPa or less. By setting the average tensile breaking strength within the above range, in addition to excellent balance between water resistance and flexibility, anisotropy is reduced, and therefore it is difficult to tear when used for clothing. By setting the average tensile breaking strength to be equal to or more than the above lower limit, sufficient water pressure resistance can be obtained, and water resistance is good. Furthermore, it is possible to suppress deterioration of handleability during film formation and processing. In addition, by setting the average tensile breaking strength to be equal to or less than the above upper limit, it is possible to suppress excessive orientation of polymer chains, and to suppress the polyolefin microporous membrane from becoming hard and losing flexibility.

[0017] The polyolefin microporous membrane according to the embodiment of the present invention preferably has a tensile modulus of 400 MPa or less in at least one of the longitudinal direction (MD) and transverse direction (TD). It is preferably 350 or less, more preferably 300 MPa or less, particularly preferably 250 or less, and most preferably 200 MPa or less. There is no particular lower limit for the tensile modulus, but it is preferably 50 MPa or more, more preferably 100 MPa or more, because it is easy to achieve compatibility with water pressure resistance. By setting the tensile modulus within the above range, it may be possible to obtain a polyolefin microporous membrane with excellent flexibility. There is no particular limit to the method of controlling the tensile modulus. For example, if the temperature condition of the first stretching step is increased, orientation in the stretching step becomes difficult, so the tensile modulus tends to decrease. In addition, if the ratio condition of the first stretching step is increased, orientation in the stretching step progresses, so the tensile modulus tends to increase. In addition, recrystallization can be suppressed by lowering the temperature of the second stretching step, so the tensile modulus tends to decrease. In addition, when the draft ratio during gel-like sheet formation is increased, the melt-oriented structure formed between the die and the cooling roll is easily formed. Furthermore, when the cooling rate is increased during gel-like sheet formation, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be stretched at a higher temperature in the first stretching step. In addition, when the weight-average molecular weight and molecular weight distribution conditions of the polyolefin microporous membrane are increased in molecular weight and narrowed in molecular weight distribution, the melt viscosity increases, so that the shape retention at high temperatures increases even when the gel-like sheet is thin, and the gel-like sheet tends to be stretched at a higher temperature in the first stretching step. The tensile modulus can be controlled within a desired range by appropriately controlling the temperature of the first stretching step, the temperature of the second stretching step, the draft ratio during gel-like sheet formation, and the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane.

[0018] The polyolefin microporous membrane according to the embodiment of the present invention preferably has a porosity of 50% or more and 75% or less. It is preferably 50% or more and 70% or less, more preferably 55% or more and 70% or less, and even more preferably 60% or more and 70% or less. By setting the porosity within the above range, it may be possible to obtain a polyolefin microporous membrane with excellent moisture permeability and water resistance. The porosity can be set within the above range by adjusting the stretching temperature, heat setting conditions, etc.

[0019] The polyolefin microporous membrane according to the embodiment of the present invention has an air permeability of 30 sec / 100 cm 3 It is preferable that the speed is 25 sec / 100 cm or less. 3 More preferably, it is 22 sec / 100 cm or less. 3 More preferably, it is 19 sec / 100 cm or less. 3 There is no particular lower limit for air permeability, but it is set to 1 sec / 100 cm because this makes it easier to balance it with water pressure resistance. 3 More than 5sec / 100cm is preferable. 3The above is more preferable. By setting the air permeability within the above range, it may be possible to obtain a polyolefin microporous membrane with excellent moisture permeability and water resistance. The method of controlling the air permeability is not particularly limited. For example, the air permeability tends to decrease when the membrane thickness decreases. In addition, if the temperature condition of the first stretching step is increased, the subdivision (refining of the pore structure) of the polyolefin resin in the stretching step can be suppressed, so the air permeability tends to decrease. In addition, if the ratio condition of the first stretching step is increased, the subdivision (refining of the pore structure) of the polyolefin resin in the stretching step progresses, so the air permeability tends to increase. In addition, if the ratio of the second stretching step is increased, the pore structure formed in the first stretching step and the washing step is coarsened, so the air permeability tends to decrease. In addition, if the draft ratio during the formation of the gel-like sheet is increased, it becomes easier to form a melt-oriented structure formed between the die and the cooling roll. Furthermore, when the cooling rate is increased during the formation of the gel-like sheet, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be stretched at a higher temperature in the first stretching step. In addition, when the weight-average molecular weight and molecular weight distribution conditions of the polyolefin microporous membrane are increased in molecular weight and narrowed in molecular weight distribution, the melt viscosity increases, so that the gel-like sheet tends to have improved shape retention at high temperatures even if it is a thin film, and to be stretched at a higher temperature in the above-mentioned first stretching step. By appropriately controlling the membrane thickness, the temperature and ratio in the first stretching step, the ratio in the second stretching step, the draft ratio during the formation of the gel-like sheet, and the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane, the air permeability can be controlled within the desired range.

[0020] The polyolefin microporous membrane according to the embodiment of the present invention has a thickness-equivalent air permeability of 7.5 sec / 100 cm 3 / μm or less. Preferably, it is 6.0sec / 100cm 3 / μm or less, and more preferably 3.5sec / 100cm 3 / μm or less, and more preferably 3.0sec / 100cm 3 / μm or less, and most preferably 2.5sec / 100cm 3 / μm or less. There is no particular lower limit for the thickness-based air permeability, but it is 0.1sec / 100cm 3 / μm or more, and 0.5sec / 100cm 3 / μm or more is preferable, and 0.8sec / 100cm 3 / μm or more is more preferable, and 0.9sec / 100cm 3 / μm or more is most preferable. By setting the thickness-equivalent air permeability in the above range, a polyolefin microporous membrane with excellent moisture permeability and water resistance can be obtained, and a filter with good pressure loss can be obtained. The method of controlling the thickness-equivalent air permeability is not particularly limited. For example, if the temperature condition of the first stretching step is increased, the subdivision (refining of the pore structure) of the polyolefin resin in the stretching step can be suppressed, so the thickness-equivalent air permeability tends to decrease. In addition, if the ratio condition of the first stretching step is increased, the subdivision (refining of the pore structure) of the polyolefin resin in the stretching step progresses, so the thickness-equivalent air permeability tends to increase. In addition, if the ratio of the second stretching step is increased, the pore structure formed in the first stretching step and the washing step is coarsened, so the thickness-equivalent air permeability tends to decrease. In addition, if the draft ratio is increased when forming the gel-like sheet, it becomes easier to form a melt-oriented structure formed between the die and the cooling roll. Furthermore, when the cooling rate is increased during the formation of the gel-like sheet, the gel-like sheet crystallizes while maintaining the above-mentioned melt-oriented structure, so that the shape retention at high temperatures is improved, and the gel-like sheet tends to be stretched at a higher temperature in the first stretching step. In addition, when the weight-average molecular weight and molecular weight distribution conditions of the polyolefin microporous membrane are increased in molecular weight and narrowed in molecular weight distribution, the melt viscosity increases, so that the gel-like sheet tends to have improved shape retention at high temperatures even if it is a thin film, and to be stretched at a higher temperature in the above-mentioned first stretching step. By appropriately controlling the membrane thickness, the temperature and ratio in the first stretching step, the ratio in the second stretching step, the draft ratio during the formation of the gel-like sheet, and the weight-average molecular weight and molecular weight distribution of the polyolefin microporous membrane, the air permeability can be controlled within the desired range.

[0021] The polyolefin microporous membrane according to the embodiment of the present invention preferably has an average pore size of 60 nm or more. It is preferably 65 nm or more, more preferably 70 nm or more. There is no particular upper limit to the average pore size, but it is preferably 140 nm or less, more preferably 110 nm or less, in terms of compatibility with water resistance. By setting the average pore size within the above range, it may be possible to obtain a microporous membrane with excellent moisture permeability and water resistance.

[0022] The polyolefin microporous membrane according to the embodiment of the present invention has a weight average molecular weight of 7.0×10 as measured by gel permeation chromatography (GPC). 5 More preferably, it is 7.5×10 5 More preferably, it is 8.0×10 5 More preferably, it is 8.5×10 5 The upper limit of the weight average molecular weight of the polyolefin microporous film is not particularly set, but from the viewpoint of flexibility, it is set to 5.0×10 6 It is preferable that the value is less than 4.0×10 6The following is more preferable. By setting the weight average molecular weight of the polyolefin microporous film in the above range, the relaxation rate is slowed down, so that in the step of forming a gel-like sheet described later, the melt-oriented structure is less likely to relax under the draft ratio conditions described later. In addition, by setting the weight average molecular weight of the polyolefin microporous film in the above range, the melt viscosity of the polyolefin is increased, so that the film can be stretched at a higher temperature in the first stretching step described later. Therefore, the inhibition of orientation in the stretching process and the fragmentation of the polyolefin resin (refining of the pore structure) are suppressed, and it may be possible to achieve both moisture permeability, film strength, and bubble point pressure. There is no particular limit to the method of controlling the weight average molecular weight of the polyolefin microporous film. For example, the weight average molecular weight of the polyolefin microporous film tends to decrease when the weight average molecular weight of the polyolefin raw material is reduced. In addition, increasing the kneading temperature promotes the degradation reaction, so the weight average molecular weight of the polyolefin microporous film decreases. By reducing the amount of antioxidant added, oxidation degradation progresses, so the weight average molecular weight of the polyolefin microporous film decreases. By appropriately controlling the weight average molecular weight of the polyolefin raw material, the kneading temperature, and additives such as antioxidants, the weight average molecular weight can be controlled within a desired range.

[0023] The polyolefin microporous membrane according to the embodiment of the present invention preferably has a molecular weight distribution (Mw / Mn) measured by GPC of 1.0 or more and 5.0 or less. More preferably, it is 2.0 or more and 5.0 or less, and even more preferably, it is 3.0 or more and 5.0 or less. By setting the molecular weight distribution of the polyolefin microporous membrane within the above range, the relaxation rate is slowed down, so that in the step of forming a gel-like sheet described later, the melt-oriented structure is less likely to relax under the draft ratio conditions described later. In addition, by setting the molecular weight distribution of the polyolefin microporous membrane within the above range, the melt viscosity of the polyolefin is increased, so that the polyolefin can be stretched at a higher temperature in the first stretching step described later. Therefore, the inhibition of orientation during the stretching process and the fragmentation of the polyolefin resin (refining of the pore structure) are suppressed, and it may be possible to achieve both moisture permeability, membrane strength, and bubble point pressure. The method of controlling the molecular weight distribution of the polyolefin microporous membrane is not particularly limited. For example, narrowing the molecular weight distribution of the polyolefin raw material tends to narrow the molecular weight distribution of the polyolefin microporous membrane. In addition, when the number of types of polyolefin raw materials used is reduced, the molecular weight distribution of the polyolefin microporous membrane tends to become narrower. By appropriately controlling the weight average molecular weight of the polyolefin raw materials and the types of the polyolefin raw materials, the molecular weight distribution can be controlled within the desired range.

[0024] Specific configurations of the polyolefin microporous membrane of the present invention will be described below, but the present invention is not necessarily limited to the embodiments described below.

[0025] The polyolefin microporous membrane according to the embodiment of the present invention is preferably mainly composed of a polyethylene resin. The main component referred to here means the component that is the most abundant in mass % among the components that constitute the polyolefin microporous membrane. The polyethylene resin component in the polyolefin microporous membrane is preferably 50 mass % or more, more preferably 80 mass % or more, even more preferably 90 mass % or more, particularly preferably 96 mass % or more, and most preferably 99 mass % or more. By setting the content of the polyethylene resin component in the polyolefin microporous membrane within the above range, the microporous membrane is excellent in membrane formability and is excellent in the balance of performance as a moisture-permeable waterproof membrane, such as water resistance, moisture permeability, and flexibility. Here, it is preferable to use one or more polyethylene resins in the polyolefin microporous membrane.

[0026] It is preferable to use ultra-high molecular weight polyethylene as the polyethylene used in the polyolefin microporous membrane according to the embodiment of the present invention. The ultra-high molecular weight polyethylene may be a homopolymer of ethylene, or may be a copolymer containing other α-olefins in order to lower the melting point as described below. Examples of α-olefins include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, and styrene. The presence and type of α-olefins can be determined by the C 13 This can be confirmed by measuring with -NMR.

[0027] The ultra-high molecular weight polyethylene in the present invention preferably has a weight average molecular weight (Mw) of 800,000 or more, more preferably 1,000,000 or more, even more preferably 1,200,000 or more, and particularly preferably 1,500,000 or more, as determined by gel permeation chromatography (GPC) measurement under the conditions described below. Also, it is preferably 10,000,000 or less, more preferably 8,000,000 or less, and even more preferably 6,000,000 or less.

[0028] The ultra-high molecular weight polyethylene in the present invention preferably has a molecular weight distribution (Mw / Mn) of 1.0 or more and 6.5 or less, more preferably 3.0 or more and 5.5 or less, which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) measured by gel permeation chromatography (GPC) under the conditions described below. When the Mw and Mw / Mn of the ultra-high molecular weight polyethylene are within the above ranges, even after the molecular weight is reduced and the molecular weight distribution is narrowed by melt kneading, it is possible to maintain the Mw and Mw / Mn of the polyolefin microporous membrane within the preferred ranges necessary for stretching under high temperature conditions described below.

[0029] The polyolefin microporous membrane may contain resin components other than the polyethylene resin and the polypropylene resin as necessary, and may further contain various additives such as antioxidants, heat stabilizers, antistatic agents, ultraviolet absorbers, antiblocking agents, fillers, crystal nucleating agents, and crystallization retarders, within the range that does not impair the effects of the present invention. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidation deterioration due to heat history of polyolefin resins. For example, it is preferable to use one or more selected from 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox" (registered trademark) 1330: molecular weight 775.2), tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 1010: molecular weight 1177.7), etc.

[0030] [Method for producing polyolefin microporous membrane] Next, the method for producing the polyolefin microporous film in the embodiment of the present invention will be described. The method for producing the polyolefin microporous film can be, for example, a dry film-forming method or a wet film-forming method. As the method for producing the polyolefin microporous film in the present embodiment, the dry film-forming method is advantageous in terms of moisture permeability because it is easy to form coarse pores, but the wet film-forming method is preferable from the viewpoint of balance with water pressure resistance and flexibility.

[0031] A wet method for producing a polyolefin microporous membrane will be described below. Note that the following description is merely an example of the production method, and the present invention is not limited to this method.

[0032] A method for producing a polyolefin microporous membrane in an embodiment of the present invention preferably includes the following steps (1) to (5) in this order, and may further include the following step (6). Alternatively, the method may further include the following step (7) after or instead of step (6). (1) A step of melt-kneading the polyolefin resin and a membrane-forming solvent to prepare a polyolefin resin composition. (2) A step of extruding the polyolefin resin composition and cooling it to form a gel-like sheet. (3) A first stretching step of preheating and stretching the gel-like sheet (4) A step of removing the membrane-forming solvent from the stretched gel-like sheet. (5) A step of drying the sheet after removing the membrane-forming solvent. (6) A second stretching step of preheating and stretching the dried sheet (7) A step of heat treating the dried sheet.

[0033] (1) Preparation of polyolefin resin composition A polyolefin resin composition is prepared by heating and dissolving a polyolefin resin in a plasticizer (membrane-forming solvent). The plasticizer is not particularly limited as long as it is a solvent that can uniformly disperse the polyolefin resin, but in order to enable relatively high-magnification stretching, it is preferable that the solvent is liquid at room temperature. Examples of the solvent include aliphatic, alicyclic or aromatic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin, and mineral oil fractions having boiling points corresponding thereto, as well as phthalic acid esters that are liquid at room temperature, such as dibutyl phthalate and dioctyl phthalate. In order to obtain a gel-like sheet with a stable content of liquid solvent, it is preferable to use a nonvolatile liquid solvent such as liquid paraffin in order to perform stretching without forming localized coarse pores. If a volatile liquid solvent is used, the solvent will escape from the phase-separated gel-like sheet, which may increase the concentration unevenness in the gel-like sheet and make it easier to form localized coarse pores.

[0034] The blending ratio of the polyolefin resin and the plasticizer is preferably 10 to 50% by mass of the polyolefin resin relative to the total mass of the polyolefin resin composition. More preferably, it is 10 to 40% by mass, further preferably, it is 10 to 30% by mass, and particularly preferably, it is 15 to 25% by mass. By setting the content of the polyolefin resin within the above range, the dispersion state of the polyolefin resin and the plasticizer becomes good, and the Mw, Mw / Mn, membrane strength, moisture permeability, and pore size of the obtained polyolefin microporous membrane become excellent. In addition, when forming into a sheet, the amount of swelling and necking at the outlet of the die becomes appropriate, and the sheet moldability and film formability are also good.

[0035] The polyolefin resin and the plasticizer are preferably melt-kneaded in a twin-screw extruder in order to obtain a uniform kneaded state. The resin temperature during kneading is preferably 150° C. or higher, more preferably 160° C. or higher, and even more preferably 180° C. or higher, with the upper limit being preferably 250° C. or lower, more preferably 240° C. or lower, and even more preferably 230° C. or lower. By keeping the temperature of the polyolefin resin composition during kneading within the above range, it is possible to prevent a decrease in strength due to deterioration of the resin, and it is possible to uniformly melt-knead the polyolefin resin and the plasticizer.

[0036] In addition, during kneading with a twin-screw extruder, Q / Ns calculated from the ratio of the extrusion mass Q (kg / hr) to the screw rotation speed Ns (rpm) is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. This makes it possible to prevent a decrease in strength due to resin deterioration during kneading. In addition, the upper limit is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less. This makes it possible to apply sufficient shear to the polyolefin resin composition and obtain a uniformly dispersed state.

[0037] (2) Gel-like sheet formation process The melt of the polyolefin resin composition is fed from the extruder to a die and extruded into a sheet. The extrusion method is preferably a T-die method. The extrusion temperature is preferably 190 to 250°C. The ratio of the cooling roll speed V(roll) to the T-die exit speed V(die) (V(roll) / V(die)) is called the draft ratio. V(die)(mpm): Die exit speed V(roll)(mpm): cooling roll speed The larger the draft ratio, the greater the melt drawing in the take-up direction of the composition discharged from the T-die until it comes into contact with the cooling roll. The draft ratio is preferably 1.5 to 4.0, and more preferably 2.0 to 3.5. The resin composition melt-extruded into a sheet is cooled and solidified by a cooling roll to become a gel-like sheet. In the cooling step, it is preferable to cool the resin composition to 10 to 50°C before the first stretching step described later. This is because it is preferable to set the final cooling temperature below the crystallization end temperature, and by making the high-order structure finer, it becomes easier to perform uniform stretching in the subsequent stretching. In addition, the cooling rate at this time is preferably 50°C / min or more, more preferably 100°C / min or more, and even more preferably 150°C / min or more. If the cooling rate is slow, the structure melt-oriented under the above draft ratio conditions will relax before crystallization, and the gel-like sheet will have difficulty in maintaining its shape during high-temperature stretching in the first stretching step described later. On the other hand, if the cooling rate is fast, the structure melt-oriented under the above draft ratio conditions will be crystallized while maintaining the structure, so that the shape retention at high temperatures will be good, and the gel-like sheet can be stretched at a higher temperature in the first stretching step described later. As a result, inhibition of orientation during the stretching process and fragmentation of the polyolefin resin (fining of the pore structure) are suppressed, making it easier to achieve both moisture permeability, membrane strength, and bubble point pressure, as well as excellent pore size, air permeability, and elastic modulus. The sheet thickness is preferably 0.3 mm to 2.0 mm, more preferably 0.4 mm to 1.7 mm, and further preferably 0.5 mm to 1.4 mm, in consideration of the film thickness, porosity, and the stretching ratio in the stretching step described below.

[0038] (3) First stretching step Next, the obtained gel-like sheet is stretched at least in one direction, but it is preferable to preheat the gel-like sheet before stretching. The preheating temperature is preferably 110 to 130°C. The lower limit is preferably 115°C or higher, more preferably 120°C or higher, and even more preferably 121°C or lower. The upper limit is preferably 129°C or lower. The gel-like sheet after preheating is preferably stretched at a predetermined magnification by a tenter method, a roll method, an inflation method, or a combination of these. The stretching may be uniaxial or biaxial, with biaxial stretching being preferred. In the case of biaxial stretching, any of simultaneous biaxial stretching, sequential biaxial stretching, and multi-stage stretching (e.g., a combination of simultaneous biaxial stretching and sequential biaxial stretching) may be used, with simultaneous biaxial stretching being preferred. The stretching ratio (area stretching ratio) in this step is preferably 16 times or more, more preferably 25 times or more. The stretching ratio is preferably 4 times or more in both the machine longitudinal direction (MD) and the machine width direction (TD), more preferably 5 times or more. The stretching ratios in the MD and TD directions may be the same or different. The area stretching ratio in this step is preferably 49 times or less, more preferably 36 times or less. By setting the area stretching ratio in the above range, the mechanical strength can be adjusted to a preferred range. The stretching temperature in this step is preferably 121° C. or higher, more preferably 122° C., even more preferably 123° C., particularly preferably 125° C. or higher, and most preferably 126° C. or higher. The upper limit is preferably 133° C. or lower, more preferably 131° C. or lower, even more preferably 130° C. or lower, and particularly preferably 129° C. or lower. When the stretching temperature is within the above range, inhibition of orientation during the stretching process and fragmentation of the polyolefin resin (refining of the pore structure) are suppressed, making it easy to achieve both moisture permeability, film strength, and bubble point pressure, and to obtain excellent pore size, air permeability, and elastic modulus.

[0039] (4) Removal of membrane-forming solvent The membrane-forming solvent is removed (washed) using a washing solvent. The polyolefin resin phase is phase-separated from the membrane-forming solvent phase. Therefore, when the membrane-forming solvent is removed, a porous membrane is obtained that is made of fibrils that form a fine three-dimensional network structure and has holes (voids) that are three-dimensionally irregularly connected. Washing solvents and methods for removing the membrane-forming solvent using the same are publicly known, so a description thereof is omitted. For example, the methods disclosed in Japanese Patent No. 2132327 and Japanese Patent Laid-Open No. 2002-256099 can be used.

[0040] (5) Drying process The polyolefin microporous membrane from which the membrane-forming solvent has been removed is dried by heat drying or air drying. The drying temperature is preferably equal to or lower than the crystal dispersion temperature (TCD) of the polyolefin resin, and more preferably 5° C. or more lower than the TCD. The drying is preferably performed until the remaining washing solvent is 5 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass (dry mass) of the total mass of the polyolefin microporous membrane.

[0041] (6) Second stretching step The dried microporous membrane is then stretched at least uniaxially at a predetermined areal stretch ratio. The stretching of the dried film (second stretching) is also called dry stretching. The stretching may be uniaxial or biaxial, but uniaxial stretching is preferred. The uniaxial stretching may be either MD or TD, but TD stretching is more preferred.

[0042] The areal stretching ratio of the dry stretching is preferably 1.0 to 3.0 times, more preferably 1.2 to 2.0 times or more, and even more preferably 1.2 to 1.7 times or more. By setting the areal stretching ratio of the dry stretching in the above range, it becomes easy to achieve both moisture permeability, membrane strength, and bubble point pressure. In addition, it becomes easy to obtain excellent pore size and air permeability by dry stretching at a predetermined ratio. Here, the areal stretching ratio described in this process indicates the product of the dry stretching ratios in the MD direction and the TD direction.

[0043] The stretching temperature in this step is preferably 80° C. or higher, and more preferably 90° C. or higher, and preferably 125° C. or lower, more preferably 110° C. or lower, and even more preferably 100° C. or lower. By setting the stretching temperature in this step within the above range, an increase in crystallinity due to relaxation and recrystallization of the resulting polyolefin microporous membrane can be suppressed, and the membrane strength, elastic modulus, and pore size can be adjusted to predetermined ranges to obtain a microporous membrane with excellent flexibility and water pressure resistance.

[0044] (7) Heat treatment process In addition, after the step (6) or instead of the step (6), the polyolefin microporous membrane after drying can be subjected to a heat treatment. The heat treatment stabilizes the crystals and makes the lamellae uniform. As the heat treatment method, a heat setting treatment and / or a heat relaxation treatment can be used. The heat setting treatment is a heat treatment in which the membrane is heated while maintaining its dimensions. The heat relaxation treatment is a heat treatment in which the membrane is thermally shrunk in the MD direction or the TD direction during heating. The heat setting treatment is preferably performed by a tenter method or a roll method. The relaxation rate in the relaxation treatment is the value obtained by dividing the dimensions of the membrane after the relaxation treatment by the dimensions of the membrane before the relaxation treatment, and both the relaxation rates in the MD and TD directions of the membrane are preferably 1.0 or less, more preferably 0.98 or less, and even more preferably 0.96 or less. In addition, from the viewpoint of the planarity of the microporous membrane, it is preferably 0.80 or more, and more preferably 0.90 or more. The heat treatment temperature is preferably performed within the range described in the previous step (6). The reason is the same as that described in the previous step (6). The microporous polyolefin membrane obtained as described above can be used for various purposes such as clothing and filters. EXAMPLES

[0045] The present invention will be described in more detail with reference to examples, but the embodiment of the present invention is not limited to these examples. Evaluations in this application were performed in an environment with a temperature of 23°C and a humidity of 65%, unless otherwise specified. The evaluation and analysis methods used in the examples are as follows.

[0046] [Measurement method] [Film thickness] The thickness of the polyolefin microporous membrane was measured at any five points within a 50 mm × 50 mm area using a contact thickness meter, Mitutoyo Corporation's "Litematic" (registered trademark) VL-50 (10.5 mmφ ultrahard spherical probe, measuring load 0.01 N), and the average value was recorded as the thickness (μm).

[0047] [Porosity] A sample was cut from the polyolefin microporous membrane into a 50 mm × 50 mm square, and its volume (cm 3 ) and mass (g). These values ​​and the film density (g / cm 3 The porosity of the polyolefin microporous membrane was calculated from the following formula. The membrane density was 0.99 g / cm 3 In this measurement, samples were cut out from three randomly selected positions on the polyolefin microporous membrane, and the average porosity was calculated. Formula: Porosity (%) = [(volume-mass / membrane density) / volume] x 100 [Air permeability] For polyolefin microporous membranes, the air permeability (sec / 100cm) was measured in an atmosphere of 25°C using an Oken air permeability meter (Asahi Seiko Co., Ltd., EGO-1T) in accordance with JIS P-8117:2009. 3 ) was measured.

[0048] In addition, the thickness converted air permeability (sec / 100cm) is calculated using the following formula: 3 / μm) was calculated. Formula: Thickness converted air permeability (sec / 100cm 3 / μm) = Air permeability (sec / 100cm 3 ) / Polyolefin microporous membrane thickness (μm) [Piercing strength] The puncture strength was measured in accordance with JIS Z 1707 (2019), except that the test speed was 2 mm / s. Using a force gauge (IMADA Co., Ltd., DS2-20N), the maximum load (mN) was measured when a polyolefin microporous membrane was punctured with a 1.0 mm diameter needle with a spherical tip (radius of curvature R: 0.5 mm).

[0049] Furthermore, the thickness-equivalent puncture strength (N / μm) was calculated using the following formula.

[0050] Formula: Thickness-converted puncture strength (N / μm)=puncture strength (N) / film thickness of polyolefin microporous membrane (μm).

[0051] [Moisture permeability] The measurement was performed according to the method specified in JIS L1099:2021. The measurement was performed in an atmosphere of temperature: 40°C and humidity: 90%, and the measurement was performed three times, and the average value was taken as the moisture permeability. The moisture permeability may be measured from either side of the film.

[0052] [Bubble point pressure] The bubble point pressure (MPa) of the polyolefin microporous membrane was determined using a perm porometer (CFP-1500A, manufactured by PMI) based on JIS K 3832: 1990. GALWICK (surface tension: 15.9 dynes / cm) was used as the impregnation liquid for the polyolefin microporous membrane, and pressure was applied to the fully immersed microporous membrane to measure the pressure at which air began to penetrate.

[0053] [Tensile breaking strength] The tensile strength (MPa) in each direction was measured using an Instron 5543 tensile tester manufactured by Instron in accordance with ASTM D882 under the following conditions. Sample shape: Rectangular shape, 100mm long x 10mm wide Chuck distance: 20mm Pulling speed: 100mm / min Grip: Instron 2702-018 Jaw Faces for Flats (Rubber Coated, 50 x 38 mm) Load cell: 500N Chuck pressure: 0.50MPa ·Temperature: 23℃±2℃ The above measurements were performed at three different points on the same film in both the MD and TD directions, and the average value of the three points was taken as the tensile breaking strength in each direction (MD tensile breaking strength, TD tensile breaking strength).

[0054] [Tensile modulus] The tensile modulus (MPa) corresponding to each direction was measured under the following conditions using an Instron tensile tester, Instron 5543. The strain used to determine the tensile modulus is the slope of the stress-strain curve for strains from 0% to 3%. Sample shape: Rectangular shape, 100mm long x 10mm wide Chuck distance: 20mm Pulling speed: 100mm / min Grip: Instron Catalog No. 2702-307 (rubber coated, width 50 x height 38 mm) Load cell: 500N Chuck pressure: 0.50MPa ·Temperature: 23℃±2℃ [Average pore diameter] The average pore size of the polyolefin microporous membrane was determined using a perm porometer (CFP-1500A, manufactured by PMI). GALWICK (surface tension: 15.9 dynes / cm) was used as the impregnation liquid for the polyolefin microporous membrane, and measurements were performed in the order of dry-up and wet-up. The average pore size (nm) was measured based on ASTM E1294-89 (1999) (half dry method), and the pore size was calculated from the pressure (KPa) at the point where the curve showing the 1 / 2 slope of the pressure and flow rate curve in the dry-up measurement intersects with the curve in the wet-up measurement. The following formula was used to convert pressure and pore size.

[0055] d=C·γ / P (In the above formula, "d (nm)" is the average pore size of the microporous membrane, "γ (dynes / cm)" is the surface tension of the impregnating liquid, "P (KPa)" is the pressure, and "C" is a constant which is set to 2860.)

[0056] [Gel Permeation Chromatography (GPC)] The weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution of the polyolefin resin and the microporous polyolefin membrane were determined by GPC under the conditions shown below.

[0057] ·Measuring device: AMR high temperature GPC device PL-GPC220 Column: PLgel 20um MIXED-A manufactured by AMR Corporation Column temperature: 160℃ Solvent (mobile phase): TCB (trichlorobenzene) Solvent flow rate: 1.0 ml / min ·Sample concentration: 0.1% by mass (dissolution conditions: 160℃ / 0.5h) Injection volume: 500μl Detector: RI detector Calibration curve: Prepared using monodisperse polystyrene standard samples.

[0058] [Water pressure resistance] Measurements were performed in accordance with JIS L 1092:2009 Method B (waterproofing test method for textile products). Specifically, a porous film was set in a water pressure tester, and a mesh with a pitch of 1000 um and a wire diameter of 500 um was placed over it, after which the porous film and mesh were fixed in the water pressure tester. Water pressure was then applied to the test piece at a pressure increase rate of 60 cm / min, and the water pressure was measured when three drops of water had appeared.

[0059] [Flexibility] Measurements were made in accordance with JISL1096:2010A method (45° cantilever method) and used as an index of flexibility.

[0060] [Polyolefin microporous membrane with a good balance of water resistance, moisture permeability, and flexibility] The balance of water resistance, moisture permeability and flexibility of the polyolefin microporous membrane was evaluated according to the following criteria. ◎: Pass all three items below and have 2 or more A's and 0 C's 〇: All three items below are passed except for ◎, and at least one item is A △: ◎, 〇, and all three of the following three items are passed ×:Other than the above Item 1 (A to C are pass.) A: Moisture permeability is 10500 (g / (m 2 ·day) or more B: Moisture permeability is 10000 (g / (m 2 ·day)) or more 10500(g / (m) 2 Less than 1 day C: Moisture permeability is 9500 (g / (m 2 ·day)) or more 10000(g / (m) 2 Less than 1 day D: Moisture permeability is 9500 (g / (m 2Less than 1 day Item 2 (A to C are pass.) A: Water pressure resistance of 0.1 (MPa) or more B: Water pressure resistance is 0.7 (MPa) or more but less than 0.1 (MPa) C: Water pressure resistance is 0.3 (MPa) or more but less than 0.7 (MPa) D: Water pressure resistance is less than 0.3 (MPa) Item 3 (A to C are pass.) A: Flexibility is 8mm or less B: Flexibility is greater than 8 mm and less than 12 mm C: Flexibility is greater than 12 mm and less than 15 mm D: Flexibility exceeds 15 (mm).

[0061] [Example 1] The polyolefin raw material is resin A with Mw of 2.8 x 10 6 100% by mass of ultra-high molecular weight polyethylene with Mw / Mn of 5.2 was used. 81% by mass of liquid paraffin was added to 19% by mass of the above polyolefin raw material, and 1.1 parts by mass of 2,6-di-t-butyl-p-cresol and 0.7 parts by mass of tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate]methane were added as antioxidants based on the mass of the above resin A and mixed to prepare a polyolefin resin composition. The obtained polyolefin resin composition was charged into a twin-screw extruder and kneaded at 180°C to prepare a polyolefin solution. The obtained polyolefin solution was fed into a T-die adjusted to 220°C, melt extruded under conditions such that the draft ratio was 2.4 (see Table 1 for detailed conditions), and cooled in a casting drum controlled to 35°C to form a gel-like sheet. The gel-like sheet was first stretched at 122°C in both MD and TD directions by 5 times using a simultaneous biaxial tenter stretching machine. The wet-stretched gel-like sheet was immersed in a methylene chloride bath to remove liquid paraffin, and then air-dried. The sheet was then secondly stretched at 110°C in the TD direction by 1.4 times using a tenter stretching machine to obtain a polyolefin microporous membrane. The film-forming conditions for the polyolefin microporous membrane are shown in Table 1, and the evaluation results for the obtained polyolefin microporous membrane are shown in Table 2.

[0062] [Examples 2 to 4, 6 to 9, Comparative Examples 1 to 4] A porous film was obtained in the same manner as in Example 1 except for the conditions shown in Tables 1 and 2. The physical properties and evaluation results of the obtained porous film are shown in Tables 2 and 4.

[0063] [Example 5] The polyolefin raw material is resin A with Mw of 2.8 x 10 6 100% by mass of ultra-high molecular weight polyethylene with Mw / Mn of 5.2 was used. 80% by mass of liquid paraffin was added to 20% by mass of the above polyolefin raw material, and 1.1 parts by mass of 2,6-di-t-butyl-p-cresol and 0.7 parts by mass of tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate]methane were added as antioxidants based on the mass of the above polyolefin raw material and mixed to prepare a polyolefin resin composition. The obtained polyolefin resin composition was charged into a twin-screw extruder and kneaded at 180°C to prepare a polyolefin solution. The obtained polyolefin solution was supplied to a T-die adjusted to 230°C, melt extruded under conditions such that the draft ratio was 3.1 (see Table 1 for detailed conditions), and cooled in a casting drum controlled to 15°C to form a gel-like sheet. The gel-like sheet was subjected to a first stretching at 126° C. and a stretching ratio of 5 times in both the MD and TD directions using a simultaneous biaxial tenter stretching machine. The wet-stretched gel-like sheet was fixed to a 30 cm x 30 cm aluminum frame, immersed in a methylene chloride bath adjusted to 25°C, and rocked for 5 minutes to remove the liquid paraffin. The sheet was then air-dried at room temperature to obtain a dry film. Subsequently, the film was stretched 1.7 times in the TD direction at 100°C using a tenter-type stretching machine as the second stretching to obtain a polyolefin microporous membrane. The film-forming conditions for the polyolefin microporous membrane are shown in Table 1, and the evaluation results of the obtained polyolefin microporous membrane are shown in Table 2.

[0064] [Comparative Examples 5 to 8] As shown in Table 3, a gel-like sheet was obtained, but since the gel-like sheet broke during the first stretching, a porous film was not obtained.

[0065] Examples and comparative examples are shown in Tables 1 to 4.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] [Table 4]

[0070] The polyolefin microporous membranes shown in Examples 1 to 9 all have preferred ranges for thickness, puncture strength, moisture permeability, and bubble point pressure. Therefore, when used as a moisture-permeable waterproof membrane for clothing, they have a better balance of water resistance, moisture permeability, and flexibility than the prior art. On the other hand, the polyolefin microporous membranes shown in Comparative Examples 1 to 4 could not achieve a balance between water resistance, moisture permeability, and flexibility because none of the above parameters could be within the preferred range. [Industrial Applicability]

[0071] According to the present invention, it is possible to provide a polyolefin microporous membrane which, when used as a moisture-permeable waterproof membrane, has a better balance of water resistance, moisture permeability, and flexibility than those of the prior art.

Claims

1. The film thickness is 1 μm or more and 30 μm or less, the puncture strength is 0.5 N or more and 1.1 N or less, and the moisture permeability is 9500 (g / (m ２ - day) or more, and a bubble point pressure of 0.3 MPa or more and 1.0 MPa or less.

2. The microporous polyolefin membrane according to claim 1, having a tensile break strength in at least one of the machine direction (MD) and the transverse direction (TD) of 40 MPa or more and 100 MPa or less.

3. 3. The microporous polyolefin membrane according to claim 1 or 2, having a tensile modulus of 400 MPa or less in at least one of the machine direction (MD) and the transverse direction (TD).

4. The microporous polyolefin membrane according to claim 1 or 2, having a porosity of 50% or more and 75% or less.

5. Air permeability is 30sec / 100cm ３ 3. The microporous polyolefin membrane according to claim 1 or 2, wherein:

6. The microporous polyolefin membrane according to claim 1 or 2, having an average pore size of 60 nm or more.

7. The weight average molecular weight Mw measured by gel permeation chromatography (GPC) is 7.0×10 ５ The polyolefin microporous membrane according to claim 1 or 2.

8. The microporous polyolefin membrane according to claim 1 or 2, having a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) measured by gel permeation chromatography (GPC) of 1.0 or more and 5.0 or less.

9. The microporous polyolefin membrane according to claim 1 or 2, which is used for a filter.

10. A filter comprising the microporous polyolefin membrane according to claim 1 or 2.

11. The microporous polyolefin membrane according to claim 1 or 2, which is used for clothing.

12. A garment comprising the polyolefin microporous membrane according to claim 1 or 2.

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