Porous film and absorptive article

Abstract

To provide a porous film which is excellent in flexibility, and an absorptive article which has a flexible rear face sheet, prevents inconvenience such as deviation when being used while being fixed to a garment, and is excellent in wearing feeling and leakage prevention property.SOLUTION: A porous film contains a low melting point olefinic resin having a melting point of lower than 80°C, wherein the low melting point olefinic resin contains an ethylene-vinyl acetate copolymer. An absorptive article 1A is used while being fixed to a garment, and adhesives 7 and 8 are attached to a fixed surface 3a to a garment. In the absorptive article 1A, a sheet 3 forming the fixed surface 3a is the porous film.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a porous film suitable for absorbent articles. [Background technology]

[0002] There are known absorbent articles such as disposable diapers and sanitary napkins, which include an absorbent body that absorbs and retains bodily fluids and a back sheet arranged on the non-skin-facing side of the absorbent body. A porous film is often used as the back sheet. An absorbent article having a back sheet made of a porous film has the advantage that moisture generated from the wearer's body is easily released to the outside through the back sheet when worn, making it less likely to become stuffy when worn.

[0003] As a porous film, moisture-permeable films formed from a resin composition containing a thermoplastic resin such as a polyolefin resin and an inorganic filler are known (Patent Documents 1 to 3). For example, Patent Documents 1 and 2 describe a moisture-permeable porous film containing a crystalline low-density polyethylene having a melting point of 50 to 100°C as measured by a differential scanning calorimeter (DSC), and also describe the use of the film as a back sheet of an absorbent article. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-1557 A [Patent Document 2] JP 2000-1556 A [Patent Document 3] JP 2019-163357 A

[0005] The back sheet of an absorbent article is required to have flexibility in addition to moisture permeability. By using a back sheet with excellent flexibility, it is expected that the wearing comfort of the absorbent article will be improved. In addition, in absorbent articles of the type that are used by fixing to clothing such as shorts, such as sanitary napkins, an adhesive is often provided as a fixing means on the fixing surface of the back sheet to the clothing. The adhesive as the fixing means is required to stably exhibit a certain level of adhesive force so that after the absorbent article is fixed to a predetermined position on the clothing via the adhesive, there is no inconvenience such as the absorbent article being displaced from the fixed position or the absorbent article being unintentionally deformed, such as twisting or turning over. A porous film that is excellent in flexibility and can stably exhibit the adhesive force of the adhesive when used as a back sheet of an absorbent article has not yet been provided. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention relates to a porous film having excellent flexibility. The present invention also relates to an absorbent article which has a flexible backsheet, which is less likely to slip when fixed to clothing, and which is excellent in comfort and leak prevention. [Means for solving the problem]

[0007] The present invention relates to a porous film comprising an olefin-based resin composition, an inorganic filler, and a fatty acid. In one embodiment of the porous film of the present invention, it is preferable that the inorganic filler is contained in an amount of 50 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the olefin-based resin composition, and the fatty acid is contained in an amount of 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the inorganic filler. In one embodiment of the porous film of the present invention, the olefin resin composition preferably contains a low-melting-point olefin resin having a melting point of less than 80°C. In one embodiment of the porous film of the present invention, the low melting point olefin resin is preferably made of a resin containing an ethylene-vinyl acetate copolymer.

[0008] The present invention is an absorbent article to be fixed to clothing when used, in which an adhesive is attached to the surface to be fixed to the clothing, and the sheet forming the fixing surface is the porous film of the present invention. Other features, advantages and embodiments of the present invention are described below. Effect of the Invention

[0009] According to the present invention, a porous film having excellent flexibility can be provided. Also, according to the present invention, an absorbent article having a flexible back sheet, which is less likely to cause problems such as slippage when fixed to clothing, and which has excellent wearing comfort and leak prevention properties can be provided. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a plan view showing a schematic view of the non-skin-facing side of a sanitary napkin, which is one embodiment of the absorbent article of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view that typically shows a cross section taken along line II (a cross section along the thickness direction and the lateral direction) of the sanitary napkin shown in FIG. [Diagram 3] FIG. 3 is a view corresponding to FIG. 1 of another embodiment of the absorbent article of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The porous film of the present invention will be described in detail below. The porous film of the present invention has a large number of micropores. The porous film of the present invention has moisture permeability due to the micropores. The porous film of the present invention also has high water resistance and high leakproofness. Furthermore, the porous film of the present invention has high flexibility and requires a small load to deform. The porous film of the present invention contains at least an olefin resin composition, an inorganic filler, and a fatty acid. In addition to these components, the porous film of the present invention may contain various additives for the purpose of improving various properties of the porous film.

[0012] In this specification, the term "olefin resin composition" includes both the case where only one type of various olefin resins is contained and the case where two or more types are contained. In addition, the term "olefin resin composition" is a concept that consists of only various olefin resins and does not contain other resins or components other than resins. In addition, the porous film of the present invention may contain resins other than olefin resins. The olefin resin composition used in the present invention is composed mainly of a polymer or copolymer of a monoolefin such as ethylene, propylene, butene, etc. Examples of such a polymer or copolymer include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, an olefin elastomer, and a mixture of any two or more of these.

[0013] In order to set the density of the olefin resin composition within the above-mentioned range, the olefin resin composition preferably contains a low-melting-point olefin resin as the olefin resin. The low-melting-point olefin resin is also used to impart flexibility to the porous film of the present invention. From the viewpoint of imparting flexibility to the porous film of the present invention, the low melting point olefin resin has a melting point of preferably less than 80° C., more preferably less than 77° C., and even more preferably less than 75° C. In order to obtain dimensional stability of the porous film, the low melting point olefin resin has a melting point of preferably 40° C. or more, more preferably 50° C. or more, and even more preferably 60° C. or more. In summary, the low melting point olefin resin has a melting point of preferably 40° C. or more and less than 80° C., more preferably 50° C. or more and less than 77° C., and even more preferably 60° C. or more and less than 75° C. Unless otherwise specified, the term "low melting point olefin resin" used in this specification refers to an olefin resin having a melting point of less than 80°C.

[0014] The melting point of the low melting point olefin resin contained in the porous film is measured by the following method. Approximately 2.0 mg of the porous film is used as a sample, and differential scanning calorimetry (DSC) is performed using a differential scanning calorimeter (DSC7000X, Hitachi High-Tech Science Corporation) under conditions of a measurement temperature range of 10°C to 260°C, a heating rate of 10°C / min, and an air environment. In the obtained DSC curve, an endothermic peak is observed in a temperature range lower than 80°C, which occurs when the low melting point olefin resin melts, and the melting point of the low melting point olefin resin is the temperature at the apex of the observed endothermic peak.

[0015] In addition, when the porous film contains components (e.g., additives) other than the object of melting point measurement (low melting point olefin resin), the above-mentioned melting point measurement method may not be able to accurately measure the melting point of the object of measurement. In such a case, the additives are collected from the porous film by the following method, and their melting points are measured, making it possible to distinguish the melting point of the object of measurement measured separately from the melting points of other components (additives). First, a porous film is kneaded at 160° C. and 30 rpm for 10 minutes using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.) to obtain a resin mass. Next, using a lab press (manufactured by Toyo Seiki Seisakusho), the resin block is pressed at 150° C. and 13 MPa for 1 minute, and then cold pressed at room temperature and 13 MPa for 1 minute to obtain a pressed film with a thickness of approximately 0.5 mm. Finally, the pressed film is stored in an environment of 50°C for one week. By doing so, more additives bleed out onto the surface of the pressed film than in the porous film state, so the additives can be collected efficiently. Methods for collecting the additives from the surface of the pressed film include, for example, wiping them off with a wipe or scraping them off with a spatula.

[0016] The porous film of the present invention contains a low melting point olefin resin as described above, and therefore has excellent flexibility. As the low melting point olefin resin, considering only the flexibility of the porous film, for example, a copolymer of ethylene and α-olefin (hereinafter also referred to as "ethylene-α-olefin copolymer") is preferable, and the α-olefin includes propylene, 1-butene, 1-pentene, and 1-hexene. However, according to the findings of the present inventors, when an adhesive used as a fixing means for an absorbent article such as a sanitary napkin to clothing such as shorts is applied to the surface of a porous film to which a low polarity elastomer that contributes to improving the flexibility of the porous film, such as an ethylene-α-olefin copolymer, is added, the adhesive strength of the adhesive may decrease over time. Such a problem of deterioration over time of the adhesive, which is specific to a porous film whose flexibility is improved due to the raw material resin, is not described in Patent Documents 1 to 3.

[0017] One possible method for solving the above problem is to increase the amount of adhesive applied to the porous film compared to conventional methods, but this method has the risk of causing discomfort to the wearer when the absorbent article fixed to clothing via the adhesive is peeled off from the clothing, as the adhesive remains on the clothing.

[0018] The present inventors conducted various studies to solve the above problems, and found that the cause of the deterioration over time of the adhesive coated on the surface of the porous film is that the low molecular weight components of the adhesive are absorbed by a low polarity elastomer such as an ethylene-α-olefin copolymer contained in the porous film for the purpose of improving flexibility.Further studies based on this finding led to the finding that by using a high polarity elastomer, ethylene-vinyl acetate copolymer (EVA), instead of the low polarity elastomer conventionally used, as the raw material resin (low melting point olefin resin) contained in the porous film for the purpose of improving flexibility, the above problem of deterioration over time of the adhesive can be solved while ensuring the flexibility of the porous film.

[0019] The porous film of the present invention was made based on the above findings, and is characterized in that the low melting point olefin resin contained in the porous film contains EVA. As a low melting point olefin resin and a highly polar elastomer, there is, in addition to EVA, for example, ethylene-methyl acrylate copolymer (EMA), but according to the findings of the present inventors, EMA is less effective than EVA.

[0020] The low melting point olefin resin used in the present invention may contain EVA, and the content of EVA in the low melting point olefin resin is not particularly limited. That is, the porous film of the present invention may contain other low melting point olefin resins in addition to EVA as the low melting point olefin resin. However, from the viewpoint of achieving both the flexibility of the porous film and the effect of preventing the deterioration of the adhesive over time at a high level, the higher the content of EVA in the low melting point olefin resin, the more preferable, and the whole of the low melting point olefin resin is EVA, that is, the content of EVA in the low melting point olefin resin is most preferably 100% by mass.

[0021] The vinyl acetate content in the low-melting point olefin-based resin used in the present invention is preferably 25 mass% or more, more preferably 27 mass% or more, and even more preferably 30 mass% or more, relative to the total mass of the low-melting point olefin-based resin, from the viewpoint of further improving the effect of preventing deterioration of the adhesive over time as described above.

[0022] In addition, the vinyl acetate content in the low-melting point olefin-based resin used in the present invention is preferably less than 50 mass%, more preferably 45 mass% or less, and even more preferably 40 mass% or less, relative to the total mass of the low-melting point olefin-based resin, from the viewpoint of suppressing the odor of acetic acid liberated from EVA during long-term storage.

[0023] When the porous film of the present invention contains a high-melting-point olefin resin described later, the low-melting-point olefin resin is preferably a random copolymer in order to obtain good compatibility with the high-melting-point olefin resin.

[0024] The olefin resin composition used in the present invention preferably contains the above-mentioned low melting point olefin resin in 100 parts by mass of the olefin resin composition, since it can provide the porous film of the present invention with satisfactory flexibility and can keep the residual strain after elongation deformation small.In order to make this advantage more prominent, the low melting point olefin resin is more preferably contained in 100 parts by mass of the olefin resin composition in 15 parts by mass or more, more preferably contained in 20 parts by mass or more. In addition, the olefin resin composition used in the present invention preferably contains the above-mentioned low melting point olefin resin in an amount of 90 parts by mass or less per 100 parts by mass of the olefin resin composition, since blocking is unlikely to occur in the porous film of the present invention. From the viewpoint of making this advantage more prominent, the low melting point olefin resin is more preferably contained in an amount of 85 parts by mass or less, and even more preferably contained in an amount of 80 parts by mass or less per 100 parts by mass of the olefin resin composition. In summary, the olefin resin composition used in the present invention contains the above-mentioned low melting point olefin resin in an amount of preferably 10 parts by mass or more and 90 parts by mass or less, more preferably 15 parts by mass or more and 85 parts by mass or less, and even more preferably 20 parts by mass or more and 80 parts by mass or less, per 100 parts by mass of the olefin resin composition.

[0025] The olefin resin composition used in the present invention preferably contains a high melting point olefin resin in addition to the low melting point olefin resin described above, in order to further impart heat resistance, morphological stability, and processability to the porous film of the present invention. The high melting point olefin resin used in the present invention has a melting point of preferably 80° C. or higher, more preferably 90° C. or higher, and even more preferably 95° C. or higher so as to realize rapid molding of the melt-molded porous film and solidification in a short time. In addition, from the viewpoint of imparting flexibility to the porous film, the high melting point olefin resin has a melting point of preferably 130° C. or lower, more preferably 127° C. or lower, and even more preferably 124° C. or lower. In summary, the melting point of the high melting point olefin resin is preferably 80° C. or higher and 130° C. or lower, more preferably 90° C. or higher and 127° C. or lower, and even more preferably 95° C. or higher and 124° C. or lower.

[0026] The melting point of the high melting point olefin resin contained in the porous film is measured by the following method. Approximately 2.0 mg of the porous film is used as a sample, and differential scanning calorimetry (DSC) is performed using a differential scanning calorimeter (DSC7000X, Hitachi High-Tech Science Corporation) under conditions of a measurement temperature range of 10°C to 260°C, a heating rate of 10°C / min, and an air environment. An endothermic peak that occurs when the high melting point olefin resin melts is observed in the temperature range of 90°C or higher on the obtained DSC curve, and the apex of the endothermic peak is the melting point of the high melting point olefin resin. The method for distinguishing the additives contained in the porous film from the high melting point olefin resin is the same as the method for distinguishing the additives contained in the porous film from the low melting point olefin resin described above.

[0027] From the viewpoint of achieving both the flexibility of the porous film and the effect of the high melting point olefin resin (such as the effect of imparting heat resistance), it is preferable that the high melting point olefin resin has a relatively low density, specifically, preferably 0.950 g / cm 3 More preferably, 0.940 g / cm 3 More preferably, 0.930 g / cm 3 In order to prevent blocking, the density of the high melting point olefin resin is 0.900 g / cm or less. 3In summary, the density of the high melting point olefin resin is preferably 0.900 g / cm or more. 3 More than 0.950g / cm 3 More preferably, 0.900 g / cm 3 More than 0.940g / cm 3 More preferably, 0.900 g / cm 3 More than 0.930g / cm 3 The following is the result.

[0028] As the high melting point olefin resin having the above density, it is preferable to use polyethylene such as low density polyethylene or linear low density polyethylene, and in particular, it is preferable to use linear low density polyethylene because it improves heat resistance during stretching and enables uniform stretching. In particular, linear low density polyethylene polymerized by a metallocene catalyst is more preferable because it further improves the strength of the film against tearing, punch-through, etc. The metallocene catalyst is a combination of a metallocene, which is a compound having a structure in which a transition metal such as titanium, zirconium, or hafnium is sandwiched between unsaturated cyclic compounds containing a π-electron system cyclopentadienyl group or a substituted cyclopentadienyl group, and a cocatalyst such as an aluminum compound. Examples of the metallocene include titanocene and zirconocene. Examples of the aluminum compound include alkylaluminoxane, alkylaluminum, aluminum halide, and alkylaluminum halide.

[0029] The olefin resin composition used in the present invention preferably contains 10 parts by mass or more of the high melting point olefin resin having the above-mentioned density in 100 parts by mass of the olefin resin composition, from the viewpoint of imparting further heat resistance, morphological stability, and processability to the porous film.From the viewpoint of making this advantage more prominent, the high melting point olefin resin is more preferably contained in 100 parts by mass of the olefin resin composition in an amount of 15 parts by mass or more, and even more preferably contained in 20 parts by mass or more. In addition, the olefin resin composition used in the present invention preferably contains the above-mentioned high melting point olefin resin in an amount of 90 parts by mass or less per 100 parts by mass of the olefin resin composition, from the viewpoint of achieving both the flexibility of the porous film and the action and effect of the high melting point olefin resin (such as the effect of imparting heat resistance). In order to make this advantage more prominent, the high melting point olefin resin is more preferably contained in an amount of 85 parts by mass or less, and even more preferably 80 parts by mass or less, per 100 parts by mass of the olefin resin composition. In summary, the olefin resin composition used in the present invention contains a high melting point olefin resin having the density described above, preferably in an amount of 10 parts by mass or more and 90 parts by mass or less, more preferably 15 parts by mass or more and 85 parts by mass or less, and even more preferably 20 parts by mass or more and 80 parts by mass or less, per 100 parts by mass of the olefin resin composition.

[0030] The inorganic filler used in the present invention is a substance that causes peeling at the interface with the olefin resin composition to form micropores. From this viewpoint, the inorganic filler has an average particle diameter D 50 is preferably 30 μm or less, more preferably 10 μm or less, and is preferably 0.5 μm or more, and even more preferably 1.0 μm or more. 50 refers to the weight cumulative particle size at a cumulative weight of 50% by mass as measured by a laser diffraction / scattering particle size distribution measurement method.

[0031] Examples of inorganic fillers include calcium carbonate, gypsum, talc, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium phosphate, aluminum hydroxide, zinc oxide, titanium oxide, alumina, mica, zeolite, carbon black, and mixtures thereof. In particular, it is preferable to use calcium carbonate because it is easy to adjust the particle size to the above-mentioned size.

[0032] The inorganic filler is preferably contained in an amount of 50 parts by mass or more per 100 parts by mass of the olefin resin composition in order to form a sufficient amount of fine pores and sufficiently increase the moisture permeability of the porous film, more preferably 60 parts by mass or more, and even more preferably 80 parts by mass or more. In addition, the inorganic filler is preferably contained in an amount of 400 parts by mass or less per 100 parts by mass of the olefin resin composition, from the viewpoint of sufficiently enhancing the leakproofness of the porous film, more preferably 350 parts by mass or less, and even more preferably 200 parts by mass or less.

[0033] The fatty acid used in the present invention is a substance that functions as a dispersant for inorganic fillers. As a dispersant, a substance that can hydrophobize the surface of inorganic fillers is preferably used from the viewpoint of fully exerting such a function. From this viewpoint, it is preferable to use, for example, fatty acids as a dispersant, and particularly stearic acid is preferable. Other fatty acids include, for example, caprylic acid, palmitic acid, capric acid, oleic acid, myristic acid, lauric acid, etc. In particular, when the porous film contains a metal soap described below, it is preferable that the chain length of the hydrocarbon chain in the fatty acid is the same as that of the fatty acid constituting the metal soap, since this allows the metal soap to be more smoothly transferred to the inorganic filler surface-modified with the fatty acid. In particular, it is preferable that both the fatty acid and the fatty acid constituting the metal soap described below are stearic acid.

[0034] The porous film of the present invention preferably contains the fatty acid in an amount of 0.5 parts by mass or more relative to 100 parts by mass of the inorganic filler in order to enhance the dispersibility of the inorganic filler. In order to make this advantage more prominent, the fatty acid is more preferably contained in an amount of 0.6 parts by mass or more, and even more preferably contained in an amount of 0.7 parts by mass or more relative to 100 parts by mass of the inorganic filler. In addition, the porous film of the present invention preferably contains the above-mentioned fatty acid in an amount of 5.0 parts by mass or less per 100 parts by mass of the inorganic filler, from the viewpoint of not impairing the formability of the film. In order to make this advantage more prominent, the fatty acid is more preferably contained in an amount of 4.0 parts by mass or less, and even more preferably contained in an amount of 3.0 parts by mass or less per 100 parts by mass of the inorganic filler. In summary, the porous film of the present invention preferably contains 0.5 parts by mass or more and 5 parts by mass or less of the above-mentioned fatty acid per 100 parts by mass of inorganic filler, more preferably 0.6 parts by mass or more and 4.0 parts by mass or less, and even more preferably 0.7 parts by mass or more and 3.0 parts by mass or less.

[0035] The porous film of the present invention may further contain a pore opening promoter in addition to the above-mentioned olefin resin composition, inorganic filler and fatty acid. The pore opening promoter is used for the purpose of smoothly stretching the resin film containing the olefin resin composition and inorganic filler to generate micropores. As mentioned above, the olefin resin composition contains a low melting point olefin resin and has a low density, which gives flexibility to the porous film of the present invention, and the low density olefin resin tends to be less likely to cause interfacial peeling with the inorganic filler. Therefore, by using a pore opening promoter in addition to the low melting point olefin resin as the raw material of the porous film, such interfacial peeling can be promoted. As the pore opening promoter, a substance known as a release agent between metal and resin is preferably used. Specific examples include metal soap, silicone, fluororesin, fatty acid amide, hydrocarbon paraffin wax, etc. In particular, it is preferable to use metal soap, since it can more smoothly form fine pores.

[0036] As the metal soap, metal salts of saturated or unsaturated fatty acids are preferably used, and zinc stearate is particularly preferred. Fatty acids include, for example, caprylic acid, palmitic acid, stearic acid, capric acid, oleic acid, myristic acid, lauric acid, etc. Metal salts include calcium, aluminum, magnesium, zinc, etc. salts of these fatty acids.

[0037] Fatty acids themselves are known as substances similar to metal salts of fatty acids and are incorporated into porous films. As mentioned above, fatty acids are used to enhance the dispersibility of inorganic fillers. However, fatty acids do not have the function of promoting interfacial peeling between olefin resin compositions and inorganic fillers. Therefore, in the present invention, fatty acid metal salts and fatty acids are clearly distinguished from each other in terms of substance and function.

[0038] In particular, it is preferable to use a metal soap having a melting point of 200° C. or less, from the viewpoint that the metal soap is sufficiently melted and uniformly mixed in the molten resin during kneading of the compound in the manufacturing process of the porous film of the present invention. From this viewpoint, the melting point of the metal soap is more preferably 180° C. or less, and even more preferably 160° C. or less.

[0039] In addition, in relation to the above-mentioned olefin resin composition, it is preferable to use a metal soap having a precipitation temperature higher than the solidification temperature of the olefin resin composition, from the viewpoint of successfully forming micropores and obtaining a porous film having high moisture permeability and high water resistance. In detail, since the precipitation temperature of the metal soap is higher than the solidification temperature of the olefin resin composition, the metal soap precipitates earlier than the olefin resin composition solidifies, and the metal soap can smoothly migrate to the surface of the inorganic filler. As a result, the releasability between the inorganic filler and the olefin resin composition during stretching is improved, and micropores are smoothly formed. In order to make this advantage more prominent, when the precipitation temperature of the metal soap is Ts (°C) and the solidification temperature of the olefin resin composition is Tp (°C), the value of Ts-Tp is preferably greater than 0°C, more preferably 1°C or more, and even more preferably 2°C or more. In addition, the value of Ts-Tp is preferably 50°C or less.

[0040] Provided that the value of Ts-Tp is within the aforementioned range, the precipitation temperature Ts of the metal soap is preferably 80°C or higher and 180°C or lower, more preferably 90°C or higher and 170°C or lower, and even more preferably 100°C or higher and 160°C or lower. On the other hand, the solidification temperature Tp of the olefin resin composition is preferably 60°C or more and 130°C or less, more preferably 70°C or more and 120°C or less, and even more preferably 80°C or more and 115°C or less, provided that the value of Ts-Tp is within the above-mentioned range.

[0041] The precipitation temperature Ts of the metal soap is measured using a hot stirrer and a thermocouple as follows. Using a hot stirrer, 0.43 g of the metal soap is added to 5.0 g of paraffin oil, and the mixture is heated while stirring until the metal soap dissolves. After stopping stirring the liquid with the stirrer, the temperature of the paraffin oil is lowered at a rate of 0.2°C / min, and the temperature of the paraffin oil when the metal soap begins to precipitate is read with a thermocouple, and this temperature is defined as the precipitation temperature of the metal soap. Note that if the metal soap does not dissolve in the paraffin oil despite the paraffin oil being heated to 210°C, the precipitation temperature is defined as 210°C. On the other hand, the solidification temperature Tp of the olefin resin composition is measured by the following method in accordance with JIS K 7121 (method of determining extrapolated crystallization end temperature). Using a porous film of about 2.0 mg as a sample, differential scanning calorimetry (DSC) is performed using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Co., Ltd.) under the conditions of a measurement temperature range of 30°C to 260°C, a heating rate of 10°C / min, a heating rate of 50°C / min, an air environment, and a data sampling period of 0.5 s. In the temperature drop process of the obtained DSC curve, an exothermic peak that occurs when the olefin resin composition solidifies (crystallizes) is observed. The solidification temperature of the olefin resin composition is the temperature at the intersection of a straight line extending the baseline on the lower side of the peak temperature to the higher side for the peak with the highest heat generation during the temperature drop process, and an approximation straight line drawn between the data of the two points where the slope of the curve on the lower side of the peak is maximum. When two or more overlapping exothermic peaks exist, for example, the software PeakFIT v4.12 (manufactured by Hulinks Corporation) is used to separate the peaks, and then the solidification temperature is determined by the above-mentioned method.

[0042] In the porous film of the present invention, the metal soap is preferably contained in an amount of 0.5 parts by mass or more per 100 parts by mass of the olefin resin composition, from the viewpoint of successfully generating micropores. From the viewpoint of making this advantage more prominent, the metal soap is more preferably contained in an amount of 1.0 part by mass or more, and even more preferably contained in an amount of 2.0 parts by mass or more per 100 parts by mass of the olefin resin composition. In addition, in the porous film of the present invention, the metal soap is preferably contained in an amount of 20 parts by mass or less relative to 100 parts by mass of the olefin resin composition in order to maintain good moldability. In order to make this advantage more prominent, the metal soap is more preferably contained in an amount of 15 parts by mass or less, and even more preferably contained in an amount of 10 parts by mass or less, relative to 100 parts by mass of the olefin resin composition. In summary, in the porous film of the present invention, the metal soap is preferably contained in an amount of 0.5 parts by mass or more and 20 parts by mass or less, more preferably contained in an amount of 1.0 parts by mass or more and 15 parts by mass or less, and even more preferably contained in an amount of 2.0 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the olefin resin composition.

[0043] The amount of metal soap contained in the porous film of the present invention is also related to the amount of inorganic filler contained in the porous film. In detail, in the porous film of the present invention, the metal soap is preferably contained in an amount of 0.5 parts by mass or more per 100 parts by mass of inorganic filler, from the viewpoint of successfully generating micropores. From the viewpoint of making this advantage more prominent, the metal soap is more preferably contained in an amount of 1.5 parts by mass or more, and even more preferably contained in an amount of 2.0 parts by mass or more per 100 parts by mass of inorganic filler. In addition, in the porous film of the present invention, the metal soap is preferably contained in an amount of 15 parts by mass or less per 100 parts by mass of the inorganic filler in order to maintain good moldability. In order to make this advantage more pronounced, the metal soap is preferably contained in an amount of 10 parts by mass or less, more preferably 9.0 parts by mass or less, and even more preferably 8.0 parts by mass or less per 100 parts by mass of the inorganic filler. In summary, in the porous film of the present invention, the metal soap is preferably contained in an amount of 0.5 parts by mass or more and 15 parts by mass or less per 100 parts by mass of inorganic filler, more preferably 0.5 parts by mass or more and 10 parts by mass or less, even more preferably 1.5 parts by mass or more and 9.0 parts by mass or less, and even more preferably 2.0 parts by mass or more and 8.0 parts by mass or less.

[0044] The porous film of the present invention may contain additives. Additives that can impart various additional properties to the porous film are used. Examples of such additives include plasticizers, water repellents, antioxidants, ultraviolet absorbers, and colorants.

[0045] The plasticizer is used for the purpose of imparting flexibility and suppleness to the porous film of the present invention, and preventing the porous film of the present invention from generating a rustling sound. As the plasticizer, monoester, polyester, ethylene-α-olefin co-oligomer, low molecular weight polyethylene, olefin oligomer, liquid polyisoprene, liquid polybutadiene, etc. are preferably used. A monoester is a compound obtained from a monobasic acid and a monohydric alcohol. On the other hand, polyester is a compound obtained by any combination of a polybasic acid and a monohydric alcohol, a monobasic acid and a polyhydric alcohol, or a polybasic acid and a polyhydric alcohol. Ethylene-alpha olefin co-oligomers are low molecular weight copolymers of ethylene with alpha olefins such as propylene, 1-butene, 1-pentene and 1-hexene.

[0046] As the above-mentioned monobasic acid, polybasic acid, monohydric alcohol, and polyhydric alcohol, for example, the following are preferably used. The monobasic acid may be, for example, a monocarboxylic acid of a long-chain hydrocarbon having 10 to 22 carbon atoms. Examples of the polybasic acid include dicarboxylic acids, tricarboxylic acids, and tetracarboxylic acids. The monohydric alcohol may be, for example, a long-chain hydrocarbon monoalcohol having 10 to 22 carbon atoms. Examples of polyhydric alcohols include diols, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol, and sucrose.

[0047] Particularly preferred polyesters include, for example, polyesters of diethylene glycol and dimer acid in which the carboxylic acid or alcohol at both ends is partially or completely blocked with stearyl alcohol or stearic acid, polyesters of 1,3-butanediol and adipic acid, hexaesters of trimethylolpropane-adipic acid-stearic acid, octaesters of pentaerythritol-adipic acid-stearic acid, and dodecaesters of dipentaerythritol-adipic acid-stearic acid.

[0048] On the other hand, particularly preferred monoesters include esters having a total of 30 or more carbon atoms obtained by dehydrating a monocarboxylic acid having 1 to 40 carbon atoms and a monoalcohol having 1 to 40 carbon atoms. Among them, those having a total of 30 or more carbon atoms obtained from a monocarboxylic acid and a monoalcohol are preferred, and monoesters having 38 or more carbon atoms and having a branched chain are more preferred. Specific examples include isodecyl stearate, isodecyl behenate, isotridecyl stearate, 2-octadecyl stearate, 2-decyl tetradecyl laurate, 2-decyl tetradecyl stearate, 2-octadecyl behenate, stearyl isostearate, esters of stearic acid and C20 Guerbet alcohol, and esters of α-branched fatty acids (having 18 to 40 carbon atoms) and monoalcohols (having 6 to 36 carbon atoms).

[0049] As the water repellent, it is preferable to use triglyceride, which enhances the water repellency of the porous film surface and improves leak resistance. From the viewpoint of making the advantage of using triglyceride more prominent, the content of triglyceride in the porous film of the present invention is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 parts by mass or more, relative to 100 parts by mass of the olefin resin composition. Also, from the viewpoint of film formability, the content of triglyceride is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the olefin resin composition. In summary, the content of triglyceride in the porous film of the present invention is preferably 0.1 parts by mass or more and 30 parts by mass or less, more preferably 0.5 parts by mass or more and 25 parts by mass or less, and even more preferably 1.0 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the olefin resin composition.

[0050] A preferred example of the triglyceride used in the present invention is a triglyceride that "contains a group derived from a fatty acid having 16 to 22 carbon atoms, and the group is a hydrocarbon group that has no unsaturated bonds or substituents" (hereinafter, also referred to as a "specific triglyceride"). The "hydrocarbon group having no unsaturated bonds" refers to a hydrocarbon group having neither a carbon-carbon double bond nor a triple bond. In other words, it refers to an alkyl group. The "hydrocarbon group having no substituents" refers to a hydrocarbon group in which the hydrogen atoms contained in the hydrocarbon group are not substituted with other atoms or atomic groups (e.g., hydroxyl groups). Therefore, the "hydrocarbon group having no unsaturated bonds or substituents" is synonymous with an unsubstituted alkyl group.

[0051] The specific triglyceride is preferably one in which the number of carbon atoms in the fatty acid residue is adjusted, and specifically, for example, it is preferably the following (a) or (b). (a) A triglyceride containing a mixture of a triglyceride containing at least a group derived from a fatty acid having 16 carbon atoms (i.e., palmitic acid) in one molecule (the group is a hydrocarbon group having no unsaturated bonds and no substituents) and a triglyceride containing at least a group derived from a fatty acid having 18 carbon atoms (i.e., stearic acid) in one molecule (the group is a hydrocarbon group having no unsaturated bonds and no substituents). (b) A triglyceride containing at least one group derived from a fatty acid having 16 carbon atoms and one group derived from a fatty acid having 18 carbon atoms in one molecule.

[0052] The specific triglyceride is preferably a natural oil. The specific triglyceride of natural oil has a diverse molecular structure, and therefore can provide higher liquid repellency than other specific triglycerides such as synthetic oils. An example of the specific triglyceride of natural oil is highly hydrogenated rapeseed oil.

[0053] Next, a preferred method for producing the porous film of the present invention will be described. The method for producing a porous film of the present invention includes a step of stretching, at least in one direction, a resin sheet obtained by melt molding a compound containing at least an olefin resin composition, an inorganic filler, and a fatty acid. The details of the olefin resin composition, inorganic filler and fatty acid contained in the compound are as described above.The amount of the olefin resin composition, inorganic filler and fatty acid contained in the compound is the same as the amount of these components contained in the porous film.Furthermore, the type and amount of optional components such as metal soap contained in the compound are the same as the type and amount of optional components contained in the porous film.

[0054] The porous film of the present invention can be efficiently produced, for example, by the following method. First, the components constituting the compound described above are premixed using a Henschel mixer, a super mixer, or the like, and then kneaded and pelletized using a single-screw or twin-screw extruder. The pellets obtained are then formed into a film using a molding machine to obtain a resin sheet. For example, a T-die type or an inflation type molding machine can be used.

[0055] The dispersant may be used alone and mixed with other components constituting the compound, but it is preferable to attach the dispersant to the surface of the inorganic filler in advance to produce a surface-modified inorganic filler, and then mix this surface-modified inorganic filler with other components constituting the compound to prepare the compound. In this way, the resin sheet can be successfully stretched while suppressing the occurrence of unintended pinholes, and a porous film having both high moisture permeability and high water resistance can be obtained.

[0056] The resin sheet described above is stretched uniaxially or biaxially, whereby the interfacial peeling between the olefin resin composition and the inorganic filler occurs, making the sheet porous. For this stretching, a roll method capable of stretching in the machine direction, or a tenter method capable of stretching in the film width direction in addition to the machine direction, etc. are used. In this way, the porous film of the present invention is obtained. The resin sheet is stretched at least uniaxially preferably by 1.1 times or more, more preferably by 1.5 times or more, and even more preferably by 2.0 times or more, so that the area increases with stretching. In addition, from the viewpoint of avoiding a decrease in tear strength due to excessive molecular orientation caused by excessive stretching, the resin sheet is stretched preferably by 5.0 times or less, more preferably by 4.5 times or less, and even more preferably by 4.0 times or less.

[0057] In either case of uniaxial stretching or biaxial stretching, the temperature of the resin film during stretching is set to preferably 30°C or higher and 100°C or lower, more preferably 35°C or higher and 95°C or lower, and even more preferably 40°C or higher and 90°C or lower, from the viewpoint of being able to uniformly stretch the film without breaking the film.

[0058] The porous film produced by the above method has high flexibility and high breathability. When the degree of flexibility is expressed by the degree of flexibility deformation, the porous film of the present invention preferably has a degree of flexibility deformation in the machine direction of 0.12 N / (mm (g / m 2 )) or less, and more preferably 0.10 N / (mm (g / m 2 )) or less, more preferably 0.08 N / (mm (g / m 2 From the viewpoint of maintaining the strength of the porous film of the present invention, the lower limit of the degree of flexible deformation is preferably 0.005 N / (mm (g / m 2 ))That's all.

[0059] The degree of flexible deformation of the porous film is measured by the following method. The porous film to be measured is cut into three pieces measuring 150 mm in the machine direction and 30 mm in the width direction. The cut test pieces are fixed to a tensile tester (product name: AG-1S, manufactured by Shimadzu Corporation) so that the initial length L0 of the test piece is 100 mm. After fixing, the load read by the tensile tester is set to zero, and the test piece is elongated to 1.3 times L0 at a deformation rate of 200 mm / min, and then immediately contracted to L0 at a deformation rate of 200 mm / min to perform a cyclic test. From the obtained data, the load (F3%) at 1.03 times deformation during the elongation process is read, and the degree of flexible deformation (N / (mm (g / m 2 ))). Degree of flexibility (N / (mm (g / m 2 ))) = F3% (N) / (0.03 × 30 (mm) × film weight (g / m 2 ))

[0060] The moisture permeability of the porous film of the present invention is preferably 0.1 g / (100 cm 2 h), more preferably 0.15 g / (100 cm 2 h) or more, and more preferably 0.2 g / (100 cm 2·h) or more. This allows the porous film of the present invention to have high moisture permeability and to properly dissipate moisture inside the absorbent article to the outside. On the other hand, the upper limit of the moisture permeability of the porous film is preferably 4.5 g / (100 cm) so as not to lose the necessary leakproofness of the back sheet due to excessive porosity. 2 h) or less, more preferably 3.5 g / (100 cm 2 h) or less, more preferably 3.0 g / (100 cm 2 h) or less.

[0061] The moisture permeability of the porous film is measured by the following method in accordance with JIS L1099A-2. Diameter 2.03cm (area 3.23cm 2 Approximately 25 mL of ion-exchanged water is placed in a 100% glass bottle (Labolan Screw Bottle No. 8, AS ONE), the mouth of the glass bottle is covered with a single test piece (the porous film to be measured) leaving no gaps, and the test piece is secured to the glass bottle with a rubber band to create an evaluation sample. After measuring the mass (W1) of the evaluation sample, the sample is stored in a thermostatic chamber controlled at 40°C and 20% RH for 10 to 15 hours. After storage, the mass (W2) of the evaluation sample is measured and the storage time (T1, unit: h) is recorded, and the moisture permeability is calculated using the following formula. Moisture permeability (g / (100cm 2 h)) = (W1 - W2) / (T1 x 3.23) ×100

[0062] The basis weight of the porous film of the present invention depends on its application, but for example, when it is used as a back sheet of an absorbent article, it is preferably 5 g / m 2 More preferably, 10 g / m 2 More than 100 g / m 2 Less than 50 g / m 2 The thickness of the porous film of the present invention depends on its application, but for example, when it is used as a back sheet of an absorbent article, it can be about 4 μm or more and 90 μm or less.

[0063] The porous film of the present invention may be a single layer film or a laminated film in which a plurality of layers are laminated in the thickness direction. When the porous film of the present invention is a laminated film, at least one of the layers constituting the laminated film may be a porous film having the above-mentioned configuration.

[0064] The porous film of the present invention has excellent flexibility, moisture permeability, and high leak-proofness against liquids, especially water, and therefore can be applied to, for example, leak-proof sheets for absorbent articles such as disposable diapers and sanitary napkins, waterproof sheets for rain gear, etc. In particular, as described later, it is useful as a back sheet of an absorbent article.

[0065] The absorbent article of the present invention will be described below based on preferred embodiments with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are basically schematic, and the ratios of the dimensions may differ from the actual ones.

[0066] 1 and 2 show a sanitary napkin 1A, which is one embodiment of the absorbent article of the present invention. The napkin 1A is an absorbent article that is fixed to clothing (not shown) when used, and has adhesives 7, 8 attached to a fixing surface 3a to the clothing.

[0067] As shown in FIG. 1, the napkin 1A has a longitudinal direction X that corresponds to the front-rear direction of a wearer and extends from the wearer's abdomen through the crotch region to the back, and a lateral direction Y that is perpendicular to the longitudinal direction X. The napkin 1A is divided into three parts in the longitudinal direction X: a longitudinal central region M including a portion facing the excretory part (excretion point) facing the excretory part such as the vaginal opening of the wearer, a front region F located closer to the wearer's abdomen (front side) than the portion facing the excretory part, and a rear region R located closer to the wearer's back (rear side) than the portion facing the excretory part. The longitudinal central region M can be the region located in the middle when the napkin 1A in an unfolded and maximally stretched state is divided into three equal parts in the longitudinal direction X.

[0068] As shown in FIG. 2, the napkin 1A comprises an absorbent body 4 that absorbs and retains bodily fluids, a liquid-permeable top sheet 2 that is arranged on the skin-facing side of the absorbent body 4 and can come into contact with the wearer's skin, and a leak-proof back sheet 3 that is arranged on the non-skin-facing side of the absorbent body 4.

[0069] In this specification, the "skin-facing side" refers to the side of the absorbent article or its constituent member (e.g., absorbent body 4) that faces the wearer's skin when the absorbent article is worn, i.e., the side relatively closer to the wearer's skin, and the "non-skin-facing side" refers to the side of the absorbent article or its constituent member that faces the opposite side to the skin when the absorbent article is worn, i.e., the side relatively farther from the wearer's skin. Note that "when worn" here refers to the normal, proper wearing position, i.e., a state in which the absorbent article is maintained in the correct wearing position.

[0070] In the napkin 1A, the absorbent body 4 is composed of an absorbent core 40 mainly made of a water-absorbing material, and a liquid-permeable core wrap sheet 41 covering the outer surface of the absorbent core 40. Examples of the water-absorbing material that can be used include hydrophilic fibers such as pulp fibers, water-absorbing polymer particles, and mixtures thereof. The absorbent core 40 has a shape elongated in the vertical direction X in a plan view as shown in FIG. 1, and the longitudinal direction of the absorbent core 40 coincides with the vertical direction X of the napkin 1A, and the width direction of the absorbent core 40 coincides with the horizontal direction Y of the napkin 1A. The absorbent core 40 and the core wrap sheet 41 may be bonded together with an adhesive such as a hot melt adhesive. The core wrap sheet 41 may be omitted.

[0071] 2, the topsheet 2 covers the entire skin-facing surface of the absorbent body 4. Meanwhile, the backsheet 3 covers the entire non-skin-facing surface of the absorbent body 4 and further extends outward in the lateral direction Y from both side edges of the absorbent body 4 along the longitudinal direction X to form side flap portions 5, 5 together with side sheets 6 described below. The side flap portions 5 are portions of the napkin 1A made of members extending outward in the lateral direction Y from the absorbent body 4.

[0072] The napkin 1A has a pair of wing portions 5W, 5W in the vertical central region M. The wing portions 5W are portions of the side-flap portions 5 that extend outward in the horizontal direction Y beyond the peripheral portions. The wing portions 5W are trapezoidal in plan view as shown in Fig. 1, and the length in the vertical direction X gradually decreases from the inside to the outside in the horizontal direction Y. When the napkin 1A is fastened to clothing such as shorts, the wing portions 5W are folded back toward the outer surface (non-skin-facing surface) of the crotch portion of the clothing.

[0073] The napkin 1A has a pair of side sheets 6, 6 which, together with the top sheet 2, form the skin-facing surface of the napkin 1A. The top sheet 2 forms the central region in the transverse direction Y of the skin-facing surface of the napkin 1A, and the side sheets 6 form the side regions of the skin-facing surface of the napkin 1A. The pair of side sheets 6, 6 are each joined to another member (the back sheet 3 in the illustrated embodiment) by a known joining means such as an adhesive at joining lines (not shown) extending in the longitudinal direction X. As the top sheet 2 and the side sheet 6, various types of sheets conventionally used in absorbent articles such as sanitary napkins can be used without any particular restrictions. As the top sheet 2, a single-layer or multi-layer nonwoven fabric, a perforated film, etc. can be used. As the side sheet 6, a sheet having liquid impermeability (a property that does not allow liquid to pass through at all) or liquid-difficulty permeability (a property that does not go as far as to be liquid impermeable, but does not allow liquid to pass through easily) can be used.

[0074] The napkin 1A has a fixing surface 3a for attachment to clothing such as shorts. The fixing surface 3a is the non-skin facing surface of the backsheet 3 and is the outer surface of the napkin 1A. Adhesives 7 and 8 are attached to the fixing surface 3a. The adhesive 7 is disposed in an area of ​​the fixing surface 3a that overlaps with the absorbent body 4 in a plan view. The adhesive 8 is disposed in an area of ​​the fixing surface 3a that does not overlap with the absorbent body 4, specifically, in the wing portions 5W. Both adhesives 7 and 8 are directly attached to the backsheet 3. The adhesives 7 and 8 are means for fixing the napkin 1A to clothing, and are covered with a release sheet (not shown) made of film, nonwoven fabric, paper, or the like before use.

[0075] 1, in the napkin 1A, the adhesive 7 has a shape long in the horizontal direction Y in plan view, specifically a rectangular shape, and is arranged at intervals in the vertical direction X from the front region F to the rear region R of the region overlapping with the absorbent body 4 in plan view, with its longitudinal direction coinciding with the horizontal direction Y. The adhesive 8 has a quadrangular shape in plan view, and is arranged on the non-skin-facing surface of the wing portion 5W. Note that, since the wing portion 5W is folded back toward the outer surface of the crotch portion of the garment when in use, the non-skin-facing surface of the wing portion 5W faces the wearer's skin during use (while the napkin 1A is being worn), and serves as the skin-facing surface.

[0076] In the absorbent article of the present invention, the arrangement pattern of the adhesives 7, 8 is not limited to the arrangement pattern shown in Fig. 1, and may be appropriately set in consideration of the function as a fixing means, etc. In the napkin 1B shown in Fig. 3, the adhesive 7 has a long strip shape in the vertical direction X in a plan view, and is arranged intermittently in the horizontal direction Y in a region overlapping with the absorbent body 4 in a plan view, with its longitudinal direction coinciding with the vertical direction X.

[0077] The adhesives 7 and 8 may be any adhesive capable of releasably fixing the napkin 1A to clothing such as shorts, and any adhesive conventionally used for such purposes in absorbent articles such as sanitary napkins may be used without any particular limitations. A preferred example of the adhesives 7 and 8 is a hot melt adhesive containing a styrene elastomer. For example, styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butylene-ethylene block copolymer (SEBS) or the like is used as the base polymer of the hot melt adhesive containing a styrene elastomer, and for example, hydrogenated petroleum resin is used as the tackifier, and for example, paraffin oil is used as the plasticizer for adjusting the melt viscosity. In this composition, the tackifier and plasticizer correspond to the low molecular weight components of the adhesive. The hot melt adhesive preferably contains a total of 30% by mass or more of the plasticizer and the tackifier, and more preferably contains a total of 40 to 75% by mass.

[0078] The napkins 1A and 1B are characterized in that the back sheet 3, which forms the fixing surface 3a with the clothing and is a sheet to which the adhesives 7 and 8 are attached, is the porous film of the present invention described above. As described above, the porous film of the present invention contains a low-melting point olefin resin containing EVA and having a melting point of less than 90 degrees, so that it is excellent in flexibility and the adhesive strength of the adhesive is unlikely to deteriorate over time even when the adhesive is attached. Therefore, the adhesives 7 and 8 attached to the back sheet 3 are unlikely to decrease in adhesive strength over time, and can stably maintain adhesive strength sufficient for practical use for a long period of time. Therefore, the back sheet 3 of the napkins 1A and 1B is flexible, and when used by fixing it to clothing via the adhesives 7 and 8, inconveniences such as slippage, twisting, and turning over are unlikely to occur, and the napkins are excellent in wearing comfort and leak prevention.

[0079] Although the present invention has been described based on the embodiment, the present invention is not limited to the embodiment and can be modified as appropriate. The absorbent article of the present invention broadly includes articles used to absorb bodily fluids discharged from the human body (menstrual blood, urine, loose stool, sweat, etc.), and includes not only the sanitary napkins mentioned above, but also panty liners, panty liners, incontinence pads, disposable diapers, etc.

[0080] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "parts" means "parts by mass".

[0081] [Examples 1 to 3, Comparative Examples 1 to 2] A porous film was produced by the following procedure. (1) Compound manufacturing The components shown in the "Film composition (parts)" column in Table 1 below were weighed out in the amounts shown in the same column. These were mixed in a Henschel mixer (Kawata Corporation). The resulting mixture was kneaded in a twin-screw extruder at a set temperature of 180°C and a screw rotation speed of 180 rpm to obtain a pelletized compound. (2) Manufacturing of resin sheets A film was formed from the molten compound using an inflation molding machine with a slit diameter of 100 mm at the die discharge part and a gap of 0.9 mm. The inflation die set temperature and take-up speed are as shown in Table 1. The molding conditions for Example 1 were an inflation die set temperature of 190°C and a take-up speed of 4 m / min. The molding conditions for Examples 2 and 3 were an inflation die set temperature of 205°C and a take-up speed of 5 m / min. The molding conditions for Comparative Examples 1 and 2 were an inflation die set temperature of 190°C and a take-up speed of 6 m / min. (3) Manufacturing of porous films The film was uniaxially stretched in the machine direction using a roll stretching machine to obtain a porous film having the basis weight shown in Table 1. The stretching ratio and stretching temperature are as shown in the same table.

[0082] Details of the raw materials used in the production of the porous film are as follows: Elastomer A (low melting point olefin resin): EVA (melting point 74°C, vinyl acetate content 28% by mass) Elastomer B (low melting point olefin resin): EVA (melting point 65°C, vinyl acetate content 32% by mass) Elastomer C (low melting point olefin resin): EVA (melting point 72°C, vinyl acetate content 41% by mass) Elastomer D (low melting point olefin resin): Ethylene-1-butene copolymer produced with a metallocene catalyst (melting point 44°C, vinyl acetate-free, density 0.864g / cm 3 ) High melting point olefin resin: Linear low density polyethylene produced with metallocene catalyst (melting point 116°C, vinyl acetate-free, density 0.924g / cm 3 ) Inorganic filler: Calcium carbonate (average particle size D 50 is 1.8μm) Fatty acid: stearic acid · Hole opening promoter (metal soap): Zinc stearate (melting point 124℃, precipitation temperature Ts102℃) Water repellent (specific triglyceride): Hardened rapeseed oil (among the constituent fatty acids, the ratio of saturated fatty acids with 16 carbon atoms is 4% by mass, the ratio of saturated fatty acids with 18 carbon atoms is 93% by mass, the ratio of saturated fatty acids with 20 carbon atoms is 2% by mass, the ratio of saturated fatty acids with 22 carbon atoms is 1% by mass, and it does not contain fatty acids with unsaturated bonds or hydroxyl groups.) The solidification temperature Tp of the olefin resin composition (a mixture of a low melting point olefin resin and a high melting point olefin resin) used in Examples 1 to 3 was 95°C.

[0083] [Evaluation test] For the porous films of each Example and Comparative Example, the degree of flexible deformation in the machine direction and the moisture permeability were measured by the above-mentioned methods. In addition, for the porous films of each Example and Comparative Example, the moldability, initial adhesive strength, and adhesive strength retention rate were evaluated by the following methods. The results are shown in Table 1.

[0084] <Method of evaluating moldability> In the above "(3) Manufacturing of porous film", when the resin sheet was uniaxially stretched in the machine direction, if it could be stretched, it was rated as A (pass), and if it could not be stretched due to the resin sheet breaking or the like, it was rated as B (fail).

[0085] (Preparation of composite film) A composite film to be used for measuring the initial adhesive strength and adhesive strength retention rate described below is prepared by the following procedure: A hot melt adhesive containing a styrene-based elastomer is applied in a predetermined pattern to the release-treated surface of a release film, and the release film and the porous film to be measured are integrated via the adhesive to prepare a composite film. As the release film, "Single-sided release film PET25 2010" manufactured by Lintec Corporation is used. As the adhesive, a hot melt type adhesive is used, which uses a styrene-butadiene copolymer as a base polymer and is blended with hydrogenated petroleum resin as a tackifier and paraffin oil as a plasticizer for adjusting the melt viscosity. In this composition, the hydrogenated petroleum resin and paraffin oil correspond to the low molecular weight components of the adhesive. The coating pattern of the adhesive is such that the coated and uncoated parts of the adhesive are alternately arranged in the machine direction (MD) of the release film, and the coated and uncoated parts each have a length of 2 mm in MD and extend over the entire length of the release film in the direction (CD) perpendicular to the MD. The coating amount of the coated part is 50 g / m 2 Let us assume that. The release film and the porous film are integrated by the following procedure. That is, the release film is placed with its adhesive coated surface facing up, and the porous film to be measured is placed on the adhesive coated surface so that the MD / CD of the release film and the MD / CD of the porous film coincide with each other. Then, the rubber roller is moved along the MD of the porous film while contacting the circumferential surface of the rubber roller with the upper surface of the porous film (the surface opposite to the surface facing the release film), and the release film and the porous film are integrated via the adhesive to obtain the target composite film. By such an integration operation, the adhesive coated on the release film is transferred to the porous film while maintaining the coating pattern. The rubber roller is moved back and forth once on the upper surface of the porous film in the MD, and the linear pressure of the rubber roller is 800 N / m and the moving speed of the rubber roller is 5 mm / sec.

[0086] <Method for measuring initial adhesive strength> First, adhesive tape (Nichiban Co., Ltd., Cellotape (registered trademark), No. 405) was applied to the entire non-coated surface of the adhesive in the composite film, and the film was left to stand for 10 minutes in an environment with an ambient temperature of 40°C. After that, a rectangular shape in plan view with an MD length of 120 mm and a CD length of 20 mm was cut out from the composite film to prepare a measurement sample precursor. Next, the measurement sample precursor is left to stand in an environment of 24°C ambient temperature and 50% RH relative humidity for 30 minutes, and then the release film is peeled off from the measurement sample precursor, and in the same environment, a cotton cloth (Kanakin No. 3) is attached to the transfer surface of the adhesive in the porous film constituting the measurement sample precursor (the surface facing the release film) using a rubber roller to obtain a measurement sample. In the cotton cloth attachment work, the rubber roller is moved back and forth in the MD of the porous film, and the linear pressure of the rubber roller is 300 N / m and the moving speed of the rubber roller is 10 mm / sec. Then, using a tensile tester in an environment of an atmospheric temperature of 24°C and a relative humidity of 50%RH, the porous film and the cotton cloth in the measurement sample are T-shaped peeled along the MD of the porous film at a peeling speed of 5 mm / sec, and the peeling force at that time is measured. In the measurement sample, the adhesive-coated part with a length of 2 mm in the MD and the adhesive-uncoated part with a length of 2 mm in the MD are alternately arranged in the MD, so that in the T-shaped peeling, a peak value of the peeling force appears every 2 mm. The five-point average value of such peak values ​​of the peeling force is taken as the initial adhesive force of the measurement sample. For each type of porous film to be measured, three measurement samples are prepared, and the initial adhesive force of each is measured by the above procedure, and the average value of the three measured values ​​is taken as the initial adhesive force of the porous film to be measured.

[0087] <Method for measuring adhesive strength retention rate> The composite film used was stored in a thermostatic chamber at an internal temperature of 50°C for one week, and the measurement sample was subjected to T-shaped peeling in the same manner as in the above <Method of measuring initial adhesive strength> to measure the five-point average of the peak peel strength, and the average of the five-point average of the three measurement samples was taken as the adhesive strength of the porous film to be measured after the storage test. The ratio of the adhesive strength after the storage test to the initial adhesive strength of the porous film to be measured was taken as the adhesive strength retention rate. The higher the adhesive strength retention rate, the less likely the adhesive strength of the adhesive would deteriorate over time, and the higher the evaluation.

[0088] [Table 1]

[0089] As shown in Table 1, the porous films of the Examples used EVA (elastomers A to C) as the low-melting-point olefin-based resin, and therefore had almost the same degree of flexible deformation and flexibility as those of Comparative Example 1, which used elastomer D that did not contain EVA as the low-melting-point olefin-based resin, but showed adhesive strength retention rates equal to or higher than those of the porous film of Comparative Example 2, which did not contain a low-melting-point olefin-based resin and had low flexibility. This shows that the use of EVA as the low-melting-point olefin-based resin makes it possible to achieve both flexibility and the effect of preventing deterioration of the adhesive over time. [Explanation of symbols]

[0090] 1A, 1B Sanitary napkins (absorbent articles) 2 Surface sheet 3 Back sheet 3a Fixed surface with clothing 4. Absorber 7,8 Adhesive

Claims

1. A porous film comprising an olefin-based resin composition, an inorganic filler, and a fatty acid, The inorganic filler is contained in an amount of 50 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the olefin-based resin composition, and the fatty acid is contained in an amount of 0.5 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the inorganic filler, The olefin resin composition contains a low-melting-point olefin resin having a melting point of less than 80°C, The porous film contains an ethylene-vinyl acetate copolymer as the low-melting-point olefin-based resin.

2. The porous film of claim 1 , wherein the porous film is a monolayer film.

3. The porous film according to claim 1 or 2, wherein the low-melting-point olefin-based resin has a vinyl acetate content of 25% by mass or more.

4. The porous film according to claim 1 or 2, wherein the low-melting-point olefin-based resin has a vinyl acetate content of less than 50% by mass.

5. The porous film according to claim 1 or 2, wherein the olefin-based resin composition contains a high-melting-point olefin-based resin having a melting point of 80°C or higher.

6. The porous film according to claim 5 , wherein the high melting point olefin resin is polyethylene.

7. The porous film according to claim 5 , wherein the high melting point olefin resin comprises linear low density polyethylene.

8. The porous film according to claim 7 , wherein the linear low-density polyethylene comprises linear low-density polyethylene polymerized using a metallocene catalyst.

9. The degree of flexible deformation in the machine direction is 0.12 N / (mm·(g / m ２ 3. The porous film according to claim 1, wherein the porous film has a viscosity of 1000 MPa or less.

10. 3. An absorbent article to be used by being fixed to clothing, wherein an adhesive is attached to the surface to be fixed to the clothing, and the sheet forming the surface to be fixed to the clothing is the porous film according to claim 1 or 2.

11. The absorbent article according to claim 10, wherein the pressure-sensitive adhesive is a hot-melt pressure-sensitive adhesive containing a styrene-based elastomer.

Images