JP5013857B2 - Moisture permeable sheet and method for producing the same - Google Patents

Description

  The present invention relates to a moisture-permeable sheet that is liquid impermeable but water vapor permeable, and a method for producing the same.

Various liquid impermeable and water vapor permeable moisture permeable sheets made of polyolefin resins are known. This type of moisture-permeable sheet is formed by stretching a sheet (film) made of a composition mainly composed of a polyolefin resin and an inorganic filler in a uniaxial or biaxial direction, thereby forming fine through holes in the sheet. Moisture is imparted. For example, in Patent Document 1, when an inorganic filler having a specific surface area of 16000 to 24000 cm ² / g is used in an amount of 100 to 300 parts by mass with respect to 100 parts by mass of the polyolefin-based resin, the moisture permeability is high and the water resistance is also high. It is described that a high and sufficient strength sheet can be obtained.

However, when manufacturing the above moisture-permeable sheet, in the conventional manufacturing method, a pinhole having a minute hole diameter of about 100 μm to 1 cm may occur in the manufactured sheet. The sheet in which the pinhole is generated cannot be used as a leak-proof sheet for an absorbent member such as a diaper because a hole is formed in the sheet. When the basis weight of the manufactured sheet is generally more than 30 g / m ² , the thickness of the sheet increases, and the above-described pinhole problem does not substantially occur. However, if the basis weight is too large, flexibility and moisture permeability may be reduced. Therefore, in the manufacturing process of moisture-permeable sheets that require high flexibility and moisture permeability, it is necessary to attach sensor detection marks for discharging the parts with pinholes, or discard sheets and diapers with pinholes. there were. This reduced productivity and increased production costs.
JP 2004-99665 A

  An object of the present invention is to provide a method for efficiently producing a moisture permeable sheet by suppressing the generation of pinholes. Moreover, it aims at providing the liquid-impermeable moisture-permeable sheet which suppressed generation | occurrence | production of a pinhole.

  The inventors of the present invention are concerned with the specific surface area and addition amount of the inorganic filler in the raw material and the content of the fatty acid or metal salt thereof in relation to the occurrence of pinholes during molding, and these factors have a specific relationship. It has been found that the above object can sometimes be achieved.

The present invention has been made on the basis of the above knowledge. Polybasic acid and polyhydric alcohol are used with respect to 100 parts by mass of polyolefin resin component containing 25 to 55% by mass of polyolefin resin and 45 to 75% by mass of inorganic filler. And 1-30 parts by mass of a polyester with a monobasic acid having 14 to 22 carbon atoms and / or a monohydric alcohol having 12 to 22 carbon atoms, and 0.5 to 5 parts by mass of a fatty acid or a metal salt thereof. Is a method for producing a moisture-permeable sheet, wherein the sheet is stretched twice or more by a uniaxial or biaxial stretching method, and the basis weight is 10 to 25 g / m ^2. The object is achieved by providing a method for producing a moisture-permeable sheet in which the specific surface area and content of the filler and the content of the fatty acid or metal salt thereof satisfy the following relational expression.
1,800,000> (A × S) ÷ B> 1,400,000 (wherein A represents the content (mass%) of the inorganic filler in the composition, and S represents the specific surface area of the inorganic filler (cm ² / g). And B represents the content (% by mass) of the fatty acid or its metal salt in the composition.)
Moreover, this invention achieves the said objective by providing the moisture-permeable sheet | seat produced with said manufacturing method.

In the manufacturing method of the moisture-permeable sheet of this invention, generation | occurrence | production of a pinhole can be suppressed, As a result, a moisture-permeable sheet can be produced efficiently and cheaply.
Further, the moisture-permeable sheet of the present invention can be suitably used as a leak-proof sheet for absorbent members such as diapers because the occurrence of pinholes is remarkably reduced and liquid-impermeable.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The manufacturing method of the moisture-permeable sheet | seat of this invention is a polybasic acid, polyhydric alcohol with respect to 100 mass parts of polyolefin resin components containing 25-55 mass% of polyolefin resin and 45-75 mass% of inorganic fillers. A resin composition comprising 1 to 30 parts by mass of a polyester with a monobasic acid having 14 to 22 carbon atoms and / or a monohydric alcohol having 12 to 22 carbon atoms, and 0.5 to 5 parts by mass of a fatty acid or a metal salt thereof. A sheet formed by molding the sheet by a uniaxial or biaxial stretching method to stretch the area by 2 times or more to have a basis weight of 10 to 25 g / m ² , the specific surface area of the inorganic filler And content and content of the said fatty acid or its metal salt satisfy | fill the following relational expression.
1,800,000> (A × S) ÷ B> 1,400,000 (wherein A represents the content (mass%) of the inorganic filler in the resin composition, and S represents the specific surface area of the inorganic filler (cm ² / g). And B represents the content (% by mass) of the fatty acid or its metal salt in the resin composition.

  In the present invention, a resin composition comprising 100 parts by mass of a polyolefin-based resin component containing a polyolefin resin and an inorganic filler, 1 to 30 parts by mass of a specific polyester, and 0.5 to 5 parts by mass of a fatty acid or a metal salt thereof. Is a raw material.

  Examples of the polyolefin resin used in the present invention include, for example, those mainly composed of monoolefin polymers and copolymers such as ethylene, propylene and butene, such as linear low density polyethylene (LLDPE) and branched low density. Examples include polyethylene (LDPE), high density polyethylene, polypropylene, ethylene-propylene copolymer, polybutene, ethylene-vinyl acetate copolymer, and mixtures thereof. Among these, LLDPE is preferable because it is supple and tough.

Further, LLDPE having a melt index (hereinafter also referred to as MI) of 1 to 5 g / 10 min and a density of 0.920 to 0.935 g / cm ³ , MI of 6 to 15 g / 10 min, and a density of 0.910 to 0. Using a mixture of 930 g / cm ³ LDPE with a LLDPE blending amount of 80 to 99% by mass and a LDPE blending amount of 1 to 20% by mass, the sheet formability is good, the width direction and the flow direction. This is preferable because there is little unevenness in thickness, the appearance is good, and the moisture permeable sheet has an excellent balance of moisture permeability, strength and flexibility.

  In the present invention, the inorganic filler used together with the polyolefin resin is used for imparting moisture permeability by making the moisture-permeable sheet of the present invention porous. 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, aluminum powder, iron powder and the like. These can be used alone or in combination of two or more. Of various inorganic fillers, calcium carbonate and barium sulfate are preferably used, and calcium carbonate is particularly preferably used. These inorganic fillers preferably have an average particle size of 0.3 to 8 μm and a maximum particle size of 20 μm or less from the viewpoint of ensuring the strength of the moisture-permeable sheet obtained and preventing sheet breakage during production. More preferably, the particle size is 0.5-5 μm and the maximum particle size is 15 μm or less.

In the present invention, the specific surface area of the inorganic filler is preferably 20000 to 22000 cm ² / g, more preferably 20500 to 22000 cm ² / g. Even if the specific surface area is too large or too small, a sheet having high moisture permeability and high water resistance, that is, a sheet having a large number of dense holes and difficult to ooze liquid and having sufficient strength cannot be obtained. In the present invention, the specific surface area of the inorganic filler is measured by the brane method (based on JIS R 5201) in a measurement environment at a temperature of 23 ° C. and a humidity of 50%. For example, the measuring device can be measured by using a Blaine air permeation fineness measuring device manufactured by Tsutsui Rika Chemical Instruments Co., Ltd. The standard material is 102K, a standard material for measuring fineness of Cement Association / Laboratory, and the filter paper is No. 1 for the Brain Method of Tsutsui Rika Chemical Instruments Co., Ltd. 5-A is used. The measurement sample is calculated by a general formula described in JIS R 5201, with a quantity of 2.15 g, a specific gravity ρ of 2.7 g / cm ³ and a porosity of 0.5. As a measurement sample, 500 g of an inorganic filler is prepared, from which specific surface areas of three measurement samples (one sample is 2.15 g) are measured, and the average value of the measurement values of each sample is taken as the specific surface area of the inorganic filler. did.

In the present invention, it is preferable that the distribution of the specific surface area of the inorganic filler to be used is narrow since pinholes can be suppressed. For example, in the measurement of the specific surface area by the above-mentioned Blaine method, if the maximum value is MAX and the minimum value is MIN among the measurement values of three measurement samples, the R value of the difference MAX−MIN is preferably 500 cm ² / g. Within 300 cm ² / g.

  The inorganic filler used in the present invention may be a treated product that has been surface-treated with a dispersant in advance, or may be an untreated product, but in the case of a treated product, the moisture-permeable sheet has a smaller content than the untreated product. This is preferable because the occurrence of pinholes can be suppressed. As the surface treatment agent for the inorganic filler, those capable of hydrophobizing the surface of the inorganic filler are preferable, and examples thereof include fatty acids or metal salts thereof described later.

  The content ratio of the inorganic filler to the polyolefin resin is 25:75 to 75:45, preferably 30:70 to 60:40, more preferably 35:65 to 45, in terms of polyolefin resin: inorganic filler (mass ratio). : If the amount of the inorganic filler is 55 is too small relative to the polyolefin resin, the moisture permeability of the resulting sheet will be insufficient, and if it is too large, the water resistance of the sheet will be reduced, and the liquid will be liable to bleed. However, the strength decreases and the moldability also deteriorates.

  The resin composition used in the present invention contains a fatty acid or a metal salt thereof for the purpose of uniformly dispersing the inorganic filler. Examples of the fatty acid or metal salt thereof used in the present invention include stearic acid, magnesium stearate, calcium stearate and the like. The fatty acid or the metal salt thereof is 0.5 to 5 parts by mass, preferably 0.5 to 4.0 parts by mass, more preferably 1.0 to 3.0 parts by mass with respect to 100 parts by mass of the polyolefin resin component. It is contained.

In the present invention, the content (mass%) of the inorganic filler in the resin composition is A, the specific surface area (cm ² / g) of the inorganic filler is S, and the fatty acid or metal salt thereof in the resin composition. When the content (mass%) B is satisfied, the following formula is satisfied.
1.8 million> (A × S) ÷ B> 1.4 million The above (A × S) ÷ B is
It is preferable that 1.8 million> (A × S) ÷ B> 14.5 million is satisfied,
More preferably, 1.8 million> (A × S) ÷ B> 1.5 million is satisfied.

  In the present invention, the content of the fatty acid and the inorganic filler and its specific surface area satisfy the above relational expression, so the reason for reducing the pinhole of the manufactured sheet is not yet clear, I think so. In other words, if the melt viscosity of the resin during sheet molding fluctuates, the resin before cooling and curing will not be stable, and shaking and vibration will occur, and if the molten sheet deforms due to this shaking and vibration, there will be holes in that part. Open pinhole. On the other hand, in the present invention, by satisfying the above formula, the amount of fatty acid and the like adsorbed on the surface of the inorganic filler and the amount of fatty acid remaining in the resin are controlled within an appropriate range, and during sheet (film) molding (For example, when a melt is used for inflation molding described later), the melt viscosity of the composition in the molten state is controlled to be constant, and pinholes are reduced by preventing the phenomenon of resin shaking and vibration before cooling and curing. It is estimated that

  In the resin composition used in the present invention, in addition to the above-mentioned polyolefin resin, inorganic filler, and fatty acid or metal salt thereof, a specific polyester is blended to give a supple texture and improve stretchability. To do. This polyester is a polyester of a polybasic acid, a polyhydric alcohol, a monobasic acid having 14 to 22 carbon atoms, and / or a monohydric alcohol having 12 to 22 carbon atoms. By blending this polyester, the moisture-permeable sheet obtained has a supple texture. In addition, since the stretchability is good, it is uniformly whitened with no unevenness and looks good in appearance, and moisture permeability can be obtained by opening a large number of fine holes. The combination of each component constituting the polyester is selected in consideration of the number of ester groups in the polyester constant mass and the degree of branching of the hydrocarbon chain, from the balance of the affinity with the polyolefin resin and the inorganic filler.

  As the monobasic acid in the polyester, a long-chain hydrocarbon monocarboxylic acid having 14 to 22 carbon atoms or the like is used. As the polybasic acid, dicarboxylic acid, tricarboxylic acid, tetracarboxylic acid and the like are used. As the monohydric alcohol, a long-chain hydrocarbon monoalcohol having 12 to 22 carbon atoms is used. As the polyhydric alcohol, diols, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol, sucrose and the like are used. When the carbon number of monobasic acid is 12 or less, or the carbon number of monohydric alcohol is 10 or less, the balance of affinity for polyolefin resin and inorganic filler is shifted, and polyester is partially concentrated during film molding. Unevenness may occur during stretching, and the vertical tear strength may decrease.

  The polyester is a polyester obtained by dehydrating and condensing a polybasic acid and a polyhydric alcohol. When the terminal is a carboxylic acid, most of the polyester is a long-chain hydrocarbon monoester such as stearyl alcohol, oleyl alcohol, gerve alcohol, It is preferably esterified with alcohol. In the case where the terminal is an alcohol, most of the terminal is preferably an end-capped polyester esterified with a monocarboxylic acid of a long chain hydrocarbon such as stearic acid, hydroxystearic acid, oleic acid, and isostearic acid. However, even in these cases, not all ends need to be blocked. More preferred are esters containing branched acids or alcohols as ester constituents.

  Examples of preferred specific polyesters include 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, 1,3-butanediol and adipic acid Polyester having both ends of the polyester blocked with hydroxystearic acid, hexaester composed of trimethylolpropane-adipic acid-stearic acid, octaester composed of pentaerythritol-adipic acid-stearic acid, dipentaerythritol-adipic acid-stearin Dodecaester consisting of acid, polyester using dimer acid or hydrogenated dimer acid instead of adipic acid, which is a component of the polyester, and isostearic acid instead of stearic acid It was a polyester or the like.

  The polyester is preferably blended in an amount of 1 to 30 parts by mass, particularly 2 to 20 parts by mass with respect to 100 parts by mass of the polyolefin-based resin component, from the viewpoint of supple texture and stretchability.

  In addition to the above-described components, the resin composition used in the present invention may contain a plasticizer, a stabilizer, an antioxidant, an ultraviolet absorber, and the like as long as the effects of the present invention are not hindered.

In the manufacturing method of the moisture-permeable sheet of this invention, a moisture-permeable sheet is manufactured as follows using said resin composition, for example.
Each component constituting the above resin composition is premixed using a Henschel mixer or a supermixer, and then kneaded with a single or twin screw extruder to obtain a molten resin composition.
Next, the molten resin composition is formed into a film using a molding machine. In this case, the melt index (MI) of the molten resin is preferably 10 g / 10 min or less, and more preferably 9 g / 10 min or less. MI is measured under the conditions of a temperature of 190 ° C. and a load of 21.18 N according to the method defined in ASTM D-1238-57T (E). The temperature at the time of film formation is not particularly limited, but is preferably 140 to 200 ° C. Moreover, it is preferable to shape | mold the basic weight of a film to 20-70 g / m < ² >.

  As a molding machine, generally used T-die molding or inflation molding can be used to form a molten resin composition into a film. The obtained film is uniaxially or biaxially stretched to cause interfacial peeling between the resin and the inorganic filler to make it porous, thereby obtaining the moisture-permeable sheet of the present invention. A roll method or a tenter method is used for stretching. The draw ratio is 2 times or more, preferably 2 to 4 times, and particularly preferably 2.0 to 3.5 times.

The moisture permeable sheet of the present invention has a moisture permeability of preferably 3600 to 8400 g / (m ² · 24 h), more preferably 4000 to 8400 g / (m ² · 24 h), and further preferably 5000 to 8400 g / (m ² · 24 h). )

The moisture permeable sheet of the present invention has a basis weight of 10 to 25 g / m ² . As will be described later, the basis weight of the moisture permeable sheet is preferably 15 to 25 g / m ² , more preferably 17 to 23 g / m ² in the form of a composite sheet bonded to a fiber sheet such as a nonwoven fabric on one surface. a m ^2. When the basis weight is too small, the strength of the sheet is lowered, and the transportability becomes a problem, or the water resistance is lowered due to perforation. Moreover, when there is too much basic weight, a softness | flexibility will fall or it will become a sheet | seat in which moisture permeability fell.

  The moisture-permeable sheet of the present invention is used, for example, as a sanitary material, a medical material, or a clothing material. Moreover, the moisture-permeable sheet | seat of this invention can also be used as said material in the form of the composite sheet bonded together with the fiber sheets, such as a nonwoven fabric, on the one surface. In particular, the moisture-permeable sheet of the present invention suppresses pinholes that allow water to pass therethrough, while fine moisture-permeable holes that allow water vapor to pass but not allow water to pass therethrough can be made dense, Alternatively, as a composite sheet bonded to a fiber sheet, when used as a constituent material of absorbent articles such as disposable diapers and sanitary napkins, it is possible to prevent an increase in humidity in the clothing and rash occurs on the wearer's skin. This can be effectively prevented. These absorbent articles generally include a liquid-permeable top sheet, a liquid-impermeable back sheet, and a liquid-retaining absorbent disposed between the two sheets. The composite sheet bonded with the fiber sheet is used as the back sheet, for example.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this.
In the following examples, “parts” means “parts by mass” unless otherwise specified.

[Examples 1-6 and Comparative Examples 1-3]
(1) Preparation of polyolefin-based resin composition Raw materials prepared by mixing the materials shown in Table 1 below with the composition shown in Table 1 are premixed with a Henschel mixer, then superheated with a twin-screw extruder, and melted. A master batch (MI = 8) of the composition was produced. The set temperature of the twin screw extruder was 180 ° C.

(2) Molding of moisture-permeable sheet A sheet was molded with an inflation molding apparatus using this master batch. The set temperature of the circular die was 160 ° C., and the blow ratio was 2.5.
The obtained sheet was stretched 2.6 times in the sheet flow direction using a uniaxial stretching machine to produce a moisture-permeable sheet having a basis weight of 20 g / m ² . The stretching temperature was 70 ° C. and the annealing temperature was 80 ° C. The return rate in annealing was set to 10%.
Further, the moisture permeable sheets of the examples and comparative examples were measured in accordance with JIS Z 0208 under conditions of a temperature of 30 ° C. ± 0.5 ° C. and a humidity of 90 ± 2% RH. It was 6 g / 100 cm ² · h. Further, the tear strength in the machine direction (MD) measured according to JIS K 7128-2 Elmendorf tear method was about 9 cN in all cases.

Each material shown in Table 1 is as follows.
(1) Polyolefin resin: “UZ2520F (trade name)” manufactured by Prime Polymer Co., Ltd.
(2) Calcium carbonate A: A product obtained by classification of “Escalon # 2000 (trade name)” manufactured by Sankyo Seimitsu Co., Ltd. (average particle size 1 μm)
MAX-MIN of specific surface area distribution = 300 cm ² / g
(3) Calcium carbonate B: “Escalon # 2000 (trade name)” manufactured by Sankyo Seiko Co., Ltd.
MAX-MIN of specific surface area distribution = 650 cm ² / g
(4) Polyester: “Exepal TM20-AS (trade name)” manufactured by Kao Corporation
(5) Fatty acid: “Lunac S-40 (trade name)” manufactured by Kao Corporation
In Table 1, “parts” represents parts by mass. The unit of the specific surface area is cm ² / g.
Moreover, Formula 1 is as follows.
(A × s) ÷ b (Formula 1)
However, a: Compounding quantity (mass%) of calcium carbonate in the resin composition, s: Specific surface area (cm ² / g) of calcium carbonate, b: Compounding quantity (mass%) of fatty acid in the resin composition

[Performance evaluation]
For moisture-permeable sheet obtained in Examples and Comparative Examples, were counted in the presence or absence of pinholes per moisture permeable sheet 10000 m ^2, a liquid-permeable by dividing the number without the number of available number of available pinholes The incidence of pinholes (having a hole diameter of 0.2 mm or more) was measured, and the productivity was shown in four stages: ◎, ○, Δ, and ×. Those above Δ are at a level that can be produced practically without any problems. These results are shown in Table 2 below. The pinhole generation rate in Table 2 indicates the pinhole generation rate per 10,000 m ^{2 of} the moisture permeable sheet.

  As is clear from the results shown in Table 2, it can be seen that the moisture permeable sheets of the examples (products of the present invention) have a pinhole generation rate of 50% or less and are excellent in productivity. On the other hand, in the moisture permeable sheet of the comparative example, the incidence of pinholes exceeded 50%, which was a problem level in industrial production.

Claims (2)

Polybasic acid, polyhydric alcohol, monobasic acid having 14 to 22 carbon atoms and 100 mass parts of polyolefin resin component containing 25 to 55 mass% of polyolefin resin and 45 to 75 mass% of inorganic filler A sheet formed by molding a resin composition containing 1 to 30 parts by mass of a polyester with a monohydric alcohol having 12 to 22 carbon atoms and 0.5 to 5 parts by mass of a fatty acid or a metal salt thereof is uniaxial or A biaxial stretching method is a method for producing a moisture-permeable sheet, in which the area is stretched by 2 times or more, and the basis weight is 10 to 25 g / m ² .
The difference between the maximum value and the minimum value in the specific surface area of the inorganic filler is within 500 cm ² / g,
A method for producing a moisture permeable sheet, wherein the specific surface area and content of the inorganic filler and the content of the fatty acid or metal salt thereof satisfy the following relational expression.
1,800,000> (A × S) ÷ B> 1,500,000 (wherein A represents the content (mass%) of the inorganic filler in the resin composition, and S is the specific surface area of the inorganic filler (cm ² / g). And B represents the content (mass%) of the fatty acid or metal salt thereof in the resin composition.) The method for producing a moisture-permeable sheet according to claim 1, wherein the inorganic filler has a specific surface area of 20000 to 22000 cm ² / g .