JPH0977901A - Porous sheet, method for producing the same, and absorbent article using the same - Google Patents

Abstract

(57) [Summary] [Purpose] Good physical properties such as mechanical strength, flexibility and breathability required for backing materials of absorbent articles such as disposable diapers and sanitary products, and frictional force is reduced. A porous sheet. The moisture-permeable porous sheet of the present invention is 50-90 parts by weight of a crystalline polyolefin resin and a crystalline polyolefin resin which is miscible with the crystalline polyolefin resin under melting of the crystalline polyolefin resin. A sheet formed from a mixture containing 50 to 10 parts by weight of an organic compound that undergoes phase separation below the crystallization temperature of 1.2 to 5 times at least uniaxially to obtain a stretched sheet having a thickness of 10 to 100 μm. The stretched sheet is embossed so that the difference between the concave portion and the convex portion of the stretched sheet is 10 μm to 5 μm.
It is characterized by being obtained by forming an uneven pattern of 00 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous sheet, a method for producing the same, and an absorbent article using the same, more specifically, it has an uneven pattern, has a good texture, and has a frictional force. The present invention relates to a reduced porous sheet, a method for producing the same, and an absorbent article using the same.

[0002]

2. Description of the Related Art A porous film can be obtained by mixing a polyolefin resin and an inorganic filler, stretching a film obtained by film formation, and then embossing the film. Is known. However, the porous film obtained by such a method has a defect that it has low mechanical strength and is easily broken.

It is also possible to obtain a porous film by melt-blending a crystalline thermoplastic resin with a compound miscible with the crystalline thermoplastic resin, stretching the obtained film, and then embossing the film. Are known. For example,
Japanese Unexamined Patent Publication No. 62-68459 and Japanese Unexamined Patent Publication No. 2-504 disclose a technique for producing a porous film by stretching a formed film and subsequently performing embossing. However, since the embossed portion of the porous film obtained by such a method becomes translucent, when the porous film is used as, for example, the backing material of a disposable diaper, the color of excrement passes through the porous film. It has a drawback that it can be seen through from the outside and impairs the cleanliness of the disposable diaper. Further, since the porous film has a very small difference in unevenness in the thickness direction,
The texture was inferior and could not be said to give a high-class image. Further, the porous film has a drawback that it has a large frictional force and is easily broken during secondary processing due to a very small difference in unevenness in the thickness direction.

Therefore, the object of the present invention is to achieve good physical properties such as mechanical strength, flexibility, and air permeability required for the backing material of absorbent articles such as disposable diapers and sanitary products, and to reduce frictional force. It is to provide a reduced porosity sheet. Another object of the present invention is to provide a method capable of easily and inexpensively producing the above-mentioned porous sheet.

[0005]

[Means for Solving the Problems] In order to achieve the above object,
As a result of intensive studies by the present inventors, a sheet formed from a specific composition is subjected to a stretching step and an embossing step that follows, and a specific uneven pattern, specifically, a difference between a concave portion and a convex portion is obtained. It was found that the various physical properties described above can be imparted to the sheet by forming the uneven pattern of 10 μm to 500 μm.

The present invention has been made based on the above findings, and is 50-90 parts by weight of the crystalline polyolefin resin and the crystalline polyolefin resin which is miscible with the crystalline polyolefin resin under melting. Organic compounds that undergo phase separation below the crystallization temperature of the polyolefin resin 50
A step of forming a sheet from a mixture containing 10 to 10 parts by weight, and a step of stretching the sheet at least uniaxially by 1.2 to 5 times to obtain a stretched sheet having a thickness of 10 to 100 μm.
The method for producing a porous sheet having moisture permeability, comprising the step of embossing the stretched sheet to form an uneven pattern in which the difference between the concave portion and the convex portion is 10 μm to 500 μm. The above object is achieved by providing the following.

The present invention also provides a preferable porous sheet produced by the above method, which is compatible with 50 to 90 parts by weight of the crystalline polyolefin resin and the crystalline polyolefin resin under melting of the crystalline polyolefin resin. A sheet formed from a mixture containing 50 to 10 parts by weight of an organic compound that undergoes phase separation at a crystallization temperature of the crystalline polyolefin resin or less is stretched at least uniaxially by 1.2 to 5 times to have a thickness of 10 to 100 μm. A porous sheet having moisture permeability, which is obtained by obtaining a sheet, and then subjecting the stretched sheet to embossing to form an uneven pattern in which the difference between the concave portion and the convex portion is 10 μm to 500 μm on the stretched sheet. It provides a seat.

Furthermore, the present invention provides an absorbent article comprising a liquid-permeable surface material, a leak-proof backing material, and an absorber disposed between them, wherein the backing material is the above-mentioned material. It is intended to provide an absorbent article characterized by using a porous sheet.

The porous sheet obtained by the method of the present invention can be used in applications requiring waterproofness and moisture permeability, such as waterproof clothing, waterproof covers and packaging materials, but especially disposable diapers and menstruation. It is preferably used as a backing material for absorbent articles such as napkins.

The method of the present invention will be described in detail below.

The method of the present invention comprises: i) 50 to 90 parts by weight of a crystalline polyolefin resin and the crystalline polyolefin resin which is miscible with the crystalline polyolefin resin under melting and the crystallization temperature of the crystalline polyolefin resin. In the following, a first step of forming a sheet from a mixture containing 50 to 10 parts by weight of an organic compound that undergoes phase separation, ii) a second step of stretching the sheet at least uniaxially by 1.2 to 5 times, and ii.
i) It comprises three steps of a third step of embossing the stretched sheet to form an uneven pattern in which the difference between the concave portion and the convex portion is 10 μm to 500 μm. Each of these steps will be described.

First, the first step will be described.
In the first step, first, 50 to 90 parts by weight of the crystalline polyolefin resin and the crystalline polyolefin resin which is miscible with the crystalline polyolefin resin under melting and is equal to or lower than the crystallization temperature of the crystalline polyolefin resin. A mixture containing 50 to 10 parts by weight of an organic compound that phase separates is prepared.

The crystalline polyolefin resin, which is one component of the mixture, will be described below. Examples of the crystalline polyolefin include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, and ethylene-vinyl acetate. Copolymer, ethylene-
Examples thereof include, but are not limited to, acrylic acid copolymer, polypropylene, ethylene-propylene copolymer, propylene-butene copolymer, ionomer resin and blends thereof. Among these, it is particularly preferable to use a polypropylene resin, a blend of a polypropylene resin and an ethylene-propylene copolymer resin, or a blend of a polypropylene resin and a polyethylene resin. The crystalline polyolefin may be blended with a polyester resin such as polyethylene terephthalate or polybutylene terephthalate as long as the intrinsic properties are not impaired.

The melt index of the crystalline polyolefin resin is preferably 3 g / 10 minutes or less, and more preferably 0.2 to 3 g / 10 minutes. By setting the melt index of the crystalline polyolefin resin to 3 g / 10 minutes or less, a necessary melt tension is obtained at the time of sheet forming, and a sheet can be formed stably at high speed. The melt index is 0.2 g /
If the time is less than 10 minutes, there is a case that a large power is required in the extrusion molding at the time of sheet molding, and the productivity may be reduced. Therefore, the above range is preferable. In the present invention, the melt index is defined as ASTM D-1.
According to 238, for polypropylene and polypropylene-based copolymer, it refers to a value measured under a load of 230 ° C. and a load of 2.16 kgf.
2. A value measured under a load of 16 kgf.

Explaining the organic compound which is another component of the mixture, the organic compound is miscible with the crystalline polyolefin resin under melting of the crystalline polyolefin resin and the crystalline polyolefin resin. At temperatures below the crystallization temperature of, the phases are separated.
Examples of the organic compound include liquid paraffin and α
-Olefin oligomers, mineral oils, synthetic lubricating oils, various hydrocarbons such as mineral spirits and paraffin wax, and aliphatic carboxylic acids such as dioctyl phthalate, diethyl phthalate, trimethylol propane laurate, distearyl adipate and tetraoctyl pyromellitate Examples thereof include various esters of polyhydric alcohol and polyhydric alcohol, but are not limited thereto. Of these, especially
It is preferable to use mineral oils, synthetic lubricating oils, paraffin waxes and esters of aliphatic carboxylic acids with polyhydric alcohols. When using the above mixture, a small amount of a water repellent such as silicone oil may be used in combination as long as the original properties are not impaired.

The mixing ratio of the crystalline polyolefin resin and the organic compound in the mixture is 50 to 90 parts by weight of the organic compound to 50 to 90 parts by weight of the crystalline polyolefin resin. If the compounding ratio of the organic compound is less than 10 parts by weight, a porous sheet having sufficient moisture permeability cannot be obtained, and if it exceeds 50 parts by weight, the mechanical strength of the obtained sheet becomes insufficient, and for a long period of time. It is not practical because the organic compound bleeds out from the sheet during storage. The blending ratio is preferably 40 to 20 parts by weight of the organic compound with respect to 60 to 80 parts by weight of the crystalline polyolefin resin, more preferably 60 to 75 parts by weight of the crystalline polyolefin resin. 40 to 25 parts by weight of organic compound.

In addition to the crystalline polyolefin resin and the organic compound, other additives can be added to the mixture as needed. Particularly preferred as such additives are crystal nucleating agents. Use of such a crystal nucleating agent is preferable because the crystallinity of the crystalline polyolefin can be increased. The nucleating agent is used in an amount of 0.0
It is preferable to mix 1 to 3 parts by weight, more preferably 0.05 to 1 part by weight. If the compounding amount of the above crystal nucleating agent is less than 0.01 part by weight, a sufficient crystal nucleating effect may not be obtained, and if it exceeds 3 parts by weight, the moisture permeability of the obtained porous sheet is insufficient. Therefore, it is preferable that the amount is within the above range.

The crystal nucleating agent is, for example, 1.
3,2,4-dibedylidene sorbitol, 1,3,2 ・
4-bis (p-methylbenzylidene) sorbitol, 1
3,2,4-bis (p-ethylbenzylidene) sorbitol, sodium bis (4-t-butylphenyl) phosphate, adipic acid, benzoic acid, sodium benzoate, talc, titanium oxide, kaolin and the like. However, the present invention is not limited to these.

When the above crystal nucleating agent is blended, it is preferably blended as a crystal nucleating agent masterbatch.

In addition to the above crystal nucleating agent, additives that can be added to the above mixture include, for example, inorganic fillers such as calcium carbonate, stabilizers such as antioxidants, antistatic agents, and the like.
Examples include organic pigments and dyes. These additives can be blended preferably in an amount of 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on the mixture.

In the first step, a sheet is formed from the mixture. The sheet forming method is not particularly limited, and a conventionally known sheet forming method can be used. For example,
The mixture may be inflation-molded or extruded from a T-die to form a sheet, or the sheet may be formed by cast molding or calendar molding. For example, when a sheet is formed by inflation molding, the above-mentioned mixture containing the above-mentioned crystalline polyolefin, the above-mentioned organic compound and optional additives is fed from a hopper to a single-screw or twin-screw kneader and heated in the kneader. A melt-kneaded product is obtained by kneading. Such a melt-kneaded product is once pelletized, and the pellet is supplied as a raw material to a single-screw extruder and extruded from a ring die connected to the tip, and the extruded melt-kneaded product is pulled upward to form a tube, and the tube Blow air into the inside of the to form a sheet.

The above-mentioned sheet molded in this manner is
In order to make the difference between the concave portion and the convex portion 10 μm to 500 μm in the embossing in the third step described later, the thickness thereof is 20 to 600 μm (more preferably 40 to 360 μm).
μm) is preferable.

Next, the second step will be described. In the second step, the sheet obtained in the first step is 1.2 to 5 times in at least one axial direction (area ratio).
Stretch. By this stretching step, continuous fine pores are formed in the sheet, and moisture permeability is imparted. If the draw ratio is less than 1.2 times, the formation of fine pores is insufficient and sufficient moisture permeability cannot be obtained, and if the draw ratio exceeds 5 times, stretch breakage occurs or the sheet becomes fragile and stable. Then, it becomes difficult to manufacture. The draw ratio is 1.2 to
It is more preferable that the amount is 3 times, because a better texture and sufficient moisture permeability can be obtained.

In the stretching step, the sheet may be stretched in at least one direction. For example, in the case of uniaxial stretching, a uniaxial roll stretching machine can be used,
In the case of biaxial stretching, simultaneous biaxial stretching or sequential biaxial stretching can be performed using a tenter stretching machine or a mandrel stretching machine. At this time, the sheet to be stretched may be stretched while being heated.

In this way, a stretched sheet having a thickness of 10 to 100 μm is obtained. If the thickness is less than 10 μm, sufficient strength cannot be obtained, and if it exceeds 100 μm, the flexibility and texture are deteriorated. The thickness is preferably 20-6
It is 0 μm, more preferably 25 to 50 μm.

Next, the third step will be described. In the third step, the stretched sheet obtained in the second step is embossed to form a concavo-convex pattern in which the difference between the concave portion and the convex portion is 10 μm to 500 μm.

As the embossing roll, a pair of rolls generally composed of an engraving roll and a smooth roll can be used. As the engraving roll, for example, an iron roll having various patterns engraved on its surface can be used. On the other hand, as the smooth roll, for example,
A paper roll, a cotton roll, a rubber roll, an iron roll, or the like can be used.

In the embossing, the sheet before embossing can be preheated with a heating roll. It is also possible to heat the embossing roll itself and interpose the sheet between the heated rolls for embossing. At the time of heating, it is preferable to set the temperature of the embossing roll to a temperature lower by 10 ° C. or more than the melting point of the crystalline polyolefin resin.

The engraving roll of the embossing roll will be described in detail. The pattern on the surface of the engraving roll, that is, the embossing pattern, preferably has a difference in unevenness of 15 μm to 800 μm. When the difference between the unevenness is less than 15 μm, the unevenness due to the thickness unevenness of a normal sheet approaches, and it is not possible to make a sufficient difference in the unevenness, and the effect cannot be expected. On the other hand, if the difference between the irregularities exceeds 800 μm, the sheet may be broken during embossing, which makes it unsuitable for industrial production. Therefore, it is preferably within the above range. By using such an embossing roll, the stretched sheet has a difference between the concave portion and the convex portion of 1
An uneven pattern of 0 μm to 500 μm can be formed. When the difference between the concave portion and the convex portion is less than 10 μm, the frictional force of the sheet cannot be reduced, and even if the sheet actually has moisture permeability, it has moisture permeability in appearance. It is not possible to give the user the impression that. On the other hand, when the difference between the concave portion and the convex portion exceeds 500 μm, not only does the sheet have a stiff texture, but also the sheet is easily broken in terms of strength. The difference between the concave portion and the convex portion is preferably 2
0 to 300 μm, more preferably 30 to 200 μm
m.

Explaining the embossed pattern on the engraving roll, various patterns can be used as the embossed pattern. However, it is a mechanical aspect of the sheet that the convex portion on the surface of the engraving roll is a continuous pattern. It is preferable from the viewpoint of improving strength. In particular, embossing a continuous pattern such as a lattice pattern or a mesh pattern having continuous convex portions is preferable because the mechanical strength in the direction perpendicular to the stretching direction in the second step is improved. Further, the continuous pattern is a striped pattern composed of a number of substantially parallel straight lines, and the striped pattern is 0 to 90 with respect to the sheet forming direction.
Having an angle of degrees is also preferable from the viewpoint that the strength balance in the direction perpendicular to the stretching direction can be changed by the angle of the striped pattern. When the angle is 0 or 90 degrees, an embossed sheet having a vertical stripe pattern or a horizontal stripe pattern is obtained, which is more preferable from the viewpoint of appearance and texture. Another example of the embossed pattern is preferably one in which the convex portion on the surface of the engraving roll is a pattern pattern (for example, a dot pattern or a turtle shell pattern).

The linear pressure during the embossing depends on the thickness of the sheet to be embossed, the heating temperature, and the running speed.
As a general range, it is preferably 5 to 150 kg / cm.

Further, the area (emboss area ratio) of the portion embossed by the embossing is preferably 20 to 80% with respect to the area of the entire sheet, and 30
More preferably, it is 70%. If the above-mentioned embossed area ratio is less than 20%, the embossment of the sheet wound into a roll is deteriorated, the frictional force of the sheet cannot be reduced, and the sheet may be broken during the secondary processing. .
Further, if it exceeds 80%, the moisture permeability may be deteriorated by embossing and the moisture permeability necessary for practical use may not be obtained.

The method for producing the porous sheet of the present invention has been described in detail above. However, in the method of the present invention, other steps may be carried out, if necessary, in addition to the above first to third steps. Good. For example, the sheet may be further embossed to further reduce the frictional force of the sheet to improve the appearance and texture, or hydrocarbons such as normal hexane or 1,1,2,2-trichloro. The organic compound may be extracted from the embossed sheet using halogenated hydrocarbons such as -1,2,2-trifluoroethane, trichlorofluoromethane and dichlorofluoromethane.

Next, a preferred porous sheet produced by the above-mentioned method of the present invention will be described with reference to the drawings. Here, FIG. 1 is a schematic view showing a cross section of a preferable porous sheet produced by the method of the present invention. As shown in FIG. 1, the preferred porous sheet 20 manufactured by the method of the present invention has a difference d between the concave portion 22 and the convex portion 24 of 10 μm to 500 μm (preferably 20 to 20) due to the stretching process and the embossing process. 300 μm,
More preferably, an uneven pattern of 30 to 200 μm) is formed. As a result, the preferred porous sheet produced by the method of the present invention, unlike conventional porous sheets,
The frictional force is extremely reduced. The above-mentioned porous sheet with reduced frictional force has the advantages that the running property of the sheet is improved and it is less likely to break during secondary processing.

Further, the porous sheet has fine pores from one surface to the other surface, and exhibits moisture permeability through the fine pores. The water vapor transmission rate of the above-mentioned porous sheet is 600-9600 g /
(M ² · day) is preferable, and more preferably 1
It is 200 to 6000 g / (m ² · day). Be insufficient to use the moisture permeability is less than 600g / (m ² · day) as moisture-permeable sheet, 9600g / (m ² ·
If it exceeds 10 days, the water pressure resistance and tear strength may be insufficient, so it is preferable to set it within the above range.

Further, the porous sheet 2 having the above-mentioned moisture permeability.
The thickness d _{S of} 0 (see FIG. 1) depends on the application, but is 1
It is preferably about 0 to 100 μm, more preferably 20.
〜60 μm. When the thickness is less than 10 μm, sufficient strength cannot be obtained, and when the thickness exceeds 100 μm, the flexibility and the texture may be deteriorated.

Furthermore, the porous sheet 2 having the above-mentioned moisture permeability.
The apparent thickness d _{E of} 0 (see FIG. 1) is preferably about 20 to 600 μm, and more preferably 40 to 360 μm, although it depends on the application.

As described at the beginning, the above-mentioned porous sheet having moisture permeability can be used for applications requiring waterproofness and moisture permeability such as waterproof clothing, waterproof covers and packaging materials. It is suitably used as a backing material for absorbent articles such as disposable diapers and sanitary napkins. Therefore, as a particularly preferable application of the porous sheet, an example in which the porous sheet having moisture permeability is used as a backing material of an absorbent article will be described below with reference to the drawings. Here, FIG. 2 is a perspective view showing a disposable diaper as an example of the absorbent article, and FIG. 3 is a partially cutaway development view of the disposable diaper shown in FIG.

The disposable diaper 1 shown in FIG. 2 and FIG.
It comprises a liquid-permeable front surface material 2, a leakproof back surface material 3, and an absorber 4 arranged therebetween, and the porous sheet is used as the back surface material 3.

More specifically, the disposable diaper 1 is
As shown in FIG. 3, the back surface waist portion 5 ′, the abdominal waist portion 5 and the back surface material 3, the back surface material 3, and the absorbent body 4 which are each molded in an overflowing hourglass shape,
The leg portion 6 is formed. In addition, the elastic body 7 is provided between the front surface material 2 and the back surface material 3 in the abdominal waist portion 5, the back waist portion 5'and the leg portion 6, respectively.
Further, a pair of tape fasteners 10 are fixed to the left and right side edges of the back waist portion 5 ', thereby improving the function and performance as a diaper. Further, as shown in FIG. 3, the disposable diaper 1 is formed to be long in the vertical direction, and the surface material 2 and the back surface material 3 are formed to have substantially the same length and width. .

The surface material 2 generally has a basis weight of 15
Although a non-woven fabric of -40 g / m ² is used, a film or a net may be used as long as it is liquid permeable, and it is particularly preferable that the periphery is water repellent and the central portion is hydrophilic.

As the absorbent body 4, a cotton-like material obtained by crushing softwood kraft pulp is generally covered with water-absorbent paper, and one containing superabsorbent polymer particles is particularly preferable. The weight of the cotton-like material is generally about 10 g-40
g. The superabsorbent polymer used in the absorbent may be located in any of the upper, middle and lower layers of the absorbent, or may be mixed with the pulp. Examples of the superabsorbent polymer include starch-based, cellulose-based, and synthetic polymer-based polymers, and examples thereof include starch-acrylic acid (salt) graft copolymers, saponified starch-acrylonitrile copolymers, and sodium carboxymethyl cellulose. Suitable are cross-linked products, acrylic acid (salt) polymers, and the like. The particles of such a high-absorbent polymer have a liquid-absorption retention force of 20 times or more of the own weight and have a gelling property.

Examples of the elastic body 7 include generally polyurethane, natural rubber and the like in the form of strings, ribbons, etc., and threads which develop elasticity after being wetted with water. As described above, it is preferable that the number of the devices is approximately five. Further, the attachment length of the elastic body 7 is usually about 30 to about 60% of the length of the diaper, and the extension degree is preferably about 1.3 to about 2.0 times the free length.

Although the flat type disposable diaper has been described as an example of the absorbent article, the absorbent article is not limited to this, and other absorbent articles such as sanitary napkins and incontinence can be used. The porous sheet can be similarly applied to pads, pants-type diapers and the like.

[0045]

EXAMPLES The method for producing a moisture-permeable porous sheet of the present invention and the specific structure of the moisture-permeable porous sheet obtained by the method will be described below with reference to examples.

Example 1 70 parts by weight of polypropylene [Cisso Petrochemical Co., Ltd.] having a density of 0.91 g / cm ³ and a melt index of 0.5 g / 10 min, mineral oil [PW-9]
0, Idemitsu Petrochemical Co., Ltd.] 30 parts by weight and a crystal nucleating agent [EC-1, EC Chemical Co., Ltd.] 0.13 part were kneaded with a twin screw type kneader to prepare pellets. The obtained pellets were supplied to an inflation molding machine to mold an inflation sheet having a thickness of 44 μm. The obtained inflation sheet was stretched at a stretching temperature of 50 ° C. at a stretching ratio of 1.5 times using a roll stretching machine. The thickness of the stretched sheet was approximately 36 μm. The stretched sheet,
Embossing pressure of 10 kg / cm between a pair of embossing rolls made of a combination of a metal engraving roll (heating temperature 80 ° C.) having a hexagonal pin pattern with a groove depth of 0.25 mm and a silicon smoothing roll, running Speed 5mm /
Embossing was performed through min. Using the porous sheet thus obtained as a backing material, a disposable diaper shown in FIGS. 2 and 3 was produced.

[Examples 2 to 4] The embossing temperature and pressure in the embossing step of Example 1 were changed to the conditions shown in Table 1 to obtain embossed sheets having different recesses and protrusions.

Comparative Example 1 A porous sheet was obtained by the same operation as in Example 1 except that the embossing step in Example 1 was not performed.

<Performance Evaluation> In order to evaluate the performance of the porous sheets obtained in Examples and Comparative Examples, the difference between the concave portion and the convex portion, the tensile strength, the frictional force, the moisture permeability, the water pressure resistance, and the texture were evaluated. It was measured. Table 1 shows the results. The measurement was performed according to the following procedure.

<Moisture Permeability> The moisture permeability is measured according to JIS Z-
According to 0208, it was measured at a temperature of 30 ° C. and a relative humidity of 90 ± 2%.

<Water resistance> Water resistance is measured according to JIS L-
Measured in accordance with the A method of 1092, the constant water pressure method (water column 2
m) was evaluated for water resistance for 10 minutes.

<Hand feeling> The following criteria were used for evaluation. ⊚: High-class appearance, seemingly breathable to the eye, and having a very good feel to the touch ○: Appearing breathable to the eye and having a good feel to the touch △: Seemingly breathable and not likely to look I feel a little sticky

<Difference between concave and convex> Difference d between concave and convex is
It was measured by subtracting the sheet thickness d _S from the sheet thickness (apparent thickness d _E ) after embossing.

<Tensile Strength> The tensile strength was measured by measuring the tensile strength in the direction perpendicular to the forming direction (longitudinal direction) of the porous sheet (horizontal direction) and using the breaking strength of the test sheet as the tensile strength. The dimension width of the test sheet is set to 10 mm, a tensile force universal tester is used, and the distance between chucks is 50 m as a tensile condition.
m, tensile speed 300 mm / min, and room temperature.

<Frictional force> The frictional force is measured by the rotary drum type frictional resistance measuring device (HEIDON-16 type, Shinto Kagaku) shown in FIG.
(Manufactured by KK). That is, one sheet-shaped test piece 30 (width 30 mm, length 300 mm) is attached to the rotating drum 33.
/ 4 round winding, weight 35 on one side of the sheet-shaped test piece 30
A load of 50.6 g was applied to the other side, and the load converter 31 was attached to the other side through the test piece connector 34 and the spring 32. By rotating the rotating drum 33 at a constant rotation speed, friction was generated on the contact surface between the rotating drum 33 and the sheet-shaped test piece 30, and the resistance force was measured. The rotary drum 33 is made of aluminum and has a diameter of 57.3 mm and a width of 40 mm and is polished and finished. Rotation speed is 30
m / min.

[0056]

[Table 1]

As is clear from the above results, a sheet formed from a specific composition is subjected to a stretching step and an embossing step that follows, so that the difference between the concave portion and the convex portion falls within a specific range. It can be seen that the processed porous sheets obtained by the method of the present invention (Examples 1 to 4) have good texture and reduced frictional force while maintaining high moisture permeability. On the other hand, the porous sheet (Comparative Example 1) obtained by performing only the stretching process without performing the embossing process has a high frictional force. In addition, although it has moisture permeability, it gives the impression that it does not look like it. Further, it had a slightly sticky feel.

[0058]

As described above in detail, the porous sheet having moisture permeability obtained by the method of the present invention has a mechanical strength required for a backing material in absorbent articles such as disposable diapers and sanitary napkins, It has flexibility and moisture permeability. Moreover, the frictional force is reduced, and it is less likely to tear during secondary processing. Further, the above-mentioned porous sheet gives the user the impression that it has a good texture due to the embossing process and that it also has breathability in appearance. Further, unlike the conventional porous sheet, the porous sheet hardly becomes translucent due to the effect of the uneven pattern formed by embossing. Further, according to the method of the present invention, such a porous sheet can be mass-produced easily and inexpensively.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of a preferable porous sheet produced by the method of the present invention.

FIG. 2 is a perspective view showing a disposable diaper as an example of an absorbent article.

FIG. 3 is a partially cutaway exploded view of the disposable diaper shown in FIG.

FIG. 4 is a schematic view showing an apparatus used for measuring a frictional force.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Disposable diaper 2 Liquid-permeable surface material 3 Leak-proof backing material 4 Absorber 5 Abdominal waist part 5'Back waist part 6 Leg part 7 Elastic body 10 Tape fastener 20 Porous sheet 22 Concave part 24 Convex part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B29K 105: 04 (72) Inventor Yoshihiro Sakai 2606 Kabane-cho, Haga-gun, Tochigi Kao Stock Company Research Institute (72) Inventor Kazuo Fujita 2606 Akabane, Kai Town, Haga-gun, Tochigi Prefecture

Claims (8)

[Claims] 1. An organic compound which is miscible with 50 to 90 parts by weight of a crystalline polyolefin resin and the crystalline polyolefin resin under melting, and phase-separates below the crystallization temperature of the crystalline polyolefin resin. Forming a sheet from a mixture containing 50 to 10 parts by weight of a compound and 1.2 to 5 at least uniaxially the sheet.
A step of double stretching to obtain a stretched sheet having a thickness of 10 to 100 μm, and a step of embossing the stretched sheet to form a concavo-convex pattern in which the difference between the concave portion and the convex portion is 10 μm to 500 μm. A method of manufacturing a porous sheet having moisture permeability, comprising: 2. The manufacturing method according to claim 1, wherein the difference between the concave portion and the convex portion in the uneven pattern is 20 μm to 300 μm. 3. The moisture permeability of the porous sheet is 600-9.
The production method according to claim 1 or 2, which is 600 g / (m ² · day). 4. The production method according to claim 1, wherein the crystalline polyolefin resin is polypropylene, a blend of polypropylene and a propylene-ethylene copolymer, or a blend of polypropylene and polyethylene. 5. The method according to claim 1, wherein the organic compound is a mineral oil, a synthetic lubricating oil, a paraffin wax, or an ester of an aliphatic carboxylic acid and a polyhydric alcohol. 6. An organic compound which is miscible with 50 to 90 parts by weight of a crystalline polyolefin resin and the crystalline polyolefin resin under melting, and phase-separates below the crystallization temperature of the crystalline polyolefin resin. A sheet formed from a mixture containing 50 to 10 parts by weight of a compound is stretched at least uniaxially by 1.2 to 5 times to have a thickness of 10
Moisture permeability obtained by obtaining a stretched sheet having a thickness of up to 100 μm, and then subjecting the stretched sheet to embossing to form a concavo-convex pattern having a difference between recesses and protrusions of 10 μm to 500 μm on the stretched sheet. Having a porous sheet. 7. The mixture further comprises a crystal nucleating agent,
The porous sheet according to claim 6. 8. An absorbent article comprising a liquid-permeable front surface material, a leakproof back surface material, and an absorbent body disposed between these materials, and the back surface material according to claim 6. An absorbent article, characterized in that a porous sheet is used.