JPH0455072B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) The present invention particularly relates to a method for manufacturing a vapor-permeable and liquid-impermeable backsheet for disposable diapers that has excellent flexibility, tensile strength, and tear strength. (Prior Art) In recent years, disposable diapers mainly composed of a liquid-permeable sheet, a liquid absorber, and a liquid-impermeable back sheet have become extremely popular because they are convenient and easy to handle. Such a back sheet for disposable diapers must not only be liquid impermeable and vapor permeable, but also have moisture permeability, flexibility,
Functions such as tensile and tear strength are required. Conventionally,
Regarding the back sheet of disposable diapers, for example, a sheet made by melting a resin composition consisting of polyolefin and barium sulfate, forming a film, and then stretching it (Japanese Patent Laid-Open No.
60-185803), a film in which fine pores are created by stretching a film of a composition consisting of a polyolefin, a filler, and a liquid or wax-like hydrocarbon polymer (Japanese Patent Application Laid-open No. 149303/1989), or Sheet with specified physical properties (JP-A-57-205505
No. 59-69906), etc. have been proposed. However, the disposable diaper back sheet proposed above does not satisfy all the required functions. In particular, the back sheets of disposable diapers that have been given flexibility generally have relatively low tensile and tear strength, and therefore have the problem of breakage in practical use. (Problems to be Solved by the Invention) Therefore, in view of the above-mentioned problems, the object of the present invention is to provide a material having excellent physical properties such as liquid impermeability, vapor permeability, flexibility, and strength, especially tear strength in the width direction. An object of the present invention is to provide a back sheet for disposable diapers which is a porous sheet. (Means for Solving the Problems) As a result of intensive studies to solve the above problems, the present inventors have found that a porous sheet obtained by biaxially stretching a sheet-like material of a specified polyolefin resin composition is disposable. It was discovered that the material has desired physical properties suitable for use as a diaper backsheet, and the present invention was proposed. That is, the present invention has an air permeability of 500~
5000 seconds/100c.c., moisture permeability 1000-6000g/ ^m2・24hr,
This back sheet for disposable diapers is made of a biaxially stretched polyolefin sheet having a tensile strength of 50 to 400 Kg/cm ² , a tear strength of 50 to 250 g, a flexibility of 20 to 60 mm, and a thickness of 20 to 80 μm. Such a back sheet for disposable diapers of the present invention is made by forming a composition consisting of 100 parts by weight of a polyolefin resin, 50 to 400 parts by weight of a filler, and 0.1 to 10 parts by weight of a silicone oil and/or a polyglycerin fatty acid ester surfactant into a sheet. After molding, the stretching ratio is 1.1 to 2.5 times.
It can be obtained by a method of stretching in axial and biaxial directions. Specifically, the back sheet for disposable diapers of the present invention has an air permeability of 500 to 5000 based on JIS P8117 method.
seconds/100c.c., preferably 600-3000 seconds/100c.c., JIS
Moisture permeability at 40℃ and 90% relative humidity based on Z0208 method is 1000-6000g/ ^m2・24hr, preferably
3000~5000g/ ^m2・24hr, tensile strength based on JIS P8113 method is 50~400Kg/ ^cm2 , preferably 70~380
Kg/ ^cm2 , tear strength based on JIS L1085A-1 method
50-250g, preferably 70-230g, flexibility based on JIS L1079 Clark method 20-60mm, preferably 20
~50mm and thickness 20~80μ, preferably 20~
It is important that it is 60μ. That is, as a back sheet for disposable diapers, the air permeability of the sheet is
Greater than 5000 seconds/100c.c. or moisture permeability 1000g/
If it is smaller than ^m2・24hr, it is insufficient to prevent stuffiness when wearing disposable diapers, and the air permeability is smaller than 500 seconds/100 c.c. or the moisture permeability is too low.
If it is larger than 6000g/m ² ·24hr, there is a fear of liquid leakage, and at the same time physical properties such as tear strength deteriorate, which is not preferable. Also, if the tensile strength is less than 50Kg/cm ² or the tear strength is less than 50g, it will break easily.On the contrary, it is desirable that the tensile strength and tear strength are high, but if the tensile strength is greater than 400Kg/cm ² ,
If the tear strength is greater than 250g, the moisture permeability and flexibility will be impaired, resulting in a decrease in the fit to the skin when worn. In particular, the disposable diaper back sheet of the present invention has tensile strength and tear strength in uniaxial and biaxial directions of 50 kg/cm ² respectively.
It is preferable that the weight is 50 g or more since this improves the releasability of the tape attached to the backsheet. In addition, if the sheet of the present invention has a flexibility less than 20 mm, the strength will be significantly reduced and defects such as easy tearing will occur, and if the flexibility is more than 60 mm, it will feel stiff. This is undesirable because the fit during installation deteriorates. Furthermore, if the sheet of the present invention is thinner than 20μ, it will have poor strength, and if it is thicker than 80μ, it will have poor flexibility, making it unsuitable as a back sheet for disposable diapers. As for other physical properties, it is preferable that the water pressure resistance according to JIS L1092 method is 5000 mmH ₂ O or more. The back sheet for disposable diapers of the present invention having the above-mentioned physical properties can be produced by forming a composition comprising a polyolefin resin, a filler, a silicone oil and/or a polyglycerin fatty acid ester surfactant into a sheet shape, and then biaxially stretching the composition. Suitably obtained. As the polyolefin resin used in the present invention,
Homopolymers or copolymers of olefins such as ethylene, propylene, butene-1, etc. can be used without particular restriction, but medium-density polyethylene and linear low-density polyethylene are particularly preferred, especially those with low density.
0.910-0.940g/ ^cm2 with melt flow index (MFI) of 0.1-10g/10 min, preferably 0.1-5g/cm2.
Ten minute linear low density polyethylene is preferably used. In addition, in the present invention, it is also possible to add and mix a small amount of one or more of, for example, high density polyethylene, polypropylene, polybutene-1, etc. to the above-mentioned linear low density polyethylene, and the addition,
The thickness of the stretched sheet obtained by mixing can be adjusted, and in particular, the physical properties such as tensile/tear strength and flexibility can be adjusted as desired. As the filler used in the present invention, calcium carbonate is generally preferred, and is generally less than 5μ, particularly 0.1 to
Used as a powder with an average particle size of about 3μ.
If a filler having an average particle diameter that is too large is used, the resulting stretched sheet will have poor pore density and poor water resistance. In addition, when a filler having an average particle diameter that is too small is used, stretching tends to be uneven and a good porous sheet cannot be obtained. The blending ratio of filler is
The amount is 50 to 400 parts by weight, preferably 60 to 300 parts by weight, based on 100 parts by weight of the polyolefin resin. If it is less than 50 parts by weight, the resulting porous sheet will have fewer communicating pores, resulting in lower moisture permeability. Moreover, if it exceeds 400 parts by weight, it becomes difficult to form and stretch a sheet-like product. The silicone oil used in the present invention is generally not particularly limited as long as it has heat resistance to the extent that it does not volatilize at the melting temperature of the polyolefin resin, but has a viscosity of 50 to 500,000 centistrokes (cst), preferably 500 to 100,000 cst For example, polydimethylsiloxane, polymethylphenylsiloxane, etc. are preferably used.
In addition, the polyglycerin fatty acid ester surfactant is an ester compound of polyglycerin and fatty acid obtained by dehydration condensation of glycerin, and the degree of condensation of glycerin is usually 3 to 10.
Higher fatty acids, such as those partially or completely esterified with _C12 to _C17 carboxylic acids, have an HLB of 6
Below, those of 3 or less are preferably used in order to obtain good volatility. In the present invention, by blending at least one of the above silicone oil and polyglycerol fatty acid ester surfactant with the above resin and filler, a stretched sheet having a uniform predetermined thickness can be obtained satisfactorily. Therefore, it is possible to obtain a sheet having desired physical properties. The amount of the silicone oil and/or polyglycerol fatty acid ester surfactant is 0.1 to 10 parts by weight, particularly 1 to 10 parts by weight, based on 100 parts by weight of the polyolefin resin.
5 parts by weight is preferred; if it is less than 0.1 parts by weight, uniform whitening will not occur during uniaxial stretching, so-called stretching unevenness will occur, and if it is more than 10 parts by weight, extrusion moldability will become non-uniform. It is difficult to obtain a sheet material with a certain thickness. In the present invention, the polyolefin resin composition is generally prepared using a high-speed stirring (mixing) machine such as a Henschel mixer, after adding and mixing silicone oil and/or polyglycerin fatty acid ester surfactant to the filler. A silicone oil and/or a polyglycerol fatty acid ester-based interface is added to a mixture of a polyolefin resin powder or pellets and a filler using the above-mentioned mixer. After adding and mixing the activator,
This is done by kneading using a mixing roll or screw extruder. In such preparations, small amounts of stabilizers,
Pigments or stearic acid and its metal salts for imparting fluidity can be mixed simultaneously or separately. A method of biaxially stretching the above-mentioned polyolefin resin composition after forming it into a sheet is to form a sheet by, for example, an inflation molding method, an extrusion molding method using a tie die or an annular die, and then, for example, by a roll stretching method. After uniaxial stretching, a method of biaxial stretching using a tenter stretching machine, an air inflation method, a mandrel stretching method, etc. can be used without particular limitation. Therein, the polyolefin resin composition was formed into a cylindrical sheet by an air inflation method, and then the sheet was stretched in the uniaxial (longitudinal) direction by a roll stretching method, and then in the biaxial (horizontal) direction by a mandrel stretching method. (1) As a method for manufacturing unstretched raw sheets, the inflation method for manufacturing cylindrical sheets is slightly inferior to the T-die method, but it is a simple die method. By rotating the roll, a final product with good winding appearance and less edge loss can be obtained. (2) As a biaxial stretching method, the cylindrical stretching method has great economic merits, such as lower equipment costs and lower utility than the tenter method. The following two points are particularly preferably adopted. Uniaxial stretching is performed below the softening point of polyolefin resin.
It is stretched 1.1 to 2.5 times, preferably 1.2 to 2 times. In the mandrel stretching method, the stretching temperature is 1.1 to 2.5 times, preferably below the softening point of the polyolefin resin.
Stretch 1.2 to 2 times. The biaxially stretched sheet may be slit as is and then wound up, or the sheet may be heat treated to improve its dimensional stability and then slit and wound up. (Effects) The sheet thus obtained has the following properties: Air permeability 500-5000 seconds/100c.c. Moisture permeability 1000-6000g/m2 ^24hr Tensile strength 50Kg/ ^cm2-400Kg / ^cm2 Tear strength 50g-250g Flexibility A material with a thickness of 20 to 60 mm and a thickness of 20 to 80 μm has good air permeability, moisture permeability, and water resistance, and is flexible and has high tensile strength and tear strength in both the longitudinal (MD) and transverse (TD) directions. This sheet has excellent strength and is suitable as a back sheet for disposable diapers. (Example) Examples and comparative examples will be shown below, and their physical properties were measured by the method shown below. Tensile strength and elongation: Measured according to JIS P8113 (tensile speed 200mm/mm) Tear strength: Measured according to JIS L1085A-1 method Moisture permeability: 40℃, relative humidity 90%, JIS Z0208
Water resistance: Measured according to JIS L1092B method (hydrostatic pressure method) Air permeability: Measured according to JIS P8117 Flexibility: Measured according to JIS L1079 method (Clark bending test method) Tape removability: Sellotape with a width of 19 mm was applied to the sheet in each of the MD and TD directions, and the state of peeling when quickly peeled off was evaluated based on the following criteria. ○: No tearing in any direction. Δ: Partial tearing occurs in either direction. ×: Tears occur. Diaper fitting test; adult diaper (commercially available)
Cut out the back sheet as shown in Figure 1, weld a sample sheet to each trace,
We conducted a wetness test. (Evaluation) Three adults wore the sheets and evaluated whether they felt stuffiness using the non-perforated back sheet as a standard as follows. ○: Effective in preventing stuffiness (all 3 people) △: 〃 (1 to 2 people) ×: 〃 None Example 1 and Comparative Examples 1 and 2 Linear low-density polyethylene (manufactured by Sumitomo Chemical Co., Ltd., Sumikasen L FA201- 0, MFI = 2) 100 parts by weight, 120 parts by weight of heavy calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., Whiten SSB (red), particle size 1.2μ) and silicone oil (manufactured by Toshiba Silicon Co., Ltd., TSF-
451, viscosity 10,000 cst) was mixed in a super mixer and pelletized in a twin screw extruder. Screw this pellet with a diameter of 50
Using an inflation extruder with mmφ and die diameter of 150mmφ, the thickness is 50μ and the folding diameter is 380m/m under the following conditions.
A cylindrical sheet was formed. (Extrusion conditions) - Cylinder temperature: 160, 170, 175℃ - Adapter: 180℃ - Die: 180℃ - Screw rotation speed: 60rpm - Take-up speed: 10m/min Next, the folded sheet is stretched at 60℃ using a roll stretching machine. It was uniaxially stretched to 1.4 times. Furthermore, this uniaxially stretched sheet was biaxially stretched using a biaxial stretching machine having the following structure. That is, as a biaxial stretching device, the preheating section and the widening stretching section are
The mandrel is suspended, the mandrel is externally heated by an air ring, and the stretched sheet is taken up by a take-up roll. With this biaxial stretching device, the fold diameter after uniaxial stretching is 350.
A sheet of 1.0 mm thick was stretched in the transverse direction at 80° C. by a factor of 1.4, cooled, and rolled up. The obtained sheet had a thickness of 40 μm, and the actual stretching ratio of the sheet was 1.4×1.3 times. In addition, the thickness of the die lip was changed in Comparative Examples 1 and 2, and inflation raw sheets with a thickness of 20 μm in Comparative Example 1 and 120 μm in Comparative Example 2 were similarly uniaxially and biaxially stretched. . Table 1 shows the results of measuring the properties of the obtained sheet. Comparative Examples 3 and 4 The same composition as in Example 1 was extruded by inflation under the same conditions as in Example 1, and then uniaxially stretched to 1.4 times and 2.6 times, biaxially stretched to 1.0 times, and wound up. . The obtained sheet width is 350 when it is 1.4 times
mm, it was 315 mm when magnified 2.6 times. The properties of the obtained sheet are shown in Table 1. Comparative Examples 5 and 6 Table 1 shows the physical properties of commercially available breathable backsheets for disposable diapers and non-porous backsheets for disposable diapers. From the results of Example 1 and Comparative Examples 1 to 6, Example 1 has superior tensile strength in the transverse direction and tear strength in the longitudinal direction compared to the commercially available breathable backsheet (Comparative Example 5).
When a tape peel test was carried out, Comparative Example 5 was easily torn in the longitudinal direction by the tape peel test, whereas Example 1 only stretched the sheet and did not peel and tear between the tape and the sheet. Moreover, Example 1 clearly had a stuffiness prevention effect in the diaper wearing test compared to Comparative Examples 6 and 3. Further, in Comparative Examples 1 and 2, when the sheet thickness was thin, a decrease in strength was observed, and when the sheet was thick, the flexibility was poor. In Comparative Example 4, the tape releasability was poor due to the high stretching ratio.

[Table] Examples 2, 3, 4 and Comparative Examples 7, 8 100 parts by weight of linear low-density polyethylene (manufactured by Sumitomo Chemical Co., Ltd., Sumikasen L-FA201-0, MFR=2) and heavy calcium carbonate (Shiraishi Silicone oil (made by Toshiba Silicone Co., Ltd.) with varying amounts of Whiten SSB (red), particle size 1.2μ, made by Calcium Co., Ltd.
After adding 3 parts by weight of TSF-451 (viscosity 6000cst) and longitudinally stretching at 60°C in the same manner as in Example 1,
The cylindrical shape was horizontally stretched along a mandrel at 80°C to a ratio of 1.4 times. The results obtained are shown in Table-2.

[Table] Examples 5, 6, 7 and Comparative Examples 9, 10 90 parts by weight of linear low-density polyethylene (manufactured by Sumitomo Chemical Co., Ltd., Sumikasen L, MFR=2) and high-density polyethylene (manufactured by Showa Denko Co., Ltd.) , Shorex N5008,
MFR=0.9) 100 parts by weight of a resin mixture, 100 parts by weight of heavy calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., Whiten SSB (red) 1.2μ) and silicone oil (manufactured by Toshiba Silicone Corporation, TSF) −433, viscosity
A composition consisting of 3 parts by weight (450 cst) was granulated in the same manner as in Example 1, and after forming an extruded sheet, the uniaxial stretching ratio was varied, and the composition was further biaxially stretched in the same manner as in Example 1. The results obtained are shown in Table-3. From the results obtained, the stretched sheet obtained in Comparative Example 9 had somewhat poor thickness accuracy and low moisture permeability.
Examples 5, 6, and 7 all had good strength and moisture permeability. Comparative Example 10 had poor tear strength and tape removability. Examples 8 and 9 and Comparative Examples 11 and 12 After extrusion molding in the same manner as in Example 5 at the same blending ratio,
After keeping the uniaxial stretching constant at 1.5 times at 60°C, keeping the diameter of the preheated part of the cylindrical mandrel constant, and increasing the ratio of the maximum width part of the mandrel widening part to 1.6 times, 2.2 times, and 3.4 times, Lateral stretching was performed. The results are shown in Table-3.
In Examples 8 and 9, stretched sheets with good properties were obtained, but with a mandrel 3.4 times larger than that in Comparative Example 12, stretching was difficult and the sheets broke immediately. Also, comparative example 11
was a sheet that was only uniaxially stretched, and this sheet had low air permeability and moisture permeability.

【table】

[Table] Examples 10 to 14 and Comparative Examples 13 to 15 Calcium carbonate (Shiraishi Manufactured by Calcium Co., Ltd.
Add 120 parts by weight of Whiten SSB (particle size 1.2μ),
Furthermore, silicone oil (manufactured by Toshiba Silicone Corporation,
TSF451−10000), decaglyceryl decaisostearate (manufactured by Nikko Chemicals Co., Ltd., Decagrin 10−
Biaxial stretching was carried out in the same manner as in Example 1 while changing the amount of IS) added. The results are shown in Table-4. Comparative example 13
In the case of uniaxial stretching, stretching unevenness was large and a uniformly whitened sheet could not be obtained. Also, comparative example
In Nos. 14 and 15, the thickness accuracy was poor during extrusion, and breakage occurred at the biaxially stretched portion, making it impossible to obtain a biaxially stretched sheet.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of the diaper used in the diaper wearing test.

Claims (1)

[Claims] 1 100 parts by weight of polyolefin resin, 50 to 400 parts by weight of calcium carbonate, and silicone oil and/or polyglycerin fatty acid ester surfactant
1. A method for producing a backsheet for disposable diapers, which comprises forming a composition containing 0.1 to 10 parts by weight into a sheet, and then stretching the sheet in uniaxial and biaxial directions at a stretching ratio of 1.1 to 2.5 times.