STRETCHED POROUS FILM AND MANUFACTURING METHOD THEREFOR

Abstract

An object of the present invention is to provide a stretched porous film having all of air permeability, water resistance, and flexibility. A stretched porous film in accordance with an embodiment of the present invention contains a resin composition containing a specific polyethylene-based resin and a thermoplastic elastomer at a certain mass ratio, and has a water vapor transmission rate of not less than 1400 g/m.Math..24 h.

Claims

1. A stretched porous film comprising a resin composition, the resin composition containing: a polyethylene-based resin having a density of not less than 0.900 g/cm.sup.3 and not more than 0.940 g/cm.sup.3; not less than 1.0 parts by mass and not more than 16 parts by mass of a thermoplastic elastomer relative to 100 parts by mass of the polyethylene-based resin; and an inorganic filler, the stretched porous film having a water vapor transmission rate of not less than 1400 g/m.sup.2.Math.24 h as measured at 40 C. and at a relative humidity of 60% in accordance with ASTM E96.

2. The stretched porous film as set forth in claim 1, wherein the thermoplastic elastomer is an olefin-based elastomer and/or a styrene-based elastomer.

3. The stretched porous film as set forth in claim 1, wherein the stretched porous film has a strength in a machine direction of not less than 0.3 N/25 mm and not more than 2.5 N/25 mm as measured when pulling the stretched porous film in the machine direction in accordance with HS K 7127 with a chuck-to-chuck distance of 50 mm and at a pulling speed of 200 mm/min has increased the chuck-to-chuck distance by 5%.

4. The stretched porous film as set forth in claim 1, wherein the resin composition has a melt mass flow rate of not less than 2.0 g/10 min as measured at 190 C. in accordance with JIS K 7210.

5. The stretched porous film as set forth in claim 1, wherein the stretched porous film has an air permeability of not less than 300 sec/100 ml and not more than 2000 sec/100 ml as measured by Oken-type air permeability tester method in accordance with JIS P 8117.

6. The stretched porous film as set forth in claim 1, wherein the resin composition further contains a paraffin-based oil.

7. A method for producing a stretched porous film, comprising: a mixing step of mixing (i) a polyethylene-based resin having a density of not less than 0.900 g/cm.sup.3 and not more than 0.940 g/cm.sup.3, (ii) not less than 1.0 parts by mass and not more than 16 parts by mass of a thermoplastic elastomer relative to 100 parts by mass of the polyethylene-based resin, and (iii) an inorganic filler to prepare a resin composition; a forming step of forming the resin composition into the form of a film; and a porosification step of stretching, at least in a machine direction, the film obtained by the forming step to porosify the film.

8. The method as set forth in claim 7, wherein a stretch magnification at which the film is stretched in the machine direction in the porosification step is represented by the following formula II:
1.4Y0.075X+2.5 (II) where X represents a mixing ratio (parts by mass) of the thermoplastic elastomer to 100 parts by mass of the polyethylene-based resin and Y represents a stretch magnification (times).

Description

EXAMPLES

[0070] The following description will discuss the present invention in more detail based on Examples. Note, however, that the present invention is not limited to such Examples.

[0071] [Evaluation Method]

[0072] Physical property values of each of stretched porous films in accordance with the Examples and the Comparative Examples, which will be described later, were measured in the following manner.

[0073] (1) Melt Mass Flow Rate

[0074] A melt mass flow rate of the resin composition was measured by the A method in accordance with JIS K 7210, selecting 190 C. as a measurement temperature. Note that the melt mass flow rate will be hereinafter referred to as MI (melt index).

[0075] (2) Weight Per Unit Area

[0076] A sample in a size of 10 cm10 cm was cut out from the stretched porous film, and a mass of the sample was measured with use of a balance. From an area and the mass of the sample, a weight per unit area was calculated.

[0077] (3) Water Vapor Transmission Rate

[0078] Ten samples each in a size of 10 mm10 mm were taken from the stretched porous film. Water vapor transmission rates of the respective samples were measured at 40 C. and a relative humidity of 60% for a measurement time of 24 hours under the conditions of the pure water method in accordance with ASTM E96, and an average value of the water vapor transmission rates was calculated.

[0079] (4) Air Permeability

[0080] An air permeability was measured by the Oken-type air permeability tester method in accordance with JIS P 8117.

[0081] (5) Strength at 5% Stretch

[0082] A sample of 25 mm in width and 150 mm in length in a machine direction was taken from the stretched porous film in accordance with JIS K 7127. As a strength at 5% stretch, a strength of the sample was measured when the sample was stretched by 5% by being pulled in the machine direction with a chuck-to-chuck distance of 50 mm and at a pulling speed of 200 mm/min. That is, a stress in the machine direction when the chuck-to-chuck distance increased by 2.5 mm was measured.

[0083] (6) Thermal Shrinkage Rate in Machine Direction

[0084] A sample in a size of 15 cm15 cm was taken from the stretched porous film. Lines were marked on the sample such that a distance between the marked lines along the machine direction was 10 cm. The sample was left for 24 hours at 50 C. and then cooled down to a room temperature, and a distance between the marked lines was measured. A thermal shrinkage rate in the machine direction was calculated by the following formula (formula I).

Thermal shrinkage rate in the machine direction (%)={(10 cmDistance between the marked lines after cooling (cm))/10 cm}100 (I)

[0085] (7) Blocking Strength

[0086] Two samples each in a size of 25 mm80 mm were taken from the stretched porous film. The samples were placed so as to overlap with each other by 40 mm to be used as a test piece. In a constant temperature/humidity chamber, the test piece was left for 24 hours at a temperature of 40 C. and a relative humidity of 70% in a state where a load of 10 kg was applied to an overlapping portion of the test piece. After 24 hours, the test piece was cooled down to a room temperature, and a blocking strength was determined with use of a tension testing machine.

[0087] [Components Used]

[0088] A: Linear low-density polyethylene [manufactured by The Dow Chemical Company, product name: DOWLEX 2047, density: 0.917 g/cm.sup.3, MI: 2.3 g/10 min]

[0089] B: Linear low-density polyethylene [manufactured by The Dow Chemical Company, product name: DOWLEX 2035G, density: 0.919 g/cm.sup.3, MI: 6.0 g/10 min]

[0090] C: Linear low-density polyethylene [manufactured by The Dow Chemical Company, product name: DOWLEX 2036P, density: 0.935 g/cm.sup.3, MI: 2.5 g/10 min]

[0091] D: Linear low-density polyethylene [manufactured by The Dow Chemical Company, product name: DOWLEX 2045G, density: 0.920 g/cm.sup.3, MI: 1.0 g/10 min]

[0092] E: Very-low-density polyethylene [manufactured by Tosoh Corporation, product name: Lumitac 22-7, density: 0.900 g/cm.sup.3, MI: 2.0 g/10 min]

[0093] F: Very-low-density polyethylene [manufactured by Tosoh Corporation, product name: Lumitac 43-1, density: 0.905 g/cm.sup.3, MI: 8.0 g/10 min]

[0094] G: Very-low-density polyethylene [manufactured by Mitsui Chemicals, Inc., product name: TAFMER A-4085S, density: 0.885 g/cm.sup.3, MI: 3.6 g/10 min]

[0095] H: High-density polyethylene [manufactured by Tosoh Corporation, product name: Nipolon Hard 4200, density: 0.961 g/cm.sup.3, MI: 2.3 g/10 min]

[0096] I: High-density polyethylene [manufactured by Japan Polyethylene Corporation, product name: NOVATEC HD HF560, density: 0.963 g/cm.sup.3, MI: 7.0 g/10 min]

[0097] J: Branched low-density polyethylene [manufactured by Du Pont-Mitsui Polychemicals Co., Ltd., product name: Mirason 16P, density: 0.917 g/cm.sup.3, MI: 3.7 g/10 min]

[0098] K: Branched low-density polyethylene [manufactured by Asahi Kasei Chemicals Corporation, product name: L1850K, density: 0.918 g/cm.sup.3, MI: 6.8 g/10 min]

[0099] L: Thermoplastic elastomer [JSR Corporation, product name: EXCELINK 1301 N, density: 0.880 g/cm.sup.3, MI: 7.0 g/10 min]

[0100] M: Thermoplastic elastomer [KURARAY PLASTICS CO., Ltd., product name: EARNESTON JG2ONS, density: 0.890 g/cm.sup.3, MI: 2.6 g/10 min]

[0101] N: Thermoplastic elastomer [KURARAY PLASTICS CO., Ltd., product name: EARNESTON JS2ON, density: 0.890 g/cm.sup.3, MI: 15 g/10 min]

[0102] O: Thermoplastic elastomer [KURARAY CO., LTD., product name: SEPTON 2063, density: 0.880 g/cm.sup.3, MI: 0.4 g/10 min]

[0103] P: Calcium carbonate [manufactured by IMERYS Minerals, product name: FL-520]

[0104] Q: Barium sulfate [manufactured by Sakai Chemical Industry Co., Ltd., product name: BARIACE B-54]

[0105] R: Additive [a mixture of 50% by mass of titanium oxide (manufactured by HUNTSMAN, product name: TR28), 20% by mass of a hindered phenol-based thermal stabilizer (manufactured by Ciba Japan K.K., product name: IRGANOX3114), and 30% by mass of a phosphorus-based thermal stabilizer (manufactured by Ciba Japan K.K., product name: IRGAFOS 168)].

Example 1

[0106] Polyethylenes, a thermoplastic elastomer, an inorganic filler, and an additive written in Tables 1 and 2 were mixed together to prepare a resin composition. The resin composition was granulated, and then film formation was carried out.

[0107] The granulation (preparation of pellets) was carried out in the following manner. With use of a 30-mm diameter twin-screwed extruder having a vent, the resin composition was extruded into the form of strands at a cylinder temperature of 180 C., and was cooled in a water tank. Then, the resin composition thus extruded was cut into pieces of approximately 5 mm and dried to prepare pellets.

[0108] Subsequently, a film was formed out of the pellets with use of a 400-mm diameter T-die film formation machine. Note that a lip clearance was 1.5 mm, a die temperature was 230 C., an air gap was 105 mm, a take-off speed was 10 m/min, and a cast roller temperature was 20 C. The film thus obtained was further subjected to uniaxial stretching (stretch magnification: 1.8 times) only in a machine direction with use of a roller stretching machine which had been set to 40 C., and then was subjected to in-line annealing with use of a heat-setting roller which has been set to 90 C. (heat fixation time: 4 seconds). A thermal shrinkage rate in the machine direction when the heat fixation was carried out was 8%.

Examples 2 through 18 and Comparative Examples 1 through 6

[0109] In Examples 2 through 18 and Comparative Examples 1 through 6, a film was formed in the same manner as Example 1 except that a mixing ratio of components or a stretching condition (stretch magnification or heat fixation temperature) was changed as shown in Table 1.

TABLE-US-00001 TABLE 1 Density of Polyethylene-based resin: mixing ratio entire (% by mass) polyethylene- LLDPE VLDPE HDPE LDPE based resin A B C D E F G H I J K (g/cm.sup.3) Ex. 1 30 42 28 0.918 Ex. 2 31 45 24 0.918 Ex. 3 29 41 30 0.918 Ex. 4 31 44 25 0.906 Ex. 5 31 45 24 0.906 Ex. 6 31 45 24 0.918 Ex. 7 73 27 0.917 Ex. 8 31 45 24 0.918 Ex. 9 31 45 24 0.918 Ex. 10 31 45 24 0.918 Ex. 11 44 28 28 0.922 Ex. 12 46 27 27 0.929 Ex. 13 30 43 27 0.907 Ex. 14 30 43 27 0.907 Ex. 15 31 45 24 0.918 Ex. 16 31 45 24 0.918 Ex. 17 31 45 24 0.918 Ex. 18 29 41 30 0.918 Comp. 31 45 24 0.918 Ex. 1 Comp. 31 45 24 0.918 Ex. 2 Comp. 31 45 24 0.951 Ex. 3 Comp. 75 25 0.893 Ex. 4 Comp. 31 45 24 0.918 Ex. 5 Comp. 31 45 24 0.918 Ex. 6

TABLE-US-00002 TABLE 2 Raw material: mixing Resin Thermoplastic ratio (parts by mass) com- elastomer Calcium posi- Stretch- mixing ratio carbon- Barium Addi- tion MI ing (parts by mass) ate sulfate tive (g/10 condi- L M N O P Q R min) tion Ex. 1 8.0 135 2.0 2.3 *1 Ex. 2 4.0 124 2.0 2.3 *1 Ex. 3 11 142 2.0 2.3 *1 Ex. 4 4.0 135 2.0 2.2 *1 Ex. 5 2.0 130 2.0 2.5 *1 Ex. 6 3.0 125 2.0 3.2 *1 Ex. 7 5.0 143 2.0 2.5 *1 Ex. 8 12 115 2.0 2.4 *1 Ex. 9 4.0 124 2.0 2.6 *1 Ex. 10 4.0 124 2.0 2.3 *2 Ex. 11 5.0 149 2.0 2.4 *1 Ex. 12 5.0 143 2.0 2.4 *1 Ex. 13 8.0 134 2.0 2.2 *1 Ex. 14 8.0 134 2.0 2.3 *1 Ex. 15 4.0 124 2.0 2.3 *3 Ex. 16 9.0 115 2.0 2.7 *1 Ex. 17 2.0 6.0 120 2.0 2.8 *1 Ex. 18 11 142 2.0 2.3 *3 Comp. 115 2.0 2.5 *1 Ex. 1 Comp. 18 155 2.0 2.5 *1 Ex. 2 Comp. 4.0 124 2.0 2.3 *1 Ex. 3 Comp. 4.0 135 2.0 2.0 *4 Ex. 4 Comp. 4.0 124 2.0 1.0 *1 Ex. 5 Comp. 4.0 124 2.0 2.3 *5 Ex. 6

[0110] Note that Polyethylene-based resin: mixing ratio (% by mass) indicates a mixing ratio of polyethylenes to 100% by mass of the polyethylene-based resin contained in the resin composition. Mixing ratio (parts by mass) of the thermoplastic elastomer indicates a mixing ratio of the thermoplastic elastomer relative to 100 parts by mass of the polyethylene-based resin. Further, L, M, and N used in the present Examples are each a thermoplastic elastomer mixture containing not only a thermoplastic elastomer but also a component (e.g., a paraffin-based oil) other than the thermoplastic elastomer. As such, the mixing ratio of each thermoplastic elastomer in Table 2 indicates a mixing ratio of a thermoplastic elastomer component calculated on the basis of a published mixing ratio of each product. A mixing ratio of each of calcium carbonate, barium sulfate, and an additive written in Table 2 is relative to 100 parts by mass of a total of the polyethylene-based resin and the thermoplastic elastomer.

[0111] Further, a stretching condition *1 indicates a stretch magnification of 1.8 times and a heat fixation temperature of 90 C. A stretching condition *2 indicates a stretch magnification of 2.3 times and a heat fixation temperature of 90 C. A stretching condition *3 indicates a stretch magnification of 3.2 times and a heat fixation temperature of 90 C. A stretching condition *4 indicates a stretch magnification of 1.8 times and a heat fixation temperature of 60 C. A stretching condition *5 indicates a stretch magnification of 1.3 times and a heat fixation temperature of 90 C.

[0112] [Results]

[0113] The stretched porous films obtained in Examples 1 through 18 and Comparative Examples 1 through 6 were measured in terms of weight per unit area, water vapor transmission rate, air permeability, strength at 5% stretch, and thermal shrinkage rate. Measured results are shown in Table 3.

TABLE-US-00003 TABLE 3 Physical properties of film Weight Water Air per vapor per- Thermal unit transmis- meabil- Strength at shrinkage area sion rate ity 5% stretch rate (g/m.sup.2) (g/m.sup.2 .Math. 24 h) (s/100 ml) (N/25 mm) (%) Note Ex. 1 18 1,850 600 1.3 2.8 Ex. 2 18 2,050 550 1.7 2.0 Ex. 3 15 1,450 1,050 0.8 3.0 Ex. 4 18 1,750 600 1.3 3.0 Ex. 5 18 1,950 500 1.5 3.0 Ex. 6 18 1,450 1,100 1.8 2.0 Ex. 7 18 1,900 500 1.2 3.0 Ex. 8 18 2,000 500 2.0 2.5 Ex. 9 18 1,750 600 1.4 1.6 Ex. 10 18 2,550 400 1.9 1.5 Ex. 11 18 2,250 450 1.3 2.5 Ex. 12 18 1,550 950 1.7 3.2 Ex. 13 18 1,500 1,050 1.5 4.0 Ex. 14 18 1,950 500 0.8 3.0 Ex. 15 18 2,600 300 2.8 1.5 Ex. 16 18 1,850 600 2.2 2.0 Ex. 17 18 1,700 650 1.8 2.0 Ex. 18 18 1,700 650 2.4 2.5 Comp. 18 1,950 500 2.9 2.0 Ex. 1 Comp. 18 *6 Ex. 2 Comp. 18 3,400 100 2.9 3.2 Ex. 3 Comp. 18 2,600 250 0.7 13.8 Ex. 4 Comp. 18 1,200 1,300 1.8 2.7 Ex. 5 Comp. 18 200 4,000 1.6 2.0 Ex. 6 Note that Note *6 indicates that a draw resonance occurred.

[0114] The stretched porous films of Examples 1 through 18 each exhibited a good water vapor transmission rate of not less than 1400 g/ m.sup.2.Math.24 h and had a good texture. Further, the stretched porous films of Examples 1 through 18 each had a low value of strength at 5% stretch and a low value of thermal shrinkage rate.

[0115] Note that a comparison of Examples 1 through 3 indicates that as the mixing ratio of the thermoplastic elastomer decreases, the water vapor transmission rate increases and the air permeability and the thermal shrinkage rate decrease. Further, a comparison of Examples 4 and 5 also indicates that as the mixing ratio of the thermoplastic elastomer decreases, the water vapor transmission rate increases and the air permeability decreases.

[0116] A comparison of Example 2 and Examples 6 and 9 indicates that Example 2, which had a lower melt mass flow rate, had a higher water vapor transmission rate and a lower air permeability.

[0117] A comparison of Examples 2 and 10 indicates that Example 10, which had a higher stretch magnification, had a higher water vapor transmission rate, a lower air permeability, and a lower thermal shrinkage rate.

[0118] A comparison of Examples 3 and 18 indicates that, as with the comparison of Examples 2 and 10, Example 18, which had a higher stretch magnification, had a higher water vapor transmission rate, a lower air permeability, and a lower thermal shrinkage rate.

[0119] Examples 11 and 12 used respective polyethylene resins that differed from each other in density. Polyethylene having a density of 0.961 g/cm.sup.3 was used in Example 12. Example 12, in which the polyethylene having the higher density was added, had a lower water vapor transmission rate and a higher air permeability than Example 11. Further, Example 12 had a higher strength at 5% stretch. However, there is no problem with these results, and Example 12 was excellent in heat resistance.

[0120] Examples 13 and 14 used respective different inorganic fillers. Barium sulfate has a high specific gravity, and a volume ratio of the inorganic filler per unit volume of the resin composition was therefore small. Accordingly, fewer holes were formed in Example 13 than in Example 14. As such, Example 14 had a higher water vapor transmission rate and a lower air permeability than Example 13. Further, Example 13 had a higher volume ratio of the resin component, and therefore had a higher stress during stretching. Accordingly, Example 13 had a higher strength at 5% stretch.

[0121] Note that Example 15, which had a stretch magnification not satisfying the formula II, had a higher strength at 5% stretch than Examples 1 through 14 and 16 through 18 each of which had a stretch magnification satisfying the formula II. However, Example 15 exhibited a better strength at 5% stretch than Comparative Examples.

[0122] A comparison of Examples 8 and 16 indicates that Example 8, in which the amount of the thermoplastic elastomer was higher than Example 16, had a higher water vapor transmission rate and a lower air permeability. Further, due to the increase in the amount of the thermoplastic elastomer, Example 8 had a lower strength at 5% stretch. A comparison of Examples 16 and 17 indicates that Example 17, in which a paraffin-based oil was contained, had a lower strength at 5% stretch.

[0123] Comparative Example 1 used no thermoplastic elastomer. This resulted in a stretched porous film having a higher strength at 5% stretch and poor flexibility.

[0124] In Comparative Example 2, the thermoplastic elastomer was used in a large amount, so that a draw resonance occurred. This inhibited evaluation of physical properties.

[0125] In Comparative Example 3, a polyethylene-based resin which as a whole had a density of more than 0.940 g/cm.sup.3 was used. This resulted in a stretched porous film having a higher strength at 5% stretch and poor flexibility. In Comparative Example 4, a polyethylene-based resin having a density of less than 0.900 g/cm.sup.3 was used. This resulted in a stretched porous film having a high thermal shrinkage rate.

[0126] In each of Comparative Examples 5 and 6, a stretched porous films obtained had a low water vapor transmission rate and thus had a poor air permeability.

[0127] Aspects of the present invention can also be expressed as follows:

[0128] [1] A stretched porous film containing a resin composition, the resin composition containing: a polyethylene-based resin having a density of not less than 0.900 g/cm.sup.3 and not more than 0.940 g/cm.sup.3; not less than 1.0 parts by mass and not more than 16 parts by mass of a thermoplastic elastomer relative to 100 parts by mass of the polyethylene-based resin; and an inorganic filler, the stretched porous film having a water vapor transmission rate of not less than 1400 g/m.sup.2.Math.24 h as measured at 40 C. and at a relative humidity of 60% in accordance with ASTM E96.

[0129] [2] The stretched porous film as set forth in [1], wherein the thermoplastic elastomer is an olefin-based elastomer and/ or a styrene-based elastomer.

[0130] [3] The stretched porous film as set forth in [1] or [2], wherein the stretched porous film has a strength in a machine direction of not less than 0.3 N/25 mm and not more than 2.5 N/25 mm as measured when pulling the stretched porous film in the machine direction in accordance with JIS K 7127 with a chuck-to-chuck distance of 50 mm and at a pulling speed of 200 mm/min has increased the chuck-to-chuck distance by 5%.

[0131] [4] The stretched porous film as set forth in any one of [1] through [3], wherein the resin composition has a melt mass flow rate of not less than 2.0 g/10 min as measured at 190 C. in accordance with JIS K 7210.

[0132] [5] The stretched porous film as set forth in any one of [1] through [4], wherein the stretched porous film has an air permeability of not less than 300 sec/100 ml and not more than 2000 sec/100 ml as measured by Oken-type air permeability tester method in accordance with JIS P 8117.

[0133] [6] The stretched porous film as set forth in any one of [1] through [5], wherein the resin composition further contains a paraffin-based oil.

[0134] [7] A method for producing a stretched porous film, including: a mixing step of mixing (i) a polyethylene-based resin having a density of not less than 0.900 g/cm.sup.3 and not more than 0.940 g/cm.sup.3, (ii) not less than 1.0 parts by mass and not more than 16 parts by mass of a thermoplastic elastomer relative to 100 parts by mass of the polyethylene-based resin, and (iii) an inorganic filler to prepare a resin composition; a forming step of forming the resin composition into the form of a film; and a porosification step of stretching, at least in a machine direction, the film obtained by the forming step to porosify the film.

[0135] [8] The method as set forth in [7], wherein a stretch magnification at which the film is stretched in the machine direction in the porosification step is represented by the following formula II:

1.4Y0.075X+2.5 (II)

where X represents a mixing ratio (parts by mass) of the thermoplastic elastomer to 100 parts by mass of the polyethylene-based resin and Y represents a stretch magnification (times).

INDUSTRIAL APPLICABILITY

[0136] The present invention is suitably applicable to, for example, a personal care product such as a diaper.