NL8403798A - METHOD FOR MANUFACTURING POROUS FILMS - Google Patents

Description

a/ * .

tat t

Process for the production of porous films.

Background of the Invention a) Field of the Invention

The invention relates to an improved process for the production of porous films, more in particular to a process for the production of porous films, which comprises mixing a polyolefin resin with barium sulphate as a filler, melting the resin composition obtained and forming the composition into a film and then at least uniaxially stretching the film.

B) Description of the prior art

There are a variety of known processes for manufacturing porous films by molding a resin composition containing a polyolefin resin and one of several incompatible fillers into a film and then drawing the film. For example, Japanese Patent Laid-Open Nos. 733/82 and 203520/82 disclose a method of manufacturing porous films, which comprises melting a resin composition obtained by mixing a polyolefin resin with a filler and liquid rubber 20 8403798 *. -2-.

or a hydroxylated poly-saturated hydrocarbon, molding the molten resin composition into a sheet or film and then drawing this sheet or film. Japanese Patent Laid-open No. 15538/83 discloses a method of manufacturing porous films comprising melting a resin composition obtained by mixing a low density linear polyethylene resin with a filler and a liquid or waxy hydrocarbon polymer to form the molten resin composition into a sheet or film and then draw 10 of this sheet or film. However, the films produced by these processes are disadvantageous because they exhibit surface tack due to the aforementioned component, which is present next to the polyolefin resin and the filler, and because they can be used practically only in relatively great thickness due to the low mechanical strength.

Furthermore, it is disclosed in Japanese Patent Laid-Open No. 1 9303/83 that such porous films can be used as a puncture resistant sheet in disposable diapers, porous films used as the puncture resistant sheet of a disposable diaper are manufactured by mixing 100 wt. parts of a polyolefin resin with 28 to 200 wt. parts of a filler and 10 to 70 parts by weight of a liquid or waxy hydrocarbon polymer, forming the resulting resin composition into a film, and then stretching this film at least uniaxially with a factor of 1.2 or greater. However, this method of manufacturing porous films has the drawback that some types of fillers give poor stretchability and consequently fail to provide completely uniform pores, and that the resulting film tends to produce an unpleasant noise. Moreover, the simultaneous use of a hydrocarbon polymer makes this process unsatisfactory because the hydrocarbon polymer tends to sweat out of the film surface and cause a tacky feel.

Such porous films are also useful as 8403798 m "3" - ft * i puncture resistant sheet in sanitary towels. Typically, a paper sheet made impermeable to liquid using a synthetic resin such as polyethylene is used for this purpose. However, the sanitary towels obtained have the drawback that they feel unpleasant during prolonged use due to the lack of permeability to water vapor.

Summary of the invention

Accordingly, an object of the invention is to provide an improved method of manufacturing porous films.

Another object of the invention is to provide a method of manufacturing porous films having sufficiently high porosity. and therefore have a high permeability to moisture and gas while maintaining an excellent resistance to water.

Yet another object of the invention is to provide a method of manufacturing porous films which are free from surface tack, have excellent softness and exhibit little reduction in strength.

Another object of the invention is to provide an improved puncture resistant sheet for use in disposable diapers.

Another object of the invention is to provide an improved puncture resistant sheet for use in sanitary towels.

Other objects of the invention will become apparent from the following description.

According to the invention there is provided a method of manufacturing porous films, which comprises melting a resin composition consisting essentially of 100 parts by weight of a polyolefin resin and 50 to 500 parts by weight of barium sulfate, forming the molten resin composition into a film and then at least uniaxially stretching the film 35 by a factor of 1.5 to 7.

8403798 τ? - U - w. -. By "a resin composition consisting essentially of 100 parts by weight of a polyolefin resin and 50 to 500 parts by weight of barium sulfate" is meant here that the resin composition may further contain (1) at least one additive selected from conventional stabilizers, antioxidants, colorants, ultraviolet light absorbers and lubricants and / or (2) in addition to the barium sulfate other inorganic fillers (such as calcium carbonate and the like) or conventional inorganic and organic modifiers in an amount less than the amount of barium sulfate used (e.g. no more than 20 fo, based on the amount of barium sulfate used), but the addition of liquid rubber, a hydroxylated polysaturated hydrocarbon or a hydrocarbon polymer as described in the aforementioned Japanese Patent Laid-Open Nos. 733/82, 203520/82 , 15538/83 and 11303/83 should be positively avoided in order to get a porous sheet which is free from surface tackiness.

According to the invention, porous films which are free from surface tackiness and have excellent properties and which cannot be obtained according to the prior art can be produced without using any of the above-described additives, which the technique be used. This can be done simply by specifying the type of the filler, the amount used, and preferably the average particle diameter thereof; preferably by using a low density polyethylene resin with a specific melt index and density and most preferably a linear low density polyethylene resin (in particular a linear low density polyethylene resin containing a copolymer of ethylene and hexene and / or octene ), which preferably has a specific melt index and density; and providing the film with a specific factor.

DETAILED DESCRIPTION OF THE INVENTION The polyolefin resins disclosed in the present invention are 8403798-5.

* * invention can be used, include homopolymers such as polypropylene, low density polyethylene, high density polyethylene, a linear low density polyethylene, polybutene, etc .; copolymers such as ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, etc.

and mixtures thereof.

Of these resins, low density polyethylene resins are preferred and have a melt index of 0.5 to 7 (0.5 to 8.5 for linear low density polyethylene resins) and a density of 0.915 to 0.935.Although preferred to use a single resin, any a mixture of polyethylene resins of different densities can be used. Most preferably, the melt index is in the range of 1 to 5. When the melt index is less than 0.5 or greater than 7 (8.5 for low density linear polyethylene resins), the resin will have markedly reduced film formability and may they fail to produce a film of small and uniform thickness.

On the other hand, when the density is less than 0.915 or greater than 0.935, the resin will have a reduced stretchability and stiffness and may fail to provide a soft film.

Bleacher preferred polyolefin resins are low density linear polyethylene resins. Low density linear polyethylene resins are copolymers of ethylene and one or more α-olefins and are different from low density polyethylene resins prepared by the conventional high pressure process. Low density linear polyethylene resins are prepared by the low pressure process and suitable α-olefins are butene, hexene, octene, decene and the like.

The difference between the low-density polyethylene resins prepared by the high-pressure process and the low-density polyethylene resins prepared by the low-pressure process lies in the fact that, from the point of view of chemical structure, the first resins are highly branched polymers, 84037981. -6.-. , While the last resins are straight chain polymers.

Of these low density linear polyethylene resins, octene copolymers of ethylene and hexene and / or are particularly preferred.

In the practice of the present invention, it is preferable to use barium sulfate having an average particle diameter of 0.1 to 7 µm, and most preferably 0.5 to 5 µm. When the average particle diameter is less than 0.1 µm, well-defined pores are not obtained. On the other hand, when the average particle diameter is greater than 7 µm, the resulting film will have poor stretchability, and therefore well-defined pores can hardly be obtained, as well as in cases where the average particle diameter is small.

The barium sulfate is used in an amount of 50 to 500 wt. parts and preferably 100 to h-00 wt. parts, per 100 parts by weight of the polyolefin resin. When the amount of barium sulfate used is less than 50 wt. parts, a sufficiently high porosity cannot be obtained, while when the amount is greater than 500 parts by weight, the resulting film cannot be completely stretched because of the greater rigidity and therefore will show a reduction in porosity.

It is preferable to subject the barium sulfate to a surface treatment with a fatty acid or a metal salt thereof, silicone, silane, a resin acid, and the like, because this treatment is effective in improving dispersibility in the resin and forming well-defined pores.

Insofar as the effects of the present invention are not affected, other inorganic fillers such as calcium carbonate and the like or conventional inorganic and organic modifiers can be used in addition to the barium sulfate. However, these additives must be used in an amount no greater than 20% based on the amount of resin sulfate used.

The present method of manufacturing porous films will now be described in more detail below.

Depending on the need, at least one additive selected from stabilizers, antioxidants, colorants, ultraviolet light absorbers and lubricants is added to a polyolefin resin and barium sulfate.

These ingredients are mixed with a Henschel mixer, super mixer or tumble mixer. Then, using a conventional single screw or twin screw extruder, the resulting mixture is mixed and pelleted.

Then, using an inflation extruder or a T-die extruder, these pellets (alone or mixed with polyolefin resin pellets) are melted at a temperature higher than the melting point of the polyolefin resin (preferably 20 ° C or more higher) and lower than a decomposition temperature thereof, formed into a film In some cases, the aforementioned mixture can be formed directly into a film with an extruder, rather than being pelleted 20. Then the film is stretched at least uniaxially with a factor of 1.5 to 7 by a conventional method, such as rolling, stretching in a stretcher, etc. This stretching may take place in steps and / or in two or more directions, however, in case of biaxial stretching, it deserves it is preferable to draw the film simultaneously in both directions To increase the morphological stability of the pores, the stretched film m be tempered by heating.

The porosity is determined by the amount of barium sulfate used, the stretching factor and the like.

When the stretching factor is less than 1.5, a sufficiently high porosity cannot be obtained, while when it is greater than 7, a porous film. cannot be manufactured constantly due to the frequent fracturing during the stretching process.

5403798 ï * - 8 - - ··

Films produced by the method of the invention are characterized by high porosity, excellent softness and little reduction in strength.

In addition, since the good affinity between the poly-olefin resin and the barium sulfate provides good stretchability, not only good processability can be obtained, but also an even distribution of the pores, and therefore a porous film can be produced constantly.

Particularly when a low density polyethylene resin is used as the base resin, the resulting film will show very little reduction in strength. Thus, it is possible to produce porous films that are thinner (e.g., about 10 µm in thickness) than those made by the known processes.

Moreover, since the resin composition does not contain liquid rubber, hydroxylated poly-saturated hydrocarbons and hydrocarbon polymers used in the known processes, the resulting porous film is free from surface tackiness.

Thus, the porous films of the invention have a sufficiently high porosity and, consequently, they exhibit good moisture and gas permeability while maintaining excellent water resistance so that they can be used in clothes and sanitary applications.

Moreover, they can also be used as a filter medium due to the uniform distribution of the pores.

The invention is now further illustrated in the following examples. However, these examples are for illustrative purposes only and not to limit the scope of the invention.

In the examples, the melt index (M1) was determined according to ASTM D-1238 and density according to ASTM D-1505.

In the examples, the film properties were further evaluated according to the following methods: 35 (1) Strength and elongation 8403798 -9-., * Rf1 w

Using a Tensilon tensile test machine, a piece of film measuring 25 mm (wide) x 100 mm (long) was tested at a drawing speed of 200 mm / min. The strength and elongation at break were determined in the 5 maehine direction (MD) and the transverse direction (TD).

(2) Permeability to moisture

Moisture permeability was determined according to ASTM E90 (Method D).

(3) Softness; The softness was evaluated by feeling and rated according to the following criteria: As very soft and smooth B = Fairly soft and smooth C = Hard and rough.

Examples 1-19 and Comparative Examples 1-9

Each of the fillers listed in Table A was added to the corresponding base resin in the amount listed in Table A and mixed therewith using a Henschel mixer. Then, using a twin-screw mixer, the resulting mixture was thoroughly mixed and pelleted. Then, using a T-die extruder, these pellets were melted at a temperature 80 ° C higher than the melting point of the base resin and formed into a film. This film was stretched uniaxially or biaxially (Example III) with the factor listed in Table A to obtain a porous film of the thickness listed in Table A. However, the film was not stretched in Comparative Example 1 and could not be stretched into a porous film in Comparative Examples 2 and 9 In the Comparative Examples 5 and 8, the film could only be stretched with a factor of up to 2. In Comparative Examples 3 and 7, sampling was not possible due to frequent fracturing during the stretching process.

The strength, elongation, moisture permeability and softness of the films thus obtained were evaluated according to 8403798 J * - 10 - the methods described above and the results are shown in Table A.

8403798 "1 1".

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Table A

- Basic resin type1 ^ trade name melt— density (manufacturer) index (g / cm.3) (g / 10 min)

EXAMPLE 1 IDENT REXLOID - 1 - 1 (Nippon 5.0 0S923

Petrochemicals Co.,

Ltd.)

It It IT tl 11 it 3ίΧΧ ^ II> it ιι ”IV" MIBASON k5 (Mitsui 1,5 0.920

Polychemicals Co.,

Ltd.)

I! γ II II It II

VI UBE POLYETHYLENE 0.9 0.912 F0191 (Ube Kosan K.K.) "VII Neo-zex ^ -330 (Mitsui 3.0 0.9 ^ 0

Petrochemical Industries,

Inc.) / UBE POLYETHYLENE VFk30 (Ube Kosan K.K.) = __ 2 / 1_, r VIII L-LDPE NUCG-5511 (Nippon 1.0 0.920

Unicar Co., Ltd.) if n it it it

"X Ultzex 2020L (Mitsui 2.1 M

Petrochemical Industries,

Inc.) it ££ II it »t

II xn II 'I II

II XIII II, 1 If fj8403798 J * - 12 -

Table A (continued) - Filler _. Stretch- Film thickness

Type average amount _,,, \ particles phr factor [µm] diameter (µm)

^ aSO ^ 0.8 150 4 ifO

ff TT! t ^ TT

"" "2x2" "1,2 130 5 50" 5,0 120 "" "1 s2" 33) "n" 100 k "1« 1 1 11 11 "" 150 5 15 "U, 2 50 6, 5 1 ^ 0 "0.8 150 5" "0.5 100 7 10

300 3 HO

8403798 -13-.

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Table A (continued) * strength (kg / 25 mm) elongation {%) - - Permeability Softness MD TD MD TD for moisture (g / no / 24 hours)

6.0 1.5 80 350 3,500 A.

6.5 1.3 6θ 300 4,200 A

4.9 "4.5 200 200 3,900 A

5.5 1.5 120 450 3,000 A

5.0 1.3 100 390 "A

3.9 1.0 55 390 1,100 B

4.5 "50, 200 2,000 C

3.5 1.2 100 420 3,900 C

2.5 0.8 '80 400 5,000 A.

7.8 1.4 65 170 2.800 A

6.5 1.8 130 510 7,500 A

2.3 0.7 4θ 120 8,500 A

5.3 1.5 78 360 5-500 A.

8403798 j m - iU - · - -

Table A (continued)

Base resin type1 ^ trade name melt density (manufacturer) index (g / cm ^) (g / 10 min.)

Example XIV L-LDPE Uitzex 301OF (Mitsui 1.3 0.930

Petrochemical Indus- _tn.es, Ine.) _ "XV" From zex 2020L (Mitsui 2.1 0.920

Petrochemical Industry- _tries, Inc.) _ "XVI" From zex 20100J (Mitsui 8.0 0.920

Petrochemical Industry- _tries, Inc.) _ "XVII HDPE Hi-zex HZ5000S (Mitsui 0.9 0.95 ^

Petrochemical Indus- 'tries, Inc.) _ "XVIII PP MITSUI E0BLEN JS-G 1,5 0.890 (Mitsui Toatsu _Chemicals, Ine.) _" XIX EPC MITSUI N0BLEK MJS-G "" (Mitsui Toatsu ________Chemicals, Ine.) _ '_

Compare L-LDPE. Ultzex 2020L (Mitsui 2.1 0.920 kings- Petrochemical Indus example 1_tries, Inc.) __ tt 2 · »tt tt ti tt 2" 11 "" "tt tt tt tt tt £ J tt tt tt tt" 6 "ÏUCG- 5511 (Nippon 1.0 ”__Unicar Co., Ltd.) ___ tt Y tt tt tt tt" 3 tt tt tt tt "9 LDPE PETROSEN 207 (Toyo 8 0.92h

Soda Manufacturing Co., Ltd.

«Q '.....

8403798 * - 15 -

Table A (continued)

Filler * -r-t— stretch film thickness

Type of average amount of 'fakfcor (µm) particles phr' diameter fyam) __- _

BaSO ^ 5.0 150 5 50 ”0.5 500 2 5 + 0" 0.8 200 3 "” tf 15Ö 5 "\

It IT It IT It

If It It It It ", T" not provided 50 V »" 11 600 not provided 150 8 ^ -CaCO3 1.0 "1+ T0 glass beads 1.2 120 2 * ^ 50

BaSO ^ "30 5 5 + 0" "100 86) glass beads" "27 ^ 60

BaSQ ^ "130 not provided 8403798 J ** - 16 -

Table A (continued) strength (kg / 25 mm) elongation% --- permeability MD TD MD TD prepuce moisture softness (g / m / 21 hours)

5.1 1.1 110 400 6,700 A.

5.0 1.0 35 20 5,000 A

5.5 1Λ 105 ^ 20 1,700 A

8.0 2.2 70 100 1,500 C

10.3 2.5 90 350 1,900 C

9.1 2.3 88 520 1,000 C

2.5 2.3 570 180 15 A

1.3 0.8 20 100 3,000 C

1.5 0.7 110 290 30 C

1.5 1.0 105 130 15 C

1.0 0.5 10 100 lo C

8403798 - 1T -,

Notes: 1) LDPE = low density polyethylene ϊ, -LDPE = linear low density polyethylene PP = polypropylene 5 EPC * ethylene-propylene copolymer 2) Wt. parts of the filler per 100 wt. parts of the base resin 3), 5) & 7) The maximum value at which stretching can take place constantly.

10 4) & 6) Sampling was not possible due to frequent breaking during the stretching process

Porous films produced by the method of the invention have a high porosity and excellent softness, and furthermore show little reduction in strength, so that they are very suitable for use as a leak-resistant sheet in disposable diapers. Although such a leak-resistant sheet is generally used as the outer layer of a disposable diaper, a material (such as a conventional perforated film or steric embossed sheet) which does not affect moisture permeability may be applied to the outside of the puncture resistant sheet to give it the appearance of a cloth.

In such disposable diapers, any of the conventional liquid absorbents can be used, including fluff consisting of pulp fibers, such as fluff wrapped in absorbent paper and the like, polymeric absorbents with high water absorbency and the like.

As the liquid-permeable sheet, which will be in indirect contact with the skin, a non-woven fabric consisting of polyester fibers, nylon fibers, polyolefin fibers and the like can preferably be used.

In addition, pressure sensitive tapes can be used to attach the diaper and elastic members such as rubber members are applied along the sides to prevent leakage.

Disposable diapers are manufactured by applying a liquid absorbent to the aforementioned puncture resistant sheet and stacking a liquid pervious sheet thereon.

In disposable diapers, in which the porous film of the invention has been used as the puncture resistant sheet, the outer puncture resistant trap has a large number of pores. Since these pores allow water vapor to pass through them, while holding back 10 drops of water, the child's skin is not damaged, but kept in a dry state, resulting in a slight tendency to develop diaper rash. In addition, they can also have the advantage of being difficult to tear, because of the high strength and soft enough not to cause unpleasant noise.

The following examples illustrate the use of the porous film of the invention as a puncture resistant sheet in disposable diapers.

Examples XX-XXII and Comparative Examples 10-1U 20 Barium sulfate with an average particle diameter of 1.5 µm or any of the other fillers listed in Table B was added to 100 wt. parts of low density polyethylene (LDPE) with a melt index (M1) of 3 (examples XX and XXI) or linear low density polyethylene (L-LDPE) 25 with a melt index (M1) of 5 (example XXII and comparative examples 10 -1 ^) in the amounts listed in Table B and mixed therewith using a scale mixer. The resulting mixture was then thoroughly mixed and pelleted using a twin-screw mixer. Then, the pellets were melted at 130 ° C using a T-die extruder and formed into a film. This film was stretched uniaxially between a preheat roll heated to 50 ° C and a draw roll, with the factor listed in Table B, to obtain a 50 µm thick porous film. The properties of the porous films thus obtained were evaluated and the results are 8403798-19 "? Listed in Table B. Disposable diapers were prepared by placing a filling of down-like pulp and a nonwoven polyester cloth on each of the porous films obtained in Examples XX-XXII and Comparative Examples 10, 13, 5 and 1k, and then fitted with pressure sensitive tapes and rubber members.

The disposable diapers of Examples XX-XXII were superior in strength, moisture permeability and softness, compared to that of Comparative Examples 10, 13 and 10 14, so that in use they produce only a slight rustle and feel comfortable. When these disposable diapers were tested for practical use in children, the diapers of Examples XX-XXII did not cause a rash on the wearer's skin. In contrast, the disposable diapers of Comparative Examples 10, 13, and 1k 'caused a strong rash or a minor appearance (Comparative Example 13).

Example XXIII

Using a biaxial stretch machine heated to T0 ° C, the unstretched film made in Example XX was simultaneously stretched in both the machine direction and the crosswise direction (with 2x2 factors) to obtain a porous film with a thickness of 50 µm. The properties of this porous film were evaluated and the results are shown in Table B. Disposable diapers

using this porous film as the puncture resistant sheet showed good behavior as well as that of Example XX. Example XXIV

The same resin composition as used in Example XXII was formed into a film. Using a roll heated to 50 ° C, this film was stretched uniaxially with a factor k to obtain a porous film 15 µm thick. The properties of this porous film were evaluated and the results are reported in Table B.

34 0 3 7 98 -20 ----

The exterior of this porous film was a 70 µm thick LDPE film with 1mm (20 µm / cm) diameter openings all over the surface. Disposable diapers using this composite material 5 as the puncture resistant sheet showed as good performance as that of Examples XX-XXIII.

84037 98> -21-.

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Table Β basic resin filler type quantity type quantity (parts) (parts)

Example XX LDPE 100 BaSO ^ 150 it XXX ^ ^ ** ^ "XXIX L-LDPE" "200" XXIII LDPE "” 150 w XXIV L-LDPE "" 200 comparison example 10 n "" 150

. ” 11 »t. 1 »g0Q

u 12 «" "150" 13 "" CaCO "" ih "" glass beads 120 8403798 -22-.

Table B (continued) stretch factor permeability (MD / TD) pre-moisture softness _ (kg / 25 mm) _ (g / m2 / 2l hours) _

k 6.0 / 1.5 3,500 A.

5 6.5 / 1.3 ^ -. 200 A

3 5.5 / 1.3 ^ .600 A

2x2 b, 9 / k, 5 3,900 A.

U 6.7 / 0.9 '.700 A

not provided 2.3 / 2.2 15 A.

not provided - - __ - _ -

k b, 3 / 0.8 3,000 C

2s *) 1.5 / 0.7 .30 C

2c) ..

An attempt was made to stretch this film with a factor of 8, but testing was not possible due to frequent breaking during the stretching process.

The film could not be supplied with a factor greater than 2.

*. «!„ <F -W Q

- 23 - "Comparative example 15 120 Gev. parts of calcium carbonate with an average particle diameter of 1.2 µm and 20 parts by weight of a hydroxylated poly-saturated hydrocarbon (liquid polybutadiene 5 GI-2000; Nippon Soda Co., Ltd) were added to 100 parts by weight.

parts of linear low density polyethylene (L-LDPE) with a melt index (M1) of 5 and mixed therewith using a Henschel mixer. The resulting mixture was then thoroughly mixed and pelleted using a twin-screw mixer. These pellets were then formed into a film using an inflation extruder with a diameter of 00 mm. This film was rolled at 80 ° C with a factor of 3.0 to obtain a porous film with a thickness of 50 yam. This porous film 15 varied in moisture permeability depending on the location and showed a low degree of surface tack. Disposable diapers using this porous film as the puncture resistant sheet caused a slight rash on the skin of children.

20 Comparative example 16

The procedure of Comparative Example 15 was repeated except that liquid polybutadiene (Nisso PBG; Nippon Soda Co., Ltd) or rubbery EPR (Toughmer POU80; Mitsui Petrochemical Industries, Ine.) Was used as the hydroxylated poly-saturated carbon hydrogen. Thus, films with a thickness of 50 µm were obtained. These porous films showed surface tackiness and varyed moisture permeability depending on location. Disposable diapers using each of these porous films as the puncture resistant sheet caused a slight rash on the skin of children.

Porous films obtained by the process according to the invention have a high porosity and an excellent softness and, in addition, they show a slight decrease in strength despite their small thickness, so that they are very suitable for use. as a puncture resistant sheet in sanitary towels. Conventional sanitary towels are made such that a liquid absorbent, for example, downy pulp, cotton, absorbent resin and the like, is partially covered with a film of paper rendered liquid impermeable by treatment with a synthetic resin such as polyethylene and the like and the resulting structure is then wrapped in a nonwoven cloth. In sanitary towels using the porous film of the invention as the leak-proof sheet, this leak-resistant sheet has a large number of pores that allow water vapor to pass through it. As a result, they were able to keep the user's skin dry and do not cause any discomfort, even with prolonged use.

The following examples illustrate the use of the porous film according to the invention as a puncture resistant sheet in sanitary towels.

Examples XXV - XXVII

Barium sulfate with an average particle diameter of 0.8 µm was added to 100 parts by weight of low density lirphene polyethylene (L-LDPE) with a melt index (M1) of 2.1 in the amount listed in Table C and mixed with a Henschel mixer. Then, using a twin screw mixer, the resulting mixture was thoroughly mixed and pelletized. These pellets were then melted at 230 ° C using an extruder and formed into a film. This film was stretched uniaxially between a preheated roller heated to 80 ° C and a stretching roll with the factor listed in Table C.30 to obtain a 20 µm thick porous film.

The properties of this porous film were evaluated and the results are shown in Table C. Sanitary towels were prepared by partially covering a downy pulp filling with each of the porous films obtained in Examples XXV-XXVII, wrapping the structure obtained 8403798 -25 - ~ a non-woven cloth and then thermal welding of the overlapping parts. When these sanitary towels and the commercially available cloths with a liquid-impermeable film of polyethylene-coated paper were tested comparatively by practical use over a long period of time, the sanitary towels according to the invention did not cause an uncomfortable stuffiness.

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Claims (13)

1. A method of manufacturing porous films, which comprises melting a resin composition consisting essentially of a polyolefin resin and a filler incompatible therewith, forming the molten resin composition into a film and then drawing at least uniaxially of the film, characterized in that the incompatible filler is barium sulfate, the barium sulfate is used in an amount of 50 to 500 parts by weight per 100 parts by weight of the polyolefin resin and the film is stretched with a factor of 1.5 up to 7 The method according to claim 1, characterized in that the mean particle diameter of the barium sulfate is in the range of 0.1 to 7 Process according to claim 2, characterized in that the mean particle diameter of the barium sulfate is in the range of 0.5 to 5 µm. The method according to claim 1, characterized in that the barium sulfate is used in an amount of 100 to 100 parts by weight per 100 parts by weight of the polyolefin resin. Process according to claim 1, characterized in that the barium sulfate is subjected to a surface treatment with a fatty acid or a metal salt thereof, silicone, silane or a resin acid. Process according to claim 1, characterized in that the polyolefin resin is a polyethylene resin. A process according to claim 6, characterized in that the polyethylene resin is a low-density polyethylene resin with a melt index of 0.5 to 7 and a density of 0.915 to 0.935. 8. Process according to claim 7, characterized in that the low-density polyethylene resin is a single resin. 9. Process according to claim 7, characterized in that the low-density polyethylene resin is a mixture of. x ____ 8403798 - 28 - ώ · τ polyethylene resins of different densities. Process according to claim J, characterized in that the melt index is in the range from 1 to 5. A method according to claim 6, characterized in that the polyethylene resin is a linear low density polyethylene resin. 12. Process according to claim 11, characterized in that the linear low density polyethylene resin has a melt index of 0.5 to 8.5 and a density of 0.915 to 0.935 Process according to claim 11, characterized in that the low density linear polyethylene resin is a copolymer of ethylene and hexene and / or octene. 15 1U. Porous film with water resistance, moisture permeability and gas permeability, which is produced by the method according to any one of claims 1-13. Use of the porous film according to claim 1¾ as a puncture resistant sheet in disposable diaper. Use of the porous film according to claim 14 as a puncture resistant sheet in sanitary towels. c 6403798