Note: Descriptions are shown in the official language in which they were submitted.
- ~ZS~'7~
I
SPECIFICATION
Title o~ the Invention:
Process for Producing Porous Films
Background of the Invention:
a) Field of the Invention:
This invention relates to an improved process
for producing porous films. More particularly,
it relates to a process for producing porous films
which comprises blending a polyolefin resin with
barium sulfate as a filler, melting the result-
ing resin composition and forming it into a film,
and then stretching the film at least uniaxially.
b) Description of the Prior Art:
Conventionally, there are a large number of
well-known processes for producing porous films by
forming a resin composition comprising a poly-
oleFin resin and any of various noncompatible
fillers into a fiIm and then stretching this film.
For example, Japanese Patent Laid-Open Nos. 47334/
'82 and 203520/'82 laid open March 18, 1982 and
December 13, 1982 (both in the name of Mitsubishi
Chemical Industries Ltd.) disclose a process for
producing porous films which comprises melting a
resin composition obtained by blending a poly-
olefin resin with a filler and liquid rubber or
a hydroxylated poly-saturated-hydrocarbon, forming
the molten resin composition into a sheet or film,
~q
~ ~ S ~ 7 ~ ~
and then stretching this sheet or film. Moreover,
Japanese Patent Laid-Open No. 15538/'83 laid open
January 28, 1983 in the name of Mitsubishi Chemical
Industries Ltd. discloses a process for producing
porous films which comprises melting a resin compo-
sition obtained by blending a linear low-density
polyethylene resin with a filler and a liquid or
waxy hydrocarbon polymer, forming the molten resin
composition into a sheet or film, and then stretch-
ing this sheet or film. However, the fiIms produced
by these processes are disadvantageous in that they
exhibit surface tackiness due to the aforesaid
component contained in addition to the polyolefin
resin and the filler and in that they can only be
practically used in relatively large thickness
because of their low mechanical strength.
Furthermore, it is described in Japanese Patent
Laid-Open No. 149303/'83 laid open September 15, 1983
in the name of Kao Corporation that such porous
films can be used as a leakproof sheet in disposable
diapers. Porous fiIms for use as the leak?roof
sheet of a disposable diaper are produced by blending
100 parts by weight of a polyolefin resin with 28 to
200 parts by weight 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 by
~Z5~24
a factor of 1.2 or greater. However, this process for
producing porous films has the disadvantages that some types
of fillers give poor stretchability and hence fail to pro-
vide fully uniform pores and that the resulting film tends
to produce a disagreeable noise. Moreover, the concurrent
use of a hydrocarbon polymer makes this process unsatisfactory
because the hydrocarbon polymer tends to bloom to the film
surface and causes a sticky sensation.
Such porous films are also useful as a leakproof
sheet in sanitary napkins. Conventionally, a sheet of paper
which has been rendered liquid-impermeable by means of a
synthetic resin such as polyethylene has been used for this
purpose. However, the resulting sanitary napkins have the
disadvantage of causing a disagreeable sensation during
prolonged use because of their lack of permeability to water
vapor.
Summary of the Invention:
Accordingly, it is an object of an aspect of the
present invention to provide an improved process for pro-
ducing porous films.
It is an object of an aspect of the present inven-
tion to provide a process for producing porous films which
have sufficiently high porosity and thereby exhibit high
moisture permeability and gas permeability while retaining
excellent water resistance.
It is an object of an aspect of the present inven-
_4_ ~S~4
tion to provide a process for producing porous filmswhich are free from surface tackiness, have excellent
softness and show little reduction in strength.
It is an object of an aspect of the present
invention to provide an improved leakproo~ sheet for use
in disposable diapers.
It is an object of an aspect of the present
invention to provide an improved leakproof sheet for
use in sanitary napkins.
Other objects of the present invention will be
apparent from the following description.
An aspect of the invention is as follows:
In a process for producing porous films which
comprises melting a resin composition consisting
essentially of a polyethylene resin and a filler
noncompatible therewith, and with or without a
hydrocarbon-free lubricant, forming the molten resin
composition into a film and then stretching the film at
least uniaxially, the improvement in which the
polyethylene resin is either a high-pressure-processed
low-density polyethylene resin having a melt index of
0.5 to 7 and a density of 0.915 to 0.935, a linear low-
density polyethylene resin having a melt index of 0.5 to
~.5 and a density of 0.915 to Q.935, or a mixture
thereof; the filler is barium sulfate having an average
particle diameter of O.1 to 7 ~m and the barium sulfate
is used in an amount of 50 to 500 parts by weight per
100 parts by weight of the polyethylene resin; and the
film is stretched by a factor of 1.5 to 7~
According to another aspect of the present
invention, there is provided a process for producing
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, fo~ming the molten resin composition into a
film, and then stretching the film at least uniaxially
by a factor of 1.5 to 7.
The expression "a resin composition consisting
essentially of 100 parts by weight o~ a polyolefin resin
and 50 to 500 parts by weight of barium sulfate"
12S~7~
as used herein means that the resin composition may
further contain (1) at least one additive selected
from common stabilizers, antioxidants, colorants,
ultraviolet light absorbents and laubricants and/or
(2), in addition to the barium sulfate, other
inorganic fillers (such as calcium carbonate and
the like) or common inorganic and organic modifiers
in an amount less than that of barium sulfate used
(for example, not greater than 20~ based on the
amount of barium sulfate used), but the addition
of liquid rubber, a hydroxylated poly-saturated-
hydrocarbon or a hydrocarbon polymer as described
in the aforementioned Japanese Patent Laid-Open Nos.
47334/'82, 203520/'82, 15538/'83 and 149303/'83 should
be positively avoided in order to obtain a porous
film free from surface tackiness.
According to the present invention, porous
films which are free from surface tackiness and
have excellent properties and which have been un-
obtainable in the prior art can be produced withoutusing any of the above-described additives used in
the prior artO This can be accomplished simply by
specifying the type of the filler, i~s amount used
and preferably its average particle diameter;
preferably using a low-density polyethylene resin
having a specific melt index and density and more
5~ 29~
preferably a linear low-density polyethylene resin
(in particular, a linear low-density polyethylene
resin comprising a copolymer of ethylene and hexene
and/or octene) which most preferably has a specific
melt index and dansity; and stretching the film by
a specific factor.
Detailed Description of the Invention:
The polyolefin resins which can be used in
the present invention include homopolymers such as
polypropylane, low-density polyethylene, high-density
polyethylene, linear low-density polyethylene,
polybutylene, etc.; copolymers such as ethylene-
propylene copolymer, ethylene-butylene copolymer,
ethylene vinyl acetate copolymer, etc.; and blends
thereof.
Among these resins, low-density polyethylene
resins having a melt index of 0.5 to 7 (0.5 to 8.5 for
linear low-density polyethylene resins) and a density
of O.91S to 0.935 are preferred. Although it is
preferable to use a single resin, any blend of poly-
ethylene resins having different densities may be
used. More preferably, the melt index is in the
range of 1 to 5. If the melt index is less than 0.5
or greater than 7 (8.5 for linear low~density poly-
ethylene resins), the resin will have significantly
1~5~72~
decreased formability into a film and may fail to
yield a film of small and uniform thickness.
On the other hand, if the density is lower
than 0.915 or higher than 0.935, the resin will have
decreased stretchability and increased rigidity
and may fail to yield a soft film.
Particularly preferred polyolefin resins
are linear low-density polyethylene resins. Lineax
low-density polyethylene resins are copolymers of
ethylene and one or more a-olefins, and differ from
low-density polyethylene resins prepared by the
conventional high-pressure process. Lineax low-density
polyethylene resins are prepared by the low-pressure
process, and useful a-olefins include butene, hexene,
octene, dPcene and the like. The difference between
high-pressure-processed low-density polyethylene
resins and low-pressure-processed low-density poly-
ethylene resins lies in the fact that, when seen
from the viewpoint of chemical structure, the former
ones are highly branched polymers while the latter
ones are straight-chain polymers Among such liear
low~density polyethylene resins, copolymers of
ethylene and hexene and/or octene are particularly
preferred.
In the practice of the present invention,
it is preferable to use barium sulfate having an
~S~24
average particle diameter of 0.1 to 7 ~m and more
preferably 0.5 to 5 ~m. If the average particle
diameter is smaller than 0.1 ~m, well-defined pores
cannot be obtained. On the contrary, if it is larger
than 7 ~m, the resulting film will have poor
stretchability and, therefore, well-defined pores
can hardly be obtained just as in cases where the
average particle diameter is too small.
The barium sulfate is used in an amount
of 50 to 500 parts by weight, and preferably 100 to
400 parts by weight, per 100 parts by weight of the
polyolefin resin. If the amount of barium sulfate
used is less than 50 parts by weight, sufficiently
high porosity cannot be obtained, while if it is
greater than 500 parts by weight, the resulting film
cannot be fully stretched because of its increased
rigidity and, therefore, will show a reduction in
porosity.
It is preferable to subject the barium
sulfate to surface treatment with a fatty acid or a
metallic salt thereof, silicone, silane, a resin
acid or the like, because this treatment is effective
in improving its dispersibility in the resin and
producing well-defined pores.
So far as the effects of the present inven-
tion are not impaired, other inorganic fillers such as
`` ~IL25~17z~
_ 9 _
calcium carbonate and the like or common inorganic
and organic modifiers may be used in addition to
the barium sulfate. However, these additives should
be us~d in an amount of not greater than 20% based
on the amount of barium sulfate used.
Now, the pres~nt process for producing
porous films will be specifically described
hereinbelow.
According to the need, at least one additive
selected from stabilizers, antioxidants, colorants,
ultraviolet light absorbents and lubricants is added
to a polyolefin resin and barium sulfate. These
ingredients are mixed with a Henschel mixer, super-
mixer or tumbling mixer. Thereafter, using an
ordinary single-screw or twin-screw extruder, the
resulting mixture is blended and pelletized. Then,
using an inflation extruder or T-die extruder, these
pelle~s (alone or in admixture with polyolefin
resin pellets) are melted at a temperature higher
than the melting point of the polyolefin resin (prefer-
ably, by 20C or more) and lower than the decomposition
temperature thereof, and formed into a film. In some
cases, the aforesaid mix~ure may be directly formed
into a film with an extruder, instead of being
pelletized. Subsequently, the film is a~ least
unaxially stretched by a factor of 1.5 to 7 according
~S()72~
-- 10 --
to a conventional technique such as roll stretching,
tentering or the like. This stretching may be
performed in steps and~or in two or more directions.
In the case of biaxial stretching, however, it is
preferabl~ to stretch the film simultaneously in the
two directions. In order to enhance the morphological
stability o~ pores, the stretched film may be
annealed by heating.
~he porosity is determined by the amount
of barium sulfate used, the stretching factor and
the like. If the stretching factor is less than
1.5, sufficiently high porosity cannot be obtained,
while if it is greater than 7, a porous film cannot
be steadily produced because of its frequent breakage
during the stretching process.-
Porous films produced by the process of thepresent invention are characterized by high porosity,
excellent softness and little reduction in strength.
Moreover, since the good affinity between
the polyolefin resin and barium sulfate provides good
stretchability, not only good workability but also an
even distribution of pores can be achieved and,
therefore, a porous film can be produced steadily.
Especially when a linear low-density polyethylene
resin is used as the base resin, the resulting film
will show very little reduction in strength. Thus, it
~ZS~4
11 --
is possible to produce porous films which are thinner
(for example, approximately 10 ~m in thickness)
than those produced by the prior-art processes.
Furthermore, since the resin composition
does not contain any of the liquid rubber, hydroxylated
poly-saturated-hydrocarbons and hydrocarbon polymers
used in the prior~art processes, the resulting porous
film is free from surface tackiness.
Thus, the porous films of the present
invention have sufficiently high porosity and hence
exhibit good moisture permeability and gas
permeability while retaining excellent water resis-
tance, so that they can be used in clothing and
sanitary applications. In addition, they can also be
used as a filtering medium owing to their even
distribution of pores.
The present invention is further illustrated
by the following examples. However, these examples
a~e given for purposes of illustration only and are
not to be construed to limit the scope of the inven-
tion.
In the examples, melt index (MI) was
determined according to ASTM D-1238 and density was
determined according to ASTM D-1505.
Also in the examples t film properties were
evaluated according to the following procedures:
~L~S~Z~
-- 12 --
~1) Strength and elongation
Using a Tensilon tensile testing machine,
a piece of film measuring 25 mm (wide) x 100 mm tlong)
is tested at a straining rate of 200 mm/min. Its
strength and elongation at breakage are determined
with respect to the machine direction (MD) and the
transverse direction (TD).
(2) Moisture permeability
Moisture permeability is tested according
to ASTM E36(Method D).
(3) Softness
Softness is evaluated ~y the feel and rated
according to the following cristeria:
A = Very soft and smooth
B = Rather soft and smooth
C = Hard and rough
Examples 1-19 and Comparative Examples 1-9
Each of the fillers given in Table 1 was
added to the corresponding base resin in the amount
given in Table 1, and mixed therewith by means of a
Henschel mixer. Thereafter, using a twin-screw
mixer, the resulting mixture was intimately blended
~LZ5~7~4~
- 13 -
and formed into pellets. Then, using a T-die extruder,
these pellets were melted at a temperature 80C higher
than the melting point of the base resin and formed
into a film. This film was uniaxially or biaxially
(Example 3~ stretched by the factor given in Table 1
to obtain a porous film having the thickness given
in Table 1. 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
Comparative Examples 5 and 8, the film could only be
stretched by a factor of up to 2. In Comparative
Examples 3 and 7, no sampling was possible because
of frequent breakage during the stretching process.
The strength, elongation, moisture permea-
bility and softness of the porous films thus obtained
were evaluated according to the above-described
procedures and the results are shown in Table 1.
~;~S~7~
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Table 1
. .
_ . __ _ _
Base resin
_ _
T 1) Trade name Melt Density
YP (manufacturer) ( /10 min) (g/cm3)
~ g. _
REXLON F-41*(Nippon
Example 1LDPE Petxochemicals Co., 5.0 0.923
. ._ _ ~ _
" 2 ll .. .. ..
. . _ .. __ . _
.. 3 ., .. .. ..
. ... _
MIRASON 45*~Mitsui
.. ~ .. Polychemicals Co., 1.5 0.920
Ltd.~
_ . _ ., _ . _
.. 5 .. .. .. .,
. . __ . . _
UBE POLYETHYLENE
" 6 ll F0191*(Ube Kosan 0.9 0.912
K.K.)
... _ . _
Neo-zex 4330*(Mitsui
Petrochemical Indus-
7 .. tries, Inc.)/UBE 3.0 0.940
POLYETHYLENE VF430
. (Ube Kosan K.K.)=2/1
.. . .~ _ _
" 8 L-LDPE Unicar Co., Ltd.) 1.0 0.920
_ _ _ .................................. _
" .9~ .. ._ _"_ .. ". ._ _
Ultzex 202OL*(Mitsui
" 10 ~ Petrochemical Indus- 2.1 ..
tries, Inc.) _
" 11 .. .. " "
_
" 12 .. .. ,. "
. . _
" 13 .. .. ~ ,. " _
* trade marks or trade designations
~L~S~7~
- 15 -
Ta~le 1 (Cont'd)
.
Fiiïer _
_
Average 2) Stretchingl Film
Type particle dia- Amount factor I thickness
meter (~m) (phr) __ (~m) _
BaSO4 0.8 150 4 ¦ 40
. 5 _ ~
_ .. .. 2 X 2 ~ _
,. 1.2 130 . 5 50 _
,. 5.0 120 . ll ,. _
.~ 1.2 ,- 33) I ..
. . .__ _
.. .. 100 4 I ..
_ . 30 _
.. 150 . . _ -lS------- _
. . _ _ ._
- .. 4.2 50 6.5 40
.. 0.8 _ 150~ 5 --- _ _
0.5 100 . 7 ._10 _
300 . 3 40 _
~25~
- 16 -
Table 1 (Cont'a)
. _
__ ._ _
(kg/25 mm) Elongation (%) Moisture
permeability Soft-
= _ ~D MD rD (g/m /24 hr) ness
6.0 1.5 80 350 3,500 A
6.5 1.3 60 300 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 n 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 0.880 400 5,000 A
... _ ._ _ _ .____
7.8 1 4 65 170 2,800 a
6.5 1 1.8 130 510 7,530 A
2.3 1 0.7 !40 120 8,500 A
5.3 1.5 78 360 5,500 A
~2S~37Z4
- 17 -
Table 1 (Cont'd)
_ . ~ _
Base resin
. _ _ ,_ _.. __ _
1)Trade name Melt Density
Type (manufacturer) lndex 3
(g/l0 mln) ~g/cm )
. ~ __ .. ___ _
Ultzex 3010F*(Mitsui
Example 14 L-LDPE Petrochemical Indus- 1.3 0.930
tries, Inc.)
_ _ . ._ _ . _
Ultzex 2020L*(Mitsui
- 15 ll Petrochemical Indus- 2.l 0.920
tries, Inc.)
, _ _ _
Ultzex 20100J*
" 16 ll (Mitsui Petrochemical 8.0 0.920
Industries, Inc.)
_ ._ . . _ ..... ._ _ __ _
Hi-zex ~Z5000S*
" 17 HDPE (Mitsui Petrochemical 0.9 0.954
Industries, Inc.)
.. __ _ _ ._ ............................. _
MITSUI NOBLEN JS-G*
" 18 PP (Mitsui Toatsu 1.5 0.890
Chemicals, Inc.)
. , _
MITSUI NOBLEN MJS-G
" 19 EPC (Mitsui To~tsu ll ,.
Chemicals, Inc.) _ _
.
* trade marks or trade designations
lZ5~
- 18 -
Table 1 (Cont'd)
-
. _ ._ . _ _
Filler l r-
_ Average _ Stretching ¦ Film
Type particle dia- Amount factor I thickness
meter (~m) (Phr) l (~m)
__ _ ... __ _
BaSO4 5.0 150 5 50 _
~. 0.5 500 2 40
_ _
.. _ _ _ b ~ ~ -
_ . _ ._ . _ _
~` = ~-
~LZ5~
-- 19 --
Table 1 (Cont'd)
. .
.
Strength Elongation (~) Moisture
_ . permeability Soft-
MD TD MD TD (g/m /24 hr) ness
5.1 1.4 110 400 6,700 A
.__ ._ .
; D 1.0 35 ~ 5,000 A
5.5 1.4 105 420 4,700 A
~ ~ - 2.2 ' ~,~0~ C -
10.3 1 2.5 90 1 350 4,900 C
.. .. _ .__
9.1 2.3 88 1 520 14,000 C
~2~ Z4
- 20 -
Table 1 (Cont'd)
. . . . . . _ _ .
Base resin
_ _ _ _ , __ _
Type ) Trade name index Density
(manufacturer) (g/10 min) (g/cm3)
._ . ._ _ _
t- .~
6 ..NUCG-5511*(Nippon 1 0
Unicar Co., Ltd.)
" 7 __ _
" 8 .._ '' ~ - _ ~ = _
PETROSEN 207*(Toyo
.. g LDPESoda Manufacturing 8 0.924
__ Co., Ltd. _ _
Notes: 1) LDPE = low-density polyethylene.
L-LDPE= linear low-density polyethylene.
PP = Polypropylene
EPC = ethylene-propylene copolymer.
2) Parts by weight of the filler per 100 parts by
weight of the base rein.
3), 5) & 7) The maximum value at which stretching
can be performed steadily.
4) ~ 6) No sampling was possible because of frequent
breakage during the stretching process.
* trade marks or trade designations
~5~24
- 21 -
Table ' (Cont'd)
. . _ . .
- ._ , ~ _
Filler
. I
Average21 I Stretching I Film
Type particle dia- Amount l factor Ithickness
meter (~ml(Phr) l l (~m)
.__ ._ ~ _
BaSO4 0.8 150 ¦ Unstretch- 50
.. _ _
.. .. 600 ¦ Unstretch-
.. _ _ _ 150 84~- _~ -
CaCO3 1.0 .. ¦ 4 70
. ._ _ _
beads 1.2 120 _ _ _
BaSO4 .. 30 ¦ 5 40
_ 100 86) _ _
beads . _ 27) 60 _
BaSO4 l30 ACI _ _
12S~7~
- 22 -
Table 1 (Cont'd)
Strength Elongation (~) Moisture
(kg/25 mm) . ~ permeability Soft-
MD TD MD TD (g/m /24 hr) ness
. ._ _ ..
2.5 2.3 570 480 15 A
.
_ _ _ _ _
_ __
_ _ ~ _
4.3 0.8 20 100 3,000 C
1.5 0.7 140 290 30 C
. _ _ _ _
4.5 1.0 105 430 15 C
- _ _ __
. . . . _
1.0 0.5 40 100 40 C
. _ _ .. ... _ __
_ _ _ _
.__ . _ . _
12~iU~
- 23 -
Porous films produced by the proces~ of
the present invention have high porosity and excellent
softness and, moreover, show little reduction in
strength, so that they are very suitable for use as a
leakproof sheet in disposable diapers. Although such
a leakproof sheet is generally used as the outermost
layer of a disposable diaper, a material (such as
a common punched film or sterically embossed sheet)
not impairing its moisture permeability may be super-
posed on the outer side of the leakproof sheet toimpart a cloth-like appearance thereto.
In such disposable diapers, there may be
used any of common liquid absorbers including fluff
composed of pulp fibers, such fluff wrapped in
absorbent paper or the like, polymeric absorbers
having high water absorbency, and the like.
As the liquid-permeable sheet which will
be in direct contact with the skin, there may
preferably be used a non-woven fabric composed of
polyester fibers, nylon fibers, polyolefin fibers or
the like.
In addition, there may be used pressure-
sensitive tapes for fastening the diaper, and elastic
members (such as rubber members) provided along the
side edges to prevent leakage.
Disposable diapers are made by placing a
3LZS~37~
- 24 -
liquid absorber on the aforesaid leakproof sheet,
and stacking a liquid-permeable sheet thereon.
In disposable diapers using the porous
film of the present invention as the leakproof sheet,
the outermost leakproof sheet has a large number of
pores. Since these pores allow water vapor to pass
therethrough while retaining water droplets, the
skin of the infant is not dampened but kept in a dry
state, resulting in little tendency to develop diaper
rash. Moreover, they also have the advantages of
being hardly torn because of their high strength and
being soft enough to produce no disagreeable noise.
The following examples illustrate the use
of the porous film of the present invention as a
leakproof sheet in disposable diapers.
Exam les 20-22 and Comparative Examples 10-14
p
Barium sulfate having an average particle
diameter of l.S ~m or each of the other fillers given
in Table 2 was added to 100 parts by weight of low-
density polyethylene (LDPE) having a melt index (~$I)
of 3 (Examples 20 and 21) or linear low-density
polyethylene (L-LDPE) having a melt index (MI) of 5
(Example 22 and Comparative Examples 10-14) in -the
amount given in Table 2, and mixed therewith by
means of a ~enschel mixer. Thereafter, using a
~LZ~72~
- 25 -
twin-screw mixer, the resulting mixture was intima-tely
blended and formed into pellets. Then, using a T-die
extruder, these pellets were melted at 130C and
formed into a film. This film was uniaxially
stretched between a preheating roll heated to 50C
and a ^qtretching roll by the factor given in Table 2
to obtain a porous film having a thickness of 50 ~m.
Properties of the porous films thus obtained were
evaluated and the results are shown in Table 2.
Disposable diapers were made by placing a filling
of fluffy pulp and a non-woven polyester fabric on
each of the porous films obtained in Examples 20-22
and Compara~ive Examples 10, 13 and 14, and then
providing it with pressure-sensitive tapes and rubber
members.
The disposable diapers of Examples 20-22
were superior in strength, moisture permeability and
softness to those of Comparative Examples 10, 13 and
14, 50 that they produced only a slight rustling
noise during use and felt comfortable to the touch.
When these disposable diapers were tested by using
them practically in infants, those of Examples 20-22
caused no rash on the skin of the wearer. In contrast,
the disposable diapers of Comparative Examples 10,
13 and 14 caused an extensive rash or a slight rash
(Comparative Example 13).
3L25~7Z~
- 26 -
Example 23
Using a biaxial stretching machine heated
to 70C, the unstretched film formed in Example 20
was simultaneously stretched in both the machine
and the transverse direction (by factors of 2 x 2) to
obtain a porous film having a thickness of 50 ~m.
Properties of this porous film were evaluated and
the results are shown in Table 2. Disposable diapers
using this porous film as the leakproof sheet
exhibited as good performance as those of Example 20.
Example 24
The same resin composition as used in
Example 22 was formed into a film. Using a roll
heated to 50C, this film was uniaxially stretched
by a factor of 4 to obtain a porous film having a
thickness of 15 ~m. Properties of this porous film
were evaluated and the results are shown in Table 2.
On the outer side of this porous film was
superposed a LDPE film of 70 ~m thickness having
apertures of 1 mm diameter (20/cm2) all over its
surface. Disposable diapers using this composite
material as the leakproof sheet also exhibited as
good performance as those of Examples ~0-23.
~Z5~)72~
- 27 -
Table 2
_ .
Base resin Filler _
Amount Amount
Type (parts by Type (parts by
weight) weight) _
Example 20 LDPE 100 BaSO4 150 _
_ . . ___ _
' 22 L-LDPE ll .. ~00
. ._ . _ . . _
" 23 LDPE .. .. 150
" 24 L~LDPE 200 _
Comparative .. -:~ _
" 11 .. .. .. 6Q0
. __ _ _
" 12 .. .. " __ 150 _
" 13 . CaCO3 _
" 14 beads 120 _
*) An attempt was made to stretch the film by a
factor of 8, but no sampling was possible because
of frequent breakage during the stretching
processO
**) The film could not be stretched by a factor of
more than 2.
lZ5~'729L
- 28 -
Table 2 (Cont'd)
_ _ Strength Moisture
Stretching ~MD/TD] permeability ~Softness
(kg/25 mm) (g/m /24 hr)
.. _ .. _ ._
4 6.0/1.5 . 3,500
, . .. _
6.5/1.3 4,200 A
35.5/1.3 4,600 _
2 X 2 4.9/4.5 3,900 A
6.7/0.9 4,700 _ __
Unstretch- 2.3/2~2 15 A
,
Unstretch- _
8*) _ _
44.3/0.8 3,000 C
**) .__ _
. 1.5/0.7 _ _
~L~S~ 4
- 29 -
Comparative Exam~e 15
.
120 parts by w~ight of calcium carbonate
having an average particle diameter of l.2 ~m and 20
parts by weight of a hydroxylated poly-saturated-
hydrocarbon (Liquid Polybutadiene GI-2000; Nippon
Soda Co., Ltd.) were added to lO0 parts by weight of
linear low-density polyethylene IL-LDPE) having a
melt index (MI) of 5, and mixed therewith by means
of a Henschel mixer. Thereafter, using a twin-
screw mixer, the resulting mixture Wa5 intimatelyblended and formed into ~ellets. Then, using a 40 mm~
inflation extruder, these pellets were formed into a
film. This film was roll stretched at 80C by a
factor of 3.0 to obtain a porous film having a thick-
ness of 50 ~m. This porous film varied in moisturepermeability according to th~ location and exhibited
a slight degree of surface tackine~s. Disposable
diapers using this porous film as the leakproof
sheet caused a slight rash on the skin of infants.
Comparative Example 16
The procedure of Com~arative Example 15 was
repeated except that liquid Polybutadiene (Nisso PBG;
Nippon Soda Co., Ltd.) or rubbery EPR (Toughmer
(19
P0480; ~itsui Petrochemical Industries, Inc.) was
used as the hydroxyla~ed poly-saturated-hydrocarbon.
12~ 4
- 30 -
Thus; there were obtained films having a thickness
of 50 ~m. These porous films exhibited surface
tackiness and varied in moisture permeability
according to the location. Disposable diapers using
each of these porous films as the leakproof sheet
caused a slight rash on the skin of infants.
Porous films obtained by the process of
the present invention have high porosity and excellent
softness and, moreover, show little reduction in
strength in spite of their small thickness, so that
they are very suitable for use as a leakproof sheet
in sanitary napkins. Conventional sanitary napkins
are so constructed that a liquid absorber such as
fluffy pulp, cotton, absorbent resin or the like is
partially covered with a film of paper having been
rendered liquid-impermeable by treatment with a
synthetic resin such as polyethylene or the like and
the resulting structure is then wrapped in a non-
woven fabric. In sanitary napkins using the porous
film of the present invention as the leakproof sheet,
this leakproof sheet has a large number of pores
which allow water vapor to pass therethough. Accord-
ingly, they can keep the skin of the user in a dry
state and cause no disagreeable sensation even during
prolonged use.
The following examples illustrate the use of
~zs~
- 31 -
the porous film of the present invention as a leakproof
sheet in sanitary napkins.
Examples 25-27
-
Barium sulfate having an average particle
diameter of 0.8 ~m was added to 100 parts by weight
of linear low-density polyethylene (L-LDPE) having a
melt index (MI) of 2.1 in the amount given in Table 3,
and mixed therewith by means of a Henschel mixer.
Thereafter, using a twin-screw mixer, the resulting
mixture was intimately blended and formed into
pellets. Then, using a T-die extruder, these pellets
were melted at 230C and formed into a film. This
film was uniaxially stretched between a preheating
roll heated ~o 80C and a stretching roll by the
factor given in Table 3 to obtain a porous film
having a thickness of 20 ~m. Properties of this
porous film were evaluated and the results are
shown in Table 3. Sànitary napkins were made by
covering a filling of fluffy pulp partially with
each cf the porous films obtained in Examples 25-27,
wrapping the resulting structure in a non-woven
fabric and then heat sealing its overlapping portions.
When these sanitary napkins and commercially available
ones having a liquid-impermeable film of polyethylene-
coated paper were comparatively tested by using them
lZS~)~7~2~
- 32 -
practically for prolonged periods of time, the sanitary
napkins in accordance with the present invention
did not cause a disagreeable, stuffy sensation.
~5~Z~.
.
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