Microporous shaped article and process for preparation thereof

Disclosed is a microporous shaped polyolefin article comprising a polyolefin and synthetic resin particles dispersed therein and having a softening temperature or a decomposition temperature higher than the shaping temperature of the polyolefin resin, said article having a network structure composed of open-cellular pores with a maximum pore diameter of not more than 5 micromoters, having a porosity of 20 to 90% and being molecularly oriented by stretching. A process for its production is also provided.

BACKGROUND OF THE INVENTION 
This invention relates to a microporous shaped article having fine network 
open-cellular pores. 
Microporous shaped articles of various shapes having fine network 
open-cellular pores have been known. For example, microporous films have 
been widely used as a battery separator or a diaphragm of a capacitor, and 
hollow filaments have been widely used an air filter, a gas separation 
membrane, and a membrane for blood purification in a therapeutic field, 
and as a dialysis membrane. Typically, for production, a cellulose ester 
or polyester resin is dissolved in a solvent, and the solution is extruded 
from a spinneret of a double-walled tube and guided into a coagulating 
liquid. Another known method of production comprises mixing a filler 
composed of an inorganic compound typified by calcium carbonate and silica 
with a polyolefin, shaping the mixture in the molten state, and then 
stretching the shaped product (Japanese Patent Publication No. 
49405/1986). The first-mentioned method is easy and can give a shaped 
article having excellent permeation property. But the shaped article lacks 
chemical resistance and has inferior mechanical strength and particularly 
inferior break strength and elongation. In incorporating the hollow 
filament membranes in a helical or U-shape into a module, the hollow 
filaments tend to break and lose the excellent mechanical properties of 
the material. The latter method can give shaped articles form which the 
above defects have been removed to some extent. But the chemical 
resistance of the shaped article by the latter method is not sufficient. 
Furthermore, its pore size cannot be controlled, and its porosity cannot 
be increased above a certain limit. Thus, it is difficult to have the 
shaped article exhibit sufficient separation and permeation properties. 
It is an object of this invention therefore to provide a microporous shaped 
article having excellent mechanical strength and chemical resistance in 
which the pore diameter is controlled to a uniform value. 
Another object of this invention is to provide a technique of making a 
microporous shaped article having excellent separating and permeating 
abilities easily at low cost. 
Other objects of this invention will become apparent from the following 
description. 
According to this invention, there is provided a microporous shaped article 
comprising a polyolefin and synthetic resin particles dispersed therein 
and having a softening temperature or a decomposition temperature higher 
than the shaping temperature of the polyolefin, said article having a 
network structure composed of open-cellular pores with a maximum pore 
diameter of not more than 5 micrometers, having a porosity of 20 to 90% 
and being molecularly oriented by stretching. 
The microporous shaped article of this invention is composed mainly of a 
polyolefin and synthetic resin particles dispersed in the polyolefin. 
The polyolefin is not particularly limited, and any conventional 
polyolefins can be used. Typical examples of polyolefins that can be used 
particularly suitably include homopolymers of alpha-olefins such as 
polyethylene, polypropylene, polybutene-1 and polymethylpentene, 
copolymers of alpha-olefins and other copolymerizable monomers, and 
mixtures of these. In view of the thermal stability of the microporous 
article of the invention as well as shapeability, a propylene homopolymer, 
copolymers of propylene with other copolymerizable monomers and mixtures 
of these are preferred. 
The copolymers of alpha-olefins generally contain at least 90% by weight of 
an alpha-olefin, particularly propylene and not more than 10% by weight of 
another copolymerizable monomer. The copolymerizable monomers are not 
particularly limited, and any known monomers may be used. Generally, 
alpha-olefins having 2 to 8 carbon atoms, especially ethylene and butene, 
are preferred. 
The synthetic resin particles used in this invention act to induce peeling 
in the interface with the polyolefin and form open-cellular pores. 
Accordingly, the synthetic resin particles used have a softening 
temperature or a decomposition temperature higher, preferably at least 
10.degree. C., especially at least 100.degree. C. higher, than the shaping 
temperature of the polyolefin. Preferably, the synthetic resin particles, 
when mixed with the polyolefin, are not agglomerated but are dispersed 
uniformly. 
The synthetic resin particles used in this invention may be particles of 
any known synthetic thermosetting and thermoplastic resins which perform 
the above function. Above all, particles of thermosetting resin having a 
crosslinked structure are preferably used. If the softening or 
decomposition temperature of the synthetic resin particles is lower than 
the shaping temperature of the polyolefin, the synthetic resin particles 
may be softened or decomposed to evolve gases during the formation of a 
shaped article, and a microporous shaped article cannot be obtained. 
Specific examples of the synthetic resin particles preferably used in this 
invention include polyamides such as 6-nylon and 6,6-nylon; 
fluorine-containing resins such as polytetrafluoroethylene and 
tetrafluoroethylene-hexafluoropropylene copolymer; polyimides, silicone 
resins; phenolic resins; benzoguanamine resins; and crosslinked copolymers 
of styrene, acrylic acid, methacrylic acid, methyl acrylate or methyl 
methacrylate and a divinyl compound such as divinylbenzene. Particularly a 
crosslinked polymer is preferably used. Above all, the silicone resins are 
most preferably used because the interface between the polyolefin and the 
synthetic resin particles has good peelability, and by stretching, the 
shaped article can be easily rendered porous. 
The synthetic resin particles should have an average particle diameter of 
0.01 to 5 micrometers. If the average particle diameter of the synthetic 
resin particles falls outside the above range, the synthetic resin 
particles are difficult to disperse in the polyolefin, or they have too 
large a maximum pore diameter so that the resulting product cannot be used 
for such applications as liquid separation, reverse osmosis, 
ultrafiltration and gas separation. To obtain porous shaped articles that 
can be preferably accepted in such applications, the synthetic resin 
particles preferably have an average particle diameter of 0.03 to 3 
micrometers. Preferably, the synthetic resin particles have as narrow a 
particle size distribution as possible because with narrower particle size 
distribution, a more uniform pore size can be obtained. Generally, if the 
particle size distribution is expressed by S.sup.2, namely the average of 
the square of the difference from the average 
##EQU1## 
S.sup.2 is preferably not more than 1.5, especially not more than 0.1. The 
shape of the synthetic resin particles may be any. Usually, they are 
preferably in the form of a spherical or elliptical particle having a 
long-to-short diameter ratio of from 1 to 2 because pores having a uniform 
diameter can be obtained. The above ratio is especially preferably from 1 
to 1.5. 
Since the synthetic resin particles used in this invention are synthesized 
industrially, the above-mentioned uniform particles can be obtained. This 
uniformity brings about the following advantage over non-uniform particles 
of an inorganic compound obtained, for example, by crushing fine particles 
of the compound. Generally, when an inorganic compound is used as a 
filler, the largest amount of the filler to be added is about 40% by 
volume based on the polyolefin. Unexpectedly, however, when synthetic 
resin particles are used as the filler, 55% by volume or even more of them 
can be filled into the polyolefin. As a result, the porosity of the 
microporous shaped article obtained can reach even 90%. Moreover, since 
they have a uniform particle diameter, the dispersion of these particles 
in the resin is good, and the pores in the microporous shaped article can 
be controlled nearly to a uniform pore diameter. Another important 
advantage is that while the inorganic compound has insufficient chemical 
resistance, the synthetic resin particles have high chemical resistance 
and are not limited in use for lack of chemical resistance. 
The blending ratio between the polyolefin (a) and the synthetic resin 
particles (b) constituting the microporous shaped article may be 
determined properly depending upon the properties required of the final 
microporous shaped article. Most broadly, the proportion of (a) is 
generally 20 to 80% by weight, preferably 30 to 70% by weight, and the 
proportion of the synthetic resin particles (b) is generally 80 to 20% by 
weight, preferably 70 to 30% by weight. The above proportions of the 
component (a) and the component (b) are important for maintaining the 
properties of the microporous shaped article within the above-specified 
ranges and producing the microporous shaped article industrially 
advantageously. If the proportion of component (b) is lower than the 
above-specified lower limit, the formation of pores in the resulting 
microporous shaped article is not sufficient, and the desired porosity 
sometimes cannot be obtained. If, on the other hand, the proportion of 
component (b) is higher than the specified upper limit, the shapability of 
the starting composition tends to become poor. Consequently, sometimes, 
stretching tends to be unable to be carried out sufficiently, and a 
sufficient porosity tends to be unable to imparted to the shaped article. 
Since the particle diameter of the microporous shaped article is affected 
by the particle diameter of the synthetic resin particles, its required 
particle diameter can be obtained by controlling the particle diameter of 
the synthetic resin particles obtained. Generally, when synthetic resin 
particles having an average particle diameter of 0.01 to 5 micrometers are 
used, the resulting microporous shaped article has a maximum pore diameter 
of not more than 5 micrometers and an average particle diameter of 
generally 0.02 to 3 micrometers. Because the synthetic resin particles are 
uniformly dispersed in the polyolefin, the pores of the microporous shaped 
article are of a network structure composed of open-cellular pores. The 
porosity of the microporous shaped article is determined depending upon 
the blending proportion of the synthetic resin particles, the stretch 
ratio, etc. and can generally be selected from the range of 20 to 90%, 
preferably the range of 35 to 80%. 
Other properties of the microporous shaped articles arc the same 
irrespective of their shapes, if the production conditions are the same. 
However, since the shape and the mode of use of the microporous shaped 
article frequently differ according to usages, some typical properties and 
shapes are exemplified below. 
When the microporous shaped article is in the form of a hollow fiber 
The pores of the microporous hollow fiber are small and have excellent 
uniformity. They have a nitrogen gas permeating amount of generally 100 to 
100,000 liters/m.sup.2 .multidot.hr.multidot.0.5 atm. It can also be 1000 
to 100,000 liters/m.sup.2 .multidot.hr.multidot.0.5 atm. 
The small maximum pore diameter and the high porosity of the microporous 
hollow fiber have closely to do with the above desirable amount of 
nitrogen gas permeated. The above amount of nitrogen gas permeation has 
closely to do with the water permeability of the hollow fiber of this 
invention, and generally, the amount of water permeation through the 
hollow fiber is 1 to 1000 liters/m.sup.2 .multidot.hr.multidot.atm. 
Since the above maximum pore diameter and the porosity are related to each 
other, it is not always proper to point out the defects of the hollow 
fiber if independently these properties fall outside the specified ranges. 
However, the following can be stated generally. 
If the maximum pore diameter exceeds 5 micrometers, the hollow fiber 
frequently exhibits higher permeation properties for nitrogen and water 
than the above-specified upper limits. But this is not a preferred 
embodiment because the hollow fiber in this embodiment is decreased in 
separation ability between liquid/solid, liquid/gas, liquid/liquid and 
gas/solid. On the other hand, if the maximum pore diameter is less than 
0.01 micrometer, the hollow fiber has excellent separation ability, but 
the amounts of nitrogen gas permeation and the amount of water permeation 
markedly decrease, and they are not feasible for practically application. 
If the porosity becomes lower than the lower limit, the amounts of 
nitrogen gas permeation and the amounts of water permeation decrease. If 
the porosity becomes higher than the upper limit, the strength of the 
hollow fiber becomes weak, and its separation ability might be reduced 
undesirably. Furthermore, since the upper limit of the porosity is 
affected by the amount of the synthetic resin particles blended in the 
method of production. It is not advisable to obtain microporous hollow 
fibers having a higher porosity than the upper limit by an industrial 
method of production. 
Furthermore, the microporous hollow fiber usually can be produced so as to 
have a water resistant pressure of as high as 10000 to 50000 mmH.sub.2 O. 
However, where hydrophobic microporous hollow fibers having such water 
resistant pressures are disadvantageous, it is easy to decrease the water 
resistant pressure, and even to nearly 0 mmH.sub.2 O. For example, the 
water resistant pressure can be reduced by immersing the hydrophobic 
microporous hollow fiber in an aqueous solution containing a small amount 
(for example, 1 to 3%) of a non-ionic surface-active agent having an HLB 
of 10 to 15, or by adding the above surfactant in advance to a material 
for the microporous hollow fiber and shaping the mixture. 
When the microporous shaped article is in the form of a film 
The microporous shaped article in the form of a film exhibits is highest 
performance as a battery separator. Such a microporous polyolefin film can 
have an air permeability of 5 to 3000 seconds/100 cc, preferably 5 to 300 
seconds/100 cc. Its electrical resistance in propylene carbonate 
containing 2 moles of lithium perchlorate can be 0.01 to 100 
ohms/cm.sup.2, preferably 0.01 to 50 ohms/cm.sup.2. 
The water resistant pressure of the microporous film product, like the 
above microporous hollow fiber, can be 10000 to 50000 mmH.sub.2 O, and if 
required, can be decreased to nearly 0 mmH.sub.2 O by treatment with a 
nonionic surfactant having an HLB of 10 to 15. 
It is an important requisite that the microporous shaped article of this 
invention is molecularly oriented by stretching. The pores of the 
microporous shaped article of the invention has great uniformity. As will 
be clearly seen from the following description of the manufacturing 
process, this uniformity is induced by stretching the polyolefin 
containing a large amount of the synthetic resin particles. For the 
uniform occurrence of the pores, the stretch ratio is a very important 
factor, although it is also an important factor to select an additive for 
finely dispersing the synthetic resin particles in the polyolefin. 
Preferably, the stretch ratio of the microporous shaped article of the 
invention is 1.5 to 30 in terms of an area stretch ratio. It is not always 
necessary to stretch the article in two directions, and monoaxial 
stretching alone may give a shaped article having sufficiently good 
properties. When the shaped article is stretched only in one direction 
(the longitudinal direction of the hollow filaments), the stretch ratio is 
preferably 1.5 to 12, preferably 3 to 7. When it is to be stretched 
biaxially, the stretch ratio in one direction (the longitudinal direction 
of the hollow fibers) is generally at least 1.2, preferably at least 1.5, 
and the stretch ratio in the other direction (the circumferential 
direction of the hollow filaments) is generally at least 1.2, preferably 
at least 1.5. Most preferably, the shaped article is stretched in the 
first direction at a stretch ratio of 2 to 5, and in the second direction 
at a stretch ratio of 2 to 7. 
When the microporous shaped article is in the form of a hollow fiber, its 
outside diameter is 50 micrometers to 5 mm, and its thickness is 10 
micrometers to 0.5 mm. If it is in the form of a film, its thickness may 
be 5 to 200 micrometers. 
To obtain the microporous shaped articles, the polyolefin, the synthetic 
resin particles and the additive must be used in specific combinations of 
types and amounts. Typical manufacturing processes will now be described 
in detail. 
A process which comprises melt-shaping a mixture composed of 20 to 80% by 
weight of (a) a polyolefin, 80 to 20% by weight of (b) synthetic resin 
particles having an average particle diameter of 0.01 to 5 micrometers and 
having a softening temperature or a decomposition temperature higher than 
the shaping temperature of the polyolefin, and 0.1 to 20 parts by weight, 
per 100 parts by weight of the components (a) and (b), of a plasticizer 
into a desired shape such as a film or hollow fibers, and then stretching 
the shaped article at an area stretch ratio of 1.5 to 30 times its 
original area may be typically pointed out. It is generally difficult to 
mix a large amount of the component (b) uniformly with the component (a). 
To remove this difficulty, it is important to add a specific amount of the 
plasticizer at the time of mixing the components (a) and (b). The amount 
of the plasticizer (c) is 0.1 to 20 parts by weight per 100 parts by 
weight of the components (a) and (b) combined. 
The amount of the plasticizer (c) to be added affects the properties of the 
microporous shaped articles to a greater extent than the proportions of 
the components (a) and (b) do. If the amount of the plasticizer (c) is 
smaller than the above lower limit, the dispersion of the synthetic resin 
particles in the polyolefin is not good, and a microporous shaped article 
having uniform pores cannot be obtained. If the amount of the plasticizer 
(c) is larger than the upper limit, the plasticizer partly flows out 
during the shaping, and the thickness and diameter of the shaped article 
cannot be controlled. Consequently, the desired porous shaped article 
cannot be obtained. 
Many plasticizers for use in various synthetic resins are known. Any of 
these known plasticizers may be used as the plasticizer (c) in this 
invention. Preferred plasticizers generally used are polyester-type 
plasticizers and epoxy-type plasticizers. Examples of such plasticizers 
are described below. 
The polyester-type plasticizers are preferably those obtained by 
esterification reaction of aliphatic or aromatic dibasic or tribasic acids 
having 4 to 8 carbon atoms with linear dihydric alcohols having 2 to 5 
carbon atoms. Specific examples of the polyesters which are particularly 
preferably used include polyester compounds derived from dibasic or 
tribasic acids such as sebacic acid, adipic acid, phthalic acid, azelaic 
acid and trimellitic acid and ethylene glycol, propylene glycol, butylene 
glycol, neopentyl glycol and long-chain alkylene glycols, especially 
polyester compounds derived from adipic acid or sebacic acid and propylene 
glycol, butylene glycol or long-chain alkylene glycols. Compounds obtained 
by epoxidizing the double bonds of monobasic linear unsaturated acids 
having 8 to 24 carbon atoms are most preferred as the epoxy-type 
plasticizers. Specific examples include epoxidized soybean oil and 
epoxidized linseed oil. These plasticizers may be used singly or in 
combination. 
In a preferred embodiment, a silane-type dispersing agent (d) may be 
further used in a suitable amount in addition to the plasticizer (c) in 
order to improve shapability, or to improve the dispersibility of the 
component (b). The preferred amount of the component (d) is 0.01 to 5 
parts by weight per 100 parts by weight of the components (a) and (b) 
combined. 
The additive (d) is not essential, but generally the addition of the 
component (d) frequently produces favorable results. If, however, the 
amount of the silane-type dispersant (d) exceeds 5 parts by weight per 100 
parts by weight of the components (a) and (b) combined, the silane-type 
dispersant will partly flow out during the shaping as does the 
plasticizer. Hence, the amount of the component (d) should preferably be 
up to 5 parts by weight. 
The silane-type dispersing agent may be any of known silane compounds, and 
examples of preferred silane compounds include alkoxysilane compounds of 
the formula R.sub.4-n .multidot.Si(OR').sub.n in which R and R' each 
represent an alkyl group such as a methyl, ethyl or propyl group, and n is 
an integer of 2 or 3. Especially preferred are methyltrimethoxysilane, 
ethyltrimethoxysilane dimethyldimethoxysilane and diethyldimethoxysilane 
in which R and R' are a methyl or ethyl group. 
Mixing of the components (a), (b) and (c) and optionally (d) may be 
performed by using any known mixing method. For example, the above 
components may be simultaneously mixed by using a mixer such as a 
supermixer or a Henschel mixer. It is possible to mix components (c) and 
(d) with component (b), and then melt-knead the polyolefin (a) with the 
mixture by, for example, a single-screw or twin-screw extruder, and cut 
and pelletize the extrudate. 
It is frequently a desirable embodiment to add known additives such as a 
coloring agent, a lubricant, an antioxidant, a degradation inhibitor, a 
hydrophilizing agent and a hydrophobizing agent at the time of mixing the 
above components, so long as it does not impair the production of the 
desired microporous shaped articles. 
When the above mixture (composition) is melt-shaped into an article of the 
desired shape and then stretched, the microporous shaped article of the 
invention is obtained. 
When the microporous shaped article of the invention is to be obtained in 
the form of a hollow fiber, it is generally possible to use a known 
extruder for hollow fiber production which is equipped with a known 
double-walled cylindrical spinneret. In the production of hollow fibers 
generally, the shaped article is monoaxially stretched by a roll 
stretching method. Or as required, after monoaxial stretching the article 
is consecutively stretched in the lateral direction by a known tenter 
stretcher. Alternately, it may be simultaneously stretched in the machine 
and transverse directions. 
When the microporous shaped article is to be shaped into a film or sheet, a 
sheet-like article is first produced by a general inflation molding method 
or an extrusion method using a T-die. Then, the sheet-like material is 
monoaxially stretched by a general roll stretching method. Or after the 
monoaxial stretching, it is consecutively stretched in the transverse 
direction by a tenter stretcher or an air inflation stretcher. 
Alternatively, there may be employed a method in which it is stretched 
simultaneously in the machine and transverse direction. 
Preferably, the microporous shaped article obtained by the above stretching 
procedure is further heat-treated under tension, for example, at a 
temperature above the stretching temperature but below the melting point, 
to set it, and then cooled to room temperature to obtain the final 
product. In a further preferred embodiment, to improve adhesion, the 
product is surface-treated by, for example, corona discharge treatment, 
hydrophilizing treatment or hydrophobizing treatment. 
As a result of the polyolefin having been molecularly oriented by 
stretching or having been further heat-set, the microporous shaped article 
has markedly increased thermal resistance and improved mechanical 
strength. When heat-set, the product has markedly improved dimensional 
stability at room temperature and high temperatures. 
By choosing shapes, the microporous shaped articles of the invention may be 
widely used in various applications. For example, the microporous shaped 
articles in the form of a hollow fiber can be used as an air filter for 
dust removal or removing microbes; a gas separation membrane; for water 
treatment; for production of clean water in the food industry, electronics 
industry and pharmaceutical industry; as household water purifying device; 
for blood purification and as artificial lungs and dialysis membrane in 
the field of medical therapy. They can also be suitably used as a support 
for precision filtration, ultrafiltration, reverse osmosis or 
pervaporation. The microporous shaped articles in the form of a film may 
be suitably used as a battery separator, and also a capacitor, an 
artificial leather, a synthetic paper-like sheet, a packaging film for a 
heat-insulating pack, a packaging film for a moisture absorber pack, a 
bandage, a wear for a surgeon, a face mask, a back sheet for a 
pharmaceutical paste, and a gas purification filter. 
The following Examples and Comparative Examples illustrate the present 
invention more specifically. The present invention are not to be limited 
to these Examples. 
The various properties of the microporous shaped articles in these examples 
were measured or determined by the following methods. 
Maximum pore diameter (micrometers) 
Measured by the methanol bubble point method. 
Average pore diameter (micrometers) 
Measured by a mercury porosimeter method. 
Porosity (%) 
With respect to a microporous film, it was determined by specific gravity 
measuring method and calculated from the following equation. 
##EQU2## 
With respect to a microporous hollow fiber, it was calculated from the 
following equation in accordance with the mercury porosimeter method. 
EQU Porosity=(Pore volume/volume of the microporous hollow fiber).times.100(%) 
Tensile strength and break elongation 
By using an autography made by Shimazu Seisakusho Co., Ltd., the sample 
(hollow fiber) was pulled at a pulling speed of 200%/min. with an 
interchuck distance of 50 mm, and the strength and elongation of the 
sample were measured at break. 
Amount of nitrogen gas permeated 
Ten microporous hollow fibers were bundled, and by cementing the open 
portions of the hollow fibers with an epoxy resin, a module was 
constructed. The effective length of the hollow fibers excepting the epoxy 
resin-embedded portions was adjusted to 15 cm. A pressure of 0.5 atm was 
applied 25.degree. C. to the hollow fibers of the module with nitrogen 
gas. The amount of nitrogen gas which passed through the wall surface of 
the hollow fibers was measured. The membrane area was determined on the 
basis of the inside diameters of the fibers. 
Amount of water permeated 
Ten microporous hollow fibers were bundled, and by cementing the open 
portions of the hollow fibers with an epoxy resin, a module was 
constructed. The effective length of the hollow fibers excepting the epoxy 
resin-embedded portions was adjusted to 15 cm. prior to measuring the 
water permeating property of the module, the module was immersed in a 2% 
ethanol solution of a nonionic surfactant having an HLB of 21. Then, water 
under a pressure of 1 atm was applied, and the amount of water which 
passed through the wall surface of the hollow fibers was measured. The 
membrane area was based on the inside diameter of the hollow fibers. 
Air permeability (sec/100 cc) 
Measured by JIS-P-8117 (Gurley's Air permeability) 
Water resistant pressure (mmH.sub.2 O) 
Measured by JIS-K-6328. 
Electrical resistance 
A pure platinum plate was used as an electrode plate. As an organic 
electrolyte solution for a lithium cell, 2 moles of lithium perchlorate 
was dissolved in a propylene carbonate solution, and the electrical 
resistance was measured at 25.degree. C. at an alternate current of 1 KHz. 
Shapability 
An unstretched film or hollow fiber was observed visually or by a finger 
touch, and the results were rated on the following scales. 
Good: The surface was free from thickness unevenness and raisings and 
depressions. 
Fair: the surface slightly had thickness unevenness or surface raisings or 
depressions. 
Poor: The sample had thickness unevenness and surface raisings and 
depressions. 
Dispersibility 
The microporous shaped article obtained after stretching was observed 
visually, and the presence of fish eyes was determined on the following 
scales. 
Good: The sample was free from fish eyes. 
Poor: Fish eyes were observed. 
Stretchability 
In the case of a film, the unstretched film was stretched monoaxially 
and/or biaxially, and the stretched state was evaluated. 
In the case of a hollow fiber, the unstretched hollow fiber was stretched 
longitudinally, and the stretched state was evaluated. 
Good: no cutting and break occurred, and the stretching was carried out 
uniformly. 
Slightly poor: The stretching could be done, but an unstretched portion 
remains partly. 
Impossible of stretching: cutting or break occurred, and stretching failed. 
In the following Examples and Comparative Examples, the resins, the 
synthetic resin particles, the plasticizers and the silane-type dispersing 
agents used were the following commercial products. 
Polypropylene: PN-120 (tradename) made by Tokuyama Soda Kabushiki Kaisha, 
density 0.91 g/cm.sup.3, intrinsic viscotity (measured in tetralin at 
135.degree. C.) 2.38 dl/g, melting point 160.degree. C. 
Propylene/ethylene copolymer: MS-624 (tradename) produced by Tokuyama Soda 
Kabushiki Kaisha, density 0.09, instrinsic viscosity (measured in tetralin 
at 135.degree. C., ethylene content 4.7% by weight. 
Polyethylene: High density Polyethylene Hizex 1200J (tradename) produced by 
Mitsui Petrochemical Industries, Ltd., melt index 1.3 g/10 minutes, 
softening temperature 135.degree. C. 
Silicone resin (A): XC99-301 (tradename) produced by Toray Silicone Co., 
Ltd., spherical particles having an average particle diameter of 4 
micrometers, dispersion 1.5, heat decomposition temperature 450.degree. C. 
Silicone resin (B): XC99-501 (tradename) producted by Toray Silicone Co., 
Ltd., spherical particles having an average particle diameter of 2 
micrometers, dispersion 0.007, heat decomposition temperature 450.degree. 
C. 
Silicone resin (C): XC-651 (tradename) produced by Toray Silicone Co., 
Ltd., spherical particles having an average particle diameter of 1.3 
micrometers, dispersion 0.01, heat decomposition temperature 450.degree. 
C. 
Silicone resin (D): XC99-621 (tradename) produced by Toray Silicone Co., 
Ltd., spherical particles having an average particle diameter of 0.8 
micrometer, dispersion 0.008, heat decomposition temperature 450.degree. 
C. 
Silicone resin (E): XC99-789 (tradename) produced by Toray Silicone Co., 
Ltd., spherical particles having an average particle diameter of 0.3 
micrometer, dispersion 0.007, heat decomposition temperature 450.degree. 
C. 
Methylmethacrylic acid/divinylbenzene copolymer: MP3000 (tradename) 
produced by Soken chemical Co., Ltd., spherical particles having an 
average particle diameter of 0.4 micrometer, dispersion 0.007, heat 
decomposition temperature 250.degree. C. 
Styrene/acryllic acid/divinylbenzene copolymer: Microgel (tradename) 
producted by Japan Paint Co., Ltd., spherical particles having an average 
particle diameter of 0.2 micrometer, dispersion 0.007, heat decomposition 
temperature 270.degree. C. 
Benzoguanamine resin (A): Eposter-R-S (tradename) produced by Japan 
Catalytic Chemical Industry Co., Ltd., spherical particles having an 
average particle diameter of 0.8 micrometers, dispersion 0.1, heat 
decomposition temperature 300.degree. C. 
Benzoguanamine resin (B): Eposter-R-L (tradename) produced by Japan 
Catalytic Chemical Industry Co., Ltd., spherical particles having an 
average particle diameter of 15 micrometers, dispersion 0.3, heat 
decomposition temperature 300.degree. C. 
Polyester-type plasticizer: PN-150 (tradename) produced by Adeka-Argus Co., 
Ltd. 
Epoxy-type plasticizer: Epocizer W100EL (tradename) epoxidized oil produced 
by Dainippon Ink and Chemicals, Inc. 
Silane-type Dispersing agents 
Methyltrimethoxysilane: TSL 8113 (tradename) produced by Toshiba Silicone 
Co., Ltd. 
Methyltriethoxysilane: TSL 8123 (tradename) produced by Toshiba Silicone 
Co., Ltd. 
Dimethyldidmethoxysilane: TSL 8117 (tradename) produced by Toshiba Silicone 
Co. Ltd.