CA1084663A - Microporous film and method for preparing the same - Google Patents
Microporous film and method for preparing the sameInfo
- Publication number
- CA1084663A CA1084663A CA255,022A CA255022A CA1084663A CA 1084663 A CA1084663 A CA 1084663A CA 255022 A CA255022 A CA 255022A CA 1084663 A CA1084663 A CA 1084663A
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- Prior art keywords
- film
- polyolefin
- set forth
- microporous film
- molecular weight
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/0066—Use of inorganic compounding ingredients
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
- C08J2201/0542—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition
- C08J2201/0543—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition the non-solvent being organic
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
- C08J2201/0545—Precipitating the polymer by adding a non-solvent or a different solvent from an aqueous solvent-based polymer composition
- C08J2201/0546—Precipitating the polymer by adding a non-solvent or a different solvent from an aqueous solvent-based polymer composition the non-solvent being organic
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Electrochemistry (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
- Cell Separators (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A microporous film comprising a 40 to 90 volume percent polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000 and a 10 to 60 volume percent inorganic filler and having a void space rate or porosity of 30 to 75 volume percent based on the volume of the film. The microporous film of such specific composition and structure has a desired wettability and much reduced electrical resistance as low as 0.0006 .OMEGA.dm2/sheet, keeping sufficient flexibility and mechanical strength and is useful in wide variety of applications, especially with great advantage for separators of battery or electrolytical apparatuses etc. Such microporous material is prepared by blending the specified polyolefin, the inorganic filler and an organic liquid in amounts of 10 to 60 volume percent, 6 to 35 volume percent and 30 to 75 volume percent, respectively based on the whole volume of the blend, the amount of the polyolefin being 2/3 to 9 multiple of the amount of the inorganic filler; subjecting the blend to molding to form a film; and extracting from the film said organic liquid.
A microporous film comprising a 40 to 90 volume percent polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000 and a 10 to 60 volume percent inorganic filler and having a void space rate or porosity of 30 to 75 volume percent based on the volume of the film. The microporous film of such specific composition and structure has a desired wettability and much reduced electrical resistance as low as 0.0006 .OMEGA.dm2/sheet, keeping sufficient flexibility and mechanical strength and is useful in wide variety of applications, especially with great advantage for separators of battery or electrolytical apparatuses etc. Such microporous material is prepared by blending the specified polyolefin, the inorganic filler and an organic liquid in amounts of 10 to 60 volume percent, 6 to 35 volume percent and 30 to 75 volume percent, respectively based on the whole volume of the blend, the amount of the polyolefin being 2/3 to 9 multiple of the amount of the inorganic filler; subjecting the blend to molding to form a film; and extracting from the film said organic liquid.
Description
-~v~
This invention relates to a microporous film, and more particularly to a microporous film comprising a matrix composed of a polyolefin and an inorganic filler and void spaces formed therein and having overall a microporous structure.
here have heretofore been proposed:
(1) a porous film prepared by the method kneading and molding a polyvinyl chloride resin, a solvent for the resin, a plasticizer and silica into a film, and then subjecting the molded film to drying process (See, for example Japanese Patent Application Publication No. 2922/1962):
This invention relates to a microporous film, and more particularly to a microporous film comprising a matrix composed of a polyolefin and an inorganic filler and void spaces formed therein and having overall a microporous structure.
here have heretofore been proposed:
(1) a porous film prepared by the method kneading and molding a polyvinyl chloride resin, a solvent for the resin, a plasticizer and silica into a film, and then subjecting the molded film to drying process (See, for example Japanese Patent Application Publication No. 2922/1962):
(2) a porous film prepared by sintering a mixture of powder : polyvinyl chloride resin and finely divided silica (See, for example Japanese Patent Application Publication No. 3092/1960);
15 ~ and (3) a porous film prepared by molding a mixture of a polyolefin having a standard load melt index of 0 and a viscosity average molecular weight of 300,000 or more, silica and a plasticizer into a film and extracting the plasticizer from the molded film. (See, for example U.S.
patent specification 3,351,4~5).
In case a porous film is employed for example as a separator of a lead accumulator, the film is required to . have a small electrical resistance in the e].ectrolyte. For . a high-performance separater, the film should have an electrical resistance lower than 0.0006 Qdm2/sheet. To meet this re-quirement, the film should have high void space rate or porosity to enjoy anelectrical resistance as low as 0.0003 Qdm2/O.lmm(in thickness) or less and be formed to have a thickness of about 0.2 mm. In case the electrical resistance . 30 is higher than 0.0003Qdm2/ 0.1 mm, the film should be .~ .
6~;3 ., -formed extremely thin, to wit, less than 0.2 mm thick.
n this connection, it is to be noted that the conventional porous films (1) and (2) made of a polyvinyl chloride resin as mentioned above can be imparted with an electrical resistance as low as 0.0003 Qdm2/0.1mm but they have such defects as being brittle and lacking flexibility so that they are extremely difficult to be formed in a film of practical use having a thickness of less than 0.4 mm. On the other hand, the ; conventionally proposed porous film made of an ordinary polyolefin and a vast amount of inorganic filler fails to have flexibility and is too brittle to be practically utilizable.
Then, there has been proposed the method as mentioned above referring to the film (3) to solve the problem of brittleness and lack of flexibility. This method~ however, encounters another drawback of poor moldability which causes difficulty ` to form a thin film because there is employed in the method a super high molecular weight polyolefin of low flow characteristics such as a polyolefin having a standard load melt index of 0 and a viscosity average molecular weight (it is nearly equal to a weight average molecular weight) of 300,000. Furthermore, the film (3) has inevitably an electrical resistance higher than 0.0003Q dm2/0.1 mm. Thus, it is difficult to produce a high-performance separator having an electrical resistance as low as 0.0006 Qdm2/sheet or less from the conventional films.
Accordingly, one and principal object of the present invention is to provide a microporous film having a high mechanical strength and great flexibility and, in addition, wetting characteristics, showing much reduced electrical resistance in an electrolyte.
~01346~3 The inventors of the present application have made an intensive and extensive study with a view to obtaining a microporous film of high void space rate or porosity while keeping sufficient mechanical strength and flexibility, and surprisingly found that with use of a- polyolefin having a molecular weight of a specified range there can be effectively produced, with a good molding processability a microporous film having excellent properties.
In one aspect of the present invention, there is provided a microporous film which comprises 40 to 90 volume percent of a polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000 and 10 to 60 volume percent of an inorganic filler; and which has a void space rate of 30 to 75 volume percent based on the volume of the film. The microporous film of the present invention has a mechanical strength and flexibility sufficient for various uses, particularly for an electrochemical or electrolytical separator or battery separator. With this microporous thin film, the electrical resistance of a separator is by far reduced to 1/10 of the resistance of separator made of the conventional film such as polyvinyl chIoride-sintered film, polyvinyl chloride-extracted film, etc.
The foregoing and other objects, features and advantages of the invention will be better understood from the following detailed description and appended claims taken in connection with the accompanying drawings in which:
Fig. 1 (a) is an enlarged diagrammatical view of a microporous film of the present invention, shown in the state the inorganic filler is extracted;
Fig. 1 (b) is an enlarged diagrammatical view of a portion x-y-z as shown in Fig. 1 (a);
Fig. 1 (c) is an enlarged diagrammatical view of a portion S as shown in Fig. 1 (b), illustrating the web structure defining a network of void;
Fig. 2 is a scanning electron photomicrographic ( x 10,000 ) plan view of the microporous film obtained in Example 3, with the silica extracted;
Fig. 3 is a similar scanning electron photomicrographic ( x 10,000 ) plan view of the film obtained in Comparative Example 5, with the silica extracted; and ~ .
Fig. 4 is a similar sc~ng electron photomicrographic ( x 10,000 ) plan view of the film obtained in Comparative ` Example 7, with the silica extracted.
The most important characteristic feature of the present invention is in the polyolefin employed. According to the present invention, there should be employed a polyolefin having a number average molecular weight of 15,000 or more, preferably, 17,000 to 50,000 and a weight average molecular weight of less than 300,000, preferably ranging from 85,000 .
to 250,000. There may be employed a polyolefin having a standard load melt index of 0.01 or more, preferably 0.03 to 1. With use of such specific polyolefin, it is possible to form a flexible thin film having a thickness ranging from 0.05 to 1 mm. In contrast, when a polyolefin having a number average molecular weight of less than 15,000 is employed, a porous material obtained i5 poor in stretchability and brittle.
Whereas, in case a polyolefin having a weight average molecular weight of 300,000 or more is employed, there are caused ; 30 problems as to moldability because of its poor flow characteristics ; - 5 -~B~663 in the molten state and as to electrical resistance of the film produced therefrom because the void space rate or porosity is lowered.
The term "polyolefin" used herein is intended to include homopolymers and copolymers of olefins, for example, poly- - -ethylene, polypropylene, polybutene, ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-p.~opylene-butene tercopolymers, and mixturés thereof so long as they have a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000. Of these resins, polyethylene or a copolymer of ethylene as a ;
main component with another olefin is most preferable.
The inorganic filler employed serves to impart wetting characteristics to the prepared film and the filler is pre-ferably finely divided particles or porous particles having an average particle diameter ranging from 0.005 to 0..5~ and a specific surface area of 50 to 500, preferably 150 to 400 m /g. ~s specific examples of the inorganic fillers, there can be mentioned silica, calcium silicate, aluminum silicate, aluminum oxide, calcium carbonate, magnesium carbonate, kaolin clay, pulverized talc, titanium oxide, diatomaceous earth, carbon black, etcO Two or more kinds of fillers may be employed in combination. In this case, one of the fillers is to have a hydrophi~ic property. For an electrolytic ~;
separator and a lead accumulator which uses acid electrolyte, silica is preferably employed.
In the microporous film of the present in/ention the : ' g,~
~^ cm/p~
.
.. . , :, ~4L6~i3 amount ratio of the polyolefin and the inorganic filler is 40 to 90 volume percent to 10 to 60 volume percent. For use as a separat~r, the ratio is preferably 50 to 80 volume percent (polyolefin) to 20 to 50 volume percent (filler) and more preferably 60 to 70 volume percent to 30 to 40 volume percent. In case the amount of the filler employed exceeds 60 volume percent, the film obtained is poor in flexibility ; and not practically employable even if a polyolefin having a number average molecular weight of 15,000 or more is employed.
Whereas, in case the amount of the filler employed is less than I0 volume percent, the strength of the film obtained increases but the wetting characteristics thereof is so reduced that the film cannot be ulitized for a separator.
~ .
Referring to Fig. 1 there is shown enlarged diagrammatic views of a microporous film , with the silica extracted, .
; of the present invention. As seen from Fig. 1, especially from Fig. 1 (c), the microporous film has such a structure that the polyolefin constitutes a web structure 1 and a void ` 2 defined by the polyolefin web structure i5 formed in network. The void opens at the surface of the film and an average diameter of the opening portion of the void is in the range of 0.05 to 0.5 ~u. The network void contains the filler attached thereto, leaving a space forming a path communicating from one surface of the film to the opposite ~; 25 surface of the film.
The term "void" used herein has a meaning as apparent from the above description and more illustratively it means a void portion defined by the polyolefin web structure but having the filler contained therein. The term "void space"
used herein has a meaning as apparent from the above description 6~3 and more illustratively it means a space left in the void and formed by cooperation between the particles of filler contained therein and cooperation between the wall of the void and the particles of filler contained therein. The term "void space rate" used herein is intended to mean a volume rate of void spaces formed in the overall structrure of the microporous film.
The actual average diameter of the void in,the state - where the filler is attachedly disposed, namely the average diameter of the opening portion of the void space is as small as 0.01 to 0.1 ~u. The thus formed film of the present invention has a void space rate of 30 to 75 volume percent based on the volume of the film. In case the void space rate is less than 30 volume percent, the electrical resistance increases and the film obtained can not be effectively employed for the separator. Whereas, in case the void space rate exceeds 75 volume percent, the strength of the film obtained is so reduced that the film can not be practically utilized. To meet the requirements both of strength and electrical resistance, the void space rate is preferably within the range of 45 to 6S volume percent. Further, in order that the microporous material may have a desired electrical resistance and a void space of a size suitable for ~; preventing the passage of solid materials and permitting ions to pass through while maintaining a mechanical strength,tthe average diameter of the void is to be in the range of 0.05 to 0.5 and more preferably in the range of 0.08 to 0.3 JU.
The microporous film of the present invention has a thickness of 0.05 to 1 mm. The film thickness may be for a separator preferably within the range of 0.10 to 0.30 mm in ' :, ' '.
view of imparting good moldability and sufficient strenyth j to the resulting film.
~ Thus, to the film of the present invention having a I high porosity with fine void spaces or pores formed in the j~
network structure, sufficient mechanical strength and excellent flexibility is further imparted with an unexpected low electrical resistance (as low as 0.0006 Q dm2/sheet). This film can be employed with great advantage for a separator, by far enhancing the separator performance.
Referring to Fig. 2, there is shown a scanning electron photomicrographic plan view of the present microporous film, ¦, in comparison with those of conventional porous films as shown in Figs. 3 and 4. As is seen from these Figures, the present microporous film has definite pores of a suitable size and of a number as many as 4 to 6 x 10 /cm2, leading to a desired electrical resistance as low as 0.0006 Q dm /sheet while maintaining high mechanical strength, as opposed to -the con- j ~i ventional porous films in which there are formed pores of -too small a size to distinguish, which exerts unfavourable influence on the electrical resistance, increasing the same.
Due to the excellent properties as mentioned above, the . i .
microporous film of this invention has a wide variety of uses, ¦
for example, as a battery separator, filter, liquid retainer, wrapping material, synthetic paper, etc. In view of its extremely low electrical resistance in an electrolyte, the microporous film of the present invention is useful with grea-t advantage especially for a battery separa-tor and a separator j in various electrochemical or electrolytical apparatuses.
The microporous film of the present invention formed of . ' , ,, i ~ . .
-. '~
''' ' .
.
~ _ g _ ; cm/~
, ' ~34~63 .
', ~
a polyolefin and an inorganic filler is produced, for example, by a process as given below. i~
Accordingly, as another aspect of the present invention ¦' there is provided a process for preparing a microporous film j~
which comprises: blending a polyolefin having a number j average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000, an inorganic ~ ,l - filler and an organic liquid in amounts of 10 to 60 volume ~ I I
~,:
percent, 6 to 35 volume percent and 30 to 75 volume percent, ;
respectively, based on the whole volume of the polyolefin-filler-liquid composition, the amount of the polyolefin being 2/3 to 9 multiple of the amount of the inorganic filler;
sub~ecting the resulting blend to molding to form a film; ~
and extracting from said film said organic liquid. , -Based on the total volume of the polyolefin, the inorganic filler and the organic liquid, 6 to 35 volume percent inorganic filler and 30 to 75 volume percent organic . ~ , .
liquid are blended using an ordinary mixer such as a Henschel mixer or V-shaped tumbler to absorb the organic liquid onto the surface of the filler particles. The conditions of the above blending vary slightly according to kind and rotation speed of the mixer used, but usually the blending is accomplished at room temperature for about one minute. A polyolefin is then mixed with the above obtained blend in an amount of 10 to 60 percent by volume but 2/3 to 9 multiple by weight based on the inorganic filler. The above-mentioned blending of three com-ponents i5 effected in a two-stage operation, bu-t a one-stage blending operation may be employed. When the two-stage blènding is employed, good handling characteristics . ., . .
~' ', ~
.; , ' "". ':
:
cm/p~ - 10 - ~
., I , .
, and cxcellent dispersioll of the component can be attained Whilst, when the one-stage blendiny is employed, the ~` polyole1n tends to be wetted with the organ.ic liqu.id so that good dispersion of the components cannot be attained In such case, however, the dispersion of the three components can be attained by adjusting rotation speed of the mixer, b].ending time, etc ~:
The resulting polyolefin-filler-liquid blend is kneaded by a kneading machine such as an extruder, a sanbury mixer, am~ing twin roll, a kneader, etc The so kneaded material is subjected to molding to be formed in a film having a thickness of 0.05 to lmm. Typical examples of the molding are extrusion molding employing a T~die or inflation method, calender molding, compressi.on molding, ` injection molding, etc The T-die extrusion molding is especially preferable to form a film as thin as 0.05 to lmm :~
The molding may be effected under molding conditions as ordinarily employed in molding of polyolefins as far as the molding i.s effected at a temperature higher than the melting point of the polyolefin employed and below the boiling point of the organic liquid employed.
The kneading step as described above is optional , in the method of the present invention, Particularly, in the extrusion molding in which the kneadiny is also conducted simultaneously, the separate step for kneading is not necessary~ But when the kneading step is positively employed, the bulk density of the blend can be appropriately controlled and, at the same time, good dispersion of the components can be attained, leading to i.mprovement of handling characteristics and reduction of pin holes of the product film. Such reduction * Trademark bm: .
: :
~iL084L16~3 . . . :
' of pin holes is particularly important for a battery separator and separators of various electrolytical apparatus.
The organic liquid is extracted from the molded film 1~
at a temperature below a melting point of the polyolefin ~y a ~ ~-solvent OL the organic liquid employed, to form a final micro-porous film made of 40 to 9a vo]ume percent polyolefin and 10 to 60 volume percent inorganic filler and having a void space rate of 30 to 75 volume percent based upon the film volume.
The organic liquid employable in the present invention ¦-is preferably kept in a liquid stata at the time of the molding;
it is readily soluble in general organic solvents or water and is easily extractible.from the molded film. The organic --liquid is selected from ones having a solubility parameter (hereinafter referred to as "SP") of 8.4 to 9.9, preferably from 8.6 to 9.4. An organic liquid having an SP of more than 9.9, when used in the method of the present invention, forms .. . .
~`, coarse pores or voids of more than 0.5 ~ in average diameter I --, and the resultant film has a poor elongation and is brittle.
On the other hand, when an organic liquid having an SP of less than 8.4 is used, the breaking strength and elongation l; are improved but the electrical resistance is also increased. ~j It should be noted that, according to the present invention, with use of an organic solvent having an SP of 8.4 to 9.9 as well as a polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000, there is obtained a microporous film of a specific construction in which the 1!
polyolefin constitutes a web structure defining a network of voids in which the filler is attachedly contained, leaving ' .
cm/~ - 12 -.' ':' ,~ . . :
, . . ,-: - , .. . :. ~
.
~L~1346~i3 , . a space to form a path communicating from one surface of the film to the opposite surface thereof, said voids hav;ng l~-~ an average void diameter ranging from 0.05 to 0.5 ;~ Representative examples of the organic liquid having ~
an SP ranging from 8.4 to 9.9 are phthalic acid esters such ,J
as diethyl phthalate (DEP), dibutyl phthalate (DBP), and ¦, dioctyl phthalate (DOP); fatty acid esters such as dioctyl ~ ;
sebacate (DOS) and dioctyl adipa-te (DOA); maleic acid es-ters ~ such as dibutyl maleate; trimetallitic acid esters such as - 10 trioctyl trimellitate (TOTM); phosphoric acid esters such as r tribu-tyl phosphate (TBP), octyl diphenyl phosphate, tricresyl phosphate (TCP); other esters; and glycols such as polyethylene glycol.
The solvent employable for extracting the organic liquid from the molded film is selected from those capable ' ` of dissolving the organic liquid but not dissolving the poly- ¦;
I olefin used. ¦
Representative examples of the solvent-to be employed ~
for extracting the organic liquid include alcohols such as ~j methanol, ethanol and iso-propanol; ketones such as acetone;
j and chlorine-substituted hydrocarbons such as trichloroethylene and l,l,l-trichloroethàne. The extraction of the organic ~' liquid from the molded film may be conducted employing various ¦
methods ordinarily employed in the art, for example batch type dipping method, counter-flow method and the like (U.S.
Patent Specification No. 3,351,495 may be referred to).
Since the average diameter of the voids of the present i ` porous film is in an appropriate range, i.e. 0.05 to 0.5 ~ li and the SP value of the organic liquid employed in the presen-t ., . ;., . "' , , ,: : ' : . " . .' '~
cm/ ~ - 13 -~.'.
, .
, ' , . .
:, , ' ' ,, '. ' . .
.
invention is 8.9 or more, far from the SP value of polyolefin of 7.9 to 8.0, almost all the organic liquid, e.g., 98% or more of the organic liquid is easily extracted at room temperature in a few minutes.
According to the present invention, it is not necessary to remove by extraction all of the organic liquid used and there may remain in the product film an amount of the organic r liquid such that the properties of the film are not impaired. -However, if the extraction is not effected sufficiently, the porosity or void space rate is lowered, which is of course undesirable in a film to be used as a separator. The acceptable resldual rate of the organic liquid is generally 5% or less, preferably 2~ or less.
After extraction of the organic liquid, the film is subjected to drying, for example drying at room temperature i.
under atmospheric or reduced pressure, heated air drying ' -or contact heating drying.
Though the microporous film of the present invention is substantially formed of a polyolefin and an inorganic j filler and has fine pores, an antioxidant, lubricant or , plastici~er may be added in amount such that the properties of the film are not spoiled. ¦;
The present invèntion will now be described in detail I `
by reference to the following Examples that by no means limit the scope of the present invention. ;¦
The properties shown in Examples were measured in the following method.
, Weight average molecular weight (Mw), Number average molecular weight ~Mn):
.. .'.' ":'' , i; .:. '. , . ' " . '',' ~, . ,.' ! -cm/p~
' i ~
- :
, . .
6~
GPC measuring apparatus - Model 200 manufactured by Waters Assoc. Co.
Column - G 7000S - G 3000S manufactured by Toyo Soda Kogyo K.K.
Solvent - trichlorobenzene Measuring temperature - 135C
Viscosity average molecular weight (Mv):
'~ (Mw -~ Mv?
Measured by using decalin at a temperature of 135 C
[~] = 6.20 x 10 4Mv0'70 (Formula of Chiang) Thè average molecular weig~t-of polyethylene - -having SLMI of 0 was measured according to .
this method and then calculated.
Compositlon ratio (volume percent):
Calculated from the value obtained by dividing the amount of the respective materials charged by their respective true specific gravities.
~, , , :; Porosity (Void space rate) (~):
Void space volume/film volume x 100 (Void space volume = Wet volume - oven dry weight) .: .
Average void diameter (,u):
Weighted average calculated from averages of long and short diameters of the opening of the voids measured from-scanning electron photomicrograph of the porous ilm where both the organic liquid and the inorganic filler are extracted.
346;~3 Specific suxEacc~ area (m2/g) Measured accordlncJ to BET adsorption method Average void space diameter (~
Calculated from specific suxface area measured by BET
adsorption method d: diameter t~) -d _ 2V S: specific surface area (m2/g) . .
. V: void space volume (ml/g) Breakillg strength (kg/cm2) and Breaki.ng elongation (%): - -Measured according to ASTM D-882 except that there is employed an initial strain rate = 2,0 mm/rnm^min. with - .
Instron type tension tester , -~ Electrical resistance (Qdm2/sheet): .
'` Measured by using dilu~e sulfuric acid having a specific ~ --gravity of 1.200 according to JIS-C-2318 Folding endurance (times):
Measured by MIT type folding tester (0,3kg tension/15mm width) according to ASTM D-2176 ~
.,.~ . .
Melt index (MI):
, . . .
20 Measured accordin~ to ASTM - 1238 - 65T (Condition E) . , - .: .
Solubility parameter (SP): ~-, Calculated by the formula d~G ~.
M :
. ; .
." , .' . - ,:
: , ' .' ~.:
~1 -16- .
.
* Trademark ~
bm: . , .
,;, - . . , . ', ~ , . . . .
her~ill G: molal- at:tr.act.ion constant d: specific gravity m: molecular welyht Permeability (sec/lOOml) Measured accordin~ to ASTM D-726, Method A
Example 1 15 vol % of fi.nely divided silica [Aerosil #
200(trademark) : Specific surface area 175 m2/g, avera~e diameter of particles 16 m~] and 61 vol.~ of dioctyl phthalate (DOP SP=8, 9) were mixed in the l~enschel mixer and : further mixed wlth 24 vol.% of polyethylene [Suntec A-360 (trademark): Mw=85,000, Mn=21,000 and SLMI=l] in this mixer. - .
By a twin extruder having a diameter of 30mm, the blend was kneaded, extruded and pelletized These pellets were extruded to form a film using an extruder having a T die of 420 mm diameter attached thereto~ at an extruding rate of -12 kg/hr, an extruding speed of 2 m/min and a resin pressure of 70 kg/cm20 The extruded film was immersed in 1,1,1- -trichloroethane (chlorocene) for 5 minutes to extract DOP~
The porous film thus obtained had a thickness of 0.13 mm and a void s~ace rate of 58 %. The substrate of the porous film consisted of 61.5 vol % of polyethylene, 38,3 vol,%
of finely divided silica and 0,2 vol.% of DOP, The porous ~ :
film had a breaking strength of 29 kg/cm2, a breaking elongation of 106 % and a folding endurance of 2400 runs, showing an excellent elongation and flexibility, The web structure of the porous film composed of the resin was examined by an electron microscope and found to contain void having an average diameter of 0,10~.
, ' ': ' ' . . ' .
:, " ' -17~
,~ ,, , , ~ , . . . .
,- , , , :
;6~ ~
The porous film lna(led wi.th the finely d:ivlded si:Lica had a void space of average diameter of 0.02~ which was measured by BET method and a maximum diameter of 0.09~ This film had a by far reduced electrical resistance as low as 0.00022 Qdm2/sheet. The moment water was dropped on the film, it was absorbed.
xample 2 Procedures of Example 1 were repeated except that 13 vol.% of finely divided silica, 34 vol.% of polyethylene and 53 vol.~ of octyl trimellitate were used. The porous film obtained had 72,2 vol~% of resin, 27.5 vol % of finely divided silica and 0.3 vol~% of octyl trimellitate. The porous film had a void space rate of 49 % and a thickness of `~ 0 085 mm, showing a breaking strength of 62 kg/cm2, a `~ breaking elongation of 201%, a folding endurance of more than ~0,000 runs, an electrical resistance of 0.00033Qdm2/sheet and good wettability in water Example 3 Procedures of Example 1 were repeated except that 13.6 vol,~ of finely divided silica [Nipsil VN-3(trade name):
specific surface area 280 m2/g and average diameter of particles 16 m~, 60,8 vol % of DOP and 25.6 vol ~O of polyethylene [Suntec S-360(trademark): Mw=85~000, Mn=21,000 and SMLI-l] were used. The obtained porous film showed an excellent breaking strength, elongation and film characters as shown in Table 1. The porous film from which the silica , . .
was extracted had 4 to 6 x 108/cm2 openings of average diameter of 0,14 ~ on the surface of the ~ilm The scanning electron microphotograph of the openings on the film surface was shown in Fig, 2 . :
~18-bm:
r~ cL~:!"'V~ '1,. ' Proc~ure.s of l~xample 3 were rep~clted except that a mix~ure of po:L~e-thylene (Sl,M~=0,].) consis-tincJ of 7 parts by weight of one class of polyethylene (~w--180,000, ~n=17,000 and SLMI-0.04) and 3 parts by we:ight of another c]ass o:E
polyethylene (Mw=85,000, ~n=21,000 and SLM:C=l) was used, The film obtai~ed had a strength higher than that of ~xamp].e
15 ~ and (3) a porous film prepared by molding a mixture of a polyolefin having a standard load melt index of 0 and a viscosity average molecular weight of 300,000 or more, silica and a plasticizer into a film and extracting the plasticizer from the molded film. (See, for example U.S.
patent specification 3,351,4~5).
In case a porous film is employed for example as a separator of a lead accumulator, the film is required to . have a small electrical resistance in the e].ectrolyte. For . a high-performance separater, the film should have an electrical resistance lower than 0.0006 Qdm2/sheet. To meet this re-quirement, the film should have high void space rate or porosity to enjoy anelectrical resistance as low as 0.0003 Qdm2/O.lmm(in thickness) or less and be formed to have a thickness of about 0.2 mm. In case the electrical resistance . 30 is higher than 0.0003Qdm2/ 0.1 mm, the film should be .~ .
6~;3 ., -formed extremely thin, to wit, less than 0.2 mm thick.
n this connection, it is to be noted that the conventional porous films (1) and (2) made of a polyvinyl chloride resin as mentioned above can be imparted with an electrical resistance as low as 0.0003 Qdm2/0.1mm but they have such defects as being brittle and lacking flexibility so that they are extremely difficult to be formed in a film of practical use having a thickness of less than 0.4 mm. On the other hand, the ; conventionally proposed porous film made of an ordinary polyolefin and a vast amount of inorganic filler fails to have flexibility and is too brittle to be practically utilizable.
Then, there has been proposed the method as mentioned above referring to the film (3) to solve the problem of brittleness and lack of flexibility. This method~ however, encounters another drawback of poor moldability which causes difficulty ` to form a thin film because there is employed in the method a super high molecular weight polyolefin of low flow characteristics such as a polyolefin having a standard load melt index of 0 and a viscosity average molecular weight (it is nearly equal to a weight average molecular weight) of 300,000. Furthermore, the film (3) has inevitably an electrical resistance higher than 0.0003Q dm2/0.1 mm. Thus, it is difficult to produce a high-performance separator having an electrical resistance as low as 0.0006 Qdm2/sheet or less from the conventional films.
Accordingly, one and principal object of the present invention is to provide a microporous film having a high mechanical strength and great flexibility and, in addition, wetting characteristics, showing much reduced electrical resistance in an electrolyte.
~01346~3 The inventors of the present application have made an intensive and extensive study with a view to obtaining a microporous film of high void space rate or porosity while keeping sufficient mechanical strength and flexibility, and surprisingly found that with use of a- polyolefin having a molecular weight of a specified range there can be effectively produced, with a good molding processability a microporous film having excellent properties.
In one aspect of the present invention, there is provided a microporous film which comprises 40 to 90 volume percent of a polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000 and 10 to 60 volume percent of an inorganic filler; and which has a void space rate of 30 to 75 volume percent based on the volume of the film. The microporous film of the present invention has a mechanical strength and flexibility sufficient for various uses, particularly for an electrochemical or electrolytical separator or battery separator. With this microporous thin film, the electrical resistance of a separator is by far reduced to 1/10 of the resistance of separator made of the conventional film such as polyvinyl chIoride-sintered film, polyvinyl chloride-extracted film, etc.
The foregoing and other objects, features and advantages of the invention will be better understood from the following detailed description and appended claims taken in connection with the accompanying drawings in which:
Fig. 1 (a) is an enlarged diagrammatical view of a microporous film of the present invention, shown in the state the inorganic filler is extracted;
Fig. 1 (b) is an enlarged diagrammatical view of a portion x-y-z as shown in Fig. 1 (a);
Fig. 1 (c) is an enlarged diagrammatical view of a portion S as shown in Fig. 1 (b), illustrating the web structure defining a network of void;
Fig. 2 is a scanning electron photomicrographic ( x 10,000 ) plan view of the microporous film obtained in Example 3, with the silica extracted;
Fig. 3 is a similar scanning electron photomicrographic ( x 10,000 ) plan view of the film obtained in Comparative Example 5, with the silica extracted; and ~ .
Fig. 4 is a similar sc~ng electron photomicrographic ( x 10,000 ) plan view of the film obtained in Comparative ` Example 7, with the silica extracted.
The most important characteristic feature of the present invention is in the polyolefin employed. According to the present invention, there should be employed a polyolefin having a number average molecular weight of 15,000 or more, preferably, 17,000 to 50,000 and a weight average molecular weight of less than 300,000, preferably ranging from 85,000 .
to 250,000. There may be employed a polyolefin having a standard load melt index of 0.01 or more, preferably 0.03 to 1. With use of such specific polyolefin, it is possible to form a flexible thin film having a thickness ranging from 0.05 to 1 mm. In contrast, when a polyolefin having a number average molecular weight of less than 15,000 is employed, a porous material obtained i5 poor in stretchability and brittle.
Whereas, in case a polyolefin having a weight average molecular weight of 300,000 or more is employed, there are caused ; 30 problems as to moldability because of its poor flow characteristics ; - 5 -~B~663 in the molten state and as to electrical resistance of the film produced therefrom because the void space rate or porosity is lowered.
The term "polyolefin" used herein is intended to include homopolymers and copolymers of olefins, for example, poly- - -ethylene, polypropylene, polybutene, ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-p.~opylene-butene tercopolymers, and mixturés thereof so long as they have a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000. Of these resins, polyethylene or a copolymer of ethylene as a ;
main component with another olefin is most preferable.
The inorganic filler employed serves to impart wetting characteristics to the prepared film and the filler is pre-ferably finely divided particles or porous particles having an average particle diameter ranging from 0.005 to 0..5~ and a specific surface area of 50 to 500, preferably 150 to 400 m /g. ~s specific examples of the inorganic fillers, there can be mentioned silica, calcium silicate, aluminum silicate, aluminum oxide, calcium carbonate, magnesium carbonate, kaolin clay, pulverized talc, titanium oxide, diatomaceous earth, carbon black, etcO Two or more kinds of fillers may be employed in combination. In this case, one of the fillers is to have a hydrophi~ic property. For an electrolytic ~;
separator and a lead accumulator which uses acid electrolyte, silica is preferably employed.
In the microporous film of the present in/ention the : ' g,~
~^ cm/p~
.
.. . , :, ~4L6~i3 amount ratio of the polyolefin and the inorganic filler is 40 to 90 volume percent to 10 to 60 volume percent. For use as a separat~r, the ratio is preferably 50 to 80 volume percent (polyolefin) to 20 to 50 volume percent (filler) and more preferably 60 to 70 volume percent to 30 to 40 volume percent. In case the amount of the filler employed exceeds 60 volume percent, the film obtained is poor in flexibility ; and not practically employable even if a polyolefin having a number average molecular weight of 15,000 or more is employed.
Whereas, in case the amount of the filler employed is less than I0 volume percent, the strength of the film obtained increases but the wetting characteristics thereof is so reduced that the film cannot be ulitized for a separator.
~ .
Referring to Fig. 1 there is shown enlarged diagrammatic views of a microporous film , with the silica extracted, .
; of the present invention. As seen from Fig. 1, especially from Fig. 1 (c), the microporous film has such a structure that the polyolefin constitutes a web structure 1 and a void ` 2 defined by the polyolefin web structure i5 formed in network. The void opens at the surface of the film and an average diameter of the opening portion of the void is in the range of 0.05 to 0.5 ~u. The network void contains the filler attached thereto, leaving a space forming a path communicating from one surface of the film to the opposite ~; 25 surface of the film.
The term "void" used herein has a meaning as apparent from the above description and more illustratively it means a void portion defined by the polyolefin web structure but having the filler contained therein. The term "void space"
used herein has a meaning as apparent from the above description 6~3 and more illustratively it means a space left in the void and formed by cooperation between the particles of filler contained therein and cooperation between the wall of the void and the particles of filler contained therein. The term "void space rate" used herein is intended to mean a volume rate of void spaces formed in the overall structrure of the microporous film.
The actual average diameter of the void in,the state - where the filler is attachedly disposed, namely the average diameter of the opening portion of the void space is as small as 0.01 to 0.1 ~u. The thus formed film of the present invention has a void space rate of 30 to 75 volume percent based on the volume of the film. In case the void space rate is less than 30 volume percent, the electrical resistance increases and the film obtained can not be effectively employed for the separator. Whereas, in case the void space rate exceeds 75 volume percent, the strength of the film obtained is so reduced that the film can not be practically utilized. To meet the requirements both of strength and electrical resistance, the void space rate is preferably within the range of 45 to 6S volume percent. Further, in order that the microporous material may have a desired electrical resistance and a void space of a size suitable for ~; preventing the passage of solid materials and permitting ions to pass through while maintaining a mechanical strength,tthe average diameter of the void is to be in the range of 0.05 to 0.5 and more preferably in the range of 0.08 to 0.3 JU.
The microporous film of the present invention has a thickness of 0.05 to 1 mm. The film thickness may be for a separator preferably within the range of 0.10 to 0.30 mm in ' :, ' '.
view of imparting good moldability and sufficient strenyth j to the resulting film.
~ Thus, to the film of the present invention having a I high porosity with fine void spaces or pores formed in the j~
network structure, sufficient mechanical strength and excellent flexibility is further imparted with an unexpected low electrical resistance (as low as 0.0006 Q dm2/sheet). This film can be employed with great advantage for a separator, by far enhancing the separator performance.
Referring to Fig. 2, there is shown a scanning electron photomicrographic plan view of the present microporous film, ¦, in comparison with those of conventional porous films as shown in Figs. 3 and 4. As is seen from these Figures, the present microporous film has definite pores of a suitable size and of a number as many as 4 to 6 x 10 /cm2, leading to a desired electrical resistance as low as 0.0006 Q dm /sheet while maintaining high mechanical strength, as opposed to -the con- j ~i ventional porous films in which there are formed pores of -too small a size to distinguish, which exerts unfavourable influence on the electrical resistance, increasing the same.
Due to the excellent properties as mentioned above, the . i .
microporous film of this invention has a wide variety of uses, ¦
for example, as a battery separator, filter, liquid retainer, wrapping material, synthetic paper, etc. In view of its extremely low electrical resistance in an electrolyte, the microporous film of the present invention is useful with grea-t advantage especially for a battery separa-tor and a separator j in various electrochemical or electrolytical apparatuses.
The microporous film of the present invention formed of . ' , ,, i ~ . .
-. '~
''' ' .
.
~ _ g _ ; cm/~
, ' ~34~63 .
', ~
a polyolefin and an inorganic filler is produced, for example, by a process as given below. i~
Accordingly, as another aspect of the present invention ¦' there is provided a process for preparing a microporous film j~
which comprises: blending a polyolefin having a number j average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000, an inorganic ~ ,l - filler and an organic liquid in amounts of 10 to 60 volume ~ I I
~,:
percent, 6 to 35 volume percent and 30 to 75 volume percent, ;
respectively, based on the whole volume of the polyolefin-filler-liquid composition, the amount of the polyolefin being 2/3 to 9 multiple of the amount of the inorganic filler;
sub~ecting the resulting blend to molding to form a film; ~
and extracting from said film said organic liquid. , -Based on the total volume of the polyolefin, the inorganic filler and the organic liquid, 6 to 35 volume percent inorganic filler and 30 to 75 volume percent organic . ~ , .
liquid are blended using an ordinary mixer such as a Henschel mixer or V-shaped tumbler to absorb the organic liquid onto the surface of the filler particles. The conditions of the above blending vary slightly according to kind and rotation speed of the mixer used, but usually the blending is accomplished at room temperature for about one minute. A polyolefin is then mixed with the above obtained blend in an amount of 10 to 60 percent by volume but 2/3 to 9 multiple by weight based on the inorganic filler. The above-mentioned blending of three com-ponents i5 effected in a two-stage operation, bu-t a one-stage blending operation may be employed. When the two-stage blènding is employed, good handling characteristics . ., . .
~' ', ~
.; , ' "". ':
:
cm/p~ - 10 - ~
., I , .
, and cxcellent dispersioll of the component can be attained Whilst, when the one-stage blendiny is employed, the ~` polyole1n tends to be wetted with the organ.ic liqu.id so that good dispersion of the components cannot be attained In such case, however, the dispersion of the three components can be attained by adjusting rotation speed of the mixer, b].ending time, etc ~:
The resulting polyolefin-filler-liquid blend is kneaded by a kneading machine such as an extruder, a sanbury mixer, am~ing twin roll, a kneader, etc The so kneaded material is subjected to molding to be formed in a film having a thickness of 0.05 to lmm. Typical examples of the molding are extrusion molding employing a T~die or inflation method, calender molding, compressi.on molding, ` injection molding, etc The T-die extrusion molding is especially preferable to form a film as thin as 0.05 to lmm :~
The molding may be effected under molding conditions as ordinarily employed in molding of polyolefins as far as the molding i.s effected at a temperature higher than the melting point of the polyolefin employed and below the boiling point of the organic liquid employed.
The kneading step as described above is optional , in the method of the present invention, Particularly, in the extrusion molding in which the kneadiny is also conducted simultaneously, the separate step for kneading is not necessary~ But when the kneading step is positively employed, the bulk density of the blend can be appropriately controlled and, at the same time, good dispersion of the components can be attained, leading to i.mprovement of handling characteristics and reduction of pin holes of the product film. Such reduction * Trademark bm: .
: :
~iL084L16~3 . . . :
' of pin holes is particularly important for a battery separator and separators of various electrolytical apparatus.
The organic liquid is extracted from the molded film 1~
at a temperature below a melting point of the polyolefin ~y a ~ ~-solvent OL the organic liquid employed, to form a final micro-porous film made of 40 to 9a vo]ume percent polyolefin and 10 to 60 volume percent inorganic filler and having a void space rate of 30 to 75 volume percent based upon the film volume.
The organic liquid employable in the present invention ¦-is preferably kept in a liquid stata at the time of the molding;
it is readily soluble in general organic solvents or water and is easily extractible.from the molded film. The organic --liquid is selected from ones having a solubility parameter (hereinafter referred to as "SP") of 8.4 to 9.9, preferably from 8.6 to 9.4. An organic liquid having an SP of more than 9.9, when used in the method of the present invention, forms .. . .
~`, coarse pores or voids of more than 0.5 ~ in average diameter I --, and the resultant film has a poor elongation and is brittle.
On the other hand, when an organic liquid having an SP of less than 8.4 is used, the breaking strength and elongation l; are improved but the electrical resistance is also increased. ~j It should be noted that, according to the present invention, with use of an organic solvent having an SP of 8.4 to 9.9 as well as a polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000, there is obtained a microporous film of a specific construction in which the 1!
polyolefin constitutes a web structure defining a network of voids in which the filler is attachedly contained, leaving ' .
cm/~ - 12 -.' ':' ,~ . . :
, . . ,-: - , .. . :. ~
.
~L~1346~i3 , . a space to form a path communicating from one surface of the film to the opposite surface thereof, said voids hav;ng l~-~ an average void diameter ranging from 0.05 to 0.5 ;~ Representative examples of the organic liquid having ~
an SP ranging from 8.4 to 9.9 are phthalic acid esters such ,J
as diethyl phthalate (DEP), dibutyl phthalate (DBP), and ¦, dioctyl phthalate (DOP); fatty acid esters such as dioctyl ~ ;
sebacate (DOS) and dioctyl adipa-te (DOA); maleic acid es-ters ~ such as dibutyl maleate; trimetallitic acid esters such as - 10 trioctyl trimellitate (TOTM); phosphoric acid esters such as r tribu-tyl phosphate (TBP), octyl diphenyl phosphate, tricresyl phosphate (TCP); other esters; and glycols such as polyethylene glycol.
The solvent employable for extracting the organic liquid from the molded film is selected from those capable ' ` of dissolving the organic liquid but not dissolving the poly- ¦;
I olefin used. ¦
Representative examples of the solvent-to be employed ~
for extracting the organic liquid include alcohols such as ~j methanol, ethanol and iso-propanol; ketones such as acetone;
j and chlorine-substituted hydrocarbons such as trichloroethylene and l,l,l-trichloroethàne. The extraction of the organic ~' liquid from the molded film may be conducted employing various ¦
methods ordinarily employed in the art, for example batch type dipping method, counter-flow method and the like (U.S.
Patent Specification No. 3,351,495 may be referred to).
Since the average diameter of the voids of the present i ` porous film is in an appropriate range, i.e. 0.05 to 0.5 ~ li and the SP value of the organic liquid employed in the presen-t ., . ;., . "' , , ,: : ' : . " . .' '~
cm/ ~ - 13 -~.'.
, .
, ' , . .
:, , ' ' ,, '. ' . .
.
invention is 8.9 or more, far from the SP value of polyolefin of 7.9 to 8.0, almost all the organic liquid, e.g., 98% or more of the organic liquid is easily extracted at room temperature in a few minutes.
According to the present invention, it is not necessary to remove by extraction all of the organic liquid used and there may remain in the product film an amount of the organic r liquid such that the properties of the film are not impaired. -However, if the extraction is not effected sufficiently, the porosity or void space rate is lowered, which is of course undesirable in a film to be used as a separator. The acceptable resldual rate of the organic liquid is generally 5% or less, preferably 2~ or less.
After extraction of the organic liquid, the film is subjected to drying, for example drying at room temperature i.
under atmospheric or reduced pressure, heated air drying ' -or contact heating drying.
Though the microporous film of the present invention is substantially formed of a polyolefin and an inorganic j filler and has fine pores, an antioxidant, lubricant or , plastici~er may be added in amount such that the properties of the film are not spoiled. ¦;
The present invèntion will now be described in detail I `
by reference to the following Examples that by no means limit the scope of the present invention. ;¦
The properties shown in Examples were measured in the following method.
, Weight average molecular weight (Mw), Number average molecular weight ~Mn):
.. .'.' ":'' , i; .:. '. , . ' " . '',' ~, . ,.' ! -cm/p~
' i ~
- :
, . .
6~
GPC measuring apparatus - Model 200 manufactured by Waters Assoc. Co.
Column - G 7000S - G 3000S manufactured by Toyo Soda Kogyo K.K.
Solvent - trichlorobenzene Measuring temperature - 135C
Viscosity average molecular weight (Mv):
'~ (Mw -~ Mv?
Measured by using decalin at a temperature of 135 C
[~] = 6.20 x 10 4Mv0'70 (Formula of Chiang) Thè average molecular weig~t-of polyethylene - -having SLMI of 0 was measured according to .
this method and then calculated.
Compositlon ratio (volume percent):
Calculated from the value obtained by dividing the amount of the respective materials charged by their respective true specific gravities.
~, , , :; Porosity (Void space rate) (~):
Void space volume/film volume x 100 (Void space volume = Wet volume - oven dry weight) .: .
Average void diameter (,u):
Weighted average calculated from averages of long and short diameters of the opening of the voids measured from-scanning electron photomicrograph of the porous ilm where both the organic liquid and the inorganic filler are extracted.
346;~3 Specific suxEacc~ area (m2/g) Measured accordlncJ to BET adsorption method Average void space diameter (~
Calculated from specific suxface area measured by BET
adsorption method d: diameter t~) -d _ 2V S: specific surface area (m2/g) . .
. V: void space volume (ml/g) Breakillg strength (kg/cm2) and Breaki.ng elongation (%): - -Measured according to ASTM D-882 except that there is employed an initial strain rate = 2,0 mm/rnm^min. with - .
Instron type tension tester , -~ Electrical resistance (Qdm2/sheet): .
'` Measured by using dilu~e sulfuric acid having a specific ~ --gravity of 1.200 according to JIS-C-2318 Folding endurance (times):
Measured by MIT type folding tester (0,3kg tension/15mm width) according to ASTM D-2176 ~
.,.~ . .
Melt index (MI):
, . . .
20 Measured accordin~ to ASTM - 1238 - 65T (Condition E) . , - .: .
Solubility parameter (SP): ~-, Calculated by the formula d~G ~.
M :
. ; .
." , .' . - ,:
: , ' .' ~.:
~1 -16- .
.
* Trademark ~
bm: . , .
,;, - . . , . ', ~ , . . . .
her~ill G: molal- at:tr.act.ion constant d: specific gravity m: molecular welyht Permeability (sec/lOOml) Measured accordin~ to ASTM D-726, Method A
Example 1 15 vol % of fi.nely divided silica [Aerosil #
200(trademark) : Specific surface area 175 m2/g, avera~e diameter of particles 16 m~] and 61 vol.~ of dioctyl phthalate (DOP SP=8, 9) were mixed in the l~enschel mixer and : further mixed wlth 24 vol.% of polyethylene [Suntec A-360 (trademark): Mw=85,000, Mn=21,000 and SLMI=l] in this mixer. - .
By a twin extruder having a diameter of 30mm, the blend was kneaded, extruded and pelletized These pellets were extruded to form a film using an extruder having a T die of 420 mm diameter attached thereto~ at an extruding rate of -12 kg/hr, an extruding speed of 2 m/min and a resin pressure of 70 kg/cm20 The extruded film was immersed in 1,1,1- -trichloroethane (chlorocene) for 5 minutes to extract DOP~
The porous film thus obtained had a thickness of 0.13 mm and a void s~ace rate of 58 %. The substrate of the porous film consisted of 61.5 vol % of polyethylene, 38,3 vol,%
of finely divided silica and 0,2 vol.% of DOP, The porous ~ :
film had a breaking strength of 29 kg/cm2, a breaking elongation of 106 % and a folding endurance of 2400 runs, showing an excellent elongation and flexibility, The web structure of the porous film composed of the resin was examined by an electron microscope and found to contain void having an average diameter of 0,10~.
, ' ': ' ' . . ' .
:, " ' -17~
,~ ,, , , ~ , . . . .
,- , , , :
;6~ ~
The porous film lna(led wi.th the finely d:ivlded si:Lica had a void space of average diameter of 0.02~ which was measured by BET method and a maximum diameter of 0.09~ This film had a by far reduced electrical resistance as low as 0.00022 Qdm2/sheet. The moment water was dropped on the film, it was absorbed.
xample 2 Procedures of Example 1 were repeated except that 13 vol.% of finely divided silica, 34 vol.% of polyethylene and 53 vol.~ of octyl trimellitate were used. The porous film obtained had 72,2 vol~% of resin, 27.5 vol % of finely divided silica and 0.3 vol~% of octyl trimellitate. The porous film had a void space rate of 49 % and a thickness of `~ 0 085 mm, showing a breaking strength of 62 kg/cm2, a `~ breaking elongation of 201%, a folding endurance of more than ~0,000 runs, an electrical resistance of 0.00033Qdm2/sheet and good wettability in water Example 3 Procedures of Example 1 were repeated except that 13.6 vol,~ of finely divided silica [Nipsil VN-3(trade name):
specific surface area 280 m2/g and average diameter of particles 16 m~, 60,8 vol % of DOP and 25.6 vol ~O of polyethylene [Suntec S-360(trademark): Mw=85~000, Mn=21,000 and SMLI-l] were used. The obtained porous film showed an excellent breaking strength, elongation and film characters as shown in Table 1. The porous film from which the silica , . .
was extracted had 4 to 6 x 108/cm2 openings of average diameter of 0,14 ~ on the surface of the ~ilm The scanning electron microphotograph of the openings on the film surface was shown in Fig, 2 . :
~18-bm:
r~ cL~:!"'V~ '1,. ' Proc~ure.s of l~xample 3 were rep~clted except that a mix~ure of po:L~e-thylene (Sl,M~=0,].) consis-tincJ of 7 parts by weight of one class of polyethylene (~w--180,000, ~n=17,000 and SLMI-0.04) and 3 parts by we:ight of another c]ass o:E
polyethylene (Mw=85,000, ~n=21,000 and SLM:C=l) was used, The film obtai~ed had a strength higher than that of ~xamp].e
3 and excellent properties as shown in Table 1.
Example 5 Procedures of Example 1 were repeated except that ; an ethylene-propylene copolymer (ethylene : propyle~le = 99,1 ~ -: 0.9 by weiglr~) was used, The film obtained had an excellent mechanical strength and good film prope~ties as shown in Tab].e 1.
Examples 6,7 and 8 are also summarized in Table 1 and the films ob-tained had excellent mechanical strengths . . - .
and good film properties.
Comparative Example 1 Procedures of Example 1 were repeated except that a polyethylene (Mw=120,000, Mn=ll,000 and SLMI=0.3) was used, The porous film obtained was composed of 61,4 vol.% of polyethylene and 38.5 vol,% of finely divided silica, and had a void space rate of 56 % and a thickness of 0,28 mm, The porous film had a breaking strength of 21 kg/cm~, a breaking elongation of 11 % and a folding endurance of 2 runs, Thus, the film was brittle and poor in flexibility, The electrical resistance of the film was 0.00042Qdm2/sheet.
Comparative Example 2 Procedures of Example 1 were repeated except that a polyethylene [Suntec F-160(trade mark): Mw=83,000~
bm:
' ,, . .", '' ' , ' '. ' ' ~ ;:
.
16~3 .
Mn=7,500 and ~LMI-0,9] was used. The ob~ained film was extremely brittle. The breaking elonyation was 7~ and the folding endurance was null, The film properties are shown in Table 1.
Comparative Example 3 is summarized in Table 1.
Comparative Exam~le 4 Procedures of Example 3 were repeated except that ., .
a polyethylene (Mw=330~000, Mn=20,000 and SLMI=0) was used. ~:
The porous film obtained had a breaking strength of 48 kg/cm2 and a breaking elongation of 242%, which were higher than those of Example 3 But the film of this Comparative Example had a void space rate as low as 52%, and an electrical resistance as high as 0 00033 Qdm2/0.1 mm and ~ ~:
0 0083 QdmZ/sheet Comparative Example 5 Procedures of Example 3 were repeated except that polyethylene (~1w=600,000 and SLMI=O) was used. The porous ; film prepared was as thick as 0,3 mm because of difficulty ~ in molding due to higher molecular weight of the resin - 20 employed. The breaking strength and the breaking elongation were as large as 63 kg/cm2 and 195~, respectively, but the porous film of this Comparative Example had a lower void space rate of 51% and a higher electrical resistance of 0 00040Qdm2/0 1 mm and 0,0012Qdm2/sheetO The porous film with the silica extracted has 0 03~ average diameter of void or opening on the surface of the polyethylene web structure, which was by far reduced as compared with 0,14~ average diameter of the opening of Example 3, The opening area is al50 reduced, The scanning electron microphotograph of the openings of the surface was shown in Fig, 3.
bm:
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Comparative Example 6 Procedures of Example 1 were repeated except that a 15 'ivol.~ of`polyethylene (Mw=330,000 and Mn=20,000-), a 15 vol%
of finely divided silica [Nipsil VN-3(trade name) ]and a 70 5vol.~ of process oil (SP = 7.9) were used. Petroleum ether - - wa's-used for an extraction of the process oil. The obtained porous film showed slightly lower values in strength and elongation than that of Comparative Example 4. For all the `' ' ' amounts of the process oil employed, the obtained porous ; 10film had a little lowered void space rate of 56 % and higher electrical resistance.
Comparative Example 7 Procedures in Comparative Example 6 were repeated except that polyethylene (Mw=600,000) was used. mhe poxous 15film'prepared had a higher tensile strength, a lower void , .
space rate of 52 % and a higher elec~rical resistance. The . - .
openings on the film surface were extremely fine as shown in Fig. 4 and could not be obserbed by an scanning electron '~ microscope.
20r Example 9 Procedures of Example 3 were repeated except that dibutyl phthalate (DBPV SP=9.4) was used. The porous film prepared had openings of average diameter of 0.3 ~, by far larger than that of Example 3, but good in other properties.
' 25 Examples 10 to 16 Procedures of Example 3 were repeated except that organic liquids having different SP values were used. The properties of the film obtained were shown in Table 2. As the Sp value of the liquid decreased towards 7.9 of polyethylene 30 ' ~ SP value, the mechanical strength of the film was increased 6~3 .
but the other film properties were degraded.
Comparative Example 8 Procedures of Example 3 were repeated except that dimethyl phthalate (DMP: SP=10.5) was used as an organic liquid. The porous film prepared had openings of an extremely large average diameter of 0.62 ~ with a distructed web structure. The film was brittle insomuch as it showed a . ~, breaking strength of 17.3 kg/cm2 and a breaking elongation of 40 %. See Table 2.
' ~ 10 Comparative Example 9 ( corresponding to Example 6 ) Procedures of Example 3 were repeated except that a .
process oil (SP=7.8) was used. Petroleum ether was used~for the extraction of the process oil. In the porous film ~` 15 prepared, 5.6 % of process oil remained unextracted. The film was improved in strength and elongation, but the void .
space rate was decreased to 50 % and the electrical resistance was increased to 0.00074 ndm2/0.1 mm. The diameters oE the openings on the surface of the film were so small that they -~' 20 could not be measured by an electron microscope. See Table 2.
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Example 5 Procedures of Example 1 were repeated except that ; an ethylene-propylene copolymer (ethylene : propyle~le = 99,1 ~ -: 0.9 by weiglr~) was used, The film obtained had an excellent mechanical strength and good film prope~ties as shown in Tab].e 1.
Examples 6,7 and 8 are also summarized in Table 1 and the films ob-tained had excellent mechanical strengths . . - .
and good film properties.
Comparative Example 1 Procedures of Example 1 were repeated except that a polyethylene (Mw=120,000, Mn=ll,000 and SLMI=0.3) was used, The porous film obtained was composed of 61,4 vol.% of polyethylene and 38.5 vol,% of finely divided silica, and had a void space rate of 56 % and a thickness of 0,28 mm, The porous film had a breaking strength of 21 kg/cm~, a breaking elongation of 11 % and a folding endurance of 2 runs, Thus, the film was brittle and poor in flexibility, The electrical resistance of the film was 0.00042Qdm2/sheet.
Comparative Example 2 Procedures of Example 1 were repeated except that a polyethylene [Suntec F-160(trade mark): Mw=83,000~
bm:
' ,, . .", '' ' , ' '. ' ' ~ ;:
.
16~3 .
Mn=7,500 and ~LMI-0,9] was used. The ob~ained film was extremely brittle. The breaking elonyation was 7~ and the folding endurance was null, The film properties are shown in Table 1.
Comparative Example 3 is summarized in Table 1.
Comparative Exam~le 4 Procedures of Example 3 were repeated except that ., .
a polyethylene (Mw=330~000, Mn=20,000 and SLMI=0) was used. ~:
The porous film obtained had a breaking strength of 48 kg/cm2 and a breaking elongation of 242%, which were higher than those of Example 3 But the film of this Comparative Example had a void space rate as low as 52%, and an electrical resistance as high as 0 00033 Qdm2/0.1 mm and ~ ~:
0 0083 QdmZ/sheet Comparative Example 5 Procedures of Example 3 were repeated except that polyethylene (~1w=600,000 and SLMI=O) was used. The porous ; film prepared was as thick as 0,3 mm because of difficulty ~ in molding due to higher molecular weight of the resin - 20 employed. The breaking strength and the breaking elongation were as large as 63 kg/cm2 and 195~, respectively, but the porous film of this Comparative Example had a lower void space rate of 51% and a higher electrical resistance of 0 00040Qdm2/0 1 mm and 0,0012Qdm2/sheetO The porous film with the silica extracted has 0 03~ average diameter of void or opening on the surface of the polyethylene web structure, which was by far reduced as compared with 0,14~ average diameter of the opening of Example 3, The opening area is al50 reduced, The scanning electron microphotograph of the openings of the surface was shown in Fig, 3.
bm:
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Comparative Example 6 Procedures of Example 1 were repeated except that a 15 'ivol.~ of`polyethylene (Mw=330,000 and Mn=20,000-), a 15 vol%
of finely divided silica [Nipsil VN-3(trade name) ]and a 70 5vol.~ of process oil (SP = 7.9) were used. Petroleum ether - - wa's-used for an extraction of the process oil. The obtained porous film showed slightly lower values in strength and elongation than that of Comparative Example 4. For all the `' ' ' amounts of the process oil employed, the obtained porous ; 10film had a little lowered void space rate of 56 % and higher electrical resistance.
Comparative Example 7 Procedures in Comparative Example 6 were repeated except that polyethylene (Mw=600,000) was used. mhe poxous 15film'prepared had a higher tensile strength, a lower void , .
space rate of 52 % and a higher elec~rical resistance. The . - .
openings on the film surface were extremely fine as shown in Fig. 4 and could not be obserbed by an scanning electron '~ microscope.
20r Example 9 Procedures of Example 3 were repeated except that dibutyl phthalate (DBPV SP=9.4) was used. The porous film prepared had openings of average diameter of 0.3 ~, by far larger than that of Example 3, but good in other properties.
' 25 Examples 10 to 16 Procedures of Example 3 were repeated except that organic liquids having different SP values were used. The properties of the film obtained were shown in Table 2. As the Sp value of the liquid decreased towards 7.9 of polyethylene 30 ' ~ SP value, the mechanical strength of the film was increased 6~3 .
but the other film properties were degraded.
Comparative Example 8 Procedures of Example 3 were repeated except that dimethyl phthalate (DMP: SP=10.5) was used as an organic liquid. The porous film prepared had openings of an extremely large average diameter of 0.62 ~ with a distructed web structure. The film was brittle insomuch as it showed a . ~, breaking strength of 17.3 kg/cm2 and a breaking elongation of 40 %. See Table 2.
' ~ 10 Comparative Example 9 ( corresponding to Example 6 ) Procedures of Example 3 were repeated except that a .
process oil (SP=7.8) was used. Petroleum ether was used~for the extraction of the process oil. In the porous film ~` 15 prepared, 5.6 % of process oil remained unextracted. The film was improved in strength and elongation, but the void .
space rate was decreased to 50 % and the electrical resistance was increased to 0.00074 ndm2/0.1 mm. The diameters oE the openings on the surface of the film were so small that they -~' 20 could not be measured by an electron microscope. See Table 2.
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Claims (24)
1. A microporous film which comprises 40 to 90 volume percent of a polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000 and 10 to 60 volume percent of an inorganic filler; and which has a void space rate of 30 to 75 volume-percent based on the volume of the film.
2. A microporous film as set forth in claim 1, wherein said polyolefin has a weight average molecular weight ranging from 85,000 to 250,000.
3. A microporous film as set forth in claim 1, wherein said polyolefin has a number average molecular weight of 17,000 to 50,000.
4. A microporous film as set forth in claim 1, wherein said polyolefin has a standard load melt index of 0.01 or more.
5. A microporous film as set forth in claim 4, wherein said standard load melt index is in the range of 0.03 to 1.
6. A microporous film as set forth in claim 1, which has a thickness ranging from 0.05 to 1mm.
7. A microporous film as set forth in claim 6, wherein the film thickness is in the range of 0.10 to 0.30mm.
8. A microporous film as set forth in claim 1, wherein said polyolefin is an olefin homopolymer.
9. A microporous film as set forth in claim 1, wherein said polyolefin is an olefin copolymer.
10. A microporous film as set forth in claim 8, wherein said polyolefin is polyethylene.
11. A microporous film as set forth in claim 9, wherein said polyolefin is an ethylene copolymer.
12. A microporous film as set forth in claim 11, wherein said ethylene copolymer is an ethylene-propylene copolymer, an ethylene-butene copolymer or an ethylene-propylene-butene terpolymer.
13. A microporous film as set forth in claim 1, wherein said polyolefin is a copolymer of ethylene as a main component with other olefin.
14. A microporous film as set forth in claim 1, wherein said polyolefin has a web structure defining a network void in which said inorganic filler is attachedly contained, leaving a space to form a path communication from one surface of the film to the opposite surface thereof.
15. A microporous film as set forth in claim 14, wherein said void has an average void diameter ranging from 0.05 to 0.5 µ.
16. A microporous film as set forth in claim 15, wherein said average void diameter is in the range of 0.08 to 0.3
17. A method for preparing a microporous film which comprises: blending a polyolefin having a number average molecular weight of 15,000 or more and a weight average molecular weight of less than 300,000, an inorganic filler and an organic liquid having a solubility parameter ranging from 8.4 to 9.9 in amounts of 10 to 60 volume percent, 6 to 35 volume percent and 30 to 75 volume percent, respecitvely, based on the whole volume of the polyolefin-filler-liquid composition, the amount of the polyolefin being 2/3 to 9 multiple of the amount of the inorganic filler;
subjecting the resulting blend to molding to form a film;
and extracting from said film the organic liquid.
subjecting the resulting blend to molding to form a film;
and extracting from said film the organic liquid.
18 . A method as set forth in claim 17, wherein said polyolefin has a weight average molecular weight from 85,000 to 250,000.
19. A method as set forth in claim 17, wherein said polyolefin has a number average molecular weight of 17,000 to 50,000,
20. A method as set forth in claim 17, wherein said polyolefin has a standard load melt index of 0.01 or more.
21 A method as set forth in claim 17, wherein said standard load melt index is in the range of 0.03 to 1.
22. A method for preparing a microporous film as set forth in claim 17, wherein said solubility parameter is in the range of 8.6 to 9.4.
23. A method for preparing a microporous film as set forth in claim 17, wherein said organic liquid is dioctyl phthalate or trioctyl trimellitate.
24. A method as set forth in claim 17, wherein said molding is effected using an extrusion molding method employ-ing a T-die.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP50073031A JPS5819689B2 (en) | 1975-06-18 | 1975-06-18 | Takoumaku |
| JP50-73031 | 1975-06-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084663A true CA1084663A (en) | 1980-09-02 |
Family
ID=13506561
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA255,022A Expired CA1084663A (en) | 1975-06-18 | 1976-06-16 | Microporous film and method for preparing the same |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4335193A (en) |
| JP (1) | JPS5819689B2 (en) |
| CA (1) | CA1084663A (en) |
| DE (1) | DE2627229C3 (en) |
| FR (1) | FR2316279A1 (en) |
| GB (1) | GB1527385A (en) |
| IT (1) | IT1061840B (en) |
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| GB2014184B (en) * | 1978-01-10 | 1982-05-19 | Asahi Chemical Ind | Method of separating oil from oil-containing liquid |
| PT69761A (en) * | 1978-06-16 | 1979-07-01 | Amerace Corp | Improved process for producing flexible microporous composition rubber base articles and articles so produced namelya battery separator |
| US4331622A (en) * | 1978-08-01 | 1982-05-25 | Asahi Kasei Kogyo Kabushiki Kaisha | Method for manufacturing a microporous film having low electrical resistance and high durability |
| NL8000423A (en) * | 1979-02-12 | 1980-08-14 | Grace W R & Co | BATTERY SEPARATOR. |
| US4287276A (en) * | 1979-06-08 | 1981-09-01 | W. R. Grace & Co. | Alkaline battery with separator of high surface area |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3536796A (en) * | 1967-11-29 | 1970-10-27 | Grace W R & Co | Process for reducing shrinkage in preparing porous plastic sheet |
| US3956020A (en) * | 1968-10-31 | 1976-05-11 | General Electric Company | Ultrafine porous polymer articles |
| JPS4922472A (en) * | 1972-06-22 | 1974-02-27 | ||
| JPS4937878A (en) * | 1972-08-11 | 1974-04-08 | ||
| US3962205A (en) * | 1973-03-06 | 1976-06-08 | National Research Development Corporation | Polymer materials |
| JPS5937292B2 (en) * | 1977-10-03 | 1984-09-08 | 旭化成株式会社 | Polyolefin resin porous membrane, alkaline storage battery separator, and microfilter |
-
1975
- 1975-06-18 JP JP50073031A patent/JPS5819689B2/en not_active Expired
-
1976
- 1976-06-10 GB GB24072/76A patent/GB1527385A/en not_active Expired
- 1976-06-14 IT IT24280/76A patent/IT1061840B/en active
- 1976-06-16 CA CA255,022A patent/CA1084663A/en not_active Expired
- 1976-06-17 FR FR7618450A patent/FR2316279A1/en active Granted
- 1976-06-18 DE DE2627229A patent/DE2627229C3/en not_active Expired
-
1979
- 1979-02-28 US US06/016,176 patent/US4335193A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| US4335193A (en) | 1982-06-15 |
| FR2316279B1 (en) | 1981-11-06 |
| IT1061840B (en) | 1983-04-30 |
| FR2316279A1 (en) | 1977-01-28 |
| JPS5270988A (en) | 1977-06-13 |
| JPS5819689B2 (en) | 1983-04-19 |
| DE2627229C3 (en) | 1978-10-26 |
| GB1527385A (en) | 1978-10-04 |
| DE2627229B2 (en) | 1978-03-02 |
| DE2627229A1 (en) | 1977-03-10 |
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