CA1150873A

CA1150873A - Oxidation protected olefinic polymer battery separator

Info

Publication number: CA1150873A
Application number: CA000344453A
Authority: CA
Inventors: Nathan Sugarman
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co Conn
Priority date: 1979-02-12
Filing date: 1980-01-28
Publication date: 1983-07-26
Also published as: CH634172A5; IT1127349B; DE3004659C2; DE3004659A1; GB2044516A; GB2044516B; IT8047862A0; ES488460A1; NL8000423A; SE8001065L; FR2448791A1; BE881658A; FR2448791B1

Abstract

ABSTRACT OF THE DISCLOSURE

Battery separators having polyolefin as the primary structural material protected from oxidative attack by an oil having an aromatic content of 40% or more of its weight.

Description

~15(~8'73 BACKGROU~D OF m~E I~ENTI~I
The invention of the present application is con-cerned with battery separators havina as a primary struc-tural material a polyolefin which when su~jected to substantial oxidative attack undergo a deterioration in physical strength that is deleterious to the battery separator's life and thus to battery life. ~Jhile poly-olefins tend to be resistant to the acids or alkalis em-ployed in batteries, they are not totally resistant over normal battery life. Thus the addition of the aromatic factors of the present invention in the preferred ranges extends the useful life of the separator and concurrently extends battery life. An important factor in the present invention is that the aromatic materials of the present invention may be used without any substantial direct dam-age to the electrical resistance and, in the preferred ranges in particular, actually inexplicably provide a small amount of ER benefit.
United States Patent 3,351,495 teaches the use of plasticizers including oil in the manufacture of battery separators having polyolefins as a primary structural mate-rial, see the bottom of Col. 4 and top of Col. 5. The oils actually taught were, however, paraffinic and had aromatic contents of no more than about 20~. Fuel oils are mention-ed and some fuel oils have high aromatic contents. It is believed however that the fuel oils that would normally be thought of for use in practicing the teaching of United States Patent 3,351,495 would be those that did not ., llS0873 have high aromatic contents because of the desirability of having a flash point not much lower than 400~F to avoid spontan-eous ignition during processing under the teaching of U.S. Pat-ent 3,351,495. Generally those fuel oils that have aromatic contents above 20~ either have a flash point significantly below 4Q0F or are waxes. U.S. Patent 4,024,323 also teaches the use of petroleum oil as a preferred plasticizer and more specifically mineral oil was given as preferred at Col. 4 lines 14 et seq.
and 61 et seq. The mineral oil given in Example 1 of TT.~. ~at-o B ent 4,Q24,323 is Shellflex 412 which is listed in the literature as a naphthenic oil but has an aromatic content of about 35% of its molecular ~reight.
U.S. Patent 4,024,323 teaches the use of the plasticizers of U.S. Patent 3,351,495 in the manufacture of battery separators having polymeric mixtures of polyolefins including those with polymer of acrylic and methacrylic acid. German patent publicat-ion DT-OS 25 44 303 shows in Example 4 forming a battery separ-ator from 64% polyproplyene, 11% silica and 25% polyethylene-glycol plasticizer with the polyethyleneglycol being extracted.
2Q Other polymers were mentioned for use in place of polypropylene, for example, polystyrene, acrylonitrile-butadiene-styrene, polysulfone, polyvinylidene fluoride, and vinyl chloride-vinyl-idene chloride copolymer.
Another composition ~Ihich would benefit from the present invention is the one taught ~y German patent publication DT OS-26 27 229, This German patent publication shows forming microporous films by mixing 4Q to 90% by volume of a polyolefin, 10-60~ inorganic filler and 3Q-75% of an organic liquid such as

-2 1 15~)~73 phthalic acid esters, as diethyl phthalate, dibutyl phthalate or dioctyl phthalate, fatty acid esters as the dioctyl esters of sebacic acid and adipic acid, maleic acid esters as dibutyl maleate, trimellitic acid esters as trioctyl trimellitic acid ester, phosphoric esters as tributyl phosphoric ester and octyl diphenyl phosphoric esters and glycols as polyethylene glycol and then extracting the organic liquid.
Summary of the Invention By an aspect of the invention a battery separator is prov-ided that has an olefinic polymer as a primary binding material and a material to protect the olefinic polymer. The protective material is an oil present in an amount between about 5 to about 25%, more preferably about 8 to about 20%, of the separ-ator weight. The oil has a high aromatic content, at least about 40% of the oil's weight, preferably about 45 to about 90~, and more preferably about 45 to about 80% of the oil's weight.
The aromatic content in the battery separator, exclusive of any aromatic content in the binding polymer, is preferably about 2 to about 10% of the battery separator weight, more preferably about 4 to about 8% of the battery separator weight.
The battery separator is preferably microporous and prefer-ably contains an inorganic filler, preferably a siliceous mater-ial, in an amount of at least about 30% of the battery separator weight. The preferred olefinic polymer is a homopolymer or copolymer of ethylene and is preferably present in an amount of at least about 20% of the separator weight. The separator is particularly advantageous for use in acid batteries.

~150873 By another aspect of the invention a process is provided that is particularly advantageous for producing a hattery separator. The process includes forming a mass comprised of the polymer described above and an aromatic oil as described above. The aromatic oil is preferably present in an amount in excess of about 10% of the mass's gross weight. Preferably the mass has an inorganic filler present in an amount of at least about 10% of the mass weight, and the polymer content is at least about 10% of the mass weight and the aromatic oil content is at least about 30% of the mass weight and the battery separator is formed by forming the mass into a sheet and thereafter removing at least about 50% of the aromatic oil weight therefrom.
By yet another aspect a process is provided for modifying a bat-tery separator structure. The process includes providing a battery separator structure comprised of olefinic polymer and having an aromatic oil content of less than 5% of the battery separator structure weight and coating exposed surfaces of the battery separator structure with an aromatic oil to a resid-ual level of between about 5 to about 25% of the battery separator structure weight including the aromatlc oll.
Preferred Embodiment The battery separator of the present invention has as its primary structural material a polyolefin. This primary structural material is protected by providing an aromatic oil in the battery separator in an amount of between 5 and 25% of the battery separator's weight, preferably between 8 and 20% of the total battery separator weight should be aromatic oil. The aromatic oils claimed for the invention of this application are those having an aromatic content of at least 40% of the oil's weight, preferably hetween 45 and 90%. Because of economics and viscosity, the more usual aromatic contents in the oil may be found in preferred practice to be 40 to 80% or even 40 to 70~. The high aromatic content greatly improves oxidative resist-115t~873 ance as measured hy retention of physical strength after battery life or accelerated oxidation test. In addition lower ER's (electrical resistance) are found with the preferred aromatic oil content of between 5 and 25% of the battery separator weight and particularly with the preferred aromatic oil content of between 8 and 20% of the battery separator weight. The aromatic content of the oil is believed to be the primary beneficient factor in the oil and should preferably be present in the battery separator in an amount ranging between 2 and 10% more preferably 5 and 8% of the battery separator weight.
The term "aromatic oil" when used in this application means an oil having an aromatic content of at least about 40% as determined by the ASTM procedure of the next following paragraph.
The aromatic content of the oil is determinable by either ASTM
D2007 or D2549-68. In this application if the aromatic content determined by either ASTM method falls within a claimed range the content is to be under-stood as containing the designated aromatic content. Furthermore if either the starting oils aromatic content or the extracted oils aromatic content falls within a claimed range the content is to be understood as containing the designated aromatic content. The method of extraction of the aromatic content (of the oil not the polyolefin binder) is to extract with pentane and then proceed as described in the ASTMs. Normally in the petroleum industry ASTM D2007 is preferred.
The preferred polymers are the polyolefins. Representative of polyolefins of high and low molecular weight operable in the instant invent-ion are polyethylene, polypropylene, polybutene, polystyrene, ethylene-propylene copolymers, ethylene-hexylene copolymers, ethylene-butene copoly-115~873 mers, propylene-butene copolymers and ethylene-propylene-butene copolymers and copolymers of ethylene or propylene with an ethylenically unsaturated monocarboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof. The most preferred polymer is a homopolymer or copolymer of polyethylene and most preferably the homopolymer.
Polyethylene offers both good per se resistance to oxidative damage in acid battery environments and good processability at economical cost. The polymer is preferably present in the finished battery separator in an amount of at least 20% of the battery separator weight. While the preferred binder from an oxidation resistance standpoint is the homopolymer of ethylene, some copoly-mers of ethylene are more easily and economically processed. It is with these copolymers that the present invention is most critical for use because of their relatively poor oxidative resistance. The invention of the present application make it practical to use binders that formerly were not useful in the more oxidative battery applications as well as further enhancing the usefulness of binders that already performed well.
The preferred battery separators contain water insoluble inorganic fillers, for example those listed in U.S. Patent 3,351,495, Col. 4, lines 9-23. The preferred inorganic filler is finely divided silica. The inorganic filler is preferably present in an amount of at least 30% of the weight of the finished battery separator.
It is contemplated that the oil will be supplied in the battery separator by either one of two methods. In the first method the oil is used as an ingredient in the procedure for producing the battery separator by form-ing a mass comprising the polymer and the aromatic oil, and typically, also a mineral filler. A typical preferred mass comprises an aromatic oil in an amount in excess of 10% of the mass's gross weight. The polymer is preferably present in an amount of at least 10% of the mass weight with the mineral filler being present in an amount of at least 10% of the mass weight.
This mass is formed into a sheet and the aromatic oil is then extracted down to the desired levels previously enumerated to provide the desired porosity in the battery separator with the remaining residual oil providing the oxidative properties desired and improved ER characteristics. At least 50% of the aromatic oil weight is removed from the sheet. Examples of this general procedure of manufacture, but using non-aromatic oils, are given in greater detail in U.S. Patent 3,351,495 and U.S. Patent 4,n24,323.
The second method for supplying the oil in the battery separator involves taking a separator made from a polymer of the previously described character and coating the exposed polymer surfaces in the pores of the battery separator with the aromatic oil of this invention by, for example, dipping the battery separator in oil-solvent solution and removing the solv-ent, or roller coating the battery separator using oil alone or with diluent or spraying the battery separator oil alone or mixed with diluent.
Unless otherwise stated, percents in this application are by weight based upon 100% end composition weight. Thus 10% of the battery separator weight of an aromatic oil means that the aromatic oil constitutes 10 weight parts out of every 100 weight parts of the total battery separator weight, leaving 90 weight parts of other ingredients.
The following examples further illustrate the nature and ad-vantages of the present invention.
EXAMPLE I
The antioxidative effectiveness of the aromatic oil was tested on battery separators composed essentially of polyethylene and amorphous silica made by W. R. Grace ~ Co., sold under the trademark DARAMIC and made accord-ing to the teachings of U.S. Patent 3,351,495. The battery separators were prepared by thoroughly washing with Hexane to remove substantially all of the residual paraffinic oil as determined by incremental weight loss on extended extraction using Soxhlet extraction apparatus. The battery separat-ors were then soaked in hexane solutions of the oils specified in Table 1 A and dried to yield the oil contents given. The naphthen c oil was Shellflex 411 (a product of Shell) and the aromatic oil was Dutrex 357 (a product of Shell). The hexane solutions of the oils contained 6 weight percent of the specified oil. The residual oil content was determined by weight difference after extended hexane extraction using a Soxhlet extraction apparatus.
The battery separators were then cut into samples 2 1/2 inch square and subjected to electrolysis in sulfuric acid (1.400 sp. gr.) for 24 hours at 9 amps to simulate the degradative chemical effects during the life of a lead acid battery. This will be referred to as ROX or Rapid Oxidat-ion Comparative procedure. The 9 amps ROX for Table I for all of the samples was carried out at the same time to obtain increased reliability. The test was repeated except the current was raised from 9 amps to 11 amps and the time was increased as indicated in Table I.
The tensile strength (T) and elongation (E) in the cross machine direction was determined by die cutting samples 0.375 inch x 2.5 inch from the center of the specimen and measuring the breaking strength (in lbs/sq. in.) and elongation (as a % of starting length) at break using a tensile testing machine having a jaw gap of 1.0 inches and cross head speed of 12.0 inches per minute.

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~lS0873 Characterist;cs of Oils Name of Oil Shellflex 411 Shell Dutrex 357 .
Type Designation Naphthenic Aromatic Visc. sus @ 100F 523 459 Flash CPC F 410 395 Pour point, F -5 35 Aniline point, F 207 74 Volatility:22 hrs./225F 0.7 0.4 Clay-Gel analysis, %
Polar Compounds 1 10 Aromatics 20 72 Saturates 79 18 ... ,~
_g_ 115~873 Table 1 ROX 24 hrs.t9 amps Oil Content Before ROX After ROX Percent Loss in Sample % T E T E T E
Naphthenic 7.7%
Sample 1 1307 760843 480 35.536.8 2 1241 703747 341 39.851.5

3 1252 641872 498 30.322.3

4 1352 787730 369 46.053.1 Average: 37.940.9 Aromatic 7.3%
Sample 1 1327 5691115 530 16.0 6.9 2 1351 6571121 537 17.0 18.3 3 1207 492106~ 504 12.0 0.0 4 1306 7271099 511 15.8 29.7 Average: 15.2 13.7 ROX 48 Hrs./ll amps Naphthenic 7.7%
Sample 1 1387 642865 388 37.6 39.6 2 1312 583853 387 3~.0 33.6 3 1357 603925 381 31.8 36.8 4 1376 641886 298 35.6 53.5 Average: 35.0 40.9 Aromatic 7.3%
Sample 1 1463 6271096 356 25.1 43.7 2 1274 4831049 401 17.7 17.0 3 1457 5981113 446 23.6 25.4 4 1392 5291175 474 15.6 10.4 Average: 20.5 24.1 The retention of tensile strength and ability to elongate hefore breaking are obviously very much improved hy the aromat;c oil.
Example 2 The procedures of Example 1 were repeated except the polymer in the battery separator was a 1:1 blend of polyethylene ~Hercules Hifax 1900) and B an ethylene-hexylene copolymer. (Allied Chemicals Co. EC 50-003). The ROX was at 9 amps for 24 hours.
In addition the impregnating oils were as shown in Table II.

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115~873 Example 3 The procedure of Example 1 was repeated except enough battery separat-ors were treated for the assembly of complete batteries. The batteries were group 24 batteries composed of 9 regular antimonial plates per cell ~4 pos-itives and 5 negatives per cell) with 6 cells per battery. Three alternate cells were equipped with the battery separators containing the aromatic oil while the remaining cells were equipped with naphthenic oil treated separat-ors for comparison purposes. The battery separators were subjected to the oxidative effect of the SAE life cycle test according to an adaptation of Society of Automotive Engineers Tech Report J-537f with the following results.
The cold performance results (done basically as described in Tech Report J-537f) showed the aromatic oil treated separators were .03 volts/cell less than the naphthenic oil treated separators (1.29 vs. 1.32 respectively).
The cells with the aromatic oil averaged two weeks longer (287 vs 227 cycles) on SAE life cycle. After cycling, these same aromatic oil treated battery separators showed significantly higher elongations in both the machine and cross machine directions than the naphthenic oil treated battery separators (350% vs 42% MD and 118% vs 9% CMD). Throughout testing, the aromatic oil treated battery separator cells gave cadmium voltages which were more negative, which is a desirable attribute.

115t~873 Example 4 Battery separators manufactured by F.vans Products, Inc., it is believed according to U.S. Patent 4,024,323, were treated and tested as in Example 1. The untreated separators as received contained essentially no oil. The results are as shown in Table III.
T A B L E III
Battery Separator Battery Separator Untreated Battery treated w/ 10% of treated w/ 10% of Separator the naphthenic oil the aromatic oil Tensiles, MD (~si) Initial 947 947 947 Final 0 0 324 % Loss 100 100 66 Elongation (%) Initial 305 305 305 Final 0 0 <10 % Loss lnO 100 ~97 Tensiles CMD (psi) Initial 564 564 564 Final 0 0 305 % Loss 100 100 46 Elongation (%) -Initial 150 150 150 Final 0 5 % Loss 100 100 97 115~)873 The beneficial effect of the aromatic oil on battery separator properties can he seen by comparing the tensile and the elongation values of Table III.
Experimental work to date seems to clearly support the view that oxidation resistance and ER are improved by the aromatic oil. The ex-perimental work to date is inconclusive with regard to whether life cycle test results indicates some degree of improvement or some degree of harm in this aspect of battery performance.
Taken as a whole it may be seen that quite unexpectedly and uniquely there is a protective effect provided by including an oil having an aromatic content in excess of the minimums specified in this application in battery separators having olefinic binder materials. This supplies aromatic compon-ents exclusive of the binder polymer and is not related to any aromatic content in the binding polymer itself.
While in accordance with the patent statutes, what is considered to be the best mode of carrying out the invention has been described, it will be obvious to those skilled in the art that numerous changes and modifications may be made therein without departing from the invention and it is therefore aimed in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of the invention.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A battery separator comprising olefinic polymer and between about 5 to about 25% of the battery separator weight of an oil having an aromatic content of at least about 40% of the oil's weight.

2. The battery separator of Claim 1 wherein said oil has an aromatic content of about 40 to about 90% of the oil's weight.

3. The battery separator of Claim 2 wherein said oil has an aromatic content of about 45 to about 80% of the oil's weight.

4. The battery separator of Claim 2 comprising siliceous material in an amount of at least about 30% of the battery separator weight and wherein said olefinic polymer is present in an amount of at least about 20% of the battery separator weight and said oil is present in an amount of between about 8 to about 20% of the battery separator weight.

5. The battery separator of Claim 4 wherein said olefinic polymer is a homopolymer or copolymer of ethylene and said oil has an aromatic content of 40 to about 70% of the oil's weight.

6. The battery separators of Claim 2 wherein said olefinic polymer is chosen from the group consisting of polyethylene, polypropylene, polybutene, polystyrene, ethylene-propylene copolymers, ethylene-hexylene copolymers, ethylene-butene copoly-mers, proplyene-butene copolymers and ethylene-propylene-butene copolymers and copolymers of ethylene or propylene with an ethylenically unsat-urated monocarboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof.

7. A battery separator comprising olefinic polymer and an aromatic oil constituent to protect the olefinic polymer, characterized in that the battery separator has an aromatic content, exclusive of said olefinic polymer, of about 2 to about 10% of the battery separator weight.

8. The battery separator of claim 7 wherein said aromatic content, ex-clusive of said olefinic polymer, is about 4 to about 8% of the battery separa-tor weight.

9. In an acid battery a microporous battery separator comprised of olefinic polymer, the improvement comprising including about 5 to about 25% of the battery separator weight of an oil in the battery separator, said oil hav-ing an aromatic content of at least about 40% of the oil's weight.

10. The battery of claim 9 wherein said oil has an aromatic content of about 40 to about 90% of the oil's weight.

11. The battery of claim 10 wherein said olefinic polymer comprises an alpha olefin homo or copolymer present in an amount of at least about 20% of the separator weight, said oil is present in an amount of about 8 to about 20%
of the separator weight and said battery separator comprises an inorganic fill-er present in an amount of at least about 30% of the battery separator weight.

12. The process of producing a battery separator comprising forming a mass comprising an olefinic polymer and an oil in an amount in excess of about 10% of the mass's gross weight with the oil having an aromatic content of at least about 40% of the oil's weight and forming a battery separator using said mass.

13. The process of Claim 12 wherein said oil has an aromatic content of about 40 to about 90% of the oil's weight.

14. The process of Claim 13 wherein said oil has an aromatic content of about 45 to about 90% of the oil's weight.

15. The process of Claim 13 wherein said olefinic polymer comprises a polyethylene homo or copolymer and is present in an amount of at least about 10% of the mass weight, said mass comprises an inorganic filler present in an amount of at least about 10% of the mass weight, said oil is present in an amount of at least about 30% of the mass weight and said forming of said battery separator using said mass comprising forming said mass into a sheet and thereafter removing at least about 50%
of the oil's weight.

16. The process of modifying a battery separator structure comprising providing a battery separator structure comprised of olefinic polymer and having an aromatic oil content of less than about 5% of the battery separator structure weight and coating exposed surfaces of the battery separator structure with an aromatic oil to a residual level of between about 5 to about 25% of the battery separator structure weight including the aromatic oil.

17. The process of Claim 16 wherein said oil has an aromatic content of about 40 to about 90% of the oil's weight.

18. The process of Claim 17 wherein said oil has an aromatic content of about 45 to about 80% of the oil's weight.

19. The process of Claim 17 wherein said olefinic polymer comprises a homo or copolymer of ethylene and is present in an amount of at least 20% of said battery separator structure, and said battery separator structure comprises inorganic filler in an amount of at least about 30% of said battery separator structure, and said aromatic oil residual level is between about 8 to about 20% of the said battery separator structure.