WO2001034388A1

WO2001034388A1 - Graft polymerization, separators, and batteries including the separators

Info

Publication number: WO2001034388A1
Application number: PCT/US2000/041656
Authority: WO
Inventors: Wai Ming Choi
Original assignee: Hollingsworth & Vose Company
Priority date: 1999-10-29
Filing date: 2000-10-27
Publication date: 2001-05-17
Also published as: EP1265748A1; JP2003514135A; AU2748201A; TW590887B; US6384100B1; EP1265748A4; CN1399594A

Abstract

A method for producing an acrylic graft polymer on the surface of a polyolefin article is disclosed. The method comprises the steps of immersing the polyolefin article in a solution of a photoinitiator in a volatile solvent, allowing the volatile solvent in the photoinitiator solution to vaporize, immersing the polyolefin article in a solution of an acrylic monomer, and subjecting the polyolefin article, while in a suitable atmosphere, which can be air or can be inert, to ultraviolet irradiation to cause the acrylic monomer to graft to the polyolefin surface. A method which involves subjecting a polyolefin article to corona discharge, immersing the article, after corona discharge treatment, in a solution of a photoinitiator and an acrylic monomer in a volatile solvent, and subjecting the article to ultra violet irradiation to cause the acrylic monomer to graft to the polyolefin surface is also disclosed. The latter method improves the ammonia trapping capacity of the grafted article.

Description

TITLE

GRAFT POLYMERIZATION, SEPARATORS, AND BATTERIES INCLUDING THE SEPARATORS

s BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The piesent inv ention lelates generally to the field ot gi att polymerization and, moie specifically, to gi att polymerization ot non-woven polyolefm fiber sheets, and to battenes in w hich giatt polymerized non-woven polyoletin tibei sheets constitute

10 sepaiatoi s w hich are positioned between the positive and negative plates DESCRIPTION OF THE PRIOR ART

Battei) sepaiatoi s which aie non-woven sheets ot polyoletin fibers with an aciylic giatt polymei on the tibei surfaces aie known, being disclosed in a papei piesented at the 1986 Povv ei Souices Symposium held in Chen y Hill, New Jersey, J Polym Sci 34, 671 i ( 1959). and in WO 93/01622, published January 21. 1 93 The Symposium papei discloses the use ot ionizing ladiation to pioduce such sepai atoi s. while WO 93/01622 discloses a method tor pioducing such separatoi s which involves immeision ot non-woven sheets ot polyoletin tibei s in a solution ot an aciylic monomei which also contains a photoinitiatoi . followed by ultiaviolet π iadiation ot the sheets Vanous publications, e g .

20 Yao and Ranby. Journal of Applied Po ei Si win e, Vol 41 , 1469- 1478 ( 1990) disclose w i k earned out at the Royal Institute ot Science. Stockholm, Sweden which involv ed mimei sing poly olet in tibei s and films in solutions ol aci ylic monomei s and benzophenone, followed by ultiaviolet n radiation of the fibers and films to produce an aci ylic giatt polymei on the surfaces ot the tibei s and films Another publication,

2s Join nal of Po met St win e, Po m i Letrei s Edition, Vol 19, pages 457-462 ( 1981 ) discloses the immei sion ot polyolefin films in an acetone solution ot benzophenone and attei di ving ot the films, v apoi phase and liquid phase copolymeuzation ot an aciylic monomei v ith the polypiopylene suitaces ot the films to pioduce acrylic giatt polymei s

30 A Journal aiticle entitled "Chemical Absorptive Piopeities ot Acrylic Acid

Gi atted Non-woven Battei y Sepai atoi s". refers to woik earned out by Leblanc et al (citing P Leblanc, Ph Blanchard, S Senyaπch, Abstract No 261 ESC/ISE meeting. Pans, ( 1997) and P Leblanc, Ph Blanchard, S Senyaπch, Elec ti oche Sot 145. 846. (1998)) as showing that ammonia in a NiMH cell diamatically reduces the selt- dischaige performance, and cites the lattei reference tor the statements

"It was also demonstrated that this effect could be significantly leduced it the tiee ammonia in the cell could be removed The tests showed that by using an acrylic acid grafted separator with an ammonia absoiption ot over 15 x 10⁴ mol/g then all the tree ammonia could be eliminated, and the self-discharge performance impioved to the levels noimally associated with NiCd cells " The leteience then leteis to the piocess ot WO 93/01622 as ' capable ol giatting non- wovens ot all constiuctions^" and states

"A study was earned out to examine the etlect ot the non-woven type on the sepaialor^'s ability to absorb ammonia using K|eldhal s technique (see table 1 ) All the grafted materials were giatted to the same level using the same grafting conditions The lesults show tiistly that an aciylic acid giatt is necessaiy for a non-woven to posses the ability to absoib ammonia Fuithermore. the amount of absoiption is a lunction ot the base non-woven matenal The stiongest correlation is with the tibie size ot the non- woven, and theietoie also suit ace aiea, with tine sepaiatois absoibing the most ammonia

"Samples ot the PP fine tibie spunbond weie also piepaied with two ditteient graft levels and then ammonia absorption measured (see table 2) These lesults show that the ammonia absoiption is independent ot the total amount ot aciylic acid grafted onto the polymei backbone, and is further evidence that it is the base non woven which contiols the degiee ot ammonia absoiption "

THE INSTANT INVENTION

The instant invention is based upon the discovery that a non-woven sheet ot polyoletin tibeis can be immeised in a solution ot benzophenone, dried, immersed in a solution ot aciylic acid, and subjected to ultraviolet uiadiation, while the acrylic acid solution is still on its surfaces, to pioduce an acrylic graft copolymer on the surfaces of the fibers, and that the reaction proceeds more rapidly than when the non-woven sheet of polyolefin fibers is immersed in a solution of benzophenone and aci ylic acid, and subjected to ultraviolet irradiation while the solution of aci ylic acid and benzophenone is still on the surfaces of the fibers. In a further aspect, the invention is based upon the discovery that a non-woven sheet of polyolefin fibers can be immersed in a solution of benzophenone. dried, immersed in a solution of acrylic acid, and subjected to ultraviolet irradiation, while the acrylic acid solution is still on its surfaces, and while the non-woven sheet with the acrylic acid solution on its surfaces is in contact with either air or an inert atmosphere, to produce an acryl ic graft copolymer on the surfaces of the fibers.

In a still further aspect, the invention is based upon the discovery that a non-woven sheet of polyolefin fibers can be immersed in a solution of benzophenone, dried, immersed in a solution of acrylic acid, and subjected to ultraviolet irradiation, while the acrylic acid solution is still on its surfaces, and while the non-woven sheet with the acrylic acid solution on its surfaces is inside a polyethylene bag or tube, and is in contact either with air or with an inert atmosphere, to produce an acrylic graft copolymer on the surfaces of the fibers. In a preferred embodiment, after the volatile solvent in the photoimtiator solution vaporizes, a web of the polyolefin article is advanced through the solution of the acrylic monomer, and through a region where it is subjected to ultraviolet irradiation to cause the acrylic monomer to graft to the polyolefin surface, and sheets of a polyolefin such as polyethylene which are wider than the web are introduced above and below the web and the adjacent edges of the polyolefin sheets are sealed to one another to form a tube which surrounds the web. and it is the web surrounded by this tube which is advanced through the region where the web is subjected to ultraviolet irradiation. In yet another aspect, the invention is based upon the discovery that the ammonia absorption capacity of a non-woven sheet composed of polyolefin fibers which have been graft polymerized with acrylic acid can be increased significantly by subjecting the sheet to corona discharge before the fibers are graft polymerized with acrylic acid.

In still another aspect, the invention is based upon the discovery of a method for producing a non-woven sheet of polyolefin fibers which is hydrophilic in at least one part and hydrophobic or hydrophilic to a different degree in at least one part. The sheet which is hydrophilic in at least one part and hydrophobic in at least one part can be produced by applying a solution ot benzophenone or ot anothei photoimtiator to a selected pait oi to selected paits ot a non-woven sheet composed ot polyoletin tibeis, immersing the sheet, attei evapoiation ot the solvent tiom the benzophenone oi the like solution thereon, in an aciylic acid solution, lemoving the sheet tiom the acrylic acid solution, and uiadiating the lesulting sheet ith ultia violet the niadiation causes the aciylic acid to graft polymerize to the surfaces ot the tibeis wheie the benzophenone oi the like solution was applied, making them hydiophilic. but does not cause graft polymei ization to the surfaces ot the tibeis wheie benzophenone oi the like was not applied, so that they remain hyidiophobic The sheet which is hvdiophi c in at least one pait and hydiophilic to a ditteient degiee in at least one pan can be pioduced by applying a solution ot benzophenone or ot anothei photoinitiatoi to a selected pait oi to selected parts of a non-woven sheet composed ot polyolelm tibeis, applying a solution having a dilteient concentiation ot benzophenone oi ot anothei photoinitiatoi to a ditleient selected pait oi to ditteient selected parts, lmmeising the sheet, altei evapoiation ot the solvent tiom the benzophenone oi the like solutions theieon. m an aciylic acid solution lemoving the sheet tiom the aciylic acid solution, and uiadiating the lesulting sheet with ultia violet the niadiation causes the acrylic acid to giatt polymenze to the surfaces ot the tibeis wheie the benzophenone oi the like solution was applied, making them hydiophilic, but the degiee to which giatt polymei ization to the surfaces ot the tibeis makes them hydiophilic depends upon the concentiation ot the benzophenone oi the like in the solution which was applied When a recombinant battei y is assembled in which non-woven sheets ot polyoletin tibeis which aie hydiophobic in paits and hydiophilic in paits aie used as a sepaiatoi between adμcent plates, the hydiophilic poitions of the sheets aie wet by the electiolyte, but the hydiophobic poitions aie not As a consequence, poitions ot the plates aie wet by the electiolyte, which saturates adμcent poitions ot the sepaiatoi, but gas evolved at one of the plates is tiee to migiate through the hydiophobic poitions ot the sepaiatoi to an adμcent one ot the plates

Non-woven sheets ot polyolef tibeis which can be used as staiting materials in piacticing the instant invention aie pioduced commeicially by numeious piocesses which have been classified as "diy-laid systems" and as "melt spun systems" Recognized "diy- laid systems aie known as "random air laid", as "caided web systems" and as ' spun lace systems", while lecogmzed ' melt spun systems" aie known as "spunbonded" and "melt blown piocesses These methods are all well known, and are disclosed in the literature, e g in ^'Inti oduction to Nonwovens". Albin Tui bak. TAPPI Pi ess, Atlanta. Georgia, 1998 (see m pai ticulai pages 32-39) OBJECTS OF THE INVENTION

It is. thei etore, an object ot the invention to piovide an lmpioved method tor s pioducing a graft polymer on the surfaces of polyoletin fibers and films

It is another object to pi ovide an impioved method tor producing an aci ylic graft polymer on the surfaces of polyoletin fibers and films

It is a tui thei ob|ect to pi ovide a method toi pioducing a non woven sheet ot polyoletin fibers which has at least one region in which the fibers aie hydi ophilic as a 0 consequence ot an acrylic acid gi att polymei on fiber surfaces and at least one region in which the fibers are hydi ophobic

It is still a turthei object to piovide a non-woven sheet ot polyoletin fibers which has at least one legion in which the fibers ai e hydiophilic as a consequence of an acrylic acid gi att polymei on fiber surfaces and at least one l egion in which the fibers aie i s hydi ophobic

Othei ob|ects and advantages will be apparent tiom the descnption which follows, which is intended only to illustrate and disclose, and not to limit, the invention DISCLOSURE OF THE PREFERRED EMBODIMENTS

In the following Examples, and elsewheie heiein. the terms "peicent" and ' parts" 20 l etei to pei cent and pai ts by weight, unless othei wise indicated, and "g" means gram oi gi ams 'ml means millihtei oi mil htei s ' m means metei oi metei s, ' cm" means centimetei oi centimetei s "mm" means mil metei oi millimeters, "μm^* means mici ometei oi mici ometei s "KV" means kilov olts, "KW" means kilowatts

25 Example 1

A sample ot a non-woven tabi ic which is commercially available under the designation "TR 1827E 1 ^" was immersed in a solution of 15 g benzophenone in 285 g acetone, was removed from the solution, and was allowed to stand under ambient conditions of about 25°C tor five minutes until the acetone evaporated The fabric 30 sample w as appioxnnatelv 5 inches ( 12 7 cm) by 30 inches (76 2 cm) and 0 007 inch (0 178 mm) thick, its avei age unit area weight was 50 g per m^~, it was composed of 40 peicent ot polypiopylene fibers having an avei age diametei of 12 μm and 60 percent ot sheath coie tibeis having an aveiage diametei ot 16 μm. and composed ot a polypropylene coie enclosed within a polyethylene sheath The tabnc sample was then immeised in an aqueous solution which contained 35 percent ot aciylic acid, and was placed inside a polyethylene bag Nitiogen was then intioduced into the bag to puige the s an that was onginally piesent theiein, and to establish a nitrogen atmosphere inside the bag The bag was then closed, and was moved undei a UV lamp which was 8 inches (203 cm) in length at a speed ot 8 to 10 teet per minute (244 to 305 m per minute) The distance tiom the UV souice to the sample surface ninged tiom 4⁷/ inches to 5'/_ inches The sample was then lemoved tiom the polyethylene bag After the grafting 0 which occuned dunng the pioceduie desciibed above, thiee samples weie found to have gained an aveiage 175 peicent in weight, and to have an average ion exchange capacity in meq g ' ot 0689

Foi puiposes ot compaiison, but not in accoidance with the instant invention, the pioceduie ot Example 1 was lepeated, except that the step ot immersing the non-woven s tabnc sample in an acetone solution ot benzophenone was omitted, and, instead, the tabnc. as leceived. was immeised in a solution composed ot 35 percent ot aciylic acid. 636 peicent ot H_:0.05 peicent ol a surfactant that is commercially available under the designation "Tnton X 100^" and 085 percent ot benzophenone Attei the grafting which occuned dunng the pioceduie desciibed above, two samples weie found to have gained 0 an aveiage ot 132 peicent in weight, and to have an aveiage ion exchange capacity in meq -l ot 0291 Example 2

The pioceduie desciibed in Example 1 was lepeated. except that the solution in which the tabnc sample was immeised, attei it was lemoved tiom the benzophenone 2s solution in acetone and allowed stand until the acetone evapoiated, contained 35 percent ot aciylic acid, 645 percent ot watei, and 05 peicent ot the surfactant which is available undei the designation Triton XI 00 Attei the giatting. two samples weie found to have gained an aveiage 1815 peicent in weight, and to have an aveiage ion exchange capacity in meq g ' ot 0641 30 Example 3

The piocedure desciibed in Example 1 was also lepeated, except that the sample was immeised in a 5 peicent solution ot benzophenone in methylene chloride After the methylene chlonde evapoiated, the sample was immeised in the aqueous solution which contained 35 percent ot acrylic acid, and was placed inside the polyethylene bag and, attei a nitiogen atmospheie was established inside the bag and the bag was closed, was moved undei the UV lamp Attei the giatting. two samples which weie exposed to the UV niadiation tor 15 seconds weie found to have gained an aveiage ot 194 percent in weight, and to have an aveiage ion exchange capacity in meq g ' ot 0542 A sample which was exposed to UV u radiation toi 10 seconds was found to have gained 1042 peicent in weight, and to have an ion exchange capacity in meq g ' of 0251 Example 4 Samples which weie appioximately 5 inches (127 cm) by 30 inches (762 cm) and

0007 inch (0178 mm) thick ot vaiious non-woven tabiics other than that which is available under the designation "TR1827E1 ^' have been tieated by a proceduie similai to that desciibed in Example 1, ditteiing in that the fabrics were immersed in a solution containing 5 g benzophenone in 150 g methanol. the acrylic acid solution in which the tabiics weie immersed was composed ot 90 g acrylic acid.3 g methanol and 207 g watei. and the polyethylene bags in which the tabnc samples weie placed attei having been immeised in the aciylic acid solution weie not pinged with nitiogen so that theie was an in contact with the tabnc samples dunng niadiation with UV The tibeis in the tabiics that weie tieated weie polypiopylene tibeis having an aveiage diameter ol 12 μm ("PP tibeis^"). and sheathcoie tibeis composed ot a polypropylene core and a polyethylene sheath aveiage diametei 1 μm (' PE/PP tibeis")

Non-woven webs weie pioduced by opening bales ot the tibeis identified above, carding the tibeis. and bonding the caided tibeis to one anothei at points ot contact in a flow thiough type an oven maintained at a tempeiatuie sufficiently high that the tibeis bind to one anothei. but not so high that sticking occuis This temperatuie is usually in the lange of 120 to 126° C . but the pi ease tempeiatuie requued in any given case can be determined with simple expenmentation The webs were composed ot the PE/PP tibeis identified above, in the propoitions indicated in the following table, where the teim "Diylaid" leteis to webs pioduced as desciibed. and the teim "Spunlace" leteis to such webs and to wet laid webs which have been sub|ected to hydroentanglement by high velocity watei jets, toi example, using equipment known to those skilled in the art, and letened to as "Fleissnei-Aquajet" appaiatus Repiesentative ones of the non-woven polyoletin tabiics that weie tieated with benzophenone and acrylic acid solutions and then inadiated with ultia violet as desciibed above aie identified in the following table

The basis weights (Weight, g/nr) given in the toiegomg table aie nominal values tor the

Diylaid and Meltblown matenals, aie based upon actual deteimmalions toi the SMS,

Spunlace and Diy laid/meltblo n Composite matenals

The divlaid/meltblown composite identified in the loregomg table was pioduced by depositing meltblown PP tibeis on top ot a diylaid sheet composed ot PP tibeis and PE/PP tibeis theie was a surface size on the tibeis ol the diylaid sheet, but not on the meltblown PP tibei poition ot the matenal

The matenal designated "SMS^" in the toiegomg table is composed ot thiee layeis two t a known matenal called spunbond and an intei mediate ' Meltblown ^' layei The lesults achieved in Example 4 aie summanzed in the following table wheie

"IEC^" means the ion exchange coefficient ot the grafted sheet in milliequivalents pei

Example 5

The Diylaid and Spunlace webs produced as described above were subjected to coiona dischaige at a powei level ol 08 KW by advancing them at a speed ot about 10 yaids pei minute ovei a giounded i il and beneath metal shoes which weie chaiged by s alternating cuπent and weie spaced a traction ot an inch abo e the webs The appaiatus used to subject the Diylaid and Spunlace webs to coiona dischaige is commercially available tiom Corotec Coiporation, Collinsville, Connecticut, under the designation "HFT-10

The webs weie then immeised in a 35 percent aqueous solution ot aciylic acid 0 which also contained 08 peicent ot benzophenone and placed in polyethylene bags

Nitiogen was used to jmige an tiom the bags, and the bags weie sealed with a nitrogen atmospheie inside in contact with the webs The sealed bags weie then moved under a 300 watt UV lamp so that the major surfaces ot the webs were about 5 inches from the lamp, inveited, and moved undei the lamp a second time with the web surfaces about 5 s inches tiom the lamp This pioceduie subjected each majoi surface ot each web to UV iπadiation toi about 10 seconds to cause graft polymei ization of the aciylic acid to the tibei surfaces

Diylaid and Spunlace webs which had not been subjected to corona discharge weie also immeised in the 35 jieicent aqueous solution ot aciylic acid which also 0 contained 08 ]3eιcenl ot benzophenone and placed in polyethylene bags Nitrogen was used to ptuge an tiom the bags and the bags weie sealed with a nitiogen atmospheie inside in contact with the webs The sealed bags weie then moved undei a 300 watt UV lamp, using the pioceduie described in the previous paiagraph. so that each major surface ot each web was subjected to UV niadiation toi about 10 seconds to cause graft 2s polymei ization ot the aciylic acid to the fiber surfaces

The ion exchange coefficient and the ammonia absoiption ot the sepaiatoi weie then determined foi the sepaiatoi which had been subjected to coiona dischaige pnoi to graft polymei ization with acrylic acid and foi the separatoi which had not been so subjected pnoi to giatt polymerization The ion exchange coefficient was determined in 30 milliequivalents pei giam ot sepaiatoi, while the ammonia absorption was determined in mole NH pei gram ot separatoi on the basis ot a Kjeldhal determination ot the total nitiogen in the sepaiatoi attei it had been in contact with an electiolyte which contained ammonia The lesults ot this testing aie summaiized in the following table

It will be appieciated that the pioduction of Spunlace and Diylaid webs, then tieatment by coiona dischaige, and then giatt polymenzation with an aciylic monomei lend themselves to a continuous piocess

The hydioentanglement technique used as desciibed above to produce Spunlace webs also lends itself well to the pioduction ot non-woven tabiics having a high surface aiea Foi example, tibeis composed ot a pltuality ot alternate polyethylene and polypiopvlene segments say toui polyethylene and toui polypropylene segments, aie available hav mg been pioduced by extiusion Such tibeis can be used to pioduce eithei drylaid oi wetlaid. non-woven tabiics. and the tabiics can be subjected to hydi entanglement as desciibed which sepaiates the segments tiom one anothei gieatly lncieasing the surface aiea ot the tibeis in the tabiics, and the surface aiea ot non-woven tabiics having aciylic giatt polymeis on then surfaces which can be pioduced theietiom By way ot example, the tibeis ot a non-woven tabnc made tiom 3 deniei tibeis composed ot eight jiolyethylene and eight polypi ojiylene segments, attei hav mg been subjected to hydioentanglement can have a deniei ot about 01875 or less Example 6

Rotaiy scieen coating is used to apply in a desued pattern, a solution containing 5 g benzophenone in 150 g methanol to one ot the surfaces ot the sheets of the Spunlace and ot the Diylaid matenal desciibed above The benzophenone solution is sprayed I I fi om inside a cylindrical screen of the coating apparatus onto a first major surface of the Spunlace and Drylaid sheets, which are approximately 5 inches ( 12.7 cm) by 30 inches (76.2 cm) and 0.007 inch (0. 178 mm) thick as they pass between the cylindrical screen and a roller which is adjacent the screen, passing through openings in the screen. The sheets are

5 then stacked on a screen support, and allowed to stand until the methanol in the benzophenone solution evaporates, and are then immersed in an acryl ic acid solution which is composed of 90 g acrylic acid, 3 g methanol and 207 g water, and are conveyed through a chamber having an air atmosphere where they are irradiated for 5 seconds on each side w ith ultra violet from a source having an output of 400 watts per inch. The

10 cyl indrical screen has circular openings extending therethrough in a regular pattern which provide an open ai ea which constitutes 30 pei cent ot the area ot the inside of the screen. The apparatus is described in Chapter 5. entitled "Rotary Screen Coating", pages 8 1 and following, of a book entitled "Web Processing and Conv erting Technology and Equipment", published by VanNostrand and Reinhold. New York, New York 10020,

I S 1984. ISBN 0442281773.

Example 7

The procedure described in Example 6 is repeated, except that the webs, after the coating is applied to the first ma|or surface of the Spunlace and Drylaid webs, as

20 described, is advanced between a second cyl indrical screen and a second roller, and a dit ferent benzophenone solution is sprayed through the second cylindrical screen onto the second major surface thereof. In a speci fic embodiment, the benzophenone solution sprayed onto the second ma|or surface of the webs contains 3 g benzophenone in 150 g methanol. and the second cylindrical screen has circular ojienings extending

25 therethrough in a regular pattern which provide an open area which constitutes 30 percent of the area of the inside of the screen, and is indexed so that the regions of second major surfaces of the webs to w hich the benzophenone solution is applied do not overlie the regions of the first major surfaces of the webs to which the benzophenone solution is applied.

30 Example 8

A web ot the pieviously identified non-woven tabnc which is commercially available undei the designation "TRI827EI" is impiegnated with a solution of benzophenone in methanol which contains about 32 peicent ot benzohpenone. and passed thiough an oven which is maintained at about 80° C to vaponze the methanol The web. with benzophenone on the tibeis theieot is then advanced thiough an aqueous aciylic acid solution containing 35 jiercent ot aciylic acid and 2 peicent ot methanol and between souices. above and below the web. toi ultiaviolet niadiation which are about live inches tiom the web and have an output ot 400 watts pei inch Each side ot the web is exposed to this ultiaviolet niadiation toi a total ot about 5 seconds Attei the web leaves the aciylic acid impiegnatmg tank polyethylene sheets which aie widei than the web aie intioduced theieabove and theiebelow. and the adjacent edges ot the polyethylene sheets aie heat sealed togethei to toim a tube which sunounds the web After the ultiaviolet niadiation ot the tub and web, the polyethylene tube is slit vapors which weie confined inside the tube aie lecoveied and a mil ot the web ol non-woven polyoletin tibeis with an acrylic giatt copolymei on the fiber surfaces is collected

Battenes in which sepaiatoi pioduced as desciibed in Example 6 is positioned between jwsitive and negative electi des has sepaiatoi legions which aie hydiophilic and legions which aie hydiophobic so that t eie is electiolyte absoibed by the sepaiatoi in some 'egions, adjacent the plates as lequired to make the battenes opeiable. but theie is no electiolvte in othei legions of the sepaiatoi as a consequence gases leleased al one electiode can pass tieely into contact with the othei electiode tor lecombmation and the hydiophobic/hydiophilic natuie of the sepaiatoi can be tailoied by vaiymg the piopoitions ot the two legions to the peitoimance chaiactenstics desued in the batteiy Even moie tailoiing is possible in sepaiatoi pioduced bv the method of Example 7. and the sepaiatoi can be matched to the dittenng needs ot positive and negative plates

It will be appieciated that various changes and modifications of the invention as specificalh disclosed above aie jxissible without depaitmg tiom the spuit and scope theieot as defined in the tollowmg claims and that, in its essential details, one embodiment theieot is a method foi pioducing Λ\Λ aciylic giatt polymei on the surface ot a polyoletin aiticle The method compnses the steps ot immersing the polyoletin article in a solution ot a photoinitiatoi in a volatile solvent, allowing the volatile solvent in the photoimtiator solution to apouze tiom the polyoletin aiticle, immersing the polyoletin article in a solution ot an acrylic monomer, and subjecting the polyoletin article to ultraviolet ni adiation to cause the aciylic monomei to giatt to the polyolefin surface The ]3θlyoletιn aiticle can be subjected to ultraviolet ni adiation while in an inert s atmospheie. or while in contact with air, it is pieteiably carried out while the aiticle is in a closed chambei so that v ajioi s formed during n iadiation ai e confined, do not contaminate the woi k area, and can be sciubbed from air or an inert atmospheie lemov ed tiom the closed chamber

The pi etened photoinitiatoi s aie benzophenone and anthi aquinone, although 0 benzoy l jiemxide, ethy l-phenyl ketone, aceto-phenone, n-pmpyl phenyl ketone, ISO- piopyl phenyl ketone. n-butyl pheny l ketone and iso-butyl phenyl ketone and the like can also be used

In the toiegomg examples, acetone, methylene chlonde and methanol weie used as solvents toi benzophenone So tar as is known, the identity ot the solvent is not i s iiϊφoitant. so long as it has a sufficiently high paitial piessure that it evaporates in a comparativ ely short time, and is inert to the benzophenone or other photoi tiator

Aciy lic acid is giatted to polyoletin surfaces in the pioceduies desci ibed in the toi egomg examples Equivalent amounts ot methacryhc acid, acrylamide and other aci ylic monomei s can also be used, as can, in the language ot WO 93/01622, equivalent 20 amounts ot a vinyl monomei capable ot leading with an acid oi a base to toi m a sail duectly oi mdiiectly so that the product ot the icaction can function as an ion exchange matenal

Refeience has been made heiein to sheathcoie tibei s, pai ticulai ly ones compi ismg a jiolypiopy lene coie and a jiolyethylene sheath It will be appieciated that 25 the sheath and the coie ot these tibeis can be concentnc oi eccentnc and that, in the toimer case, the sheath effectively sunounds the coie while, in the latter, a region ot the coie may be exposed along one side, and the pmportion ot exposed core will vary, depending upon the degree ot eccentncity

When UV n i adiation in the process ot the instant invention is earned out in an 30 ineit atmosphere, nitiogen. as is indicated by the foregoing examples, is satisfactory, but other gases can also be used, tor example, helium, neon, aigon, xenon and radon, hydiocarbons such as methane, hydmgen and the like There is, however, no advantage to using helium, neon, argon, xenon and ladon, so then gieater expense is not wananted oi to using hydiocaibons, hydmgen and the like, so theie is no leason to run the risk caused by then susceptibility to combustion and explosion

In anothei embodiment, the instant invention also involves toiming tibeis tiom a polyoletin and a photoinitiatoi, and then imineismg the fibers in a solution ot an acrylic or the like monomei and subjecting the fibers to UV uradiation while the acrylic acid or the like monomei solution is on their surfaces

In still another embodiment, the invention involves toiming fibers fmm a polyoletin. applying an othei wise conventional sizing composition which contains benzophenone, acetophenone oi the like photoinitiator to the tibeis. and then immeising the fibers in a solution ot an aciylic oi the like monomei and subjecting the tibeis to UV iπadiation oi to ionizing ladiation while the aciylic oi the like monomei solution is on then surfaces

In yet anothei embodiment, the invention invol es using a plasma to effect giatt polvmenzation ot an aciylic oi the like monomei with polyoletin tibeis. tor example, by lntioducing the tibeis to be giatt polymerized into an aigon oi helium plasma to form tiee ladicals on the tibei surfaces and then bunging an aciylic oi the like monomer into contact with the tiee radicals on the tibei surfaces

In a tuithei embodiment the invention involves mtmduung the polyoletin tibeis into a plasma and vaiying the gas and plasma conditions to make the tibei surfaces hydiophilic

In another embodiment, the invention involves introducing an acrylic monomei into a plasma to cause it to undergo polymei ization and intioducing polyoletin tibeis into the plasma so that then surfaces contact and adheie to the polymei In still a tuither embodiment, the invention involves ti eating a non-woven sheet ot polyoletin tibeis with a plasma to generate active sites, vaponzing an acrylic monomei oi ohgomei, feeding the vaponzed monomei oi ohgomei thiough a slot die and into contact with the non-woven sheet so that the monomei or ohgomer condenses on the surfaces ot the jiolyoletin tibeis. and exposing the monomer oi ohgomei on the polyoletin tibei surfaces to electron beam oi ultiaviolet radiation to cuie the monomer oi ohgomei on the tibei surfaces IS

Vaiious changes and modifications can be made tiom the specific details ot the invention as disclosed heiein without depaitmg tiom the spiiit and scope theieot as set foith in ihe following claims

Claims

I claim:

1 A method toi pioducing an aciylic giatt polymei on the surface ot a polyolefm aiticle said method compnsmg the steps ot immersing the polyoletin aiticle in a solution ot a photoinitiatoi in a volatile solvent, allowing the volatile solvent in the photoinitiatoi solution to vaponze. immersing the polyoletin article in a solution ot an aciylic monomei. and subjecting the polyoletin article to ultiaviolet irradiation to cause the aciylic monomei to graft to the polyoletin surface

2 A method as claimed in claim 1 in which the polyolefin aiticle is a non-woven tabnc coirφosed of polyoletin tibeis

3 A method as claimed in claim 2 in which the photoinitiator is benzophenone

4 A method as claimed in claim 3 m which the benzophenone photoinitiator is dissolved in acetone

5 A method as claimed in claim 3 m which the benzophenone photoinitiatoi is dissolved m methanol

6 A method as claimed in claim 4 in which the

lie monomei is aci vlic acid

7 A method as claimed in claim 5 in which the aciylic monomei is aciylic acid

8 A method as claimed in claim 1 in which the polyoletin aiticle. when subjected to ultiaviolet niadiation to cause the aciylic monomei to giatt to the polyoletin surface, is m an atmospheie of an

9 A method as claimed in claim 1 in which the polyoletin aiticle. when subjected to ultiaviolet niadiation to cause the aciylic monomei to giatt to the polyoletin surface, is in an ineit gas atmospheiL

10. A method for producing an acrylic graft polymer on the surface of a polyolefin article, said method comprising the steps of subjecting the polyolefin article to corona discharge, immersing the article, after corona discharge treatment, in a solution of a photoinitiator and an acrylic monomer in a volatile solvent, and subjecting the polyolefin article to ultraviolet irradiation to cause the acrylic monomer to graft to the polyolefin surface.

I 1 . A method as claimed in claim 10 in which the polyolefin article is a non- woven fabric comprising polyolefin fibers.

12. A method as claimed in claim 1 I in which the polyolefin article, after havint been immersed in the solution of a photoinitiator and an acrylic monomer, is in an inert atmosphere during ultra violet irradiation.

13. A non-woven sheet of polyolefin fibers having an acrylic graft polymer on the surfaces of the fibers of the sheet, said sheet having been produced by a method which comprises the steps of subjecting a non-woven sheet of polyolefin fibers to corona discharge, immersing the article, after corona discharge treatment, in a solution of a photoinitiator and an acrylic monomer in a volatile solvent, and subjecting the polyolefin article to ultraviolet irradiation to cause the acrylic monomer to graft to the polyolefin surface, said sheet of polyolefin fibers having an increased ammonia trapping capacity by comparison with an identical sheet produced by the same method, but without the corona dischaige treatment.

14. In a metal hydride battery comprising a plurality of plates, suitable electrical connections, an electrolyte, and a separator between adjacent ones of said plates and a case, the improvement wherein the separator is a non-woven sheet of polyolefin fibers having an acrylic graft polymer on the surfaces of the fibers of the sheet, said sheet having been produced by a method which comprises the steps of subjecting a non- woven sheet of polyolefin fibers to corona discharge, immersing the article, after corona discharge treatment, in a solution of a photoinitiator and an acrylic monomer in a volatile solvent, and subjecting the polyolefin article to ultraviolet irradiation to cause

I S the aci y lic monomei to gi att to the polyoletin tibei surf aces, said sheet ot polyoletin fibers having an lnci eased ammonia trapping capacity by comparison with an identical sheet pi oduced by the same method, but without the corona discharge treatment

s 15 A non-woven sheet ot polyoletin tibei s having opposed major surfaces wherein some aieas ot one ot the ma]or surfaces aie hydrophilic as a consequence of an acrylic gratt polymerized with the surfaces ot the fibers in those areas while the fibers in othei areas ot that majoi surface are tree ot the gratt and. as a consequence, remain hydi ophobic

10

16 A non-woven sheet as claimed in claim I 5 wherein some aieas ot both ot the ma|θi surfaces aie hydiophilic as a consequence ot an acrylic gratt polymerized with the surfaces ot the tibei s in those areas while the fibers in other aieas ot the major surfaces ai e tiee ot the giatt and. as a consequence, remain hv diophobic. and wherein the sum ot i s the aieas ot one majoi surface that aie hydi ophilic div ided by the sum ot the aieas ot that mj|oι surface that are hydrophobic is ditteient from the sum ot the areas ot the second majoi surface that aie hydi ophilic divided by the sum ot the areas ot the second major surface that are hydrophobic

20 17 A non-woven sheet ot jiolyoletin tibeis having opposed major surfaces whei cin both ot the majoi surfaces aie hydiophilic as a consequence ot an aciylic gi aft |X)lymenzed with the surfaces ot the tibeis adjacent that surface, and wherein one ot the majoi surface has a given ion exchange coefficient measuied in milliequivalents per gram, while the othei majoi surface has an ion exchange coefficient measured in

25 milliequivalents pei gram, that is at least 10 percent different

18 A method as claimed in claim I w heiein, after the volatile solvent in the photoinitiatoi solution vaponzes, a web ot the polyoletin aiticle is advanced through a solution ot an acrylic monomei , and thiough a legion where it is subjected to ultiaviolet 30 lπ adiation to cause the aciylic monomei to gratt to the polyoletin surface, and sheets ol a polyoletin which aie wider than the web are introduced above and below the web and the adjacent edges ot the polyoletin sheets are sealed to one another to form a tube which surrounds the web, and it is the web surrounded by the tube which is advanced through the region where the web is subjected to ultraviolet irradiation.

19. A method as claimed in claim 18 wherein the polyolefm sheets which are intioduced above and below the web are polyethy lene sheets.