Patent Application: US-43628503-A

Abstract:
a method for producing a separator material for rechargeable alkaline batteries . the method includes providing a base material , forming a polymer having a molecular structure that includes at least one functional group having a titrimetrically determined binding property for ammonia of at least 0 . 3 mmole nh 3 / g polymer powder . the method further includes introducing the polymer in particle form to the base material in a quantity of 1 to 50 g / m 2 . in addition , a separator material that includes a base material and a polymer disposed on the base material in particle form . the polymer includes a molecular structure that includes at least one functional group having a titrimetrically determined binding property for ammonia of at least 0 . 3 mmole nh 3 / g polymer powder .

Description:
referring to fig1 a method for producing a separator material for rechargeable alkaline batteries is illustrated , in which a base material is provided in step 1 . the base material may be , for example a non - woven fabric , a microporous sheeting , or a woven polymer fabric ( i . e . a woven fabric of one or more polymers ). in step 2 , a polymer is formed having molecules that include at least one functional group having a titrimetrically determined binding property for ammonia of at least 0 . 3 mmole nh 3 / g polymer powder . the polymer may be formed , for example , by copolymerization or grafting by reactive extrusion . in step 3 , the polymer is introduced in particle form to the base material , either by being applied onto the base material or by being introduced into the base material . specific embodiments of the present invention are described in more detail below on the basis of several examples . the base material is a precalendered , smooth polyolefin wet non - woven fabric having a mass per unit area of 50 g / m 2 and a thickness of 150 μm . to this , one applied a powder of a copolymer between polyethylene and polyacrylic acid having particle sizes & lt ; 250 μm in quantities of 10 g / m 2 . the material was sintered thereto at 130 ° c . using a calender , at a line pressure of 10 n / mm . the thickness of the resultant separator material amounted to 250 μm , a clear “ two - sidedness ” being apparent between the partially melted polymer “ membrane ” and the non - woven fabric side . nevertheless , the material still exhibited a good porosity . the measured binding property for ammonia amounted to 0 . 15 mmole nh 3 per g separator material . as a base material , a precalendered , smooth polyolefin wet non - woven fabric having a mass per unit area of 50 g / m 2 is used . to this , one applied a powder made up of a copolymer between polyethylene and polyacrylic acid having particle sizes of 250 μm & lt ;×& lt ; 500 μm in quantities of 10 g / m2 . the material was sintered thereto at 130 ° c . using a calender at a line pressure of 10 n / mm . the thickness of the resultant separator material amounted to 300 μm , a clear “ two - sidedness ” once again being apparent . this material was also porous . the measured binding property for ammonia amounted to 0 . 13 mmole nh 3 per g separator material . as a base material , a precalendered , smooth polyolefin wet non - woven fabric having a mass per unit area of 50 g / m 2 is used . to this , one applied a powder made up of a copolymer between polypropylene and polyacrylic acid having particle sizes & lt ; 250 μm in quantities of 10 g / m 2 . the material was sintered thereto at 130 ° c . using a calender , at a line pressure of 10 n / mm . the thickness of the separator material formed amounted to 350 μm , the particles of the polymer still being clearly perceptible . the measured binding property for ammonia amounted to 0 . 13 mmole nh 3 per g separator material . the existing binding property for ammonia reveals that the functionality of the polymer in this case is not masked by the melted components of the binding fibers . as a base material , a precalendered , smooth polyolefin wet non - woven fabric having a mass per unit area of 50 g / m 2 was used . a dispersion of a copolymer was applied thereto , between polypropylene and polyacrylic acid ( particle sizes & lt ; 1 μm ) in quantities of 5 g / m 2 . the task was carried out using a squeezing apparatus at ambient temperature . in this case , there was no thermal post - bonding . this type of application did not alter the thickness of the separator material , which still amounted to 150 μm . the typical “ non - woven fabric ” character was retained . the measured binding property for ammonia amounted to 0 . 11 mmole nh 3 per g separator material . in addition , the attempt was made to remove the particles , which were deposited in this manner , from the surface using compressed air . for this , a finished non - woven fabric was treated for 10 s with compressed air having a pressure of 0 . 4 mpa . this non - woven fabric &# 39 ; s binding property for ammonia still amounted to 0 . 09 mmole nh 3 per g separator . therefore , the assumption may be made that , following this treatment , the major share of the particles is still present on the non - woven fabric surface as a base material , a precalendered , smooth polyolefin wet non - woven fabric having a mass per unit area of 50 g / m 2 was used , to which a thin layer of an epoxide binder ( mass per unit area of 0 . 5 g / m 2 ) was applied . to this , one subsequently applied a powder of a copolymer between polyethylene and polyacrylic acid having particle sizes & lt ; 250 μm in quantities of 10 g / m 2 . the separator material was subsequently calendered at t = 50 ° c . and at a line pressure of 80 n / mm between two teflon rollers , to a thickness of 200 μm . the measured binding property for ammonia amounted to 0 . 14 mmole nh 3 per g separator material . as a base material , an uncalendered , relatively open polyolefin wet non - woven fabric having a mass per unit area of 40 g / m 2 and a thickness of 400 μm is used . to this , one applied a powder of a copolymer between polyethylene and polyacrylic acid having particle sizes & lt ; 250 μm in quantities of 10 g / m 2 . in this case , due to the open character , the powder was able to attain the interior of the non - woven fabric . the material was sintered thereto at 140 ° c . using a calender , at a line pressure of 10 n / mm , and the non - woven fabric was bonded . the thickness of the separator material formed amounted to 200 μm . in this case , there was no two - sidedness . the material formed had good porosity . the measured binding property for ammonia amounted to 0 . 18 mmole nh 3 per g separator material . as a base material , an uncalendered , relatively open polyphenylene sulphide ( pps ) wet non - woven fabric having a mass per unit area of 50 g / m 2 and a thickness of 380 μm is used . pps has a melting point of & gt ;& gt ; 200 ° c . to this , one applied a powder of a copolymer between polypropylene and polyacrylic acid having particle sizes & lt ; 250 μm in quantities of 10 g / m 2 . as described in example 6 , due to the open character , the powder was able to attain the interior of the non - woven fabric . the material was sintered thereto at 140 ° c . using a calender , at a line pressure of 10 n / mm , and the non - woven fabric was bonded . the thickness of the separator material formed amounted to 210 μm . in this case as well , there was no two - sidedness . the material formed had good porosity . the measured binding property for ammonia likewise amounted to 0 . 15 mmole nh 3 per g separator material . here , a powder of the copolymer between polyethylene and polyacrylic acid having particle sizes 250 μm & lt ;×& lt ; 500 μm was suspended together with the fibers , and the wet non - woven fabric was laid . the open product formed , having a mass per unit area of 50 g / m 2 ( 40 g / m 2 fibers ; 10 g / m 2 powder ) was subsequently sintered at 140 ° c . and calendered ( line pressure of 10 n / mm ). in this case , the depth distribution of the polymer was homogeneous . the material formed had good porosity . the measured binding property for ammonia amounted to 0 . 18 mmole nh 3 per g separator material . as a base material , an uncalendered , relatively open polyolefin dry non - woven fabric having a mass per unit area of 50 g / m 2 and a thickness of 450 μm was used . to this , one applied a powder of a copolymer between polyethylene and polyacrylic acid having particle sizes & lt ; 250 μm in quantities of 10 g / m 2 . as described in example 5 , in this case , due to the open character , the powder was able to attain the interior of the non - woven fabric . the material was sintered thereto at 140 ° c . using a calender , at a line pressure of 10 n / mm , and the non - woven fabric was bonded . the thickness of the separator material formed amounted to 220 μm . in this case as well , there was no two - sidedness . the material formed had good porosity . the measured binding property for ammonia likewise amounted to 0 . 15 mmole nh 3 per g separator material . for this example , the same wet non - woven base material was used as in examples 1 - 4 ( weight of 60 g / m 2 ). the ascertained binding property for ammonia (“ blank value ”) amounted to less than 0 . 009 mmole nh 3 per g separator material . the same wet non - woven base material was used as in examples 1 - 4 ( weight of 60 g / m 2 ). as polymer powder , one used copolymer pe and maleic anhydride having a binding property for ammonia of & lt ; 0 . 01 mmole nh 3 per g polymer powder or copolymer pe and polyacrylic acid ( different manufacturer ) having a binding property for ammonia of & lt ; 0 . 01 mmole nh 3 per g polymer powder . the ascertained binding property for ammonia amounted to less than 0 . 009 mmole nh 3 per g separator material . in accordance with the present invention , polymers are employed in particle sizes of & lt ; 250 μm , where the ascertained binding property for ammonia amounts to 0 . 52 or 0 . 55 mmole nh 3 per g polymer powder . it should be noted in this connection that , due to the application on a wet non - woven fabric , the observed binding property for ammonia lies above the theoretical value . thus , for example , a base non - woven fabric having a mass per unit area of 50 g / m 2 , which is finished with 10 g / m 2 of a polymer having a binding property of 0 . 52 mmole / g , should theoretically have a binding property of 0 . 087 mmole / g . the value of 0 . 15 mmole / g ascertained in example 1 lies clearly above the theoretically expected value of 0 . 095 mmole / g . moreover , the influence of the polymer particle size is much less than expected ( compare examples 1 and 2 ). the separators in accordance with example 1 and example 8 were each installed in 22 nickel / metal hydride cells of the aa type . a set of 11 cells each was fully charged and stored for a specific period of time at a defined temperature . following this storage period , the residual charge remaining and , thus , the self - discharge were determined . as a comparison , one measured cells finished with fluorinated separator material which did not have any absorption capacity for ammonia . moreover , one observed the self - discharging of cells having separator material , which had a high absorption capacity for ammonia ( materials treated by uv - induced grafting with acrylic acid or sulfonation ). it turns out that , at ambient temperature , the self - discharging is equally slight for all cells . however , at higher temperatures , cells having ammonia - binding separator material exhibit a distinctly lower self - discharging . a high self - discharging is especially useful for batteries used in notebooks , for example , or for starter batteries used in motor vehicles . wet non - woven fabric wet non - woven fluorinated finished with fabric finished wet non - powder with powder wet non - woven sulfonated woven ( according to ( according to fabric grafted with wet non - fabric example 1 ) example 8 ) acrylic acid woven fabric absorption 0 0 . 15 0 . 18 0 . 25 0 . 3 capacity for ammonia ( mmole / g ) self - 25 24 24 25 24 discharging 28 days at 20 ° c . self - 33 25 24 24 22 discharging 7 days at 45 ° c . self - 65 33 32 32 33 discharging 3 days at 60 ° c . 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