NZ199582A

NZ199582A - Producing porous material;battery separators and filter material

Info

Publication number: NZ199582A
Application number: NZ199582A
Authority: NZ
Inventors: H L Stoehr
Original assignee: Grace Gmbh
Priority date: 1981-01-28
Filing date: 1982-01-27
Publication date: 1986-01-24
Also published as: DE3102735A1; DE3102735C2; AU7984982A; AU552123B2; ATE14171T1; EP0057841A3; BR8200457A; CA1179459A; JPS57182964A; EP0057841B1; EP0057841A2; ZA82379B

Abstract

1. Process for the production of porous bodies containing no binder in the pores with air resistant values, variable within wide limits, as a measure for the pore size from coarse-pored substrates obtained by any production process and fillers, characterized in that the substrate is filled with a binder-free dispersion of a micronized agglomeratable filler having a particle size of not more than 5x10**-3 mm and subsequently the dispersion medium is removed.

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number 1 99582 1 995 8 Priority Date(s): JBJ. Complete Specification Filed: pU. . Cass: P.O/i .. ii.OJ, 3 /3fi LQ^/J^y.. £)£ tfJjjth... Publication Date: .. .'Z .4 JAN J98fi P.O. Journal, No: . "PROCESS FOR PRODUCING POROUS MATERIALS' AND THE USE THEREOF" I ,VJE GRACE GMBH, a German company, of Erlengang 31, 2000 Norderstedt, Federal Republic of Germany, hereby declare the invention, for which-T/we pray that a patent may be granted to ge/us, ,and the method by which it is to be performed, to be particularly described in and by the following statement:- NO DRAWINGS Patents Form No.5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION 199S The invention relates to a process for producing porous materials with air resistance values which are variable within wide limits and which serve as a measure of the pore size of the porous material. More specifically it relates to porous materials having a reduced air permeability achieved by agglomerating inorganic fillers in a coarse-pored structure of preshaped dimensions. The porous materials produced according to the process of this invention are suitable inter alia particularly as battery separators and filter mats or felts of different types. It is known in the art to apply fillers or powders having a small particle size to the surface of porous substrates and to fix them to the substrate by means of bonding agents, condensible resins or sintering to obtain a layer having a smaller pore size, which is partially anchored in the substrate layer. As a result, the material is obtained having a smaller pore size than is possible with the substrate production process. The disadvantage of this process is that in the case of high filler loadings, or when using sintering, the adhesion of the filler to itself or to the substrate is incomplete, so that it can only undergo limited.mechanical loading and is manifested as apparent sensitivity to vibration and/or abrasion. However, when high proportions of bonding agents are used there is a risk of obtaining areas that are completely dense, due to excessive local concentrations, and prejudicial to the intended purpose. It is also known to mix fillers with condensible resins and to fill an existing coarse-pored substrate with the mixture. On condensing the resin, the filler is anchored to the substrate due to the resin layer connecting them. The disadvantages of this process are (1) the limited capacity of commercial resins for fillers due to the viscosity increases occurring with higher filler concentrations, (2) the partial blocking of the surface of the fillers by resin films and (3) the change undergone by the substrate by the introduction of a condensible resin. Thus, for example, it is only possible under difficult conditions to combine a low-melting polymer substrate with a resin WB -2- 199582 which can only be condensed at a satisfactory speed at elevated temperatures, without the low-melting polymer losing its shape. This invention is directed at a process for producing a porous material with air resistance values, variable within wide limits, and which serve as a measure of the pore size of the type defined in the claims. According to the invention, there is provided a process for producing porous materials with air resistance values, variable within wide limits, as a measure for the pore size, but containing no binder in pores thereof, characterised in that a coarse-pored substrate obtained by random production process is filled with a dispersion of a micronized agglomera-table non-fibrous filler dispersed in a liquid medium and subsequently the liquid medium is removed causing the filler to agglomerate. A substrate with a pore size of more than 10 mm preferably is used. The micronized fillers used may have a particle size of 10 ® to 10 ^ mm. The substrate, referred to a substrate thickness of 2 0.1 mm, may be loaded with 0.1 to 100 g/m , preferably with 2 1 to 60 g/m of filler. The substrate may be loaded with a quantity of filler such that the air resistance value of the substrate increases by a factor of 1 to 1000, preferably of 1 to 600 and most preferably of 1 to 200. The invention also provides for the use of manufactured porous material, obtained by the process of the invention, as battery separator for alkaline or acid electrolytes. In one form, such use as a battery separator for acid electrolytes is characterized in that the substrate is a cellulose fibre tangled fleece impregnated with phenolic resin, the substrate is 2 loaded with 1 to 200 g/m and the substrate loaded with filler has air resistance values of 10 to 2000 seconds. In another form, such use as a battery separator for acid electrolytes is characterized in that the substrate is a sintered polyvinyl 2 chloride material, the substrate is loaded with 1 to 200 g/m and the substrate loaded with filler has air resistance vaL^i^^J^, 'j ' of 10 to 2000 seconds. In a further form, such use as a o battery separator for acid electrolytes is characterized ;ian o -H BL - 3 - tn .>°/ \.V- 199582 that the substrate consists of synthetic fibres or of mixtures of natural and synthetic fibres, the substrate is loaded with 2 1 to 500 g/m and the substrate loaded with filler has air resistance values of 10 to 5000 seconds. Air resistance values in the sense of this application are the times, determined by means of suitable measuring instruments, necessary for forcing a given quantity of air under a predetermined pressure through a testpiece of a specified area. The smaller the pores in the testpiece, the longer the time required for passing the given quantity of air. The air resistance values given in the description and claims relate to an air quantity of 300 ml, at a pressure of 124.2 mm of water and employing a surface area of 6.45cma. A type 4110 Gurley densimeter was used in which the indicated air quantities are forced through the testpiece by means of an inner cylinder weighing 567 grams moved through an outer cylinder. In the process of this invention a given substrate, whose shape and pore structure are fixed by some other method, is treated with a dispersion of micronized fillers in a liquid phase in such a way that the filler is introduced into the coarse-pored structure and during the subsequent removal of the liquid phase is agglomerated in the pores, so that the coarse-pored structure of the substrate holds back the agglomerated filler in a plurality of "cages". This leads to a substantially mechanical retention of the filler so that there is generally no need for a separate chemically bonding agent. The substrates to be treated by the process of this invention can be of various types and have very different pore shapes and sizes by virtue of the fact that the filler agglomerate being formed adapts to the substrate pore shape. The examples of substrates which can be used are, for example, cellulose fibre tangled fleeces, fleeces of synthetic fibres, mineral fibres or mixtures of said fibr^gg=^. sintered shaped articles of metal, plastic, glass or otlSerli ° kb 3 H- - i 20 19 MAR 1985 199582 materials, porous materials obtained by fleece formation, sintering or extraction processes, etc. It is obvious that this list of examples is only representative and not complete. The lower pore size limit results from the minimum size of the filler particles present in the dispersion and this is in the range of approximately 10~6 to 10~5 mm in the case of silicia based fillers. However, due to rising costs in the production of the dispersion and reduced efficiency regarding the loading of the substrates (grams of filler/m2 of substrate) there is minimum practical limit of approxi- _3 mately 10 mm for the pore size of the substrate. Suitable fillers for the process according to this invention are all substances dispersible in liquid mediums and which agglomerate on removing the liquid medium while being compatible with the intended use of the end product. It is mainly a question of using inorganic fillers such as calcium carbonate, kaolins, silicon dioxide, talc, diatoma-ceous earth, etc. Depending on the type of filler, the secondary particles present in the filler as received are broken up by means of stirrers of different types. In particular, it is possible to use high speed, high efficiency stirrers with very high shear forces, turbine stirrers, oirurbine homogenisers, etc., with the Ultraturrax apparatus eing used in the tests described hereinafter. In this ,<>// apparatus, the particles are micronized by the shear forces •t occurring between the fixed stator and a rotor, rotating at high speed. Many fillers are supplied in dispersed form and addi- 30 tional mechanical treatment is unnecessary because the particles are already in the micronized form making it possible to directly use the dispersions. As stated hereinbefore, the minimum size for the filler particles present in the dispersion is between — 6 "5 approximately 10 and 10 mm. In the case of commercially obtainable dispersions of e.g. silicic acid obtained by flame hydrolysis or precipitated silicic acid, the particle -5 -4 size range is 10 to 10 mm. Filler dispersions with 39 particle sizes in this range are very well suited to the WB 199582 process of the invention. In general terms, it is pointed out that fillers with a particle size of approximately 10~"* ;mm are suitable, but that the size should not extend much -3 ;over 5 x 10 mm. ;The fillers used according to the invention with the indicated small particle size (primary particles) have the capacity to agglomerate to larger aggregates. The agglome- ;-5 ;rates (secondary particles) can have a size of 5 x 10 to approximately 10 ^mm. The agglomerate size of the preferred ;-4 -2 ;fillers used is in the range of 5 x 10 to 10 mm. These agglomerate size values are those given by the manufacturers and can vary from the agglomerate sizes actually found in the porous materials produced according to the invention, because in practice it is not possible to determine the agglomerate size in the porous materials according to the invention. ;The fillers are mixed at preferably 1 to 40% weight (weight weight) concentrations, depending on the filler type with the dispersing agent, which for cost reasons is generally water, followed by batchwise or continous dispersion . . v. for a particular time determined by tests. The substrates •°,"^are then filled by known processes, e.g. filtration pro- . rAesses, sponging rollers, dipping processes, washing on, MAR 1985 spraying on, applying to the surface of the dispersion, ;i, o ""/''etc. As a function of the nature of the process used, the ~• filler, its particle size and the pore size and wettability of the substrate, the dispersion penetrates the pores at a higher or lower speed. However, the penetration must ensure that the air in the pores can escape. ;The dispersing agent can be removed by various prior art processes. In particular, it is possible to use e.g. drying processes by supplying heat, by evaporation in moving gas streams, by evaporation in vacuo, etc. The temperatures, vacuums, gas speeds, etc. which are used are dependent on the dispersing agent, the filler, and the coarse-pored substrates. ;Substrates filled in this way are suitable as battery separators, particularly lead - acid accumulators, as well as for other uses. The conventionally used cellulose ;WB ;b ;199582 ;or sintered PVC separators or more modern separators made from tangled fleeces produced from synthetic fibres constitute the presently acceptable compromise of operating efficiency (cold starting behaviour), service life and costs. As a result of the pore sizes of approximately ;-3 -2 ;5 x 10 to 5 x 10 nun present in such separators, the life is limited by dendrite growths (short-circuits). To guarantee an acceptable life, the separators must have a certain, undesired thickness. The* separators produced according to the invention lead to an improvement in the life for the same substrate thickness or the same life with reduced substrate thickness or a random combination of both values. The preferred absolute loading and air resistance values can be gathered from the claims directed at the use of the porous materials produced according to the invention as battery separators. Example 1 32g of precipitated silicic acid (FK 320 DS, DEGUSSA, primary particle size approx. 18mm) and 368g of water are treated for 60 seconds with an Ultraturrax apparatus and poured into a flat dish. A previously cut approximately 0.6mm thick substrate of a cellulose fibre fleece impregnated with phenolic resin and cured out is placed on the surface of the dispersion. Thorough wetting takes place within a few seconds. The thus prepared sheet is allowed to drip and is then dried for 15 minutes at 110°C. Any silicic acid particles on the surface can be brushed off. The weight increase obtained was 14g/m2. The air resistance value rose from 15 seconds for the substrate to approximately 170 seconds for the filled sheets (measurement with a type 4110 Gurley apparatus, 300ml air throughput, 567g applied weight, = 124.2mm water column, 6.45cm2 measuring surface. By using solutions with a higher or lower concentration, other dispersing processes and/or conditions, etc. any desired air permeability values can be obtained, so that the filtering action of the substrate obtained can be adapted to the intended use. To check the suitability of the thus obtained WB 7 .';,l-':V;~Z '5';'.'iit-.: i'r"'r-V.-'if'■ /; 10 20 9AJ&v;. H£>- - 30 40 199582 substrate for use in lead - acid batteries both the untreated substrate and the filled substrate were incorporated into lead - calcium elements Cfour positive and five negative plates, with a 1.0mm plate spacing) and subjected to the service life -test of DIN 43 539. The elements separated with unfilled substrates did suffer from a definite capacity loss after 94 cycles and no longer met standard after 117 cycles. However, the elements with the filled substrates only failed after 141 cycles. Evaluation of the substrates after the test revealed that the unfilled substrates, despite the smaller number of cycles, had a larger number and more severe short-circuits through the substrate, whereas the filled substrates prevented short-circuits due to the smaller pore sizes. Unfilled Filled substrate substrate Cold starting values after 94 cycles Cold starting values after 117 cycles Cold starting values after 141 cycles EXAMPLE 2 1.33V/72 sec. failed failed 1.48V/106 sec 1.4 0V/74 sec. failed 45 g precipitated silicic acid (FK 320 DSl and 255 g of water were treated as in example 1 and used for filling an identical substrate to that of example 1. The weight 2 increase here was 35g/m . The air resistance values of the substrate rose from 11 seconds to approximately 150 seconds. The thus obtained separators were incorporated into lead - acid battery element groups in order to determine their service life. Unlike in example 1, a grid alloy containing 3.5% antimony was used in order to determine the varying nature of the material adhesion and the structure of the deposited material. The elements were comprised of four positive plates and five negative plates, welded with a 1.0mm plate spacing and subjected to a cycle test according to DIN 4 3 539. The results again show a clear performance advantage KL -X 8 199582 in the case of elements with a filled substrate. Cold starting values after 118 cycles Cold starting values after 141 cycles Cold starting values after 153 cycles Unfilled substrate Filled substrate 1.43V/131 sec. 1.45V/128 sec 1.29V/69 sec. 1.39V/101 sec failed 1.36V/81 sec. test broken off. Assessment of the separators after the test revealed moderate to serious short-circuits with the unfilled substrates and no short-circuits with the filled substrates. Example 3 A 15% by weight suspension of precipitated silicic acid (FK 320 DS) in water was treated for 30 seconds with an Ultraturrax apparatus and then further used as given in example 1. The weight increase was 65g/m2, the air resistance value rising from 4 seconds on the untreated substrate to 220 seconds for the filled substrate. Example 4 A 5% by weight suspension of precipitated silicic acid (FK 320 DS) was prepared in the manner described in example 1. A sheet of an approximately 0.4mm thick sintered polyvinylchloride material was fillied with it. The weight increase was 7g/m2 and the air resistance value rose from 20 to 100 seconds. The thus produced porous material was suitable as a battery separator for acid electrolytes. Example 5 A 35% by weight dispersion of silicic acid (Aerosil K342, DEGUSSA, primary particle size approx. 30nm) was used in the form supplied for filling an approximately 0.5mm thick substrate constituted by a mixture of synthetic polymer fibres (45% polyethylene, 10% polyester) and glass fibres (36%). The dispersion was not mechanically prepared and the other conditions were as in example 1. The weight increase was 270g/m2, the air resistance WB </div>

Claims

<div class="application article clearfix printTableText" id="claims"> fc. 199582 value rising from 5 seconds to approximately 2700 seconds. The porous material produced was suitable as a battery separator for acid electrolytes. EXAMPLE 6 A 20% .by weight dispersion of precipitated silicic acid (VN-2, DEGUSSA, primary particle size approximately 28nm) was treated for 10 minutes with an Ultraturrax apparatus A substrate of the type indicated in example 5 was filled . 2 with this dispersion. The weight increase was 130g/m and 10 the air resistance value rose from 5 to 410 seconds. The porous material produced was suitable as a battery separator for acid electrolytes. 20 mssz WHAT WE CLAIM IS: 1. A process for producing porous materials with air resistance values, .as a measure for the pore size, but containing no binder in pores thereof, characterised in that a coarse-pored substrate is filled with a dispersion of a micronized agglomeratable non-fibrous filler dispersed in a liquid medium and subsequently the liquid medium is removed causing the filler to agglomerate. 10
2. A process as in claim 1, characterized in that a substrate with a pore size of more than 10~5 mm is used.
3. A process as in claim 1 or claim 2, characterized in that fillers which are dispersible in water are used.
4. A process as in any one of claims 1 to 3, characterized in that calcium carbonate, kaolins, silicon dioxide, talc and/or diatomaceous earth are used as fillers.
5. A process as in any one of claims 1 to 4, characterized in that micronized fillers with a particle size of 10~ to 10 mm are used. 20
6. A process as in any one of claims 1 to 5, characterized in that the micronized filler is introduced into the substrate by dipping, sponging on, filtration, washing on or spraying on.
7. A process as in any one of claims 1 to 6, wherein 0.1 2 to 100 g/m of filler is incorporated into said substrate per 0.1 mm of substrate thickness.
8. A process as in claim 7, wherein said substrate is 2 loaded with 1 to 60 g/m of filler.
9. A process as in any one of claims 1 to 8, characterized in that the substrate is loaded with a quantity of filler such 30 that the air resistance value of the substrate increases by a factor of 1 to 1000.
10. A process as in claim 9, wherein the quantity of filler is such that the air resistance value increases by a factor of 1 to 200.
11. Use of manufactured porous material, obtained by the process according to any one of claims 1 to 10, as a battery separator for alkaline or acid electrolytes.
12. Use according to claim 11 as a battery separator for 39 acid electrolytes, characterized in that the substrate is a BL 11 199592 cellulose fibre tangled fleece impregnated with phenolic resin, 2 the substrate is loaded with 1 to 200 g/m of filler per 0.1 mm of substrate thickness and the substrate loaded with filler has an air resistance value of from 10 to 2000 seconds.
13. Use according to claim 11 as a battery separator for acid electrolytes, characterized in that the substrate is a sintered polyvinyl chloride material, the substrate is loaded 2 with 1 to 200 g/m of filler per 0.1 mm of substrate thickness and the substrate loaded with filler has an air resistance value of from 10 to 2000 seconds.
14. Use according to claim 11 as a battery separator for acid electrolytes, characterized in that the substrate consists of synthetic fibres or of mixtures of natural and synthetic 2 fibres, the substrate is loaded with 1 to 500 g/m of filler per 0.1 mm of substrate thickness and the substrate loaded with filler has an air resistance value of from 10 to 5000 seconds.
15. Use of the porous material manufactured by the process according to any one of claims 1 to 10 as a filter mat or felt.
16. A process for producing porous materials substantially as specifically described herein in any one of the examples.
17. Use of manufactured porous material substantially as specifically described herein in any one of the examples.
18. Manufactured porous material substantially as specifically described herein in any one of the examples. 'attorneys SON & CAREY BL 12 </div>