CA1303788C

CA1303788C - Process for the production of a sinterable finely divided molding compound with a polyvinyl chloride base and its use

Info

Publication number: CA1303788C
Application number: CA000553509A
Authority: CA
Inventors: Heimo Bieringer; Klaus Engel
Original assignee: Huels AG
Current assignee: Huels AG
Priority date: 1986-12-06
Filing date: 1987-12-04
Publication date: 1992-06-16
Anticipated expiration: 2009-06-16
Also published as: JPS63154709A; US4828946A; NO875074D0; DE3761980D1; NO875074L; NO168045B; DE3641815A1; EP0273112A1; NO168045C; EP0273112B1; ATE51236T1

Abstract

ABSTRACT OF THE DISCLOSURE
Sinterable finely divided polyvinyl chloride powder is produced by suspension polymerization of vinyl chloride. The polymerization is carried out at 40 to 80°C using an oil-soluble radical initiator in the presence of 0.5 to 1% by weight (based on the monomer) of a suspension stabilizer. The suspension stabil-izer is a mixture of a sulfated carbohydrate ester and a cellulose ether. The sulfated carbohydrate ester has the carbohydrate ester moiety of the formula:
(wherein n is 0 to 99 and R is an aliphatic polyol esterified with a long chain aliphatic carboxylic acid) and is 10 to 95% sulfated.
The cellulose ether is methylcellulose, methylhydroxyethylcellu-lose, methylhydroxypropylcellulose, hydroxyethylcellulose or hydroxypropylcellulose.

Description

13 03 7a 8 23443-355 Process for the production of a sinterable finely divided molding compound with a polyvinyl chloride base and its use The invention relates to a process for the production of finely divided polyvinyl chloride by homopolymerization of vinyl chloride in aqueous suspension, and its use for the production of sintered molded articles.
It is known to use molding compounds basedon polyvinyl chloride for the production of sintered molded articles, for example, of separator plates for electric cells.
A process is described in DE-C3-23 10 431 in which for the production of the suspension polymer a free emulsifier acid is used, besides usual suspension stabilizers and nonionic surfac-tants. From these polymers sintered plates with good wettability and good mechanical properties can indeed be producedbuttheir electrical resistance is comparatively high.
In DE-A-33 34 667 a process is described, in which after vinyl chloride polymerization, before drying of the finely divided polymer, at least one nonionic surfactant and one nonsurfactant acid are added. Even with polymers of this type, it is not pos-sible to produce sintered plates with good mechanical propertiesand a slight electrical resistance.
In the course of optimizing the performance character-istics of electric cells, especially of batteries for use in motor vehicles, it was found that the cold starting performance of a batttery can be considerably improved by a reduced electrical 3~

1303'788 resistance. It is thus desirable to produce sintered plates, which exhibit as small electrical resistance at possible. It i5 also desired that sintered plates with given plate thickness and strength exhibit a high porosity. A high porosity of the sintered plate means higher acid storage volumes and reduction of the battery volume.
It has now been found that sintered plates with slight electrical resistance and high porosity can be produced by using a finely divided polyvinyl chloride which is produced by suspension polymerization of vinyl chloride at 40 to 80DC in the presence of at least one oil-soluble radical polymerization initiator option-ally together with a molecular weight modifier as well as a parti-cular suspension stabilizer. The suspension stabilizer is in an amount of 0.5 to 1% by weight (based on the vinyl chloride) and is a mixture consisting of:
a) 10 to 90% by weight (based on the suspension stabilizer mixture) of a sulfated carbohydrate ester, which has a carbohy-drate ester moiety of the following formula ~\ _ ~ _ 0~ _ OH _nR

~ 3443-355 (in which n is an integer of from 0 to 99 and R is an aliphatic linear or branched polyol with 2 to 6 hydroxyl groups and 2 to 12 carbon atoms, esterified wi~h a saturated or unsaturated linear or branched aliphatic carboxylic acid with 6 to 24 carbon atoms) and which is 10 to 95% sulfated, and b) 90 to 10% by weight (based on the suspension stabilizer mixture) of a cellulose ether selected from the group consisting of methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, hydroxyethylcellulose and hydroxy propylcellulose, said cellulose ether in 2% by weight aqueous solution at 20C exhibiting a viscosity of 15 to 500- 10 3 Pa s.
Another aspect of the invention provides a method of producing a sintered molded article, which comprises: molding the polyvinyl chloride produced by the process into a molded article, and, sintering the molded article under sintering conditions.
In a preferred embodiment of the process, component b) consists of 90 to 10% by weight of methylcellulose, methylhydroxy-ethylcellulose or methylhydroxypropylcellulose, each with a molar degree of substitution of methyl group of 1.4 to 2.4 and a molar degree of substitution of the optionally present hydroxyalkyl group of 0.08 to 0.28; or hydroxyethylcellulose or hydroxypropyl-cellulose with a molar degree of substitution of 1 to 3.5, which in the 2~ by weight a~ueous solution at 20C exhibits a viscosity of 15 to 500- 10 3 Pa s.

; . T~ ~ .

Preferably component a) is used in amounts of 20 to 80%
by weight, in relatlon to the suspension agent mixture. A
particularly favourable combination of properties of the polyvinyl chloride resin is obtained with the suspension stabilizer mix-- 3a -'~' t ~

i303788 tures, which contain as component b) a methylhydroxypropylcell-ulose with a viscosity of 50 to 100 mPa s and which contain 20 to 80 and especially 70 to 30% by weight of component b).
In a preferred embodiment of the process the degree of sulfation of the carbohydrate ester is 20 to 90%.
The degree of esterification of the carbohydrate ester is suitably 10 to 95%, especially 20 to 90%.
The sulfated carbohydrate ester to be used as component a) can be obtained, for example, by sulfation of a carbohydrate ester produced according to DE-OS 24 23 278. A general descrip-tion of the sulfation is found in E.E. Gilbert, Sulfonation and Related Reactions, page 336, Interscier.ce Publishers, New York-London-Sydney (1965).
The carbohydrate serving as the basis of the carbohy-drate ester is built up from aglycone and carbohydrate radical.
The carbohydrate radical contains 1 to 100, preferably 1 to 50, especially 1 to 15, anhydroglycose units, which are linked to one another through alpha- or beta-glucoside bonds. The carbohydrate radical can have a homogeneous molecular structure, but preferably it is a mixture of carbohydrates with a different number of anhydroglycose units.
The aglycone R-OH is an aliphatic linear or branched polyol with 2 to 6 hydroxyl groups and 2 to 12 carbon atoms. The following are suitable, for example:
ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerin, trimethylpropane, erythritol, pentaerythritol, penti-tols, as, e.g., arabitol and xylitol, hexitols as, e.g., sorbitol, mannitol and dulcitol.
The carbohydrate, made up of aglycone and anhydroglycose units, can be esterified with saturated or unsaturated, linear or branched aliphatic carboxylic acids or carboxylic acid mixtures, which contain 6 to 24 carbon atoms.
As such carboxylic acids there can be used, for example:
caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lingnoceric acid, palmitoleic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, ricinoleic acid or mixtures corresponding to their natural triglycerides, as, e.g., colza oil fatty acid, tall oil fatty acid, coconut oil fatty acid, soybean oil fatty acid, castor oil fatty acid, palm nut oil fatty acid, palm oil fatty acid, peanut oil fatty acid, cottonseed oil fatty acid, sunflower oil fatty acid, linseed oil fatty acid, tallow fatty acid and fish oil fatty acid.
The molar amount of fatty acids present in the carbo-hydrate ester is at least 1 mol, in relation to the carbohydrate, preferably 0.5 to 2 mol per anhydroglycose unit, and is limited upward by the total number of OH groups available in aglycone and anhydroglycose units, i.e., in the total carbohydrate.
The sulfation reaction of the carbohydrate ester is performed so that degrees of sulfation of 10 to 95~, preferably 20 to 90~, result. The extent of the sulfation can be controlled by the choice of the reaction temperature, reaction period and the molar ratio of, e.g., chlorosulfonic acid to carbohydrate ester.
The degree of sulfation reacted can be determined ~303788 according to a method of analysis described in K. Lindner, Tenside--TextiLhilfsmittel--Waschrohstoffe [Surfactants-Textile Auxiliaries--Detergent Base Materials], Vol. III, 3058, Wissen-schaftliche Verlagsgesellschaft mbH, (1971).
The polymerization of the vinyl chloride in aqueous suspension is usually performed in the presence of 0.001 to 3% by weight (which is well known in the art), preferably 0.01 to 0.3 by weight, in relation to the vinyl chloride monomer, of the radical initiator (which is well known in the art), such as, e.~., diaryl, diacyl peroxides, such as diacetyl, acetyl benzene, dilauroyl, dibenzoyl, bis-2,4-dichlorobenzoyl, bis-2-methyl benzoyl peroxide; dialkyl peroxides, such as di-tert-butyl peroxide; peresters, such as tert-butyl percarbonate, tert-butyl peracetate, tert-butyl peroctoate, tert-butyl perpivalate dialkylperoxide carbonates, such as diisopropyl diethylhexyl, dicyclohexyl, diethylcyclohexyl peroxydicarbonates; mixed anhydrides of organic sulfoperacids and organic acids, such as acetylcyclohexylsulfonyl peroxide; known azo compounds which are known as polymerization initiators can be used such as azoiso-butylnitrile, optionally together with persulfates such aspotassium, sodium, or ammonium persulfate, hydrogen peroxide, tert-butylhydroperoxide or other water-soluble peroxides as welll as mixtures of different catalysts. The peroxide radical initi-ators can also be used in the presence of 0.012 to 1% by weight, in relation to monomer, of one or more reducing substances, which are suitable for building up of a redox catalyst system, such as, e.g., sulfites, bisulfites, dithionites, thiosulfates, aldehyde sulfoxilates, e.g., Na formaldehyde sulfoxilate.
The polymerization is performed at 40 to 80~C, preferably 50 to 70C, usually up to a monomer conversion of vinyl chloride of 60 to 95%, preferably 70 to 85%. From economical aspects, as high as possible end conversion is chosen, in which with the suspending agent system according to the invention vinyl chloride polymers are obtained, whose grain porosity (determined by plasticizer absorption at room temperature according to DIN 53 417/1) is very high even then, namely more than 25%.
After polymerization a nonionic or amphoteric wetting agent can optinally be added, before the main amount of the aqueous phase is separated and the product is fed to a drying device.
The following characteristic values are determined on the vinyl chloride polymer:
apparent density : according to DIN 53 468 plasticizer absorption : according to DIN 53 417/1 (centrifuging process) grain size distribution: according to DIN 53 734 (airjet sifting).
Futher, the object of the invention is the use of the sinterable finely divided molding compounds produced according to the new processfor the production of sintered molded articles such as insulating material, packing for cooling towers, filters, water evaporators on heating bodies or also on ion-exchangers, but especially for the production of separator plates for electric cells.

From the molding compounds produced according to the invention separator plates can be produced by sintering, which exhibit a very low electrical resistance, a high plate porosity and a good tensile strength.
The production of the sintered plates takes place in the usual way by application of a specific layer thickness of the polyvinyl chloride poweder to a steel strip, which is then put into a forced air oven (at a temperature, for instance, about 230C) for sintering. The stay time and thus the intensity of the sintering is selected so that with products according to the prior art separating plates can be obtained, whose properties correspond to those of comparison example 1.
The volume resistance of the separators is determined with a microohmeter analogously to the process described in DE-A-23 10 431. The tensile strength is determined analogously to DIN regulation 53 455.
The following examples explain the invention.
Production of the sulfated carbohydrate ester A total of 1.5 mol of chlorosulfonic acid, dissolved in 200 ml of methylene chloride, is instilled in a solution of 1.5 mol of carbohydrate ester in 1.5 liters of methylene chloride in the course of 1 hour at 0C with passing of a nitrogen stream (0.5 l/min). It is further stirred for 4 hours at O~C, and 1 liter of ice water is added. The aqueous phase is neutralized with sodium hydroxide solution and bleached with 30 ml of 30% hydrogen peroxide. The sulfated product has a degree of sulfation of 75%

and is further processed as accumulating aqueous solution.
The following amount data indicate parts by weight (pw) .
Comparison example 1 (analogously to DE-C3-23 10 431) In a 40 liter polymerization autoclave the following mixture is polymerizedat 59C and 340 rpm up to a residual pressure of 6 bars:
1000 pw of vinyl chloride 2000 pw of deionized water 4 pw of methylcellulose (viscosity 400 mPa s, 2% by weight of a solution at 20C) 1 pw of n-dodecylbenzene sulfonic acid 0.4 pw of polyoxyethylene sorbitan monolaurate 1 pw of dicetyl peroxydicarbonate The fine-grain polymerization sludge is filtered off and the polymer is dried in a vacuum cabinet.
The powder with a small grain porosity produces sintered plates with a high electrical volume resistance (Table 1).
Example 1 In a 40-liter polymerization autoclave the following mixture is polymerized at 54C and 340 rpm up to a residual pressure of 5 bars:
1000 pw of vinyl chloride 2000 pw of deionized water 5 pw of methylhydroxypropylcellulose (METHOCE ~ F 50 of DOW Chem. Co, Midland, USA) 2 pw of carbohydrate ester sulfate with a degree of sulfation i303788 of 80% on the basis of a colza oil fatty acid-polyglycosyl sorbitol ester with n~l2 and a 1:1 molar ratio of anhydroglycose to carboxylic acid.
1 pw of dicetyl peroxydecarbonate.
After degassing of the residual monomer, 1 pw of a nonionic wetting agent, namely an addition product of 3 mol of propylene oxide and 1 mol of ethylene oxide, is stirred in, the fine-grain polymerization sludge is filtered off and the polymer is dried in a vacuum cabinet.
The powder has a high grain porosity and in the processing produces sintered plates with a very low electrical volume resistance and a good tensile strength (table 1).
Example 2 In a 40-liter polymerization autoclave the following mixture is polymerized at 54C and 340 rpm up to a residual pressure of 6 bars:
1000 pw of vinyl chloride 2000 pw of deionized water 4 pw of methylhydroxypropylcellulose (METHOCE ~ F 50 of DOW. Chem. Co, Midland, USA) with the degree of molecular substitution of 2.0 and viscosity of 50 mPa s, measured in water at 20~C as a 2% by weight solution 3 pw of carbohydrate ester sulfate with a degree of sulfation of 57% on the basis of a colza oil fatty acid-polyglycosyl sorbitol ester with n=12 and a 2:1 molar ratio of anhydroglycose to carboxylic acid 1 pw of dicetyl peroxydicarbonate.

After degassing of the residual monomer, 1 pw of a nonionic wetting agent, namely an addition product of 3 mol of propylene oxide and 1 mol of ethylene oxide, is stirred in, the fine-grain polymerization sludge is filtered off and the polymer is dried in a vacuum cabinet.
The powder in the processing produces sintered plates with a very low electrical volume resistance and a good tensile strength (table 1) Comparison example 2 The procedure is as in example 1, but as carbohydrate ester sulfate 3 pw of a type with a degree of sulfation of 7% is ; used.
The powder under selected conditions cannot be sintered into plates. With changed sintering conditions exclusively nonporous, thermal~y greatly damaged, sintered plates, which are not suitable for use as battery separator plates, are obtained.

Table 1 PVC Powder Data Sintered Separator Data Apparent Plasticizer Average Electrical Tensile density absorption grain flow stren~th (g/l) (~ by wt) size K resis. (N/mm~) ~micron) ~mohm/dm2) Comp.
ex. 1 415 15 27 1.6 9.8 Comp.
ex. 2 462 22.5 35 1) 1) Ex. 1 405 30 34 0.8 10.3 Ex. 2 437 27 40 0.9 7.5 1) Powder not sinterable

Claims

1. A process for the production of a sinterable finely divided polyvinyl chloride useful as a molding compound, which comprises suspension polymerization of vinyl chloride in water at 40 to 80°C using at least one oil-soluble radical polymerization initiator in the presence of 0.5 to 1% by weight (based on the vinyl chloride monomer) of a suspension stabilizer mixture which consists of:
a) 10 to 90% by weight (based on the suspension agent mixture) of a sulfated carbohydrate ester which has the carbohy-drate ester moiety of the following formula:
(wherein n is an integer of from 0 to 99 and R is an aliphatic linear or branched polyol with 2 to 6 hydroxyl groups and 2 to 12 carbon atoms esterified with a saturated or unsaturated linear or branched aliphatic carboxylic acid with 6 to 24 carbon atoms) and which is 10 to 95% sulfated, and b) 90 to 10% by weight (based on the suspension agent mixture) of a cellulose ether selected from the group consisting of methylcellulose, methylhydroxyethylcellulose, methylhydroxy-propylcellulose, hydroxyethylcellulose and hydroxypropylcellulose, said cellulose ether in 2% by weight aqueous solution at 20°C
exhibiting a viscosity of 15 to 500?10-3 Pa s.

2. The process according to claim 1, wherein the two compon-ents of the suspension agent mixture a) and b) are used in the weight ratio of 20:80 to 80:20.

3. The process according to claim 1, wherein component b) is methylhydroxypropylcellulose with a viscosity of 50 to 100 mPa s and makes up to 30 to 70% by weight of the total suspending agent mixture.

4. Process according to claim 1, wherein the degree of sulfation of the sulfate carbohydrate ester is 20 to 90%.

5. Process according to claim 2 or 3, wherein the degree of sulfation of the sulfated carbohydrate ester is 20 to 90%.

6. Process according to claim 1, wherein the degree of esterification of the sulfated carbohydrate ester is 10 to 95.

7. Process according to claim 2, 3 or 4, wherein the degree of esterification of the sulfated carbohydrate ester is 10 to 95.

8. A process according to claim 1, wherein in component a), n is 1 to 50, the degree of esterification with the carboxylic acid is at least 1 mole per mole of the carbohydrate.

9. A process according to claim 1, wherein in component a), R is sorbitol esterified with a linear fatty acid with 6 to 24 carbon atoms.

10. A process according 1, wherein in component a), n is 1 to 15, R is sorbitol esterified with a linear fatty acid with 6 to 24 carbon atoms, the degree of esterification being from 0.5 to 2 mole per mole of the anhydroglycose unit.

11. A process according to claim 1 or 2, wherein component b) is methylcellulose, methylhydroxyethylcellulose or methylhy-droxypropylcellulose, each with a molar degree of substitution of the methyl group of 1.4 to 2.4 and a molar degree of substitution of the hydroxyalkyl group of 0.08 to 0.28, which in the 2% by weight aqueous solution at 20°C exhibits a viscosity of 15 to 500 ? 10-3 Pa s.

12. A process according to claim 8, 9 or 10, wherein component b) is methylcellulose, methylhydroxyethylcellulose or methylhydroxypropylcellulose, each with a molar degree of substi-tution of the methyl group of 1.4 to 2.4 and a molar degree of substitution of the hydroxyalkyl group of 0.08 to 0.28, which in the 2% by weight aqueous solution at 20°C exhibits a viscosity of 15 to 500 ? 10-3 Pa s.

13. A method of producing a sintered molded article, which comprises:
molding the polyvinyl chloride produced by the process of claim 1, 3 or 10, into a molded article, and, sintering the molded article under sintering conditions.

14. A method of producing a separator plate for electric cells, which comprises:
molding the polyvinyl chloride powder produced by the process of claim 1, 3 or 10, into a layer of a predetermined thickness on a steel strip, and sintering the polyvinyl chloride layer in a forced air oven at a temperature about 230°C under sintering conditions.