AU427218B2 - Resin compositions containing mainly polyvinylchloride suitable for producing battery separator - Google Patents

Description

2Q,623 t'1 This invention relates to a resin composi- tion containing mainly a 'polyvinyl chloride and being suitable for the production of a battery separator. More particularly, the invention pertains

to a polyvinyl chloride resin composition high in processability and suitable for the production of a battery separator excellent in mechanical strength and electric resistance which comprises a mixture consisting of 50 to 95 by weight of a suspension- polymerized polyvinyl chloride prepared by polymeriz- ing vinyl chloride in the presence of cellulose derivatives containing alkyl group and/or hydroxyalkyl group in their units -as a suspension stabilizer and: an anionic emulsifier-as an auxiliary suspension stabilizer, and 50 to 5 by*weight of an emulsion- polynerized polyvinyl chloride, and a nonionic antistatic agent. It is well known that a polyvinyl chloride may be used in a resin composition for battery separator. It is also well known that a polyvinyl chloride used for the production of battery separator is required to be excellent in processability during the production of separator and to give a separator prominent in mechanical strength, high -in porosity and low in electric resistance. With an aim to provide at low cost a poly- vinyl chloride resin composition excellent in pro- cessability and suitable for the production of a battery separator excellent in mechanical strength and electric resistance, the present inventors made

4 272 18

29,623 71 extensive studies to find that such a resin composi-

tion as mentioned above can be obtained by mixing (i)

100 parts by weight of a mixture composed of 50 to

by weight of a suspension-polymerized polyvinyl chloride having an average particle size of 10 to 40 ii,

and an average polymerization degree of 700 to 1,400

which has been prepared by polymerizing vinyl chloride

in the presence of at least one ellulose dervative containing alkyl group and/or/hyd~_eya~l~ group in

their units as a suspension stabilizer and at least

one anionic emulsifier as an auxiliary suspension

stabilizer, and 50 to 5 by weight of an emulsion- polymerized polyvinyl chloride having an average

polymerization degree of 700 to 1,400 in which parti-

cles having an average primary particle size of 0.1

to 1.5 L have been agglomerated to particles having an average secondary particle size of 20 to 50 1, with (ii) 0.1 to 3 parts by weight of a nonionic

antistatic agent.

The suspension-polymerized polyvinyl chloride

used in the present invention should be a resin pre-

pared by suspension-polymerizing vinyl chloride in

the presence of such a specific suspension stabilizer

system as acombination of at least one cellulose

derivative containing alkyl group and/or hyonyal

group in their units as the main suspension stabilizer

which is selected from the group .consisting of alkyl

celluloses such as methyl cellulose, ethyl cellulose

and propyl cellulose, and hydroxyalkyl celluloses such

as hydroxypropoxymethyl cellulose, hydroxyethyl

4272 18

2 9.623 /71 cellulose, hydroxypropyl cellulose and hydroxybutyl

cellulose, with at least one anionic emulsifier as an

auxiliary suspension stabilizer which is selected

from the group consisting of alkali metal salts of

alkylsulfate, dialkylsulfosuccinate and alkylbenzen-

sulfonic acids. Preferable as the said auxiliary

suspension stabilizer are sodium dodecylsulfate,

sodium dioctylsulfosuccinate and sodium dodecylbenzene-

sulfonate. The suspension stabilizer and auxiliary

suspension stabilizer are used in amounts of 0.05 to

by weight and 0.005 to 0.1 by weight, respec-

tively, based on the weight of vinyl chloride monomer.

As a suspension polymerization catalyst,

there may be used any of such known oil-soluble

catalysts as lauroyl peroxide, benzoyl peroxide,

azobisisobutyronitrile and diisopropyl peroxydi-

carbonate. Further, there may be used in the poly-

merization any of such known buffer agents as alkali

metal salts of carbonic, phosphoric and sulfurous

acids, for example, sodium carbonate, sodium bicarbonate,

potassium carbonate, sodium phosphate, sodium dihydrogen

phosphate, sodium monohydrogen phosphate, sodium sulfite,

sodium bisulfite and the like. These agents have the

effects that they facilitate the control of particle

size. Oridinarily, the suspension polymerization is

effected at a temperature of 30° to 700C.

The accompanying drawing is a scanning electron micrograph of a suspension-polymerized poly-

vinyl chloride obtained according to the above-

mentioned process. As is clear from said micrograph,

4 427218

29.623 71 the individual particles of said polymer have a

considerably uneven surface.

The reason why a resin composition containing as

one component a polyvinyl chloride prepared according

to the above-mentioned specific suspension polymerization

process gives a satisfactory battery separator has not

been elucidated yet. However, the polymer obtained

according to the aforesaid process is composed of

particles of less than 90P which have an average particle

size of 10 to 40pand a pore volume (volume of pores of

less than 73,000 l in size as measured according to

mercury injection method) of 0.2 cm 3 /g or more, and

which are considerably uneven at the surface as is

clear from the accompanying drawing. The present inventors,

therefore, consider that because of these properties,

'the polymer can be a resin high in processability and

suitable for the production of a battery separator

excellent in mechanical strength and electric resistance.

Further, not only a suspension polymerization product

obtained according to the aforesaid process is less

expensive than an emulsion polymerization product, but

also all the particles obtained can be used without any

sieving or the like operation, so that there is additionally

attained such an.advantage that a battery separator can

be produced at an extremely low cost.

Heretofore, many processes have been known for the

suspension polymerization of vinyl chloride monomers.

However, polyvinyl chloride obtained according to other

processes than the process mentioned

4-27218

29.623 171 above have such a large average particle size as 70 i

or more, so that the polymers, when used as they are,

are low in processability and cannot give but un-

satisfactory separators having coarse, through pores.

The present composition further contains as

the other resin component 50 to 5 by weight based

on the total weight of the resin components of an

emulsion-polymerized polyvinyl chloride having an

average polymerization degree of 700 to 1,400 in which

particles having an average primary particle size of

0.1 to 1.5 i have been agglomerated to particles

having an average secondary particle size of 20 to

V. By incorporation of such emulsion-polymerized

polyvinyl chloride, not only the composition can be

greatly improved, as compared with the case where the

aforesaid suspension-polymerized polyvinyl chloride

is used alone, in powder spread coating property and

roll adhesion at the time of powder spread coating,

but also a separator obtained by sintering the com-

position can be improved in surface state and re-

inforced rib-forming property. In addition, there is

attained such a processability-improving effect that

the application of processing temperature and proces-

sing speed in wide ranges can be made possible.

In case the amount of the emulsion-polymerized

polyvinyl- chloride is more than 50 by weight, the

composition can give nothingbut a separator low in

mechanical strength, while in case the amount of said

resin is less than 5 by weight, the composition is

less improved in processability.

6 427218

2 9,623/71 The emulsion-polymerized polyvinyl chloride

is obtained by emulsion-polymerizing vinyl chloride

in the presence of a known anionic emulsifier such as

alkali metal salts of alkylsulfate, dialkyl sulfo-

succinate or alkylbenzene sulfonic acids, and a known

water-soluble radical initiator such as hydrogen

peroxide, potassium persulfate or ammonium persulfate,

either singly or in combination with an organic or

inorganic reducing agent such as .0-ascorbic- acid, (cg 2 o.VaZ sO .ZZo), RongalitA ferrous sulfate or cuprous sulfate. Pre-

ferable as the said anionic emulsifier are sodium

dodecylsulfate, sodium dodecylbenzenesulfonate, sodium

di-2-ethylhexyl sulfosuccinate and sodium dibutyl

sulfosuccinate.

The suspension-polymerized and emulsion-

polymerized polyvinyl chloride used in the present

invention are those which have an average polymeri-

zation degree of 700 to 1,400. For the preparation

of polyvinyl chloride having an average polymeriza-

tion degree of 700 to 1,400, there may be adopted

such a procedure that the polymerization temperature

is controlled, that is, in case a chain transfer

agent is not used, the polymerization may be carried

out at a temperature of about 500 to 70 0 or a

halogenated hydrocarbon such as trichloroethylene,

tetrachloroethylene or tetrafluoromethane, or a

mercaptan such as dodecylmercaptan, is added to the

polymerization system. In case the average polymeri-

zation degree is less than 700, the separator obtained

from the composition is lowered in mechanical strength

4272 18

2 9.623 /1 and porosity, while in case the polymerization degree

is more than 1,400, a high temperature is required

for the sintering of the composition.

The noionic antistatic agent, which is one

component of the present composition, is used in order

to improve the processability of the composition.

Examples of the nonionic antistatic agent are block

copolymers of ethylene oxide and propylene oxide,

alkyl ethers of polyoxyethylene, alkyl esters of

polyoxyethylene, aryl ethers of polyoxyethylene, aryl

esters of polyoxyethylene, monoalkyl esters of sorbitan,

polyalkyl esters of sorbitan, and condensation pro-

ducts of mono- and poly-alkyl esters of sorbitan with

ethylene oxide, said alkyl or aryl group having 6 to

18 carbon atoms. The amount of the nonionic anti-

static agent is 0.1 to 3 parts by weight per 100

parts by weight of the resin. In case the amount of

said antistatic agent is less than 0.1 part by weight,

the composition is not improved in processability. On

the other hand, even if the amount thereof exceeds 3 parts by weight, no effect proportional thereto can

be expected. Generally, therefore, the antistatic

agent is used in an amount of less than 3 parts by

weight per 100 parts by weight of the resin.

The antistatic agent may be used in ad-

mixture with the suspension-polymerized and emulsion-

polymerized polyvinyl chloride, or may be added at

the emulsion polymerization or spray.drying step for

preparation of the emulsion-polymerized polyvinyl

chloride.

29,623 m The mixing of the suspension-polymerized

polyvinyl chloride with the emulsion-polymerized

polyvinyl chloride and the nonionic antistatic-agent

may be carried out by use of a Henschell mixer, a

ribbon blender or the like. In this case, a stabilizer,

and a filler such as silica or alumina may also be

incorporated.

For the production of a separator by use of

the polyvinyl chloride resin composition of-the present

invention, there may be adopted any of the known pro-

cesses carried out by, for example, passing the resin

composition on a comb-shaped die to mold the com-

position into a suitable shape as a battery separator,

and then sintering the molded composition in a hot air

furnace.

The process of the present invention is

illustrated in further detail below with reference to

examples, but the scope of the invention is, of

course, not limited to these examples.

Example 1 A mixture comprising 100 parts by weight of

vinyl chloride monomer, 150 parts by weight of

demineralized water, 0.1 part by weight of lauroyl

peroxide, and each one of the suspension stabilizers

and auxiliary suspension stabilizers shown in Table 1

was fed to a 5-liter, stainless steel autoclave, and

then polymerized at 600°C for 10 hours. The average particle size and pore volume of the resulting polymer

were as set forth in Table 1.

29,62 3 17r__

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m (71 c w C2 3 oc 002amw (D 3 4 0 0 C-r

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*l f%3 A -r4C cfd-1

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CD 3 ~(D0*M, %D0 0 CD CD CD

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-In 427218 p 0 o Fco (0 0 0D c+ o .1 Q H mPz0 m 0 0 H ED0 0 1 c*0 0 0Y fl 0 HP

C4 AH 0, 9 ~c1 0

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4272 18

29.623 171 As is clear from Table 1, the polymers obtained by use of the suspension stabili zer systems (Run Nos. 2 to 7) according to the present invention are smaller in average particle size and larger in pore volume than the polymers obtained by use of the substituted cellulose alone (Rin No. 1) and other suspension stabilizer systems (Run Nos. 8 and 9) than those of the present invention~.

Example 2. Using a 200-liter super mixer, the suspension- polymerized polyvinyl chloride obtained in Example 1 and/or an emulsion polymerized polyvinyl chloride were mixed for 10 minutes with an antistatic agent In such proportions as shown in Table 2. The resulting corn- position was continuously sintered at 240 0C to obtain a battery separator. The mixing conditions and pro- cessabil-ity of the composition, and the physical pro- perties of the battery separator obtained were as set forth in,Table 2.

12 427218

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14 427218 1

2 j (;22 17- 7 w~CDtd IO MD cc CD M1 C M1 ca

o 0 CaCa0 (A 0 ca C :3b 0 0 t3 0 t 0: I-0 0 I- o 0 0 0- 0

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H. 9 *003 0 a a .3 '0:00 o o- O 0 4 VA :r 0 (4 0. '0 O 0 (4 9- H. to 0- a4 0- N 0 e~.4H. O .4 P- s td a rr 0. U H. 0 a a as H DO 0. 0. 0 (4 00 H. a 0. 0 tow o 0 a 0 0 a 0 .4 (4 ~b H. 0 0 0 (4 0 o a a 'a 0 0. U H. H. N 0

(4 oO 00 W 50 a a'4 a 0 '002(4 a 40. 0t 0 W 00I-~ t~a0 U .4 a '0 0 00 a 0.0 U 0'4 0 0- 0 0 9- 0 0.0 (4 0.0. H. a a 0*0 0 C+ 0 a- 0 3 0. L. 0 a 0 (4 P- '4 a 3 w 0 a. p 0 0 0 4 0 000 a. '0 Off 0 0 (4 (4 o a f U. 0 0 0 0 (4

a '0 a '4j 0 a .4 0 27 21

0 a %A 0 0. H. (4. H. 0% 0 0 a

.4 0 a

0 0.

From Table 2, itisc1ear that the control

resin compositions (Run Nos. 18, 20, 25 and 26) con-

taining no antistatic agent or an nonlonic antistatic agent in an amount outside the. scope

of the present invention are inferior in such pro- perties as spread coating property and roll adhesion to

the present resin compositions (Run Nos. 12, 13, 14,

16and 17); that the control resin composition (Run No.

21), in which the amount of the emulsion-polymerized

polyvinyl chloride is more than 50 parts by weight based

on the total weight of the resins, is markedly low in

tensile strength; that the control resin compositions

(Run Nos. 22 and 23), in which are used suspension-

polymerized polyvinyl chlorides prepared according to

other processes than that of the present invention, are

poor in both spread coating property and electric

resistance; and that the control resin composition

(Run No. 24), in which the particle size of the emuli-:'i-

sion-polymerized polyvinyl chloride is out of the range

regulated by the present invention, is inferior in both

processability and tensile strength. When the poly-

merization degree is out of the range regulated by the

present invention (Run Nos. 27 and 28), the tensile

strength is low and the processability is inferior.

When no emulsion-polymer is contained (Run No. 19), the

prQcessability is low.

A- 4- 2 L7-28A

Claims (1)

1. 29,623 /71 The claims defining the invention are as follows:-

   1. A polyvinyl chloride resin composition high in processability and suitable for the production

   of a battery separator excellent in mechanical strength

   and electric resistance which comprises 100 parts by weight of a mixture consisting of 50 to 95 by weight of a suspension-polymerized polyvinyl chloride

   having an average particle size of 10 to 40 P, and an

   average polymerization degree of 700 to 1,400 which

   has been prepared by suspension-polymerizing vinyl

   chloride in the presence of at least one cellulose derivative containing alkyl group having 1 4 carbon atoms and/or hydroxyalkyl group having 1 4 carbon atoms as a suspension stabilizer and at least nrn

   anionic emulsifier as an auxiliary suspension stabilizer, which is selected from the group consisting of alkali metal salts

   of alkylsulfate, dialkyl sulfosuccinate and alkyl benzene

   sulphonic acids, and 50 to 5 by weight of an emulsion-polymerized polyvinyl chloride having an average polymerization

   degree of 700 to 1,400 in which particles having an

   average primary particle size of 0.1 to-l.5 P have

   been agglomerated to particles havig an average

   secondary particle size of 20 to 50 p, and (ii) 0.1 to

   3 parts by weight of a nonionic antistatic agent. A composition according to CL-uim 1, wherein the suspension stabilizer is one member selected

   18 427218

   2 9,623p71 .from the group consisting of methyl cellulose, ethyl

   cellulose, propyl cellulose, hydroxypropoxymethyl

   cellulose, hydroxyethyl cellulose, hydroxypropyl

   cellulose and hydroxybutyl cellulose.

   3. A composition according to Claim 1,

   wherein the auxiliary suspension stabilizer is one

   member selected from the group consisting of alkali

   metal salts of alkylsulfates, dialkylsulfosuccinates

   and alkylbenzenesulfonic acids.

   l. H A composition according to Claim 1,

   wherein the amount of the suspension stabilizer and

   the auxiliary suspension stabilizer is 0.05 to 0.5

   by weight and 0.005 to 1 by weight, respectively,

   based on the weight of the vinyl chloride monomer.

   A composition according to Claim 1,

   wherein the suspension polymerization is effected in

   the presence of an oil-soluble catalyst.

   6.A( A composition according to Claim 1, wherein the suspension polymerization is effected at

   a temperature of 30° to 700C.

   7A A composition according to Claim 1,

   wherein the nonionic antistatic agent is one member

   selected from the group consisting of block copolymers

   of ethylene oxide and propylene oxide, alkyl ethers of

   polyoxyethylene, alkyl esters of polyoxyethylene, aryl ne29, 3 171 ethers of polyoxyethylene, es ers of polyoxy- ethylene, monoalkyl esters of sorbitan, polyalkyl esters of sorbitan, and condensation products of mono- and poly-alkyl esters of sorbitan with ethylene oxide.

   A composition according to Claim 1, wherein the nonionic antistatic agent is polyoxyethylene

   nonylphenyl ether, sorbitan monolaurate and ethylene- oxide-propylene-oxide block copolymer.

   9-10 A composition according to Claim 1, wherein the composition additionally contains a stabilizer and a filler.

   /01-2 A composition according to Claim"i wherein the filler is silica.

   3 A composition substantially as hereinbefore described.

   DATED this 1st Day of JUNE, 1971 SUMITOMO CHEMICAL COMPANY, LIMITED By their Patent Attorneys

   CLEMENT HACK CO. Fellows Institute of Patent Attorneys of Australia.

   29, 623 1"