CA1220887A

CA1220887A - Water-swellable elastomer composition

Info

Publication number: CA1220887A
Application number: CA000466088A
Authority: CA
Inventors: Morio Nakamura; Shigeji Obayashi; Motomu Hirakawa; Hitoshi Tanaka; Shinichi Takemori
Original assignee: Seitetsu Kagaku Co Ltd
Current assignee: Sumitomo Seika Chemicals Co Ltd
Priority date: 1984-10-23
Filing date: 1984-10-23
Publication date: 1987-04-21

Abstract

ABSTRACT OF THE DISCLOSURE
Water-swellable elastomer composition consisting essentially of a homogeneous mixture of an elastomer, a water-absorbent resin and a water-soluble resin. Said composition exhibits a high degree of swelling and a high swelling rate when it is soaked in water. Also, said composition retains swellability even when it is put in contact with water for a long period of time.

Description

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1 This invention relates to a watex~swellable elastomer composition consisting essentia.lly of an elas-tomer, a water absorbent resin and a water-soluble resinO
Heretofore, there has been proposed the use of a water-swellable rubber which is produced by mixing a rubber with a water-absorbent material such as crossli~ked polyvinyl alcohol, crosslinked polyacrylate, crosslinked starch-acryla~e copolymer, crosslinked carboxyme~hyl-cellulose or the like; a water-swellable urethane resin;
a hydrophilic group-containing rubber; or the like for the purpose of the caulking or sealing of gaps or the stopping of water in civil engineering and construction works or the like, or the preservation of airtightness in machinery and apparatus [Japanese Patent Application Kokai (Laid-Open) Nos. 33,032/81 and 190,065/82~.
However, if watex-swellability is imparted to a rubber by mixing a water-absorbent material therewith, the swelling rate and degree of swelling of the rubber are low, and in addition, the rubber has also such problems that the water-absorbent material is separated off upon contacting with water for a long period of timel so that the swellability is ultimately lost, the strength is remarkably decreased, and water is polluted.
When a water-swellable urethane resin or hydro-philic gxoup-containing rubber is mixed with a rubber, ~, ~
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1 ~he water-swellability of the rubber thus obtained is inferior because these have a low degree ~f swelling and a low swelling rate, and therefore, no satisfactoxy efect can be expected.
The present inventors have conducted exten~ive research for the purpose of overcoming the above-men~ioned problems. As a result thereof, they have found that when a water-absorbent resin and a water-soluble resin are homo-geneously dispersed in an elas~omer, the water-absorbent resin can be prevented from being separated off, and a water-swelling elastomer cQmposition having an extremely high swelling rate and an extremely high degree of swelling, is obtained.
An object of this invention is to provide an elastomer which can be swollen with water.
1~ Another objec~ of this invention is to provide a water-swellable elastomer composition having an extremely high swelling rate and a high degree of swelling.
Other objects and advantages of this invention will be apparent from the following description.
~0 According to this invention, there is provided a water-swellable elastomer composition having a high swelling rate a~d a high degree of swelling, said com-position consisting essentially of a homogeneous mixture of an elastomer, 5~300 parts by weight of a water-absorbent resin per 100 parts by weight of the elastomer and wherein said water-absorbent resin absorbs water in an amount of at least 20 times the weight of the resin and has a particle size of 400 ~m or less, and 1-50 parts by weight of a water-soluble ,~ - 2 -~2~

resin per 100 parts by weight of the elastomer.
The elastomer used in this invention includes a natural rubber and a synthetic rubber. The synthe~ic rubber includes many known rubbers such as chloroprene - 2a -~ o~

1 rubbex, butadiene rubber, styrene~butadienerubber, acrylonitrile-bu~adiene xubber, isobutylene isoprene rubber, fluororubber, ~thylene-propylene rubber, chloro-sulfonated polyethylene, silicone rubber, urethane rubber, S polyaulfide rubber, acrylic rubber and thf~ like, and it is preferable to use chloroprene rubber or st:yrene-butadiene rubber from ~he standpoint of processability and economy.
These rub~ers can be properly selected depencling upon the application fields of water-swellable rubbers.
For instance, chloroprene rubber or chlorosulfonated polyethylene are suitable for the requirement of weathçr resistance, and silicone rubber or fluororubber are pre-ferred when heat resistance is required.
The water-absorbent resin used in this invention includes crosslinked products of polyacrylates, crosslinked products of starch-acrylate graft copolymers, crosslinked products of a hydrolyzate of starch-acry~onitrile graft copolymer, crosslinked products of carboxymethylcellulose, crosslinked products of polyvinyl alcohol, crosslinked products of a hydrolyzate of methyl (meth)acrylate-vinyl acetate copol~mer, crosslinked products of cellulose-sodiu~
acrylate graft copol~mer, and the like, and in particular, crosslinked products of polyacrylates have an excellent effect.
Although any of the above water-absorbent resins can be used in this invention, it i5 necessary to use a water-absorbent resin which absorbs water in an amount of at least 20 times the weight of the resin.

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1 The water soluble ~esin used in this invention includes polyethylene oxide, polyvinyl pyrrolidone, hydroxy-ethylcellulOse, hydroxypropylcellulose or ~he like. Poly ethylene oxide and polyvinyl pyrrolidone are preferably used from the standpoint of rubber-compatibility and processabi-lity because they are ~hermoplastic, and a water swellable elastomer containing polyethylene oxide or polyvinyl pyrrolidone is preferred in view of the appearance and pexformance.
The amount of the water-absorbent resin added is 5-300 parts by weight, preferably 10 200 parts by weight, per 100 parts by weight of the elastomer. If the content of the water-absorbent resin is too small, neither a sa-tisfactory swelling rate nora satisfactor~ degree of swelling are obtained. On the other hand, if the content is too large, the water~absorbent resin is separated off from the elastomer, and th composition becomes in some cases un-suitable for water stopping ox water retention.
A water-swellahle elastomer obtained by mixing an elastomer only wi~h a water-absorbent resin as i~ usual in the conventional method exhibits only a slow swelling rate and a low degree of swelling. Moreover, the water-absorbent resin is separated off from the water-swellable elastomer in some cases, and.hence, the purpose is not achieved.
However, by adding a water-soluble resin together with a water-absorbent resin to an elastomer according to this invention, a homogeneous water-swelling ',~.~1 1 elastomer composition is obtained, and when it contacts with water a swollen product which has a high degree of swelling/ is homogeneous and has a smooth surface, is obtained from the water-swelling elastomer composition.
~he amount of the water-soluble resin added is 0.5-100 parts by weight, pre~erably 1-50 parts by weight, per 100 parts of the elastomer. If the amount of the water-soluble resin is too small, the intended effect of the addition cannot be obtained and the degree of swelling of the elastomer is low. If the amount of the water-soluble resin is too large, the degree of swelling is not so much increased, and adverse effects such as elution or the like tend to take place.
The particle diameter of a wa-ter-absorbent resin used in this invention is 400 ~m or less, preferably 100 um or less. If the particle becomes finer, a more homogeneous composition is obtained, and a swollen product obtained therefrom becomes homogeneous.
When 10-100 parts by weight of water per 100 parts by weight of the water-absorbent resin is previously contain-ed in an elastomer prior to mixing the elastomer with the water-absorbent resin, a water-s~elling elastomer composi-tion having an extremely high swelling rate is obtained.
If the amount of water is too smalll the effect is not suf-ficient. Qn the other hand, if the amount of water is toolarge, mixing operation becomes difficult. As for the stage of enabling wate~ to be contained it is not always necessary to previously contain the water in the water-absorbent resin, and an equivalent effect is obtained by 1 adding water at the time of mixing The water-swellable elastomer of this invention is produced by uniformly dispersing a water-absorbent resin and a water-soluble resin in an elastomer by a mechanical procedure. For example, roll mixing~ mixing with a Banbury mixer, mixing with an extruder~ or the like are mechanical dispersing methods which are applicable to this invention. A vulcanizing agent and a vulcanization accelerator are mixed during the mixing procedure in this invention, and if necessary, a coloring agent, a filler, a plasticizer, an antioxidant and the like are incorporat-ed. The compound obtained by mixing is heat-vulcanized and molded according to a conventional method to form a water-swellable elastomer composition in the form of a plate, rod or the like depending on intended uses.
The water-swellable elastomer of this invention can be applied to various uses as water-stopping material, water-retaining material, medical supplies and the like, and suitable compounding recipes are selected depending upon uses to form compositions.
This invention is further explained in detail below referring to Examples and Comparative Examples.
However, it should not be interpreted ~hat this inven-tion be limited to the Examples.
Degree of swelling in the Examples and Compara-tive Examples is defined as follows:

Degree of swelling = -a a_ x 100 (%) a: weight before swelling b: weiyht after swelling 1 The size of a s~mple is 2 x 4 cm with a thick-ness of 1 mm.
In the Examples and Comparative Examples all parts are hy weight unless o~herwise specified.

Example 1 A compound obtained ~y roll-mixing a chloroprene rubber (Toyo Soda Mfg. Co., I,td.: "Sk~prene B-30)" as an elastomer, a crosslinked product of polysodium acrylate tSeitetu Kagaku Co., Ltd.: ~quakePp 4S, average particle diameter, 70 ~ as a water-absorbent resin and a poly-***
ethylene oxide (Seitetsu Kagaku Co., Ltd.: PEO-3~ as a water-soluble resin in the amounts shown in Table 1 was vulcanlzed at 150C at a pressure of 150 kg~m2 G
for 30 minutes to prepare a water-swellable elastomer composition. A sheet of 29 x 40 x 1 mm was formed from this elastomer composition, and soaked in ion-~xchanged water to swell the sheet.
The degrees of swelling are shown in Table 2.

* Trademark ** Trademark *** Trademark i ~ 7 -~2~
Table 1 ~ ... ~ __ _ _ Component Part __ _ _ _ __ ~ _~
Chloroprene 100 Carbon black 30 Zinc white S
~Sagnesium oxide Stearic acid Ethyl~ne thiourea 0.5 Aquakeep 4S" (trademark) 100 Polyethylene oxlde 10 __ _ _ .

Table 2 __.
Soaking Time 10 min 1 hr 24 hrs ~j _ _ _ Degree of 40 98 830 swelllng ( % ) _ _ _ _ _ _ 1 Example 2 A compound obtained by roll mixing a styrene butadiene rubber ISumitomo Chemical Co., Ltd.: Sumitomo SBR 1778S) as an elastomer, a crosslinked product of polysodium acrylate ~Seitetsu Kagaku Co., Ltd.~ "Aquakeep 4S, average particle diameter, 70 ~m) as a water-absorbent resin and a polyethylene oxide iSeitetsu Xagaku Co., Ltd.:

**
"PEO-3) as a water-soluble resin in the amounts shown in Table 3 was vulcanized at ~50~C at a pressure of * Trademark ** Trademark ;; 8 -~L2~

1 150 kg/cm2 G for 30 minukes to produce a water-swellable ela~tomer composition. The degree of swelling deter mined in the same manner as in Example 1 are shown in Table 4.

~able 3 _~ .
Component Part ~ ____ Styrene-butadiene rubber 100 Carbon black 30 Sulfur 4

2-Benzothiazyl disulfide Tetramethylthiuram disulfide Aquakeep 4S 100 Polyethylene oxide 10 Water 30 _ _ . . _ _ Table 4 ~ . .
¦ Soaking Time 10 min1 hr 24 hrs ~ _ ¦ Degree sf 75 240 1~570 I swelling (~) __ _ _ _ ~ ~ _ Comparative Example 1 A water swellable elastomer composition was prepared in the same manner as in Example 1, excep~ that the polyethylene oxide was omitted. Because of the absence of polyethylene oxide, the components were _ g ~ 2 ~

1 unable to be hsmogeneously mixed, and the water aksorbent resin was remarkably separated off from th~e elastomer 2 hours after the soaking in water.

Comparative Ex~mple 2 A water-swelling elastomer composition was prepared in the 6ame manner as in Example 2, ~xcept that the polyethylene oxide was omitted. The degxees of swelling determined in the same manner as in ~xample 1 are shown in Table 5.

Table 5 ____ Soaking Time 10 min 1 hr 24 hxs _ __ _ e ~ _ .

swelling (%) 18 _ _ 315 Example 3 A water-swellable elastomer composition was prepared in the same manner as in Example 2, except that a crosslinked product of starch acrylate graft copolymer (Sanyo Chemical Industry, ~td.: Sanwet IM-300t was used ~5 as a water~absorbent resin ins~ead of ~he crosslinked product of polysodium acrylate. The degrees o swelling determined in the same manner a in Example 1 are shown in Table 6.
* Trademark O
~'~1 Table 6 Soaking Time 10 min 1 hr24 hrs ~ _ . _ ~
Degree of 50 1701,150 swelling (%) ~
_ _ _ ~ ~

1 Example 4 A water-swellable elastomer composition was prepared in the same manner as in Example 2~ except that a hydroxyethylcellu}ose ~FU3I C~EMICAL CO., LTD.:
Fujihec AH-15) was substituted for the polyethylene oxide. The degrees of swelling determined in the same manner as in Example 1 are shown in Table 7.

Table 7 _ _ _ ~ _ Soaking Time 10 min 1 hr 24 hr~
_ _ _ _ ~ _ .

Degree of 40 150 1,050 swelling (%) _ _ _ _ ~ _ _ Example 5 A water-swellable elasto~er composition was prepared in the ~ame manner as in Example 2, except that a polyvinylpyrrolidone lKISHIDA KAGAKU: K-15 was substituted fox the polyethylene oxide.
Soaking the sheet obtained in water for a predetermined time and observing the surface state, the swollen product was fou~d to be smooth and slimeless.

* Trademark ** Trademark 1 The degrees of swelling determined in the same manner as in Example 1 are shown in Table 8.

Table 8 Soaking Time 10 min 1 hr 24 hrs ~ _ ~ _ swelling (~) 60 210 1,250 .

Examples 6 - 10 A water-swellable elastomer composition was prepared by vulcaniæing at a pressure of 150 kg/cm2 G
at 150C for 30 minutes a compound obtained by roll-mixing the components shown in Table ~ in the same manner as in Example 1. The degrees of swelling determined in ~he same manner as in Example 1 are shown in Table 10. The swollen sheets had favorable surfaces which were smooth and slimeless.

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Table ~
~Parts) __ _ __ _ _ Example No. 6 7 8 9 10 . . ___ _ _ _ _ _ Carbon black 30 30 30 30 30 Zinc white (ZnO) 3 3 5 5 Magnesium oxide ~gO) 5 Sulur (S) 1.5 2 1.5 Stearic aci.d 1 1 1 1 Vulcanization accelerator M 0.5 " TT 1~0 0.5 It BZ
" TRA 2 " DM 0.5 ,i P2 Antioxidant (Antigen NBC~ 1 Process oil 10 10 10 10 10 A~-4S' (trademark) 70 70 70 Waterlock ~-100" (trademark) 70 Sumikagel S-50" (trademark) 70 Water 35 35 35 35 35 PVP 15 15 15 ~5 15 ~ _ _ ___ Trademark Nste:
~ Com~ound Trade Mark ~
EPT- Ethylene-propylene Esprene 505" Sumitomo Chem.
terpolymer rubber NR- Natural rubber ~ -CSM: Chlorosulfonated ~ypalone 40" Dupont polyethylene rubber NBR: Nitrile rubber "Nipole 1042" ~ippon Zeon obutylene-isoprene ~SSOBUTY~ 268 Esso. Chem.
rubber M: 2-Mercaptoben20-thiazole TT: Tetramethylthiuram disulfide BZ: Zinc dibutyl-dithiocarbamate TRA: Dipentamethylene-thiuram tetrasulfide DM: Dibenzothiazyl disulfide PZ: Zinc dimethyl-dithiocarbamate Anti- Nickel dibutyl- "~nt,lgen oxidant dithiocarbamate NBC Sumitomo Chem.
AK-4S: Crosslinked product "Aquakeep 4S" Seitetgu of polysodium Ragaku acrylate "Water Crosslinked saponi Grain-lock * fication product proce~sing -A100:" of starch-acrylo- Corp.
nitrile copolymer "Sumikagel Crcsslinked saponi- Sumitomo Chem.
5~50:"** fication product o methyl acrylate-vinyl acetate copolymex PVP: Polyvinylpyrrolidone ~ 15 KISHIDA K~GAKU

* Trademark - 14 --** Trademark ~0~
Table 10 Soaking Tlme 10 min 1 hr 24 hrs _ _._ __ _ _ _ ._ Example 6 30 70 580 ,- 7 25 65 520 " 8 30 70 600 ,. 9 20 60 500 " 10 30 75 530

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A water-swellable elastomer composition consisting essentially of a homogeneous mixture of an elastomer, 5-300 parts by weight of a water-absorbent resin per 100 parts by weight of the elastomer and wherein said water-absorbent resin absorbs water in an amount of at least 20 times the weight of the resin and has a particle size of 400 µm or less, and 1-50 parts by weight of a water-soluble resin per 100 parts by weight of the elastomer.

2. The composition of claim l wherein the particle size of said water-absorbent resin in 100 µm or less.

3. A composition according to claim 1, wherein the amounts of the water-absorbent resin and the water-soluble resin are, respectively, 10-200 parts by weight and 1-50 parts by weight per 100 parts by weight of the elastomer.

4. A composition according to claim 1, wherein the elastomer is a chloroprene rubber, a butadiene rubber, a styrene-butadiene rubber, an acrylonitrile-butadiene rubber, an isobutylene-isoprene rubber, a fluororubber, an ethylene-propylene rubber, a chlorosulfonated polyethylene, a silicone rubber, an urethane rubber, a polysulfide rubber, an acrylic rubber or a natural rubber.

5. A composition according to claim 1, wherein the elastomer is a chloroprene rubber.

6. A composition according to claim 1, wherein the elastomer is a styrene-butadiene rubber.

7. A composition according to claim 1, wherein the water-absorbent resin is a crosslinked product of poly-acrylate, a crosslinked product of starch-acrylate graft copolymer, a crosslinked product of a hydrolyzate of starch-acrylonitrile graft copolymer, a crosslinked pro-duct of a carboxymethylcellulose, a crosslinked product of polyvinyl alcohol, a crosslinked product of a hydrolyzate of methyl (meth)acrylate-vinyl acetate copolymer or a crosslinked product of cellulose-sodium acrylate graft copolymer.

8. A composition according to claim 1, wherein the water-absorbent resin is a crosslinked product of polyacrylate.

9. A composition according to claim 1, wherein the water-absorbent resin is a crosslinked product of starch-acrylate graft copolymer.

10. A composition according to claim 1, wherein the water-soluble resin is a polyethylene oxide, a polyvinylpyrrolidone, a hydroxyethylcellulose or a hydroxypropylcellulose.

11. A composition according to claim 1, wherein the water-soluble resin is a polyethylene oxide.

12. A composition according to claim 1, wherein the water-soluble resin is a polyvinyl pyrrolidone.

13. A composition according to claim 1, wherein the water-absorbent resin is in the form of a powder having a particle diameter of 100 µm or less.

14. A composition according to claim 1, wherein the water absorbent resin and the water-soluble resin are homogeneously dispersed in the elastomer.

15. A composition according to claim 1, wherein the water-absorbent resin is a water-absorbent resin having previously absorbed therein 10-100 parts by weight of water per 100 parts by weight of the water-absorbent resin.