Sealing material which swells when treated with water

Details Sealing material which swells when treated with water Sealing material which swells when treated with water

2000-07-07

2002-03-19

Acquah, Samuel A. (Department: 1711)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C524S027000, C524S028000, C524S035000, C524S047000, C524S056000, C524S057000, C524S058000, C524S081000, C524S082000, C524S186000, C524S457000, C524S543000, C525S054240, C525S054260, C525S054310, C525S055000, C525S088000, C525S185000, C525S191000, C521S056000, C521S059000, C428S034300, C428S035200, C428S035800, C428S036100, C428S304400, C428S423900, C428S424200

Reexamination Certificate

active

06358580

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention is directed to water-swellable seal compositions for producing preformed seals for structural, civil and technical engineering, especially for joint sealing and for compensating dimensional changes in structural components. The seal compositions include elastomers and, embedded in their matrix, a combination of strongly water-absorbing materials such as polysaccharides and hydrophilic polymers which are known as superabsorbents.
BACKGROUND OF THE INVENTION
Water-swellable seal compositions are well known.
DE-A-42 26 198 describes a water-swellable seal material, particularly for joint sealing and for compensating dimensional changes in structural, civil and technical engineering or in other technical areas. The seal material is producible by polymerization of a reaction mixture of monomeric water-soluble or water-miscible acrylic and/or methacrylic acids and/or derivatives thereof. The sealing materials described have the disadvantage of using toxic raw materials which will partly remain in the sealing material even after the tape has cured and pollute the environment.
DE-A-36 10 645 discloses a water-swellable seal material which includes as the polymeric base material not a hydrophobic polymer such as rubber but a hydrophilic addition product of a low molecular weight polyolefinpolyol and ethylene oxide that contains reactive hydroxyl groups. The composition includes as water-absorbing polymers hydrolyzed PVA-sodium acrylate copolymers, CMC, hydrolyzed polyacrylic acids, mixtures of starch and hydrolyzed polyacrylonitriles or mixtures of starch and sodium polyacrylates. Crosslinking is effected using isocyanate.
DE-A-35 32 961 describes a seal material which includes a water-swellable material comprising a mixture of water-absorbing polymer and rubber or synthetic resin. Water-absorbing polymers mentioned are CMC, starch-polyacrylonitrile hydrolyzate, starch-polyacrylate, sodium polyacrylate hydrolyzate. The water-swellable material may be foamed so that its specific density is 0.1 to 0.9 g/cm
3
.
EP-A-160 438 describes a water-swellable caulking material which comprises a body of water-swellable polymer material and non-water-swellable material that is surrounded by a layer which is impervious to neutral water, but previous to alkaline water. The body includes a water-insoluble rubbery polymer and a strongly water-absorbent resin, e.g. crosslinked polyacrylic acid salts, reaction products of starch and polyacrylic acid.
U.S. Pat. No. 5,011,875 is directed to water-swellable caulking compositions of rubber, thermoplastic polymers and water-absorbent material, such as polymers based on acrylic acid, starch-polyacrylic acid graft copolymers, starch-polyacrylonitrile graft copolymers, CMC.
U.S. Pat. No. 5,075,373 discloses a water-swellable seal material which comprises, embedded in a matrix of rubber or synthetic polymers, particles of a water-absorbent resin, for example crosslinked polyacrylic acid salts, starch-acrylic acid graft copolymers, starch-ethyl acrylate graft copolymers, CMC.
EP-A-118 998 is directed to a water-swellable seal comprising chloroprene rubber blended with hydrophilic water-absorbing polymers such as starch-polyacrylate graft copolymers, polyacrylates, poly(meth)acrylic acid salts, maleic anhydride copolymers.
EP-A-055 848 discloses a water-absorbing rubber mixture composed of a 1,3-diene rubber and, dispersed therein, a resin of high water absorbency, for example maleic anhydride copolymers, crosslinked alkali metal salts of polyacrylic acid.
EP-A-410 669 describes a water-swellable seal composition comprising a vulcanized rubber material, a strongly water-absorbent resin, such as poly(acrylic acid)-based resins, maleic anhydride copolymers, basic water-absorbing inorganic material, plasticizers, vulcanizing agents and customary auxiliaries.
DE-A-196 19 709 discloses a seal material comprising a metal sheet with an overcoat of a superabsorbent polymer, fibers and rubber.
JP-A-6-157839 discloses a water-swellable seal composition which comprises an unvulcanized resin component comprising a specific noncrosslinked thermoplastic olefinic elastomer and a hydrogenated diene copolymer, the composition also including a water-absorbing resin and, if desired, cellulose fibers.
However, the known seal materials have disadvantages, especially when used in composite seals. Inorganic aggregates lead to severe equipment wear when producing and processing the seals. Frequently, the requisite extensibility and elasticity is lost on drying. Most seal materials have a relatively high specific density (>1 g/cm
3
) and the elasticity is limited. They further frequently include toxic constituents.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a water-swellable seal material for preformed seals that is primarily produced from nontoxic raw materials and is readily processible into preformed seals, including composite seals. Furthermore, machine problems, such as abrasion, shall be avoided in the production of the seals. The swellability shall be conformable to specific requirements in structural, civil and technical engineering.
SUMMARY OF THE INVENTION
This object is achieved by water-swellable seal compositions for preformed seals comprising a matrix of elastomer component(s) and embedded particulate water-absorbent material, characterized in that the water-absorbent material is a combination of (A) polysaccharide(s) selected from microcrystalline or amorphous cellulose, starch, starch derivatives except grafted starch, amylose, amylopectin, dextrans, pectins, insulin, chitin, xanthan, alginic acid, aglinates, carragheenan, pustulan, callose, laminarin, guluronic acid, pullulan, lichenin or mixtures thereof with (B) water-superabsorbent synthetic polymer selected from polymers based on (meth)acrylate, poly(meth)acrylic acid and salts thereof, polyacrylamide, polyalcohols or copolymers thereof, and the seal composition is foamed by means of a blowing agent and heating to 100° C. or higher and the elastomer components is (are) crosslinked.
It is also possible to use mixtures of water-superabsorbent synthetic polymers.
The water-swellable seal compositions include 6.67 parts by weight to 600 parts by weight of polysaccharide(s) and 2.67 parts by weight to 100 parts by weight of water-superabsorbent synthetic polymer(s) per 100 parts by weight of elastomer component(s).
The seal compositions of the invention include a blowing agent and are expanded by heating to 100° C. or higher.
After the vulcanizing or crosslinking of rubber(s) to elastomer(s) as elastomer component(s), the seal compositions of the invention will increase in volume by 5-600% by volume on exposure to water for 3 to 7 days.
It is particularly preferable, through appropriate choice of type and fraction of polysaccharide and superabsorbent synthetic polymer, of the porosity, of the crosslinking, of the hardness of rubber and elastomer, to set the swellability, more particularly to construct relatively low-swelling preformed seals having a volume increase of 5-30% by volume, particularly preferably having a volume increase of 10-20% by volume, and/or strongly swelling preformed seals having a volume increase of above 50% by volume to 500% by volume.
The preformed composite or noncomposite seals can be constructed as tapes, round cords, endless profiles with a variety of cross sections.
The composite or noncomposite seals of the invention can be used for sealing constructions in structural, civil or tunnel engineering, industrial engineering, but also in other applications requiring water-swellable seals.
The invention also provides a process for producing preformed seals which swell under the action of water, from seal compositions comprising a matrix of elastomer component(s) and an embedded particulate water-absorbent material which comprises mixing the constituents on mixing rolls, in an internal mixer or extruder and then forming and foaming and crosslinking the elastomer component(s) so that the volume increase on expo

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