Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-10-04
2004-08-03
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S209000, C523S212000, C524S588000, C524S432000, C524S431000
Reexamination Certificate
active
06770690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to silicone rubber compositions for use in rubber construction materials such as sealants, coatings and gaskets.
2. Prior Art
Synthetic rubber sealants are commonly used to fill concrete joints, joints in window and door sashes, and around the edge of glass panels in buildings and other structures. A variety of such sealants are known, including silicone, polysulfide, polyurethane, acrylic rubber, styrene-butadiene rubber (SBR) and butyl rubber sealants. Of these, condensation-curing silicone sealants are widely used on account of their adhesive properties, heat and weather resistance, and durability. Solid gaskets used in construction are often made of peroxide-vulcanized silicone. In addition, techniques have recently been disclosed for overcoating peroxide-vulcanized silicone gaskets with a UV-curable silicone coating, and for fabricating gaskets integral to glass by placing a mold over the glass, pouring a platinum-catalyzed addition-curing silicone rubber composition into the mold, then curing the composition and bonding it to the glass.
However, one problem associated with the silicone sealants and gaskets used until now in exterior wall joints has been the spread of stains near the joints. This depends to a large extent on the site conditions (external environment, orientation) of the building and the joint design (shape, adhesion substrate), and has generally been found to correlate closely with the degree of air pollution around the building, the manner in which rainwater flows down over the building, and the degree of dryness after a rainfall. Solutions to prevent staining include changing the design of the joint to one which does not come into direct contact with rain, such as a hidden joint or a recessed joint, and using a coating to create a barrier on the surface of the sealant after it has cured or on the surface of the gasket. The former approach entails changes in the design specifications, leaving problems to be resolved with the decorative details of the building, whereas the latter approach requires the addition of a coating operation that increases overall construction costs. For these reasons, neither approach is in common use today.
We earlier disclosed that, when a rubber construction material such as a sealant, coating or gasket is made of the cured form of a silicone rubber composition containing dispersed particles having a photocatalytic activity, such as titanium oxide or zinc oxide, exposure to ultraviolet light modifies the surface, rendering it hydrophilic and non-staining (JP-A 9-227779). Yet, although this method marked a significant improvement in non-staining ability over other prior-art silicone sealants, there exists a need for good shelf stability during product distribution and for better and longer lasting non-staining properties.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide silicone rubber compositions for rubber construction materials which have excellent non-staining properties and outstanding shelf stability.
We have found that, in a silicone rubber composition for use in rubber construction materials which contains dispersed photocatalytically active particles typically made of titanium oxide or zinc oxide, surface-treating the particles with a compound that can easily be deteriorated by the photocatalytic activity under outdoor exposure to ultraviolet light facilitates the removal of moisture without a loss in the activity of the photocatalytically active particles, thus improving the shelf stability of the composition.
We have also discovered that a particularly remarkable degree of improvement in non-staining properties can be achieved by surface treating the photocatalytically active particles together with a non-surface-treated fumed silica having a specific surface of at least 50 m
2
/g, or by also including in the composition an oil-absorbing filler which is not surface treated and has a dioctyl phthalate (DOP) oil absorption of at least 20 ml/100 g.
Accordingly, the invention provides a silicone rubber composition for use in rubber construction materials, which composition contains dispersed particles having a photocatalytic activity. The particles are surface-treated with a compound that can easily be deteriorated by the photocatalytic activity upon outdoor exposure to ultraviolet light.
DETAILED DESCRIPTION OF THE INVENTION
The silicone composition of the invention typically contains a diorganopolysiloxane as the base polymer, and may be cured by any suitable mechanism. Examples include compositions vulcanized using a known organic peroxide, condensation-curing compositions, platinum-catalyzed addition-curing compositions and radiation-curable compositions.
The diorganopolysiloxane used in the silicone composition is preferably one having the average compositional formula R
a
SiO
(4-a)/2
. In the formula, each R group is independently a substituted or unsubstituted C
1-12
, and preferably C
1-10
, monovalent hydrocarbon group selected from among alkyl groups (e.g., methyl, ethyl, propyl, butyl, 2-ethylbutyl, octyl), cycloalkyl groups (e.g., cyclohexyl, cyclopentyl), alkenyl groups (e.g., vinyl, hexenyl, allyl), aryl groups (e.g., phenyl, tolyl, xylyl, naphthyl, diphenyl) aralkyl groups (e.g., benzyl, phenylethyl), any of the foregoing groups in which some or all of the hydrogens bonded to the carbons have been substituted (such as with halogen atoms or cyano), or groups substituted with or containing, for example, amino groups, ether groups (—O—), carbonyl groups (—CO—), carboxyl groups (—COOH) or sulfonyl groups (—SO
2
—) (e.g., chloromethyl, trifluoropropyl, 2-cyanoethyl, 3-cyanopropyl). The letter a in the above formula is from 1.90 to 2.05.
If the silicone rubber composition is a condensation-curing composition, a diorganopolysiloxane in which both ends of the molecular chain are capped with hydroxyl or organooxy groups is used as the base polymer of the composition. A composition that provides a cured product having good rubber properties and an excellent mechanical strength may be advantageously achieved by the use of a diorganopolysiloxane having a viscosity at 25° C. of at least 25 cs, and preferably from 100 to 1,000,000 cs.
A silane or siloxane compound having at least two hydrolyzable groups per molecule is typically used as the crosslinking agent for the diorganopolysiloxane. Illustrative examples of the hydrolyzable groups include alkoxy groups (e.g., methoxy, ethoxy, butoxy), ketoxime groups (e.g., dimethyl ketoxime groups, methyl ethyl ketoxime groups), acyloxy groups (e.g., acetoxy), alkenyloxy groups (e.g., isopropenyloxy, isobutenyloxy), amino groups (e.g., N-butylamino, N,N-diethylamino), and amide groups (N-methylacetamide groups). The crosslinking agent is typically included in an amount of 2 to 50 parts, and preferably 5 to 20 parts, per 100 parts of the diorganopolysiloxane capped at both ends with hydroxyl or organoxy groups. Unless noted otherwise, all parts here and below are by weight.
A curing catalyst is typically used in the above condensation-curing silicone rubber composition. Illustrative examples of suitable curing catalysts include alkyltin ester compounds such as dibutyltin diacetate, dibutyltin dilaurate and dibutyltin dioctoate; titanic acid ester or titanium chelate compounds such as tetraisopropoxytitanium, tetra-n-butoxytitanium, tetrakis(2-ethylhexoxy)titanium, dipropoxybis(acetyl-acetonato)titanium and titanium isopropoxyoctylene glycol; organometallic compounds such as zinc naphthenate, zinc stearate, zinc 2-ethyloctoate, iron 2-ethylhexoate, cobalt 2-ethylhexoate, manganese 2-ethylhexoate, cobalt naphthenate and alkoxyaluminum compounds; aminoalkyl-substituted alkoxysilanes such as 3-aminopropyltriethoxysilane and N-&bgr;(aminoethyl)-&ggr;-aminopropyltrimethoxysilane; amine compounds and their salts, such as hexylamine and dodecylamine phosphate; quaternary ammonium salts such as benzyltriethylammonium acetate; lower fatty acid salts of alkali metals, s
Araki Tadashi
Fujiki Hironao
Kimura Tsuneo
Birch Stewart Kolasch & Birch, LLP.
Moore Margaret G.
Shin-Etsu Chemical Co. , Ltd.
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