Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2001-01-11
2002-10-08
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S447000, C428S448000, C428S450000, C106S287100, C524S801000, C524S806000, C524S849000, C524S588000
Reexamination Certificate
active
06461735
ABSTRACT:
This invention relates to a coated article comprising substrate, an undercoat and an overcoat sequentially applied onto the substrate, and more particularly, to such a coated article which exhibits a high degree of weather and water resistance sufficient to withstand long-term outdoor exposure, due to a firm bond between the overcoat and the undercoat.
BACKGROUND OF THE INVENTION
From the standpoints of currently much concerned environmental pollution and safe working environment, a need exists in the paint and coating fields to replace organic solvent systems by aqueous systems.
To meet such a demand, emulsion systems resulting from emulsion polymerization of radical-polymerizable vinyl monomers, as typified by acrylic resin systems, are now widely used as the base of coating compositions because of their good film-forming ability and chemical resistance. However, coating compositions of this type essentially lack water resistance and weather resistance.
On the other hand, silicone resins resulting from hydrolytic condensation of silane compounds now draw attention as coating compositions since they are able to form coatings having good physical and chemical properties including a high hardness, weather resistance, water resistance, chemical resistance, heat resistance and water repellency. However, the silicone resins are poor in film-forming ability, alkali resistance and film flexibility and lack storage stability on account of silanol groups having high condensation activity. Additionally, the silicone resins are generally used as solutions in organic solvents, which involve fire and explosion hazards, toxicity to humans, and environmental pollution. A need exists to develop emulsion type compositions.
In order to overcome the above-mentioned drawbacks, U.S. Pat. No. 5,973,068, U.S. Pat. No. 6,114,400 and JP-A 11-130962 disclose coating compositions based on composite emulsions in which a silicone resin is incorporated into an acrylic resin. These compositions form coating possessing both the advantages of silicone and acrylic resins, and especially markedly improved weather resistance. These coatings are thus suitable as topcoats on outdoor buildings, structures and articles which are exposed to sunlight and weather and thus required to have long-term durability.
In such applications subject to long-term outdoor weathering, however, the weather resistance of the coating itself is insufficient and its adhesion to the substrate and undercoat layer, if any, is requisite. The above silicone/acrylic composite resin emulsion coatings have good adhesion to glass, metals and similar materials due to the inclusion of silanol groups or polar groups in the silicone resin, however their adhesion to plastics, organic resins and porous inorganic substrates such as slates is not necessarily satisfactory.
From the past, epoxy base primers have been used in order to improve the adhesion of coatings to substrates. Where the primers are applied to porous brittle surfaces such as those of autoclaved light-weight concrete (ALC) substrates, the coatings are prone to cracking.
Meanwhile, the silicone/acrylic composite resins rich in siloxane component serving as the overcoating agent have coating physical properties largely differing from conventional well-known topcoat resins such as vinyl polymers having hydrolyzable silyl groups on side chains (typically having a silicon content of less than 10%) and essentially fail to establish a firm bond to the underlying substrate.
SUMMARY OF THE INVENTION
An object of the invention is to provide a coated article having improved adhesion between an undercoat layer and an overcoat layer and a high degree of weather and water resistance sufficient to withstand long-term outdoor exposure.
It has been found that by subsequently applying an undercoat agent of a composition (I) having hydrolyzable silyl groups and an overcoat agent of a composition (II) having more silanol groups onto a substrate, a drastically enhanced adhesion is established between the undercoat and the overcoat because silanol groups resulting from hydrolysis of the hydrolyzable silyl groups in composition (I) form siloxane bonds with silanol groups in the composition (II). The coated substrate thus exhibits a high degree of weather resistance and water resistance sufficient to withstand long-term outdoor exposure as well as good coating properties such as heat resistance, water repellency, film-forming ability, mar resistance, and chemical resistance.
The invention provides a coated article comprising a substrate, an undercoat and an overcoat sequentially applied onto the substrate. The undercoat is formed of a composition (I) comprising a compound having a hydrolyzable group-bearing silyl group represented by SiX
3−a
and/or a partial hydrolyzate thereof, wherein X is a hydrolyzable group and “a” is equal to 0, 1 or 2. The overcoat is formed primarily of a silicone resin-containing emulsion composition (II) comprising a silicone resin-containing emulsion (A). The silicone resin-containing emulsion (A) results from emulsion polymerization of a mixed solution containing (A-1) 100 parts by weight of a silanol group-bearing silicone resin comprising 30 to 100 mol % of structural units (T units) represented by the formula: R
1
—SiZ
3
, and based on the entire T units, 30 to 80 mol % of structural units (T-2 units) containing only one silanol group represented by the general formula: R
1
—Si(OH)Z′
2
, the silicone resin having a number average molecular weight of at least 500, and (A-2) 10 to 1,000 parts by weight of a radical-polymerizable vinyl monomer. Herein R
1
is a substituted or unsubstituted monovalent hydrocarbon group, Z is a hydroxyl group, hydrolyzable group or siloxane residue, at least one of the Z groups being a siloxane residue, and Z′ is a siloxane residue.
As a first feature, the coated article has a topcoat or overcoat formed of a silicone/acrylic emulsion composition having the following advantages. (i) In emulsion particles, the silicone resin forms an interpenetrating polymer network (IPN) with the acrylic resin so that both the resins may complement their shortcomings. The emulsion has a good film-forming ability and provides a uniform cured coating having satisfactory properties including mar resistance, weather resistance, and chemical resistance. (ii) In emulsion particles, polymers are intertwined in a solventless state, restricting the freedom of silanol groups which have rich condensation activity. As a consequence, condensation of silanol groups is suppressed even in systems having a high content of silanol groups, contributing to storage stability. Since the silicone resin used are water insoluble, the silicone resin is completely incorporated in particles, so that a satisfactory level of stability is maintained. (iii) Since silanol groups are restrained within emulsion particles, they retain high crosslinking or curing activity until curing, achieving effective cure even at relatively low temperatures. (iv) Because of the substantial absence of solvent, a dry and fully cured coating is obtained. A sound working environment is insured since the volatilization of harmful solvent is eliminated. The emulsion is kept fully stable since it is free of an alcohol component that promotes demulsification.
As a second feature, the coated article has an undercoat of the specific composition having the following advantage below the overcoat of the silicone/acrylic emulsion composition. (v) In the event of substrates having less active groups contributing to adhesion on the surface such as stainless steel and plastics, and porous substrates allowing water to penetrate therethrough such as slates, the interposition of the undercoat layer containing hydrolyzable silyl groups prevents swelling upon immersion in hot water, achieving a significant improvement in adhesion to the substrates.
The coated article, in which the undercoat composition cooperates with the overcoat composition to dramatically improve the adhesion between the undercoat and the overcoat,
Furuya Masahiro
Iwasaki Satoshi
Yamamoto Akira
Yamaya Masaaki
Yoshikawa Yuji
Dawson Robert
Feely Michael J.
Shin-Etsu Chemical Co. , Ltd.
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