Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-09-08
2001-09-25
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S100000, C525S101000, C525S123000, C525S125000, C525S127000, C525S154000, C525S155000, C525S157000, C525S455000
Reexamination Certificate
active
06294607
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an acrylic coating composition. More particularly, the invention relates to an ultra-high-solids acrylic coating composition derived from a polyol blend that comprises a liquid acrylic polyol and a resinous polyol having a T
g
greater than 25 ° C.
BACKGROUND OF THE INVENTION
Hydroxy-functional acrylic resins have been widely and increasingly used in high performance coatings, particularly in automotive topcoats, due to their excellent durability and outstanding physical properties. They are usually crosslinked with a multifunctional isocyanate or a melamine to form acrylic-urethane or acrylic-melamine coatings.
Hydroxy-functional acrylic resins are usually copolymers of a hydroxyalkyl acrylate or methacrylate and one or more ordinary alkyl acrylates or methacrylates. Commonly used hydroxyalkyl acrylates and methacrylates include hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxyethyl methacrylate (HEMA), and hydroxypropyl methacrylate (HPMA).
Usually, a combination of two types of ordinary alkyl acrylates and methacrylates are used to achieve optimal resin properties. The first type are acrylates and methacrylates whose homopolymers have low glass transition temperatures (T
g
below 25° C.), e.g., n-butyl acrylate (T
g
: −54° C.), n-butyl methacrylate (T
g
: 20° C.), and 2-ethylhexyl methacrylate (T
g
: −10° C.). The second type includes acrylates and methacrylates whose homopolymers have high T
g
s (greater than 50° C.), such as methyl methacrylate (T
g
: 100° C.). Styrene is also often incorporated into acrylic resins as a high T
g
monomer (T
g
: 99° C.). High T
g
monomers increase the coating's gloss and hardness, while low T
g
monomers impart toughness and flexibility.
In general, high-solids acrylic resins have a hydroxyl number from 60 to 160 mg KOH/g, and a number average molecular weight (Mn) from 1,000 to 5,000. Lowering the molecular weight of the hydroxy-functional acrylic resin can reduce its solution viscosity. This is desireable because it reduces the amount of solvent required to make the coatings sprayable. Solvents are regulated as volatile organic compounds (VOCs) by the U.S. EPA and most coatings have VOC content limits imposed on them. However, the molecular weight reduction must be compensated by an increase in resin hydroxyl number to maintain the coating performance. The increased hydroxyl number increases hydrogen bonding within the resin which increases viscosity. The current solids level of sprayable acrylic-urethane or acrylic-melamine coatings is about 50% to 55% by weight.
Newly developed hydroxyl acrylic resins from allylic alcohols have significantly reduced viscosity, and their melamine and urethane coatings can achieve about 60% solids (see, e.g., U.S. Pat. No. 5,646,213). However, ultra-high-solids (65%-70%) acrylic-urethane and acrylic-melamine coatings are needed.
SUMMARY OF THE INVENTION
The invention is an ultra-high-solids coating composition. The coating is formulated from a polyol blend that comprises a liquid acrylic polyol and a resinous polyol. The liquid polyol has Mn within the range of about 500 to about 10,000, hydroxyl number within the range of about 20 mg KOH/g to about 500 mg KOH/g, and T
g
within the range of about −70° C. to about 0° C. The resinous polyol has Mn within the range of about 500 to about 10,000, hydroxyl number within the range of about 20 mg KOH/g to about 500 mg KOH/g, and T
g
greater than about 25° C. The ultra-high-solids coating also includes a crosslinker selected from multifunctional isocyanates, melamines, and silanes. It uses less than about 35% by weight of an organic solvent, i.e., greater than about 65% by weight of solids at a viscosity of about 95 centistokes at 25° C.
The invention includes an A-B two-component ultra-high-solids acrylic-urethane coating. Component A comprises a blend of a liquid acrylic polyol and a resinous polyol as described above. Component B comprises a multifunctional isocyanate selected from 1,6-hexamethylene diisocyanate (HDI), polymeric HDIs, isophorone diisocyanate (IPDI), polymeric IPDIs, and HDI- or IPDI-based isocyanate-terminated prepolymers of polyethers, polyesters, or acrylic resins. The ratio of OH equivalent in Component A/NCO equivalent in Component B is within the range of 0.8 to 1.2, and the solids % of the combination of Components A and B is greater than about 65% by weight at a viscosity of about 95 centistokes at 25° C.
The invention also includes an ultra-high solids acrylic-melamine coating. The coating comprises a blend of liquid acrylic polyol and a resinous polyol as described above, a melamine crosslinker, and an organic solvent. The ratio of the polyol blend/melamine is within the range of 1/1 to 15/1 by weight. The coating has a solids % greater than about 65% by weight at a viscosity of about 95 centistokes at 25° C.
We have surprisingly found that the coating compositions of the invention have a significantly higher solids % at the same viscosity than that of coatings formulated from a single resin whose composition and molecular weight are similar to the polyol blend.
DETAILED DESCRIPTION OF THE INVENTION
Ultra-high-solids acrylic coatings of the invention comprise a polyol blend, a crosslinker, an organic solvent, and an optional crosslinking catalyst.
The polyol blend comprises a liquid acrylic polyol and a resinous polyol. The liquid acrylic polyol has a number average molecular weight (Mn) within the range of about 500 to about 10,000, a hydroxyl number about 20 mg KOH/g to about 500 mg KOH/g, and a glass transition temperature (T
g
) about −70° C. to 0 ° C. The liquid acrylic polyol preferably comprises recurring units of a hydroxyl functional monomer. The hydroxyl functional monomer is used in an amount sufficient to give the polyol the desired hydroxyl number. It is preferably used in an amount within the range of about 2% to about 60% by weight of the liquid polyol.
The hydroxyl functional monomer is preferably selected from allylic alcohols, alkoxylated allylic alcohols, hydroxyalkyl acrylates and methacrylates, and the like, and mixtures thereof. Examples include allyl alcohol, methallyl alcohol, propoxylated allyl alcohol, ethoxylated allyl alcohol, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. Allylic alcohols, alkoxylated allylic alcohols, and hydroxyalkyl acrylates are preferred because they offer the liquid polyol lower T
g
than hydroxyalkyl methacrylates. Lowering T
g
usually reduces viscosity of the liquid polyol. Monomers having a secondary OH group such as propoxylated allylic alcohols are also preferred. These monomers contribute low viscosity to the liquid polyol compared to those having primary OH group due to weak hydrogen bonding. Secondary hydroxyl functionality is also preferred in ultra-high-solids systems because it slows the curing rate and extends pot life. Allyl alcohol monopropoxylate is most preferred due to its secondary OH functionality and the low T
g
of its homopolymer. A mixture of secondary and primary OH monomers may be used to achieve low viscosity, acceptable pot life, and fast drying of the coating.
The liquid acrylic polyol preferably comprises also recurring units of one or more C
1
to C
20
alkyl acrylates or methacrylates whose homopolymers have a T
g
below 25° C. It is important to select an acrylate or methacrylate that has low homopolymer T
g
because otherwise the liquid polyol would have a high T
g
and would not stay liquid at room temperature. Examples of suitable commercial alkyl acrylates and methacrylates include n-butyl acrylate, n-butyl methacrylate, lauryl acrylate, lauryl methacrylate, tridecyl acrylate, tridecyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and the like, and mixtures thereof. The proportion of recurring units of C
1
to C
20
alkyl acrylates or methacrylates in the liquid acrylic polyol depends on many factors, but most important among these are the desired hydroxyl number and T
Guo Shao-Hua
Pourreau Daniel B.
Wang Wei
Arco Chemical Technology L.P.
Guo Shao
Niland Patrick D.
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