Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1998-01-22
2003-04-08
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C427S385500, C428S422800, C428S423100
Reexamination Certificate
active
06545117
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new coating composition based on an oxazolidine functional compound, an isocyanate functional compound, and a compound selected from a mercapto and a sulfonic acid functional compound.
BACKGROUND OF THE INVENTION
Coatings used for painting motor vehicles and repairing the original paint are required to have good physical properties such as hardness, mechanical strength, and resistance to water, acids, and solvents. The coatings are also required to have good appearance properties, which means that films must be smooth and have a high gloss and high distinctness of image (DOI). It is also desirable that all properties be retained under prolonged outdoor weathering.
For environmental reasons, it is required to use a coating composition which can be applied easily using spray application at a low volatile organic content (VOC). Coatings with a lower organic solvent content emit lower levels of solvent when they are used and so the atmosphere becomes less polluted.
One way to achieve a lower solvent content is to use so-called high-solids compositions. Such compositions comprise a relatively high level of non-volatile materials, such as film forming polymer, pigments and fillers, and a relatively low level of organic solvent. A problem when formulating high-solids coating compositions is that such compositions have an unacceptably high viscosity due to the high molecular weight of the conventional film forming polymer. The high viscosity gives rise to problems in spray application with poor paint atomization and poor flow-out and, consequently, low gloss levels and poor appearance.
The use of low-molecular weight film forming polymers, which results in adequate application viscosities, has as a disadvantage that the resulting coating is soft and marks easily. The hardness build-up of the coating is therefore unacceptable.
Another way to reduce the amount of volatile organic compounds in coating compositions is the use of reactive diluents. Examples of reactive diluents include aldimines and ketimines. In EP-A-0 686 654 such compounds are discussed. Other reactive diluents, such as oxazolidines, are mentioned but it is stated that they have limited utility as a sole reaction partner with isocyanate because of generally slow setting film properties.
Aldimines are used as reactive diluents for low VOC paint systems. These diluents are commercially available and use of such aldimines is referred to in U.S. Pat. No. 5,214,086 and EP-A-0 686 654. In general these reactive diluents offer good cure and hardness development. However, they are known to cause skin irritation and to cause adhesion failure when applied in low VOC clearcoats.
Bicyclic oxazolidines are also used as reactive diluents for low VOC paint systems. These diluents are commercially available and use of such bicyclic oxazolidines are referred to in WO 95/14528. In general, these reactive diluents offer good durability and color stability and low toxicity. However, compositions based on bicyclic oxazolidines may exhibit an unacceptably long time to cure.
Monocyclic oxazolidines are also used as reactive diluents for low VOC paint systems. Coating compositions based on monocyclic oxazolidines are also referred to in EP 0 499 188 A1. Monocyclic oxazolidines and dimers of the same are commercially available. Coating compositions based on monocyclic oxazolidines may exhibit a loss of adhesion over time.
While the use of mono- or bi-cyclic oxazolidines has been described (see, e.g., U.S. Pat. No. 5,126,421), nowhere is there described the use of both monocyclic and bicyclic oxazolidines. WO 92/13907 refers to the use of monocyclic and bicyclic oxazolidines (page 7, lines 20-21), but this reference relates to the use of these compounds in the alternative and does not disclose a mixture of the two oxazolidines.
U.S. Pat. No. 5,506,328 refers to a two-component system with side A being an aliphatic polyisocyanate and side B being a tertiary amine catalyst and optionally an isocyanate-reactive compound selected from the group consisting of monoahls, polyols, imines, oxazolidines, or combinations thereof. The monoahl can be an -SH compound. The examples show only alcohols as monoahls. It has not been recognized by this disclosure that the combination of an oxazolidine functional compound, an isocyanate functional compound, and a mercapto functional compound shows improved and unexpected results over the use of the combination of an oxazolidine functional compound and an isocyanate functional compound alone.
Surprisingly, it was found that the addition of a mercapto functional compound to a coating composition comprising an oxazolidine functional compound and an isocyanate functional compound results in an increased potlife while maintaining the drying characteristics of the composition or results in increased drying rate while maintaining acceptable potlife.
It was also found that the addition of a sulfonic acid functional compound to a coating composition comprising an oxazolidine functional compound and an isocyanate functional compound results in improved curing characteristics of the coating composition, even at low relative humidity (e.g., 30% and below), without loss of potlife and, in some cases, with increased potlife.
It was also found that the use of mixtures of bicyclic and monocyclic oxazolidines as reactive diluents in low VOC coatings provide properties that can compete with those of imines, but without loss of adhesion.
A lower VOC at the same viscosity and a higher pot life/drying balance is obtained when using coating compositions of the present invention while other paint properties remain on the same level.
SUMMARY OF THE INVENTION
The present invention relates to a coating composition comprising:
(a) at least one oxazolidine functional compound,
(b) at least one isocyanate functional compound, and
(c) at least one compound selected from the group consisting of a mercapto functional compound, a sulfonic acid functional compound, and mixtures thereof.
Component (a) comprises at least one oxazolidine functional compound which may be a monocyclic oxazolidine functional compound, a bicyclic oxazolidine functional compound, and, preferably, mixtures thereof.
Component (b) comprises at least one isocyanate functional compound which may be an isocyanurate, a uretdione, a biuret, an allophonate, an adduct, a NCO prepolymer, or mixtures thereof.
Component (c) may be a mercapto functional compound, preferably a mercapto functional silane, most preferably &ggr;-mercapto-propyl-trimethoxysilane. Component (c) may also be a sulfonic acid functional compound, preferable p-toluene sulfonic acid or dodecyl benzene sulfonic acid. Component (c) more preferably comprises a mixture of mercapto and sulfonic acid functional compounds, most preferably a mixture of &ggr;-mercapto-propyl-trimethoxysilane and p-toluene sulfonic acid.
The composition may also further comprise:
(d) a resin comprising a functional group selected from hydroxyl and amine.
The invention further relates to a method of coating a substrate with the coating composition and to a substrate coated with the coating composition.
DETAILED DESCRIPTION OF THE INVENTION
Component (a) comprises at least one oxazolidine functional compound. Preferably, the oxazolidine functional compound has the formula:
wherein
x and y are independently selected from 0 to 10, with the proviso that x and y cannot both be 0;
n is selected from the integers 2 or 3;
m and p are independently selected from the integers 1 or 2;
R
1
, R
2
, R
3
, R
4
, R
5
and R
6
may be the same or different and are selected from the group of hydrogen, linear or branched (cyclo)alkyl, and linear or branched aryl, optionally substituted;
R
1
and R
2
, R
3
and R
4
, and R
5
and R
6
may be joined together to form a 5 or 6 carbon ring with the attached carbon atom of the ring in the formula, i.e. R
1
and R
2
, R
3
and R
4
, and R
5
and R
6
collectively represent a tetramethylene or a pentamethylene group; and
R
7
is a mono- or multivalent aliphatic
Crutchfield Traci Lynne
Ernst Moos Jan Wilhelm
Gerardus van Engelen Antonius Hendrikus
Weaver Jason Donald
Akzo Noble N.V.
Gorr Rachel
McGillycuddy Joan M.
Morris Louis A.
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