Compositions – Compositions containing a single chemical reactant or plural... – Organic reactant
Reexamination Certificate
1999-12-30
2002-11-19
Toomer, Cephia D. (Department: 1714)
Compositions
Compositions containing a single chemical reactant or plural...
Organic reactant
Reexamination Certificate
active
06482333
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of polyaspartic ester mixtures, and more particularly to the use of polyaspartic ester mixtures in polyurea coating applications.
BACKGROUND OF THE INVENTION
Two-component polyurea coating compositions containing a polyisocyanate in combination with a polyaspartic ester component are known. They are suitable for the formation of coatings and can be adjusted to produce coatings that are hard, elastic, abrasion resistant, solvent resistant, and especially weather resistant. Despite their wide-spread use, however, known coating compositions contain disadvantages which limit their use in important applications.
Coating compositions with an appreciable amount of polyaspartic esters with dimethyl groups would be desired because dimethyl groups would add desired properties to coatings made from such compositions. U.S. Pat. No. 5,126,170 discloses a process for making polyurethane coatings in which an isocyanate-reactive component b) includes a polyaspartic ester mixture made from an optionally-substituted maleic or fumaric acid ester and a primary amine. Although the patent teaches that maleic acid or fumaric acid ester can be substituted with dimethyl, diethyl and di-n-butyl esters, it has been observed that during the Michael Addition Reaction of dimethyl maleate and primary amines, dimethyl maleate isomerizes to dimethyl fumarate in the presence of amines, according to the following geometric isomerization reaction:
The dimethyl fumarate forms long needle-like crystals which no longer participate in the Michael Addition Reaction and prevent the reaction from completing. Although the resulting reaction produces yields of only about 30 to 40%, the entire composition is useless for commercial purposes. This is because the composition contains a mixture of compounds that preclude the formation of a suitable coating. The crude mixture generally contains (i) dimethyl fumarate crystals, (ii) starting diamine material, (iii) mono-primary-amine-monoaspartate and (iv) diaspartate. The presence of crystals in such a mixture prevents the formation of a coating. Filtering the crystals from the mixture has not been an option because filtration removes an appreciable amount of starting material, thereby adding substantial costs. Also, a filtrated mixture contains unreacted primary amines whose presence undesirably speed the crosslinking reaction.
U.S. Pat. No. 5,126,170 teaches preparing its polyaspartic esters in a solvent. The use of a 50% methanol reaction medium, however, is not practical in a production situation for the following reasons. First, the use of a 50% solution means that yields of product are half of what could be achieved if the reaction was run without solvent. Second, the methanol is highly flammable and its presence in manufacturing would be a safety hazard. Finally, in order for the polyaspartic ester to be used with polyisocyanates, the methanol would have to be completely removed. Even small, residual amounts of methanol would react with polyisocyanates to form urethanes, which would decrease the crosslink density of the films and so cause a decrease in properties.
For the foregoing reasons, it has been desired to develop a method for making a polyurea coating ingredient that contains an appreciable amount of dimethyl-substituted polyaspartic esters.
SUMMARY OF THE INVENTION
The invention relates to a method for making an asymmetric polyaspartic ester mixture by sequentially (a) forming an ester mixture containing a dimethyl-substituted first ester component and a second ester component substituted with an alkyl group having at least two carbon atoms and (b) reacting the ester component with a propylene oxide amine component, such that the equivalent number ratio of the first ester component and the second ester component is sufficient to prevent the formation of a reaction-stopping crude mixture containing dimethyl fumarate crystals. The invention also relates to a polyurea coating composition containing a polyisocyanate component, the ester component used to make the polyaspartic ester mixture, and the asymmetric polyaspartic ester mixture, a method for making a coating with the polyaspartic ester mixture, and a coating made with the asymmetric polyaspartic ester mixture. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DESCRIPTION OF THE INVENTION
The invention is based on the surprising discovery that the crystallization that has been observed during the reaction of dimethyl-substituted maleic acid or dimethyl-substituted fumaric acid and a propylene oxide amine can be substantially reduced or eliminated altogether by reacting the propylene oxide amine with a mixture containing dimethyl maleate and a small amount of at least one dialkyl maleate having two or more carbon atoms, e.g., diethyl maleate, dipropyl maleate. By practicing the invention, polyaspartic esters based on dimethyl maleate can now be made simply and directly, without crystallization and without the need for solvents. The asymmetric polyaspartic ester mixtures produced can then be used as isocyanate-reactive components in coating compositions for making polyurea coatings having a novel structure and improved properties.
Maleic acid esters and fumaric acid esters include suitable dialkyl maleates or dialkyl fumarates. Suitable dialkyl maleates include dimethyl maleate, diethyl maleate, dipropyl maleate, dibutyl maleate, methyl propyl maleate, ethyl propyl maleate, and the like. Suitable dialkyl fumurates include dimethyl fumurate, diethyl fumurate, dipropyl fumurate, dibutyl fumurate, methyl propyl fumurate, ethyl propyl fumurate, and the like.
The propylene oxide amine component includes any propylene oxide amine that can accomplish the objects of the invention. Suitable polypropylene oxide amines generally include difunctional and multi-functional amines with polypropylene oxide groups. These amines are well known and can be prepared by methods such as those described in German Offenlegungsschrift No.1,193,671, U.S. Pat. No. 3,236,895, French. Pat. No.1,466,708. Suitable examples of such difunctional amines include polypropylene oxide diamine can be obtained from Huntsman Corporation under the marks Jeffamine D-2000. Examples of suitable trifunctional polypropylene oxide amines include polyoxypropylene triamine, (Jeffamine T-403), Jeffamine T-3000 and Jeffamine T-5000, also available from Huntsman. It is believed that multifunctional propylene oxide amines, e.g., tetrafunctional polypropylene oxide amines, can also be used.
The equivalent number ratio of (i) the dimethyl maleates (or the dimethyl fumurates) to (ii) the dialkyl maleates (dialkyl fumurates) that have at least 2 carbon atoms is sufficient to prevent the formation of a reaction-stopping crude mixture containing dimethyl fumarate crystals. I Generally, the equivalent number ratio is from less than about 7:3, preferably from about 5:5 to more than 0:10, more preferably from about 4.5:5.5 to 1:9, and even more preferably from about 4:6 to about 2:8. Stated in a number percentage basis, the amount of the dimethyl-substituted maleic acid ester or fumaric acid ester is present from less than about 70% to more than 0%, preferably less than 50% to more than 0%, preferably from about 45% to about 10%, and even more preferably from about 40 to about 20%, based on the total number of esters. It has been discovered that these following ranges are critical to accomplish the objects of the invention. The equivalent number ratio of the propylene oxide amine component to the ester component is generally about 1:1. As such, the ratio of the first ester component and the second ester component must be greater than 0:10.
The polyisocyanate component used to react with the polyaspartic ester mixtures includes any polyisocyanate, which, when used in accordance with the invention, meets the object of the invention. Suitable polyisocyanates for use as polyisocyanate component in acc
Roesler Richard R.
Squiller Edward P.
Bayer Corporation
Eyl Diderico van
Gil Joseph C.
Roy Thomas W.
Toomer Cephia D.
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