Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2002-03-27
2004-05-04
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C427S385500, C525S123000, C525S409000, C525S440030, C528S045000, C528S067000, C528S073000
Reexamination Certificate
active
06730405
ABSTRACT:
The invention relates to an optionally masked polyisocyanate composition of relatively low viscosity having a high mean functionality of at least 3 or more.
The invention also relates to a process for the preparation of a polyisocyanate composition of low viscosity having a high mean functionality in isocyanate groups.
The invention additionally relates to crosslinkable coating compositions, in particular to a polyurethane coating composition, of use in particular in the field of automotive finishing.
Masked or nonmasked polyisocyanate compositions having a mean functionality of greater than 2 are generally obtained by catalytic cyclotrimerization of diisocyanates and comprise compounds comprising isocyanurate groups.
Such compositions and processes for their preparation are disclosed in, for example, U.S. Pat. No. 4,324,879 and U.S. Pat. No. 4,412,073. Although these compositions have noteworthy properties, they have, however, a high viscosity which requires that they be diluted with organic solvents.
One of the solutions recommended for this purpose is to halt the cyclotrimerization reaction at a very low degree of trimerization in order to increase the amount of monoisocyanurate polyisocyanates and to reduce the amount of isocyanurate polyisocyanates having more than one isocyanurate ring.
Thus, patent U.S. Pat. No. 4,801,663 discloses a process for the cyclotrimerization of 1,6-hexamethylene diisocyanate (HDI) in which the trimerization is halted at a low degree of conversion.
The disadvantage of such a process is, however, a significant decrease in the overall yield of the reaction, which requires the removal from the final reaction product of a significant amount of unreacted monomers, the effect of which is to greatly increase the cost of the process.
Another solution provided consists in subjecting the isocyanate monomers to a cyclodimerization reaction before, after or during the cyclotrimerization stage, in order to result in a polyisocyanate composition having isocyanate compounds comprising isocyanurate groups and isocyanate compounds comprising uretidinedione (1,3-diazetidine-2,4-dione) groups, in particular monouretidinedione compounds.
The disadvantage of this process is, however, a reduction in the mean functionality with regard to NCO groups of the reaction product, due to a greater or lesser proportion of uretidinedione compounds.
Another solution recommended in U.S. Pat. No. 4,810,820 consists in adding an alcohol to the reaction mixture before, after or during the trimerization reaction, in order to obtain a polyisocyanate mixture comprising isocyanurate groups and allophanate groups.
However, as above, the disadvantage of this method lies in a decrease in the functionality of the final polyisocyanate composition, in particular due to the presence of “true” allophanates, compounds composed of two monomer chains of isocyanates and of an allophanate functional group, the functionality of which is 2 in the case of diisocyanates, or of polyallophanates.
Such polyisocyanate compositions with high functionality and with low viscosity can be of use in the formation of coating, for example of polyurethane type, in particular in the automobile industry.
Generally, the original finish on a motor vehicle consists of several coating layers. Usually, the first layer is zinc phosphate or iron phosphate, to prevent corrosion. The second layer is a primer deposited electrostatically, in order to obtain a better appearance and to improve the adhesion, a base coating or a coating colored with pigments being applied to this second layer in order to protect the quality of the finishing on the panel. Coatings based on acrylic polyol are particularly useful as final coating to give a solid and lasting finish.
Motor vehicle finishing coatings are used in the motor vehicle after-sales service, for example as forming part of repair processes for reproducing the appearance and the durability of the original finishes of motor vehicles. However, the process for the application of the repair finishing coating is different from that for the original finishing coating. In the original manufacturing process, the body of the motor vehicle can be coated and crosslinked at high temperature. In contrast, the repair finishing does not make possible crosslinking temperatures of greater than 80° C., since some parts of the motor vehicle itself, such as the tires, cannot withstand a higher temperature. This is why repair finishing coatings are usually formulated so as to be able to crosslink at ambient temperature.
There is an ongoing interest in the fact of reducing the drying time at ambient temperature of motor vehicle repair finishing coatings based on acrylic polyol, in order to reduce the adhesion of dust to the surface of the paint and to increase production, without compromising the desired characteristics of these coatings, for example the hardness, the durability and the appearance.
Numerous efforts have been made to increase the rate of drying by adjusting the acrylic polyol component (see, for example, U.S. Pat. No. 5,759,631 and U.S. Pat. No. 4,758,625). Generally, the decrease in the surface drying results from the increase [lacuna] the glass transition temperature (T
g
) of the polyol (see, for example, U.S. Pat. No. 5,279,862 and U.S. Pat. No. 5,314,953). However, a high T
g
can produce harmful effects on the properties of the coating, such as greater brittleness.
Another means of increasing the rate of drying is to adjust the isocyanate component. Isocyanurate oligomers derived from 1,6-hexamethylene diisocyanate (HDI) are often used, because of their high reactivity, as crosslinking agents for motor vehicle repair finishes based on acrylic polyol. To increase the rate of surface drying, other oligomers, usually trimers, of isophorone diisocyanate (IPDI) can be incorporated in the formulation. By virtue of the higher glass transition temperatures for the IPDI oligomers than for the HDI isocyanurates, the surface hardness develops faster than that of the compositions not comprising IPDI oligomers and, consequently, the apparent rate of drying is higher. However, as the reactivity of the IPDI oligomers is lower than that of the HDI oligomers, the core drying (correlated with the rate of crosslinking of the body of the material) is lower for a composition comprising an IPDI oligomer.
There therefore exists a need to provide polyurethane coating compositions, in particular aliphatic polyurethane coating compositions, which exhibit surface drying, and core drying, at ambient temperature, which is rapid, without, however, compromising the desired properties of a coating composition, such as, for example, a long pot life, or alternatively the desired properties of the crosslinked coating originating from the coating composition, such as, for example, the properties of hardness, of flexibility and of surface impact of the coating.
Thus, one aim of the present invention is to provide an optionally masked polyisocyanate composition of reduced viscosity having a high functionality of at least 3, preferably of greater than 3, in the case where it is obtained by polycondensation of diisocyanates, and an even higher functionality in the case of triisocyanates.
Another aim of the present invention is to provide an optionally masked polyisocyanate composition of reduced viscosity having a reduced content of monouretidinedione polyisocyanates, this content advantageously being less than 5% by weight, with respect to the weight of the isocyanates of the polyisocyanate composition.
Yet another aim of the present invention is to provide an optionally masked polyisocyanate composition of reduced viscosity having a reduced content of polyisocyanates comprising isocyanurate groups, in particular monoisocyanurate compounds, this content advantageously being not greater than 45%, preferably not greater than 40%, by weight, with respect to the weight of the isocyanates of the polyisocyanate composition.
Yet another aim consists in providing a polyurethane coating composition with rapid drying
Bernard Jean-Marie
Chen Ming J.
Han Qiwen
Rhodia Chimie
Short Patricia A.
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