Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-11-09
2002-12-03
Cooney, Jr., John M. (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C252S182200, C548S951000, C548S952000, C560S027000, C560S334000, C560S336000, C560S359000
Reexamination Certificate
active
06489503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a liquid methylene bis(phenylisocyanate) composition having improved storage stability.
2. Description of Prior Art
Polyisocyanate compositions including a high concentration of methylene bis(phenylisocyanate) (“MDI”), particularly 4,4′-methylene bis(phenylisocyanate) (“4,4′-MDI”), while useful for various cellular and non-cellular polyurethane applications often pose a processing problem in that they are normally a solid at room temperature, i.e., about 25° C. The material, therefore, has to be melted and maintained in order to be useful as a liquid.
Unfortunately, methylene bis(phenylisocyanate) compositions having relatively high levels of 4,4′-MDI are also known to have a limited life due to the formation of diphenylmethane uretdione, otherwise referred to herein as uretdione. Uretdione tends to couple with the 4,4′-MDI molecules contained in methylene bis(phenylisocyanate) compositions, thereby forming a substantially insoluble precipitate over time. For example, 4,4′-MDI compositions maintained at about 43° C. for 14 days have exhibited uretdione concentrations above the generally acceptable saturation concentration of 0.5%. The formation of high concentrations of uretdione have heretofore rendered the methylene bis(phenylisocyanate) compositions substantially useless.
Interestingly, the uretdione reaction is both temperature and phase dependent. For example, as the temperature of a 4,4′-MDI composition is increased above about 43° C., the rate of uretdione formation increases. Further, the rate of uretdione formation is accelerated when the methylene bis(phenylisocyanate) is in the solid state as compared to a liquid composition at 43° C.; such formation being generally attributed to the alignment of the isocyanate groups in the crystal lattice structure.
In an effort to limit the formation of uretdione, methylene bis(phenylisocyanate) compositions, particularly 4,4′-MDI compositions, are often frozen and stored at temperatures below about 0° C. While this temporarily retards the formation of uretdione dimer, refrigerating the compositions for extended periods of time prior to use can be expensive and introduces logistic considerations which must be addressed.
It is, therefore, an object of the present invention to provide a liquid methylene bis(phenylisocyanate) composition which is storage stable at temperatures above about 30° C.
It is a further object of the invention to provide a liquid methylene bis(phenylisocyanate) composition which increases the saturation concentration of uretdione.
It is another object of the present invention to provide a methylene bis(phenylisocyanate) having a reduced freezing point.
It is still another object of the present invention to provide a liquid methylene bis(phenylisocyanate) composition which can be used in the preparation of all types of polyurethanes for which pure MDI is currently employed.
In view of the foregoing, the development of a liquid storage stable methylene bis(phenylisocyanate) composition including a high concentration of 4,4′-MDI that could be shipped in bulk, thereby reducing the high costs associated with shipping frozen drummed compositions would be highly desirable.
SUMMARY OF THE INVENTION
The foregoing objects, among others, are achieved by the methylene bis(phenylisocyanate) compositions of the present invention comprising a mixture of a) a methylene bis(phenylisocyanate) component including at least about 90.0 weight percent 4,4′-MDI; and b) an uretonimine. Under preferred embodiments, the uretonimine will be present in positive amounts of less than about 5.0 weight percent, based on the weight of the methylene bis(phenylisocyanate) composition. More preferably the uretonimine is present in amounts ranging from about 0.1 to less than about 5.0 parts per 100.0 parts of methylene bis(phenylisocyanate) composition, with amounts ranging from about 0.25 parts to about 2.5 parts being highly preferred. As will be described in greater detail below, a catalyst may be employed to cause the formation of uretonimine in situ. The amount of catalyst will generally range from about 0.0001 to about 5.0 parts, preferably about 0.0002 to about 2.5 parts, per 100.0 of methylene bis(phenylisocyanate).
The invention also provides a method of preparing storage stable liquid methylene bis(phenylisocyanate) compositions by admixing a methylene bis(phenylisocyanate) component including at least about 90.0 weight percent 4,4′MDI with an uretonimine to form a liquid methylene bis(phenylisocyanate) composition which is storage stable at temperatures as low as about 30° C.
Another method of the present invention relates to the in situ formation of uretonimine in liquid methylene bis(phenylisocyanate) composition including at least about 90.0 weight percent 4,4′-MDI.
DETAILED DESCRIPTION OF THE INVENTION
The methylene bis(phenylisocyanate) composition of the present invention comprises a) a methylene bis(phenylisocyanate) component including at least about 90.0 weight percent 4,4′-MDI; and b) an uretonimine.
The methylene bis(phenylisocyanate) component a) which includes at least about 90.0 weight percent 4,4′-MDI, more preferably will include at least about 95.0 weight percent 4,4′-MDI and under a highly preferred embodiment will include at least about 98.0 weight percent 4,4′-MDI. Generally, in addition to the 4,4′-MDI, the component a) may include 2,4′-MDI; 2,2′-MDI and other isomers, the 2,4′-MDI isomer being the predominant specie therein. The 2,4′-MDI isomer (and other MDI isomers) may make up the balance of the component a). Preferably, however, these isomers are limited to relatively low levels, i.e., about 2% or less by weight of component a).
The amount of methylene bis(phenylisocyanate) component a) in the composition of the present invention may be as low as about 80 weight percent, based on the total weight of the methylene bis(phenylisocyanate) composition. However, compositions of the present invention preferably comprise at least about 90.0 weight percent, more preferably at least about 95 weight percent, most preferably at least about 99 weight percent, of the methylene bis(phenylisocyanate) component.
In another aspect of the present invention, the source of uretonimine to the composition may contribute additional amounts of methylene bis(phenylisocyanate) isomers (predominantly 4,4′-MDI) to raise the level of methylene bis(phenylisocyanate) component in the composition, as described below. As such, the amount of methylene bis(phenylisocyanate) component a) in the composition of the present invention may be at least 97.5 weight percent, based on the total weight of the methylene bis(phenylisocyanate) composition, preferably at least about 98.75 weight percent, and still more preferably, at least about 99.75 weight percent. As described above, this component a) will predominantly comprise the 4,4′-MDI isomer, with the remainder of the methylene bis(phenylisocyanate) component (preferably 2% or less) comprising 2,4′-MDI and other isomers.
The methylene bis(phenylisocyanate) component a) can be produced by any of the commonly employed processes including the distillation of crude mixtures of isocyanate obtained by phosgenating a mixture of polyamines generally obtained by acid condensation of aniline and formaldehyde.
The uretonimine b) may be introduced into the methylene bis(phenylisocyanate) composition as part of an organic isocyanate blend or may be formed in situ in the methylene bis(phenylisocyanate) component to form the composition of the present invention. The uretonimine b) is generally formed by initially reacting, for example, 4,4′-MDI with a suitable catalyst such as a phospholene oxide with heating to give MDI carbodiimide. The MDI carbodiimide then reacts with excess 4,4′-MDI to give uretonimine groups as illustrated by the following reaction:
Thus, in the presence of excess 4,4&pri
Loop Cynthia
Lunato Anthony
Narayan Thirumurti
Nevejans Filip
Peters David D.
BASF Corporation
Borrego Fernando A.
Cooney Jr. John M.
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