Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-10-29
2004-03-02
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S137000, C521S170000, C428S308400, C428S319300, C428S423100
Reexamination Certificate
active
06699916
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to rigid polyurethane foams, particularly rigid polyurethane foams that are useful as reinforcement materials, such as in the auto industry.
Rigid foams have been used in the auto and other industries for a number of purposes. For example, rigid foams have been used for structural reinforcement, preventing corrosion and damping sound and vibration. These foams are typically formed by applying a reactive foam formulation to a part and allowing the formulation to foam in place. The part is often already assembled onto a vehicle when the foam is applied. This means that the foam formulation must be easy to mix and dispense, must cure rapidly before it runs off the part, and preferably initiates curing at moderate temperatures. To minimize worker chemical exposure, the formulation is preferably is low in volatile organic compounds, especially volatile isocyanates and amines. The individual components are preferably storage-stable at room temperature for an extended period.
One foaming system for these applications is based on the prepolymer described by Rizk et al. in U.S. Pat. No. 5,817,860. The prepolymer described in that patent is made by reacting an isocyanate with a monofunctional alcohol and a polyol. Foams are made from this prepolymer by reacting it with water. While good quality foam can be made using this approach, it has several drawbacks. Because the prepolymer is cured with a water stream, the volume ratio of the reactants (prepolymer and water) is often quite high, such as 15:1 or more. Much of the commercially available dispensing equipment cannot handle such high component ratios. This can be alleviated somewhat by replacing the water with a higher equivalent weight polyol. But the equivalent weight of the polyol must be so high, if volume ratios are to be reduced significantly, that the resulting foam is flexible, unstable, or both.
It would therefore be desirable to provide a rigid polyurethane system that can be applied at lower volume ratios and which provides stable, rigid foam.
SUMMARY OF THE INVENTION
In one aspect, this invention is a method of making a rigid hybrid polyurethane foam, comprising mixing an isocyanate component with a polyol component in the presence of (i) a blowing agent, (ii) at least one polyfunctional (meth)acrylate compound containing an average of at least 2 acrylate or methacrylate groups per molecule and a weight per acrylate or methacrylate group of about 300 daltons or less and (iii) at least one catalyst for the reaction of a polyol or water with a polyisocyanate and, subjecting the mixture to conditions sufficient to cause the isocyanate component and polyol component to react and the polyfunctional (meth)acrylate compound to polymerize, thereby forming a rigid hybrid polyurethane foam having a bulk density of 45 pounds per cubic foot (720 kg/m
3
) or less.
In a second aspect, this invention is a two-component reactive system for making a hybrid polyurethane foam, comprising
(a) a isocyanate component that contains at least one polyisocyanate compound ant at least one polyfunctional (meth)acrylate compound containing an average of at least 2 acrylate or methacrylate groups per molecule and a weight per acrylate or methacrylate group of about 300 daltons or less; and
(b) a polyol component that contains one or more polyols and an effective amount of a blowing agent;
wherein the system is further characterized by
(i) a volume ratio of isocyanate component to polyol component of between 1:4 to 4:1,
(ii) a ratio of isocyanate groups in the isocyanate component to isocyanate-reactive groups in the polyol component from about 0.8:1 to about 1.5:1 and
(iii) at least one of the isocyanate component or the polyol component contains a catalyst for the reaction of an isocyanate with a polyol or water.
The process of this invention provides a method by which rigid hybrid polyurethane foam can be prepared at convenient mix ratios while still allowing the production good quality, rigid foam. The method and resulting foam is especially suitable for making foamed-in-place reinforcing and sound- or vibration-dampening foam, especially for automotive applications, as it is easily foamed in place where reinforcement is needed. Through the selection of appropriate catalysts, the reactive system can be formulated with low levels of volatile compounds, in particular low levels of volatile amines and isocyanates.
DETAILED DESCRIPTION OF THE INVENTION
In this invention, an isocyanate component and a polyol component are reacted in the presence of a blowing agent, catalyst and a polyfunctional (meth)acrylate compound to form a rigid foam. The “polyfunctional (meth)acrylate compound” is a compound or mixture of compounds that have a plurality of polymerizable acrylate or methacrylate groups. The polyfunctional (meth)acrylate compounds preferably each have at least 2 such groups per molecule and preferably have on average from about 2.2 to about 5 such groups per molecule. It is more preferred that the polyfunctional (meth)acrylate compounds contain an average of at least 2.5, more preferably at least 2.8, such polymerizable acrylate or methacrylate groups per molecule. The polyfunctional (meth)acrylate compound has a weight of up to 300 daltons per acrylate or methacrylate group, preferably between about 100 and 200, especially between about 100 and 150. It is preferred that the polyfunctional (meth)acrylate compound be substantially devoid of groups (i.e., hydroxyl, primary or secondary amine, carboxylic acid, thiol groups, among others) that will react with an isocyanate group under the conditions of the foaming reaction.
The polyfunctional (meth)acrylate compound will typically be incorporated into the isocyanate component. In order to facilitate mixing and the preparation of a good quality hybrid foam, it is preferred that the polyfunctional (meth)acrylate compound be miscible with the isocyanate component at the proportions that are present.
Suitable polyfunctional (meth)acrylate compounds include esters of acrylic acid and/or methacrylic acid and one or more polyalcohols that have on average at least 2 alcohol groups per molecule. The polyols are generally of low equivalent weight so that the weight of the polyfunctional (meth)acrylate compound per acrylate or methacrylate group is as described before. These polyfunctional (meth)acrylate compounds can be prepared by reacting the acid, corresponding acid halide or corresponding alkyl ester (especially methyl or ethyl ester) with the polyalcohol in the presence of an esterification catalyst or transesterification catalyst. Suitable polyfunctional (meth)acrylate compounds are commercially available under the trade name Sartomer™, and include trimethylolpropane trimethacrylate (Sartomer 350), trimethylolpropanetriacrylate, di(trimethylolpropane) tetracrylate (Sartomer 355), di(trimethylolpropane) tetramethacrylate and similar compounds.
The amount of polyfunctional (meth)acrylate compound that is used is selected in conjunction with the amounts of the other components so that the resulting foam is rigid and stable. In the preferred two-component method of making the foam, the amount of the polyfunctional (meth)acrylate compound is also selected in conjunction with the amounts of other components so the volume ratio of the isocyanate component to the polyol component is within the ranges described below. The precise amount that is required will depend on the relative equivalent weights of the isocyanate component and the polyols in the polyol component. However, these volume ratios are generally achieved when the polyfunctional (meth)acrylate compound constitutes from about 1, preferably about 3, more preferably about 5, to about 35, preferably to about 30 percent of the total weight of the foam formulation. To obtain a stable, rigid foam, the polyfunctional (meth)acrylate compound preferably constitutes at least about 15% of the total weight of the foam formulation. When, as preferred, the polyfunctional (meth)acrylate compound is incorporated
Billotto Frank V.
Lekovic Huzeir
Cooney Jr. John M.
Dow Global Technologies Inc.
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