Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-03-29
2004-10-12
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, C428S308800, C428S319300, C428S423100
Reexamination Certificate
active
06803390
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 Rizak 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. First, 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. Second, in order to get a sufficiently fast reaction with this system, it is often necessary to preheat the components to temperatures of 80° C. or more. This increases energy costs, exposes workers to high temperature reactants and reduces the viscosity of the system, thereby promoting run-off.
It would therefore be desirable to provide a rigid polyurethane system that can be applied at lower volume ratios and can be applied at lower operating temperatures.
SUMMARY OF THE INVENTION
In one aspect, this invention is a method of making a rigid polyurethane foam, comprising mixing a polyisocyanate component with a polyol component in the presence of at least one catalyst for the reaction of a polyol or water with a polyisocyanate and subjecting the mixture to conditions sufficient to cause it to cure to form a polyurethane foam having a bulk density of 45 pounds per cubic foot (720 kg/m
3
) or less, wherein
(a) the polyisocyanate component contains an isocyanate-terminated prepolymer made by reacting an excess of an organic polyisocyanate with (i) at least one polyol and (ii) at least one hydroxy-functional acrylate or methacrylate,
(b) the polyol component containing an effective amount of a blowing agent and isocyanate-reactive materials that have an average functionality of at least about 2.3 and include at least one polyol and,
(c) the volume ratio of the polyisocyanate component to the polyol component is no greater than 10:1, and
(d) the ratio of isocyanate groups in the polyisocyanate component to the number of isocyanate-reactive groups in the polyol component is from about 0.8:1 to about 1.5:1.
In a second aspect, this invention is an isocyanate-terminated prepolymer which is the reaction product of an excess of an organic polyisocyanate with (i) at least one polyol and (ii) at least one hydroxy-functional acrylate or methacrylate.
In a third aspect, this invention is a reactive system comprising
(a) a polyisocyanate component that contains an isocyanate-terminated prepolymer made by reacting an excess of an organic polyisocyanate with (i) at least one polyol and (ii) at least one hydroxy-functional acrylate or methacrylate,
(b) a polyol component containing an effective amount of a blowing agent and isocyanate-reactive materials that have an average functionality of at least about 2.3 and include at least one polyol,
wherein the system is further characterized by
(c) a volume ratio of polyisocyanate component to polyol component of no greater than 10:1,
(d) a ratio of isocyanate groups in the polyisocyanate component to isocyanate-reactive groups in the polyol component from about 0.8:1 to about 1.5:1 and
(e) at least one of the polyisocyanate component or the polyol component containing a catalyst for the reaction of an isocyanate with a polyol or water.
The process of this invention provides a method by which rigid polyurethane foam can be prepared at convenient mix ratios and at moderate operating temperatures while still allowing the formulation to cure quickly into good quality 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.
DETAILED DESCRIPTION OF THE INVENTION
The polyisocyanate component comprises an isocyanate-terminated prepolymer that is made from an excess of an organic polyisocyanate, a hydroxy-functional acrylate or methacrylate, and a polyol. The equivalent ratio of the hydroxy-functional acrylate or methacrylate to polyol is advantageously from about 0.5:1, preferably from about 0.75:1 and more preferably from about 1.25:1 to about 4:1, preferably to about 3:1, even more preferably to about 2:1. The total number of equivalents of hydroxy-functional acrylate or methacrylate plus polyol(s) to the equivalents of starting organic polyisocyanate is advantageously such that the prepolymer has an isocyanate equivalent weight of from about 150, preferably from about 175, to about 500, preferably to about 350, more preferably to about 250. These isocyanate equivalent weights correspond to NCO contents of from about 28-8.4%, preferably from 24-12%, more preferably from about 24-16.8%.
Suitable polyisocyanates that can be used in preparing the prepolymer include aromatic, aliphatic and cycloaliphatic polyisocyanates. Aromatic polyisocyanates are generally preferred based on cost, availability and properties, although aliphatic polyisocyanates are preferred in instances where stability to light is important. Exemplary polyisocyanates include, for example, m-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate (TDI), the various isomers of diphenylmethanediisocyanate (MDI), hexamethylene-1,6-diisocyanate, tetra methylene-1,4-diisocyanate, cyclohexane-1,4-diisocyanate, hexahydrotoluene diisocyanate, hydrogenated MDI (H
12
MDI), naphthylene-1,5-diisocyanate, methoxyphenyl-2,4-diisocyanate, 4,4′-biphenylene diisocyanate, 3,3′-dimethyoxy-4,4′-biphenyl diisocyanate, 3,3′-dimethyldiphenylmethane-4,4-diisocyanate, 4,4′,4″-triphenylmethane diisocyanate, polymethylene polyphenylisocyanates, hydrogenated polymethylene polyphenylisocyanates, toluene-2,4,6-triisocyanate, and 4,4′-dimethyldiphenylmethane-2,2′,5,5′-tetraisocyanate. Preferred polyisocyanates include TDI, MDI and the so-called polymeric MDI products, which are a mixture of polymethylene polyphenylene isocyanates in monomeric MDI. Especially suitable polymeric MDI products have a free MDI content of from about 5 to about 40% by weight, more preferably about 10 to about 25% by weight, and have an average functionality (number of isocyanate groups per molecule) of about 2.7 to 4.0, more preferably about 2.8 to about 3.4. Such polymeric MDI products are available from The Dow Chemical Company under the trade name PAPI®.
Hydroxy-functional acrylates and methacrylates contain an acrylate (CH
2
═CH—C(O)—) or methacrylate (CH
2
═C(CH
3
)—C(O)—) group and an isocyanate-reactive hydroxyl group. Suitable hydroxy-functional acrylates and methacrylates include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate (HEMA), 2-hydroxylpropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxy-n-butyl acrylate, 2-hydroxy-n-butyl acrylate, 2-hydroxy-n-butyl methacrylate, 4-hydroxy-n-butyl methacrylate, poly(oxyethylene)-
Billotto Frank V.
El-Khatib Ali J.
Lekovic Huzeir
Cooney Jr. John M.
Dow Global Technologies Inc.
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