Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
1994-06-17
2001-03-06
Sellers, Robert E. L. (Department: 1712)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S257000, C264S258000, C264S297500, C264S328100
Reexamination Certificate
active
06197242
ABSTRACT:
BACKGROUND OF THE INVENTION
Reaction injection molding (RIM) has become an important process for the manufacture of a wide variety of moldings. The RIM process is a process which involves the intimate mixing of a polyisocyanate component and an isocyanate-reactive component followed by the injection (generally under high pressure) of the mixture into a mold with subsequent rapid curing. U.S. Pat. No. 4,218,543 describes one particularly commercially significant RIM system, which requires the use of a specific type of aromatic amine as a crosslinker/chain extender. The preferred amine described in the '543 patent is diethyl toluene diamine (DETDA).
In the automotive industry, the application of RIM technology has been primarily to produce vertical parts (e.g. fenders and fascias) and has typically not been used in the production of horizontal body parts (e.g., trunks, hoods and roofs). In order to be useful for the production of horizontal body parts, the molded product 1) must have high stiffness, 2) must have a high quality surface, and 3) must be able to withstand the heat generated during further processing of the part (e.g., painting and curing the paint). Typically, such a part must have a flexural modulus of 750,000 psi or higher.
Fiber glass reinforcement of polyurethane RIM parts is known. See, e.g., U.S. Pat. Nos. 4,435,349, 4,792,576, and 4,871,789. When utilizing such fiber glass reinforcement, several problems are generally encountered, not the least of which is the production of a smooth surface (see, e.g., U.S. Pat. Nos. 4,610,835, 4,644,862, 4,781,876, 4,810,444, 4,952,358, 4,957,684, and 5,009,821).
Recently, a process was developed for preparing Class A surface, fiber-reinforced molded articles (U.S. Pat. No. 5,391,344 issued on Feb. 21, 1995, based on U.S. application Ser. No. 159,891, filed on Dec. 1, 1993 which is a Continuation-in-Part of U.S. patent application Ser. No. 07/798,479, filed on Nov. 26, 1991 now abandoned). The process broadly comprised injecting a specific formulation into a mold, allowing the formulation to fully react and removing the molded part from the mold. The formulation broadly required the use of a polymethylene poly(phenyl isocyanate) and a mixture of hydroxyl functional materials. While adequate for many applications, the formulation tended to blister after being subjected to further heat treatment at 150° C. (which is typical for curing of the paint).
Hindered amines are known for a variety of use in the polyurethane art (see, e.g., U.S. Pat. Nos. 4,146,688, 4,595,742, 4,631,298 and 5,059,634).
DESCRIPTION OF THE INVENTION
The present invention is directed to an improved process for preparing a Class A surface, fiber reinforced molded article which has excellent high temperature properties and which exhibits little or no blistering when subjected to temperatures as high as 180° C. The process can be used to produce horizontal, as well as vertical, automotive parts. The improved process comprises:
(A) providing a mold, having a cavity therein for forming the fiber reinforced molded article, wherein at least a portion of the mold cavity defines a mold cavity surface against surface the article is to be molded,
(B) laying one or more fiber surfacing veils against the mold cavity surface,
(C) laying one or more layers of fiber reinforcing mat over said surfacing veil,
(D) laying one or more fiber surfacing veils over said fiber mat,
(E) closing the mold,
(F) injecting a reaction mixture via the RIM process into said mold cavity,
(G) allowing the reaction mixture to fully react, and removing the resultant molded product from the mold,
the improvement wherein said reaction mixture comprises
(1) one or more polymethylene poly(phenyl isocyanates) (i) having a diisocyanate content of from 25 to less than 50% by weight, (ii) containing less than 2% by weight of 2,4′-methylene bis(phenyl isocyanate), and (iii) containing less than 0.5% by weight of 2,2′-methylene bis(phenyl isocyanate), and
(2) a blend of active hydrogen containing compounds comprising:
(a) at least one polyether polyol having an hydroxyl functionality of from 2 to 8 and a molecular weight of from 350 to below 1800,
(b) at least one hydroxyl functional organic material containing from 2 to 8 hydroxyl groups and having a molecular weight below 350, components (a) and (b) being used in a weight ratio of from about 10:1 to about 1:10,
(c) no more than 45% by weight based on the total weight of components (a), (b), and (c), of one or more active hydrogen containing compounds having a molecular weight of 1800 or more, and
(d) from about 20% to about 40% by weight, based upon the total weight of components (a), (b), (c) and (d) of one or more hindered amines of the formula:
where each R may be the same or different and represents an alkyl group, preferably of from 1 to 20 carbon atoms and most preferably from 1 to 6 carbon atoms,
each R′ may be the same or different and represents H or any substituent which does not adversely affect polyurethane formation, more preferably an alkyl group of from 1 to 6 carbon atoms or H,
n=2 or 3, preferably 2,
p=2 or 3, preferably 2,
q=0 to 2,
r=0 to 4,
s=0 to 5,
t=3 or 4, and
X is an alkylene or alkylidene,
with the amounts of components (1) and (2) being such that the isocyanate index is from about 70 to about 130.
The mold cavity surface preferably has an SPI-SPE polished rating of at least 3. Furthermore, the surfacing veils are preferably glass fiber veils. In each of steps (B) and (D), the amount of veil used is preferably at least 0.1 kilogram per square meter. In addition, the amount of reinforcing mat is preferably at least 0.5, and most preferably at least 1.0, kilograms per square meter. The total amount of surfacing veils and reinforcing mat is preferably such that the total amount of fiber in the molded article is from 15 to 45% by weight, and most preferably from 20 to 35% by weight, based upon the total weight of the molded product. When the reaction mixture is introduced into the mold, it fills the mold cavity, simultaneously impregnates the reinforcing mat and deforms the veil into intimate contact with the mold cavity surface.
In general, the final thickness of the molded part is no thicker than 120 thousands of an inch. The surface of the part is a Class A surface, and the flexural modulus of the part is in excess of about 5.16 GPa (i.e., in excess of about 750,000 psi). Finally, the part is able to withstand heat over a broad range of temperatures up to about 180° C.
The components (i.e., (1) and(2)) useful herein are known in the art. The isocyanates, the hydroxy functional materials and the relatively high molecular weight active hydrogen containing materials are described in U.S. Pat. No. 4,792,576, the disclosure of which is herein incorporated by reference.
Starting polyisocyanate components (1) suitable for use in the present invention are polymethylene poly(phenyl isocyanates) (i) having a diisocyanate content of from 25 to less than 50% by weight, (ii) containing less than 2% by weight of 2,4′-methylene bis(phenyl isocyanate), and (iii) containing less than 0.5% by weight of 2,2′-methylene bis(phenyl isocyanate). The isocyanates generally have isocyanate group contents of from 25 to 35% by weight, and preferably from 27 to 32% by weight.
The blend of active hydrogen containing compounds (2) used according to the present invention must include (a) a polyether polyol having a molecular weight of from 350 to below 1800 and (b) a polyhydroxy material having a molecular weight below 350, and may include (c) up to 45% by weight of one or more active hydrogen containing compounds having molecular weights of more than 1800 and having functionalities of 2 to 8.
Polyethers having molecular weights of from 350 to below 1800 containing two to four hydroxy groups are preferred as component (2)(a).
Useful polyethers are known and are obtained, for example, by the polymerization of epoxides, such as ethylene oxide, propylene oxide, butylene ox
Lesko Merle W.
Mitesser Richard W.
Parks Kristen L.
Rains Randall C.
Sanns, Jr. Frank
Bayer Corporation
Brown N. Denise
Gil Joseph C.
Sellers Robert E. L.
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