US-12624147-B2 - Dimensionally stable polyurethanes and composites

US12624147B2US 12624147 B2US12624147 B2US 12624147B2US-12624147-B2

Abstract

Rigid polyurethanes and composites are made from a reaction mixture containing an aromatic polyisocyanate and a mixture of polyols. The mixture of polyols has an average hydroxyl equivalent weight of 125 to 275 and an average hydroxyl funtionality of 2.5 to 4 hydroxyl groups per molecule. 5 to 33% of the weight of the mixture of polyols is triisopropanolamine. Rigid polyurethanes made from such a reaction mixture have excellent dimensional stability, even when cured at or near room temperature.

Inventors

Paolo Diena
Thomas Mosciatti
Andrea Benvenuti

Assignees

DOW GLOBAL TECHNOLOGIES LLC

Dates

Publication Date: 20260512
Application Date: 20210823
Priority Date: 20200831

Claims (12)

1 . A composite comprising a continuous resin phase and 8 to 85% by weight, based on the weight of the composite, of a discontinuous phase comprising filler particles, reinforcing fibers or both filler particles and reinforcing fibers, wherein the continuous resin phase is a cured polyurethane which is the reaction product of a polyurethane-forming reaction mixture characterized by an isocyanate index of 95 to 150, the reaction mixture comprising A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175; B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 12 to 33 weight percent of the mixture of polyols, wherein the reinforcing fibers are selected from one or more of a group consisting of glass fibers, boron fibers, ceramic fibers, carbon fibers, and metal fibers, and wherein the cured polyurethane has a glass transition temperature of at least 80° C.
2 . The composite of claim 1 wherein the discontinuous phase comprises reinforcing fibers having diameters of 0.5 to 10 μm and lengths of 2 mm to 150 mm.
3 . The composite of claim 1 wherein the fibers are glass fibers.
4 . The composite of claim 3 wherein the discontinuous phase further comprises filler particles.
5 . The composite of claims 1 which contains 2 to 15% by weight reinforcing fibers, 30 to 70% by weight of filler particles and 20 to 50% by weight of the continuous resin phase.
6 . The composite of claim 1 which has a void volume of no greater than 65%.
7 . A process for preparing a composite of claim 1 , comprising (i) introducing reinforcing fibers and/or filler particles and a polyurethane-forming reaction mixture into a cavity of a mold or onto a form, closing the mold or applying mechanical pressure to the form such that the reinforcing fibers and/or filler particles become embedded in the polyurethane-forming reaction mixture and (ii) curing the polyurethane-forming reaction mixture in the presence of the reinforcing fibers and/or filler particles in the mold cavity or on the form to form the composite, wherein the polyurethane-forming reaction mixture is characterized by an isocyanate index of 95 to 150 and comprises A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175; B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 12 to 33 weight percent of the mixture of polyols, wherein the reinforcing fibers are selected from one or more of a group consisting of glass fibers, boron fibers, other ceramic fibers, carbon fibers, and metal fibers, and wherein the cured polyurethane has a glass transition temperature of at least 80° C.
8 . The process of claim 7 wherein the step of curing the polyurethane-forming reaction mixture is performed at a temperature of no greater than 40° C.
9 . The process of claim 7 wherein the composite has a void volume of no greater than 65%.
10 . The process of any of claim 7 wherein the polyurethane-forming reaction mixture contains reinforcing fibers having diameters of 0.5 to 10 μm and lengths of 2 mm to 150 mm.
11 . The process of any of claim 7 wherein the composite contains 2 to 15% by weight reinforcing fibers, 30 to 70% by weight of filler particles and 20 to 50% by weight of the continuous resin phase.
12 . The process of any of claim 7 , wherein step (i) is performed by wetting the reinforcing fibers with the polyurethane-forming reaction mixture, dispensing the reinforcing fibers wetted with the polyurethane-forming reaction mixture into the mold or onto a form, closing the mold or applying mechanical pressure to the polyurethane-forming reaction mixture on the form and curing the polyurethane-forming reaction mixture in the mold.

Description

This invention relates to polyurethanes and polyurethane composites, and method for making them. Rigid polyurethanes and composites made with rigid polyurethanes are useful as load-bearing members in many types of construction. They have the advantages of having great strength and low weight compared to construction metals like steel. As such, they have found uses as deck planking, automotive and other vehicular structural beams, I-beams and other beams for building construction, manhole covers and road decking, among others. The rigid polyurethanes are made by curing precursor materials that include one or more polyisocyanates and one or more polyols. Curing can take place at about room temperature or at some elevated temperature. Curing at a somewhat elevated temperature such as 50 to 80° C. offers some advantages, as curing times in the mold are shorter and a more complete cure can be obtained. Unfortunately, elevated temperature curing adds to manufacturing costs, because of increased energy and equipment expenses. These additional costs can become quite substantial, particularly when manufacturing very large parts. Some manufacturers prefer to avoid these extra costs by using a room temperature cure. However, parts made using a room temperature cure often exhibit inadequate dimensional stability. They tend to exhibit an unwanted amount of thermal expansion and contraction. When used in hot environments or in settings in which there is no temperature control and temperatures can vary considerably with the time or day or the season of the year, the parts can exhibit a significant amount of expansion or shrinkage. It would be desirable to provide a rigid polyurethane or polyurethane composite that exhibits greater dimensional stability, particularly when produced without using an elevated temperature cure. This invention is in a first aspect composite comprising a continuous resin phase and 8 to 85% by weight, based on the weight of athe composite, of a discontinuous phase comprising filler particles, reinforcing fibers or both filler particles and reinforcing fibers, wherein the continuous resin phase is a cured polyurethane which is the reaction product of a polyurethane-forming reaction mixture characterized by an isocyanate index of 95 to 150, the reaction mixture comprising A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175;B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 5 to 33 weight percent of the mixture of polyols. The invention is also a process for preparing the foregoing composite, comprising (i) introducing reinforcing fibers and/or filler particles and a polyurethane-forming reaction mixture into a cavity of a mold or onto a form, closing the mold or applying mechanical pressure to the form such that the reinforcing fibers and/or filler particles become embedded in the polyurethane-forming reaction mixture and (ii) curing the polyurethane-forming reaction mixture in the presence of the reinforcing fibers and/or filler particles in the mold cavity or on the form to form the composite, wherein the polyurethane-forming reaction mixture is characterized by an isocyanate index of 95 to 150 and comprises A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175;B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 5 to 33 weight percent of the mixture of polyols. The polyurethane and composite of the invention have remarkably good dimensional stability as determined by the method described herein, even when cured at room temperature or only slightly above room temperature. The mixture of polyols and aromatic polyisocyanate exhibit a curing profile that is well-suited for making large moldings. The mixture of polyols and aromatic polyisocyanate perform well when used to make fiber-reinforced composites in a casting process such as an LFI (long fiber injection) process, as well as other processes such as S-RIM, resin transfer molding and others. The polyurethane-forming reaction mixture contains a mixture of polyols, one of which is triisopropanolamine (TIPA). The amount of TIPA is based on the weight of the polyols only, not on the weight of other ingredients as may be present in the polyurethane-forming reaction mixture. TIPA constitutes 5 to 33 weight percent of the mixture of polyols Within this broad r