Dimensionally stable polyurethane and composite materials

Abstract

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

Description

[0001] This invention relates to polyurethane and polyurethane composites and methods for their preparation.

[0002] Rigid polyurethane and composites made from rigid polyurethane can be used as load-bearing components in many types of buildings. Compared to building metals such as steel, they have the advantages of high strength and low weight. Therefore, they can be used as deck slabs, structural beams for motor vehicles and other vehicles, I-beams and other beams used in building construction, manhole covers, and road paving, etc.

[0003] Rigid polyurethanes are prepared by curing precursor materials comprising one or more polyisocyanates and one or more polyols. Curing can be carried out at approximately room temperature or at slightly elevated temperatures. Curing at slightly elevated temperatures, such as 50°C to 80°C, offers some advantages, as the curing time in the mold is shorter and more complete curing can be achieved. Unfortunately, high-temperature curing increases manufacturing costs due to the increased energy and equipment expenses. These additional costs can become quite substantial, especially when manufacturing very large parts.

[0004] Some manufacturers prefer to avoid these additional costs by using room temperature curing. However, parts prepared using room temperature curing often exhibit insufficient dimensional stability. They tend to show undesirable amounts of thermal expansion and contraction. When used in hot environments or in environments without temperature control where temperatures can vary greatly over time, date, or season, parts may exhibit significant expansion or contraction.

[0005] It is desirable to provide a rigid polyurethane or polyurethane composite that exhibits greater dimensional stability, especially when produced without the use of high-temperature curing.

[0006] The invention, in a first aspect, is a composite material comprising a continuous resin phase and a discontinuous phase comprising filler particles, reinforcing fibers, or both, in an amount of 8% to 85% by weight based on the composite material, wherein the continuous resin phase is a cured polyurethane, said cured polyurethane being a reaction product of a reaction mixture forming a polyurethane characterized by an isocyanate index of 95 to 150, the reaction mixture comprising...

[0007] A) Aromatic polyisocyanates or mixtures of aromatic polyisocyanates, wherein the aromatic polyisocyanates or mixtures of aromatic polyisocyanates have an isocyanate functionality of 2 to 4 and an isocyanate equivalent of 80 to 175.

[0008] B) A polyol mixture having an average hydroxyl equivalent of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine accounts for 5% to 33% by weight of the polyol mixture.

[0009] The present invention also relates to a method for preparing the aforementioned composite material, comprising (i) introducing reinforcing fibers and / or filler particles and a reaction mixture for forming polyurethane into a cavity of a mold or onto a model, closing the mold or applying mechanical pressure to the model such that the reinforcing fibers and / or filler particles become embedded in the reaction mixture for forming polyurethane, and (ii) curing the reaction mixture for forming polyurethane in the presence of the reinforcing fibers and / or filler particles in the mold cavity or on the model to form the composite material, wherein the reaction mixture for forming polyurethane is characterized by an isocyanate index of 95 to 150 and contains

[0010] A) Aromatic polyisocyanates or mixtures of aromatic polyisocyanates, wherein the aromatic polyisocyanates or mixtures of aromatic polyisocyanates have an isocyanate functionality of 2 to 4 and an isocyanate equivalent of 80 to 175.

[0011] B) A polyol mixture having an average hydroxyl equivalent of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine accounts for 5% to 33% by weight of the polyol mixture.

[0012] The polyurethanes and composites of this invention exhibit excellent dimensional stability, as determined by the methods described herein, even when cured at room temperature or only slightly above room temperature. The polyol mixtures and aromatic polyisocyanates demonstrate curing profiles highly suitable for preparing large-scale molded articles. The polyol mixtures and aromatic polyisocyanates perform well when used in the preparation of fiber-reinforced composites in casting processes such as LFI (long fiber injection molding) and other processes such as S-RIM, resin transfer molding, and others.

[0013] The reaction mixture forming the polyurethane comprises a mixture of polyols, one of which is triisopropanolamine (TIPA). The amount of TIPA is based solely on the weight of the polyols, and not on the weight of other components that may be present in the reaction mixture forming the polyurethane. TIPA accounts for 5% to 33% by weight of the polyol mixture. Within this wide range, increasing the amount of TIPA from 5% by weight to about 20% to 25% by weight tends to improve dimensional stability; therefore, a lower amount of at least 10%, at least 12%, or at least 15% by weight is preferred.

[0014] TIPA can be provided as a pure or substantially pure material comprising 95% to 100% TIPA by weight. Commercial grades containing 98% to 99.5% TIPA are suitable. Such highly concentrated grades of TIPA are room-temperature solids and can be melted for blending with other components of the polyol blend if desired. Mixtures or solutions of TIPA in suitable solvents can be used if desired. Such mixtures or solutions may, for example, comprise 80% to 97% by weight of TIPA and correspondingly 3% to 20% by weight of another material, such as water, a polyol different from TIPA, or a non-isocyanate reactive solvent. If TIPA is provided as a mixture with water, it is preferable to keep the total amount of water (including water provided with TIPA) in the reaction mixture forming the polyurethane within the amounts mentioned below. Any polyols present in such mixtures or solutions are counted by weight of the polyol mixture, not by weight of TIPA. TIPA itself has a molecular weight of about 191.3 and a hydroxyl functionality of 3.

[0015] Most preferably, triethanolamine (TEOA) is absent or constitutes at most 2% by weight, 0.5% by weight, or 0.1% by weight of the polyol mixture.

[0016] The polyol mixture comprises at least one additional polyol other than TIPA and TEOA, such that the polyol mixture has an average hydroxyl equivalent of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule. The average hydroxyl equivalent may be at least 140 (hydroxyl number 400.7 mg KOH / g), at least 150 (hydroxyl number 374), at least 160 (hydroxyl number 350.6), and may, for example, be up to 250 (hydroxyl number 224.4), up to 225 (hydroxyl number 249.3), up to 210 (hydroxyl number 267.1), or up to 200 (hydroxyl number 280.5). The hydroxyl equivalent of the polyol mixture can be determined by measuring the number of hydroxyl groups in the blend using a well-known titration method, or it can be calculated from the equivalent and / or the number of hydroxyl groups of the individual polyols.

[0017] The polyol mixture preferably contains no more than 5% by weight, and more preferably no more than 2% by weight, of an amine-containing polyol other than TIPA and / or TEOA. The polyol mixture may contain no more than 1% by weight, no more than 0.5% by weight, or no more than 0.25% by weight of another amine-containing polyol, and may not contain any other amine-containing polyols.

[0018] One or more additional polyols in the polyol mixture may have a hydroxyl equivalent of 31 to 3000 or higher, and a hydroxyl functionality of 2 to 8 or higher, preferably 2 to 6, provided that the polyol mixture has the average hydroxyl equivalent and functionality as described above. Preferably, no more than 25% by weight of the polyol mixture is one or more polyols with a functionality of 5 or higher. The polyol mixture may contain up to 10% by weight, up to 5% by weight, or up to 2% by weight of polyols with a functionality of 5 or higher, and may not contain any such polyols.

[0019] The polyol mixture preferably contains no more than 10% by weight of polyols other than TIPA with a hydroxyl equivalent of less than 70. It may contain no more than 5% by weight, no more than 2% by weight, or no more than 1% by weight of polyols other than TIPA with a hydroxyl equivalent of less than 70.

[0020] In some embodiments, the additional polyol comprises at least one polyol having 2 to 4, preferably 3 to 4 hydroxyl groups and a hydroxyl equivalent of 150 to 300, preferably 175 to 275 or 175 to 225, and being nitrogen-free. One or more such polyols may comprise at least 50% by weight, at least 60% by weight, or at least 70% by weight of the polyol mixture and at most 95% by weight or at most 90% by weight. This particular additional polyol is preferably a polyether polyol prepared by alkoxylation of a starting material having 2 to 4, preferably 3 to 4 hydroxyl groups. Preferably, 1,2-propylene oxide, ethylene oxide, or both 1,2-propylene oxide and ethylene oxide are used for alkoxylation of the starting material, but other polymerizable ethylene oxides may also be used. In some embodiments, the polyol mixture comprises only TIPA and at least one polyol having 2 to 4, preferably 3 to 4 hydroxyl groups and a hydroxyl equivalent of 150 to 300, preferably 175 to 275 or 175 to 225, and being nitrogen-free.

[0021] Aromatic polyisocyanate compounds used to prepare polyurethane polymer matrices are compounds containing two or more isocyanate groups linked in an aromatic manner per molecule. Preferred isocyanates are diphenylmethane diisocyanate (MDI), and more preferred isocyanate compounds are polymeric MDI. "Polymeric MDI" refers to a mixture of MDI and polymethylene polyphenyl isocyanate containing at least three phenyl isocyanate groups. MDI can be a 2,4'- or 4,4'- isomer, or a mixture of both. MDI or polymeric MDI can be modified by carbodiimide, urea-ketimide, urethane, urea, or biuret bonds.

[0022] Aromatic polyisocyanate compounds preferably have an isocyanate equivalent of 125 to 168 and an average isocyanate functionality of 2.2 to 4.0. Examples of usable polyisocyanates are polymeric MDI having an isocyanate equivalent of about 130 to 168, particularly 130 to 150, and an isocyanate functionality of about 2.2 to about 3.5, particularly 2.5 to 2.75.

[0023] A polyisocyanate is provided to the reaction mixture forming the polyurethane to provide an isocyanate index of 95 to 150. In some embodiments, the isocyanate index is at least 100 or at least 102 and up to 125, up to 115, or up to 110. The isocyanate index is 100 times the ratio of the equivalent of isocyanate groups to the equivalent of isocyanate reactive groups provided to the reaction mixture forming the polyurethane.

[0024] The reaction mixture forming the polyurethane preferably includes at least one urethane catalyst, i.e., a catalyst for the reaction of the isocyanate group with the hydroxyl group. Examples of urethane catalysts include, for example, tertiary amine compounds, cyclic amidines, and various metal carboxylates, particularly tin carboxylates and tetravalent tin compounds. Amine catalysts preferably have 0 or at most 1 hydroxyl group.

[0025] The choice and amount of catalyst can be selected to provide a polyurethane-forming reaction mixture with desired curing properties. For the production of large parts in casting or spraying methods, the polyurethane-forming reaction mixture can exhibit, for example, a cream time of at least 20 seconds, preferably 20 to 40 seconds; a gel time of at least 90 seconds, preferably 100 to 150 seconds; and a tack-free time of at least 120 seconds, preferably at least 140 seconds, and preferably up to 200 seconds; all measured in the manner described in the examples below. In such embodiments, the type and amount of catalyst are selected to obtain these values.

[0026] Representative amine catalysts include trimethylamine, triethylamine, dimethylethanolamine, N-methylmorpholine, N-ethylmorpholine, N,N-dimethylbenzylamine, N,N-dimethylethanolamine, N,N,N',N'-tetramethyl-1,4-butanediamine, N,N,N',N”,N”-pentamethyldiethylenetriamine, N,N-dimethylpiperazine, 1,4-diazabicyclo-2,2,2-octane, bis(dimethylaminoethyl) ether, bis(2-dimethylaminoethyl) ether, 4,4'-(oxydi-2,1-ethanediyl)bismorpholine, triethylenediamine, pentamethyldiethylenetriamine, N,N-dimethylcyclohexylamine, N-acetyl-N,N-dimethylamine, N-coco-morpholine, N,N-dimethylaminomethyl-N-methylethanolamine, N,N,N' -Trimethyl-N'-hydroxyethyl bis(aminoethyl) ether, N,N-bis(3-dimethylaminopropyl)N-isopropanolamine, (N,N-dimethyl)aminoethoxyethanol, N,N,N',N'-tetramethylhexanediamine, 1,8-diazabicyclo-5,4,0-undecene-7,2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimorpholinodiethyl ether, N-methylimidazolium, dimethylaminopropyldipropanolamine, bis(dimethylaminopropyl)amino-2-propanol, tetramethylaminobis(propylamine), (dimethyl(aminoethoxyethyl))((dimethylamino)ethyl) ether, tri(dimethylaminopropyl)amine, dicyclohexylmethylamine, bis(N,N-dimethyl-3-aminopropyl)amine, 1,2-ethylidene piperidine, and methyl-hydroxyethylpiperazine.

[0027] Examples of available tin catalysts include stannous octanoate, dibutyltin diacetate, dimethyltin diacetate, dimethyltin dilaurate, dibutyltin dilaurate, dibutyltin dithiol, dialkyltin dialkylmercapto acid, dibutyltin oxide, dimethyltin dithiol, dimethyltin diisooctylmercaptoacetate, dibutyltin diisooctylmercaptoacetate, tin octanoate, dibutyltin dioctanoate, dimethyltin dioctanoate, etc.

[0028] Catalysts are typically used in small amounts. For example, the total amount of catalyst used may be 0.0015 to 5, preferably 0.01 to 2 parts by weight per 100 parts by weight of the polyol mixture. Metal catalysts are typically used in amounts less than 0.5 parts by weight of the polyol mixture.

[0029] The reaction mixture forming the polyurethane may contain a blowing agent. Water is the preferred blowing agent, but other chemical (exothermic) and physical (endothermic) blowing agents may be used instead of or supplemented with water. Available physical blowing agents are compounds with a boiling point of 10°C to 50°C, including hydrocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, hydrofluoroolefins, and hydrochlorofluoroolefins, as described, for example, in US2007 / 0100010, and other low-boiling-point compounds such as diethyl ether. Those with low or zero global warming potential and low or zero ozone depletion potential are preferred. Water may be used as the sole blowing agent in an amount of 0.25 to 1.5 parts by weight per 100 parts by weight of the polyol mixture.

[0030] When used, the foaming agent is preferably used in an amount that gives the composite a void volume of no more than 75 vol%, preferably no more than 65 vol%. Higher void volumes tend to result in the composite lacking the physical properties required for structural applications. Void volume can be any low amount, including 0. For structural applications, a void volume of 25 vol% to 65 vol% typically provides a good balance between product weight and structural strength, although void volumes can be as low as 0%. Void volume can be determined by microscopic instruction or calculated by comparing the density of the composite with the expected density of a fully dense composite made from the same materials excluding the foaming agent.

[0031] In some embodiments, the density of the composite material is at least 250 kg / m³. 3 Or at least 350 kg / m 3 In certain embodiments, the density of the composite material can be up to 1500 kg / m³. 3 Up to 1250 kg / m 3 Up to 1000 kg / m 3 Up to 800 kg / m 3 Or up to 700 kg / m 3 .

[0032] Foam-stabilizing surfactants can be present in the reaction mixture that forms polyurethane. A wide variety of silicone surfactants commonly used in the preparation of polyurethane foams can be used. An example of such silicone surfactants is the trade name Tegostab. TM (Evonik Niax TMMomentive Performance Materials and Dabco TM Commercially available from Evonik. Various other non-organosilicon anionic, cationic, amphoteric, and nonionic surfactants are also available. Examples of available nonionic surfactants include block copolymers of ethylene oxide and higher epoxides such as 1,2-epoxypropane and 1,2-epoxybutane. Such block copolymers may contain, for example, 40% to 90% by weight of ethylene oxide units and have a molecular weight of 1,500 to 12,000. Such block copolymers may have one or more hydroxyl groups. Examples of suitable block copolymers include those produced by The Dow Chemical Company using Tergitol. TM Those block copolymers sold under trademarks, and those produced by BASF under Pluronics TM Those block copolymers sold under the trademark.

[0033] Surfactants (if used) are typically present in amounts such as 0.25 to 2.5 parts by weight per 100 parts by weight of the polyol mixture.

[0034] Another optional component of the reaction mixture forming the polyurethane is a combustion modifier. The combustion modifier may be solid or liquid. It may include non-halogenated flame retardants and / or halogenated flame retardants. Exemplary combustion modifiers include melamine, halogen-free phosphorus compounds such as tris(1-chloro-2-propyl) phosphate, halogen-free aluminum-containing compounds, halogen-free nitrogen-based compounds, chlorinated compounds, brominated compounds, expandable graphite, boron derivatives, and polyurea. The combustion modifier (if present) may be present in amounts of at least 1 part by weight, or at least 3 parts by weight and up to 45 parts by weight, up to 25 parts by weight, up to 10 parts by weight, or up to 5 parts by weight per 100 parts by weight of the polyol mixture.

[0035] Based on the weight of the composite material, the composite material of the present invention comprises 8% to 85% by weight of a discontinuous phase, said discontinuous phase comprising at least one granular filler and / or at least one fiber. Both filler particles and reinforcing fibers may be present.

[0036] The "filler" differs from reinforcing fibers in that it has an aspect ratio of less than 3.0, and preferably less than 2.0. The filler is in particulate form, preferably having a longest dimension of 50 nm to 1 mm. More preferably, the filler particles have a longest dimension of 250 nm to 500 μm, as measured using laser diffraction. The filler particles are made of inorganic or organic materials that are thermally stable at the processing temperatures encountered during the curing step (i.e., do not undergo changes in physical state or participate in chemical reactions). Examples of suitable fillers include calcium carbonate, talc, wollastonite, various clays, frosted glass, carbon black, titanium dioxide, iron oxide, aluminum hydroxide, magnesium hydroxide, etc. Calcium carbonate is a preferred filler.

[0037] Before forming the composite material, the particulate filler is conveniently blended with a polyol mixture or at least one of its components before use. In this case, a wetting agent may be present, as its presence can significantly reduce the viscosity of the blend. Suitable wetting agents include ammonium salts of certain acidic polyesters and acidic copolymers, such as those sold by BykUSA (a member of the Altana Group) under the trade names BYK W985 and BYK W969. The amount of wetting agent available is typically in the range of about 0.25% to 3% by weight, preferably 0.5% to 2% by weight, of the particulate filler.

[0038] The reinforcing fibers have an aspect ratio of at least 3 and may have a diameter in the range of 0.5 to 100 μm, preferably 2 to 50 μm. The reinforcing fibers are made of a material that does not melt or thermally degrade at temperatures below 200°C and is harder than the polyurethane polymer matrix. The diameter of the reinforcing fibers is taken as the diameter of a circle of equivalent area. The fibers may be a roving composed of multiple primary fibers having such a diameter. Suitable fibers include, for example, glass fibers, boron fibers, other ceramic fibers, carbon fibers, metal fibers, natural fibers such as cotton and wool fibers, and synthetic polymer fibers with the desired thermal stability and melting temperature. Glass rovings and fibers are preferred based on cost, availability, and performance. In some embodiments, the fibers have a length-to-diameter ratio of at least 20, preferably at least 100. The fibers may have a length of 2 mm or longer, or 5 mm or longer. Randomly oriented fibers in the composite material preferably have a length of 5 to 150 mm or 5 to 50 mm.

[0039] The reinforcing fibers may be present in the presence of the preformed mat, and the fibers may be, for example, woven, knitted, needle-punched, or otherwise bonded together. Continuous long fibers are available, such as continuous fiber bundles, random or even non-randomly oriented long (length greater than 150 mm) and short (length less than 150 mm, such as 5 to 150 mm or 5 to 50 mm) fibers as described in US 6,656,405.

[0040] Based on the weight of the composite material, the composite material of the present invention comprises 8% to 85% of a discontinuous phase (i.e., blended fillers and reinforcing fibers). The filler particles themselves may account for, for example, 0% to 60%, 5% to 60%, or 25% to 50% of the weight of the composite material, and in such embodiments, the reinforcing fibers themselves may account for, for example, 0% to 60%, 2% to 60%, 3% to 25%, 3% to 15%, or 3% to 10% of the total weight of the composite material, provided that the total amount of the discontinuous phase is 8% to 85% of the weight of the composite material, i.e., blended fillers and reinforcing fibers.

[0041] The composite material of the present invention is formed by compounding a polyol mixture with a polyisocyanate and optionally one or more other optional components (such as those described herein) to produce a reaction mixture for forming a polyurethane, and curing the reaction mixture for forming a polyurethane in the presence of reinforcing fibers and / or filler particles. The filler particles may be incorporated into the isocyanate, or preferably, into the polyol mixture. The reinforcing fibers may be incorporated into the isocyanate, into the polyol mixture, or incorporated into the reaction mixture for forming the polyurethane during molding or after molding but before curing. The process is carried out in such a manner that the reaction mixture for forming the polyurethane fills at least some of the spaces between the individual fibers and / or particles. After curing, the reinforcing fibers and / or filler particles are embedded in the polyurethane polymer matrix.

[0042] Composite materials can be prepared using various methods. A preferred method is long fiber injection molding (LFI). In LFI, short fibers (up to 150 mm, preferably 2 to 150 mm, more preferably 5 to 150 mm, and even more preferably 5 to 50 mm) are wetted with a polyurethane-forming reaction mixture, and the wetted fibers are dispensed into an open mold or model. Filler particles may also be incorporated into the reaction mixture, typically by blending them with one or both of a polyisocyanate and a polyol mixture. The fibers and the polyurethane-forming reaction mixture are conveniently dispensed through a mixing head, and are typically dispensed together into the mold or model by spraying, pouring, or injection. Fibers are sometimes supplied to the process in the form of continuous rovings. In that case, the rovings are cut to discrete lengths just before being wetted with the polyurethane-forming reaction mixture. In some processes, the fibers are introduced into a chamber closely adjacent to the mixing head, where a polyol mixture and a polyisocyanate are mixed to form the polyurethane-forming reaction mixture. The fibers and the polyurethane-forming reaction mixture are then dispensed together from the mixing head into the mold or model. In other cases, the fibers and the reaction mixture forming the polyurethane are dispensed separately from the mixing head, but into each other, such that the dispensed fibers become wetted as they travel toward the mold surface. Once the mold is filled, it is closed, and the reaction mixture forming the polyurethane is cured within the mold to form the polyurethane composite. If a form is used instead of a mold, mechanical pressure is applied during the curing process. A “form” refers to any open (non-closed) surface on which the fibers and the reaction mixture forming the polyurethane are dispensed; a form can be, for example, a stationary surface or a moving surface such as a conveyor belt.

[0043] Preferred types of mixing heads for long fiber injection molding processes include high-pressure impact mixers, through which the polyol mixture and polyisocyanate are contacted, rapidly mixed, and brought into contact with the fibers. The fibers can be supplied in the form of continuous rovings, which are cut to the desired length before being introduced into the mixing head. The resulting wetted fibers are sprayed, poured, or injected into a mold or template. These types of mixing heads are commercially available. They include the "LFI" mixing head from Krauss-Maffei or the "Interwet" mixing head from The Cannon Group (Milan, Italy).

[0044] Other suitable methods include, for example, structural reaction injection molding (SRIM), which includes the following steps: (A) introducing reinforcing fibers (typically in the form of pre-formed woven or non-woven pads) into a mold cavity; (B) introducing a polyurethane-forming reaction mixture into the mold such that the polyurethane-forming reaction mixture permeates between the reinforcing fibers; and then (C) curing the polyurethane-forming reaction mixture in the presence of the reinforcing fibers in the mold. Filler particles may also be present, preferably incorporated into one or both of a mixture of polyisocyanates and polyols prior to molding the polyurethane-forming reaction mixture.

[0045] Another suitable manufacturing method is a reinforced reactive injection molding (RRIM) process, in which short (typically up to 1 mm, preferably about 0.1 to 0.5 mm) fibers or sheet-like reinforcing materials are dispersed in a liquid polyurethane precursor (typically a polyol mixture), passed through a mixing head in which the precursor is mixed with other reactants, and then injected into a closed mold in which the reaction mixture is cured to form a polyurethane polymer matrix in which fibers are embedded.

[0046] In any of the foregoing processes, once the mold or model has been filled with wetted fibers, mechanical pressure is applied (by closing the mold or otherwise) and the reaction mixture forming polyurethane is cured in the presence of the fibers and / or filler particles. The mold or model can be heated together with the applied wetted fibers to elevated temperatures such as 40°C to 100°C for curing. In this case, the mold or model is typically preheated to the curing temperature. However, a significant advantage of the present invention is that high-temperature curing is not necessary to obtain dimensionally stable parts. Therefore, in the preferred process of the present invention, the curing temperature is no greater than 40°C, particularly no greater than 35°C or 32°C, and can be, for example, 15°C to 32°C or 15°C to 28°C. The curing temperature is the temperature applied to the outside of the mold or model during the curing process. The curing reaction mixture typically generates heat during an exothermic reaction, which can raise the temperature of the reaction mixture and also heat the mold. In a typical process, the mold or model during the curing process is kept in an atmosphere at a temperature not exceeding 40°C, particularly not exceeding 35°C or 32°C, and may be, for example, 15°C to 32°C or 15°C to 28°C, and no additional heating or cooling is applied to the mold or model or the curing reaction mixture.

[0047] The reaction mixture forming the polyurethane is allowed to cure for a sufficient time so that the composite material can be demolded or removed from the mold without permanent deformation or damage. The curing step typically takes 0.5 to 60 minutes, depending on factors such as the specific reaction mixture forming the polyurethane, the size of the part, and the curing temperature. The mechanical pressure applied during the curing step is sufficient to prevent undesirable expansion of the mold contents.

[0048] The resulting composite material can have any arbitrary geometry and size. Specific shapes and sizes may be required for particular applications. However, the present invention is particularly suitable for manufacturing large articles, such as deck slabs, structural beams for motor vehicles and other vehicles, I-beams for buildings, manhole covers and road or pavement paving, wind turbine blades, and so on. The composite material portion of such articles may have a maximum dimension of at least 0.5 meters, at least 1 meter, or at least 2 meters and up to 10 meters, up to 7.5 meters, or up to 5 meters.

[0049] The composite material of the present invention may have a thickness of at least 5 mm, at least 10 mm, at least 12 mm or greater, at least 15 mm, at least 18 mm or at least 25.4 mm. In some embodiments, the thickness is up to 100 mm or up to about 50 mm.

[0050] If desired, the composite material of the present invention can be produced with a textured surface, such as a wood grain pattern or other arbitrary pattern.

[0051] The composite material of the present invention can constitute the entire article. However, the article may also include one or more additional layers, such as coatings on some or all of the outer surfaces of the polyurethane composite material. Coatings may impart useful properties, such as climate stability, a higher coefficient of friction (for anti-slip or non-slip purposes), or may be present for aesthetic reasons. An anti-slip or non-slip coating on at least one surface is generally advantageous. Such a coating may be a polyurethane polymer layer. Some products may have, for example, an elastomeric polyurethane coating applied to the composite material of the present invention and one or more colored coatings outside the elastomeric polyurethane.

[0052] The coating can be produced in various ways, such as by applying a powder coating, in-mold paint, thermoplastic film, and / or gel coating composition to the surface of a mold or model via methods such as casting or spraying, then introducing a fiber-reinforced material and a composition forming a polyurethane into the mold or model and curing the composition to form a polyurethane (and coating, if necessary). The coating can also be applied after the curable composition of the present invention has cured using techniques such as high-pressure injection in-mold coating processes or via post-demolding coating or coating methods.

[0053] The polyurethane or polyurethane matrix of the composite material of the present invention preferably has a glass transition temperature of at least 80°C and more preferably at least 130°C, as measured by dynamic mechanical analysis.

[0054] The following examples are provided to illustrate the invention, but are not intended to limit the scope of the invention. Unless otherwise specified, all parts and percentages are by weight.

[0055] Example 1 and Comparative Sample AH

[0056] Polyurethane composites were prepared by reacting a formulated polyol blend with polymeric MDI in a mold with a cavity of 1000 × 30 × 50 mm. In all cases, the mold temperature was 22–24 °C, except for Comparative Sample B, where the mold temperature was 54 °C. Fibers were omitted in these experiments to simplify the formulation and minimize the potential impact of uneven fiber distribution when using laboratory equipment.

[0057] All ingredients except the polyisocyanate were blended to produce the formulated polyol blend. TIPA, solid at room temperature, dissolved in polyol A during mixing. The mold cavity was lined with a polyethylene film. The formulated polyol blend and polyisocyanate were equilibrated to 22-24°C and then mixed on a high-speed mixer for 20 seconds to produce a reaction mixture for forming polyurethane. Approximately 740 g of the reaction mixture was poured into the lined mold cavity. A second piece of polyethylene film was placed on top of the reaction mixture in the mold cavity, and the mold was closed. The reaction mixture was allowed to cure in the mold for 20 minutes while maintaining it at the aforementioned temperature. The resulting composite material was demolded and stored at approximately 22-24°C for 24 hours. The molded part had a strength of 400 to 650 kg / m³. 3 Density within the range.

[0058] The reaction mixture for each case was prepared from the components shown in Table 1.

[0059] Polyol A is propoxylated glycerol. It has a nominal hydroxyl functionality of 3 and a number of hydroxyl groups of 274 mg KOH / g (205 equivalents).

[0060] Propoxylated TMP is a propoxylated form of trimethylolpropane. It has a nominal functionality of 3 and a number of hydroxyl groups of 950 mg KOH / g (59 equivalents).

[0061] The surfactant is a surfactant used for stabilizing organosilicon foam.

[0062] TIPA is a 99% triisopropanolamine product.

[0063] Catalyst A is a solution of 33% by weight of triethylenediamine in dipropylene glycol.

[0064] Catalyst B is benzyldimethylamine.

[0065] TCPP is tris(1-chloro-2-propyl) phosphate.

[0066] CaCO3 is calcium carbonate powder.

[0067] Polymerized MDI A has an isocyanate content of 31.45% by weight and an average isocyanate functionality of 2.7.

[0068] Polymer MDI B has an isocyanate content of 30.2% by weight and an average isocyanate functionality of 2.85.

[0069] Table 1

[0070]

[0071]

[0072] *Comparative example. 1 The polyol is polyol A, plus TIPA, glycerin, ethylene glycol, propoxylated TMP and tripropylene glycol, as present under each specific condition, excluding other components.

[0073] The dimensional stability of sample AG and each of Example 1 was evaluated and compared as follows: The length of each component was measured after equilibration at 22-24°C for 24 hours. The component was then placed horizontally in an oven and heated to 80°C for 72 hours. Its length was measured immediately after removal from the oven. The component was then cooled to 22-24°C for approximately 1 hour, and its length was measured again. The results are shown in Table 2.

[0074] Determine the glass transition temperature (T) of each of the comparison sample AG and Example 1. g The results for T and storage modulus (at 70°C) are also included in Table 2. g The peak value of the tanδ curve was determined and taken by dynamic mechanical analysis (three-point bending test).

[0075] Table 2

[0076]

[0077] Comparative sample A represents the baseline. When molded at 54°C, this formulation exhibits excellent dimensional stability. However, when molded at 22-24°C, the product experiences a significant increase in length and does not accurately recover its original length upon recooling. The difference in results between molded articles prepared at curing temperatures of 54°C and 22-24°C indicates that dimensional stability is related to the degree of curing that occurs during the molding step.

[0078] Comparative sample BG represents various methods for improving dimensional stability. In comparative sample B, a higher-functionality polyisocyanate was used to attempt to promote greater crosslinking during the molding step. The results were worse than the baseline.

[0079] In comparative sample C, the filler content was increased by 20%, as higher filler levels typically impart greater dimensional stability to the composite. Again, the results were worse than the baseline.

[0080] The comparison sample D included an additional catalyst, but the results were worse than the baseline.

[0081] Comparative samples E, F, and G represent attempts to increase in-mold curing by increasing the exothermic effect of the system (by reducing the average equivalence of the polyol and increasing the amount of polyisocyanate). In comparative sample F, a mixture of tripropylene glycol and propoxylated TMP was used due to the high viscosity of propoxylated TMP; the tripropylene glycol modifies the viscosity and also increases exothermic effect due to its low equivalence relative to polyol A. Comparative sample E performed similarly to the baseline, while comparative samples F and G showed only minor improvements. Comparative samples E and F also exhibited surface defects upon demolding.

[0082] Results obtained using comparative sample BG indicate that various methods aimed at promoting better in-mold curing at low mold temperatures have failed to significantly improve dimensional stability. Increasing crosslink density by using higher functionality polyisocyanates is ineffective, as is reducing the equivalent by adding various low-equivalent polyols and additional amine catalysts.

[0083] Example 1 unexpectedly exhibited significantly better dimensional stability than the baseline and all other comparative samples. Expansion during heat treatment was only about one-third that of the baseline and only half that of the best among the other comparative samples. Similar improvement was observed upon recooling. The product demolded well, producing a high-quality surface.

[0084] When the formulation includes triisopropanolamine, T g The data for both energy storage modulus and energy storage modulus showed a significant increase in both values. Other attempts to improve in-mold curing had relatively minor beneficial effects (if any) (comparing Comparative Example BG to Comparative Example A), thus highlighting the unique benefits of TIPA in the formulation.

[0085] Examples 2-5

[0086] Repeat Example 1, varying the amount of triisopropanolamine and adjusting the amount of polyol A by weight exchange. The formulation is shown in Table 3. Example 1 is included as a reference. The dimensional stability of the molded articles was evaluated as in the aforementioned samples, and the results are shown in Table 3.

[0087] Table 3

[0088]

[0089]

[0090] The results shown in Table 3 indicate that triisopropanolamine improves dimensional stability when used over a wide range of loadings. Within this range, dimensional stability improves with increasing triisopropanolamine loading.

[0091] Comparison Sample HK

[0092] Triethanolamine is commonly used as a crosslinking agent in polyurethane foam formulations. It is chemically similar to triisopropanolamine because both contain a single tertiary nitrogen atom and both have three hydroxyl groups. The formulation for the polyurethane composite comparative sample HK corresponds to the formulations in Examples 2-5, except that triethanolamine (TEOA) is used instead of triisopropanolamine (measured by weight exchange).

[0093] The emulsification, gelation, and surface drying times of samples A and HK, as well as Examples 2-5, were evaluated and compared. In each case, this was achieved by forming a formulated polyol blend of all components except the polyisocyanate and equilibrating the polyol blend to 40°C. The polyisocyanate was equilibrated separately to 25°C. The polyisocyanate and polyol blends were mixed on a high-speed laboratory mixer for 12 seconds and poured into a cup. The emulsification time was the time after pouring when a visible reaction was observed. The gelation time (the time it took for the polymer strings to adhere to a spatula after mixing) was assessed by periodically pressing a metal rod onto the surface of the cured reaction mixture and removing it. The surface drying time (the time it took for the polymer to no longer adhere to the finger after mixing) was assessed by periodically pressing a human finger onto the surface of the cured reaction mixture and removing it. Those results are shown in Table 4.

[0094] Table 4

[0095]

[0096] *Comparative Examples

[0097] As the data in Table 4 indicate, adding these amounts of TIPA causes only a slight reduction in milking, gelling, and surface drying times across the entire loading range. On the other hand, TEOA causes a very large reduction in each of those times, indicating a very large increase in system reactivity. Due to its lower reactivity, TIPA-containing systems are better suited for preparing large molded parts in casting processes than TEOA-containing systems. The slight increase in the reactivity of TIPA systems allows them to be readily used in such processes.

Claims

1. A composite material comprising a continuous resin phase and a discontinuous phase comprising filler particles, reinforcing fibers, or both, in an amount of 8% to 85% by weight based on the weight of the composite material, wherein the continuous resin phase is a cured polyurethane, the cured polyurethane being a reaction product of a reaction mixture forming a polyurethane characterized by an isocyanate index of 95 to 150, the reaction mixture comprising... A) An aromatic polyisocyanate or a mixture of aromatic polyisocyanates, wherein the aromatic polyisocyanate or the mixture of aromatic polyisocyanates has an isocyanate functionality of 2 to 4 and an isocyanate equivalent of 80 to 175. B) A polyol mixture having an average hydroxyl equivalent of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine accounts for 10% to 33% by weight of the polyol mixture.

2. The composite material according to claim 1, wherein the discontinuous phase comprises reinforcing fibers with a diameter of 0.5 to 10 μm and a length of 2 mm to 150 mm.

3. The composite material according to claim 1 or 2, wherein the fiber is glass fiber.

4. The composite material according to claim 2, wherein the discontinuous phase further comprises filler particles.

5. The composite material according to claim 1 or 2, comprising 2% to 15% by weight of reinforcing fibers, 30% to 70% by weight of filler particles, and 20% to 50% by weight of the continuous resin phase.

6. The composite material according to claim 1 or 2, wherein the void volume is not greater than 65%.

7. A method for preparing the composite material according to claim 1, comprising (i) introducing reinforcing fibers and / or filler particles and a reaction mixture for forming polyurethane into a cavity of a mold or onto a model, closing the mold or applying mechanical pressure to the model such that the reinforcing fibers and / or filler particles become embedded in the reaction mixture for forming polyurethane, and (ii) curing the reaction mixture for forming polyurethane in the presence of the reinforcing fibers and / or filler particles in the mold cavity or on the model to form the composite material, wherein the reaction mixture for forming polyurethane is characterized by an isocyanate index of 95 to 150 and contains A) An aromatic polyisocyanate or a mixture of aromatic polyisocyanates, wherein the aromatic polyisocyanate or the mixture of aromatic polyisocyanates has an isocyanate functionality of 2 to 4 and an isocyanate equivalent of 80 to 175. B) A polyol mixture having an average hydroxyl equivalent of 125 to 275 and an average hydroxyl functionality of 2.5 to 4 hydroxyl groups per molecule, wherein triisopropanolamine accounts for 10% to 33% by weight of the polyol mixture.

8. The method of claim 7, wherein the step of curing the reaction mixture forming the polyurethane is carried out at a temperature not exceeding 40°C.

9. The method according to claim 7 or 8, wherein the composite material has a void volume of not more than 65%.

10. The method according to claim 7 or 8, wherein the reaction mixture forming the polyurethane comprises reinforcing fibers with a diameter of 0.5 to 10 μm and a length of 2 mm to 150 mm.

11. The method according to claim 7 or 8, wherein the composite material comprises 2% to 15% by weight of reinforcing fibers, 30% to 70% by weight of filler particles, and 20% to 50% by weight of the continuous resin phase.

12. The method according to claim 7 or 8, wherein step i) is performed by: wetting the reinforcing fiber with the polyurethane-forming reaction mixture, dispensing the reinforcing fiber wetted with the polyurethane-forming reaction mixture into the mold or onto the model, closing the mold or applying mechanical pressure to the polyurethane-forming reaction mixture on the model, and curing the polyurethane-forming reaction mixture in the mold.

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