Patent Application
20080090921
The present invention will now be described for purposes of illustration and not limitation. Except in the operating examples, or where otherwise indicated, all numbers expressing quantities, percentages, OH numbers, functionalities and so forth in the specification are to be understood as being modified in all instances by the term “about.” Equivalent weights and molecular weights given herein in Daltons (Da) are number average equivalent weights and number average molecular weights respectively, unless indicated otherwise.
The present invention provides a reaction system for the preparation of a fiber reinforced composite according to the pultrusion process made from continuous fiber reinforcing material and a polyurethane formulation containing a polyisocyanate component including at least one polyisocyanate and an isocyanate-reactive component including at least one double metal cyanide (“DMC”)-catalyzed polyol.
The present invention also provides a pultrusion process for preparing a fiber reinforced polyurethane composite, the process involving continuously pulling a roving or tow of continuous fiber reinforcing material successively through an impregnation chamber and a die, continuously feeding a polyurethane formulation containing a polyisocyanate component including at least one polyisocyanate and an isocyanate-reactive component including at least one double metal cyanide (“DMC”)-catalyzed polyol to the impregnation chamber, contacting the fiber reinforcing material with the formulation in the impregnation chamber such that substantially complete wetting of the material by the formulation occurs, directing the fiber reinforcing material through a die heated to reaction temperature to form a solid composite and drawing the composite from the die, wherein conditions in the impregnation chamber are such that substantially no polymerization takes place.
The art is silent regarding the effect on pultrusion processing of low unsaturated polyols prepared via double metal cyanide (“DMC”) catalysts as the polyol component in polyurethane pultrusion formulations. Because polyols prepared via DMC catalysis are free of monols and have a higher functionality, they show improved properties relative to the corresponding base (KOH)-catalyzed polyols in pultrusion systems.
Among the benefits of the inventive formulations are: (1) the pultruded parts have a smoother surface in some embodiments which prevents defects from arising on the finished surface, especially those parts having complex profiles; (2) generally lower pull forces are required; (3) the pultrusion process can be stopped or paused for longer time periods without “locking up” in the die; (4) the pot life of the system is increased; and (5) the pultruded parts are lighter and more uniform in color.
Further, in contradistinction to the teaching in the art, exemplified by the patents mentioned hereinabove that require a high degree of polymerization occur within the impregnation die, the present inventors find it desirable to have essentially no reaction occur inside of the impregnation die. Although the gel time of any resin, not just a polyurethane, is important, the inventors herein have determined that it is not the key factor in determining pultrusion processability.
Pultrusion of the inventive polyurethane formulations with fiber reinforced composites is preferably performed by feeding the polyisocyanate and isocyanate-reactive components to a mix/metering machine for delivery in a desired ratio to a mixing apparatus, preferably a static mixer, to produce a polyurethane formulation. This polyurethane formulation is fed to an injection die where it can be used to impregnate fibers being pulled concurrently into the injection die. The conditions in the injection die are such that little, or more preferably no polymerization of the polyurethane formulation will occur. The resulting uncured composite is pulled through a zoned heating die, attached directly to the injection die, having a desired cross-section where it is shaped and cured. The dynamic forces needed to pull the composite through the forming die are provided by a pulling machine which has gripping devices that contact the cured composite profile (or the glass fibers therein) and give the traction necessary to pull the composite profile through the die. The machine may also have a device that develops a force in the desired direction of pull that gives the impetus necessary to pull the composite profile continuously through the die. The resulting composite profile upon exiting the pulling machine may be cut to the desired length by an abrasive cut off saw.
A long fiber based reinforcing material provides mechanical strength to the pultruded composite, and allows the transmission of the pulling force in the process. Fibers should preferably be at least long enough to pass though both the impregnation and curing dies and attach to a source of tension. The fibrous reinforcing material suitable in the instant invention may be any fibrous material or materials that can provide long fibers capable of being at least partially wetted by the inventive polyurethane formulation during impregnation. The fibrous reinforcing structure may be single strands, braided strands, woven or non-woven mat structures, combinations of these, or the like. Mats or veils made of long fibers may be used, in single ply or multi-ply structures. Suitable fibrous materials known in the pultrusion art, include, but are not limited to, glass fibers, glass mats, carbon fibers, polyester fibers, natural fibers, aramid fibers, nylon fibers, basalt fibers, combinations thereof. Particularly preferred in the present invention are long glass fibers. The fibers and/or fibrous reinforcing structures may be formed continuously from one or more reels feeding into the pultrusion apparatus and attached to a source of pulling force at the outlet side of the curing die. The reinforcing fibers may optionally be pre-treated with sizing agents or adhesion promoters as is known in the art.
The weight percentage of the long fiber reinforcement in the pultruded composites of the present invention may vary considerably, depending on the end use application intended for the composite articles. Reinforcement loadings may be from 30 to 95% by weight, preferably from 40 to 90% by weight of the final composite, more preferably from 60 to 90% by weight, and most preferably from 70 to 90% by weight, based on the weight of the final composite. The long fiber reinforcement may be present in the pultruded composites of the present invention in an amount ranging between any combination of these values, inclusive of the recited values.
In some embodiments of the present invention, the polyisocyanate component and the isocyanate-reactive component may be the only components that are fed into the impregnation die in the pultrusion process. The polyisocyanate component or the isocyanate reactive composition may be premixed with any optional additives. However, it is to be understood that the optional additives that are not themselves polyfunctional isocyanate reactive materials are to be considered (counted) as entities separate from the isocyanate-reactive component, even when mixed therewith. Likewise, if the optional additives, or any part thereof, are premixed with the polyisocyanate component, these are to be considered as entities separate from the polyisocyanate component, except in the case where they are themselves polyfunctional isocyanate species.
The pultrusion apparatus preferably has at least one impregnation die and at least one curing die. Because no polymerization is to take place in the impregnation die, the curing die necessarily will operate at a higher temperature than the impregnation die. The pultrusion apparatus may optionally contain a plurality of curing dies, or zones. Different curing zones may be set at different temperatures, if desired, but all the zones of the curing die will be higher in temperature than the impregnation die. The pultrusion apparatus may optionally contain a plurality of impregnation dies. Preferably, there is just one impregnation die, and this preferably is situated immediately prior to the first curing die (or zone). As mentioned hereinabove, the impregnation die is set at a temperature that provides for substantially no reaction (polymerization) between the polyisocyanate component and the polyisocyanate-reactive component in the inventive polyurethane formulation before the fibrous reinforcing structure, which has been at least partially impregnated with the inventive polyurethane formulation, enters the first curing die (or zone).
The isocyanate-reactive component of the present invention includes one or more double metal cyanide (“DMC”) catalyzed polyols. Suitable examples of methods for the preparation of DMC catalysts and the use thereof in the manufacture of polyether polyols can be found in U.S. Pat. Nos. 3,278,457, 3,404,109, 3,941,849 and 5,158,922, 5,482,908, 5,783,513, 6,613,714, 6,855,658, the entire contents of which are incorporated herein by reference thereto. The DMC-catalyzed polyols useful in the inventive isocyanate-reactive component preferably have an unsaturation of less than 0.02 meq/g, more preferably less than 0.01 meq/g, and most preferably less than 0.005 meq/g, Starter compounds suitable in producing the DMC-catalyzed polyol included in the inventive isocyanate-reactive component are any compounds having active hydrogen atoms. Preferred starter compounds include those compounds having number average molecular weights between 18 to 2,000 Da, more preferably, between 32 to 2,000 Da, and having from 1 to 8 hydroxyl groups. Any monofunctional or polyfunctional active hydrogen compound may be oxyalkylated for inclusion in the inventive isocyanate-reactive component. Suitable monofunctional initiators include, but are not limited to, methanol, ethanol, propanol, butanol, pentanol, phenols, C6-C36 branched or linear alcohols, and monofunctional ethers of polypropylene glycols, polyethylene glycols, polybutylene glycols, and polyoxyalkylene glycol copolymers. Polyfunctional initiators include, but are not limited to, water, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, propanediol, glycerine, trimethylolpropane, butanediol isomers, pentaerythritol, polypropylene glycols, polyethylene glycols, polybutylene glycols, and polyoxyalkylene glycol copolymers.
The alkylene oxides useful in producing the DMC-catalyzed polyol contained in the isocyanate-reactive component of the present invention include, but are not limited to, ethylene oxide, propylene oxide, 1,2- and 2,3-butylene oxide, isobutylene oxide, epichlorohydrin, cyclohexene oxide, styrene oxide, and the higher alkylene oxides such as the C5-C30 α-alkylene oxides. Other polymerizable monomers may be used as well, e.g. anhydrides and other monomers as disclosed in U.S. Pat. Nos. 3,404,109, 3,538,043 and 5,145,883, the contents of which are herein incorporated in their entireties by reference thereto.
Suitable polyisocyanates are known to those skilled in the art and include unmodified isocyanates, modified polyisocyanates, and isocyanate prepolymers. Such organic polyisocyanates include aliphatic, cycloaliphatic, araliphatic, aromatic, and heterocyclic polyisocyanates of the type described, for example, by W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136. Examples of such isocyanates include those represented by the formula,
Q(NCO)n
in which n is a number from 2-5, preferably 2-3, and Q is an aliphatic hydrocarbon group containing 2-18, preferably 6-10, carbon atoms; a cycloaliphatic hydrocarbon group containing 4-15, preferably 5-10, carbon atoms; an araliphatic hydrocarbon group containing 8-15, preferably 8-13, carbon atoms; or an aromatic hydrocarbon group containing 6-15, preferably 6-13, carbon atoms.
Examples of suitable isocyanates include ethylene diisocyanate; 1,4-tetramethylene diisocyanate; 1,6-hexamethylene diisocyanate; 1,12-dodecane diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3- and -1,4-diisocyanate, and mixtures of these isomers; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate; e.g. German Auslegeschrift 1,202,785 and U.S. Pat. No. 3,401,190); 2,4- and 2,6-hexahydrotoluene diisocyanate and mixtures of these isomers; dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI, or HMDI); 1,3- and 1,4-phenylene diisocyanate; 2,4- and 2,6-toluene diisocyanate and mixtures of these isomers (TDI); diphenylmethane-2,4′- and/or -4,4′-diisocyanate (MDI); naphthylene-1,5-diisocyanate; triphenylmethane-4,4′,4″-triisocyanate; polyphenyl-polymethylene-polyisocyanates of the type which may be obtained by condensing aniline with formaldehyde, followed by phosgenation (crude MDI), which are described, for example, in GB 878,430 and GB 848,671; norbornane diisocyanates, such as described in U.S. Pat. No. 3,492,330; m- and p-isocyanatophenyl sulfonylisocyanates of the type described in U.S. Pat. No. 3,454,606; perchlorinated aryl polyisocyanates of the type described, for example, in U.S. Pat. No. 3,227,138; modified polyisocyanates containing carbodiimide groups of the type described in U.S. Pat. No. 3,152,162; modified polyisocyanates containing urethane groups of the type described, for example, in U.S. Pat. Nos. 3,394,164 and 3,644,457; modified polyisocyanates containing allophanate groups of the type described, for example, in GB 994,890, BE 761,616, and NL 7,102,524; modified polyisocyanates containing isocyanurate groups of the type described, for example, in U.S. Pat. No. 3,002,973, German Patentschriften 1,022,789, 1,222,067 and 1,027,394, and German Offenlegungsschriften 1,919,034 and 2,004,048; modified polyisocyanates containing urea groups of the type described in German Patentschrift 1,230,778; polyisocyanates containing biuret groups of the type described, for example, in German Patentschrift 1,101,394, U.S. Pat. Nos. 3,124,605 and 3,201,372, and in GB 889,050; polyisocyanates obtained by telomerization reactions of the type described, for example, in U.S. Pat. No. 3,654,106; polyisocyanates containing ester groups of the type described, for example, in GB 965,474 and GB 1,072,956, in U.S. Pat. No. 3,567,763, and in German Patentschrift 1,231,688; reaction products of the above-mentioned isocyanates with acetals as described in German Patentschrift 1,072,385; and polyisocyanates containing polymeric fatty acid groups of the type described in U.S. Pat. No. 3,455,883. It is also possible to use the isocyanate-containing distillation residues accumulating in the production of isocyanates on a commercial scale, optionally in solution in one or more of the polyisocyanates mentioned above. Those skilled in the art will recognize that it is also possible to use mixtures of the polyisocyanates described above.
In general, it is preferred to use readily available polyisocyanates, such as 2,4- and 2,6-toluene diisocyanates and mixtures of these isomers (TDI); polyphenyl-polymethylene-polyisocyanates of the type obtained by condensing aniline with formaldehyde, followed by phosgenation (crude MDI); and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups, or biuret groups (modified polyisocyanates).
Isocyanate-terminated prepolymers may also be employed in the present invention. Prepolymers may be prepared by reacting an excess of organic polyisocyanate or mixtures thereof with a minor amount of an active hydrogen-containing compound as determined by the well-known Zerewitinoff test, as described by Kohler in “Journal of the American Chemical Society,” 49, 3181(1927). These compounds and their methods of preparation are well known to those skilled in the art. The use of any one specific active hydrogen compound is not critical; any such compound can be employed in the practice of the present invention.
The polyisocyanate composition preferably contains organic polyisocyanates having a number averaged isocyanate (NCO) functionality of from at least 1.8 to 4.0, more preferably from 2.0 to 3.0, most preferably from 2.3 to 2.9. The NCO functionality of the polyisocyanate composition may be in an amount ranging between any combination of these values, inclusive of the recited values.
The polyisocyanate composition preferably has a free isocyanate group content (NCO content) in the range of from 5% to 50% by weight, more preferably from 8% to 40%, most preferably from 9% to 35% by weight. The NCO content of the polyisocyanate composition may be in an amount ranging between any combination of these values, inclusive of the recited values.
The reaction mixture may optionally contain a catalyst for one or more of the polymer forming reactions of polyisocyanates. Catalyst(s), where used, is/are preferably introduced into the reaction mixture by pre-mixing with the DMC-catalyzed polyol.
Catalysts for the polymer forming reactions of organic polyisocyanates are well known to those skilled in the art. Preferred catalysts include, but are not limited to, tertiary amines, tertiary amine acid salts, organic metal salts, covalently bound organometallic compounds, and combinations thereof.
Examples of preferred tertiary amine catalysts include triethylenediamine, N,N-dimethyl cyclohexylamine, bis-(dimethylamino)-diethyl ether, N-ethyl morpholine, N,N,N′,N′,N″-pentamethyl diethylenetriamine, N,N-dimethyl aminopropylamine, N-benzyl dimethylamine, and aliphatic tertiary amine-containing amides of carboxylic acids, such as the amides of N,N-dimethyl aminopropylamine with stearic acid, oleic acid, hydroxystearic acid, and dihydroxylstearic acid.
Examples of suitable tertiary amine acid salt catalysts include those prepared by the at least partial neutralization of formic acid, acetic acid, 2-ethyl hexanoic acid, oleic acid, or oligomerized oleic acid with a tertiary amine such as triethylenediamine, triethanolamine, triisopropanolamine, N-methyl diethanolamine, N,N-dimethyl ethanolamine, mixtures of these amines, and the like.
Examples of preferred organic metal salts for use as catalysts include potassium 2-ethyl hexanoate (potassium “octoate”), potassium oleate, potassium acetate, potassium hydroxide, bismuth octoate, zinc neodecanoate, dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioleate, and other organotin carboxylate catalysts.
Other metal-based catalysts, which are suitable for use in the invention, include zinc carboxylates, such as zinc stearate and zinc neodecanoate, and bismuth carboxylates. Further examples of useful catalysts suitable for use in the invention include amido amine compounds derived from the amidization reaction of N,N-dimethyl propanedimine with fatty carboxylic acids.
Mixtures of tertiary amine, amine acid salt, organometallic, and/or metal salt catalysts may be used. The use of mixed catalysts is well known to those skilled in the art. It is sometimes desirable to include in the mixing activated chemical formulation one or more catalysts for the trimerization of isocyanate groups.
The levels of the preferred catalysts required to achieve the needed reactivity profile for pultrusion processing will vary with the composition of the formulation and must be optimized for each reaction system (formulation). Such optimization would be well understood by persons of ordinary skill in the art. The catalysts preferably have at least some degree of solubility in the polyol blends used, and are most preferably fully soluble in the polyol blend at the use levels required.
The inventive reaction mixture may contain other optional additives, if desired. The optional additives are preferably added to the isocyanate-reactive material (typically, this is a polyol blend) prior to processing, although it is within the scope of the invention to premix all or any part of the optional additives package with the polyisocyanate composition under the proviso that it does cause the polyisocyanate to self-react or otherwise interfere with pultrusion processing of the reaction system. Examples of additional optional additives include particulate or short fiber fillers, internal mold release agents, fire retardants, smoke suppressants, dyes, pigments, antistatic agents, antioxidants, UV stabilizers, minor amounts of viscosity reducing inert diluents, combinations of these, and any other known additives from the art. In some embodiments of the present invention, the additives or portions thereof may be provided to the fibers, such as by coating the fibers with the additive.
Suitable fillers include, for example, calcium carbonate, barium sulfate, clays, aluminum trihydrate, antimony oxide, milled glass fibers, wollastonite, talc, mica, flaked glass, silica, titanium dioxide, molecular sieves, micronized polyethylene and combinations thereof.
Other preferred optional additives for use in pultrusion processing of mixing activated isocyanate-based polymer systems include moisture scavengers, such as molecular sieves; defoamers, such as polydimethylsiloxanes; coupling agents, such as the mono-oxirane or organo-amine functional trialkoxysilanes; combinations of these and the like. The coupling agents are particularly preferred for improving the bonding of the matrix resin to the fiber reinforcement. Fine particulate fillers, such as clays and fine silicas, are often used at thixotropic additives. Such particulate fillers may also serve as extenders to reduce resin usage.
Fire retardants are sometimes desirable as additives in pultruded composites. Examples of preferred fire retardant types include, but are not limited to, triaryl phosphates; trialkyl phophates, especially those bearing halogens; melamine (as filler); melamine resins (in minor amounts); halogenated paraffins and combinations thereof.
The stoichiometry of mixing isocyanate-based polymer forming formulations, containing an organic polyisocyanate and a polyfunctional isocyanate reactive resin is often expressed by a quantity known in the art as the isocyanate index. The index of such a mixing activated formulation is simply the ratio of the total number of reactive isocyanate (—NCO) groups present to the total number of isocyanate-reactive groups (that can react with the isocyanate under the conditions employed in the process). This quantity is often multiplied by 100 and expressed as a percent. Preferred index values in the inventive formulations range from 70 to 150%. A more preferred range of index values is from 90 to 125%.
As those skilled in the art are aware, pultrusion of polyurethane and polyisocyanurate systems with fiber reinforced composites is performed by supplying the polyisocyanate and isocyanate-reactive components to a mix/metering machine for delivery in a desired ratio to a mixing apparatus, preferably a static mixer, to produce a reaction mixture. The reaction mixture is supplied to an injection die where it can be used to impregnate fibers being pulled concurrently into the injection die. The resulting uncured composite is pulled through a zoned heating die, attached directly to the injection die, having a desired cross-section where it is shaped and cured. The curing die has two to three heated zones equipped with electrical heating coils individually controlled to maintain the desired temperatures. The entrance to the die is cooled to prevent premature polymerization. The temperature at the hottest zone generally ranges from about 350° F. to about 450° F. The dynamic forces needed to pull the composite through the forming die are supplied by the pulling machine. This machine typically has gripping devices that contact the cured composite profile (or the glass fibers therein) and give the traction necessary to pull the composite profile through the die. The machine also has a device that develops a force in the desired direction of pull that gives the impetus necessary to pull the composite profile continuously through the die. The resulting composite profile upon exiting the pulling machine is then cut to the desired length typically by an abrasive cut off saw.
The present invention is further illustrated, but is not to be limited, by the following examples. All quantities given in “parts” and “percents” are understood to be by weight, unless otherwise indicated. The following materials were used in the formulations of the examples:
The formulations in Table 1 were processed on several different commercial pultrusion machines with different die profiles and found to process well over a range of speeds and temperatures compared to the comparative example. The inventive formulations containing DMC-catalyzed polyols (Examples 2-8) yielded parts with better edge details on complex window lineal profiles, could be paused for long times without lockup, gave parts with a lighter color and smoother surface versus the comparative example (C1) containing polyols made by base catalysis.
The foregoing examples of the present invention are offered for the purpose of illustration and not limitation. It will be apparent to those skilled in the art that the embodiments described herein may be modified or revised in various ways without departing from the spirit and scope of the invention. The scope of the invention is to be measured by the appended claims.
