HYBRID PHENOL-FORMALDEHYDE AND ISOCYANATE BASED RESINS

Abstract: Hybrid resins formed of an acylated phenol-formaldehyde (PF) resin and an isocyanate component have extended shelf stability, yet cure at a rate faster than any of its components when used in conventional flakeboard, strandboard or other board making processes.

Description: HYBRID PHENOL-FORMALDEHYDE AND ISOCYANATE BASED RESINS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the field of adhesives, more particularly to adhesives useful in the area of forest products, such as plywood, chipboard, waferboard, strandboard, etc. Methods of synthesis, the resulting adhesive and methods of using the adhesive are within the scope of the invention. 2. Description of the Related Art Forest products, especially products which are manufactured into useful materials through the use of adhesives are generally known. Chipboard, waferboard, strandboard, plywood and other composites made through the addition of an adhesive to forest products or byproducts is well established. Generally, the adhesive comprises a phenol-formaldehyde (PF) resin. Another commonly used resin is a liquid polymethylene poly(phenyl isocyanate) (pMDI). Although aqueous, alkaline phenol-formaldehyde resins show good durability, relatively low cost and relatively low toxicity, they are known to exhibit slower press times and, in general, produce products with higher thickness swell properties than the same products composed of a pMDI binder. Although isocyanate resins can exhibit some enhanced performance, they are more costly than PF resins. An additional drawback to production in manufacturing plants is the huge capital costs associated with the press and associated equipment, including steam generation equipment which provides the heat during the pressing process. Yet the press itself is a bottleneck in the process because of the dwell time of the product required in the press in order to cure the adhesive. Thus, any manner of reducing dwell time would be of commercial importance to the board making industry. Thus, there exists a need for suitable adhesive compositions for the manufacture of improved wood products, especially exterior grade products, such as waferboard and oriented strandboard. SUMMARY OF THE INVENTION It is, therefore, an object of the invention to provide novel adhesive systems which avoid the problems associated with the known adhesives. It is a further object of the invention to provide a hybrid resin comprising the combination of a PF resin and an isocyanate component that forms a single phase liquid material, and which has both shelf stability, and fast cure times when used in conventional board making processes. We have found that by combining a protected PF resin and an isocyanate component we can obtain a storage life of greater than 2 weeks at room temperature. The hybrid resin of the invention can be applied to forest products by applying, e.g., by spraying, blending or otherwise mixing the adhesive and lignocelluosic material, such as wood flakes, wood fibers, wood particles, wood wafers, strips or strands, or other comminuted lignocellulosic materials while the materials are tumbled or agitated in a blender or similar apparatus. Once blended, the materials are formed into a loose mat which, optionally after orientation of the lignocellulosic materials, is compressed between heated platens or plates to set the binder and bond the flakes, strands, strips, pieces, etc. together in densified form. Conventional processes are carried out at elevated temperatures of from about 120 to 225°C, by using a source of heat, such as steam, to heat the platens, or even to inject the steam into the mat, to cure the resin. Alternatively, the blended material may be fed to molds for the purpose of forming molded articles in which the resin and particles are bonded under heat and pressure. However, notwithstanding the particular shaping process employed, the resin of the invention has a faster cure time than its individual components. The adhesive of the invention has other utilities, such as being coated upon veneers or strips of wood, laminates, etc. by roll coating, knife coating, curtain coating or spraying the adhesive onto the veneer surface(s). A plurality of veneers are then laid-up to form sheets of the required thickness and subjected to heat and pressure to effect consolidation and curing of the materials into a board. Synthesis of the novel adhesives of the invention are also disclosed in more detail in connection with the description of the preferred embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Phenol-formaldehyde resins are generally well known to fall into two classes depending upon the phenol to formaldehyde ratio and being generally termed "novolacs" or "novolaks" (which are thermoplastic) and "resoles" (which are thermosetting). Suitable polyisocyanates which may be used in forming the isocyanate compositions in accordance with the present invention include monomeric diisocyanates, NCO prepolymers, and preferably liquid polyisocyanates and polyisocyanate adducts, and mixtures thereof. Suitable monomeric diisocyanates may be represented by the formula R(NCO) 2 in which R represents an organic group obtained by removing the isocyanate groups from an organic diisocyanate having a molecular weight of about 56 to 1 ,000, preferably about 84 to 400. Diisocyanates preferred for the process according to the invention are those represented by the above formula in which R represents a divalent aliphatic, hydrocarbon group having 4 to 12 carbon atoms, a divalent cycloaliphatic hydrocarbon group having 6 to 13 carbon atoms, a divalent araliphatic hydrocarbon group having 7 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. Preferred monomeric diisocyanates are those wherein R represents an aromatic hydrocarbon group. Examples of the suitable organic diisocyanates include 1 ,4-tetramethyIene diisocyanate, 1 ,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1 ,6-hexamethylene diisocyanate, 1 ,12-dodecamethylene diisocyanate, cyclohexane-1 ,3- and -1 ,4- diisocyanate, 1 -isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3- isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis(4-isocyanatocyclohexyl) methane, 2,4'-dicyclohexyImethane diisocyanate, 1 ,3- and 1 ,4-bis(isocyanatomethyl) cyclohexane, bis(4-isocyanato-3-methyl-cycIohexyl) methane, ,α,α',α'-tetramethyl-1 ,3- and/or -1 ,4-xylylene diisocyanate, 1 -isocyanato- 1 -methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- and/or 2, 6-hexahydrotoluene diisocyanate, 1 ,3- and/or 1 ,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate, 2,4'- and/or 4,4'-diphenylmethane diisocyanate, 1 ,5-diisocyanato naphthalene and mixtures thereof. Aromatic polyisocyanates containing 3 or more isocyanate groups such as 4,4',4"-triphenylmethane triisocyanate and polymethylene poly(phenylisocyanates) obtained by phosgenating aniline/formaldehyde condensates may also be used. In accordance with the present invention, at least a portion of the polyisocyanate component may be present in the form of an NCO prepolymer, semi- prepolymer or a polyisocyanate adduct. Suitable polyisocyanate adducts are those containing isocyanurate, uretdione, biuret, urethane, allophanate, carbodiimide and/or oxadiazinetrione groups. The polyisocyanate adducts have an average functionality of 2.0 to 4 and an NCO content of 5 to 30% by weight. Suitable adducts/prepolymers include the following type of components: 1 ) Isocyanurate group-containing polyisocyanates which may be prepared as set forth in DE-PS 2,616,416, EP-OS 3,765, EP-OS 10,589, EP-OS 47,452, US- PS 4,288,586 and US-PS 4,324,879. The isocyanato-isocyanurates generally have an average NCO functionality of 3 to 4.0, preferably of from 3.2 to 3.6, and an NCO content of 5 to 30%, preferably 10 to 25% and most preferably 15 to 25% by weight. 2) Uretdione diisocyanates which may be prepared by oligomerizing a portion of the isocyanate groups of a diisocyanate in the presence of a, i.e., trialkyl phosphine catalyst and which may be used in admixture with other aromatic, aliphatic and/or cycloaliphatic polyisocyanates, particularly the isocyanurate group- containing polyisocyanates set forth under (1) above. 3) Biuret group-containing polyisocyanates which may be prepared according to the processes disclosed in U.S. Patents 3,124,605; 3,358,010; 3,644,490; 3,862,973; 3,906,126; 3,903,127; 4,051 ,165; 4,147,714; or 4,220,749 by using co-reactants such as water, tertiary alcohols, primary and secondary monoamines, and primary and/or secondary diamines. These polyisocyanates preferably have an NCO content of 18 to 22% by weight and an average NCO functionality of 3 to 3.5. 4) Urethane group-containing polyisocyanates which may be prepared in accordance with the process disclosed in U.S. Patent 3,183,112 by reacting excess quantities of polyisocyanates, preferably diisocyanates, with low molecular weight glycols and polyols having molecular weights of less than 400, such as tripropylene glycol, trimethylol propane, glycerine, 1 ,2-dihydroxy propane and mixtures thereof. The urethane group-containing polyisocyanates have a most preferred NCO content of 12 to 20% by weight and an (average) NCO functionality of 2.5 to 3. 5) Allophanate group-containing polyisocyanates which may be prepared according to the processes disclosed in U.S. Patents 3,769,318, 4,160,080 and 4,177,342. The allophanate group-containing polyisocyanates have a most preferred NCO content of 12 to 28% by weight and an (average) NCO functionality of 2 to 4. 6) Isocyanurate and allophanate group-containing polyisocyanates which may be prepared in accordance with the processes set forth in U.S. Patents 5,124,427, 5,208,334 and 5,235,018; the disclosures of which are herein incorporated by reference. 7) Carbodiimide group-containing polyisocyanates which may be prepared by oligomerizing di- or polyisocyanates in the presence of known carbodiimidization catalysts as described in DE-PS 1 ,092,007, US-PS 3,152,162 and DE-OS 2,504,400, 2,537,685 and 2,552,350. Preferred polyisocyanate adducts are the polyisocyanates containing urethane groups, isocyanurate groups, biuret groups or mixtures of isocyanurate and allophanate groups. The NCO prepolymers, which may also be used as the polyisocyanate component in accordance with the present invention, are prepared from the previously described polyisocyanates or polyisocyanate adducts, preferably monomeric diisocyanates, and organic compounds containing at least two isocyanate-reactive groups, preferably at least two hydroxy groups. These organic compounds include high molecular weight compounds having molecular weights of 500 to about 6,000, preferably 1 ,000 to about 4,000, and optionally low molecular weight compounds with molecular weights below 400. The molecular weights are number average molecular weights (M n ) and are determined by end group analysis (OH number). Products obtained by reacting polyisocyanates exclusively with low molecular weight compounds are polyisocyanate adducts containing urethane groups and are not considered to be NCO prepolymers, but instead are considered adducts. It is preferred that the polyisocyanates of the present invention are aromatic polyisocyanates. Some examples of suitable aromatic poly-isocyanates are 1 ,3- and/or 1 ,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate, 2,4'- and/or 4,4'-diphenylmethane diisocyanate, 1 ,5-diisocyahato naphthalene and mixtures thereof. "Polymeric MDI" as used herein, refers to polymethylene poly(phenyl- isocyanate) which in addition to monomeric diisocyanate (i.e., two-ring compounds) contains three-ring and higher ring containing products. Also suitable are mixtures of polyisocyanate compositions as described above with adducts of MDI including, for example, allophanates of MDI as described in, for example, U.S. Patents 5,319,053, 5,319,054 and 5,440,003, the disclosures of which are herein incorporated by reference; urethanes of MDI as described in, for example, U.S. Patents 5,462,766 and 5,558,917, the disclosures of which are herein incorporated by reference; and carbodiimides of MDI as described in, for example, U.S. Patents 2,853,473, 2,941 ,966, 3,152,162, 4,088,665, 4,294,719 and 4,244,855, the disclosures of which are herein incorporated by reference. Particularly preferred components to be used as the isocyanate component in the present invention include those selected from the group consisting of: (a) a polymethylene poly(phenylisocyanate) component having an NCO group content of about 30 to 33%, preferably a polymethylene poly(phenylisocyanate) having a viscosity of less than about 2,000 cps at 20 ° C, and most preferably a polymethylene poly(phenylisocyanate) having a functionality of about 2.1 to about 3.5, an NCO group content of from about 30% to about 33%, and a monomer content of from about 30% to about 90% by weight, wherein the content of the monomer comprises from up to about 5% by weight of the 2,2'-isomer, from about 1 % to about 20% by weight of the 2,4'-isomer, and from about 25% to about 65% by weight of the 4,4'-isomer, based on the entire weight of the polyisocyanate; and (b) a semi-prepolymer of a polymethylene poly(phenylisocyanate) having an NCO group content of about 25 to 33%, preferably a semi- prepolymer of a polymethylene poly(phenyl isocyanate) having a urethane group content of about 0.5 to 6% and a viscosity of less than about 2,000 cps at 20°C, and being prepared by reacting a polymethylene poly(phenylisocyanate) with polyols or by blending a polymethylene poly(phenylisocyanate) with prepolymers from monomeric methylene bis(phenyl-isocyanate). The polyisocyanates of the present invention have a functionality of from about 2.1 to about 3.5, preferably 2.3 to 3.0 and most preferably of 2.6 to 2.8, and an NCO group content of about 30% to about 33%, preferably about 30.5% to about 32.5%, and a monomer content of from about 30% to about 90% by weight, preferably from about 40% to about 70%, wherein the content of monomer comprises up to about 5% by weight of the 2,2'-isomer, from about 1 to about 20% by weight of the 2,4'-isomer, and from about 25 to about 65% by weight of the 4,4'- isomer, based on the entire weight of the polyisocyanate. The polymeric MDI content of these isocyanates varies from about 10 to about 70% by weight, preferably from about 30% to about 60% by weight, based on the entire weight of the polyisocyanate. Other suitable polymeric MDI components include, for example, those described in U.S. Patents 3,666,953; 5,008,359; 5,140,086; 5,143,768; and 5,204,176, the entire disclosures of which are herein incorporated by reference. A preferred polymethylene poly(phenylisocyanate) blend has a functionality of from 2.2 to 2.4, an NCO group content of from about 31.2 to about 32.8% by weight, and a monomer content of from about 55% to about 80%, wherein the content of monomer comprises no more than about 3% by weight of the 2,2'-isomer, from about 15% to about 20% by weight of the 2,4'-isomer and from about 40% to about 55% by weight of the 4,4'-isomer, based on the entire weight of the polyisocyanate. This polyisocyanate blend comprises from about 20 to about 45% by weight, based on the entire weight of the polyisocyanate, of polymeric MDI. Most preferred polyisocyanates include, for example, polymethylene poly(phenylisocyanate) blends having an average functionality of from about 2.5 to about 3.0, preferably about 2.6 to about 2.8, an NCO group content of about 30 to 32% by weight, and a monomer content of from about 40 to 50% by weight, wherein the content of monomer comprises no more than about 1 % by weight of the 2,2'- isomer, from about 2 to about 10% by weight of the 2,4'-isomer and from about 35 to about 45% by weight of the 4,4'-isomer, based on the entire weight of the polyisocyanate. This isocyanate blend comprises from about 50 to about 60% by weight, based on the entire weight of the polyisocyanate, of polymeric MDI. Suitable polyisocyanates of the present invention also include, for example, mixtures of polyisocyanate blends as described above with adducts of MDI including, for example, allophanates of MDI as described in, for example, U.S. Patents 5,319,053, 5,319,054 and 5,440,003, the disclosures of which are herein incorporated by reference, and carbodiimides of MDI as described in, for example, U.S. Patents 2,853,473, 2,941 ,966, 3,152,162, 4,088,665, 4,294,719 and 4,244,855, the disclosures of which are herein incorporated by reference. Suitable semi-prepolymers of polymethylene poly(phenylisocyanate) to be used in the present invention include those semi-prepolymers having an NCO group content of 25 to 30% by weight. These semi-prepolymers have a urethane group concentration of about 0.5 to 6% and a viscosity of less than about 2,000 cps at 20°C. Typically, suitable semi-prepolymers can be prepared by reacting a polymethylene poly(phenylisocyanate) with a polyol, or by blending the polymethylene poly(phenylisocyanate) with a prepolymer of monomeric methylene bis(phenylisocyanate) as described in, for example, U.S. Patents 5,462,766 and 5,714,562, the disclosures of which are herein incorporated by reference. It is also possible to prepare suitable semi-prepolymers from a mixture of monomeric and polymeric MDI and an isocyanate-reactive material having from about 2 to about 4 hydroxyl groups and a molecular weight of from about 500 to about 6,000. These isocyanate-terminated prepolymers are formed by reacting a polyisocyanate mixture and an isocyanate-reactive compound having from about 2 to about 4 hydroxyl groups and a molecular weight of from about 500 to about 6,000 in amounts such that the ratio of equivalents of hydroxyl groups to isocyanate groups is from about 0.001 :1 to about 0.20:1 , preferably from about 0.004:1 to about 0.1 :1. The polyisocyanate mixture preferably comprises a mixture of polyphenylene polymethylene polyisocyanate(also known as polymeric MDI) and a mixture of diphenylmethane diisocyanate isomers. The polymethylene poly(phenylisocyanate) must be present in the polyisocyanate mixture in an amount of from 50 to about 60% by weight (based on the total weight of the polyisocyanate mixture), preferably from about 50 to about 58% by weight, and most preferably from about 52 to about 56% by weight. The mixture of diphenylmethane diisocyanate isomers is present in an amount of from about 40 to 50% by weight (based on the total amount of polyisocyanate mixture), preferably from about 42 to about 50%. The isomer mixture of diphenylmethane diisocyanate is composed of (a) from about 4 to about 30% by weight (based on the total weight of the isomeric diphenylmethane diisocyanate mixture), preferably from about 5 to about 28% by weight of 2,4'-diphenyImethane diisocyanate and (b) from about 70 to about 96% by weight (based on the total amount of the diphenylmethane diisocyanate isomer mixture), preferably from about 72 to about 95% by weight of 4,4'-diphenylmethane diisocyanate. The polyisocyanate mixture may be produced in accordance with any of the techniques known in the art. The isomer content of the diphenymethane diisocyanate may be brought within the required ranges, if necessary, by techniques which are well known in the art. One technique for changing isomer content is to add monomeric MDI to a mixture of MDI containing an amount of polymeric MDI which is higher than desired. Polymeric isocyanates prepared from residues of the toluene diisocyanate production process may optionally be included in the binder composition of the present invention. Such residues are described, for example, in U.S. Patent 5,349,082. The isocyanate-reactive compound which is used to produce the prepolymer of the present invention must have from about 2 to about 4 hydroxyl groups, and most preferably from about 2 to about 3 hydroxyl groups and a molecular weight of from about 500 to about 6,000, preferably from about 1 ,000 to about 4,000. Any of the known isocyanate-reactive materials containing hydroxyl groups which satisfy these criteria may be used. Suitable isocyanate-reactive materials include but are not limited to any of the known polyesters and polyethers. Polyesters which may be used to produce the prepolymers of the present invention include the reaction products of polyhydric (preferably dihydric) alcohols with polybasic (preferably dibasic) carboxylic acids, polycarboxylic acid anhydrides or polycarboxylic acid esters of lower alcohols. The polycarboxylic acid may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally be substituted (e.g., by halogen atoms) and/or unsaturated. Specific examples of suitable carboxylic acids and their derivatives are succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic acid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride, endomethylene tetrahydrophthalic acid anhydride, glutaric acid anhydride, maleic acid, maleic acid anhydride, fumaric acid anhydride, dimerized and trimerized unsaturated fatty acids(optionally in admixture with monomeric unsaturated fatty acids such as oleic acid), terephthalic acid dimethyl ester and terephthalic acid-bis- glycol ester. Specific examples of suitable alcohols are 1 ,2-propylene glycol, 1 ,3- propylene glycol, 1 ,4-butylene glycol, 2,3-butylene glycol, 1 ,6-hexanediol, 1 ,8- octanediol, neopentyl glycol, 1 ,4-bis-hydroxy-methyl cyclohexane, 2-methyl-1 ,3- propanediol, glycerol, trimethylol propane, 1 ,2,6-hexanetriol, 1 ,2,4-butanetriol, trimethylol ethane, pentaerythritol, quinitol, mannitol, 1 ,4-cyclohexanedimethylol, sorbitol, formitol, methyl glycoside, diethylene glycol, triethylene glycol, tetraethylene glycol, higher polyethylene glycols, dipropylene glycol, higher polypropylene glycols, dibutylene glycol and higher polybutylene glycols. The polyester may contain terminal carboxyl groups or a small portion of monofunctional ester capped functionalities. Polyesters of lactones (e.g., ε-caprolactone) or of dihydroxy carboxylic acids (e.g., ω-hydroxy caproic acid) may also be used. Preferred polyesters are prepared from mixtures of phthalic, isophthalic and terephthalic acids with ethylene glycol, diethylene glycol and higher polyethylene glycols. Polyethers which may be used to produce the prepolymers of the present invention may be produced, for example, by polymerizing epoxides themselves in the presence of a Lewis acid catalyst or by the addition of an epoxide to starter components containing reactive hydrogen atoms such as water, alcohols, ammonia or amines. Epoxides which may be used include ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide and epichlorohydrin. Ethylene oxide, propylene oxide and combinations thereof are particularly preferred. Specific examples of suitable starter components include: ethylene glycol, 1 ,3-propylene glycol, 1 ,2-propylene glycol, trimethylol propane, glycerol, sorbitol, 4,4'-dihydroxy diphenyl propane, aniline, ethanolamine, substituted ethanolamines such as methyl ethanolamine and methyl diethanolamine, ethylene diamine, and sucrose. The starter component may be used alone or in admixture with other starter components. Preferred polyethers are polypropylene oxide adducts started on an amine such as ammonia, ethylene diamine, and substituted ethanolamines. The polyisocyanate mixture and isocyanate-reactive material used to produce the prepolymers of the present invention are each used in quantities such that the ratio of equivalents of hydroxyl groups to isocyanate groups is from about 0.001 :1 to about 0.20:1 , preferably from about 0.004 to about 0.1 :1 , most preferably from about 0.005 to about 0.02:1. The prepolymer of the present invention may be prepared by reacting the polyisocyanate mixture and hydroxyl compound at temperatures of from about 10 to about 250°C, preferably from about 60 to about 120°C for a period of from about 1 to about 1500 minutes, preferably from about 30 to about 200 minutes. To mediate the undesirable properties of PF and an isocyanate component when used individually, the inventors thought to combine the two resin systems. However, the physical combination of the two binders is problematic because of differences in polarity and incompatible chemical functional groups. A strategy to produce a hybrid resin by emulsification of the pMDI in PF resin and chemical modification of the NCO functional group of the pMDI proved not to give a satisfactory combination of storage life and performance. Thus, the inventors conceived of the invention by modifying the PF resin. The inventors protected the functional group of the PF resin, e.g., by acylating the PF resin, and found that the esterfication of the phenolic oxygen greatly diminished the reactivity of the PF portion of the mixture when combined with an isocyanate component, preferably pMDI, to form a single phase liquid material with a storage life of greater than 2 weeks at room temperature. The diminished reactivity of the PF portion is well illustrated by its gel time in excess of 350 hours at 125°C. The gel time of the pMDI alone, or with added water to mimic the conditions needed to cure the hybrid resin is in excess of 100 min. at 121°C. However the gel time with added water of the acylated PF/pMDI system is about 10 min. The acyl PF resin can be produced by any known method of hydroxyl group acylation, to yield an organic-soluble anhydrous clear liquid. The acylated PF resin can then be added to any isocyanate component, specifically any commercially available pMDI resin, or a pMDI resin prepared to customer's specifications. When the acyl group is a carboxylic ester, it acts as a protecting group that permits reactivity of the hydroxyl oxygens with the NCO functionality of the isocyanate component. Under conditions of temperature and moisture encountered during manufacture of boards, such as strandboard, the PF and isocyanate component can react with one another. A particularly preferred ester comprises a component having an acetic acid ester group. There is a wide combination of phenolic resins and acyl groups that can be employed to render the PF resin inactive toward reaction with isocyanate groups as disclosed in U.S. Patents 5,051 ,454 and 5,340,888, the entire disclosures of which are herein incorporated by reference. Because of the inherent protecting nature of the acyl groups, the acyl PF resin can be used in combination with any isocyanate resin that is useful in commercial panel production. We have found that the two resins may be combined in amounts of from 10- 80 wt % PF resin based on the weight of the whole resin system. However, we have also found that hybrid resins comprised of 10-50 wt % PF exhibit better lack of viscosity advancement over a period of four weeks. With the addition of water in acetone, a 30 wt % PF/pMDI hybrid resin will react at 121 °C to form a gel, which hardens to form a single phase material. We have also found that strandboard panels produced with a 40 wt % PF/60 wt % pMDI hybrid resin exhibit cure speeds that appear much faster than either of the two individual components above. This synergistic effect was not expected by us. Accordingly, the hybrid resins of the present invention preferably comprise from about 10 to 80% by weight, and more preferably from about 10 to 50% by weight of the phenol formaldehyde component, and preferably from about 90 to 20% by weight, and more preferably from about 90 to 50% by weight, of the isocyanate component, with the sum of the % by weight of phenol formaldehyde component and isocyanate component totaling 100% by weight of the hybrid resin. In addition, the present invention relates to mixtures comprising from about 50 to 95% (preferably 60 to 90%) by weight of the hybrid resins described above, and from about 5 to 50% (preferably 10 to 40%) by weight of a solvent or a hydrophobic diluent, with the combined weights of hybrid resin and solvent or diluent totaling 100% by weight of the mixtures. Suitable components to be used as solvents and/or diluents in the present invention include those components selected from the group consisting of (a) liquid hydrophobic diluents having a flash point above 250°C and which are only slightly or negligibly soluble in water, (b) liquid cyclic alkylene carbonates, and (c) high boiling solvents which are free of Zwittemoff-active hydrogen atoms. The liquid hydrophobic diluents suitable for the present invention are those having a flash point above 250°F, preferably above 325°F and most preferably above 375°F, and that are only slightly or negligibly soluble in water, and are preferably insoluble in water. In the context of the present invention, the term "hydrophobic" is defined as being insoluble, negligibly or only slightly soluble in water. As many manufacturers use these terms without defining limits, as used herein "hydrophobic" refers to compounds that do not dissolve in water or do not dissolve in water in amounts greater than 2% by weight, preferably less than 1 % by weight, and most preferably less than 0.1 % by weight at room temperature. Viscosity of the hybrid resins may be reduced by adding the hydrophobic diluents of the present invention. It is preferred that the viscosity of the mixtures of the hybrid resins and hydrophobic diluents be in the range of 10 to 2,000 cps, preferably 50 to 1 ,000 cps, and most preferably 100 to 700 cps. Suitable liquid hydrophobic diluents to be used in the mixtures according to the present invention include those compounds having a flash point above 250°F, preferably above 325°F and most preferably above 375 and that are only slightly soluble in water or have negligible solubility in water, and preferably insoluble in water. Some examples of suitable liquid hydrophobic diluents include compounds such as, for example, aromatic sulfonamides, aromatic phosphate esters, alkyl phosphate esters, dialkylether aromatic esters, dialkylether diesters, polymeric polyesters, polyglycol diesters, polyester resins, alkyl alkylether diesters, aromatic diesters, aromatic triesters, aliphatic diesters, alkylether monoesters, alkyl monoesters, halogenated hydrocarbons, chlorinated paraffin, aromatic oils often used as processing aids, and phthalates often used as plasticizers including, for example, dialkyl phthalates, etc. In the context of the present invention, hydrophobic diluents are defined as those that are not soluble in water or water is not soluble in them in amounts greater than 2% (pbw), preferably less than 1 % and most preferably less than 0.1 %. Although less preferred, it is possible to add a small portion of diluents that are not hydrophobic provided that the amount of these present does not increase the thickness swell of the lignocellulosic composites prepared using the binders of the present invention. Illustrative examples of diluents that are not hydrophobic would be the cyclic carbonates including ethylene-, propylene-, and butylene-carbonate, ethers, ketones, and alkyl acetates. It is also possible, but less preferred, to add a portion of diluent in which the hybrid resin is not fully miscible, providing that the mixture of diluents solubilizes the resin. Illustrative examples of these materials include paraffinic oils, and napthenic oils containing a minimum of about 50% saturated hydrocarbon radicals, or in other words, those containing less than about 50% aromatic compounds. Suitable aromatic compounds are typically blends of high boiling aryl, alkylaryl and arylalkyl hydrocarbons obtained from coal tar or in the distillation of petroleum or in the recovery from the solvent extracts of petroleum-based products. Included are hydrogenated, partially-hydrogenated and non-hydrogenated light and heavy cracked distillates, napthenic oils, and paraffinic oils. These materials typically are comprised of complex mixtures of arylalkyl, alkylaryl, and polycyclic aromatic compounds containing these substituents. Illustrative examples of alkylaryl hydrocarbons are octylphenyl-, nonylpheny-, and dodecylphenyl-substituted aromatic and polycyclic aromatic compounds. Illustrative examples of arylalkyl hydrocarbons include phenylhexyl- and napthyldodecyl-substituted aromatic hydrocarbons. Illustrative examples of aryl and polycyclic aromatic compounds include substituted napthalenes, anthracenes, phenanthrenes, pyrenes, perylenes, coronenes, and the like. Examples of hydrogenated aromatic compounds include substituted dihydronapthalenes, tetralins and their higher ring analogues. Examples of other aromatic compounds include substituted fluorenes, fluoranthrenes, biphenyl, and further substituted biphenyl compounds. The aromatic compounds of the present invention are seldom separated and are most often obtained as blends with varying amounts of the individual components. The boiling points for the individual components range between about 150°C and about 500°C. The components typically have carbon numbers from about C 9 to about C 36 and often contain from about four to six condensed unsaturated rings. Some suitable phthalates to be used as diluents in accordance with the present invention include compounds such as, for example, diisobutyl phthalate, dibutyl phthalate, di-2-ethylhexyl azelate, di-2-ethylhexyl phthalate, dibutyl sebacate, diphenyl octyl phosphate, dioctyl phthalate, di-2-ethylhexyl sebacate, diphenyl-2- ethylhexyl phosphate, dioctyl azelate, dioctyl sebacate, diisodecyl phthlate, etc., wherein phthalate denotes the ortho-, meta- and para-isomers and mixtures thereof. Other suitable compounds to be used as diluents in the present invention include 2,2,4-trimethyl-1 ,3-pentanediol monoisobutyrate, 2,2,4-trimethyl-1 ,3-pentanediol diisobutyrate, 2,2,4-trimethyl-1 ,3-pentanediol dipropionate, 2,2,4-trimethyl-1 ,3- pentanediol dibutyrate, 2,2,4-trimethyl-1 ,3-pentanediol dicaproate, 2,2,4-trimethyl- 1 ,3-pentanediol dicaprionate, 2,2,4-trimethyl-1 ,3-pentanediol dioctanoate, etc. Preferred diluents for the present process include dioctyl phthalate, di-2- ethylhexyl phthalate, 2-hydroxybenzenesulfonic acid esters and 4-hydroxy- benzenesulfonic acid esters which contain, for example, from 1 to 24 carbon atoms in the ester group. It is preferred that these contain from 6 to 16 carbon atoms in the ester group, and most preferred that these contain from 8 to 12 carbon atoms in the ester group. Some examples of suitable diluents include compounds such as, for example, Mesamoll (CAS RN = 39406-18-3), a processing oil, commercially available from Bayer AG. Viplex 885, a petroleum distillate blend, commercially available from Crowley Chemical Corporation (CAS RN = 64741-81-7) as an aromatic hydrocarbon oil that it typically used as a processing oil, is a preferred diluent. Suitable compounds to be used a liquid cyclic alkylene carbonates in the present invention include, for example, propylene carbonate, butylene carbonate, and mixtures thereof. Suitable high boiling solvents which are free of Zwitternoff-active hydrogen atoms. These high boiling solvents include compounds such as, for example, N- methyl pyrrolidinone, dimethyl formamide, dimethyl sulfoxide, glycol ethers, glycol ether acetates, and liquid esters of alkoxyaliphatic carboxylic acids, including ethyl 3- ethoxypropionate, butyl 3-ethoxypropionate and butyl 3-butoxypropionate, high- boiling ketones including isophorone and cyclic ketones, and dibasic esters and blends of dibasic esters, particularly diethyl malonate, dimethyl adipate, dimethyl glutarate and dimethyl succinate, a mixture of the dibasic esters comprising dimethyl adipate, dimethyl glutarate and dimethyl succinate, commercially available from E. I. duPont and Company under the trade designation DBE. The advantages of the invention will become apparent by reference to the following examples: Example 1 Phenyl acetate and aniline were combined in a reaction vessel in approximately equimolar amounts. The temperature was raised to 121 ° C for 5 minutes to simulate the interior of a strandboard panel during hot pressing. Acetanilide, the product of actuation by aniline was identified as a major reaction product demonstrating that, under these conditions, the PF portion would be activated toward condensation and reaction with the isocyanate component. Example 2 An acetylated PF resin prepared from the treatment of a commercially available PF resin (sold under the description AcmeFlow®2012) with acetyl chloride and triethylamine was combined with a commercial polymeric MDI resin. Combinations in the weight ratios of 10%, 25% and 33% acyl PF (with the balance being polymeric MDI) produced clear homogeneous solutions that did not advance in viscosity noticeably over the test period of two weeks. Example 3 A mixture of 30 wt % PF/70 wt % pMDI with 0.25 mol. eq. of water/NCO was heated at 121°C. Samples were collected after 5 min. and 8 min. at which point the mixture was a soft gelatinous material. The material was removed from the heat source and after 2-3 minutes, the sample appeared to be a single phase hard solid. This example is consistent with the co-reactivity of the two resins. Example 4 A resin composition of 40 wt % acyl PF/60 wt % pMDI with an intrinsic viscosity of 75 cps at 25°C and 300 cps at 40°C was applied to wood particles using the standard procedure for making composite panels. The following resins were compared to determine how the performance of the hybrid resin compared to that of a commercially available polymeric MDI resin. Resin Description 1 polymeric MDI wood moisture = 2.7 wt % 2 Acyl PF/polymeric MDI 40 wt %:60 wt %; wood moisture = 2.7 wt % 3 Acyl PF/polymeric MDI 40 wt %:60 wt %; wood moisture = 5.6 wt % Results of thickness swell and internal bond Press temperature: 430 °C The results of the board study demonstrate that the resin of the invention is capable of producing a panel with acceptable thickness swell properties and internal bond strengths within press times that are commercially viable. One of the surprising features is that the same process used to provide greater room temperature stability in the hybrid resin appears to also offer faster cure speed in board production. The cure speed of the hybrid (mixed) resin appears to be faster than that of either component individually. Past experience with PF resoles indicates that they are always slower than pMDI in cure time. The acylated PF resins are even slower than ordinary PF resoles. Yet, when used in combination with pMDI, the result is a faster cure time. This attribute has great commercial advantage in reducing the dwell time in the consolidating press, thereby making the process of producing a board more productive. This greatly improves the production for a fixed capital investment in press apparatus and related equipment. While it will be apparent to those skilled in the art that various modifications and other embodiments of the invention can be made upon review of the foregoing disclosure, such modifications and embodiments do not depart from the spirit or scope of the invention as defined in the appended claims.

Claims: We claim: 1. A hybrid resin comprising a protected phenol-formaldehyde resin and an isocyanate component selected from the group consisting of diisocyanates, polyisocyanates, prepolymers thereof, adducts thereof, and mixtures thereof. 2. The hybrid resin of claim 1 , wherein said protected phenol- formaldehyde resin comprises an acylated phenol-formaldehyde. 3. The hybrid resin of claim 2, wherein the protecting group on the phenol-formaldehyde resin comprises an ester group. 4. The hybrid resin of claim 3, wherein the ester group comprises an acetic acid ester group. 5. The hybrid resin of claim 1 , wherein the phenol-formaldehyde resin is a resole. 6. The hybrid resin of claim 1 , wherein the isocyanate component comprises hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethylene diisocyanate, diphenylmethane diisocyanate, oligomers of diphenylmethane diisocyanate, polymethylene poly(phenylisocyanate), toluene diisocyanate, a prepolymer thereof, or an adduct thereof. 7. The hybrid resin of claim 1 , wherein the isocyanate component is selected from the group consisting of : (A) a polymethylene poly(phenylisocyanate) having an NCO group content of from about 30 to 33% by weight, and (B) a semi-prepolymer of polymethylene poly(phenylisocyanate) having an NCO group content of from about 25 to about 32% by weight. 8. The hybrid resin of claim 7, wherein (B) said semi-prepolymer has a viscosity of less than 1500 cps at 25°C and an NCO group content of from about 25 to about 32% and comprises the reaction product of: 1 ) a polyisocyanate mixture comprising: (a) from 50 to 60% by weight, based on the total weight of 1 ), of polymethylene poly(phenylisocyanate), (b) from 40 to 50% by weight, based on the total weight of 1 ), of an isomeric mixture of diphenylmethane diisocyanate comprising: (i) from about 4 to about 30% by weight, based on 100% by weight of 1)(b), of 2,4'-diphenylmethane diisocyanate, and (ii) from about 70 to about 96% by weight, based on 100% by weight of 1)(b), of 4,4'-diphenylmethane diisocyanate; and 2) at least one polyol having from 2 to 4 hydroxyl groups and a molecular weight of from about 500 to about 6,000, in amounts such that the ratio of equivalents of hydroxyl groups to equivalents of isocyanate groups is from about 0.001 :1.0 to about 0.20:1.0. 9. The hybrid resin of claim 7, wherein (A) said polymethylene poly(phenylisocyanate) has a functionality of about 2.1 to about 3.5, and a monomer content of from about 30 to about 90% by weight, wherein the monomer comprises up to about 5% by weight of the 2,2'-isomer, from about 1 % to about 20% by weight of the 2,4'-isomer and from about 25% to about 65% by weight of the 4,4'-isomer, based on the entire weight of the polyisocyanate. 10. The hybrid resin of claim 1 , wherein the amount of the protected phenol formaldehyde to the isocyanate component is from about 10% to about 80% by weight of the protected phenol formaldehyde, to about 90% to about 20% of the isocyanate component. 11. The hybrid resin of claim 10, wherein the amount of the protected phenol formaldehyde to the isocyanate component is from about 10 % to 50% by weight of the phenol formaldehyde to about 50% to 90 % by weight of the isocyanate component. 12. The hybrid resin of claim 1 having a storage stability of at least two weeks at room temperature. 13. A mixture comprising (1 ) from about 50 to about 95% by weight of the hybrid resin of claim 1 , and (2) from about 5 to about 50% by weight of a solvent or a hydrophobic diluent, wherein the combined weight of (1 ) and (2) totals 100% by weight of the mixture. 14. The mixture of Claim 13, wherein (2) is selected from the group consisting of (a) a liquid hydrophobic diluent having a flash point above 250°F and which is only slightly or negligibly soluble in water, (b) a liquid cyclic alkylene carbonate and (c) at least one high boiling solvent, which is free of Zwitternoff-active hydrogen atoms. 15. The mixture of claim 13, wherein (1 ) is present in an amount of from 60 to 90% by weight, and (2) is present in an amount of from 10 to 40% by weight, wherein the combined weight of (1) and (2) totals 100% by weight of the mixture. 16. A method of manufacturing a board made of lignocellulosic particles comprising mixing said particles with a hybrid resin according to claim 1 , forming the resulting mixture of lignocellulosic particles and resin into a loose mat and consolidating the mat under heat and pressure to cure the resin. 17. The method of claim 16, wherein the hybrid resin is present in an amount of from 1 to 20% by weight, based on the combined weight of lignocellulosic particles and of hybrid resin. 18. The method of claim 16, wherein the reaction occurs in the presence of moisture carried by the lignocellulosic particles. 19. The method of claim 18, wherein said lignocellulosic particles contain from 2 to 25% by weight of moisture (based on 100% by weight of the combined hybrid resin and any solvent or diluent present). 20. The method of claim 16, wherein the reaction occurs by reason of moisture provided by injection of steam through the mat during pressing. 21. The method of claim 16, wherein the phenol formaldehyde reacts with the isocyanate component at a temperature in excess of 120°C. 22. The method of claim 16, wherein the cellulosic particles are selected from the group consisting of wood flakes, wood fibers, wood wafers, wood strips, wood strands, wood veneers and mixtures thereof. 23. A method of manufacturing a board made of lignocellulosic particles comprising mixing said particles with the mixture of claim 13, forming the resulting mixture of lignocellulosic particles and resin into a loose mat and consolidating the mat under heat and pressure to cure the resin. 24. A method of preparing a hardened hybrid resin comprising providing a phenol formaldehyde resin, protecting the reactive oxygens of the phenol formaldehyde resin, mixing the protected phenol formaldehyde resin with an isocyanate component having reactive NCO groups, and permitting the protected phenol formaldehyde resin to react with the isocyanate component, thereby obtaining a hardened resin. 25. The method of claim 24, including mixing the hybrid resin with lignocellulosic material before the reaction step. 26. The method of claim 24, wherein reaction is achieved under conditions of elevated heat, elevated pressure and in the presence of moisture. 27. The method of claim 24, including the step of storing the mixture for more than two weeks at room temperature before said reaction step. 28. The method of claim 24, wherein the mixing step comprises mixing 10 wt % to 80 wt % of the protected phenol formaldehyde with 90 wt % to 20 wt % of the isocyanate component. 29. The method of claim 24, wherein the phenol-formaldehyde is a resole and the isocyanate component is polymethylene poly(phenyl isocyanate). 30. The method of claim 24, wherein the mixing comprises mixing 10 wt % to 40 wt % of the protected phenol formaldehyde with 90 wt % to 60 wt % of the isocyanate component. 31. The method of claim 24, wherein the protecting step results in an acylated phenol formaldehyde resin.

Inventors: CREEL LEWIS D, DETLEFSEN WILLIAM D, MILLER TODD R, CREEL, LEWIS, D., DETLEFSEN, WILLIAM, D., MILLER, TODD, R.
Applicants: BAYER AG, BORDEN CHEM INC, CREEL LEWIS D, DETLEFSEN WILLIAM D, MILLER TODD R, BAYER CORPORATION, BORDEN CHEMICAL, INC., CREEL, LEWIS, D., DETLEFSEN, WILLIAM, D., MILLER, TODD, R.
Application year: 2001
Main classification: B27N3
IPC codes: B27N1, B27N3, C08G8, C08G18, C08L61, C09J161, C09J175