Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Reexamination Certificate
2001-03-23
2003-04-15
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
C528S256000, C528S486000, C524S789000, C524S858000, C525S480000
Reexamination Certificate
active
06548625
ABSTRACT:
TECHNICAL FIELD
The invention relates to a process for making liquid melamine urea formaldehyde (“MUF”) resins, liquid suspension hardeners, and adhesive compositions containing these materials. In particular, the invention relates to a liquid MUF resin that is stable for a significant period of time.
BACKGROUND OF THE INVENTION
MUF resins are widely used in the woodworking industry for gluing wood or as binders for the production of wood-based materials, including particle board, plywood, various fiber boards, and the like. These resins are the products of reactions of urea and melamine with formaldehyde. The resin is then set or cured with a hardener, such as ammonium salts or acids.
The resins, however, can often quickly solidify once the reaction between the melamine, urea, and formaldehyde is complete, sometimes in a matter of hours or minutes. This solidifying before the hardener is added, is problematic in that the resin cannot be stored for later use.
U.S. Pat. No. 4,536,245 to Shiau et al. discloses a MUF resin with a formaldehyde to urea equivalent molar ratio of 0.7:1 to 1.3:1. Urea equivalent is calculated by determining the moles of urea used and adding to that value 1.5 times the moles of melamine used. Thus, the urea equivalent molar ratio will be smaller than a straight formaldehyde to urea and melamine molar ratio.
U.S. Pat. No. 4,603,191 to Kong discloses a process for preparing a urea-formaldehyde resin having a very low mole ratio of formaldehyde to urea. It teaches a formaldehyde to urea molar ratio of 1:1 to 1.3:1.
U.S. Pat. No. 4,997,905 to Druet et al. teaches a process for producing a melamine urea-formaldehyde resin in three stages wherein the melamine is added at the first stage, second stage, or both. The final ratio of formaldehyde to amino groups ratio is 0.3:1 to 0.5:1.
U.S. Pat. No. 5,008,365 to Druet et al. teaches a process for producing a urea-formaldehyde resin with no more than 10% melamine. The final ratio of formaldehyde to amino groups is 0.5:1 to 0.575:1.
U.S. Pat. No. 5,162,462 to Barthomieux et al. teaches a process for producing aminoplast resins with 2-ureido-4,6-diaminotriazine-1,3,5 and optionally added melamine. The result is a resin with very low formaldehyde emission rates.
U.S. Pat. No. 5,681,917 to Breyer et al. discloses a method for preparing an MUF resin with a low formaldehyde content. The resin has a formaldehyde to urea and melamine molar ratio of 0.5:1 to 1.1:1.
E.P. Application No. 0501174 discloses a hardening composition for a urea-formaldehyde adhesive that includes an aqueous solution of an ammonium salt as a polymerization catalyst and a polyvinyl acetate resin in an emulsion.
PCT Application No. WO 99/48991 discloses a hardener for use in urea-formaldehyde and urea-melamine-formaldehyde based adhesives that includes a polyvinyl acetate emulsion together with a metal chloride and an ammonium salt.
A urea formaldehyde resin with a high melamine content is described by in “Melamine Modified Urea-formaldehyde Resin For Bonding Flakeboards,” Proceedings of a Symposium on Wood Adhesives Before the Forest Products Research Society, pp. 155-59, Madison, Wis., 1990. The resins contained 9.5 to 34.4 percent melamine by weight. These resins, however, had a shelf life of less than 1 day.
The focus of the art up to this point has been to produce a resin that has very low formaldehyde emission rates. These resins either do not have good wet bonding strength or have insufficient stability to be stored for extended periods of time. Thus, there is a need for liquid resins that are stable for extended periods of time, can be stored for later use, and are resistant to moisture in wood bonding applications. Resins that contain a higher level of formaldehyde and melamine are generally less stable than those that contain less formaldehyde and melamine. There is also a need in the art for a liquid resin and liquid hardener that can be used in both thermal and radio frequency curing conditions.
SUMMARY OF THE INVENTION
The invention relates to a method of preparing a stable melamine urea formaldehyde resin, including the steps of: providing a first aqueous solution of formaldehyde, heating the solution, adding in a single step about 0.35 to 0.65 molar equivalents of urea based on the amount of formaldehyde provided in the first aqueous solution to form a UF mixture, adding acid to the UF mixture to adjust the pH to a value of about 4 to 7 to provide an acidified UF mixture, monitoring the viscosity of the acidified UF mixture until it reaches a value of about 150 to 1000 cps, adjusting the pH of the acidified mixture to a value of about 8 to 10 to provide a basic UF mixture, adding a second aqueous solution including about 0.24 to 1.27 molar equivalents of formaldehyde based on the amount of formaldehyde provided in the first aqueous solution to the basic UF mixture, adjusting the pH of the basic UF mixture to a value of about 8 to 10, adding in a single step about 0.15 to 0.55 molar equivalent of melamine based on the amount of formaldehyde provided in the first aqueous solution to the basic UF mixture to form an MUF mixture, monitoring the viscosity of the MUF mixture until it reaches a value of about 150 to 1000 cps, and adjusting the pH to a value of about 9 to 10 to provide the melamine urea formaldehyde resin having a viscosity that is less than about 1500 cps for about 14 days.
In one embodiment, the preparation further includes adding up to about 0.13 molar equivalents of methanol based on the amount of formaldehyde provided in the first aqueous solution to the MUF mixture. In a preferred embodiment, the added acid is formic acid. The pH may be adjusted with sodium hydroxide. In a preferred embodiment, the viscosity of the acidified UF mixture is monitored until the viscosity reaches a value of about 150 to 400 cps. The aqueous mixture of formaldehyde is preferably formalin.
In another embodiment, the method includes preparing a melamine urea formaldehyde resin and adding a hardener to the resin to form an adhesive. In one embodiment, the hardener or adhesive is combined with a filler selected from the group of wood flour, pecan shells, organically modified cellulose, various starches, insoluble fibrous carbohydrate fillers, tricalcium phosphate, clay, barium sulfate, and hydrated aluminum magnesium silicates.
The invention further relates to a MUF resin having a formaldehyde to melamine and urea molar ratio of about 1.5:1 to 2.5:1, a melamine to urea molar ratio of about 0.25:1 to 1.5:1, and a viscosity of less than about 1500 cps for about 14 days. In a preferred embodiment, the formaldehyde to melamine and urea molar ratio is about 1.75:1 to 2.3:1, the melamine to urea molar ratio is about 0.5:1 to 0.75:1, the viscosity is about 200 cps to 400 cps, and the viscosity of the resin remains at a value of less than about 1500 cps for at least about 3 weeks.
The invention also relates to a liquid hardener including a catalyst, a filler, a thickener, and water, wherein the filler remains suspended in the hardener for at least about 14 days. In a preferred embodiment, the hardener includes about 6% to 30% of the catalyst, about 7% to 50% of the filler, and about 0.8% to 10% of the thickener. The catalyst is selected from the group consisting of a Lewis acid, a Bronsted acid, an ammonium salt, a substituted ammonium salt, or a combination thereof. Preferably, the catalyst includes AlCl
3
, NH
4
Cl, or a combination thereof; the filler includes pecan shells, wood flour, or a combination thereof; and the thickener includes polyurethane, polyvinyl alcohol, fumed silica, or a bentone clay. In another embodiment, the liquid hardener further includes an anti-foaming agent.
The invention also relates to an adhesive composition including a hardener and an MUF resin, the resin having a formaldehyde to melamine and urea molar ratio of about 1.5:1 to 2.5:1, a melamine to urea molar ratio of about 0.24:1 to 1.27:1, wherein the viscosity of the adhesive is less than about 1500 cps for at least about 14 days. In one embodiment, the composition in
Jacobs, III William
Lees Robert G.
Mendonca Luis
Rasch Roger C.
Zhu Huide Dennis
Cytec Technology Corp.
Didamo Valerie T.
Jubinsky James A.
Schultz Claire M.
Truong Duc
LandOfFree
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