Claims
- 1. A process for preparing a urea-formaldehyde resin precursor having an F/U mole ratio of 5:1 to not below 2.5:1, that comprises an acidic condensation as a first step, which condensation comprises
- slowly charging urea to an acidic aqueous formaldehyde solution having an initial pH of from about 0.5 to about 1.0 while maintaining the temperature of the solution in the range from about 50.degree. C. to about 98.degree. C., until the initial F/U mole ratio is not above 5:1 and not below 3.0:1, and then
- neutralizing the reaction mixture to a pH of 7.2 to 8.0.
- 2. The process of claim 1 wherein urea is charged at a temperature not above 95.degree. C., the reaction mixture is neutralized to a pH of 7.2 to 7.9, then a final charge of urea is added to adjust to a final F/U mole ratio to 3.25:1 to 2.5:1.
- 3. A process in accordance with claim 2 wherein the reaction mixture is neutralized to a pH in the range of 7.7 to 7.9, and the F/U mole ratio after the addition of the final charge of urea is 2.6:1 to 2.5:1.
- 4. A process according to claim 3 wherein the solids content of the product obtained is from 60% to 69% by weight.
- 5. The process of claim 1 wherein urea is charged at a temperature not above 95.degree. C., and sufficient urea is added that the F/U mole ratio of the product is from 3.25:1 to 3.0:1.
- 6. The process of claim 5 wherein the F/U mole ratio of the product is 3.1:1.
- 7. The process of claim 5 wherein the reaction mixture is neutralized to a pH in the range of 7.7 to 7.9, and the F/U mole ratio after the addition of the final charge of urea is 2.6:1 to 2.5:1, and wherein the reactants are selected and added so that the solids content of the product is from 60% to 64% by weight of the product.
- 8. A process according to claim 2 wherein the viscosity of the final product of the process as produced is from 30 cps to 100 cps, as measured on a Brookfield RVF viscometer using a No. 1 spindle at 90 rpm at 25.degree. C.
- 9. A process according to claim 8 wherein, after the final charge of urea is added, the pH is adjusted to 7.2 to 8.0.
- 10. A process for preparing a urea-formaldehyde resin precursor having an F/U mole ratio of 3.25:1 to 2.5:1, comprising:
- slowly charging urea to an acidic aqueous formaldehyde solution having a pH of 0.8 to 1.0, while maintaining the temperature of the solution in the range from about 50.degree. C. to about 98.degree. C., to form a condensate having an initial F/U mole ratio from 5:1 to 3.0:1, and then
- adjusting the pH of the condensed reaction mixture to 7.2 to 8.0, then
- adding more urea to attain an F/U mole ratio in the range from 3.25:1 to 2.5:1, and then
- adjusting the pH of the final reaction product to 7.2 to 8.0.
- 11. The process of claim 10 wherein the urea is added to the acidic formaldehyde solution at a temperature not above 85.degree. C. and sufficient urea is initially added to the acidic formulation that the F/U mole ratio of said condensate is from 3.25:1 to 3.0:1.
- 12. The process of claim 11 wherein, in the step of adding more urea to the condensate, urea is added to attain a final F/U mole ratio of the resin precursor of from 3.0:1 to 2.5:1.
- 13. A process according to claim 12 wherein the resin precursor product as produced has a viscosity in the range from 30 cps to 100 cps, is adjusted to a pH of 7.4 to 7.9, and has a solids content of from 60% to 69%.
- 14. The process of claim 11 wherein, in the step of adding more urea to the condensate, urea is added to attain a final F/U mole ratio of the resin precursor of 3.0:1 to 2.5:1, the viscosity of the final reaction product as produced is in the range from 30 cps to 100 cps, the pH is adjusted to the range from 7.4 to 7.9, and the solids content is in the range from 60% to 69%.
- 15. The process of claim 14 wherein urea is added to a final F/U mole ratio of 2.6:1 to 2.5:1, and wherein the solids content of the final reaction product is in the range from 60% to 66%.
- 16. A urea-formaldehyde condensation product produced by the process of claim 1.
- 17. A urea-formaldehyde resin precursor product produced by the process of claim 10.
- 18. A urea-formaldehyde resin precursor product produced by the process of claim 15.
- 19. A urea-formaldehyde condensate that is characterized by having an initial F/U mole ratio of from 5:1 to 2.5:1, produced by an initially acidic reaction between urea and formaldehyde at an initial pH less than about 1.0, said condensate being adjusted to a pH of 7.2 to 8.0, having a solids content of 60% to 69%, and having a storage life at 72.degree. F. greater than 102 days without becoming cloudy or settling.
- 20. A urea-formaldehyde condensate according to claim 19 wherein said initially acidic reaction is at a temperature not above 85.degree. C., the F/U mole ratio is in the range 3.25:1 to 3.0:1, and the pH is adjusted to 7.2 to 7.9.
- 21. The condensate of claim 20 wherein the F/U mole ratio is 3.1:1.
- 22. A urea-formaldehyde resin precursor that has a final F/U mole ratio in the range from 3.25:1 to 2.5:1, a solids content of from 62% through 69%, a pH of 7.2 to 8.0, and a storage life at 72.degree. F. that is greater than 102 days, without becoming cloudy or settling.
- 23. The precursor of claim 22 wherein the mole ratio is 3.0:1 or less, the solids content is at least 63%, and the pH is 7.4 or higher.
- 24. The precursor of claim 22 in the form of an aqueous dispersion having a viscosity as produced in the range from 30 cps to 100 cps.
- 25. The precursor of claim 23 wherein the solids content is not above 66%, and said precursor is in the form of an aqueous dispersion having a viscosity as produced in the range from 30 cps to 100 cps.
- 26. A urea-formaldehyde resin precursor produced from the condensate of claim 20, that has a final F/U mole ratio in the range of 3.0:1 to 2.5:1, a solids content of from 62% through 69%, a pH of 7.2 to 8.0, and a storage life at 72.degree. F. that is greater than 102 days, without becoming cloudy or settling.
- 27. An aqueous dispersion of a urea-formaldehyde resin precursor having a molar ratio of formaldehyde to urea in the range from about 3.25:1 to about 2.5:1, said dispersion being characterized by having a solids content in the range 62% to 69%, a pH of 7.2 to 8.0, and a viscosity not in excess of about 200 cps as measured on a Brookfield Viscometer Model RVF, No. 1 spindle, at 20 rpm and at 25.degree. C., after storage, following its production, for 102 days at a temperature of 72.degree. F.
- 28. The aqueous dispersion of claim 27 of a urea-formaldehyde resin precursor that is formed from a condensation product of urea and formaldehyde having a molar ratio of formaldehyde to urea in the range from about 3.25:1 to about 3.0:1, formed by the addition of urea to an aqueous solution of formaldehyde at an initial pH of 1 or less, and at a temperature not above 85.degree. C., said precursor having a final F/U mole ratio of 3.0:1 to 2.5:1 and having been produced from a reaction at a temperature of 50.degree. C. to 85.degree. C., then adjusted to a pH of 7.2 to 8.0, and characterized by having a viscosity as produced in the range from about 35 cps to about 100 cps, as measured on a Brookfield Viscometer Model RVF, Spindle No. 1, at 20 rpm and at 25.degree. C., which viscosity is stable to a viscosity not in excess of 200 cps after storage at a temperature of 72.degree. F. for at least 102 days.
- 29. The aqueous dispersion of claim 28 having a pH of 7.6 to 7.9, and a solids content of 62% to 66%.
RELATED APPLICATION
This application is a continuation-in-part of my earlier patent application, Ser. No. 416,573, filed Sept. 10, 1982, now U.S. Pat. No. 4,410,685, which is expressly incorporated herein by reference. My earlier application disclosed a process for the production of a low emission urea-formaldehyde resin useful as an adhesive. The adhesive was particularly useful as a binder for wood particles and chips.
US Referenced Citations (12)
Foreign Referenced Citations (2)
Number |
Date |
Country |
532326 |
Oct 1956 |
CAX |
1168882 |
Apr 1964 |
DEX |
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
416573 |
Sep 1982 |
|