Claims
- 1. A process for making paper having high dry and wet strength, which comprises adding to paper stock before sheet formation or applying to a surface of a paper sheet, a cationic urea/formaldehyde resin produced by condensing urea and formaldehyde in molar ratio of from 1:1.5 to 1:3 in the presence of polymers which contain not less than 1 mol % of polymerized vinylamine units and have K values of from 5 to 300 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25.degree. C. and at a polymer concentration of 1% by weight), in an amount of from 5 to 50 g, based on 1 mole of urea in the end product, where the mixture is first:
- a) precondensed at a pH of from 8 to 14, then acidified, and
- b) concondensed at a pH of from 1 to 5 until gel formation begins,
- c) then 0.3 to 1.5 moles of formaldehyde are added per mole of urea used,
- d) post-condensation is carried out and
- e) the resin solution is subsequently neutralized.
- 2. The process of claim 1, wherein for the cationic urea/formaldehyde resin, said polymerized vinyl amine units have the formula: ##STR4## where R is H or C.sub.1 -C.sub.6 -alkyl.
- 3. The process of claim 1, wherein cationic urea/formaldehyde resin has a K value of from 15 to 150.
- 4. The process of claim 1, wherein said cationic urea/formaldehyde resin contains structural units of the formula: ##STR5## where R is H and which resin has a K value of from 20 to 95.
- 5. The process of claim 1, wherein the polymer containing vinylamine units is obtained by:
- a) copolymerizing from 1 to 99 mol % of N-vinylamides and from 99 to 1 mol % of vinyl acetate, vinyl propionate, C.sub.1 -C.sub.4 -vinyl ethers, ethylene, esters, nitriles or amides of acrylic acid or methacrylic acid, N-vinylpyrrolidone or mixutes thereof, and
- b) subsequently hydrolyzing amide groups of poymerized untis produce in step a) to produce amino gorups.
- 6. The process as claimed in claim 5, wherein said N-vinylamides are selected from the group consisting of N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylpropionamide and N-vinylbutyramide.
- 7. The process as claimed in claim 5, wherein from 10 to 90 mol % of N-vinylamides are used.
- 8. The process as claimed in claim 5, wherein in step a) a pH of from 9 to 11 is used.
- 9. The process as claimed in claim 5, wherein in step a), said urea and formaldehyde are precondensed at a temperature of from 60.degree. to 100.degree. C.
- 10. The process as claimed in claim 5, wherein in step b), said urea and formaldehyde are condensed at a pH of from 2 to 4.5.
- 11. The process as claimed in claim 5, wherein in step b), said urea and said formaldehyde are condensed at a temperature of form 60.degree. to 100.degree. C.
- 12. The process as claimed in claim 5, wherein in step d), said post-condensation is effected at a temperature of from 60.degree. to 100.degree. C.
Priority Claims (1)
Number |
Date |
Country |
Kind |
39 27 812.3 |
Aug 1989 |
DEX |
|
Parent Case Info
This is a Division of application Ser. No. 07/775,928 filed on Nov. 6, 1991, which was filed as International Application No. PCT/EP90/01399, filed Aug. 22, 1990.
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
3275605 |
Eastes et al. |
Sep 1966 |
|
3752781 |
Muzyczko et al. |
Aug 1973 |
|
4663379 |
Fischer et al. |
May 1987 |
|
Divisions (1)
|
Number |
Date |
Country |
Parent |
775928 |
Nov 1991 |
|