Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1998-08-31
2000-12-12
Lipman, Bernard
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621682, 5253282, D21H 1700
Patent
active
061593400
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the use of partially hydrolyzed polymers of N-vinylcarboxamides as paper, paperboard and cardboard dry strength enhancers.
U.S. Pat. No. 2,721,140 discloses using polyvinylamine hydrochloride as an assistant in papermaking. The papers obtained have high wet strength.
U.S. Pat. No. 4,421,602 discloses partially hydrolyzed, water-soluble polymers of N-vinylformamide, which contain N-vinylformamide units and vinylamine units. The polymers are used as agents for enhancing flocculation, retention and drainage rate in papermaking.
EP-A-0 216 387 discloses agents for enhancing the dry strength of paper. They are water-soluble copolymers which contain vinylamine units and which are obtainable by copolymerizing N-vinylformamide with monoethylenically unsaturated monomers selected from the group consisting of vinyl acetate, vinyl propionate, C.sub.1 - to C.sub.4 -alkyl vinyl ethers, the esters, nitriles and amides of acrylic acid and methacrylic acid and N-vinylpyrrolidone and elimination of the formyl groups from the copolymers. The preferred N-vinylformamide copolymers are with vinyl acetate and have each of their monomer units hydrolyzed 30-100 mol %.
For the production of paper having high dry strength it is known to apply dilute aqueous solutions of synthetic polymers acting as dry strength enhancers to the surface of paper and drying the paper thus impregnated. The amounts of dry strength enhancer, ideally applied uniformly to the surface of the paper, range in general from 0.1 to 4% by weight, based on dry paper. Suitable dry strength enhancers are known for example from DE-B-2 741 753, EP-B-0 013 969 and EP-B-0 036 993. Since the dry strength enhancers are applied to the surface of the paper in the form of a dilute aqueous polymer solution, in which the polymer concentration is generally from 1 to 10% by weight, a considerable amount of water has to be evaporated in the subsequent drying process. The drying step is therefore very energy-intensive. Yet the capacity of the customary drying facilities on papermaking machines is not so large that papers having improved dry strength can be produced by application of aqueous polymer solutions at the maximum production speeds of the papermaking machines. On the contrary, the production speed of the papermaking machine has to be reduced when dry strength enhancers are applied to the surface of paper in order that the paper may dry sufficiently.
EP-B-0 251 182 discloses copolymers containing vinylamine groups in salt form, vinylformamide and acrylonitrile groups and optionally small amounts of acrylamide and acrylic acid groups. These copolymers are used for example in papermaking and act as drainage and retention aids and also as agents for enhancing the dry strength of paper.
It is an object of the present invention to provide a further processing aid for papermaking which leads to enhanced dry strength.
We have found that this object is achieved according to the invention by the use of hydrolyzed polymers of N-vinylcarboxamides obtainable by sole polymerization of N-vinylcarboxamides of the formula ##STR3## where R.sup.1 and R.sup.2 are each hydrogen or C.sub.1 - to C.sub.6 -alkyl, and elimination from the polymers of from 0.5 to 100 mol % of the groups of the formula ##STR4## where R.sup.1 is hydrogen or C.sub.1 - to C.sub.6 -alkyl, as paper, paperboard and cardboard dry strength enhancers.
Suitable monomers for preparing the polymers are N-vinylcarboxamides of the formula ##STR5## where R.sup.1 and R.sup.2 are identical or different and are each hydrogen or C.sub.1 - to C.sub.6 -alkyl. Suitable monomers include for example N-vinylformamide (R.sup.1 =R.sup.2 =H in formula I), N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinyl-N-methylpropionamide and N-vinylpropionamide. The polymers can be prepared by polymerizing the monomers mentioned either alone or mixed with each or one another. Preference is given to homopolymers of N-vinylformamide.
The polymerization is carried out ac
REFERENCES:
patent: 2721140 (1955-10-01), Weisgerber
patent: 4421602 (1983-12-01), Brunnmueller et al.
Niessner Manfred
Nilz Claudia
Rubenacker Martin
Schuhmacher Rudolf
Utecht Jens
BASF - Aktiengesellschaft
Lipman Bernard
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