Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-04-15
2004-04-06
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S221000, C525S222000, C525S231000, C525S240000, C525S241000
Reexamination Certificate
active
06716922
ABSTRACT:
The present invention relates to heat-curable polymer dispersion powders and to their use as binders for moldings.
The consolidation of sheetlike fiber structures, examples being fiber webs, moldings such as fiberboard or chipboard panels, etc., is frequently done chemically using a polymeric binder. In this way, shaped parts of high mechanical strength, especially of high resistance to wetness and heat, are obtained. Besides liquid polymeric binders such as polymer solutions or polymer dispersions, use is also made of polymer powders. These powders lead to a lower energy requirement in the course of thermal curing, relative to the liquid binders, since there is no need to evaporate the, dispersion medium.
Heat-curable polymer powders and their use as binders are already known. DE 22 14 450 specifies powderous copolymers consisting of ethylene and maleic anhydride and, as crosslinkers, of compounds having 1 to 4 hydroxyl groups and at least one amine or amide group. The thermal crosslinking of such a composition takes place at from 110 to 300° C.
WO 90/14457 describes the use of thermoplastic polymer powders, e.g., polypropylene, polyesters or polyamide, as binders for glass fibers. AU 36659/89 recommends for this application polymer powders based on polyester or polystyrene. A disadvantage is the low strength of the fiber structures thus bound on contact with water or solvents.
The consolidation of powderous crosslinkable polymers based on phenol-formaldehyde resins is described in U.S. Pat. No. 4,612,224. A disadvantage with this binder system is the high level of formaldehyde emission during the preparation and use of the fiber materials thus consolidated.
Heat-curable copolymers based on acrylic esters and/or vinyl esters, further comprising (meth)acrylic esters of mono- and polyfunctional hydrbxycarboxylic acids and N-alkoxyalkyl(meth)acrylamide as crosslinker components are described in DE 27 01 490 as powderous coating compositions.
DE 43 06 808 specifies vinyl acetate copolymers or (meth)acrylate copolymers having a glass transition temperature of from −20 to +60° C. as powderous fiber binders. The copolymers contain from 0.1 to 10% by weight of N-methylol(meth)acrylamide as crosslinkable units, and crosslinking takes place at temperatures from 100 to 200° C. Owing to the presence of the hydroxymethylated monomer units, formaldehyde is given off in the course of thermal crosslinking.
EP 601 518 describes crosslinkable, water-dispersible dispersion powders based on carboxyl-containing acrylate copolymers which are dried in the presence of polyvinyl alcohol and may, for the purpose of crosslinking, contain polyvalent metal ions. Similar crosslinkable dispersion powders are known, too, from U.S. Pat. No. 3,409,578, in which polymer compositions comprising carboxyl-containing polymers and/or carboxyl-containing protective colloids are crosslinked in the presence of polyvalent metal ions. A disadvantage of these systems is that compositions of this kind frequently release acid in the presence of water and tend toward premature crosslinking, especially on contact with moisture. Moreover, the wet strength and dimensional stability of the resultant shaped parts under humid conditions is in many cases unsatisfactory.
EP 723 975 discloses crosslinkable dispersion powders based on copolymers containing epoxide groups. For the purpose of crosslinking, external crosslinkers, examples being polyamines, polycarboxylic acids, hydroxy-functionalized polymers, and also polyvalent metal salts, are added. A problem when using polyamines or polyvalent metal salts is the low stability on storage. The use of polycarboxylic acids or hydroxy-functionalized polymers does not impair the storage stability; however, for reaction with the epoxy groups, it is necessary to operate at an increased temperature, since otherwise the stabilization of the dispersion powders that is specified in the application using customary protective colloids would not be possible.
EP 721 004 discloses crosslinkable, redispersible powder mixtures which comprise film-forming polymer particles containing at least one functional, crosslinkable group. The crosslinkable group may also be introduced by way of the protective colloids. For crosslinking, this document, too, recommends the addition of an external crosslinker that comprises at least one reactive component which with the functional groups forms nonionic bonds after the mixture is redispersed in water.
EP 894 821 specifies polymer powders consisting of from 30 to 95% by weight of a water-insoluble polymer 1, from 5 to 70% by weight of a water-soluble polymer 2, and from 0.01 to 5% by weight of a phase transfer catalyst, the polymers 1 and/or 2 containing reactive groups which react with one another or with a crosslinker. Reactive groups specified include the following: alkoxysilane epoxy, isocyanate, hydroxyl, carboxyl, thiol, amino or aldehyde groups. Examples of the crosslinkers that are suitable include polyamines, polycarboxylic acids, and polyalcohols. Examples of suitable phase transfer catalysts are quaternary amines, phosphonium salts, and crown ethers. The compositions possess a high level of stability on storage and, after thermal curing, lead to shaped parts of high strength. Owing to the phase transfer catalyst present, the water absorption of the shaped parts is unsatisfactorily high and the resistance under humid conditions, accordingly, is low.
EP 894 822 describes polymer powders composed of from 30 to 95% by weight of a water-insoluble polymer 1 with from 0.5 to 10% by weight of reactive monomer, from 5 to 70% by weight of a water-soluble polymer 2, and a crosslinker which is present in salt form. Preferred reactive monomers are compounds containing carbonyl, epoxy, anhydride, isocyanate, and aziridine groups. Crosslinkers employed are hydrazides, hydrazines, hydrazones, amines, and hydroxylamine esters, examples being hexamethylenediamine phosphate and adipic dihydrazide acetate. The blocking of the crosslinkers in salt form ensures high storage stability of the compositions, with crosslinking ensuing only when a strong base is added or at elevated temperatures. The water resistance of the resultant fiber parts, and their resistance under humid conditions, however, are low.
DE-A-197 92 161 describes heat-curable aqueous compositions comprising at least one polymer (A1) containing in copolymerized form from 0 to 5% by weight of an &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acid and being obtainable by free-radical polymerization in the presence of
a) at least one polymer (A2) obtainable by free-radical polymerization and containing in copolymerized form from 15 to 100% by weight of an &agr;,&bgr;-ethylenically unsaturated mono- or dicarboxylic acid, and
b) at least one amine comprising at least one long chain having at least six carbon atoms,
the weight ratio (based on solids) of polymer (A1) to polymer (A2) being in the range from 7:1 to 1:7 and the weight ratio of polymer (A2) to long-chain amine being in the range from 20:1 to 2:1. Powders based on this composition are not described.
It is an object of the present invention to provide powderous formaldehyde-free binders for bound substrates, such as moldings, for example. These binders should be suitable especially for fibrous and particulate substrates. Preferably, they should give the substrate high mechanical strength and dimensional stability even under humid conditions. The powderous binder should also have high stability on storage.
We have found that this object is achieved, surprisingly, by a heat-curable polymeric binder in powder form, comprising
from 87.5 to 12.5% by weight, based on the overall weight of the polymeric binder, of at least one water-insoluble polymer A1,
from 12.5 to 87.5% by weight, based on the overall weight of the polymeric binder, of at least one water-soluble polymer A2 composed of
from 50 to 100% by weight, based on the polymer A2, of at least one ethylenically unsaturated mono- and/or dicarboxylic acid,
from 0 to 50% by weight, based
Dreher Stefan
Gerst Matthias
Laubender Matthias
Reck Bernd
Sack Heinrich
BASF - Aktiengesellschaft
Nutter Nathan M.
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