Coating processes – Particles – flakes – or granules coated or encapsulated
Reexamination Certificate
2000-02-17
2001-10-09
Cameron, Erma (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
C427S389900, C427S393000
Reexamination Certificate
active
06299936
ABSTRACT:
The present invention relates to using thermally curable aqueous compositions comprising a low-acid and an acid-rich polymer component and also a hydroxyalkylated amine as binders for shaped articles.
Sheetlike fibrous structures, for example fiber webs, shaped articles such as chipboard, etc., are frequently consolidated chemically using a polymeric binder. To enhance the strength, especially the wet and heat resistance strengths, binders are frequently used that comprise formaldehyde-eliminating crosslinkers. This means, however, that there is a danger of formaldehyde emissions.
Various alternatives to prior art binders have been proposed to avoid formaldehyde emissions. For instance, U.S. Pat. No. 4,076,917 discloses binders comprising polymers containing carboxylic acid or carboxylic anhydride, with &bgr;-hydroxyalkylamides as crosslinkers. The molar ratio of carboxyls to hydroxyls is preferably 1:1. A disadvantage is the relatively costly production of the &bgr;-hydroxyalkylamides.
EP-A-445 578 discloses sheets composed of finely divided materials, for example glass fibers, in which mixtures of high molecular mass polycarboxylic acids and polyhydric alcohols, alkanolamines or polyvalent amines act as binders. The described high molecular mass polycarboxylic acids are polyacrylic acid, copolymers of methyl methacrylate
-butylacrylate/methacrylic acid, and of methyl methacrylate/methacrylic acid. Polyhydric alcohols and alkanolamines employed are 2-hydroxymethyl-1,4-butanediol, trimethylolpropane, glycerol, poly(methyl methacrylate-co-hydroxypropyl acrylate), diethanolamine and triethanolamine. However, the sheets obtained are not sufficiently water-resistant.
EP-A-583 086 discloses formaldehyde-free aqueous binders for producing fiber webs, especially glass fiber webs. The binders comprise a polycarboxylic acid containing at least two carboxyls with or without anhydride groups. Polyacrylic acid in particular is used. The binder further comprises a polyol, for example glycerol, bis[N,N-di(&bgr;-hydroxyethyl)]adipamide, pentaerythritol, diethylene glycol, ethylene glycol, gluconic acid, &bgr;-D-lactose, sucrose, polyvinyl alcohol, diisopropanolamine, 2-(2-aminoethylamino)ethanol, triethanolamine, tris(hydroxymethylamino)methane and diethanolamine. These binders require a phosphorus-containing reaction accelerant to obtain glass fiber webs having adequate strengths. It is noted that the presence of such a reaction accelerant can only be dispensed with if a highly reactive polyol is employed. &bgr;-Hydroxyalkylamides are mentioned as highly reactive polyols.
EP-A-651 088 describes corresponding binders for substrates composed of cellulose fiber. For these binders the inclusion of a phosphorus-containing reaction accelerant is mandatory.
EP-A-672 920 describes formaldehyde-free binding, impregnating or coating compositions comprising a polymer, constituted by from 2 to 100% by weight of an ethylenically unsaturated acid or acid anhydride as comonomer, and at least one polyol. The polyols are substituted triazine, triazinetrione, benzene or cyclohexyl derivatives, the polyol radicals always being located in positions 1,3,5 of the rings mentioned. Despite a high drying temperature, the binders provide only low wet breaking strengths on glass fiber webs. Amine-containing crosslinkers and predominantly linear polyols were tested too as part of comparative experiments. It is noted that amine-containing crosslinkers have a flocculating effect and that the predominantly linear polyols lead to weaker crosslinking than the cyclic polyols.
DE-A-22 14 450 describes a copolymer constituted by from 80 to 99% by weight of ethylene and from 1 to 20% by weight of maleic anhydride. The copolymer, in powder form or in dispersion in an aqueous medium, is used for surface coating together with a crosslinker. The crosslinker used is an amino-containing polyalcohol. Crosslinking of the system, however, requires heating at up to 300° C.
EP-A-257 567 describes a polymer composition which is obtainable by emulsion polymerization of ethylenically unsaturated monomers, such as olefins, vinylaromatic compounds, &agr;,&bgr;-ethylenically unsaturated carboxylic acids and their esters, ethylenically unsaturated dicarboxylic anhydrides and vinyl halides. In the course of polymerization a water- or alkali-soluble or —dispersible resin having a number-average molecular weight of from about 500 to about 20,000 is added in order to influence the flow properties of the polymer composition. The resin is composed of olefins, vinylaromatic compounds, &agr;,&bgr;-ethylenically unsaturated carboxylic acids and the esters thereof or ethylenically unsaturated dicarboxylic anhydrides. Ammonium hydroxide is indicated as an alkaline medium in which said resin should be soluble or dispersible The composition can be used to produce formaldehyde-free coatings on wood substrates.
EP-A-576 128 describes repulpable adhesive compositions comprising an acid-rich polymer component and a low-acid polymer component. The acid-rich component is based on a monomeric mixture of from 40 to 95% of an alkyl acrylate or alkyl methacrylate and from 5 to 60% of an ethylenically unsaturated acid such as acrylic or methacrylic acid. The low-acid component is based on a monomer mixture of from 90 to 100% of an alkyl acrylate or alkyl methacrylate and from 0 to 10% of an ethylenically unsaturated acid. The composition is prepared by aqueous emulsion polymerization, the acid-rich polymer component being polymerized in the presence of the low-acid polymer component, or vice versa. The pH of the composition is adjusted to the desired level by adding ammonium hydroxide or sodium hydroxide. The composition can be used as a pressure-sensitive adhesive, laminating adhesive, textiles adhesive, tile adhesive and packaging adhesive and as a wood glue.
U.S. Pat. No. 4,420,583 and EP-A-098 091 both describe a binder composition comprising an acid-rich polymer dispersion and a solution polymer. The basis of the latex is a monomer composition of vinylaromatic compounds and alkyl (meth)acrylates and up to 20% of an ethylenically unsaturated acid. The solution polymer contains at least 10% of a monomer comprising (halohydroxypropyl)ammonium groups. The composition is stable on storage and cures at room temperature after base (NaOH or the like) has been added. It is used for formaldehyde-free binders, adhesives and coatings.
U.S. Pat. No. 5,314,943 describes a mixture consisting of a polymer dispersion and a water-soluble copolymer, and its use as a binder for fiber webs. The polymer includes not only vinylaromatic compounds and alkyl (meth)acrylates but also preferably bifunctional monomers such as butadiene and vinyl acrylates. The mixture's content of solution polymer is up to 5%, and the polymer itself consists of 25-60% of an ethylenically unsaturated monocarboxylic acid and 40-75% of an ethylenically unsaturated dicarboxylic acid. Disadvantages are the high temperatures required for curing.
U.S. Pat. No. 4,868,016 describes a composition based on at least one thermoplastic latex polymer, insoluble in aqueous alkaline medium, and at least one alkali-soluble polymer, which is incompatible with the latex polymer. The latex polymer is an aqueously dispersed polymer which can be composed of acrylic or methacrylic esters, vinylaromatic compounds and vinyl esters and which additionally comprises from 0.5 to 3% by weight of an ethylenically unsaturated carboxylic acid, in copolymerized form. The alkali-soluble polymer is composed of the same monomers but contains from 10 to 60% by weight of an ethylenically unsaturated carboxylic acid. To establish a pH of >7 the composition can contain ammonia, triethylamine, ethylamine or dimethylhydroxyethylamine. One of its possible uses is to provide substrates with a coating.
It is an object of the present invention to provide formaldehyde-free binders for shaped articles, which permit rapid curing at low temperature and impart good mechanical properties and high climatic resistance to the substrate.
We have
Beckerle Wilhelm Friedrich
Dreher Stefan
Reck Bernd
Roser Joachim
Türk Johannes
BASF - Aktiengesellschaft
Cameron Erma
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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