Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-10-11
2002-12-10
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S839000, C524S840000, C525S440030
Reexamination Certificate
active
06492457
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to two-component systems comprising water-soluble polyesters and blocked isocyanates that are suitable as binders for aqueous baking varnishes.
BACKGROUND OF THE INVENTION
Baking varnishes comprise reactive resin binders and curatives which only on baking, i.e., at relatively high temperatures, react with the reactive groups of the resins to form crosslinked structures. Aqueous baking binders are known, for example, from EP-A 0 218 906, which describes combinations of copolymers of free-radically polymerizable monomers and crosslinker resins such as amino resins, phenolic resins or blocked isocyanates. Blocking agents mentioned for the isocyanates are aliphatic and aromatic monoalcohols such as methanol, ethanol, butanol, (cyclo)hexanol and benzyl alcohol, oximes, lactams and phenols. The binder is a water-dilutable mixture comprising mass fractions of from 60 to 95% of the copolymer and from 40 to 5% of the crosslinker. By adding pigments it is also possible to prepare pigmented paints possessing high storage stability. The blocking of the isocyanates is so efficient that the crosslinking reaction in the mixture does not proceed with any notable speed at standard (room) temperature.
EP-A 0 496 210 discloses two-component systems for producing baking coatings which comprise aqueous/organic solutions of anionically modified polyacrylate resins and organic polyisocyanates which are not blocked and therefore no blocking agents are liberated on curing.
According to EP-A 0 537 568, certain aqueous polyester resins containing sulfonate and hydroxyl groups may be formulated to aqueous two-component binders using polyfunctional isocyanates containing free isocyanate groups as curatives. Water-dilutable paints in the form of two-component systems based on water-soluble polyesters or other water-soluble resins and unblocked isocyanates in combination with water-soluble or water-dispersible, partially etherified amino resins are known from Austrian patent application A-2173/99.
When unblocked isocyanates are used, however, a number of disadvantages arise. For instance, in the paint, the aqueous solvent always competes with the OH groups of the resin for reaction with the unblocked isocyanate groups within the processing period. This activity may lead on the one hand to formation of unwanted secondary products (by reaction of water and isocyanate, substantially amines, and subsequently ureas); on the other hand, the carbon dioxide formed when the isocyanates are decomposed by the action of water produces gas bubbles which often result in defects in the baked paint film. The secondary products formed (amines, ureas) may also additionally impair the properties of the baked paint film.
The losses of isocyanate groups as a result of secondary reactions are normally compensated by using stoichiometric excess—often considerable—of the isocyanates. This is economically undesirable. The processing of unblocked isocyanates in the two-component process, moreover, also presents workplace hygiene (toxicological) problems.
In practice, usually unblocked, polyfunctional aliphatic isocyanates are used in two-component systems. The reaction between water and the unblocked aromatic isocyanates is generally so rapid that processing within the necessary time is impossible. Aromatic unblocked isocyanates are therefore not usually used for a 2K application.
SUMMARY OF THE INVENTION
It has been found that not only aliphatic but also aromatic polyfunctional isocyanates can in fact be used in two-component systems if they are blocked with blocking agents which lead to highly reactive reaction products which undergo deblocking at comparatively low baking temperatures. The isocyanates blocked in this way may be so reactive that formulation with water-soluble, hydroxyl group-containing resins (e.g., polyesters) in the form of one-component systems is no longer possible because of their instability to hydrolysis. On the other hand, curing of two-component paints which comprise these isocyanates to give crosslinked films is possible at baking temperatures which are all the lower. Compounds which have been found particularly appropriate for use as blocking agents are highly activated C-H acidic compounds, certain reactive alcohols, and certain oximes, as elucidated later on below. Similar adducts with aliphatic isocyanates are described for example in Houben-Weyl, Methoden der Organischen Chemie, Vol. XIV/2, Makromolekulare Stoffe [macromolecular substances], 4
th
ed. 1963, pages 62 and 63.
The present invention therefore provides aqueous two-component binders, its first component comprising a water-dilutable polyester AB having a hydroxyl number of at least 10 mg/g and its second component comprising a blocked polyfunctional isocyanate C, wherein the blocked isocyanate C is prepared by reaction of an aromatic isocyanate C1 and a blocking agent C2 for the isocyanate, C2 being selected from primary alcohols C21 having 3 to 10 carbon atoms, in which the carbon atom adjacent to the hydroxymethylene group carries a double bond, oximes C22 of linear, branched or cyclic aliphatic ketones having 3 to 15 carbon atoms, CH-acidic compounds C23, in which the carbon atom which carries the active hydrogen carries at least one further group selected from R
1
—CO—, R
2
—O—CO—, —NO
2
and R
3
—SO
2
—, R
1
, R
2
and R
3
independently of one another denoting linear, branched or cyclic alkyl groups having 1 to 18 carbon atoms or aryl groups having 5 to 15 carbon atoms, and NH-acidic compounds C24 such as, for example, 3,5-dimethylpyrazole, succinimide or phthalimide. Examples of suitable blocking agents C21 are hydroxyacetone, allyl alcohol, 2-methylallyl alcohol (&bgr;-methallyl alcohol), 3-methyl-2-buten-1-ol, 2-penten-1-ol and 2-hexen-1-ol. Examples of suitable blocking agents C22 are the oximes of acetone, 2-butanone, 2- and 3-pentanone and methyl isobutyl ketone. Particularly suitable blocking agents C23 are acetyl acetone, acetoacetates, malonates and cyanoacetates.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The water-dilutable polyesters AB may be prepared either conventionally by polycondensation of polyfunctional, especially difunctional, organic hydroxy compounds AB1 and polyfunctional, especially difunctional, organic acids AB2 or by partial condensation of hydroxyl group-containing compounds B which per se are insoluble in water with organic compounds A containing acid groups, especially carboxyl groups. The compounds A are per se soluble in water or dispersible in water following at least partial neutralization of the acid groups. Partial condensation means here that the reaction of the compounds A and B is conducted to a point such that the resulting condensation product AB still contains both hydroxyl groups and acid groups. The amount of the acid groups in AB corresponds preferably to an acid number of from about 10 to 60 mg/g, preferably from 15 to 55, and in particular from 20 to 50 mg/g. The amount of the hydroxyl groups in AB corresponds to a hydroxyl number of at least 10 mg/g, preferably from 15 to 200 mg/g, and in particular from 25 to 150 mg/g. The polycondensate AB normally has a Staudinger index J
0
of from 5 to 25 cm
3
/g, preferably from 7 to 22, and in particular from 10 to 20 cm
3
/g, as measured in dimethylformamide at 20° C.
A substance termed “water-soluble” here is one which in contact with ten times the amount of water at room temperature (20° C.) is dissolved in the aqueous phase to an extent such that the mass fraction of this substance in the aqueous phase after equilibrium has been reached is not less than 1%. A substance termed “water-dispersible” is one which with ten times the mass of water forms—under shearing—a dispersion which when stored at room temperature shows no macroscopic separation over a period of 14 days. Substances referred to as “water-dilutable” are soluble in water and/or dispersible in water.
The compounds or resins A containing carboxyl groups are preferably selected from polyester resins A1, polyurethane resin
Dworak Gert
Feola Roland
Gmoser Johann
Kuttler Ulrike
Niland Patrick D.
ProPat L.L.C.
Solutia Austria GmbH
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