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
2001-05-18
2003-01-21
Gorr, Rachel (Department: 1711)
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...
C524S901000, C522S096000, C205S224000, C205S229000, C427S458000, C427S473000, C526S301000, C528S049000, C528S075000
Reexamination Certificate
active
06509411
ABSTRACT:
The invention concerns anodically precipitable, aqueous electrodeposition lacquers that can be cured by high-energy radiation and provide the advantage of good full cure even with elevated coating thicknesses and good mechanical properties together with, in particular, a high resistance in the industrial atmosphere. It also concerns their preparation and use for lacquering electrically conductive substrates, e.g. consisting of metal, electrically conducting plastics, e.g. metallised plastics, or electrically conducting coatings.
Coatings applied by the electrodeposition method display the advantage that they contain only a small quantity of residual water. Therefore the coating obtained need not be pre-dried after any adhering bath material has been rinsed away but can instead be cured by high-energy radiation after possible blowing-off of water drops.
EP-A-0 473 169 describes aqueous, heat-curable unsaturated polyurethane compositions having a weight-average molecular weight Mw of 20000 to 60000, which are used for example as top coats by spray application. They can also be cured by UV radiation, amongst other methods. The polyurethane compositions are obtained by chain extension of an isocyanate prepolymer containing unsaturated groups in the form of allyl groups and other ethylenically unsaturated groups, particularly in the form of unsaturated polyesters, with chain extenders having active hydrogen atoms. It has emerged that full cure of the coatings obtained in this way by irradiation with high-energy radiation is insufficient, particularly in the case of elevated coating thicknesses. Furthermore, the coatings are in need of improvement in terms of mechanical and chemical resistances, particularly their brittleness and resistance in an industrial atmosphere. At the same time, although it is mentioned that the polyurethane compositions can also be used for electrodeposition lacquering, it has emerged that the coatings obtained in this way exhibit inadequate flow.
The object underlying the invention was therefore to provide anodically precipitable, aqueous electrodeposition lacquers that do not exhibit these deficiencies, that cure fully by high-energy radiation even with elevated coating thicknesses and deliver lacquer films with improved properties in comparison to the prior art, particularly in regard to elasticity and resistance in an industrial atmosphere.
It has emerged that this object can be achieved with the anodically precipitable, aqueous electrodeposition lacquer forming a subject of the invention, which contains
A) an aqueous dispersion containing one or more anionically modified polyurethane (meth)acrylates (a1) having terminal ethylenically unsaturated (meth)acrylic double bonds, and one or more reactive thinners (a2) having at least two ethylenically unsaturated (meth)acrylic double bonds, whereby the (meth)acrylic double bonds from the mixture comprising (a1) and (a2) correspond to a bromine number of 20 to 150 g bromine/100 g solids, and
B) optionally one or more photo-initiators and/or optionally one or more thermally activable radical initiators,
whereby the terminal ethylenically unsaturated (meth)acrylic double bonds from the polyurethane (meth)acrylates are bonded to the anionically modified polyurethane prepolymer via urethane, urea, amide or ester groups,
and optionally conventional auxiliary substances and additives, pigments and/or fillers.
The term (meth)acrylic refers here to acrylic and/or methacrylic.
An aqueous anionic polyurethane dispersion consisting of, for example, 40 to 85 wt. % of component (a1), calculated as solid resin, and 15 to 60 wt. % of component (a2) is used as component (A). The aqueous anionic polyurethane dispersion (A) has, for example, a solids content (polyurethane (meth)acrylate plus reactive thinner) of 30 to 70 wt. %, preferably 40 to 55 wt. %. Its content of terminal ethylenically unsaturated (meth)acrylic double bonds corresponds to a bromine number of 20 to 150, preferably 20 to 80 g bromine/100 g solids (polyurethane (meth)acrylate plus reactive thinner).
The aqueous dispersion (A) can for example be prepared by the following method:
An anionically modified urethane prepolymer with terminal NCO groups is first prepared by reacting
i) one or more aliphatic, cycloaliphatic, araliphatic and/or aromatic polyisocyanates, whereby the aromatic polyisocyanates preferably exhibit a molecular weight above 174,
ii) one or more higher-molecular polyhydroxyl compound(s) having a number-average molecular weight (Mn) of, for example, 400 to 5000, preferably 1000 to 2500,
iii) one or more compound(s) exhibiting one anionic group and two groups that are functional in respect of isocyanates and
iv) optionally one or more low-molecular polyhydroxyl compounds, for example having a number-average molecular weight (Mn) of 60 to below 400.
The reaction can for example be performed in a one-stage or multi-stage process solvent-free or in a polar solvent that is inert in respect of NCO groups.
The quantities of components (i) to (iv) are chosen, for example, such that the ratio of NCO groups to OH groups is between 4:1 and 1.1:1.
The ethylenically unsaturated groups are then attached to the free NCO groups. This is achieved, for example, by reaction with compounds (v) exhibiting one or more ethylenically unsaturated (meth)acrylic groups and one or more groups that are reactive in respect of isocyanates, whereby the stoichiometric ratios of groups that are reactive in respect of NCO groups to isocyanate groups is chosen such that no free NCO groups remain.
In order to regulate the functionality (number of ethylenically unsaturated (meth)acrylic double bonds) compounds (vi) can additionally be used that exhibit one or more, preferably one, group that is reactive in respect of isocyanates, but contain no (meth)acrylic double bonds. They can contain other ethylenically unsaturated double bonds or can be free from them. The compounds (vi) can for example be introduced into the reaction following the reaction of components (i) to (iv) to produce a urethane prepolymer, before, along with or after reaction with component (v).
Alternatively, however, the free NCO groups can first be reacted with compounds containing, in addition to a group that is reactive in respect of isocyanates, one or more other reactive groups, which in turn can react with complementarily reactive groups of ethylenically unsaturated (meth)acrylic compounds, such as, for example, hydroxycarboxylic acid with glycidyl (meth)acrylate. In this way (meth)acrylic double bonds bonded to the polyurethane prepolymer can be introduced via ester groups, for example.
The anionically modified polyurethane (meth)acrylates having terminal ethylenically unsaturated (meth)acrylic double bonds (a1) exhibit for example a number-average molecular weight Mn of 800 to 5000 and/or a weight-average molecular weight Mw of 5000 to 20000, preferably below 20000. Their acid value is preferably from 5 to 50, particularly preferably from 10 to 35. Their content of terminal ethylenically unsaturated (meth)acrylic double bonds is preferably from 4 to 80 g bromine/100 g solid resin, particularly preferably 5 to 35 g bromine/100 g solid resin.
The component (a1) obtainable as described above is diluted with the reactive thinner (a2), at least partially neutralised and converted to the aqueous phase. At least 25% of the acid groups are present in neutralised form. The neutralising agent can be added before or with the water, or alternatively it can be introduced in advance into the water in which the polymer is dispersed. No addition of external emulsifiers is required. High-speed stirring disc units, rotor stator mixers or high-pressure homogenisers, for example, are used for conversion to the aqueous phase. The inert solvent is then optionally distilled off under vacuum.
The reactive thinner (a2) can alternatively be added subsequently to the already aqueous dispersion. In this case the aqueous dispersion is prepared as described above, whereby initially component (a1) is not yet diluted with the reactive t
Fieberg Andreas
Rekowski Volker
Saatweber Dietrich
Simmrock Hans-Ulrich
Vogt-Birnbrich Bettina
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Gorr Rachel
LandOfFree
Aqueous electrodeposition coating, the production and use... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous electrodeposition coating, the production and use..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous electrodeposition coating, the production and use... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3012347