Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1996-09-06
2002-06-25
Sergent, Rabon (Department: 1711)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C528S045000, C528S049000, C528S059000, C528S060000, C528S061000, C528S065000, C528S067000, C528S068000, C528S085000, C560S024000, C560S025000, C560S336000, C560S358000, C560S359000
Reexamination Certificate
active
06410095
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substantially solvent free binder composition containing a polyisocyanate component containing heteroallophanate groups and an isocyanate-reactive component, and to its use two-component coating compositions.
2. Description of the Prior Art
Binder compositions, other than epoxide systems, which are used in architectural protective coatings, in particular for high quality flexible coatings, are those prepared from polyisocyanates and isocyanate-reactive compounds such as polymeric polyols. The requirements in such applications are for coatings with an increased film thickness, which largely excludes the use of products containing solvents.
Binder compositions based upon solvent-free aliphatic polyisocyanates exhibit excellent yellowing resistance in such applications. However, in comparison to polyisocyanates having aromatically-bound isocyanate groups, they cure slowly. Furthermore, the coatings obtained from these products do not have sufficient hardness.
In combination with polymeric polyols, aromatic polyisocyanates exhibit rapid curing and development of hardness. However, relatively thick films may be cured without blistering only if special hydrophobic polyester polyols are used.
The required low viscosity of the polyisocyanate component may be achieved in the previously used aromatic systems only by dilution with monomeric diisocyanates. For toxicological reasons, only those products based upon diisocyanato-diphenylmethane may be used for dilution. The diluted polyisocyanate component may be combined with polyols based on castor oil to form binder compositions. However, due to its inadequate saponification resistance, this binder composition cannot be applied directly as a two-component system onto basic substrates. It is thus restricted to the preparation of intermediate layers and topcoat layers.
Polyisocyanates containing allophanate groups and based on aliphatic or aromatic diisocyanates are known and have been described, for example, in GB-A-994,980, EP-A-303,150, EP-A-194, DE-A-2,009,179 and 2,040,645 and U.S. Pat. No. 3,769,318. However, these publications do not describe solvent-free binder compositions which cure to yield blister-free coatings having good hardness in thick layers. Due to their slow curing, excessively high intrinsic viscosity and excessive susceptibility to blistering, the polyisocyanates having aromatically-bound isocyanate groups and containing homoallophanate groups and the polyisocyanates having aliphatically-bound isocyanate groups, which are described in these publications, are not suitable in binder compositions with polyols.
Accordingly, it is an object of the present invention to provide solvent-free binder compositions, which are suitable in particular for sealing concrete and which rapidly cure, even in thick layers, to yield blister-free coatings having good hardness.
This object may be achieved with the binder compositions according to the invention containing low viscosity isocyanate-reactive compounds and solvent-free aromatic polyisocyanates containing heteroallophanate groups.
According to the invention, polyisocyanates containing “heteroallophanate groups” are understood to be products having allophanate groups, the majority of which are prepared from one aliphatic and one aromatic isocyanate group.
In contrast, polyisocyanates containing “homoallophanate groups” are understood to be compounds having allophanate groups which are prepared from two aliphatic or two aromatic isocyanate groups.
SUMMARY OF THE INVENTION
The present invention relates to substantially solvent-free binder compositions containing
a) a polyisocyanate component containing heteroallophanate groups and having aromatically-bound isocyanate groups,
i) an NCO content of 3 to 16%,
ii) an average functionality of 1.8 to 4,
iii) an allophanate group content (calculated as C
2
HN
2
O
3
, MW: 101) of 5 to 35% and
iv) a hydrocarbon chain content of 10 to 65%, wherein the hydrocarbon chains are attached to allophanate groups via oxygen and have an average of 2 to 23 carbon atoms and
b) an isocyanate-reactive component.
The present invention also relates to the use of these binder compositions in one- and two-component coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
In the binder compositions according to the invention, polyisocyanate component a) has
i) an NCO content of 3 to 16, preferably of 5 to 13 and more preferably of 7 to 10.5%,
ii) an average functionality of 1.8 to 4, preferably of 1.9 to 3 and more preferably of about 2.0,
iii) an allophanate group content (calculated as C
2
HN
2
O
3
, molecular weight MW: 101) of 5 to 35%, preferably of 10 to 23% and
iv) a hydrocarbon chain content of 10 to 65%, preferably of 18 to 53% and more preferably of 30 to 53%, wherein the hydrocarbon chains may be linear, branched, saturated or unsaturated, are attached to allophanate groups via oxygen, have an average of 2 to 23, preferably 8 to 23 and more preferably 16 to 23 carbon atoms, and may optionally contain oxygen atoms.
Polyisocyanate component a) used in the coating compositions according to the invention is produced by reacting a linear aliphatic diisocyanate component a1) with a hydroxyl component a2) in an NCO/OH equivalent ratio of 1.0:1.0 to 0.5:1.0, preferably 1.0:1.0 to 0.6:1.0 and more preferably 1.0:1.0. The reaction is performed at a temperature of 40 to 140° C., preferably 60 to 120° C.
The compounds or mixtures of compounds containing urethane groups obtained in this manner have a number average molecular weight of 250 to 4000, preferably 300 to 2000 and more preferably 300 to 1000, which may be determined from the stoichiometry of the starting components.
If an excess of hydroxyl component a2) is used during urethanization, a portion of hydroxyl component a2) remains in the reaction product. In one embodiment of the process, this excess amount of hydroxyl component a2) (or a portion thereof) may be added when diisocyanate component a3) has been added. The excess reacts with diisocyanate component a3) to yield urethane and ultimately allophanate groups.
The urethane produced from components a1) and a2) may also be produced from the amine on which the isocyanate component a1) is based by using known phosgene-free urethane syntheses described, for example, in EP-A-27,940, EP-A-27,952, EP-A-27,953, EP-A-323,514 and EP-A-355,443. However, this is less preferred.
The urethane component prepared from components a1) and a2) is reacted with diisocyanate component a3) in an NCO/urethane equivalent ratio of 3:1 to 100:1, preferably 6:1 to 60:1 and more preferably 8:1 to 30:1, at a temperature of 20° C. to 150° C., preferably 50° C. to 120° C. and more preferably 60° C. to 90° C. The allophanatization reaction is preferably accelerated using conventional catalysts known from the literature.
Examples of usable catalysts are tetraalkylammonium hydroxides or arylakylammonium hydroxides; metal salts such as iron(III) chloride and potassium octoate; zinc compounds such as zinc stearate, zinc octoate, zinc naphthenate and zinc acetylacetonate; tin compounds such as tin(II) octoate, tin(l) ethylhexanoate and tin(II) laurate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate; manganese, cobalt and nickel compounds together with mineral acids such as trifluoroacetic acid, sulphuric acid, hydrochloric acid, hydrobromic acid, phosphoric acid and perchloric acid; aluminum tri(ethylaceto-acetate); and mixtures thereof.
Strong acids, such as those described in EPA-194, may also be used for the reaction of urethane groups with aromatic isocyanate compounds. However, this is less preferred.
The catalysts may be added before the allophanatization reaction or before urethanization. They are used at a concentration of 0.001% to 5%, preferably 0.005% to 1%, based on the weight of the reaction components. Where possible, the catalyst may be removed from the reaction mixture by distillation. However, it is als
Brahm Martin
Ruttmann Gerhard
Schmalstieg Lutz
Bayer Aktiengesellschaft
Eyl Diderico van
Gil Joseph C.
Roy Thomas W.
Sergent Rabon
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