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
1999-09-16
2001-01-23
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...
C524S539000, C524S839000, C524S840000
Reexamination Certificate
active
06177509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aqueous dispersions with reduced triethylamine content, a process for the preparation of such dispersions, and their use as binders for coatings.
2. Description of the Prior Art
With the aim of reducing emissions of organic solvents, aqueous coating compositions are increasingly replacing solvent-containing compositions. These aqueous compositions contain polymers, which are similar to those used in solvent-containing coatings with the exception that they contain hydrophilic groups to render the polymers water soluble and/or water dispersible. It is advantageous if these hydrophilic groups are incorporated into the polymer (“internal emulsifiers”), instead of being physically mixed with the polymer (“external emulsifiers”).
The internal hydrophilic groups are anionic groups usually formed, e.g., from a carboxylic acid and a base. It is known from U.S. Pat. No. 3,412,054 to hydrophilically modify polyurethanes by incorporating compounds containing hydroxy and carboxylic acid groups, such as dimethylolpropionic acid, and neutralizing the
Bases (for example, metal salts such as alkali metal hydroxides or amines) are used to neutralize the incorporated hydrophilic groups. Amines have an advantage over metal salts because they evaporate and, thus, do not remain in the dried paint film after application of the binder. Therefore, the hydrophilicity and water sensitivity of the coating is significantly reduced. However, primary and secondary amines have the disadvantage that they react with isocyanates.
Isocyanate group-containing compounds are used for preparing aqueous dispersions. Particularly in the preparation of polyurethane dispersions (see for example D. Dieterich, Prog. Org. Coatings 9, 281 (1981), EP-A 220,000, EP-A 511,547 and WO 98/05696), prepolymers are often obtained in intermediate stages that contain free isocyanate groups as well as neutralizing bases.
Also, in the application of aqueous two-component polyurethane coating compositions containing polyisocyanate crosslinking agents and aqueous polyol dispersions (see for example EP-A 358,979, EP-A 537,568 and EP-A 542,105) neutralizing agents and isocyanate groups from the crosslinking agent come into contact with one another.
Particularly in these two cases, tertiary amines free of hydroxyl groups are increasingly used as neutralizing agents since they do not react with isocyanate groups. Due to its ready availability, triethylamine is generally used as the neutralizing amine. However, the release of corrosive triethylamine from aqueous coating compositions is a disadvantage for ecological reasons. Accordingly, paint users as well as paint manufacturers have attempted to reduce the triethylamine content in aqueous dispersions with out impairing paint quality.
Replacement of triethylamine with ammonia, primary and secondary amines, hydroxyl group-containing tertiary amines and tertiary amines having relatively long alkyl substituents alternatives have not been successful.
Ammonia reacts rapidly with isocyanate groups. In addition, ammonia-neutralized binders in pigmented paints exhibit considerably worse pigment wetting.
Primary and secondary amines, as well as hydroxyl group-containing tertiary amines, react with isocyanates. Hydroxyl group-containing tertiary amines are also considerably less volatile than triethylamine, which is reflected in the poorer water resistance of the coating in the first few days after paint application.
Tertiary amines with relatively long alkyl substituents also have the disadvantage compared to triethylamine of insufficient volatility. Experience has also shown that resins neutralized with long chain tertiary amines are more difficult to disperse than triethylamine-neutralized resins.
An object of the present invention is to provide an amine for neutralizing aqueous dispersions that is at least an equivalent replacement for the ecologically less desirable triethylamine, but which does not have the disadvantages of the previously discussed alternative neutralizing amines for aqueous dispersions.
This object may be achieved according to the present invention by using N,N-diisopropyl-N-ethyalmine as the neutralizing amine in the preparation of aqueous dispersions.
SUMMARY OF THE INVENTION
The present invention relates to aqueous polymer dispersions containing anionic salt groups neutralized with 0.05 to 5 wt. % of N,N-diisopropyl-N-ethylamine and 0 to 1.5 wt. % of other tertiary amines, wherein the preceding percentages are based on the weight of the aqueous polymer dispersions.
The present invention also relates to one- and two-component coating compositions containing these aqueous polymer dispersions.
DETAILED DESCRIPTION OF THE INVENTION
The aqueous polymer dispersions according to the invention accordingly contain hydrophilic salt groups neutralized with 0.05 to 5 wt. %, preferably 0.25 to 2 wt. % and more preferably 0.4 to 1.5 wt. % of N,N-diisopropyl-N-ethylamine and 0 to 1.5 wt %, preferably 0 to 0.9 wt %, of other tertiary amines. The neutralizing agents may be present in either protonated or neutral form.
Suitable aqueous polymer dispersions for use according to the invention include polyacrylate, polyurethane, polyester, polyolefin and/or polyepoxy resin dispersions, preferably urethane group-containing dispersions, mixed dispersions of the preceding types and mixtures of dispersions.
The aqueous polymer dispersions according to the invention are prepared by neutralizing an acid group-containing polyacrylate, polyurethane, polyester, polyolefin and/or polyepoxy resin with N,N-diisopropyl-N-ethylamine, optionally mixed with other amines, and then dispersing the neutralized resin in water.
In a particularly preferred embodiment isocyanate group-containing prepolymers are neutralized with N,N-diisopropyl-N-ethylamine without the addition of other amines and then dispersed in water and chain extended, as described, for example, in EP-A 220,000, EP-A 511,547 or WO 98/05696.
The aqueous polymer dispersions according to the invention that contain N,N-diisopropyl-N-ethylamine are especially suitable as paint binders. Preferably, they are used as binders in physically drying one-component coating compositions that crosslink by radiation or atmospheric oxygen. More preferably they are used as the polyol component in aqueous two-component polyurethane coating compositions.
Preferred aqueous polymer dispersions are polyurethane dispersions containing
A1) polyisocyanates,
A2) polymeric polyols having number average molecular weights of 400 to 6000,
A3) optionally monoalcohols,
A4) polyols, aminopolyols and polyamines having a number average molecular weight of less than 400,
A5) mono-, di- or polyols and/or mono-, di- or polyamines that have a salt group (anionic group) or a functional group that can be converted into a salt group (potential anionic group).
Suitable polyisocyanates A1) include diisocyanates corresponding to the formula, R
1
(NCO)
2
, wherein R
1
represents an aliphatic hydrocarbon radical having 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon radical having 6 to 15 carbon atoms, an aromatic hydrocarbon radical having 6 to 15 carbon atoms, or an araliphatic hydrocarbon radical having 7 to 5 carbon atoms. Examples include tetramethylene diisocyanate, hexamethylene diisocyanate, 4,4′-diisocyanatodiphenylmethane, 2,4′-diisocyanato-diphenylmethane, 2,4-diisocyanatotoluene, 2,6-diisocyanato-toluene and &agr;,&agr;,&agr;′,&agr;′-tetramethyl-m- or p-xylylene diisocyanate as well as mixtures of the aforementioned diisocyanates. Preferred diisocyanates include 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate) and 4,4′-diisocyanato-dicyclohexylmethane.
Also suitable as polyisocyanates A1) are polyisocyanates that contain isocyanurate, biuret, uretdione and/or carbodiimide groups. Such polyisocyanates may have high functionalities, for example, of 3 or more.
Suitable polymeric polyols A2) are known and include polyols having a numbe
Gil Joseph C.
Niland Patrick D.
Roy Thomas W.
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