Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2000-06-08
2002-07-16
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C252S182200, C252S182210, C252S182220, C528S055000, C528S059000, C528S060000, C528S065000, C528S066000, C528S067000, C528S073000, C528S085000, C544S067000, C544S068000, C544S193000, C544S222000, C560S115000, C560S157000, C560S158000, C560S330000, C560S336000, C560S355000, C560S357000, C560S166000, C564S044000, C564S045000
Reexamination Certificate
active
06420508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polyisocyanate mixtures that are soluble in non-polar solvents, to a process for their production and to their use as starting components for the production of polyurethane plastics, which are highly dilutable with non-polar solvents, in particular, as crosslinking agents for lacquer binders and/or binder components having isocyanate-reactive groups.
2. Description of the Prior Art
Polyisocyanates having aliphatically or cycloaliphatically bound isocyanate groups may be used as high-grade, non-yellowing two-component (2K) polyurethane (PU) coating compositions in many areas of application, for example in automotive coatings or in the construction sector. Due to their relatively high viscosity, these (so-called light-fast) lacquer polyisocyanates are generally used in a form diluted in solvents.
Since it is desired to reduce emissions of toxicologically or environmentally questionable solvents from lacquers and coatings, repeated attempts have been made in recent years to replace these solvents with alternative products, for example with non-polar, environmentally compatible solvents, such as mineral spirits or turpentine. It has not previously been possible to dilute 2K PU coating compositions with these non-polar solvents because they are not sufficiently compatible with the known aliphatic or cycloaliphatic polyisocyanate crosslinking agents.
The aliphatic or cycloaliphatic polyisocyanates, which contain biuret, isocyanurate and/or uretidione groups, are prepared from commercially available diisocyanates, such as hexamethylene diisocyanate (HDI) and/or 4,4′-diisocyanatodicyclohexylmethane, and are particularly important for the production of light-fast polyurethane coatings, are all only sparingly soluble non-polar organic solvents.
In contrast, allophanate-modified polyisocyanurates are much more readily soluble in non-polar solvents. These polyisocyanates may be obtained according to EP-A 238,013, EP-A 496,208, EP-A 524,500, EP-A 524,501, EP-A 566,037, U.S. Pat. No. 4,789,705, U.S. Pat. No. 5,086,175, U.S. Pat. No. 5,258,482, U.S. Pat. No. 5,290,902, U.S. Pat. No. 5,380,792, JP 0 403 621 8 A, JP 0 413 012 4 A, JP 0,413 017 1 A, JP 6 107 201 3 A or JP 901 266 0 A by reacting aliphatic and/or cycloaliphatic diisocyanates with linear or branched aliphatic or cycloaliphatic monoalcohols or diols in the presence of trimerization catalysts. However, when producing such allophanate trimers from monomeric diisocyanates, the reaction becomes exothermic after an unpredictable latency period. When using batch methods, it is thus necessary to dissipate the resultant heat of reaction, which is not always simple to achieve. Moreover, the allophanate-modified polyisocyanurates described in the stated publications, in particular those based on monoalcohols, give rise to coatings having considerably poorer resistance to solvents and chemicals than corresponding unmodified polyisocyanurates.
Pure allophanate polyisocyanates or so-called heteroallophanates, which are described, for example, in EP-A 807,623, also have good solubility in non-polar solvents. However, these products also result in coatings having only moderate resistance characteristics and, thus, are not well suited as crosslinking components for high-grade coating compositions. This also applies to urethanes that are prepared from di- or polyisocyanates and long-chain monoalcohols or dimer diol, even though according to the teachings of U.S. Pat. No. 5,086,175, JP 0 413 278 2 A, JP 0 423 065 1 A and JP 0 726 805 9 A, they exhibit good compatibility with hydrocarbons.
Trimers of special diisocyanates having lipophilic residues, for example cycloaliphatic diisocyanates having a long-chain aliphatic residue attached to the cycloaliphatic ring (EP-A 818,485), branched linear aliphatic diisocyanates (DE-A 3,151,855) or saturated aliphatic or cycloaliphatic diisocyanates having 11-20 carbon atoms (JP 0 324 462 3 A) have also been suggested as polyisocyanate crosslinking agents dilutable with non-polar solvents. However, these special diisocyanates are not available on a large industrial scale and are thus costly.
DE-A 3,613,064, U.S. Pat. No. 3,304,286 and JP 0 230 247 9 A describe isocyanate-functional prepolymers, which are prepared from polyisocyanates and polyols and are readily soluble in non-polar solvents. These products frequently have only a low content of free isocyanate groups and a low functionality. They are consequently less suitable as a crosslinking component for 2K PU systems, but are instead preferably used as the sole binder in moisture-curing one-component systems.
No light-fast polyisocyanates are known, which exhibit good solubility in non-polar solvents and meet all property requirements, i.e. in particular result in highly crosslinked coatings resistant to solvents and chemicals, and which may be obtained in a simple, low-cost process.
An object of the present invention is to provide novel polyisocyanate mixtures having aliphatically and/or cycloaliphatically-bound isocyanate groups and do not suffer from the disadvantages of the prior art.
This object may be achieved with the polyisocyanate mixtures according to the invention, which are described in greater detail below along with a process for their production. The polyisocyanate mixtures according to the invention are based on the surprising observation that, by reacting aliphatic and/or cycloaliphatic polyisocyanates having a low monomer content with alcohols under allophanatization conditions, it is possible to produce highly functional polyisocyanate mixtures which are readily soluble in non-polar solvents even at low temperatures and which, in combination with hydroxy-functional lacquer binders, result in coatings distinguished by outstanding resistance characteristics.
Although some publications relating to the production of polyisocyanates containing allophanate groups, for example EP-A 000,194, EP-A 303,150 and EP-A 682,012, do make general mention of polyisocyanates having a functionality of >2, such as trimerization products of HDI or IPDI, within long lists of suitable starting polyisocyanates, it is not taught or suggested in any of the above-stated publications that reaction products of polyisocyanates having low monomer contents with alcohols produced under allophanatization conditions exhibit particularly good solubility characteristics in non-polar solvents.
SUMMARY OF THE INVENTION
The present invention relates to polyisocyanate mixtures prepared from aliphatic and/or cycloaliphatic diisocyanates and having
a) an average isocyanate functionality of at least 2.0,
b) a content of isocyanate groups (calculated as NCO; molecular weight=42) of 4.0 to 28.0 wt. % and
c) a content of alkoxy groups having up to 36 carbon atoms of 2.0 to 37.5 wt. %,
wherein the alkoxy groups are constituents of allophanate groups or optionally urethane groups, provided that >50 mol % of the alkoxy groups are a constituent of allophanate groups that are connected to at least two polyisocyanate molecules which are each prepared from at least two diisocyanates.
The present invention also relates to a process for preparing these polyisocyanate mixtures by reacting
A) a polyisocyanate component having an average NCO functionality of 2.0 to 5.0, a content of aliphatically and/or cycloaliphatically bound isocyanate groups (calculated as NCO; molecular weight=42) of 8.0 to 27.0 wt. % and a content of monomeric diisocyanates of less than 1 wt. % with
B) (cyclo)aliphatic alcohols having up to 36 carbon atoms,
at an NCO/OH equivalent ratio of 1.9:1 to 80:1 such that >50% of the urethane groups formed by the NCO/OH reaction are converted to allophanate groups.
The present invention further relates to coating compositions, which are highly diluted or dilutable with non-polar solvents and contain these polyisocyanate mixtures and lacquer binders or binder components optionally containing isocyanate-reactive groups.
DETAILED DESCRIPTION OF THE INVENTION
Polyisocyanat
Danielmeier Karsten
Jahn Reinhard
Laas Hans-Josef
Mertes Harald
Schmalstieg Lutz
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
Sergent Rabon
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