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
2000-12-29
2003-09-30
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...
C525S123000, C525S440030, C528S080000
Reexamination Certificate
active
06627726
ABSTRACT:
The invention relates to a composition comprising at least one isocyanate which is essentially free from allophanate groups and has an average functionality or more than 3.5 and a viscosity of from 4000 to 50000 mPas at from 20° C. to 50° C. and at least one compound having more than at least 5 functional groups which are reactive toward isocyanates with formation of urea or urethane and leading to polyurethanes combining improved hardness, scratch resistance and acid resistance with good reflow behavior. The invention further relates to a process for preparing such a composition and to the use of certain polyisocyanatoisocyanurates for preparing such compositions.
With polyurethane coating materials, especially those intended for use in the automotive or furniture sectors, particular value is generally placed on the resistance of such coatings to different environmental influences. Examples of criteria frequently employed to evaluate such coatings are their hardness, the scratch and acid resistance, and also the reflow behavior.
The reflow behavior is the ability of a cured surface coating (finish) to compensate for relatively small damage sites (in the &mgr;m range) which have come about by scratching or impact on the finish by cold flow of the finish into the damage site.
To improve the scratch resistance, use has frequently been made in the past of oligomeric polyisocyanatoisocyanurates based on hexamethylene diisocyanate (HDI) as the isocyanate component. The polyurethane finishes produced therefrom are generally soft and therefore possess good reflow behavior. A disadvantage of such finishes, however, is their inadequate acid resistance.
Hard and acid resistant polyurethane finishes are generally obtained when the polyisocyanate component used comprises, for example, IPDI or the oligomeric polyisocyanatoisocyanurates of IPDI. However, the scratch resistance and reflow behavior or such products is generally inadequate. A further disadvantage of the IPDI based products in respect of a large scale use for the production of mass products is their high price in comparison to that of HDI.
It is an object of the present invention to provide a composition which can be used as a polyurethane coating material and which, after curing, gives surface coatings combining good hardness, scratch resistance and acid resistance with good reflow behavior.
CA-A 2,163 591 relates to polyisocyanate mixtures containing allophanate and isocyanurate groups. Such isocyanate compounds are prepared, for example, by adding a certain amount of a monoalcohol having a molecular weight of up to about 2500 g/mol to a suitable amount of hexamethylene diisocyanate. Subsequent heat treatment of such a mixture produces the corresponding polyisocyanates containing allophanate groups. The reaction with monoalcohols, however, leads to polyisocyanates whose isocyanate group content per molecule (based on the molecular weight) is lower than the isocyanate group content of polyisocyanates prepared without adding monoalcohols. Owing to this reduced number of isocyanate groups per molecule, the functionality required for network formation is reduced, resulting in a lower network density with reductions in the desired properties. Moreover, the document gives no information on the reflow behavior of surface coatings produced with isocyanates containing allophanate groups, nor their acid resistance.
U.S. Pat. No. 4,419,513 relates to mixed isocyanurates obtainable by mixed trimerization of HDI and IPDI. It is stated that the mixed trimers described have desirable properties in respect of hardness and elasticity. A disadvantageous effect with these mixed trimers is that, owing to the IPDI fraction, the isocyanate group content (based on the molecular weight) is lower than in the case of straight HDI trimers, which brings economic disadvantages.
U.S. Pat. No. 4,454,317 mentions polyisocyanatoisocyanurates obtainable, for example, by trimerizing HDI. Described by way of example is an HDI trimer having an NCO content of 20.8% and a viscosity of 14 Pas at room temperature. The document says nothing about the possibility of preparing polyurethanes having improved chemical resistance by combining such polyisocyanatoisocyanurates with appropriate polyols.
EP-A 0 646 608 relates to polyisocyanates obtainable by cyclic trimerization of at least one aliphatic or alicyclic diisocyanate either following its reaction with a polyfunctional alcohol or by trimerization in the presence of such an alcohol. Although such isocyanates have high viscosities, the fraction of polyfunctional alcohol in the polyisocyanate molecule prepared produces a fall in the weight fraction of isocyanate groups per molecule. When the polyisocyanate is used, this necessitates the employment of a larger amount of isocyanate, which is economically undesirable.
U.S. Pat. No. 4,801,675 relates to polyisocyanatoisocyanurates having an isocyanate content of from 10 to 30% by weight and to their reaction with polyols which have an average functionality of from 1.8 to 5.
As stated, it is an object of the present invention to provide a composition which possesses excellent hardness, scratch resistance and acid resistance in conjunction with good reflow behavior.
We have found that this object is achieved by a composition which comprises at least one polyisocyanatoisocyanurate which is essentially free from allophanate groups and has an average NCO functionality of more than 3.5 and a viscosity of more than 4000 mPas up to 50000 mPas at from 20° C. to 50° C. and at least one compound having on average more than 5 functional groups which are reactive toward isocyanates with formation of urea or urethane and which leads to surface coatings which possess excellent hardness, scratch resistance and especially acid resistance coupled with good reflow behavior.
The invention accordingly provides a composition comprising components A and B, comprising
a) as component A at least one polyisocyanatoisocyanurate which is essentially free from allophanate groups and has an average NCO functionality of more than 3.5 and a viscosity of more than 4000 mPas up to 50000 mPas at from 20° C. to 50° C., measured with a rotational viscometer in accordance with DIN 53019, and
b) as component B at least one compound containing on average more than 5 functional groups which are reactive toward isocyanates with formation of urea, urethane, thiourethane or amide.
The term “essentially free from allophanate groups” refers to compounds whose fraction of allophanate groups is less than 10% in relation to isocyanurate groups.
A polyisocyanatoisocyanurate is a compound possessing at least one isocyanurate ring and at least 2, preferably at least 3, isocyanate groups. The number of isocyanurate rings and the NCO functionality are always calculated as an average of the overall mixture of compounds used as component A. Since the trimerization of diisocyanates generally leads not to pure products but rather to compounds having different degrees of oligomerization, the functionality of the resulting compounds can only be stated as an average value.
It is known that isocyanates may be converted into isocyanurates with the aid of catalysts.
The literature describes numerous catalysts for the cyclization of isocyanates to isocyanurates. Examples of such catalysts are strong bases such as quaternary ammonium hydroxides, e.g., benzyltrimethylammonium hydroxide, alkali metal hydroxides, e.g., sodium or potassium hydroxide, alkali metal alkoxides, e.g., sodium methoxide or potassium isopropoxide, trialkylphosphines, e.g., triethylphosphine, alkylaminoalkylphenols, e.g., 2,4,6-tris(dimethylaminomethyl)phenol, 3- or 4-substituted pyridines or mixtures thereof, e.g., 3- or 4-methylpyridine, organometallic salts, e.g., tetrakis(hydroxyethyl)sodium borate, Friedel-Crafts catalysts, e.g., aluminum chloride, iron(III) chloride, boron trifluoride and zinc chloride, and alkali metal salts of weak organic acids and nitrophenoxides, e.g., potassium octoate, potassium 2-ethylhexoate, potassium benzoate, sodium picrate and p
Baumgart Hubert
Bitter Simone
Bruchmann Bernd
Mohrhardt Günter
Poth Ulrich
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sergent Rabon
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