Isocyanate-based hardenable preparations

Details Isocyanate-based hardenable preparations Isocyanate-based hardenable preparations

2001-06-20

2002-11-12

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S097000, C528S049000, C528S075000, C526S301000, C428S422800, C428S423100, C427S385500

Reexamination Certificate

active

06479564

ABSTRACT:

The present invention relates to curable, in particular radiation-curable, compositions comprising a prepolymer based on a polyisocyanate and isocyanate-reactive ethylenically unsaturated compounds, to their use for coating substrates and to the coated substrates obtainable in this way.
Radiation-curable compositions have achieved wide use in industry, in particular as high-quality coating materials for surfaces. For the purposes of the present invention, radiation-curable compositions are compositions which comprise ethylenically unsaturated polymers or prepolymers and which, if appropriate after a physical drying step, are cured by action of high-energy radiation, for example by irradiation with UV light or by irradiation with high-energy electrons (electron beam).
Radiation-curable compositions are used predominantly in the coating of wood, paper and plastics. The coatings obtained should be very flexible and abrasion-resistant. For exterior applications, the coatings should also be stable to weathering and not undergo yellowing. Further requirements are a high scratch resistance and chemical resistance.
Thermally curing polyurethane compositions are used, for example, in surface coatings for automobiles.
Known curable polyurethane compositions frequently comprise aliphatic isocyanurates as isocyanate component, e.g. on the basis of isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HDI). However, the products based on HDI have the disadvantage of a poor chemical stability while the products based on IPDI have unsatisfactory scratch resistance. On the other hand, urethane acrylates based on aromatic isocyanates have a high tendency to undergo yellowing.
It is an object of the present invention to provide curable compositions based on a polyisocyanate and isocyanate-reactive ethylenically unsaturated compounds which lead to coatings having a high scratch resistance, good chemical stability, low tendency to undergo yellowing and good weathering resistance.
We have found that this object is achieved by a curable composition comprising a prepolymer which comprises, in copolymerized form:
(a) a bifunctional or polyfunctional isocyanate based on a compound of the formula I
 where R
1
and R
2
are independently C
1
-C
12
-alkylene,
(b) an ethylenically unsaturated compound containing isocyanate-reactive groups and
(c) if desired, a saturated compound containing isocyanate-reactive groups.
Preferably, R
1
and R
2
are independently C
1
-C
4
-alkylene such as methylene, 1,2-ethylene, 1,2-propylene, 1,3-propylene or 1,4-butylene.
The composition of the present invention generally comprises:
from 20 to 100% by weight, preferably from 20 to 80% by weight, of prepolymer,
from 0 to 80% by weight, preferably from 10 to 50% by weight, of reactive diluent
from 0 to 80% by weight of solvent or a solvent mixture,
from 0 to 20% by weight, preferably 0.1-10% by weight, of initiator and
from 0 to 20% by weight of further auxiliaries.
The prepolymer is the reaction product of an on average at least bifunctional polyisocyanate based on a compound of the formula I and an ethylenically unsaturated compound containing isocyanate-reactive groups, if desired with concomitant use of saturated compounds containing isocyanate-reactive groups.
The bifunctional or polyfunctional isocyanate is either a compound of the formula I or preferably an oligomerization product, in particular a trimerization product, thereof. Such polyisocyanates are obtained in a manner known per se by oligomerization of a compound of the formula I, preferably to an NCO content of the reaction mixture of from 40 to 20% by weight, in particular from 39 to 30% by weight, and subsequent stopping of the reaction and, if desired, removal of unreacted compound of the formula I by distillation. The oligomerization can be carried out in the presence of suitable catalysts such as quaternary ammonium salts, e.g. N,N,N-trimethyl-N-(2-hydroxypropyl)ammonium 2-ethylhexanoate or N,N,N-trimethyl-N-(2-hydroxypropyl)ammonium hydroxide. To stop the oligomerization reaction, the catalyst is decomposed thermally or a suitable substance which deactivates the catalyst is added. Substances which are suitable for this purpose are, for example, acids such as p-toluenesulfonic acid or dibutyl phosphate.
Preferred polyisocyanates based on a compound of the formula I contain at least one uretdione, isocyanurate, biuret and/or allophanate group per molecule.
Particularly preferred representatives of compounds of the formula I are 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane and mixtures thereof.
The polyisocyanates based on compounds of the formula I may, if desired, be present in admixture with other polyisocyanates. The other polyisocyanates are preferably used in such an amount that less than 50%, in particular less than 30%, of the total number of NCO groups originate from the polyisocyanates which do not correspond to the formula I. The other polyisocyanates are usually tetramethylene diisocyanate, hexamethylene diisocyanate (1,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexane diisocyanate or tetramethylhexane diisocyanate, 1,4-, 1,3- or 1,2-diisocyanatocyclohexane, 4,4′-di(isocyanatocyclohexyl)methane, 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane (isophorone diisocyanate), 2,4- or 2,6-diisocyanato-1-methylcyclohexane, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, tetramethylxylylene diisocyanate, 1, 4-diisocyanatobenzene, 4,4′- and 2,4′-diisocyanatodiphenylmethane, p-xylylene diisocyanate and isopropenyldimethyltolylene diisocyanate. Preference is given to the aliphatic and cycloaliphatic diisocyanates. Here too, the oligomerization products of these diisocyanates, which generally contain a uretdione, isocyanurate, biuret and/or allophanate group, are particularly useful. The adducts of diisocyanates with trifunctional alcohols such as glycerol, trimethylolethane, trimethylolpropane, etc., or with triamines are also suitable.
“Isocyanate-reactive groups” are functional groups which can undergo an addition reaction with OCN groups to form a covalent bond, i.e. particularly OH, SH, NH
2
or COOH groups.
OH-containing ethylenically unsaturated compounds for reaction with the polyisocyanates are generally selected from among the esters of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, acrylamidoglycolic acid, methacrylamidoglycolic acid and vinylacetic acid with a diol or polyol having preferably 2-20 carbon atoms, e.g. ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, tripropylene glycol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-methylpentane-1,5-diol, 2-ethylbutane-1,4-diol, 1,4-dimethylolcyclohexane, glycerol, trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerythritol, ditrimethylolpropane, erythritol and sorbitol, as long as the ester has at least one OH group which is reactive toward isocyanate. Furthermore, it is also possible to use the amides of the abovementioned ethylenically unsaturated carboxylic acids with aminoalcohols, e.g. 2-aminoethanol, 3-amino-1-propanol, 1-amino-2-propanol or 2-(2-aminoethoxy)ethanol, and also the vinyl, allyl and methallyl ethers of the abovementioned diols or polyols, as long as they still have a free OH group. Preference is given to the esters of acrylic acid and of methacrylic acid, e.g. 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 1,4-butanediol mono(meth)acrylate, neopentylglycol mono(meth)acrylate, trimethylolpropane mono- and di(meth)acrylate, pentaerythritol di- and tri(meth)acrylate. Particular preference is given to esters selected from among 2-hydroxyethyl acrylate, hydroxypropyl acrylate and 1,4-butanediol monoacrylate.
In addition, concomitant use can be made of saturated amine or alcohol components. Suitable saturated alcohol components are, for example, linear monools, diols and polyols having 1-14 c

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