Moisture-Hardening Varnishes With an Isocyanate Resin Base

1. Field of the Invention

This invention relates to moisture-hardening varnishes based on derivatives of aliphatic diisocyanate mixtures.

2. Description of the Prior Art

Moisture-hardening resins based on aromatic polyisocyanates are known and can be produced in several manners. Unfortunately, these resins have a tendency to yellow upon exposure to sunlight.

Cyclic polyisocyanates, such as e.g. isophoronediisocyanate or methylene-bis-(4-cyclohexylisocyanate) are used for more demanding applications. However, the isocyanurate or the propanetriol prepolymer of these cyclic diisocyanates merely form hard, brittle films following moisture hardenings.

Based on cyclic polyisocyanates and, e.g., higher molecular polyols, NCO terminated adducts can be produced that provide hard or soft films, in each case elastic films, following moisture hardening. But the resins are inactive and must be activated with additions of, e.g., 0.1 to 0.2% tin catalysts, which limits the weathering resistance of the hardened films. The hardened films have excellent thermal and oxidative stability, but have no outstanding solvent stability.

Aliphatic polyisocyanates through their floating, NCO end groups introduce highly reactive moisture-hardening resins in the form of their isocyanurate or their propanetriol prepolymers, which, following hardening, form hard, elastic weather and solvent resistant films. However, their thermal and oxidative stability and compatibility with other products are problematical, as e.g., also with solvents and pigments which are present especially in cyclic polyisocyanate resins.

Hence, a need clearly continues to exist for moisture-hardening varnishes with both excellent thermal and oxidative stability, and resistance to solvent attack. Also, it is necessary for these moisture-hardening varnishes to have excellent storage stability.

Accordingly, it is an object of the present invention to provide a moisture-hardening varnish which has excellent thermal and oxidative stability, and which also has excellent solvent stability.

It is also an object of this invention to provide a moisture-hardening varnish which has excellent compatibility with solvents, pigments, reactants or auxiliary products.

According to the present invention, the foregoing and other objects are attained by providing a moisture-hardening varnish with an isocyanate resin base of adducts of a mixture of diisocyanates, wherein said diisocyanate mixture has about 88 to 99% by weight of 2-methyl-1,5-diisocyanatopentane and about 12 to 1% by weight 2-ethyl-1,4-diisocyanatobutane.

According to the present invention, it has now been surprisingly found that resin derivatives of the 2-methyl-1,5-diisocyanatopentane (MPDI)/2-ethyl-1,4-diisocyanatobutane (EBDI) mixture possess quality properties which considerably surpass those of the conventionally used aliphatic isocyanate resins.

The moisture-hardening varnishes with an isocyanate resin base according to this invention contain adducts of a diisocyanate mixture having the composition of about 88 to 99% by weight of 2-methyl-1,5-diisocyanatopentane (MPDI) and about 12 to 1% by weight of 2-ethyl-1,4-diisocyanatobutane (EBDI), according to the following formulas: ##STR1##

The resins are produced by trimerization of the MPDI/EBDI mixture to the corresponding isocyanattoisocyanurate or by reaction of the MPDI/EBDI mixture with propanetriols in NCO:OH equivalents of about 2:1.

These resins are chemically hardened through the effects of atmospheric moisture and provide films and coatings of superior quality.

The isocyanate mixture is the result of phosgenation of the corresponding diamine mixture, whereby the latter is formed by hydrogenation of the corresponding dinitrile mixture. The mixture is obtained, e.g., as a by-product in the adipodinitrile production through reaction of butadiene with HCN or by dimerization of acrylonitrile.

The isocyanurate or the propanetriol prepolymers here are understood to be adducts.

The moisture-hardening varnishes according to the invention have the following qualities:

1. Thermooxidation stability

2. Storage stability of pigmented systems

3. Compatibility with solvents, pigments, reactants or auxiliary products

4. Solvent resistance

The present invention will be further illustrated by certain examples and references which are provided for purposes of illustration only and are not intended to limit the present invention.

The thermooxidation stability of the resins applied according to the invention, as shown in Table 1, is not typical of aliphatic isocyanate resins and comparable with that shown by the indicator diagram of cyclic isocyanate resins.

The storage stability especially of white pigmented resins, which require a high pigment volume concentration, is extraordinary considering the high reactivity of the resins used according to the invention (Table 2).

The results of the severe storage test at 60.degree. C. permit the empirical conclusion of an over 10 times greater shelf life at 25.degree. C.

The very limited storage life of the HDI prepolymers as well as their low gloss value at 20.degree. C. Gardner indicate clear incompatibility of this system with pigments, reaction products and solvents. This incompatibility of HDI prepolymers or additives becomes evident when such prepolymers are to be modified by partial oxyester additives.

Thus, e.g., not only hard substrates, such as metal, concrete and parquet flooring have to be coated but also softer substrates, such as PVC floor coverings and the like. Softer resin adjustments can be made very advantageously if the resin systems according to the invention are chemically reacted with small amounts of oxyester additives and moisture-hardening of the coating takes place only thereafter. Surprisingly, the resins used according to the invention permit such a modification while standard types of aliphatic isocyanates, such as HDI derivatives, coagulate after a few hours' storage at room temperature.

In view of the good compatibility of the resins used according to the invention, their excellent solvent resistance is surprising compared with the premium gasoline sensitivity of the well compatible 5-methyl-1,4-dicyanatononane (MMDI) (Table 4).

The resins used according to the invention provide directly applied reactive, cold-hardening, hard but elastic coatings. If necessary, hardening can also take place in the presence of heat.

134 g of trimethylolpropane (1 mol) and 504 g of a mixture of MPDI and EBDI (3 mol) in 343 g of ethyl glycol acetate are reacted for 6 hours at 80.degree. C.

Yield: 978 g of prepolymer, NCO content: 12.79% (theoretical 12.84%), of a highly viscous, practically colorless resin.

The following data were obtained following moisture hardening:

Triisocyanatoisocyanurate of MPDI and EBDI mixture.

Resin Preparation: 65 parts by weight of isocyanurate (MPDI+EBDI)

NCO content: 16.2%

35 parts by weight of ethyl glycol acetate

0.01 part by weight of DBTL

0.2 parts by weight of DABCO

The following data were obtained following moisture-hardening:

Solvent resistant to EGA, xylene, MEK, acetone, premium gasoline.

By reaction of the monomer diisocyanate mixture consisting of MPDI and EBDI with linear oxyesters, preferably those of molecular weights of about 1000 in NCO:OH equivalents=2:1, resins are obtained that, following moisture-hardening, form soft, tacky films and are not particularly suitable for immediate use. But these NCO end prepolymers are excellently suited for modification according to examples 1 and 2 to obtain less hard films on flexible substrates:

1,016.9 g of resin (produced by reaction of PCP 210 with (MPDI+EBDI) in the equivalence ratio OH:NCO=1:2) NCO content: 4.13%; and 2,616.8 of resin according to example 1 are homogenized and provide the following data after moisture-hardening:

Analogously to example 3, both resins are mixed but in a 1:1 ratio.

The following data are obtained following moisture-hardening:

Analogous mixtures according to examples 3 and 4 of the isocyanurate (MPDI+EBDI) and of the linear prepolymer (produced by reactions of PCP 210 with MPDI/EBDI mixtures in OH:HCO equivalents 1:2) following moisture-hardening provide numerically analogously equivalent sheet steel and foil data.

The outstanding performance of the adducts of the MPDI/EBDI mixture used according to the invention result from the fact that oxyester prepolymers as shown in example 6 provide high reactivity, good compatibility, and remarkable mechanical film data but are inadequate as regards storage stability and solvent resistance.

Prepolymer produced from

210 g of oxyester (1 mol of TMP, 2 mol of PS, 2 mol of HMG)

OHZ=266.7

168 g of MPDI/EBDI

378 g of ethyl glycol acetate (PA=phthalic acid; HMG=hexamethylene glycol)

Colorless resin, NCO content: 5.55%

Following catalytic activation with 0.02% DBTL and 0.2% DABCO and moisture-hardening, the following film data and properties have been determined.

Having now fully described this invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.