EP0000963B1 - Isocyanurates containing blocked isocyanate groups, and process for their preparation - Google Patents

Description

Description and examples

The present invention relates to a process for the preparation of new compounds with an adjusted isocyanurate group content, and to the compounds obtainable by this process.

The production of masked isocyanates, also called isocyanate releasers, is known and is described in Houben-Weyl, Methods of Organic Chemistry XIV / 2 pp. 61-70. Tertiary alcohols, phenols, acetoacetic esters, malonic esters, actylacetone, phthalimide, imidazole, hydrogen chloride, hydrogen cyanide and e-caprolactam are known as blocking agents.

These blocked isocyanates have the property of reacting like isocyanates at elevated temperature. The more acidic the H atom of the masking group is, the easier it is to split off. Such blocked isocyanates are described in DT-A-21 66 423. Terminal-blocked isocyanates which additionally contain uretdione groups have also been described in DE-A 25 02 934, they are dimerizates, not trimerizates, only the latter catalyzing the subsequent deblocking.

From FR-A 2 292 724 it is known to use blocked hexamethylene diisocyanate. However, this is highly viscous and therefore difficult to introduce.

Furthermore, it is known from FR-A 2 299 354 to block monomeric 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate-IPDI) with dimethyl ketoxime, but this product is only of limited use because of its low melting point.

Finally, NL-A 7 403 748 relates to the production of isocyanate trimers, but IPDI is not mentioned as the diisocyanate.

Surprisingly, there is no information in the literature about isocyanurate groups and terminally blocked isocyanate groups containing isophorone diisocyanate. Blocked aromatic isocyanurates for the production of heat-resistant, abrasion-resistant urethane stoving enamels, especially for electrical wire insulation, are listed in JA-A 73.30453. In contrast, the production of aliphatic polyisocyanates containing isocyanurate groups blocked in this way has hitherto been unknown.

The invention relates to a process for the preparation of blocked isocyanate groups and isocyanurate group-containing compounds from polyisocyanates and monofunctional, acidic hydrogen-containing blocking agents, characterized in that first 3 - isocyanatomethyl - 3,5,5 - trimethyl-cyclohexyl isocyanate in a known manner an isocyanurate mixture containing more than 2 free isocyanate groups is transferred and this intermediate is then reacted with dimethyl ketoxime as a monofunctional, acidic hydrogen-containing blocking agent at 50-120 ° C., the dimethyl ketoxime being used in amounts such that an NCO group equivalent is used Equivalent dimethyl ketoxime is coming. One variant is that the intermediate product obtained is first freed of the monomeric polyisocyanate and then the practically monomer-free polyisocyanate is then blocked in the manner described.

The invention further relates to a mixture containing blocked isocyanate groups and isocyanurate groups, consisting of at least 10% by weight of an isocyanurate containing 3-isocyanatomethyl-3,3,3-trimethyl and containing more than 2 isocyanate group-containing blocks prior to blocking cyclohexyl isocyanate and, if appropriate, an amount of the monomeric 3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl isocyanate blocked with dimethyl ketoxime and adding to 100% by weight, the total content of unblocked NCO groups being <0.6% by weight lies.

The monomeric polyisocyanate is therefore identical to that which was used to prepare the isocyanurate. The isocyanurate can also be a mixture of the trimeric and higher addition product of the monomeric polyisocyanate. The isocyanurate group content in the compounds produced according to the invention is 2-8% by weight.

These starting materials for the process according to the invention are then subjected to trimerization in a known manner, as described for example in GB-PS 1 391 066 and DT-A 23 25 826. The trimerization of the cycloaliphatic isocyanate is a catalytic reaction. Metal compounds from the group consisting of salts and bases and homeopolar metal compounds wide metal naphthenates, sodium benzoate in DMF, alkaline earth metal acetates, formates and carbonates, metal alkoxides, AICI ₃ and Fe acetylacetonate can be used as catalysts. The proposed catalyst system composed of N, N'-endoethylene piperazine and propylene oxide is particularly suitable for trimerization. The trimerization can be carried out in bulk or in inert organic solvents. To carry out the trimerization process, it is essential to terminate the reaction at a certain isocyanate content of the mixture, preferably when 30-50% of the NCO groups have reacted with trimerization. The unreacted isocyanate then becomes thin Layer distillation separated from the isocyanurate formed.

In the process according to the invention, the isocyanurate isocyanates thus accessible can be used either as the exclusive isocyanate component or else in a mixture with isocyanurate-free polyisocyanate. The addition of isocyanurate-free polyisocyanate allows the properties of the process products, in particular their melting point, to be varied in a desired manner in a simple manner.

It is particularly advantageous to use the triisocyanate mixture prepared in situ as isocyanurate component in the process according to the invention, which mixture is accessible by partial trimerization.

The isocyanurate group-containing polyisocyanate thus obtained, the triisocyanate, or deodorant mixtures with isocyanurate group-free polyisocyanate, is the precursor to the process products according to the invention referred to above as an intermediate.

In a further step of the process according to the invention, this intermediate stage is then converted into the process product according to the invention and terminally blocked isocyanate groups as described below without further modification.

Dimethyl ketoxime has proven to be particularly suitable since it easily undergoes an addition reaction with the compounds containing isocyanate groups at temperatures above 50 ° C., preferably between 80-120 ° C. The addition products thus obtained in a mixture with non-volatile primary hydroxyl-containing polyols react at temperatures between 100 and 200 ° C. with the liberation of dimethyl ketoxime with the non-volatile polyols with formation of urethane.

To carry out the blocking reaction, the isocyanate component is generally introduced and the blocking agent is added. The reaction can be carried out in bulk or in the presence of suitable (inert) solvents. The blocking reaction is generally carried out at 80-120 ° C. The dimethyl ketoxime is used in such amounts that there is one equivalent of blocking agent per NCO group equivalent. The customary isocyanate polyaddition reaction accelerating catalysts, such as tin (11) octoate, can also be used. The catalysts are generally used in an amount between 0.001 and 1% by weight, based on the amount of compounds having hydrogen atoms which are reactive toward isocyanates.

The process products according to the invention are generally compounds of the molecular weight range 300-3000, preferably 400-2000. The process products have melting points or ranges from 30-200 ° C, preferably 60-170 ° C. The preferred polyisocyanates containing isocyanurate groups according to the invention are moreover characterized by a content of isocyanurate groups (calculated as (CO-N-) 3) of 2% by weight to 14% by weight, preferably 3-10% by weight and a content of terminally in blocked form present isocyanate groups (calculated as NCO) of 2-18, preferably 10-17% by weight.

The compounds of the invention described above are particularly suitable because of their low melting points and at the same time higher molecular weights than cocatalysts for the anionic polymerization of _E- caprolactam.

The process products are also suitable as hardeners for higher functional thermoplastic compounds containing Zerewittinoff active hydrogen atoms. In combination with such compounds having Zerewitinoff active hydrogen atoms, the process products form above 120 ° C., preferably at 160-200 ° C., systems curable to high-quality plastics. The most important field of application for such systems is their use as binders for (PUR) powder coatings. The process products according to the invention are also well suited for the production of storage-stable one-component stoving enamels (especially for coil coating).

The invention is illustrated by the following examples:

Example 1: a. Preparation of the trisocyanurate:

100 parts by weight Isophorone diisocyanate (IPDI) was mixed with 0.5 part by weight. the catalyst system from 1,4 - -diazobicyclooctane [2,2,2] (also Dabco @ gennant) and propylene oxide heated at 120 ° C for 3 h. During this time, the NCO content fell from 37.8% (corresponding to 100% IPDI) to 28.4% (50% IPDI sales). To deactivate the catalyst, the reaction mixture was cooled to 40 ° C. and stripped with nitrogen at this temperature for 1/2 h. The NCO content of the reaction mixture changed slightly to 28.2%.

b. Blocking the triisocyanurate:

To 100 parts by weight this isocyanato-isocyanurate mixture was 49 parts by weight at 100 ° C. Dimethylketoxime added in portions so that the reaction temperature did not rise above 120 ° C. To complete the reaction, the reaction mixture was kept at 120 ° C. for a further 2 hours.

Fig. 1 shows the IR spectrum of the reaction product.

Example 2: a. Production of the triisocyanurate:

100 parts by weight IPDI were 0.75 parts by weight. a catalyst system according to Example 1 a heated at 120 ° C for 2 h. During this time, the NCO content fell from 37.8% to 29.4%. To deactivate the catalyst, evacuation was carried out at 120 ° C. and 30 torr for 15 minutes. During this time the NCO content of the reaction mixture changed to 27%.

b. Blocking the triisocyanurate:

To 100 parts by weight this isocyanato-isocyanurate mixture was 46.9 parts by weight at 100 ° C. Dimethylketoxime added in portions so that the reaction temperature did not rise above 120 ° C. To complete the reaction, the reaction mixture is kept at 120 ° C. for a further 2 hours.

Fig. 2 shows the IR spectrum of the reaction product.

Example 3: a. Production of the triisocyanurate:

100 parts by weight IPDI were with 0.5 parts by weight. of the catalyst described in Example 1 heated at 120 ° C for 4.5 h. The progress of the trimerization was followed using the refractive index, viscosity or NCO content. With an NCO content of 25.8%, evacuation was carried out at 20 torr for half an hour. After cooling, the reaction mixture had an NCO content of 25%.

b. Blocking the triisocyanurate:

To 100 parts by weight This isocyanato-isocyanurate mixture was 43.4 parts by weight at 120 ° C. Dimethylketoxim slowly metered in with good stirring. After the addition of dimethyl ketoxin, the reaction mixture was heated at 130 ° C. for a further hour.

Fig. 3 shows the IR spectrum of the reaction product.

Example 4: a. Production of the triisocyanurate:

An isocyanato-isocyanurate mixture (with deactivated cat. 1), the NCO content of which was 20.9%, was prepared from IPDI by the process described in 1a-3a.

b. Blocking the triisocyanate:

To 100 parts by weight this mixture (NCO: 20.9%) was 36.3 parts by weight at 140 ° C with vigorous stirring. Dimethylketoxime added so that the mixture was kept at 140 ° C by the heat of reaction. After the addition of dimethyl ketoxime, the reaction was heated at 140 ° C. for a further 1 h.

Fig. 4 shows the IR spectrum of the reaction product.

Claims (3)

1. Process for production of blocked isocyanate groups and isocyanurate group-containing compounds of polyisocyanates and monofunctional, acid hydrogen-containing blocking agents, characterized in that one first converts 3 - isocyanatomethyl - 3,5,5 - trimethyl - cyclohexylisocyanate in known manner into a mixture consisting of an isocyanurate containing more than 2 free isocyanate groups and then transforms this intermediate product with dimethylketoxime as monofunctional, acid hydrogen-containing blocking agent at 50-120°C, where the dimethylketoxime is introduced in such quantities that to an NCO group-equivalent there corresponds an equivalent of dimethylketoxime.

2. Process according to Claim 1, characterized in that one frees the remaining intermediate product of monomeric polyisocyanate and blocks the then practically monomer-free polyisocyanate in the described manner.

3. Blocked isocyanate group- and isocyanurate group-containing mixture consisting of

at least 10 wt.% of an isocyanurate of 3 - isocyanatomethyl - 3,5,5 - trimethyl - cyclohexylisocyanate containing more than 2 isocyanurate groups before the blocking with dimethylketoxime

and, if necessary, a quantity making up the rest of the 100 wt.% of a dimethylketoxime- blocked monomeric 3 - isocyanatomethyl - 3,5,5 -trimethyl -cyclohexylisocyanate,

whereby the total content of unblocked NCO- groups is <0,6 wt.%.

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