HK1062560B - Process for preparing low-monomer-content tdi trimers - Google Patents

Description

Method for preparing TDI trimer with low monomer content

Cross reference to related patent applications

According to U.S. c. § 119(a) to (d), the present application claims priority from german patent application 10229780.0 filed on 7, 3, 2002.

Technical Field

The invention relates to a novel method for producing low-monomer-content trimers based on 2, 4-and 2, 6-diisocyanatotoluene (TDI) and to the use thereof in coatings.

Background

Processes for preparing polyisocyanates containing isocyanurate groups have been known for a long time and are described in numerous publications and patents (Houben-Weyl, Methoden der organischen Chemie Volume 8, p.136ff., Georg Thieme verlag Stuttgart 1952; H.Wagner, H.F.Sarx, Lackkunsharze 5)^thEdition, page 153ff., CarlHanser Verlag Munich 1971; DE-A4428107, US-PS2,993,870; DE-C1201992; DE-A2456328; j.prakt.chem.336, pp.185 to 200, 1994). Aliphatic diisocyanate trimers and aromatic diisocyanate trimers are widely used as coatings and also as polyurethane elastomers and polyurethane foams.

From the viewpoint of occupational hygiene, low monomer content terpolymer product grades are preferred. These products can be obtained either by distillative separation of the excess monomer after the trimerization or by stirring the trimerization to high conversions until the monomer has undergone very significantly conversion to higher oligomeric isocyanurates. The latter process is particularly successful when the diisocyanate used carries two isocyanate groups of different reactivity, as in the case of toluene 2, 4-diisocyanate. Such solvent-containing products can be prepared by this process with a monomeric TDI (sum of isomeric toluene diisocyanates) content of < 0.5% (e.g.^®Desmodur IL, commercial product from Bayer AG, 50% butyl acetate, NCO content: 8.0%).

Due to the fastening effect of the marked TDI based products, products substantially free of monomeric grades, i.e. products with a TDI content of < 0.1%, are of great interest. To achieve this, the starting substrate of the TDI-based coating system must contain substantially < 0.5 wt.% TDI, preferably < 0.1 wt.%.

In principle, this object can be achieved simply by continuing the trimerization reaction to even higher conversions and thus higher molecular weights. However, this will lead to an increase in viscosity and, on the other hand, to products which are obtained which contain less and less reactive isocyanic acid centers. In addition, for an increased range, the compatibility of the product obtained in this way in admixture with other coating substrates can be adversely affected.

Attempts have also been made to reduce the monomer content in other ways. The use of non-solvents in terpolymers for changing the equilibrium is described, for example, in JP-A56059828. The distillation of "thin-film TDI trimers" (e.g.DE-A3420923, DE-A19618230) and the use of pretreatment and aftertreatment, such as subsequent urethanization, are described in the literature (De-A3928503, U.S. Pat. No. 3,3,384,624, DE-A2414413, DE-A19523657). An even particularly gentle process for selective trimerization at low temperatures has been discussed (JP-A63260915). However, all of the above processes result in very complex, often multi-step industrial processes that are associated with long reaction times, poor space/time yield, and/or inability to transition from laboratory to industrial scale.

EP-A0416338 catalyzes the trimerization of TDI in coating solvents, in particular using Mannich bases. However, the addition of alcohols which are considered essential leads to the formation of urethane groups which exert a strong co-catalytic effect on the trimerization reaction and thus destroy the selectivity necessary to obtain low TDI contents. Similarly, the use of alcohols in combination with other catalyst systems (e.g.US-A5,905,151) has been described, but products having a monomer content of < 0.1% have not been obtained.

DE-A2452532 describes in particular a similar TDI trimerization using a Mannich base. In this case, the reaction must be carried out with the addition of carbamate, which leads to deactivation of the catalytic system at high temperatures, thus preventing "runaway" of the reaction. However, only high monomer content products are obtained, and essentially no monomer-free TDI trimer is obtained.

Disclosure of Invention

The object of the present invention was therefore to provide a simple process for preparing a terpolymer solution which is substantially free of monomers, without additional process steps or physical separation of the monomer TDI.

This object has been achieved by the process of the invention as detailed below.

The invention provides a process for preparing solvent-and/or diluent-containing polyisocyanates based on toluene 2, 4-and/or 2, 6-diisocyanate, containing isocyanurate groups and < 0.1% by weight of monomeric diisocyanate, characterized by the following mixture:

A) 20 to 80% by weight of a diisocyanate component containing at least 80% by weight of 2, 4-and/or 2, 6-diisocyanatotoluene, and

B)20 to 80 wt.% of a solvent and/or diluent, and also

C) Phenol catalysts containing dialkylaminomethyl groups, which catalyze the trimerization reaction in the absence of aliphatic hydroxyl groups and urethane groups at temperatures of 55 to 120 ℃ and are then quenched, if appropriate, with a catalytic poison.

The process of the present invention is used to prepare a polyisocyanate solution containing isocyanuric acid and preferably < 0.10% by weight free TDI, more preferably < 0.05% free TDI.

In one aspect, the present invention provides a process for the preparation of a solvent and/or diluent-containing polyisocyanate based on 2, 4-and/or 2, 6-diisocyanatotoluene, said polyisocyanate containing isocyanurate groups and < 0.1% by weight of monomeric diisocyanate, which process comprises:

a) carrying out catalytic trimerization reaction on a diisocyanate component in the presence of a solvent component and a catalyst to obtain a mixture, wherein the catalyst is a Mannich base containing a dialkylaminomethyl group and a phenolic OH group;

wherein the mixture contains 20 to 80% by weight of a diisocyanate component,

wherein the diisocyanate component comprises 80% of 2, 4-and/or 2, 6-diisocyanatotoluene,

wherein the mixture comprises 20 to 80 wt% of a solvent and/or diluent,

wherein the mixture comprises a phenol catalyst containing dialkylaminomethyl groups, and

wherein the catalytic trimerization reaction is carried out in the absence of aliphatic hydroxyl groups and urethane groups at a temperature of from 70 ℃ to 120 ℃, and

b) the reaction is then optionally terminated with a catalytic poison.

In another aspect of the present invention, there is provided the process as described above, wherein the di-C of the catalyst used_1-3The alkylaminomethyl groups and the phenolic OH groups are located in one molecule.

In another aspect of the present invention there is provided the process described above wherein the catalyst used is a Mannich base based on phenol, p-isononylphenol or bisphenol a obtained by reaction with dimethylamine and formaldehyde.

In another aspect of the present invention there is provided the process described above wherein toluene 2, 4-diisocyanate and/or a mixture of toluene 2, 6-diisocyanate in a weight ratio of from 3: 2 to 9: 1 is used as the starting diisocyanate.

In another aspect of the present invention, there is provided the process described above wherein 2, 4-diisocyanatotoluene is used as the starting diisocyanate.

The invention also provides a process for preparing polyurethane paints, coatings, adhesives, inks, sealants and polyurethane moulding compounds, which comprises adding to the formulation the polyisocyanates containing isocyanate groups prepared by the process of the invention.

Detailed description of the invention

As used herein, unless otherwise specifically indicated, all numerical ranges, amounts, values and percentages, such as amounts of material, times and temperatures of reaction, quantitative ratios, molecular weight values and other portions of the specification which follow, are preceded by the word "about", although such values, amounts or ranges are not expressly stated herein by the term "about".

According to the invention, the diisocyanate component A) consists of 2, 4-diisocyanatotoluene and/or 2, 6-diisocyanatotoluene, optionally containing up to 20% by weight, preferably up to 10% by weight, of further compounds containing isocyanate groups. They may be used alone or in a mixture with another compound.

The mixtures of 2, 4-and 2, 6-diisocyanatotoluene of diisocyanate component A) are preferably used in a weight ratio of from 3: 2 to 9: 1.

The 2, 4-and/or 2, 6-diisocyanatotoluene of diisocyanate component A) may also comprise, if appropriate:

monoisocyanates containing aliphatic, cycloaliphatic, araliphatic or aromatic branched isocyanate groups, such as isostearyl cyanate, naphthyl isocyanate,

diisocyanates containing aliphatic, cycloaliphatic, araliphatic and/or aromatic branched isocyanate groups, e.g. 1, 4-diisocyanatobutane, 1, 6-diisocyanatohexane (HDI), 2-methyl-1, 5-diisocyanatopentane, 1, 5-diisocyanato-2, 2-dimethylpentane, 2, 4-or 2, 4, 4-trimethyl-1, 6-diisocyanatohexane, 1, 10-diisocyanatodecane, 1, 3-and 1, 4-diisocyanatocyclohexane, 1, 3-and 1, 4-di (isocyanatomethyl) cyclohexane, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 4, 4' -diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4 (3) -isocyanatomethylcyclohexane (IMCI), bis (isocyanatomethyl) norbornane, 2, 4 '-and 4, 4' -diisocyanatodiphenylmethane and higher homologs, 1, 5-diisocyanatonaphthalene, dipropylene glycol diisocyanate, triisocyanates and/or higher functional isocyanates such as 4-isocyanatomethyl-1, 8-diisocyanatooctane (triisocyanatononane), 1, 6, 11-triisocyanatoundecane, or any desired mixtures of such isocyanate compounds and isocyanate compounds known as modified isocyanates, derived from the aforementioned diisocyanates and triisocyanates, can be prepared by oligomerization (e.g., trimerization).

Preference is given to using mixtures of 2, 4-and 2, 6-diisocyanatotoluene.

As solvents B), it is possible to use the diluents and solvents customary in polyurethane chemistry, such as toluene, xylene, cyclohexane, chlorobenzene, butyl acetate, ethyl glycol acetate, amyl acetate, hexyl acetate, methoxypropyl acetate, tetrahydrofuran, dioxane, acetone, N-methylpyrrolidone, methyl ethyl ketone, white spirit, higher-substituted aromatic hydrocarbons, such as those prepared from SolventNaphtha^®、Solvesso^®、Shellsol^®、Isopar^®、Nappar^®And Diasol^®Those solvents sold, heavy benzenes, tetrahydronaphthalenes, decahydronaphthalenes and alkanes containing more than 6 carbon atoms, conventional plasticizers, such as phthalates, sulfonates and phosphates, and also mixtures of these solvents and diluents. The concentrations of the diluents and solvents described here are from 20 to 80% by weight, preferably from 40 to 60% by weight.

Further suitable solvents B) are also polyisocyanates based on aliphatic diisocyanates, as described in DE-A4428107. In this way, dilute, low monomer content TDI trimers can be obtained which are free of readily evaporable solvents or diluents.

Suitable phenol catalysts C) for initiating and accelerating the trimerization include special systems which contain a so-called negative temperature effect and which lead to selective incorporation of TDI even at relatively high temperatures. Catalyst systems of this type have a catalyst system which is associated with the aromatic hydrocarbon (alkyl: substituted by oxygen or substituted by oxygen)Sulfur-interrupted, independent alkyl or alkylene chains containing up to 18 carbon atoms) to a phenolic OH group and an N, N-dialkylaminomethyl group. These groups may be distributed in two or more molecules on one or more benzene-containing aromatic hydrocarbons. As the catalyst system, a compound containing both a hydroxyl group and a dialkylaminomethyl group in one molecule is preferably used. Particular preference is given to using dialkylaminomethyl radicals (alkyl ═ C1 to C₃Chain) is located ortho to the aromatic hydroxyl group. Examples which may be mentioned include the following Mannich bases which are obtained, for example, on the basis of phenol, p-isononylphenol or bisphenol A, for example according to DE-A24525319 by heating 188 parts by weight of phenol with 720 parts of 25% aqueous dimethylamine solution and 425 parts by weight of 40% formaldehyde solution at 80 ℃ for two hours, separating the aqueous phase and distilling the organic phase at 90 ℃/10 torr.

The trimerization reaction of the present invention is carried out at elevated temperatures, which for the trimerization of aromatic isocyanates is generally from 55 to 120 ℃, preferably from 70 to 110 ℃, more preferably from 75 to 90 ℃.

In order to obtain an advantageous increase in selectivity at elevated temperatures, the present invention is carried out in the absence of aliphatic hydroxyl group-containing alcohols and any urethane groups formed therefrom.

The catalyst C) can be used in pure form or in solution, suitably in two or more fractions. For the preparation, the total amount of active catalyst used is from 0.003 to 2.0% by weight, preferably from 0.01 to 0.5% by weight. The reaction time is generally between 1 and 100 hours, preferably 10to 25 hours.

The trimerization reaction is preferably stopped at the end by adding a catalytic poison, such as a protic acid, an acid chloride or a methylated compound, such as methyl tosylate.

Surprisingly, in the process of the present invention, when a specific catalyst C) is used in combination with the TDI trimerization in the temperature range of the present invention, an effect contrary to the well-known conventional results is observed, obtaining a more selective incorporation of monomers at relatively high temperatures. According to the process of the invention, it is surprisingly possible to obtain trimer solutions which are substantially free of TDI, even when 2, 6-TDI is used.

Furthermore, after the trimerization reaction is complete, the reaction product can be modified with low molecular weight substances and/or hydroxyl-containing polymeric compounds.

The polyisocyanates obtained by the process of the invention are preferably used for the preparation of coatings which can be cured under the influence of atmospheric humidity. They are used for the production of adhesion promoters, adhesives, inks, sealants and polyurethane moulding compounds, can be added to formulations for the production of these products, and for the production of paints and coatings. More preferably, they are used as crosslinkers for 2-component systems containing isocyanate-reactive compounds known per se. These include, for example, hydroxy-functional polyethers, polyesters, polyamides, polycarbonates, polyacrylates, polybutadienes and hybrid combinations of the above hydroxy-functional polymers. Low molecular weight substances di-and polyols, dimer fatty alcohols and trimer fatty alcohols and amino functional compounds can also be used in 2K (two-component) systems. With the block isocyanate reactive compound, a single-component system can also be prepared; similarly, the products obtained by the process according to the invention can also be used in block form in coatings. In this case, drying may occur at relatively high temperatures up to about 200 ℃.

In addition to the products of the process of the invention, other auxiliaries and additives can also be used in the coating materials, such as customary wetting agents, leveling agents, antiskinning agents, antifoams, solvents, flatting agents (such as silica, aluminum silicates and high-boiling paraffins), viscosity regulators, pigments, dyes, UV absorbers and heat and oxidative degradation stabilizers.

The resulting coatings can be used to coat any desired substrate, such as wood, plastic, leather, paper, textiles, glass, ceramic, gypsum, masonry, metal, or concrete. They can be applied by conventional methods, such as spraying, brushing, dipping, pouring, dipping and rolling. The coating can be used in the form of a clear coating or else in the form of a pigmented paint.

The coating produced by the product of the invention can be cured into a high-quality coating at 20 ℃ for several minutes to several hours. Alternatively, curing can be done at lower temperatures (as low as-5 ℃) or accelerated at higher temperatures (up to 200 ℃).

Examples

All numbers given as "parts" and "%" are by weight. As is known to the skilled worker, the NCO content is determined by titration.

Comparative example 1

(not according to the invention, example 1 of EP-A0416338 was repeated)

In a stirred apparatus, 375g Desmodur^®T80 (a mixture of 80% toluene 2, 4-diisocyanate and 20% toluene 2, 6-diisocyanate) was mixed at 50 ℃ with 19.8g 2-ethylhexanol and stirred until the mixture contained 44% NCO. It is then diluted with 394g of butyl acetate, mixed with 1.0g of catalyst solution (40% strength Mannich base in xylene, based on phenol/dimethylamine) and stirred. After 3,8 and 12 hours, a further 0.7g of catalyst solution were added, respectively, and the mixture was stirred at 50 ℃ for 10 hours until the NCO content had fallen to 8.05%. To terminate the trimerization, the product obtained is mixed with 1.0g of methyl tosylate and heated at 80 ℃ for 1 hour. The product had the following characteristics:

NCO content: 7.95 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1250mPas

Free TDI content: 0.35% (by GC)

Example 1(method of the invention)

500g of butyl acetate and 500g of toluene 2, 4-diisocyanate were mixed and stirred at 75 ℃ with 1.5g of catalyst solution, based on bisphenol A/dimethylamine, in a 40% strength dilution of a Mannich base in xylene (40% butyl acetate), in a stirring apparatus. After 4, 8 and 12 hours, half the amount of the second catalyst was added and the mixture was stirred at 75 ℃ for 10 hours until the NCO content had fallen to 8.1%. To terminate the trimerization reaction, the product obtained was mixed with 1.5 times the weight (based on the amount of catalyst added) of methyl tosylate and heated at 80 ℃ for 1 hour. The product had the following characteristics:

NCO content: 8.07 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1300mPas

Free TDI content: < 0.03% (by GC)

Example 2(method of the invention)

In a stirred apparatus, 500g of butyl acetate and 500g (1.35eq) of Desmodur are introduced^®T80 (mixture of 80% toluene 2, 4-diisocyanate and 20% toluene 2, 6-diisocyanate) was mixed with 1.34g of catalyst (a dilution of 40% Mannich base in xylene based on bisphenol A/dimethylamine (40% butyl acetate)) at 80 ℃ and stirred. After 3,8, 10 and 14 hours, 30% of the initial amount of catalyst was added and the mixture was stirred at 80 ℃ for 6 hours until the NCO content had fallen to 8.05%. To terminate the trimerization reaction, the product obtained was mixed with 1.5 times the weight (based on the amount of catalyst added) of methyl tosylate and heated at 80 ℃ for 1 hour. The product had the following characteristics:

NCO content: 8.02 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1250mPas

Free TDI content: 0.04% (determined by GC)

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (6)

1. A process for the preparation of a solvent and/or diluent-containing polyisocyanate based on 2, 4-and/or 2, 6-diisocyanatotoluene, said polyisocyanate containing isocyanurate groups and < 0.1% by weight of monomeric diisocyanate, which process comprises:

a) carrying out catalytic trimerization reaction on a diisocyanate component in the presence of a solvent component and a catalyst to obtain a mixture, wherein the catalyst is a Mannich base containing a dialkylaminomethyl group and a phenolic OH group;

wherein the mixture contains 20 to 80% by weight of a diisocyanate component,

wherein the diisocyanate component comprises 80% of 2, 4-and/or 2, 6-diisocyanatotoluene,

wherein the mixture comprises 20 to 80 wt% of a solvent and/or diluent,

wherein the mixture comprises a phenol catalyst containing dialkylaminomethyl groups, and

wherein the catalytic trimerization reaction is carried out in the absence of aliphatic hydroxyl groups and urethane groups at a temperature of from 70 ℃ to 120 ℃, and

b) the reaction is then optionally terminated with a catalytic poison.

2. The process according to claim 1, wherein the di-C of the catalyst used_1-3The alkylaminomethyl groups and the phenolic OH groups are located in one molecule.

3. The process according to claim 1, wherein the catalyst used is a Mannich base based on phenol, p-isononylphenol or bisphenol A obtained by reaction with dimethylamine and formaldehyde.

4. A process as claimed in claim 1, wherein 2, 4-diisocyanatotoluene and/or 2, 6-diisocyanatotoluene mixtures in a weight ratio of from 3: 2 to 9: 1 are used as starting diisocyanates.

5. A process according to claims 1 to 3, wherein 2, 4-diisocyanatotoluene is used as starting diisocyanate.

6. A process for the preparation of polyurethane paints, coatings, adhesives, inks, sealants and polyurethane molding compounds which comprises adding to the formulation a polyisocyanate containing isocyanate groups according to claim 1.