HK1062561B - Process for preparing low-monomer-content tdi trimers - Google Patents

Description

Method for preparing TDI trimer with low monomer content

Cross Reference to Related Applications

According to U.S.C. § 119(a) to (d), the present application claims priority from german patent application 10229781.9 filed 2, 7/2003.

Technical Field

The invention relates to a novel process for preparing low-monomer-content trimers based on 2, 4-and/or 2, 6-diisocyanatotoluene (TDI).

Background

Processes for preparing polyisocyanates containing isocyanurate groups have been known for a long time and are described in numerous publications and patents (e.g.Houben-Weyl, Methoden der organischen Chemie Volume 8, p.136ff., Georg Thieme Verlag Stuttgart 1952; H.Wagner, H.F.Sarx, Lackkunsharze 5th Edition, page 153ff., CarlHanser Verlag Munich 1971; DE-A4428107, U.S. Pat. No. 3,699; DE-A1201992; DE-A2452532; 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% EtOHButyl acid, NCO content: 8.0%).

Due to the fastening effect of the labeled TDI based products, products substantially free of monomer 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, on the one hand, low viscosity is expensive and, on the other hand, the process is such that the product obtained contains less and less reactive isocyanate groups. In addition, this measure greatly affects the compatibility of the product with other coating substrates.

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 terpolymers" (e.g.DE-A3420923, DE-A19618230, DE-A712840) and the use of pretreatment and aftertreatment, such as subsequent urethanization, are also known (e.g.De-A3928503, US-A3,384,624, DE-A2414413, DE-A19523657, JP-A2000273142). 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.

Disclosure of Invention

The object of the present invention was therefore to provide a simple process for preparing trimer solutions which essentially do not need to contain 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-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, B)20 to 80% by weight of a solvent, and C)0 to 20% by weight of an alcohol component, and also D) a phenol catalyst containing dialkylaminomethyl groups,

the catalytic trimerization is carried out at a temperature of from 20 ℃ to 120 ℃ and in one or more steps from 0.1 to 25% by weight, based on the amount of diisocyanate used, of monomeric 2, 4-diisocyanatotoluene is metered in, followed by termination of the reaction, where appropriate, with the aid of a catalytic poison.

In one aspect of the present invention there is provided a process for the preparation of a solvent-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) reacting the following mixture at a temperature of 20 ℃ to 120 ℃:

A) 20 to 80% by weight of a diisocyanate component containing at least 80% by weight of 2, 4-and/or 2, 6-diisocyanatotoluene, B)20 to 80% by weight of a solvent, and C)0 to 20% by weight of an alcohol component, and also D) a phenol catalyst containing dialkylaminomethyl groups;

b) during the trimerization reaction, from 0.1 to 25% by weight, based on the amount of diisocyanate used, of the monomeric toluene 2, 4-diisocyanate are metered in one or more steps;

c) the reaction is terminated by the addition of a catalytic poison.

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".

The process of the invention is clearly in conflict with reducing the residual monomer content of the product. The general idea is that increasing the reaction time entails increasing the monomer conversion, while shortening the reaction time entails the opposite. Therefore, when additional monomers are measured during the reaction, some of the monomers can only be reacted for a shorter time, and the monomer content must relatively tend to rise. However, experimental measurements showed that the addition of additional toluene 2, 4-diisocyanate resulted in a significant reduction of the residual monomer fraction to < 0.1 wt.%.

The process of the invention is used for preparing polyisocyanate solutions containing isocyanurate groups and < 0.1% by weight of free diisocyanate, preferably < 0.05% by weight of free TDI.

In the process of the present invention, the amount of monomeric 2, 4-diisocyanatomethylbenzene additionally metered in during the trimerization carried out is preferably from 10 to 20% by weight, more preferably from 1 to 10% by weight, based on the amount of diisocyanate used.

As diisocyanate component A) it is possible according to the invention to use compounds containing isocyanate groups and mixtures thereof, which contain at least 80% by weight of 2, 4-and/or 2, 6-diisocyanatotoluene, preferably at least 90% by weight. More preferably, 2, 4-and/or 2, 6-diisocyanatotoluene is used, preferably without blending with other isocyanate components.

In addition to 2, 4-and/or 2, 6-diisocyanatotoluene, the isocyanate component A) may also comprise:

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 2, 6-diisocyanatotoluene (TDI), 2, 4 '-and 4, 4' -diisocyanatodiphenylmethane and the 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.

In addition to the TDI in the mixture as isocyanate component A), so-called modified isocyanate compounds may be used which are derived from the above-mentioned diisocyanates and triisocyanates and which can be prepared by oligomerization reactions such as polyurethane reactions, biuret reactions, urethanic reactions or trimerization reactions.

Particular preference is given to using mixtures of 2, 4-and 2, 6-diisocyanatotoluene, in particular mixtures of 75 to 85% by weight of 2, 4-TDI and 25 to 15% by weight of 2, 6-TDI. In this mixture, the weight ratio of 2, 4-TDI to 2, 6-TDI is preferably from 3: 2 to 9: 1.

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

Further suitable solvents B) may be polyisocyanates based on aliphatic diisocyanates, as described in DE-A4428107 and DE-A506004. In this way, dilute TDI trimers with low monomer content can be obtained which are free of readily evaporable solvents.

Suitable catalysts D) for initiating and accelerating the trimerization include special systems which lead to selective incorporation of TDI even at relatively high temperatures. Catalyst systems of this type have a C atom of up to 18 carbon atoms interrupted by oxygen or sulfur with an aromatic hydrocarbon₁-C₃Alkyl chain or alkylene chain) and an N, N-dialkylaminomethyl group.

These groups may be distributed in two or more molecules, on one or more 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 C₁-C₃Catalyst system in which the dialkylaminomethyl group is 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 by reacting the compounds with aqueous dimethylamine solution and formaldehyde according to DE-A2452531 or Synth.

The trimerization reaction of the present invention is carried out at from 20 to 120 ℃ and preferably from 50 to 80 ℃.

The criterion of the present invention is single, and when appropriate, the addition of 2, 4-diisocyanatotoluene to the reaction phase during the trimerization reaction results in a significant reduction in the residual TDI content of the product. The 2, 4-diisocyanatotoluene may be pure or as a mixture with other diisocyanate components A) according to the invention or as a solution in the solvents B) according to the invention.

The diisocyanate is generally added to obtain a TDI residual monomer content of less than 5% by weight, preferably less than 2% by weight, particularly preferably less than 1% by weight; less than 10% by weight, particularly preferably less than 5% by weight, based on the total amount of diisocyanate components used, is preferably added. The residual monomer content can be determined by gas chromatography. In the experimental context, this can also be determined by linking the residual monomer content to the NCO content.

The catalyst D) can be used in pure form or in solution, suitably in two or more fractions or continuously. For the preparation, the total amount of active catalyst D) 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 10 to 25 hours. The temperature is preferably from 50 to 80 ℃.

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.

During the trimerization of TDI according to the invention, it has surprisingly been observed that when additionally monomeric diisocyanates, preferably toluene 2, 4-diisocyanate, are added, the final TDI content of the polyisocyanate does not rise, but falls. Very surprisingly, with this process it is possible to prepare a trimer solution which is substantially free of monomeric TDI.

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 useful coatings which cure under the influence of atmospheric humidity. They are useful for the production of adhesion promoters, adhesives, inks, sealants and polyurethane molding compounds.

They are particularly preferably 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 materials diols and polyols, dimer fatty alcohols and amino functional compounds may 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

In a stirred apparatus, 500g of butyl acetate and 500g of Demodur^®T80 (mixture of 80% toluene 2, 4-diisocyanate and 20% toluene 2, 6-diisocyanate) was mixed continuously with 4.4g of the catalyst solution (based on bisphenol A/dimethylamine, a dilution of 35% Mannich base in xylene (40% butyl acetate)) at 50 ℃ and stirred. The reaction was stirred until the NCO content had fallen to 8.0%. 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 solids content was adjusted to 50% by adding solvent. The product had the following characteristics:

NCO content: 8.0 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1100mPas

Free TDI content: 0.30% (by GC)

Comparative example 2

In a stirred apparatus, 500g of butyl acetate and 500g of Desmodur^®T80 (mixture of 80% toluene 2, 4-diisocyanate and 20% toluene 2, 6-diisocyanate) was mixed continuously with 4.5g of the catalyst solution (80% dilution of butyl acetate Mannich base based on bisphenol A/dimethylamine) at 50 ℃ and stirred. The reaction was stirred until the NCO content had fallen to 8.0%. 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 solids content was adjusted to 50% by adding solvent.

The product had the following characteristics:

NCO content: 8.0 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1400mPas

Free TDI content: 0.53% (by GC)

Example 1 (Process according to the invention)

In a stirred apparatus, 500g of butyl acetate and 500g of Desmodur^®T80 (mixture of 80% toluene 2, 4-diisocyanate and 20% toluene 2, 6-diisocyanate) was mixed continuously with 5.9g of the catalyst solution (based on bisphenol A/dimethylamine, a dilution of 35% Mannich base in xylene (40% butyl acetate)) at 50 ℃ and stirred. At an NCO content of 10.45% and 8.7%, 40g and 20g of toluene 2, 4-diisocyanate were added in this order. The reaction was further catalyzed and stirred until the NCO content dropped to 8.0%. 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 solids content was adjusted to 50% by adding solvent. The product had the following characteristics:

NCO content: 8.0 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1300mPas

Free TDI content: < 0.05% (by GC)

Example 2 (method of the invention)

In a stirred apparatus, 500g of butyl acetate and 500g of Desmodur^®T80 (mixture of 80% toluene 2, 4-diisocyanate and 20% toluene 2, 6-diisocyanate) was mixed continuously with 6.17g of the catalyst solution (based on bisphenol A/dimethylamine, a dilution of 35% Mannich base in xylene (40% butyl acetate)) at 50 ℃ and stirred. At an NCO content of 9.05%, 30g of toluene 2, 4-diisocyanate were added. The reaction was further catalyzed and stirred until the NCO content dropped to 8.0%. 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 solids content was adjusted to 50% by adding solvent. The product hasThe characteristics are as follows:

NCO content: 8.0 percent

Solid content: 50 percent of

Viscosity at 23 ℃: 1500mPas

Free TDI content: < 0.09% (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 (7)

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

a) reacting the following mixture at a temperature of 20 ℃ to 120 ℃:

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

B)20 to 80% by weight of a solvent, and

C)0 to 20% by weight of an alcohol component, and also

D) A phenol catalyst containing a dialkylaminomethyl group;

b) during the trimerization reaction, from 0.1 to 25% by weight, based on the amount of diisocyanate used, of the monomeric toluene 2, 4-diisocyanate are metered in one or more steps;

c) the reaction is terminated by the addition of a catalytic poison.

2. The process according to claim 1, wherein the amount of further monomeric 2, 4-diisocyanate metered in during the trimerization reaction is from 10 to 20% by weight.

3. The process according to claim 1, wherein the amount of further monomeric 2, 4-diisocyanate metered in during the trimerization reaction is from 1 to 10% by weight.

4. 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.

5. A process according to claim 4, wherein the catalyst used comprises a Mannich base obtained from phenol, p-isononylphenol or bisphenol A by reacting it with dimethylamine and formaldehyde.

6. The process according to claim 1, wherein the trimerization reaction is carried out at a temperature of from 50 to 80 ℃.

7. 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.