Use of special isocyanates for preparing aqueous polyurethane coatings

Abstract

The invention relates to the use of 4-isocyanatomethyloctane 1,8-diisocyanate isocyanatononane, (TIN) and TIN-containing mixtures for preparing polyurethane lacquers and coatings which can be applied from an aqueous medium.

Description

FIELD OF THE INVENTION

The invention relates to the use of 4-isocyanatomethyloctane-1,8-diisocyanate (triisocyanatononane, TIN) and TIN-containing mixtures for preparing polyurethane lacquers and coatings which can be applied from an aqueous medium.

BACKGROUND OF THE INVENTION

The preparation and use of water-dispersible polyisocyanates, i.e., isocyanates with at least two NCO groups in the molecule, is well-known (see EP-A 540,985 and documents cited therein). They are gaining increasing economic importance for the preparation of lacquers and coating agents based on polyurethane which emit a substantially lower proportion of volatile organic components (VOC), in particular solvents, during application. Due to their low tendency to become yellow under the influence of light, representatives which contain exclusively (cyclo)aliphatically bonded NCO groups are gaining particular importance for the preparation of high quality lacquer raw materials and coating agents.

A variety of substances and methods are available for dispersing in water those polyisocyanates which are hydrophobic, per se, and react with water, these being known from "classical" two-component technology, i.e., those normally requiring substantially non-aqueous conditions.

Thus, it is possible to disperse classical polyisocyanate hardeners, e.g., derivatives of aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) or hydrogenated 4,4'-diphenylmethane diisocyanate (H.sub.12 MDI, Desmodur.RTM. W=a commercial product from Bayer AG) in water by using extremely high shear forces. The last two compounds mentioned, however, always require the use of solvents since the 100% solids systems are solids or highly viscous oils. These dispersions produce high quality coatings which are substantially equal to those which result from the use of non-aqueous processing technologies (see L. Kahl, M. Bock, E. Jurgens and H. -J. Laas in "Farbe und Lack", 102nd issue, March 1996, pages 88-100 and literature cited therein).

The disadvantage of these is the cost of the nozzle jet dispersion process since these technologies are not available in all fields of application, in particular car repair lacquering.

On the other hand, according to the disclosure in EP-A 540,985, the chemical incorporation of hydrophilic components into the above-mentioned classical polyisocyanate hardeners has been proposed in order to overcome the hydrophobic nature of these species which cannot be directly dispersed under the effect of low shear forces (e.g., stirring in by hand). The incorporation of these hydrophilic components, however, often takes place by using the free NCO groups in the polyisocyanate (e.g., by urethenization with specific, e.g., monofunctional, polyethers). Thus the provision of hydrophilic characteristics is naturally associated with a lowering of the NCO functionality of the polyisocyanate hardener and therefore a drop in the concentration of valuable NCO groups which are available for cross-linking to the substrate.

Furthermore, polyisocyanates have also been rendered hydrophilic by adding so-called "external" emulsifiers (e.g., EP-A 557,844 and documents cited therein). Apart from the economic disadvantage of an additional process step, this method involves the critical disadvantage that the external emulsifiers used have to remain in the lacquer film and tend to affect its physical properties disadvantageously, e.g., due to so-called "sweating," due to the higher degree of hydrophilicity and, resulting from that, a greater sensitivity of the lacquer or coating towards the effects of water, odor problems due to the frequently intense and unpleasant intrinsic odor of the emulsifiers or of the products formed from it, etc.

It is known that the viscosity of (poly)isocyanates is connected with their water dispersibility (e.g., EP-A 0,358,979). That is, low viscosity should generally lead to better dispersibility. However, this relationship is not generally applicable as can be seen from a few comparative trials (1.c. Example 1).

Also, explicit reference is made for example in EP-A 0,358,979 (p.2,line 54 to p.3, line 1) that the NCO-reactive components, and the optional auxiliary substances and additives which are used, have to be present before adding the isocyanate component to the aqueous polymer solution and/or dispersion. Thus, it can be assumed that these auxiliary substances and additives do not have an uncritical effect on the dispersibility of the polyisocyanate which itself is not water dispersible in the absence of additives.

The object of the present invention is to provide water-dispersible polyisocyanates or polyisocyanate mixtures which are characterized by ease of incorporation, even at low shear forces (e.g., "stirring by hand"), and which contain no hydrophilic additives.

SUMMARY OF THE INVENTION

The object of the invention is achieved by the use of 4-isocyanatomethyloctane-1,8-diisocyanate (triisocyanatononane, in the following called TIN) or TIN-containing mixtures with other lacquer polyisocyanates known, per se, from the prior art. More specifically, the invention is directed to a method-for making an aqueous polyurethane lacquer composition, the isocyanate component used to make the lacquer composition, and coatings made from the lacquer composition.

DETAILED DESCRIPTION OF THE INVENTION

The invention is based on the surprising observation that 4-isocyanato-methyloctane-1,8-diisocyanate (triisocyanatononane, or TIN) can be readily dispersed in water even without the use of high shear forces or hydrophilic additives and, in addition, is capable of "incorporating" a certain amount of other polyisocyanates of the above-mentioned type which are hydrophobic, per se, in the aqueous dispersion or emulsion.

As such, the present invention provides the use of 4-isocyanatomethyloctane-1,8-diisocyanate (triisocyanatononane, TIN) to prepare aqueous polyurethane lacquers and coatings. The present invention also provides corresponding use of TIN mixed with other isocyanate group-containing conventional polyisocyanates from the group of biurets, uretdiones ("dimers"), allophanates and isocyanurates, iminooxadiazinediones ("trimers") of hexamethylene diisocyanate, isophorone diisocyanates, hydrogenated diphenylmethane diisocyanates and other, optionally cyclic, aliphatic diisocyanates, wherein the proportion of conventional polyisocyanate in the mixtures used according to the invention does not exceed 50 wt. %.

TIN can be prepared from the parent triamine, optionally, after conversion into a derivative which is easier to phosgenate, such as, e.g., a (tris)hydrochloride, carbaminate, etc, by a phosgenating process, known from the prior art, in condensed phase or in the gas phase (e.g., DE-A 3,109,276 and EP-A 749,958). Phosgene-free processes for preparing this compound have also been proposed (U.S. Pat. No. 5,189,205). The triisocyanate is produced as a high-boiling, virtually odorless liquid with an NCO concentration of 48 to 51 wt. % when titrated in accordance with DIN 53 185 and has a purity of not less than 95% when determined using gas chromatography.

The theoretical NCO content of TIN is 50.16%. If a slightly higher NCO content is found, e.g., when titrating in accordance with DIN 53 185, this means that there are impurities in the TIN which have a higher concentration of amine-reactive functional groups than TIN itself, e.g., unsaturated C.sub.9 triisocyanates.

A certain concentration of impurities, however, does not affect the use of TIN in accordance with the invention in the fields of application described here as can be demonstrated by using model experiments with very pure TIN and deliberately contaminated material.

TIN can be combined with all known NCO-reactive components which are suitable for use in aqueous systems. Examples of these types or reaction partners are OH- and NH-functional polyethers, polyesters, polyacrylates, polyamines and polycarbonates, optionally mixed with each other. Examples of the preparation and use of these types of reaction partners can be found, inter alia, in DE-A 4,137,896 and 3,829,587.

High quality polyurethane lacquers and coatings are obtained using TIN or TIN-containing mixtures according to the invention and these are characterized, as compared with products from the prior art, by a number of other advantages in addition to the advantage which is an essential part of the invention, and has already been mentioned, of better emulsifiability in water. It is difficult to express the positive qualities which are immediately obvious to a trained person skilled in the art which result from the use or joint use of TIN as quantitatively measurable properties. Therefore, at this point only qualitative expressions such as fullness, uniformity and transparency of the coating will be mentioned. However, the (measurable) lacquer properties such as improved resistance to chemicals and water, greater hardness and an earlier increase In hardness during setting and also rapid drying are qualities which come to the fore when using or jointly using TIN as compared with products from the prior art.

Other auxiliary substances and additives may also be used in the coatings which use TIN or TIN-containing mixtures according to the invention, such as wetting agents, flow control agents, skin preventing agents, antifoaming agents, matting agents, viscosity regulating substances (thickeners, thixotropic agents), pigments, colorants, UV-absorbers and stabilizers against thermal and oxidative effects.

The use of TIN or TIN-containing mixtures according to the invention may serve to coat a number of materials, e.g., wood, plastics, leather, metal, paper, concrete, brickwork, ceramic, textiles, etc.

The invention is further described in the following illustrative examples. All parts are by weight unless otherwise indicated.

EXAMPLES

The dynamic viscosities were obtained at 23.degree. C. with a rotary viscometer and a ball and plate measuring arrangement PK 100 from the Haake Company (Example 1) or were performed by the DIN methods specified in the details. As a result of measurements at different rates of shear, it was shown that the flow behavior of polyisocyanate mixtures according to the invention and also of the comparison products corresponded to that of ideal Newton liquids. The data on rates of shear can therefore be omitted.

Determining the NCO content was performed in accordance with DIN 53 185.

In all the examples, the measurements and observations which are an essential part of the invention were made using an example of TIN, or mixtures of TIN with HDI polyisocyanates mainly of the isocyanurate-type ("trimers") as highly viscous components. This was to provide better comparability of the results obtained and does not mean that the invention is restricted to these products. The same applies to mixtures based on other (poly)isocyanates and/or other structural types than the isocyanurate polyisocyanates ("trimers").

Example 1

Each of the following is placed in a test tube:

1. TIN 2. hexamethylene diisocyanate (HDI) 3. isophorone diisocyanate (IPDI) 4. a mixture of 50% TIN and 50% of an HDI/isocyanurate polyisocyanate with an NCO content of 23.3% and a viscosity of 1180 mPa.multidot.s, prepared in accordance with the disclosure in DE-A 3,806,276 (viscosity of the mixture: 70 mPa.multidot.s) 5. a mixture of 50% TIN and 50% of an HDI/isocyanurate polyisocyanate with an NCO content of 21.8% and a viscosity of 3080 mPa.multidot.s, prepared in accordance with the disclosure in DE-A 3,806,276 (viscosity of the mixture: 100 mPa.multidot.s) 6. a mixture of 70% TIN and 30% of an HDI/isocyanurate polyisocyanate with an NCO content of 23.3% and a viscosity of 1180 mPa.multidot.s, prepared in accordance with the disclosure in DE-A 3,806,276 (viscosity of the mixture: .ltoreq.50 mPa.multidot.s) 7. a mixture of 70% TIN and 30% of an HDI/isocyanurate polyisocyanate with an NCO content of 21.8% and a viscosity of 3080 mPa.multidot.s, prepared in accordance with the disclosure in DE-A 3,806,276 (viscosity of the mixture: .ltoreq.50 mPa.multidot.s) in such a way that the levels in all the test tubes are roughly identical. This level is marked and each liquid is very carefully covered with approximately the same volume of deionized water (two phases), then sealed with a stopper and shaken vigorously for a few seconds until a milky white suspension is produced.

Next, the time to de-mixing of the suspensions is measured, i.e., until the isocyanate-containing lower phase has reached approximately 80% of the previously marked full level. This produces the following results:

1. about 10 minutes 2. about 30 seconds 3. about 40 seconds 4. about 1 min. 30 sec. 5. about 40 seconds 6. about 2 min. 40 sec. 7. about 2 min. 30 sec.

It can be seen from this example that on the one hand TIN has an outstanding dispersibility in water and on the other hand that the viscosity of the (poly)isocyanate may not be the only critical parameter for good water dispersibility since the isocyanates from Examples 1, 2 and 3 have approximately the same low viscosity (up to 10 mPa.multidot.s), the degree of inaccuracy of the measurement of the method described at the beginning is too great in this range for them to be differentiated any further, and for the same reason only an upper limit is quoted for the viscosity of the mixtures used in Experiments 6 and 7).

Example 2

With Comparison Examples

The use of pure TIN (according to the invention, Formulation 3) and TIN mixed with an HDI trimer polyisocyanate (Desmodur.RTM. VP LS 2025/1, product of Bayer AG, called LS 2025/1 in the following, according to the invention, Formulation 4) in aqueous lacquers as compared with products from the prior art (pure LS 2025/1 without added TIN, comparison example, Formulation 1) and a hydrophilic modified polyisocyanate (Bayhydur.RTM. 3100 from Bayer AG, called 3100 in the following, comparison example, Formulation 4).

A polyacrylate in accordance with DE-A 3,829,587 (Bayhydrol.RTM. VP LS 2235, product of Bayer AG), which is suitable for use in aqueous two-component PUR lacquers was used as the polyol component (binder) in all the formulations.

______________________________________Formulation # 1 2 3 4______________________________________Desmodur .RTM. LS -- TIN LS 2025/1 2025/1 + TIN(1:1)Bayhydur .RTM. -- 3100 -- --80% in Proglyde .RTM. DMM.sup.1) --> --> --> -->Component 1Bayhydrof .RTM. VP LS 2235 64.14 58.28 67.51 67.51Surfynol .RTM. 104.sup.2) 1.24 1.21 1.16 1.250% BGBorchigel .RTM. PW 25.sup.3) 0.08 0.08 0.08 0.0825% PG/H.sub.2 OBaysilone .RTM. OL 31.sup.4) 1.0 1.0 1.0 1.010% BGDemin. H.sub.2 O for flow time -- -- -- --DIN 6 = 50"______________________________________ .sup.1) dipropyleneglycoldimethylether, product of the Dow Chemical Co. .sup.2) commercial substrate wetting agent, product of the Air Products Co. .sup.3) commercial thickener, product of the Borchers Co. .sup.4) commercial slip additive, product of Bayer AG ______________________________________Formulation # 1 2 3 4______________________________________Component 2Hardener, 80% strength 12.59 15.63 9.46 11.35Water for spray viscosity 20.95 23.80 20.79 18.86Total 100.0 100.0 100.0 100.0Spray dilution H.sub.2 O H.sub.2 O H.sub.2 O H.sub.2 ONCO:OH 1.5 1.5 1.5 1.5Solids (wt. %) 40.3 40.0 39.3 42.9Co-solvent (wt. %) 9.04 9.18 8.64 9.04VOC g/l 183 187 180 174Density (kg/l) 1.0 1.0 1.0 1.0pH 8.2 8.0 8.0 7.9______________________________________ ______________________________________Aqueous 2-component PUR clear lacquer, hardener incorporation 30"2000 rpm/Dissolver disc .phi. 40 mm for a dispersive volume of500 g in a 1000 ml vessel (simulated "incorporation by hand")Formulation # 1 2 3 4______________________________________Bayhydrol .RTM. VP LS 2235 --> --> --> -->Desmodur .RTM. LS -- TIN LS 2025/1 2025/1 + TIN (1:1)Bayhydur .RTM. -- 3100 -- --Viscosity 35/8.0 35/8.0 35/8.0. 35/8.0Comp. 1 DIN 6(sec)/pHViscosity component 1 + 2 (DIN 4)//Ph//opacity (0-5)Immediately 15/7.8/5 16/7.9/3 15/8.0/1 16/8.1/4after 30 min 15/8.1/4 16/7.9/0 15/7.9/0 16/7.9/0after 60 min 15/8.0/4 15/7.8/0 17/7.7/0 18/7.7/0after 120 min 15/7.8/4 15/7.8/0 19/7.5/0 20/7.4/0after 180 min 16/7.5/4 15/7.5/0 22/7.3/0 25/7.3/0Drying (h)T1 1.5 1.5 1 1.5T3 5 5 4 4.5______________________________________ ______________________________________Formulation # 1 2 3 4______________________________________Drying 2//0 2//0 1//0 1//0(0-5)30'60.degree. C.//30'60.degree. C. + 1hTurbidity 4//4 1//1 1//1 2//2(0-5)30'60.degree. C.//30'60.degree. C. + 1hPendulum hardness 57 23 39 49(s)(RT = RoomTemperature) 69 36 53 69Pendulum hardness 19 14 32 41(s)30'60.degree. C. + 2h RT+ 46 29 81 75+ 60 43 106 102Solvent resistance on ALU + base lacquer + clear lacquer.sup.1)1d RT 3344 3355 2233 23333d RT 2343 2355 2222 22337d RT 1233 1233 1121 112130'60.degree. C. + 2h RT 4555 4555 2344 2334+ 1d RT 2344 2344 1111 1111+ 3d RT 1233 1245 1000 1111+ 7d RT 1233 1233 0000 0011Solvent resistance on glass plate + clear lacquer (60 .mu.m dryfilm).sup.1)3d RT 3444 4455 4233 4344+ 7d RT 3333 4233 4121 422230'60.degree. C. + 3d RT 4444 4344 2222 2222+ 7d RT 3233 4233 1000 0000______________________________________ ______________________________________Formulation # 1 2 3 4______________________________________Alkali (A) and acid (S) resistance on ALU +base lacquer + clear lacquer5h A/S 1/1 1/1 1/1 1/13d RT5h A/S 1/1 1/1 1/1 1/17d RT5h A/S 1/2 1/2 1/1 1/130'60.degree. C. + 3d RT5h A/S + 1/1 1/1 1/1 1/17d RTAlkali and acid resistance onGlass plate + clear lacquer (60 .mu.m dry film).sup.2)1h//5h + 3d RT 44//44 11//44 34//44 44//441h//5h + 7d RT 44//- 44//- 44//- 44//-16h + 7d RT 21//- 11//- 11//- 11//-1h//5h 41//43 44//44 21//32 33//3330'60.degree. C. + 3d RT1h//5h + 7d RT 44//- 44//- 44//- 44//-16h + 7d RT 12//- 12//- 11//- 11//-Flow RT//30'60.degree. C. 3/3 2/1 0/0 1/1Visual gloss 2-3 2 0 1assessmentGloss 20.degree. RT 89 92 91 91Haze RT 37 <20 <20 <20Gloss 20.degree. 30'60.degree. C. 90 91 91 90Haze 30'60.degree. C. 24 24 <20 30Flake tough, soft tough, averag. hard of 1 & 2 or 3______________________________________ 0 = positive//5 = negative .sup.1) 1h H.sub.2 O/5' super petrol/5' methoxypropyl acetate/5' xylene .sup.2) 2% caustic soda solution//2 % sulfuric acid Spraying: HVLP pistols // sprayed perpendicular to the surface // one spray process, 15 min. drying in air, second spray process, 30 min. drying in air, drying at room temperature or 30 min at 60.degree. C.

The advantages of the use according to the invention are better emulsifiability, more rapid drying and higher degree of hardness of the coating produced (e.g., pendulum hardness, stability to weathering, resistance to solvents, etc).

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.

Claims

1. A method for making an aqueous polyurethane lacquer composition comprising the steps of:

(a) forming an isocyanate component by dispersing 4-isocyanatomethyloctane 1,8-diisocyanate in water, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is homogeneously dispersed throughout the water; and

(b) combining the isocyanate component with an isocyanate-reactive component.

2. The method of claim 1, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is mixed with a polyisocyanate comprising a component selected from the group consisting of isocyanurates based on 1,6-hexamethylene diisocyanate, iminooxadiazinediones based on 1,6-hexamethylene diisocyanate, biurets based on 1,6-hexamethylene diisocyanate, uretdione based on 1,6-hexamethylene diisocyanate-urethane pre-polymers based on 1,6-hexamethylene diisocyanate, and allophonates based on 1,6-hexamethylene diisocyanate, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is present in an amount that is at least 50 wt. %, based on the weight of the polyisocyanate component.

3. The method of claim 1 wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is mixed with a polyisocyanate comprising a component selected from the group consisting of isocyanurates based on isophorone diisocyanate, iminooxadiazinediones based on isophorone diisocyanate, biurets based on isophorone diisocyanate, uretdione based on isophorone diisocyanate, urethane pre-polymers based on isophorone diisocyanate, and allophonates based on isophorone diisocyanate, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is present in an amount that is at least 50 wt. %, based on the weight of the polyisocyanate component.

4. The method of claim 1 wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is mixed with a polyisocyanate comprising a component selected from the group consisting of isocyanurates based on hydrogenated diphenylmethane diisocyanate, iminooxadiazinediones based on hydrogenated diphenylmethane diisocyanate, biurets based on hydrogenated diphenylmethane diisocyanate, uretdione based on hydrogenated diphenylmethane diisocyanate, urethane pre-polymers based on hydrogenated diphenylmethane diisocyanate, and allophonates based on hydrogenated diphenylmethane diisocyanate, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is present in an amount that is at least 50 wt. %, based on the weight of the polyisocyanate component.

5. The method of claim 1 wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is dispersed in the water under low shear conditions.

6. The method of claim 5 wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is dispersed without any hydrophilic agents.

7. The composition of claim 1.

8. A method for making an isocyanate component for a two component aqueous polyurethane lacquer composition comprising mixing a 4-isocyanatomethyloctane 1,8-diisocyanate component in water to homogeneously disperse throughout the 4-isocyanatomethyloctane 1,8-diisocyanate component throughout the water.

9. The method of claim 8, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is mixed at low shear conditions.

10. The method of claim 8, wherein the 4-isocyanatomethyloctane 1,8-diisocyanate is mixed without a hydrophilic agent.

11. The method of claim 8, wherein after the 4-isocyanatomethyloctane 1,8-diisocyanate component is homogeneously dispersed in the water, the 4-isocyanatomethyloctane 1,8-diisocyanate component remains homogeneously dispersed for at least 5 minutes.

12. The method of claim 8, wherein the water contains a hydrophilically-modified isocyanate-reactive component.

13. The isocyanate component of claim 8.

14. A method for making an isocyanate component for a two-component aqueous polyurethane lacquer composition comprising mixing a 4-isocyanatomethyloctane 1,8-diisocyanate component under low shear conditions in water without an appreciable amount of a hydrophilic agent to homogeneously disperse throughout the 4-isocyanatomethyloctane 1,8-diisocyanate component throughout the water;

wherein the 4-isocyanatomethyloctane 1,8-diisocyanate component remains homogeneously dispersed for at least 5 minutes after being homogeneously dispersed in the water.

15. The method of claim 14 further comprising the step of mixing the isocyanate component with an Isocyanate-reactive component to form a two-component composition.

16. The isocyanate component of claim 14.

17. The two-component composition of claim 15.