FROST-RESISTANT WATER PAINTS BASED ON POLYISOCYANATES

Abstract

The present invention relates to the use of hydrophilized polyisocyanates for the production of water-diluted coating compositions.

Claims

1. A coating composition comprising a water-thinned isocyanate component A having an isocyanate concentration between 2% by weight and 40% by weight, defined as a proportion by weight of the isocyanate group in the overall molecule that contains at least one hydrophilized polyisocyanate, the isocyanate groups of which are in direct contact with water, wherein the coating composition has a content of polymeric polyols of not more than 10% by weight.

2. The coating composition as claimed in claim 1, wherein the hydrophilized polyisocyanate has been hydrophilized by an external emulsifier not covalently bonded to the polyisocyanate.

3. The coating composition as claimed in claim 1, wherein the hydrophilized polyisocyanate has been hydrophilized by an internal emulsifier covalently bonded to the polyisocyanate.

4. The coating composition as claimed in claim 1, wherein the polymeric polyols have a number-average molecular weight of at least 20 000 g/mol.

5. The coating composition as claimed in claim 1, wherein the water content used to thin the isocyanate component A is such that the viscosity, determined to M014-ISO 3219/A.3, of the thinned isocyanate component A is lowered by at least 40% compared to an otherwise identical but anhydrous isocyanate component A.

6. The coating composition as claimed in claim 1, wherein the isocyanate component A is in the form of a dispersion having an average particle size of not more than 5 m or of an aqueous solution.

7. The coating composition as claimed in claim 1, additionally comprising a trimerization catalyst C.

8. The coating composition as claimed in claim 1, additionally comprising an isocyanate-reactive component B having a molecular weight of not more than 1800 g/mol.

9. The coating composition as claimed in claim 8, wherein the isocyanate-reactive component B comprises at least one of glycerol, monoethylene glycol, butane-1,4-diol, trimethylolpropane, butane-1,3-diol, butane-1,2-diol, neopentyl glycol, and diethylene glycol.

10. The coating composition as claimed in claim 8, additionally comprising a urethanization catalyst D.

11. (canceled)

12. A method of producing a coating, comprising the steps of a) thinning an isocyanate component A containing at least one hydrophilized polyisocyanate with water, such that the isocyanate groups of the hydrophilized isocyanate are in direct contact with water; b) applying the coating composition obtained in method step a), wherein at least 90% of the free isocyanate groups of the isocyanate component A that were present at the start of method step a) are still present at the start of method step b), to a surface; and c) curing the coating composition, with the proviso that the curing coating composition has a content of polymeric polyols of not more than 10% by weight.

13. The method as claimed in claim 11, wherein, in method step a), the isocyanate component A is mixed with a water-dissolved isocyanate-reactive component B prior to performance of method step b).

14. The method as claimed in claim 12, wherein the isocyanate component is thinned in method step a) with an amount of water in such a way that its viscosity is lowered by at least 40%.

15. A substrate coated with a coating obtained by the method as claimed in claim 12.

Description

EXAMPLES

Description of the Test Methods for Examples 1 to 14

[0268] Pendulum hardness analogously to DIN EN ISO 1522: the pendulum damping test is a method of determining the viscoelastic properties of coatings to DIN EN ISO 1522 in a pendulum damping instrument and is thus a measure of the hardness thereof. It consists of a sample table on which a pendulum can swing freely on a sample surface and a counter. The number of swings in a defined angle range is a measure of the hardness of a coating and is reported in seconds or number of swings.

[0269] Abrasion resistance in the Taber Abraser instrument with CS10 friction rolls (moderate hardness). The paints are applied to specimens. After the appropriate curing time, the test is conducted. The specimen (substrate with coating) is weighed and the starting weight is ascertained. The number of friction cycles after which the weight of the specimens and hence the abrasion is weighed is fixed beforehand. The specimen is secured in the sample holder, the friction rolls and suction are applied, and the abrasion test is started. For the determination of abrasion resistance, the weight loss is measured. The specimen is scratched with a fixed number of rotation cycles and the proportion of the sample abraded is ascertained by difference weighing.

[0270] Chemical Stability

[0271] Paint surface stability to test substance: The cured paint films are examined for their resistance to test substances. The paint film is generally on a glass plate. A small cottonwool bud is soaked with the test substance and placed onto the paint surface. Evaporation of the test substance is prevented by covering it, for example by means of a watch glass or test tube. The cottonwool bud or cellulose does not dry out. After a contact time fixed beforehand, the bud soaked with test substance is removed, the contact site is dried off, and an immediate assessment is made in order to anticipate regeneration of the paint surface. The test surface is checked for changes visually and by touching by hand. An assessment is then made as to whether and what changes have occurred on the test surface.

[0272] Softening and discoloration of the paint surface are assessed.

[0273] 0=no changes detectable

[0274] 1=only visible change

[0275] 2=minor softening/slight change in hue

[0276] 3=distinct softening/moderate change in hue

[0277] 4=significant softening/significant change in hue

[0278] 5=coating completely destroyed without outside action/very significant change in hue

[0279] Formulation:

[0280] The paints of the invention are mixed in 2 stages. First the component (A) containing the hydrophilized isocyanate and, in parallel, the aqueous component (B), each in a dissolver at 1500 rpm for at least 2 min. Thereafter, the two components are again mixed by means of a dissolver at 1500 rpm in the desired composition for at least 1 min.

[0281] The sequence of addition of the constituents to the dissolver for components A and B and for the mixture of A and B is:

[0282] A, isocyanate phase: 1. hydrophilized isocyanates, 2. further organic constituents, 3. additives, 4. fillers, 5. catalysts.

[0283] B, water phase: 1. water, 2. organic constituents, 3. additives, 4. fillers, 5. catalysts. A+B: 1. component A, 2. component B

[0284] Application:

[0285] The paints were drawn down on the desired substrates in the desired thickness by means of a drawdown bar 15 min after mixing. After curing at 80 C. for 90 minutes, and optionally then at 140 C. for 30 minutes, and optionally at 23 C. for 1 or 2 days, pendulum hardness (s) and chemical stability are measured.

[0286] Raw Materials Used:

[0287] Hydrophilized Isocyanates:

[0288] Hydrophilic Polyisocyanate 1:

[0289] Hydrophilic aliphatic polyisocyanate based on hexamethylene diisocyanate, having a viscosity of 35001000 mPa.Math.s M014-ISO 3219/A.3 at 23 C., NCO content 20.3-21.3% by weight M105-ISO 11909, 11909, Hazen color number <60 M017-EN 1557, monomeric HDI'0.24% M106-ISO 10283, flashpoint about 192 C. DIN EN ISO 2719, density about 1.16 g/cm.sup.3 DIN EN ISO 2811, sourced as Bayhydur XP 2655 from Covestro Deutschland AG

[0290] Isocyanates:

[0291] Polyisocyanate 1:

[0292] Aliphatic polyisocyanate (low-viscosity HDI trimer), NCO content 23.00.5% M105-ISO 11909, viscosity at 23 C. 1200300 mPa.Math.s M014-ISO 3219/A.3, color number (Hazen) <40 M017-EN 1557, monomeric HDI0.25% M106-ISO 10283, viscosity at 25 C. about 1100 mPa.Math.s M014-ISO 3219/A.3, equivalent weight about 183, flashpoint about 158 C. DIN 53 213/1, density at 20 C. about 1.16 g/ml DIN EN ISO 2811, sourced as Desmodur N 3600 from Covestro Deutschland AG

[0293] Polyols

[0294] Ethylene glycol, butane-1,3-diol, butane-1,4-diol, diethylene glycol, trimethylolpropane, neopentyl glycol, glycerol, 1,1,1-trimethylolpropane were sourced from Aldrich.

[0295] Polyol 1:

[0296] Linear aliphatic polycarbonate ester diol, acid number 3 mg KOH/g DIN EN ISO 2114, viscosity at 23 C. 30 5005500 mPa.Math.s DIN EN ISO 3219, hydroxyl content 6.50.45% DIN 53 240/2, water content 0.1% DIN 51 777/1, equivalent weight about 260, density at 20 C. about 1.17 g/ml DIN EN ISO 2811-2, flashpoint about 150 C. DIN EN ISO 2719, sourced as Desmophen C 1100 from Covestro Deutschland AG

[0297] Polyol 2:

[0298] Polyester polyurethane dispersion, about 41% in water/N-methylpyrrolidone, neutralized with dimethylethanolamine, about 53.5:4.5:1, acid number 6.5-8.5 mg KOH/g DIN EN ISO 2114, viscosity at 23 C., D=about 40 s.sup.1, 500-1500 mPa.Math.s DIN EN ISO 3219/A.3., solids content (1 g/l h/125 C.) 40-42% DIN EN ISO 3251, pH (1:3 in demineralized water) 7.8-8.8 DIN ISO 976, OH content, solvent-free about 2.5% DIN 53 240/2, minimum film formation temperature MFT about 0 C. DIN ISO 2115, average particle size about 50 nm photon correlation spectroscopy, density at 20 C. about 1.10 g/ml DIN EN ISO 2811-2, visual appearance opaque to milky blue, cloudy, sourced from Covestro Deutschland AG as Bayhydrol U 241

[0299] Polyol 3:

[0300] Aliphatic hydroxy-functional polyester polyurethane dispersion, about 55% in water/NMP/DMEA, about 42:2:1, viscosity at C., D=about 240 s.sup.1 250-650 mPa.Math.s DIN EN ISO 3219/A.3, pH, 10% in water 7.0-7.5 DIN ISO 976, acid number about 10.5 mg KOH/g DIN EN ISO 2114, density at 20 C. about 1.07 g/ml DIN EN ISO 2811, OH content about 0.8%, minimum film formation temperature (MFT) <0 C. DIN ISO 2115, sourced from Covestro Deutschland AG as Bayhydrol U 355.

[0301] Polyol 4:

[0302] Anionic polyester polyurethane dispersion as a white, low-viscosity dispersion in water having a solids content of about 40%, flow time 23 C. 4 mm DIN cup <70 s AFAM 2008/10503, pH 6.51 DIN ISO 976, solids content (0.9-1.1 g /1 h/125 C.) 40 1%, density at 23 C. 1.1 g/ml DIN EN ISO 2811 501% DIN EN ISO 3251, sourced from Covestro Deutschland AG as Impranil DLN

[0303] Polyol 5:

[0304] Aliphatic polycarbonate ester/polyether/polyurethane dispersion as a white aqueous dispersion having low viscosity and a solids content of 60%, pH 81 DIN ISO 976, solids content (0.9-1.1 g/1 h/125 C.) 602% DIN EN ISO 3251, density at 23 C. about 1.1 g/ml DIN EN ISO 2811, sourced from Covestro Deutschland AG as Impranil DLU

[0305] Additives

[0306] Additol XW 395 (wetting agent) was sourced from Allnex

[0307] BYK 028 (defoamer) was sourced from BYK

[0308] DBTL (catalyst) was sourced from TIB Chemicals as TIBKAT 218

[0309] 3-Methoxy-n-butyl acetate (cosolvent) sourced from Celanese.

TABLE-US-00001 Experiment 1* 2* 3* 4* 5* 6* 7* Composition Isocyanate phase (component A) Hydroph. polyisocyanate 1(g) 70 70 70 70 70 70 70 3-Methoxy-n-butyl acetate (g) 14 14 14 14 14 14 14 Water phase (component B) Glycerol (g) 8.75 Monoethylene glycol (g) 7.5 Butanediol (g) 10.45 Trimethylolpropane (g) 10.28 Butane-1,3-diol (g) 10.45 Neopentyl glycol (g) 12.2 Diethylene glycol (g) 12.02 Additol XW 395 (g) 0.56 0.56 0.56 0.56 0.56 0.56 0.56 BYK 028 (g) 0.02 0.02 0.02 0.02 0.02 0.02 0.02 DBTL (g) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Water (g) 6 6 6 3.95 6 3.51 6 Experiment 8* 9* 10* 11* 12* 13* 14* Composition Isocyanate phase (component A) Hydroph. polyisocyanate 1 (g) 35 35 35 35 35 35 35 3-Methoxy-n-butyl acetate (g) 10 10 10 10 10 10 10 Water phase (component B) Glycerol (g) 4.38 Monoethylene glycol (g) 3.75 Butanediol (g) 5.23 Trimethylolpropane (g) 5.15 Butane-1,3-diol (g) 5.23 Neopentyl glycol (g) 6.10 Diethylene glycol (g) 6.02 Additol XW 395 (g) 0.28 0.28 0.28 0.28 0.28 0.28 0.28 BYK 028 (g) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 DBTL (g) 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Water (g) 50 50 50 50 50 50 50 Example 1* 2* 3* 4* 5* 6* 7* Pendulum hardness (s), amount applied 0.12 mm wet with doctor blade, on glass, curing at 80 C. for 90 min and at 140 C. for 30 min. Then 2 days at 23 C. 90 min at C. +30 min at 140 C. +2 days at 23 C. 175 195 157 189 180 180 176 Example 8* 9* 10* 11* 12* 13* 14* Pendulum hardness (s), amount applied 0.18 mm wet with doctor blade, on glass, curing at 80 C. for 90 min and at 140 C. for 30 min. Then 1 day at 23 C. and 90 min at 80 C. +1 day at 23 C. 48 42 123 108 113 49 41 90 min at 80 C. +30 min at 140 C. 167 169 141 122 139 64 147 +1 day at 23 C. 172 182 169 167 178 185 179 Chemical stability (soaked cottonwool bud, under bell jar, visual assessment, 0 = unchanged, 5 surface destroyed) Example 8* 9* 10* 11* 12* 13* 14* Applied by knife coating at 0.18 mm wet, drying for 90 min at 80 C. + 30 min at 140 C. + 14 d at 23 C. Water (24 h) 0 0 Ethanol (5 min/30 min) 1/1 0/0 Acetone (1 min/5 min) 0/0 0/0 2-Propanol (5 min/10 min) 1/1 0/0 Xylene (5 min/10 min) 0/0 0/0 Sodium hydroxide solution (10%/24 h) 5 0 0 5 0 0 0 Sulfuric acid (38%/24 h) 0 0 0 0 0 0 0 Comparative example: 15 Composition Isocyanate phase (component A) Hydroph. polyisocyanate (g) 15 3-Methoxy-n-butyl acetate (g) 5 Water phase (component B) Polyol 1 (g) 25 Additol XW 395 (g) 0.28 BYK 028 (g) 0.01 DBTL (g) 0.02 Water (g) 50 Pendulum hardness (s), amount applied 0.18 mm wet with doctor blade, on glass, curing at C. for 90 min and at C. for 30 min. Then 1 day at C. 90 min at C. <10 +30 min at C. +1 day at C. <10 Inventive examples are identified by *.

[0310] In no case was it possible to use the insufficiently water-soluble or dispersible polyol 1 to produce a homogeneous film having a pendulum hardness after drying of >10 (s).

[0311] All formulations of the invention consisting of a hydrophilized isocyanate-containing component A and an aqueous component B and produced clear homogeneous films having a high hardness after drying.

[0312] In a further experiment, the freezing stability of various formulations was examined.

[0313] For this purpose, an isocyanate-reactive component was mixed at 23 C. under shear with a dissolver at 1500 rpm for 2 min with water, 0.3 g of Additol XW 395, 0.01 g of BYK 028 and 0.02 g of DBTL to give a component B. Thereafter, component B was treated at a constant temperature of 10 C. for 1 h and at 50 C. for 1 h, in 5 repetitions of each.

[0314] The isocyanate-reactive component B was formulated in each case for the freezing stability test so as to result in a solids content of 20% by weight. The hydrophilized isocyanate-containing component A consisting of a mixture of 15 g of hydrophilic polyisocyanate 1 and 5 g of 3-methoxy-n-butyl acetate was added in such an amount that an index of 1:1 was achieved for the low molecular weight polyols and a weight ratio of the solid components in each case for the polyurethane polyester dispersions of 1:10.

TABLE-US-00002 Freezing Inventive formulations of components B* stability Glycerol 25 g thinned with 75 g of water OK Monoethylene glycol 25 g thinned with OK 75 g of water Butanediol 25 g thinned with 75 g of water OK Trimethylolpropane 25 g thinned with 75 g OK of water Butane-1,3-diol 25 g thinned with 75 g of OK water Neopentyl glycol 25 g thinned with 75 g OK of water Diethylene glycol 25 g thinned with 75 g OK of water

[0315] Comparative Examples of the Formulations of Component B

TABLE-US-00003 Polyol 1 25 g thinned with 75 g of water separate phase Polyol 2 38 g thinned with 62 g of water coagulated Polyol 3 31 g thinned with 69 g of water coagulated Polyol 4 34 g thinned with 36 g of water coagulated Polyol 5 29 g thinned with 71 g of water coagulated

[0316] After a cold cycle of 1 h at 10 C. and 1 h at 50 C., in 5 repetitions, all noninventive formulations of component B showed distinct instability manifested by complete coagulation and/or irreversible separation between water phase and polyol phase.

[0317] On the basis of polyols of low water solubility and only poor dispersibility, no frost and shear-stable aqueous components B are obtained. If these phases were mixed with an inventive component A after the frost cycle, only poor inhomogeneous or tacky films are were obtained after drying.

[0318] Inadequate frost and shear stability was observed when conventional aqueous dispersions and emulsions were used as component B. These products, which are known to be of excellent suitability for use as 2K polyurethane paints, thus exhibit poor freezing stability, and therefore complex precautionary measures, for example temperature control, have to be taken in transport and storage.

[0319] By contrast, the inventive components B for use in combination with an isocyanate phase comprising a hydrophilized isocyanate in component A exhibit excellent freezing and shear stability. This is manifested in that, even after freezing or high shear stress, the blends in component B form stable phases which, if required, can be converted back to their original form after complete freezing and thawing by simple stirring. It is thus possible for the first time, on the basis of the formulations of the invention, to produce transport- and freezing-stable 2-component isocyanate-based aqueous paint formulations.

[0320] 1K Systems

[0321] Description of the Test Methods and Raw Materials

[0322] Solvent and water stabilities were ascertained to DIN EN ISO 4628-1:2016-07. For the test of the solvent stabilities, the solvents xylene (also abbreviated hereinafter to Xy), methoxypropyl acetate (also abbreviated hereinafter to MPA), ethyl acetate (also abbreviated hereinafter to EA) and acetone (also abbreviated hereinafter to Ac) were used. The contact time was 5 min in each case. For the measurement of the water stabilities, the contact time in each case was 24 h. The specimens were made in accordance with the standard cited. The test surface is assessed visually and via scratching, using the following classification: 0=no change apparent; 1=swelling ring, hard surface, only visible change; 2=swelling ring, slight softening; 3=distinct softening (possibly slight blistering); 4=significant softening (possibly severe blistering), can be scratched through to the substrate; 5=coating completely destroyed without outside influence.

[0323] Pendulum hardness analogously to DIN EN ISO 1522: the pendulum damping test is a method of determining the viscoelastic properties of coatings to DIN EN ISO 1522 in a pendulum damping instrument and is thus a measure of the hardness thereof. It consists of a sample table on which a pendulum can swing freely on a sample surface and a counter. The number of swings in a defined angle range is a measure of the hardness of a coating and is reported in seconds or number of swings.

[0324] Monomeric hexamethylene diisocyanate and Bayhydur 3100 were sourced from Covestro, Leverkusen. Bayhydur 3100 is a hydrophilized oligomeric polyisocyanate formed from hexamethylene diisocyanate and having an NCO content of 17.4% by weight and a residual monomer content of less than 0.15% by weight. Borchi Kat 22 was sourced from Borchers, Langenheim. All further chemicals not cited in detail here were purchased from Sigma-Aldrich and used without further purification.

Example 15: Preparation of Polyisocyanate 2

[0325] The polyisocyanate 2 used here was prepared in accordance with example 11, patent specification EP-A 330 966. The reaction was stopped by adding dibutyl phosphate at an NCO content of the crude product of 40% by weight. Subsequently, unconverted HDI was removed by means of thin-film evaporation at a temperature of 130 C. and a pressure of 0.2 mbar. A product was obtained with the following properties:

[0326] NCO content: 21.8%

[0327] Monomeric HDI: <0.1%

[0328] Viscosity (23 C.): 3000 mPa.Math.s

Example 16

[0329] 100 g of polyisocyanate 2 was admixed with 2-[[2-(dimethylamino)ethyl]methylamino]ethanol (75.9 g) and the reaction was stirred at 80 C. until an NCO content of less than 0.3% was attained. A product was obtained with the following properties:

[0330] NCO content: <0.3%

[0331] Monomeric HDI: <0.1%a

[0332] Coating 1

[0333] The hydrophilic polyisocyanate Bayhydur 3100 (15.9 g) was admixed with BYK 331 (0.15 g), BorchiKat 22 (1.5 g, 10% by weight in MPA) and the catalyst from example 16 (0.9 g, 10% by weight in MPA). Subsequently, the mixture was admixed with water (7.49 g) and mixed in a Speedmixer at 2500 rpm for 1 min. The emulsion was then applied to a glass slide with a doctor blade (50 m).

[0334] Coating 2

[0335] Bayhydur 3100 (14.1 g) was admixed with BYK 331 (0.14 g), BorchiKat 22 (1.41 g, 10% by weight in MPA) and the catalyst from example 16 (0.85 g, 10% by weight in MPA). Subsequently, the mixture was admixed with water (8.47 g) and mixed in a Speedmixer at 2500 rpm for 1 min. The emulsion was then applied to a glass slide with a doctor blade (50 m).

[0336] Coating 3

[0337] Bayhydur 3100 (13.4 g) was admixed with BYK 331 (0.13 g), BorchiKat 22 (1.34 g, 10% by weight in MPA) and the catalyst from example 16 (0.80 g, 10% by weight in MPA). Subsequently, the mixture was admixed with water (9.36 g) and mixed in a Speedmixer at 2500 rpm for 1 min. The emulsion was then applied to a glass slide with a doctor blade (50 m).

[0338] Reference 1

[0339] Bayhydur 3100

[0340] Results

[0341] The table below summarizes the results for the three coating systems. In the series of experiments, it was found that polyisocyanates can be crosslinked from aqueous solutions in the presence of a zinc carboxylate catalyst. This shall be illustrated by experiment no. 1. In the presence of the zinc catalyst Borchi Kat 22, after baking at 120 C., complete curing of the film with pendulum hardnesses of 120 s and very good solvent stabilities were achieved. Without catalyst, by contrast, no crosslinking of the material was observed.

[0342] Aqueous coating formulations based on polyisocyanates.

TABLE-US-00004 Reference 1 Coating 1 Coating 1 Coating 2 Coating 2 Coating 3 (noninventive) Experiment No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Baking 120 140 120 140 140 140 temperature ( C.) Appearance OK OK OK OK OK Film thickness 50 50 50 50 50 (m) Pendulum 179 193 178 191 21 <15 hardness (s) Surface solubility 1 1 4 4 1 0 1 4 1 1 4 4 1 0 1 4 4 4 4 4 5 5 5 5 (Xy, MPA, EA, Ac)