FORMATION OF COATINGS BY SEPARATE APPLICATION OF POLYISOCYANATE COMPOSITIONS AND CROSSLINKING CATALYSTS

Abstract

The invention relates to processes for coating surfaces by alternatingly applying polyisocyanate compositions and suitable crosslinking catalysts, followed by catalytically crosslinking the polyisocyanate composition.

Claims

1-15. (canceled)

16. A process for coating surfaces containing the steps of a) applying a polyisocyanate composition A) to a surface; b) applying a composition B containing at least one crosslinking catalyst B1 to the same surface; and c) curing the polyisocyanate composition A by catalytic crosslinking of the polyisocyanate composition A; with the proviso that the process steps a) and b) are performed in any desired sequence or else simultaneously but prior to process step c).

17. The process as claimed in claim 16, wherein the polyisocyanate composition A is applied such that the layer formed thereby has an application weight of not more than 150 g/m.sup.2.

18. The process as claimed in claim 16, wherein the catalytic crosslinking in process step c) has the result that at least 30% of the isocyanate groups present in the polyisocyanate composition A are converted into isocyanurate structural units.

19. The process as claimed in claim 16, wherein the polyisocyanate composition A contains at least ≥50% by weight of aliphatic polyisocyanates.

20. The process as claimed in claim 16, wherein the process step a) or the process step b) is carried out at least twice.

21. The process as claimed in claim 20, wherein between the repetitions of the process step carried out at least twice the respective other process step is performed at least once.

22. The process as claimed in claim 20, wherein the process step a) is carried out at least twice and in at least two repetitions polyisocyanate compositions A containing different polyisocyanates are applied.

23. The process as claimed in claim 16, wherein the crosslinking catalyst B1 is basic.

24. The process as claimed in claim 23, wherein the composition contains a carboxylate or an alkoxide.

25. The process as claimed in claim 16, wherein the polyisocyanate composition A contains blocked polyisocyanates.

26. The process as claimed in claim 16, wherein the polyisocyanate composition A is applied only to a portion of the surface covered by the composition B or the composition b is applied only to a portion of the surface covered by the polyisocyanate composition A.

27. The process as claimed in claim 16, wherein the process step c) is performed entirely at room temperature and at least 30% of the isocyanate groups react to afford isocyanurates or uretdiones.

28. The process as claimed in claim 16, wherein the curing in process step c) is carried out in two stages with the proviso that the reaction temperature in a process step c1) is 60° C. to 300° C. and in a process step c2) is 10° C. to 59° C.

29. The process as claimed in claim 16, wherein the ratio of the sum of free and reversibly blocked isocyanate groups to the sum of the isocyanate-reactive groups in the reaction mixture that is present on the surface at commencement of the process step c) is at least 3 to 1.

30. A surface coated by the process as claimed in claim 16.

Description

EXAMPLES

[0147] Methods and Employed Materials:

[0148] NCO Number Determination by FT-IR Spectrometer Fitted with an ATR Unit

[0149] Determination of the NCO number employed an FT-IR spectrometer (Tensor II) from Bruker fitted with a platinum ATR unit.

[0150] In all experiments the components were applied to a glass plate and subsequently subjected to the temperature program. To effect measurement either the liquid or the film was lifted from the glass plate and subsequently contacted on the platinum ATR unit. To this end the films were placed with their front side on the 2×2 mm sample window of the ATR unit and pressed down with a tamper. For liquid samples the window was wetted with a droplet.

[0151] Depending on the wavenumber the IR radiation penetrates 3-4 μm into the sample during the measurement. An absorption spectrum was then obtained from the sample.

[0152] In order to compensate nonuniform contacting of the samples of different hardness, both a baseline correction and a normalization using the evaluation program OPUS were performed on all spectra.

[0153] The normalization was based on the CH.sub.2 and CH.sub.3 bands. To this end, the wavenumber range of 2600 to 3200 was chosen. The program determined the highest peak in this region and scaled the entire spectrum such that this maximum peak has a value of 2.

[0154] To determine the NCO number the peak in the wave number range from 2170 to 2380 (NCO-Peak) was integrated.

[0155] Determining Conversion of NCO Groups

[0156] To determine the conversion of the NCO groups a reference value is initially required. To this end, the isocyanate component was initially measured by FTIR without any thermal treatment and without reaction. For Desmodur® N3600 an NCO number of 878 was obtained (see example 1). The percentage conversion was obtained by dividing the NCO number determined after an experiment by 878, subtracting the obtained value from 1 and subsequently multiplying the result by 100. Thus for example an NCO number of 830 was measured in example 2. This then resulted in:

830/878=0.9453

1−0.9453=0.05467

0.05467*100%=5.467

[0157] The rounded conversion level in example 2 is thus 5.5%.

[0158] Droplet Weight Determination

[0159] The majority of applied materials was applied using a digital printer (Dimatix DMP 2831, printing head DMC-11610 (16 nozzles and a nominal droplet size of 10 pp). Since the actual droplet volume and thus the droplet weight is dependent on many parameters this was determined before application. To this end, 3 million droplets were printed into a previously weighed plastic dish before immediately determining the net weight. The following droplet weights were determined for the examples.

[0160] Isocyanate component: 6.81289*10.sup.−9 g/droplet

[0161] Catalyst mixture: 6.31944*10.sup.−9 g/droplet

[0162] Desmodur® N3600

[0163] Solvent-free polyisocyanurate based on HDI having an NCO content of 23.0±0.5% (according to M105-ISO 11909) and a viscosity at 23° C. of 1.200±300 mPa.Math.s (according to M014-ISO 3219/A.3.)

[0164] Butyl Acetate (BA)

[0165] Butyl acetate 98/100 from Azelis, Antwerp;

[0166] BYK® 141 and BYK® 331

[0167] Additives from BYK Additives & Instruments, Wesel

[0168] BYK 141 is a silicon-containing defoamer for solvent-containing and solvent-free polyurethane-based paint systems and cold-curing plastics applications.

[0169] BYK 331 is a silicone-containing surface additive for solvent-containing, solvent-free and aqueous paints and printing inks for intermediate reduction of surface tension and intermediate increasing of surface smoothness.

[0170] Isocyanate Ink

[0171] 70 parts by weight of Desmodur®, 30 parts by weight of butyl acetate, 0.4 parts by weight of BYK® 141 and 0.03 parts by weight of BYK® 331

[0172] Potassium Acetate

[0173] Potassium acetate having a purity of ≥99% was obtained from Acros

[0174] 18-Crown-6

[0175] 18-Crown-6 having a purity of ≥99% from Sigma Aldrich.

[0176] Diethylene Glycol

[0177] Diethylene glycol having a purity of 99% from Sigma Aldrich.

[0178] Catalyst Mixture

[0179] 177 parts by weight of potassium acetate, 475 parts by weight of 18-Crown-6 and 3115 parts by weight of diethylene glycol. Potassium acetate is initially charged before initially the crown ether and subsequently the diethylene glycol are added. The dissolving time was 2 days wherein the mixture was in each case manually shaken once per hour during the eight hour working time and left to stand overnight

[0180] The raw materials were used without further purification or pretreatment unless otherwise stated.

[0181] Procedure:

[0182] The catalyst and the isocyanate ink were consecutively applied by means of a digital printer (Dimatix DMP 2831, printing head DMC-11610 (16 jets and a nominal droplet size of 10 pl)) to a previously washed and dried glass sheet such that the layers were disposed one on top of the other. The ratio of the two components was adjusted by setting different DPI values. After application the coated glass sheets were flashed off for 10 minutes and subsequently cured at 180° C. for 10 minutes in a recirculating drying cabinet. After curing an ATR-FT-IR instrument was used to determine the NCO number at the surface of the coating.

[0183] As a comparison 50 μm of a premixed system having a comparable mixing ratio was blade coated onto a glass sheet. After application the coated glass sheets were flashed off for 10 minutes and subsequently cured at 180° C. for 10 minutes in a recirculating drying cabinet before an ATR-FT-IR instrument was used to determine the NCO number at the surface of the coating.

[0184] In the investigation of the different application weights the same number of catalyst layers as subsequent isocyanate ink layers was always printed.

[0185] In further comparative examples only the isocyanate component was applied: [0186] after application of the isocyanate component the sample was flashed off for 10 minutes, then heat treated at 180° C. for 10 minutes in the recirculating drying cabinet before the NCO number at the surface was determined [0187] after application of the isocyanate ink the sample was flashed off for 10 minutes, then heat treated at 180° C. for 10 minutes in the recirculating drying cabinet before the NCO number at the surface was determined

[0188] Results:

TABLE-US-00001 NCO number at the Converted NCO Example Application Description/remarks surface/result groups [%]  1 Desmodur ® N3600 without Determination of baseline 878 0 (comparative) heating value for pure polyisocyanate  2 Desmodur ® N3600, 10′ flash Determination of baseline 830 5.5 (comparative) off, 10′ at 180° C. in value for pure recirculating drying cabinet polyisocyanate  3 Desmodur ® N3600 (70% in Determination of baseline 800 8.9 (comparative) butyl acetate), 10′ flash off, value for 70% 10′ at 180° C. in recirculating polyisocyanate in butyl drying cabinet acetate with subsequent thermal treatment  4 Blade coating of 50 μm of a Comparative example for a 7 99.2 (comparative) Desmodur ® N3600 premixed system applied to (pure)/catalyst mixture a glass sheet by blade (mixing ratio 33/1), 10′ flash coating. The polyisocyanate off, 10′ at 180° C. in was employed in undiluted recirculating drying cabinet form  5 Blade coating of 50 μm of a Comparative example for a 47 94.6 (comparative) mixture of Desmodur ® N3600 premixed system applied to (70% in butyl acetate) and a glass sheet by blade catalyst (mixing ratio 33/1, coating. The polyisocyanate neglecting solvent), 10′ flash was employed as 70% in off, 10′ at 180° C. in butyl acetate recirculating drying cabinet  6 Layer 1: cat (211 DPI) Calculated application 17 98.1 Layer 2: isocyanate ink weight: Isocyanate ink: (1400 DPI) 20.7 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 14.5 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 0.44 g/m.sup.2  7 Layer 1: isocyanate ink Calculated application 147 83.3 (1400 DPI) weight: Isocyanate ink: Layer 2: cat (211 DPI) 20.7 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 14.5 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 0.44 g/m.sup.2  8 Layer 1: cat (149 DPI) Calculated application 26 97.0 Layer 2: isocyanate ink weight: Isocyanate ink: (1400 DPI) 20.7 g/m.sup.2 (wet) Layer 3: cat (149 DPI) 14.5 g/m.sup.2 (solid) 10′ flash off, 10′ curing at Catalyst ink: 180° C. in recirculating drying 2 * 0.22 g/m.sup.2 cabinet  9 Layer 1: isocyanate ink Calculated application 236 73.1 (990 DPI) weight: Isocyanate ink: Layer 2: cat (211 DPI) 2 * 10.3 g/m.sup.2 (wet) Layer 3: isocyanate ink 2 * 7.2 g/m.sup.2 (solid) (990 DPI) Catalyst ink: 10′ flash off, 10′ curing at 0.44 g/m.sup.2 180° C. in recirculating drying cabinet 10 Layer 1: 2x cat (211 DPI) Calculated application 11 98.7 Layer 2: 2x isocyanate ink weight: Isocyanate ink: (1400 DPI) 41.4 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 29.0 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 0.87 g/m.sup.2 11 Layer 1: 3x cat (211 DPI) Calculated application 24 97.3 Layer 2: 3x isocyanate ink weight: Isocyanate ink: (1400 DPI) 62.1 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 43.5 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 1.31 g/m.sup.2 12 Layer 1: 4x cat (211 DPI) Calculated application 61 93.1 Layer 2: 4x isocyanate ink weight: Isocyanate ink: (1400 DPI) 82.8 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 58.0 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 1.74 g/m.sup.2 13 Layer 1: 5x cat (211 DPI) Calculated application 36 95.9 Layer 2: 5x isocyanate ink weight: Isocyanate ink: (1400 DPI) 103.5 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 72.4 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 2.18 g/m.sup.2 14 Layer 1: 6x cat (211 DPI) Calculated application 67 92.4 Layer 2: 6x isocyanate ink weight: Isocyanate ink: (1400 DPI) 124.2 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 86.9 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 2.62 g/m.sup.2 15 Layer 1: 7x cat (211 DPI) Calculated application 289 67.1 Layer 2: 7x isocyanate ink weight: Isocyanate ink: (1400 DPI) 144.9 g/m.sup.2 (wet) 10′ flash off, 10′ curing at 101.4 g/m.sup.2 (solid) 180° C. in recirculating drying Catalyst ink: cabinet 3.05 g/m.sup.2 16 Layer 1: cat (211 DPI), Calculated application A clear image full surface weight: Isocyanate ink: is obtained Layer 2: isocyanate ink 20.7 g/m.sup.2 (wet) (1400 DPI), image 14.5 g/m.sup.2 (solid) 10′ flash off, 10′ curing at Catalyst ink: 180° C. in recirculating drying 0.44 g/m.sup.2 cabinet, wash off excess catalyst with butyl acetate 17 Layer 1: isocyanate ink Calculated application A clear image (1400 DPI), full weight: Isocyanate ink: is obtained surface 20.7 g/m.sup.2 (wet) Layer 2: cat (211 DPI), image 14.5 g/m.sup.2 (solid) 10′ flash off, 10′ curing at Catalyst ink: 180° C. in recirculating drying 0.44 g/m.sup.2 cabinet, wash off excess isocyanate ink with butyl acetate 18 Layer 1: cat (211 DPI), Calculated application A severely image weight: Isocyanate ink: distorted Layer 2: isocyanate ink 20.7 g/m.sup.2 (wet) image is (1400 DPI), full 14.5 g/m.sup.2 (solid) obtained surface Catalyst ink: 10′ flash off, 10′ curing at 0.44 g/m.sup.2 180° C. in recirculating drying cabinet, wash off excess isocyanate ink with butyl acetate 19 Layer 1: isocyanate ink Calculated application A slightly (1400 DPI), image weight: Isocyanate ink: distorted Layer 2: cat (211 DPI), 20.7 g/m.sup.2 (wet) image is full surface 14.5 g/m.sup.2 (solid) obtained 10′ flash off, 10′ curing at Catalyst ink: 180° C. in recirculating drying 0.44 g/m.sup.2 cabinet, wash off excess catalyst with butyl acetate

[0189] When the Desmodur® N3600 merely undergoes the temperature program about 5.5% of the isocyanate groups are converted (example 2). When the polyisocyanate is first diluted to a solids content of 70% with butyl acetate about 9% of the NCO groups are converted during the flash off and heat treatment steps (example 3). However, in both cases the product remains liquid. Only when a catalyst is employed (comparative examples 4 and 5 and inventive examples 6 to 15) are tack-free films obtained.

[0190] It is apparent from the examples that conversions of at least 50% are achievable independently of the sequence of application and up to an application weight (solid) even at a layer thickness of 100 g/m.sup.2.

[0191] Post-curing at room temperature would result in complete conversion of the remaining isocyanate groups too.

[0192] Examples 4 to 6 show that comparable results are obtained irrespective of whether the catalyst is previously incorporated or whether said catalyst is initially printed separately with printing of the isocyanate ink occurring only subsequently.

[0193] Examples 6 to 9 verify that it can be particularly advantageous to print the catalyst first and to print the isocyanate ink in the second step.

[0194] Examples 16 to 19 show that it is also possible to carry out full surface application of one component and only local application of the other component before washing off the uncured proportion. The examples clearly show that image sharpness is always markedly better when the partial coating (for example an image) is applied with the second layer.