COATING OF WIRES WITH CATALYTICALLY CROSSLINKED BLOCKED POLYISOCYANATES

Abstract

The present invention relates to the coating of wires with coatings which are obtained by crosslinking blocked polyisocyanates. The coatings are characterized in that they are substantially free of urethane groups and the crosslinking of the monomers is predominantly effected by isocyanurate groups.

Claims

1. Process for coating wires, comprising the steps of a) providing a reaction mixture comprising (i) a polyisocyanate composition A containing blocked isocyanates, where the blocking agent is selected from the group consisting of phenols, oximes and lactams, and (ii) at least one crosslinking catalyst B; b) applying the reaction mixture provided in process step a) to a wire; and c) curing the reaction mixture, with crosslinking of the isocyanate groups of the polyisocyanate composition A by at least one structure selected from the group consisting of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and oxadiazinetrione structures; with the proviso that the molar ratio of blocked and unblocked isocyanate groups to groups that are reactive toward isocyanate and are present in compounds containing more than one such group in the reaction mixture at the start of process step b) is at least 80%:20%.

2. Process according to claim 1, wherein the reaction mixture does not contain more than 0.2 wt.-% of organic and inorganic compounds of iron, lead, tin, bismuth and zinc.

3. Process according to claim 1, wherein the blocked polyisocyanates in the polyisocyanate composition A have a low level of monomers.

4. Process according to claim 1, wherein at least 50% of the blocked isocyanates in the polyisocyanate composition A are aliphatic isocyanates.

5. Process according to claim 1, wherein the coating obtained in process step c) has a glass transition temperature of at least 80° C.

6. Process according to claim 1, wherein the crosslinking catalyst B comprises a carboxylate.

7. Process according to claim 6, wherein the carboxylate is potassium 2-ethylhexanoate.

8. Process according to claim 1, wherein the curing in process step c) is conducted at a temperature of at least 180° C.

9. Coated wire obtainable by the process according to claim 1.

10. Use of blocked polyisocyanates for coating of wires, wherein the blocking agent is selected from the group consisting of phenols, amines, oximes and lactams.

11. Use according to claim 10, wherein the crosslinking of the blocked polyisocyanates is brought about by a crosslinking catalyst B comprising a carboxylate.

Description

EXAMPLES

Example 1

[0121] 303.4 g of a polyether polyol with an OH number of 44 were prepared via simultaneous ethoxylation and propoxylation (EO/PO ratio of 2:8) of a 2:1 mixture of propylene glycol and glycerine, and 3-chloroproponic acid (0.02 g). The obtained polyether was reacted with 41.4 g of a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (80:20 mixture), by using a flask with a thermomether, a mechanical stirrer, a dropping funnel and a reflux condenser. The reaction mixture was heated to 80° C. until a theoretical NCO content of 2.9 wt % was obtained. The prepolymer was blocked with 4-nonylphenol (55.1 g) in the presence of N,N-dimethyldodecylamine (10 mg) and quenched with benzoyl chloride (10 mg). [0122] Blocked NCO content: 2.46 wt. % [0123] viscosity (23° C.): 75.000 mPa.Math.s

[0124] Methods

[0125] Testing of Pencil Hardness

[0126] Pencil hardness is a scratch-testing method to ascertain paint film hardness, particularly in the case of smooth surfaces. The hardness corresponds here to that of the hardest pencil that does not damage the surface of the coating. Fine abrasive paper (400 grit, 600 grit or 800 grit) is used in order to produce a smooth surface for pencils with different hardnesses (6B to 7H). The testing of painted test specimens is conducted at room temperature (23-28° C.), relative air humidity 50%±20%. The pencil tips are ground away to a flat surface with abrasive paper. At an angle of 45°, the pencil of moderate hardness (HB) is pushed over a few millimetres of the paint film to be tested, over which a very substantially constant force should be applied. The operation is repeated with a harder pencil each time until the edge of the pencil damages the coating. If the coating is damaged by a pencil of moderate hardness (HB), a softer pencil is used each time to approach the value where no damage occurs.

[0127] Pendulum Damping

[0128] Pendulum damping was measured according to DIN EN ISO 1522:2007-04 and is determined according to K6nig. All measurements have been conducted at 50% air humidity and 23° C.

[0129] Solvent Resistance

[0130] Resistance of the coatings against organic solvents and water was determined according to DIN EN ISO 4628-1 to -5:2016-07. Organic solvents tested were xylene (Xy), 1-Methoxy-2-propanyl acetate (MPA), ethyl acetate (EA) and acetone (AC). Solvent resistance has been determined on a scale from 0 to 5, 0 being the best value and 5 the worst.

[0131] Microhardness

[0132] Microhardness was determined by an indentation test according to DIN EN ISO 14577-1 to -4:2017-04. The indenter is pyramid-shaped with a square base (according to Vickers). It is pressed with continuously increasing force into the surface of the sample. This was done with a Fischerscope HM2000 with a Vickers-indenter made by Fischer. The indentation measurement was conducted with a load/indentation depth, having an incremental force ramp from Fmin to Fmax with Fmin=0.4 mN and Fmax=7 mN and a ramp of 10 sec.

[0133] DMA Measurements

[0134] Dynamic mechanical analysis (DMA) is specified in DIN EN ISO 6721-1:2011-08. The measurements were conducted with a DMA Q800 by TA-Instruments. Measurements on free film stripes (15 mm×6 mm×13 μm) were performed within a temperature range of −100° C. to 250° C. at a heating rate of 2K.Math.min-1, an excitation frequency of 10 Hz, and a deformation amplitude of 10 μm.

[0135] Differential Scanning Calorimetry

[0136] Differential scanning calorimetry (DSC) is specified in DIN EN ISO 55672-1:2016-03. A DSC-7 calorimeter by Perkin Elmer was used for the analysis. Three heating cycles with temperatures between room temperature and 300° C. were used. The heating rate was 20 K.Math.min-1 and the cooling rate 320K.Math.min-1. Cooling was achieved with a compressor and flushing of the cell with nitrogen (30 ml.Math.min-1).

[0137] Thermogravimetric Analysis

[0138] Thermogravimetric analysis (TGA) was conducted according to DIN EN ISO 11358-1:2014-10. A thermogravimetric analyzer TGA-7 by Perkin-Elmer was used. The sample was analyzed in an open Pt-pan 45. Analysis was performed in a temperature range between 23° C. and 600° C. with a heating rate of 20 K min-1. Analysis was done based on the weight profile.

[0139] The abbreviation n.d. stands for non-determinable. In the context of the measurement of pendulum hardness n.d. stands for pendulum damping values of less than 15 seconds.

[0140] Materials

[0141] Blocked polyisocyanates, BL 3175, BL 4265, PL 350 and BL 3272, have been purchased from Covestro AG. Unless otherwise specified, all other chemicals were obtained from Sigma-Aldrich.

[0142] Catalyst 1

[0143] The catalyst was dissolved in MPA and contains 10% by weight of catalyst (potassium octoate/18-crown-6 equimolar). For the preparation of polyisocyanurates from blocked polyisocyanates, there was a study of which blocking agents are suitable for the preparation of polyisocyanurates. Standard blocking agents such as methyl ethyl ketoxime (MEKO), ε-caprolactam, 4-nonylphenol and 1,3-dimethylpyrazole (DMP) were used; the results are collated in Table 1.

[0144] The studies showed that MEKO-blocked (nos. 1-5), e-caprolactam-blocked (nos. 6-10) and phenol-blocked (no. 17) polyisocyanates are converted to polyisocyanurates in the presence of potassium octoate; DMP-blocked polyisocyanates, by contrast, could not be converted to polyisocyanurates in the presence of this catalyst. In view of the suitability of pyrazoles as blocking agents for polyurethane systems, which has been described in principle in the literature, this result is surprising and shows that the findings relating to conventional polyurethane systems cannot be applied directly to the isocyanurate-crosslinked systems according to the invention.

[0145] The pendulum damping, pencil hardness and solvent resistance of the various systems are each within comparable ranges. However, it can be seen that pendulum damping increases with increasing IPDI content.

TABLE-US-00001 TABLE 1 Crosslinking of blocked polyisocyanates with 0.1% by weight of catalyst 1 and subsequent determination of pendulum damping, pencil hardness and solvent resistance of the films. Sample temperature at 220° C., 10 min (oven temperature at 250° C.). Films were prepared on glass substrates. Pendulum Ratio hardness (BL 3175:BL Blocking according to König Pencil Solvent assay No. Sample 4265) agent (s) hardness (Xy/MPA/EA/Ac) 1 BL 3175 SN/BL 4265 SN 10:0  MEKO 174 6H 1 0 1 1 2 BL 3175 SN/BL 4265 SN 9:1 MEKO 159 6H 1 1 1 1 3 BL 3175 SN/BL 4265 SN 8:2 MEKO 173 6H 1 1 1 1 4 BL 3175 SN/BL 4265 SN 5:5 MEKO 181 6H 1 1 1 1 5 BL 3175 SN/BL 4265 SN  0:10 MEKO 191 n.d. 4 4 4 4 6 BL 3272 MPA/BL 2078/2 SN 10:0  ε-caprolactam 151 6H 0 1 0 1 7 BL 3272 MPA/BL 2078/2 SN 9:1 ε-caprolactam 158 6H 1 0 0 1 8 BL 3272 MPA/BL 2078/2 SN 8:2 ε-caprolactam 169 7H 0 1 1 2 9 BL 3272 MPA/BL 2078/2 SN 5:5 ε-caprolactam 180 7H 4 4 4 4 10 BL 3272 MPA/BL 2078/2 SN  0:10 ε-caprolactam 194 n.d. 4 4 4 5 11 PL 340 BA/SN/PL 350 MPA/SN 10:0  DMP n.d. n.d. n.d. 12 PL 340 BA/SN/PL 350 MPA/SN 9:1 DMP n.d. n.d. n.d. 13 PL 340 BA/SN/PL 350 MPA/SN 8:2 DMP n.d. n.d. n.d. 14 PL 340 BA/SN/PL 350 MPA/SN 5:5 DMP n.d. n.d. n.d. 15 PL 340 BA/SN/PL 350 MPA/SN  0:10 DMP n.d. n.d. n.d. 16 example 1 (with catalyst 1) — 4- n.d. n.d. n.d. nonylphenol 17 example 1 — 4-  38 3B 3 3 4 5 nonylphenol n.d. = not determinable; MPA = methoxypropyl acetate; SN (solvent naphtha)

[0146] The glass transition points confirm the results of the pendulum damping measurements: with increasing IPDI content, there is a rise in the glass transition point of 116° C. for the pure HDI-based polyisocyanurate to 254° C. for HDI/IPDI with a ratio of 2:8 (Table 2, no. 4). For polyisocyanurate no. 1 and no. 2, a second glass transition temperature at around 230° C. was observed.

TABLE-US-00002 TABLE 2 glass transition temperature T.sub.g of different mixtures. Catalyst 1 was used for all experiments. Sample temperature at 220° C., 10 min (oven temperature at 250° C.). Films were prepared on glass substrates. decom- ratio posi- (BL 3175/ catalyst T.sub.g tion No. sample BL 4265) (wt. %) (° C.) (° C.) 1 BL 3175 SN / BL 4265 SN 10:0 0.7 116 / 229 280 2 BL 3175 SN / BL 4265 SN  8:2 2.0 161 / 233 280 3 BL 3175 SN / BL 4265 SN  5:5 2.0 221 280 4 BL 3175 SN / BL 4265 SN  2:8 0.1 254 225

[0147] As depicted in Table 2, DSC and TGA measurements gave surprisingly high glass transition temperatures and thermal stabilities. Glass transition points of standard polyurethane coatings for automobiles (OEM coatings) are in the range of 40 to 60° C. In addition, these coatings usually start to decompose at around 200° C.

TABLE-US-00003 TABLE 3 DMA and microhardness results. sample was cured at 220° C., for 10 min; oven temperature at 250° C.. films prepared on glass substrates and then removed to give free films for DMA measurements. E″max = loss modulus. microhardness measurement ratio DMA-Tg storage modulus (nanoindentation) (BL 3175: BL (dynamic Tg) (rubber plateau) surface film depth 4265) E″.sub.max tan δ DSC-Tg E′.sub.Gummi hardness hardness hardness No. Gew.-% ° C. ° C. ° C. MPa (0.4 mN) (1 mN) (7 mN) 1 10:0  113.5 124.5 116 14.80 177 N/mm.sup.2 162 N/mm.sup.2 146 N/mm.sup.2 2 8:2 163.0 175.0 161 17.16 198 N/mm.sup.2 173 N/mm.sup.2 160 N/mm.sup.2 3 2:1 192.0 207.5 183 25.77 — — — 4 1:1 218.0 234.5 221 31.39 218 N/mm.sup.2 194 N/mm.sup.2 180 N/mm.sup.2

[0148] The values of the glass transition temperatures of the DMA measurements are in line with the previously reported DSC measurements (Table 3). In addition, it was found that the storage modulus at the rubber plateau increases with BL 4265 content. The microhardness measurements showed the same trend, as the surface hardness increases from 177 N/mm.sup.2 (No. 1) to 218 N/mm.sup.2 (No. 4) with increasing BL 4265 amount.

[0149] The results of the polyisocyanurate coatings (vide supra) were compared to U.S. Pat. No. 6,133,397A. In this patent, the authors do not specify to polyisocyanates the experiments were performed with. Since Desmodur© N 3300 was mentioned in the patent description, we decided to use this polyisocyanate for comparative studies. In this experimental series, experiment no. 1 (Table 4) is reproduced from U.S. Pat. No. 6,133,397A, column 9, example 6. All reaction parameters were kept in accordance to this patent.

TABLE-US-00004 TABLE 4 Desmodur © N 3300 chosen according to descriptions of US6133397A. “Monoahl” (Lutensol ® XL 70, Fa. BASF), an ethoxylated and propoxylated alcohol with an average molecular weigt of 560 g/mol was used, as described in the patent. According to the procedure, the coating formulation was cured at 135° C., 30 min and afterwards stored for 2 weeks at room temperature. After this period of time, characterizations of the coatings were conducted. Formulation details: Desmodur © N 3300 (17.83 g), Lutensol XL 70 (4.71 g), trioctylphosphine (0.03 g), DBTL (0.27 g), BYK 331 (0.03 g) und MPA (6.69 g). solvent catalyst pencil decomposition resistance No. catalyst (wt. %) monoahl hardness Tg (° C.) (° C.) (Xy/MPA/EA/Ac) 1 trioctylphosphine 0.2 yes H 34 170 2 2 2 3 2 catalyst 1 0.2 yes H 31 175 2 2 2 3 3 catalyst 1 0.2 no 3H 56 170 0 0 0 1

[0150] Our comparative study revealed for experiment no. 1 (patent example) and experiment no. 2 (catalyst 1 was used instead of trioctylphosphine) that both materials give the same glass transition temperature; the glass transition temperature of the coating known to the art is suitable for auto OEM coatings and auto refinish. In experiment no. 3, the coating was cured without monoahl. An increased glass transition temperature of around 55° C. was observed, still well below the glass transition temperatures which were observed for curing at 220° C. (Table 2). In addition, the decomposition of the coating materials in Table 4 showed an up to 100° C. lower decomposition temperature than the high temperature cured systems (Table 2). Hence, these coating systems cannot be used for high temperature applications.

[0151] The deblocking temperature of blocked polyisocyanates can be lowered by addition of suitable catalysts. Accelerated deblocking inevitably enables faster crosslinking of the polyisocyanates. Table 5 summarizes the results of the studies on catalytic deblocking: the addition of DBTL in the presence of the crosslinking catalyst reduces the film hardnesses. This is equally true of the addition of 0.1% by weight of DBTL and 1.0% by weight of DBTL.

TABLE-US-00005 TABLE 5 Effect of DBTL as cocatalyst on curing and crosslinking 220° C., 10 min Pendulum Ratio Amount damping (HDI: (% by according No. Sample IPDI) Catalyst wt.) to König (s) 1 BL 3175 SN / BL 4265 SN 10:0 KOc 0.1 174 2 BL 3175 SN / BL 4265 SN  9:1 KOc 0.1 159 3 BL 3175 SN / BL 4265 SN  8:2 KOc 0.1 173 4 BL 3175 SN / BL 4265 SN  5:5 KOc 0.1 181 5 BL 3175 SN / BL 4265 SN  2:8 KOc 0.1 191 6 BL 3175 SN / BL 4265 SN 10:0 KOc / 0.1 / 0.1 159 DBTL 7 BL 3175 SN / BL 4265 SN  9:1 KOc / 0.1 / 0.1 162 DBTL 8 BL 3175 SN / BL 4265 SN  8:2 KOc / 0.1 / 0.1 140 DBTL 9 BL 3175 SN / BL 4265 SN  5:5 KOc / 0.1 / 0.1 168 DBTL 10 BL 3175 SN / BL 4265 SN  2:8 KOc / 0.1 / 0.1 173 DBTL 11 BL 3175 SN / BL 4265 SN 10:0 KOc / 0.1 / 1 87 DBTL 12 BL 3175 SN / BL 4265 SN  9:1 KOc / 0.1 / 1 135 DBTL 13 BL 3175 SN / BL 4265 SN  8:2 KOc / 0.1 / 1 95 DBTL 14 BL 3175 SN / BL 4265 SN  5:5 KOc / 0.1 / 1 118 DBTL 15 BL 3175 SN / BL 4265 SN  2:8 KOc / 0.1 / 1 164 DBTL

[0152] The reduced hardness is probably attributable to the formation of urea groups. FIG. 1 shows the IR spectra of three samples based on BL 3175 SN. Sample no. 1 has been crosslinked exclusively with the crosslinking catalyst, catalyst 1, and has a sharp maximum of the isocyanurate group. Sample nos. 6 and 10, containing 0.1% by weight and 1.0% by weight of DBTL, show a shoulder at 1630 cm.sup.−1 (CO stretch vibration of urea) and a band for the NH deformation vibration at 1580 cm.sup.−1; this demonstrates the activation of the NCO group which is known from the literature and, hence, leads to an easier breakdown in the presence of moisture.