COATINGS FROM POLYISOCYANURATE COATINGS (RIM) AND THEIR USE IN INJECTION MOLDING PROCESSES

Abstract

The present invention relates to the use of polyisocyanate compositions and trimerization catalysts for production of coatings by reaction injection molding, to the coatings obtained by the use and to correspondingly coated workpieces.

Claims

1. The use of a reaction mixture having a molar ratio of isocyanate groups to isocyanate-reactive groups of at least 3:1 for coating workpieces by reaction injection molding, wherein the reaction mixture contains a) at least one polyisocyanate composition A and b) at least one trimerization catalyst B and at least 30 mol % of the free isocyanate groups present in the reaction mixture are converted into isocyanurate groups.

2. The use of the reaction mixture as claimed in claim 1, wherein the reaction mixture additionally contains at least one isocyanate-reactive compound selected from the group consisting of mono- or polyhydric alcohols, amines, amino alcohols and thiols.

3. The use as claimed in claim 1 or 2, wherein the polyisocyanate composition A consists to an extent of at least 70% by weight, based on its total weight, of polyisocyanates which comprise exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

4. The use as claimed in any of claims 1 to 3, wherein the polyisocyanate composition A contains at least one blocked polyisocyanate whose blocking agent is selected from the group consisting of lactams, oximes, cyclopentanone 2-alkyl esters and phenols.

5. The use as claimed in any of claims 1 to 4, wherein the workpiece consists of at least one material selected from the group consisting of thermoplastic polymers, thermosetting polymers, wood and metal.

6. A process for coating a workpiece, comprising the steps of a) introducing a workpiece into a mold which surrounds at least a portion of the workpiece and has dimensions such that the distance between the surface of the workpiece and the inside of the mold corresponds to the thickness of the coating; b) injecting at least one reaction mixture as defined in any one of claims 1 to 4; and c) curing the reaction mixture injected in process step b) at a temperature between 60° C. and 300° C., wherein at least 30 mol % of the free isocyanate groups present at commencement of process step c) are converted.

7. The process as claimed in claim 6, wherein process step c) is performed at a temperature between 80° C. and 130° C.

8. The process as claimed in claim 6 or 7, wherein process step c) is performed for 10 seconds to 900 seconds and the coated workpiece is demoldable.

9. The process as claimed in any of claims 6 to 8, wherein the workpiece to be coated consists to an extent of at least 90% by weight of a thermoplastic and said workpiece was produced by injection molding not more than 5 minutes before commencement of process step a).

10. The process as claimed in any of claims 6 to 9, wherein the distance between the surface of the workpiece and the inside of the mold is 50 μm to 5 mm.

11. The process as claimed in any of claims 6 to 9, wherein the polyisocyanate composition A contains at least one silane-functional polyisocyanate.

12. A coating obtained or obtainable by the process according to any of claims 6 to 11.

13. The coating as claimed in claim 12, characterized in that the ratio of the absolute peak heights of the CH.sub.2 band and the NH-δ band is at least 0.85:1 and the ratio of the absolute peak heights of the isocyanurate band and the NH-δ band is at least 5.5:1 and the coating has a Tg of 40° C. to 300° C.

14. The coating as claimed in claim 12 or 13, characterized in that it has a density of at least 0.95 g/cm.sup.3.

15. A workpiece coated with the coating as claimed in any of claims 12 to 14.

Description

[0168] FIG. 1A shows a workpiece (diagonally hatched) having a cutout (grey) viewed from above.

[0169] FIG. 1B shows a cross section of the workpiece having a cutout.

[0170] FIG. 1C shows the cross section of the workpiece after coating. The workpiece and the cutout are now covered by the coating (black).

[0171] FIG. 1D shows a coated workpiece where an article (hatched horizontally) was inserted into the originally present cutout.

[0172] The working examples which follow serve merely to illustrate the invention. They are not intended to limit the scope of protection of the claims in any way.

WORKING EXAMPLES

[0173] The tests were carried out on a Battenfeld HM 370/1330 injection molding machine combined with a laboratory piston metering system for 2 components. The mold used was an A5 plate mold which was coated with a mass of about 41 g of lacquer which corresponds to a lacquer layer thickness of 280 μm to 390 μm.

[0174] The following materials were used: [0175] Desmophen XP 2488, branched polyester polyol available from Covestro Deutschland AG having the following properties:

TABLE-US-00001 Hazen color number ≤100    Acid number ≤4.0 mg KOH/g Viscosity at 23° C. 12 250 ± 1 750 mPa s Hydroxyl content 16.0 ± 0.6 % Water content ≤0.1 % Equivalent weight about 105 g/eq Density at 20° C.  about 1.12 g/cm.sup.3 Flashpoint about 127 ° C. [0176] Desmophen C1100, linear, aliphatic polycarbonate polyester available from Covestro Deutschland AG having the following properties:

TABLE-US-00002 Hazen color number ≤150 Acid number about 0.1 mg KOH/g Viscosity at 23° C. 3 200 ± 1 300 mPa s Hydroxyl content 3.3 ± 0.3 % Water content about 0.05 % Equivalent weight about 515 g/eq Density at 20° C. about 1.1 g/cm.sup.3 Solidification temperature about 15 ° C. [0177] Polyisocyanate B1 [0178] The isocyanurate-containing HDI polyisocyanate B1 was produced according to EP-A 330 966, example 11, wherein 2-ethylhexanol was employed as the catalyst solvent instead of 2-ethyl-1,3-hexanediol. Removal of the excess monomeric HDI by thin-film distillation afforded an HDI polyisocyanate having an NCO content of 22.9%, a viscosity of 1200 mPas at 23° C. and an average NCO functionality of 3.1 (calculated from NCO content and number-average molecular weight determined by GPC measurement). [0179] Makrolon 2405/901510, black polycarbonate [0180] The catalyst was produced according to EP 333 7836, example 1a.

[0181] The following materials were used for the lacquer:

[0182] Component A

TABLE-US-00003 Desmophen C1100 20.6 g  Desmophen XP 2488 8.8 g Catalyst 3.0 g

[0183] The polyols Desmophen C1100 and Desmophen XP 2488 were used in a mass ratio of 70:30. The employed amount of catalyst corresponds to a concentration of 2.91% by weight based on the total mass (component A+component B), calculated for a degree of crosslinking of 3.

[0184] Component B: Polyisocyanate B1, amount see table 1.

[0185] Both components were heated to about 90° C. before the test. The surface temperature of the mold was 117° C. The thermoplastic was melted in the extruder at 290° C. and injected into the mold at an established mold temperature of 120° C. The experimental release agent L9500021 from Votteler was applied manually to the plate mold, but any external release agent for polyurethane systems is suitable in principle.

[0186] Different degrees of crosslinking were used for the coating of the test panels. The degree of crosslinking was calculated based on the theoretical isocyanate and OH contents:

[0187] Degree of crosslinking 1=ratio of NCO groups to OH groups of 1:1

[0188] Degree of crosslinking 3=ratio of NCO groups to OH groups of 3:1

[0189] The following parameters were used for the coating tests:

TABLE-US-00004 TABLE 1 Overview of employed mixing ratios of polyol (A) to isocyanate (B), degrees of crosslinking achieved therewith and parameters established Mixing Temperature Mold Degree of ratio A:B Material closing No. crosslinking (volume) A/B time 1 1.3 100:100 90/90 90 s (comp.) 2 2 100:145 90/90 90 s 3 3 100:215 90/90 90 s 4 4 100:285 90/90 90 s 5 5 100:360 90/90 90 s 6 6 100:430 90/90 90 s

[0190] At least 6 parts were produced for each degree of crosslinking.

[0191] For each degree of crosslinking the residual NCO content for at least one article was determined by IR after the following times. To this end, an unreacted mixture of components A and B mixed at room temperature according to the degree of crosslinking was measured and the peak for the NCO group contained therein at about 2200 cm.sup.−1 was normalized to 100%.

[0192] Measurements were made on a Bruker Tensor II infrared spectrometer using a Platinum ATR unit. The spectrometer was controlled with the instrument software OPUS Version 7.5, which was also used for the evaluation. After baseline correction (rubber band method) and normalization to CH.sub.2/CH.sub.3 (min-max normalization in the range 2800-3000 cm.sup.−1) a straight line was applied between 2380 cm.sup.−1 and 2170 cm.sup.−1 for area integration and the area thereabove calculated.

TABLE-US-00005 TABLE 2 Overview of percentage content of residual NCO in articles having different degrees of crosslinking measured after different time intervals When the average value was below 5%, development was not pursued further. 2 weeks + Degree of 16 h @ crosslinking 3 h 1 day 1 week 2 weeks 60° C. 1.3 0.00% 0.00% 2 0.38% 0.65% 0.00% 3 11.72% 7.83% 2.89% 2.14% 4 20.80% 15.51% 9.32% 7.39% 3.57% 5 39.01% 22.43% 15.53% 10.57% 3.24% 6 43.48% 25.37% 17.11% 12.73% 4.48%

[0193] The ratios of the absolute peak heights of different signals were also compared, wherein in each case the greatest absolute intensity of the band was determined. The measurement range for CH.sub.2 was between 2900 and 3000 cm.sup.−1, for NH-5 between 1480 and 1600 cm.sup.−1 and for isocyanate between 1590 and 1700 cm.sup.−1. The peak heights were correspondingly related to the other signal. Exclusively fully cured articles were used for this investigation, i.e. the measurements were carried out about 6 months after production. An overview is shown in table 3.

TABLE-US-00006 TABLE 3 Overview of ratios of peak heights of CH2 to NH-δ and isocyanurate to NH-δ for different degrees of crosslinking. Degree of crosslinking CH2:NH-δ ratio Isocyanurate:NH-δ ratio 1.3 0.81 3.81 2 0.80 4.56 3 0.84 5.5 4 0.85 5.82 5 0.90 6.16 6 0.89 6.05

[0194] The following coatings technology tests were carried out on the lacquers: [0195] Hazen color numbers were determined using a micro-haze plus instrument from Byk-Gardner GmbH, Geretsried, Germany at an angle of 20°. [0196] The gloss of obtained coatings was measured by reflectometry according to DIN EN ISO 2813:2014 at an angle of 20°. [0197] Glass transition temperature (TG) by differential scanning calorimetry (DSC) [0198] The measurements were performed using a Perkin Elmer DSC 8500 calorimeter. Temperature calibration was carried out on indium and lead (melt onset) and heat of reaction calibration was carried out on indium (melt area integral). Three heatings from −65° C. to +150° C. were performed at a heating rate of 20 K/min. Between heatings the sample was cooled at a cooling rate of 320 K/min. The measurements were performed under nitrogen and a closed aluminum crucible was used as the sample vessel for solid samples. [0199] Solvent resistance [0200] A small amount of the relevant solvent (xylene, 1-methoxyprop-2-yl acetate (MPA), ethyl acetate or acetone) was added to a test tube and provided with a cotton pad at the opening, so that an atmosphere saturated with solvent was formed inside the test tube. The test tubes were then applied to the lacquer surface by the cotton pad and remained there for 5 minutes. After wiping off the solvent, the film was examined for damage/softening/loss of adhesion and visually assessed from 0 (no change) to 5 (lacquer surface destroyed). [0201] Pendulum damping was measured after König according to DIN EN ISO 1522 (01-04-2007 edition), wherein the test panels are described according to DIN 1514. [0202] Cross-cut adhesion tests were carried out according to DIN EN ISO 2409 (01-09-2019 edition) with a grid line spacing of 3 mm. [0203] Sun cream resistance was determined based on the Ford test USA PV 3964 (Engineering Material Specification/Soiling and Cleanability FLTM BN 112-08, ISO 105-A02/AATCC). The sun cream was applied to the lacquer surface to be tested and then stored at 70° C. for 4 hours. The test surfaces were wiped off with a cosmetic tissue immediately after exposure. After wiping off the sun cream, the film was checked for destruction/softening/loss of adhesion and visually assessed from 0 (no change) to 5 (lacquer surface destroyed).

TABLE-US-00007 TABLE 4 Overview of test results on direct coating articles having different degrees of crosslinking. The tests were performed as described above. No. 1 (comp.) 2 3 4 5 6 Degree of 1.3 2 3 4 5 6 crosslinking Gloss 20° 81 85 86 85 87 80 [GU] Haze 20° 21 18 21 19 24 47 TG [° C.] 12 34 50 65 77 82 Pendulum 13 68 162 176 182 186 damping [s] Cross-hatch 3 2 1 1 1 1 Solvent 3/3/3/3 3/3/3/3 2/1/2/2 2/1/2/2 2/1/2/2 2/1/2/2 resistance 1 minute Xylene/ MPA/ethyl acetate/ acetone Sun cream 4 4 4 1-2 1 1 resistance

[0204] The evaluation of the data reported in table 4 shows that a higher degree of crosslinking is correlated with a higher glass transition temperature TG and a higher pendulum damping. It is also apparent that the properties of the lacquer surfaces in respect of resistance to sun cream and solvents improve with increasing degree of crosslinking. The jump in properties is particularly evident above a degree of crosslinking of 3.