NL2014667B1 - An RMA crosslinkable composition with reduced yellowing. - Google Patents

Abstract

The invention relates to an RMA crosslinkable composition comprising a component A with at least two acid protons CH in activated methylene or methine groups, a component B with at least two activated unsaturated C = C groups, a catalyst C, capable of an RMA activate cross-linking reaction between components A and B, optionally comprising reactivity moderators and optionally comprising one or more organic solvents or a mixture of organic solvents, wherein yellowing is enhanced by higher C = C to CH ratios and lower amounts of the specified catalyst and certain choices for catalysts moderator D.

Description

A RMA NETWORKABLE COMPOSITION WITH A REDUCED YELLOW

The invention relates generally to RMA crosslinkable compositions, in particular coating compositions, with reduced yellowing.

RMA crosslinkable compositions are compositions comprising at least one crosslinkable component comprising reactive components A and B, each comprising at least 2 reactive groups wherein the at least 2 reactive groups of component A are acid protons (CH) in activated methylene - whether methine groups (RMA donor group) and the at least 2 reactive groups of component B are activated unsaturated groups (C = C) (RMA acceptor group). These reactive groups react to cross-link by Real Michael Addition (RMA) reaction between said at least one cross-linkable component in the presence of a basic catalyst (C).

Such RMA cross-linkable compositions are described in EP 2 556 108 of the same applicant. Described herein is a special catalyst C which is a substituted carbonate catalyst that decomposes into a coating layer to generate carbon dioxide that evaporates from the applied curing coating layer and a strong base that initiates the RMA crosslinking reaction. The catalyst ensures a long shelf life in the pot and at the same time a high reactivity.

EP 2 764 035 from the same applicant discloses similar compositions that further comprise an XH group that includes reactivity moderating component (D) which is also a Michael Addition donor capable of reacting with component B under the action of catalyst C, wherein X is C, N, P, O or S. This reactivity moderating component improves the open time and hardness development of the coating. Preferred examples of components D described in the prior art are acetoacetate, succinimide, triazole and benzotriazole.

For the present application, the description of RMA crosslinkable composition, in particular components A, B, C and D, definitions and measurement techniques in EP 2 556 108 and EP 2 764 035 apply and are included herein. by reference.

The underlying problem of the invention is that known RMA crosslinkable compositions can suffer from undesired yellowing, both during heating (thermal or dark yellowing) and during exposure to UV radiation (UV yellowing). During the application life of a coating, a coating is subjected to heat radiation from the sun or to thermal heating, for example when the coating is in the vicinity of, for example, combustion engines or electric motors. Moreover, the coating can also be exposed to UV radiation if it is exposed to sunlight. All these external influences can not only cause yellowing, but can also damage the coating and decrease the gloss value and / or cause the surface to crack.

Thus, there is a particular need for RMA crosslinkable composition that does not have these mentioned problems, or at least has less extensive. Acceptable yellowing levels should be comparable or lower than existing urethane reference systems. Most preferably, the total color difference dE is lower than 1 and the comparison index db is also lower than 1.

However, on the other hand, a low yellowing formulation cannot provide the best balance between yellowing, chemical resistance, and mechanical properties, and it is objective to find an improvement in which said performance parameters are not substantially compromised by the low yellowing RMA -composition.

According to the invention, at least one of the problems is solved by providing a cross-linkable composition comprising: a. A component A with at least two acid protons C-H in activated methylene or methine groups, b. a component B with at least two activated unsaturated C = C groups, c. a catalyst C capable of activating an RMA cross-linking reaction between component A and B, d. optionally comprising one or more organic solvents or a mixture of organic solvents, wherein yellowing is enhanced by one or more characteristics selected from the group of characteristics i) to iv) i. the molar ratio of activated unsaturated C = C groups of component B to CH in activated methylene or methine groups of component B is higher than 0.8, preferably higher than 0.85, 0.9 or 0.92 and less than 1, 2, preferably less than 1.1 or 1, and ii. the catalyst C is 0 quaternary ammonium salt or bicarbonate or alkyl carbonate, or 0 is a salt or a basic anion X- of an acidic XH group-containing compound wherein X is N, P, O, S, or C, anion X- a Michael Addition is donor that can react with component B and anion X- is characterized by a pKa (C) of the corresponding acid XH of more than two units lower than the pKa (A) of the main component A, iii) the amount of catalyst C is between 0.03 and 0.08, more preferably between 0.04 and 0.06 and most preferably 0.045 and 0.055 meq / g of solid resin, and iv) optionally a reactivity moderator D comprising an XH group which is also a Michael is an addition donor capable of reacting with component B under the action of catalyst C, where X is C, N, P, O or S, where in the case of acetoacetate the amount is less than 7, 5, 3 or even 1 mg / g of solid and in the case of benzotriazole the amount is less than 6, 4, 3, 2, 1 or even 0.5 mg / g of solid .

It was found that the yellowing resistance can be considerably reduced and it was found that in various yellowing tests the DE was reduced for compositions according to the prior art described in EP 2 556 108 from 2-20 to 0.5 - 1 or for top layers even in the range of 0.2 and 1. Preferably, the total color difference dE is lower than 1, preferably lower than 0.7, or even 0.5. Preferably the yellowing index db is less than 1.5, preferably less than 1.2 or more preferably less than 1 and most preferably even less than 0.7.

It was found that within the described narrow ranges good yellowing resistances with good mechanical and chemical coating properties could be obtained. Of course, variations within the ranges can be used to optimize certain properties, so that the catalyst amount can be chosen higher if the C = C / CH ratio is chosen sufficiently high, etc. Acetoacetate is preferred in view of yellowing resistance or benzotriazole is completely omitted, but since this has a negative impact on the appearance, especially when thick layers are applied, it is preferred to add other reactivity moderators D, for example 1,2,4 triazole or succinium. nimide that do not have a negative yellowing effect.

According to the invention, the C = C / C-H reactivity group ratio, most preferably the acryloyl to malonate ratio, is between 0.8 and 1.5. The ratio normally used (about 0.75) is preferably increased to at least 0.8 or 0.9 and most preferably to 0.95 and preferably also to less than 1.5, 1.3 or even 1.1. The upper limit is mainly determined by the activated C = C component B, in particular because the acryloyl component is expensive and because the XLD goes down due to related mechanical disadvantages.

It is surprising that a relatively high ratio and thus high amounts of unsaturated C = C groups reduce yellowing because yellowing is normally associated with the presence of unsaturated C = C groups but in the present invention the reverse was found.

Brief description of the drawings Figure 1: shows the measurement of the Hardness (65 microns) after one day of RT (red) and thermal yellowing (after 24 hours at 120 ° C) depending on the ratio between acryloyl groups and malonate hydrogen in RMA crosslinked -able composition.

Figure 1 shows that to avoid thermal (dark) yellowing of the coating, the acryloyl / malonate ratio is preferably between 0.8 and more preferably> 0.9, with a ratio between 0.8 and 1.2 hardness also very good and the RMA composition surpasses even the isocyanate based systems.

Very good yellowing levels can be obtained in RMA formulations (dE = 0.4 after 1 day at 120 ° C) similar to (urethane) reference systems (dE = 3.66 for a commercial clear coat after 1 day at 120 ° C or dE = 1.1 after 150 h at 120 ° C for a white base layer).

The dependence on yellowing and mechanical and chemical properties depends on the ratio of acrylolyl to malonate and is shown in Table 2. The results clearly show an optimal balance of opposing properties for the ratio between 0.8 and 1.2.

Table 2. Influence of acryloyl / CH ratio on RMA coating ** properties.

** catalyst = 0.05 meq / g, succinimide / cat. = 1,1,2,4-triazole / cat = 4, P / B = 0.6; # 1 = very bad, 5 = very good; * performed on panels with a 24 hour aging at 120 ° C; $ after 2 days It was found that to improve the yellowing resistance, it is preferred to reduce the amount of catalyst to amounts below 0.06 meq per g of solid resin, preferably below 0.055, 0.05, 0.045 or even lower than 0.04, but taking into account catalyst activity, the amount is preferably at least 0.01.02 or 0.03 meq per g of solid resin.

When optimizing the yellowing resistance, care should be taken, given the chemical resistance (MEK resistance test), that the conversion of the reactive groups upon curing is at least 60%, preferably 65, 70 or even 75% by weight to obtain sufficient cross-linking. IR spectroscopy measurements and PCA analysis can be used to confirm that sufficient conversion of the formulation has taken place. Too low a conversion will sacrifice many positive improvements that RMA can offer.

A higher conversion can be achieved, for example, at higher catalyst levels but also at longer reaction times and temperatures. Because curing is preferably carried out at room temperature and longer reaction time is not desired in practice, a larger amount of catalyst is preferred. To achieve sufficient conversion, it is preferred that the amount of catalyst is at least 0.04 meq / g, preferably at least 0.05, more preferably at least 0.06, or even 0.07 meq / g. g. At catalyst levels of 0.05 or even 0.04 meq / g, a better yellowing resistance is obtained, but this can cause too low a conversion. A good balance is therefore between 0.04 and 0.06, preferably between 0.045 and 0.055 meq / g, in particular in the malonate / acryloyl systems.

Results are shown in Table 1 which indicate a trend that more catalyst results in more yellowing, harder films, higher conversion and thus better MEK resistance in the malonate / acryloyl system.

Table 1. Influence of amount of catalyst on RMA coating ** properties

** acryloyl / CH = 0.95, succinimide / cat. = 1,1,2,4-triazole / cat = 6, P / B = 0.8; # 1 = very bad, 5 = very good; * determined by PCA at the 1410 cm -1 peak; $ after 2 days It was found that some reactivity moderators D result in yellowing and others not; in particular, it was found that a decrease in acetoacetate content reduces thermal yellowing, that a reduction in benzotriazole content reduces UV yellowing and that triazoles and succinimides have good reactivity moderating properties without yellowing.

In particular, it is preferred to reduce benzotriazole levels to below 6, 4, 3, 2, 1 or even 0.5 mg / g of solid. In view of the moderation of the reactivity of the cross-linking reaction, 1,2,4-triazole is preferably used which does not have that cross-linking problem but does have the advantage of the moderator D with an improved open time.

It was further found that acetoacetate can be used as moderator D and that better results are obtained if the amount of acetoacetate normally used as moderator between 10 and 30 mg / g of solid is reduced to 0, so preferably lower than 7, 5, 3 or even 1 mg / g of solid).

Description of the illustrative embodiments The following is a description of certain embodiments of the invention, given by way of example only.

The malonate functional resin PE is a polyester resin that was transesterified with diethyl malonate. This resin is prepared as follows: 382 g of neopentyl glycol, 262.8 g of hexahydrophthalic anhydride and 0.2 g of butyl tin hydroxy oxide were introduced into a reactor with a distillation column filled with Raschig rings. The mixture was polymerized at 240 ° C under nitrogen to an acid number of 0.2 mg KOH / g. The mixture was cooled to 130 ° C and 355 g of diethyl malonate was added. The reaction mixture was warmed to 170 ° C and ethanol was removed under reduced pressure. Succinimide containing a malonate functional group PE in Table 1 was prepared by adding succinimide to the method described above; when the viscosity at 100 ° C has reached 0.5 Pa.s, the material was cooled to 140 ° C and 11.2 g of solid succinimide was added. This mixture was stirred until all of the succinimide was dissolved. The products (with and without succinimide) were further cooled and diluted with butyl acetate to 85% solids.

The FCT catalyst is a mixture of tetrabutylammonium bicarbonate, diethyl carbonate and n-propanol with a concentration of 0.928 prepared as described in EP 2 556 108 (catalyst C5).

Examples 1 to 3 and comparative experiment 1-3 Formulations 1 to 6 of examples 1 to 3 and comparative experiments 1 to 3 were prepared as described in Table 1.

Table 1

* Mix 32.0% Miramer M410 with 65.1% Kronos 2310 and 2.9% disperserk 163 and grind until the particle size is less than 10 µm ** mix 24.0% Miramer M410 with 72, 7% Kronos 2310 and 3.3% disperbyk 163 and grind until the particle size is less than 10 µm A paint was prepared by mixing Part 1 in Table 1 of the formulations F1 - F6 shortly before application to a substrate with Part 2 comprising the catalyst. Ditrimethylolpropane tetra-acrylate (di-TMPTA: Mamer M410) was used as component B in such an amount that the specific C = C / C-FI ratio was obtained and was added separately and / or with the pigment paste.

The resulting paint was applied to a metal panel with a dry film thickness of 60 µm. After drying, the color was measured. The panel was then heated at 120 ° C for 1 day. After cooling, the color was measured again, which showed a certain degree of yellowing. For formulations F1, F2 and F5, a second panel of the same paint and the same layer thickness was exposed to UV-B radiation in UVCON for 100 and 600 h and yellowing was determined by known techniques. The results are shown in Table 2.

Yellowing was measured using Flunterlab coloration meter using Hunter L, a, b color scale before and after the yellowing test to evaluate the db as a deviation to yellowing and the dE deviation as a measure of total color difference, db is comparable with dE as mentioned above and is determined.

Table 2 shows examples 1 to 3 (formulations F1 - F3) show low yellowing (db) with comparative examples (formulations F4 - F6) showing increased thermal yellowing; in F4 this is caused by a higher amount of catalyst and in F6 by a lower acryloyl / malonate ratio. In F5 the thermal yellowing was still acceptable but the UV yellowing was not.

Table 2

Example 4 and Comparative Examples 4 and 5 A formulation F1 as described in Table 1 was prepared (listed as Acure in Table 1) and compared to prior art aspartate and isocyanate polyol systems. The focus was on averaging control of the curing chemistry in systems with relatively high concentrations of functional groups. As a result, coatings with very high crosslinking densities (XLD) of typically 2.5-3 mmol / cc were obtained. These XLDs are a factor 3 higher relative to high side, e.g., on 4% OH isocyanate-based systems, even if high isocyanate amounts are used (see Table 4 comparing isocyanate amounts in this study).

Table 3. View immediately after application and after aging for 24 hours at 120 ° C (DFT: 45 ± 4 µm on Q-panel) 4% OH- 4% 4%

Acure Aspartate NCO A OH- OH-

NCO B NCO C

Spray viscosity 30 24 20 20 25 SC@ Toegep.visc (g / l) 81 83 71 72 76 NCO weight% - 29.0 17.4 17.4 22.0 on solids NCO: OH, NH - 1.05 1 , 1 1.1 1.05

Curing temp. RT RT RT 60 80

Long wave 12 4 21 4 6

Short wave 8 3 5 2 4 DOI 91 93 94 94 94

Turbidity (HU) 11 10 10 21 16

Gloss 20 ° (GU) 80 85 90 88 90

Gloss 60 ° (GU) 90 93 95 95 97

Foam limit (pm)> 240> 240> 160 ~ 100 ~ 110

Turbidity * (HU) 34 314 63 78 32

Gloss 20 ° * (GU) 78 49 83 81 85

Gloss 60 ° * (GU) 90 83 94 99 95

* 24 hours at 120 ° C

Table 3 compares the view data, including the effect of thermal (dark) aging. Note that the RMA cross-linkable paint (Acure) was applied at the highest spray viscosity (DIN-4). The aspartate coating deteriorated significantly over time when exposed for 24 hours at 120 ° C. An additional advantage of the RMA cross-linkable paint is its relative insensitivity in view as a function of the applied thickness of the layer. In contrast to OH-isocyanate-containing systems, there are no foam-generating reactions with water and subsequent risk of small holes.

The invention has thus been described with reference to certain embodiments as discussed above. It is recognized that these embodiments are subject to various modifications and alternative forms well known to those skilled in the art. Variants that can be used are described in detail in the prior art disclosed herein by the same inventors or applicant Nuplex and are hereby incorporated by reference.

Claims (8)

1. A cross-linkable composition comprising: a. a component A with at least two acidic protons C-H in activated methylene or methine groups, b. a component B with at least two activated unsaturated C = C groups, c. a catalyst C capable of activating an RMA cross-linking reaction between component A and B, d. optionally comprising one or more organic solvents or a mixture of organic solvents, wherein yellowing is enhanced by one or more characteristics selected from the group of characteristics i) to iv) i. the molar ratio of activated unsaturated C = C groups of component B to CH in activated methylene or methine groups of component B is higher than 0.8, preferably higher than 0.85, 0.9 or 0.92 and less than 1, 2, preferably less than 1.1 or 1, and ii. the catalyst C is 0 a quaternary ammonium salt of bicarbonate or alkyl carbonate or 0 a salt or a basic anion X- of an acidic XH group-containing compound wherein X is N, P, O, S, or C, anion X- a Michael Addition is a donor that can react with component B and anion X- is characterized by a pKa (C) of the corresponding acid XH of more than two units lower than the pKa (A) of the main component A, iii. the amount of catalyst C is between 0.03 and 0.08, more preferably between 0.04 and 0.06 and most preferably 0.045 and 0.055 meq / g of solid resin and iv. optionally a reactivity moderator D is present which includes an XH group that is also a Michael Addition donor that can react with component B under the action of catalyst C, wherein X is C, N, P, O or S, where in the case of acetoacetate is the amount <7, 5, 3 or even 1 mg / g of solid and in the case of benzotriazole the amount is less than 6, 4, 3, 2, 1 or even 0.5 mg / g of solid .