HK1151051B - Epoxy curing system and coatings obtained thereof - Google Patents

Description

Epoxy curing system and coatings obtained therefrom

The present invention relates to a curing system comprising a compound having at least one epoxy group, a polyamine, and a co-curing agent. The invention also relates to a method for curing the system and to coatings obtained therefrom.

Coating compositions based on compounds having epoxy groups have limited heat resistance and decompose above 160 ℃.

A method of modifying a resin having an ethylenically unsaturated bond by combination with bismaleimide is described in US 5,198,515. According to this method, a polymer having heat resistance of up to 500 ℃ can be obtained using 1, 3-bis (citraconimidomethylene) benzene. The product can be tradenameAndand (4) obtaining.

Flexlink has the formula:

wherein D represents 1, 3-dimethylenebenzene and R is methyl.

The crosslinking accelerator of the curing system is a peroxide. However, for polymers with epoxy groups which are not cured in the presence of peroxides but in the presence of amine-functional compounds, only small amounts of Flexlink may be used. Due to its limited solubility, Flexlink is present in the curing system in an amount of less than about 20%. At higher concentrations, Flexlink formed a sediment in the cured system.

Epoxy resin adhesives have been disclosed in US4,837,295, in which polyoxyalkylene polyamines are used as curing agents and mono-or diunsaturated maleimides are present, but N, N' -hexamethylenebiscitraconimide, which is not sought to be protected, is also mentioned. However, the maleimides of US4,837,295 are toxic and carcinogenic compounds and moreover have a different reactivity compared to the biscitraconimides of the invention. A further disadvantage of these compounds is that they cannot be used in low-temperature applications, since they are insoluble and solidify at room temperature in the curing system.

The synthesis of biscitraconimide compounds having both ether and sulfone groups is disclosed in JP01-186865, for example 4, 4' -bis (3-citraconimidophenoxy) diphenyl sulfone. Such compounds are not useful in the present invention.

There is a need for peroxide-free curing systems with much higher amounts of bismaleimides than are possible with Flexlink. It is therefore an object of the present invention to provide such a system which is less toxic and carcinogenic than known systems.

To this end, the invention relates to a peroxide-free curing system comprising 20 to 89.5 wt% of a compound having at least one epoxy group, 0.5 to 30 wt% of a polyamine, and 10 to 50 wt% of a co-curing agent, wherein the co-curing agent has the formula I:

and/or tautomeric forms thereof, IIa and/or IIb:

and/or formula III:

or a tautomer thereof;

and/or oligomers thereof; wherein

D represents branching (CR)₁R₂)_nOr

Wherein p is independently 0 or 1, and X is CH₂O or SO₂And

represents a meta-or para-phenyl group;

r is independently H or C₁-C₄An alkyl group; r₁And R₂Independently is H or (CH)₂)_mCH₃(ii) a Wherein at least one group R₂Is (CH)₂)_mCH₃And m is 0 to 2; n is 1 to 10; and n + m is 4 to 14; r' -CH₂Is R; and P represents phenyl or C unsubstituted or substituted by hydroxy_1-6Alkyl or C_2-6An alkenyl group; with the proviso that at least one R is C_1-4An alkyl group.

Examples of D are:

-(CH₂)₂-CH(CH₃)-(CH₂)₂-；-(CH₂)₄-CH(CH₃)-(CH₂)₄-；

-CH₂-CH(CH₃)-CH₂-CH(CH₃)-CH₂-

the co-curing agent is citraconimide (citraconimide) and one of the two maleimide moieties may be in their tautomeric itaconimide form. These citraconimides (and tautomers thereof) may be present as described, but may also readily form dimers, trimers or higher oligomers. When referring to the co-curing agent citraconimides, also included are tautomers thereof and oligomers formed from 2 to 10 molecules of formula I, IIa, IIb and/or III. Parts by weight are based on the weight of the peroxide-free curing system.

The invention further relates to a process for obtaining a cured polymer by heating the curing system to a temperature and for a time sufficient to co-cure the co-curing agent and the epoxy group-containing compound. In this system, polyamines can act as crosslinkers and curing catalysts, and optionally other ingredients can be added to the system. Such other ingredients may be monoamines, which do not react as cross-linkers, but may still be effective curing catalysts or co-catalysts.

The curing system may contain other ingredients such as nanoparticles, for example carbon nanotubes or modified hydrotalcites, adhesion modifiers which are well known compounds or compositions that improve the adhesion of coatings to surfaces, such as silane coupling agents, titanium coupling agents, zirconia coupling agents, aluminum coupling agents, organopolysiloxane compositions or those described in US4,389,432, and other additives such as dyes, pigments, and the like.

It may also be useful to use mixtures of biscitraconimides and/or biscitraconimides (I, IIa, IIb) and monomeric maleimides or itaconimides III. Such a mixture of monomers and dimers, for example 1-20% by weight of monomer III of the co-curing agent in the curing system, results in a cured polymer having a more flexible network. Higher amounts, up to 100%, result in very soft to extremely soft networks. Furthermore, maleimide may also be used instead of moieties I, IIa, IIb and/or III. This further increases the heat resistance of the coating and also creates unique curing possibilities, such as fast fixing at room temperature (mainly citraconimide curing), optionally followed by post-hardening at elevated temperature (mainly maleimide curing).

Curing is carried out by simply mixing a mixture comprising at least one biscitraconimide of formula (I), if desired as a mixture with IIa and/or IIb or (III), or tautomers or oligomers thereof, epoxides, polyamines and optionally other ingredients such as monoamines, nanoparticles and the like, optionally heated to a temperature sufficient to co-cure the (bis) citraconimide and the epoxy group containing compound and maintaining the temperature at that level for a time sufficient to cure the material into a polymeric product. The temperature and time can be readily determined by one skilled in the art using conventional means. Curing can be accomplished at 20 ℃ to 150 ℃. Typically, curing is accomplished at a temperature below 130 ℃, preferably at room temperature. The curing time varies depending on the amount of polyamine and the type of material present and can be readily determined by standard analytical techniques.

Additional nitrogen-containing curing catalysts for maleimide systems may be employed, such as amine-containing catalysts.

The system comprises compounds containing at least one epoxy group, however compounds having one or more epoxy groups in combination with an ethylenically unsaturated isocyanate or urethane group may also be used.

Examples of co-curing agents are known from US 5,198,515, but none of these generically mentioned compounds are disclosed as being suitable in the curing system of the peroxide-free epoxy group-containing compound of the invention.

Has the chemical name 1, 3-bis (citraconimidomethylene) benzene and is available from Flexsys, Brussels, Belgium. Lowering the melting point of Flexlink by isomerization (tautomerization) provides modified Flexlink and improved for room temperature cure applicationsStabilizing the solubility of the product in the formulation. Instead of less than 10-20% Flexlink, more than 25% of the modified Flexlink is soluble in epoxy-modified 2K (two-component) curing systems at room temperature without forming sediment on storage. Thus a solvent-free, room temperature compatible and stable 2K system is obtained. This means that tautomerization of Flexlink is a prerequisite for obtaining higher concentrations of Flexlink in stable formulations. Optionally, a suitable reactive or non-reactive solvent may also be added.

Particularly suitable biscitraconimides have the formula I, wherein D is branched C₆-an alkylene group which is liquid at room temperature. Thus, the molecule can be used even directly without isomerization, in very high concentrations (> 50%). Isomerization further increases solubility. These aliphatic citraconimides produce clear coatings and are color stable and resistant to outdoor conditions such as ultraviolet light. In order to obtain a clear coat from a commercially available Flexlink, the standard obtained grade must be recrystallized.

Compounds having reactive epoxy groups, glycidyl ethers and esters such as Epikote 827/828 and Epikote 1001 (available from Hexion Specialty Chemicals, Columbus, OH, USA) orTautomeric Flexlink of EPS (manufacturer: Akzo Nobel, Netherlands) combinations.

Conventional commercially available 2K systems based on epoxy resins can be heated up to 160 ℃. These curing systems decompose at higher temperatures. The addition of a modified Flexlink to such formulations improves heat resistance and stability. By means of the modified citraconimide formulation, high temperature resistance up to 250 ℃ can be obtained, while curing can be carried out at room temperature. The modified (tautomeric) citraconimide Flexlink has a melting point (ratio citraconimide: itaconimide approximately 45: 55) of about 60-70 ℃. To be provided withCommercially available unmodified citraconoyl imidesThe melting point of the amine (citraconimide: itaconimide ratio of about 95: 5) was about 90 ℃. Preferably, the citraconimide comprises 6 to 50% of one or both tautomeric itaconic isomers.

In addition to improved heat resistance, the coatings obtained from the cured systems of the present invention also exhibit improved chemical and scratch resistance and self-healing properties.

The curing system also comprises a polyamine. These act as promoters and/or comonomers. Suitable polyamines are compounds having at least two primary and/or secondary amino groups, and also mixtures of such polyamines. Amine-containing oligomers and polymers may also be used, e.g., commercially available(available from Huntsman, Salt Lake City, USA), and other nitrogen-containing basic molecules. The cure system of the present invention allows for a high concentration of co-curing agent, which should be at least 10% of the composition, but can easily be as high as 50%, preferably 20-40% by weight of the composition. Further examples of polyamines are given in the experimental part.

The citraconimides of the invention produce transparent coatings and are color stable and resistant to outdoor conditions such as UV light. The addition of high concentrations of co-curing agents results in improved heat resistance and stability, which is enhanced when the amount of co-curing agent in the system is higher.

On addition of nanoparticles such as modified hydrotalcite, automated topographic 3D landscape (landscapes) formation was observed on many substrates. This may be attractive for decorative applications. Scratch resistance and slip resistance are also improved. The layer thickness of the coating varies from 50 micrometers to several millimeters. The thicker the layer, the more pronounced the aesthetic effect is obtained.

The compositions of the present invention can be applied to a variety of surfaces, especially softwood and hardwood, man-made wood such as composite wood and the like, glass, aluminum, stainless steel, iron, plastics such as PVC, polycarbonate, polyester, polyamide, polyethylene and polypropylene, concrete, stone, latex surfaces, conventional paint surfaces, natural and synthetic fibers such as aliphatic and aromatic polyamides, polyester, cotton, and the like.

Applications for the new coating compositions are clear coats, adhesives, sealants, fillers, and combinations thereof.

The invention will be further illustrated with reference to the following examples, which should not be construed as limiting the scope of the invention.

Example 1

General method for modifying Flexlink

Will be sold on the market(available from Flexsys, Belgium) is mixed with the weak base N-phenylimidazole (or any other weak base) used as a catalyst (in a concentration range of 0.05-5% m/m), preferably 0.1-3.0% m/m, most preferably 0.5-1.0% m/m, and heated in an oven at about 130 ℃ for about 10-20 hours or at 140 ℃ for 3-4 hours. The higher the temperature, the more oligomeric homo (pre) polymers are formed.

Various types of amines may be used as curing agents. For very fast cure times, small amines such as Ethylenediamine (EDA), Diethylenetriamine (DETA), triethylenetetramine (TETA), Tetraethylenepentamine (TEPA), Pentamethylenehexamine (PEHA), and the like, and functionally similar homologs or derivatives, can be used.

Example 2

Fast curing System 2K System

Mixture 1: 15 g of the tautomeric Flexlink were melted in an oven (70-90 ℃) and mixed and homogenized with 15 g of an epoxy curing agent (Epikote 827/828 or 1001). Optionally, 0.5 to 3 grams of a coupling agent such as trialkoxyglycidyl silane is added to the mixture for improving adhesion on metal surfaces.

Mixture 2: in another cup, 15 grams of TEPA was prepared.

The two mixtures were mixed with each other. An exothermic reaction (> 100 ℃ C.) occurred. During this heating also a certain amount of Flexlink tautomerizes. Within minutes, the coating system can be applied as a thin layer coating, filler, backing or adhesive to a surface such as wood, metal, etc. These 2K systems can also be sprayed and mixed in nozzles for professional application.

If more elasticity is desired in the final cure system, 2-5 grams can be addedEPS, and/or less epoxide may be used (e.g., 13-10 grams instead of 15 grams).

If long working times are required, e.g. hours instead of minutes, more fatty amine derivative should be added (e.g. to the reaction mixture)Homologues; the manufacturer: akzo Nobel) and less EDA or homologues thereof.

The coupling agent may also be applied separately by first activating the metal surface with caustic soda (by a washing procedure) and thereafter degreasing the surfaces together in the presence of the coupling agent. In this case, coupling agents are present in particular for the adhesion of the metal to the coating.

Example 3

Slow curing 2K systems

Mixture 1: 15 g of the tautomeric Flexlink were melted in an oven (70-90 ℃), mixed with 15 g of an epoxy curing agent (Epikote 827/828 or 1001) and homogenized.

Optionally, 0.5 to 3 grams of a coupling agent (e.g., trialkoxyglycidylsilane) is added to the mixture for improving adhesion on the metal surface.

Mixture 2: in a separate cup 15 grams of cocopropylenediamine (Duomeen CD) or other Duomeen type (monosubstituted propylenediamine homolog) were prepared. The two mixtures were mixed with each other. A slightly exothermic reaction occurred, so that the temperature rose to about 30-50 ℃.

The coating system is applied as a thin layer coating to the surface of, for example, wood, metal or other materials, for an operating time of at least several hours, as a filler, a backing or as an adhesive. After drying at room temperature for 10-15 hours, the system hardens. These 2K systems can also be sprayed and mixed in a nozzle for professional application.

If greater elasticity is desired in the final cure system, 2-5 grams of thioplastEPS may be added, and/or less epoxide may be used (e.g., 13-10 grams instead of 15 grams).

For example, TETA and less Duomeen homologues may be added if shorter operating times are desired, e.g., half an hour rather than several hours.

The coupling agent may also be applied separately by first activating the metal surface with caustic soda (by a washing procedure) and thereafter degreasing the surfaces together in the presence of the coupling agent. In this case, coupling agents are present in particular for the adhesion of the metal to the coating.

If water-repellent properties (anti-corrosion etc.) are required, aliphatic (poly) amines and derivatives thereof may be used. A variety of amines were tested for each of the amines,tri-and linear and branchedGood results were obtained (monosubstituted tripropylene tetramine, manufacturer: Akzo Nobel).

By using a combination of different amines, such as short chain amines and fatty amines, the curing time is adjustable. Jeffamines (polyoxyalkyleneamines), dendrimers and/or polyaminoamides may also be used.

Example 4

Nanotechnology application for three-dimensional automated landscape formation

The composition of example 3 was used as a base formulation.

To the mixture 1 (imide/epoxy moiety) was additionally added 0.1 to 10% m/m, preferably 0.5 to 5% m/m, most preferably 1 to 4% m/m of the modified hydrotalcite F100 and thoroughly mixed. 4 grams of HTC F100 were added to mixture 1.

This mixture 1 was aged for at least half an hour to defoliate (defoliation) before being mixed with mixture 2.

The mixture, operating for several hours, is coated on metal (aluminum or stainless steel), wood, concrete or other surfaces.

Standing (drying) for 5-10 hours at room temperature to automatically form an automatic landscape. After 24 hours, a dry three-dimensional clear coating having an alligator skin appearance was obtained. Optionally, 0.1-1% dye or 20-30% pigment may be added for providing an aesthetic color. Color bodies are mainly concentrated on islands and rarely on (street) streets. This means that an aesthetically pleasing color distribution and separation is also obtained.

Claims (13)

1. A peroxide-free curing system comprising 20 to 89.5 weight percent of a compound having at least one epoxy group, 0.5 to 30 weight percent of a polyamine, and 10 to 50 weight percent of a co-curing agent, wherein the co-curing agent has the formula I:

and/or tautomeric forms thereof, IIa and/or IIb:

and/or formula III:

or a tautomer thereof;

and/or oligomers thereof; wherein

D represents branching (CR)₁R₂)_nOr

Wherein p is independently 0 or 1, and X is CH₂O or SO₂Andrepresents a meta-or para-phenyl group;

r is independently H or C_1-4An alkyl group; r₁And R₂Independently is H or (CH)₂)_mCH₃(ii) a Wherein at least one group R₂Is (CH)₂)_mCH₃And m is 0 to 2; n is 1 to 10; and n + m is 4 to 14; r' -CH₂Is R; and P represents phenyl or C unsubstituted or substituted by hydroxy_1-6Alkyl or C_2-6An alkenyl group; with the proviso that at least one R is C_1-4An alkyl group.

2. The curing system according to claim 1 wherein R is methyl and R' is H.

3. The curing system according to claim 1, wherein 6 to 50% of the co-curing agent has the formula IIa and/or IIb.

4. A curing system according to claim 2, wherein 6 to 50% of the co-curing agent has formula IIa and/or IIb.

5. The curing system of claim 1 comprising 20 to 40% by weight of the composition of a co-curing agent.

6. A curing system according to claim 2 comprising 20 to 40% by weight of the composition of a co-curing agent.

7. The curing system of any of claims 1 to 6, wherein the co-curing agent has a structural moiety D representing a branched C6-alkylene group, or wherein the co-curing agent is 1, 3-bis (citraconimidomethyl) benzene.

8. The curing system according to any one of claims 1 to 6, further comprising nanoparticles and/or adhesion improvers.

9. The curing system according to claim 7, further comprising nanoparticles and/or adhesion improvers.

10. A coating comprising a crosslinked polymer obtainable from the curing system of any one of claims 1 to 9, wherein the compound having at least one epoxy group is crosslinked by the polyamine.

11. A method of curing the curing system of any one of claims 1-9 by heating the curing system to a temperature and for a time sufficient to co-cure the co-curing agent, the compound having at least one epoxy group, and the polyamine.

12. The method of claim 11, wherein the curing is performed at a temperature of less than 130 ℃.

13. The method of claim 12, wherein the curing is performed at room temperature.