WO2009128957A1

WO2009128957A1 - Water-reducible radiation-curable acrylate oligomers and their cured coatings

Info

Publication number: WO2009128957A1
Application number: PCT/US2009/002469
Authority: WO
Inventors: Michael L. Gould; Sheldon X. Zhang; Hilbert Esselbrugge
Original assignee: Ashland Licensing And Intellectual Property Llc
Priority date: 2008-04-18
Filing date: 2009-04-21
Publication date: 2009-10-22

Abstract

The invention pertains to multifunctional acrylate oligomers comprising the reaction product of a Michael donor and an acceptor wherein the multifunctional acrylate oligomer is hydrophilic. The Michael donor and/or acceptor may be ethoxylated. The multifunctional acrylate oligomers may be incorporated into coating compositions and water may be used for viscosity reduction. The coating compositions are typically curable, by chemical means, thermally or by the application of energy, such as, by exposure to ultraviolet radiation or electron beam radiation.

Description

WATER-REDUCIBLE RADIATION-CURABLE ACRYLATE OLIGOMERS AND THEIR CURED COATINGS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Patent Application No. 61/124,706, filed April 28, 2008. U.S. Patent Application No. 61/124,706 is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The invention concerns water-reducible multifunctional acrylate oligomers formed by the reaction of acrylate monomers and oligomers with β- keto esters (e.g., acetoacetates), β-diketones (e.g., 2,4-pentanedione), β-keto amides (e.g., acetoacetanilide, acetoacetamide), and/or other β-dicarbonyl compounds that can participate in the Michael addition reaction as Michael donors. The constituents of the Michael addition reaction impart hydrophilicity to the resulting oligomer. The invention further pertains to coatings comprising multifunctional acrylate oligomers. Background of the Invention

[0003] Multifunctional acrylates and methacrylates are commonly utilized in the preparation of crosslinked films, adhesives, foundry sand binders, composite materials, and the like. Uncrosslinked resins prepared via the Michael addition reaction of β-dicarbonyl compounds with multifunctional acrylates have been disclosed in the art. For example, trimethylol propane triacrylate (TMPTA) can be reacted in a 2:1 molar ratio with ethyl acetoacetate (EAA) in the presence of 1 ,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to make the photoactive oligomer shown in Fig. 1.

[0004] An advantage of energy-cured acrylic systems is that such systems can be applied and cured with little or no solvent, thus reducing the total amount of HAPS/VOCs released to the environment. A limitation in solvent-free coating systems, however, is achieving sufficient wetting and laydown of liquid films at viscosities suitable for spray application and other typical applications. Medium molecular weight oligomers typically provide robust physical properties to their cured formulated coatings. But, with higher molecular weight comes higher viscosity, in most cases. The viscosity may be reduced with diluent monomers (e.g., HDDA, NPGDA, DPGDA, TRPGDA, etc.) although this often gives rise to worker exposure issues. Thus, when monomer exposure is of concern and if the advantages of solvent-free application are desired, solvent other than organic solvent, such as water, must be chosen to moderate viscosity and improve coating performance.

[0005] Water, however, may not be an effective option to reduce the viscosity for typical oligomers and many monomers as a milky, unstable suspensions of particles generally result. This is, for example, the result when water is used to decrease the viscosity of the Michael oligomer discussed above that is shown in Fig. 1. When the Michael addition oligomer of Fig. 1 is mixed with water to reduce viscosity the formation of large particles with significant settling results in a matter of minutes. Such results when viscosity thinning with water are disadvantageous for many practical applications.

[0006] All parts and percentages set forth in this specification are on a weight by weight basis unless otherwise specified. SUMMARY OF THE INVENTION

[0007] The water-reducible multifunctional acrylate oligomers are formed through the Michael addition reaction between Michael "acceptors", such as acrylate monomers and oligomers, and Michael "donors", such as β-keto esters (e.g., acetoacetates), β-diketones (e.g., 2,4-pentanedione), β-keto amides (e.g., acetoacetanilide, acetoacetamide), and/or other β-dicarbonyl compounds that can participate in the Michael addition reaction as Michael donors. The constituents of the Michael addition reaction, i.e. the acceptor and/or donor compounds, have structural features that impart hydrophilicity to the resulting oligomer.

[0008] In a particular embodiment, the acceptor compounds and/or Michael donor compounds in the Michael addition reaction comprise non-charged moieties, typically ethoxylated species, which results in an oligomer that is hydrophilic. In this embodiment, the ethoxylated chain segments impart water affinity to each molecule and levels of ethylene oxide concentrations will impart sufficient water affinity to develop hydrophilicity. The reaction product may be in the form of a stable emulsion, such as a water-in-oil emulsion or an oil-in- water emulsion, depending on the level of water dilution. [0009] The oligomers resulting from the Michael addition reaction between ethoxylated Michael donors and/or acceptors can by cured by chemical means, thermally, or by the application of energy, such as exposure to UV or electron beam radiation. Generally low doses of UV radiation under standard UV-cure conditions, with or without prior removal of water, and with or without photoiniators will cure the oligomers. Thus, resins comprising the oligomer compounds can be used as coatings for a variety of substrates including metal, plastic, wood, paper, glass and the like, in addition to other substrates as would be appreciated by one skilled in the art. Final film properties (e.g., water sensitivity, solvent resistance, hardness, scratch resistance and the like, to name a few) will dictate whether or not water removal prior to cure is necessary.

[0010] Formulations comprising the resins and oligomers may further comprise other functional materials, additives and fillers. For example, such formulations may comprise both reactive materials (like conventional polyacrylates) and non-reactive materials (like solvents) to enhance the coating properties. These additives include a variety of acrylic monomers and oligomers, primary and secondary amines, organonitro compounds, acid-functional monomers and oligomers, organic and inorganic fillers, silicones, waxes and elastomers, among others. Thus, the invention encompasses coating formulations comprising at least^' the oligomers disclosed herein as well as formulations comprising the oligomers, the functional additives and fillers as discussed herein, and, optionally, other materials which would be recognized by one skilled in the art as beneficial in coating formulations.

[0011] In certain applications viscosity thinning of the oligomer resulting from the Michael addition reaction between ethoxylated Michael donor and/or acceptor and/or resins comprising these oligomers require thinning, i.e. reduction in viscosity. The oligomer and/or resin may be thinned with solvent, in particular water. In certain embodiments, relatively little amounts of water can provide a significant reduction in oligomer viscosity, thereby making application by spray, flood coat or gravure techniques practical. An example of an application is UV lithographic inks from self-photoinitiating resins, in particular, for food applications, such as incorporation of the oligomers into lithographic ink formulated, either alone or with other monomers, such as, propoxylated glycerol triacrylate, for food packaging applications. DETAILED DESCRIPTION OF THE DRAWINGS [0012] Fig. 1 shows a reaction sequence comprising trimethylol propane triacrylate (TMPTA) reacted in a 2:1 molar ratio with ethyl acetoacetate (EAA) in the presence of 1 ,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to make a prior art photoactive oligomer which is then combined with monomer and solvent and subjected to UV radiation to form a cured network. [0013] Fig. 2 shows a reaction sequence comprising ethoxylated trimethylol propane triacrylate (TMPTA) having an ethoxylation number of 3 reacted in a 2:1 molar ratio with ethyl acetoacetate (EAA) in the presence of 1,8- diazabicyclo [5.4.0]undec-7-ene (DBU) to make a photoactive oligomer in accordance with the invention which can then be combined with monomer and solvent and subjected to UV radiation to form a cured network. [0014] Fig. 3 shows a reaction sequence comprising trimethylol propane triacrylate (TMPTA) reacted in a 2:1 molar ratio with an ethoxylated methoxy polyethylene glycol (MPEG) having an ethoxylation number of 5.2 in the presence of 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) to make a photoactive oligomer in accordance with the invention which is then combined with monomer and solvent and subjected to UV radiation to form a cured network. [0015] Fig. 4 shows a reaction sequence comprising ethoxylated trimethylol propane triacrylate (TMPTA) having an ethoxylation number of 3 reacted in a 2:1 molar ratio with an ethoxylated methoxy polyethylene glycol (MPEG) having an ethoxylation number of 5.2 in the presence of 1 ,8-diazabicyclo [5.4.0]undec- 7-ene (DBU) to make a photoactive oligomer in accordance with the invention which is then combined with monomer and solvent and subjected to UV radiation to form a cured network.

DETAILED DESCRIPTION OF THE INVENTION

[0016] One or more of the acceptors and/or Michael donors applied in the Michael addition reaction which results in the oligomer is preferably ethoxylated. For example, the reaction can proceed with a) one or more acceptors that are not ethoxylated and one or more Michael donors wherein at least one Michael donor is ethoxylated, b) one or more acceptors, wherein at least one acceptor is ethoxylated, and one or more Michael donors that are not ethoxylated or c) one or more acceptors and one or more Michael donors wherein at least one acceptor and at least one Michael donor is ethoxylated. In embodiments of the invention, the ethoxylated species in the reaction, i.e. the ethoxylated acceptor and/or ethoxylated Michael donor, has an ethoxylation number (EO) of between about 1 and about 30. The reaction results in an ethoxylated oligomer and/or resin comprising an ethoxylated oligomer which has water affinity and/or is hydrophilic.

[0017] An embodiment of the invention concerns an oligomer comprising three ethylene oxide side chain units, made by the reaction sequence shown in Fig. 2. The Michael addition reaction oligomer shown in Fig. 2 possesses a greater degree of water affinity than non-ethoxylated compounds, such as the prior art oligomer discussed above and shown in Fig. 1 , but may not possess as much water affinity as other ethoxylated Michael addition reaction oligomers, such as those of Fig. 3 and Fig. 4. The ethoxylated oligomer resulting from the reaction sequence shown in Fig. 2 is capable of aqueous viscosity reduction as a "water-in-oil" emulsion that is stable enough for coating over a period of hours. Based on the turbidity of the emulsion the inventors theorize without wishing to be bound to any theory, that water forms discreet domains within the mixture stabilized by the ethoxylated side chains of the starting monomer. Separation of resin from water occurs very slowly over a period of hours. [0018] In a further embodiment, non-ethoxylated (i.e., hydrophobic) trimethylol propane triacrylate (TMPTA) monomer is reacted with an ethoxylated (i.e., hydrophilic) Michael donor as shown in Fig. 3 to create an ethoxylated oligomer. The degree of ethoxylation is controlled by selection of the starting methoxy polyethylene glycol (MPEG) alcohol prior to acetoacetylation. In this case, reduction with water is very efficient and the resulting "water-in-oil" mixture is completely clear. Based on the lack of turbidity the inventors theorize without wishing to be bound to any theory that the mixture is very stable, owing in large part to the 'surfactant-like' EO tail on each oligomer. Separation of resin from water occurs, generally over a period of days. [0019] In another embodiment, a hydrophilic ethoxylated Michael acceptor (TMPEO3TA) having three ethoxylation molecules per unit is reacted, as shown in Fig. 4, with an ethoxylated hydrophilic Michael donor methoxy polyethylene glycol 350 acetoacetate (MPEG350AA), having an ethoxylation number of 5.2, to form a completely water-soluble oligomer. This oligomer remains clear and stable at any level of dilution in water. The oligomer may remain clear and stable even weeks after mixing at ratios up to about 25% resin to about 75% water. [0020] The invention demonstrates the advantageous use of these uncrosslinked resins alone or modified by reaction/blending with additional materials in water-reducible coating formulations on a variety of substrates. These additional materials include a variety of acrylic monomers and oligomers, primary and secondary amines, organonitro compounds, acid- functional materials, siloxanes, elastomers, waxes and others to modify and improve coating performance.

[0021] The oligomers of the invention can be cured by all methods typically used to crosslink acrylic materials, though most advantageously by exposure to UV radiation. Cure, or crosslinking, is usually accomplished through a free radical chain mechanism, which may require any of a number of free radical- generating species such as peroxides, hydroperoxides, REDOX complexes, and the like, which decompose to form radicals when heated, or at ambient temperature in the presence of amines or transition metal promoters. Electron beam (EB) radiation is another energy source suitable for initiating reaction of acrylic moieties.

[0022] The oligomers described herein, particularly the ethoxylated oligomers, offer significant advantages over traditional multifunctional acrylic oligomers. For example, viscosity can be reduced by either diluent monomers or water and the oligomers can be cured upon exposure to UV radiation without additional photoinitiator. The amount of water necessary for a desired viscosity reduction will be a function of the specific application, such as a specific coating application technique. The amount of water needed for effective viscosity reduction may be low, in certain embodiments about 5% to about 10% water by weight may be sufficient for effective viscosity reduction. [0023] The resins and blends disclosed herein exhibit performance properties that make them effective coating materials and these properties can be modified greatly depending upon composition. Resins can be produced that show excellent adhesion to metals, plastics, wood, paper and glass while exhibiting wide ranges of hardness, toughness, flexibility, tensile strength, stain resistance, scratch resistance, impact resistance, solvent resistance, and the like. Nearly any desired coating performance parameter can be attained by proper selection of raw material building blocks.

EXAMPLES

[0024] The resin products described in the following examples can be "reduced" with common solvents or water for spray application to substrates, or applied at 100% solids by means consistent with article shape and constitution. Application of the resins to a variety of substrates in these examples was accomplished by the "draw down" technique to produce films of varying thickness, unless otherwise noted. Cure was affected by exposure to a single 600W Fusion "H" bulb at the specified dose. Impact, water and chemical resistance assessments were done on steel panels; adhesion is substrate- specific as indicated.

[0025] Resin performance properties were measured by a variety of different test methods. For purposes of defining properties by means familiar to others skilled in the art, the following test methods were utilized:

Property J ASTM or Measurement Method

Dynamic Viscosity (Poise @ i Brookfield CAP 2000 cone and plate temperature) I viscometer

[0026] The following are the evaluation protocol and criteria utilized for assessment of resins in the following examples:

Dynamic Viscosity - value in Poise at the defined temperature and water level based on constant shear cone and plate measurement.

Cure Response - value assignment of 1 (wet; uncured), 2 (sticky), 3 ("greasy surface", easily marred), 4 (tack-free, can be marred with cotton swab), or 5 (tack-free/mar-free) based on assessment of coating following exposure to defined dose.

MEK resistance - Number of MEK double rubs required to break through or significantly mar the coating.

Water "Flash" - 5 minutes at 5O⁰C (forced air oven with open door).

Water Sensitivity - qualitative observation of "blushing", erosion or blistering after 60 minute exposure to deionized water at room temperature (under a watch glass).

[0027] The following examples illustrate the constitution, application, cure and performance properties of the multifunctional acrylate oligomers.

Example 1 (Comparative) [0028] Trimethylol propane triacrylate (TMPTA), ethyl acetoacetate (EAA) and diazabicycloundecene (DBU) were combined in the reaction sequence shown in Fig. 1 according to the methods described in U.S. Patent Nos. 5,945,489 and 6,025,410, which are incorporated in their entirety herein by reference, to obtain the oligomer shown in Fig. 1 and discussed above. The reactor temperature was set to 80 ⁰C and held at that temperature for approximately four hours. When the reaction was judged to be complete according to refractometry, the resin was discharged from the reactor and allowed to cool. Neat resin viscosity at room temperature was measured by a Brookfield viscometer (spindle # 4, 50 rpm). Additional resin samples were diluted with deionized water to 95% and 90% solids and their viscosities were determined and compiled in the data table below. The neat and water-reduced resin products were applied to steel panels and irradiated with UV light from a medium pressure mercury lamp (Fusion "H" bulb) at a total dose of 500 mJ/cm². Table 1 provides the results of the performance testing for the resins and cured films of this example. Water is not effective to reduce viscosity of this oligomer.

Table 1

Example 2

[0029] Hydrophilic monomer, ethoxylated trimethylol propane triacrylate (TMPEO3TA), ethyl acetoacetate (EAA) and diazabicycloundecene (DBU) were combined in the reaction sequence shown in Fig. 2 in accordance with the methods described in Example 1 and the incorporated references to obtain the oligomer shown in Fig. 2 and discussed above. Resin samples were characterized neat and diluted with deionized water to 95% and 90% solids. The neat and water-reduced resin products were then applied to steel panels and cured with a single UV dose of 500 mJ/cm². Table 2 provides the results of the performance testing for the resins and cured films of this example.

Table 2

Example 3

[0030] Trimethylol propane triacrylate (TMPTA), ethoxylated hydrophilic Michael donor, methoxy polyethylene glycol 350 acetoacetate (MPEG350AA) and diazabicycloundecene (DBU) were combined in the reaction sequence shown in Fig. 3 in accordance with the method described in Example 1 and the incorporated references to obtain the oligomer shown in Fig. 3 and discussed above. Resin samples were characterized neat and diluted with deionized water to 95% and 90% solids. The neat and water-reduced resin products were then applied to steel panels and cured with a single UV dose of 500 mJ/cm². Table 3 provides the results of the performance testing for the resins and cured films of this example. Water is very effective in reducing viscosity of this oligomer.

Table 3

Example 4

[0031] Hydrophilic monomer, ethoxylated trimethylol propane triacrylate (TMPEO3TA), hydrophilic Michael donor, ethoxylated methoxy polyethylene glycol 350 acetoacetate (MPEG350AA), and diazabicycloundecene (DBU) were combined in the reaction sequence shown in Fig. 4 in accordance with the methods described in Example 1 and the incorporated references to obtain the oligomer shown in Fig. 4 and discussed above. Resin samples were characterized neat and diluted with deionized water to 95% and 90% solids. The neat and water-reduced resin products were then applied to steel panels and cured with a single UV dose of 500 mJ/cm². Table 4 provides the results of the performance testing for the resins and cured films of this example. Water is completely effective in reducing viscosity of this oligomer. Table 4

[0032] In the examples, the self-initiating photocurable oligomers that range in degree of water affinity (from dispersible with limited emulsion stability to highly water soluble and stable in solution) were made via the Michael addition reaction of β-ketoesters and polyacrylate monomers. The more highly hydrophilic the Michael donor, the more soluble and stable the final oligomer in aqueous media. Water sensitivity of cured films followed the inverse trend. [0033] An additional benefit of cured films made from these oligomers is that they are very tough and flexible, much more than would be expected from standard free radical-cured acrylic systems based on ethoxylated monomers. Degree of cure can be influenced by additional components in order to boost cure response (i.e., cure "speed") on lines with or without infrared, RF or standard "driers".

Claims

CLAIMSWe claim:

1. A multifunctional acrylate oligomer comprising the reaction product of a Michael donor and an acceptor wherein the multifunctional acrylate oligomer is hydrophilic.

2. The multifunctional acrylate oligomer of claim 1 wherein the reaction product is a water-in-oil emulsion or an oil-in-water emulsion.

3. The multifunctional acrylate oligomer of claim 1 wherein the Michael donor is a β-dicarbonyl compound.

4. The multifunctional acrylate oligomer of claim 1 wherein the β- dicarbonyl compound is selected from the group consisting of β- keto esters, β-diketones and β-keto amides.

5. The multifunctional acrylate oligomer of claim 1 wherein the acceptor is selected from the group consisting of acrylate monomers and oligomers.

6. The multifunctional acrylate oligomer of claim 1 wherein either a) at least one Michael donor is ethoxylated, b) at least one acceptor is ethoxylated, or c) at least one Michael donor and at least one acceptor are ethoxylated.

7. The multifunctional acrylate oligomer of claim 6 wherein the ethoxylated Michael donor or the ethoxylated acceptor has an ethoxylation number between about 1 and about 30.

8. The multifunctional acrylate oligomer of claim 6 wherein both the ethoxylated Michael donor and the ethoxylated acceptor have an ethoxylation number between about 1 and about 30.

9. The multifunctional acrylate oligomer of claim 1 wherein the acceptor comprises ethoxylated trimethylol propane triacrylate.

10. The multifunctional acrylate oligomer of claim 1 wherein the Michael donor comprises ethoxylated methoxy polyethylene glycol.

11. The multifunctional acrylate oligomer of claim 1 further comprising water.

12. A coating formulation comprising the multifunctional acrylate oligomer of claim 1 , functional additives and fillers.

13. The coating formulation of claim 12 wherein the viscosity of the multifunctional acrylate oligomer is decreased by the addition of water to the coating formulation.

14. The coating formulation of claim 13 wherein the amount of water is about 5% to about 10% by weight.

15. A method of curing a composition comprising the steps of a. providing a coating composition having i) a multifunctional acrylate oligomer comprising the reaction product of a Michael donor and an acceptor wherein the multifunctional acrylate oligomer is hydrophilic and ii) water; and b. curing the coating composition.

16. The method of claim 15 wherein the curing is accomplished by exposing the coating composition to ultraviolet radiation or electron beam radiation.

17. The method of claim 15 wherein either a) at least one Michael donor is ethoxylated, b) at least one acceptor is ethoxylated, or c) at least one Michael donor and at least one acceptor are ethoxylated.

18. The method of claim 15 wherein the coating composition comprises about 5% to about 10% by weight water.

19. A cured composition made by the method of claim 15.

20. An ultraviolet curable lithographic ink comprising the multifunctional acrylate oligomer of Claim 1 and propoxylated glycerol triacrylate.