PL244107B1 - Method for producing an epoxy(meth)acrylate varnish binder and a film-forming composition based on an epoxy(meth)acrylate binder - Google Patents

Abstract

The subject of the application is a method for producing an epoxy(meth)acrylate varnish binder, which consists in a solvent-free reaction of the addition of (meth)acrylic acid to compounds containing epoxy groups in an inert gas atmosphere, at elevated temperature, in the presence of a catalyst and an inhibitor of (meth)acrylic acid polymerization. The essence of the invention is that 1,4-cyclohexyl dimethanol diglycidyl ether is used as a compound containing epoxy groups, and the molar ratio of epoxy groups to carboxyl groups is 1:1. The addition reaction is carried out at a temperature of 70°C - 130°C. and ends with an acid number below 30 mg KOH/g, obtaining a cycloaliphatic epoxy(meth)acrylate resin with at least two functional groups, including at least one epoxy and at least one acrylic. The subject of the application is also a coating composition based on an epoxy(meth)acrylate binder, containing a photoinitiator, which is characterized by containing an epoxy(meth)acrylate varnish binder obtained according to the method described above in an amount from 30 to 99.9% by weight, a radical photoinitiator and/or cationic in an amount from 0.1 to 7% by weight and photoreactive additives in an amount from 0 to 70% by weight, with the percentage of all components of the varnish composition being 100%.

Description

The subject of the invention is a method for producing an epoxy(meth)acrylate varnish binder and a coating composition based on an epoxy(meth)acrylate binder.

Photoreactive resins are increasingly used in industry due to the practical, economic and ecological advantages of their hardening process. Among them, the most noteworthy are epoxyacrylate resins, which combine the advantages of epoxy and (meth)acrylate resins and are characterized by a favorable set of mechanical properties combined with chemical and thermal resistance. Newly developed photoreactive epoxyacrylate varnish binders containing both epoxy and (meth)acrylate groups in the molecule are obtained using a solvent-free method in a one-step process involving the addition of acrylic or methacrylic acid to 1,4-cyclohexyldimethanol diglycidyl ether. New epoxyacrylates can be the basis of photoreactive varnish compositions that can be hardened according to two different photopolymerization mechanisms (cationic and radical). From the description of the invention US3989610A, a photoreactive composition based on epoxyacrylate resins is known, used to produce protective films that can be used for the production of printed circuit boards, for precise metalworking or as components of adhesives, paints, etc. The ingredients of this composition are mainly compounds (meta )acrylate, a photoinitiator capable of polymerizing unsaturated (meth)acrylate bonds, and also a compound containing at least two epoxy groups and compounds used to harden epoxy groups, i.e. dicyanodiamide, diphenylamines or compounds containing at least two carboxyl groups - polycarboxylic anhydrides and their mixtures. This composition was called epoxyacrylate because it is a mixture of epoxy and acrylate components. Park and co-workers ("Preparation and characterization of dual curable adhesives containing epoxy and acrylate functionalities, Reactive and Functional Polymers 73, 641-646, 2013) produced a series of dually cross-linked mixtures (using ultraviolet radiation and thermal), in which the compositions contain both epoxy and acrylate groups. The developed compositions consist of acrylate derivatives of bisphenol A (vinyl ester resins), glycidyl methacrylate and acrylic acid mixed in various proportions. Moreover, an amine addition reaction catalyst (triethylamine), a cross-linking agent in the form of a multifunctional acrylate monomer (trimethylpropane triacrylate) and a photoinitiator (2-Hydroxy-2-methyl-1-phenyl-1-propanone) are introduced into the mixture in constant amounts.

Some information can be found in the literature regarding the method of obtaining unsaturated epoxyacrylate resins (also known as vinylester resins) which are the product of the addition of (meth)acrylic acid to diglycidyl ether of bisphenol A (DGEBA) or epoxy resins based on bisphenol A, produced by polycondensation of diane with epichlorochydrin in an alkaline medium . Known vinyl ester resins constitute a group of products for the preparation of which acid is used in an amount that is stoichiometric or close to stoichiometric in relation to the epoxy groups. From the publications Matynia T., Kutyła R., Księżopolski J., Kurys K., "Research on the synthesis and properties of unsaturated polyester resins of the vinyl ester type", a method for producing vinyl ester resins based on medium molecular weight solid epoxy resins and methacrylic acid is known, and further its modification with maleic anhydride. The acid addition reactions, used in a stoichiometric amount in relation to the epoxy groups, were carried out in an inert gas atmosphere, using a temperature gradient of 80-120°C, in the presence of an amine catalyst (2,4,6-tris(dimethylaminomethyl)phenol and a methacrylic acid polymerization inhibitor (hydroquinone). From the publication Parsania P. H., Bhat R. D., Patel J. P.: Synthesis and Evaluation of some physical properties of epoxy methacrylate of bisphenol-C: a comparative study with commercial resin Aeropol-7105, Polymer Bulletin (2020) a method for synthesizing epoxymethacrylate is known by reacting methacrylic acid with bisphenol C epoxy resin in a molar ratio of 2:1 mol/mol, at a temperature of 80°C, in the presence of a catalyst (triethylamine). The produced epoxyacrylate resins are characterized by a low acid value of ~6 mg KOH/g, and thus the very high degree of reaction of carboxyl and epoxy groups. From the publication Feng Y., Hu J., Wang F., Qi H., Peng C., Xu Z., Synthesizing promising epoxy acrylate prepolymers applied in ultraviolet adhesives based on esterification reaction, Materials Research Express (2018) and Yildiz Z., Gungor A., Onen A., Usta I., Synthesis and characterization of dual-curable epoxyacrylate binders for polyester cord/rubber applications, Journal of Industrial Textiles (2015) there is a known method for the synthesis of epoxyacrylate binders based on epoxy resins containing bisphenol A by adding acrylic acid stabilized with hydroquinone dropwise.

The description of the invention US3377406A concerns a method for preparing hydroxy-substituted polyesters from epoxy prepolymers having more than one epoxy group, i.e. polyhydric glycidyl-phenolic polyether with a carboxylic acid such as methacrylic acid, in the presence of an onium salt, e.g. products hardened by polymerization of unsaturated groups and their applications, in particular for the production of coatings, adhesives, reinforced plastics, shapes and the like. The description of the invention US 5677398A describes a method for obtaining an epoxyacrylate resin from a carboxylic acid or its anhydride and an epoxy resin obtained by reacting 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindan with epichlorohydrin in presence of dehydrogenohydrin. According to the description of the invention, it is advantageous to carry out the modification in the presence of a catalyst, inhibitor and solvent. The product is obtained in the form of an epoxyacrylate resin with 100% reacted epoxy groups (for systems in which the molar ratio of epoxy groups to carboxyl groups is 1:1 mol/mol or those in which an excess of acid is used > 1 mol of carboxyl groups) or a resin epoxyacrylate (for systems in which the molar ratio of epoxy groups to carboxyl groups is 1:0.9 mol/mol, it is preferable to use such an undersize that will not significantly affect the quality of the composition hardened by radical polymerization). The final product has an acid value in the range of 20 to 300 mg KOH/g, more preferably in the range of 30 to 250 mg KOH/g, and most preferably in the range of 50 to 150 mg KOH/g. Compositions based on the obtained epoxyacrylate resin are hardened by polymerization of unsaturated groups. An undoubted disadvantage of the method according to the invention from US 5677398A is the use of a solvent in the synthesis process, and thus the need to remove it after the process, e.g. by distillation.

From the description of the invention US 3450613, epoxyacrylates are known containing both epoxy and meth(acrylate) groups in their structure, i.e. there is >1 mole of epoxy groups per 1 mole of carboxyl groups. Moreover, from Park Y.J., Lim D.H., Kim. H.J., Park D.S., Sung I.K., "UV and thermal-curing behaviors of dual-curable adhesives based on epoxy acrylate oligomers" (International Journal of Adhesion & Adhesives 29, 710-717, 2009) there is a known method for synthesizing epoxyacrylate based on diglycidyl ether bisphenol A (DGEBA) and acrylic acid, using the catalyst - triphenylphosphine (TPP). Epoxyacrylates were obtained from 0.2; 0.4; 0.6; 0.8 and 1 molar ratio of acrylic acid to DGEBA epoxy groups. The authors of the discussed work do not provide information on the reaction conditions and the amount of catalyst. From Cho C. H., Son I., Yoo J. Y., Kim J. H., Lee B., Moon G., Lee E., and Lee J. H. "New UV/heat dual-curable sealant containing acrylate epoxy hybrid resin for highly adhesive liquid crystal device ” there is a known method of modifying a low-molecular-weight epoxy resin based on bisphenol A with 2-carboxyethyl acrylate, where 1 mole of 2-carboxyethyl acrylate is used per 1 mole of resin. The modifications are carried out in the presence of a catalyst - triphenylphosphine. The reaction product is an epoxyacrylate resin characterized by the presence of two functional groups: epoxy and acrylate. The authors of the discussed work do not provide information on the conditions for carrying out the modification and the amount of catalyst. In the article Srivastava A., Neelam P., Sudha A. and Rai J. S. P. published in Advances in Polymer Technology, Vol. 24, 1-13 (2005), the authors discussed the influence of tertiary amines: triethylamine, tripropylamine and tributylamine on the mechanism and kinetics of the reactions occurring in the system: epoxy resin based on bisphenol A - methacrylic acid. The final reaction product was an epoxy resin with a ratio of epoxy groups to carboxyl groups of 1/0.4 mol/mol. Products known from patent US 3450613, publication Park Y.J. et al., Cho C.H. et al., Srivastava A. et al. concern the synthesis of epoxyacrylates based on diglycidyl ethers or low molecular weight epoxy resins based on bisphenol A. Only a few literature items concern the modification of epoxy resins with a larger number of functional groups, e.g. by reacting a trifunctional epoxy resin based on 4-(3,3-dihydro-7- hydroxy-2,4,4-trimethyl-2H-1-benzopyran-2-yl)-1,3-benzenediol and epichlorochydrin (THBPBTH-EPOXY) with acrylic acid (Photopolymerization kinetics and properties of a trifunctional epoxy acrylate, Li C. , Cheng J., Chang W. and Nie J., Designed Monomers and Polymers, 2013) or by reacting a tetrafunctional epoxy resin based on 4,4'-methylenebis(N,N-diglycydlaniline) (MBDGA) with acrylic acid (Tetra- functional epoxy-acrylate as crosslinker for UV curable resins: Synthesis, spectral and thermomechanical studies, Mohdtadizadeh F., Zohuriaan-Mehr M.J. ShirkavandHadavand B., Dehghan A., progress in Organic Coatings, 2015).

From the description of the invention US2824851A, a liquid composition is known consisting of at least one glycidyl ether containing at least one epoxy group in the molecule, acrylic or methacrylic acid and an amine catalyst in an amount of 0.01-7.0% in relation to the weight of the ether. As a result of thermal hardening, a hard, thermally resistant solid is obtained. In the technology of polymeric materials, the method of ionic cross-linking of epoxy resins in the presence of cationic photoinitiators is also known. L.W. Dickson and A. Singh in the review publication entitled Radiation curing of epoxies, from 1988 (Radtat. Phys. Chem. Vol 31, No 4-6, pp 587-593) described a number of articles on cross-linking of epoxy compounds, epoxyacrylate compounds and mixtures of epoxy compounds with vinyl compounds, using electromagnetic radiation . From the description of the invention EP0843685A4, ionically photopolymerizable compositions are known, consisting of an epoxy resin, a cationic initiator, such as a diaryliodonium or triarylsulfonium salt with specific anions, and an additive increasing the mechanical strength, i.e. a thermoplastic polymer, a thermoplastic oligomer containing hydroxyl or epoxy groups, a reactive plasticizer, an elastomer or their mixture. These compositions are hardened under the influence of high-energy ionizing radiation such as electron beam, X-ray or gamma radiation. In turn, from the description of the invention US4014771A, a composition is known consisting of an epoxyacrylate resin (30-95% by weight), produced by reacting the epoxy component with (meth)acrylic acid, at least one (meth)acrylate ester (5-70% by weight). ) containing 3-6 (meth)acrylate groups in the structure derived from (meth)acrylic acid and alcohol containing 3-6 hydroxyl groups and a radical photoinitiator (0.2-10% by weight in relation to the weight of the resin and ester). This composition is cross-linked by UV radiation, according to the radical mechanism, in a very short time. From the publication of M. Xiao, Y. He, J. Nie (2008): Novel Bisphenol A Epoxide-Acrylate Hybrid Oligomer and Its Photopolymerization, Designed Monomers and Polymers, 11:4, 383-394, compositions based on epoxyacrylate oligomers prepared as a result of the reaction of bisphenol A epoxy resin with (meth)acrylic acid, triarylsulfonium salts, which act as an effective cationic photoinitiator. The authors point out that the salts used are also capable of generating free radicals that initiate the polymerization of unsaturated bonds, therefore they are very suitable for the photopolymerization of epoxyacrylate monomers. It should be noted that the epoxyacrylates that are the subject of our invention are, however, prepared based on cycloaliphatic diglycidyl ether.

The solutions known from the state of the art lack those that allow obtaining binders for the production of varnish coatings by simple synthesis, without the need to add reagents dropwise and without the need to remove the solvent. Additionally, there are no binders in which (meth)acrylate and epoxy groups occur simultaneously, which will enable crosslinking by two separate mechanisms: radical and cationic polymerization.

The method for producing an epoxy(meth)acrylate varnish binder, according to the invention, consists in a solvent-free, one-step reaction of addition of (meth)acrylic acid to compounds containing epoxy groups - 1,4-cyclohexyldimethanol diglycidyl ether, in an inert gas atmosphere, at elevated temperature, in the presence of catalyst and polymerization inhibitor of (meth)acrylic acid. The essence of the invention is that the molar ratio of diglycidyl ether of 1,4-cyclohexyldimethanol to (meth)acrylic acid is equal to 1:1, i.e. the molar ratio of epoxy groups to acrylate groups is equal to 2:1, and the addition reaction is carried out in temperature of 70°C-130°C and ends with an acid number below 30 mg KOH/g, obtaining a cycloaliphatic epoxy(meth)acrylate resin with two functional groups at the same time, including one terminal epoxy and one terminal (methacrylic and formula 1 or with formula 2.

Preferably, the catalyst is used in an amount of 0.1%-1.5% by weight based on the weight of (meth)acrylic acid, and the radical polymerization inhibitor is used in an amount of 0.006%-0.015% by weight based on the weight of ether and acid.

Preferably, triphenylphosphine, triphenylstibine or amine addition reaction catalysts are used as a catalyst.

Preferably, triethylamine, tetrabutylammonium bromide, benzyltriethylammonium chloride, 2,4,6-tris(N,N-dimethylaminomethyl)phenol, 1-benzyl-1,1-dimethylamine, 1,8-diazabicyclo[5.4. 0]undec-7-ene, or triethylbenzyl ammonium chloride.

Preferably, hydroquinone, tert-butylhydroquinone, benzoquinone, diphenylpicrylhydrazyl, phenothiazine or 4-methoxyphenol is used as a radical polymerization inhibitor.

Preferably, the acid is removed after completion of the addition reaction by distillation or extraction, or the product is used without prior purification.

The coating composition based on an epoxy(meth)acrylate binder, according to the invention, contains a photoinitiator and is characterized by the fact that it contains an epoxy(meth)acrylate varnish binder obtained according to the method described above in an amount from 93 to 99% by weight, a radical and/or cationic photoinitiator in amounts from 1 to 7% by weight. The composition may contain a (meth)acrylate oligomer, an epoxy resin and/or a photoreactive diluent (to modify the desired properties). If necessary, varnish compositions may additionally contain auxiliary substances, such as anti-foaming agents, UV absorbers, antioxidants, polymerization inhibitors, wettability improving agents, etc. and inorganic fillers, coloring pigments, dyes, etc. The percentage of all components of the varnish composition is 100%. The percentage of all ingredients of the varnish composition is 100%.

Preferably, the cationic photoinitiator is an onium salt, including an aryl diazonium salt, a diaryl iodonium salt, an alkoxy pyridinium salt, an alkoxy isoquinoline salt, a phosphonium salt, a triarylsulfonium salt, a phenacyl anilinium salt, a phenacyl ammonium salt, a phenyl pyridinium salt or a dialkyl phenacyl sulfonium salt.

Preferably, the radical photoinitiator is an α-hydroxy ketone, an α-hydroxyalkylphenone, an α-aminoalkylphenone or benzoin derivatives.

The composition has the ability to cross-link according to the cationic and radical mechanism, under the influence of UV or LED radiation.

The new varnish binders are characterized by low viscosity, no yellowing and the ability to create varnish coatings hardened in a short time using pro-ecological methods, in the photopolymerization reaction according to the radical or cationic mechanism. Surprisingly, it turned out that the use of 1,4-cyclohexyldimethanol diglycidyl ether also leads to obtaining coatings with excellent properties, in particular coatings with low yellowness, e.g. compared to coatings obtained on the basis of bisphenol A diglycidyl ethers. The varnish composition was obtained on the basis of the newly developed epoxy( meth)acrylate varnish binder creates colorless polymer films that are easily spread in the form of a thin layer with excellent self-leveling ability, and the hardened coatings are characterized by good physicochemical and mechanical properties. The obtained film hardens in a short time under a UV or LED lamp. The coatings obtained in this way can be used to protect against mechanical damage, giving them favorable aesthetic values. Curing coatings using UV/LED technology shortens the time to achieve surface dryness and full hardening of the coating, reduces the energy input of the process and is a pro-ecological solution compared to conventional methods of coating hardening, i.e. chemical hardening, thermosetting, because in each of the mentioned methods the hardening process takes longer, requires increased energy inputs and involves the emission of solvents into the atmosphere. In the proposed invention, the substrate for synthesis is cycloaliphatic diglycidyl ether, and the reaction product is cycloaliphatic epoxyacrylate resin.

The invention is illustrated in more detail by the following embodiments, where examples 1-2 concern new varnish binders and methods of obtaining them, while examples 3-4 concern methods of obtaining coatings based on new compositions. The varnish binders according to the examples presented below were characterized by low viscosity, no yellowing and the ability to create varnish coatings hardened in a short time using pro-ecological methods, in the photopolymerization reaction according to the radical or cationic mechanism.

Example 1

The following substrates are introduced into the reactor equipped with a mechanical stirrer, a temperature measurement probe and a reflux condenser: 1,4-cyclohexyldimethanol diglycidyl ether in an amount of 39.3 g (1 mol) and methacrylic acid in an amount of 10.7 g (1 mol) and hydroquinone in the amount of 0.01 and triphenylphosphine in the amount of 0.0869 g. The reaction was carried out at a set temperature of 90°C, in a nitrogen atmosphere, with intensive stirring (120 rpm) for 5 hours. The product had an acid value of 15 mg KOH/g. The unreacted acid is removed from the reaction mixture by extraction.

Example 2

The following substrates are introduced into the reactor equipped with a mechanical stirrer, a temperature measurement probe and a reflux condenser: 1,4-cyclohexyldimethanol diglycidyl ether in an amount of 40.34 g (1 mol) and acrylic acid in an amount of 9.66 g (1 mol) and tert-butylhydroquinone in the amount of 0.005 and 2,4,6-tris(N,N-dimethylaminomethyl)phenol in the amount of 0.128 g. The reaction was carried out at a set temperature of 70°C, nitrogen atmosphere, with intensive stirring throughout (120 rpm). for 7 hours. The product had an acid value of 21 mg KOH/g. Unreacted acid is removed from the reaction mixture by distillation.

Example 3

The photocurable varnish composition for obtaining a coating consists of 9.3 g (93% by weight) of the new epoxy(meth)acrylate varnish binder described in Example 1, and 0.7 g (7% by weight) of a cationic diaryliodonium photoinitiator containing a hexafluoroantimony anion (Sylanto-7MS, Synthos SA, Poland). The composition obtained in this way was applied using a slot applicator with a slot thickness of 120 μm (BYK Gardner) onto an aluminum substrate and cured under a UV lamp (Aktiprint T lamp (Technigraf, Germany), emitting radiation in the UVA range and a radiation dose of 650 mJ/cm ^{2 )} . The created polymer film hardens within 25 seconds, thus creating a durable varnish coating with good aesthetic and decorative properties and high hardness, adhesion, gloss and low yellowness.

Example 4

The photocurable varnish composition for obtaining the coating consists of 9.9 g (99 wt.%) of the new epoxy(meth)acrylate varnish binder described in example 2, and 0.1 g (1 wt.%) of a radical photoinitiator in the form of diphenyl oxide (2,4,6-trimethylbenzyl)phosphines (Omnirad TPOL, IGM resins). The composition obtained in this way was applied using a slot applicator with a slot thickness of 120 μm (BYK Gardner) onto an aluminum substrate and hardened under an LED lamp (365 nm, 36 W). The created polymer film hardens within 60 seconds, thus creating a durable varnish coating with good aesthetic and decorative properties and high hardness, adhesion, gloss and low yellowness.

Claims (10)

1. A method for producing an epoxy(meth)acrylate varnish binder consisting in a solvent-free reaction of the addition of (meth)acrylic acid to 1,4-cyclohexyldimethanol diglycidyl ether in an inert gas atmosphere, at elevated temperature, in the presence of a catalyst and an inhibitor of the polymerization of (meth)acrylic acid, characterized in that the molar ratio of 1,4-cyclohexyl dimethanol diglycidyl ether to (meth)acrylic acid is equal to 1:1, i.e. the molar ratio of epoxy groups to acrylate groups is equal to 2:1, and the addition reaction is carried out at a temperature of 70° C-130°C and ends with an acid number below 30 mg KOH/g, obtaining a cycloaliphatic epoxy(meth)acrylate resin with two functional groups at the same time, including one terminal epoxy group and one terminal (meth)acrylate group and of formula 1 or formula 2. 2. A method for preparing a photoreactive epoxy(meth)acrylate binder according to claim. 1, characterized in that the catalyst is used in an amount of 0.1%-1.5% by weight relative to the weight of (meth)acrylic acid, and the radical polymerization inhibitor is used in an amount of 0.006%-0.015% by weight relative to the weight ether and acid. 3. A method for preparing a photoreactive epoxy(meth)acrylate binder according to claim. 1, characterized in that the catalyst used is triphenylphosphine, triphenylstibine or amine addition reaction catalysts. 4. A method for preparing a photoreactive epoxy(meth)acrylate binder according to claim. 3, characterized in that the amine catalysts used for the addition reaction are triethylamine, tetrabutylammonium bromide, benzyltriethylammonium chloride, 2,4,6-tris(N,N-dimethylaminomethyl)phenol, 1-benzyl-1,1-dimethylamine, 1,8 -diazabicyclo[5.4.0]undec-7-ene, or triethylbenzyl ammonium chloride. 5. A method for preparing a photoreactive epoxy(meth)acrylate binder according to claim. 1, characterized in that the radical polymerization inhibitor is hydroquinone, tert-butylhydroquinone, benzoquinone, diphenylpicrylhydrazyl, phenothiazine or 4-methoxyphenol. 6. A method for preparing a photoreactive epoxy(meth)acrylate binder according to claim. The process of claim 1, wherein the acid is removed after completion of the addition reaction by distillation or extraction. PL 244107 Β1 7. A coating composition based on an epoxy(meth)acrylate binder, containing a photoinitiator, characterized in that it contains an epoxy(meth)acrylate varnish binder obtained according to the method described in claims 1-6 in an amount from 93 to 99% by weight, a radical photoinitiator and/ or cationic in an amount from 1 to 7% by weight, with the percentage of all components of the varnish composition being 100%. 8. Film-forming composition according to claim. 7, characterized in that the cationic photoinitiator is an onium salt, including an aryl diazonium salt, a diaryl iodonium salt, an alkoxy pyridinium salt, an alkoxy isoquinoline salt, a phosphonium salt, a triarylsulfonium salt, a phenacyl anilinium salt, a phenacyl ammonium salt, a phenyl pyridinium salt or a dialkyl phenacyl salt. sulfonate. 9. Film-forming composition according to claim. 7, characterized in that the radical photoinitiator is α-hydroxyketone, α-hydroxyalkylphenone, α-aminoalkylphenone or benzoin derivatives. 10. Film-forming composition according to claim. 7, characterized in that it has the ability to cross-link according to the cationic and radical mechanism, under the influence of UV or LED radiation.