Thermosetting resin composition

Abstract: A thermosetting resin composition comprising i) an advanced resin product obtainable by reacting a) a diglycidylester of an alpha,alpha'-dibranched dicarboxylic acid with b) an alpha,alpha'-dibranched dicarboxylic acid, and ii) a curing compound.

Description: The invention relates to a thermosetting resin composition and to the use thereof, particularly in coatings. Diglycidyl esters of alpha,alpha'-dibranched dicarboxylic acids having both alpha carbon atoms with respect to the carbonyl groups substituted with alkyl, halogen or aryl groups have been described for use in thermosetting resin compositions in US patent No. 3,629,295. These diglycidyl esters were found to have improved hydrolytic stability and resistance to transesterification, presumably due to the presence of the sterically hindered ester linkages. According to said US patent curing of the diglycidyl esters can be performed using any type of polyfunctional curing agent which is capable of adding to an epoxy compound such as primary or secondary amines and carboxylic acid anhydrides. European patent application publication No. 366205 also relates to diglycidyl esters of alpha,alpha'-dibranched dicarboxylic acids. It shows inter alia some favourable properties of castings (good hardness and clear coloured) and of a film (good adhesion to metal and high initial gloss) that were prepared from the diglycidyl ester of thiodipivalic acid using isophoronediamine (IPD) or diphenyldiaminomethane (DDM) as curing agent. However, in spite of the above mentioned advantageous properties inherent to the use of diglycidyl esters of alpha,alpha'-dibranched dicarboxylic acids in the cured resin systems, these systems were found to suffer from a major deficiency i.e. insufficient weathering resistance, which in fact precludes their use in automotive topcoats and in other end uses requiring a high degree of outdoor durability. Therefore it is an object of the present invention to find thermosetting resin compositions based on diglycidyl esters of alpha,alpha'-dibranched dicarboxylic acids which not only show hydrolytic stability and resistance to transesterification but also show improved weathering resistance. The invention therefore relates to a thermosetting resin composition comprising i) an advanced resin product obtainable by reacting a) a diglycidyl ester of an alpha,alpha'-dibranched dicarboxylic acid of the general formula I with b) an alpha,alpha'-dibranched dicarboxylic acid of the general formula II wherein n is 0 or 1, wherein R is independently selected from the group consisting of straight and branched chain alkyl, cycloalkyl, arylalkyl and aryl, or both R's may form part of a substituted or unsubstituted cycloaliphatic ring system comprising 5, 6 or 8 carbon atoms, in which case n should be 0, wherein R 1 is independently a hydrogen atom or a methyl group, wherein R 2 is a single bond, substituted or unsubstituted alkylene or arylene or a radical of the formula III ―(R 3 ) m 1 ―X―(R 3 ) m 2 ― wherein m 1 and m 2 are independently 0 or 1, wherein R 3 is independently selected from the group consisting of substituted or unsubstituted alkylene, and X is a single bond or one of the following bridging groups I to V wherein R 4 is independently selected from the group consisting of C 1 to C 4 alkyl, with the proviso that when X is bridging group (IV), m 1 is 0 and when X is bridging group (V), m 2 = 0 and when n is 0, R 2 is a single bond, the advanced resin having a number average molecular weight in the range of from 600 to 7000 ; and ii) a curing compound selected from the group consisting of amino resins, blocked or unblocked (cyclo)aliphatic isocyanates, alpha,alpha'-dibranched cyclic anhydrides, acid-functional polyesters containing only alpha,-dibranched acid and ester groups, (cyclo)aliphatic amines, (cyclo)aliphatic polyamino amides, blocked or unblocked Lewis acids, and tertiary amines. It was surprisingly found that the combination of i) an advanced resin product of a diglycidyl ester of an alpha,alpha'-dibranched dicarboxylic acid with an alpha,alpha'-dibranched dicarboxylic acid and ii) a curing agent which cures via the hydroxyl and/or epoxy groups of the advanced resin product and which does not form any "weak" ester linkages (which are formed when curing with conventional anhydrides or polycarboxylic acids), has a significant positive effect on the weathering resistance of the resulting cured matrix. Advancing of a) with b) is generally carried out at a temperature of between 60 °C and 160 °C and the molar ratio of a) and b) applied preferably lies within the range of from 0.5 to 2.0. It is preferred to react a) and b) in the absence of a solvent, however, if necessary a non-interfering solvent may be added to the reaction mixture, such as ketones, alcohols, ethers and aromatic hydrocarbons such as toluene and xylene. In general no catalyst is needed in advancing a) with b). However, if required any suitable catalyst may be added to the reaction mixture, for example tertiary phosphines and amines, quaternary phosphonium and ammonium salts and metal salts such as chromium salts. The branched dicarboxylic acid b) may be the same or different branched dicarboxylic acid wherefrom compound a) is derived. If desired mixtures of a) and/or b) can be used. Depending on the ratio of components a) and b) applied in the advancing process the advanced resin product will generally be a mixture of essentially linear compounds carrying carboxy- or epoxy end groups. The number average molecular weight of the advanced product formed by reacting a) with b) generally lies within the range of from 600 to 7000; this of course depends on the sort of starting compounds a) and b) and their molar ratio in the reaction mixture. The advanced resin product may vary from oil type liquid to highly viscous or solid products. Terminal epoxy - or carboxy groups of the advanced resin product may be converted into secondary hydroxyl groups. This can be achieved during the reaction of a) with b) or after completion of the reaction of a) with b). To that end the epoxy end groups can be reacted with a stoichiometric quantity of an alpha-branched monocarboxylic acid such as dimethylolpropionic acid, hydroxypivalic acid or one of the commercially available tertiary monocarboxylic acids containing of from 5 to 10 carbon atoms known as VERSATIC acids (VERSATIC is a trade mark), likewise carboxy end groups can be reacted with a stoichiometric quantity of a monoglycidyl ester of an alpha-branched monocarboxylic acid such as for example one of the commercially available glycidyl esters of the VERSATIC acids, known as CARDURA (CARDURA is a trade mark). Compounds a) can be prepared by methods known in the art e.g. as described in US patent No. 3,644,431. As preferred compounds a) and b) can be mentioned those wherein R is C 1 to C 4 alkyl, R 1 is hydrogen, R 3 is C 1 to C 4 alkyl. R 4 is methyl and X is a single bond or a sulpho group. Typical compounds a) are the diglycidyl esters of dimethylmalonic acid, diethylmalonic acid (DEMA), dibenzylmalonic acid, tetrapropyladipic acid (TPAA), tetramethylenecyclohexyladipic acid, 1,1-dicarboxy-2-phenyl-4-methyl cyclohexane, 1,1-dicarboxy-2-ethyl-4-methyl cyclohexane, 2,2,6,6-tetramethyl-3-keto-4-oxapimelic acid and 1,4-dicarboxy-1,4-dimethyl cyclohexane. Preferred compounds a) are the diglycidyl esters of DEMA TMAA and TPAA. Similarly, typical and preferred compounds b) are the dicarboxylic acids mentioned above in connection wiht the typical compounds a). The advanced epoxy resin product can be used alone or in combination with other curable epoxy resin compounds in the thermosetting resin composition of the invention. The thermosetting resin composition of the invention comprises a curing compound which cures via the hydroxyl and/or epoxy groups of the advanced product, in such a way that ether, amine, urethane or alpha,-dibranched ester linkages are formed but unbranched ester linkages are avoided. Typical curing agents are melamine-formaldehyde resins, urea-formaldehyde resins, glycoluryl resins, alcohol-blocked isophorone diisocyanates, 3,3,4,4-tetramethylsuccinic anhydride, isophorondiamine. Versamid 100 (an aminoamide), dicyandiamide, borontrifluoride-ethylamine complex, and N,N,N',N'-tetramethyl-1,6-diaminohexane. A particularly preferred curing compound is hexamethoxymethylmelamine (HMMM). Depending on the choice of curing compound the cure can be effected in one or more cycles at temperatures of from 80 °C to 200 °C, preferably of from 140 to 170 °C for a period of from 5 to 30 minutes. Although cross linking mainly takes place between the OH groups and the curing compound, the epoxy or carboxy end groups present in the advanced resin product may also participate in the cross-linking. It is furthermore possible to use accelerators in the curing reaction, suitable accelerators for amino type curing agents are e.g. acids such as phosphoric acid, para-toluene sulphonic acid (pTsa), Lewis acids and blocked Lewis acids such as BF 3 -amine adducts; suitable accelerators for isocyanate type curing agents are e.g. tertiary amines, phosphines and metal salts such as dibutyl tindilaurate. The thermosetting resin composition of the invention may further at any stage before cure be mixed with usual modifiers such as extenders, fillers pigments, dyestuffs, organic solvents, flow control agents and agents for conferring thixotropy. Suitable organic solvents useful for modifying the curable thermosetting composition of the invention are e.g. toluene, xylene, n-propanol, butylacetate, acetone, methyl-ethyl ketone, diacetone-alcohol, ethylene glycol monomethyl ether and ethylene glycol monobutyl ether. The thermosetting resin compositions of the invention can be used in solvent or water borne paints as well as in powder coating systems, which can be cured into insoluble and infusible weathering resistant coatings. Due to the α,-dibranched ester structures the resin compositions of the invention are especially suitable for the production of water borne paints of high hydrolytic stability. Typical enduses of the composition of the invention are seen in decorative paint systems e.g. for automotive topcoats. The following examples are presented to illustrate certain specific embodiments of the present invention but are not to be considered limitative thereto. EXAMPLES Advanced resins 1 to 6 according to the invention and 7 to 8 for comparison were prepared as follows: 1. Resin based on DGEDEMA and DEMA General structure: DGEDEMA-[DEMA-DGEDEMA] 3 Composition: a) 4 moles diglycidylester (DGE) of diethylmalonic acid (DEMA) b) 3 moles DEMA Preparation: a+b are reacted at 120 °C for 2.5 hours. Final epoxy group content is 1.25 meq/g and final acid value is < 0.05 meq/g. 2. Resin based on DGETMAA and DEMA General structure: DGETMAA-[DEMA-DGETMAA] 3 Composition: a) 4 moles DGE of 2,2,5,5-tetramethyladipic acid (TMAA) b) 3 moles DEMA Preparation: a+b are reacted at 120 °C for 2.5 hours. Final epoxy group content is 1.15 meq/g and final acid value is < 0.05 meq/g. 3. Resin based on DGESDPA and DEMA General structure: DGESDPA-[DEMA-DGESDPA] 3 Composition: a) 4 moles DGE of sulfodipivalic acid (SDPA) b) 3 moles DEMA Preparation: a+b are reacted at 120 °C for 1.0 hours. Final epoxy group content is 0.91 meq/g and final acid value is < 0.05 meq/g. 4. Resin based on DGETMAA and TMAA General structure: DGETMAA-[TMAA-DGETMAA] 3 Composition: a) 4 moles DGETMAA b) 3 moles TMAA Preparation: a+b are reacted at 140 °C for 1.0 hours. Final epoxy group content is 1.01 meq/g and final acid value is < 0.05 meq/g. 5. Resin based on DGEDEMA and DEMA General structure: DEMA-[DGEDEMA-DEMA] 3 Composition: a) 3 moles DGEDEMA b) 4 moles DEMA Preparation: a+b are reacted at 120 °C for 1.0 hours. Final epoxy group content is < 0.05 meq/g and final acid value is 1.60 meq/g. 6. Resin based on DGEDEMA, DEMA, and V5 General structure: V5-DGEDEMA-[DEMA-DGEDEMA] 3 -V5 Composition: a) 4 moles DGEDEMA b) 3 moles DEMA c) 2 moles pivalic acid (V5) d) catalyst AMC-2 (AMC-2 is a trade mark, available from CORDOVA Chemicals) (0.25% on solid resin) Preparation: a+b+c+d are reacted at 120 °C for 2.5 hours. Final epoxy group content is < 0.05 meq/g and final acid value is < 0.05 meq/g. 7. Resin based on DGEDEMA and AA General structure: DGEDEMA-[AA-DGEDEMA] 3 Composition: a) 4 moles DGEDEMA b) 3 moles adipic acid (AA) c) catalyst AMC-2 (0.25% on solid resin) Preparation: a+b are reacted at 120 °C for 1.0 hours. Final epoxy group content is 1.26 meq/g and final acid value is < 0.05 meq/g. 8. Resin based on DGEDEMA and PA General structure: DGEDEMA-[PA-DGEDEMA] 3 Composition: a) 4 moles DGEDEMA b) 3 moles phthalic acid (PA) c) catalyst AMC-2 (0.25% on solid resin) Preparation: a+b are reacted at 140 °C for 0.45 hours. Final epoxy group content is 1.26 meq/g and final acid value is < 0.05 meq/g. Coating compositions comprising DGEDEMA or one of the advanced resins 1 to 8, HMMM: hexamethoxymethyl melamine (Cymel 301; ex. American Cyanamid Inc.) as curing agent and p-toluenesulphonic acid as catalyst were prepared and applied on bare steel panels type QD-36, size 76x152x5 mm (precoated with a 10 µm thick epoxy primer). The cure schedule employed was 10 min for flash off followed by 10 min at 100 °C and 20 min at 160 °C. The thickness of the top coatings varied from 40 to 50 microns. Properties of the coating compositions are shown in table I. Table I shows the excellent weathering resistance of the coatings comprising the thermosetting resin composition of the invention, (Nos. 1-6) in comparison to the performance of comparative systems 7 and 8 that were based on acids not containing alpha,-dibranching.

Claims: Claims for the following Contracting States : BE, DE, FR, GB, IT, NL, SE A thermosetting resin composition comprising i) an advanced resin product obtainable by reacting a) a diglycidyl ester of an alpha,alpha'-dibranched dicarboxylic acid of the general formula I with b) an alpha,alpha'-dibranched dicarboxylic acid of the general formula II wherein n is 0 or 1, wherein R is independently selected from the group consisting of straight and branched chain alkyl, cycloalkyl, arylalkyl and aryl, or both R's may form part of a substituted or unsubstituted cycloaliphatic ring system comprising 5, 6 or 8 carbon atoms, in which case n should be 0, wherein R 1 is independently a hydrogen atom or a methyl group, wherein R 2 is a single bond, substituted or unsubstituted alkylene or arylene or a radical of the formula III wherein m 1 and m 2 are independently 0 or 1, ―(R 3 ) m 1 ―X―(R 3 ) m 2 ― wherein R 3 is independently selected from the group consisting of substituted or unsubstituted alkylene, and X is a single bond or one of the following bridging groups I to V wherein R 4 is independently selected from the group consisting of C 1 to C 4 alkyl, with the proviso that when X is bridging group (IV), m 1 is 0 and when X is bridging group (V), m 2 = 0 and when n is 0, R 2 is a single bond, the advanced resin having a number average molecular weight in the range of from 600 to 7000; and ii) a curing compound selected from the group consisting of amino resins blocked or unblocked (cyclo)aliphatic isocyanates, alpha,alpha'-dibranched cyclic anhydrides, acid-functional polyesters containing only alpla,alpha'-dibranched acid and ester groups, (cyclo)aliphatic amines, (cyclo)aliphatic polyamino amides, blocked or unblocked Lewis acids, and tertiary amines. A thermosetting resin composition as claimed in claim 1 wherein the molar ratio of compounds a) and b) lies in the range of from 0.5 to 2.0. A thermosetting resin composition as claimed in claim 1 or 2 wherein compound a) is the diglycidyl ester of compound b). A thermosetting resin composition as claimed in any one of the claims 1 to 3 wherein compound b) is reacted with a molar excess of a) in the presence of a stoichiometric quantity of an alpha branched monocarboxylic acid. A thermosetting resin composition as claimed in any one of the claims 1 to 3 wherein compound a) is reacted with a molar excess of b) in the presence of a stoichiometric quantity of a glycidylester of an alpha-branched monocarboxylic acid. A thermosetting resin composition as claimed in any one of claims 4 and 5 wherein the alpha-branched monocarboxylic acid is pivalic acid. A thermosetting resin composition as claimed in any one of the claims 1 to 6 wherein compound a) is selected from the group consisting of the diglycidyl ester of diethylmalonic acid, 2,2,5,5-tetramethyladipic acid and tetrapropyladipic acid. A thermosetting resin composition as claimed in any one of the claims 1 to 7 wherein compound b) is selected from the group consisting of diethylmalonic acid, 2,2,5,5-tetramethyladipic acid, and tetrapropyladipic acid. A thermosetting resin composition as claimed in any one of the claims 1 to 8 wherein the curing compound is selected from the group consisting of melamine-formaldehyde resins, urea-formaldehyde resins, glycoluril resins, and alcohol blocked isophorone diisocyanates. A thermosetting resin composition as claimed in claim 9 wherein the curing compound is hexamethoxymethylmelamine. Claims for the following Contracting State : ES Process for the preparation of a thermosetting resin composition, comprising i) reacting a) a diglycidyl ester of an alpha,alpha'-dibranched dicarboxylic acid of the general formula I with b) an alpha,alpha'-dibranched dicarboxylic acid of the general formula II wherein n is 0 or 1, wherein R is independently selected from the group consisting of straight and branched chain alkyl, cycloalkyl, arylalkyl and aryl, or both R's may form part of a substituted or unsubstituted cycloaliphatic ring system comprising 5, 6 or 8 carbon atoms, in which case n should be 0, wherein R 1 is independently a hydrogen atom or a methyl group, wherein R 2 is a single bond, substituted or unsubstituted alkylene or arylene or a radical of the formula III wherein m 1 and m 2 are independently 0 or 1, wherein R 3 is independently selected from the group consisting of substituted or unsubstituted alkylene, and X is a single bond or one of the following bridging groups I to V wherein R 4 is independently selected from the group consisting of C 1 to C 4 alkyl, with the proviso that when X is bridging group (IV), m 1 is 0 and when X is bridging group (V), m 2 = 0 and when n is 0, R 2 is a single bond; and reacting the obtained advanced resin having a number average molecular weight in the range of from 600 to 7000, with ii) a curing compound selected from the group consisting of amino resins blocked or unblocked (cyclo)aliphatic isocyanates, alpha,alpha'-dibranched cyclic anhydrides, acid-functional polyesters containing only alpha,alpha'-dibranched acid and ester groups, (cyclo)aliphatic amines, (cyclo)aliphatic polyamino amides, blocked or unblocked Lewis acids, and tertiary amines. A process as claimed in claim 1 wherein the molar ratio of compounds a) and b) lies in the range of from 0.5 to 2.0. A process as claimed in claim 1 or 2 wherein compound a) is the diglycidyl ester of compound b). A process as claimed in any one of the claims 1 to 3 wherein compound b) is reacted with a molar excess of a) in the presence of a stoichiometric quantity of an alpha branched monocarboxylic acid. A process as claimed in any one of the claims 1 to 3 wherein compound a) is reacted with a molar excess of b) in the presence of a stoichiometric quantity of a glycidylester of an alpha-branched monocarboxylic acid. A process as claimed in any one of claims 4 and 5 wherein the alpha-branched monocarboxylic acid is pivalic acid. A process as claimed in any one of the claims 1 to 6 wherein compound a) is selected from the group consisting of the diglycidyl ester of diethylmalonic acid, 2,2,5,5-tetramethyladipic acid and tetrapropyladipic acid. A process as claimed in any one of the claims 1 to 7 wherein compound b) is selected from the group consisting of diethylmalonic acid, 2,2,5,5-tetramethyladipic acid, and tetrapropyladipic acid. A process as claimed in any one of the claims 1 to 8 wherein the curing compound is selected from the group consisting of melamine-formaldehyde resins, urea-formaldehyde resins, glycoluril resins, and alcohol blocked isophorone diisocyanates. A process as claimed in claim 9 wherein the curing compound is hexamethoxymethylmelamine.

Inventors: KOOIJMANS PETRUS GERARDUS, SMAARDIJK ABRAHAM ADRIAAN, VERBURG ANTOON, KOOIJMANS, PETRUS GERARDUS, SMAARDIJK, ABRAHAM ADRIAAN, VERBURG, ANTOON
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1992
Main classification: C08G59
IPC codes: C09D163, C08G59