WO2008045892A1

WO2008045892A1 - Cyclic anhydride grafted epoxy resins and thermoset derivatives derived therefrom

Info

Publication number: WO2008045892A1
Application number: PCT/US2007/080843
Authority: WO
Inventors: Maurice J. Marks
Original assignee: Dow Global Technologies Inc.
Priority date: 2006-10-10
Filing date: 2007-10-09
Publication date: 2008-04-17
Also published as: TW200831554A

Abstract

The present invention is directed to the preparation of a self-curing curable epoxy resin composition comprising the reaction product of an epoxy resin starting material containing an initial concentration of cyclic dimer and a sufficient amount of a cyclic anhydride to reduce the concentration of cyclic dimer in the resulting epoxy resin reaction product to a level 50 % or greater than that of the epoxy resin starting material. The compositions of the present invention are cyclic anhydride grafted epoxy resins bearing terminal epoxy groups and having been reacted with sufficient amounts of cyclic anhydride to significantly reduce the concentration of cyclic dimer without causing crosslinking or gelling. These cyclic anhydride grafted epoxy resins form coatings having excellent properties and are useful in various applications including can and coil coatings.

Description

CYCLIC ANHYDRIDE GRAFTED EPOXY RESINS AND THERMOSET DERIVATIVES

DERIVED THEREFROM

Cross-Reference to Related Applications This application claims priority to U.S. Provisional Application Serial No. 60/850,479, filed

October 10, 2006, the contents of which are incorporated by reference in their entirety.

Field of Invention

The present invention relates to cyclic anhydride grafted epoxy resins and thermoset derivatives derived therefrom; and to coatings prepared therefrom. More specifically, the present invention relates to cyclic anhydride grafted epoxy resins prepared from solid epoxy resins and sufficient amounts of cyclic anhydride such that the resulting cyclic anhydride grafted epoxy resins have significantly reduced concentrations of undesirable low molecular weight species such as cyclic dimer. Coatings prepared from the cyclic anhydride grafted epoxy resins of the present invention, either with or without added crosslinker, have an excellent balance of properties and are useful in can and coil applications, among other applications.

Background of the Invention

Protective coatings for metals is one of the premier applications for epoxy resins, and their use as internal coatings for metal food and beverage containers is one of their largest markets. Typically, internal protective coatings for metal food and beverage containers are made from high molecular weight epoxy resins. And, typically, such high molecular weight epoxy resins are made by reacting a low molecular weight epoxy resin such as a diglycidyl ether of bisphenol A with a hydroxyl-containing monomer such as bisphenol A. A cyclic reaction product of bisphenol A and bisphenol A diglycidyl ether, the so-called cyclic dimer, often precipitates from coating formulation solutions causing fouling of process equipment and comcomitant loss of productivity and waste generation. The food and beverage can industry has been seeking technologies which can reduce or eliminate this problem from processes for producing epoxy thermoset interior container coatings.

Given this problem, it would be desirable to provide a non-crosslinked cyclic anhydride grafted epoxy resin, such as a cyclic anhydride grafted epoxy (CAGE) resin, for use in coating formulations having significantly reduced levels of cyclic dimer.

It is well known to prepare thermosets by curing epoxy resins with various anhydrides. For example, GB 777,255 discloses a composition prepared from the reaction of epoxy resins and anhydrides to form crosslinked epoxy-anhydride thermosets. Bolson, Harry B., SPE Journal (1962),

19, 780-4 also discloses thermoset compositions resulting from the reaction of solid epoxy resins and anhydrides to form epoxy-anhydride thermosets. Neither of the above two references describe a non-crosslinked cyclic anhydride grafted epoxy resin. U.S. Patent No. 4,638,038 discloses anhydride grafted phenoxy resins. The compositions of

U.S. Patent No. 4,638,038 are cyclic anhydride grafted phenoxy resins which do not contain terminal epoxy groups.

WO 0228939A2 discloses compositions which are CAGE resins using < 10 wt. % (< 0.25 moles/eq. resin-OH) cyclic anhydride and thus the CAGE resins of WO0228939A2 retain significantly high concentrations of cyclic dimer. The CAGE resins disclosed in WO 0228939 A2 are prepared for the purpose of forming aqueous epoxy resin dispersions. WO 0228939A2 discloses making dispersion precursors from 1- to 7-type SERs.

In both U.S. Patent No. 4,638,038 and WO 0228939A2, only up to about 10 wt. % cyclic anhydride is used to achieve the desired dispersion stability. Similar half-esters are prepared from epoxy-ester resins which in turn are made by capping the terminal epoxy groups of SERs with carboxylic acids as described in W. J. van Westrenen; L. A. Tysall, J. Oil Col. Chem. Assoc. 1968,

51, 108.

It would be desirable to provide compositions using a sufficient amount of cyclic anhydride which unexpectedly achieves significant cyclic dimer reduction without crosslinking or gelling the epoxy functional composition.

Summary of the Invention

One aspect of the present invention is directed to cyclic anhydride grafted epoxy (CAGE) resins prepared by reacting solid epoxy resins (SER) with cyclic anhydrides such as succinic anhydride (SA) and trimellitic anhydride (TMA), in sufficient amounts to significantly reduce the concentration of cyclic dimer in the resultant CAGE resin product. The compositions of the present invention are cyclic anhydride grafted epoxy resins bearing terminal epoxy groups and which have been reacted with sufficient amounts of cyclic anhydride to significantly reduce the concentration of cyclic dimer but without causing crosslinking or gelling. Another aspect of the present invention is directed to cured coatings derived from the CAGE resins. Still another aspect of the present invention includes a process for preparing the CAGE resins. In the process of the present invention for preparing CAGE resins pendant hydroxyl groups of solid epoxy resins are grafted by a cyclic anhydride to form half-esters with minimal reaction of the terminal epoxy groups of the epoxy resin starting material. The cyclic dimer bears two pendant hydroxyl groups per molecule and it is believed that the formation of its half-ester derivative renders the cyclic dimer less crystallizable and more reactive in coatings formulations. High concentrations of cyclic anhydrides (e.g. greater than 10 weight %, levels which typically are used to crosslink epoxy resins) are required to achieve the desired level of cyclic dimer reduction (e.g. less than 50 % of that in the starting epoxy resin). When the reaction is conducted in a controlled manner, the CAGE product is unexpectedly free of crosslinked or gelled by-products. The cyclic anhydride grafted epoxy resins prepared by the process of the present invention can be cured to form coatings having excellent properties. The resultant cured coating can be cured with or without an added crosslinker.

One of the objectives of the present invention is to reduce the cyclic dimer in epoxy resins, particularly in 7-type and higher solid epoxy resins, which have the highest concentrations of cyclic dimer.

Detailed Descriptions of the Preferred Embodiments

In one embodiment, the present invention includes an epoxy resin composition that is the reaction product of an epoxy resin and an anhydride, wherein the reaction product contains residual oxirane groups, after the reaction, available to participate in further crosslinking reactions. The epoxide equivalent weight (EEW) of the resultant epoxy resin composition preferably is not significantly changed, compared to the unreacted epoxy resin starting material, to an extent that would cause any undesirable crosslinking of the resin. The resulting resin composition of the present invention may be used as a coating or may be formulated with other components to create a coating composition.

The epoxy resin used in the present invention includes a backbone with pendant oxirane and pendant hydroxyl functional groups. In general, the reaction of the epoxy resin and the anhydride takes place in an organic medium under conditions selected such that the pendant oxirane groups remain substantially intact and the pendant hydroxyl groups react with the anhydride to form ester linking groups on the backbone of the epoxy resin. The thus-formed ester linking groups have pendant carboxyl functional groups.

The epoxy resins useful in the present invention may vary widely depending on the intended application. The epoxy resin includes a pendant oxirane group and a pendant hydroxyl functional group on a backbone. A representative epoxy resin is shown in Formula I as follows:

FORMULA I

Where B represents the backbone, X is an oxirane group, Y is a hydroxyl functional group, and n and m are independently at least 1, preferably at least 2.

In one embodiment, the epoxy resin is a reaction product of an epoxide and a dihydroxy compound. The epoxide can be for example epichlorohydrin. The dihydroxy compound used to make the epoxy resin may vary widely depending on the intended backbone structure needed in the epoxy resin. Preferably, the dihydroxy compound is selected from bisphenol A, bisphenol F, bisphenol, resorcinol and the like, and bisphenol A is particularly preferred.

Commercially available epoxy resins that are suitable for the present invention include those available under the trade designations D. E. R. 66x epoxy resins available from The Dow Chemical Company and Epon lOOy epoxy resins available from Hexion Corporation, where x, y = 1 - 9. Examples of epoxy resins useful in the present invention include D.E.R. 667 and D.E.R. 669E epoxy resins.

Preferred epoxy resins have a number average molecular weight (Mn) of about 500 to about

10,000 and an epoxy equivalent weight (EEW) of about 250 to about 5000. Most preferred epoxy resins have an average number molecular weight of about 500 to about 8,000 and an epoxy equivalent weight of about 250 to about 4000.

Suitable cyclic anhydrides used in the present invention to react with the epoxy resin to form the resin composition of the present invention may vary widely depending on the epoxy resin selected and the reaction conditions. Examples of useful anhydrides include succinic anhydride (SA), methyl succinic anhydride, tricarballylic anhydride, phthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride (TMA), itaconic anhydride, maleic anhydride and mixtures thereof.

Dianhydrides, such as, for example, benzophenone tetracarboxylic dianhydride (BTDA) or pyromellitic dianhydride, may also be used, and in the thermoset derivative may increase cure rate and form a more densely crosslinked reaction product. When dianhydrides are used care should be taken to ensure that no undesirable gelation of the CAGE resin occurs.

To prepare the CAGE resin compositions of the invention, the epoxy resin and the anhydride are reacted in a liquid medium under reaction conditions such that the reaction between the anhydride and the hydroxyl functional groups is substantially preferred over the reaction between the anhydride and the oxirane groups. The progress of the reaction can be monitored through methods such as nuclear magnetic resonance (NMR), infrared resonance (IR), liquid chromatography (LC), or other methods known in the art.

The resulting CAGE reaction product has oxirane groups available for further crosslinking reactions, and the reaction product's EEW preferably is moderately changed, compared to the unreacted epoxy resin starting material, but not to an extent that it would cause any undesirable gelling or crosslinking of the resin. Preferably, the resulting reaction product's EEW is no more than about 100% higher than that of the starting epoxy resin. More preferably, the resulting reaction product's EEW is no more than about 80% higher than that of the starting epoxy resin. Most preferably, the resulting reaction product's EEW is no more than about 60 % higher than that of the starting epoxy resin.

The anhydrides react with the pendant hydroxyl groups on the epoxy resin to generate ester acids. This reaction is represented in Formula II below:

FORMULA II Where B is the resin backbone, X is an oxirane group, Y is a hydroxyl group, L is an ester linking group, Q is a reactive carboxyl functional group, m and n are as previously defined, p is at least 1 , preferably 2, and the sum m-p is at least 0.

The liquid medium used to prepare the resin compositions of the present invention is preferably selected from aprotic solvents such as ketones, ethers, aryl ethers, ether esters and alkyl ethers, aromatic hydrocarbons (for example, toluene, xylene and the like), used alone or as mixtures.

Suitable solvents or solvent mixtures have between about 2 and about 8 carbon atoms.

Suitable ketones or esters include aliphatic compounds containing between 3 and 8 carbon atoms, such as, for example acetone, diethyl ketone, methylethyl ketone, methylpropyl ketone, methylbutyl ketone, methylamyl ketone, methylhexyl ketone, ethylpropyl ketone, ethylbutyl ketone, ethylamyl ketone, dioxane, tetrahydrofuran (THF), methoxy acetone and mixtures thereof.

Dialkyl ethers of alkylene glycols and polyethylene glycols, such as glyme, diglyme, and the like, may also be used as the solvent. Suitable alkyl ethers of diethylene glycol may contain between 1 and 4 carbon atoms in the alkyl group. Preferred liquid media include l-methoxy-2-propanol acetate, methyl ethyl ketone (MEK), cyclohexanone, and mixtures thereof.

Reaction temperatures for synthesizing the CAGE resin compositions of the present invention are typically less than about 12O⁰C. The preferred temperature range is from about 40°C to about 120°C. More preferably, the temperature range is from about 60°C to about 120°C, and most preferably, from about 80°C to about HO⁰C. Generally, reaction times are less than about 20 hours and preferably less than about 8 hours. Preferably, the reaction time is between about 0.25 hour and about 8 hours, and most preferably, between about 1 hour and about 4 hours.

A catalyst is preferably used to prepare the resin compositions of the present invention. While not wishing to be bound by any theory, the catalyst is believed to selectively enhance the formation of the ester linking groups between resin backbones via reaction of the hydroxyl group with the anhydride group, and limit the reaction between the carboxyl functional groups on the opened anhydride and the oxirane groups on the resin backbone. Preferably, the catalyst is a tertiary amine. Suitable catalysts include, but are not limited to, methyl diethylamine, triethylamine, dimethyl propylamine, methyl dipropylamine, tripropylamine, methyl diisopropylamine, methyl dibutylamine, ethyl dibutylamine, tributylamine, N,N-diethyl benzylamine, N-methylmorpholine, 1,4- diazabicyclo[2,2,2]octane (DABCO), l,8-diazabicyclo[5,4,0]undec-7-ene (DBU) and mixtures thereof. Preferably, the catalyst used in the present invention is l,4-diazabicyclo[2,2,2]octane (DABCO).

The catalyst is preferably used in an amount of from about 0.01 wt % to about 0.5 wt %, more preferably from about 0.02 wt % to about 0.3 wt %, and most preferably from about 0.03 wt % to about 0.1 wt %, based on the total weight of reactants.

Other components which can optionally be added to the reaction mixture may include for example acidic compounds such as phosphoric acid to neutralize the amine catalyst or adsorbents such as silica or molecular sieves to adsorb the amine catalyst after completion of the reaction.

The epoxy resin compositions of the present invention, CAGE resins, preferably have an

EEW of about 500 to about 10,000, more preferably from about 1,000 to about 8,000. The resin compositions preferably have a weight average molecular weight (Mw) of about 2,000 to about 20,000, more preferably from about 2,000 to about 15,000. The resin compositions preferably have a number average molecular weight (Mn) of about 1,000 to about 10,000, more preferably from about 1 ,000 to about 8,000.

The resin compositions of the present invention preferably have an acid number (AN) (expressed in conventional units of mg KOH/g) greater than about 55, more preferably greater than about 57 and most preferably greater than about 59.

The amount of cyclic anhydride reacted with the epoxy resins required to achieve the CAGE resins of the present invention is greater than 10 weight %, preferably at least about 12 weight %, and most preferably at least about 15 weight % based on the amount of epoxy resin used. In terms of the number of moles of cyclic anhydride per equivalent of resin hydroxyl groups (HEW, where

HEW = [285 x EEW]/[EEW-170]), the amount of cyclic anhydride required to achieve the CAGE resins of the present invention is from about 0.26 to about 1.00, preferably from about 0.35 to about 0.70, and most preferably from about 0.45 to about 0.65.

The concentration of cyclic dimer remaining in the CAGE resins of the present invention is less than about 50 % of that in the starting epoxy resin, preferably less than about 60% of that in the starting epoxy resin, and most preferably less than about 70% of that in the starting epoxy resin. For example, in a 7-type or 9-type SER resin, the concentration of the cyclic dimer in the epoxy resin may be about 6000 ppm and after the reaction is carried out to form the CAGE resin the concentration of cyclic dimer is reduced to at least about 3000 ppm for a 50% reduction or conversion as described in the examples which follow.

The resin composition of the present invention may be used as a coating composition. These coating compositions may include other additives and agents to provide formulations that can be applied to substrates such as, for example, metal containers. These materials may include additives such as carriers, emulsifiers, pigments, fillers, anti-migration aids, curing agents, coalescents, wetting agents, biocides, plasticizers, crosslinking agents, antifoaming agents, colorants, waxes, anti-oxidants, or combinations thereof. The coating composition may be applied to a substrate and subsequently baked to form a fully cured coating.

However, to reduce the amount of volatile organic compounds (VOCs) evolved during the baking step, in another embodiment of the present invention the resin composition is optionally mixed with water and a water-soluble base such as, for example, a tertiary amine, to form a water- based coating composition.

The coating composition may optionally contain a crosslinking agent to assist in curing the composition. Suitable crosslinking agents that may be used in the coating compositions of the present invention include, for example, amino resins, phenolic resins, blocked isocyanates, and the like. Some specific examples of suitable amino resins include fully or partially alkylated melamine- formaldehyde resins, benzoguanamine-formaldehyde resins, urea-formaldehyde resins, and Glycoluril-formaldehyde resins. More specifically, suitable crosslinkers include commercial materials available from Cytec industries under the trade designations Cymel 303, Cymel 325, Cymel 1123, Cymel 1125, Cymel 1156, Cymel 1170, Cymel 5010, Beetle 1 5 80, and Beetle 1054, and those available under the trade designation Mepranel MF 800 from Hoechst.

Some specific examples of phenolic resins that may be used in the coating compositions of the present invention include phenol-formaldehyde resins, cresole-formladehyde, bisphenol formaldehyde resins, and un-alkylated, partially-alkylated or fully-alkylated formaldehyde resins. Some more specific examples include those available from Oxychem under the trade designations Varcum 94-607, Varcum 29-116, Varcum 29-159, those available under the trade designations HRJ 11206, HRJ 2527 from Schenectady, those available under the trade designation EP 560 from Solutia, and those available under the trade designation Uravar FB 210 from Schenectady. Blocked isocyanates can be, for example, aliphatic, cyclo-aliphatic, or aromatic poly- functional isocyanates, blocked with, for example, MEK- Oxime, epsilon- caprolactam, uretedione, alcohols, glycol ethers, and the like. More specific examples include compounds available from Degussa under the trade designations Vestanat B 1358, Vestanat B 1370, Vestagon B 1530, and Vestagon BF 1540.

If desired, the coating composition of the present invention may optionally comprise an additional resin, such as a poly-hydroxy or phenoxy group containing resin. For example, epoxy or phenoxy resins having two or more hydroxy groups may be utilized. Typically, such resins will have epoxy or phenoxy end groups. The presently preferred epoxide equivalent weight (EEW) of such optional resins is greater than about 1,000. Examples of suitable such additional resins include those available from Shell under the trade designations EPON 1001, 1004, 1009 and those available under the trade designation DER 684 EK 40 from The Dow Chemical Company. In one embodiment the coating composition comprises (i) from about 20 to about 100 parts by weight of the resin of the present invention; (ii) up to about 80 parts by weight of a suitable additional resin having epoxy or phenoxy groups; and (iii) up to about 20 parts of a suitable crosslinking agent.

The coating compositions of the present invention may be applied to a substrate by any procedure known in the art, including spray coating, roll coating, and the like. Preferably, the coating is applied to a metal sheet or coil or the interior of a metal can using an airless spray.

After application to a substrate, the coating composition is heated in a baking process to form a cured coating. During the bake, the ester acids react with the hydroxyl groups and the oxirane groups both inter- molecularly and/or intra-molecularly to form a crosslinked network bound together by ester linking groups.

The baking steps used to cure the coating compositions of the present invention may occur in discrete or combined steps. For example, substrates can be dried at ambient temperature (about 25 ⁰C) to leave the coating compositions in a largely un-crosslinked state. The coated substrates can then be heated to fully cure the compositions to provide a hard coating. More preferably, the coating compositions of the present invention are dried and heated in one step.

The temperature used in the baking process preferably ranges from about 60°C up to the decomposition temperature of the composition. Generally, baking at about 120⁰C to about 400°C for a period of time between about 3 seconds to about 15 minutes is sufficient to provide a fully cured composition. For the present invention, heat treatment at about 150°C to about 220°C for about 1 minute to about 10 minutes is preferred.

The cured coatings of the present invention are particularly well suited as coatings for metal cans or containers. The containers may be coated with at least one layer of the cured coating, and the layers may be present on the inside of the containers, the outside of the containers, and the ends of the containers. The cured coatings adhere well to metal and provide substrates with high levels of resistance to corrosion or degradation that may be caused by food or beverage products.

The cured coatings also find utility in the general packaging field, such as in the coating of aerosol cans. These coatings have also been found to be comparable to the presently commercially available coatings that are based on epoxy/phenolic crosslinker and/or amino crosslinker. The coatings show, for example, good flexibility, and good resistance to blush and corrosion.

In particular, the coating show reduced cyclic dimer concentration of levels of less than about 50%, preferably less than about 60% and more preferably less than about 70% compared to the coating prepared from the unmodified starting epoxy resin.

In order to provide a better understanding of the present invention including representative advantages thereof, the following Examples are offered.

Various terms, abbreviations and designations for raw materials used in the following Examples are explained as follows:

"SER" stands for Solid Epoxy Resin.

D.E.R.™ 667 (EEW = 1850) and D.E.R.™ 669E (EEW = 3290) are SERs commercially available from The Dow Chemical Company.

Methylon 75108 is a methylolphenyl allyl ether commercially available from Occidental Chemical Company. Super phosphoric acid (105 %), methylethyl ketone (MEK), lactic acid, cyclohexanone, 2- butoxyethanol (Dowanol™ EB), diglyme, Dowanol™ PMA, benzyldimethylamine (BDMA), 1,4- diazobicyclo[2.2.2]octane (DABCO), succinic anhydride (SA), succinic acid, and trimellitic anhydride (TMA) are chemicals commercially available from Aldrich Chemical Company.

"HPLC" stands for High Pressure Liquid Chromatography. HPLC grade water, acetonitrile (ACN), and tetrahydrofuran (THF) are commercially available

Dowanol* PMA is a propylene glycol methyl ether acetate, commercially available from The Dow Chemical Company. The various standard test methods and procedures used in the Examples to measure certain properties are as follows:

Residual monomer and cyclic dimer analyses are carried out by HPLC using an Agilent 1100 LC system comprising a quaternary pump system, an on-line solvent degasser, an autosampler, a column heater set at 4O⁰C , and a variable wavelength detector set at 228 nanometers (nm). Analysis of bisphenol A (BA), bisphenol A diglycidyl ether (BADGE), and cyclic dimer employ a 4.6 millimeters (mm) x 250 mm Waters YMC ODS-AQ S-5 120 A column or equivalent and a 1 mL/minute water/ACN gradient elution program (0 minutes, 50% ACN; 25 minutes, 68% ACN; 26 - 33 minutes, 20% ACN and 80% tetrahydrofulon (THF); 34 minutes, 50% ACN) with stop time at 34 minutes, post time of 10 minutes, and a data acquisition stop time at 29 minutes 10 μL aliquots of about 1 wt. % solution of samples prepared in 60/40 ACN/THF (v/v) are injected. BA and BADGE are calibrated using peak area values of equally weighted external standards with a linear curve type forced through the origin. The response factors for the two cyclic dimer peaks are assumed equal to that for BADGE.

HPLC analyses for residual succinic anhydride and by-product succinic acid are carried out using the above Agilent 1100 LC system with ultraviolet (UV) detection at 200 nm and an isocratic 95 % water/5 % ACN elution over 15 minutes followed by a linear gradient to 20 % water over the next 5 minutes and ending with a 70 % THF flush.

Epoxide equivalent weight (EEW) and acid number (AN) titrations are carried out according to work procedures equivalent to ASTM D- 1652-97 and ASTM D 1639-90, respectively.

EXAMPLES

General Procedure for the Preparation of CAGE Resin Composition

Several SA and TMA derived CAGE resins were prepared in order to determine cyclic dimer reduction by the present derivatization procedure and to subsequently evaluate the new resins in coatings formulations. Both the SA and TMA anhydrides are approved for use in food coatings (SA for epoxy coatings, TMA for vinyl coatings). Levels of anhydride were used to achieve an ultimate level of cyclic dimer reduction.

To a 1 liter (L) resin kettle fitted with a mechanical stirrer, condenser, and thermocouple connected to a programmable controller were added 250 grams (g) SER and 250 g solvent to form a mixture. The mixture was warmed to approximately 14O⁰C using heat lamps (one connected to the controller, the other to a rheostat) to dissolve the SER resin. Azeotropic removal of water from the resulting solution was not needed; vacuum oven dried SER was used. The solution was allowed to cool to the desired reaction temperature and a cyclic anhydride was added in the amounts described in Table I below and allowed to dissolve. Then 0.26 g of amine catalyst was added to the solution while controlling the reaction temperature with the heat lamps. Samples of the reaction solution were removed periodically for analysis (EEW and monomers). The results of analysis are shown in

Table I.

Examples 1 -12 and Comparative Examples A-C - Preparation of Resin Composition

Table I. Reaction Conditions and Analytical Results for Succinic Anhydride (SA) Grafted D.E R.

669E.

bor = based on resin Table I. (continued) Reaction Conditions and Analytical Results for Succinic Anhydride (SA)

Grafted D.E.R. 669E.

*bor = based on resin

Comparative Example A in Table I above used D.E.R. 669E SER, succinic anhydride (SA), and the conditions described in Examples 1 - 6 of WO 02/28939 with BDMA catalyst, about 50 % solids in Dowanol PMA solvent, and a reaction temperature of 77⁰C. As described in WO 02/28939 these reactions conditions require prolonged reaction times to reach completion. The relatively low amounts of anhydride (6 - 10 wt. % based on resin) used are effective in the preparation of epoxy dispersions but are insufficient to achieve high cyclic dimer conversion.

With 12% SA, as shown in Example 1, the cyclic dimer conversion reaches 50%. Conducting the reaction at 100⁰C using 18% SA, and diglyme solvent, as shown in Example 2, achieves complete conversion within 5 hours as determined by analysis for residual SA and cyclic dimer conversion. Example 3 describes the use of more SA (24%) with the same amount of cyclic dimer conversion. The EEW of the resulting products increases with the amount of SA used indicating some reaction of the carboxylic acid group of the half-ester product and/or dicarboxylic acid byproduct with the resin terminal epoxy groups.

The use of DABCO as a catalyst and diglyme as a solvent proved more effective reaction conditions for the preparation of CAGE resins. A much higher cyclic dimer conversion was achieved using 6% SA under these conditions (see Table I, Comparative Example B compared to Comparative Example A). At 100⁰C the reaction was complete within an hour and the product eventually gelled with prolonged heating (Comparative Example C). Example 7 shows that cyclohexanone is also an effective solvent. Hydroxylic solvents which would compete with the resin hydroxyl groups in the reaction with anhydrides should be avoided. An about 10 fold reduction in reactant concentration resulted in a slower reaction rate and lower cyclic dimer conversion shown in Example 10. Liquid chromatograph (LC) analysis of SA-g-D.E.R. 669E resins and the cured derivative were carried out. The LC of the CAGE resin shows residual BA (6.6 min.) and BADGE (17.8 min.) and very small dimer peaks (23.7 and 24.1 min). No major new peaks are observed in the LC of this sample. Overall the concentration of species having an apparent molecular weight < 1000 Daltons is very low in this extract. About 90% conversion of cyclic dimer is achieved using SA.

The acid numbers of CAGE resins made using D.E.R. 669E and succinic anhydride are: 10 wt. % SA (Example 4): AN = 52, 12 wt. % SA (Example 5): AN = 63, and 18 wt. % SA (Example 6): AN = 106.

Similar results were obtained in the preparation of SA grafted D.E.R. 667 (SA-g-D.E.R. 667) resins as shown in Table II. Each of these Examples used diglyme as solvent and DABCO as catalyst; were conducted at 100⁰C. Cyclic dimer conversion was proportionate to the amount of SA used. Because of the slightly higher HEW of D.E.R. 667 the mole SA/mole resin OH in these examples are slightly larger than that for D.E.R. 669E resins using the same amount of SA. About 90% cyclic dimer conversion is again achieved using an amount of SA slightly over the theoretical stoichiometric value.

Examples 13-14 and Comparative Example D - Preparation of Resin Composition

Table II. Reaction Conditions and Analytical Results for Succinic Anhydride (SA) Grafted

D.E.R. 667.

bor = based on resin

Examples 15 - 16 and Comparative Example E - Preparation of Resin Composition

Examples of CAGE resins were prepared using trimellitic anhydride (TMA) as shown in Table III. The molecular weight of TMA is about twice that of SA, so the mole TMA/mole resin OH and cyclic dimer conversion is about a factor of two less for the same mass of anhydride used. The reaction of TMA with D.E.R. 669E using BDMA catalyst at 77⁰C converted about 20% of the cyclic dimer (Comparative Example E). Two examples were prepared using 18 wt. % TMA; the reaction was complete within 2 hours at 100⁰C using DABCO catalyst and the cyclic dimer conversion was about 65% (Examples 15 andl6).

bor = based on resin

Example 17-34 and Comparative Examples F-I - Preparation of Coating Formulations

Tin free steel (TFS - single reduced electrolytic chromium coated sheet), type L, T4CA, surface 50, obtained from Weirton Steel Corporation were used in these Examples. General Procedure for the Preparation and Testing of Coated Steel Panels

Coating formulations were applied to tin-free steel (TFS) panels using a draw-down bar according to ASTM D 4147-99 and cured to give 0.20 +/- 0.02 mil coating thickness. The coated 0 panels were tested for MEK resistance according to the test procedure ASTM D 5402-93 and wedge- bend flexibility according to the test procedure ASTM D 3281-84. Lactic acid pasteurization resistance was done using wedge bend panel samples (about 170 ° bend with coating in tension) immersed in vials containing 2 wt. % lactic acid and heated in an autoclave at 120⁰C for 30 minutes. The following rating system shown in Table A, was used to describe the coating performance. AU 5 tests were performed in duplicate and the average values of the results are reported herein.

Table A. Rating System for the Lactic Acid Pasteurization Resistance Test. Rating Observation

5 No blush or blisters on bent or flat sections 4 No blush or blisters on flat section 3 Blush but no blisters on flat section

2 Blush with few small blisters on flat section 1 Blush with many large blisters on flat section

0 Total coating destruction

Coatings based on CAGE resins were prepared with either a standard phenolic resole hardener and/or the CAGE resin alone using H₃PO₄ catalyst as shown in Table IV. Properties of the control coatings prepared using 5, 10, and 15 wt. % hardener and D. E. R. 669E are shown in Comparative Examples -F-H. With increasing % hardener the coating solvent resistance increases (albeit with a high variation), flexibility decreases, and pasteurization resistance increases marginally. This evaluation of the CAGE resin coatings was done using the properties of 85% D.E.R. 669E/15% hardener coating as the target values.

Table IV. Properties of D.E.R. 669E-Based CAGE Resin Coatings.

Table IV. (Continued) Properties of D.E.R. 669E-Based CAGE Resin Coatings.

The acid catalyzed curing of high molecular weight SERs with phenolic resole hardeners involves the reaction of the pendant hydroxyl groups with the resole methylol groups to form ethers. The analogous reaction of the CAGE resins is expected to form the same products by reaction of remaining hydroxyl groups and esters by coupling the pendant carboxylic acid groups with the methylol groups. In the absence of added hardener the CAGE resins can cure by themselves by reaction of the carboxylic acid groups with the epoxy terminal moieties and remaining hydroxyl groups to form other esters.

Achieving a significant degree of cure of the coatings formulations containing no added hardener as estimated by the MEK resistance tests required a higher catalyst concentration and usually longer cure times than used in standard conditions. Typically 2.5 wt. % H₃PO₄ catalyst and 20 minute cure time were used in these examples. The thusly treated 6 wt. % SA-g-D.E.R. 669E resin (Table IV Comparative Example I had less solvent resistance but otherwise closely matched the control properties (Table IV Comparative Examples -F-H). The 10 wt. % SA derivative and 15 wt. % hardener in Example 18 gave a coating which met the control criteria. The self-cured 12 wt. % SA-g-D.E.R. 669E coating (Example 19) had good solvent resistance, less flexibility, and better pasteurization resistance compared to the control. The coating made from this resin and 5 wt. % hardener (Example 20) also had a good balance of properties. The coating made using 15 wt. % hardener achieved (Examples 21 and 22) improved pasteurization resistance with additional cure time. The 18 and 21 wt. % SA-g-D.E.R. 669E based coatings showed a good balance of coating properties. Both self-cured resins (Examples 23 and 27) had good solvent and pasteurization resistance, but the 21 wt. % resin coating was less flexible than the control. Noteworthy is the 18 wt. % SA resin self-cured for 10 minutes; this coating had good solvent resistance, adequate flexibility, and improved pasteurization resistance. Coatings from the higher SA resins and hardener showed good properties. As in the 12% SA resin additional curing increased pasteurization resistance at the expense of flexibility, Pasteurization resistance can be strongly affected by coating composition, including the presence of additives such as surfactants and lubricants, and cure schedule.

The properties of the coatings prepared from the 18 wt. % TMA-g-D.E.R. 669E resin also compared favorably to the control. The half-esters from TMA bear two carboxylic acid groups and are thereby more reactive than the SA analogs, so these resins can self-cure at lower acid concentrations. The use of 5 wt. % hardener also gave a coating having a good match to the control . The CAGE resins of the present invention using relatively high concentrations of anhydride precursors and concomitant high cyclic dimer conversions were prepared by a high solids, amine catalyzed solution process. Anhydride grafted D.E.R. 669E and 667 resins were prepared in solutions having > 50 wt. % solids using either BDMA or DABCO catalysts. Ether, ester, and ketone solvents are applicable but alcoholic solvents are expected to interfere with the reaction. The reaction of D.E.R. 669E and 18 wt. % SA in diglyme at 100⁰C using DABCO as catalyst was complete within 2 hours, and achieved about 90% conversion of the cyclic dimers to half-esters. CAGE resins were also prepared using TMA as the anhydride, which on a weight basis gave less cyclic dimer reduction than SA. The CAGE resins of the present invention can be self-curable or can be cured with 5 - 15 wt. % phenolic resole hardener. To achieve coating properties which match those of the control a higher H₃PO₄ catalyst concentration was required for self-curing. The self-cured coating prepared from 18 wt. % SA grafted D.E.R. 669E had properties very similar to those of the control coating. Self-curing of CAGE resins can also be catalyzed using basic compounds, such as amines. Coatings prepared from CAGE resins and hardener tended to have good solvent resistance and flexibility.

The CAGE resins of the present invention offer a new approach to food can coatings having better processability and equivalent or better coating properties compared to known coatings. The present invention provides a practical process for the preparation of CAGE resins and of coating formulations which meet specific food can application requirements, as well as regulatory requirements.

While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the present invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A self-curing curable epoxy resin composition comprising the reaction product of an epoxy resin and a sufficient amount of a cyclic anhydride to prepare a CAGE resin product having a reduced concentration of cyclic dimer to a level of less than about 50 % of that in the starting epoxy resin.

2. The composition of Claim 1 wherein the epoxy resin comprises a high molecular weight epoxy resin.

3. The composition of Claim 1 wherein the epoxy resin comprises a solid epoxy resin.

4. The composition of Claim 1 wherein the cyclic dimer comprises the reacted product of a bisphenol A and a bisphenol diglycidyl ether.

5. The composition of Claim 1 wherein the resin composition's epoxide equivalent weight has not been significantly changed compared to the unreacted epoxy resin, to an extent that would cause any undesirable gelling or crosslinking of the resin.

6. The composition of Claim 1, wherein the reaction is conducted in an aprotic solvent.

7. The composition of Claim 1, wherein the epoxy resin comprises a backbone having at least one pendant oxirane groups and at least one pendant hydroxyl functional group.

8. The composition of Claim 7, wherein the epoxy resin comprises at least two hydroxyl functional groups.

9. The composition of Claim 7, wherein the backbone is derived from a compound selected from the group consisting of bisphenol A, bisphenol F, bisphenol, and resorcinol.

10. The composition of Claim 9, wherein the compound comprises bisphenol A.

11. The composition of Claim 1, wherein the anhydride is selected from the group consisting of phthalic anhydride, trimellitic anhydride, maleic anhydride, succinic anhydride, itaconic anhydride, and benzophenone tetracarboxylic dianhydride.

12. The composition of Claim 1, wherein the reaction is conducted in the presence of a tertiary amine catalyst.

13. The composition of Claim 12, wherein the catalyst comprises DABCO.

14. The composition of Claim 1, wherein the resin composition has an epoxide equivalent weight of between about 1,000 to about 8,000.

15. The composition of Claim 1, wherein the resin composition has an acid number greater than about 55.

16. A coating composition comprising the resin composition of Claim 1 and further comprising an additional separate crosslinker.

17. The coating composition of Claim 16, wherein the additional separate crosslinker is selected from the group consisting of an amino resin, a phenolic resin or a blocked isocyanate.

18. The coating composition of Claim 16, wherein the composition comprises (i) between about 20 and about 100 parts of the reaction product of an epoxy resin and an anhydride; (ii) up to about 80 parts by weight of an additional resin having epoxy or phenoxy groups; and (iii) up to about 20 parts of a suitable crosslinking agent.

19. A coating composition comprising the resin composition of Claim 1, further including a base or acid catalyst.

20. A container having a coating applied to at least one surface thereof, wherein the coating comprises the resin of Claim 16 or 19.

21. A process for making a resin composition, comprising: providing an epoxy resin with a backbone having attached thereto at least one pendant oxirane group and at least one pendant hydroxyl group; and reacting the epoxy resin with an anhydride in an organic liquid medium to form a resin composition, wherein the resin composition has an epoxide equivalent weight that is substantially the same as the epoxide equivalent weight of the epoxy resin.

22. The process of Claim 21, wherein the organic medium comprises an aprotic solvent.

23. The process of Claim 21, wherein the epoxy resin and the anhydride are reacted at a temperature of less than about 125⁰C.

24. The process of Claim 21, wherein the epoxy resin and the anhydride are reacted in the presence of a catalyst.

25. The process of Claim 24, wherein the catalyst is a tertiary benzylic amine.

26. The process of Claim 21, further comprising the step of: adding water and a base, wherein sufficient water is added to form a coating composition comprising a continuous aqueous phase and a discontinuous organic phase comprising the resin composition.

27. The process of Claim 26, wherein the discontinuous organic phase comprises particles of the resin composition with a particle size of less than about 0.5 micron.

28. The process of Claim 21, further comprising the steps of: applying the resin composition to a substrate and baking the resin composition.

29. The process of Claim 21, wherein the epoxy resin is a reaction product of an epoxide and a dihydroxy compound.

30. The process of Claim 29, wherein the dihydroxy compound is selected from the group consisting of bisphenol A, bisphenol F, bisphenol and resorcinol.