EPOXY RESIN COMPOSITIONS CONTAINING AN INTERNAL MOLD RELEASE AGENT

Abstract

Alkoxylated hydrophobes that include a poly(alkylene oxide) chain of at least 5 oxyalkylene units having a terminal secondary hydroxyl group or a terminal C.sub.1−8 hydrocarbyl group are effective internal mold release agents for epoxy resin moldings. The alkoxylated hydrophobe, when mixed with an epoxy resin, forms a mixture that is highly stable when heated to 80 to 100° C. and held at that temperature for a period of as much as 22 days.

Claims

1. An epoxy resin mixture comprising at least one epoxy resin mixed with 0.2 to 5 parts by weight, per 100 parts by weight of the at least one epoxy resin, of one or more alkoxylated hydrophobes that include a poly(alkylene oxide) chain of at least 5 oxyalkylene units having i) a terminal hydroxyl group, provided that at least 50% of the hydroxyl groups provided by the one or more alkoxylated hydrophobes are secondary hydroxyl groups, or ii) a terminal C.sub.1−8 hydrocarbyl group, the poly(alkylene oxide) chain being bonded at one end through a linking group to a hydrophobe that includes an unsubstituted aliphatic hydrocarbyl group of at least 10 carbon atoms.

2. The epoxy resin mixture of claim 1, wherein the hydrophobe is a straight-chain alkyl group having 10 to 24 carbon atoms; a straight-chain mono-, di- or tri-alkene having 10 to 24carbon atoms; or an alkyl- or alkenyl-substituted phenyl in which the alkyl or alkenyl group is a straight-chain group having 10 to 24, carbon atoms.

3. The epoxy resin mixture of claim 1, wherein the poly(alkylene oxide) chain is a poly(1,2-propylene oxide), a block copolymer having an internal poly(ethylene oxide) block and a terminal poly(1,2-propylene oxide) block, a block copolymer having an internal poly(ethylene oxide) block and a terminal poly(1,2-butylene oxide) block, a block copolymer having a poly(1,2-propylene oxide) block and a poly(1,2-butylene oxide) block or a random copolymer of 1,2-propylene oxide and 1,2-butylene oxide.

4. The epoxy resin mixture of claim 1, wherein the alkoxylated hydrophobe is made by alkoxylating a straight-chain alkyl group having 10 to 18 carbon atoms with a mixture of 1,2-propylene oxide and 1,2-butylene oxide.

5. The epoxy resin mixture of claim 1, wherein the alkoxylated hydrophobe is made by sequentially alkoxylating a straight-chain alkyl group having 10 to 18 carbon atoms with ethylene oxide and then 1,2-propylene oxide.

6. The epoxy resin mixture of claim 1 wherein the alkoxylated hydrophobe has hydroxyl groups, and at least 85% of the hydroxyl groups of the alkoxylated hydrophobe are secondary hydroxyl groups.

7. The epoxy resin mixture of claim 1 wherein the epoxy resin contains 80 to 100 weight percent, based on the weight of the epoxy resin, of a polyglycidyl ether of a polyphenol having a number average of 1.8 to 3 epoxy groups per molecule and a number average epoxy equivalent weight of 125 to 225.

8. The epoxy resin mixture of claim 1, further comprising an alkali metal, ammonium or phosphonium salt of a phosphate ester.

9. A method for making a cured epoxy resin, comprising filling a mold with a curable epoxy resin composition and curing the curable epoxy resin composition in the mold, wherein the curable epoxy resin composition includes a hardener and an epoxy resin mixture that contains at least one epoxy resin mixed with 0.5 to 5 parts by weight, per 100 parts by weight of the at least one epoxy resin, of an alkoxylated hydrophobe that includes a poly(alkylene oxide) chain of at least 5 oxyalkylene units having i) a terminal hydroxyl group, provided that at least 50% of the hydroxyl groups provided by the one or more alkoxylated hydrophobes are secondary hydroxyl groups, or ii) a terminal C.sub.1−8 hydrocarbyl group, the poly(alkylene oxide) chain being bonded at one end through a linking group to a hydrophobe that includes an unsubstituted aliphatic hydrocarbyl group of at least 10 carbon atoms.

10. The method of claim 9, wherein the epoxy resin mixture is preheated to a temperature of 50 to 100° C., and then mixed with the hardener.

11. The method of claim 10, wherein the epoxy resin mixture is preheated to a temperature of 50 to 100° C. for a period of at least one day, and then mixed with the hardener.

12. The method of claim 9, wherein the hydrophobe is a straight-chain alkyl group having 10 to 24 carbon atoms, a straight-chain mono-, di- or tri-alkene having 10 to 24 carbon atoms; or an alkyl- or alkenyl-substituted phenyl in which the alkyl or alkenyl group is a straight-chain group having 10 to 24 carbon atoms.

13. The method of claim 9, wherein the poly(alkylene oxide) chain is a poly(1,2-propylene oxide), a block copolymer having an internal poly(ethylene oxide) block and a terminal poly(1,2-propylene oxide) block, a block copolymer having an internal poly(ethylene oxide) block and a terminal poly(1,2-butylene oxide) block, a block copolymer having a poly(1,2-propylene oxide) block and a poly(1,2-butylene oxide) block or a random copolymer of 1,2-propylene oxide and 1,2-butylene oxide.

14. The method of claim 9 wherein the alkoxylated hydrophobe has hydroxyl groups, and at least 85% of the hydroxyl groups of the alkoxylated hydrophobe are secondary hydroxyl groups.

15. The method of claim 9, wherein the alkoxylated hydrophobe is made by alkoxylating a straight-chain alkyl group having 10 to 18 carbon atoms with a mixture of 1,2-propylene oxide and 1,2-butylene oxide.

16. The method of claim 9, wherein the alkoxylated hydrophobe is made by sequentially alkoxylating a straight-chain alkyl group having 10 to 18 carbon atoms with ethylene oxide and then 1,2-propylene oxide.

17. The method of claim 9 wherein the epoxy resin contains 80 to 100 weight percent, based on the weight of the epoxy resin, of a polyglycidyl ether of a polyphenol having a number average of 1.8 to 3 epoxy groups per molecule and a number average epoxy equivalent weight of 125 to 225.

18. The method of claim 9, further comprising an alkali metal, ammonium or phosphonium salt of a phosphate ester.

Description

SCREENING EXAMPLES 1 AND 2 AND COMPARATIVE SAMPLES A-D

[0089] 50/50 by weight mixtures of an epoxy resin and an IMR agent are prepared as indicated in Table 1.

[0090] The IMR candidates are separately mixed with an equal weight of an epoxy resin and stirred at room temperature until mixed. The large amount of IMR candidate, well in excess of typical use levels, is chosen so the reaction between the IMR candidate and the epoxy resin, if any, could be detected easily by differential scanning calorimetry (DSC). The stability of the resulting epoxy resin/IMR mixtures is evaluated by DSC. The enthalpy of reaction is an indication of the extent of the reaction between the IMR agent and the epoxy resin, with higher enthalpies indicating more reaction.

TABLE-US-00001 TABLE 1 DSC evaluation of 50/50 IMR/Epoxy Resin Mixtures Epoxy Enthalpy of Designation Resin IMR agent Reaction Comp. Sample A A A 50 J/g Comp. Sample B B A 55 J/g Comp. Sample C A B 10 J/g Comp. Sample D A C 53 J/g Ex. 1 A D 0 J/g Ex. 2 A E 0 J/g

[0091] IMR agents A-C each react significantly with Epoxy Resin A. IMR agent A reacts similarly with Epoxy Resin B. Conversely, no reaction is detected between Epoxy Resin A and either of IMR agents D and E, even at the very high concentrations of IMR candidate used in these experiments.

EXAMPLES 3-6 AND COMPARATIVE SAMPLES E-H

[0092] IMR candidates are mixed with epoxy resins as indicated in Table 2, in a weight ratio of 2:100. These mixtures are stored at 80° C. under air with stirring for 22 days. They are inspected visually for the formation of particulates. The formation of particulates is indicative of instability in the resin/IMR mixture. Results are as indicated in Table 2

TABLE-US-00002 TABLE 2 Stability of 2% IMR mixtures at 80° C. Epoxy Particle Designation Resin IMR agent Formation? Comp. Sample E A A After 1 day Comp. Sample F A B Not Determined Comp. Sample G A C After 1 day Example 3 A D None after 20 days Example 4 A E None after 20 days Comp. Sample H C A None after 20 days Example 5 C D None after 20 days Example 6 C E None after 20 days

[0093] As can be seen by comparing the results in Tables 1 and 2, the DSC results correlate well with observed elevated temperature stability of the IMR/epoxy resin mixtures. IMR agents A, B and C all show significant reactivity with Epoxy Resin A on DSC, and mixtures of those IMR agents with Epoxy Resin A also form particles when stored at 80° C. The 80° C. storage conditions are typical of conditions encountered in industrial scale composite production equipment. This equipment typically includes a heated storage tank in which the epoxy resin/IMR mixture is stored at elevated temperature for periods that can extend until several days. The formation of particles in each of Comparative Samples A-D demonstrates that those epoxy resin/IMR mixtures are too instable to be processed on such production equipment under these conditions. The use of these IMR candidates therefore requires them to be added as separate streams to be mixed with the epoxy resin and hardener in the mixhead of the production apparatus. The small volume of the IMR stream leads to difficulties in metering the material accurately, and leads to inconsistent release characteristics, with frequent adhesion of the parts to the mold.

[0094] By contrast, mixtures of Epoxy Resin A with either of IMR agents D or E show no sign of reactivity on either the DSC test (Ex. 1 and 2) or upon storage at 80° C. for up to 20 days (Ex. 3 and 4). Mixtures of Epoxy Resin C with either of IMR agents D or E show no sign of reactivity upon storage at 80° C. for up to 20 days (Ex. 5 and 6). These mixtures are easily processed on industrial composite production equipment.

EXAMPLES 7-12 AND COMPARATIVE SAMPLES I-L

[0095] Examples 7-12 are made and tested according to the following general procedure. The epoxy resin and internal mold release candidates as set forth in Table 3 are combined at room temperature and stirred to form a uniform mixture. Separately, a triethylene tetraamine product containing less than 0.3 weight percent aminoethylethanolamine (TETA-E from The Dow Chemical Company) is combined with triethylenediamine at a mole ratio of 10:1.

[0096] A portion of each epoxy resin mixture is heated to a temperature 80° C. and blended with a room temperature portion of the triethylene tetraamine mixture. The mixing ratio is indicated in Table 3. The resulting curable epoxy resin composition is blended by hand for about 30 seconds and poured onto a preheated (130° C.) hot plate to form a disk. The hot plate temperature is maintained at 130° C. until the epoxy resin composition has cured. A line is scored through the disk periodically with a pallet to follow the extent of cure. When the disk has cured enough that it cannot be scored with the pallet knife, the cured disk is removed from the hot plate surface using a spatula. The release characteristics are assessed qualitatively. A “very good” rating is indicated by minimal if any sticking. A “good” rating is indicated by a small amount of sticking, although the disk is nonetheless easily removed. A “fair” rating indicates that the disk could be removed from the hot plate with significant effort. A “poor” rating indicates that the disk could be removed only with substantial effort that leads to permanent deformation of the cured resin. The glass transition temperature of each disk is measured by DSC. The sample is heated from room temperature to 200° C. at 20° C./minute, held at 200° C. for 3 minutes, cooled to room temperature at a rate of 20° C./minute, and then again heated to 200° C. at 20° C./minute. Glass transition temperature is measured on the second heating segment as the midpoint of the transition.

[0097] Where indicated in Table 3, the remaining amounts of each of the epoxy resin/IMR candidate mixtures are heated continuously at 80° C. with stirring for 22 days. Samples are withdrawn after 1, 8, 12 and 22 days heating, and used to make cured disks as described above. The release characteristics and glass transition temperature are measured in each case. Results are as indicated in Table 3.

TABLE-US-00003 TABLE 3 Comp. Comp. Comp. Comp. Samp. I Ex. 7 Ex. 8 Ex. 9 Ex. 10 Samp. J Samp. K Samp. L Ex. 11 Ex. 12 Epoxy Resin A, 98 A, 98 A, 98  A, 98 A, 98 A, 98 A, 98 C, 98 C, 98 C, 98 (type, pbw) IMR Candidate A, 2  D, 2  D, 1.5 E, 2  E, 2  B, 2  C, 2  A, 2  D, 2  E, 2  (type, pbw) Phosphate Salt  0  0    0.5  0    0.5 0 0  0  0  0 (pbw) Epoxy/Hardener 100:16.2 100:16.2 100:16.2 100:16.2 100:16.2 100:16.2 100:16.2 100:14.1 100:14.1 100:14.1 Ratio 0 Days Storage Results Release Rating Very Good Very Good Very Poor Good Very Good Good good Good Good Good T.sub.g, ° C. 122 120 130 127 130 N.D. N.D. 124 122 131 1 Day Storage Results Release Rating Fair Good N.D. N.D. N.D. N.D. N.D. Very Good Good Good T.sub.g, ° C. 119 120 N.D. N.D N.D. N.D. N.D. 124 122 131 8 Days Storage Results Release Rating Poor Good N.D. N.D. N.D. N.D. N.D. Good Good Good T.sub.g, ° C. 119 120 N.D. N.D. N.D. N.D. N.D. 123 122 131 12 Days Storage Results Release Rating Poor Good N.D. N.D. N.D. N.D. N.D. Good Good Good T.sub.g, ° C. 119 120 N.D. N.D. N.D. N.D. N.D. 122 122 131 22 Days Storage Results Release Rating Poor Good N.D. N.D. N.D. N.D. N.D. Good Good Good T.sub.g, ° C. 113 120 N.D. N.D. N.D. N.D. N.D. 120 122 131

[0098] The data in Table 3 shows the performance of various IMR candidates in Epoxy Resin A (Ex. 7-10 and Comp. Samples I, J and K) and Epoxy Resin C (Ex. 11-12 and Comp. Sample L).

[0099] Comp. Sample I represents a commercial benchmark. In this case, IMR candidate A provides very good release before the epoxy resin/IMR mixture is heat-aged. The glass transition temperature of Comp. Sample I is 122° C. before the epoxy resin/IMR mixture is heat aged. As shown in Table 3, heat aging of the epoxy resin/IMR mixture has a large adverse effect on release properties and glass transition temperature. The deterioration of these properties is consistent with a reaction of epoxy and resin and IMR candidate A as it is heat-aged.

[0100] Example 7 (containing IMR candidate D) does not release quite as well as Comp. Sample I before heat aging, and has a slightly lower glass transition temperature. But heat aging causes no deterioration of either of these properties. After only one day aging, Example 7 performs better on both counts than Comp. Sample I. Even better results are obtained when IMR candidate D is used together with a phosphate ester salt, as in Example 8. Even before heat aging, release is comparable to that of Comp. Sample I, and the glass transition temperature is considerably higher.

[0101] Comparative Sample J releases poorly, even without heat aging. Comparative Sample K releases well before heat aging, but as shown above, IMR candidate C is very reactive with Epoxy Resin A and is expected to perform worse with heat aging.

[0102] Comparative Sample L and Examples 11-12 compare the performance of various IMR candidates in Epoxy Resin C. Epoxy Resin C contains a significant fraction of monohydrolyzed species, and as such cures more slowly than Epoxy Resin A or B and may be disfavored when a very rapid cure is needed. IMR candidate A performs well before heat aging, but as with Comp. Sample I, those properties deteriorate with heat aging, albeit more slowly in this case. With IMR candidate D (Ex. 11), initial performance is similar to Comp. Sample I, but there is no deterioration of properties with heat aging. IMR candidate E provides comparable release and a higher glass transition temperature with no deterioration of those properties with heat aging.