METHOD FOR MANUFACTURING ULTRA-LOW-TEMPERATURE, FAST-CURABLE EPOXY RESIN, AND POWDER COATING COMPOSITION COMPRISING RESIN MANUFACTURED THEREBY

Abstract

The present disclosure relates to a method for manufacturing an ultra-low-temperature, fast-curable epoxy resin and a powder coating composition comprising a resin manufactured thereby and, specifically, to a method for manufacturing an ultra-low-temperature, fast-curable epoxy resin and a powder coating composition comprising a resin manufactured thereby, wherein the epoxy resin is curable in conditions of 110-130° C./10 min and thus can be used even in a material, of which the temperature is difficult to raise or which is sensitive to heat.

Claims

1. A method for manufacturing a low-temperature curable epoxy resin of the following Chemical Formula 1 by synthesizing an oligomer using an organic acid containing one or more phenol groups and an alcohol containing three or more hydroxy groups and reacting the synthesized oligomer and a bisphenol resin with a bisphenol epoxy resin of the following Chemical Formula 2: ##STR00002## where n is a real number from 0.1 to 30, R1 and R2 are each independently a hydrogen, substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, and X is an ester linkage containing 1 or more hydroxy groups or 20 to 30% of X as an CR.sub.1R.sub.2 group is an ester linkage containing a hydroxy group.

2. The method of claim 1, wherein the bisphenol epoxy resin has an epoxy equivalent weight of 150 to 300 g/eq, preferably, 180 to 250 g/eq, and the bisphenol resin is bisphenol-A or/and bisphenol-F.

3. The method of claim 1, wherein the bisphenol epoxy resin is 60 to 80 parts by weight, the synthesized oligomer is 15 to 30 parts by weight, the bisphenol resin is 5 to 15 parts by weight, and the epoxy resin has an equivalent weight of 400 to 1,000 g/eq.

4. The method of claim 1, wherein R1 and R2 of the epoxy resin in Chemical Formulae 1 and 2 are hydrogen or methyl, and n is a real number from 1 to 15.

5. The method of claim 1, wherein the oligomer is produced by reacting a monocarboxylic acid containing a phenol group or a derivative thereof with an aliphatic or alicyclic polyalcohol having 3 to 4 hydroxy groups.

6. The method of claim 5, wherein the monocarboxylic acid containing a phenol group or the derivative thereof is 65 to 75 parts by weight, and the aliphatic or alicyclic polyalcohol having 3 to 4 hydroxy groups is 25 to 35 parts by weight.

7. The method of claim 5, wherein the monocarboxylic acid containing a phenol group or the derivative thereof is selected from a group consisting of 4-hydroxyphenyl acetic acid, diphenolic acid, 4-hydroxybenzoic acid, and combinations thereof, and the aliphatic polyalcohol is selected from a group consisting of trimethylolpropane, trimethylolethane, glycerol, 3-hydroxy-2-(hydroxymethyl)-2-methyl propanoate, sorbitol, and combinations thereof.

8. The method of claim 5, wherein the acid value of the oligomer is 0 to 4 mg KOH/g, preferably, 0 to 2 mg KOH/g, and the number average molecular weight (Mn) thereof is 500 to 1,500, preferably 600 to 1,200.

9. A powder coating composition comprising a phenolic hardener or a 2-cyanoguanidine or polyester hardener in an amount of 2 to 200 parts by weight per 100 parts by weight of an epoxy resin manufactured by the method of claim 1.

10. The powder coating composition of claim 9, further comprising one or more selected from a group consisting of a pigment, a filler, an optical stabilizer, a hardening accelerator, a flow enhancer, and a defoamer.

Description

MODE FOR INVENTION

[0054] Hereinafter, the present disclosure will be described in more details through an exemplary embodiment.

[Synthesis Example 1]: Manufacture of Oligomer

[0055] 795 g of 4-hydroxyphenyl acetic acid, 352.5 g of trimethylolpropane, and 2.295 g of a metallic organotin compound (AP-CAT0041, FTC Korea) as a catalyst were put into a four-neck flask where a condenser with a nitrogen gas pipe and a cooling device, an agitator, a thermometer, and a heater were installed, and the temperature was gradually raised. When the temperature reached 100° C. or higher, condensate flowed out and its temperature was raised up to about 220 to 230° C. to induce a reaction, thereby manufacturing an oligomer with an acid value of 2 mg KOH/g or lower and a number average molecular weight of 799.

[Synthesis Example 2]: Manufacture of Epoxy Resin

[0056] 69.42 g of bisphenol-A epoxy resin (YD-128, Kukdo Chemical), 21.38 g of the synthesized oligomer produced in Synthesis Example 1, 9.2 g of bisphenol-F resin, and 0.046 g of ethyl triphenyl phosphonium iodine were put into a four-neck flask where a condenser with a nitrogen gas pipe and a cooling device, an agitator, a thermometer, and a heater were installed, and the temperature was gradually raised. After reacting them at 150° C. for 4 hours, an epoxy resin was manufactured which had an epoxy equivalent weight of 646.3 g/eq, a melt viscosity of 3,079 cps at 150° C., a softening point of 85° C., and a number average molecular weight of 1,608.

[Synthesis Example 3-6]: Manufacture of Epoxy Resin

[0057] An epoxy resin was synthesized by applying the procedure of Synthesis Example 2, except that the components and contents given in the following Table 1 were used.

TABLE-US-00001 TABLE 1 Components for epoxy resin synthesis and their contents Synthesis Examples (g) Components 2 3 4 5 6 YD-128 (epoxy 69.42 69.8 70.71 67.04 67.83 equivalent weight of 187) Oligomer of 21.38 30.5 19.29 26.46 25.67 Synthesis Example 1 Bisphenol F 92 — 10 6.5 6.5 ETPPI* 0.046 0.031 0.029 0.033 0.048 *Ethyl triphenyl phosphonium iodine

[Text Example 1]: Measurement of Physical Properties of Epoxy Resin

[0058] The physical properties of the epoxy resins of the present disclosure manufactured in Synthesis Examples 2 to 6 were measured. Their equivalent weights were measured using a 0.2N—HCl Dioxane solution, and their melt viscosities (cps) were measured at 150° C. using a Brookfield viscometer. Their softening points were measured using a ring-and-ball method, and their number average molecular weights were analyzed by gel permeation chromatography. The results of the physical properties of the epoxy resins measured according to this test are shown in the following Table 2.

TABLE-US-00002 TABLE 2 Physical Properties of Epoxy Resins Synthesis Examples (g) Components 2 3 4 5 6 Equivalent weight [g/eq] 646.3 507 607.8 691 652.7 Melt viscosity [cps] 3079 1750 1450 4317 — Softening point [° C.] 85.0 71.9 75.7 88.9 96.3 Number average 1608 1238 1197 1892 2189 molecular weight [Mn]

[Test Example 2]: Measurement of Gel Time of Epoxy Resins

[0059] The gel times of the epoxy resins of the present disclosure manufactured in Synthesis Examples 2 to 6 were measured after the components were mixed according to the compositions in Table 3. A bisphenol-A hardener (KD-410J, Kukdo Chemical) or a polyester hardener (HC-5501, INOPOL) was used as the hardener.

TABLE-US-00003 TABLE 3 Gel Times of Epoxy Resins Embodiments (g) Components 1 2 3 4 5 6 Synthesis Example 2 7.17 Synthesis Example 3 8.00 Synthesis Example 4 8.88 Synthesis Example 5 9.45 14.55 Synthesis Example 6 14.38 KD-410J 2.83 5.45 5.62 HC-5501 12.00 11.12 10.55 2-MI* 0.1 Embodiment (mins′ secs″) Gel time 1 2 3 4 5 6 120° C. 1′48″ 3′42″ 6′53″ 4′47″ 3′32″ 3′08″ 110° C. 2′27″ 5′17″ 4′21″ *2-methly imidazole

[0060] The gel time of the epoxy resin of the present disclosure of Synthesis Example 2 and the gel time of 650 to 725 g/eq of a bisphenol-A epoxy resin (KD-242G, Kukdo Chemical) for general-use powder coatings were measured after the components were mixed according to the compositions in Table 4. A bisphenol-A hardener (KD-410J, Kukdo Chemical) or a polyester hardener (HC-5602, INOPOL) was used as the hardener.

TABLE-US-00004 TABLE 4 Measurement of Gel Times of Epoxy Resins Embodiments (g) Comparative Examples (g) Components 7 8 1 2 Epoxy resin of 7.23 4.592 Synthesis Example 2 KD-242G 7.293 4.671 KD-410J 2.77 2.707 HC-5602 5.408 5.329 2-MI 01. 0.1 0.1 0.1 Gel Time Embodiment (mins′ secs″) 150° C. 41.16″ .sup.  52.94″ .sup.  1′12″ 1′30″ 130° C. 1′11″ 1′29″ 2′24″ 2′54″ 120° C. 1′46″ 2′11″ 2′35″ 3′57″ 110° C. 2′20″ 4′22″

[0061] As shown in Table 4, the measurement results of the gel times at different curing temperatures of the epoxy resin manufactured according to the method of the present disclosure and the bisphenol-A epoxy resin for general-use powder coatings showed that the gel times in Embodiments 7 and 8 were much shorter than those in Comparative Examples 1 and 2.

[0062] The gel time required to bind the epoxy resin and the hardener to a sufficiently high degree is preferably 2 minutes 20 seconds or shorter. At ultra-low temperatures (110 to 130° C.), the gel times in Embodiments 7 and 8 were short enough to satisfy the above requirement, whereas the gel times in Comparative Examples 1 and 2 were longer.

[Test Example 3]: Manufacture of Powder Coatings

[0063] A powder coating composition was manufactured as shown in the following Table 5 by using the epoxy resin manufactured in Synthesis Example 2. A bisphenol-A hardener (KD-410J, Kukdo Chemical) or a polyester hardener (HC-5602, INOPOL) was used as the hardener. Examples 9 and 10 used the epoxy resin manufactured by Synthesis Example 2 of the present disclosure, and Comparative Examples 3 and 4 used 650 to 725 g/eq of the bisphenol-A epoxy resin for general-use powder coatings (KD-242G, Kukdo Chemical).

TABLE-US-00005 TABLE 5 Manufacture of Powder Coatings Embodiments (g) Embodiments (g) Components 9 10 3 4 Epoxy resin of 216.9 137.8 Synthesis Example 2 KD-242G 217.7 141 KD-410J 83.1 82.3 HC-5602 162.2 159 Benzoin 2 2 2 2 TiO.sub.2 150 150 150 150 BaSO.sub.4 48 48 48 48 2-MI 3 3 3 3 Benzoin: Anti-pinhole agent TiO.sub.2: White pigment BaSO.sub.4: Extender pigment

[0064] The components were mixed according to the compositions shown in Table 5 and then the mixture was passed through an extruder to get the components completely mixed. The obtained substance was broken into fine particles and then applied onto metal surfaces using a Nordson Encore® LT electrostatic spray gun (60 kV), thus forming coating films.

Test Example 4: Measurement of Physical Properties of Powder Coatings

[0065] The powder coatings of Embodiments 9 and 10 manufactured as shown in Table 5 were used for curing on metal surfaces at 110° C./10 mins, 120° C./10 mins, and 130° C./10 mins, and the powder coatings of Comparative Examples 3 and 4 were used for curing on metal surfaces at 110° C., 120° C., 130° C., and 180° C., thereby manufacturing coating specimens with a coating thickness of 60 to 80 μm. The outer appearance and mechanical properties of the manufactured coating specimens were measured, and the results were shown in Tables 6 and 7.

TABLE-US-00006 TABLE 6 Physical Properties of Powder Coating Films (Embodiments of the Disclosure) Embodiments Physical properties 9-1 10-1 9-2 10-2 9-3 10-3 Curing condition 110° C./min 120° C./min 130° C./min Outer Pinhole Good Good Good Good Good Good appearance Gloss 90 37 109 61 106 90 Mechanical Adhesion 100/100 100/100 100/100 100/100 100/100 100/100 properties Flexibility 7.2 mm 1.05 mm 8.89 mm 7.84 mm 9.34 mm 9.52 mm Impact 500 g/50 cm 500 g/50 cm >500 g/100 cm 500 g/55 cm >500 g/100 cm >500 g/100 cm Hardness F HB F HB F HB

TABLE-US-00007 TABLE 7 Physical Properties of Powder Coating Films (Comparative Examples) Comparative Examples Physical properties 3-1 4-1 3-2 4-2 3-3 4-3 3-4 4-4 Curing condition 110° C./min 120° C./min 130° C./min 180° C./min Outer Pinhole Good Good Good Good Good Good Good Good appearance Gloss 120 94.1 120 88.2 120 98.4 116 97.8 Mechanical Adhesion 100/100  70/100 100/100 100/100 100/100 100/100 100/100 100/100 properties Flexibility 0.4 mm 0.69 mm 0.78 mm 0.97 mm 2.76 mm 8.54 mm 8.02 mm 8.62 mm Impact 500 g/10 cm 500 g/10 cm 500 g/15 cm 500 g/30 cm 500 g/30 cm 500 g/30 cm 500 g/50 cm 500 g/100 cm Hardness 2B HB HB HB HB F HB HB

[0066] As shown in Tables 6 and 7, powder coatings obtained by using the epoxy resin manufactured according to the method of the present disclosure and the bisphenol-A epoxy resin for general-use powder coatings having a conventional 150-180° C. curing system were cured in the same manner under a low-temperature curing condition. The results showed that the physical properties of the coating films obtained by curing at 110° C. (Embodiment 9-1) which is an ultra-low temperature, satisfied all of the outer appearance and mechanical property requirements for the current powder coating market, and that especially the coating films obtained by curing at 120° C. or higher (Embodiments 9-2 and 9-3) exhibited far better mechanical properties than the powder coatings obtained by curing under the conventional curing condition (Comparative Examples 3-4). The coating film according to Embodiment 10-2 in which the curing was performed at 120° C. exhibited similar mechanical properties to the coating film according to Comparative Example 4-4 in which the curing was performed at 180° C.

[0067] On the other hand, the coating films according to Comparative Examples 3-1, 3-2, 3-3, 4-1, 4-2, and 4-3 exhibited a poor impact resistance of 500 g/50 cm or lower under a low-temperature curing condition and showed similar differences in flexibility.

[0068] Although the present disclosure has been described above with respect to particular modes of practice and exemplary embodiments of the present disclosure, the present disclosure is not limited to the techniques described in the foregoing embodiments. Rather, various changes and modifications may be made based on the foregoing embodiments so that best powder coatings according to the present disclosure that have physical properties required for the powder coating market can be obtained by means of an ultra-low temperature curing system of 110° C./min. However, it will be evident from the appended claims that all of these changes and modifications fall within the scope of the present disclosure.