Highly branched liquid epoxy resin, its preparation method and application

Abstract

This invention relates to a highly branched liquid epoxy resin. The process involves first performing a transesterification reaction between 1,3,5-tris(2-hydroxyethyl)cyanuric acid and dimethyl octanoate in xylene solvent to extend the chain. Then, pyromellitic acid is added for further symmetrical chain extension to obtain a rigid polyhydroxy compound. This compound is then reacted with epichlorohydrin and sodium hydroxide, undergoing sequential ring-opening and ring-closing reactions to obtain the highly branched liquid epoxy resin. When used in a 50 / 50 powder coating system to replace part of the E-12 epoxy resin, the resulting coating exhibits good hardness, scratch resistance, and water resistance. It is applied directly externally without affecting the original powder coating system. Furthermore, the hardness range of the coating can be adjusted by the amount added, making it convenient to use, widely applicable, and with promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin technology, specifically to a highly branched liquid epoxy resin, its preparation method, and its application. Background Technology

[0002] Currently, powder coatings, as environmentally friendly coatings, are characterized by solvent-free production, 100% film formation, and low energy consumption, and have been widely used in various fields such as furniture and home appliances in recent years. In the indoor furniture sector, 50 / 50 mixed-type powder coatings offer superior overall performance and cost advantages, occupying a significant share of indoor furniture coatings. However, because they are used in indoor coating applications, such as alloy furniture and wardrobes, they are frequently subjected to minor collisions and scratches, making the coating film susceptible to damage. Therefore, developing high-hardness, scratch-resistant 50 / 50 mixed-type coatings is a necessary direction for industry development. Since 50 / 50 blended powder coatings consist of 50% polyester resin and 50% E-12 epoxy resin by weight, and the properties of E-12 epoxy resin are relatively fixed, they are often produced by modifying polyester resin. Although some polyester resin products can achieve high-hardness coatings, they require special high-hardness polyester resin formulations and varieties. The raw material and manufacturing costs of polyester resins are high, and the film hardness is difficult to adjust by the amount added, thus limiting its application range. Developing an additive method to improve the film hardness of 50 / 50 indoor blended powder coatings, with flexible adjustment of film hardness through addition, has broad market application prospects and research value. Summary of the Invention

[0003] To address current market demands and the aforementioned problems, this invention relates to a highly branched liquid epoxy resin, its preparation method, and its applications. This liquid epoxy resin is prepared by first reacting 1,3,5-tris(2-hydroxyethyl)cyanuric acid with dimethyl octanoate in xylene solvent via transesterification to obtain a chain-extended product. Then, trimellitic acid is added for further symmetrical chain extension. After the trimellitic acid reaction is complete, a rigid polyhydroxy compound is obtained. This compound is then reacted with epichlorohydrin and sodium hydroxide, undergoing ring-opening and ring-closing reactions sequentially to obtain the highly branched liquid epoxy resin. When used in 50 / 50 ordinary powder coating systems to replace part of the E-12 epoxy resin, it can improve the hardness and scratch resistance of the coating film, and also enhance its water resistance.

[0004] A highly branched liquid epoxy resin comprising the following raw materials in molar amounts:

[0005]

[0006] The raw materials also include catalyst 1, catalyst 2 and an appropriate amount of water.

[0007] Preferably, catalyst 1 is tetrabutyl titanate, and the amount used is 0.5-0.8% of the mass of dimethyl octanoate; catalyst 2 is boron trifluoride diethyl ether solution, and the amount used is 2-3% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0008] The method for preparing a highly branched liquid epoxy resin as described above includes the following steps:

[0009] A. Add the prescribed amount of xylene, 1,3,5-tris(2-hydroxyethyl)cyanuric acid and catalyst 1 into the reaction vessel, start stirring, heat to 130-135℃, and then add the prescribed amount of dimethyl octanoate dropwise from the high-level tank to carry out the transesterification reaction. The dropwise addition is completed in 0.8-1.2 hours, and then the reaction is kept at the temperature.

[0010] B. The content of dimethyl octanoate was detected by gas chromatography. When the content of dimethyl octanoate was less than 1%, the amount of chain extender pyromellitic acid was added according to the formula, and the temperature was raised to the boiling point of xylene solvent to carry out reflux dehydration esterification chain extension reaction.

[0011] C. Detect the acid value of the reactants in the system. When the acid value of the reactants is less than 2 mg KOH / g, start the vacuum system to remove xylene solvent under reduced pressure, and maintain the temperature at 140-145℃.

[0012] D. After no obvious xylene solvent has evaporated, release the vacuum system, cool down to 95-100℃, then add the prescribed amount of epichlorohydrin and catalyst 2, and after fully dissolve and homogenize, continue the ring-opening reaction at 95-100℃ for 2-3 hours.

[0013] E. Sampling and testing: When the content of free epichlorohydrin in the system no longer decreases, cool down to 50-55℃. At this time, add sodium hydroxide to carry out the ring-closing reaction. After all the sodium hydroxide is added, continue to keep warm to carry out the ring-closing reaction for 1-1.5 hours.

[0014] F. Then cool to room temperature, filter to remove solid sodium chloride from the system, obtain filtrate, wash the filtrate with water, remove the aqueous phase by separation, heat to 120-125℃, and use a high vacuum system to fully remove excess epichlorohydrin and water. When the volatile content is less than 1%, stop the vacuum system and discharge the material at high temperature to obtain highly branched liquid epoxy resin.

[0015] Preferably, in step C, the vacuum is controlled between -0.096 MPa and -0.098 MPa; in step F, the vacuum is controlled between -0.098 MPa and -0.099 MPa; in step E, sodium hydroxide is added in three batches to carry out the closed-loop reaction, with each batch spaced 20 minutes apart; in step F, the filtrate is washed three times with water equal to one-fifth of the filtrate mass to remove the aqueous phase by separation.

[0016] For example, a method for preparing a highly branched liquid epoxy resin includes the following steps:

[0017] A. Add the prescribed amount of xylene, 1,3,5-tris(2-hydroxyethyl)cyanuric acid and catalyst 1 into the reaction vessel, start stirring, heat to 130-135℃, and then add the prescribed amount of dimethyl octanoate dropwise from the high-level tank to carry out the transesterification reaction. The dropwise addition is completed in 0.8-1.2 hours, and then the reaction is kept at the temperature.

[0018] B. The content of dimethyl octanoate was detected by gas chromatography. When the content of dimethyl octanoate was less than 1%, it indicated that the transesterification reaction was completed. The amount of chain extender pyromellitic acid was added and the temperature was raised to the boiling point of xylene solvent for reflux water separation esterification chain extension reaction.

[0019] C. Detect the acid value of the reactants in the system. When the acid value of the reactants is less than 2 mg KOH / g, it indicates that the chain extension reaction of trimesic acid is basically completed. At this time, start the vacuum system, remove xylene solvent under reduced pressure, maintain the temperature at 140-145℃, and control the vacuum at -0.096 MPa to -0.098 MPa.

[0020] D. After no obvious xylene solvent is evaporated (less than 1 drop within 20 seconds), release the vacuum system, cool down to 95-100℃, then add the prescribed amount of epichlorohydrin and catalyst 2, and after fully dissolve and homogenize, continue the ring-opening reaction at 95-100℃ for 2-3 hours.

[0021] E. Sampling and testing: When the content of free epichlorohydrin in the system no longer continues to decrease, it indicates that the ring-opening intermediate has been completely reacted. Cool down to 50-55℃, and add sodium hydroxide in 3 batches to carry out the ring-closing reaction, with an interval of 20 minutes between each batch. After all the sodium hydroxide is added, continue to keep warm to carry out the ring-closing reaction for 1-1.5 hours.

[0022] F. Then cool to room temperature, filter to remove solid sodium chloride from the system, and obtain filtrate. Wash the filtrate three times with water equal to one-fifth of the filtrate mass to remove the aqueous phase. Heat to 120-125℃ and use a high vacuum system to remove excess epichlorohydrin and water. Control the vacuum degree at -0.098Mpa to -0.099Mpa. When the volatile content is less than 1%, stop the vacuum system and discharge at high temperature to obtain highly branched liquid epoxy resin with an average branching functionality of about 9.

[0023] The resulting product is a pale yellow, transparent, viscous liquid with an epoxy equivalent of 285-335 g / mol.

[0024] The molecular structure diagram of the product is as follows:

[0025]

[0026] The present invention also relates to the application of the highly branched liquid epoxy resin as described above or the highly branched liquid epoxy resin obtained by the preparation method described above in a 50 / 50 indoor mixed powder coating system; it is used by direct external addition.

[0027] As described above, in the 50 / 50 indoor hybrid powder coating system, a highly branched liquid epoxy resin replaces part of the E-12 epoxy resin and is used in combination with polyester resin.

[0028] For example, the 50 / 50 mixed powder coating formulation can be formulated as follows by weight: 300 parts polyester resin; 200 parts E-12 epoxy resin; 60 parts epoxy resin prepared in this invention; 200 parts titanium dioxide; 180 parts barium sulfate; 10 parts leveling agent; 10 parts gloss enhancer; and 4 parts benzoin.

[0029] Coating preparation method: Mix all materials according to the above powder coating formula, extrude, press, and crush them using a twin-screw extruder, and then crush and sieve the sheet to make powder coating; spray the powder coating onto the surface-treated tinplate substrate with an electrostatic spray gun, and cure it to obtain the coating.

[0030] Beneficial effects:

[0031] This invention relates to a highly branched liquid epoxy resin, its preparation method, and its application. The liquid epoxy resin is prepared by first reacting 1,3,5-tris(2-hydroxyethyl)cyanuric acid with dimethyl octanoate in xylene solvent via transesterification to obtain a chain-extended product. Then, trimellitic acid is added to continue symmetrical chain extension. After the trimellitic acid reaction is complete, a rigid polyhydroxy compound is obtained. This compound is then reacted with epichlorohydrin and sodium hydroxide, respectively, to undergo ring-opening and ring-closing reactions sequentially, resulting in the highly branched liquid epoxy resin. It is evident that this liquid epoxy resin possesses both rigid isocyanuric acid rings and benzene rings provided by pyromellitic acid, exhibiting a well-symmetrical structure and high rigidity. When used in a 50 / 50 powder coating system to replace part of the E-12 epoxy resin, it can improve the hardness and scratch resistance of the coating film, and also enhance its water resistance. Furthermore, its direct external application does not affect the original powder coating system, and the hardness range of the coating film can be adjusted by controlling the amount added. It is very convenient to use, has a wide range of applications, and shows promising prospects. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0033] All raw materials described in this invention are commercially available.

[0034] Preparation Example 1

[0035] A highly branched liquid epoxy resin comprising the following raw materials in molar amounts:

[0036]

[0037] Catalyst 1 is tetrabutyl titanate, and its amount is 0.8% of the mass of dimethyl octanoate;

[0038] Catalyst 2 is a boron trifluoride diethyl ether solution, used in an amount of 3% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0039] A method for preparing highly branched liquid epoxy resin includes the following steps:

[0040] A. Add the prescribed amount of xylene, 1,3,5-tris(2-hydroxyethyl)cyanuric acid and catalyst 1 into the reaction vessel, start stirring, heat to 135℃, and then add the prescribed amount of dimethyl octanoate dropwise from the high-level tank to carry out the transesterification reaction. The addition is completed in 1 hour, and then the reaction is kept at the temperature.

[0041] B. The content of dimethyl octanoate was detected by gas chromatography. When the content of dimethyl octanoate was less than 1%, it indicated that the transesterification reaction was completed. The amount of chain extender pyromellitic acid was added and the temperature was raised to the boiling point of xylene solvent for reflux water separation esterification chain extension reaction.

[0042] C. Detect the acid value of the reactants in the system. When the acid value of the reactants is less than 2 mg KOH / g, it indicates that the chain extension reaction of pyromellitic acid is basically completed. At this time, start the vacuum system, remove xylene solvent under reduced pressure, maintain the temperature at 145℃, and control the vacuum at -0.098 MPa.

[0043] D. After no obvious xylene solvent is evaporated (less than 1 drop within 20 seconds), release the vacuum system, cool down to 100°C, and then add the prescribed amount of epichlorohydrin and catalyst 2. After fully dissolving and homogenizing, continue the ring-opening reaction at 100°C for 3 hours.

[0044] E. Sampling and testing: When the content of free epichlorohydrin in the system no longer continues to decrease, it indicates that the ring-opening intermediate has been completely reacted. Cool down to 55°C, and add sodium hydroxide in 3 batches to carry out the ring-closing reaction, with an interval of 20 minutes between each batch. After all the sodium hydroxide is added, continue to keep warm to carry out the ring-closing reaction for 1.5 hours.

[0045] F. Then cool to room temperature, filter to remove solid sodium chloride from the system, and obtain filtrate. Wash the filtrate three times with water equal to one-fifth of the filtrate mass to remove the aqueous phase. Heat to 125°C and use a high vacuum system to remove excess epichlorohydrin and water. Control the vacuum degree at -0.098 MPa. When the volatile content is less than 1%, stop the vacuum system and discharge the material at high temperature to obtain highly branched liquid epoxy resin.

[0046] The prepared liquid epoxy resin is a pale yellow viscous liquid with an epoxy equivalent of 303 g / mol.

[0047] Preparation Example 2

[0048] A highly branched liquid epoxy resin comprising the following raw materials in molar amounts:

[0049]

[0050] Catalyst 1 is tetrabutyl titanate, and its amount is 0.8% of the mass of dimethyl octanoate; catalyst 2 is boron trifluoride diethyl ether solution, and its amount is 3% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0051] The preparation method is the same as in Preparation Example 1.

[0052] The prepared liquid epoxy resin is a pale yellow viscous liquid with an epoxy equivalent of 314 g / mol.

[0053] Preparation Example 3

[0054] A highly branched liquid epoxy resin comprising the following raw materials in molar amounts:

[0055]

[0056] Catalyst 1 is tetrabutyl titanate, and its dosage is 0.6% of the mass of dimethyl octanoate;

[0057] Catalyst 2 is a boron trifluoride diethyl ether solution, used in an amount of 2.5% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0058] The preparation method is the same as in Preparation Example 1.

[0059] The prepared liquid epoxy resin is a pale yellow viscous liquid with an epoxy equivalent of 327 g / mol.

[0060] Preparation Example 4

[0061] A highly branched liquid epoxy resin comprising the following raw materials in molar amounts:

[0062]

[0063]

[0064] Catalyst 1 is tetrabutyl titanate, and its amount is 0.8% of the mass of dimethyl octanoate;

[0065] Catalyst 2 is a boron trifluoride diethyl ether solution, used in an amount of 3% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0066] The preparation method is the same as in Preparation Example 1.

[0067] The prepared liquid epoxy resin is a pale yellow viscous liquid with an epoxy equivalent of 292 g / mol.

[0068] Examples 1-4 (obtained from the epoxy resins prepared in Examples 1-4, respectively)

[0069] The application testing of the product of this invention is based on an indoor 50 / 50 mixed powder coating formulation, which is typically as follows by weight:

[0070]

[0071] The polyester resin used is the 50 / 50 mixed low-cost, economical polyester resin from Anhui Shenjian New Material Co., Ltd., model SJ3C. The E-12 epoxy resin used is the ordinary E-12 epoxy resin (model 604) from Anhui Hengyuan Technology Co., Ltd.

[0072] Comparative Example 1

[0073] Similar to the liquid epoxy resin in Example 3, only the amount of the liquid epoxy resin of the present invention added was adjusted. In the above 50 / 50 mixed powder coating formulation, the E-12 epoxy resin was increased to 250 parts by weight, and the epoxy resin of the present invention was reduced to 30 parts by weight.

[0074] Comparative Example 2

[0075] In the above 50 / 50 mixed powder coating formulation, the E-12 epoxy resin is increased to 300 parts by weight, and the epoxy resin of the present invention is not used.

[0076] Comparative Example 3

[0077] In the 50 / 50 mixed powder coating formulation, commercially available E-51 liquid epoxy resin was used instead of the epoxy resin of the present invention as Comparative Example 2.

[0078] Coating preparation: Mix all materials according to the above powder coating formula, extrude, press, and crush using a twin-screw extruder, then pulverize and sieve the sheet (150-180 mesh) to produce powder coating. Apply the powder coating to a surface-treated tinplate substrate using an electrostatic spray gun, achieving a film thickness of approximately 80 μm. Curing is then performed at 180℃ for 15 minutes to obtain the coating layer.

[0079] Performance Comparison

[0080] The coating index testing is based on GB / T 21776-2008 "Guideline for Testing Standards of Powder Coatings and Their Coatings". Pencil hardness testing is conducted according to GB / T 6739-2006 "Determination of Hardness of Paints and Varnishes by Pencil Method". The pencil hardness parameters are 5B-4B-3B-2B-B-HB-FH-2H-3H-4H-5H, with the hardness grade gradually increasing from left to right.

[0081] The polyester resins prepared in the above embodiments and comparative examples were used to prepare coatings according to the coating formulations provided by the present invention. The coating performance results are shown in Table 1 below.

[0082] Table 1 Performance of Powder Coating Film

[0083]

[0084]

[0085] As can be seen from Table 1, the products corresponding to the embodiments of the present invention have a high degree of branching. The 50 / 50 powder coatings involved in the product have a smooth and flat appearance after curing, excellent impact resistance, gloss of about 93%, and a hardness of 2H or above, with most at the 3H level. Due to the participation of highly branched epoxy resin in curing, the coating has high density and excellent boiling water resistance. After boiling in water for 2 hours, the coating showed no change and had good overall performance.

[0086] In Comparative Example 1, the highly branched epoxy resin of the present invention was reduced from 60 parts by mass to 30 parts by mass, and the hardness of the coating film decreased. Compared with Example 1, the hardness of the coating film decreased from 2H to H level, indicating that the hardness of the coating film can be adjusted by adjusting the amount of external additives to meet the needs of different customers for the hardness of the coating film.

[0087] Comparative Example 2 does not use the highly branched epoxy resin of the present invention. The coating film is prepared according to the current normal 50 / 50 mixed powder coating. It uses a low-cost and economical polyester resin, and its hardness only reaches the F level. It also shows a very slight loss of gloss after boiling in water for 2 hours.

[0088] Comparative Example 3 uses commercially available linear liquid epoxy resin E-51 instead of the epoxy resin of this invention. Due to the low branching degree and small molecular weight of E-51 epoxy resin, the final coating film is not fully cured, and cracking occurs during backflow. Moreover, the coating film hardness is significantly lower than that of the ordinary 50 / 50 powder coating in Comparative Example 2, only reaching the HB level. The coating film shows obvious loss of gloss after boiling in water for 2 hours, and cannot meet the requirements of this invention to improve the coating film hardness.

[0089] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A highly branched liquid epoxy resin, characterized in that, Including the following raw materials in molar amounts: The raw materials also include catalyst 1, catalyst 2, and water; Catalyst 1 is tetrabutyl titanate, and its dosage is 0.5-0.8% of the mass of dimethyl octanoate; catalyst 2 is boron trifluoride diethyl ether solution, and its dosage is 2-3% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid. The preparation method of highly branched liquid epoxy resin includes the following steps: A. Add the prescribed amount of xylene, 1,3,5-tris(2-hydroxyethyl)cyanuric acid and catalyst 1 into the reaction vessel, start stirring, heat to 130-135℃, and then add the prescribed amount of dimethyl octanoate dropwise from the high-level tank to carry out the transesterification reaction. The dropwise addition is completed in 0.8-1.2 hours, and then the reaction is kept at the temperature. B. The content of dimethyl octanoate was detected by gas chromatography. When the content of dimethyl octanoate was less than 1%, the amount of chain extender pyromellitic acid was added according to the formula, and the temperature was raised to the boiling point of xylene solvent to carry out reflux dehydration esterification chain extension reaction. C. Detect the acid value of the reactants in the system. When the acid value of the reactants is less than 2 mg KOH / g, start the vacuum system to remove xylene solvent under reduced pressure, and maintain the temperature at 140-145℃. D. After no obvious xylene solvent has evaporated, release the vacuum system, cool down to 95-100℃, then add the prescribed amount of epichlorohydrin and catalyst 2, and after fully dissolve and homogenize, continue the ring-opening reaction at 95-100℃ for 2-3 hours. E. Sampling and testing: When the content of free epichlorohydrin in the system no longer decreases, cool down to 50-55℃. At this time, add sodium hydroxide to carry out the ring-closing reaction. After all the sodium hydroxide is added, continue to keep warm to carry out the ring-closing reaction for 1-1.5 hours. F. Then cool to room temperature, filter to remove solid sodium chloride from the system, obtain filtrate, wash the filtrate with water, remove the aqueous phase by separation, heat to 120-125℃, and use a high vacuum system to fully remove excess epichlorohydrin and water. When the volatile content is less than 1%, stop the vacuum system and discharge the material at high temperature to obtain highly branched liquid epoxy resin.

2. The method for preparing a highly branched liquid epoxy resin as described in claim 1, characterized in that, Includes the following steps: A. Add the prescribed amount of xylene, 1,3,5-tris(2-hydroxyethyl)cyanuric acid and catalyst 1 into the reaction vessel, start stirring, heat to 130-135℃, and then add the prescribed amount of dimethyl octanoate dropwise from the high-level tank to carry out the transesterification reaction. The dropwise addition is completed in 0.8-1.2 hours, and then the reaction is kept at the temperature. B. The content of dimethyl octanoate was detected by gas chromatography. When the content of dimethyl octanoate was less than 1%, the amount of chain extender pyromellitic acid was added according to the formula, and the temperature was raised to the boiling point of xylene solvent to carry out reflux dehydration esterification chain extension reaction. C. Detect the acid value of the reactants in the system. When the acid value of the reactants is less than 2 mg KOH / g, start the vacuum system to remove xylene solvent under reduced pressure, and maintain the temperature at 140-145℃. D. After no obvious xylene solvent has evaporated, release the vacuum system, cool down to 95-100℃, then add the prescribed amount of epichlorohydrin and catalyst 2, and after fully dissolve and homogenize, continue the ring-opening reaction at 95-100℃ for 2-3 hours. E. Sampling and testing: When the content of free epichlorohydrin in the system no longer decreases, cool down to 50-55℃. At this time, add sodium hydroxide to carry out the ring-closing reaction. After all the sodium hydroxide is added, continue to keep warm to carry out the ring-closing reaction for 1-1.5 hours. F. Then cool to room temperature, filter to remove solid sodium chloride from the system, obtain filtrate, wash the filtrate with water, remove the aqueous phase by separation, heat to 120-125℃, and use a high vacuum system to fully remove excess epichlorohydrin and water. When the volatile content is less than 1%, stop the vacuum system and discharge the material at high temperature to obtain highly branched liquid epoxy resin.

3. The method for preparing a highly branched liquid epoxy resin as described in claim 2, characterized in that, In step C, the vacuum is controlled between -0.096 MPa and -0.098 MPa; in step F, the vacuum degree is controlled between -0.098 MPa and -0.099 MPa.

4. The method for preparing a highly branched liquid epoxy resin as described in claim 2, characterized in that, In step E, sodium hydroxide is added in three batches to carry out the ring-closing reaction, with each batch spaced 20 minutes apart.

5. The method for preparing a highly branched liquid epoxy resin as described in claim 2, characterized in that, In step F, the filtrate is washed three times with water equal to one-fifth of the filtrate mass to remove the aqueous phase by separation.

6. The application of the highly branched liquid epoxy resin as described in claim 1 or the highly branched liquid epoxy resin obtained by the preparation method according to any one of claims 2-5 in a 50 / 50 indoor mixed powder coating system.

7. In the application described in claim 6, in the 50 / 50 indoor hybrid powder coating system, a highly branched liquid epoxy resin replaces a portion of the E-12 epoxy resin and is used in combination with polyester resin.

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