Polyester resin for triglycidyl trimesic acid ester curing powder coating and preparation method of polyester resin

Abstract

The invention discloses polyester resin for a triglycidyl trimesic acid ester curing powder coating and a preparation method of the polyester resin. The polyester resin is obtained by esterification and condensation polymerization of trimesic acid, terephthalic acid, glycidyl methacrylate, glycidyl neodecanoate, palmitic acid, neopentyl glycol and behenyl alcohol. The cleaning agent comprises the following components in parts by mass: 5-15 parts of trimesic acid; 10 to 25 parts of terephthalic acid; 3 to 17 parts of glycidyl methacrylate; 8 to 12 parts of glycidyl neodecanoate; 3 to 7 parts of palmitic acid; 5 to 19 parts of neopentyl glycol; and 3 to 7 parts of behenyl alcohol. According to the invention, terephthalic acid and neopentyl glycol are used as framework monomers, and glycidyl methacrylate and glycidyl neodecanoate are used for modifying polyester resin, so that an obtained coating is higher in gloss and better in fineness; behenyl alcohol and palmitic acid are adopted to reduce the softening point of the polyester resin, reduce the difference between a curing agent and polyester in softening flow, increase the wettability of a film forming matter to pigments, fillers and a base material, and improve the gloss and fineness of a coating.

Description

Technical Field

[0001] The invention relates to the technical field of polyester resins for powder coatings, in particular to a polyester resin for triglycidyl trimesic acid-cured powder coatings and a preparation method thereof. Background Art

[0002] Outdoor powder coatings are more favored by downstream customers due to their good weather resistance and water boiling resistance. At present, outdoor powder coatings are divided into two categories according to their curing system: triglycidyl isocyanurate (TGIC) and hydroxyalkylamide (HAA).

[0003] In the prior art:

[0004] CN118772384A discloses a polyester resin for high-hardness, high-temperature resistant powder coatings and its preparation method and application. The invention uses p-cresol, phenol, furfural residue, formaldehyde, dimethyl adipate, 1,3-dihydroxybutane, ethylmalonic acid, 1,1-cyclohexanediacetic acid and the like as raw materials for polymerization to obtain a polyester resin. The resin has good heat resistance and the raw materials are environmentally friendly, but its application is mainly focused on the heat resistance and hardness of the polyester coating, and does not involve fineness and gloss;

[0005] CN112048235A discloses a long-lasting weather-resistant, chloride-corrosion-resistant polyester powder coating and a preparation method thereof. The invention adopts polyester resin, TGIC, triglycidyl trimesic acid, titanium dioxide, barium sulfate, a brightener and a leveling agent to prepare a powder coating with long-lasting weather resistance and chloride-corrosion resistance. The powder coating prepared by TGIC has high paint film hardness, no pinholes when thickly coated, good weather resistance and yellowing resistance; in addition, since it has good compatibility with polyester, small molecule TGIC will produce a strong plasticizing effect after being added to polyester, so TGIC will greatly reduce the Tg of the powder, thereby affecting its storage stability; its fatal disadvantage is that it is potentially carcinogenic.

[0006] HAA has a highly active amide hydroxyl structure. Its advantages are non-toxicity, good mechanical properties, and basically no reduction in powder Tg. Its disadvantages are that due to its inherent chemical structure, it has poor anti-yellowing performance, is prone to pinholes when thickly coated, has poor compatibility with polyester resins, and has low board gloss and poor fineness.

[0007] In order to overcome the defects of HAA yellowing, poor fineness and TGIC carcinogenicity, some domestic manufacturers have developed triglycidyl trimesic acid, which is made of trimesic acid and allyl chloride through the epoxidation of meta-chloroperbenzoic acid. It overcomes the sensitization problem of TGIC and the problem of HAA yellowing pinholes, but its melting point (80°C) is quite different from the softening point of existing polyester (105-125°C). During the melt extrusion process, triglycidyl trimesic acid (TOTC) curing agent and polyester are difficult to mix into a homogeneous phase, resulting in phase separation. Under extrusion conditions, it is difficult to wet the pigments and fillers, which will result in poor fineness, low gloss and granularity of the final coating. In addition, its chemical structure is quite different from the existing polyester main chain structure, which is also one of the reasons for its low gloss, poor fineness and poor leveling.

[0008] In summary, in view of the poor fineness, low gloss and granular feel of the existing cured powder coatings, it is urgent to develop a polyester resin for high-gloss and high-fineness powder coatings cured with triglycidyl trimesic acid. Summary of the invention

[0009] The purpose of the present invention is to provide a polyester resin for a triglycidyl trimesic acid (TOTC)-cured powder coating in view of the fact that triglycidyl trimesic acid (TOTC) curing agent and polyester in the prior art are difficult to mix into a homogeneous phase, resulting in phase separation, and it is difficult to wet the pigments and fillers under extrusion conditions, resulting in poor fineness of the final coating, low gloss, and a grainy feeling on the board surface;

[0010] Another object of the present invention is to provide a method for preparing a polyester resin for curing powder coatings with triglycidyl trimesic acid.

[0011] The technical solution adopted to achieve the purpose of the present invention is:

[0012] A polyester resin for trimesic acid triglycidyl ester-cured powder coating, wherein the polyester resin is obtained by esterification and polycondensation of trimesic acid, terephthalic acid, glycidyl methacrylate, glycidyl neodecanoate, palmitic acid, neopentyl glycol and behenyl alcohol, and the mass fractions of each component are as follows:

[0013] Trimesic acid: 5-25 parts;

[0014] Terephthalic acid: 10-35 parts;

[0015] Glycidyl methacrylate: 3-31 parts;

[0016] Glycidyl neodecanoate: 8-18 parts;

[0017] Palmitic acid: 3-11 parts;

[0018] Neopentyl glycol: 5-29 parts;

[0019] Behenyl alcohol: 3-14 parts.

[0020] As a further improvement of this solution, the acid value of the polyester resin is 50-70 mgKOH / g and the viscosity is 1000-3000 mPa.s / 200°C.

[0021] As a further improvement of this solution, the components also include 0.08-0.2 parts of a catalyst, and the catalyst is zinc acetate.

[0022] As a further improvement of the present solution, the components further include an anti-aging agent which is an environmentally friendly phenol-free pentaerythritol diisotridecyl diphosphite, and the added amount is 0.1-0.2 parts.

[0023] As a further improvement of the present solution, the components further include auxiliary agents, and the auxiliary agents include a curing accelerator, an antioxidant and a pigment dispersing auxiliary agent.

[0024] As a further improvement of this scheme, the curing accelerator is di(tert-butylcyclohexane)-18-crown-6, and the addition amount is 0.03-0.13 parts. The antioxidant is di(tert-butylcyclohexane)-18-crown-6, and the addition amount is 0.1-0.5 parts. The pigment dispersing aid is SA506, and the addition amount is 0.05-0.25 parts.

[0025] A method for preparing a polyester resin for a triglycidyl trimesic acid cured powder coating comprises the following steps:

[0026] Step 1, according to the formula, glycidyl methacrylate, neopentyl glycol, behenyl alcohol and a catalyst are added into a reaction kettle, heated to melt and stirred;

[0027] Step 2, adding trimesic acid, terephthalic acid, and an anti-aging agent to the mixed material obtained in step 1 in sequence, raising the temperature for esterification under protective gas conditions, separating the gas phase material, removing small molecules, gradually reaching chemical equilibrium, and obtaining oligomers;

[0028] Step 3, detecting the acid value of the oligomer obtained in step 2, and when the acid value is 8-15 mgKOH / g, adding glycidyl neodecanoate, continuing to heat, and keeping the temperature to react until the gas phase material temperature is lower than 50° C.;

[0029] Step 4, detecting the acid value of the polymer obtained in step 3, and performing reduced pressure vacuum polycondensation when the acid value is 40-55 mgKOH / g, until the acid value of the polymer reaches 25-45 mgKOH / g;

[0030] Step 5, adding a formulated amount of palmitic acid to the polymer obtained in step 4, capping again, and keeping warm until the acid value of the obtained polyester resin reaches 50-70 mgKOH / g and the viscosity reaches 1000-3000 mPa.s;

[0031] Step 6, cooling the polyester resin obtained in step 5, adding an auxiliary agent, stirring and opening a vacuum, the vacuum degree is 300-600 mmHg, stirring, discharging, cooling and tableting.

[0032] As a further improvement of this scheme, the melting temperature in step 1 is 240-255°C, the esterification temperature in step 2 is 230-235°C, the protective gas is argon, the argon flow rate is 15-45mL / min, the insulation temperature in step 5 is 230-235°C, in step 6, the vacuum stirring time is 50-100mins, and the discharge temperature is 190-195°C.

[0033] A powder coating is obtained by weighing, mixing, melting, extruding, tableting, crushing and screening prepared polyester resin, triglycidyl trimesic acid, titanium dioxide, precipitated barium sulfate, PLA-200 and benzoin.

[0034] As a further improvement of this solution, the particle size of the powder coating is 30-60 μm.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The invention adopts terephthalic acid and neopentyl glycol as skeleton monomers, and glycidyl methacrylate and glycidyl neodecanoate to modify the polyester resin, so that the polyester resin has better compatibility with the environmentally friendly curing agent triglycidyl trimesic acid, and the coating has higher gloss and better fineness; behenyl alcohol and palmitic acid are adopted to reduce the softening point of the polyester resin, reduce the difference between the curing agent and the polyester in softening flow, increase the wettability of the film-forming material to the color filler and the substrate, and improve the gloss and fineness of the coating; zinc acetate and phenol-free pentaerythritol diisotridecyl diphosphite are used to improve the environmental protection of the polyester resin and reduce the harm to the environment and the toxicity to the human body. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Table 1 shows the specific components and physical and chemical properties of the polyester resins of Examples 1-4 of the present invention. Each of the examples of the present invention adopts the following preparation method:

[0039] A method for preparing a polyester resin for a triglycidyl trimesic acid cured powder coating comprises the following steps:

[0040] Step 1: Add glycidyl methacrylate, neopentyl glycol and behenyl alcohol into a reaction kettle according to the formula amount, heat to melt and stir to obtain a mixed material.

[0041] Step 2, add trimesic acid, terephthalic acid and a catalyst to the mixed material obtained in step 1 in sequence, raise the temperature for esterification and keep warm under argon protection, separate the gas phase material through a packed tower, remove small molecules, gradually reach chemical equilibrium, and obtain oligomers.

[0042] Step 3, detecting the acid value of the oligomer obtained in step 2, when the acid value is 8-15 mgKOH / g, adding glycidyl neodecanoate, continuing to heat, and keeping the temperature to react until the gas phase material temperature is lower than 50°C.

[0043] Step 4, when the acid value of the polymer in step 3 is 40-55 mgKOH / g, perform reduced pressure vacuum polycondensation until the acid value of the polymer reaches 25-45 mgKOH / g.

[0044] Step 5, adding a formulated amount of palmitic acid to the polymer obtained in step 4, capping again, and keeping warm until the acid value of the polyester resin reaches 50-70 mgKOH / g and the viscosity reaches 1000-3000 mPa.s.

[0045] Step 6, cooling to 200°C, adding additives, stirring for 10 minutes, opening the vacuum, the vacuum degree is 300-600 mmHg, stirring for 50 minutes, discharging, cooling and tableting to obtain a polyester resin for powder coating cured with triglycidyl trimesic acid.

[0046] Table 1

[0047]

[0048]

[0049] As can be seen from Table 1, through Examples 1-4 and Comparative Examples 1-2, it can be found that the embodiments of the present invention use terephthalic acid and neopentyl glycol as skeleton monomers, and glycidyl methacrylate and glycidyl neodecanoate to modify the polyester resin, so that the polyester resin and the environmentally friendly curing agent triglycidyl trimesic acid are more compatible, and the coating has higher gloss and better fineness; behenyl alcohol and palmitic acid are used to reduce the softening point of the polyester resin, greatly reducing the viscosity of the powder melt system, forming a better leveling effect, and in addition, it is also beneficial to the dispersion of pigments and fillers in the resin system and the spreading of the powder on the metal substrate, so that the coating has excellent interlayer adhesion.

[0050] The polyester resins prepared in Examples 1-4 and Comparative Examples 1-2 and commercially available polyester resin 4412 (acid value of 54.21 mgKOH / g, viscosity of 4510 mPa.s / 200°C, softening point of 113°C, Foshan Ax New Materials Co., Ltd.) were weighed 480 g, triglycidyl trimesic acid 120 g, titanium dioxide 250 g, precipitated barium sulfate 130 g, PLA-200 10 g, and benzoin 4 g. The above materials were weighed, mixed, melted, extruded, tableted, crushed, and sieved, wherein the mesh number of the sieve was 250 meshes, and a powder with a particle size of 30-60 μm was obtained. The powder was electrostatically sprayed and placed in an oven at 200°C*15 min to obtain a coating. The test results of the obtained coating are shown in Table 2 below.

[0051] Table 2

[0052]

[0053] As shown in Table 2, the polyester resin cured by trimesic acid triglycidyl ester prepared by the formula of the present invention has a molecular main chain with more benzene and glycidyl ester structures, which can significantly improve the compatibility of polyester resin and trimesic acid triglycidyl ester, facilitate the homogeneous mixing of the two during extrusion, and completely cure with trimesic acid triglycidyl ester at 200℃*15min. The resulting coating has high gloss, excellent fineness and good leveling, and the board surface is flat and free of graininess. In addition, due to the use of high-grade fatty monomers such as behenyl alcohol and palmitic acid, the viscosity and softening point of the polyester are reduced, the anti-bending performance of the coating is outstanding, the adhesion is level 0, and the wettability with the metal substrate is excellent. The use of additives such as zinc acetate and phenol-free pentaerythritol diisotridecyl diphosphite improves the environmental protection of the polyester resin synthesis and use process, reduces the harm to the environment and the toxicity to the human body, and expands the application field of the resin of the present invention. Compared with commercially available polyester and comparative polyester, the polyester obtained by the present invention has excellent board surface effect and mechanical properties in the triglycidyl trimesic acid curing system, and can be used as a supporting polyester for an environmentally friendly curing agent.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A polyester resin for triglycidyl trimesic acid curing powder coating, characterized in that: The polyester resin is obtained by esterification and polycondensation of trimesic acid, terephthalic acid, glycidyl methacrylate, glycidyl neodecanoate, palmitic acid, neopentyl glycol and behenyl alcohol, and the mass fractions of each component are as follows: Trimesic acid: 5-25 parts; Terephthalic acid: 10-35 parts; Glycidyl methacrylate: 3-31 parts; Glycidyl neodecanoate: 8-18 parts; Palmitic acid: 3-11 parts; Neopentyl glycol: 5-29 parts; Behenyl alcohol: 3-14 parts.

2. The polyester resin for triglycidyl trimesic acid curing powder coating according to claim 1, characterized in that: The polyester resin has an acid value of 50-70 mgKOH / g and a viscosity of 1000-3000 mPa.s / 200°C.

3. The polyester resin for triglycidyl trimesic acid curing powder coating according to claim 1, characterized in that: The components also include 0.08-0.2 parts of a catalyst, which is zinc acetate.

4. The polyester resin for triglycidyl trimesic acid curing powder coating according to claim 1, characterized in that: The components also include an anti-aging agent which is an environmentally friendly phenol-free pentaerythritol diisotridecyl diphosphite, and the added amount is 0.1-0.2 parts.

5. The polyester resin for triglycidyl trimesic acid curing powder coating according to claim 1, characterized in that: The components also include auxiliary agents, which include curing accelerators, antioxidants and pigment dispersing auxiliary agents.

6. The polyester resin for triglycidyl trimesic acid curing powder coating according to claim 5, characterized in that: The curing accelerator is di(tert-butylcyclohexane)-18-crown-6, and the addition amount is 0.03-0.13 parts. The antioxidant is di(tert-butylcyclohexane)-18-crown-6, and the addition amount is 0.1-0.5 parts. The pigment dispersing aid is SA506, and the addition amount is 0.05-0.25 parts.

7. The method for preparing a polyester resin for a triglycidyl trimesic acid cured powder coating according to claim 1, characterized in that: The following steps are involved: Step 1, according to the formula, glycidyl methacrylate, neopentyl glycol, behenyl alcohol and a catalyst are added into a reaction kettle, heated to melt and stirred; Step 2, adding trimesic acid, terephthalic acid, and an anti-aging agent to the mixed material obtained in step 1 in sequence, raising the temperature for esterification under protective gas conditions, separating the gas phase material, removing small molecules, gradually reaching chemical equilibrium, and obtaining oligomers; Step 3, detecting the acid value of the oligomer obtained in step 2, and when the acid value is 8-15 mgKOH / g, adding glycidyl neodecanoate, continuing to heat, and keeping the temperature to react until the gas phase material temperature is lower than 50° C.; Step 4, detecting the acid value of the polymer obtained in step 3, and performing reduced pressure vacuum polycondensation when the acid value is 40-55 mgKOH / g, until the acid value of the polymer reaches 25-45 mgKOH / g; Step 5, adding a formulated amount of palmitic acid to the polymer obtained in step 4, capping again, and keeping warm until the acid value of the obtained polyester resin reaches 50-70 mgKOH / g and the viscosity reaches 1000-3000 mPa.s; Step 6, cooling the polyester resin obtained in step 5, adding an auxiliary agent, stirring and opening a vacuum, the vacuum degree is 300-600 mmHg, stirring, discharging, cooling and tableting.

8. The method for preparing a polyester resin for a triglycidyl trimesic acid cured powder coating according to claim 7, characterized in that: The melting temperature in step 1 is 240-255°C, the esterification temperature in step 2 is 230-235°C, the protective gas is argon, and the argon flow rate is 15-45mL / min. The insulation temperature in step 5 is 230-235°C, and in step 6, the vacuum stirring time is 50-100min, and the discharge temperature is 190-195°C.

9. A powder coating containing the polyester resin according to claim 1, characterized in that The powder coating is obtained by weighing, mixing, melting, extruding, tableting, crushing and screening the polyester resin described in claim 1, triglycidyl trimesic acid, titanium dioxide, precipitated barium sulfate, PLA-200 and benzoin.

10. The powder coating according to claim 9, characterized in that The particle size of the powder coating is 30-60 μm.

Images