A polyester resin particle used for an environment-friendly powder coating without phosphating treatment

Abstract

The application belongs to the technical field of paint and discloses polyester resin particles which can be used for environment-friendly powder paint without phosphating treatment, and the raw materials of the polyester resin particles are composed of the following components in parts by weight: dibasic acid 55-60 parts; dibasic alcohol 30-40 parts; acidolysis agent 2-10 parts; polyhydric alcohol 0.1-1 part; catalyst 0.01-0.5 part; heat stabilizer 0.1-1 part; antioxidant 0.1-1 part; modified phosphate ester 0.1-1 part. The polyester paint produced by the application does not need phosphating treatment on the coating surface when used, greatly reduces the pollution to the environment in the spraying process, simultaneously simplifies the process steps, shortens the process time, reduces the cost, and has a broad application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to polyester resin particles and phosphating-free environmentally friendly powder coatings based thereon. Background Art

[0002] Since its invention by British artist Waross in 1869, the phosphating process has evolved over a long period of time and is now highly mature. It has found numerous applications on metal surfaces, including rust prevention in paint bases, friction reduction and lubrication, and surface decoration. Despite these promising applications, however, the process has struggled to overcome its inherent drawbacks: phosphates and heavy metals are the raw materials for phosphating solutions; nitrites are often used as accelerators in the film-forming process; and significant waste is generated during production. These challenges have hindered the development of the phosphating process, and to date, a fundamental solution remains unresolved.

[0003] In recent years, metal surfaces need to be treated with ceramics (such as Chinese patent CN 114622196A) or phosphating (such as Chinese patent CN 111945142B) before spraying coatings. The traditional phosphating process is complicated and cumbersome. The discharged industrial wastewater contains a large amount of phosphorus, which can cause eutrophication of water bodies. The phosphating solution contains heavy metal ions and nitrites, which have strong carcinogenic effects. Therefore, the discharge of phosphorus-containing wastewater is subject to increasingly strict control, which greatly limits its application. The phosphating process still has many problems such as slow speed, thin phosphating film, and poor corrosion resistance of the film. Even the ceramic process after optimization and modification still has many defects such as complex process, low adhesion, high raw material cost, and poor self-repair ability. Whether from the perspective of environment or energy saving, this high-pollution and high-energy-consuming process is in urgent need of optimization and improvement. However, after years of development, these problems have not been solved, and eliminating this process is the future development direction. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a polyester resin particle and a phosphating-free environmentally friendly powder coating based thereon, aiming to enable it to be directly sprayed on an unphosphated metal surface to solve the pollution problem in the traditional process.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A polyester resin particle is characterized in that the raw materials are composed of the following components in parts by weight: 55-60 parts of dibasic acid; 30-40 parts of diol; 2-10 parts of acidolysis agent; 0.1-1 part of polyol; 0.01-0.5 part of catalyst; 0.1-1 part of heat stabilizer; 0.1-1 part of antioxidant; and 0.1-1 part of modified phosphate ester.

[0007] Furthermore, the dibasic acid is a combination of one or more of terephthalic acid (PTA), adipic acid (ADA) and cyclohexanedicarboxylic acid; and the acidolysis agent is isophthalic acid (IPA).

[0008] Furthermore, the diol is a combination of one or more of neopentyl glycol (NPG), 2-methyl-1,3-propanediol (MPO), 2-butyl-2-ethyl-1,3-propanediol (BEPD), diethylene glycol (DEG) and 1,4-cyclohexanedimethanol.

[0009] Furthermore, the polyol is a combination of one or more of trimethylolpropane (TMP), pentaerythritol and 1,2,4,5-benzeneteterol.

[0010] Furthermore: the catalyst is a combination of one or more of monobutyltin oxide, dibutyltin oxide, stannous oxalate and tetrabutyl titanate; the thermal stabilizer is triphenyl phosphite (TPP); and the antioxidant is a combination of one or more of hindered phenol antioxidants and phosphite antioxidants.

[0011] Furthermore, the modified phosphate ester is a combination of one or more of Grace DC118 and JSC-7300 produced by Hangzhou Jessica Chemical Co., Ltd.

[0012] Trimellitic anhydride (TMA) is highly harmful to the human body. Data show that if exposure is prolonged and no intervention measures are taken, trimellitic anhydride can cause serious and permanent damage to lung function. Therefore, when synthesizing polyester powder, the present invention abandons the conventional TMA end-capping method. Although the water generated by the esterification reaction is not absorbed by TMA, the addition of modified phosphate esters increases the overall polarity of the polyester to achieve the purpose of improving adhesion. This can save the phosphating step during the subsequent coating process. The process flow chart is shown below. Figure 1 At the same time, since modified phosphate is added to the raw material, this raw material contains not only amide groups but also phenyl groups. The lone pair electrons on the N atom in the amide group attract the template. The principle diagram is shown in Figure 2 As shown. The amide group is also a polar group, carrying a large electron cloud, which attracts the metal in the sample and helps improve the coating's adhesion. The phenyl side chain in the modified phosphate ester raw material provides a shielding and protective effect on the groups on the main chain, reducing damage to the main chain during salt spray resistance testing, thereby improving the coating's salt spray resistance.

[0013] The present invention also discloses a preparation method of the polyester resin particles, comprising the following steps: adding a dibasic acid, a diol and a catalyst into a reaction kettle according to a proportion, heating to 230-245° C. under nitrogen protection, carrying out a constant temperature reaction until the acid value of the system reaches 20-30 mgKOH / g, then adding an acidolysis agent, a polyol, a modified phosphate ester, an antioxidant and a heat stabilizer, continuing the constant temperature reaction until the acid value of the system reaches 30-50 mgKOH / g, evacuating and continuing the constant temperature reaction for 0.5-2 hours, discharging the material after the reaction is completed, cooling, and crushing to obtain the polyester resin particles.

[0014] The present invention further discloses a phosphating-free environmentally friendly powder coating based on the polyester resin particles, which comprises the following raw materials in parts by weight:

[0015] 30-40 parts of polyester resin particles;

[0016] 20-30 parts of epoxy resin;

[0017] 0.8-1.2 parts of powder leveling agent;

[0018] Brightening agent 0.8-1.2 parts;

[0019] Pigment 0.5-25 parts;

[0020] 10-40 parts of inorganic filler;

[0021] 0.1-0.5 parts of benzoin.

[0022] Furthermore: the polyester resin particles of the present invention can be cross-linked and cured with epoxy resin without the need for additional curing agent; the powder leveling agent is an acrylic leveling agent; the pigment is a combination of one or more of sericite, TiO2, carbon black, permanent red and phthalocyanine blue; and the inorganic filler is precipitated BaSO4.

[0023] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0024] 1. Currently, general powder coatings need to be vitrified or phosphated before spraying. The present invention obtains polyester resin particles with excellent performance through scientific and reasonable formula design. The powder coating based on the polyester resin particles does not need to be vitrified or phosphated before spraying. This is not only beneficial to saving energy, reducing energy consumption, and reducing pollution problems caused by the production process, but also can protect the substrate from corrosion, thereby expanding the application field of polyester powder coatings.

[0025] 2. To address the curing issue, the present invention adopts a two-component blending method, in which the polyester resin and epoxy resin cross-link to complete the curing. By abandoning the traditional curing agent and using two components to complete the curing, it saves costs and protects the environment.

[0026] 3. After the metal sample is phosphated, an "anchor point" will be formed on the surface. Although this anchor point can be tightly combined with the coating, and tightly fix the surface side layer like an anchor, the coating cannot wrap the anchor point as a whole around the anchor point. There will be a certain gap between the sample, the coating and the anchor point. In the salt spray atmosphere, Cl- enters these gaps with the air flow, thus bypassing the protective layer of the coating and directly invading the surface of the plate. When using the coating of the present invention, the metal surface does not need to be phosphated, and no raised structure will be formed on the surface of the metal sample. The coating and the metal are more tightly bonded. The coating relies on its self-repairing properties to repair surface scratches and prevent corrosive salt spray from further invading the interior of the metal. The amide group in the coating carries a large amount of electron cloud, which attracts the metal sample, improves the adhesion of the coating, and makes its salt spray resistance more excellent. Figure 2 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart;

[0028] Figure 2 Comparison of phosphating and treatment-free sample plates after salt spray corrosion, where: (a), (b), (c) are actual pictures of the sample plates after salt spray test; (d), (e), (f), (g) are diagrams of the salt spray resistance mechanism of phosphating treatment; (h), (i), (j), (k) are diagrams of the salt spray resistance mechanism of non-phosphating treatment. DETAILED DESCRIPTION

[0029] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0030] The reagents and instruments used in the following examples can all be purchased from commercial sources.

[0031] The antioxidants used in the following examples are hindered phenol antioxidant 1076, hindered phenol antioxidant 1010 and phosphite antioxidant 168.

[0032] The epoxy resin used in the following examples is EP-12 produced by Huangshan Meijia New Materials Co., Ltd.

[0033] The powder leveling agent used in the following examples is GLP588 produced by Ningbo Nanhai Chemical Co., Ltd.

[0034] The brightener used in the following examples is 701B produced by Ningbo Nanhai Chemical Co., Ltd.

[0035] The preparation method of the polyester resin particles in the following embodiment comprises the following steps:

[0036] A dibasic acid, diol, and catalyst were added to a reactor according to the ratio. The reaction was heated to 245°C under nitrogen protection and allowed to react at this temperature until the acid value of the system reached 20-30 mgKOH / g. An acidolyzer, polyol, modified phosphate ester, antioxidant, and thermal stabilizer were then added. The reaction was continued at this temperature until the acid value of the system reached 30-50 mgKOH / g (specific values ​​are shown in Table 1). The reaction was then continued at this temperature for 1 hour under vacuum to remove excess esterification product water from the system and increase the reaction rate. This stage primarily involves polymerization between chain segments, resulting in a slight decrease in the acid value and no significant change. After the reaction, the material was cooled and pulverized to produce polyester resin particles.

[0037] The method for preparing a polyester powder coating based on polyester resin particles involves mixing the raw materials according to a specific ratio and then extruding them through a twin-screw extruder. The feeding zone (Zone I) is set at 110°C, and the mixing and extrusion zone (Zone II) is set at 115°C. The extruded powder coating is then ground in a coffee grinder and screened through a series of screens to select a 180-200 mesh coating powder for spraying. Finally, the coating is cured at 180°C for 30 minutes. After the sample is prepared, gloss, film thickness, leveling, impact performance, and salt spray resistance are tested.

[0038] Examples 1 to 3 and Comparative Example 1

[0039] The composition of the components of the polyester resin particles in Examples 1 to 3 and Comparative Example 1 in parts by weight is shown in Table 1, and the physical properties of the obtained polyester are also shown in Table 1.

[0040] Table 1 Raw material composition, dosage and physical properties of polyester resin particles

[0041]

[0042] In Table 1: the acid value was determined according to GB / T 6743-2008; the viscosity was determined according to GB / T 9751.1-2008; and the Tg was determined according to GB / T 19466.2-2004.

[0043] The composition of the components of the powder coatings prepared based on the polyester resin particles of the above embodiments in parts by weight is shown in Table 2, and the physical properties of the obtained coatings are also shown in Table 2.

[0044] Table 2 Raw material composition, dosage and physical properties of polyester resin powder coating during curing stage

[0045]

[0046] The standard used for impact strength is GB / T 1732-1997; the standard used for gloss measurement is GB / T 9754-2003; the standard used for coating adhesion is GB / T 9286-202-2a; the standard used for leveling measurement is JB / T 3998-1999; and the standard used for neutral salt spray resistance measurement is GB / T 1771-2007.

[0047] Table 2 shows that the powder coating curing process involves baking the sample in an oven at 180°C for 30 minutes. Powder Coatings D and H, used as comparative examples, did not contain modified phosphate esters in the polyester resin. Consequently, after 500 hours of neutral salt spray corrosion resistance testing, the coatings exhibited significant flaking. Adding modified phosphate esters to the polyester raw material improved the coating's adhesion, demonstrating that the introduction of amide groups effectively enhances adhesion between the coating and the sample. This demonstrates that, even after process optimization, the optimized powder coating exhibits excellent neutral salt spray resistance, even without the vitrification and phosphating steps. Furthermore, its leveling, gloss, and impact resistance are significantly improved. By skipping the surface phosphating step, the coating process significantly reduces environmental pollution, simplifies the process steps, shortens processing time, and reduces costs, offering broad application prospects.

[0048] The above descriptions are all preferred embodiments of the present invention, which are intended to help illustrate the present invention and do not describe all details in detail. They are not intended to limit the present invention in any substantial way. It should be noted that any equivalent embodiments or modifications that do not depart from the spirit of the present invention are included within the scope of protection of the present invention.

Claims

1. A polyester resin particle that can be used for phosphating-free environmentally friendly powder coating, characterized in that: The raw materials are composed of 55-60 parts by weight of dibasic acid, 30-40 parts of diol, 2-10 parts of acidolysis agent, 0.1-1 part of polyol, 0.01-0.5 part of catalyst, 0.1-1 part of heat stabilizer, 0.1-1 part of antioxidant and 0.1-1 part of modified phosphate ester. The diol is a combination of neopentyl glycol and 2-butyl-2-ethyl-1,3-propanediol. The modified phosphate ester is a combination of one or more of Grace DC118 and Hangzhou Jessica Chemical JSC-7300.

2. The polyester resin particles according to claim 1, wherein: The dibasic acid is a combination of one or more of terephthalic acid, adipic acid and cyclohexanedicarboxylic acid; and the acidolysis agent is isophthalic acid.

3. The polyester resin particles according to claim 1, wherein: The polyol is a combination of one or more of trimethylolpropane, pentaerythritol and 1,2,4,5-benzeneteterol.

4. The polyester resin particles according to claim 1, wherein: The catalyst is a combination of one or more of monobutyltin oxide, dibutyltin oxide, stannous oxalate and tetrabutyl titanate; the heat stabilizer is triphenyl phosphite; and the antioxidant is a combination of one or more of hindered phenol antioxidants and phosphite antioxidants.

5. A method for preparing the polyester resin particles according to any one of claims 1 to 4, characterized in that: The steps include: Add dibasic acid, diol and catalyst into the reactor according to the proportion, heat to 230-245°C under nitrogen protection, and react at constant temperature until the acid value of the system reaches 20-30 mgKOH / g, then add acidolysis agent, polyol, modified phosphate ester, antioxidant and heat stabilizer, continue to react at constant temperature until the acid value of the system reaches 30-50 mgKOH / g, vacuum and continue constant temperature reaction for 0.5-2h, discharge the material after the reaction is completed, cool and crush to obtain polyester resin particles.

6. A phosphating-free environmentally friendly powder coating, characterized by: Prepared from the polyester resin particles according to any one of claims 1 to 4.

7. The phosphating-free environmentally friendly powder coating according to claim 6, characterized in that: The coating comprises the following raw materials in parts by weight: 30-40 parts of polyester resin particles; 20-30 parts of epoxy resin; 0.8-1.2 parts of powder leveling agent; Brightening agent 0.8-1.2 parts; Pigment 0.5-25 parts; 10-40 parts of inorganic filler; 0.1-0.5 parts of benzoin.

8. The phosphating-free environmentally friendly powder coating according to claim 7, characterized in that: The powder leveling agent is an acrylic leveling agent; the pigment is a combination of one or more of sericite, TiO2, carbon black, permanent red and phthalocyanine blue; and the inorganic filler is precipitated BaSO4.

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