Synthesis of polyester resins for powder coatings prepared for polyester (PET) recycling materials

Zeng calendar 1, 2, Li Yong 1, 2, Liu Liang 1, 2, Li Xiaoqiang 1, 2, Tao Zhirong 1, 2, Shi Yuanrong 1, 2
1. China Electrical Science Research Institute Co., Ltd.
2. Guangzhou Dynasky Materials Technology Co., Ltd.
Summary: introduced how to use polyester (PET) recycled materials for powder coating polyester resin. In the process of preparing polyester, the effects of polyester recovery materials and polyol types on alcohol solution reaction were examined, and the effects of polyol types and polyester recycled materials on polyester resin properties were also discussed. The resulting synthetic polyester resin has the same properties as conventional polyester and can meet the requirements of indoor coating

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With the rapid development of polymer materials, polymer materials represented by polyester plastics in the field of engineering plastics and bottling materials have been large-scale applications, their use increased year by year, these materials after the completion of the use of value will produce a large number of waste, environmental protection caused great pressure. How to deal with or reuse these wastes is an urgent problem to be solved, and has received more and more attention from all over the world. In the production of polyester resin for powder coatings, the raw material type is basically the same as the raw material used in the production of polyester resin for plastic, and the use of polyester recycling material degradation to prepare polyester resin for powder coating is a subject worth studying. In recent years, in order to improve the ecological environment, the country has introduced a variety of policies and measures to protect the environment, including the paint industry for the "paint-to-powder" policy is of great significance to the protection of the environment. With the continuous implementation of the policy, powder coating use gradually increased, the major polyester resin enterprises are also increasing production capacity, the demand for raw materials is also growing, while the powder coating polyester industry competition is fierce, enterprises in order to sustainable development have to strictly control production costs, recyclable polyester plastic applied to powder coating polyester resin preparation, not only can reduce the production costs of enterprises, but also to solve the problem of secondary utilization of polyester waste, reduce the dependence of polyester resin manufacturers on petroleum-based raw materials.
At present, there are more research and applications on polyester recycling materials in liquid coatings, and the liquid coatings that can be prepared using waste polyester as raw materials are mainly polyester resin coatings, epoxy resin coatings, aolate resin coatings and polyurethane coatings. However, the relevant literature on polyester resins used in the preparation of powder coatings using polyester recycled material alcohol is rare, among which Wang Xiaoyan and others reported on the polyester resins used in PET alcohol solution legal polyester/epoxy mixed powder coatings, and discussed the control factors of polyester resin synthesis process and The effect of monomer on film coating performance, Song Hongxuan and others reported that under the aid of microwave, the use of new glycol to disprove waste PET, the product after esterification, prepared can be used for polyester-epoxy powder coating polyester resin. In this paper, by studying the alcohol solution reaction of polyester recycled materials, and using the products obtained by alcohol solution as raw materials for polyester resins used in the preparation of powder coatings, the final preparation of polyester resins has good comprehensive properties.
1 Experimental part
1.1 Experiment main raw materials
polyester recycling material, new glycol (NPG), glycol (EG), glycol (DG), 2-methyl-1, 3-propylene glycol (MPD), For benzoic acid (PTA), trihydroxymethyl propane (TMP), paraben terabyte (TMA), monobutyl tin oxide, E-12 epoxy resin, titanium dioxide powder, vanadium sulfate, leveling agent, sabbath, the above materials are industrial grade.
1.2 polyester resin preparation
in the reactor, nitrogen protection, according to the amount of formula added polyester recycling material, polyols and alcohol-dissoling catalyst for alcohol solution reaction, reaction to material clear and transparent; Then add a polyic acid and esterification catalyst, nitrogen continues to heat up the reaction, about 180 degrees C esterified water began to generate and distillate, and then gradually heated to 230 degrees C for esterification dehydration reaction, until no further water distillation, and then cooling for vacuum shrinking React and pull out the small molecular by-product until the desired acid value and molten viscosity are reached, then cool down and add the ratio of the acid antidote to seal the end reaction, until the acid value reaches about 50 mg KOH/g, and finally add the appropriate amount of additives, stirring evenly can be produced.
1.3 Preparation of powder coatings and coating models
synthetic polyester resins, E-12 epoxy resins, pigments, leveling agents and degassing agents are weighed according to table 1 formulation and added to the mixer, after the ingredients, premixed, melted extruded, cooled press, crushed, crushed through the sieve can obtain a certain particle size of powder coating samples. The prepared powder coating is applied to the treated cold-rolled steel plate by electrostic spraying, and the coating model is obtained by curing 10min to 15min at 180 to 200 oC.
1.4 Analysis and test
acid value: test the acid value of polyester resin by GB/T 6743-2008; Viscosity: Test the melt viscosity of polyester resin according to ASTM D4287; Glassing temperature: according to GB/T 19466.2-2004 test polyester resin glass temperature, heating speed of 10K/min; Reactive: tested by GB/T 16995-1997; Impact performance: According to GB/T 1732-1993, the coating film is positive and reverse-punched by the lacquer film impactor, and the cracking of the coating film is observed; Gloss: According to GB/T 9754-2007, the coating 60 degrees gloss is tested with a 60-degree gloss tester; Adhesion test according to GB/T 9286-1998; Neutral salt spray test (500h) according to GB/T 1771-91 test; Pencil hardness test according to GB/T 6739-2006 test; Test the coating gloss after boiling the coating in boiling water for 2h to assess the coating's water resistance.
2 Results and discussion of the effects of
2.1 polyester recycled materials on alcohol-relief reactions
Due to the many types of polyester plastics on the market, there are many sources of polyester recycled materials, their structural composition and relative molecular mass are also different, the reaction conditions are not the same when alcohol solution. In order to investigate the influence of different polyester recycled materials on alcohol solution reaction, several representative polyester recovery materials were selected in this paper, NPG's alcohol solution reaction was studied, and in order to reflect better contrast, the alcohol solution temperature of this study was unified at 210 degrees C, and the results were shown in Table 2.
As can be known from Table 2, the polyester recovery material of the above-mentioned brand has different relative molecular mass and melting point, and its reactivity varies when the meldi reaction occurs, which is reflected in the high molecular weight of polyester recovery material, and when the alcohol is fully delysed, the consumption of new glycol More, this is because the process of alcoholation reaction is to degrade polymers with high molecular weight into small molecular lymers with low molecular weight, which means that the higher the molecular mass of polyester recovery material, in the case of alcohol to small molecules of similar molecular weight lysum, the reaction consumes more alcohol.
2.2 Effects of polyols on alcohol solution reactions
In the preparation of polyester resins for powder coatings, different polyols, common such as NPG, EG, DG and MPD, are involved in formulation design, depending on the resin performance requirements. In order to learn more about the mellow reaction of different polyols and polyester recyclers, this paper studies the alcohol solution reactions of several commonly used polyols and polyester recyclers, and also examines the dosing and alcohol solution temperature required for different polyols at the time of reaction. In the experiment, 200g polyester recycled material (brand 881) was selected as the subject of the study, and the results were found in Table 3.
table 3 shows that when alcohol is dissophedged with exactly the same quality polyester recycled material, the amount of molars required for different polyols is different, and the temperature of alcohol solution is not the same. This is due to differences in the structure of polyols resulting in different reaction activity, as shown by the different temperature required for the meldiol reaction. From the results of the study, it can be found that the same quality of polyester recovery material, NPG requires the least amount of molar, and EG requires the lowest temperature of the alcohol solution reaction. Due to the low reaction activity of DG itself, its dosing is the highest and the highest temperature of alcohol solution.
2.3 Effect of polyols on polyester resin performance
In this paper, in order to investigate the effect of polyols on polyester resin performance of polyester resins in the study of polyester recycling material preparation, the experiment was conducted on the premise of the same polyester recovery material, fixed polyester recycling material and polyic acid type and dosing, and the polyols of the same amount of mols were synthesized with the same acid value (49 to 52) in order to investigate the effect of polyester on polyester resin performance.
table 4 shows that polyester resins prepared with different polyols behave at exactly the same glassesized transition temperature (Tg) and melting viscosity under conditions of the same acid value. Generally speaking, there are several factors affecting polymer Tg, including the structure of the polymer main chain, the influence of the side chain and the inter-molecular force produced by the polar group, the greater the rigidity of the resin molecular main chain, the greater the resistance of the side chain base group, the stronger the inter-molecular force, the more difficult the rotation of the chain segment, the higher the Tg. Because there are two side methyls on the NPG monostructure, there is a greater bit resistance than EG, DG and MPD, making the rotation of the chain segment more difficult and Tg performing higher. From the molecular structure, DG is composed of two EG molecules dehydrated and reduced, is a long straight chain flexible monosome, the molecule is easy to rotate around a single bond, increasing the activity of the chain segment, thereby reducing the resin Tg. The bit resistance of EG and MPD monomer structure is between NPG and DG, and the Tg represented by resin is also somewhere in between, wherein MPD monomer has a side methyl, the rotation of its main chain is more difficult than EG, so its preparation of polyester resin Tg is higher. The melt viscosity of polyester resin is also related to molecular structure, and the effect of fatty family binary alcohol with side chain or asymmetric structure on the viscosity of resin melt is greater than that of straight chain. Under the condition of obtaining the same acid value, the larger the bit resistance, the greater the viscosity of the resulting resin melt. Among the above polyols, the position resistance of NPG monosome is the largest, so the resin fuse viscosity is the largest, DG has a longer chain segment relative to EG, the free movement of its chain segment is easier, and the melt viscosity of the prepared resin is lower.
2.4 Effect of polyester recycled material on polyester resin performance
In order to investigate the effect of polyester recycled material on polyester resin performance, this study synthesized polyester resin with the same acid value (49 to 52) by adding polyester recovery material with different mass fractions, on the premise of ensuring consistent formulation composition.
as can be known from Table 5, the viscosity, relative molecular mass and glassy transition temperature of polyester resins increased gradually with the increase of polyester recycled materials under the premise that the acid values were consistent. Generally speaking, the molecular weight of polyester resins used in conventional powder coatings is about 4000, while the relative molecular mass of polyester resins used as engineering plastics is relatively large (generally around 30,000), polyester recycling materials as waste after use of polyester plastics, in the recovery process almost The properties of the resin relative to the molecular weight are retained, therefore, when using polyester recycling materials to prepare polyester resins for powder coatings, their dosing will directly affect the relative molecular quality of polyester resins, and the molecular weight of polyester resins will increase significantly with the increase of polyester recycling material content. The viscosity of polyester resin is related to the relative molecular mass, which usually increases with the increase of relative molecular mass. In the synthesis process, due to the addition of polyols and end-end agents, destroyed the regulation of polyester chain segment, the final synthetic resin is anaplastic polyester resin, but due to the molecular weight of polyester recycling material is too large, structural symmetry is too strong, so that anaetic polyester resin chain segment activity is reduced, Tg is relatively high.
2.5 Compared with the performance of conventional polyester resins
Combining the above experimental results, this paper synthesizes polyester resins for powder coatings using polyester recycled materials, and prepares powder coatings for them, as compared to the properties of conventional polyester resins in Table 6.
From the test results of Table 6, the basic properties of polyester resins and cured coating properties of powder coatings prepared from polyester recycled materials in this paper are comparable to between the performance of conventional polyester products and can fully meet the requirements of daily use.
3 Conclusion
In this paper, in the study of polyester recycling material preparation powder coating polyester resin experiments found that different types of polyester recycled materials in the meldiation of the amount of polyols required to vary, due to differences in monomer activity, different amounts of polyols required There are differences in the temperature of alcoholation, the variety of polyols used in the process of alcoholation has different effects on the performance of polyester resins, the experimental results show that NPG-prepared resins have higher Tg and molten viscosity, while DG-prepared polyester resins have lower Tg and molten viscosity. Summarizing the above experimental results, the performance index of polyester resin prepared from polyester recycling material meets or approaches the performance of conventional polyester resin, which greatly reduces the production cost of resin under the premise of meeting the performance requirements of powder coating.