Electron beam curing polyester powder coating as well as preparation method and application thereof

Abstract

The invention discloses an electron beam curing polyester powder coating as well as a preparation method and application thereof, and belongs to the field of powder paints.The electron beam curing polyester powder coating comprises the following components in parts by mass: 54 parts of methyl-acrylic polyester, 2 parts of alicyclic diacrylic polyester, 28 parts of highlight barium sulfate, 10 parts of titanium dioxide, 1 part of a flatting agent, 1.5 parts of benzoin and 1 part of a toughening plasticizer. 0.3 part of a brightening agent, 0.5 part of a defoaming agent, 1 part of an electricity increasing agent and 0.7 part of an anti-caking agent. The adopted film-forming substance methyl-acrylic polyester is unsaturated polyester, and during electron beam radiation curing, after double bonds are broken, the methyl-acrylic polyester can be self-polymerized or copolymerized with an active reaction curing agent alicyclic diacrylic polyester, or both the methyl-acrylic polyester and the alicyclic diacrylic polyester are self-polymerized or copolymerized, so that the film-forming property is improved; more cross-linking reaction binding sites can be provided for polymerization reaction, the cross-linking density of a final coating film is improved, and the mechanical property and the medium resistance of the coating film can be obviously improved.

Description

Technical Field

[0001] The invention belongs to the field of powder coatings, and in particular relates to an electron beam cured polyester powder coating and a preparation method and application thereof. Background Art

[0002] Since the 1970s, powder coatings and coating technology have become recognized as 4E-type coatings that meet the requirements of high production efficiency, excellent coating performance, ecology, and economic benefits due to their characteristics of saving petrochemical resources, being pollution-free, high production efficiency, and easy to realize automated spraying. They have become the fastest growing variety among all types of coatings. Powder coatings are divided into thermoplastic powder coatings and thermosetting powder coatings based on the curing type. Thermosetting powder coatings are divided into epoxy, epoxy-polyester, polyester powder coatings, etc. based on the resin type. Since the introduction of powder coatings in my country in the mid-1990s, my country has made great progress in both the scale of powder coating production and the equipment related to powder coating production for more than half a century of technological development and scale expansion, making China the world's largest producer and user of powder coatings. Among them, polyester powder coatings have a wide range of raw materials, are not overly dependent on fossil fuels, and the overall product price is relatively cheap, making it the fastest growing branch of powder coatings.

[0003] Although polyester powder coatings account for 40% of the total amount of thermosetting powder coatings, these powder coatings generally require a baking temperature of 180-200℃ and a time of 15-20min. At present, some powder manufacturers have developed low-temperature curing powder coatings, but the curing temperature is still 140-160℃. For heat-sensitive substrates such as solder, electronic components, and substrates such as PVC, MDF, and plastics, the scope of use is still very limited. In recent years, UV-curing powder coatings developed with reference to liquid coatings have successfully solved the problem that ordinary powder coatings need high-temperature baking to be completely cured. In theory, the application range of powder coatings has been broadened, but in actual use, it is still subject to great limitations. For example, the UV curing process will cause accelerated aging of materials that are not resistant to UV light. For example, in yellow powder coatings, the absorption of ultraviolet light by pigments will cause insufficient absorption of initiators, resulting in incomplete curing of the yellow powder coating or only the surface coating has achieved cross-linking and curing, and the bottom coating has not achieved cross-linking and curing. Specifically, the film has poor impact strength, corrosion resistance, chemical resistance, and film adhesion. UV curing technology only performs well in thin powder coatings (30-50μm) and powder varnishes, but in order to effectively ensure the strength, medium corrosion resistance, wear resistance and decorative properties of the powder coating, pigments and fillers are indispensable in polyester powders.

[0004] Electron beam curing technology is a technology that uses an electron accelerator to emit high-energy electron beams (unidirectional high-speed electron flows with energy). Through the energy of the high-energy electron beams, the liquid coating film on the material surface undergoes an instant cross-linking polymerization reaction to form a polymerized three-dimensional network structure, thereby forming a high-performance coating. Different from thermal curing and photo-curing, electron beam curing technology is a cold processing technology that does not generate heat itself and is very suitable for the processing applications of heat-sensitive materials. At the same time, the electron beam is hardly affected by pigments and fillers, and can completely cure the surface, middle, and bottom of the coating film. This technology can play an important role in the fields of printing inks, coatings, adhesives, composite decorative panels (plastic sheets, billboards, etc.), electronic materials, and wood decorative panels. Summary of the Invention

[0005] The object of the present invention is to provide an electron beam curing polyester powder coating and its preparation method and application to meet the needs of spraying powder coatings on heat-sensitive materials, heat-sensitive materials, and special materials with low-temperature curing requirements.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: An electron beam curing polyester powder coating, comprising the following components in parts by mass: 54 parts of methyl-acrylic polyester, 2 parts of alicyclic diacrylate polyester, 28 parts of high-gloss barium, 10 parts of titanium dioxide, 1 part of leveling agent, 1.5 parts of benzoin, 1 part of toughening and plasticizing agent, 0.3 part of brightening agent, 0.5 part of defoaming agent, 1 part of charge-increasing agent, 0.7 part of anti-caking agent; The glass transition temperature Tg of the methyl-acrylic polyester is 103 °C, and its synthesis process is as follows: (1) Add toluene into a reaction kettle equipped with a stirrer, a condenser, a monomer dropping tube, and a thermometer. Mix methyl methacrylate (MAA), n-hexyl methacrylate (n-BMA), glycidyl methacrylate (GMA), and styrene (St) to form a mixed monomer, and then load it into the monomer dropping tube in advance; (2) After starting the stirrer and stirring, heat the reaction kettle until toluene starts to reflux, and slowly drop the initiator and the mixed monomer; (3) After dropping is completed within 3 h, continue to react for 1 h, and test the hydroxyl value every half hour. The hydroxyl value is controlled at 40-60 mg KOH / g; (4) Put the reactant after the reaction into an intermediate tank. Under the premise of controlling the temperature at 170 °C by starting the thin-film evaporator equipment, slowly add the reactant in the intermediate tank into the thin-film evaporator to volatilize the solvent to form a molten resin liquid. The solvent is recovered into the recovery tank for reuse; (5) The molten resin liquid enters the molten resin tank. Open the roller pressing and cooling belt below the discharge port to perform molten pressing, cooling and crushing on the slowly discharged resin liquid, and then weigh and package it.

[0007] Furthermore, in step (1), the usage ratio of toluene, methacrylic acid, n-hexyl methacrylate, glycidyl methacrylate and styrene is 100:50:15:10:25.

[0008] Furthermore, the leveling agent is GLP504 leveling agent from Ningbo Nanhai Chemical, the toughening plasticizer is TL600 toughening plasticizer from Guangzhou Tianlong Chemical, the brightener is BCL701 brightener from Ningbo Nanhai Chemical, the defoaming agent is YPE defoaming agent from Hubei Laisi Chemical, the charge increasing agent is PW-180 charge adjusting agent from Deqian Chemical, and the anti-caking agent is M-5 fumed silica from Degussa.

[0009] The present invention also provides a method for preparing the electron beam cured polyester powder coating, comprising the following steps: (1) Accurately weigh methyl-acrylic polyester, alicyclic diacrylate polyester, high-gloss barium, titanium dioxide, leveling agent, benzoin, toughening plasticizer, brightener, defoamer, charge enhancer, and anti-caking agent, put them into a premixing tank, stir and crush for 180 seconds to obtain powder; (2) Turn on the main power of the extruder, control the temperature of the extruder zone A to 95°C, the temperature of the extruder zone B to 100°C, and the temperature of the extruder zone C to 105°C, adjust the screw frequency to 50HZ speed requirement, put the powder in the premix tank into the extruder, and the extruded melt is quickly cooled and solidified by the air cooling device to obtain fragments, which are then connected to the water-cooled storage box for cooling treatment; (3) The fragments processed in step (2) are ground by an ACM air mill. After the particle size and the residue on the sieve meet the index requirements, the product is automatically weighed and packaged.

[0010] The present invention also provides the use of the electron beam cured polyester powder coating in coating heat-sensitive substrates, wherein the heat-sensitive substrates include but are not limited to density fiberboard, plastic, paper and electronic components.

[0011] Compared with the prior art, the beneficial technical effects of the present invention are: The present invention uses an unsaturated polymer methyl - acrylic polyester containing double bonds as a reactive film - forming substance, an alicyclic diacrylate polyester as an active reactive curing agent, and an initiator that absorbs radiation waves to initiate the cross - linking reaction of the polymer. Compared with traditional thermosetting polyester powder coatings, electron - beam - cured polyester powder coatings do not need to be baked for 10 - 15 minutes under curing conditions of 180 - 200 °C. After electrostatically spraying the powder onto the material, only 110 °C needs to be applied first to make the powder form a molten state, and then the electron beam is used to cross - link and cure the molten film. The molten film is not directly cured, and the open time of the film is longer, providing more sufficient time for leveling and defoaming, and the film leveling is better. Compared with photo - cured powder coatings (UV curing), the lamp reflector of UV curing needs to be connected to a blower and a water - cooling system to ensure that the system temperature during the photo - curing process will not be too high to damage the lamp or the processed product. However, electron - beam curing belongs to a cold - processing process and does not generate heat, which is suitable for the processing of heat - sensitive materials. Secondly, affected by the absorption of ultraviolet light waves by pigments and fillers, the ultraviolet - light - curing technology only performs well in thin powder coatings (30 - 50 μm) and powder varnishes. However, to effectively guarantee the strength, medium - corrosion resistance, abrasion resistance, and decoration of the powder coating film, pigments and fillers are essential in polyester powder. In contrast, electron - beam curing is basically not affected by pigments and fillers, and the cross - link density of the cured film is higher, and the physical properties of the film are better.

[0012] The film - forming substance methyl - acrylic polyester prepared in the present invention is an unsaturated polyester containing double bonds. When cured by electron - beam radiation, after the double bonds break, they can self - polymerize or copolymerize with the active reactive curing agent alicyclic diacrylate polyester, or both methyl - acrylic polyester and alicyclic diacrylate polyester can self - polymerize or copolymerize, which can provide more cross - linking reaction binding sites for the polymerization reaction, increase the cross - link density of the final film, and significantly improve the mechanical properties and medium - resistance properties of the film.

[0013] The Tg value of the methyl methacrylate of the film - forming substance prepared in the present invention is 103 °C. The Tg values of traditional polyester resins, epoxy resins, and acrylic resins are mostly between 50 - 90 °C. In powder coatings, the higher the glass transition temperature value of the resin, the better the anti - caking property, hardness, and stain - resistance of the prepared powder coating. The electron - beam - cured polyester powder coating prepared in the present invention has good anti - caking property and good powder looseness. After electrostatic spraying, rapid curing can be achieved in 3 - 6 minutes through the molten leveling plus electron - beam curing technology, which is very suitable for the production mode of rapid - processing assembly lines and is also applicable to the processing and application on non - metals, heat - sensitive materials, and special materials with ultra - low - temperature curing requirements.

[0014] In the present invention, the alicyclic diacrylate polyester is an active reaction curing agent, which replaces the traditional triglycidyl isocyanurate (TGIC) curing agent for carboxyl-terminated polyester resin. TGIC has the characteristics of moisture absorption and high carcinogenicity. The alicyclic diacrylate polyester is convenient for storage and avoids the physical harm to coating production employees caused by this highly carcinogenic curing agent during storage, transportation and production, meeting the environmental protection requirements of EU countries.

[0015] For the electron beam-curable polyester powder coating of the present invention, when electrostatically sprayed on a material, only by applying 110 °C to make the powder form a molten state, the electron beam can crosslink and cure the molten film. At this temperature, benzoin in the product will expel the gas in the molten film but will not cause the film to turn yellow due to high temperature, and the color of the entire film is more saturated and bright. During the electron beam curing process, benzoin (diphenylglycol ketone) can also act as an initiator to undergo a free radical reaction under the action of the electron beam, further increasing the crosslinking density of the film.

[0016] The electron beam-curable polyester powder coating of the present invention has non-toxic and easily available raw materials. There is no VOC release throughout the whole process of coating production and construction application. The recycled powder can be recycled and reused, and the theoretical utilization rate of the product is over 95%. It is suitable for industrialized and large-scale production. Detailed implementation mode

[0017] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Embodiment (1)Preparation of methyl - acrylic polyester: Add 10 kg of toluene into a reaction kettle equipped with a stirrer, a condenser, a monomer dropping pipe, and a thermometer. Mix 5 kg of methacrylic acid (MAA), 1.5 kg of n - hexyl methacrylate (n - BMA), 1 kg of glycidyl methacrylate (GMA), and 2.5 kg of styrene (St) to form a mixed monomer, and then load it into the monomer dropping pipe in advance. After starting the stirrer and stirring, heat the reaction kettle until toluene starts to reflux, and slowly drop the initiator and the mixed monomer. After dropping is completed within 3 h, continue the reaction for 1 h, and test the hydroxyl value every half hour, with the hydroxyl value controlled at 40 - 60 mg KOH / g. The reactant after the reaction is put into an intermediate tank. Under the premise of controlling the temperature of the thin - film evaporator equipment at 170 °C, slowly add the reactant in the intermediate tank into the thin - film evaporator to volatilize the solvent to form a molten resin liquid, and the solvent is recovered into the recovery tank for reuse. The molten resin liquid enters the molten resin tank, and the roller - press cooling belt below the discharge port is opened to perform melt - pressing, cooling, and crushing on the slowly discharged resin liquid, and then it is weighed and packaged.

[0019] (2)Preparation of electron - beam - cured polyester powder coating: Accurately weigh 5400 g of methyl - acrylic polyester, 200 g of alicyclic diacrylate polyester, 2800 g of high - gloss barium, 1000 g of titanium dioxide, 100 g of leveling agent, 150 g of benzoin, 100 g of toughening and plasticizing agent, 30 g of brightening agent, 50 g of defoaming agent, 100 g of charge - increasing agent, and 70 g of anti - caking agent, and put them into a premixing tank. Stir and crush for 180 s to obtain a powder material. Turn on the main power of the extruder, control the temperature of zone A of the extruder at 95 °C, zone B at 100 °C, and zone C at 105 °C, adjust the screw frequency to the rotational speed requirement of 50 HZ, put the powder material in the premixing tank into the extruder, and the extruded melt is quickly cooled and cured by an air - cooling device to obtain fragments, which are then connected to a water - cooling storage tank for temperature reduction treatment. Use an ACM air mill to grind the treated fragments. After detecting that the particle size and sieve residue of the ground powder meet the index requirements, perform automatic weighing and packaging of the product.

[0020] In this example, the alicyclic diacrylate polyester is produced by Hangzhou Zhongfa Powder Resin Co., Ltd., the high - gloss barium is produced by Shanxi Hongji Powder Co., Ltd., the titanium dioxide is Zhonghe R2195 rutile titanium white, the benzoin and the leveling agent are produced by Hangzhou Zhongshun Chemical Co., Ltd., the leveling agent is GLP504 leveling agent of Ningbo Nanhai Chemical Co., Ltd., the toughening and plasticizing agent is TL600 toughening and plasticizing agent of Guangzhou Tianlong Chemical Industry Co., Ltd., the brightening agent is BCL701 brightening agent of Ningbo Nanhai Chemical Co., Ltd., the defoaming agent is YPE defoaming agent of Hubei Laisi Chemical Industry Co., Ltd., the charge - increasing agent is PW - 180 charge regulator of Delon Chemical Co., Ltd., and the anti - caking agent is M - 5 fumed silica of Degussa.

[0021] The electron beam-cured polyester powder coating prepared in this example was electrostatically sprayed onto a heat-sensitive substrate. After baking at 110°C for 3 minutes for melting and leveling, it entered the electron radiation area for irradiation for 3 - 6 minutes to complete curing. It was tested according to the type I, class 1 standard of thermosetting powder coatings HG / T 2006 - 2022, and the results are shown in Table 1.

[0022] Table 1 Test results of the coating properties of the examples Comparative example Preparation of thermosetting polyester powder coating: Accurately weigh 5400 g of carboxyl-terminated polyester, 400 g of triglycidyl isocyanurate, 2600 g of high-gloss barium, 1000 g of titanium dioxide, 100 g of leveling agent, 150 g of benzoin, 100 g of toughening and plasticizing agent, 30 g of brightening agent, 50 g of defoaming agent, 100 g of charge-increasing agent, and 70 g of anti-caking agent. Put them into the premixing tank, check and close the tank lid and the discharge port, and start stirring and crushing for 180 s to obtain powder; Turn on the main power supply of the extruder, control the temperature of zone A of the extruder at 95°C, zone B at 100°C, and zone C at 105°C, adjust the screw frequency to 50 HZ rotation speed requirement, put the powder in the premixing tank into the extruder, and the extruded melt is quickly cooled and cured by an air-cooling device to obtain fragments, which are connected to a water-cooling storage tank for temperature reduction treatment; Use ACM air mill to grind the treated fragments, and after detecting that the particle size and sieve residue of the ground powder meet the index requirements, carry out automatic weighing and packaging of the product.

[0023] In this comparative example, the type of carboxyl-terminated polyester is P5200, with an acid value of 33 - 38 and a ratio of 93 / 7, produced by DSM; Triglycidyl isocyanurate (TGIC) is produced by Niutang Chemical Co., Ltd., high-gloss barium is produced by Shanxi Hongji Powder Co., Ltd., titanium dioxide is Zhonghe R2195 rutile titanium white, benzoin and leveling agent are produced by Hangzhou Zhongshun Chemical Co., Ltd., and toughening and plasticizing agent, brightening agent, defoaming agent, charge-increasing agent, and anti-caking agent are produced by Ningbo Nanhai Chemical Co., Ltd.

[0024] The thermosetting polyester powder coating prepared in the comparative example was cured by baking at 180°C for 15 minutes. It was tested according to the type I, class 1 standard of thermosetting powder coatings HG / T 2006 - 2022, and the results are shown in Table 2.

[0025] Table 2 Test results of the coating properties of the comparative example It was found by comparing Table 1 and Table 2 that compared with traditional thermosetting powder coatings, the electron beam-cured powder coatings can meet the requirements of the type I, class 1 standard of thermosetting powder coatings HG / T 2006 - 2022 in terms of chemical resistance and mechanical properties. The difference is that the electron beam-cured powder coatings do not require high-temperature baking and can be used for the processing and application of heat-sensitive materials such as heat-sensitive materials and electronic components.

[0026] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the technical solutions and concepts of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electron beam curable polyester powder coating, characterized in that, Comprising the following components in parts by mass: 54 parts of methyl-acrylic polyester, 2 parts of alicyclic diacrylate polyester, 28 parts of high-gloss barium, 10 parts of titanium dioxide, 1 part of leveling agent, 1.5 parts of benzoin, 1 part of toughening and plasticizing agent, 0.3 part of brightening agent, 0.5 part of defoaming agent, 1 part of charge-increasing agent, 0.7 part of anti-caking agent; The glass transition temperature Tg of the methyl-acrylic polyester is 103 °C, and its synthesis process is as follows: (1) Add toluene into a reaction kettle equipped with a stirrer, a condenser, a monomer dropping tube, and a thermometer. Mix methylacrylic acid (MAA), n-hexyl methacrylate (n-BMA), glycidyl methacrylate (GMA), and styrene (St) to form a mixed monomer, and then load it into the monomer dropping tube in advance; (2) After starting the stirrer and stirring, heat up the reaction kettle until toluene starts to reflux, and slowly drop the initiator and the mixed monomer; (3) After dropping is completed within 3 h, continue the reaction for 1 h, and test the hydroxyl value every half hour. The hydroxyl value is controlled at 40 - 60 mg KOH / g; (4) Put the reactant after the reaction into an intermediate tank. Under the premise of controlling the temperature of the thin-film evaporator equipment at 170 °C, slowly add the reactant in the intermediate tank into the thin-film evaporator to volatilize the solvent to form a molten resin liquid. The solvent is recovered into the recovery tank for reuse; (5) The molten resin liquid enters the molten resin tank. Open the roller press cooling belt below the discharge port, and perform melt pressing, cooling and crushing on the slowly discharged resin liquid, and then weigh and package it.

2. An electron beam curable polyester powder coating according to claim 1, characterized in that: In step (1), the dosage ratio of toluene, methylacrylic acid, n-hexyl methacrylate, glycidyl methacrylate, and styrene is 100:50:15:10:

25.

3. The electron beam curable polyester powder coating according to claim 1, characterized in that: The leveling agent is GLP504 leveling agent of Ningbo Nanhai Chemical, the toughening and plasticizing agent is TL600 toughening and plasticizing agent of Guangzhou Tianlong Chemical Industry, the brightening agent is BCL701 brightening agent of Ningbo Nanhai Chemical, the defoaming agent is YPE defoaming agent of Hubei Laisi Chemical Industry, the charge-increasing agent is PW-180 charge regulator of Delon Chemical, and the anti-caking agent is M-5 fumed silica of Degussa.

4. The preparation method of an electron beam-curable polyester powder coating according to claim 1, characterized in that, Including the following steps: (1) Accurately weigh methyl-acrylic polyester, alicyclic diacrylate polyester, high-gloss barium, titanium dioxide, leveling agent, benzoin, toughening and plasticizing agent, brightening agent, defoaming agent, charge-increasing agent, and anti-caking agent, put them into a premixing tank, and stir and crush for 180 s to obtain powder; (2) Turn on the main power of the extruder, control the temperature of zone A of the extruder at 95 °C, the temperature of zone B at 100 °C, and the temperature of zone C at 105 °C. Adjust the screw frequency to 50 HZ rotation speed requirement, put the powder in the premixing tank into the extruder, and the extruded melt is quickly cooled and solidified by an air-cooling device to obtain fragments, which are connected to a water-cooling storage tank for temperature reduction treatment; (3) Use ACM air mill to grind the fragments processed in step (2). After detecting that the particle size and sieve residue of the ground powder meet the index requirements, perform automatic weighing and packaging of the product.

5. The application of an electron beam-curable polyester powder coating as described in claim 1 in coating a heat-sensitive substrate, wherein the heat-sensitive substrate includes but is not limited to density fiberboard, plastic, paper, and electronic components.

Images