Powder coating for refrigerated container door plate and preparation method of powder coating

Abstract

The invention belongs to the technical field of thermosetting powder coatings, and particularly relates to a powder coating for a refrigerated container door plate and a preparation method thereof. Polyester resin, a curing agent, a flatting agent, benzoin, an infrared reflection pigment, a core-shell impact modifier and titanium dioxide are premixed, melt extrusion, crushing and sieving are performed, and the powder coating for the refrigerated container door plate is obtained. The prepared powder coating for the refrigerated container door plate solves the problems that a conventional water-based coating is poor in adhesive force and impact resistance and the like, efficient, automatic, low-carbon, environment-friendly and the like of door plate coating can be achieved, meanwhile, the heat insulation and heat preservation performance of the door plate is improved, and the coating has excellent salt spray corrosion resistance, impact resistance and adhesive force and is suitable for large-scale popularization and application. The door plate is suitable for special use environments of refrigerated container door plates.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder coatings, and particularly relates to a powder coating for the door panels of refrigerated containers and a preparation method thereof. Background Art

[0002] The door panels of refrigerated containers are in harsh environments such as low temperature, high humidity, and salt spray for a long time, and have extremely high requirements for the performance of the coating. Existing waterborne coatings are prone to problems such as embrittlement and decreased adhesion in low-temperature environments, resulting in coating cracking and peeling, which affect the service life and appearance of the containers. In addition, the corrosion resistance and impact resistance of traditional coatings also fail to meet the requirements of the door panels of refrigerated containers.

[0003] In the prior art, although there are some improved waterborne coatings, their performance in low-temperature environments is still insufficient, and the construction period is long, making it difficult to achieve automated production. Therefore, developing a powder coating suitable for the door panels of refrigerated containers has important practical significance. It has the advantages of easy construction, convenient use, low cost, environmental protection, etc.; the preparation method is simple and is easy to mass-produce on an industrial scale by an assembly line. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a powder coating for the door panels of refrigerated containers and a preparation method thereof, aiming to solve the technical problems of the long construction period, poor impact resistance and adhesion of conventional waterborne coatings.

[0005] A powder coating for the door panels of refrigerated containers includes a polyester resin, a curing agent, a leveling agent, benzoin, an infrared reflective pigment, a core-shell impact modifier, and titanium dioxide.

[0006] In certain embodiments, it includes the following components by mass percentage: 60 - 70% of polyester resin, 4 - 5% of curing agent, 0.8 - 1.2% of leveling agent, 0.4 - 0.6% of benzoin, 2 - 6% of infrared reflective pigment, 3 - 6% of core-shell impact modifier, and 20 - 30% of titanium dioxide.

[0007] In certain embodiments, the polyester resin is a saturated carboxyl polyester resin; the model can be selected as C2441-2.

[0008] In certain embodiments, the curing agent is an epoxy resin based on a glycidyl ester mixture; the model can be selected as ARALDITE PT 910.

[0009] In certain embodiments, the leveling agent is an acrylic copolymer; the model can be selected as Nanhai GLP588.

[0010] In certain embodiments, the benzoin is benzil; the model is Benzoin.

[0011] In some embodiments, the titanium dioxide is rutile titanium dioxide; the model is Longmang R996.

[0012] In some embodiments, the infrared reflective pigment is a specially modified rutile titanium dioxide. The material manufacturer and model are VENATOR, W400. Its principle is mainly based on its special modification, and the pigment particles have a more regular approximate microsphere structure, so it has a high reflectivity to infrared rays, can effectively reflect the infrared part in sunlight, thereby reducing the heat absorption of the coated object. It plays the role of heat preservation and insulation, and at the same time has excellent weather resistance.

[0013] In some embodiments, the core-shell impact modifier is a core-shell copolymer prepared by emulsion polymerization of methyl methacrylate, butadiene and styrene.

[0014] The model is TMS-2672. Its principle is that the core layer is usually copolymerized by butadiene and styrene, has flexibility and elasticity, and provides a toughening effect; the shell layer is usually copolymerized by methyl methacrylate and styrene, has higher hardness and compatibility, and provides good processing performance and surface performance; the core-shell impact modifier is provided in the form of a free-flowing powder, which is convenient for thermosetting powder coating formulation designers to have greater formulation freedom. This product is based on a unique technology and is easily dispersed in the resin. Adding less than 15% of the total formulation will not affect the viscosity of the system; the core-shell structure can significantly improve the impact resistance, transparency and processing performance of the material by adjusting the composition ratio of the core layer and the shell layer.

[0015] I. Raw material composition and dosage of the core-shell impact modifier

[0016] 1. Main raw materials of the core layer (butadiene-styrene copolymer elastomer):

[0017] Butadiene: 40-60 wt% (based on the total mass of the core layer)

[0018] Styrene: 30-50 wt%

[0019] Crosslinking agent (such as divinylbenzene, DVB): 1-3 wt% (enhancing the crosslinking degree of the core layer)

[0020] Emulsifier (such as sodium dodecyl sulfate, SDS): 1-2 wt%

[0021] Initiator (such as potassium persulfate, KPS): 0.1-0.5 wt%

[0022] Deionized water: The dosage is 2-3 times the total amount of monomers (as the reaction medium)

[0023] 2. Main raw materials of the shell layer (methyl methacrylate homopolymer or copolymer):

[0024] Methyl methacrylate: 80 - 95 wt% (based on the total mass of the shell layer)

[0025] Functional monomer (such as acrylic acid, AA): 5 - 20 wt% (enhance compatibility with the matrix resin)

[0026] Emulsifier (such as OP - 10): 0.5 - 1 wt%

[0027] Initiator (such as ammonium persulfate, APS): 0.1 - 0.3 wt%

[0028] Chain transfer agent (such as dodecyl mercaptan, DDM): 0.05 - 0.1 wt% (control molecular weight)

[0029] 3. Total system core - shell mass ratio:

[0030] Generally 3:7 to 4:6 (the core layer accounts for 30 - 40%)

[0031] II. Preparation process flow of core - shell impact modifier

[0032] 1. Core layer synthesis (emulsion polymerization)

[0033] a. Pre - emulsification:

[0034] Mix butadiene, styrene, cross - linker (DVB) with emulsifier (SDS) and deionized water, and pre - emulsify for 30 minutes by high - speed stirring (1000 - 1500 rpm) to form a stable monomer emulsion.

[0035] b. Initiation reaction:

[0036] Add the pre - emulsified liquid into the reaction kettle, heat up to 70 - 75 °C, add the initiator (KPS), and purge with nitrogen to remove oxygen. Reaction time: 4 - 6 hours, control the pressure (butadiene is a gas, and a closed - high - pressure reaction is required).

[0037] c. Core layer post - treatment:

[0038] After the reaction, cool down to 40 °C and adjust the pH to neutral to obtain styrene - butadiene latex (core layer particle size is about 50 - 100 nm).

[0039] 2. Shell layer coating (seed emulsion polymerization)

[0040] a. Premixing of shell monomers:

[0041] Mix MMA, functional monomer (AA), emulsifier (OP - 10), chain transfer agent (DDM) with deionized water and pre - emulsify for 20 minutes.

[0042] b. Gradient dropping:

[0043] Slowly drop the shell pre-emulsion into the core emulsion (dropping rate: 1 - 2 mL / min), maintain the temperature at 75 - 80 °C, and add the initiator (APS). Reaction time: 3 - 5 hours. Monitor the particle size growth to 100 - 200 nm by dynamic light scattering (DLS).

[0044] c. Terminate the reaction:

[0045] Add the terminator (such as hydroquinone), cool to room temperature, and adjust the pH to 6 - 7.

[0046] 3. Post-treatment and drying

[0047] a. Demulsification and coagulation: Add an electrolyte (such as a CaCl2 solution) or an acid (such as hydrochloric acid) to the emulsion to destroy the emulsion stability and precipitate the particles.

[0048] b. Washing and drying: Wash repeatedly with deionized water until the conductivity < 50 μS / cm, centrifuge, and dry in vacuum (50 - 60 °C, 12 - 24 hours) to obtain the white powdery MBS core-shell modifier.

[0049] The polyester and the curing agent are used as the main materials, and are melt-crosslinked and cured into a film. The leveling agent is used to eliminate the surface depressions of the coating film, the benzoin eliminates the pinholes of the coating film, the titanium dioxide is a white pigment to improve the whiteness and covering power of the coating, the infrared reflection pigment has the function of reflecting infrared rays and can achieve the effect of heat insulation, and the core-shell impact modifier can improve the hardness of the coating film and enhance the impact resistance.

[0050] The present invention also includes the following preparation method of the powder coating for the refrigerated container door panel:

[0051] Step 1: Weigh the raw materials: Premix the polyester resin, curing agent, leveling agent, benzoin, infrared reflection pigment, core-shell impact modifier, and titanium dioxide, and then perform melt extrusion, crushing, and sieving to obtain the powder coating for the refrigerated container door panel;

[0052] Step 2: Premixing: Sequentially put the polyester resin, curing agent, leveling agent, benzoin, infrared reflection pigment, core-shell impact modifier, and titanium dioxide into the premixer. The main stirring paddle speed of the premixer is 150 rpm / min for 6 minutes; the secondary stirring paddle speed is 3000 rpm / min for 3 minutes, and the mixing temperature is at room temperature;

[0053] Step 3: Melt extrusion: The premixed material is fed through the hopper to the extruder for melt extrusion. The temperature of the extruder is set as follows: Zone I is the feeding section with a temperature of 85 - 90 °C; Zone II is the melt extrusion section with a temperature of 100 - 110 °C; the screw speed is 250 - 280 rpm / min;

[0054] Step 4: Crushing: The sheet materials after melt extrusion are crushed by a grinding mill. The main grinding speed of the grinding mill is 45HZ, and the secondary grinding speed is 28 - 30HZ; the mesh screen for sieving is 180 meshes.

[0055] The present invention has the following effects: The powder coating for the refrigerated container door panel prepared by the present invention can completely replace the existing water-based coating, significantly improve the production efficiency of the cold box manufacturing factory, meet the conditions of intelligent manufacturing on the automated production line, be green and low-carbon, and can achieve green intelligent manufacturing, with obvious economic and technological value. Brief Description of the Drawings

[0056] Figure 1 is a flow chart of the preparation method of the powder coating for the refrigerated container door panel of the present invention;

[0057] Figure 2 is a practical application scenario case of the powder coating for the refrigerated container door panel of the present invention. Detailed Description of the Invention

[0058] To make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the following further details the present invention with reference to specific embodiments and the attached Figure 1 , and further elaborates on the present invention.

[0059] Example 1

[0060] This example provides a preparation method of a powder coating for a refrigerated container door panel, including the following steps:

[0061] Step S1: Weigh the raw materials according to the weight percentage:

[0062] Polyester resin 60%;

[0063] Curing agent 4.6%,

[0064] Leveling agent 0.8%;

[0065] Benzoin 0.6%;

[0066] Infrared reflective pigment 6%;

[0067] Core-shell impact modifier 5%;

[0068] Titanium dioxide 23%;

[0069] Among them, the polyester resin is a saturated carboxyl polyester resin, with the model C2441-2: the curing agent model is ARALDITE PT 910; the leveling agent model is GLP588; the benzoin model is Benzoin; the infrared reflective pigment model is W400; the core-shell impact modifier model is TMS-2672; the titanium dioxide model is R996;

[0070] Step S2: Put the weighed raw materials into the premixer one by one according to the formula sequence;

[0071] Step S3: Premix. The parameters of the premixer are set as follows: the rotation speed of the main stirring paddle is set at 150 rpm / min for 6 minutes; the rotation speed of the auxiliary stirring paddle is set at 3000 rpm / min for 3 minutes to obtain the premixed material;

[0072] Step S4: Melt extrusion. Melt extrude the premixed material. The temperature of the extruder is set as follows: Zone I is 85 - 90 °C; Zone II is 100 - 110 °C; the screw rotation speed is set at 250 - 280 rpm / min to obtain the extruded sheet;

[0073] Step S5: Crushing. Crush the extruded sheet. The grinding parameters are: the main grinder is 45 HZ, and the auxiliary grinder is 28 - 30 HZ;

[0074] Step S6: Screening. Screen the powdered material after grinding. The mesh screen selected is 180 mesh.

[0075] This embodiment also provides a powder coating for the door panel of a refrigerated container prepared by the above method.

[0076] Example 2

[0077] This embodiment provides a preparation method of a powder coating for the door panel of a refrigerated container, including the following steps:

[0078] Step S1: Weigh the raw materials according to the weight percentage:

[0079] Polyester resin 65%;

[0080] Curing agent 4.9%,

[0081] Leveling agent 1.1%;

[0082] Benzoin 0.5%;

[0083] Infrared reflective pigment 2.5%;

[0084] Core-shell impact modifier 4%;

[0085] Titanium dioxide 22%;

[0086] Among them, the polyester resin is a saturated carboxyl polyester resin, and the model is C2441-2; the model of the curing agent is ARALDITE PT 910; the model of the leveling agent is GLP588; the model of benzoin is Benzoin; the model of the infrared reflective pigment is W400; the model of the core-shell impact modifier is TMS-2672; the model of titanium dioxide is R996;

[0087] Step S2: Put the weighed raw materials into the premixer one by one according to the formula sequence;

[0088] Step S3: Premixing. The parameters of the premixer are set as follows: the rotational speed of the main stirring paddle is set at 150 rpm / min for 6 minutes; the rotational speed of the secondary stirring paddle is set at 3000 rpm / min for 3 minutes to obtain the premixed material.

[0089] Step S4: Melting and extrusion. The premixed material is melted and extruded. The temperature of the extruder is set as follows: Zone I: 85 - 90 °C; Zone II: 100 - 110 °C; the rotational speed of the screw is set at 250 - 280 rpm / min to obtain the extruded sheet.

[0090] Step S5: Crushing. The extruded sheet is crushed. The parameters of the grinding are: the main grinder is at 45 HZ, and the secondary grinder is at 28 - 30 HZ.

[0091] Step S6: Screening. The ground particles are screened, and a 180 - mesh screen is selected.

[0092] This embodiment also provides a powder coating for the door panel of a refrigerated container prepared by the above method.

[0093] Example 3

[0094] This embodiment provides a method for preparing a powder coating for the door panel of a refrigerated container, which includes the following steps:

[0095] Step S1: Weigh the raw materials according to the weight percentages:

[0096] Polyester resin: 67%

[0097] Curing agent: 4.2%

[0098] Leveling agent: 0.8%

[0099] Benzoin: 0.4%

[0100] Infrared reflective pigment: 4.6%

[0101] Core - shell impact modifier: 3%

[0102] Titanium dioxide: 20%

[0103] Among them, the polyester resin is a saturated carboxyl polyester resin, with the model C2441 - 2; the curing agent has the model ARALDITE PT 910; the leveling agent has the model GLP588; the benzoin has the model Benzoin; the infrared reflective pigment has the model W400; the core - shell impact modifier has the model TMS - 2672; the titanium dioxide has the model R996.

[0104] Step S2: Put the weighed raw materials into the premixer one by one according to the formula sequence.

[0105] Step S3: Premixing. The parameters of the premixer are set as follows: the rotation speed of the main stirring paddle is set at 150 rpm / min for 6 minutes; the rotation speed of the auxiliary stirring paddle is set at 3000 rpm / min for 3 minutes to obtain the premixed material.

[0106] Step S4: Melting and extrusion. The premixed material is melted and extruded. The temperature of the extruder is set as follows: Zone I: 85 - 90 °C; Zone II: 100 - 110 °C; the screw rotation speed is set at 250 - 280 rpm / min to obtain the extruded sheet.

[0107] Step S5: Crushing. The extruded sheet is crushed. The parameters of the grinding are: the main grinder is at 45 HZ, and the auxiliary grinder is at 28 - 30 HZ.

[0108] Step S6: Screening. The ground particles are screened, and a 180 - mesh sieve is selected.

[0109] This embodiment also provides a powder coating for the door panel of a refrigerated container prepared by the above method.

[0110] Example 4

[0111] This embodiment provides a preparation method of a powder coating for the door panel of a refrigerated container, which includes the following steps:

[0112] Step S1: Weigh the raw materials according to the weight percentage:

[0113] Polyester resin: 64%;

[0114] Curing agent: 4.8%,

[0115] Leveling agent: 0.8%;

[0116] Benzoin: 0.4%;

[0117] Infrared reflective pigment: 5%;

[0118] Core - shell impact modifier: 5%;

[0119] Titanium dioxide: 20%;

[0120] Among them, the polyester resin is a saturated carboxyl polyester resin with the model C2441 - 2; the curing agent has the model ARALDITE PT 910; the leveling agent has the model GLP588; the benzoin has the model Benzoin; the infrared reflective pigment has the model W400; the core - shell impact modifier has the model TMS - 2672; the titanium dioxide has the model R996.

[0121] Step S2: Put the weighed raw materials into the premixer one by one according to the formula sequence.

[0122] Step S3: Premixing. The parameters of the premixer are set as follows: the rotational speed of the main stirring paddle is set at 150 rpm / min for 6 minutes; the rotational speed of the auxiliary stirring paddle is set at 3000 rpm / min for 3 minutes to obtain the premixed material.

[0123] Step S4: Melting and extrusion. The premixed slurry is subjected to melting and extrusion. The temperature of the extruder is set as follows: Zone I is 85 - 90 °C; Zone II is 100 - 110 °C; the rotational speed of the screw is set at 250 - 280 rpm / min to obtain the extruded sheet.

[0124] Step S6: Crushing. The extruded sheet is crushed. The parameters for grinding are as follows: the main grinder is at 45 HZ, and the auxiliary grinder is at 28 - 30 HZ.

[0125] Step S6: Screening. The ground particles are screened, and a 180 - mesh sieve is selected.

[0126] This embodiment also provides a powder coating for the door panel of a refrigerated container prepared by the above method.

[0127] Comparative Example

[0128] The comparative example provides a conventional powder coating and its preparation method, including the following steps:

[0129] Step S1: Weigh the raw materials according to the weight percentages:

[0130] 65% of polyester resin;

[0131] 4.8% of curing agent,

[0132] 1.0% of leveling agent;

[0133] 0.4% of benzoin;

[0134] 28.8% of titanium dioxide;

[0135] The polyester resin is a saturated carboxyl polyester resin, with the model C2441 - 2; the curing agent model is ARALDITE PT910; the leveling agent model is GLP588; the benzoin model is Benzoin; the titanium dioxide model is R996;

[0136] Step S2: Put the weighed raw materials into the premixer one by one in the formula order;

[0137] Step S3: Premixing. The parameters of the premixer are set as follows: the rotational speed of the main stirring paddle is set at 150 rpm / min for 6 minutes; the rotational speed of the auxiliary stirring paddle is set at 3000 rpm / min for 3 minutes to obtain the premixed material.

[0138] Step S4: Melt Extrusion. The premix is subjected to melt extrusion. The temperature of the extruder is set as follows: Zone I: 85 - 90 °C; Zone II: 100 - 110 °C; the screw speed is set at 250 - 280 rpm / min to obtain extruded sheet materials.

[0139] Step S5: Crushing. The extruded sheet materials are crushed. The grinding parameters are as follows: main grinder: 45 HZ, secondary grinder: 28 - 30 HZ.

[0140] Step S6: Screening. The ground granules are screened, and a 180 - mesh sieve is selected.

[0141] The powder coatings for the refrigerated container door panels in the examples and the coatings in the comparative examples are sprayed onto the experimental MGSS plates with the specification of 75 * 150 * 1.6 mm using an electrostatic spray gun and cured. The curing conditions are 180 °C * 15 minutes. The performance of the coatings in the examples and comparative examples is tested using a film thickness gauge (BYK), a gloss meter (BYK), an impact tester (Guangdong Biaogeda), an artificial weathering tester (Q - LAB), and a salt spray tester (Q - LAB). The test results are shown in Table 1.

[0142] Table 1 Test Indexes and Performance of the Coatings in the Examples and Comparative Examples

[0143]

[0144]

[0145] As can be seen from the above table, the powder coatings for the refrigerated container door panels in Example 4 have significantly better performance than ordinary coatings, especially in terms of outdoor weather resistance, heat insulation performance, adhesion, and anti - mechanical impact strength.

[0146] In summary, the powder coatings for the refrigerated container door panels prepared by the present invention can be directly used for the painting of cold box door panels, replacing the existing painting methods. It can significantly improve the production efficiency of cold box manufacturers, realize intelligent manufacturing on an automated production line, be green and low - carbon, and have obvious economic and technological value.

[0147] It can be widely promoted in the fields of refrigerated container door panels and accessories, etc.

[0148] The above are only the preferred and feasible embodiments of the present invention, and it is not a limitation to the present invention. The present invention is not limited to the above examples either. Those skilled in the art of this technology, within the scope of the essence of the present invention, the changes, modifications, additions, or substitutions made should also fall within the protection scope of the present invention.

Claims

1. Powder coating for the door panel of a refrigerated container, characterized in that: It includes polyester resin, curing agent, leveling agent, benzoin, infrared reflective pigment, core-shell impact modifier and titanium dioxide.

2. The powder coating for the door panel of a refrigerated container according to claim 1, wherein: It includes the following components by mass percentage: 60-70% of polyester resin, 4-5% of curing agent, 0.8-1.2% of leveling agent, 0.4-0.6% of benzoin, 2-6% of infrared reflective pigment, 20-30% of titanium dioxide, and 3-6% of core-shell impact modifier.

3. The powder coating for the door panel of a refrigerated container according to claim 1, wherein: The polyester resin is a saturated carboxyl polyester resin with an acid value of 30-36 (mg KOH / g).

4. The powder coating for the refrigerated container door panel according to claim 1, characterized in that: The curing agent is an epoxy resin based on a glycidyl ester mixture.

5. The powder coating for the door panel of a refrigerated container according to claim 1, characterized in that: The leveling agent is an acrylic copolymer.

6. The powder coating for the refrigerated container door panel according to claim 1, wherein The infrared reflective pigment is modified rutile titanium dioxide; The modification process is as follows: Rutile titanium dioxide is doped with aluminum ions and then coated with SiO2. Specifically, TiCl4 and Al(NO3)3 are mixed at a molar ratio (Ti:Al = 95:5), and co-precipitated with ammonia water, washed and dried to obtain an Al-TiO2 precursor; the precursor is calcined at 950 °C for 2 hours to obtain aluminum ion-doped rutile TiO2; Al-TiO2 is dispersed in ethanol, tetraethoxysilane is added, and ammonia water is used to catalyze hydrolysis to form a SiO2 coating layer; Finally, it is calcined at 500 °C for 1 hour to enhance the bonding force of the coating layer, and finally modified rutile titanium dioxide is obtained.

7. The powder coating for the door panel of a refrigerated container according to claim 1, characterized in that, The core-shell impact modifier is a core-shell copolymer prepared by emulsion polymerization of methyl methacrylate, butadiene and styrene.

8. The preparation method of the powder coating for the refrigerated container door panel according to claims 1-7, characterized in that: The preparation method is as follows: Step 1: Weigh the raw materials: The polyester resin, curing agent, leveling agent, benzoin, infrared reflective pigment, core-shell impact modifier and titanium dioxide are premixed, and then melt-extruded, crushed and sieved to obtain a powder coating for refrigerated container door panels; Step 2: Premixing: The polyester resin, curing agent, leveling agent, benzoin, infrared reflective pigment, core-shell impact modifier and titanium dioxide are sequentially put into a premixer. The main stirring paddle of the premixer rotates at a speed of 150 rpm / min for 6 minutes; the auxiliary stirring paddle rotates at a speed of 3000 rpm / min for 3 minutes, and the mixing temperature is at room temperature; Step 3: Melt extrusion: The premixed material is fed into an extruder through a hopper for melt extrusion. The temperature of the extruder is set as follows: Zone I is the feeding section with a temperature of 85-90 °C; Zone II is the melt extrusion section with a temperature of 100-110 °C; the screw speed is 250-280 rpm / min; Step 4: Crushing: The sheet material after melt extrusion is crushed by a grinding mill. The main grinding of the grinding mill is 45 HZ, and the secondary grinding of the grinding mill is 28-30 HZ; the sieve mesh for sieving is 180 mesh.

Images