Photochromic low-temperature curing polyester resin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a photochromic low-temperature curing polyester resin as well as a preparation method and application thereof, dihydric alcohol, dibasic acid and a hydroxyl-containing spiropyrane modified photochromic monomer are subjected to step-by-step esterification reaction and vacuum polycondensation, a curing accelerator is introduced after polycondensation, and the polyester resin is prepared. According to a coating test, the weak light transmittance of the coating is larger than 75%, the strong light shading rate of the coating is larger than 80%, the heat conductivity coefficient of the coating is smaller than 0.04 W / (m.K), and the coating has good mechanical performance and is suitable for low-temperature sensitive base materials such as light alloy and plastic composite boards. Good application prospects are realized.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a photochromic low-temperature curing polyester resin, its preparation method, and its application. Background Technology

[0002] Powder coatings are solid coatings that use thermosetting resins as the main film-forming substance. They are applied by electrostatic spraying, followed by heating to melt, level, and cure into a film. They are widely used in construction, furniture, and automotive industries, especially in building envelopes to provide both protection and decoration. Polyester resin, as the core component of powder coatings, is typically prepared by esterification and vacuum polycondensation of diols and diacids. It possesses excellent weather resistance, superior mechanical properties, and is environmentally friendly and solvent-free, playing a crucial role in the performance of powder coatings.

[0003] However, the curing temperature of existing polyester resin powder coatings is typically 180-200℃, making them difficult to adapt to low-temperature sensitive substrates. Furthermore, their limited functionality makes it difficult to achieve both light transmittance regulation and thermal insulation effects. Currently, conventional powder coating systems using polyester resins with epoxy or isocyanate curing agents achieve basic protective performance, but these solutions have high curing temperatures, easily damaging substrates such as lightweight alloys or plastic composite panels. Alternatively, photochromic materials or insulating fillers, such as glass microspheres, are added through physical mixing to attempt to achieve light transmittance regulation or thermal insulation effects. However, these commonly used solutions cannot effectively solve the problem of poor compatibility between photochromic monomers and polyester resins, leading to uneven color change and easy migration. The addition of insulating fillers often affects the leveling and mechanical properties of the coating, failing to achieve a good balance between light-response regulation and efficient thermal insulation.

[0004] In summary, developing polyester resins for powder coatings that combine low-temperature curing, photochromism, and thermal insulation has become a pressing challenge for the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a photochromic low-temperature curing polyester resin and its preparation method.

[0006] Another objective of this invention is to provide an application of photochromic low-temperature curing polyester resin in thermal insulation and energy-saving powder coatings.

[0007] This invention provides a photochromic low-temperature curing polyester resin, which is prepared from the following raw materials in parts by weight:

[0008] Diol 4.0-4.4 parts;

[0009] Dicarboxylic acid 6.6-7.0 parts;

[0010] Esterification catalyst: 0.008-0.012 parts;

[0011] 0.3-0.6 parts of spiropyran-modified hydroxyl photochromic monomer;

[0012] Antioxidant 0.03-0.05 parts;

[0013] Curing accelerator 0.02-0.04 parts.

[0014] In the above-mentioned photochromic low-temperature curing polyester resin, the diol is one or more of neopentyl glycol, 1,4-cyclohexanediol, 2-butyl-2-ethyl-1,3-propanediol, or 1,6-hexanediol. Preferably, the diol is a mixture of neopentyl glycol, 1,4-cyclohexanediol, 2-butyl-2-ethyl-1,3-propanediol, and 1,6-hexanediol in a mass ratio of 3.5-3.9:0.3-0.5:0-0.3:0-0.1.

[0015] In the above-mentioned photochromic low-temperature curing polyester resin, the dicarboxylic acid is one or more of terephthalic acid, isophthalic acid, or adipic acid; preferably, the dicarboxylic acid is a mixture of terephthalic acid, isophthalic acid, and adipic acid in a mass ratio of 5.3-5.7:0.9-1.2:0.1-0.3.

[0016] In the above-mentioned photochromic low-temperature curing polyester resin, the esterification catalyst is one of monobutyltin oxide or stannous oxalate.

[0017] In the above-mentioned photochromic low-temperature curing polyester resin, the spiropyran-modified hydroxyl photochromic monomer is 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran.

[0018] In the above-mentioned photochromic low-temperature curing polyester resin, the antioxidant is one or more of antioxidant 168, antioxidant 1076, antioxidant 626 or antioxidant 1010.

[0019] In the above-mentioned photochromic low-temperature curing polyester resin, the curing accelerator is one or more of triphenylphosphine, ethyltriphenylphosphine bromide, propyltriphenylphosphine bromide, or benzyltriphenylphosphine bromide.

[0020] In the above-mentioned photochromic low-temperature curing polyester resin, the photochromic low-temperature curing polyester resin has an acid value of 30-35 mgKOH / g, a viscosity of 4000-6000 mPa·s, and a glass transition temperature of 61-64℃.

[0021] The present invention provides a method for preparing the photochromic low-temperature curing polyester resin, comprising the following steps:

[0022] 1) The diol is added to the reaction vessel and heated to melt, then the diacid and esterification catalyst are added and mixed evenly to carry out the pre-esterification reaction;

[0023] 2) Add a dicarboxylic acid and a spiropyran-modified hydroxyl photochromic monomer to the reaction vessel for copolyesterification reaction;

[0024] 3) Reduce the system pressure to carry out vacuum polycondensation reaction. After the reaction is completed, add antioxidants and curing accelerators to obtain photochromic low-temperature curing polyester resin.

[0025] In step 1) of the above preparation method, the reaction temperature of the pre-esterification reaction is 235-240℃, and the reaction continues until the acid value of the system is 5-10 mgKOH / g and the viscosity is 500-1000 mPa·s.

[0026] In step 2) of the above preparation method, the reaction temperature of the copolyesterification reaction is 220-230℃, and the reaction continues until the acid value of the system is 42-45 mgKOH / g and the viscosity is 1000-1500 mPa·s.

[0027] In steps 1) and 2) of the above preparation method, the mass ratio of the amount of dicarboxylic acid in step 1) to that in step 2) is 5.3~6:0.7~1.5.

[0028] In step 3) of the above preparation method, the reaction pressure of the vacuum polycondensation is -0.09 to -0.1 MPa, the reaction time is 1-2 h, and the reaction temperature is 220-230 °C.

[0029] In step 3) of the above preparation method, the feeding temperature is 180-200℃ and the feeding time is 10-30min.

[0030] This invention provides an application of the photochromic low-temperature curing polyester resin in thermal insulation and energy-saving powder coatings.

[0031] This invention provides a thermal insulation and energy-saving powder coating, which is prepared from the following raw materials in parts by weight:

[0032] 75-82 parts of photochromic low-temperature curing polyester resin;

[0033] Triglycidyl isocyanurate (TGIC) 5-7 parts;

[0034] 10-18 parts of silane-modified hollow glass microspheres;

[0035] Leveling agent 1.0-2.0 parts;

[0036] Benzoin 0.3-0.8 parts;

[0037] 0.3-0.8 parts of wetting accelerator.

[0038] The leveling agent is GLP588.

[0039] The wetting accelerator is BLC701B wetting accelerator.

[0040] The preparation method of the silane-modified hollow glass microspheres includes the following steps:

[0041] (1) Hollow glass microspheres are pretreated by acid washing, water washing and drying to obtain pretreated microspheres;

[0042] (2) Mix silane coupling agent with ethanol at a mass ratio of 1:8-12, add 3-5wt% hydrochloric acid or nitric acid to adjust the pH to 4-5, and hydrolyze to obtain silane solution;

[0043] (3) Immerse the pretreated microbeads in silane solution at a solid-liquid ratio of 1g / 9~11mL and react at 50-80℃ for 1-3h.

[0044] (4) Centrifuge, wash and dry to obtain silane-modified hollow glass microspheres;

[0045] The silane coupling agent mentioned in step (2) is one or more of KH-570, KH-550 or A-171.

[0046] The hollow glass microspheres have a particle size of 1~5μm.

[0047] The present invention also provides a method for preparing the aforementioned thermal insulation and energy-saving powder coating, the method comprising the following steps:

[0048] The thermal insulation and energy-saving powder coating is obtained by mixing, screw extrusion, crushing, grinding and sieving the raw materials of the powder coating.

[0049] In the above-mentioned method for preparing thermal insulation and energy-saving powder coatings, the parameters of the screw extrusion are:

[0050] Zone I temperature: 95-105℃; Zone II temperature: 105-120℃; Zone III temperature: 95-110℃; Feeding speed frequency: 25-35Hz; Screw speed frequency: 35-45Hz.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] 1. By introducing spiropyran-modified hydroxyl photochromic monomers directly chemically grafted onto the polyester backbone, since they are part of the same molecular chain, there is no problem with compatibility. The leveling, adhesion, gloss appearance and mechanical properties of the coating will not be affected by the independent addition of spiropyran-modified hydroxyl photochromic monomers. Moreover, because the color-changing groups are uniform and the content is controllable, the chemically grafted resin is more likely to maintain high light transmittance under weak light conditions.

[0053] 2. The insulation layer is constructed by using silane-modified hollow glass microspheres, which improves the resin compatibility and interfacial bonding force, ensuring thermal insulation and light transmittance. The resulting thermal insulation and energy-saving powder coating achieves sensitive and uniform photochromic response, excellent thermal insulation performance, and can be cured at a low temperature of 150℃. It has good leveling properties, a balance between hardness and toughness, and is suitable for lightweight low-temperature sensitive substrates.

[0054] 3. In the preparation process of photochromic low-temperature curing polyester resin, the rigidity of the ring structure and the flexibility of the molecular chain are combined to balance the hardness and toughness of the polyester resin, thereby improving the impact resistance and bending performance of the coating under low-temperature curing conditions. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0057] The acid value test of the following examples and comparative examples is based on standard GB / T 6743-2008; the viscosity test is based on standard GB / T 9751.1-2008; and the glass transition temperature (Tg) test is based on standard GB / T 19466.2-2004.

[0058] The preparation steps of the silane-modified hollow glass microspheres used in the following application examples and comparative examples are as follows:

[0059] (1) Hollow glass microspheres with a particle size of 5 μm were pretreated by acid washing, water washing and drying to obtain pretreated microspheres;

[0060] (2) Mix KH-550 and ethanol at a mass ratio of 1:8, add 5wt% hydrochloric acid or nitric acid to adjust the pH to 5, and hydrolyze to obtain a silane solution.

[0061] (3) The pretreated microbeads were immersed in silane solution at a solid-liquid ratio of 1g / 10mL and reacted at 80℃ for 3h.

[0062] (4) The product obtained in step (3) is centrifuged, washed and dried to obtain silane-modified hollow glass microspheres.

[0063] Example 1

[0064] A method for preparing a photochromic low-temperature curable polyester resin specifically includes the following steps:

[0065] 1) By mass, add 3.8 parts of neopentyl glycol and 0.4 parts of 1,4-cyclohexanediethanol to the reaction vessel, heat to melt, start stirring, then add 5.7 parts of terephthalic acid and 0.011 parts of stannous oxalate, raise the temperature to 236℃ and maintain the reaction until the acid value is 6.2 mg KOH / g and the viscosity is 520 mPa·s;

[0066] 2) Cool down to 222℃, add 1.0 part of isophthalic acid, 0.2 part of adipic acid, and 0.6 part of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, and maintain the reaction until the acid value is 42.8 mg KOH / g and the viscosity is 1050 mPa·s;

[0067] 3) Under -0.092 MPa conditions, vacuum polycondensation was carried out for 1.2 h, followed by cooling to 182 °C. 0.01 parts of antioxidant 626, 0.03 parts of antioxidant 1010, and 0.025 parts of ethyltriphenylphosphine bromide were added. The reaction conditions were maintained for 15 min to obtain a photochromic low-temperature curing polyester resin. The resulting resin had an acid value of 32.5 mg KOH / g, a viscosity of 4600 mPa·s, and a glass transition temperature of 62.8 °C.

[0068] Example 2

[0069] A method for preparing a photochromic low-temperature curable polyester resin specifically includes the following steps:

[0070] 1) By weight, add 3.8 parts of neopentyl glycol, 0.1 parts of 1,6-hexanediol and 0.3 parts of 1,4-cyclohexanediethanol to a reaction vessel, heat to melt, start stirring, then add 5.6 parts of terephthalic acid and 0.01 parts of stannous oxalate, raise the temperature to 238℃ and maintain the reaction until the acid value is 8.5 mg KOH / g and the viscosity is 850 mPa·s;

[0071] 2) Cool down to 227℃, add 1.1 parts of isophthalic acid, 0.15 parts of adipic acid, and 0.5 parts of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, and maintain the reaction until the acid value is 44.1 mg KOH / g and the viscosity is 1380 mPa·s;

[0072] 3) Under -0.096 MPa conditions, vacuum polycondensation was carried out for 1.8 h, followed by cooling to 195 °C. 0.03 parts of antioxidant 626, 0.02 parts of antioxidant 1010, and 0.035 parts of benzyltriphenylphosphine bromide were added, and the reaction conditions were maintained for 28 min to obtain a photochromic low-temperature curing polyester resin. The resulting resin had an acid value of 33.1 mg KOH / g, a viscosity of 4870 mPa·s, and a glass transition temperature of 63.5 °C.

[0073] Example 3

[0074] A method for preparing a photochromic low-temperature curable polyester resin specifically includes the following steps:

[0075] 1) By weight, add 3.7 parts of neopentyl glycol, 0.1 parts of 2-butyl-2-ethyl-1,3-propanediol, and 0.4 parts of 1,4-cyclohexanediethanol to a reaction vessel, heat to melt, start stirring, then add 5.5 parts of terephthalic acid and 0.01 parts of monobutyltin oxide, raise the temperature to 240℃ and maintain the reaction until the acid value is 9.1 mg KOH / g and the viscosity is 980 mPa·s;

[0076] 2) Cool down to 230℃, add 1.2 parts of isophthalic acid, 0.2 parts of adipic acid, and 0.4 parts of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, and maintain the reaction until the acid value is 43.5 mg KOH / g and the viscosity is 1120 mPa·s;

[0077] 3) Under -0.099 MPa conditions, vacuum polycondensation was carried out for 1.5 h, followed by cooling to 188 °C. 0.02 parts of antioxidant 626, 0.02 parts of antioxidant 1010, and 0.03 parts of ethyltriphenylphosphine bromide were added. The reaction conditions were maintained for 22 min to obtain a photochromic low-temperature curing polyester resin. The resulting resin had an acid value of 31.8 mg KOH / g, a viscosity of 4680 mPa·s, and a glass transition temperature of 63.1 °C.

[0078] Example 4

[0079] A method for preparing a photochromic low-temperature curable polyester resin specifically includes the following steps:

[0080] 1) By weight, add 3.6 parts of neopentyl glycol, 0.1 parts of 2-butyl-2-ethyl-1,3-propanediol, and 0.5 parts of 1,4-cyclohexanediethanol to a reaction vessel, heat to melt, start stirring, then add 5.4 parts of terephthalic acid and 0.009 parts of monobutyltin oxide, raise the temperature to 235℃ and maintain the reaction until the acid value is 7.3 mg KOH / g and the viscosity is 760 mPa·s;

[0081] 2) Cool down to 225℃, add 1.2 parts of isophthalic acid, 0.3 parts of adipic acid, and 0.5 parts of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, and maintain the reaction until the acid value is 44.9 mg KOH / g and the viscosity is 1470 mPa·s;

[0082] 3) Under -0.095MPa conditions, vacuum polycondensation was carried out for 1 hour, followed by cooling to 200℃. 0.03 parts of antioxidant 626, 0.01 parts of antioxidant 1010, 0.03 parts of ethyltriphenylphosphine bromide, and 0.01 parts of benzyltriphenylphosphine bromide were added. The reaction conditions were maintained for 12 minutes to obtain a photochromic low-temperature curing polyester resin.

[0083] The resulting resin had an acid value of 34.2 mg KOH / g, a viscosity of 4950 mPa·s, and a glass transition temperature of 62.5℃.

[0084] Comparative Example 1

[0085] A method for preparing a polyester resin specifically includes the following steps:

[0086] 1) By weight, add 3.7 parts of neopentyl glycol, 0.1 parts of 2-butyl-2-ethyl-1,3-propanediol, and 0.4 parts of 1,4-cyclohexanediethanol to a reaction vessel, heat to melt, start stirring, then add 5.5 parts of terephthalic acid and 0.01 parts of monobutyltin oxide, raise the temperature to 236℃ and maintain the reaction until the acid value is 6.9 mg KOH / g and the viscosity is 730 mPa·s;

[0087] 2) Cool down to 225℃, add 1.1 parts of isophthalic acid, 0.2 parts of adipic acid, and 0.1 parts of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, and maintain the reaction until the acid value is 43.3 mg KOH / g and the viscosity is 1220 mPa·s;

[0088] 3) Under -0.096 MPa conditions, vacuum polycondensation was carried out for 2 hours, followed by cooling to 195℃. 0.02 parts of antioxidant 626, 0.02 parts of antioxidant 1010, and 0.01 parts of benzyltriphenylphosphine bromide were added. The reaction conditions were maintained for 20 minutes to obtain polyester resin. The resulting resin had an acid value of 33.1 mg KOH / g, a viscosity of 4710 mPa·s, and a glass transition temperature of 62.3℃.

[0089] Comparative Example 2

[0090] A method for preparing a polyester resin specifically includes the following steps:

[0091] 1) By weight, add 3.6 parts of neopentyl glycol, 0.5 parts of 1,4-cyclohexanediol, and 0.2 parts of 2-butyl-2-ethyl-1,3-propanediol to a reaction vessel, heat to melt, start stirring, then add 5.3 parts of terephthalic acid and 0.008 parts of monobutyltin oxide, raise the temperature to 238℃ and maintain the reaction until the acid value is 7.7 mg KOH / g and the viscosity is 660 mPa·s;

[0092] 2) Cool down to 220℃, add 1.2 parts of isophthalic acid and 0.1 parts of adipic acid, and maintain the reaction until the acid value is 45.7 mg KOH / g and the viscosity is 1020 mPa·s;

[0093] 3) Under -0.09 MPa conditions, vacuum polycondensation was carried out for 1 h, followed by cooling to 180 °C. 0.3 parts of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, 0.02 parts of antioxidant 626, 0.02 parts of antioxidant 1010, and 0.03 parts of propyltriphenylphosphine bromide were added. The reaction conditions were maintained for 10 min to obtain a polyester resin. The resulting resin had an acid value of 34.4 mg KOH / g, a viscosity of 4550 mPa·s, and a glass transition temperature of 61.6 °C.

[0094] Application Example 1

[0095] A thermal insulation and energy-saving powder coating, wherein the thermal insulation and energy-saving powder coating comprises the following raw materials in parts by weight:

[0096] 78 parts of the photochromic low-temperature curing polyester resin prepared in Example 1;

[0097] Triglycidyl isocyanurate (TGIC) 5.9 parts;

[0098] 13.6 parts of silane-modified hollow glass microspheres;

[0099] Leveling agent GLP588, 1.5 parts;

[0100] 0.5 parts benzoin;

[0101] 0.5 parts of wetting accelerator BLC701B.

[0102] A method for preparing a thermal insulation and energy-saving powder coating, the method comprising the following steps:

[0103] After the above raw materials are fully premixed, they are extruded through a twin-screw extruder with the parameters set as follows: Zone I temperature 98℃, Zone II temperature 108℃, Zone III temperature 97℃, feeding speed frequency 28Hz, and screw speed frequency 38Hz. The extruded flakes are crushed, ground, and sieved through a 200-mesh screen to obtain the thermal insulation and energy-saving powder coating.

[0104] Application Example 2

[0105] A thermal insulation and energy-saving powder coating, wherein the thermal insulation and energy-saving powder coating comprises the following raw materials in parts by weight:

[0106] 80 parts of the photochromic low-temperature curing polyester resin prepared in Example 2;

[0107] Triglycidyl isocyanurate (TGIC) 6.0 parts;

[0108] 12.3 parts of silane-modified hollow glass microspheres;

[0109] Leveling agent GLP588 1.1 parts;

[0110] Benzoin 0.3 parts;

[0111] 0.3 parts of wetting accelerator BLC701B.

[0112] A method for preparing a thermal insulation and energy-saving powder coating, the method comprising the following steps:

[0113] After the above raw materials are fully premixed, they are extruded through a twin-screw extruder. The parameters are set as follows: zone I temperature 103℃, zone II temperature 115℃, zone III temperature 107℃, feeding speed frequency 33Hz, screw speed frequency 42Hz. The extruded sheet is crushed, ground, and sieved through a 200-mesh screen to obtain the heat-insulating and energy-saving powder coating.

[0114] Application Example 3

[0115] A thermal insulation and energy-saving powder coating, wherein the thermal insulation and energy-saving powder coating comprises the following raw materials in parts by weight:

[0116] 82 parts of the photochromic low-temperature curing polyester resin prepared in Example 3;

[0117] Triglycidyl isocyanurate (TGIC) 6.2 parts;

[0118] 10.0 parts of silane-modified hollow glass microspheres;

[0119] Leveling agent GLP588 1.0 part;

[0120] 0.4 parts of benzoin;

[0121] 0.4 parts of wetting accelerator BLC701B.

[0122] A method for preparing a thermal insulation and energy-saving powder coating, the method comprising the following steps:

[0123] After thorough premixing, the material is extruded through a twin-screw extruder with the following parameters set: Zone I temperature 101℃, Zone II temperature 112℃, Zone III temperature 102℃, feed speed frequency 31Hz, and screw speed frequency 40Hz. The extruded sheet is then crushed, ground, and sieved through a 200-mesh screen to obtain the thermal insulation and energy-saving powder coating.

[0124] Application Example 4

[0125] A thermal insulation and energy-saving powder coating, wherein the thermal insulation and energy-saving powder coating comprises the following raw materials in parts by weight:

[0126] 75 parts of the photochromic low-temperature curing polyester resin prepared in Example 4;

[0127] Triglycidyl isocyanurate (TGIC) 5.6 parts;

[0128] 17.1 parts of silane-modified hollow glass microspheres;

[0129] Leveling agent GLP588 1.3 parts;

[0130] 0.4 parts of benzoin;

[0131] 0.6 parts of wetting accelerator BLC701B.

[0132] A method for preparing a thermal insulation and energy-saving powder coating, the method comprising the following steps:

[0133] After thorough premixing, the material is extruded through a twin-screw extruder with the following parameters set: Zone I temperature 105℃, Zone II temperature 119℃, Zone III temperature 109℃, feed speed frequency 35Hz, screw speed frequency 44Hz, and screw speed frequency 35-45Hz. The extruded sheet is then crushed, ground, and sieved through a 200-mesh screen to obtain the thermal insulation and energy-saving powder coating.

[0134] Application Comparative Example 1

[0135] A powder coating comprising the following raw materials in parts by weight:

[0136] 85 parts of polyester resin prepared in Comparative Example 1;

[0137] Triglycidyl isocyanurate (TGIC) 6.4 parts;

[0138] 7.0 parts of silane-modified hollow glass microspheres;

[0139] Leveling agent GLP588 1.0 part;

[0140] Benzoin 0.3 parts;

[0141] 0.3 parts of wetting accelerator BLC701B.

[0142] A method for preparing a powder coating, the method comprising the following steps:

[0143] After thorough premixing, the material is extruded through a twin-screw extruder with the following parameters set: Zone I temperature 100℃, Zone II temperature 110℃, Zone III temperature 110℃, feed speed frequency 30Hz, and screw speed frequency 40Hz. The extruded sheet is then crushed, ground, and sieved through a 200-mesh screen to obtain the thermal insulation and energy-saving powder coating.

[0144] Application Comparative Example 2

[0145] A powder coating comprising the following raw materials in parts by weight:

[0146] 80 parts of polyester resin prepared in Comparative Example 2;

[0147] Triglycidyl isocyanurate (TGIC) 6.0 parts;

[0148] 12.4 parts of silane-modified hollow glass microspheres;

[0149] Leveling agent GLP588 1.0 part;

[0150] Benzoin 0.3 parts;

[0151] 0.3 parts of wetting accelerator BLC701B.

[0152] A method for preparing a powder coating, the method comprising the following steps:

[0153] After thorough premixing, the material is extruded through a twin-screw extruder with the following parameters set: Zone I temperature 105℃, Zone II temperature 115℃, Zone III temperature 105℃, feed speed frequency 30Hz, screw speed frequency 40Hz, and screw speed frequency 35-45Hz. The extruded flakes are then crushed, ground, and sieved through a 200-mesh screen to obtain the powder coating.

[0154] Application Comparative Example 3

[0155] A powder coating comprising the following raw materials in parts by weight:

[0156] 80 parts of the polyester resin prepared in Example 1;

[0157] Triglycidyl isocyanurate (TGIC) 6.0 parts;

[0158] 12.4 parts of hollow glass microspheres;

[0159] Leveling agent GLP588 1.0 part;

[0160] Benzoin 0.3 parts;

[0161] 0.3 parts of wetting accelerator BLC701B.

[0162] A method for preparing a powder coating, the method comprising the following steps:

[0163] A method for preparing a powder coating, the method comprising the following steps:

[0164] The comparison example for this application is the same as that for application comparison example 1.

[0165] Test Example 1

[0166] The powder coatings prepared in each embodiment and comparative example were cured at 150°C for 20 minutes to form sample coatings. Corresponding tests were conducted according to relevant standards, as follows: adhesion test of the samples was performed according to standard GB / T9286-1998; impact test was performed according to standard GB / T 1732-2020, including frontal impact strength and back impact strength, abbreviated as forward impact and reverse impact; bending test was performed according to GB / T 1731-2021; thermal conductivity test was performed according to standard GB / T 10294-2008; visible light transmittance under weak light and shading rate under strong light were performed according to standard GB / T 2680-2021; leveling performance was obtained by comparing with a PCI standard plate, and the specific indicators are shown in Table 1.

[0167] Table 1. Performance of Powder Coatings Prepared with Polyester Resins in Each Example

[0168]

[0169] Comparative Example 1 used a smaller amount of spiropyran-modified hydroxyl photochromic monomer and silane-modified hollow glass microspheres. Comparative Example 2 used polyester resin synthesized using a different process. Comparative Example 3 used conventional hollow glass microspheres as the insulation filler. The test results show that the resins in Examples 1-4 can achieve good low-temperature curing. The cured coatings exhibit good adhesion, impact resistance, and flexural strength. Under strong light, the photochromic coating shows color while blocking light, with a light-blocking rate greater than 80%, effectively reducing indoor temperature. Under weak light, it fades and transmits light, with a light transmittance greater than 75%. Utilizing natural light for insulation, the silane-modified hollow glass microspheres construct a sealed insulation layer, and the coating's thermal conductivity is less than 0.04 W / (m·K).

[0170] Comparative Example 1 used a smaller amount of spiropyran-modified hydroxyl photochromic monomer and silane-modified hollow glass microspheres. The test results show that its light transmittance under weak light is 88.5%, and its light blocking rate under strong light is only 49.8%, indicating that the photochromic response amplitude is significantly insufficient and it cannot effectively achieve the effect of color development and light blocking under strong light. At the same time, the thermal conductivity is 0.09 W / (m·K), which is significantly higher than that of the example, indicating that due to the insufficient amount of silane-modified hollow glass microspheres, an effective sealed insulation layer was not formed, resulting in poor thermal insulation performance. In addition, its reverse impact strength is only 30 kg·cm, and its mechanical properties have also decreased.

[0171] Comparative Example 2 used a method of adding spiropyran-modified hydroxyl photochromic monomer in the later stage of polyester resin synthesis, i.e., after the polycondensation reaction. The test results show that its shading rate under strong light was only 60%, far lower than the 80.6%-83.8% of Examples 1-4, and its transmittance under weak light was 70%, also lower than the 76.5%-80.3% of the Examples. This indicates that due to the low reaction temperature and short reaction time during later addition, the spiropyran-modified hydroxyl photochromic monomer failed to fully undergo a chemical grafting reaction with the polyester backbone, existing only in a physical mixing form, resulting in a weak photochromic response and a small color change amplitude. Simultaneously, its thermal conductivity was 0.035 W / (m·K), comparable to the Examples, indicating that the addition of silane-modified hollow glass microspheres still provides good thermal insulation.

[0172] Comparative Example 3 uses conventional hollow glass microspheres. The test results show that its thermal conductivity is 0.11 W / (m·K), which is significantly higher than that of the Example. At the same time, the light transmittance under weak light is 73.5%, which is lower than that of the Example, and the light blocking rate under strong light is 68.1%, which is significantly lower than that of the Example. This indicates that conventional glass microspheres cannot effectively coordinate photochromism and heat preservation functions due to interface defects and scattering losses.

[0173] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0174] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A photochromic low-temperature curing polyester resin, characterized in that, The photochromic low-temperature curing polyester resin is prepared from the following raw materials in parts by weight: Diol 4.0-4.4 parts; Dicarboxylic acid 6.6-7.0 parts; Esterification catalyst: 0.008-0.012 parts; 0.3-0.6 parts of spiropyran-modified hydroxyl photochromic monomer; Antioxidant 0.03-0.05 parts; Curing accelerator 0.02-0.04 parts.

2. The photochromic low-temperature curing polyester resin according to claim 1, characterized in that, The diol is one or more of neopentyl glycol, 1,4-cyclohexanediol, 2-butyl-2-ethyl-1,3-propanediol, or 1,6-hexanediol; the diacid is one or more of terephthalic acid, isophthalic acid, or adipic acid; the esterification catalyst is one or more of monobutyltin oxide or stannous oxalate; the antioxidant is one or more of antioxidant 168, antioxidant 1076, antioxidant 626, or antioxidant 1010; and the curing accelerator is one or more of triphenylphosphine, ethyltriphenylphosphine bromide, propyltriphenylphosphine bromide, or benzyltriphenylphosphine bromide.

3. The photochromic low-temperature curing polyester resin according to claim 1, characterized in that, The spiropyran-modified hydroxyl photochromic monomer is 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran.

4. The photochromic low-temperature curing polyester resin according to claim 1, characterized in that, The photochromic low-temperature curing polyester resin has an acid value of 30-35 mgKOH / g, a viscosity of 4000-6000 mPa·s, and a glass transition temperature of 61-64℃.

5. A method for preparing the photochromic low-temperature curing polyester resin as described in any one of claims 1-4, characterized in that, Includes the following steps: 1) The diol is added to the reaction vessel and heated to melt, then the diacid and esterification catalyst are added and mixed evenly to carry out the pre-esterification reaction; 2) Add a dicarboxylic acid and a spiropyran-modified hydroxyl photochromic monomer to the reaction vessel for copolyesterification reaction; 3) Reduce the system pressure to carry out vacuum polycondensation reaction. After the reaction is completed, add antioxidants and curing accelerators to obtain photochromic low-temperature curing polyester resin.

6. The method for preparing the photochromic low-temperature curing polyester resin according to claim 5, characterized in that, The reaction temperature of the pre-esterification reaction in step 1) is 235-240℃, and the reaction continues until the system acid value is 5-10 mgKOH / g and the viscosity is 500-1000 mPa·s; the reaction temperature of the copolyesterification reaction in step 2) is 220-230℃, and the reaction continues until the system acid value is 42-45 mgKOH / g and the viscosity is 1000-1500 mPa·s; the reaction pressure of the vacuum polycondensation in step 3) is -0.09 to -0.1 MPa, the reaction time is 1-2 h, and the reaction temperature is 220-230℃; the feeding temperature is 180-200℃, and the feeding time is 10-30 min; the mass ratio of the dicarboxylic acid in step 1) to the dicarboxylic acid in step 2) is 5.3~6:0.7~1.

5.

7. The application of the photochromic low-temperature curing polyester resin as described in claim 1 in thermal insulation and energy-saving powder coatings.

8. A thermal insulation and energy-saving powder coating, wherein the thermal insulation and energy-saving powder coating is prepared from the following raw materials in parts by weight: 75-82 parts of the photochromic low-temperature curing polyester resin as described in claim 1; 5-7 parts of triglycidyl isocyanurate; 10-18 parts of silane-modified hollow glass microspheres; Leveling agent 1.0-2.0 parts; Benzoin 0.3-0.8 parts; 0.3-0.8 parts of wetting accelerator.

9. The thermal insulation and energy-saving powder coating according to claim 8, characterized in that, The preparation method of the silane-modified hollow glass microspheres includes the following steps: (1) Hollow glass microspheres were pretreated by acid washing, water washing and drying to obtain pretreated microspheres; (2) Mix silane coupling agent with ethanol at a mass ratio of 1:8-12, add 3-5wt% hydrochloric acid or nitric acid to adjust the pH to 4-5, and hydrolyze to obtain silane solution; (3) Immerse the pretreated microbeads in silane solution at a solid-liquid ratio of 1g / 9~11mL and react at 50-80℃ for 1-3h; (4) Centrifuge, wash and dry to obtain silane-modified hollow glass microspheres; The silane coupling agent mentioned in step (2) is one or more of KH-570, KH-550 or A-171.

10. A method for preparing the aforementioned thermal insulation and energy-saving powder coating, the method comprising the following steps: The thermal insulation and energy-saving powder coating is obtained by mixing, screw extrusion, crushing, grinding and sieving the raw materials of the powder coating.

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