High gloss high flow impact resistant polylactic acid based powder coating and method of making the same

Abstract

The application discloses a high-gloss high-flow anti-impact polylactic acid-based powder coating and a preparation method thereof. The powder coating is prepared by the following steps: uniformly mixing polylactic acid resin, polyester resin, natural wax, a polylactic acid compatilizer, an anti-hydrolysis agent and an environmentally-friendly antioxidant, extruding and granulating the mixture through a double-screw extruder, drying the modified polylactic acid resin master batch, mixing and pressing the modified master batch with TGIC, pigments, fillers and additives, and crushing and screening the mixture to obtain the polylactic acid-based powder coating. The compatibility among the components of the resin is improved, and the film-forming performance of the powder coating is improved through the synergistic effect of the natural wax and the polylactic acid compatilizer during the resin modification and the film-forming process of the powder coating, so that the coating layer has good impact resistance and gloss.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a high-gloss high-flow flat impact-resistant polylactic acid-based powder coating and a preparation method thereof. BACKGROUND

[0002] The powder coating is a new type of 100% solid powder coating without solvent, which is prepared by physical mixing and melt extrusion of specific chemicals. At present, polyester powder coating is the highest yield and most widely used powder coating product in the market. In the formulation of polyester resin powder coating, polyester resin is one of the main film-forming substances, and the performance of polyester resin is the key to realizing the performance of powder coating.

[0003] The synthesis raw materials of polyester resin mainly come from fossil resources such as petroleum, coal, and natural gas. However, fossil resources are non-renewable, and the conversion and application of fossil resources cause the "greenhouse effect". The conversion and utilization of biomass resources is an effective way to protect the environment and reduce the greenhouse effect. Polylactic acid, a biodegradable polymer derived from biomass conversion, not only has biodegradability, non-toxicity, and good biocompatibility, but also has good mechanical and weather resistance, and is a potential raw material for preparing high-performance bio-based powder coating. However, the inherent brittleness of unmodified polylactic acid limits its application as a resin in powder coating. At the same time, the melt viscosity of polylactic acid is high, and the flowability of the coating during solidification is poor. During the resin solidification and film formation process, it is difficult for small molecules such as air and moisture in the substrate surface and melt pores to overflow, resulting in defects in the appearance and bulk of the cured coating film, which cannot meet the use requirements. SUMMARY

[0004] The present application provides a high-gloss high-flow flat impact-resistant polylactic acid-based powder coating and a preparation method thereof, which aims to improve the compatibility between the components of the resin and the melt film-forming performance of the powder coating through the synergistic effect of natural wax and polylactic acid compatibilizer during resin modification and powder coating melt film formation, so that the coating has good impact resistance and gloss.

[0005] To achieve the purpose, the present application adopts the following technical solutions:

[0006] The present application first provides a high-gloss high-flow flat impact-resistant polylactic acid-based powder coating, which is characterized in that: the raw materials of the powder coating include, in mass fraction: modified polylactic acid resin 50-70 parts; TGIC 3-6 parts; titanium dioxide 20-25 parts; filler 15-20 parts; leveling agent 0.5-1 part; brightener 0.5-1 part; degassing agent 0.2-0.5 part.

[0007] In some embodiments of the present application, the raw materials for preparing the modified polylactic acid resin include: 10-90 parts of polylactic acid resin; 10-90 parts of polyester resin; 1-3 parts of natural wax; 5-8 parts of polylactic acid compatibilizer; 1-2 parts of hydrolysis-resistant agent; and 0.1-0.5 parts of environmentally-friendly antioxidant.

[0008] In some embodiments of the present application, the polylactic acid resin has a melt mass flow rate of 20-50 g / 10 min under the test conditions of a temperature of 190℃ and a load weight of 2.16 Kg, a notched impact strength of 2-4 kJ / m 2 , a tensile strength of 40-60 MPa, an elongation at break of 4-10%, a molecular weight of 20000-80000 g / mol, a melting point of 155-180℃, and a density of 1.2-1.3 g / cm 3 .

[0009] In some embodiments of the present application, the polyester resin has a melt mass flow rate of 3-50 g / 10 min under the test conditions of a temperature of 190℃ and a load weight of 2.16 Kg, an acid value of 20-50 mg KOH / g, a viscosity of 2000-8000 mPa·s / 200℃, a molecular weight of 2000-8000 g / mol, and a glass transition temperature ≥ 60℃.

[0010] In some embodiments of the present application, the natural wax is selected from one or more mixtures of beeswax, palm wax, rice bran wax, candelilla wax, soy wax, and coconut wax, all having a molecular weight of 300-1000 g / mol.

[0011] In some embodiments of the present application, the polylactic acid compatibilizer includes one or both of polylactic acid grafted glycidyl methacrylate compatibilizer and polylactic acid grafted maleic anhydride compatibilizer; and the grafting rate of the polylactic acid compatibilizer is 1-3%.

[0012] In some embodiments of the present application, the hydrolysis-resistant agent is a polymeric carbodiimide hydrolysis-resistant agent, and the carbodiimide content is not less than 12%.

[0013] In some embodiments of the present application, the environmentally-friendly antioxidant includes a primary antioxidant and a secondary antioxidant, the primary antioxidant is tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, the secondary antioxidant is tris(2,4-di-tert-butylphenyl)phosphite, and the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1-2.

[0014] In some embodiments of the present application, the TGIC is a microfine modified TGIC, having an average particle size D50 of 50-200 μm, an epoxy equivalent weight ≤ 110 g / mol, and a melting point of 90-115℃.

[0015] In some embodiments of the present application, the titanium white powder is one or more of rutile titanium white powder and anatase titanium white powder, with an average particle size D50 of 0.2-0.4 μm, a TiO2 content of 94-98%, a pH value of 6.5-8.0, an oil absorption value of 15-20 g / 100 g, and a density of 4.0-4.1 g / cm 3 .

[0016] In some embodiments of the present application, the filler is one or more of precipitated barium sulfate, matt barium sulfate and light calcium carbonate, with an average particle size D50 of 0.1-2 μm, a pH value of 7.0-9.0, an oil absorption value of 10-22 g / 100 g, a loss on ignition of ≤1.50%, and a density of 4.4-4.5 g / cm 3 .

[0017] In some embodiments of the present application: the leveling agent is one or more of an acrylate homopolymer, an acrylate copolymer, a silicone-modified acrylate polymer and a polysiloxane. The gloss agent is an acrylate copolymer, with a ring and ball softening point of 95-125℃. The degassing agent is benzoin or a modified product thereof, with a melting point of 134-138℃ and a density of 1.3-1.4 g / cm 3 .

[0018] In some embodiments of the present application, the modified polylactic acid resin is prepared by the following steps:

[0019] The polylactic acid resin, polyester resin, natural wax, polylactic acid compatibilizer, hydrolysis-resistant agent and environmentally-friendly antioxidant are added to a high-speed mixer in proportion, and high-speed mixed at a rotation speed of 1000-1500 r / min for 5-10 min to obtain a mixed material;

[0020] The mixed material is subjected to shearing mixing and plasticizing in a twin-screw extruder at an extrusion temperature of 170-190℃ and a screw rotation speed of 100-300 r / min, and then subjected to water cooling, stretching, air drying and granulation to obtain the modified polylactic acid resin master batch.

[0021] The present application further provides a preparation method of the high-gloss high-leveling impact-resistant polylactic acid-based powder coating, comprising the following steps:

[0022] The modified polylactic acid resin, TGIC, titanium white powder, filler, leveling agent, gloss agent and degassing agent are added to a high-speed mixer in proportion, and mixed at a mixing speed of 1000-1500 r / min for 5-10 min, and then subjected to melt shearing in a twin-screw extruder at an extrusion temperature of 100-120℃ and a screw rotation speed of 400-600 r / min, and then subjected to cooling and tabletting and coarse crushing to obtain the primary powder coating.

[0023] The primary powder coating is finely pulverized by an ACM pulverizer under the conditions of main mill 4000-6000 r / min and secondary mill 2000-3000 r / min, and then the particle size is screened by a 100-140 mesh standard test sieve to obtain the high-gloss high-flow flat impact-resistant polylactic acid-based powder coating.

[0024] The present application has the following beneficial effects:

[0025] The present application first prepares modified polylactic acid resin masterbatch by blending polylactic acid resin, polyester resin, natural wax, polylactic acid compatibilizer and antioxidant, then the masterbatch is mixed and extruded into tablets with pigments, fillers and additives, and the polylactic acid-based powder coating is obtained by crushing and sieving. The present application improves the interfacial bonding strength and compatibility of polylactic acid and polyester resin through the synergistic effect of natural wax and polylactic acid compatibilizer during resin modification and powder coating melting and film forming, effectively improves the impact resistance of the coating, and endows the coating with good impact resistance. At the same time, the lubricity of natural wax effectively reduces the melt viscosity of the resin, improves the leveling and film forming performance of the resin melt during coating film forming, and makes the air in the substrate surface and the melt pore have enough time to escape from the coating film. The coating formed after the melt film forming has high gloss, which can meet the application requirements in the field of biological-based powder coating of household appliances, metal furniture and automotive interior decoration. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described in detail below with specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification without departing from the spirit of the present application.

[0027] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified by the present application, each numerical range has two endpoints and any number between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application are consistent with the mastery of the prior art by those skilled in the art and the description of the present application, and any method, equipment and material of the prior art similar or equivalent to the method, equipment and material described in the embodiments of the present application can be used to realize the present application.

[0028] Note that, unless otherwise specified, the “%” and “parts” described herein refer to “mass %” and “mass parts”, respectively.

[0029] The application provides a high-gloss high-flow flat impact-resistant polylactic acid-based powder coating and a preparation method thereof.

[0030] The high-gloss high-flow flat impact-resistant polylactic acid-based powder coating comprises, in mass fraction, 50-70 parts of modified polylactic acid resin, 3-6 parts of TGIC, 20-25 parts of titanium white, 15-20 parts of filler, 0.5-1 part of flow agent, 0.5-1 part of brightener and 0.2-0.5 part of degassing agent.

[0031] The raw material of the modified polylactic acid resin comprises, in mass fraction, 10-90 parts of polylactic acid resin, 10-90 parts of polyester resin, 1-3 parts of natural wax, 5-8 parts of polylactic acid compatibilizer, 1-2 parts of hydrolysis-resistant agent and 0.1-0.5 part of environment-friendly antioxidant.

[0032] In the following examples of the application, the polylactic acid resin used has a melt mass flow rate of 30 g / 10 min under the test conditions of a temperature of 190 DEG C and a load weight of 2.16 Kg, a molecular weight of 20000 g / mol, a notched impact strength of 3 kJ / m 2 , a tensile strength of 50 MPa, an elongation at break of 4%, a melting point of 175 DEG C and a density of 1.24 g / cm 3 . Specifically, the polylactic acid resin used in the following examples is FY201 of Anhui Fengyuan Futai Lai Polylactic Acid Co., Ltd.

[0033] In the following examples of the application, the polyester resin used has a melt mass flow rate of 40 g / 10 min under the test conditions of a temperature of 190 DEG C and a load weight of 2.16 Kg, an acid value of 30-36 mg KOH / g, a viscosity of 6000-8000 mPa·s / 200 DEG C, a molecular weight of 2000 g / mol and a glass transition temperature of greater than or equal to 65 DEG C. Specifically, the polyester resin used in the following examples is YC8600 of Anhui Yongchang New Material Co., Ltd.

[0034] In the following examples of the application, the natural wax is refined and purified beeswax with a molecular weight of 300 g / mol.

[0035] In the following examples of the application, the polylactic acid compatibilizer is polylactic acid grafted glycidyl methacrylate (PLA-g-GMA) with a grafting rate of 2%. Specifically, the polylactic acid compatibilizer used in the following examples is V105 of Foshan Fankuo Chemical Co., Ltd.

[0036] In the following examples of the present application, the anti-hydrolysis agent used is a polymeric carbodiimide anti-hydrolysis agent, and the carbodiimide content is 12.5%, the density is 1.05 g / cm 3 , and the melting temperature is 100℃. Specifically, the anti-hydrolysis agent used in the following examples is Hyadimide 100 from Rhein-Schafer, Germany.

[0037] In the following examples of the present application, the environmentally friendly antioxidant used includes a primary antioxidant and a secondary antioxidant, the primary antioxidant is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and the secondary antioxidant is tris(2,4-di-tert-butylphenyl)phosphite. Further, the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1.

[0038] In the following examples of the present application, the TGIC used is a micro-modified TGIC, the average particle size D50 of which is 50μm, and the micro-modified TGIC has an epoxy equivalent weight ≤110g / mol and a melting point of 90-115℃. The micro-modification treatment increases the specific surface area of TGIC, significantly increases its reactivity, reduces the activation energy required for the reaction, and improves the dispersion of TGIC in the resin, thereby improving the comprehensive performance of the coating. Specifically, the TGIC used in the following examples is T-4005 from Dongguan Longxin Innovational Material Technology Co., Ltd.

[0039] In the following examples of the present application, the titanium dioxide used is a rutile titanium dioxide, the average particle size D50 of which is 0.3μm, and the TiO2 content is 95%, the pH value is 7.0, the oil absorption value is 20g / 100g, and the density is 4.1g / cm 3 . The rutile titanium dioxide as a pigment has good leveling property for the coating, and the gelation time is relatively short, which is more conducive to curing and film formation. Specifically, the rutile titanium dioxide used in the following examples is NTR-760 from Ningbo Nanhai Chemical Co., Ltd.

[0040] In the following examples of the present application, the filler used is precipitated barium sulfate, the average particle size D50 of which is 0.79μm, and the pH value is 7.0-9.0, the oil absorption value is 14-22g / 100g, the loss on ignition is ≤1.50%, and the density is 4.5g / cm 3 . The precipitated barium sulfate has the smallest oil absorption, which is beneficial to improving the melt flowability and gloss of the coating. Specifically, the precipitated barium sulfate used in the following examples is HY-A03 from Shenzhen Haiyang Powder Technology Co., Ltd.

[0041] In the following examples of the present application, the leveling agent used is an acrylate homopolymer, which can significantly reduce the surface tension of the powder coating used in the present application, avoiding the appearance of orange peel or shrinkage on the coating film. Specifically, the leveling agent used in the following examples is GLP303 from Ningbo Nanhai Chemical Co., Ltd.

[0042] In the following examples of the present application, the brightener used is a copolymer of butyl acrylate and methyl methacrylate, and the ring and ball softening point of the copolymer of butyl acrylate and methyl methacrylate is 95-125℃, which contains a certain amount of polar groups, has good wetting effect on pigments, fillers and substrates in the powder coating, and can effectively eliminate shrinkage and promote leveling. Specifically, the brightener used in the following examples is PLC701 from Ningbo Nanhai Chemical Co., Ltd.

[0043] In the following examples of the present application, the degassing agent used is benzoin, and the melting point of benzoin is 136℃, the density is 1.31g / cm 3 , which can play the role of a solid solvent in the powder coating used in the present application, allowing sufficient time for air to escape from the coating film. Specifically, the degassing agent used in the following examples is WK315 from Ningbo Weikai Chemical Co., Ltd.

[0044] The present application will be explained in more detail by reference to the following examples, which should not be construed as limiting. Suitable modifications can be made within the scope of the main idea of the present application, which all fall within the technical scope of the present application.

[0045] Example 1

[0046] Step S1, 10 parts of polylactic acid resin, 90 parts of polyester resin, 1 part of beeswax, 5 parts of PLA-g-GMA, 2 parts of anti-hydrolysis agent and 0.3 parts of environmentally friendly antioxidant were added to a high-speed mixer in proportion, and high-speed mixing was carried out at a speed of 1000r / min for 5min to obtain a mixture;

[0047] Step S2, the mixture prepared in step S1 was sheared and mixed in a twin-screw extruder at an extrusion temperature of 180℃ and a screw speed of 200r / min, and then subjected to water cooling, stretching, air drying and granulation processes to obtain a modified polylactic acid resin master batch;

[0048] Step S3, 60 parts of the modified polylactic acid resin prepared in step S2, 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener, and 0.3 parts of a degassing agent are added to a high-speed mixer in proportion, mixed at a mixing speed of 1000 r / min for 5 min, then subjected to melt shearing through a twin-screw extruder at an extrusion temperature of 110°C and a screw rotation speed of 500 r / min, and then subjected to a cooling and tabletting process and a coarse crushing process to obtain a primary powder coating;

[0049] Step S4, the primary powder coating prepared in step S3 is subjected to fine crushing of the material through an ACM crusher at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min, and then the particle size is sieved through a 120-mesh standard inspection sieve to obtain a high-gloss high-leveling impact-resistant polylactic acid-based powder coating.

[0050] Example 2

[0051] Step S1, 90 parts of a polylactic acid resin, 10 parts of a polyester resin, 3 parts of beeswax, 8 parts of PLA-g-GMA, 2 parts of a hydrolysis-resistant agent, and 0.3 parts of an environmentally friendly antioxidant are added to a high-speed mixer in proportion, and mixed at a rotation speed of 1000 r / min for 5 min to obtain a mixture;

[0052] Step S2, the mixture prepared in step S1 is subjected to shearing, mixing, and plasticizing in a twin-screw extruder at an extrusion temperature of 180°C and a screw rotation speed of 200 r / min, and then subjected to a water-cooled drawing, air drying, and granulation process to obtain a modified polylactic acid resin master batch;

[0053] Step S3, 60 parts of the modified polylactic acid resin prepared in step S2, 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener, and 0.3 parts of a degassing agent are added to a high-speed mixer in proportion, mixed at a mixing speed of 1000 r / min for 5 min, then subjected to melt shearing through a twin-screw extruder at an extrusion temperature of 110°C and a screw rotation speed of 500 r / min, and then subjected to a cooling and tabletting process and a coarse crushing process to obtain a primary powder coating;

[0054] Step S4, the primary powder coating prepared in step S3 is subjected to fine crushing of the material through an ACM crusher at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min, and then the particle size is sieved through a 120-mesh standard inspection sieve to obtain a high-gloss high-leveling impact-resistant polylactic acid-based powder coating.

[0055] Example 3

[0056] Step S1, 50 parts of polylactic acid resin, 50 parts of polyester resin, 2 parts of beeswax, 6 parts of PLA-g-GMA, 2 parts of anti-hydrolysis agent and 0.3 parts of environmentally friendly antioxidant are added into a high-speed mixer in proportion, and high-speed mixing is carried out at a rotating speed of 1000 r / min for 5 min to obtain a mixture;

[0057] Step S2, the mixture prepared in step S1 is subjected to shearing mixing plasticization in a twin-screw extruder at an extrusion temperature of 180℃ and a screw rotating speed of 200 r / min, and then after the processes of water cooling, air drying and granulation, a modified polylactic acid resin master batch is obtained;

[0058] Step S3, 60 parts of the modified polylactic acid resin prepared in step S2 are added into a high-speed mixer in proportion with 5 parts of TGIC, 20 parts of titanium white, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener and 0.3 parts of a degassing agent, and after mixing at a mixing speed of 1000 r / min for 5 min, the mixture is subjected to melt shearing in a twin-screw extruder at an extrusion temperature of 110℃ and a screw rotating speed of 500 r / min, and then after the processes of cooling and tabletting and coarse crushing, a primary powder coating is obtained;

[0059] Step S4, the primary powder coating prepared in step S3 is subjected to fine crushing of materials in an ACM crusher at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min, and then the particle size is sieved through a 120-mesh standard inspection sieve to obtain a high-gloss high-leveling impact-resistant polylactic acid-based powder coating.

[0060] Example 4

[0061] Step S1, 50 parts of polylactic acid resin, 50 parts of polyester resin, 2 parts of beeswax, 6 parts of PLA-g-GMA, 2 parts of anti-hydrolysis agent and 0.3 parts of environmentally friendly antioxidant are added into a high-speed mixer in proportion, and high-speed mixing is carried out at a rotating speed of 1000 r / min for 5 min to obtain a mixture;

[0062] Step S2, the mixture prepared in step S1 is subjected to shearing mixing plasticization in a twin-screw extruder at an extrusion temperature of 180℃ and a screw rotating speed of 200 r / min, and then after the processes of water cooling, air drying and granulation, a modified polylactic acid resin master batch is obtained;

[0063] Step S3, 50 parts of the modified polylactic acid resin prepared in step S2 are added into a high-speed mixer in proportion with 5 parts of TGIC, 20 parts of titanium white, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener and 0.3 parts of a degassing agent, and after mixing at a mixing speed of 1000 r / min for 5 min, the mixture is subjected to melt shearing in a twin-screw extruder at an extrusion temperature of 110℃ and a screw rotating speed of 500 r / min, and then after the processes of cooling and tabletting and coarse crushing, a primary powder coating is obtained;

[0064] Step S4, the primary powder coating prepared in step S3 is finely pulverized by an ACM pulverizer under the conditions of a main mill of 5000 r / min and a secondary mill of 2500 r / min, and then the particle size is screened through a 120-mesh standard test sieve, to obtain a high-gloss high-flow impact-resistant polylactic acid-based powder coating.

[0065] Example 5

[0066] Step S1, 50 parts of polylactic acid resin, 50 parts of polyester resin, 2 parts of beeswax, 6 parts of PLA-g-GMA, 2 parts of anti-hydrolysis agent, and 0.3 parts of environmentally friendly antioxidant are added to a high-speed mixer in proportion, and high-speed mixing is performed at a rotation speed of 1000 r / min for 5 min, to obtain a mixture;

[0067] Step S2, the mixture prepared in step S1 is sheared, mixed, and plasticized in a twin-screw extruder at an extrusion temperature of 180°C and a screw rotation speed of 200 r / min, and then after the processes of water cooling, stretching, air drying, and granulation, a modified polylactic acid resin master batch is obtained;

[0068] Step S3, 70 parts of the modified polylactic acid resin prepared in step S2, 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener, and 0.3 parts of a degassing agent are added to a high-speed mixer in proportion, and mixing is performed at a mixing speed of 1000 r / min for 5 min, and then melt shearing is performed in a twin-screw extruder at an extrusion temperature of 110°C and a screw rotation speed of 500 r / min, and then after the processes of cooling, tabletting, and coarse pulverization, a primary powder coating is obtained;

[0069] Step S4, the primary powder coating prepared in step S3 is finely pulverized by an ACM pulverizer under the conditions of a main mill of 5000 r / min and a secondary mill of 2500 r / min, and then the particle size is screened through a 120-mesh standard test sieve, to obtain a high-gloss high-flow impact-resistant polylactic acid-based powder coating.

[0070] Comparative Example 1

[0071] Step S1, 50 parts of polylactic acid resin, 50 parts of polyester resin, 6 parts of PLA-g-GMA, 2 parts of anti-hydrolysis agent, and 0.3 parts of environmentally friendly antioxidant are added to a high-speed mixer in proportion, and high-speed mixing is performed at a rotation speed of 1000 r / min for 5 min, to obtain a mixture;

[0072] Step S2, the mixture prepared in step S1 is sheared, mixed, and plasticized in a twin-screw extruder at an extrusion temperature of 180°C and a screw rotation speed of 200 r / min, and then after the processes of water cooling, stretching, air drying, and granulation, a modified polylactic acid resin master batch is obtained;

[0073] Step S3, 60 parts of the modified polylactic acid resin prepared in step S2, 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener, and 0.3 parts of a degassing agent were added to a high-speed mixer in proportion, mixed at a mixing speed of 1000 r / min for 5 min, and then subjected to melt shearing through a twin-screw extruder at an extrusion temperature of 110°C and a screw rotation speed of 500 r / min. After cooling, pressing, and coarse crushing, a primary powder coating was obtained.

[0074] Step S4, the primary powder coating prepared in step S3 was subjected to fine crushing of the material through an ACM crusher at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min. After sieving the particle size through a 120-mesh standard inspection sieve, a powder coating was obtained.

[0075] Comparative Example 2

[0076] Step S1, 50 parts of a polylactic acid resin, 50 parts of a polyester resin, 2 parts of beeswax, 2 parts of a hydrolysis-resistant agent, and 0.3 parts of an environmentally friendly antioxidant were added to a high-speed mixer in proportion, and mixed at a rotation speed of 1000 r / min for 5 min to obtain a mixture.

[0077] Step S2, the mixture prepared in step S1 was subjected to shearing, mixing, and plasticizing in a twin-screw extruder at an extrusion temperature of 180°C and a screw rotation speed of 200 r / min. After water cooling, stretching, air drying, and granulation, a modified polylactic acid resin master batch was obtained.

[0078] Step S3, 60 parts of the modified polylactic acid resin prepared in step S2, 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of a leveling agent, 1 part of a brightener, and 0.3 parts of a degassing agent were added to a high-speed mixer in proportion, mixed at a mixing speed of 1000 r / min for 5 min, and then subjected to melt shearing through a twin-screw extruder at an extrusion temperature of 110°C and a screw rotation speed of 500 r / min. After cooling, pressing, and coarse crushing, a primary powder coating was obtained.

[0079] Step S4, the primary powder coating prepared in step S3 was subjected to fine crushing of the material through an ACM crusher at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min. After sieving the particle size through a 120-mesh standard inspection sieve, a powder coating was obtained.

[0080] Comparative Example 3

[0081] Step S1, 60 parts of polylactic acid resin, 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of leveling agent, 1 part of brightener and 0.3 parts of degassing agent were added to a high-speed mixer in proportion, mixed at a mixing speed of 1000 r / min for 5 min, then melt sheared by a twin-screw extruder at an extrusion temperature of 110°C and a screw speed of 500 r / min, and then cooled, pressed, and coarsely crushed to obtain a primary powder coating.

[0082] Step S2, the primary powder coating prepared in step S1 was finely pulverized by an ACM pulverizer at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min, and then the particle size was sieved by a 120 mesh standard test sieve to obtain a powder coating.

[0083] Comparative Example 4

[0084] Step S1, 50 parts of polylactic acid resin, 50 parts of polyester resin, 2 parts of beeswax, 6 parts of PLA-g-GMA, 2 parts of anti-hydrolysis agent and 0.3 parts of environmentally friendly antioxidant were added to a high-speed mixer in proportion, and mixed at a speed of 1000 r / min for 5 min to obtain a mixture.

[0085] Step S2, 60 parts of the mixture prepared in step S1 were added to a high-speed mixer in proportion with 5 parts of TGIC, 20 parts of titanium dioxide, 15 parts of precipitated barium sulfate, 1 part of leveling agent, 1 part of brightener and 0.3 parts of degassing agent, mixed at a mixing speed of 1000 r / min for 5 min, then melt sheared by a twin-screw extruder at an extrusion temperature of 110°C and a screw speed of 500 r / min, and then cooled, pressed, and coarsely crushed to obtain a primary powder coating.

[0086] Step S3, the primary powder coating prepared in step S2 was finely pulverized by an ACM pulverizer at a main mill speed of 5000 r / min and a secondary mill speed of 2500 r / min, and then the particle size was sieved by a 120 mesh standard test sieve to obtain a powder coating.

[0087] Test Example

[0088] The powder coatings prepared in Examples 1-5 and Comparative Examples 1-4 were used to prepare coating samples by high-voltage electrostatic spraying method: first, 200 g of powder coating sample powder was loaded into an electrostatic spraying gun, the spraying gas pressure was set to 0.38 MPa, the electrostatic high voltage was set to 76 KV, then the powder coating was uniformly sprayed on the substrate by opening the spraying gun, the film thickness was controlled at 80-90 μm, then the sprayed substrate was placed in an oven for curing treatment at 200°C for 10 min to form a coating sample. The substrate selected was a tinplate with a size of 50 mm x 120 mm x 0.3 mm, and the surface was polished with sandpaper before spraying to remove the oxide skin.

[0089] The powder coating layers prepared in the above-mentioned examples and comparative examples were tested, and the performance parameter test methods were as follows:

[0090] Coating film appearance: tested according to the standard of GB / T 37356-2019 “Illumination conditions and methods for visual evaluation of paint and varnish coatings”;

[0091] Impact resistance: tested according to the standard of GB / T 1732-2020 “Determination of impact resistance of paint film”;

[0092] Gloss: tested according to the standard of GB / T 9754-2007 “Determination of 20°, 60° and 85° specular gloss of paint films of non-metallic pigmented paints and varnishes”;

[0093] Leveling grade: according to the PCI leveling grading standard;

[0094] Adhesion: tested according to the standard of GB / T 9286-1998 “Crosshatch test for paint and varnish films”;

[0095] The coating performances of the powder coatings obtained in the above-mentioned examples and comparative examples are shown in Table 2.

[0096] Table 2, Performance comparison of product coating films in examples and comparative examples

[0097]

[0098] As shown in Table 2, by comparing the performances of the coatings in comparative examples 1-3 and examples 1-5, it can be found that the gloss of the powder coating layers in examples 1-5 is significantly higher than that of the coatings in the comparative examples, indicating that the gloss of the polylactic acid-based powder coating is improved. The leveling grade of the examples is also significantly higher than that of the comparative examples, indicating that the leveling property of the material is significantly improved, and the impact resistance of the coating in the examples can mostly pass, indicating that the impact resistance of the material is improved. By comparing the performances of the coatings in example 3 and comparative example 1-2, it can be found that the performance difference is large after only adding natural wax or polylactic acid compatibilizer to modify the polylactic acid resin / polyester resin blend, which cannot meet the application requirements of the powder coating. The reason is that it is difficult to balance the compatibility between the resin components and the leveling and film-forming properties of the resin melt. Example 3 and comparative example 4 have the same formulation but different preparation processes, and the performance difference is large. The reason is that the traditional preparation method of powder coating is difficult to realize the effective regulation of the polylactic acid compatibilizer to the interface of the polylactic acid resin / polyester resin blend and the controllable dispersion of the natural wax in the matrix, which reflects the superiority of the preparation process.

[0099] Thus, from the gloss, leveling grade and impact resistance results in various embodiments and comparative examples, it can be seen that the application uses polylactic acid resin / polyester resin blend as the matrix, through the synergistic effect of natural wax and polylactic acid compatibilizer in the process of resin modification and powder coating melt film formation, the interfacial bonding strength and compatibility between the components of the resin are improved, at the same time, the lubricity of natural wax is used to effectively reduce the melt viscosity of the resin, the leveling and film forming properties of the resin melt during the coating film forming process are improved, the air in the substrate surface and the melt pore has enough time to escape from the coating film, the coating formed after the melt film forming has good impact resistance and gloss, the application range and field of polylactic acid-based powder coating are expanded, especially in the fields of household appliances, metal furniture and automotive interior decoration which have higher requirements for appearance gloss and impact resistance.

[0100] The above description is only the preferred embodiment of the present application and the explanation of the applied technical principles, and those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept, for example, the technical solutions formed by replacing the above features with the technical features disclosed in the present application (but not limited to) having similar functions.

[0101] In addition to the technical features described in the specification, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present application, the remaining technical features will not be described here.

Claims

1. A high gloss, high flow, impact resistant polylactic acid based powder coating, characterized in that, The raw materials of the powder coating include, in mass fraction: modified polylactic acid resin 50-70 parts; TGIC 3-6 parts; titanium white powder 20-25 parts; filler 15-20 parts; leveling agent 0.5-1 part; brightener 0.5-1 part; degassing agent 0.2-0.5 part; The raw materials of the modified polylactic acid resin include, in mass fraction: polylactic acid resin 10-90 parts; polyester resin 10-90 parts; natural wax 1-3 parts; polylactic acid compatibilizer 5-8 parts; hydrolysis inhibitor 1-2 parts; environmentally friendly antioxidant 0.1-0.5 part; The polylactic acid compatibilizer includes one or both of polylactic acid grafted glycidyl methacrylate compatibilizer and polylactic acid grafted maleic anhydride compatibilizer, and the grafting rate of the polylactic acid compatibilizer is 1-3%. The modified polylactic acid resin is prepared by the following steps: The polylactic acid resin, polyester resin, natural wax, polylactic acid compatibilizer, hydrolysis inhibitor and environmentally friendly antioxidant are added into a high-speed mixer in proportion, and high-speed mixing is carried out at a rotating speed of 1000-1500 r / min for 5-10 min to obtain a mixture; The mixture is subjected to shearing mixing plasticization in a twin-screw extruder at an extrusion temperature of 170-190 ℃ and a screw rotating speed of 100-300 r / min, and then is subjected to water cooling, air drying and granulation to obtain modified polylactic acid resin masterbatch.

2. A high gloss, high flow, impact resistant polylactic acid based powder coating according to claim 1, characterized in that, The melt mass flow rate of the polylactic acid resin is 20-50 g / 10 min under the test conditions of a temperature of 190 ℃ and a load weight of 2.16 Kg.

3. A high gloss, high flow, impact resistant polylactic acid based powder coating according to claim 1, wherein, The polyester resin has an acid value of 20-50 mg KOH / g, a viscosity of 2000-8000 mPa·s / 200℃, and a molecular weight of 2000-8000 g / mol.

4. A high gloss, high flow, impact resistant polylactic acid based powder coating according to claim 1, wherein, The natural wax is selected from one or more mixtures of bee wax, palm wax, rice bran wax, candelilla wax, soybean wax and coconut wax, all having a molecular weight of 300-1000 g / mol.

5. A high gloss, high flow, impact resistant polylactic acid based powder coating according to claim 1, wherein, The hydrolysis inhibitor is a polymeric carbodiimide hydrolysis inhibitor, and the carbodiimide content is not less than 12%.

6. A high gloss, high flow, impact resistant polylactic acid based powder coating according to claim 1, wherein, The environmentally friendly antioxidant includes a primary antioxidant and a secondary antioxidant, the primary antioxidant is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and the secondary antioxidant is tris(2,4-di-tert-butylphenyl)phosphite, and the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1-2.

7. A process for the preparation of a high gloss, high flow, impact resistant polylactic acid based powder coating according to any one of claims 1 to 6, characterized in that, The following steps are included: The modified polylactic acid resin, TGIC, titanium white powder, filler, leveling agent, brightener and degassing agent are added into a high-speed mixer in proportion, and mixing is carried out at a mixing speed of 1000-1500 r / min for 5-10 min, and then the primary powder coating is obtained by melt shearing in a twin-screw extruder at an extrusion temperature of 100-120 ℃ and a screw rotating speed of 400-600 r / min, and then is subjected to cooling and tabletting and coarse crushing. The primary powder coating is finely pulverized by an ACM pulverizer under the conditions of 4000-6000 r / min of main grinder and 2000-3000 r / min of secondary grinder, and then is screened by a 100-140 mesh standard test sieve to obtain the high-gloss high-flow flat impact-resistant polylactic acid-based powder coating.

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