Silicone modified bifunctional polyester resins and weather resistant powder coating compositions formulated therefrom

Abstract

The invention relates to organic silicon modified bifunctional polyester resin and a weather-resistant powder coating composition prepared from the organic silicon modified bifunctional polyester resin. Specifically, the silicone-modified bifunctional polyester resin has a molecular backbone derived from a polyol component, a polyacid component, a capping component, and a silicone component, in which the silicone-modified bifunctional polyester resin has an acid value in the range of 20 to 40 mg KOH / g, a hydroxyl value in the range of 5 to 15 mg KOH / g, and a hydroxyl value in the range of 5 to 15 mg KOH / g. The organic silicon component is organic silicon resin with a structure as shown in a formula (I). The weather-resistant powder coating composition disclosed by the invention has excellent weather resistance, such as QUVB of more than 500 hours, and also has excellent leveling property and high glossiness. (RSiO3 / 2) a (R2SiO2 / 2) b (R3SiO1 / 2) c (SiO4 / 2) d (XO1 / 2) e (HO1 / 2) g (I)

Description

Technical Field

[0001] This application relates to a bifunctional polyester resin and its application in the formulation of weather-resistant powder coating compositions. Specifically, this application relates to a silicone-modified bifunctional polyester resin capable of providing excellent weather resistance, leveling, and high gloss, and its application in the formulation of weather-resistant powder coating compositions. Background Technology

[0002] Powder coatings are coating compositions existing in the form of fine powder, possessing a completely different form from conventional coatings and using no solvents. Therefore, compared to traditional liquid coatings, powder coatings have several advantages: 1) Better environmental performance: Powder coatings do not contain solvents, so they do not release harmful volatile organic compounds (VOCs) during application and curing, thus helping to reduce environmental pollution and complying with increasingly stringent environmental regulations in terms of efficiency and cost; 2) Higher utilization rate: Because powder coatings exist in the form of fine powder, the uncured portion of the coating during application can be recycled, thus improving the utilization rate of powder coatings. These advantages are the main driving force behind the gradual replacement of liquid coatings by powder coatings. Furthermore, compared to conventional coatings, powder coatings typically form harder, more wear-resistant, and more resistant to chemical corrosion. They can achieve various gloss levels and colors to meet different decorative needs, thus having a particularly wide range of applications. They can be applied to various substrates such as metal, wood, and plastics, as well as various industries such as furniture, construction, automobiles, and electrical appliances, and even in heavy-duty anti-corrosion fields such as marine and shipbuilding. Therefore, in today's world where sustainable development is increasingly valued, powder coatings are becoming an ideal alternative to traditional liquid coatings due to their environmental friendliness, high efficiency, and superior performance.

[0003] As a film-forming resin for powder coatings, polyester resins are mainly divided into two categories: carboxylated polyesters and hydroxylated polyesters. In China, because carboxylated polyesters use triglycidyl isocyanate (TGIC) as a curing agent, powder coatings formulated with them are significantly cheaper than those formulated with hydroxylated polyesters and blocked isocyanate curing agents. Currently, carboxylated polyesters account for approximately 95% of the market share, far exceeding that of hydroxylated polyesters.

[0004] Today's market demands superior performance from polyesters, particularly excellent weather resistance. As the most common modifier to improve the heat resistance of polyester resins, silicone materials can be combined with polyester resins through physical or chemical methods. Physical methods, such as physical blending, combine polyester resins and silicone raw materials, but the resulting coatings tend to have poor leveling and appearance. Chemical methods, such as solvent polymerization and bulk polymerization, combine polyester resins and silicone raw materials. Compared to physical methods, chemically synthesized coatings offer improved leveling and appearance. However, solvent polymerization is unacceptable for traditional powder coating polyester resin manufacturers due to environmental pollution and increased operating costs. Bulk polymerization faces challenges such as rapid viscosity increases and difficulty in process control due to gelation.

[0005] Currently, known technologies for improving polyester resins using organosilicon resins via chemical methods include Dow Chemical's WO 2022 / 120566 (hereinafter referred to as the 566' patent), Zhejiang Guanghua Technology's CN 110903471 (hereinafter referred to as the 471' patent), and Anhui Shenjian New Materials' CN 110527073 (073' patent). The 566' patent synthesizes an organosilicon resin and uses it for bulk polymerization to synthesize a polyester resin for powder coatings, thereby improving the heat resistance of the powder coatings. This patent synthesizes a carboxyl polyester with an acid value of 10-60 mg KOH / g and hydroxyl groups less than 5 mg KOH / g. However, this patent makes no mention of bifunctional polyesters, nor of the influence of the type of end-capping component on the synthesis of organosilicon-modified bifunctional polyester resins, or how to improve the weather resistance of powder coatings. The 471' patent discloses a method for synthesizing a hydroxyl polyester for powder coatings via bulk polymerization using the organosilicon resin mentioned in the 566' patent, thereby improving the heat resistance of the powder coatings. The hydroxyl polyester synthesized in this patent has a hydroxyl value of 35-45 mg KOH / g and an acid value of less than 5 mg KOH / g. Similarly, this patent makes no mention of difunctional polyesters, nor of the influence of the type of end-capping agent on the performance of silicone-modified difunctional polyester resins, or how to improve the weather resistance of powder coatings. Patent 073' discloses a high-temperature resistant and ultra-weather-resistant silicone-containing polyester resin for powder coatings. This patent uses easily hydrolyzable silanes as silicone-containing raw materials. These silicone-containing raw materials are easily hydrolyzed during the synthesis of silicone-containing polyester resins, and their dosage should not be too high; otherwise, the synthesis process will be difficult to control and gelation will easily occur. Furthermore, although patent 073' synthesizes silicone-modified difunctional polyester resins, it employs a complex end-capping process, including not only carboxylic acid end-capping but also polyol end-capping, resulting in unnecessary additional process costs. Moreover, this patent makes no mention of the influence of the type of end-capping agent on the performance of silicone-modified difunctional polyester resins, or how to improve the weather resistance of powder coatings.

[0006] Therefore, the powder coating industry still needs improved organosilicon-modified bifunctional polyester resins that can significantly enhance the weather resistance of powder coatings. Summary of the Invention

[0007] To address the aforementioned technical problems, the inventors of this application have designed a novel bifunctionalized polyester resin for powder coatings, modified with an organosilicon resin having the structure of formula (I), using bulk polymerization. (RSiO 3 / 2 ) a (R2SiO 2 / 2 ) b -(R3SiO 1 / 2 ) c (SiO 4 / 2 ) d(XO 1 / 2 ) e (HO 1 / 2 ) g (I) The coating formed by curing the polyester resin with a single TGIC curing agent or a combination of TGIC and a blocked isocyanate curing agent can provide superior weather resistance, while also providing good leveling and gloss.

[0008] Therefore, this application provides a silicone-modified bifunctional polyester resin, wherein the silicone-modified bifunctional polyester resin has a molecular backbone derived from a polyol component, a polyacid component, a capping component, and a silicone component, wherein,

[0009] The organosilicon-modified bifunctional polyester resin has an acid value in the range of 20 to 40 mg KOH / g and a hydroxyl value in the range of 5 to 15 mg KOH / g.

[0010] The organosilicon component is an organosilicon resin having the structural formula (I):

[0011] (RSiO 3 / 2 ) a (R2SiO 2 / 2 ) b (R3SiO 1 / 2 ) c (SiO 4 / 2 ) d (XO 1 / 2 ) e (HO 1 / 2 ) g (I)

[0012] In the above formula (I)

[0013] Each R is independently a monovalent hydrocarbon group having 1 to 30 carbon atoms, each X is independently an alkyl group having 1 to 5 carbon atoms, a>0, b≥0, c>0, d≥0, e>0, g≥0, a / (a+b+c+d) is 0.5 to 0.9, b / a is 0 to 1, c / a is 0.1 to 1, d / a is 0 to 0.25, and e / (a+b+c+d) is 0.2 to 2; wherein the organosilicon resin has an average number of silicon-bonded alkoxy groups and silicon-bonded hydroxyl groups per molecule in the range of 2 to 4, and contains less than 2% by weight of silicon-bonded hydroxyl groups based on the weight of the organosilicon resin; and wherein 50 mol% or more of the silicon atoms in the organosilicon resin are linked to aryl groups.

[0014] Another aspect of this application provides a weather-resistant powder coating composition comprising at least one organosilicon-modified bifunctional polyester resin according to the first aspect of this application, a curing agent component, and additional additives.

[0015] The inventors of this application were surprised to discover that, when modifying polyester resin with an organosilicon resin having the above-described structural formula (I), the weather resistance of the cured film of powder coatings formulated from the resulting organosilicon-modified bifunctional polyester resin can be effectively improved by specifically selecting the type of end-capping component and / or the type of polyol. Furthermore, the inventors of this application were even more surprised to discover that, based on the above formulation, by controlling the amount of the organosilicon resin and combining it with a combination of triglycidyl isocyanate (TGIC) and blocked isocyanate as a curing agent, the weather resistance of the cured film of powder coatings formulated from the resulting organosilicon-modified bifunctional polyester resin can be further effectively improved, even achieving a weather resistance of 700 hours or longer, which was previously unforeseen.

[0016] Details of one or more embodiments of this application are set forth in the following description. Other features, objectives, and advantages of this application will become clear from the description and claims.

[0017] definition

[0018] In this document, unless otherwise stated, the terms “a,” “this,” “at least one,” and “one or more,” as well as the absence of quantifiers, are used interchangeably. Thus, for example, a coating composition containing “a” additive can be interpreted as meaning that the coating composition contains “one or more” additives.

[0019] When a composition is described as including or comprising specific components, it is anticipated that optional components not covered by the present invention are not excluded from the composition, and that the composition may be constituted or composed of the components involved. Similarly, when a method is described as including or comprising specific process steps, it is anticipated that optional process steps not covered by the present invention are not excluded from the method, and that the method may be constituted or composed of the process steps involved.

[0020] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0021] The term "powder" herein refers to a substantially dry solid substance at room temperature and atmospheric pressure that has been reduced to a fine, loose particulate state, wherein the maximum particle size of a single particle at 23°C and atmospheric pressure is preferably at most 200 μm, more preferably at most 180 μm, even more preferably at most 160 μm, most preferably at most 150 μm, particularly at most 140 μm, more particularly at most 130 μm, most particularly at most 120 μm, for example at most 110 μm, for example at most 100 μm, for example at most 90 μm; and the minimum particle size of a single particle at 23°C and atmospheric pressure is preferably at least 10 μm, more preferably at least 15 μm, even more preferably at least 20 μm, most preferably at least 25 μm, particularly at least 30 μm, more particularly at least 35 μm, most particularly at least 40 μm, for example at least 45 μm, for example at least 50 μm, for example at least 60 μm, for example at least 70 μm. Particles are defined as small objects that: a) have an average linear size as described herein and b) behave as a single unit in terms of transport and performance. The method used to measure the particle size of the powder coating compositions of the present invention is sieving.

[0022] In the context of this invention, "composition" means: a combination and / or mixture of different chemical substances and / or components that form a whole.

[0023] In the context of this invention, "powder coating composition" refers to a multi-component mixture capable of forming a powdery material, which is solid or semi-solid at room temperature and capable of forming an irreversible cross-linked network (the so-called cured form). In the powder coating composition of this invention, cross-linking is achieved by forming permanent covalent bonds through a chemical reaction between the functional groups of a polyester having functional groups that can react with, for example, epoxy or isocyanate groups, and the functional groups of a cross-linking agent (also commonly referred to as a curing agent, which is a compound having, for example, epoxy or isocyanate groups). If other resins are also present in the powder coating composition of this invention, their functional groups (if they can react with epoxy or isocyanate groups) can also react with the cross-linking agent. The result of these cross-linking reactions is that the cured form of the powder coating composition (the cross-linked powder coating composition) becomes a "fixed" material, i.e., a material that can no longer flow or melt.

[0024] In the context of this invention, the term "powder coating" refers to a partially or completely cured (crosslinked) form of the powder coating composition of this invention. In other words, a powder coating is obtained from a partially or completely cured powder coating composition.

[0025] In the context of this invention, the functional group in the polyester that can react with epoxy or isocyanate groups is the terminal group (=terminal group) located at the end of the polyester macromolecular structure of each polyester molecule (including terminal groups on side chains that form part of the main chain and longer chain (compared to the side chain) of the macromolecule).

[0026] In the context of this application, the term "bifunctional polyester" refers to a polyester macromolecular structure whose terminal groups include both carboxyl and hydroxyl groups, thus enabling it to react simultaneously with both carboxyl and hydroxyl reactive groups. Only polyesters with both a hydroxyl value and an acid value greater than 5 mg KOH / g can be classified as "hydroxy-carboxyl bifunctional polyesters." Therefore, in embodiments of this application, "bifunctional polyester" can also be referred to as "hydroxy-carboxyl bifunctional polyester," and the two terms can be used interchangeably.

[0027] When referring to "hydroxy-carboxyl bifunctionalized polyester," the term "acid value" (AV) refers to the measured AV of the resin. According to the present invention, the acid value (AV) of the polyester (mg KOH / g polyester) is determined based on ISO 2114 according to the TM-2400 test method. The acid value of a polyester resin is a measure of the amount of carboxylic acid groups in the polyester resin.

[0028] When referring to "hydroxyl-carboxyl bifunctional polyester," the term "hydroxyl value" (OHV) refers to the measured OHV of the resin. According to the present invention, the hydroxyl value (OHV) of the polyester (mg KOH / g polyester) is determined based on ISO 2114 according to the TM-2433 test method. The hydroxyl value of a polyester resin is a measure of the amount of hydroxyl groups in the polyester resin.

[0029] When referring to “hydroxy-carboxyl bifunctional polyesters”, the term “glass transition temperature” (Tg) is the determined Tg of the polyester. According to the present invention, the glass transition temperature of the polyester is measured by differential scanning calorimetry (DSC) according to the TM-2433 test method based on ISO 11357, ISO 16805, and ASTM E1356 at a heating rate of 5 °C / min.

[0030] When referring to “hydroxy-carboxyl-bifunctionalized polyester”, the term “viscosity” or its equivalent “melt viscosity” refers herein to the melt viscosity (in Pa·s) at 160 °C. Viscosity measurements were performed at 160 °C using a Brookfield CAP 2000+H Viscometer. The applied shear rate was 21 s. -1 It uses a 19.05mm spindle (conical rotor CAP-S-05 (19.05mm, 1.8°)).

[0031] When referring to the use of "hydroxy-carboxyl bifunctional polyester", the amount of silicone component refers to the mass percentage of the amount of silicone component added based on the total amount of material used to prepare the polyester resin.

[0032] When referring to the use of "hydroxy-carboxyl bifunctional polyester", the phrase "the end-capping component of the silicone-modified bifunctional polyester resin is free of isophthalic acid, tetrahydrophthalic anhydride and trimellitic anhydride" means that none of the intentionally added isophthalic acid, tetrahydrophthalic anhydride and trimellitic anhydride are present in the end-capping component used in the synthesis of the bifunctional polyester.

[0033] In the context of this invention, "curing agent" refers to a compound capable of reacting with a hydroxy-carboxyl difunctional polyester to cure a powder coating composition formulated from the polyester and the hydroxy-carboxyl difunctional polyester, thereby becoming a "fixed" material. In the case of hydroxy-carboxyl difunctional polyesters, common curing agents are curing agents containing epoxy functional groups or a combination of curing agents containing epoxy functional groups and curing agents containing isocyanate functional groups.

[0034] When referring to the use of "curing agent," the term "epoxy equivalent" is a parameter expressing the curing agent such as triglycidyl isocyanurate (TGIC) and TGIC-based epoxy resins, and refers to the mass of curing agent containing 1 mol of epoxy groups. Generally, the lower the epoxy equivalent, the more epoxy groups the curing agent contains, and the higher its reactivity. According to the present invention, the epoxy equivalent of the curing agent can be determined according to GB4612-84.

[0035] When referring to the use of "curing agent," the term "isocyanate content" is a parameter expressing the reactivity of the blocked isocyanate as a curing agent, and is a measure of the amount of active isocyanate groups in the blocked isocyanate. According to the present invention, the isocyanate content (NCO%) of the curing agent is determined according to HG / T2409-2023.

[0036] In this invention, the term "cure" may be used interchangeably with the terms "crosslinking" or "curing," and the powder coating is the object obtained when the weather-resistant powder coating composition of this invention is cured. "Cure" herein refers to the process of becoming a "fixed" material.

[0037] In this invention, heat cure is used interchangeably with the term "thermal cure." Preferably, only heat energy (thermal cure) is used for curing the weather-resistant powder coating composition. In the context of this invention, the term "thermal energy" does not include UV or electron beam-induced curing.

[0038] In this invention, the PCI leveling index is a parameter used to measure the leveling properties of a coating formed from the powder coating composition according to the invention. It is determined by comparing the waviness of a sample measured using the reflection of a light source with the smoothness of a series of 60-micron thick powder coating visual smoothness standard panels (ACT Test Panels Inc., APR22163(A) Batch: 50708816). Generally, the higher the PCI leveling index, the better the leveling properties of the powder coating. A PCI leveling index greater than or equal to 5 is considered acceptable, while a lower index is considered unacceptable.

[0039] In this invention, "weathering time" is an effective parameter for measuring the weather resistance of a coating. According to this invention, the weathering time of a coating refers to the time period during which the coating can withstand a cyclic test of 4 hours in a UV state (at 50°C) and 4 hours in a condensed state in a QUV-B aging test, provided that the coating's gloss retention is not less than 50% or its color difference is not greater than or equal to 3. When the coating's gloss retention is less than 50% or its color difference is greater than or equal to 3, the aging time experienced by the coating until the end of the test is determined as the coating's weathering time. Generally, powder coatings with a weathering time of 500 hours or more are considered acceptable, and powder coatings with a weathering time of 700 hours are considered excellent.

[0040] For any upper and lower bounds of the parameters given herein, the boundary values ​​are contained within each range of each parameter. All combinations of the minimum and maximum values ​​of the parameters described herein can be used to define the parameter ranges of various embodiments and preferred examples of the invention.

[0041] In this document, "curing" refers to the process by which a material becomes "fixed" to form an irreversible cross-linked network (the so-called "cured form" or "cured composition"), in which the material no longer flows, melts, or dissolves. The terms "curing" and "cross-linking" are used interchangeably in this document.

[0042] "Powder coating" in this document refers to a cured powder coating composition in the form of a coating. A powder coating is obtained after the powder coating composition has been cured.

[0043] When used herein, the term "comprising" means that the following enumeration is not exhaustive and may or may not include any other suitable additional items, such as suitable one or more further features, components, and / or substituents. The term "comprising" is used interchangeably with the term "containing." When used herein, "substantially comprising" or "comprising substantially" means that a component or the listed components are present in a given material in an amount greater than or equal to about 90% by weight of the total amount of the given material, preferably greater than or equal to about 95% by weight of the total amount of the particular material, more preferably greater than or equal to about 98% by weight of the total amount of the particular material, and even more preferably greater than or equal to about 99% by weight of the total amount of the particular material. When used herein, the term "comprising" means that the following list is exhaustive and does not include additional items.

[0044] Unless the context clearly indicates otherwise, the plural form of terms used herein (e.g., polyester resin, curing agent, powder coating composition, component) may be interpreted as including the singular form, and vice versa.

[0045] In this invention, the numerical range defined by the endpoints includes all values ​​within that range. For example, the range of 1 to 5 encompasses the values ​​1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. Moreover, the disclosed numerical range includes all subsets of the wider range. For example, the range of 1 to 5 includes subranges 1 to 4, 1.5 to 4.5, 1 to 2, etc.

[0046] The terms "preferred" and "ideally" refer to embodiments of the invention that provide certain benefits in certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention. Detailed Implementation

[0047] According to a first aspect of the present invention, an organosilicon-modified bifunctional polyester resin is provided, wherein the organosilicon-modified bifunctional polyester resin has a molecular backbone derived from a polyol component, a polyacid component, a capping component, and an organosilicon component, wherein...

[0048] The organosilicon-modified bifunctional polyester resin has an acid value in the range of 20 to 40 mg KOH / g and a hydroxyl value in the range of 5 to 15 mg KOH / g.

[0049] The organosilicon component is an organosilicon resin having the structural formula (I):

[0050] (RSiO 3 / 2 ) a(R2SiO 2 / 2 ) b (R3SiO 1 / 2 ) c (SiO 4 / 2 ) d (XO 1 / 2 ) e (HO 1 / 2 ) g (I)

[0051] In the above formula (I)

[0052] Each R is independently a monovalent hydrocarbon group having 1 to 30 carbon atoms, each X is independently an alkyl group having 1 to 5 carbon atoms, a>0, b≥0, c>0, d≥0, e>0, g≥0, a / (a+b+c+d) is 0.5 to 0.9, b / a is 0 to 1, c / a is 0.1 to 1, d / a is 0 to 0.25, and e / (a+b+c+d) is 0.2 to 2; wherein the organosilicon resin has an average number of silicon-bonded alkoxy groups and silicon-bonded hydroxyl groups per molecule in the range of 2 to 4, and contains less than 2% by weight of silicon-bonded hydroxyl groups based on the weight of the organosilicon resin; and wherein 50 mol% or more of the silicon atoms in the organosilicon resin are linked to aryl groups.

[0053] As shown in the background section, most research on silicone-modified polyester resins using the formula (I) structure focuses on improving the heat resistance of powder coatings, with very little research on the weather resistance of powder coatings. The inventors of this application have designed a novel silicone-modified bifunctionalized polyester resin for powder coatings using bulk polymerization of the silicone resin with the formula (I) structure. The coating film formed by curing this polyester resin with a single TGIC curing agent or a combination of TGIC and a blocked isocyanate curing agent can provide superior weather resistance, while also offering good leveling and gloss.

[0054] As described above, the silicone-modified bifunctional polyester resin according to embodiments of this application has a molecular backbone derived from the polyol component, the polyacid component, the end-capping component, and the silicone component. The molecular backbone of the polyester resin can have any suitable structural configuration. This backbone can have different structural configurations, depending on various factors such as the materials used to form the backbone, cost, and the desired end use of the polymer. Unless otherwise stated herein, the term "molecular backbone derived from the polyol component, the polyacid component, the end-capping component, and the silicone component" strictly refers to a polyester backbone formed solely from the polyol component, the polyacid component, the end-capping component, and the silicone component.

[0055] In this application, "organosilicon component" is understood to be a silicon-containing component capable of participating in the synthesis of polyester resin, wherein the fragments in the silicon-containing component capable of participating in the synthesis of polyester resin are mainly alkoxy groups bonded to silicon atoms. In an embodiment of the present invention, an organosilicon resin having the structure of formula (I) is used as the organosilicon component:

[0056] (RSiO 3 / 2 ) a (R2SiO 2 / 2 ) b (R3SiO 1 / 2 ) c (SiO 4 / 2 ) d (XO 1 / 2 ) e (HO 1 / 2 ) g (I)

[0057] In the above formula (I)

[0058] Each R is independently a monovalent hydrocarbon group having 1 to 30 carbon atoms, each X is independently an alkyl group having 1 to 5 carbon atoms, a>0, b≥0, c>0, d≥0, e>0, g≥0, a / (a+b+c+d) is 0.5 to 0.9, b / a is 0 to 1, c / a is 0.1 to 1, d / a is 0 to 0.25, and e / (a+b+c+d) is 0.2 to 2.

[0059] In formula (I), each R can be the same or different and is independently a monovalent hydrocarbon group with 1 to 30 carbon atoms, 1 to 12 carbon atoms, or 1 to 6 carbon atoms, which can be saturated or unsaturated. Suitable monovalent hydrocarbon groups of R can be alkyl groups and aromatic groups, such as aryl groups and aralkyl groups, provided that 50 mol% or more of silicon atoms in the silicone resin are attached to one or more aryl groups, for example, 52 mol% or more, 55 mol% or more, 58 mol% or more, 60 mol% or more, 62 mol% or more, 65 mol% or more, 68 mol% or more, or even 70 mol% or more in the silicone resin, and simultaneously 90 mol% or less, 88 mol% or less, 85 mol% or less, 82 mol% or less, or even 80 mol% or less of silicon atoms are attached to one or more aryl groups. Alkyl groups may include, for example, methyl, ethyl, propyl (e.g., isopropyl and / or n-propyl), butyl (e.g., isobutyl, n-butyl, tert-butyl and / or sec-butyl), pentyl (e.g., isopentyl, neopentyl and / or tert-pentyl), hexyl, heptyl, octyl, nonyl and decyl, as well as branched alkyl groups; and cycloalkyl groups, such as cyclopentyl and cyclohexyl. Preferably, the alkyl group has 1 to 6 carbon atoms or 1 to 3 carbon atoms, such as methyl, ethyl and propyl. Examples of suitable aryl groups include cyclopentadienyl, phenyl, anthraceneyl and naphthyl. Monocyclic aryl groups may have 5 to 9 carbon atoms, 6 to 7 carbon atoms, or 5 to 6 carbon atoms. Polycyclic aryl groups may have 10 to 17 carbon atoms, 10 to 14 carbon atoms, or 12 to 14 carbon atoms. A preferred aryl group is phenyl. Suitable aryl groups may include, for example, tolyl, xylyl, benzyl, phenethyl, phenylpropyl, and phenylbutyl. In formula (I), each R may be independently selected from the group consisting of alkyl groups, aryl groups, or mixtures thereof. Preferably, each R is independently selected from methyl and phenyl.

[0060] In formula (I), each X is independently an alkyl group having 1 to 5 carbon atoms, 1 to 3 carbon atoms, or 1 to 2 carbon atoms. Suitable X can be methyl, ethyl, propyl, or a combination thereof. Preferably, X is ethyl.

[0061] In equation (I), “a” can have a value of 0.5 or greater, 0.55 or greater, 0.6 or greater, 0.65 or greater, 0.7 or greater, 0.75 or greater, or even 0.8 or greater, while having a value of 0.9 or less, or 0.85 or less.

[0062] In equation (I), “b” can have a value of 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, or even zero.

[0063] In equation (I), “c” can have a value of 0.5 or less, 0.45 or less, 0.4 or less, 0.35 or less, 0.3 or less, 0.25 or less, 0.2 or less, 0.15 or less, or even 0.1 or less.

[0064] In equation (I), “e” can have values ​​of 0.2 or greater, 0.22 or greater, 0.25 or greater, 0.28 or greater, 0.3 or greater, 0.32 or greater, 0.35 or greater, 0.38 or greater, 0.4 or greater, 0.42 or greater, 0.45 or greater, and can also have values ​​of 2 or less, 1.9 or less, 1.8 or less, 1.5 or less, 1.2 or less, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less.

[0065] In equation (I), “g” can have values ​​of 0.2 or less, 0.18 or less, 0.15 or less, 0.12 or less, 0.1 or less, 0.08 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or even zero.

[0066] In equation (I), the value of (a+b+c+d) can be 1.

[0067] The silicone resin of the present invention has an average number (hereinafter referred to as "number-average molecular functionality") of alkoxy (i.e., OX) groups and hydroxyl (OH) groups per silicon molecule in the range of 2 or more, 2.1 or more, 2.2 or more, 2.3 or more, 2.4 or more, or even 2.5 or more, and simultaneously 4 or less, 3.9 or less, 3.8 or less, 3.7 or less, 3.6 or less, 3.5 or less, 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, or even 3 or less. Preferably, the average number of OH groups per silicon molecule is less than 1, less than 0.8, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, less than 0.15, less than 0.12, less than 0.1, less than 0.05, or even zero. See the relevant description of the number-average molecular functionality of the silicone resin in patent 566.

[0068] The silicone resin of the present invention optionally contains silicon-bonded hydroxyl groups (also referred to as "silanol groups"). Preferably, the silicone resin does not contain (i.e., is free of) silicon-bonded hydroxyl groups. Based on the weight of the silicone resin, the silicone resin may contain less than 2% by weight, less than 1% by weight, less than 0.7% by weight, less than 0.3% by weight, less than 0.1% by weight, or even zero silicon-bonded hydroxyl groups. The weight percentage w(OH) of silicon-bonded hydroxyl groups can be found in the relevant description of the 566' patent.

[0069] The organosilicon resin of the present invention may have a number-average molecular weight (Mn) in the following range: 700 g / mol to 2,000 g / mol, for example 700 g / mol or more, 720 g / mol or more, 750 g / mol or more, 780 g / mol or more, 800 g / mol or more, 820 g / mol or more, 850 g / mol or more, 880 g / mol or more, 900 g / mol or more, 950 g / mol or more, 1,000 g / mol or more, 1,100 g / mol or more, or even 1,200 g / mol or more, and simultaneously 2,000 g / mol or less, 1,900 g / mol or less, 1,800 g / mol or less, 1,700 g / mol or less, 1,600 g / mol or less, 1,500 g / mol or less, 1,400 g / mol or less, or even 1,300 g / mol or less. Mn can be determined using GPC analysis as described in the Examples section below.

[0070] Based on the weight of the silicone resin, the silicone resin of the present invention may contain the following amounts of silicon-bonded alkoxy groups: 4.5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 12% or more, or even 15% or more, and simultaneously 25% or less, 24% or less, 23% or less, 22% or less, 21% or less, or even 20% or less. The weight percentage w(OX) of the silicon-bonded alkoxy groups in the silicone resin can be found in the relevant description of patent 566'.

[0071] Silicone resins having the structure of formula (I) are commercially available products, such as DOWSIL 2080 from Dow, with an ethoxy content of 15% by weight.

[0072] The inventors of this application have discovered that the addition of an organosilicon resin having the structure of formula (I) can significantly reduce the glass transition temperature of a polyester resin. Considering that an excessively low glass transition temperature of the polyester resin used in powder coatings can cause agglomeration, making subsequent powder coating preparation and spraying difficult, the glass transition temperature of the polyester resin should not be lower than 40°C. Therefore, in this application, the organosilicon component is present in an amount not exceeding 37 wt% relative to the total weight of the feed used to form the polyester resin. Furthermore, the amount of organosilicon resin should not be too low, otherwise the desired effect of improving the weather resistance of the powder coating cannot be achieved. Preferably, the organosilicon component is present in an amount of 30-37 wt% relative to the total weight of the feed used to form the polyester resin. Exemplarily, the organosilicon component is present in amounts of 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, or 39 wt% relative to the total weight of the feed used to form the polyester resin, or any range consisting of any two of the above values.

[0073] The inventors of this application have also discovered that by controlling the mass percentage of the organosilicon resin having the structure of formula (I) relative to the total weight of the feed used to form the polyester resin within a specific range, for example, in the range of 35-37 wt%, and by curing the resulting organosilicon-modified bifunctionalized polyester resin together with a dual curing agent, the weather resistance of the resulting powder coating can be significantly improved, achieving a QUVB weathering time of 700 hours or higher, which was previously unforeseen.

[0074] In this application, "polyacid component" is understood to be a component capable of providing two or more carboxyl functional groups, including compounds, oligomers, or polymers having at least two carboxyl functional groups. In the field of resin synthesis, the polyacids used to synthesize conventional polyester resins are diverse, including but not limited to diacids or their anhydrides, such as phthalic acid and its anhydrides, isophthalic acid, terephthalic acid, succinic acid, adipic acid, octanoic acid, azelaic acid, sebacic acid, tetrachlorophthalic acid, tetrabromophthalic acid, maleic acid, fumaric acid, mesocarboxylic acid, citrate, dichloromaleic acid; tricarboxylic acids or their anhydrides, such as trimellitic acid; tetracarboxylic acids or their anhydrides, such as phenylmethyltetracycline anhydride; and combinations thereof, as well as other polyacids or anhydrides known to those skilled in the art to be used in the preparation of polyester resins.

[0075] The inventors of this application have surprisingly discovered that, when modifying polyester resins with organosilicon resins having the above-described structural formula (I), selecting specific types of carboxylic acids is crucial for the successful synthesis of the organosilicon-modified bifunctional polyester resin according to the present invention. In some embodiments of the present invention, the polybasic acid component of the organosilicon-modified bifunctional polyester resin includes aromatic dicarboxylic acids and their anhydrides, including but not limited to phthalic acid and its anhydrides, isophthalic acid, and terephthalic acid, preferably including isophthalic acid.

[0076] Preferably, the polybasic acid component is present in an amount of 25-35 wt% relative to the total weight of the feed used to form the polyester resin. Exemplarily, the polybasic acid component is present in an amount of 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, or 34 wt% relative to the total weight of the feed used to form the polyester resin, or any range consisting of any two of the above values.

[0077] In this application, "polyol component" is understood to be a component capable of providing two or more hydroxyl functional groups, including compounds, oligomers, or polymers having at least two hydroxyl functional groups. In the field of resin synthesis, the polyols used to synthesize conventional polyester resins are also diverse, including but not limited to diols, triols, tetraols, or alcohols having more hydroxyl functional groups. Examples of diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-methylpropanediol, 2-butyl-2-ethylpropanediol, 2-ethyl-1,3-hexanediol, 1,3-neopentylene glycol (NPG), 2,2-dimethyl-1,3-pentanediol, 1,6-hexanediol, 1,2- and 1,4-cyclohexanediol, 1,2- and 1,4-bis(hydroxymethyl)cyclohexane (1,2- and 1,4-CHDM), bis(4-hydroxycyclohexyl)methane, ether alcohols (e.g., diethylene glycol, triethylene glycol, or dipropylene glycol), or any combination thereof. Examples of triols, tetraols, and alcohols with more hydroxyl functional groups include trimethylolpropane, trimethylolethane, trimethylolhexane, glycerol, hexanetriol, pentaerythritol, mannitol, sorbitol, and combinations thereof.

[0078] The inventors of this application have discovered that when modifying polyester resin with an organosilicon resin having the structure of formula (I) above, selecting a polyol component including CHDM is important to ensure that the resulting polyester resin has an appropriate glass transition temperature. Furthermore, the inventors of this application have also discovered that when modifying polyester resin with an organosilicon resin having the structure of formula (I) above, selecting a polyol component including CHDM can significantly improve the weather resistance of the resulting powder coating. Therefore, in one embodiment of the present invention, the polyol component of the organosilicon-modified bifunctionalized polyester resin includes 2,2-dimethyl-1,3-propanediol (NPG), 1,4-cyclohexanediethanol (CHDM), and combinations thereof. Preferably, the 1,4-cyclohexanediethanol (CHDM) is present in an amount not less than 40 wt% relative to the total weight of the polyol component, and more preferably in an amount in the range of 40-45 wt%.

[0079] Considering that incorporating 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) into the polyol component would significantly reduce the weather resistance of the resulting powder coating, the polyol component of the silicone-modified bifunctional polyester resin does not contain 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD).

[0080] Preferably, the polyol component is present in an amount of 29-40 wt% relative to the total weight of the feed used to form the polyester resin. Exemplarily, the polyol component is present in an amount of 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, or 39 wt% relative to the total weight of the feed used to form the polyester resin, or any range consisting of any two of the above values.

[0081] In this application, "end-capping component" is understood to be a component that is added to the reaction system at the final stage of polyester resin synthesis to adjust the resulting polyester molecular structure, hydroxyl value, and / or acid value. In the conventional synthesis of polyester resins, the compound used as the end-capping component can be one or more of the polybasic acids or anhydrides (acid hydrolysants) defined above. However, the inventors of this application were surprised to find that when modifying polyester resins with organosilicon resins having the above-described formula (I), choosing hexahydrophthalic anhydride as the end-capping component significantly improves the weather resistance of the resulting powder coating compared to tetrahydrophthalic anhydride, which was previously unforeseen. Moreover, the inventors of this application were also surprised to find that when modifying polyester resins with organosilicon resins having the above-described formula (I), using tribasic or more polybasic carboxylic acids or their anhydrides (e.g., trimellitic anhydride) or dibasic carboxylic acids (e.g., isophthalic acid) as end-capping components results in a gelled system or an unclear and opaque reaction product, thus failing to successfully obtain organosilicon-modified polyester resins. Therefore, in one embodiment of the invention, the end-capping component of the silicone-modified bifunctional polyester resin includes hexahydrophthalic anhydride, but does not contain dicarboxylic acids, tricarboxylic acids, or more polycarboxylic acids or their anhydrides. In a particularly preferred embodiment of the invention, the end-capping component of the silicone-modified bifunctional polyester resin is hexahydrophthalic anhydride.

[0082] Preferably, the end-capping component is present in an amount of 5-7 wt% relative to the total weight of the feed used to form the polyester resin. Exemplarily, the end-capping component is present in an amount of 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, or 7 wt% relative to the total weight of the feed used to form the polyester resin, or any range consisting of any two of the above values.

[0083] In embodiments of the present invention, the silicone-modified difunctional polyester resin has a specific acid value. In this invention, the acid value of the silicone-modified difunctional polyester resin is an important parameter, affecting the leveling and gloss of the weather-resistant powder coatings formulated with it. The inventors of this application have found that excessively high or low acid values ​​of the silicone-modified difunctional polyester resin can adversely affect the leveling and gloss of the powder coatings formulated with it. Therefore, in embodiments of the present invention, the acid value of the silicone-modified difunctional polyester resin is selected in the range of 20-40 mg KOH / g, preferably in the range of 25-35 mg KOH / g. In some preferred embodiments of the present invention, the acid value of the silicone-modified difunctional polyester resin is selected in the range of 29-31 mg KOH / g.

[0084] In embodiments of the present invention, the silicone-modified bifunctional polyester resin also has a specific hydroxyl value. In this invention, the hydroxyl value of the silicone-modified bifunctional polyester resin is an important parameter that can adjust the leveling and gloss of the weather-resistant powder coatings formulated therefrom. Therefore, in embodiments of the present invention, the acid value of the silicone-modified bifunctional polyester resin is selected to be in the range of 5-15 mg KOH / g, preferably in the range of 5-10 mg KOH / g, and more preferably in the range of 8-8.5 mg KOH / g.

[0085] In some embodiments of the present invention, the silicone-modified bifunctional polyester resin may have a suitable glass transition temperature. Optionally, the Tg of the silicone-modified bifunctional polyester resin is at most 120°C, more preferably at most 100°C, even more preferably at most 90°C, most preferably at most 85°C, for example at most 80°C, for example at most 75°C, for example at most 70°C. Further optionally, the Tg of the silicone-modified bifunctional polyester resin is at least 40°C, more preferably at least 45°C. In some preferred embodiments of the present invention, the silicone-modified bifunctional polyester resin may have a glass transition temperature (Tg) in the range of 40-60°C, preferably in the range of 40-50°C. As described above, in the present invention, the glass transition temperature (Tg) of the hydroxy-carboxyl bifunctional polyester is the measured Tg of the resin. According to the present invention, the glass transition temperature of polyester is measured by differential scanning calorimetry (DSC) according to ISO 11357, ISO 16805 and ASTM E1356 at a heating rate of 5 °C / min.

[0086] In some embodiments of the present invention, the silicone-modified difunctional polyester resin may have a wide range of viscosity or melt viscosity. Optionally, the viscosity of the silicone-modified difunctional polyester resin at 160°C is at most 20 Pa·s, more preferably at most 15 Pa·s, even more preferably at most 12.5 Pa·s, more preferably at most 8 Pa·s, even more preferably at most 7 Pa·s, and most preferably at most 5 Pa·s. Preferably, the viscosity of the silicone-modified difunctional polyester resin at 160°C is at least 3 Pa·s, more preferably at least 4 Pa·s. In some preferred embodiments of the present invention, the silicone-modified difunctional polyester resin may have a melt viscosity of 3-7 Pa·s, preferably 3.5-5 Pa·s. As mentioned above, the melt viscosity is measured at 160°C on a Brookfield CAP 2000+H Viscometer.

[0087] The organosilicon-modified bifunctional polyester resin according to the present invention can be prepared by esterification or transesterification using a polycondensation process for preparing conventional polyester resins, optionally in the presence of an esterification catalyst (e.g., dibutyltin oxide, butylstannic acid, or tetrabutyl titanate). Typically, the organosilicon-modified bifunctional polyester resin can be obtained by a three-step process comprising: mixing an organosilicon component and a polyol component and reacting them; next, adding a polyacid component and reacting it to form a hydroxyl-functionalized polyester resin at the end of the first step; and next, further reacting the hydroxyl-functionalized polyester resin with a selected end-capping component to obtain a polyester resin.

[0088] The synthesized organosilicon-modified bifunctional polyester resin is suitable for formulating powder coating compositions and can significantly improve the weather resistance of the resulting powder coating.

[0089] Therefore, according to a second aspect of the present invention, a weather-resistant powder coating composition is provided, comprising at least one organosilicon-modified bifunctional polyester resin according to the first aspect of the present application, a curing agent component, and additional additives.

[0090] In embodiments according to this application, the weather-resistant powder coating composition comprises at least one organosilicon-modified bifunctional polyester resin according to the first aspect of this application.

[0091] In some embodiments of the invention, the at least one organosilicon-modified bifunctionalized polyester resin is present in an amount of 40 wt% to 95 wt% relative to the total weight of the weather-resistant powder coating composition.

[0092] In an embodiment of the present invention, the weather-resistant powder coating composition comprises at least one curing agent having a specific content of carboxyl reactive functional groups (including but not limited to epoxy functional groups and isocyanate functional groups), thereby being combined with the above-mentioned organosilicon-modified bifunctionalized polyester resin.

[0093] Therefore, in embodiments of the invention, when the at least one curing agent is a curing agent with epoxy functional groups, such as triglycidyl isocyanurate (TGIC) or an epoxy resin based on triglycidyl isocyanurate (TGIC), the at least one curing agent has an epoxy equivalent of no more than 200 g / eq. Considering the source of the curing agent, the epoxy equivalent of the at least one curing agent is at least 50 g / eq. In some embodiments of the invention, the epoxy equivalent of the at least one curing agent is in the range of 50 g / eq to 180 g / eq, preferably in the range of 80 g / eq to 150 g / eq. The epoxy equivalent is determined according to GB4612-84. Alternatively, in an embodiment of the invention, when the at least one curing agent is a curing agent with isocyanate functional groups, such as a blocked isocyanate, the content of the hydroxyl reactive functional group isocyanate group (NCO) of the blocked isocyanate is no more than 20% but at least 10%, preferably, the NCO content of the at least one curing agent is in the range of 12% to 18%.

[0094] In some embodiments of the invention, the curing agent may comprise triglycidyl isocyanurate (TGIC) or a combination of triglycidyl isocyanurate (TGIC) and a blocked isocyanate. The inventors of this application have surprisingly discovered that using a combination of triglycidyl isocyanurate (TGIC) and a blocked isocyanate as a curing agent can significantly improve the weather resistance of the resulting powder coating. Therefore, in a preferred embodiment of the invention, the curing agent is a combination of triglycidyl isocyanurate (TGIC) and a blocked isocyanate. These curing agents may be homemade or commercially available, such as those from Huntsman Polyurethanes (China) Co., Ltd. PT 810 (epoxy equivalent of 100-108 g / eq), or Crelan VP LS2256 (NCO content of approximately 15%) purchased from Covestro (Shanghai) Investment Co., Ltd.

[0095] The amount of curing agent can be adjusted according to factors such as the acid value and hydroxyl value of the polyester resin used, the epoxy equivalent and isocyanate content of the curing agent, and the required gelation time. Based on the total amount of the coating composition, the amount of curing agent is 2-10% by weight, preferably 3-8% by weight, more preferably 4-7% by weight, and even more preferably 5-7% by weight.

[0096] In embodiments of the invention, the weather-resistant powder coating composition further comprises any additional additives suitable for the powder coating composition. Examples of additional additives suitable for the powder coating composition may include one or more of organic / inorganic pigments and fillers, organic light stabilizers, free radical blockers, dispersants, leveling agents, wetting agents, defoamers, adhesion promoters, inhibitors, and catalysts, preferably present in an amount from 1 wt% to 58 wt% relative to the total weight of the weather-resistant powder coating composition.

[0097] In some embodiments of the invention, the weather-resistant powder coating composition comprises inorganic pigments and fillers. As an example, the weather-resistant powder coating composition may comprise rutile titanium dioxide (TiO2) pigment, such as Ti-Pure commercially available from Chemours. TM (Chuntai TM R-960; precipitated barium sulfate (1250 mesh), such as precipitated barium sulfate commercially available from Shanghai Yuejiang Titanium Dioxide Chemical Products Co., Ltd. In some embodiments of the invention, the weather-resistant powder coating composition includes benzoin as an antifoaming agent to eliminate air bubbles in the molten powder coating. In some embodiments of the invention, the weather-resistant powder coating composition includes a leveling agent to improve the leveling properties of the coating composition. Examples of leveling agents include, but are not limited to, leveling agent GLP503 / 588 from Ningbo Nanhai Company, leveling agent Modaflow Powder Ⅲ / 2000 from Solutia, leveling agent PV88 / P67 from Worlee-chemie, and leveling agent Resiflow PV5 from EHWorlèe & Co. (GmbH & Co.) KG. Those skilled in the art can determine the type and amount of additives based on the desired product properties (e.g., coating color, hardness, roughness, etc.).

[0098] On the other hand, the present invention also relates to a method for preparing the weather-resistant powder coating composition of the present invention. Misev described the preparation of the weather-resistant powder coating composition in "Powder Coatings, Chemistry and Technology" (pp. 224-300; 1991, John Wiley), which is incorporated herein by reference.

[0099] A common method for preparing weather-resistant powder coating compositions is as follows: the weighed components are mixed in a premixer, the resulting premix is ​​heated (e.g. in a kneader, preferably in an extruder, to obtain an extrudate), the resulting extrudate is cooled until it solidifies, and then it is crushed into small particles or flakes, further ground to reduce the particle size, and then properly sorted to obtain a weather-resistant powder coating composition with suitable particle size.

[0100] The obtained powder particles are sprayed onto a suitable substrate using an electrostatic spray gun and then cured in an oven at a specific temperature. After curing, a powder coating is obtained. The powder coating can be a primer, topcoat, or intermediate coating.

[0101] When heating the powder coating composition to cure it, the heating of the powder coating composition can be carried out at a certain temperature and continued for a suitable time to cure the powder coating composition of the present invention.

[0102] Heating of the powder coating composition can be carried out using conventional methods, such as using a convection oven and / or (N)IR lamp, and / or using infrared laser and / or microwave equipment.

[0103] Preferably, the curing time of the weather-resistant powder coating composition according to the invention is at most 60 minutes, more preferably at most 45 minutes, even more preferably at most 30 minutes, most preferably at most 20 minutes, and particularly at most 15 minutes.

[0104] Preferably, the weather-resistant powder coating composition according to the invention is cured at a temperature in the range of 220-250°C for a period of 5-30 minutes.

[0105] Therefore, the present invention also provides an article comprising a substrate partially or wholly coated with the powder coating composition according to the present invention. Those skilled in the art will select and determine suitable materials as the substrate based on actual needs.

[0106] The substrate may be, for example, glass, ceramic, fiber cement board, or metal (e.g., aluminum, copper, or steel).

[0107] This invention also relates to powder coatings as described herein in powder coating, in-mold powder coating, 3D printing, automotive applications (automotive parts, agricultural machinery, composite structures, ceramic structures, etc.), marine applications (ships, vessels), aerospace applications (aircraft, helicopters, composite structures, ceramic structures, etc.), medical applications (artificial joints, nets, woven or nonwoven sheets, strips, ribbons, cords, cables, tubular products such as ligament substitutes, composite structures, ceramic structures, etc.), protective applications (bulletproof equipment, bulletproof vests, bulletproof vests, bulletproof helmets, bulletproof vehicles, composite structures, ceramic structures, etc.), and sports / recreation applications (fencing, skating, skateboarding, skis, slings in sports parachutes, paragliders, kites, kite sports). Applications include kite strings, mountaineering equipment, composite structures, ceramic structures, etc., architectural applications (windows, doors, (false) walls, cables, etc.), bottle applications, household applications (home appliances, white goods, furniture, computer casings, etc.), mechanical applications (can and bottle handling machine parts, moving parts of textile machines, bearings, gears, composite structures, ceramic structures, computer casings, etc.), can applications, roll applications, energy applications (for example, wind, tidal, or solar generators), textile applications (for example, fabrics, which can be very broad, from impregnation-technical textiles to, for example, all composite materials, both as coatings and as adhesives for composite materials), and electrical applications (for example, in cabinets for wires or distribution panels).

[0108] Test methods

[0109] Unless otherwise indicated, the following test methods are used in the following embodiments.

[0110] gloss

[0111] This test, used to measure the gloss of a coating formed from the powder coating composition according to the present invention, is determined according to ASTM D523.

[0112] Leveling

[0113] This test measures the leveling properties of coatings formed from powder coating compositions according to the present invention, typically expressed as the PCI leveling index. It is determined by comparing the waviness of a sample, measured using the reflection of a light source, with the smoothness of a series of 60-micron thick powder coating visual smoothness standard panels (ACT Test Panels Inc., APR22163(A) Batch: 50708816). Generally, a higher PCI leveling index indicates better leveling properties of the powder coating, where a PCI leveling index greater than or equal to 4 is considered acceptable, and vice versa. The PCI value is determined according to PCAII-002V009EN.

[0114] Weather resistance (QUVB)

[0115] This test is used to measure the weather resistance of the cured coating. Artificial acceleration is adopted to determine the weather resistance of the coating according to GB / T 1766-2008. Generally, the longer the weathering time, the higher the weather resistance of the powder coating. The powder coating with a weathering time greater than or equal to 500 hours is regarded as qualified, otherwise it is unqualified. Specifically, the weather resistance is determined as follows: After measuring the gloss and color difference of the prepared sample panel, it is placed in an accelerated aging chamber, and the parameters of the aging chamber are set as follows: 4 hours in the UV state, the temperature is set at 50 °C, 4 hours in the condensation state, one cycle every 8 hours, and the power is 0.75 W / m 2 / nm. Measure the gloss and color difference of the sample panel every other day when the machine is in the UV state. When the light retention rate < 50% or when the value of the color difference ΔE ≥ 3, take out the sample panel and calculate the weathering time.

[0116] Example

[0117] Next, the content disclosed in the present invention will be described more specifically through examples. These examples are only for illustrative purposes and cannot be construed as limiting the protection scope of the present invention, because various modifications and changes within the scope of the content disclosed in the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available and can be used directly without further treatment.

[0118] Material

[0119] The materials used are listed in Table 1 below.

[0120] Table 1: Materials Used and Related Information

[0121]

[0122] Organosilicon-modified bifunctional polyester resins (resins A, B, and C, and comparative resin AG)

[0123] Under an inert atmosphere, the polyol, catalyst, and organosilicon intermediates as shown in Table 1 are added to the reactor. While stirring, the material is heated, ensuring the column top temperature does not exceed 78°C. When the reaction temperature in the reactor reaches 180-190°C, it is maintained for 3-4 hours. Once the column top temperature drops below 40°C and the recovered distillate is approximately 15% of the total input organosilicon intermediate mass, isophthalic acid is added, and the material is slowly heated to 240°C. During this period, the column top temperature is controlled to not exceed 105°C. Samples are taken when the material becomes clear and transparent and the column top temperature is below 40°C. When the acid value is below 10 mg KOH / g and the hydroxyl value is between 50-60 mg KOH / g, the material temperature is lowered to 200°C. When the material cools to 200°C, a vacuum is slowly applied, maintaining a vacuum level below 100 mbar, and samples are taken every fifteen minutes. Vacuuming is stopped when the hydroxyl value is between 30-40 mg KOH / g. Add the amounts of the final agent shown in Table 1 to the reactants, and stir until homogeneous. Take samples every 15 minutes to test the hydroxyl value of the samples. When the hydroxyl value of the system is below 10 mg KOH / g, cool the reactants to 190°C, add the formulated amounts of 2,6-di-tert-butyl-4-methylphenol and triphenylphosphine bromide, stir for 30 minutes, and then discharge the resin to obtain the polyester resin AC of each embodiment and the polyester resin AG of each comparative example.

[0124] According to the testing standards described above, the acid value, hydroxyl value, viscosity, and Tg of the polyester resins obtained in each example and comparative example were determined. The results are summarized in Table 1.

[0125]

[0126] By analyzing the results in Table 1 above, the following conclusions can be drawn:

[0127] 1) By comparing the results of comparative polyester A with those of examples A and B, it is evident that the addition of silicone intermediates significantly lowers the glass transition temperature of the polyester resin. When the amount of silicone intermediates exceeds 37% of the total formulation, the resulting comparative polyesters B and C are unsuitable for powder coating formulation due to their excessively low glass transition temperatures. Generally, the glass transition temperature of polyester resins suitable for powder coatings should not be lower than 40°C.

[0128] 2) By comparing the results of polyester E and example polyester B, it can be seen that using trimellitic anhydride as the end-capping component causes the sample to gel, making it impossible to obtain a polyester resin suitable for powder coatings.

[0129] C) By comparing the results of polyester G and example polyester B, it can be seen that using isophthalic acid as the end-capping component results in samples that are not clear and transparent, and polyester resins suitable for powder coatings cannot be obtained.

[0130] Powder Coating Composition

[0131] According to the dosages shown in Table 2, various polyester resins, curing agents, leveling agents, benzoin, and titanium dioxide were placed together in a plastic sample bag and shaken well. The extruder temperature was set to 120℃ and the speed to 400 rpm. The mixed sample was poured into the extruder at a uniform speed. After passing through the extruder, a molten and mixed sample was obtained. The sample was then placed in a crusher for pulverization. The pulverized sample was then sieved through a 90μm sieve to obtain a sample with a particle size <90μm.

[0132] Then, the powder coating compositions obtained in the above embodiments and comparative examples were sprayed onto the surface of an aluminum substrate using an electrostatic spray gun. The coatings were then cured in an oven at 220°C for 15 minutes. After the required curing time was reached, the samples were removed, yielding a powder coating with a thickness of 60-80 μm. These powder coatings were tested using the experiments described in the above testing section, and the results are summarized in Table 2.

[0133]

[0134] By analyzing the results in Table 2 above, the following conclusions can be drawn:

[0135] 1) By comparing the results of Comparative Examples 2 and 4 and Examples 2 and 4 involving Comparative Polyester D and Example Polyester B, it is evident that when modifying polyester resins with silicone resins having the structure of formula (I) above, selecting a polyol component including CHDM is important to ensure that the powder coating formed using the resulting polyester resin achieves a weather resistance of at least 500 hours. When 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) is incorporated into the polyol component, the powder coating of Comparative Example 2 formed with the resulting polyester resin exhibits significantly reduced weather resistance compared to the powder coating of Example 2, for example, QUVB decreased by 183 hours.

[0136] 2) By comparing the results of Comparative Examples 3 and 5 and Examples 2 and 4 involving Comparative Polyester F and Example Polyester B, it is evident that when modifying polyester resins with silicone resins having the structure of formula (I) above, selecting end-capping components including hexahydrophthalic anhydride is important to ensure that the powder coating formed using the resulting polyester resin achieves a weather resistance of at least 500 hours. When tetrahydrophthalic anhydride is used as the end-capping component, the powder coating of Comparative Example 3 formed with the resulting polyester resin exhibits significantly reduced weather resistance compared to the powder coating of Example 2, for example, QUVB decreased by 156 hours.

[0137] 3) By comparing the results of Examples 1-6, it can be seen that by controlling the mass percentage of the silicone resin having the structure of Formula (I) relative to the total weight of the feed used to form the polyester resin within a specific range, such as 35%-37 wt%, and curing the resulting silicone-modified bifunctionalized polyester resin together with a dual curing agent, the weather resistance of the resulting powder coating can be significantly improved by up to 17%, achieving a QUVB weather resistance time of 700 hours or higher, which was difficult to anticipate before this application.

[0138] Although the present invention has been described with reference to numerous embodiments and examples, those skilled in the art will recognize that other embodiments can be designed based on the disclosure of the present invention without departing from the scope and spirit of the invention.

Claims

1. A silicone-modified bifunctional polyester resin, wherein the silicone-modified bifunctional polyester resin has a molecular backbone derived from a polyol component, a polyacid component, a capping component, and a silicone component, wherein, The organosilicon-modified bifunctional polyester resin has an acid value in the range of 20 to 40 mg KOH / g and a hydroxyl value in the range of 5 to 15 mg KOH / g. The organosilicon component is an organosilicon resin having the structural formula (I): (RSiO 3 / 2 ) a (R2SiO 2 / 2 ) b (R3SiO 1 / 2 ) c (SiO 4 / 2 ) d (XO 1 / 2 ) e (HO 1 / 2 ) g (I) In the above formula (I) Each R is independently a monovalent hydrocarbon group having 1 to 30 carbon atoms, each X is independently an alkyl group having 1 to 5 carbon atoms, a>0, b≥0, c>0, d≥0, e>0, g≥0, a / (a+b+c+d) is 0.5 to 0.9, b / a is 0 to 1, c / a is 0.1 to 1, d / a is 0 to 0.25, and e / (a+b+c+d) is 0.2 to 2; wherein the organosilicon resin has an average number of silicon-bonded alkoxy groups and silicon-bonded hydroxyl groups per molecule in the range of 2 to 4, and contains less than 2% by weight of silicon-bonded hydroxyl groups based on the weight of the organosilicon resin; and wherein 50 mol% or more of the silicon atoms in the organosilicon resin are linked to aryl groups.

2. The organosilicon-modified bifunctional polyester resin as described in claim 1, wherein, The organosilicon-modified bifunctional polyester resin has a glass transition temperature of at least 40°C, preferably 40-60°C, which is determined using ASTM-2076.

3. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The silicone resin has a number-average molecular weight in the range of 700 g / mol to 2,000 g / mol.

4. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The silicone resin contains 4.5% to 25% by weight of silicon-bonded alkoxy groups.

5. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The organosilicon component is present in an amount not exceeding 37 wt%, preferably in an amount of 30 wt% to 37 wt%, and more preferably in an amount of 35 wt% to 37 wt%, relative to the total amount of feed used to form the organosilicon-modified bifunctionalized polyester resin.

6. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The organosilicon-modified bifunctional polyester resin contains a polyacid component including aromatic dicarboxylic acids and their anhydrides.

7. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The polyol component of the organosilicon-modified bifunctional polyester resin does not contain 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD).

8. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The polyol component of the organosilicon-modified bifunctional polyester resin includes 2,2-dimethyl-1,3-propanediol (NPG), 1,4-cyclohexanediethanol (CHDM), and combinations thereof. Preferably, the 1,4-cyclohexanediethanol (CHDM) is present in an amount of not less than 40 wt% relative to the total weight of the polyol component, and more preferably in an amount in the range of 40-45 wt%.

9. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The end-capping component of the organosilicon-modified bifunctional polyester resin includes hexahydrophthalic anhydride.

10. The organosilicon-modified bifunctional polyester resin as described in claim 1 or 2, wherein, The end-capping components of the organosilicon-modified bifunctional polyester resin do not include isophthalic acid, tetrahydrophthalic anhydride, and trimellitic anhydride.

11. A weather-resistant powder coating composition comprising at least one silicone-modified bifunctional polyester resin as described in any one of claims 1 to 10, a curing agent component, and additional additives.

12. The weather-resistant powder coating composition of claim 11, wherein, The at least one organosilicon-modified bifunctional polyester resin is present in an amount of 40 wt% to 95 wt% relative to the total weight of the weather-resistant powder coating composition.

13. The weather-resistant powder coating composition according to any one of claims 11 or 12, wherein, The curing agent component includes either triglycidyl isocyanurate (TGIC) alone or a combination of TGIC and a blocked isocyanate.

14. The weather-resistant powder coating composition of claim 13, wherein, The epoxy equivalent of the triglycidyl isocyanate (TGIC) is no more than 200 g / eq and at least 50 g / eq. Preferably, the epoxy equivalent of the epoxy resin based on triglycidyl isocyanate (TGIC) is in the range of 50 g / eq to 180 g / eq, more preferably in the range of 80 g / eq to 150 g / eq. Alternatively, the content of the hydroxyl reactive functional group isocyanate group (NCO) of the blocked isocyanate is no more than 20% but at least 10%. Preferably, the NCO content of the at least one curing agent is in the range of 12% to 18%.

15. The weather-resistant powder coating composition according to any one of claims 11 to 12, wherein, The curing agent component is present in an amount of 2 wt% to 10 wt% relative to the total weight of the weather-resistant powder coating composition.

16. The weather-resistant powder coating composition according to any one of claims 11 to 12, wherein, The additional additives are selected from one or more of organic / inorganic pigments and fillers, organic light stabilizers, free radical blockers, dispersants, leveling agents, wetting agents, defoamers, adhesion promoters, inhibitors and catalysts, and are preferably present in an amount of 1 wt% to 58 wt% relative to the total weight of the weather-resistant powder coating composition.

17. The weather-resistant powder coating composition according to any one of claims 11 to 12, wherein, The weather-resistant powder coating composition can be cured at a temperature of 220-250°C.

18. The weather-resistant powder coating composition according to any one of claims 11 to 17, wherein, The powder coating formed from the weather-resistant powder coating composition exhibits a weathering time of 500 hours or more, preferably 700 hours or more, in the QUV-B aging test, the weathering time being determined according to GB / T 1766-2008.

19. The weather-resistant powder coating composition according to any one of claims 11 to 18, wherein, The powder coating formed from the weather-resistant powder coating composition has a gloss level of over 90% at 60° and a PCI leveling index of grade 4 or higher, which is determined according to PCAII-002V0009EN.

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