A matting agent for powder coatings and its application, matting powder coatings and their applications

Abstract

This invention provides a matting agent for powder coatings and its application, as well as matting powder coatings and their applications, belonging to the field of coating technology. The matting agent for powder coatings of this invention comprises a hydroxyl-containing functional group component and a carboxyl-containing functional group component. The matting agent can achieve a matting effect of <30% gloss (60°) in HAA system powder coatings. The matting agent has low resin selectivity and can achieve excellent matting effects when used with different carboxyl-based film-forming resins. The matting effect of the matting agent is stable, and the prepared matting powder coating can achieve a stable matting effect under different curing conditions.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, and in particular to a matting agent for powder coatings and its application, and matting powder coatings and their applications. Background Technology

[0002] HAA system powder coatings refer to powder coating systems that use carboxylated polyesters as the main film-forming substance and a class of hydroxyalkylamide compounds as curing agents. These hydroxyalkylamide compounds can be synthesized from ester compounds and corresponding alcohol-amine compounds. The ester compounds include dimethyl adipate, diethyl adipate, methyl benzoate, etc., and the alcohol-amine compounds include diethanolamine, diisopropanolamine, etc. The synthesis process can be carried out using solvents or under solvent-free conditions. Invention patents such as US5101073, EP0473380B1, DE19823925, CN1160311C, CN1315785C, US5101073A, US6235933B1, US20040260123A1, and CN1042739C all disclose the synthesis of these hydroxyalkylamide compounds. Powder coatings prepared using the aforementioned hydroxyalkylamide compounds as curing agents are mostly high-gloss powder coatings, such as the invention patent US6767479B1. Invention patent US6767479B1 discloses a hydroxyalkylamide curing agent mixture and a powder coating prepared therefrom. The composition of the hydroxyalkylamide curing agent mixture includes a tetrafunctional hydroxyalkylamide compound and a difunctional hydroxyalkylamide compound, and the resulting powder coating has a gloss >90% (60°). Therefore, it can be seen that powder coatings prepared using a combination of difunctional and tetrafunctional hydroxyalkylamide compounds as curing agents are high-gloss powder coatings.

[0003] HAA-based powder coatings can easily achieve high gloss, but in some coating fields that require low-gloss powder coatings, such as aluminum profiles, automotive parts, agricultural machinery, metal fences, hardware, and lighting fixtures, current technology cannot adjust the esterification reaction rate between carboxylated polyester resin and hydroxyalkylamide curing agent. Therefore, HAA-based powder coatings are difficult to meet the requirements for low gloss.

[0004] Acrylic resin is a commonly used raw material for preparing matte powder coatings. Most acrylic resins used to prepare matte powder coatings are carboxylated acrylic resins and glycidyl ester acrylic resins (GMA resins). Hydroxyl functional polyacrylic resins have not been found to be used to prepare matte powder coatings, especially HAA system powder coatings with hydroxyalkylamide compounds as film-forming resins.

[0005] Invention patents CN113621263A and CN114621617A both utilize carboxylated acrylic acid and epoxy-based acrylic resins (GMA resins) to prepare matting agents and achieve the matting effect of HAA system powder coatings. The matting agents are based on acrylic resins, polybasic acids, accelerators, synthetic waxes, etc., and the acrylic resins include epoxy-based acrylic resins and carboxylated acrylic resins. The HAA system matting schemes disclosed in invention patents CN113621263A and CN114621617A can stably achieve a matting effect of <10% HAA system powder coatings, and no hydroxyl functional components are observed, particularly the application of hydroxyl acrylic resins in matting powder coatings, especially HAA system matting powder coatings.

[0006] Invention patent CN101880490B discloses a matting curing agent, a powder coating containing the matting curing agent, and their uses. The matting curing agent is a polymer component polymerized from carboxyl monomers and basic monomers. The matting curing agent is a carboxyl acrylic resin with an acid value ≥118mgKOH / g. The carboxyl monomer is selected from one or more of itaconic acid monobutyl ester, itaconic acid, acrylic acid, methacrylic acid, and butylated acrylate. The matting curing agent can achieve a medium gloss (20-30%) and relatively smooth coating film in the HAA system.

[0007] US Patent 10517064 discloses a semi-gloss powder coating composition comprising a carboxyl polyester, a glycidyl acrylate copolymer (GMA resin), and a curing agent having a reaction capability with the carboxyl groups of the polyester. This composition can be used to achieve a semi-gloss matte effect in HAA (hybrid allergen-based) powder coatings.

[0008] The carboxyl groups in polybasic acids can also undergo crosslinking reactions with the hydroxyalkylamide curing agents in HAA system powder coatings. Therefore, theoretically, polybasic acids can be used to participate in the chemical crosslinking process of hydroxyalkylamide compounds. As seen in the aforementioned invention patents CN113621263A, CN114621617A, and CN103694766A, polybasic acid (anhydride) compounds are used to prepare matte HAA system powder coatings. The polybasic acids (anhydrides) include pyromellitic dianhydride, long-chain dicarboxylic acids, pyromellitic tricarboxylic acid, etc. In all these polybasic acid (anhydride) matting schemes, epoxy-based acrylic resins are used to react with the aforementioned polybasic acids (anhydrides) to achieve the matting effect. That is, in the polybasic acid (anhydride) matting schemes, the HAA system matte powder coatings undergo crosslinking reactions with different reaction rates during the crosslinking process, thereby achieving the matte effect of the HAA system powder coating. The crosslinking reactions in the HAA system matte powder coatings include two completely different reaction mechanisms: the reaction between carboxyl groups and epoxy groups, and the reaction between carboxyl groups and hydroxyalkylamides.

[0009] Invention patent CN100491445C discloses an ester amide condensation product as a matting agent for powder coatings. This ester amide condensation product is synthesized from a tetrafunctional β-hydroxyalkylamide compound and a polybasic acid (anhydride) compound to form a substance with a special structure, which can achieve a matting effect in powder coatings. When the matting powder coating is a polyester-Primid powder coating, the achievable gloss is only 52% (60°).

[0010] Currently, it is difficult to achieve the desired matting effect for HAA-based powder coatings using the aforementioned matting methods. Therefore, it is essential to develop a matting solution for HAA systems that offers stable matting effects, adjustable gloss, and low resin selectivity. Summary of the Invention

[0011] The purpose of this invention is to provide a matting agent for powder coatings and its application, as well as matting powder coatings and their applications. The matting agent can achieve a gloss effect of 5-30% in HAA system powder coatings, and the matting effect is stable with low resin selectivity.

[0012] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0013] This invention provides a matting agent for powder coatings, comprising the following components in weight percentage:

[0014] The component containing hydroxyl functional groups is 50-86%, and the component containing carboxyl functional groups is 14-50%.

[0015] The hydroxyl-functionalized component comprises 30-62% hydroxyl-functionalized compound and 38-70% hydroxyl-functionalized polyacrylic acid resin;

[0016] The hydroxyl functional compound is a hydroxyalkylamide compound with a functionality of ≥2;

[0017] The carboxyl functional group component has a carboxyl functionality greater than 2; the carboxyl functional group component includes one or more of carboxyl functional compounds, carboxylates, and carboxyl functional polyacrylic resins.

[0018] Preferably, the hydroxyl-functionalized compound has the structure described in Formula 1:

[0019]

[0020] In Formula 1, R is an alkyl, aryl, or olefinic group containing 1 to 60 carbon atoms; R1 is hydrogen or an alkyl group containing 1 to 5 carbon atoms; and R2 is hydrogen or an alkyl group containing 1 to 5 carbon atoms.

[0021] Alternatively, R may have the structure shown in Equation 2:

[0022]

[0023] In Formula 2, B is an alkyl, aryl, or olefinic group containing 1 to 60 carbon atoms, R3 is hydrogen or an alkyl group containing 1 to 5 carbon atoms, R4 is hydrogen, an alkyl group containing 1 to 5 carbon atoms, or a hydroxyalkyl group containing 1 to 5 carbon atoms, and X = 0 to 2 and X is an integer.

[0024] Preferably, the hydroxyl-functional polyacrylic acid resin has a weight-average molecular weight of 4,000 to 1,500,000, a hydroxyl value of 10 to 150 mg KOH / g, and a glass transition temperature of 40 to 145°C.

[0025] Preferably, the carboxyl functional compound includes one or more of pyromellitic acid, ethylenediaminetetraacetic acid, trimellitic acid, butanetetracarboxylic acid, triamic acid, cyclohexanetetracarboxylic acid, pyromellitic dianhydride, and trimellitic anhydride; the carboxylate includes pyromellitic acid-2-phenylimidazoline salt or trimellitic acid imidazoline salt; the carboxyl functional group-containing polyacrylic acid resin has a weight-average molecular weight of 2000-8000, an acid value range of 150-300 mgKOH / g, a glass transition temperature of 40-110℃, and a softening point of 80-150℃.

[0026] This invention provides the application of the matting agent for powder coatings described in the above technical solution in powder coatings.

[0027] This invention provides a matte powder coating, the raw materials of which include: a carboxyl-containing polyester resin, a hydroxyalkylamide curing agent, a matting agent, and additives; the mass of the carboxyl-containing polyester resin is 40-60% of the total mass of the matte powder coating; the mass of the matting agent is 4-10% of the total mass of the matte powder coating; the mass ratio of the hydroxyalkylamide curing agent to the carboxyl-containing polyester resin is 4-6:94-96; and the matting agent is the matting agent for powder coatings described in the above technical solution.

[0028] Preferably, the acid value of the carboxyl-containing polyester resin is in the range of 10-100 mg KOH / g, and the glass transition temperature (Tg) is 40-80℃.

[0029] Preferably, the carboxyl-containing polyester resin is formed by the condensation of a diacid and a polyol; the diacid includes terephthalic acid, isophthalic acid, 1,4-cyclohexyldicarboxylic acid, adipic acid, maleic acid, or succinic acid; the polyol includes ethylene glycol, diethylene glycol, propylene glycol, hexanediol, neopentyl glycol, cyclohexyldiethanol, or trimethylolpropane.

[0030] Preferably, the hydroxyalkylamide curing agent has the structure shown in Formula 3:

[0031]

[0032] In Formula 3, A is hydrogen, an alkyl, aryl or olefinic group containing 1 to 60 carbon atoms, R5 is hydrogen, an alkyl group containing 1 to 5 carbon atoms or a hydroxyalkyl group containing 1 to 5 carbon atoms, R6 is hydrogen or methyl, n' is an integer from 0 to 2, and n is an integer from 1 to 10.

[0033] This invention provides the application of the matte powder coating described above in the field of low-gloss powder coating, wherein the low gloss has a gloss level of 5-30%.

[0034] This invention provides a matting agent for powder coatings, comprising a hydroxyl-containing functional group component and a carboxyl-containing functional group component. Unrestricted by any reaction theory, the hydroxyl-containing and carboxyl-containing functional group components in the matting agent of this invention undergo an esterification reaction. The reaction rate of this esterification reaction differs from the reaction rate of the carboxyl polyester resin and hydroxyalkyl amide compound in HAA system powder coatings. This difference in reaction rate is the main reason why the matting agent of this invention can achieve the excellent matting effect of HAA system powder coatings. The matting agent disclosed in this invention does not involve crosslinking reactions between epoxy and carboxyl groups, unlike HAA system matting schemes that use epoxy-based acrylic resins (GMA resins). Furthermore, the matting agent of this invention does not require the synthesis of new special structural substances to achieve the matting effect of the HAA system.

[0035] The matting agent described in this invention has the following beneficial effects:

[0036] 1. The matting agent can achieve a matting effect of <30% gloss (60°) in HAA system powder coatings; specifically, the gloss of HAA system powder coatings can be adjusted by adjusting the amount of matting agent added to achieve a gloss adjustment of 5-30%;

[0037] 2. The matting agent resin has low selectivity and can achieve a good matting effect when used in combination with different carboxyl film-forming resins;

[0038] 3. The matting agent has a stable matting effect, and the prepared matting powder coating can achieve a stable matting effect under different curing conditions;

[0039] 4. The matting agent can be used to prepare HAA system matting powder coatings in a one-step extrusion process, which is simple to operate. Attached Figure Description

[0040] Figure 1 A graph showing the relationship between the amount of matting agent III-5 added and the gloss of powder coatings;

[0041] Figure 2 The images show the matting effect of the powder coating prepared in Example 27 under different curing conditions. Detailed Implementation

[0042] This invention provides a matting agent for powder coatings, comprising the following components in weight percentage:

[0043] The component containing hydroxyl functional groups is 50-86%, and the component containing carboxyl functional groups is 14-50%.

[0044] The hydroxyl-functionalized component comprises 30-62% hydroxyl-functionalized compound and 38-70% hydroxyl-functionalized polyacrylic acid resin;

[0045] The hydroxyl functional compound is a hydroxyalkylamide compound with a functionality of ≥2;

[0046] The carboxyl functional group component has a carboxyl functionality greater than 2; the carboxyl functional group component includes one or more of carboxyl functional compounds, carboxylates, and carboxyl functional polyacrylic resins.

[0047] In this invention, the mass percentage of the hydroxyl-functionalized component is 50-86%, preferably 70-76%; the hydroxyl-functionalized component comprises 30-62% of a hydroxyl-functionalized compound and 38-70% of a hydroxyl-functionalized polyacrylic acid resin; the mass percentage of the hydroxyl-functionalized compound is preferably 38.9-40.7%, more preferably 39.1-40.0%, and the mass percentage of the hydroxyl-functionalized polyacrylic acid resin is preferably 38.9-41.2%, more preferably 40.0-40.7%.

[0048] In this invention, the hydroxyl-functionalized compound preferably has the structure described in Formula 1:

[0049]

[0050] In Formula 1, R is an alkyl, aryl, or olefinic group containing 1 to 60 carbon atoms; R1 is hydrogen or an alkyl group containing 1 to 5 carbon atoms; and R2 is hydrogen or an alkyl group containing 1 to 5 carbon atoms.

[0051] Alternatively, R may have the structure shown in Equation 2:

[0052]

[0053] In Formula 2, B is an alkyl, aryl, or olefinic group containing 1 to 60 carbon atoms, R3 is hydrogen or an alkyl group containing 1 to 5 carbon atoms, R4 is hydrogen, an alkyl group containing 1 to 5 carbon atoms, or a hydroxyalkyl group containing 1 to 5 carbon atoms, and X = 0 to 2 and X is an integer.

[0054] In this invention, R is more preferably aryl, and even more preferably substituted or unsubstituted phenyl; R1 and R2 are preferably the same or different, and more preferably, R1 and R2 are both methyl.

[0055] In this invention, the hydroxyl functional compound is preferably:

[0056] (N,N-Di(2-hydroxypropyl)benzamide)

[0057] (N,N,N',N'-Tetra(2-hydroxypropyl)hexamethylenediamide).

[0058] In this invention, the hydroxyl functionalized compound is preferably synthesized according to published invention patents, such as US20040260123 and CN109553547A; or purchased from the market, with specific models not described further. The hydroxyl functionalized compounds used in the embodiments of this invention are N,N-bis(2-hydroxypropyl)benzamide and N,N,N',N'-tetra(2-hydroxypropyl)hexamethylenediamide (Anhui Huaan Import & Export Co., Ltd.).

[0059] In this invention, the weight-average molecular weight of the hydroxyl-functionalized polyacrylic acid resin is preferably 4,000 to 1,500,000, the hydroxyl value is preferably 10 to 150 mg KOH / g, and the glass transition temperature is preferably 40 to 145 °C.

[0060] In this invention, the hydroxyl-functional polyacrylic resin is preferably obtained by copolymerization of hydroxyl-containing monomers and acrylate comonomers; the hydroxyl-containing monomers are preferably a mixture of allyl alcohol structural monomers and propoxylated allyl alcohol structural monomers in any proportion.

[0061] In this invention, when the hydroxyl-containing monomer is an allyl alcohol monomer, the general structural formula is CH2=CY-CH2-OH, where Y is hydrogen or an alkyl group with 1 to 5 carbon atoms, preferably one or more of allyl alcohol, methanalyl alcohol, and 2-ethyl-2-propen-1-ol. When the hydroxyl-containing monomer is a propoxylated allyl alcohol monomer, the general structural formula is CH2=CZ-CH2-(A). a -OH, A is an oxypropylene group, Z is hydrogen or an alkyl group with 1 to 5 carbon atoms, and a is the average number of oxypropylene groups in propoxylated allyl alcohol, a = 1 to 2.

[0062] In this invention, the acrylate comonomer is preferably methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, dodecyl acrylate, dodecyl methacrylate, benzyl acrylate, benzyl methacrylate, or vinyl monomers; the vinyl monomer is preferably styrene and / or methylstyrene.

[0063] The present invention does not impose any particular restrictions on the polymerization conditions for the copolymerization of the hydroxyl-containing monomer and the acrylate comonomer. Methods known to those skilled in the art, such as bulk polymerization, free radical solution polymerization, emulsion polymerization, and suspension polymerization, can be used. Free radical solution polymerization is preferred. An initiator is preferably added during the polymerization process. The initiator is preferably azobisisobutyronitrile, benzoyl peroxide, tert-butyl hydroperoxide, or dicumyl peroxide.

[0064] In this invention, the hydroxyl-functionalized polyacrylic acid resin is preferably obtained commercially. The hydroxyl-functionalized polyacrylic acid resin used in this invention is... The series of products (Bolier Chemical Co., Ltd.) and other types of hydroxyl-functionalized polyacrylic resins are also available through market purchases; specific models will not be listed here.

[0065] In this invention, the mass percentage of the component containing carboxyl functional groups is 14-50%, preferably 18.7-22.2%, and more preferably 19.8-20.0%.

[0066] In this invention, the carboxyl functionality of the component containing carboxyl functional groups is >2; the component containing carboxyl functional groups includes one or more of carboxyl functional compounds, carboxylates, and carboxyl functional polyacrylic resins. When the component containing carboxyl functional groups comprises two or more of the above, this invention does not have a special limitation on the proportions of different components, and any proportion is acceptable.

[0067] In this invention, the carboxyl-functionalized compound preferably includes one or more of pyromellitic acid, ethylenediaminetetraacetic acid, trimellitic acid, butanetetracarboxylic acid, triamic acid, cyclohexanetetracarboxylic acid, pyromellitic dianhydride, and trimellitic anhydride; the carboxylate preferably includes pyromellitic acid-2-phenylimidazoline salt or trimellitic acid imidazoline salt; the weight-average molecular weight of the carboxyl-functionalized polyacrylic acid resin is preferably 2000-8000, more preferably 3000-7000, and even more preferably... The preferred step value is 4000–6500 mg KOH / g; the preferred acid value range is 150–300 mg KOH / g, more preferably 170–280 mg KOH / g, and even more preferably 200–260 mg KOH / g; the preferred glass transition temperature is 40–110 °C, more preferably 50–100 °C, and even more preferably 60–90 °C; the preferred softening point is 80–150 °C, more preferably 90–120 °C, and even more preferably 97–115 °C.

[0068] In this invention, the carboxyl-functionalized acrylic resin is preferably obtained by copolymerization of carboxyl-containing monomers and acrylate comonomers. The mass of the carboxyl-containing monomers is preferably 25-40% of the total mass of the carboxyl-containing monomers and acrylate comonomers, more preferably 30-35%. The mass of the acrylate comonomers is preferably 60-75% of the total mass of the carboxyl-containing monomers and acrylate comonomers, more preferably 65-70%.

[0069] In this invention, the structural formula of the carboxyl-containing monomer is shown in formula a:

[0070]

[0071] In formula a, S is preferably H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or tert-butyl.

[0072] In this invention, the acrylate comonomer is preferably methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, dodecyl acrylate, dodecyl methacrylate, benzyl acrylate, benzyl methacrylate, or vinyl monomers; the vinyl monomer is preferably styrene and / or methylstyrene.

[0073] In this invention, the carboxyl-functionalized polyacrylic resin is preferably obtained by polymerization of carboxyl-containing monomers and acrylate comonomers. This invention does not impose any particular restrictions on the polymerization conditions, and methods well known in the art, such as bulk polymerization, free radical solution polymerization, emulsion polymerization, and suspension polymerization, can be used. Free radical solution polymerization is preferred. During the polymerization process, an initiator is preferably added. The initiator is preferably azobisisobutyronitrile, benzoyl peroxide, tert-butyl hydroperoxide, or dicumyl peroxide.

[0074] In this invention, the carboxyl-functionalized polyacrylic resin is preferably purchased from the market. The partially carboxyl-functionalized acrylic resins used in this invention are LZ5005, LZ7007 (Baoding Lanzhu Chemical Co., Ltd.), and JONCRYL 843 (BASF). Other types of carboxyl-functionalized polyacrylic resins are also purchased from the market, and the specific models will not be described in detail.

[0075] The present invention does not impose any special limitation on the preparation method of the matting agent for powder coatings. The materials can be mixed evenly according to the methods known in the art. In the embodiments of the present invention, all the raw materials of the matting agent are ground and pulverized separately and then passed through a 140-mesh sieve. According to the formula composition (mass percentage) of the matting agent, all the pulverized and sieved raw materials are put into a high-speed mixer and dispersed evenly to obtain the corresponding matting agent.

[0076] This invention provides the application of the matting agent for powder coatings described in the above technical solution in powder coatings.

[0077] This invention provides a matte powder coating, the raw materials of which include: a carboxyl-containing polyester resin, a hydroxyalkylamide curing agent, a matting agent, and additives; the mass of the carboxyl-containing polyester resin is 40-60% of the total mass of the matte powder coating; the mass of the matting agent is 4-10% of the total mass of the matte powder coating; the mass ratio of the hydroxyalkylamide curing agent to the carboxyl-containing polyester resin is 4-6:94-96; and the matting agent is the matting agent for powder coatings described in the above technical solution.

[0078] In this invention, the mass of the carboxyl-containing polyester resin is preferably 45-55% of the total mass of the matte powder coating, more preferably 50-54%, and even more preferably 51.9-53.1%; the mass of the matting agent is 4-10% of the total mass of the matte powder coating, more preferably 5-9%, and even more preferably 6.7-7.4%; the mass ratio of the hydroxyalkylamide curing agent to the carboxyl-containing polyester resin is preferably 4-6:94-96, more preferably 4.5-5.5:94.5-95.5, and even more preferably 5-5.2:95.

[0079] In this invention, the acid value range of the carboxyl-containing polyester resin is preferably 10-100 mg KOH / g, more preferably 20-80 mg KOH / g, and even more preferably 25-40 mg KOH / g; the glass transition temperature Tg is preferably 40-80℃, more preferably 45-65℃, and even more preferably 50-65℃.

[0080] In this invention, the carboxyl-containing polyester resin is preferably formed by the condensation of a diacid and a polyol; more preferably by the condensation of a diacid and an equivalent amount of a diol; the diacid preferably includes terephthalic acid, isophthalic acid, 1,4-cyclohexyldicarboxylic acid, adipic acid, maleic acid, or succinic acid; the polyol preferably includes ethylene glycol, diethylene glycol, propylene glycol, hexanediol, neopentyl glycol, cyclohexyldiethanol, or trimethylolpropane.

[0081] The carboxyl-containing polyester resin described in this invention is preferably a commercially available product, such as SJ5122 and SJ5100 from Anhui Shenjian.

[0082] In this invention, the hydroxyalkylamide curing agent has a structure different from that of the hydroxyalkylamide compounds in the matting agent.

[0083] In this invention, the hydroxyalkylamide curing agent has the structure shown in Formula 3:

[0084]

[0085] In Formula 3, A is hydrogen, an alkyl, aryl or olefinic group containing 1 to 60 carbon atoms, R5 is hydrogen, an alkyl group containing 1 to 5 carbon atoms or a hydroxyalkyl group containing 1 to 5 carbon atoms, R6 is hydrogen or methyl, n' is an integer from 0 to 2, and n is an integer from 1 to 10.

[0086] In this invention, the alkyl group containing 1 to 60 carbon atoms is preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, eicosyl, triacontyl, tetradecyl, pentadecanyl, or hexadecyl; the aryl group is preferably phenyl or naphthyl; and the olefinic group is preferably vinyl, isopropenyl, 1,3-dimethyl-3-propenyl, 1,2-dimethyl-2-propenyl, 3-carboxy-2-propenyl, or 3-ethoxycarbonyl-2-propenyl.

[0087] In this invention, the alkyl group containing 1 to 5 carbon atoms is preferably methyl, ethyl, n-propyl, n-butyl, isobutyl, tert-butyl, or pentyl; the hydroxyalkyl group containing 1 to 5 carbon atoms is preferably hydroxyethyl, 3-hydroxypropyl, 2-hydroxypropyl, 4-hydroxybutyl, 3-hydroxybutyl, 2-hydroxy-2-methylpropyl, 5-hydroxypentyl, 4-hydroxypentyl, 3-hydroxypentyl, or 2-hydroxypentyl.

[0088] In this invention, n is preferably 1 or 2; A is preferably (CH2). m m is an integer from 1 to 10, more preferably from 2 to 8, and even more preferably 4.

[0089] In this invention, the hydroxyalkylamide curing agent is preferably at least one of N,N,N',N'-tetra(β-hydroxyethyl)hexamethylenediamide and N,N,N',N'-tetra(β-hydroxypropyl)hexamethylenediamide; when the hydroxyalkylamide curing agent is two of the above, this invention does not have a special limitation on the ratio of the two, and can be adjusted according to actual needs; the N,N,N',N'-tetra(β-hydroxyethyl)hexamethylenediamide is preferably a commercially available product, such as EMS's Primid XL552, Ningbo Nanhai Chemical's T105, or Degussa's Vestagon HA320; the N,N,N',N'-tetra(β-hydroxypropyl)hexamethylenediamide is a commercially available product, such as EMS's Primid QM 1260.

[0090] In this invention, the additives preferably include leveling agents, plasticizers, stabilizers, or degassing agents; the stabilizers are preferably stabilizers that prevent UV degradation; the degassing agents are preferably benzoin; this invention does not have any special limitations on the specific models and amounts of the leveling agents, plasticizers, and stabilizers, and the amounts of corresponding additives well known in the art can be adjusted according to actual needs.

[0091] In this invention, the components of the matte powder coating preferably also include pigments; the pigments are preferably TiO2, iron oxide red, iron oxide yellow, chromium pigment, carbon black, phthalocyanine blue, azo, anthraquinone, thioindigo, benzanthrone, triphenyldiane or quinacrine; more preferably pigments that have the function of resisting outdoor exposure.

[0092] The present invention does not impose any special limitation on the addition ratio of the additives and pigments; they can be added to the powder coating as needed.

[0093] In this invention, the matte powder coating is preferably prepared by a one-step extrusion method: the raw materials are mixed evenly, and then subjected to hot melt mixing, tableting, crushing and sieving in sequence, wherein the sieve mesh number is 80-200 mesh (Chinese standard sieve); preferably 100-180 mesh, more preferably 140-180 mesh.

[0094] In this invention, the preferred temperature for hot melt mixing is 90–120°C.

[0095] The present invention does not impose any special limitations on the specific preparation conditions of the matte powder coating, and can be carried out according to the process known in the art; in the embodiments of the present invention, the specific steps are as follows: the raw materials of the powder coating are mixed according to the ratio (mass percentage), placed in a plastic bag and manually mixed for 3 to 5 minutes, added to a twin-screw test extruder (model: SLJ-30A, Yantai Donghui) for melting and homogenization, pressed into tablets, cooled, and then ground into fine powder and passed through a 180-mesh standard sieve.

[0096] In this invention, based on existing theories, in HAA system powder coatings, the hydroxyl groups in the hydroxyl-functional polyacrylic resin cannot undergo cross-linking reactions with the carboxyl groups in the film-forming resin and the matting agent, nor can they react with the curing agent in the powder coating formulation. Therefore, theoretically, the hydroxyl-functional polyacrylic resin will not affect the addition ratio of carboxyl film-forming resin and hydroxyalkylamide curing agent in the powder coating formulation, nor will it affect the cross-linking reaction process between carboxyl groups and hydroxyalkylamide compounds. However, in practice, this invention adds hydroxyl-functional polyacrylic resin to the matting agent, which can further enhance the matting effect of the matting agent, resulting in a matte powder coating with lower gloss. At the same time, it can also improve the leveling performance of the coating after curing, thus overcoming technical bias.

[0097] Esterification reactions between carboxyl and hydroxyl groups typically require temperatures above 225°C or the presence of a strong catalyst. However, in the crosslinking chemistry of hydroxyalkylamides, the esterification reaction between hydroxyalkylamide compounds and carboxyl groups in carboxylated polyester resins is due to the activation of hydroxyl groups by the amide groups in the hydroxyalkylamide compounds. This activation leads to the formation of an oxazolium intermediate structure upon heating. Subsequently, this oxazolium intermediate undergoes a ring-opening reaction with the carboxyl groups in the carboxylated polyester resin to yield the esterified product. However, the oxazolinium ring exhibits unique reactivity, capable of undergoing ring-opening reactions with both electrophilic and nucleophilic reagents. Therefore, this invention proposes that the presence of hydroxyl-functionalized components may lead to a reaction between hydroxyl groups and the oxazolium ring, thus affecting the reaction rate between carboxyl groups and the oxazolium ring, resulting in a rate difference. In particular, the addition of hydroxyl-functionalized polyacrylic acid resins affects the ring-opening reaction process between the oxazolium intermediate and the carboxyl groups. In this invention, this manifests as the presence of hydroxyl-functionalized polyacrylic acid resins resulting in HAA-based matte powder coatings with lower gloss and better leveling properties.

[0098] This invention provides the application of the matte powder coating described above in the field of low-gloss powder coating, wherein the low gloss has a gloss level of 5-30%.

[0099] The matte powder coating of the present invention is preferably applied by electrostatic powder gun, friction gun spraying, fluidized bed dip coating and hot melt sintering to adhere it to the substrate (such as metal substrate), and then cured by heating or radiation to form a coating film. The coating thickness is preferably selected as needed, more preferably 50-400 μm, and even more preferably 60-80 μm.

[0100] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0101] Example

[0102] All matting agents are prepared according to the following method: all raw materials of the matting agent are ground and pulverized separately and then passed through a 140-mesh sieve. According to the formula composition (mass percentage) of the matting agent, all the pulverized and sieved raw materials are put into a high-speed mixer and dispersed evenly to obtain the corresponding matting agent.

[0103] Preparation method of powder coating: Mix the raw materials of powder coating according to the ratio (mass percentage), put them in a plastic bag and mix manually for 5 minutes. Add them to a twin-screw test extruder (model: SLJ-30A, Yantai Donghui) and melt and homogenize at 90-120℃. Press into sheets, cool, and then grind into fine powder. Pass through a 180-mesh standard sieve. After electrostatic spraying the low-gloss powder coating composition onto degreased cold-rolled steel plate, cure at 200℃ for 10 minutes. Test after curing.

[0104] Performance testing methods

[0105] 1. Coating thickness

[0106] The thickness was measured directly using a magnetic thickness gauge (Q Nix4500 from Automation Dr. Nix GmbH, Germany) in accordance with GB / 4957 standard.

[0107] 2. Gloss

[0108] The reflectance was measured directly using the German BYK Micro-gloss 60° 4442, according to the GB / T1743 standard.

[0109] 3. Impact strength

[0110] The test shall be conducted in accordance with GB / T1732 standard and using a hammer impact tester. A 1kg 50cm impact tester that passes both forward and reverse impacts is marked as 50+, a pass in forward impact is marked as 50, and a failure in either forward or reverse impact is marked as <50, and so on.

[0111] 4. Leveling

[0112] PCI classification is performed by visual inspection, with 10 being the best and 0 being the worst.

[0113] Table 1 Information on the main raw materials used in the embodiments.

[0114]

[0115]

[0116]

[0117] Matting agents were prepared using carboxylates and hydroxyl functional compounds as raw materials. The formulation of the matting agents is shown in Table 2.

[0118] Table 2 Formulation composition of matting agents I-1 and I-2

[0119] matting agent Ⅰ-1 Ⅰ-2 2-Phenylacetic acid 54.1％ 44.4％ N,N,N',N'-Tetra(2-hydroxyethyl)hexamethylenediamide 45.9％ N,N-Di(2-hydroxypropyl)benzamide 55.6％ total 100.0％ 100.0％

[0120] The formulation composition and application test results of matting powder coatings composed of matting agents I-1 and I-2 are shown in Table 3.

[0121] Table 3. Composition and test results of matting powder coatings composed of matting agents I-1 and I-2.

[0122]

[0123]

[0124] As shown in Table 3, the matte powder coating prepared with matting agent I-1 (Example 1) has a lower leveling grade after curing, while the matte powder coating prepared with matting agent I-2 (Example 2) has a lower gloss and a higher leveling grade.

[0125] As shown in Example 2, the combination of 2-phenyl-2-imidazoline pyromellitic acid and N,N-bis(2-hydroxypropyl)benzamide can achieve excellent matting effects in HAA system powder coatings, but the leveling effect is still insufficient, and the cured coating exhibits obvious pinholes and orange peel defects. Carboxyl-functionalized polyacrylic resin is one of the commonly used matting agent raw materials in the field of powder coating technology. Therefore, based on matting agent I-2, carboxyl-functionalized polyacrylic resins with different acid values ​​are added to the matting agent formulation to enhance the matting effect and improve the leveling performance of the coating. The formulation composition of the new matting agent is shown in Table 4.

[0126] Table 4. Formulation composition of matting agents II-1 to II-8

[0127]

[0128]

[0129] The formulation composition and application test results of matting powder coatings composed of matting agents II-1 to II-8 are shown in Table 5.

[0130] Table 5. Composition and test results of matting powder coatings composed of matting agents II-1 to II-8.

[0131]

[0132]

[0133] As can be seen from Examples 3-10, matting agents composed of polyacrylic acid resins with different acid values, combined with 2-phenyl-2-imidazoline pyromellitic acid and N,N-bis(2-hydroxypropyl)benzamide, can achieve good matting effects. However, this also leads to a significant deterioration in the impact resistance of the cured coating, which cannot meet the actual application requirements.

[0134] To eliminate the influence of carboxyl-functionalized acrylic resin on the impact performance of the cured coating, hydroxyl-functionalized polyacrylic resin was added to the matting agent formulation. Based on matting agent I-2, hydroxyl-functionalized polyacrylic resin was added to the matting agent formulation, resulting in six matting agents III-1 to III-6 prepared by combining hydroxyl-functionalized compounds with hydroxyl-functionalized polyacrylic resin and carboxylates. The composition of these matting agent formulations is shown in Table 6.

[0135] Table 6. Formulation composition of matting agents III-1 to III-6

[0136]

[0137] The hydroxyl-functional polyacrylic resin used in the above-mentioned matting agent III was purchased from Shanghai Bolier Chemical Co., Ltd. The formulation composition and application test results of the matting powder coating composed of matting agents III-1 to III-6 are shown in Table 7.

[0138] Table 7. Composition and test results of matting powder coatings composed of matting agents III-1 to III-6.

[0139]

[0140]

[0141] As shown in Table 7, the HAA system matting powder coatings prepared with matting agents III-1 to III-7 can all achieve excellent matting effects, with matting agent III-5 being the preferred matting agent. In Example 15, the addition amount of matting agent III-5 was 5.4%, which achieved a matting effect of 16.5%. The matting effect achieved by matting agent III-2, which has the same raw materials as matting agent III-5, at an addition amount of 7.4% (Example 12) is similar to that of Example 15. However, the leveling grade of the coating after curing in Example 12 is slightly lower than that in Example 15, indicating that matting agent III-5 is a more preferred matting agent.

[0142] Furthermore, a comparison of the examples in Tables 7 and 5 shows that the matting agents III-1 to III-7 prepared with hydroxyl-functionalized polyacrylic acid resins exhibit better impact resistance after curing than the matting agents prepared with carboxyl-functionalized polyacrylic acid resins in Table 5 (comparative Examples 3-7 and Examples 11-15). This demonstrates that the hydroxyl-functionalized polyacrylic acid resin in this invention can synergistically work with 2-phenyl-2-imidazoline pyromellitic acid (carboxylate) and N,N-bis(2-hydroxypropyl)benzamide (hydroxyl-functionalized compound) to achieve the desired matting effect of HAA system powder coatings without affecting the curing effect or film-forming properties of the coating.

[0143] As demonstrated in Examples 16 and 17, stearic acid diethanolamide or N,N,N',N'-tetra(2-hydroxypropyl)hexamethylenediamide combined with 2-phenyl-2-imidazoline pyromellitic acid and hydroxyl-functionalized polyacrylic acid resin can also achieve the matting effect of HAA system powder coatings, with gloss levels of 27.9% and 28.7%, respectively. These gloss levels are higher than those of the combination of 2-phenyl-2-imidazoline pyromellitic acid, N,N-di(2-hydroxypropyl) and hydroxyl-functionalized polyacrylic acid resin (Comparative Examples 11-15).

[0144] In addition to the polybasic acid compound 2-phenyl-2-imidazoline pyromellitic acid mentioned above, seven matting agents, IV-1 to IV-7, were prepared by using other polybasic acid (anhydride) compounds in combination with N,N-bis(2-hydroxypropyl) and hydroxyl-functionalized polyacrylic acid resins. The formulations of the matting agents are shown in Table 8.

[0145] Table 8 Formulation composition of matting agents IV-1 to IV-7

[0146] Matting agent number Ⅳ-1 Ⅳ-2 Ⅳ-3 Ⅳ-4 Ⅳ-5 Ⅳ-6 Ⅳ-7 Pyromellitic acid 19.8％ Trimeric triglyceride 20.0％ aminetriacetic acid 20.0％ EDTA-1,5-diaminetetraacetic acid 22.2％ Triamic acid 18.7％ Butanetetracarboxylic Acid 18.7％ Cyclohexanetetracarboxylic acid 20.0％ BM666 41.2％ 40.0％ 40.0％ 38.9％ 40.7％ 40.7％ 40.0％ N,N-Di(2-hydroxypropyl)benzamide 39.1％ 40.0％ 40.0％ 38.9％ 40.7％ 40.7％ 40.0％ total 100.0％ 100.0％ 100.0％ 100.0％ 100.0％ 100.0％ 100.0％

[0147] The formulation composition and application test results of matting powder coatings composed of matting agents IV-1 to IV-7 are shown in Table 9.

[0148] Table 9. Composition and test results of matting powder coatings composed of matting agents IV-1 to IV-7.

[0149]

[0150]

[0151] As shown in Examples 18-24 of Table 9, different polybasic acid (anhydride) compounds combined with N,N-bis(2-hydroxypropyl) and hydroxyl-functionalized polyacrylic acid resins can all achieve excellent matting effects in the HAA system. However, compared with Example 15, the gloss of the matting powder coatings of Examples 18-24 is higher than that of Example 15, indicating that Example 15 is the powder coating composition with the best matting effect. That is, the combination of 2-phenyl-2-imidazoline pyromellitic acid, N,N-bis(2-hydroxypropyl), and hydroxyl-functionalized polyacrylic acid resin is the preferred matting agent composition, and matting agents III-5 are the preferred matting agents. The matting effect of other polybasic acids (anhydrides) used to replace 2-phenyl-2-imidazoline pyromellitic acid is deteriorated.

[0152] Therefore, the matting effect of powder coatings with different matting agent addition amounts was tested based on matting agent Ⅲ-5. The test formula and test results of matting powder coatings are shown in Table 10.

[0153] Table 10 Composition and test results of matte powder coatings with different matting agent III-5 addition amounts

[0154]

[0155]

[0156] As shown in Table 10, with the increase of matting agent III-5 in the formulation, the final gloss of the powder coating will decrease, and the matting effect will change linearly with the amount of matting agent added (see Table 10). Figure 1 ).

[0157] The powder coating prepared in Example 27 was cured under different curing conditions, and its gloss was tested. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the gloss difference of the powder coating prepared with matting agent III-5 after curing under different curing conditions is not significant, indicating that the prepared powder coating has high gloss stability and can achieve a stable matting effect without significant fluctuations with changes in baking temperature. Based on a curing condition of 200℃, the gloss change value of the cured coating at different curing temperatures is < ±2 gloss units, and the gloss fluctuation with changes in baking conditions is very small. In addition, the powder coating prepared with matting agent III-5 can also achieve high-temperature rapid curing without affecting the matting effect of the matting agent.

[0158] Selectivity test of matting resin

[0159] Different polyester resins were combined with matting agent III-5 to test their matting effect. The powder coating formulation and test results are shown in Table 11.

[0160] Table 11. Matting Effects of Different Polyester Resins Combined with Matting Agent III-5

[0161]

[0162] As can be seen from the comparison of Example 26 in Table 11, different polyester resins combined with matting agent III-5 can achieve a matting effect of less than 20% in HAA system powder coatings, which is a matting effect that none of the previously disclosed matting agents can achieve.

[0163] In summary, the matting agent of the present invention can stably achieve matting of HAA system powder coatings, and the gloss can be adjusted by adjusting the amount of matting agent. It has a wide range of curing conditions, low resin selectivity, and stable matting effect, making it the preferred solution for achieving matting of HAA system powder coatings.

[0164] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A matting agent for HAA system powder coatings, characterized in that, The components include the following components by mass percentage: The component containing hydroxyl functional groups is 50-86%, and the component containing carboxyl functional groups is 14-50%. The hydroxyl-functionalized component comprises 30-62% hydroxyl-functionalized compound and 38-70% hydroxyl-functionalized polyacrylic acid resin; The hydroxyl functional compound is a hydroxyalkylamide compound with a functionality of ≥2; The carboxyl functional group component has a carboxyl functionality > 2; the carboxyl functional group component includes one or more of carboxyl functional compounds, carboxylates, and carboxyl functional polyacrylic resins. The hydroxyl-functionalized compound has the structure shown in Formula 1: Formula 1; In Formula 1, R is an alkyl, aryl, or olefinic group containing 1 to 60 carbon atoms; R1 is hydrogen or an alkyl group containing 1 to 5 carbon atoms; and R2 is hydrogen or an alkyl group containing 1 to 5 carbon atoms. Alternatively, R may have the structure shown in Equation 2: Formula 2; In Formula 2, B is an alkyl, aryl, or olefinic group containing 1 to 60 carbon atoms, R3 is hydrogen or an alkyl group containing 1 to 5 carbon atoms, R4 is hydrogen, an alkyl group containing 1 to 5 carbon atoms, or a hydroxyalkyl group containing 1 to 5 carbon atoms, and X = 0 to 2 and X is an integer. The hydroxyl-functional polyacrylic acid resin has a weight-average molecular weight of 4,000 to 1,500,000, a hydroxyl value of 10 to 150 mg KOH / g, and a glass transition temperature of 40 to 145 °C. The carboxyl functionalized compounds include one or more of pyromellitic acid, ethylenediaminetetraacetic acid, trimellitic acid, butanetetracarboxylic acid, triamic acid, cyclohexanetetracarboxylic acid, pyromellitic dianhydride, and trimellitic anhydride.

2. The matting agent for HAA system powder coatings according to claim 1, characterized in that, The carboxylate includes pyromellitic acid-2-phenylimidazoline salt or trimellitic acid imidazoline salt; the weight-average molecular weight of the carboxyl-functionalized polyacrylic acid resin is 2000~8000, the acid value range is 150~300mgKOH / g, the glass transition temperature is 40~110℃, and the softening point is 80~150℃.

3. The application of the matting agent of the HAA system for powder coatings according to any one of claims 1 to 2 in powder coatings.

4. A matte powder coating, characterized in that, The raw materials for preparation include: carboxyl-containing polyester resin, hydroxyalkylamide curing agent, matting agent, and additives; the mass of the carboxyl-containing polyester resin is 40-60% of the total mass of the matte powder coating; the mass of the matting agent is 4-10% of the total mass of the matte powder coating; the mass ratio of the hydroxyalkylamide curing agent to the carboxyl-containing polyester resin is 4-6:94-96; the matting agent is the matting agent for HAA system powder coatings according to any one of claims 1-2.

5. The matte powder coating according to claim 4, characterized in that, The acid value of the carboxyl-containing polyester resin is in the range of 10~100mg KOH / g, and the glass transition temperature Tg is 40~80℃.

6. The matte powder coating according to claim 4 or 5, characterized in that, The carboxyl-containing polyester resin is formed by the condensation of a dicarboxylic acid and a polyol; the dicarboxylic acid includes terephthalic acid, isophthalic acid, 1,4-cyclohexyldicarboxylic acid, adipic acid, maleic acid, or succinic acid; the polyol includes ethylene glycol, diethylene glycol, propylene glycol, hexanediol, neopentyl glycol, cyclohexyldiethanol, or trimethylolpropane.

7. The matte powder coating according to claim 4, characterized in that, The hydroxyalkylamide curing agent has the structure shown in Formula 3: Formula 3; In Formula 3, A is hydrogen, an alkyl, aryl or olefinic group containing 1 to 60 carbon atoms, R5 is hydrogen, an alkyl group containing 1 to 5 carbon atoms or a hydroxyalkyl group containing 1 to 5 carbon atoms, R6 is hydrogen or methyl, n' is an integer from 0 to 2, and n is an integer from 1 to 10.

8. The application of the matte powder coating according to any one of claims 4 to 7 in the field of low-gloss powder coating, wherein the low gloss has a gloss of 5 to 30%.

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