High-coating-rate coiled material back coating composition, high-coating-rate coiled material back coating prepared from high-coating-rate coiled material back coating composition and application of high-coating-rate coiled material back coating composition

Abstract

The invention discloses a high-coating-rate coiled material back coating composition, a high-coating-rate coiled material back coating prepared from the high-coating-rate coiled material back coating composition and application of the high-coating-rate coiled material back coating composition. The high-coating-rate coiled material back coating composition comprises the following components in percentage by mass: 30-80% of film-forming resin selected from polyester resin, 4-15% of amino resin, 1-30% of pigment, 0-10% of filler, 1-10% of auxiliaries and a solvent, wherein the number-average molecular weight Mn of the polyester resin is 2000-3000, the hydroxyl value is 100-120mg KOH / g, the acid value is 3-5mg KOH / g, the Tg is 10-30 DEG C, and the solid content is greater than or equal to 75wt%. A back paint coating formed after the back paint prepared from the back paint composition is subjected to film forming has high coating rate, high bonding strength and excellent flexibility and machinability, and the emission load of organic compounds VOCs is low.

Description

Technical Field

[0001] The present invention relates to the technical field of back paints for coils. More specifically, it relates to a high coating rate coil back paint composition, a high coating rate coil back paint prepared therefrom, and applications thereof. Background Art

[0002] Pre-coated coils, also known as color steel plates, have a broad market and application space due to their efficient, energy-saving, and environmentally friendly characteristics, and are widely used in industries such as construction, household appliances, and automotive manufacturing. Conventional color steel plates are multi-coating systems, including a front anti-corrosion primer, a functional topcoat, and a back paint according to application characteristics. The main function of the back paint is to protect the back of the color steel plate, preventing the back paint and the topcoat from being anti-stuck, indented, or even scratched and chipped on the front of the paint film due to relative displacement forces after stacking, which may affect subsequent processing. In addition, the back paint is also required to have good foam layer adhesion performance, especially in the fields of building sandwich panels, household appliance back panels, etc.

[0003] Traditional epoxy back paints have a low coating rate, a relatively hard paint film, and slightly poor processability; while polyester back paints are the opposite, with excellent processing performance, but poor solvent resistance and foam layer adhesion performance, and a narrow range of use. By combining the advantages of both, a back paint film based on epoxy-modified polyester resin not only has good processing performance and excellent foaming performance, but also has low cost and high economic benefits, and is more in line with the market development trend.

[0004] The current coil market is highly competitive, and customers have higher and higher performance evaluations for coil production lines. To further improve the competitiveness of products, the coating rate, environmental friendliness, and foam bonding performance of back paint coatings are all key factors for seizing the market. However, in the existing improvement schemes for the performance of high coating rate coil back paints, they mainly focus on: while improving the coating rate of the back paint, improving its adhesion, flexibility, surface smoothness, and scratch resistance, etc. But these methods have limited improvement effects on the coating rate, and these schemes cannot well improve the foam bonding property of the paint film. Summary of the Invention

[0005] Based on the above facts, the purpose of the present invention is to provide a high coating rate coil back paint composition, a high coating rate coil back paint prepared therefrom, and applications thereof. After being coated on the back of the coil and forming a film, the back paint coating formed has both a high coating rate, high bonding strength, excellent flexibility and processability, etc., and a low emission of volatile organic compounds (VOCs).

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] On the one hand, the present invention provides a high coating rate coil back paint composition, and by mass percentage, its components include:

[0008] A film-forming resin, selected from polyester resins, with a content of 30 - 80%;

[0009]

[0010] A solvent;

[0011] Among them, the number-average molecular weight Mn of the polyester resin is 2000 - 3000, the hydroxyl value is 100 - 120 mg KOH / g, the acid value is 3 - 5 mg KOH / g, the Tg is 10 - 30 °C, and the solid content is ≥ 75 wt%.

[0012] Furthermore, the viscosity of the polyester resin is 3000 - 7000 mPa·s.

[0013] Furthermore, the polyester resin contains active end-group functional groups.

[0014] Furthermore, the active end-group functional groups are hydroxyl groups, carboxyl groups, etc.

[0015] Furthermore, the polyester resin is selected from the ETERKYD 5093-R-75 polyester resin of Changxing Company.

[0016] Furthermore, the amino resin is selected from one or a mixture of methylated melamine resin or butylated melamine resin; and the amino resin contains imino groups.

[0017] Furthermore, the mass ratio of the polyester resin to the amino resin is (3 - 6):1.

[0018] Furthermore, the additive contains an adhesion promoter.

[0019] Furthermore, the adhesion promoter is an acid ester adhesion promoter.

[0020] Furthermore, the adhesion promoter is an epoxy phosphate adhesion promoter.

[0021] Furthermore, in the components, the mass percentage content of the adhesion promoter is 0.5 - 5%.

[0022] Furthermore, the additive also contains one or several of a dispersant, a catalyst, an antifoaming agent, and a leveling agent.

[0023] Furthermore, by mass percentage, the high coating rate coil backside coating composition contains:

[0024]

[0025] In another aspect, the present invention provides a high coating rate coil back coating, which is prepared from the high coating rate coil back coating composition as described above.

[0026] In another aspect, the present invention provides a method for preparing the high coating rate coil back coating as described above, comprising the following steps:

[0027] Mix the polyester resin, part of the additives, pigments, fillers and part of the solvents, and grind them until the fineness of the materials is dispersed below 10 μm to obtain a mixture;

[0028] Add the amino resin to the mixture, mix well, then add the remaining additives, mix well again, and then add the remaining solvents, and adjust the viscosity to obtain the high coating rate coil back coating.

[0029] In another aspect, the present invention provides a structure comprising a substrate and a coating bonded to the surface of the substrate;

[0030] Wherein, the coating is obtained by coating with the high coating rate coil back coating as described above.

[0031] Further, the substrate is selected from coils.

[0032] Further, the substrate is selected from pre-coated board coils.

[0033] Further, the coating method comprises the following steps:

[0034] Roll coat the high coating rate coil back coating on the substrate and bake it in an oven at 320 °C for 30 s, wherein the substrate metal plate temperature PMT: 224 - 232 °C, to form a paint film, thus obtaining the coating.

[0035] Further, a chromium-free primer is provided or not provided on the substrate.

[0036] The beneficial effects of the present invention are as follows:

[0037] After the high coating rate coil back coating composition of the present invention is used to prepare a high coating rate back paint coating, a specific performance polyester resin and amino resin are used in combination in the formula, so that after the back paint coating is cured, it can have a high coating rate. And on the basis of ensuring the protection of the back paint, the obtained back paint also has excellent processability and foaming adhesiveness. In addition, compared with the current back paint products on the market, the back paint coating of the present invention has a higher coating rate in the production line, lower production cost and lower VOCs emissions, meeting the environmental protection requirements. Detailed embodiments

[0038] To more clearly illustrate the present invention, the present invention will be further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0039] In order to provide a coil back paint with high coating rate, good foaming adhesiveness, low VOC and good processability, a specific embodiment of the present invention provides a high coating rate coil back coating composition. By mass percentage, its components include:

[0040] Film-forming resin, selected from polyester resins, with a content of 30-80%;

[0041]

[0042] Among them, the number average molecular weight Mn of the polyester resin is 2000-3000, the hydroxyl value is 100-120 mg KOH / g, the acid value is 3-5 mg KOH / g, the Tg is 10-30 °C, and the solid content is ≥75 wt%.

[0043] In this coating composition, the film-forming resin is a polyester resin. The appropriate hydroxyl value, acid value, etc. in this polyester resin make the probability of the back coating prepared from this coating composition reacting chemically with the foaming binder to form chemical bonds high, the bonding strength high, and the foaming adhesion performance good. Moreover, the paint film obtained after curing of this resin has a high cross-linking structure, greatly improving the scratch resistance, solvent resistance and other properties of the coating formed by curing the back coating.

[0044] In some examples, the viscosity of the polyester resin is 3000-7000 mPa·s. The polyester resin has a high solid content, low viscosity and a light dry film specific gravity, which helps to improve the coating rate of the back coating. And the polyester resin has a low VOC emission during the curing process, which can solve the problem of high VOC emission of solvent-based coatings at the source and meet the requirements of national environmental protection regulations.

[0045] In this embodiment, the polyester resin preferably contains active end group functional groups. The active end group functional groups contained in the polyester resin remain after the back coating is cured to form a coating. The more residual active groups, the higher the probability of reacting chemically with the foaming binder to form chemical bonds, the higher the bonding strength, and the better the foaming adhesion performance. Exemplary active end group functional groups include, but are not limited to, hydroxyl groups, carboxyl groups, etc. In some more specific examples, the polyester resin includes, but is not limited to, the ETERKYD 5093-R-75 polyester resin from Changxing Company.

[0046] Exemplarily, in the coating composition, the mass percentage content of the polyester resin includes but is not limited to 40-70%, 43-70%, 43-69%, 43-45%, 45-69%, 43%, 45%, 69%, etc.

[0047] In some examples, the amino resin is selected from one or a mixture of methylated melamine resin or butylated melamine resin; and, the amino resin contains imino groups, preferably high imino groups. In some preferred examples, the amino resin is a methylated or butylated amino resin containing high imino groups. Specifically, the amino resin containing high imino groups includes but is not limited to Cytec CYMEL 325 amino resin, etc. This resin can self-polymerize, thereby increasing the dosage of the amino resin crosslinker and increasing the hardness of the paint film. In addition, this resin can react quickly at low temperatures, reducing the possibility of volatilization of low molecular weight resins. When combined with the specific polyester resin in this embodiment, the exhaust gas emissions during the baking process of the back coating are relatively lower, and the VOCs emissions more meet the environmental protection requirements.

[0048] Exemplarily, in the coating composition, the mass percentage content of the amino resin includes but is not limited to 4-12%, 8-12%, 10-12%, 10%, 12%, etc.

[0049] According to some preferred technical solutions of this embodiment, the mass ratio of the polyester resin to the amino resin is (3-6):1. The coating composition obtained at this time has better foaming adhesiveness on the basis of a high coating rate. In some more specific solutions, the mass ratio of the polyester resin to the amino resin includes but is not limited to (3.5-6):1, (3.5-5.75):1, (3.5-4.5):1, (4.5-5.75):1, 4.5:1, 5.75:1, 3.58:1, etc.

[0050] In some embodiments of the present invention, the pigments include but are not limited to commonly used pigments in this technical field such as titanium dioxide, carbon black, etc. Pigments suitable for use with the high coating rate coil back coating composition of the present invention are generally known to those skilled in the art and can be selected according to the desired coating color or appearance change, including but not limited to pigments such as titanium dioxide R-902, R-960 provided by DuPont Company, and carbon black COLOUR BLACK FW200 provided by Degussa Company.

[0051] In some embodiments of the present invention, the fillers include, but are not limited to, calcined kaolin, light calcium carbonate and other commonly used fillers in the technical field. Fillers suitable for use with the high coating rate coil backside coating composition of the present invention are generally known to those skilled in the art and can be selected according to the desired change in the dry film specific gravity of the coating, including but not limited to fillers such as the ultrafine calcined kaolin CK-400 and light calcium carbonate powder (1250 mesh) provided by Guangfu Building Materials Company. In the coating composition, the mass percentage content of the filler includes, but is not limited to, 0, 1-10%, 2-6%, etc.

[0052] In some examples, the additives include an adhesion promoter. Preferably, the adhesion promoter is an acid ester adhesion promoter. Exemplary adhesion promoters include, but are not limited to, epoxy phosphate esters, polyester phosphate esters and other commonly used promoters in the technical field. The phosphoric acid monoester in the epoxy phosphate ester adhesion promoter suitable for the present invention is not easily hydrolyzed under the action of alcohol, acid or base and can be stably dispersed in the solvent. In some specific examples, the adhesion promoters suitable for the present invention include, but are not limited to, Lubrizol 2063, etc.

[0053] Exemplarily, in the coating composition, the mass percentage content of the adhesion promoter is 0.5-5%.

[0054] In some embodiments of the present invention, the additives further include one or more selected from dispersants, catalysts, defoamers and leveling agents. Among them, the dispersant can effectively improve the dispersion performance of the material and maintain the relative stability of the dispersion system; the catalyst can promote the reaction and increase the reaction rate; the defoamer can be used to prevent surface defects such as shrinkage holes, orange peel, foaming, pinholes, etc., and prevent the residue of boiling marks to achieve excellent leveling; the wettability, defoaming property and dispersibility of the leveling agent can enhance the gloss of the coating and improve the long-wave leveling effect, slightly reduce the surface tension, and do not affect the recoatability and interlayer adhesion. By mass percentage, the high coating rate coil backside coating composition contains:

[0055]

[0056] The mass percentage content of the above components is preferably 1-5% in total.

[0057] Specifically, the dispersants include, but are not limited to, dispersants with models BYK-170, BYK110, BYK115, BYKP-104, SOLSPERSE 2000 provided by BYK Company, and the dispersant with model DA-1040 provided by Yisheng Company. In some specific examples, in the coating composition, the mass percentage content of the dispersant includes, but is not limited to, 0, 0.2-3%, 0.5-2%, 0.5-1%, 1-2%, etc.

[0058] In this embodiment, exemplary catalysts include, but are not limited to, organotin catalysts such as Nacure 1051. In some specific examples, in the coating composition, the mass percentage content of the catalyst includes, but is not limited to, 0.5 - 1%, 0.5%, 1%, etc.

[0059] In this embodiment, exemplary defoamers include, but are not limited to, AFCONA 2720. In some specific examples, in the coating composition, the mass percentage content of the defoamer includes, but is not limited to, 0, 0.1 - 0.5%, 0.5%, etc.

[0060] In this embodiment, exemplary leveling agents include, but are not limited to, AFCONA - 3773. In some specific examples, in the coating composition, the mass percentage content of the leveling agent includes, but is not limited to, 0.8 - 1%, 1%, etc.

[0061] In the present invention, the solvent in the high - coating - rate coil back - side coating composition is selected from one or more of cyclohexanone, propylene glycol methyl ether acetate, ethylene glycol butyl ether, xylene, n - butanol, solvent oil S - 100, solvent oil S - 150, trimethylbenzene solvent oil, and dibasic acid ester mixture (DBE).

[0062] In some preferred examples, the solvent is a mixture of solvent oil S - 100, n - butanol, propylene glycol methyl ether acetate, and DBE, and the mixing ratio is preferably 6:1:2:2. In some more preferred examples, in the coating composition, by mass percentage, it contains 6% of solvent oil S - 100, 1% of n - butanol, 2% of propylene glycol methyl ether acetate, and 2% of DBE.

[0063] According to another specific embodiment of the present invention, there is provided a high - coating - rate coil back - side coating prepared from the high - coating - rate coil back - side coating composition as described above.

[0064] In this embodiment, the back - side coating is the topcoat in the back - paint.

[0065] According to another specific embodiment of the present invention, there is provided a preparation method of the high - coating - rate coil back - side coating as described above, including the following steps:

[0066] Mix the polyester resin, part of the additives, pigments, fillers, and part of the solvent, and then grind until the fineness of the material is dispersed to less than 10 μm to obtain a mixture;

[0067] Add amino resin to the mixture, mix well, then add the remaining additives, mix well, and then add the remaining solvent, and adjust the viscosity to obtain the high - coating - rate coil back - side coating.

[0068] In some preferred examples, the preparation method comprises the following steps:

[0069] (1) Polyester resin, partial additives, pigments, fillers and partial solvents are successively added into a reaction vessel, stirred at a speed of 500 - 700 r / min for 5 min, and the obtained mixture is ground at a speed of 1500 - 2000 r / min until the fineness of the material is dispersed to below 10 μm to obtain a mixture;

[0070] (2) Amino resin is added to the mixture obtained in the reaction vessel, and stirred at a speed of 500 - 700 r / min for 5 min; then the remaining additives are added and stirring is continued at a speed of 500 - 700 r / min for 5 min, and the remaining solvent is added. The viscosity of the obtained mixture is adjusted with the solvent so that when measured with a coating - 4 cup viscometer, the viscosity value is in the range of 100 - 120 s, thus obtaining the high - coating - rate coil back - side coating composition.

[0071] A specific embodiment of the present invention further provides a structure, which comprises a substrate and a coating bonded to the surface of the substrate;

[0072] Among them, the coating is obtained by coating with the high - coating - rate coil back - side coating as described above.

[0073] In some examples, the substrate is selected from coils, preferably pre - coated sheet coils.

[0074] In some specific examples, the coating method comprises the following steps:

[0075] The high - coating - rate coil back - side coating is roll - coated on the substrate and baked in an oven at 320 °C for 30 s, wherein the substrate metal plate temperature PMT: 224 - 232 °C, to form a paint film, thus obtaining the coating.

[0076] In some examples, the thickness of the coating is 5 ± 1 μm.

[0077] In some specific examples, a chromium - free primer is provided or not provided on the substrate.

[0078] The technical solutions of the present invention are described below in conjunction with some specific embodiments:

[0079] Example 1: High - coating - rate coil back - side coating 1

[0080] Prepare the high - coating - rate coil back - side coating 1 of the present invention according to the formula in Table 1 below:

[0081] Table 1 Weight parts of raw materials in Example 1

[0082]

[0083] The preparation of the high coating rate coil back coating 1 includes the following steps:

[0084] In a reaction vessel, polyester resin, dispersant, pigment, filler and half of the dosage of S-100 and all of the propylene glycol methyl ether acetate are added in sequence, stirred at a speed of 500 - 700 r / min for 5 min, and the obtained mixture is ground at a speed of 1500 - 2000 r / min until the fineness of the material is dispersed to less than 10 μm to obtain a mixture;

[0085] Amino resin is added to the mixture obtained in the reaction vessel, and stirred at a speed of 500 - 700 r / min for 5 min; then other additives are added and stirred continuously at a speed of 500 - 700 r / min for 5 min, and the remaining solvent is added. The viscosity of the obtained mixture is adjusted with the solvent so that when measured with a coating - 4 cup viscometer, the viscosity value is in the range of 100 - 120 s, and the high coating rate coil back coating 1 is obtained.

[0086] The performance detection method of the high coating rate coil back coating 1 includes the following steps:

[0087] Coating and plate making: The obtained high coating rate coil back coating 1 is directly coated on a galvanized sheet with a wire bar roller and baked in an oven at 320 °C for 30 s, and the metal plate temperature PMT: 224 - 232 °C, to obtain a paint film 1 with a film thickness of 5 μm.

[0088] The performance of the paint film 1 is detected, and the detection results are shown in Table 8.

[0089] Example 2: High coating rate coil back coating 2

[0090] Prepare the high coating rate coil back coating 2 of the present invention according to the formula in Table 2 below:

[0091] Table 2 Raw material weight parts of Example 2

[0092]

[0093]

[0094] The preparation of the high coating rate coil back coating 2 includes the following steps:

[0095] In a reaction vessel, polyester resin, dispersant, pigment and half of the dosage of S-100 and all of the propylene glycol methyl ether acetate are added in sequence, stirred at a speed of 500 - 700 r / min for 5 min, and the obtained mixture is ground at a speed of 1500 - 2000 r / min until the fineness of the material is dispersed to less than 10 μm to obtain a mixture;

[0096] Add amino resin to the mixture obtained in the reaction vessel and stir at a speed of 500 - 700 r / min for 5 min; then add other additives and continue to stir at a speed of 500 - 700 r / min for 5 min. Add the remaining solvent and adjust the viscosity of the resulting mixture so that when measured with a Coat-4 cup viscometer, the viscosity value is in the range of 100 - 120 s, thus obtaining the high coating rate coil backside coating 2.

[0097] The performance testing method of the high coating rate coil backside coating 2 includes the following steps:

[0098] Coating plate making: Roll coat the obtained high coating rate coil backside coating 2 on a galvanized plate with a wire bar, bake it in an oven at 320 °C for 30 s, and the metal plate temperature PMT: 224 - 232 °C, to obtain a paint film 2 with a film thickness of 5 μm.

[0099] Test the performance of the paint film 2, and the test results are shown in Table 8.

[0100] Example 3: High coating rate coil backside coating 3

[0101] Prepare the high coating rate coil backside coating 3 of the present invention according to the formula in Table 3 below:

[0102] Table 3 Raw material weight parts of Example 3

[0103]

[0104]

[0105] The preparation of the high coating rate coil backside coating 3 includes the following steps:

[0106] Add polyester resin, dispersant, pigment, filler and half of the dosage of S-100, and all of the propylene glycol methyl ether acetate into the reaction vessel in sequence, stir at a speed of 500 - 700 r / min for 5 min, and grind the obtained mixture at a speed of 1500 - 2000 r / min until the fineness of the material is dispersed to below 10 μm to obtain a mixture;

[0107] Add amino resin to the mixture obtained in the reaction vessel and stir at a speed of 500 - 700 r / min for 5 min; then add other additives and continue to stir at a speed of 500 - 700 r / min for 5 min. Add the remaining solvent and adjust the viscosity of the resulting mixture so that when measured with a Coat-4 cup viscometer, the viscosity value is in the range of 100 - 120 s, thus obtaining the high coating rate coil backside coating 3.

[0108] The performance testing method of the high coating rate coil backside coating 3 includes the following steps:

[0109] Coating and plate making: The obtained back coating 3 of the high coating rate coil is roll-coated on the existing chromium-free primer galvanized plate with a wire bar roller, and baked in an oven at 320 °C for 30 s. The metal plate temperature PMT is 224 - 232 °C, and a paint film 3 with a film thickness of 5 μm is obtained.

[0110] The performance of the paint film 3 is detected, and the detection results are shown in Table 8.

[0111] Example 4: Back coating 4 of the high coating rate coil

[0112] Prepare the back coating 4 of the high coating rate coil of the present invention according to the formula in Table 4 below:

[0113] Table 4 Raw material weight parts of Example 4

[0114]

[0115] The preparation of the back coating 4 of the high coating rate coil includes the following steps:

[0116] In a reaction vessel, polyester resin, dispersant, pigment, filler, and half of the amount of S-100 and all of the propylene glycol methyl ether acetate are added in sequence, stirred at a speed of 500 - 700 r / min for 5 min, and the obtained mixture is ground at a speed of 1500 - 2000 r / min until the fineness of the material is dispersed to less than 10 μm to obtain a mixture;

[0117] Add amino resin to the mixture obtained in the reaction vessel, stir at a speed of 500 - 700 r / min for 5 min; then add other additives, continue to stir at a speed of 500 - 700 r / min for 5 min, add the remaining solvent, and adjust the viscosity of the obtained mixture with the solvent so that when measured with a coating - 4 cup viscometer, the viscosity value is in the range of 100 - 120 s, thus obtaining the back coating 4 of the high coating rate coil.

[0118] The performance detection method of the back coating 4 of the high coating rate coil includes the following steps:

[0119] Coating and plate making: The obtained back coating 4 of the high coating rate coil is directly roll-coated on the galvanized plate with a wire bar roller, and baked in an oven at 320 °C for 30 s. The metal plate temperature PMT is 224 - 232 °C, and a paint film 4 with a film thickness of 5 μm is obtained.

[0120] The performance of the paint film 4 is detected, and the detection results are shown in Table 8.

[0121] Comparative Example 1: Coating 1 as a comparative example

[0122] Prepare Coating 1 of the present invention as a comparative example according to the formulation in Table 5 below. Its preparation method, steps, detection method and steps are the same as those in Example 1:

[0123] Table 5 Parts by weight of raw materials for Comparative Example 1

[0124]

[0125] It should be noted that in this comparative example, the polyester resin used is the resin with model 3754H provided by Sanmu Company, and its solid content is 60%. The too low solid content of the polyester resin results in a low coating rate and high VOC emissions during the baking process.

[0126] Comparative Example 2: Coating 2 as a comparative example

[0127] Prepare Coating 2 of the present invention as a comparative example according to the formulation in Table 6 below. Its preparation method, steps, detection method and steps are the same as those in Example 1:

[0128] Table 6 Parts by weight of raw materials for Comparative Example 2

[0129]

[0130]

[0131] It should be noted that in this comparative example, the polyester resin used is the resin with model NL301-75 provided by Shanghai Kangming Chemical Industry. Its hydroxyl value is 60 mg KOH / g. The too small hydroxyl value results in poor solvent resistance of the paint film and insufficient foaming bonding strength.

[0132] Comparative Example 3: Coating 3 as a comparative example

[0133] Prepare Coating 3 of the present invention as a comparative example according to the formulation in Table 7 below:

[0134] Table 7 Parts by weight of raw materials for Comparative Example 3

[0135]

[0136] It should be noted that in this comparative example, the amino resin CYMEL 303 is not a high-imino-containing amino resin. Although the amino resin CYMEL 303 can ensure the processability, solvent resistance and other properties of the paint film, the obtained paint film has poor foaming bonding performance.

[0137] Test results

[0138] Detection method and detection standard

[0139] 1. Detection method

[0140] The coating composition is directly cured (single coat) or combined with a chromium-free primer (double coat), and then cured by high-temperature baking to form the corresponding coating of the coating composition, and the coating performance is tested.

[0141] 2. Detection Standards

[0142] Unless otherwise stated, the following examples are all tested according to the national standard GB / T 13448-2006, and the results meet the requirements of the national standard GB / T 13448-2006. Specifically:

[0143] (1) The requirements for the MEK rubbing test are carried out according to the specimen preparation, test environment, and test procedures specified in 10.2 of GB / T 13448-2006. That is, by the manual method, wrap the index finger with a cotton gauze and immerse it in the MEK solution, and rub it 100 times on the sample plate with an arm force of about 10 N, and then compare it with the unrubbed part. There should be no visible color difference and coating damage on the part of the coating surface wiped by the organic solution MEK. The specific test method can refer to the enterprise standard Q / HR 0502008-2009 of Haier Group.

[0144] (2) The detection method of the foaming adhesion test is required to be carried out according to the specimen preparation, test environment, and test procedures specified for the flexible materials in the T peel strength test method for adhesives in GB / T 2791-1995. Apply the two-component polyurethane adhesive evenly on the entire width of the bonding part surface of each reference color plate and the tested color plate sample, with the coating length of 155 mm, and then conduct the adhesion test piece. Use the recording device of the tensile machine to record the peel load curve and evaluate the percentage of the cohesive failure area.

[0145] (3) The detection method of volatile organic compounds (VOC) requires the determination of the content of organic compounds (VOC) according to GB 30981-2020.

[0146] The tests are carried out according to GB / T 13448-2006 and the above detection standards, and the coating performance test results of Examples 1-4 and Comparative Examples 1-3 shown in Table 8 are obtained.

[0147] Table 8 Coating Performance Test Results of the Above Examples and Comparative Examples

[0148]

[0149] The test results in Table 8 show that:

[0150] (1) The high coating rate coil back coating composition of the present invention has a high coating rate, low VOC emissions during baking, and the cured coating can firmly combine with the pre-coated board, with good interlayer adhesion and high hardness, fully meeting the protective function of the back paint. In addition, the coating also has excellent processing performance and foaming bonding performance.

[0151] (2) The low solid content of the polyester resin selected in Comparative Example 1 results in a low coating rate and high VOC emissions during crosslinking curing, failing to meet environmental protection standards.

[0152] (3) The hydroxyl value of the polyester resin used in Comparative Example 2 is on the low side, with insufficient reactivity. Therefore, the back paint coating obtained based on this resin fails to meet the requirements in terms of solvent resistance and foaming bonding performance.

[0153] (4) The type of amino resin selected in Comparative Example 3 is not a high-imine-containing amino resin, with insufficient active groups, and the foaming bonding performance fails to meet the requirements.

[0154] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation modes of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all implementation modes here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A high coating rate coil backside coating composition, characterized in that, by mass percentage, its components include: Film-forming resin, selected from polyester resin, with a content of 30-80%; Solvent; Among them, the number average molecular weight Mn of the polyester resin is 2000-3000, the hydroxyl value is 100-120mg KOH / g, the acid value is 3-5mg KOH / g, the Tg is 10-30°C, and the solid content is ≥75wt%.

2. The high coating rate coil backside coating composition according to claim 1, characterized in that, the viscosity of the polyester resin is 3000-7000mPa.s; Preferably, the polyester resin contains active end group functional groups.

3. The high coating rate coil backside coating composition according to claim 1, characterized in that, the amino resin is selected from one or a mixture of methylated melamine resin or butylated melamine resin; and, the amino resin contains imino groups.

4. The high coating rate coil backside coating composition according to any one of claims 1-3, characterized in that, the mass ratio of the polyester resin to the amino resin is (3-6):

1.

5. The high coating rate coil backside coating composition according to claim 1, characterized in that, the additives also include one or several of adhesion promoters, dispersants, catalysts, defoamers and leveling agents; Preferably, by mass percentage, the high coating rate coil backside coating composition contains:

6. A high coating rate coil backside coating, characterized in that, it is prepared from the high coating rate coil backside coating composition according to any one of claims 1-5.

7. The preparation method of the high coating rate coil backside coating according to claim 6, characterized in that, comprises the following steps: Mix the polyester resin, part of the additives, pigments, fillers and part of the solvent, and grind them until the fineness of the materials is dispersed to less than 10μm to obtain a mixture; Add the amino resin to the mixture, mix well, then add the remaining additives, mix well, and then add the remaining solvent, and adjust the viscosity to obtain the high coating rate coil backside coating.

8. A structure, characterized in that, comprises a substrate and a coating bonded to the surface of the substrate; Among them, the coating is obtained by coating with the high coating rate coil backside coating according to claim 6.

9. The structure according to claim 8, characterized in that, the substrate is selected from coils; Preferably, the substrate is selected from pre-coated sheet coils.

10. The structure according to claim 8, characterized in that, the coating method comprises the following steps: Roll coat the high coating rate coil backside coating on the substrate, and bake it in an oven at 320°C for 30s, wherein the substrate metal plate temperature PMT: 224-232°C, to form a paint film, thus obtaining the coating; Preferably, a chromium-free primer is provided or not provided on the substrate.

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