A low-VOC baking paint and its preparation method

Abstract

The present invention discloses a low-VOC baking paint. By weight, its raw materials include the following components: 42-55 parts of acrylic resin, 12-18 parts of crosslinking resin, 1-2 parts of dispersion aid, 20-35 parts of pigment, 0.2-0.4 parts of catalyst, 7-9 parts of solvent A and 1-2 parts of solvent B. This paint features high solid content, low viscosity, and low VOC. The VOC emission during construction can be reduced to 430 g / L, which is 30% or more lower than that of common baking paints currently on the market. Meanwhile, it is applicable to various substrates, with less diluent consumption and low viscosity during the spraying process, and has relatively low requirements for VOC treatment of coating equipment, showing good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of baking coatings. More specifically, it relates to a low-VOC baking coating and a preparation method thereof. Background Art

[0002] Volatile organic compounds, abbreviated as VOC (Volatile Organic Compounds), are usually used as solvents for coatings in daily industrial production. After use, they are emitted into the atmosphere, causing great impact on the environment. With the development of the times, the environmental problems brought about by industrial production have become increasingly prominent. Therefore, the VOC emissions during the coating construction process have attracted more and more attention. The lower the VOC content during the coating construction process, the lower the emissions will be, and the smaller the impact on the environment.

[0003] At present, the baking coatings used in the market have great deficiencies in terms of VOC during construction:

[0004] 1. The VOC content is generally relatively high (most are > 500 g / L), and when spraying, the usage amount (dilution ratio) of the diluent is relatively high (≥ 30%), and this emission has a greater impact on the environment;

[0005] 2. The current VOC treatment equipment of coating enterprises cannot reach the VOC emissions of the coatings currently on the market. If the VOC treatment capacity of the equipment needs to be improved, it is necessary to upgrade and replace in terms of technology and equipment, which requires a large amount of expense. This will be a great burden for coating enterprises.

[0006] Therefore, it is an urgent requirement for coating enterprises to develop a low-VOC baking coating with a significantly reduced VOC content, low requirements for upgrading and transforming the VOC treatment equipment of coating enterprises, and high performance in terms of various properties of the product. Summary of the Invention

[0007] An object of the present invention is to provide a low-VOC baking coating. The main resin acrylic resin in this coating is a special molecular structure, high-solid content, low-viscosity thermosetting resin. Under the action of a solvent with high solubility and a crosslinking assistant, while ensuring the use performance of the coating, high solid content, low viscosity and low VOC are achieved.

[0008] Another object of the present invention is to provide a preparation method of a low-VOC baking coating.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a low-VOC baking paint, and in terms of parts by weight, the raw materials thereof include the following components:

[0011]

[0012] Optionally, the viscosity of the acrylic resin is less than 1500 Mpa·s, the solid content is 66-70%, the number-average molecular weight is 8000-9000, the acid value is <11, and the hydroxyl value is 55-65 mgKOH / g.

[0013] Optionally, the crosslinking resin is a butyl etherified resin.

[0014] Further, the crosslinking resin is a n-butyl etherified melamine formaldehyde resin or a mixed etherified melamine formaldehyde resin.

[0015] Optionally, the catalyst is selected from p-toluenesulfonic acid or dodecylnaphthalenesulfonic acid.

[0016] Optionally, the solvent A includes methyl isobutyl ketone and propylene glycol monomethyl ether acetate; the solvent B is n-butanol.

[0017] Further, the 8-10 parts of the solvent A includes 4-5 parts of methyl isobutyl ketone and 3-4 parts of propylene glycol monomethyl ether acetate.

[0018] Optionally, the viscosity value of the low-VOC baking paint measured by a Stormer viscometer is 65-70 KU / 20 °C.

[0019] Optionally, the amount of diluent used during spraying of the low-VOC baking paint is 10-15 wt% of the low-VOC baking paint.

[0020] Optionally, the solid content of the low-VOC baking paint is ≥70%

[0021] In a second aspect, the present invention provides a preparation method of a low-VOC baking paint, and the preparation process includes:

[0022] S1: Mix 42-55 parts of acrylic resin, 1-2 parts of dispersion aid, and 4-5 parts of solvent A, and stir at 400-600 rpm for 10-15 min; add 20-35 parts of pigment filler under stirring, and stir at 400-600 rpm for 10-15 min;

[0023] S2: Add 3-4 parts of solvent A under stirring, and continue to stir until uniform; then grind and disperse to a suitable fineness;

[0024] S3: Then add 12-18 parts of crosslinking resin and 0.2-0.4 parts of catalyst, and stir at 400-600 rpm for 10 min;

[0025] S4: Add 1 - 2 parts by weight of Solvent B and stir evenly to obtain the product.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention provides a low - VOC baking paint, which comprises an acrylic resin with special molecular treatment, high solid content and low viscosity properties, a solvent with strong dissolving power, and a cross - linking resin with a lower cross - linking temperature. This paint has the characteristics of high solid content, low viscosity and low VOC. Its VOC emission can be reduced to 430 g / L, which is 30% or more lower than that of the commonly used baking paints on the current market. At the same time, this baking paint has excellent compatibility with primers such as epoxy primer and electrophoretic primer, good applicability to substrates such as iron, aluminum and stainless steel, and all physical and chemical properties of the paint film are not lower than those of the current baking paint products on the market; it has relatively low requirements for VOC treatment of coating equipment and can be used without large - scale transformation of the equipment; and the amount of thinner used during spraying can be reduced to 10 - 15 wt%, without affecting the spraying viscosity and effect. Specific Embodiments

[0028] To make the technical solutions and advantages of the present invention clearer, the following will explain them in combination with specific embodiments and examples. 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.

[0029] It should be noted that except for special instructions, other reagents used in the present invention can be obtained through commercial channels.

[0030] One possible implementation is that a low - VOC baking paint, by weight, its raw materials contain the following components:

[0031]

[0032] The content of the main resin, acrylic resin, in the low - VOC baking paint provided by the present invention is very high. In a preferred embodiment, the acrylic resin is an acrylic resin with a special molecular structure, high solid content and low viscosity. The physical properties of the acrylic resin used include: viscosity lower than 1500 Mpa.s, solid content of 66 - 70%, number - average molecular weight of 8000 - 9000, acid value < 11, and hydroxyl value of 55 - 65 mgKOH / g. The special molecular structure design of the acrylic resin, combined with a solvent with strong dissolving power and a cross - linking resin with a lower cross - linking temperature, can obtain a paint with high solid content and low viscosity, so as to reduce the VOC content introduced due to the resin in the paint.

[0033] One possible implementation is that the cross-linked resin is a butyl etherified resin, more preferably a n-butyl etherified melamine formaldehyde resin or a mixed etherified melamine formaldehyde resin. In the specific application process, the butyl etherified resin can be directly purchased commercially. For example, the n-butyl etherified melamine formaldehyde resin with the model number NP 001RAM325 produced by Youke can be selected, or the low-viscosity mixed etherified melamine formaldehyde resin, such as the CYMEL1130 produced by Changxin Resin, can be selected.

[0034] The catalyst affects the reaction rate and degree and directly affects the cross-linking density, and can also affect other properties such as hardness, impact resistance, and adhesion after the paint forms a film. One possible implementation is that the catalyst is selected from p-toluenesulfonic acid or dodecylnaphthalenesulfonic acid. The catalyst can be directly purchased commercially. For example, it can be selected from the p-toluenesulfonic acid with the model number NACURE produced by King Industries and the dodecylnaphthalenesulfonic acid with the model number CAT6000 produced by Nanjing Shengda Chemical Industry. Further, the 7-9 parts of solvent A includes 4-5 parts of methyl isobutyl ketone and 3-4 parts of propylene glycol methyl ether acetate.

[0035] The dissolving power of the solvent has an important influence on the solid content, viscosity in the paint, and the amount of diluent added during use. In combination with the characteristics of the main resin, acrylic resin, in a preferred implementation of the present invention, solvent A obtained by mixing methyl isobutyl ketone and propylene glycol methyl ether acetate and solvent B containing n-butanol are selected. Solvent A has good solubility for the main resin and pigments and fillers. Under the action of the dispersing aid, the main resin and pigments and fillers can be evenly dispersed in the solvent, and then, under the action of the catalyst, fully cross-link with the cross-linked resin to obtain a paint with low viscosity and a stable dispersion system. Finally, adding solvent B can make the formed paint system stably dispersed in solvent B to obtain a paint with appropriate viscosity. At the same time, the above solvents have little impact on the environment when meeting the dissolving power, reduce the increase in VOC caused by adding solvents in the formula, and reduce the amount of diluent added during the later painting of the paint, further reducing VOC.

[0036] While achieving high solid content and low VOC, it is also necessary to ensure the low viscosity of the paint. In the present invention, the viscosity value of the low-VOC baking paint measured by a Stormer viscometer is 65-70 KU / 20 °C. In a preferred implementation, the solid content of the low-VOC baking paint is ≥70%.

[0037] The high solid content and low viscosity enable the low-VOC baking paint in the present invention to be applicable to the existing painting equipment of paint coating manufacturers. Without major modifications to the VOC emission treatment device of the coating manufacturers, the VOC emission meets the environmental protection emission requirements, reducing the pressure on the enterprise's investment in VOC.

[0038] One possible implementation is that the amount of diluent required for the low-VOC baking paint during spraying is 10-15 wt% of the low-VOC baking paint. During the spraying process of the paint, a diluent containing organic solvents needs to be added to ensure the leveling and anti-sagging properties of the paint film. The low-VOC baking paint in the present invention has a low viscosity while maintaining a high solid content. Therefore, during the spraying process, a large amount of diluent does not need to be used to reduce the viscosity, further reducing the VOC.

[0039] One possible implementation is the preparation method of the above-mentioned low-VOC baking paint, and the preparation process includes:

[0040] S1: Mix 42-55 parts of acrylic resin, 1-2 parts of dispersing aid, and 4-5 parts of solvent A, and stir at 400-600 rpm for 10-15 min; add 20-35 parts of pigment and filler under stirring, and stir at 400-600 rpm for 10-15 min;

[0041] S2: Add 3-4 parts of solvent A under stirring, and continue to stir until homogeneous; then grind and disperse to a suitable fineness;

[0042] S3: Then add 12-18 parts of crosslinking resin and 0.2-0.4 part of catalyst, and stir at 400-600 rpm for 10 min;

[0043] S4: Add 1-2 parts of solvent B, stir evenly, and obtain.

[0044] In the specific implementation process, first dissolve the relevant raw materials with part of solvent A, then add the remaining solvent A to obtain a uniformly distributed main resin dispersion, then add the crosslinking resin, and obtain the paint under the action of the catalyst. Add solvent B to obtain a paint with a specific viscosity.

[0045] The above technical solutions will be described below in conjunction with specific embodiments.

[0046] Embodiment

[0047] Example 1

[0048] A white low-VOC baking paint, 100 kg of the paint is prepared according to the following method, and its specific formula is shown in Table 1:

[0049] S1: Add 43.6 kg of acrylic resin, 4.7 kg of solvent A, and 1.1 kg of dispersing aid into a container of appropriate size, and stir (400-600 rpm) for 10-15 minutes; add 33.2 kg of titanium white pigment under stirring, and stir (400-600 rpm) for 10-15 minutes;

[0050] S2: Add 3 kg of Solvent A under stirring, and continue stirring for 30 min until homogeneous; then start grinding and dispersing on a specified sand mill until the fineness meets the requirements;

[0051] S3: Add 12.3 kg of crosslinking resin and 0.2 kg of catalyst, and stir at 400 - 600 rpm for 10 min;

[0052] S4: Add 1.9 kg of Solvent B to adjust its viscosity to 67 - 70 KU / 20 °C (Stormer viscometer), thus obtaining the product.

[0053] Examples 2 - 4

[0054] The preparation method of the low - VOC baking paint in Examples 2 - 4 is exactly the same as that in Example 1, except that the weights of the added substances are changed. For details, please refer to Table 1 and Table 2.

[0055] Table 1 Components of the low - VOC baking paint in Examples 1 - 4

[0056]

[0057] Table 2 Components of the low - VOC baking paint in Example 5

[0058]

[0059]

[0060] Test Examples

[0061] Test Example 1

[0062] Apply the paints in Examples 1 - 5 for painting construction, specifically as follows:

[0063] 1) After degreasing, cleaning, and phosphating the steel plate, apply electrophoretic primer and dry at 140 °C, then cool for preparation;

[0064] 2) Spray the low - VOC baking paint and dry at 140 °C;

[0065] 3) Cool the workpiece to complete the painting.

[0066] Conduct performance tests on the paint films formed by painting, and the obtained results are shown in Table 3.

[0067] Table 3 Properties of the paint films of the low - VOC baking paint on steel plates in Examples 1 - 4

[0068]

[0069] The results in Table 3 show that the acrylic resin with a special molecular structure design provided in the present invention is dissolved in a solvent with high dissolving power, and can undergo a good cross-linking reaction with butyl etherified cross-linking resin and mixed etherified cross-linking resin with relatively low cross-linking temperature at 140-160°C, and all performance indicators of the formed paint film can reach high standards. At the same time, this paint has a low VOC, and on the premise that the equipment does not require major modifications, the VOC emissions can meet the environmental protection emission standards.

[0070] Test Example 2

[0071] The white low-VOC baking paint prepared in Example 1 was applied to iron, aluminum, and stainless steel substrates, and its performance was tested. The substrates were cleaned, degreased, and surface-treated, and then sprayed. The test results are shown in Table 4.

[0072] Table 4 Film properties of the white low-VOC baking paint in Example 1 when applied to iron, aluminum, and stainless steel

[0073]

[0074] The results in Table 4 show that the low-VOC baking paint provided by the present invention has good wettability and leveling property for various metal substrates with different surface tensions, and the formed paint film has a good appearance effect; moreover, in the process of forming the paint film, the acrylic resin with a special molecular structure design in the low-VOC baking paint can form an excellent connection effect with the surfaces of metal substrates such as iron, aluminum, and stainless steel through cross-linking-generated functional groups, further improving the performance of the paint film.

[0075] Test Example 3

[0076] Phosphatized SPCC board was selected as the material, and the white low-VOC baking paint prepared in Example 1 was paired with the room-temperature curing epoxy primer ORGA SELECT 30NC primer P-3 produced by Nippon Paint to make a board. The specific board-making conditions are as shown in Table 5.

[0077] Table 5 Board-making conditions for Test Example 3

[0078] Coating Name Film Thickness PMT Coating Method ORGA SELECT 30NC Primer P-3 (Nippon Paint) 10 - 15μm 140°C for 20 minutes Spraying Low VOC White Baking Coating 30 - 35μm 140°C for 20 minutes Spraying

[0079] Test Example 4

[0080] Phosphatized SPCC board was selected as the material, and the white low-VOC baking paint prepared in Example 1 was paired with the baking epoxy primer NIPPE POWERBIND all-purpose primer produced by Nippon Paint to make a board. The specific board-making conditions are as shown in Table 6.

[0081] Table 6 Board-making conditions for Test Example 4

[0082]

[0083] Test the products obtained in Test Examples 3 and 4, and the obtained results are shown in Table 7.

[0084] Table 7 Product Performance Results of Test Examples 3 and 4

[0085]

[0086] The results in Table 7 show that the low-VOC baking-type coating provided by the present invention can form excellent interlayer compatibility with both room-temperature curing epoxy primer and baking-type epoxy primer, and the obtained products can all meet the requirements.

[0087] Comparative Example

[0088] Comparative Example 1

[0089] Compared with Example 1, the acrylic resin in Comparative Example 1 is different. The acrylic resin used in Comparative Example 1 has a viscosity of 1100 - 13000 Mpa·s and a solid content of 48 - 51%. The viscosity is close to that of the acrylic resin in Example 1, and the solid content is 20% lower.

[0090] Table 8 Components of the Baking-Type Coating in Comparative Example 1

[0091]

[0092]

[0093] Comparative Example 2

[0094] Compared with Example 1, Solvent A in Comparative Example 2 is S-100 solvent.

[0095] Table 9 Components of the Baking-Type Coating in Comparative Example 2

[0096] Material Type Material Name Manufacturer Name Comparative Example 2 Acrylic Resin Acrylic Resin Youke 43.6 kg Crosslinking Resin n-Butyl Etherified Melamine Formaldehyde Resin Youke 12.3 kg Dispersing Aid Wetting Dispersant BYK-Chemie 1.1 kg Pigment Titanium White Pigment DUPONT 33.2 kg Catalyst p-Toluenesulfonic Acid King Industries 0.2 kg Solvent A S-100 Solvent Hualun Chemical 7.7 kg Solvent B Isobutanol Dow Chemical 1.9 kg

[0097] Comparative Example 3

[0098] Prepare a white baking-type coating containing other acrylic resins. The preparation process of 100 kg of this coating is as follows:

[0099] S1: Put 42.2 kg of acrylic resin (DIC WEG-581), 5.13 kg of solvent (S-100 solvent oil), 1.49 kg of solvent (n-butanol), and 0.8 kg of dispersion aid into a container of appropriate size, stir (400 - 600 rpm) for 10 - 15 minutes; while stirring, add 33.2 kg of titanium white pigment, and after adding the pigment, stir (400 - 600 rpm) for 10 - 15 minutes;

[0100] S2: While stirring, add 0.81 kg of solvent (methyl isobutyl ketone), 0.81 kg of solvent (S-100 solvent oil), and 0.85 kg of solvent (n-butanol) along the container wall, and continue stirring for 30 minutes until homogeneous; start grinding and dispersing on a specified sand mill until the fineness meets the requirements;

[0101] S3: Add 12.06 kg of butylated amino resin (Changchun Chemical BR 20SE), and stir (400 - 600 rpm) for 10 minutes;

[0102] S4: Use 3.43 kg of solvent (S-100 solvent oil) to adjust the product viscosity value to 70 KU / 20 °C (Stormer viscometer), and the finished product is thus obtained.

[0103] Comparative Example 4

[0104] Prepare a white baking paint containing polyester resin. The preparation process of 100 kg of this paint is as follows:

[0105] S1: Put 45.18 kg of polyester resin (R-4304 produced by Nippon), 4.25 kg of solvent (isobutanol), 2.13 kg of solvent (DBE), 0.53 kg of solvent (n-butanol), and 0.53 kg of dispersion aid into a container of appropriate size, and stir (400 - 600 rpm) for 10 - 15 minutes; while stirring, add 33.2 kg of titanium white pigment, and after adding the pigment, stir (400 - 600 rpm) for 10 - 15 minutes;

[0106] S2: While stirring, add 0.53 kg of solvent (S-100 solvent oil) and 0.53 kg of solvent (n-butanol) along the container wall, and continue stirring for 30 minutes until homogeneous; start grinding and dispersing on a specified sand mill until the fineness meets the requirements;

[0107] S3: Add 12.45 kg of butylated amino resin (Changchun Chemical BR 20SE), and stir (400 - 600 rpm) for 10 minutes; add 0.2 kg of acid catalyst during stirring (400 - 600 rpm), and after adding, stir (400 - 600 rpm) for 10 minutes;

[0108] S4: Use 0.47 kg of solvent (S-100 solvent oil) to adjust the product viscosity value to 70 KU / 20 °C (Stormer viscometer), and the finished product is thus obtained.

[0109] Conduct performance tests on the baking paints obtained in Comparative Examples 1 - 4, and the results are shown in Table 10.

[0110] Table 10 Performance of the baking paints in Example 1 and Comparative Examples 1 - 4

[0111]

[0112]

[0113] The above results show that:

[0114] 1) At the same viscosity, the specific gravities of the products of the comparative examples are close. The solid content of Example 1 is significantly higher than that of Comparative Examples 1-4, which means that the VOC content of Example 1 is lower than that of Comparative Examples 1-4;

[0115] 2) When the original paint has the same viscosity and is diluted with the same thinner to the same construction viscosity, the amount of thinner used in Example 1 is 50% of that in Comparative Examples 2, 3, and 4, and is lower than that in Comparative Example 1. During the construction process, the VOC emissions added later will be further reduced;

[0116] 3) For Example 1, which uses a high-solid, low-viscosity acrylic resin with a special molecular structure design, the gloss of the product is higher than that of Comparative Example 1 and 3 using conventional baking acrylic resins and Comparative Example 4 using conventional baking polyester coatings.

[0117] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A low-VOC baking-type coating, characterized in that, by weight, it is composed of the following raw materials: The viscosity of the acrylic resin is less than 1500 Mpa.s, the solid content is 66-70%, the number-average molecular weight is 8000-9000, the acid value < 11, and the hydroxyl value is 55-65 mg KOH / g; The cross-linking resin is selected from n-butyl etherified melamine formaldehyde resin or mixed etherified melamine formaldehyde resin; The solvent A is methyl isobutyl ketone and propylene glycol methyl ether acetate; the solvent B is n-butanol; Among the 7-9 parts of solvent A, it includes 4-5 parts of methyl isobutyl ketone and 3-4 parts of propylene glycol methyl ether acetate; The low-VOC baking-type coating is prepared according to the following steps: S1: Mix 42-55 parts of acrylic resin, 1-2 parts of dispersing aid, and 4-5 parts of solvent A, and stir at 400-600 rpm for 10-15 min; add 20-35 parts of pigment under stirring, and stir at 400-600 rpm for 10-15 min; S2: Add 3-4 parts of solvent A under stirring, and continue to stir until uniform; then grind and disperse to a suitable fineness; S3: Then add 12-18 parts of cross-linking resin and 0.2-0.4 part of catalyst, and stir at 400-600 rpm for 10 min; S4: Add 1-2 parts of solvent B, and stir evenly to obtain.

2. The low-VOC baking-type coating according to claim 1, characterized in that, The catalyst is selected from p-toluenesulfonic acid or dodecylnaphthalenesulfonic acid.

3. The low-VOC baking-type coating according to claim 1, characterized in that, The viscosity value of the low-VOC baking-type coating measured by a Stormer viscometer is 65-70 KU / 20 °C.

4. The low-VOC baking-type coating according to claim 1, characterized in that, The solid content of the low-VOC baking-type coating ≥ 70%.

5. The low-VOC baking-type coating according to claim 1, characterized in that, The amount of diluent used when the low-VOC baking-type coating is sprayed is 10-15 wt% of the low-VOC baking-type coating.

6. A preparation method of a low-VOC baking-type coating according to any one of claims 1-5, characterized in that, The preparation process includes: S1: Mix 42-55 parts of acrylic resin, 1-2 parts of dispersing aid, and 4-5 parts of solvent A, and stir at 400-600 rpm for 10-15 min; add 20-35 parts of pigment under stirring, and stir at 400-600 rpm for 10-15 min; S2: Add 3-4 parts of solvent A under stirring, and continue to stir until uniform; then grind and disperse to a suitable fineness; S3: Then add 12-18 parts of cross-linking resin and 0.2-0.4 part of catalyst, and stir at 400-600 rpm for 10 min; S4: Add 1-2 parts of solvent B, and stir evenly to obtain.

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