Water-based coating paint for PP (polypropylene) base material and preparation method of water-based coating paint

Abstract

A formula of the water-based PP coating comprises the following components in parts by weight: 20-70 parts of anionic polyurethane acrylic resin; 1-3 parts of an initiator; 3-10 parts of a bifunctional monomer; 3-8 parts of a solvent; 0.2-1 part of a neutralizer; 40 to 60 parts of water; and 0.02 to 0.08 part of a leveling agent. The water-based PP film coating paint has excellent adhesion to a PP base material, meets the environmental protection requirement, and has good chemical resistance and water resistance. The invention also provides a preparation method of the water-based PP film coating paint.

Description

Technical Field

[0001] The invention relates to the field of ultraviolet (UV) curing coatings, in particular to coatings used for vacuum coatings, and more specifically to water-based primer coatings used for vacuum coatings. Background Art

[0003] Plastic products are widely used in many fields, such as lamp parts, automobile decorative parts, cosmetic boxes, toys and daily commodities. In order to improve the surface decoration of plastic products and present a metallic effect, vacuum coating is usually used to form a metal film on the surface of the plastic substrate. However, the vacuum-plated metal film must be matched with a primer (primer) and a topcoat (topcoat). The primer is located between the metal film layer and the plastic substrate to improve the adhesion of the coating.

[0004] Polypropylene (PP) is a commonly used substrate. However, since it is a non-polar material, the coating used for PP substrate must have good adhesion, which is also one of the technical difficulties in the industry. In order to improve the adhesion of coatings on PP substrates, the industry has proposed a variety of solutions, such as coating adhesion promoters on the surface of PP substrates, or using some means (such as plasma) to treat the surface of PP substrates. Although these solutions have some effects, they increase the operating procedures and costs.

[0005] Some technologies have also proposed improvements to coatings, for example, improving PVD primers to meet the adhesion requirements for PP substrates. However, the current technical system is an oily system. Although there are no obvious deficiencies in terms of technology and performance, the biggest disadvantage is that the VOC is too high and does not meet green environmental protection requirements.

[0006] In summary, for the coating system used for PP substrates, it is expected that a water-based system can replace the existing oil-based system to reduce VOC content and meet environmental protection requirements. However, the current water-based primer system requires the use of emulsifiers, has poor adhesion to PP substrates, and has poor chemical resistance and water resistance. Summary of the invention

[0007] The present invention aims to solve the above problems of the prior art and provides a water-based PP coating, the formula of which comprises, by weight:

[0008]

[0009]

[0010] The present invention proposes to use anionic polyurethane acrylic resin in water-based PP coating, whose molecular structure carries an electric charge and has a self-emulsification effect, so the coating of the present invention does not contain an emulsifier component. Therefore, the water-based PP coating of the present invention abandons the use of emulsifiers and eliminates the decrease in adhesion caused by the use of emulsifiers. At the same time, the coating of the present invention has good adhesion to the PP substrate and is a water-based coating. Compared with the existing oily PP substrate coating, the water-based PP coating of the present invention has great environmental significance.

[0011] The amount of anionic polyurethane acrylic resin added cannot be too much, otherwise the emulsion will be too sticky. In addition, since the resin contains a large number of ester bonds and is a hydrophilic group, excessive use of anionic polyurethane acrylic resin will lead to poor water resistance, easy hydrolysis, and poor storage stability of the coating. Anionic polyurethane acrylic resin is the main component of the system, providing adhesion and required resistance. Too little use will result in insufficient adhesion, low viscosity, poor film-forming properties, and low hiding power.

[0012] The addition of difunctional monomers is to adjust the viscosity and wettability of the emulsion system. It has low skin irritation, low shrinkage, high activity, strong dilution ability, fast photocuring rate and low price. However, if it is added in excess, the wetting of the coating will be poor, and it will also cause problems with resistance such as water resistance and poor storage stability. The preferred difunctional monomer is hexanediol diacrylate.

[0013] Preferably, the water-based PP coating coating of the present invention comprises, by weight, the following formula:

[0014]

[0015] The preferred solvent of the present invention is a mixed solvent of propylene glycol methyl ether and propylene glycol methyl ether acetate.

[0016] The solvent, neutralizer, leveling agent and initiator of the present invention can be selected from commonly used solvents, neutralizers, leveling agents and initiators known to those skilled in the art, and are not limited to the specific examples given in the embodiments herein.

[0017] The preparation method of the water-based PP coating coating according to the present invention comprises: adding anionic polyurethane acrylic resin, initiator, difunctional monomer and solvent into a container, mixing and heating for 15-20 minutes, stirring, adding neutralizer and leveling agent according to the neutralization degree requirement, stirring, adding water until the viscosity becomes maximum, adding water while stirring with a glass rod, and then slowly adding water, emulsifying with an emulsifier, and slowly adding water while emulsifying.

[0018] The technical effects obtained by the present invention are:

[0019] 1. The water-based PP coating coating of the present invention is a water-based system. Compared with the oil-based coating commonly used for PP substrates in the current industry, the coating of the present invention is more environmentally friendly and meets the current trend of the coating industry to expect more environmental protection.

[0020] 2. The water-based PP coating of the present invention has good adhesion to the PP substrate, which is a technical effect that the current water-based coatings in the industry have not yet achieved. DETAILED DESCRIPTION

[0021] [Preparation method]

[0022] 20 parts by weight of anionic polyurethane acrylic resin (hexafunctional polyurethane acrylic resin), 2 parts by weight of initiator (initiator 184), 6 parts by weight of difunctional monomer (hexanediol diacrylate), 4 parts by weight of propylene glycol methyl ether, and 2 parts by weight of propylene glycol methyl ether acetate are added into a container, mixed and heated for 15-20 minutes, stirred, and a neutralizer (triethylamine) and a leveling agent (acrylic resin) are added according to the neutralization degree requirements, stirred, and water is added until the viscosity reaches the maximum, and water is added while stirring with a glass rod, and then water is slowly added, and emulsified using an emulsifier, and water is slowly added while emulsifying, to finally prepare a water-based PP coating coating according to Example 1 of the present invention.

[0023] [Example]

[0024] According to the preparation method described above and the formulation given in Table 1, water-based PP coating primers according to Examples 1-5 of the present invention were prepared.

[0025] Table 1, Primer formulation composition according to Examples 1-5 of the present invention (parts by weight)

[0026]

[0027] [Comparative Example]

[0028] According to the preparation method described above, the water-based PP coating primers of Comparative Examples 1-5 were prepared according to the formulations given in Table 2 and Table 3. A commercially available oily PP coating (PM-5230 (PP)) was selected as Comparative Example 6.

[0029] Table 2: Comparative Examples 1-5 coating compatibility, in parts by weight

[0030]

[0031] [Test method]

[0032] 1. The appearance performance of the primer coatings of Examples 1-5 and Comparative Examples 1-6 was tested.

[0033] Test storage performance, refrigerate at 5℃, heat store at 50℃ for one week, and store at room temperature for 180 days. Visual inspection shows that there is no problem with the appearance (no precipitation, no precipitation, no stratification). After spraying and curing on the PP substrate, visual inspection shows that if there is no shrinkage hole or leakage on the PP flat film, it is OK, otherwise it is NG.

[0034] Test the pH, particle size and distribution of the coating: The pH of the coating is measured by a pH meter to determine whether the coating is acidic or alkaline. Our coating is generally alkaline. At the same time, the pH after storage can be compared. If the pH changes too much after storage, it means that the coating has deteriorated. The particle size and distribution are tested by a particle size measuring instrument. The narrower the distribution of the coating, the more evenly the coating is dispersed. Too large a particle size of the coating will lead to unstable storage and easy precipitation. It can also be compared with the particle size and distribution after storage as a basis for judging whether the coating storage is stable.

[0035] 2. Primer curing: After flame treatment of the PP substrate (PP flat plate and PP orange cover), apply the treatment agent (1-2μm, bake at 60℃ for 1min), then spray the primer (18-20μm, bake at 60℃ for 6min), and cure (800-1200mj / cm 2 energy curing).

[0036] After the primer is cured, the adhesion of the primer film is measured using the Baige method.

[0037] 3. Primer + Aluminum Plating + Topcoat: On the PP substrate (PP flat plate and PP orange cover), after flame treatment, apply the treatment agent (1-2um, 60℃ baking for 1min), then spray the primer (18-20um, 60℃ baking for 6min), and cure (800-1200mj / cm 2 Energy curing), aluminum plating, spraying topcoat (10-12um, 60 degrees Celsius baking 3min), curing (500-600mj / cm 2 energy curing).

[0038] Adhesion test (100-grid method, 3M600 tape): ISO Grade 1 and ASTM4B standards, small pieces of paint peel off along the edges of the grid or at the intersection of the knife marks, and the actual damage in the grid area is ≤5%.

[0039] Water boiling resistance: After boiling at 70℃ for 8 hours, the adhesion is measured by the hundred grid method.

[0040] 4. Wettability: After the primer is cured, measure the wettability. PP plate - flame - spray treatment agent - spray primer - cure - observe the wettability to see if there are shrinkage holes or leakage. If so, the wettability is judged to be NG.

[0041] [Test results]

[0042] The test results of the coating samples of the embodiments of the present invention are shown in Table 3, and the test results of the coating samples of the comparative examples are shown in Table 4.

[0043] Table 3. Test results of coatings of Examples 1-5

[0044]

[0045] Table 4. Test results of coatings of comparative examples 1-6

[0046]

[0047] After testing, the appearance performance of the coating samples of the embodiment of the present invention and the comparative example are both milky white opaque liquids. However, in terms of storage performance, the embodiment of the present invention is significantly better than the comparative example. Comparative examples 1-5 all had shrinkage holes and leakage after spraying, whether they were stored in cold storage, hot storage, or room temperature storage. Comparative example 6 is an oily PP primer, which has good ability to adhere to the PP substrate, and other performances such as storage performance and paint film appearance are good. Compared with the present invention, its disadvantage is that it is not environmentally friendly.

[0048] In terms of the technical problem to be solved by the present invention, the adhesion of the embodiments of the present invention is very good. Whether it is sprayed on a PP plate or a PP orange cover, the adhesion test of the primer after curing is 5B. In addition, in the case of primer + aluminum plating + topcoat, the adhesion test page is 5B after the topcoat is cured.

[0049] In comparison, among the comparative examples, only the comparative example 6 of the oily PP primer can achieve such an effect. For the other comparative examples 1-5, the adhesion of both tests (primer spraying only, primer+aluminum plating+topcoat) after curing is lower than 5B.

[0050] After being boiled in water, the adhesion of each sample was measured. The adhesion of each embodiment of the present invention was 5B, while the adhesion of comparative examples 1-5 was much lower than 5B.

[0051] From the wettability test, the samples of Examples 1-5 of the present invention had no defects, while the samples of Comparative Examples 3-5 had defects such as shrinkage cavities and bottom leakage.

[0052] Although this specification describes specific embodiments of the present invention, the present invention is not limited to the specific embodiments disclosed, and it is obvious to those skilled in the art that various changes may be made to the present invention without departing from the scope of the present invention as defined by the claims.

Claims

1. A water-based coating for a PP substrate, the formula of which, by weight, comprises: The preparation method of the water-based coating for PP substrate comprises: The anionic polyurethane acrylic resin, the initiator, the difunctional monomer and the solvent are added to a container, mixed and heated for 15-20 minutes, stirred, the neutralizer and the leveling agent are added according to the neutralization degree requirements, stirred, and water is added until the viscosity reaches the maximum, and water is added while stirring with a glass rod, and then the water is slowly added, and an emulsifier is used for emulsification, and water is slowly added while emulsifying.

2. The water-based coating for PP substrate according to claim 1, wherein the formula thereof comprises, by weight:

3. The water-based coating for PP substrate according to claim 1, wherein: The difunctional monomer is hexanediol diacrylate.

4. The water-based coating for PP substrate according to claim 1, wherein: The solvent is a mixed solvent of propylene glycol methyl ether and propylene glycol methyl ether acetate.

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