WANG Jing, GAO Lei, YU Jie
(Production Base of Marine Chemical Research Institute, Qingdao 266111, Shandong, China)
Abstract: Waterborne peelable protective coatings are temporary protective coatings for automobiles, ships, large-scale instruments and equipment during painting, transportation and storage. In this paper, we studied the peelability, the temporary protection effect and the effect on gloss and adhesion of the waterborne peelable protective coatings applied on different substrates and different coatings. The results show it can be used on various substrates with good peelability, and have little effect on the gloss, adhesion and surface state of the protected coatings.
Ships, automobiles, various large-scale precision instruments, equipment, etc. are often scratched, worn, and polluted during the process of painting, manufacturing, transportation, storage, etc., causing their surfaces to be damaged to varying degrees, causing loss or affecting life . Applying peelable protective coating on the surface of these instruments and equipment is an effective, convenient and economical method to solve this problem. This not only provides the necessary protection, but can also be removed manually when protection is not needed.
At present, the peelable protective coatings that are available on the domestic market are mainly solvent-based. Due to the dissolution of the solvent, its use on physical-drying coating films is limited, and the VOC content is high, which volatilizes into the air and causes pollution and harm to the environment. Human health and waste of resources. Therefore, the development of environmentally friendly, pollution-free water-based peelable protective coatings has great development potential and social significance.
At present, there are not many domestic literatures on water-based peelable protective coatings, and there are few products on the market that meet the requirements for use and are commercially available. Based on this, this paper experimentally screens suitable resins, pigments, fillers, additives, etc. to develop a Water-based peelable protective coating with good temporary protection and easy peeling.
1 Experimental part
1.1 Main raw materials
(1) Resin: Water-based peelable resin, domestic, industrial grade.
(2) pigments and fillers: titanium dioxide, silicon powder, etc., domestic, industrial grade.
(3) Auxiliaries: Wetting and dispersing agents, imported, industrial grade; thickeners, defoamers, etc., domestic, industrial grade.
(4) Coatings: various polyurethane topcoats, white water-based epoxy topcoats, Changsheng green chlorinated rubber topcoats, etc., Marine Chemical Research Institute Co., Ltd.
(5) Reagents: hydrochloric acid, sodium hydroxide, domestic, analytical grade.
1.2 Instrument and Equipment
Electronic Balance BS2202, Beijing Sartorius Instrument Co., Ltd .; SFJ-400 Grinding and Dispersing Multi-purpose Machine, Shanghai Modern Environment Engineering Co., Ltd .; Microcomputer Controlled Electronic Universal Testing Machine, Jinan Zhongluchang Testing Machine Manufacturing Co., Ltd .; QFH Scale , Tianjin Material Testing Machine Factory; Gloss Meter, Tianjin Xinguang Technology Development Company; Bending Tester, Guangxi Wuzhou Chemical Instrument Factory; Coating Film Impactor, Tianjin Material Testing Machine Factory.
1.3 Basic formula and preparation process of water-based peelable protective coatings
Table 1 shows the basic formula of water-based peelable protective coatings.
Preparation process: Weigh pigments, fillers and auxiliaries (except thickeners) according to the proportion, mix, add an appropriate amount of water and stir uniformly, use a grinding and dispersing machine to add grinding media to grind to ≤70 μm, and filter. The filtered color paste is added to the film-forming substance under low-speed dispersion, and the dispersion is uniform, and the thickener is used to adjust the viscosity to a proper amount, and is used for future use.
1.4 Preparation of test samples of water-based peelable protective coatings
(1) Spray solvent-based polyurethane coatings, alkyd coatings, epoxy coatings, and water-based epoxy topcoats on low-carbon steel plates polished by sandpaper to remove oil and rust, and dry for 3 weeks .
(2) Brush the water-based peelable protective coating on the coatings of polyurethane coatings, alkyd coatings, epoxy coatings, and water-based epoxy topcoats with a dry film thickness of 100 μm or more.
(3) Brush water-based peelable protective coating on the substrates such as low-carbon steel plate polished by sandpaper, degreasing and rust removal, with a dry film thickness of 100 μm or more.
1.5 Testing of basic properties of water-based peelable protective coatings
According to various national standards, the performances of coatings and coating films were tested. The results are shown in Table 2.
2 Results and discussion
2.1 Selection of water- based emulsion
In water-based peelable protective coatings, the film-forming substance is the most important component, and its performance determines the basic properties of the coating. The water-based peelable protective coating is formed on the surface of the object to form a protective film to prevent the surface of the object from being scratched, stained, discolored, powdered, etc., thereby providing temporary protection. When the protection task is completed, the protective film can be easily peeled off by hand. In order to achieve the peelability of the coating, the film-forming substance is required to have a certain elasticity and tear resistance. The current water-based elastic emulsions are mainly styrene-acrylic emulsions, polyurethane emulsions, polyvinyl alcohol and liquid rubber, etc.. In this experiment, several emulsions were selected, and brushed on dry glass and polyurethane topcoats, and their peelability was examined, as shown in Table 3.
It can be seen from Table 3 that A emulsion has good peelability on both smooth glass and polyurethane topcoats, so A emulsion was selected as the emulsion of the peelable protective coating.
2.2 Film-forming and peelability of water-based peelable protective coatings on different substrates
The emulsions screened in 2.1 were used to make water-based peelable protective coatings according to 1.3. Apply the water-based peelable protective coating on the surface of different substrates (glass, aluminum plate, carbon steel plate) and different coating films (solvent-based polyurethane coating, alkyd coating, epoxy coating, water-based coating), and dry at room temperature for 7 days Test film formation and peelability. It can be seen from Table 4 and Figure 1 that the water-based peelable protective coating can be continuously formed on the substrate and different coating film surfaces used in the experiment, and can be completely peeled off. It has excellent peelability and can meet the requirements for use.
2.3 Influence of water-based peelable protective coatings on the gloss of the protected coatings
Water-based peelable protective coatings not only need to have excellent peelability, but also satisfy the performance of the protected coatings when the protection is over.
In this experiment, dark gentian blue and light-colored gardenia white solvent-based polyurethane topcoats, physically dry Changsheng green chlorinated rubber topcoats, and water-based white epoxy topcoats were selected as the protective coatings. After covering the water-based peelable protective coating, the protective coating is peeled off according to different protection times, and the effect of the protection time on the gloss of the protected coating is examined. The results are shown in FIG. 2.
It can be seen from Figure 2 that whether it is a dark gentian blue polyurethane topcoat or a light-colored gardenia white polyurethane topcoat, whether it is a solvent-based coating or a water-based coating, whether it is physical drying or chemical crosslinking curing drying, Within the experimental range, the protection time of the water-based peelable protective coating has almost no effect on the gloss of its coating film.
2.4 Effect of coating thickness of water-based peelable protective coating on gloss of protected coating film
Brush-coating water-based peelable protective coating on polyurethane topcoat, control thickness is 40 μm, 80 μm, 120 μm, 160 μm, 200 μm, peeled off after 7 d, and measured the gloss of the coating film and compared it with the unpeelable protective coating. The results are shown in FIG. 3.
It can be seen from FIG. 3 that the thickness of the water-based peelable protective coating has little effect on the gloss of the protective coating film.
2.5 The influence of water-based peelable protective coating on the adhesion of the protected coating
The surface of solvent-based polyurethane topcoat and water-based epoxy topcoat is coated with a water-based peelable protective coating (100 μm thickness) and peeled off after 1 month of protection. The adhesion between the protective coating film and the substrate was measured by the grid method and recorded. The comparison with the uncoated water-based peelable protective coating is shown in Figure 4.
It can be seen from FIG. 4 that after peeling the water-based peelable protective coating, the adhesion between the protected coating and the substrate is not significantly different from that of the uncoated protective coating. The adhesion of the wood has no effect.
2.6 Water resistance of water-based peelable protective coatings
Solvent-based polyurethane coatings and water-based epoxy coatings are used as protective coatings. After applying water-based peelable protective coatings for 7 days, they are immersed in distilled water. Soak for 10 days, no blistering, no penetration, and no effect on peeling (see Figure 5).
2.7 Acid and alkali resistance of water-based peelable protective coatings.
Solvent-based polyurethane coatings and water-based epoxy coatings are used as protective coatings. After applying water-based peelable protective coatings for 7 days, they are immersed in 5% HCl solution and 5% NaOH solution During immersion for 7 days, there was no blistering or penetration, and it did not affect peeling (see Figures 6 and 7).
2.8 Low flame spread performance test of water-based peelable protective coatings
Prepare samples according to the standard requirements and send them to the Far East Fire Center for low flame spread performance measurement. The surface flammability test was performed in accordance with the relevant requirements of Part 5 of Annex 1 of the 2010 FTP Code. The experimental results (Table 5) show that the water-based peelable protective coating meets the requirements of Chapter II-2 of the SOLAS Convention and has a low flame spread surface material.
(1) The water-based peelable protective coating prepared in this experiment can be peeled on the surface of aluminum plates, glass, etc. as well as complete peeling on solvent-based coatings and water-based coatings. It has high tensile strength and tear strength, good peelability and Does not affect the gloss and adhesion of the substrate coating.
(2) The water-based peelable protective coating has good acid and alkali resistance and water resistance.
(3) The water-based peelable protective coating has passed the determination of low flame spread performance and is a surface material with low flame spread conforming to the requirements of Chapter II-2 of the SOLAS Convention.