Abstract: A water-based imitation metal paint for plastic surface coating was prepared by using water-based emulsion as film-forming material and aluminum powder and copper-gold powder as effect pigments. The effects of the types and amounts of resins, effect pigments and anti-settling agents on the comprehensive properties of coatings were investigated . The results show that when the self-made single-component self-crosslinking acrylic emulsion B is used as the film-forming base material, the effect pigments are aluminum powder paste XH330 and copper gold powder K, and the dosage is 8%, and the water-based wax emulsion F is used as anti-sedimentation agent, the obtained Silver powder paint and gold powder paint have better storage stability, the adhesion of the paint film reaches 0 grade, and the pencil hardness reaches 3H, showing a good imitation metal appearance effect.
With the continuous improvement of living standards, people are more and more fond of decoration with luxurious metal texture. The emergence of metal-like plastic paint has alleviated the contradiction between people's pursuit of metal texture and the shortage of metal resources. This kind of coating can give plastic a metal-like appearance and texture. It not only replaces metal materials with light and cheap plastic products , but also satisfies people's pursuit of luxurious metal effects, and is deeply loved by the public[1]. At present, the plastic coatings on the market are mainly , which seriously pollute the environment and consume a lot of energy [2]. Therefore, the development and application of environmentally friendly water-based plastic coatings is imperative. According to reports, the global annual demand for water-based plastic coatings is increasing at a rate of more than 10%, and the growth rate of plastic water-based coatings in the United States has reached 17% [3].
The development of water-based metal-like plastic paints not only has to overcome the problems of slow drying rate, low hardness, poor scratch resistance, and poor adhesion paints are mostly weakly alkaline and easy to corrode metal effect pigments. , such as copper-gold powder with copper and zinc as the main raw materials is easy to tarnish and unstable in storage, and aluminum powder slurry reacts to generate hydrogen gas, which makes the paint bulge during storage [4] . In addition, metallic pigments have a high density and are easy to settle, which will affect the stability of metallic paints. Whether the metal particles can be arranged regularly in the wet film will also affect the metal-like effect of the paint film. At present, the research on water-based metal-like plastic paint is still in its infancy, and few research results have been publicly reported. However, as plastic products replace metal materials on a large scale, metallized coating on the surface has become the focus of paint workers [5] . In this paper, on the basis of the developed high-performance self-crosslinking water-based resin, a water-based imitation metal paint that can be applied to plastics such as PET (polyethylene terephthalate), PVC (polyvinyl chloride), and Some basic issues , and useful explorations are made for making plastics replace metals to a certain extent and reducing VOC (volatile organic compound) emissions.
1 experiment
1.1 Main raw materials and instruments
Water-based aluminum powder paste 6730, copper gold powder U35, industrial grade, Gulf Chemicals; water-based aluminum powder paste XH330, industrial grade, Hisense aluminum pigment; hydroxyl-containing polyacrylic acid emulsion A2470, water-based polyisocyanate curing agent XP2655, industrial grade, Bayer Company; One-component water-based acrylic resin 1637, industrial grade, Jiuwei Trading Co., Ltd.; wetting and dispersing agent Dispers655W, water-based rheology control agent F, industrial grade, BYK; defoamer oamStarA34, leveling agent Levelling620, industrial grade, Haichuan Chemical; water-based wax emulsion F, industrial grade, Degussa; fumed silica, industrial grade, Degussa; single- component self-crosslinking acrylic emulsion B [6], copper gold powder K [7], deionized water, Self-made; PET plastic sheet L701, Kaiben Plastic Film Co., Ltd.
SDF400 Experimental Dispersion Sand Mill, Changzhou Tengjiao Machinery Factory; JB300-I Powerful Electric Mixer, Shanghai Specimen Model Factory; MG268-F2 Gloss Meter, Quanzhou Keshijia Photoelectric Instrument Co., Ltd.; ZAHN Cai En Cup 4# Viscosity Meter, Guangzhou Demanyi Instrument Co., Ltd.; X-Rite-MA68 II multi-angle Spectrophotometer , American X-Rite Company.
1.2 Preparation of paint and coating film
Add 0.30% wetting and dispersing agent, 15.0% deionized water and 6.0% ~ 12.0% effect pigment in sequence according to the system mass fraction (the same below) in a container with a stirring device, mix at a speed of 300 r/min, and stir for 20 min to get the effect pigment paste. Mix 75.0% acrylate emulsion, 0.2% defoamer, 0.2% leveling agent, 0.5% water-based rheology control agent, 1.5% anti-settling agent and water to make up the balance, and stir at a speed of 1 000 r/min for 20 After the dispersion is uniform, add the dispersed effect pigment slurry under stirring at 300 r/min, and disperse for 20 minutes to obtain the water-based imitation metal plastic paint. According to GB/T 1727-1992 "General Preparation Method of Paint Film", the samples were prepared by spraying on a clean PET plastic plate, the thickness of the paint film was controlled at about 20 μm, and dried at (25 ± 5) °C for 7 days before use.
1. 3 Performance testing
1. 3. 1 Coating properties
According to GB/T 1721-2008 "Varnishes, Varnishes and Thinners Appearance and Transparency Determination Method", visually inspect the physical properties of the samples such as color, state, uniformity, and transparency The solid content and storage stability of the samples were determined according to GB/T 1725-2007 "Determination of Non-volatile Content of Paints, Varnishes and Plastics" and GB/T 6753.3-1986 "Test Method for Storage Stability of Paint . According to GB/T 1723-1993 "Determination of Viscosity of Coatings", the viscosity of the sample at 25 °C was measured with a Tu-4 cup.
1. 3. 2 Film properties
Respectively according to GB/T 6739-2006 "Determination of paint film hardness by pencil method of paints and varnishes", GB/T 9286-1998 "Cross-cut test of paint films of paints and varnishes ", GB/T 1743-1979 (1989) " "Determination of paint film gloss" and GB/T 1728-1979 (1989) "Determination of drying time of paint film and putty film " to test the pencil hardness, adhesion, gloss and drying time of the paint film. Measure the water resistance of the coating film according to GB/T 1733-1993 "Determination of Water Resistance of Paint Films"
sex. Use a mixture of rosin and paraffin to seal the edge of the coated substrate to prevent water immersion, then soak it in water, and record the time of whitening and wrinkling of the coating.
Use a multi-angle Spectrophotometer to measure the gloss of the coating film at 15°, 45° and 110°, namely L 15 , L 45 and L 110 , and substitute it into formula (1) to calculate the metallic sparkle index
2 Results and discussion
Water-based metal imitation plastic paint requires good adhesion of the paint film on the plastic surface, high hardness and gloss, and good metal imitation effect. Therefore, it is a major difficulty to choose a resin that can meet its performance requirements. In addition, it is necessary to investigate the main raw materials in the formula so that the metallic pigments can be stably aligned in the paint film, so as to exhibit excellent metallic effects. This paper discusses the effects of emulsion, effect pigments and additives on the properties of waterborne metal-like plastic paints.
2.1 The effect of emulsion on the performance of waterborne metal-like plastic paint
At present, the water-based resins that can be used for plastic products on the market mainly include acrylic acid, epoxy, polyurethane, polyurethane acrylic composite resin, etc., which are mainly used on the surface of ABS (acrylonitrile-butadiene-styrene copolymer), PET, PVC and other surfaces [8 ]. This paper mainly focuses on PET and PVC, using commercially available two -component water-based polyurethane resin A, one-component water-based acrylic resin 1637 and self-made one-component self-crosslinking acrylic emulsion B as film-forming materials respectively, and the dosage of aluminum powder paste XH330 is 8.0%, the anti-settling agent is water-based wax emulsion F, and other conditions are the same, the imitation metal paint is prepared, and the basic performance test results are shown in Table 1.
It can be seen from Table 1 that the coating made of resin A has a short service life, because it is mixed with a curing agent containing isocyanate groups and a polyacrylic Film-forming substances are formed and the degree of cross-linking continues to increase, which finally leads to the solidification of the paint solution and cannot be used any longer. Resin B is a stable enamine structure formed from the acetoacetate group and amino group in the self-crosslinking monomer under alkaline conditions.
As the pH drops, the reaction proceeds in reverse, acetoacetate groups are regenerated and self-crosslinking reactions occur, so the coatings prepared have a relatively long shelf life.
The appearance of the water-based imitation metal paint film prepared by resin B is metallic silver, and the gloss and metallic sparkle index are higher than those of the paint films prepared by resin A and resin 1637. The higher the metal scintillation index, the more regular the arrangement of the aluminum powder particles, and it can be inferred that the alignment effect of the metal particles in the emulsion B is better, because the resin B has a chelating group, which is adsorbed on the The surface of the metal particles is wrapped, so it can significantly promote the regular arrangement of the metal particles in the wet film. The paint film made by resin B has excellent comprehensive properties such as hardness, adhesion, water resistance, long service life and better metal effect, so it is selected as the film-forming base material of this system.
2. 2 Effect pigment type and dosage on the performance of water-based metal-like plastic paint
The reason why the water-based imitation metallic paint has a special metallic effect is that effect pigments are added to the paint. Under light irradiation, effect pigments achieve the effect of different colors with angles through regular reflection, transmission or interference [9]. The selection of aluminum powder and copper-gold powder for water-based imitation metal paint is very strict. In this paper, a variety of aluminum powder and copper-gold powder are selected as effect pigments and the dosage is 8.0%. Water-based wax emulsion F is used as anti-settling agent. Other conditions are the same. See Table 2 for the basic performance test results of several water-based imitation metal-plastic paints.
从表 2 可知，在弱碱性的水性漆液体系中，铝粉浆 6730 由于被腐蚀而产生了氢气，造成贮存容器内部压力升高，出现胀桶现象，而且所制漆膜的光泽度也大大降低。铝粉浆 XH330 制备的涂料有较好的贮存稳定性且漆膜光泽较高。铜金粉 U35 由于被呈弱碱性的体系腐蚀，释出 Cu 2+ 而使漆液呈蓝色，并且导致漆膜光泽下降。铜
金粉 K 经过有机−无机双重包覆处理 [7, 10] ，包覆层可以在腐蚀环境下有效保护铜金粉，所以可以稳定使用。综上，选定铝粉 XH330 和铜金粉 K 分别作为银粉漆和金粉漆的效应颜料。
效应颜料的用量需要恰当，既要能够遮盖底材，又不能互相堆积，这样才能有良好的仿金属效果。以铝粉浆 XH330 为效应颜料，水性蜡乳液 F 为防沉剂，进行了仅铝粉用量不同的对比试验，结果见表 3。从表 3 可知，当效应颜料用量较少时，涂膜遮盖力不足，需要喷涂多道来保证其遮盖力，易造成浪费。当效应颜料用量过多时，漆膜发黑，铅笔硬度和附着力均有所下降。这是因为效应颜料用量过多，金属粒子容易相互团聚，影响了其定向排列，导致漆膜发黑，间接表现为光泽度下降。另外颜料过多，其表面不能达到饱和吸附，空余点会造成颜料絮凝，体系稳定性变差，附着力降低 [11] 。因此效应颜料用量以 8.0%为宜
2. 3 防沉剂对涂料性能的影响
由于效应颜料密度大，随着放置时间延长，混合在乳液及水中的颜料会渐渐沉降，聚积在底部，甚至发生团聚，更甚者会团结成大颗粒，使涂料变质，丧失原有性能。为防止效应颜料沉降，需加入防沉剂使其能够较长时间地均匀悬浮在涂料中。以 8.0%铝粉浆 XH330 为效应颜料，采用 2 种不同特性的防沉剂进行对比试验，结果如表 4 所示。
从表 4 可知，2 种防沉剂均可起到防沉作用，其中水性蜡乳液 F 的防沉效果更优。水性蜡乳液 F 的结构为聚酰胺蜡，可在体系中形成强大的网状结构，具有优异的触变性和防沉效果。加入气相二氧化硅后，漆膜光泽下降明显，而加入水性蜡乳液 F 后，漆膜光泽有所上升，这是因为气相二氧化硅具有消光性，而蜡助剂能够促进效应颜料更好地定向排列，继而获取良好的金属效果。另外，加入水性蜡乳液 F 还提高了漆膜的铅笔硬度。蜡颗粒分散在涂膜表面，形成细微粗糙的表面，与外平面接触时，蜡颗粒起到支撑骨架的作用，减少了漆膜接触面积，可抵抗外力刮伤 [12] 。因此选择水性蜡乳液 F 为防沉剂。
2. 4 水性仿金属塑料漆的综合性能
按很好配方制备了水性仿金属塑料漆，并测试了其性能见表 5，因为国家尚未出台水性仿金属塑料涂料标准，所以与溶剂型塑料仿金属涂料的标准对比 [13] 。从表 5 可见，所制涂料能满足标准要求，综合性能较好。
图 1 显示了水性仿金属漆在 PET 塑料上的涂饰效果。其漆膜平整光亮，赋予了塑料底材优异的仿金属外观。
结语
以单组分自交联丙烯酸乳液 B 为成膜基料，水性聚酰胺蜡防沉剂 F 为防沉助剂，与贮存稳定性较好的铝粉浆 XH330 和铜金粉 K 分别制备了水性仿金属银粉漆和金粉漆，所得涂料具有较好的贮存稳定性，其漆膜综合性能优良，金属效果明显，满足性能要求。
参考文献：
[1] 刘登良. 塑料和橡胶用涂料与涂装技术[M]. 北京: 化学工业出版社, 2001: 1-115.
[2] 曹逸辰. 塑料用水性树脂及涂料的研制及应用[J]. 涂料技术与文摘, 2010, 31 (4): 13-17.
[3] 陆丽浓, 欧宗和, 陈铃红. 塑料用水性涂料的研究进展[J]. 涂料工业, 2010, 40 (3): 61-63.
[4] 李利君, 皮丕辉, 文秀芳, 等. 溶胶−凝胶法制备纳米 SiO 2 包覆的铝颜料[J]. 华南理工大学学报(自然科学版), 2007, 35 (11): 72-76.
[5] 刘浏, 张彪, 徐戈文. 环保型塑料涂料的研究及应用现状[J]. 涂料技术与文摘, 2010, 31 (2): 5-8.
[6] 雷亮, 夏正斌. 乙酰乙酰基丙烯酸酯聚合物乳液的合成及室温交联改性[J]. 高校化学工程学报, 2014, 28 (3): 561-566.
[7] 合肥旭阳铝颜料有限公司. 水性铜金粉的制备方法: 201310290409.7 [P]. 2013–10–02.
[8] 廖阳飞, 张旭东, 邢俊恒, 等. 塑料涂料研究进展[J]. 上海涂料, 2008, 46 (8): 14-18.
[9] RINK H P, MAYER B. Water-based coatings for automotive refinishing [J]. Progress in Organic Coatings, 1998, 34 (1/2/3/4): 175-180.
[10] Liu Hui, Ye Hongqi, Lin Tianquan. The effect of double coating on the corrosion resistance of aluminum powder [J]. Material Protection, 2008, 41 (1): 38-40.
[11] TIARKS F, PRECHEN T, KIRSCH S, et al. Formulation effects on the distribution of pigment particles in paints [J]. Progress in Organic Coatings, 2003, 48 (2/3/4): 140-152 .
[12] Zhang Shengwen, He Lifan, Li Xiaoyu. Application of wax additives in waterborne wood coatings [J]. Coating Industry, 2007, 36 (10): 62-66.
[13] Liang Zengtian. Coatings for Plastics [M]. Beijing: Chemical Industry Press, 2001: 25-27
