超细粉末涂料用丙烯酸树脂的制备和应用
制备了聚丙烯酸酯树脂及其超细粉末涂料，采用红外光谱、热重分析、差损扫描量热等方法对聚丙烯酸酯树脂的结构进行了表征，对制备的粉末涂料和涂膜的性能进行了测试，考察了超细粉末涂料的粉碎性、带电性、流动性、储存稳定性和施工性能，并展望了超细粉末涂料的应用前景。
1、简介
随着环境问题的日益严重，绿色涂料越来越受到人们的关注和重视。粉末涂料是一种新型的无溶剂 100% 固体粉末涂料，以其低污染、高效率、性能优异、节约能源和资源、粉末可回收等特点，引起了世界各国的广泛关注。
其中，丙烯酸树脂基粉末涂料属于低毒性产品，具有一系列优点：装饰性优异、耐户外风化、耐老化、耐腐蚀和耐污染、表面硬度高、柔韧性好，目前已广泛应用于汽车家电等领域，未来丙烯酸粉末涂料将成为汽车装饰面漆的主要品种之一。
超细粉末涂料由于粒径及其分布与普通粉末涂料的性能差异和特殊性，如涂料具有涂层薄、表面平整度和光泽度好等特点，可达到与液体涂料相似的效果，使得超细粉末涂料能够满足对粉末涂料更为严格的要求，为粉末涂料在各个领域的推广和应用进一步拓展了发展空间。
丙烯酸超细粉末涂料性能优异，将具有良好的发展前景和巨大的市场需求，因此，研究丙烯酸超细粉末涂料意义重大。
2、实验部分
2.1 实验原材料
甲基丙烯酸甲酯 (MMA)、甲基丙烯酸丁酯 (BMA)、甲基丙烯酸缩水甘油酯 (GMA)、 甲基丙烯酸环己酯 (CHMA)甲基丙烯酸异冰片酯 (IBOMA)、偶氮二异丁腈 (AIBN) 和十二烷二酸 (DDDA) 均为分析纯；苯和甲苯为化学纯。
2.2 丙烯酸树脂的合成
在本实验中，丙烯酸树脂是通过均相溶液聚合法合成的。聚合前，通过减压蒸馏从聚合阻断剂中去除所有单体。将甲基丙烯酸甲酯 (MMA)、甲基丙烯酸丁酯 (BMA)、甲基丙烯酸缩水甘油酯 (GMA)、甲基丙烯酸环己酯 (CHMA) 和甲基丙烯酸异冰片酯 (IBOMA) 混合，倒出一小部分单体混合物留作后续使用；将引发剂偶氮二异丁腈 (AIBN) 加入剩余的单体混合物中，搅拌至完全溶解。
在四颈烧瓶中加入甲苯，加热至 80°C，恒温回流 0.5 小时。通入 N2 进行保护，滴加引发剂单体混合物 2 小时，保持反应 0.5 小时。再滴加剩余单体混合物 0.5h，滴加完毕，保温反应 1.5110 反应结束，得到含甲苯的聚丙烯酸酯树脂溶液。
将上述产品趁热倒入单瓶中，用旋转蒸发仪在 80℃/0.098MPa的真空度下基本蒸发掉所有溶剂，将聚丙烯酸酯树脂倒在盘子表面，置于真空干燥箱中干燥 24h 即可得到洁净的白色聚丙烯酸酯树脂。
2.3 超细粉末涂层的制备
超细粉末涂料的制备需要采用超细研磨分级系统，所用设备有ACM325超细磨粉机、SCX400超细分级机、高效旋风除尘器、脉冲布袋除尘器和离心风机。超细丙烯酸粉末涂料的制备步骤如下：
(1) 将聚丙烯酸酯树脂初步粉碎；
(2) 预混合聚丙烯酸酯树脂、十二烷二酸（DDDA）、匀染剂和其他添加剂；
(3) 混合材料在双螺杆挤压机中熔化并挤出；
(4) 冷却后，挤出的薄膜与 A1203 在破碎机中进行破碎和混合；
(5) 第二次挤压上述材料并压片；
(6) 在超细研磨系统中加入 0.5%、3% A1203 进行破碎和分级；
2.4 涂层制备
用丙酮对基材表面进行脱脂处理后，用砂纸除锈并擦拭干净，然后放入鼓风烘箱中烘烤 2 分钟。然后，采用静电喷涂工艺和设备制备丙烯酸超细粉末涂料。将预处理好的样板放入喷粉柜中，用电晕放电静电喷枪进行喷涂，喷涂后保持样板垂直，放入鼓风干燥箱中固化，然后在室温下放置 24h 进行性能测试。
2.5 结构特性和性能测试
(1) 树脂的结构特征
红外光谱（IR）用于定性分析和识别分子中可能含有的官能团和化学键，并定量确定其数量。试样的制备采用压片法，即在玛瑙研钵中将少量树脂样品研磨成细粉，并与溴化钾干粉充分混合，然后装入模具中压片，再在红外光谱仪上扫描，收集红外光谱。
(2) 树脂性能测试
玻璃转化温度 (Tg)
当发生玻璃化转变时，聚丙烯酸酯树脂的性质会发生突变。差示扫描量热法（DSC）是一种表征玻璃化转变温度随温度升高和热流变化而变化的方法。本实验采用 DSC 法测定树脂的玻璃化转变温度，使用的热分析仪为美国公司的 DS02910 系列产品，测试条件如下表所示。
图片
热稳定性
热重分析（TG）是一种测量物质的质量随温度（或时间）变化的方法，它通过聚合物链受热后因氧化、侧基分解、主链断裂或结构变化引起的质量变化来反映聚合物的热稳定性。本实验采用 TA-2000 系列热重分析仪分析聚合物的热稳定性，测试条件如下：扫描温度范围为 25~600℃，加热速率为 10℃/分钟。
(3) 超细粉末涂料的可碾碎性测试
粉末涂料的粒度由英国马尔文公司的 MS2000 激光粒度分析仪进行分析，确定产品的平均粒度小于 15 和小于 30。
(4) 涂膜性能测试
外观：目测；机械性能：铅笔法测量硬度，漆膜划线试验测量附着力，漆膜弯曲试验（圆柱轴）测量柔韧性，漆膜冲击试验机测量抗冲击性。
3、结果与讨论
3.1 丙烯酸树脂的合成
(1) 选择聚合方法
粉末涂料用丙烯酸树脂的分子量分布应尽可能窄，而悬浮聚合或乳液聚合合成的树脂分子量较大，分子量分布较宽，同时树脂中会残留水溶性物质，如：分散剂、乳化剂、稳定剂等，微量杂质会影响树脂的性能，导致无法达到粉末涂料的高质量要求，因此这两种方法较少使用。
虽然无需去除溶剂，但聚合体系会随着反应的进行变得越来越粘稠，反应过程中会释放出大量热量，容易发生剧烈聚合，反应过程难以控制。
丙烯酸树脂的合成主要采用自由基聚合法，与四大自由基聚合法相比，由于溶液聚合反应在回流温度下进行，并有氮气保护，反应过程中的搅拌和溶剂回流会带走反应产生的热量，可有效避免局部温度过高甚至剧烈聚合，故反应温度易于控制，反应转化率较高，体系较稳定，聚合物分子量易于控制。聚合物的分子量易于控制。虽然溶液聚合法所用的溶剂一般都有毒，但去除溶剂比较容易，所以本论文的树脂合成方法是溶液聚合法。
(2) 选择共聚单体
丙烯酸树脂一般采用五元共聚法合成，需要硬单体、软单体、交联剂一起在一定温度下交联聚合。可用作合成丙烯酸树脂原料的单体种类很多，每种单体对树脂的性能都有不同的影响。可以通过选择单体的种类和调整单体之间的比例来改变树脂的玻璃化温度，从而改善树脂的破碎性能和抗结块性能，并提高涂层的流平性。
因此，为了确保目标树脂的综合性能达到预期效果，综合考虑各种单体对树脂性能的影响，以及不同类型单体的配比对树脂玻璃化转变温度的影响，本文选择 MMA 作为硬单体，BMA 作为软单体，GMA 作为交联单体，将环氧基团引入树脂中，并选择 IBOMA 降低聚合物的粘度。
(3) 启动剂的选择和用量
聚丙烯酸酯树脂合成常用的引发剂有偶氮二异丁腈（AIBN）和过氧化苯甲酰（BPO）。其中，BPO 的正常使用温度为 70、100 ℃，AIBN 的使用温度为 60、80 ℃。在合成丙烯酸树脂时，首选 AIBN 的原因如下：
① BPO is easy to induce decomposition reaction, the primary radicals are easy to capture the hydrogen, chlorine and other atoms or groups on the macromolecular chain, and then the introduction of branched chains on the macromolecular chain to make the molecular weight distribution broader; AIBN decomposition of free radicals generated by the activity of the smaller than the BPO, generally no induced decomposition reaction, so that the molecular weight of the polymer obtained from the distribution of the narrower;
② Benzoyl radical decomposition for highly active benzene radical initiated polymerisation, the polymer end group is poor outdoor durability, the coating film will yellow for a long time; and AIBN initiated polymer end group is (CH3)3C-, good outdoor durability;
③ The two free radicals C6H5C00- and C6H5 produced by the decomposition of BPO will undergo a coupling reaction, which inactivates most of the initiator and reduces the efficiency of the initiator.
④ At 60, 100 ℃, the half-life of AIBN is shorter than that of BPO, indicating a high reaction rate, and the peroxide residue will lead to oxidative yellowing of the resin.
The amount of initiator is also critical. Too little, resulting in polymer molecular weight is too large, the resin melt viscosity is too high, processing performance is bad, based on the resin coating leveling is poor, and the formation of the film is prone to orange peel phenomenon; initiator dosage is too large, the molecular weight of the polymer is small, although easy to process, but the coating film’s mechanical properties and impact resistance deterioration.
(4) Selection of solvent
AIBN does not induce decomposition reaction, so the solvent for the initiator decomposition rate is very small. Therefore, only the boiling point of the solvent and the chain transfer ability on the molecular weight and its distribution of the impact. The solvents commonly used in the synthesis of acrylic resin are benzene, toluene, xylene and butyl acetate, etc., while the toxicity and cost of xylene are higher, so benzene and toluene are chosen as mixed solvents. Among them, benzene has a boiling point of 80°C and plays the role of reflux, while toluene plays the role of chain transfer.
The glass transition temperature (Tg) of the resin is directly related to the storage stability of the powder coating, the higher the Tg, the better the storage stability, but the Tg is too high will make the processing performance of the powder coating as well as the decrease of levelling, so the Tg of the resin used for powder coating needs to be adjusted appropriately, and the Tg of the polyacrylate resin used for powder coating is generally in the range of 40-100℃, and the more optimized range is 40-60℃. The glass transition temperature of the copolymer can be used to make a preliminary design of the Tg of the polyacrylate resin through the Fox equation to better guide the experiment.
3.2 Performance analysis of ultrafine powder coatings
(1) Crushability
Ultrafine powder coatings and ordinary powder coatings production process is similar, mainly including the pre-mixing of raw materials, melt extrusion, cooling and crushing, fine crushing and grading sieve, product packaging and other processes. Only in the degree of crushing and grading and the selection of flow-assisting agent is different.
The experimental results show that the powder coating particle size less than 15μm accounted for more than 80%, less than 30m accounted for more than 90%, and the average particle size is smaller, below 10μm. This indicates that the system has a better effect on the crushing and grading of acrylic powder and reaches the level of ultrafine. It also indicates that the ACM impact pulveriser with internal classification and the SCX ultrafine classifier are feasible for the new process route of pulverisation and classification for the preparation of ultrafine powders. This ultrafine powder crushing and grading system can well meet the requirements of the product on particle size and yield after multiple processes such as ultrafine crushing, coarse grading and fine grading.
(2) Fluidisation
Ultrafine powder coating with a small particle size, the particle mass itself is reduced, the relative surface area increases, the inter-particle force (mainly Van der Waals force) greatly enhanced, it is very easy to form agglomerates. In the electrostatic spraying process into the fluidisation problems caused by difficulties, easy to block the pipeline, storage stability is not good, clusters lead to particle size increase and lose the excellent performance of ultra-fine powder. Therefore, it is necessary to solve the fluidisation problem of ultrafine powders to eliminate the limitation of the promotion and application of ultrafine powders.
According to the current literature, the main method to improve the fluidisation of ultrafine powder is to introduce some guest particles in the main ultrafine powder, which are much smaller than the ultrafine powder itself, as a flow-assisting agent, in order to change the interaction force between the particles of the ultrafine powder, so that the ultrafine powder is easy to be dispersed, and play a role in improving the fluidisation.
Common flow-assisting agents include alumina, aluminium hydroxide, calcium oxide, silicon dioxide, zinc oxide, wrong oxide, platinum trioxide, titanium dioxide, ornamental dioxide, tungsten trioxide, and aluminium silicate, and a combination of at least two of these substances will improve the fluidisation properties of the ultrafine powder coating. Therefore, it is necessary to select the type, particle size, and addition ratio of the added nanofluidising agent. The flow aid should not be added in excess or the coating properties will be affected, and the type of flow aid also has an effect on the fluidisation effect and other properties of the coating.
Through comparison, A1203 was found to be the most effective, and A1203 was selected as the flow aid. In the production of ultrafine powder coatings, in the crushing process added 0.5%, 3% of the nanoparticles of A1203, making the ultrafine powder fluidisation performance is good, and improve the storage stability.
(3) Chargeability
Ultrafine powder quality is small resulting in not easy to powder, in order to improve the powder rate, the theory should be added to some electrifying agent. However, in practice, it is found that a low powdering rate improves the selectivity of spraying, that is, the particle size of the particles on the spray is similar, and the coating thickness obtained is more uniform.
Ordinary coarse powder recycling powder in the high content of fines, repeated use will be holding, spit powder and other fluidisation problems, usually need to be recycled powder and new powder mixed at a certain ratio. Ultra-fine powder has solved the fluidisation problem, so the recycled powder can be used normally even if the particle size is too fine. Powder coating powder can be recycled after spraying, and its powder rate is good, the powder rate of ordinary coarse powder can reach more than 95%, and the powder rate of ultra-fine powder coating is more than 98%, which avoids the waste of resources.
(4) Construction performance
Comparison of the comprehensive performance test results of the coating and film is shown in the table below.
图片
It can be seen from the above table:
Appearance: The long wave on the surface of the coating film formed by ultra-fine powder is much lower than that of ordinary coarse powder, which largely eliminates the phenomenon of orange peel inherent in powder coatings. The surface of the coating film formed by ordinary powder coatings is not flat enough, and the surface gloss of the coating film formed by ultra-fine powder coatings is much higher, which can meet the high decorative requirements.
Mechanical properties: thin coating of fine powder and thick coating of coarse powder have the same effect in adhesion, corrosion resistance, etc. Thin coating of fine powder has better pencil hardness and impact resistance. Under the same thickness, the coating formed by fine powder has better corrosion resistance.
Levelling: ultra-fine powder coating particle size is smaller, after solving the problem of agglomeration, it is not easy to appear the problem of hanging, the fluidisation performance is very excellent, compared with the ordinary coarse powder, the formation of the coating film is more flat.
Construction performance: ultra-fine powder coatings can form thinner coatings due to smaller particle size, so covering the same area of the substrate, not only the amount of raw materials is greatly reduced and the surface roughness is also significantly reduced. Even if a very rough substrate is covered with ultrafine powder coating, there will be no obvious orange peel, which cannot be done with ordinary coarse powder.
And the thin coating of ultrafine powder dries faster, saves time and shortens the construction week after 2 or 3 layers of ordinary coarse powder and ultrafine powder are sprayed, the ordinary coarse powder has no covering power problem because of the thick coating, and the thin coating of ultrafine powder appears to have insufficient covering power, so you can choose to apply the appropriate thick coating or choose the pigment with strong covering power, but you should pay attention to the amount of pigment added should not be too much, or else it will be unevenly fused phenomenon.
(5) Storage stability
Powder acrylic resin is easy to store and transport, the transport cost is lower than solvent-based acrylic resin, storage and transport process security. However, there are some common disadvantages of powder coatings, such as paint storage and transport process pressure or moisture resulting in bonding, need to be kept at low temperatures and dry powder.
Powder acrylic resin is more easily accepted by the construction unit, and some models of solid acrylic resin has thixotropic, made of paint and ordinary latex paint has the same effect of opening the can and construction performance. High-grade solid acrylic resin, because the main monomer is methacrylate, in the ultraviolet radiation will not degrade, so its weather resistance is more prominent. Resin thermal stability of 170 ℃ or more, individual varieties up to 260 ℃ which is difficult to reach the ordinary solvent-based thermoplastic acrylic resin.
4, Conclusion
In summary, ultra-fine acrylic powder coatings and coating has a series of advantages: small pollution; good light and colour retention, excellent decorative; electrostatic coating effect is good, can be thinly coated; spraying efficiency is high, the powder can be recycled; good adhesion, without primer; heat resistance, maroon resistance, chemical resistance, not easy to turn yellow; good physical and mechanical properties.
Ultra-fine powder coatings can be widely used in all areas where powder coatings are used, and can meet more stringent requirements, such as highly decorative coating requirements in the automotive field, high weathering requirements for outdoor products, corrosion resistance requirements in the field of ships and containers, decorative and economic requirements for furniture and home appliances, and ultra-thin coating requirements for fine instrument components, and so on.
The environmental protection, economy and superior performance of ultrafine acrylic powder coatings will also make its application fields expanding, its extensive development prospects and huge market potential, will bring a new round of development opportunities for the powder coating industry.
| 聚硫醇/聚硫醇 | ||
| DMES 单体 | 双（2-巯基乙基）硫醚 | 3570-55-6 |
| DMPT 单体 | THIOCURE DMPT | 131538-00-6 |
| PETMP 单体 | 季戊四醇四(3-巯基丙酸酯) | 7575-23-7 |
| PM839 单体 | 聚氧（甲基-1,2-乙二基） | 72244-98-5 |
| 单官能团单体 | ||
| HEMA 单体 | 甲基丙烯酸 2-羟乙基酯 | 868-77-9 |
| HPMA 单体 | 甲基丙烯酸羟丙酯 | 27813-02-1 |
| THFA 单体 | 丙烯酸四氢糠酯 | 2399-48-6 |
| HDCPA 单体 | 氢化双环戊烯丙烯酸酯 | 79637-74-4 |
| DCPMA 单体 | 甲基丙烯酸二氢双环戊二烯酯 | 30798-39-1 |
| DCPA 单体 | 丙烯酸二氢双环戊二烯酯 | 12542-30-2 |
| 二氯丙烯酰亚胺单体 | 甲基丙烯酸二环戊氧基乙酯 | 68586-19-6 |
| DCPEOA 单体 | 丙烯酸二环戊烯基氧基乙基酯 | 65983-31-5 |
| NP-4EA 单体 | (4) 乙氧基化壬基酚 | 50974-47-5 |
| LA 单体 | 丙烯酸十二烷基酯/丙烯酸十二烷基酯 | 2156-97-0 |
| THFMA 单体 | 甲基丙烯酸四氢糠酯 | 2455-24-5 |
| PHEA 单体 | 2-苯氧基乙基丙烯酸酯 | 48145-04-6 |
| LMA 单体 | 甲基丙烯酸月桂酯 | 142-90-5 |
| IDA 单体 | 丙烯酸异癸酯 | 1330-61-6 |
| IBOMA 单体 | 甲基丙烯酸异冰片酯 | 7534-94-3 |
| IBOA 单体 | 丙烯酸异冰片酯 | 5888-33-5 |
| EOEOEA 单体 | 2-(2-乙氧基乙氧基)丙烯酸乙酯 | 7328-17-8 |
| 多功能单体 | ||
| DPHA 单体 | 双季戊四醇六丙烯酸酯 | 29570-58-9 |
| DI-TMPTA 单体 | 二（三羟甲基丙烷）四丙烯酸酯 | 94108-97-1 |
| 丙烯酰胺单体 | ||
| ACMO 单体 | 4-丙烯酰基吗啉 | 5117-12-4 |
| 双功能单体 | ||
| PEGDMA 单体 | 聚乙二醇二甲基丙烯酸酯 | 25852-47-5 |
| TPGDA 单体 | 三丙二醇二丙烯酸酯 | 42978-66-5 |
| TEGDMA 单体 | 三乙二醇二甲基丙烯酸酯 | 109-16-0 |
| PO2-NPGDA 单体 | 丙氧基新戊二醇二丙烯酸酯 | 84170-74-1 |
| PEGDA 单体 | 聚乙二醇二丙烯酸酯 | 26570-48-9 |
| PDDA 单体 | 邻苯二甲酸二乙二醇二丙烯酸酯 | |
| NPGDA 单体 | 新戊二醇二丙烯酸酯 | 2223-82-7 |
| HDDA 单体 | 二丙烯酸六亚甲基酯 | 13048-33-4 |
| EO4-BPADA 单体 | 乙氧基化 (4) 双酚 A 二丙烯酸酯 | 64401-02-1 |
| EO10-BPADA 单体 | 乙氧基化 (10) 双酚 A 二丙烯酸酯 | 64401-02-1 |
| EGDMA 单体 | 乙二醇二甲基丙烯酸酯 | 97-90-5 |
| DPGDA 单体 | 二丙二醇二烯酸酯 | 57472-68-1 |
| 双-GMA 单体 | 双酚 A 甲基丙烯酸缩水甘油酯 | 1565-94-2 |
| 三官能单体 | ||
| TMPTMA 单体 | 三羟甲基丙烷三甲基丙烯酸酯 | 3290-92-4 |
| TMPTA 单体 | 三羟甲基丙烷三丙烯酸酯 | 15625-89-5 |
| PETA 单体 | 季戊四醇三丙烯酸酯 | 3524-68-3 |
| GPTA ( G3POTA ) 单体 | 丙氧基三丙烯酸甘油酯 | 52408-84-1 |
| EO3-TMPTA 单体 | 三羟甲基丙烷三丙烯酸乙氧基化物 | 28961-43-5 |
| 光阻单体 | ||
| IPAMA 单体 | 2-异丙基-2-金刚烷基甲基丙烯酸酯 | 297156-50-4 |
| ECPMA 单体 | 1-乙基环戊基甲基丙烯酸酯 | 266308-58-1 |
| ADAMA 单体 | 1-金刚烷基甲基丙烯酸酯 | 16887-36-8 |
| 甲基丙烯酸酯单体 | ||
| TBAEMA 单体 | 2-(叔丁基氨基)乙基甲基丙烯酸酯 | 3775-90-4 |
| NBMA 单体 | 甲基丙烯酸正丁酯 | 97-88-1 |
| MEMA 单体 | 甲基丙烯酸 2-甲氧基乙酯 | 6976-93-8 |
| i-BMA 单体 | 甲基丙烯酸异丁酯 | 97-86-9 |
| EHMA 单体 | 甲基丙烯酸 2-乙基己酯 | 688-84-6 |
| EGDMP 单体 | 乙二醇双(3-巯基丙酸酯) | 22504-50-3 |
| EEMA 单体 | 2-甲基丙-2-烯酸 2-乙氧基乙酯 | 2370-63-0 |
| DMAEMA 单体 | 甲基丙烯酸 N,M-二甲基氨基乙酯 | 2867-47-2 |
| DEAM 单体 | 甲基丙烯酸二乙氨基乙酯 | 105-16-8 |
| CHMA 单体 | 甲基丙烯酸环己基酯 | 101-43-9 |
| BZMA 单体 | 甲基丙烯酸苄酯 | 2495-37-6 |
| BDDMP 单体 | 1,4-丁二醇二（3-巯基丙酸酯） | 92140-97-1 |
| BDDMA 单体 | 1,4-丁二醇二甲基丙烯酸酯 | 2082-81-7 |
| AMA 单体 | 甲基丙烯酸烯丙酯 | 96-05-9 |
| AAEM 单体 | 甲基丙烯酸乙酰乙酰氧基乙基酯 | 21282-97-3 |
| 丙烯酸酯单体 | ||
| IBA 单体 | 丙烯酸异丁酯 | 106-63-8 |
| EMA 单体 | 甲基丙烯酸乙酯 | 97-63-2 |
| DMAEA 单体 | 丙烯酸二甲胺基乙酯 | 2439-35-2 |
| DEAEA 单体 | 2-(二乙基氨基)乙基丙-2-烯酸酯 | 2426-54-2 |
| CHA 单体 | 丙-2-烯酸环己基酯 | 3066-71-5 |
| BZA 单体 | 丙-2-烯酸苄酯 | 2495-35-4 |