Wide application of Glycidyl Methacrylate GMA in powder coatings

Wide application of Glycidyl Methacrylate GMA in powder coatings

Powder coatings are solid powdered synthetic resin coatings composed of solid resins, pigments, fillers and additives. Unlike ordinary solvent-based coatings and water-based coatings, its dispersion medium is not solvent and water, but air. It has the characteristics of no solvent pollution, 100% film formation and low energy consumption. Powder coatings are divided into two categories: thermoplastic and thermosetting. The film appearance (gloss and leveling) of thermoplastic powder coatings is poor, and the adhesion between them and metal is also poor, so they are rarely used in the field of automotive coatings. Automotive coatings generally use thermosetting powder coatings. Thermosetting powder coatings use thermosetting synthetic resins as film-forming materials. During the drying process, the resin first melts and then solidifies into a flat and hard coating film after chemical cross-linking. The appearance of the paint film formed by this kind of coating, various mechanical properties and corrosion resistance can meet the requirements of automotive finishing.

Powder coatings are completely different from general coatings. They exist in the form of fine powder. Because no solvent is used, it is called powder coatings. The main features of powder coatings are: harmless, high efficiency, resource saving and environmental protection.

It has two major categories: thermoplastic powder coatings and thermosetting powder coatings.

Thermoplastic powder coatings are composed of thermoplastic resins, pigments, fillers, plasticizers and stabilizers. Thermoplastic powder coatings include: polyethylene, polypropylene, polyester, polyvinyl chloride, chlorinated polyether, polyamide series, cellulose series, polyester series, etc.

Thermosetting powder coatings are composed of thermosetting resins, curing agents, pigments, fillers and additives. Thermosetting powder coatings include: epoxy resin series, epoxy-polyester series, polyester series, polyurethane series, acrylic resin series, etc.

Disadvantages: uneven powdering of corners, difficult to cover up coating defects after curing, high curing conditions, and limited use of substrates.

There are many classification standards, and the names of various types of powders on the market are uneven. According to the properties of the film-forming material, it is divided into two categories: thermoplastic powder coatings and thermosetting powder coatings. Or it can be divided into matte type, high gloss type, art type, etc. according to the appearance of the film-forming material. It can also be divided into two categories according to the use environment: indoor type and outdoor type.

Although the varieties of powder coatings are not as numerous as solvent-based coatings, there are also many polymer resins that can be used as powder coatings. In general, they can be divided into two categories: thermosetting type and thermoplastic type. [2]

1. Thermosetting powder coating refers to a coating that uses thermosetting resin as the film-forming material and adds a curing agent that reacts with a cross-linking reaction to form an infusible hard coating after heating. Even at high temperatures, the coating will not soften like a thermoplastic coating, but will only decompose. Since the resin used in thermosetting powder coatings is a prepolymer with a low degree of polymerization and a low molecular weight, the coating has better leveling properties and better decorative properties. In addition, after curing, the low molecular weight prepolymer can form a network of cross-linked macromolecules, so the coating has better corrosion resistance and mechanical properties. Therefore, thermosetting powder coatings have developed particularly rapidly.

1.1 Epoxy powder coatings. Due to its excellent metal adhesion, corrosion resistance, hardness, flexibility and impact strength, it is the first type of thermosetting powder coating to be used. Epoxy powder coating is composed of epoxy resin, curing agent, pigment, filler and other assistants. The contribution of these components to the performance of the powder coating is mutually restricted and influenced. A suitable formula is actually the result of the coordination of various components.

1.2 Polyester powder coating. Compared with other types of powder coatings, polyester powder coating has unique properties. It is better than epoxy resin in weather resistance and UV resistance [2]. In addition, since polyester resin has polar groups, its powder coating rate is higher than epoxy resin. It is not easy to yellow during baking, has high gloss, good leveling, full paint film, light color and other characteristics, so it has good decorative properties. It is generally used in refrigerators, washing machines, vacuum cleaners, instrument housings, bicycles, furniture and other fields.

1.3 Acrylic powder coating. There are two types of acrylic resin powder coatings: thermoplastic and thermosetting. The biggest advantage of thermosetting acrylic resin powder coatings is that they have excellent weather resistance, color retention, pollution resistance, strong metal adhesion, and excellent coating appearance, making them suitable for decorative powder coatings.

2. Thermoplastic powder coatings. Thermoplastic powder coatings began to appear in 1950. They melt at the spraying temperature and solidify into a film when cooled. Due to the simple processing and spraying methods, powder coatings only need to be heated to melt, leveled, cooled or extracted to solidify into a film, and no complex curing device is required. Most of the raw materials used are common polymers on the market, which can meet the requirements of performance under most conditions. However, there are also some shortcomings, such as high melting temperature, low coloring level, and poor adhesion to metal surfaces. Despite this, commonly used thermoplastic powder coatings still show some unique properties, among which polyolefin powder coatings have excellent solvent resistance; polyvinylidene fluoride coatings have outstanding weather resistance; polyamide has excellent wear resistance; polyvinyl chloride has a good price/performance ratio; thermoplastic polyester powder coatings have the advantages of beautiful appearance and high artistry. These characteristics make thermoplastic powder coatings occupy a large proportion in the coating market.

2.1 Polyvinyl chloride powder is one of the cheapest polymers produced on an industrial scale. It has excellent solvent resistance, good corrosion resistance to water and acid, impact resistance, salt spray resistance, can prevent food contamination and has high insulation strength for electrostatic spraying. It is mainly used for coating metal mesh, steel furniture, chemical equipment, etc.

2.2 Polyethylene powder coating has excellent corrosion resistance, chemical resistance, excellent electrical insulation and UV radiation resistance. The disadvantage is that the mechanical strength is not high and the adhesion to the substrate is poor. It can be used for chemical tanks, impellers, pumps, pipe inner walls, instrument housings, metal plates, refrigerator inner mesh, automotive parts, etc.

2.3 Nylon powder coating. Nylon (Nylon) is also called polyamide. Since the N atoms of the chlorine group on the molecular chain easily form hydrogen bonds with the hydrogen atoms on the adjacent chain segments, the melting point of polyamide resin is generally high. Nylon has the advantages of high mechanical strength, impact resistance, hardness, wear resistance, low friction coefficient, low dust absorption, etc., and can be used for parts with special requirements. For example, it can be used for water pump impellers, textile machinery parts, diesel engine starting piston parts, motor sailboat propeller impellers, car wheels, motorcycle brackets, agricultural machinery, construction and sports equipment, etc. In addition, due to nylon's resistance to salt water and inertness to mold and bacteria, it is very suitable for making coatings immersed in or in contact with seawater. At the same time, nylon powder coatings are non-toxic, odorless, not corroded by mold, and will not promote bacterial growth. They are very suitable for spraying food industry parts, drinking water pipes and food packaging.

2.4 Fluororesin powder coatings. There are many types of powder coatings that can be prepared from fluorinated polymers, such as polytetrafluoroethylene (PTFE), polytrifluorochloroethylene (PTFCE), polyvinylidene fluoride (PVDF), etc. The melting point of polytetrafluoroethylene is as high as 327℃. It can be used for a long time in the range of -250～250℃. In addition, it has excellent corrosion resistance, and it is not corroded even in aqua regia. It has excellent dielectric properties, extremely low friction coefficient and self-lubricating properties, so it is known as the "King of Plastics". It is widely used in petroleum, chemical anti-corrosion coatings, seals, bearing lubricating materials, electronic and electrical materials, ship launching rails and non-stick pan coatings. The price of polytrifluorochloroethylene is cheaper than PTFE, the processing temperature can be reduced, and the coating can be used for a long time below 130℃. The ability to resist alkali and hydrogen fluoride corrosion is better than acid-resistant enamel, and the ability to resist hydrochloric acid, dilute sulfuric acid, hydrogen chloride and chlorine is better than stainless steel equipment. It has been widely used in anti-corrosion equipment in chemical plants, pesticide plants, pharmaceutical plants, detergent plants, etc. The biggest advantage of polyvinylidene fluoride powder coating is its excellent weather resistance, high resistance to degradation in outdoor exposure, and it does not absorb dust and is easy to maintain its original gloss. 5 Chlorinated polyether powder coating. Chlorinated polyether has excellent chemical stability. The coating has good corrosion resistance and dissolution resistance to various acids, alkalis and solvents. Its chemical stability is second only to polytetrafluoroethylene. Its mechanical and friction properties are also very good. Chlorinated polyether powder coatings are mainly used in chemical equipment, pipeline linings, instrument equipment shells, etc. Its disadvantage is that it has poor adhesion to metals. Adding additives can improve the adhesion to metals.