Characteristics and Application of Fluorine Coatings in Metal Packaging

In the world of Metal Packaging, the application of fluorine coatings has become more and more extensive. As large as containers, container drums, small convenience buckets, metal cans, etc., the use has expanded to the entire industry of metal Packaging. However, in China, the use of fluorine coating metal packaging products is still very limited, mainly for the internal coating of steel drums, and most of the internal coating of steel drums have not used fluorine coating. Therefore, fluorine coatings have a promising future in the field of metal packaging in China.

This article clarifies the excellent characteristics of fluorine coating for metal packaging, and the classification and application of metal packaging fluorine coating. It mainly discusses the development status of China's metal packaging fluorine coating, and the problems of China's metal packaging fluorine coating, and so on.

First, the excellent characteristics of metal packaging fluorine coating

In fluoropolymers, fluorine atoms are first substituted for hydrogen atoms and surround the carbon chain to form a close protective layer, making the carbon chain less vulnerable to external attack and making the entire molecular chain harder and spiraling; There are a large number of high-bonding C-F (460 kj/mol) bonds, which are the main reasons for the thermal stability and chemical inertness of fluoropolymers.

In addition, because the energy of the visible and ultraviolet parts of the solar energy that destroys the organic matter cannot destroy the F-C covalent bond, the polymer does not absorb the visible light and the ultraviolet light, and almost entirely passes through the fluoropolymer film. The coating film exhibits excellent weather resistance (When a pigment filler is selected, super weather resistance is selected, otherwise, the pigment filler itself affects the weather resistance of the entire fluoropolymer film).

Due to the excellent thermal stability, chemical resistance and super weatherability of fluoropolymers, the development and application of fluoropolymers are increasingly valued. The world and even our country have developed fluoropolymers for decades. However, the high crystallinity and insolubility of fluoropolymers that were developed early limited their practical application.

Second, the classification and application of metal packaging fluorine coating

Fluorine paints are divided into powder coatings and liquid coatings (suspensions, emulsion dispersions, solvent solvents). However, according to the use of our country, the fluorine coatings are divided into high-temperature curing fluorocarbon coatings and room temperature curing fluorocarbon coatings.

1. High-temperature curing fluorocarbon coating The high-temperature curing fluorocarbon coating needs high-temperature baking, dissolution and hardening. Such coatings include: PTFE coating, PVF, and PVDF coating.
● PTFE is mainly used in the fields of non-sealing and coating of metal packagings with low hygiene requirements, such as containers and food containers.
● PVF is resistant to all kinds of oils, acid and alkali salts and pesticides. It is commonly used for the inner wall coating of steel drums and small packaging containers. Such as bulk oil, food and pesticide packaging container wall.
● PVDF has super weather resistance and has the following advantages in the application of large-scale transport packaging:
1 long-term use of the coating does not fade; 2 excellent corrosion resistance; 3 good toughness; 4 excellent resistance to chalking and stain resistance.

2, room temperature curing fluorocarbon coating

The room-temperature curing fluorocarbon coating is a vinyl fluoride-vinyl ether (FEVE) coating. The introduction of -CL, -OH, -COOH and other active groups makes the resin not only soluble in solvents, but also can be cured at room temperature. In addition, the wettability of pigment fillers has been improved, making its application widely popularized.

Third, the status of China's metal packaging fluorine coating

China's fluorine coating mainly includes high temperature curing and room temperature curing.

High-temperature-curing Fluxetritol mainly refers to PVDF. Due to China's modernization and improvement of living standards in recent years, some manufacturers in Jiangsu, Zhejiang, and Guangdong have introduced advanced metal plate production lines abroad, which require corresponding supporting fluorine coatings (ie, PVDF), which is now coated with the outer layer of some large packaging containers. However, the fluorine coatings required by these metal plate production lines are technically demanding. In addition, most of the imported production lines comply with the foreign fluorine coating technical parameters, plus other reasons, making this application area mostly dominated by foreign products.

Domestic fluorine coatings mainly include powdered fluoropolymers from Shanghai Organic Institute, polyvinyl fluoride coatings from Zhejiang Chemical Industry Institute and PVDF from Shanghai San Aifu. However, due to the long-term technical accumulation of these products, and because of construction restrictions, these fluorine coatings are almost all room temperature curing type. This is because the industrialization and commercialization of room-temperature curing fluororesin in this year and two years, together with the ad propaganda of advertisements, made it fierce overnight and became a new star in the coating industry, and it also became a panacea for all kinds of film defects.

However, according to its synthetic raw materials, domestic and foreign products are somewhat different. For example, in Japan, a copolymer is synthesized from chlorotrifluoroethylene and alkyl vinyl ether. Its structure is a strictly alternating polymer; in China, it is synthesized from chlorotrifluoroethylene and alkyl vinyl ester. Hard to get alternating polymers. In addition, domestic resin products are of a single type, and there are no industry and national standards, and they are independent of each other and cannot provide a unified and ideal resin quality assurance. As for the room temperature-curable fluororesin, it gives a feeling that commercial hype is very strong.

Fourth, the domestic metal packaging fluorine coating problems

In 2003, the annual dosage of high-temperature-cured fluorocoatings in China was 1,000 tons, and the annual amount of normal-temperature-cured fluorocoatings was 300 tons. In the field of high-temperature fluorocarbon coatings, the speed of development of domestic production enterprises is much lower than that of the domestic market. High-temperature PVDF With the development of domestic packaging and other industries, its annual consumption ranges from 0 to 1,000 tons in 5 years, but domestic coatings have not yet seized the opportunity and the market share is very low.

Normal-temperature curing fluorocarbon coatings enter the disorder when the market has not yet formed. High-temperature curing fluorine coatings have been operating for 30 years, but still have considerable technical requirements of difficulty and complexity. Therefore, foreign mainstream plants adopt strict quality commitments and safeguard systems for the benefit of their customers. It is the resin manufacturer that issues the license to the coating manufacturer and the coating manufacturer grants the license to the coating company.

On the one hand, the license promises product quality, and on the other hand, it also promises to control the quality of downstream customers' products. This way, the end-user quality commitment includes the guarantees and commitments of several companies, which are heavier and more convincing.

Domestic enterprises do not have uniform standards and performance parameters, nor do they provide technical support for coating companies. Although most of the products of the paint factory are subject to artificial aging tests, they do not pay attention to communicating with metal packaging companies, do not pay attention to the collection and arrangement of outdoor exposure data, and do not have persuasive data and cases. (The most important feature of foreign products is the use of outdoor This time-consuming accumulation of exposure to evaluate paint performance).

Currently in the fluorine coating market at room temperature curing fluorine coating, no foreign intervention, this market is generally recognized by the good performance of high-temperature fluorine coating, and this metal packaging industry users did not really appreciate. In addition, room-temperature curing coatings have greater technical arbitrariness and difficulty in construction. This is manifested in: poor resin stability in the resin production process; wide range of pigments and auxiliaries in the coating; no uniform requirement for fluorine content (plus little fluorine Also called fluororesin). Therefore, it is necessary to strengthen the basic research of the resin on the one hand; on the other hand, it is necessary to cooperate with the coating industry and the application side to ensure the superiority of the fluorine coating itself. The current pressing need is an industry standard - a common standard.