Abstract: Hydroxypolyester/Tetramethoxymethylurea (TMMGU) wrinkle powder coating, although not a new product, is widely used due to the high cost of raw materials, and there is little research and development work on this system of powder coatings. Based on extensive experimental research and practical application experience, the author provides a detailed introduction to the performance and application of the powder coating system. In addition to the familiar wrinkle powder coating, the hydroxypolyester/TMMGU system can also be used to prepare fine art powder coatings such as mesh, turtle, and peacock patterns, and is suitable for both indoor and outdoor powder coatings.

1. Preface

Wrinkle powder coatings have various names in the industry, such as Mianmian paint, water-based powder coatings, etc. The coating surface has a special texture effect and excellent decorative performance. Therefore, wrinkle powder coating is widely used for the coating of indoor and outdoor products such as hardware, furniture, electrical appliances, anti-theft doors, etc. Wrinkle powder coatings are divided into two types: epoxy/dicyandiamide type and hydroxypolyester/tetramethoxymethylurea type, which are respectively used for the coating of indoor decorative products and outdoor durable decorative products.

The raw materials for preparing epoxy/dicyandiamide wrinkle powder coatings are abundant in the domestic market, with convenient procurement and low prices. Therefore, this type of powder coating has been widely used and promoted in the domestic market since its launch. However, due to the need to import key raw materials, there are only a few domestic suppliers for the hydroxypolyester/tetramethoxymethylurea (TMMGU) wrinkle powder coating. The research and development technology is completely monopolized by foreign companies, and the sales price is jointly controlled by foreign manufacturers and domestic traders, resulting in extremely high raw material prices that completely exceed the acceptable capacity of domestic powder coatings and related consumer markets. Therefore, outdoor wrinkle powder coatings have almost no foothold in the domestic market, and the market has shrunk significantly. So far, there are very few companies that can develop and sell such products.

With the development of domestic powder coating raw material technology, this passive stalemate has been broken, and the selling price of key raw materials will be reduced by more than 50%. Raw material procurement will become simple, easy, and effortless! It will inevitably bring a storm to the promotion and application of outdoor wrinkle powder coatings in the domestic market!

2. Outdoor Wrinkle Powder Coating Technology

Durable wrinkle powder coating has excellent outdoor weather resistance and anti-aging degradation, which can be used for painting indoor and outdoor products. The current method for preparing outdoor durable wrinkle powder coatings is to combine low hydroxyl polyester resin with TMMGU resin, and form a coating with wrinkle effect under the catalysis of WL series amine blocking sulfonic acid. The structure of the formula for outdoor wrinkle powder coating is very similar to that of indoor wrinkle powder coating, with typical formulas shown in Table 1.

From the formula in Table 1, it can be seen that the formula structure of outdoor wrinkle powder coating is similar to that of indoor powder coating, mainly manifested in the following aspects:

(1) All adopt a main resin design formula. The main resin used for indoor wrinkle powder coating is universal bisphenol A epoxy resin, while outdoor wrinkle powder coating uses a hydroxyl value of 30; 5mgKOH/g low hydroxyl polyester resin. At present, the polyester resins used for P/TMMGU wrinkle powder coating include EL-1000H from the production association company and CRYLCOAT 2920-0 from the cyanide company. It should be noted that the hydroxyl polyester resin suitable for P/TMMGU wrinkle powder coating has a hydroxyl value of 30; 5mgKOH/g is optimal. The increase in resin hydroxyl value is not conducive to the formation of wrinkles on the surface of the coating. Hydroxyl value 40± Hydroxypolyester resin with a concentration of 5mgKOH/g can be used, but it should be avoided as much as possible. Hydroxyl value 50± Polyester resin with a concentration of 5mgKOH/g is mainly used for polyurethane powder coatings and is not suitable for P/TMMGU powder coatings.

(2) Both use a main crosslinking agent with a slower crosslinking reaction rate with the main resin. The curing agent for indoor wrinkle powder coating is ordinary melamine, and cannot replace or accelerate melamine, otherwise it will not form a wrinkle surface effect. The curing agent for outdoor wrinkle powder coating is TMMGU resin, which is the only type of amino resin applied to powder coatings. TMMGU resin was first developed by Cyanamid Corporation in the United States and has always had a high selling price in China. Now Taiyuan Keyuanda Company in Shanxi Province has localized TMMGU resin and conducted multiple batches of stability tests, which can fully meet the use of P/TMMGU wrinkle powder coatings. The resin price is much lower than that of similar imported products.

(3) All formulas use

Reaction catalyst promotes the formation of wrinkles on the surface of the coating. The catalyst used in indoor wrinkle powder coating is aluminum acetylacetonate, which has a strong catalytic effect on epoxy ring opening curing. XG605-1A from Nanhai Chemical, Wuhan Yanhuang, MCD from Dongguan Zhongtian, and SA208 from Jietongda all belong to this category of products. The catalyst used in outdoor wrinkle powder coating is amine blocking sulfonic acid catalyst, which is very expensive, such as ACTIRON&reg from SYNTRON in France; 32-18A (active ingredient of approximately 50%), ADDITOL&reg from Cyanide Company using resin as a carrier; 920 (active ingredient 5%), the WL series catalyst pioneered by the author in China (active ingredient 65%± 2%) is currently in the process of applying for a national patent. The WL series catalysts have comparable performance to similar imported catalysts, with high content of effective active ingredients, low dosage, and a price that is basically half of imported products, which is conducive to reducing formulation costs.

(4) Reaction rate regulators are used in the formula. The use of reaction rate regulators in wrinkle powder coatings can improve the fluctuations in the physical and mechanical properties of the coating caused by the increase or decrease in catalyst dosage, which helps to enhance the gloss of the coating. The indoor wrinkle powder coating uses a 6/4 polyester resin with a medium acid value (52-58mgKOH/g) and medium speed reaction. This polyester was originally designed for epoxy/polyester hybrid powder coatings. The outdoor wrinkle powder coating uses closed or internally closed isocyanate resin as a reaction rate regulator. This type of isocyanate resin is dominated by products from Degussa and Bayer, with higher prices. Hangzhou Jintian Chemical Co., Ltd. in China has developed a closed isocyanate resin; TS280， It has been pushed to the market. This product has a relatively low selling price and is suitable for the development of outdoor wrinkle powder coating products by domestic enterprises.

(5) Wrinkle powder coating has selectivity towards fillers. In the formulation design of wrinkle powder coatings, different types or levels of fillers can more or less affect the gloss and texture effect of the coating. When designing wrinkle powder coatings for indoor and outdoor use, product designers must recognize the impact of fillers on the gloss and texture of the coating. The author believes that ultrafine barium sulfate is the best choice and does not recommend precipitation flow barium sulfate, extinction barium sulfate (with coarse particle size), and weakly alkaline calcium carbonate (including heavy and light types) as fillers for such powder coatings.

(6) The curing conditions are similar. The curing conditions of thermosetting powder coatings depend on slow reacting components. Wrinkle powder coatings of epoxy and hydroxyl polyester systems both have slow reacting crosslinking components, so the curing conditions are 15min@200 Above ℃.

3. Extension development and innovation of outdoor wrinkle powder coating

Outdoor wrinkle powder coating (P/TMMGU type) is widely used in foreign-funded enterprises. Due to technological, raw material, and price monopolies, domestic enterprises have been unable to widely and effectively develop, apply, and innovate P/TMMGU type wrinkle powder coating. At present, the raw materials for developing outdoor wrinkle powder coatings in China have been basically solved, with sufficient supply and low prices, which is conducive to the development of such products. As P/TMMGU wrinkle products are no longer considered new products, this article will not delve into the product design of P/TMMGU wrinkle powder coatings in detail.

3.1 Mesh powder coating

Mesh powder coating is a type of powder coating developed on the basis of wrinkled powder coating, which has a net like texture appearance effect. The net like texture is very clear (Figure 1 and Figure 2). The formula for outdoor mesh powder coating is shown in Table 2.

Formula 2 indicates that the mesh powder coating is obtained by adding a mesh agent (usually using a floating agent as the mesh agent) on the basis of the wrinkle powder coating formula. Under normal circumstances, the film-forming substance content in the formula of mesh powder coating is higher than that in the formula of wrinkled powder coating, and with the increase of film-forming substance content, the coating pattern clarity is higher and the pattern is larger.

3.2 Turtle Pattern Powder Coating

Turtle pattern powder coating is also based on the principle of incompatibility, and there are various methods for preparing turtle pattern powder coating: (1) epoxy type turtle pattern powder coating, which is prepared by adding turtle pattern agent on the basis of epoxy type wrinkle powder; (2) Epoxy/polyester type turtle grain powder coating, made of special 6/4 polyester resin, combined with an appropriate amount of acetylacetone aluminum (wrinkle catalyst) and externally added turtle grain agent; (3) Low acid value carboxyl polyester resin and extinction type GMA acrylic resin are prepared in a specific ratio, with the addition of a turtle grain agent Low hydroxyl value hydroxyl polyester resin and TMMGU are catalyzed by WL amine blocking sulfonic acid, and externally added with a turtle like agent to form a very stable turtle like effect coating. The appearance of the coating is shown in Figure 3-4, and the typical formula is shown in Table 3.

P/TMMGU type turtle grain powder coating is also obtained by adding turtle grain agent on the basis of wrinkle powder coating. The difference from the mesh formula is that the external mixed additive used is turtle grain agent instead of mesh agent. Compared with wrinkle and mesh powder coating formulas, the film-forming substance content of turtle pattern powder coating formulas is significantly higher than that of wrinkle and mesh powder formulas. Generally, the higher the film-forming substance content, the larger the particle size of the turtle pattern agent, and the less the amount used, the more obvious the turtle pattern effect formed, and the larger the pattern.

3.3 Peacock Pattern Powder Coating

P/TMMGU wrinkle powder coating and epoxy/DICY wrinkle powder coating have different film-forming substances and curing mechanisms, resulting in P/TMMGU wrinkle powder being more distinctive and having better decorative properties than epoxy/DICY wrinkle powder. If you carefully observe the appearance of the two types of wrinkle coatings, you can find subtle differences in their texture, that is, different patterns. A more intuitive difference is that the P/TMMGU powder, under the catalytic action of WL amine blocked sulfonic acid, can form a peacock pattern (spotted effect) appearance by adding some pollen externally, as shown in Figures 5-6. And this special peacock pattern effect cannot be achieved by other types of powder coatings. The formula of peacock pattern powder coating is shown in Table 4.

Peacock pattern powder coating is a variant or extension of dot flower powder coating, formed by mixing a wrinkle base powder with one, two or more types of dot pollen. Epoxy wrinkle powder coating cannot achieve a peacock like appearance effect, and pollen cannot show color effects in epoxy wrinkle powder coating. In P/TMMGU wrinkle powder coating, the color display of dot pollen is similar or better than that in hammer powder or other ordinary flat powder coatings, thus forming a peacock like appearance effect. Affected by the bottom powder pattern, the P/TMMGU type peacock pattern has a significantly different effect from the pattern of ordinary dot pollen powder, and is more like the color effect of peacock feathers.

4. Application and Research of Epoxy Polymers in Outdoor Mesh and Turtle Pattern Powder Coatings

Blocked isocyanates are widely used in P/TMMGU type wrinkle, mesh, turtle and peacock pattern powder coatings, which can not only adjust the reaction rate, but also effectively reduce; Node” The occurrence of defects. P/TMMGU powder coating, under the catalytic action of amine blocking sulfonic acid, blocking isocyanate is not the only coating surface modifier. Epoxy polymers, such as TGIC, PT910, PT912, GMA acrylic resin, etc., have a dual regulating effect on the pattern and gloss of P/TMMGU type mesh and turtle pattern powder coatings. Bisphenol A epoxy resin is the most typical representative. The experimental formula is shown in Table 5, and the results of the coating performance test are shown in Table 6. The coating baking conditions during the test are as follows: 15min@200 ℃.

The experimental results in Table 6 indicate that adding different amounts of epoxy resin to the formula of P/TMMGU wrinkle powder coating will significantly affect the coating's surface gloss, texture, and mechanical properties. It should be noted that when the epoxy resin addition is 4%, the coating exhibits a regular pattern; Crocodile Skin” Appearance effect, which is commonly referred to as“ Turtle pattern; Effect, but no“ was added to the formula at this time; Turtle line agent;. The results in Table 6 also indicate that when the amount of epoxy resin added in the formula exceeds 6%, the wrinkling effect of the coating film basically disappears and the mechanical properties significantly decrease. Therefore, it can be preliminarily confirmed that the addition amount of epoxy resin in P/TMMGU wrinkle powder coating is below 6%.

Amine blocking sulfonic acid is a special catalyst. During the baking and curing process of P/TMMGU powder coating, it will decompose into two compounds: organic acids and amines. Amine volatile compounds will evaporate with heating, and organic acids will effectively catalyze the reaction between TMMGU resin and hydroxyl groups. In fact, during the powder baking process, amines cannot be completely evaporated, and residual amines can have an impact on; Acid catalyzed TMMGU hydroxyl reaction; Generate a blocking effect. Due to the presence of tertiary amine structure in the amine produced by catalyst decomposition, it has a catalytic effect on the ring opening of epoxy groups. Therefore, the addition of epoxy resin consumes residual amines and also consumes a small amount of carboxyl groups on the hydroxyl polyester. With the sharp decrease in the number of amine and polyester carboxyl groups, the catalytic effect of organic acids on the reaction process reaches its limit, which is beneficial for reducing the gloss of the coating. But with the increase of epoxy resin, excessive epoxy resin is not conducive to catalytic action, which will once again lead to an increase in gloss.

Due to; Hydroxypolyester+TMMGU+WL catalyst; The reaction mechanism of the powder coating is very complex, and the addition of epoxy resin will cause certain interference, which to some extent affects the appearance of the final coating. Therefore, the absence of a turtle like agent in the powder coating formula also produces a turtle like effect. The characteristic of epoxy polymer makes it easy to design turtle grain powder coatings. If mesh or turtle grain agents are used, different coating effects will be presented.

5. Application and Research of Outdoor Wrinkle Powder Coating

Compared with epoxy wrinkle powder coating, a significant feature of P/TMMGU wrinkle powder coating is its excellent weather resistance, which can be used for the coating of indoor and outdoor metal products. This is the reason why P/TMMGU wrinkle powder coating is widely used. Another use of P/TMMGU wrinkle powder coating cannot be ignored, which is that it can be cured in a direct fired oven, with slight changes in coating gloss and texture.

When using a direct fired baking oven for curing, the fuels used in the direct fired baking oven are coal, petroleum, natural gas, coal gas, etc. During the combustion process, inorganic oxides such as C, S, P, N are produced, which have a certain catalytic effect and side effects on the coating being crosslinked and cured. If such inorganic oxides enter the furnace, they will undoubtedly affect the film-forming process of coating melting and solidification, especially the cross-linking reaction process, causing changes in the physical and chemical properties and appearance of the coating, such as adhesion, gloss, color, coating texture and appearance, ultimately leading to peeling, poor interlayer adhesion, large-scale loss of gloss, yellowing and discoloration of the coating, texture changes, etc. Whether it is outdoor P/TMMGU wrinkle powder coating or indoor epoxy/DICY wrinkle powder coating, the wrinkle appearance effect is formed under the action of specific catalysts. Practical applications have shown that some coating factories, due to direct fired baking ovens, experience serious loss of gloss and reduced texture when using epoxy/DICY wrinkled powder coating, resulting in serious consequences such as product coating failure! Powder manufacturers and coating companies are at a loss about this. During the process of providing on-site technical services to customers, the author found that using P/TMMGU wrinkle powder coating can solve the problems of severe loss of gloss and significant changes in texture caused by baking of epoxy/DICY wrinkle powder coating. So when customers cannot change the oven conditions, using P/TMMGU wrinkle powder coating for coating is an inevitable choice!

6. Summary

P/TMMGU powder coating is a unique type of powder coating, and many of its properties and applications are yet to be developed. We believe that there will be more related products in the industry in the near future.

For the Chinese nation, who love colorful and vibrant lifestyles, the love for P/TMMGU powder coatings is innate. I believe that with the significant reduction in the prices of related raw materials, this type of powder coating will have broad development space in China.