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Development of Amino Baking Paint Used in Transformer Coating Equipment

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Release time:

2021-06-17 19:40

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0 Preface

Amino baking paint is one of the important varieties of transformer protective coatings. At present, the baking temperature of amino baking paint used in this industry is generally above 100 ℃, even as high as 180 ℃, curing time is generally 60 to 120 min, and the amount of formaldehyde emission is relatively high. Large, with a distinct pungent smell. With the development of society, more people pay attention to human health and energy saving. This article focuses on the improvement of traditional amino baking varnishes such as high curing temperature, long curing time and large formaldehyde emission.

In this paper, through the selection of amino resin, catalyst, stabilizer and solvent and the optimization of the dosage, various amino baking paints with good performance are prepared, which reduces the curing temperature and curing time of the amino baking paint, and the formaldehyde of the amino baking paint The release amount is significantly reduced. The reduction of curing temperature and curing time reduces the requirements of amino baking paint for the use conditions, expands the construction window, and lays the foundation for the expansion of the market application of amino baking paint; the significantly reduced formaldehyde emission makes the amino baking paint move towards environmental protection A step away.

1 Test part

1.1 Main raw materials

Amino resin, hydroxy alkyd, catalyst, stabilizer, dispersant, leveling agent, defoamer, rheological agent, are all industrial products.

1.2 Preparation process

Stir hydroxy resin, pigment filler, dispersant, defoamer, leveling agent and appropriate amount of thinner evenly, grind to fineness ≤ 25μm, after the paint temperature drops below 30 ℃, add stabilizer, amino resin and catalyst in sequence , Stir evenly, and finally add rheological additives under stirring, and ensure that it is evenly dispersed before packaging.

1.3 Performance testing standards

Viscosity: GB/T 1723, adhesion: GB 1720, pendulum hardness: GB/T 1730, impact resistance: GB/T 1723, flexibility: GB/T 1731.

2 Results and discussion

Amino resins play a very important role in improving the gloss, hardness, and chemical resistance of the paint film. Although amino resin occupies a small proportion in amino paint, the improvement of amino paint performance is achieved by adjusting its dosage and variety. While amino resins bring excellent performance, they also bring formaldehyde, which is harmful to people's health. There are two ways that amino resins can bring formaldehyde. 1) Amino resins themselves contain a certain amount of formaldehyde, and 2) Amino resins produce formaldehyde during curing. In order to reduce the amount of formaldehyde produced during the production and curing of the amino paint, two tasks need to be done. First, select an amino resin with low formaldehyde content, and secondly, by inhibiting the occurrence of related reactions during the curing process.

The curing temperature and time of the amino baking paint also have a negative impact on the energy demand and the convenience of construction. Adding a catalyst to the system can reduce the curing temperature and curing time, but the addition of the catalyst will bring about the storage stability of the amino paint. In order to eliminate such unfavorable factors, a stabilizer is introduced into the amino paint, so that the amino paint has good storage stability and at the same time has a lower curing temperature and a shorter curing time.

The solvent system as a storage medium also has a certain impact on the stability of the amino paint.

Therefore, this article discusses the influence of the types and amounts of amino resins, catalysts, stabilizers, and solvents on amino paints, and determines their types and the best amount in amino paints through experiments.

2.1 The influence of the type and amount of amino resin on the formaldehyde emission and performance of amino baking paint

The content of formaldehyde in the atmospheric environment has a greater impact on the construction personnel, and the impact of formaldehyde on the health of the construction personnel is shown in Table 1.

The free formaldehyde contained in the amino resin and the formaldehyde produced during the curing process of the amino resin are the main sources of formaldehyde released during the curing process of the amino baking paint. Therefore, the selection of the amino resin variety is the main means to reduce the formaldehyde emission of the amino baking paint. Choosing different amino resins has different effects on amino baking paint. For this reason, we compare the formaldehyde emission and the influence on the performance of amino baking paint with several commercially available products. See Table 2 respectively, 582 and 582- 2 The content of free formaldehyde in amino resin is relatively high and should not be used. The other 3 kinds of amino resin have relatively low free formaldehyde content and can be considered for use.

In addition, the type and content of functional groups in amino resins are one of the important sources of formaldehyde released during the construction of amino baking paints. Generally, the active functional groups of amino resins are alkoxy, imino and hydroxymethyl groups. Among them, hydroxymethyl is in the paint. Formaldehyde removal reaction easily occurs when the film is cured: ~N(CH2OCH3) CH2OH→ ~NHCH2OCH3+HCHO.

At present, the main functional groups of the 917, 717 and 525 types of commercially available amino resins are alkoxy and imino groups. Amino baking paints prepared using these amino resins release very little formaldehyde during curing, so these three types are used. The amino resin was tested with paint, and the performance of the formulated amino baking paint is shown in Table 3.

It can be seen from Table 3: Use 917 amino resin, the paint film hardness is low, so it is not suitable; use 525 amino resin and 717 amino resin, the overall performance of the paint film is better, both can be used in low-temperature curing amino paint; amino resin The dosage is about 30% of the amount of alkyd resin. If the dosage is too small, the cross-linking density of the paint film is not enough, resulting in low hardness; on the contrary, the hardness is too high, impact resistance, and cost increase.

2.2 The choice of catalyst

When the amino baking varnish is cured, the amino resin and the matrix resin mainly undergo the following two cross-linking reactions:

~NCH2OR + NH~→ ~N CH2N~ + ROH (self-crosslinking)

~NCH2OR+HOR, →~NCH2OR, +ROH (cross-linked with base resin)

In order to reduce the curing temperature of the amino baking varnish, only the high-activity amino resin cannot meet the requirements. Therefore, a catalyst needs to be added to reduce the curing temperature of the coating. H+ catalyzes the cross-linking and curing reaction of the amino baking varnish, so an acid catalyst is introduced to reduce the curing temperature. The curing temperature of the paint film is cross-linked, the curing temperature of the amino baking paint is reduced to (90±2) ℃, different H+ catalysts are selected, and the effects of different catalysts and dosages on the new performance of the coating are verified. The results are shown in Table 4.

Note: KC color is nearly water white, HAH, 2403 are reddish brown

It can be seen from Table 4 that the catalytic effect of the catalyst weakens according to KC, HAH, and 2403; the catalytic effect of 2403 is poor, and the color is dark, so give up; the amount of KC is large, but the color is light, so it is suitable for light-colored paint; on the contrary, HAH is used for dark paint.

2.3 The choice of stabilizer

Although the introduction of highly active amino resins and catalysts has a very good effect on reducing the curing temperature of amino baking paints, it also brings great negative effects, mainly in the deterioration of storage stability. In this case, a method is often used, which is to seal the acid catalyst with a stabilizer. After the sealing, a latent catalyst is formed. Under the baking conditions, the latent catalyst will decompose, and the acid catalyst will be effective to complete the curing process of the paint film. While improving the storage stability of amino baking paint, this kind of stabilizer has no obvious influence on the catalytic curing effect of the catalyst. The selection of different stabilizers has different effects on the performance of amino baking paint. The results are shown in Table 5.

It can be seen from Table 6 that when the proportion of xylene in the solvent system is higher, the viscosity of the paint during storage rises faster, which is not conducive to storage stability; when the ratio of butanol increases, the viscosity of the paint rises slowly during storage. , The storage stability is obviously improved; after the test, it is found that the solvent system adopts xylene:butanol=7:3, which can ensure the storage stability while making the viscosity appropriate.

2.5 The effect of curing temperature and time of amino baking varnish on coating performance

Before and after the use of high-activity amino resin and catalyst for the amino baking paint (referred to as before and after use), under different baking and curing conditions, the performance of the paint film is shown in Table 7.

It can be seen from Table 7 that at the same baking temperature (such as 1# and 3#), the high-activity amino resin needs a shorter baking time than before it is used, that is, it only consumes less energy; When the baking time is the same (such as 1# and 4#), the high-activity amino resin needs a significantly lower baking temperature (such as 90 ℃) after use than before use. Generally, the baking equipment only needs steam heating. Electric heating reduces unsafe factors.

3 Conclusion

Through the selection of amino resin, catalyst, stabilizer and solvent and the optimization of the dosage, various amino baking paints with good performance were prepared. The curing temperature of the prepared amino baking paint was reduced to 90 ℃, and the curing time was reduced to 30 min. The formaldehyde emission of amino baking paint is significantly reduced. The reduction of curing temperature and curing time expands the construction window and lays a foundation for the expansion of the market application of amino baking paint; the formaldehyde emission of the amino baking paint is significantly reduced, which makes the amino baking paint one step closer to environmental protection.