Abstract: The paper gives a systematic research on coupling agents’ application and function in powder coatings. The two active groups of coupling agents play its roles in flowing, dispersion, shrinkage resistance, compatibility, deaeration, raising the fullness and reflection clarity of coating surface.

Keywords: Powder Coating, rheological agents, Polar Group, Wetness, dispersion

 

The powder coating’s property of film formation largely depends on solution’s fluidity and flowing during the process, and the main influences include surface tension, wet film tension and the uniform degree of coating surface tension. An effective means to modifier the flowing property is to add leveling agent and rheological agent in powder coating.

With raw materials’ soaring prices in recent years, and the rapid growth of powder coating, a large demand of leveling agent appears in market, the large cost price and the fierce market competition, all this factors lead a poor quality of the leveling agent for powder coating, which limit the improvement of powder coating in domestic market. In order to help the enterprises (in line with powder coating) to improve powder coatings’ quality, with principle of win-win effect, confirmed by plenty of tests, we successfully develop coupling agent, which own comprehensive properties in mass of rheological agents.

 

CH3-(CH2)n-CH2  CH3-(CH2)n-CH2  CH3-(CH2)n-CH2  CH3-(CH2)n-CH2         

              COOH              NH2             OH

The coupling agent newly researched by Zhihua Chemical contains at least 2 active groups, one is CH3-(CH2)n-CH2- non-polar group, and it can accelerate the coupling agent to fuse with resin; The other is hydrophilic polar group that contains -OH、-COOH, which can raise compatibility to base metals and accelerate the wetting dispersiveness of filler pigment. A paper points that, molecular center (the space between hydrophobic groups) contain hydrophilic group’s surface active agent, and the wetting property is super well. The coupling agent developed by us contains hydrophilic group in molecular center, molecular structure is as below, it has good wetting & dispersing property, and it can also accelerate adhesion.  

 

CH3-(CH2)n-CH2  CH3-(CH2)n-CH2  CH3-(CH2)n-CH2  CH3-(CH2)n-CH2         

              COOH              NH2             OH

The molecular structure determined it owns double-functions of flowing and wet-accelerating. This is the real reason that the agent can well improve flowing and anti-shrinkage. Also -OH、-COOH of coupling agent in powder coating can be combined with functional groups of resin by every form, which can greatly raise the resin function of wetting, enhance the compatibility with base resin, improve the whole transference trend of the coating surface, increase the gloss, fullness and clarity of surface.

In process of powder coating’s fusion and leveling to form layer, small molecule compound produced in process of curing reaction by air and water in coating may evaporate and detrain, leading to the growth of pinholes, and other holes. This phenomenon can be solved with dosage of anti-blowing agent (benzoin 0.3% wt of total), or with large dosage of Ethylene distearic amide. The coupling agent we developed contains a certain quantity of amide, which can effectively avoid pinholes and other defects’ appearance; it can substitute benzoin, and can solve the problem of yellowing when baked in high temperature with using benzoin

With special double-group structure of hydrophilic and hydrophobic groups, it can form super thin monolayer in process of forming coating surface and surface transference, which accelerate the flowing and dispersion of pigment with fully complete the pigment’s function, and it can obtain obvious effect in powder coatings contain metal pigment. The coupling agent has good compatibility with pigment, it can modifier the vivid color of coating surface. The technical specification is as below (table 1):

Table 1: technical data for coupling agent

 

 

We do large quantity research to prove the function and chemism of coupling agent. Prescriptions and usage effects are listed in table 2:

 

Table 2 shows the coupling agent has double-functions of improving flowing and degasification, and it can raise the gloss in powder coating.

Proved by lots of tests, with dosage 1 share coupling agent 3 share of resin can be reduced, and we can use fillers to replace resin. The result shows that the powder coating’s comprehensive quality is as good as sample powder coating.

 

Ø The function of coupling agent upon powder coating is comprehensive. In recent market with uneven quality of resin and fillers, the successfully development of coupling agent can modifier the powder coating’s comprehensive function. It has several functions in summary as below:

Ø Strong anti- interference property, which can greatly reduce the interference by different kinds of powder coating, it can also avoid the interference caused by organic silicon powder.

Ø High effective dispersity and compatibility. Which can raise the share of filler; reduce the dosage of resin, improving the function of metal powder. Under condition of lower dosage of metal powder, it can receive better textural quality of coating surface.

Ø Improve the clarity and fullness of coating surface, with dosage of active silicane in high-gloss powder can obviously raise the gloss of coating surface. With dosage of active silicane coupling agent applied to matting or dulling powder can improve the clarity of surface, no influence to gloss of surface; With 0.2% wt dosage of active silicane coupling agent in art-type powder coating, it can obtain the same or better effect.

Ø Eliminate the crater and pinhole caused by materials’ inter-compatibility, resins’ unevenly distribution, or poor dispersion by extruder screw

Ø Increase coverage of powder, an obvious effect can obtain in super fine powder’s extrusion

                   

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[2] Xiaoming Xia，Functional Powder Coating Additives，Beijing：Chemical Industry Press，75~84

[3] Zhenfa Chen, Techniques of Powder coating and Paint Coating，Shanghai: Shanghai Scientific and Technological Literature Publishing House，87~93