The effect of the special leveling agent of powder coating on its physiculation performance was studied

Abstract: The classification, content, monosome and infrared map IR of the special leveling agent of powder coating are introduced, and the effects of different leveling agents on the surface surface of powder coating under the same system and the same amount of addition, melting viscosity, static coefficient of friction, inter-layer adhesion, glaching temperature Tg, gel time, fresh doI, leveling R, short wave Sw, long wave Lw and gloss are described.
0 Introduction
leveling agent is a very important additive in powder coatings and has an irreplaceable position. Leveling agent is often referred to as "interface active agent", because of its resin compatible is limited is excluded to the gas/liquid interface, so that the surface pressure of the coating in a balanced state, thus overcoming the surface defects caused by the difference in surface pressure .
this study selected a number of well-known suppliers at home and abroad leveling agent, by comparing its effective ingredient content, monosome and infrared map IR, it can be more intuitive and clear to see its similarities and differences; The test data reflect the effect of different leveling agents on the surface strength, melting viscosity, static friction coefficient, inter-layer adhesion, Tg, fresh-reflection DOI and leveling R, and then find a more suitable for the customer's field application in subsequent formulation design. The following experimental tests were conducted under the same addition 1%, hybrid system, extruse conditions, particle size, film thickness, spray conditions, and baking conditions.
1 leveling agent
1.1 classification
powder coating leveling agent can be divided into reactive and non-reactive type according to reaction type: general non-reactive leveling agent is more commonly used such as ESTRON Resiflow®P 67, Resiflow®PL-200, Ningbo South China Sea GLP588, etc., while reactive leveling agents are less used and more expensive such as ESTRON Resiflow®PH-240, etc.; Structures can be divided into acrylics and polyethers, which are more commonly used such as ESTRON Resiflow®P67, Resiflow®PL-200, Resiflow® -240, Ningbo South China Sea GLP588, PV88, polyethers are often used in transparent powder and more expensive such as Powdermate®486CFL, Powdermate®570FL and so on.
Because acrylic molecule polymerization is low, at room temperature is a liquid, so it is necessary to adsorption in the gas phase silicon dioxide carrier to make powder coating leveling agent, its effective content is usually 60% to 70%;
1.2 and monosome
This study selected 6 well-known leveling agents at home and abroad, and showed table 1 by Fourier Transform infrared spectrum FTIR and MRI spectrum NMR.
comparison can be found: PL-200, P67, GLP588, PH-240 belong to acrylic leveling agent, only PH-240 contains HEA monomer, this leveling agent is reactive leveling agent, and several other non-reactive leveling agent;
1.3 IR infrared map
can be compared by infrared map: PL-200, P67, GLP588, PH-240 acrylate leveling agent characteristic absorption peak consistent, map basic re-fit;
2 Chemical and chemical performance study
2.1 surface stress
surface stress is the sum of polar force and dispersion force, dispersion force is mainly Van der Hua force, polar force is mainly even moment, hydrogen bond, acid-base binding force. Surface stress has an important influence on the wetting of the substrate and inter-layer adhesion, low surface pressure contributes to the wetting of the substrate, high surface pressure contributes to the leveling of the powder coating, and this paper compares the coating surface pressure with the blank test by adding the same amount of 1% of different varieties of leveling agents in the Hybrid system.
can be compared by test data: acrylic leveling agent for the coating surface stress is slightly improved, can strengthen the inter-layer adhesion between flour and base powder, and polyether leveling agent 486CFL can Significantly reduce the surface pressure of the coating film, which has a great influence on inter-layer adhesion, re-painting and leveling, while the polyether leveling agent 570FL is a branching modified on the basis of the molecular structure of 486CFL to improve its re-painting performance.
2.2 Melt viscosity
Melting viscosity curve is a very important reference index for powder leveling and curing process, the melting viscosity curve can generally be divided into three stages: the first stage is the initial melting of powder, the second stage is powder melting and leveling, and the third stage is powder curing. The melting viscosity of the first and second stages of the powder decreases sharply with the temperature, which helps the powder wet, spread and level, and the third stage of the powder begins to cross-curing reaction at high temperature, the system viscosity begins to gradually increase, the surface pressure of the powder in this process will not change, but the leveling resistance will increase rapidly, which is basically no help for powder leveling.
this study compared the powder molten viscosity curve with the blank test in hybrid system by adding different varieties of leveling agents of the same amount of 1%.
It has long been generally believed that leveling agent can reduce the melting viscosity of the powder system, but as can be seen from the melting viscosity curve mentioned above, the main factor affecting the melting viscosity of the system is the temperature, as the temperature rises, the viscosity of the system drops sharply.
Through the comparison of molten viscosity curve, it can be found that acrylic leveling agents have slightly improved the effect of melting viscosity on powder systems, but the effect of polyether lysate on the melting viscosity of powder systems has been slightly reduced, and the changes have not been significant. Therefore, the leveling agent has less effect on the melting viscosity of the powder system, only that the leveling agent reduces the temperature at which the system begins to melt, thus prolonging the flow time after melting the powder coating and increasing its melting fluidity, which can be reflected in the slope of the melting viscosity curve.
2.3 static coefficient of friction
coefficient of friction refers to the ratio of friction between two surfaces and the vertical force acting on one of its surfaces, which is related to the roughness of the surface and the size of the contact area. The greater the roughness, the greater the coefficient of friction.
coefficient is a very important consideration for dual coating system and recoated system. The greater the coefficient of friction on the primer coating surface, the better the adhesion between it and the coating layer, so the choice of leveling agent in a dual coating system is also particularly important.
Through the comparison of test data, it can be known that: different leveling agents have a greater impact on the coefficient of static friction of the coating film, acrylic leveling agents for the coefficient of static friction of the coating film are showing a trend of increasing, while PL-200 and PH-240 are specifically designed to increase inter-layer adhesion of the leveling agent, the largest coefficient of friction; Reducing its coefficient of friction, coupled with its coating surface pressure reduction is also the largest, and through laboratory testing its re-painting performance is also the worst;
2.4 Glassed temperature Tg
glassed temperature refers to the transition temperature of a non-stereotyped polymer from a glass state to a highly bulleted state, and is the minimum temperature at which a large chain segment of a non-stereotyped polymer can move freely, usually expressed in Tg. Glass temperature is a very critical index for the storage stability of powder coating, it is generally believed that powder Tg is higher than 55 degrees C and its storage stability is better, of course, it is closely related to its resin content, particle size, type and dosage of desiccant, transportation environment and storage environment. This paper analyzes and compares the effects of different leveling agents of the same amount added on powder Tg in the Hybrid system.
Through the comparison of test data, it can be seen that different categories and varieties of leveling agents will reduce their powder Tg, that is, affect the stability of their powder storage, but from Figure 5, it can be seen that different leveling agents have less effect on powder Tg, all within 1 degree C, so leveling agent is not the main factor to reduce powder Tg.
2.5 gel time (200 degrees C)
gel time is an important index to reflect the powder coating, gel time measurement is a relatively simple and effective method of coating properties and quality control, but not as the actual curing time in the customer site construction process, only as a reference for powder leveling and curing time for research and development workers.
Through the comparison of test data, it can be found that acrylic leveling agent has a greater impact on the gel time of the powder, can greatly extend the time of powder melting leveling, while the polyether leveling agent has a smaller impact on the gel time of the powder, and contributes less to the time of powder melting level, mainly because of the influence of its surface pressure, and the driving force of powder melting level is mainly surface stress.
2.6 leveling R, short-wave Sw, long-wave Lw
BYK Wave Scan dual orange peeler is designed to express the appearance of coating film leveling, orange peel, freshness and other performance. Orange peel is a high-gloss surface composed of bright and dark areas of the ripple image, through optical scanning ripple image can simulate the visual perception of ripples, wave structure size of 0.1 to 30mm wavelength is called orange peel or level is not good. The higher the R value, the better the leveling, and the smaller the Sw and Lw values, the better the leveling.
According to the Navier Stokes equation, the leveling of powder coatings is mainly determined by the melting viscosity and surface tensivity of the system, which is inversely inversely related to the viscosity of the system and is directly related to the surface tension. The effect of different leveling agents on coating surface strength and system viscosity has been detailed in the first half of the article.
can be compared by test data: polyether leveling agent 486CFL, 570FL leveling is mainly due to its large impact on the coating surface stress, while acrylic leveling agent PL-200, P67 , GLP588, PH-240 and blank test phase is better mainly because of the less viscosity impact of its surface pressure is increased, there is also a reason that the addition of leveling agent extends the melting leveling time of the powder system, can be verified by the gel time.
2.7 Freshness DOI and Glossy
Freshness DOI can also be described as brightness, contour clarity, or clarity, influenced by very fine structures (i.e., obscurity) that our eyes can't argue about, and some ultra-short waves, Wa and Wb, also affect DOI, which together with obscurity are calculated to measure DOI. The higher the DOI value, the higher the freshness and the higher the film brightness.
as the surface characteristics of an object, depends on the surface-to-light specular reflectivity, so-called specular reflection refers to the reflection angle and the incoming angle of the same reflection phenomenon. Gloss is the physical amount that evaluates the ability of the surface of a material to reflect light under a set of geometric conditions. Therefore, it expresses a reflective nature with directional selection.
Through the comparison of test data can be found: acrylic, polyether leveling agents can improve the DOI value of the coating film, that is, clarity, and different leveling agents on the clarity of the impact is also greater, PH-240 is the most prominent, so in doing some high-brightness high-definition products can choose the appropriate leveling agent to achieve the best results;
3 conclusion
special leveling agent for powder coatings is essential in the formulation design process, and its principle of action is very complex. With the continuous updating of testing equipment and testing methods, the research of special leveling agents for powder coatings is also in-depth. This study illustrates the effects of different leveling agents on the physiculative properties of powder coatings by a large number of test equipment, and also hopes to give some reference opinions to researchers through test data, and then select the leveling agent suitable for the customer's field application.
Wen /Wen Jiajun, Tang Lintong, Guangdong Huacai Powder
Co., Ltd.