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Selection principle and characteristics of powder coating matting agent

 2.1 determine the luster of several factors
When the surface when exposed to light, the surface roughness is different, part of the light reflected by the surface, a part of a diffuse, and part of the object itself is absorbed. Therefore, the fact that the surface of the object reflects the light is reflected. If the light is reflected, the more light the surface of the object, the size of the reflective ability can be measured by means of a gloss instrument and expressed as a percentage. Obviously, the more uneven surface of the object, the higher the light scattering or refraction, the lower the. Therefore, the surface roughness increases can make objects produce extinction, which is the essence of powder coating for extinction, so to speak, to make the powder coating to produce specific extinction must increase the film surface roughness, as we design different curing systems or different curing agents to provide a broad space.
2.2 powder coating matting method
It is more difficult to solve the extinction of powder coating compared with liquid coating. Pigment migration to the surface of dry coating in liquid coatings, due to pigment aggregation leads to increased roughness and the extinction effect established, however, powder coating because it does not contain solvents in the curing process, the viscosity is quite large, that from low viscosity to solid phase migration is not likely to happen, not in the accumulation of pigment and filler coating on the surface, so the powder coating matting has a certain particularity. But generally speaking, the extinction of powder coating can be obtained by the following methods:
2.2.1 filler addition method
Join the BaSO4, such as CaCO3, kaolin, barite, fumed silica, mica powder in the coating component in filling material. In theory can produce surface extinction effect from high light to light, but with the increase of mechanical properties of filler coating decreased sharply, leveling deterioration, so this method is only suitable for coating in the preparation of more than 60 degrees luster, limited scope of application.
2.2.2 add incompatible substances
Will not be compatible with the resin material adding component, the high temperature baking stage they can flow freely but is non homogeneous state, after cooling from the system arrangement in the homogeneous distribution of non precipitation surface, rough surface scattering of light so as to reduce the formation of light. Such as polyethylene acetate fiber derivatives, cellulose esters, etc.. In this system without leveling agent and select appropriate incompatible substances, the viscosity decreases sharply during the cooling process, when the precipitation from the system can also produce surface wrinkles (Yi Shiman, CAB is this kind of material). Add the appropriate catalyst in the wax matting agent will strengthen the extinction effect, this is because the accelerator in the curing process to strengthen the surface contraction produced a fine uneven wave structure leads to system gloss further reduced, such as Hefei Ketai chemical KT109 is this kind of matting agent, which is composed of modified polyethylene wax and composite the catalyst can be used for TGIC or mixed system, adjust the extinction effect formula can produce 30%~60%, and will not have a negative impact on weather resistance. But the addition of incompatible substances of extinction has its limitations, the first is difficult to prepare less than 30% gloss powder, add excess wax compounds but also easy to cause the seeping from the surface to the processing trouble; second component uneven distribution is often affected by the extrusion conditions, which lead to the fluctuation of gloss. Hefei Ketai chemical industry developed on the basis of low wax content outdoor matting agent KT209P has a certain reaction, because the wax content can be prepared and black system can get below the film gloss 15%, is on the wax matting agent for a successful improvement.


2.2.3 dry mixed method
Dry mixing of two different reactive powders or two incompatible types of powders can produce the extinction effect. In order to improve the mixing effect of two kinds of powder will usually be crushed together instead of the two kinds of powder simple mechanical dry mix, two kinds of powder, the gel time is not the same, some fast reaction powder first reticulated structure, reduced the liquidity of the system. Limiting the subsequent reaction to the activity of the lower powder cross linking, the two different responses of the stress contraction to the formation of microscopic rough surfaces lead to extinction. A good example is the mixture of two different reactive polyester powders such as polyester based /TGIC 90:10 and 96:4 powders, polyester / hydroxy amide 90:10 and 96:4 (96.5:3.5) powders. In general, the larger the difference of the reaction activity, the better the extinction effect.
Mixing with a different chemical reaction mechanism, melt viscosity, surface tension of the powder will lead to the film surface roughness (sometimes referred to as pollution) to produce extinction. A simple example is the mixed type and TGIC high gloss polyester hybrid and pure epoxy, polyurethane /TGIC system of dry mix, these combinations can produce 30%~40% ranging from extinction, which greatly affect the sensitivity of different gloss polyester resin.
Dry mixing extinction is a very time consuming method. Sometimes, because of the difference of the mixing effect, it will cause the phenomenon of bad reproduction, and sometimes produce uneven surface.
2.2.4 primary extrusion
The primary extrusion method overcomes the instability of the dry mixing method, which contains at least two chemical reactions with different reaction rates. It is based on the following principle: the curing agent of a resin and a bifunctional or a resin and a curing agent two, or two kinds of resin and a curing agent, or different resin and two (three) curing agent. In general, the greater the difference in reaction rate, the lower the gloss of the film.
A curing agent that has two functional groups. The most classic is to generate the familiar polycarboxylic acid and ring amidine salts (such as benzoic acid and 2- phenyl -2- four imidazoline). That is, Degussa's vestagon B68, B55. B68 is a single salt, the structure is as follows:

The B55 is a double salt, the structure is as follows:


It is often used as a pure epoxy and a hybrid type of curing agent. The mechanism is that, in the amount of curing agent, amidine is not enough to completely cured epoxy resin, only part of the pre crosslinking, as the temperature continues to rise, the response to low activity of carboxylic acid and epoxy reaction because of polyfunctional carboxylic acid, so the reaction must with strong contraction of molecules. However, this phenomenon is offset by the pre crosslinked resin portion, which limits its further mobility. Further crosslinking can not be compensated by the uniform shrinkage of the film. Therefore, the final contraction retardation phenomenon will lead to uneven shrinkage on the surface of the film, resulting in extinction.
In addition to the above reaction in the mixed system, the amine structure of the curing agent also plays a catalytic role in the epoxy and polyester, but the actual reaction mechanism is more complex:



As mentioned above, if the system is not completely cured or cured at different temperatures will produce significant gloss differences. This difference does not mean that the curing agent is not good, to a large extent depends on the complexity of these multi component systems. Because the formula must have the reactants and the reaction of curing agent enough, so polyester in this complex system also plays an extremely important role, its physical and chemical properties have great influence on the extinction effect of different manufacturers, in other words the polyester similar will not produce the same effect of extinction. Therefore, it is very important to select suitable polyester. In the mixed system, the amount of the matting agent should take into account the amount of epoxy resin consumed at the end of the polyester reaction.
Must pay attention to join in the delustrant excess is not suitable for the use of the matting agent, because the ring amidine matting agent in excess of if enough in the epoxy resin curing system, the coating will be the formation of a high luster, because at this time, with the increase of temperature and not excess carboxylic acid epoxy reaction, it will not shrink the effect of this film occurred.
Polycarboxylic acid matting agent containing cyclic amidines can provide excellent leveling effect, and also has good effect on block water and surfactant. However, due to the shrinkage of the film, so the mechanical properties (such as impact performance) is poor. At the same time because of cyclic amidines, coating during baking yellowing tendency is very serious. In addition, the baking temperature is an important factor affecting the extinction of the system. Too low or too high baking temperature is not conducive to the low extinction effect. General recommendations for ideal 170220 in C. Due to have high activity of cyclic amidines of extinction in the curing agent, so the extrusion temperature should not be too high, extrusion temperature will lead to part of the pre crosslinking powder is too high, the extinction effect and leveling, the monitoring results show that the cyclic amidines began to produce the reaction with epoxy is at 120 DEG C, so the suitable temperature control is a must the.
Two price of cyclic amidines and polycarboxylic acid salt can lead to extinction effect of 18 - 25, also known as Matt delustrant, such as Hefei Ketai chemical KT55. PMA and 2- can also 2-phenylimidazoline of salt, but the general effect can only obtain the extinction effect of more than and 30 degrees.
The German SKW has developed a new pc45 Dyhard extinction curing agent, which is composed of a 2- phenyl -2- imidazoline (component A) and a mixture of three triazine derivatives (group B). Can be used with epoxy or polyester / epoxy curing system, the initial component A crosslinking, surface tension forming region, the B component is then completed completely cured, punctate protuberance on the surface of the tiny curing to extinction. Adjust the A and B components to achieve a minimum of 10% extinction effect.
Thomas Swan Casamid 142 is also a mixture of curing agents in epoxy system can provide the extinction effect of 5% and the mixed system of the extinction effect of 15%.
Another based on multistage reaction mechanism of delustrant is a polyfunctional epoxy for naphthenic acid and mixed type of extinction. This product can obtain the extinction effect of 0 - 50%, high functional groups leads to non-uniformity of the crosslinking density, and the characteristics of alicyclic also determines the miscibility and containing aromatic polyester and epoxy has poor. Aliphatic carboxylic acid reaction is slower than aromatic carboxylic acid. Therefore, the reaction film has been partially crosslinked, resulting in the coating due to blockage of the film. Further study showed that the gloss and curing conditions were not related. Therefore, it is concluded that the incompatibility and the immiscibility ratio are more important than the reaction activity. Huntsman's DT3357 is the kind of product. The extinction effect of "5%" can be obtained in the epoxy and mixed system, and no yellowing phenomenon will be produced. Because of the low activity of the reaction, a special catalyst is needed to initiate the reaction. Therefore, it is very important to adjust the formula and choose the suitable catalyst in order to get a good effect. Its chemical structure is as follows: 
[2,2,6,6-tetra(β-carboxyl ethyl) cyclohexanone]
In 1997, Bayer invented the light within the closed type polyurethane powder system, the principle of this system is two (n d ketone uretdione curing agent and long chain carboxylic acids or mixtures). Uretdione and hydroxyl polyester reaction. Two yuan TGIC or carboxylic acid and hydroxyl alkyl amide (HAA) reaction, crosslinking reaction will be parallel at different rates and influence each other, leading to confusion and extinction of the film, 10 - 15%, to obtain the extinction effect by adjusting the proportion of the minimum.
In 1999, Bayer was also prepared as a near complete light free polyurethane coating, which contained two functional groups, namely isocyanate and carboxyl group. The sample number is Crelan VPLS 2181/1. These groups allow the two parallel reactions to occur, the reaction of blocked isocyanate and hydroxyl polyester, and the reaction of hydroxyl amide or TGIC and carboxyl groups. Such as hydroxyl polyester 50.4 parts (hydroxyl value of 30), Crelan VPLS2181/1 10.8pbw, Araldite PT910 1.8pbw. can produce light extinction.
The chemical extinction structure of Crelan VPLS2181/1 is as follows:

It can also be a combination of two hydroxyl resin and curing agent can also produce good matting effect. Such as hydroxyl value of 30 and of hydroxyl resin and curing agent Crelan VPLS214 in nitrogen butyl ketone (uretdione) combination can produce 15 - 20% extinction effect.
The use of carboxyl polyester and acrylic acid glycidyl ester and acrylic acid copolymer with GMA can also produce a very good extinction, in the system of polymerization of GMA and hydroxyl polyester reaction. In order to obtain better mechanical properties can also be combined with HAA or TGIC to complete. This system can produce a minimum extinction effect of 5%. High temperature baking is also very excellent, the typical products of Hefei Elcoteq KT188, CP550 Worlee. This product is the main defect of poor mechanical properties, surface scratch resistance effect is unsatisfactory (now there has been a great change in the preparation of > 15%), gloss, reproducibility is not stable.
The high extinction effect is often due to the microstructure of the surface, and the DSC analysis of the curing process indicates that the reaction has a wide exothermic reaction. It can be inferred that there are multiple reactions leading to the extinction of the surface, so the GMA based reaction can be referred to as the multistage curing reaction.
Another based on multistage reaction mechanism of delustrant is a polyfunctional epoxy for naphthenic acid and mixed type of extinction. This product can obtain the extinction effect of 0 - 50%, high functional groups leads to non-uniformity of the crosslinking density, and the characteristics of alicyclic also determines the miscibility and containing aromatic polyester and epoxy has poor. Aliphatic carboxylic acid reaction is slower than aromatic carboxylic acid. Therefore, the reaction film has been partially crosslinked, resulting in the coating due to blockage of the film. Further study showed that the gloss and curing conditions were not related. Therefore, it is concluded that the incompatibility and the immiscibility ratio are more important than the reaction activity. South Sea Co XG633 is such products. The extinction effect of "5%" can be obtained in the epoxy and mixed system, and no yellowing phenomenon will be produced. Because of the low activity of the reaction, a special catalyst is needed to initiate the reaction. Therefore, it is very important to adjust the formula and choose the suitable catalyst in order to get a good effect.
A low molecular weight SMA (styrene maleic anhydride) copolymer can also be used for the extinction of epoxy resins. It is also based on two kinds of reactions produced by micro shrinkage surface and extinction. Fast reaction between epoxy resin and SMA, faster response and faster reaction can be provided through a combination of epoxy and dicyandiamide. In the hybrid system, the components of epoxy, SMA and polyester resins must be well balanced to achieve better balance performance.
The following chemical equations describe the main reactions experienced by the functional groups of SMA resins in the mixed system:

Through our experiments show that the SMA resin can generate extinction but the extinction effect and mechanical properties are not completely balanced, sometimes adding catalyst is a must, and resistance to yellowing and now the mainstream delustrant than no advantage.
A new type of 2.2.5. yellow stain resistant agent
The early anti yellowing agent Huntsman extinction DT3357 products in a hybrid system, extinction effect of this product is very good, but the fatal flaw is to obtain good mechanical properties need to start 3357 of the catalyst, filler is critical, adding acids need extra epoxy to balance, so different you need a different gloss epoxy / polyester and 3357 proportion to, so it is very troublesome, 3357 and a painful disadvantage is the long time storage powder luster will rise, until the publication of DT3360 to solve this problem, this is a mixed system with non yellowing matting agent, do not need to change the proportion of epoxy polyester can provide 15 - 40 extinction effect luster, also is our country now popular so-called "physical matting agent", but the mechanism and composition of China is not the same. The first to launch this type of delustrant is Jietongda company, now the so-called "physical extinction" products, more rich. Here are Hefei Ketai company KT108S and general physics delustrant agent 68 performance comparison
project KT205 Ordinary physical extinction agent B68 Remarks
Consumption,% 1-4 1-5 1-5 Total weight of formula
gloss, %, 60° 5-50 5-70 1-70  
Powder system blend blend Epoxy and mixed  
Required polyester 50/50 & 60/40 60/40 & 50/50 50/50&60/40 &70/30  
thermal stability excellent excellent Poor-general  
 
Flow and appearance
good Good or general good Depends on the use of polyester resin
Gloss change rate% weak(170-220degree) large large  
Effect of baking temperature change
Film hardness excellent Good to general excellent  
Scratch Resistance excellent commonly excellent  
Stain resistant good good good  
Curing condition 170-230 180 170-230 Centigrade
Impact performance good good commonly  
storage stability good commonly excellent  
High temperature storage
Price High performance to price ratio Depends on the price Depends on the price  
Based on my experience, there are probably some of the following mechanisms in the market for physical matting agents:
Pure physical extinction of A. catalyst,
B. contains certain reactive acrylic resins (generally containing epoxy groups) and complexes,
C. with a chemical reaction characteristic but does not change the proportion of epoxy polyester special matting agent.
The chemical type of delustrant D. has the characteristics of chemical reaction to participate fully in the resin reaction, such as the KT208G KT268G kotai.
C is the matting agent and the D type Elcoteq Hefei provides, most new varieties of delustrant KT208G and KT268G can be less than 3 degrees. The extinction effect requires proper excess epoxy resin and hedge matting agent application reaction. The A and C chemical equilibrium and physical extinction of D agent in the reaction of epoxy polyester resin of the whole system in the strict sense, but not the balance of type B only use special functional groups and epoxy or polyester acrylic resin to obtain competitive reactions leading to extinction so crosslinking is incomplete, the extinction I think that there are hidden dangers that luster will change over time (of course there are other factors that can lead to gloss change). As far as physical extinction is concerned, we believe that the carboxyl containing acrylic epoxy excess extinction agent has excellent storage stability.
Like vestagon, in the mixed system of physical type of polyester delustrant is selective, i.e. different resin will produce different extinction effect, which in addition to external structure and resin itself is closely related to internal polyester and additives. At present, no physical matting agent can be found, but the overall effect is getting better and better.
Physical extinction is the most headache is its storage stability, for now, or 68 type extinction stability is slightly better, of which the most users are worried about the following issues:
1 the stability of the process, that is, the impact of the processing technology on the gloss and surface, the impact of the extrusion conditions on the gloss is the most important problem of the current extinction agent, and some varieties will have an impact on the flat,
2 gloss baking temperature on physical extinction also have a relatively large impact, some varieties of more than 68 series of sensitive (series Hefei Ketai can keep good stability in the range of 170-220 degrees).
3 compatibility problems, physical extinction and 68 series powder compatibility is not very good and even repulsive and relatively strong, which is decided by their different curing mechanism by which is why physical extinction can not completely replace one of the reasons for the 68 series, but this compatibility problem has solutions more compromise, although not yet can reach the ideal state,
4 physical storage stability, delustrant storage stability is still a problem, the specific performance in the powder after stored for a period of time (especially hot weather) will increase or gloss leveling deterioration, at this point the 68 series of relatively stable lot, this is the biggest obstacle to fully replace the 68 series, now Hefei Ketai series have been walking in front of the.
The 5 part of the product in the black poor levelling system.
The latest physical matting agent has made a lot of progress, for example, the selectivity of the resin, low temperature curing some varieties have a good performance, which is gradually replacing the traditional direction of future matting agent.
Selection and effect evaluation of 2.2.6 yellowing resistant matting agent
According to our understanding and experience of physical extinction, we should pay attention to the following points:
1 first determines that it is a purely physical type and reaction type, this is very important, because it relates to the physical property and storage stability, the use of pure physical extinction do not contain large amounts of catalyst can be assured as long as do a preliminary assessment on it.

2 storage stability
Some matting agent with extinction effect is very good, but can not withstand the long time storage especially after the hot summer after a sharp rise in gloss powder leveling deterioration, which will cause a huge loss with late, the products of different manufacturers are different, it is important to do the evaluation work,
3 curing conditions
Any matting agent has certain conditions such as curing, curing time, curing temperature range, the product is more controllable obviously has wide curing interval, this can provide in the test or supplier data,
4 machining performance is an important problem to be considered
Physical extinction is the most vexing problem will occur after the gloss powder extrusion to rapidly rise or leveling deterioration, which will bring production more trouble and not in control, especially in the color phase, the products of different manufacturers will show significant differences,
5 Determination of the amount of added
The extinction properties of different matting agent is not the same, we should do a series of tests in the test, such as from 1% to 5% the amount of testing, so you can determine the extinction properties of the entire interval so as to make more scientific judgment,
6 selective for polyester
Physical extinction has greater selectivity of polyester delustrant, different polyester performance results may be exactly the opposite, so for a particular pet can achieve better results, so as to choose different matting agent, leveling in black system is relatively weak, especially in the sub light, matting agent different manufacturers have different performance, the. The design problem of matting agent,
7 surface hardness
The surface hardness of indoor extinction due to the characteristics of different matting agent will show great differences.
8 evaluation of outdoor extinction agents
Outdoor selection of matting agents also need to do a complete test, determine the performance of adding the extinction effect range and final powder, such as whether it is easy to agglomerate yellowing, with some of the matting agent reactive to determine whether there is great selectivity of the resin, gloss dependence on temperature is strong and so on. How are these weather resistance, should be determined by test.