How to establish systematic thinking in the selection of additives?
Plastic additives occupy a particularly important position in the plastic molding process, including plasticizers, heat stabilizers, antioxidants, light stabilizers, flame retardants, foaming agents, antistatic agents, anti-mold agents, colorants and whitening agents (see pigments), fillers, coupling agents, lubricants, mold release agents, etc..
Among them, colorants, whitening agents and fillers are not plastic-specific chemicals, but general-purpose matching materials.
How to choose additives?
In order to design a high-performance, easy-to-process, low-priced formula, there are many factors to consider when selecting additives, selecting the right additives according to the purpose to be achieved, and the additives added should be able to give full play to their expected effectiveness and meet the required indicators.
The specific choice of additives range as follows.
◆ Toughening – select elastomers, thermoplastic elastomers and rigid toughening materials.
◆ Reinforcement – select glass fiber, carbon fiber, whisker and organic fiber.
◆ flame retardant – bromine (ordinary bromine and environmental protection bromine), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardants, antimony trioxide, hydrated metal hydroxide.
▲ antistatic – various types of antistatic agents.
▲ conductive – carbon (carbon black, graphite, carbon fiber, carbon nanotubes), metal fibers and metal powder, metal oxides.
▲ magnetic – ferrite magnetic powder, rare earth magnetic powder including samarium cobalt type (SmCo5 or Sm2Co17), neodymium iron boron type (NdFeB), samarium iron nitrogen type (SmFeN), aluminum nickel.
★ Thermal conductivity – metal fibers and metal powders, metal oxides, nitrides and carbides; carbon materials such as carbon black, carbon fibers, graphite and carbon nanotubes; semiconductor materials such as silicon and boron.
★ heat resistance – glass fibers, inorganic fillers, heat-resistant agents such as substituted maleimides and beta crystal nucleating agents.
How do the additives match with plastics?
☆ Red phosphorus flame retardants are effective for PA, PBT and PET.
☆ Nitrogen-based flame retardants are effective for oxygen-containing classes, such as PA, PBT, PET, etc.
☆Nucleating agents are effective for copolymerized polypropylene
☆ Glass fiber heat-resistant modification is effective for crystalline plastics, but poor for amorphous plastics.
☆ Carbon black filled conductive plastic works well in crystalline resins.
The same composition of the additives, their different forms, the impact of the role of modification is also very large.
(1) the shape of additives
o fibrous additives to enhance the effect of good (the degree of fibrillation of additives can be expressed in terms of length to diameter ratio, the greater the L / D, the better the enhancement effect, which is why we add glass fibers to join from the exhaust hole)
○Melting state is better than powder form to maintain the aspect ratio and reduce the chance of fiber breakage.
○The round spherical additives have good toughening effect and high brightness. Barium sulfate is a typical round spherical additives, so the filling of high gloss PP choose barium sulfate, small rigid toughening.
(2) particle size of additives
① The effect of particle size of additives on mechanical properties.
the smaller the particle size, the more beneficial to the tensile strength and impact strength of the filler material.
(2) the effect of additives particle size on flame retardant properties.
The smaller the particle size of the flame retardant, the better the flame retardant effect. For example, the smaller the particle size of hydrated metal oxides and antimony trioxide, the less the amount added to achieve the same flame retardant effect.
③ The effect of particle size of additives on color matching.
The smaller the particle size of the colorant, the higher the coloring power, the stronger the covering power, the more uniform the color.
④ additives particle size on the impact of electrical conductivity.
Carbon black, for example, the smaller the particle size, the easier it is to form a network of conductive pathways to achieve the same conductive effect of the amount of carbon black added to reduce. However, as with colorants, particle size also has a limit, particle size is too small to gather easily and difficult to disperse, the effect is not good.
(3) surface treatment of additives
All inorganic additives after treatment of the surface, the modification effect will be improved. In particular, the filler is the most obvious, and other glass fibers, inorganic flame retardants, etc..
Surface treatment is based on coupling agents and compatibilizers, coupling agents specifically such as silanes, titanates and aluminates, and compatibilizers for the resin corresponding to the maleic anhydride graft polymer.
Our formulation design is actually the same, in the design of the formulation must have a systematic way of thinking, this time we will take the selection of defoamer to talk about the importance of systematic thinking.
When it comes to defoaming we have to mention the famous Stokes formula: the bubble rate of rise is proportional to the square of the radius of the bubble, and inversely proportional to the viscosity of the system.
Then we solve the whole system of defoaming when “viscosity” is the main line of systematic thinking throughout the system.
So let’s see
What are the additives in the system have an impact on viscosity.
Dispersants
If your system is a color filler, the different selection of dispersant will have a significant impact on the rheological properties of the whole system, this impact in the general system may not account for a large proportion of the impact, or we do not feel.
But in fact, it still has a significant impact on our defoaming and leveling.
The weight of this effect in high solids or solvent-free systems is so large that it has to be seriously considered. Let’s visualize the effect of dispersant on the overall rheological properties of the system in solvent-free or high-solids systems.
It can be seen that in the solvent-free or high-solids epoxy system either organic pigments or inorganic pigments suitable for the system of deflocculation type of dispersant can do the rheological type of the system to Newtonian (the sample on the right of the photo), it can be seen that the system in the case of such rheological properties no matter how high the viscosity of the system, the bubbles in the system is still able to rise.
However, in the case that the dispersant dosage is not added on the left or the dispersant is not selected properly and the dispersant dosage is not enough, the thixotropy of the system will have a serious impact on the defoaming and leveling of the later body. It is very difficult for the bubbles to move up and finally break in such a system.
Not added & dispersant selection problem
3%SOP BYK-DISPERBYK-110*
So what is the situation for the more common solvent-containing systems? Actually, the large amount of solvent “washes out” and masks the unfavorable situation of defoaming and leveling as shown in the photo on the left.
The large amount of solvent as a carrier makes the weight of this effect much lower, and sometimes we can not even consider the dispersant viscosity reduction factor. But the real situation is that when our solvent-based coatings are sprayed onto the surface of the workpiece, a large amount of solvent has already evaporated into the atmosphere, and the state of the coating on the work surface is much closer to the high solids state.
This brings us back to our previous discussion of the effect of dispersant viscosity reduction on later defoaming and leveling performance. However, if the defoaming and leveling has been completed while containing sufficient solvent carrier, it seems that we can ignore the effect of this factor. In fact, not because it may lead to the cost of your defoamer and leveling agent additives rise.
If the system contains a large number of matting powder and no good matte powder special dispersant protection, will have a great negative impact on the choice of defoamer later. As shown in the figure.
The negative impact of matting powder on defoaming and leveling.
Substrate wetting agent & leveling agent stabilization tendency factors on the system of the final defoamer impact.
The vast majority of our substrate wetting agents and leveling agents are more or less bubble stability. Because these substances are substances with interfacial activity. The presence of these substances will make the bubble wall as shown below.
So the choice of surface additives that do not stabilize the bubbles, or even the surface additives that can defoam the choice of defoamer is very important. Especially in high solids or solvent-free systems. The following chart: BYK surface additives with antifoaming properties. Usually the stronger the ability to reduce surface tension, the more stable the foam. However, BYK-378 is an exception, which can both strongly reduce surface tension and achieve relatively unstable foam.
Influence of rheology additives
Both rheology additives based on the principle of intermolecular hydrogen bonding and intermolecular entanglement will have a relatively large negative impact on the flow level and defoaming of the whole system (Figure below).
Therefore, when choosing rheology additives, it is important to understand the purpose of adding rheology additives in order to choose the additives that have as little negative impact on the system as possible.
No anti-sagging additive
Adding anti-sagging additives
For example: in the selection of anti-sagging agent, it is best to choose the A point viscosity is higher and B point viscosity is lower rheology additives is good. Such rheology additives will have a very good anti-sink effect, while the minimum impact on the system of defoaming leveling.
