Calcium carbonate, as the largest inorganic powder material, is used directly in plastic to cause dust to fly and severely damage the production environment. Meanwhile, since it is a hydrophilic material, the dispersibility is poorly added directly to the lipophilic resin, Calcium carbonate powder, the general need to be processed into masterbatch beforehand to provide customers, so that you can solve the production environment and compatibility problems. Calcium carbonate masterbatch generally by the carrier resin, calcium carbonate powder, dispersant, coupling Agents, lubricants, antistatic agents, antioxidants, etc., the specific choice of each component is as follows.
1, the choice of calcium carbonate
Calcium carbonate is the core of the masterbatch, which determines the basic properties of the masterbatch Calcium carbonate masterbatch calcium carbonate powder content, the general content of about 80% with a twin-screw extruder with a continuous mixer to produce the general content About 88%.
There are many varieties of calcium carbonate, the major categories can be divided into heavy calcium carbonate and light calcium carbonate, and heavy calcium carbonate can be divided into calcite calcium carbonate, calcium carbonate and dolomite calcium carbonate, calcite and calcium carbonate can be divided into large calcite Calcium carbonate and calcite Calcium carbonate.
Specific design formula how to choose heavy calcium carbonate and light calcium carbonate? From the oil value considerations: light calcium carbonate oil absorption value is much larger than heavy calcium carbonate, if the formula contains liquid additives, should use heavy calcium carbonate From the performance point of view: light calcium carbonate on the impact strength modification is beneficial, and heavy calcium carbonate contribution to the tensile strength.From the price considerations: the same size of heavy calcium carbonate cheaper than light calcium carbonate 30 % .From the resin filled: PVC products preferred light calcium carbonate, because of the more alkaline light calcium carbonate, can absorb the decomposition of acid HCl in time to improve the thermal stability of PVC processing.
If you determine the choice of heavy calcium carbonate, the specific choice of what kind of heavy calcium carbonate? According to the need to select different types of modified calcium carbonate performance, as shown in Table 1.
Table 1 compares the performance of four different calcium carbonate filled PP
Although the specific varieties of calcium carbonate have been selected, but the same type of calcium carbonate, different origin of different quality, with different milling equipment out of calcium carbonate powder particle size distribution of different particle appearance and shape, so the modification effect is also large the same.
2, the choice of carrier resin
Calcium carbonate masterbatch carrier resin selection of several basic principles are as follows:
(1) The carrier resin should be compatible with the matrix resin
In theory, in order to ensure adequate compatibility of the carrier resin with the matrix resin, choose the same resin as possible, such as PE PE, PP choose PP. However, sometimes the same resin can not choose, only select other resins with good compatibility , Such as PE choose PP, POE, EVA and other good compatibility of the resin, PVC, PC, PET, PA and other commonly used EVA resin carrier resin compatibility.
(2) The carrier resin should be more fluid than the matrix resin
In theory, the carrier resin fluidity is higher than the matrix resin, and the higher the better, the only way to ensure that the masterbatch in the matrix resin has good dispersion, but in fact, the choice of carrier in the dispersion and filling The balance between the strength of the composite material is chosen such that the larger the MI of the carrier resin, the better the dispersibility of the masterbatch, but the lower the strength of the composite product, so the MI of the carrier is as small as possible to ensure decentralized conditions, Masterbatch MI select the substrate close to the resin; Another example is the non-woven fabric filled masterbatch carrier selection copolymer PP, the best and non-woven raw material close to the technical indicators, MI close, so you can ensure the strength of the normal conditions, the carrier resin MI is greater than the matrix resin 10g / 10min above the best.
(3) The carrier resin has a lower melting temperature than the base resin
Carrier resin melting temperature is lower than the matrix resin, at least not higher than the matrix resin, to ensure that the carrier resin melts before the matrix resin melts, so as to facilitate the dispersion of inorganic powder in the masterbatch.Based on this principle, PP and HDPE can choose LDPE, LLDPE, HDPE, PP or blend as carrier, LLDPE and LDPE can only choose LLDPE, LDPE or blend as carrier, remember that LDPE can not choose HDPE and PP as carrier, that is, if HDPE As carrier, can not be used for LDPE and LLDPE matrix resin, only for HDPE or PP matrix; if copolymerization PP is used as carrier, it can only be used for HDPE or PP matrix resin.
(4) the best choice of a variety of resin composition mixed carrier
Based on the above principles, calcium carbonate filled masterbatch carrier with high melt index of LDPE, HDPE, LLDPE, PP as the main body, according to performance needs often use a mixture of these carriers to increase the carrier functionality, such as LDPE / HDPE , HDPE / LLDPE, LDPE / LLDPE, PP / HDPE, etc. According to the performance requirements, mLLDPE, POE, EVA, etc. can be properly added as required. Can significantly improve the impact strength of the film, EVA, PCL can improve the heat seal strength.
Finally, the best choice of powder resin, powder resin and inorganic powder particle size close to more easily mixed.
3, the choice of additives
In addition to the carrier resin and inorganic powder, additives must be added to the formula aluminum coupling agent, polymer wax dispersants, lubricants, etc. In general, the finer the inorganic powder, the above-mentioned amount of the relative increase See Table 2 for details.
Table 2 different particle size calcium carbonate masterbatch formula
(1) Coupling agent
The purpose of adding the coupling agent in the formula is to change the hydrophilicity of the inorganic powder into lipophilicity, increase the compatibility with the lipophilic resin, increase the thickness of the interface, improve the performance of the filler material or reduce the influence on the performance of the filler material .
Coupling treatment before buying powder to pay attention to the status of treatment:
◆ If treated with stearic acid, pay attention to different and then titanate coupling agent treatment, this will reduce the coupling effect;
◆ If you add water-based grinding aids, and then treated with a lipophilic coupling agent, can form a parent function, the treatment effect is good, for example, calcium carbonate can reduce the oil absorption value to 22%, the viscosity decreased by 3 times, Image shows the interface thicker thickened.
◆ If the surface has not been processed, any method can be used for subsequent processing.
Whether the coupling agent is added to the formula, if the composite material added with inorganic powder is not satisfactory in strength, it may be considered not to add.
For calcium carbonate, the best type of coupling agent is aluminate, which is supplied by powder and added in an amount of about 1% of the powder. Another coupling agent that can be used is titanate, The disadvantage is that the product has a taste, the liquid supply of the product is difficult to join in the powder, and the two kinds of coupling agents can also be combined and the effect is improved.
The amount of coupling agent is generally controlled at about 1% of the powder, the smaller the particle size, the larger the specific surface area, the amount of coupling agent should also be increased accordingly.Carbonate powder with large oil absorption will lead to the need to deal with even For example, increasing the oil absorption of calcium carbonate from 40 ml / 100 mg to 50 ml / 100 mg results in a 30% increase in the amount of coupling agent.
(2) Dispersant
The role of dispersant is to promote the powder evenly dispersed in the substrate, different carriers choose different dispersants, the main carrier resin with the corresponding wax, PE PE wax or PP wax, PP PP wax for use, medium pole Resin such as PS, ABS with polyethylene oxide wax, polar resins such as PC, PET, PA and other EVA wax.
The quality of the wax is mainly reflected in the size of the molecular weight, the molecular weight of about 5000 is best, generally not less than 3000. Detection method for the normal quality of the wax melting point in the range of 110-120 ℃, if added to 100 ℃ water to melt the quality is not Qualified.Wax melting point is greater than 110 ° C, to prevent the wax molecular weight is too low or doped with small molecular weight paraffin.But low-grade products can also join all 58 degrees paraffin as a dispersant, to ensure adequate lubrication of the powder extrusion, But a large number of low molecular weight paraffin wax will affect the heat seal strength, surface printing performance, film extrusion residue increases, the nose increased volatile smoke.
Many lubricants such as stearic acid, EBS, etc. have varying degrees of dispersant role, if the formula contains can reduce the amount of dispersant. Dispersed wax also has some internal and external lubricant effect, if the formula contains dispersant wax, Can reduce the amount of lubricant. Dispersant added depends on the following factors:
◆ Particle size: The larger the particle size, the smaller the specific surface area, the easier to disperse, adding dispersant dosage can be reduced, if the particle size is greater than 800 mesh can be considered without adding dispersant. The smaller the particle size of the powder, the greater the specific surface area, the more Difficult to disperse evenly, the more you need to add more dispersant.
◆ Particle Shape: The higher the spherical shape of calcium carbonate powder, the easier it is to disperse. The order of dispersion is particle (marble calcium carbonate)> columnar (light calcium carbonate, calcite calcium carbonate), so the appearance of the calcium carbonate particles is sphericity High, the less the amount of dispersant.
(3) lubricant
Internal lubrication can reduce the friction between materials and promote material flowability; External lubrication can reduce the friction between materials and equipment, can reduce scratches on the surface of products to ensure the surface brightness of the masterbatch and filled products. Internal and external lubrication with the use of internal and external lubrication to maintain the balance between the main external lubrication with paraffin, stearic acid and EBS, etc., the general internal lubrication with zinc stearate, calcium stearate, dispersant polyethylene wax also played outside Lubricant, so the formula lubricant with a dispersant can be reduced.Compared with light calcium carbonate, heavy calcium carbonate lubricant can be added less because the light calcium carbonate absorption value, light calcium carbonate Liquidity is not good, so both inside and outside lubricants should be added.If the appearance of the light from the masterbatch to consider, you can join a white oil or 1-2 parts of paraffin, more conducive to improving product brightness.
The addition of external lubricant should include two parts: one is the amount of external lubricant needed in the process of processing the masterbatch and the other is the amount of external lubricant needed in the subsequent processing of the product, such as film, but the external lubricant If you add too much, it will affect the printing of film products and heat sealing performance.
(4) Stabilizer
It is best to add calcium / zinc composite stabilizer, but because of the price of zinc stearate is generally added as a heat stabilizer, and both the role of the internal lubricant.If the selling price of the product, you can also add a small amount of calcium and zinc stabilizer. Antioxidants generally can not join, unless the strength of the filled products require high, or product requirements are white.
Can promptly eliminate high-speed hybrid materials, static electricity, but also to follow-up products to provide anti-static effect, specific products such as woven bags, non-woven fabrics and so on.
Above introduced the principle of selection of various additives, and finally talk about the problem of small molecule additives.We formula in the small molecule additives for the coupling coating, lubrication and dispersion added, the specific varieties of aluminate, White oil, paraffin wax, polyethylene wax, stearic acid, zinc stearate, EBS, etc. However, small molecule additives have two fatal flaws: First, small molecule additives can reduce the strength of the composite material, Allow appropriate small molecule additives, fill the pipe is to strictly control the content of small molecule additives, or the intensity decreased; Second, small molecule additives will release VOC gas, seriously affecting the environmental cleanliness. Therefore, should minimize the small molecule help The amount of agent used, of course, requires special equipment to cooperate.