The key of formula design is four elements: material selection, collocation, dosage and stirring. Seemingly simple on the surface, it actually contains many internal connections. It is not easy to design a formula with high performance, easy processing and low price, and there are many factors to consider. The author has accumulated many years of experience in formula design, and provides the following factors for readers' reference.

1, selection of resin

Selection of (1) resin varieties

The variety whose performance is closest to the purpose of modification should be selected to save the amount of additives. Wear-resistant modification, three wear-resistant resins, PA, POM, UHMWPE；; , should be considered first. Another example is transparent modification. The first thing to consider is PS, PMMA and PC.

(2) the choice of resin brand

The performance of different brands of the same resin is very different, so the brand closest to the modification purpose should be selected. For example, heat-resistant modified PP can be selected within the thermal deformation temperature range of 100 ~ 140℃, and we should choose heat-resistant PP 140℃, such as PP-40 12 of Korea Petrochemical Company.

(3) Selection of resin fluidity

The viscosity of various plasticizing materials in the formula should be close to ensure the processing fluidity. For materials with different viscosities, transition materials should be added to reduce the viscosity gradient. For example, PA6 is often added as transition material in PA66 toughening and flame retardant formula, and HDPE is often added as transition material in PA6 toughening and flame retardant formula.

Different processing methods require different fluidity.

Different kinds of plastics have different fluidity. Therefore, plastics are divided into high fluidity plastics, low fluidity plastics and non-fluidity plastics, as follows:

High fluidity plastics -PS, HIPS, ABS, PE, PP, PA, etc.

Low fluidity plastics -PC, MPPO, PPS, etc.

Non-flowing plastics-PTFE, UHMWPE, polyphenylene ether, etc.

The same plastic also has different fluidity, mainly because of the different molecular weight and molecular chain distribution, so the same raw material is divided into different brands. Different processing methods have different requirements for liquidity, so brands are divided into injection grade, extrusion grade, blow-molding grade, calendering grade and so on.

Different modification purposes require different fluidity. For example, high filling requires good fluidity, such as magnetic plastics, fillers and halogen-free flame retardant cable materials.

(4) Selectivity of resin to additives

For example, PPS can not add additives containing lead and copper, and PC can not use antimony trioxide, which will lead to depolymerization. At the same time, the acidity and alkalinity of the additive should be consistent with the acidity and alkalinity of the resin, otherwise a reaction will occur.

2. Selection of additives

(1) Choose additives according to the purpose to be achieved.

According to the purpose to be achieved, appropriate additives should be selected, and the added additives should be able to give full play to their expected efficacy and reach the specified indicators. The specified indicators are generally the national and international standards of products, or the performance requirements put forward by customers. The specific selection range of auxiliaries is as follows:

Toughening-choose elastomers, thermoplastic elastomers and rigid toughening materials.

Strengthening-choose glass fiber, carbon fiber, whisker and organic fiber.

Flame retardant-bromine (common bromine and environmental protection bromine), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardant, antimony trioxide, hydrated metal hydroxide.

Antistatic-all kinds of antistatic agents.

Conductivity-carbon (carbon black, graphite, carbon fiber, carbon nanotube), metal fiber and metal powder, metal oxide.

Magnetic-ferrite magnetic powder and rare earth magnetic powder include samarium cobalt (SmCo5 or Sm2Co 17), NdFeB, samarium ferronitrogen (SmFeN) and Al-Ni-Co magnetic powder.

Heat conduction-metal fibers and metal powders, metal oxides, nitrides and carbides; Carbon materials such as carbon black, carbon fiber, graphite and carbon nanotubes; Semiconductor materials such as silicon and boron.

Heat-resistant glass fiber, inorganic filler, heat-resistant agent such as substituted maleimide and beta crystal nucleating agent.

Transparent nucleating agent sorbitol series Millad 3988, α nucleating agent, has the best effect on PP.

Wear-resistant-graphite, molybdenum disulfide, copper powder, etc.

Insulated calcined kaolin.

Barrier mica, montmorillonite, etc.

(2) Additives are selective to resins.

Red phosphorus flame retardant is effective for PA, PBT and PET. Nitrogen flame retardant is effective for oxygen-containing compounds, such as PA, PBT and PET. Nucleating agent has a good effect on polypropylene; Heat-resistant modification of glass fiber has good effect on crystalline plastics, but poor effect on amorphous plastics; Conductive plastics filled with carbon black have a good effect in crystalline resin.

3, the form of additives

Different forms of additives with the same composition have great influence on the modification.

(1) shape of auxiliary agent

Fiber additives have good reinforcement effect. The degree of fibrosis of additives can be expressed by the ratio of length to diameter. The greater the L/D, the better the reinforcement effect, which is why we add glass fiber through the exhaust hole. Compared with powder, the molten state is beneficial to maintain the aspect ratio and reduce the probability of fiber fracture.

The spherical additive has good toughening effect and high brightness. Barium sulfate is a typical spherical additive, so barium sulfate can be used to fill high-gloss PP, and barium sulfate can also be used for small-scale rigid toughening.

(2) Particle size of additives

A. Effect of particle size of additives on mechanical properties

The smaller the particle size, the better the tensile strength and impact strength of the filler. For example, the influence of 20% wollastonite with different particle sizes on the mechanical properties of PA6 is shown in Table 3.

For another example, as far as impact strength is concerned, the impact strength will increase by 1 times when the particle size of antimony trioxide decreases by1μ m.

B. Effect of particle size of additives on flame retardancy

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 oxide and antimony trioxide, the less the amount added to achieve the same flame retardant effect.

For another example, adding 4% antimony trioxide with a particle size of 45μm to ABS has the same flame retardant effect as adding 1% antimony trioxide with a particle size of 0.03 μ m.

C. 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 hiding power and the more uniform the color. However, the particle size of colorant is not as small as possible, and there is a limit value, and the limit values of different properties are different. For coloring power, the limit particle size of azo colorant is 0.65438 0 μ m, and that of phthalocyanine colorant is 0.05 μ m. For hiding power, the limit particle size of colorant is about 0.05 μ m.

D. Effect of particle size of additives on conductivity

Taking carbon black as an example, the smaller the particle size, the easier it is to form a network conductive path, and the amount of carbon black added to achieve the same conductive effect is reduced. However, like colorants, particle size also has a limit. If the particle size is too small, it is easy to aggregate and not easy to disperse, but the effect is not good.

(3) Surface treatment of additives

The compatibility between additives and resin is good, so as to ensure the dispersion of additives and resin according to the expected structure, ensure the completion of design indicators, and ensure its long-term, anti-extraction, anti-migration and anti-precipitation in the service life. For example, most formulations require that the additives be uniformly dispersed with the resin, while for barrier formulations, it is desirable that the additives be distributed in the layers of the resin. Except for a few additives such as surfactant, good compatibility with resin is the key to exert its efficacy and increase its dosage. Therefore, we must try to improve its compatibility, such as surface activation with compatibilizer or coupling agent.

After surface treatment of all inorganic additives, the modification effect will be improved. In particular, fillers are the most obvious, and others include glass fibers and inorganic flame retardants.

The surface treatment is mainly based on coupling agent and compatilizer, the coupling agent is silane, titanate and aluminate, and the compatilizer is maleic anhydride graft polymer corresponding to the resin.

4. Reasonable addition of additives

(1) Some additives should be added as much as possible.

Such as flame retardant, toughening agent, magnetic powder, barrier agent, etc. The more you add, the better.

(2) Some additives have the best dosage.

Such as conductive additives, can be formed in the electrical path, and then adding them can not achieve any effect; Another example is the coupling agent, which can be coated on the surface, and it is useless to add it; Another example is antistatic agent, which can form a charge release layer on the surface of the product.

5, the relationship between additives and other components

The additives selected in the formula should not deteriorate or minimally affect the efficacy of other additives while exerting their own functions, and it is best to have a synergistic effect with other additives. In a specific formula, a variety of additives with different uses may be added, and the relationship between these additives is very complicated. Some additives have synergistic effect, while others have antagonistic effect.

5. 1 Synergy

Synergy means that the effect of adding two or more additives together in plastic formula is higher than the average value of adding them separately.

(1) In the anti-aging formula, the specific synergistic effects are as follows:

The combination of two phenolic antioxidants with different steric hindrance of hydroxyl ortho-substituents has synergistic effect;

The combination of two amine antioxidants with different structures and activities has synergistic effect;

The compound use of amine and phenol antioxidants with different antioxidant properties has synergistic effect;

Completely hindered phenols and phosphite antioxidants have synergistic effect;

Semi-hindered phenol has synergistic effect with thioester antioxidant, which is mainly used in indoor products;

Hindered phenolic antioxidants and hindered amine light stabilizers;

Hindered amine light stabilizer and phosphorus antioxidant;

Hindered amine light stabilizer and ultraviolet absorber.

(2) There are many examples of synergistic effects in flame retardant formulations, mainly including:

In the halogen/antimony composite flame retardant system, halogen flame retardant can react with Sb2O3 to generate SbX3, which can isolate oxygen, thus increasing the flame retardant effect.

In the halogen/phosphorus composite flame retardant system, the two flame retardants can also react to generate high-density gases such as PX3, PX2 and POX3, which can isolate oxygen. In addition, the two flame retardants can promote each other in gas phase and liquid phase respectively, thus improving the flame retardant effect.

5.2 confrontation

Antagonism means that the effect when two or more additives are added together in the plastic formula is lower than the average value when they are added alone.

(1) There are many antagonistic examples in the formula of anti-aging plastics, mainly including:

HALS light stabilizer can not be used with thioether auxiliary antioxidant, because the acidic components produced by thioether will inhibit the light stability of HALS.

Aromatic amines and hindered phenols antioxidants are generally not used together with carbon black ultraviolet shielding agent, because carbon black can catalyze the direct oxidation of amines or phenols and inhibit the antioxidant effect.

There is antagonism between common antioxidants and some sulfides, especially polysulfides. The reason is also that polysulfides contribute to oxidation.

If HALS cannot be used with acidic additives, acidic additives will react with alkaline HALS, resulting in HALS failure; In the presence of acidic additives, usually only ultraviolet absorbers can be selected.

(2) In the formula of flame retardant plastics, there are also antagonistic examples, mainly including:

The combination of halogen flame retardant and silicone flame retardant will reduce the flame retardant effect; The combination of red phosphorus flame retardant and silicone flame retardant also has antagonistic effect.

(3) Other examples of confrontation are:

Lead salt additives cannot be used with sulfur-containing compounds, otherwise lead pollution will be caused. Therefore, lead stearate lubricant and organotin mercaptan must not be added to PVC processing formula together; Tin thiolate stabilizer cannot be used for the insulation layer of copper cable, otherwise it will cause copper pollution; For example, in the filling formula containing a lot of oil-absorbing fillers, the amount of oil additives such as DOP and lubricant should be increased accordingly to make up for the absorbed part.

6. The ingredients of the formula should be mixed evenly.

(1) Some components should be added in stages.

For the formula with too much filler, it is best to add filler twice. The first time in the hopper, the second time in the middle side feed inlet. If 150 parts of aluminum hydroxide is added to PE, it must be added twice, otherwise it cannot be granulated.

The coupling agent treatment of filler usually needs to be sprayed three times to disperse evenly, and the coupling effect is good.

(2) Reasonable arrangement of feeding sequence

In the formulation of PVC or filler masterbatch, the feeding sequence of various materials is very important. In the formula of filling masterbatch, filler should be added first, and the water in it can be removed after mixing and heating, which is beneficial to the subsequent coupling treatment. In PVC formula, external lubricant should be added later to avoid affecting the uniform mixing of other materials.

7. Negative effects of formula on other properties

The designed formula should not deteriorate or minimally affect the basic physical and mechanical properties of the resin, at least keep the original properties, and it is best to improve some properties of the original resin by the way. However, the objective fact is that everything has two sides. If one performance is improved, it may reduce other performance, which can be described as taking care of one thing and losing the other. Therefore, when designing the formula, we must consider it comprehensively and try not to affect other properties. For example, the high filling formula has a great influence on the mechanical properties and processability of composites, the impact strength and tensile strength are greatly reduced, and the processing fluidity is poor. If the product has specific requirements for the mechanical properties of composite materials, specific compensation should be made in the formula, such as adding elastomer materials to make up for the impact properties and adding lubricants to improve the processability.

The following are some performances that are often affected.

(1) influence

Most inorganic materials and some organic materials will reduce the impact properties of the formula. In order to compensate the impact strength, it is necessary to add elastomer when designing the formula. Such as PP/ talcum powder /POE formula in the filling system and ABS/ decabromoantimony trioxide/toughening agent formula in the flame retardant system.

(2) Transparency

Most inorganic materials have an influence on transparency, and choosing inorganic materials with similar refractive index to resin will have less influence on transparency. Transparent filling masterbatch is popular recently, which is mainly used for HDPE plastic bags. Adding special kinds of talcum powder has little effect on transparency, but it is not absolutely without effect.

Organic materials will also affect transparency, such as PVC toughening, only MBS does not affect transparency, while CPE, EVA and ACR all affect its transparency.

In inorganic flame retardant materials, colloidal antimony pentoxide does not affect transparency.

(3) Color

Some resins themselves are dark, such as phenolic resin itself is brown, and conductive resin such as polyaniline itself is black. Some additives are colored, such as carbon black, carbon nanotubes, graphite, molybdenum disulfide, red phosphorus is dark red, and various colorants are colorful.

When designing the formula, we must pay attention to the color and discoloration of additives. Some additives are dark in color, which will affect the color of products, and it is difficult to process light-colored products. If carbon black is black, only dark products can be processed; Others, such as graphite, red phosphorus, molybdenum disulfide, metal powder, industrial slag, etc., all have their own colors, so pay attention to them when choosing. There are also some additives that are white in themselves, but change color due to high temperature reaction during processing. For example, wollastonite itself is white, but it turns light gray after being filled into resin and processed.

(4) Other attributes

The thermal conductivity of plastics is generally modified by adding metal and carbon thermal conductivity agents, but these thermal conductivity agents are also conductive agents, which will improve the thermal conductivity and electrical conductivity, thus affecting insulation. Heat conduction is widely used in materials that need insulation, such as circuit boards, connectors and packaging materials. Therefore, insulation and heat conduction can only be added with insulation and heat conduction agents, such as ceramic metal oxides, but not with electrical and heat conduction agents.

8. The formula should be processable.

The formula should ensure proper processing performance to ensure product molding, and it has no adverse impact on processing equipment and use environment. Additives in composite materials have good heat resistance and will not evaporate and decompose at processing temperature (except crosslinking agent, initiator and foaming agent); The addition of additives has little effect on the original processability of the resin; The wear and corrosion of the added additives to the equipment should be as small as possible, and toxic gases cannot be released during processing, which will damage the health of the processing personnel.

(1) liquidity

Most inorganic fillers affect the processability. If the amount of inorganic fillers is large, processing modifiers need to be added accordingly to make up for the loss of fluidity, such as adding lubricants.

Organic additives generally promote processability, such as decabromodiphenyl ether and tetrabromobisphenol A flame retardants, which can promote processing fluidity, especially tetrabromobisphenol A.

Generally, a proper amount of lubricant needs to be added to modify the formula.

(2) Heat resistance

Ensure that additives do not decompose during processing, except foaming agent, initiator and crosslinking agent, which must be decomposed due to functional requirements. Also note the following points:

Aluminum hydroxide has a low decomposition temperature, so it is not suitable for PP and can only be used for PE.

Tetrabromobisphenol A has a low decomposition temperature and is not suitable as a flame retardant material for ABS.

Most organic dyes have low decomposition temperature and are not suitable for engineering plastics processed at high temperature.

The decomposition temperature of spices is low, generally below 150℃, and only resins with low processing temperature such as EVA can be used as carriers.

Because of the strong shearing effect in processing, the modified plastic formula needs to add antioxidants to prevent the raw materials from yellowing due to thermal decomposition.

9. Environmental protection of plastic formulation components

The specific requirement is that all kinds of additives in the formula are harmless to operators, equipment, users and contact environment. In the past, the scope of environmental protection requirements was very small, but it was non-toxic to food, medicine and other parts that contacted the human body. Now the requirements are high, even if it comes into indirect contact with the human body, it will not pollute the environment, such as soil, water and atmosphere.

(1) human health

The resin and selected additives should be absolutely nontoxic, or their contents should be controlled within the specified range.

(2) Environmental pollution

The selected components shall not pollute the environment. For example, lead salt can't be used for water pipes and cable sheaths, because the components will penetrate into the soil from buried water pipes and overhead cable sheaths through rainwater, be absorbed by crops and be eaten by future generations.

Several plasticizers DOA and DOP cannot be used in toys and food packaging films.

Heavy metals such as lead, cadmium, hexavalent chromium and mercury cannot be used, which pollutes the soil.

Do not use polybrominated biphenyls and polybrominated diphenyl ethers, resulting in dioxins and air pollution.

10, price and source of additives

On the basis of meeting the above requirements, the lower the formula price, the better. In the specific choice of additives, we must choose low-priced types for similar additives. For example, lead salt stabilizer should not be used in PVC stabilizing formula; In the formula of flame retardant, zinc borate can be selected, but antimony trioxide or molybdenum oxide is not selected. Specifically, the following principles should be followed:

Choose raw materials with low prices as much as possible-reduce product costs.

Try to choose raw materials in stock-don't buy them.

Choose local raw materials as much as possible-low transportation costs can reduce inventory and save liquidity.

Choose domestic raw materials as much as possible-imported raw materials are greatly influenced by foreign exchange, trade policy, transportation time and other factors.

Try to choose common raw materials-new raw materials are few in distribution units, difficult to buy and unstable in performance.