Formulation Principles and Performance Improvement of Polyolefin Masterbatch

Formulation Principles and Performance Improvement of Polyolefin Masterbatch

1. Focus on performance of polyolefin masterbatch

Polyolefin masterbatch is an intermediate material in plastics processing industry, so properties of customer's plastic, resin, and thermoplastic elastomer must be taken into account, and color masterbatch provided must match raw material used by customer. Important considerations are compatibility, diffusion and dispersion between masterbatch and resin used by customer. Thus, the melt flow rate of polyolefin masterbatch has become a very important control parameter in manufacture of color masterbatch. It not only affects process of injection molding, extrusion, blow molding, etc. It is smooth, and it will affect degree of dispersion and uniformity of pigment when mixing resin to be dyed!

Formulation Principles and Performance Improvement of Polyolefin Masterbatch

Strength brother's note. We hope that carrier resin should be as small as possible and amount of masterbatch should not be too large, so that performance of our matrix material will not be greatly affected.

Second, principles for developing color polyolefin masterbatches

2.1. Carrier resin selection

2.1.1. The carrier resin must have good compatibility with matrix resin

Theoretically, to ensure full compatibility between carrier resin and matrix resin, as many of same resin as possible should be selected, such as PE for PE and PP for PP. However, sometimes same resin cannot be selected, and only other resins with good compatibility can be selected, such as PE, PP, POE, EVA and other resins with good compatibility, often choose PVC, PC, PET, PA, etc. with good compatibility EVA is used as carrier resin.

Note from Tough Brother. Generally, color masterbatch with EVA resin as carrier is sometimes referred to as universal color masterbatch.

2.1.2. The fluidity of carrier resin is higher than that of matrix resin

Theoretically, fluidity of carrier resin should be higher than fluidity of matrix resin, and higher better, this is only way to ensure good dispersion of masterbatch in matrix resin. But in fact, choice of carrier must be balanced between dispersion and strength of composite material being filled. The higher MI of carrier resin, better dispersion of masterbatch, but lower strength of composite product. . Therefore, provided that dispersion is ensured, lower MI of carrier, better. For example, to fill MI masterbatch for filling tubes, select a resin close to base material, and for masterbatch carrier for filling nonwoven fabric, select copolymer polypropylene, which is preferably close to technical index and MI of raw material for nonwoven fabric. to ensure strength. Under normal conditions, it is best that MI of carrier resin exceed 10 g/10 min of matrix resin.

Strength issue: If melt index of carrier resin is too high, is it possible that carrier resin is compatible with matrix resin, which may lead to slippage and poor dispersion of coated toner. ? Can an expert answer it?

2.1.3. The melting temperature of carrier resin must be lower than melting temperature of matrix resin

The melting point of carrier resin should be lower than that of matrix resin, at least not higher than that of matrix resin, to ensure that carrier resin is melted before matrix resin is melted, which is conducive to dispersion of inorganic powder in masterbatch . Based on this principle, LDPE, LLDPE, HDPE, PP or mixtures thereof can be used as carriers forFor PP and HDPE, and LLDPE, LDPE or mixtures can be used as carriers for LLDPE and LDPE. Please note that HDPE and PP cannot be used as carriers. for PVD. That is, if HDPE is selected as carrier, it cannot be used for LDPE and LLDPE matrix resins, but can only be used for HDPE or PP matrix resins; if PP copolymer is selected as carrier, it can only be used for HDPE or PP matrix resins.

2.1.4. It is best to choose different resins to form a mixed carrier

Based on above principles, calcium carbonate filler masterbatch carrier is mainly composed of LDPE, HDPE, LLDPE and high melting index PP. According to performance requirements, these media are often used in combination to enhance functionality of media. LDPE/HDPE, HDPE/LLDPE, LDPE/LLDPE, PP/HDPE, etc. According to performance requirements, mLLDPE, POE, EVA, etc. can also be added respectively. film toughness, and EVA and PCL can improve heat resistance. - tightness. Finally, it is best to choose resin powder so that particle size of resin powder and inorganic powder is close, and it is easier to mix evenly.

Reminder from Brother Toughness: PP powder is available from petrochemical companies, but PE powder still needs to be ground, right? Is cost too high?

2.2. Selection and dosage of filling materials

Filling additives form basis of polyolefin masterbatch. It is one of key factors affecting cost, dispersibility and efficiency of masterbatch. Usually we choose calcium carbonate powder as filler, and usual amount of additive is about 10%-70% when produced by twin screw extruder.

There are many varieties of calcium carbonate, which can be divided into heavy calcium carbonate and light calcium carbonate, and heavy calcium carbonate can be divided into calcite calcium carbonate, marble calcium carbonate and dolomite calcium carbonate, and calcite calcium carbonate can be divided into Divided into coarse calcite calcium carbonate and fine calcite calcium carbonate.

How to choose heavy calcium carbonate and light calcium carbonate when formulating? Considering oil absorption index: The oil absorption index of light calcium carbonate is much higher than that of heavy calcium carbonate. If formula contains liquid additives, heavy calcium carbonate should be used. In terms of performance: light calcium carbonate is useful for modifying toughness, while heavy calcium carbonate greatly contributes to strengthand for stretching. Considering price: heavy calcium carbonate with same particle size is about 30% cheaper than light calcium carbonate. As for filled resin: light calcium carbonate is first choice for PVC products, because light calcium carbonate is more alkaline and can absorb decomposed HCl acid substance in time to improve thermal stability of PVC processing.

If you decide to choose ground calcium carbonate, which type of ground calcium carbonate should you choose? Depending on characteristics of modification, different types of heavy calcium carbonate should be selected.

Although certain grades of calcium carbonate have been selected, quality of same type of calcium carbonate differs depending on origin. Calcium carbonate powders obtained with different grinding equipment have different particle size distribution and different particle shape , so effect is also excellent. not same.

Recommended Reading: A detailed comparison of properties of heavy and light calcium and choice of calcium carbonate in rubber and plastics industry?

2.3. Types and dosage of dyes

As we all know, most original and most important function of masterbatch is coloring, so pigment is main component of masterbatch, different types and properties of pigments and their content will affect melting index of masterbatch in different ways.

Pigments for polyolefin masterbatch include inorganic pigments and organic pigments, and dyes are rarely used to color polyolefins. Inorganic pigments are usually metal oxides, sulfides and sulfates, chromates, aluminates and other salts, and carbon black. Titanium dioxide and carbon black are two very important inorganic pigments used to color plastics. Carbon black is reported to be pigment that has greatest impact on melt index (MI) of masterbatch.

Compared with inorganic pigments, organic pigments have advantages of high coloring power, good dispersibility, bright color, full color spectrum and low relative density. According to molecular structure, they can be divided into azo pigments, phthalocyanine pigments, and heterocyclic pigments, lake pigments, fluorescent pigments, fluorescent whitening agents and so on. Because of its better compatibility with polyolefins, higher color strength and better cost-effectiveness, it has become main source of pigments in polyolefin masterbatch. The influence of organic pigments and inorganic pigments on flow of polyolefin masterbatches is mainly due to factors such as pigment particle structure, pore size and distribution, specific surface area and oil absorption.

Obviously, what wouldThe closer structure of pigment particles to a dense spherical shape, larger average pore size, smaller specific surface, and lower oil absorption, less its effect on pigment melt index. masterbatch.

2.4. Choice of additives

Because most polyolefin processing and molding processes use granular resins, it is difficult for powdered lubricants to mix uniformly with granular resins and colored masterbatches, so lubricants and other additives are usually added to colored masterbatches as part of functional masterbatches.

There are two types of friction in polymer processing: internal friction between polymer melt molecules, pigments and additives, and external friction between polymer melt and surface of processing machine. These frictions reduce melt flow and reduce processing efficiency. At same time, strong friction can make surface of product rough, glossless or form flow lines. The addition of lubricant is to reduce above two kinds of friction. Lubricants mainly include saturated hydrocarbons, halogenated hydrocarbons, fatty acids, fatty acid esters, aliphatic amides, metal soaps, fatty alcohols and polyols, etc. The most commonly used metal soaps and aliphatic amides, such as solid calcium stearate, stearate magnesium, zinc stearate. , stearamide, oleamide, erucamide, EBS, etc.

Other additives include antioxidants, UV absorbers, antistatic agents, etc. The purpose of their addition is to provide thermal and oxygen stability in preparation and processing of masterbatches, thermal and oxygen stability and light stability in processing of finished product, and antistatic properties. . Experience has shown that addition of almost all lubricants and additives increases MI of polyolefin masterbatch, ie improves flowability of polyolefin masterbatch. The characteristics of a dispersant are mainly determined by its polarity, melting point, density, molecular weight and its distribution, melt viscosity and crystallinity. The most important parameters are polarity, molecular weight and its distribution. Common masterbatch dispersants include low molecular weight waxes, ionic polymers, stearates, etc. Low molecular weight waxes include polyethylene wax, polypropylene wax, oxidized polyethylene wax, EVA wax, etc.

Recommended Reading: Lubricant against crooked impacts: calcium stearate

Generally speaking, lower polarity of dispersant (eg, polyethylene wax), greater amount, lower molecular weight, and wider molecular weight, higher MI of resulting polyolefin masterbatch. relatively smooth and moist. However, unlike a carrier with a high MI, since dispersant usually has a low molecular weight, tooa large amount of dispersant may precipitate and adhere to surface of masterbatch after being added to masterbatch formulation system due to poor carrier compatibility. as a coating, resulting in a gray and cloudy appearance of masterbatch.

Internal lubrication can reduce friction between materials and increase fluidity of materials; external lubrication can reduce friction between materials and equipment, can reduce scratches on surface of product, and ensure whiteness of surface of masterbatch and products. The formula design uses internal and external lubrication together to maintain a balanced ratio between internal and external lubrication. The external lubricant mainly uses paraffin, stearic acid and EBS, etc. The internal lubricant generally uses zinc stearate and calcium stearate, and polyethylene dispersant wax also acts as an external lubricant, so lubricant formula with dispersant can reduce amount. Compared with filling with light calcium carbonate, grease filled with heavy calcium carbonate can be added less, because light calcium carbonate has a large oil absorption rate, and fluidity of light calcium carbonate is poor, so more internal and external lubricants are included. . If you consider bright appearance of masterbatch, you can add an appropriate amount of white oil or paraffin, which is more conducive to improving brightness of product.

Third, polyolefin masterbatch production and quality control

3.1 high speed mixer

a. Order of addition: Calcium carbonate should be added first for dehydration, and then other components will be added after completion. Add calcium carbonate and mix for about 5 minutes (material temperature reaches 60-80°C); add polypropylene carrier and polypropylene wax and mix for 2 minutes; add grease and mix for 2 minutes.

b.Mixing moisture control:The temperature must reach a certain height to remove moisture adsorbed on calcium carbonate surface so that it can be controlled below 0.3%.

c. Eliminate static electricity: Calcium carbonate easily causes frictional electrification during mixing, especially calcium carbonate with an obvious sheet structure, which causes serious particle aggregation and affects dispersion effect. When using masterbatch, small white spots appear on product. The first solution is to add a small amount of antistatic agent to formula, and second is to let quick mix material sit for 20 hours before using it.

3.2, filter

The filter is necessary, although it has a great effect, but it is often ignored. Filter mesh can convert rotating material into linear motionuse high shear operation to further plasticize material, adjust melt pressure in machine head, filter out impurities and decompose material.

Filter nets usually have a three or four layer structure, in particular, such as 80/120/80, 100/140/100, 100/120/140/100, etc.. As a rule, it is changed every 2 hours, and thrown away at a time, it is not recommended to burn and reuse it. If filter is too thin, it will cause extruder pressure to increase, current to increase, and output to decrease.

3.3, masterbatch moisture control

Moisture and its low molecular weight volatile matter must be controlled below 0.3% to ensure that there is no water pulsation during production. A special control method uses a magnifying glass to observe masterbatch. If it is dense and does not have obvious foaming voids, surface of product is very bright.

3.4 density control

The denser masterbatch, better it can completely remove moisture or low molecular weight volatiles, making surface of subsequent composite filling product brighter. The compactness is mainly achieved by increasing melt pressure of screw extruder's granulation head, which can specifically lower melt temperature, increase feeding rate, and so on.

Brother Toughness: The original author believes masterbatch is made from single screw granulate. If it is a twin screw granulator, you may consider vacuuming to extract low molecular weight substance to increase compactness. masterbatch.

Source: Internet, thanks to first author, very interesting!

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