Pearlescent Pigments for Plastic Applications OUTLINE 1. 2. 3. 4. Introduction Raw Materials Manufacturing Process
Issues and Solutions 1. 2. 3. 4. 3 INTRODUCTION Forty years ago, anything made of plastic was considered "cheap. However with the development of high quality plastics this is not true today. Plastics are used in thousands of products ranging from computers, automobile parts and important medical equipment, to toys, cookware, sports equipment, and even clothes. Plastic Products Packaging: Products: Personal care products
Electronics Automotive Household Films Toys Sports Packaging: Personal care products Food Household Sanitary Toys 5 Plastic Applications Plastics Raw Materials
PE LDPE / MDPE / HDPE / LLDPE PVChard PVC / soft PVC PP Homo Polymer / Copolymer EVA ABS semi transparent ABS/transparent ABS TPU PS HIPS / GPPS TPE PC PEEK PA PA6 / PA66 / PA46 PPS PBT PI PET PMMA POM Plastic Properties Density Transparency Gloss Elongation Flexibility
Impact Melt Flow Deflection temperature Molding Temperature Acid and alkali resistance Flammability Electronic properties MANUFACTURING FLOW Pearl Forming Colorant Master batch Pumping tablet
Color paste Forming Extrusion Molding Extrusion is the most common processes used to form plastics. A heated plastic compound is forced continuously through a forming die made in the desired shape, like squeezing toothpaste from a tube, producing a long, usually narrow, continuous product. The formed plastic cools under blown air or in a water bath and hardens on a moving belt. Rods, tubes, pipes and toys such as Slinkys. Sheet and thin films (such as food wraps) are extruded then coiled or cut to desired lengths. Extrusion Molding Machine parameters for best results with pearlescent pigments Masterbatches or compounds are usually used to color the molten mass with effect pigments. For a satisfactory result in plastic extrusion with effect pigments, a balanced ratio must be maintained between the mixture energy and pigments which are as undamaged as possible. Excessive shear from mixing sections or inappropriate screws or filters destroy effect pigments and dramatically decrease the pearl luster effect. The orientation of the pigments is a requirement for an even effect. This has to be ensured in the process through a corresponding engineering and design of the machinery. Injection Molding Injection moulding Is the second most widely used process to form plastics. The plastic compound, heated to a semi fluid state which is injected into a mould under great pressure and cools and hardens quickly. The mould is opened and the part is released. This process can be repeated as many times as necessary and is particularly suited to mass production methods. Injection moulding is used for a wide variety of plastic products, from small cups and toys to large objects weighing or more. Injection Molding For best results with pearlescent pigments
In injection molding, flow processes in the molten mass cause the orientation of pigment platelets. By a technically well engineered tool construction the Effect pigments can orientate perfectly and showing nearly no flowline or welding effects. Another point to optimize the effect appearance is the position of the injection gate. Circular, centralized and edge minimized forms are perfectly suited for Effect pigments. In cases, where this is not possible we recommend, using our Diamond Effect pigment series in a low concentration. It shows a strong sparkling effect and decreases the optical perception of irregularities. Blow Molding Blow molding is where gas pressure is used to form hollow objects, such as the soda pop bottles, in a direct or indirect method. For direct blow-molding, a partially shaped, heated plastic form is inserted into a mold. Air is blown into the form, forcing it to expand to the shape of the mold. For indirect blow-moulding, a plastic sheet or special shape is heated then clamped between a die and a cover. Air is forced between the plastic and the cover and presses the material into the shape of the die. In this process Effect pigments develop their full optical effect. Blow Molding For best results with pearlescent pigments
Effect pigments are excellently suited to the extrusion blow moldingprocess, since the extrusion process guarantees that platelet-shapedeffect pigments are aligned evenly to the surface so they can developtheir full optical effect. Co-extrusion is an efficient option for combining high coverage and good effects. Strong pearl luster and other effects can be achieved with a thin outer layer, while the desired opacity is created by the covering inner layer. Blow Molding Phenomenon of Effect pigments and the interesting FrostEffect. Due to the soft heating during the blow molding process, its elasticity isnot very high. Effect pigments are now elastic anyway due to theirinorganic composition. The stretches form voids between the stretchedpolymer and the unstretchable effect pigments.The larger the pigmentsand the higher the stretching ratio, the more obviously the vacuoles are.Effect pigments can be used at stretching ratios of up to 3:1. In addition,1-level or 1.5-level processes are more suitable, because the plastic isstill in a semi-viscous state. In general this void effect is broadly used for the so-called frost effect in PET bottles. This frost effect gives the surface an appearance like it comes directly out of the fridge. Manufacturing Equipment
Twin-screw machine Single Screw Machine Injection molding machine Blow Molding Machine Trombone Mixer Factors Affecting Pigment Effects
Plastic resins transparency and gloss Brightness of the forming die Product surface treatment Product size and structure Pearlescent pigment quality Pearlescent pigment dispersion The extent of damageof pearl during the manufacturing process Effect from Enhancer and filler Pearl dosage COMMON ISSUES PEARLESCENT PLASTIC
Color changing/ stability Black spots /pearly spots Flow lines Weld lines Yellowing Poor pearlescent effects Crazes Bubbles Effect Issue Analysis Formula Raw material Equipment
Pearlescent pigment Issue Investigation What is the raw material used
Pearlescent Pigments dosage in Master Batch Dispersion used Equipment Used Manufacturing reference such as pressure, temperature, etc. Timing If the issue is regular Pearlescent pigment coating is single layer or dual layer? The thickness of the layer Pearl total dosage Final product structure and size Issue Reasons and Solutions
Black Spots Solutions: Reduce pearl dosage in master batch Improve dispersion Reduce grinding damage Clean the equipment Use pre-dispersed pigments Use proper filtering Choose correct pearlescent pigments Possible Reasons: Poor dispersion Damage caused by grinding Impurities Accumulation Incorrect choice ofpearlescent pigments Problems and Solutions
Yellowing Possible Reasons: Non-yellowing resistantpearlescent pigments The yellow resistant coatinglayer is damaged duringgrinding Chemical damage of the yellowresistant coating layer Solutions: Choose proper yellowresistant pearlescentpigments Mix the pearls properly, donot grind which destroys theyellowing resistant coatinglayer Yellowing Is an reaction between Titanium and Phenol antioxidant.
Occurs withouthumidity or lights. Is a Reversible chemical process. The speed and strength of this reaction depends on the activity ofPhenol group, such as BHT. Temperature affects its speed and strength. When pearlescent pigments are used with polycarbonates yellowingissues may occur Specially treated Yellow Resistant pearlescent pigments arerecommended for polycarbonates Flow Lines Solutions: Possible Reasons: Dispersion improvement
Poor master batch dispersion Equipment problems Waves created by moisture Processing temperaturetoo low Mold temperature too low Solutions: Dispersion improvement Adjust manufacturingreferences such astemperature, speed andpressure Increase the processing andmold temperature temperature Dry raw material Weld Lines Possible Reasons: Solution: Mold structure
Pearlescent pigment andits dosage Solution: Weld lines are not avoidable butcan reduced Improve the mold structure Cautions Pearlescent pigments need to be dispersed first, except to mix intodirectly with PVC power plastic Plastic pieces require wetting with % adhesive first thenmixed in with pearlescent pigments. Polyolefin. when it used with titanium power, reacts with phenolsand may cause yellowing. PVC requires all transparent ingredients with pearlescentpigments mixed in at the last step. When Gold and Ironpearlescent pigments areused with PVC a lab test is required PMMA, PC, PA: requiring drying first before use. Exterior applications Only yellowing / weather resistant productsare recommended.