Prior to injection or extrusion molding process, coloring agents can be added to resins during blending or on-site mixing with the pellets to attain desirable color. This flexibility is a major advantage in plastic processing—which allows pre-coloring and on-site coloring. There are multiple plastic coloring methods, and coloring agents can come in the forms of master batches, dyes, pastes, and so on.

Pre-Coloring

Pre-coloring refers to when the toner has already been blended into the resins prior to the extrusion. The coloring process is completed before delivering the resins to customer. The advantage of this method is that the coloring material can sufficiently ensure the stability of the color and the customer does not need to have coloring equipment and processing; the disadvantage of pre-coloring is its relatively higher cost.

Master batch Coloring

Another method is to add master batch coloring into the plastic. Master batch is a highly concentrated coloring agent that can be directly added into the plastic metering device during processing by injection molding or extrusion. Compared to pre-coloring, this reduces color deviations caused by the heat repeatedly generated through processing and has less impact on the mechanical properties of the plastic. Another advantage is that the same kind of plastic can be formulated based on different colors required by the customer, this gives customers greater flexibility with their plastic stock; the disadvantage of this method is that it requires a mixing nozzle or screw design to help with color dispersion.

Dye Coloring

Similar to master batch coloring, dye coloring can also avoid the problem caused by repeated heat generation during the coloring process.  The powdered colorant can be directly added into the plastic.

Paste Coloring

Paste coloring is similar to master batch coloring with the only difference that the paste is liquid. During injection, the paste is typically added to the hopper of the injection molding machine and the base material of the paste must be hydrophobic as moisture can cause degradation to the plastic molding and affect the material properties.

  Impact of Opaque Colorants on Material’s Physical Properties:

Highly concentrated opaque colorants will affect the physical properties of material. For instance, titanium dioxide (TiO2) is a natural white colorant typically used for shading effect. When TiO2 is added, however, the impact resistance of the material will decrease. Although it is unusual to add pearl coloring agent to copolyester, most of the mica in these colorants is coated with Ti02, and as such, the physical properties of the material will be compromised.

  Color Variation

Both pre-coloring or on-site coloring can achieve very good coloring results; however different wall thickness on the product may produce different colors. Even colorants from the same lot/batch may also result in color variation; differences in processing times, processing conditions, equipment sizes, and shear forces of screw will all affect the final color effect.

Injection molded products, extruded products or other thermoplastic products can be coated with metal to achieve the same metallic appearance. For a single metal or plastic to achieve this effect is quite difficult, whether in terms of effort or costs. Metal coating is more economical than metal polishing technology but can still achieve its mirror-like metallic effect. Moreover, the weight of electroplated plastics is far lower than that of metal products.

When applying ultrasonic welding on electroplated products, pay attention to the electroplated layer as it may affect the strength of welding. Electroplating of plastic products comes in two forms: vacuum electroplating and electroplating.

Vacuum Plating

The first step of vacuum plating is to pre-treat (prime) the product so as to improve the adhesion between the metal and plastic surface. Priming also helps remove surface defects on the plastic; then, a very thin metal coating is applied in a vacuum chamber. Finally, a coating of finish is applied upon the metal surface to improve abrasive resistance.  This final coating also prevents oxidation of the metal or even to change the color (vacuum aluminum products can be turned into a more noble gold or copper color through a transparent topcoat coloring).

Vacuum plating is more environmentally friendly than ordinary electroplating.

Vacuum plating has been successfully applied to Eastar, Spectar and Eastalloy copolyesters.

Electroplating

This method involves electrolysis which separates metal ions such as copper and nickel as well as a process of chemical disposition which covers the surface with a layer of metal.

Electroplating requires a good affinity between the plastic substrate and metal. This should not be a problem for the plastic materials which contain catalyst of strong affinity with metal.  The catalyst remains in the plastic from the synthetic process. However, there is no catalyst in copolyester synthesis so it is not suitable for ordinary electroplating. Patented data indicates that copolyester can be coated with a surface layer of ABS, thereby solving the copolyester electroplating issue.

Copolyester plastics are modified PET materials. The processing of copolyesters is incredibly easy.

Eastman is currently the main copolyester manufacturer, producing PCTG, PCTA and Tritan®, in addition to PETG. The current market price ranges from RMB10-40 per kg, varying by brands and grades. The primary copolyester supplier for Shanghai and Zhejiang is Shanghai Chengzhong Plastics Co., Ltd. Copolyesters are characteristically highly transparent and environmentally friendly. It can replace materials such as PVC, PMMA, TABS, K-plastics and PC.

Drying

NewMat engineering plastics must be dried before molding. Drying can be done through an ordinary hot air circulating dryer or a dehumidifier. For best results, choose the latter.

Startup and Shutdown

The startup procedure is similar to that of other thermoplastics; first set the hopper and nozzle temperature to the desired melting temperature.

For caution’s sake, purge the melt resin generated during the heating stage. Test again to determine optimal mold parameters.

Prior to long-term shutdown, empty all remaining material inside the hopper.

Use of Recycled Materials

In molding NewMat engineering plastics, runners and scrap produced can be recycled. While the ratio of recycled material should be determined in accordance with the specific test results and quality requirements, the recycled ratio is generally limited to 25%.

Recycled material must be clean and dry.  It should be dried again before molding, even when it has been stored in a dry place.  Moisture in the molding process will result in material degradation.

Note: When recycled materials are added to the new material it will cause variations in the melt rheological properties, demolding, shrinkage and the mechanical properties of the product.

Injection Molding Conditions

Molding Temperature (oC) / Time (hour):

Mold Temperature

The mold temperature of NewMat engineering plastics is typically between 80 and 100℃, while the mold temperature required by for the CP1201and DK series is lower than 40℃.

Appropriate control on mold temperature is an important condition for obtaining a highquality product.

Mold temperature impacts the final products in a number of ways including surface glossiness, dimensional tolerance, deformation, and internal stress etc.

Duration in Hopper

Plastic degradation takes place in high temperature environment.

The length of time in which the plastic remains in the hopper is a determining factor of product quality. If the time is too short, it may cause inadequate plasticization; if the time is too long, it may cause thermal degradation.

Thermal degradation will lower the product’s impact strength, cause discoloration, flow marks and other such undesirable qualities.