There are many plastic products around us, such as plastic bottles, stationery, and food containers (trays). These plastic products are not originally colored. Plastics (resin) are nearly colorless (milky-white). Colorants such as pigments are added to produce plastic products in various colors.
There are roughly two methods of coloring: external coloring and internal coloring. External coloring is a method of coloring the surface of plastics. It applies to printing, coating, and plating. Internal coloring is a method of coloring plastics by kneading colorants into them. Unlike external coloring, materials are colored evenly up to the inside, because colorants are mixed with plastics. Colorants used for internal coloring are generically called Plastic Colorants.
Roles and functions of plastic colorants
Plastic colorants do not just add color to our lives, they are helpful for creating a product's image, as well as improving usability and quality.
The effect of coloring is most noticeable in the decoration. In the case of cosmetics, home appliances, and automobile interiors, skillfully create an impression, such as a sense of luxury and dignity, by devising color and luster depending on the materials.
Coloring also plays a role of identification. Using an example from our daily lives, the lid of plastic bottles for hot drinks is uniformly orange colored. Therefore, we can identify hot drinks immediately. Colors are also specified based on the global standards for clearly identifying products at the time of construction or in the event of emergency such as blue for water pipes, and yellow for gas pipes.
Moreover, colors are used effectively to protect contents. For example, the outside of a product is colored black to shield it from UV rays and prevent the deterioration of its contents.
In the meantime, plastic colorants do not only add color, but play a role in enhancing the functionality of products more directly, known as functional plastic colorants.
For example, automobile bumpers and containers use carbon black as plastic colorants to improve weather resistance (*Resistance to temperature change, wind, and rain.)
Also, it is possible to add such functions as conductivity and antistatic performance to plastic colorants. In the case of products including PCs and testing equipment incorporating precision equipment such as IC chips, even a slight current causes malfunction and breakdown. However, plastic materials that protect them tend to be charged with electricity. You can see it from the dust attracted when you rub a plastic sheet. In this case, it is possible to knead plastic colorants with high conductivity into plastics to release electricity outside, lowering the risk of breakdown.
Other usage examples include the use of white plastic colorants for back sheets of solar cells in order to improve power generation efficiency by reflecting light inside.
Types of plastic colorant
Types of plastic colorants mainly include masterbatches, colored pellets, colored compounds, Dry Color, Paste Colors, and Liquid Masterbatch. They are mixed with natural pellets (*plastics in a grain form before colorants are added) and molded to produce plastic products.
Plastic colorants in pellet (grain) form. Pigments are kneaded inside at a high concentration. Easily change color tones by adjusting the amount of mixing with natural pellets. They feature excellent dispersion, and even and beautiful coloring. Also, there is no need to worry about scattering and contamination of machinery and materials, and it is easy to handle. They outperform colored pellets in terms of cost performance.
Colored Pellets, Colored Compounds
Plastic colorants in pellet form. Unlike masterbatches, they are set at the same concentration (hue) as the final products. Therefore, there is no need to mix them with natural pellets. They also have no trouble mixing and an ease of stably in producing the desired color. However, the cost is higher than other products.
Plastic colorants in powder form are produced by mixing pigments with metal soaps and suchlike. They are the most inexpensive colorants, because there is no trouble with production. However, they have several weak points in handling, such as scattering easily, easily dirtying machinery and materials, and difficulties in measurement.
Paste Colors, Liquid Masterbatch
Plastic colorants in a liquid form. Paste Colors are different from Liquid Masterbatch in terms of viscosity. Paste Colors are mainly used when the base resin is in a liquid form such as vinyl chloride. Liquid Masterbatch is used in the case that a customer wants to color products lightly, such as semi-transparent color overseas.
Features and advantages for each type of plastic colorant
|Masterbatch||Colored pellet||Colored compound||Dry color||Paste color
|Pigment concentration||10 - 70%||< 5%||< 5%||30 - 80%||30 - 60%|
|Dispersibility (coarse particles)||◎||○ - ◎||○ - ◎||△||○|
|Dispersibility (color unevenness)||○||◎||◎||○||○|
|Coloring with high pigment concentration||◎||◎||◎||×||×|
|Metricability||◎||no need||no need||△||△|
|Molding property||○||◎||◎||△ - ○||△|
|Versatility||○||×||×||○||△ - ○|
Manufacturing process of masterbatch
Plastic colorants currently used in Japan are mainly masterbatches featuring an excellent overall balance, which can be produced with relatively light facilities. Masterbatches can provide various colors and functions by kneading colorants, such as pigments or functional materials, into pellets as a base (resin materials).
(1) Preparation and stirring
Measure base resin for materials, colorants such as pigments, and functional materials as specified in the designed formula, put them into a mixer and mix them evenly.
Put the mixed materials into an extruder to dissolve, mix and knead. The colored resin will come out of the tip of the extruder in a long bar, similar to spaghetti.
Put the extruded colored resin bars in the water tank, and cool and harden them.
Pelletize them in around 3 to 5 mm by using a pelletizer to finish the masterbatches.
Pack the masterbatches and load them in pallets using robot arms. Preparation for shipping is complete.
Types of plastic
There are various types of plastics to be mixed with plastic colorants. Thermoplastic (*mold by melting in heat) plastics which are often used for daily necessities and are divided into two categories—crystalline and non-crystalline. Each of features a variety of properties, which must be taken into consideration when designing products.
For example, polyethylene (PE) that is strongly resistant to heat and chemicals among crystalline plastics is used for films and buckets. Highly transparent and durable polyethylene terephthalate (PET) is used for plastic bottles and egg cartons.
Example of plastics
|Classification||Material type||Abbreviations||Character||Product example|
|Crystalline plastic||Polyethylene||PE||Strong against heat and chemicals||Film, bucket, etc.|
|Polyethylene terephthalate||PET||High transparency and strong||PET bottle, egg pack, etc.|
|Amorphous plastic||Polyvinyl chloride||PVC||Hard to burn and strong||Hose, electric wire, etc.|
|ABS resin||ABS||Opaque, resistant to cracking and heat||Furniture, PC, etc.|
Molding methods of plastic
There are various methods of molding plastics: compression molding and injection molding, calendar molding, extrusion molding, blow molding, and vacuum molding.
Pour melted resin into a mold just like injecting with a syringe. This method is used for producing containers and caps.
Turn a screw inside the machine, and extrude melted resin forward for molding. This method is used for producing tubes and pipes.
Blow compressed air inside melted resin to mold it into the shape of a mold. This method is used for bottles and syringes.
Mold while kneading resin with heated rolls to stretch. This method is used for making films and sheets.
Mold while melting the resin added to a mold with heat and by applying pressure. This method is mainly used for producing containers.
After resin in a board form is heated to soften, mold it into the shape of a mold using vacuum suction. This method is used for producing containers.
- Colorants Sales Division
Toyocolor Co., Ltd.
- TEL : +81-3-3272-0834