PLASTIC PRODUCTS ARE DISCOLORED: CAUSES AND TREATMENT
I.1 The need for colored plastic products
🔹 Since ancient times, people have tried to create many different colors to put into everyday products and objects. From cuisine like five-colored sticky rice to clothes, blankets... Color plays an important role in stimulating human emotions and psychology.
🔹 To meet human needs, plastic products are also produced in a variety of colors.
I.2 Methods of coloring plastic products
To color the product, people will have to mix plastic with pigment / color masterbatch in a certain ratio to create the required color.
🔹 Powder color
Powder color is the original state of the prepared pigment. The specific surface area is large and it tends to agglomerate, it is very dusty, has problems with automatization and does not disperse completely during the coloring process. It does not affect the properties of the tinted product and is cheap. Although it has many limitations, it is easy to process and easy to formulate for many colors, especially with small quantities of products with many different colors. Unlike masterbatch, it is not limited by the type of base resin and color. Therefore, it is widely used in small and medium-sized plastic manufacturing companies. You need to be precise when measuring the powder color otherwise it will be easy to get the wrong color. Therefore, to minimize errors, it is necessary to use electronic scales as accurately as possible.
🔹 Granular color
Compound granules are a colorful component prepared by the process of melting, mixing, and extrusion. After mixing primary plastic with other additives. It can be used in many direct processing methods, especially in thermoplastics. Furthermore, Compound granules have very good color distribution and stable quality. Therefore, it is widely used in tinting home appliances and car vehicle components, which require strict tinting quality. Compound granules have a high price because the amount of color to be mixed has been used in the mixing resin. It is an effective color mixing method in the field of modified plastics, engineering plastics, composite plastics, high-quality plastics, etc.
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I.3 Problems when producing colored plastic products
As stated above, to create colored plastic products, you will have to mix color masterbatch/pigment with primary plastic beads to create the right color. If this mixing process is not good, the product color will be inconsistent
II. Method of mixing plastic when producing colored plastic products - mix before putting into plastic injection machine
Use a stirred tank mixer or a screw quantitative mixer.
Stirring tank mixer: The resin and color masterbatch are weighed outside and then poured into the tank in a certain ratio. The machine will stir to mix the two types together. The advantage is that the device is simple and cheap. The disadvantage is that it is not possible to accurately control the level of color mixing.
Screw quantitative plastic mixer: Mixing two types of plastic together using a screw mechanism, the advantage is the mixing ratio and high mixing accuracy, the disadvantage is the complicated equipment.
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III. Method of mixing plastic when producing colored plastic products - mixing in a plastic injection machine
The characteristic of this method is to disrupt the flow of molten plastic in the screw cylinder of the press. Which method is highly effective because the plastics are mixed together in a liquid state, the possibility of mixing the two types is much higher when mixed outside.
In a plastic injection machine, there are many components that can be designed to both ensure its basic function and also have the function of mixing plastic.
III.1 Mixing screw
Two- helical groove screw shaft
The secondary spiral groove is usually only in the compression zone or the metering zone, but there are also special cases where the spiral groove starts in the compression zone and extends to the end of the metering zone.
🔹 Screw with mixing head
In addition to the screw spiral area, the shaft is designed with an additional zone-shaped section to allow for plastic mixing.
III.2 Mixing tipset
🔹 Create the mixing part at the rocket head (Srew head)
🔹 Create a mixing part at the plastic stop ring (Checkring)
🔹 Create a mixing part at the Sealring
III.3 Mixing nozzle
🔹 The core is designed to create turbulent flow.
IV. Process for handling problems when the product has uneven color errors
Step 1: Control input materials - Check whether the materials are contaminated with impurities, whether the drying mode has been achieved, whether the color mixing ratio is correct, and whether the color mixing is thorough enough.
Step 2 If you have handled step 1 but the problem has not been resolved, depending on the severity of the uneven color, you can improve the nozzle with mixing function and the screw head set with mixing function because this is faster and lower cost. The improvement of the screw has the function of mixing.
Step 3: If the above two steps have not been completed, the screw shaft will need to be redesigned and a plastic mixing function added to the screw shaft. If the screw shaft design is not suitable, the plastic or color particles will not be fully matured, affecting the color mixing ability.
The problem of uneven color on the product is a serious problem. When encountering this error, it is necessary to have a reputable unit with fast processing speed to meet the requirements of creating an ok product and processing schedule.
ASG Vietnam Engineering Company Limited is a unit specializing in handling plastic injection problems with more than 10 years of experience. We are always ready to listen to your questions 24/7 via hotline 0917.54.88.11