Question 1

The 3 categories of plastic injection dyeing methods

Accepted Answer

Choosing the right color for plastic products is the key to improving product texture. In the process of plastic injection, the common plastic dyeing methods are divided into three categories, : toner, masterbatch, and full extraction.

Before understanding the principle of plastic dyeing, let us first have an understanding of the basic concept of the original colors of different plastic raw materials. The following are the natural colors of several common plastic raw materials, The natural color of PP is milky white and transparent, PS and PC are completely transparent, ABS is of ivory white and opaque, and PA (Nylon) has a slightly transparent light yellow color.

If you want to produce products with a sense of transparency, it is recommended to use raw materials with a transparent color, such as PP and PC.

There are three categories of common plastic dyeing methods, namely "toner" dyeing, " masterbatch " dyeing and "full extraction" dyeing.

Toner dyeing

Before production, the raw materials and toner are uniformly stirred to allow the toner to fully adhere to the raw materials, and then poured into the machine, and the raw materials are heated, melted and mixed by the material tube. This is a very common dyeing method. Although the cost is the lowest, the color of the manufactured product is more likely to have color difference and uneven mixing.

Masterbatch dyeing

After the toner is made into a granular shape, it is mixed with the raw materials evenly. Then, pour into the machine, then melt and mix the mixture through the material tube. The stability of color masterbatch is higher than that of toner, but because the purchase of color masterbatch has a requirement of minimum order quantity, when the quantity of the product is small, the unused color masterbatch may become excess stock.

Full extraction dyeing

First, the raw materials and a certain proportion of dyes are melted and mixed, and then re-made into plastics of designated colors, and then poured into the production machine. This method has the highest color stability, and there will be no uneven mixing, but the minimum order quantity is much higher than that of color masterbatches, so when the number of products is small, it is rarely used due to cost considerations.

The following is a comparison form of three plastic dyeing methods. Among them, the cost of toner is the lowest, and the stability of full extraction dyeing is the best. As to which dyeing method is a better choice, you would need to take into consideration the cost of the product, the amount of product, and the quality of color requirements of the product.

Question 2

Principles of Plastic Injection Molding (Plastic Processing Process)

Accepted Answer

Plastic is everywhere around us. In our daily life, more than 60% of daily necessities are made of plastics. The most common production method of plastic products is "plastic injection molding."

What is plastic injection?
Simply put, plastic injection molding is composed of three main categories: "plastic material", "plastic mold" and "plastic injection machine". These three main categories then expands into many different sub-categories due to different manufacturing requirements.

(The 3 main categores of injection molding)
→Plastic material
Crystalline material: PP, PE, PA…
Amorphous material: PS, ABS, PC…

→Plastic mold
Two plate mold, three plate mold and hot runner

→Plastic injection machine
Hydraulic crankshaft, two-plate direct pressure, all-electric

Before understanding the process of injection molding, let's begin with a breif introduction of the structure of the injection machine:

Barrel: where the raw materials are stored
Material pipe: the passage of raw materials to the mold
Screw: the material tube is covered with a "screw". The function of the screw is to melt and mix the plastic and inject a certain amount of plastic into the mold.
Mold: It is like making a chocolate model, in which raw materials are poured into it to form a product with a specific shape.
Thimble: "thimble" is a part of the mold, and its main function is to remove the molded product from the mold

The 5 steps of plastic injection molding

The plastic injection molding process can be simplified into a "5 stages, continuous cycle" process, which are:
Plasticizing → filling → holding pressure → cooling → ejection

Manufacturing process of plastic injection

• Plasticizing
The raw materials are melted in the material pipe (the screw works to evenly mix the raw materials)

• Filling
"Filling" the raw material into the mold through the screw

• Holding pressure
After the raw materials are filled into the mold, in order to avoid backflow of the raw materials, the space in the mold is continuously pressurized to ensure the compactness of the raw materials.

• Cooling
The product is quickly cooled and shaped in the mold.

• Ejection
Push the cooled product out of the mold through the thimble on the mold As we mentioned in the episode of "3D Printing VS Plastic Injection", the principle of plastic injection molding is like making chocolate. The raw materials are poured into the machine, heated and melted, and then injected into the model. After the product is cooled, demolded, and the finished product is completed.

Plastic injection is an easy and rapid prototyping processing method, but because the plastic itself has the characteristics of "cooling shrinkage", it requires the technology and experience that the product designer and processing manufacturer holds to be able to produce the required size and appearance of the product, hence guaranteeing the precision and quality of every single mass produced product.