Introduction: Two-color injection molding is a classic molding process. It uses two materials to inject into a product, which can achieve different colors and touch appearance effects. In this article, I will mainly introduce everything about two-color injection molding.

What is Two-Color Injection Molding?

The so-called two-color injection molding is called double injection molding refers to the molding method of injecting two plastics of different colors into the same mold. It can make the plastic parts appear in two different colors, and can make the plastic parts present regular patterns or irregular cloud patterns to improve the practicality and aesthetics of the plastic parts.

What are the Characteristics of the Two-Color Injection Production Process?

The two-color injection molding machine is composed of two sets of plasticizing injection devices with the same structure and specifications. The nozzle should have a special structure according to the production method, or be equipped with two sets of molding molds with the same structure that can be rotated and transposed.

During plasticizing injection, the process parameters such as melt temperature, injection pressure, and injection melt volume in the two sets of plasticizing injection devices are required to be the same, and the fluctuation difference of the process parameters in the two sets of devices should be minimized.

Compared to regular plastic injection molded products, the melt temperature and injection pressure of two-color injection molded plastic products should use higher parameter values during injection. The main reason is that the mold flow channel in two-color injection molding is longer, the structure is more complicated, and the injection melt flow resistance is greater.

When making two-color injection molded plastic products, you need to use raw materials with good thermal stability and low melt viscosity. This is to avoid decomposition due to high melt temperature and long residence time in the flow channel. The most commonly used plastics are polyolefin resins, polystyrene, and ABS materials.

When two-color plastic products are injection molded, you need to use a higher melt temperature, higher mold temperature, higher injection pressure, and higher injection rate to make the two different colors of melts melt well in the mold during molding and ensure the molding quality of the injection molded products.

What are the Key Points of Two-Color Injection Design?

Molding part; The molding part of the two-color injection mold is basically the same as the general injection mold. The difference is that it is necessary to consider the consistency of the convex mold of the injection mold at two positions, and the concave mold should cooperate well with the two convex molds. Generally, the plastic parts molded in this way are smaller.

Demolding mechanism; Because two-color plastic parts can only be ejected after the secondary injection, the ejection mechanism on the primary injection machine cannot be used.

For horizontally rotating injection molding machines, the ejection mechanism of the injection molding machine can be used for ejection, while for vertically rotating injection molding machines, the ejection mechanism of the injection molding machine cannot be used. In this case, a hydraulic ejection mechanism can be set on the rotary table.

Casting system; Because it is two-color injection molding, the casting system is divided into a casting system for primary injection and a casting system for secondary injection, which come from two injection molding devices respectively.

Mold body; Because the two-color injection molding method is relatively special, it requires mutual cooperation and coordination. The size and precision of the two mold guide devices must be consistent.

For horizontally rotating injection molding machines, the closing height of the mold must be consistent, and the centers of the two molds should be on the same rotation radius and 180 degrees apart. For vertically rotating injection molding machines, the two molds must be on the same axis.

What are the Requirements for Two-Color Injection Molding?

Material requirements: The materials you use for two-color injection molding need to meet two basic compatibility conditions: bonding compatibility and processing compatibility.

Process requirements: The melting points of the two materials in the soft and hard glue double-shot design must have a certain temperature difference. It is generally recommended to be 60℃, and it is recommended to be at least 30℃.

The melting point of the first shot material is high. Generally, the first shot is PC or PC/ABS, and the second shot is TPU or TPE. The PC thickness is 0.6-0.7mm, and the software is 0.4mm or more.

Try to increase the contact area, make grooves, etc. to increase the adhesion, or use core pulling for the first shot, and inject part of the material into the first shot in the second shot. The surface of the first shot mold is as rough as possible.

Transparent and non-transparent double-shot design: Dual-injection molding for small lens design: the first injection is for non-transparent material, and the second injection is for lens material. The first injection should use PC with a high melting point as much as possible, and the second injection should use PMMA.

Dual-injection molding for transparent and non-transparent decoration: the first injection is for non-transparent material, and the second injection is for transparent material.

Non-transparent materials commonly use PC with a high material temperature, and PMMA or PC is used for transparent materials in the second injection. PC needs to be sprayed with UV for protection, PMMA can choose UV or strengthen, if there are characters on the surface, UV must be selected.

Soft and hard double shot design; The two materials need to have a certain temperature difference in melting point, generally recommended to be 60℃, and at least 30℃ is recommended. The melting point of the first shot material is high. Generally, the first shot is PC or PC/ABS, and the second shot is TPU or TPE. The PC thickness is 0.6-0.7mm, and the software is more than 0.4mm.

Try to widen the contact area, make grooves to increase adhesion, or use core pulling for the first shot, and inject part of the second shot material into the first shot. The surface of the first shot mold should be as rough as possible.

Mold requirements; Two-color mold: Two plastic materials are injected on the same injection molding machine, molded in two times, but the product is only ejected once. This molding process is also called double-material injection molding, which is usually done by a set of molds and requires a special two-color injection molding machine. It usually has the following requirements:

The two shapes of the master mold must be different, forming a product respectively, while the two shapes of the male mold must be exactly the same;The front and rear molds of the mold must match after rotating 180° around the center .

The total thickness of the front mold panel plus the A plate cannot be less than 170mm. The maximum mold thickness, minimum mold thickness, KO hole distance, etc. need to be carefully checked;The sprue of the three-plate mold should preferably be designed to be able to automatically demold;

When designing the master mold for the second injection molding, in order to avoid the second master mold from scratching the glue position of the first molded product, a part of the airtightness can be designed.

However, the strength of each sealing position must be carefully considered (i.e., during injection molding, will the plastic deform under high injection pressure, resulting in the possibility of a second injection having a front edge?) .

When you do two-shot molding, the first shot can be a little bigger so it can be pressed tighter with the other half of the mold to make a seal ; Watch out for the plastic flow from the second shot that might push the first shot out of shape; Watch out for the front mold slide or the stripper plate crushing the part before the A and B plates come together .

Try to get the water lines in the two female molds and the male mold as even and balanced as possible ; In 99% of the cases, you shoot the hard plastic part of the part first and then shoot the soft plastic part because the soft plastic is easy to deform.

What is the Working Principle of Two-Color Injection Molding?

Debugging of injection molding machine: First, you need to adjust the injection pressure, injection speed, holding time and temperature of the injection molding machine according to the product requirements, and install the two-color injection mold.

Preparing Injection Material: Get two different colors of melted plastic pellets and put them in the hopper of the injection molding machine through the feed hopper.

Feeding and melting: When the feeder is working, the two colors of plastic particles are respectively sent to the screw of the injection molding machine. When the screw rotates, the plastic particles gradually melt at high temperature.

Injection: When the two colors of plastic particles are completely melted, the screw of the injection molding machine goes forward and shoots the melted plastic into the hole of the injection mold.

Cooling of plastic: In the injection mold, the molten plastic starts to cool and solidify. If necessary, a cooling system or cooling nozzle can be used to speed up the cooling of the plastic. Opening and removal of the mold: When the plastic is completely cooled, the injection mold is opened and the finished product is taken out.

What is the Process of Two-Color Injection Molding?

The process of two-color injection molding usually goes like this:

Mold prep: Make a mold that fits the product design. The mold has to have two different injection cavities so you can inject two materials separately.

Material selection: Choose two materials that are suitable for the product’s requirements. Make sure the materials work well together so you don’t run into any issues when you’re molding.

In the injection molding machine, one material is first injected into the first cavity, and after it cools to a certain temperature, the second material is injected into the other cavity of the mold. This process requires the control of injection pressure, temperature and time to ensure the smooth flow and molding of the material.

Cooling and demolding: After molding is completed, the mold is cooled to the appropriate temperature before demolding. When demolding, make sure the bonding parts of the two materials are intact without stratification or falling off.

What are the Advantages of Two-Color Injection Molding Technology?

Strong functionality: Through two-color injection molding technology, you can combine plastic materials with different functions to form products with multiple functions. For example, in electronic products, you can use two-color injection molding technology to combine conductive plastics and insulating plastics to achieve the electrical isolation and conductive functions of the product.

Durable: Two-color injection molding technology can make different parts of the product have different material properties, thereby improving the durability of the product. For example, in automotive accessories, two-color injection molding technology can be used to combine hard plastics and soft rubbers, so that the product has both sufficient strength and good elasticity.

Environment protection and energy saving: Two-color injection molding technology adopts one-time molding method, which reduces material waste and energy consumption during processing. Meanwhile, products made of environmentally friendly materials are also in line with the green development concept of modern society.

Cost savings: Traditional injection molding technology requires multiple production and assembly steps, while two-color injection molding can complete the manufacturing of products in one injection molding cycle, saving labor and equipment costs. Additionally, two-color injection molding can also reduce scrap rates and production costs.

Boost efficiency: Two-color injection molding not only makes it possible to produce products with different colors and materials in a single injection molding cycle, but also cuts down on the number of steps on the production line and increases production efficiency. Plus, two-color injection molding also trims production time, so you can meet customer needs faster.

Make better products; two-color injection molding can make products more precise and consistent. That’s because two-color injection molding can put different materials into the same mold at the same time and make the mold at the same temperature and pressure .

So the product is the same every time.In the Ordinary injection molding , flexible resin material and soft rubber are used as molten material to fill the mold cavity to achieve high-quality molding effects.

Make it look better; two-color injection molding can make products look better. Two-color injection molding can make parts of different colors and materials on the same product, making the product look better and more attractive. In addition, two-color injection molding can also make products with special effects, such as gradient colors, shiny surfaces, matte surfaces, etc.

What are the Application Areas of Two-Color Injection Molding?

Automotive industry; In the car manufacturing industry, two-color mold injection molding is widely used in the production of car parts, such as fancy parts and inside parts of dashboards, door handles and other parts. By using different colors and materials for combined design, the product looks more beautiful and special.

Electronics industry; With the fast growth of the electronics market and the rise in innovation needs, two-color mold injection molding has also been widely used in the production process of electronic parts and shells. For example, the two-color design concept of the shell of a mobile phone can bring better visual effects and user experience.

Medical Industry; The production and manufacturing of medical devices and equipment also requires the use of high-precision and high-quality two-color mold injection products to meet their functional requirements and hygiene standards.

Packaging industry; For the packaging design of some high-end products, in order to meet the aesthetic needs of consumers and the need to enhance the brand image, some special materials and color matching methods will be used to complete the design and production of the outer packaging.

Summary

This article will give you a brief introduction to the two-color injection molding process. It is a process of injecting two different colored or different material plastics into the same mold to form beautiful and practical plastic parts. The process includes mold preparation, material selection, injection molding and cooling demolding.

The material used for two-color injection molding must have good thermal stability and fluidity. The advantages of two-color injection molding are strong functionality, durability, environmental protection, cost savings, and improved production efficiency. It is widely used in industries such as automobiles, electronics, medical, and packaging to meet the diverse needs of the market.