The creation of clear plastic injection molding part is a set of complex tasks that are different from those that are faced in injection molding with non-transparent materials. The choice of materials is critical not only to their properties but also to their performance during the production process and in the end product. While working with non-transparent materials, some defects can be hidden to a certain extent, but when it comes to transparent injection molding, the precision of the design and manufacturing processes should be perfect.

However, it is important to note that planning and preparation are very important in the injection molding process before going into the details of the materials used. This entails proper preparation of raw materials, proper calibration of equipment, proper tooling, and proper molding procedures, which are crucial in the production of clear molded parts.

The first criterion that is taken into consideration while practicing clear injection molding is the ability to see the particles. Clear plastics do not mask defects that are likely to be made during molding as compared to opaque plastics. Hence, it is crucial to keep every area of the production cycle as clean as possible to achieve the best quality of the final product. It is important to store the materials properly so that they do not get contaminated and the raw materials are of good quality.

Material Selection For Clear Plastic Injection Molding Process

When it comes to selecting materials for translucent and clear injection molding, several options offer distinct advantages:

Acrylic (PMMA): Acrylic is a versatile material that can be used to injection mold clear as well as colored products. It is well known for its nontoxicity, scratch resistance, and UV resistance and is widely used in outdoor equipment, lighting fixtures, and decorative items. However, the rigidity of acrylic and its brittle nature requires proper drying to avoid moisture which affects the molding process and the final product. Go to Acrylic injection molding page to know more about PMMA molding.

High-density Polyethylene (HDPE): It is UV resistant and can be molded into translucent parts which is an advantage of HDPE. It is more resistant to breakage than acrylic and is relatively cheaper hence suitable for use in containers, bottles, and pipes among others. Nevertheless, HDPE is not recommended for high-pressure applications because of its relatively low impact strength.

Polycarbonate (PC): Polycarbonate is clear, resistant to UV light, and is more resistant to impact than acrylic. It is widely used in safety clothing, windows, containers, and other applications that require high-impact strength and transparency. Like in the case of acrylic, PC also needs to be dried before injection molding to get the best performance. learn more about Polycarbonate injection molding.

Polyetherimide (PEI): PEI is a high-performance material that exhibits excellent resistance to UV, heat, and chemical environments. It is widely used in high-performance applications like medical instruments, automotive parts, and aerospace components where high mechanical performance and thermal characteristics are desirable. However, due to its high cost and the requirement of specialized manufacturing processes such as the use of steel molds, PEI is most appropriate for applications that require high performance.

Polypropylene (PP): PP is a very useful material that is characterized by flexibility, electrical conductivity, and chemical stability. It is used in numerous industries for uses like fabrics, packaging, electronics, and chemical uses. Due to the hinge-like characteristic, PP is best suited for applications where flexibility and resilience are required and the part is not expected to bear any load.

Liquid Silicone Rubber (LSR): LSR is a biocompatible material with good thermal, chemical, and electrical stability. It is widely applied in medical equipment, electrical parts, and automobile manufacturing industries where strength and efficiency are vital. Due to its flexibility and enhanced characteristics, LSR is well suited for applications where high accuracy in molding and high performance are required.

Optical Silicone Rubber (OLSR): OLSR is an advanced material that is used for improving the light transmission and clarity of optical parts. It has better non-yielding characteristics and hence can be used in outdoor fixtures and other applications where the product is exposed to extreme weather conditions. Due to its good stability of optical transmittance over time, OLSR is suitable for clear optical parts where light transmission is important.

All these materials have their own benefits and challenges when it comes to clear injection molding, and they are suitable for use in different applications across various industries. The choice of materials, design, and manufacturing techniques are well thought out and implemented to produce clear molded parts that are of high quality, performance, and appearance.

Polyethylene (PE)

HDPE is made through a process in which petroleum is exposed to heat and pressure and is a type of thermoplastic. While acrylic has its advantages, HDPE has UV resistance, is incredibly versatile, and is easy to mold. Because of these advantages and the fact that it is relatively cheaper to manufacture, HDPE is commonly used in large-scale production of products such as bottles, pipes, and containers.

Elastomeric Resins

TPR is one of the elastomeric resins which are a combination of plastic and rubber that can be easily processed through injection molding. TPR has uses in products such as fluid dispensers, flexible hoses, catheters, and equipment that need to have resistance to liquids such as acids. For these applications, it is preferred due to its flexibility and ability to withstand tough conditions.

Thermoplastic Polyurethane (TPU)

Thermoplastic Polyurethane (TPU) is characterized by high tensile and tear strength, softness, and elasticity. This makes TPU suitable for use in the development of products that need to have a firm handle while at the same time being comfortable to hold. Even though TPU is comparatively costlier than the other resins, it is widely used for creating parts with rubber-like attributes.

clear plastic molding covers

Common Issue With clear injection Injection molds

Some of the common defects that are evident in clear plastic parts and the possible solutions include the following:

Plastic parts that are transparent are vulnerable to different kinds of defects during the molding process. It is important to know these defects and how to avoid them in order to manufacture high-quality transparent products. Here are some of the most common defects and their respective solutions: 

1. Air Traps

When molding the resin, it is not uncommon for air pockets to be locked into the material, which will be evident in the final product. This is usually a result of poor venting or low pressure during injection of the material.

Solution: The air traps can be reduced and the product transparency increased by enhancing the mold design to incorporate the correct channels for venting and by increasing the injection pressure. 

2. Flow Lines

Flow lines are those lines or streaks on the surface of the clear plastic parts that are formed due to the difference in the flow of the material during the injection molding process. These lines can mar the beauty of the product.

Solution: Changing the injection speed and pressure and also the gate design can be used to minimize flow lines and enhance the general surface finish of the part. 

3. Sink Marks

Sink marks are small indentations on the surface of the plastic part, which are usually formed due to differences in the cooling rate or improper filling of the resin during the solidification process.

Solution: Reducing cooling time, controlling packing pressure, and applying proper mold temperature control measures can go a long way in reducing sink marks and enhancing the quality of the part.

4. Surface Scratches

Some of the surface defects that may be observed include scratches or marks that may be caused by handling or ejection of the molded parts and this will affect the degree of transparency and surface finish of the parts.

Solution: Proper handling and ejection procedures, mold release agents, or surface treatments can help avoid surface scratches and ensure product clarity. 

5. Hazing or Cloudiness

Misting or clouding of clear plastic components can be caused by several factors, such as inadequate drying of the raw material, contamination, or high moisture content during the molding process.

Solution: To avoid hazing and obtain clear, transparent parts, it is necessary to pay attention to the correct handling and storage of materials, the use of dry resins, and the correct processing conditions.

If these defects are corrected and the right solution is applied, manufacturers can create clear plastic parts with good clarity and aesthetic value.

clear plastic corner molding

Surface Finishing Selection and Design Tips For Clear Injection Molds

In as much as the clarity of the plastic parts is concerned, choosing the right surface finish is very important. Manual sanding and polishing are useful for rougher designs that do not have fine details, but they are not efficient for creating clear products. If the production run is low or if the prototype or project is a one-off or off, then the SPI-A2 finish may be adequate, especially if surface finish is not a consideration when evaluating a prototype. It was also seen that if the concept of surface finish is deferred to the production level, then a lot of time and money could be saved.

For flat or nearly flat transparent parts such as windows or lenses, the best surface finish is the resin coating. However, it is crucial to understand that the use of a release agent is disadvantageous to the part’s surface and should not be used. It is important to note that lead times and costs of surface finishing may differ depending on the project.

As for the recommendations for the design of the clear or translucent parts, several aspects should be taken into account. It is also important to keep the wall thicknesses constant throughout the part to keep the clarity consistent. Other considerations include designing gate runners that are wide enough and placing gates in such a way that they will accommodate the contraction process. The lack of sharp corners, especially for PC products, helps to avoid gaps and make the transitions clearer.

Furthermore, maintaining a smooth surface of the mold and proper cooling will reduce the surface defects and the decline in the clarity of the plastic in clear plastic injection molding. To get more specific design recommendations for transparent injection molding, it is suggested to read more about it.

If You Require Clear Plastic Injection Molding, Then Sincere Tech is The Company To Turn To.  

Non-transparent molding is more critical and needs more attention than non-transparent molding when it comes to the production of clear plastic parts through injection molding. Clear polymers have different characteristics, such as different strengths, different temperature limits, and different chemical resistance. Thus, the choice of the most appropriate clear plastic material for a given project should be made depending on these factors.

Sincere Tech is one of the top 10 plastic injection molding companies in China that focuses on helping clients determine the best clear plastic material for their parts. Whether you require help with the creation of a prototype or have questions about clear plastic resins and injection molding, our team is ready to help. Please get in touch with us now to share your project specifications with us.