Polyethylene Terephthalate Glycol (PETG) Injection Molding at Mythentec
Polyethylene terephthalate glycol, or PETG for short, is a transparent thermoplastic copolyester that combines a high-quality appearance with good toughness and reliable processability. In PETG injection molding , it can be used to produce clear or colored plastic components with smooth surfaces, complex geometries, and reproducible dimensions. PETG is used in particular in applications where transparency alone is not sufficient, but where increased impact resistance, an attractive surface finish, and cost-effective mass production are also required.
To achieve a successful result, the material type, component design, mold design, and process control must be consistently coordinated. Mythentec supports projects from plastic-specific development through mold and process design to documented series production.
SERVICES PROFILE
- 15 injection molding machines
- Single- and two-component technology
- Clamping force from 50t to 420t
- Part weight from 0.01 g to 1 kg
- Fully automated with 3-axis and 6-axis robots
- Digitized by Leitrechnersystem:
– IST parameter recording
– Batch tracking
– Planning and monitoring - Production in ISO 7 and ISO 8 clean rooms in accordance with EN ISO 14644
- Qualified injection molding machines and validated processes
- Processing of high-performance plastics
- Processing environmentally friendly "plastics"
- Tool storage in separate fire compartment
PETG Material Profile
PETG is a glycol-modified variant of polyethylene terephthalate. This modification largely suppresses the material’s crystallization during processing. As a result, the material remains amorphous and can achieve high transparency as well as a uniform, glossy surface.
Compared to standard PET, PETG can often be processed into transparent components within a wider processing window. At the same time, the material has good toughness and is less prone to breakage than various other transparent plastics. However, the properties achieved in a specific component always depend on the selected PETG grade, the wall thickness, the component geometry, and the processing conditions.
The combination of optical, mechanical, and processing properties makes PETG an attractive material for a variety of technical production parts.
Key features include:
- High transparency and a high-quality surface finish
- Good impact resistance even with more complex component geometries
- relatively low processing shrinkage
- Good mold filling with appropriate process and mold design
- Option for transparent or opaque coloring
- Good resistance to selected media and cleaning agents
- thermoplastic processability and limited reusability of suitable production returns
PETG is available in various material grades and modifications. Depending on the application, variants with enhanced temperature resistance, UV stabilization, specific medical properties, or approvals for certain food contact applications, among others, can be used.
Processing PETG in Injection Molding
Processing PETG requires careful material preparation and controlled thermal stress. As a polyester, PETG can absorb moisture. If too much residual moisture enters the melt, the polymer may suffer hydrolytic damage during processing. The potential consequences range from streaks and bubbles to a deterioration in mechanical properties.
Proper drying and a closed-loop material supply system are therefore essential for stable PETG injection molding. The required drying conditions depend on the specific material type and the specifications provided by the raw material manufacturer. Generic temperatures or drying times are not appropriate, as different copolyesters sometimes have significantly different requirements.
Mythentec has a centralized drying and material supply system that allows the prepared material to be transported in a controlled manner to the injection molding machine. This reduces the reabsorption of moisture between the drying and processing stages.
Component Design for PETG Injection Molding
A component design optimized for plastic manufacturing facilitates mold filling, reduces internal stresses, and lays the groundwork for cost-effective mass production. For transparent PETG components, design details are particularly important, as sink marks, weld lines, flow lines, or localized stresses may become visible.
Wall thicknesses that are as uniform as possible promote consistent flow and cooling behavior. Significant changes in wall thickness should be smoothed out with gentle transitions. Areas with large accumulations of material can cause extended cooling times, sink marks, or internal stresses.
Rounding the inner and outer edges improves material flow and reduces notch effects. Sharp corners, on the other hand, can create stress peaks that have a negative impact under mechanical stress or when in contact with certain media. Ribs and domes should be dimensioned so that they achieve the required stability without causing noticeable indentations on the opposing visible surface.
Adequate draft angles reduce the forces generated during ejection and protect delicate surfaces. For textured or polished visible surfaces, the necessary draft must be taken into account during the design phase.
The subsequent assembly process also influences the design. Screw connections, snap hooks, weld seams, and bonded surfaces each generate different local stresses. Especially for components exposed to chemical stress, sustained high assembly stresses should be avoided. Mythentec provides support in the developing and optimizing components suitable for plastics , taking into account the material, manufacturing process, and subsequent function as a unified whole.
Tooling Concept for PETG Injection-Molded Parts
For PETG injection-molded parts, the gate system, venting, temperature control, mold surface, and ejection system must be specifically tailored to the required part quality.
For transparent visible parts, special attention is paid to the mold surface. Machining marks, contaminants, or local variations in the polish can be directly visible on the molded part. The required surface finish is therefore specified during the mold design phase.
The tool steels and the design of moving components must also be suited to the material and the planned production volume. For highly polished visible surfaces, the tool must also be designed to ensure reliable demolding without scratches, grinding marks, or localized ejector marks.
Surfaces and Post-Processing of PETG Components
PETG is suitable for clear, translucent, colored, and opaque parts. Depending on the mold surface, high-gloss, matte, or textured surfaces can be produced. For transparent components, the quality of the cavity in particular determines how clear and uniform the final surface will appear.
Coloring can be transparent, translucent, or opaque. The selection of pigments or color masterbatches must be tailored to the specific material type and the application requirements. With transparent coloring, differences in wall thickness and flow path are more noticeable, as they can affect the perceived color depth.
After injection molding, PETG components can be further processed depending on their geometry and application. Possible methods include printing, laser marking, bonding, mechanical joining, and various welding methods. Whether a particular method is suitable depends on the specific material grade, the component geometry, and the functional requirements.
Adhesives, cleaning agents, printing inks, and coatings must be tested for potential interactions with the material. Under internal or external stress, unsuitable substances can cause stress cracks or changes to the surface.
Applications and Industries for PETG Injection Molding
In PETG injection molding often produces transparent or translucent mass-produced components, where, in addition to geometry, requirements regarding appearance, impact resistance, cleanability, and reproducible manufacturing are also taken into account.
Typical areas of application include, among others:
- Mechanical Engineering and Plant Engineering
Viewing windows, protective covers, inspection areas, or transparent housing components designed to allow the condition of a component behind them to remain visible.
- Electrical Engineering and Electronics
Display covers, light-emitting surfaces, housing components, or transparent control elements for electronic assemblies and devices.
- Medical and Laboratory Technology
Housings, covers, containers, or functional components that require transparent sections and documented manufacturing processes. Medical suitability, biocompatibility, and resistance to cleaning or sterilization procedures must be ensured through the use of an appropriately qualified material type.
- Packaging and Dispensing Systems
Transparent containers, closure components, dispensing components, or high-quality packaging elements. For food, cosmetic, or pharmaceutical applications, the required approvals for the specific material must be taken into account.
- Consumer and Capital Goods
Visible parts, housings, displays, covers, or decorative functional components that require a combination of aesthetic appeal and mechanical robustness.
- Lighting and Display Technology
Light covers, translucent components, or presentation elements with specific requirements for light transmission, surface appearance, and coloration.
The specific choice of material always depends on the conditions of the particular application. Factors such as mechanical stress, continuous operating temperature, UV exposure, chemical environment, cleaning methods, or required certifications influence the decision regarding the appropriate PETG grade or an alternative transparent plastic.
Project Process: From Component Design to Mass Production
In PETG injection molding, material behavior, part geometry, optical requirements, and mold design must be coordinated. To this end, Mythentec follows a clearly defined process that takes technical feasibility, process stability, and documentation into account early in the project.
- Inquiry and Technical Clarification
During the inquiry phase, we identify the basic requirements for the component. These include technical drawings or 3D data, functional and aesthetic requirements, planned production volumes, and the intended operating conditions. Requirements regarding transparency, color, chemical resistance, certifications, and documentation are also taken into account. Based on this information, we conduct an initial technical assessment of the feasibility of PETG injection molding.
- Material and Process Concept
Based on the requirements, a suitable PETG or copolyester grade is selected. Factors such as impact strength, temperature range, transparency, chemical resistance, and required compliance standards are taken into account. At the same time, an initial concept is developed for material preparation, the injection molding process, and quality assurance. - Part and Mold Coordination
In this phase, the part design and mold concept are coordinated. Wall thicknesses, radii, ribs, draft angles, and assembly features are taken into account, as are gate location, venting, temperature control, and mold surface finish. The goal is a design optimized for plastic injection molding that supports cost-effective and repeatable production. - Tooling, Prototyping, and Process Validation
Once the mold is complete, the first sample parts are produced. During this process, mold filling, dimensional accuracy, surface finish, transparency, and functionality are inspected. The processing parameters are adjusted step by step and documented to establish a robust process window for subsequent mass production. - Approval and Start of Mass Production
Following successful sample testing and component approval, mass production is ramped up. Material handling, machine parameters, inspection procedures, and, if applicable, downstream process steps are formally defined. Relevant process parameters can be monitored and documented during production. - Production Support and Change Management
During series production, Mythentec provides support for technical adjustments, material changes, tooling optimizations, or requalifications. The traceable documentation of the manufacturing and
