Renowned for its exceptional thermal and chemical resistance, PPS injection molding has emerged as a preferred method for manufacturing components that demand high performance in extreme environments.
PPS (Polyphenylene Sulfide) injection molding is a manufacturing process that uses PPS polymer to create highly durable and precise parts for various industries. This process benefits from the excellent dimensional stability of PPS, allowing it to maintain its shape and resist deformation under varying environmental conditions. Additionally, PPS is inherently flame retardant, achieving high flammability ratings without the need for additional additives.
From automotive components to electronic devices, the process ensures reliability and efficiency in producing complex, high-quality parts.
What is Polyphenylene Sulfide (PPS) Materials?
Polyphenylene sulfide (PPS), full name of Polyphenylene sulfide, English name Polyphenylene sulfide, referred to as PPS (hereinafter referred to as polyphenylene sulfide or PPS).
The molecular structure of polyphenylene sulfide is relatively simple, the main chain of the molecule is alternately arranged by benzene ring and sulfur atoms, a large number of benzene rings give polyphenylene sulfide with rigidity, and a large number of sulfur ether bonds provide flexibility. The molecular structure is symmetrical, easy to crystallize, non-polar, good electrical properties, no water absorption.
PPS Characteristics
General Performance
PPS is a kind of white, high crystallinity, hard and brittle polymer, pure PPS is relatively dense.
The degree is 1.3, but it will increase after modification.
PPS has a very small water absorption, generally only about 0.03%.
The flame retardancy of PPS is inherently flame retardant, with an oxygen index as high as 44%, and does not require additional flame retardant additives.
Mechanical Properties
The mechanical properties of PPS are not high, especially the impact strength is relatively low. After reinforced with glass fiber, the impact strength will be greatly improved, increasing from 27J/m to 76J/m, increasing by 3 times.
The tensile strength is doubled from 6Mpa to 137Mpa.
The rigidity of PPS is very high, which is rare in engineering plastics.
The bending modulus of pure PPS can reach 3.8Gpa and 12.6Gpa after inorganic filling modification, which increases by 5 times.
PPS has good creep resistance under load.
High hardness: high resistance, the wear at 1000 RPM is only 0.04g, and it will be further improved after filling F4 and molybdenum disulfide; PPS
It also has certain self-moistening properties.
The mechanical properties of PPS are less sensitive to temperature, and it maintains its shape and integrity even under extreme conditions, making it ideal for applications that demand tight tolerances.
Thermal Properties
PPS exhibits exceptional thermal performance, capable of withstanding short-term exposure to temperatures up to 260°C and maintaining long-term usability at 200–240°C. The heat deflection temperature (HDT) of PPS, which is the temperature at which the material deforms under a specified load, is significantly enhanced by fiber reinforcement, making it more suitable for demanding thermal applications.
Its high melting point further emphasizes its temperature resilience and stability at elevated temperatures, maintaining its properties even above 200°C. Its heat resistance is comparable to PI (Polyimide) and second only to PTFE (Teflon), a rarity even among thermosetting plastics.
Electrical Properties
PPS boasts outstanding electrical properties. Compared to other engineering plastics, it has a lower dielectric constant and dielectric loss tangent, with minimal variation across a wide range of frequencies and temperatures.
Additionally, PPS demonstrates excellent arc resistance, rivaling thermosetting plastics, making it ideal for electrical insulation materials. PPS is widely used in electrical applications, accounting for approximately 30% of its overall usage.
Environmental and Chemical Resistance Properties
One of the most notable features of PPS is its excellent chemical resistance, which is a key aspect of its physical properties, with chemical stability second only to PTFE. It also has strong radiation resistance, further enhancing its durability in challenging environments.
PPS Injection Molding Process Explained
Process Characteristic
The glass transition temperature of the crystalline polymer PPS is 85℃, the exothermic peak of crystallization is 127℃, the high melting point is 285℃, and the injection molding temperature is 280~320℃.
PPS is a crystalline resin, and its crystallinity significantly influences properties like shrinkage, impact strength, heat resistance, surface hardness, and creep resistance.
In PPS molding, controlling mold temperature allows for precise crystallinity adjustments based on product requirements, eliminating the need for maximum crystallinity. This flexibility is a key advantage of PPS.
Wide molding temperature, good fluidity.
PPS Injection Molding Mold
1. Product design
Since PPS is a crystalline resin, stress concentration will occur at the corners and wall thickness changes of the product. Cracking is easy to occur in these parts, the size changes, and the impact strength decreases. Therefore, when designing, pay attention to adding R on the corner of the product, and try to make the wall thickness uniform. Adding reinforcement in the appropriate position can increase the strength and rigidity of the product, eliminate residual stress, and improve fluidity.
2. Mold Material Selection
PPS is primarily molded at high temperatures, so mold materials should be chosen based on a mold temperature range of 140–150°C. For mass production, high-melting steel or materials like SK, SKD, or SKH are recommended. The surface finish should be controlled to below 10S for optimal results.
3. Runner and Gate Design
The mold’s runner shape should ideally be round or trapezoidal, with cold slug wells included. For products prone to weld lines, an overflow zone can be set at the weld line location to alter the resin flow direction and improve weld line strength.
4. Molding Shrinkage
As a crystalline resin, PPS exhibits exceptional dimensional stability, allowing it to maintain precise tolerances during the molding process. Its crystallinity varies with mold temperature, which in turn affects its molding shrinkage. The shrinkage rate differs between the flow direction (0.1%–0.3%) and the perpendicular direction (0.4%–0.8%). Additionally, the impact of annealing on dimensional changes must be considered.
5. Venting
PPS products are prone to defects like bubbles, reduced performance, discoloration, and surface roughness due to poor venting or burn marks. Proper venting slots with a depth of 0.015–0.02 mm and a width of 2 mm are necessary to produce high-quality products.
6. Mold Temperature Control
Production molds typically use electric rod heaters. To prevent heat loss, asbestos insulation boards are installed on both outer sides of the mold.
PPS Injection Molding Parameter Setting
1. Material Drying Process
Although PPS has a low moisture absorption rate (around 0.03%), thorough drying is essential to reduce nozzle leakage, silver streaks, and bubbles. Early versions of PPS with low molecular weight were primarily used for specialist coating applications and had a simpler manufacturing process. A dehumidifying dryer should be used, with a drying temperature of 160°C for 3–4 hours.
2. Barrel Temperature
The barrel temperature should be set between 280–320°C, adjusted based on the material type and product structure. Reinforced materials require higher temperatures than pure materials, and thin-walled parts require higher temperatures than thick-walled ones.
3. Injection Pressure and Speed
Injection pressure and speed significantly affect melt flow and play a crucial role in mold filling and product quality. The typical injection pressure is 80–130 MPa. Faster injection speeds improve surface smoothness but can cause issues like warping or burning, so moderate injection speeds are generally recommended.
4. Screw Speed and Back Pressure
To ensure consistent product quality, applying some back pressure is beneficial. During molding, the screw speed is typically set to 60–100 rpm. For high-cycle molding, speeds above 200 rpm can be used, but this increases the risk of resin overheating, requiring a lower barrel temperature setting.
5. Mold Temperature
The mold temperature is generally maintained between 120–140°C.
6. Cooling Time
Cooling time typically ranges from 20–50 seconds. For thin-walled parts, even in high production volumes, each cycle requires 10–30 seconds.
7. Insert Preheating
The preheating temperature for inserts is generally between 80–100°C.
PPS Injection Molding After Process
In order to eliminate the internal residual stress of the product, improve the dimensional stability and the binding force with the insert, the product should be annealed. The annealing condition depends on the thickness of the product, generally 160~200℃, 2h. The annealing temperature of the product with low die temperature is reduced correspondingly.
Applications of PPS Injection Molding
In order to eliminate the internal residual stress of the product, improve the dimensional stability and the binding force with the insert, the product should be annealed. The annealing condition depends on the thickness of the product, generally 160~200℃, 2h. The annealing temperature of the product with low die temperature is reduced correspondingly.
Automobile industry
PPS is used in the automotive industry for about 45%. PPS grades refer to the different formulations of PPS that are tailored for specific automotive applications, ensuring optimal performance and durability.
- Pump impeller,
- pneumatic regulator,
- Temperature sensor,
- carburetor,
- Igniter,
- lamp holder,
- bearing,
- Automobile generator coil skeleton and bracket, etc.
Electronic appliance
PPS can account for 30% in the electronic and electrical industry
- Brushes on engines and generators,
- miniature electronic component packages,
- side connectors,
- connectors,
- IC sockets,
- computers,
- stereoscopic printed circuit boards,
- trimmer capacitors, etc.
Household appliance
PPS can replace metal, ceramic, etc
- Electric fan,
- Microwave stand!
- Clothes dryer, Coffee cooker,
- Rice cooker, Hot air dryer,
- Hair iron, Air conditioning compressor copy
- Machine, printer,
- Electric kettle accessories and parts.
Machinery Industry
- Used for shell,
- Structural parts,
- Wear-resistant parts and sealing materials.
- Pump body, pump shell,
- Pump wheel, tile, gear
- Pulley, universal head, gasket flange
- Counter, level, valve, bearing
- Bearing bracket, piston ring and gear, etc.
Matters Needing Attention
1.Glass fiber reinforced PPS and other glass fiber reinforced engineering plastics, because of its wear with the barrel and screw, so special corrosion resistant, wear resistant barrel and screw should be selected.
2. The cleaning after forming should first choose glass fiber reinforced polysulfone and polycarbonate with high forming temperature, and finally clean with high-density polyethylene.
3. The proportion of gate and flow material used depends on the performance required by the product, the general proportion is less than 20%, and the powder should be screened out.