Plastic Injection Molding Processing Conditions

injection-parts

ABS processing conditions

Generic Class
ABS (Acrylonitrile-Butadiene-Styrene)

Typical Applications
Automotive (instrument and interior trim panels, glove compartment doors, wheel covers, mirror housings, etc.), refrigerators, small appliance housings and power tools applications (hair dryers, blenders, food processors, lawnmowers, etc.), telephone housings, typewriter housings, typewriter keys, and recreational vehicles such as golf carts and jet skis.

Injection Molding Processing Conditions
Drying ABS grades are hygroscopic and drying is required prior to processing. Suggested drying conditions are 80 – 90 C (176 – 195 F) for a minimum of 2 hours. The material moisture content should be less than 0.1%
Melt Temperature 200 – 280 C (392 – 536 F); Aim: 230 C (446 F)
Mold Temperature
25 – 80 C (77 – 176 F). (Mold temperatures control the gloss properties; lower mold temperatures produce lower gloss levels)
Material Injection Pressure
50 – 100 MPa
Injection Speed
Moderate – High

Chemical and Physical Properties
ABS is produced by a combination of three monomers: acrylonitrile, butadiene, and styrene. Each of the monomers impart different properties: hardness, chemical and heat resistance from acrylonitrile; processibility, gloss, and strength from styrene; and toughness and impact resistance from butadiene. Morphologically, ABS is an amorphous material.

The polymerization of the three monomers produces a terpolymer which has two phases: a continuous phase of styrene-acrylonitrile (SAN) and a dispersed phase of polybutadiene rubber. The properties of ABS are affected by the ratios of the monomers and molecular structure of the two phases. This allows a good deal of flexibility in product design and consequently, there are hundreds of grades available in the market. Commercially available grades offer different characteristics such as medium to high impact, low to high surface gloss, and high heat distortion.

ABS offers superior processibility, appearance, low creep and excellent dimensional stability, and high impact strength.

HDPE processing conditions

Generic Class

HDPE (High Density Polyethylene)

Typical Applications

Containers in refrigeration units, storage vessels, household goods (kitchenware), seal caps, bases for PET bottles, etc. Major use is in blow-molding applications (packaging applications)

Injection Molding Processing conditions

Drying Not normally necessary if stored properly.
Melt Temperature 180 – 280 C (356 – 536 F); for high molecular weigh grades, the suggested melt temperature range is 200 – 250 C (392 – 482 F)
Mold Temperature 20 – 95 C (68 – 194 F) (higher temperatures for wall thickness of up to 6 mm; lower temperature for wall thicknesses greater than 6 mm.) The cooling rate should be uniform to minimize shrinkage variations. For optimum cycle times, the cooling channel diameters should be at least 8 mm and must be within a distance of 1.3 d from the mold surface (where “d” is the diameter of the cooling channel).
Material Injection Pressure 70 – 105 MPa
Injection Speed High injection velocity is recommended; profile injection velocity can be used to reduce warpage in the case of components with a large surface area.

Runners and Gates

Diameters of runners range from 4 – 7.5 mm (typically 6 mm). Runner lengths should be as short as possible. All types of gates may be used. Gate lands should not exceed 0.75 mm in length. Ideally suited for hot runner molds; an insulated hot tip runner is preferred when there are frequent color changes.

Chemical and Physical Properties

High density polyethylene is produced from polymerization of ethylene (lower temperature and pressure conditions are used compared to the production of low density polyethylene). The material is free from branching and this is made possible by the use of stereospecific catalysts. Because of molecular regularity, HDPE has a high level of crystallinity (compared to LDPE).

Higher levels of crystallinity contribute to higher density, tensile strength, heat distortion temperature, viscosity, and chemical resistance. HDPE is more resistant to permeability than LDPE. The impact strength is lower. The properties of HDPE are controlled by the density, and molecular weight distributions. Injection molding grades typically have a narrow molecular weight distribution.

When the density is 0.91 – 0.925 g/cm^3, the material is known as Type 1; Type 2 materials have densities in the range of 0.926 – 0.94 g/cm^3, and Type 3 materials have densities in the range of 0.94 – 0.965 g/cm^3.

The material flows easily and the MFR ranges from 0.1 – 28. Higher molecular weights (lower MFR grades) have better impact resistance.

Being a semicrystalline material, the molding shrinkage is high (order of 0.015 – 0.04 mm/mm or 1.5 – 4%). This is dependent on the degree of orientation and level of crystallinity in the part (which in turn are dependent on processing conditions and part design).

PE is susceptible to environmental stress cracking, which can be minimized by reducing internal stresses by proper design and using the lowest MFR material at a particular density level. HDPE is soluble in hydrocarbons at temperatures greater than 60 C, but resistance to these materials is greater than that for LDPE.

LDPE processing conditions

Generic Class

LDPE (Low Density Polyethylene)

Typical Applications

Closures, bowls, bins, pipe couplings.

Injection Molding Processing Conditions

Drying Not usually necessary
Melt Temperature 180 – 280 C (355 – 535 F)
Mold Temperature 20 – 70 C (68 – 158 F)
For uniform and economic heat removal, it is recommended that the cooling channel diameters be at least 8 mm and the distance from the surface of the mold to the edge of the cooling channel be not more than 1.5 times the diameter of the cooling channel.
Material Injection Pressure Up to 150 MPa
Pack Pressure Up to 75 MPa
Injection Speed Fast speeds are recommended; profiled speeds can limit warpage problems of large surface area parts.

Runners and Gates

All conventional types may be used; LDPE is well suited for hot runner molds. Insulated hot tip runners are preferred for frequent color changes.

Chemical and Physical Properties

Low density polyethylene is produced by the polymerization of ethylene at high pressure and temperature. The material is semicrystalline-crystalline. The crystallinity level is low because of chain branching. The material is tough but possesses moderate tensile properties and exhibits creep. However, it has good impact and chemical resistance. It is an easy flow material because of long chain branching.

Commercial materials have densities in the range of 0.91 – 0.94 g/cm^3. LDPE is permeable to gases and vapors. Very close tolerances are not possible with this material and its relatively large coefficient of thermal expansion makes it less suitable for long term applications.

Shrinkage is of the order of 0.02 – 0.05 mm/mm (2 – 5%) when density is between 0.91 – 0.925 g/cm^3. When density is between 0.926 -.04 g/cm^3, the shrinkage is of the order of 1.5 – 4%. Actual shrinkage values are dependent on the molding conditions.

LDPE is resistant to many solvents at room temperatures but aromatic and chlorinated hydrocarbons cause swelling. Like HDPE, it is also susceptible to environmental stress cracking.

PA12 processing conditions

Generic Class

PA12 (Polyamide 12 or Nylon 12)

Typical Applications

Gear wheels for water meters and business machines, cable ties, cams, slides, and bearings.

Injection Molding Processing Conditions

Drying The moisture content must be below 0.1% prior to processing. If the material is exposed to air, drying in a hot air oven at 85 C (185 F) for 4 -5 hours is recommended (3-4 hours in a desiccant dryer). If the container is unopened, it may be used directly for molding after 3 hours of equilibration to shop floor temperature.
Melt Temperature 230 – 300 C (446 – 580 F); Not to exceed 310 C (590 F) for standard grades and 270 C (518 F) for flame retardant grades
Mold Temperature 30 – 40C (86 – 104 F) for unreinforced grades; for thin walled or large surface area components, 80 -90 C (176 – 194 F) may be used; 90 – 100 C (194 – 212 F) for reinforced grades. Increasing the mold temperature increases the crystallinity level. It is very important to precisely control the mold temperature.
Material Injection Pressure Up to 100 MPa  Low hold pressures and high melt temperatures are recommended.
Injection Speed High (high speeds give better finish on glass-filled grades)

Runners and Gates

Runner diameters for unfilled grades may be as small as 3 – 5 mm because of the material’s low viscosity. Reinforced grades require larger diameters (5 – 8 mm). The runner shape should be the full round type. Sprues should be as short as possible.

A variety of gates may be used. Small gates for large parts should be not be used, in order to avoid highly stressed components or excessive shrinkage. The thickness of the gate should preferably be equal to the part thickness. When using submarine gates, the minimum recommended diameter is 0.8 mm.

Hot runner molds may be used effectively but precise temperature control is necessary to prevent material drooling or freezing off at the nozzle. When hot runners are used, the size of the gates may be smaller than in the case of cold runners.

Chemical and Physical Properties

PA12 is a linear, semicrystalline-crystalline thermoplastic derived from butadiene. It has properties similar to PA11 but its crystal structure is different. PA12 is a good electrical insulator and its properties are not as sensitive to humidity as other polyamides. It has good resistance to shock and resistant to many chemicals. It is extensively modified with plasticisers and reinforcements. In comparison to PA6 and PA66, these materials have a lower melting point, density, and much lower moisture regain. It is not resistant to strong oxidizing acids.

Viscosity is determined by water content, temperature, and residence time. This material flows easily. Shrinkage is of the order of 0.005 – 0.02 mm/mm (0.5 – 2%). This is dependent on the specific grade, wall thickness, and processing conditions.

PA6 processing conditions

Generic Class

PA6 (Polyamide 6, or Nylon 6, or Polycaprolactam)

Applications

Used in many structural applications because of its good mechanical strength and rigidity. It is used in bearings because of its good wear resistance.

Injection Molding processing conditions

Drying Since PA6 absorbs moisture readily, care should be taken to ensure its dryness prior to molding. If the material is supplied in watertight packaging, the containers should be kept closed. If the moisture content is >0.2%, drying in a hot air oven at 80 C (176 F) for 16 hours is recommended. If the material has been exposed to air for more than 8 hours, vacuum drying at 105 C (221 F) for more than 8 hours is recommended.
Melt Temperature 230 – 280 C (446 – 536 F); 250 – 300 C (482 – 572 F) for reinforced grades
Mold Temperature 80 – 90 C (176 – 194 F). Mold temperature significantly influences the crystallinity level which in turn affects the mechanical properties. For structural parts, a high degree of crystallization is required and mold temperatures of 80 – 90 C (176 – 194 F) are recommended. High mold temperatures are also recommended for thin-wall parts with long flow lengths. Increasing the mold temperature increases the strength and hardness, but the toughness is decreased. When the wall thickness is greater than 3 mm, a cold mold is recommended (20 – 40 C / 68 – 104 F), which leads to a higher and more uniform degree of crystallinity. Glass reinforced materials are always processed at mold temperatures greater than 80 C (176 F).
Material Injection Pressure Generally between 75 – 125 MPa (depends on material and product design)
Injection Speed High (slightly lower for reinforced grades)

Runners and Gates

The gate location is important because of very fast freeze-off times. Any type of gate may be used; the aperture should not be less than half the thickness of the part. When hot runners are used, the size of the gates can be smaller than when cold runners are used, because premature freeze-off is prevented. When using submarine gates, the minimum diameter of the gate should be 0.75 mm.

Chemical and Physical Properties

The molecular structure of polyamides consist of amide (CONH) groups joined by linear aliphatic sections (based on methylene groups). The toughness, rigidity, crystallinity, and thermal resistance of polyamide materials are due to the strong interchain attraction caused by the polarity of the amide groups. The CONH groups also cause a lot of moisture absorption.

Nylon 6 is produced by polymerization of caprolactam. The chemical and physical properties are similar to that of PA66. However, its melting point is lower than PA66 and it has a wider processing temperature range. Its impact strength and solvent resistance are better than PA66, but its moisture absorption is higher. Many properties are affected by moisture absorption, which must be taken into account when designing with this grades. Various modifiers are added to improve mechanical properties; glass is one of the most commonly used fillers. Addition of elastomers such as EPDM or SBR improves impact resistance.

For unfilled grades, shrinkage is of the order of .01 – .015 mm/mm (1 – 1.5%). Addition of glass fibers reduce the shrinkage to as low as 0.3% in the flow direction (but could be as high as 1% in the cross-flow direction). The post-molding shrinkage is affected mainly by the crystallinity level and moisture absorption. The actual shrinkage is a function of part design, wall thickness, and processing conditions.

PA66 processing conditions

Generic Class

PA66 (Polyamide 66, or Nylon 66, or poly (hexamethylene adipamide))

Applications

Competes with PA6 for most applications. PA66 is heavily used in the automotive industry, appliance housings, and generally where impact resistance and strength are required.

Injection Molding Processing conditions

Drying Drying is not required if the material is sealed prior to molding; however, if the containers are left open, drying in a hot air oven at 85 C (185 F) is recommended. If the moisture content is > 0.2%, vacuum drying at 105 C (220 F) for 12 hours is recommended.
Melt Temperature 260 – 290 C (500 – 554 F); 275 – 280 C (527 – 536 F) for glass filled grades; melt temperatures above 300 C (572 F) should be avoided
Mold Temperature 80 C (176 F) suggested. Mold temperature affects crystallinity level which in turn affects physical properties. In the case of thin walled parts, crystallinity changes with time if mold temperatures of less than 40 C (104 F) are used. In such cases, annealing may be needed to retain dimensional stability.
Material Injection Pressure Generally between 75 – 125 MPa, depends on material and product design
Injection Speed High (slightly lower for reinforced grades)

Runners and Gates

The gate location is important because of very fast freeze-off times. Any type of gate may be used; the aperture should not be less than half the thickness of the part. When hot runners are used, the size of the gates can be smaller than when cold runners are used, because premature freeze-off is prevented. When using submarine gates, the minimum diameter of the gate should be 0.75 mm.

Chemical and physical properties

PA66 homopolymer is produced by the polymerization of hexamethylene diamine and adipic acid (a dibasic acid). Among commercially available polyamides, PA66 has one of the highest melting points. It is a semicrystalline-crystalline material. The grades have strength and stiffness which is retained at elevated temperatures. It does absorb moisture after molding, but the retention is not as much as in the case of PA6. Moisture absorption depends on the composition of the material, wall thickness, and environmental conditions. Dimensional stability and properties are all affected by the amount of moisture absorption which must be taken into account for product design.

Various modifiers are added to improve mechanical properties; glass is one of the most commonly used filler. Addition of elastomers such as EPDM or SBR improves impact resistance.

The viscosity is low and therefore, it flows easily (but not as easily as PA6). This allows molding of thin components. The viscosity is very sensitive to temperature. Shrinkage is of the order of 0.01 – 0.02 mm/mm (1 – 2%). Addition of reinforcing glass fibers reduces the shrinkage to 0.2 – 1%. Differential shrinkage in the flow and cross-flow directions is quite high. Mineral fillers yield more isotropic moldings. PA66 is resistant to most solvents but not to strong acids or oxidizing agents.

PBT processing conditions

Generic Class

PBT (Polybutylene Terephthalates)

Typical Applications

Household appliances (food processor blades, vacuum cleaner parts, fans, hair dryer housings, coffee makers, etc.), electronics (switches, motor housings, fuse cases, key caps for computer keyboards, connectors, fiber optic buffer tubing, etc.), automotive (grilles, body panels, wheel covers, and components for doors and windows, etc.)

Injection Molding Processing Conditions

Drying This material is sensitive to hydrolysis at high temperatures. It is therefore important to dry the material prior to molding. Suggested drying conditions (in air) are 120 C (248 F) for 6 – 8 hours (or 150 C (300 F) for 2 – 4 hours). Moisture levels must be below 0.03%. When using a desiccant dryer, drying at 120 C (248 F) for 2.5 hours is recommended.
Melt Temperature >220 – 280 C (428 – 536 F); aim: 250 C (482 F)
Mold Temperature 40 – 60 C (104 – 140 F) for unreinforced grades. For other grades, a wide range of temperatures can be used, depending on the grade (15 – 80 C / 59 – 176 F). Cooling channels should be properly designed to minimize part warpage. The heat removal must be fast and uniform. Cooling channels of 12 mm diameter are recommended.
Material Injection Pressure Moderate (up to maximum of 150 MPa).
Injection Speed Fastest possible speeds should be used (due to fast solidification of PBTs)

Runners and Gates

Full round runners are recommended to impart maximum pressure transmission (rule of thumb: runner diameter = part thickness + 1.5 mm). A wide variety of gates may be used. Hot runners may also be used, taking care to avoid drool and material degradation. Gate diameters or depths should preferably be between 0.8 – 1.0 times the part thickness. When using submarine gates, the minimum recommended diameter is 0.75 mm.

Chemical and Physical Properties

PBT is one of the toughest engineering thermoplastics. It is a semicrystalline material and has excellent chemical resistance, mechanical strength, electrical properties (high dielectric strength and insulation resistance), and heat resistance, all of which are stable over a broad range of environmental conditions. It has very low moisture absorption.

PBT, which is a polyester, is produced by the polycondensation reaction of dimethyl terephthalate an butanediol.

Tensile strength ranges from 50 MPa (7,250 psi) for unfilled grades to 170 MPa (24,650 psi) for glass reinforced grades. High levels of glass fillers make the material more brittle. Crystallization is rapid and this could cause warpage due to non-uniform cooling. In the case of glass filled grades, shrinkage is reduced in the flow direction, but in the cross-flow direction it may be equal to that of the generic grade. Shrinkage is of the order of 0.015 – 0.028 mm/mm (1.5 -2.8%). A 30% glass-filled material has a shrinkage range of 0.3 – 1.6%. The melting point (approximately 225 C / 437 F) and heat distortion temperatures are lower than that of PET. The Vicat softening point is approximately 170 C (338 F). The glass transition temperature ranges from 22 – 43 C (71 – 109 F).

The melt viscosity is fairly low and due to fast crystallization rates, cycle times are typically low.

PC processing conditions

Generic Class

PC (Polycarbonate)

Typical Applications

Electronic and business equipment (computer parts, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation (head lights, tail lights, instrument panels, etc.).

Injection Molding Processing Conditions

Drying PC grades are hygroscopic and pre-drying is important. Recommended drying conditions are 100 – 120 C (212 – 248 F) for 3 to 4 hours. Moisture content must be less than 0.02% prior to processing.
Melt Temperature 260 – 340 C (500 – 644 F); higher range for low MFR grades and vice-versa
Mold Temperature 70 – 120 C (158 – 248 F); higher range for low MFR grades and vice-versa
Material Injection Pressure As high as possible for rapid molding
Injection Speed Slow injection speeds when small or edge gates are used; high speeds for other types of gates

Chemical and Physical Properties

Polycarbonate is a polyester of carbonic acid. All general-purpose polycarbonates are based on bisphenol A. The bisphenol A component of the molecule contributes to the high glass transition temperature (150 C / 302 F). The rotational mobility of the carbonyl group within the molecule contributes to the high ductility and toughness of the material.

PC is an amorphous engineering material with exceptionally good impact strength, heat resistance, clarity, sterilizability, flame retardancy, and stain resistance. The notched Izod impact strength of PC is very high and mold shrinkage is low and consistent (.1 -.2 mm/mm).

High molecular weight PCs (which translate to low melt flow rate) have higher mechanical properties, but processibility of such grades becomes difficult. The type of PC chosen for a particular application should be based on the desired criteria (for high impact properties, use a low-MFR PC; conversely, for optimal processibility, use a high-MFR PC).

The melt viscosities are typically Newtonian up to shear rates of 1000 1/s and decrease beyond that. The Heat Deflection Temperature Under Load is typically between 130 -140 C (266 – 284 F) and the Vicat Softening Point is typically around 155 C (311 F).

PC+ABS processing conditions

Generic Class

PC+ABS (Polycarbonate-Acrylonitrile-Butadiene-Styrene Blend)

Typical Applications

Computer and business machine housings, electrical applications, cellular phones, lawn and garden equipment, automotive components (instrument panels, interior trim, and wheel covers)

Injection molding processing information

Drying Drying is required prior to processing. Moisture content should be less than 0.04 % to ensure stable processing parameters. Drying at 90 – 110 C (194 – 230 F) for 2 to 4 hours is recommended.
Melt Temperature 230 – 300 C (446 – 572 F)
Mold Temperature 50 – 100 C (122 – 212 F)
Material Injection Pressure Part dependent
Injection Speed As high as possible

Chemical and Physical Properties

PC+ABS offers combined properties of PC and ABS (high processibility of ABS along with excellent mechanical properties and impact and heat resistance of PC). The ratio of the two components affects the heat resistance. The blend exhibits excellent flow characteristics.

PC+PBT processing conditions

Generic Class

PC+PBT (Polycarbonate + Polybutyleneterephthalate blend)

Typical Applications

Gear cases, automotive (bumpers); applications which require chemical and corrosion resistance, high heat resistance, high impact strength over wide temperature ranges, and high dimensional stability.

Injection Molding Processing Conditions

Drying 110 – 135 C (230 – 275) F for approximately 4 hours .
Melt Temperature 250 – 280 C (482 – 536 F); Depends on specific grade
Mold Temperature 40 – 85 C (104 – 185 F)

Chemical and Physical Properties

PC+PBT blends offers a combination of properties of PC and PBT – high toughness and dimensional stability of PC and good chemical and heat resistance and lubricity of crystalline PBT.

PEI processing conditions

Generic Class

PE2 (Polyetherimide)

Typical Applications

Automotive (engine components: temperature sensors, fuel and air handling devices), electrical/electronics (connector materials, printed circuit boards, circuit chip carriers, explosion proof boxes), packaging applications, aircraft (interior materials), medical (surgical staplers, tool housings, non implant devices)

Injection molding processing information

Drying PEI absorbs moisture and can cause material degradation. Moisture content should be less than 0.02%. Suggested drying conditions are 150 C (302 F) for 4 hours in a desiccant dryer (6 hours for reinforced and blended grades)
Melt Temperature 340 – 440 C (644 – 824 F) unreinforced grades
340 – 415 C (644 – 780 F) reinforced grades
Mold Temperature 70 – 175 C (158 – 347 F); Aim: 140 C
Material Injection Pressure 70 – 150 MPa Typical
Injection Speed As high as possible

Chemical and Physical Properties

PEIs are amorphous materials whose chemical structure consists of repeating aromatic imide and ether units. This accounts for its high temperature resistance. It also leads to high stiffness, and modifiers are used to make the material processible. PEIs are very stiff and strong even without reinforcements. They have excellent thermal stability making it possible to use them in high temperature applications. They have good flame and chemical resistance and good electrical insulation properties. The glass transition temperature is high (215 C / 419 F). It exhibits low shrinkage and highly isotropic mechanical properties.

PET processing conditions

Generic Class

PET (Polyethylene terephthalate)

Typical Applications

Automotive (structural components such as mirror backs, and grille supports, electrical parts such as head lamp reflectors and alternator housings), electrical applications (motor housings, electrical connectors, relays, and switches, microwave oven interiors, etc.), industrial applications (furniture chair arms, pump housings, hand tools, etc.).

Injection molding processing conditions

Drying Drying is essential prior to molding. PETs are very sensitive to hydrolysis. Recommended drying conditions are 120 – 165 C (248 – 329 F) for 4 hours. The moisture content should be less than 0.02%.
Melt Temperature 265 – 280 C (509 – 536 F) for unfilled grades
275 – 290 C (527 – 554 F) for glass reinforced grades
Mold Temperature 80 – 120 C (176 – 248 F); preferred range: 100 – 110 C (212 – 230 F)
Material Injection Pressure 30 -130 MPa
Injection Speed High speeds without causing embrittlement

Runners and Gates

All conventional types of gates may be used; gates should be 50 – 100% of the part thickness.

Chemical and Physical Properties

PET is an aromatic polyester produced from polymerization of either terephthalic acid (TPA) or dimethyl ester terephthalic acid (DMT) and ethylene glycol (EG). The glass transition is approximately 165 C (330 F) and the material crystallizes over a temperature range from 120 – 220 C (248 -428 F).

PET is highly sensitive to moisture at high temperatures and exhibits excessive warpage when reinforced with glass fibers. Promotion of crystallinity is achieved through adding nucleating agents and crystal growth accelerators. Crystalline moldings exhibit high modulus, gloss, and heat distortion temperatures. Warpage is minimized by addition of particulate fillers such as mica. When low mold temperatures are used, transparent moldings

PETG processing conditions

Generic Class

PETG (Glycol-modified PET; Copolyesters)

Typical Applications

PETGs offer a desirable combination of properties such as clarity, toughness, and stiffness. Applications include medical devices (test tubes and bottles), toys, displays and lighting fixtures, face shields, and refrigerator crisper pans.

Injection molding processing conditions

Drying Drying is essential for PETG prior to injection molding. The moisture level must be below 0.04%. Drying temperature is not to exceed 66 C (150 F). Drying at approximately 65 C (149 F) for 4 hours is recommended.
Melt Temperature 220 – 290 C (428 – 554 F); The melt temperature is grade specific
Mold Temperature 10 – 30 C (50 – 86 F); Recommended: 15 C (60 F)
Material Injection Pressure 30 -130 MPa
Injection Speed High speeds without causing embrittlement

Chemical and Physical Properties

PETGs (or copolyesters) are glycol modified PETs; the modification is done by adding a second glycol during polymerization. The resulting molecular structure is irregular and the material is clear and amorphous with a glass transition temperature of 88 C (190 F). PETGs can be processed over a wider processing range than conventional PETs and offer good combination of properties such as toughness, clarity, and stiffness.

PMMA processing conditions

Generic Class

PMMA (Polymethyl methacrylate)

Typical Applications

Automotive (signal light devices, instrument panels, etc.), medical (blood cuvettes, etc.), industrial (video discs, lighting diffusers, display shelving, etc.), consumer (drinking tumblers, stationery accessories, etc.)

Injection Molding Processing Conditions

Drying PMMA is hygroscopic and must be dried prior to molding. Drying at 90 C (194 F) for 2-4 hours is recommended.
Melt Temperature 240 – 280 C (460 – 536 F)
Mold Temperature 35 – 80 C (90 – 176 F)
Injection Speed Moderate

Chemical and Physical Properties

Pellets for injection molding are made either by bulk polymerization of methyl methacrylate followed by extrusion and pelletization or by polymerization in an extruder. Formulations vary by molecular weight and physical properties such as flow rate, heat resistance, and toughness. Higher molecular weight grades are tougher than lower molecular weight grades. High flow formulations are generally preferred for molding.

Heat deflection temperature under load varies from 75 C (167 F) for high flow materials to 100 C (212 F) for low flow (high molecular weight) materials.

PMMA has excellent optical properties and weatherability. The white light transmittance is as high as 92%. Molded parts can have very low birefringence which makes it ideally suited as a material for video discs.

PMMA exhibits room temperature creep. The initial tensile strength is high but under long term, high stress loading, it exhibits stress craze. Impact strength is good but it does show some notch sensitivity.

POM processing conditions

Generic Class

POM (Polyacetal or Polyoxymethylene)

Applications

Acetals have a low coefficient of friction and good dimensional stability. This makes it ideal for use in gears and bearings. Due to its high temperature resistance, it is used in plumbing (valve and pump housings), and lawn equipment.

Injection Molding processing conditions

Drying Not usually required but the material should be stored in a dry atmosphere.
Melt Temperature 180 – 230 C (356 – 446 F) for homopolymer; 190 – 210 C (374 – 410 F) for copolymer
Mold Temperature 50 – 105 C (122 – 221 F); Higher mold temperatures are preferred for precision molding which reduce post-molding shrinkage
Material Injection Pressure 70 – 120 MPa
Injection Speed Medium – High

Runners and Gates

Any type of gate may be used. When using tunnel gates, the short type is preferred. Insulated, hot tip runners are preferred for homopolymers; both internally and externally heated hot runners may be used in the case of copolymers.

Chemical and Physical Properties

Acetals are tough, resilient materials and exhibit good creep resistance, dimensional stability, and impact resistance even at low temperatures. Acetal grades are either homopolymers or copolymers. Homopolymers have better tensile strength, fatigue resistance and hardness but are difficult to process. Copolymers have better thermal stability, chemical resistance and processibility. Both homopolymers and copolymers are crystalline and have low moisture absorption.

Copolymers may be used continuously at air temperatures up to 100 C (212 F); homopolymers have slightly higher temperature resistance. Many grades of acetal materials are available, tailored to different applications.

High crystallinity levels of acetals lead to relatively high shrinkage levels of 0.02 – 0.035 mm/mm. Differential shrinkage is observed with reinforced grades.

PP processing conditions

Generic Class

PP (Polypropylene)

Typical Applications

Automotive (mostly mineral-filled PP is used: dashboard components, ductwork, fans, and some under-hood components), appliances (doorliners for dishwashers, ductwork for dryers, wash racks and lids for clothes washers, refrigerator liners, etc.), consumer products (lawn/garden furniture, components of lawn mowers, sprinklers, etc.).

Injection Molding Processing Conditions

Drying Not normally necessary if proper storage is used
Melt Temperature 220 – 280 C (428 – 536 F); not to exceed 280 C
Mold Temperature 20 – 80 C (68 – 176 F); suggested: 50 C (122 F) The crystallinity level is determined by the mold temperature.
Material Injection Pressure Up to 180 MPa

Injection Speed

Typically, fast injection speeds are used to minimize internal stresses; if surface defects occur, slow speed molding at a higher temperature is preferred. Machines capable of providing profiled speed is highly recommended.

Runners and Gates

In the case of cold runners, typical diameters range from 4 – 7 mm. Full round sprues and runners are recommended. All types of gates can be used. Typical pin gate diameters range from 1 – 1.5 mm, but diameters as low as 0.7 mm may be used. In case of edge gating, the minimum gate depth should be half the wall thickness and the width should be at least double the thickness. Hot runners can readily be used for molding PP.

Chemical and Physical Properties

PP is produced by the polymerization of propylene using stereospecific catalysts. Mainly, isotactic PP is produced (the methyl groups lie on one side of the carbon chain). This linear plastic is semicrystalline because of ordered molecular structure. It is stiffer than PE and has a higher melting point. The PP homopolymer becomes very brittle at temperatures higher than 0 C (32 F) and for this reason, many commercially available grades are random copolymers with 1 – 4% ethylene or block copolymers with higher ethylene content. Copolymers have a lower heat distortion temperature (approximately 100 C / 212 F), less clarity, gloss, and rigidity, but greater impact strength. The material becomes tougher as the ratio of ethylene increases. The Vicat softening point is approximately 150 C (302 F). Because of high levels of crystallinity, the surface hardness and scratch resistance is higher for these materials.

PP does not have environmental stress cracking problems. PP is usually modified by addition of glass fibers, mineral fillers, or thermoplastic rubbers. The MFR of PP ranges from 1 to 40; lower MFR materials have better impact strength but lower tensile strength. The copolymer is tougher than the homopolymer of the same MFR. The viscosity is more shear and temperature sensitive than PE.

Due to crystallinity, the shrinkage is relatively high (order of 0.018 – 0.025 mm/mm or 1.8 – 2.5%). The shrinkage is more uniform than PE-HD (the difference in flow and cross-flow shrinkage is typically less than 0.2%). Addition of 30% glass reduces the shrinkage to approximately 0.7%.

Both homopolymer and copolymer PP offer excellent resistance to moisture and good chemical resistance to acids, alkalis, and solvents. However, it is not resistant to aromatic hydrocarbons such as benzene, and chlorinated hydrocarbons such as carbon tetrachloride. It is not as resistant to oxidation at high temperatures as PE.

PPE processing conditions

Generic Class

PPE/PPO (Polyphenylene Ether Blends)

Typical Applications

Household appliances (dishwasher, washing machine, etc.), electrical applications such as control housings, fiber-optic connectors, etc.

Injection Molding Processing Conditions

Drying Recommend drying before molding for approximately 2 – 4 hours at 100 C (212 F). PPOs have low levels of moisture absorption can typically be molded as received.
Melt Temperature 240 – 320 C (464 – 608 F); higher ranges for grades with higher levels of PPO
Mold Temperature 60 – 105 C (140 – 220 F)
Material Injection Pressure 60 – 150 MPa

Runners and Gates

All gates can be used; tab and fan gates are preferred

Chemical and Physical Properties

PPO is poly(2,6 dimethyl p-phenylene) oxide. The ether linkages offer easier processibility. Copolymers are referred to as PPEs (Polyphenylene Ethers). Typically, the commercially available PPOs (or PPEs) are blended with other thermoplastic materials such as PS (or HIPS), Nylon, etc. These blends are still referred to as PPOs or PPEs.

The blends offer superior processibility compared to pure PPOs. Their viscosities are lower. A range of properties can be obtained depending on the ratios of PPO and PS. Blends with nylons (PA 6/6) offer improved chemical resistance and perform well at high temperatures. The water absorption is low and the molded products have excellent dimensional stability.

Blends with PS are amorphous whereas blends with Nylons are crystalline. The addition of glass fibers reduces shrinkage levels to 0.2%. These materials have excellent dielectric properties and a low coefficient of thermal expansion. The viscosity level depends on the ratio of the components in the blend; higher PPO levels increase the viscosity.

PS processing conditions

Generic Class

PS (Polystyrene)

Typical Applications

Packaging, housewares (tableware, trays, etc.), electrical (transparent housings, light diffusers, insulating film)

Injection Molding Processing Conditions

Drying Not usually required unless stored improperly. If drying is needed, the recommended conditions are 2-3 hours at 80 C (176 F).
Melt Temperature 180 – 280 C (356 – 536 F); upper limit is 250 C for flame retardant grades (19 – 158 F)
Mold Temperature Suggested: 20 – 70 C (68 – 158 F)
Material Injection Pressure 20 – 60 MPa
Injection Speed Fast speeds are recommended

Runners and Gates

All types of conventional gates may be used.

Chemical and Physical Properties

General-purpose PS is produced by the polymerization of styrene. Most commercial grades are clear, amorphous polymers. PS offers excellent dimensional and thermal stability, optical clarity, and very little tendency to absorb moisture. It has good dielectric properties. It is resistant to water and dilute inorganic acids, but is attacked by strong oxidizing acids such as concentrated sulfuric acid, and is swollen by some organic solvents.

Processing shrinkage is typically between 0.4 – 0.7%.

PVC processing conditions

Generic Class

PVC (Polyvinyl Chloride)

Typical Applications

Water distribution piping, home plumbing, house siding, business machine housings, electronics packaging, medical apparatus, packaging for foodstuffs, etc.

Injection Molding Processing Conditions

Drying Not usually necessary as PVC absorbs very little water.
Melt Temperature 160 – 220 C (320 – 428 F)
Mold Temperature 20 – 70 C (68 – 158 F)
Material Injection Pressure Up to 150 MPa
Packing Pressure Up to 100 MPa
Injection Speed Relatively slow, to avoid material degradation

Runners and Gates

All conventional gate types may be used; pin-point and submarine gates are used for molding small components and fan gates are typically used for thick sections. The minimum diameter of pin-point or submarine gates should be 1 mm and the thickness of fan gates should not be less than 1 mm.

Sprues should be as short as possible; typical runner sizes are 6 – 10 mm and should have a full round cross-section. Insulated hot runners and certain types of hot sprue bushings may be used with PVC.

Chemical and Physical Properties

Rigid (unplasticised) PVC is one of the most widely used plastic materials. It is produced from sodium chloride and natural gas. The repeat chemical structure is vinyl chloride. Additives are mixed with PVC to make it processible. PVC grades produced by suspension or mass polymerization techniques are the major types used for melt processing. PVC is substantially an amorphous material.

Some of the additives used include stabilizers, lubricants, processing aids, pigments, impact modifiers, and fillers. Some features of PVC include low combustibility, toughness (designed to be virtually unbreakable), good weatherability (including good color and impact retention, and no loss in stiffness), and excellent dimensional stability. PVC is highly resistant to oxidizing and reducing agents, and strong acids. However, unplasticised PVC is not recommended for environmental and continuous use above 60 C (140 F). It is not resistant to concentrated oxidizing acids such as sulfuric or nitric acid and is unsuitable for use with aromatic and chlorinated hydrocarbons.

It is very important to process the material at the correct melt temperature; otherwise severe problems from decomposition (which produces hydrochloric acid which in turn accelerates decomposition) could result.

PVC is a relatively stiff flow material and has a narrow processing range. The molecular weight determines the flow characteristics. Higher molecular weight materials are more difficult to process (this could be modified by addition of lubricants). Typically, however, relatively low molecular weight grades are used in molding).

Shrinkage is fairly low (0.002 – 0.006 mm/mm or 0.2 – 0.6%).

SAN processing conditions

Generic Class

SAN (Styrene Acrylonitrile)

Typical Applications

Electrical (receptacles, mixer bowls, housings, etc. for kitchen appliances, refrigerator fittings, chassis for television sets, cassette boxes, etc.), automotive (head lamp bodies, reflectors, glove compartments, instrument panel covers, etc.), household appliances (tableware, cutlery, beakers, etc.), cosmetic packs, etc.

Injection Molding processing Conditions

Drying Under improper storage conditions, SAN absorbs moisture; it is recommended that it be dried at 80 C (176 F) for 2-4 hours prior to molding.
Melt Temperature 200 – 270 C (392 – 518 F); 230 – 260 C (446 – 500 F) for most applications; lower end of the range is used for molding thick wall components
Mold Temperature 40 – 80 C (104 – 176 F); SAN solidifies rapidly at higher temperatures; for reinforced grades, the mold temperatures should not be less than 60 C (140F).
The cooling system must be well designed because the mold temperature affects the parts appearance and shrinkage and warpage.
Material Injection Pressure 35 – 130 MPa
Injection Speed High speeds are recommended

Gates design

All conventional gate types may be used. The gates must be of proper size which aid in processing and do not cause streaks, burn marks, or voids.

Chemical and Physical Properties

SAN copolymers are produced by the polymerization reaction of styrene and acrylonitrile. They are strong, transparent materials. The styrene component imparts clarity, stiffness, and processibility and the acrylonitrile component imparts chemical and thermal resistance.

They have excellent load bearing capacity, rigidity, good resistance to chemicals, heat deformation, and cyclic temperature loads, and dimensional stability. The properties are dependent on the acrylonitrile content and commercial grades offer different acrylonitrile molecular masses. The addition of glass fibers enhances rigidity and resistance to heat deformation, and decreases the coefficient of linear thermal expansion.

The Vicat softening point is approximately 110 C (230 F) and the deflection temperature under load is approximately 100 C (212 F).

Shrinkage ranges from 0.003 – 0.007 mm/mm (0.3 – 0.7%).