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PBT

Tereftalato de Polibutileno

PBT·Polyesters·Semi-crystalline

PBT (Polybutylene Terephthalate) is the technical thermoplastic that quietly became the world's #1 material for automotive electrical connectors. If you pop the hood of any modern car, most of the black connectors (sensors, ECU, lights, fuel system) are PBT with 30% glass fiber (PBT-GF30). Why? High mechanical strength, excellent dimensional stability under humidity and temperature changes (where PA6-GF moves 0.6%, PBT-GF barely moves 0.05%), stable dielectric properties, V0 flame-retardant grades available, and very fast crystallization giving short cycle times in high-volume production.

You also know it by its brand names: Valox (SABIC), Ultradur (BASF), Crastin (DuPont/Distrupol), Pocan (Lanxess). Here we have compiled the reference ranges from the PDS, plus the questions that come up over and over on the shop floor: PBT vs PET (despite being the same polyester family, they're different), mandatory drying, hydrolysis at high temperature + humidity, GF grades, HR (hydrolysis resistant) and FR (flame retardant) grades, and when PBT vs PA6-GF makes sense for connectors.

Share your experience in the comments — ranges vary by manufacturer and grade, and collective discussion is what gets us out of trouble on the floor.

The ranges shown in these data tables were compiled by the MVPS team from various parameter sheets and literature, integrating the lower and upper limits for each material type.

This information must be carefully reviewed when developing injection molding processes. Final ranges and processing tolerances are the responsibility of the engineer in charge.

These ranges are not recommended for developing specific process tolerances. MVPS always recommends requesting and consulting the supplier's data sheet.

General Properties

Chemical StructureSemi-crystalline
Specific Gravity (Density)1.34:1
L/D Ratio18 – 24
Compression Ratio2.5 – 3
Tonnage Factor4.63 – 6.18kN/cm²
Thermal Diffusivity0.1206mm²/s
Max Shear Rate50,0001/s
Shrinkage0.5 – 2%
Regrind20%
Heat Deflection (HDT) @ 1.82 MPa121°C
Glass Transition (Tg) @ 10°C/min48°C
Vicat Softening @ 50N65°C

Drying

Drying Temperature121 – 138°C
Drying Time3 – 5h
Recommended Moisture0.05%
Recommended Dryer TypeDesiccant
Dew Point-40°C

Temperatures

Melt229 – 271°C
Nozzle243 – 266°C
Front241 – 266°C
Middle235 – 254°C
Rear229 – 249°C
Demolding57 – 91°C
Mold (Cooling)41 – 79°C
Feed Throat35 – 79°C

Processing

Back Pressure3.4 – 6.9bar
Screw Speed50 – 80RPM
Injection SpeedHigh
Barrel Occupancy25 – 75%
Injection Pressure1,500 – 2,500Pbar
Holding Pressure375 – 2,000Pbar
Cushion6.4 – 12.7mm

Mold

Runner Diameter4.06 – 7.11mm
Gate Diameter0.76 – 2.03mm
Gate Area0.46 – 3.24mm²
Wall Thickness0.08 – 4.06mm

Venting

Depth (Vent Depth)0.0406 – 0.2032mm
Land (Vent Land)0.508 – 1.02mm
Width (Vent / Clearance)3.05 – 7.62mm
Relief (Relief Channel)0.127 – 0.254mm

Frequently asked questions

PBT (Polybutylene Terephthalate) is a semi-crystalline engineering thermoplastic in the aromatic polyester family. Synthesized by polycondensation of 1,4-butanediol (BDO) + terephthalic acid or dimethyl terephthalate. Its linear chain with aromatic rings provides rigidity + thermal stability, while the butylene segment (4 carbons) provides chain flexibility allowing very fast crystallization during molding. Density ~1.31 g/cm³ (1.53 with 30% GF). Melting point ~225°C, HDT 60°C unfilled, 200°C+ with GF30.
No. Same family (both polyethylene/butylene terephthalate), but key difference: crystallization speed. PBT crystallizes fast (seconds) → ideal for injection. PET crystallizes slowly without nucleating agents → virgin PET stays amorphous in fast injection (the bottle one) and only crystallizes with sustained heat. Practical result: PBT dominates technical injection (connectors, housings). PET dominates extrusion of bottles/films/textile fibers. PET-G (modified) is used in transparent thermoforming. For comparable injection grades: PET needs nucleants/GF to crystallize as fast — a PET-GF30 can compete with PBT-GF30 at similar cost but with higher HDT.
PBT is hygroscopic (0.08–0.5% absorption at equilibrium) and sensitive to hydrolysis at injection temperature (240–270°C). Moisture >0.03% reacts with the polymer chain → hydrolytic chain scission → loss of 20–40% impact, silver streaks, brittle parts. Mandatory conditions: desiccant at 120°C for 3–4 h (virgin material) or 4–6 h (regrind), dew point ≤ –20°C, target ≤0.03% moisture. For PBT-GF grades, drying at 130°C is common in industrial production.
30% glass fiber loading (typical for PBT). Results: tensile strength 145–230 MPa (vs 50–60 MPa unfilled PBT), modulus 10,000 MPa, HDT 205°C (vs 60°C unfilled), low shrinkage 0.4–0.6% (vs 1.5–2.5% unfilled), low CTE (important for connectors seeing thermal cycles), CTI (comparative tracking index) 350V — fundamental for electrical certification. Key point: unlike PA6-GF, PBT-GF maintains its dimensions under changing humidity — a connector that goes into an engine sensor full of oil/water/cyclic temperature needs this. Combined with HR (Hydrolysis Resistant) and FR (Flame Retardant V0) grades, it dominates under-hood applications.
PBT-GF wins on: dimensional stability under humidity (key for IP67 sealed connectors), low creep, better processability with fast cycle, better chemical resistance to fuels/oils, higher CTI (electrically safer). PA6-GF wins on: superior toughness and impact (PBT is somewhat brittle), higher continuous use temperature (105–110°C vs 95°C for standard PBT), better fatigue resistance, cost (~15–25% cheaper). Rule of thumb: sealed connectors, under-hood, high voltage → PBT-GF. Mechanical brackets, structural housings under impact → PA6-GF. Consumer electronics housings → PBT-GF (better aesthetics and dimensional).
The PDS marks 38–79°C unfilled, 80–120°C for PBT-GF. Mold temperature is critical for PBT because it controls final crystallinity. Cold (38–55°C) = amorphous/partially crystalline parts that post-crystallize in storage (= unstable dimensions). Hot (70–90°C unfilled, 90–110°C with GF) = full crystallization in the mold, final dimensions, better stiffness/HDT. For electrical connectors: always 90–110°C. For non-critical parts: 60–80°C. Good news: PBT is one of the resins that benefits the least from advanced mold cooling because it crystallizes so fast that the process window is very wide.
Not by default — pure PBT yellows and loses toughness under UV in a few months. For outdoor use you need grades with UV stabilizers (HALS + carbon black typically). Automotive exterior grades (mirrors, handles, grilles) have special formulations with UV + thermal stabilization. For under-hood connectors (that see heat but not direct UV), HR (hydrolysis resistant) grades are sufficient. For exterior exposed connectors (tail lights, roof antennas, front ADAS sensors) → always UV-stabilized grade, typically with carbon black.
HR (Hydrolysis Resistant): standard PBT can degrade under hot water + sustained temperature (e.g., connector in cooling system). HR grades (Lanxess Pocan HR, DuPont Crastin HR) have additives that extend service life from 1000 h to 3000–5000 h at 85°C/85% RH. Critical for automotive under-hood. FR (Flame Retardant) V0: add retardants (typically brominated or organic phosphorus) for UL94 V0 classification. Required for high-voltage connectors, EV battery housings, appliances. Modern ones are halogen-free per European regulation. PBT-GF30-FR-V0-HR is the holy grail for electrical automotive.
The PDS marks 30% as recommended maximum. Each cycle slightly degrades molecular weight and increases hydrolysis sensitivity. For critical parts (certified connectors, parts with legal liability) → many OEMs forbid regrind or limit to 10%. Important: PBT regrind needs more aggressive re-drying (4–6 h at 120–130°C) than virgin — absorbed moisture from ambient air between operations, and starting with wet material on PBT is a guarantee of a brittle part. Closed-bag PBT regrind handling with desiccant until consumption is industry standard.
POM wins on: even better dimensional stability (POM <0.25% absorption vs PBT 0.08–0.5%), lower coefficient of friction, better wear resistance, better stiffness in unfilled parts. PBT wins on: higher temperature resistance with GF, better for parts with electrical detail (high CTI), better paintable and bondable, no formaldehyde risk. Rule of thumb: for gears and bushings in mass mechanical production → POM. For parts with electrical + mechanical function (housings with contacts, connectors with clip) → PBT-GF. For parts requiring painting (handles, exteriors) → PBT painted vs POM which is hard to paint/bond.

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