How to Read a PC Resin Datasheet for Design

Why a Standard Datasheet Is Not Enough

A generic polycarbonate datasheet lists average properties for a commodity grade. That data rarely matches the specific resin lot you will mold. When engineers design a part, they need to read the grade-specific sheet provided by the supplier. The values shift between grades. A low-impact grade may flow differently than a high-heat grade. A standard reading of a polycarbonate datasheet often skips these nuances. Engineers who only check the headline numbers miss the details that cause flash, sink marks, or brittle failure. This guide breaks down the process. It treats the datasheet as a working tool for design decisions.

What to Check Before You Start

Before opening the document, confirm the exact resin grade. The supplier code matters. A sheet for grade A and grade B may look identical at first glance. They are not. The formulation changes. One may contain nucleating agents for faster cooling. The other may be a pure amorphous polymer. Verify the supplier part number against your purchase order. Also check the revision date. Old sheets list outdated processing windows. Always work from the current technical data sheet. If the sheet lists a batch number, note it. Moisture content varies by lot. You will need this information later for drying time calculations.

Step 1: Verify the Heat Deflection Temperature

Start with the heat deflection temperature, or HDT. This number tells you the temperature at which the material deforms under a specific load. For polycarbonate, this is the first number engineers check. A standard HDT sits in a mid-range, but specific grades vary. If your part holds a motor or a heated component, the HDT must exceed the operating temperature with a safety margin. Look at the load condition. Some sheets list HDT under a low load. Others use a high load. A higher load produces a lower HDT. This difference changes your design tolerance. Do not compare an HDT under 0.46 psi to one under 1,470 psi. They measure different things. Choose the HDT value that matches the actual stress in your part. If the operating temperature is close to the HDT, increase the wall thickness or add ribs. Do not rely on the material alone.

Step 2: Check Thermal Stability and Degradation

The HDT shows static load behavior. Thermal stability shows how the resin ages over time at elevated temperatures. Look for the long-term stability data. Some grades retain their strength after months at high heat. Others degrade faster. If your part stays in a hot environment, like near a light fixture or an engine bay, this data matters. Check for any yellowing or embrittlement notes. Polycarbonate can yellow when exposed to UV light. If the part is outdoors, verify the UV stability rating. If the sheet does not mention UV, assume the resin will degrade over time. Plan for a protective coating or a UV-stabilized grade. This prevents field failures that a short-term HDT check would miss.

Step 3: Match Melt Flow Index to the Mold

The melt flow index, or MFI, is the second critical number. It measures how easily the resin flows through the mold at a set temperature and pressure. A low MFI means the resin is stiff. It requires higher injection pressure and temperature. A high MFI means the resin flows easily. It is easier to mold but may shrink more. Match the MFI to your mold complexity. A thin-walled part with long runners needs a higher MFI. A thick boss on a housing needs a lower MFI to reduce sink marks. Check the recommended injection temperature range. If the MFI is low, you may need to run the barrel hotter. But do not exceed the maximum processing temperature. That causes degradation. Balance the flow rate with the machine’s screw diameter. A large screw can handle a low MFI resin. A small screw may struggle.

Step 4: Review Chemical Resistance Limits

Polycarbonate is tough, but it has chemical limits. Look at the chemical resistance table. Some grades resist hydrocarbons well. Others swell in contact with ketones or esters. If your part holds a fluid, match the chemical to the resistance rating. Do not assume all polycarbonate grades are the same. A resin modified for impact may have lower chemical resistance. A resin optimized for clarity may be more brittle in the presence of solvents. Check the temperature of the chemical. Resistance at room temperature is not the same at boiling point. If the datasheet lists a limit, use that limit as your design boundary. If it is missing, request a sample for a chemical immersion test. Do not guess. Chemical swelling causes part distortion and seal failure.

Step 5: Assess Optical and Impact Properties

If the part is a lens, a visor, or a cover, check the optical clarity. Look for haze and light transmission values. A clear grade has high light transmission and low haze. A frosted grade has the opposite. These values depend on the resin’s crystallinity and additives. For impact resistance, check the Charpy impact test results. Polycarbonate is known for high impact strength. But specific grades vary. A standard grade may chip at low temperatures. A low-temperature grade maintains impact strength in cold environments. If your part sees sub-zero temperatures, verify the impact resistance at low temperatures. Do not use room temperature values. The resin stiffens as it cools. This changes the failure mode from ductile to brittle.

Step 6: Verify Moisture and Purity Requirements

Polycarbonate is hygroscopic. It absorbs moisture from the air. Even a fresh bag can hold enough moisture to cause porosity and splay marks. Check the recommended drying time and temperature. The datasheet will list a maximum moisture content for molding. Usually, this is a low percentage. Verify that your dryer can hold that level. If the resin sits in the hopper for long periods, moisture returns. Plan for continuous drying. Also check the purity level. Some grades are for standard parts. Others are for medical or food contact. The purity requirements differ. A medical grade has lower extractables. A standard grade may contain higher levels of stabilizers. Match the purity level to your application. Do not use a standard grade for a medical device.

Common Mistakes Engineers Make

Engineers often skip the load condition for HDT. They use the wrong value for their part. They also compare MFI values without checking the test method. Different suppliers use different methods. A high MFI from one supplier may not equal a high MFI from another. This leads to mold flow simulation errors. Another mistake is ignoring the chemical resistance table. Engineers see “polycarbonate” and assume it resists everything. It does not. Finally, many engineers skip the moisture check. They assume the resin is dry. It is not. They mold wet resin and wonder why the part is full of bubbles. Always verify the lot. Always verify the drying process. The datasheet is the baseline. The process is where it breaks.

Final Verification Step

Before releasing the design, run a design review. Pull the specific resin grade. Check the HDT, MFI, and chemical resistance against the part’s operating conditions. Confirm the drying time. Verify the purity level. If the part has optical requirements, check the haze. If it sees low temperatures, check the impact resistance. If it holds a chemical, check the swelling limit. Sign off on the datasheet values. Store the document with the design file. When production starts, compare the actual resin lot to the datasheet. If the values match, mold the part. If they do not, stop. Re-evaluate the grade. Do not proceed with a mismatched resin. The datasheet is your contract. Read it like one.

How to Use This Guide

This process applies to any engineering plastic. Polycarbonate is just one example. The same steps work for polyamide, polypropylene, and polybutylene terephthalate. Read the grade-specific sheet. Match the properties to the part. Verify the process. When in doubt, ask the supplier for the technical data sheet. Do not rely on a generic brochure. The details are in the sheet. Read them. Design accordingly.