Каковы характеристики акрилового материала？

What are the characteristics of acrylic material?

Acrylic (PMMA) is a transparent thermoplastic prized for optical clarity, weather resistance, and rigidity. If you are comparing vendors, our injection molding supplier sourcing guide covers RFQ prep and qualification.

For a broader look at проектирование пресс-форм для литья под давлением, our pillar guide covers tooling structure, thermal control, and manufacturability tradeoffs.

Acrylic — officially known as polymethyl methacrylate (PMMA) — is an amorphous thermoplastic valued for its glass-like clarity, weather resistance, and rigidity. It transmits up to 92% of visible light, weighs half as much as glass, and can be machined, polished, or литьё под давлением into complex shapes. But behind these headline numbers are processing realities that catch engineers off guard: narrow melt temperature windows, sensitivity to moisture, and a tendency to develop internal stresses if cooling is rushed. With 20+ years of injection molding experience across 400+ materials, we have seen firsthand how acrylic rewards careful process design — and punishes shortcuts.

This article covers the mechanical, thermal, and optical properties that matter for production, explains how acrylic compares to polycarbonate and glass, and walks through the литьевая форма² design and processing parameters that determine whether your acrylic parts come out clear and dimensionally stable — or cloudy, stressed, and scrapped.

What are the physical and mechanical properties of PMMA?

The physical and mechanical properties of pmma are the main categories or options explained in this section. PMMA is an amorphous thermoplastic with a density of 1.18 g/cm3, a glass transition temperature (Tg) of approximately 105°C, and a tensile strength of 65-75 MPa. Unlike semi-crystalline plastics, it does not have a sharp melting point — it gradually softens above Tg, which gives processors a wider forming window but also means dimensional stability drops off quickly above 80-90°C. The table below compares key properties of PMMA against two common alternatives: polycarbonate (PC) and general-purpose polystyrene (GPPS).

Looking at the numbers, three things stand out. First, acrylic wins on optical clarity — 92% light transmission edges out both PC and GPPS. Second, PC dominates impact resistance by a factor of 25–35x, which is why you see PC in safety goggles and acrylic in display cases. Third, PMMA has higher water absorption than PC or GPPS, which means you must pre-dry the resin (typically 80–90°C for 3–4 hours) before processing to avoid splay marks and bubbles in clear parts.

In our Shanghai factory, we run 47 injection molding machines from 90T to 1850T, and we process acrylic across a wide range of part geometries — from thin-wall light guides to thick optical lenses. The key is dialing in the drying, melt temperature, and mold cooling before the first shot goes in.

How does acrylic compare to polycarbonate and glass?

If you are choosing between acrylic, polycarbonate, and glass for a transparent component, the decision comes down to three questions: How much impact resistance do you need? What temperature will the part see in service? And how important is scratch resistance versus polishability?

Acrylic vs Polycarbonate

Polycarbonate is the go-to when impact resistance is the priority. PC withstands 10–20 times more impact energy than PMMA, and it maintains toughness down to -40°C. But PC has tradeoffs: it yellows faster under UV exposure unless stabilized, it costs 20–40% more per kilogram, and it is harder to achieve the same level of optical clarity — PC typically tops out around 88–90% light transmission versus acrylic’s 92%. If your part needs to survive drops (safety equipment, riot shields, aircraft windows), choose PC. If your part sits still and needs to look crystal clear (display cases, light fixtures, lenses), acrylic is the better call.

Acrylic vs Glass

Glass still wins on hardness and scratch resistance — a Mohs hardness of 6+ versus acrylic’s 2–3. Glass also handles higher temperatures without deforming. But acrylic has practical advantages that matter in manufacturing: it weighs roughly half as much as glass (1.18 vs 2.5 g/cm3), it can be machined and drilled without cracking, and it can be injection molded into complex shapes that would be impossible or prohibitively expensive in glass. For production runs above a few hundred units, injection-molded acrylic parts typically cost 40–60% less than equivalent glass components.

What are the key processing parameters for acrylic injection molding?

Processing PMMA is not difficult, but it is unforgiving. The material has a narrow processing window, and the margin between “perfectly clear” and “burned or cloudy” is smaller than with most engineering resins. Here are the parameters that matter most, based on our experience across hundreds of acrylic production runs:

Drying Requirements

PMMA absorbs 0.3–0.4% moisture in 24 hours at room conditions. If you skip drying, you get silver streaks (splay), bubbles, and reduced clarity in transparent parts. The standard protocol is 80–90°C for 3–4 hours in a dehumidifying hopper dryer, targeting a dew point below -20°C and final moisture content below 0.02%. In humid climates like Shanghai in summer, we extend drying to 4–5 hours to be safe.

Melt and Mold Temperature

The recommended melt temperature range is 230–260°C, depending on the specific grade. Go below 230°C and you risk short shots, high internal stress, and poor surface reproduction. Go above 260°C and the resin starts to degrade — you will see yellowing, gas burns, and a drop in mechanical properties. Mold temperature should be 60–80°C. Higher mold temperatures improve surface finish and reduce residual stress (critical for optical parts), but they extend cycle time.

Скорость и давление впрыска

Acrylic has relatively high melt viscosity compared to materials like PP or PE. This means you need higher injection pressure (typically 800–1500 bar) and moderate-to-fast injection speed to fill the mold before the material freezes. However, too-fast injection causes jetting and surface blemishes. For thick optical parts, a profiled speed (slow start, then ramp up) usually produces the best results. Holding pressure is critical — maintain 60–80% of peak injection pressure for 3–8 seconds (depending on wall thickness) to compensate for volumetric shrinkage and prevent sink marks.

What gate and mold design considerations apply to acrylic?

Because acrylic parts are often transparent, gate location and design directly affect cosmetic качество³. Edge gates and fan gates are common for flat display parts — they distribute flow evenly and minimize visible witness marks. For small optical lenses, a pinpoint or submarine gate may be preferred for automatic degating. Avoid placing gates on appearance surfaces; the stress-whitening around the gate is impossible to hide on clear parts.

Draft angles of 1–2° per side are recommended for polished cavities. Ejection should use large-area ejector pins or stripper plates rather than small-diameter pins, which can cause stress cracking or white marks on the part surface. Cooling channels should be placed to ensure uniform temperature across the cavity — uneven cooling creates internal stress that shows up as birefringence (optical distortion) under polarized light inspection.

What are the common applications of acrylic in injection molding?

Acrylic injection molding serves industries where optical clarity, surface finish, and design flexibility are the primary requirements. Here are the applications we see most frequently in production:

Lighting and optics: Light guides, lenses, light pipes, and diffusers for LED lighting systems. PMMA’s 92% light transmission makes it the standard choice for automotive taillight lenses, backlight guides in displays, and medical diagnostic windows.

Потребительская электроника: Transparent covers, display windows, touch-panel substrates, and protective lenses. Acrylic’s polishability and UV stability keep screens and windows clear over years of use.

Медицинские изделия: Curettes, tubing connectors, fluid-handling components, and diagnostic equipment housings. PMMA is biocompatible (USP Class VI grades available) and can withstand common sterilization methods including ethylene oxide and gamma irradiation.

Point-of-purchase displays: Retail fixtures, product stands, brochure holders, and display cases. Injection-molded acrylic provides glass-like appearance with the durability and cost advantages of plastic for volume production.

Автомобили: Interior trim, gauge covers, light covers, and decorative panels. Color-matched acrylic (using Pantone, RAL, or customer samples) is standard for branded interior components.

What are the limitations and disadvantages of acrylic?

No material is perfect, and acrylic is no exception. Engineers who choose PMMA without understanding its limitations end up with field failures and customer complaints. Here are the tradeoffs you need to weigh:

Low impact resistance: At 17–25 J/m notched Izod, PMMA is brittle compared to PC (600–850 J/m). It cracks under sharp impact rather than deforming. This rules it out for safety-critical applications like helmets, safety shields, or any component subject to drop tests above 1 meter on to hard surfaces.

Poor scratch resistance: With a Mohs hardness of 2–3, acrylic scratches easily. For applications where the surface will be handled frequently (handheld devices, tabletop items), you either need a hard coat (which adds cost and can yellow) or you should consider a harder material like glass or hardened PC.

Limited thermal resistance: The glass transition temperature of 105°C means acrylic parts start to soften and deform above 80–90°C under load. If your part will see sustained temperatures above 80°C (automotive engine compartments, sterilization in autoclaves, hot-fill packaging), PMMA is the wrong choice. PC, PEEK, or PPSU would be more appropriate.

Chemical sensitivity: PMMA is attacked by alcohols, ketones (acetone, MEK), esters, and aromatic and chlorinated hydrocarbons. It resists dilute acids and alkalis, but solvents commonly used in cleaning, painting, or assembly can craze or dissolve the surface. Always verify chemical compatibility before specifying acrylic for applications involving fluid contact.

When should you choose acrylic for your injection molding project?

Choose acrylic when your part needs optical clarity above all else and the operating temperature stays below 80°C. It is the right material for light guides, lenses, display covers, and decorative components where surface finish and color fidelity matter more than toughness. If you need clarity and impact resistance, consider PC. If you need clarity and heat resistance, consider glass-filled PC or PC/PMMA blends.

What are frequently asked questions about acrylic material?

Часто задаваемые вопросы

What are the main characteristics of acrylic material?

Acrylic transmits 92% of visible light, slightly better than polycarbonate at 88-90%. It weighs half as much as glass and costs 40-60% less than equivalent glass components in volume production runs. However, it scratches more easily than glass (Mohs 2-3 vs 6+) and has much lower impact resistance than polycarbonate (17-25 J/m vs 600-850 J/m). Choose acrylic for stationary applications needing optical clarity, choose PC for impact-critical parts, and choose glass for scratch-critical or high-temperature applications where thermal stability matters.

How does acrylic compare to glass and other plastics?

The main disadvantages of acrylic are: low impact resistance (it cracks rather than deforms under sharp impact), poor scratch resistance (Mohs hardness of 2-3 requires surface protection or hard coating for handled parts), limited thermal resistance (Tg of 105°C means parts soften above 80-90°C under load), and chemical sensitivity (attacked by alcohols, ketones like acetone, esters, and aromatic hydrocarbons). For applications requiring higher impact strength or heat resistance, polycarbonate or PC/PMMA blends are generally more appropriate despite their slightly lower optical clarity and higher material cost.

What are the disadvantages of acrylic plastic?

The main disadvantages of acrylic are: low impact resistance (it cracks rather than deforms under sharp impact), poor scratch resistance (Mohs hardness of 2-3 requires surface protection or hard coating for handled parts), limited thermal resistance (Tg of 105°C means parts soften above 80-90°C under load), and chemical sensitivity (attacked by alcohols, ketones like acetone, esters, and aromatic hydrocarbons). For applications requiring higher impact strength or heat resistance, polycarbonate or PC/PMMA blends are generally more appropriate despite their slightly lower optical clarity.

What temperature is needed for acrylic injection molding?

Acrylic requires melt temperatures of 230-260°C and mold temperatures of 60-80°C for optimal results. The resin must be pre-dried at 80-90°C for 3-4 hours in a dehumidifying dryer to reach moisture content below 0.02%. Processing below 230°C causes short shots and high internal stress in the finished parts, while temperatures above 260°C cause yellowing and material degradation. Injection pressure of 800-1500 bar is typical due to PMMA high melt viscosity. Higher mold temperatures (70-80°C) improve surface finish and reduce residual stress in optical-quality parts.

Is acrylic recyclable?

Yes, acrylic (PMMA) is recyclable through standard thermoplastic reprocessing methods and carries recycling code 7. It can be reground, re-melted, and reformed into new products. Recycled acrylic (rPMMA) is commercially available for non-optical applications, though it typically shows slightly reduced clarity and may have minor color variations compared to virgin material. For sustainability-focused projects, PMMA production scrap from injection molding can be reground and reused in non-critical components, which reduces both material waste and overall manufacturing cost in volume production environments.

1. литьё под давлением: injection molding refers to the manufacturing process that melts plastic resin, injects it into a mold cavity under pressure, cools and solidifies the part, then ejects it — repeating the cycle for volume production. ↩

2. литьевая форма: injection mold refers to the precision steel tool that defines part geometry, gate location, cooling channel layout, ejection method, and surface finish for every shot. ↩

3. качество: Качество — это производственная дисциплина, объединяющая DFM, валидацию формы, технологические окна, планы контроля и корректирующие действия для получения повторяемого результата. ↩