Epoxy Resin Zero Bubble! Defoaming Test of 3 Viscosity Grades

Solve bubble challenges in epoxy potting, coatings and composite materials, full coverage from 500cps to 200,000cps


Epoxy resin is a thermosetting polymer based on bisphenol A or novolac epoxy resin. Formulated by adding curing agents, reactive diluents and functional fillers, it features outstanding bonding strength, electrical insulation, chemical resistance and dimensional stability. Epoxy resin is widely used in electronic potting, composite molding, floor coatings, structural bonding and mold manufacturing. However, air is easily entrapped during dispensing, mixing and pouring. Coupled with wide viscosity range and exothermic curing reaction, residual bubbles may cause insulation failure of potting parts, surface pinholes and composite delamination. SIENOX delivers high-efficiency defoaming solutions for various epoxy resins via self-developed planetary mixing and defoaming technology.


◆ Material Properties

Common Resin Matrix

Bisphenol A type (E-51/E-44), novolac type, alicyclic epoxy resin

Curing Agent Types

Modified aliphatic amines, acid anhydrides, aromatic amines, imidazole accelerators

Viscosity Range

500~200,000+ cps, covering diluent to high-viscosity paste

Filler Loading

0~85 wt%, commonly alumina, silica, glass microspheres

Curing Conditions

Room temperature cure / medium temp 80-120℃ / high temp 150-180℃

Defoaming Difficulties

High-filled systems feature high viscosity and strong thixotropy; curing exotherm accelerates bubble expansion


◆ Mature Application Fields

🔌 Electronic Potting

Potting protection for power modules, transformers, LED drivers, sensors, connectors and other electronic components (viscosity 500~8,000cps)

✈️ Composite Materials

Resin infiltration and molding for carbon fiber / glass fiber prepregs, aerospace structural parts, wind turbine blades and sports equipment

🏭 Industrial Flooring

Epoxy self-leveling floor, anti-static floor, anti-corrosion floor coating (viscosity 10,000~50,000cps, film thickness 1-5mm)

🔧 Structural Bonding

Structural bonding of metal/ceramic/concrete, building reinforcement, bridge anchoring adhesive (viscosity 5,000~30,000cps)

🎨 Crafts / Molds

Epoxy ornaments, river tables, silicone mold reproduction, crystal drop resin crafts (viscosity 1,000~5,000cps)

🏗️ Building Anti-Corrosion

Concrete crack grouting, steel structure anti-corrosion coating, tank/pipeline lining anti-corrosion (high-solid high-viscosity system)

💎 Optical Lenses

LED packaging lenses, optical lens bonding, transparent encapsulated parts (low-viscosity high-clarity system with strict bubble requirements)

⚡ Insulating Materials

Dry-type transformer casting, high-voltage switch insulators, cable accessories (high-filled flame-retardant system, arc resistance required)

🚗 Automotive Components

Lightweight carbon fiber auto parts, battery potting, motor winding insulation treatment (medium & high temperature curing system)


◆ Core Problems Caused by Bubbles

⚡ Degraded Insulation Performance

Internal bubbles in potting parts form discharge channels, causing local electric field concentration. Breakdown voltage drops by over 50%, resulting in electrical insulation failure

🔘 Surface Pinhole Defects

Dense pinholes and fish eyes appear on coating/casting surfaces, damaging appearance and flatness, leading to rework or scrapping

📉 Reduced Mechanical Strength

Bubbles act as stress concentration points and reduce bonding and impact resistance. Interlaminar shear strength of composites drops by 30-60%

🔍 Loss of Transparency & Uniformity

Microbubbles scatter light in optical encapsulations and transparent crafts, lowering light transmittance and causing whitening, downgrading product grade


◆ Recommended Process — Planetary Mixing & Defoaming

Step 1 Weighing & Proportioning

Weigh epoxy resin and curing agent by formula ratio. Preheat resin component separately (40-60℃) to reduce viscosity for better subsequent defoaming

Step 2 Vacuum Mixing & Defoaming

Put mixture into mixing cup, set vacuum at -95KPa and planetary mixing parameters. The machine completes mixing and vacuum defoaming synchronously in one run

Step 3 Pouring / Coating

Perform pouring or coating immediately after defoaming. Pour slowly along vessel wall to avoid secondary air entrapment. Finish operation within pot life

Step 4 Curing & Forming

Cure under specified temperature & duration. For large-volume castings, staged heating is recommended to prevent secondary foaming from excessive exothermic peak


◆ Recommended Equipment

  1. MIX60 — Capacity 5~60g, suitable for lab R&D and small-batch potting sample defoaming; remarkable defoaming effect for low-viscosity epoxy systems (500~8,000cps)

  2. MIX90 — Capacity 20~500g, suitable for medium-batch production and medium-viscosity epoxy structural adhesives (5,000~30,000cps); high homogeneity of planetary mixing

  3. MIX1000PLUS — Capacity 100~1,000g, suitable for mass production and high-viscosity high-filled epoxy systems (30,000~200,000+ cps)

  4. MIX2000 — Capacity 500~2,000g, suitable for industrial continuous production and batch defoaming of large castings (e.g. transformers, insulators)


◆ Test Cases

▶ Case 1: Defoaming of Low-Viscosity Electronic Potting Adhesive

Test Material

Bisphenol A epoxy E-51 + methylhexahydrophthalic anhydride curing system (electronic potting adhesive with silica powder filler)

Initial Viscosity

2,500 cps (25℃)

Test Model

MIX60

Vacuum Level

-95 KPa

Rotation Speed

1,500 rpm

Defoaming Time

3 minutes

Material Temperature

25℃ (Ambient)

✅ Defoaming Result: Mixing and defoaming finished within 3 minutes. No visible bubbles on potting section, excellent surface leveling, breakdown voltage＞25KV/mm, meets standards for electronic component potting.


▶ Case 2: Defoaming of Medium-Viscosity Composite Structural Adhesive

Test Material

Toughened epoxy structural adhesive (for carbon fiber composite bonding, with rubber toughener and nano silica)

Initial Viscosity

15,000 cps (25℃)

Test Model

MIX90

Vacuum Level

-95 KPa

Rotation Speed

2,000 rpm

Defoaming Time

5 minutes

Material Temperature

40℃ (preheated for viscosity reduction)

✅ Defoaming Result: Mixing and defoaming completed within 5 minutes. No obvious interlayer bubbles in carbon fiber bonded parts, lap shear strength increased by 22%, good wetting of composite laminates, meeting bonding requirements for aerospace structural components.


▶ Case 3: Defoaming of High-Viscosity Flooring / Casting Compound

Test Material

High-filled epoxy self-leveling coating (containing quartz sand, heavy calcium and other aggregates, thick paste casting system)

Initial Viscosity

80,000 cps (25℃)

Test Model

MIX1000PLUS

Vacuum Level

-95 KPa

Rotation Speed

2,500 rpm

Defoaming Time

8 minutes

Material Temperature

50℃ (preheated for viscosity reduction)

✅ Defoaming Result: Mixing and defoaming completed within 8 minutes. No pinholes or fish eyes on self-leveling coating surface. Cross-section porosity＜1% at 3mm thickness, coating gloss＞90%, meeting high-standard industrial flooring requirements.


◆ Comparison Before & After Improvement

Comparison Item

Before Defoaming

After Defoaming

Surface Quality

Dense pinholes, fish eyes, shrinkage cavities

Smooth & dense surface, no visible defects

Internal Density

Cross-section porosity 5-15%

Cross-section porosity＜1%, uniform & dense structure

Insulation Performance

Unstable breakdown voltage, high partial discharge risk

Stable breakdown voltage＞25KV/mm, reliable insulation

Bonding / Mechanical Strength

Stress concentration at bubbles, large strength discreteness

Lap shear strength increased by 20%+, high data consistency

Transparency (Optical Parts)

Light scattered by microbubbles, whitening & haze

Light transmittance＞98%, optically clear

Yield Rate

High rework rate, poor batch consistency

Yield＞99%, stable & controllable batches


🎯 Free Sample Test    
      Send us your epoxy samples. We will test defoaming parameters and issue a test report