Fish Eyes and Pinholes on Carbon Fiber Parts: Resin Problem or Release Agent Problem?

# 1. What do fish eyes and pinholes look like?

# 1.1 Fish Eyes

Typical characteristics:

• Circular craters or volcano-like depressions on the surface
• Little or no resin in the center, or visible resin shrinkage
• A clear dewetting or repelling appearance

Root cause: Uneven surface tension prevents the resin from spreading uniformly.

# 1.2 Pinholes

Typical characteristics:

• Many tiny holes distributed across the surface
• Usually more obvious after curing or after coating or painting
• Can appear uniformly or as locally dense clusters

Root cause: Gas is not fully evacuated, or volatiles are released during cure.

# 2. Analysis of possible causes

# 2.1 Release agent factors

Common issues:

• Over-application
• Uneven wiping
• Insufficient cure
• Incompatibility with the resin system
• Oil or silicone contamination on the mold surface

Mechanism: A release agent is essentially a low-surface-energy film. If it is applied incorrectly, it can lead to:

• Reduced resin wetting -> fish eyes
• Local isolation -> pinholes or bubbles

# 2.2 Resin factors

Common issues:

• Viscosity is too high
• Mixing ratio is inaccurate
• Mixing is incomplete
• Moisture or volatiles are present
• Cure reaction is too fast

Mechanism:

• Poor wet-out -> fibers are not fully impregnated
• Gas release during cure -> pinholes
• Surface-tension differences -> fish eyes

# 2.3 Process and environmental factors

Even if the materials themselves are not the main problem, the following can still cause defects:

• High humidity (moisture absorption)
• Low mold temperature
• Insufficient vacuum
• Poor lay-up practice
• Dust contamination in the air

# 3. Verification method: use A/B tests to isolate the cause quickly

To avoid guesswork, an A/B test approach is recommended:

# 3.1 Test A: change only the release agent

• Keep the resin and process unchanged
• Switch the release agent or reduce the application amount

How to judge the result:

• Defect disappears -> release agent issue
• Defect remains -> likely resin or process issue

# 3.2 Test B: change only the resin

• Keep the release agent and process unchanged
• Change to a lower-viscosity resin or a different resin system

How to judge the result:

• Defect improves -> resin issue
• No obvious change -> release agent or process issue

# 3.3 Test C: process optimization test

• Increase mold temperature
• Improve vacuum level
• Extend degassing time

# 3.4 Interpreting the results

• Fewer pinholes -> gas or process issue
• Fish eyes remain -> surface contamination or release-agent issue

# 4. Repair and optimization recommendations

# 4.1 Solutions for release-agent-related issues

• Use thin, multiple coats (wipe-on / wipe-off)
• Allow each coat to cure fully
• Choose a semi-permanent release agent that matches the resin
• Clean the mold regularly to avoid buildup

# 4.2 Solutions for resin-related issues

• Use lower-viscosity resin to improve wetting
• Strictly control mix ratio and mixing uniformity
• Degas before use
• Avoid moisture exposure during storage

# 4.3 Process optimization recommendations

• Keep mold temperature within a suitable range
• For vacuum infusion, aim for >= -0.095 MPa
• Keep ambient humidity below 60%
• Optimize lay-up and operating procedures

# 5. Symptom-cause-solution reference table

Symptom	Possible cause	Recommended action
Fish eyes	Too much release agent	Reduce application amount and wipe evenly
Fish eyes	Surface contamination	Clean the mold
Fish eyes	Resin incompatibility	Change resin or release agent
Pinholes	Air entrapment	Improve vacuum and degassing
Pinholes	Resin viscosity too high	Use lower-viscosity resin
Pinholes	Moisture or volatiles	Control humidity and improve storage
Fish eyes + pinholes	Process parameters are not reasonable	Optimize temperature, pressure, and time

# Summary

Fish eyes and pinholes are not random defects. They are process problems that can be diagnosed systematically and controlled effectively.

Instead of changing materials blindly, build a scientific method:

• A/B verification
• Material-compatibility evaluation
• Standardized process control

Only by correctly identifying whether the problem comes from the resin, the release agent, or the process can you truly achieve:

• Improve surface quality
• Increase yield
• Reduce total production cost