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High-transparency TPU has become a preferred material for consumer electronics, wearable devices, protective gear, and medical components. Its exceptional clarity, flexibility, abrasion resistance, and biocompatibility make it a versatile choice.

Yet manufacturers working with transparent TPU films, molded TPU parts, and high-clarity elastomer components know a different side of the story: transparent TPU is one of the most challenging materials to demold. Sticking during demolding often leads to surface defects, reduced transparency, longer cycle times, and inconsistent product quality.

Even with optimized parameters—adjusted melt temperature, slower injection speed, improved mold polish—many factories still struggle with sticking, haze, drag marks, glossy spots, and unstable appearance. These problems not only reduce yield but also disrupt production continuity.

This article explains why high-transparency TPU is notoriously difficult to process and introduces a new silicone-based release additive technology that is redefining the standard for optical TPU parts — offering clean release,and stable surface quality without affecting mechanical durability or yellowing resistance.

1. Why Is High-Transparency TPU So Hard to Demold?

Compared with conventional TPU grades, transparent TPU typically falls in the 85A–95A hardness range and features a more regular polymer chain structure to achieve optical clarity.
This structure significantly narrows the processing window. During molding, transparent TPU becomes highly viscoelastic, resulting in stronger adhesion to the mold surface.

As a result, manufacturers frequently encounter:

1) Severe Mold Sticking and Difficult Ejection

The high adhesion between TPU and polished mold surfaces leads to:

deformation during ejection

surface tearing or whitening

stress marks on thin-wall sections

For transparent TPU phone cases, thin shields, and wearable components, these defects are unacceptable.

2) Haze Caused by External Release Agents

Traditional oily release sprays often leave trace residues that interfere with optical clarity. Even a thin film of residue can cause:

loss of gloss

increased haze

uneven transparency

sticky or oily surface feel

In high-end transparent products, such contamination is a critical quality failure.

3) Flow-Related Defects: Drag Marks, Silver Streaks, Bright Spots

Non-uniform cooling or insufficient melt flow leads to:

streaks along the flow path

water-wave drag marks

silver lines

localized bright spots or optical distortion

These defects may persist even when the mold is polished to a mirror finish.

4) Low and Unstable Yield Rates

Manufacturers often report:

cycle-to-cycle inconsistency

frequent mold cleaning

unpredictable defect rates

irregular shrinkage or warpage

This is especially problematic in mass production of high-transparency parts.

2. Why External Release Agents Fail for Transparent TPU

Many factories attempt to solve demolding issues using external release agents. However, for transparent TPU, this approach typically causes additional problems.

1) Residue Migration Leads to Optical Distortion

Oily layers disrupt the uniformity of the transparent TPU surface. As they migrate, haze increases and optical clarity declines.

2) Instability at High Temperatures

At TPU injection temperatures (190–220°C), release agent residue may:

carbonize on the mold surface

cause burn marks or bright spots

reduce surface consistency

3) Poor Compatibility with Secondary Processing

Residual release agents negatively affect:

bonding

printing

painting

coating

overmolding

For these reasons, many OEMs prohibit external release agents for optical-grade components.

The industry is shifting toward internal mold-release modification rather than surface spraying.

3. How to Solve the Problem of High-Transparency TPU Being Difficult to Demold?

Material-Level Breakthrough: A New Demolding Approach for High-Transparency TPU
SILIKE Copolysiloxane Additives — High-Lubrication Silicone-Based Release Modifier (SILIMER 5150)

Although SILIMER 5150 was originally developed as a high-lubrication silicone wax to enhance scratch resistance, surface gloss, and texture retention in plastics such as PA, PE, PP, PVC, PET, ABS, TPEs, polymer alloys, and WPC, market feedback has revealed unexpected success in high-transparency TPU demolding applications.

TPU Processors have discovered that the easy-to-use pelletized additive provides:

improved melt flow

better mold filling

enhanced abrasion resistance

smoother surface finish

TPU mold release improvement

These benefits collectively upgrade TPU processing efficiency far beyond the additive’s initial design scope.

Why SILIMER 5150 Works as a High-Performance Release Additive for TPU

SILIMER 5150 is a functionally modified silicone wax engineered with a unique molecular structure that ensures excellent compatibility with TPU. It delivers strong lubrication performance without precipitation, blooming, or compromising transparency.

Instead of applying chemicals externally on the mold surface, the TPU is internally modified so that adhesion naturally decreases during molding.
This eliminates the haze, residue, or instability normally associated with external release agents.

4. Practical Guide: How to Optimize Demolding for High-Transparency TPU

To achieve defect-free, stable demolding, manufacturers should optimize material, mold, and process parameters.

(1) Material Optimization

Use internally modified TPU with Silicone-Based additive SILIMER 5150.

Maintain moisture below 0.02%.

Select TPU grades with enhanced flow for thin-wall parts.

(2) Process Parameter Optimization

Mold temperature: 30–50°C

Melt temperature: 195–210°C

Injection speed: medium–high for uniform flow

Cooling time: ensure full stabilization before ejection

Back pressure: moderate to avoid overheating

Balanced parameters help prevent drag marks, poor filling, and sticking.

5. Benefits of Using Copolysiloxane Additive and Modifier SILIMER 5150 for High-Transparency TPU Demolding 

This Silicone-Based Release Modifier technology is particularly effective for high-hardness, high-transparency TPU grades, which are traditionally the most difficult to demold. By integrating this additive solution, TPU manufacturers gain an immediate competitive advantage — achieving higher-quality surfaces, lower rejection rates, and more consistent production performance. Its benefits extend across TPU applications in electronics, sporting goods, automotive interiors, and medical packaging, where clarity, surface aesthetics, and processing stability are critical.

For inquiries about TPU release additive, sample requests of the best additive for TPU demolding, or technical support on how to fix TPU sticking in molding, please contact SILIKE. Get your TPU sticking problem solution and TPU mold release improvement.

Tel: +86-28-83625089, Email: amy.wang@silike.cn, Website: www.siliketech.com