Medical-Grade vs. Cosmetic-Grade Plastic Parts: Three Key Differences to Consider in Mold Design

 

 

In the manufacturing of high-end packaging and medical devices, the choice of plastic material directly determines product success or failure. While medical-grade and cosmetic-grade materials may appear similar, they differ fundamentally from material selection criteria to mold design logic. This article, drawing on international certification standards such as FDA and REACH, as well as industry case studies, analyzes the key differences between these two types of materials in mold design, helping injection mold manufacturers mitigate development risks.

Difference 1: Material Certification Standards and Mold Compatibility Design

 

Core Conflict

 

Medical-grade: Must meet mandatory certifications such as FDA 21 CFR and ISO 10993 biocompatibility. Materials must withstand high-temperature steam sterilization (e.g., PC must withstand temperatures above 120°C).

 

Cosmetic-grade: Focusing on EU regulations such as EC 1223/2009, materials must be compatible with alcohol wipes and fragrance penetration (e.g., PMMA requires higher chemical resistance).

 

Mold Design Impact

Hot Runner System Optimization:

 

Medical materials (such as PEEK) have a low melt index, requiring a large hot runner cross-section to prevent cold material blockage. A YUDO hot nozzle with a PID temperature control module is recommended.

 

Cosmetic materials (such as AS) have good flowability, so a needle-valve hot runner can be used for precise dispensing and reduced weld lines.

 

Cooling Water Path Differences:

 

Material Type

 

Cooling Requirements

 

Mold Steel Recommendations

 

Medical Grade (such as TPU)

 

Fast Cooling to Avoid Crystallization Defects

 

S136 Mirror Steel (HRC ≥ 52)

 

Cosmetic Grade (such as ABS)

 

Slow Cooling to Ensure Surface Gloss

 

NAK80 Pre-hardened Steel

 

Differentiation Point 2: Surface Treatment and Mold Life Management

 

Functional Requirements Comparison

 

Medical Grade: The surface must achieve a mirror finish of Ra ≤ 0.2μm to prevent microbial adhesion, and nickel plating is prohibited (to avoid allergic reactions).

 

Cosmetic-grade: For high-gloss textures (such as diamond grain and IMD transfer), a 0.05-0.1mm etching margin should be reserved [citation:9].

 

Key Process Implementation Points

Differences in Steel Pretreatment:

 

Medical molds require electro-discharge machining (EDM) followed by mirror polishing to eliminate microscopic pores; cosmetic molds can be directly CNC-engraved.

 

Maintenance Cycle Management:

 

Medical molds require plasma cleaning every 5,000 cycles, while cosmetic molds require routine maintenance every 20,000 cycles.

 

Difference Point 3: Tolerance Accuracy and Mold Structure Design

Precision Standard Comparison

Indicators

 

Medical Grade (e.g., IV Connectors)

 

Cosmetic Grade (e.g., Lipstick Tubes)

 

Dimensional Tolerance

 

±0.01mm

 

±0.03mm

 

Coaxiality Requirements

 

≤0.005mm

 

≤0.02mm

 

Parting Surface Matching Accuracy

 

Zero-Step Design

 

Permitted Step ≤0.05mm

 

Mold Structure Solutions

Guide System Enhancement:

 

Medical molds require ball guide pins with taper positioning, achieving a repeatability of ±0.002mm; cosmetic molds can use conventional guide pins.

 

Exhaust System Design:

 

The porosity of medical products must be less than 0.1%. A 0.003mm stepped exhaust system with a vacuum-assisted system is recommended; cosmetic molds use conventional exhaust grooves.

 

Conclusion: Risk Control Strategies for Cross-Discipline Material Applications

Dual-Track Verification Mechanism: New projects must undergo simultaneous ISO 13485 medical device quality management system validation and cosmetics GMP review.

 

Digital Collaboration: Moldflow mold flow analysis software was used to simulate the filling stability of medical materials and the surface flow mark index of cosmetic materials.

 

Supply Chain Audit: Medical material suppliers must provide USP Class VI certification, and cosmetic materials must pass 26 allergen tests.