PET กับ PETG สำหรับ ISBM: เรซินชนิดใดเหมาะสมกับการใช้งานในขวดของคุณ

1. Why PET and PETG Are Often Confused

PET and PETG share an almost identical chemical foundation. Both are polyethylene terephthalate based polyesters. Both exhibit excellent transparency. Both carry FDA and KFDA approval for food contact applications. Both recycle under the universal resin identification code 1 or 7 respectively. To a procurement manager reading spec sheets, the two materials appear interchangeable.

This similarity produces expensive selection mistakes. Korean manufacturers routinely specify PET for applications that require PETG’s impact resistance, then absorb 15-30% scrap rate from brittle bottle failures. Others specify PETG for commodity beverage applications, then carry a 200-400 KRW per bottle material premium that destroys the pricing position.

The technical reality is that one small molecular modification, the addition of cyclohexanedimethanol glycol to the polyester backbone, produces substantially different processing behavior, bottle performance characteristics, and commercial positioning. Understanding this modification is the foundation of resin selection discipline.

2. Molecular Structure & Material Chemistry

PET: Semi-Crystalline Homopolymer

Polyethylene terephthalate (PET) is a semi-crystalline thermoplastic polymer produced through polycondensation of terephthalic acid (TPA) and ethylene glycol (EG). The resulting polymer chain is regular and symmetric, which allows polymer chains to align into crystalline regions during cooling below the glass transition temperature.

This crystallization behavior is simultaneously PET’s greatest strength and its processing challenge. Biaxial orientation during ISBM stretching organizes polymer chains into oriented crystalline structures that deliver exceptional bottle strength, gas barrier properties, and dimensional stability. However, uncontrolled crystallization during cooling produces opacity and haze that ruins bottle appearance.

PETG: Amorphous Glycol-Modified Copolyester

PETG is produced by substituting approximately 30% of the ethylene glycol in the PET polymerization with cyclohexanedimethanol (CHDM). This substitution disrupts the regular polymer chain geometry and prevents crystalline alignment during cooling. The resulting material is amorphous, meaning it does not form crystalline regions regardless of cooling rate.

The amorphous structure produces exceptional optical clarity in thick-wall applications where PET would haze. It also produces superior impact resistance because amorphous polymer chains absorb energy through chain slippage rather than crystalline crack propagation. The trade-off is reduced barrier properties (no crystalline structure to impede gas permeation) and lower service temperature (no crystalline melt transition to resist deformation).

3. ISBM Processing Parameters Comparison

The molecular differences translate directly to measurably different ISBM processing windows. Operators switching between PET and PETG on the same platform must adjust five parameter groups.

The single most important processing difference is the drying temperature. PET absorbs moisture aggressively and requires high-temperature desiccant drying at 165-170°C to reach <50 ppm residual moisture. PETG handles moisture more gracefully and only requires 65-70°C drying. Operators switching from PET to PETG must reset drying profiles or risk polymer degradation.

The second key difference is stretch temperature tolerance. PET requires precise preform temperature control in a narrow 90-110°C window for optimal biaxial orientation without overheating into crystallization. PETG offers a wider forgiving window because it does not crystallize regardless of stretch conditions. This makes PETG significantly easier to process reliably, particularly for operators new to ISBM.

4. Bottle Performance Properties

The finished bottle performance differences are substantial and drive most application decisions.

Three performance dimensions drive most Korean selection decisions:

• ▸Thick-wall clarity: for premium cosmetic jars with 5-10mm wall thickness, PETG delivers glass-like clarity that PET cannot match. This single property drives K-beauty premium segment selection toward PETG.
• ▸Impact resistance: PETG bottles survive drops that shatter PET bottles, particularly at refrigeration temperatures. This matters for refrigerated beauty products and premium ready-to-drink beverages.
• ▸Gas barrier: PET biaxial crystalline structure creates excellent CO2 and O2 barrier for carbonated beverages, beer, and oxygen-sensitive products. PETG lacks this barrier and is unsuitable for carbonated applications.

5. Application Decision Matrix

The following decision matrix maps common bottle applications to the optimal resin choice based on the performance characteristics discussed above.

6. Cost & Supply Chain Analysis

Material cost is one of three cost components that differ meaningfully between PET and PETG bottle production. Supply chain structure and processing cost also contribute to total economics.

The 200-400 KRW per bottle cost differential is meaningful for commodity beverage products where retail pricing is tightly constrained. For premium K-beauty applications where retail prices range 25,000-80,000 KRW per SKU, the PETG premium is absorbed easily and justified by visual quality and brand positioning.

Korean PETG supply primarily depends on Eastman (US-origin Tritan/Eastar) imports with SK chemicals providing domestic supply. This creates longer lead times than PET, where SK geocentric and Lotte Chemical provide abundant domestic supply with 2-4 week lead times typical.

7. Ever-Power Platform Matching

All Ever-Power ISBM platforms handle both PET and PETG through configurable temperature profiles and drying system adjustment. Specific platforms are optimized for each material based on typical application envelope.

For operators producing mixed PET and PETG portfolios on a single platform, the HGY150-V4-EV full-servo premium platform offers the widest processing window flexibility. The full-servo architecture enables precise temperature profile switching between materials without mechanical adjustment, reducing changeover time to 30-45 minutes versus 2-3 hours on hydraulic platforms.

Mould design considerations also differ between materials. PETG requires slightly more generous vent clearance to accommodate larger thermal expansion during cooling. For operators developing new bottle formats in either material, custom one-step ISBM mould service engineers tooling specifically for the target resin.

8. Recycling & Sustainability

Recyclability increasingly factors into Korean brand decisions as K-EPR compliance and global sustainability commitments tighten. PET and PETG have meaningfully different recycling infrastructure profiles.

PET Recycling Infrastructure

PET carries resin identification code 1 and recycles through mature global infrastructure. Korean collection and bottle-to-bottle recycling systems handle PET at scale, with SK geocentric and domestic recyclers providing commercial rPET supply from 30% to 100% recycled content. K-EPR compliance for beverage and water bottles is well-supported through PET.

For comprehensive understanding of rPET processing considerations in ISBM, see our dedicated guide on recycled PET production for Korean operators in the K-EPR compliance era.

PETG Recycling Challenges

PETG carries resin identification code 7 (other plastics) and lacks dedicated recycling streams in most markets including Korea. When PETG bottles mix with PET recycling streams, the amorphous copolyester contaminates PET recyclate and degrades recycled material properties. Korean brands pursuing closed-loop sustainability commitments typically cannot use PETG at scale without dedicated collection infrastructure.

This recycling gap is one reason Korean premium K-beauty brands increasingly evaluate alternatives. Some brands reserve PETG only for ultra-premium low-volume SKUs while using PET with high rPET content for mainstream SKU portfolios.

9. Korean Market Applications

10. คำถามที่พบบ่อย

11. บทสรุป

PET and PETG are not competing materials. They are complementary resins that serve structurally different application requirements. PET dominates high-volume commodity production, carbonated beverage, mineral water, and standard cosmetic applications where cost efficiency and gas barrier matter most. PETG dominates premium thick-wall cosmetic jars, alcohol-containing fragrance bottles, medical device packaging requiring gamma sterilization, and applications where amorphous clarity or impact resistance is essential.

The correct Korean manufacturing approach is not choosing between the two materials universally, but matching each SKU to the optimal material based on performance requirements, retail positioning, and sustainability considerations. Ever-Power ISBM platforms handle both materials with appropriate temperature profile configuration, and the HGY150-V4-EV full-servo platform specifically enables rapid changeover between materials for mixed-portfolio contract fillers.