33/400 Aluminum PE Lined Caps
Neck Specification 33-400: Standard continuous thread (diameter 33 mm, thread pitch 400)
33/400 Aluminum PE Lined Caps are widely used standard packaging sealing solutions in the beverage, condiment, and pharmaceutical industries.
The 33/400 aluminum-plastic PE lined cap is one of our factory’s mature and core products. It utilizes aluminum to provide structural strength and a base for plastic sealing, while the plastic shell offers ease of use and brand display. The core PE liner fulfills the most critical function of airtight and liquid-tight sealing. Through precise manufacturing processes, strict quality control, and continuous material R&D, we are committed to providing customers with high-quality cap solutions that are reliably sealed, easy to open, visually appealing, compliant with safety standards, and cost-competitive—meeting the sealing needs of packaging across beverages, food, condiments, pharmaceuticals, and more.
Type: Aluminum-Plastic Composite Cap. This is a composite-structure cap that combines the strength of metal (aluminum), the sealing reliability of plastic, and the ease of opening and aesthetic qualities of plastic (typically PP or HDPE).
Core Specification: 33/400. This clearly specifies the neck finish the cap is compatible with:
- 33: Indicates the outer diameter of the bottle neck is 33 mm. This is the most critical dimension of the bottle mouth, determining the basic inner diameter of the cap.
- 400: Refers to a standard continuous thread with a pitch of 4.00 mm. This determines the matching design of the inner thread of the cap, ensuring smooth screwing and reliable sealing.
- Core Functional Component: PE Liner. This is the key material layer for sealing the bottle mouth, usually made of food-grade Low-Density Polyethylene (LDPE) or Linear Low-Density Polyethylene (LLDPE), forming an airtight and liquid-tight seal with the bottle top through heat sealing or pressure.
33/400 Aluminum PE Lined Caps – Structure and Materials
| Component Name | Material | Function | Manufacturing Process |
| Aluminium Shell / Outer Cap | Food-grade aluminum alloy coil (e.g., 8011, 8079), typically 0.20–0.25mm thick | Structural Body: Provides overall strength and rigidity | Precision stamping + deep drawing of aluminum coil |
| Sealing Base: Inner top serves as the carrier for the PE liner | High-precision mold required to ensure dimensional stability and burr-free edges | ||
| Plastic Sealing Base: Skirt acts as base for plastic over-molding | |||
| Tamper-Evident Ring Carrier: Located at the lower edge of the skirt | |||
| Plastic Overcap / Shell | Mainly food-grade PP, with some applications using HDPE | User Interface: Provides screw-on grip and aesthetic design (e.g., texture, shape) | Secondary injection molding over the aluminum cap |
| Protective Appearance: Covers aluminum shell exterior, allows brand printing | Molten PP over-molded onto the skirt | ||
| Opening Convenience: Softer feel than aluminum, more comfortable to use | Precise temperature and mold matching ensure tight fit | ||
| PE Liner / Sealing Wad | Food-grade LDPE or LLDPE (sometimes special formulation) | Core Sealing: Fits against bottle mouth to prevent leakage, gas escape, and contamination | Extrusion coating method: Mainstream process where molten PE is extruded onto inner top of aluminum cap and cooled to form; thickness approx. 0.2–0.6mm |
| Cushion Protection: Prevents bottle mouth from damage | Punched wad method: Used in some plastic caps; higher cost, lower efficiency | ||
| Tamper Evident Band (TEB) | Integrated with aluminum cap, over-molded with plastic | Tamper Indicator: Bridge breaks upon first opening, leaving the band on the neck as visual proof | Fracture bridge structure formed during aluminum cap stamping |
| Plastic over-molding avoids fracture line to ensure functionality |
HC Aluminum Common Neck Size Aluminum-Plastic Bottle Caps
| Item | 20-410 Aluminum Cap | 24-410 Aluminum Cap | 28-410 Aluminum Cap | 38-400 Aluminum Cap |
| Neck Specification | Outer diameter 20mm, pitch 410 (1.5 threads/mm) | Outer diameter 24mm, pitch 410 | Outer diameter 28mm, pitch 410 | Outer diameter 38mm, pitch 400 (single-turn thread) |
| Applicable Containers | Small-capacity bottles: essential oils, dropper bottles, reagent bottles, etc. | Cosmetics: lotion, essence, mist spray, etc. | Daily chemicals: shampoo, body wash, detergent, etc. | Food/Oil: soy sauce, edible oil, beverage bottles, etc. |
| Aluminum Cap Size Range (Height x Diameter) | Approx. 15–18mm height, 20mm diameter | Approx. 20–22mm height, 24mm diameter | Approx. 22–25mm height, 28mm diameter | Approx. 25–30mm height, 38mm diameter |
| Skirt Structure | Shorter skirt, simpler tamper-evident design | Medium skirt, with standard tamper-evident bridges | Reinforced skirt, suitable for enhanced sealing on daily chemical bottles | Widened skirt, suitable for thick bottle necks, enhanced structure |
| PE Liner Size | Small-diameter discs, commonly using extrusion coating | Standard diameter liner, suitable for lotion-type sealing needs | Often paired with leak-proof reinforcement ring (anti-back pressure) | Thickened PE liner, suitable for high-viscosity/oily contents |
| Plastic Cap Coverage | Generally covers skirt and top | Fully covers skirt, top can be printed or embossed | Often features textured anti-slip surface | Enlarged top surface, suitable for large-area brand printing |
| Tamper-Evident Ring Design | Simple bridge-type tamper-evident design | Standard 3–5 bridge-point structure | Reinforced fracture structure, suitable for thick plastic bottles | Reinforced + slotted fracture structure, easy to identify opening |
PE Liner Matching: Small diameters (e.g., 20mm) mainly use lightweight structures, while large diameters (e.g., 38mm) require reinforced liners to maintain pressure sealing—particularly important for carbonated beverages or high-oil content products (such as olive oil).
33/400 Aluminum PE Lined Caps – Quality Control
Dimensional Accuracy:
- Inner Diameter & Thread: Must strictly conform to the 33mm diameter and 4.00mm thread pitch standard. Tolerances are extremely tight (typically within ±0.10mm). This is fundamental for matching the standard 33/400 bottle neck and ensuring smooth screwing and sealing. Requires high-precision molds and stable stamping processes.
- Overall Height: Affects grabbing and capping on the filling line.
- Tamper Ring Position and Size: Ensures correct fit with bottle neck ring and smooth breakaway or release upon first opening.
Sealing Performance:
- PE Liner Material and Thickness: Select the most suitable PE grade and thickness based on product characteristics (carbonated, non-carbonated, hot-fill, cold-fill, acidity/alkalinity, oiliness). LLDPE is the mainstream choice.
- Liner Uniformity: The extrusion coating process must ensure uniform liner thickness, no bubbles, no impurities, and strong adhesion to the aluminum substrate.
- Heat Seal Performance (if applicable): For heat-seal caps, it is necessary to precisely control sealing temperature, pressure, and time to ensure the liner forms an immediate and firm seal with the bottle mouth after capping.
- Sealing Tests: Strict sealing performance tests must be conducted before shipment, such as vacuum decay test, pressure test (simulating carbonation pressure), and torque retention test.
Opening Torque & Application Torque:
- Opening Torque: Must be controlled within a user-friendly range (typically target value between 10–35 Ncm), neither too tight nor too loose. It depends on thread design, plastic cap texture, liner friction coefficient, etc.
- Application Torque: The torque applied by the capping machine on the filling line must be sufficient to ensure sealing, but not excessive to avoid cap deformation or liner over-compression failure. Recommended torque values should be provided for different applications.
- Torque Consistency: Torque values must remain highly consistent within the same batch and across different batches.
Tamper Evidence:
- Bridge Strength: Must ensure no accidental breakage during normal transportation but allows smooth separation upon first opening.
- Release/Break Performance: The tamper-evident band should clearly and completely remain on the bottle neck, providing a visible indication of opening.
- Plastic Overmolding: The plastic cap must firmly cover the upper part of the tamper-evident band to prevent easy prying or tampering.
Appearance & Printing:
- Plastic Cap Surface: Smooth, defect-free, no flash, with uniform color.
- Printing: Graphics and text must be clear, accurately registered, richly colored, with strong adhesion (passing abrasion and alcohol wipe tests), and comply with food safety standards (ink migration test).
33/400 Aluminum PE Lined Caps Applications
The 33/400 aluminum-plastic PE lined cap is widely used due to its excellent sealing performance, tamper resistance, aesthetics, and cost-effectiveness in:
Carbonated Soft Drinks (CSD): Requires high gas barrier and pressure resistance (liner formula is usually specially designed). Bottled Water: Requires good water-tightness and hygiene. Juice, Tea Beverages, Functional Drinks: Requires good sealing; some must withstand hot filling (caps and liners must be heat-resistant). Edible Oil, Condiments (e.g., soy sauce, vinegar): Requires excellent oil resistance and chemical resistance. Pharmaceuticals, Health Supplements: Requires high sealing standards and material safety.
Why Choose HC Aluminum?
- Professional Mold Development: Experienced team in mold design and manufacturing ensures precise implementation of 33/400 specifications.
- Precision Manufacturing Capability: Equipped with high-precision stamping, injection molding, coating production lines, and automated assembly equipment.
- Strict Quality Control System: Full-process monitoring from raw material entry to finished product delivery (IQC, IPQC, FQC), with advanced testing equipment (projector, torque tester, seal tester, migration testing instruments, etc.).
- Customized Formulation Capability: Able to develop customized PE liner formulas for specific products (e.g., high-acidity juices, high-carbonation beverages).
- Custom Printing Services: Offers multi-color printing, hot stamping, UV and other surface treatments.
- Technical Support: Provides cap application recommendations, filling line compatibility support, and troubleshooting services.
- Stable Supply: Capable of large-scale, stable, and timely delivery.
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