38mm Aluminum ROPP Cap

38mm ROPP (Roll On Pilfer Proof) aluminum cap is a widely used metal sealing solution for various liquid packaging applications. With its excellent sealing performance, tamper-evident functionality, and recyclability, it has become the preferred packaging component in industries such as food and beverage, pharmaceuticals and healthcare, and cosmetics.

The 38mm aluminum ROPP (Roll-On Pilfer Proof) cap is a specially designed sealing system used for securely capping bottles, especially in industries that require tamper resistance and durability. Its name derives from its manufacturing process ("roll-on") and anti-tampering function ("pilfer-proof"). Made from lightweight aluminum, this cap is widely used for packaging beverages, pharmaceuticals, and specialty liquids due to its reliability and safety.

38mm ROPP Aluminum Cap Specifications and Dimensions

Dimension Parameter	Value	Tolerance Range	Measurement Position
Outer Diameter	38mm	±0.2mm	Maximum diameter at the top
Height	16.5-18mm	±0.15mm	Vertical distance from top to bottom
Thread Diameter	37.7mm	±0.15mm	Root diameter of the thread
Thread Effective Length	Approximately 12mm	±0.5mm	Effective engagement portion of the thread
Tamper-Evident Band Width	Approximately 3mm	±0.3mm	Widest part of the tamper-evident band
Cap Blank Diameter	66mm	±0.5mm	Size of the raw material blank

The dimensional design of the 38mm ROPP aluminum cap fully considers compatibility and usability with various containers, including bottle neck matching design, ergonomic design, manufacturing process adaptability, and tamper-evident functionality.

Material and Structure of 38mm Aluminum ROPP Cap

Material of 38mm Aluminum ROPP Cap

Main Material

3004 Aluminum Alloy: An Al-Mn-Mg series alloy with good formability, corrosion resistance, and strength.
5052 Aluminum Alloy: An Al-Mg series alloy with excellent corrosion resistance and cold working properties.

Liner Materials

PE (Polyethylene): Offers good flexibility and chemical stability.
EVA (Ethylene-Vinyl Acetate Copolymer): Provides better elasticity and sealing performance.
Silicone: Excellent heat resistance, cold resistance, and chemical stability.

Material Selection Recommendations for 38mm ROPP Aluminum Caps

According to different application scenarios and product characteristics, HC Aluminum recommends suitable material combinations for customers:

General Beverage Packaging
3004 aluminum alloy body combined with PE liner offers high cost performance and is suitable for most non-carbonated beverages and food packaging.
Carbonated Beverage Packaging
5052 aluminum alloy body combined with EVA liner provides better pressure resistance and sealing performance, capable of withstanding the internal pressure of carbonated drinks.
High-Temperature Sterilized Products
3004 aluminum alloy body combined with silicone liner can withstand high-temperature sterilization without deformation or performance degradation.

Structure of 38mm Aluminum ROPP Cap

Component Name	Material Description	Functional Description
Cap Body	Aluminum (generally corrosion-resistant aluminum alloy suitable for roll-forming)	Surface includes pre-formed knurling for hand grip and easy twist-off, providing strong bottleneck protection.
Liner	Optional materials: PE (Polyethylene), EPE (Expanded Polyethylene), TPE, PVDC, etc.	Provides sealing function to prevent liquid leakage; liner material is selected based on liquid type (e.g., carbonated beverages, juice, pharmaceuticals) for compatibility.
Tamper Evidence Band	Aluminum perforated ring, connected to the lower end of the cap body	Breaks off as the cap is opened, leaving visible signs of opening, preventing unauthorized access, ensuring package integrity and consumer safety.
Knurled Skirt	Embossed or pre-patterned texture on the outer aluminum shell	Provides friction for twisting open/close, enhancing user experience during opening.
Threading	Threads formed by roll-forming on the inner wall of the aluminum shell	Matches the bottle neck threading to ensure tight fit and repeated twist sealing.

Skirt and tamper band: Begins as a smooth skirt with a frangible lower band (pilfer band). Upon first opening, this band breaks—providing visible tamper evidence .
Liner assembly: Usually includes an inner liner made of elastomeric or EPE/PP materials, ensuring leak-proof sealing and content compatibility. Can be L-type (for carbonated drinks), epoxylite, or elastomer-lined depending on application .

38mm Aluminum ROPP Cap Compatibility

Standard diameter of 38mm, suitable for glass bottles, plastic bottles, and aluminum bottles
Can be adapted to containers with diameters ranging from 20–70mm (customized equipment required)

38mm Aluminum ROPP Cap Liner System

Includes a liner (usually PVC, foam, or cork) to enhance sealing performance.
Liner selection depends on the application: heat resistance (e.g., hot-filled beverages), chemical compatibility (e.g., pharmaceuticals), or gas barrier properties (e.g., carbonated beverages).

Liner materials are selected based on the contents. Common liners include:

Liner Material	Application Field	Characteristics
EPE (Expanded Polyethylene)	Beverages, water	Good elasticity, reliable sealing
TPE / PVC liner	Spirits, condiments	Suitable for high alcohol content liquids
No liner / Aluminum foil seal	Disposable packaging or induction sealing	Low cost, suitable for mass production

Difference Between 38mm and 42mm Aluminum ROPP Caps

Comparison Dimension	38mm ROPP Cap	42mm ROPP Cap
Size and Structure	Diameter: 38mm	Larger diameter (42mm), requires wider bottleneck
Size and Structure	Height: 17.0–17.7mm	Height may increase (approx. 19–20mm) to maintain sealing strength
Application Scenario	Mainly used for juice, beer, functional drinks (below 500ml)	Suitable for large-volume containers (e.g., beverages over 1L, sauce bottles), requires higher pressure resistance
Production Process Adjustments	Rolling machine mold adapted to 38mm threading	Requires customized larger rolling molds
Production Process Adjustments	Smaller printing area	Larger printing area, may require adjustments in printing equipment precision
Material and Cost	Approx. 2g aluminum per cap, lower cost	Increased aluminum usage (approx. 2.5–3g), cost rises by 10–15%
Sealing Performance	Fits standard PET/glass bottles (GPI-1650 neck finish)	Requires thicker liner or enhanced coating to accommodate internal pressure of larger bottles

Gold 38mm Aluminum ROPP Bottle Cap

Application Scenarios of 38mm ROPP Aluminum Cap

Which industries commonly use the 38mm Aluminum ROPP Cap?

Widely used across various industries, including:

Spirits, wine, beer, cider, and soft drinks.
Edible oils, pharmaceuticals, cosmetics, agrochemicals, and lubricants.
Contents: Juice, soft drinks, coffee, alcoholic/non-alcoholic beverages.
Containers: Sealed glass bottles and aluminum containers.
Customization needs: Printable logo, customizable color options such as white.

38mm Aluminum ROPP Cap Packaging for Glass Bottles

Item	Description
Bottle Neck Outer Diameter	Typically 38mm (±0.2mm), requires precise measurement
Thread Type	Such as GPI, MCA, BVP, etc., with different pitch standards
Bottle Neck Height	Affects the skirt height and sealing position of the cap
Bottle Neck Shape	Presence of tamper-evident ring lock or chamfer, directly impacts aluminum cap design

How to Choose the Right Size for 38mm Aluminum ROPP Cap?

ROPP caps refer not only to bottle neck diameter, but also include height, thread pitch, and other complete parameters:

Cap Specification	Typical Application	Height (mm)	Features
38×18 mm Aluminum ROPP Cap	Juice, alcoholic beverages	18	Commonly paired with glass bottles, moderate height
38×15 mm Aluminum ROPP Cap	Pharmaceuticals, food	15	Shorter, lightweight design
38×21 mm Aluminum ROPP Cap	High-pressure contents	21	Deeper skirt, stronger sealing performance

Aluminum caps typically require a 3–5 mm allowance for the skirt fold, so the cap height should be adjusted according to the bottle neck height.

Reference Applications of 38mm Aluminum ROPP Cap

Scenario	Glass Bottle Size	Recommended Cap
Beverage/Juice	38mm MCA bottle neck	38×18 mm aluminum cap, EPE liner
Spirits/Condiments	38mm standard thread	38×21 mm, with tamper-evident ring, PVC liner
Pharmaceuticals/Tinctures	38mm short neck	38×15 mm, TPE liner or aluminum foil liner

Silver 38mm Aluminum ROPP Bottle Cap

Advantages of 38mm ROPP Aluminum Cap

Tamper-evidence: Clearly indicates unauthorized access.
Enhanced safety: ROPP design prevents tampering and provides clear evidence of unauthorized opening.
Durability: Aluminum structure ensures the cap can withstand handling, transport, and environmental factors without performance degradation.
Resealability: After opening, the cap can be re-tightened to maintain freshness and prevent spillage.
Barrier sealing: Provides moisture/oxygen protection and leak resistance when properly lined.
Compatibility: Suitable for glass or PET bottles that can withstand thread-forming pressure.
Aesthetic appeal: Sleek metallic surface is attractive on retail shelves and enhances brand presentation.
Product preservation: Excellent sealing helps maintain product freshness and prevent contamination.
Customization: Available in multiple colors with options for embossing, debossing, or printed logos/text.
Recyclability: Aluminum is 100% recyclable, supporting sustainability goals.

Production and Quality of 38mm ROPP Aluminum Cap

Manufacturing Process of 38mm Aluminum ROPP Cap

Process Step	Description
Aluminum Material Selection	Uses 3-series aluminum alloy for its good ductility and corrosion resistance, suitable for stamping forming
Coating Treatment	Inner layer: Epoxy resin (anti-corrosion)
	Outer layer: Polyester resin (abrasion resistance)
	Pre-coated slip layer (e.g., PP) to optimize capping performance
Liner Preparation	Specialized equipment melts non-PVC materials (e.g., TPE/PE), forms a bead, and compresses it into the cap to form a liner
Sealing Adaptability	Liner must fit tightly, withstand high-temperature sterilization (e.g., pasteurization) or cold filling environments, ensuring sealing performance
Surface Printing	Custom branding with silk screen printing, hot stamping, UV printing, etc., for logo, anti-counterfeit mark, and graphics
Curing Process	Post-printing curing by hot air/UV to enhance scratch and weather resistance of printed graphics
Thread Forming	Cap is placed on the bottle neck, and thread structure is rolled into the cap body using rolling equipment
Tamper-Evident Ring Forming	Simultaneously forms the tamper-evident band which breaks upon first opening to provide evidence of tampering
Quality Inspection	Inspects printing quality, liner integrity, and visual defects, and verifies dimensional tolerance

How to Ensure the Quality of 38mm Aluminum ROPP Cap?

Six Key Elements to Ensure the Quality of ROPP Caps

Stage	Core Measures
Raw Material	Select high-quality aluminum, control thickness and surface finish
Forming Process	Use high-precision molds and automated equipment to avoid deformation and errors
Surface Treatment	Ensure uniform coating with strong adhesion
Dimensional Accuracy	Strict tolerance control to match sealing equipment requirements
Sealing Test	Ensure tight seal with the bottle and reliable tamper-evidence
Packaging & Shipment	Scratch-resistant and anti-oxidation packaging, with inspection report attached

Selection Process of 38mm Aluminum Cap

Confirm bottle neck diameter, thread type, and height
Choose matching aluminum cap height
Select liner material based on bottle contents
Opt for tamper-evident structure and knurling process
Check compatibility with capping equipment

The 38mm aluminum ROPP cap combines functionality, security, and environmental responsibility. Its tamper-proof design, cross-industry adaptability, and recyclable material make it the preferred choice for brands prioritizing product safety and sustainability.

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