블로그 약 Sponge Rubber Gains Traction in Manufacturing and Beyond

Imagine a world without cushioned sneakers, soundproofed cars, or comfortable mattresses. Our daily lives would be significantly less comfortable without sponge rubber, this seemingly ordinary yet ubiquitous material that quietly enhances our quality of life and safety. But what exactly is this remarkable material, and what makes it so special?

This article delves into the fascinating world of sponge rubber, exploring its manufacturing history, production processes, physical properties, and diverse applications to reveal why it has become an indispensable material in modern industry.

Sponge rubber, also known as cellular rubber, foam rubber, or expanded rubber, is a rubber material characterized by its internal structure filled with air pores. This unique structure gives sponge rubber its lightweight, highly elastic, cushioning, insulating, and soundproofing properties. Commercial sponge rubber typically uses synthetic rubber, natural latex, or polyurethane as its primary raw materials.

• Natural latex sponge rubber: Based on natural rubber, widely used in mattress manufacturing due to its exceptional durability.
• Polyurethane sponge rubber: A thermosetting polymer composed of methyl diisocyanate and chemical additives like polyethylene, known for its excellent wear resistance and chemical corrosion resistance.

The invention of sponge rubber wasn't accidental but rather an inevitable result of technological progress. In 1929, two research chemists from Dunlop Rubber Company—E. A. Murphy and Eric Owen—first successfully produced sponge rubber by whipping latex. This groundbreaking discovery laid the foundation for industrial-scale sponge rubber production.

In 1937, isocyanate-based materials were first applied in sponge rubber manufacturing. After World War II, styrene-butadiene rubber gradually replaced much of the natural rubber as the primary raw material for sponge rubber production. Since the 1940s, sponge rubber began seeing widespread commercial applications.

In the 1950s, Charles C. Price invented polyether polyurethane rubber and patented it. Today, polyurethane foam accounts for over 90% of the polyurethane market by weight. Polyurethane finds extensive applications in construction, transportation, furniture, noise reduction, vibration damping, and carpeting. The construction industry consumes 27% of polyurethane, while transportation uses 21%. In terms of application forms, flexible foam constitutes 44% of total production, while rigid foam accounts for 28% of the U.S. market.

The production of sponge rubber involves multiple critical stages, each significantly impacting the final product's quality and performance.

1. Material Preparation: Liquid and solid raw materials typically arrive via rail or truck. Liquid materials are stored in heated tanks after unloading. For sheet production, two or more polymer streams are usually employed.
2. Mixing: Open pouring, also called continuous dispensing, primarily forms rigid, low-density foam. Specific amounts of chemicals are mixed in a mixing head resembling an industrial blender. The foam is then poured onto a conveyor belt for curing and cutting.
3. Curing and Cutting: After curing on the conveyor belt, the foam is forced through a horizontal band saw that cuts it to specified dimensions. For example, the construction industry commonly uses 4ft×12ft×2in sheets.
4. Further Processing: After cutting and curing, sheets can be sold directly or undergo lamination to become rigid foam panels used in metal roof insulation, oven insulation, and other durable products.

• Polymer Mixing: Advanced mixing technologies like high-shear mixers and twin-screw extruders ensure uniform polymer mixing, optimizing product quality and consistency while reducing waste and improving efficiency.
• Post-Curing Heat Treatment: Some foam products undergo secondary heat treatment (post-curing) to enhance durability and dimensional stability, particularly important for automotive and aerospace applications.
• Surface Coatings: Various surface coatings like flame retardants or UV-resistant layers are applied to improve performance, especially for outdoor applications exposed to sunlight or harsh conditions.
• Recycling and Sustainability: Many manufacturers adopt closed-loop systems that recycle waste foam back into production, minimizing waste and creating more environmentally friendly processes.
• Quality Control: The manufacturing process includes multiple quality checks like visual inspections, density tests, and stress-strain tests to ensure products meet performance, safety, and durability standards.

Sponge rubber's widespread applications stem from its unique physical properties:

• Lightweight: The air-filled pores make sponge rubber significantly less dense than solid rubber, greatly reducing product weight.
• Buoyancy: Its low density and closed-cell structure provide excellent buoyancy for life-saving equipment and water toys.
• Cushioning: The elastic structure effectively absorbs and disperses impact forces, providing superior protection in sneakers, protective gear, and packaging.
• Thermal Insulation: Air pores effectively block heat transfer, making it ideal for building insulation, pipe insulation, and thermal clothing.
• Sound Insulation: The porous structure absorbs and dampens sound waves, reducing noise transmission in soundproof walls, enclosures, and automotive interiors.
• Vibration Damping: Effectively absorbs and reduces vibrations, lowering operational noise and extending product lifespan in machinery, automotive chassis, and electronics.
• Cost-Effectiveness: Compared to other high-performance materials, sponge rubber offers an economical yet practical solution.

Cross-linking technology also plays a crucial role in EVA-based foam formation, including LLDPE, LDPE, HDPE, PP, and TPE. Cross-linking—the chemical bonding between polymer chains—is essential in sponge rubber production to stabilize bubble expansion, enhance resistance to thermal collapse, and improve physical properties.

Thanks to its exceptional properties and versatility, sponge rubber finds applications across numerous industries:

• Household Items: Mattresses, pillows, sofa cushions, and carpet underlays for comfortable sleep and relaxation.
• Automotive Industry: Seats, interior trim, soundproofing materials, and vibration dampers to enhance comfort and safety.
• Sports and Leisure: Sneakers, protective gear, sports mats, and swimming equipment for impact protection and performance.
• Packaging and Shipping: Cushioning pads, shockproof packaging, and insulated containers to protect products during transit.
• Construction: Soundproofing materials, insulation, and sealing strips to improve building comfort and energy efficiency.
• Healthcare: Medical mattresses, surgical pads, and rehabilitation equipment for supportive comfort and protection.
• Electronics: Vibration dampers, sealing rings, and insulating materials to protect components and improve reliability.

The diverse chemical nature of polyurethane makes sponge rubber recycling challenging. Currently, the most common method involves reusing sheet foam as carpet backing—shredding waste material and bonding small flakes into sheets. Other methods include breaking foam into particles and dispersing them into polyol mixtures to mold parts identical to originals. Sponge rubber recycling continues to evolve, with new, simpler methods likely emerging in the future.

With its exceptional performance and wide-ranging applications, sponge rubber plays an indispensable role in modern industry. As technology advances and environmental awareness grows, manufacturing processes will continue refining while applications expand. There's every reason to believe sponge rubber will keep enhancing our lives with greater comfort, safety, and convenience in the years ahead.