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2021

Tips for Using Natural Rubber in EVA Foam Soles

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1. Control the amount of natural rubber used.

The rational use of natural rubber in EVA soles can significantly enhance the overall performance of the soles. However, in actual production, increasing the amount of natural rubber does not necessarily lead to better results. It is understood that the foaming efficiency of EVA foam soles is closely related to the amount of natural rubber used: as the amount of natural rubber increases, the foaming rate steadily declines. Moreover, as the amount of natural rubber rises, the melt viscosity of the blended material—2LLYY0313-SJ—also increases, which in turn makes it more difficult for the foaming material to degas and leads to uneven foaming. Consequently, the shrinkage of the finished EVA foam sole becomes markedly greater.

Generally, in the production of EVA-natural rubber foamed soles, the amount of natural rubber should not exceed 20 parts to ensure uniform foaming of the EVA foamed sole and reduce shrinkage of the finished product.

2. Types of Compounding Agents for EVA-Natural Rubber Foamed Soles

The addition of a small amount of natural rubber to EVA foam soles can significantly improve the elasticity and elongation at break of the foam sole, thereby markedly enhancing its comfort. When preparing foam soles using an EVA-natural rubber blend, rubber product manufacturers who opt for peroxide vulcanization—such as DCP—will achieve better physical and mechanical properties in the blended material. Alternatively, selecting AC as a foaming agent allows for better coordination between the vulcanization rate and the foaming rate, further improving both the foaming efficiency and the uniformity of the foamed rubber sole.

Elastomer-rubber composites offer superior performance at lower costs and are now widely used. The inclusion of a small amount of natural rubber in EVA foam shoe soles can significantly enhance the overall performance of the soles. In foamed sole formulations based primarily on EVA, other elastomers such as cis-butadiene rubber and styrene-butadiene rubber can also be employed. In actual production, rubber product manufacturers not only need to carefully control the amounts of natural rubber and compounding agents in EVA foam sole formulations but also must appropriately adjust the vulcanization and foaming processes for the soles, taking into account the processing characteristics of both rubber and EVA materials. Regarding issues encountered during the production and processing of EVA-natural rubber foamed shoe soles, our editor will be glad to continue discussing them with you at a later time.

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What’s the difference between rubber foaming and EVA foaming?

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What’s the difference between rubber foaming and EVA foaming?

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Tips for Using Natural Rubber in EVA Foam Soles

EVA, or ethylene-vinyl acetate copolymer, is currently a commonly used material in footwear manufacturing companies for producing both shoe soles and uppers. EVA foam soles boast excellent moisture absorption, heat resistance, abrasion resistance, weather resistance, and oil resistance. However, when worn, they tend to slip easily on wet surfaces and become relatively stiff at low temperatures—both of which are inherent defects of the material itself. With the continuous development and advancement of rubber-plastic compounding technology, the appropriate incorporation of natural rubber into EVA soles can significantly mitigate issues such as slipping and low-temperature brittleness, while also enhancing the puncture resistance of rubber soles. 1. Controlling the Amount of Natural Rubber Used Reasonable use of natural rubber in EVA soles can markedly improve their overall performance. However, in actual production, more natural rubber does not necessarily mean better results. It’s been observed that the foaming efficiency of EVA foam soles is closely linked to the amount of natural rubber used: as the proportion of natural rubber increases, the foaming rate steadily declines. Moreover, an increase in natural rubber content leads to a rise in the melt viscosity of the compounded material, which in turn makes it harder for the foaming material to degas uniformly and results in uneven foaming. Consequently, the shrinkage of the finished EVA foam sole becomes significantly greater. Generally speaking, in the production of EVA-natural rubber foam soles, the amount of natural rubber should not exceed 20 parts to ensure uniform foaming and reduce shrinkage in the final product. 2. Types of Compounding Agents for EVA-Natural Rubber Foam Soles The addition of a small amount of natural rubber to EVA foam soles can significantly enhance the elasticity and elongation at break of the foam sole, greatly improving its comfort. When preparing foam soles from EVA-natural rubber blends, if rubber manufacturers choose peroxides such as DCP for vulcanization, the compounded material will exhibit superior physical and mechanical properties. Alternatively, using AC blowing agents can better coordinate the relationship between vulcanization speed and foaming speed, further improving the foaming efficiency and uniformity of the foam rubber sole. Rubber-plastic composites offer improved performance and lower costs, making them widely adopted today. The inclusion of a small amount of natural rubber in EVA foam soles can significantly enhance the overall performance of the sole. In foam sole formulations based primarily on EVA, other elastomers such as cis-butadiene rubber and styrene-butadiene rubber can also be used. In actual production, rubber manufacturers must not only carefully control the amounts of natural rubber and compounding agents in the EVA foam sole formulation but also appropriately adjust the vulcanization and foaming processes according to the processing characteristics of both rubber and EVA materials. Regarding specific challenges encountered during the production and processing of EVA-natural rubber foam soles, we’ll be happy to continue discussing these topics with you in future articles.

What’s the difference between rubber foaming and EVA foaming?

1. The two have different definitions. Rubber foaming: As the name suggests, this foaming method uses pure natural rubber as the primary material, supplemented by other auxiliary materials and a specific foaming agent. After undergoing certain processing techniques, the result is a corresponding product. EVA: This is a material produced by the copolymerization of ethylene (E) and vinyl acetate (VA). Its specific molecular formula is (C2H4)x·(C4H6O2)y. At room temperature, it is solid; however, when heated to high temperatures, it transforms into a liquid with a certain viscosity. 2. They have different advantages. Rubber foaming: It has low costs, simple operation, and requires less labor. EVA foaming: It is environmentally friendly, non-toxic, and does not absorb water. Additionally, it boasts excellent properties such as shock resistance, cushioning, thermal insulation, and corrosion resistance. 3. Their applications differ. Rubber foaming: This product can be used to make relatively soft rubber items such as shoe insoles, anti-slip mats, shoulder pads, and similar products. EVA: Its applications are quite extensive, finding use in medical devices, the electronics industry, architectural decoration, luggage and footwear, and many other fields. Do you now clearly understand the differences between rubber foaming and EVA foaming? Due to space limitations in this article, there are still significant differences in the characteristics of these two materials that we will explore in greater detail at a later time.

Application of PE (polyethylene) wax in rubber

As a rubber processing aid, it can enhance the dispersion of fillers, increase the extrusion molding rate, boost die flow, facilitate demolding, and improve the surface gloss and smoothness of the finished product after demolding. Rubber: It protects rubber from the erosion of static electricity and ozone, and enhances the dispersibility of carbon black in rubber. The recommended addition amount is 2-5 phr. PE wax used in rubber is a chemical material whose polyethylene wax appears as tiny white beads or flakes, formed through the polymerization of rubber processing agents. It features a relatively high melting point, great hardness, high gloss, and a snow-white color. The application of PE wax in rubber involves its widespread use as a low-molecular-weight homopolymer or copolymer in coatings. The term "wax" here refers to a polymer that ultimately floats on the coating surface in the form of microcrystals, exhibiting an appearance similar to paraffin wax yet possessing many additional properties beyond those of paraffin wax. The primary functions of PE wax in rubber-based solvent-borne coatings include: matting, scratch resistance, abrasion resistance, anti-polishing, anti-imprint, anti-sticking, anti-sedimentation, thixotropy, excellent lubricity, good processability, and metallic pigment compatibility. 1. Lubrication and Dispersion In general, when compounding rubber or silicone, fillers such as carbon black, calcium carbonate, talc powder, etc., are added. For applications requiring high transparency, white carbon black or similar materials are often used. Adding polyethylene wax can provide certain lubricating and dispersing effects. 2. Anti-Sticking and Demolding Most rubbers tend to be sticky and easily adhere to molds! Polyethylene wax can serve as an external lubricant to reduce this adhesion. 3. Antiozonant—A physical antioxidant for rubber products, migrating into the rubber to form a protective film that provides antiozonant protection. 4. Proper addition can lower the Mooney viscosity of the compounded rubber, acting as a plasticizer; however, excessive amounts may negatively affect the mechanical properties of the compound. 5. It improves the fluidity of the compound during extrusion, calendering, and vulcanization molding processes. 6. Enhances the uniformity of the compounded rubber: Its self-lubricating properties both internally and externally help disperse inorganic additives, improving the overall mixing uniformity of the compound. However, most manufacturers do not choose polyethylene wax for the following reasons: 1. Relatively High Melting Point Some rubber compounds are mixed at temperatures ranging from 70°C to 120°C, while polyethylene wax has a high melting point and is difficult to melt, thus failing to perform effectively. (Generally, polyethylene wax with a softening point around 70°C to 100°C is preferred.) 2. Prone to Exudation Rubber is a high-molecular-material, whereas polyethylene wax molecules are relatively small. If too much is added, it tends to exude; if too little is added, the effect will be insufficient. (An addition level of 2–4 phr is ideal.) 3. Narrow Application Range This is mainly limited by its melting point. 4. Impacts Product Transparency 1. Antiozonant Aging Resistance: Polyethylene wax exudes onto the rubber surface, forming a protective film. 2. Plasticizing and Improving Processing Performance: Polyethylene wax has a much lower molecular weight than rubber; once added, its molecular chains easily intercalate between rubber molecular chains, making the rubber chains more mobile. 3. Lubrication (internal + external lubrication), improving extrusion performance and reducing shrinkage: Same as item 2. 4. Making the compound easier to mix uniformly: Polyethylene wax enters between rubber molecular chains, increasing the distance between them and carrying low-molecular-weight compounding agents into the rubber molecular chains, thereby facilitating better dispersion of other additives. Protective waxes are classified according to their intended use. PE wax, paraffin wax, and microcrystalline wax can all be used as protective waxes. PE wax, or polyethylene wax (PE-WAX), is a very low-molecular-weight polyethylene. Polyethylene wax generally falls into four categories: oligomeric wax, pyrolysis wax, polymerized wax, and blended wax. Among these, oligomeric wax is commonly produced domestically, while pyrolysis wax, polymerized wax, and blended wax are mostly manufactured overseas. Theoretically, polymerized wax has superior performance compared to pyrolysis wax; specific usage depends on the compatibility with the product. Generally, it is primarily used to improve the flowability of polyolefin plastics, enhance the dispersion of fillers and additives, and also serves as an internal lubricant for rubber and plastic materials.

Xinhan (Taiwan) International Trading Co., Ltd. was established in 2004 and is one of Taiwan’s leading manufacturers of high-quality rubber and plastic raw materials.

Our company is headquartered in Dongguan City, Guangdong Province, and we also have a subsidiary named “Xinhan Rubber Technology (Shenzhen) Co., Ltd.” located in Shenzhen. Our primary business activities include international trade in rubber raw materials as well as the import and export of rubber raw materials by our company. In addition, we have established a factory in Wanjiang District, Dongguan City, Guangdong Province, specializing in the production of various rubber raw materials and pre-dispersed masterbatch granules. The factory covers an area of 5,000 square meters and is equipped with several production lines for manufacturing pre-dispersed rubber and plastic masterbatch granules, along with a variety of testing equipment. Monthly output can reach up to 500 tons. We also have distribution partners and agents in Sichuan, Wenzhou, Fujian, Jiangsu, Hebei, Xiamen, and other regions, serving customers across the entire country. To better meet customer needs, in 2014 we set up offices in Vietnam and Cambodia, providing local and existing customers with professional technical expertise and product services.

Processing aids, tackifying resins, accelerators, anti-aging agents, yellowing-resistant agents, antioxidants, active agents, fillers, zinc oxide powder, wear-resistant agents, EVA processing aids, EVA additives, and other chemical products.

Currently, we primarily sell rubber and plastic products—including processing aids, tackifying resins, accelerators, antioxidants, yellowing-resistant agents, anti-oxidants, active agents, fillers, zinc oxide powder, wear-resistant agents, EVA processing aids, EVA additives, and other chemical products. Since its establishment in 2004, Xinhan Company has adhered to the sole corporate mission of “quality as the foundation, innovation as the goal, and integrity as the brand,” guided by the business philosophy of “innovative technology, supreme quality.” We continuously upgrade our production technologies and enhance and refine our sales services. Our company collaborates with well-known raw material manufacturers both domestically and internationally, and is equipped with a dedicated rubber materials production line and a professional technical team. We are committed to providing customers with higher-quality, innovative, and environmentally friendly products, reducing customer costs, strengthening quality assurance, and helping customers maintain their global competitiveness. We sincerely hope to develop and cooperate together with both new and existing customers in the rubber and plastic industry, creating win-win outcomes for all!

Warmly celebrate the official establishment of Xinhan Rubber Technology’s Vietnam office.

Warmly celebrate the establishment of Xinhan Rubber Technology’s Vietnam office: TEL: 0084-854100104 FAX: 0084-854100104 ADD: Sky Garden 1, Floor 8, Room 1B38, Nguyen Van Linh Street, District 7, Ho Chi Minh City Contact: Mr. Huang, Deputy General Manager +84 1267547819

Unified compilation

53,633,481

Phone

+886 4 22435557

vivi@twxinhan.com

Address

No. 955, Section 4, Wenxin Road, Taichung City, 10th Floor, Unit 4

Website

http://www.twxinhan.com

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