Let’s take a look at how rubber soles are made.

Summary Description:

The manufacturing process for rubber shoe soles: raw material weighing—massive‑force mixing—open mill refining—sheet extrusion—storage (minimum 24 hours)—bulk compound preparation—formulation weighing—open mill refining—sheet extrusion—cutting—vulcanization—(for foam soles) secondary vulcanization—rough grinding—cutting—edge trimming—finishing—shipping.

1. Rubber Manufacturing Process
Raw material weighing—mixing in a high‑power mixer—open mill processing—sheet extrusion on the open mill—storage (minimum 24 hours)—batching—formulation weighing—open mill processing—sheet extrusion on the open mill—cutting—vulcanization—(for foam soles) secondary vulcanization—rough trimming—cutting—edge finishing—finishing—shipping.

2. Basic recipe ingredients

• Rubber (NR and SR). Rubber (natural rubber, synthetic rubber);
• promoting agent. Promoter;
• Curing agent. A vulcanizing agent, also known as a bridging agent;
• Activator. Activating agent;
• Others: Additives (fillers, processing aids, preservatives, colorants, etc.).

 

3. Natural rubber

• Ingredients: 80% liquid glue, 20% solid glue;
• Characteristics: Very high viscosity; easier to process than synthetic rubber.
• It exhibits excellent tear strength, tensile strength, heat resistance, and high elasticity, with a favorable structure; however, its physical properties are not sufficiently stable.
• Types: Raw Rubber No. 3, Standard Rubber;
• Origin: Native to subtropical and tropical rainforest regions (e.g., Malaysia, Thailand, Brazil).

 

4. Accelerator

• Type: D, DM, TS, MBT, M;
• Functions: shortens vulcanization time, reduces the amount of vulcanizing agent required, and acts as a retarder to prevent premature vulcanization and scorching.

5. Surfactant

• It activates the accelerator and is also referred to as a vulcanization aid.
• Common examples include ZnO, oxidizing agents, and fatty acids.

 

6. Vulcanizing Agent

• Function: Enables crosslinking of rubber molecules.
• Common ones include: DCP, sulfur, and the liquid form of 231.
• DCP is generally used to produce transparent and light-colored adhesive bases.
• Sulfur is commonly used to produce dark-colored rubber soles.

 

7. Fillers

• Types: Reinforcing fillers mainly include white carbon black, carbon black, and magnesium carbonate; non-reinforcing fillers mainly include calcium carbonate and rubber powder.
• Function: Reduces rubber consumption, lowers costs, and enhances material properties, particularly wear resistance, hardness, tensile strength, and tear resistance.

 

8. Processing aids

• Function: Enhance the efficiency of the mixing process;
• Main ingredients: softening agent, adhesion promoter.

 

9. Additives

• Pigments are classified into two types: organic pigments and inorganic pigments.
• Retarders: substances that slow down the vulcanization rate, primarily including PVI and BC;
• Foaming agents: Used in rubber foam bases; common ones include ADC, DPT, and DD.

 

10. Classification of Rubber Soles : Rubber sole, foamed rubber sole, micro-foamed sole.