E06.Shoe Manufacturing Process: Midsole Process

Shoe Manufacturing Process: Midsole Process

In the shoe manufacturing process, the midsole plays a crucial role and is one of the key factors determining the quality and comfort of the shoes when worn by customers. Let’s explore the production process of the midsole process, one of the stages in the shoe manufacturing process. Please take a look at the diagram below first and visualize the process.

shoe manufacturing process

1.1. The Significance of Midsoles

The durability and comfort of shoes rely on the midsole. Midsoles protect the feet and absorb external impacts, providing comfortable wear. The quality of midsoles can become a criterion for customers when choosing a product. This is because a company’s midsoles with good cushioning can secure loyal customers based on whether they are suitable for individuals.

1.2. Purpose of the Article

The purpose of this article is to provide a brief overview of various types of insoles and their production processes. By understanding how insoles are made and their characteristics, especially for those who are not familiar with shoes, readers can get a big picture of the process.

Midsoles can be categorized into different types based on materials and production methods. They are divided into EVA (Ethylene Vinyl Acetate) series, including Phylon and IP, and PU (Polyurethane) series. Here, we will explore the characteristics of three main types of midsoles.

2.1. EVA Series (Phylon, IP)

The advantages of EVA series midsoles include lightweight and comfort. In the case of non-brand shoes, you may feel the weight when wearing them. However, EVA series shoes are lightweight and provide a comfortable cushioning during walking. Therefore, they are popular among many people.

Characteristics of EVA (Ethylene Vinyl Acetate)

• Lightweight: EVA is a lightweight material, making the shoes feel incredibly light.
• Elasticity and Flexibility: EVA offers excellent elasticity and flexibility, enhancing comfort during walking or running.
• Durability: EVA is highly durable, maintaining the shape and functionality of the shoes over time.
• Chemical Stability: EVA is chemically stable, performing consistently in various environmental conditions.
• Ease of Processing: EVA is easy to process, allowing for a variety of shapes and designs.
• Eco-Friendly: EVA is an eco-friendly material, recyclable, and minimizes environmental impact during production.

2.2. PU Series (Polyurethane)

PU series midsoles are known for their durability and versatility in design. Here are some specific characteristics:

Characteristics of PU (Polyurethane)

• Durability: PU is highly durable, maintaining the shape and function of shoes over a long period.
• Various Designs: PU midsoles can be manufactured in various designs and styles to meet diverse customer demands.
• Comfortable Fit: PU material is flexible and conforms to the shape of the feet, providing a comfortable fit.
• Heat and Impact Resistance: PU midsoles maintain their shape even at high temperatures and offer excellent shock absorption.
• Flexibility and Elasticity: PU exhibits outstanding flexibility and elasticity, adapting to foot movements.
• Adhesion and Easy Processing: PU adheres well to other materials, ensuring stable assembly in shoe production.
• Eco-Friendly: PU is an eco-friendly material, contributing to environmental protection through recyclability.

The production process for each type of midsole varies depending on the materials and techniques used. As mentioned earlier, let’s explore the key processes and differences based on the characteristics of the three midsole types.

3.1. Phylon

Production Process

• Phylon midsoles are produced using high-density EVA material by applying heat and pressure. This allows for the adjustment of the midsole’s density and elasticity.
• The process begins with the CMP (Chemical Mechanical Polishing) step, where the EVA material is dispensed and foamed. At this stage, the midsole takes on a somewhat amorphous shape.
• After foaming, the CMP midsole undergoes buffing to create a rough surface texture before being transferred to the Phylon process.
• In the Phylon process, the midsoles go through both heating and cooling steps using molds to achieve their final shape.
• Following this, the midsoles are subjected to cleaning and UV treatment processes to complete the Phylon process.

3.1.1. Selection of EVA Material

The production process of Phylon midsoles is based on EVA (Ethylene Vinyl Acetate) material. EVA is an ideal material due to its lightweight nature and exceptional elasticity, which enhances the durability and comfort of the shoes.

3.1.2. Molding Stage

Phylon midsoles are initially molded from EVA material under high-temperature and high-pressure conditions in the CMP process. After this molding step, they go through a maturation process and are buffed to create a rough surface texture. The buffing process is essential to remove the surface layer and prepare the midsoles for the next step, ensuring the proper quality of Phylon foam.

Next, they are transferred to a machine known as the Phylon Press. In this machine, the midsoles are heated for a specific period in the mold and then rapidly moved to the cooling mold. Under these conditions, the unique characteristics of Phylon material become apparent, transforming the previously amorphous CMP midsoles into well-shaped Phylon midsoles.

3.1.3. Cleaning and Pre-treatment

Midsoles removed from the molds often have residues of the mold release agent and other foreign substances on their surfaces. Therefore, a cleaning process is crucial to remove these impurities. The cleaning process ensures that the midsoles are free from any contaminants that could interfere with the adhesive properties.

After cleaning, the midsoles undergo pre-treatment through UV processes. They are preheated and then coated with a UV primer, followed by drying. This pre-treatment ensures that the midsoles maintain optimal conditions for adhesive bonding during subsequent manufacturing steps.

Application Equipment and Characteristics

• CMP Press: Used in the initial stage for foaming EVA material.
• Buffing Machine: Ensures a textured surface for proper molding.
• Phylon Press: Combines heat and cold molding to shape the midsole.
• Cleaning Machine: Removes impurities and residues.
• UV Line: Applies UV primer and ensures proper curing.

파이론 프레스 : 미드솔 설비 / Phylone Press

3.2. IP (Injection Preform)

Production Process

• The IP (Injection Preform) process is a method for producing midsoles by processing EVA material into pellet form, melting it, and injecting it into molds, similar to an injection molding process.

3.2.1. Molding Stage

• After removing moisture from the EVA pellet raw material, it is transferred to the equipment’s hopper.
• The transferred raw material is melted into a liquid state inside the injector.
• The molten material is injected into the molds, and after a specific period, it is extracted as a product.
• The extracted midsoles are then transferred to a maturation chamber, where they are allowed to mature for a certain period before proceeding to the cleaning process.
• In the case of IP midsoles, dimensional measurements are inspected again due to significant variations caused by shrinkage, ensuring that they meet the specifications.
• They are subsequently transferred to the UV spray process, similar to the Phylon midsole production process.

Application Equipment and Characteristics

• IP Machine: Responsible for injecting EVA material into molds.
• Aging Chamber: Allows the midsole to mature.
• Cleaning Machine: Removes impurities from the midsole.
• UV Line: Applies UV primer and ensures proper curing.

IP 머신 :미드솔 설비 / IP Machine

3.3. PU (Polyurethane)

Production Process

• PU midsole production can be easily understood by likening it to the process of making fish-shaped pastries sold on the streets during winter in Korea – refer below video.
• PU raw material is mixed in the right proportion and poured into molds.
• After covering the top of the mold, it is allowed to flow for a specific period.
• The product is extracted, cleaned, and dried.
• The process is finished by removing any protruding fur (flash) from the surface of the midsole and conducting inspections.

Application Equipment and Characteristics

• PU Material Mixing and Blending: Ensures proper mixing of PU raw materials.
• Pouring Machine: Pours the PU material into molds.
• Cleaning Machine: Ensures the midsole is free of impurities.
• Trimming Equipment: Removes any protruding material and ensures a smooth finish.

PU머신 : 미드솔 설비 / PU Machine

Taking another look at the overall process of making shoes from the beginning will be even more helpful for better understanding.