Learn more about the types of shoe soles (Features of different types of shoe soles)
Basically, a shoe sole should have the following characteristics:
Beauty: Give the shoes a beautiful shape to be attractive to the buyer of the shoes. The influence and role of shoe shape on the choice of buyers of sports and formal shoes is more evident today.
Impact absorption: In other words, a shoe sole should make the foot feel comfortable.
High abrasion resistance: Replacing the soles of worn and worn leather shoes with elastic indicates the need for soles with high abrasion resistance. For example, a tennis player tends to use a shoe sole that is highly resistant to abrasion.
High flexural strength: Walking and running expose the soles of shoes to bending. Customers expect the soles of their shoes not to be easily damaged during exercise and walking in different temperatures and environments.
High slip resistance: In other words, the amount of friction or coefficient of friction between the materials of different types of soles and different flooring materials should be high to prevent the person from slipping. Special footwear, such as safety shoes, should provide maximum protection for workers’ feet.
Depending on the type and condition of the work environment, the soles of the shoes should be resistant to solvents, oils, petroleum products, hydrolysis, static electricity and abrasion. Antistatic, antibacterial, etc. agents added to the polymer improve its properties.
Materials used in the production of shoe soles:
Rubber: The soles of shoes can be natural or artificial. The characteristics of different types of rubber shoe soles include the following:
- High durability
- Easier and cheaper to produce than leather
Today, most types of rubber shoe soles are synthetic rather than natural rubber soles that used to be made from trees.
Rubber soles are usually a combination of several additives to rubber to control the physical properties of the sole.
Some black compounds may cause blackening of the foam (depending on the type of carbon black used). Shoe soles are used in a variety of products from shoes such as industrial shoes to parliamentary shoes.
Natural rubber or (NR)
Prominent elastic properties and excellent properties of natural rubber allow all types of soles to remain soft and flexible in the cold. Resistance to tearing, puncturing and slipping of natural rubber is higher compared to PVC outsole. Natural rubber is resistant to chemicals such as bases, acids, alcohols and water-based solutions. Because natural rubber is a hydrocarbon, it does not have high resistance to prolonged contact with petroleum and gasoline solvents. NR safety shoe soles are used in food, transportation, facilities, construction and agriculture.
Styrene-butadiene rubber soles: (SBR)
Styrene-butadiene rubber is the most common and cheapest synthetic rubber. It is very weak if you do not add filler. Compared to natural rubber, it has higher abrasion resistance but weaker fatigue resistance.
Nitrile rubber shoe soles: (NBR)
NBR insole or nitrile elastomer is a copolymer of butadiene and acrylonitrile, which is mainly suitable for use in applications where the sole of the shoe requires high resistance to gasoline and petroleum products. NBR cumin has high resistance to minerals and vegetable oils but low resistance to oxygenated solvents such as acetone, methyl ethyl ketone and other ketones.
NBR outsole is highly resistant to acids and bases. Its heat resistance to corrosion compared to natural rubber is an advantage for NBR outsoles.
As the acrylonitrile content in the NBR substrate increases, the resistance to solvents increases but the flexibility decreases at low temperatures. Flexibility at foot temperature NBR outsole is lower than natural foot rubber. Although the performance of NBR low temperature flexibility can be improved by adding compounds, the advantage of NBR outsole lies in its resistance to oil and solvents. In most cases, when it comes to resistance to oil, gasoline and aromatic hydrocarbons, NBR rubber is used instead of natural rubber soles.
Neoprene chloroprene rubber 🙁 CR)
Neoprenees are a large family of synthetic rubbers that have characteristics similar to natural rubbers but have higher resistance to oil, grease, oxidation, and fire resistance than natural rubbers. Although they have lower tensile strength at high temperatures than natural rubber, they have a longer lifespan and do not soften when exposed to heat.
Neoprene rubber, like natural rubber, is used to make soft, high-strength shoe soles in other combinations. The high density of neoprene substrate increases its price and high cost. Neoprene outsole does not have the properties of natural rubber flexibility at low temperatures and limits its use for shock and shock absorption applications. CR substrate is resistant to animal fats, blood, oil, oils, certain acids, alcohols and other solvents.
Thermoplastic elastomer sole: (TPE)
While vulcanized rubbers derive their structural strength from the sulfur crosslinkers that connect the chains at the double bonding sites, the strength of thermoplastic elastomers is derived from crystals that act as the physical crosslinking between the chains. Slowly In the case of thermoplastics (TPU) polyurethane, the crystals are formed by the deposition of a compound (polystyrene) from a polymer network (styrene butadiene). Thermoplastic vulcanization (TPV), which is a double cross-linking process caused by a temperature process, is not discussed here due to its low consumption.
Thermoplastic polyurethane shoe soles:
Polyurethane polyester shoe soles, which are produced by reaction with MDI by mold injection method, have excellent abrasion resistance properties. Thermoplastic polyurethane shoe soles are mostly used in the production of sports shoe soles.
On the other hand, polyester thermoplastic polyurethanes are more resistant to hydrolysis and degradation in contact with water, but their wear resistance is slightly lower.
Cyrillic styrene butadiene styrene 🙁 SBS)
SBS synthetic rubber is made up of a series of styrene butadiene polymers. This rubber is composed of a combination of polystyrene and polyutadiene blocks. The polystyrene phase provides the hardness of the sole, while the polybutadiene phase provides the adhesion and integrity of the sole. The most important descriptive parameter of the SBS shoe sole is the ratio of styrene to butadiene composition.
The share of styrene in the composition is about 29 to 55%, which low amount of styrene to soft grade and high amount of styrene leads to the production of firm cumin.
PVC is the most important material for the production of synthetic shoe soles. PVC polymer is very hard but when used for shoe soles it softens with additives. PVC subsoil is usually produced by direct injection.
Features of PVC underlay include the following:
- Slippery and slippery in cold weather
EVA shoe soles
Ethylene vinyl acetate or EVA sole is one of the most popular materials used in the production of shoe soles due to its cheapness and light weight. The solid co-polymer of vinyl acetate and ethylene expands during the shoe sole production process using a gas as a puffing agent. The resulting closed cell foam gives the shoe sole a high impact absorption property. EVA outsole can be produced by mold injection and extrusion method. Extruded sheets with different hardness and colors can be laminated to the desired thickness with a flame and cut into a specific shape.
Features of EVA outsoles include the following:
- It is much lighter and more durable than micro-cellular rubber soles. It has high flexibility and reversibility.
- Good thermal insulation to protect the feet from the cold.
- Use in midsole for sports shoes
- Use for outdoor soles for lightweight shoes
Polyurethane shoe soles: Polyurethane materials are produced in two parts from a combination of two liquids at high pressure by injection machine and then injection into the shoe sole mold.
The product is open cell foam that is not as cheap and light as EVA substrate.
Due to the open cell of polyurethane outsole, its impact absorption property is not as significant as EVA foam. However, the PU outsole pressure is lower than the EVA outsole so the life of the PU outsole is longer.
PU or polyurethane shoe soles include two types of polyester and polyester, which have been discussed in other articles. Polyurethane materials used in all types of shoe soles have a soft and flexible cell structure.
PUK polymer outsole is very strong and durable and resistant to many chemicals. The production of various types of safety shoe soles with polyurethane materials is very important.
Its features include the following.
- High flexibility, flexibility and high flexibility
- High thermal insulation against cold
- The most durable cumin
Leather outsole: Despite its vulnerability, leather insole is one of the most popular insoles in house shoes.
The cow skin is about half a centimeter thick.
The advantages and disadvantages of leather soles include the following:
- High abrasion resistance
Expensive: Leather soles are usually more expensive than rubber and plastic soles.
For this reason, it is mainly used in the production of quality shoes.
- It is less durable than other types of shoe soles:
Leather soles are bought more because of their high attractiveness than for durability, because they are less durable than other shoe soles.
Composite PVC is one of the most widely used and cheapest materials in the production of footwear, sandals and slippers. Subsoil density varies from 0.75 to 1.3 g / cm3 and hardness varies from 45 shore A to 95 shore A 95. When PVC materials are combined with thermoplastic polyurethane (TPU) materials, the substrate is obtained with high abrasion resistance and flexibility. PVC outsole is highly resistant to animal fats, acids, alcohols, gasoline, oil and bases.
PVC outsole is not suitable for working in environments exposed to aldehydes and ketones. The combination of PVC with nitrile rubber powder (NBR) gives the shoe soles a higher resistance to oil and therefore can be used in the molding of shoe soles in the production of safety shoes.
The following features of thermoplastic rubber shoes can be mentioned as follows:
- Feeling comfortable in the foot
- Lighter weight compared to PVC and rubber soles
- High elasticity
- High resistance to cold
- To be cheap
Physical characteristics of shoe soles:
All the materials and compounds mentioned above have unique physical characteristics in the production of various types of shoe soles.
In the following table, we compare the physical characteristics of different types of shoe soles:
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