RUBBER FOR SHOES

Luis TormentoFebruary/2017

Introduction• Although they have several appearances and purposes of use, basically

the shoes are manufactured with the same component, among them sole, intermediate sole, buttress, insole (except for women's shoes that normally do not have insoles).

• The midsole is usually made of an expanded material such as polyurethane (PU), ethylene vinyl acetate (EVA), polyolefin elastomer (POE), rubber and PVC, thermoplastic polyurethane (TPU), which provide the necessary cushioning for this use .

• In terms of performance, thermoplastic materials are considered the best, however, new materials are emerging in the market, seeking ease of production and low weight.

• The midsole often has a much lower density (0.2-0.5 g / cm³) than the outer sole, to maintain the lightness of the footwear.

Introduction• The outer sole provides the properties of traction, durability and a little

damping and can not be made from the same material as the intermediate sole: it may be a microcellular foam, however, with a higher density (0.6 g / cm³ or more) For reasons of durability; May also be solid, with a density of 1.0-1.2 g / cm 3).

• In certain footwear, the midsole and outer sole are combined into a single component; This type of sole is usually glued to the body of the footwear.

• With this variety of footwear, the consumer usually asks himself: what is the best footwear in terms of properties?

• Of course, this answer depends on the use that will be proposed for the footwear. A person looking for a running shoe obviously looks for properties different from those looking for a shoe for everyday use. However, several properties tend to be universally demanded: fashion and a beautiful look are extremely important.

Introduction• External crepe-like outer soles remain popular even if they are not made of

natural rubber, but PVC, PU and TPU. Bright and light colored soles are still the high point in shoe sales.

• The low weight of footwear is very important, even in heavy use footwear such as hiking and working. This led to the development of microcellular foams with a new variety of materials: EVA, POE, PVC, TPU, TPE and rubbers.

• A sole that is appropriate for a particular sport is critical in athletic footwear. Examples are: high traction required for hiking shoes, good wet traction for water sports footwear, light weight and good traction for running shoes and high durability while sliding into tennis.

• The very high durability for external soles can be obtained with the use of carbon black as a filler, however, dark soles leave marks on floors and sports surfaces, which is undesirable, so silica and light loads are the most used in many shoes, And the carbon black was relegated to the function of a pigment.

Materials for Shoes• Leather was one of the first materials used in soles and its use today continues in

work and feminine shoes and in limited types of footwear. However, as the market became more diversified and new materials were developed, its use diminished.

• The use of unvulcanized materials, such as natural crepe, began around 1920, followed by vulcanized rubber in the 1930s.

• The use of vulcanized synthetic rubber began in the 1940s, after the development of SBR rubber and its own vulcanization equipment.

• Soles with resins of high styrene content were also developed at this time.

Materials for Shoes• In the 1950s the use of PVC was started, with the development of new softer

types and the use of synthetic plasticizers. In Table 1 we can see, through the decades, the new materials introduced in soles for footwear. From the table we conclude that every decade we have a new material developed until the 70's, when several new materials were developed: TPU, PU and TPE. Materials developed since the 1980s include EVA and POE: both used in microcellular soles. EVA is often used with a little rubberquantity to increase its physical properties in external soles.

Materials for Shoesfootwear materials over the decades

1930 1940

1950 1960 1970 1980 1990 2000

C C C C C C C C NR NR NR NR NR NR NR

BV BV BV BV BV BV BV

PVC PVC PVC PVC PVC PU PU PU PU TPE TPE TPE TPE TPU TPU TPU TPU EVA EVA EVA LR LR POE

C Leather NR Natural rubberBV Vulcanized rubber PVC Polyvinylkl chloridePU Polyurethane TPE Thermoplastic rubberPU Thermoplastic Polyurethane EVA Ethylene Vynil Acetate

LR Látex POE Polyolefin elastomers

Table 1. Use of footwear materials over the decades.

Materials for Shoes

Materials used in soles, kTon/ano

1970 1975 1980 1985 1990 1995 2000 2005

Leather 264 292 295 265 268 258 298 280

Rubber 694 804 767 617 618 686 833 1000

PVC 129 208 576 955 1292 1344 1450 1550

TPE 0 64 250 393 476 480 625 800

TPU 1 88 119 141 175 243 313 430

Others 112 130 185 205 241 360 491 640

Total 1188 1656 2192 2576 3070 3371 4010 4700

Table 2. Materials used in soles since 1970

Characteristics of materials used in soles

• A) Leather– It was the first material to be used in shoes recently had a 4% reduction in

its consumption. Despite being a material of animal origin, it has a high cost and does not meet the traction characteristics needed by many current shoes.

– Studies with the injection of polyurethane on the leather, improve the traction characteristic and can reinvigorate its use by the ecological factor.

Características dos materiais utilizados em solados

• B) Thermoplastic materials– They account for approximately 50% of the soles and include: TPE, TPU, EVA, PVC

and POE. Their advantage lies in the fact that they can be processed using inexpensive plastic injection molding machines.

– B1) Thermoplastic rubbers have experienced a 15% increase in their consumption since 1970, while PVC, for ecological reasons, has declined. Among the thermoplastic rubbers we highlight SBS and SEBS, which, in addition to providing properties similar to those of vulcanized rubber, still have softness, flexibility and resilience.

– B2) PVC is a rigid hard material composed of 35-50% of a plasticizer, often a phthalate, the most common of which is DOP plus stabilizers and process aids, to leave the material with useful properties.

– PVC accounts worldwide for 36% of all material used in soles. It is used pure or in mixtures with other thermoplastics such as POE and TPU, or with rubber type NBR or NBR / SBR, which give it special characteristics such as resistance to grease and better resistance to abrasion.

Characteristics of materials used in soles

• C) Vulcanized materials– C1) EVA - crosslinked and expanded, competes with vulcanized rubber in

microcellular soles; Its advantages include: ease of production, lower cost and density; Its main disadvantage is the poor physical properties. EVA is also used in soles, mixed with SBR, IR and NR / HSR (high styrene resin) that improve its physical properties.

– C2) Vulcanized rubber - Among the many rubber used in the manufacture of soles, the most commonly used are SBR, NBR, NBR / PVC, BR and NR, each one with a characteristic peculiar to the application. For example, natural rubber is widely used in crepe-type (unvulcanized) soles and in many other applications, especially in men's shoes. Due to the high cost of NR, SBR has taken much of its use for decades and is now considered the leading elastomer in the footwear industry.

Characteristics of materials used in soles

• C) Vulcanized materials– Special applications require different elastomers; Among them we can

mention NBR and NBR / PVC for military and safety shoes, and miscellaneous applications such as mountaineering, which makes use of polyurethane rubber, use in contact with oils where polychloroprene and other elastomers are used as diverse as their application: In outer space, on the moon, or in the polar cold.

Contact

LT QuimicosAv. Pedro Severino Jr., 366 Cjto 35

04310-060 – São Paulo – SP – BrasilLuis TormentoNPD Director

Luis.tormento@LTQquimicos.com.brTel: +55 (11) 5581-0708