PROCESS FOR TREATING SHOE SOLES THROUGH ULTRAVIOLET RADIATION AND OZONE

OBJECT OF THE INVENTION

The present invention is aimed at a process for the treatment of shoe soles using ultraviolet radiation combined with ozone.

With this process, adhesive properties are improved, on the surface area of materials used in the manufacture of soles, such as (synthetic vulcanized and non vulcanized rubbers, thermoplastic rubbers, ethylene mixed polymers and vinyl acetate (EVA), polyurethane foams, etc..) used in the footwear industry.

BACKGROUND OF THE INVENTION

In the footwear sector, the synthetic rubbers and polymers (for example, EVA mixed polymers, polyurethane foams) are widely used in the manufacture of soles. However, the majority of these materials have low superficial energies (below 30 mJ/m2), which necessitates the undertaking of a superficial treatment when joining to the cutting material by means of an adhesive (generally polyurethane or polychloroprene). In addition to this, different components of the rubber and polymers formulation may lead to superficial energy values below 30 mJ/m2, making the adhesive process even more complex.

Halogenation is the superficial treatment most widely used in the footwear sector for the chemical modification of the surface area of rubber materials due to its effectiveness, low cost and easy application. There are different methods of halogenation of vulcanised synthetic rubbers. All of them are based on the use of solutions of a halogenant agent (a chlorine or bromine organic or inorganic donor) in an organic solvent, of either chlorine or bromine vapours. The trychloroisocyaniric acid (TCI) - 1,3,5- trychloro- 1,3,5, -tryacin - 2,4 6, tryona is currently the most widely used halogenant agent in the footwear sector and is applied from a ketone or ester type organic solvent in solution.

The halogenation is made by applying the halogenant solution with a brush on top of the sole. After between 20 and 45 minutes has elapsed the adhesive in solution is applied. This adhesive is also applied with a brush. After 30 minutes the dry film of the adhesive reacts and joins with the cutting material.

However, halogenation has certain limitations:

• Potential toxicity of halogenant solution owing to chlorine vapour emanations during handling and application of the halogenant agent.
• The halogenant solutions have very limited stability, and have therefore to be prepared shortly before use.
• Treatment requires relatively long periods of time (around 6 hours) to achieve optimum output.
• The nature and formulation of rubber used affects the halogenation treatment effectiveness.
• The use of a high concentration of halogenant agent causes a loss of adhesion as a consequence of the degradation of the most external superficial load of the rubber and the depositing of halogenant agent remains on the surface area.
• The halogenation implies the use of organic solvents, with the consequent damage, both environmental and for the operator.
• The adhesive cannot be immediately applied after treatment, one must wait for at least one hour.

DESCRIPTION OF THE INVENTION

The process of the invention provides technological advantages compared with the halogenation process regularly used in joining soles with polyurethane or polychloroprene adhesives:

• ■ The superficial treatment time is shortened from around one hour to minutes.
• ■ No chemical residues occur, nor are solvents used.
• ■ Excellent adhesive joints are obtained with many sole materials.
• ■ It is a versatile superficial treatment, which may be used in a continuous or discontinuous production system. Therefore, it may be integrated into an automated production chain.
• ■ Improvement in the quality of the finished shoe
• ■ The adhesive may be applied immediately after completion of treatment.

The process consists in applying UV radiation between 130 and 185 nm with high treatment power per area unit (at least 20 mW/cm2) on a shoe sole, using an appropriate discharge lamp with or without a reflective, for a variable time of between several seconds and several minutes. The sole may be composed of a synthetic, vulcanised rubber or not, a EVA mixed polymer which is expanded or not, an open or closed pore polyurethane foam, of any density, or any sole material used in the manufacture of any type of shoe.

The process is applied with a lamp situated inside a closed chamber into which the sole to be treated is placed. The distance between the sole and the lamp is variable, using any type of device to raise or lower the sole and/or the lamp.

The chamber has a continuous air inlet which, when in contact with the UV lamp, continuously generates ozone, which is essential for producing an appropriate treatment efficiency. The ozone is continuously or discontinuously evacuated from the chamber to avoid undesirable concentrations of the same in contact with the metallic parts of the chamber.

The sole is placed in the chamber using a continuous (for example conveyor belt) or discontinuous system. Moreover, once the sole has been treated, it is removed from the chamber using a continuous or discontinuous system.

The polyurethane, polychloroprene or any other adhesive used in the manufacture of shoes, may be applied to the sole using any process (brush, pistol, curtain, roller or any other) immediately after undertaking treatment or after any amount of time (either minutes or months) from completion of treatment.

Once the adhesive has been applied the joint is made to any sole material used in shoe manufacture (such as fabric, leather, pseudo-leather, or any other) using any process already known and which is not the aim of the invention.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a perspective view of the device where the invention process is activated.

PREFERRED EMBODIMENT OF THE INVENTION

The process for the treatment of shoe soles is applied in the device (1) which is made up of a chamber (2), the format of which is preferably prismatic.

On at least one of the lateral faces of the chamber are one or several forced air inlets (3) whilst in at least another different lateral face is a forced air outlet (4).

The air inlet may be continuous and/or discontinuous.

On the inside of the chamber there is a UV lamp (5) whilst opposite the lamp is a conveyor belt (6) on which the surface area of the sole (7) to be treated is placed.

The chamber has an access for inserting the sole and placing it on the conveyor belt and an exit opposite this through which the sole goes out once it has been treated.

The distance between the lamp and the sole is variable which means that it uses any type of device to comfortably vary this distance and fix the displaced element into place, whether it be the lamp or the conveyor belt.