WO2017186787A1

WO2017186787A1 - Thermoplastic product for footwear parts, and relevant manufacturing process

Info

Publication number: WO2017186787A1
Application number: PCT/EP2017/059919
Authority: WO
Inventors: Bruno Cardinali
Original assignee: Tecnofilm S.P.A.
Priority date: 2016-04-29
Filing date: 2017-04-26
Publication date: 2017-11-02

Abstract

A thermoplastic product for producing footwear parts, obtained by injection molding of an extruded product comprising a Styrene-Butadiene-Styrene (SBS) block copolymer and lubricant, wherein said molded thermoplastic product is submitted to an ultraviolet (UV) radiation treatment in such manner to obtain a bondability with polyurethane adhesives higher than 4N/mm measured in compliance with the UNI EN 1392 standard.

Description

Thermoplastic product for footwear parts, and relevant manufacturing process.

The present patent application for industrial invention relates to a thermoplastic product having a high bondability with polyurethane adhesives, as well as to a manufacturing process of said thermoplastic product. Said thermoplastic product is especially suitable for being used to produce footwear parts, such as soles, uppers, midsoles and heels, which are intended to be glued with polyurethane adhesives.

As it is known, footwear soles are generally obtained from vulcanized products derived from both natural and synthetic materials. Among such vulcanizable products, the following are generally used: Natural Rubber (NR), Polylsoprene cis (PI cis), Polystyrene Butadiene random (SBr), PolyAcryloNitrileButadiene random (NBr) and PolyButadiene (PB). In such a case, polyurethane adhesives are largely used to glue the sole to an upper and other footwear parts, such as midsoles and heels.

In recent times, compounds based on Styrene-Butadiene-Styrene copolymer blocks, which are generally known as SBS, have been largely used in the footwear industry. They are thermoplastic polymers and can advantageously replace the vulcanized products. As a matter of fact, being of thermoplastic type, the SBS copolymer blocks can be recycled several times and are therefore more environmental-friendly than vulcanized products.

However, the non-polar nature of these products, which are obtained with SBS copolymer blocks, requires specific treatments in order to provide a suitable bonding with the polyurethane adhesives that are largely used in the footwear industry.

On the other hand, the same surface treatments that are used for SBS elastomers are also known for vulcanized elastomers because the chemical characteristics of vulcanized elastomers are very similar to the ones of thermoplastic elastomers, being related to the presence of double olefinic bonds deriving from Butadiene and Isoprene-based polymer segments.

The surface treatments provide for chemical treatments, such as halogenation or chlorination. Halogenation is used in the footwear industry because it is a simple, yet effective technology that provides long-lasting mechanical results, while meeting the essential requirements for the use of the material in applications with polyurethane adhesives.

The main factors that have determined the choice of halogenation surface treatments are especially related to the composition of the thermoplastic mixtures that are used to make footwear parts. Such a composition has changed over time with the use of new polymeric and non- polymeric additives that have negatively changed the capability of SBS copolymer blocks to adhere to the most commonly used adhesives, such as Neoprene and Polyurethane.

Approximately 30 years ago, PolyButadiene 1 -2 Syndiotactic (for the sake of brevity, PB syndio) started to be used in SBS mixtures. The presence of PB syndio has considerably reduced the bondability of the SBS compounds with polyurethane adhesives.

On the other hand, the use of PB syndio in thermoplastic compounds has proved necessary in order to eliminate the difference that exists in the surface of vulcanized products and thermoplastic products. In fact, the surface of vulcanized rubber products is very matt; whereas, the surface of SBS products is very shiny.

PB syndio has a lower density than SBS and a different solubility parameter. Therefore, when PB syndio is mixed with SBS, the PB syndio tends to stratify in the surface, thus giving the desired matt effect to the final product.

The halogenation surface treatment provides for a chlorination reaction that proceeds by adding hypochlorous acid to the double bonds of the polymer unsaturated segments, with formation of ethylenic and dichloro Chloridrines. Butyl Acetate, Ethyl Acetate or Methyl Ethyl Ketone (MEK), or a mixture of them, are generally used as solvent in such a chlorination reaction. The solvent facilitates the penetration of the reactant in the lower layers with respect to the surface, thus increasing the quantity of adhesion sites.

However, PB syndio is less soluble than SBS in these solvents or in other polar solvents. This makes the penetration of chlorinant in the non- surface layers difficult, reducing the number of adhesion sites.

Moreover, the reactivity of the double olefinic bonds of the thermoplastic mixture must be considered. The Cis and Trans position is favored in the chlorination with respect to the 1 -2 vinylic position of the PB syndio. This is another unfavorable factor for bondability.

The applicant made some experimental tests on samples that were submitted to chlorination according to the prior art, and measured bondability in compliance with the UNI EN 1392 standard.

The UNI EN 1392 standard measures the force of traction (peeling) of a 10 mm-wide bovine leather strip that is glued on the surface of a plate obtained from the tested sample, with a traction speed of 100 mm/min. The result is expressed in Newton/strip width. The strip width is expressed in mm.

Samples of SBS based products with different weight percentages of PB syndio that were previously submitted to chlorination according to the prior art were prepared for the tests. In these tests a bovine leather support was adhered with polyurethane adhesive to different samples.

The bondability results are shown in Table 1 below. In the following description the percentages refer to the weight percentage with respect to the total weight of the final product.

Table 1

As indicated in Table 1 , in spite of chlorination, the SBS compounds with an increasing weight percentage of PB syndio showed a decreasing bondability to the bovine leather support. One sample with 25% weight percentage of PB syndio showed a bondability of 5-7 N/mm.

However, it must be considered that for sports footwear the ISO/TR 20880/2007 standard requires a bondability equal to or higher than 4 N/mm. Therefore, with any adhesion system, the minimum bondability required for footwear must be 4 N/mm in order to meet the ISO/TR 20880/2007 standard.

As shown in Table 1 , in spite of the high decrease in bondability when the PB syndio increases, the minimum bondability requirement (higher than 4 N/mm) is complied with. Therefore chlorination solves the bondability problem in footwear.

However, the chlorination process generates a high emission of toxic substances, the characteristics and effects of which for the health of the operators that are directly involved in the chlorination process are still partially unknown.

BRP10701866A2 discloses the production of a compound made of SBS,

1 ,2 PolyButadiene syndiotactic, Mineral Oil and a photoinitiator. Said material can be processed by injection, extrusion or compression and can be used to manufacture products, for example footwear soles, that will partially cross-link when submitted to irradiation, for example with UV radiations, changing the base structure of the polymeric components and increasing their molecular weight. Such a process is suitable for changing some thermo-mechanical characteristics of the products (abrasion, tensile strength, etc.), but it is not suitable for providing bondability with polyurethane adhesives, if these products contain white pigments and were not previously treated with chlorinating solutions.

BRP10701866A2 also discloses SBS hydrogenated derivatives, i.e. SEBS and similar polymers, as possible polymer components of the compound, but these components are to be avoided if the product is to be glued after being manufactured. As a matter of fact, being PolyOlefins with very low surface tension like PolyEthylene and PolyPropylene, SEBS, SEPS, SEEPS and the like cannot be used to obtain a sufficient adhesion with polyurethane- based adhesives. BRP10701866A2 discloses a UV radiation that is suitable for creating radicals from the photoinitiators contained in the compound, but such radicals are completely insufficient to modify the surface tension of the product to be glued if white pigments are present. The UV radiation is used to decompose the photoinitiator (for example R-R1 ) that is present in the compound. The photoinitiator decomposes in radicals, R(.) and R1 (.), both of them with a very low molecular weight, which extract Hydrogens from the polymer P molecule with homolytic reaction of the C-H bond with formation of RH, R1 H (inactive molecules) and polymeric radicals P(.), P1 (.) etc. The extraction of hydrogens generally takes place on the C-H bonds in allylic position to the double bond and the polymeric radicals (P(.) and P1 (.)) can bind to originate a new P-P1 polymer with higher molecular weight than the initial individual polymers. The radicals R(.) and R1 (.), which are inactivated by the extraction of Hydrogens coming from the polymer, become polar contaminants with low molecular weight that do not modify the surface tension of the polymeric surface of the product. For this reason, the use of the chlorant is necessary to obtain the necessary bondability with polyurethane adhesives. Such an increase process in the molecular weights of the compound justifies the corresponding increase in the thermo-mechanical characteristics of these products, without solving, however, the problem of bondability with polyurethane adhesives.

Two scientific publications by Maria D. Romero Sanchez et al. are known: "UV treatment of syndetic styrene-butadiene-styrene rubber" (Journal of Adhesion science and technology; vol. 17 No. 1 ) and "Addition of ozone in the UV radiation treatment of syndetic styrene-butadiene-styrene (SBS) rubber" (International Journal of adhesion and adhesives, Elsevier Vol. 25 No. 4).

These scientific publications provide a detailed description of the behavior of an SBS-based compound plasticized with mineral oil, known as S6, which is submitted to separate 03 and UV treatments, and also to simultaneous 03 UV treatments. These publications do not consider the presence of any other additives in addition to SBS, such as for example white pigments, and in particular mineral photoactive pigments (such as Titanium Dioxide). They disclose an ideal mixture that cannot be used or is rarely used in the footwear industry to make footwear soles. In fact, in the footwear industry, it is necessarily required that the products can be matt (high presence of 1 ,2 PolyButadiene Syndiotactic) and colorable and possibly protected against the action of visible and ultraviolet radiations (presence of white pigments).

Therefore, if PolyButadiene syndiotactic (in concentration of 25% in order to obtain a good matt finish), coloring additives, such as white pigments like as Ti02 (in concentration higher than 0.5%) and anti-UV are added to the compound of S6 type as protectors, and this product is submitted to the processes described in the two aforesaid publications, the final result will be a product with a strong adhesive deficiency to the adhesion test, with values lower than 4 N/mm, which is the minimum value accepted for footwear production. Such a poor bondability result is shown below in Tables 2-7 of this patent application, which indicate the adhesion values obtained on compounds produced using various SBS combinations with the aforementioned additives.

Therefore, said scientific publications take into consideration a product only made of SBS (S6), which is difficult to be used for footwear parts, such as soles, that require a great variety of characteristics, such as glossy or matt surface and a wide range of colors, that negatively affect the proposed adhesive treatment.

The three treatments disclosed in these publications - i.e. treatment with 03, with UV and with 03 and UV simultaneously - are all ineffective for the SBS compounds that are modified with the aforesaid additives. As a matter of fact, these publications do not describe a sequential treatment, i.e. they do not disclose the execution of the 03 treatment, followed by the UV treatment.

CN101200621 discloses SBS products, without disclosing their bondability with polyurethane adhesives. Moreover, CN101200621 does not describe additives such as PolyButadiene 1 -2 Syndiotactic and/or titanium dioxide pigments, or the sequential use of treatments with 03 and UV.

The purpose of the present invention is to eliminate the drawbacks of the prior art by providing a thermoplastic product and a manufacturing process of said thermoplastic product that does not require any treatment with the emission of toxic substances for the operators, in order to make the thermoplastic product suitable for a polyurethane-based adhesive treatment.

Another purpose of the present invention is to provide a thermoplastic product and a manufacturing process of said thermoplastic product that ensures effective, reliable and foreseeable bondability with polyurethane adhesives.

These purposes are achieved according to the invention with the characteristics of the independent claims.

These purposes are obtained using a system for modifying the surface of the thermoplastic product based on a chemical-physical treatment, without emitting hazardous substances for the operators. The modification is suitable for the following polyurethane-based adhesive treatment, avoiding any other action and eliminating the need for the chlorination phase.

Advantageous embodiments of the invention appear from the dependent claims.

The use of ozone (O3) is known at experimental level to increase the bondability of thermoplastic materials. As a matter of fact, the ozone binds with the double bonds of SBS-based compounds by means of a ionic mechanism, forming Ozonures that successively decompose, generating carbonylic, acid and hydroperoxy groups that increase the surface tension of the product and its predisposition to bond with polyurethane adhesive.

In view of the above, the applicant made some experimental tests in compliance with the UNI EN 1392 standard, gluing a bovine leather support with polyurethane adhesive to SBS products having a gradually increasing weight percentage of PB syndio from 0 to 25% and previously treated with ozone. The final bondability obtained with such a technique was comprised in a range from 2 to 5 Newton/mm. Therefore, such an ozonization treatment did not guarantee the minimum value of 4 N/mm that is requested by the ISO/TR 20880/2007 standard to obtain very good adhesion results.

A surface treatment with UV radiation is known at experimental level to increase the bondability of thermoplastic materials. In view of the above, the applicant made some experimental tests in compliance with the UNI EN 1392 standard, by gluing a bovine leather support with polyurethane adhesive to SBS products having a gradually increasing weight percentage of PB syndio from 0 to 25% and previously treated with UV radiation. The test results were surprisingly better compared to the ozone treatment, with bondability values that were clearly higher than the 4 N/mm required by the ISO/TR 20880 standard. After the UV treatment, bondability increases with an increasing percentage of PB syndio.

However, such a UV treatment cannot be applied to all SBS and PB syndio-based compounds.

As a matter of fact, in order to obtain SBS-based products with a very matt surface and an intense white color, it is necessary to use Dioxide Titanium white pigments (TiO2 with a concentration of approximately 1 %), in addition to using high concentrations of PB syndio (approximately 25%). From the experimental tests, the applicant surprisingly discovered that when the TiO2 white pigments exceed the weight percentage of 0.5%, the UV treatment is ineffective and the product treated with UV radiation does not meet the minimum bondability value of 4 N/mm when submitted to the adhesion test in compliance with the ISO/TR 20880 standard.

In fact, the high concentration of TiO2 produces an intense white coloration in the product and this causes two different types of phenomena. The first one is the reflection of the majority of the UV radiation and the second one is the absorption of the remaining part of radiation for photo-chemical activities that are specific of Dioxide Titanium, subtracting the radiation from the desired surface modification.

Moreover, the applicant performed a simultaneous treatment of UV radiation and Ozone on samples of SBS-based products with PB syndio (approximately 25%) and TiO2 (approximately 1 %). Successively, these samples were submitted to tests in compliance with the UNI EN 1392 standard. Also the result of said tests was unsatisfactory, because a bondability lower than 4 N/mm was measured. In fact, the Ozone is an oxidizing gas and a barrier to the UV radiation that is blocked by the Ozone for its well-known photolytic reaction that occurs in the high layers of the earth's ionosphere. Therefore, also in this case, the results of the adhesion tests are contradictory and not constant, and therefore such a treatment cannot be used for the adhesion of soles in the footwear industry.

Based on these experimental tests, the applicant discovered that the main problem in the application of ozone and UV radiation treatments is represented by the presence of two additives in the SBS-based mixture:

PB syndio, which comprises vinylic groups that are highly resistant to the adding action of the Ozone, and

ΤΊΟ2, which is a white pigment with a very high refraction index and high photo-synthesis capabilities, which highly reflects the UV radiation.

In order to solve these problems, when an intense white color is to be obtained, according to the invention, the ΤΊΟ2 is replaced in the SBS and PB- based mixture, either completely or partially, with other types of white pigments that are different from ΤΊΟ2 and have a much lower reflection of the UV radiation. These white pigments that are different from TiO2 can be, for example, zinc sulfide (ZnS) or barium sulfate (BaSO4).

Such a product is superficially treated first with 03 and then with UV radiation.

In such a way, the Ozone, which is not affected by reflection due to the white color of the surface, attacks the unsaturated bonds of the SBS and of the PB syndio, forming Ozonures in quantities that are not massive, but can considerably change the surface of the thermoplastic product. Whereas such an ozone treatment does not make the product suitable for gluing, it creates the conditions for advantageously completing such an adhesion characteristic with a UV treatment.

The following UV radiation treatment attacks the double bonds, the vinylic bonds and the Cis and Trans bonds, in a sufficient quantity to increase the sites that are necessary for a strong adhesion; however, this is possible only if the concentration of the TiO2 white pigment does not reach the critical threshold value of 0.5% with respect to the weight of the final product. As a matter of fact, the energetic radiant effect of the UV radiation is considerably low for TiO2 higher than 0.5%. The applicant prepared several sample mixtures, the compositi which is indicated in Table 2 below.

Table 2

These samples were prepared by mixing SBS granules with mineral oil and eventually with PB syndio granules and Ti02 white pigments in an extruder. The extruded product was molded in molds by means of injection molding.

Table 3 shows the aesthetic characteristics of the samples.

Table 3

High white index indicates an intense white obtained with a TiO2 percentage of 1 %. Instead, low white index indicates a poorly intense white obtained with a TiO2 percentage of 0.5%.

All samples S1 - S6 were submitted to a UV radiation treatment for 30 minutes. The UV-treated samples were tested to measure bondability in compliance with the UNI EN 1392 standard. The results of the tests are indicated in Table 4 below. SAMPLE BONDABILITY

(N/mm)

S1 10-12

S2 12-16

S3 9-1 1

S4 6-8

S5 2-4

S6 2-4

Table 4

As shown from the results of Table 4, the first four samples (S1 -S4) comply with the ISO/TR 20880 standard because they are not white or they have a low white index.

On the contrary, the last two samples (S5, S6) do not comply with the

ISO/TR 20880 standard because they have a high white index. Therefore, as it was expected, problems were encountered with samples having a high white index.

Since samples S5 and S6 did not pass the test, the applicant submitted these samples first to an ozone treatment for 10 minutes, and then to a UV radiation treatment for 10 minutes. The samples treated with ozone and UV radiation were tested to measure bondability in compliance with the UNI EN 1392 standard. The results of said tests are shown in Table 5 below.

Table 5

As shown in Table 5, the double treatment (first ozone and then UV radiation) complied with the ISO/TR 20880 standard for sample S5. On the contrary, the sample S6 did not pass the ISO/TR 20880 standard because the combination of PB syndio with TiO2 percentages higher than 0.5% makes the double treatment (first ozone and then UV radiation) ineffective. The applicant repeated the test on sample S6, increasing the treatment time and submitting the sample S6 to ozone treatment for 20 minutes and to UV radiation treatment for 30 minutes. After such a prolonged treatment, a bondability of 3-6 N/mm was obtained, which is slightly higher than the shorter treatment, but is still insufficient to comply with the ISO/TR 20880 standard.

Therefore the applicant understood that, in order to obtain a matt product with a high white index, a Ti02 percentage higher than 0.5% cannot be used and it is necessary to replace Ti02, either partially or completely, with another white pigment, such as ZnS and/or BaS04.

It must be considered that a ZnS weight percentage that is two times higher than the Ti02 weight percentage must be used in order to obtain the same white index. Consequently, the applicant prepared the following sample as indicated in Table 6 below.

Table 6

The sample S7 is matt and has a high white index, just like the sample S6, which did not pass the tests of the ISO/TR 20880 standard.

The applicant submitted sample S7 to three types of treatments and made tests to measure bondability in compliance with the UNI EN 1392 standard. The results of the tests are indicated in Table 7 below.

Table 7 As shown in Table 7, the sample S7 did not pass the ISO/TR 20880 standard for a treatment with UV radiation only, whereas it passed the ISO/TR 20880 standard after a double treatment with 03 for 10 minutes and with UV radiation for 10 minutes. Even better results were obtained with a longer treatment.

In view of the tests, the applicant developed the thermoplastic product according to the invention, as well as its manufacturing process.

Such a thermoplastic product is obtained by means of injection molding of an extruded product and ultraviolet (UV) radiation treatment of the molded product, in such a way to obtain a bondability with polyurethane adhesives that is higher than 4N/mm measured in compliance with the UNI EN 139 standard.

The extruded product comprises a mixture of Styrene-Butadiene- Styrene (SBS) block copolymer and lubricant, such as mineral oil. The lubricant can be in a weight percentage of 20-30% with respect to the final product.

The extruder is preferably a twin-screw extruder with two counter- rotating screws. The mixture is heated to a temperature of approximately 180° during extrusion. An extruded product in granules is obtained from the extruder. The extruded granules are used in a mold, with an injection molding process, to obtain the desired product. The mold can have a suitable shape in order to obtain, for example, a footwear sole.

In order to obtain a very matt product, PB syndio can be added to the SBS and lubricant mixture in a weight percentage comprised between 20 and 35%.

In order to obtain a non-matt product with low white index, TiO2 white pigments can be added to the SBS and lubricant mixture in a weight percentage comprised between 0.1 and 0.5%.

In order to obtain a matt product with low white index, TiO2 white pigments can be added to the SBS, lubricant and PB syndio mixture in a weight percentage comprised between 0.1 and 0.5%.

These molded thermoplastic products, which can be non-matt, matt and with a low white index, are submitted to a UV radiation treatment process. In order to obtain a non-matt product with high white index, Ti02 white pigments can be added to the SBS and lubricant mixture in a weight percentage higher than 0.5% and lower than or equal to 1 %. In such a case, the molded product is submitted first to an ozone flow treatment, and then to the UV radiation treatment.

In order to obtain a matt product with high white index, ZnS and/or BaS04 white pigments and/or other white pigments that are different from Ti02 can be added to the SBS, lubricant and PB syndio mixture in a weight percentage higher than 1 %. Alternatively, in order to obtain a matt product with high white index, Ti02 white pigments up to a maximum of 0.5% and ZnS and/or BaS04 white pigments and/or other white pigments that are different from Ti02 can be added to the BSB, lubricant and BP syndio mixture. In these cases, the molded product is submitted first to an ozone flow treatment, and then to the UV radiation treatment.

In any case, in the aforementioned examples, the Ti02 can be replaced, either partially or completely, with ZnS and/or BaS04 white pigments and/or other white pigments that are different from Ti02, in a weight percentage of 1 :2.

In the case of products with high white index, these products must be submitted to a two-phase double treatment.

The first treatment phase consists in the exposure of the surface area of the product intended to be glued. Such a surface area of the product is exposed to an Ozone gas flow with concentration comprised between 40 and 60 g/m³, preferably 50 g/m³, in an Oxygen gas flow with 10% v/v Nitrogen contents. Such an exposure is made at ambient temperature for a time comprised between 10 and 30 minutes, preferably 20 minutes, according to the specific purpose to be achieved. The ozone flow can be obtained from a ozonizer of the type that is commonly found on the market.

The ozone treatment system can be made continuously and simultaneously on several articles in a dynamic way. In this case the articles are positioned on a conveyor belt that passes through a tunnel wherein the ozone flow is fed. A slight depression is created inside the tunnel. Such a depression can be obtained by feeding the Ozone gas at the entrance of the tunnel in the same forward traveling direction as the conveyor belt and by means of extraction at the exit of the tunnel.

The second phase provides for treating the surfaces of the thermoplastic product that were previously exposed to Ozone with an ultraviolet (UV) radiation, the main radiation of which having a wavelength of 254 nanometers. Such a treatment can be made in a tunnel of the same type as the one previously described for 03. However, in this case, ultraviolet (UV) radiation lamps are positioned inside the tunnel. The UV lamps can be commonly found on the market and have an irradiation power of approximately 10 mW/cm² at a distance of 10 cm.

The position of the lamps can vary in height, being preferably parallel to the traveling direction of the conveyor belt, continuously covering the entire length of the conveyor belt inside the tunnel.

The UV treatment can last from 5 to 40 minutes, preferably 30 minutes, according to the bondability to be obtained.

The two treatments must be sequential in case of a weight percentage of white pigments higher than 0.5%: first the 03 treatment and then the UV treatment. In fact, 03 is an excellent filter for the UV radiation that decompose the 03 into 02 and nascent O (as demonstrated by the 03 layer in the Ozonesphere that acts as filter for the UV radiation from the sun). The nascent oxygen is very active as oxidant, its reaction proceeds with radicalic course in concurrence and is very similar to the effect caused by the UV radiation, and the two effects are summed.

According to the process of the invention, without the co-participation of the UV radiation, the 03 treatment proceeds by ionic way, attacks the double bonds of Butadiene and of other reactive groups, modifying their nature with the formation of polar products, such as aldehydes, acids and hydroxyls, and the following UV treatment is summed to this effect, making the surface suitable for adhesion with PolyUrethane adhesives only. The product according to the invention is surface-modified by means of a sequential 03 and UV treatment in order to make it suitable for adhesion with PolyUrethane adhesives, without requiring a previous Chlorination treatment.

It must be considered that, according to the prior art, the white or whitish color of footwear soles is obtained by using a mineral pigment - TiO2 - at a high concentration, at least 1 % in weight. However, TiO2 is photoactive and therefore it interferes with the penetration of both solar and ultraviolet radiation. Moreover, this type of white pigment also exerts a phenomenon of almost total reflection with respect to both the luminous and the UV radiation. Furthermore, the product may contain various anti-UV additives that are suitable for blocking the radiation necessary for the formation of polar groups by double unsaturated bonds that are encountered both in the SBS and PolyButadiene polymers.

This problem is solved by the present invention in two different ways:

- by using only an UV treatment in case of a low weight percentage of white pigments (max. 0.5%);

- by using a sequential treatment, first with 03 and then with UV, in case of a high weight percentage of white pigments (higher than 0.5%).

If photoactive white pigments, such as Titanium Dioxide (TiO2) are used, the TiO2 weight percentage must not exceed 1 %. In the case of non photoactive white pigments, such as zinc sulfide (ZnS) and/or barium sulfate (BaSO4), the weight percentage can exceed 1 %.

Numerous variations and modifications can be made to the present embodiments of the invention, which are within the reach of an expert of the field, falling in any case within the scope of the invention as disclosed by the attached claims.

Claims

1 . Thermoplastic product for manufacturing footwear parts obtained by injection molding of an extruded product comprising:

- a Styrene-Butadiene-Styrene (SBS) block copolymer

- lubricant, and

- white pigments;

wherein said molded thermoplastic product was submitted to:

A) an ultraviolet (UV) radiation treatment, when the weight percentage of white pigments is lower than or equal to 0.5%;

B) sequentially, first to an exposure treatment to an Ozone (03) gas flow and then to an ultraviolet (UV) radiation treatment, when the weight percentage of white pigments is higher than 0.5%;

in such manner to obtain a thermoplastic product having a bondability with polyurethane adhesive higher than 4N/mm measured in compliance with the UNI EN 1392 standard.

2. The thermoplastic product of claim 1 , wherein said extruded product also comprises Syndiotactic 1 ,2 PolyButadiene in a weight percentage comprised between 20% and 35%.

3. The thermoplastic product of claim 1 or 2, wherein said extruded product comprises titanium dioxide (TiO2) white pigments in a weight percentage comprised between 0.1 % and 1 %.

4. The thermoplastic product of any one of the preceding claims, wherein said extruded product comprises non-photo active white pigments different from titanium dioxide (TiO2).

5. The thermoplastic product of claim 4, wherein said non photoactive white pigments that are different from titanium dioxide (TiO2) are in a weight percentage higher than 1 %.

6. The thermoplastic product of claim 4 or 5, wherein said non photoactive white pigments that are different from titanium dioxide (TiO2) comprise zinc sulfide (ZnS) and/or barium sulfate (BaSO4).

7. The thermoplastic product of any one of the preceding claims, wherein said thermoplastic product is a footwear sole.

8. Manufacturing process of a thermoplastic product for footwear parts, comprising the following steps:

- extrusion of a mixture comprising a Styrene-Butadiene-Styrene (SBS) block copolymer, lubricant and white pigments in such manner to obtain an extruded product;

- injection molding of the extruded product in order to obtain a molded thermoplastic product;

wherein said molded thermoplastic product is submitted to

B) sequentially, first to an exposure treatment to a Ozone (03) gas flow and then to an ultraviolet (UV) radiation treatment, when the weight percentage of white pigments is higher than 0.5%;

in such manner to obtain a thermoplastic product with bondability with polyurethane adhesive higher than 4N/mm measured according to the UNI EN 1392 standard.

9. The process of claim 8, wherein said Styrene-Butadiene-Styrene (SBS) block copolymer is mixed with Syndiotactic 1 ,2 Polybutadiene in a weight percentage comprised between 20% and 35%.

10. The process of claim 8 or 9, wherein said white pigments comprise titanium dioxide (TiO2) in a weight percentage comprised between 0.1 % and 1 %.

1 1 . The process of any one of claims 8 to 10, wherein said white pigments comprise non-photo active white pigments different from titanium dioxide (TiO2).

12. The process of claim 1 1 , wherein said non photoactive white pigments that are different from titanium dioxide (TiO2) are in a weight percentage higher than 1 %.

13. The process of claim 1 1 or 12, wherein said non photoactive white pigments that are different from titanium dioxide (TiO2) comprise zinc sulfide (ZnS) and/or barium sulfate (BaSO4).

14. The process of any one of claims 8 to 13, wherein said thermoplastic product is exposed to UV radiation for a time comprised between 5 and 40 minutes.

15. The process of any one of claims 8 to 13, wherein said thermoplastic product is exposed to an Ozone (03) gas flow for a time comprised between 10 and 30 minutes.