VULCANIZATION SYSTEM DESCRIPTION

Technical field of the invention

The present invention relates to a polyurethane material wherein the surface thereof is treated in such a way as to improve the adhesion to a polymeric material with a cross-linkable unsaturated chain and a vulcanizing system. The invention finds particular application in the manufacture of pneumatic tyres wherein a layer of polyurethane is inserted in order to reduce the noise generated by vehicles.

Background

Polyurethane is a polymer widely used in various industries due to the many advantageous properties thereof. One of the most interesting properties of expanded polyurethane is acoustic insulation, i.e., the ability to be able to isolate sounds. For this reason, during recent years, an effort has been made to use polyurethane based materials in order to try to eliminate, or at least reduce, the noise generated by vehicles, in particular the noise generated by the rolling of pneumatic tyres. However, the application of polyurethane materials in pneumatic tyres has been found to be extremely limited due to the lack of adhesion of this type of material to those materials commonly used in the manufacture of a pneumatic tyre.

The patent publications EP1950057 A1 and US2010038005 A1 describe systems for reducing the noise associated with the rolling of pneumatic tyres, based upon the use of materials made from polyurethane foams that are attached to the inner surface of the pneumatic tyre using mechanical means or using thermoplastic adhesives.

The patent publication EP2423247 A1 describes a particular aqueous resorcinol- formaldehyde-latex dispersion wherein reinforcing fibers are immersed in order to improve the adhesion thereof to cross-linked rubbers or elastomers in pneumatic tyres.

One object of the invention is to provide the means and processes in order to ensure that polyurethane materials with acoustic insulation properties can adhere effectively to those materials used in the construction of a pneumatic tyre. Summary

The technical problem underlying the present invention is therefore that of providing a system for the adhesion of polyurethane layers to polymeric materials with a cross-linkable unsaturated chain and a vulcanizing system such as those commonly used in the compounds for the manufacture of pneumatic tyres.

The object of the present invention is a polyurethane material according to claim 1 and a process for the preparation thereof according to claim 12. Preferred characteristics of the invention are the subject of the dependent claims.

Brief description of the figures

Reference will be made to the figures of the accompanying drawings, wherein:

■ Figure 1 shows a cross-sectional view of a part of the pneumatic tyre according to an embodiment of the present invention;

■ Figure 2 shows a photograph of a detail of the pneumatic tyre according to an embodiment of the present invention;

■ Figure 3 shows a schematic representation of the layout of the internal PBN test;

■ Figure 4 is a graph showing the level of PBN expected at 80 km/h of a standard pneumatic tyre and of a pneumatic tyre manufactured according to the embodiment of Figure 2;

■ Figure 5 is a graph showing a comparison of the representative MIC spectra at 80 km/h of a standard pneumatic tyre and of a pneumatic tyre manufactured according to the embodiment of Figure 2;

■ Figure 6 shows the layer of polyurethane after the treatment in the oven following the application of the RFL solution;

■ Figure 7 is a photograph showing the assembly of the Cellasto® + CPD sandwich as described in the examples at points 1.1 -1.3;

■ Figure 8 shows a diagram of the final layout as described in the examples at points 1.1 -1.3;

■ Figure 9 is a photograph that refers to the ASTM D143 methodology used in the example of point 1 .3;

■ Figure 10 is a photograph showing the lack of adhesion using Cellasto® that is not treated with RFL; ■ Figure 1 1 shows a diagram of a comparison between a conventional pneumatic tyre (Figure 11 A) and the embodiment of Figure 2 (Figure 1 1 B);

■ Figure 12 is a photograph showing the cutting of the layer of Cellasto® for the replacement of the undertread.

Detailed description of the invention

Consistent with the consolidated terminology in the field, within the present context: tread refers to the portion of the pneumatic tyre that is in contact with the road surface. Undertread refers to the portion of the tread compound between the bottom of the tread grooves and the upper part of the layers of fabric that form the carcass of the pneumatic tyre.

Cap ply refers to the upper layer of fabric carcass of the pneumatic tyre.

The term polyurethane (PU) refers to a broad family of polymers wherein the polymer chain is composed of urethane -NH-(C0)-0 bonds.

Belt. The belts of the pneumatic tyre are an assembly of fabrics and/or wires used to reinforce the tread area of the pneumatic tyre.

The present invention relates to a polyurethane material wherein at least a part of the surface thereof, and preferably the entire surface thereof, is treated with a composition with adhesive properties in relation to a cross-linkable elastomeric element (A) and in relation to a polyurethane material (B).

According to the invention, the treated polyurethane material is chemically modified on the treated surface by means of the chemical bonding of the polyurethane with a first component of the composition, that is able to bind itself to the polyurethane material (B); a second component of the composition that is able to chemically bind itself to a cross-linkable elastomeric element (A) remains available for such binding on the modified polyurethane surface.

In other words, the composition of the treatment is able to bind itself on the one hand to the surface of the polyurethane material, and on the other hand it is able to bind itself to a cross-linkable elastomeric element, such as the inner surface of a pneumatic tyre, thus constituting a union between the polyurethane and the pneumatic tyre. The bonding of the polyurethane material with the composition of the treatment consists in a surface modification of the polyurethane which, after such treatment, has an exposed surface that is suitable for the chemical bond with the cross-linkable elastomers. The composition of the treatment according to the invention, therefore, chemically modifies the surface of the polyurethane, rendering it suitable for chemical bonding with a cross-linkable elastomer. For example, the composition of the treatment of the invention will comprise:

a) a chain with a base polymer (C) comprising at least one chemically active site in relation to the polyurethane material (B);

b) a chain with an unsaturated base polymer (D) comprising at least one chemically active site in relation to a cross-linkable elastomeric element (A) and at least one chemically active site in relation to said chain with a base polymer (C). Preferably, the chain with a base polymer (C) comprises at least one hydrogen acceptor/donor site and/or wherein said chain with an unsaturated base polymer (D) comprises at least one hydrogen donor/acceptor site. According to one embodiment, the composition will comprise:

a) a chain with a base polymer with one chemically active site in relation to the polyurethanes;

b) a chain with a base polymer comprising at least one hydrogen acceptor/donor site; and

c) a cross-linkable chain comprising at least one hydrogen acceptor/donor site, i.e., capable of forming a hydrogen bond. The material can, for example, be treated by means of immersion within the composition. According to one embodiment, such a composition is a solution comprising resorcinol, formaldehyde and latex (RFL). For example with a solution of resorcinol, formaldehyde, latex and ammonia. For example with a solution of resorcinol, formaldehyde, latex and ammonia in the following ratios:

The polyurethane may have a closed or open cell structure, preferably the polyurethane will be a microcellular polyurethane elastomer, even more preferably the polyurethane will be used that is marketed by BASF under the trade name Cellasto®.

A second object of the present invention is a product, in particular a pneumatic tyre, comprising a polyurethane material treated as mentioned above, further comprising a polymeric material comprising a cross-linkable unsaturated chain and a vulcanizing system, and wherein said polymeric material adheres to said polyurethane material. In a preferred embodiment, the polyurethane material according to the present invention will be used in the manufacture of a pneumatic tyre 1 in order to decrease the noise generated by rolling. The polyurethane material can be inserted in order to form one or more layers within any one of the portions of the pneumatic tyre that is not in contact with the exterior. The expression "not in contact with the exterior" refers to all of the internal parts of the pneumatic tyre, i.e., not in direct contact with the external environment or with the road surface. For example, as schematically shown in the embodiment of figure 1 the polyurethane layer 4 is positioned between the tread 2 and the layer commonly defined as the cap ply 3. Alternatively, when the cap ply 3 is not present within the pneumatic tyre, the polyurethane layer 4 is positioned between the portion of tread in contact with the exterior and the belts. In the embodiment shown schematically in figure 1 , the portion commonly defined as the undertread comprises or consists in at least one layer of polyurethane material 4 treated as described herein.

The overall thickness of the polyurethane layer 4 will preferably be at least 0.3 mm, even more preferably between 0.5 mm and 10 mm. The tread 2 may be mono- or multicompound, for example, it may consist of three compounds A, B and C such as those shown in the examples.

The pneumatic tyre 1 may comprise all of the other elements that are commonly used in the layout of these products such as for example a body ply, two beads, a tread belt comprising at least two plies, an innerliner and any other layers of additional functional material arranged between the innerliner and the inner cavity of the pneumatic tyre.

A further object of the present invention is a process for the production of a material as described herein comprising a step wherein a polyurethane material is treated, preferably by means of immersion, with a composition comprising:

a) a chain with a base polymer (C) comprising at least one chemically active site in relation to the polyurethane material (B);

b) a chain with an unsaturated base polymer (D) comprising at least one chemically active site in relation to a cross-linkable elastomeric element (A) and at least one chemically active site in relation to said chain with a base polymer (C). According to a preferred embodiment, the composition used in the process is a solution comprising resorcinol, formaldehyde and latex (RFL). The process may provide for an additional step wherein the material is dried in such a way as to remove the solvent and to promote the uniform distribution of the RFL over the entire surface. The drying may for example be performed in an oven at a temperature of at least 100-120 degrees for at least 10-15 minutes.

A further object of the present invention is a process for the production of a pneumatic tyre, wherein during the step of preparing the "green” pneumatic tyre, a layer of the polyurethane material according to any one of the embodiments described herein is inserted into any of the portions of the pneumatic tyre not in contact with the exterior.

In the process described above, said one or more polyurethane layers 4 may be positioned between the tread 2 and the layer commonly defined as the cap ply 3 or, alternatively, when the cap ply 3 is not present within the pneumatic tyre, they may be positioned between the tread portion in contact with the exterior and the belts.

The present invention has heretofore been described with reference to preferred embodiments. It is understood that there may be other embodiments which refer to the same inventive concept and which fall within the scope of the following claims. EXAMPLES

1.1 Description of the selected polyurethane layer

For the polyurethane layer, a high performance microcellular polyurethane elastomer was selected that is marketed by BASF under the trade name Cellasto® and has a thickness of 2.5 mm and a density of 0.6 g/cm ³ .

1 .2 Description of the selected polyurethane layer

The Cellasto® polyurethane layer was initially treated with the resorcinol- formaldehyde-latex solution (RFL) by means of a brush. It was then dried in an oven for 15 minutes at 120 °C in order to remove the solvent and to promote the uniform distribution of the RFL over the entire surface.

The following is the composition of the RFL solution used:

1.3 Tests on a laboratory scale The Cellasto layer was assembled (fig. 7) together with a CPD layer (CPD A/B/C) in a dedicated mold in order to replicate in the laboratory a vulcanization condition similar to that used for the manufacture of a pneumatic tyre.

The composition of the CPD layer (CPD A/B/C) is shown in detail below:

The three Cellasto + CPD sandwiches were then vulcanized in a press for 25 minutes at 160 °C and at 20 bar. The final arrangement of the assembly is depicted in figure 8. After the vulcanization, the vulcanized layers (Cellasto + CPD) were cut into thin sheets and the forces of adhesion between Cellasto/CPD A, Cellasto/CPD B, Cellasto/CPD C were measured according to the ASTM D413 procedure in order to demonstrate the adhesion capacity (fig. 9). For comparative purposes, the same procedure was repeated but in skipping the treatment step with the RFL solution described in paragraph 1.2. Flowever, in this case, there was no adhesion between the Cellasto and each of the CPD layers (figure 10), and it was not possible perform the adhesion test.

The levels of adhesive strength are shown in table 1 and show a clear advantage of the use of the treatment with RFL in improving the adhesion between the rubber and the layer of polyurethane.

Table 1 .

1 .4 Production of the pneumatic tyre On the basis of the laboratory results mentioned above, the aforesaid method was adapted to a passenger car pneumatic tyre (Bridgestone Turanza 225/50R17) in order to also confirm the validity of the results obtained using finished products.

The objective was to replace the compound of the rubber of the undertread with a layer of Cellasto as shown in the diagram of fig. 1 1 .

The Cellasto layer was cut in such a way as to replicate the geometry of a corresponding undertread layer of the pneumatic tyre. The width of the Cellasto® strips was optimized for a better finish, avoiding the trapping of air, and in particular strips of 150 mm and 190 mm in width were used. The treatment with RFL and the subsequent oven drying were performed according to the procedure described at point 1 .2.

The Cellasto layer was then embedded within the layout of the pneumatic tyre during the manufacturing step of the pneumatic tyre. Thereafter the pneumatic tyre was vulcanized at 160 TD for 15 minutes using standard vulcanization settings. After vulcanization the pneumatic tyre was cut open in order to verify the effective adhesion between the Cellasto and the surrounding components (Tread and CPS). Interfaces were observed that were homogeneous and without defect (fig. 2).

EXAMPLE 2 experimental measurements

2.1 Noise emission test

The acoustic evaluation of the pneumatic tyre produced as described in example 1 was performed within a semi-anechoic environment with the dimensions: 8m (L) x 6m (W) x 3.5m (H), ISO 3744 certified (Sound Power Test). The rubber was loaded by means of a pneumatic tyre support onto the drum covered in resin shells that replicate the asphalt used for the pass-by noise (PBN) approval test performed on the vehicle on the track.

The measurement setup is composed of a series of angularly equally spaced microphones for evaluating the directionality of the noise, as shown below. The post processing algorithm calculates the expected external PBN value at 80 km/h. The test described above is schematically represented in figure 3, whilst in figures 4 and 5 the measurements are shown in graph form that were obtained with a conventional pneumatic tyre without a layer of polyurethane and the pneumatic tyre produced according to example 1. The results indicate that the pneumatic tyre manufactured according to the present invention is effective in reducing external noise, in particular: - On the basis of the sound pressure level spectrum, it is clear that it has effective insulating properties insofar as it reduces the inputs from both the geometry of the tread pattern and the roughness of the road.

- In relation to an equivalent volume of a standard compound, it reduces the overall PBN by an additional 0.4 dB.