Rubber coating composition for application as a coating to a substrate and a rubber solution

Abstract

The present application relates to a rubber coating composition for application as a coating to a substrate. The rubber coating composition derives from a rubber solution, which is suitable for use as a coating for different substrates.

Description

RUBBER COATING COMPOSITION FOR APPLICATION AS A COATING TO A SUBSTRATE AND A RUBBER SOLUTION

[0001] This application relates to a rubber coating composition for application as coating to a substrate and a rubber solution.

[0002] The population growth of recent decades has led to an ever-increasing waste production. Worldwide, around one billion vehicle tires reach the end of their life in terms of performance and safety each year [1]. In 1999, the accumulation of end-of-life tires (ELTs) in landfills was banned in Europe due to environmental and health risks. Since then, sustainable alternatives that promote the management and recovery of this waste have been encouraged [2,3].

[0003] The production of rubber granulates, mainly used in sport and recreational fields, is the most common method of tire recycling [4]. However, this end-market is expected to be regulated and limited due to an increasing concern regarding microplastic accumulation and release of harmful chemicals [5-7]. Thus, the creation of alternatives is necessary.

[0004] Natural and synthetic rubber have been largely used as raw materials for surface coating, along with solvents and chemical agents to facilitate its application. The resulting coatings can present different properties and are mainly used in construction applications [8-15]. On the other hand, recycled rubber from tires presents an additional challenge because of the vulcanization process. Before being used in tires, rubber must be vulcanized, i.e., subjected to sulfur treatment, to resist the extreme temperature and abrasion conditions. Due to vulcanized rubber's high chemical and thermomechanical stability, the subsequent recovery and use of the recycled material is complex.

[0005] To overcome this limitation, Tran et al. (2021)

[0016] suggested the addition of terminal functional groups to the rubber polymer chain, to coat surfaces containing silica through the formation of covalent bonds. In a simpler yet effective approach, Durães et al. (2022) [1] and Lamy-Mendes et al. (2022)

[0017] proposed the dissolution of vulcanized rubber granulate in an alcoholic solution of peracetic acid, resulting in a rubber sol with colloidal particles, that was later used in the synthesis of silica-rubber aerogel composites for thermal insulation. However, the studies focused on producing and characterizing the aerogel composites and did not characterize the rubber sol. In addition, the use of the rubber solution for coating was not explored and thus coated materials were not developed or characterized.

[0006] In this context, some studies have proposed the valorization of recycled rubber as coatings, with interesting properties such as impermeability and anti-corrosion, but using more complex strategies to overcome the stability of vulcanized rubber [18-20], namely chemical devulcanization techniques or the addition of cross-linkers.

[0007] To further exploit the advantages of the more straightforward technology of Durães et al. (2022) [1, 17] for dissolving rubber, this patent presents the application of liquid rubber as waterproof coatings through a simple and low-cost procedure. The full characterization of the liquid rubber and the coated substrates has shown that the apolar chains of rubber ensure a waterproofing character of the coating, while the polar functional groups provided by the oxidation with peracetic acid secure the adhesion of the coating to diversified substrates (metals, polymers, glass, wood). This coating is therefore versatile and presents a novel composition compared to existing technologies.

[0008] The present application relates to a rubber coating composition for application as a coating to a substrate, comprising dissolved oxidized rubber, wherein the elemental composition of the resulting coating is:

[0009] Carbon in a quantity between 55-80 wt%

[0010] Oxygen in a quantity between 20-30 wt%

[0011] Sulfur in a quantity between 1-3 wt%.

[0012] In one embodiment, the rubber coating composition is obtained from a rubber solution comprising oxidized rubber in a quantity between 0.6 and 6.5% w / v, a alcohol in a quantity between 60 and 98% v / v, an oxidizing agent in a quantity between 0.83 and 1.05% w / v.

[0013] In one embodiment, the substrate is selected from wood, glass, aluminum, steel, stainless steel, polypropylene, polyvinyl chloride, polystyrene, expanded polyethylene or polycarbonate.

[0014] The application also relates to a rubber solution comprising:

[0015] Dissolved oxidized rubber in a quantity between 0.6 and 6.5% w / v;

[0016] Alcohol in a quantity between 60 and 98% v / v;

[0017] Oxidizing agent in a quantity between 0.83 and 1.05% w / v.

[0018] In one embodiment, the alcohol is selected from ethanol, methanol, n-propanol, isopropanol, or mixtures thereof.

[0019] In one embodiment, the rubber is obtained from rubber granules of vulcanized rubber mixtures of different polymeric basis, such as Natural Rubber and Styrene-Butadiene Rubber.

[0020] The application also relates to the use of the rubber solution for application as a coating to a substrate selected from wood, glass, aluminum, steel, stainless steel, polypropylene, polyvinyl chloride, polystyrene, expanded polyethylene or polycarbonate.General description

[0021] The present application discloses a rubber coating composition for application as a coating in a substrate. The rubber coating composition is derived from a rubber solution, and is fully characterized in its elemental composition. The rubber solution is obtained from recycled rubber granules dissolved in an alcohol solution comprising an oxidizing agent.

[0022] The oxidation observed in the dissolution process of the rubber promotes the interaction of the obtained rubber solution with different substrates, allowing its application as a coating. It was found that when this rubber solution, as a coating composition, is applied on different substrates, it provides a hydrophobic, smooth, thoroughly connected, and homogeneous rubber coating of low thickness covering the substrate and making it waterproof. The additional hysteresis friction provided by the rubber coating also grants grip to the substrate.

[0023] For easier understanding of this application, figures are attached in the annex that represent the preferred forms of implementation, which nevertheless are not intended to limit the technique disclosed herein.

[0024] shows (a) Original wood substrate. Wood substrate after application of (b) 1 and (c) 3 layers of rubber coating composition.

[0025] shows SEM images of rubber coating composition on glass substrate: (a) dripping method, magnified in (b); and (c) film applicator method, magnified in (d).

[0026] shows SEM images of (a) rubber coating on aluminum substrate, magnified in (b); (c) rubber coating on stainless steel substrate; and (d) rubber coating on polypropylene substrate.

[0027] shows scratch tests of glass substrate with (a) 1 and (b) 3 layers of rubber coating obtained by dripping method and (c) 3 layers of rubber coating obtained by film applicator method.

[0028] shows signals of corrosion in steel substrate after coating.

[0029] shows the evolution of coefficient of friction (COF) throughout scratch test in glass with 1 layer of rubber coating, obtained by dripping method. Dashed black curve is the moving average calculated with 500 points and dashed red bar is the point where coating failure was first observed.

[0030] Now, preferred embodiments of the present application will be described in detail with reference to the annexed drawings. However, they are not intended to limit the scope of the invention.

[0031] The rubber solution is obtained by dissolving rubber granules with a particle diameter of less than 1 mm in a solution comprising an alcohol with a concentration between 85 and 95% v / v, and further comprising an oxidizing agent with a concentration between 2.5% and 7.5% v / v. The solution is stirred for a time between 1 and 30 hours at a temperature between 15 and 30ºC. The solution is then filtered to remove non-dissolved additives originating from the rubber. The rubber granules can be recycled and may be vulcanized.

[0032] In one embodiment, the rubber granules are sourced from tire rubber or vulcanized rubber mixtures of different polymeric basis, such as Natural Rubber (NR) and Styrene-Butadiene Rubber (SBR), with varying proportions and tire additives.

[0033] The rubber solution of the present application comprises:

[0034] Dissolved oxidized rubber in a quantity between 0.6 and 6.5% w / v;

[0035] Alcohol in a quantity between 60 and 98% v / v;

[0036] Oxidizing agent in a quantity between 0.83 and 1.05% w / v.

[0037] In one embodiment, the alcohol is selected from, but not limited to, ethanol, methanol, n-propanol, isopropanol, or mixtures thereof.

[0038] In one embodiment, the oxidizing agent is selected from paracetic acid.

[0039] In one embodiment, the rubber solution is suitable to be applied as a coating to a substrate. The substrate can be selected from, but not limited to, wood, glass, aluminum, steel, stainless steel, polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), expanded polyethylene (EPE) or polycarbonate, among others.

[0040] The dissolution of rubber is observed in the first hours of contact with the oxidizing agent in the alcoholic solvent. The rubber granulates are gradually destroyed and the solution changes its color into black. The dissolution is achieved due to the oxidation of the rubber chains, consuming the oxidizing agent almost completely. At the end of the dissolution step, it is possible to observe the non-dissolved rubber and additives (from tires) dispersed as particles in the black solution. After filtration, the rubber solution is easily applied on substrates to obtain coated surfaces.

[0041] A rubber coating composition is then derived from the rubber solution.

[0042] The rubber coating composition for application as a coating to a substrate comprises dissolved oxidized rubber, wherein the elemental composition of the resulting coating is:

[0043] Carbon in a quantity between 55-80 wt%

[0044] Oxygen in a quantity between 20-30 wt%

[0045] Sulfur in a quantity between 1-3 wt%.

[0046] The rubber coating composition is obtained from a rubber solution comprising oxidized rubber in a quantity between 0.6 and 6.5% w / v, an alcohol in a quantity between 60 and 98% v / v, an oxidizing agent in a quantity between 0.83-1.05% w / v.

[0047] The resulting coating is formed by evaporation of the alcohol.

[0048] In one embodiment, the alcohol is selected from, but not limited to, ethanol, methanol, n-propanol, isopropanol, or mixtures thereof.

[0049] In one embodiment, the oxidizing agent is selected from paracetic acid.

[0050] In one embodiment, other elements such as hydrogen, sodium, fluorine, magnesium, aluminum, silicon and zinc can also be part of the rubber coating composition.

[0051] In one embodiment, the substrate is selected from, but not limited to, wood, glass, aluminum, steel, stainless steel, polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), expanded polyethylene (EPE) or polycarbonate, among others.

[0052] In one embodiment, the methods to apply the rubber coating composition as a coating in surfaces are selected from, but not limited to, manual application by pouring the solution, or with manual or automatic film applicators.

[0053] The rubber coating composition presents a dual behavior. The oxidation of the rubber chains during dissolution facilitates the interaction between the solution and different substrates, allowing the adhesion of a rubber coating when the solution is applied to a surface and then dried. Due to the apolar part of the rubber chains, the coating presents a hydrophobic behavior. The rubber layers are also closely connected and thoroughly cover the surface, resulting in a waterproof coating on the substrate. The distinctive rubber effect of hysteresis friction is also present in the coating, providing it with grip. The smoothness, homogeneity and low thickness of the coating applied with a film applicator are also advantageous features for applications in which the visual aspect is important.

[0054] The circular economy approach of the proposed rubber solution and coating is also an attractive aspect, due to the use of recycled rubber granulates as raw material. The technology constitutes an alternative path for waste management of ELTs.Examples

[0055] 1. Materials

[0056] Recycled rubber granulates (diameter < 0.8 mm, Genan), ethanol (99% vol., C2H5OH, Valente e Ribeiro Lda.), peracetic acid (38-40%, CH3CO3H, Merck), sodium hydroxide (98.7%, NaOH, Fisher Chemical), sulfuric acid (>95%, H2SO4, Fisher Chemical), Ferroin solution (0.025 M, C36H24FeN6O4S, PanReac AppliChem), cerium(IV) sulfate (0.1 N standardized solution, Ce(SO4)2, Thermo Scientific), potassium iodide (>= 99.5%, KI, Fisher Chemical), maize starch (general purpose grade, (C6H10O5)n, Fisher Chemical) and sodium thiosulfate (0.1 N standardized solution, Na2S2O3, Thermo Scientific) were used as purchased, without additional purification. Uniform and flat rectangular pieces of different materials were used as substrates for coating, including wood, glass, aluminum, steel, stainless steel, polypropylene, polyvinyl chloride (PVC), polystyrene, expanded polyethylene (EPE) and polycarbonate, among other possible metallic, polymeric or ceramic substrates. Surface areas of the tested substrates varied between 50-150 cm2, but larger substrates can also be used.

[0057] 2. Preparation of the rubber solution

[0058] The first step is the dissolution of the rubber granulates. For that, 0.5 g of rubber granules was dissolved in 10 mL of a 5% peracetic acid solution with ethanol as solvent, resulting in a rubber concentration in solution of 5% w / v.

[0059] The mixture was stirred at 200 rpm for 24 h, at a temperature between 15 and 30ºC [1,17]. After that, the rubber solution was separated from the non-dissolved tire additives by vacuum filtration (particle retention of filter: 11 or 22 µm, with the yield of separated dissolved rubber in solution increasing with the size of the filter).

[0060] 3. Application of the solution as a coating on different substrates

[0061] Two coating methods were tested. In the first one, the rubber solution was slowly poured into the top surface of each substrate to obtain a fine layer of rubber, using a plastic Pasteur pipette (referred to as “dripping method”). In the second one, a film applicator (Elcometer 3570 / 1 Micrometric Film Applicator) was used to apply the rubber solution on the top surface of each substrate, controlling the thickness of the rubber layer (referred to as “film applicator method”). This applicator can be used in manual or automatic modes. After the solution deposition, the substrate was dried for 6-48 h, preferably 24 h, at 20-50 ºC, preferably 30 ºC, resulting in a dried rubber layer covering the entire surface by this solvent casting procedure. The procedure was repeated to obtain multiple layers of rubber coating to ensure complete cover and impermeabilization. One to three layers were tested, but there is no limitation in the number of layers that can be applied.

[0062] 4. Characterization of the rubber solution

[0063] The quantification of peracetic acid in the rubber solution (after oxidation of rubber) was performed with two consecutive titrations. First, the analyte solution was prepared by adding 1.25 mL of rubber solution and 4.0 mL of sodium hydroxide solution (0.1 mol L-1) to 450 mL of deionized water. Then, pH was adjusted to 3.5 with the sodium hydroxide solution and the volume was completed with deionized water until 500 mL. For the first titration, 30 mL of the analyte solution was mixed with 20 mL of deionized water, 5 mL of sulfuric acid solution (10%) and 3 drops of Ferroin indicator, and the obtained solution was immediately titrated with cerium(IV) sulfate solution (0.1 N) until a blue color was observed. Then, 0.5-1.0 g of potassium iodide and 5 mL of starch solution (5 g L-1) were added to the peracetic acid solution, and it was immediately titrated with a sodium thiosulfate solution (0.1 N) until a bright orange color was observed. The concentration of peracetic acid was calculated with the volume of sodium thiosulfate solution used.

[0064] 5. Characterization of obtained coatings

[0065] The substrates were weighed before and after the application of the rubber coating to compare the mass difference. The thickness of the rubber coating was determined by measuring the thickness of the substrate before and after applying the rubber coating, with an electronic digital micrometer (0-25 mm, 0.001 mm) and a thickness gauge (0-12 mm, 0.0005 mm).

[0066] The hydrophobicity was evaluated by measuring the contact angle with water, before and after applying the rubber coating. A drop of water of 15 µL was added to the surface and the contact angle was measured with the image processing program ImageJ.

[0067] The composition of the rubber layer was determined with elemental analysis (EA 1108 CHNS-O, Fision Instruments), in terms of C, N, H and S elements. This analysis was also performed for the original rubber and the non-dissolved tire additives retained in the filter (see section 2) for comparison.

[0068] Scratch tests were performed with a multifunctional tribometer (MFT-5000, Rtec instruments) to assess coating adhesion. A standard Rockwell C diamond indenter with 0.2 mm of radius was used. The test was performed with progressive loading from 50 mN to 850 mN, a total scratch distance of 16 mm, and a typical sliding speed of 0.1666 mm s-1. The coefficient of friction (COF) was measured throughout the test and the scratches were observed with panoramic imaging using an optical microscope with a 10x objective.

[0069] Scanning electron microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS) was performed to visualize the coating morphology and characterize its composition, using a Compact / VPCompact FESEM (Zeiss Merlin) microscope, with an XMaxN from Oxford for EDS. In some observation it was also possible to inspect the thickness of the coatings.

[0070] 6. Discussion of results

[0071] After 24 h of dissolution, the composition of the rubber solution was between 60-98% v / v of alcohol, (e.g. 87.5% v / v of ethanol), between 0.6-6.5 % w / v of rubber (e.g. 3.1% w / v of dissolved oxidized rubber), between 0.83-1.05 % w / v of peracetic acid (e.g. 0.94% w / v of peracetic acid), and other substances with minor concentrations including acetic acid, hydrogen peroxide and water. The original rubber granulates presented approximately 60% of rubber, along with additives, and the dissolution method was capable of dissolving 51% of the rubber granulates, suggesting that nearly all rubber was successfully dissolved.

[0072] Tables 1, 2 and 3 show the elemental composition of the recycled rubber granulates, the rubber coating and the non-dissolved substances that remained in the filter after filtration (presented as “non-dissolved tire additives” – carbon black, silica, metal-containing phases), determined by elemental analysis and SEM-EDS.

[0073] The increase of oxygen in the non-dissolved rubber tires and mostly in the rubber coating, in comparison to recycled rubber granulates, is observed in Table 2. It is explained by the oxidation of the rubber chains by peracetic acid during dissolution, leading to the creation of new functional groups that increase the reactivity of rubber and reduce slightly his hydrophobicity. Although oxygen was not directly determined by elemental analysis (Table 1), the significant decrease of the total percentage of rubber carbon also indicates the increased presence of another element, likely oxygen.

[0074] Table 1. Elemental composition (w / w) of recycled rubber granulates, rubber coating and non-dissolved tire additives determined by elemental analysis.N / %C / %H / %S / %Total / %Recycled rubber granulates0.448 ± 0.00480 ± 17.6 ± 0.22.1 ± 0.190Rubber coating0.55 ± 0.0560 ± 56.4 ± 0.63 ± 170Non-dissolved tire additives0.42 ± 0.0485 ± 46.4 ± 0.31.9 ± 0.593

[0075] Table 2. Elemental composition (w / w) of recycled rubber granulates, rubber coating and non-dissolved tire additives determined by SEM-EDS (only majoritarian elements).C / %O / %S / %Total / %Recycled rubber granulates85 ± 56 ± 21.6 ± 0.393Rubber coating76.2 ± 0.622 ± 11.00 ± 0.0289Non-dissolved tire additives80 ± 111.2 ± 0.51.9 ± 0.193

[0076] Table 3. Elemental composition (w / w) of recycled rubber granulates, rubber coating and non-dissolved tire additives determined by SEM-EDS (other elements).Recycled rubber granulatesRubber coatingNon-dissolved tire additivesF / %-0.5 ± 0.21.9 ± 0.8Na / %0.19 ± 0.030.15 ± 0.000.15 ± 0.02Mg / %0.19 ± 0.060.04 ± 0.000.10 ± 0.03Al / %0.12 ± 0.070.10 ± 0.070.23 ± 0.08Si / %0.7 ± 0.60.2 ± 0.11.44 ± 0.18Zn / %1.74 ± 0.830.8 ± 0.31.42 ± 0.08K / %0.14 ± 0.05-0.11 ± 0.03Ca / %0.34 ± 0.18-0.54 ± 0.08Fe / %4 ± 4-0.7 ± 0.2Mn %0.21 ± 0.00--

[0077] Both elemental analysis and SEM-EDS (Tables 1 and 2) show the decrease in the concentration of carbon in the rubber coating sample, due to the separation of carbon black additive, which is not dissolved and remains in the filter along with other non-dissolved tire additives and non-dissolved rubber with higher colloid size. The increase of oxygen (as observed in Table 2) also contributes to the mathematical decrease of the carbon percentage in the sample.

[0078] The concentration of sulfur is approximately similar in all samples (Tables 1 and 2), indicating that the degree of vulcanization is not significantly affected by the dissolution process. The exception is the higher sulfur concentration in non-dissolved tire additives measured by SEM-EDS, which can be attributed to a specific region with a higher proportion of sulfur in the sample. In fact, the quantification of elements with low amounts by SEM-EDS should be seen as semi-quantitative, due to the limited representativeness of the analyzed areas.

[0079] Regarding the other elements shown in Table 3, the higher percentages of Al, Mg and, above all, Zn and Si confirm that most tire additives were retained in the filter. Again, it is important to note that SEM-SDS focuses only on specific regions of the samples. For example, particles with different morphology were found in the non-dissolved tire additives, with significantly higher percentages of Zn.

[0080] Except for porous substrates, the obtained coatings presented the same opaqueness and black color after drying. Wood and EPE partially absorbed the liquid rubber, and cross-sectional SEM images showed a penetration of up to 350 µm in wood. The opaque and black aspect gradually increased as more layers were added, as can be seen in. The film applicator allowed the achievement of more smooth and homogeneous coatings.

[0081] The SEM images ofallow the comparison between the two application methods based on the coating morphology (on a glass substrate). A smoother surface is obtained with the film applicator, as already observed in the macroscopic scale. On both surfaces, spherical cavities of different sizes can be observed. They can be explained by the formation of solvent bubbles during drying that are either destroyed or covered by the subsequent layer of coating.

[0082] The other coated substrates present similar morphology, but with varying uniformity of the coating. For instance,(a) and (b) shows aluminum substrates coated with the film applicator.(c) and (d), on the other hand, shows how the coating adheres to stainless steel and polypropylene substrates, respectively. Especially in the case of stainless steel (see(c)), it can be observed that the coating is fixed to the substrate.

[0083] The rubber coating increased the hydrophobicity of all substrates, as observed by the variation of the contact angle in Table 4. The use of the film applicator led to higher contact angles in most of the substrates, which can be explained by the homogeneity of the coating with this application method, leading to an even hydrophobic rubber coating on top of the substrate. In the case of EPE, it was not possible to apply the liquid rubber with the film applicator due to the softness of the material.

[0084] Table 4. Contact angle between original substrates and water, and rubber coating (3 layers) and water, per substrate and application method.Contact angle / ˚Original substrateDrippingFilm applicatorWood(immediately absorbed)96.4 ± 0.397.7 ± 0.2Glass43.8 ± 0.278.4 ± 0.281.6 ± 0.2Aluminum74.3 ± 0.182.5 c 0.283.5 ± 0.2Steel72.8 ± 0.180.9 ± 0.182.3 ± 0.2Stainless steel63.3 ± 0.282.5 ±0.286.9 ± 0.1Polypropylene70.0 ± 0.272.3 ± 0.379.9 ± 0.2PVC69.8 ± 0.180.8 ± 0.284.4 ± 0.2Polystyrene73.5 ± 0.374.4 ± 0.375.6 ± 0.2Polycarbonate69.3 ± 0.274.1 ± 0.178.7 ± 0.2EPE64.2 ± 0.269.5 ± 0.1-

[0085] Comparing the rubber coatings (Table 4) with the original rubber (contact angle of 117.5 ± 0.8˚), the lower contact angle observed in the coatings can be justified by the oxidation of the rubber chains during dissolution, reducing its hydrophobicity, but retaining an intermediate contact angle. Nevertheless, the rubber coatings are clearly more hydrophobic in comparison with the original surfaces. This duality allows the interaction and thus adhesion of the coating to the substrates (with the polar part), and, at the same time, makes the substrates waterproof (with the apolar part).

[0086] The mass variation and the coating thickness are shown in Table 5 comparing both application methods. The film applicator allowed to obtain coatings with comparable mass variation, while the dripping method led to irregular coatings. In the case of wood, a negative mass variation is observed, probably because the contact of wood with the alcoholic solution of peracetic acid provokes the release of wood extractives. The thickness was also more controllable when using the film applicator, and reached significantly lower values for every substrate.

[0087] Although it is not the only reason, the use of a more reliable measuring instrument (thickness gauge) can partially explain the lower variation. In the case of EPE, it was not possible to compare the thickness due to the soft nature of the material.

[0088] Table 5. Mass variation and thickness of rubber coating (3 layers) per substrate and application method. The mass variation was calculated as the difference between the mass of the substrate after and before applying the coating divided by the top surface area covered by the coating.Mass variation / (g cm-2)Coating thickness / µmDrippingFilm applicatorDripping(a)Film applicator(b)Wood-0.0116-0.00652212Glass0.00510.00164120Aluminum0.00660.001011523Steel0.00990.001112334Stainless steel0.00400.001011412Polypropylene0.00570.00128323PVC0.00650.00136825polystyrene0.00370.00104523Polycarbonate0.00170.00178418EPE0.0046---

[0089] (a)Thickness measured with electronic digital micrometer.(b)Thickness measured with thickness gauge.

[0090] The thickness of the coating was also measured with SEM, but resulted in lower values in comparison with the thickness of Table 5. In the case of the glass substrate, the thickness measured in the SEM images was 15 ± 3 µm for the dripping method, and 13 ± 4 µm for the film applicator method. Since the thickness was measured on scraped parts of the sample, it is possible that these values do not represent the entire coating. Either way, it was possible to observe that the thickness of the coating varies slightly throughout the surface, and the film applicator allows to obtain coatings with lower thickness.

[0091] Scratch tests were then performed to assess the coating adhesion to the substrates.shows the comparison between the scratch tests on coated glass substrate. The rubber coating is more easily removed in the case of application of 3 layers with film applicator (in(b)) and 1 layer with dripping method (in(a)). Adding more layers of coating by dripping method avoids the coating removal, without clear failure points, and only the scratch is visible. Signals of corrosion were observed in the case of steel (light orange color around the scratch), as seen in, however, they were not present in stainless steel.

[0092] The critical load, under which failure of the coating occurs, is shown in Table 5. Comparing the results, it can be concluded that, regarding the dripping method, the addition of more layers hampers the removal of the coating, demonstrated either by the increase of the critical load, i.e., a higher load is required to provoke failure of the coating, or by the lack of a failure point. Comparing samples with 3 layers applied by the two different application methods, the film applicator leads to coatings more prone to failure, which is justified by the lower thickness of these coatings. Comparing the different substrates, the adhesion varied according to the application method. In general, plastic substrates led to coatings easier to remove, while glass and metal substrates resulted in coatings with better adhesion, with few exceptions.

[0093] Table 6. Critical load of scratch test for all substrates, comparing 1 and 3 layers of coating.Critical load / mNDrippingFilm applicator1 layer3 layers3 layersWood(a)(a)(b)Glass502 ± 67(a)403 ± 17Aluminum(a)(a)561 ± 134Steel135 ± 21408 ± 30416 ± 23Stainless steel452 ± 2(a)518 ± 45Polypropylene223 ± 60659 ± 19375 ± 71PVC(a)(a)371 ± 6Polystyrene(a)(a)(a)Polycarbonate742 ± 37(a)(b)

[0094] (a) Critical load was not determined because the scratch did not present a clear failure point.

[0095] (b) Scratch test was not performed.

[0096] Regarding the evolution of the COF in the scratch tests, a similar trend was observed for the different substrates. The average COF increased for loads higher than the critical load, from which the coating is removed, i.e., when the indenter is presumably in contact with the substrate. The lower COF of the coated substrates in comparison with the original substrates indicates a slight decrease in friction, as can be seen in, and as expected due to the soft nature of rubber.

[0097] However, the additional hysteresis friction provided by the rubber coating is an important feature for applications that require grip, such as sports equipment grips. It is, therefore, one of the possible applications of the rubber coating developed in this work.References

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[0118] This description is of course not in any way restricted to the forms of implementation presented herein and any person with an average knowledge of the area can provide many possibilities for modification thereof without departing from the general idea as defined by the claims. The preferred forms of implementation described above can obviously be combined with each other. The following claims further define the preferred forms of implementation.

Claims

A rubber coating composition for application as a coating to a substrate, comprising dissolved oxidized rubber, wherein the elemental composition of the resulting coating is:Carbon in a quantity between 55-80 wt%Oxygen in a quantity between 20-30 wt%Sulfur in a quantity between 1-3 wt%.The rubber coating composition according to the previous claim, wherein the rubber coating composition is obtained from a rubber solution comprising oxidized rubber in a quantity between 0.6 and 6.5% w / v, an alcohol in a quantity between 60 and 98% v / v, an oxidizing agent in a quantity between 0.83 and 1.05% w / v.The rubber coating composition according to the previous claim, wherein the substrate is selected from wood, glass, aluminum, steel, stainless steel, polypropylene, polyvinyl chloride, polystyrene, expanded polyethylene or polycarbonate.A rubber solution comprising:Dissolved oxidized rubber in a quantity between 0.6 and 6.5% w / v;Alcohol in a quantity between 60 and 98% v / v;Oxidizing agent in a quantity between 0.83 and 1.05% w / v.The rubber solution according to the previous claim, wherein the alcohol is selected from ethanol, methanol, n-propanol, isopropanol, or mixtures thereof.The rubber solution according to any of the claims 4 to 5, wherein the rubber is obtained from rubber granules of vulcanized rubber mixtures of different polymeric basis, such as Natural Rubber and Styrene-Butadiene Rubber.Use of the rubber solution described in any of the claims 4 to 6, for application as a coating to a substrate selected from wood, glass, aluminum, steel, stainless steel, polypropylene, polyvinyl chloride, polystyrene, expanded polyethylene or polycarbonate.

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