Electrostatic spray coating process for a substrate or metallic surface intended to receive an elastomer, kit and associated tool

Abstract

A method for coating a substrate or metallic surface intended to receive an elastomer by electrostatic spraying, comprising at least the following steps: preparing a composition A comprising at least one fluoroethylenepropylene (FEP) in micro-powder form; preparing a composition B comprising at least one polyetheretherketone (PEEK) in micro-powder form; intimately mixing the two compositions A and B to form a composition AB (50) in fine powder form; applying the mixture AB obtained in step c) by electrostatic spraying (60) onto the substrate or metallic surface; polymerizing (70) said composition AB. Figure for the abstract: [Fig. 1]

Description

Title of the invention: Method for coating a substrate or metallic surface intended to receive an elastomer by electrostatic spraying, kit and associated tool technical field

[0001] The invention relates to the field of fluoropolymer coatings of substrates or metallic surfaces intended to receive an elastomer such as, for example, tire rubber. In particular, the invention relates to a method for coating tire molds. Prior state of the art

[0002] In this field, it is known to apply a fluoropolymer coating, particularly to tire molds, in order to obtain a surface with anti-adhesion and sliding properties during tire manufacturing. Thus, during the vulcanization of the rubber, it is easier to separate the rubber from the metal surface of the mold.

[0003] The prior art includes, for example, application WO81 / 001375 A1, which discloses a composite material comprising a protective outer layer deposited by sintering and consisting of polytetrafluoroethylene (PTFE) particles dispersed in a polyimide lacquer. The composition comprises 90 to 80% by volume of sand-cured thermosetting polyimide lacquer and 10 to 20% by volume of self-lubricating additives such as PTFE.

[0004] A known solution is to use Xylan® 8840 as a coating. However, molds with such a coating deteriorate rapidly, and their mechanical properties diminish, resulting in a loss of their non-stick and sliding properties. Re-treatments of these coatings are also known, but they can only be carried out three to four times, after which the molds are no longer reusable. These re-treatments consist of pyrolyzing the molds, then sandblasting them, and reapplying the Xylan® 8840 coating. These re-treatments are unsatisfactory, particularly because they involve energy expenditure and damage the molds.

[0005] Furthermore, for certain applications, Xylan® 8840 is unsatisfactory because it does not allow for a sufficiently thin coating layer (30 to 50 µm with Xylan 8840) that retains satisfactory mechanical strength properties. Indeed, due to the counterboring of these molds, it is preferable that the applied coatings be as thin as possible while still having sufficient mechanical strength to not not to be damaged during demolding operations. The use of a thin coating is advantageous in the manufacture of tires with fine grooves.

[0006] For substrates with complex geometries, it is difficult to obtain a uniform and very thin coating less than 20 pm, preferably on the order of 5 to 10 pm, when fluoropolymers in liquid form are used. Similarly, it is not easy to visualize this application, particularly if the liquid composition, comprising at least one fluoropolymer, is transparent. Description of the invention

[0007] The invention aims to remedy the drawbacks of the prior art and in particular to propose an improved coating process.

[0008] To this end, the invention proposes a method for coating a suitable metallic substrate or surface intended to subsequently receive an elastomer such as tire rubber by electrostatic spraying, said method being characterized in that it comprises the following steps:

[0009] a) the preparation of a composition A comprising at least one fluoroethylenepropylene (FEP) in micro-powder form

[0010] b) the preparation of a composition B comprising at least one polyetheretherketone (PEEK) in micro-powder form

[0011] c) mix the two compositions A and B thoroughly so as to form a composition AB in the form of a fine powder

[0012] d) apply by electrostatic spraying the AB mixture obtained in step c) onto the substrate or the metallic surface

[0013] e) polymerization of said composition.

[0014] Advantageously, said substrate or said metallic surface intended to receive an elastomer is made of steel.

[0015] The micro-powder composition (also referred to as composition or mixture AB) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) overcomes the drawbacks of the prior art in terms of slip resistance and non-stick effect, as well as in terms of mechanical strength and coating thickness, while facilitating the application of said composition to the substrate. It also allows for easier cleaning of the molds and thus preserves the lifespan of the molds used.

[0016] Indeed, the projection of a micro-powder is very advantageous compared to a liquid product because it allows for the uniform treatment of parts with complex geometries. Furthermore, the application of the micro-powder mixture creates a whitish effect on the part before polymerization, ensuring proper curing. application over the entire desired surface. This has the primary advantage of not creating excess thickness and also saving on coating.

[0017] Furthermore, these micro-powders are not currently subject to European REACH legislation concerning solvents in products since they are used without solvents, and preferably pure.

[0018] By "suitable metallic surface or substrate" is meant a surface sufficiently resistant to the treatments related to the application and polymerization of the micro-powder composition comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK).

[0019] In particular, the high curing temperatures used to polymerize the fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) mixture do not damage such a surface. For example, a metallic substrate or one with a metallic surface adapted to withstand such curing temperatures, such as 400°C or 380°C, may, among other things, be intended to subsequently receive an elastomer such as tire rubber.

[0020] “Coating”: refers to a layer of material, preferably solid, covering totally or partially a surface in order to protect and / or provide particular physico-chemical properties to said surface.

[0021] “Surface” or “Substrate”: refers to the visible part of a material on which can be used to deposit the AB micro-powder composition (comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK)). Non-limiting examples of substrates include materials used in: aeronautics (e.g., airplanes, helicopters); railways; automobiles; marine and naval vessels; wind energy; passenger spaces (e.g., airplanes, buses, subways); or building construction (exterior or interior surfaces).

[0022] The term "electrostatic spraying" refers to any means of projecting, spraying, or transferring a micro-powder onto a substrate and holding it in place by means of electrostatic charges. This may be achieved using an electrostatic gun, an electrostatic fluidized bath, an electrostatic fluidized bed, or any technically equivalent means known to those skilled in the art.

[0023] According to another feature of the invention, said micro-powder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), preferably between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of FEP relative to the total weight of said composition and between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of PEEK relative to the total weight of said composition.

[0024] According to another embodiment, said micro-powder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) in a proportion of 50 / 50 by weight relative to the total weight of said composition.

[0025] The applicant has discovered, surprisingly, that the FEP / PEEK mixture has the following advantages over state-of-the-art coatings: anti-stick, anti-friction, chemical inertness, electrical insulation, thermal resistance and low thickness.

[0026] Advantageously, said FEP fluoropolymer has a particle size of between approximately 1 and 7 pm, preferably 4 pm.

[0027] Preferably, the fine particles of PEEK polyetheretherketone have a particle size between approximately 2pm and 50pm.

[0028] According to another feature of the invention, step d) of applying said composition is carried out by electrostatic gunning or electrostatic spraying. That is to say, the application means, such as an electrostatic gun, is adapted to spray said composition of the invention onto the surface of said substrate or surface. By way of example, a WAGNER® electrostatic gun can be used as an application means.

[0029] According to another embodiment, step d) of applying said composition is carried out by the use of an electrostatic fluidized bath.

[0030] Preferably, said FEP or PEEK micro-powder used is obtained by evaporating the aqueous phase solution of liquid FEP or PEEK, then ground and / or sieved or by micro-grinding a powder to obtain the usable particle size.

[0031] Advantageously, step e) of polymerization is carried out at a temperature between about 360°C and 420°C, preferably about 380°C, until total polymerization of said fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) mixture, preferably for 1 hour.

[0032] In addition, the process according to the invention may include preliminary preparation steps for step a), such as a thermal penetrant step and / or a masking step and / or a sandblasting step, at least partial, of the surface to be coated.

[0033] Preferably, the process includes, prior to step a), a sandblasting step and / or a degreasing step, at least partial, of the metal surface to be coated.

[0034] The invention also relates to a coating kit using a mixture of at least one fluoropolymer and a polyetheretherketone (PEEK) of a suitable substrate or metallic surface intended to receive an elastomer such as a rubber of tire, configured for the implementation of a process as described above, comprising: - a micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), - a means for applying said composition by electrostatic spraying (60) onto said surface, - preferably a polymerization means (70) of said composition.

[0035] The invention also relates to a substrate or a metallic surface, comprising a surface coated with a micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), obtained by the process defined above and intended to receive an elastomer.

[0036] Furthermore, the invention relates to a composition, preferably in the form of a micro-powder, suitable for carrying out the process according to the invention. That is to say, a homogeneous micro-powder composition comprising at least fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), more particularly a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), preferably in a proportion between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of FEP relative to the total weight of said composition and between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of PEEK relative to the total weight of said composition.

[0037] The object of the present application also relates to the use of such a composition, preferably comprising at least fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) in micro-powder form as a coating in order to obtain a surface having anti-stick, anti-friction, chemical inertness, electrical insulation, thermal resistance and / or slip properties.

[0038] Another object of the invention consists of a mechanical tool comprising a suitable metallic surface coated with composition AB comprising a mixture of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) obtained by the process as described above and intended to receive an elastomer such as a tire rubber.

[0039] More specifically, the invention also relates to a mechanical tool comprising a suitable metallic surface coated with a mixture of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) and intended to receive an elastomer such as a tire rubber, having the following characteristics together or separately: - only one layer of the mixture of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) is applied; - the layer of the mixture of micro-powders of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) applied with a thickness of between 3 pm and 20 pm, preferably between 5 pm and 15 pm, preferably about 10 pm. - the mixture of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) is a micro-powder composition comprising between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of fluoroethylenepropylene (FEP) relative to the total weight of said composition and between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of polyetheretherketone (PEEK) relative to the total weight of said composition.

[0040] According to another embodiment, said micro-powder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) in a proportion of 50 / 50 by weight relative to the total weight of said composition.

[0041] Such a tool may be a tire mold or a tool intended to come into contact with an elastomer such as, for example, a tool for cutting an elastomer. Brief description of the figure

[0042] [Fig.1] illustrates a method according to a variant of the invention describing steps 10 to 80. Other features, details and advantages of the invention will become apparent from reading the following description, with reference to [Fig.1]. Detailed description of an implementation method

[0043] According to the representation in [Fig. 1], the process preferably begins with a step (10) of thermal penetrant testing of the part to be treated using methods known to those skilled in the art, under operating conditions that do not degrade the substrate. This thermal penetrant testing step eliminates impurities that may be present on the part to be treated and hinder the adhesion of the coating according to the invention.

[0044] Advantageously, a sandblasting step (30) can be carried out to prepare the substrate surface. The sandblasting is carried out by any suitable means and in particular by electro-fused crystallized aluminum oxide of very high purity, obtained by melting calcined aluminum oxide; such as, for example, by means of grade 80 white corundum.

[0045] The sandblasting pressure is adjusted according to the substrate to avoid damaging it, for example between approximately 2 and 3 bar. For a metallic substrate, a A pressure of 3 bars is preferred. One or more passes of the sandblasting equipment can be implemented according to the operator's wishes, depending on the nature of the substrate and the desired result.

[0046] Subsequently, a cleaning step (40) can be carried out, for example, by blowing compressed air onto the appropriate surfaces, in order to remove the corundum residues and / or loose material from the substrate.

[0047] Optionally, a masking step (20) may be implemented before and / or after the sandblasting step (30) to delimit the area to be sandblasted and / or the area for applying the composition according to the invention to the substrate surface. Masking may be performed mechanically or manually using methods known to those skilled in the art, such as applying a mask to areas of the surface that are not to be treated, for example, using sandblasting tape. In particular, areas that are not to be coated are protected by such masking.

[0048] Finally, step (60) of applying the composition according to the invention by electrostatic spraying is carried out using an electrostatic gun, at a rate of about 50 g / m2 to 150 g / m2, preferably about 100 g / m2.

[0049] The micro-powder composition according to the invention will have been previously prepared during step (50) in [Fig.1], by mixing micro-powders of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) obtained by grinding and then sieving the dry matter obtained after evaporation of FEP and liquid PEEK or by micro-grinding the powders in order to obtain the desired particle size.

[0050] These micro-powders can be purchased commercially or manufactured locally. However, the applicant noted that it is very difficult to find commercially available micro-powders with the characteristics, particularly the particle size, suitable for the present invention. It therefore appears preferable to produce them in-house according to the protocol described in this application.

[0051] Said mixture of FEP and PEEK micro-powders is made in the following proportions: between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of FEP relative to the total weight of said composition and between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of PEEK relative to the total weight of said composition.

[0052] According to another embodiment, said micro-powder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) in a proportion of 50 / 50 by weight relative to the total weight of said composition.

[0053] Furthermore, the composition according to the invention may comprise other compounds provided that they do not interfere with the application and polymerization of the composition according to the invention. By way of example, one can cite: colorants such as graphite, and / or lubricating agents, and / or hardening agents.

[0054] Finally, a polymerization step (70) is carried out at a temperature suitable for the substrate, generally between approximately 360°C and 420°C, preferably between 360°C and 385°C, more preferably at approximately 380°C, for 30 to 90 minutes, preferably between 45 and 60 minutes; preferably about 1 hour, using methods known to those skilled in the art, such as an oven or infrared radiation. This curing process forms a layer that adheres to all or part of the metal surface.

[0055] The coated substrate is subsequently cooled, for example until it reaches ambient temperature, and then quality checks (80) can be carried out.

[0056] These checks may consist of dimensional measurements, preferably at several points on the coated surface. These measurements are taken, for example, using a permascope. This makes it possible to verify the coating thickness and its uniformity. It is also possible to check for blisters or traces of oxidation. Advantageously, a cross-section test on a tracer specimen can be carried out.

[0057] In some cases, it is preferable to start the process with an alkaline degreasing step of the substrate surface before said thermal penetrant (or pyrolysis) step.

[0058] According to the representation in [Fig.1], the process according to a variant of the invention preferably begins with a step (30) of sandblasting the part to be treated, optionally preceded by a sparing step (20).

[0059] Next, a cleaning step (40) is preferably carried out, for example by blowing compressed air onto the appropriate surfaces, in order to remove the corundum and / or metal residues.

[0060] The sandblasting (30) and / or cleaning (40) steps can be carried out under the control, for example visual, of an operator.

[0061] The coating according to the invention is generally transparent but compounds can be added to modify its color. Examples:

[0062] EXAMPLE 1: Unsuccessful attempt to coat metal parts with a mixture of FEP and PTFE:

[0063] The micro-powder composition comprising a mixture of 75% fluoroethylenepropylene (FEP) (compound A) and 25% polytetrafluoroethylene (PTFE) (compound B), hereinafter referred to as DELTAFLON, did not provide good adhesion to the metal according to the cross-section test carried out on the substrate according to the International Standard ISO 2409:2007 well known to those skilled in the art.

[0064] In particular, the following drawbacks were observed during the initial tests consisting of simply applying DETAFLON powder to the steel wheel linings, and the initial results were very disappointing: - Problem of DELTAFLON powder detaching from steel molds (harder metal and therefore difficult to achieve good adhesion). - Corrosion problem under the coating because one of the components of DELTAFLON powder (PTFE) is microporous and therefore allows moisture to pass through. - Appearance problem because DELTAFLON powder is smooth and therefore gives a shiny appearance to the tire.

[0065] EXAMPLE 2: modification of example 1

[0066] The unsuccessful trials described in Example 1 led the inventors to seek solutions to resolve the technical problem. These solutions consisted of modifying the following steps:

[0067] Modification of sandblasting parameters (grain size and pressure) in order to improve adhesion.

[0068] Modification of the percentage between agents A and B in the powder composition described in example 1.

[0069] The tests are measured using the cross-cut test as described in International Standard ISO 2409:2007, which is well known to those skilled in the art. This International Standard describes a test method for evaluating the resistance of paint coatings to separation from their substrates when a cross-cut is made in the coating down to the substrate. The property evaluated by this empirical method depends, among other things, on the adhesion of the layer to either the preceding layer or the substrate.

[0070] The apparatus required for these measurements can be a single-blade cutting tool suitable for all types of coatings applied to hard or soft substrates. A multi-blade tool can also be used but is not suitable for thick (> 120 µm) or hard coatings, nor for coatings applied to soft substrates.

[0071] The evaluations are carried out according to a classification into six classes represented in Table 1 below:

[0072] Table 1:

[0073] The numerous plate tests did not give conclusive results as as shown in Table 2 below:

[0074] [Tables2] Plate number Coating Sandblasting pressure (bar) Media Ra after sandblasting Ra after application (pm) Thickness pm Grid Observation 1 Primer powder -i-PTFE powder 3 sü 1.49- 1.61 1.11 - 1.23 7 to 10.7 Class G The finish failed to adhere to the primer. The information transmitted concerns only the primer. There was a reversal of the test specimens, nc3 corresponds to test n'1 and vice versa. Liquid primer t: PTFE powder .3 80 1.63-2.05 1.36-1.49 17.1 to :23.3 Class G mats imprint the tape left a Liquid primer + liquid PTFE ..3. 80' 1:56-1.5S 1.1.9-1.33 8.4 a 16.2 Class G. There was a reversal of the specimens, the mi corresponds to test no. 3 Powder Objective Ru after coating ISO coated aluminium elements 36 3.54-09 1.32-1.72 26' to 36 J Clause 0 The significant increase in sandblasting had an impact on the thickness.

[0075] EXAMPLE 3: Positive test for a mixture according to the invention

[0076] The micro-powder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), preferably between 70 and 90 wt% FEP and 10 to 30 wt% PEEK. After permascope reading of a coated metallic substrate, the following data were obtained: 1. Coefficient of friction: from 0.08 to 0.2 2. Maximum operating temperature: 210°C 3. Thickness: 10µm + / - 5µm 4. Hue: Depends on the substrate.

[0077] Method: Permascope

[0078] 100% visual inspection: YES

[0079] Results: Compliant - The results measured using the cross-section test according to International Standard ISO 2409:2007 as described in Example 2, all gave a result equal to class O.

[0080] Numerous combinations can be considered without departing from the scope of the invention; a person skilled in the art will choose one or another according to the economic, ergonomic, dimensional, or other constraints to be respected. For example, a person skilled in the art will adapt the temperatures to the thermal masses of the parts.

Claims

Demands

1. A method for coating a substrate or a metallic surface intended to receive an elastomer by electrostatic spraying comprising at least the following steps: a) the preparation of a composition A comprising at least one fluoroethylenepropylene (FEP) in the form of a micro-powder having a particle size of between 1 and 7 pm; b) the preparation of a composition B comprising at least one polyetheretherketone (PEEK) in the form of a micro-powder having a particle size of between 2 pm and 50 pm; c) the intimate mixing of the 2 compositions A and B so as to form a composition AB (50) in the form of a fine powder; d) the application by electrostatic spraying (60) of the mixture AB obtained in step c) onto the substrate or metallic surface; e) polymerization (70) of said composition AB.

2. A method according to claim 1, characterized in that said substrate or said metallic surface intended to receive an elastomer is made of steel.

3. A process according to claim 1 or 2, characterized in that said micro-powder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), preferably between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of FEP relative to the total weight of said composition and between 10% and 90%, preferably between 20% and 80%, even more preferably between 30% and 70%, preferably between 40% and 60% by weight of PEEK relative to the total weight of said composition.

4. A method according to any one of the preceding claims, characterized in that step d) of applying said composition is carried out by electrostatic spraying.

5. A process according to any one of the preceding claims, characterized in that step e) of polymerization is carried out at a temperature between about 360°C and 420°C, preferably 380°C, until total polymerization of said fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) mixture, preferably for 1 hour.

6. A method according to any one of the preceding claims, characterized in that it comprises, prior to step a), a thermal penetrant step (10) and / or a masking step (20) and / or a sandblasting step (30), at least partial, of the surface to be coated.

7. A process according to any one of claims 2 to 6, characterized in that said FEP or PEEK micro-powder used is obtained by evaporating the aqueous phase of liquid FEP or PEEK and then grinding and / or sieving or by micro-grinding a powder to obtain the usable particle size.

8. A coating kit for a substrate or metallic surface intended to receive an elastomer, configured for carrying out a process according to any one of claims 1 to 7, comprising: • a micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), • a means for applying said composition by electrostatic spraying (60) onto said surface, • preferably a means for polymerizing said composition (70).

9. Metallic substrate or surface comprising a surface coated with a micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), obtained by the process according to any one of claims 1 to 7.

10. Composition for coating suitable for carrying out the process according to any one of claims 1 to 7.

11. Use of a composition according to claim 10 as a coating to obtain a surface having anti-stick, anti-friction, chemical inertness, electrical insulation, thermal resistance and / or slip resistance properties.

12. Mechanical tooling comprising a suitable metallic surface coated with the micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), obtained by the process according to any one of claims 1 to 7

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