FR3140780A1 - Process for coating a substrate or a metal surface intended to receive an elastomer by electrostatic projection, associated kit and tool - Google Patents

Abstract

Process for coating a substrate or a metal surface intended to receive an elastomer by electrostatic projection comprising at least the following steps: the preparation of a composition A comprising at least one fluoroethylenepropylene (FEP) in the form of micro-powder the preparation of a composition B comprising at least one polyetheretherketone (PEEK) in the form of a micro-powdermix the two compositions A and B intimately so as to form a composition A-B (50) in the form of a fine powderapply the mixture by electrostatic projection (60) A-B obtained in step c) on the substrate or the metal surface (70) polymerization of said composition A-B. Figure for abstract: [Fig. 1]

Description

Process for coating a substrate or a metal surface intended to receive an elastomer by electrostatic projection, associated kit and tool

The invention relates to the field of coatings with fluoropolymers of substrates or metal surfaces intended to receive an elastomer such as, for example, tire rubber. In particular, the invention relates to a process for coating tire molds.

State of the prior art

In this field, it is known to apply a fluoropolymer coating, in particular to tire molds, in order to have a surface having anti-adhesion and sliding properties during the manufacture of tires. Thus when the rubber is vulcanized, it is easier to separate the rubber from the metal surface of the mold.

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

A known solution is to use Xylan® 8840 as a coating. However, molds comprising such a coating are quickly damaged and their mechanical properties decrease so that the anti-adhesion and sliding functions fade. Reprocessing of these coatings is also known but can only be done three to four times after which the molds are no longer reusable. These reprocessings consist of pyrolizing the molds, then sandblasting them and reapplying the coating with Xylan® 8840. These reprocessings are not satisfactory in particular because they involve energy expenditure and deterioration of the molds.

Furthermore, for certain applications, Xylan® 8840 is not satisfactory because it does not provide a sufficiently thin layer (30 to 50 µm with Xylan 8840) of coating which retains satisfactory mechanical resistance properties. Indeed, due to the countersinking of these molds, it is preferable that the coatings applied are as thin as possible while having sufficient mechanical strength so as not to be damaged during demoulding operations. The use of a thin coating is of interest in the manufacture of tires with fine grooves.

For substrates having a complex geometry, it is difficult to obtain a uniform and very thin coating of less than 20 μm, preferably of the order of 5 to 10 μm when fluoropolymers in liquid form are used. Likewise, it is not easy to visualize this application in particular if the liquid composition, comprising at least one fluoropolymer, is transparent.

The invention aims to remedy the drawbacks of the state of the art and in particular to propose an improved coating process.

To do this, the invention proposes a process for coating a substrate or a suitable metal surface intended to subsequently receive an elastomer such as tire rubber by electrostatic projection, said process being characterized in that it comprises the following steps :

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

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

c) thoroughly mix the 2 compositions A and B so as to form a composition A-B in the form of a fine powder

d) apply by electrostatic projection the A-B mixture obtained in step c) on the substrate or the metal surface

e) polymerization of said composition.

Advantageously, said substrate or said metal surface intended to receive an elastomer is made of steel.

The micro-powder composition (also called composition or mixture A-B) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) makes it possible to overcome the disadvantages of the prior art in terms of sliding and non-stick effect but also in terms of mechanical resistance and fineness of the coating, while facilitating the application of said composition to the substrate. It also allows easier cleaning of the molds and thus preserves the lifespan of the molds used.

In fact, the projection of a micro-powder is very advantageous compared to a liquid product because it allows parts of complex geometries to be uniformly treated. In addition, the application of the mixture of micro-powders creates a whitish effect on the part before polymerization, ensuring good application over the entire desired surface. This has ^{the first} advantage of not creating excess thickness and also of saving on coating.

In addition, these micro-powders are currently not subject to European REACH legislation regarding solvents in products since they are used without solvents, and preferably pure.

By “suitable metal surface or substrate” is meant a surface sufficiently resistant to treatments linked to the application and polymerization of the micro-powder composition comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK).

In particular, the high baking temperatures, used to polymerize the mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), do not deteriorate such a surface. By way of example, a metallic substrate or having a metallic surface adapted to withstand said cooking temperatures such as 400°C or even 380°C, which may, among other things, be intended to subsequently receive an elastomer such as tire rubber.

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

“Surface” or “Substrate”: refers to the visible part of a material on which the deposit of the micro-powder composition A-B (comprising the mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK)) can be placed. artwork. Non-limiting examples of substrates include a material used: in the field of aeronautics (airplane, helicopter, for example), in the railway field, in the automotive field, in the nautical and naval field; in the field of wind power; in passenger spaces (planes, buses, metro, for example); or in the building sector (exterior or interior surfaces).

By “electrostatic projection” we mean any means making it possible to project, spray or transfer a micro-powder onto a substrate and to hold it in place by means of electrostatic charges. To do this, an electrostatic gun, an electrostatic fluidized bath, an electrostatic fluidized bed or any technically equivalent means known to those skilled in the art can be used.

According to another characteristic 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.

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

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

Advantageously, said FEP fluoropolymer has a particle size of between approximately 1 and 7 μm, preferably 4 μm.

Preferably, the fine PEEK polyetheretherketone particles have a particle size of between approximately 2µm and 50µm.

According to another characteristic of the invention, step d) of applying said composition is carried out by electrostatic spraying or electrostatic spraying. That is to say that the application means, such as an electrostatic gun, is adapted to spray on the surface of said substrate or of said surface, said composition of the invention. For example, a WAGNER® electrostatic gun can be used as an application means.

According to another embodiment, step d) of applying said composition is carried out by using an electrostatic fluidized bath.

Preferably, said micro-powder of FEP or PEEK used is obtained by evaporation of the aqueous phase solution of FEP or liquid PEEK, then crushed and/or sieved or by micro-grinding of a powder in order to obtain the usable particle size.

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

In addition, the method according to the invention may comprise preliminary preparation steps in step a), such as a thermal penetrant step and/or a sparing step and/or a sandblasting step, at least partially , of the surface to be coated.

Preferably, the method comprises, prior to step a), a sandblasting step and/or a degreasing step, at least partially, of the metal surface to be coated.

• une composition de micro-poudre (50) comprenant un mélange de fluoroéthylènepropylène (FEP) et de polyétheréthercétone (PEEK),
• un moyen d'application de ladite composition par projection électrostatique (60) sur ladite surface,
• de préférence un moyen de polymérisation (70) de ladite composition.

The invention also relates to a kit for coating with a mixture of at least one fluoropolymer and a polyetheretherketone (PEEK) of a substrate or a suitable metal surface intended to receive an elastomer such as tire rubber. , configured for the implementation of a method as described above, comprising:

• a micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK),
• means for applying said composition by electrostatic projection (60) onto said surface,
• preferably a means (70) for polymerizing said composition.

The invention also relates to a substrate or a metal 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 below. -above and intended to receive an elastomer.

Furthermore, the invention relates to a composition, preferably in the form of micro-powder, suitable for carrying out the process according to the invention. That is to say a homogeneous micro-powder composition comprising at least fluoroethylene propylene (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.

The subject 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-adhesion, anti-friction, chemical inertia, electrical insulation, thermal and/or slip resistance properties.

Another object of the invention consists of a mechanical tool comprising a suitable metallic surface coated with the composition A-B comprising the 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 tire rubber.

• une seule couche du mélange d’au moins un fluoroéthylènepropylène (FEP) et de polyétheréthercétone (PEEK) est appliquée ;
• la couche du mélange de micro-poudres d’au moins un fluoroéthylènepropylène (FEP) et de polyétheréthercétone (PEEK) appliquée selon une épaisseur comprise entre 3 µm et 20 µm, de préférence comprise entre 5 µm et 15 µm, préférentiellement d’environ 10 µm.
• le mélange d’au moins un fluoroéthylènepropylène (FEP) et de polyétheréthercétone (PEEK) est une composition de micro-poudres comprenant entre 10% et 90%, préférentiellement entre 20% et 80%, encore plus préférentiellement entre 30 et 70%, de préférence entre 40% et 60% en poids de fluoroéthylènepropylène (FEP) par rapport au poids total de ladite composition et entre 10% et 90%, préférentiellement entre 20% et 80%, encore plus préférentiellement entre 30 et 70%, de préférence entre 40% et 60% en poids de polyétheréthercétone (PEEK) par rapport au poids total de ladite composition.

More specifically, the invention also relates to mechanical tooling 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 tire rubber, comprising the following characteristics together or separately:

• a single 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 to a thickness of between 3 µm and 20 µm, preferably between 5 µm and 15 µm, preferably around 10 µm.
• the mixture of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) is a composition of micro-powders comprising between 10% and 90%, preferably between 20% and 80%, even more preferably between 30 and 70%, of 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.

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

Such a tool can 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

illustrates a method according to a variant of the invention describing steps 10 to 80. Other characteristics, details and advantages of the invention will emerge on reading the description which follows, with reference to the .

Detailed description of an embodiment

According to the representation of the , the process preferably begins with a step (10) of thermal penetrating the part to be treated according to means known to those skilled in the art under operating conditions which do not degrade the substrate. This thermal penetrant step makes it possible to eliminate impurities which could be found on the part to be treated and hinder the adhesion of the coating according to the invention.

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

The sandblasting pressure is adjusted according to the substrate so as to avoid damaging it, for example between approximately 2 to 3 bars. For a metal substrate, a pressure of 3 bars is preferred. One or more passes of the sandblasting means can be implemented according to the operator's wishes depending on the nature of the substrate and the desired result.

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

Optionally a saving step (20) can then be implemented before and/or after the sandblasting step (30) in order to delimit the zone of sandblasting and/or application of the composition according to the invention on the surface of the substrate. The saving can be mechanical or manual according to means known to those skilled in the art such as affixing a mask to surface parts that one does not wish to treat, for example using tape. sandblasting. In particular, areas that should not be coated are protected by such savings.

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

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

Said micro-powders can be purchased commercially or manufactured on site. However, the applicant has noted that it is very difficult to find commercially micro-powders having the characteristic, in particular the particle size, suitable for the present invention. It therefore appears preferable to produce them yourself according to the protocol described in this application.

Said mixture of FEP and PEEK micro-powders is produced 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% in 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 to the total weight of said composition.

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

In addition, the composition according to the invention may comprise other compounds provided that they do not oppose the application and the polymerization of the composition according to the invention. By way of example, we can cite: dyes such as graphite, and/or lubricating agents, and/or hardening agents.

Finally, a polymerization step (70) is carried out at a temperature adapted to the substrate generally between approximately 360°C and 420°C, preferably 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 approximately 1 hour, according to means known to those skilled in the art such as for example using an oven or infrared radiation. This cooking makes it possible to form a layer which adheres to all or part of the metal surface.

The substrate thus coated is subsequently cooled, for example until reaching ambient temperature, then quality controls (80) can be carried out.

Said checks may consist of dimensional readings preferably at several points of the surface thus coated. These readings are carried out, for example, using a permascope. It is thus possible to ensure the thickness of the coating and its uniformity. We can also check if there are blisters or traces of oxidation. Advantageously, a grid test on a tracer specimen can be carried out.

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

According to the representation of the , the method according to a variant of the invention preferably begins with a step (30) of sandblasting the part to be treated, optionally preceded by a saving step (20).

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

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

The coating according to the invention is generally transparent but compounds can be added to modify the color.

Examples:

EXAMPLE 1 : unsuccessful attempt to cover metal parts with a FEP and PTFE mixture:

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

• Problème de décollement du DELTAFLON poudre sur des moules en acier (métal plus dur et donc difficile de faire une bonne accroche).
• Problème de corrosion sous le revêtement car l’un des composants du DELTAFLON poudre (le PTFE) est microporeux et donc laisse passer l’humidité.
• Problème d’aspect car le DELTAFLON poudre est lisse et donc donne un aspect brillant au pneu.

In particular, the following disadvantages were noted during the first tests of simply applying DETAFLON powder to the steel wheel linings and the first results were very disappointing:

• Problem of detachment of DELTAFLON powder from steel molds (harder metal and therefore difficult to get a good grip).
• Corrosion problem under the coating because one of the components of DELTAFLON powder (PTFE) is microporous and therefore allows humidity to pass through.
• Appearance problem because DELTAFLON powder is smooth and therefore gives a shiny appearance to the tire.

EXAMPLE 2 : modification of example 1

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

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

Modification of the percentage between agents A and B in the powder composition described in Example 1.

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

The equipment required for these measurements may be a single blade cutting tool which is suitable for all types of coatings applied to hard or soft substrates. A tool with several blades can also be used but is not suitable for thick (> 120 pm) or hard coatings, nor for coatings applied to soft substrates.

The evaluations are carried out according to a classification into six classes represented in table 1 below:

Table 1:

The numerous tests on plates did not give convincing results as indicated in table 2 below:

Plate number Coating Sandblasting pressure (bar) Media Ra after sandblasting (μm)2 Ra after application (μm) Thickness μm Grid Observation 1 Primer powder + PTFE powder 3 80 1.49 - 1.61 1.11 - 1.23 7 to 10.7 Class 0 The finish failed to stick to the primer. The information transmitted only concerns the primary. There was a reversal of the test pieces, number 3 corresponds to test number 1 and vice versa 2 Liquid primer + PTFE powder 3 80 1.63 - 2.05 1.36 - 1.49 17.1 to 23.3 Class 0 but the tape left an imprint 3 Liquid primer + liquid PTFE 3 80 1.56 - 1.58 1.19 - 1.33 8.4 to 16.2 Class 0 There was an inversion of the test pieces, number 1 corresponds to test number 3 4 Deltaflon Powder Objective
Ra after coating
iso coated aluminum elements 5 36 3.54-4.09 1.32-1.72 26 to 36.1 Class 0 The significant increase in sandblasting affected the thickness.

EXAMPLE 3 : positive test for a mixture according to the invention

1. Coefficient de frottement :de 0.08 à 0.2
2. Température maximum d’utilisation :210°C
3. Epaisseur :10µm +/-5µm
4. Teinte : Dépend du support.

The micropowder composition comprises a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK), preferably between 70 to 90% by weight of FEP and 10% to 30% by weight of PEEK. After permascope reading of a metal substrate covered with a coating, the following data were obtained:

1. Coefficient of friction: from 0.08 to 0.2
2. Maximum use temperature: 210°C
3. Thickness: 10µm +/-5µm
4. Color: Depends on the support.

Method: Permascope

100% visual inspection: YES

Results : Compliant – The results measured using the grid test according to International Standard ISO 2409:2007 as described in Example 2, all gave a result equal to class O.

Numerous combinations can be envisaged without departing from the scope of the invention; the skilled person will choose one or the other depending on the economic, ergonomic, dimensional or other constraints to be respected. Those skilled in the art will, for example, adapt the temperatures to the thermal masses of the parts.

Claims (12)

Process for coating a substrate or a metal surface intended to receive an elastomer by electrostatic projection comprising at least the following steps:
a) the preparation of a composition A comprising at least one fluoroethylenepropylene (FEP) in micro-powder form
b) the preparation of a composition B comprising at least one polyetheretherketone (PEEK) in micro-powder form
c) thoroughly mix the 2 compositions A and B so as to form a composition AB (50) in the form of a fine powder
d) applying by electrostatic projection (60) the mixture AB obtained in step c) on the substrate or the metal surface
e) polymerization (70) of said composition AB. Method according to claim 1, characterized in that said substrate or said metal surface intended to receive an elastomer is made of steel. Method 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. Method according to one of the preceding claims, characterized in that step d) of applying said composition is carried out by electrostatic spraying. Process according to one of the preceding claims, characterized in that step e) of polymerization is carried out at a temperature between approximately 360°C and 420°C, preferably 380°C, until total polymerization of said fluoroethylenepropylene mixture ( FEP) and polyetheretherketone (PEEK), for preferably 1 hour. Method according to one of the preceding claims, characterized in that it comprises, prior to step a), a thermal penetrant step (10) and/or a saving step (20) and/or a step of sanding (30), at least partially, of the surface to be coated. Method according to one of claims 2 to 6, characterized in that said micro-powder of FEP or PEEK used is obtained by evaporation of the aqueous phase of FEP or liquid PEEK then crushed and/or sieved or by micro-grinding of a powder in order to obtain the usable particle size. Kit for coating a substrate or a metal surface intended to receive an elastomer, configured for the implementation of a method according to one of claims 1 to 7, comprising:

• a micro-powder composition (50) comprising a mixture of fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK),
• means for applying said composition by electrostatic projection (60) onto said surface,
• preferably a means (70) for polymerizing said composition.

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 one of claims 1 to 7. Composition for coating suitable for carrying out the process according to one of claims 1 to 7. Use of a composition according to claim 10 as a coating in order to obtain a surface having anti-adhesion, anti-friction, chemical inertia, electrical insulation, thermal resistance and/or sliding properties . Mechanical tool comprising a suitable metallic surface coated with the composition according to claim 7 comprising the mixture of at least one fluoroethylenepropylene (FEP) and polyetheretherketone (PEEK) and intended to receive an elastomer such as tire rubber.