WO2014125180A1

WO2014125180A1 - Process for coating a metallic surface intended to receive an elastomer, and associated kit and tool

Info

Publication number: WO2014125180A1
Application number: PCT/FR2014/050095
Authority: WO
Inventors: Benjamin Morin
Original assignee: Fluorotechnique
Priority date: 2013-02-13
Filing date: 2014-01-20
Publication date: 2014-08-21
Also published as: PL414815A1; FR3001901B1; FR3001901A1; PL236872B1

Abstract

The invention relates to a process for coating, with fluoropolymers, a suitable metallic surface intended to receive an elastomer such as a tyre rubber, comprising steps for: a- applying (60) in a layer a first resin A comprising fine particles of fluoro ethylene propylene in suspension, then b- polymerising (61) the first resin A, c- cooling the resin A, d- applying (64) a mixture A-B comprising the first resin A and a second resin B which itself comprises fine particles of polytetrafluoroethylene in suspension, then e- polymerising (65) the mixture A-B, f- cooling the mixture A-B. The invention also relates to a coating kit and a tool coated with said fluoropolymers.

Description

METHOD FOR COATING A METAL SURFACE FOR RECEIVING AN ELASTOMER, KIT AND TOOL THEREFOR

TECHNICAL FIELD OF THE INVENTION

The invention relates to the field of fluoropolymer coatings of metal surfaces for receiving an elastomer such as for example a tire eraser. In particular, the invention relates to the field of coating tire molds.

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

STATE OF THE PRIOR ART

The state of the art includes for example the application WO 1981/001375 A1, which discloses a composite material which comprises a protective outer layer deposited by sintering and consisting of polytetrafluoroethylene particles (PTFE) dispersed in a polyimide lacquer. The composition comprises from 90 to 80% by volume of thermosetting polyimide lacquer and from 10 to 20% by volume of self lubricating additives such as PTFE.

This document is limited to an application of PTFE in a composition comprising predominantly polyimide.

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 functions of anti-adhesion and sliding fade. Reprocessing of these coatings are also known but they can be done only three to four times after which the molds are no longer reusable. These reprocessors consist of pyrolizing the molds, then sandblasting them and applying the Xylan® 8840 coating again. These reprocessings are not satisfactory, in particular because they induce energy expenditure and deterioration of the molds.

In addition for some applications, the Xylan® 8840 is not satisfactory because it does not allow to have a sufficiently thin layer (30 to 50μιη with Xylan 8840) coating that retains mechanical strength properties satisfactory. Indeed, because of the countersinking of these molds, it is preferable that the applied coatings are as thin as possible while having sufficient strength to not be damaged during demolding operations. The use of a thin coating is of interest in the manufacture of tires having fine grooves.

Alternatively, when the release properties are no longer sufficient, it is known to add release agents. This generates an induced cost and a decrease in productivity during the production of tires.

SUMMARY OF THE INVENTION

The invention aims to overcome the disadvantages of the state of the art and in particular to provide an improved coating process.

To this end, a fluoropolymer coating process is proposed for a suitable metal surface for subsequently receiving an elastomer such as a tire rubber, comprising steps for:

a-layer a first resin A comprising fine particles of fluoroethylenepropylene in suspension, then

b- polymerize the first resin,

c- cool the first resin A

d- applying a mixture comprising the first resin A and a second resin B which itself comprises fine particles of polytetrafluoroethylene in suspension, then

e-polymerize the mixture,

cool the mixture A-B.

The fluoropolymers in suspension of the invention can overcome the disadvantages of the prior art in terms of slip and nonstick effect but also in terms of mechanical strength and fineness of the coating.

By "suitable metal surface" is meant a sufficiently resistant surface treatments related to the application and polymerization of fluoropolymers. In particular, the high firing temperatures used to polymerize the fluoropolymers do not deteriorate such a suitable surface. In some embodiments, a tool comprising the appropriate metal surface is also adapted to support said cooking temperatures.

According to a variant, the first resin comprises 50% by mass or more of fine particles of fluoroethylenepropylene suspended in water. In addition Preferably, the AB mixture comprises 50% of the first resin and 50% of a second resin which itself comprises 50% polytetrafluoroethylene in fine particles suspended in water. In particular the fluoropolymers have mass concentrations of 50% or more. Preferably, the fine particles of fluoroethylenepropylene have a granulometry of between about 0.1 and 0.3 .mu.m.

According to an interesting aspect, the first resin and / or the mixture is applied su r a thickness between about 1 and 3 μ ιη, preferably 2μιη.

Advantageously, the first resin is polymerized at a temperature between about 345 and 375 ° C, preferably 360 ° C.

According to another interesting aspect, the first resin is polymerized for about 30 to 60 minutes, preferably for 45 minutes.

Preferably, the fine particles of polytetrafluoroethylene has a granulometry of about 0.25 μιη. In a variant, the mixture A-B is polymerized at a temperature between about 365 and 395 ° C., preferably at 380 ° C.

In another aspect, the A-B mixture is polymerized for 30 to 90 minutes, preferably for 60 minutes.

Advantageously, the mixture A-B has a viscosity, according to ASTM D2196, of 20 cP.

[0021] Preferably, the process comprises, prior to step a), a pyrolysis step and / or a sandblasting step and / or a step of degreasing, at least partially, the metal surface to be coated. .

These steps allow better preparation of the metal surface for the coating. The pyrolysis step can be carried out at the temperatures and rees of the polymerization steps. These temperatures and times vary depending on the thermal mass of the workpiece. For example, the pyrolysis step is conducted at temperatures between 380 and 400 ° C, preferably for about one hour. This pyrolysis removes impurities that may be on the surface of the room. The invention also relates to a fluoropolymer coating kit of a suitable metal surface intended to receive an elastomer such as a tire eraser, configured for the implementation of a method as described above, comprising:

a first resin comprising, preferably 50% by mass or more, fine particles of fluoroethylenepropylene in suspension,

a mixture comprising the first resin and a second resin which itself comprises fine particles of polytetrafluoroethylene in suspension,

preferably means for polymerizing the first resin and / or the mixture. Another object of the invention is a mechanical tool comprising a suitable metal surface coated with fluoropolymers and intended to receive an elastomer such as a tire rubber, obtained by the method as described above.

More specifically, the invention also relates to a mechanical tool comprising a suitable metal surface coated with fluoropolymers and intended to receive an elastomer such as a tire rubber, characterized in that the fluoropolymers comprise:

at least one layer of a first polymerized resin comprising, preferably 50% by mass or more, fine particles of fluoroethylenepropylene in suspension, at least one layer of a polymerized mixture comprising the first resin and a second resin which comprises itself fine particles of polytetrafluoroethylene in suspension.

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. Alternatively, it can be provided to use perfluoroalkoxy instead of fluoroethylenepropylene.

BRIEF DESCRIPTION OF THE FIGURE

Other features, details and advantages of the invention will become apparent from reading the description which follows, with reference to Figure 1 attached, which illustrates a method according to a variant of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

According to the representation of the single figure, the method according to a variant of the invention preferably begins with a step 40 of sandblasting the workpiece, optionally preceded by a saving step 30. Advantageously, the method may include, prior to sanding, pyrolysis 20 of the workpiece.

In the case of savings, a mask is disposed on surface portions where it is not desired to perform sandblasting. Saving can be mechanical or manual, for example using a sandblasting tape. In particular, areas that should not be paved are protected by such savings.

Sandblasting 40 is for example by means of white corindon® grade 120. The sanding pressure is for example 2 to 3 bar. A pressure at 3 bar is preferred. Only one passage of sanding means can be implemented. Then, it is preferably carried out a cleaning step 50 for example by blowing compressed air on the appropriate surfaces, to remove residues of corundum and / or metal.

The sanding steps 40 and / or cleaning 50 can be done under control, for example visual, an operator. Then one carries out a step 60 of applying a fluorinated ethylene propylene resin (FEP) layer preferably of 1 to 2 μιη. At this moment the savings can be removed (30 '). The FEP resin preferably contains more than 50% by mass of FEP particles. The particles of FEP advantageously measure from 0.1 to 0.3 μm. In particular, FEP particles are suspended in water. Another solvent and / or other amounts of FEP may be used as long as they do not oppose the application of the first resin and the polymerization of FEP.

The application 60 is preferably by means of a pneumatic gun. Baking is then carried out at a temperature of between 340 and 375 ° C., preferably at 360 ° C. The cooking can be done for 40 to 55 minutes, preferably for 45 minutes. This firing induces the polymerization 61 of the FEP to form a layer that adheres to all or part of the metal surface, depending on the possible savings.

Then it is allowed to cool 62 for example to room temperature (of the order of 20 ° C), then we can set up 63 a second saving. This step 63 is optional.

Next, a step 64 is performed to apply a layer of a mixture of FEP (in particular of the first resin) and of PTFE (second resin) at 50% by weight, to a thickness of between approximately 1. and 3 μιη, preferably 2μιη. In the second resin, the PTFE particles advantageously measure about 0.25 μιη. In particular, the FEP particles of the second resin are in suspension in water preferably at a concentration of 50% or more by mass. Another solvent and / or other amounts of PTFE and / or FEP may be used as long as they do not oppose the application of the resin mixture and its polymerization. The application 64 is preferably by means of a pneumatic gun.

Preferably the viscosity of the mixture is 20cP according to ASTM D2196 (Brookfield Viscometer). At this time the second savings can be removed (63 '). The mixture is then fired at a temperature of between 360 and 395 ° C., preferably at 380 ° C. Cooking can be done for 30 to 90 minutes, preferably for 60 minutes. This firing allows the polymerization 65 of the FEP-PTFE mixture to form a layer fixed on all or part of the metal surface, depending on the possible savings.

Then it is allowed to cool 66, for example, until the ambient temperature is reached, and then checks 70 can be made before packaging the tool.

The controls 70 may consist of dimensional readings preferably at several points of the surface thus coated. These surveys are done for example at the permascope. It is thus possible to ensure the thickness of the coating, its uniformity. We can also check for blisters or oxidation. It is also possible to perform a grid test on a tracer test specimen.

In some cases, it is preferable to begin the process with a step 10 of alkaline degreasing of the parts, followed by a step 20 thermal penetration (or pyrolysis) parts. This bleeding step can be done at 380 ° C, for example for 30 to 60 minutes depending on the thermal mass of the treated parts. This pyrolysis removes impurities that may be on the workpiece and interfere with the adhesion of the fluoropolymer layers.

Example: [0044] The coating according to the invention is generally transparent but compounds can be added to modify the color.

The following data was obtained:

- coefficient of friction: 0.02; -Maximum operating temperature: 220 ° C continuous / 260 ° C intermittently;

- Thickness: 3 to 6μ;

- Hue: Depends on the support.

Many 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. The person skilled in the art will, for example, adapt the temperatures to the thermal masses of the parts.

Claims

A method of coating with fluoropolymers a suitable metal surface for subsequently receiving an elastomer such as a tire rubber, comprising steps for:

a- applying (60) in layer a first resin A comprising fine particles of fluoroethylenepropylene in suspension, then

b-polymerizing (61) the first resin A,

c- cool the resin A

d- applying (64) a mixture A-B comprising the first resin A and a second resin B which itself comprises fine particles of polytetrafluoroethylene in suspension, then

e-polymerizing (65) the mixture A-B,

cool the mixture A-B.

2. Method according to claim 1, characterized in that the first resin A comprises 50% by mass or more of fine particles of fluoroethylenepropylene suspended in water.

3. Process according to claim 2, characterized in that the mixture AB comprises 50% of the first resin A and 50% of a second resin B which itself comprises 50% of polytetrafluoroethylene in fine particles suspended in water. water.

4. Method according to one of claims 1 to 3, characterized in that the fine particles of fluoroethylenepropylene have a particle size of between about 0.1 and 0.3 μιη.

5. Method according to one of claims 1 to 4, characterized in that the first resin A and / or the mixture A-B is applied to a thickness between about 1 and 3 μιη, preferably 2μιη.

6. Method according to one of claims 1 to 5, characterized in that the first resin A is polymerized at a temperature between about 345 and 375 ° C, preferably 360 ° C.

7. Method according to one of claims 1 to 6, characterized in that the first resin A is polymerized for about 30 to 60 m inutes, preferably for 45 m in utes.

8. Process according to one of claims 1 to 7, characterized in that the fine particles of polytetrafluoroethylene have a granulometry of about 0.25 μιη.

9. Process according to one of claims 1 to 8, characterized in that the mixture A-B is polymerized at a temperature between about 365 and 395 ° C, preferably at 380 ° C.

10. Method according to one of claims 1 to 9, characterized in that the mixture A-B is polymerized for about 30 to 90 minutes, preferably for 60 minutes.

11. Method according to one of claims 1 to 10, characterized in that the mixture A-B has a viscosity, according to ASTM D2196, of 20 cP.

12. Method according to one of claims 1 to 11, characterized in that it comprises, prior to step a), a pyrolysis step and / or a sanding step and / or a degreasing step, at least partially, of the metal surface to be coated.

13. A fluoropolymer coating kit of a suitable metal surface for receiving an elastomer such as a tire tire, configured for carrying out a method according to one of claims 1 to 12, com taking:

a mixture comprising the first resin and a second resin which comprises, preferably 50% by weight or more, polytetrafluoroethylene in fine particles in suspension,

preferably means for polymerizing the first resin and / or the mixture.

14. Mechanical tools comprising a suitable metal surface coated with fluoropolymers and intended to receive an elastomer such as a tire rubber, obtained by the method according to one of claims 1 to 12.