FR2796388A1 - surface treatment for aerospace applications, etc includes changing surface roughness measured perpendicular and in plane of surface before applying adhesive or decorative material - Google Patents

Abstract

Treatment of a surface prior to applying an adhesive or decorative material includes changing its roughness measured perpendicular to and in the plane of the surface. An Independent claim is included for the following: (a) A system for performing as above. Preferred Features: The treatment produces peaks and troughs having a desired heightand depth and a desired spatial distribution. The treatment is by photoablation using a patterned mask or by producing moire fringes on the surface. Alternatively, the treatment is by electro-erosion. Alternatively, where the material being treated is amorphous silicon, the treatment is by total or partial crystallisation of the surface.

Description

The present invention relates to a method for preparing surfaces prior to deposition of an adhesive or decorative product. It also aims systems for the implementation of this method.

There is a growing demand, particularly in the aeronautical industry and many other industrial sectors, for high performance bonding techniques on high technology materials such as carbon fiber materials or light alloys. Although now-proven gluing techniques already satisfy a large part of the industrial needs, the fact remains that the demand for ever higher performances is leading, on the one hand, to research work aiming to better understand the physical mechanisms involved. used in bonding processes and, secondly, development work aimed at proposing new techniques for bonding and preparing surfaces to be bonded.

To explain the performance of collages, recent work [1] has highlighted a suction effect created by tiny bubbles enclosed between the surface of objects and glue. The roughness of a hard material is translated, on a microscopic scale, by an alternation of mountains and valleys whose difference in altitude is of the order of the um, the distance between two peaks not exceeding the tens of um. An adhesive film also has a roughness with wider corrugations, 5um high and spaced 100pm apart. This work shows that the interaction between the surface roughness at the micron scale and the suction effect can lead to much higher energies than surface thermodynamic energies. With regard to the preparation of the surfaces before bonding, there are already preparation methods for bonding epoxy-carbon composites comprising solvent cleaning and manual abrasion.

In addition, work has been carried out on the preparation of surfaces by interaction of laser beams and on the qualitative improvements obtained on the collages applied to surfaces thus treated [2]. Thus, surface treatments were carried out by means of a 248 nm wavelength laser used in pulsed mode at a frequency ranging from 1 to 200 Hz. The treatment of a surface is performed by adding a predetermined number firing, then moving the processed sample by a beamwidth. It should be noted that other types of laser can be used to perform similar operations.

It is in this context that the invention is located, the objective of which is to present a new concept of surface preparation before depositing an adhesive or decorative product, which contributes to better performances than those obtained with the preparation processes. based on the most recent results in terms of understanding physical mechanisms while proposing a new approach to the industrialization of surface preparation.

The aforementioned objectives are achieved with a method for preparing a surface before depositing an adhesive or decorative product, characterized in that it comprises a treatment of this surface to adapt the roughness to the adhesive or decorative product to be applied, in terms of depth perpendicular to said surface and spatial distribution in the plane of said surface.

This provides a particularly efficient preparation process, providing in practice a repeatability of the expected phenomena and thus an industrialization of the process, and a reduction in the constraints related to the preparation of surfaces before bonding. In addition, this method makes it possible to improve the industrial economy of gluing, since it can be used on bonded surfaces bounded within larger surfaces.

It should be noted that there have long been techniques for surface preparation before bonding, using mechanical means to modify the roughness of the surface to be treated. The control of the result is related to the qualification of the abrasives, the duration of the friction, and to the pressure exerted during the operations. By way of example, the rasp cleaning of a bicycle inner tube after a puncture may be mentioned before a patch is put in place. However, these mechanical preparation techniques do not make it possible to obtain a predetermined spatial distribution aimed at adapting the roughness to the vulcanization glue.

A particularly advantageous mode of implementation of the preparation method according to the invention consists for example in the use of optical means to adjust the roughness of the surface of the material to be prepared.

In a first exemplary embodiment corresponding to this optical mode, a known ablation phenomenon is put into play and management of the spatial distribution of the energy is assumed. It should be noted that the depth of ablation is directly related to the difference in energy per surface element between the most illuminated points and the least illuminated points. As an indication, a ablation of 0.1 μm can be obtained by laser firing.

The management of the spatial distribution of energy can also implement a method of laser granularity, also referred to as "Speckle", in which the beam of a non-monochromatic laser interferes with the surfaces it illuminates. . The pitch of the interferences is directly related to the laser surface distance and can be determined by a direct projection of the beam, with adjustment of the distances, or by an optical combination modifying it. These interferences naturally modulate the surface energy within the illuminated area. This modulation, coupled with the cumulative duration of illumination, makes it possible to control the depth of photoablation. As an indication, we can obtain a transverse pitch between O, Olpm and lmm.

To overcome the randomness of the distribution of "mountains" and "valleys" on the treated surface obtained by implementing the laser granularity method, the preparation method according to the invention may include a control of the location of the "mountains" and "valleys" by scanning the focused laser beam on the surface or at very close distance, using mechanical means (eg deflecting mirrors) or optoelectronic means (crystal modulators or opto-acoustic tanks, for example) ). The value of the energy of the beam can then be coupled to the deflection of the beam. It should be noted that stereolithography techniques fall within this framework. The transverse pitch corresponding to these techniques is in practice greater than 0.1 μm.

The image projection technique can also be implemented to achieve a spatial distribution of energy on the surface to be prepared. This technique consists in projecting on the sample to prepare an image containing information of surface distribution of the energy.

In a first exemplary embodiment of a preparation method according to the invention implementing an image projection technique, a two-dimensional grid is used, itself illuminated by a constant or variable energy wavefront. . This wavefront crosses the grid. An image of the grid is made on the surface to be treated. It can also be provided that this grid is used in reflection. In a variant of this first exemplary embodiment, the image grid comprises more or less opaque bars, obtained for example by a variable thickness of the object grid, or by a focus defect.

In a second exemplary embodiment, the grid is advantageously replaced by a hologram, the spatial distribution of the light areas and dark areas being more random, the edges of the area less abrupt. In practice, it is possible to achieve 2000 lines per mm.

In a third embodiment, the object projected onto the surface to be prepared is the image of a ground glass absorbing at the wavelength of the light beam. A frosted glass, because of its structure, has a random distribution of its grains. By projecting the surface of the etched glass onto the sample, the geometry of the grains of the sample is managed in the plane of its surface. By the differential transmission of the frosted glass between its hollow parts and its solid parts, coupled with the cumulative duration of exposure, the depth of modulation of the sample is managed. It should be noted that, in this exemplary embodiment, it is important to perform a decoupling between, on the one hand, the support function performed by the body of this glass and, on the other hand, the modulation function performed by the layer. superficial thin of this glass, which has the effect of frosted. Thus, a very small thickness of the modulation glass relative to the overall thickness of the glass piece is used for absorption purposes. The frosted material can be obtained either by rubbing, or by sanding or else by a chemical etching, in particular based on picric acid. According to a variant of this embodiment, the ground glass is coupled with another optical component, glued or not, which makes it possible to increase or decrease the effects of the transmission coefficient of the optical glass.

The material of the ground glass can be advantageously chosen so as to be adapted by its nature and its transmission to the absorption effects that it wants to play.

In the context of the optical embodiment, it is also possible to use known moiré techniques which can make it possible to project variable-pitch energy onto a sample. A particularity of the application of these moiré techniques to the preparation of surfaces before bonding lies in the fact that a projected linear array can cause a differential bonding effect, in both directions parallel and perpendicular to the direction of the linear array.

It is also possible, in the context of the application of moiré techniques, to superimpose two linear arrays at least, of different directions, these directions possibly being adjustable with respect to the sample. The pitch obtained with the implementation of a moire technique is in practice greater than 0.0 lm.

In a second embodiment of the method according to the invention, the phenomenon of total or partial crystallization of this surface obtained under the effect is used to change the roughness of the surface of a substrate such as amorphous silicon. an excimer laser. The adaptation of the surface roughness is obtained by adjustments of the laser in intensity, possibly in duration and in number of pulses. The crystallization rate and the crystallization depth are closely correlated with the energy parameters. The step discounted with this technique is of the order of 0.1 μm per grain. Crystallization can also be carried out by chemical or physical means other than optical, for this example and other supports.

Other embodiments of the method according to the invention make use of point techniques. In a first exemplary embodiment, lasers capable of ablating or crystallizing a surface or used for drilling materials are used to stitch the surface to be bonded. The step obtained is in practice less than 0.01 with the use of a microscope objective.

These lasers are focused on or near the surface. The surface energy can then be considerably greater than that of the beams with little or no focus. This allows the use of low energy lasers, but requiring a high repetition rate to cover sufficient surfaces in reasonable time.

The beam impacts in the material are treated one by one, or in a matrix manner, with deterministic or random spatial distribution, by optical division of the initial beam. The array of beams can also be generated from a multibeam laser cavity.

The geometric distribution of the roughness is obtained by conventional optical means or fiber guide beams or beams, the depth of modulation by the combined effects of the energy density and the cumulative duration of illumination.

A third mode of implementation of the preparation method according to the invention consists in the use of mechanical means.

In a first embodiment, a stamping or punching technique is used. The surface to be treated is punched under the effect of a punch or die. The punch can be a pointed object moved point by point across the entire surface. it is also possible to use a matrix making it possible to obtain a surface having the desired roughness in a single stamping operation, for example according to a technique for producing a pressed hologram, with the desired modulations both in depth and on the surface.

The pressed hologram may include details at a pitch of 500 lines per mm and a depth of up to 1 μm.

In a second exemplary embodiment, mechanical projection techniques are used, such as sandblasting, microbeading, starch spraying or other equivalent techniques already used elsewhere for stripping and surface hardening. These techniques can be advantageously used for their surface modulation performance for the preparation of a surface before bonding or decoration by providing an adhesive or decorative material.

In a fourth embodiment of the method according to the invention, electrical techniques are used, among which the electroerosion which makes it possible to obtain on the surface of certain materials a granularity that can be used in the surface preparation, and the electrophoresis.

In a fifth mode of implementation, chemical techniques are used to obtain a modulation at the surface and at depth.

In a first embodiment implementing chemical techniques, it is possible to use acidic or basic active products which are applied to the surface. The pH of the product used and the duration of the interaction are key parameters of the expected results in terms of valley depth. By way of example, it is possible to envisage the application of picric acid used in mirrors to polish glasses. In a second embodiment, the so-called Langmuir layer technique, in which a monolayer or multilayer film whose molecules are oriented and distributed is deposited. The molecules used have a length and a diameter of a few nanometers. The roughness of the treated surface depends on several parameters including the hydrophilic or hydrophobic character, the size of the molecules forming the film, as well as the density in number of molecules per unit area.

Other features and advantages of the invention will become apparent in the description below. In the accompanying drawings given as non-limiting examples: FIG. 1 schematically illustrates the general steps of a bonding process including a method according to the invention; FIG. 2 is a synoptic view of a preparation system according to the invention in optical mode, implementing a photoablation technique; FIG. 3 is a synoptic view of a first exemplary embodiment of the preparation system according to the invention of the optical type illustrated in FIG. 2, implementing an image projection technique; FIG. 4 is a synoptic view of a second exemplary embodiment of the system illustrated in FIG. 2, implementing a moiré technique; FIG. 5 is a synoptic view of a preparation system according to the invention of the photocrystallization type; FIG. 6 is a synoptic view of a preparation system according to the invention of the point type; and FIG. 7 is a block diagram of the essential steps of the preparation process according to the invention, in one embodiment involving Langmuir layers.

We will first describe the general principle of the preparation process according to the invention, with reference to Figure 1. Consider (1) a sample E of bonding material have a natural roughness RN. This sample E is subjected (2) to a treatment equipment for obtaining (3) on the surface to be bonded a controlled roughness RP having a predetermined depth P and a spatial distribution of the cavities or nipples determined according to a matrix or a random distribution of treatment MT. It is then possible to apply (4) a layer of adhesive C having a specific RC roughness greater than that of the material to be bonded. The pitch L of the controlled roughness at the surface of the prepared material is in practice less than or much less than the average distance between two depressions at the surface of the glue layer.

We will now describe a first embodiment of the preparation method according to the invention, from optical means, with reference to FIGS. 2 to 4. The general principle of this optical mode, illustrated in FIG. using a beam generated by a laser equipment L, which is transferred by a transfer optical system S to a beam control optical system MF, applying a beam thus controlled on the surface of a sample E to be prepared in order to obtain a suitable or controlled roughness RP by photoablation.

The optical beam control system may be an image projection system, with reference to FIG. 3. This image projection system SP comprises an illumination device EG, a GR gate and a CO optical conjugation device. of the grid with sample E to prepare. It is also possible to provide a beam control optical system implementing a moiré method with interference generation from two mirrors, as illustrated in FIG. 4. The interference generation system SM comprises at the output of FIG. a laser generator L, a lens L and two mirrors M1, M2 spatially offset so as to produce, on the surface of a sample E to be treated, a set of interferences contributing to obtaining a suitable roughness.

The adaptation of the roughness to the surface of a sample E of substrate type (for example in amorphous silicon) can also be obtained by photocrystallization by means of a HF beam homogenization system arranged between the optical transfer system S and the sample to be treated, with reference to FIG.

In the case of the use of point methods, the beam control system SC comprises, with reference to FIG. 6, an optical device GE for managing the energy of the laser beam coupled to an optical device GP for managing the beam. position of the laser beam which is applied to the surface of the sample E to be treated.

An example of the implementation of a chemical preparation method using Langmuir layers will now be described with reference to FIG.

(A) A CU filled with a BA bath is used on the surface of which floats a layer of Langmuir CL. A sample E to be treated is then immersed (B) in the tank CU. Sample E passes through the CL layer and becomes impregnated with this layer by penetrating the bath.

When the sample E is removed (C) from the bath BA, it then has on its surface a molecular layer CI whose macroscopic structure is shown schematically in (D). This CI molecular layer provides a roughness that can be adapted to the needs of the collage or the decoration of the sample E.

Thanks to the wide variety of possible methods for implementing the preparation method according to the invention, a significant technical choice is offered to the operator of this process, which will have to be carried out according to the physical characteristics of the material to be treated, its geometry and its own dimensions of the bonding area, and the characteristics of the adhesive or decorative product used.

Thus, the optical methods will be particularly favorable when it comes to preparing a very limited bonding zone within a complex piece, whereas the chemical method will be interesting in the case where the entire external surface of a room will have to be treated. Electrical methods will be used for the treatment of parts made of electrically conductive material.

Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention. Thus, many variants of the described optical beam control systems can be envisaged. Likewise, the geometry of the roughness profiles can vary according to the characteristics of the glues used.

 REFERENCES [l <B>] </ B> L.LEIBNER and C.GAY Theory of Tackiness Physical Review Letters, Vo1.82, No. 5, February 1, 1999 <b> 1999 </ B> [2] JC HENRI Preparation and Cleaning surface treatment by laser: application to the bonding of composite materials and metals Club "Lasers de Puissance" Newsletter n 26

Claims (31)

1. A process for preparing a surface before deposition of an adhesive or decorative product, characterized in that it comprises a treatment of this surface to adapt the roughness to the adhesive or decorative product to be deposited, especially in terms of depth perpendicular to said surface and spatial distribution in the plane of said surface. 2. Method according to claim 1, characterized in that it further comprises a spatial management of the interactions implemented in this treatment. 3. Method according to one of claims 1 or 2, characterized in that the treatment of the surface comprises a creation in a given area of a set of valleys or valleys and a set of peaks or mountains according to a spatial distribution and a predetermined depth-dip depth. 4. Method according to claim 3, characterized in that the energy used for the treatment of the surface is applied to said surface optically from a laser beam source, and in that the adaptation of the roughness of said surface is obtained by photoablation. 5. Method according to claim 4, characterized in that the treatment of the surface comprises a direct projection of a laser beam on said surface so as to produce interference by laser granularity effect. 6. Method according to claim 4, characterized in that the treatment of the surface comprises a scanning of said surface with a laser beam focused on said surface or very close to said surface. 7. Method according to claim 4, characterized in that the treatment of the surface comprises a projection on said surface of an image produced by transmission and / or reflection of a laser beam through a projection optical system. 8. Method according to claim 4, characterized in that the treatment of the surface comprises an application on said surface of a moiré produced by a method of interference from a laser beam. 9. Method according to one of claims 1 to 3, applied to a substrate, for example amorphous silicon, characterized in that the surface treatment induces a total or partial crystallization of the surface of said substrate, by application of a beam laser. 10. Method according to one of claims 1 to 3, characterized in that it comprises a set of point operations of impacts of a laser beam at points of a surface to be treated. 11. The method of claim 10, characterized in that laser beam impacts are made one by one at distinct points of the surface. 12. Method according to one of claims 10 or 11, characterized in that laser beam impacts are performed in a matrix or random manner by optical division of an initial laser beam. 13. Method according to one of claims 10 to 12, characterized in that laser beam impacts are performed in a matrix or random manner according to a beam matrix generated from a multibeam laser cavity. 14. Method according to one of claims 1 to 3, characterized in that the adaptation of the roughness of a surface to be treated is obtained by stamping said surface by means of a matrix or stamping tool. 15. Method according to one of claims 1 to 3, characterized in that the adaptation of the roughness of a surface to be treated is obtained by a point by point movement of a punch on the whole of said surface. 16. Method according to one of claims 1 to 3, characterized in that the treatment of the surface comprises an electroerosion of said surface, operated so as to cause a granularity on said surface. 17. Method according to one of claims 1 to 3, characterized in that the surface treatment is performed by depositing on said surface of a monolayer or multilayer film whose molecules are oriented and distributed so as to provide a suitable roughness adhesive or decorative product. 18. The method of claim 17, characterized in that the deposition of the monolayer or multilayer film is obtained by implementation of the so-called Langmuir layer technique. 19. System for preparing a surface before depositing an adhesive or decorative product, implementing the method according to any one of the preceding claims, characterized in that it comprises means for adapting the roughness of the surface to the adhesive product. or decorative to deposit, in particular in terms of depth perpendicular to said surface and spatial distribution in the plane of said surface. 20. System according to claim 19, characterized in that it further comprises means for managing interactions implemented in this treatment. 21. System according to claim 20, characterized in that it comprises means for generating a laser beam and means for controlling this laser beam and applying it to the surface to be prepared, for an adaptation of the roughness of said surface by photoablation. 22. System according to claim 21, characterized in that it further comprises means for directly projecting the laser beam on the surface to be prepared. 23. System according to claim 21, characterized in that it further comprises means for scanning the surface to be prepared with a laser beam focused on said surface or at very close distance therefrom. 24. System according to claim 21, characterized in that it further comprises means for projecting onto the surface to be prepared an image produced by transmission and / or reflection of a laser beam through a grid. 25. System according to claim 21, characterized in that it further comprises means for producing on the surface to be prepared a set of interference moire from a laser beam. 26. The system of claim 21, adapted for the preparation of a substrate, characterized in that it further comprises means for applying to the surface of said substrate a laser beam set to cause total or partial crystallization of the surface of said substrate. substrate. 27. System according to one of claims 19 or 20, characterized in that it further comprises means for producing a set of laser beam impacts. at points of a surface to be treated. 28. System according to one of claims 19 or 20, characterized in that it further comprises means for stamping a surface to be prepared by means of a matrix arranged to obtain a predetermined spatial distribution and depth of the roughness of said surface. 29. System according to any one of the preceding claims, characterized in that it further comprises means for performing electroerosion of the surface to be prepared. 30. System according to any one of the preceding claims, characterized in that it further comprises means for depositing on the surface to be treated a monolayer or multilayer film whose molecules are oriented and distributed so as to provide a roughness adapted to adhesive or decorative product. 31. System according to claim 30, characterized in that the deposition means implement the so-called Langmuir layer technique.