CH716042A2 - Production of elastomer parts produced by duplication, from a standard reference model. - Google Patents

Abstract

The invention relates to the production of a textured molding impression, in particular for the molding of elastomer parts comprising a surface texturing. This method is based on the acquisition of a texture from a natural model of which it is desired to reproduce a surface state on an elastomer part, by overmolding said model between two calendered sheets of elastomeric material and vulcanization for a period of between 20 minutes and 60 minutes at a temperature between 80 ° C and 200 ° C. The invention also relates to a molding impression of elastomeric material thus obtained and a method of molding a textured elastomeric part obtained by vulcanization in the impression of the invention of a sheet of green calendered elastomeric material on a base element of the invention. the same partially vulcanized elastomeric material. Finally, the invention relates to a textured elastomeric part obtained according to the inventive molding process.

Description

Technical area

The present invention relates to the field of the manufacture of elastomer parts. It relates more particularly to a process for creating a molding impression of an elastomer part comprising a surface texturing, in particular a texturing of the natural material type or a texturing obtained by own know-how.

[0002] The invention also relates to a method of molding a part of elastomeric material comprising a surface texturing from such an impression.

[0003] The invention can advantageously be applied to the field of watchmaking, luxury goods, leather goods, packaging, window displays, in particular trim or to other industrial fields using rubber or various elastomers.

State of the art

[0004] It is known to manufacture parts such as watch straps, in natural or synthetic rubber, or in various plastics. These bracelets are generally made by molding, the mold possibly comprising structures allowing graphic elements, such as a mark or a logo, or sometimes even a local or more extensive surface texture intended to provide an effect to appear on the bracelet. particular aesthetic and / or tactile. Only the relief makes it possible to discern the shape or the inscription, both visually and tactilely.

[0005] However, it turns out that the current molding methods do not make it possible to provide a local or heard surface texturing of an elastomeric part providing a faithful rendering of a texture of a natural material such as a leather, a feather, flaking skin, bark, etc ... such that the rendering of the textured part can, at least to the naked eye and / or to the touch, be confused with said natural material.

[0006] This is due in particular to the fact that the molding impressions known to date do not make it possible to sufficiently faithfully reproduce the textural fineness of natural materials, for lack of resolution of the methods of acquiring and / or reproducing the surfaces of these. natural materials.

[0007] Indeed, the molding impressions of elastomeric materials are conventionally obtained by removal of material using laser according to digital models obtained by computer-aided design or by shaping (stamping, molding) of a rigid impression of metal or plastic material resistant to vulcanization temperatures of the elastomeric materials to be molded. Unfortunately, these techniques do not make it possible to produce in an industrial manner, other than by manual final machining, surface states of the molds comprising pitches of less than a millimeter, even less than a tenth of a millimeter. However, a number of natural or synthetic biological materials such as feathers, skins, hair for example exhibit such dimensional variations in surface, or simply individual dimensions so small that they cannot be molded or reproduced faithfully.

The object of the present invention is to overcome the drawbacks of the methods for obtaining parts made of textured elastomers, such as bracelets, but not only, mentioned above.

Disclosure of the invention

[0009] To achieve these aims, the invention relates to a method, the characteristics of which are mentioned in the claims.

[0010] More particularly, according to a first object, the invention relates to a method for producing a textured molding impression, in particular for the molding of elastomer parts comprising a surface texturing, comprising the following steps: Provide a natural model whose surface condition is to be reproduced on an elastomer part; Arrange the natural model between two sheets of a first calendered elastomeric material to form an impression acquisition assembly; Arranging the fingerprint acquisition assembly between two sheets of a second calendered elastomeric material different from the first elastomeric calendered elastomeric material so as to cover the impression acquisition assembly; Place the whole between two compression plates of a steaming shuttle and close said shuttle by clamping the two said plates against each other so as to compress the sheets of second calendered material on the acquisition assembly of imprint between said plates; Heat the steaming shuttle for a period of between 20 minutes and 60 minutes at a temperature of between 80 ° C and 200 ° C to at least partially vulcanize each sheet of first calendered elastomeric material and overmold said natural pattern in one side of those -this ; Open the shuttle and remove the natural pattern from between the impression acquisition blocks to obtain two textured mold impressions comprising a sheet of at least partially vulcanized vulcanized calendered elastomeric material.

[0011] This method thus advantageously makes it possible to produce a mold imprint in flexible elastomer material and textured in the mass, making it possible to obtain an extremely faithful negative, without alteration or finishing by machining, of the surface texture of n ' any basic model, natural or not, in order to transfer this texture to a later molded elastomeric part, unlike the hard molds known from the prior art.

[0012] The invention also relates, moreover, according to a second object, to a flexible molding impression obtained by this method.

Finally, according to a third object, the invention relates to a method of molding a part of elastomeric material and an elastomer part obtained by this method, which comprises the following steps: <tb> <SEP> a) Provide a molding impression according to one of claims 6 to 8, <tb> <SEP> b) Arranging a sheet of green calendered elastomeric material in said mold cavity; <tb> <SEP> c) Arrange on the sheet of green calendered elastomeric material an element of partially vulcanized pre-molded elastomeric material having substantially the shape of the part that is to be obtained, and <tb> <SEP> d) Place the molding impression in which the sheet of raw elastomer material and the pre-molded element have been superimposed between two compression plates of a steaming shuttle and tighten the two said plates one against the other so as to compress the sheet of green elastomer material and the element pre-molded in the impression, <tb> <SEP> e) Heat the shuttle after closing to a temperature between 150 ° C and 220 ° C, preferably between 160 ° C and 200 ° C, for at least 30 minutes to vulcanize the sheet of green elastomeric material and the element pre-molded together to form a textured elastomeric part; <tb> <SEP> f) After firing, separate the textured elastomeric part thus formed, the face of which resulting from the raw calendered material before curing in contact with the impression is textured.

Brief description of the drawings

Other characteristics of the present invention will emerge more clearly on reading the following description, made with reference to the accompanying drawings, in which:

- Figure 1 shows schematically the different steps of the method of forming a molding impression according to the invention and

[0016] FIG. 2 schematically represents the various steps of a method for molding a textured elastomeric part using an impression obtained according to the method of FIG. 1.

Mode (s) for carrying out the invention

In the following description, the method of making a molding impression and then the process of molding a textured elastomer part using an impression thus obtained will be described in particular in relation to the production of 'a strand of a watch strap. However, this application will not be able to be adopted as limiting the scope of the present invention, which will apply equally to the production of molding impressions and of textured elastomer molded parts of all kinds and for all applications.

Referring firstly to Figure 1, the invention relates according to a first object to a method of making a textured molding impression. In contrast with the molding impressions known from the prior art and their manufacturing techniques, the invention proposes the manufacture of impressions, that is to say of flexible molds, themselves made of elastomeric material, which were overmolded on a natural model in order to acquire the texture in its smallest details, such as a negative, to then transfer the texture thus acquired to a molded part of elastomer during a molding process described below in relation of Figure 2 in particular.

The production of textured elastomer imprints and their implementation for the molding of textured elastomeric parts also constitute essential characteristics of the methods proposed by the invention.

[0020] According to the block diagram given in FIG. 1, the invention relates firstly to a method of acquiring a textured molding imprint, in particular for the molding of elastomer parts comprising a surface texturing.

Prior to the actual impression taking, it is necessary in a first step 1 to provide a model of which one wishes to reproduce a surface condition on an elastomer part. Such a model can be of any nature and origin and have a very diverse surface condition but preferably not smooth, that is to say having roughness. Said asperities can be of extremely small dimensions, in particular of the order of a few tenths of a millimeter in depth or length / width, such as coarser, of the order of several millimeters, or even centimeters. The model to be reproduced may in particular preferably be a natural material of an animal, plant, lithographic or other nature. Mention may be made, among others, without limitation: skins, leathers, coats, feathers, bark, rocks, etc.

Once the model has been selected, it is then appropriate in a second step 2 to place it between two sheets of a first green calendered elastomer material to form a set of impression acquisition by vulcanization of said sheets of first elastomeric material calendered.

The use of sheets of raw calendered elastomeric material, that is to say unvulcanized and obtained by lamination of elastomeric material to form calibrated strips and / or sheets is of particular importance for the process of invention. Indeed, such sheets make it possible to adjust the thickness and the material of the impression produced according to the model chosen, without altering the latter but by "printing" the surface texture perfectly, by overmolding, as will be. described later.

In the context of the invention, use will be made in particular for the production of the impression acquisition assembly of calendered sheets with a thickness preferably between 0.5 mm and 10 mm, more preferably included between 1 mm and 3 mm.

Each sheet of first calendered material, calibrated aims to provide a flexible half-mold of the overmolded model, half-mold whose thickness must be at least 10% greater than half the thickness of the model. Also, the invention, although not specifically limited to the overmolding of a model with a thickness greater than 10 mm, is in practice particularly suitable for obtaining textured impressions from models of relatively small thicknesses, less than a centimeter, a thickness which makes it particularly overmolding by hard materials more delicate in practice.

The first elastomer material constituting these calendered sheets will also be chosen from a fluorinated elastomer material, in particular of the FKM type, or nitrile (NBR). A fluoroelastomer will be suitable in particular for overmolding and the acquisition of texture from relatively dense and resistant materials such as leathers, bark or stones, while nitrile will be more suitable for overmolding fragile materials and rough edges. fine surface such as fur or feathers.

Once the model is sandwiched between two sheets of first calendered elastomeric material, a so-called impression acquisition assembly is thus obtained, which is then in a third step 3 to be placed between two sheets of a second calendered elastomeric material, which is different from the first calendered elastomeric material, so as to cover the impression acquisition assembly. The second calendered elastomeric material should be of a different nature from the first and preferably consists of raw or partially vulcanized ethylene propylene diene monomer (EPDM). Such a material has the advantage of not adhering to the first elastomeric material during the subsequent baking of the impression.

The assembly thus formed must then be passed in an oven to cook, and therefore vulcanize, the sheets of first material calendered around the model for which it is desired to acquire a texture. To do this, in a fourth step 4 the said assembly is placed between two compression plates of a steaming shuttle, which is closed and clamped against each other so as to compress the sheets together. acquisition of imprint between said sheets of second calendered material and the plates of the shuttle.

Advantageously, the clamping plates of the shuttle each comprise an internal silicone compression sole, said sole having a different Shore A hardness, in practice preferably between 20 ° and 30 ° Shore A for a first sole and between 40 ° and 50 ° Shore A for a second sole.

Such a difference in hardness between the soles is particularly advantageous because it provides better compression of the impression acquisition assembly, therefore better overmolding of the model in the sheets of first calendered elastomeric material, by a thrust effect. of the harder sole on said impression acquisition assembly taken from the EPDM sheets in the softer sole.

Once the plates of the shuttle are then placed in a fifth step 5 said shuttle in an oven in order to heat it and its contents for a period of between 20 minutes and 60 minutes at a temperature of between 80 ° C. and 200 ° C to at least partially vulcanize each sheet of raw calendered first elastomeric material and overmold said pattern in one face thereof.

For a majority of materials and models, baking for 30 to 45 minutes between 160 ° C and 200 ° C will be perfectly suited to obtain complete vulcanization of the first calendered material and to obtain perfectly textured half-molds of the surface of the chosen model. However, for fragile models, prolonged cooking up to 60 min at a lower temperature, between 120 ° C and 150 ° C, may be preferred.

Once the cooking is complete, it suffices to remove the shuttle from the oven (or oven) and open it in a sixth step 6 to release the sheets of second calendered elastomeric material and release each half-mold textured imprint thus formed around the pattern obtained from the first vulcanized calendered elastomeric material.

The quality of said impressions thus obtained from the 1st molding is then checked, in particular their integrity and quality of texturing. In the event of a defect 7, the manufacturing process is recommenced as described above from new sheets of first and second calendered elastomer materials, and of course so on until impressions of satisfactory quality are obtained.

Once the satisfactory imprints obtained 8, one can then if necessary proceed to a subsequent engraving or finishing step 9, in particular to possibly integrate certain additional textures or markings into the imprint, then the latter is stored for use. in a molding process as described below. Unsatisfactory molded impressions are discarded and recycled.

Once a flexible textured elastomeric imprint obtained as described above, the invention also provides a method of molding a part of elastomeric material, for example without limitation a strand of a watch strap, textured according to the model obtained by the flexible impression. Such a molding process is shown schematically in Figure 2.

The molding process of the invention begins (a) by providing a molding imprint as previously obtained, as well as a first pre-molded elastomer element, having substantially the shape of the part that one wishes to obtain. This first pre-molded element can result from a previous molding, for example, by compressing an elastomer in a mold having the desired geometry, at a temperature which does not allow the elastomer to vulcanize.

A second step of the method consists (b) in placing a sheet of green calendered elastomeric material, that is to say unvulcanized, in the molding cavity, then (c) in placing thereon in said imprint the first elastomer element referred to above. The sheet of green calendered elastomeric material will thus serve to take the texture of the molding impression and simultaneously coat the first elastomeric element during molding and be fused therein by vulcanization as described below.

It will be noted that the sheet of green calendered material and the first pre-molded elastomeric element can be of different colors in order to create particular aesthetic effects where appropriate. However, advantageously, the sheet of green calendered material and the pre-molded element will both be made of an elastomeric material of the same nature in order to be able to be jointly vulcanized and to provide a complete mechanical bond during the molding. Preferably, a green sheet and a pre-molded element of ethylene propylene diene monomer (EPDM) may be chosen, the pre-molded element itself being partially vulcanized, in particular at least at T30 and at most at T80 before the start of the process. final molding.

The next step (d) consists, once this preparation has been carried out, to have the molding impression in which the sheet of green elastomeric material and the pre-molded element have been superimposed between two compression plates of a steaming shuttle.

This steaming shuttle can be of a similar nature to that used for the formation of the molding imprint as described above. Each clamping plate forming the steaming shuttle may in particular include an internal silicone compression sole, each one preferably of different Shore A hardness and in ranges of Shore A hardness as previously mentioned.

Then insert (e) the shuttle in a molding press to clamp the two said plates against each other so as to compress the sheet of green elastomer material and the pre-molded element in the imprint molding and heated to a temperature between 150 ° C and 220 ° C, preferably between 160 ° C and 200 ° C, for at least 30 minutes to vulcanize the sheet of green elastomeric material and the pre-molded member together .

This heating may result from heating by convection in an oven or, preferably, from heating by conduction of the press jaws in contact with the metal parts of the plates of the shuttle. This second heating method is in practice the most optimal in terms of controlling the heating temperature in the heart of the shuttle, and therefore the vulcanization temperature of the sheet of raw material on the pre-molded element. . It is in fact possible to adjust the heating according to an electronically regulated setpoint at the level of the clamping press, thermocouples being integrated into the press jaws to continuously measure the contact temperature with the clamping shuttle and transmit the measurements to the electronic device. control of the press for possible adjustment of the heating temperature taking into account a desired heating profile as a function of the thermal resistance parameters of the materials of the shuttle.

The jaws of the molding press apply during the molding on the compression plates of the steaming shuttle a pressure of at least 5 tons, preferably at least 7 tons, throughout the heating operation. Such pressure proves in practice necessary to ensure good bonding of the materials, without creeping out of the molding cavity during the vulcanization of the green sheet on the pre-molded element.

It should also be noted that the molding of several pre-molded elements can be carried out simultaneously without affecting the quality thereof. For this, it suffices to stack, between as many compression plates as necessary, a plurality of indentations in each of which will have been placed a said sheet of green calendered elastomer material and a pre-molded element to be coated and textured. Advantageously, up to 6 elastomeric parts can thus be molded simultaneously, thus using 6 impressions and 7 compression plates, thus forming a stepped shuttle inserted between the jaws of the molding press.

In such a simultaneous multi-molded configuration, care will then be taken to advantageously place silicone spacers between each compression plate and molding cavity on the one hand and the pre-molded element on the other hand, in order to apply the most uniform pressure on each stage of feed.

Once the baking is complete, the molding press is then opened and the shuttle is taken out. The compression plates are then separated to access the elastomeric part (s) thus molded, bearing a texture imparted by transfer of the molding imprint onto the portion resulting from the sheet of calendered material. flood vulcanized in the mass on the pre-molded element, now fully vulcanized.

It is then sufficient to recover (f) the parts thus molded for checking, deburring, possible final machining and then packaging with a view to subsequent final use.

The above description has been given by way of nonlimiting illustration of the invention, a preferred purpose of which may be to produce watch strap strands of elastomeric material. Those skilled in the art will however be able to adapt it without departing from its scope of the invention, in particular to produce various components of timepieces, such as inserts intended to be housed in watch crowns, or parts of backs. boxes or any other parts which may be made of elastomers and on which it may be advantageous to affix a decorative textured element.

Claims (15)

1. Method for producing a textured molding impression, in particular for the molding of elastomer parts comprising surface texturing, comprising the following steps: - Provide (1) a natural model for which one wishes to reproduce a surface condition on an elastomer part; - Arrange (2) the natural model between two sheets of a first calendered elastomeric material to form an impression acquisition assembly; - Arranging (3) the impression acquisition assembly between two sheets of a second calendered elastomeric material different from the first elastomeric calendered elastomer material so as to cover the impression acquisition assembly; - Arrange (4) the whole between two compression plates of a steaming shuttle and close said shuttle by clamping the two said plates against each other so as to compress the sheets of second calendered material on the impression acquisition assembly between said plates; - Heat the steaming shuttle for a period of between 20 minutes and 60 minutes at a temperature of between 80 ° C and 200 ° C to at least partially vulcanize each sheet of first calendered elastomeric material and overmold said natural model in a face of these; - Open the shuttle and remove the natural model from between the impression acquisition blocks to obtain two textured mold impressions comprising a sheet of first vulcanized elastomeric material at least partially vulcanized. 2. Method according to claim 1, characterized in that the first calendered elastomeric material is chosen from a fluorinated elastomer material, in particular of the FKM type, or nitrile (NBR). 3. Method according to claim 1 or 2, characterized in that the second calendered elastomeric material is ethylene propylene diene monomer (EPDM). 4. Method according to one of claims 1 to 3, characterized in that the clamping plates of the shuttle each comprises an internal silicone compression sole, said sole having a different Shore A hardness. 5. Method according to claim 4, characterized in that a first sole has a hardness of between 20 ° and 30 ° Shore A and a second sole has a hardness of between 40 ° and 50 ° Shore A. 6. Molding impression obtained by a production method according to one of claims 1 to 5. 7. A molding impression according to claim 6, characterized in that it comprises a first layer of a first elastomeric material comprising a textured molding shape and a second layer of a second calendered elastomeric material different from the first vulcanized to the first layer on a side thereof opposite to that having the textured molding form. 8. Molding impression according to claim 6 or 7, characterized in that the first calendered elastomer material comprises a fluoroelastomer material, in particular of the FKM type, or nitrile (NBR) and the second calendered elastomer material comprises ethylene propylene. monomeric diene (EPDM). 9. A method of molding a piece of elastomeric material, comprising the following steps: at. Provide a molding impression according to one of claims 6 to 8, b. Disposing a sheet of green calendered elastomeric material in said mold cavity; vs. Arranging on the sheet of green calendered elastomeric material an element of partially vulcanized pre-molded elastomeric material having substantially the shape of the part which is desired to be obtained, and d. Arrange the molding cavity in which the sheet of green elastomer material and the pre-molded element have been superimposed between two compression plates of a steaming shuttle and clamp the two said plates against each other of so as to compress the sheet of green elastomeric material and the pre-molded element in the impression, e. Heat the shuttle after closing to a temperature between 150 ° C and 220 ° C, preferably between 160 ° C and 200 ° C, for at least 30 minutes to vulcanize the sheet of green elastomeric material and the pre-molded member together to form a textured elastomeric part; f. After firing, separate the textured elastomeric part thus formed, the face of which resulting from the raw calendered material before firing in contact with the impression is textured. 10. The method of claim 9, characterized in that the sheet of green calendered material and the pre-molded element consist of an elastomeric material of similar chemical nature, so as to be able to be crosslinked together. 11. The method of claim 9 or 10, characterized in that the sheet of green calendered material and the pre-molded element consist of ethylene propylene diene monomer (EPDM). 12. Method according to one of claims 9 to 11, characterized in that the compression plates are held against each other under a pressure of at least 5 tonnes, preferably at least 7 tonnes, during the heating operation. 13. Method according to one of claims 9 to 12, characterized in that the pre-molded element is vulcanized at least at T30 and at most at T80 before the heating step. 14. Method according to one of claims 9 to 13, characterized in that there are silicone spacers between a compression plate and the molding cavity on the one hand and the other compression plate and the pre-molded element on the other hand. 15. Textured elastomeric part obtained according to the method of one of claims 9 to 14.