CH711883B1 - Process of impregnating a plastic part. - Google Patents

Abstract

The invention relates to a process for impregnating a finished plastic part through the core with an additive, comprising the following steps: - dissolving the additive in a carrier liquid to form a solution; - placing the plastic part at ambient pressure in an enclosure which can be pressurized; - hermetically close the enclosure; - impregnating the plastic part of the solution with carbon dioxide under conditions close to supercritical conditions, that is to say at a pressure slightly below its critical value so as to obtain a liquid vapor mixture, in the enclosure at a pressure of 4 MPa, and at a temperature between 50 ° C and 60 ° C for a period of between 5 min and 10 min; - Release the pressure in the chamber so that the carrier liquid diffuses outside the plastic part and to trap the additive inside the plastic part.

Description

Field of the invention

The present invention relates to a method for impregnating a plastic part with an additive using a supercritical fluid. More specifically, the invention relates to a process for impregnating timepieces, as well as the parts obtained.

Background of the invention

[0002] Supercritical CO2 has known commercial applications, such as the thorough cleaning of industrial parts or the extraction of caffeine from coffee.

[0003] Many impregnation processes using a supercritical fluid have been the subject of patents and are known for their speed and their lower costs. Carbon dioxide is often used for its low cost and the very low risks when handling it.

[0004] Thus, it is known from document EP 0 200 197 to impregnate parts made of thermoplastic polymer material with an odorous material using a fluid in or near supercritical conditions of temperature and pressure. In this document, the impregnation is carried out at a pressure of 17 MPa and at a temperature between 25 ° C and 60 ° C for polymers such as polypropylene, polyethylene, ethylene-vinyl acetate (EVA) copolymers and ethylene ethyl acrylate copolymers.

[0005] Document EP 0 683 804 also discloses a process for impregnating a polymeric substrate with an additive by means of a supercritical fluid. In this document, the impregnation is carried out at a pressure of preferably between 7 MPa and 30 MPa and at a temperature of between 30 ° C and 60 ° C for polymers such as polyolefins, polyamides, polyurethanes, silicones, albumin, polymers of lactic and glycolic acid, and combinations thereof.

[0006] Thus, impregnation processes using supercritical CO 2 have already been described in the prior art. However, none of them describes a rapid process, easy to implement and usable regardless of the type of polymer materials to be impregnated. Indeed, the methods described are relatively long, two hours or more, and the pressure used is very high, between 7 MPa and 30 MPa.

[0007] According to the findings of the inventor, these processes in particular do not allow impregnation of timepieces made from polymeric materials while maintaining a satisfactory quality of these parts for the watch industry ( fine dimensional tolerances, surface quality and color quality), and more specifically for copolymer materials such as methyl methacrylate-acrylonitrile-butadiene-styrene (M-ABS) and thermoplastic polyurethane (TPU) materials.

[0008] In fact, after experiments, the inventor observed that the pressure and temperature parameters used in the prior art to impregnate certain materials led to numerous defects in the materials, even significant deformations or foaming of the part, which is particularly troublesome for the manufacture of plastic timepieces for example.

Summary of the invention

[0009] The object of the invention is in particular to overcome the various drawbacks of these known techniques for application in the watchmaking or jewelery world.

[0010] More precisely, an objective of the invention is to provide a method making it possible to rapidly impregnate finished plastic parts with an additive which would be too sensitive to temperature or to shear to be added during a classic mixing or molding process. Such a process also makes it possible to gain flexibility for production. With such a process, one can easily set up by model the molding of a single reference of white or transparent color without additive. This reference is then colored or functionalized (that is to say provided with a new property) by the process according to the needs of the market.

Another objective of the invention is to provide a method making it possible to reduce the times and costs of manufacturing plastic watches.

[0012] These objectives, as well as others which will emerge more clearly below, are achieved according to the invention using a process for impregnating to the heart of a finished plastic part with at least one additive. According to the invention, the method comprises the following steps: <tb> - <SEP> dissolving at least one additive in a carrier liquid to form a solution; <tb> - <SEP> placing the plastic part at ambient pressure in an enclosure which can be pressurized; <tb> - <SEP> hermetically close the enclosure; <tb> - <SEP> impregnate the plastic part of the solution with carbon dioxide under conditions close to supercritical conditions, that is to say at a pressure slightly below its critical value so as to obtain a liquid vapor mixture, in the chamber at a pressure of between 4 MPa and 6 MPa, and at a temperature of between 50 ° C and 60 ° C for a period of between 5 min and 10 min; <tb> - <SEP> release the pressure in the enclosure so that the carrier liquid diffuses outside the plastic part and to trap at least part of the additive inside the material part plastic.

[0013] According to other advantageous variants of the method according to the invention: <tb> - <SEP> the material is chosen from thermoplastic polyurethanes, polyamides, methyl acrylonitrile butadiene styrene or polymethyl metacrylates; <tb> - <SEP> the carrier liquid is chosen from hexane, isopropanol, D-limonene; <tb> - <SEP> the additive is chosen from colorants, anti-odor agents, fragrances, cosmetic active additives; <tb> - <SEP> the plastic material is impregnated with a combination of at least two additives; <tb> - <SEP> the impregnation is carried out under constant flow; <tb> - <SEP> the method comprises a step of washing the plastic part after releasing the pressure in the chamber to remove the residues; <tb> - <SEP> the washing step is carried out with clean water and by means of a brush or the like.

The invention also relates to all timepieces and jewelry made of copolymer material obtained by the process according to the invention.

Brief description of the drawings

Other characteristics and advantages of the invention will emerge more clearly on reading the following description of a particular embodiment of the invention, given by way of simple illustrative and non-limiting example, and the appended figures , among : <tb> - <SEP> FIG. 1 is a photo of plastic timepieces illustrating the results of a first test; <tb> - <SEP> FIG. 2 is a photo of plastic timepieces illustrating the results of a second test; <tb> - <SEP> FIG. 3 is a photo of a section of a plastic timepiece illustrating the results of a third test; <tb> - <SEP> FIG. 4 is a photo of a plastic timepiece illustrating the results of a fourth test; <tb> - <SEP> Figure 5 is a photo of a plastic timepiece illustrating the results of a fifth test; <tb> - <SEP> FIG. 6 is a photo of a plastic timepiece illustrating the results of a sixth test; <tb> - <SEP> Figure 7 is a photo of plastic timepieces illustrating the results of a seventh test. <tb> - <SEP> FIG. 8 is a photo of a plastic timepiece illustrating the results of an eighth test; <tb> - <SEP> Figure 9 is a photo of a plastic timepiece showing the results of a ninth test.

Detailed description of the preferred embodiments

The invention relates to a process for impregnating a finished piece of plastic material with at least one additive. According to the invention, the method comprises the following steps: <tb> - <SEP> dissolving at least one additive in a carrier liquid to form a solution; <tb> - <SEP> placing the plastic part at ambient pressure in an enclosure which can be pressurized; <tb> - <SEP> hermetically close the enclosure; <tb> - <SEP> impregnate the plastic part of the solution with carbon dioxide under conditions close to supercritical conditions, that is to say at a pressure slightly below its critical value so as to obtain a liquid vapor mixture, in the chamber at a pressure of 4 MPa, and at a temperature between 50 ° C and 60 ° C for a period of between 5 min and 10 min; <tb> - <SEP> release the pressure in the enclosure so that the support liquid diffuses outside the plastic part and to trap the at least one additive inside the plastic part.

By fluid under supercritical conditions, or supercritical fluid, is meant within the meaning of the present invention a fluid used at a temperature and a pressure above its critical value so as to place it in its supercritical state and thus disperse it more easily in a material, such as polymers, copolymers or elastomers.

By fluid close to supercritical conditions is meant within the meaning of the present invention a fluid used at a pressure slightly below its critical value so as to obtain a liquid vapor mixture.

By core impregnation is meant penetration of the additive into the thickness of the material so as to have a wear-resistant coloring of the part.

By finished part is meant any machined part originating for example from an operation of injection, extrusion, thermoforming, molding, and ready to be assembled.

There are many supercritical fluids to impregnate materials, and preferably a non-reactive and non-toxic supercritical fluid such as CO2 will be used, on the one hand to avoid altering certain additives and, on the other hand, to treat materials intended to be in contact with the skin and to prevent skin reactions.

The CO 2 also makes it possible to limit the costs of the impregnation operation by virtue of its temperature and its pressure to reach the supercritical state.

The pressure is between 3 MPa and 6 MPa, and the temperature is between 25 ° C and 65 ° C.

The inventor has found that beyond these parameters many defects were present in the material of the plastic part depending on the polymers used, and in particular for the following thermoplastics which are commonly used to make watches in plastic: thermoplastic polyurethanes, polyamides, methyl acrylonitrile butadiene styrene, polymethyl methacrylates.

For the purposes of the present invention, the term “additive” is understood to mean any organic or inorganic additive with a density of less than 3 and with a particle size of less than 50 micrometers, whether it is soluble or sparingly soluble in a liquid medium. This process is therefore not limited to additives soluble in a liquid medium.

[0026] According to one embodiment of the invention, the additive can be a dye or a pigment (organic or inorganic). Mention may be made, by way of example, of azo dyes.

[0027] The additive can also be an active substance in cosmetics, for example hyaluronic acid or ceramides may be mentioned.

[0028] The additive can also be an anti-odor agent such as zinc pyrithium or else a fragrance such as essential oils for example.

[0029] According to the invention, the plastic material can be impregnated with a combination of additives. The plastic material can, for example, be impregnated with a dye and an anti-odor agent.

By carrier liquid is meant within the meaning of the present invention, a co-solvent such as hexane, isopropanol or even D-limonene.

According to a preferred embodiment of the invention, the method is implemented under a constant flow of supercritical CO 2, that is to say that all the reagents are brought together simultaneously and the supercritical CO 2 is injected for a period of time determined. For example, in the fourth step of the invention, supercritical CO 2 is injected for a predetermined time into the chamber receiving the mixture obtained during the first step and the plastic part to be impregnated.

[0032] According to one embodiment of the invention, the material to be impregnated is chosen from the family of acrylates or polyurethanes.

The first step of the process according to the invention allows for the intimate mixture of the additive and the co-solvent before the diffusion step. By intimate mixture is meant a mixture in which the additive and the co-solvent are found uniformly distributed (either a dispersion or a dissolution) within the mixture obtained. The first step therefore makes it possible to optimize the impregnation and obtain better results. The mixture obtained at the end of the first step is therefore preferably a liquid mixture so as to reduce the impregnation time during the fourth step. The first three steps of the process are carried out at room temperature and pressure.

The fourth step of the process according to the invention makes it possible to impregnate the material with the additive. The fourth step is carried out in a hermetically sealed enclosure. The mixture obtained during the first step is introduced into an enclosure with the plastic part to be impregnated, before closing the enclosure hermetically. During the third and fourth step of the process, the enclosure is closed, pressurized and brought to the desired temperature for the time necessary for the CO2 then in near-supercritical form to allow the plastic part to be impregnated. with the additive at the desired content. The longer the treatment, the more the plastic part will be impregnated with, however, a saturation phenomenon when the porosities of the plastic part are filled.

During the fourth step, the plastic part to be impregnated remains in solid form. The temperature during the fourth stage is between 25 and 65 ° C. Such temperatures make it possible to prevent deterioration of the plastic material during impregnation.

The pressure during the fourth step is between 3 MPa and 6 MPa, for example equal to 4 MPa. Such pressures have the advantage of being able to use inexpensive infrastructures compared to the state of the art.

In a particular embodiment, the contact time during the fourth step is preferably between one minute and fifteen minutes, and more preferably between one minute and ten minutes, for example equal to five minutes. Such a processing time makes it possible to rapidly impregnate the plastic parts and therefore to process a larger quantity of parts.

Depending on the desired coloring, the impregnation time or the pressure can be adjusted so as to obtain a lighter or darker coloring.

The fifth step makes it possible to recover and isolate the impregnated plastic part obtained following the fourth step and optionally to separate the additive which has not impregnated the plastic part. For this, the enclosure used is depressurized and gradually cooled. It is then maintained at ambient pressure for 2 minutes.

According to the invention, the method may include a step of washing the plastic part, after releasing the pressure in the chamber, to remove the residues remaining on the surface such as a surplus of dye for example.

[0041] According to a preferred embodiment of the invention, the washing step is preferably carried out with clean water and by means of a brush or equivalent. One could also use low pressure water jets or pass the impregnated parts in a bath. The agitation of the bath can also be provided and adapted to the necessary cleaning.

The plastic part impregnated with the additive can be used in the manufacture of timepiece or jewelry, and more particularly plastic timepieces or jewelry. In particular, the process can be used in the manufacture of watch cases, bracelets, bezels, crowns, dials, pushers, crystals, buckles, or even any plastic part forming part of a watch or of a jewel. The present invention also relates to a piece of timepiece or jewelry made of plastic, in solid form, and impregnated with an additive by the process according to the present invention as described above.

[0043] Thus, the watch or jewelery components in plastic already molded or machined can be impregnated by this process while retaining the initial properties of the component, in particular the dimensions and the mechanical characteristics.

The following examples are given as an indication and are not limiting. The coloring and impregnation treatments were carried out on watch cases injected into the materials indicated.

Table 1:

[0045] <tb> Test 1 <SEP> Acrylonitrile Butadiene Styrene <SEP> 8.3 <SEP> 60 <SEP> 45 <SEP> 10 <SEP> none <SEP> Foaming of the part <tb> Test 2 <SEP> Thermoplastic polyurethane (polyether base) 65shore A <SEP> 7.6 <SEP> 50 <SEP> 30 <SEP> 10 <SEP> 6.6% hexane <SEP> Foaming of the part <tb> Test 3 <SEP> Acrylonitrile Butadiene Styrene <SEP> 6.2 <SEP> 55 <SEP> 10 <SEP> 2 <SEP> 1.6% hexane <SEP> Foaming of the part <tb> Test 4 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 5.5 <SEP> 35 <SEP> 10 <SEP> 2 <SEP> 1.6% hexane <SEP> Foaming of the part <tb> Test 5 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 4 <SEP> 35 <SEP> 10 <SEP> 2 <SEP> 1.6% hexane <SEP> Coloring only on 100 micrometers in the thickness <tb> Test 6 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 1.5 then 5.5 <SEP> 45 <SEP> 5 then 10 <SEP> 2 <SEP> 1.6% in hexane <SEP> Incomplete coloring in the thickness

Table 2:

[0046] <tb> Test 7 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 5.5 <SEP> 60 <SEP> 13 <SEP> 2 <SEP> 1.6% hexane <SEP> Light foaming giving a whitish appearance <tb> Test 8 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 4 <SEP> 100 <SEP> 10 <SEP> 10 <SEP> 1.6% hexane <SEP> Very significant foaming <tb> Test 9 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 4 <SEP> 60 <SEP> 10 <SEP> 10 <SEP> 1.6% hexane <SEP> Nice color, but very light bleaching on the surface <tb> Test 10 <SEP> Methylmetacrylate Butadiene Styrene / Thermoplastic polyurethane <SEP> 4 <SEP> 50 <SEP> 10 <SEP> 10 <SEP> 1.6% hexane <SEP> Homogeneous color without foaming, but slight bleaching on the surface <tb> Test 11 <SEP> Methylmetacrylate Butadiene Styrene <SEP> 4 <SEP> 50 <SEP> 5 <SEP> 5 <SEP> 1.6% hexane <SEP> Homogeneous color slightly lighter <tb> Test 12 <SEP> Thermoplastic polyurethane (polyether base) 65shore A <SEP> 4 <SEP> 50 <SEP> 5 <SEP> 5 <SEP> 1.6% hexane <SEP> Homogeneous color

In these two tables, the same additives were used, namely an azo dye, chromophtal®, and an aromatic hydrocarbon, anthraquinone (oracet®). A single co-solvent is used, hexane, and three plastics have been tested, acrylonitrile butadiene styrene, thermoplastic polyurethane (polyether base) and methylmetacrylate butadiene styrene.

In Figure 1 corresponding to tests 1 and 2, we can observe a complete deformation of the part due to foaming and non-uniform coloring. These same results are observed in FIG. 2 for tests 3 and 4; deformations are visible on the parts.

In Figure 3 corresponding to test 5, it is observed that the part is colored only on the surface and to a very shallow depth; the dye did not penetrate deep enough to provide correct and lasting coloration over time despite wear.

In Figure 4, corresponding to test 7, there is a bleaching of the part after impregnation, which is not acceptable.

In Figure 5 corresponding to test 8, there is significant foaming of the part after impregnation which makes it unusable.

Figure 6 illustrates the result of test 9, a slight is observed on the surface of the part following the impregnation due to the migration of waxes used in the MABS plastic as a processing agent, however the coloring is satisfactory.

FIG. 7 illustrates parts colored according to the conditions of test 10. A homogeneous coloring of good quality is observed without any deformation of the plastic parts. However, a very slight white veil is visible on the surface, indicating the start of migration of certain plastic additives.

FIG. 8 illustrates two parts of styrene butadiene methacrylate corresponding to test 11. A homogeneous coloring is observed without deformation and without bleaching.

FIG. 9 illustrates two thermoplastic polyurethane parts corresponding to test 12. A homogeneous coloring is observed without deformation and without bleaching.

Of course, the present invention defined by the claims is not limited to the example illustrated and is susceptible of various variants and modifications which will appear to those skilled in the art.

Claims (9)

1. A process for impregnating a finished plastic part with at least one additive to the core, characterized in that it comprises the following steps: - dissolving the at least one additive in a carrier liquid to form a solution; - placing the plastic part at ambient pressure in an enclosure which can be pressurized; - hermetically close the enclosure; - impregnate the plastic part of the solution with carbon dioxide under conditions close to supercritical conditions, that is to say at a pressure slightly below its critical value so as to obtain a liquid vapor mixture, in the enclosure at a pressure of 4 MPa, at a temperature between 50 ° C and 60 ° C for a period of between 5 min and 10 min; - Releasing the pressure in the enclosure so that the support liquid diffuses outside the plastic part and to trap at least one additive inside the plastic part. 2. The method of claim 1, wherein the material is chosen from polyurethane thermoplastics, polyamides, methyl acrylonitrile butadiene styrene, polymethyl methacrylates. 3. Method according to one of claims 1 and 2, wherein the carrier liquid is chosen from hexane, isopropanol or D-limonene. 4. Method according to one of claims 1 to 3, wherein the additive is chosen from colorants, anti-odor agents, fragrances, cosmetic active additives. 5. The method of claim 4, wherein the plastic is impregnated with a combination of at least two additives. 6. Method according to one of claims 1 to 5, wherein the impregnation is carried out under constant flow. 7. Method according to one of claims 1 to 6, comprising a step of washing the plastic part to remove residues. 8. The method of claim 7, wherein the washing step is performed with clean water and by means of a brush. 9. Watchmaker or jeweler component in plastic material obtained by the process according to claims 1 to 8.