Method for impregnation of a part made of plastic material

Abstract

A method for core impregnation of a finished part made of plastic material with an additive, including: dissolving the additive in a liquid medium to form a solution; placing the plastic part at ambient pressure in a pressure enclosure; hermetically sealing the chamber; impregnating the plastic part with the solution by a fluid at supercritical or near supercritical conditions in the enclosure at a pressure between 3 MPa and 6 MPa, at a temperature between 25 C. and 65 C. for a duration between 1 minute and 15 minutes; releasing the pressure inside the enclosure so that the liquid medium diffuses outside the plastic part and to trap the additive inside the plastic part.

Claims

1. A method for core impregnation of a finished part made of plastic material with at least one additive, the method comprising: dissolving the at least one additive in a liquid medium to form a solution; placing a plastic part at ambient pressure in a pressure enclosure; hermetically sealing the chamber; impregnating the plastic part with the solution by carbon dioxide in the enclosure at a pressure between 3 MPa and 6 MPa, at a temperature between 40 C. and 65 C. for a duration between 1 minute and 10 minutes; releasing the pressure inside the enclosure so that the liquid medium diffuses outside the plastic part and to trap the at least one additive inside the plastic part, wherein the plastic part is a watch case, a watch wristband, a watch bezel, a watch crown, a watch dial, a watch push-button, a watch crystal, or a watch loop.

2. The method according to claim 1, wherein the material is a thermoplastic material chosen from polyurethanes, polyamides, methyl acrylonitrile butadiene styrene, or poly(methyl methacrylate).

3. The method according to claim 1, wherein the liquid medium is chosen from hexane, isopropanol, or d-limonene.

4. The method according to claim 1, wherein the additive is chosen from dyes, anti-odour agents, or fragrances.

5. The method according to claim 4, wherein the additive includes a combination of at least two additives.

6. The method according to claim 1, wherein the impregnation is carried out with the carbon dioxide under constant flux.

7. The method according to claim 1, further comprising washing the part made of plastic material to eliminate residues.

8. The method according to claim 7, wherein the washing is carried out with clean water and using a brush.

9. The method according to claim 1, wherein the impregnating includes impregnating the plastic part with the solution by the carbon dioxide in the enclosure at the pressure of 4 MPa, at the temperature between 50 C. and 60 C. for a duration between 5 minutes and 10 minutes.

10. The method according to claim 1, wherein the additive is a hyaluronic acid or ceramide.

11. A method for core impregnation of a finished part made of plastic material with at least one additive, the method comprising: dissolving the at least one additive in a liquid medium to form a solution, wherein the at least one additive is a hyaluronic acid or ceramide; placing a plastic part at ambient pressure in a pressure enclosure; hermetically sealing the chamber; impregnating the plastic part with the solution by carbon dioxide in the enclosure at a pressure between 3 MPa and 6 MPa, at a temperature between 40 C. and 65 C. for a duration between 1 minute and 10 minutes; releasing the pressure inside the enclosure so that the liquid medium diffuses outside the plastic part and to trap the at least one additive inside the plastic part.

12. The method according to claim 11, wherein the material is a thermoplastic material chosen from polyurethanes, polyamides, methyl acrylonitrile butadiene styrene, or poly(methyl methacrylate).

13. The method according to claim 11, wherein the liquid medium is chosen from hexane, isopropanol, or d-limonene.

14. The method according to claim 13, wherein the additive includes a combination of at least two additives.

15. The method according to claim 11, wherein the impregnation is carried out with the carbon dioxide under constant flux.

16. The method according to claim 11, further comprising washing the part made of plastic material to eliminate residues.

17. The method according to claim 16, wherein the washing is carried out with clean water and using a brush.

18. The method according to claim 11, wherein the impregnating includes impregnating the plastic part with the solution by the carbon dioxide in the enclosure at the pressure of 4 MPa, at the temperature between 50 C. and 60 C. for a duration between 5 minutes and 10 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the invention will appear more clearly upon reading the following description of a specific embodiment of the invention, given simply by way of illustrative and non-limiting example, and the annexed Figures, among which:

(2) FIG. 1 is a photograph of timepieces made of plastic material illustrating the results of a first test.

(3) FIG. 2 is a photograph of timepieces made of plastic material illustrating the results of a second test.

(4) FIG. 3 is a photograph of a cross-section of a timepiece made of plastic material illustrating the results of a third test.

(5) FIG. 4 is a photograph of a timepiece made of plastic material illustrating the results of a fourth test.

(6) FIG. 5 is a photograph of a timepiece made of plastic material illustrating the results of a fifth test.

(7) FIG. 6 is a photograph of a timepiece made of plastic material illustrating the results of a sixth test.

(8) FIG. 7 is a photograph of timepieces made of plastic material illustrating the results of a seventh test.

(9) FIG. 8 is a photograph of a timepiece made of plastic material illustrating the results of an eighth test.

(10) FIG. 9 is a photograph of a timepiece made of plastic material illustrating the results of a ninth test.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(11) The invention concerns a method for the core impregnation of a finished part made of plastic material with at least one additive. According to the invention, the method includes the following steps: dissolving at least one additive in a liquid medium to form a solution; placing the plastic part at ambient pressure in a pressure enclosure; hermetically sealing the chamber; impregnating the plastic part with the solution by means of a fluid at supercritical conditions or near supercritical conditions in the enclosure at a pressure comprised between 3 MPa and 6 MPa, at a temperature comprised between 25 C. and 65 C. for a duration preferably comprised between 1 minute and 15 minutes, and even more preferentially between 1 minute and 10 minutes; releasing the pressure in the enclosure so that the liquid medium diffuses outside the plastic part and to trap the at least one additive inside the plastic part.

(12) For the purposes of the present invention, a fluid at supercritical conditions, or supercritical fluid means a fluid used at a temperature and pressure higher than its critical point, so that it is placed in a supercritical state and thus more easily dispersed in a material, such as polymers, copolymers or elastomers.

(13) For the purposes of the present invention, a fluid near supercritical conditions means a fluid used at a pressure slightly lower than its critical point to obtain a liquid-vapour mixture.

(14) Core impregnation means penetration of the additive into the thickness of the material to obtain wear-resistant colouring of the part.

(15) A finished part means any ready-to-use machined part, for example following an injection, extrusion, thermoforming or moulding operation.

(16) There are many supercritical fluids for impregnating materials, and a non-reactive and non-toxic supercritical fluid will preferably be used, such as CO.sub.2, on the one hand to avoid degrading certain additives, and, on the other hand to treat materials intended to be in contact with the skin to avoid skin reactions.

(17) CO.sub.2 also limits the costs of the impregnation operation given the temperature and pressure required to reach its supercritical state.

(18) According to the invention, the pressure is comprised between 3 MPa and 6 MPa, and the temperature is comprised between 25 C. and 65 C.

(19) The inventor found that, beyond these parameters, numerous defects were present in the material of the plastic part according to the polymers used, and particularly for the following thermoplastics which are commonly used to make plastic watches: thermoplastic polyurethanes, polyamides, methyl acrylonitrile butadiene styrene, poly(methyl methacrylate).

(20) An additive means, within the meaning of the invention, any organic or inorganic additive, with a density of less than 3 and particle size of less than 50 microns, whether soluble or poorly soluble in a liquid medium. This method is not, therefore, limited to additives soluble in a liquid medium.

(21) According to one embodiment of the invention, the additive may be a dye or a pigment (organic or inorganic). Azo dyes can be mentioned as an example.

(22) The additive may also be an active cosmetic ingredient: hyaluronic acid or ceramides can be mentioned as examples.

(23) The additive may also be an anti-odour agent such as zinc pyrithione, or a fragrance such as essential oils, for example.

(24) According to the invention, the plastic material can be impregnated with a combination of additives. For example, the plastic material can be impregnated with a dye and an anti-odour agent.

(25) For the purposes of the invention, a liquid medium means a cosolvent such as hexane, isopropanol or d-limonene.

(26) According to a preferential embodiment of the invention, the method is implemented under constant flux of supercritical CO.sub.2, i.e. all the reactants are simultaneously present, and the supercritical CO.sub.2 is injected for a determined duration. For example, in the fourth step of the invention, supercritical CO.sub.2 is injected for a predetermined duration into the enclosure that receives the mixture obtained in the first step and the part made of plastic material to be impregnated.

(27) According to one embodiment of the invention, the material to be impregnated is chosen from the acrylate or polyurethane family.

(28) The first step of the method according to the invention allows to achieve the intimate mixture of the additive and the cosolvent prior to the diffusion step. Intimate mixture means a mixture in which the additive and cosolvent are uniformly distributed (either by dispersion or by dissolution) within the mixture obtained. The first step thus allows to optimise impregnation and obtain better results. The mixture obtained at the end of the first step is thus preferably a liquid mixture to reduce the impregnation time in the fourth step. The first three steps of the method are performed at ambient temperature and pressure.

(29) The fourth step of the method according to the invention allows to impregnate the material with the additive. In a particular embodiment, the fourth step is performed in a hermetically sealed enclosure. The mixture obtained in the first step is introduced into an enclosure with the plastic part to be impregnated, before the enclosure is hermetically sealed. In the third and fourth step of the method, the enclosure is sealed, placed under pressure and brought to the desired temperature for the time necessary for the CO.sub.2, which is then near supercritical, to allow the desired degree of impregnation of the plastic part with the additive. The longer the treatment, the more the plastic part will be impregnated, with, however, saturation occurring when the pores of the plastic part are filled.

(30) During the fourth step, the plastic part to be impregnated remains in solid form. In a particular embodiment of the invention, the temperature in the fourth step is comprised between 25 and 65 C. Such temperatures avoid deterioration of the plastic material during impregnation.

(31) In another particular embodiment, the pressure during the fourth step is comprised between 3 MPa and 6 MPa, for example equal to 4 MPa. The advantage of such pressures is that inexpensive infrastructures can be used compared to the prior art.

(32) In a particular embodiment, the contact time in the fourth step is preferably comprised between one minute and fifteen minutes, and more preferentially between one minute and ten minutes, for example equal to five minutes. Such a treatment time allows the plastic pieces to be impregnated quickly and therefore a greater quantity of pieces to be treated.

(33) Depending upon the desired colour, the impregnation time or pressure can be adjusted to obtain a lighter or darker colour.

(34) The fifth step allows to recover and isolate the impregnated plastic part obtained after the fourth step and possibly to separate the additive which has not impregnated the plastic part. For this purpose, the enclosure used is gradually depressurized and cooled. It is then kept at ambient pressure for 2 minutes.

(35) According to the invention, the method may include a step of washing the plastic part, after releasing the pressure inside the enclosure, to eliminate surface residues, such as excess dye for example.

(36) According to a preferential embodiment of the invention, the washing step is preferably performed with clean water and using a brush or equivalent. Low pressure water jets could also be used, or the impregnated pieces could be placed in a bath. The bath could also be stirred and adapted to the cleaning required.

(37) The plastic part impregnated with the additive can be used in the manufacture of timepieces or pieces of jewellery, and more particularly plastic timepieces or pieces of jewellery. In particular, the method can be used in the manufacture of watch cases, wristbands, bezels, crowns, dials, push-buttons, crystals, loops, or any plastic part forming part of a watch or piece of jewellery. The present invention also concerns a timepiece or piece of jewellery made of plastic material, in solid form, and impregnated with an additive by the method according to the present invention as described hereinbefore.

(38) Thus, pre-moulded or pre-machined plastic watch or jewellery components can be impregnated by this method while maintaining the initial properties of the component, particularly its dimensions and mechanical characteristics.

(39) The following examples are given by way of non-limiting illustration. The colouring and impregnation treatments were carried out on watch cases injected, moulded using the materials mentioned.

(40) TABLE-US-00001 TABLE 1 P T Treatment Aeration Material (MPa) ( C.) (mins) (mins) Cosolvent Results Test Acrylonitrile 8.3 60 45 10 None Foaming of part 1 Butadiene Styrene Test Thermoplastic 7.6 50 30 10 6.6% Foaming of part 2 polyurethane hexane (polyether base) 65 Shore A Test Acrylonitrile 6.2 55 10 2 1.6% Foaming of part 3 Butadiene Styrene hexane Test Methyl methacrylate 5.5 35 10 2 1.6% Foaming of part 4 butadiene styrene hexane Test Methyl methacrylate 4 35 10 2 1.6% Colouring only to 5 butadiene styrene hexane depth of 100 microns Test Methyl methacrylate 1.5 45 5 then 10 2 1.6% Colouring not 6 butadiene styrene then hexane complete throughout 5.5 thickness

(41) TABLE-US-00002 TABLE 2 P T Treatment Aeration Material (MPa) ( C.) (mins) (mins) Cosolvent Results Test Methyl methacrylate 5.5 60 13 2 1.6% hexane Slight foaming giving 7 butadiene styrene whiteish appearance Test Methyl methacrylate 4 100 10 10 1.6% hexane Very significant 8 butadiene styrene foaming Test Methyl methacrylate 4 60 10 10 1.6% hexane Good colour, but very 9 butadiene styrene slight surface whitening Test Methyl methacrylate 4 50 10 10 1.6% hexane Homogeneous colour 10 butadiene styrene/ with no foaming, but Thermoplastic slight surface polyurethane whitening Test Methyl methacrylate 4 50 5 5 1.6% hexane Slightly lighter 11 butadiene styrene homogeneous colour Test Thermoplastic 4 50 5 5 1.6% hexane Homogeneous colour 12 polyurethane (polyether base) 65 Shore A

(42) In both of these tables, the same additives were used, namely an azo dye, Chromophtal, and an aromatic hydrocarbon, anthraquinone (Oracet). Only one cosolvent is used, hexane, and three plastic materials were tested: acrylonitrile butadiene styrene, thermoplastic polyurethane (polyether base) and methyl methacrylate butadiene styrene.

(43) In FIG. 1, which corresponds to tests 1 and 2, complete deformation of the part due to foaming and a non-uniform colour can be seen. These same results are seen in FIG. 2 for tests 3 and 4; deformations are visible in the parts.

(44) In FIG. 3, which corresponds to test 5, it is seen that the part is only coloured on the surface and to a very shallow depth; the dye has not penetrated sufficiently deeply to provide satisfactory and long-lasting colouring despite wear.

(45) In FIG. 4, corresponding to test 7, whitening of the part is seen after impregnation, which is unacceptable.

(46) In FIG. 5, corresponding to test 8, significant foaming of the part is seen after impregnation, which makes it unusable.

(47) FIG. 6 illustrates the result of test 9, slight whitening is seen at the surface of the part following impregnation due to migration of waxes used in the MABS plastic as agent for implementation; however, the colouring is satisfactory.

(48) FIG. 7 illustrates parts coloured according to the conditions of test 10. Homogeneous, good quality colouring is seen with no deformation of the plastic parts. However, a very slight white cloudiness is visible at the surface, indicating the start of migration of some plastic additives.

(49) FIG. 8 illustrates two methacrylate butadiene styrene parts corresponding to test 11. Homogeneous colouring with no deformation and no whitening is seen.

(50) FIG. 9 illustrates two thermoplastic polyurethane parts corresponding to test 12. Homogeneous colouring with no deformation and no whitening is seen.

(51) Of course, the present invention is not limited to the illustrated example and is capable of various variants and modifications that will appear to those skilled in the art.