FR2669264A3 - Luminescent viscoelastic substrate, and articles and films obtained with such a substrate - Google Patents

Abstract

Non-stick viscoelastic substrate comprising natural rubber obtained from a latex, in which at least one luminescent pigment of the mineral type is dispersed directly and in a homogeneous manner. Films made from such a substrate are obtained by directly mixing and kneading together a latex and a powder of the luminescent pigment, coacervating on a support a layer of the mixture thus obtained, and removing the water from the layer thus obtained, in order to obtain the film.

Description

Luminescent visco-elastic substrate, articles
and films obtained with such a substrate
The present invention relates to a non-adhesive, visco-elastic substrate comprising an elastomeric material in which is homogeneously dispersed at least one luminescent pigment. The invention relates to all kinds of articles obtained with such a substrate, but is more particularly, although not exclusively, concerned with thin films or elastic sheets, elastic in all directions, formed at least by such a substrate , and conformed to all items such as gloves, balloons, and condoms.

 By "luminescence", or "luminescent", is meant the property of emitting more or less bright light, after having received an excitation which may be light (UV, visible, IR), radioactive, of the X-ray domain, and even thermal, chemical, or electrical.

 In accordance with document FR-A-2 492 393, films having a thickness of between 1 and 5 mm have been described, which can be used as a wall covering, the elastomer material of which is silicone rubber, therefore synthetic, in which is homogeneously dispersed a luminescent pigment of mineral nature, for example zinc sulfide, cadmium sulfide, gallium arsenide, etc.

 In accordance with document US-C-4 652 395, an adhesive film for floor coverings has been described, for example, obtained by drying an emulsion in water of a synthetic elastomer (styrene-butadiene rubber), improperly called latex, since this term must be reserved for natural rubber emulsions. In this film are uniformly dispersed particles or grains of resin (high density polyethylene), in which is incorporated a fluorescent organic pigment.

 For certain uses and applications, in which the substrate made of elastomeric material must be in contact with the skin or living tissue, many synthetic elastomeric materials cannot be retained, in particular because of their allergenic nature. In these cases, a natural rubber obtained from a latex must be used, taking into account the total harmlessness of this material, and in particular its hypoallergenic nature.

 Some of these uses, such as articles such as gloves and condoms, require very small thicknesses of the elastic film, between 1 and 10 hundredths of a millimeter.

 By an experimental protocol reported below, the present invention discovered and demonstrated, unexpectedly and surprisingly, that luminescent mineral pigments could be dispersed in natural rubber substrates, obtained from latex, and in particular in relatively small thicknesses, between 1 and 10 hundredths of a millimeter.

 These results appear surprising for several reasons.

 We know first of all that a latex, plant secretion and therefore natural product consists of an emulsion of natural rubber particles in water, generally ammonia-containing, to avoid any bacterial or microbial development, and consequently any coagulation or premature coacervation.

As such, a latex cannot be compared or assimilated to a synthetic rubber, generally obtained in bulk, that is to say in particular without an aqueous or other medium, of dispersion or dissolution. And the physicochemical properties of a latex cannot be deduced from those of a synthetic elastomer having an identity and or a chemical structure comparable to that of natural rubber in suspension.

Regarding the incorporation or homogeneous dispersion of dyes or pigments in rubbers, the preceding statement is corroborated by the consultation of the work
Bristish compounding ingredients for rubber (second edition)
W. Heffer and Sons Ltd, Cambridge
According to this book, it appears possible and known to incorporate all kinds of luminescent pigments or dyes, including minerals, in synthetic rubbers. On the other hand, for natural latexes or rubbers, only non-luminescent dyes, in particular organic dyes, are described or prescribed for these elastomers.

 Also, if we refer to the technical notices of the manufacturers and suppliers of latex, for example to the technical notice (brochure issued by the French company COMERTEX SA) relating to a pre-vulcanized natural rubber latex, marketed under the brand "Revultex" , it is found that only dyes can be incorporated into a latex, and again on the condition of having previously crushed said dyes in a ball mill. It is also observed that hot vulcanization can deteriorate the dye. It is therefore unexpected that a luminescent pigment can be incorporated directly, that is to say without prior additional grinding, into a latex.

 Next, the fragility or relative instability of a latex is known, capable of precipitating or coagulating under the action of various external agents, such as impurities, fillers, adjuvants, or other additives. Given the crystalline nature of the luminescent pigments used, there was reason to fear precipitation or instability of the latex; this is not the case, subject to certain operational precautions described below.

 It was also feared to significantly alter or modify the physical, mechanical and chemical properties of the elastic film obtained, taking into account the heterogeneous nature of the luminescent mineral pigment; we know in particular that certain cations can be real poisons of natural rubber. Again, still with certain precautions set out below, this was not the case.

 The very low fragility of certain luminescent mineral pigments is also known, with regard to the preservation of these same luminescent properties, which appear to depend on the maintenance of the crystalline integrity of the pigment. Taking into account the treatments inflicted on a latex to obtain a natural rubber, such as heating, evaporation, etc., it was not a priori immediate that the crystal structure, or in any case the luminescent properties of the pigment, could be preserved in the final product, namely the visco-elastic substrate, in bulk, or in film.

 Finally, more specifically with regard to elastic films, all of these fears were reinforced by the fact that the latter were also thin, which a priori reinforces the fragility of the elastic film, and makes it more difficult to obtain good dispersion of the luminescent pigment.

The present invention also has the following additional technical characteristics
- when the visco-elastic substrate is shaped according to a film, the thickness of the latter is limited between 1 and 10 hundredths of a millimeter
the luminescent pigment is chosen from the group comprising zinc sulfide, a mixed zinc and cadmium sulfide, and a mixed calcium and strontium sulfide
- the luminescent pigment content is between 0.1% and 10% by weight of the substrate
- the particles of the dispersed luminescent pigment have a size at most equal to one micron
- for a film of the substrate according to the invention, the quantity of luminescent pigment dispersed in said substrate is less than 80 g / m2
- with the films of the substrate according to the invention, all kinds of articles can be made, such as gloves, condoms and balloons
- From the substrate according to the invention, it is also possible to obtain elastic threads, but also elastic foams.

Finally, the process for obtaining a film according to the invention is of the so-called "dip" type and generally consists
- directly mixing and kneading together a latex and a powder of said luminescent pigment
- to coacerve on a support a layer of the mixture thus obtained
- removing water from the layer thus obtained to obtain a film
- Optionally vulcanizing the film thus obtained, when the starting latex is not pre-vulcanized.

 The present invention is now described from the following example.

 The latex used is a pre-vulcanized natural rubber latex, containing approximately 60% of centrifuged natural rubber in suspension, and 40% of ammoniacal water. It is a latex as sold under the brand "Revultex" by the company COMERTEX SA.

Regarding luminescent pigments, the following materials have been selected
- mixed sulfide of calcium and strontium, emitting a blue color,
- zinc sulfide, emitting a green color,
- mixed zinc and cadmium sulfide, emitting an orange or yellow color.

 For applications of the elastic film type in contact with the human body, all of these pigments have been retained, because of their great stability with respect to bodily fluids or secretions such as perspiration, saliva, etc.

 The articles or objects to be produced are generally obtained according to the known technique known as "dipping".

 A charge of the retained luminescent pigment is introduced into the liquid emulsion of pre-vulcanized latex in the form of a powder. The whole is then kneaded for forty-eight hours in a row, so as to obtain a perfect liquid mixture, in which the particles of the luminescent pigment are very fine, of the order of a few thousandths of a millimeter.

 The objects or articles to be manufactured are molded on the porcelain forms or supports, previously soaked in a coagulating or coarcervating agent (calcium nitrate for example), by immersing said forms in the mixture or emulsion obtained previously.

 The coated forms are placed in an oven where the latex is cooked at 80 "C-90" C, to remove the water and obtain vulcanization.

 The object or article thus obtained is removed from the form or its support.

 Of course, it appears possible to mix several different luminescent pigments, depending on the desired luminescence color, and the intensity of the latter depends on the quantities of pigments used.

According to this process, different test pieces are obtained, which are then subjected to the following chemical resistance tests.
- heating at 70 "C for one hour, in a solution of 9 g of sodium chloride per liter, at a pH of 1
- heating at 70 "C for one hour, in a solution of 9 g of sodium chloride per liter, at a pH equal to 8.

The components of the luminescent pigments are then dosed in the preceding sodium chloride solutions, and the following result is obtained for zinc sulfide.
- pH = 1, Zn = 0.038% of the quantity initially present in the test piece
- pH = 8, Zn = 0.002% relative to the initial amount of zinc in the test piece.

 As can be seen, despite the severe attacks, the pigment and natural rubber resisted well, which is no doubt due to the insolubility of the pigment and the protective power of the natural rubber film.

 Furthermore, the luminescence of the pigment remains preserved in the article or object thus obtained, which shows that these pigments resist immersion in the ammoniacal latex emulsion, mixing with the latter, and vulcanization at hot.

 Qualitatively, the mechanical qualities of the finished objects appear excellent.

Claims (11)

 1 / Non-adhesive visco-elastic substrate comprising an elastomeric material in which is homogeneously dispersed at least one luminescent pigment of mineral nature, characterized in that the chosen elastomeric material is a natural rubber obtained from a latex.  2 / A substrate according to claim 1, characterized in that the luminescent pigment is chosen from the group comprising zinc sulfide, a mixed sulfide of zinc and cadmium, a mixed sulfide of calcium and strontium.  3 / Substrate according to claim 1, characterized in that the content of luminescent pigment is between 0.1% and 10% by weight of the substrate.  4 / A substrate according to claim 1, characterized in that the particles of the dispersed luminescent pigment have a size at most equal to 1 µm.  5 / elastic film constituted at least by a substrate according to any one of claims 1 to 4.  6 / film according to claim 5, characterized in that the amount of 2 luminescent pigment dispersed in the substrate is less than 80 g / m2.  7 / film according to claim 5, characterized in that the thickness of the substrate is between 1 and 10 hundredths of a millimeter.  8 / Article such as glove, condom and balloon, produced with a film according to any one of claims 5 to 7.  9 / elastic thread constituted at least by a substrate according to any one of claims 1 to 4.  10 / elastic foam constituted at least by a substrate according to any one of claims 1 to 4.  11 / A method of obtaining a film according to any one of claims 5 to 7, characterized in that  - a latex and a powder are mixed directly and kneaded together  of said luminescent pigment  - Coating on a support a layer of the mixture thus obtained  - Water is removed from the layer thus obtained to obtain said film  - The film thus obtained is optionally vulcanized.