This invention relates to a method for the manufacture of adhesive multi-layer substrates which can be bonded to the skin to form self-adhesive hair prostheses, and multi-layer prostheses so obtained.
At the present time various types of hair prostheses which are normally used by many tens of thousands of people affected by baldness are available on the market. These prostheses can be summarily allocated to two main categories: rigid and elastic.
Rigid prostheses are characterised by a substrate of composite material (polyurethane and/or silicone) into which the hairs are inserted; these are appreciably thick and rigid, being of the order of a few millimetres. These prostheses are generally custom-made on an expanded polyurethane cast obtained by filling an impression of the user's head and matching the shape of his baldness.
Elastic prostheses are made using an extremely soft and elastic polyurethane (from 20 to 300 microns) which are suitably preformed into a cap of standard size into which the hairs are inserted. The roots of the hairs projecting from the underside are secured to the substrate by a spread layer of polyurethane which embeds them. These “standard” prostheses are suitably cut to the shape of the user's typical baldness using a cast custom-made on customer's heads with a thin film of polyethylene and an adhesive layer with a glass fibre core. The elasticity of the substrate means that the shaped prostheses can be perfectly adjusted to the surface of the head.
In both cases, for both rigid and elastic prostheses, adhesion to the user's head is achieved through an adhesive bonding system. These systems may use adhesive tape or liquid adhesive spread with a brush.
The main disadvantage of these conventional prostheses/head adhesion systems lies in the fact that in contact with sebaceous fat and the acidity of sweat the adhesive used tends to come loose, with the result that the prosthesis is progressively detached from the user's head.
For these reasons, and in addition the hygiene problems due to sebum and sweat remaining between the prosthesis and the skin, the prostheses have to be removed periodically for cleaning and replacement of the adhesive.
This “maintenance” operation, also known as the “hygienic phase”, performs the function of rendering the skin and the prosthesis hygienic.
The problems deriving from the present technological situation for hair prostheses can be summarised in the main as: adhesion time, lack of an effective transpiration system, large thicknesses and long times for the hygienic phase.
As far as adhesion times are concerned, the systems presently in use allow periods between hygienic phases which vary from a few days up to ⅔ weeks, depending upon the pH of the sweat and the amount which the user sweats. In addition to this, conventional adhesives are attacked by physiological components of the user's skin such as sweat and sebum and ultimately detach from the head and bind to the hair, giving rise to an adverse aesthetic image and wholly losing adhesion.
As far as the problem of transpiration is concerned, it is pointed out that both adhesive strips and adhesive liquids form an impermeable film on the skin which wholly prevents transpiration, holding back sebum and sweat, thus encouraging significant bacterial growth, which in addition to being unhygienic produces unpleasant smells.
As far as prostheses are concerned, it is impossible to achieve effective transpiration and sufficient drainage of sebum and sweat using present manufacturing technology. Rigid prostheses, although drilled to permit the circulation of air between the prosthesis and the hair-bearing skin, are absolutely ineffective in ensuring any transpiration. Elastic prostheses are wholly impermeable to sweat, which remains between the prosthesis and the skin, because of the polyurethane spread to fix the hairs to the substrate and the subsequent application of liquid adhesives to provide adhesion.
In addition to this, these prostheses are of substantial thickness, some 400/600 microns, while the market requires continuous reductions in thickness to achieve greater more natural hair and greater comfort for users.
Finally, present-day technology provides that the time needed for the periodical hygienic phases is approximately 50/60 minutes, in addition to the time needed to cut the hair, that is an excessively long time.
The main object of this invention is therefore to provide a substrate which can be bonded to the skin to form self-adhesive hair prostheses suitable for producing a multi-layer prosthesis capable of overcoming the abovementioned disadvantages of the prostheses currently in use.
In particular, according to a principal characteristic of this invention, it provides a method for the manufacture of a substrate which can be bonded to the skin in order to form self-adhesive hair prostheses through the use of a liquid adhesive, comprising the stages of:
adding 0% or 0.5% by weight of micronized silver powder or a stoichiometrically quantitative equivalent of Ag+ ions to the adhesive,
intimately mixing the Ag powder and/or the Ag+ ions and the adhesive,
blowing microbubbles of air into this liquid mixture during the mixing stage,
spreading the said mixture on a thermoformable silicone film which can be quite easily or readily detached with the formation of a film having thicknesses of 5 to 80 microns in a single spreading operation.
According to a further feature of the invention it provides for application of a polyurethane membrane which allows transpiration through microperforation of the same to that film, and subsequently inserting hair onto that polyurethane membrane to form the hair prosthesis, and subsequent application of the said prosthesis onto one of the previously-shaped bondable substrates.
Further features and advantages of this invention will be more apparent in the course of the following description, made with reference to the appended drawings, provided by way of a non-restrictive example of this invention, in which:
With reference to
At this point, to form the prosthesis the flat sheet formed in this way is cut to a suitable size for “standard” prostheses, which are suitable for almost all types of baldness; these cut portions are heated to temperatures of the order of 80° C., and using a press in the form of male and female spherical cups are curved so as to obtain a cap shape, as illustrated in
At this point, as more particularly illustrated in
At this point protective film 1 is removed from the sandwich so obtained, and is positioned on a non-stick silicone head 5, as illustrated in
At this point the product in
When the prosthesis is applied to the skin, a tractive force is exerted upon it, breaking the bubbles, creating openings in the adhesive, which when the prosthesis is applied to the user's head allows the skin the transpire.
The surface bubbles which remain partly closed create hemispherical cups which when applied to the skin are subjected to a pressure which allows the air present within them to escape, creating a vacuum effect like small suction cups.
In addition to this, the bubbles which remain enclosed within the adhesive, still full of air/solvent mixture, open up when attacked by sebum and/or sweat and carry out an oxidation reaction on the molecules penetrating within them, appreciably reducing their acidity and thus their ability to attack the adhesive.
In the variant in
Of course this invention is not restricted to the embodiments illustrated and described, which are given purely by way of examples of the invention. Thus for example the product in
Number | Date | Country | Kind |
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GE2008A000100 | Dec 2008 | IT | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP09/66118 | 12/1/2009 | WO | 00 | 7/13/2011 |