Patent Application
20130115449
The invention proposes a method of grafting monomers in a deep layer in an organic material by using an ion beam.
The invention seeks in particular to create hydrophobic barriers that are thick, to improve significantly the adhesion of water-based varnishes on elastomers, to constitute antibacterial barriers that are characterized by their effectiveness over a long duration. The invention finds applications in the field of pharmaceutical packaging, where, by way of example, it is desired to prevent ambient humidity from being diffused through bottles, so as to avoid degradation of the active principles that are contained therein. The invention also finds applications in any industry that, by way of example, uses water-based varnishes applied to elastomers, where it is desired firstly to improve mechanical compatibility (between the varnish and the elastomer) by reinforcing the hardness thereof, and secondly to increase the hydrophilic character of the elastomer so as to encourage the varnish to adhere to the elastomer (e.g. windshield wiper blade). Another application consists in treating the PEEK sheaths of electric cables used in the oil industry, so as to reinforce their ability to withstand oxidation in extreme temperature and humidity conditions.
The term “organic” means a material constituted by carbon atoms bonded together or to other atoms via covalent bonds. By way of example, this category includes materials belonging to the family of polymers, elastomers, or resins. Such organic materials have the specific feature of generally being electrical insulators and being capable of producing free radicals under the effect of ionizing radiation; this includes ultraviolet (UV), X-ray, or gamma (γ) ray radiation, electron beams, and ion beams.
As an example, under ionizing radiation, a covalent bond of the C═C type produces two free radicals, denoted (.), each located on one carbon atom (.C—C.) and each being capable of combining with other molecules (for example O2) in radical reactions characterized by three steps, the first being initiation, the second being propagation, and the third being inhibition.
The term “monomer” means a simple molecule used for the synthesis of polymers. In order to be capable of being grafted to an organic material, these monomers must have unsaturated bonds (for example a double bond) that are capable of reacting with the free radicals produced in the organic material by the ionizing radiation.
Exposing a polymer material to ionizing radiation of the electron bombardment or gamma radiation type creates free radicals (ionization reaction) that can either combine together by reactions known as cross-linking reactions, thereby creating new covalent bonds between atoms of the organic material, or that can be used to graft monomers from outside with the atoms of the organic material. The free radicals react with monomers having a vinyl or acrylic type unsaturated bond. The ionizing radiation by electronic bombardment or gamma radiation and associated irradiation units can be used to graft supports in very different formats: films, textile surfaces, compound-filled granules, medical devices, for example. A monomer carrying a graftable vinyl, allyl, or acrylic type unsaturated bond may be bonded onto a carbon chain under the effect of ionizing radiation. Depending on the other chemical functions (or ligands) carried by the monomer, the support material may be permanently endowed with particular characteristics: antiseptic properties, ion exchange properties, adhesion promoting properties, etc.
Electronic bombardment or gamma radiation grafting methods may, however, suffer from disadvantages linked to the means for producing the ionizing particles and to their range, which has the effect of greatly limiting their use.
Units producing gamma rays are extremely difficult to manage from both a technical and a safety standpoint. They consist of a radioactive cobalt-60 source in the form of rods confined in a shielded compartment made of concrete with 2 m [meter] thick walls. The compartment also houses a pool for storing the source stock, intended to provide biological protection when the source is in the “rest” position. In the “working” position, an overhead conveyor carrying containers (also known as trays) moves the items to be treated around the source suspended in the cell and also transfers the items between the interior and the exterior of the compartment. The labyrinthine configuration ensures that the radiation is confined while allowing the items to pass through continuously. The power of the source may reach several million Curies.
All units producing electron beams are also difficult to use. Thick shielding systems must be provided to stop the intense X rays that are produced by deceleration of electrons in the material. Further, the electron beams may cause breakdowns by an accumulation of electrostatic charges in the core of an insulating organic material.
Another disadvantage, this time physical, is linked to the excessive penetrating power of gamma radiation (several meters) and of electrons (several mm [millimeter]). Penetrating powers of such magnitudes are not suitable for a treatment where it is the surface that is to be treated, but without modifying the bulk properties of the organic material. In fact, it is not desirable for an elastomer to lose its bulk elastic properties and to increase in stiffness to a point where it could no longer, for example, match the shape of a shaped surface (a windshield, for example).
A further grafting method exists, this time acting at the extreme surface using a cold plasma. Cold plasmas are ionized media obtained by exciting a gas (in general under low vacuum) under the effect of an electrical discharge: radiofrequency plasmas (kHz to MHz [kilohertz to megahertz]) and microwave plasmas (2.45 GHz [gigahertz]) are the most widely used. A mixture is obtained thereby that is constituted by neutral molecules (in the majority), ions (negative and positive), electrons, radical species (chemically very active), and excited species. Such plasmas are termed “cold” since they are media that are not in thermodynamic equilibrium, where the energy is essentially captured by the electrons, but where the “macroscopic” temperature of the gas remains close to ambient temperature. The electrons emitted by the electrode collide with the molecules of the gas and activate them. Ionization or dissociation then occurs with the creation of radicals. These excited species diffuse into the chamber of the reactor and in particular reach the surface of the substrate. There, a number of types of surface reaction may occur: implantation at very low energies (a few nm [nanometers]), energy transfer, and the creation or destruction of bonds. Depending on the type of reaction occurring at the surface, the surface may be activated, a layer may grow, or etching may occur. Chemical grafting with cold plasmas consists in operating with gases such as oxygen, nitrogen, air, ammonia, or tetrafluorocarbon with active species that react chemically with the macromolecular chains of the polymer to lead to the formation of covalent bonds (C—O, CN, C—F, etc.) that are characteristic of the treatment gas. That type of treatment affects the first nanometers only of the surface exposed to the plasma. The surface of a polymer that has been activated in that manner may then be brought into contact with specific biocompatible molecules (heparin, phospholipids, etc.) to bind them via chemical bonds. In general, chemical grafting is carried out by placing the material to be treated outside the zone where the discharge is created (post-discharge). Because the graft thicknesses are very small, the treatment has a limited lifespan. It is also sensitive to the service conditions (wear, friction, abrasion) that may cause it to disappear very early on.
This gives rise to a need for a method of deep layer grafting of an organic material, preferably using methods that are readily industrializable, in order to be able to offer such organic materials in significant quantities and at reasonable cost.
The invention aims to offer a method of deep layer grafting an organic material that is inexpensive and that can be used to treat surfaces complying with the needs of many applications.
Thus, the invention proposes a method of deep layer grafting an organic material by means of an ion beam, which method comprises two steps:
a) ionic bombardment, wherein:
b) a step of grafting monomers, consisting in diffusing the monomers from the surface towards the reservoir of free radicals at a diffusion temperature that is carefully selected to graft them to molecules present in said reservoir. The diffusion temperature must be selected so as to:
In one implementation, the glass transition temperature Tg appears to be the most suitable. Another implementation allows the option of exploring temperatures intermediate between the glass transition temperature Tg and the melting temperature, subject to precautions being taken concerning cooling conditions to ensure that the properties of the original organic material are regained. Finally, a third implementation allows the option of exploring temperatures included between ambient temperature and the glass transition temperature if the density and reactivity of the free radicals and the rate of diffusion of the monomers are sufficiently high to greatly shorten the grafting periods. The choice of diffusion temperature depends greatly on the nature of the organic material and the graftable monomer.
The choice of ions and the bombardment conditions of these ions in accordance with the invention can advantageously be used to identify a reservoir of free radicals with an optimized density for deep layer grafting of monomers over a thickness of the order of one micrometer and at high density, which monomers may have properties that are hydrophobic, hydrophilic, antibacterial, or even conductive. It is thus possible to create thick, highly effective barriers of a hydrophobic, hydrophilic, antibacterial, or even conductive nature. Examples that may be mentioned are:
The inventors have been able to show that the ranges selected in the invention for the acceleration voltage and for the ion dose per unit area can be used to select optimized experimental conditions where deep layer grafting is possible by means of ionic bombardment, while treating thicknesses of the order of one micrometer.
Furthermore, they have been able to show that the method of the invention may be used “cold”, in particular at ambient temperature, and that the temperature of the organic material remains less than or equal to the melting temperature during implementation of the method. Thus, advantageously, it is possible advantageously to avoid physico-chemical modification of the organic material or self-combination of the free radicals.
The method of the invention has the advantage of modifying the surface characteristics of the organic material over a thickness of the order of one micrometer without altering its bulk properties.
The choice of the ion dose per unit area in the range of doses of the invention may result from a previous calibration step where a sample constituted by the envisaged organic material is bombarded with one of the ions selected from He, B, C, N, O, Ne, Ar, Kr, and Xe. Bombardment of this organic material may be carried out in different zones of the material using a plurality of ion doses within the range of the invention, and the change of the surface resistivity of the treated zones over time is measured under ambient conditions in order to identify a resistive jump that is characteristic of very rapid oxidation of the reservoir of free radicals underlying the surface, with this happening after a period that is linked to the diffusion of oxygen in the organic material.
The inventors have been able to show that the magnitude of the resistive jump provides an estimate of the density of free radicals present in the reservoir, and that the choice of dose for a given organic material must be based on that which induces the greatest resistive jump.
The measurement of surface resistivity in the treated zones, expressed as Ω/□ [ohm per square], is carried out in accordance with IEC standard 60093.
Without wishing to be bound by any particular scientific theory, it may be considered that this phenomenon of resistive jump can be explained by the diffusion of oxygen from the air towards the reservoir of free radicals, followed by its very rapid combination, by radical mechanisms, with the molecules present in that zone. This oxidation process has the effect of suddenly reducing the density of free radicals, or in other words the surface conductivity. When the change with time of the surface resistivity of the organic material is analyzed, this is shown up by a resistive jump exhibited in the form of a step. At a higher dose, these free radicals disappear, leaving amorphous carbon in place with electrical properties that are very stable over time. The change of surface resistivity of the organic material then remains constant over time. The method of the invention is capable of identifying a resistive jump indicating the presence of this deep layer reservoir of free radicals. The magnitude of the step provides an estimation of the density of free radicals present in this reservoir and should be selected so as to be as great as possible.
In addition to reinforcing the hydrophobic, hydrophilic and antibacterial properties intimately linked to deep layer grafting of monomers, the method of the invention can simultaneously be used to harden the surface of the organic material over a thickness of one micrometer or less by creating an extreme surface layer of amorphous carbon. This amorphous carbon layer may be obtained by adjusting the implanted dose of ions in order to cross-link the organic material completely at the extreme surface and in order to cross-link it partially at a greater depth. The inventors have been able to show that this effect is particularly reinforced for multi-energy, multi-charged ions obtained from an electron cyclotron resonance (ECR) source. It appears that ions with lower charges, which are thus less energetic, participate in the total cross-linking of the extreme surface organic material (layer of amorphous carbon), while the ions with the higher charges, which are thus more energetic, participate in creating a deep layer reservoir of free radicals. It is thus possible to create two successive layers, an extreme surface layer that is completely cross-linked in the form of amorphous carbon, and the other, deeper layer that can subsequently be grafted with monomers.
This copolymerization is advantageously capable of supplying distinct pairs of improvements (hardness/hydrophobic nature; hardness/adhesion; hardness/antibacterial nature, etc.).
The method of the invention has the advantage of creating hydrophobic or antibacterial barriers that are thick and thus effective for long-term use or under severe conditions of use without modifying the bulk properties of the organic material. In fact, it might be possible to replace glass bottles with plastics bottles that, after treatment, have been rendered impermeable to ambient humidity. In another example, the method of the invention has the advantage of providing elastomers with excellent wettability (hydrophilic) properties combined with a surface hardness that is highly suitable for applying an aqueous based lacquer.
In various implementations, which may be combined together:
Other features and advantages of the present invention appear from the following description of non-limiting implementations, in particular with reference to the accompanying drawings, in which:
In the implementational examples of the present invention, samples of polycarbonate were studied for treatment with helium ions emitted by an ECR source.
The ion beam with a current of 5 mA [milliamp] comprised He+ and He2+ ions with a distribution (He+/He2+)=10; the extraction and acceleration voltage was 35 kV; the He energy was 35 keV [kilo electron volt] and that of He2+ was 90 keV.
The sample to be treated was moved relative to the beam at a movement rate of 40 mm/s [millimeters per second] with a lateral advance on each return of 1 mm. In order to reach the necessary dose, the treatment was carried out in several passes.
The change with time of the surface resistivity of the polycarbonate was carried out in application of IEC standard 60093, which recommends measuring, after one minute, the electrical resistance existing between two electrodes, one constituted by a disk with a diameter d, the other by a ring centered on the disk and with an internal radius D. These electrodes were placed on the surface of the polycarbonate and subjected to a voltage of 100 V [volt]. D was equal to 15 mm and d was equal to 6 mm. Measurement of the surface resistivity was only possible for values of less than 1015Ω/□.
In accordance with a first implementational example of the present invention, samples of PP (polypropylene) were used to study grafting with acrylic acid for a treatment with helium ions emitted by a ECR source.
The ion beam with a current of 300 μA [microamp] comprised He and He2+ ions with a distribution (He+/He2+)=10; the extraction and acceleration voltage was 35 kV; the He energy was 35 keV and that of He2+ was 90 keV. The sample to be treated was moved relative to the beam at a movement rate of 80 mm/s with a lateral advance on each return of 3 mm. In order to reach the necessary dose, the treatment was carried out in several passes.
The samples of polypropylene PP were bombarded with different doses corresponding to 2×1014 ions/cm2 [ions per square centimeter], 5×1014 ions/cm2, and 1015 ions/cm2.
A single grafting condition was used: immersion for 24 h [hour] in an acrylic acid solution (CH2═CH—COOH) dosed in an amount of 10% by weight, maintained at 40° C.
Measurements of the contact angles of droplets allowed the modification in the wettability of the surface following grafting to be validated, characterized by the change from a hydrophobic behavior to a hydrophilic behavior. These results are summarized in Table 1.
The behavior of the PP changed—the untreated sample had somewhat hydrophobic behavior (contact angle) 76°, while the behavior of the treated samples tended somewhat towards being hydrophilic (contact angle smaller, at 64′). It can be seen that the hydrophilic behavior was substantially improved for doses in the range 5×1014 ions/cm2 to 1015 ions/cm2. It can be seen that FTIR [Fourier transform infra-red] analysis of the PP treated with He indicated a dose of the same order of magnitude as those observed by measuring the surface conductivity on polycarbonate PC treated with He.
In a second implementational example of the invention, samples of polypropylene were used for grafting studies with acrylic acid for a treatment with nitrogen ions emitted by an ECR source.
The ion beam with a current of 300 μA comprised N+, N2+, and N3+ ions, with respective distributions of 60%, 40%, and 10%; the extraction and acceleration voltage was 35 keV; the energy of N+ was 35 keV, that of N2+ was 90 keV, and that of N3+ was 105 keV.
The PP samples were bombarded with different doses at 2×1014 ions/cm2, 5×1014 ions/cm2, 1015 ions/cm2 and 5×1015 ions/cm2.
The sample to be treated was moved relative to the beam at a movement rate of 80 mm/s with a lateral advance on each return of 3 mm. To obtain the required dose . . .
Two grafting conditions were employed; the results are summarized in Table 2:
It should be observed that grafting did indeed occur for all of the samples treated and immersed in an acrylic acid solution at 40° C. or 60° C. Untreated samples immersed in the grafting solution did not exhibit any changes in terms of wettability, which reveals that ionic bombardment under the conditions recommended by the method of the invention is clearly the origin of the grafting. For doses of less than 1015 ions/cm2, the contact angles appear to be relatively comparable, plus or minus 2°. For doses of 1015 ions/cm2, 5×1015 ions/cm2, an inverse effect was observed: for a dose of 1015 ions/cm2 and immersion at 60° C., the contact angle of the droplet of water was smaller than for immersion at 40° C. (70°<75°); for a dose of 5×1015 ions/cm2 and immersion at 60° C., the contact angle of the droplet of water was greater than for immersion at 40° C. (65°<75′). Without wishing to be bound by any particular scientific theory, it may be considered that the stabilizing layer is thinner at lower doses (2×1014 ions/cm2, 5×1014 ions/cm2). Acrylic acid molecules pass through this layer in a relatively short time, both at 40° C. and at 60° C., before the onset of self-combination of free radicals can occur, even in the core of the reservoir created by the ionic bombardment. Grafting of the acrylic acid with the free radicals from the reservoir is then total. The contact angle has a tendency to increase at the same time as the thickness of the stabilizing layer that separates the reservoir of free radicals from the surface. When the dose is increased, in other words when the thickness of the stabilizing layer reaches a certain threshold, the temperature acts somewhat in favor of self-combination of free radicals, to the detriment of grafting. Thus, the acrylic acid has no more time to reach the reservoir of free radicals for grafting therein. In fact, the contact angle of the droplet at 60° C. is higher than at 40° C. The inventors have been able to conclude that it is then preferable to graft at 40° C. or even at ambient temperature rather than at 60° C.
Grafting of the acrylic acid was also confirmed by a more refined mode of investigation, FTIR analysis. The IR [infrared] spectrum of the samples at different doses showed an absorption peak at about 1710 cm−1 [per centimeter] (absorption peak of carbonyl group: C═O); and the appearance of an absorption peak at approximately 3200 cm−1 (absorption peak of the hydroxyl group (OH)). These two functional groups, carbonyl and hydroxyl, are absent from PP and thus could only have come from the acrylic acid. Tables 3 and 4 below show the results obtained at respective immersion temperatures of 40° C. and 60° C.:
It can be seen that the optimum dose for which the absorption peak (reduction of transmittance) was the highest was located at about 5×1014 ions/cm2.
92%
89%
It can be seen that for immersion at 60° C., the optimized dose for which the absorption peak (reduction in transmittance) was the highest was located at about 1015 ions/cm2. This is true both for the CO groups (1710 cm−1) and for the OH groups (3200 cm−1). The absorption peaks were lower at 60° C. than at 40° C., thus confirming that a portion of the free radicals had partially self-combined under the effect of the temperature.
The inventors have been able to show, on the basis of preliminary tests and extrapolation, that it is possible, for any type of ion with a given energy, to calculate the dose corresponding to the highest resistive jump step, using the results obtained under the same conditions for another type of ion with a different energy. The relationship is as follows:
N1×Eion(E1)=N2×Eion (E2)
where:
This ionization energy is a function of the nature and of the energy of the ion and of the nature of the polymer. Methods and data for carrying out these calculations are in particular disclosed in the publications “The Stopping and Range of Ions in Matter” by J. F. Ziegler, volumes 2-6, Pergamon Press, 1977-1985, “The Stopping and Range of Ions in Solids” by J. F. Ziegler, J. P. Biersack and U. Littmark, Pergamon Press, New York, 1985 (new edition in 2009) and J. P. Biersack and L. Haggmark, Nucl. Instr. and Meth., vol. 174, 257, 1980.
Further, software has been developed and sold for facilitating or carrying out such calculations, such as, for example the software supplied with the names “SRIM” (“The Stopping and Range of Ions in Matter”) and “TRIM” (“The Transport of Ions in Matter”), developed in particular by James F. Ziegler.
As an example, the following correspondence table, Table 5, is obtained for PP (polypropylene):
The first row of the table reiterates known experimental data: He is the type of ion employed, with the energy of the ion used being 35 keV; the ionization energy of the helium at the start of its trajectory in the PP is 10 eV/Å [electron volts per {dot over (a)}ngström] (provided by TRIM&SRIM). The 1015 ions/cm2 dose is the dose identified by the experiment corresponding to the resistive jump step of PC, knowing that PC has an ionization energy of (9.5 eV/Å), almost identical to that of PP.
In the second row, the nature of the ion is known, N, its energy is 50 keV, and its ionization energy, estimated by TRIM&SRIM, is 20 eV/Å. The dose corresponding to the highest resistive jump step is deduced by applying the relationship N=(10×1015)/20=5×1014 ions/cm2. This dose is relatively close to that deduced by FTIR for PP (see Table 3).
The third row constitutes another example of grafting with argon that has to be validated. In this row, a dose corresponding to the highest resistive jump step is deduced that is about 5×1014 ions/cm2, in other words relatively close to that obtained with the nitrogen beam
The method of the invention is characterized by the following advantages:
Two implementations exist for creating a grafted layer storing and releasing ions known for their bactericidal action such as, for example, silver ions (Ag+), copper ions (Cu2+), or zinc ions (Zn2+). The choice of implementation depends essentially on cost: examples of modes that may be mentioned are the cost of the monomers to be grafted, and the number of operations to be carried out to obtain the antibacterial effect (immersion in one or two solutions).
The first implementation consists in bombarding the polymer with ions then immersing it in a solution of metal salts such as, for example, in a metal acrylate solution (CH2═CH—COO−+(M+)) or (2 CH2═CH—COO−+(M2+)). Examples that may be used are copper acrylate, silver acrylate, or zinc acrylate. Copper acrylate is known to have biocidal properties; it is in particular used in anti-fouling paints for boat hulls. The aim is to prevent the marine organism from attaching itself. In maritime legislation, for environmental impact reasons, copper leaching must not exceed 20 micrograms per day per cm2 in the first 14 days of contact with sea water. The principle of antibacterial grafting is as follows: the acrylate reacts with the free radicals to bond to the substrate, bringing with it the bactericidal metal ion weakly attached to the CO2− terminus. The metal ion may then be released to the outside in order to exert its bactericidal action.
The second implementation comprises two steps:
In both implementations, the grafted antibacterial layer acts as a bactericidal ion exchanger, and its features may advantageously be adjusted in order to:
The inventors have developed a model for grafting and storing metal ions that can be used to establish a useful formula for making predictions about the metal ion storage capacity as a function of the bombardment parameters.
This model is based firstly on the specific nature of the grafted layer, as could be observed experimentally (reservoir of free radicals flush with the surface and protected by a stabilizing layer of amorphous carbon), and secondly on steric hindrance considerations, the effect of which is to limit grafting independently of the number of free radicals present.
This model integrates the following points:
From these assumptions, the inventors have been able to establish the following formula:
N
ion=(½).6.02×1023.Ep.(ρ/Mmol).K.A
where:
K=(2×(Lp/Lg)−1)/2.
The charge per unit area Cs, defined as the mass of bactericidal metal ions stored and releasable per unit area, can be deduced:
Cs=(Nion/Nat)×ρ
where
Using this formula, it is possible to obtain estimates of the number of ions that are stored in and can be released from a grafted layer of polymer, to evaluate and predict the bactericidal effect over a given volume of fluid.
Consideration is given, for example, to a PP (polypropylene) bombarded with three types of ions, He, N, Ar with the same energy, with different doses calculated to obtain a stabilizing layer and an optimized reservoir of free radicals (highest resistive jump step), which is then grafted with acrylic acid, and which is finally immersed in a solution of silver or copper. The parameters of the formula are initialized with the following values:
The calculation of the surface loading of bactericidal metal ions that are stored and released, combined with knowledge of the bactericidal concentration thresholds, means that it is possible to predict the volume of fluid that can effectively be provided with a bactericidal action.
As an example, for fixed bombardment and grafting parameters, followed by immersion in a solution of Ag+ ions, the surface loading estimates shown in Table 6 are obtained:
It can be seen that the surface loading of Ag+ ions stored and releasable by a layer bombarded with He, grafted with acrylic acid and then immersed in a solution of Ag+ ions, has highly bactericidal characteristics when treating a volume of fluid of approximately 1.9 cm3 (the bactericidal concentration of Ag+ is 20 ppm, in other words 20 μg/cm3). For bombardment with N, the surface loading of stored and releasable Ag+ ions is lower, but is still effective for treating 0.65 cm3. For bombardment with Ar, the surface loading of stored and releasable Ag+ ions can be used to effectively treat a film of fluid 2 mm thick. Thus, the bactericidal properties of a surface treated in accordance with the method of the invention can be modulated as a function of the envisaged applications whether this applies to a drop of fluid, or a film of fluid, etc.
For fixed bombardment and grafting parameters followed by immersion in a solution of Cu2+ ions, the surface loading estimates shown in Table 7 are obtained:
In the same manner as for the Ag+ ions, it can be seen that the load of Cu2+ ions stored and releasable by a layer bombarded with He, grafted with acrylic acid, and then immersed in a solution of Cu2+ ions has highly bactericidal characteristics for treating a volume of fluid of approximately 2.1 cm3 (the bactericidal concentration threshold for Cu2+ is 10 ppm, in other words equal to 10 μg/cm3).
Another approach for a given ion type consists of adjusting the energy of the ion, in other words of adapting the depth of the thickness of the treatment Ep, to store and release a load of bactericidal metal ions that is sufficient to exceed the bactericidal concentration threshold (specific to the bactericidal metal ions) into a fluid with a given volume and contact surface. The load of metal ions that can be released into the fluid is proportional to the contact area of the fluid with the bactericidal surface.
As an example, for PP bombarded with a single type of nitrogen ion with three possible energies of 35 keV, 50 keV, 70 keV and grafted with acrylic acid, and then immersed in a solution of Cu2+ copper, the respective surface loadings of stored and releasable Cu2+ ions can be estimated with the aim of identifying the energy that can exceed a bactericidal concentration threshold equal to (10 μg/cm3) in a volume of fluid of 1 cm3 with a contact surface of 1 cm2. The estimates of the surface loading are shown in Table 8:
It can be deduced from this table that an energy of approximately 60 keV is required to create a sufficient bactericidal charge of 10 μg/cm2 in order to treat 1 cm3 extending over 1 cm2.
The method of the invention can be used to determine the ionic bombardment parameters for creating a grafted layer that has optimized characteristics (hydrophilic, hydrophobic, antibacterial, metal ion exchanger), leaving open the many implementational conditions: nature, temperature, and concentration of solutions of monomers to be grafted, metal ions to be loaded into the grafted layer. These implementational conditions act only on the chemical kinetics (speed of obtaining a result). These conditions have little or no effect on the result per se. These implementational conditions are within the remit of the industrialist who should adjust them during preliminary tests to match then to a production rate, economic costs, etc. As a general rule, the inventors recommend preliminary tests with solutions that do not exceed 40° C. in order to avoid the free radicals combining before grafting, and concentrations of less than 10% by volume in order to produce good homogeneity of the solution during grafting or during loading with bactericidal ions.
The spectra of action of the Ag+ and Cu2+ ions on the bacterial or fungal agents overlap in part, the first being more effective, or even not at all compared with the second in treating a bacterium or fungus. In several embodiments of a bactericidal surface, the spectrum of action of these ions can be broadened, for example by immersing a PP bombarded and grafted with acrylic acid in bactericidal Cu2+ and/or Ag+ metal ion solutions simultaneously or sequentially in one direction or another with the aim of obtaining, in the end, specific stored proportions of bactericidal metal ions, for example storing bactericidal metal ions constituted by 70% silver ions (Ag+) and 30% copper ions (Cu2+).
1) untreated organic material, which by nature is highly insulating (curve 1);
2) the same organic material treated using the method of the invention to provide it with an optimized reservoir of optimum free radicals that are readily identified by a resistive jump step (h) that occurs after a period (d) (curve 2). The delay corresponds to the time for ambient oxygen to diffuse through the layer of amorphous carbon (1). The delay is longer when this layer is thicker; and
3) the same organic material treated with a higher dose producing a thick amorphous carbon layer by cross-linking, which has low resistivity and which is extremely stable over time (curve 3).
The abscissa (T) represents time and the ordinate (R) represents the surface resistivity, expressed as Ω/□.
In various implementations of the method of the present invention, which may be combined one with another:
| Number | Date | Country | Kind |
|---|---|---|---|
| 1002989 | Jul 2010 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2011/051551 | 7/1/2011 | WO | 00 | 1/15/2013 |
