WO2008046165A2

WO2008046165A2 - Anti-adhesive and antistatic composition

Info

Publication number: WO2008046165A2
Application number: PCT/BE2007/000113
Authority: WO
Inventors: Alexandre Beigbeder; Daniel Bonduel; Michäel CLAES; Myriam Devalckenaere; Philippe Dubois
Original assignee: Nanocyl S.A.
Priority date: 2006-10-18
Filing date: 2007-10-18
Publication date: 2008-04-24
Also published as: WO2008046165A3

Abstract

The present invention relates to the use of composition as an anti-adhesive coating that comprises a polysiloxane-based cross-linked copolymer and at least one nanocylindrical charge.

Description

ANTI-ADHESIVE AND ANTISTATIC COMPOSITION

Object of the invention

The present invention relates to a nonstick and antistatic composition which gives the surfaces or supports, on which it is applied, a resistance to soiling.

State of the art [0002] Any surface, whatever it is, is potentially exposed to fouling of any kind, a fortiori if it is an outside surface exposed to the bad weather. This is particularly the case for interior or exterior surfaces of structures made of brick, stone, wood or metal, exposed for example to rain, mud, dust, grease, air pollution, or even surfaces that may also be covered with unwanted or unauthorized graffiti or posters.

[0003] Surfaces are usually freed from their soiling by more or less frequent cleaning, which often requires the use of abrasives, strong detergents and / or solvents.

To facilitate cleaning and / or reduce their frequency, the use of coatings or antifouling varnishes is well known, especially coatings or varnishes based on halogenated polymers or silicone polymers which may or may not include , mineral charges.

[0005] Of the halogenated polymers, fluoropolymers are the most commonly used, in particular polytetrafluoroethylene, or PTFE, which has excellent chemical resistance, low coefficient of friction and excellent abrasion resistance. Silicone polymers have, for their part, mechanical and chemical strengths equivalent to those of fluoro-polymers, but are much cheaper to produce. Polydimethylsiloxane, or PDMS, is the most commonly used silicone polymer. The antifouling nature of a coating or varnish is closely related to the non-stick or hydrophobic nature of the substance or substances that compose it. In a very conventional way, the non-stick nature of a coating is judged by measurements of the contact angle with a drop of a liquid and by surface energy calculations.

The contact angle accounts for the ability of a liquid to spread over a surface by wettability and its determination is made by measuring the angle θ between the tangent to the liquid drop at the point of contact and the flat solid surface on which the drop is deposited (diagram 1).

Diagram 1

[0009] Generally, the liquid used is ultra-pure water, which makes it possible to determine the hydrophilic or hydrophobic nature of a surface, but by using different liquids, this measurement also makes it possible to determine the free surface energy. of a surface according to different models described in the literature. The PDMS is intrinsically hydrophobic, however, applied in film form, it has a contact angle of the order of 100 ° to 110 °. However, during prolonged contact with water, it appears that the PDMS undergoes a modification of its surface, which makes it more hydrophilic, less hydrophobic, and therefore less anti-adhesive. [00113] To improve the anti-adhesive properties of PDMS, Meihua Jin, in an article entitled "Super-hydrophobic PDMS Surface with Ultra-low adhesive force" published in Macromolecular Rapid Communication, 2005, 26, pages 1805-1809, proposes to use a surface property commonly called the "lotus effect" and reproduce on the PDMS film microspheres have on the surface of the lotus leaves and allow these leaves to slide the foreign elements on their surface without being able to adhere . Thus, a laser etching of the surface of the PDMS makes it possible to obtain a coating having a contact angle with the water of more than 160 ° and having a sliding angle of less than 5 °. Nevertheless, this technique is unsuitable for most of the potential applications of such a modified PDMS. In addition, it is a difficult technique to implement and remains very expensive because of the use of a laser.

Aims of the invention

The present invention aims to provide a nonstick composition which does not have the disadvantages of the state of the art. It aims in particular to provide a non-stick composition facilitated implementation. It also aims to provide a nonstick composition that retains its non-stick properties even when subjected to prolonged contact with water.

It also aims to provide a nonstick composition which gives the supports, on which it is applied, a resistance to soiling.

It also aims to provide a nonstick composition that reduces the frequency of cleaning of the media on which it is applied, and to reduce the intervention time.

Summary of the invention

The present invention relates to the use of a composition comprising a crosslinked polysiloxane-based polymer and at least one nanocylindrical filler as a release coating.

According to particular embodiments, the latter comprises one or some combination of several of the following features:

the nanocylindrical filler represents between 0.01 and 5% by weight of the total weight of said composition and, preferably, it represents between 0.01 and 1% by weight of the total weight of said composition;

the nanocylindrical charge comprises sepiolite;

the sepiolite represents between 0.01 and 3.5% by weight of the total weight of said composition;

the nanocylindrical feedstock comprises carbon nanotubes, preferably carbon nanotubes chosen from the group of single-walled carbon nanotubes

(SWNTs), double wall (DWNTs) or multiple wall (MWNTs);

the composition comprises both sepiolite and carbon nanotubes.

The present invention also relates to a nonstick and antistatic composition comprising a crosslinked polysiloxane polymer and a concentration of carbon nanotubes of between 0.1% and 1% by weight, said composition having an electrical resistivity of less than 100,000,000 Ohm. cm. Preferably, the nonstick and antistatic composition comprises a polysiloxane-based crosslinked polymer and a multiwall wall nanotube concentration of between 0.5% and 1% by weight, said composition having an electrical resistivity of less than 250,000 Ohm. cm.

The invention also discloses the use as antistatic coating of a composition comprising a polysiloxane-based crosslinked polymer, said composition comprising a concentration of multi-wall carbon nanotubes of between 0.01 and 5% by weight, and preferably between 1.1 and 1% by weight.

Brief description of the figures

Figure 1 shows the differences in contact angle values of a PDMS coating without load before and after immersion in water. FIGS. 2a to 2c show atomic force microscopy images of a PDMS coating comprising no filler before immersion in water (FIG. 2a), after immersion (FIG. 2b) and after immersion. and drying (Fig.2c).

Figure 3 schematically shows the structural modification that can undergo a polysiloxane chain in a very polar environment. FIG. 4 represents the values of the surface contact angle of a PDMS coating comprising 3.5% and 10% by weight, of sepiolite and of a PDMS coating comprising 1 to 10% of partition 30, before and after immersion in water. FIGS. 5a to 5c show atomic force microscopy images, before immersion in water, of a PDMS coating comprising no charge (FIG. 5a), a PDMS coating comprising 3.5% by weight of sepiolite (Fig.5b) and a PDMS coating 10% by weight of sepiolite (Fig.5c).

FIGS. 6a to 6c show atomic force microscopy images after immersing in water a PDMS coating comprising no filler (FIG. 6a), a PDMS coating comprising 3.5% by weight. sepiolite weight (Fig.6b) and a PDMS coating 10% by weight of sepiolite (Fig.6c).

FIG. 7 represents the values of the surface contact angle of a PDMS coating comprising 0.01% to 5% of multi-walled carbon nanotubes and a coating.

PDMS comprising 1 to 5% of partition 30B, before and after immersion in water.

FIG. 8 represents the surface energy of a PDMS coating comprising no charge and a PDMS comprising from 0.01% to 5% of carbon nanotubes.

FIG. 9 represents the variation of the electrical resistivity, as a function of the percentage of multi-walled carbon nanotubes of a PDMS coating comprising 0.01 to 5% of carbon nanotubes. It is remarkable to note that the surface resistivity is already less than 100,000 Ohm. cm for a concentration of carbon nanotubes of less than 1% by weight in the PDMS. In addition, a surface resistivity of less than 1,000,000 Ohm is already achieved. cm with a concentration of carbon nanotubes of less than 0.3% by weight in the PDMS. Resistivity is already below 100.000.000 Ohm. cm for a concentration of carbon nanotubes of 0.1% by weight in the PDMS. FIG. 10 represents the peel strength of PDMS coatings comprising 0.01 to 5% of carbon nanotubes.

FIGS. 11a and 11b show the electron microscopy images of the adhesive tapes of the peel test of a composition comprising a) 1% of carbon nanotubes, b) 5% of carbon nanotubes.

FIG. 12 represents the viscosity variation of the polymer precursor as a function of the amount of filler for composites comprising carbon nanotubes, sepiolite or partitioning.

3OB.

FIG. 13 represents the variation in viscosity of the precursor of the polymer as a function of the amount of filler for compositions comprising carbon nanotubes of different types.

DETAILED DESCRIPTION OF THE INVENTION In order to meet the problem of obtaining an easy-to-use release composition which gives the supports and surfaces on which it is applied a resistance to soiling, and which retains its properties. Even when it is subjected to prolonged contact with water, the invention proposes in an original manner the use of a nanocylindrical filler in a polysiloxane-based crosslinked polymer.

The term "support" means any material that can be covered with a polymer and "surface" any surface, whether internal or external, vertical or horizontal of any body or object. Without being limiting, the supports concerned may be flexible supports, especially fibrous, woven or not, which may be covered with at least one reinforcing layer, for example textile fabrics, or non-flexible supports, for example metal, plastic or ceramic parts, or else polymeric or elastomeric supports, in particular plastic films, such as for example packaging films. protection. It can also be the surface of any object, for example the internal or external surfaces of a building, a dwelling or a vehicle.

The term "nanocylindrical charge" means a charge having the shape of a cylinder, a needle or fiber, and two of the three dimensions of the charge are less than 100nn, or even of the order of one a few tens of nanometers.

According to a preferred embodiment of the invention, the polysiloxane-based polymer used is Sylgard 184 from Dow Corning, a resin that crosslinks by hydrosilylation.

By resin is meant by cross-linking by hydrosilylation, a resin obtained from two polysiloxane precursors, one comprising the vinyl groups and the other hydrosilane groups.

The crosslinking consists of an addition reaction of the hydrosilane groups on the vinyl groups

(diagram 2).

Figure 2 The composition of the Dow Corning Sylgard 184 resin is given in Table 1 and the chemical structure of the components is given in Schemes 3 to 6.

Table 1: Composition of the resin

CH ₂ = CH- (CH ₂ ) _n - (SiO) - Si - (CH ₂ ) _2n CH = CH

434

Scheme 3: SFD 117, polysiloxane carrying vinyl groups

Even

- (- If O -) - (- If O -) "

Me H

Scheme 4: Polysiloxane Polymer Carrying Hydrosilane Groups

Scheme 5: Crosslinking inhibitor

Scheme 6: VQM matrix comprising a polydimethyl siloxane microarray.

The nanocylindrical charge is any suitable charge in the form of a cylinder, a needle or a fiber, and two of the three dimensions of the charge is less than 100 nm, or even of the order of one a few tens of nanometers. Preferably, it is sepiolite or carbon nanotubes, or a combination of sepiolite and carbon nanotubes. Sepiolite is a clay with a fibrous structure of formula Mg ₄ Si ₆ O ₅ (OH) ₂ * 6H ₂ O. It generally consists of fibers of the order of 0.1 to 5 μm in length and 5 at 30 nm in diameter. Carbon nanotubes are a particular crystalline structure of carbon atoms, tubular, hollow and closed, of the order of 0.1 to 10 microns long and 2 to 30nm in diameter. It may be single-walled carbon nanotubes (SWNTs), double-walled

(DWNTs) or multiple wall (MWNTs). Preferably, it is multi-walled carbon nanotubes (MWNTs). Preferably, it is multi-walled carbon nanotubes of

1.5 to 1.7 μm in length and 7 to 12 nm in diameter, having undergone no post-synthetic treatment, in particular no purification.

Preferably, the nanocylindrical filler represents by weight between 0.01% and 5% of the total weight of said composition. Different compositions were prepared and their release properties were studied by contact angle measurements with water. Among these compositions, some include no charge, others include nanocylindrical charges, sepiolite between 3.5 and 10% or carbon nanotubes between 0.01 and 5%, others finally include platelet charges, montmorillonite between 1 and 10%

(partition 30B). Unlike carbon nanotubes and sepiolite, montmorillonite is a charge in which only one of the three dimensions is less than 100 nm. Montmorillonite is a mineral composed of hydrated aluminum silicate and magnesium, belonging to the family of phyllosilicates. Conventionally, the compositions based on polysiloxane are obtained from precursors A and B which are mixed with stirring, for 30 minutes for example, in a solvent with a ratio of 10 to 1 (10 parts of precursor A for a part of the precursor B). Charges, for compositions that include, are added to precursor A with stirring, for example at 500 rptn for 30 minutes, before the addition of precursor B. The mixture thus obtained is deposited on microscope slides which are heated at 70 ^° C. for 1 hour and then at 105 ^° C. for 8 hours and finally at 70 ⁰ C for 8h under vacuum. The coating thicknesses thus obtained are of the order of 150 μm. The lamellae are then cut to obtain lcm ² samples. Some are immersed in demineralized water for 48 hours or a week, others are not and serve as a control.

In another embodiment, the compositions based on polysiloxane can also be obtained from precursors A and B which are mixed beforehand with stirring, for example for three minutes, in a proportion of 10 parts of precursor A for a part of the precursor B. The charges, for the compositions which comprise it, are added to the precursor A with stirring, for example at 500 rpm for 30 minutes, before the addition of the precursor B. The mixture thus obtained is deposited on strips for microscope which are brought to 105 ⁰ C for 20 hours. The coating thicknesses thus obtained are of the order of 0.2 to 4 mm. The lamellae are then cut to obtain lcm ² samples. Some are immersed in demineralized water for 48 hours or a week, others are not and serve as a control.

The surface appearance of these samples is studied under an atomic force microscope and their wettability is determined by contact angle measurements with water, before and after prolonged contact with water which can be 48 hours or a week for example. The calculation of surface energy is done using the model of Owens, Wendt and Rabel. Atomic force microscopy images were made by a Nanoscope IHa microscope (Veeco, Inc.) operating at room temperature in air using cantilevers having a spring constant of 30 Nm-I and a resonant frequency about 300 kHz and operating in "tapping" mode (TMAFM), that is to say in a mode where the working frequency is smaller than the resonance frequency. The images obtained are then digitized with a maximum resolution of 512x512 pixels, then analyzed using the atomic force microscope software.

The wettability of the samples is determined using a Kruss DSA 10 device using the "sessile drop" technique. The hydrophobic character of the polymeric coating is evaluated by angle measurements between the surface of the coating and drops of ultrapure water. The results obtained are expressed as an average of at least five measurements. As shown in Figure 1, before prolonged contact with water, a PDMS coating, which includes no charges, has a contact angle of about 101 °. After prolonged contact for one week with distilled water, the angle changes from 101 ° to 89 °, indicating that the surface of the coating is more hydrophilic. Nevertheless, after drying at room temperature for 24 hours, the coating regains its hydrophobic character.

Figures 2a to 2c show interestingly that the surface of the coating is smooth, homogeneous and without particular structural features, while after prolonged contact with water, the surface of the coating has a significant change; Microporous structures or cavities of about 200 ± 50 nm in diameter and about 3 to 4 nm in depth appear. Nevertheless, after drying coating, its surface returns to its original appearance (Fig.2c). It thus appears that the presence of these cavities causes the hydrophobicity of the surface of the coating to decrease. The modification of the surface of an unloaded PDMS coating is a well-known phenomenon. Generally, such a result is achieved by employing additives or oxidizing the PDMS. Nevertheless, in the present case, neither additives nor oxidation have been used. This structure modification, which also results in the appearance of microporous cavities (FIG. 2b), can be explained by the fact that a PDMS polymer chain has a helical structure in which the methyl groups of the Siloxane units are free from rotation. However, these methyl groups, which are responsible for the low surface tension of the PDMS, can, in a very polar environment, be pushed back inside the helix, thus exposing the skeleton of the polysiloxane chain (FIG. this may result in a change in the wettability of the PDMS coating.

As shown in FIG. 4, the contact angle and therefore the wettability of an uncharged PDMS or a PDMS comprising sepiolite or partition 30B are substantially identical, namely, an angle of about 100 °. Nevertheless, after being immersed in water, all PDMS do not have the same behavior. It is remarkable to note that a PDMS comprising 3.5% sepiolite has a contact angle substantially identical to that of an uncharged PDMS which would not have been in prolonged contact with water, whereas a PDMS comprising 1% or 3.5% of partition 30B shows a significant decrease in the contact angle, a more pronounced decrease for a PDMS comprising 10% of partition 30B. So, the presence of 3.5% sepiolite in the PDMS matrix makes it possible to prevent the decrease in hydrophobicity of the surface after prolonged contact with water, which does not allow the partition 30B.

As shown in Figure 5 (before immersion) and Figure 6 (after immersion), coatings comprising no charge or comprising sepiolite have microporous cavities. Nevertheless, the cavities observed for the coating comprising 3.5% of sepiolite are smaller than those observed for the coating comprising no filler or comprising 10% of sepiolite.

In the coating comprising 3.5% sepiolite, it seems that the polysiloxane chains are less mobile and their ability to reorganize in a polar environment is decreased because of sepiolite. Thus, the size of the cavities is smaller and the coating thus appears more hydrophobic. In a coating comprising 10% of sepiolite, the size of the cavities is larger and the coating appears more hydrophilic because at this loading rate the poor dispersion of the sepiolite in the polymer matrix and the presence of aggregates decreases the number favorable interactions between sepiolite and polymer. The polysiloxane chains are then freer and reorganize more easily than in a coating comprising 3.5% sepiolite.

As shown in Figure 7, it is remarkable to note that the contact angle, and therefore the wettability, of a PDMS comprising 0.01% to 5% by weight of multiwall carbon nanotubes, with or without has been placed in prolonged contact with water, is substantially identical to that of an unloaded PDMS coating that has not been immersed, contrary to what can be observed for the bulkhead 30B. Similarly, the surface energy of coatings PDMS comprising 0.01 to 5% of carbon nanotubes is substantially identical to that of a PDMS coating comprising no charge, ie around 5.10 ^"3 N / m, and remains constant when the carbon nanotube loading rate increases. (Fig.8).

In addition, it is also interesting to note that the surface of the PDMS-based coatings comprising at least 0.1% multi-walled carbon nanotubes already shows an antistatic behavior which is confirmed from 0.3% (FIG. .9). This is explained by the good quality of the dispersion of carbon nanotubes within the PDMS matrix. FIG. 9 represents the variation of the electrical resistivity as a function of the percentage of multi-walled carbon nanotubes of a PDMS coating comprising 0.01% to 5% of carbon nanotubes.

The value of the electrical resistivity drops already considerably for a concentration of carbon nanotubes as low as 0.1% (82,000,000 Ohm / cm) and the electrical resistivity is already 36,000 Ohm / cm for a concentration of nanotubes of carbon of 1% by weight in PDMS. Moreover, an electrical resistivity of 560,000 Ohm / cm is already achieved with a concentration of carbon nanotubes of 0.3% by weight in the PDMS.

Table 2: Values in Figure 9 Thus, the type of charge of the composition is an important element because a composition based on PDMS which comprises a platelet clay load, in this case montmorillonite (30B partition), does not provide the results. obtained with compositions comprising a nanocylindrical filler. It appears that only a nanocylindrical filler makes it possible to maintain the hydrophobic character of the coating in which it is incorporated. Among the compositions comprising 0.01 and 5% of carbon nanotubes, discrimination can be performed on the basis of an adhesion test, or peel test or "peeling test". In this test, the adhesion of the PDMS coatings is evaluated by applying an adhesive tape (Tesa 07476) on the different coatings and measuring the force required to detach it. It seems

(FIG. 10) that the peel strength remains constant for carbon nanotube loading rates of less than 1%, or at least the peel strengths for these charge levels are not significantly different from one another, whereas above 1% the difference is clearly marked. This is explained by the fact that the higher the content of carbon nanotubes, the higher the viscosity increases, resulting in poor dispersion of different parts constituting the PDMS matrix subjected to crosslinking. This explains why at high loading rates in carbon nanotubes the crosslinking will be incomplete. Polymer chains left free, due to incomplete crosslinking, can adhere to the adhesive tape placed on the surface of the PDMS matrix during the "peeling test". These polymer free chains can be torn off the surface of the PDMS matrix as the adhesive strip is removed, resulting in greater peel strength of that surface (Fig.ll). So, the The percentage of carbon nanotubes is advantageously less than 1% and is preferably between 0.01 and 0.5%.

The effect of carbon nanotubes on the viscosity of a composition based on PDMS, in particular on the viscometric properties of the precursor A ₇ makes it possible to envisage the application by brush of this precursor for particular embodiments. of the invention in which the nanocylindrical filler of the composition comprises at least carbon nanotubes, that is to say in a composition in which the nanocylindrical filler comprises carbon nanotubes and one or more other nanocylindrical fillers which are not not carbon nanotubes, or a composition in which the nanocylindrical filler is made of carbon nanotubes.

The effect of the carbon nanotubes on the viscosity of the constituents of the polymer in which they are incorporated, in particular of the precursor A, is illustrated in FIG. 12. The viscosity of the precursor A containing multi-walled carbon nanotubes is significantly increased by compared to more conventional compositions containing clay fillers. As shown in FIG. 13, the viscosity of precursor A varies according to various parameters such as the size, the diameter and the purity of the carbon nanotubes.

It appears that a feed rate of less than 1% by weight of carbon nanotubes allows a significant increase in viscosity and more particularly with carbon nanotubes having undergone no post-synthetic treatment. These result in a significant increase in the viscosity of the polymer with very low levels of filler between 0.2% and 0.3% by weight. This surprising increase in viscosity is explained by the very high affinity of the crude carbon nanotubes for the polysiloxane polymer, as shown by the measurements made by means of a so-called "bound rubber" test (Table 3). The experimental procedure of this test consists of extracting 3.5 g of precursor A / carbon nanotubes mixture with 30 ml of solvent (heptane) for 4 hours at 25 ° C. After centrifugation and evaporation of the solvent, the dry residue is weighed to determine the amount of PDMS polymer bound to the carbon nanotubes. Table 3 shows that the crude nanotubes have a much greater affinity with the precursor A than sepiolite and much greater than platelet loading.

Table 3: Affinity of carbon nanotubes for the polymeric matrix of the composition

Thus, the viscometric properties of the precursor A loaded weakly carbon nanotubes allow its application by brush to coat the surface of a material. Nevertheless, the application of the composition according to the invention on a support or a surface can be done by any suitable means. For example, the application can be by injection, or by casting.

Claims

Use as a non-stick coating of a composition comprising a polysiloxane crosslinked polymer and at least one nanocylindrical filler.

2. Use of a composition according to claim 1, wherein said nanocylindrical filler is between 0.01% and 5% by weight of the total weight of said composition.

3. Use of a composition according to claim 2, wherein said nanocylindrical filler is between 0.01% and 1% by weight of the total weight of said composition.

4. Use of a composition according to any one of claims 1 to 2, wherein the nanocylindrical filler comprises sepiolite.

5. Use of a composition according to claim 4, wherein the sepiolite is between 0.01% and 3.5% by weight of the total weight of said composition.

6. Use of a composition according to any one of claims 1 to 3, wherein the nanocylindrical filler comprises carbon nanotubes.

7. Use of a composition according to any one of the preceding claims, wherein said composition comprises sepiolite and carbon nanotubes.

8. Use of a composition according to any one of claims 6 or 7, wherein the carbon nanotubes are selected from the group of single wall carbon nanotubes (SWNTs), double wall (DWNTs) or multiple wall (MWNTs).

9. Anti-adhesive and antistatic composition comprising a crosslinked polysiloxane polymer and a concentration of multiwall nanotubes of between 0.1% and 1% by weight, said composition having an electrical resistivity of less than 100,000,000 Ohm. cm.

10. Anti-adhesive and antistatic composition according to claim 9, characterized in that the concentration of multiwall carbon nanotubes is between 0.3% and 1% by weight, said composition having an electrical resistivity of less than 1,000,000 Ohm. cm.

11. Anti-adhesive and antistatic composition according to claim 10, characterized in that the concentration of multi-wall carbon nanotubes is between 0.5% and 1% by weight, said composition having an electrical resistivity of less than 250,000 Ohm. cm.

12. Use as antistatic coating of a release composition comprising a polysiloxane crosslinked polymer, said composition comprising a concentration of multiwall carbon nanotubes of between 0.01 and 5% by weight.

13. Use as antistatic coating of a non-stick composition according to claim 12, characterized in that said composition comprises a concentration of multiwall nanotubes of between 0.1 and 1% by weight.