Patent Application
20070275245
The invention relates to a process for activating the surface of glass to make it more receptive to subsequent treatments, generally for the deposition of coats, for instance a hydrophobic coat.
Hydrophobic properties are desired for glazing and windshields in the transportation field, in particular for motor vehicles and aircraft, and also for glazing in the construction field. For applications in the transportation field, rain-repelling properties are desired, the drops of water on windshields thus needing to run easily along the glass wall in order to be removed, for example under the effect of the air and wind when the vehicle is running, with the aim of improving the visibility and, consequently, the safety, or to facilitate the cleaning, to remove frost easily, etc. It is estimated that the surface of a substrate is hydrophobic if the angle of contact of a drop of water with the substrate is greater than 60° or 70°, without the drop of water becoming crushed or spread. Specifically, glazing is said to be functional as long as this angle is greater than 60° for aviation and 70° for motor vehicles. However, it is appropriate in practice to exceed in all cases a value of 90°, the ideal being to obtain running of the drops that allows the water to be removed so quickly that the windshield wipers can be dispensed with as much as possible in the motor vehicle field. Moreover, the improvement of the hydrophobic properties that is thus sought should not take place to the detriment of the conservation of the other properties, such as the resistance to mechanical constraints: tangential friction resistance (Opel test, standardized under dry conditions), the abrasion resistance (Taber), the resistance to wiping with windshield wipers (test simulating the sweep cycles of a windshield wiper); the resistance to environmental constraints (WOM test of resistance to UVA or Xenon test; QUV test of resistance to UVB for aircraft; BSN test of resistance to neutral saline fog); the resistance to chemical constraints: test of resistance to acidic and basic detergents; and the optical properties.
The Applicant has observed that coats of diverse nature (including hydrophobic coats) held less well when the surface of a glass substrate showed a certain degree of ageing in ambient air. Such ageing undoubtedly arises from the change in the chemical state of the surface. The coats deposited on an aged surface present overall less adhesion, and less uniform adhesion. It is estimated that a surface is substantially aged once it has spent at least one hour in ambient air below 100° C. Thus, any glass object that has been normally stored in order to be taken later to apply a deposit has a surface that is aged within the meaning of the invention. This type of aged surface may especially be the surface of curved glazing, especially for motor vehicles, for example motor vehicle side window glass. It is noted that the surface of a glass coming directly from a flat glass forming plant naturally has an activated and thus non-aged surface. If it is not left for too long, a coat may thus be deposited directly onto such a surface without it being necessary to perform an activation treatment.
The activation process according to the invention is applied directly to the surface of the glass without it being necessary either to heat or to apply a particular undercoat in order to regenerate the surface. According to the invention, the surface is regenerated (or “activated” or “buffed”) by abrasion, i.e. removal of material, even if this abrasion may be so light that its effects are not visible to the naked eye or even, where appropriate, to a scanning electron microscope. Thus, this abrasion may even be of the order of an atomic monocoat. This abrasion is thus applied directly to the glass surface not containing any coats (a coat may optionally be present on the face that is not to be activated). This treatment is applied to the entire surface, i.e. especially to the periphery and the central area. The use of any chemical product that attacks glass, for instance an acid, is not necessary to activate the surface, neither before, nor during, nor after the present abrasion treatment, even before the application of any surface coat or undercoat.
This abrasion may especially be performed by treating the surface with a plasma or an ionized gas at reduced or atmospheric pressure, chosen from air, oxygen, nitrogen, argon, hydrogen, helium and ammonia, or a mixture of these gases, or an ion beam.
This abrasion may also be performed by rubbing the surface with a polishing abrasive. The abrasive comprises abrasive grains. The term “polishing” is slightly incorrect in the present context since the abrasive will make the surface slightly coarse, such that, in general, the surface is slightly coarser after polishing than before. Nevertheless, it is “polishing” abrasives that may be used. The abrasive material may especially be very fine cerium oxide (particle size: for example 0.1 to 5 μm). Preferably, the grains of abrasive are fine enough not to create scratches that are visible to the naked eye. Preferably, the abrasion does not produce any scratches that are visible to the naked eye.
The polishing treatment may be performed manually. In this case, an operator passes an orbital sander fitted with a pad of the Scotchbrite type or a cotton pad over the surface, which has also received a dispersion comprising a liquid, generally an aqueous liquid, and an abrasive powder, for instance a cerium oxide powder. The dispersion may contain, for example, 5% to 30% by weight of cerium oxide. The surface is then rinsed with water. A composite abrasive at the same time comprising a support acting as matrix for the abrasive grain held on the surface of the support may also be used. In this case, during the polishing operation, it suffices to add water to the surface to be treated. The composite abrasive may also be applied to the orbital sander by an operator. After rinsing, the glass is dried.
The polishing treatment may also be performed automatically. To do this, a composite abrasive described above may preferably be used. This abrasive may have the form, for example, of a disk and may be driven in a rotational motion during the polishing action. A belt, generally closed on itself, may also be used as abrasive.
The machine fitted with the polishing belt may be one of those usually used for flashing or deburring metal components.
The glass may be handled by a robot. The robot grips the glass by means of suction pads applied to the main face (which is generally concave) opposite the face to be treated. Water is continuously sprayed onto the surface and the polishing belt during the treatment so as to gradually remove the cerium oxide and also the polishing debris. The robot applies half of the glass against the traveling belt, and optionally rotates it by 180° to again apply it to the other half. The pressure of the belt on the glass is controlled at all times by compliance means so as to ensure homogeneous buffing.
The activation treatments that have just been described activate the surface so much that the coats deposited thereafter adhere better and more homogeneously to the glass. This activation of the surface of the glass is reflected by a strong hydrophilic nature. This hydrophilic nature is witnessed by observing whether sprayed water spreads out well and homogeneously on the surface, or by means of surface tension measurements, for example using calibration liquids of the Plasmatreat® type. The activation treatment according to the invention leads to an activated and hydrophilic surface with a surface tension of at least 62 mN/m at any point.
After activation according to the invention, the activated surface may especially be coated with a hydrophobic coat. Generally, the hydrophobic coat itself is preceded by a mineral undercoat comprising silicon coordinated to at least one other chemical element such as O, and/or C, and/or N, said undercoat serving as primer for the grafting of the molecules of hydrophobic nature, generally fluorinated silane molecules.
The undercoat containing Si may especially consist of a compound chosen from SiOx with x less than or equal to 2, SiOC, SiON, SiOCN and Si3N4, hydrogen possibly being combined in any proportion with SiOx with x less than or equal to 2, SiOC, SiON and SiOCN. It may contain aluminum, in particular up to 8% by weight, or alternatively carbon, Ti, Zr, Zn or B. Mention may also be made of undercoats consisting of scratchproof varnish, such as polysiloxanes, which have been applied as a coat to polycarbonate substrates. The undercoat containing Si has a thickness especially of between 1 nm and 250 nm and especially between 2 nm and 100 nm. The coat containing silicon can be deposited onto the substrate, without heating, by cathodic sputtering, under vacuum, preferably assisted by a magnetic field and/or an ion beam, or by PECVD at low pressure or at atmospheric pressure, or alternatively under hot conditions by pyrolysis.
This coat of silica may also be produced by applying a solution of an alkoxysilane, for instance tetraethyl orthosilicate (or tetraethoxysilane) of formula Si(OCH2CH3)4, commonly known as TEOS. A solution of TEOS in isopropanol may especially be applied. This operation may be performed at room temperature by manual wiping by an operator.
After application of the undercoat, the hydrophobic coat should be applied without delay. The reason for this is that, if there is too much of a delay, the surface of the undercoat tends to become deactivated (in the same way as the glass substrate before the activation according to the invention), and the surface of the undercoat would thus have to be reactivated. In practice, it is recommended to apply the hydrophobic coat as quickly as possible after applying the undercoat. For the case of an application of TEOS dissolved in isopropanol, the evaporation of the solvent and the reaction of the TEOS are quick enough for it not to be necessary to perform a particular drying treatment before applying the hydrophobic coat.
The hydrophobic coat may also be applied by manual wiping by an operator.
To make the hydrophobic coat, it is possible to apply a compound chosen from:
(a) the alkylsilanes of formula (I):
CH3(CH2)nSiRmX3-m (I)
in which:
An example of an alkylsilane of formula (I) is octadecyltrichlorosilane (OTS). The preferred hydrophobic agents are fluorinated silanes (c), in particular those of formula (II), particular examples of the latter being those of formula:
CF3—(CF2)n—(CH2)2—Si(OR4)3
in which:
It may especially be CF3 (CF2)7CH2CH2Si(OCH2CH3)3.
The hydrophobic agent may generally be applied manually by wiping, i.e. using a cloth impregnated with this agent.
The hydrophobic coat especially has a thickness of between 1 and 100 nm and preferably between 2 and 50 nm. The fluorinated hydrophobic coat may have a mass thickness of grafted fluorine of between 0.1 μg/cm2 and 3.5 μg/cm2 and in particular between 0.2 μg/cm2 and 3 μg/cm2.
The Opel test for characterizing the resistance of the coat(s) on the glass substrate is as follows: Construction Standard En 1096-2 of January 2001, which consists in applying onto a part of the coated surface 9.4 cm long—this part being referred to as the track—a felt 14 mm in diameter, 10 mm thick and with a mass per unit volume of 0.52 g/cm2, under a load of 39.22 MPa (400 g/cm2), the felt being subjected to a translation (50 to-and-fro motions over the entire length of the track per minute) combined with a rotation of 6 rpm (1 cycle=1 to-and-fro motion).
After these various treatments, it is generally desired for the glass to maintain good transparency, especially in the case of window glass for motor vehicles (or for other vehicles).
The invention relates to all glass surfaces, more particularly the window glass of motor vehicles, for instance windshields and sliding window glass and more especially side window glass. The surface of the activated glass may have an area of at least 0.25 m2 and even at least 0.3 m2 and even at least 0.35 m2 and even at least 0.4 m2.
Thus, the invention also relates to a pane comprising a hydrophobic coating applied to a pane having the activated surface according to the invention, an undercoat containing Si possibly being applied between the glass and the hydrophobic coat. Such a pane provided with a hydrophobic coating may have a resistance in the Opel test at 5000 cycles of at least 80° (water drop angle). The invention also relates to a windshield or sliding window glass of a vehicle, comprising a pane equipped with a hydrophobic coating according to the invention.
The surface of two window glasses is activated by abrasion. One is treated automatically with a belt as described for
The automatic polishing leads to a surface tension of 72 mN/m (measured with Plasmatreat®). The manual polishing leads to a surface tension of 65 mN/m, which reflects a less hydrophilic nature than in the case of the automatic polishing (it should be noted that an identical window glass that is not activated but simply degreased with an RBS soap gives a surface tension of between 50 and 60 mN/m).
Identical treatments are applied to the window glasses, first a coat of silica by wiping with TEOS in isopropanol, followed by a hydrophobic coat by wiping with a solution of a fluorosilane of formula CF3(CF2)7CH2CH2Si(OCH2CH3)3. This solution was prepared by mixing together 2% by weight of silane and 98% by weight of a solvent. This solvent contained 90% by weight of 2-propanol and 10% by weight of 0.3N HCl in water.
The resistance of the coats is then measured by the Opel test. The angle of contact of a drop of water with the substrate after a certain number of cycles (5000, 7500 and 10000 cycles) is measured. The table below collates the results:
| Number | Date | Country | Kind |
|---|---|---|---|
| 0404531 | Apr 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR05/50281 | 4/27/2005 | WO | 1/22/2007 |
