FR3103807A1 - LAMINATED GLASS FOR CAMERA - Google Patents

Abstract

The invention relates to a device for shooting by a camera through a glazing, comprising a camera and a laminated glazing comprising two sheets of glass separated by a polymer material, the two sheets of glass being of the fusion draw type. The device is particularly suitable for equipping vehicles, the camera being integrated into a vehicle driving assistance system or an autonomous vehicle driving system.

Description

LAMINATED GLASS FOR CAMERA

The invention relates more particularly to the field of glazing for vehicles and more particularly glazing of very good optical quality, in particular that which must provide visibility to a camera.

Currently laminated glazing for cars is mostly produced from two sheets of “float” glass. This term means that each sheet of glass is obtained by the process of floating the glass on a bath of liquid tin called the “float process”. However, this type of glass has characteristic geometric imperfections, both in terms of flatness and thickness but also of orientation along the glass sheet. Good optical quality of laminated glazing is thus difficult to obtain because of the flatness and thickness defects of the glass sheets it contains.

In the "float" process, liquid glass is cast on a tin bath and the glass is stretched longitudinally and laterally in order to obtain sheets of thin thicknesses used in automotive laminated products (typically one of the thicknesses sizes: 2.6 mm, 2.1 mm, 1.8 mm, 1.6 mm, 1.4 mm, 1.1 mm, 0.7 mm). The glass sheets thus produced have two types of geometric imperfections which are parallel to the direction of longitudinal stretching. These are flatness defects and thickness defects.

The optical transmission quality of glazing depends on the way incident rays are deflected when they pass through the glass sheet. The optical quality in transmission is particularly affected when the two faces of the glass sheet are not parallel. Conversely, a glazing with only flatness defects (but no thickness defects) will have a much better optical quality, especially when the incident rays are not too grazing in relation to the surface of the glazing.

The optical transmission quality of laminated glazing depends on the properties of the glass sheets it contains. Two types of defects can be distinguished for an individual sheet: 1) thickness defects and 2) flatness defects. In general, flatness and thickness defects are present simultaneously in glasses manufactured using the float process. They are present in the longitudinal direction of the process and are named under the generic term “float lineage” (“draw lines” in English). A lack of thickness of a sheet produces a strong optical distortion at the level of this sheet. On the other hand, a lack of flatness of a sheet is not at the origin of a strong optical distortion of this sheet. However, even if the two sheets of glass assembled in a laminated glazing do not have a thickness defect but only flatness defects, these defects are a local loss of parallelism between the two external faces of the glazing, which ultimately leads to a lack of thickness in the final glazing (see explanations in Figure 5). We can therefore say that the assembly operation transforms the defects of parallelism of the two sheets of glass that compose it into a defect of thickness. If the starting sheets also have thickness defects, except in the unlikely case where these would be in phase opposition in the final laminated glazing, the latter would be of low optical quality in transmission.

Furthermore, the thermoplastic spacer material that is placed between the two sheets of glass to manufacture laminated glazing (generally PVB) is not perfectly liquid at the time of assembly and does not marry the two surfaces perfectly. of glass with which it is in contact. Thus, the PVB "erases" part of the flatness defects of longer wavelengths, those which do not require a lot of mechanical effort to be "straightened" by bending the glass sheet. The assembly is said to “iron out” (like an iron ironing out the ripples in a garment) long wavelength flaws. Nevertheless, the undulation defects of the float glass of relatively short wavelength are only very partially "ironed" by the assembly operation.

In practice, it is therefore found that laminated glazing is particularly affected by “float lineage”. This effect is all the greater when the angle of incidence of the light rays is grazing relative to the surface of the laminated glazing. Thus, and in order to improve the optical quality of automotive products, windshields are preferably manufactured taking into account the "float lineage". A windshield is thus mounted on a vehicle so that the float lineage is parallel to the median vertical plane of the vehicle (vertical plane of symmetry of the vehicle passing through the middle of the windshield and the middle of the entire vehicle). By definition, the residual distortions of the glazing slightly distort the people and objects that make up the scene seen by the driver. With a vertical float alignment, these deformations are minimized when the driver is looking straight ahead and they are greater when the driver is looking at an angle through the windscreen, on the passenger side for example. In addition, the driver's vision is significantly affected when the shape of an object present in his field of vision changes dynamically and in an unnatural way (an object will be alternately slightly smaller then larger and so on) during the movement of the vehicle. However, when the vehicle is moving, the various elements of the scene seen by the driver move mainly from bottom to top along an essentially vertical line (except for the elements which laterally leave the driver's field of vision). Thus, the shape of objects or people, possibly slightly affected by the residual distortions of the glazing, changes little during their movement in the driver's field of vision.

For the same reasons, and for the most demanding customers in terms of optical quality, the laminated side windows of vehicles are preferably produced with a horizontal "float line". Indeed and contrary to the case of the windshield, for a side window, the elements present in the driver's field of vision move essentially horizontally.

Cameras on board motor vehicles have developed very rapidly in recent years, and motor vehicle manufacturers have increased their degree of requirement concerning the optical quality in transmission of the glazing, in particular in the upper central zone in the state mounted on the vehicle. , especially windshields. With the development of driving aids (“ADAS”) which “take control” of the driver, particularly in the event of emergency braking, and the forthcoming advent of autonomous driving vehicles, it is important to minimize the risk of possible failure of the system for recognizing objects in the path of the vehicle and more generally functions that could affect the safety of passengers or people outside the vehicle. This is why it is useful to improve the transmission optics of the glazing, at least in the areas equipped with cameras.

Float lineage poses a particularly difficult problem for stereoscopic cameras because the latter must combine two images taken from two points located on either side of the axis of symmetry of the vehicle and on a horizontal line, and are particularly affected by the vertical alignment of windshields.

An alternative process to the “float” process is the “fusion draw” process, in which liquid glass overflows on both sides of an elongated tank. The two glass flows meet and rejoin in a single sheet flowing under the tank. This process is suitable for forming thin sheets, typically with a thickness of less than 2.6 mm and is renowned in the electronics industry because its two faces have only been in contact with air and have no defects. physical, nor tin gradient as is the case with the "bath" side of a float glass. This glass resulting from the “fusion draw” process is also free from optical defects of the “float lineage” type. It is considered that the expression “fusion draw” can be rendered in French by the expression “fusion par étirement vertical”, the latter meaning more precisely “formed by overflow from a weir and vertical drawing downwards in the air”. Such a method is described in particular in the patent application FR1432363A. A sheet made by this process does not have a face comprising a tin gradient whose concentration decreases from the surface towards the core. Indeed, when it was formed into flat glass, the sheet froze in the air without contact with a metal bath or with any tool.

Also, if a float glass is assembled with glasses resulting from the “fusion draw” process, this assembly is of better optical quality than a similar glazing whose two glasses would come from a float.

The invention consists in manufacturing laminated glazing intended to provide vision for a camera, in particular for a vehicle, and of which two sheets of glass, on either side of an interlayer sheet of polymer material, are obtained from the process of "fusion draw" manufacturing.

The invention relates to a device for taking pictures by a camera through a glazing, comprising a camera and a laminated glazing comprising two sheets of glass separated by a polymer material, the two sheets of glass being of the fusion draw type.

The benefits include:

• the thickness of the “fusion draw” glass sheets is compatible with those used for the manufacture of vehicle glazing, which are generally less than or equal to 2.6 mm thick;
• the optical transmission is particularly improved compared to the sheets manufactured by the float process.

According to the invention, in a laminated glazing unit, at least two sheets of "fusion draw" glass are assembled, separated by a sheet of polymeric material (generally PVB), the thickness of each of these sheets of glass possibly being comprised in the range from from 0.5 to 3 mm. Preferably, the thinnest glass is in the glazing so as to be placed on the side of the interior of the vehicle. The polymer material between two sheets of glass may have a thickness comprised in the range from 0.3 to 1 mm in the final laminated glazing. In particular, the invention relates to a windshield whose outer and inner glasses (when mounted on the vehicle) respectively have the thickness:

- from 1.4 to 2.3 mm for the exterior glass (not located on the side of the camera), and

- from 0.7 to 1.8 mm for the interior glass (located on the side of the camera).

In particular, the invention relates to a windshield whose outer and inner glasses (when mounted on the vehicle) are respectively 2.1 and 1.6 mm thick.

The glass sheets may or may not be covered with one or more thin layers such as one or more anti-IR layers, for example with silver, or one or more so-called Low-E layers: these layers are not taken into account in the aforementioned thickness ranges.

At least one glass sheet of the laminated glazing may be tinted. At least one sheet of glass of the laminated glazing, or even two sheets of glass of the laminated glazing, can be chemically reinforced (by chemical toughening).

Laminated glazing is generally curved.

The laminated glazing can be manufactured by conventional techniques for assembling laminated glazing comprising bringing the glass sheets into contact with the interlayer sheet made of polymer material to separate them, degassing and passing the assembly through an autoclave. An adhesion is thus created between the sheet of polymeric material and the sheets of glass. In the final laminated glazing, the sheet of polymer material is placed between the two sheets of glass. One side of the sheet of polymeric material is in contact and adhesively bonded to one sheet of glass, while the other side of the sheet of polymeric material is in contact and adhesively bonded to the other sheet of glass.

The spacer material located between the two sheets of glass is advantageously PVB (that is to say polyvinyl butyral) which makes it possible to give good mechanical performance to the laminated glazing over a wide temperature range and thus to satisfy the tests. of the "ECE R43" standard which defines the minimum properties that glazing for automotive applications must satisfy.

The standard PVB material has a certain level of stiffness. According to the invention, the PVB used preferably has a higher rigidity. Indeed, the use of a more rigid PVB makes it possible to better "iron" the defects of parallelism between the two sheets of glass during their assembly operation. It therefore makes it possible to further improve the optical quality in transmission of the glazing produced. More specifically, during the degassing step around 100-110°C and in the autoclave around 110-140°C, rigid PVB has a higher viscosity, so it has both:

• more difficulty thinning out in areas where, if alone, the two sheets of glass would be closer to each other;
• more difficulty in migrating to fill the spaces where, if they were alone, the two sheets of glass would be farther apart.

The higher the viscosity of the PVB between 100 and 140° C., the less these displacements of PVB between the two sheets of glass can take place. As a result, two effects are achieved:

• in the distribution of the different wavelengths of the parallelism defects existing between the two sheets of glass, a rigid PVB "passes" a wider range of defects, until reaching defects of lower wavelength, compared to a standard stiffness PVB;
• at a given wavelength, each defect is “ironed” more efficiently.

The rigidity of PVB is, to the first order, characterized by its glass transition temperature which can be effectively measured by a method of dynamic mechanical analysis (or dynamic mechanical analysis , DMA in English) and by the determination of the temperature where the loss angle is maximum (see article https://en.wikipedia.org/wiki/Dynamic_mechanical_analysis for more information). For PVB, it is recommended to carry out such an analysis at low frequency, typically 1 Hz, in order to properly identify the deformation modes taking effect when the stress on the material is slow.

By this method, and as documented in the technical article "Spacers for laminated glass", Gérard SAVINEAU, "Engineering techniques", Ref. N4404-V1, 10-02-2013, it is possible to characterize several types of PVB including:

• “soft” PVBs with enhanced acoustic properties have a glass transition temperature between 16-18°C;
• "standard" PVB whose glass transition temperature is between 28-32°C;
• “rigid” PVB whose glass transition temperature is between 40-45°C.

Of course there are PVBs with glass transition temperatures intermediate to the three categories just mentioned.

According to the invention, glazing with improved optics can be produced with “soft” PVB if the acoustic performance is paramount before the optical properties. The improvement in optical quality then comes essentially from the use of two sheets of flat glass formed by the “fusion draw” process.

According to the invention, the glazing with improved optics is manufactured from sheets of flat glass formed by the "fusion draw" process and preferably with standard PVB, the glass transition temperature of which, determined at 1Hz by the DMA method, is included in the range from 28 to 32°C.

According to the invention, the glazing with improved optics is manufactured from sheets of flat glass formed by the "fusion draw" process and more preferably with more rigid PVB whose glass transition temperature determined at 1 Hz by the DMA method is above 32°C.

According to the invention, the polymer material may comprise a PVB having a glass transition temperature determined at 1Hz by the DMA method greater than 28°C or even greater than 32°C.

The use of too rigid PVB can possibly lead to a loss of mechanical resistance and to a negative ball drop test described in the ECE R43 standard. Also, it is necessary to rigorously qualify the glazings when they are produced with PVB whose glass transition temperature determined by DMA is higher than 40°C.

The invention also relates to a vehicle comprising the device according to the invention. In particular, the vehicle is generally such that the glazing delimits the passenger compartment and the exterior of the vehicle, the camera being in the passenger compartment. In particular, the laminated glazing is generally the windshield of the vehicle.

In the following figures, flatness and parallelism defects are deliberately exaggerated to facilitate understanding. The thicknesses of the different constituents (glass and polymer material) are not to scale. The camera can be integrated into a vehicle driving assistance system or an autonomous vehicle driving system.

Figure 1 gives a representation of float glass flatness defects.

Figure 2 gives a representation of float glass thickness defects.

Figure 3 illustrates how the optical quality in transmission is affected when the two sides of a sheet of glass are not parallel.

Figure 4 illustrates the fact that two parallel incident rays can come out almost parallel from a sheet of glass with a simple waviness defect but whose two faces are parallel.

Figure 5 illustrates how the operation of assembling a laminated glazing comprising two sheets of glass and a sheet of material transforms the defects of parallelism of the two sheets of glass into a thickness defect of the final laminated glazing.

FIG. 6 illustrates a device comprising curved laminated glazing and a camera arranged to be able to take shots through the glazing.

Figure 1 gives a representation (deliberately exaggerated) of float glass flatness defects. The glass sheet 1 has corrugations parallel to the longitudinal edges of the float ribbon, that is to say parallel to the direction of flow of the glass (arrow 2) during its forming in a float enclosure. The 3 peaks and 4 valleys of the glass have been highlighted with a dotted line. This representation is naturally simplified compared to a real sheet of glass where there are a plurality of flatness defects having different wavelengths. Real glass therefore has flatness defects characterized by a distribution of wavelengths, which the figure does not show.

Figure 2 gives a representation (deliberately exaggerated) of the thickness defects of float glass. The glass sheet 5 has overthicknesses and underthicknesses parallel to the longitudinal edges of the float ribbon, that is to say parallel to the direction of flow of the glass (arrow 2). The 6 peaks and 7 valleys of the sample have been underlined with a dotted line. As in the case of figure 1, this representation of the thickness defects is simplified compared to a real glass sheet presenting a plurality of thickness defects characterized by a distribution of wavelengths.

A real glass sheet is therefore characterized by the combination of flatness defects and thickness defects, each type of defect being characterized by a wavelength distribution.

Figure 3 illustrates how the optical quality in transmission is affected when the two sides of a sheet of glass are not parallel, this defect being of course exaggerated in the figure. We actually have a lens in some places.

Figure 4 illustrates the fact that two parallel incident rays can come out almost parallel from a sheet of glass with a simple waviness defect but whose two faces are parallel. Such a sheet has good optical quality in transmission. This statement is all the more correct when the incident rays are perpendicular to the glass sheet and becomes less and less correct when the incident rays form an increasingly acute angle with the surface of the glass.

FIG. 5 illustrates the structure of a laminated glazing 13 made by assembling two sheets of glass 10 and 11 with a sheet of polymer material 12. The two sheets do not have any thickness defect, the sheet 10 being perfectly flat and the sheet 11 having undulations. It is assumed for simplicity that the sheet of polymeric material behaves like a perfectly liquid material and which hugs the two surfaces of the sheets of glass with which it is in contact. Each sheet of glass taken separately has good optical quality in transmission, but the assembly operation has transformed the lack of parallelism of the two sheets in the final laminated glazing 13 into a lack of thickness. We finally find ourselves in a case of defect similar to that of figure 3. Thus, the assembly operation transforms the defects of parallelism of the two sheets of glass into a defect of thickness at the level of the final laminated glazing.

FIG. 6 illustrates a device according to the invention comprising a curved laminated glazing 30, and a camera 31 arranged to be able to take shots through the glazing 30. The glazing here is a motor vehicle windshield and the camera is fixed to the glazing by a base 34. The laminated glazing comprises a sheet of glass 32 outside the cabin located on the side opposite to that of the camera, and a sheet of glass 33 inside the cabin located on the side of the camera. The outer sheet 32 is thicker in the figure but could be of the same thickness as the inner sheet 33. These two sheets of glass are of the fusion draw type. They are assembled in the laminated glazing with a sheet 35 of polymeric material, generally PVB. In this laminated glazing, the sheet of polymeric material is in contact and adhesively bonded by each of its faces to the two sheets of glass.

Claims (17)

Device for shooting by a camera through a glazing (30), comprising a camera (31) and a laminated glazing (30) comprising two sheets of glass (32,33) separated by a polymer material (35), characterized in that the two sheets of glass are of the fusion draw type. Device according to the preceding claim, characterized in that the thickness of each of the two sheets of glass is included in the range going from 0.5 to 3 mm. Device according to one of the preceding claims, characterized in that the thickness of the sheet located on the side of the camera has a thickness included in the range from 0.7 to 1.8 mm and the thickness of the other sheet has a thickness in the range from 1.4 to 2.3 mm. Device according to one of the preceding claims, characterized in that one or both glass sheets are chemically reinforced. Device according to one of the preceding claims, characterized in that at least one sheet of glass is tinted. Device according to one of the preceding claims, characterized in that the polymer material comprises a PVB having a glass transition temperature determined at 1Hz by the DMA method above 28°C. Device according to one of the preceding claims, characterized in that the polymer material comprises a PVB having a glass transition temperature determined at 1Hz by the DMA method above 32°C. Device according to one of the preceding claims, characterized in that the polymer material has a thickness comprised in the range from 0.3 to 1 mm. Device according to one of the preceding claims, characterized in that the glazing is the windscreen of a vehicle. Vehicle comprising the device of one of the preceding claims. Vehicle according to the preceding claim, characterized in that the glazing delimits the passenger compartment and the exterior of the vehicle, the camera being in the passenger compartment. Vehicle according to one of the preceding vehicle claims, characterized in that the camera is integrated into a vehicle driving assistance system or an autonomous vehicle driving system. Laminated glazing (30) comprising two sheets of glass (32,33) separated by a polymer material (35), characterized in that the two sheets of glass are of the fusion draw type and in that the polymer material comprises a PVB having a glass transition temperature determined at 1Hz by the DMA method greater than 32°C. Glazing according to the preceding claim, characterized in that the polymer material has a thickness comprised in the range from 0.3 to 1 mm. Glazing according to one of the preceding glazing claims, characterized in that the thickness of each of the two sheets of glass is within the range from 0.5 to 3 mm. Glazing according to one of the preceding glazing claims, characterized in that one or both sheets of glass are chemically reinforced. A vehicle comprising the glazing of one of the preceding glazing claims.