Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2002-06-12
2004-10-26
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S300400, C428S300700, C428S480000, C428S430000
Reexamination Certificate
active
06808797
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to interlayers used for the production of laminated glazing intended for fitting into motor vehicles. Such glazing usually consists of two glass sheets separated from each other by a plastic interlayer, such as a sheet of polyvinyl butyral (PVB).
More particularly, although the invention is not limited to such applications, it applies to side windows linked to “raising-lowering” systems defining a sliding movement of the said windows in the doors of motor vehicles.
BACKGROUND OF THE INVENTION
Usually, such side windows consist of a sheet of so-called “safety” or “security” glass, that is to say glass meeting European Regulation No. 43. Such windows have weaknesses with regard to the actual security of the vehicle since it is possible to break such windows and get inside the vehicle, either to steal the vehicle or to remove articles or accessories from the passenger compartment.
For a number of years now, anti-theft systems have been developed either in the form of an audible alarm or which allow the vehicle to be immobilized. Although such systems may possibly prevent the vehicle from being stolen, they are often ineffective against a simple break-in, by smashing the window in order to steal articles left in the passenger compartment.
In order to respond to and prevent this type of break-in, it has already been proposed to use laminated glazing consisting, for example, of two glass sheets separated by a plastic interlayer, as mentioned above.
The use of such laminated glazing is advantageous for solving the security problem. This is because the presence of the plastic sheet enormously complicates the breaking of the glass; in the case of laminated glazing comprising two glass sheets separated from each other by a sheet of PVB, when one or both glass sheets are broken, the laminated structure remains in place, the broken glass sheets remaining fast to the interlayer.
However, in the event of an attempted break-in, during which an individual attempts using a tool to smash the laminated glazing by repeated blows, it may happen that the glazing becomes deformed such that the edges of the latter come free of the lateral jambs into which it is set. This is more particularly true in the case of opening windows, such as those which slide vertically in the doors of motor vehicles; in the closed position, the lateral parts and the top of the window are not fixed to the door frame but set in the guide rails and the top of the frame. A large and repeated compressive force using a blunt instrument, such as a club or baseball bat, may thus result in the deformation of the window, which bends and comes free of the door frame, at least on one of its sides. It then merely remains to push or pull the window in order to expose an opening into the interior of the vehicle.
To limit or retard the deformation of such a window, when one or both glass panes are broken, it has already been envisaged to use a rigid interlayer which has a high flexural strength and therefore prevents the window from bending. However, such interlayers have large thicknesses which make them incompatible with the applications in question or at the very least require very significant modification to the door frames. The inventors were thus tasked with the objective to produce an interlayer consisting of at least one soft plastic film, as opposed to the abovementioned rigid interlayers, for the purpose of producing laminated glazing that can be used as a motor-vehicle window in standard structures, the said interlayer increasing the resistance of the window to deformation, or in other words increasing its “residual rigidity”.
SUMMARY OF THE INVENTION
The present invention relates to an interlayer for a laminated glazing, consisting of at least two sheets of polyvinyl butyral (PVB), a reinforcement being inserted between the said two sheets of PVB, the said reinforcement giving the interlayer a tensile strength such that the elastic energy (Et
r
) needed to deform the interlayer in tension is at least 80 J/m
2
, in all directions in the plane of the interlayer.
Preferably, this elastic energy Et
r
is greater than 120 J/
2
.
This elastic energy needed to deform the interlayer in tension, which illustrates the tensile strength of the interlayer, is expressed in the following way:
Et
r
=&sgr;
e
2
X/
2
Y
(
I
)
with &sgr;
e
: tensile yield strength of the reinforcement,
Y: Young's modulus
x: cross section of the reinforcement per unit length.
The elastic energy Et
r
of a sheet of PVB having a standard thickness for producing laminated glazing intended for motor-vehicle applications is very small and virtually equal to 0 J/m
2
.
Unlike the techniques envisaged hitherto, the interlayer has an almost non-existent flexural strength, yet it makes it possible to limit the deformation of the laminated window broken when pressure is exerted on it, because of the increase in its tensile strength, or more precisely because of the higher value of the elastic energy needed to deform the interlayer in tension.
In fact, during their studies the inventors have been able to demonstrate that, as soon as breakage of the glass sheet occurs, at least two pieces or fragments of glass are formed in the region where the force is exerted. The boundary or line separating these two pieces becomes a site of flexure allowing the window to deform. However, as soon as this deformation occurs, the two pieces of glass bear against each other and this results, since the interlayer remains fast to the glass sheets, in the said interlayer being stressed in tension, at least in one direction, and not only in bending.
According to a first embodiment of the invention, the reinforcement inserted between the sheets of PVB consists of yarns, such as glass yarns or nylon yarns, arranged in at least two directions, for example in order to form a grid or mesh.
In the case of such a reinforcement, the parameter x in formula (I) for Et
r
is such that x=IIr
2
n:
with
r: radius of the yarn
n: number of yarns present per unit length.
According to another embodiment of the invention, the reinforcement inserted between the sheets of PVB consists of a polyester film, such as a polyethylene terephthalate (PET) film having a thickness of greater than 70 &mgr;m.
According to this embodiment, the parameter x in formula (I) for Et
r
is equal to the thickness of the sheet or film of the reinforcement.
The use of a polyethylene terephthalate film has in particular the advantage of possessing a tensile strength which remains high over a wide temperature range, at least up to 50° C.
Advantageously, the reinforcement consists of the combination of at least two polyester films. This embodiment makes it possible in particular to retain good developability of the reinforcement in the form of film, when it is desired to increase the thickness of the said film in order to further improve the tensile strength. This is because increasing the thickness of such a film increases its stiffness and makes its developability less certain, especially if the window has a significant sphericity. The association or combination of two films results substantially in the same reinforcement in terms of tensile strength as a film having a thickness equal to the sum of the thicknesses of the two films in question and each of the films still having a developability compatible with windows having possibly very pronounced sphericities.
Also preferably, in the case of two polyester films joined together, these are separated by a sheet of PVB which ensures good cohesion of the assembly.
The invention also proposes laminated glazing consisting of at least two glass sheets and of an interlayer as described above having a tensile strength such that the elastic energy needed to deform it in tension is at least 80 J/m
2
in all directions in the plane of the said interlayer.
Such laminated glazing therefore comprises two glass sheets which form the outer surfaces of the glazing and between which the interlayer may consist of two sheets of PVB be
Blackwell-Rudasill G.
Jones Deborah
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Gobain Glass France
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