Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1998-05-01
2001-08-28
Niland, Patrick D. (Department: 1714)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C296S084100, C296S077100, C296S146100, C428S213000, C428S214000, C428S215000, C428S423300, C428S425500, C428S425600, C428S426000
Reexamination Certificate
active
06280847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to glazings, and in particular to laminated glazings having a high intrusion resistance.
2. Summary of Related Art
Glazings for automotive use comprise safety glass which may be laminated (widely used for windscreens) or toughened (widely used for sidelights and backlights). Both types of glazing provide some degree of impact resistance, with laminated glazings having certain advantages over toughened glass so that, although laminated glazings are more expensive to manufacture than toughened glass, it would be desirable for all automotive glazings to be laminated to give improved intrusion resistance and to improve occupant retention in collisions. However, while conventional laminated glass (using polyvinylbutyral interlayer) provides better intrusion resistance than toughened glass, it will not resist a sustained attack especially when (as in the case of opening side lights) it is not permanently secured around its periphery by the glazing system used.
Attempts have been made to improve the impact resistance of laminated glazings by incorporating polycarbonate as an impact resistant ply in the laminate. Unfortunately, a polycarbonate ply at least 3 mm thick is required because polycarbonate is prone to stress cracking at lower thicknesses. However, while a 3 mm polycarbonate layer provides sufficient impact resistane for most purposes in a laminated glazing, when a 3 mm polycarbonate is laminated between glass panes (to provide the durability required for most uses) the resultant glazing becomes relatively thick and heavy, making it unsuitable for general automotive use.
A new family of engineering thermoplastic polymers have become available in recent years, the rigid thermoplastic polyurethanes, (RTPU), which are finding use in load-bearing engineering applications. Unfortunately, such polymers have poor resistance to ultra violet radiation, presumably due to inclusion of aromatic units in the polymer chains (the flexible thermoplastic polyurethanes currently used in aircraft glazings are aliphatic in character, and do not suffer the same deterioration on exposure to ultra-violet radiation). Thus they would not normally be considered suitable for use in external glazings.
We have now found that a rigid thermoplastic polyurethane ply may be satisfactorily protected from ultra-violet radiation so that it becomes suitable for external use by incorporating it in a laminate with an ultra-violet absorbing and/or reflecting ply outside (i.e. between the rigid thermoplastic ply and the source of incident ultra-violet light, normally the sun) the rigid thermoplastic ply, providing a durable, impact resistant glazing, suitable for automotive use, without the disadvantages of thickness and weight referred to above.
BRIEF SUMMARY OF THE INVENTION
According to the present invention there is provided a laminated glazing including an impact resistant ply of rigid thermoplastic polyurethane sensitive to ultra-violet radiation and, outside said ply, an ultra-violet reflecting or absorbing ply. The laminated glazing may be for automotive use.
The use of a thermoplastic material for the impact resistant layer facilitates the production of curved laminates, as it may be thermoformed to the required shape of the laminate during lamination.
The rigid thermoplastic polyurethanes have a Youngs (tensile) modulus of greater than 500 MPa, and the preferred materials have a modulus of at least 1000 MPa so that adequate stiffness can be achieved using layers no more than about 1 mm thick; in an especially preferred embodiment the tensile modulus of the impact resistant layer is about 2000 MPa or greater. The modulus values referred to herein are as measured in accordance with ASTM D638.
The rigid thermoplastic polyurethane ply will normally have a thickness of at least 0.20 mm (in order to provide adequate impact resistance) with thicknesses in the range 0.5 to 2 mm, especially 0.5 to 1.5 mm being appropriate for most applications. For applications where unnecessary weight and thickness are undesirable, it will preferably have a thickness in the range 0.4 to 0.8 mm.
The ultra-violet reflecting or absorbing ply or plies used should transmit no more than about 20% (measured in accordance with ISO 9050) of the incident ultra-violet solar radiation and preferably less than 10% and especially less than 5%. The non-transmitted ultra-violet will normally be substantially absorbed by a ply or plies of the laminate on the outside of the impact resistant ply, although it may be at least partially reflected, for example, by incorporating a reflective metal coating in the laminate outside the impact resistant ply.
A pane of high performance solar control glass (such as OPTIGRUN™ 90 or EZ-KOOL™ glass) may be used to absorb ultra-violet light, usually in conjunction with an additional ply, between an outer glass ply and the impact resistant layer, of an ultra-violet absorbing interlayer material. Such an interlayer material may itself be a thermoplastic polyvinylbutyral or polyurethane (normally an aliphatic polyurethane and much softer than the rigid thermoplastic polyurethane used for the impact resistant ply) for example, Morton PE 399 (available in commerce from Stevens Urethane of Holyoke, Mass., USA) or Tecoflex AG-8451 primerless film (available in commerce from Lehmann & Voss & Co of Hamburg, Germany). The Tecoflex primerless film has particularly good ultra-violet absorbing properties (with a 0.38 mm thick film absorbing substantially all the incident solar ultra-violet radiation measured in accordance ISO 9050) and is preferred as it may be used in thin layers without any additional absorption provided by an outer glass or reflecting metal layer.
While certain plastics, such as polycarbonates, polyurethanes and polyvinylacetals have properties which make them useful in glazing applications, for most glazing applications it is preferred to use such plastics plies in conjunction with glass outer plies because of the good optics and high durability of glass. Where the plastic plies are thermoset, as for example, acrylics, they may be bonded to glass either by incorporating a thermoplastics interlayer ply between the thermoset plastics ply and the glass and autoclaving, or by using a curable “cast-in-place” interlayer material to form an interlayer in-situ between the thermoset ply and the glass, the interlayer so formed adhering to both the thermoset ply and the glass and bonding them together. Where the plastics plies are thermoplastic, they are normally bonded directly to glass by heating the plies together under pressure in an autoclave.
Thus, it was anticipated that the rigid thermoplastic polyurethanes used in the present invention would be bonded directly to glass outer plies by autoclaving, avoiding the need to use a separate bonding layer. However, it has been found that much better adherence can be achieved, with the laminate displaying greatly enhanced energy absorption and impact resistance, if the rigid thermoplastic polyurethane ply is bonded to a glass outer ply using a relatively low modulus interlayer material, preferably a thermoplastic material to which the glass and rigid thermoplastic plies are bonded by heating under pressure.
It is found that the use, as an adhesive, of an interlayer, preferably a preformed thermoplastic interlayer, of low modulus (for example, less than 100 MPa, preferably less than 10 MPa) between the glass and the high modulus rigid polyurethane prevents cracks propagating through an outer glass ply into the rigid interlayer; it is believed that a low tensile modulus adhesive does this by blunting the crack tip. A thin adhesive layer having a thickness of as little as 10 microns and ideally about 100 microns or more can be used for this purpose, although the ready availability of suitable soft adhesive materials in greater thicknesses e.g. 0.38 mm may make it more convenient to use somewhat thicker layers (for example up to 0.4 mm) than necessary.
Thus, according to a further aspect of the
Corkhill Philip Harold
Green Malcolm Francis
Holmes Paul Arthur
Winstanley Neil
Marshall & Melhorn LLC
Niland Patrick D.
Pilkington plc
LandOfFree
Laminated glazings does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laminated glazings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laminated glazings will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2451304