Electrically heated laminated car windscreen.

p0001The invention relates to a heating laminated pane electrically, in particular an automobile pane, comprising two glass sheets joined by a thermoplastic polyvinylbutyral sheet of which is coated on its surface located thin layers of polyvinyl butyral side deposited by a method namely sputtering one silver layer, an anti-reflective zinc oxide layer having optionally an intermediate layer of a metal or a substoichiometric metal oxide, and a layer for improving the bond with polyvinylbutyral placed on the anti-reflective zinc oxide layer.

p0002It is known and proven to form layers for electrically heated auto glass through sputtering methods assisted by a magnetic field or by reactive sputtering also magnetron. A particularly effective composition comprises firstly an anti-reflective zinc oxide layer on the glass surface and a silver layer deposited on zinc oxide and finally a surface layer also anti-reflective and also made of 'zinc oxide. Such a combination is the subject of patents Us 4654067, 4668270 and 4744844.

p0003multiple layers of the same type are also known in which there is interposed between the silver layer and the antiglare surface layer a thin layer of a metal or a metal oxide sub-oxidized. Its function is to protect the money from the action of oxygen during the reactive deposition of the anti-reflective surface layer (European Patent EP 0104870).

p0004Also known through the European patent application EP 0263623 a laminated glazing unit of the type described above wherein there is added to the surface layer of a zinc oxide layer to improve adhesion to the polyvinyl butyral (PVB) . It is in this case a layer of chromium oxide having a thickness between 2.5 and 10 nanometers. But it is in fact in the presence of a complex or a mixture of metallic chromium and oxides with different oxidation levels (CrO, CrO₂, CrO₃ and Cr₂O₃). The function of this surface layer based on chromium oxides is to provide the solution well known to specialists related to aging laminated glasses with thin layers in contact with the PVB when exposed to light and radiation ultraviolet. It is found under these conditions degradation of adhesion such that the laminated glass of the performance becomes insufficient for a safety glass.

p0005The invention's mission is to enable the production of laminated glazing of the type described above, which is equipped layers improving adhesion to polyvinyl butyral and has adhesion properties equivalent to or better than those of glazing with chromium oxide layers mentioned above and which moreover can be manufactured without difficulty by sputtering techniques.

p0006The object of the invention is achieved by a new thin layer which improves the adhesion to the PVB, it consists of metals of group IV, V or VIII of the periodic table or an oxide of the same metals.

p0007The technique of the invention to achieved improvements in adhesion performance between the thin layers and the polyvinyl butyral which are the same as those of the adhesion between a blank glass surface and the same PVB. This is achieved with both metals with their oxides.

p0008One of the requirements to be met by adhesion layers is not to change the optical performance of multiple layers ie light transmission as well as the intensity and spectral distribution of the reflected light. The metal layers, however, have an important influence on the transmission and light reflection. That is why when the adhesion layer is made of a metal, it is important that the thickness remains low by example from 1 to 3 nanometers.

p0009It is found that the metal oxides have a transparency much higher than those of metals and therefore greater the rate of oxidation of metal layer is high and its thickness can be increased. The metal oxide layers of which the metal is fully oxidized, it means that the stoichiometry is reached, can have a thickness much greater than 3 nanometers. The required performance of the laminated glazing ie no or little change in the light transmission and the lack of influence on color both in transmission and in reflection can be obtained adhesion layers made of metal oxides stoichiometric even when their thickness, which depends on the nature of the metal reaches 10 nanometers.

p0010Is obtained very good results from the viewpoint of adhesion and optical properties of the laminated glass where the layer of the invention is composed of titanium, nickel or an alloy of nickel and chromium or a oxide of one of these metals. Was obtained particularly good results with an adhesion layer of tantalum or tantalum oxide. Obviously alloys of mentioned metals or mixtures of their oxides can be used and the results obtained and then the final laminated glass properties are the same.

p0011The operation of the invention will be clear with the drawing and the examples which follow.

p0012The drawing shows the construction of an automobile windshield of the invention. This is a cut.

p0013The unitary glass sheet is equipped on one side of the multiple layer 2. The sheet is placed outside the car when the windshield is laying. Multiple layer 2 is in contact with the thermoplastic interlayer sheet 3 of polyvinylbutyral to which it is linked. On the side of the windshield inside the car is placed in unit glass sheet 4 which is it, in direct contact with the tab 3 to which it adheres. The various components of the laminated glazing are associated with each other in a known manner through the heat and pressure provided by an autoclave.

p0014Multiple layer 2 comprises first layer 21 of zinc oxide having a thickness of 35 nanometers. It is placed on the glass surface. On to the next layer 22 of silver with a thickness of approximately 8 nanometers and finally the protection antireflection layer 23 also made of zinc oxide with a thickness of about 35 nanometers. The adhesion layer 24 made of a metal or a metal oxide is provided on the antireflection layer 23. When the layer 24 is metal, it has a thickness of 1 to 3 nanometers. If on the contrary it is made of an oxide thickness is between 1 and 10 nanometers.

p0015The improved properties of adhesion to the polyvinyl butyral as well as optical measurements are given during the presentation of the following examples.

p0016Measuring the light transmission is carried out using the usual measuring instruments. To measure the adhesion between the surface of glass equipped its layers and the PVB sheet a current test was used in the laminated glass industry, the pummel test. This test involves subjecting a sample of laminated glass that has been heated to a temperature of -20 ° C to the action of a 300 gram hammer and then determine the fraction of fragments which continues to adhere to the plastic sheet. When no fragment does not adhere to the PVB pummel value is zero. But if all the fragments continue to adhere, the pummel value is 10. The windshields of safety standards require that pummel the value is at least 4, which corresponds to 40% of fragments that retain their grip on the PVB at the end of the test.

p0017The procedure was to pummel tests after long term exposure to a light (100, 200, 300 and 400 hours). The lighting conditions were those of "Light Stability Test 1" (American National Standards Institute, ANSI Z 26.1a - 1980).

p0018In all cases, it was heated windshields equipped ZnO-Ag-ZnO layers; with the exception of comparative glazing all windscreens were equipped with the adhesion layer.

Comparative Example

p0019The comparison was made with a laminated glass which does not contain the adhesion layer. Its light transmission was 77%. Before light exposure, the pummel the coated glass interface - PVB was 3. At the end of the first 100 hours exposure the Pummel was already down to a value of 1. This value exists for all illumination up to 400 hours. On the other side of the polyvinyl butyral ie the PVB interface - glass, the value was from 8 and even after 400 hours illumination she had hardly fallen.

EXAMPLE 1

p0020The sample here equipped with a substantially metallic titanium adhesion layer having a thickness of 2 nanometers. The transmission measurement carried out on the finished laminated glass was 77%. The pummel value was at the beginning of approximately 8 and decreased after 200 hours and after 400 hours 7 6.

EXAMPLE 2

p0021This time the adhesion layer was made of titanium oxide having a thickness of approximately 4 nanometers. This layer was obtained by reactive cathodic sputtering from a metallic titanium cathode in an atmosphere having a low partial pressure of oxygen. Again transmission remained unchanged at 77%. The pummel value was 7.5 before irradiation decreased to 6.5 after 200 hours and about 5 after 400 hours.

EXAMPLE 3

p0022The sample was provided with an adhesion layer in substantially metallic nickel chromium, it is obtained by sputtering from a target made of an alloy of nickel and chromium in the proportions 80-20. The thickness of this layer was about 1.5 nanometers. The light transmission had decreased to 75.4%. Pummel test before exposure to the light was approximately 4. This value remained virtually unchanged throughout the irradiation.

EXAMPLE 4

p0023A specimen was provided with an adhesion layer of tantalum metal. This layer had a thickness of about 1.5 nanometers. In comparison with the reference sample, the measurement of the light transmission was unchanged but with a slight tendency to increase. Before the start of the irradiation Pummel test was 8 this value has not changed in subsequent illumination of steps and even after 400 hours a pummel 8 remained.

EXAMPLE 5

p0024By a technique of reactive cathodic sputtering from a tantalum target was deposited an adhesion layer of tantalum oxide having a thickness of about 5 nanometers. The finished sample showed a slight increase of light transmission in comparison with the reference sample. Similarly the adhesion values ​​measured using the pummel test showed that the collage was particularly strong since pummel value of 8 was still observed after irradiation of 400 hours.