GB2045681A

GB2045681A - Manufacture of glass laminates

Info

Publication number: GB2045681A
Application number: GB8003718A
Authority: GB
Original assignee: Saint Gobain Vitrage SA
Current assignee: Saint Gobain Vitrage SA
Priority date: 1979-02-05
Filing date: 1980-02-04
Publication date: 1980-11-05
Also published as: FR2447807A1; FI65769C; ES488266A1; FI65769B; IT1129991B; FR2447807B1; GB2045681B; BE881531A; DE3001987C2; FI800336A; DE3001987A1; IT8019665A0

Abstract

A glass laminate is made by forming a stack 1 of glass sheets and an intermediate thermoplastics layer in which any intermediate spaces are isolated from the surrounding atmosphere by U-shaped sealing member 2 and member 6 which are connected to a degassing duct 9, the stack is put in an autoclave 8 without degassing and with the duct opening to the atmosphere outise and autoclave, the pressure in the autoclave is raised to expel the air 3 from the intermediate spaces at a temperature less than the softening temperature of the plastics material and the pressure and temperature are then regulated to values allowing adhesion. <IMAGE>

Description

SPECIFICATION Manufacture of glass laminates The invention relates to manufacture of glass laminates in which the different glass sheets are assembled together by means of one or more intermediate layers of thermoplastics material. Using the method of the invention, after having formed a stack of sheets in which the intermediate spaces are isolated from the external atmosphere and connected to a duct for degassing, the assembly thus formed may be placed in an autoclave without a previous degassing operation, the duct may be joined to a conduit opening to the exterior before closing the autoclave and the sheets of the stack may be joined together by the action of heat and pressure.

Laminated panes are commonly made by a method in two stages during which, after the stack of sheets has been formed, air is re moved from the spaces between the different sheets and a certain preliminary adhesion is achieved.

The first stage of this method may be carried out by introduction of the stack of sheets at a temperature from 80 to 1 00 C, between pressing rollers made of rubber. It is also possible to subject the stack to vacuum with, as the case requires, an increase in temperature. In this case, it is known to carry out initial degassing inside the autoclave itself, placing the stack without pre-assembly there and subjecting the autoclave to vacuum before application of pressure. This method, known under the name of the "vacuum process", is described for example in French Patent Publication 1 095 476.As it is necessary first of all to put under vacuum the whole of the autoclave, the operation requires a relatively long time and a consumption of energy which is not negligible For this reason it is preferred to carry out subjection to vacuum by means of a pump for aspirating air from between the different sheets of the stack inside a separate reservoir, in a bag of rubber, or by means of an elastic profile member having a U section provided with a degassing duct and placed around the edges of the stack.During the second stage, the stack of sheets which has already been subjected to initial assembly is placed in an autoclave where it is subjected to a temperature which causes softening of the thermoplastics intermediate layers and which is of the order of 1 40 C if there is used polyvinylbutyral, whereupon the pressure is raised to a value of the order of 7 to 14 bars to obtain final adhesion.

It is also known to subject the intermediate spaces to vacuum inside the autoclave during a part, at least, of the second stage, by means of an aspiration duct connecting the intermediate spaces to a vacuum pump situated out side the autoclave to continue degassing of the pre-assembled stack or to achieve sealing of the edges; the autoclave is put under pressure directly or is itself subjected initially to a vacuum which is possibly greater. Such variations of this method are described in French Patent Publication 1 159 216 and 2 231 631.

Finally, there is also known from United States Patent 3 074 466 an analogous method using a single stage, according to which the stack of sheets surrounded by an elastic profile member is directly subjected to vacuum inside the autoclave from the exterior and and without initial degassing, even though the stack is subjected to heat under pressure.

Thus all these methods require the use of a vacuum pump which represents a significant investment and consumes a certain amount of energy.

The invention has the object of providing a method having a single stage allowing opera tion in a time as short as possible with a minimum of expense in equipment and en ergy.

According to the invention there is provided a method of making a glass laminate in which sheets of glass are assembled together with one or more intermediate layers of thermo plastics material to form a stack, any interme diate spaces in the stack are isolated from the surrounding atmosphere and connected to a degassing duct, the stack is placed in a auto clave without previous degassing, with the duct in communication with the atmosphere outside the autoclave and the sheets and layers are adhered together by the action of heat under pressure; in a first stage the pres sure being elevated sufficiently for any air in the intermediate spaces to be expelled there from at a temperature less than the softening temperature of the thermoplastic material and in a second stage the pressure and tempera ture being regulated to sufficient values to cause adhesion.

It has been found that, when such a method is carried out and contrary to that which takes place in all the known methods, it is necessary to provide a supplementary aspi ration of occluded air or any other operation intended to obtain a preliminary adhesion. By increasing, inside the autoclave, the pressure for expelling the air which is in the intermedi ate spaces of the stack of sheets to the exterior atmosphere through a degassing duct providing between a flexible profile member and the edge of the sheets there is achieved without auxiliary steps, expulsion of the oc cluded air as is required to obtain adhesion without faults.The method according to the invention may be used with success for glass sheets of particularly large dimensions and for glass sheets which are curved in dies which are more or less complex for which there have been preferred up to now, instead of auto clave methods, complicated methods described for example in French Patent Publications 2034 169 and 2090 176.

In the case, which is common nowadays, where there are used intermediate layers formed of polyvinylbutyral, there may be employed with advantage a temperature less than 350"Kelvin and exterior pressures greater than 2 bars. The temperatures and pressures necessary and also their duration of application depend on the dimensions of the panes to be made: as the surface area of the latter is larger the greater is the resistance opposed to escape of the air and consequently the greater will be the excess pressure employed for removing this air.

The rugosity of the surface of the thermoplastics layer used plays a role; in fact the rugosity of all the thermoplastics layers which at present are readily available for manufacture of laminated panes is sufficient.

Preferably, the pressure necessary for final adhesion is exercised initially substantially at room temperature and the temperature is then raised.

In an advantageous arrangement the duct for degassing of each of several stacks of sheets, rendered airtight, is conducted separately outside the autoclave; thus when a plurality of stacks are treated at the same time, a possible fault in airtightness of one of the stacks will not have unfavourable repercussions on the others.

To close off in an airtight manner the intermediate space, it is possible to use a profile member of flexible material such as rubber of U section, of annular shape, arranged around the periphery of the stack.

However in numerous cases it is sufficient to deposit a part of such a profile member having a duct for degassing on one part only of the periphery of the stack, the remainder of the periphery being closed by means of an adhesive band which is airtight. It is thus possible to dispense with the use of costly rubber annuli adapted in each case to the shape of the pane and, for example, make in a simple manner panes of complicated shape arranging such a part of a profile member along one longitudinal edge of a stack of sheets and closing the other sides comprising the transverse edges by means of an adhesive band; the degassing duct of the U shaped profile member is preferably obturated in advance at each of its two ends.

Methods according to the invention will be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a stack of sheets handled according to one embodiment of the invention inside an autoclave under pressure; Figure 2 is a vertical section of the stack along line A-A of Fig. 1; Figure 3 is a pressure/temperature diagram relating to the method.

EXAMPLE 1 This example relates to manufacture of a laminated safety pane intended to serve as a windscreen for a car. This pane has a width of 280 cm and a height of 140 cm. It has a curved shape of which the middle part is substantially cylindrical with a radius of curvature of 1000 cm, and of which the edges have a radius of curvature of the order of 1 5 cm.

Two sheets of silicate glass previously curved together are placed one on the other with interposition of an intermediate layer of polyvinylbutryal of 0.75 mm thickness. The sheet of glass on the convex surface has a thickness of 3 mm, and that on the concave surface a thickness of 2.6 mm.

The edges of the stack thus formed are surrounded by an annulus of elastic material having a U-shaped section of which the lips are applied closely to the glass sheets; this annulus has an outlet suitable to be connected to a pipe.

The assembly thus prepared is mounted on a convenient support and placed in the autoclave.

Inside the autoclave, the outlet of the profile member of U shape is connected, by means of a reinforced pipe to a duct connected to an airtight connection and which passes through the wall of the autoclave to open into free air; it is thus connected to the exterior atmosphere. The autoclave is then closed and put under pressure; finally the heating is started.

The temperature should initially be lower than the temperature at which the superficial sharp parts of a thermoplastic sheet, between which the air may escape, disappear allowing the intermediate layer to adhere to the glass sheets and rendering airtight the edge of the stack causing air to escape with greater difficulty or even preventing escape altogether.

The pressure/temperature cycle has the following course: Time Pressure Temperature mn bars K 0 1 298 5 3 298 10 8 298 15 10.5 323 20 12 408 30 12 408 40 12 408 50 12 408 60 8 380 After 90 mn the autoclave is opened to free air, and the laminated pane, after leaving the autoclave, is ready for use.

EXAMPLE 2 The description of this example refers initially to Fig. 1.

There is formed a stack of sheets 1 analogous to that of Example 1, with the sheets having similar dimensions. Along one of the longitudinal edges of the stack of sheets is arranged a portion of airtight profile member 2 in the form of a U. This profile member has a duct for removal of air 3 closed at each end of the profile member to prevent the fluid for pressurizing the autoclave penetrating into the member and, in its middle, an outlet for degassing 4 connected to a pipe 5. Outside the airtight profile member 2 an adhesive band 6 is mounted on the edge of the stack of sheets to close in an airtight manner the space separating the two glass sheets. The assembly thus prepared is placed on a stand 7 inside an autoclave 8, having a duct 9 which opens to free air outside and, inside, is connected to an airtight connection 10.Once the stack of sheets has been put in the autoclave, this connection 10 is connected to a complementary stem with which the free end of the pipe 5 is provided, then the autoclave is crossed hermetically and there is carried out a cycle of treatment corresponding to the pressure/temperature diagram shown in Fig. 3.

This treatment cycle comprises the following stages: -at the instant TO and at introduction of compressed air, the autoclave is rapidly brought to elevated pressure whereas the temperature remains of the order of ambient temperature; -at instant T1, that is to say at the end of 1 2 mn, the pressure is raised to a value of 10 bars; there is then started the heating inside the autoclave. At the end of several minutes, at an instant T2, the temperature has reached 408"K, whereas the pressure has increased to 1 2 bars. The autoclave is maintained under this pressure and at this temperature for about 45 mn, that is to say up to instant T3; -at instant T3, the heating is stopped and the pressurization by compressed air is interrupted, and cooling water is passed through a cooling circuit. Because of the reduction in temperature and faults in airtightness of the system, the pressure is reduced slowly; -at instant T4, the autoclave is opened, the pressure falls rapidly to 1 bar and the temperature is decreased. The finished laminated pane is then extracted from the autoclave.

Claims

1. A method of making a glass laminate in which sheets of glas are assembled together with one or more intermediate layers of thermoplastics material to form a stack, any intermediate spaces in the stack are isolated from the surrounding atmosphere and connected to a degassing duct, the stack is placed in an autoclave without previous degassing, with the duct in communication with the atmosphere outside the autoclave and the sheets and layers are adhered together by the action of heat under pressure; in a first stage the pressure being elevated sufficiently fo any air in the intermediate spaces to be expelled therefrom at a temperature less than the softening temperature of the thermoplastics material and in a second stage the pressure and temperature being regulated to sufficient values to cause adhesion.

2. A method according to claim 1, in which the thermoplastics material comprises polyvinylbutyral, and the pressure is raised above 2 bars and the temperature is less than 350"K in the first stage.

3. A method according to claim 2, in which the pressure in the autoclave is first raised to 10 bars in 1 2 minutes without heating, then the temperature is raised to the value required for adhesion, while the pressure is increased to a value of about 1 2 bars and the temperature and pressure are held at said values for from 30 to 60 minutes.

4. A method according to any one of claims 1 to 3, in which a plurality of stacks is treated simultaneously in the same autoclave and the intermediate spaces therein are connected to the atmosphere separately.

5. A method according to any one of claims 1 to 4, in which the intermdiate spaces are isolated from the surrounding atmosphere by means of a flexible annulus of U-shaped section provided with a degassing duct.

6. A method according to any one of claims 1 to 4, in which the intermediate spaces are isolated from the surrounding atmosphere by means of a flexible profile member of U-shaped section provided with a degassing duct and mounted on a part of the periphery of the stack, whereas the rest of this periphery is closed by means of an airtight adhesive strip.

7. A method according to claim 6, in which the profile member has a degassing duct obturated at two ends.

8. A method according to claim 6 or 7, in which the adhesive strip used to close the edges is left in place after adhesion to form a protective strip on the edges of the laminate.

9. A method of making a glass laminate, substantially as hereinbefore described with reference to the accompanying drawings.