GB2236277A - Producing laminated sheet glass - Google Patents

Abstract

A process for producing laminated sheet glass and in which a suitable interlayer disposed between two sheets of glass material is fed through one or more sets of pinch rollers and heated, as it moves, to cause the interlayer to bond to each sheet; characterised by the features: (a) that both sheets and the interlayer are initially unbonded to one another and are heated and rolled simultaneously throughout the process; and (b) that the interlayer is heated at least to and preferably above its plastic temperature.

Description

BONDING LAMINATIONS Field of the Invention The invention relates to a process and apparatus for laminating sheets of glass.

Laminated glass is presently made by pressing together the sheets which are to form the laminated structure with a bonding plastics interlayer between them. The known process involves heating the component sheets under pressure in an autoclave at a raised temperature. The sheets are subjected to this temperature and pressure for several hours and then allowed to cool undisturbed for a further considerable time.

As a practical matter, the use of an autoclave restricts this technique to a batch process. The continuous raising of temperature and pressure and subsequent release to atmosphere at the end of each cycle is wasteful in energy. An object of the present invention is to provide a glass laminating process which is continuous and requires less energy to laminate a given area and thickness of glass than known processes, especially the ones involving a final-stage autoclaving.

Review of Art known to the Applicant There is extensive prior art dealing with glass laminated processes of the kind in question. Amongst those prior documents personally known to the applicant at this stage are the following: 1. GB A 2 198 087 (STAINED GLASS SYSTEMS) Specifies "heating up to 100CC" (but not beyond it). Also specifies "gentle heating and rolling" with no figures at all given for the rolling pressure. Is an essentially low temperature and low-pressure sheet-rolling process".

2. GB A 2 058 662 (BFG) Shows again that the basic concept of rolling and heating two panes of glass either side of a PVB interlayer to form a laminate is known. But this isn't a laminating-only process; it specifies the need for a final-stage autoclaving. And there are no temperature or pressure ranges given in the entire specification.

3. GB 1 463 452 (UBE) Shows chemically how to make polymers which - amongst other uses - could clearly be used as the interlayer in a glass-laminating process. But goes no way towards teaching under what conditions of temperature and pressure should we attempt to use such polymers for making glass laminates. There's nothing here to do with glass-making.

The Figure 3 example is notable (a) in that it concerns laminating metal plates - irrelevant in that the stated temperatures, etc, can't be assumed to apply to glass - and (b) that it's not a "one-shot" laminating process; first the polymer is heat-laminated to one of the plates and then the other is pressed against it.

4. GB 1 461 236 (UBE) Same for this.

5. GB 1 312 136 (THOMAS BENNETT) Is not a laminating-only process; this ends with an autoclaving step "occupying five hours" and hence is anything but a continuousproduction system.

6. US 3 647 592 (MALLORY & CO) Shows, again, a method of bonding a (specifically) polyester film to a (i.e. single) substrate; not sandwich-laminating a glass sheet. Glass is said to be one suitable substrate but there's no specific example given; and no suggestion of simultaneous-sandwich-laminating. Vacuumpreheating of the polyester is said to be essential (see claim l).

Electrifying (claim 2) highly advantageous. Pressures of "about 2 psi" are used to press the film to the sheet.

Summary of the Invention It is clearly known from the prior art reviewed above to produce a bonded composite laminate by disposing a suitable interlayer between two sheets of material and rolling and heating these components to cause them to bond to one another. But what is not known is such a process in which the interlayer and two sheets of glass are initially unbonded to one another and are heated and rolled simultaneously throughout the process with the interlayer being heated at least to and preferably above its plastic temperature.

If the process is characterised by the just-recited features then the sheets and the interlayer will bond sufficiently for any further heat treatment - such as autoclaving - to be unnecessary; thereby turning a multi-stage batch-production process into a single-stage continuousproduction one as well as achieving considerable energy savings and optimising the efficiency of the whole process.

Preferably the interlayer is heated to between 100 C and 180 C as temperatures falling within this range have been found, with appropriate rolling pressures, to optimise the balancing of time, energy and adequacy of final bond. The final bond of course occurs as the hot laminate emerges from the end-stage of the process and cools.

Preferably also the necessary heating means are subdivided into separately operable units arranged transversely with respect to the direction of movement of the laminate. This allows the temperature across the sheets to be substantially evened out and otherwise controlled efficiently.

Where the invention is embodied in a pilot plant, for example a manually-operated plant, to prove the basic operating principle, then part of the set-up procedure for the plant apparatus may involve sending a sheet of heat-conductive material between the rollers and the heating means before the laminate is passed through. The sheet serves to even out the temperature distribution within the apparatus.

Successive sheets of glass with their respective interlayers then follow one another through the apparatus, almost touching each other, in the normal fully-automated production plant. But if for any reason a significant delay is experienced, the heat-conductive sheet can be reintroduced.

Description of the Preferred Embodiment The invention can be put into practice in several ways. In its developed version, it envisages fully automated and controlled operation. But to illustrate the principles, a manually-controlled pilot plant apparatus will now be described with reference to the accompanying drawings.

Brief Description of the Drawings.

Figure 1 is a side view of laminating apparatus in accordance with the invention; Figure 2 is a end view of the apparatus of Figure 1; Figure 3 is a plan view of the apparatus of Figure 1; Figure 4 is a schematic diagram of a hydraulic system used to urge compressing rollers together; and Figure 5 is a schematic representation of the configuration of heating elements in the apparatus of Figure 1.

Description of the Preferred Embodiment Referring to Figures 1 to 3 of the drawings, laminating apparatus for bonding a laminate 11 of sheets of glass and an interlayer of hot melt adhesive comprises a bed 10 on which are mounted a set of four adjustable lower pinch rollers 12. Generally aligned with a plane defined by the top of the lower pinch rollers 12 is a set of conveyor rollers 14. An upper pinch roller 16 is adjustably mounted above each lower pinch roller 12.

Each of the rollers 12 and 16 comprises a steel inner body covered by a 3 mm layer of silicone rubber, giving an overall diameter of 200 mm. The rollers are spaced with 500 mm between centres.

Each upper roller 16 is journalled on each side in a journal block 18 having slots which are vertically movable over guides 19 in a bearing housing plate 20.

A hydraulic piston and cylinder device 22 is mounted on each side of the bed between separate pairs of upper rollers 16. The cylinder end of the device 22 is removably pivotably held with respect to the bed by means of a pin 26 projecting through a hole in a mounting plate 24 which is itself fixed to the bed.

The piston end of the device 22 is removably pivotably attached to a crossbar 27 by means of another pin 26 passing through a hole in the bar. The position of securement of the piston- and ends of the device 22 to both the bed and the rocking crossbar can be shifted by relocating the pins in any of the series of further respectively adjacent holes.

The crossbar 27 bears on each of the journal bearing blocks 18 through a connecting rod 28. The rod 28 rides in a yoke 30 above the bearing. The force exerted by the device 22 can be controlled by limiting the extent of travel of the rod 28 by means of an adjustable nut 32 threadedly received on each rod 28 which abuts the top of the yoke 30.

In between the rollers 12 and 16 are disposed banks of infrared heaters 34. The heaters are separately controlled by thyristor banks in patterns as illustrated in Figure 5. The commonly lettered heating elements are connected to a common thyristor controller. -It is found that ceramic elements sold by the company Pearlco of Units 1-4, Derwent Yard, Derwent Road, Ealing, London, W54 TW as "FSR Elements" provide adequate control of the heat.

It has also been found that other forms of heating can be used, e.g. common electrical bar elements can be used in place of the more expensive ceramic elements although with less precise control. As a compromise an assortment of both types of heater is preferable in which the ceramic elements are used in the middle of each bank and the electric bar elements used outside of these.

The wattage of each row of heaters, as indicated by the broken lines in Figure 5, is 375, 325, 250, 200, 250, 325 and 375 watts from one end of the bank of heaters to the other. It is possible to use banks of heaters switched on and off using on/off control, but the degree of control obtained by the above arrangement is preferable.

The rollers 12 and 16 are driven by a three-phase electric motor 35 and a triple reduction gearbox 36 having a 12.5:1 ratio controllable to rotate the rollers via gear wheels 38 at between 1 and 12 rev/min.

Clearly, the thickness of the composite.of materials making up the laminate will determine the speed of the motor for a given case along with the power of the heating elements.

The banks of heaters 34 are mounted between the rollers 12 and 16 within reflective aluminium foil lined insulated compartments 40 to enhance their efficiency.

It may also be preferable to install a vent flap in the top of each compartment in order to derive further control of the heat at the glass and to prevent the rollers 12 and 16 from overheating by providing a means of ventilation for them. The flaps would also prove useful in hastening cooling of the apparatus when no glass is present. The bases of the longitudinally spaced walls 42 of the compartments are flared outwardly at the lower ends and beneath the upper rollers 16 in order further to protect the upper roller surfaces. Similar flared skirts 43 are positioned adjacent the lower rollers to protect them from the heat from the heaters 34.

The spacing of the rollers 12 and 16 and the heaters 34 is a compromise between the need to pinch the glass as close together as possible along the laminating direction and to provide enough space for the heaters in between. If the rollers are too far spaced apart the glass constituents of the heated laminate tend to bow outwardly between pairs of pinch rollers and become detached from the hot melt adhesive interlayer.

At the outlet end of the apparatus the laminated glass is fed onto a receiving table 44.

Referring to Figure 4 each pair of piston and cylinder devices 22 on either end of the pairs of roller sets are charged by means of a hand pump P through an isolating valve 50. The pressure exerted on the device 22 is indicated by a gauge 52. The pressure is maintained by means of a charged accumulator 56 also connected in the line, which also absorbs displacement of the upper rollers as the glass passes between them.

The hot melt adhesive used is a plastics material known as polyvinylbutyral (PVB). In place of this could be used ultra-violet stabilised styrene-butadiene block copolymer (K-resin), polycarbonate or ethylene-vinyl acetate copolymer (EVA). These materials require differing temperatures and pass rates according to their characteristics. The polycarbonate and the EVA also tend to go cloudy if the layer is too thick and this needs to be taken into consideration when a thickness of laminate is being determined.

As an example of the use of the apparatus according to the invention, a laminate of two pieces of 3 mm thick glass and an inner hot melt adhesive layer of .38 mm PVB were laminated using the above apparatus.

Before proceeding with the actual laminating process a black anodised aluminium sheet is passed through the apparatus. It is found that the warmed up heaters tend to cause the heat inside the apparatus to accumulate at either end. By passing the aluminium sheet through, the localised heating is more evenly distributed before the glass enters the apparatus.

The rollers were set to a gap of 1 mm less than the total thickness of the laminate. The piston and cylinder devices applied a pressure of up to about 3,000 psi on each roller pair which is equivalent to a localised loading on the layers of glass of about 10 tonnes. The temperature of the bonding layer was raised to between 120 and 150 OC or even up to 1800C.

The resulting bonded laminate was clear when it emerged onto the receiving table where there were no impurities existing between the layers. It was noted that water or any other contaminates between the layers tended to impair the quality of the finished laminate. In order to avoid this it is preferable that the glass and the PVB are thoroughly cleaned and dried before the laminating begins. One method of achieving this is to use ultrasonic cleaning.

In an alternative form the rollers may be adjusted to have gradually closer gaps along the direction of travel of the glass. The rollers may indeed be grouped together in a bank with no heaters between them. In this case the heater is preferably before the roller banks. It may also, in some situations, be that a heater may be disposed on either side of the bank of rollers.

The apparatus according to the invention is both highly efficient in terms of the power consumed in a laminating run and by virtue of the fact that it is essentially a continuous process. The apparatus is also very flexible and can be easily adjusted to accommodate different glass or adhesive layers.

As previously stated, this illustrated apparatus is a manually controlled pilot plant. A continuous-scale production plant would be equipped with advanced measuring equipment for monitoring and controlling such variables as (a) temperature across the laminate at multiple points (b) pressure on each roller or combination of pinch/drive rollers (c) speed of the moving laminate through the machine.

The necessary sensors in such an automated plant would connect to a controller which monitors and adjusts the conditions in line with the equasion of temperature, time and pressure arrived at by experimentation and development of the specific apparatus built in any one production instance.

Other modifications would of course be made to the apparatus illustrated in final production mode. For example the vent flaps previously referred to would eventually together with the heaters and drives to each roller be microprocessor controlled. And the receiving table 44 may well comprise an equivalent part of a continuous system.

It will also be appreciated that the so-called hot melt adhesive layer is the "interlayer" of the invention in its broadest aspect.

Claims (6)

CLAIMS:

1. A process for producing laminated sheet glass and in which a suitable interlayer disposed between two sheets of glass material is fed through one or more sets of pinch rollers and heated, as it moves, to cause the interlayer to bond to each sheet; characterised by the features: (a) that both sheets and the interlayer are initially unbonded to one another and are heated and rolled simultaneously throughout the process; and (b) that the interlayer is heated at least to and preferably above its plastic temperature.

2. A process as claimed in Claim 1 wherein the interlayer is heated to between 100 C and 1800 C.

3. A process as claimed in Claim I or Claim 2, wherein the heating means are subdivided into separately operable units arranged transversely with respect to the direction of movement.

4. A process as claimed in any preceding Claims wherein a sheet of heat conductive material is passed between the rollers and heating means before the laminate.

5. A process substantially as described herein, with reference to, and as illustrated in, the accompanying drawings.

6. Apparatus substantially as described herein, with reference to and as illustrated in the accompanying drawings.