Manufacture of insulated glass units

Abstract: An insulated glass unit (20) comprises two sheets of glass separated by spacers, a thermosetting resin seal­ ant such as a polysulphide or polyurethane sealant or a hot melt butyl sealant being applied around the edges of the unit to seal the sheets together. Curing or melt-bonding of the sealant is accelerated by the application of micro­ wave energy, suitably by passing the unit through a tunnel (26) with microwave generators (30) on each side thereof. The unit passes through the tunnel on a conveyor (28), held upright by pinch chains (32). The conveyor and pinch chains are made of a nonpolar material such as polypropyl­ ene.

Description: This invention relates to a method for the rapid production of insulated glass units, and in particular to the accelerated heat bonding or curing of the edge sealants of such units. In a conventional insulated glass unit, two sheets of glass are placed parallel to one another with a small gap therebetween, this gap being maintained by longitudinal spacers between the sheets positioned just inside the peripheral edges of the sheets. The spacers generally contain a desiccant which is in communication with the gap between the glass sheets to absorb residual moisture. liquid sealant such as a polysulphide, polyurethane or silicone sealant is then applied around the outside of the spacer between the peripheral edges of the sheets to seal the unit. These sealants are typically two-component systems, the base and the curing agent being mixed just prior to application to the glass. More recently, integral sealing strips have been developed which comprise for example an extrusion of "hot melt butyl" which may incorporate a desiccant and optionally also a spacer, suitably in the form of an aluminium strip. Such strips can be supplied in rolls, stored in airtight containers. In the manufacture of such units the sealant may require a long cure time, typically 2 to 4 hours, before the unit can be passed on to the next manufacturing stage. This creates particular problems in a continuous production line process since units have to be removed from the production line and stood for several hours. There arises the further possibility with liquid sealants that these may tend to flow during this cure period, particularly since the insulated glass (IG) units are generally in a vertical position during curing. Also, if a sealant system with a fast cure (and hence a short pot life) is used difficulties will arise if there is any delay in the IG unit production line. One way of overcoming this difficulty has been to use one part hot melt sealant systems, such as the hot melt butyl strips discussed above, instead of the conventional two part systems which cure at room temperature. Hot melt systems however require high temperature and pressure to effect adhesion. There is therefore a need for a method of putting energy into the chemically curing sealant to accelerate the cure. Straightforward heating in a hot air oven is however unsatisfactory since this also results in heating of the air in the cavity between the glass sheets which therefore has to be vented. Such heating also increases the temperature of the whole unit, including for example plastics spacers and corner pieces, which can also cause problems. The use of direct infra-red radiation, disclosed for example in GB-A-2114859, also causes heating and expansion of the air in the cavity unless the heating is focussed precisely on the sealant. US-A-4110148 discloses a process in which the edge sealants of double-glazed units are cured by capacitative high-frequency heating in the kHz-MHz range, electrodes being placed in close proximity to the sealant. It is known from the prior art that microwave energy can be used to accelerate the curing of some polar resins. US-A-4011197 discloses the microwave curing of organosiloxane compositions and US-A-3936412 discloses the curing of thermosetting sealants such as polysulphides and polyurethanes using a high-frequency alternating electric field, the exemplified frequency of which is 27 MHz. The present invention consists in a method of manufacturing an insulated glass unit wherein two glass sheets are positioned adjacent one another and spaced apart by spacers of aluminium or of plastics material of low polarity to define an air gap between them and wherein an uncured sealant is applied between the edges of the sheets to form a sealed unit and subsequently cured or melt-bonded with the input of radiant energy, characterised in that the radiant energy is provided in the form of microwave energy in the frequency range from 900 to 5000 MHz. It has been found that, using selected materials and selected conditions, cure times of 2 to 4 hours can be reduced to as little as 1 to 2 minutes in this way. The invention has been found to be particularly applicable to polysulphide sealants, preferably cured with manganese dioxide. Good results are also obtained with epoxide-polysulphide sealants and polyurethane sealants, as well as one part hot melt sealants such as those based on butyl rubber or polyisobutylene. The curing of the silicone sealants tested has been found to be less affected by such radiation but the use of such sealants is nevertheless contemplated within the scope of the present invention. An important advantage of the method of the invention is that only the sealant is heated significantly by the microwave energy. The glass, the spacers and the air space are not heated, except where they come into direct contact with the heated sealant. The present inventors have now devised a system for applying microwave energy to insulated glass units as part of a continuous production line process which does not have to be interrupted to allow the sealant to cure. This system will be described in more detail hereinafter. The microwave energy used is in the frequency range from 900 to 5000 MHz, preferably 2000 to 3000 MHz and typically 2450 MHz. The total power input will preferably be within the range from 750 to 2000W. Standard microwave generators can be used, these typically having an output of some 750W. The microwave generators can be positioned on one or both sides of a tunnel through which the IG unit is passed, at selected heights to ensure that the whole unit is subjected to the radiation. Typically three 750W generators will be used, a total operating power of for example 1500W being tapped off from these. Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein FIG. 1 shows a sealed double glazed unit of the type to which the process of the present invention may be applied; FIG. 1a shows an enlarged detail of one corner of the unit; FIG. 2 is an enlarged cross section on the line II-II in Figure 1; FIG. 3 is a perspective view of one corner of a double glazing unit incorporating an alternative form of sealant supplied as an integral strip with a built-in spacer; and FIG. 4 is a schematic plan view of a tunnel used to apply microwave energy to an IG unit in accordance with the invention. Referring first to Figures 1 and 2, two glass sheets 10 and 11 are secured together in a parallel configuration with elongate spacers 12 between them. The spacers are positioned parallel to each of the peripheral edges of the sheets, a small distance in from the respective edge so as to leave space for a sealant, and joined together by corner keys 22. The spacers are filled with a desiccant 16, which is in communication with the gap 24 between the sheets through elongate slots 16 or a series of apertures so as to absorb moisture. The sheets 10, 11 are preliminarily bonded to the spacers by a butyl sealant 18 or the like to hold them in position during curing. The peripheral gap between the sheets outside the spacers is then filled with an uncured sealant material 21. The spacers may suitably be made from aluminium but may also be of plastics material of low polarity such as polycarbonate or polypropylene. Nylon has however been found unsuitable for this purpose since it tends to heat up too fast owing to its high polarity. Surprisingly, aluminium spacers heat up less fast and can be used in the process of the invention. Aluminium spacers should however be connected by metal corner keys (suitably also aluminium) to prevent arcing. Alternatively, a single length of aluminium- pacer can be bent to the desired shape. One advantage of plastics, for example polycarbonate, spacers over aluminium ones is that the plastics spacers allow the desiccant to absorb microwave energy and warm up, giving additional background heating, without overheating, to accelerate the cure. Figure 3 shows an alternative form of double glazing unit wherein two parallel glass sheets 40, 41 are sealed together by a one component extrude sealing strip 42 of hot melt butyl rubber or the like. The strip incorporates an aluminium spacer in the form of a strip which has an undulating shape to impart rigidity in the transverse direction. Such strips are obtainable from Tremco Inc of Cleveland, Ohio, USA, under the Registered Trade Mark SWIGGLE STRIP. The strip is positioned around the edges of one sheet, laid flat, and the other sheet is then laid on top. The unit thus formed is then subjected to microwave heating in accordance with the invention. Referring now to Figure 4, there is shown schematically a tunnel 26 through which an insulated glass unit 20 is passed on a polypropylene track 28 to be subjected to microwave energy. As shown in Figure 4, the IG unit passes through in a vertical position. In Figure 4, the microwave generators 30 are shown positioned on both sides of the tunnel. They could however be positioned on only one side, in any suitable configuration. The inner walls of the tunnel 26 are preferably of reflective material such as polished stainless steel, so as to distribute the microwave radiation throughout the tunnel. Sensors may be provided to detect the size of the unit to be treated before it enters the tunnel, so that the total output of microwave energy can be adjusted accordingly. For example, if a unit of small height is to be treated, the uppermost microwave generators might be switched off altogether. Means may also be provided for stirring the air within the tunnel so as to obtain a more uniform distribution of energy. A typical apparatus as shown in Figure 4 might be designed to accommodate IG units ranging in size from 300mm x 300mm to 2.5M x 1M. To hold the IG unit in its vertical position and, if necessary, to press the two sheets together to maintain adhesion, a pinch chain system 32 is provided. This comprises polypropylene chains on each side of the IG unit designed to exert an inward pressure on the unit. The pinch chains may suitably be made of polypropylene carried on end sprockets and supported along their length by a polypropylene structure (not shown). The conveying chain 28 which supports the unit is also suitably made of polypropylene. The use within the tunnel of components made from a low-polarity polymer such as polypropylene ensures that these components do not themselves absorb microwave energy. Microwave chokes 34 are provided at each end of the tunnel. IG units may be passed in series through the tunnel in a continuous process, each unit as it leaves the tunnel passing on to a second guide track where it is unloaded from the equipment to be passed on to the next production stage. It is envisaged that the present invention may be used with a wide variety of sealants including those based on liquid polysulphides such as LP32 manufactured by Morton International Inc, epoxy-modified liquid polysulphides, liquid polysulphide/epoxy adducts, polyurethane resins, one-part hot melt butyls and indeed all sealants designed to be susceptible to microwave heating. Such a design may include the addition of an amount of water or other polar materials to facilitate the absorption of microwave energy into the sealant to accelerate the cure. The residence time of the IG unit in the tunnel may be varied by varying the track speed and/or the power output. A typical residence time will be 60 to 120 seconds, at the end of which the sealant should be substantially cured. The following trials were carried out using IG units of 300mm x 300mm with Thermobar polycarbonate spacers containing Duosorb desiccant. The sealant used was Evode 2850, a polysulphide based sealant, applied by hand. The sealant was mixed with a spiral blade for 3 minutes prior to application. Trials 1 to 6 were carried out in a batch process, were the IG units were not rotated continuously. The microwave supply was 620W. The following results were obtained. TRIAL 1 Full power 1 min, Max sealant temperature 120°C, Min sealant temperature 30°C. Non-uniform cure, some bubbling visually apparent. TRIAL 2 310 watts for 90 secs. Sealant temperature 40-45°C sealant not cured. Further 90 secs. Sealant not cured. Further 90 secs. Sealant temperature 50°C. Good cure. Unit handleable. TRIAL 3 465 watts 30 secs. Unit rotated through 90° (not checked for cure) Further 30 secs. Sealant temperature variable, 40-70°C. Sealant not cured. Further 30 secs. Sealant temperature 55-70 °C. Good cure. Unit handleable. TRIAL 4 465 watts 45 secs. Unit rotated through 90° (not checked for cure). Further 45 secs. Sealant temperature 55-70 °C./Excellent cure. TRIAL 5 465 watts 1 minute. Unit rotated through 90° (not checked for cure). Further 1 minute sealant temperature 90°C. Some foaming on joint face otherwise excellent cure. TRIAL 6 This unit was made at the end of the sealant's work life (45 minutes after end of mixing). 465 watts 45 secs. Unit turned through 90°. Further 45 secs. Good cure, no bubbling. A power output of 465 watts was thus found to be suitable for such a small unit. The output can of course be increased as required to accommodate larger units. Trials 7-14 were conducted on units 510mm x 360mm on a conveyor, horizontal bed microwave tunnel. Fixed travel speed. This final test shows the desiccant to be a high energy absorber.

Claims: A method of manufacturing an insulated glass unit (20) wherein two glass sheets (10,11) are positioned adjacent one another and spaced apart by spacers of aluminium or of plastics material of low polarity to define an air gap (24) between them and wherein an uncured sealant (21) is applied between the edges of the sheets to form a sealed unit and subsequently cured or melt-bonded with the input of radiant energy, characterised in that the radiant energy is provided in the form of microwave energy in the frequency range from 900 to 5000 MHz. A method according to Claim 1 wherein a thermosetting liquid sealant (21) is applied around the outside of the spacers (12) separating the glass sheets (10,11). A method according to Claim 2 wherein the liquid sealant is a polysulphide, epoxide-polysulphide or polyurethane sealant. A method according to Claim 1 wherein the sealant is a hot melt sealant. A method according to Claim 4 wherein the hot melt sealant is fitted between the glass sheets (40,41) in the form of a preformed strip (42). A method according to Claim 5 wherein the sealant strip (42) is made from a hot melt butyl rubber or polyisobutylene sealant. A method according to Claim 5 or Claim 6 wherein a sealant strip (42) incorporating an integral spacer (44) is fitted between the glass sheets. A method according to any one of Claims 1 to 6 wherein the spacers (12) are made from aluminium and are connected by metal corner keys (22). A method according to any one of Claims 1 to 7 wherein the spacers are made from a single continuous length of aluminium (44) bent to the desired shape. A method according to any one of Claims 1 to 7 wherein the spacers are made from a polyolefin or polycarbonate resin. A method according to any preceding claim wherein the microwave energy used is in the frequency range from 2000 to 3000 MHz. A method according to any preceding claim wherein the microwave energy is applied at a total power input of 750 to 2000 W. A method according to any preceding claim wherein the microwave energy is applied by passing the insulated glass unit (20) through a tunnel (26) with one or more microwave generators (30) positioned on one or both sides thereof. A method according to Claim 13 wherein the insulated glass unit (20) is conveyed through the tunnel (26) on a conveyor of nonpolar plastics material, held upright by pinch chains also of nonpolar plastics material.

Inventors: LEE TIMOTHY CHARLES PHILIP, LOWE GEORGE BERNARD, LEE, TIMOTHY CHARLES PHILIP, LOWE, GEORGE BERNARD
Applicants: MORTON INT LTD, MORTON INTERNATIONAL LIMITED
Application year: 1990
Main classification: E06B3
IPC codes: B29C35, H05B6, E06B3, C03C27