DE3871939T2 - MULTIPLE GLAZING. - Google Patents

Description

This invention relates to insulating, sealed, multiple-layer units for building cladding incorporating insulating spacers therefor, and wherein the multiple layers are typically made of a transparent glazing material.

Insulating glass units consist of two or more parallel panes of glass spaced apart from one another, with the space between the panes sealed along the perimeter of the panes to enclose an air space between them. Spacer bars are arranged along the perimeter of the space between the two panes. These spacer bars are usually long, hollow, perforated metal sections, most often made of an aluminum alloy, either extruded or rolled from a flat strip material. The hollow interior of the spacer contains a desiccant which serves to absorb any residual moisture that may be present in the enclosed air and to soak up any additional moisture that may enter the sealed unit over time. The spacers or spacers are assembled into an overall rectangular frame using typical corner wedges.

Units are constructed with either a single or double seal. Single seal units combine structural sealing and air and moisture vapor barrier in a single seal. Sealants commonly used in single seal construction include either thermoplastic, such as butyl, or thermosetting, such as polysulphide and polyurethane. In general, thermosetting sealants are more permeable to moisture vapor than thermoplastic sealants.

In double seal units, there is an inner seal as well as the main outer seal, with the inner seal acting as an additional moisture vapor barrier. The inner seal in double seal units is typically a thermoplastic material, such as polyisobutylene, and a bead of the polyisobutylene is attached to the sides of the spacer adjacent to the glass panes. The spacer frame is then placed between the panes and heat and/or pressure is applied to ensure that the polyisobutylene is compressed and fully wetted onto the surface of the glass. For the second, outer seal, it is common to use a thermosetting sealing material, such as silicone or polysulphide, which is placed in the outward-facing peripheral channel between the two glass panes.

In sealed units manufactured in the conventional manner using corner wedges, approximately 50 percent of the moisture vapor entering the sealed unit enters through the corner joints. Similarly, in sealed units filled with low-conductive gas, approximately 50 percent of the gas loss from the sealed units occurs through the corner joints. To improve the durability of the sealed units, the corner joints can be eliminated and the metal spacer bar bent or formed by stretching it around the corners. To complete the bent-corner spacer frame, the two ends of the metal spacer can be welded or soldered together. With the advent of automated equipment, bent-corner spacer frames can be manufactured most efficiently.

With conventional sealed glazing units, there is the difficulty that, given the high conductivity of the aluminium spacer, a thermal bridge between the glazing layers and this can lead to fogging along the perimeter or the formation of ice under extreme weather conditions. The metal spacer also causes glass stresses, particularly in glass with a low emissive coating. On cold, sunny days the center of the inner glass heats up and expands but because the material is held in place by the cold glass of the perimeter, stress is created in the glass. Under extreme conditions this stress can be enough to break the glass. These problems associated with the use of a conductive metal spacer are now becoming even more acute with the introduction of high thermal performance glazing. Compared to conventional double glazing (R-2 center glazing), high thermal performance units range in performance from R-4 to R-12 (center glazing). This increased thermal performance is achieved through various combinations of low emissive coatings, low conductive gas filling and additional glazing layers.

For high thermal performance glazing, one possibility is to apply the low emissivity coating to a shrink-fit film that is installed inside two outer layers of glazing. The method for making this type of sealed glazing unit is described in U.S. Patent 4,335,166. A particular manufacturing problem is that to avoid wrinkling of the film at the corner following the heat shrink process, steel spacers are used rather than aluminum because the steel spacer has greater stiffness and rigidity.

Especially in buildings with a high risk of vandalism, plastic films can be used instead of glass in the manufacture of the sealed unit. The advantages of using plastic instead of glass are greater safety, lower maintenance costs and increased protection without the risk of glass breakage.

The main disadvantage of using plastic instead of glass is early failure of the sealed unit, caused primarily by two factors. One is increased moisture accumulation and desiccant degradation resulting from the relatively high permeability of the plastic glazing material. A second is premature seal failure due to increased expansion of the glazing layers due to the higher coefficient of expansion of the plastic glazing material. Another disadvantage is that, due to moisture accumulation within the sealed unit, high performance, low emissivity coatings cannot typically be incorporated into sealed plastic glazing units because the quality of these coatings degrades rapidly. In addition, due to the permeability of the glazing material, a low conductivity gas fill cannot be provided within the sealed glazing unit because the gas diffuses out of the unit over time.

For glazing that offers high security, laminated films of glass and plastic are used. However, because of the higher expansion coefficient of the plastic, the plastic films are typically sandwiched between two panes of glass to hold the plastic films evenly and help prevent delamination of the glazing layers.

Although most multi-glazed units incorporate conventional hollow metal spacers, there are other, more specialized types and designs of sealed units with metal spacers. Two special Special designs of sealed units are particularly highlighted.

A special type of sealed glazing unit used as structural spacer glazing includes a channel-like metal spacer used with a deformable sealant tape containing a desiccant. The two legs of the spacer are bonded to the glazing layers by means of a silicone structural sealant. The construction of structural spacer glazing units is described in detail in U.S. Patent 4,552,790.

An interesting application for structural spacer glazing is in flush glazed windows that can be opened. In this type of window construction there is no need for a separate window frame and the hardware for opening the window, the window seal and similar components are attached directly to the sealed unit. A key advantage of this type of construction for high thermal performance glazing is that there is greater energy efficiency without the supporting frame. Firstly, there is better solar utilization due to the increased glazing area. Secondly, heat losses are reduced due to the reduced perimeter frame area. A particular problem with using a metal spacer for flush glazed windows is that holes cannot be drilled into the metal spacer because the metal spacer acts as a moisture barrier and the integrity of the moisture vapor barrier must be maintained in order to maintain the integrity of the edge seal. Consequently, it is relatively difficult to attach the various window components, such as hinges and opening hardware, to the sealed unit.

A second special design of a sealed unit is made with a continuous strip product in which the spacer and the sealing element are combined in a single product. The metal spacer is a flat metal strip bent into a continuous zigzag profile and embedded within an elongated band of deformable sealant containing a desiccant. The product, described in U.S. Patent 4,431,691 to Greenlee, is sold commercially by Tremco Inc., Cleveland, Ohio under the name "Swiggle Strip" (TM).

As with conventional sealed units, the main problem with using metal spacers for these specialty structures is that the highly conductive metal spacer acts as a thermal bridge causing heat loss and condensation around the inner perimeter of the sealed unit. This difficulty with heat loss along the perimeter edge is now becoming more pronounced, again as with conventional units, with the introduction of high thermal performance glazing units.

To address this problem with heat loss along the peripheral edge, various attempts have been made over the past twenty years to use less conductive plastics instead of metals to make the spacer strip. However, these efforts to replace conventional thermoplastics have not proven successful, as plastics are generally unsuitable as a material for making spacer strips. The main disadvantages of conventional plastics include a high coefficient of thermal expansion, poor UV stability, high moisture, vapor and gas transmission, low rigidity or Stiffness, poor thermal stability with volatile outgassing and stress relaxation, etc.

To overcome these disadvantages associated with conventional thermoplastics, more complex spacer designs have been developed using reinforced engineering grade plastics. In one case, shown in U.S. Patent 4,479,988, an extruded polycarbonate filled with glass fiber is used. The advantage is that the coefficient of expansion of the glass fiber filled polycarbonate is somewhat reduced. However, the coefficient of expansion is still greater than glass.

Another approach, documented in US Patent 4,551,364 and US Patent 4,564,540, uses glass fiber pultrusion. The advantage is again that the expansion coefficient of pultruded glass fiber is reduced and in this case is almost the same as the thermal expansion coefficient of glass.

These efforts to develop reinforced plastic spacers have not proven to be commercially successful at present. There appear to be five main factors responsible for the lack of commercial success of reinforced plastic spacer strips.

One factor is that the cost of manufacturing reinforced plastic spacers is relatively high for both extruded and pultruded spacers. For the extruded spacer, the production and material costs are high because each spacer must be individually extruded from engineering grade glass fiber filled resins and because the glass fiber filling requires the extrusion dies to be replaced at regular intervals. For the pultruded spacers, the set-up costs for producing a specific profile are high. In addition, the walls of the pultruded profile are relatively thick and contain a high percentage of glass fiber content, so consequently the material costs are relatively high and again the molds have to be replaced at regular intervals.

A second factor is that the reinforced plastics remain relatively permeable even with the reinforcement in the form of the glass fiber fill. Therefore, there is a concern that over time moisture vapor can penetrate through the walls and corner joints of the plastic spacer frame into the sealed unit and that in the long term this transfer of moisture will lead to deterioration of the desiccant and eventual failure of the sealed unit. This problem is particularly significant when silicone is used as an external sealing material in the manufacture of the sealed unit. Similarly, with gas filled units there is a concern that the low conductive gas will penetrate the plastic spacer and that this will lead to reduced thermal performance over time.

A third factor is that reinforced plastic spacers can cause increased stress on the sealant material, and this increased stress can lead to premature failure of the sealed unit. In the extruded reinforced spacer, the increased stress on the sealant is due to the fact that the coefficient of expansion of the fiber-filled polycarbonate is higher than the coefficient of expansion of the glass. With regard to the pultruded spacer, some sealed unit manufacturers believe that there is increased sealant stress due to the extreme rigidity and stiffness of the thick-walled spacer profile.

A fourth factor is that reinforced plastic spacers can cause manufacturing difficulties. In the case of the extruded spacer, the thin cross-section with glass fiber fill means that the spacer cannot be easily heat welded together if desired. With regard to the pultruded spacer, the high percentage of glass fiber fill means that very high levels of dust are generated when the spacer is cut with a saw. The spacers are difficult to clean of the fine dust for clean assembly of sealed units.

A fifth factor is that the extruded polycarbonate spacer does not solve the problem of volatile outgassing at high temperatures and that sealed units made using the polycarbonate spacer currently have difficulty passing certain sealed unit durability testing requirements.

It has been found that by making a multi-glazed sealed unit with an insulating spacer made of oriented thermoplastic polymeric material, the problems existing in the prior art have been overcome. In particular, it has been found that some of the apparent disadvantages of using an oriented thermoplastic material for the manufacture of insulating spacers can be used to advantage in the design of the product.

The present invention accordingly provides a multi-layer sealed unit comprising at least two glazing layers which are in mutual spaced parallel to each other, and an insulating spacer made of a highly oriented thermoplastic polymeric material and disposed between them adjacent the periphery of the glazing layers. The required physical properties of the insulating spacer are substantially controlled by controlling the degree and directions of the oriented molecular structure of the thermoplastic material or materials from which it is formed. Typically, the orientation of the polymer comprising the insulating spacer is largely along the longitudinal axis of the spacer.

The present invention also provides an insulating spacer for multilayer sealed units formed from a highly oriented thermoplastic polymeric material. The thermal conductivity, coefficient of thermal expansion, and butt bending properties of the spacer, among other physical properties of the spacer, are controlled by controlling the degree and directions of orientation of the molecular structure of the material from which it is formed.

Various processes can be used to produce the oriented thermoplastic material, and most often these processes involve some form of drawing or stretching of the isotropic material. This process of drawing or stretching the thermoplastic material aligns or orientates the molecular structure of the isotropic polymer, and the result is a material with substantially modified properties. These modified properties are anisotropic. The properties of the material in the drawing direction are very different from the properties of the material perpendicular to the drawing direction. The material properties also differ clearly depending on the type of polymer and in particular on whether the polymer is crystalline or amorphous in its molecular structure. Overall, it is the more crystalline polymers that are most influenced by the orientation process of the polymer structure. In addition, the higher the stretch ratio, the greater the degree of modification of the physical properties of the oriented thermoplastic polymer.

As for insulating spacers, the modified and improved properties of the oriented thermoplastic material make it possible to make insulating spacers from conventional thermoplastics, usually without the need for additional reinforcement. The use of oriented thermoplastic material results in four main improvements.

One improvement is greater strength and stiffness in the stretch direction. The advantage of these improved structural properties is that the oriented thermoplastic spacer profile wall thickness can be thin without the need for glass fiber reinforcement, reducing the cost and weight of the spacer and also reducing the loss due to heat dissipation through the thin walled profiles. The increased stiffness of the insulating spacer profiles also speeds up the process of assembling the sealed unit as the spacer frame can be more easily laid down on the glass so that the sides of the frame are parallel to the edges of the glazing panes.

A second improvement is the increased resistance to deterioration caused by ultraviolet (UV) radiation. The advantage of the improved weather resistance is that for certain types of thermoplastics it is unnecessary to provide a separate UV blocker, and that the front face of the oriented plastic spacer does not dust or chip even if it is exposed to sunlight for a long time. The color fading of the plastic is also reduced.

A third improvement is increased high temperature resistance. One benefit of better temperature resistance is that the spacer is not deformed by the application of a hot sealing material during the manufacture of the sealed unit. On a related note, the improved thermal stability of the oriented thermoplastic helps prevent outgassing at elevated temperatures, which causes the sealed unit to fog up as volatile plastics condense on the internal cold surfaces of the glass. The improved thermal stability of the material also eliminates the problem of stress relaxation.

A fourth improvement is increased barrier properties. The benefit of a lower level of moisture vapor transmission is that certain types of oriented plastics have the necessary barrier properties to ensure long-term performance of the sealed unit without the need for a separate barrier coating. Similarly, the improved barrier properties of the oriented thermoplastic help to reduce the loss of low-conductive gas from the sealed unit.

The manufacturing process for the oriented spacer not only leads to the above-mentioned improved properties, but also to modified material properties that do not initially appear to be obviously advantageous or at all compatible with the requirements of an insulated spacer for sealed glazing units.

One such property is that the thermal conductivity parallel to the stretch direction is increased. The conductivity perpendicular to the stretch direction is, however, somewhat reduced. We have now found that if the orientation direction is ensured to be mostly on the long axis of the spacer, the lower conductivity perpendicular to the stretch direction can be taken advantage of, with the result that the heat loss via the edge seal is reduced.

A second property considered a disadvantage is negative thermal expansion along the stretching direction. To avoid stressing the sealing material in an insulated spacer, the thermal expansion coefficient of the polymeric material should be substantially equal to the positive expansion coefficient of the glass within the temperature range of -30ºC to +60ºC. Our research has shown that this negative expansion problem can be overcome and the expansion coefficient along the long axis can be fine-tuned to match the expansion coefficient of glass.

A third property that is considered a disadvantage is that the polymeric oriented material has butt bending properties in the stretch direction. The material can be dented by impact like metal. However, an insulated spacer can benefit from this "troublesome" property. An example of this is a spacer frame made by cold forming or bending the spacer strip around the corners or partially cutting or V-notching the spacer and then bending the spacer strip around the corners. The advantages of a spacer frame with a bent corner are more efficient assembly of the sealed unit, particularly by automated manufacturing methods and improved Durability of the sealed unit with reduced moisture vapor transmission and reduced loss of low conductive gas at the corners.

The process used to produce the oriented plastic sheets or profiles does not alter other key properties of the polymeric material that make thermoplastics more suitable than metals as a material for producing spacer strips. These improved properties include light weight, non-corrosive, weldable, easy handling, etc.

The suitability of the oriented thermoplastic spacer for welding is particularly advantageous for three reasons. First, when making a bent corner spacer frame, it is easy to weld the final joint joining the two ends of the spacer bar. Second, in gas-filled units, after the gas-filler nozzles are removed, it is easy to seal the holes. Third, when making sealed units with laminated glass and plastic glazing films or plastic glazing films or sheets, the thermoplastic spacer can be bonded to the plastic glazing material.

According to a feature of the present invention, the sealed unit may incorporate a sealing material which adheres and wetting to the spacer and to at least one or both of the glazing layers, depending on the design of the spacer. The sealed unit may also incorporate additional inner glazing layers which are spaced parallel to the outer glazing layers. The glazing layers may be glass sheets or thermoplastic films or shrink-fit plastic films. If thermoplastic glazing films or films are used, These thin films or foils can be directly bonded to the spacer made of oriented thermoplastic material.

Where the outer glazing layers consist of plastic films or laminated films of glass and plastic, the oriented thermoplastic spacer may be bonded to the outer glazing films around the perimeter and no sealant is required to create the sealed unit.

The use of the oriented plastic spacer, particularly in sealed plastic glazing units, results in significant performance improvements of the sealed unit, especially when the outer glazing films are also made of clear oriented thermoplastic sheet material.

First, the manufacture of the glazing unit is simplified because an external sealing material is not required. Second, the durability of the sealed plastic glazing unit is improved because of the better barrier properties of the oriented thermoplastic polymer. Third, heat loss through the edge seal is reduced compared to a solid sealant; the thin walls of the oriented thermoplastic spacer create a minimal thermal bridge. Fourth, the energy efficiency of the sealed plastic glazing unit can be significantly improved because low-emissive coatings and a low-conductive gas fill can be included because of the better barrier properties of the plastic glazing. In addition, because of the strength of the oriented plastic glazing, it is possible to manufacture sealed units with thick air spaces incorporating multiple layers of shrink-fit plastic films with low-emissive coatings. Compared to conventional Double glazing (R-2), the thermal performance of these multi-layer, sealed plastic glazing units with low conductive gas fill can exceed R-16. A particular advantage of using these high thermal performance sealed plastic glazing units for flush glazed windows that can be opened is that various window components, such as opening hardware, hinges and window seals, can be easily connected to the oriented thermoplastic glazing and spacer.

For sealed plastic glazing units, the outer plastic glazing sheets are typically made from a biaxially oriented thermoplastic material or from biaxially oriented thermoplastic material bonded to glass sheets. Unlike conventional laminated glass and plastic glazing, the biaxially oriented thermoplastic material does not need to be sandwiched between glass sheets because the elongation coefficient of the oriented thermoplastic material can be finely tuned to match the elongation coefficient of glass. The advantage is that the manufacture of the sealed unit is facilitated because the oriented plastic spacer can be bonded directly to the inward facing plastic layers of the laminated glazing sheets.

In manufacturing the spacer frame for the insulated glazing unit, the oriented thermoplastic spacer strips may be assembled in a conventional manner using corner wedges to form an overall rectangular shaped frame. Alternatively, the spacer frame may be formed by cold forming or bending the spacer strip around the corners or by partially cutting or V-notching the spacer strip and then bending the spacer strip around the corners. To complete the spacer frame with a curved corner, the two ends of the spacer bar can then be welded or sealed together.

Conventional hollow profile spacers made of oriented thermoplastic material can be manufactured in a variety of ways, including extruding the spacer into individual profiles, with the material being oriented as part of the production process, or alternatively by roll forming the spacer from flat strips of already oriented thermoplastic sheet material. The oriented thermoplastic material typically has increased butt bending properties only in the stretching direction. In the case of the spacer obtained by roll forming, in addition to orientation along the longitudinal axis of the spacer, there must also be some degree of orientation perpendicular to the longitudinal axis of the spacer so that the spacer profile can be formed by rolling and also bent. This biaxial orientation can be achieved in a variety of ways, including by biaxially orienting the film during manufacture or by creating a stack of two or more layers of oriented thermoplastic films such that the stretch direction of one film is perpendicular to the stretch direction of the other.

The biaxially oriented films can be manufactured by using a cross-roll stretching process in which the material is oriented in opposite diagonal directions to the longitudinal axis of the sheet. In this case and with this manufacturing process, the required material properties can be achieved on the longitudinal axis of the spacer, whereby the main orientation direction does not necessarily lie mostly in a direction longitudinal to the axis of the spacer.

Overall, when the sealed unit is manufactured, the hollow profile spacer contains a desiccant and the air-facing side of the spacer typically includes perforated holes or a slot so that the desiccant material can absorb moisture from the air within the sealed unit. If the profiles are roll formed, one option is to intermittently heat weld the edges of the plastic sheet together, creating a continuous but perforated seam on the air-facing side of the spacer.

The spacer can be made from various types of thermoplastic polymeric materials. One possibility, which involves no sealing material being used, or alternatively using a very permeable external sealing material such as silicone, is to make the spacer from a thermoplastic material which already has very good barrier properties and to further improve these properties by the orientation process. A preferred material is vinylidene chloride (Saran (TM)) and another advantage of using Saran (TM) in addition to its very good barrier properties is that all common types of sealants adhere strongly to it.

Depending on the type of thermoplastic material used for the spacer, the spacer may have its own moisture vapor film or coating or a separate UV barrier on the face. If the spacer is formed from flat strips cut from sheet material by roll forming, one or both surfaces of the sheet material are first laminated or coated with the required coatings or films. The hollow profile spacer is then manufactured in such a way that the coatings or thin foils are located on the correct surface of the spacer after roll forming of the hollow profile spacer.

For different specialized sealed glazing applications, different profile shapes of the oriented thermoplastic polymer spacer can be used. One example is where the spacer is used for structural spacer glazing. A second example is where the spacer is a continuous, zig-zag bent flat strip embedded within an elongated band of deformable sealant containing a desiccant.

Building panels used as part of the building envelope are not currently manufactured as multi-layer sealed units. However, with advances made in the development of high thermal performance sealed glazing units, there are now advantages in using the same edge sealing technology developed for glazing units to manufacture opaque insulating panels. The advantages of using sealed opaque panels for the building envelope include the ease with which the thermal performance of the building envelope can be upgraded in the future and the ease with which the air barrier built into the building envelope can be maintained and repaired. These panels can provide more insulation per unit thickness than conventional insulation materials currently used in the building envelope. The outer opaque layers used to make these high thermal performance sealed panels can be made from a variety of impermeable materials, including thin slices of stone or marble on a metal backing or sheets of biaxially oriented thermoplastic material.

The following is a description of certain embodiments of the present invention by way of example with reference to the accompanying drawings. In the drawings:

Figure 1 is a drawing of a spacer made of oriented thermoplastic material obtained by roll forming;

Figure 2 shows a detail of a double glazed unit with double seal in cross section incorporating a spacer made of oriented thermoplastic material;

Figure 3 shows a detail of a double glazed unit with a single seal in cross section incorporating a spacer made of oriented thermoplastic material ;

Figure 4 shows a detail of a triple-glazed unit in cross-section with an inner, flexible, shrink-fit film arranged in layers between two spacers made of oriented thermoplastic material;

Figure 5 shows plan views of details of three alternative corner designs of spacer frames made from oriented thermoplastic polymers;

Figure 6 is a cross-sectional detail of a triple glazed unit incorporating a shrink-fit film in which the oriented thermoplastic spacers are bonded directly to the glazing layers;

Figure 7 is a detail of a double glazed unit in cross-section for structural spacer glazing incorporating a channel-shaped spacer made of oriented thermoplastic material; and

Figure 8 shows a corner detail of a double glazed unit incorporating an edge seal of deformable sealing material with a spacer strip of oriented thermoplastic material.

Figure 1 shows a spacer 30A for sealed units having multiple layers used in applications such as windows. The insulating spacer, while of conventional cross-section, is made of oriented thermoplastic material in accordance with the invention rather than metal, conventional plastic or reinforced plastic.

There are essentially two known methods for producing oriented polymeric material. One method involves producing an oriented, elongated structure in the polymer melt or solution, followed by or accompanied by crystallization which may include the formation of a liquid crystal phase. A second method for producing an oriented polymeric material relies on solid-state deformation and concomitant orientation of the orientable thermoplastic polymers. Solid-state deformation methods include pultrusion, tensile stretching, hydrostatic extrusion, die extrusion, deep drawing and roll-press stretching. In general, the various methods involve stretching or elongation of the isotropic material in some way or another. As an example, the specific technique of deep drawing is described in GB Patent 2 060 469.

The present oriented thermoplastic spacer is typically made using solid-state forming processes. For solid-state forming processes, the extent of orientation is largely determined by the stretch ratio; although other factors such as temperature, pressure and the nature of the manufacturing process also play a role. The process of orienting the isotropic material promotes critical properties of the thermoplastic polymeric material and it is these modified properties that allow the insulating spacer to be manufactured from commodity or intermediate grade thermoplastic polymeric materials.

If an insulating spacer is to function satisfactorily within a sealed glazing unit, a number of demanding material requirements must be met. We have found that these demanding requirements can be met by controlling the degree and directions of orientation of the molecular structure of the thermoplastic material from which the spacer is made.

A necessary property that the insulating spacer 30A must have is strength and stiffness along the long axis of the spacer, as shown by arrow 34. Overall, the higher the stretch ratio, the greater the strength and stiffness of the material in the stretch direction, which should be parallel to the long axis of the spacer. However, compared to other uses of highly stretched, oriented thermoplastics, very high stretch ratios are not necessarily required to make an insulating spacer, since the necessary strength and stiffness must be balanced against the other requirements of an insulating spacer.

A second property that an insulating spacer must have is the dimensional stability in the longitudinal direction of the spacer, as shown by arrow 34. In particular, if the outer glazing layers are glass, the thermal expansion coefficient of the oriented glass spacer should be thermoplastic material must be essentially adapted to the positive expansion coefficient of glass between temperatures of -30º C and +60º C.

At high stretch ratios, most crystalline thermoplastics have a negative overall thermal expansion coefficient. However, this negative thermal expansion coefficient of the oriented thermoplastic material in the stretch direction can be fine-tuned to match the positive thermal expansion coefficient of glass. This can be done in three main ways.

First, the type of polymeric material used must be carefully selected, as the coefficient of thermal expansion differs significantly depending on the type of oriented thermoplastic material used. Materials such as high density polyethylene have a very high degree of negative thermal expansion, while materials such as polypropylene have a lower degree. Second, the degree of negative thermal expansion increases with the stretch values. At low stretch values, the degree of thermal expansion is positive, while at high values it becomes negative. By careful optimization, the coefficient of expansion can easily be made positive, again matching the coefficient of expansion of glass. Third, the coefficient of thermal expansion can also be increased by heat treating the oriented thermoplastic material at high temperatures.

A third necessary property of the insulating spacer is low permeability to moisture, vapor and gas. Research has shown that the permeability of oriented thermoplastics responds to the stretch ratio. In the case of polyethylene, for example, the permeability of the polymer decreases dramatically when the stretch ratio is increased from 5 to 10.

A fourth necessary property is low conductivity perpendicular to the long axis of the spacer (shown by arrow 33). The thermal conductivity of the oriented material perpendicular to the stretch direction decreases overall with increasing stretch ratio, although after a stretch ratio of about 5, increasing the stretch ratio typically does not result in further significant reductions in thermal conductivity.

Other required properties include heat stability and UV resistance, and it has been shown that these properties are also enhanced by increasing the stretch ratio.

If the spacer is used to manufacture spacer frames with curved corners, the spacer 30A must also have the property of being able to be stretch-formed or bent around the corners (see Figure 5).

By properly controlling the stretch ratio and manufacturing conditions, and these optimal ratios and conditions vary from material to material, a number of different types of thermoplastics can provide the necessary properties for an insulating spacer. These include polypropylene, high density polyethylene and polyethylene terephthalate.

Hollow profile insulating spacers 30A as shown in Figure 1 can be manufactured in a variety of ways, including by extruding the spacer into profile shape so that the material is oriented as part of the manufacturing process, or by roll forming the hollow profile spacer from flat strips cut from previously oriented sheet material. The specific embodiment shown in Figure 1 is for a roll formed spacer.

The hollow profile spacer 30A is roll formed from flat strips of oriented thermoplastic material using similar manufacturing processes as used to make roll formed metal spacers. As shown in Figure 1, after roll forming the hollow profile, the two edges of the flat strip of material are heat welded together to form an invisible seam 28 parallel to the longitudinal axis of the spacer as shown by arrow 34. The seam 28 is located on the back surface 31 of the spacer as shown in Figure 1, although the seam 28 may alternatively be located on one of the sides 27 of the spacer or on the end face 32 along the longitudinal axis of the spacer.

When installed within the sealed unit, the spacer 30A typically incorporates a desiccant contained within the hollow profile. The desiccant must be in moisture contact with the air space enclosed by the glazing layers. One way to achieve this with either the extruded or roll formed spacer is, as shown in Figure 1, to incorporate perforations 29 on the face 32 of the spacer 30A. A second way, particularly for roll formed spacers, is to incorporate a continuous slot along the face 32 of the spacer 30A. A third method, again particularly suitable for roll formed spacers, is to intermittently weld the edges of the oriented thermoplastic sheet together, creating a continuous but perforated seam. Compared to a continuous slot, the advantage of an intermittently welded slot is a stiffer profile which it makes it possible to reduce the wall thickness of the spacer.

If the spacer is roll formed from flat strips, the sheet material must have butt bending properties both parallel and perpendicular to the longitudinal axis of the spacer, as shown by arrows 34 and 33. To achieve butt bending properties in two directions, it is typically necessary that the thermoplastic material also be oriented in at least two directions. This arrangement can be achieved in a variety of ways.

One possibility is to make the strips from oriented thermoplastic films where the material is at least biaxially oriented. The biaxially oriented films can be made using some type of cross-roll stretching process in which the material is oriented in two opposite diagonal directions from the longitudinal axis of the spacer. It should be noted that by balancing the degree and directions of orientation of the sheet material obtained by the cross-roll manufacturing process, the necessary properties of the spacer in the direction of the longitudinal axis can still be achieved, although the main direction and extent of orientation may not be mostly on the longitudinal axis of the spacer, as shown by arrow 34.

A second possibility is to cut the strips from sheet material of an oriented thermoplastic material which is a laminate of at least two layers. One of the layers may be more oriented than the other and the layer with the higher degree of orientation is arranged so that the direction of stretching is parallel to the longitudinal axis of the spacer, as shown by arrow 34. The second sheet is arranged so that the stretching direction (shown by arrow 33) is perpendicular to the longitudinal axis of the spacer.

In roll forming the spacer from the layered sheet material, the first layer, where the orientation direction is along the axis, should become the outer surface on the side 27 of the spacer adjacent the glazing layers (see Figure 3), and the second layer should become the inner surface of the spacer. This arrangement is preferred because the reduced thermal conductivity layer on the outside of the spacer 30A helps prevent heat flow to the inner layer of increased thermal conductivity.

Although the process of orienting the thermoplastic material improves the overall barrier properties of the material, for certain applications where no external sealing material is used or where, as an alternative, a very permeable external sealing material such as silicone is used, there is a need to further improve the barrier properties of the spacer.

One way to improve the barrier properties is to make the spacer 30A from a thermoplastic material which already has very good barrier properties and to further improve these properties by the orientation process. A preferred material is polyvinylidene chloride (Saran (TM)) and in addition to its very good barrier properties, another advantage of using Saran (TM) is that all common types of sealing material adhere strongly to it. A second way to improve the barrier properties is to add a separate moisture, vapor and gas barrier film or coating to at least the back 31 and sides 27 of the spacer 30A.

Compared to an extruded profile, a particular advantage of a roll formed spacer 30A made from strips cut from sheets of oriented thermoplastics is that the sheets can be more easily laminated or coated with one or more layers of high barrier materials. These high performance barrier materials and coatings can include EVA, EVOH (Eval (TM)), polyvinylidene chloride (Saran (TM)) and metallized coatings on PET film.

In addition to the need to provide a separate barrier film or coating, it may also be necessary for certain types of plastics to provide a separate UV resistant film or coating on the face 32 of the spacer 30A.

Figure 2 shows a double seal assembly with a spacer 30B made of an oriented thermoplastic polymer. As with a conventional double seal assembly, beads of polyisobutylene sealant 36 are attached to the sides of the hollow profile spacer 30B. The spacer 30B is formed into a spacer frame, as will be explained in more detail below. The prefabricated spacer frame is positioned between the first glazing layer 37A and the second glazing layer 37B adjacent the perimeter of the glazing layers. The orientation of the polymeric material of the spacer 30B is typically mostly along the longitudinal axis of the spacer.

A sealing material 40A is inserted into the outwardly facing groove around the periphery of the glazing panes 37A and 37B. The sealing material 40A must adhere to the back surface 31 of the spacer 30B and with certain types of thermoplastics it may be necessary to Spacer 30B may be treated or prepared to ensure good adhesion. Spacer 30B contains desiccant 39 and typically has perforations 29 incorporated therein to allow air flow between desiccant 39 and the air or low conductivity gas 38 within the sealed unit.

Figure 3 shows a cross-section of a single gasket double glazed unit incorporating a hollow profile spacer 30A of oriented thermoplastic material. The outer sealing material 40B may be any sealant having good barrier properties, such as high melting point butyl, polysulphide or polyurethane. Therefore, in this construction, given the lower permeability of the outer sealing material 40B, there is typically not the same need or requirement for the spacer 30A to be made of an oriented plastic having excellent barrier properties or, alternatively, to be coated with a separate moisture, vapor and gas barrier film or coating.

Figure 4 shows a detail of a cross-section through a triple glazed sealed unit where two spacers 30C of oriented thermoplastic material support a shrink-fit plastic film 51 between two spaced apart parallel glazing sheets 37A and 37B. The shrink-fit plastic film 51 is typically polyethylene terephthalate (PET). The outer sealing material 40C is typically a polyurethane sealant. The sealed unit as a whole is manufactured using a known process, for example that outlined in U.S. Patent 4,335,166. The particular advantage of using spacers 30C of an oriented thermoplastic polymer for this application is is that the spacers can be as stiff and rigid as steel spacers used heretofore. A further advantage is that the film 51 can be heat bonded to the spacers 30C and this can simplify the assembly of multi-glazed units incorporating shrink-fit flexible films.

Figure 5 shows plan views of three alternative corner details of spacer frames. In Figure 5A, the two spacers 30A are connected in a conventional manner by corner wedges 42. In Figure 5B, the spacer 30A is cold worked or bent around the corners 43 at room or slightly elevated temperatures. In making the spacer frame from hollow sections of oriented thermoplastic material, similar equipment to that used for corner bending metal spacers can be used. The two ends of the rigid plastic spacer 30E can be welded together as a butt joint 45 to ensure a continuous moisture vapor and gas barrier around the perimeter of the sealed unit. In an alternative, as shown in Figure 5C, the spacer 50 can be partially cut out and then bent around the corners 44. The special corner detail shown in Figure 5C is for structural spacer glazing (see Figure 7).

Other alternative spacer frame corner details not shown in the drawings include: heat welding and sealing the spacers at the corners using a conventional miter joint and V-notching the spacer and then bending the spacer around the corner.

Figure 6 shows a detail of a cross-section through a triple glazed sealed unit where two spacers 30G made of oriented thermoplastic material are placed between two parallel, spaced apart glazing sheets 52A and 52B support a shrinkable film 51. The glazing sheets 52A and 52B may be biaxially oriented thermoplastic polymeric films or laminated films of glass and biaxially oriented thermoplastic polymeric material. When laminated films are used, the oriented thermoplastic material is on the side of the glazing facing the air spaces 38A and 38B. The hollow profile spacers 30G contain desiccant 39 and are bonded to the outer plastic films 52A and 52B as well as to the film 51 and each other.

Various methods can be used to directly bond the spacer to the plastic glazing sheets 52A and 52B, including magnetic heat sealing, adhesive bonding, ultrasonic sealing and solvent welding. No external sealing material is used and therefore the spacers must have a very low level of permeability to moisture, vapor and gas. As previously explained, this can be achieved by either making the spacers out of oriented thermoplastic material from materials such as vinylidene chloride which have good barrier properties or by incorporating a separate high performance barrier layer. Similarly, for long term durability of the sealed unit, the plastic glazing sheets 52A and 52B must have a very low degree of moisture, vapor and gas permeability and, as with spacer 30G, this can again be achieved by making the glazing sheet from an oriented thermoplastic material having very good barrier properties, such as polyvinylidene chloride, or by incorporating a separate high performance transparent barrier layer.

Since no external sealing material is used in the manufacture of the spacer frame, the corners must be hermetically sealed. This can be achieved by either manufacturing the spacer frame using the corner bending method as described in Figure 5B or by assembling the frame from separate pieces and hermetically welding the corners.

The biaxially oriented thermoplastic glazing films 52 can be made from a variety of thermoplastic materials. In addition to plastic glazing materials such as polycarbonates and acrylic resins that are commonly used, other materials such as polypropylene and polyethylene can also be used because the process of orienting the material improves optical clarity.

The sealed unit in Figure 6 incorporates a shrink-fit film 51, typically PET, which is also bonded to the spacers 30G. Although only a single film 51 is shown in Figure 6, multiple parallel layers of shrink-fit film may be incorporated into the sealed unit. Extremely high energy sealed units (R-18 center glazing) may be made by using low-emissivity coating glazing films or shrink-fit flexible films and filling the sealed unit with a low-conductive krypton gas fill that allows for reduced spacing between the glazing layers. With these thick airspace sealed plastic glazing units, there is no concern about breakage caused by pressure fluctuations within the sealed unit, as the outer glazing sheets are made of a substantially non-breakable, rigid, oriented thermoplastic polymer material.

When the sealed plastic unit is used for flush glazed opening windows, the window seals, window fittings and hinges can be connected directly to the plastic glazing and spacer. The unit is self-supporting and there is no need for a separate window frame. Consequently, the cost of producing a flush glazed opening window is reduced.

Although the glazing films 52A and 52B are typically translucent, the layers may be translucent or opaque. If the films are opaque, one option is to select laminated films consisting of biaxially oriented thermoplastic material bonded to thin films of stone or marble.

Various profile designs of the spacer made of an oriented thermoplastic polymer can be used for a wide variety of special designs of sealed glazing units. One special design is for structural spacer glazing.

Figure 7 shows a detail of a cross-section through an oriented thermoplastic spacer 50 for a structural spacer glazing unit where the spacer is U-shaped in profile, creating a recessed channel 56 around the perimeter of the sealed glazing unit. The channel 56 is partially covered with a butyl tape 52 containing a desiccant. The spacer is bonded to the glazing sheets 37A and 37B with a structural silicone sealant 53. In addition to the reduced heat loss along the perimeter, a particular advantage of using an oriented thermoplastic spacer for this application is that the spacer frame can be manufactured very efficiently. As shown in Figure As shown in Figure 5C, the oriented thermoplastic gutter spacer is partially cut through the rear legs of the U-gutter and bent at the corners. The two ends of the gutter spacer are then welded together at a butt joint, creating a rigid frame with a bent corner.

Figure 8 is a detailed drawing of a second specific design for the oriented thermoplastic spacer, which for this application is a spacer 55 incorporated within an edge sealing strip product 57. The continuous spacer 55 of corrugated configuration is embedded within an elongated strip of deformable sealing material containing a desiccant. The edge sealing strip product 57 is disposed around the periphery of the glazing layers 37A and 37B. The oriented thermoplastic material is used for the spacer particularly because of its butt bending properties along the longitudinal axis, which allow the oriented material to be very easily bent or folded to create the necessary zigzag profile. However, unlike the conventional spacer, heat loss through the edge seal in the direction perpendicular to the longitudinal axis of the spacer is reduced.

The drawings described here illustrate only a very small representative sample of some of the possible construction designs for multi-glazed, sealed units incorporating the oriented thermoplastic spacer strip.

Furthermore, for the various sealed unit designs illustrated here, in order to improve high thermal performance, it is recommended to fill the air spaces with a low-conductive gas filling, to provide a glazing surface in each separate compartment with a low-conductive gas filling, emitting high performance coating and, if necessary, to incorporate a further glazing layer or layers between the outer glazing layers to create additional air spaces. In order to avoid repetition in the description of the drawings, it has not been specifically stated in every case that the sealed units may incorporate these features. It should also be noted that in the foregoing the space enclosed by the spacer and the glazing layers has been referred to as an air space and that this in particular does not exclude the possibility that the space may be filled with an inert gas such as argon or that, in the alternative, no air may be enclosed and a partial vacuum maintained between the glazing layers. To obtain good thermal performance when using air or argon gas, the optimum distance between the glazing layers is about 14 mm. If a low conductive krypton gas is used, the optimum distance between the glazing layers is reduced to about 7 mm.

Claims (10)

1. Insulating spacer made of thermoplastic, polymeric material arranged between at least first and second glazing layers of a sealed multi-glazing unit, characterized in that the material of the spacer is highly oriented (anisotropic), wherein, among other physical properties, in particular the thermal conductivity, the thermal expansion coefficient, the flexural properties, the rigidity and strength, the UV resistance, the moisture and gas permeability are determined by controlling the extent and direction of the orientation of the molecular structure of the material. 2. A spacer according to claim 1, wherein the extent and directions of orientation of the molecular structure of the thermoplastic material are such that the thermal conductivity of the spacer perpendicular to its longitudinal axis is less than its thermal conductivity along its longitudinal axis. 3. Spacer according to claim 1, wherein the extent and directions of orientation of the molecular structure of the thermoplastic material are such that the thermal expansion coefficient in the direction of the longitudinal axis of the spacer substantially corresponds to the thermal expansion coefficient of the glazing layers of the sealed unit between at least temperatures of -30ºC and +60ºC. 4. A spacer according to claim 1, wherein the extent of orientation of the molecular structure of the material in the direction perpendicular to the longitudinal axis of the spacer is such that the proper roll forming and bending properties of the material are achieved. 5. A spacer according to claim 1, which is formed by rolling from oriented thermoplastic polymeric disc material which is oriented in at least two directions and highly oriented in at least one direction. 6. A spacer according to claim 1, wherein said multi-glazed sealed unit comprises at least one heat shrinkable plastic film between outer glazing layers, and wherein said spacer is characterized by a rigidity and strength comparable to conventional hollow steel spacers. 7. A spacer according to claim 1, wherein said glazing layers are oriented thermoplastic sheets and said spacer is bonded thereto. 8. Spacer according to claim 1, which is substantially U-shaped in cross section, thereby creating a receptacle for fastening means. 9. A spacer according to claim 1, wherein it is formed as a curled flat strip embedded in an elongated strip of deformable sealing material containing desiccant material. 10. Multi-layer sealed glazing unit with an insulating spacer made of thermoplastic material between two glazing layers, characterized in that the material of the spacer has a molecular structure which is highly oriented in the longitudinal direction of the spacer.