Field of the Invention

The present invention relates to laminated glass comprising a polyvinylchloride interlayer, to a polyvinylchloride film for use as an interlayer in laminated glass, and to methods for preparing the same.

Background of the Invention

Laminated glass has many applications as a construction material. It can for example be used to form windows, walls, doors, screens and splashbacks. It can also be used for the construction of articles such as coffee tables, and other small articles of furniture. Laminated safety glass is specified or desired in a number of applications as a result of its inherent safety characteristics compared to normal glass sheets. Laminated glass is commonly formed by joining two sheets of glass using a polyvinyl butyral (PVB) interlayer. The production process normally involves two steps. In the first step the interlayer is placed between two sheets of glass and the resulting sandwich type structure is heated as it passes through nip rollers that squeeze the glass sheets into contact with the softened interlayer. A further step involves the treatment of the laminate so formed in an autoclave to complete the bonding process.

A key function of an interlayer within a laminated glass structure is to prevent or at least minimise dispersion of dangerous glass fragments should the glass break. Desirable properties of such an interlayer include the following: sufficient shear and tear strength to prevent or at least minimise rupture of the interlayer by the broken glass; sufficient adhesion to the glass to prevent or at least minimise dispersion of the broken glass; acceptable thermal stability and acceptable weatherability.

In many applications it is desirable to colour the laminated glass, and in some applications render it translucent or opaque. The colouring can be for the purposes of decoration or can serve a functional purpose by partially or completely obscuring the view through the glass sheet. As used throughout this specification the term "colour" refers to either a solid colour or a substantially solid colour that is textured or patterned, for example to have a wood grain, marble onyx or other effect including effects obtained using interference pigments and pearl pigments.

Previous attempts to produce coloured laminated glass have involved painting or screen printing the finished product. These techniques do not provide a solid or completely uniform colour which makes the appearance unsatisfactory, especially in applications with backlighting. Other attempts to produce coloured laminated glass have involved introducing a coloured acetate film into the laminate usually between two sheets of interlayer. The coloured laminated glass produced in this way suffers from the disadvantage of lack of uniformity of colour. Furthermore, the acetate layer may deleteriously affect the integrity of bond strength between layers within the laminated glass.

Films made from plasticised PVB are considered to be particularly suited for use as an interlayer in laminated glass products due to their ability to strongly adhere with glass, their transparency and their sound physical and mechanical properties over a broad range of temperatures. However, there are several disadvantages to using plasticised PVB films as an interlayer. A major disadvantage is that such films are relatively expensive. PVB films are also hygroscopic and must be handled under controlled atmospheric conditions to prevent excessive moisture uptake. The use of PVB as an interlayer material therefore adds considerable expense to the final laminated glass product.

A further disadvantage of using PVB as an interlayer material is that the polymer itself is not particularly well suited to pigmentation or decoration.

Polyvinylchloride (PVC) has been considered as a potential replacement for PVB as an interlayer material. PVC is a commercial polymer that is readily available and relatively inexpensive. PVC can be easily calendered to a range of thicknesses, it can be plasticised to give a range of hardness values, it has suitable physical and mechanical properties for use as an interlayer and it can be pigmented or decorated to give a wide range of colours. In addition, PVC is not water sensitive and unlike PVB, does not require storage in a special controlled humidity environment. However, the use of PVC in laminated glass structures has been limited due to the polymer having practically no inherent ability to adhere to glass.

Attempts have been made to promote adhesion between glass and PVC within laminated glass structures. For instance, US 4,277,583 and US 6,180,246 disclose the use of organosilane compounds as adhesion promoters. Such compounds are typically coated on the surface of the PVC film or dispersed within the PVC film itself. Although the adhesion promoters do initiate a bond between the glass and the PVC, there are many practical problems associated with the effective use of such compounds. For example, additional manufacturing steps are often required in order to apply the technology. Furthermore, the process of achieving an appropriate bond between the PVC and the glass is subject to many complex variables such as surface energy of the PVC film, stability of the silane during lamination and the concentration of the silane available at the surface of the PVC film.

US 4,600,627 discloses a laminated glass structure wherein an ethylene vinylacetate (EVA) polymer is used to bond a PVC interlayer to the glass sheets. However, it has been reported that silane adhesion promoters are required to be used in conjunction with EVA in order to obtain adequate bond strength.

Accordingly, there remains an opportunity to design and develop a laminated glass that meets acceptable quality standards and which can be prepared in an effective and efficient manner using PVC as an interlayer material.

Summary of the Invention

In one aspect, the invention provides a laminated glass comprising two glass sheets, a polyvinyl chloride interlayer located between the two glass sheets, and an adhesive layer located between the interlayer and each of the two glass sheets, wherein at least one of the adhesive layers is formed from a material comprising a polyurethane, a polyester or a combination thereof, said polyurethane and polyester having a Tg of less than about 100°C.

In a further aspect, the invention provides a polyvinylchloride film for use as an interlayer in laminated glass, the film comprising a polyvinylchloride interlayer having first and second opposing sides and an adhesive layer formed from a material comprising a polyurethane, a polyester or a combination thereof provided on the first opposing side thereof, said polyurethane and polyester having a Tg of less than about 100°C.

In another aspect, the invention provides a method of preparing a laminated glass comprising a polyvinylchloride interlayer located between two sheets of glass, which method comprises heat bonding the interlayer to the glass sheets using an adhesive layer located between the interlayer and each glass sheet, wherein at least one of the adhesive layers is formed from a material comprising a polyurethane, a polyester or a combination thereof, and wherein the Tg of the polyurethane and polyester is selected such that said at least one of the adhesive layers develops initial green tack with, and promotes bonding of, the interlayer and the glass before the interlayer undergoes substantial reversion to a less oriented state.

In yet a further aspect, the invention provides a method of preparing a polyvinylchloride film comprising a polyvinylchloride interlayer having first and second opposing sides for use as an interlayer in laminated glass, the method comprising applying an adhesive layer formed from a material comprising a polyurethane, a polyester or a combination thereof to the first opposing side of the interlayer, said polyurethane and polyester having a Tg of less than about 1000C.

It has been found that an adhesive layer formed from a material comprising a polyurethane, a polyester, or a combination thereof, having a relatively low Tg can be used in an advantageously robust and simple manufacturing process to heat bond a PVC interlayer to glass sheets to form a laminated glass structure which has excellent performance characteristics.

As will be described in more detail below, PVC interlayers used to manufacture glass laminates in accordance with the invention often have a degree of in-built orientation that can cause undesirable shrinkage of the interlayer during the lamination process. Such shrinkage results from the interlayer undergoing reversion to a less orientated state upon being subjected to the elevated temperatures at which the lamination process is typically conducted. Shrinkage of the interlayer during the lamination process can cause the laminated glass product to have poor interfacial bond strength between the layers, promote undesirable air ingress between the layers, result in edge cracking of the glass sheets during lamination, and render the manufacture process uneconomic due to the need to trim non-laminated edges of the laminated glass product.

By selecting the Tg of the polyurethane and polyester adhesive materials such that the adhesive layer develops initial green tack with, and promotes bonding of, the interlayer and the glass before the interlayer undergoes substantial reversion to a less oriented state, the aforementioned disadvantages associated with interlayer shrinkage can be advantageously minimised, if not avoided all together.

Description of the Preferred Embodiments

The adhesive layer in accordance with the invention can bond an interlayer to another interlayer and an interlayer to glass sheets in a laminated glass. At least one of the adhesive layers in accordance with the invention is formed from a material comprising a polyurethane, a polyester or a combination thereof. Where only one of the adhesive layers is formed from a material comprising a polyurethane, a polyester or a combination thereof, other adhesive materials known to promote adhesion between glass -and PVC may be used to complete the bonding system in the laminated glass. However, it is preferred that each adhesive layer in accordance with the invention is formed from a material comprising a polyurethane, a polyester or a combination thereof. As the invention contemplates the use of a polyurethane, a polyester or a combination thereof as an adhesive material, it will of course be possible to use various arrangements of these materials to bond an interlayer between the glass sheets. For example, a polyurethane and a polyester may be used to respectively bond opposing sides of the interlayer in the laminated glass.

For the sake of clarity, reference hereinafter to an "adhesive layer" or an "adhesive material", unless stated otherwise, should be taken as a reference to an adhesive layer/material formed from a material comprising a polyurethane, a polyester or a combination thereof having a Tg of less than about 100°C.

As will be discussed in more detail below, during general handling of PVC interlayers for use in accordance with the invention, for example wind-up/out of interlayer rolls and/or coating of the adhesive layer on the interlayer, the interlayers are often subjected to tensile forces which can downgauge their thickness and in turn impart a degree of in-built orientation. The PVC interlayers may also have a degree of in-built orientation derived solely from the interlayer manufacturing process itself.

Those skilled in the art will appreciate that the reversion rate of an orientated polymer varies as a function of the temperature at which the polymer is exposed. In general, the rate of reversion becomes more pronounced with an increase in temperature.

During the manufacture of the glass laminates in accordance with the invention, the PVC interlayers can be subjected to oven temperatures of up to 130°C or higher. These temperatures have been found to raise the temperature of the interlayer sufficiently high to cause pronounced reversion of the interlayer during lamination resulting in undesirable shrinkage of the interlayer in the direction of the in-built orientation.

Such reversion of PVC interlayers can be suppressed to some extent by applying a compressive pressure to the outer glass sheets during lamination. However, pressure that can be practically applied to the glass sheets by nip rollers in a commercial laminating line during the initial stages of the lamination process is generally insufficient to prevent substantial reversion of the interlayer.

By selecting the adhesive layer such that it has a Tg of less than about 1000C, the layer can advantageously develop initial green tack with, and promote bonding of, the interlayer and the glass before the interlayer undergoes substantial reversion to a less oriented state.

By developing "initial green tack" is meant development of the primary or initial bond that occurs between the glass, adhesive layer and the interlayer during the lamination process. Primary bonding will generally be promoted by passing the layed-up laminate structure through and oven at elevated temperature under compressive pressure applied by a series of nip rollers. Such bonding is to be distinguished from the secondary or final bonding that occurs between the glass, adhesive layer and the interlayer. The secondary bonding process is generally promoted by autoclaving the primary bonded laminated structure under compressive pressure at elevated temperatures for a period of time, and generally provides the laminated glass with the required interfacial adhesion between the layers for it to safely function as a laminated glass product.

Without wishing to be limited by theory, it is believed that the bonding force provided by the initial green tack of the relatively low Tg adhesive layer, alone or in conjunction with any compressive pressure applied to the outer glass sheets, is sufficient to overcome substantial reversion of the interlayer during lamination.

By "substantial reversion" of the PVC interlayer is meant an amount of reversion that would result in the glass laminate having unacceptable commercial qualities. Generally, substantial reversion would result in a shrinkage of the interlayer in the direction of the in¬ built orientation of about 15 % during the lamination process. In other words, reversion which results in shrinkage of the interlayer in the direction of the in-built orientation of up to about 15% can be acceptable. Preferably reversion results in only up to about 10%, more preferably up to about 5%, most preferably up to about 3% shrinkage of the interlayer in the direction of the in-built orientation. Those skilled in the art will appreciate that the "Tg" of a polymer is a narrow range of temperature over which an amorphous polymer (or the amorphous regions in a partially crystalline polymer) changes from a relatively hard and brittle state to a relatively viscous or rubbery state. Although not the case with all polymers, in the case of the adhesive layers contemplated in the present invention, the Tg also corresponds well with the temperature above and below which the adhesive develops a tacky or non-tacky character, respectively. As used herein, the Tg of the adhesive material is that which is determined by Differential Scanning Calorimetry (DSC).

Preferably, the Tg of the adhesive layer is less than about 8O0C, more preferably less about 50°C, most preferably in the range of about 25°C to about 35°C.

Preferably, the adhesive layer is used to bond a single PVC interlayer directly to the glass sheets. In this case, the glass laminate may be viewed as a structure comprised of five layers, that is glass/adhesive layer/interlayer/adhesive layer/glass.

Alternatively, multiple interlayers may be used. For example a glass laminate may be formed using two interlayers resulting in a 7 layer structure, that is glass/adhesive layer/interlayer/adhesive layer/interlayer/adhesive layer/glass. In this case, the glass laminate can be designed to display a different colour from opposed faces by using different coloured interlayers.

Accordingly, the invention also provides a laminated glass comprising two glass sheets, at least two polyvinylchloride interlayers located between each of the two glass sheets, and an adhesive layer located between adjacent interlayers and also between the interlayers adjacent to each of the two glass sheets, wherein at least one of the adhesive layers is formed from a material comprising a polyurethane, a polyester or a combination thereof, said polyurethane and polyester having a Tg of less than about 100°C. The use of multiple interlayers can also extend to structures where glass layers are placed between the interlayers. For example, a 9 layer structure such as glass/adhesive layer/interlayer/adhesive layer/glass/adhesive layer/interlayer/adhesive layer/glass. Laminated glass structures of this type have the added advantage of exhibiting improved impact resistance.

Where the adhesive layer of the invention is formed from polyurethane, the polyurethane is preferably an aliphatic polyurethane, more preferably a thermoplastic aliphatic polyurethane. Where the adhesive layer of the invention is formed from a polyester, the polyester is preferably an aliphatic polyester, more preferably a thermoplastic aliphatic unsaturated polyester.

Preferably the adhesive layer is derived from a waterborne or water reducible emulsion. By "water reducible emulsion" it is meant that the emulsion is not entirely waterborne and may also contain organic solvents. A water reducible emulsion will nevertheless be capable of being diluted with water.

A particularly preferred adhesive layer formed from polyurethane or polyester for use in accordance with the invention is an aliphatic polyester-polyurethane.

For the sake of clarity, unless stated otherwise reference herein to a "polyester- polyurethane" is intended to be a reference to a subclass of both polyester and polyurethane.

The excellent performance characteristics of glass laminates provided by the invention may be attained using relatively thin layers of the adhesive material. Preferably, the bond between the respective layers has sufficient strength to transfer loads placed on the glass to the interlayer without delamination or ingress of air occurring.

Without wishing to be limited by theory, it is believed that the silanol (-Si-OH) rich surface of glass and the polar pendant chloride groups residing on the surface of interlayer from the PVC interact with the polyurethane and/or polyester to form a strong green tack and ultimate bond through hydrogen bonding. For this reason, hydroxy functionalised polyurethanes and polyesters are preferred.

The adhesive layers may be formed from a combination of polyurethane and polyester. By a "combination" is meant a mixture or a blend of both a polyurethane and a polyester. Where a combination of polyurethane and polyester is used in the methods of preparing the glass laminate or polyvinylchloride film in accordance with the invention, it will be important that the combined adhesive material has suitable properties to enable it to be applied in the manufacturing process. For example, if the polyurethane and polyester are initially in the form of separate waterborne or water reducible emulsions, a blend of these materials may be used in the manufacturing process provided the resultant blend maintains a stable emulsion.

Suitable emulsified polyesters include, but are not limited to, products sold by Solutia under the product name of Resydrol® having the required Tg. Some Resydrol® products contain an aliphatic unsaturated sulphonate-substituted oil free polyester. By "oil free polyester" is meant a polyester that has been manufactured without any hydrocarbon oil extenders. The sulphonate substituents of such polyesters are believed to further assist in the adhesive properties of the coating.

Suitable emulsified polyesters preferably have a solids content ranging from about 40 weight percent to about 44 weight percent, a dynamic viscosity (230C, 10s"1) ranging from about 500 mPas to about 3000 mPas, a pH ranging from about 3 to about 5, and a hydroxyl number of about 25 mg KOH/g solids.

The polyurethane is preferably an aliphatic polyurethane. Those skilled in the art will appreciate that such polyurethanes may be provided in the form of a polyether- polyurethane, a polycarbonate-polyurethane, an acrylic-modified polyurethane and a polyester-polyurethane. All such classes of polyurethane may be used in accordance with the invention. A particularly preferred class of polyurethane (and polyester) is an aliphatic polyester-polyurethane. A particularly preferred aliphatic polyester-polyurethane comprises a hexane diol adipate polyurethane. The polyester-polyurethane is also preferably provided in the form of a waterborne or water reducible emulsion.

Suitable emulsified polyester-polyurethanes include, but are not limited to, products sold by Stahl USA such as RU41-347X, and by Solutia under the product name of Daotan®, having the required Tg. Suitable emulsified polyester-polyurethanes have a viscosity from about 5 to about 250 cps and a solids content from about 30 weight % to about 45 weight %, more preferably about 39 weight %.

The polyester-polyurethane preferably has a tensile strength from about 1800 psi to about 2200 psi, more preferably about 2000 psi, an elongation from about 300% to 350 %, more preferably 325 %, a modulus at 100 % elongation from about 1100 psi to about 1300 psi, more preferably about 1200 psi, a modulus at 200 % elongation from about 1300 psi to about 1500 psi, more preferably about 1400 psi, and a modulus at 300 % elongation from about 1700 psi to about 1900 psi, more preferably about 1800 psi.

To assist application of the adhesive and/or processing of the polyvinylchloride film during or after manufacture, the adhesive material may contain one or more additives such as antiblocking agents, defoamers, surfactants, leveling agents and viscosity modifiers to assist in producing a coating that is substantially free of defects such as bubbles, craters and thin spots.

The adhesive material preferably comprises a wetting agent promoter ranging in an amount of between 1 % w/w to about 5 % w/w. More preferably, the wetting agent is present in amount of about 3 % w/w. A preferred wetting agent promoter includes Additol® VXW 6214 which is sold by Solutia.

The adhesive material may also comprise a silane coupling agent to further promote adhesion to the glass and/or the interlayer. Preferred silane coupling agents include epoxysilanes, mercaptosilanes, and amino silanes. Gamma glycidoxypropyl trimethoxysilane, aminoethylaminopropyl trimethoxysilane, styrylaminosilane and a product sold under the name of Silquest A-187 by Crompton Corporation USA are particularly preferred coupling agents. When a silane coupling agent is employed, it is preferable that it is prehydrolysed to form silanol monomers, silanol dimers, silanol oligomers or mixtures thereof. The prehydrolysed coupling agents are believed to be more effective at promoting adhesion.

When preparing the glass laminate, the adhesive material may be applied where necessary to effect bonding between the layer(s) within the laminate. For example, the adhesive material may be applied on one or both sides of the glass sheets and/or the interlay er(s). More preferably, the adhesive material is applied to both sides of the interlayer(s). Preferably, the adhesive material is applied as a substantially continuous coating on one or both sides of the glass sheets and/or the interlayer(s).

Dyes and/or pigments can be added to the adhesive material provided there is no adverse effect on the bond strength between the interlayer and the glass or between two or more interlayers. By adding dyes and/or pigments to the adhesive layer the glass laminate can advantageously be provided in a variety of colours. This technique for colouring the glass laminate provides an alternative to colouring the interlayer material itself. The adhesive material may be dyed or pigmented to provide solid (opaque) colours or novel pigments may be used to provide special effects. Examples of novel pigments can include so called "interference pigments" or "colour variable pigments" which provide a differing colour perception depending on the viewing angle.

Application of the adhesive material onto the glass sheets or interlayer is typically achieved by some form of coating means. Preferred coating means include spray, knife coating, blanket flexographic coating, rotogravure and reverse roll coating.

The invention provides for a polyvinylchloride film comprising a polyvinylchloride interlayer having first and second opposing sides and an adhesive layer provided on the first opposing side thereof. An adhesive layer may also be provided on the second opposing side of the interlayer which may be selected from other adhesives known to promote adhesion between glass and PVC within laminated glass structures. However, it is preferred that when an adhesive layer is provided on both sides of the interlayer, each adhesive layer is formed from the adhesive material defined herein.

The process of applying a liquid form of adhesive material has been found to be advantageously robust and simple. In this case, the adhesive material is typically applied to one surface of the interlayer, using coating means well known in the art, as part of continuous coating process. Once coated, the interlayer is transferred to a means for drying or curing the adhesive layer, the interlayer is then returned for coating on the reverse side and after this coat has been dried or cured, the resulting coated interlayer is typically coiled and stored ready for use in a subsequent lamination process.

Drying or curing of the adhesive layer during the coating process may be achieved by means well known in the art. Preferred drying or curing means include transferring the "wet" coated interlayer through an oven or past an application of hot air. During the drying or curing process, it is preferable that the interlayer undergoes a minimum degree of orientation or downgauging. To minimise orientation or downgauging, a balance needs to be obtained between the temperature that interlayer reaches during the process and the force applied to the interlayer by the transferring means during its transit through the process. Preferably, the drying or curing process should not cause more than about 10 % orientation of the interlayer, more preferably not more than about 5% orientation, most preferably not more than about 3% orientation.

Where an oven is used to dry or cure a solvent based adhesive layer, the temperature in the oven preferably ranges from about 30°C to about 7O0C, more preferably from about 400C to about 600C. Where an oven is used to dry or cure a water based adhesive layer, the temperature in the oven preferably ranges from about 500C to about 900C, more preferably from about 800C to about 900C. Preferably, the adhesive material is applied to the glass sheets and/or interlayer(s) at a thickness ranging from about 5 GMS (dry) to about 70 GMS (dry), more preferably from about 10 GMS (dry) to about 50 GMS (dry), most preferably about 10 GMS (dry).

After the adhesive material has been applied to at least one side of the interlayer, the so formed, coated self-adhering interlayer (ie the polyvinylchloride film in accordance with one aspect of the invention) is typically coiled or stacked in the form of die-cut blanks for further application of adhesive on a non-coated side or convenient storage and subsequent use in a lamination process. In this case, blocking can sometimes cause a problem with the subsequent separation of the sheets of interlayer. Blocking is a form of autoadhesion whereby the cured coated interlayer sticks to itself. It is a phenomenon that increases with storage time, pressure and temperature. Due to the relatively high force that can be required to separate "blocked" interlayers, the process of separation can it self result in undesirable orientation of the interlayer.

If blocking of the coiled or stacked self-adhering interlayer occurs, a suitable interleaf material, such as a polyethylene sheet, can be used to assist in parting of the sheets of interlayer. The adhesive material can also be formulated to avoid or at least minimise blocking. In this case, the adhesive material preferably comprises an antiblocking or dulling agent. For example, a silica (SiO2) based agent, such as Stahl WD2863 sold by Stahl USA, or polyurethane micro-beads, such as Stahl WTl 3-485 sold by Stahl USA, may be incorporated in the adhesive formulation to minimise blocking.

Provided that there is no net detrimental effect on the adhesive characteristics of the adhesive material, any additive(s) commonly used in the adhesive formulation that may contribute to blocking can also simply be left out of the formulation. For example, it may be preferable to exclude tackifiers from the adhesive formulation.

An adhesive material that incorporates an antiblocking or dulling agent preferably comprise about 1 to about 15 weight % of the agent, more preferably about 5 to 15 weight %, most preferably the agent is present in an amount of about 10 weight %. An additional or alternative technique that may be used to avoid or at least minimise blocking involves embossing the PVC interlayer prior to applying the adhesive material. In this case the embossing preferably creates a multitude of valleys in the surface of the interlayer with a peak-to-valley height of about 70 microns, more preferably with a peak- to-valley height of about 50 microns, most preferably with a peak-to-valley height of about 30 microns.

Advantageously, embossing has also been found to facilitate air egress during the glass lay-up and sandwich pressing steps of the glass laminating process.

Those skilled in the art will appreciate that as the Tg of the adhesive material is reduced, the propensity for a self-adhering interlayer coated with such an adhesive material to block is increased. Despite the disadvantages associated with blocking of the self-adhering interlayers, it is particularly preferred that the adhesive material used in accordance the invention has a Tg which renders the coated interlayer prone to blocking. Such adhesive materials are believed to be particularly effective at developing initial green tack during the lamination process and suppressing substantial reversion of the interlayer. In this case, it is also preferred that an interleaf is used in conjunction with such a coated interlayer to minimise blocking of the interlayer.

When the Tg of the adhesive layer is less than about 800C, more preferably less about 500C, most preferably in the range of about 25°C to about 35°C, the self adhering interlayer is preferably used in conjunction with an interleaf to minimise blocking.

By virtue of the strong initial green tack and final adhesive characteristics of polyurethane/polyester toward both the glass and the interlayer, glass laminates in • accordance with the invention may be provided with an extremely thin layer of adhesive material. Preferably, the adhesive layer has a thickness ranging from about 5 microns (dry) to about 70 microns, more preferably from about 10 microns (dry) to about 30 microns (dry), most preferably the adhesive layer is about 10 microns (dry) thick. The polyvinylchloride film of the present invention can advantageously be used as a "drop in" substitute for a conventional PVB interlayer, and processed using standard laminating techniques. However, it is preferable to use a slightly higher temperature during pressing of the laminate than that used in a conventional PVB laminating process. In particular, temperatures ranging from about 10 to 2O0C higher than that used in a conventional PVB laminating process are preferred. The slightly higher temperatures allow the adhesive layer and the interlayer to soften, which in turn facilitates the removal of entrapped air between layers, assists in the removal of creases or undulations in the interlayer and ensures that a satisfactory bond between the interlayer(s) and the glass is obtained.

Once the layers of the laminate have been physically assembled, pressing of the laminate typically involves moving the composite between nip rollers exerting a pressure of around 1000 psi through an oven operating at a temperature of approximately 12O0C to 2300C. This process softens the adhesive layers which in turn initiates bonding (green tack) between the layers.

The use of nip rollers during the laminating process facilitates removal of entrapped air in the laminated sheet and the removal of creases or undulations in the interlayer. In order maintain a good level of adhesion between the coated interlayer and the glass sheets during the laminating process, the pressing nip rollers located after the oven are preferably positioned closer to the oven compared with the position of such nip rollers in a conventional laminating line.

The laminated sheets so formed are then transferred to an autoclave which typically operates at a temperature of about 135 0C and a pressure of about 1 150 psi. Autoclaving is used to complete the bonding process between the layers and typically takes around 4.5 hours.

The autoclave process provides uniform pressure that allows for further pressing of the adhesive layer and the interlayer intimately against the glass. The uniform pressure prevents flow differentials that could otherwise stretch the interlayer and distort a decorative pattern or effect.

Alternatively, the assembled laminated structure can be placed in a sealed vacuum bag to minimise air bubbles from being entrapped within the laminate. The "bagged" structure is then pre-pressed and/or pre-evacuated before the assembly is placed in an autoclave and heated to approximately 135°C for 4.5 hours.

To facilitate the removal of entrapped air within the glass laminate during manufacture, the inclusion of a cold pressing stage prior to any heat treatment of the assembled composite structure has been found to be particularly useful. Such a cold pressing stage typically involves passing the composite at ambient temperature between nip rollers that exert a pressure of around 175 psi. The cold pressed composite may then be subjected to heat treatment as described above.

To reduce the degree of in-built orientation of an interlayer, the interlayer can be annealed before it is bonded to a glass sheet. By the term "annealed" it is meant that the interlayer is heated to a temperature (typically above about 4O0C) for a sufficient period of time such that the interlayer relaxes to a less oriented state. Given that drying of the adhesive layer coated onto the interlayer can impart orientation, the annealing process is preferably performed on the coated interlayer after the drying step.

The interlayer used in accordance with the present invention is a PVC interlayer. The PVC interlayer may contain other components such as additives. The PVC interlayer may also contain other polymers. However, the inclusion of other components should not deleteriously effect the physical and/or mechanical properties of the interlayer.

As mentioned above, PVC can readily be calendered to a range of thickness. Accordingly, calendered PVC film is a particularly preferred form of PVC for use as an interlayer in accordance with the present invention. Calendered PVC interlayers coated with the adhesive material can advantageously be used as a "drop-in" replacement for PVB interlayers in standard laminating processes. Accordingly, no additional manufacturing costs or modifications are required to conventional glass laminating equipment.

The PVC interlayers used in accordance with the invention preferably have a thickness ranging from about 0.2 mm to about 1 mm, more preferably from about 0.3 mm to about 0.8 mm, most preferably the PVC interlayer has a thickness of about 0.4 mm to about 0.6 mm.

The PVC used in the manufacture of the interlayers is preferably substantially free of impurities and sensitisers such as initiators, which can lead to excessive degradation and yellowing of the interlayer and can have a detrimental effect on the long term heat stability of the interlayer. In order to minimise the presence of these impurities and sensitisers, the PVC used in the manufacture of the interlayers is preferably made by suspension polymerisation.

Interfacial adhesion is a critical performance property for the glass-interlayer-glass system. During cutting of laminated glass, any delamination becomes highly visible and manifests itself as a type of 'edge whitening'. Even with good interfacial adhesion the tendency for edge delamination will increase with increasing hardness of the interlayer. In order to reduce the tendency for edge whitening, PVC used in the manufacture of the interlayer is preferably plasticised PVC.

Some plasticisers used for plasticising PVC are renowned for their tendency to migrate to the surface of a PVC product over time. Excessive migration of plasticiser from the PVC of the interlayer used in accordance with the present invention may interfere with the interfacial bonding between the interlayer and the layers of glass. Accordingly, if present, plasticiser(s) used in the PVC of the interlayer preferably have a low tendency for migration. Preferred low migration plasticisers include di-octyl adipate and polymeric plasticisers such as polyphthalates and polyadipates. The PVC used for the interlayer preferably has a number average molecular weight of at least 40,000 Dalton and a plasticiser concentration ranging from about 60 phr to about 230 phr. An interlayer comprising plasticised PVC preferably has a hardness ranging from about 15 BSS (British Standard Softness) to about 50 BSS.

Techniques to colour or decorate PVC are well known in the art. PVC may be pigmented to provide for solid (opaque) colours or novel pigments may be used to give special effects. Examples of novel pigments can include so called "interference pigments" or "colour variable pigments" which provide a differing colour perception depending on the viewing angle. PVC is also well suited to printing which can be used to apply an endless array of decorative effects. The decorative effect can be of any suitable colour or finish for example, marble, gloss, satin, translucent or flat. An interlayer comprising PVC can for example be produced with a black finish on one side and a white finish on the other side. This has the advantage of being able to use a single interlayer to produce a laminated glass which for example appears black on one side and white on the other.

An interlayer used in accordance with the present invention is preferably pigmented, coloured, printed or decorated in some way. Particularly preferred interlayers are those which are pigmented and which have had a printing design applied to one or both surfaces.

An interlayer used in accordance with the present invention preferably contains between about 2 to 4 phr of a primary heat stabilizer including an organometallic compound, such as salts of alkaline metals including barium, calcium, tin, and zinc. The primary heat stabilizer preferably includes a zinc salt of an organic acid or a barium, calcium or tin salt of an organic acid, or mixtures thereof. The primary heat stabilizer more preferably includes from about 1.6 to about 4.0 % atomic zinc as a zinc salt of an organic acid.

To maximise the long term thermal and colour stability of the interlayer, the primary heat stabilizer also preferably includes from about 2.0 weight % to about 4.0 weight % phosphorus in the form of a phosphite. A. preferred phosphite is triphenyl phosphite. The interlayer may also contain a UV stabilizer and/or a UV inhibitor to protect the PVC against the damaging effects of UV radiation.

The interlayer may also contain dyes, inorganic fillers, inorganic pigments, interference pigments and optical brighteners.

The interlayer in accordance with the present invention may also comprise a PVC copolymer such as polyvinylchloride co-vinylacetate. In this case, the vinylacetate content of the copolymer preferably ranges from about 15 molar % to about 40 molar %. A suitable example of a vinyl chloride/vinyl acetate copolymers that is commercially available includes, but is not limited to, MPR-TSN from Nissin Chemicals, Nitta-Gun, Japan, which is a copolymer of 87 molar % vinyl chloride and 13 molar % vinyl acetate with a degree of polymerisation of 400.

The invention will now be described with reference to the following non-limiting example which is included for the purpose of illustrating the invention only and is not to be construed as limiting the generality hereinbefore described.

Example

Tests commonly used to evaluate glass laminates include the following:

Impact Test The most critical test for grade-A laminated safety glass to comply with is the impact test as defined in AS2208-96. In this test a 46 kg bag of lead shot is swung through a pendulum arc at a vertical sheet of glass from a pendulum drop height of 300 mm. If the glass panel cracks into small pieces and deforms but is still held together in a safe manner, it is deemed to pass the test. It must retain the shards of annealed glass in an accident, limiting lacerations. Boil Test In the boil test (which is a part of AS2208), the sample (in triplicate) is immersed vertically on edge in water at 660C for 3 minutes and then quickly transferred to and immersed similarly in boiling water. The sample is kept in the boiling water for 2 hours, then removed and examined for bubbles and other defects. This test can highlight the presence of entrapped air. The degree of adhesion, yellowness and haze are also measured after the samples are subjected to a boil test.

Sample tested The laminate was prepared using the following components:

Glass Sheet used Commercially available float glass having a thickness of about 4 mm.

PVC interlavers used 45 BSS PVC sheet of 0.6-0.64 mm thickness comprising approximately 30 parts per hundred (phr) of DOP (dioctyl phthalate - also known as DEHP) embossed on one side only with a peak-to-valley height of about 30 microns.

Polyurethane (polyester) coating used A waterborne polyester-polyurethane sold as RU41-347X by Stahl USA, Massachusetts, USA having a Tg in the range of 25°C to 35°C.

Coating application details Coatings were applied to both sides of the PVC substrate using rotogravure roll coating process. Only one coat was applied in each case. The final coating thickness was 8 GSM (dry) which approximates to a coating thickness of about 8 microns. The coating was cured in an oven at about 70-90 0C for 1-3 minutes. Lamination procedure followed The float glass sheets were first cleaned thoroughly with dilute soap in an industrial glass washing plant. The coated self-adhering interlayer was placed on top of a glass sheet and a further glass sheet was placed on top of the interlayer to make a sandwich type structure. The layed-up structure was then passed between nip rollers through an oven operating at a temperature of approximately 23O0C at a speed of about 2.3 m/min. When being passed through the oven, the glass reached a temperature of about 9O0C. The lead nip rollers provided a lmm compression whereas the rear nip rollers provided a 1.7 mm compression. The resulting primary bonded laminated was then heated in an autoclave for 4.5 hrs at 1350C and a pressure of about 1150 psi to complete the heat bonding process.

Preparation of samples where the glass temperature reached about 1200C or higher resulted in thermal degradation of the PVC interlayer. It is therefore preferred that the temperature of the glass sheet be maintained at about IOOC or less in order to ensure that good initial green tack and final bond strength is obtained.

Test Results

*The glass shatters and splinters as a result of the impact but the broken glass is safely retained by the PVC interlayer.