Method of manufacturing fire-resistant safety glass

A fire-resistant safety glazing product comprising at least two sheets of glazing material, e.g. glass, bonded together with an interlayer of adhesive binder material and metallic wire mesh of the type used in "wired glass" embedded in the interlayer, and methods of manufacturing the same.

FIELD OF THE INVENTION 
This invention relates to a fire-resistant safety glazing product and to 
the manufacture or production of a fire-resistant safety glazing product 
in which reinforcing wire mesh is incorporated in the glazing product. 
BACKGROUND OF THE INVENTION 
Wired glass has been in production for many years and in general provides a 
greater measure of security than ordinary clear or obscure annealed glass. 
In particular wired glass is widely used as glass balustrading, the wire 
being effective in preventing people or objects falling completely through 
the glass when the glass is broken. Wired glass is also used in glass pass 
doors to act as a barrier for preventing a hand or arm going through the 
glass accidentally and to hold the glass together longer when exposed to 
fire and heat. In this latter respect all glass will melt at a high enough 
temperature. However the wire in the wired glass holds the melting and 
sagging glass in its original position much longer than unwired glass. 
There are three common types of wired glass, namely "Georgian" wired glass 
which has a square mesh, "Hexagonal" wired glass which has a hexagonal 
mesh, and "Diamond" wired glass which has a diamond shaped mesh. The wires 
of the meshes are welded together, e.g. electrically welded together, at 
their intersecting or cross-over points and are typically made of steel, 
e.g. chemically treated steel. With "georgian" wired glass the area of 
each square mesh opening is typically about 155 mm.sup.2 (wires spaced 
12.5 mm apart), and the wires typically have a gauge of 0.46 mm. Such wire 
mesh has good reinforcing properties, improves the fire-resisting 
properties of the glass and does not obstruct or impair the view through 
the glass to any great extent. 
Known wired glass is generally manufactured by the same basic method of 
feeding wire mesh into the glass as it passes in a fairly molten state 
between rollers of a roller system and then cooling the glass to solidify 
it. However this process is unsatisfactory in three respects. Firstly, the 
pull on the wire mesh as it is fed into the molten glass distorts the wire 
mesh so that, with square mesh for instance, the cross wires are not 
completely straight but become bent. Secondly, the wire mesh tends not to 
be positioned centrally in he solidified glass. Thirdly the process is 
costly, especially if the wired glass subsequently has to be further 
treated, e g. by grinding and polishing to produce "polished plate" glass. 
In 1982 the British Standards Institute published BS 6262:1982 relating to 
codes of practice for glazing for buildings. This standard took 
recognition of the danger of serious accidents which could occur from 
ordinary glass when glazed in certain locations and recommends that safety 
glass or material should be used in these locations, "safety glass" being 
specified as laminated or toughened glass. A simple laminated glass 
comprises two sheets of glass bonded together by an interlayer of 
reinforcing material. The interlayer is able to absorb impact shock and to 
hold the glass in position when broken or cracked thus preventing spalling 
of glass fragments and preventing any part of a person's body going 
through the glass and causing a series injury. 
Conventional wired glass was not deemed by the British Standards Institute 
to constitute a "safety glass" since it was unable to meet their required 
safety standard. In particular it is unable to retain or hold splinters or 
slivers of glass brought about by impacting and fracturing wired glass. 
In the prior art it is known to incorporate wire in laminated glass to 
fulfil three differing purposes. Firstly, to render the glass visible by 
incorporating in the interlayer fine wires running parallel in one 
direction only at approximately 30 mm centres. Secondly, to provide an 
electric heater or alarm circuit by incorporating a continuous thin wire 
filament in the interlayer. Thirdly, to provide a fire-resistant glass in 
which a conventional wired glass is laminated to another sheet of glass. 
However such glass is less fire-resistant than ordinary solid (monolithic) 
wired glass and is considerably more expensive to produce. 
It has also previously been proposed in GB-A-2078166 to incorporate a wire 
mesh in a safety glass, the wire mesh acting as a reinforcement. However 
the mesh is adhered between two sheets of material to form therewith a 
sandwich type interlayer and is not therefore truly embedded in the 
interlayer and does not act to hold the interlayer together if subjected 
to intense heat, e.g. in a fire. Indeed the action of heat could well 
cause the interlayer to delaminate. 
It is also known from GB-A-2125732 to provide a fine-mesh wire net in a 
laminated glass to act as a microwave shield. However visibility through 
the fine-mesh wire net is poor and its presence does not significantly 
reinforce the glass or assist in rendering the glass fire-resistant. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an improved 
fire-resistant safety glazing product incorporating wire mesh. A further 
object of the invention also is to provide a glazing product which is able 
to withstand impact shock (preferably being able to comply with BS 
6206:1981 for a flat glazing product) and which is fire-resistant 
(preferably being able to withstand a half-hour integrity fire test 
according to BS 476 Part 8). 
According to one aspect of the present invention a fire-resistant safety 
glazing product comprising two sheets of glazing material bonded together 
with an interlayer of adhesive binder material and a reinforcing wire mesh 
consisting of metallic wires welded together at intersecting or cross-over 
points, is characterized in that the reinforcing wire mesh is completely 
embedded in the interlayer. 
The interlayer can be clear (transparent), coloured or tinted. The glazing 
product is preferably flat but may alternatively be formed from bent 
glass, domes or other curved glass or glazing material. 
Preferably the wire mesh comprises a first set of chemically treated, 
spaced apart, parallel first straight steel wires arranged at an angle, 
e.g. perpendicular, to a second set of chemically treated, spaced apart, 
parallel second straight steel wires, the criss-crossing first and second 
straight steel wires being electrically welded together at each cross-over 
point to provide rectangular, square or diamond shaped meshes. 
Alternatively, however, the wires of the wire mesh may be arranged to 
provide hexagonal meshes. Preferably the wire is made of steel (e.g. 
galvanised or stainless steel) as mentioned above, but other metallic 
wires, e.g. of copper, bronze, zinc, brass, gold or lead, may be employed. 
The thickness of the interlayer is determined at least in part by the gauge 
of the wire of the wire mesh. With wire having a gauge of 0.46 mm, the 
interlayer can have a thickness as small as from 1.00 to 1.20 mm. However, 
the interlayer thickness may be greater, e.g. up to 2.00 mm, or smaller, 
e.g. down to 0.25 mm with less preferred smaller gauge wire. 
There are various types of resin or resinous material which can be used to 
provide the interlayer and which can have varying degrees of clarity and 
performance, e.g. for rendering the laminate fire-resistant. Preferably 
the interlayer comprises a methacrylate resin with additives but other 
resins, such as polyester or silicate resins, can be employed. 
Although the interlayer is preferably formed by the setting, polymerization 
or solidification of a liquid resin material introduced between spaced 
apart glazing sheets, it is conceivable to provide a sheet of polyvinyl 
butyral (PVB) having the desired wire mesh embedded therein and to bond 
glazing sheets thereto in a conventional manner using an autoclave, or in 
any similar manner of compressing and melting and laminating a wire mesh 
embedded interlayer between glazing sheets. Similarly two thinner sheets 
of PVB can be set on either side of the wire mesh and melted and laminated 
together, the melting and laminating ensuring that the wire mesh becomes 
completely embedded in the interlayer as a coherent interlayer in the 
finished product. However this last-mentioned method has proved less than 
satisfactory under test conditions, the lamination being imperfect. 
Therefore laminating or bonding using resinous material is preferred. 
According to another aspect of the present invention a method of 
manufacturing a fire-resistant safety glazing product comprising bonding 
together two sheets of glazing material with an interlayer of adhesive 
binder material, the bonding process including setting of the binder 
material from a flowable condition, a reinforcing wire mesh consisting of 
metallic wires welded together at intersecting or cross-over points being 
between the outwardly facing surfaces of the two sheets of glazing 
material, is characterized in that the adhesive binder material when in 
its flowable condition flows around the reinforcing wire mesh so that the 
latter is completely embedded in the binder material when the latter sets. 
Preferably the adhesive binder material is introduced in liquid form into a 
cavity provided between the two glazing sheets, the cavity being at least 
partly peripherally sealed in a liquid tight manner and containing the 
wire mesh. Alternatively, one of the sheets of glazing material is 
positioned substantially horizontally and provided with a peripheral seal, 
the wire mesh is positioned on top of the said one sheet and liquid 
adhesive binder material is poured onto said one sheet inside said 
peripheral seal and finally the other sheet of glazing material is 
positioned on top of the peripheral seal and the assembly allowed to set. 
In this case the bottom sheet may be urged downwards in its centre, e.g. 
by the natural weight of the glazing material or with the use of suction 
cups or the like, to assist in the containment of the liquid adhesive 
binder material. 
Conveniently the wire mesh is under tension during setting of the adhesive 
binder material, or alternatively depending on the gauge rigidity and 
tension of the wire, it can be left free to adopt its own position in the 
interlayer when the adhesive binder material is in its liquid form. In 
fact is has been found that the surface tension and viscosity of the 
liquid adhesive binder material ensure that in most applications the wire 
mesh is embeds itself centrally in the interlayer. This phenomenon of the 
wire mesh "floating" in the liquid adhesive material is extremely 
important in respect of the quality of the finished product in large scale 
manufacture, the tensioning of the wire being time consuming and 
impractical for large scale, fast production. In tests it has been found 
that the wire mesh "freely floats" into a centralized position when wire 
mesh having a gauge of from 0.46 to 0.70 mm is selected, the cavity or 
interlayer thickness being from 1 mm to 2 mm and the liquid adhesive 
binder material when introduced into the cavity having a kinematic 
viscosity in the range of from 2.59 cSt to 5.97 cSt at 20.degree. C. It is 
believed that the surface tension of the adhesive binder material prevents 
the wire mesh from breaking the surface of the adhesive material and 
ensures that the wire mesh remains suspended within the interlayer. Thus 
with adhesive binder material having a pouring kinematic viscosity of 
2.593 cSt, and using 12.5 mm square wire mesh having a wire gauge of 0.46 
mm with a 1 mm thickness interlayer, the wire mesh is suspended 
approximately 0.25 mm from the surface of the binder material. Thus using 
an interlayer thickness of only from 1.0 mm to 1.2 mm, a reasonable 
centralization of the wire mesh within the encapsulating adhesive binder 
material is obtained. Centralization may not be obtained if substantially 
thicker interlayers are used. 
Typically the manufacturing method is similar to that described in 
GB-B-2155856 in my own name. 
Peripheral sealing of the sheets of glazing material in a liquid tight 
manner may be provided by double sided adhesive tape or strip which is 
either solid (i.e. gas impervious) or gas permeable. Alternatively solid 
mastic, butyl tapes or extrusions may be employed for peripheral sealing, 
although care has to be taken to avoid chemical reactions with the 
interlayer material. Indeed any suitable material can be used which will 
seal the periphery satisfactorily and will remain unaffected by, or will 
not affect, e.g. optically, the chemical interlayer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a first method of manufacturing a fire-resistant safety glazing product 
according to the invention, a first glazing pane 1, typically of glass, of 
the desired thickness, e.g. 3 mm, and size is cleaned and laid 
horizontally, e.g. on a table. A selected metallic wire mesh 2 having 
crossing wires welded together at their cross-over points, is cut to a 
smaller size than the glazing pane 1 and is then laid horizontally on top 
of the pane 1. The mesh 2 is positioned so that there is an uncovered 
peripheral b order 3, consisting of end border regions 3a and 3b and side 
border regions 3c and 3d, extending around the entire periphery of the 
pane 1 as shown in FIG. 1A. If desired a short length 4 of very fine wire 
is attached to each corner of the wire mesh 2 and the wire lengths 4 are 
then taken round the edges of the glazing pane 1 over the end border 
regions 3a and 3b and are bonded to the opposite face of the pane 1 by any 
temporary adhesive method, e.g. with the use of adhesive tape 5 as shown 
in FIG. 1B. Before adhering the wire lengths 4 to the pane 1, the lengths 
are slightly tensioned to ensure that the mesh 2 will remain reasonably 
flat, without kinks. 
Lengths of double-sided adhesive strip material, e.g. Normount V2500 
flexible adhesive tape (Normount being a trade name of the U.S. company 
Normount Performance Plastics), or flexible adhesive tape No. 910 from 
Technibond Ltd., are then adhered to the border regions 3a-3b but not 
quite along the full length of border region 3b. Thus small air gaps, each 
typically about 2 mm wide, are left in the strip material at opposite ends 
of the border region 3d. Non-adhesive backing layers on the lengths of 
strip material are then peeled back a short way and a pre-cleaned second 
glazing pane 7 (see FIG. 1C) of similar size to, and typically the same 
thickness e.g. 3 mm, of the first glazing panel 1, is positioned on, so as 
to be supported by, the lengths of strip material so as to be in 
face-to-face relationship with the pane 1. The non-adhesive backing layers 
on the lengths of strip material covering border regions 3a-3c are then 
peeled off and the glazing panes pressed together so that the strip 
material is adhered to both glazing panes and provides a peripheral seal. 
The first and second glazing panes and the peripherally sealing strip 
material define a cavity in which the wire mesh 2 is located. The cavity 
thickness is determined by the thickness of the peripheral strip material 
and may typically be from 0.5 mm to 2.5 mm thick, or as desired, e.g. 1.2 
mm thick. 
The assembly of sealed glazing panes is raised into an inclined position, 
e.g. from 15 degrees to 65 degrees, typically from 20 degrees to 40 
degrees, with its unsealed edge (i.e. along border region 3d) uppermost. 
The unsealed edge is carefully prized apart, i.e. the second glazing panel 
is lifted clear of the underlying length of strip material which still has 
its non-adhesive backing layer in place, and a broad but thin spout of a 
pouring funnel is inserted therein. 
A predetermined quantity of settable liquid bonding material is then poured 
through the funnel into the cavity between the first and second glazing 
panes. The funnel is then removed, the backing layer is removed from the 
last length of strip material, and the upper edges of the glazing panes 
are pressed together. The glazing pane assembly is then lowered, e.g. into 
a horizontal position or into a reverse inclination, so that the 
introduced liquid bonding material flows towards the one, two or more air 
gaps in the peripheral "seal", expelling air as it moves towards the air 
gaps. When the liquid bonding material reaches the air gaps, the latter 
are sealed, e.g. with suitable filling material, and the assembly is moved 
into (or retained in) a horizontal position during setting of the bonding 
material. This method follows substantially the laminating method 
disclosed in my Patent GB-B-2155856 and further details of steps of the 
laminating technique given in that patent specification. 
After the bonding material has set, the projecting ends of the wire lengths 
4 are removed. The finished product is in the form of a fire-resistant 
"Safety Glass" (see FIG. 1C) comprising two glazing panels 1, 7 bonded 
together by an interlayer 8 in which a metallic wire mesh is embedded 
centrally. The peripheral seal is then cut and removed to provide the 
final product. 
The use of the wire lengths 4 for tensioning the wire mesh 2 may be 
dispersed with if the wire mesh is of suitable gauge and reasonable 
rigidity, whereby the phenomena of the relationship between the wire mesh, 
surface tension and viscosity effect of the resin as previously described 
ensures consistent centralization of the wire mesh on completion of the 
setting or polymerization of the adhesive resin. 
A fire-resistant safety glass produced by the method described above and 
consisting of two glass sheets bonded together by a methacrylate resin and 
additive having wire mesh embedded therein, has passed the half-hour 
integrity test and a one hour stability test under BS 476: Part 8: 1972 
(Certificate No. J8053/3 of Yarsley Technical Centre, Redhill, Surrey, 
United Kingdom)--although this is not absolutely necessary 
commercially--and Safety Test BS 6206 1982. For the fire test certificate 
a 1 mm interlayer thickness was employed with two 3 mm thick glass panels. 
12.5 mm square steel wire mesh of the type used in conventional "Georgian" 
wired glass was used for the wire mesh. The liquid bonding material was a 
clear methacrylate resin having a pouring kinematic viscosity at 
20.degree. C. of 2.593 cSt. 
The liquid bonding material may be of any suitable type used in glass 
laminating techniques and examples of suitable resin or resinous bonding 
materials, such as methacrylate resin (the presently preferred resin) or 
polyester resin, are given in GB-B-2155856 and GB-A-2178363. It should 
also be added that additives may be employed in the resins to increase the 
fire-resistance of the cured resin material. Some resin materials cure 
adequately at room temperatures while other require higher temperatures 
(e.g. IR heaters or warm air) or need to be exposed to UV radiation (e.g. 
for windscreen repairs) or radiation at microwave frequencies, e.g. from 
1000-2500 MHz. In general the use of resin heating to the particular 
optimum temperature of the resin can accelerate curing by up to 80 per 
cent. In production, to enable reproducible results, it is preferred to 
heat the glazing products to a specific temperature so that the room 
temperature (which may vary) does not influence curing. Examples of 
methacrylate resin are "Naftolan" sold by Chemetall (West Germany) and 
"Plexmon 900" sold by Rohm (West Germany). Other examples of usable resins 
are diethylene glycol bis allyl carbonate (e.g. "Nouryset 200" sold by 
Akzo Chemie, Holland, or "Allymer CR 39"), polyester resin, liquid PVB 
(e.g. "Butvar"), poly(ethylene-vinyl acetate) and 
poly(ethylene-methyl-methacrylate). However nearly all these compositions 
are not as attractive as methacrylate resin. 
The strip material described herein for the peripheral seal is 
gas-impervious or non-gas permeable and the provision of air holes or gaps 
in the peripheral seal is required to allow the release of air from the 
cavity. However other types of peripherally sealing material may be 
employed, for example gas-pervious or gas-permeable tape, which is known 
in the art, in which air, but not the liquid bonding material, is able to 
pass therethrough. With such a peripheral seal the air holes or gaps in 
the seal can be dispensed with. The perimeter seal can also be achieved 
using, polyisobutylene (cored or uncored), butyl tape or butyl, silicone 
which can also be used on the external perimeter edges of the glass, 
numerous mastics and tapes metallizing the edges, for example with metal 
arc spray or similar, in fact any perimeter binder which will contain the 
interlayer liquid or otherwise. 
Although a hand pouring technique has been described for introducing the 
liquid bonding material into the cavity, other liquid introducing 
techniques may be employed such as machine injection, with resin mixing 
and metering machines, using either one filling hole, or a number of holes 
for air release or the gas-permeable liquid barrier. 
Other techniques may be employed for keeping the wire mesh in a reasonably 
flat position during setting of the liquid bonding material. For example 
the wire mesh may be oversize and laid over the entire glazing pane 1. The 
edges of the wire mesh are then bent over and around the edges of the pane 
1 either prior to or after application of the peripheral seal. 
In all instances the sealing edges of the mesh "reinforced", 
fire-resistant, laminated safety glass can be cut and removed if desired. 
Also the glass can be cut to desired sizes by the same methods used to cut 
ordinary laminated glass. Because of this ability to peripherally trim the 
glass, it is also possible to use a wider peripheral seal and to trap 
reinforcing wire mesh under the peripheral seal, the wire mesh, however, 
not extending outwardly of the glazing panes, or alternatively sandwiching 
the extended mesh between two adhesive binders of requisite thickness. 
FIGS. 2A and 2B illustrate steps of a second method of producing laminated 
fire-resistant safety glass according to the invention. This second method 
is almost the same as the first method, but is generally simpler. 
Typically interlayers of from 0.5 mm to 2 mm between the spaced apart 
glazing panes can be employed, depending on the gauge of wire mesh 
selected. 
In the second method, the first pane 1 of glass or other glazing material 
has a peripheral seal 6 applied thereto. The wire mesh 2 is cut to a size 
to fit inside the peripheral seal 6 and is laid on the horizontal pane 1 
in a position just short of the peripheral seal 6 as shown in FIGS. 2A and 
2B. The second pane (not shown) is then placed in position and the 
procedure followed as in the first method described above. 
It should be noted that, in the methods described herein, when the liquid 
resin or other settable liquid bonding material is introduced into the 
interlayer between the spaced apart glazing panes, the liquid bonding 
material flows around the wire mesh and suspends the latter within the 
bonding material. This is described as a "free floating suspension 
method". When the bonding material fully cures, the wire mesh is 
reasonably centrally positioned within the interlayer, although this is 
not necessary for the finished product. 
The glazing panes are preferably supported on a table which can be manually 
or automatically tilted, e.g. with a two way tilting mechanism, generally 
termed concentric (i.e. enabling simultaneous tilting in the horizontal 
and vertical planes) or merely with the use of a simple horizontally 
tilting table. Alternatively an ordinary static table can be used with the 
glazing panes being tilted up and down relative to the table. 
Another method of producing safety glass according to the invention 
involves following the procedure set out in the description of 
GB-B-2155856 until the position is reached where the envelope of glazing 
panes is assembled in position prior to the removal of the backing tapes 
from the peripheral seals. The bottom backing tape is then removed and the 
two side backing tapes are partially removed until approximately two 
thirds of the adhesive tape is exposed on either side. The glazing panes 
are then pressed together to form a peripheral seal on the bottom edge and 
partially up to the two sides. The "envelope" is then opened up 
sufficiently at the top to permit a sheet of wire mesh, which has been cut 
to fit inside the peripheral seal, to be slid down into the envelope which 
is in the inclined position. The remaining parts of the side backing tape 
are then removed and the laminating procedure continues normally, e.g. as 
described in the first method of this description. This particular method 
is more suitable for smaller size areas of laminating. 
For large glazing areas, the two glazing panes can be sealed around their 
perimeters and laid on to a tilting table fitted with hydraulic or 
pneumatic clamps which hold the glass together around the edges to prevent 
leakage (which is more likely with large areas). The resin can be can be 
machine mixed and dispensed, e.g. under pressure, via a nozzle into the 
interlayer cavity which will be in an inclined position on the tilting 
table. When the desired amount of liquid bonding material is deposited in 
the cavity, the table is lowered, e.g. to the horizontal position, for air 
venting and setting of the bonding material. 
Another method which can be used for very large areas of glazing panes, is 
a method employing a slightly concave tilting table. A large pane of glass 
is laid on the table and sealing material as previously described is laid 
around the glass perimeter. Preferably a complete, gas permeable 
peripheral seal is provided. However is non-gas permeable material is 
used, vent openings to expel air must be used. The glass, because of its 
large area, has the ability to bend and sink to an extent into the concave 
table. Alternatively, the centre of the glass pane can be pulled downwards 
by means of one or more rubber suction cups which can hold the horizontal 
glass in a concave manner. Wire mesh of a size slightly smaller than the 
glass pane is laid horizontally on the glass pane inside the previously 
sealed perimeter. The desired amount of resin, e.g. methacrylate resin, is 
poured or dispensed by machine into the centre of a glass concave. Another 
similarly sized glass pane is then placed exactly over the first pane, 
usually by means of rubber suckers, and the peripheral edges pressed 
together. The concave bottom pane is then released from its depressed 
position, by either moving the table back to a horizontal condition or 
releasing the underneath suction cups. The central pool of the resin layer 
then expands outwards until the perimeter sealing is reached. The wire 
mesh "floats" in the resin and is unaffected by this movement. 
One of the drawbacks of this method is that the glass may break from 
physical stress although this would not occur if plastic, e.g. acrylic or 
polycarbonate, sheets were used. 
It is possible to locate two panes of glass vertically for cavity 
filling/curing. Expelling of air is speeded up and pressure plates on 
either side of the glass panes prevent outward bulging. 
A semi-automatic production line can be set up to manufacture laminated 
fire-resistant glass comprising a line of rubber castor tables on to which 
are fed, from two rubber castor concentric tilting or ordinary tilting 
tables, the bonded and filled glazing sheets. The glazing sheets are 
assembled on the rubber castor tilting table in the horizontal position, 
as previously described. The tilting table is then raised to the desired 
tilted position for resin filling by hand or machine. The perimeter edge 
or filling opening(s) are sealed or left with vent holes as desired and 
the table returned to its horizontal position. The wire mesh "floats" to 
the desired central position due to the resin viscosity and interlayer 
thickness. The glass is rolled away on the rubber castor tables for final 
curing. Machine dispensing of resin is particularly suitable if glass 
sizes are repetitive. 
The glazing panes may be of glass, annealed glass, toughened glass, 
emissivity glass or plastics material, e.g. acrylic, perspex, PVC, 
polycarbonate or the like. The panes may be clear, patterned, tinted or 
coloured. 
Instead of the glazing panes being permanently secured to the interlayer, 
one of the panes may be releasable therefrom, e.g. by treating its face 
with a release agent prior to laminating. Resin such as diethylene glycol 
bis allyl carbonate with additive(s) are particularly suitable for this 
method. 
In all applications the wire mesh acts to reinforce the glazing product, 
although its main purpose is to provide the glazing product with a degree 
of fire resistance by retaining the interlayer in a coherent form even 
when it begins to melt in the presence of intense heat. The wire mesh can 
also expand in the resilient interlayer when subjected to heat absorption 
without causing the glass to break--a common problem with conventional 
wired glass. Also the peripherally exposed edges of the wire mesh are less 
likely to rust since the wire does not become detached from the resin 
interlayer and the rusting will not spread back along the wires. Tinted 
wired glass is usually not produced with conventional wired glass since it 
has an increased heat absorption, the different coefficients of expansion 
of the glass and wire resulting in cracking of the wire. However a 
resinous interlayer can absorb the increased heat expansion. Furthermore 
the fire-resistant safety glazing product of the invention can be used as 
a roof covering since, even if the glass cracks, water will not penetrate 
through the resin interlayer. 
Conventional chemically treated steel wire mesh used in conventional wired 
glass produced by Pilkington Brothers PLC is the preferred wire mesh. This 
mesh has a grid of wires providing a 13 mm.sup.2 (or 12.5 mm.sup.2) square 
mesh size with the wires being electrically welded together at each 
intersecting or cross-over point. However other types of reinforcing mesh 
may be employed provided that it consists of metallic wires welded 
together at intersecting or cross-over points. The steel wire may be 
galvanised or stainless steel. Other types of metal which may be used are 
copper, bronze, zinc, brass, gold or lead. The mesh shape may be 
rectangular, square, hexagonal or diamond shaped. 
It is also conceivable to produce a PVB sheeting with a wire mesh embedded 
therein, bonding of the interlayer being achieved with an autoclave. 
Similarly the mesh could be laid between two PVB sheets and processed 
through the autoclave in the normal manner, resulting in the wire mesh 
becoming completely embedded in the interlayer. 
The invention finds application in the manufacture of fire-resistant safety 
glass or glazing products incorporating wire mesh. The glazing products 
can be produced more cheaply than conventional wired glass. Furthermore 
the wire mesh is not distorted during the manufacturing process.