Note: Descriptions are shown in the official language in which they were submitted.
~35~ 66
A Method of Producing a Laminate
This invention relates to a method of producing a laminate.
Laminates provide a way oF strengthening frangible material,
for example glass, so as to extend its uses and to render it
safer to use in certain circumstances. Thus laminated glass
products can be used for car windscreen~, glass doors 9
balustrades, bulletproofing and many other uses where the
glass product mu5t be strong and/or shatterproof.
In conventional laminated glass products a sheet of glass
is bonded to a layer of polymer, and a further shePt or layer
of material is bonded to the other side of the polymer layer,
so that the polymer is "sandwiched" between two outer layers.
If the glass sheet is then struck a blow it cracks or breaks,
but does not shatter into small sharp pieces as the broken
pieces are still bonded to and held in place by the polym~r
layer. If the laminated glass is used in a car windscreen,
therefore, occupants of the car are not showered with broken
glass on breakage of the windscreen.
Some previously-proposed methods of producing laminates suffer
from the disadvantage that they require considerable capital
expenditure to set up the necessary apparatus. One particular
method involves the various stage8 of providing a pre-formed
~heet of vinyl polyrner, placing the vinyl sheet between
planar face8 of two 8heet8 of gla89, passing the resulting
"sandwich" through a mangle to Compre88 the vinyl sheet again
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the glass sheets, and bonding the vinyl sheet to the glass
sheets by heating in an oven and then cooling. This method
uses costly equipment and is inefficient as it involves a
series of operations with transport of the composite from
5 one apparatus to another.
The disadvantagesinherent in this previously-proposed
method have been dealt with in U.S. Patents Nos. 3,334,008
(Park et al) and 3,50Y,015 (Wismer et al) in which a method
10 is described for producing laminated glass by sealing the
periphery of two parallel glass sheets with pressure-sensitive
tape and forcing resinous material under pressure into the
inter-sheet space. The resinous material is forced through a
self-closing valve held in place with the tape while
15 trapped air escapes through an aperture in the taped seam
at the top of the cell.
U.5. Patent No. 4,125,669 (Triebel et al) describes a similar
method in which two glass panes are sealed all round except
20 for a filling opening and an aeration opening, and introducing
a binder material into the envelope thus formed in an
amount calculated to exactly fill the envelope. Putty is
applied to the openings just before emergence of the binder
on laying the filled envelope flat.
~.S. Patent No. 3,315,035 (Appelgath et al) described a method
involving maintaining the glass sheets in opposite relationship,
heating the sheets to ~out 200 F and injecting a resin
composition containing a hardening agent, preheated to about
~0 200F, into the inter-sheet space and curing the assembled
article.
While these above methods overcome the disadvantage of
high equipment costs and transfer of the laminate from one
35 apparatus to another, nevertheless they themselves have various
drawbacks which the present invention seeks to overcome.
In particular, a very considerable problern exists in
producing a laminate which can be made to an exact finished
~ize and whose interlayer is free from air bubbles, as in
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practice the methods of the ebove-identified patents involve
the operator in very precise and difficult estimation of the
point at which the envelope formed between the sheets is complete-
ly filled with the interlayer liquid without overFlowing, and
at which all the air bubbles have been eliminated.
In the above-described methods one or two openings are
provided in the envelope for fiIling and air bubble removal,
but in each ca8e removal of bubbles must be certain and
filling achieved precisely befor~e the openings are sealed.
Slight overfilling results in loss of resin and an inferior
product, while slight underfilling results in air being
trapped in the envelope. Thus measurement of the amount of
resin required before its introduction is only effective if
the envelope i8 fully sealed at the crucial moment when the
resin exactly fills the envelope and after complete rmeoval
of air bubbles.
,
The air bubble removal is difficult with these previou81y-
proposed methods as the opening must be suffiently small to
allow accurate estimation of the point at which the envelope
i8 just filled, but this necessarily restricts the effectiveness
of bubble removal as bubbles must be directed to this small
opening~or become trapped at the envelope periphery; direction
of the bubbles in this manner can be time-consuming and
difficult
According to the pre8ent invention there is provided a method
of producing a laminate comprising placing a pair of sheets
of frangible material in face-to-face relationship,
introducing between the ~heets a liquid which on solidifying
forms a polymer of greater resistance to Fracture than the
sheets and adheres to the sheets, forming around the peripher~
of the sheets a continuous barrier to passage of the liquid
thereby to retain the liquid between the sheets, wherein at
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1135166
least part of the barrier is gas-permeable, expelling air from
: the intersheet space through the barrier so as to cause the
liquid to fill the intersheet space, and solidifying the
- liquid to form a bonded laminate
: 5
- Further according to the present invention there is provided
a method of produoing a laminate compri~ing placing a pair
~ of ~heet of frangib~le material~in spaced face-to-face relation-
- : ~ ship, sealing the sheets together around~part of their
~10 periphery to form an envelope, tilting the envelope so that the
uns~ealed portion of the sheets i~ uppermost, introducing into
the envelope through the unsealed porti~on;a mea~sured quantity
of a liquid which on olidifying forms a polymer of greater
resistance to fracture than the s~heets and adheres to the
sheets, sealing the unseale~d portion to Form around the periphery
of the sheets a continuous barrier to pass~a~ge af the liquid,
at least an upper portion of the barrier being permeable
to~air, allowing air to escape from the e`nvelope through
the barrier so as to cause the liquid to fill the intersheet
~pa*e and ~olidifving the liquid e* ~*rm a b*nded la
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li3Sl66
5 _
By providing a yas-permeable seal for forming th~ envelope
the drawbacks of the prior art are overcome, as the method
of this invention requires no expensive equipment, and
makes it no longer necessary to judge when the liquid
5 exactly fills the envelope and contains no air bubbles.
After the liquid is introduced the envelope can be completely
sealed immediately, and trapped air escapes through the gas-
permeable seal, which can if desired extend all round the
sheets, until the space within the envelope is fiIled
1~ entirely with the liquid. As the seal is gas-per~eable and
not liquid-permeable the liquid is retained within the
envelope, and a measured amount of liquid can be guaranteed to
produce a precise desired thickness of interlayer for the
laminates without any likelihood of human error after its
15 introduction.
Gas-permeable materials which are suitable for the purpose
of this invention are known, and preferably the material used
adheres to the sheets. In this respect the material may
20 be a fine-pored strip having pressure-sensitive adhesive
faces, and a particularly suitable material is "Scotchmount"
which is marketed by 3M.
The seal may be gas permeable over any portion or the whole
25 of the sheets periphery, but the greater the extent of the
permesbility the easier it is for air to escape without
directing it to any particular outlet portion of the seal.
Thu~, if the liquid is introduced into the envelope with the
~heet9 inclined to the horizontal, for example by pouring
30 under gravity, the sheets can be immediately laid flat to
provide even thickness of the interlayer, allowing the trapped
air to eacape around the periphery by passage through the
gas-permeable material.
35 The sheets of frangible material can be of any material
which it is desired to strengthen by means of lamination with
a polymer; they may be, for example, glass, polymethyl
methacrylate or polycarbonate, although other materials which
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- il35~ 66
can bond with the polymer may al50 be used. The method of the
invention is of considerable benefit when the material is glass
because of the wide range of uses for laminated glass.
5 When the frangible material is translucent, as for example
glass, and the polymer formed by solidifying the liquid is
also translucent, it is o,ften of advantage for the two
materials to be selected as having similar refractive
indices. This is particularly effective when the sheet of
10 frangible material has one non-planar surface, for example
in the case of one or both sheets being of a patterned
glass, and it is desired to produce a laminate which does
not distort light passing through it, as the liquid can be applied
to a depth sufficient to cover completely the non-planar
15 surface.- If the liquid layer is then solidified the similar
refractive indices of the sheet and polymer will cause the
overall optical properties of the laminate to be similar to
those of a sheet having parallel planar surfaces. An advantage
of this is that if a planar sheet of suitable size is not
20 available for a translucent laminate a non-planar sheet
can be used instead in combination with a translucent
polymer of similar refractive inde'x.
The polymer produced on solidification can be any having
25 the desired properties for the laminate provided that it can
be made to adhere to the sheet of frangible material used
and it has greater resistance to fracture than the sheet.
For ease of manufacture it should be a polymer which doe~
not shrink on curing. Curing may be effected with the aid
~0 of for example heat, UV liyht or of a catalyst. Polymers which
have been found to be suitable in various situations are
polyester~ vinyl polymers and epoxy resins. The thickness of
the polymer layer can be selected a9 desired, but from 0.4 to
3 mm has been found to be effective in rnany cases; thicker
35 layers can be used for soundproofing purposes.
A polymer which has been found to be e~pecially effective
in the present method is manufsctured by Warwick Chemical
Limited under the trade name UVAC 2721. Thi~ is a resin
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made from glycols, polyols, dibasic acids and polyfunctional
acids and having a very small degree of shrinkage on curing. The
resin is prepared by mixing the ingredients in a resin
kettle, polymerised to a closely controlled molecular weight
5 which is in the highly viscous liquid stage after cooling. The
mixture is thinned down to pourable liquid by the addition
of monomers such as styrene,methylmethacrylate, vinyl
toluene and other acrylates. Cure is begun by adding an
initiator, usually an organic hydroperoxide such as methyl
10 ethyl ketone peroxide. Typically, promoters and accelerators
are added (UVAC 2721 contains cobalt naph.) to promote
the decomposition of the initiator at room temperature
and, thus, rapid low temperature curing. Cure takes place
in two stages: the initial formation of soft gel is followed
15 by polymerisation to give a transparent tough product not
unlike natural rubber.
The most important properties of the UVAC 2721 system include
ease of handling, low temperature curing with no volatile
20 ~nvolved, light colours and generally good mechanical and
physical properties.
A primer can be employed to improve the bond. The primer
may be in the form of an adhesion promoter or coupling agent,
25for example a silicon-based compound such as ~-methacryloxypropyl-
trimethoxysilane or a compound sold by Bondaglass-Voss
Limited under the trade name "G4". The primer can either be
applied directly to the sheet before application of the liquid
or applied to the sheet in admixture with the liquid.
Psrticularly when the polymer is a polyester it has been found
that adhesion i8 best achieved to an inorganic material such as
glass, and if an organic sheet is used it is best to use a
primer, for example a silane, impregnated with quartz or other
35 inorganic material. In this case a chain of bonds is formed from
the organic sheet through the primer to the quartz and from the
quartz to the polymer, so that the polymer forms a direct
bond with the inorganic quartz while the bonding chain ensures
that the polymer and the sheet are held together.
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An ef~ective method of producing a laminate by the present
invention is by placing two or more inclined sheets of frangible
material in face-to-face relationship, temporarily sealing
around all but one of the common edges of the sheets with
5 gas-permeable tape so as to form an envelope, optionally
prising apart the sheets along the remaining unsealed
edge, pouring a liquid resin between the sheets into the
included angle therebetween, expelling the resin towards the
unsealed edge by application of pressure to the sheets or
10 by laying the sheets flat, sealing the unsealed edge with
gas-permeable tape and allowing the resin to set while
maintaining the pressure to form a laminate.
When the sheets are held upright or at an angle to the horizontal
15 during pouring of the liquid resin, glass tends to "balloon"
outwards under the weight of the resin. If the sheets are
vertical, a pair of vertical plates may be pressed against
the sheets to counteract the "ballooning" and hold the
sheets planar during curing of the resin, and this can be
2û achieved in the case of angled sheets by placing weights
on the "ballooned" position. Alternatively the sheets can be
lowered to reduce their angle to the horizontal so that the weight
of the upper sheet counteracts the "ballooning".
25 If desired, the polymer may be transparent.
There are several ways in which the method of the present
invention can be put into practice, and examples of these
will now be deBcribed by way of practical illustration.
EXAMPLE l
A pair of clear rectangular glass sheets are cleaned,
degreased and dried and placed in face-to-face relationship
with a 3mm thick gas-permeable tape "Scotchmount" between
35 them around three sides to form a liquid seal. The sheets
are then held at an angle of 10 to the vertical with the
unsealed edges uppermost and a 4" strip of glass of the same
width as the sheets and of the same thickness as the bottom
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9 _
sheet is affixed with adhesive tape to the top edge of the
bottom sheet in the same plane as that sheet, as shown in
Fig. 1 in which the sheets are 10 and 11, the gas-permeable tape
is 12 and the strip is 13.
A measured amount of a mixture of UVAC 2721 resin, 1o of
silane A172 and 1~ of methyl ethyl ketone sufficient to fill
the inter-sheet space is then poured onto the strip 13
so as to flow down into the space between the two sheets 10
10 and 11, and this causes a lower portion of the sheets 10
and 11 to "balloon" outwards under the weight of the resin.
When the resin has been poured into the space the -top
edges of the sheets 10 and 11 are sealed together with "Scotch-
15 mount" tape and weights are placed on the upper sheet 10, thelower sheet 11 being supported in order to counteract the
"ballooning" of the sheets and to expel air through the
gas-permeable tape. The strip 13 of glass can then be removed.
The resin cantains ~ -methacryloxpropyltrimethoxysilane
20 as a primer to achieve a good bond between the sheets.
The resin cures with minimum shrinkage to a clear thermoset
sheet sandwiched between the glass sheets, so that a laminated
glass is formed suitable for use in many situations as a
25 safety glass.
As an alternative to placing weights on the upper sheet,
the a8sembly can be lowered to form a greater angle to the
v8rtical after expulsion of the air, whereby the weight of
30 the upper sheet may be sufficient to counteract the "ballooning".
The 4" 8trip of glass is used to assist in pouring the resin
between the sheets~ but other methods can be used, for sxample
a funnel or open channel extending into the inter-shéet space,
35 or providing one of the sheets longer than the other so as to
extend above it, the longer sheet forming the lower of the
two when the resin is being poured; the excess glass can be
trimmed to BiZe after the resin has cured.
1135~66
~o
EXAMPLE 2
The method described in Example 1 is carried out with
the exceptions that one of the glass sheets has a non-planar
face, this faoe being the one adjacent the face of the other
5 sheet, and the resin used is selected to have a refractive
index similar to that of the glass.
Care is taken to ensure that the faces of the sheets are
not in direct contact~with one another, and the result is
10 the production of a laminated glass which has an appearance
similar to a laminate in which both glass sheets have
planar surfaces, the effect of the resin being not only to
bond the sheets together but also to complement the non-planar
face thereby preventing distortion of light passing through the
15 18minate.
EXAMPLE 3
-
Two rectangular sheets of glass are cleaned using a glass
washing machine and gas-permeable "Scotchmount" tape is applied to
20 all four edges of the perimeter of one of the sheets. The paper
protecting the adhesive faces of the tape is removed from the
bottom edge and both upright edges, and the second sheet of
- glass i8 laid in position on the first sheet so as to adhere
to the tape. The two face-to-face sheets are then laid on
25 an inclined tilting table, both sheets of glass are prised
apart 8t their free edges and a funnel is inserted between
the~n.
1,6 of ~ilane A172 adhe8ion promoter i8 added to an amount
of UVAC 2721 resin calculated a8 correct for filling the
inter8heet volume. 16 of methyl ethyl Ketone peroxide
cataly~t i~ then added to the re8in/silane mixture with
gentle bUt thorough mixing and the mixture is allowed to stand
until all air bubbles have escaped. The mixture is then poured
slowly between the sheets through the funnel.
When the mixture has settled in the lower part of the
cavity the funnel is removed and a wedge inserted to keep
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1135166
11
the sheets apart. The protective paper is then removed from the
tape at the top edge of the sheets and the table lowered
until nearly horizontal; at the same time the space at the top
is decreased. Pressure is theo applied to the top edges of
5 the glass until the liquid mixture has filled the entire
intersheet volume and the table is made hori~ontal. The
resin is then allowed to set and a laminate is obtained.
Faster curing of the resin can be achieved by increasing
10 the amount of catalyst to a maximum of 3O~ by raising the
temperature, or by adding a small quantity of cobalt
naphthenate (although care should be taken to prevent this
substance from contacting the catalyst.)
.
15 In other embodiments of this invention the resin may bP tinted
with one or more colours, and/or other bodies may be included
in the resin layer for example wire mesh, coloured or patterned
cloth, flakes of metal or other material, or other decorative
means, and in this way an attractive laminate may be produced
20 easily and cheaply.
The method of the invention can also be used to form curved
laminates of glass, polymethyl methacrylate, polycarbonate or
other sheet material. An effective method of doing this is to
25 hold face-to-face curved sheets apart at an angle to the
vertical as with the flat sheets of Example 3 and to pour the
liquid therebetween, the sheets being sealed at their peripheries
by gas-permeable material.
30 In some instances the present method may be used to form
laminates on existing sheets of frangible material in situ,
for example by laminatit)g existing glags doors or windows without
removing them from their frarnes.
~5 If desired, a glass laminate having additional properties
similar to those of toughened glass can be produced by the
rnethod of the invention by using a liquid which shrinks to a
certain extent on solidifying. An example of such a laminate
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1135~66
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can be made by the method of Example l with the exception
that the UVAC 2721 resin is replaced by a resin~which shrinks
to a significant degree, the silane primer still being
present. On curing, the resin bonds through the silane primer
5 to the two glass sheets, at the same time undergoing shrinkage
so that the effect is to put the surfaces of the glass sheets
under tension; the resulting laminate is capable of withstanding
greater impact than that of Example l, and when it does
break it forms fragments similar to those of tempered or
lO toughened glass.
"Scotchmount" gas-permeable tape is of polyurethane material
and a further example of a gas-perm~eable tape which is suitable
for use in the method of this invention is "Inseal 5250"
15 PVC tape manufactured by D.R.G. Inseal Products.
.
In the method of EXAMPLE 3 it is sometimes of benefit, after
ths introduction of the resin mixture between the sheets, to
tilt the table further than horizontal whereby the resin
20 flows towards the originally unsealed edge of the sheets
and forces air out under its weight. This is particularly
useful when the resin mixture is viscous.
The present invention can be use~ in the manufacture of
25 one-way mirrors in which case one of the sheets is
coated on its inner face with a thin layer of silvering
prior to the manufacture of the laminate. The laminate thus
formed isolates the silvering from the atmosphere and prevents
deterioration of the thin film. This overcomes the problem
30 with conventional one-way mirrors in which the silvering
is protected only by tape around the periphery of the sheets
and no resin interlayer is present. Under these conditions
the silvering gradually becomes oxidised and discoloured.
.
