Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
SPG 75206
'703
Description
1 METHOD AND APPARATUS FOR PRODUCING LAMINATED GLASS
Field of Invention
The present invention relates to a method and
apparatus for producing laminated safety glass and, in
particular, laminated automobile windshields, and the like.
Background of the Invention
Aut~mobile windshields ordinarily consist of two
sheets of glass and an interposed layer of a thermoplastic
material, such as polyvinyl butyral, bonded to one another
by heat and pressure to form a composite unit. The bondin~
is usually accomplished in a two-step operation by first
subjecting the assembled laminations to a preliminary
pressing to remove the air from between the laminations and
effect superficial bonding thereof, and then to a final
heating and pressing in an autoclave filled with oil or air
to completely bond the laminations together.
Different methods have been employed for initially
removing the air from between the laminations. One of
these consists in passing the glass-plastic assembly
between squeeze rollers to force the entrapped air from
between the lamination~. Another is to provide a flexible
channel shaped member in engagement with the marginal edge
portions only of the assembly, in spaced relation to at
least part of the periphery of the assembly, to provide a
conduit through which the air can be withdrawn. Still
another is to place the assembly in a flexible bag, seal
the bag and apply a vacuum thereto to withdraw the air from
within the bag as well as from between the laminations.
These bags are usually formed of films or sheets of a
plastic material, such as polyvinyl alcohol.
Outline of the Invention
This invention is concerned with the so-called
-~ bagging method and has for its primary object the
~'
SPG 75206
~2~77~3
1 provision of ~ new and improved vacuum bag formed of a
special material which will facilitate the evacuation of
air from th~ bag interior and cause it to exert a uniform
pressure on the entire surface of the glass sheets when
vacuum is applied thereto, thereby permitting the escape of
all of the air within the bag, as well as from between the
laminations.
Another object of the invention is to provide a
laminating bag of the type disclosed in which it is
possible not only to effect a preliminary pressing of the
laminations but to completely laminate the glass-plastic
assembly while retained within the bag.
The i~proved vacuum bag herein provided is formed of
fiber glass cloth impregnated with a silicon-rubber sealant
applied to the outer surface thereof.
Fiber glass cloth impregnated with cilicon-rubber
sealant is elastic and resilient and retains this
characteristic under environmental demands that cause other
elastomer compounds to fail. Such a bag is tougher and
harder to tear in the vacuum lamination of glass
windshields than bags heretofore used. Also, ozone aging
has little or no affect on silicon-rubber fiber glass
cloth. T~is silicon-rubber coated fiber glass bag can
easily withstand higher temperatures, moisture and
oxidation, qualities that are ~ignificant in the autoclave
vacuum lamination of glass. Further, this composite bag
contains no acid producing chemicals and is not corrosive.
Brief DescriPtion of the Drawings
Fig. 1 is an end view of a glass-plastic assembly.
Fig. 2 is a front elevation of a vacuum bag provided
by the invention in which the glass-plastic assembly,
indicated in broken lines, is processed,
Fig. 3 is a cross sectional view taXen substantially
on line 3--3 of Fig. 2, and
Fig. 4 is an enlarged cross sectional view showing
the bag construction and the glass-plastic assembly located
therein taken ~ubstantially on line 4--4 of Fig. 2.
.. ~.
SPG 75206
177~3
--3--
1 Detailed DescriPtiOn
Referring to the drawings, there is disclosed in Fig.
1 a glass-plastic assembly representing an automobile
windshield and composed of the top and bottom sheets of
glass 10 and 11 and an interposed layer 12 of a
thermoplastic material, such as polyvinyl butyral.
According to the invention, the three laminae 10, 11
and 12 are laid freely one upon the other in properly
assembled relationship to form a sandwich and the assembly
then introduced into the vacuum bag 13 shown in Figures 2
and 3. The bag is substantially rectangular and formed of
the two ~ide panels 14 and 15 sealed together along one
side edge 16 and the two end edges 17 and 18. The other
side edge 19 i8 left open and forms the entrance through
which the laminated assembly is introduced into the bag.
As illustrated in Fig. 4, the side panels 14 and 15
of the bag are composed of sheets o~ fiber glass cloth 20
to the outer surfaces of which are applied a layer of
silicon-rubber 21, preferably by spraying, which renders
the side panel impervious to air and moisture. The
silicon-rubber is air dried, being preferably of the ~TV
type (trademark of General Electric Co. for silicone rubber
compounds of the room temperature vulcanizing type).
To secure the side panels 14 and 15 together there is
also applied to the inner surfaces thereof around the
relatively narrow marginal portions a coating 22 of the
silicon-rubber. The side edge 16 and end edges 17 and 18
of the panels are then brought together and pressed into
sealing relation with one another, leaving the edge 19 open
to receive the laminated assembly. The bag edges may be
pressed together by hand, by mechanical means or in any
other desired manner.
The laminated assembly is then placed within the bag
13 through the open edge 19 and a vacuum hose 23 arranged
around the periphery of the assembly in spaced relation
thereto. The hose 23 is provided with a series o~ spaced
openings 24 and is connected to a vacuum pump (not shown)
through an outlet hose 25.
....
SPG 75206
12~776)3
--4--
1 The bag panels 14 and 15 at the open side 19 are then
brought together and closed and a vacuum established in the
bag. This vacuum will initially draw the edges of the
panels into tight sealing engagement with one another and
will then completely withdraw the air from within the bag,
as well as from between the laminations through the hose
23.
While maintaining the vacuum thereon, the bag is
placed in a sealed heating oven and subjected to a
temperature sufficient to bring about a softening oE the
plastic interlayer 12 and superficial adhesion of the
plastic interlayer to the glass sheets. By way of example,
the assembly may be heated in the oven at a temperature of
about 150 to 225F. for a period of about 20 minutes.
The bag, with the vacuum still on, is then trans-
ferred from the oven to an autoclave wherein it is sub-
jected to an air pressure gage (PSIG) in the neighborhood
of 100 to 250 pounds per square inch for a period of about
10 minutes to effect final and complete bonding of the
laminations throughout the entire area of the assembly. ~o
additional heating i8 provided in the autoclave, the resi-
dual heat rstained from the heating oven being sufficient.
When the pressing cycle is completed, the bag is removed
from the autoclave and the completed product removed from
the bag. Thus the entire laminating process can be accom-
plished while the laminated assembly remains in the bag.
The silicon-rubber coating that is applied to the
outside surface of the bag will seal the interstices
between the glass fibers but will not completely penetrate
them thereby leaving the inside surface of the bag bare and
the individual fibers exposed as shown in Fig. 4. The
exposed fibers form an uneven surface due to the weave and
which, when brought into face-to-face contact with the
glass sheetq, result in innumerable small channels through
which the air can escape. This greatly facilitates the
total withdrawal of the air and causes the bag to exert
uniformily distributed pressing force on the entire
surfaces of the glass sheets so that breakage of the glass
SPG 75206
:121~3
--5--
1 and the presence of air bubbles in the completed product
are minimized.
While the invention is not restricted to use of glass
fiber cloth of any specific weave, it has been found that
the glass fiber cloth supplied by J.P. St~vens & Co. of New
York under ~o. 7628/38 performs very well in practice.
This glass cloth weights 6.00 oz. per square yard, has a
thickness of .0065 inch, and a thread count of per square
inch of 44 warp and 32 fill. The thickness of the
silicon-rubber coating is in the neighborhood of .010 inch,
with the overall thickness of the coated bag being about
.017 inch.
It will be understood that the specific thicknesses,
temperatures and pressures given above are by way of
example only and that variations thereof may ~e resorted to
without departing from the spirit of the invention or scope
of the claims.
