Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates generally to a
method and apparatus for applying a layer of plastic
material to a glass sheet and, in particular, to a method
for producing an anti-lacerative window assembly for use in
automotive vehicles.
It has been found that the addition of a plastic
layer bonded to the inboard glass surfase of a conventional
laminated windshleld can further increase the safety
effec~iveness of the windshield. This plastic layer has
typically been termed an anti-laceration shield since it has
been found that the additional plastic layer will
appreciably reduce the number and severity of lacerative
in~uries to persons thrown against the windshield under all
impact conditions. Further, it has been found that the
anti-laceration shield, when produced under certain
conditions of manufacture, improves the ability of the
laminated windshield to decelerate movement of a person
thrown against the windshield, while also increasing the
penetration resistance of the windshield as compared to
conventional laminated windshields. Also, the laceration
shield reduces the amount of fly~ng glass and thus the
in~ury to car occupants as a result of objects that may be
thrown against the windshield from overpasses or elsewhere
outside the vehicle.
An example of one type of anti-lacerative
windshield is disclosed in United States Patent No.
4,242,403. In this patent, the laceration sh~eld includes a
penetration resisting multi-layer body consisting of an
inner layer of relatively soft, extensible plastic material
Sr~
such as polyvinyl butyral, which is adhered to the inboard
surface of the windshield, an intermediate layer of more
durable plastic such as polyester, and an outer coating of
an abrasion resistant material. Another type of
anti-lac~rative windshield is disclosed in United States
Patent No. 3,808,077 wherein a single layer of polyurethane
is utilized as an anti-laceration shield.
While the effectiveness of a laminated windshield
having an anti-laceration shield is obvious, very few
vehicles utilize such a windshield. The chief reason for
this limited use has been the difficulty experienced in
trying to manufacture a windshield with an anti-laceration
shield on a production basis. In the automotive industry,
the standard for windshields is very high, especially as to
optical qualities, and it has been very difficult to
manufacture a windshield having an anti-laceration shield
which is free of optical defects. Even when the individual
sheets of the laminated assembly are free from optical
defects before bonding them together, it is difficult to
~oin them and preserve the optical qualities.
The present invention concerns a unlque method for
producing an anti-lacerative glass assembly. The initial
step involves assembling a glass substrate sheet having a
predetermined curvature, an anti-laceration sheet and a
glass cover sheet having substantially the same curvature as
a glass substrate sheet into a stacked arrangement. In the
preferred embodiment of the invention, the anti-laceration
sheet is a plastic composite sheet which includes an inner
layer of polyvinyl butyral adapted to abut the glass
substrate sheet, an intermediate layer of polyester, and an
outer layer of an abrasion resistant material adapted to
abut the gla~s cover sheet. Once the stacked arrangement of
individual laminae have been assembled, a vacuum ring is
placed about the peripheral edges of the laminated glass
assembly and is coupled to a vacuum source to de-air the
assembly and urge the individual laminae toward one another.
Next, the assembly is placed in an autoclave unit
wherein the laminated glass assembly is heated to a
predetermined temperature in the range of 285~ F to 305 F,
while simultaneously pressure is applied to the exterior
surfaces of the laminated assembly. It has been discovered
that, when a plastic composite anti-laceration sheet of the
type described above is utilized, the autoclave bonding
temperature is very critical. For example, the autoclave
temperature must be sufficiently high to enable the
intermediate polyester layer to properly bond to the inner
polyvinyl butyral layer, and the temperature must be
sufficlently low to prevent crazing of the abrasion
resistant coating~
Once a predetermined temperature and a
predetermined pressure have been reached in the autoclave,
these levels are maintained for a predetermined time period.
At the end of this time period, the temperature in the
autoclave is reduced while the pressure is maintained at the
predetermined level. After the temperature has fallen below
a predetermined point such as 125 F9 the pressure then can
be reduced, and the laminated assembly can be removed from
the autoclave.
The present invention also concerns the use of a
vacuum ring having a unique construction. The vacuum ring is
provided with a check valve means such that the vacuum ring
can be disconnected from a vacuum source while mainta1ning
~2~3~
the vacuum within the ring. If desired, the vacuum ring can
then be reconnected to the vacuum source.
The method of the present invention can further
include the step of, subsequent to producing an
anti-lacerative glass assembly, removlng a selected portlon
or portions of the anti-laceration sheet from the glass
substrate sheet to define an exposed glass surface which can
be used either to mount the windshield within an associated
frame, or to mount a rear view mirror assembly.
Alternatively, the invention concerns th~ use of a
unique cover sheet utilized to position the anti-laceration
sheet in a selected position on the glass sheet to wh~ch the
anti-laceration sheet is to be bonded.
According to the present invention, there is
provided a method of producing an anti-lacerative glass
assembly comprising the steps of:
a) assembling into a stacked arrangement
individual laminae including a glass substrate sheet
having a predetermined curvature, a plastic composite
anti-laceration sheet having one surface abutting the
glass substrate sheet, and a glass cover sheet having
substantially the same curvature as the glass substrate
sheet and abutting the opposite surface of the
composite anti-laceration sheet, thereby producing a
laminated glass assembly, the plastic composite
anti-laceration sheet including an inner layer of
polyvinyl butyral adapted to abut the glass substrate
sheet, an intermediate layer of polyester, and an outer
layer of an abrasion resistant material adapted to abut
3~ the glass cover sheet;
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b) urging the individual laminae of th~ glass
assembly toward one another;
c) simultaneously with step (b), heating ~he
laminated glass assembly to a predetermined temperature
ln the range o~ 285F to 305~, for a predetermined
period and then subsequently reducing the temperature,
said predetermined temperature being sufficiently high
to cause the intermediate layer of polyester to bond to
the inner layer of polyvinyl butyral and to cause the
inner layer of polyvinyl butyral to bond to the glass
substrate sheet and being sufficiently low to prevent
crazing of the abrasion resistant coating; and
d) removing the glass cover sheet from the
laminated glass assembly to produce the anti-lacerative
glass assembly.
Also9 according to this invention, there is
provided an apparatus intended for use in bonding a plastic
sheet to a glass substrate sheet having a predetermined
curvature and having an outer periphery larger than the
perlphery of the plastic sheet, comprising: a glass cover
sheet havlng substantially the same curvature as the glass
substrate sheet and adapted to abut an outwardly facing
surface of the plastic sheet, said glass cover sheet
lncluding a positioning means located on one surface thereof
for positioning and maintaining at least a portion of the
marginal edge of the plastic sheet in inwardly spaced
relationship relative to the marginal edge of the glass
substrate sheet, said positioning means adapted to sealingly
contact the glass substrate sheet to prevent the plastic
sheet from flowing across and bonding to a predetermined
portioll of the marginal edge surface of the glass substrnte
33~
sheet contacted by said positioning means during the bonding
operation.
In the accomanying drawings:
Fig. 1 is a rear elevational view of a laminated
window assembly produced by the method of the present
invention;
Fig. 2 is a fragmentary sectional view taken along
the line 2-2 of Fig. l;
Fig. 3 is an enlarged sectional view taken along
the line 3-3 of Fig. 2 and illustrating the individual
laminae which comprise the plastic composite anti-laceration
sheet;
Fig. 4a is a fragmentary sectional view
illustrating the individual laminae which comprise the first
sub-assembly utilized in the method of the present
invention;
Fig. 4b is a fragmentary sectional view
illustrating the individual laminae which comprise the
second sub-assembly utilized in the method of the present
invention;
Fig. 5 is a plan view of the laminated glass
assembly having a vacuum ring attached thereto which is
utilized to evacuate any air spaces between the individual
laminae;
Fig. 6 is a fragmentary sectional view taken along
the line 6-6 of Fig. 5 and illustrating the laminated glass
assembly having the vacuum ring positioned about the
peripheral edge thereof; and
Fig. 7 is a diagram illustrating the preferred
pressure-temperature sequence wh$ch occurs during the
autoclave operation.
It should be noted at the outset of this
descrlption that, whlle the embodiment of the invention
illLlstrated in the drawings and described herein concerns an
anti-lacerative window assembly consisting of two laminated
sheets of glass, it will be appreciated that the method and
apparatus of the present invention can readily be adapted to
produce an anti-lacerative window consisting of a single
sheet of glass. Also~ while the preferred embodiment of the
invention is described as a vehicle windshield, it will be
appreciated that the anti-lacerative window can also be used
as a side or rear vehicle window, or as a window in other
types of safety applications.
Referring to Figs. 1 through 3, there is shown one
type oE laminated glass assembly, such as an automotive
windshield 10, which can be produced by the method of the
present invention. The windshield 10 includes two sheets of
glass 12 and 14 which are bonded together by means of a
plastic interlayer 16 positioned therebetween. The plastic
interlayer 16 is typically a sheet of relatively soft
extensible plastic material in the range of 0.025 to 0.040
inch thick and capable of being bonded to a glass surface.
In the preferred embodiment of ~he invention, the plastic
interlayer 16 is a sheet of polyvinyl butyral approximately
0.030 to 0.0375 inch thick. Also, the glass sheets 12 and
14 are preferably sheets of float glass, in thicknesses in
the range of 0.070 inch to 0.125 inch. In ~he preferred
embodiment of the invention, the glass sheets 12 and 14 are
approximately 0.100 inch thick. IE a single ply
anti-lacerative window is to be produced, the single sheet
of glass is typically in the range of 0.090 to 0.150 inch
thick.
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Additionally, the glass sheet 14, which is
adapted to face the interior of the vehicle, has a plas-
tic composite anti-laceration sheet 18 bonded to the in-
board glass surface 14a. As shown in the enlarged sec-
tional view of Fig. 3, the anti-laceration sheet 18 is a
three layer composite sheet comprising a layer 20 of a
relatively soft extensible plastic material, a layer 22
. of a more durable plastic material, and an outer CQating
or layer 24 of an abrasion resistant plastic material.
In the preferred embodiment of the invention, the soft
extensible plastic layer 20 is approximately 0.015 inch
thick and can be polyvinyl butyral, for example, while
the more durable plastic layer 22 is approximately 0.002
to 0.007 inch thick and can be a heat treated polyester,
for example. if a single ply anti-lacerative window is
to be produced, the inner layer of polyvinyl butyral is
typically 0.030-0.045 inch thick.
The abrasion resistance coating 24 is relative-
ly thin as compared to the layers 20 and 22 and can be
cured, organopolysiloxane compound reinforced with silica.
More specifically, the plastic layers 20 and 22 and the
abrasion resistant coating 24 may be of the types des- ~
cribed in United States Patents 3,900,673; 4,059,469;
4,112,171; 4,177,315; and 4,242,403. A plastic composite
anti-laceration sheet of the type utilized in the prefer-
red embodiment of the invention is available from the
E.I. Du Pont De Nemours and Company, Wilmington, Delaware,
U.S.A.
As previously mentioned, the present invention
concerns a unique method for producing a laminated glass
! assembly of the type as illustrated in Figs. l through 3.
In the method of the present invention, the individual
3~*
laminae which comprise the laminated assembly are first
assembled in two separate sub assemblles. The flrst
sub-assembly 26, illustrated in Fig. 4a, comprises a stacked
arrangement which includes the pair of glass sheet 12 and 14
having the plastic interlayer 16 positioned therebetween.
The second sub-assembly 28, illustrated in Fig. 4b, includes
the plastic composite anti-laceration sheet 18 which is
placed on a surface 30a of a glass cover sheet 30 having
substantially the same curvature as the glass sheets 12 and
14. The composite anti-laceration sheet is placed on the
cover sheet 30 such that the abrasion rèsistance coating 24
abuts the surface 30a. Typically, the cover sheet 30 is
formed of a sheet of float glass. As will be discussed, the
cover sheet 30 is utilized to produce a laminated glass
assembly of high optical quality by assisting in bonding the
anti-laceration sheet 18 to the outer surface 14a of the
glass sheet 14.
It has been dlscovered that, in producing an
anti-laceration windshield of the type shown in Figs. 1
through 3, it is desirable that the anti-laceration sheet 18
not cover selected portions of the inboard glass surface 14a
such that those selected portions provide an exposed glass
surface. For example, in Fig. 1, the marginal edge of the
laceration sheet 18 is spaced inwardly from the marginal
edge of the glass sheet 14 to define a peripheral edge
portion 14b having an exposed glass surface. It has been
discovered that such an exposed glass surface is desirable
when mounting the windshield in an associated vehicle frame,
since the adhesives typically utilized to secure the
windshield within the frame have been found to adhere more
readily to a glass surface than to the plastic surface of
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the anti~laceration sheet. Also, in Fig. 1, a circular
cutout is provided in the anti-laceration sheet 18 to define
a circular portion 14c havlng an exposed glass surface. The
circular portion 14c can be utllized for securing a rear
view mirror mount assembly to the windshield.
In addition to providing a better adhesive
surface, the selected exposed glass surfaces also provide
other advantages. For example, in the event a windshield
must be temporarily removed from the vehicle, or a mirror
mount must be replaced, any damage to the anti-laceration
sheet is avoided. Also, if the vehicle window frame or the
mlrror mount was adhered directly to the anti-laceration
sheet, any separation of the frame or mirror mount from the
windshield tends to separate the anti-laceration sheet from
the glass substrate sheet, thereby causing distortion in
those areas.
While the anti-laceration sheet 18 can be bonded
to the entire glass surface 14a, and selected portions of
the laceration sheet can subsequently be removed from the
glass surface 14a to provide the selected exposed glass
surface portions 14b and 14c, the removal of selected
portions of the anti-laceration sheet can be a relatively
time consuming task and can effect damage to the glass
substrate sheet. Preferably, the anti-laceration sheet is
initially precut to predetermined dimensions such that, when
the anti-laceration sheet is properly positioned and bonded
to the glass sheet 14, the selected portions of the glass
surface 14a will remain exposed and there is no need for any
subsequent trimming and removal of portions of the
anti-laceration sheet.
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In order to assist in positioning the anti-laceration
sheet 18 on the glass surface 14a, the method of the present
invention utilizes a cover sheet 30 of a unique design. More
specifically, the glass cover sheet 30 of the present invention
includes a positioning means such as a dam or gasket 32, for
example, which is secured about the peripheral edges of the
surface 30a to define a boundary within which the anti-
laceration sheet 18 is to be placed. The gasket 32 is
constructed of a resilient material having a thickness
approximately equal to the overall thickness of the anti-
laceration sheet. While the gasket 32 can be constructed of
cork, silicone, fiber-reinforced silicon, or rubber, it has
been found desirable to construct the gasket of Teflon*.
Typically, the surface of the Teflon* gasket which is to be
secured to the glass surface of the cover sheet is specially
treated to assist in the adhesion of the gasket to the cover
sheet. It has been found that a conventional epoxy provides
a suitable means for securing the Teflon~ gasket to the glass
surface.
The location on the cover sheet surface 30a to which the
gasket 32 is secured corresponds to the peripheral edge portion
14b on the glass surface 14a which is to remain exposed. In
addition to the peripheral gasket 32, a circular gasket 34 is
secured to the surface 30a at the location corresponding the
exposed circular portion 14c for the mirror mount assembly.
Thus, in the preferred embodiment of the invention, the plastic
composite anti-laceration sheet 18 is precut to dimensions
which enable the sheet l~ to be placed on the cover sheet
surfac~ 30a within the boundary of the peripheral gasket 32.
MoreoverJ as shown in Fig. 4b, a circular cutout portion 18a
~ Trade mark of E.I. Dupont de Nemours ~ CoO
LCM:jj 11
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is provided in the anti-laceration sheet at the location
corresponding to the circular gasket 34.
It has been found that, prior to placing the
anti-laceration sheet 18 on the surface 30a of the glass
cover sheet 30/ it is desirable to apply a release agent to
the surface 30a to enable the cover sheet 30 to be easily
removed from the anti-laceration sheet after the
anti-laceration sheet has been bonded to the glass sheet 14.
- While the release agent can be a conventional silicone wax,
it is preferable to utili~e a silane having the formula
R -Si(OR)4 wherein R is an alkyl group and n is a number
from 1 to 3. In this connection, good results have been
obtained with the use of an alkyl-trialkoxy silane and
particularly n-propyl-trimenthoxy silane, and
dialkyl-dialkoxy silanes, particularly diethyl-diethoxy
silane.
After the two individual sub-assemblies as
illustrated in Figs. 4a and 4b are produced, the two
individual sub-assemblies are assembled to produce a
laminated glass assembly whereln the polyvinyl butyral layer
of the anti-laceration sheet 18 of the second sub-assembly
28 abuts the outwardly facing glass surface 14a of the first
sub-assembly 26. Prior to assembling the two
sub-asse~blies, it is preferable to apply a primer to the
outer glass surface 14a to assist in bonding the
anti-laceration sheet 18 to the glass sheet 14. The primer
can be a silane solution which includes 0.5 to 3% by volume
of silane in a solvent such as isopropyl alcohol. The
silane can be gamma-aminopropyltriethoxysilane which is
available from Union Carbide Corporation, Danbury,
Connecticut, U.S.A. under the trade designation A-1100.
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After the first and second sub-assemblles have
been positioned together to form the laminated glass
assernbly, the air spaces betwsen the individual lamlnae are
evacuated to urge the individual laminae toward one another.
This can be accomplished by positioning a vacuum ring 36, as
shown in Figs. 5 and 6, about the peripheral edge of the
laminated glass assembly. The vacuum ring 36 dcfines an
interior chamber 36a in communication with a flexible
conduit 37 which is adapted to be coupled to a vacuum source
(not shown). The vacuum ring 36 can ~e constructed of
silicone or neoprene3 for example.
The method of the present invention utilizes a
vacuum ring having a unique construction. More
specifically, the vacuum ring is provided with a
quick~disconnect coupling 38 having a check valve means
incorporated therein. Such a coupling is commercially
available from Crawford Fitting Co. of Solon, Ohio, U.S.A.,
as Part No. SS-QC-4-D-4HC. After the vacuum ring 36 has
been positioned about the laminated glass assembly and
coupled to a vacuum source for a predetermined period of
time to de-air the assembly, the vacuum ring can be
disconnected from the vacuum source, and the check valv~
means will continue to maintain the vacuum in the chamber
36a.
The laminated assembly having the vacuum ring
attached is then placed in an autoclave unit (not shown)
which is designed to apply pressure to the exterior surfaces
of the laminated assembly, while simultaneously heating the
entire laminated assembly to a predetermined temperature to
cauge the plastic interlayer 16 to bond to the pair of glass
sheets 12 and 14 and ~o cause the PVB layer of the
anti-laceration sheet 18 to bond to the surface 14a of the
glass sheet 14. In the event a plastic composite
anti-laceration sheet of the type shown in Fig. 3 i8 used,
the autoclave operation also causes the intermediate
polyester layer 22 to bond to the inner polyvinyl butyral
layer 20. While in the autoclave, the vacuum ring 36 can be
connected to the vacuum source to maintain the vacuum within
the chamber 36a during the bonding operation.
Typically, the pressure in the autoclave is in the
range of 20~ to 275 psi, while the temperature is in the
range of 250 F to 325 F. This temperature and pressure
are typically maintained for approximately twenty to thirty
minutes to assure an effective bonding between the
individual laminae.
It has been discovered that, in the event a
plastic composite anti-laceration sheet of the type shown in
Fig. 3 is used, the autoclave bonding temperature is very
critical. For example, the autoclave temperature must be
sufficiently high to enable the intermediate polyester layer
22 to properly bond to the inner polyvinyl butyral layer 20,
and the temperature must be sufficiently low to prevent
crazing of the abrasion resistance coating 240 It has been
found that an autoclave temperature in the range of 285 F
to 305 F provides satisfactory results. For optimum
reeults, a temperature of approximately 295 F should be
used.
Fig. 7 illustrates a time diagram of the preferred
temperature/pressure sequence for the autoclave bonding
operation of an anti-laceration window assembly utilizing
the composite anti-laceration sheet of Fig. 3. As shown Ln
Fig. 7, after the laminated assembly has been placed in the
37~
autoclave and the autoclave has been sealed, the pressure
and temperature is increased until the pressure reaches 250
p.s.i. and the temperature reaches 295 F. The pressure and
temeprature are then maintained at these levels ~or
approximately 25 minutes.
After the 25 minute period, the temperature is
reduced while the pressure is maintained at 250 p. 8 .i. to
ensure that the surface 30a of the cover sheet 30 is
maintained in complete contact with the anti-laceration
sheet. Otherwise 9 reducing the pressure before the
laminated assembly has sufficiently cooled can cause the
cover sheet to pull away from the anti-laceration sheet in
certain areas, thereby causing increased distortion in those
areas. After the temperature has fallen below a
predetermined point, the pressure can then be reduced, and
the laminated assembly can be removed from the autoclave.
It has been found that allowing the temperature to fall
below 125 F before reducing the pressure provides
satisfactory results.
After the laminated assembly has been removed from
the autoclave, the vacuum ring 36 is removed. Next, the
cover sheet 30 can be removed from the laminated assembly
such that the remaining portion of the laminated assembly
constitutes the anti-laceration windshield 10 of Fig. 1.
In accordance with the provisions of the patent
statutes, the principle and mode of operation of the present
invention have been illustrated and described in what is
considered to represent the preferred embodiment. ~owever,
it should be understood that the present invention can be
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practiced otherwise than as specifically illustrated and
described wlthout departing from the scope of the following
claims.
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