Note: Descriptions are shown in the official language in which they were submitted.
~L~59~373
Various glass bending techniques have been developed
in recent years to accommodate the numeroua~ gla~is con~lgurations
incorporated in ~he design of automobiles, such as the commcnly
referred to "cap" and~"wrap-around" windshields and backlights.
Sometimes it i~ desirable ~o shape or form the glass compatible
wl~h Ftyling features~found ln the ad~acent sheet metal panel '
in or'der to create the appearance of unity between the gla58
and the sheet metal. By wsy of example, it may be desirable to ~ I
provide a generally vertically extending sharp bend in a wlnd-
. . . ., ~ 10 shield or backlight in continuation of a bead or molding strip
on, the surface ~f the hood, roof panel or deck lid. At time~
' it~may al~o be des,irable to form a aharp bend in either a hori-
zontal or vertical direction to effect wrap-ar,ound of the wind-
ahield or backlight into the roof line of the vehicle or the
' sidé surfaces thereof. The formation of,~uch bend~, i.e.,
"~ Y-sha~ped bends'or bends having very ~mall radii of curvQtures,
pose pro'blems in fabrication.
The glass bending methoda disclosed and clalmed in
Uni~ed States patent~ No~. 3,762,903 and 3,762,904, provided a
', 20 solution to thes~ problem~ by utillYing an improved method for
~ angularly bandin~ one or more glas~ ~heet~ a~ a relatively ~harp
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~L~5~23'73
angle wiehOut adversely affectlng or dlstorting portions of the
glass ad~acent the bend. To this end, an electrically conduct-
ing path is formed on at leasL one surface of the glass sheet
along a line about which lt i8 desired to bPnd the sheet. Subse-
quently, an electrical potential is applied acro~s such path of
a sufficient magnitude and for a time adequate to heat the sheet
in the area immediately ad;acent said path to a temperature
above the bending point of the glass, causing the glass sheet to ~ ~ ;
bend along the line of the electrically conducting path to form --
the desired relatively sharp angle therein,
The electrically conducting path i8 formed by apply~
ing to a~ least one surface of the glass, a conductive metallic
paste, such as a silver paste material, along the line about
which the bend is desired. While such a silver paste provides
an efficlent electrically conductive path to provide the neces-
sary localized heat~ng at the V-shaped bend, it adheres to the
finished bent glass as an integral part thereof in the form of
an elongated narrow stain or line having a yello~-brown appear-
ance. This yellowish-brown stain is ob~ectionable from the
standpoint of design and aesthetics) often presenting a harsh
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contrast to the color or combination of colors employed on the
automobile body, roof, etc., to detract from the general appear-
ance thereof.
It i8 accordingly, an ob~ect of the pre~ent invention ;~
to provide a method for altering the appearance of the residual
stain normally remaining along the relatively sharp angular bend
in~a glas~ sheet as a result of the fusing of the electrically
conductive metallic paste to the glass sheet initially applied
thereto for localized heating.
:
It i8 another obJect of this invention to interpose
an undercoating of a coloring agent between the glass sheet sur-
face and the foregoing electrlcally conductive paste material to
alter the color of the resldual stain resulting from the fusion
of the electrically conductive paste material to the glass sheet.
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It Ls a further obJect of the present invention to
provide an undercoating for the foregoing electrically conductive
paste material to preclude adherence of the latter to the glas~
interface. ~ ~
According to the present invention, there is provided ~ -
a process for treating a glass sheet adapted to be bent to a
relatively sharp angle, characterized by applying a band of
coloring agent to at least one surface of the sheet along the
line about which it i8 desired to bend the sheet, superimposing
an electrically conducting path on said band lengthwise thereof
heating the sheet to a temperature above the strain point of the
glass but below the bending temperature thereof to fuse the
coloring agent and electrically conducting path to the glass, `
and applying an electrical potential across said path of a suffi~
cient magnitude and for a time adequate to heat the sheet in the
area immediately adJacent said path to a temperature above ~he -
bendlng point of the glass causing said sheet to bend along said
line and forming a stain ~herealong of desired appearance. -
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In the accompanying drawings: -
~'~ Fig. 1 is a perspective view of an automobile includ-
ing a bent glass back window or backlight produced in accordance
i with the present invention;
i Fig. 2 is a perspective view of the backlight illus-
trated in Fig. l; i~
j Fig. 3 is a sectional view taken along the line 3--3
- o~ Fi8. 2, showing the application oE an undercoa~ing beneath
¦ the electrically conducting path formed on the inner gurfsce of
the backlight; '
Fig. 4 is a perspectlve view ~howing a glass sheet
in position on a mold prior to initiation of the bending process;
- Fig. 5 iB a sectional view taken along the line 5--5
of Fig. 4; and
Fig. 6 is a sectional view showing the glass ~heet
supported on the mold upon the conclusion oE the bending proces~.
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11~5~373
~eferring now in detail to the illustrative embodiment
depicted in the accompanying drawing, there is shown in Fig. 1,
a backligh~ 10 constructed in accordance with this invention as
it appears from the outside of an automobile 11 in ~hich the
backlight is mounted. The backlight 10 i9 comprised of a single
glass sheet 12 of V-3haped configuration, belng bent along a
straight line path indicated generally at 13 extending from one
longitudinal edge sf the glass shee~ to the other, intermediate
of and parallel to ~he transverse edges. The path or axis of
the bend is defined by a fired electrically conducting frit line
14, hereinafter described in detail. While it will be conven-
ient to de~cribe the method of this invention in connection with
the formation of the backlight 10, lt should b~ understood that
the principles o~ this invention are equslly applicable in the
production of multiple layered sheets of glass, such a8 in the - ~ ;
conventional laminated construction of a windshield ~or example,
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which generally comprises two sheets of glass and a non-brittle
thermoplaatic interlayer, all bonded together to form an inte-
gral 8 tructure.
The glaaa sheet 12 can be bent upon a ring or skeleton
type mold indicated generally at 15 in Figs.~ 4 and 6. Molds of
., ~
this type are conventionally used for the bending of glass and
have a peripheral rail 16, the top edge of which forms the shap- -
ing surface for forming the gla~s. In ~ccordance with pre~ent-
day practice, the rail 16 may be either a substantially single
piece s~ationary member, as shown, or formed of articulated ~ec-
tions which are moved during the bending of the glasa from an
open glass recei~ing position to a closed~ flnal position.
Prior to po~itioning the glsss sheet on the bending
30 ~ mold 15, the electrically conducting frit line or re2istance
el~ment 14 can be formed thereon in accordance with the method
set forth in United States patent No. 3,762,903. If desired, a
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~L~5~37~
groove may be formed in one or both surfaces of the glass sheet
12 along the line of the sub~equent bend to facilita~e the bend-
ing operation as set forth in detail in United States patent No.
39762,904, and the electrically conducting frit line 14 may then
be formed in such~groove. While various materi21s m3y be u~ed
to form these electrically conducting paths or resistance heat-
ing element~ 14, preferred compositiona are compri~ed of con-
ductive metal pa~tes. The~e materials, sometimes 8190 referred ?
i to a9 inks, are applied to the gla5~ sheet by conventional silk
screen processes, painting, or other conveDtional uniform c03t-
ing method~ and then are heated or fired to fuse the moterial to
the sheet.
Typically, the paste3 compri~e conductive metal par-
ticles, e.g., silver, glas~ f~it particles and organic binder~
and solvent. The glass frit, in addition to fusing the heating
elements or strips to the sheet, al30 serves as an extender by
~ which the desired conductivity or resistivity ~ 8 achieved in the
- paths or element~ 14. Thus, for a given cro~s sectional area
of the elements, the silver, which imparts electrical conductivity
thereto, can be diluted or extended with the glass frit to attain
~f, ' the deslred resistance which in turn determines the heat devel~
oped in the paths and glass immediately ad~arent thereto.
Although the conductive silver pa3tes are ideally
suited for forming the electrically conducting paths, other
conductlve metal pastes may be used, e.g., tho~e containing
- gold, palladium, platinum and alloy~ thereof. In addition, air
drying dispersions of conductive metals may be employed. One
par-ticular material of this type which has been u~ed 3ucces~fully ~;~
is "Dag 422", a di~persion of silver plus graphite in a water
carrier obtained from the Acheson Colloids Company, Port Huron,
Michigan, U.S.A. Al~o, materials auch as electrically conduc~-
ing t3pe~ which may or may not be removed after the bending
step can be employed.
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lOS43'73
After the electrically conducting llne or resi3tance
element 14 has been satisfactorily laid down, the glas~ sheet 12
~s positioned on the bending mold by supporting the ~ransverse
edges of the sheet on a shaping surface of the mold (Fig. 4).
Leads 17 and 18 from a suitable electrical power source (not
shown~ are then placed in electrical contact with the line 14
through alligator cllps or the like 19 and 20, respectively,
(Figs. 4 and 5).
Prior to supplying power to the leads 17 and 18, the
bending mold and glass sheet carried thereby are preferably ~ ~
heated to a relatively high temperature, for example, above the ~ -
strain point of the glass but below the bending point or the
temperature at which the glass bends to any significant degree.
In this respect, temperatures in the range from approximately
900F. to 1150~. have been found satisfactory. The purpose
of this preliminary heating, whlch may be accomplished by con-
veying the mold through a furnace, is to fuse the metal-glass
frit suspension to the glass, prevent the formation of permanent
stresses in the glass, obviate the tendency of the glass to - ;
crack when subsequently heated locally along the electrically
conducting line 14 to its bending ~emperature, and also to -~ ~
enable the accomplishment of this latter step within a time ~ ~ -
acceptable frsm a commercial standpoint and wlth the use of a
reasonable amount ~f electrical energy.
Upon the glass sheet reaching the desired over-all
temperature, power is supplied to the leads 17 and 18 and con-
sequently ~o the resis~ance element 14. This ln turn heats the
glass sheet immediately adjacent resistance element 14 to a tem-
perature above the bending temperature of the glass, for example,
above approximately 1200F., at which time the sheet bends
sharply along the path 13 and settles by gravity into the gen-
erally V-shaped configuration illustrated in Fig. 6. The sheet
is then allowed to cool at room temperature.
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1~5~373 ~ -
A8 a result of the preheating of the glass sheet
prior ~o the application of power ~hrough the elec~r~cally
conducting path, thP silver paste material forming the latter
adheres to the glass sheet and forms an objectionable
yellow-brown stain thereon extending longitudinally of the bend.
It is desirable that such stain be at least altered to obtain a
color pattern less ob~ectlonable from the standpoint of aesthet~
ics and more compatible with the color combinations of the auto-
mobile body so as to enhance the general appearance of the auto-
~, ...
mobile.
It has been found that the application of a suitablecoloring agent as an undercoating or substrate for the electrical-
ly cDnducting silver paste material serves to alter the residual
silver stain sufficiently to yield a more compatible color wlth
automobile body design requirements. To this end, and in ac-
cordance with this invention, prior to forming the electrically -
conducting path or resistance element 14 on the glass surface9 a ;;
coloring agent is applied to at least one surface of the glass
sheet 12 along a strip or band 21 ~Fig. 3) upon which the elec- ;~
trically conducting path will be formed and about which it is
desired to bend the shee~. Whlle various materlals, such as
blue, red and green pigments and various shades the~eof, may be
used to form this undercoating, preEerred compositlons comprise ~
pure black pigments and mixtures of pure black pigments and black - ; ;
enamels, i. e., black pigments containing a minor percentage of
frit. These materials can be applied ~o the glass sheet surface ;~
by conventional silk screen processes, painting or other known
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roating processes and then allowed to dry at room temperature.
A preferred specific coloring agent, which has yield-
.: . .
ed good results, is a fritless, pure black pigment composition
sold by Drakenfeld Company, a division of Hercules Incorporated, ~-
Washington, Pennsylvania, U.S.A., under the designation of
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59~3~73
Drakenfeld 1795 Black which i~ a composition comprised of ap-
pro~imately 30% by weight of chrome oxide, 32% by weight of
cobalt oxide, and 382 by weight of iron oxide. Thls composition
is employed in an oily mixture of pine oil and resln sold under
the tradename of Drakenfeld 900 to form a mixture designated
"Drakenfeld 1795 Black Oxlde in 900 Oil".
AB a specific example of altering the residual stain
remaining along the Y-shaped bend in a ~inlshed glass sheet as
a result of the firing of the conductive metallic paste initial-
ly applied thereto for localized heating in accordance with the
method of this invention, a glass sheet of nominal 0.235 inch
thickness was procured. A uniform coating of a fr~tless pure
black pigment, such as that referred to above as Drakenfeld ;~
1795 Black Oxide in 900 Oil, was applied by a silk screen print-
ing process in a band or strip having a width of one-half inch
to one surface of the glass sheet along the line abou~ which the ; ~;~
glass sheet was to be bent, the band ex~ending in~ermediate the
opposite edges of the sheet and parallel thereto. After the `
band of pigment dried at room temperature, a silver composition
comprised of abou~ 85% by weight of conductive silver particles,
and the remainder composed of solvent, binder and frit, marketed
by E. I. duPont de Nemours and Company, Wilmington, Delaware,
U.S.A., under the designation "8966", was then superimpo3ed in ~ ;
a width of .120 inch on the band of black pigment lengthwise
thereof by a conventional silk screen printing process.
This sheet was supported at the two opposite or
transverse edgee only on a mold and heated in a furnace set to a
temperature of 1150F. During this heating, the finely divided
metal ceramic frit fused onto tha glass surface. The glass and "
integral frit line were then allowed to cool to room temperature
and electrical connections such as those shown in Figs. 4, 5 and
6 were made to the frit line and the mold supported sheet again
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~L~54373
placecl in the furnace and heated to a temperature of 1150F.
When this temperature was obtained, electrical energy was sup-
plied to the frit line, and more particularly, a current of 16
ampere~ was passed therethrough. This current was supplied for
approximately one minute at which time the sheet had assumed a
generally V-shaped appearancP, the bend occurring at and along
the frit line or electrically conducting element 14. The sheet
was then removed from the. furnace and cooled quickly to produce
a tempered structure. ~;
It should be noted that it is not nece~sary that the
sheet be allowed to cool down aEter firing of the frlt and then ;
reheated for the bending operation. The electrical connections
may be made prlor to the firlng step, which firing step can be
accomplished during preheating of the sheet to fuse the metal-
ceramic frit onto the glass surace.
After the finished glass sheet had cooled sufficient~ ~ ~
ly, only that por~ion of the black oxide pigment directly beneath -~ -
the silver paste material, indicated at 21a in Flg. 3, adhered
to the glass surface and the remainder, shown in dotted outline,
was readily removed as by wiping, for example. This yielded a ~ -
glass sheet product having a long, relatively narrow line along
the sharp bend which appeared white on the surface to which the
electrically conductive paste material was applied and black on
the opposite surface, i.e., the glass side of the sheet O Also , . -'
it was found that vigorous rubbing would remove all traces of
the silver paste material, even though it initially contained ;
glass frit~ resulting in a line which appear~d black when view0d
~: .
from both sides of the finished glass product and is especially
desirable in some applications.
Since the coloring agent di~posed outwardly of the
marginal edges of the frit line is easily removed, the strip 21
- of coloring agent can be quickly applied in a relatively wide
band without special regard to lndexing, i.e., accurate alignment
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~II;IS~373
of its marginal edges with those of the subsequently applied
re~istance elen-ent 14. Thls saves time and becomes especially
advantageous in a ma3s production operation.
Another conductlve paste material which was success-
fully employed in combination with the pure black pigment des-
cribed above was a fritless, conductive silver paste preparation
comprlsed of approximately 85% by weight of silver pal;ticles,
the remainder consisting of a suitable solvent and binder,
marketed by E. I. DuPont de Nemours and Company under the desig-
10 nation "9105". It wa~ found that the utilization of a fritless
silver paste material a~ the electrlcally conductive path 0n-
ables the residual ~ilver stain ~o be completely removed, thu~
leaving only a black line visible on the opposite surfaces of
: the finished gla~s product, which ha3 beeD found desirable in
many design applications.
While the pure black oxide pigment de73cribed above
i9 preferable, it should be understood that the black pigments
:,
containing frit can be successfully employed as colorln~ agents
in carry~ng out the method of the pre~ent invention. One such
.
`~ 20 coioring agent is available under the tradename "Drakenfeld
24-339" in 175 oil. This is a black pigment -- glass frit com-
positlon or enamel containing approximately 10% by weight of
gla~s frit. The Drakenfeld 24-339 composi~tlon and Drakenfeld
1795 pure black pigment composition were blended in the follo~7-
ing ratios: 10/90; 25t75; and 50/50. These blended compo~ttions
~, , .
were applied, such a7 by suitable F7ilk screen prlnting proces3e3
for example, in a one-half inch wide band acros77 the gla373 sheet.
After beine dried at room temperature, a silver paste prepara-
- tion, identified a3 duPont "8966'7~ W~8 superimposed on the band
.: . .
30 as a line llaving a width of .120 inch extending lengthwis2 of
the band
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~C~5~373
After firing the electrically conductive material to
effect the relatively sharp bend as de~cribed above, it was
found that the 10/90 a~d 25/75 mixtures fused to the gla~ only
in the area beneath ~he electrically conductive path as defined
by the silver paste material. The excess of the 10/90 mixture,
i.e., those portions disposed outwardly beyond the marginal
edges of the silver paste line could be readily removed, as by
wiping for e~ample, while removal of the ex~ess 25J75 mixture
required slightly more effort. In both instances, the sllver
electrically conductive material adhered to the glaa8 surface
which appeared as a black line when viewed from the glass alde,
l.e., the surface opposite of that to which the electrically
conductive mate~ial was applied and white when viewed from the
opposite side oi the gla~s. -~
All of the 50/50 mixture fused to the glass, creating
a relatively wide band across the surface of the finished gl~s~
prcduct. Thus, the lesser the percentage of frit contained in
j
-~ the coloring agent undercoating, the lesser the pos~lbillty of
adherence to the glass with consequent easier removal of the
exce~s portions of the coloring agent.
From the foregoing, it is apparent that the ob~ects of
the invention have been fully accomplished. By interposing an
undercoating of coloring agent between ~he electrically conduc- ;
tive paste ma~erial and the ~urface o the glasa sheet, the un-
desirable color of the residual stain resulting from the firing
thereo can be altered in accordance with optically acceptable ~
specification~ without adversely affecting the appear~nce o the
windshield or backlight or obstructing visibility therethrough.
It should be u=derstood that when lt ia deslred to apply elec-
trically conducting paths to the opposlte surfaces of a gla~s
sheet, or lnto a groove formed thP~rein, the coloring sgent al90 .
would be appl~ed to such oppoaite aurface~ or into such groo~e,
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1~5~373
re~pecti~ely~ as a substrate or undercoating for the elertrically
conduccive materlsl forming ssid p~ths,
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