Note: Descriptions are shown in the official language in which they were submitted.
10~36~3
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POLYVINYL BUTYRAL COMPOSITE INT~RLAY~R
FOR LAMINAT~D SAF~TY GLASS
BACKGROUND OF T~E INVERTION
1. Field of the Invention
The present invention relates to a polyvinyl butyral composite
interlayer for laminated safety glass and a process for preparation ~,
thereof. Morespecifically, the present in-
vention relates to a composite interlayer for laminated safety glass which
contains a color gradient.
2. Description of the Prior Art
Polyvinyl butyral sheet material is well known as an interlayer for
the laminated safety glass used in vehicles, especially windshields, and in
architectural applications. In many applications the interlayer is tinted
with an ink so as to provide a colored laminate. One of the major uses for
tinted laminates is in automobile windshields. In these applications the
interlayer i~ tinted with a color gradient which is positioned so as to form
a glare-reducing color gradient band at the top of the laminated windshield.
The gradient printing operation for the interlayers, used in wind-
shields~ usually involves printing ink in the form of dots on the surface of
the polyvinyl butyral sheet. The sheet is then dusted with a material such
as sodium bicarbonate to minimize undesirable ink transfer. Prior to use as
an interlayer, the sodium bicarbonate dust is washed off the sheet which is
then dried and laminated to the glass. Printing the interlayer material
gives rise to the need to dust and then wash the sheet. Noreover, the adhesion
of the printed portion of the sheet to glass may be adversely effected by the
printing step.
A definite need exists in the art for a polyvinyl butyral inter-
layer material having a color gradient with desired adhesion to glass and
which does not re~uire dusting and washing prior to use.
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SUMMARY OF THE INVE~TION
The present invention solves the aforementioned pro-
blems heretofore known in the prior art by providing a process
for preparing a composite polyvinyl butyral interlayer which
does not require dusting and washing prior to use.
The interlayer prepared by this process comprises
combining at least two sheets of polyvinyl butyral wherein
at least a portion of at least one of the sheets of polyvinyl
butyral is tinted with an ink applied to the side of the sheet
which is in face-to-face contact with the other sheet of
polyvinyl butyral.
In a preferred embodiment of the present invention
there is provided a process for preparing a composite inter-
layer for laminated safety glass which comprises:
A. passing a first continuous sheet of thermoplastic material
between nip rolls to impart machine direction, sheet
tension and drawdown into the sheet;
B. adjusting the temperature of the sheet to a.temperature
in the ranqe of from 32 to 82C;
C. removing any wrinkles from the sheet; and then
D. combining the first continuous sheet.with a second con-
tinuous sheet which is tinted wherein the second sheet
has received substantially the same treatment as out-
lined in process steps A to C above;
E. cooling the resulting composite.
In a further preferred embodiment of the present
invention, there is provided a process for preparing a com-
posite interlayer for laminated safety glass which comprises:
A. (1) passing a first continuous sheet of polyvinyl
butyral between a first set of nip rolls to impart
machine direction, sheet tension and drawdown
into the sheet;
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10~;~133
(2) adjusting the temperature of the first sheet to a
temperature in the range of from 32 to 82C while
removing any wrinkles in the sheet;
~3) allowing the first sheet to droop in a catenary
loop between a second and third set of nip rolls;
(4) adjusting the temperature of the first sheet to a
temperature in the range of from 32 to 82C; and
simultaneous with steps 1 to 4 above;
~. (1) passing a second continuous sheet of polyvinyl
butyral which is printed on one side with a color
gradient, between a set of nip rolls and
(2) allowing the second sheet to droop in a catenary
loop between the nip rolls;
(3) adjusting the temperature of the second sheet to a
temperature in the range of from 32 to 82C; and
C. (1) passing the-first and second sheets into a combining
nip where they are combined wherein the printed
surface of the second sheet of polyvinyl butyral
is combined to the first sheet so as to provide a
composite wherein the bond strength between the
first and second sheet is at least 0.Z95 Kg/cm;
(2) cooling the resulting composite;
wherein the process steps outlined in A and B above are con-
trolled to provide substantially the same line speed, sheet
tension and temperature in each of the first and second sheets
of polyvinyl butyral being fed into the combining nip.
~ESCRIPTION OF THE DRAWINGS
Figures I to IV inclusive, illustrate cross sections
of the composite interlayers of the present invention.
Figure I illustrates a sheet of polyvinyl butyral 11
printed with an ink 12 wherein the printed side is in face-to-
face contact with a second sheet of polyvinyl butyral 13.
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~0436~33
Figure II illustrates two sheets of polyvinyl
butyral 11, each of which is printed with an ink 12, wherein
the printed sides are combined.
Figure III illustrates a sheet of polyvinyl butyral
11, printed on both sides with an ink 12, wherein the printed
sides are combined to two other sheets of polyvinyl butyral
13.
Figure IV illustrates a colored wedge shaped sheet
of polyvinyl butyral 14, which is sandwiched between two
sheets of polyvinyl butyral 13.
Other variations on the above composite configura-
tions will become apparent to those skilled in the art upon
reading the present specification. .
Figure V is a schematic diagram illustrating the
extrusion of molten polyvinyl butyral onto the surface of a
sheet of polyvinyl butyral which has been printed with a
gradient.
Figure VI is a schematic diagram illustrating the
combining of two sheets of polyvinyl butyral, one of which
has been printed with a gradient wherein the gradient is
at the interface of the resulting composite.
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C-06~12-0364 10~3
Figure VII is a schematic diagram illustrating another more de-
tailed process for combining tuo s-heets of polyvinyl buty~al, one of uhich
has been printed with a gradient ~herein the gradient i8 at the interface of
the resulting composite.
DESCRIPTION OF THE PREPERRED EHRODIMENTS
In general the polyvinyl butyral resins employed in the present
invention have Staudinger molecuIar weights ranging from about 50,000 to
600,000 and preferably from 150,0aO to 270,000 and may be considered to be
made up, on a weig~t ~asis, o~ from 5 to 30% hydroxyl groups, calculated as
polyvinyl alcohol, O to 10% ester groups, calculated as polyvinyl ester, and
the balance substantially butyraldehyde. The polyvinyl butyral resin will
preferably contain, on a weight basis, from 9 to 25Z hydroxyl groups, cal-
culated as polyvinyl alcohol and from O to 3% acetate groups, calculated as
polyvinyl acetate, the ~alance being substantially butyraldehyde.
It is conventional to ad~ust the alkaliniq titer of the polyvinyl
butyral resin so as to optimize the impact strength of the resulting laminate.
Methods for adjusting the alkalin$ty titer are d$scussed in U.S.P. 3,262,835,
3,294,490, 3,396,074, 3,271,235 and 3,231,461 as well as in other patents.
The polyvinyl butyral resin is plasticized with from about 20 to 80
parts plasticizer per 100 parts res$n and more commonly between 30 and 50
parts for normal uindshield use. This latter concentration i8 generally used ~;with polyvinyl butyrals containing 18 to 23% vinyl alcohol by weigh~. In
general, the plasticizers which are commonly employed are esters of a poly-
basic acid or a polyhydric alcohol. Particularly suitable are triethylene
glycol di(2-ethylbutyrate), dibutyl sebacate, and di(betabutoxyethyl~ adipate.
The resulting plasticized resin mixture is then generally extruded in the form
of sheets which are then printed as described below.
The thickness of the individual polyvinyl butyral sheets used to
prepare the composites of the present ~nvention is in the range of from 5 to
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C~06-12-0364 10~83
1.~24 Dun wlth a range Or from 0.127 to 0.762 n~n bel~ ~rer~rr~
for use in auto-
mobile windshields. The choice of thickness of the individual sheets will
ultimately depend on the thickness desired in the composite sheet and those
skilled in the art can readily select sheets o~ appropriate thickness for
any given application.
In one embodiment of th~ present invention the surface of the sheet
to be printed, which is the surface which will ultlmately be in laminated con-
tact with another sheet of polyvinyl butyral, is relatively smooth so as to
provide a better surface for printing. On the other hand, the surface of the
polyviuyl butyral sheet which will ultimately be in laminated contact with
the glass member of the laminated safety glass will preferably have a con-
ventionally rough surface so as to prevent blocking of the rolled sheet, and
to facilitate deairing of the laminate. The above mentioned surfaces are
well known in the art and need no further discussion here.
The processes for tinting automobile windshield interlayer material
are usually designed to give a color gradient. In the gradient printing
process the ink is printed in a pattern such that there is a dark section at
the top of the interlayer which gradually and uniformly fades off into a clear
section at the bottom of the interlayer. In the resulting laminated wind-
shield the dark portion of the gradient is at the top of the windshield. In
automobile wintshields the darkest portion of the color gradient usually has
an optical density in the range of from 1.70 to 0.70 which corresponds to a
percent light transmission of from 2 to 20~, respectively. Preferably, the
light transmission in the darkest portion of the gradient is in the range of
from 4 to 10~.
The present invention is also applicable to those polyvinyl butyral
printing operations which do not require a color gradient. These usually
involve non-windshield application wherein the sheet is uniformly tinted.
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C-06-12-0364
Referring to the drawings, ~igure y illustrate~ ~ne embod~ment of
the present invention wherein molten pol~vinyl butyral is extruded onto the
printed surface of the polyvinyl ~utyral sheet. In Figure V polyvinyl
butyral sheet material 50 is passed over an idler roll 51 through a printing
station 52 wherein one side of the sheet is printed. The printed sheet is then
passed over a series of drive rolls 53 and idler rolls 51 to a nip formed by
the outlet of the extruder 56 and a die roll 57 where molten polyvinyl butyral
is extruded onto the printed gurface of the polyvinyl sheet. The resulting
composite is passed over the die roll 57, past a stripper roll 54 and a take-
off roll 55 and an idler roll 51 to a winder 58. The resulting gradient
composite 59 is then transferred to storage or shipping.
Referring again to Figure V, polyvinyl butyral sheet material mayoptionally be fed to the printing station directly from an extruder or other
sheet making apparatus thereby eliminating the necessity of winding and
unwinding the sheet material prior to feeding it to the printing station.
~ igure VI illustrates a sheet combining operation wherein two 15
mil sheets of polyvinyl butyral are combined to form a 30 mil composite
having a printed gradient at the interface of the composite sheet. The first
sheet 60 is clear material having conventional surfaces on both sides while
the second sheet 61 is printed on one side with a gradient which is designed
to appear as the tinted color band at the top of a windshield in the resulting
laminate. Preferably, the printed side ls relatively smooth while the
opposite side of the sheet has a conventional rough surface.
The clear sheet 60 enters the top section of the combining unit
through the upper tension rolls 62. These tension rolls serve two purposes:
(1) they act as a positive, constant speed driving section; and (2) they are
driven at a slower line speed than the combining rolls 65 to impart a desired
amount of sheet tenæion and drawdown in the clear sheet 60 to prevent cross
machine direction wrinkles and to control curl. This sheet tension is re-
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1043683
~-06-12-0364
quired to elimlnate wrinkles in the c~mbined sheet due to sheet growth during
heating and to match the amount of drawdown in the upper clear sheet 60 to
the drawdown in the lower printed sheet 61. The drawdown is usually deter-
mined by measuring the width change of the gheet. If the drawdo~n in the
upper sheet does not ~atch that of the luwer sheet, the final product will
have excessive curl. The upper tension rolls are run 1% to 30% slower than
the combining rolls 65 with 4~ to 1~% slower heing typical values.
The clear sheet 60 then passes under a ~ank of electric infra-red
pre-heaters which adjust the temperature of the incoming sheet to a temperature
in the range Or from 21 to 82C. The p~eferred temper~ture is
43 to 71C
as measured w~th an infra-red pyrometer ~ust after the bowed flexible rolls 63.
After being pre-heated, the sheet passes over a flexible bowed roll 63 (Mt.
Hope Vari-Bow Roll) which serves to spread the sheet in a cross-machine
direction, eliminating any wrinkles which may have formed due to sheet growth
during heating.
The clear sheet 60 is then carried to the upper lay-on roll 64
which transfers the sheet to the upper com~ining rolls 65. The lay-on roll
64 is operated at anywhere from zero nip pressure Cnip open) to a nip pressure
of 2.95 Kg/cm dependin4 on the parttculz~r 6heet used as w~l]. ~6 other
operating conditions. The clear sheet 60 wraps the upper combining roll 65
from 15 to 154C until lt reaches the comblnin~ nip 69. The combinlr~
rolls are heated at from 32C to 82C wlth 43 to 71c belng preferred.
The comblning nip pressure run~ rrom ~.48 ~g/c~ to 8,85 K~/c~ ~1th
2.95 to
5.90Kg/cm being preferred. The upper combining roll 65 surface is slightly
less tacky than the bottom combining roll 65 surface to facilitate sheet
transfer to the bottom roll.
Polyvinyl butyral sheet printed with a gradient sheet 61 enters the
unit through the bottom relaxing nip 66, generally at a temperature of from
21 to 49C with a drawdown of from 10% to 35%. The sheet is allowed to
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1~436~3
C-06-12 0364
relax between the relaxing nip 66 and the lo~er tension ni~ 62 by running the
lower tension nip 3% to 20% slower than the relaxing nip. The printed sheet
61 goes through the lower tension rolls 62, which are run at a line speed
equal to or less than the combining roll li~e speed and preferably at the
same line speed as the upper clear sheet 60. The lower tension rolls serve
the same purpose as the upper tension rolls, namely they build in machine
dire~tion sheet tension to prevent cross-machine d~rection wrinkles and to
control curl. The lower tension roll speed is from lZ to 30~ less than the
combining roll speed with from 4% to 16% less being preferred.
The gradient printed sheet 61 then passes under electric infra-red
preheaters which are set to give temperatures equal to the temperature achieved
in the top section. The printed sheet 61 is then transferred to the lower
combining roll 65 by the lower lay-on roll 64, operating in a manner similar
to ~he upper lay-on roll. The sheet wraps the lower combining roll 65 from
about 15 to 154C\ Which lS heated to the same temPerature as the
upper combinlnF roll.
After passing through the combining nip 69, the combined sheet (0.762
nun j is transferred to a cooling roll 67, which it wraps from 15 to
154C. The cooling roll surface is usually kept below 21C. After leaving
the cooling roll 67, the sheet is wound and packaged.
While Figure VI refers to the combining of two Q03~hnnsheets to
form a 0.762nncomposite, it is apparent that other sheet thicknesses can be
used. In addition, wide variation in sheet surfaces and sheet composition
is permissible as well as wide variations in the printing of the sheets. In
regard to the latter, one or both sheets may be printed with any desired
pateerns, designs or colors.
One of the ma;or problems in sheet combining is wrinkling of the
sheet in both the machine direction and cross-machine direction. These
wrinkles are caused by sheet growth on the combining rolls during heating
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C-06-12-0364 ~0~3
on the roll and by vapars released from the surface of the sheet which are
trapped between the sheet and the roll surface 6ehind the combining nip. The
wrinkles caused by sheet growth during heating can be controlled by restricting
the temperature rise of the sheet on the com~ining roll to less than 17oC by
preheating the sheet before it gets to the combining roll or by introducing
machine direction and cross~machine direction stresses into the sheet before
it reaches the com6ining rolls. ~y preh ating within IlC of the sheet
combining ~emperature, the sheet growth on the com6ining rolls i9 limited to
an amount insufficient to cause wrin~les. A com6ination of the two techniques
is preferred.
In addition, the tension, both in the machine and cross-machine
directions, the temperature and the line speed of the sheets to be combined
should be as evenly matched as possible.
Figure VII illustrates a s~eet com6ining process similar to that
shown in Figure VI above, except that several tension, catenary loop and
temperature controls have been added. These process controls are designed to
match the tension, temperature and line speed of the sheets to be combi~ed so ~;;
as to provide optimum properties in the resulting composite interlayer.
Clear sheet 80 enters the upper section of the combining unit
through a first upper tension nip 82. This tension nip controls the sheet
tension through the pre-conditioning section comprising pre-conditioning - -
heaters and a dewrinkling section where the sheet is dewrinkled using con-
ventional means. Sheet tension in the pre-conditioning section is controlled
at a minimum level by a first upper tension sensor 83.
A first upper temperature sensor 84 controls the pre-conditioning
heaters to obtain a sheet temperature in the range of 32C to 82C with
~3C to 71C being preferred.
The clear sheet then passes through a second upper tension nip 85
into a rela~ing section where the sheet is allowed to droop in a controlled
catenary loop 6etween the second upper tension nip 85 and the third upper
tenslon nip 88. Tension nips 85 and 88 control the tension and
catenary loop _ g _ : -
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C-06-12-0364
in the relaxing section. ~le speed of these ~ension rolls, w~ich form
tension nips 85 and 88, is controlled ~y the catenary loop sensor 86. The
catenary loop is maintained in the relaxing section to relax out as much
inherent sheet stress as possible so that the clear sheet, which enters this
section with a shrink level o~ from 4% to 24%, leaves with a shrink level
of less t~an 4%. Also included in the relaxing section is a second upper
temperature sensor 87.
The third upper tension nip 88 controls the tension through the
sheet stressing section to achieve drawdown levels in the range of from 1%
to 30~ wLth 4Z to 16% being preferred. This nip is controlled by a second
upper tension sensor 89.
After the relaxing section the sheet passes through a heating
section where the sheet temperature is again adjusted in the range of from
32C to 82C, wlth 43C to 71C being preferred.
The clear sheet 80 then passes over a lay-on roll 90 onto a
temperature control roll 91 in order to adjust the sheet temperature to the
desired co~b~n~ng temperature. T~e temperature of the sheet just before
combining is measured and controlled by a third temperature sensor 93,
which is located just before the com~ining nip 94. After leaving the
temperature control roll91, the clear sheet 80 passes over an upper flexible
bowed roll 92 for dewrinkling and then passes into the combining nip 94.
Meanwhile, polyvinyl butyral sheet which has been printed with a
gradient 81 enters the lower section of the sheet combining unit which is
essentially the same as that described above.
The printed sheet 81 enters the lower section of the combining ~ -
unit through a first lower tension nip 95 and then through a pre-conditioning
section which comprises pre-conditioning heaters and a dewrinkling unit.
This section may not be needed in an inline operation where the sheet is con-
ditioned to a certain temperature and dewTinkled just prior to printing and
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1Q43683
C-06-12-03~4
then fed directly int~ the combining un~t. Al80 located in the pre-
- conditioning unit is a first lower tension sensor 96 and a first lower
temperature sensor 97, The printed sheet 81 then pasges into a relaxing
section formed by a second lower tension nip 98 and a third lower tension nip
101. In the relaxing section the sheet is allowed to droop in a controlled
catenary loop where a lower catenary loop sensor 99 and a second lower tem-
perature sensor 100 measure the droop and the temperature of the sheet,
respectively.
Upon leaving the third lower tension nip 101, the sheet passes into
a preheating section similar to that discussed above. The sheet which is
preheated as in the upper section, passes over a lay-on roll 103 onto a lower
temperature control roll 104 and then over a lower fl.exible bowed roll 105
into the combining nip 94. A third lower temperature sensor 106 is located -
between the flexible bowed roll lOS and the combining nip 94.
Referring again to Figure VII, a control section 109 is provided to
receive tension, temperature and catenary loop data from the sensors ln the
upper and lower section and to ad~ust these variables so that the tension,
temperature and degree of relaxation in the catenary loop is matched for the
. ~ .
upper and lower sections so as to provide opti~um properties in the laminate.
In the combining nip 94 the clear sheet ôO is press-tacked to the
gradient sheet 81 so as to form a composite where the printed surface is
at the interface of the two sheets.
After combining, the composite sheet 108 passes over a number of
cooling rolls 107, which reduce the sheet temperature to less than 27C with
a temperature of less than 21C being preferred. The composite sheet is
then wound and transferred to shipping or storage.
The roll speeds, nip pressures and temperatures used in reference
to the process illustrated in Figure VII are the same as those given in re-
ference to the process illustrated by Figure VI unless otherwise specified.
The above description of Figure VII refers to an upper and lower
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7 C_06-l2-0364 10~83
section. However, it is understood that the operation can be carried out
side by side in which case the upper and lower sections would become the left
and right ~ections or first and second sections of the operation.
It is also possible to com~ine two printed sheets using the above
processes.
In the case of a three ply composite the middle layer can be printed
on both sides and then laminated between two clear sheets, using modifications
of the processes outlined above. Other such modifications will become apparent
to those skilled in ~he art upon reading the present specification.
The heating steps referred to throughout the specification may be
carried out by those means that are well known in the art. The sheet may be
heated by any of those various means which include electrical heaters, IR
heaters, hot air devices, steam heated devices, hot water heated devices,
etc. Conversely, any cooling steps which are needed to adjust sheet tempera-
ture would use conventional means such as cool air, chill rolls, etc. Like-
wise, the degree of wrap around any given roll may be varied within broad
limits.
The composites of the present invention are press-tacked to provide
a bond strength, as measured by a 180 degree pull apart test, of at least
20 0.295 Kg/cm, The bond should be sufficient to maintain the unitary nature
of the composite during shipping, storage, handling and fabrication into
laminated safety glass. During the glass laminating step the heat and
pressure used to make the laminate also serve to increase the band strength
of the composite interlayer.
Preferably, the co~posite sheet has a curl value of less than 20.
The curl value is measured by cutting a sample approximately 508 cm X 2 cm
from the machine direction of composite. The test sample is then placed in
a circulating air oven maintained at 43C. ~ 1C. for ten minutes. In the
oven one-half of the test sample is supported on a flat shelf while the other
half hangs down unsupported. The sample is then removed from the oven after
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10436~3 , ~
C-06-12-0364
10 minutes and placed on a flat tahle with the ~urface of the sheet that was ~;
supported in the oven placed face down on the table. Tfie sample is examined ~;
and if the ends of the sample curl bac~ from the table surface, the distance
from the end of the sample to the point that is still in contact with the
table i8 measured in millimeters. T~e measurements for each end of the sample
are averaged and the percent curl is determined by the following formula:
mm of curled sheet/original length (millimeters) X 100 = X curl ;-
A curl value greater than 20% indicates that there are residual
stresses in the sheet which will cause the sheet to curl thereby causing
processing difficulties in the glass laminating operations. More preferably, -
the composlte sheet has a curl value of less than 15% and most preferably,
less than 10%.
A 30 ml. composite gradient sheet prepared by the process illustrated
in ~igure Vl, having a bond strength of Q2 95 K~/om and a curl value of 3% is
laminated between two sheets of glass of the type conventionally used ln the
preparation of automob~le windshields. The resulting laminated safety glass
is evaluated for optical density, sheet beauty and adhesion and compared to
glass laminates prepared using a single ply Q762~polyvinyl butyral inter- ~ -
layer prepared by conventional methods. The properties of the glass laminates
2~ prepared using the camposite interlayer of the present invention are compar-
able to the properties of those laminates prepared using a conventional single
ply polyvinyl butyral interlayer.
While the foregoing description has been dlrected to polyvinyl
;~ butyral interlayers, one skilled in the art will readily recognize that the
present invention is readily adaptable to preparing composites of other
thermoplastic materials which couid be used aH interlayers for laminated
safety glass. Examples of other suitable interlayer material include
polyurethanes, polyamides, poly(ethylene-vinyl acetate), poly(ethylene-vinyl
alcohol), etc.
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C-06-12-0364 104~83
From the foregoin~ description of the present invention, it will
become apparent that many variations and modifications are possible without
departing from the spirit and scope thereof.
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