Note: Descriptions are shown in the official language in which they were submitted.
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Attorney Docket No.: 1691.001
FLEXIBLE REFLECTIVE MATERIAL
AND PROCESS FOR MAKING TIIE SAME
BACKGROUND OF T~E INVENTION
The present invention relates to the field of reflective polymer products, and
methorls of m~nllfactllring the same. In particular, the present invention provides a low
cost altemative to tr~ition~l glass mirrors, and may be formed into a variety of useful
10 and orn~m~ont~l shapes.
BACKGROUND OF T~E rNVENTlON
P~epl~cem~nt reflective products are increasingly desirable to ~limin~te the cost,
- weight, and potential danger of traditional mirrored glass. Additionally, plastic
reflective products that can be molded into useful articles, such as p1ates or automobile
vent shades, are h~cleasingly sought. Such alternative reflective products currently
available are frequently constructed of chrome materials or with metallic particles
embedded in a polymer base. Although desirably light-weight, the currently available
reflective polymer products do not provide a satisfactory reflective image. The
appearance of prior art reflective polymer products is relatively dull and characterized by
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Attorney Docket No.: 1691.001 2
transverse optical chatter lines or waves that distort the reflective image. Available
reflective polymer products are not snfficiently flexible to resist cracking. DeiAminAtion
of polymer layers is also a common problem with existing reflective products. In
addition, current reflective polymer products are not moldable to s~tisf~ctory dimen~;ons
5 without thinning or splittin~ into unusable forms or beco.,.in~ so,,,c~l~l cloudy in
appearance. These shortcomings in the prior art are due to the currently available
compositions of reflective particles and polymer substrates, as well as ~nC~ ctory
means for mAnllfActuring such products.
Consequently, there is a need in the art for a flexible reflective polymer material
that is substantially free from optical chatter to provide an undistorted reflective image.
There is also a need for a flexible reflective product that is stronger than other known
compositions and can, therefore, be molded into usefi~l forms without splitting or
del~l.linAl;on. Furthermore, there is a need in the art for improved methods of
15 mAnuf~ctllring such a flexible reflective material.
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Attorney Docket No.: 1691.001 3
SUMMARY OF TIIE lNVENTlON
The present invention provides a flexible reflective material s~ lly free
from optical chatter. The invention provides such a material having a reflective layer
5 adjacent to a substrate layer comprising polyethylene te~tph~ lq-te. The reflective layer
is pref~-ably constructed of metallic particles disposed on â tran~Uc~nt polymer layer,
and the substrate layer is p~efe.ably a glycol modified polyethylene te.~ph~ qte The
reflective layer can also have an acrylic layer therein.
The invention also provides a process of making a flexible multi-layered polymer
material comprising heating a substrate polymer to at least its melting point, extruding
the polymer between a first and a second cylindrical roller, each .. ~ i ed at selected
temperatures and positioned a selected ~listqnce apart while rotating in sy~.c~"oni~alion.
A lqminqte layer is supplied under tension to the rollers along with the molten substrate
15 polymer, and the Iqminqte layer and substrate polymer are combined under a selected
high pressure to form a multi-layered polymer product.
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Attorney Docket No.: 1691.001 4
BR~EF DESCR~PTION OF T~E DRAWTNGS
Fig. 1 is a side view of one embodiment of the flexible reflective material of the present
5 invention.
F;g. 2 is a side view of an alternative embodiment of the flexible reflective material of
the present invention.
10 Fig. 3 is a side view of an alternative embodiment of the flexible reflective material of
the present invention.
Fig. 4 is a side view of an alternative embodiment of the flexible reflective material of
the present invention.
lS
Fig. 5 is a side view of an alternative embodiment of the flexible reflective material of
the present invention.
Figs. 6A and 6B are side views ofthe m~chine for m~mlf~cturing a multi-layered
20 polymer material of the present invention, connected by a match line.
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Attorney Docket No.: 1691.001 5
Fig. 7 is a top view of the portion of the m~chine for m~nuf~cturing a multi-layered
polyrner material of the present invention, corresponding to that shown in Fig. 6A.
Fig. 8 is a opposite side view of a portion of the m~ ine for making the multi-layered
5 material, showing the roller gears.
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Attorney Docket No.: 1691.001 6
DETA~LED DESCRIPTION OF T~E JNVENTION
As used herein "a" means one or more than one. The following examples are
5 int~nded to describe various embodiments of the invention but are not intçnded to limit
the scope ofthe claims. The present invention provides a flexible reflective material 10.
The material 10 is preferably substantially free from optical chatter. By "optical chatter"
- is meant transverse lines or waves of distorted reflective image app~ ;ng on the surface
ofthe material 10. By "sl~b~ ly free from optical chaner" is meant that sub~ ;ally
10 no image distorting transverse lines appear in the material 10 to the unaided eye viewing
the reflective material 10 securely mounted to a planar surface. This effect is achieved
by the combination of ~lem~nts in the reflective material 10, the "~r.hine and the process
for the manufacture of the reflective material 10, described below.
As seen in Fig. 1, the material 10 has a reflective layer 12 co~ ;ng a first
acrylic layer 14, a tr~nclllcPnt polymer layer 16, and a first metal layer 18 that is
disposed between the acrylic layer 14 and the tr~nclucent polymer layer 16. The
material 10 also has a substrate layer 20 adjacent to the reflective layer 12. The
substrate layer 20 can be a variety of polymers, but is p. efel dbly acrylic or a polyester,
20 such as, a polyethylene terephthalate (PET). In preferred emborlim~nts, the material 10
is between 15 to 60 mil thick.
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Attorney Docket No.: 1691.001 7
In another embodiment shown in Fig. 2, the substrate layer 20 is disposed
adjacçnt the polymer layer 16, and the material 10 further has a second acrylic layer 22
disposed between the polymer layer 16 and the substrate layer 20. In another
embodiment shown in Fig. 3, the substrate layer 20 is disposed adjacent the polymer
layer 16, and the material 10 further has a second metal layer 24 disposed between the
polymer layer 16 and the substrate layer 20. In another p.er.,.-ed embodiment, the first
metal layer 18 is adjacent the acrylic layer and the polymer layer 16, and the second
metal layer 24 is adjacent the second acrylic layer 22 and the polymer layer 16.
In another preferred embodiment shown in Fig. 4, the substrate layer 20 is
disposed adjacent the polymer layer 16, and the material 10 further has a second metal
layer 24 disposed between the polymer layer 16 and the substrate layer 20 and a second
acrylic layer 22 disposed between the second metal layer 24 and the substrate layer 20.
In another embodiment shown in Fig. 5, the material 10 further comprises a third
acrylic layer 26 adjacent the substrate layer 20 opposite the reflective layer 12. In some
preferred embodiments, the first metal layer 18 is adjacent the first acrylic layer 14 and
the polymer layer 16. The invention cont~mplates a variety of additional layer
co...binalions, not exemplified herein.
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Attorney Docket No.: 1691.001 8
Referring more generally to Figs. 1-~, the first, second or third acrylic layers 14,
22, 26 can generally be an acrylic comonomer or copolymer, such as acrylic acid, methyl
acrylic acid, and derivatives thereof. A description of such acrylics is, for example, in
U.S. Patent No. 5,035,945, which is hereby incorporated by reference in its entirety.
The metals in the metal layers 18, 24 can be selected from ai~ln~inl-m~ silver,
gold, pl~tinum, chromium, zinc, copper, nickel, p~ Ai~m, and tit~nhlrn~ and alloys
thereof, for example. The deposit of such metals on a polymer layer 16 can be
performed by a variety of conventional m~t~llising teçhnigues, for example, by
10 deposition from a suspension of finely divided metallic particles in a suitable liquid
vehicle, or by electrode beam evaporation, electrolysis plating, or by vacuum deposition.
The tr~n~luc~nt polymer layer 16 is generally a film of polymeric material, such
as polyethylene ter~hth~l~te ~PET). The composite reflective layer 12 is co,~ ..,rcially
15 available from MEI (Agawam, ~f~cs~chnsetts) as a Melinex-type product (e.g., Melinex-
453). In preferred embotlim~ontc, the reflective layer 12 is between 1 to 5 mil. thick.
The material 10 also has a substrate layer 20 adhered to the reflective layer 12,
which can comprise a polyester. In particular, the polyester can be a polyethylene
20 terephthalate (PET), poly ( l ,4-cyclohexylene dimethylene terephthalate) (PCT), or a
combination thereof. The substrate layer 20 can also be modified by a variety of
chemical processes, such as glycol modification discucced in more detail below. Jn
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Attorney Docket No.: 1691.001 9
plefelled embo-lim~nts, the substrate layer 20 is between I to 250 mil. thick. The
substratê layer 20 can comprise a pigment to provide color, such as black, to the
material 10. ~-ldition~l additives can also be added to the substrate 20, such as
ultraviolet light stabilizers, anti-oxidants, fire lela.dan~s, acrylics, tedlar coating or
5 adhesives, etc. The invention cont~mrl~tçs that a conventional heat-activated adhesive
can also be used to secure the layers 20, 12, ~Ithol~gh the emb~iments described herein
do not contain such an adhesive. Another substrate malerial may be added to the
substrate 20, as by means of a co-extruder 46 assembly, as described below with
rël~ence to the m~hine and process for the m~nl-f~ re ofthe material 10. In one
10 embo~liment7 the substrate layer 20 is 1,4-cyclohexylene-dimethylene-e~ lene
ter~ph~ te (PCT-G). PCT-G is co-----,~,.~ially available as PCTG Kodar copolyester
5445 from Eastman Chemical Company (Kingsport, Tenn~ssee). PCT-G is an
amorphous (non-crystalline) thermoplastic polyester of the PCT family. The "G" in the
PCT-G design~tion in~ic~t~s the use of a second glycol in making the polymer.
In a prefe. ~ ~,d embo~im~nt~ the polyester of the substrate layer 20 is ethylene-
1,4-cyclohexylene-dimethylene terephthalate (PET-G). PET-G is co-,ul~ ,;ally
available as PETG Kodar copolyester 6763 from ~Stm~n Chemical Comr~ny
(Kingsport, Tçnnçssee). PET-G is an amorphous (noncrystalline) thermoplastic
20 polyester of the PET family. The "G" in the PET-G designation in~ic~t~s the use of a
second glycol (1,4-cyclohexane~i-neth~nol, or CHDM) in making the polymer. A PET-
G substrate layer 20 results in a preferred flexible reflective material 10 that is especially
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Astorney Docket No.: 1691.001 10
substantially free from optical chatter and exhibits suprisingly high optical clarity.
Some of the physical properties of PET-G are generally as follows. PET-G has a
tensile strength at break of about 4,000 psi (28 MPa), and a tensile strength at yield of
5 about 7,300 psi (50 MPa). The elongation at break is about 130%. The mod~ s and
elasticity in bending is 2.9 x 105 psi (2,000 ~a). The flexular strength is about 10,000
psi (69 MPa). PET-G can be extrusion cast into film in thic~n~cc.os as light as about
0.025 mm (I mil) and into sheet thicLnesses greater than 6.4 mm (250 mils) on
conventional extrusion eql~iprn~nt Film and 5heçting products of 0.254 mm (10 mils) or
10 more will prel;.ably be nip-polished on a three-roll stack to ensure better gauge control
and improved surface appearance. PET-G must be predried, but not to the degree
required for normal PET. Good heat stability permits processing te ..p~al,~res to vary
as required for di~- ~nt gauges and output rates.
The flexible reflective material 10 comprising PET-G of the present invention
poss~ses many unique qualities. For example, the present material 10 permits vacuum
molding to about 30% deeper than similar previous products. Previous products can
not be drawn deeper than 1/2" at a 45 degree angle without failure, such as split~ing of
the substrate 20 or reflective layer 12. The present invention, howeva, can be drawn
20 over a rolled edge about I inch at an 80 degree angle without failure. The material 10 is
heat sealable and sonic weldable, unlike prior products which crack or peel during such
procedures. The PET-G substrate 20 adhesion to the reflective layer 12 is about 20%
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Attorney Docket No.: 1691.001 l l
higher than other products, which avoids peeling and de~ g product failures. The
low melting point of PET-G (about 178~F) assists in the layer adhesion process.
The materials of the present invention are made by a - ~hine shown generally in
5 Figs. 6-8 by a process as follows. PET substrate 20 pellets should be dried before
extrusion for about four to six hours at about 300~F. PET-G substrate 20 pellets should
be dried before extrusion for about four to six hours at about 150~F. PCT-G substrate
- 20 pellets should be dried before extrusion for about four hours at about 160~F. Acrylic
substrate 20 pellets should be dried before extrusion for about six hours at about 190~F.
10 As seen in Fig. 6A, a dehllmidifying-type hopper dryer 30 should plefelably be used to
produce a dewpoint of-38~F with an air flow for PET, PET-G, PCT-G and acrylic of
about 1200 to 1800 cfm. Drying equipm~nt should ~rerèl ably be fitted with a dewpoint
meter and an alarm. Care should be exercised in the drying-hopper design to ensure
uniform pêilet and air flow, i.e., no çh~nn~ling While moisture bubblês or streaks
15 become readily visible in extruded substrate 20 if the moisture content is exc~ssively
high, an un~cceFtable ievel of moisture may be present, but not obvious during
extrusion. The moisture level of the pellets just before extrusion should preferably not
exceed about 0.08%. Higher levels will result in a signifi~nt reduction in molecular
weight, and thus, cause the substrate 20 to have considerably lower toughness that can
20 be obtained with properly dried pellets. This higher moisture level can also result in
processing problems such as substrate 20 sticking to the chill roll stack 50 and die lip 44
buildup.
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Attorney Docket No.: 1691.001 12
The primary dryer 30 preferably has a conventional desicc~nt bed (features not
detailed) with a molecular sieve for water adsorption, blowers to provide airflow,
heaters to vaporize the water, filters to remove dust and fines, an after-cooler to remove
water from the air, and a hopper which serves as a drying container and provides a base
5 cone for uniform pellet flow. The most co-l.--lon type of d~o~icc~nt used in plastics
drying is an alkali metal alumino-silicate molecular sieve with a chemic~l formula
(Nal2[(AI02)12(SiO2)l2)]. Molecular sieve is generally available in powder form, in 1/16"
and 1/8" pellets, 8" x 12" and 4" x 8" beads, and 14" x 30" mesh (Union Carbide Corp.,
Tarrytown, NY).
Preferably, the dryer 30 is a fully automatic, self-contained adsorption type
dehllmi~lifier co.~ g two molecular sieve desicc~nt beds, one supplying dPhllm;~ified
air while the other is being regenerated. Such a dryer 30 is available from Universal
Dynamics, Inc. (Woodbridge, Virginia) as a DHD-60. The dçh~m;~ifi~r preferably has a
15 microprocessor (Ornni II-E) for control of process air flow and temperature, which is in
turn monitored and controlled by a central processing unit ("CPUn, not shown)
described in more detail below. To assure moisture free substrate 20, a second dryer
(not shown) also monitored and controlled by the CPU can be inc~lled intermedi~tely
between the first dryer 30 and the extruder 32.
An extruder 32, shown in Figs. 6A and 7A, receives the dried substrate 20
pellets and heats the material 10 to a molten consistency. The extruder 32 is hollow
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Attorney Docket No.: 1691.001 13
and elone~ted, having a first substrate receiving end 34, a second substrate extruding -
end 36, at least one heater element (not detailed) along the length thereof, and a screw
means (not shown) for moving the substrate 20 therethrough. Such an extruder 32jS
available from Cin~inn~ti Milicrom, Inc. The extruder 32 preferably has six heater zones
5 along the length thereof in thermal comm~nication with the substrate 20, which are each
monitored and controlled by the CPU. At the extruding end, the molten substrate 20 is
moved through at least one screen pack 38, a pump 40, at least one adapter 42, a static
mixer 43 and across the die lip 44.
As with other polymers, the substrate 20 W;ll soften and becorne tacky as it
approaches its glass transition te.l.p~,.al~lre(TB). For PET-G, the T8 is 81 ~C (178~F).
For PCT-G, the TBjS 88~C (190~F). PET-G and PCT-G have better hydrolytic stability
than PET and, cor-cequ~ontly, their molecular weight will not break do~hn as readily
during extrusion. The nominal target inherent viscosity (I.V.) of PET~ and PCT-G
15 pellets is 0.75. When pellets are dried and extruded under the suggested conditions, the
resulting I.V. should be about 0.71 to 0.73, and the extruded substrate 20 should exhibit
excellent toughness If the pellets are not properly dried or are extruded at too high a
te.npe.~lure, the resulting I.V. may be too low, and the substrate 20 may be somewhat
brittle and contain surface distortions.
The molecular weight of a polymer is an important p, opc. ly because it is an
indication ofthe toughness (or brittlen~ss) ofthe extruded substrate 20. The higher the
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Attorney Docket No.: 1691.001 14
molecular weight, the tougher the substrate 20. Molecular weight is very difficult to
determine directly. However, inherent viscosity is a direct indication of molecular
weight, and it is much easier to measure. While the measurement of I.V. is rather simple
colllpal~d to dete...-i~ g molecular weight, it can be hazardous because ofthe
5 ch~m:~lc involved. A safer technique is to determine the flow rate of the substrate 20,
which can then be converted to I.V. by using a correlation curve. This method is known
to those skilled in the art.
A minimnm extrusion barrel length to diameter ratio (L/D) of 24/1 is suggested
10 for optimum stability and production rate. The extruder 32 drive motor (not shown)
should be sized according to the output desired, and a properly de~igne~ screw (not
shown) should be used. An output of approximately 3.6 to 4.5 kg/hr (8 to lO Ib/hr) per
horsepower can be expected for eq~ipm~nt designed for PET-G or PCT-G. However,
screws specifically designed for other polymers may yield con~id~rably less output per
1 5 horsepower.
This screw is pl~fel~bly characterized by a double-flighted section that provides
a channel for llnmelted pellets as well as one for the molten substrate 20. This
separation of melted and unmelted substrate 20 results in more efficient melting and
20 helps prevent overheating. For example, the output rate for a 3 1/2-in. extruder 32 with
a barrier screw having an L/D ratio of 24/1 and operating at 95 rpm is greater than 318
kg (700 Ib) per hour. The drive power required under these conditions is less than 75
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Attorney Docket No.: 1691.001 15
hp. Preferably, the extruder 32 drive motor has about 250 hp rotating about 4.5 in.
double-ftighted screw having a L/D ratio of 30/1.
Gauge variation in the m~hine direction of substrate 20 extruded from virgin
5 material is approximately +4%. When extruding substrate 20 it may be helpful to use
internal screw cooling in the first three or four feed flights. This will help prevent pellet
bridging in the hopper throat and in the screw feed section and will provide uniform
feeding. Screws cooled along their entire length are not reco,~ f ~~de~ The
temperature zones l eco-. --.-f nded for extruding the various substrates are dicc~ l~sed in
10 more detail below in Table I . The extruder 32 tenlpf;l al-lres, rate of screw rotation and
internal pump 40 pressure are all monitored and controlled by the CPU.
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Attorney Docket No.: 1691.001 16
The following screen 38 pack is suggested for extrusion of substrate 20:
MESH QUANTl~IY
24X24
60X60
24X24
More pl ere. ably, the following screen 38 pack is sugeested for the extrusion of
PET-G when making a reflective material sul.s~ ly free of optical chatter:
MESH QUANTITY
60X60
80X80
100 X 100
150 X 150
80X80
40 X 40
The melt pump 40 is a positive displ~cem~nt pump that runs at a co~ l speed.
20 There is a pressure sensor on both sides of the pump 40. The pressure between the
extruder 32 and pump 40 is called the suction pressure, and the pressure between the
pump 40 and the die lip 44 is called the discharge pressure. When the suction pressure
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Attorney Docket No.: 1691.001 17
drifts away from the preset pressure, the extruder 32 screw speed ~utoln~tir.~lly
increases or decreases to bring the pressure back to the set point. When the extruder 32
supplies a con~a.ll amount of material 10 to the pump 40, the suction pressure and
screw speed will remain constant. The melt pump 40 distributes an even flow of
5 substrate to the die lip 44 to insure accurate gauge without air bubbles or pits. The melt
pump 40 pressure and extruder 32 screw speed are monitored and controlled by the
CPU.
An even flow of substrate 20 will result in a uniform gauge in the m~chine
10 direction, typically about ~4%. Since the control system automatically co".pensates for
~h~nges in the extruder 32 output rate, changes in the size and amount of regrind
substrate 20 have very little effect upon film gauge. The pump 40 can be a Luwa Model
45/45 which is capable of processing up to about 400 kg/hr (900 Ib/hr) of substrate 20.
The melt pump 40 should be capable of 20 to 35 rpms. The melt pump 40 receives
15 molten substrate at a pressure of about 800 to 1000 psi and extrudes the substrate 20 at
about 1,000 to 2,500 psi, and prerel~bly at 1,500 psi. The pump 40 is ~l~fe.ably further
equipped with a heating means for m~int~ining a temperature which is shown in Table I
with respect to specific substrates. All of the temperatures shown in Table I are
monitored and controlled by the CPU.
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Attorney Docket No.: 1691.001 18
The static mixer 43, preferably a bow-tie model, is important to provide a
consistent temperature throughout the substrate 20. A co-extruder 46 assembly (shown
in Fig. 7A) can optionally be provided to feed another molten substrate into the die lip
44 extruding the molten first polymer substrate 20. For example, an acrylic can be co-
S extruded into a line of polyester to form a multi-functional substrate layer 20.
Fc~çnti~lly, the co-extruder assembly 46 is a smaller scale duplic~te of the main extruder
assembly 32 .
A flexible film extrusion die lip 44 having a two-piece body is suggested for
10 extruding substrate 20. For sheeting. a flexible die lip 44 with a strP~mlined restrictor
bar is suggested. For film, the land length should be about 25 to 32 mm (1.0 to 1.25
in.), and for sheet, the land should be much longer, e.g., about 89 mm (3.5 in.) when
making roughly 6.35 mm (250 mil) sheet. For film, a die lip 44 orifice of about 1,016 ~o
1,270 microns (40 to 50 mils) is suggested. For sheeting, the orifice should be at least
15 about 25% greater than the desired sheet th;~k neSs The face of the die lip 44 should be
tapered rather than square-faced to permit a short side to chill roll air gap. The die lip
44 should have a good surface finish (two or four microinches) on all flow surfaces,
have no hang-up areas or areas where flow is dead, and be free of all nicks and
scratches.
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Attorney Docket No.: 1691.001 19
Substrate 20 can be extruded either horizontally or vertically from the die lip 44
to the chill roll stack 50. However, the horizontal setup is pl~relled because of its ease
of operation. While a three-roll stack 50 arrangement is pl ~fel I ed to produce heavy film
and sheeting of high quality, a two-roll, S-wrap technique is usually employed for
5 thinner films. With such a unit, the chill rollers 52, 54, 56 diAmeters can be in the 256-
to 510-mm (10- to 20-in.) range, depending upon the production rate desired.
A plefelled ... ~.hi.~e embodiment has a three chrome roller stack 50, which
receives the molted bead of substrate 20 and ~cco..-p~ .ying l~min~te reflective layer 12
10 and co--l~l~Jses them into a single flexible reflective material 10 between the first (top)
52 and second (middle) rollers 54. The die lip 44 extrudes the molten substrate 20
between the top roller 52 and the middle roller 54. The top roller 52 is prefc.ably about
12 inches di~m~t~r and is ,~,~inl~ined at constant t~ .llp~.dlule, depen~lin~ upon the
substrate 20 type, discnsced below. The middle roller 54 is preferably about 18 inches
15 di~meter and is ,..Ain~ined at conslallt temperature, depending upon the substrate 20
type, dicc~lssed below. The material 10 can be further passed around a third (lower)
roller 56, that is pleftl~bly about 18 inches diAm~t~r and is ,,,A;nlAi.ltd at conctAnt
temperature, depending upon the substrate 20 type, discllsced below. The plefe-led
ratio of the sizes of the top:middle:lower rollers 52, 54, 56 is 2:3 :3 . More preferably,
20 the temperatures of the respecli~e rollers 52, 54, 56 are achieved by circulating heat
e~cch~nged water therethrough, which is monitored and controlled by the CPU. The top,
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Attorney Docket No.: 1691.001 20
middle and lower rollers 52, 54, 56 are respectively cooled or warmed to prevent
sticking of the material 10 to the previous roller as it is passed thereover. The rollers
52, 54, 56 pl efe-~bly have a smooth chrome finish of two to four mi- l oh~ches to prevent
substrate 20 and reflective layer 12 sticking thereto.
S
The low melt strength of PET-G and PCT-G make it plere.able that a short die
lip 44 to chill roll stack 50 ~li5t~nce be used. An air gap that is too long produces
excessive web sag and web instability between the die lip 44 and chill roll stack 50. This
can cause the web to drag over the lower die lip 44 (as in the case of horizontal
10 extrusion) producing an excessive number of die lines in the extruded sh~etin~
When extruding PET-G or PCT-G, the takeoffunit should be such that it can be
moved to within about 6 mm (l/4 in.) ofthe die lip 44 to ..~ ;,e the die lip 44 to chill
roll stack 50 air gap. In addition, the vertical position of the chill rollers 52, 54, 56
15 should be ~djust~ble, as by the third hydraulic means 76, ~lisrl-ssed below. When
extruding horizontally with the two-roll techn;qu~, the top of the second chill roll 54
should be about 6 to 12 mm (1/4 to l/2 in.) above the centerline ofthe die lip 44. When
using a three-roll stack, the nip point between the top (first) 52 and middle (second) 54
chill rolls should be on or slightly below the centerline of the die lip 44.
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Attorney Docket No.: 1691.001 21
The top and middle rollers 52, 54 are rotated in syn~hrolu~alion, preferably at a
rate of about l O to 50 fpm, dep~nding upon the substrate 20 being extruded and
thickness desired. The top and middle rollers 52, 54 preferably rotate at about 20 to S0
fpm for thin PET and PET-G substrate 20 (I to 25 mil), and rotate at about 10 to 20
5 fpm for thicker PET and PET-G substrates 20 (25 to 60 mil) and all gauges of PCT-G
and acrylic substrate 20.
The means for rotating the rollers 52, 54, 56 is l~refe,ably a seven helical gear
system available from Ko~ollm~nn Gear Corp. (New Jersey), shown in Fig. 8. The gears
10 preferably have a did..lel-ical pitch of about 2.25, a pressure angle of about 14.5
degrees, a helix angle of about 25.84 degrees and a circular tooth thicl~ncss of about
0.1386 to 0.1396 inches. The helical nature ofthe gears is believed to contributeto the
smooth rotation ofthe rollers 52, 54, 56 and hence, to provide a reflective material 10
that is subst~nti~lly free from optical chatter.
The preferred gear system comprises: a first gear 58 affixed to a drive means
(not shown) rotatable in a first direction and having circu...felenlially disposed helical
gear teeth; a second gear 60 having circu---fel elllially disposed helical gear teeth
rotatable in a second direction in commnnic~tion with the first gear 58 teeth; a third
20 gear 62 affixed to the first roller 52 and having circumferentially disposed helical gear
teeth rotatable in the first direction in communication with the second gear 60 teeth; a
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Attorney Docket No.: 1691.001 22
fourth gear 64 having circul.,felellLially disposed helical gear teeth rotatable in the
second direction in conlm~ ic~tion with the second gear 60 teeth; a fi~h gear 66 affixed
to the second roller 54 and having circull,ferenlially disposed helical gear teeth rotatable
in the first direction in communication with the fourth gear 64 teeth; a sixth gear 68
5 having circunlfel e~ ally disposed helical gear teeth rotatable in the second direction in
comm--n;c~tion with the fourth gear 64 teeth; and a seventh gear 70 affixed to the third
roller 56 and having circu,,,~ele~ ally disposed helical gear teeth ~otalable in the first
direction in comm~ tion with the sixth gear 68 teeth, thereby rotating the first,
second and third rollers 52, 54, 56 in synchronization. The helical orientation of the
10 gear teeth, as opposed to standard lateral gear teeth, is believed to conllil,ule to a
material 10 that is subs~ ly free of optical chatter.
The dictpnce between the top and the middle rollers 52, 54 is determined by a
first pair of hydraulic positioning means 72 located on the top roller 52. The ~ict~nce
15 between the lower roller 56 and the middle roller 54 can also be determined by a second
pair of hydraulic positioning means 74 located on the lower roller 56. The position of
the middle roller 54 is fixed within the roll stack 50, however, the entire stack 50 can be
moved vertically relative to the die lip 44 by a third pair of hydraulic positioning means
76. The location and pressure of the first, second and third pairs of hydraulic
20 positioning means 72, 74, 76 are monitored and controlled by the CPU. A linear
potentiometer (not shown) monitors the distances. These hydraulic systems provide a
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Attorney Docket No.: 1691.001 23
much more consistent and controllable means for m~int~ining the rlist~nce between
rollers than conventional pneum~tic means. Preferably, the first hydraulic positioning
means 72 provides at least about 500 pli, more preferably at least 1000 pli and more
~lerel~bly about 1,300 pli, between ~djacent top and middle rollers 52, 54.
As seen in Fig. 6B, the m~chirle can further be equipped with a first tensioning
roll 78 for providing l~min~tes, such as the reflective layer 12, to the extruded substrate
20 as it is being passed between the top 52 and middle rollers 54. A second ten~ nine
roll 80 may be provided to supply a protective m~sl~in~ polymer larninate 82 to the
10 finished material 10 as it is being passed from the lower roller 56 through a pair of
material 10 receiving rollers 84, 86. The first and second tensioning rolls 78, 80 are
preferably controlled by pne~m~tic brakes, (not shown) preferably capable of applying a
tensioning pressure between 30 and 160 psi. For a reflective layer 12 cont~inir~ an
~Inmimlm metal having a gold colored acrylic coat, the plefell~;d braking on the first
15 tensioning roll 78 is about 40 to 60 psi. For a reflective layer 12 col.lail~ing only an
~lumimlm metal, the preferred braking on the first tensioning roll 78 is about 100 to 140
psi. For m~s~ing l~min~te 82 the preferred braking on the second ten~ionine roll 80 is
about 10 psi.
The material 10 is delivered along a conveyor 88 to a pair of opposed receiving
rollers 84, 86 which rotate in the direction of the top and middle stack rollers, 52, 54
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Attorney Docket No.: 1691.001 24
respectively, to receive the material 10. The pa;r of receiving rollers 84, 86 preferably
have a rubber surface for gripping the reflective material 10 and a means for adjusting
the rlict~nce therebetween corresponding to the gauge ofthe reflective material 10. The
material 10 is thus tensioned by setting the rate of rotation of the receiving rollers 84, 86
5 p,ef~-dbly up to 50% greater, relative to the rate ofthe rotation ofthe top 52 and
middle rollers 54 (fpm). For thinner PET and P~T-G substrates 20, the receiving
rollers 84, 86 are p-efe~ dbly set at about a 6 to 9% greater rate than the chrome rollers
52, ~4. For thicker PET and PET-G substrates 20 and all gauges of acrylic and PCT-G
substrate 20, the receiving rollers 84, 86 are preferably set at about a 10 to 12% greater
10 rate than the chrome rollers 52, ~4. These higher rate settings for the receiving rollers
84, 86 permit app.op.iate tensioning ofthe material 10, without indu~ng distorting
strain. The actual rotation rate of the receiving rollers 84, 86 however, remains in
synchroni~lion with the top and middle rollers ~2, 54.
As stated previously, the preferred setup for producing heavy material 10 [0.254
mm (10 mils) or heavier] and sheeting is the three-roll stack ~0. With this setup, nip-
polishing (sometim~s called kiss-polishing or c~l~nd~ring) will yield considerably higher
quality film or sheet that can be obtained with the two-roll, S-wrap technique. When
lining out the equipment to make material 10, it is strongly suggested that the die lip 44
20 be adjusted to obtain uniform thickness across the die lip 44 width prior to bringing the
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Attorney Docket No.: 1691.001 25
polishing roll stack 50 into position. Failure to do so can result in poor quality material
10 having nonuniform strain and substantial optical surface distortion.
High pressures between the first and second rollers 52, 54 are necessO, y for
5 proper nip-polishing. Previously suggested roller pressures range from about 175 pli for
heavy sheet, up to about 350 pli for lighter gauges. However, the hydraulic means 72 of
the present invention provides a pressure of at least 500 pli and more ple~l~bly about
1,300 pli between the first and second rollers 52, 54, which yields a reflective material
10 sub~ ly free from optical chatter and which prevents dPI~...ir.~;on ofthe layers
10 12, 20. Due to these high pressure requirements, the rolls 52, 54 should be fabricated
and hardened to about 48 to 50 Rockwell C hardness prior to chrome plating or else
worm-tracking or grooving will occur.
Material 10 produced by the nip-polishing techni1ue not only has excellent
15 optical qualities, but it also possesses snap-back, which results from internal strains
induced in the material 10 during the polishing operation. Snap-back is highly desirable
in material 10 being produced for subseq-lPnt thermoforming because it reduces the
amount of sag in the material 10 during heat-up for thermoforming and .~.;..;...;,~ s
webbing. Nip-polished material 10 can be examined for strain uniformity by using
20 polarized light.
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Attorney Docket No.: 1691.001 26
The equipment used for winding material 10, such as the pair of receiving rollers
84, 86 previously mentioned, should be capable of precise tension control. Sudden
changes in tension or uneven tension ate likely to produce wrinkles or optical chatter in
the material 10. ~vlinimllm tension should be used when winding the material 10 to
5 reduce blocking tendenri~s
Devices for removing static electricity from the material 10 sbould be positioned
at strategic locations in the extrusion line to ~ nilll;~e dirt and dust pickup, electric
shock, film ~linein~, and film blocking. Strategic locations would be just downstream
10 from the nip rolls, and just before windup. In Fig. 6B, a static bath station 92 familiar to
those skilled in the art is shown for providing long-lasting protection against static.
Conditions similar to those given in Table 1 are suggested for extruding material
10 from substrate 20 PET and PET-G. In the majority of cases, the rolls 52, 54, 56
15 should be run at te.llpe.dlLIres just below the point at which sticking would occur.
When downr~ting is being used, the top roll 52 should usually be run at least about 15
to 18~F cooler than the middle roll 54 so that the material 10 will follow the middle roll
54 and release easily from the top roll 52. With a two-roll, S-~vrap setup, the first roll
52 should be run as hot as possible without film stic~in~ and the second roll 54 should
20 be ~djusted to obtain the desired material 10 flatness. The temperatures and parameters
described herein are provided as p, ~;r~l . ed examples only, and are not int~nded to limit
the scope ofthe invention. Each temperature in Table I is monitored and controlled by
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Attorney Docket No.: 1691.001 27
the CPU. The temperatures are believed to be variable by at least about + 5~F while
ill~ g the operability ofthe invention.
TABLE I
SPROCESS TEMPERATU~ES (~F)
1-25 mil 40-60mil 1-25 mil 40-60mil Allgage Allgage
PET-G PET-G PET PET Ac~x!ic PCT-G
ExtruderZone I 480 450 520 520 405 510
Extruder Zone 2 490 460 550 560 420 540
10 Extruder Zone 3 500 470 560 560 445 540
Extruder Zone 4 490 460 550 540 430 530
Extruder Zone 5 485 460 540 530 450 520
Extruder Zone 6 485 450 530 530 450 520
Screen Changer 485 450 530 520 450 520
15 Adapter 485 450 530 520 450 520
Melt Pump 485 450 530 520 450 520
Static Mixer 485 450 530 520 450 520
Co-Ex Block 485 450 530 520 450 520
Adapter 485 450 530 520 450 520
20 Die Zones 470 450 480 460470 420 470
Die Lip 470 460 480 460470 400 470
Top Roller 80-90 65-85 90 70-80 180 125
Middle Roller 110-130 90-120 110 100-120 200 130
Bottom Roller 145 145 145 145 220 180
Such a CPU computer monitoring and control system is available from FACTS,
Inc. (2737 Front Street, Cuyahauga Falls, OH 44221). For exa~nple, a FACTS, Inc.
1500 Plus System is a versatile interactive data acquisition and control system
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Attorney Docket No.: 1691.001 28
specifically designed for extrusion line applications. The system has a broad range of
capabilities including digital VO and analog inputs, temperature and speed loop control,
and PID loops that can be mixed and m~tched or c~sc~ded together to provide complete
extruder control. The system's configuration for di~rerel.~ products may be stored as
5 user defined product codes, allowing the user to change his entire system at the touch of
a button to run a JilI~lelll product.
Therefore, the 1500 PLUS control system can be tailored to specific
applications. This ple~lled system is composed ofthree major components: 1. Central
10 Processing Unit and I/O Panel Cabinet with Color Touch Information Display "TID"
monitor screen; 2. Parameter control Panels; and 3. Software (Base system & Specials
if desired). Software can be custom written to provide the various control ranges for
temperatures, rotation rates, pressures, etc. described herein.
Before extruding substrates 20, the extruder 32 and die lip 44 should be cleaned
thoroughly. Any nicks or scratches on the die lip 44 flow surfaces should be polished.
In addition, the surfaces of the chill rollers 52, 54, 56 should be cleaned thorouL~hly.
Before start-up, polymer substrate 20 drying conditions should again be
20 chec~ed In addition, extruder 32 and die lip 44 temperatures should be checked to see
that they are at the proper settings and that simple heat soaking has taken place.
,~.cSIlmin~e that the extruder 32 is ready to start, screw rotation should be started at 15 to
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Attorney Docket No.: 1691.001 29
25 rpm with the dryer 30 hopper throat closed. The extruder 32 should be starve-fed
until extrudate exits the die 44. The purpose of starve-feeding is to prevent drive
overloading and stalling (especially during an initial run). Normally, an extruder 32 with
no substrate 20 in the barrel will overload more quickly than one with substrate 20 left
~ S in it. On s lbseq-lçnt runs, it is not usually necçss~. y to starve-feed the extruder 32
because plastic substrate 20 remains in the barrel from the previous run.
Af'ler the extruder 32 has been started and a good web is observed coming from
the die lip 44, the screw should be stopped and the die lip 44 cleaned before the web is
10 put on the chill rollers 52,54. It is eSs~nti~l that the e,.lre.-,;lies ofthe die lip 44 be
clean in order to minimi7e die lines in the extruded substrate 20. The die lip 44 should
be cleaned first with a brass spatula. It should then be cleaned with a light abrasive
hous~hold cleaner such as that used for brass or copper pots, and then finally wiped with
a clean cloth. If the lip 44 needs to be cleaned inside, a thin brass spatula can be used.
15 After the die lip 44 is thoroughly cleaned, the die lip 44 eAlle---ilies plus the orifice
opening should be sprayed with a uniform, heavy coat of silicone release agent.
A~er the die lip 44 is cleaned, the chill roll stack 50 takeoff unit should be
brought into the casting position as quickly as possible and the extruder 32 screw
20 restarted. If this is not done quickly, molten substrate 20 will drool from the die lip 44
and stick to the die lip 44 eAIlelniLies, requiring recle~ning To f~cilit~te threading ofthe
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Attorney Docket No.: 1691.001 30
takeoffequipment, it is desirable to have the unit pre-threaded with a leader of film or
kraft paper. This will normally prevent the extrudate from rolling up on the die lip 44 as
it first exits. As soon as the screw is restarted and polymer begins corning from the die
lip 44, the chill roll stack 50 can be started and the pre-threaded leader will pick up the
5 hot web and carry it through the m~chine.
An alternative method ofthreading the takeoffunit which works as well as the
above technique is as follows: with the chill roll stack ~0 backed away from the die lip
44 slightly, a piece of stiff cardboard (the same length as the die lip 44 and about 12
10 inches wide) is placed against the die lip 44 just under the orifice. When the melt first
exits the die lip 44, it is caught on cardboard and carried onto the chill rollers 52, 54.
For a horizontal setup, this prevents melted material 10 from rOl Illhlg a bead and
sticking to the die lip 44. Once the web is on the chill rollers 52, 54, a,r pins for holding
the web edges and an knife can be positioned (not shown). At this point in the start-up,
15 the web should be observed for the presence of die lines. Some lines will probably be
present. If they are large and excessive in number, the face of the die lip 44 should be
~Y~mined for polymer clinging to them and scrubbing against the web. If polymer is
found on the die lip 44, an attempt should be made to remove it by carefully pushing it
into the web with a thin spatula, and thus, allowing the web to carry it away.
As stated previously, a clean start-up is necess~ry to obtain substrate 20 with
minimum die lines, particularly when the substrate 20 will not be nip-polished. If a ver~
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Attorney Docket No.: 1691.001 31
dirty start-up is experienced and many die lines are observed, it is suggested that the
start-up instructions described here be repeated, beginning with the die lip 44 cle~nin~
procedure.
During start-up with a two-roll, S-wrap unit, the first chill roller 52 should be
run cooler than norrnal, since sticking is likely to occur on a freshly cleaned roller. After
10 to 15 min-ltec, a white substance will form on the roller 52, and this plate-out will aid
the release of the film from the chill roller 52. As plate-out covers the roller 52, the
t~ y~ ure of the roller 52 should then be increased. The white. plate-out should be
allowed to remain on the roller 52 unless an excessive amount causes a problem. If
spotty pickoffofthe plate-out occurs, the chill roller 52 temperature should be
increased. This will remove the excessive plate-out from the roller surface. ARer a few
minllt~S~ the roller 52 tenlpelatLJre can then be lowered to its previous setting (or slightly
higher) to prevent excess buildup from reoccurring.
The edges ofthe material 10 should be l~hllllled with razor blade slitters located
somewhere along the extruded web. The blades should be sharp industrial types, rigidly
mounted to prevent optical chatter. The innl~lded angle of the cutting edge with the
sheeting should be fairly small to prevent heavy edge buildup on the finished wound roll
20 go
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Attorney Docket No.: 1691.001 32
The start-up suggestions listed above for a two-roll, S-wrap unit will also apply
when starting a three-roll stack, with the exception of the portion dealing with plate-out.
As with the two-roll setup, the die lip 44 should be cleaned and the extruder 32 started
as soon as possible after the roll stack S0 is brought into position. Also, the use of a
S leader of film or kraft paper will facilitate threading the takeoffunit. Once the m~chine
is running, the line and screw speeds should be adjusted to yield the desired gauge and
production rate.
Next, gauge ~.,.iro,~ y should be chec~d and die af~ stments made to yield and
10 extrudate having minimal thickness variation across the web. Cut a piece of substrate 20
from the web which covers the entire width of the web. Measure the t~ic~n~ocs at two-
inch intervals and mark the readings on the substrate 20 at each point checked. This will
give a visual indication of the areas needing adjustm~nts over that portion of the
substrate 20 from which the sample was taken. Determine which bolts (not shown) on
15 the die lip 44 need adjusting by laying the substrate 20 over a full scale die lip 44 bolt
location pattern attached to a table near the extruder 32. By having bolt locations on
the pattern and bolts on the die lip 44 itself numbered, one can quickly see exactly which
bolts should be adjusted. Bolts in heavy areas should be tightened and bolts in thin areas
should be loosened. This procedure should be repeated until the gauge variation across
20 the width is no greater than +5%, except possibly at the edges, which can be trimmed.
Edges should be adjusted as well as possible; if the edges are too thick, they can hold
the nip roller 52, 54 apart causing additional gauge problems.
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Attorney Docket No.: 1691.001 33
Once these die lip 44 adjustments are made, the polishing roll stack S0 should be
brought into position, and only minor ~djustm~nts should be needed. Bringing the
polishing chill roll stack 50 into position at the beginning of start-up and prior to
arljustine the die lip 44 will require more time and result in more scrap generation during
5 line-out. Furthermore, the proper lie-out procedure should also ~ e the pos~;bil;ly
of producing substrate 20 with nonuniform strain caused by thick and thin areas.
As previously mentioned, a short die lip 44 to chill roll stack 50 air gap is needed
- to 1-1;1-;-11i7~ sagging ofthe extrudate. If excess sag occurs and the extrudate contacts
10 the chill roll stack 50 too far ahead ofthe nip point, air can be ellllapped between the
extrudate and the chill roll stack 50 and result in random unpolished areas. If the sag
has been l..;.~ d with a short air gap and low melt te.,-pe-~ re, and air e~,l.a~ e~JL is
still a problem, the chill roller 52, 54, 56 should be lowered relative to the die lip 44 so
that the extrudate will go straight into the nip and be contacted by both polishing rollers
15 52, 54 siml~lt~neollsly. If this is not properly accomplished, the reflective material 10
will contain optical distortions.
Quality control is very important in any substrate 20 extrusion operation,
çspeci~lly with the most preferred reflective material 10. There are at least three things
20 that should be checked routinely at various times during all production runs. These
include gauge uniformity, strain level, and flow rate or I.V. Substrate 20 gauge should
be checked in both the m~rhine (M.D.) and transverse (T.D.) directions. Both of these
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Attorney Docket No.: 1691.001 34
should be controlled to within +5% of the target thickness. The strain level is important
because it has as an effect upon the manner in which the substrate 20 reacts during and
after thermoforming. Too little strain results in a minimllrn of snap-back, and thus, the
rate at which the substrate 20 sags will be too great. If the strain is too great, the
5 substrate 20 can shrink too much and actually pull out of the chains which carry the
substrate 20 in thermoforming. Too much strain can also cause other forming problems
such as localized sl,l 1 ~e of the substrate 20 during thermofc,.li~hlg that results in
nonuniform gauge and/or wrinkles. In addition, substrate 20 with too much strain will
not be as tough as it should be.
Probably the simplest method of determining the strain level is by checl~in~ M.D.
shrinkage. For blister paç~eing applications, the M.D. shrinkage should be about 8 to
10%. For applications in which the substrate 20 will be used in its extruded condition
and not thermoformed, M.D. shrinkage should be minimi7ed and should Dot exceed
15 about 4 to 5%. It is important that strain be both minimal and uniform in the extruded
product. The use of polarized light is an excellent nondestructive techn:que for
qualitatively ch~c~ing extruded substrate 20 (or formed parts) for the presence and
u n;ro.,.lily of strain. In fact, a simple polarized light apparatus can be monnted in line
with the extruder 32 to monitor strain.
As stated earlier, the toughness of substrate 20 made from PET, PET-G, or,
PCT-G is dependent upon its l.V ~as well as other factors such as strain and the
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Attorney Docket No.: 1691.001 35
environment). Checking the I.V. is rather complicated and is not suggested as a quality
control test. However, a relatively simple flow rate test, along with a conversion chart,
will provide essenti~lly the same data as the I.V. test. Such tests are known to those
skilled in the art.
When processing substrate 20 into material 10, it is suggested that long runs be
made and that frequent stops and restarts be avoided. Even though interruptions in
production can be tolerated without degradation becoming a problem, they should be
avoided as much as possible to ..~;.l;...;~e the presence of die lines or optical chatter in
10 the finished product as well as the cost of the waste substrate 20.
Polyesters can be s~ticf~ctorily purged from the extruder 32 with either
polyethylene or polypropylene. If a cleanup is to be made, the die lip 44 can be opened
and cleaned while it is still hot without purging. The extruder 32 barrel, however,
15 should be purged before cleaning. This is suggested because polyester has a tendency to
stick to metal and can be somewhat difficult to remove from the screw. These and other
features of the invention will be appare"l to one skilled in the art.
