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Патент USA US3084673

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April 9, 1963
E. WARNER
3,084,663
DOCTOR BLADE FOR COATING APPARATUS
Filed Aug. 29. 1960
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Patented Apr. 9, 1963
2
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within the holder. Thus the doctor rod structure of the
present invention is self-cleaning, capable of coating uni
3,684,663
DOCTOR BLADE FUR COATING APl’ARATUh
Edgar Warner, Middletown, Qhio, assignor to Champion
Papers Inc, a corporation of Qhio
Filed Aug. 29, 1960, Ser. No. 52,438
8 Claims. (tCi. 118-—1l18)
The present invention relates to the manufacture of
coated webs or coated sheet material and has particular
application to the manufacture of such webs or sheets
wherein the coating composition is an adhesive substance
or contains an adhesive which acts to bind the coating
substance to the web or sheet or if pigmented, the pig
ment particles to each other and to a web, a case in point
being the manufacture of coated paper for high grade
printing purposes. In particular, the invention relates
to an improved doctor blade which may be used in such
manufacturing processes. The invention may be classi?ed
formly, while at the same time all of the advantages of
the prior art devices are retained.
The present structure therefore represents an improve
ment over the prior art referred to above in that it per
mits of the application of a greater weight of coating
composition to the web being processed than has hereto
fore been possible with doctor devices, and differs from the
fore-running doctoring devices in that this result is ob
tained by utilizing a relatively small diameter doctor rod
provided with a series of alternately arranged annular
ribs and grooves on its surface and mounted the rod in a
holding structure such that the annular grooves are self
cleaning and are in and of themselves, are doctored of
excess coating over and above that which has been
deposited upon the web being coated.
The details of the invention will become more apparent
from the following description thereof in which reference
as an improvement over the doctor blade structure shown
will be made to the accompanying drawing wherein,
20
in Warner Patent 2,598,733 dated June 3, 1952 as well
FIG. 1 is a front elevation of the doctor blade com
as that disclosed in Warner Patent 2,729,192 dated Janu
prising the present invention,
FIG. 2 is a sectional view taken along the line 2-2
ary 3, 1956.
Since the manufacture of coated paper is an excellent
of FIG. 3,
example of the usefulness of the invention and illustrates
FIG. 3 is a sectional view similar to P16. 2, but show
its advantages, this medium will serve to illustrate the 25 ing a modi?ed form of the invention,
invention, its use and its advantages over known struc
tures, though it will be understood the invention is capable
of much broader application and utility.
The manufacture of coated paper by a doctoring process
usually comprises the application of an excess of an aque
ous dispersion of a mineral pigment and an adhesive to
the surface of a moving web and subsequent removal of
the surplus over and above the amount (of coating com
FIG. 4 is a view ‘similar to FIG. 3 but illustrating a
further modi?ed form of the invention, and ?nally
FIGS. 5 and 6 are schematic diagrams illustrating the
manner in which the invention may be incorporated into
several representative coating processes.
Referring now in particular to FIGS. 1 and 2, it will be
seen that the doctor blade comprises essentially two parts,
the doctor rod 10 and a holder 20 therefor. The doctor
position) required to form a coating of the desired dry
rod 10 is formed from a steel rod which has been ma
weight on (of coating) the surface of the web. In the 35 chined, rolled or otherwise worked by one or the other of
processes disclosed in the aforesaid patents, the paper web
several methods to modify its normally smooth cylindrical
absorbs aqueous vehicle from the portion of the applied
surface, such that it is comprised of a series of concentric
coating layer in contact therewith to form what is therein
alternately interdigitated circumferential hills 2 and valleys
called a ?lter cake, which is ?rm enough to resist the
4 of generally thread-like pro?le con?guration. It is most
wiping action of the doctor which then rides on the sur
face of the ?lter cake and wipes off the overlying ?uid
coating composition.
signi?cant to note that these valleys and grooves are de
?ned as thread-like. They do not comprise a thread in that
there is no spiral progression of the valley as is the case
of a thread wherein the valley between adjacent ribs would
When utilizing a doctor coating process in accordance
with the aforesaid patents it was found to be difhcult to 45 be continuous throughout the length of the article pro
secure ?lter cake heavy enough to form coating of the
vided with the thread from one end to the other. Rather
desired dry weight. Attempts have been made to secure
in the present invention each valley between any two
the passage of more coating under the doctor by using
adjacent ribs is an annular recess extending around the
wire-wound or vertically threaded doctor rods which were
circumference of the rod and singularly each circumfer
intended to pass under the doctor an amount of ?uid coat 60 ential groove is completely independent one from the
ing metered by the number, form, and depth of the
grooves between the threads or wires.
The use of such
wire wound or threaded doctor rods with paper coating
compositions containing adhesive and mineral pigment
other. As has been stated the pro?le con?guration of the
hills and valleys 2 and 4 may be thread-like in pro?le
appearance. It has been found for example a standard
Witworth pro?le performs, a satisfactory function. Of
was almost always disappointing because of the tendency 55 course the thread pro?le may assume a variety of con
of the coating to pack ?rmly into the grooves and reduce
?gurations, for example, the Witworth pro?le itself may
the space and the amount of coating passed therethrough.
be modi?ed such that the tops of the ribs and the bottoms
Additionally, if the spirally wound devices of the prior
of the valleys may be slightly rounded rather than as
angulated as shown in the drawing. Thus in general, it
art are mounted in a close ?tting holder, the clogging of
the threads tends to build up coating within the holder
may be said that the thread~like pro?le of these alternat
ing ribs and valleys should be such that the included angle
which can and does actually cause the rod to be displaced
between any two adjacent surfaces de?ning a valley should
from its seat with obviously adverse results. Attempts to
cure this difficulty have not proved successful to any great
approximate 90° for most favorable results.
The doctor rod, as has also been stated is preferably
degree because devices capable of cleaning the threads
continuously are expensive and in addition to the men 65 manufactured from a steel rod, of about 1A to 1/3 inch
in diameter, generally of tool steel characteristics. The
tioned difficulties the spiral type of rod has an inherent
rod is chromium plated by any suitable process after the
tendency to creep laterally from the holder.
described pro?le has been imparted to its surface. The
The present device obviates these dllTlClllil?S because
depth from top of the ribs 2 to the floor of the valleys 4
there is no tendency for the rod to creep laterally and the
design of the holder for the rod is such that it acts as a 70 may be varied for the purpose to be de?ned hereinafter,
though satisfactory results have been obtained when this
doctoring device to clean the grooved surface thereof thus
dimension approximates about '.003-.0O4 inch.
preventing both build up of coating in the grooves and
sea
4
As the pro?lt depth may be varied so also may the
in holder 26 preferably at an extremely low rate of speed,
number of ribs per inch length of rod be varied. For
on the order of from 2/3 foot per minute surface speed.
example very successful results have been obtained with
This enhances the self-doctoring feature of the device on
the speci?ed depth and within the range of from 50 to
a continuous basis and additionally distributes wear evenly
150 ribs or “threads” per inch along the entire length of 5 throughout the length of the rod 10. The driving mecha
the doctor rod 10 though this dimension may also vary as
nism may be conventional, such as an electric motor
will be indicated subsequently.
Again referring to FIGS. 1 and 2, it will be seen that
the doctor rod holder 20 may comprise a pair of compli
coupled to the end of the rod through a speed reduction
device.
In FIG. 1 a drive mechanism is illustrated sche
matically as comprising a large sprocket 14 driven from
mentarily shaped clamping elements 16 and 18. These 10 small sprocket 8 via chain or belt 12; the large sprocket
clamping elements may assume several forms, as illus
trated in FIGS. 3 and 4. Each element de?nes a generally
semicircular socket half, such that, when the two ele
ments are joined in complimentary relation they will de?ne
a cylindrical socket in which the doctor rod 10 is firmly
secured. It is extremely important to note that the ter
minal edges 22 and 24 of each of the socket de?ning por
tions of each holder elements is deformed somewhat in
that these edges are bent inwardly to exert a de?nite
being mounted on the end of rod 19; the smaller sprocket
being carried on shaft 6 driven by a conventional motor
M. If desired the same shaft 6 could be connected to the
opposite end of rod 10 such that the rod 10 is driven from
both ends simultaneously. This arrangement is desirable
to prevent torsional stresses from being developed in the
rod 10 where the device is utilized in coating wide webs,
such as in the paper making art.
In FiGS. 1 and 2 the doctor device is shown as a so
pressure against the rod 1%) rather than merely de?ning a
called “rigid” doctor rod. As seen the two holder ele
support as does the greater portion of the socket formed
ments l6 and 18 are ?rmly clamped between a pair of bar
by the holder elements 16 and 18. In addition it will also
members, 30, 301 such that there is little or no ?exure of
be noted that these edges 22 and 24 are spaced apart by
the rod 14? or holder 29. This arrangement is clearly
a distance less than the diameter of the rod 10 such that
shown in Patent No. 2,598,733.
the rod will be physically locked into the holder, yet leav 25
On the other hand FIG. 3 illustrates the present inven
ing a substantial portion of the rod exterior exposed for
tion as utilized as a ?exible doctor rod, the holders 16, 18
contact with he web or other coating means as the case
being riveted or otherwise ?xed to a ?exible support mem
may be.
ber 48. This arrangement is clearly shown in Patent No.
It will also be apparent from an inspection of FIGS. 1
2,729,192.
and 2, the inwardly directed terminal edges 22 and 24 30
FIG. 4, is a further modi?cation of the structure in that
are provided with serrated inner surfaces comprised of
the doctor rod 10 is mounted in holder elements 4-2 and
ribs and valleys 32 and 34 and 26 and 28 respectively.
44 wherein the major portion of the socket de?ned be
The pro?le con?guration of these serrated edges is com
tween them in assembled relation is embodied in holder
plementary to that of the doctor rod such that the ribs 25
element 44 and a minor portion in holder 42‘. Again the
and 32 respectively ride in each of the valleys 4 provided 35 terminal ends 45, 46 of these elements 42 and 44 are
on the doctor rod 1%. Due to the deformation of the
crimped or deformed inwardly to assure close association
edges 22 and 24 inwardly it will be seen that the serrated
of the serrated inner edges 4-7 and 48‘ with the grooved
edges will always be pressed against doctor rod 10 such
surface of the rod 10. This arrangement is particularly
that the ribs 28 and 34 thereon will be pressed into close
useful in connection with the ?exible mounting arrange
contact within the valleys 4 on the doctor rod it}.
There we various methods to produce the proper con
?guration of the serrated edges of the holder elements 16
and 18. However, one method of producing the desired
close ?t between these edges and the doctor rod 16 is
derived by manufacturing the holders of stainless steel
sheet of suitable forming characteristics which is softer
than the rod, assembling the rod 10 in holder 20 and there
after rotating the rod it}. Obviously the pressure of the
ment of FIG. 3.
FIGS. 5 and 6 illustrate but several of the many ways
of utilizing the invention.
FIG. 5 illustrates a simple tension blade coater wherein
the web W passes over a rotating applicator roll 50 which
carries coating from pan 51 onto the web, the coating be
ing smoothed and metered to the correct weight as the
web thereafter passes under tension over rod 10‘. In this
case either the rigid mounting of FIG. 2, or the ?exible
crimped in edges 22 and 24 causes wear on these edges
mounting means of FIG. 3 may be used.
principally at the points of contact between ribs 2 against 50
In FIG. 6, the doctor apparatus is incorporated in a
these edges 22‘ and 24. As rotation is continued the ex
coating apparatus where the web W again contacts an
treme edges of the holder elements wear until the ser
applicator roll 53 rotating in pan 54>. Thereafter the web
rations, ribs 28 and 34-, are gradually worn-in the surface
passes through the nip de?ned between a resiliently
with the result that there is extremely close contact be
covered back-up roll 55 and the doctor blade 10 which
tween rod 10 and the edges of holder 20‘. This extremely 55 preferably will be incorporated in the type of holder as
close ?t is of the utmost importance to the successful
shown in FIG. 4.
operation of the invention.
From the above description of the invention it will be
As has been mentioned the present invention represents
appreciated that changes and modi?cations therein are
an improvement over the prior art, smooth surfaced doctor
Within the purview of one skilled in the art, all of which
rods in that it permits of the application of greater coat 60
are
within the spirit and scope of the invention, limited
ing weights per unit area than any of these devices. This
as it is only as de?ned hereinafter wherein.
is because the circumferential grooves operate as a series
What is claimed is:
of metering devices allowing coating to pass between the
1. A doctor device for the application of coating com
individual chambers formed by these grooves and the web
as it contacts the tops of the ribs. Thus the amount of 65 positions to moving webs and sheets comprising a doctor
rod, a ?exible holder for said rod, support means ai'?xed
coating applied is a direct function of groove size which
to said holder, said doctor rod having a surface com
is in turn a function of groove depth and the number of
prised of a series of closely spaced alternately arranged
thread-like grooves provided per inch of doctor rod length.
circumferential ribs and grooves, said holder de?ning a
It has been found that by application of coating with the
present device a known amount of coating weight may be 70 partial elongated, channel-like socket receiving said rod
applied in a uniform mannerand at such a solids content
‘that the pattern that might be expected does not form but
‘ratherthe coating completely ?ows out on the surface of
the web within a few seconds after application.
As illustrated in FIG. 1, the rod 10 is driven or rotated 75
throughout its length and having spaced apart terminal
edges only conforming to the surface pro?le of said rod
and in close engagement therewith and spaced apart a
distance less than the diameter of the rod when said rod
is emplaced within said socket.
3,084,663
5
2. A doctor device as de?ned in claim
means ‘for rotating said rod in said socket.
3. A doctor device as de?ned in claim 1,
support means is rigid.
4. A doctor device as de?ned in claim 1
support means is ?exible.
5. A doctor device as de?ned in claim 1
1 including
wherein said
6
eter of said rod to expose a minor portion of the surface
thereof to de?ne a working surface, the terminal edges
only of said socket being provided with a serrated con
?iguration corresponding to the pro?le con?guration of
said rod and being in close engagement with all points on
the surface of said rod.
7. A doctor device for the application of coating com
wherein said
positions
to moving sheets and webs as de?ned in claim
holder is comprised of a pair of complementary elements
6 wherein the depth of the grooves de?ned between any
joined together to de?ne a partial socket.
6». A doctor device for the application of coating com 10 two adjacent ribs is from .003 to .004 inch.
8. A doctor device as de?ned in claim 6 wherein the
positions to moving webs and sheets comprising a doctor
surface of said doctor rod is provided from 50 to 150 cir
rod, a holder for said rod, said rod having a thread-like
cumferential ribs per each inch of length.
surface pro?le de?ned by alternatingly and successively
wherein said
arranged, circumferential grooves and ribs, the grooves
and ribs being of generally V-shaped cross-sectional con
?guration such that the included angle de?ned between
any two adjacent surfaces de?ned a groove is approxi
mately 90°, said holder comprising an elongated socket
receiving said rod throughout its length and embracing
a major portion thereof and having a pair of parallel
terminal edges spaced apart a distance less than the diam
References Cited in the ?le of this patent
UNITED STATES PATENTS
1,980,961
2,598,733
2,729,192
Sommer _____________ __ Nov. 13, 1934
Warner _______________ __ June 3, 1952
Warner _______________ __ Ian. 3, 1956
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