Process for removing ink-bearing fines from dry-deinked secondary fiber sources

A method of deinking comprises: (a) mechanically fiberizing a secondary fiber source in a substantially dry state, preferably air dry, thereby producing a fibrous material consisting of substantially discrete fibers and ink-bearing fines: (b) depositing the fibrous material onto a moving screen or wire which retains fibers and allows fines to pass therethrough; and (c) lifting the fibrous material above the screen with upwardly directed forced air and redepositing the material onto the screen, whereby upon re-deposition of the material, additional fines pass through the screen.

BACKGROUND OF THE INVENTION 
This application relates to copending application Ser. No. 554,174 filed 
Nov. 22, 1983 now abandoned, entitled "Process for Dry Deinking of 
Secondary Fiber Sources". 
The commercial production of various types of paper requires the use of 
recycled paper as a source of papermaking fibers due to the expense of 
virgin fibers. Prior to using such secondary fiber sources for making a 
commercial product, it is necessary to treat the fiber source to remove 
unwanted chemical constituents which adversely affect the quality of the 
final paper product. The most notable contaminants to be removed are inks 
or dyes which adversely affect the color and brightness of secondary 
fibers used as a feedstock. Ink deposits on paper are extremely thin and 
roughly have a thickness of only about 0.0001 inch. Chemically, the inks 
are generally a mixture of pigment or organic dye, binder, and solvent. 
Some inks also contain metallic driers, plasticizers, and waxes to impart 
desired properties. Hence, their chemical make-up can be very complex. 
However, inks are not to be equated with other additives or contaminants 
such as varnishes, sizes, and plasticizers, which are chemically and 
physically of a different nature as those skilled in the art of deinking 
will appreciate. 
The prior art has addressed secondary fiber clean-up generally by 
subjecting secondary fiber sources to a variety of treatments. The most 
common form of treatment is chemical wet deinking. However, wet deinking 
processes can be expensive and produce large quantities of sludge, which 
creates a disposal problem. In addition, there are certain types of papers 
which cannot be successfully deinked at all by conventional wet methods 
because they are chemically unreactive with the deinking agents. 
Other treatments of secondary fibers have been directed toward separating 
other contaminants besides inks from the secondary fibers, such as plastic 
coatings and miscellaneous particulates. For example, French Pat. No. 
1295608 (1961) teaches recovery of waste paper coated with synthetic 
materials or plastic films by wetting the waste paper and subjecting the 
slurry to attrition in a beating device. The hydrophobic plastic particles 
can be separated from the hydrophylic fibrous material, which has been 
disintegrated by the attrition mill into particles (fibers) which are 
smaller than the plastic particles. British Pat. No. 940,250 (1963) 
teaches a method for recovering fibrous materials from waste paper 
products which have been coated with synthetic resins in the form of a 
rigid film. The waste material is exposed to vigorous mechanical treatment 
in the presence of less than 70 weight percent water to fiberize the 
material, while leaving the synthetic resin film in relatively large 
pieces. British Pat. No. 1228276 (1971) teaches a method for recovering 
fibrous material from plastic coated or plastic-containing wastepaper. The 
wastepaper is fiberized in water whereby the plastic separates from the 
fibers in small particles. The plastic particles are then separated from 
the fibers. A Russian article entitled "Dry Comminution of Waste Paper:, 
M. V. Vanchakov, V. N. Erokhin, M. N. Anurov (Jan. 14, 1981) teaches dry 
grinding of wastepaper in a hammermill as a pretreatment prior to a 
hydropulper to separate large contaminants such as fasteners, cloth, 
polyethylene film, and others. The ground material was passed through 
separator screens having 4 mm. and 8 mm. diameter holes and the fractions 
passing through the screens were defiberized in a hydropulper. However, as 
suggested previously, none of these methods are directed to deinking. All 
are concerned with removal of plastic films and coatings, which separate 
out as relatively large pieces. Also, except for the Russian article, all 
of these methods use water and accordingly are not suggestive of a dry 
process. On the other hand, the Russian article does not suggest deinking, 
but rather is directed toward removal of large contaminants rather than 
fines. 
Still other prior methods of treating waste papers use different 
approaches. For example, U.S. Pat. No. 3,736,221 (1973) to Evers et al 
teaches a method for making shaped bodies from wastepaper by fiberizing 
the wastepaper in a hammermill, coating the fibers with an aqueous binder, 
compressed under pressure, and baked. No effort is made to remove the ink 
from the wastepaper. U.S. Pat. No. 4,124,168 (1978) to Bialski et al 
teaches a method for recovering different types of wastepaper from a mixed 
source by fragmenting the source materials and separating the various 
components by their fragmentability. This method only serves to classify 
various types of wastepaper present in a mixed sample and does not attempt 
to remove the ink from the wastepaper. German Pat. No. 1097802 (1961) 
teaches a method for reclaiming wastepaper by tearing the paper and 
cleaning it, crimping and rolling the torn paper in a practically dry 
state, and defibering in the dry state, optionally in the presence of dry 
steam. This method seeks to overcome difficulties in fiberizing 
wastepapers coated with hydrophobic materials which do not respond well to 
aqueous methods. There is no teaching, however, that inks can be removed 
by such a dry treatment. 
The previously mentioned copending application Ser. No. 554,174 also 
published in Belgian Pat. No. 898,500, issued Jan. 16, 1984, describes an 
invention which has overcome the disadvantages of the abovesaid prior 
deinking methods. The process involves fiberizing an ink-containing 
secondary fiber source, substantially dry, wherein individual fibers and 
ink-containing fines are produced. The fibers and fines are then separated 
by any suitable means, such as by depositing the material on a moving wire 
and drawing the fines down through the wire with a vacuum on the underside 
of the wire. However, it has been found that the initial deposition of the 
fibrous material onto the screen may not necessarily remove all of the 
fines present in the fibrous material, particularly if the resulting layer 
of fibers is too thick. Therefore, improvements to the separation step can 
be useful. 
SUMMARY OF THE INVENTION 
In general, the invention resides in a method for deinking a secondary 
fiber source comprising: (a) mechanically fiberizing the secondary fiber 
source in a substantially dry state, preferably air dry, thereby producing 
a fibrous material consisting of substantially discrete fibers and 
ink-bearing fines; (b) depositing the fibrous material onto a moving 
screen or wire which retains fibers and allows fines to pass therethrough; 
and (c) lifting the fibrous material above the screen with upwardly 
directed air and redepositing the material onto the screen, whereby upon 
re-deposition of the material, additional fines pass through the screen. 
It has been observed that repeating step (c) above can increase the amount 
of fines removed. The fines being removed can be in the form of ink 
particles, fiber fragments bearing ink, or other particulate matter 
bearing ink, such as fillers and paper size fragments, fiber fragments 
formed during the fiberization, fiber fragments initially present in the 
secondary fiber source, and particulate filler materials initially present 
in the secondary fiber source. 
For purposes herein, "secondary fiber source" means cellulosic products 
bearing or containing ink, such as printed waste paper, reclaimed for use 
as a source of papermaking fibers. 
"Air dry" means the moisture content of the secondary fiber source is in 
equilibrium with the atmospheric conditions to which it is exposed. 
"Substantially discrete fibers" means essentially individual fibers, with 
allowance for some fiber aggregates, which are many times longer than 
their diameter. 
"Substantially dry state" means that there is insufficient free water or 
moisture present on or within the fibers or fines to cause the fibers and 
fines to substantially adhere to each other. Typical secondary fiber 
sources may contain from about three to nine weight percent moisture and, 
for purposes of this invention, it is preferred that no additional water 
be present or added to the secondary fiber source to be fiberized. It has 
been found that as the water content of the paper increases, the energy 
requirements of the fiberization apparatus increases rapidly. This energy 
increase tends to destroy the fibers resulting in unacceptable fiber 
degradation. Also, as the water content within the fiberizer increases, 
the fibers and fines within the fiberizer will adhere to each other and 
plug up the apparatus. Hence, "substantially dry state" may include the 
presence or addition of water, but not so much as to cause an unacceptable 
or uneconomical amount of fiber degradation or energy consumption or 
plugging of the fiberizer. A specific numerical limitation for the water 
content will depend on the characteristics of the specific secondary fiber 
source and the operation and economics of the specific fiberization 
apparatus, which can differ greatly. These limitations can be determined 
without undue experimentation by those skilled in the art. In general, 
however, a total moisture content of about 20 weight percent based on 
solids is believed to be the upper practical limit for most situations. 
The process of this invention is particularly useful for removing inks from 
secondary fiber sources which have been treated or coated with a surface 
size or a barrier material. The size serves as a holdout to the ink in 
such a manner as to prevent the ink from directly contacting the surface 
of the fibers upon application of the ink to the secondary fiber source. 
In such cases, at least some of the size or coating is removed with the 
ink fines during fiberization. Examples of barrier coatings or surface 
sizes include starches, casein, animal glue, carboxymethyl cellulose, 
polyvinyl alcohol, methyl cellulose, wax emulsions, and a variety of resin 
polymers. 
The discrete fibers obtained by the process of this invention, which do not 
exhibit hydration (which is characteristic of fibers obtained by wet 
deinking methods), are suitable as secondary fiber and can be recycled for 
the manufacture of cellulosic products such as tissue, papers, pads, 
diapers, or other products made from fibrous webs or batts.

DETAILED DESCRIPTION OF THE DRAWING 
FIG. 1 illustrates the internal working chamber of a suitable fiberizer 1 
for forming the fibrous material from the secondary film source. The 
specific apparatus illustrated and used for purposes herein was a Pallman 
Ref. 4 fiberizer and is illustrated in U.S. Pat. No. 3,069,103. Shown is 
the serrated, grooved working surface 8 against which the feed material is 
abraded by the action of the moving rotor blades 9 driven by a suitable 
drive means 2. Cooling water is provided to the fiberizer through inlet 6 
and outlet 7. The working surface 8 is also present on the hinged cover 
10, shown in the open position. Although not clearly shown in this Figure, 
there is a space between the serrated working surface and the blades in 
which cellulosic materials are buffeted about. The blade position relative 
to the working surface 8 is adjustable to add a degree of control over the 
extent of fiberization, which is also controlled by the rotor speed, the 
residence time, and nature of the working surface. The working surface 8 
consists of six removable segments. These can be replaced by a greater or 
fewer number of segments having a different design or configuration with 
respect to the surface. This flexibility provides an infinite number of 
choices for altering and optimizing the fiberization. However, the 
configuration illustrated herein has worked very satisfactorily. More 
specifically, the grooves of each segment as shown are parallel to each 
other and are spaced apart by about 2 millimeters (mm.), measured 
peak-to-peak. Each groove is about 1.5 mm. deep. The radial width of each 
segment is about 10 centimeters (cm.). These dimensions are given only for 
purposes of illustration and are not limiting, however. Also partially 
shown is the working surface on the inside of the hinged cover 10, which 
is substantially identical to the other working surface 8 already 
described. When the cover is closed, the two working surfaces provide an 
inner chamber in which the feed material is fiberized. 
FIG. 2 is a cross-sectional, cut-away view of the fiberizer schematically 
illustrating its operation. The arrows indicate the direction of flow of 
air and fibers. More specifically, secondary fiber source 15 is introduced 
into the feed inlet 3 where it is contacted by the rotating blades 9. The 
air flow directs the secondary fiber source between the rotor blades and 
the working surface 8 such that the secondary fiber source is comminuted 
into smaller and smaller particles, eventually being reduced to 
substantially discrete fibers and fines. The centrifugal forces created by 
the rotor blades tend to force the particles, preferentially the larger 
particles, to the apex 16 between the angled working surfaces. These 
forces tend to keep the larger particles from escaping before they have 
been completely fiberized. Upon substantially complete fiberization, the 
comminuted solid materials are carried through the orifice 11 of the 
removable plate 12. The fan impellers 13 then force the airborne fibers 
out through the exit port 4. 
FIG. 3 illustrates the fiberizer previously described in continuous 
operation as would likely be required for commercial operation. In this 
embodiment, the feed inlet 3 is shown as a tubular inlet which will 
provide a continuous supply of shredded secondary fiber sources material 
of suitable size and quality. Generally speaking, such a material can be 
in the form of sheets of from about 2 to about 4 inches square or less and 
should be free of debris to protect the fiberization apparatus. However, 
the particle size and shape of the feed will depend on the capabilities of 
the particular fiberizer being used and is not a limitation of this 
invention. Rip shears can be and were used, for example, for shredding the 
secondary fiber sources. Also illustrated is the continuously moving 
screen 18 which collects the fibers in the form of a web or batt 19. The 
mesh of the screen is selected to allow the fines to pass through, 
preferably aided by a vacuum box 20 which collects fines and channels them 
to an appropriate recovery site. A wire cloth from W. S. Tyler 
Incorporated having a mesh of 150 (150 openings per linear inch), a wire 
diameter of 0.0026 inch, an opening width of 0.0041 inch, and an open area 
of 37.4% has been found to work best when producing a web having a basis 
weight of about 12 lb./2880 square feet or less. Thicker webs tend to trap 
the fines within the web itself regardless of the size of the wire 
openings. Shown in phantom lines is a modified exit port 4 which has been 
widened to accommodate the width of the moving screen. In actual practice 
on a continuous basis, for example, shredded wastepaper was fed to the 
Pallman fiberizer at a rate of 1.5 pounds per minute. The fiberizer was 
set up with a 3 mm. clearance between the serrated working surface and the 
rotor blades. A removable plate having an orifice of 140 mm. was installed 
behind the impeller, which travelled at 4830 rounds per minute (r.p.m.) 
with no load. Air flow through the fiberizer was about 365 cubic feet per 
minute. Cooling water was fed to the cooling jacket at the rate of 2 
liters per minute. Initial water temperature measured 59-60 degrees 
Fahrenheit (.degree.F.) and levelled off at 66.degree.-68.degree. F. after 
an extended run. The wire had a mesh size of 150 mesh, which was large 
enough to permit the fines to pass through yet small enough to retain the 
fibers. The speed of the wire receiving the fiberized material from the 
fiberizer was set at 350 feet per minute. Vacuum under the wire measured 
0.6 inch of water. About 18.85% of the secondary fiber source passed 
through the wire as fines, whereas the remainder was collected on the wire 
as a dry deinked product. The fines portion contained about 75 weight 
percent fiber particulates and about 25 weight percent clay (filler). Both 
portions contained ink. 
FIG. 4 schematically illustrates one embodiment of the process of this 
invention. Shown is the fiberizer 1 receiving suitably sized shredded 
ink-containing wastepaper which is fiberized into a fibrous material 19 as 
previously described and deposited onto a moving screen or wire 18. The 
fines 21 filter through the screen into a vacuum chamber 23 wherein a 
vacuum is maintained on the underside of the screen in a suitably enclosed 
space by a vacuum pump 24 and suitably-spaced orifices and piping to 
provide sufficient vacuum throughout the vacuum chamber to hold the 
fibrous material onto the screen. 
After the initial deposition of the fibrous material onto the moving 
screen, the fibrous material is then acted upon by a series of air showers 
31, 32, 33, and 34. Each of the air showers consists of a tube positioned 
with its length in the cross-machine direction of the travelling screen 
and suitably connected to a source of pressurized air 35. The air pressure 
can be measured with a pressure gage 37. Each air shower tube contains a 
multiplicity of spaced apart orifices positioned below the screen such 
that forced air is directed upwardly through the screen in a manner to 
momentarily lift the fibrous material above the screen as illustrated. The 
force of the air must be such that the vacuum present below the fabric is 
able to prevent the raised fibers from being blown away and thereby 
pulling the raised fibers back down onto the screen as shown. As a result, 
some fines 21 previously present in the fibrous material 19 pass through 
the screen and are removed from the system via the vacuum pump. This 
process can be repeated as many times as necessary to sufficiently remove 
the fines. In fact, a distinct advantage of this method is the flexibility 
available to process operators to adjust the air flow as needed for any 
given situation. By providing a multiplicity of air showers, the 
capability to obtain the highest degree of fines removal is available as 
desired. 
In actual practice, it is important to keep the thickness of the fibrous 
layer on top of the screen as thin as possible or otherwise the fibers act 
as a filter and prevent the fines from reaching the screen. As an example, 
at a moving screen speed of about 650 feet per minute and a fibrous 
material deposition rate of about 2 pounds per minute, the height or 
thickness of the fibrous material on top of the screen was about 1/16 
inch. A vacuum of about 3 inches of water was maintained on the underside 
of the screen, which consisted of 150 mesh stainless steel screen as 
previously described about 6 inches wide. An air pressure of about 15 psi 
was maintained at the pressure gauge 37. The air shower tubes were 11/4 
inch 0.D. copper tubing and extended the full width of the screen. The 
first air shower 31 had a series of orifices of 0.05 inch in diameter 
spaced apart 0.1 inch, center-to-center. The second air shower 32 had 
0.037 inch diameter orifices spaced apart 0.1 inch, center-to-center. The 
third and fourth air showers 33 and 34 had 0.037 inch diameter orifices 
spaced apart 0.75 inch, center-to-center. Under these conditions, the 
fibrous material laying on top of the moving screen was lifted above the 
screen about 1 inch by each of the air showers, which were spaced apart by 
about 4 inches. This spacing permitted the vacuum chamber to pull the 
fibers back down onto the screen in between air showers as illustrated and 
thereby remove fines at the same time. By operating in this manner, 
additional fines can be removed from the fibrous material initially 
deposited on the screen. When the desired amount of fines has been 
removed, the fibers remaining on the travelling screen are suitably 
removed, as by a suction box 39 as shown and directed to fiber recovery. 
FIG. 5 illustrates two alternative means for providing upwardly directed 
air to lift the fibrous material above the screen, each of which means can 
be used alone or in combination with each other or in combination with the 
air shower. More specifically, the two alternative means are a sub-screen 
surface, represented by a cylindrical rod 40, or an above-screen surface, 
represented by a foil 50. The operating principle behind the function of 
these alternative means is that the speed of the travelling screen causes 
a stream of air to be carried with the screen. When this airstream 
contacts a solid surface, it is diverted one way or the other. Depending 
on the shape of the surface, the airstream can be directed upwardly and 
thereby lift or pull the fibrous material above the screen as shown. 
In the case of the rod 40, the airstream moving with the underside of the 
travelling screen 18 becomes compressed as it enters the tapering "pocket" 
41 formed between the screen 18 and the leading surface of the rod 40. 
This causes air to be forced upwardly through the screen and lift the 
fibers above the screen as shown. More than one rod can be positioned in 
series to repeat the process as necessary. The shape of the tapering 
pocket can influence its effectiveness. It is believed that too small of a 
pocket, as created by a rod with too small of a diameter, will not trap 
enough air to cause a sufficient pressure build-up to lift the fibers. A 
cylindrical rod having a diameter of 11/4 inch positioned in contact with 
the underside of the travelling screen has been found to work well, but 
other sizes and shapes can be successfully used with minimal 
experimentation. An advantage of this embodiment is its mechanical 
simplicity in that a source of compressed air and air nozzles are 
unnecessary. On the other hand, adjustment of the upward air flow is not 
as easily made, although some adjustment can be made by changing the 
position of the rod. 
In the embodiment wherein a foil 50 is used, the airstream moving with the 
upper surface of the travelling screen creates a zone of lower pressure 
beneath the trailing edge of the foil, known as the Bernoulli effect, 
thereby causing an upward flow of air which raises the fibers above the 
screen as shown. As with the previous embodiment, the design of the foil 
must be optimized to meet the needs of the particular situation. One or 
more foils can be used in series, or the foil(s) can be used in 
combination with sub-screen surface or the air shower. 
It will be appreciated that the specific shapes of the above-screen surface 
and the sub-screen surface can be optimized according to aerodynamic 
principles.