GB2133817A - Dry deinking of secondary fibres - Google Patents

Abstract

Ink-bearing secondary fibre feedstocks are deinked by mechanically fiberizing the feedstocks in a substantially dry state to produce substantially discrete fibres and fines and separating the fines from the fibres. The feedstock may be shredded printed waste paper. Fiberisation may be effected in any conventional fiberisation equipment. Separation of fines from fibres may be carried out using a mesh bag, or a continuously moving wire screen, preferably with the assistance of a vacuum box. The fibres recovered may be cleaned by aqueous centricleaning, or by wet deinking methods.

Description

SPECIFICATION Process for dry deinking of secondary fibre sources This invention relates to the deinking of secondary fibre sources to enable them to be used, for example, for the production of paper.

The commercial production of various types of paper requires the use of recycled paper as a source of papermaking fibres due to the expense of virgin fibres. Prior to using such secondary fibre sources for making a commercial product, it is necessary to treat the fibre 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 colour and brightness of secondary fibres 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 fibre clean-up generally by subjecting secondary fibre sources to a variety of treatments, the most common form of which is chemical wet deinking. For example, United States Patent No. 3,098,784 teaches a process for deinking printed paper wherein the printed paper is slurried in water containing 0.2 to 5.0 percent (based on the weight of the paper) of a water-soluble non-ionic surface active agent at a temperature of from about 900 to 1 800F. The treatment is carried out in standard pulp fiberizing equipment wherein the paper stock is reduced to substantially individual fibres. However, this and other wet deinking processes can be expensive and produce large quantities of sludge, which creates a disposal problem.In addition, there are certain types of paper which cannot be successfully deinked at all by conventional wet methods because they are chemically unreactive with deinking agents.

Other treatments of secondary fibres have been directed toward separating other contaminants besides inks from the secondary fibres, such as plastic coatings and miscellaneous particulates.

However, 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, the methods use water and accordingly are not suggestive of a dry process.

Accordingly, there remains a need for a deinking process which avoids or minimizes sludge formation and chemical costs. Although various prior art treatments of waste paper have attempted to satisfy this need, none of the methods have been successful.

A method of deinking in accordance with the invention comprises: (a) mechanically fiberizing an ink-bearing secondary fibre source of feedstock in a substantially dry state, preferably air dry, thereby producing substantially discrete fibres and fines; and (b) separating the fines from the fibres.

Fiberization is conducted when the secondary fibre source is air dry or sufficiently dry to prevent adhesion of the resulting fibres and fines.

Such a method is simpler and more economical than the commonly used wet deinking methods.

The fines, which may include the ink-bearing fines, can be removed or separated from the fibres, for example, by screening through a screen having mesh openings sufficiently small to retain the fibres, yet large enough to permit the fines to pass through. The fines may comprise ink particles, fibre fragments bearing ink, other particulate matter bearing ink, such as loading or filler materials, fibre fragments formed during the fiberization, fibre fragments initially present in the secondary fibre source, and particulate loading or filler materials present in the secondary fibre source. It is understood, however, that in all instances at least a portion of the fines would include ink-bearing fines or ink particles.

The terms, as used herein and in the appended claims, have the following meanings: "Secondary fibre 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.

Typically, secondary fiber sources contain from about three to nine weight percent moisture, which, for purposes of this invention, is about the range for air dry paper. It, therefore, is preferred in carrying out the invention, 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 requirement of the fiberization apparatus increases rapidly. This energy increase tends to destroy the fibers resulting in unacceptable fiber degradation. Also, as the water content increases, the fibers and fines formed during fiberization tend to agglomerate or adhere to each other, which can plug up the apparatus, hinder separation and diminish the yield of useable fiber.Hence, the secondary fiber source is in a substantially dry state when fiberization is conducted, and although water may be present or added, it should not be 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 mainly on the characteristics of the secondary fibre source and the operation and economics of the fiberization apparatus used in the process. These limitations can be determined by experimentation by those skilled in the art. In general, however, a moisture content of about 20 weight percent based on solids is believed to be a practical limit for most situations.

The process of this invention is particularly useful for removing inks from secondary fibre 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 provide resistance to passage of the ink after application to the secondary fibre source. In such cases, at least some of the size or coating is removed with the ink fines during fiberization and separated from the fibres. 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 fibres obtained by the process of this invention, which do not exhibit hydration (which is characteristic of fibres obtained by wet deinking methods), are suitable as secondary fibre and can be recycled for the manufacture of cellulosic products such as tissue, papers, pads, batting, sheeting, newsprint, and the like.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of an example of a fiberizer apparatus used to carry out a process in accordance with this invention; Figure 2 is a perspective view of the fiberizer of the type of Figure 1 with the front lid opened to expose the impeller blades and the serrated working surface; Figure 3 is a cut-a-way perspective view of the opened fiberizer with the impeller removed to expose the orifice through which the processed fibres are withdrawn from the working chamber; Figure 4 is a side elevation of the fiberizer partially in section illustrating its operation; Figure 5 is a perspective view of a fiberizer modified to operate in a continuous mode.

Figure 6 is a schematic flow diagram illustrating a process in accordance with this invention, and Figure 7 is a block diagram illustrating the use of this invention in connection with making paper.

Referring first to Figure 1, the fiberization apparatus generally illustrated is a turbomill. However, those skilled in the art will appreciate that a variety of fiberization apparatus is available to carry out the process of this invention, such as hammermills, disc mills, pin mills, wing beater mills, etc.

In general, the fiberizer 1 comprises a housing which encloses rotating rotor blades 9, (see Figure 2) driven by a suitable drive means 2. The secondary fibre source, e.g., printed waste paper, which may be shredded, is fed to the fiberizer through a feed inlet 3 and the waste paper is comminuted or fiberized substantially to individual fibres and fines.

An internally disposed fan draws air in through the feed inlet 3 along with the waste paper, and expels the air through exit port 4 carrying the fibres and fines along with the air. The fibres are collected in a tubular meshed bag 5 which permits the fines to pass through the mesh openings while retaining the fibres. The specific meshed bag 5 material which was found to work satisfactory had a mesh size of 50x60 openings per inch. The wire diameter of 0.009 inch and the openings were 0.006 inch by 0.012 inch. The open area of the screen was 23 percent of the surface area.

Also shown in Figure 1 is a cooling means having a water supply inlet 6 and exit ports 7 for removing heat generated due to friction by the shearing of the fibre feedstock. Aside from the tubular meshed bag, fiberizers are illustrated in Figure 1 are commercially available equipment. Such a fiberizer is illustrated in U.S. 3,069,103. The specific apparatus illustrated and used-for purposes herein was a Pallman Ref 4 fiberizer.

Figure 2 illustrates the internal working chamber of the fiberizer, primarily illustrating the position of the rotor blades. There is shown a serrated, grooved working surface 8 against which the feed material is abraded by the action of the moving rotor blades 9. Although not clearly shown in this Figure, there is a space between the serrated working surface and the blades in which cellulosic materials are buffetted 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.

Figure 3 is cut-a-way perspective of the fiberizer with the rotor removed to expose the orifice 11 through which the fiberized material passes before exiting through the exit port 4. The size of the orifice is a variable which controls the degree of fiberization by increasing or decreasing the air flow rate and hence the residence time within the fiberizer. The orifice is contained within a removable plate 1 2 for convenient changing of the orifice size. An orifice diameter of 1 60 mm. has been found to be suitable in conjunction with an air flow rate of about 10 cubic meters per minute. Also shown in Figure 3 are the impeller blades 13 of the fan which provides the flow of air through the fiberizer.

Figure 4 is a cross-sectional, cut-a-way view of the fiberizer schematically illustrating its operation. The arrows indicate the direction of flow of air and fibers. More specifically, secondary fiber source 1 5 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 or fiberized 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 1 6 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 1 3 then force the airborne fibers out through the exit port 4.

Figure 5 illustrates the operation of the fiberizer previously described, but slightly modified for continuous operation as would likely be required for commercial operation. In this embodiment, the feed inlet 3 is shown as a tubular inlet rather than the hopper as shown in Figure 1. The feed tube will provide a continuous supply of shredded secondary fiber sources material of suitable size and quality.

Generally speaking, such a material can be in 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 fibre sources used to gather the data presented in Tables I-Ill.

A further modification illustrated is the continuously moving screen 1 8 which collects the fibres in the form of a web or batt 1 9. 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 percent has been found to work best when producing a web having a basis weight of about 12 lb./2800 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 litres per minute. Initial water temperature measured 59 to 50 degrees Fahrenheit ( F.) and levelled off at 66 to 680 F., after an extended run. The speed of the wire receiving the fiberized material from the fiberizer was set at 350 feed per minute. Vacuum under the wire measured 0.6 inch of water. About 1 8.85 percent of the secondary fibre 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).

Figure 6 schematically illustrates an overall view of a process in accordance with this invention.

More particularly, it shows a source of secondary fibers 1 5 being fed. to a fiberizer 21 identical to cr similar in function to the type described in the previous Figures. As previously suggested, for most fiberizers it is probably preferable to first shred the secondary fiber source. In the fiberizer the secondary fiber source, whether shredded or not, is substantially reduced to individual or discrete fibers and fines and deposited on a moving screen 18. Deposition of the fibers onto the screen is aided by a vacuum box 20 which facilitates fines removal. The fines include much of the ink present in the raw feed and are collected in a suitable receptacle 22 for disposal. Vacuum for the vacuum box is provided by fan 23, which pulls the fines through the screen and blows them into the receptacle 22.The fibrous mass or batt of fibers deposited on the moving screen is thereafter recovered by metering to a uniform thickness in a suitable metering device 24 and thereafter converted into bales of pulp in a baler 25 or alternatively, fed directly into a pulper to form a pulp slurry for making paper in the conventional manner. In addition, the recovered fibers can be fed directly to an air-forming apparatus for producing air laid webs or batts. Those skilled in the art will recognize that a variety of apparatus or equipment can be used in performing the functions illustrated herein.

Figure 7 further illustrates the process of this invention with a block diagram showing the overall process for making paper using fibers recovered from a dry-deinked secondary fiber source. As shown, an ink-bearing secondary fiber source (such as printed waste paper) is fiberized air dry to produce substantially discrete fibers and fines. The fines are separated from the fibers in any suitable manner leaving the recovered fibres to be used as desired. There are at least several options. As shown, the fibers can be baled for subsequent pulping as shown by the phantom lines. They also can be fed directly to an air-former to produce air-laid webs. Alternatively, the fibers can be cleaned, as by aqueous centricleaning (illustrated in Tables IV and V), or by wet deinking methods which are well known in the industry.In either case, the resulting fibres can be pulped by slurrying with water and diluted into papermaking stock of an appropriate consistency. The papermaking stock is then wetlaid to form a fibrous web and dried to form a paper sheet. The specific papermaking steps can vary but are also well known in the art. The dry-deinked fiber of this invention is useful as a secondary fiber for tissue, fine paper, printing paper, and other papers.

Examples In order to illustrate the effectiveness of the process of this invention, six different secondary fiber sources were mechanically fiberized in accordance with this invention as previously described using the fiberizer illustrated in Figures 1-4. The six different samples were computer printout. Xerocopy Boned,1 ink-coated board cured by ultra-violet light (UV-coated board), lacquered board, newsprint, and magazines. The second, third, and fourth samples mentioned above are virtually untreatable by standard wet deinking processes. All of the secondary fiber sources were air dry and were processed at room temperature. However, it will be appreciated that certain inks and sizes can be more optimally processed at higher temperatures when they are more friable and therefore form finer particles more easily.On the other hand, some inks or sizes may be thermoplastic and therefore can be more easily processed at lower temperatures. The optimum processing temperatures will therefore depend upon the properties of the specific predominant secondary fiber source and the economics of providing a suitable temperature.

Deinked fibers recovered by subjecting each sample to the process of this invention (Test) and non-deinked fibers (Control) recovered by shredding each sample into small pieces and slurrying in warm water (1 100F.) with gentle mixing to break the fiber-to-fiber bonds of the sample were each used in an aqueous slurry as a pulp for making paper handsheets in a conventional manner. The handsheets so formed were then tested for brightness using an Elrepho Photoelectric Reflectance Photometer (ISO 3688) and ash content (a measuring of coating and/or filler removal (TAPPI T2 11 M-58)).

In addition,1the Test and Control pulps were also tested for their drainage properties (Canadian Standard Freeness TAPPI T227 m-58). The results are set forth in Tables I, II, and Ill below.

Table I (Canadian Standard Freeness (ml.)) Sample Control Test Computer printout 380 590 Xerocopy 500 700+ UV-coated board 500 700+ Lacquered board 500 700+ Newsprint 100 270 Magazine 130 280 Table II (Ash Content (weight percent)) Sample Control Test Computer printout 10.3 6.2 Xerocopy 9.3 4.6 UV-coated board 4.6 2.4 Lacquered board 5.1 3.2 Newsprint Magazine 23 1 5 Table III (Brightness) Sample Control Test Computer printout 72 77 Xerocopy 81 85 UV-coated board 75 78 Lacquered board 79 82 Newsprint 35 44 Magazine 51 58 1Husky2 Xerocopy Bond, (Eastman Kodak) photocopy paper As is clear from the resulting data, the brightness and ash content of the final sheet were improved when the fibers recovered from the process of this invention were used to form the sheet.In addition, the drainage properties (freeness) of the pulp was also improved by the dry-deinking process of this invention. The dry-deinked samples also exhibited a dramatic reduction in the number of visible ink specs when compared to the untreated samples. Although not specifically measured, this improvement is at least partially reflected in the brightness measurements.

In addition to being a sole treatment for a secondary fiber source to be used as a feedstock for papermaking, the dry deinking process of this invention can also be used as a pretreatment to be followed by further cleaning of the fibers or a conventional wet deinking process. As a pretreatment, this process will decrease wet sludge formation during the wet deinking process (which minimizes the disposal problem created by the sludge formation) and reduces chemical costs since a portion of the inks will have already been removed prior to the subsequent wet deinking treatment. Tables IV and V contain comparative data for deinked cigarette cartons, illustrating improvement in some of the physical properties of two secondary fiber sources (cigarette cartons) when dry-deinked and subsequently cleaned in a hydroclone (centricleaning).

Table IV (WINSTON Cigarette Cartons) Dry Deinking Wet Dry plus Deinking Deinking Centricleaning Freeness 616 619 700 Elrepho brightness 76.5 75.3 77.6 Ash,% 3.3 1.8 Table V (SALEM Cigarette Cartons) Dry Deinking Wet Dry plus Deinking Deinking Centricleaning Freeness 636 658 699 Elrepho brightness 81.2 79.5 79.9 Ash, % 3.0 2.1 In each Table the first column contains physical property data for the product obtained by subjecting the particular sample to a conventional wet deinking process. The particular process used is of no consequence with respect to the process of this invention, but merely serves as a benchmark for purposes of comparison. Specifically, the deinking solution comprised 3.0 grams sodium hydroxide, 0.2 grams tetrasodium pyrophosphate, 0.2 grams Armak Ethofat 242/25 surfactant, and 1667 ml.

water. The deinking solution was heated to 1 800 F. and 50 grams of oven dried waste paper cut or torn into half inch pieces was added with mixing. After fiberization of the sample occurred, the sample was washed three times by diluting with water to a consistency of 1%. The washed product was then tested for Canadian Standard Freeness and formed into handsheets for the brightness tests.

The second column contains corresponding data for the products of the dry deinking process of this invention as previously described.

The third column contains corresponding data for the products obtained by centricleaning the fibers obtained from the dry deinking step of the second column. In particular, the dry deinked fibers were slurried with water to a feed consistency of about 0.5 dry weight percent. The slurried fibers were fed under 42 pounds per square inch gauge (psig.) pressure to a Bauer "600N" Centricleaner at a rate of approximately 40 gallons per minute. The particular apparatus referred to is a hydroclone (liquid cyclone) of a nylon construction having a generally conical shape with a 3 inch nominal internal diameter at the top and a height of approximately 36 inches. The centricleaner serves to separate the fibers from smaller and more dense particulates in a manner well known to those familiar with mechanical separations.

These results illustrate the effectiveness of the dry deinking process of this invention as a pretreatment followed by cleaning, especially with regard to fines reduction as measured by the increased freeness in both samples. In addition the brightness of both washed samples was slightly improved over the dry-deinked product.

Although not illustrated, the dry-deinked fibers can also be subsequently wet-deinked by conventional means well known to those skilled in the art of deinking. For example, the dry-deinked fibers can be slurried in the deinking solution previously described herein for a period of time to remove additional ink and washed and/or centricleaned.

It therefore is appreciated that the invention has application either as a deinking process, perse, or as a process in combination with other paper-making processes. Further, the invention has numerous advantages not achieved by the prior art.

Claims (16)

Claims

1. A method of deinking an ink-bearing secondary fibre source comprising mechanically fiberizing the secondary fibre source to produce substantially discrete fibres and fines, said fiberizing occurring when the secondary fibre source is substantially air dry or sufficiently dry to prevent adhesion of the resulting fibres and fines, and then separating the fines from the fibres.

2. A method as claimed in Claim 1 wherein the secondary fibre source contains no more than about 20 weight percent moisture.

3. A method as claimed in Claim 1 wherein the secondary fibre source is air dry.

4. A method as claimed in any of the preceding claims wherein the fines are separated from the fibres by fiberizing the fines through a screen having a mesh size sufficiently small to prevent passage of the fibres.

5. A method as claimed in any of the preceding claims wherein the separated fibres are directly slurried in water for making a cellulosic product.

6. A method as claimed in any of Claims 1 to 4 wherein the separated fibres are fed directly to an air-former.

7. A method as claimed in any of Claims 1 to 4 wherein the separated fibres are formed into a substantially uniform batt and baled.

8. A method as claimed in any of the preceding Claims 1 to 5 wherein the separated fibres are cleaned in an aqueous solution.

9. A method as claimed in Claim 6 wherein the separated fibres are cleaned in a hydroclone.

10. A method as claimed in Claim 6 wherein the separated fibres are cleaned by a wet deinking method.

11. A method as claimed in any of the preceding claims wherein the secondary fibre source is computer printout paper, photocopy paper, ink-coated board cured by ultra-violet light, lacquered board, newsprint, cigarette cartons, or magazines.

12. A method of deinking an ink-bearing secondary fibre source having a surface size which comprises mechanically fiberizing the secondary fibre source to produce substantially discrete fibres and fines comprising ink and size, said fiberizing occurring when said secondary fibre source is substantially air dry or sufficiently dry to prevent adhesion of the resulting fibres and fines, and separating the fines from said fibres, whereby said fibres are suitable as secondary fibre.

13. A process for making paper from an ink-bearing secondary fibre source comprising: (1) mechanically fiberizing the secondary fibre source to produce substantially discrete fibres and fines, said fiberizing occurring when said secondary fibre source is substantially dry to prevent adhesion of the resulting fibres and fines; (b) separating said fines from said fibres; (c) slurrying said fibres with water to form a papermaking stock; (d) wet-laying the papermaking stock to form a web of fibres; and (e) drying the web.

14. A secondary fibre useful in recycle for the manufacture of cellulosic product and produced from an ink-bearing secondary fibre source comprising discrete fibres obtained by mechanical fiberization of said fibre source when air dry or sufficiently dry to prevent adhesion of the resulting fibres and fines and obtained separately from the resulting fines, and said discrete fibres exhibiting no hydration which is characteristic of fibres obtained from wet recycle.

1 5. Deinking fibres produced by a method as claimed in Claims 1 to 13.

16. A method of deinking an ink-bearing secondary fibre source substantially as hereinbefore described.