JPS6352154B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for producing improved groundwood pulp from wood in the form of logs or chips. BACKGROUND OF THE INVENTION It is known to produce groundwood pulp by contacting logs or chips with a rotating grindstone. The resulting fiber suspension is usually treated in a bull screen to remove coarse particles, which are treated in a fibrillator, e.g. a diskcliff ironer, and returned to the fiber suspension; Sent to main screening department.
The rejects obtained in the main screening section are normally returned to the disc refiner, and the passthroughs, optionally purified in a vortex cleaner and optionally bleached, are directed to a wet or paper machine. DISCLOSURE OF THE INVENTION Groundwood pulp is used in the production of plain newsprint and other types of printing paper, and also in the production of soft crepe paper. In the production of papers of these qualities, high demands are placed on a low bound fiber content, ie a partially defibrated wood residue content. In paper manufacturing, high binding fiber content causes web breakage, imparts a high degree of surface roughness to the paper, and develops printing irregularities. Therefore, a significant challenge in the production of groundwood pulp is to reduce the cohesive fiber content to a desirable low level. The pulp used for the production of paper of said quality is ground to a relatively low freeness, ie to 70 to 200 mlC.SF. Groundwood pulp is also used in the manufacture of cardboard and paperboard, and here again it is desirable to obtain a pulp with a low binding fiber content. The groundwood pulp used to make cardboard must have a relatively high freeness, ie 250 to 400 ml C.SF. However, the disadvantage of milling to high freeness is that the pulp has a relatively high cohesive fiber content and is relatively weak. In recent years, a chemical mechanical pulp called chemothermomechanical pulp, abbreviated as CTMP, has been developed. This pulp has a very high freeness, ie 400 to 700 ml C.SF, and a low cohesive fiber content, making it highly suitable for the production of absorbent products. 500mlC.SF in groundwood pulp mill using grindstone and today's technology
It is not possible to produce a practical pulp with higher freeness. Groundwood pulp with such high freeness contains only a small percentage of fibers and consists mainly of bound fibers and debris and cannot be used to make absorbent products. Solution The above-mentioned problem is solved by forming a fiber suspension by grinding wood in a grinder, and dividing the resulting fiber suspension into a coarse screen fraction and a coarse screen-passed fraction in a coarse screen. In the method for producing groundwood pulp, the fraction passing through the coarse screen is screened in the main screening section, and the fraction not passing through the coarse screen is treated in a fibrillation means and then returned to the coarse screen. In the screening section, 30% by weight or more of the crude screen passing fraction is intentionally removed from the crude screen passing fraction as a main screening section nonpassing fraction, and the main screening nonpassing fraction is separated in the first separation means. ,4
Bundled fibers and fragments having a length of more than 8 mm, preferably more than 8 mm, are separated as a fraction that does not pass through the first separation means and are returned to the roughing screen after being treated in the fibrillation means. The fraction passing through the first separating means is separated in the second separating means by: (a) a long fiber fraction containing at least 80% of the fibers remaining on the Bauer, mucknet screen having 59 meshes/cm; and (b) a long fiber fraction having 59 meshes/cm. The fibers passing through the Bauer-Macknet screen with cm are separated into a short fiber fraction containing 15 to 60%, and the long fiber fraction (a) is dehydrated and removed from the process for use for specific purposes. However, this problem is solved by the present invention, which relates to a method for producing groundwood pulp, which is characterized in that the short fiber fraction (b) is mixed with the fraction that has passed through the main screening section. Benefits With the proposed method, extremely low surface roughness, suitable for the production of e.g. LWC paper (LWC = lightweight coated paper) with low energy consumption, and suitable for blending into other high-quality printing papers. A groundwood pulp of high opacity and virtually free of cohesive fibers is obtained. The separated removed long fiber fraction, produced with very low energy consumption, has a low resin content and high freeness (approximately 200 to 700 ml C.S.
F.) and can be very suitably mixed into pulps intended for use in absorbent products of high bulk and good absorption rate and extremely high absorption capacity and for the production of cardboard or paperboard. . By the method according to the invention it is possible to bring the properties of groundwood pulp to the level of CTMP pulp while keeping the low energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the production of groundwood pulp according to the known technology, and FIG. 2 is a block diagram of the method according to the invention. Preferred Embodiments of the Invention According to the known technique shown in FIG. 1, logs or wood chips are ground in a grinder 1. The fiber suspension leaving the grinder contains knots, splinters and other coarse wood residues and is sent through conduit 2 to a coarse screening section in the form of a bull screen 3 (knotter). The bull screen may consist of a so-called vibrating screen, ie a screen structure with vibrating screen plates provided with holes or slots. The coarse screened coarse material, typically having a length of about 50 mm or more, is passed through conduit 4 to a defibration means 5, such as a disk cliff eyer, and the defibrated material is then passed through conduit 6 The fiber suspension leaving the grinder is returned, for example to conduit 2. The fiber suspension, free of coarse wood residue, is removed from the bull screen via conduit 7 and sent to the main screening section 8. In its simplest form, the portion 8 may be a perforated screen plate, for example.
It can consist of a pressurized screen with a hole diameter of 1.75 mm. Up to about 20% by weight of the fiber suspension entering the main screening section is separated as a reject and optionally passed through a defibration means 5 before passing through a conduit 6, as shown in FIG. It is then returned to the circuit. The flow obtained in the main screening section is withdrawn through conduit 10 and typically has a freeness of 70 to 200 ml C.SF and a freeness of 0.08
It has a binding fiber content of 0.20% to 0.20%. The flowthrough is optionally cleaned in a vortex cleaner before being sent to a wet machine. During the production of groundwood pulp according to the invention (Second
(Fig.), logs or wood chips are ground in a grinder 1. The fiber suspension leaving the grinder is sent through a conduit 2 to a bull screen 3, and the wood residue separated by the screen 3 is sent through a conduit 4 to a defibration device 5, for example a disc refiner, The material defibrated from it is the first
It is returned to the suspension leaving the grinder through conduit 6 in the same manner as illustrated in the figure. In the main screening part 8, which in its simplest form can be a pressurized screen, for example by increasing the throughflow (larger opening of the valve 17) or by reducing the hole diameter of the screen plate. or by a combination of both, the amount of rejects is increased such that between 30 and 80% by weight of the fiber suspension arriving through conduit 7 is separated as rejects.
The resulting reject pulp fraction is passed through conduit 9 to 4
The remaining bundled fibers and fragments having a length of more than mm, preferably more than 8 mm, are sent to the first separating means 11 for separation. The first separating means can be, for example, a vibrating screen with a smaller hole diameter than the vibrating screen 3. The rejects from the first separation means 11 are returned via conduit 12 to the defibration means 5, from where the fraction is returned to the suspension leaving the grinder, eg to conduit 2. On the other hand, the passed pulp fraction passes through conduit 13 to 59
At least the fibers retained on the screen by Bauer and Matsukunet with mesh/cm
In order to fractionate the passed-through fraction into a long fiber fraction containing 80% and a short fiber fraction containing 15 to 60% of the fibers passing through a Bauer-Macknet screen with 59 meshes/cm, for example, centrifugation is performed. It is passed to a second separating means 14 which can be a screen or a curved screen. The long fiber fraction is removed through conduit 16, while the short fiber fraction is removed through conduit 15 and a second
is sent to the throughflow in conduit 10 leaving the main screening section so as to form a short fiber fraction of . In order to produce the effect sought according to the invention, the outgoing material streams B and C of the process should have a weight ratio between long fiber fraction and short fiber fraction of 1:3 to 3:1. must be adjusted to fit the range. According to a particularly preferred embodiment of the invention, the white water obtained when dewatering the long fiber fraction is returned to the first separation means 11 as dilution water and, if desired, a separation filter can be incorporated into the circuit. It has a fiber content of less than 200 mg/ml. Since a larger amount than usual is removed from the main screening section 8, the short fiber fraction obtained through the conduit 10 has a very low binding fiber content according to the invention, in the range of 0.0 to 0.05%. The corresponding known groundwood pulp of comparable freeness is
It has a binding fiber content of 0.08 to 0.20%. A cohesive fiber content of this order significantly impairs the usefulness of the pulp in the manufacture of printing paper, contributes to imparting surface roughness to the paper, and renders the paper non-uniformly ink absorbent. In addition, the short fiber fraction obtained according to the present invention has a fiber distribution different from that of ordinary groundwood pulp, which means that the paper made from said fraction is better than the paper made from ordinary groundwood pulp. Achieve the benefit of having higher tensile index and opacity in printing papers. It is therefore highly suitable for the production of top quality printing papers. The long fiber fraction according to the invention obtained through conduit 16 has a high freeness (200 to 750 mlC.SF)
and has a low resin content of less than 0.3% DKM (below 0.15% DKM after bleaching), and of said fraction.
80 to 100% Bauer with 59 mesh/cm;
Consists of fibers left on the screen by matskunet. This long fiber fraction has excellent properties for the manufacture of absorbent products, offering high bulk, good absorption rate and very good absorption capacity. In the process according to the invention, 15 to 75% of the incoming wood is recovered as the long fiber fraction. Thus, instead of producing a single product which is inferior to chemothermomechanical pulp (CTMP), when carrying out the process according to the invention two products are obtained, each of which has very good properties; The total energy consumption when producing the long fiber fraction according to the invention is 300 to 300 liters per ton of dry pulp.
500kwh, while the corresponding value for chemi-thermomechanical pulp is approximately 1000kwh per ton of dry pulp.
As such, such products are produced using less energy and with higher yields. When producing short fiber fractions, the energy consumption is between 1300 and 1500 kwh per t of dry pulp, whereas the corresponding value for CTMP of corresponding quality is about 2000 kwh per t of dry pulp. When practicing the present invention, at least 96% of the wood is converted to pulp (92-94% for CTMP). The long fiber fraction produced according to the invention is well suited for blending with other pulps such as sulfite pulps, sulfate pulps and chemical mechanical pulps. It is highly suitable for the production of cardboard and paperboard and also for the production of absorbent products. Other fiber materials such as recycled fibers, peat fibers and synthetic fibers can also be mixed with the long fiber fraction. The method according to the invention can also be applied with good results to the production of pressed groundwood pulp, in which case the energy consumption is even lower, approximately 10% lower. The invention is illustrated in the following examples. EXAMPLE Groundwood pulp was produced from spruce according to known techniques (see FIG. 1). Spruce was ground in a grinder 1 and the fiber suspension with a concentration of 2.1% was passed through a conduit 2 to a vibrating screen 3 of the Zienson type with a screen plate drilled with holes of 6 mm diameter.
where the coarse wood residue was removed. Approximately 3% by weight of the incoming fiber suspension obtained in vibrating screen 3 and consisting of coarse debris and bundled fibers.
A concentration of 5% is transferred through the transport conduit 4.
The coarse raw material was then sent to Disccliff Iner 5 for defibration into individual fibers. The defibrated reject pulp was returned to the vibrating screen 3 through conduit 6 and conduit 2. The pass-through from the vibrating screen 3 has a concentration of 1.3% and is sent through a conduit 7 to a pressurized screen 8, i.e. a screen with a fixed cylindrical screen basket, against whose cylindrical inner surface the pulp suspension is is sent under overpressure. The screen was equipped with internal rotating scraper means and the holes in the perforated screen plate of the pressurized screen had a diameter of 1.75 mm. The flow of the fiber suspension to the pressurized screen is such that 20% by weight of the fiber content of the fed fiber suspension remains on the screen plate, and further passes through valve 17, conduit 9, conduit 4, and passes through valve 17, conduit 9, conduit 4, It was further processed at , and was controlled to be returned to conduit 2 . The pulp concentration in conduit 9 was 1.9%. The pass through from the pressurized screen had a pulp concentration of 1.1% and was removed through conduit 10 and further cleaned in a vortex cleaner. A sample, here designated A, was removed for determination of bundled fiber content and fiber composition. In accordance with the present invention, the groundwood pulp manufacturing method was modified as shown in FIG. Therefore, the fiber suspension arriving from the grinder 1 via conduit 2 and having a concentration of 2.1% is coarsely screened in a vibrating screen 3 with a hole diameter of 6 mm, and 3% by weight of the incoming fiber suspension is The occupying rejects are sent through conduit 4 to a disc pulp ironer 5 with a pulp concentration of 5%, after which the defibrated reject pulp having a consistency of 5% is passed through conduits 6 and 2 to a vibrating screen 3. was returned to. The pass-through from vibrating screen 3 had a concentration of 1.3% and was sent via conduit 7 to pressurized screen 8.
In this case the screen plate of the pressurized screen was changed to a hole diameter of 1.60 mm instead of the 1.75 mm hole diameter in the previous case. At the same time, valve 17 was opened further and the amount of non-passing pulp was increased to 70% by weight of the fiber content of the incoming fiber suspension. Pressurized screen 8
The non-passage pulp fraction obtained had a freeness of 245mlC.SF and a bound fiber content of 2.95 according to Somerville.
%, 7.9 mesh/cm not passed 33.1%, 59 mesh/cm not passed 41.5%, and 59 mesh/cm passed
It had a fiber composition of 25.4% by Bauer and Matsukunet. Pulp concentration of non-passable pulp is 1.5%
and through conduit 9, a hole diameter of 3.0
to a first separating means in the form of a vibrating screen 11 equipped with a screen plate having a diameter of 2 mm. The vibrating screen 11 was adjusted so that the rejects were 0.8% by weight of the incoming fiber suspension. The non-passage pulp obtained from the vibrating screen 11 had a Somerville bound fiber content of 73% and was sent through conduit 12 for further processing in the disk cleaner 5 and returned through conduit 6 and conduit 2. . The pulp concentration in conduits 6 and 2 was the same as in tests conducted according to known methods. The pass-through pulp from the vibrating screen 11 was given a pulp consistency of 1.2% and was sent through conduit 13 to a second separation means 14 where it was fractionated. The fractionation means consists of a centrifugal screen of the Cowan type, ie a screen having a stationary cylindrical screen bucket, against the cylindrical inner surface of which the fiber suspension is launched by means of a rotating device. Unlike vibrating screens, centrifugal screens are constructed to take advantage of the mutual self-growth effect of fibers on the screen surface and have larger hole diameters. The centrifugal screen is 1.50
It had a hole diameter of mm. The pass-through fraction obtained from the screen has a freeness of 140 mlC.SF and a bound fiber content of 0.04% according to Somerville; It had a percentage of 82% that did not pass through cm and a percentage of 14% that passed 59 meshes/cm. The pass-through fraction is given a pulp concentration of 0.9%,
It is then sent through conduit 15 to the pass-through from pressurized screen 8, which has a freeness of 90 ml C.SF, a binding fiber content of 0.01%, and a 7.9
2.3% of meshes/cm not passed, 63.7% of 59 meshes/cm not passing, and 34% of 59 meshes/cm passing.
Hauer and Matsukunet had a fiber distribution. Pressurized screen 8 and centrifugal screen 14
The mixed pass-through fiber fraction from was removed through conduit 10 for cleaning in a vortex cleaner (not shown). 20% of the fiber suspension leaving the vibrating screen 11 through conduit 13 was removed as a throughput in the centrifugal screen 14. A sample, here designated B, was taken from the short fiber fraction in conduit 10 for measurements of bundled fiber content and fiber distribution. The amount of short fiber fraction calculated for the incoming wood raw material is 44%, of which 31.2%
was in conduit 15. The non-passage fraction from centrifugal screen 14 accounted for 80% of the fiber suspension leaving vibrating screen 11, giving a pulp concentration of 1.9%, and was removed through conduit 16 as the long fiber fraction. The ratio of short fiber fraction to long fiber fraction is 1:
It was 2.2. A sample, here designated C, was removed through conduit 16 for determination of bundle fiber content and fiber composition. Table I below shows the bundled fiber content and fiber distribution of the samples taken. A represents the known groundwood pulp, B and C represent the groundwood pulp according to the invention, of which B represents the short fiber fraction and C represents the long fiber fraction. Chemothermomechanical pulp D
Representative values of (CTMP) are also shown for comparison.

Table I shows that the short fiber fraction produced according to the invention has a very low binding fiber content. The long fiber fraction produced according to the invention has very high freeness, low binding fiber content and very high long fiber content. That is, as shown in Table I, the short fiber fraction B produced according to the present invention has a fiber distribution similar to that of the known groundwood pulp A, and the long fiber fraction C produced according to the present invention has a fiber distribution similar to that of the known groundwood pulp A. It has a fiber distribution similar to Chemothermomechanical Pulp D. They can therefore be used for the same purpose as the corresponding known groundwood pulps and chemi-thermomechanical pulps, respectively, as is clear from the tests presented below. A portion of the sample taken was bleached with 3% by weight hydrogen peroxide per t of dry pulp, washed with water, dehydrated and dried on laboratory sheets and analyzed for extractables content and whiteness. A portion of the laboratory sheet was ground into a fluffed pulp in a disk cliff iner and the bulk, absorption rate and absorption capacity were measured. The results obtained are shown in the table below. Sample E relates to cyphite pulp, which is a chemical pulp.

[Table] From the table, it can be seen that the long fiber fraction C produced according to the invention has very high values for bulk and absorbent capacity, and a high yield, which was previously considered the best for the production of absorbent products. Comparable to chemi-thermomechanical pulp. The properties of the long fiber fraction are significantly better than that of sulfite pulp. The long fiber fraction also has a significantly lower resin content than CTMP,
And at the same time it has a fairly high degree of whiteness. This high degree of whiteness is surprising because of the low light scattering coefficient of this pulp. Paper was produced from samples A and B and the technical properties of the paper were evaluated. The results are shown in the table below.

Table: The short fiber fraction produced according to the invention thus had a higher tensile index and significantly higher opacity than ordinary groundwood pulp. Therefore, when carrying out the method according to the invention, through the groundwood pulp production process, fine pulp for the production of high quality printing paper and coarse pulp for the production of fluff and cardboard are produced for a wide range of applications. It is possible to produce improved pulps consuming less energy than usual.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a method for producing groundwood pulp according to a known technique, and FIG. 2 is a block diagram of a method for producing groundwood pulp according to the present invention. 1 is a grinder, 3, 8, 11, and 14 are screens, 5 is a disk tiner, and 17 is a valve.

Claims (1)

[Claims] 1. A fiber suspension is formed by grinding wood in a grinder, and the resulting fiber suspension is divided into a fraction that does not pass through the coarse screen and a fraction that passes through the coarse screen. In the method for producing groundwood pulp, the fraction passing through the coarse screen is screened in the main screening section, and the fraction not passing through the coarse screen is treated in a fibrillation means and then returned to the coarse screen. In the screening section, 30% by weight or more of the crude screen passing fraction is intentionally removed from the crude screen passing fraction as a main screening section nonpassing fraction, and the main screening nonpassing fraction is separated in the first separation means. , more than 4mm,
Preferably, bound fibers and fragments having a length exceeding 8 mm are separated as a fraction that does not pass through the first separating means and are returned to the roughing screen after treatment in the defibrating means, The pass-through fraction is separated in the second separation means by: (a) a Bauer having 59 meshes/cm, a long fiber fraction containing at least 80% of the fibers remaining on the screen by the mucknet, and (b) a Bauer having 59 meshes/cm. , a short fiber fraction containing 15 to 60% of the fibers that pass through the screen with the matskunet, dewatering the long fiber fraction (a) and removing it from the process for use for a specific purpose; A method for producing groundwood pulp, which comprises mixing the fiber fraction (b) with the fraction that has passed through the main screening section. 2 The weight ratio of the long fiber fraction to the short fiber fraction is 1:
3 to 3:1. 3. The first, characterized in that 15 to 75% of the incoming wood material is removed as the long fiber fraction.
Section method. 4. The method of item 1, wherein the screening and fibrillation operations are carried out in such a manner that the short fiber fraction has a bound fiber content of 0.05% or less.