CA1096676A - Process and apparatus for improving the properties of a thermomechanical paper pulp - Google Patents
Process and apparatus for improving the properties of a thermomechanical paper pulpInfo
- Publication number
- CA1096676A CA1096676A CA301,414A CA301414A CA1096676A CA 1096676 A CA1096676 A CA 1096676A CA 301414 A CA301414 A CA 301414A CA 1096676 A CA1096676 A CA 1096676A
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- Prior art keywords
- pulp
- paper pulp
- filler
- raw material
- paper
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21B1/00—Fibrous raw materials or their mechanical treatment
- D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
- D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
- D21B1/14—Disintegrating in mills
- D21B1/16—Disintegrating in mills in the presence of chemical agents
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Mechanical Engineering (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
Process for improving the properties of thermomechanical paper pulp, characterized in that a filler is added to said paper pulp when it is still in a plasticized and softened condition. And an apparatus for producing such thermo-mechanical paper.
Process for improving the properties of thermomechanical paper pulp, characterized in that a filler is added to said paper pulp when it is still in a plasticized and softened condition. And an apparatus for producing such thermo-mechanical paper.
Description
The present invention relates to a process and an appa-ratus for improving the properties of thermomechanical paper pulp.
Thermomechanical paper pulp is generally produced in a refiner, preferably one utilizing mutually opposed grinding discs which rotate relative to each other, the paper pulp I
therein being heated as a result of the friction from the grinder or some other equivalent friction-causing effect so that the plasticisable constituents which are present in the pulp, such as lignin, hemicellulose or the like become plas-ticised and softened causing the fibers of the pulp to separate at least partially.
To serve as basis for the present invention, the manufac-turing process of hot ground pulp is briefly presented in the following.
The preparation of hot ground wood is usually accomplished in two grinding steps, of which the primary grinding is carried out in a grinder carrying overpressure. The pressure varies hereby between 1.5 and 3.5 bar (absolute) and the temperature in the grinder is the saturated steam temperature corresponding to this pressure. The secondary grinder operates at atmospneric pxessure.
In the hot grinding process, the chips, after washing with water, are fed by means of a plug screw or rotary seal into the preheater, where the chips are heated with steam.
The same pressure as in the primary grinder prevails in the preheater. From the preheater the chips are conveyed by screws into the grinder, whence the fibres are blown by aid of steam generated therein, to the second grinding step.
The steam and ibre material are separated by means of a cyclone prior to grinding.
-~667~i From -the cyclone, the fib~es are supplied by the aid of screws into the secondar~ grinder, whence the fibres are usually conducted into a pumping tank under the grinder, wbere the pulp stock is dil~ted to desi~ed consi /
-/
/
/ ' , /
:' la -`' . . .
6~i~76 whence the stock is pumped to a sorting step. ~Iereafter the stock represents finished raw material for paper manufacturing.
The above method was developed in the recent years and this constitutes a new mechanical wood defibrating method which takes advan-tage of the long known fact that the soften-ing of the lignin with the aid of heat permits the production of long, pliant and undamaged fibers. This particular deflbration method described above resulted in a completely new mechanical pulp brand which is designated as "thermome-chanical pulp" or "thermo-groundwood". The production of this thermomechanical pulp or groundwood similarly to the preparation of groundwood by means of grinding stones, results in a yield which is almost equal in weight to the weight of the origlnal wood consumed~ The diffe,rence between this thermomechanical pulp or thermo-groundwood (hereinafter reference will only be had with respect to the term "thermo-mechanical pulp") and chemical pulp is that in thermomechani-cal pulp the lignin remains in the pulp itself and therefore also in the paper which is manufactured therefrom.
It is well known that wood contains 20 to 30%
of lignin. Lignin is a generic term for the cellulose-like substance which lines woody fibers and includes lignose, lignon and lignin, which is a high weight, large molecule aromatic substance. Lignin resembles glue somewhat and acts to bind the wood fibers together. The proportion of lignin in the-wood is highest in the intercellular central lamellae.
When the lignin is heated and softened in the manner described above, the wood fibers can be made to become detached from each other in comparatively intact condition.
There are several differences between groundwood , and thermomechanical pulp. Thus, groundwood has a higher content of null fiber and the long fibers found therein are partly damaged. In addition, typical fiber bundles occur.
In the case of thermomechanical pulp, on the other hand, long fibers are intact to a much greater extent than in groundwood and are also longer -than in groundwood.
Recent studies have shown that thermomechanical pulp appears to consist of long, pliant, opened fibers, which are able to form a great number of bonds in the sheet. The fines present in the pulp consist mainly of long fibrils or parts of fibrils, which contribute to the establishment of bonds between long fibers.
Up to quite recently, in the manufacture of newsprint, about 75% of pulp defibrated with the aid of grinding stones has been used, together with 25% of chemically produced cellulose-which was added to improve the properties of the pulp. One of the drawbacks recognized in the use of such newsprint is that in chemical defibration the pulp yield is only about one-half the weight of the wood which is consumed.
It has been suggested that this drawback might be overcome by the use as newsprint of thermomechanical pulp by itself. The use of -thermomechanical pulp alone for the raw material of newsprint results in a gain both in the avoidance of the use of poor yield cellulose component as part of the newsprint and in better printability characteristics of the paper. Furthermore, by the use of thermomechanical pulp it has been possible to develop ~ new light newsprint quality having a base weight substantially lower than that of commonly used newsprint, which was on the order of about 50g per m2.
A further advantage of the use of thermomechanical pulp resides in the fact that as raw material it is possible to utilize partly such materials as, for example, sawdust, which heretofore has been inappropriate for the production of paper pulp in general and of mechanical pulp in particular.
7~
Thus, amon~ the advan-tages of thermomechanical pulp, are the ~ollowing:
1. It is possible to use small size timber, sawdust, and o-ther timber dressing residues, as well as pine and birch which are not suitable for the production of groundwood, in the production of thermomechanical pulp.
Thermomechanical paper pulp is generally produced in a refiner, preferably one utilizing mutually opposed grinding discs which rotate relative to each other, the paper pulp I
therein being heated as a result of the friction from the grinder or some other equivalent friction-causing effect so that the plasticisable constituents which are present in the pulp, such as lignin, hemicellulose or the like become plas-ticised and softened causing the fibers of the pulp to separate at least partially.
To serve as basis for the present invention, the manufac-turing process of hot ground pulp is briefly presented in the following.
The preparation of hot ground wood is usually accomplished in two grinding steps, of which the primary grinding is carried out in a grinder carrying overpressure. The pressure varies hereby between 1.5 and 3.5 bar (absolute) and the temperature in the grinder is the saturated steam temperature corresponding to this pressure. The secondary grinder operates at atmospneric pxessure.
In the hot grinding process, the chips, after washing with water, are fed by means of a plug screw or rotary seal into the preheater, where the chips are heated with steam.
The same pressure as in the primary grinder prevails in the preheater. From the preheater the chips are conveyed by screws into the grinder, whence the fibres are blown by aid of steam generated therein, to the second grinding step.
The steam and ibre material are separated by means of a cyclone prior to grinding.
-~667~i From -the cyclone, the fib~es are supplied by the aid of screws into the secondar~ grinder, whence the fibres are usually conducted into a pumping tank under the grinder, wbere the pulp stock is dil~ted to desi~ed consi /
-/
/
/ ' , /
:' la -`' . . .
6~i~76 whence the stock is pumped to a sorting step. ~Iereafter the stock represents finished raw material for paper manufacturing.
The above method was developed in the recent years and this constitutes a new mechanical wood defibrating method which takes advan-tage of the long known fact that the soften-ing of the lignin with the aid of heat permits the production of long, pliant and undamaged fibers. This particular deflbration method described above resulted in a completely new mechanical pulp brand which is designated as "thermome-chanical pulp" or "thermo-groundwood". The production of this thermomechanical pulp or groundwood similarly to the preparation of groundwood by means of grinding stones, results in a yield which is almost equal in weight to the weight of the origlnal wood consumed~ The diffe,rence between this thermomechanical pulp or thermo-groundwood (hereinafter reference will only be had with respect to the term "thermo-mechanical pulp") and chemical pulp is that in thermomechani-cal pulp the lignin remains in the pulp itself and therefore also in the paper which is manufactured therefrom.
It is well known that wood contains 20 to 30%
of lignin. Lignin is a generic term for the cellulose-like substance which lines woody fibers and includes lignose, lignon and lignin, which is a high weight, large molecule aromatic substance. Lignin resembles glue somewhat and acts to bind the wood fibers together. The proportion of lignin in the-wood is highest in the intercellular central lamellae.
When the lignin is heated and softened in the manner described above, the wood fibers can be made to become detached from each other in comparatively intact condition.
There are several differences between groundwood , and thermomechanical pulp. Thus, groundwood has a higher content of null fiber and the long fibers found therein are partly damaged. In addition, typical fiber bundles occur.
In the case of thermomechanical pulp, on the other hand, long fibers are intact to a much greater extent than in groundwood and are also longer -than in groundwood.
Recent studies have shown that thermomechanical pulp appears to consist of long, pliant, opened fibers, which are able to form a great number of bonds in the sheet. The fines present in the pulp consist mainly of long fibrils or parts of fibrils, which contribute to the establishment of bonds between long fibers.
Up to quite recently, in the manufacture of newsprint, about 75% of pulp defibrated with the aid of grinding stones has been used, together with 25% of chemically produced cellulose-which was added to improve the properties of the pulp. One of the drawbacks recognized in the use of such newsprint is that in chemical defibration the pulp yield is only about one-half the weight of the wood which is consumed.
It has been suggested that this drawback might be overcome by the use as newsprint of thermomechanical pulp by itself. The use of -thermomechanical pulp alone for the raw material of newsprint results in a gain both in the avoidance of the use of poor yield cellulose component as part of the newsprint and in better printability characteristics of the paper. Furthermore, by the use of thermomechanical pulp it has been possible to develop ~ new light newsprint quality having a base weight substantially lower than that of commonly used newsprint, which was on the order of about 50g per m2.
A further advantage of the use of thermomechanical pulp resides in the fact that as raw material it is possible to utilize partly such materials as, for example, sawdust, which heretofore has been inappropriate for the production of paper pulp in general and of mechanical pulp in particular.
7~
Thus, amon~ the advan-tages of thermomechanical pulp, are the ~ollowing:
1. It is possible to use small size timber, sawdust, and o-ther timber dressing residues, as well as pine and birch which are not suitable for the production of groundwood, in the production of thermomechanical pulp.
2. It is possible to use dry wood as the raw material because the chipped wood may be wetted.
- 3. The process is easily controllable and pulp of uniform quality can be produced.
4. The space requirements of the plant and number of operating personnel can be kept low.
5. When thermomechanical pulp is used in place of groundwood both the strength and the bulk of the paper improve.
6. The quantity of added cellulose may be reduced or even completely omitted.
7. The dewatering of the pulp improves and the - speed of the paper machine may be increased to impart to the ~-improvement in the dewatering of the pulp.
However, despite all of the considerable advantages of thermomechanical pulp, there are several drawbacks in its use, including the following:
1. The lignin becomes plastic at high temperatures and this causes blackening upon the calendering treatment t which is due to the fact that the paper becomes more trans-parent in spots, a change which the eye registers as a darker spot.
2. Paper made from thermomechanical pulp has a yellowish color which becomes intensified by solar effect as the paper ages.
3. Although there has been remarkable development~
~6~;76 in recent -times in mechanical pulp manufacture, ~any problems still exist which require solution. One of these problems is the bleaching of the mechanical pulp and the preserva~ion of the light color obtained.
Mineral fillers have been used in the production of paper, primarily because they improve the properties of the paper with respect to printing. The addition of filler is accomplished in one of two differen~ ways, either by pulp filling or by coating.
0 In pulp filling the filler is added in the form of a suspension to the pulp slurry prior to the slurries rival onto the paper machine. This is accomplished by introducing the filler, for example as a 30 to 40% aqueous suspension, into a mixing tank preceding the high consistency slurry tank. Talc, for example, may be added in the form of an aqueous suspension on the intake side of the so-called headbox pump.
Depending upon the type of paper, the material quantities employed in pulp filling vary between about 2%
and 40% calculated with respect to the weight of the completed paper. The most common filler contents are between 5 and 20% by weight.
Among the common fillers which are used are talc, clay (kaolin), chalk, and other equivalent substances, Recently there has been an increase in the use of high quality fillers such as titanium oxide and zinc sulfide for the purpose of increasing the opacity of the paper. The use of fillers results in improvement in the opaci-ty and lightness of color of the paper as well as an increase in absorption of the printer's ink. Still further, such fillers improve the smooth-ness and burnishability of the paper surface.
Among the disadvantages of fillers is that the same 6~d~i impair the stength of paper. Furthermore, the fillers, particularly talc, settle rapidly and thus cause problems with respect to the maintaining of a homogeneous'filler mixture. Among the drawbacks of filler addition procedures known prior to the present invention are the poor adhesion thereof to the paper which manifes-ts itself in a poor retention or leakage of fillers through the wire along with the water removed from the web. The poor adhesion has caused, in finished paper, one sidedness of the fillers and the rising of dust from the paper.
Generally speaking, in accordance with the inven-tion, fillers are added to thermomechanical paper pulp during the production thereof at such time that the filler is in contact with the pulp when the plasticisable constituents thereof are in plasticised and softened condition so that the filler adheres thereto and has the effect of improving the properties of the resulting thermomechanical pulp. Thus, for example, the filler can be added to the thermomechanical pulp before the same is frictionally acted upon, for example by grinding between grinding discs, or during the grinding, or shortly after the grinding while the plasticisable constituents thereof such as the lignin or hemicellulose is in softened condition.
Accordingly, it is a primary object of the present invention to provide a method whereby considerable quantities of filler can be made to become bound to thermomechanical pulp.
It is another object of the present invention to provide a method which can result in increase in the lightness and color and opacity of thermomechanical pulp. It is yet another object of the present invention to reduce the blacken-ing tendency of paper made from thermomechanical pulp when the same is calendered at water contents higher than 10 to 11%.
....
~6~7~;
It is still another object of the present invention to reduce the one-sidedness or assymetry and dust raising tendency of pulps which are filled with fillers.
Still further, it is an object of the present invention to reduce the energy losses in the grinding process in the production of thermo~echanical pulp, it being known that in con-nection with production of thermomechanical pulp an excess of thermal energy is produced, the dissipation of which has given rise to considerable problems.
bther objects and advantages of the present invention - will be apparent from a further reading of the specification and of the appended claims.
According to the present invention, there is provided a process for improving the properties of thermomechanical paper pulp, characterized in that a filler is added to said paper pulp when it is still in a plasticized and softened condition.
According to the present invention there is also provided an apparatus or producin~ an improved thermomechanical paper pulp comprising means for heating the paper pulp in such a way that the constituants thereof are in a plasticized and softened condition, and means for adding a filler to said paper pulp when it is still in its plasticized and softened condition.
... ~
As indicated abo~e, the plasticisable constituent of wood - is mainly lignin and throughout the discussion which follows, reference will generally be had to lignin as this substance which undergoes softening and plasticising as a result of the rise in temperature during the grinding of the pulp. How-ever, it must be noted that certain paper pulps ~
i ~ 7 contain other constituents than lignin, such as hemicellulose, which are plasticised in an equivalent manner to the plasti-cising of lignin, and from the standpoint of the present invention any such plasticisable constituen-t in the wood is af~ected in the same manner by the process o~ the inven-tion.
Thus, for example, hardwood pulps and paper pulp made of bagasse contain large quantities of hemicellulose, which behaves in the same manner as lignin from the standpoint of the present invention.
It should also be understood -that any filler which is commonly added to paper pulp may be utilized as a filler for the purposes of the present invention,-and although specific examples of specific fillers are mentioned, it is to be understood that the invention is not limited thereto.
Thus, for example, among the more commonly used fillers in the manufacture of paper pulp, all of which may be used for the purposes of the present invention, are kaolin, talc, calcined gypsum, chalk, precipitated calcium carbonate, barium sulfate in cylindrical granular form known as blanc fix, barium sulfate in arthorhombic form known as baryte, silica, titanium dioxide (anatase or rutile~, zinc, sulfide, etc.
Also, the mount of filler which is added according to the present invention varies depending upon the final - product for which the paper is to be used, in the same manner as the addition of filler in ordinary processes. In general, the content of filler, analyzed in terms of ash content, in the pulp slurry, will vary between about 1-7% by weight, and as indicated abovè, the amount is dependent upon the intended use of the final product.
The aqueous pulp slurry which is subjected to the
However, despite all of the considerable advantages of thermomechanical pulp, there are several drawbacks in its use, including the following:
1. The lignin becomes plastic at high temperatures and this causes blackening upon the calendering treatment t which is due to the fact that the paper becomes more trans-parent in spots, a change which the eye registers as a darker spot.
2. Paper made from thermomechanical pulp has a yellowish color which becomes intensified by solar effect as the paper ages.
3. Although there has been remarkable development~
~6~;76 in recent -times in mechanical pulp manufacture, ~any problems still exist which require solution. One of these problems is the bleaching of the mechanical pulp and the preserva~ion of the light color obtained.
Mineral fillers have been used in the production of paper, primarily because they improve the properties of the paper with respect to printing. The addition of filler is accomplished in one of two differen~ ways, either by pulp filling or by coating.
0 In pulp filling the filler is added in the form of a suspension to the pulp slurry prior to the slurries rival onto the paper machine. This is accomplished by introducing the filler, for example as a 30 to 40% aqueous suspension, into a mixing tank preceding the high consistency slurry tank. Talc, for example, may be added in the form of an aqueous suspension on the intake side of the so-called headbox pump.
Depending upon the type of paper, the material quantities employed in pulp filling vary between about 2%
and 40% calculated with respect to the weight of the completed paper. The most common filler contents are between 5 and 20% by weight.
Among the common fillers which are used are talc, clay (kaolin), chalk, and other equivalent substances, Recently there has been an increase in the use of high quality fillers such as titanium oxide and zinc sulfide for the purpose of increasing the opacity of the paper. The use of fillers results in improvement in the opaci-ty and lightness of color of the paper as well as an increase in absorption of the printer's ink. Still further, such fillers improve the smooth-ness and burnishability of the paper surface.
Among the disadvantages of fillers is that the same 6~d~i impair the stength of paper. Furthermore, the fillers, particularly talc, settle rapidly and thus cause problems with respect to the maintaining of a homogeneous'filler mixture. Among the drawbacks of filler addition procedures known prior to the present invention are the poor adhesion thereof to the paper which manifes-ts itself in a poor retention or leakage of fillers through the wire along with the water removed from the web. The poor adhesion has caused, in finished paper, one sidedness of the fillers and the rising of dust from the paper.
Generally speaking, in accordance with the inven-tion, fillers are added to thermomechanical paper pulp during the production thereof at such time that the filler is in contact with the pulp when the plasticisable constituents thereof are in plasticised and softened condition so that the filler adheres thereto and has the effect of improving the properties of the resulting thermomechanical pulp. Thus, for example, the filler can be added to the thermomechanical pulp before the same is frictionally acted upon, for example by grinding between grinding discs, or during the grinding, or shortly after the grinding while the plasticisable constituents thereof such as the lignin or hemicellulose is in softened condition.
Accordingly, it is a primary object of the present invention to provide a method whereby considerable quantities of filler can be made to become bound to thermomechanical pulp.
It is another object of the present invention to provide a method which can result in increase in the lightness and color and opacity of thermomechanical pulp. It is yet another object of the present invention to reduce the blacken-ing tendency of paper made from thermomechanical pulp when the same is calendered at water contents higher than 10 to 11%.
....
~6~7~;
It is still another object of the present invention to reduce the one-sidedness or assymetry and dust raising tendency of pulps which are filled with fillers.
Still further, it is an object of the present invention to reduce the energy losses in the grinding process in the production of thermo~echanical pulp, it being known that in con-nection with production of thermomechanical pulp an excess of thermal energy is produced, the dissipation of which has given rise to considerable problems.
bther objects and advantages of the present invention - will be apparent from a further reading of the specification and of the appended claims.
According to the present invention, there is provided a process for improving the properties of thermomechanical paper pulp, characterized in that a filler is added to said paper pulp when it is still in a plasticized and softened condition.
According to the present invention there is also provided an apparatus or producin~ an improved thermomechanical paper pulp comprising means for heating the paper pulp in such a way that the constituants thereof are in a plasticized and softened condition, and means for adding a filler to said paper pulp when it is still in its plasticized and softened condition.
... ~
As indicated abo~e, the plasticisable constituent of wood - is mainly lignin and throughout the discussion which follows, reference will generally be had to lignin as this substance which undergoes softening and plasticising as a result of the rise in temperature during the grinding of the pulp. How-ever, it must be noted that certain paper pulps ~
i ~ 7 contain other constituents than lignin, such as hemicellulose, which are plasticised in an equivalent manner to the plasti-cising of lignin, and from the standpoint of the present invention any such plasticisable constituen-t in the wood is af~ected in the same manner by the process o~ the inven-tion.
Thus, for example, hardwood pulps and paper pulp made of bagasse contain large quantities of hemicellulose, which behaves in the same manner as lignin from the standpoint of the present invention.
It should also be understood -that any filler which is commonly added to paper pulp may be utilized as a filler for the purposes of the present invention,-and although specific examples of specific fillers are mentioned, it is to be understood that the invention is not limited thereto.
Thus, for example, among the more commonly used fillers in the manufacture of paper pulp, all of which may be used for the purposes of the present invention, are kaolin, talc, calcined gypsum, chalk, precipitated calcium carbonate, barium sulfate in cylindrical granular form known as blanc fix, barium sulfate in arthorhombic form known as baryte, silica, titanium dioxide (anatase or rutile~, zinc, sulfide, etc.
Also, the mount of filler which is added according to the present invention varies depending upon the final - product for which the paper is to be used, in the same manner as the addition of filler in ordinary processes. In general, the content of filler, analyzed in terms of ash content, in the pulp slurry, will vary between about 1-7% by weight, and as indicated abovè, the amount is dependent upon the intended use of the final product.
The aqueous pulp slurry which is subjected to the
- 8 -ti7~
grinding in the production of the thermomechanical pulp of the present invention preferably has a solids content of 20-25%, which solids content has been found to be most suitable for practical application of the production of thermomechanical pulp. Thus, the filler content of -the slurry at the grinding stage will vary between about 0.2% and 18% by weight, al-though further variations may be made depending upon the type of filler, the purpose for which the filler is added and the purpose for which the flnal paper is to be used. The particu-lar filler used among those mentioned above and o-thers is used for improving various properties of the paper including the printing properties, the opacity, the lightness of color, the absorption of printer's ink, the surface smoothness and the feel of the paper. The particular filler is dependent upon which properties are of greatest importance, and of course also on price.
The basis of the present invention is that the filler is added to the pulp for thermomechanical paper pulp at such time that it is contact therewith while the plasti~
cisable constituents of the pulp are in softened and plasti-cised condition as a result of the heat resulting from the friction during the grinding. Thus, the filler can be added before the pulp reaches the grinder, in the grinder itself, or substantially immediately after leaving the grinder but while the lignin or other plasticisable constituent thereof is still in plasticised and sof-tened condition. This latter method of adding the filler after the pulp has left the grinder but while the lignin, hemicelluLose or other plasti-cisable constituent is still in plastic condition is used in the case that the grinding process is too strongly disturbed by the presence of the ~illers.
For a fuller understanding of the invention, refer-_ g _ ~
"
Ei6~6 ence is had to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 constitutes a block diagram illustrating the method of the present invention;
FIG. 2 diagrammatically illustrates an apparatus for carrying out the process of the present invention, Referring more particularly to the figures, in both FIGS.
1 and 2, the symbol ~in refers to the entr~ of the pulp, and MoUt refers t~ the exit o the pulp.
Block 20 represents the stage of preheating of the pulp, while block 21 represents the first grinding stage and block 22 represents the second grinding stage. The pulp from the second grinding stage 22 is conducted to the straining and purifying stage 23. The reject from this straining stage 23 is conducted to the reject gLinding stage ~5 from which it is returned through conduit C to the straining and purifying stage 23.
After the second grinding stage 22 proper a part of the pulp is returned through conduit B to the input side of the second .
grinding stage 22~
The.illers from block 24 are added to the process through :-pipes or conduits al, a2, a3 and a4.
The fillers may be introduced into the process at 26 between the first grinding stage 21 and the second grinding stage 22 through conduit al.
Conduits a2 and a3 represented by the dotted lines illus-trate embodiments o.the invention according to which the f1llers may in part or in whole be introduced directly into the first grinder 21 through conduit a2 or at its input side through con-duit a3.
According to still another embodiment of the invention, as discussed abovel the fillers may also be introduced into the process immediately 10 ~
':
6i~
after the grinding stages 21 and 22, for example -through conduit a4. According to this method of introduction the plasticisable constituent of the pulp must be in'softened plasticised condition at the time of the addition of the filler through a4.
The apparatus and me-thod of producing the thermo-mechanical pulp of improved properties according to the present invention is illustrated in greater detail in connec-tion with FIG. 2.
0 As shown in FIG. 2 a grinder 10 is utili~ed to produce the thermomechanical pulp. The grinder 10 comprises two opposed, metallic grinding discs 11 and 12 which are rotated in mutually opposite directions by mèans of electric motors 15 and 16, respectively. The pulp, for example, in the form of an aqueous slurry of 20-25% solids content is introduced into the grinder by means of the positive feed screw conveyer 13. The selected fillers, for example, talc or chalk in an amount of about 0.2-18% of the slurry is introduced into the screw conveyer 13 at 26, the filler being supplied from block 24 through conduit al.
As shwon in FIG. 2, the pulp raw material, such as wood chips, is fed into the preheater 20 through rotary valve 29. In the preheater 20 the chips are heated to about 100-130C. The preheater 20 includes a screw conveyer and the preheated wood chips leave the preheater 20 through the rotary valve 19 and are subse~uently conducted through the steam separator 17 to the screw conveyer 13 by which the preheated chips are positively fed into the grinder 10. The screw conveyer 13 is so arranged that the steam can be conducted in countercurrent with respect to the direction of movement of the chips.
Fresh steam is introduced into the process as - 11 - ~ , ,' ,:
- -: ' - - - . ~ , .:.
.
7~
required through -the control valve 28 and the pressure in the preheater 20 is controlled by means of con-trol valve 27. The pressure in steam separator 17 is controlled by a similar valve.
As is shown in FIG. 2, the wood chip particles and/or the sawdust particles are subjected to powerful mechanical treatment in the gap ~ between the grinding discs 11 and 12 which rotate in opposite direction. This -trea-tment takes place partly by their contact with the rapidly rota-ting grinding discs, but mainly as a result of their mutual contact with each other, the friction resulting therefrom causing heating of the chips. This heating of the chips results in the softening and plasticising of the lignin (or hemicellulose or other equivalent plasticisable constituent of the wood). The softening of the lignin occurs more easily in the case of wood having a higher water content.
The fillers are admixed with the plasticised lignin in the grinder 10 and adhere to the surface of the fibers at the softened lignin, creating from the lignin and the other plastic constituents of the wood an opaque, ligh-t colored mass.
The fillers may be supplied into the grinder 10 also in the form of an aqueous suspension thereof.
As indicated above, all fillers commonly used in the art may be used for the purposes of the present invention.
-One of the most suitable of such illers is talc which is a particularly soft mineral wi-th a greasy feel, white and of flaky structure. Talc is particularly appropriate due -to its slipperiness which results in reduced energy losses in the grinding process.
A further advantage of the present invention is that wood fibers are preserved in intact condition better by the process of the present invention than in conventional processes.
In general, the me-thod of -the present invention may be applied in all cases in which thermomechanical pulp has previously been used, particularly in the case of such pulp brands in which fillers have already conventionally been used, -though not in-troduced in the manner of the present inven-tion. This includes the use thereof for photogravure and off-set printing paper. In addition, the process of the present invention is suitable for the production of pulp products in which fillers have not hitherto been used but in which it is now possible to use fillers due to the advantages of the method of the present invention. Such applications include, for example, newsprint papers, particularly when it is desired to reduce the base weight of the-paper which is of considerable importance at this time. This becomes possible with the method of the present invention due to the improved opacity of the produced paper.
While the invention has been illustrated in parti-~ular with respect to specific methods of improving of the properties of photomechanical pulp, it is apparent that variations and modifications can be made in accordance with this invention.
.
grinding in the production of the thermomechanical pulp of the present invention preferably has a solids content of 20-25%, which solids content has been found to be most suitable for practical application of the production of thermomechanical pulp. Thus, the filler content of -the slurry at the grinding stage will vary between about 0.2% and 18% by weight, al-though further variations may be made depending upon the type of filler, the purpose for which the filler is added and the purpose for which the flnal paper is to be used. The particu-lar filler used among those mentioned above and o-thers is used for improving various properties of the paper including the printing properties, the opacity, the lightness of color, the absorption of printer's ink, the surface smoothness and the feel of the paper. The particular filler is dependent upon which properties are of greatest importance, and of course also on price.
The basis of the present invention is that the filler is added to the pulp for thermomechanical paper pulp at such time that it is contact therewith while the plasti~
cisable constituents of the pulp are in softened and plasti-cised condition as a result of the heat resulting from the friction during the grinding. Thus, the filler can be added before the pulp reaches the grinder, in the grinder itself, or substantially immediately after leaving the grinder but while the lignin or other plasticisable constituent thereof is still in plasticised and sof-tened condition. This latter method of adding the filler after the pulp has left the grinder but while the lignin, hemicelluLose or other plasti-cisable constituent is still in plastic condition is used in the case that the grinding process is too strongly disturbed by the presence of the ~illers.
For a fuller understanding of the invention, refer-_ g _ ~
"
Ei6~6 ence is had to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 constitutes a block diagram illustrating the method of the present invention;
FIG. 2 diagrammatically illustrates an apparatus for carrying out the process of the present invention, Referring more particularly to the figures, in both FIGS.
1 and 2, the symbol ~in refers to the entr~ of the pulp, and MoUt refers t~ the exit o the pulp.
Block 20 represents the stage of preheating of the pulp, while block 21 represents the first grinding stage and block 22 represents the second grinding stage. The pulp from the second grinding stage 22 is conducted to the straining and purifying stage 23. The reject from this straining stage 23 is conducted to the reject gLinding stage ~5 from which it is returned through conduit C to the straining and purifying stage 23.
After the second grinding stage 22 proper a part of the pulp is returned through conduit B to the input side of the second .
grinding stage 22~
The.illers from block 24 are added to the process through :-pipes or conduits al, a2, a3 and a4.
The fillers may be introduced into the process at 26 between the first grinding stage 21 and the second grinding stage 22 through conduit al.
Conduits a2 and a3 represented by the dotted lines illus-trate embodiments o.the invention according to which the f1llers may in part or in whole be introduced directly into the first grinder 21 through conduit a2 or at its input side through con-duit a3.
According to still another embodiment of the invention, as discussed abovel the fillers may also be introduced into the process immediately 10 ~
':
6i~
after the grinding stages 21 and 22, for example -through conduit a4. According to this method of introduction the plasticisable constituent of the pulp must be in'softened plasticised condition at the time of the addition of the filler through a4.
The apparatus and me-thod of producing the thermo-mechanical pulp of improved properties according to the present invention is illustrated in greater detail in connec-tion with FIG. 2.
0 As shown in FIG. 2 a grinder 10 is utili~ed to produce the thermomechanical pulp. The grinder 10 comprises two opposed, metallic grinding discs 11 and 12 which are rotated in mutually opposite directions by mèans of electric motors 15 and 16, respectively. The pulp, for example, in the form of an aqueous slurry of 20-25% solids content is introduced into the grinder by means of the positive feed screw conveyer 13. The selected fillers, for example, talc or chalk in an amount of about 0.2-18% of the slurry is introduced into the screw conveyer 13 at 26, the filler being supplied from block 24 through conduit al.
As shwon in FIG. 2, the pulp raw material, such as wood chips, is fed into the preheater 20 through rotary valve 29. In the preheater 20 the chips are heated to about 100-130C. The preheater 20 includes a screw conveyer and the preheated wood chips leave the preheater 20 through the rotary valve 19 and are subse~uently conducted through the steam separator 17 to the screw conveyer 13 by which the preheated chips are positively fed into the grinder 10. The screw conveyer 13 is so arranged that the steam can be conducted in countercurrent with respect to the direction of movement of the chips.
Fresh steam is introduced into the process as - 11 - ~ , ,' ,:
- -: ' - - - . ~ , .:.
.
7~
required through -the control valve 28 and the pressure in the preheater 20 is controlled by means of con-trol valve 27. The pressure in steam separator 17 is controlled by a similar valve.
As is shown in FIG. 2, the wood chip particles and/or the sawdust particles are subjected to powerful mechanical treatment in the gap ~ between the grinding discs 11 and 12 which rotate in opposite direction. This -trea-tment takes place partly by their contact with the rapidly rota-ting grinding discs, but mainly as a result of their mutual contact with each other, the friction resulting therefrom causing heating of the chips. This heating of the chips results in the softening and plasticising of the lignin (or hemicellulose or other equivalent plasticisable constituent of the wood). The softening of the lignin occurs more easily in the case of wood having a higher water content.
The fillers are admixed with the plasticised lignin in the grinder 10 and adhere to the surface of the fibers at the softened lignin, creating from the lignin and the other plastic constituents of the wood an opaque, ligh-t colored mass.
The fillers may be supplied into the grinder 10 also in the form of an aqueous suspension thereof.
As indicated above, all fillers commonly used in the art may be used for the purposes of the present invention.
-One of the most suitable of such illers is talc which is a particularly soft mineral wi-th a greasy feel, white and of flaky structure. Talc is particularly appropriate due -to its slipperiness which results in reduced energy losses in the grinding process.
A further advantage of the present invention is that wood fibers are preserved in intact condition better by the process of the present invention than in conventional processes.
In general, the me-thod of -the present invention may be applied in all cases in which thermomechanical pulp has previously been used, particularly in the case of such pulp brands in which fillers have already conventionally been used, -though not in-troduced in the manner of the present inven-tion. This includes the use thereof for photogravure and off-set printing paper. In addition, the process of the present invention is suitable for the production of pulp products in which fillers have not hitherto been used but in which it is now possible to use fillers due to the advantages of the method of the present invention. Such applications include, for example, newsprint papers, particularly when it is desired to reduce the base weight of the-paper which is of considerable importance at this time. This becomes possible with the method of the present invention due to the improved opacity of the produced paper.
While the invention has been illustrated in parti-~ular with respect to specific methods of improving of the properties of photomechanical pulp, it is apparent that variations and modifications can be made in accordance with this invention.
.
Claims (26)
1. Process for improving the properties of thermomechanical paper pulp, characterized in that a filler is added to said paper pulp when it is still in a plasticized and softened con-dition.
2. Process for improving the properties of thermomechanical paper pulp, comprising the steps:
- heating the paper pulp in such a way that the consti-tuents thereof are in a plasticized and softened condition, - adding a filler to said paper pulp when it is still in its plasticized and softened condition.
- heating the paper pulp in such a way that the consti-tuents thereof are in a plasticized and softened condition, - adding a filler to said paper pulp when it is still in its plasticized and softened condition.
3. Process according to claim 2, wherein said filler is added to said thermomechanical paper pulp before the same is frictionally acted upon.
4. Process according to claim 2, wherein said filler is added to said thermomechanical paper pulp during a grinding operation of said paper pulp.
5. Process according to claim 2, wherein said filler is added to said thermomechanical paper pulp shortly after a grinding operation of said paper pulp while it is still in a softened condition.
6. Process according to claim 2, wherein the content of said filler, analyzed in terms of ash content in the pulp, varies between about 1 to 7 % by weight.
7. Process according to claim 2, wherein said paper pulp is heated by friction during a grinding operation.
8. Process according to claim 2, wherein after the heating step of the paper pulp, the filler is introduced into said paper pulp between a first grinding stage and a second grinding stage of said paper pulp.
9. Process according to claim 2, wherein after the heating step of the paper pulp, the filler is introduced directly into said paper pulp during a first grinding stage of said paper pulp.
10. Process according to claim 2, wherein after the heating step of the paper pulp, the paper pulp is subjected to a first and a second grinding stages, and wherein said filler is intro-duced into said paper pulp after said second grinding stage.
11. Process for improving the properties of thermomechanical paper pulp, comprising the steps:
- introducing into a preheater pulp raw material, - conducting the preheated pulp raw material through a steam separator to a screw conveyor by which the preheated pulp raw material is fed in a grinder, said steam being conducted in countercurrent with respect to the direction of movement of the preheated pulp raw material, - subjecting said preheated pulp raw material to powerful mechanical treatment in said grinder such that said preheated pulp raw material is further heated, such further heating pro-viding the softening and the plasticizing of said pulp raw material, - introducing a filler into said grinder for admixion with with the pulp, said filler adhering to the surface of fibers composing the pulp when said pulp is in its plasticized and softened condition.
- introducing into a preheater pulp raw material, - conducting the preheated pulp raw material through a steam separator to a screw conveyor by which the preheated pulp raw material is fed in a grinder, said steam being conducted in countercurrent with respect to the direction of movement of the preheated pulp raw material, - subjecting said preheated pulp raw material to powerful mechanical treatment in said grinder such that said preheated pulp raw material is further heated, such further heating pro-viding the softening and the plasticizing of said pulp raw material, - introducing a filler into said grinder for admixion with with the pulp, said filler adhering to the surface of fibers composing the pulp when said pulp is in its plasticized and softened condition.
12. Process according to claim 11, further comprising the step of introducing fresh steam into said preheater.
13. Process according to claim 11, wherein said further heating of said preheated pulp raw material is provided by contact of said pulp raw material with rapidly rotating grinding discs inside said grinder, but mainly as a result of the mutual contact with each other of the particles composing said pulp material.
14. Process according to claim 11, wherein said filler is introduced into said grinder in the form of an aqueous sus-pension.
15. Process according to claim 11, wherein said pulp raw material is wood chips and said filler is talc.
16. Process according to claim 2 or 11, wherein more than one filler are added to said paper pulp, said fillers adhering to the surface of lignin particles, rendering the ligning and other plastic constituents of the wood from which is obtained said pulp, an opaque light-colored mass.
17. Process according to claim 1 or 11, wherein fillers are introduced into said process at least partly after a grinding stage at a point where lignin composing said paper pulp is in a substantially plastic condition as a result of a preceding treatment.
18. Apparatus for producing an improved thermomechanical paper pulp comprising:
- means for heating said paper pulp in such a way that the constituents thereof are in a plasticized and softened condition, - means for adding a filler to said paper pulp when it is still in its plasticized and softened condition.
- means for heating said paper pulp in such a way that the constituents thereof are in a plasticized and softened condition, - means for adding a filler to said paper pulp when it is still in its plasticized and softened condition.
19. Apparatus according to claim 18, wherein said means for heating said paper pulp is a grinder having facing grinding discs which rotate in opposite direction, the paper pulp being sub-jected to powerful mechanical treatment in the gap between said grinding discs.
20. Apparatus for producing an improved thermomechanical paper pulp, comprising:
- a preheater receiving pulp raw material for heating said pulp raw material, - a steam separator connected to said preheater, - a screw conveyer connected to said steam separator, said preheated pulp raw material being conducted through said steam separator to said screw conveyer, - a grinder connected to said screw conveyer and receiving said preheated pulp raw material, said grinder comprising means for further heating said preheated pulp raw material, such further heating providing the softening and the plasticizing of said pulp raw material, - means for adding a filler to said pulp when it is inside said grinder in a soft and plastic condition, said filler adhering to the surface of fibers composing said pulp.
- a preheater receiving pulp raw material for heating said pulp raw material, - a steam separator connected to said preheater, - a screw conveyer connected to said steam separator, said preheated pulp raw material being conducted through said steam separator to said screw conveyer, - a grinder connected to said screw conveyer and receiving said preheated pulp raw material, said grinder comprising means for further heating said preheated pulp raw material, such further heating providing the softening and the plasticizing of said pulp raw material, - means for adding a filler to said pulp when it is inside said grinder in a soft and plastic condition, said filler adhering to the surface of fibers composing said pulp.
21. Apparatus according to claim 20, wherein said screw conveyer is so arranged that the steam is conducted in counter-current with respect to the direction of movement of the pulp raw material.
22. Apparatus according to claim 20, wherein said preheater includes a screw conveyer.
23. Apparatus according to claim 20, further compris-ing means for introducing fresh steam into said preheater.
24. Apparatus according to claim 20, wherein said means for adding said filler to said pulp is located between a first grinding stage and a second grinding stage of said paper pulp.
25. Process for improving the properties of thermo-mechanical paper pulp, characterized in that a filler is added during the defiberizing process to said pulp when its lignin and equivalent constituents are still in a plasticized and softened condition.
26. Process for improving the properties of thermo-mechanical paper pulp, comprising the steps:
- heating the paper pulp in such a way that its lignin and equivalent constituents thereof are in a plasticized and softened condition, - adding a filler to said paper pulp when it is still in its plasticized and softened condition.
- heating the paper pulp in such a way that its lignin and equivalent constituents thereof are in a plasticized and softened condition, - adding a filler to said paper pulp when it is still in its plasticized and softened condition.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI771244 | 1977-04-19 | ||
| FI771244A FI54818C (en) | 1977-04-19 | 1977-04-19 | FOERFARANDE FOER FOERBAETTRING AV EN THERMOMECHANICAL MASS EGENSKAPER |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1096676A true CA1096676A (en) | 1981-03-03 |
Family
ID=8510785
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA301,414A Expired CA1096676A (en) | 1977-04-19 | 1978-04-18 | Process and apparatus for improving the properties of a thermomechanical paper pulp |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS53130301A (en) |
| AT (1) | ATA270578A (en) |
| BR (1) | BR7802442A (en) |
| CA (1) | CA1096676A (en) |
| DE (1) | DE2816566A1 (en) |
| FI (1) | FI54818C (en) |
| FR (1) | FR2388074A1 (en) |
| GB (1) | GB1603711A (en) |
| IT (1) | IT1094707B (en) |
| NO (1) | NO781361L (en) |
| SE (1) | SE7804443L (en) |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8231764B2 (en) | 2009-05-15 | 2012-07-31 | Imerys Minerals, Limited | Paper filler method |
| US10053817B2 (en) | 2010-04-27 | 2018-08-21 | Fiberlean Technologies Limited | Process for the manufacture of structured materials using nano-fibrillar cellulose gels |
| US10214859B2 (en) | 2016-04-05 | 2019-02-26 | Fiberlean Technologies Limited | Paper and paperboard products |
| US10253457B2 (en) | 2010-11-15 | 2019-04-09 | Fiberlean Technologies Limited | Compositions |
| US10294371B2 (en) | 2009-03-30 | 2019-05-21 | Fiberlean Technologies Limited | Process for the production of nano-fibrillar cellulose gels |
| US10301774B2 (en) | 2009-03-30 | 2019-05-28 | Fiberlean Technologies Limited | Process for the production of nano-fibrillar cellulose suspensions |
| US10577469B2 (en) | 2015-10-14 | 2020-03-03 | Fiberlean Technologies Limited | 3D-formable sheet material |
| US10794006B2 (en) | 2016-04-22 | 2020-10-06 | Fiberlean Technologies Limited | Compositions comprising microfibrilated cellulose and polymers and methods of manufacturing fibres and nonwoven materials therefrom |
| US11155697B2 (en) | 2010-04-27 | 2021-10-26 | Fiberlean Technologies Limited | Process for the production of gel-based composite materials |
| US11846072B2 (en) | 2016-04-05 | 2023-12-19 | Fiberlean Technologies Limited | Process of making paper and paperboard products |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4229250A (en) * | 1979-02-28 | 1980-10-21 | Valmet Oy | Method of improving properties of mechanical paper pulp without chemical reaction therewith |
| JP2528487B2 (en) * | 1987-12-10 | 1996-08-28 | 日本製紙株式会社 | Method for producing pulp having improved filler yield and method for producing paper |
| JPH02293496A (en) * | 1989-04-28 | 1990-12-04 | Oji Paper Co Ltd | Production of paper |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE426283A (en) * | ||||
| US2240017A (en) * | 1937-04-28 | 1941-04-29 | Primavesl Otto | Process for producing white mechanical wood pulp from pine wood |
| US2454532A (en) * | 1940-08-03 | 1948-11-23 | Wood Conversion Co | Process for defibering lignocellulose while subjected to steam and a digestive chemical |
| SE303088B (en) * | 1963-05-31 | 1968-08-12 | Defibrator Ab | |
| SE413684C (en) * | 1974-09-23 | 1987-05-07 | Mo Och Domsjoe Ab | PROCEDURE FOR PREPARING CELLULOSAMASSA IN THE REPLACEMENT AREA 65-95% |
-
1977
- 1977-04-19 FI FI771244A patent/FI54818C/en not_active IP Right Cessation
-
1978
- 1978-04-17 AT AT0270578A patent/ATA270578A/en not_active IP Right Cessation
- 1978-04-17 GB GB14941/78A patent/GB1603711A/en not_active Expired
- 1978-04-17 DE DE19782816566 patent/DE2816566A1/en not_active Ceased
- 1978-04-18 CA CA301,414A patent/CA1096676A/en not_active Expired
- 1978-04-18 NO NO781361A patent/NO781361L/en unknown
- 1978-04-19 BR BR7802442A patent/BR7802442A/en unknown
- 1978-04-19 FR FR7811619A patent/FR2388074A1/en not_active Withdrawn
- 1978-04-19 SE SE7804443A patent/SE7804443L/en unknown
- 1978-04-19 JP JP4546478A patent/JPS53130301A/en active Pending
- 1978-04-19 IT IT22465/78A patent/IT1094707B/en active
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Also Published As
| Publication number | Publication date |
|---|---|
| ATA270578A (en) | 1982-02-15 |
| JPS53130301A (en) | 1978-11-14 |
| IT1094707B (en) | 1985-08-02 |
| FI54818B (en) | 1978-11-30 |
| FI54818C (en) | 1979-03-12 |
| BR7802442A (en) | 1978-12-12 |
| GB1603711A (en) | 1981-11-25 |
| DE2816566A1 (en) | 1978-10-26 |
| NO781361L (en) | 1978-10-20 |
| FR2388074A1 (en) | 1978-11-17 |
| SE7804443L (en) | 1978-10-20 |
| IT7822465A0 (en) | 1978-04-19 |
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