FI92607C - Process for thermo-refining of hardwood in the manufacture of pulp - Google Patents

Description

92607

Method for grinding hardwood in pulp production

BACKGROUND OF THE INVENTION This invention relates to a process for making paper products 5 using hardwood pulps. More particularly, the invention relates to a method for treating hardwood pulps by producing a pulp which has better printability when produced into a paper product.

Paper products are made from a variety of fiber-10 sources. In the United States, paper products are usually made of either hardwood (Hardwood) or softwood (Softwood). Soft trees are evergreen trees, also known as conifers. Deciduous trees are trees that shed their leaves. Typical deciduous trees include oak, maple, 15 poplar, eucalyptus, birch, chestnut, aspen, beech and nutwood. Both conifers and deciduous trees are good sources of fiber in the manufacture of various paper products. Softwood bays have a longer fiber, about 3-4 mm, compared to hardwood fibers, which are about 1 to 1.5 mm long. However, although softwood fibers generally have a larger diameter, hardwood fibers have a smaller diameter and yield paper with a softer texture. Paper products are made from softwood pulp, hardwood pulp and mixtures of hardwood and softwood pulps.

25 The type of product to be produced and the pulp sources available often determine the composition of the pulp to be used.

In the production of higher quality printing paper, it is advantageous to use a high proportion of hardwood pulp due to its superior opacity, its ability to reduce the apparent density, its better formation and its economical economy. However, an eras problem in the use of hardwood pulp fibers is the basic structure of hardwoods. Deciduous trees basically contain two cell types. These are fibrous cells and stem cell cells. Stem cell cells are the part of the leaf-35 tree plant that carries water and nutrients to the root-tree 2 92607 ta ylds tree. Stem cells are not fibrous in nature. Accordingly, they do not increase the strength or quality of the paper. On the contrary, these lead cells are still, after cooking, bleaching and conventional grinding, mixed inside and on the surface of the paper product. The problem with weight is caused by the lead cells that remain on the surface of the paper product. The pressure roller picks up the large unbound guide cells on the surface of the sheet during printing. As a result, the ink does not adhere to all parts of the paper 10 to which it should be added, and a problem also arises when these guide cells remain on the surface of the printing roll, causing unwanted spots or openings when printing subsequent copies. The net result is printing paper that does not have the desired quality.

15 This problem caused by the detachment of duct cells in paper products during printing has long been known. This problem was observed on a large scale in the 1950s, when the use of bleached hardwood pulp in printing papers increased significantly. Over the years, 20 solutions have been tried. The only one that has had commercial success is coating a sheet of paper with a starch solution. The starch solution forms a film and / or paste which prevents the lead cells from coming off during pressing. However, this adds to the cost because 25 other substances have to be added during papermaking. It has now been found that this problem of detachment of duct cells from the surface of the paper can be alleviated by the use of a special grinding technique after the hardwood has been formed into pulp.

It has been found that if, after the hardwood has been formed into a pulp using any known thermochemical pulp cooking method, the hardwood is rubbed in a grinder with at least one of the grinding plates having an abrasive surface, which facilitates the problem of the lead cells. In the conventional treatment after hardwood cooking 3 92607, the fiber is conveyed to a refiner containing standards in metal-faced sheets. These sheets, which may have rods on their surface, push the fibers to form a flat netting mass. After one or more passes, the pulp of the 5 grinders is pumped into the headbox of the paper machine to be converted into a paper product.

Mass grinders containing abrasive surface plates are known in the art. U.S. Patent No. 4,372,495 discloses a method and apparatus for finely grinding wood chips to form a pulp using a disc mill with abrasive discs. The input material is wood chips and the final wood product is groundwood. In the example of this patent, Southern Pine chips are converted to thermomechanical pulp of this type using a plate grinder. This patent discloses the milling of large pieces of wood rather than boiled pulp.

U.S. Patent 3,117,603 discloses an apparatus for rubbing surface sectors which is used to grind effluent as well as for other uses. However, it does not show 20 grinding of pulp from deciduous trees.

U.S. Patent 3,827,934 discloses hardwood soup. The soup is followed by cooking fiber and after washing is followed by a grinding step. Neither of these grinding steps is shown to be performed on an abrasive surface plate with 25 grinders.

U.S. Patent 1,814,587 discloses a pulp mill having a pair of rotary scrapers. However, this patent does not disclose the type of pulps to be used or any particular advantage in the pulp.

SU patent 730 916 discloses an apparatus for grinding fiber suspensions in papermaking. It is shown that the fibrous material is first ground with metal ring blades and then the suspension is treated with projections of a ceramic plate. The abrasive grains on the ceramic plate are described as acting as 4,922,77 microc knives that bring the microfibrils out. However, the treatment of hardwood pulps is not presented here. It is not suggested that the fiber suspension would be an advantage in this method.

None of these patents discloses the advantage obtained by treating hardwood pulp in a grinder having one or more plates with an abrasive surface. Nor are any of these patents aimed at solving the problem of lead cell detachment in terms of hardwood fiber sources. As mentioned above, the prior art relies on the use of starch and Samanta-based materials to bind the lead cells to the surface of the paper. This is an effective solution but not ideal. The solution of this presentation approaches the ideal in that the mass is to be rubbed in any case. As a result, this is not an additional step. Grinding the pulp in a special grinder using a special technique solves the problem very effectively.

BRIEF SUMMARY OF THE INVENTION The invention relates to the grinding of hardwood pulp in a refiner in which at least one of the plates has an abrasive surface. By abrasive surface is meant that the surface of the plate, which is usually flat, may have other shapes. randomly dispersed finely divided abrasive material has been added. The abrasive material may be a carbide such as tungsten carbide or silicon carbide, alumina, zirconia, silicon oxide or diamond. Essentially, a well-known fine abrasive material can be used. The abrasive material 30 preferably has a particle size of about 20 to 120 mesh, and most preferably about 30 to about 40 mesh. The abrasive material covers about 10 to 90% of the surface of the plate in a scattered manner.

A hardwood source, usually in the form of chips, is cooked using a well-known thermochemical cooking method. This may be the sulphate process, the sulphide process or the soda process. After cooking to remove lignin, the pulp contains discrete fibers. These separate fibers are then ground in a refiner comprising at least one plate having the abrasive surface described above. Preferably, the refiner comprises a series of plates, wherein one plate has an abrasive surface and the opposite plate has a metal surface with a plurality of cross bars. There is usually no abrasive material on the surface in this le-10 vys containing a plurality of crossbars. Grinding the cooked hardwood pulp in such a grinder reduces the size of the duct cells to a size where they bind to the fibers and then remain within the fiber frame. The paper made from this pulp has less than about 5, and preferably less than about 3 / cm 2, loose conductor cells. Paper made from such pulp does not have the problem of detaching the lead cell portions from the paper during printing. This hardwood pulp can be used in the manufacture of paper products alone or mixed with softwood pulp. Mineral pigments are often added to the pulp to improve the opacity of the paper. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the unexpected invention that the size of the conductive cell portions of hardwood pulp can be effectively reduced and bonded to the fibers if the hardwood pulp is ground in a refiner having at least one of the refiner plates having an abrasive surface. It is common to grind hardwood pulp like other pulps before pumping the pulp into the headbox of a paper machine. A conventional grinder consists of 30 devices containing two or more plates, the plates having rods attached to the surface. The rods are substantially elongate rod-like projections which are attached to the surface of the sheet and extend outwardly from this surface as they fill the fibers 35 passing between the sheets. These pins are usually rectangular in shape with 6 92607. A typical refiner has one or more fixed mounted plates and one or more floating plates, or alternatively it has two or more therapy plates. In a conventional grinder, each of these 5 plates usually has rods attached to the surface of the plates and extending out of the surface.

Typical disc grinders for the use of hardwood pulp fibrillate pulp hardwood fibers. A usable mass is formed. Although the paper product made from this pulp is surface-treated with starch or some other substance, there is still a problem of detachment of the conductor cell parts from the surface during printing. In a hardwood mill, in which at least one of the plates has an abrasive surface, i.e. a board on the surface of which a finely dispersed fine sand is dispersed in a randomly dispersed material, the finely divided particles in the hardwood particles bind to the fibers and are held together by the fibers. Picking of these particles during printing of the paper product from pin-20 is prevented due to binding to the fibers. The result is a high-quality print on longer operating periods between press cleaning.

. The material to be rubbed is hardwood pulp and not hardwood chips. Hardwood pulp is the product of the thermochemical cooking of hardwood chips. The soup removes lignin and allows the fibers to separate. MikSli hardwood chips are a mixture of small and large fibers of groundwood and unremoved lignin. The lignin may be as high as 30 to about 50% of the material. The Schopper-Riegler grind of this groundwood is above 35 ° SR. It has a very poor drainage of water on a paper machine. In addition, the tSmS abrasive of the further grinding is not usable for the production of high-quality printing papers due to its tendency to turn yellow and brittle over time. This is due to its lignin content.

Essentially any plate grinder having at least one plate having finely divided and abrasive material on the surface can be used to practice the present invention. A disc available disc mill is disclosed in U.S. Patent No. 4,372,495, which is incorporated herein by reference. However, the present invention is not limited to the use of this disc mill. The fine abrasive material on the surface of the plate 10 may be as coarse as 5 mesh or as fine as 200 mesh. A 5 mesh portion of the abrasive material would just pass through a 5 mesh screen with 4 mm openings, while a 200 mesh material would pass through just a 15 200 mesh screen with 0.07 mm openings. Preferably, the size of the abrasive material is at least about 20 to about 120 mesh, and most preferably about 30 to about 40 mesh. The abrasive material may be essentially any well-known abrasive material. These include carbides such as tungsten-20 carbide and silicon carbide, aluminas, zirconia, silicon oxides and diamond. The finely divided abrasive material covers about 10 to about 90%, and preferably about 30 to about 70% of the surface area of the plate.

In the production of current hardwood pulps, the hardwood 25 kit is first conveyed to a chipper or such device to reduce the size of the logs to about 0.318 to about 5.1 cm pieces. Preferably, the pieces are about 0.94 to about 2.54 cm in size. These hardwood chips are then transported to a thermochemical cooking using the sulphate process, the sulphide process or the soda process. Which of these methods can be used to your advantage depending on your personal preferences. For example, the method described in U.S. Patent No. 3,827,934 can be used. The fibers are washed after cooking to remove cooking chemicals, and a brown pulp is obtained. The 8 92607 brown pulp is then bleached using substantially any of the known bleaching chemicals and bleaching cycles. Typical bleaching chemicals include chlorine, chlorine dioxide, sodium hypochlorite, ozone and hydrogen peroxy-5-din. Other conventionally used pulp bleaches may also be included or used to replace the bleaching process. The purpose is to produce a pulp that can be used to produce a white paper product or, by adding dyes, a set of colored papers. After spinning, the white pulp is ground to fibrillate the fibers before pumping the fiber into the head of the paper machine. It is at this stage that the hardwood fibers are ground in a grinder in which at least one of the grinder plates has a grinding material which is randomly distributed on at least 15 parts of the surface.

In the process of this invention, the bleached hardwood pulp coming out of the refiner can be transferred directly to the headbox of a paper machine or it can be mixed with the softwood pulp and the mixture transferred to the headbox of a paper machine. When mixed with softwood pulp, the softwood pulp may comprise from about 5% to about 95% of the fiber content of the mixture. Likewise, the content of hardwood pulp in such a mixture may be about 5 to about 95% by weight of the fiber content of the mixture. If desired, the softwood pulp and hardwood pulp can be mixed before grinding and the combined pulps can be ground in a single grinder with at least one plate with an abrasive surface. However, it is advantageous to rub the hardwood separately and then combine it with the softwood pulp.

The resulting hardwood pulp produced in this process preferably has a dry matter content of about 5 to about 35%, and most preferably about 10 to about 15%. The dry matter content of the pulp is the solids content of the pulp. The grinding of the pulp increases as a result of the grinding step. The more fiber is worked in the grinder, the more the pulp grows. The pulverized pulp *: 92607 9 is a measure of the rate at which water flows out of the paper. In papermaking, water runoff is important. For most papermaking applications, the pulp grinding, or ° SR (Schopper-Riegler number), should be less than about 40 ° SR, preferably less than about 35 ° SR, and most preferably less than about 30 ° SR. Pulps with a higher degree of grinding drain water on the paper machine too slowly, causing reduced productivity and increased energy consumption in the final drying of the sheet paper product. The grinding of the Leh-10 dripping mass before grinding is usually about 20 ° SR. After the grinding step, when the grinder has at least one plate having an abrasive surface as described above, the grindability of the pulp increases but remains below about 40 ° SR and preferably below about 35 ° SR on paper with a low number of detachable conductor cells. When using a conventional grinder, i.e. a grinder with a stick surface, the pulverizability of the pulp increases above about 40 ° SR when producing paper in which the problem of the detachment of the lead cells from the paper during printing is likewise reduced.

Another important factor in determining the efficiency of the grinding operation is the mSS of the shaft power days per ton of air-dry pulp produced (BHPD / ADT). The amount of BHPD / ADT is from about 1 to about 100. It is desired to minimize BHPD / ADT to produce an approved S-25 product. In the current method, the number of whole stem cell particles per gram decreases significantly with increasing power, such as the mSS of detachable stem cells per four centimeters. The use of abrasive material in one or more of the refining plates 30 reduces the total number of conductive cells per gram to less than half the level achieved when using a disc with a barbed surface in the refiner. The number of detachable stem cells / cm 2 is reduced by about 28% in the mill used with rod-coated plates and by about 96% in the use of the abrasive surface plates of the present invention. This is a significant difference. A refiner having at least one abrasive surface plate according to the present invention provides a paper product with superior quality properties. If it is desired to rub hardwood co-5, these can be used using different grinders to obtain an equivalent product, i.e. a product with a total number of lead cell parts of 100,000 or less, and preferably 60,000 or less per gram of mass, and lead cell detachments of 5 or less, preferably 3 or less, and preferably 10 or less / cm2 of paper surface area, an axial power of about 15 BHPD / ADT is used when the grinder has one or more abrasive-backed sheets, and more than 30 BDHD / ADT when the grinder has conventional stick-faced plates. This results in significant savings in electricity energy consumption in the production of a tonne of air-dried paper product.

In addition, there is the advantage that when the paper product to be produced has this number of conductive cells per 60,000 or less mass gram and detachable conductive cells 2 or less per cm 2 of paper surface area, the grinding is about 40 ° SR 20 or less, and preferably 35 ° SR or less, and most preferably about 30 ° SR or less of the pulp milled in a grinder having plates coated with abrasive material, while the pulp milled in a grinder with spiked plates has a grinding of more than about 40-25 about 50 ° SR. Therefore, the paper product from the hardwood pulp milled in the sheets coated with the abrasive material used in the refiner has improved the flow of water on the paper machine compared to the pulp milled on the wand-coated mill with the same wire.

In addition, paper made from the hardwood pulps of the present invention has a higher tensile strength as determined by the pulverized pulp. The tensile strength of the paper 35 obtained with a pulp value of less than about 30 ° SR is greater than 7.2 kg / 25 mm. This has the significant advantage that paper from which water drains better produces a paper product with higher strength.

There are still other undetected advantages in grinding hardwood pulp in a grinder using one or more sheets baled with an abrasive material. However, such advantages obtained by grinding hardwood pulp are within the scope of the present invention.

The following examples are set forth to further illustrate and illustrate the advantages of grinding in a hardwood grinder having at least one of the grinder plates having an abrasive surface.

The experimental procedure

Calculating the number of mast cells

The number of whole stem cell sections in the hardwood-15 pulp was calculated visually using a microscope. All pulp samples were stained with C-stain before counting. C-vari is a chemical supplied by the Institute of Paper Chemistry to assist in the study of wood fibers by nakoha observation. The figures are expressed as the number of whole stem cell-20 parts per mass gram.

Detachable lead cells

The stem cell shedding test was performed on hand-made sheets made of ground hardwood pulp. The handmade sheets were prepared by the method of: 25 Technical Association of the Pulp and Paper Industry (TAPPI) Standard Procedure no. 205.

The IGT Printability tester, model AC2, was used in the lead cell detachment test. The printing was done by O / S Paper Test Jay Blue -vSrillS, supplied by Capitol Ink Com-30 pany. Detachments were determined visually under a microscope. Their number is expressed as the number of detached lead cellsSaranS / cm2.

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Shopper-Riegler-j grumpy father ° SR

Shopper-Riegler grinding was determined using the method: Technical Association of the Pulp and

Paper Industry Standard no. 227 - grinding of the pulp.

5 Dry matter content

The dry matter content was determined by the method of: Technical Association of the Pulp and Paper Industry Standard no. 240 - dry matter content (concentration) of the pulp suspension.

10 Tensile strength

The tensile strength of the paper was determined by the method of: Technical Association of the Pulp and Paper Industry Standard no. 494 - Tensile properties of paper and board (using a constant speed stretcher). All stretch values 15 were determined on paper having a basis weight of 61 g / cm 2.

Example l

This example shows a typical method for producing bleached sulphate hardwood pulp in a factory-used manner. Hardwood pulp is made from leaf-20 wood sources with about 65% oak and about 35% other hardwood. The oak bay is mainly red oak and · white oak. Other deciduous trees are mostly foamy and poplar.

. Hardwood bays were chipped to a thickness of about 0.46 to 2.2 cm. The chips were dried in an oven and 4,000 g of these hardwood chips were added to the digester. The broth was prepared by combining sodium hydroxide, sodium sulfide and sodium carbonate so that the resulting solution contained about 22% by weight (should be between 19-25%). effects of the mother (calculated as Na 2 O), 20% sulfidity and 80% causticism. The cooking solution / wood volume ratio was 4: 1.

The kettle was sealed after the addition of the cooking solution and the temperature was raised to 166 ° C over 1 h. The digester was kept at this temperature for 1.5 h. The pressure in the digester 35 at this temperature was 760 kPa (7.6 bar).

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After cooking, water was released from the cooked fiber to atmospheric pressure and the cooking chemicals were drained from the pulp. The drained pulp was washed countercurrently with a stream of water to further remove the cooking chemicals and then bleached. The pulp was bleached using a chlorine / alkali extraction / sodium hypochlorite / chlorine dioxide bleaching step. The bleached pulp was washed with water to remove bleaching chemicals. The bleached pulp has a GE whiteness of about 83. This bleached pulp was then pumped into the Pera-10 box of a paper machine.

Example 2

The material bleached in this example was bleached kraft hardwood pulp taken from the production run of the plant. TMma in hardwood was ground in a Sprout-Wal-15 dron grinder, model 105A. This grinder operated at 1200 rpm and atmospheric pressure. The plate containing the abrasive material was 30.5 cm in diameter and contained about 36 mesh of tungsten carbide crumbs by plasma welding attached to a solid surface.

20 About 50-60% of the board is coated with a grit of abrasive material. A plate having an abrasive surface is a permanently mounted plate. The rotating plate is a barbed plate. Crocheted sheets are generally of the type used for grinding wood pulp into printing papers. These plates are 30.5 cm in diameter and have sticks 3.8 to 8.9 cm long on the surface in a radial system. The shaft power used ranged from 0.5 to 15 BHPD / ADT. This was controlled by increasing or decreasing the distance between the solid and rotating plate and / or by changing the dry matter content of the pulp.

Table I shows the properties of the pulp before and after the treatment in a grinder with a plate system having an abrasive surface as described above. As can be seen from this table, the number of whole stem cells and the number of detachable cells decreases greatly, from 14,000 to 60,000 / g of whole stem cells and from 25 to 1 / cm 2 of detachable cells. The higher the power used, the greater the reduction. At level 15, the number of BHPD / ADT whole vascular cells decreased by 76 5% and the number of detachable cells by 96%.

Table I

Properties of hardwood pulp Shaft power used on plate 10 with abrasive surface before and after grinding Total loose BHPD / ADT * guide cells / g guide cells / cm2 0 250 000 25 5 140 000 22 10 110 000 10 15 15 60 000 1 ‘shaft power per day / air

Example 3

The bleached kraft hardwood pulp taken from the production run of the production plant was ground in a grinder equipped with a grinding surface plate as described in Example 2 and in another grinder described in Example 2 with only conventional spun plates. One barbed plate is a fixed plate and one is a rotating plate. plate. Both refiners operate at 1,200 rpm and 25 atmospheres. The comparison results are shown in Table II.

As can be seen from this table, a plate with an abrasive surface is more efficient in terms of energy consumption, with a more efficient use of barbed and plate-less grinding, resulting in a reduction in both the number of complete conductor cells and the number of detachable conductor cells. At level 15, the total lead cells of BHPD / ADT are reduced from 250,000 to 60,000 / g using the abrasive surface plate of the present invention and 140,000 / g using the battled surface plates 35. The reduction on the abrasive surface is 76% and on the sticked surface 92%. The same is evident in the number of detachable lead cells. When a plate with an abrasive surface is used, the detachable conductor cells are reduced from 25 to 1 / cm2, with a reduction of 96%, while with conventional wood-5 embedded plates, the detachable conductor cells are reduced from 25 to 18 / cm2, with a reduction of 28%.

Table II

Comparison between pulp properties A plate with an abrasive surface compared to grinding with stick-dipped discs in hardwood Abrasive barbed “getting” surface surface used shaft 0 15 15 15 power (BHPD / ADT) * whole conductor 250,000 60,000 140,000 true cells / g loose wire 25 1 18 cells / cm2 20 'shaft power per day / air dry ton

Example 4

The bleached kraft hardwood pulp taken from the production run of the production plant was ground using the same grinder as in Example 2. The 25 grinders with a grinding surface plate and the grinder with a stick surface were similar to Example 2. The grinders operated at 1,200 rpm and atmospheric pressure. The results of the effect on grinding are shown in Table III. As explained above, it is desired that the milling be less than 35 ° SR in papermaking.

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Table III

Comparison of the obtained grinding

A plate with an abrasive surface compared to a needle-punched plate

5 grinding ° SR

target reduction abrasive barbed surface surface whole duct cells 32 48 60 000 or less / g 10 detachable duct cells 33.5 45 2 / cm2 or less in paper surface area

As shown in Table III, both plate types were able to reduce the number of whole conductor cells to the target value of 60,000 / mass gram or less. However, the grinder equipped with wood-embedded plates increased the grindability of the pulp from a non-abrasive value of 20 ° SR to 48 ° SR. This is well above the desired pulp-20 milling maximum of 40 ° SR, and the preferred milling of 35 ° SR. The grinder with a plate with an abrasive surface described here increased the grind by reducing the number of conductor cells of the same size to only 32 ° SR.

25 Both types of sheets, as shown in Table III, can also be used to reduce the number of detachable stem cells in the paper to 2 / cm2 of paper surface area or less. Grinding then increases again. The grinder with stitched plates increased the grinding mass from 20 ° SR to 45 ° SR. This is again above the maximum of 40 ° SR for the desired grind and 35 ° SR for the preferred grind. Equipped with the abrasive discs described here, the grinder only raises the grind to 33.5 ° SR.

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Example 5

The bleached kraft hardwood pulp taken from the production run of the production plant was ground using a plate grinder equipped with a plate with an abrasive surface and 5 plates with a barbed surface. The plates and their jar arrangement were the same as in Example 2. The grinder operated at a speed of 1,200 rpm with a fixed distance between the plates of 0.0076 mm and atmospheric pressure. Table IV shows the effect of the dry matter content of the pulp on the number of detachable stem cells / cm2. As can be seen from this table, the higher the dry matter content, the greater the reduction in detachable duct cells. In this example, a dry matter content of 13% was used and the number of detachable stem cells was reduced to the target value of 2 / cm 2 or less.

Table IV

Effect of hardwood pulp dry matter content on shrinkage of detachable duct cells when using a board with an abrasive surface 20 dry matter content of detachable duct cells / cm2 5 19 7 15 9 11 25 11 7 13 2

Example 6

Paper was made from bleached kraft hardwood pulp 30 milled in a grinder equipped with a grinding surface plate as described in Example 2 and another grinder equipped with the conventional spiked plates described in Example 2. The refiners operate at 1,200 rpm and il-35 sweet pressure. A comparison of the grindings and tensile strengths obtained is shown in Table V.

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Table V.

Comparison of grinding and tensile strength. A plate with a sanding surface compared to a conventional sticking plate.

5 grinding tensile strength (kg / 25 rom) plate with abrasive surface 23.5 7.2 25.0 7.6 10 26.9 8.2 28.4 8.6 32.0 9.6 plate with barbed surface 31.0 7.3 15 31 .9 7.5 41.0 8.3 46.9 8.8 48.9 8.9

As shown in Table V, the tensile strength 20 depends on the grinding developed during grinding. In this example, as the grinding, in ° SR, increases, the tensile strength increases. In general, the stronger the sheet of paper, the better. Therefore, it is important that no friction technique causes a decrease in tensile strength. Rubbing too much 25 may cause a decrease in strength.

Examining the values from the two grinding techniques, in particular the correspondences of the grinding values obtained, it is found that at a certain level of grinding the tensile strength achieved by a grinder 30 having a plate with an abrasive surface is higher than a grinder with barbed plates. At a grinding value of 30 ° SR, the tensile strength of the sheet made from the ground pulp on the abrasive surface was 9.0 kg, while the tensile strength of the pulp made from the ground pulp with barbed sheets was only 7.2 kg.

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Abrasive plate grinding has a clear advantage, resulting in higher tensile strength at a lower grinding value. Grinding values above about 40 ° SR, and preferably above about 35 ° SR, are not desirable in routine papermaking. The pulp rubbed with sticked plates to a tensile strength of 9 kg would have a grinding of 50 ° SR. Thus, a pulp with a high degree of grinding would not be suitable for routine papermaking.

Claims (15)

92607 A method for improving paper made from paper pulp containing pulp thermochemically obtained from hardwoods, characterized in that the hardwood-containing pulp is ground in a grinder having at least one finely divided abrasive material dispersed on the surface of the hardened discs, which is adhered to , the abrasive material being dispersed in 10 at least a substantial part of said surface of the sheet which most directly comes into contact with the pulp during grinding, whereby the number of whole conductive cells in grams and the number of detachable conductive cells in the as in the case where at least one of the surfaces of the plates of the refiner does not have a finely divided solid dispersed abrasive material on at least a considerable part of said surface of the plate. A method of improving paper 20 according to claim 1, characterized in that the deciduous trees are selected from oak, maple, poplar, birch, chestnut, aspen, beech, eucalyptus, walnut and mixtures thereof. A method for improving paper 25 according to claim 1, characterized in that the refiner has at least one rigid plate and at least one rotating plate. A method for improving paper according to claim 1, characterized in that the refiner has at least 2 rotating plates. Method for improving paper according to Claim 3 or 4, characterized in that at least one plate with a spiked surface is applied to the mill. A method of improving paper 35 according to claim 3, characterized in that all surfaces of all sheets in contact with the pulp have a randomly dispersed fine rubbing material. A method of improving paper 5 according to claim 3, characterized in that each plate having an abrasive surface comprises an abrasive material having a mesh size of about 5 to about 200 mesh. A method of improving paper according to claim 3, characterized in that each plate 10 having an abrasive surface comprises an abrasive material having a mesh size of about 20 to about 120 mesh. A method of improving paper according to claim 8, characterized in that each plate having an abrasive surface comprises an abrasive material having a mesh size of about 30 to about 40 mesh. A method of improving paper according to claim 1, characterized in that the abrasive material on the sheet is selected from tungsten carbide, aluminas, zirconia, silicon oxides, silicon carbide, diamond and mixtures thereof. A method of improving paper according to claim 1, characterized in that each abrasive material coated board has an abrasive material that covers about 10 to 90% of the surface area of the board in contact with the pulp. A method of curing paper according to claim 1, characterized in that each abrasive material coated board has an abrasive material that covers about 30 to 70% of the surface area of the board in contact with the pulp. A method of curing paper according to claim 1, characterized in that the pulp has a grindability of less than about 35 ° SR. An improved paper comprising paper made from a pulp containing a thermochemical pulp obtained from hardwood «92607, characterized in that the hardwood component of the pulp is ground at least once in a grinder having at least a finely divided solid dispersed material. 5 to one of the surfaces of the grinder plates, the abrasive material being dispersed in at least a substantial part of said surface of the plate which most directly comes into contact with the pulp during grinding, whereby the paper has a substantially reduced amount of loose conductive cells / cm2 of salt about 40 ° SR. 15. Improved in hardwood papermaking using thermochemically obtained hardwood pulp, characterized in that it is ground at least once in a grinder having a surface containing at least a substantially abrasive material dispersed in a randomly dispersed finely divided abrasive material adhered to at least one grinder. a portion of said plate surface most in direct contact with the pulp in grinding to produce a pulp having a substantially reduced number of whole conductive cell segments per gram of pulp and a lower grind than at least one of the surfaces of the grinding discs; material. 92607