FI92607B - Method for grinding hardwood in pulp production - 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 process for treating hardwood pulps, thereby 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 (Softwood) 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 walnut. Both softwoods and hardwoods are good sources of fiber in the manufacture of various paper products. Softwood springs 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 available pulp sources often determine the composition of the pulp 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, one problem with 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 cells are the part of the leaf-35 tree plant that carries water and nutrients from the root system to the tree. Stem cells are not fibrous in nature. Accordingly, they do not increase the strength or quality of the paper. On the contrary, these stem cells are still mixed within and on the surface of the paper product after cooking, bleaching and conventional grinding. 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 there is also the problem of these guide cells remaining 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 of 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 loose during pressing. However, this increases the cost as 25 other substances have to be added during papermaking. It has now been found that this problem of the 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 hardwood is formed into a pulp using any known thermochemical pulp cooking method, the hardwood is ground in a grinder in which at least one of the grinder plates has an abrasive surface, alleviating the problem of lead cells. In the conventional treatment, after hardwood cooking 3 92607, the fiber is conveyed to a refiner containing standard metal-faced sheets. These sheets, which may have sticks on their surface, process the fibers to form a smoother mass. After one or more passes through 5 grinders, the pulp is pumped into the box of the stern of the paper machine to be converted into a paper product.

Pulp 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 10 to form a pulp using a disc mill with abrasive discs. The feed material is wood chips and the end product is groundwood. In the example of this patent, Southern Pine chips are converted to thermomechanical pulp using this type of disc grinder. This patent discloses the grinding of large pieces of wood rather than the shredding of cooked pulp.

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

U.S. Patent 3,827,934 discloses the cooking of hardwood chips. 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 with a grinder comprising abrasive surface plates.

U.S. Patent 1,814,587 discloses a pulp mill having a pair of rotary grinding wheels relative to each other. However, this patent does not disclose the type of pulps used or any particular 3 0 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 4,926,607 microtives that bring the microtibrils out. However, the treatment of hardwood pulps is not presented here. Nor is it shown that a fiber suspension would be an advantage in this method.

5 None of these patents discloses the benefit of treating hardwood pulp in a grinder with one or more abrasive plates. Also, none of these patents are directed to solving the problem of lead cell detachment 10 for hardwood fiber sources. As mentioned above, the prior art relies on the use of starch and similar 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 must be ground in any case. Because of this, 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 grinder 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. and randomly dispersed finely divided abrasive material is added. The abrasive material may be a carbide such as tungsten carbide or silicon carbide, aluminas, zirconia, silicon oxides or diamond. Essentially any known fine abrasive material can be used. The abrasive 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 randomly distributed manner.

The hardwood source, which is usually in the form of chips, is boiled using any known thermochemical cooking method. This may be the sulfate method, the sulfide method or the soda method. After cooking to remove lignin, the pulp contains discrete fibers. These discrete 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, one plate having an abrasive surface and the opposite plate having a metal surface having a plurality of cross-members. This plate of le-10 containing a plurality of crossbars usually does not have abrasive material on the surface. 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 an 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 in which at least one of the refiner plates has an abrasive surface. It is common to grind hardwood pulp like any other pulp 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 protrusions attached to the surface of the sheet and extending outwardly from this surface as they thus process the fibers passing between the sheets. These rods are usually rectangular in shape with 6 92607. A typical refiner has one or more fixed mounted plates and one or more rotating plates, or alternatively has two or more rotating plates. In a conventional grinder, each of these 5 plates usually has rods attached to the surface of the plates and extending outward from the surface.

Typical disc grinders for handling hardwood pulps fibrillate the hardwood fibers in the pulp. A usable mass is formed. Although the paper product selected 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. By grinding in hardwood in a grinder in which at least one of the plates has an abrasive surface, i.e. a plate on the surface of which a finely dispersed finely divided abrasive material is fixed, the fine conductive cell parts in the hardwood pulp decompose into smaller particles which bind to the fibers. Picking of these particles during pin-20 printing of the paper product is prevented due to binding to the fibers. The result is a high-quality print for longer operating periods between press cleanings.

. The material to be ground 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. If hardwood chips are rubbed, the product is a mixture of small and large fibers in the groundwood and unremoved lignin. Lignin may contain up to 30 to about 50% of the material. The Schopper-Riegler grinding of this grind is above 35 ° SR. It has a very poor drainage of water on a paper machine. Moreover, even after further grinding, this grind is not available 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 disc grinder having at least one disc with finely divided and randomly abraded abrasive material on the surface can be used to practice the present invention. One available disc mill is disclosed in U.S. Patent 4,372,495, which is incorporated herein by reference. However, the present invention is not limited to the use of this disc grinder. 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 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 can be essentially any 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 sulfate method, the sulfide method or the soda method. Any of these methods can be used depending on personal preference. For example, the method described in U.S. Patent 3,827,934 can be used. The fibers are washed after cooking to remove cooking chemicals, and a brown pulp is obtained. 92607 8 brown pulp is then bleached using essentially any known bleaching chemical and bleaching cycle. 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 champion 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 an abrasive material that is randomly distributed over at least 15 parts of the surface.

In the process of the present invention, the bleached hardwood pulp coming out of the refiner can be transferred directly to the headbox of the paper machine or it can be mixed with the softwood pulp and the mixture transferred to the headbox of the paper machine. When blended with softwood pulp, the softwood pulp may comprise from about 5% to about 95% of the fiber content of the mixture. Likewise, the hardwood pulp content of such a blend may be from about 5% to about 95% by weight of the fiber content of the blend. 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 grind 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 a pulp is the solids content of the pulp. The grinding of the pulp increases as a result of the grinding phase. The more fiber is processed in the grinder, the more the pulp is more ground. The pulverized mass of the pulp *: 9 92607 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 a conventional grinder, i.e. a grinder with a stick surface, is used, 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 number of 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 acceptable product. In the current method, the number of total vascular cell particles per gram is significantly reduced with increasing power, as is the number of detachable vascular cells per square centimeter. Also, the use of abrasive material on one or more of the refiner plates 30 reduces the number of total conductor cells per gram to less than half the level achieved when using a disc with a stabbed surface in the refiner. The number of detachable stem cells / cm 2 is reduced by about 28% when using rod-coated plates in the grinder and by about 96% when using 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 grind hardwood-5 using these different grinders to obtain an equivalent product, i.e. a product with a total number of duct cells of 100,000 or less, and preferably 60,000 or less per gram of mass, and dermal 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 coated plates, and more than 30 BDHD / ADT when the grinder has conventional stick surface plates. . This results in significant savings in electrical 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 of 60,000 or less per gram of pulp and detachable conductive cells of 2 or less per cm2 of paper surface, the milling is about 40 ° SR 20 or less, and preferably 35 ° SR or less, and most preferably about 30 ° SR or less for pulp milled in a grinder with sheets coated with abrasive material, while pulp milled in a mill with barbed sheets has a grind of more than about 40-25 about 50 ° SR. Therefore, a paper product from hardwood pulp milled in a refiner using plates coated with abrasive material has improved water runoff on a paper machine compared to pulp milled with a stick-coated refiner for the same number of conductor cells and the amount of lead cells detached.

In addition, paper made from the hardwood pulps of this invention has a higher tensile strength per certain pulp grindability. 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 is a significant advantage that paper from which water drains better produces a paper product with higher strength.

There are still other as yet undetected advantages when grinding hardwood pulp in a grinder that uses one or more plates coated with abrasive material. However, such advantages obtained by grinding hardwood pulp are within the scope of this invention.

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

Test Methods

Calculating the number of mast cells

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

Detachable lead cells

The lead cell detachment test was performed on handmade sheets made of ground hardwood pulp. These 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 with O / S Paper Test Jay Blue, supplied by Capitol Ink Com-30 pany. Detachments were determined visually under a microscope. Their number is expressed as the number of detached vascular cells / cm2.

92607 12

Shopper-Riegler-j hardness ° 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 elongation values 15 were determined on paper having a basis weight of 61 g / cm 2.

Example 1 This example shows a typical process for preparing bleached sulphate hardwood pulp as used in a factory. Hardwood pulp is made from leaf-20 wood source with about 65% oak and about 35% other hardwood. The source of oak is mainly red oak and · white oak. Other deciduous trees are mostly maple and poplar.

. Hardwood springs 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 and 25%). 30 bases (calculated as Na 2 O), 20% sulfidity and 80% caustic. The cooking solution / wood volume ratio was 4: 1.

The kettle was concentrated 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 digester 35 at this temperature was 760 kPa (7.6 bar).

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After cooking, the boiled fiber was drained to atmospheric pressure and the cooking chemicals were drained from the pulp. The drained mass 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 stern-10 box of the paper machine.

Example 2

The material that was bleached in this example was bleached kraft hardwood pulp taken from the production run of the production facility. This hardwood was ground in a Sprout-Wal-15 drone 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 approximately 36 mesh of tungsten carbide crumbs by plasma welding attached at random.

20 About 50-60% of the board is coated with abrasive grit. A plate with an abrasive surface is a permanently mounted plate. The rotating plate is a barbed plate. Crocheted sheets are a type commonly 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 as a radial system. The shaft power used ranged from 0.5 to 15 BHPD / ADT. This was adjusted by increasing or decreasing the distance between the fixed 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 the abrasive surface plate system described above. As can be seen from this table, the number of whole stem cells and the number of detachable cells is greatly reduced, the number of whole stem cells is reduced from 250,000 to 60,000 / g and the number of detachable cells is from 25 to 1 / cm 2. The higher the power used, the greater the decrease. At level 15, the number of BHPD / ADT whole stem cells was reduced by 76 5% and the number of detachable cells by 96%.

Table I

Characteristics of hardwood pulp Shaft power used before and after grinding with plate 10 with abrasive surface total detachable 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 dry ton

Example 3

The production of the plant from which the bleached kraft hardwood pulp was taken 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 barbed plates. One barbed plate is a fixed plate and one is rotating. 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 having an abrasive surface is more energy efficient using a barbed and a plate miller with less power, thereby reducing both the number of complete conductor cells and the number of detachable conductor cells. At level 15, BHPD / ADT whole vascular cells are reduced from 250,000 to 60,000 / g using the abrasive surface plate of the present invention and 140,000 / g using baffled surface plates 35. The reduction is 76% for the abrasive surface and 44% for the roded surface. The same is evident in the number of detachable lead cells. When a board 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 boards, the detachable conductor cells are reduced from 25 to 18 / cm2, with a reduction of 28%.

Table II

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

Example 4

The production of the plant from which the bleached kraft hardwood pulp was ground 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 on 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 doweled plate

5 grinding ° SR

target reduction abrasive spiked 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 vascular cells to a target value of 60,000 / mass gram or less. However, the grinder equipped with stabbed 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 friction surface plate described herein increased grinding by reducing the same number of whole stem cells to only 32 ° SR.

25 Both types of sheets, as shown in Table III, can also be used to reduce the number of loose conductor cells in the paper to 2 / cm2 of paper surface area or less. The 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 40 ° SR of the desired grind and 35 ° SR of the preferred grind. The grinder equipped with the abrasive plates described here raises the grind to only 33.5 ° SR.

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Example 5

The production of the plant from which the bleached kraft hardwood pulp was ground was milled using a plate grinder equipped with a plate with an abrasive surface and 5 plates with a barbed surface. The plates and their arrangement were the same as in Example 2. The grinder operated at a speed of 1,200 rpm at a fixed distance between the plates of 0.0076 mm and at 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 the reduction of the number of detachable duct cells when using a plate 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 in another grinder equipped with conventional knife plates as described in Example 2. The refiners operate at 1,200 rpm and il-35 at sweet pressure. A comparison of the obtained grindings and tensile strengths is shown in Table V.

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Table V.

Comparison of grinding and tensile strength. A plate with an abrasive surface compared to a conventional stabbed plate.

5 grinding tensile strength (kg / 25 mm) 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 grindability, 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 the grinder 30 having a plate with a grinding surface is higher than that of a grinder with stick plates. At a grinding value of 30 ° SR, the tensile strength of the sheet made of ground pulp on the abrasive surface was 9.0 kg, while the tensile strength of the pulp made of ground pulp on sticky sheets was only 7.2 kg.

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Abrasive plate has a clear advantage in providing 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-5 papermaking. The pulp rubbed with sticked plates to a tensile strength of 9 kg would have a grinding of 50 ° SR. Pulp with such 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 a finely divided dispersed abrasive material adhering to at least one of the surfaces of the grinder plates. dispersed 10 on at least a substantial portion of said sheet surface most in direct contact with the pulp during grinding, reducing the number of total conductor cells per gram and the number of detachable conductor cells / cm2 of paper produced by the method to a lower value at a given grind (° SR) than in the case of at least one the surfaces of the refiner plates are free of fine randomly dispersed abrasive material on at least a substantial portion of said plate surface. 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 fixed 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. A method for improving paper according to claim 3 or 4, characterized in that the grinder comprises at least one plate with a stuck surface. A method of improving paper 35 according to claim 3, characterized in that all the surfaces of all sheets in contact with the pulp have a randomly dispersed fine abrasive 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 contains 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, zirconium oxides, silicas, silicon carbide, diamond and mixtures thereof. A method of improving paper according to claim 1, characterized in that each abrasive coated sheet 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 improving paper according to claim 1, characterized in that each abrasive coated sheet 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 improving 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 pulp obtained thermo-chemically from hardwoods, characterized in that the hardwood component of the pulp is ground at least once in a grinder having a finely divided dispersed abrasive material adhered to at least 5 to one of the surfaces of the grinder plates, the abrasive material being dispersed on at least a substantial portion of said plate surface most in direct contact with the pulp during grinding, the paper having a substantially reduced number of detachable guide cells / cm 2 Salo rack while the pulp remains less than about 40 ° SR. 15. An improved hardwood pulp papermaking process comprising a thermochemically derived hardwood pulp, characterized in that it is ground at least once in a grinder having a surface containing a randomly dispersed finely divided abrasive material adhered to at least one of the grinder plates, the abrasive material being substantially for 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 mast cell segments per gram of pulp and lower grinding than in the case of at least one surface of the refiner plates having finely divided randomly dispersed material. 92607