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Process for preparing mechanical pulpRelated Patent Categories: Paper Making And Fiber Liberation, Processes Of Chemical Liberation, Recovery Or Purification Of Natural Cellulose Or Fibrous Material, Treatment With Particular Chemical, OrganicProcess for preparing mechanical pulp description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070151683, Process for preparing mechanical pulp. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to a process in accordance with the preamble of Claim 1 for preparing mechanical pulp. The invention also relates to a process for decreasing the energy consumption of mechanical pulping processes based on refining chips, according to the preamble of Claim 17. [0002] Chemical and mechanical pulps possess different chemical and fibre-technical properties and thus their use in different paper grades can be chosen according to these properties. Many paper grades contain both types of pulps in different proportions according to the desired properties of the final products. Mechanical pulp is used, when necessary, to improve or to increase the stiffness, bulkiness or optical properties of the product. [0003] In paper manufacture, the wood material must first be defibred. Mechanical pulp is mainly manufactured by means of grinding and refining methods, in which the raw wood material is subjected to periodical pressure impulses. Due to friction heat, the structure of the wood is softened and its structure loosened, finally leading to the separation of the fibres from one another (Virkola, 1983). However, only a small part of the energy brought into the system is used for separating the fibres; the major part being converted into heat. Therefore, the total energy economy of the defibration is very poor. [0004] Several methods for improving the energy economy of mechanical pulping are suggested in prior art. Some of these are based on the pre-treatment of chips by, e.g., water or acid (FI Patent Specifications Nos. 74493 and 87371). Methods are also known, which comprise treating the raw material with enzymes to reduce the consumption of pulping energy. Thus, the Finnish Patent Application No. 895676 describes an experiment in which once-refined pulp was treated with a xylanase enzyme preparation. It is stated in the application that this enzymatic treatment would, to some extent, decrease the energy consumption of pulping. In the said prior art publication, the possibility of using cellulases is also mentioned but no examples of these are given nor are their effects shown. As far as isolated enzymes are concerned, in addition to hemicellulases, the interest has been focused on lignin modifying enzymes, such as laccase enzyme (Jokinen and Savolainen, 1991). A treatment using the laccase enzyme did not, however, have an effect on the energy consumption (Jokinen and Savolainen, 1991). [0005] The Patent Specification EP 0429 422 suggests the use of laccase treatments in mechanical pulping between the first and the second refining treatments. This specification states that the laccase treatment decreases the energy consumption of the refining process. The Patent Specification WO 93/23606, in turn, suggests a treatment with phenol oxidase enzymes after the last refining or grinding treatments. The said treatment had no effect on the energy consumption of the refining treatment but it has been said to have an influence on the strength of paper or board. [0006] As the energy in defibration is mainly absorbed by the amorphous part of the paper furnish only, i.e., hemicellulose and lignin, an increase in the amorphousness of the raw material improves the energy economy of the defibration. The Patent Specifications WO 94/20666 and WO 94/20667 suggest that the amorphousness of the raw material be increased in connection with mechanical pulping by treating the raw material with a suitable enzyme that reacts with the crystalline, insoluble cellulose of the raw material. The Patent Specification WO 94/20666 suggests that the raw material be treated with an enzyme preparation, the main cellulase activity of which consists of cellobiohydrolase activity. The Patent Specification WO 94/20667 suggests that an enzyme preparation be used for the same purpose, containing cellobiohydrolase activity and mannanase activity. The examples of the said specifications deal with rough wood, such as the long-fibre fraction of fractioned TMP spruce pulp, once-refined TMP spruce pulps (with freeness values of CSF 450-550) or TMP pulps refined to different freeness levels (30-300). If a synergistically acting cellulase enzyme product, i.e., cellulase, was used in connection with the manufacture of mechanical pulp, containing both cellobiohydrolase and endoglucanase, the treatment resulted in the hydrolysis of the insoluble cellulose and, thus, in the weakening of the strength properties of the pulp. [0007] The Patent Specification U.S. Pat. No. 6,267,841 describes a manufacturing method of thermo-mechanical pulp, wherein the pulp is treated with enzyme between the first and the second refining processes. It also suggests the treatment of chips with enzymes before the first refining. The specification cites enzymes, such as pectinase, xylanase, laccase, cellulase or the mixtures thereof. The specification gives no numerical values of any energy savings obtained. [0008] In addition to the afore-mentioned isolated enzymes, the application of growing white rot fungi in the manufacture of mechanical pulp has also been studied. Carried out before defibration, such a treatment with a white rot fungus has been found to decrease the specific energy consumption and to improve the strength properties of these pulps (Setliff et al., 1990, Leatham et al., 1990 and Akhtar et al., 1992). The drawbacks of these treatments with the white rot fungus are, however, the long treatment times needed (mostly weeks); the decreased yield (85 to 95%), the difficulty to control the process and the impaired optical properties. [0009] Generally, the different enzymatic treatments according to prior art have been applied to raw wood material, which has been defibred to a certain extent already during the manufacturing process. According to a general view, the enzymatic treatment is not as effective when applied to chips directly, because it is difficult to make the enzyme preparation to be effectively absorbed into the fibres of a raw material that is in the form of chips. In a native form of chips, the surface area of the raw wood material is not sufficient for an effective enzymatic treatment to take place. Another reason is that a major part of the capillaries of the wood are too small to receive any enzyme molecules (Grethlein, H. E. Biotechnology, February 1985, pp. 155 to 160). [0010] According to prior art, the pulping liquor is made to penetrate the chips used in pulp cooking by treating the chips with pressure shocks in the presence of the pulping liquor. In the Vilamo method, for example, the chips are treated in the presence of the cooking liquor by varying the pressure from a pressure of 4.5 kp/cm.sup.2 and a treatment time of 10-16 s to a pressure of 2 kp/cm.sup.2 and a treatment time of 5-6 s, the treatment being repeated 6-8 times at 1-minute intervals/Rydholm, 1965). [0011] The Patent Specification WO 95/09267 suggests treating the chips, which are used in pulp cooking, with a chemical solution by subjecting the chips to a vacuum and making the chemical solution penetrate the wood fibres by means of a pressure shock. According to the application, the chemical solution can be cooking liquor that contains, for example, catalysts and enzymes. The object of the invention is, thus, to be able to decrease the amount of lignin in order to diminish the need of decreasing the residue lignin at the final stage of cooking. However, the application does not describe in detail, whether or not the enzymes penetrate the wood cells successfully and whether or not the enzymes have any effect on the decrease of the amount of lignin. [0012] The U.S. Pat. No. 5,374,555 suggests the removal of lignin from the lignocellulose material by means of a protease enzyme. To enhance the enzymatic treatment, the patent suggests a mechanical treatment of chips, for example, in a screw clamp. The patent specification reminds that cellulase can be used as a pre-treatment enzyme for the chips or the pulp, but it does not suggest carrying out a treatment with cellulase in connection with the mechanical processes. The purpose of the patent is not to save energy but to remove lignin, and there are no observations relating to energy economy. While the application suggests a protease treatment of the wood material, which is used both in the manufacture of mechanical pulp and in that of chemical pulp, the main issue is the removal of lignin as a pre-treatment in the manufacture of chemical pulp. [0013] The Patent Specification WO 97/40194 suggests changing the structure or the composition of the wood by adding to the compressed chips fungal or bacterial cultures or products, such as enzymes obtained from them, by means of pressure. The purpose of the compression is to make cracks and fractures in the wood. When the chips are released from the compression, microbes of their products, while the chips expand, are absorbed by the structures of the wood partially by the virtue of under pressure, partially by the capillary action. The application suggests, among others, fungi from the genera Ceriposiophsis, Phanerochaete and Ophiostoma. Regarding enzymes, lipolytic, proteolytic, linginolytic, cellulolytic and hemicellulolytic enzymes are mentioned. The patent specification describes the absorption of the enzyme preparation Clariant Cartazyme HS.TM. (xylanase) into the compressed chips after releasing the pressure. Liquid was removed after the treatment, and mechanical pulp was prepared from the chips. In that case, the amount of energy consumed was 7.5% less than in the case of chips that were treated with a buffer only. In another test, the enzyme preparations Clariant Cartazyme NS.TM. (xylanase) and Sigma porcine pancreas Lipase L-3126 were treated. In that case, the amount of energy consumed was 12.5% less than when treated with a buffer only. The specification mentions no preservation of the optical properties of the pulp. According to the specification, the highest energy savings were made by combining enzyme preparations originating in different sources, of which the amount of a lipase of a mammalian origin, in particular, was considerable. The amount of the other enzymes used was also fairly high, which makes one suspect that the energy savings achieved were not particularly cost-effective. [0014] Eriksson and Heitman (1998) describe tests, wherein pieces of wood (with a size of 1.times.1.times.1.5 inches) were treated with a cellulase enzyme mixture, after which the pieces were ground and the energy consumed by the grinding was studied. The absorption of the enzyme mixture into the pieces of wood was facilitated by subjecting the pieces to a vacuum. The treatment was not observed to have any effect on the consumption of the grinding energy. [0015] One problem with the manufacturing methods of mechanical pulp according to prior art is their great energy consumption. While attempts have been made to improve the beating degree and the energy economy with the aid of enzymatic treatments, hardly any energy savings have been made and, often, they have resulted in the weakening of the strength properties of the pulp (cellulase treatment) or in the darkening of the pulp and an impairment in the optical properties (laccase treatment). Furthermore, it has not always been possible to make the enzyme solution effectively act on the wood. In some cases, the preparation of the enzyme composition used in the tests may have included time-consuming stages and/or been otherwise uneconomic. [0016] The purpose of the present invention is to remove at least some disadvantages of prior art and to provide an improved method for the manufacture of mechanical pulp. To be more precise, the object of the invention is to provide a pre-treatment method of chips to be used before preparing the mechanical pulp. [0017] In connection with the present invention, it has surprisingly been observed that chips can be pre-treated with an enzyme preparation that has synergistically acting enzyme activities. In that case, the enzyme preparation does not need to contain any certain isolated enzyme activity only, but an enzyme preparation containing different enzyme activities can be used directly as the enzyme preparation. [0018] The treatment according to the method can be applied to the chips directly. As the enzymatic treatment takes place at an early stage of the pulping process, savings in the refining energy are then as high as possible. [0019] According to the method of the present invention, the chips are pre-treated with an enzyme that is capable of degrading the structural parts of the wood, after which mechanical pulp is manufactured from the chips by refining. It is preferable to carry out the enzymatic treatment by compressing the chips and by bringing the compressed chips in a liquid phase into contact with the enzyme composition to absorb the enzyme composition into the chips. The enzyme composition preferably contains both cellobiohydrolase and endoglucanase. It is particularly preferable for the composition to contain an effective amount of both cellobiohydrolase and endoglucanase. Enzyme preparations containing cellobiohydrolase and endoglucanase in a ratio of 20:1-1:20, indicated as the weight ratio of the proteins, are preferable. [0020] According to some preferable embodiments of the invention, the amount of endoglucanase compared with that of cellobiohydrolase is higher than what is naturally produced by the industrial production strains of cellulase, such as Trichoderma, in their growth media. [0021] To be more precise, the method according to the invention is mainly characterized in that which is presented in the characterizing part of Claim 1. [0022] The method according to the invention is also characterized in that which is presented in the characterizing part of Claim 17. [0023] The invention provides several considerable advantages. When using the methods according to the preferable embodiments of the invention, considerably lower amounts of energy are consumed than in the methods according to prior art. The energy saving can be as much as 20% compared with a method, wherein the chips are not treated with the enzyme preparation. [0024] When treating the chips by the methods according to the preferable embodiments of the invention, the strength of the pulp was not weakened; on the contrary, it improved to some extent. The optical properties also remained good. Thus, when treating the chips with the methods according to the preferred embodiments of the invention, it was possible to improve the quality of the pulp. Continue reading about Process for preparing mechanical pulp... Full patent description for Process for preparing mechanical pulp Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Process for preparing mechanical pulp patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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