FIELD OF THE INVENTION

[001] The present invention relates to the field of manufacturing of paper used in electrical insulation, and more specifically to an additive and a method for improving dewatering efficiency in paper manufacturing.

BACKGROUND OF THE INVENTION

[002] In paper making, several additives (also referred to as aids, agents, chemicals etc.) are used to control properties of the stock and / or finished paper. One of the most commonly used additive is a dewatering additive, which is used for controlling removal of water in one or more stages of paper making. Dewatering additives are readily available in the market and typically obtained from a supplier(s) according to the process requirements. Various raw materials are used in preparing additives, and there is more than often a significant difference in property of the fibers of the dewatering additive and that of the pulp. Even when the additive is made from similar wooden material as that of the pulp, there is a variation due to the broad variation in the quality of different wooden raw materials. This heterogeneity affects the efficiency of one or more stages of the paper making process, as well as critical mechanical / aesthetic properties of the finished paper including density, tensile strength and color. There is accordingly a need for an additive that enhances efficiency of dewatering, while imparting desired properties to the finished paper.

SUMMARY OF THE INVENTION

[003] Various aspects of the present invention provide a dewatering additive and a method for preparing paper with the dewatering additive. The paper may be insulation paper, or pressboard having certain electrical, chemical and mechanical properties. The dewatering additive is obtained using the same wood that is used as raw material for preparing the paper (i.e. insulation paper or pressboard). In one embodiment, the dewatering additive is prepared from a pulp obtained from the wood. For example, the dewatering additive may be prepared by milling the pulp.

[004] The method for preparing paper (i.e. insulation paper or pressboard) comprises obtain the pulp from a pulping process by treating wood with fresh water. The method further comprises preparing a stock from the pulp by adding the dewatering additive obtained from the same wood that is used for preparing the pulp. Here, the dewatering additive can be prepared from the pulp obtained from the pulping process. The dewatering additive may be added in a chest box for preparing the stock. Alternately, a solution of the dewatering additive can be prepared and added for preparing the stock. In addition, the method comprises supplying the stock through a wire section, a press section and a drying section for preparing paper.

BRIEF DESCRIPTION OF DRAWING

[005] Fig. 1 is a simplified flow diagram of paper manufacturing using a dewatering additive, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[006] Insulation paper or pressboard manufacturing involves processing wood to prepare pulp, which is mixed with various chemical and mineral additives. As shown in Fig. 1, wood (102) is typically treated with fresh water (104) in pulping (106), to obtain a pulp. Depending on the process of pulping, the pulp may be a mechanical pulp or a chemical pulp. In accordance with the present invention, the same wood (which is used to prepare the pulp), or the pulp prepared by wood ( 102) may be used for preparing the dewatering additive as shown in 108, 110. The dewatering additive can be prepared by milling the pulp (i.e. obtained from the same wood / received as input material). For example, the dewatering additive can be prepared by milling the wood or pulp obtained from the wood, to have fibers with particle sizes much smaller than that of the wood / pulp.

[007] The dewatering additive thus prepared, is used as an input (112) for preparing stock (114). Optionally the dewatering additive can be used along with other chemical / mineral additives (not shown in Fig. 1). The additive can be mixed in a chest box (not shown) for stock preparation. Alternately, the solution can be prepared separately and added just before the process starts. Once the additive (or solution) is added, the stock needs to be keep continuously stirred to avoid resting of the additive. The additive concentration can vary depending on production set-up. The amount of additive added can be 0.5 % to 10% by weight of the total pulp consumed. For example, 50 kg of dewatering additive can be added with 950 kg of pulp for preparing stock.

[008] The stock is typically supplied through a flow spreader and head box (not shown in Fig. 1), as a slurry (wet web) into a wire section (116). This section is typically referred to as a wet end section, and the dewatering additive can be added in this section. Dewatering additives are used at the convenience depending on the type of paper/board manufacturing machines

[009] The wire section can have a paper making table and web of wires (e.g. twin wires arranged between rollers), where significant amount of water is removed from the slurry as the paper forming progresses, and the wet web enters into a press section (118) of the paper machine. As a result of the dewatering additive, there is a productivity enhancement due to increase in speed of the paper machine. The speed of the paper machine increases by about 5 % to 25 % as compared to the earlier speeds (i.e. without the use of the dewatering additive of the present invention). This is realized by altering machine speed to compensate for the change in level of water line in the wire section due to the use of the dewatering additive. [0010] There may be dewatering devices (such as suction devices (not shown)) for aiding in removal of water in the wire section. There are a plurality of rollers (not shown) in the press section for further removal of moisture, and strengthening / smoothening the wet web, before it enters a drying section (120) of the paper machine (e.g. through one or more rollers (not shown)).

[0011] In the drying section, several sections may be present such as dryer section, calendar section, reel building section etc., for further removal of moisture (e.g. as steam (122), finishing, creating rolls of paper (124) and so forth. As the dewatering additive is prepared from the same wood (or pulp), it leads to formation of homogenous cellulosic fibers, which provides desired pulp properties as well as in desired water removal in various stages (126). For example, due to improved water removal, there is optimal amount of water outflow from the wet web in the wire section, which helps in optimizing the speed of the paper machine. The speed of the machine can be increase in range of 5% to 25%. For example, the original speed of the machine (i.e. without the dewatering additive of the present invention) may be 30 MPM, and the speed after using the dewatering additive of the present invention may be 33 MPM, which indicates a productivity improvement of 10%.

[0012] In case of pressboard manufacturing, the process is substantially similar to that of manufacturing of insulation paper as described in relation to Fig. 1. Here, as well the dewatering additive is mixed with the pulp for stock preparation, and the stock is passed through the wire section and a press and dry section for obtaining pressboard.

[0013] Thus, by preparing and utilizing the dewatering additive manufactured from the same wood / pulp, the effect on the properties (e.g. electrical, mechanical, aesthetic etc.) of the stock and paper is minimized as there is no heterogeneity in the system (mixture of pulp fibers and additive). Accordingly, the appearance (e.g. color etc.) of the finished paper / pressboard is not affected by the dewatering additive. In addition, the paper / pressboard has desired mechanical properties (e.g. density, tensile strength etc.) due to the homogeneity in the slurry in various sections of the paper machine.