PRINT PAPER FOR INKJET PRINTER HAVING WHITE BOARD FUNCTION AND MANUFACTURING METHOD THEREOF Technical Field [1] The present invention relates to printing paper for an inkjet printer having a white board function and a manufacturing method thereof, and more particularly, to printing paper for an inkjet printer which is used for a black-and-white or color inkjet printer and has a function of writing and erasing letters or drawings on the printing paper using a board marker pen before and after printed out like a white board, and a manu¬ facturing method thereof. Background Art [2] A sheet of paper that is a general print paper for an inkjet printer or a plotter has a low durability, is easily torn, has a short lifetime, is unable to provide a detailed color representation due to ink burring, and has little glossiness so that a printing effect is lowered. [3] To overcome the above drawbacks, various studies to manufacture a superior printing paper capable of printing an image representing clear color, detailed line, vivid color, and not being easily torn or crumpled and scratched after printed out, have been performed. [4] For example, Korean Patent No. 279057 discloses a method of manufacturing printing paper for a color inkjet printer. The printing paper is manufactured by coating of soft semitransparent PVC as a dust remover on a rear surface of a textile sheet man¬ ufactured to have an interval of about 0.1 mm between plies and a thickness of about 0.2 mm. Polyvinyl Acetate and fluorescent white pigment are mixed and CMC, a de- humidifier and an adhesive, is coated twice on the surface of the textile sheet. [5] However, since the above exclusively using paper does not have a coating effect, the paper needs to be inconveniently and additionally coated when additional comments is needed on the printed material. [6] A white board refers to a board on which writing using a board marker pen and erasing thereof can be repeated. [7] As the related conventional technologies, for example, Korean Patent No. 160375 discloses a coating film for the board which exhibits a simple manufacturing process, a superior handling feature such as carrying and cutting, a superior anti-abrasion, non- glossy, use of the brush, and an erasure feature. The coating film can be attached to anywhere since an adhesive to which release paper is combined is coated on a rear surface thereof. The coating film is manufactured by coating a pigment on a polyester film capable of roll coater coating and continuously baking to a dried film thickness of 10-20 ?m and drying the baked portion, and coating a heat-resistant adhesive on a rear surface of the polyester film to a thickness of 20 - 200 ?m and drying the same, and combining the release paper thereto. [8] Also, Korean Patent Publication No. 2000-8143 discloses a white board which is made of plastic, paper, or cloth to be thin and light so that the white board is easy to carried and stored while drastically reducing a production cost. The white board can be easily attached to anywhere without an additional part, and be arbitrarily cut by a user to be used for a variety of purposes. The white board is manufactured by forming an adhesive layer protected by a release paper on a rear surface of a thin plate formed of paper, plastic, or cloth. A coated layer which is a cured surface is formed by coating on a front surface. This Korean Patent Publication No. 2000-8143 concerns a white board which is thin and light, but it is a simple white board which does not have a printing function for an inkjet printer. Disclosure of Invention Technical Problem [9] The present invention is invented to overcome the drawbacks of the conventional printing paper for an inkjet printer and provide convenience in use and superior quality of the paper to customers. A printing paper having a function to repeatedly write and erase with the paper only without an additional coating step has been developed so that the printing paper for an inkjet printer having a white board function is invented by selecting primer that is an adhesive reinforcement member and coating with various materials such as plastic, paper, soluble PVA or modified PVA. [10] Thus, the purpose of the present invention is to provide printing paper having a function to repeatedly write and erase using a board marker pen with the printing paper only without an additional coating step while providing a superior printing quality by improving the drawbacks of the conventional printing paper for an inkjet printer, and a manufacturing method thereof. Technical Solution [11] According to one aspect of the present invention, there is printing paper having a white board function for an inkjet printer, which comprises a base layer formed of paper, a plastic sheet, or a plastic film; a primer adhesive layer formed of one or more material selected from a group consisting of polyurethane resin solution, polyacryl resin solution, and polyurethane acryl resin solution, and having a solid of 1 - 5 wt% 2 and a coating amount of 1 - 3 gin in a solution state; and a soluble poly vinyl alcohol (PVA) coating layer having a solid of 5 - 20wt%, a coating thickness of 1 - 30 ?m, a weight-average molecular weight of 800 - 3,000, a saponification of 80 - 90 mole%, and a molar fraction of a cation group is preferably 0.1 - 10 mole%. [12] According to another aspect of the present invention, there is provided a method of manufacturing printing paper for an inkjet printer having a white board function, which comprises forming a primer adhesive layer by coating primer formed of one or more materials selected from a group consisting of polyurethane resin solution, polyacryl resin solution, and polyurethane acryl resin solution, and having a solid of 1 - 5 wt%, on a base layer formed of paper, a plastic sheet, or a plastic film, at a coating amount of 1 - 3 gin in a solution state, and drying the primer adhesive layer, and forming a soluble poly vinyl alcohol (PVA) coating layer having a solid of 5 - 20wt%, a coating thickness of 1 - 30 ?m, a weight-average molecular weight of 800 - 3,000, a saponification of 80 - 90 mole%, and a molar fraction of a cation group of 0.1 - 10 mole%, to a coating thickness of 1 - 30 ?m, on the primer adhesive layer. Advantageous Effects [13] The printing paper for an inkjet printer according to the present invention not only exhibits a superior printing adaptability but also provides a function to freely write and erase with the printing paper only and convenience of being used as a replacement of a white board because carrying and handling the same is easy. Description of Drawings [14] FIG. 1 is a sectional view of printing paper for an inkjet printer having a white board function according to an embodiment of the present invention. Best Mode [15] Referring to FIG. 1, printing paper according to an embodiment of the present invention includes a base layer 1, a primer adhesive layer 2 and a soluble PVA coated layer 3. The base layer 1 can be selected from paper, a plastic sheet, or a plastic film. [16] In the present invention, the paper may be laminated paper, high glossy paper, or raw paper. The plastic sheet refers to a plastic material, such as polyethyleneterephthalate(PET), polyethylene(PE), polypropylene(PP), polystyrene, or nylon, having a total thickness of 300 ?m or more. The plastic film refers to a plastic material having a total thickness of 300 ?m. The plastic sheet and plastic film can be either transparent or white. [17] The PET material is obtained by polycondensating ethylene glycol and terephthal acid while a PET film is obtained by extruding a PET material through a T-DIE type extruder and biaxially elongating the same. The PET film or sheet exhibits superior heat resistance, dimensional stability, and durability so as to be very adaptive to the printing paper for an inkjet printer. Since a general PET has superior mechanical (high tension strength and elasticity), chemical, electric, and optical characteristics, it is widely used for a food package member and industrial use. [18] The PP film is extruded by the T-DIE type extruder and biaxially elongated using a high crystalline characteristic. These plastic film and sheet having superior hardness and appropriate strength and heat resistance, chemical resistance, and oil resistance are suitable for a base of printing paper for an inkjet printer. [19] The nylon film is extruded by a T-DIE type or Blown type extruder and biaxially elongated, which exhibits high heat resistance, tenacity, and dimensional stability and is suitable for a base of printing paper for an inkjet printer. In addition, most plastic materials such as polyethylene, polystyrene, and polyvinylchloride are suitable for a base of printing paper for an inkjet printer. Also, a white plastic sheet or film is man¬ ufactured by adding a small amount of TiO to the above materials. [20] In the present invention, the thickness of the base layer 1 is not particularly limited, but is preferably between 0.05 - 0.15 mm. [21] In the present invention, the base layer 1 and the soluble PVA coated layer 3 do not adhere to each other by heat adhesion, a primer adhesive layer is used to increase an adhesive force between both layers. [22] The primer having a solid of 1 - 5 wt% is coated on the base layer 1 to a coated 2 amount of 1 - 3 gin (in a solution state) and passes through a drying hood so that water is evaporated and dried to thus form the primer adhesive layer 2. [23] The primer resin may be one or more materials selected from a group consisting of polyurethane resin solution, polyacryl resin solution, and polyurethane acryl resin solution. The solid of the resin is preferably 1 - 5 wt%. When the amount of the solid is less than 1 wt%, since the coated amount of the primer pure solid decreases and an adhesive force between the base layer 1 and the coated layer 3 is lowered. When the amount of the solid exceeds 5 wt%, viscosity of the primer solution increases so that a large amount of primer solid is coated and an adhesive force is rather lowered. [24] The liquid-coating method of the primer layer 2 on the base layer 1 is not par¬ ticularly limited, but may be a Gravure, kiss coater, dipping, spray coater, or comma method. The coated amount of the primer resin is preferably 1 - 3 gin in a solution state. When the coated amount is less than Ig per square meter, the adhesive force between the base layer 1 and the coated layer 3 is lowered. When the coated amount exceeds 3g per square meter, the adhesive force between the base layer 1 and the coated layer 3 is lowered as well. [25] The drying hood has a drying chamber having a length is typically 25 - 35 cm and has a particular temperature gradation from an entrance through the chamber. For example, the temperature gradually increases from the entrance of 5O0C, to 7O0C, 9O0C, 12O0C, and 14O0C respectively, while drying the primer layer 2. If the primer layer 2 is heated at a too high temperature from the beginning, only the outer surface thereof is dried and the inner side of the primer layer 2 is not well dried so that a uniform and homogeneous adhesion layer is not formed. Thus, the temperature of the drying hood is controlled to has a particular temperature gradation within a temperature range between 50 and 140 ° C so that the primer layer 2 is gradually heated. [26] The soluble PVA coated layer 3 having a solid of 5 - 20 wt% is coated on the primer adhesive layer 2 to a thickness of 1 - 30 ?m. The coating and drying method of the soluble PVA coated layer 3 can be performed in the same method for the primer adhesive layer 2. Also, when the thickness of the soluble PVA coated layer 3 is less than 1 ?m, a printing performance and a writing/erasing function of printing paper is deteriorated. When the thickness of the soluble PVA coated layer 3 exceeds 30 ?m, since the printing paper absorbs a large amount of moisture when being used for a long time, and the strength of the printing paper is lowered. [27] The soluble PVA coated layer 3 is formed as follows. [28] 1) One of more PVA resin is selected from a group consisting of PVA, acetyl- group modified PVA, and silane modified PVA to prepare a PVA solution having the concentration of 4 - 20%. [29] 2) Methyl meta acrylate, ethyl acrylate, vinyl monomers having an amide group in the side chain are copolymerized in a mole ratio of 10:10:1 to prepare a copolymer. [30] 3) Silica having a weight ratio of 0.1 - 0.3 compared to a polymer concentration (solid) is prepared. [31] 4) The items obtained from the above steps 1), 2), and 3) are solved in a solution of water and ethanol mixed in a ratio of 1:1 to produce a coated material. [32] In the present invention, the solid of the soluble PVA coated layer is preferably 5 - 20 wt% and accordingly the amount of the items of the steps 1) and 2) is controlled. When the amount of the solid is less than 5 wt%, the coated amount of PVA may be excessively small. When the amount of the solid exceeds 20 wt%, the amount of PVA coated PVA may be excessive. The acryl copolymer of the step 2) is soft polymer resin which is insoluble to water, and has a high moisture absorption capability, is preferably a cation, and contributes to prevention of a surface charge. In the present invention, the molar fraction of a cation group is preferably 0.1 - 10 mole%. When the molar fraction of a cation group is less than 0.1 mole%, its effect is small. When the molar fraction of a cation group exceeds 10 mole%, the adhesive force of polymer and performance of a film are deteriorated. The monomers having the cation group may be dimethyl amino ethyl (meta) acrylate, diethyl amino ethyl (meta) acrylate, and dimethyl amino ethyl (meta) acrylamid. [33] In addition, the PVA solution has a weight-average molecular weight of 800 - 3,000 and a saponification of 80 - 99 mole%, preferably, 80 - 90 mole%. [34] When the molecular weight- average of the PVA solution is less than 800, the strength of a PVA film decreases. When the molecular weight- average of the PVA solution exceeds 3,000, a solubility of PVA to water is deteriorated. Also, when the saponification is less than 80 mole%, although the solubility is good, water resistance, chemical resistance, and blocking resistance are deteriorated. When the saponification exceeds 99 mole%, hydrophil is lowered so that a film drying time is extended. [35] Since the above coated PVA layer exhibits a superior chemical resistance but an inferior water resistance, when an board marker pen(solubility in water) is used for a printing paper for an inkjet printer, a dissolving and swelling of PVA makes some letters or drawings on the printing paper. In contrast, since the coated PVA has a low wet tension, written texts can be easily erased. [36] According to the present invention, the printing paper can replace an existing white board in a conference room or seminar room and has a feature of freely writing and erasing with a board marker pen. Also, an additional coating to provide the writing and erasing function is not needed. [37] Also, as exclusively using paper for black and white, color, or a photo inkjet printers, the printing paper according to the present invention is glossy, non-smear, and capable of detailed color representation and uniform printing out. Also, the printing paper according to the present invention can be manufactured and sold in a roll state or an A4 format. [38] Thus, since the printing paper in the present invention is printing paper for an inkjet printer and also a white board which is easy to be carried and handled, it can be applied to a variety of fields. For example, during a military operation, a map of a cor- responding operation area can be printed by a plotter and descriptions relating to the operation can be freely marked on the map using a board marker pen. Also, Chinese characters, English words, or math questions or multiple table may be printed out on the printing paper so that texts or symbols can be freely marked down on the printing paper for explanation as an assistant teaching method. [39] The present invention is described in detail below, but not limited thereto. [40] A PET sheet having a 400 ?m thickness is prepared. Polyurethane resin solution 2 primer of 1 wt% is coated on the sheet in a solution state at a coated amount of 1 gin (in a solution state) and passes through a drying hood to be dried according to a particular temperature gradation, so that a primer adhesive layer is formed. A soluble PVA coated layer having a solid of 6 wt% is formed on the primer adhesive layer to a coating thickness of 20 ?m. A map is printed out on the above paper by a color inkjet printer. Writing down on a surface of the paper using a board marker pen and erasing it with a white board eraser can be easily. Also, the printed map represents clear line and colors so that the paper shows a superior print adaptability. [41] The soluble PVA resin having a solid of 6 wt% is manufactured by: [42] 1) 50g of a 4 wt% PVA solution; [43] 2) 50g of a copolymer obtained by copolymerizing methyl meta acrylate, ethyl acrylate, monomers having a cation group (dimethyl amino ethyl (meta) acrylate, diethyl amino ethyl (meta) acrylate, and dimethyl amino ethyl (meta) acrylamid) in a mole ratio of 10: 10: 1 ; [44] 3) 0.06g of silica (having a 0.1 weight ratio compared to a solid); and [45] 4) a solution of water and ethanol mixed in a ratio of 1 : 1 where the items 1), 2), and 3) are solved. Industrial Applicability [46] The printing paper for an inkjet printer having a white board function according to the present invention, and a manufacturing method thereof, can be useful in a field such as a printing paper for an inkjet printer having a function of writing and erasing on the paper using a board marker pen as in a white board before and after printing out, while being a print paper for a black-and-white or color inkjet printer.