Background Art [2] The kinds of tiles used as roofing materials for buildings are classified into female tiles, male tiles, crescent-shaped tiles placed at both sides of the ridge of a roof, ridge- end tiles, concave tiles at the edge of the eaves, convex tiles at the edge of the eaves, crest tiles, tiles for protruding corners of the eaves, eave tiles, plain tiles, roof ridge tiles, and the like according to the shapes and uses of tiles. They are also classified into clay tiles made of clay, cement tile made of a mixture of cement and sand, metal tiles made of aluminum or a galvanized steel sheet plated with zinc alloy, and the like according to the materials of tiles.

[3] Clay tiles that are mainly used in Korean-style houses, royal palaces and Buddhist temples are classified into sooty tiles treated with carbon, enamel tiles treated with enamel, glazed tiles treated with glazing lye, unglazed tiles treated with paints and pigments, and the like.

[4] A clay tile is manufactured as follows. Clay is kneaded and the kneaded clay is molded into a tile within a mold and then dried. Thereafter, the molded tile is ac- commodated in a baking furnace to bake it at a predetermined temperature.

[5] At this time, the baking is performed in a state where the molded tile is laid down on a support frame, or a supporting member is separately stuck into the molded tile that in turn is then vertically placed on the support frame. In the former case, since a great number of molded clay tiles cannot be accommodated in a limited space of the baking furnace, fuel costs increase in the baking process. This becomes a cause of increase in production costs and an obstacle to mass production. In the latter case, since the supporting member should be stuck into each of molded clay tiles to vertically place the clay tiles in the baking furnace, a great number of molded clay tiles can be ac- commodated in the baking furnace, resulting in reduced fuel costs in the baking process.

[6] However, since the supporting members are manually stuck into and removed from the clay tiles, there is a disadvantage in that labor power is considerably consumed.

[7] Further, when the clay tiles are completely manufactured and packaged by stacking them one above another, there is no engaging and fixing means between adjacent clay WO 2005/078209 PCT/KR2005/000398 tiles. Thus, there is a disadvantage in that damage or breakage occurs due to friction between upper and lower clay tiles.

[8] Moreover, when clay tiles are used in construction work, supporting stands are fixed transversely on the floor of a roof and the clay tiles are put on the supporting stands and then fixed thereto by means of nails. However, since each of the clay tiles has no catching portion, there is a disadvantage in that a shift of the clay tile in position results in inaccurate construction work.

[9] A cement tile is manufactured from a mixture of a certain amount of cement, water and sand at a proper ratio. A crack is produced at the cement tile over time, and thus, the life span of the cement tile is relatively short.

[10] Further, since a whitening phenomenon is produced, the external appearance of the cement tile is deteriorated and a portion thereof where the whitening phenomenon has occurred is transformed into a configuration and structure into which rainwater can penetrate. Accordingly, there is a disadvantage in that the cement tile is continuously and rapidly aged, resulting in a short life span.

[11] A metal tile is manufactured by forming a metal sheet into a traditional tile shape and has a light weight and superior weatherability and durability. However, upon assembly of female and male metal tiles in constructing a tiled roof, additional brackets should be installed on tight frames.

[12] When the female or male metal tiles are fixed to the tight frames via the brackets, a great deal of screwing or riveting work are involved. Thus, there are advantages in that the number of constituent parts increases, installation costs also increases and assembly is complicated.

Disclosure of Invention Technical Problem [13] The present invention is conceived to solve the aforementioned problems. An object of the present invention is to provide a tile of sand and plastics, which comprises 62 to 66 parts by weight of sand and 34 to 38 parts by weight of plastics so that the tile has improved strength and prolonged life span and is easy to be mass-produced, and a method of manufacturing the same.

Technical Solution [14] To achieve the object, the present invention provides a tile of sand and plastics, comprising 57 to 70 parts by weight of sand; and 30 to 43 parts by weight of plastics.

[15] More specifically, the tile may comprise 62 to 66 parts by weight of sand and 34 to 38 parts by weight of plastics.

[16] The present invention provides a method of manufacturing a tile of sand and plastics, comprising a sand-screening step of screening sand that can pass through a WO 2005/078209 PCT/KR2005/000398 sieve with meshes of 0.3 mm but cannot pass through a sieve with meshes of 0.1 mm; a plastic-melting step of melting plastics after the sand-screening step; a composition- mixing step of simultaneously supplying 62 to 66 parts by weight of sand and 34 to 38 parts by weight of plastics to a mixing bath and mixing them with each other to disperse the sand within the plastics in a gel state after the plastic-melting step; a composition-filling step of filling a mold with the mixed composition after the composition-mixing step; a composition-pressurizing step of applying pressure to the composition so as to compensate for volume reduction due to shrinkage during cooling of the molten plastics after the composition-filling step; a molded-product completing step of causing the molten plastics to be solidified and plasticized by cooling the mold after the composition-pressurizing step; and a molded-product separating step of separating a molded product from the mold after the molded-product completing step.

Advantageous Effects [17] As described above, since the tile of sand and plastics according to the present invention is good in view of bending fracture strength, the tile that has been employed in construction work does not need maintenance for several years like a metal or cement tile and thus can be used semi-permanently. Further, since a crack is not produced in the tile, there is no risk of a water leakage even though a heavy rain falls.

Moreover, since the plastics are used as the component of the tile, there is no need for an additional insulating material. In addition, there is an advantage in that rupture and dew condensation do not occur even in a hard winter because the tile itself does not absorb moisture.

Brief Description of the Drawings [18] Fig. 1 is a perspective view showing a tile of sand and plastics according to the present invention.

[19] Fig. 2 is a flowchart illustrating a method of manufacturing the tile of sand and plastics according to the present invention.

Best Mode for Carrying Out the Invention [20] Hereinafter, preferred embodiments of the present invention will be described in detail.

[21] Fig. 1 is a perspective view showing a tile of sand and plastics according to the present invention, and Fig. 2 is a flowchart illustrating a method of manufacturing the tile of sand and plastics according to the present invention.

[22] The tile of sand and plastics according to the present invention comprises 57 to 70 parts by weight of sand, and 30 to 43 parts by weight of plastics.

[23] The reason of limitation on the components is that if the amount of the sand is less than 50 parts by weight, the tile of sand and plastics has a light weight due to the small WO 2005/078209 PCT/KR2005/000398 amount of sand so that there may be a risk that the tile will be blown off by a strong wind when the tile has been used for a roof, whereas if the amount of the sand is greater than 70 parts by weight, the tile of sand and plastics has a heavy weight and imparts heavy load to a roof, resulting in problems by which a rafter, a girder and the like should be enlarged unnecessarily and workability is deteriorated.

[24] Meanwhile, if the amount of the plastics is less than 30 parts by weight, there is a disadvantage in that the binding force of the sand is lowered and the bending fracture strength of the tile of sand and plastics is lowered. If the amount of the plastics is greater than 43 parts by weight, there are problems in that the bending fracture strength is rapidly decreased and the weight of the tile is also reduced.

Mode for the Invention [25] A tile of sand and plastics according to another embodiment of the present invention comprises 62 to 66 parts by weight of sand and 34 to 38 parts by weight of plastics.

[26] The reason of limitation on the sand and plastics is that the tile of sand and plastics with this composition is a desirable tile which has a proper weight and a proper bending fracture strength and is not blown off by a strong wind.

[27] A method of manufacturing the tile of sand and plastics according to the present invention will be described. Preferably, a sand-screening step (step 10 in Fig. 2) is a step of screening sand to obtain sand with a proper grain size, removing impurities contained in the screened sand, and washing and drying the sand from which the impurities have been removed.

[28] As for the sand used in the present invention, sand with relatively uniform grains is required. Since sand gathered in a river or sea has many stones or the like mixed therewith, which are larger than the grains of the sand, sand with relatively uniform grains is screened by means of a sand-screening machine using a vibrating sieve. The gathered sand is transferred to a screening unit of the sand-screening machine by a conveyor or the like thereof and caused to pass through the vibrating sieve with meshes of 0.3 mm. The remaining sand that did not pass through the sieve is separately collected and the sand that passed through the sieve is caused again to pass through another vibrating sieve with meshes of 0.1 mm. The sand that passed through the other sieve is separately collected and the remaining sand that did not pass through the other sieve, i. e. , sand with a grain size of 0.1 to 0.3 mm, is used in the present invention.

[29] The reason of limitation on the grain size of the sand is that if the grain size is less than 0.1 mm, the amount of a usable part of gathered sand is small and the rate of use of the sand is also low so that production costs of the tile of the present invention increase, whereas if the grain size is greater than 0.3 mm, the surface of the tile of the WO 2005/078209 PCT/KR2005/000398 present invention is roughened and thus a problem with merchantability is caused.

[30] This step may further comprise the step of removing impurities contained in the sand and washing and drying the sand from which the impurities have been removed.

The gathered sand may include a great deal of impurities. Particularly, sand gathered in a sea contains much salt. Therefore, to remove the impurities, the sand is washed and then dried to remove moisture added to the sand during the washing process so that the sand can comprise a certain level of moisture.

[31] As an example of a method of washing the sand, there is a method of spraying tap water or underground water on the sand. In the drying step, it is possible to use a hot air drying method of passing the washed sand through a hot air drying chamber, or a natural drying method of drying the washed sand by a wind or sunbeams.

[32] After the sand-screening step, a plastic-melting step of melting the plastics (step 20 in Fig. 2) is performed. In this step, a plastic-melting machine such as an injection molding machine is used. The temperature of a cavity of the plastic-melting machine, i. e. , the temperature of a space in which the plastics are melted, should be maintained at 200 to 350°C. The reason is that the temperature is suitable to molding conditions, including melting, for polyethylene (PE), polypropylene (PP), polycarbonate (PC), poly vinyl chloride (PVC) or the like.

[33] If a colored plastic material is used in the plastic-melting step, a finished tile of sand and plastics has a color. Thus, it is possible to manufacture tiles of sand and plastics, which have a variety of colors.

[34] After the plastic-melting step, a composition-mixing step (step 30 in Fig. 2) is performed. In the composition-mixing step, the sand screened in the sand-screening step and the plastics melted in the plastic-melting step are simultaneously fed to a mixing bath. The sand is injected according to an air-jet principle employed in sandblasting and the like. The body of an injection nozzle comprises a linear sand injection port and sand suction port, which are integrally formed with each other, and a Y-shaped air suction port between the sand injection port and the sand suction port.

[35] The sand suction port of the injection nozzle comprises a sand suction tube that has an open distal end and an inner space. The air suction port of the injection nozzle comprises an air suction tube that has an inner space and a distal end coupled to a blower. The sand injection port of the injection nozzle is placed in the mixing bath and one side of the sand suction tube is placed in sand. When the blower is operated, air with high pressure generated by the blower is introduced into the air suction tube and the introduced air is injected through the sand injection port of the injection nozzle. At this time, sand is sucked through the sand suction tube and then injected together with the air into the mixing bath.

[36] The molten plastics in the cavity are caused to flow into the mixing bath through a WO 2005/078209 PCT/KR2005/000398 nozzle by a pressurizing device such as a piston or a screw.

[37] The screened sand and the molten plastics are fed into and mixed in the mixing bath. At this time, to solve nonuniformity of the mixture due to difference in specific gravities of the sand and the molten plastics, the sand and the molten plastics are mixed with each other while the plastics are in a gel state, so that the sand can be uniformly distributed in the plastics.

[38] Meanwhile, to keep the interior of the mixing bath at a predetermined temperature, the mixing bath is heated by a heater using a liquid such as water or oil. The liquid heater may absorb or uniformly apply heat from or to the mixing bath even though the temperature of the mixing bath rises above the predetermined temperature during the heating, thereby heating and cooling the mixing bath on an average.

[39] The mixed composition comprises 57 to 70 parts by weight of sand, and 30 to 43 parts by weight of plastics. The reason for limiting the composition ratio to the foregoing is that if the amount of the sand is less than 57 parts by weight, the tile of sand and plastics has a light weight due to the small amount of sand so that there may be a risk that the tile will be blown off by a strong wind when the tile has been used for a roof, whereas if the amount of the sand is greater than 70 parts by weight, the tile of sand and plastics has a heavy weight and imparts heavy load to a roof, resulting in problems by which a rafter, a girder and the like should be enlarged unnecessarily and workability is deteriorated.

[40] Meanwhile, if the amount of the plastics is less than 30 parts by weight, there is a disadvantage in that the binding force of the sand is lowered and the bending fracture strength of the tile of sand and plastics is lowered. If the amount of the plastics is greater than 43 parts by weight, there are problems in that the bending fracture strength is rapidly decreased and the weight of the tile is also reduced.

[41] It is desirable to manufacture a tile of sand and plastics comprising 62 to 66 parts by weight of sand and 34 to 38 parts by weight of plastics, which has a proper weight and a proper bending fracture strength and is not blown off by a strong wind.

[42] After the composition-mixing step, a composition-filling step (step 40 in Fig. 2) is performed. This step is a step of filling a mold with the mixed composition, wherein the mixture of the sand and the molten plastics flows from the mixing bath into the mold to fill a filling cavity of the mold therewith. The pressurizing device such as a piston or a screw advances so that the cooled and solidified mixture of the sand and the molten plastics in the mixing bath is caused to flow through a sprue, a runner and a gate into the filling cavity to fill the filling cavity therewith. In other words, the mixture of the sand and the molten plastics flows from a conical nozzle of the mixing bath into the filling cavity through the conical sprue, which is in contact with the nozzle of the mixing bath and has a small width and a taper angle of about 2 to 4°C, WO 2005/078209 PCT/KR2005/000398 through the runner, which is a short trough or passage in the form of a circle or the like in cross section, and through the gate, which has a cross section in the form of a circle or the like and is installed at a position where the mixture of the sand and the molten plastics can rapidly flow from an inlet of the filling cavity to an opposite position.

[43] After the composition-filling step, a composition-pressurizing step (step 50 in Fig.

2) is performed. This step is a step of applying pressure to the composition so as to compensate for volume reduction due to shrinkage during cooling of the molten plastics. In this step, after the filling cavity has been filled with the mixture of the sand and the plastics, the pressurizing device such as a piston or a screw further advances to apply pressure to the mixture. A shrinkage of about 25% generated when the molten plastics is changed from the molten state to a solid state, i. e. , volume reduction due to the shrinkage during the cooling of the plastics, is compensated.

[44] After the composition-pressurizing step, a molded-product completing step (step 60 in Fig. 2) is performed. This step is a step of completing a molded product by cooling the mold to solidify and plasticize the molten plastics so that the grains of the sand are positioned in place. Meanwhile, this step is a step of solidifying the molten plastics by cooling the mold, wherein cooling water is caused to pass through cooling holes or grooves formed in the molding machine or mold to remove heat from the molten plastics through the mold and to provide the molten plastics with plasticity that is a property by which deformation produced under stress above an elastic limit is not restored to its original state.

[45] After the molded-product completing step, a molded-product separating step (step 70 in Fig. 2) is performed. This step is a step of separating the molded product from the mold. That is, this step is a step of separating the completed, molded product from the mold using an ejector while separating a movable mold half from a fixed mold half, wherein the molded product is separated from the filling cavity using ejector pins that are fixed on an ejector plate and placed in the mold and advance together with the ejector plate when the mold is opened.

[46] <Example 1> [47] Tiles of sand and plastics according to the present invention were formed into Korean-style female tiles that had the same weight as a Korean-style female clay tile available on the market, and were subjected to comparison tests in view of bending fracture strength according to KSF 3510 of Korean Standards. As for a test method, a test sample was placed horizontally in a direction of the width of the tile on a test support stand so that the surface of the tile faced upward while the tile was in close contact with the support stand. Then, a supporting rod is placed at the center of the support stand and load was uniformly applied at a loading rate of about 49. ON/s.

[48] Tiles of sand and plastics according to the present invention were formed into Korean-style female tiles that had the same weight as a Korean-style female clay tile available on the market, and were subjected to comparison tests in view of resistance to freezing and thawing according to KSF 3510 of Korean Standards. As for a test method, a test sample was dipped into clear water at 20 +/-5°C for 24 hours, and taken out and put in a freezing chamber at-20+/-3°C for 8 hours. It was dipped again into the clear water at 20 +/-5°C for 6 hours and wiped by a wet piece of cloth to remove water.

Then, the test sample was observed in view of crack, and freezing and thawing.

[49] As for test instruments, since a well-known material tester and freezing chamber were used, detailed descriptions thereof will be omitted herein.

[50] The test results of the tiles of sand and plastics according to the present invention are shown in Table 1 below. <BR> <BR> <P>[51]<BR> [52] [53] Table 1 Sand (parts by Bending fracture strength Crack Freezing and weight) (kgf) thawing 47 341 No No 50 358 No No 53 368 No No 56 379 No No 59 396 No No 62 404 No No 65 398 No No 68 382 No No 71 376 No No 74 358 No No 77 350 No No [54] * The remainder except for the parts by weight of sand corresponds to the parts by weight of plastics. 52 parts by weight of sand indicates a tile comprising 48 parts by weight of plastics mixed therewith.

[55] [56] Consequently, it is found that the tile of sand and plastics according to the present invention exhibits that bending fracture strength is maximized when it comprises 62 parts by weight of sand, but that the bending fracture strength is gradually lowered as the amount of the sand further increases or decreases. It is believed that the sand was combined with the plastics at proper intervals.

[57] Industrial Applicability [58] The tile of the present invention generally has superior bending fracture strength to a clay tile with a bending fracture strength of 286kgf that meets KSF 3510 of Korean Standards.