RETARDER INCLUDING THE SAME, AND FLAME- RESISTING STYROFOAM TREATED WITH THE FLAME RETARDER AND PREPARATION METHOD THEREOF Technical Field

[1] The present invention relates to a water resistance improver, a silicate flame retardant containing the same, a Styrofoam treated with the retardant, and a method for preparing said Styrofoam, and more particularly to a water resistance improver capable of improving the water resistance of sodium silicate, a silicate flame retardant containing the water resistance improver, a flame-retardant Styrofoam treated with the silicate flame retardant, and a method for preparing the Styrofoam.

[2] Sodium silicates consist of a combination of Na20 and SiO 2, and are divided, according to the combination ratio, into various products. Particularly, liquid sodium silicate, called "water glass", is a viscous, alkaline, and transparent solution having various compositions. The molar ratio of Na20 to SiO 2 is 1: 2.064-4.300 as defined in the Korean Industrial Standard, KSM 1415.

[3] Such sodium silicates are inexpensive and have inherent adhesion ability, and thus are widely used as adhesives or grouting agents for improving soft ground. Also, the sodium silicates have an advantage in that they do not cause environmental pollution in the preparation thereof or before or after the use thereof, unlike organic adhesives. However, the greatest problem with sodium silicates is that they have insufficient water resistance and rapidly dissolve when in contact with water. Due to this problem, the use thereof is greatly limited. Background Art

[4] In the prior art for improving the water resistance of sodium silicates, Korean Patent

Application No. 1995-66598 discloses a heat-resistant, corrosion-resistant inorganic coating composition which contains, as a vehicle for a base coat, water-dispersible alkali silica, water-dispersible silica, and water-dispersible silicate coated with an organic functional silane compound, and as a vehicle for a top coat, a reaction product obtained by hydrolyzing water-dispersible alumina with an organic functional silane compound. The composition disclosed in said patent application has water resistance, but has a problem in that it cannot be applied except to special applications, because the preparation process thereof is complicated and the production cost thereof is excessively high.

[5] Korean Patent Application No. 2003-8372 discloses technology relating to a fireproof paint and adhesive which contains a sodium silicate-based ceramic binder, boric acid or borax, and, if necessary, a pigment. When this fireproof paint is applied to the surface of inflammable material, such as paper, plywood or wood, a portion thereof will be absorbed into the surface layer, and the remainder will form a coating layer having a beautiful appearance and acid resistance on the surface layer. Also, upon the occurrence of a fire, the adhesive layer will swell up like a bubble to form a heat-insulating fireproof layer, and the adhesive surface will stick to the deposited layer in a glass-like state, thereby blocking oxygen. However, the paint according to this technology has problems in that it has insufficient water resistance, and the coating layer becomes separated from the substrate with the passage of time.

[6] Korean Patent Application No. 2003-72869 discloses a water-resistant liquid sodium silicate consisting of a mixture of 10-99 wt% of liquid sodium silicate with 0.1-90 wt% of an organic or inorganic binder, such as phenol resin, rosin, PVA resin or cement powder. The liquid sodium silicate according to this technology also has problems in that water resistance, particularly initial water resistance, is insufficient, and the inherent characteristics of sodium silicate are reduced.

[7] Meanwhile, Styrofoam is an ideal heat insulation material because it is inexpensive and has light weight and has good heat insulation properties, but has a big problem of insufficient fire resistance. To solve this problem, various technologies have been suggested.

[8] The most general method among methods for making Styrofoam flame -retardant comprises attaching a nonflammable material such as gypsum, an iron board or aluminum to the outer surface of Styrofoam, however, even if this method is performed, it is impossible to present the combustion of Styrofoam present inside the structure.

[9] In technologies for making Styrofoam itself flame-retardant, Korean Patent No.

10-305711 discloses a flame-retardant, heat-insulating Styrofoam material prepared by coating the surface of unexpanded polystyrene particles with a flame retardant using halide or phosphate and subjecting the resulting material to expansion molding. Also, Korean Patent Publication No. 2001-72979 discloses a method comprising adding a flame retardant consisting of a brominated organic compound. However, said methods have problems of poor economy due to the use of expensive flame retardants, and show insufficient flame retardant effects.

[10] Also, Korean Patent No. 10-477193 discloses a technology comprising adding porous mineral particles such as zeolite, bentonite, perlite or illite in an amount of 1-800 parts by volume based on 1000 parts by volume of expanded polystyrene particles and subjecting the mixture to compression molding. However, in this

technology, the expanded polystyrene particles and the porous mineral particles having a specific gravity different from that of the expanded polystyrene particles will necessarily become separated from each other upon mixing, and thus, even if the mixture is molded by compression, the porous mineral particles will aggregate in only one portion. Thus, the products obtained using this technology have a problem with respect to uniform quality, and also cannot be expected to have sufficient flame retardancy.

[11] Korean Patent Publication No. 2003-0042299 discloses a technology for preparing flame-retardant Styrofoam, which comprises the steps of crushing Styrofoam beads to a size of about 1/2-1/8, applying the beads with a coating agent consisting of sodium silicate and calcium carbonate, and expanding the applied beads. However, this technology has problems in that the step of crushing the beads is highly complicated, and, due to the insufficient water resistance of sodium silicate, the obtained flame- retardant Styrofoam will be dissolved when in contact with water. Another problem is that, due to high-temperature steam applied upon molding to expand the beads, the coated sodium silicate will be dissolved and adhere to the mold, making a continuous process difficult to realize.

[12] Korean Patent Publication No. 2004-84006 discloses applying on the surface of polystyrene beads a flame-retardant composition containing sodium silicate, calcium carbonate, aluminum hydroxide, talc and the like, and drying the applied beads by microwave heating. This technology solves the problem of sodium silicate being dissolved by high-temperature steam upon molding and thereby adhering to the mold, but this technology requires a molding apparatus to bond the bead particles with each other, and the products obtained using this technology still have a problem of insufficient water resistance. Disclosure of Invention Technical Problem

[13] The present invention has been made to solve the above-described problems occurring in the prior art, and it is an object of the present invention to provide a water resistance improver capable of improving the water resistance of sodium silicate, a material having excellent flame retardancy. Another object of the present invention is to provide a silicate flame retardant having improved water resistance and durability. Still another object of the present invention is to provide a flame retardant Styrofoam treated with a silicate flame retardant having improved water resistance. Technical Solution

[14] The water resistance improver according to the present invention consists of 50-130 parts by weight of calcium carbonate dissolved in 100 parts by weight of 20-45%

potassium carbonate aqueous solution. [15] The silicate flame retardant according to the present invention consists of 1-200 parts by weight of the water resistance improver added to 100 parts by weight of sodium silicate. [16] The flame-retardant Styrofoam according to the present invention is obtained by coating the surface of polystyrene beads with the silicate flame retardant, drying the coated beads, and expanding and compressing the coated and dried beads in a mold using high-temperature steam.

Advantageous Effects

[17] According to the present invention, the problem of insufficient water resistance of sodium silicate, which have existed in the prior art, is completely solved, and Styrofoam can be imparted with flame retardancy. Best Mode for Carrying Out the Invention

[18] Hereinafter, the present invention will be described in detail.

[19] The water resistance improver according to the present invention consists of 50-130 parts by weight, and preferably 70-100 parts by weight, of calcium carbonate dissolved in 100 parts by weight of potassium carbonate aqueous solution having a potassium carbonate concentration of 20-45%, and preferably 30-35%. Calcium carbonate has good flame retardancy in itself and also fire-extinguishing ability because it generates carbon dioxide upon the occurrence of a fire. In all the prior technologies, such calcium carbonate is used in the form of particles. However, if it is used in the form of particles, the efficiency thereof will be decreased, and thus a large amount of calcium carbonate must be used to exhibit the desired degree of flame retardancy. In the present invention, calcium carbonate is used in a completely dissolved state. If the content of calcium carbonate exceeds the upper limit of the above- specified range, undissolved calcium carbonate will be present, so the object of the present invention will not be effectively achieved.

[20] When the water resistance improver having the above-described construction is added to sodium silicate, the water resistance of the sodium silicate will be remarkably improved. Even if the water resistance improver is added in a very small amount, the water resistance of sodium silicate will be improved, and when more than 1 part by weight of the water resistance improver is added to 100 parts by weight of sodium silicate, the water resistance of the sodium silicate will be remarkably improved. Although the precise reaction mechanism for the improvement in water resistance is not understood, it is thought that the improvement in water resistance is achieved by substituting dissolved calcium ions and potassium ions for a portion of the Si sites of a network structure consisting of SiO2 of sodium silicate.

[21] The silicate flame retardant having improved water resistance can be effectively used as a flame retardant for wood, paper and the like, and particularly, can preferably be used as a flame retardant for Styrofoam. This is because, when the silicate flame retardant is coated on polystyrene beads and then dried using a conventional drying process, it will exhibit significant water resistance and thus will not be dissolved with high-temperature steam applied for molding and bonding, and also will not dissolved even when it comes in contact with water.

[22] The suitable coating amount of the silicate flame retardant is 150-420 parts by weight based on 100 parts by weight of the beads, and, after completion of the drying, the coating amount is 70-120 parts by weight based on 100 parts by weight of the beads. If the silicate flame retardant is used in an amount below the lower limit of said range, the flame retardant effect thereof will be insufficient, and if it exceeds the upper limit of said range, the specific gravity thereof will be excessively increased and will cause difficulty in the bonding between particles upon molding.

[23] One example of methods for coating the silicate flame retardant may include placing beads together with the flame retardant in a longitudinally rotating drum-type mixer and rotating the mixer for 1-3 minutes. Due to this rotation, the flame retardant is uniformly coated on the surface of the beads. The coated beads may be naturally dried, but are preferably dried with a hot air dryer to stabilize the process.

[24] The coated and dried beads are transferred to a mold, and then expanded and bonded by high-temperature steam introduced into the mold, and thus are formed into the desired shape. In all of the prior technologies, the coated flame retardants come out of solution and stick to the mold during this molding process. Whether the coated flame retardant was dissolved can be determined by examining the color of water resulting from the cooling of high-temperature steam. If the flame retardant was dissolved, the water has a milky color, but if the flame retardant was not dissolved, the water is transparent.

[25] Hereinafter, the present invention will be described with reference to Examples.

[26] Preparation Example 1 : Preparation of water resistance improver

[27] To 100 parts by weight of 33% potassium carbonate aqueous solution, 80 parts by weight of calcium carbonate was added, and thoroughly mixed so as to be completely dissolved, thus obtaining a water resistance improver.

[28] Preparation Example 2: Preparation of silicate flame retardant

[29] To 100 parts by weight of silicate, the water resistance improver prepared in

Preparation Example 1 was added and mixed in each of amounts of 1, 3, 50, 100 and 200 parts by weight, thus obtaining flame retardants 1 to 5.

[30] Examples 1-5

[31] 200 parts by weight of each of the flame retardants 1-5 obtained in Preparation

Examples 2 was added to 100 parts by weight of polystyrene beads and coated on the surface of the beads. The coated beads were dried, and then placed in a mold and expanded and bonded by the application of high-temperature steam (105 ⁰ C), thus obtaining test samples.

[32] Water recovered by cooling the high-temperature steam applied for expansion was transparent, and thus it could be found that the coated flame retardants were not washed out. The obtained test samples were tested for flame retardancy and, as a result, the flame retardancy of the test samples exceeded flame retardancy standard 3 defined in the KS F 2271-98 test method.

[33] Comparative Example

[34] To 100 parts by weight of sodium silicate, 30 parts by weight of calcium carbonate was added and mixed, thus obtaining a flame retardant. According to the same manner as in Example, the obtained flame retardant was coated on beads in the same manner as in Example, and the coated beads were molded, thus obtaining a test sample. Water recovered by cooling high-temperature steam applied for expansion had a milky color, suggesting that the coated flame retardant had washed out. The obtained test sample was tested for flame retardancy and, as a result, the test sample did not pass the flame retardancy standard 3 defined in the KS F 2271-98 test method.

[35]