Background Art In general, rubber is used for various purposes such as a floor and interior material of various transportation means and buildings. However, conventionally, the natural or synthetic rubber, which has been used for the above purposes, has a high flammability or combustibility, and thus, in case of fire, becomes helpless and disastrous. In particular, if the public transport means such as subways, airplanes, buses, and ship, and the public place such department stores, hospitals, theaters, schools have a fire, it is apt to extend to a disastrous fire or accident and thus lead to a loss of lives. Therefore, a fire retardancy of rubber used as the floor and interior material has been of interest more and more.

Conventionally, in order to improve the fire-retardancy of rubber, a halogen based fire-retardant agent such as a bromine compound having a good fire-retardant efficiency has been blended to the rubber in order to provide an improved fire-retardancy. However, these rubbers embrace several problems. For example, they produce a greater amount of smoke when fired, and therefore the smoke or toxic gases resulted from the fire lead to casualties or a loss of lives, rather than the fire or flame itself.

Furthermore, in the case where excessive fire-retardant agent is added to the rubber to improve the fire-retardancy of

rubber, the resultant rubber composition tends to lose the inherent physical properties of rubber such as elasticity, durability, abrasion-resistance, contaminant-resistance, or the like. Korean Patent Application Nos. 1998-0063646 and 1998-0007141 disclose a rubber floor material having an incombustible and nontoxic property, which contains Al (OH) 3 as a fire-retardant agent, and antimony trioxide and phosphorous plasticizer. In case of the above rubber, also, when excessive Al (OH) 3 is used, the inherent material property of rubber is deteriorated as described above.

Accordingly, there has been a need for a nontoxic rubber composition having a good fire-retardance or incombustibility while maintaining its inherent material properties. Ceaseless attempts and efforts have been made in order to develop such a rubber composition.

Disclosure of Invention The present invention has been made to solve the above problems in the art, and it is an object of the invention to provide an incombustible and nontoxic rubber composition, in which aluminum hydroxyl compounds and antimony oxides, which are a fire-retardant agent, and trimethylol propane trimethacrylate (TMPTMA) are mixed with a rubber in an appropriate content such that the resultant composition has an incombustible and nontoxic property, while maintaining the inherent properties of rubber.

In order to accomplish the above object, according to one aspect of the present invention, there is provided a rubber composition comprising: a) 100 weight parts of rubber;

b) 150-300 weight parts of aluminum hydroxyl compounds; c) 5-20 weight parts of antimony oxides; and d) 10-30 weight parts of trimethylol propane trimethacrylate.

Preferably, the rubber may include Ethylene Propylene Diene Monomer triblock copolymer (EPDM).

In addition, according to another aspect of the invention, there is provided a molded article fabricated using the above-described rubber composition of the invention. The molded article of the invention can be used in various industries and purposes such as buildings, automobiles, or the like.

The rubber composition according to the invention has an incombustible and nontoxic property. In the case where the rubber composition is used as a floor or interior material of buildings or cars, a disastrous fire and a loss of lives by smoke and toxic gas resulted therefrom can be prevented.

Best Mode for Carrying Out the Invention The preferred embodiments of the invention will be hereafter explained in detail.

According to the invention, natural rubbers and a common synthetic rubbers such as SBR, BR, NBR, CR, IR or the like may be employed as a rubber material, which is one constituent of an incombustible and nontoxic rubber composition of the invention. However, EPDM (Ethylene Propylene Diene Monomer triblock copolymer) may be most preferably used as the rubber component. It is because the EPDM is chemically stable and has a good ozone-resistance, weather-resistance, heat-resistance, cold-resistance, solvent-resistance, chemical-resistance, vapor-resistance, aging-resistance, and the like, compared with

the natural rubber or a common synthetic rubber.

The incombustible and nontoxic rubber composition of the invention contains an aluminum hydroxyl compound. Aluminum hydroxide (Al (OH) 3), aluminum hydroxyl chloride, or the like may be employed as the aluminum hydroxyl compound. Among them, the aluminum hydroxide (Al (OH) 3) conducts the following reaction, depending on the temperature thereof. i) 2Al (OH) 3-t 2AlO-OH + 2H20 at 245°C ii) 2Al (OH) 3--> A1203 + 3H2O at 320°C iii) 2AlO-OH-+Al203+H2O SQ (470cal/g endothermic) at 550°C Aluminum hydroxide exhibits a cooling effect through the endothermic reaction as described above, and also contributes to fire-retardancy by means of the formation of A1203, which serves as a solid-phase protective layer. Due to the lower decomposition temperature of aluminum hydroxide, however, the aluminum hydroxide surrounding the heat source is pre-decomposed by the high temperature thereof, so that its fire-retardancy is deteriorated disadvantageously.

In order to solve the above problem, according to the invention, the ratio of constituents of the rubber composition is controlled to increase the hardness coefficient thereof, thereby improving its fire-retardancy.

The above solution of the invention will be more specifically described below.

Although the hardness of rubber varies with the types of the rubber, in general, it has a hardness of about 40-45 Shore, Type A. In case where additives such as oil or the like is added, the rubber has a more decreased hardness.

However, the rubber composition of the invention is configured to contain a rubber component, preferably 100 weight

parts of EPDM (Ethylene Propylene Diene Monomer triblock copolymer), 150-300 weight parts of aluminum hydroxyl compound, 5-20 weight parts of antimony oxide compound, and 10-30 weight parts of trimethylol propane trimethacrylate, so that the hardness of the rubber itself can be adjusted to 80-95 SHORE, Type A, which is in accordance with the hardness standard of Hs85 or above prescribed in ASTM F 1344-93"Standard Specification for Rubber Floor Tile." The increase in the hardness of a rubber composition means the increase of bonding strength between the molecules thereof, and thus, due to the increased bonding strength, the decomposition rate thereof at a high temperature is lowered.

According to the invention, the rubber composition is comprised as described above such that the hardness thereof can be increased and consequently its fire-retardancy can be improved.

The rubber composition according to the invention preferably contains 150-300 weight parts of aluminum hydroxyl compound with respect to 100 weight parts of rubber component.

Conventionally, it is known that an excessive addition of aluminum hydroxyl compound would deteriorate the inherent property of rubber. According to the invention, the above conventional problem can be solved by means of the specific constituents of the rubber composition of the invention and the specific contents thereof.

In addition, the rubber composition of the invention comprises an antimony oxide compound such as antimony trioxide (Sb203), antimony tetroxide (Sb204), antimony pentaoxide (Sb205) or the like as a supplemental agent to improve the fire-retardant effect of the rubber composition. According to the invention, therefore, about 5-20 weight parts of the antimony oxide compound

may be added in the rubber composition of the invention, with respect to 100 weight parts of rubber component, thereby providing more excellent flame-retardant effect.

The incombustible rubber composition of the invention contains trimethylol propane trimethacrylate (TMPTMA) as a softening agent or plasticizer. Conventionally, a common petroleum based blended oil such as aromatic oil, naphthene oil or paraffin oil has been used as the softening agent or plasticizer. In this invention, however, the trimethylol propane trimethacrylate is used so that workability and flowability of the rubber composition can be improved by means of the property of the softening agent, and also the viscosity of the rubber composition is lowered, thereby enabling an easy work such as extrusion, rolling, shaping, or the like. In addition, due to the cross-linking function of the trimethylol propane trimethacrylate, the inherent characteristics of the rubber can be maintained. Furthermore, the trimethylol propane trimethacrylate i s better in terms of heat-resistance, as compared with the above-described conventional materials used as the softening agent and plasticizer.

According to the invention, an additive maybe used in order to improve the property of the rubber composition of the invention.

The additive may be exemplified by silica. Silica has an excellent reinforcing effect among white reinforcing fillers, and has similar properties to carbon black. Preferably, the rubber composition of the invention contains around 5 weight parts of silica with respect to 100 weight part of rubber component, to thereby have an improved tensile strength, tearing strength, abrasion resistance, and hardness, which meet the

property standards prescribed in ASTM F1344.

In addition, according to the invention, zinc oxide (ZnO) and ketoamine based anti-aging agent may be added in order to modify its anti-aging power and permanent compression deformation by means of the improved heat resistance, along with anti-aging effects. Furthermore, white titanium dioxide (Ti02, anatase) may be added, preferably, in the content of 2-5 weight parts with respect to 100 weight parts of rubber component in order to reinforce abrasion-resistance.

According to the invention, a molded article may be manufactured by curing the rubber composition of the invention.

Although there is no specific limitation in the curing methods, the peroxide vulcanizing method is preferred, compared to the sulfur compounding method. In the peroxide vulcanizing method, a radical produced from the thermal decomposition of peroxide deprotonates the hydrocarbon of the rubber or is added to a double bond to thereby form a radical in the rubber molecule. In this way, the molecule is stabilized to increase the bonding interaction between molecules, thereby exhibiting the heat-resistant effect.

In the peroxide vulcanization, dicumyl peroxide (DCP-40%) is preferred.

The present invention will be hereafter explained in greater detail, with reference to the examples. However, the examples are described by way of illustration of the invention, and not construed as limiting the invention thereto.

Example A sample is prepared using the constituents listed in the following table 1. Specifically, the raw material rubber, EPDM,

was subjected to a mastication process into a thin rubber, and other additives were sprayed onto the thin rubber, which is again compressed between rollers in order for the additives to be blended into the rubber. Thereafter, the blended constituents were pressurized and heated in the mold to thereby prepare the sample. The numeral values in the table 1 are expressed in weight parts based on to 100 weight parts of EPDM.

[Table 1] Example Example Comparat Comparat Comparat Comparat Comparat 1 2 ive ive ive ive ive Example 1 Example Example Example Example 2 3 4 5 EPDM 100 100 100 100 100 100 100 Al (OH) 3 150 150 150 0 150 150 150 Sb203 10 5 10 10 0 100 10 TMPTMA 20 20 0 20 20 20 50 (SR-350) Zinc oxide 5 5 5 5 5 5 5 Anti-agin 1 1 1 1 1 1 1 g Agent* Catalyst 0.5 0.5 0.5 0.5 0.5 0.5 0.5 (TS) * Carbon 5 5 5 5 5 5 5 black Dicumyl 4 4 4 4 4 4 4 Peroxide *Anti-aging Agent-2, 2, 4-trimethyl-1, 2-dihydroquinoline, polymerized * Catalyst-Tetramethyl thiuram monosulfite

The samples as prepared above were tested for the tensile strength (kgf/cm2), the tearing strength (kgf/cm), the elongation (%), the hardness (rubber measurement shore type A), and the fire-retardancy (mm/lOmin).

The tensile strength means strength when the sample is fractured under a tensile load, and the measured value was obtained by dividing the fracture load by the initial

cross-section of the sample.

The tearing strength means strength when the sample is torn under a tensile load and the measured value was calculated by dividing the fracture load with the initial unit length of the sample.

The elongation rate means a ratio of the elongated length to the original length when a tensile load is applied, and the measured value was calculated according to the equation (elongated length/original length) X 100.

The hardness was measured using the rubber hardness tester (Shore type A).

The fire-retardancy means a length that a flame is propagated per unit time, and the length propagated for 10 min was measured in mm unit.

The tested material properties are listed in the table 2 for the samples of the examples 1 and 2, and the samples of the comparative examples 1 to 5.

[Table 2] Example Example Compara Compara Compara Compara Compara 1 2 tive tive tive tive tive Example Example Example Example Example 1 2 3 4 5 Tensile 105 98-134 110 85 69 Strength (kgf. cm3) Tearing 25 25-29 25 16 16 Strength (kgf/cm) Elongation 180 178-245 188 92 68 Hardness 92 87-87 88 94 78 (rubber measurement shore type A) Fire-retard 140 190 - 402 286 162 210 ancy (mm/l0min) - Not available

As shown in the table 2, the examples 1 and 2 have been found to have a good rubber property and fire-retardancy. In addition, the rubber composition of the invention has passed the class 1 of the self-extinguishable test in the BS 476-7 (SURFACE SPREAD OF FLAME TEST) of BS specification (BRITISH STANDARD 6853: 1999).

However, in the comparative example 1 where TMPTMA (SR-350) was not added, the material property test could not be conducted since it lost its elasticity and restoring force.

Furthermore, the comparative examples 2 and 3, in which aluminum hydroxide and antimony trioxide were not added respectively, has been found to have material properties above a certain value, but very inferior fire-retardancy.

In the comparative example 4 where antimony trioxide was excessively added, vigorous bubbling occurred in the rubber sheet, and its material properties were found to be inferior.

The comparative example 5, in which TMPTMA (SR-350) was excessively added, has been found that its material properties including the hardness and the fire-retardancy were greatly deteriorated.

Industrial Applicability As described above and shown in the above examples, the rubber composition according to the invention has good material properties and fire-retardancy. In particular, the rubber composition of the invention has a hardness and fire-retardancy

above a certain level so that it can be employed as a floor material.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.