coating of sodium percarbonate is conducted as follows . that is , on a sodium percarbonate particle , an aqueous solution of a silicate or a mixed aqueous solution of a silicate and an alkali metal carbonate is sprayed and dried to form a first coating layer , then an aqueous solution of magnesium sulfate independently or a mixed aqueous solution of magnesium sulfate and an alkali metal carbonate or sulfate is sprayed and dried to form a second coating layer . further , on a sodium percarbonate particle , the coating layer may be formed by spraying the sodium percarbonate particle simultaneously using different nozzles and drying the above aqueous solutions . when the order of spraying is reversed , i . e ., at first , a solution containing magnesium sulfate is sprayed , then a solution of a silicate and a solution of an alkali metal carbonate is sprayed , the thus obtained sodium percarbonate particle has a decreased amount of active oxygen . further , on a sodium percarbonate particle , the coating layer may be formed by spraying an aqueous solution of a silicate , an aqueous solution of magnesium sulfate and an aqueous solution containing an alkali metal bicarbonate or sulfate simultaneously or sequentially using different nozzles and drying . sodium percarbonate used in the present invention is obtained by cohesive - granulating , using a miscible - type granulator , sodium percarbonate ( water content of 6 - 15 %) produced by reacting , crystallizing and dehydrating using a known method , with a binder , then rectifying using an extruder and drying . further , sodium percarbonate which is produced by mixing wet powdery sodium percarbonate with recovered sodium percarbonate partially containing a coating agent component , such as a silicate component , magnesium sulfate component or alkali metal sulfate component recovered from granulation steps and / or coating steps , etc ., then granulating using the above - mentioned procedure , is preferably used . the composition ratio of the wet powdery sodium percarbonate and the recovered sodium percarbonate is preferably within the ratio from 50 : 50 to 99 : 1 . particularly , when the recovered sodium percarbonate is finely powdered such that the diameter of the recovered sodium percarbonate is 300 μm and below , preferably from 5 to 100 μm , the stability of sodium percarbonate further increases . the sodium percarbonate particle used in the present invention which is at the post - granulation step and pre - coating step is usually from 300 to 3000 μm , preferably from 300 to 2000 μm , more preferably from 500 to 1000 μm in diameter . as the silicate as a coating agent , a sodium salt , such as sodium orthosilicate , sodium metasilicate , water - glass no . 1 , no . 2 , no . 3 , etc ., can be used . among these , water - glasses are liquid and are preferably used in view of convenience . the coating amount of the silicate is preferably 0 . 01 mole to 0 . 06 mole based on sio 2 per mole of uncoated sodium percarbonate ( na 2 co 3 . 3 / 2h 2 o 2 ; molecular weight : 157 ). that is , the silicate is coated in an amount of 0 . 3 parts to 2 . 2 parts based on sio 2 ( molecular weight : 60 . 3 ) per 100 parts of sodium percarbonate . in the case that the coating amount of the silicate is too small , the coverage of the coating decreases , and the formulation stability with detergent becomes insufficient . in contrast , in the case where the coating amount of the silicate is too large , the solubility rate becomes slow . as the alkali metal bicarbonate as a coating agent , sodium bicarbonate , potassium bicarbonate , lithium bicarbonate , etc ., may be used . further , these can be used in combination . among these , sodium carbonate is most preferable from the viewpoint of economical efficiency . the coating amount of the alkali metal bicarbonate is preferably 0 . 05 mole to 0 . 25 mole per mole of uncoated sodium percarbonate . that is , in the case of sodium bicarbonate ( molecular weight : 84 ), the alkali metal bicarbonate is present in an amount of 2 . 7 to 13 . 4 parts per 100 parts of sodium percarbonate ( molecular weight : 157 ). in the case of 0 . 05 mole of alkali metal bicarbonate and below per mole of uncoated sodium percarbonate , the formulation stability with detergent is insufficient . in contrast , in the case of 0 . 25 mole of alkali metal bicarbonate and more per mole of uncoated sodium percarbonate , not only does the solubility rate decrease , but also economical efficiency is not preferable . as the alkali metal carbonate as a coating agent , sodium carbonate , potassium carbonate , lithium carbonate , etc ., may be used . further , these can be used in combination . among these , sodium carbonate is most preferable from the viewpoint of economical efficiency . the coating amount of the alkali metal carbonate is preferably 0 . 075 mole to 0 . 18 mole per mole of uncoated sodium percarbonate . that is , in the case of sodium carbonate ( molecular weight : 106 ), the alkali metal carbonate is from 5 parts to 12 parts per 100 parts of sodium percarbonate . in case that the coating amount of the alkali metal carbonate is 0 . 075 mole and less , the formulation stability with detergent decreases . in contrast , in the case of an alkali metal carbonate coating amount of 0 . 18 mole and more , not only does the solubility rate become slow , but also it is not preferable in view of economical efficiency . as the alkali metal sulfate as a coating agent , sodium sulfate , potassium sulfate , lithium sulfate , etc ., may be used . further , these can be used in combination . among these , sodium sulfate is most preferable from the viewpoint of economical efficiency . the coating amount of the alkali metal sulfate is preferably from 0 . 05 mole to 0 . 20 mole per mole of uncoated sodium percarbonate . that is , in the case that the alkali metal sulfate is sodium sulfate anhydride ( molecular weight : 142 ), it is present in an amount of from 4 . 5 parts to 18 parts per 100 parts of sodium percarbonate . in case that coating amount of the alkali metal sulfate is 0 . 05 mole and less , the formulation stability with detergent insufficient . in contrast , in case of an alkali metal sulfate coating amount of 0 . 2 mole and more , not only does the solubility rate become slow , but it is also not preferable in view of economical efficiency . in the present invention , as the alkali metal salt , alkali metal sulfate is preferably used in combination with alkali metal bicarbonate . as the alkali metal sulfate and alkali metal bicarbonate , the above - mentioned compounds can be used , preferably , sodium sulfate and sodium bicarbonate . the coating amount is desirably from 0 . 05 mole to 0 . 2 mole of alkali metal sulfate and from 0 . 04 mole to 0 . 17 mole of alkali metal bicarbonate per mole of uncoated sodium percarbonate . the coating amount of magnesium sulfate is preferably from 0 . 006 mole to 0 . 06 mole per mole of uncoated sodium percarbonate . that is , magnesium sulfate ( molecular weight : 120 . 3 ) is coated in an amount of from 0 . 45 parts to 4 . 5 parts per 100 parts of sodium percarbonate . in the case that coating amount of magnesium sulfate is 0 . 006 mole and less , the formulation stability with detergent becomes insufficient . in contrast , in the case of a magnesium sulfate coating amount of 0 . 06 mole and more , the solubility rate becomes slow . the ratio of each coating agent is not limited , as long as it is within the range described in the specification and recited in the claims of the present application . usually , the ratio of the alkali metal salt silicate : magnesium sulfate is within the range from 1 : 0 . 03 : 0 . 02 to 1 : 1 . 2 : 1 . 2 , preferably , from 1 : 0 . 1 : 0 . 1 to 1 : 0 . 4 : 0 . 4 , based on the mole ratio . in particular , when an alkali metal bicarbonate is used as the alkali metal salt , the ratio of the alkali metal bicarbonate : silicate : magnesium sulfate is usually within the range from 1 : 0 . 03 : 0 . 024 to 1 : 1 . 2 : 1 . 2 , preferably from 1 : 0 . 1 : 0 . 1 to 1 : 0 . 2 : 0 . 2 , based on the mole ratio . when an alkali metal carbonate is used as the alkali metal salt , the ratio of alkali metal carbonate : silicate : magnesium sulfate is usually within the range from 1 : 0 . 05 : 0 . 03 to 1 : 0 . 8 : 0 . 8 , preferably from 1 : 0 . 1 : 0 . 1 to 1 : 0 . 4 : 0 . 4 , based on the mole ratio . when an alkali metal sulfate is used as the alkali metal salt , the ratio of alkali metal sulfate : silicate : magnesium sulfate is usually within the range from 1 : 0 . 05 : 0 . 03 to 1 : 1 . 2 : 1 . 2 , preferably from 1 : 0 . 1 : 0 . 1 to 1 : 0 . 2 : 0 . 2 , based on the mole ratio . when a combination of an alkali metal sulfate and an alkali metal bicarbonate is used as the alkali metal salt , the ratio of alkali metal sulfate : silicate : magnesium sulfate : alkali metal bicarbonate is usually within the range from 1 : 0 . 05 : 0 . 03 : 0 . 2 to 1 : 1 . 2 : 1 . 2 : 0 . 85 , preferably from 1 : 0 . 1 : 0 . 1 : 0 . 4 to 1 : 0 . 2 : 0 . 2 : 0 . 85 , based on the mole ratio . additionally , besides the above - mentioned coating agent , a chelating agent or stabilizer , such as ethylenediaminetetraacetic acid ( edta ) or salts thereof ( edta - 4na , etc . ), nitrilotriacetic acid , etc ., may be used in combination with the coating agent . particularly , when a chelating agent is added into a mixture of magnesium sulfate and sodium bicarbonate , crystallization does not occur at all . that is , if a chelating agent is not added , depending upon the concentration of the aqueous solution , there is a case that crystallization appears partially several days after the preparation of the liquid . when sodium percarbonate is coated , the solvent of these coating agents is selected from solvents which dissolve the coating agent , and water , which has high solubility and is safe and cheap , is most preferable . the concentration of the coating agent at the time of spraying may be not more than the saturated concentration of solubility at the temperature in use ; however , when the concentration is too small , not only does it require time to dry , but also the calories of water vaporized becomes large , and thus a low concentration is not preferable from the viewpoint of economical efficiency . on the other hand , when the concentration is too high , crystallization may occur and block tubes or nozzles , and thus a high concentration is not preferable . thus , the liquid concentration of a silicate is preferably from 0 . 5 % by weight to 9 % by weight , more preferably from 1 % by weight to 6 % by weight , based on sio 2 . on the other hand , the liquid concentration of magnesium sulfate is preferably from 0 . 2 % by weight to 25 % by weight , more preferably from 0 . 5 % by weight to 20 % by weight . the liquid concentration of an alkali metal sulfate is preferably from 3 % by weight to 20 % by weight , more preferably from 5 % by weight to 15 % by weight . the liquid concentration of an alkali metal bicarbonate is preferably from 3 % by weight to 9 % by weight , more preferably from 5 % by weight to 8 % by weight . the liquid concentration of an alkali metal carbonate is preferably from 5 % by weight to 20 % by weight , more preferably from 7 % by weight to 15 % by weight . the temperature of the sodium percarbonate at the time of spray - drying is preferably from 40 ° to 95 ° c ., more preferably from 50 ° to 90 ° c . in case that the temperature of the sodium percarbonate is too low , particles of sodium percarbonate agglomerate , and the embodiment is not preferable . on the other hand , in the case that the temperature of the sodium percarbonate is too high , sodium percarbonate tends to decompose , and it is hard to make a uniform coating because of the growth of crystals of the coating agent . the present sodium percarbonate particle has an excellent solubility rate and has excellent formulation stability with detergent . the present sodium percarbonate is uniformly coated on its surface with a silicate , magnesium sulfate , and at least one of an alkali metal carbonate , bicarbonate , and sulfate and / or a reaction product thereof , and can show stabilizing action by cutting off water or another kicker . by using the combination of the components used in the present invention as a coating agent , a particularly excellent stabilizing effect is obtained . the sodium percarbonate particle coated in accordance with the present invention is not only excellent in its formulation stability with a zeolite or detergent which has a characteristic of a kicker , but also has an excellent solubility rate and can be used in low temperature laundry . hereinafter the present invention will be explained in more detail using examples and comparative examples . the present invention is not limited to these examples . the use of % in the examples means % by weight , unless otherwise described expressly . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , 225 g of an aqueous solution of water - glass no . 1 ( water - glass no . 1 concentration of 2 wt % based on sio 2 ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 39 minutes at a flow rate of 7 . 5 g / min . after spray completion , the sample was dried for 5 minutes , and the first coating layer was thereby formed . then , after a change of the nozzle , 500 g of a mixed aqueous solution of magnesium sulfate and sodium bicarbonate ( mgso 4 concentration of 0 . 9 wt %, nahco 3 concentration of 6 . 6 wt %) was sprayed at a flow rate of 7 . 5 g / min over 67 minutes . similarly as the above , after completion of the spraying , the sample was dried for 5 minutes , and the second coating layer was thereby formed . in the coating , the temperature of the sodium percarbonate was controlled from 73 ° to 77 ° c . the coating amount of each component as solids content was as follows : water - glass no . 1 ( as sio 2 ) in the first coating layer : 4 . 5 g ( 1 . 5 % of the sodium percarbonate to be coated ) magnesium sulfate in the second coating layer : 4 . 5 g ( 1 . 5 % of the sodium percarbonate to be coated ) sodium bicarbonate in the second coating layer : 33 . 0 g ( 11 % of the sodium percarbonate to be coated ). after cooling , the coated sodium percarbonate was taken out and no aggregate was observed . from this value , decomposition of the active oxygen at coating time was extremely small , with the coating agent being coated the same as the theoretical value . ( theoretical value : 14 . 4 %× 1 /( 1 + 0 . 14 )= 12 . 6 %) further , coated sodium percarbonate was mixed with a zeolite and detergent to investigate the storage stability test . the result together with the result of the solubility rate is shown in table 1 . formulation stability was very good , and great improvement of stability as compared with uncoated sodium percarbonate described below was recognized . 5 g of sodium percarbonate particle was charged into 1 l of water and stirred at 200 rpm . the time for the particle to dissolve completely was measured by the electrical conductance method . 1 g of synthetic zeolite 4a powder which was sufficiently absorbed with moisture for 1 day at 30 ° c ., relative humidity of 80 %, and 1 g of sodium percarbonate were charged into a polyethylene bag ( trade name : uni pack a - 4 , seisan nippon sya co ., ltd ., water permeable ) and mixed sufficiently . the mixture stood for 4 days at 30 ° c . and a relative humidity of 80 %, and active oxygen of pre - and post - storage was analyzed , and formulation stability with a zeolite was investigated . to 1300 g of commercially available compact detergent ( containing a zeolite and enzyme , etc . ), 200 g of coated or uncoated sodium percarbonate ( 13 . 3 % against the detergent ) was homogeneously mixed , put into carton board box , and then sealed with vinyl tape . the mixture was stored in a constant temperature bath for 21 days at 30 ° c . and a relative humidity of 80 %. the active oxygen amount of the samples was determined by sodium thiosulfate precipitation . the residual rate of active oxygen was calculated according to the following formula . residual rate of active oxygen (%)=( active oxygen at post - storage / active oxygen at pre - storage )× 100 coated sodium percarbonate was obtained using the same procedures as in example 1 , except that potassium bicarbonate was used instead of sodium bicarbonate as a coating agent . potassium bicarbonate : 33 . 0 g ( 11 . 0 % of sodium percarbonate to be coated ) water - glass no . 1 ( as sio 2 ): 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) this value shows that without decomposing the active oxygen at the coating time , the coating agent was coated the same as the theoretical value . further , solubility was investigated using the same procedure as in example 1 , and it was found that the sample dissolved by 2 . 5 minutes . formulation stability was investigated in the same manner as example 1 , and it was good . the result is shown in table 1 . coated sodium percarbonate was obtained using the same procedures as in example 1 , except that sodium metasilicate was used instead of water - glass no . 1 as a coating agent , the coating amount was changed , and a chelating agent corresponding to 0 . 5 % of the amount of the coating was added to the mixed solution of magnesium sulfate and sodium bicarbonate in order to stabilize the solution . sodium bicarbonate : 33 . 0 g ( 11 . 0 % of sodium percarbonate to be coated ) sodium meta silicate : 3 . 0 g ( 1 . 0 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) ethylenediaminetetraacetic acid tetrasodium salt : 1 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) active oxygen of the obtained sodium percarbonate , solubility and formulation stability were investigated , solubility was excellent , and formulation stability was good . the results are shown in table 1 . the mixed solution of magnesium sulfate , sodium bicarbonate and chelating agent was stable and did not give any precipitate after storing a day . 12 kg of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid drying apparatus ( fuji paudal co ., ltd ., &# 34 ; midget - dryer &# 34 ;), then air at 3 . 2 m 3 / min was sent to make fluidization . thereafter , by warming inlet air to from 120 ° to 150 ° c ., the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , a mixed solution of sodium bicarbonate and magnesium sulfate ( sodium bicarbonate concentration of 8 wt %, magnesium sulfate of 1 wt %) and an aqueous solution of sodium metasilicate ( 1 . 2 wt % based on sio 2 ) was sprayed simultaneously from different spray nozzles located 40 cm above the multipore plate . spraying of 12 kg of the mixed solution of sodium bicarbonate and magnesium sulfate took 150 minutes at a speed of 80 g / min . on the other hand , spraying of 10 kg of the aqueous solution of sodium metasilicate took 150 minutes at a speed of 67 g / min ., and the coating finished at almost the same time . the temperature during the coating was controlled from 73 ° to 77 ° c . after completion of the coating , heated air continued to be sent for 5 minutes to dry . next , heating from the air heater finished , and the sample was cooled with a cool air flow . after cooling , the coated sodium percarbonate was taken out , and no aggregate was observed . the coating amount of each component as solids content was as follows : nahco 3 : 0 . 96 kg ( 8 . 0 % of the sodium percarbonate to be coated ) sodium metasilicate ( as sio 2 ): 0 . 12 kg ( 1 . 0 % of the sodium percarbonate to be coated ) magnesium sulfate : 0 . 12 kg ( 1 . 0 % of the sodium percarbonate to be coated ) active oxygen of the obtained sodium percarbonate , solubility and formulation stability were investigated . the results are shown in table 1 . solubility and formulation stability in case of simultaneous spraying were both excellent as in the case of multi - spraying of examples 1 , 2 and 3 . coated sodium percarbonate was obtained using the same procedures as in example 4 , except that to the mixed solution of magnesium sulfate and sodium bicarbonate , edta - 4na as a chelating agent was added in an amount of 0 . 5 % corresponding to the coating amount , the coating amount was changed , and water - glass no . 1 was used instead of sodium metasilicate . the spray time of the two liquids was finished after about 188 minutes . active oxygen of the obtained sodium percarbonate , solubility and formulation stability were investigated . the results are shown in table 1 . nahco 3 : 1 . 2 kg ( 10 . 0 % of the sodium percarbonate to be coated ) water - glass no . 1 ( as sio 2 ): 0 . 15 kg ( 1 . 25 % of the sodium percarbonate to be coated ) magnesium sulfate : 0 . 15 kg ( 1 . 25 % of the sodium percarbonate to be coated ) ethylenediaminetetraacetic acid tetrasodium salt : 1 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) as can be seen from table 1 , sodium percarbonate produced according to the examples of the present invention was excellent in solubility ( time required to dissolve completely was fast , i . e ., from 2 to 2 . 5 min . ), and formulation stability with detergent was good ( only 10 % decomposition even after 21 days storage ) and found to have a balanced good property . active oxygen , solubility and formulation stability of uncoated sodium percarbonate which was used as a raw material in the present invention were investigated . the results are shown in table 1 for comparison . coated sodium percarbonate was obtained using the same procedures as in example 1 , except that the spraying of the second layer was not conducted . active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 1 . the formulation stability was only a little better than in the uncoated sample of comparative example 1 and did not show a great improvement like in example 1 . further , the solubility was rather bad , which may have been because of the use of only one component of sio 2 . coated sodium percarbonate was obtained using the same procedures as in example 1 , except that the spraying of the first layer was not conducted . potassium bicarbonate : 33 . 0 g ( 11 . 0 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 1 . although the solubility was good , the formulation stability did not show a great improvement like in example 1 . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , 180 g of an aqueous solution of magnesium chloride ( 10 % concentration of magnesium chloride ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 36 minutes at a flow rate of 5 g / min . after spray completion , the contents were removed from the apparatus , moved to a vacuum dryer , and dried for 4 hours at 50 ° c . under 3 mmhg . active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 1 . the formulation stability did not show a great improvement like in example 1 . in particular , the formulation stability with a zeolite was low , like the uncoated sample in comparative example 1 . further , a great decrease of active oxygen which was over the value of dilution by the coating agent was observed . also , the sample took 5 minutes to dissolve in comparative example 4 , so it is not applicable when laundry is conducted at a low temperature . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 50 ° c . after the temperature was steady at 50 ° c ., to keep it in a fluid state , 129 g of an aqueous solution of a mixed salt of sodium carbonate and sodium bicarbonate ( sesquicarbonate ) ( 8 . 6 % concentration of sodium carbonate , 3 % of sodium bicarbonate ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 26 minutes at a flow rate of 5 g / min . for 10 minutes after spray completion , only gas at the same temperature continued to be sent , and drying was completed . then , the gas was changed to cool wind , and the sample was cooled to 30 ° c . then , the coated sodium percarbonate was removed from the apparatus , and little aggregates were observed . sodium bicarbonate : 3 . 9 g ( 1 . 3 % of sodium percarbonate to be coated ) sodium carbonate : 11 . 1 g ( 3 . 7 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 1 . the solubility was preferable , but the formulation stability did not show a great improvement like in example 1 . coated sodium percarbonate was obtained using the same procedures as in example 1 , except that the coating amount of water - glass no . 1 was 12 . 5 %, after formulation of the first coating layer , the second coating layer was formulated using only an aqueous solution of magnesium sulfate , without using sodium bicarbonate , and total coating amount was the same as in example 1 . water - glass no . 1 ( as sio 2 ): 37 . 5 g ( 12 . 5 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 1 . table 1______________________________________ comparative example example 1 2 3 4 5 1 2 3 4 5 6______________________________________solubility ( min .) 2 . 5 2 . 5 2 . 0 2 . 0 2 . 5 1 . 5 3 . 5 1 . 5 5 . 0 2 . 5 9 . 0storage stability 95 90 92 91 93 30 65 78 43 48 851 (%) storage stability 92 88 90 90 91 50 59 70 75 64 702 (%) ______________________________________ 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , 600 g of mixed solution of sodium carbonate and water - glass no . 1 ( sodium carbonate concentration of 5 . 5 wt %, water - glass no . 1 concentration of 1 wt % based on sio 2 ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 75 minutes at a flow rate of 8 g / min . after spray completion , the sample was dried for 5 minutes , and the first coating layer was thereby formed . then , after a change of the nozzle , 90 g of the solution of magnesium sulfate ( 5 . 5 wt %) was sprayed at a flow rate of 5 g / min over 18 minutes . similarly as the above , after completion of the spraying , the sample was dried for 5 minutes , and the second coating layer was thereby formed . in the coating , the temperature of the sodium percarbonate was controlled from 73 ° to 77 ° c . the coating amount of each component as solids content was as follows : na 2 co 3 in the first coating layer : 33 . 0 g ( 11 % of the sodium percarbonate to be coated ) water - glass no . 1 ( as sio 2 ) in the first coating layer : 6 . 0 g ( 2 . 0 % of the sodium percarbonate to be coated ) magnesium sulfate in the second coating layer : 4 . 5 g ( 1 . 5 % of the sodium percarbonate to be coated ). after cooling , the coated sodium percarbonate was taken out , and no aggregate was observed . this shows that there was no decomposition of the active oxygen at the coating time , and that the coating agent was coated the same as the theoretical value . ( theoretical value : 14 . 4 %× 1 /( 1 + 0 . 145 )= 12 . 6 %) further , coated sodium percarbonate was mixed with a zeolite and detergent to investigate the storage stability test . the result together with the result of the solubility rate is shown in table 2 . formulation stability was very good , and a great improvement of stability as compared with uncoated sodium percarbonate described below was recognized . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that amount of the coating was changed as set forth below . sodium carbonate : 24 . 8 g ( 8 . 3 % of sodium percarbonate to be coated ) water - glass no . 1 ( as sio 2 ): 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) magnesium sulfate : 10 . 5 g ( 3 . 5 % of sodium percarbonate to be coated ) this value shows that without decomposing the active oxygen at the coating time , the coating agent was coated the same as the theoretical value . further , solubility was investigated using the same procedure as in example 1 , and it was found that the sample dissolved by 2 . 5 minutes . formulation stability was investigated in the same manner as example 1 , and it was good . the result is shown in table 2 . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that potassium carbonate was used instead of sodium carbonate and that water - glass no . 3 was used instead of water - glass no . 1 . potassium carbonate : 33 . 0 g ( 11 . 0 % of sodium percarbonate to be coated ) water - glass no . 3 ( as sio 2 ): 6 . 0 g ( 2 . 0 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) active oxygen of the obtained sodium percarbonate , solubility and formulation stability were investigated , and the results are shown in table 2 . 12 kg of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid drying apparatus ( fuji paudal co ., ltd ., &# 34 ; midget - dryer &# 34 ;), then air at 3 . 2 m 3 / min was sent to make fluidization . thereafter , by warming inlet air to from 120 ° to 150 ° c ., the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , a mixed solution of sodium carbonate and water - glass no . 1 ( sodium carbonate concentration of 16 . 5 wt %, water - glass no . 1 of 3 wt % based on sio 2 ) and an aqueous solution of magnesium sulfate ( 10 wt %) was sprayed simultaneously from different spray nozzles located 40 cm above the multipore plate . spraying of 8 kg of the mixed solution of sodium carbonate and water - glass no . 1 took about 76 minutes at a speed of 105 g / min . on the other hand , spraying of 1 . 8 kg of the aqueous solution of magnesium sulfate took 76 minutes at a speed of 23 . 7 g / min ., and the coating finished at almost the same time . the temperature during the coating was controlled from 73 ° to 77 ° c . after completion of the coating , heated air continued to be sent for 5 minutes so that the sample dried . next , heating from the air heater finished , and the sample was cooled with a cool air flow . after cooling , the coated sodium percarbonate was taken out , and no aggregate was observed . the coating amount of each component as solids content was as follows : na 2 co 3 : 1 . 32 kg ( 11 . 0 % of the sodium percarbonate to be coated ) water - glass no . 1 ( as sio 2 ): 0 . 24 kg ( 2 . 0 % of the sodium percarbonate to be coated ) magnesium sulfate : 0 . 18 kg ( 1 . 5 % of the sodium percarbonate to be coated ) active oxygen of the obtained sodium percarbonate , solubility and formulation stability were investigated . the results are shown in table 2 . in the case of simultaneous spraying , solubility was a little bit slow as compared to the multi - spray case of examples 6 , 7 and 8 . coated sodium percarbonate was obtained using the same procedures as in example 9 , except that a mixed solution of potassium carbonate and water - glass no . 3 was used instead of a mixed solution of sodium carbonate and water - glass no . 1 . potassium carbonate : 1 . 32 kg ( 11 . 0 % of sodium percarbonate to be coated ) water - glass no . 3 ( as sio 2 ): 0 . 24 kg ( 2 . 0 % of sodium percarbonate to be coated ) magnesium sulfate : 0 . 18 kg ( 1 . 5 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated , and the results are shown in table 2 . as can be understood from table 2 , sodium percarbonate produced according to the example of the present invention was shown to be good in solubility ( necessary time for complete dissolution was from 2 to 2 . 5 minutes ) and good in formulation stability ( after 21 days storage , only 10 % was decomposed ), and had a good balance in property . active oxygen , solubility and formulation stability of uncoated sodium percarbonate which was used as a raw material in the present invention were investigated . the results are shown in table 2 for comparison . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that the spraying of the second layer was not conducted . sodium carbonate : 33 . 0 g ( 11 . 0 % of sodium percarbonate to be coated ) water - glass no . 3 ( as sio 2 ): 6 . 0 g ( 2 . 0 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 2 . the formulation stability did not show a great improvement like in example 1 . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that the spraying of the first layer was not conducted . active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 2 . the formulation stability did not show a great improvement like in example 6 . further , a great decrease of active oxygen which was over the value of dilution by the coating agent was observed . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , 180 g of an aqueous solution of magnesium chloride ( 10 % concentration of magnesium chloride ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 36 minutes at a flow rate of 5 g / min . after spray completion , the contents were removed from the apparatus , moved to a vacuum dryer , and dried for 4 hours at 50 ° c . under 3 mmhg . active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 2 . the formulation stability did not show a great improvement like in example 6 . in particular , the formulation stability with a zeolite was low , like the uncoated sample in comparative example 6 . further , a great decrease of active oxygen which was over the value of dilution by the coating agent was observed . also , the sample took 5 minutes to dissolve in comparative example 9 , so it is not applicable when laundry is conducted at a low temperature . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 50 ° c . after the temperature was steady at 50 ° c ., to keep it in a fluid state , 150 g of an aqueous solution of a mixed salt of sodium carbonate and sodium sulfate ( 8 . 8 % concentration of sodium carbonate , 11 . 2 % of sodium sulfate ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 30 minutes at a flow rate of 5 g / min . for 10 minutes after spray completion , only gas at the same temperature continued to be sent , and drying was completed . then , the gas was changed to cool wind , and the sample was cooled to 30 ° c . then , the coated sodium percarbonate was removed from the apparatus , and little aggregates were observed . sodium carbonate : 13 . 2 g ( 4 . 4 % of sodium percarbonate to be coated ) sodium sulfate : 16 . 8 g ( 5 . 6 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 2 . the solubility was preferable , but the formulation stability did not show a great improvement like in example 6 . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that without using sodium carbonate , the first coating layer was formulated using only an aqueous solution of water - glass no . 1 . water - glass no . 1 ( as sio 2 ): 39 g ( 13 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 5 g ( 1 . 5 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 2 . table 2______________________________________ comparative example example 6 7 8 9 10 7 8 9 10 11 12______________________________________solubility 2 . 5 2 . 5 2 . 5 2 . 0 2 . 5 1 . 5 3 . 0 3 . 5 5 . 0 1 . 5 10 . 0 ( min . ) storage 90 90 89 91 90 30 67 35 43 48 84stability 1 (%) storage 91 90 87 90 90 50 62 55 75 55 67stability 2 (%) ______________________________________ 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , 105 g of an aqueous solution of sodium metasilicate ( concentration of 2 wt %, based on sio 2 ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 21 minutes at a flow rate of 5 g / min . after spray completion , the sample was dried for 5 minutes , and the first coating layer was thereby formed . then , after a change of the nozzle , 100 g of a mixed solution of magnesium sulfate and sodium sulfate ( magnesium sulfate of 4 . 2 wt %, sodium sulfate concentration of 15 wt %) was sprayed at a flow rate of 5 g / min over 20 minutes . after completion of the spraying , the sample was dried for 5 minutes , and the second coating layer was thereby formed . the temperature during coating was controlled from 73 ° to 77 ° c . the coating amount of each component as solids content was as follows : sodium metasilicate in the first coating layer : 2 . 1 g ( as sio 2 : 0 . 7 % of the sodium percarbonate to be coated ) magnesium sulfate in the second coating layer : 4 . 2 g ( 1 . 4 % of the sodium percarbonate to be coated ) sodium sulfate in the second coating layer : 15 . 0 g ( 5 . 0 % of the sodium percarbonate to be coated ) after cooling , the coated sodium percarbonate was taken out , and no aggregate was observed . this shows that there was no decomposition of the active oxygen at the coating time , and that the coating agent was coated the same as the theoretical value . ( theoretical value : 14 . 4 %× 1 /( 1 + 0 . 07 )= 13 . 5 %) further , coated sodium percarbonate was mixed with a zeolite and detergent to investigate the storage stability test . the result together with the result of the solubility rate is shown in table 3 . formulation stability was very good , and a great improvement of stability as compared with uncoated sodium percarbonate described below was recognized . coated sodium percarbonate was obtained using the same procedures as in example 11 , except that potassium sulfate was used instead of sodium sulfate . sodium metasilicate : 2 . 1 g ( as sio 2 : 0 . 7 % of the sodium percarbonate to be coated ) potassium sulfate : 15 . 0 g ( 5 % of the sodium percarbonate to be coated ) magnesium sulfate : 4 . 2 g ( 1 . 4 % of the sodium percarbonate to be coated ) this value shows that without decomposing sodium percarbonate at the coating time , the coating agent was coated the same as the theoretical value . further , solubility was investigated using the same procedure as in example 11 , and it was found that the sample dissolved by 2 minutes . formulation stability was investigated in the same manner as example 11 , and it was good . the result is shown in table 3 . coated sodium percarbonate was obtained using the same procedures as in example 11 , except that water - glass no . 1 was used instead of sodium metasilicate , the amount of coating agent was changed , and edta - 4na to the sodium percarbonate particle was added ( 0 . 6 % conc .) into a mixed solution of magnesium sulfate and sodium sulfate in order to stabilize the liquid . water - glass no . 1 : 4 . 5 g ( as sio 2 , 1 . 5 % of sodium percarbonate to be coated ) sodium sulfate : 15 . 0 g ( 5 . 0 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 2 g ( 1 . 4 % of sodium percarbonate to be coated ) ethylenediaminetetraacetic acid tetrasodium salt : 0 . 6 g ( 0 . 2 % of sodium percarbonate to be coated ) active oxygen of the obtained sodium percarbonate , solubility and formulation stability were investigated . the solubility was excellent , and formulation stability was good as in example 1 . the results are shown in table 3 . 12 kg of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid drying apparatus ( fuji paudal co ., ltd ., &# 34 ; midget - dryer &# 34 ;), then air at 3 . 2 m 3 / min was sent to make fluidization . thereafter , by warming inlet air to from 120 ° to 150 ° c ., the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , a mixed solution of sodium sulfate and magnesium sulfate ( sodium sulfate concentration of 15 wt %, magnesium sulfate concentration of 4 . 3 wt %) and an aqueous solution of sodium metasilicate ( 4 wt % as sio 2 ) was sprayed simultaneously from a spray nozzle located 40 cm above the multipore plate , wherein 5 . 6 kg of the mixed solution of sodium sulfate and magnesium sulfate was sprayed at a speed of 90 g / min and 2 . 1 kg of the aqueous solution of sodium metasilicate was sprayed at a speed of 34 g / min , both for 62 minutes . after completion of the coating , heated air continued to be sent for 5 minutes so that the sample dried . next , heating from the air heater finished , and the sample was cooled with a cool air flow . the temperature was controlled at from 73 ° to 77 ° c . after cooling , the coated sodium percarbonate was removed , and no aggregate was observed . the coating amount of each component as solids content was as follows : sodium sulfate : 840 g ( 0 . 7 % of the sodium percarbonate to be coated ) sodium metasilicate : 84 g ( as sio 2 : 0 . 7 % of the sodium percarbonate to be coated ) magnesium sulfate : 168 g ( 1 . 4 % of the sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 3 . in the case of simultaneous spraying , the solubility and formulation stability were good , similar to the multi - spray case of examples 11 , 12 and 13 . simultaneous spraying over 89 minutes using the same procedures as in example 14 was conducted , except that edta - 4na ( 0 . 3 wt %) to sodium sulfate particle was added into a mixed solution of sodium sulfate and magnesium sulfate , the amount of coating agent was changed , water - glass no . 1 was used instead of sodium metasilicate , and the concentration was changed . sodium sulfate : 1200 g ( 10 . 0 % of sodium percarbonate to be coated ) water - glass no . 1 : 84 g ( as sio 2 , 0 . 7 % of sodium percarbonate to be coated ) magnesium sulfate : 240 g ( 2 . 0 % of sodium percarbonate to be coated ) ethylenediaminetetraacetic acid tetrasodium salt : 24 g ( 0 . 2 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated , and the results are shown in table 3 . as can be understood from table 2 , sodium percarbonate produced according to the example of the present invention was shown to be good in solubility ( necessary time for 100 % dissolution was from 2 to 2 . 5 minutes , i . e ., fast ) and good in formulation stability with detergent ( after 21 days storage , only 10 % was decomposed ), and had a good balance in property . coated sodium percarbonate was obtained using the same procedures as in example 11 , except that mixed aqueous solution of magnesium sulfate , sodium sulfate and sodium bicarbonate ( 4 . 2 % by weight of magnesium sulfate , 10 % by weight of sodium sulfate and 5 % by weight of sodium bicarbonate ) was used instead of mixed aqueous solution of magnesium sulfate and sodium sulfate . sodium metasilicate : 2 . 1 g ( as sio 2 , 0 . 7 % of sodium percarbonate to be coated ) magnesium sulfate : 4 . 2 g ( 1 . 4 % of sodium percarbonate to be coated ) sodium sulfate : 10 . 0 g ( 3 . 3 % of sodium percarbonate to be coated ) sodium carbonate : 5 . 0 g ( 1 . 7 % of sodium percarbonate to be coated ) active oxygen of the obtained sodium percarbonate was analyzed to 13 . 4 %. further , solubility and formulation stability were investigated , and the solubility was excellent , and formulation stability was good as in example 11 . the results are shown in table 3 . active oxygen , solubility and formulation stability of uncoated sodium percarbonate which was used as a raw material in the present invention were investigated . the results are shown in table 3 for comparison . coated sodium percarbonate was obtained using the same procedures as in example 11 , except that the spraying of the mixed solution of magnesium sulfate and sodium sulfate for the second layer was not conducted . sodium metasilicate : 2 . 1 g ( as sio 2 , 0 . 7 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate was investigated . the results are shown in table 3 . the formulation stability was a little bit better than the uncoated sample of comparative example 11 , but did not show a great improvement like in example 1 . coated sodium percarbonate was obtained using the same procedures as in example 11 , except that the spraying of the aqueous solution of sodium metasilicate for the first layer was not conducted . active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 3 . the formulation stability did not show a great improvement like in example 11 . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 75 ° c . after the temperature was steady at 75 ° c ., to keep it in a fluid state , 180 g of an aqueous solution of magnesium chloride ( 10 % concentration of magnesium chloride ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 36 minutes at a flow rate of 5 g / min . after vacuum drying , active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 3 . the formulation stability did not show a great improvement like in example 11 . in particular , the formulation stability with a zeolite was low , like the uncoated sample in comparative example 11 . further , a great decrease of active oxygen which was over the value of dilution by the coating agent was observed . 300 g of sodium percarbonate having a mean diameter of 500 μm ( active oxygen : 14 . 4 %) was placed on a multipore plate of a fluid dry coater ( yamato scientific co ., ltd ., pulvis mini bed ), then air at 0 . 25 m 3 / min was sent to make fluidization . thereafter , by warming inlet air , the temperature of the fluidizing sodium percarbonate was raised to 50 ° c . after the temperature was steady at 50 ° c ., to keep it in a fluid state , 150 g of an aqueous solution of a mixed salt of sodium carbonate and sodium sulfate ( 8 . 6 % concentration of sodium carbonate , 11 . 2 % of sodium sulfate ) was sprayed from a spray nozzle located 10 cm above the multipore plate over 30 minutes at a flow rate of 5 g / min . for 10 minutes after spray completion , only gas at the same temperature continued to be sent , and drying was completed . then , the gas was changed to cool wind , and the sample was cooled to 30 ° c . then , the coated sodium percarbonate was removed from the apparatus , and little aggregates were observed . sodium sulfate : 16 . 8 g ( 5 . 6 % of sodium percarbonate to be coated ) sodium carbonate : 13 . 2 g ( 4 . 4 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 3 . formulation stability did not show a great improvement like in example 11 . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that after forming the first coating layer , without using sodium sulfate , the second coating layer was formulated using only an aqueous solution of magnesium sulfate . sodium metasilicate ( as sio 2 ): 2 . 1 g ( 0 . 7 % of sodium percarbonate to be coated ) magnesium sulfate : 19 . 2 g ( 6 . 4 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 3 . coated sodium percarbonate was obtained using the same procedures as in example 6 , except that after forming the first coating layer , without using magnesium sulfate , the second coating layer was formulated using a mixed aqueous solution of sodium sulfate and sodium carbonate . sodium metasilicate ( as sio 2 ): 2 . 1 g ( 0 . 7 % of sodium percarbonate to be coated ) sodium sulfate : 15 . 0 g ( 5 . 0 % of sodium percarbonate to be coated ) sodium carbonate : 4 . 2 g ( 1 . 4 % of sodium percarbonate to be coated ) active oxygen , solubility and formulation stability of the obtained sodium percarbonate were investigated . the results are shown in table 3 . table 3__________________________________________________________________________ example comparative example 11 12 13 14 15 16 13 14 15 16 17 18 19__________________________________________________________________________solubility ( min .) 2 . 0 2 . 0 2 . 5 2 . 5 2 . 5 2 . 5 1 . 5 3 . 5 1 . 5 5 . 0 1 . 5 4 . 0 3 . 0storage stability 1 (%) 95 91 93 95 96 96 30 50 79 43 48 68 72storage stability 2 (%) 91 89 90 92 93 95 50 54 68 75 55 72 70__________________________________________________________________________ while the invention has been described in detail and with reference to specific embodiments , it will be apparent to one skilled in the art that changes and modifications can be made therein without departing from the spirit and scope thereof .