Washing machine

Abstract

A washing machine includes a washing tub, a water tub, a drive unit, a feed-water unit, a drain unit, a water softening unit, a pH increasing unit, a pH decreasing unit, and a control unit. The water softening unit is disposed between the feed-water unit and the water tub, and is filled with a weak acid cation exchange material having weak acidic cation exchange groups with a pH from 7.5 to 14 at point of zero charge. The pH increasing unit increases the pH of washing water, and the pH decreasing unit decreases the pH of the washing water. The control unit performs the following operations: controlling the pH increasing unit to increase the pH of the washing water while the washing water is being fed; introducing the washing water with the increased pH to the water softening unit to decrease the hardness of the washing water; introducing the washing water with the decreased hardness to the washing tub; controlling, after the washing water is fed, the pH decreasing unit to decrease the pH of the washing water to a value of 5.5 to 7.0; and introducing the washing water with the decreased pH to the water softening unit.

1 . A washing machine comprising:
 a rotatable washing tub for accommodating laundry;   a water tub including the washing tub;   a drive unit attached to the water tub, the drive unit rotating the washing tub;   a feed-water unit for feeding washing water into the water tub and the washing tub;   a drain unit for draining the washing water from the water tub and the washing tub;   a water softening unit disposed between the feed-water unit and the water tub, the water softening unit being filled with a weak acid cation exchange material having weak acidic cation exchange groups with a pH from 7.5 to 14 at point of zero charge;   a pH increasing unit for increasing a pH of the washing water;   a pH decreasing unit for decreasing the pH of the washing water; and   a control unit for controlling the feed-water unit, the drive unit, and the drain unit so as to control washing, rinsing and spin-drying steps successively, wherein   the control unit performs the following operations:   controlling the pH increasing unit to increase the pH of the washing water while the washing water is being fed,   introducing the washing water with the increased pH to the water softening unit to decrease hardness of the washing water,   introducing the washing water with the decreased hardness to the washing tub,   controlling, after the washing water is fed, the pH decreasing unit to decrease the pH of the washing water to a value of 5.5 to 7.0, and   introducing the washing water with the decreased pH to the water softening unit.   
     
     
         2 . The washing machine of  claim 1 , wherein
 the weak acid cation exchange material is an inorganic material having hydroxyl groups on a surface thereof, the hydroxyl groups acting as the weak acidic cation exchange groups.   
     
     
         3 . The washing machine of  claim 1 , wherein
 the weak acid cation exchange material includes a base and an inorganic material applied on a surface of the base, the inorganic material having hydroxyl groups on a surface thereof, the hydroxyl groups acting as the weak acidic cation exchange groups.   
     
     
         4 . The washing machine of  claim 1 , wherein
 the pH increasing unit is a detergent container into which detergent is poured.   
     
     
         5 . The washing machine of  claim 1 , wherein
 the pH decreasing unit includes:
 a fabric softener container into which fabric softener is poured; and 
 a feed-water switching valve for switching between channels of the feed-water unit such that water is fed into the fabric softener container in a rinsing step, and 
   the washing water fed into the fabric softener container in the rinsing step is made to flow into the water softening unit.   
     
     
         6 . The washing machine of  claim 1 , wherein
 the pH decreasing unit is a gas dissolving unit for dissolving carbon dioxide in the air into tap water, the gas dissolving unit generating mild carbonated water with weak acidity, and then introducing the mild carbonated water to the water softening unit.   
     
     
         7 . The washing machine of  claim 1 , wherein
 the pH decreasing unit includes a pair of electrodes including an anode disposed adjacent to the weak acid cation exchange material, and the control unit having a DC voltage application function, and   the pH decreasing unit decreases a pH of water around the weak acid cation exchange material by electrolysis of water.   
     
     
         8 . The washing machine of  claim 1 , wherein
 the water softening unit is provided with an acid stronger than an acid generated by the pH decreasing unit for maintenance every after a predetermined time of use.   
     
     
         9 . The washing machine of  claim 1 , wherein
 the water softening unit is provided with a chelating agent for maintenance every after a predetermined time of use.