U.S. patent application number 13/382260 was filed with the patent office on 2012-05-03 for washing machine.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Kei Nambu, Keiko Yasui, Katsunori Zaizen.
Application Number | 20120103025 13/382260 |
Document ID | / |
Family ID | 43544107 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120103025 |
Kind Code |
A1 |
Nambu; Kei ; et al. |
May 3, 2012 |
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.
Inventors: |
Nambu; Kei; (Kyoto, JP)
; Yasui; Keiko; (Shiga, JP) ; Zaizen;
Katsunori; (Hyogo, JP) |
Assignee: |
PANASONIC CORPORATION
Kadoma-shi, Osaka
JP
|
Family ID: |
43544107 |
Appl. No.: |
13/382260 |
Filed: |
July 23, 2010 |
PCT Filed: |
July 23, 2010 |
PCT NO: |
PCT/JP2010/004710 |
371 Date: |
January 4, 2012 |
Current U.S.
Class: |
68/12.23 |
Current CPC
Class: |
B01J 39/09 20170101;
C02F 5/025 20130101; D06F 39/007 20130101; C02F 1/66 20130101; C02F
2001/425 20130101; A47L 15/4229 20130101; B01J 49/06 20170101; B01J
49/75 20170101; B01J 39/07 20170101; C02F 1/42 20130101 |
Class at
Publication: |
68/12.23 |
International
Class: |
D06F 33/02 20060101
D06F033/02; D06F 29/00 20060101 D06F029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2009 |
JP |
2009-183012 |
Claims
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.
Description
TECHNICAL FIELD
[0001] The present invention relates to a washing machine equipped
with a water softening device.
BACKGROUND ART
[0002] Washing machines generally use tap water, groundwater, or
well water, and are greatly affected by the qualities of water
used. In particular, hard water components such as calcium and
magnesium deteriorate the detergency of surfactants, thereby
adversely affecting the washing performance. Hard water does not
dissolve detergent as readily as soft water, possibly causing any
unit of a washing machine to be coated with detergent residue and
turning moldy. Hard water also contains trace amounts of polyvalent
metal ions, e.g., of iron, manganese, and aluminum, which can
interact with detergent, thereby deteriorating the detergency of
surfactants.
[0003] To address this problem, commercially available detergents
contain a water softening agent such as zeolite, which absorbs hard
water components. Zeolite easily absorbs polyvalent ions, thereby
providing some effect of water softening. Zeolite, however, is used
in a detergent dissolved in washing water, causing some of the hard
water components and metal ions to be again dissolved in the
washing water. As a result, the above-described problem remains
unsolved.
[0004] For this reason, users in hard water areas use a larger
amount of detergent than users in soft water areas to ensure the
washing performance. Detergent packages sold in hard water areas
often indicate an appropriate amount of detergent to be loaded
according to the hardness of water. There is a concern, however,
that using a large amount of detergent is not eco-friendly.
Moreover, there is no radical solution to the detergent residue in
the washing machine.
[0005] To overcome this problem, it has been suggested to remove
hard water components by mounting a water softening device such as
cation exchange resin in washing machines (see, for example, Patent
Literatures 1 and 2). The most common cation exchange resin
contains, in its surface, acidic ion exchange groups such as
sulfonic acid groups and absorbs cations by way of electrostatic
forces. Acidic ion exchange groups absorb cations at different
degrees depending on the ionic radius and valence of the cations.
Sulfonic acid groups, which are strong acidic ion exchange groups,
absorb trivalent ions most easily, followed by divalent ions, and
then monovalent ions. When the ionic valence is the same, sulfonic
acid groups tend to absorb ions with larger ionic radius. When hard
water passes through Na.sup.+ ion exchange resin, Ca.sup.2+ and
Mg.sup.2+ ions which are hard water components, are retained by the
cation exchange resin because of their higher selectivity than
Na.sup.+ ions. Instead, the same amount of Na.sup.+ ions is drawn
out.
[0006] The cation exchange resin loses its ability to soften water
when most surface charges of the acidic ion exchange groups are
saturated with hard water components. Therefore, it is necessary to
regenerate the cation exchange resin by adding a regenerant such as
salt (NaCl) to the resin at regular intervals and by passing water
that contains highly concentrated Na.sup.+ ions through the resin,
thereby exchanging Ca.sup.2+ and Mg.sup.2+ ions with the Na.sup.+
ions.
[0007] It has also been suggested to provide a water softening
device including either weak acid cation exchange resin or
chelating resin instead of a strong acid cation exchange resin
(see, for example, Patent Literature 3). These ion exchange resins
contain carboxyl groups as the ion exchange groups. Unlike the
above-mentioned sulfonic acid groups, carboxyl groups, which are
weak acidic ion exchange groups, have high selectivity for H.sup.+
ions (acid) as shown in Mathematical Formula 1:
H.sup.+Ca.sup.2+>Mg.sup.2+>K.sup.+>Na.sup.+ Mathematical
Formula 1.
[0008] Carboxyl groups have a pKa of 5 to 6. When the pH of water
to be processed is higher by at least 0.5 than the pKa of the
carboxyl groups, most of the carboxyl groups are generally
dissociated and generate negative charges, thereby absorbing
Ca.sup.2+ and Mg.sup.2+ ions. When, on the other hand, the pH of
water to be processed is lower by at least 0.5 than the pKa of the
carboxyl groups, H.sup.+ ions absorb the carboxyl groups. As a
result, most of the carboxyl groups are undissociated, and do not
absorb Ca.sup.2+ or Mg.sup.2+ ions. This specific selectivity of
carboxyl groups for H.sup.+ ions can be used to control the pH of
water to be processed. Carboxyl groups can soften water when the
water is alkaline, and regenerate the resin when the water is
acidic.
[0009] Generating acid or alkaline water using an electrolytic bath
with a diaphragm eliminates the need to add a regenerant for weak
acid ion exchange resin. This provides, in principle, a
self-regenerating water softening device.
[0010] Na.sup.+ ions have lower selectivity for cation exchange
resin than Ca.sup.2+ and Mg.sup.2+ ions. It is therefore necessary
to add to the cation exchange resin, as a regenerant, at least a
thousand times the amount of Na.sup.+ ions than Ca.sup.2+ and
Mg.sup.2+ ions that are released for exchanging. This requires the
user to take the trouble to frequently supply a regenerant such as
salt to the cation exchange resin, against their desire to reduce
the usage of detergent.
[0011] In addition, highly concentrated salt water may touch the
skin of the user for any reason, and cause the user to get shocked.
When metal is used inside the washing machine or in its peripheral
equipment such as the drain pipe, they may be corroded by highly
concentrated salt water.
[0012] Existing weak acid cation exchange resin and chelating resin
contain, as cation exchange groups, carboxyl groups with a pKa of 5
to 6. To regenerate these resins, it is necessary to generate acid
water with a pH of 4.5 to 5.5. To generate an acid with a low pH
without using a regenerant, it is necessary to mount a device for
electrolyzing water and a DC power supply on the washing machine.
It is, however, not practical to mount an electrolytic device in
domestic washing machines due to installation space
limitations.
[0013] Tap water, which generally contains at least several ppm of
chloride ions, generates oxidative hypochlorous acid during
electrolysis. Cation exchange resin, which is generally made of an
organic polymer material, is subjected to oxidative degradation for
a long time by hypochlorous acid. Since it cannot be expected that
users periodically replace components of domestic washing machines,
electrolysis may shorten the useful life of the resin and the water
softening device.
CITATION LIST
Patent Literatures
[0014] Patent Literature 1: Japanese Patent Unexamined Publication
No. H11-319383 [0015] Patent Literature 2: Japanese Patent
Unexamined Publication No. H11-70296 [0016] Patent Literature 3:
Japanese Patent Unexamined Publication No. 2005-161144
SUMMARY OF THE INVENTION
[0017] The present invention is directed to a washing machine
including the following components: 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 washing tub is rotatable and accommodates laundry. The
water tub includes the washing tub. The drive unit is attached to
the water tub, and rotates the water tub. The feed-water unit feeds
washing water into the water tub and the washing tub. The drain
unit drains the washing water from the water tub and the washing
tub. 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 the washing water. The pH decreasing unit
decreases the pH of the washing water. The control unit controls
the feed-water unit, the drive unit, and the drain unit so as to
control washing, rinsing and spin-drying steps successively. 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.
[0018] A weak acid cation exchange material with a point of zero
charge of 7.5 or more has high selectivity for H.sup.+ ions (acid),
and is less likely to absorb cations other than H.sup.+ ions. As a
result, the weak acid cation exchange material is readily
regenerated to the H.sup.+ form. A general weak acid cation
exchange resin containing carboxyl groups (COOH groups) as cation
exchange groups has a point of zero charge of 5 to 6. The weak acid
cation exchange material used in the washing machine of the present
invention can be regenerated to the H form with water at a higher
pH (about pH 7) than those ion exchange resins. A weak acid with a
pH of 7 or so can be generated by various means without using a
chemical agent or an electrolytic device. Thus, the washing machine
is equipped with the water softening device that does not require
using a special regenerant or performing electrolysis.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a configuration diagram of a washing machine
according to a first exemplary embodiment of the present
invention.
[0020] FIG. 2A shows tap water being fed before a washing step in
the washing machine according to the first exemplary
embodiment.
[0021] FIG. 2B shows tap water being fed before a rinsing step in
the washing machine according to the first exemplary
embodiment.
[0022] FIG. 3A shows tap water being fed before a washing step in a
washing machine according to a second exemplary embodiment of the
present invention.
[0023] FIG. 3B shows tap water being fed before a rinsing step in
the washing machine according to the second exemplary
embodiment.
[0024] FIG. 4 is a configuration diagram of a washing machine
according to a third exemplary embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0025] Exemplary embodiments of the present invention will be
described as follows with reference to drawings. Note that the
present invention is not limited to these exemplary
embodiments.
First Exemplary Embodiment
[0026] FIG. 1 is a configuration diagram of a washing machine
according to a first exemplary embodiment of the present invention.
The washing machine shown in FIG. 1 includes washing tub 1, water
tub 15, drive unit 16, washing unit 2, feed-water unit 3, drain
unit 4, water softening unit 5, detergent container (pH increasing
unit) 6, pH decreasing unit 7, and control unit 8.
[0027] Washing tub 1 is rotatable and accommodates laundry. Washing
unit 2 includes a motor, which stirs washing tub 1 and provides
physical washing effect. Feed-water unit 3 feeds washing water into
water tub 15 and washing tub 1. Drain unit 4 drains washing water
from water tub 15 and washing tub 1. Water softening unit 5 is
disposed between feed-water unit 3 and water tub 15 so as to soften
the washing water fed by feed-water unit 3. Water softening unit 5
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. Detergent container (pH increasing unit) 6 is disposed
between feed-water unit 3 and water softening unit 5, and
accommodates detergent. PH increasing unit 6 increases the pH of
washing water. PH decreasing unit 7, which decreases the pH of
washing water, is disposed between feed-water unit 3 and water
softening unit 5. PH increasing unit 6 and pH decreasing unit 7 are
in different paths from each other. Control unit 8 controls
feed-water unit 3, drive unit 16, drain unit 4, and other
components so as to control washing, rinsing and spin-drying steps
successively. Water tub 15 includes washing tub 1. Drive unit 16 is
attached to water tub 15 and rotates water tub 15.
[0028] The weak acid cation exchange material filled in water
softening unit 5 is made of hydroxide such as aluminum or iron. The
weak acid cation exchange material can alternatively be a metallic
material such as manganese oxide or titanium oxide, or a weak acid
mineral such as allophane or imogolite. It can further
alternatively be a material produced by coating these materials
onto another porous material and then sintering it.
[0029] The weak acid cation exchange material may alternatively be
produced by coating an inorganic material having hydroxyl groups on
its surface onto the surface of a base, so that the hydroxyl groups
act as weak acidic cation exchange groups.
[0030] In this case, amorphous metal hydroxide is particularly
weakly acidic, possibly having a point of zero charge at pH 7.5 or
more. This material generates negative charges on its surface in an
aqueous solution with a pH of 7.5 or more, and acts as a weak acid
cation exchange material. This material also generates positive
charges on its surface in an aqueous solution with a pH of 7.5 or
less, and acts as an anion exchange resin.
[0031] The above-mentioned material is more stable against
oxidation and hydrolysis than common weak acid cation exchange
resins which have a point of zero charge at about pH 8.0 to 9.0,
and which are made of an organic polymer material (such as acrylic,
styrene, or divinylbenzene). Many countries have guidelines for tap
water: the water should contain hypochlorous acid having oxidizing
properties with the purpose of sterilization. For this reason,
generally-used cation exchange resins can be subjected to oxidative
degradation for a long time. Since it cannot be expected that users
periodically replace components of domestic washing machines, it is
necessary to use an ion exchange material that lasts as long as the
washing machines themselves do. In that respect, the weak acid
cation exchange material used in the washing machine of the present
first exemplary embodiment is a suitable water softening material
for domestic washing machines.
[0032] For example, in amorphous alumina (amorphous aluminum
oxide), hydroxyl groups are dissociated and perform cation exchange
as shown in Mathematical Formula 2:
Al--OH.fwdarw.Al--O.sup.-+H.sup.+ Mathematical Formula 2.
[0033] Aluminum oxide has a point of zero charge at about pH 8 to
9. In pH levels above this range, the reaction proceeds to the
right-hand side. In other words, most of the aluminum oxide is
dissociated and performs cation exchange. In contrast, when, the pH
is in an acid region, the aluminum oxide is undissociated, that is,
becomes the --OH form. By making the pH of the aluminum oxide lower
by at least 0.5 than the point of zero charge according to this
principle, the above-described weak acid cation exchange material
can be regenerated. The weak acid cation exchange material differs
from the conventional weak acid cation exchange resin, which can be
regenerated only with very strong acid water because it contains,
as exchange groups, carboxyl groups with a point of zero charge of
5 to 6.
[0034] The above-described materials can be produced by subjecting
minerals to a comparatively easy process. As a result, they can be
produced at lower cost than the conventional cation exchange resin
made of synthetic resin. These inorganic materials are more stable
against high temperatures and oxidation degradation by an oxidizing
agent than the conventional weak acid cation exchange resin.
[0035] PH increasing unit 6 is detergent container 6 into which
detergent is poured. Common laundry detergents contain several to
40% of an alkaline chemical such as sodium carbonate or sodium
hydrogen carbonate. Therefore, when the detergent is dissolved in
the fed washing water, pH increasing unit 6 can make the pH of the
washing water higher than the point of zero charge of the weak acid
cation exchange material, allowing the weak acid cation exchange
material to generate negative charges.
[0036] PH decreasing unit 7 of the present first exemplary
embodiment is fabric softener feed unit 7 into which fabric
softener to be added to tap water is poured. Fabric softener feed
unit 7 includes fabric softener container 25 into which fabric
softener is poured, and feed-water switching valve 9. Valve 9
switches between the channels of feed-water unit 3 such that water
is fed into fabric softener container 25 in a rinsing step. The
water fed into fabric softener container 25 in the rinsing step is
made to flow into water softening unit 5. Common fabric softeners
have a neutral pH, and contain a pH adjusting agent, keeping the pH
of the washing water lower than the point of zero charge of the
weak acid cation exchange material. Fabric softeners also have the
effect of converting the weak acid cation exchange material to the
H form.
[0037] It is common, in hard water areas, to use fabric softeners
to prevent washed clothes from becoming stiff. Common fabric
softeners contain a pH adjusting agent or acid to neutralize the
alkaline chemical contained in detergent, and therefore has a pH
lower than the neutral. In general, adding fabric softener adjusts
the pH value of the washing water to 7.5 to 6, which is lower than
the point of zero charge of the weak acid cation exchange material.
The liquid with such a pH value is made to flow into water
softening unit 5, thereby regenerating the weak acid cation
exchange material used in the present first exemplary
embodiment.
[0038] Water softening unit 5, detergent container 6, and pH
decreasing unit 7 which are characteristic of the first exemplary
embodiment will be described as follows with reference to the
operations shown in FIGS. 2A and 2B. FIGS. 2A and 2B show tap water
being fed before a washing step and before a rinsing step,
respectively, in the washing machine according to the first
exemplary embodiment.
[0039] Before a washing step, as shown in FIG. 2A, tap water is
made to flow in the direction (arrow 20) to detergent container (pH
increasing unit) 6 by feed-water switching valve 9. In this case,
washing water whose pH is increased to 10 or more by the alkaline
chemical contained in the detergent dissolved in the washing water
flows into water softening unit 5. The weak acid cation exchange
material filled into water softening unit 5 is dissociated under
the alkaline conditions, and performs cation exchange. As a result,
hard water components such as calcium and magnesium ions contained
in the tap water are absorbed to the surface of the weak acid
cation exchange material by way of electrostatic forces. Assume
that 300 ppm of hard water is fed at a flow rate of 5 liters per
min. to water softening unit 5 containing 500 ml of weak acid
cation exchange material. In this case, the hardness of the water
decreases to about 100 ppm. The washing water softened in that
manner is fed into washing tub 1. The softened water can dissolve
detergent more easily than hard water, making the detergent more
powerful.
[0040] Before a rinsing step, on the other hand, as shown in FIG.
2B, tap water is made to flow in the direction (arrow 21) to pH
decreasing unit 7 by feed-water switching valve 9. PH decreasing
unit 7 is a fabric softener supplying means. In this case, washing
water whose pH is decreased to 7 or less by the pH adjusting agent
contained in the fabric softener dissolved in the washing water
flows into water softening unit 5. The weak acid cation exchange
material filled into water softening unit 5 is undissociated under
these pH conditions, and is regenerated. The hard water components
eliminated from water softening unit 5 are sent to washing tub 1
and drained with water after a rinsing step.
[0041] Thus, control unit 8 performs the following operations:
controlling pH increasing unit 6 to increase the pH of washing
water while the washing water is being fed; introducing the washing
water with the increased pH to water softening unit 5 to decrease
the hardness of the washing water; introducing the washing water
with the decreased hardness to washing tub 1; controlling, after
the washing water is fed, pH decreasing unit 7 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 water softening unit 5.
[0042] Thus, water softening unit 5 is regenerated in the ordinary
use of the washing machine. This achieves stable supply of soft
water, thereby providing stable washing performance.
[0043] There is, however, a fear that metal ions contained in tap
water such as iron and manganese are chelate-bonded to the weak
acid ion exchange material during long-term use, causing the
material not to be regenerated. To remove these metal ions, it is
necessary to add a chelating agent with a higher chelating ability
than the weak acid ion exchange material about once a year. More
specifically, at least ten times the amount of citric acid, malic
acid, or succinic acid than the weak acid ion exchange material is
poured in detergent container 6 and then the washing machine is
operated once or twice.
[0044] Thus, the regeneration of water softening unit 5 is secured
by providing water softening unit 5 with a chelating agent or an
acid stronger than the acid generated by pH decreasing unit 7 for
maintenance every after a predetermined time of use.
Second Exemplary Embodiment
[0045] In a second exemplary embodiment, components identical to
those in the first exemplary embodiment are denoted by the same
reference numerals, and these components will not be described
again in detail. The following description will be directed to
their differences. FIGS. 3A and 3B show tap water being fed before
a washing step and before a rinsing step, respectively, in a
washing machine according to the second exemplary embodiment.
[0046] The washing machine of the second exemplary embodiment
includes channel switching valve 10 between water softening unit 5
and washing tub 1. Valve 10 switches between the two channels: one
guides water to washing tub 1, and the other drains the water.
[0047] As shown in FIG. 3A, water softening unit 5 performs water
softening under alkaline conditions in the same manner as in the
first exemplary embodiment. In this case, channel switching valve
10 allows softened washing water to flow in the direction of arrow
22 so as to be fed to washing tub 1.
[0048] As shown in FIG. 3B, before a rinsing step, feed-water
switching valve 9 allows tap water to flow in the direction of pH
decreasing unit 7 (arrow 21). PH decreasing unit 7 in the present
second exemplary embodiment is a gas dissolving unit for dissolving
carbon dioxide in the air into the tap water. The gas dissolving
unit dissolves air taken through air supply unit 11 in the
direction of arrow 23 in tap water (washing water). One example of
the gas dissolving unit is an ejector. An ejector draws in the air
using the negative pressure created by water flow, generates micro
bubbles in the water, and dissolves them in the water in a short
time.
[0049] Air contains about 360 ppm of carbon dioxide. When in
equilibrium with tap water, carbon dioxide dissolved in the tap
water produces carbonic acid (Mathematical Formula 3). Some of the
carbonic acid dissociates (Mathematical Formula 4), making the tap
water weakly acidic. Thus, the gas dissolving unit is used to
generate mild carbonated water with weak acidity, which is
introduced to water softening unit 5.
CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3 Mathematical Formula 3
H.sub.2CO.sub.3.fwdarw.H.sup.++HCO.sub.3 Mathematical Formula 4
[0050] It is known that when pure water and carbon dioxide in the
air are in equilibrium, the equilibrium pH is about 5.6. The weak
acid cation exchange material can be regenerated by using
carbonated water when ordinary tap water, instead of pure water, is
used together with weak acidic cation exchange groups with a point
of zero charge of about 7.5 or more. The reason for this is as
follows. The equilibrium pH obtained when pure water and carbon
dioxide in the air are in equilibrium is lower than the point of
zero charge of the weak acid cation exchange material. This
provides the effect of converting the weak acid cation exchange
material to the H form.
[0051] The regenerated water softening unit draws out hard water
components such as Ca.sup.2+ and Mg.sup.2+ ions absorbed therein.
If these hard water components are flown into the
detergent-containing washing water, this will cause detergent
residue or make cloth fabrics stiff in rinse water. To avoid these
problems, it is desirable to prevent detergent, clothes, and
washing tub 1 from coming into contact with each other. For this
purpose, channel switching valve 10 allows the water flown from the
regenerated water softening unit to be drained through another
channel (arrow 24), instead of passing through washing tub 1. This
structure is advantageous to preventing fabric stiffness, but is
disadvantageous to saving water because the washing water used to
regenerate the water softening unit is drained without being
used.
Third Exemplary Embodiment
[0052] In a third exemplary embodiment, components identical to
those in the first exemplary embodiment are denoted by the same
reference numerals, and these components will not be described
again in detail. The following description will be directed to
their differences. FIG. 4 is a configuration diagram of a washing
machine according to the third exemplary embodiment.
[0053] PH decreasing unit 7 used in the present third exemplary
embodiment includes a pair of electrolysis electrodes and control
unit 8 having a voltage application function. The electrolysis
electrodes consist of anode 12 disposed surrounded by the weak acid
cation exchange material, and cathode 13 disposed adjacent to anode
12 with isolation film 14 therebetween.
[0054] These electrolysis electrodes are applied with no voltage
when washing water is fed. The weak acid cation exchange material
generates negative charges on its surface due to the effect of
alkaline detergent, and performs water softening function.
[0055] When, on the other hand, the electrolysis electrodes are
applied with a DC voltage while water is being fed before a rinsing
step, the hard water around anode 12 produces acid according to the
reaction shown in Mathematical Formula 5:
H.sub.2O.fwdarw.2H.sup.++1/2O.sub.2+2e.sup.- Mathematical Formula
5
[0056] The produced acid makes the washing water around the weak
acid cation exchange material lower than the point of zero charge.
As a result, the weak acid cation exchange material is converted
back to the H form.
[0057] Thus, pH decreasing unit 7 in the present third exemplary
embodiment includes a pair of electrodes including anode 12
disposed adjacent to the weak acid cation exchange material, and
control unit 8 having a DC voltage application function. PH
decreasing unit 7 decreases the pH of the washing water around the
weak acid cation exchange material by electrolysis of water.
[0058] When the conventional weak acid ion exchange resin is
converted to the H form using electrolyzed acid water, the
electrolysis produces hypochlorous acid as its by-product. The
hypochlorous acid oxidatively degrades the ion exchange resin. In
contrast, the weak acid cation exchange material used in the
present invention, which is made, for example, of metal hydroxide,
is much more stable against oxidation degradation. The weak acid
cation exchange material is converted to the H form at pH 7 or
less, thus saving energy required for electrolysis.
INDUSTRIAL APPLICABILITY
[0059] Thus, the water softening unit of the washing machine of the
present invention can be applied not only to domestic washing
machines, but also to washing machines, dishwashers, and other
types of washing devices using alkaline detergent in industrial
use. The water softening unit of the washing machine of the present
invention is particularly useful when tap water or surface water is
industrially used in hard water areas.
REFERENCE MARKS IN THE DRAWINGS
[0060] 1 washing tub [0061] 2 washing unit [0062] 3 feed-water unit
[0063] 4 drain unit [0064] 5 water softening unit [0065] 6 pH
increasing unit (detergent container) [0066] 7 pH decreasing unit
(fabric softener feed unit) [0067] 8 control unit [0068] 9
feed-water switching valve [0069] 10 channel switching valve [0070]
11 air supply unit [0071] 12 anode [0072] 13 cathode [0073] 14
isolation film [0074] 15 water tub [0075] 16 drive unit [0076] 20,
21, 22, 23, 24 arrow [0077] 25 fabric softener container
* * * * *