Aqueous compositions, aqueous cutting fluid using the same, method for preparation thereof, and cutting method using the cutting fluid

An aqueous cutting fluid which can reduce the impact on working environment and the global environment, and can achieve both preventing precipitates from becoming a hard cake and keeping high dispersibility for abrasive grains is provided. Such an aqueous cutting fluid is obtained by a method comprising dispersing abrasive grains (G) in an aqueous composition comprising a dispersion medium (M) containing a hydrophilic alcohol compound such as ethylene glycol, a lipophilic alcohol compound such as propylene glycol and water, and silica colloid particles dispersed stably in the medium. The dispersion medium (M) is odorless and not flammable. The abrasive grains (G) may settle out after a time, but they do not closely contact with one another, and therefore the resulting precipitates do not become a hard cake, which allows the re-dispersion and reuse of precipitated grains. The instant aqueous cutting fluid is inherently low viscous, and the reduction of viscosity owing to the contamination of water and the increase of viscosity owing to contamination of shavings are both moderate. As a result, the cutting fluid has a long life. And articles which have been cut using the cutting fluid can be washed with water. Further, as the dispersion medium (M) is a biodegradable low molecular weight organic compound, a waste liquid from a process using the cutting fluid can be disposed with an activated sludge.

TECHNICAL FIELD
 The present invention relates to improvement on performance stability,
 safety and waste treatability of a cutting liquid used for generally
 cutting a work, concretely an ingot of semiconductor material such as
 silicon single crystal, silicon polycrystal, compound semiconductor or the
 like, or a ceramic block or the like; to a simple, easy producing process
 for the cutting liquid; and to a cutting method with high reliability and
 safety using the cutting liquid.
 BACKGROUND ART
 In general, when a work is cut using a cutting tool such as a wire saw, a
 band saw or the like, a cutting liquid has widely been used as a lubricant
 between the cutting tool and the work, to remove a friction heat
 therebetween and clean cutting chips away from the cutting tool and the
 work. For example, when wafers are produced by slicing an ingot of silicon
 single crystal as a work, a non-aqueous cutting liquid in a slurry state,
 which is prepared by dispersing loose abrasive grains of SiC (silicon
 carbide) or the like in a dispersion medium composed of a mineral oil and
 higher hydrocarbons as major components, has widely been used.
 A wafer obtained by slicing has been cleaned with a low-priced chlorinated
 organic solvent with high detergency such as trichloroethane and
 dichloromethane.
 In this way, in a system in which cutting is performed by dynamic contact
 among a cutting tool, a work and loose abrasive grains, to increase
 dispersibility of loose abrasive grains in a cutting liquid is important
 in order to keep the cutting ability at a constant level all time. As
 methods of increasing the dispersibility, there have been available two
 methods in a broad sense: (a) a method in which a dispersing agent is
 added in a dispersion medium and (b) a method in which a thickener is
 added in a dispersion medium.
 The method (a) is to increase the dispersibility of abrasive grains
 themselves positively. Generally dispersibility of particles in a fluid is
 increased and a sedimentation speed of the particle is decreased, when
 individual particles each have a small mass, a sufficient repulsive force
 works between particles due to factors such as an electric double layer,
 or steric hindrance by absorbed molecules on a particle surface or the
 like and thereby the particles are existent as primary particles
 (particles in a non-aggregation state). Hence, an electrolyte or a
 surfactant having a lipophilic group such as an alkyl chain with a
 sufficient length has been added as a dispersing agent.
 On the other hand, the method (b) is to increase a viscosity of a
 dispersion medium and thereby hinder Brownian movement of an abrasive
 grain in order to diminish a sedimentation speed. As a thickener, there
 has been known bentonite.
 However, there are many problems to be solved for a nonaqueous cutting
 liquid.
 First of all, organic solvents which have widely been known as a dispersion
 medium for a conventional nonaqueous cutting liquid are strong in smell
 and have inflammability according to a kind thereof. Hence the organic
 solvents have causes to deteriorate a working environment.
 An intermediate product which has been obtained by cutting with a cutting
 oil, as described above, requires cleaning with an organic solvent capable
 of eliminating residue of the cutting oil on the product. However, since
 dichloroethane, for example, which has well been used in cleaning a
 semiconductor wafer is designated as a material to deplete the ozone layer
 by the Government, a usage quantity of the compound has to be decreased
 toward the perfect disuse state hereinafter, but economy and cleaning
 ability of alternatives are still short of target levels in the current
 state.
 The method (a) in which a dispersing agent is added has a problem that
 precipitate is formed as a hard cake.
 Abrasive grains which are increased in dispersibility by addition of a
 dispersing agent have, for certain, a slow sedimentation speed but are
 compressed under a load which exceeds a repulsive force while being put
 into close contact to each other in the course of sedimentation to form a
 hard cake. Once a hard cake is formed, it is hard to be again dispersed
 into a state same as the original one. Accordingly, if such a cutting
 liquid which has produced precipitate is tried to recycle after stirring
 for a long time, the cutting liquid in reuse as a result is in a state of
 a low concentration of abrasive grains, which decreases cutting ability.
 Besides, there also arise other problems that piping of a supply system of
 the cutting liquid is clogged, a tool for pulverization of a hard cake is
 worn at an earlier stage or the like.
 If the mass of each of abrasive grains is large and a repulsive force
 therebetween is small, a problem of formation of a hard cake is
 eliminated. The reason why is that abrasive grains electrically bond each
 other with multivalent ions, which are mainly existent in the dispersion
 medium, interposed therebetween and as a result, multipored, soft
 flocculates are formed, so that relatively soft precipitate (soft cake) is
 formed over time. If the precipitate is of a soft cake, redispersion is
 easy to be effected.
 However, since abrasive grains in a dispersion medium are hard to be kept
 in the primary particle state and in addition, a sedimentation speed of
 flocculates in the dispersion medium is fast, a distribution of abrasive
 grain concentration in the cutting liquid is apt to be uneven and thus
 cutting ability is easy to be unstable.
 For this reason, a cutting liquid with high dispersibility is eventually
 forced to be employed and a cutting liquid which is hard to be recycled is
 collected after the use and generally incinerated for disposal. In this
 incineration, much of carbon dioxide caused by combustion of an organic
 solvent is released, which is not preferable from the viewpoint of
 prevention of global warming.
 On the other hand, the method (b) in which a thickener is added has a
 guaranteed effect, on the assumption that a viscosity of a cutting liquid
 is unchanged, whereas the viscosity of a cutting liquid is actually
 changed due to a variety of factors.
 A viscosity of a cutting liquid is generally increased if cutting chips are
 mixed into the liquid. Since abrasive grains cannot be supplied at a
 constant rate on a cutting surface of a work in a uniform manner as a
 viscosity increases, it is necessary for the cutting liquid to be replaced
 with a new one when a mixed amount of cutting chips is accumulated to 3 to
 4% by weight of the total of the cutting liquid. This replacement
 increases a waste amount of the cutting liquid, which in turn increases an
 amount of carbon dioxide produced by incineration of the cutting liquid
 waste.
 Viscosity of a nonaqueous cutting liquid is also increased as water is
 mixed into the liquid. Therefore, in order to prevent water from mixing,
 there has been a tight restriction imposed on a cleaning operation of
 wafers and a mounting base for ingots in a wire saw machine. That is,
 since a cleaning liquid has to be an organic solvent in a system in which
 a nonaqueous cutting liquid is employed, there is a requirement that
 cleaning is operated with an independent tank filled with a cleaning
 liquid, different from a cutting liquid tank. Hence, an installment area
 for cutting facilities is increased and besides, the usage amount of an
 organic solvent is also increased, which causes not only a working
 environment but a global environment to be further deteriorated.
 To the contrary, when a molecular structure of a dispersing agent is broken
 through disconnection of an atomic bond in a molecule, viscosity of the
 nonaqueous cutting liquid is decreased and a cutting ability becomes
 unstable.
 As described above, when a nonaqueous cutting liquid is employed, it is
 very difficult to establish compatibility between achievement of high
 dispersibility of abrasive grains which is required for maintenance of a
 cutting ability and prevention of a hard cake from forming which is
 required for improvement on recyclability of the cutting liquid and
 maintainability of the facilities, while suppressing an impact on a
 working environment and a global environment.
 Therefore, the present invention, in order to solve the problems, has an
 object to propose a new aqueous composition which constitutes a base for
 an aqueous cutting liquid and provide an aqueous cutting liquid using the
 composition, producing processes for the composition and the cutting
 liquid and a cutting method using the cutting liquid.
 DISCLOSURE OF INVENTION
 An aqueous composition of the present invention is proposed in order to
 achieve the above described object, in which a polyhydric alcohol with a
 relatively low molecular weight, which is almost unharmful to human health
 and free of smell, and which is excellent in biodegradability and easy to
 be treated by an activated sludge process is used as a major dispersion
 medium, in which a quantity of water whereby it is made noninflammable is
 included, and in the dispersion medium of which a silicic acid colloid is
 dispersed in a stable manner. As a polyhydric alcohol described above, a
 hydrophilic polyhydric alcohol compound and a lipophilic polyhydric
 alcohol compound are simultaneously used.
 An aqueous cutting liquid of the present invention is a disperse system
 which is prepared by adding abrasive grains to the aqueous composition so
 as to be dispersed together with a silicic acid colloid in a stable manner
 therein. When such an aqueous cutting liquid is used, not only can
 dispersibility of abrasive grains be improved, but since sedimentation of
 abrasive grains progresses while colloidal particles of a silicic acid are
 interposed between abrasive grains, the precipitate is not formed as a
 hard cake even in the course of sedimentation of the abrasive grains over
 time, and therefore the precipitate can again be dispersed with ease.
 In order to produce such an aqueous composition of the present invention, a
 first liquid, which is a mixture of water, a hydrophilic polyhydric
 alcohol compound and a silicate, and in which a silicic acid is produced
 by a reaction, is prepared and the first liquid is mixed into a second
 liquid mainly composed of a lipophilic polyhydric alcohol compound, so
 that the silicic acid in a free state is stabilized as colloidal particles
 after the mixing.
 In order to produce an aqueous cutting liquid, an aqueous composition
 obtained as described above, is added with abrasive grains. The aqueous
 cutting liquid is preferably used in cutting a work while the work and
 cutting means are kept in dynamic contact to each other.

BEST MODE FOR PRACTICING THE INVENTION
 The present invention will further be described below. An aqueous
 composition of the present invention has as a dominating feature that
 silicic acid colloid particles in a dispersing medium are stabilized in an
 optimal balance between a hydrophilic polyhydric alcohol compound and a
 lipophilic polyhydric alcohol compound. A hydrophilic polyhydric alcohol
 compound of the present invention denotes any of a hydrophilic polyhydric
 alcohol and its derivatives. A lipophilic polyhydric alcohol compound of
 the present invention denotes any of a lipophilic polyhydric alcohol, and
 its derivatives or polymers of hydrophilic polyhydric alcohols.
 A hydrophilic polyhydric alcohol compound plays a role as a catalyst
 whereby silicic acid is produced from a silicate. As an example, a process
 in which a metasilicic acid is produced from a potassium metasilicate by
 the action of ethylene glycol is shown in the following equation (i).
 ##STR1##
 A potassium salt of ethylene glycol which is a byproduct is reproduced as
 ethylene glycol through ion exchange with water in the environs. The
 process is shown in the following equation (ii).
 ##STR2##
 A composition in which reaction products from the equations (i) and (ii)
 coexist show a gel-like appearance in the beginning, but as time elapses
 while being left, the gel state is gradually converted into a jelly state
 when water contents in compositions are very small. However, when a water
 content in a composition is large, the gel state is not converted into a
 jelly state. Judging from this phenomenon, formation of a jelly is
 considered to be caused by formation of disilicic acid or a higher polymer
 of silicic acid through dehydration/condensation. A producing process of
 disilicic acid is shown in the following equation (iii).
 ##STR3##
 When, for example, a composition is mixed with abrasive grains to prepare a
 cutting liquid for use, new abrasive grains cannot be supplied to a
 cutting surface in a smooth manner if the composition assumes a jelly
 state in this way, which decreases the cutting ability of the cutting
 liquid. Accordingly, it is required that the composition contains an
 amount of water. However, if water is too much, silicic acid colloid
 particles are perfectly ionized to be flocculated and precipitated, and
 cannot contribute to dispersion of abrasive grains.
 In this situation, what plays a role to prevent conversion to the jelly
 state from occurring is a lipophilic polyhydric alcohol compound. By
 adding a proper amount of a lipophilic polyhydric alcohol compound into a
 dispersion medium, a solubility of the metasilicic acid in water is
 decreased and contribution to stabilization of colloidal particles of
 silicic acid is effected without any ionization of the particles.
 At this point, part of the lipophilic polyhydric alcohol compound can be
 considered to work as a catalyst for production of metasilicic acid from
 potassium metasilicate in the same way as a hydrophilic polyhydric alcohol
 compound, but it is an ion exchange action by water in the environs that
 mainly produces metasilicic acid from potassium metasilicate in an
 environment strong in lipophilicity. This process is shown in the
 following equation (iv).
 ##STR4##
 However, if lipophilicity in the environs is too strong at this point,
 metasilicic acid and its potassium salt react with each other to form fine
 particles of silicon oxide. This process is shown in the following
 equation (v).
 ##STR5##
 That is, silicic acid which has once been produced cannot be retained with
 its form as produced but converted into silicon oxide (SiO.sub.2) which is
 precipitated. Accordingly, in the present invention, a balance in content
 between a hydrophilic polyhydric alcohol compound and a lipophilic
 polyhydric alcohol compound is especially important. A content of a
 lipophilic polyhydric alcohol compound is preferably selected more than
 that of a hydrophilic polyhydric alcohol compound by a factor almost in
 the range of 2.5 to 20.0.
 As a hydrophilic polyhydric alcohol compound used in the present invention,
 there can be named: ethylene glycol and glycerol, and ester derivatives
 and ether derivatives thereof. These compounds each are a compound almost
 with the number of carbon atoms of 2 to 6 in the principal chain and may
 be used singly or in combination.
 As a lipophilic polyhydric alcohol compound used in the present invention,
 there can be named: propylene glycol, and an ester derivative and an ether
 derivative thereof. These compounds each are a compound almost with the
 number of carbon atoms of 2 to 6 in the principal chain and may be used
 singly or in combination.
 The above compounds have no smell and are also of no harm to a human body.
 Since the above compounds each have a comparatively small molecular weight
 and excellent in biodegradability, the compounds can sufficiently be
 decomposed even by activated sludge which is used in ordinary polluted
 water disposal facilities. Therefore, there are no anxieties about
 necessity for an incinerator and occurrence of carbon dioxide in company
 with operation of the incinerator.
 A lipophilic polyhydric alcohol compound as described above may be a
 polymer such as a polyethylene glycol. However, when a polymer is used, it
 is required to be a liquid in room temperature and, for example, a
 polyethylene glycol with a degree of polymerization n=200 to 400 can be
 used. However, a waste treatment by activated sludge or adsorption of
 activated charcoal becomes hard to operate.
 In an aqueous composition of the present invention, it is especially
 preferred that a water content in a dispersion medium is 5% by weight or
 more and less than 50% by weight. In other words, this means that the sum
 of contents of a hydrophilic polyhydric alcohol compound and a lipophilic
 polyhydric alcohol compound in a dispersion medium is set in the range of
 50 to 95% by weight. When a water content is less than 5% by weight, there
 arise problems that a composition is converted into a jelly state or
 sufficient noninflammability and a proper cooling power cannot be
 provided. On the other hand, when a water content exceeds 50% by weight,
 all colloidal particles of silicic acid are ionized and flocculated and,
 for example, when the composition is added with abrasive grains and is
 used as an aqueous cutting liquid, dispersibility of abrasive grains is
 greatly reduced. That is, a water content is required to be selected so
 that it is short of perfect ionization of the colloidal particles of
 silicic acid, but sufficient to prevent silicic acid from gelation.
 A more preferred range of a water content is 10% by weight or more and less
 than 40% by weight.
 A content of a silicate in an aqueous composition of the present invention
 is preferably almost 0.1% by weight or more and less than 10.0% by weight.
 When a content is less than 0.1% by weight, a sufficient amount of
 colloidal particles of silicic acid is not produced and when a content is
 in excess of 10.0% by weight, the aqueous composition is easy to be
 converted to a jelly state by polymerization of free silicic acid
 molecules.
 An aqueous composition of the present invention is preferably added with a
 carboxylic acid or its derivative as a pH adjuster. As a carboxylic acid,
 a carboxylic acid with an chelate effect and high biodegradability is
 preferred and there can be exemplified: lactic acid, citric acid, gluconic
 acid and malic acid. As a derivative thereof, an alkali metal salt can
 typically be used. A preferable pH range is in the range of 5.0 to 12.0.
 When a pH is lower than 5.0, stable dispersibility of a silicic acid
 colloid which is produced cannot be attained and when a pH is higher than
 12.0, a silicic colloid is soluble and cannot hold a colloidal state. In
 any case, dispersibility of abrasive grains is deteriorated when an
 aqueous composition is used as a base for an aqueous cutting liquid and
 therefore, it is hard to prevent a hard cake of sediment from being
 formed.
 Besides, an aqueous composition may be added with fat and oil, a fatty acid
 or an ester as a lubricant according to a necessity. At this point, an
 additive amount of a lubricant is roughly limited to an amount up to 30.0%
 by weight.
 Besides, in order to raise a lubrication effect by a lubricant, a
 surfactant may be added almost up to 15% by weight.
 In order to produce such an aqueous composition of the present invention, a
 first liquid in which water, at least one of a hydrophilic polyhydric
 alcohol and its derivatives and a silicate are mixed is prepared. In the
 first liquid, silicic acid is produced from the silicate by a catalytic
 action of the hydrophilic polyhydric alcohol as shown in the above
 described equation (i).
 Then, the first liquid is mixed with a second liquid including at least one
 of a lipophilic polyhydric alcohol and its derivatives as a major
 component.
 When the above described aqueous composition is added with abrasive grains,
 an aqueous cutting liquid can be produced in which abrasive grains and a
 silicic acid colloid are both dispersed in a stable manner.
 Abrasive grains are added into an aqueous composition in the range of 1.0
 to 1.5 times that of the aqueous composition in weight. Abrasive grains
 are selected from the group consisting of corundum powder, emery, quartz
 sand, black silicon carbide, green silicon carbide, and the like, which
 are well known, according to a kind of application. Green silicon carbide
 is especially suitable for cutting of a semiconductor ingot.
 An aqueous cutting liquid of the present invention can widely be applied to
 cutting methods for cutting a work through dynamic contact between the
 work and cutting means in the presence of the aqueous cutting liquid.
 Especially, when an aqueous cutting liquid of the present invention is used
 in cutting a semiconductor ingot using cutting means such as a wire saw, a
 band saw or the like, a high precision cutting can be performed with ease.
 However, there is no specific limitation to the cutting means but a
 multiwire saw and a multiband saw, which are respectively composed of a
 plurality of wires and bands, and the like may be used; any of cutting
 means can be employed as far as cutting means uses loose abrasive grains.
 Below, concrete examples of the present invention will be described.
 EXAMPLE 1
 In this example, preparation of an aqueous composition of the present
 invention will be described.
 First, the first and second liquids described below were prepared.

&lt;The first liquid&gt;
 purified water 75.0% by weight
 ethylene glycol 8.5% by weight
 potassium silicate 16.5% by weight
 &lt;The second liquid&gt;
 propylene glycol 100% by weight
 Free silicic acid is produced in the first liquid.
 Then, the first liquid (24.0% by weight) was added to the second liquid
 (75.0% by weight) at 25.degree. C. In this step, by the presence of
 propylene glycol which is a lipophilic polyhydric alcohol and reduction in
 water content in a relative sense, free silicic acid already produced in
 the first liquid formed colloidal particles in a stable dispersion state.
 Thereafter, citric acid (1.0% by weight) as a carboxylic acid for adjusting
 a pH value was added to the mixture so that a pH value was adjusted to be
 6.5 and an aqueous composition was thus obtained.
 Thus obtained aqueous composition was free of smell.
 A water content of the above aqueous composition was finally 18.0% by
 weight and non-inflammable (boils at 123.degree. C.). Major other
 properties were as follows: a viscosity of 17.5 mPa.multidot.s (a B type
 viscometer made by Tokyo Keiki Co.), a specific gravity of 1.049, a
 surface tension of 35.9 mN/m, a COD (chemical oxygen demand) of a 1%
 aqueous solution of 6700 mg/l and a coefficient of friction of 0.110.
 The aqueous composition as thus prepared can be used with no additional
 adjustment, as a coolant for cutting by an inner diameter saw slicing
 machine, an outer diameter saw slicing machine and the like.
 EXAMPLE 2
 In the example, an aqueous cutting liquid was prepared by adding abrasive
 grains to the above described aqueous composition and its fundamental
 properties were studied.
 First, a mixing ratio of the first and second liquids which are described
 in the example 1 was changed and thereby 8 kinds of aqueous compositions
 whose water contents were ranged from 13 to 48% by weight.
 Then, three kinds of green silicon carbide with different grain sizes were
 mixed into each set of the eight kinds of aqueous compositions on a equal
 weight basis to prepare aqueous cutting liquids: the three kinds of green
 silicon carbide are GC#600 (average grain size of 20.0.+-.1.5 .mu.m),
 GC#800 (average grain size of 14.0.+-.1.0 .mu.m) and GC#1000 (average
 grain size of 11.5.+-.1.0 .mu.m) according to the nomenclature by JIS.
 Theses aqueous cutting liquids were all free of smell and noninflammable.
 Sedimentation speeds of the abrasive grains in the aqueous cutting liquids
 were slower as a water content was decreased, whereas the speeds were
 faster as a water content was increased. In any case of the aqueous
 cutting liquids, no hard cake of the abrasive grains was formed after
 sedimentation and deposition.
 Here, terms are defined; a aqueous cutting liquid which has a nature that,
 when the cutting liquid is left stationary for 8 hours, an upper surface
 of a precipitate layer of the abrasive grains remains at a height 90% or
 more of that of the free surface of the cutting liquid, is called of a
 nonsedimentation type and a cutting aqueous liquid which has a nature
 that, when the cutting liquid is left stationary for 24 hours, an upper
 surface of a precipitate layer of the abrasive grains remains at a height
 60% or less of that of the free surface of the cutting liquid, is called
 of a sedimentation type. An aqueous cutting liquid of the present
 invention has preferably an intermediate characteristic of the
 nonsedimentation and sedimentation types.
 In order to attain such an intermediate characteristic, it has been found
 that a water content is preferably 30% by weight or less. In such an
 aqueous cutting liquid, an upper surface of a precipitate layer of the
 abrasive grains after being left stationary for an 8 hour remained at a
 height 80 to 90% of that of the free surface of the cutting liquid and an
 upper surface of a precipitate layer of the abrasive grains after being
 left stationary for a 24 hour remained at a height 65 to 75% of that of
 the free surface of the cutting liquid.
 The reason why an aqueous cutting liquid of the present invention can
 retain a dispersion state of abrasive grains for a longer time than a
 conventional sedimentation type though an aqueous composition as a
 dispersion medium has a low viscosity is that the abrasive grains show an
 anionic property in the dispersion medium, while silicic acid colloidal
 particles are suspended in the dispersion medium in a state in which the
 surface of each of the silicic acid colloidal particles is also surrounded
 by a cloud made up of anionic ions (an electric double layer).
 A state of this disperse system is shown in FIG. 1. In this system, there
 are repulsive forces (zeta potential) caused by electrical charges of one
 type between abrasive grains G with electrical charges caused by anions
 surrounding them; between silicic acid colloidal particles P suspended in
 the dispersion medium M; and between a abrasive grain G and a silicic acid
 colloidal particle P in the presence of anions produced by dissociation
 accompanied with ionization in the dispersion medium M and dispersion of
 abrasive grains G is thus accelerated.
 These repulsive forces between electrical charges are retained to work in
 the precipitate. That is, adjacent silicic acid colloidal particles P
 exert repulsive forces, since a surface electrical charge density of each
 is large, so as to keep a distance therebetween all time, as shown in FIG.
 2. Besides, the repulsive forces between electrical charges becomes
 conspicuous in reproducibility and sustainability by actions of physical
 stimuli such as flow, vibration or the like and a kind of spatial matrix
 structure is formed with silicic acid colloidal particles P in the
 precipitate. Abrasive grains are separately dispersed in an incorporated
 manner in the matrix.
 However, since an aqueous cutting liquid of the present invention forms
 precipitate in a faster way than a conventional nonsedimentation type
 cutting liquid, the abrasive grains, in a practical aspect, can be
 recycled by solid-liquid separation through a natural sedimentation
 method. Therefore, there is a merit that a construction of an apparatus
 for solid-liquid separation is simple.
 In addition, in the precipitate which is obtained as a result of keeping
 the aqueous cutting liquid stationary, abrasive grains G, as shown in FIG.
 2, are not put into close contact to one another due to interposition of
 matrices of silicic acid colloidal particles P between the abrasive grains
 G and therefore, there are no chance to form a hard cake. Actually, even
 after the aqueous cutting liquid was left at room temperature for 7 days,
 precipitate was able to be again dispersed with ease.
 Incidentally, in a conventional cutting liquid, it has been experienced
 that as the liquid is more excellent in abrasive grain dispersibility,
 formation of a hard cake is conspicuously more progressive. Besides, since
 the abrasive grains cannot be recovered by a natural sedimentation method
 with ease, centrifugation has been forced to be employed for separation.
 The centrifugation has been accompanied with a vicious cycle in which
 precipitate is coagulated to a more solidified state.
 Then, viscosities of thus obtained aqueous cutting liquids were measured
 using two kinds of viscometers: a B type viscometer made by Tokyo Keiki
 Co. and a VTO4 type viscometer made by Rion Co., Ltd. A B type viscometer
 obtains a viscosity of a sample liquid from measurement of a stress
 imposed on a disk type rotor which is rotated in the sample liquid and a
 VT04 viscometer measures a viscosity of a sample liquid from measurement
 of a stress imposed on a cylinder type rotor which is rotated in the
 sample liquid. There are differences between both in measurable range and
 precision due to differences in a gyration radius of a rotor, a shape
 thereof and revolution number thereof.
 Measurement results by the B type viscometer and the VT04 are respectively
 shown in FIGS. 3 and 4.
 The abscissas of the graphs are each assigned in two ways: a water content
 in % by weight of an aqueous composition and an increment or a decrement
 thereof from a standard composition. The term standard composition denotes
 an aqueous composition which is prepared in the example 1: a water content
 of 18.0% by weight.
 On the other hand, the ordinates are each assigned to a viscosity in
 mPa.multidot.s.
 In the graphs, a solid line indicates measurement results of an aqueous
 cutting liquid including GC#600, a single dot & dash line GC#800 and a
 broken line GC#1000.
 As seen from the graphs, an aqueous cutting liquid of the present invention
 shows decrease in viscosity with increase in water content as a general
 trend, but a viscosity suitable for a practical use is still retained over
 the wide range of water contents. Especially, when abrasive grains with an
 average grain size of the order in the range of 20 to 10 .mu.m are used, a
 viscosity can be retained on the order in the range of 1/3 to 1/4 times
 the maximal viscosity value even if a water content is changed by a wide
 range up to 35% by weight.
 It is very advantageous in a practical aspect such as in cutting of a
 semiconductor ingot that when abrasive grains with a comparatively small
 size as in the case of GC#1000 is used, stability of a viscosity, as
 described above, can also be obtained. When abrasive grains with a small
 grain size are used, a cutting speed is slow as compared with the case
 where large abrasive grains are used, but a kerf loss of a work can be
 decreased. Hence, such small abrasive grains are suitable for cutting an
 expensive material such as a semiconductor ingot. Therefore, stability
 improvement of a viscosity of a aqueous cutting liquid including small
 abrasive grains contributes to not only increase in and stabilization of a
 processing quality but improvement on economy. In addition, frequency of
 change of a cutting liquid is also decreased as a result.
 That an aqueous cutting liquid of the present invention is hard to cause a
 change in viscosity according to a change in water content is also
 advantageous in the sense of enabling water cleaning of a cutting machine.
 When a semiconductor ingot is cut by a wire saw using a nonaqueous cutting
 liquid, for example, cleaning operations of a wafer and a mount base for
 an ingot of a wire saw have heretofore had to be performed outside the
 body of the saw in order to avoid a rapid increase in viscosity of the
 nonaqeous cutting liquid caused by mixing of wafer thereinto.
 However, if an aqueous cutting liquid of the present invention is used, a
 viscosity of the cutting liquid is retained near an original value in a
 stable manner, even when more or less of water is mixed thereinto and
 therefore, cleaning operations can be carried out within the wire saw
 machine, which enables great improvement of working efficiency and
 besides, decrease in floor space of the facilities to be realized.
 EXAMPLE 3
 In the example, a change in viscosity when silicon powder as a model of
 cutting chips is mixed into an aqueous cutting liquid of the present
 invention was investigated.
 Aqueous cutting liquids in use were liquids which were prepared in such a
 manner that aqueous compositions each of a standard in which three kinds
 of abrasive grains: GC#600, GC#800 and GC#1000 were respectively included
 were added with silicon powder at proportions in the range of 0 to 30% by
 weight. The silicon powder was prepared by screening silicon powder
 obtained by pulverizing ordinary silicon wafers with a stainless filter of
 a mesh number 20, whose particle size through the mesh was 75 .mu.m or
 less.
 Measurement results by the B type viscometer and the VT04 viscometer are
 respectively shown in FIGS. 5 and 6. The abscissas of the graphs are
 assigned to a silicon mixing amount in % by weight and the ordinates
 thereof are assigned to a viscosity in mPa.multidot.s. In the graphs,
 solid lines, single dot & chain lines and broken lines respectively
 indicate measurement results of aqueous cutting liquids including GC#600,
 GC#800 and GC#1000.
 In a nonaqueous cutting liquid in the past, a viscosity was generally
 increased by a great margin as large as 150 to 200%, when cutting chips of
 a work were mixed thereinto to a proportion of 3 to 4% by weight. However,
 increase in a viscosity of an aqueous cutting liquid of the present
 invention is suppressed to a level of 70 to 130% as long as an amount of
 mixed water is up to 10 to 15% by weight, which, it has been found,
 enables the aqueous cutting liquid for practical use to be realized with
 no problem.
 In the meantime, a viscosity of an aqueous cutting liquid whose viscosity
 is increased by mixing of cutting chips can again be decreased by adding
 purified water.
 EXAMPLE 4
 In the example, a silicon ingot was actually cut by a wire saw using an
 aqueous cutting liquid of the present invention and a cutting quality was
 evaluated.
 First, an aqueous cutting liquid A described below was prepared.

&lt;Aqueous cutting liquid A&gt;
 dispersing agent the aqueous composition prepared
 in the example 1
 abrasive grains GC #600, a weight equal to the
 dispersing agent
 specific gravity 1.5 to 1.6
 viscosity 70 .+-. 10 mPa .multidot. s
 Then, the aqueous cutting liquid A was used and wafers were prepared by
 slicing a silicon ingot with a diameter of 8 inches and a length of 300
 mm. Processing conditions were as follows:

&lt;Processing conditions A&gt;
 wire a music wire, a diameter of
 180 .mu.m
 wire average linear speed 500 m/min
 average cutting speed 500 .mu.m/min
 supply of a cutting liquid 60 to 100 l/min
 thickness of a wafer 860 .mu.m
 kerf loss 240 .mu.m
 pitch 1100 .mu.m
 number of wafers 272 pieces/ingot
 A bow, a wafer to wafer variation in center thickness and a taper were
 evaluated on obtained wafers.
 In this case, the term bow means a quantity in .mu.m which is defined as
 the sum of absolute values of maximal displacements in both ways on the
 plus side and the minus side which are calculated by using the least
 square method from measurements at points on a wafer surface with respect
 to a reference plane, while the wafer is left in a condition of no suction
 fixing.
 The term taper means a quantity in .mu.m which is defined as a difference
 between the maximum thickness and minimum thickness among five points
 comprised of one point 6 mm inside an orientation flat, three points
 located 6 mm inside the periphery being angularly spaced away from the one
 point along the periphery at an angle interval of 90 degrees about the
 center, and the center of a wafer. Results are compiled in Table 1.

Comparative Comparative
 Example 4 Example 5 Example 1 Example 2
 Bow (.mu.m) 15 20 20 30
 Variation of .+-.15 .+-.10 .+-.25 .+-.20
 thickness (.mu.m)
 taper (.mu.m) 20 15 30 25
 EXAMPLE 5
 In the example, a silicon ingot was cut in the same way as in the example 4
 with exception that the aqueous cutting liquid A of the example 4 was
 replaced with an aqueous cutting liquid B in which a grain size was
 smaller than that in the example 4.
 Specifications of the aqueous cutting liquid B were as follows:

&lt;Aqueous cutting liquid B&gt;
 dispersing agent the aqueous cutting liquid used in
 the example 1
 abrasive grains GC #800, a weight equal to the
 dispersing agent
 specific gravity 1.5 to 1.6
 viscosity 80 .+-. 10 mPa .multidot. s
 Processing conditions were as follows:

&lt;Processing conditions B&gt;
 wire music wire, a diameter of
 160 .mu.m
 wire average linear speed 500 m/min
 average cutting speed 400 .mu.m/min
 supply of a cutting liquid 60 to 100 l/min
 thickness of a wafer 860 .mu.m
 kerf loss 202 .mu.m
 pitch 1062 .mu.m
 number of wafers 282 pieces/ingot
 Cutting qualities of thus obtained wafers are compiled in the table 1.
 COMATIVE EXAMPLE 1
 As a comparative example of the example 4, a silicon ingot was cut
 according to the processing conditions A using the following aqueous
 cutting liquid A instead of the aqueous cutting liquid A.

&lt;Nonaqueous cutting liquid A&gt;
 dispersing agent a mineral oil 98% by weight as a
 dispersing agent with a surfactant
 2% by weight
 abrasive grains GC #600, a weight equal to the
 dispersing agent
 specific gravity 1.5 to 1.6
 viscosity 150 .+-. 50 mPa .multidot. s
 Cutting qualities of thus obtained wafers are compiled in the table 1.
 COMATIVE EXAMPLE 2
 As a comparative example of the example 5, a silicon ingot was cut in the
 same conditions as the example 5 with the exception that the following
 nonaqueous cutting liquid B was used instead of the aqueous cutting liquid
 B.

&lt;Nonaqueous cutting liquid B&gt;
 dispersing agent same as the nonaqueous cutting
 liquid A
 abrasive grains GC #800, a weight equal to the
 dispersing agent
 specific gravity 1.5 to 1.6
 viscosity 200 .+-. 50 mPa .multidot. s
 Cutting qualities of thus obtained wafers are compiled in the table 1.
 When looking at the results of the examples 4, 5 and the comparative
 examples 1, 2, more stable performances are clearly obtained in the
 examples than in the comparative examples in any of the items of a bow, a
 thickness variation and a taper. This is because increases in viscosity of
 the aqueous cutting liquids caused by mixing of silicon cutting chips of
 the examples 4, 5 were less than that of the nonaqueous cutting liquids of
 the comparative examples 1, 2.
 In the examples 4, 5, piping for cleaning water was laid down within the
 body of a wire saw machine, and wafers and an ingot mount base were able
 to be water-cleaned within the machine immediately after cutting. The
 reason why is that an aqueous cutting liquid of the present invention is
 less in increase in viscosity caused by mixing of water.
 In this way, in the examples 4, 5, change frequency of a cutting liquid was
 decreased to 1/4 to 1/5 times that of a conventional cutting liquid.
 On the other hand, in the comparative examples 1, 2, wafers after the
 cutting were required to be cleaned with an organic solvent or an alkali
 solution outside the machine. In addition, there was an oil smell.
 While the present invention is described based on the five examples, the
 present invention is not limited to the descriptions of the examples at
 all, but there are available various possibilities in regard to changes,
 selections and combinations, in a proper manner, of details of the
 examples such as components of an aqueous composition and their ratios,
 components of an aqueous cutting liquid and their ratios, kinds of work
 and processing conditions.
 Industrial Applicability
 As clearly understood from the above description, an aqueous composition of
 the present invention is constituted based on a totally new concept of a
 dispersion medium, which is comparatively of a low viscosity, and which is
 dispersed with silicic acid colloidal particles having a high
 dispersibility therein. The aqueous composition is aqueous and therefore
 does not show inflammablility. In addition, since a polyhydric alcohol
 compound which is included is free of smell, of a comparatively small
 molecular weight and excellent in biodegradability, a working environment
 is not deteriorated when the aqueous composition is used and no impact is
 given to a global environment when being wasted, either.
 Since an aqueous cutting liquid of the present invention which is composed
 of an aqueous composition and abrasive grains dispersed therein is of a
 low viscosity in an intrinsic sense, a change in viscosity caused by
 mixing of water and cutting chips is mild and a long life time in
 performance as a cutting liquid can be enjoyed. Recovery of abrasive
 grains by a natural sedimentation method is possible. If a precipitate
 layer is formed as time elapses, the precipitate layer is prevented from
 being formed as a hard cake because of interposition of silicic acid
 colloidal particles. Hence, the precipitated abrasive grains can again be
 dispersed with ease. This is very preferable from the viewpoints of
 resource conservation and reduction in maintenance cost.
 A producing process of an aqueous composition of the present invention is
 that water, a hydrophilic polyhydric alcohol compound and a silicate are
 mixed with one another to prepare a first liquid, while silicic acid is
 produced in a mixture, and then the mixture is further mixed into a second
 liquid mainly composed of a lipophilic polyhydric alcohol compound, so
 that silicic acid is stabilized as a colloid. Therefore, the aqueous
 composition can be produced with ease though any specific, large-scaled
 facilities are not required.
 In addition, an aqueous cutting liquid can be produced with ease only by
 mixing abrasive grains into the aqueous composition.
 Furthermore, according to a cutting method in which such an aqueous cutting
 liquid is employed, cutting can be performed with the resulted stable
 processing quality while frequency of change of the aqueous cutting liquid
 is decreased and thereby, economy, reliability and environment
 conservability in cutting operation can be improved.