Liquid developer for electrostatic photography

A liquid developer for use in electrostatic photography comprises toner particles, each containing a resin and a colorant dispersed in a carrier liquid. The carrier liquid comprises at least one ether compound derived from ethylene glycol or propylene group and represented by the following general formula EQU R.sub.1 --O(C.sub.n H.sub.2n O).sub.x R.sub.2 wherein R.sub.1 and R.sub.2 may be the same or different and represent an alkyl group or an aryl group, n is an integer of 2 or 3, and x is an integer of 1 to 3. The ether compound is present in the carrier liquid in the range of from 5 to 100 wt %.

BACKGROUND OF THE INVENTION 
1. Field of The Invention 
This invention relates to a liquid developer for electrostatic photography 
wherein ether compounds are used as a carrier liquid. 
2. Description of The Prior Art 
The wet developing system in electrophotography is generally carried out by 
a process which comprises subjecting a photosensitive material to charging 
and imagewise exposure to form an electrostatic latent image thereon, 
developing the electrostatic latent image with a liquid developer which 
consists of a dispersion of toner particles mainly composed of a resin and 
a colorant in aliphatic hydrocarbons, transferring the resulting toner 
image onto a transfer paper sheet, and fixing the image to form a final 
image. 
If a photosensitive paper or film having a photoconductive material, such 
as zinc oxide, coated thereon is used in the above process, it is possible 
to omit the transfer step and to directly fix the toner image on the 
photosensitive material after the development. In addition, the wet 
development is often used as a developing means such as of electrostatic 
recording systems wherein an electrostatic latent image is formed on a 
dielectric material through electric inputting without use of any 
photosensitive material. 
In the wet developing systems, a fine particle toner having a size of from 
sub-microns to several microns is dispersed, as set forth above, in a 
carrier liquid having a high electric resistivity, such as aliphatic 
hydrocarbons. The development of a latent image is based mainly on the 
electrophoretic principle. This eventually leads to the fact that images 
with a higher resolution than in dry developing systems making use of 
toner particles with a size of not smaller than several microns are likely 
to obtain. 
In the two references which Metcalfe reported at his initial stage, i.e. 
(K. A. Metcalfe, J. Sci. Instrum., 32, 74 (1955) and ibid., 33, 194 
(1956), it is stated that a great number of organic or inorganic pigments 
including carbon black, magnesium oxide and the like are usable as 
pigments of liquid developers and gasoline, kerosine, carbon tetrachloride 
and the like are usable as a carrier liquid. 
In Japanese Patent Publications issued at the time corresponding to the 
early stage of Metcalfe, there are stated the use of halogenated 
hydrocarbons as the carrier liquid (Japanese Patent Publication No. 
35-5511), and the use of polysiloxanes (Japanese Patent Publication No. 
36-14872) and ligroin and mixtures of these petroleum hydrocarbons 
(Japanese Patent Publication Nos. 38-22343 and 43-13519). 
Among patent publications which are directed to processes of making toners, 
there are a number of patent publications which deal with carrier liquids. 
Typical examples include Japanese Patent Publication Nos. 40-19186, 
45-14545 and 56-9189. The carrier liquids (which may also serve as a 
dispersion medium at the time of polymerization) set forth in these 
publications include aromatic hydrocarbons such as benzene, toluene, 
xylene and the like, esters, alcohols, and aliphatic hydrocarbons such as 
n-hexane, i-dodecane, Isoper H, G, L and V (Ekson Chem. Co., Ltd.) 
However, the hitherto proposed carrier liquids are mostly composed of 
organic solvents whose vapor pressure is high. This leads to the following 
problems: i) the vapor of carrier liquids discharged at the time of fixing 
is liable to cause environmental pollution; and ii) the vapor is very 
likely to cause ignition. 
To cope with the above problems, it may occur that in order to lower the 
vapor pressure of carrier liquids, petroleum solvents such as low vapor 
pressure hydrocarbons are used as the carrier liquid. If the molecular 
weight of hydrocarbons is increased so that the vapor pressure is lowered, 
the carrier liquid using such hydrocarbons is increased in viscosity, thus 
adversely influencing the developing speed. Moreover, since the melting 
point of the carrier liquid increases to the neighbourhood of room 
temperature, it becomes necessary to invariably heat the carrier liquid 
for use as a liquid developer. This is unfavorable from the standpoint of 
energy saving, thermal pollution and deterioration of the liquid 
developer. 
In Japanese Laid-open Patent Application No. 51-89428, there has been 
proposed the use, as the carrier liquid, of hydrocarbon solutions which 
have an electric resistivity of not lower than 10.sup.9 
.OMEGA..multidot.cm and a dielectric constant of not higher than 3.0. 
Hitherto proposed carrier liquids are predominantly composed of non-polar 
hydrocarbon solutions which have a high electric resistivity and a low 
dielectric constant. It is empirically known that if the electric 
resistivity of the carrier liquid is lower than an appropriate level, a 
latent image on a photosensitive material may be broken, or a bias leakage 
at the developing and transfer units may take place, not resulting in 
images of good quality. 
The liquid developers which contain non-polar carrier liquids having high 
electric resistivity and low dielectric constant are not always 
satisfactory with respect to the chargeability to toner and its stability 
in relation to time. More particularly, there arise the problems that the 
charge quantity of toner is reduced as time passes and that the quantity 
of a reverse polarity toner is increased. 
Thus, there have never been obtained any carrier liquids which are 
satisfactory for use in hitherto proposed liquid developers. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide a liquid developer 
which overcomes the above-stated problems or disadvantages and which 
enables one to reduce the amount of a carrier liquid to be discharged from 
copying machines or printers making use of the liquid developer. 
It is another object of the invention to provide a liquid developer making 
use of a liquid carrier which is unlikely to suffer the danger of fire and 
which has good charge characteristics and charge stability. 
It is a further object of the invention to provide a liquid developer whose 
carrier liquid is made of glycol diethers derived from ethylene glycol or 
propylene glycol whereby the carrier liquid has appropriate insulating 
properties, viscosity, solubility of a binder for toner, and low flow 
point. 
In order to obtain a liquid developer which ensures reduction in amount of 
a carrier liquid being discharged during the course of development and is 
thus substantially free of any ecological problem involved in the 
discharge, we have intensively studied carrier liquids. As a result, it 
has been found that when used as a carrier liquid, glycol diethers which 
are derived from ethylene glycol, propylene glycol, diethylene glycol, 
dipropylene glycol and the like have a low viscosity approximately equal 
to that of known carrier liquids and that the vapor of the carrier being 
generated can be significantly reduced in amount. In addition, the glycol 
diethers exhibit better charge characteristics and stability than known 
carrier liquids. 
According to the invention, there is provided a liquid developer for use in 
electrostatic photography which comprises toner particles, each containing 
a resin and a colorant dispersed in a carrier liquid, the carrier liquid 
comprising at least one ether compound of the following general formula 
EQU R.sub.1 --O(C.sub.n H.sub.2n O).sub.x --R.sub.2 
wherein R1 and R2 may be the same or different and represent an alkyl group 
or an aryl group, n is an integer of 2 or 3, and x is an integer of 1 to 3 
.

DETAILED DESCRIPTION AND EMBODIMENTS OF THE INVENTION 
In the liquid developer for electrostatic photography of the invention, the 
carrier liquid used to disperse toner particles made of resins and 
colorants therein is an ether compound of the above-indicated general 
formula. In the formula, the alkyl group represented by R.sub.1 and 
R.sub.2 may be a linear or branched alkyl group such as methyl, ethyl, 
propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl or the like, and 
a cycloalkyl group such as cyclopentyl, cyclohexyl or the like. The aryl 
group may be substituted or unsubstituted and includes, for example, an 
aryl group such as phenyl, tolyl, xylyl, naphthyl or the like, and an 
arylalkyl group such as benzyl, phenethyl or the like. 
These ether compounds have insulating properties, a viscosity, the 
solubility of a toner binder and a flow point, which are suitable for use 
as a carrier liquid of liquid developers. In addition, they are much lower 
in vapor pressure than known carrier liquids and is odorless. The reason 
for this is considered to result from the number of ether polar groups in 
the molecule chain (i.e. x+1 in the above formula) and the lengths of the 
hydrophobic groups R.sub.1 and R.sub.2 at both ends. 
The lengths of the hydrophobic groups are considered (i) to mitigate the 
interaction between polar groups, such as hydrogen bond, thereby lowering 
the viscosity of the carrier liquid, (ii) to raise the electric 
resistivity to an empirically usable extent, (iii) to increase affinity, 
for example, for olefinic binder resins, and (iv) to have interrelation 
with a vapor pressure within a certain range of the length. 
To this end, it is preferred to use one or more of ether compounds which 
have the total of carbon atoms of from 6 to 20 in the alkyl and/or aryl 
groups represented by R.sub.1 and R.sub.2. If the total carbon atoms in 
R.sub.1 and R.sub.2 are smaller in number than 6, the electric resistivity 
increased in excess and the solubility of olefinic binder resins is 
undesirably lowered. In addition, the vapor pressure may increase in 
excess. On the other hand, when the total of the carbon atoms exceeds 20, 
the viscosity of the resultant carrier liquid becomes higher than in a 
desired range, causing the developing speed of toner based on the 
electrophoretic force to be lowered. 
The number of the ether polar groups or the polar groups in the molecule is 
considered to influence the freezing point and the charge-imparting 
characteristic to toner. For instance, while linear hydrocarbons having a 
molecular weight substantially equal to that of the ether compounds of the 
invention are increased in freezing point up to the neighbourhood of room 
temperature as the molecular weight increases, the ether compounds have a 
remarkably lowered freezing point. Thus, the ether compounds 
satisfactorily function as a carrier liquid under environments of winter. 
The toner charge-imparting function is also improved over that of 
hydrocarbons having a similar molecular weight: i) the charge 
exchangeability between the toner and the carrier liquid is more promoted 
or stabilized; and ii) where a charge control agent such as a so-called 
charge director, is added, its dispersability and solubility can be 
appropriately controlled, thereby improving the charge stability of the 
developer. 
These specific characteristic features are considered to develop owing to 
the fact that since the ether compound has polar ether groups in the 
molecule chain, they can impart polarity to the carrier liquid. In this 
connection, the optimum number of glycol units in the molecule chain is in 
the range of from 1 to 3. This is because when the number of the units 
exceeds 3, the hydrophilicity of the developer system itself increases, 
resulting in an excessive increase of the electric conductivity of the 
carrier liquid. 
Specific examples of the ether compounds useful in the present invention 
are the following glycol diethers. 
Ethylene glycol diethers include ethylene glycol dipropyl ether, ethylene 
glycol dibutyl ether, ethylene glycol dipentyl ether, ethylene glycol 
dihexyl ether, ethylene glycol diheptyl ether, ethylene glycol dioctyl 
ether, ethylene glycol dinonyl ether, ethylene glycol didecyl ether, 
ethylene glycol diphenyl ether, ethylene glycol ditolyl ether, ethylene 
glycol dixylyl ether, ethylene glycol dinaphthyl ether, ethylene glycol 
dibenzyl ether, ethylene glycol butylhexyl ether, ethylene glycol 
2-ethylhexylamyl ether and the like. 
Diethylene glycol ethers include diethylene glycol dipropyl ether, 
diethylene glycol dibutyl ether, diethylene glycol dipentyl ether, 
diethylene glycol dihexyl ether, diethylene glycol diheptyl ether, 
diethylene glycol dioctyl ether, diethylene glycol dinonyl ether, 
diethylene glycol didecyl ether, diethylene glycol diphenyl ether, 
diethylene glycol ditolyl ether, diethylene glycol dixylyl ether, 
diethylene glycol dinaphthyl ether, diethylene glycol dibenzyl ether, 
diethylene glycol butylhexyl ether, diethylene glycol 2-ethylhexylamyl 
ether and the like. 
Similar triethylene glycol diethers may also be used. 
Propylene glycol diethers include propylene glycol dipropyl ether, 
propylene glycol dibutyl ether, propylene glycol dipentyl ether, propylene 
glycol dihexyl ether, propylene glycol diheptyl ether, propylene glycol 
dioctyl ether, propylene glycol dinonyl ether, propylene glycol didecyl 
ether, propylene glycol diphenyl ether, propylene glycol ditolyl ether, 
propylene glycol dixylyl ether, propylene glycol dinaphthyl ether, 
propylene glycol dibenzyl ether, propylene glycol butylhexyl ether, 
propylene glycol 2-ethylhexylamyl ether and the like. 
Dipropylene glycol diethers include dipropylene glycol dipropyl ether, 
dipropylene glycol dibutyl ether, dipropylene glycol dipentyl ether, 
dipropylene glycol dihexyl ether, dipropylene glycol diheptyl ether, 
dipropylene glycol dioctyl ether, dipropylene glycol dinonyl ether, 
dipropylene glycol didecyl ether, dipropylene glycol diphenyl ether, 
dipropylene glycol ditolyl ether, dipropylene glycol dixylyl ether, 
dipropylene glycol dinaphthyl ether, dipropylene glycol dibenzyl ether, 
dipropylene glycol butylhexyl ether, dipropylene glycol 2-ethylhexylamyl 
ether and the like. 
Similar tripropylene glycol diethers may also be used. 
The glycol diethers of the invention may be used singly or in combination 
with known carrier liquids. Examples of such known carrier liquids include 
branched aliphatic hydrocarbons commercially available under the 
designations of Isoper H, G, L, M, V and the like from Ekson Chem., Co., 
Ltd., and linear aliphatic hydrocarbons commercially available under the 
designations of Norper 14, 15, 16 and the like from Ekson Chem. Co., Ltd. 
Alternatively, waxy hydrocarbons having a relatively great molecular weight 
may also be used in combination, including n-undecane, n-dodecane, 
n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, 
n-octadecane, n-nonadecane and the like, and halogenated hydrocarbons 
thereof such as fluorocarbons. Still alternatively, silicone oils and 
modified silicone compounds may also be used for this purpose. 
The ether compounds of the invention can lower the vapor pressure of a 
liquid developer when mixed only in small amounts and can also lower the 
freezing point of paraffinic hydrocarbons having a relatively great 
molecular weight to an extent of from the neighborhood of room temperature 
to a range where no practical problem is involved. Additionally, the ether 
compounds are effective in improving charge characteristics. 
The amount of the ether compounds of the invention in the carrier liquid is 
generally in the range of from 5 to 100 wt %. If the amount is less than 5 
wt %, they do not satisfactorily serve to lower the freezing point of high 
molecular weight aliphatic hydrocarbons to be used in combination, or to 
lower the vapor pressure of paraffinic oils having a low molecular weight. 
The carrier liquid of the invention should preferably have an electric 
resistivity as high as not lower than 10.sup.10 .OMEGA..multidot.cm. If 
the resistivity is lower than 10.sup.10 .OMEGA..multidot.cm, charge on an 
electrostatic image carrier may be liable to leak. 
The resins for the toner used din the present invention may be polyolefins 
such as polyethylene, polypropylene and the like. Preferably, ethylene 
copolymers having polar groups are used including, for example, copolymers 
of an .alpha.,.beta.-ethylenically unsaturated acid selected from the 
group consisting of acrylic acid and methacrylic acid or its ester and 
ethylene, or ionomers of the copolymers which are ionically crosslinked. 
The process of preparing the copolymers of the type mentioned above is 
described in U.S. Pat. No. 3,264,272, issued to Ree, which is incorporated 
herein by reference. 
Alternatively, there may be used homopolymers of styrenes such as styrene, 
o, m, p-methylstyrene, .alpha.-methylstyrene, p-ethylstyrene, 
2,4-dimethylstyrene and the like, styrene-acrylate copolymers, or 
homopolymers or multi-component copolymers of other monomers. 
The acrylate components of the styrene-acrylate copolymers include, for 
example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl 
acrylate, iso-butyl acryiate, n-octyl acrylate, 2-ethylhexyl acrylate, 
lauryl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate 
and the like. Likewise, there may be used, instead of the acrylate 
component, methacrylates, .alpha.-methylene monocarboxylic esters such as 
dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and the 
like, betaine compounds of methacrylic acid and ammonium compounds 
thereof, and the like. 
Moreover, there may be used homopolymers of the above-indicated acrylates, 
homopolymers or copolymers with other monomers of perfluorooctyl 
(meth)acrylate, vinyl toluenesulfonic acid and its sodium acid, and vinyl 
pyridines and pyridinium salts thereof, polyamide resins based on dimer 
acids, and copolymers of dienes such as butadiene, isoprene and the like 
and vinyl monomers. In addition, polyesters and polyurethanes may be 
further used singly or in combination with the resins set out above. 
In the practice of the invention, the colorants which are dispersed in the 
resin may be any known organic or inorganic pigments or dyes. For 
instance, there may be mentioned C.I. Pigment Red 48:1, C.I. Pigment Red 
57:1, C.I. Pigment Red 122, C.I. Pigment Red 17, C.I. Pigment Yellow 97, 
C.I. Pigment Yellow 12, C.I. Pigment Blue 15:1, C.I. Pigment Blue 15:3, 
Lamp Black (C.I. No. 77266), Rose Bengal (C.I. No. 45432), carbon black, 
Nigrosine dye (C.I. No. 50415B), and mixtures thereof. Further, there may 
also be used metal oxides such as silica, aluminium oxide, magnetite, 
various ferrites, cupric oxide, nickel oxide, zinc oxide, zirconium oxide, 
titanium oxide, magnesium oxide and mixtures thereof. 
These colorants should be contained in the toner particles in an amount 
sufficient to form a visible image. Although depending on the toner 
particle size and the amount used for development, the amount is usually 
in the range of from 1 to 100 parts by weight per 100 parts by weight of 
the resin. 
For the preparation of the toner particles and the liquid developer, any 
known processes may be used. For instance, toners may be prepared 
according to the process set forth in the afore-indicated references of 
Metcalfe and various processes set out in Japanese Laid-open Patent 
Application Nos. 58-129438 and 58-152258 and also in U.S. Pat. No. 
4,794,651, to B. Landa et al, (issued on Dec. 27, 1988). 
For example, there is used a process which makes use of an appropriate 
device wherein the starting materials including the above-indicated resin, 
colorant and carrier liquid are dispersed and kneaded at temperatures at 
which the resin is plasticizable and the carrier liquid is not boiled, and 
which are lower than the decomposition temperature of the resin and/or 
colorant. More particularly, while utilizing the temperature dependence on 
the solubility of the resin in solvent, the resin and colorant are 
thermally melted in the carrier liquid by use of a planetary mixer or a 
kneader. The resultant melt is cooled under agitation to solidify and 
settle toner particles, thereby obtain a toner. 
In another process, the starting materials are placed in an appropriate 
container, such as an attritor or a heating vibration mill, e.g. a heating 
ball mill, into which granular media used for dispersion and kneading are 
charged. The container is kept at a preferable temperature ranging, for 
example, from 80.degree. to 160.degree. C., by which the materials are 
dispersed and kneaded. Examples of the granular media are those of steels 
such as stainless steels, carbon steels and the like, alumina, zirconia, 
silica and the like. 
For the preparation of a toner according to the above process, the starting 
materials which have become fluid are dispersed in the container by means 
of the granular media. Thereafter, while circulating cooling water or a 
coolant through an outer cooling jacket, the carrier liquid is cooled so 
that the resin containing the colorant therein is settled from the carrier 
liquid. It is important that the granular media be continuedly kept as 
dispersed during the course of and after the cooling, by which the toner 
particles are exerted with shear and/or impact forces from the media 
thereby rendering the particles finer in size. 
The finely divided toner obtained by the above processes should preferably 
have a volume mean size of not larger than 10 .mu.m, more preferably not 
larger than 5 .mu.m, when determined using a centrifugal settlement-type 
size distribution measuring device. If necessary, the particles may be 
shaped to have a configuration having a number of fibers thereon. The term 
"configuration having a number of fibers thereon" means toner particles 
which are shaped as having fibrous extensions, cirri and/or tentacles on 
the surfaces thereof. 
Another procedure of preparing a liquid developer comprises weighing a 
resin and a colorant at a given mixing ratio, thermally melting the resin, 
adding the colorant to the melt for dispersion and mixing, cooling the 
mixture, and dividing it by a mill such as a jet mill, a hammer mill, a 
turbo mill or the like to obtain fine particles. The thus obtained toner 
particles are dispersed in a carrier liquid. 
Alternatively, toners may be prepared by polymerization processes such as 
suspension polymerization, emulsion polymerization, dispersion 
polymerization and the like, or by coacervation, melt dispersion, emulsion 
coagulation and the like techniques, followed by dispersion in carrier 
liquids to obtain liquid developers. 
For the purposes of retaining the charge polarity of toner particles and 
uniformizing and stabilizing the charge quantity, charge control agents 
may be added to the carrier liquid or toner particles. The charge control 
agents may be those agents ordinarily used in wet developers and include 
lecithin, Basic Barium Petronate, Basic Sodium Petronate and Basic Calcium 
Petronate available from Vitoco Chemical Corp., oil-soluble petroleum 
sulfonate, alkylsuccinimides, and metallic soaps such as sodium 
dioctylsulfosuccinate, zirconium octanoate and the like. Besides, ionic 
and nonionic surface active agents, organic or inorganic salts such as 
quaternary ammonium salts, organic borates and metal-containing dyes, and 
block or graft copolymers having oleophilic and hydrophilic moieties may 
also be used. 
Aside from the charge control agent, in order to control the physical 
properties of the developer, fine particles of polymers or inorganic fine 
particles may be further dispersed, or various additives may be dispersed 
or dissolved in the liquid developer. 
The present invention is more particularly described by way of examples 
which should not be construed as limiting the invention thereto. 
Comparative examples are also described. 
EXAMPLE 1 
Copolymer of ethylene (89%)-methacrylic acid (11%) (New Krel N699 of Du 
Pont de Nemours) 40 parts by wt. 
Copper phthalocyanine pigment (Cyanine Blue-4933M of Dainichiseika Colour & 
Chemicals Mfg. Co., Ltd.) 4 parts by wt. Isoper L 100 parts by wt. 
The above formulation expect for Isoper L was charged into a stainless 
steel beaker and agitated for one hour while heating on an oil bath at 
120.degree. C., thereby obtaining a uniform melt of the resin and the 
pigment which had been completely melted. The resultant melt was gradually 
cooled down to rom temperature while agitating, to which 100 parts by 
weight of Isoper L was added. As the temperature of the mixture was 
lowered, toner particles each having the pigment included therein and 
having a size of 10 to 20 .mu.m started to settle. 
100 g of the thus settled toner was charged into a 01 type attritor 
(Mitsui-Miike Co., Ltd.) and finely divided at a revolution speed of the 
rotor of 300 rpm for about 20 hours by use of steel balls with a diameter 
of 0.8 mm. The division was continued until the size reached 2.5 .mu.m 
while monitoring a volume mean size according to a centrifugal 
settling-type size distributor measuring instrument (CA00 of Shimadzu 
Corporation). The resultant toner concentrate was provided as a base 
toner. 
20 parts by weight of the base toner (toner concentration of 18 wt %) was 
diluted with 160 parts by weight of diethylene glycol dibutyl ether so 
that the toner concentration was 2 wt %, followed by sufficient agitation. 
Moreover, Basic Barium Petronate provided as a charge director was added 
to the resultant liquid developer in an amount of 0.1 parts by weight per 
unit part by weight of the solid matter in the liquid developer, followed 
by sufficient agitation to obtain a liquid developer. 
EXAMPLE 2 
20 wt % of the base toner obtained in Example 1 was diluted with 160 parts 
by weight of ethylene glycol amylhexyl ether so that the solid content was 
made 2 wt %, followed by sufficient agitation. Basic Sodium Petronate 
provided as a charge director was added to the resultant liquid developer 
in the same amount as in Example 1, followed by sufficient agitation to 
obtain a liquid developer. 
EXAMPLE 3 
Polyester resin (obtained by polymerization of terephthalic acid and 
ethylene oxide-added hisphenol A with a weight average molecular weight, 
Mw=12000, an acid value of 5 and a softening point of 110.degree. C.) 85 
parts by weight Magenta pigment (Carmin 6B of Dainichiseika Colour & 
Chemicals Mfg. Co., Ltd.) 4 parts by weight 
The above formulation was kneaded in an extruder and finely divided by 
means of a jet mill, followed by classification with an air classifier to 
obtain toner particles having an average size of 3 .mu.m. 
This powder toner was dispersed in ethylene glycol dihexyl ether to make a 
solid content of 2 wt %. Then, Basic Calcium Petronate provided as a 
charge director was added to the liquid developer in the same amount as in 
Example 1, followed by sufficient agitation. 
EXAMPLE 4 
The general procedure of Example 1 was repeated using Pigment Yellow 17 as 
the pigment, thereby obtaining a toner concentrate. The toner had a 
particle size of 2.5 .mu.m. 
20 wt % of the toner concentrate (toner concentration of 18 wt %) was 
diluted with 160 parts by weight of diethylene glycol dibutyl ether to 
make a solid content of 2 wt %, followed by sufficient agitation. Sodium 
dioctylsulfosuccinate provided as a charge director was added in the same 
amount as in Example 1, followed by sufficient agitation to obtain a 
liquid developer. 
EXAMPLE 5 
Copolymer of ethylene (85%)-methacrylic acid (10%)-octyl methacrylate (5%) 
40 parts by weight 
Pigment Yellow 17 (Dainichiseika Colour & Chemicals Mfg. Co., Ltd.) 4 parts 
by weight 
Isoper L 100 parts by weight 
The above formulation was treated in the same manner as in Example 1 to 
obtain a base toner. 20 parts by weight of the base toner (toner 
concentration of 18 wt %) was diluted with 160 parts by weight of 
diethylene glycol dibutyl ether to make a solid content of 2 wt %, 
followed by sufficient agitation. Thereafter, a liquid developer was 
prepared in the same manner as in Example 1. 
EXAMPLE 6 
The base toner obtained in Example 1 was diluted with propylene glycol 
dihexyl ether so that the solid content was made 2 wt %, thereby obtaining 
a liquid developer. No charge director was added in this example. 
EXAMPLE 7 
The general procedure of Example 1 was repeated using carbon black (Regal 
330 of Cabot) as the pigment, thereby obtaining a liquid developer. The 
toner had a particle size of 2.5 .mu.m. 
COMATIVE EXAMPLE 1 
The general procedure of Example 1 was repeated except that the base toner 
obtained in Example 1 was diluted with Isoper L to have a solid content of 
2 wt %, thereby obtaining a liquid developer. 
COMATIVE EXAMPLE 2 
The base toner obtained in Example 1 was diluted with Isoper H to have a 
solid content of 2 wt %, followed by sufficient agitation. Soybean 
lecithin was added, as a charge director, to the resultant liquid 
developer in the same amount as in Example 1, followed by sufficient 
agitation to obtain a liquid developer. 
Assessment Tests of Liquid Developer 
A. Measurement of evaporation rate of carrier liquid 
3 g of a carrier liquid was charged into a laboratory dish with an opening 
diameter of 50 mm. The dish was allowed to stand on a hot plate at 
40.degree. C. to measure a variation in evaporation rate in relation to 
time by means of a precision balance. The evaporation rate was determined 
according to the following equation. Evaporation rate (%) 100 .times.the 
weight (g) of evaporated carrier liquid after 6 hours/3 
B. Measurement of amounts of positive polarity toner and negative polarity 
toner in developer 
3 ml of a liquid developer was placed between two parallel disk electrodes 
each of which had a diameter of 10 cm and an area of about 78 cm.sup.2 and 
which were provided at a distance of 1 mm from each other. A potential of 
1000 V was applied to the liquid developer for one second so that the 
electric field was +10.sup.4 V/cm. Thereafter, the electrodes deposited 
with the toner were placed in a vacuum dryer and dried at 120.degree. C. 
for 2 hours to completely eliminate the carrier liquid therefrom. The 
amount of the developed positive polarity toner was determined from the 
difference between the weights of the electrodes prior to and after the 
deposition. The above procedure was repeated except that the polarity of 
the applied potential was changed (i.e. electric field: -10.sup.4 V/cm), 
thereby determining the amount of the negative polarity toner. The sole 
figure shows a circuit diagram of a toner charge quantity measurement 
device used in the above procedure. In the figure, the shaded portion is a 
liquid developer placed between the disk electrodes. 
Moreover, a freezing point of carrier liquids was determined by a simple 
procedure wherein carrier liquids were allowed to stand at temperatures of 
20.degree. C., 0.degree. C., -10.degree. C. and -20.degree. C., 
respectively, to judge a temperature at which the respective liquids were 
solidified. The solidification temperature was determined as the freezing 
point. 
The compositions of the liquid developers and the results of the assessment 
tests are shown in Tables 1 and 2. 
TABLE 1 
______________________________________ 
Carrier 
Toner Composition Composition 
Charge Carrier 
Toner Resin Pigment Director Liquid 
______________________________________ 
Ex. 1 copolymer of 
copper basic diethylene 
ethylene- phthalo- barium glycol 
methacrylic cyanine petronate 
dibutyl 
acid (BBP) ether 
Ex. 2 copolymer of 
copper basic ethylene 
ethylene- phthalo- sodium glycol 
methacrylic cyanine petronate 
amylhexyl 
acid (BBP) ether 
Ex. 3 polyester Carmin 6B basic ethylene 
resin calcium 
glycol 
petronate 
dihexyl 
(BCP) ether 
Ex. 4 copolymer Pigment sodium diethylene 
of Yellow 17 dioctyl- 
glycol 
ethylene- sulfo- dibutyl 
methacrylic succinate 
ether 
acid 
Ex. 5 copolymer of 
Pigment basic diethylene 
ethylene- Yellow 17 barium glycol 
methacrylic petronate 
dibutyl 
acid-octyl (BBP) ether 
methacrylate 
Ex. 6 copolymer of 
copper nil dipropyleneg 
ethylene- phthalo- lycol 
methacrylic cyanine dihexyl 
acid ether 
Ex. 7 copolymer of 
carbon basic diethylene 
ethylene- barium glycol 
methacrylic petronate 
dibutyl 
acid (BBP) ether 
Comp. copolymer of 
copper basic Isoper L 
Ex. 1 ethylene- phthalo- barium 
methacrylic cyanine petronate 
acid (BBP) 
Comp. copolymer of 
Carmin 6B soybean 
Isoper H 
Ex. 2 ethylene- lecithin 
methacrylic 
acid 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Amount of Positive 
Amount of Negative 
Polarity Toner (mg) 
Polarity Toner (mg) 
Immediately 
7 Days Immediately 
7 Days 
Evaporation after after after after 
Rate of Carrier 
Charge Polarity 
Preparation 
Preparation 
Preparation 
Preparation 
Liquid (%) 
of Toner 
of Developer 
of Developer 
of Developer 
of Developer 
__________________________________________________________________________ 
Ex. 1 4.6 negative 
21.3 22.0 0.0 0.0 
Ex. 2 3.9 negative 
20.5 21.0 0.1 0.1 
Ex. 3 3.3 negative 
21.0 21.5 0.0 0.1 
Ex. 4 4.6 positive 
21.8 22.0 0.0 0.1 
Ex. 5 4.6 negative 
20.7 21.0 0.0 0.0 
Ex. 6 3.4 positive 
21.5 22.0 0.0 0.0 
Ex. 7 4.6 negative 
21.5 22.0 0.0 0.0 
Comp. Ex. 1 
92 negative 
10.5 10.1 1.9 3.4 
Comp. Ex. 2 
99 negative 
10.1 9.8 2.0 3.1 
__________________________________________________________________________ 
As will be apparent from Table 2, with the ether compounds of Examples 1 to 
7 used as the carrier liquid, the evaporation rate is significantly 
lowered by 1/20 to 1/30 of those of Comparative Examples 1 and 2. 
The developers of Examples 1, 2, 3, 5 and 7 exhibit good negative charging 
toner characteristics in view of the reduced amount of the negative 
polarity toner and are stabilized seven days after the preparation with 
respect to the amount of development. The developers of Examples 4 6 are 
also small in the amount of the negative polarity toner and exhibit stable 
positive charging toner characteristics in relation to the time. On the 
other hand, with Comparative Examples 1, 2, the developing amount of the 
developers is reduced by not larger than about half of those of Examples 1 
to 7, with the amount of the negative polarity toner being too large. 
EXAMPLE 8 
The base toner obtained in Example 1 was diluted with a carrier liquid 
which consisted of a mixture of equal amounts by weight of diethylene 
glycol dibutyl ether and Norper 15 thereby making a solid content of 2 wt 
%, followed by the procedure of Example 1 to obtain a liquid developer 
having a toner concentration of 2 wt %. 
EXAMPLE 9 
The base toner obtained in Example 1 was diluted with a carrier liquid 
which consisted of a mixture of equal amounts by weight of diethylene 
glycol dibutyl ether and Isoper L, thereby making a solid content of 2 wt 
%, followed by the procedure of Example 1 to obtain a liquid developer 
having a toner concentration of 2 wt %. 
COMATIVE EXAMPLE 3 
The base toner obtained in Example 1 was diluted with Norper 15 to make a 
solid content of 2 wt %, followed by the procedure of Example 1 to obtain 
a liquid developer having a toner concentration of 2 wt %. 
The results of the measurements of the evaporation rate and the freezing 
point of the liquid developers obtained above are shown in Table 3 below. 
TABLE 3 
______________________________________ 
Compo- Evaporation 
Freezing 
Composition 
sitiona Rate of Point of 
of Carrier 
1 Ratio Carrier Carrier 
Liquid (wt %) Liquid (%) Liquid 
______________________________________ 
Ex. 8 diethylene 50 2.5 &lt;-10 
glycol 
dibutyl 
ether 
Norper 15 50 
Ex. 9 diethylene 50 8.2 &lt;-20 
glycol 
dibutyl 
ether 
Isoper L 50 
Comp. Ex. 3 
Norper 15 100 2.1 0 
______________________________________ 
As will be apparent from Table 3, the carrier liquid of Example 8 has an 
evaporation rate of 2.5% and a freezing point of lower than -10.degree. 
C., thus being substantially free of any problem in practice. The 
evaporation rate of the carrier liquid of Example 9 is 8.2%, which is much 
lower than that of Comparative Example 3 using Isoper L alone. 
On the other hand, the carrier liquid of Comparative Example 3 is 0.degree. 
C. and will become waxy under environments of winter. Thus, such a liquid 
developer has to be heated on development. 
EXAMPLE 10 
The black color developing unit portion of the FX-5030 copying machine 
(Fuji-Xerox Co., Ltd.) was reconstructed for liquid development to 
evaluate a liquid developer of the invention through image reproduction. 
The images obtained using the liquid developer of Example 2 had a good high 
resolution. Moreover, the liquid developer was used for continuous 
duplication of 100 copies. The image after the 100th copy was 
substantially the same as an initial one.