JP2007156003A - Liquid developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer having high storage stability and satisfactory positive chageability. <P>SOLUTION: The liquid developer composed of a vegetable oil using positive charge type pigment as a carrier liquid contains an antioxidant composed of at least one phosphorous ester compound selected from triphenylphosphite, trioleilphosphite, diphenyl mono(2-ethyl hexyl)phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyl tetra(tridecyl)pentaerithritol tetra phosphite, and tetra(C12-C15 alkyl)4,4'-isopropylidene diphenylphosphite. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid developer used in an electrophotographic image forming apparatus used for a copying machine, a printer, or the like.

An image forming apparatus using a liquid developer has a feature that even when fine particles are used, a high-definition image can be formed without causing problems due to scattering outside the apparatus. In an electrophotographic image forming apparatus using a liquid developer, a developer in which toner containing colorant particles or a colorant and a resin as main components is dispersed in a carrier liquid is used. The electrostatic latent image formed by exposure is developed with a liquid developer.
After development, an image is formed by transferring and fixing the obtained image onto a recording medium such as paper.

In liquid developers, generally, petroleum-based volatile hydrocarbon solvents are used as carrier liquids. However, although the volatile hydrocarbon solvent is a stable substance with low electric conductivity, the volatile hydrocarbon solvent in the carrier liquid is not volatilized when fixing the toner transferred or recorded on the recording medium. It needs to be evaporated. If the evaporated volatile hydrocarbon solvent is discharged, it may cause environmental pollution.
Therefore, in order to consider the usage environment, it is necessary to provide a carrier liquid recovery means in the vicinity of the fixing device, but the image forming apparatus must be enlarged by the carrier liquid recovery means. It was disadvantageous for miniaturization.

It has also been proposed to prevent evaporation or volatilization of the carrier liquid by using non-volatile silicone oil or liquid paraffin as the carrier liquid. It will continue to exist on the recording medium. As a result, there are also problems such as a decrease in the print quality and the presence of the carrier liquid on the paper surface, resulting in a decrease in the printing performance and a writing characteristic of a writing instrument using water-based ink.
Also, when manufacturing a conventional liquid developer, each component is dispersed in a non-aqueous non-polar solvent, which is a carrier liquid, and the properties of the non-polar solvent increase the size of the apparatus and the quality of recorded matter. As a result, problems such as deterioration in storage and storage stability of the liquid developer remain.

  On the other hand, many proposals have been made to use vegetable oil as a carrier liquid instead of a volatile hydrocarbon-based organic solvent (for example, Patent Document 1). By using vegetable oil as a carrier liquid for a liquid developer, the particle size is reduced. It is said that it is small and odorless and can improve image density, resolution and fixability.

  In addition, in the case where a vegetable oil is used for the carrier liquid to produce a positively charged liquid developer, the use of a charge control agent (CCA) is indispensable for positive charging. When the amount of charge control agent used is increased, the storage stability of the dispersion becomes unstable. In particular, when a liquid metal soap is used, viscosity tends to increase during long-term storage, making it difficult to perform the function of a liquid developer. It was in.

On the other hand, when vegetable oil is used as the carrier liquid, the oxidative polymerization of the unsaturated bond of the vegetable oil causes the image transferred to the paper surface to form a stable image at an early stage, and the rate of oxidative polymerization is high. If it is large, the fluidity is lowered during storage, leading to the deterioration of the carrier liquid.
For example, in an emulsion ink used in a stencil printing method using vegetable oil as a dispersion medium, it has been proposed to add an antioxidant to a vegetable oil having an iodine value of 100 to 150, and a bisphenol antioxidant, sulfur as an antioxidant. It has been proposed to add a system antioxidant, a phosphorous acid system antioxidant, or the like (for example, Patent Document 2).
However, when it is used as a carrier liquid for a liquid developer, it has excellent image forming characteristics as a liquid developer in terms of charging characteristics and the like as well as problems such as oxidation prevention and polymerization prevention. However, in the past, antioxidants have not been studied in relation to image formation characteristics and the like.
JP 2000-19787 A JP 2003-335998 A

  The present invention relates to a positively charged liquid developer using vegetable oil as a carrier liquid, the storage characteristics are stable without impairing the chargeability of the colorant dispersed in the vegetable oil to the positive charge polarity, It is an object of the present invention to provide a liquid developer having good fixability after transfer to a toner.

The object of the present invention can be solved by a liquid developer containing an antioxidant comprising a phosphite compound in a liquid developer using a vegetable oil using a positively charged pigment as a carrier liquid.
Moreover, it is a liquid developer containing 0.2 mass%-5.0 mass% of a phosphite compound in a liquid developer.
The liquid developer containing at least 50% by mass of an oleic acid component with respect to the vegetable oil.

  Phosphites are triphenyl phosphite, trioleyl phosphite, diphenyl mono (2-ethylhexyl) phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite, tetra (C12-C15 alkyl) The liquid developer, which is at least one selected from 4,4′-isopropylidene diphenyl phosphite.

  The present invention relates to a positively chargeable liquid developer using vegetable oil as a carrier liquid. By adding a phosphite as an antioxidant, the liquid developer can be stored without adversely affecting the positive charge characteristics of the liquid developer. The deterioration of vegetable oil can be prevented, and polymerization and odor generation due to oxidative degradation can be prevented over a long period of time. As a result, a liquid developer capable of stable image formation over a long period of time can be provided.

  The present invention relates to a positively charged liquid developer using vegetable oil as a carrier liquid, and by incorporating phosphite as an antioxidant to oxidative polymerization during storage without affecting the charging characteristics of colored particles. It has been found that it is possible to solve problems such as an increase in viscosity due to, etc., and further, it has been found that image characteristics such as an increase in image contrast are improved as compared with the case where no phosphite is added. . It has also been found that the fixing characteristics of the transferred image are not deteriorated by the addition of an antioxidant.

  Although the detailed reason why the image characteristics are improved by the addition of the phosphite is unknown, the addition of the phosphite makes the charging characteristics of the pigment particles appropriate in the vegetable oil, and the positive polarity liquid. It seems to have improved the function of the developer.

Examples of vegetable oils that can be used as the carrier liquid of the liquid developer of the present invention include safflower oil, sunflower oil, soybean oil, corn oil, cottonseed oil, rapeseed oil, safflower oil, and sesame oil.
It is also known that fats and oils are esters of 1 molecule of glycerin and 3 molecules of fatty acid, that is, triglyceride, and by reacting this with alcohol or fatty acid, a transesterified oil in which the properties of the raw material fats and oils are changed can be obtained. However, the vegetable oil of the present invention includes transesterified oil produced by transesterification using vegetable oil as a raw material. The vegetable oil may be one type or a mixture of plural types, or may be a mixture of esters obtained by decomposition of the vegetable oil.
When mixing a plurality of types, it is preferable to adjust the type and mixing amount of the vegetable oil to be mixed in consideration of image contrast, fixing property, and the like.

An example of the composition of triglyceride in the vegetable oil used for the liquid developer of the present invention is expressed in mass% by the palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid which are the constituent fatty acids in the following table. It is as follows.
In Table 1, MO sunflower oil is a mid olein, that is, a triglyceride intermediate oleic acid component, and divider oil is a rapeseed oil processing oil with a high oleic acid component. Further, HOLL canola oil has a content of triglyceride of oleic acid which is a monovalent unsaturated fatty acid and a content of linoleic acid of triglyceride which is a trivalent unsaturated fatty acid, It is a kind of rapeseed oil produced from rapeseed obtained by improvement.

Table 1
Fatty acid MO rapeseed oil divider HOLL safflower oil olive oil
Sunflower oil oil canola
Palmitic acid 3.6% 4.1% 4.0% 4.2% 4.8% 10.3%
Stearic acid 3.6% 1.9% 2.1% 2.6% 1.9% 2.9%
Oleic acid 60.5% 62.7% 72.2% 73.7% 76.9% 78.8% Linoleic acid 29.7% 19.7% 16.2% 12.2% 14.9% 9%
Linolenic acid 0.3% 8.8% 4.3% 3.9% 0.2% 0.6%

Those having a high ratio of unsaturated bonds such as oleic acid, linoleic acid, and linolenic acid cause oxidative polymerization, so that the fixing means can be eliminated or simplified.
Accordingly, the vegetable oil of the carrier liquid preferably contains 50% by mass or more of oleic acid as the fatty acid component of triglyceride. Moreover, you may enlarge content of the oleic acid component in vegetable oil by adding an oleic acid ester with respect to vegetable oil with few oleic acid components.
Further, the vegetable oil of the present invention may be prepared by adding linseed fatty acid methyl ester to vegetable oil, or transesterified oil having a low oleic acid component obtained from a vegetable oil having a low oleic acid component or a transesterified oil of vegetable oil. , Oleic acid ethyl ester, oleic acid decyl ester and the like. The mixing ratio can be determined in consideration of image contrast and fixability. In addition, fatty acid derived from vegetable oil such as oleic acid may be added to adjust physical properties such as viscosity of the liquid developer.
In addition, the content of the oleic acid component of the vegetable oil in the present invention means the value obtained by the composition analysis of the fatty acid obtained by hydrolyzing the vegetable oil alone or by adding the vegetable oil to other vegetable oil-derived components. To do.

The phosphite-based antioxidant to be blended in the liquid developer of the present invention is preferably a phosphite ester that is stably present in vegetable oil, and is preferably liquid in the operating region of the liquid developer.
Specifically, triphenyl phosphite, trioleyl phosphite, diphenyl mono (2-ethylhexyl) phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite, tetra ( C12-C15 alkyl) 4,4'-isopropylidene diphenyl phosphite.
Further, the content of the phosphite compound in the liquid developer is preferably 0.2% by mass to 5.0% by mass.
When the amount is less than 0.2% by mass, the effect of improving the image contrast is small. When the amount is more than 5.0% by mass, the fixing property is deteriorated.

  In addition, the liquid developer of the present invention may contain a charge control agent, a resin, and the like, together with an antioxidant composed of a pigment and a phosphite. Specifically, as the charge control agent, tetraethyl titanate, tetraisopropyl titanate, tetra-n-propyl titanate, tetra-n-butyl titanate, tetra-tert-butyl titanate, tetra-2-ethylhexyl titanate, tetraoctyl titanate, Examples include tetramethoxy titanium and titanium chelates such as titanyl acetyl acetate, and other examples include titanate coupling agents such as isopropyl triisostearoyl titanate, isopropyl tridecyl benzene sulfonyl titanate, isopropyl tris (dioctyl). Pyrophosphate) titanate, tetraisopropyl bis (dioctyl phosphite) titanate, tetraoctyl bis (ditridecyl phosphite) titanate , Tetra (2,2-diallyloxydylmethyl-1-butyl) bis (di-tridecyl), bis (dioctylpyrophosphate) ethylene titanate, isopropyltrioctanoyl titanate, isopropyldimethacrylisostearoyl titanate, isopropylisostearoyl Examples include diacryl titanate, isopropyl tri (dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate, and isopropyl tri (N-aminoethyl-aminoethyl) titanate.

  When using resin, ethylene / vinyl acetate copolymer, polyester resin, styrene / acrylic resin, rosin modified resin, polyethylene, ethylene / acrylic acid copolymer, ethylene / maleic anhydride copolymer, polyvinyl One or more resins selected from pyridine, polyvinyl pyrrolidone, ethylene / methacrylic acid copolymer or ethylene / acrylic acid ester copolymer can be used.

  The liquid developer of the present invention is blended with vegetable oil, pigment, etc., and dispersed by an attritor, sand mill, ball mill, vibration mill, or the like, so that the primary particle diameter of the colored fine particles is a number average particle diameter of 1 μm or less. It is preferable.

Below, the measuring method of the charging characteristic of the pigment in this invention is demonstrated.
FIG. 1 is a diagram illustrating a measurement cell for charging characteristics of a pigment dispersed in a vegetable oil according to the present invention, FIG. 1 (A) is a perspective view showing the measurement cell, and FIG. 1 (B) is an electrode. It is a perspective view explaining a part.
In the measurement cell 1, an anode side electrode part 3 and a cathode side electrode part 4 are installed in a container 2 made of an electrically insulating member such as glass or synthetic resin.
The anode terminal 5 provided on the anode side electrode unit 3 is connected to a power supply anode side lead wire 6 coupled to a current supply device (not shown), and is provided on the cathode side electrode unit 4. A cathode-side lead wire 8 coupled to a current supply device (not shown) is connected to the cathode terminal 7.
The anode-side electrode portion 3 and the cathode-side electrode portion 4 are provided with a holding member mounting groove 9 for holding both electrode portions at a predetermined interval on the upper portion thereof. Is held at a predetermined interval.
A flow groove 10 is provided below the anode electrode portion 3 and the cathode electrode portion 4 so that the pigment dispersion can be smoothly supplied.

FIG. 1B illustrates the anode electrode portion, and the cathode electrode portion is also formed of the same structure and members.
As the anode electrode portion 3, a molded body in which a projection 11 for anode engagement is provided on a resin having high oil resistance and solvent resistance such as polyacetal resin (POM) is used.
An anode 12 is attached to the anode engaging projection 11 together with a spacer 13 made of an insulating member that maintains a constant distance from the counter electrode.
The anode 12 is preferably formed on a transparent glass plate by forming a transparent conductive film 14 such as ITO that does not elute due to the applied current when a current is applied. By using a transparent conductive film formed on a transparent glass plate, it is easy to optically observe and measure the pigment deposited on the anode removed from the anode electrode part after electrophoresis for a predetermined time. Can be performed.

Alternatively, the pigment concentration may be measured with a reflection densitometer or the like after the anode removed from the anode electrode portion is pressed against a transfer material such as paper or a synthetic resin film to transfer the pigment.
For each of the anode and the cathode, it is possible to determine whether it has a positive or negative charge characteristic by comparing the deposited pigment or its transferred image.
Examples of the present invention will be described below to explain the present invention.

(Preparation of liquid developer)
320 g of zirconia balls with a diameter of 5 mm in a stainless steel container with a capacity of 500 ml, 100 g of MO sunflower oil (manufactured by Nisshin Oilio Co., Ltd., triglyceride oleic acid component is 60.5% by mass), dispersant (Ajinomoto Finetechno Ajisper PA111) 0.11 g, 15 g of pigment blue 15: 3 which is a positively charged pigment as a cyan pigment, and 4.17 g of the antioxidant shown in Table 2 were mixed, and a stirrer (Turnado SM type propeller stirring blade manufactured by Chuo Rika Seisakusho Co., Ltd.) ), And a colorant dispersion was prepared by dispersing and mixing for 11 hours at a rotation speed of 504 rpm.

Diphenylmono (2-ethylhexyl) phosphite, which is a phosphite, is a transparent liquid, and 4,4′-thiobis- (2-tert-butyl-5-methylphenol) is a white crystal with a melting point of 124 ° C., dibutylhydroxy. Toluene is colorless crystals and has a melting point of 65 ° C.
Next, 5 g of the obtained colorant dispersion was added to 30 g of MO sunflower oil and mixed well to obtain three types of liquid developers. Further, a liquid developer to which no antioxidant was added was also prepared and used as comparative data.

(Evaluation of charging characteristics by electrophoresis)
The charging behavior of the pigment dispersion was examined using the charging characteristic measuring cell shown in FIG. In the measurement cell for charging characteristics, a 300 V DC voltage was applied for 10 seconds at a distance of 2 mm between the electrodes, and colored fine particles were adhered to the ITO transparent electrode by electrophoresis. Remove the ITO transparent electrode from the measurement cell, press the colored fine particles adhering to the anode and cathode onto the transfer paper (Fuji Xerox Office Supply PPC fine paper J paper), and attach the color to the electrodes. Fine particles could be obtained as a colored solid image on the transfer paper.

  The density of the obtained colored solid image was measured as the reflection density using a reflection densitometer (manufactured by X-Rite, model 520 type spectral densitometer) after being left for 1 day. The amount attached to the electrode can be evaluated from the reflection density value on the transfer paper. That is, when the reflection density on the cathode side is larger than the reflection density on the anode side, the pigment dispersed fine particles are positively charged, and when the reflection density on the anode side is larger than the reflection density on the cathode side, the pigment dispersed fine particles are negatively charged. It can be evaluated that the reflection density on the anode side and that on the cathode side are the same.

  As described above, the reflection density value of the solid image transferred from each electrode to the transfer paper was obtained, and the difference was expressed as the image contrast. It can be seen from the magnitude of the value whether the toner is sufficiently charged as a positively charged toner. The measurement results thus obtained are shown in Table 2.

Table 2
Antioxidant type Image contrast
No additive 0.62
Diphenyl mono (2-ethylhexyl) phosphite 0.72
4,4′-thiobis- (2-tertiarybutyl-5-methylphenol) 0.56
Dibutylhydroxytoluene 0.54

  According to the results in Table 2, the addition of phosphite as an antioxidant showed a higher value than the image contrast with no additive. When the phenolic antioxidant was added, the value was lower than the image contrast with no additive, resulting in a decrease in charging characteristics as a liquid developer. On the other hand, when a phosphite is added, it seems that the image contrast is enhanced by providing an appropriate charged region.

As the vegetable oil, rapeseed oil (manufactured by Nisshin Oilio, the oleic acid component of triglyceride in the vegetable oil is 62.7% by mass), and the addition amount of the phosphite shown in Table 3 in each liquid developer is 0.5% by mass. A liquid developer was prepared in the same manner as in Example 1 except for the points described above, and the charging behavior was evaluated by electrophoresis in the same manner as in Example 1. The result was calculated based on the phosphorus content in each phosphite. Is shown together with the phosphorus content expressed in mass%.
Moreover, the odor evaluation by the sensory test was performed by the following evaluation method, and the results are also shown in Table 3.

(Odor evaluation test by sensory test)
The transparent glass container containing the liquid developer was sealed and stored at 40 ° C. for 6 months, and the odor of the liquid developer after 6 months was compared with a newly prepared liquid developer having the same composition. Odor was evaluated as follows by a sensory test by 10 evaluators.
Ten evaluators evaluated the odor of each liquid developer after the storage test in four grades compared to the newly prepared liquid developer by the following score, and the weighted average of the scores of each evaluator is the result of the odor test As shown in Table 3.
0 points ... No change at all, 1 point ... A little change, 2 points ... A clear change was felt, 3 points ... A complete change, strong odor

When the phosphite of the present invention was added, the image contrast showed a higher value than when it was not added. Further, the phosphite ester having a higher phosphorus content tended to have a higher image contrast value.
Any of the phosphites added with the present invention has a weighted average of 0.1 or 0.2 and can be said to have substantially no change in odor.

Table 3
┌───────────────────┬─────┬─────┬────┐
│ Phosphorous acid ester │ Phosphorus content │ Imagecon │ Odor │
│ │ (mass%) │ Trust │Test results│
├───────────────────┼─────┼─────┼────┤
│ No additive │ 0 │ 0.58 │1.2 │
│Triphenyl phosphite │ 10.0 │ 0.81 │0.2 │
│Trioleyl phosphite │ 3.7 │ 0.59 │0.2 │
│Dilauryl hydrogen phosphite │ 6.5 │ 0.71 │0.1 │
│Diphenyl hydrogen phosphite │ 13.2 │ 0.73 │0.1 │
│Diphenyl mono (2-ethylhexyl) │ 8.6 │ 0.86 │0.2 │
│phosphite │ │ │ │
│tetra (C12-C15 alkyl) │ 5.3 │ 0.83 │0.2 │
│4-4'-isopropylidenediphenyl │ │ │ │
│phosphite │ │ │ │
│tetraphenyltetra (tridecyl) │ 8.7 │ 0.81 │0.2 │
│Pentaerythritol tetraphosphite│ │ │ │
└───────────────────┴─────┴─────┴────┘

The vegetable oil is rapeseed oil (manufactured by Nisshin Oilio, triglyceride in which oleic acid component is 79% by mass, linoleic acid component is 19.7% by mass, and linolenic acid component is 8.8% by mass). (C12-C15 alkyl) 4-4′-isopropylidene diphenyl diphosphite was used, and the liquid developer was the same as in Example 1 except that the blending amount was changed from 0.01 to 5.0 mass%. Was prepared.
The charging behavior of each colorant dispersion at room temperature at 25 ° C. was measured in the same manner as in Example 1. Table 4 shows the image contrast along with the addition amount (% by mass) of the phosphite.
In addition, images formed by the following image evaluation test were evaluated.

(Image evaluation test)
The produced liquid developer was developed, transferred, cleaned, and fixed using the image forming apparatus of the liquid development type shown in FIG.
In the image forming apparatus 20, a single layer type positively charged organic photoreceptor is used as the photoreceptor 21, and the developing roller 22 is made of an elastic member. First, the surface of the photosensitive member 21 is charged to +650 V with a scorotron 23, and a laser beam 24 controlled by an image signal is irradiated to form a latent image. Next, development is performed by applying a developing bias of +600 V to the developing roller 22. A liquid developer whose layer thickness is regulated by the regulating blade 26 is supplied to the developing roller 22 while the anilox roller 25 rotates in contact with the developing roller 22 in the same direction.

The anilox roller 25 is supplied with a liquid developer from a supply roller 27 which is a sponge-like elastic roller. The transfer bias is −950 V, and the transfer paper 28 is supplied as indicated by the arrow at a speed of 200 mm / sec while synchronizing the image transfer by the pair of supply rollers 29.
The transfer roller 30 is an elastic roller, and a transfer bias is applied through a control system. The image transferred onto the transfer paper passes between the heat fixing rollers 31 made of an oil repellent material and is fixed. The fixing temperature is set to 90 ° C., and can be set so that the toner image developed and transferred from the transfer paper is fixed to the extent that the toner image is not transferred to another member when the contact level is reached.

  When the transfer residual toner is generated, the cleaning elastic roller 32 in contact with the photoconductor removes the liquid developer adhering from the photoconductor by the cleaning blade 33 positioned above. The cleaned photoreceptor can form a monochrome image while repeating the cycle of charging, exposure, development, transfer, and cleaning again.

The image forming apparatus shown in FIG. 2 was used to print out a 5% original and a solid image using a liquid developer. The size of the solid image was 20 mm × 20 mm.
The evaluation of the fixability was made by attaching a 12mm wide adhesive tape (Sumitomo 3M Mending Tape) on the printed matter formed on the transfer paper (PPC paper J paper manufactured by Fuji Xerox Office Supply), and weighing 500g. The film was peeled after 10 reciprocations of the roll, and the density of the printed matter remaining on the transfer paper and the density before peeling were measured using a reflection densitometer (manufactured by X-Rite), and the ratio to the density before peeling was measured. In Table 4, the percentage is shown.

Table 4
Amount of phosphite added Image contrast Fixing rate
No additive 0.58 80%
0.01% by mass 0.51 80%
0.1% by mass 0.51 80%
0.2% by mass 0.60 80%
0.3% by mass 0.63 79%
0.5% by mass 0.86 79%
2.0% by mass 0.77 77%
5.0% by mass 0.69 72%

  According to the above results, when the addition amount of the antioxidant is larger than 0.2% by mass, the image contrast is increased. On the other hand, when the content exceeds 5.0% by mass, the fixing rate is greatly reduced. Therefore, the addition amount is preferably 0.2% by mass to 5% by mass.

320 g of zirconia balls having a diameter of 5 mm are placed in a stainless steel container having a capacity of 500 ml, 100 g of vegetable oil (both manufactured by Nisshin Oilio) showing the content of fatty acid components of triglyceride in Table 5, benzimidazolone pigment P.I. R. 15g of 185 and 0.23g of dispersant (Ajinomoto Fine Techno's Addisper PN411) were added and dispersed and mixed for 14 hours at a rotational speed of 504rpm using a stirrer (Turnado SM type propeller stirring blade manufactured by Chuo Rika Seisakusho). A colorant dispersion was prepared.
Next, 5 g of the obtained colorant dispersion was added to 30 g of each vegetable oil in Table 5 and mixed well, and 0.176 g of triphenyl phosphite (corresponding to 0.5 mass% added) was added as an antioxidant. Then, it was sufficiently mixed to obtain six types of liquid developers.

In the same manner as in Example 3, the charging behavior and the fixing property were evaluated in an image evaluation test, and the results are shown in Table 6 as the fixing rate.
According to the results, it was found that the image contrast tends to be relatively higher when the oleic acid component of the triglyceride is larger. The fixing rate was about 80%, and no significant difference was observed. However, the vegetable oil with a large amount of oleic acid tended to have a slightly lower fixing rate.

Table 5
Fatty acid MO rapeseed oil divider HOLL safflower oil olive oil
Sunflower oil oil canola
Palmitic acid 3.6% 4.1% 4.0% 4.2% 4.8% 10.3%
Stearic acid 3.6% 1.9% 2.1% 2.6% 1.9% 2.9%
Oleic acid 60.5% 62.7% 72.2% 73.7% 76.9% 78.8% Linoleic acid 29.7% 19.7% 16.2% 12.2% 14.9% 9%
Linolenic acid 0.3% 8.8% 4.3% 3.9% 0.2% 0.6%

Table 6
Type of vegetable oil Image contrast Fixation rate
MO sunflower oil 0.85 80%
Rapeseed oil 0.85 81%
Divider oil 0.89 80%
HOLL canola 0.90 80%
Safflower oil 0.90 79%
Olive oil 0.91 79%

The fatty acid component of triglyceride in the vegetable oil is 10.3% by weight palmitic acid, 2.9% by weight stearic acid, 78.8% by weight oleic acid, 5.9% by weight linoleic acid, and 0.6% by weight linolenic acid, respectively. 51 g of olive oil and 49 g of linseed fatty acid methyl ester (manufactured by Nissin Eulio) were added to benzimidazolone pigment P.I. R. A colored dispersion was prepared using 15 g of 185 and 0.23 g of a dispersant (Ajimoto Fine Techno's Ajisper PN411). The oleic acid component of triglyceride in the obtained dispersion was 50% by mass.
Next, diphenylmono (2-ethylhexyl) phosphite was added as an antioxidant to prepare a liquid developer having a phosphite content of 0.5% by mass.

The obtained liquid developer was developed, transferred, cleaned and fixed in the same manner as described in Example 3 using a liquid developing type image forming apparatus shown in FIG.
The change in the image quality and fixability of the 5% original printed output obtained over time was evaluated, and the results are shown in Table 7.
The solid portion fixing rate was evaluated in the same manner as described in Example 3, and then the initially printed image was stored at 25 ° C. and 50% relative humidity at 730 lux for 14 hours / day in an irradiation environment. After 6 months, the fixing rate of the solid part was measured again.
The liquid developer was also put in a beaker under the same conditions and stored for 6 months without a lid. For comparison, a liquid developer to which no antioxidant was added was prepared as a blank.

┌──────────┬────────────┬─────────────┐
│ │ Initial │ 6 months later │
│ ├─────┬──────┼──────┬──────┤
│ Evaluation sample │ Blank │ The present invention │ Blank │ The present invention │
├──────────┼─────┼──────┼┼──────┼──────┤
│ Dispersibility of liquid developer │ Good │ Good │ Solid-liquid separation │ Good │
│ 4 point type │ Readable │ Readable │ Difficult to read │ Readable │
│ Solid part fixing │ 87% │ 87% │ 91% │ 98% │
└──────────┴─────┴──────┴┴──────┴──────┘

  As described above, the storage stability of the liquid developer according to the present invention was good, and even a liquid developer stored for 6 months could read a letter having a size of 4 points. However, solid-liquid separation occurred in the comparative example in which the antioxidant composed of phosphite was not added. Even if this is stirred and then placed in the developing section of the image forming apparatus and subjected to an image forming test, sedimentation is observed, and the print quality is also deteriorated from the initial stage, making it difficult to interpret characters of 4 points in size. Met. Further, the fixability of the printed image is improved, but this is considered to be due to the progress of oxidative polymerization of vegetable oil as a carrier.

  Since the liquid developer of the present invention is formulated with a phosphite as an antioxidant in a liquid developer using vegetable oil as a carrier liquid, the storage stability is good without inhibiting the positive chargeability of the colorant. Therefore, it is possible to provide a liquid developer that can exhibit a function as a liquid developer for a long period of time and that has good development characteristics and fixability of the formed image.

FIG. 1 is a diagram illustrating a measurement cell for charging characteristics of a pigment dispersed in a vegetable oil of the present invention. FIG. 2 is a diagram illustrating a liquid developing type image forming apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Measurement cell, 2 ... Container, 3 ... Anode side electrode part, 4 ... Cathode side electrode part, 5 ... Anode terminal, 6 ... Anode side lead wire, 7 ... Cathode terminal, 8 ... Cathode side lead wire, 9 ... Holding Member mounting groove, 10 ... distribution groove, 11 ... projection for anode engagement, 12 ... anode, 13 ... spacer, 14 ... transparent conductive film, 20 ... image forming apparatus, 21 ... photoconductor, 22 ... developing roller, 23 ... scorotron, 24 ... Laser beam, 25 ... Anilox roller, 26 ... Regulator blade, 27 ... Supply roller, 28 ... Transfer paper, 29 ... Supply roller, 30 ... Transfer roller, 31 ... Heat fixing roller, 32 ... Cleaning elastic roller, 33 ... Cleaning blade

Claims (4)

A liquid developer comprising a vegetable oil using a positively charged pigment as a carrier liquid, the liquid developer comprising an antioxidant comprising a phosphite compound. The liquid developer according to claim 1, wherein the liquid developer contains 0.2 mass% to 5.0 mass% of a phosphite compound. The liquid developer according to claim 1 or 2, wherein the liquid developer contains at least 50% by mass of an oleic acid component with respect to the vegetable oil. Phosphites are triphenyl phosphite, trioleyl phosphite, diphenyl mono (2-ethylhexyl) phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite, tetra 4. The liquid developer according to claim 1, wherein the liquid developer is at least one selected from (C12-C15 alkyl) 4,4′-isopropylidene diphenyl phosphite.

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