JP2007163753A - Liquid developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developer having high storage stability and good positive charging property and fixability. <P>SOLUTION: The liquid developer composed of vegetable oil using a positive charge type pigment as a carrier liquid contains both of a phosphorous ester-based anti-oxidant and a phenolic anti-oxidant, in which the linolenic acid component of triglyceride in the carrier liquid is 10 to 60 mass%. <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 bisphenol antioxidants, sulfur as antioxidants It has been proposed to add a system antioxidant, a phosphorous acid system antioxidant, or the like (for example, Patent Document 2).

In addition, when vegetable oil is used as the carrier liquid for the liquid developer, the characteristics of the liquid developer are also affected by the characteristics of the fatty acid triglyceride contained in the vegetable oil. Among these, linolenic acid, which is a trivalent unsaturated fatty acid, is easily oxidized, and a vegetable oil containing a large amount of linolenic acid triglyceride is fast in oxidative polymerization and forms a film. On the other hand, since there are many components of unsaturated bonds, there has been a problem that oxidation proceeds during long-term storage or use, resulting in an increase in viscosity, generation of odor, coloring, and the like.
Further, the liquid developer carrier liquid is required not only to prevent oxidation or polymerization, but also to have excellent image forming characteristics as a liquid developer in addition to charging characteristics. Conventionally, antioxidants have not been studied in relation to image forming characteristics.
JP 2000-19787 A JP 2003-335998 A

  The present invention relates to a liquid developer for positive charging using vegetable oil as a carrier liquid, without impairing the charging property of the colorant dispersed in the vegetable oil to the positive charge polarity, the storage stability of the liquid developer, paper, etc. It is an object of the present invention to provide a liquid developer having both good fixability after transfer to a toner.

An object of the present invention is to provide a liquid developer using a vegetable oil using a positively charged pigment as a carrier liquid, containing an antioxidant comprising a phosphite compound, and containing 10 linolenic acid components of triglyceride in the carrier liquid. This can be solved by a liquid developer having a mass% to 60 mass%.
Vegetable oil is the above-mentioned liquid developer containing oil.
The liquid developer containing 0.01 mass% to 4.0 mass% of a phosphite antioxidant and 0.05 to 0.4 mass% of a phenolic antioxidant in the liquid developer. is there.
Phosphite ester is triphenyl phosphite, trioleyl phosphite, diphenyl mono (2-ethylhexyl) phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyl tetra (tridecyl) pentaerythritol tetraphosphite The liquid developer is at least one selected from tetra (C12-C15 alkyl) 4,4′-isopropylidenediphenyl phosphite.
The liquid development described above, wherein the phenolic antioxidant is at least one of 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-methoxyphenol. It is an agent.

  In the positively chargeable liquid developer using vegetable oil as a carrier liquid, the present invention specifies the content of a linolenic acid component that is a trivalent unsaturated fatty acid constituting triglyceride of vegetable oil, and a phosphite ester By blending both antioxidants and phenolic antioxidants, it prevents deterioration of vegetable oil during storage without adversely affecting the positive charge characteristics of the liquid developer, and prevents long-term polymerization and odor generation due to oxidative degradation. Can be prevented over. As a result, a liquid developer capable of stable image formation over a long period of time can be provided.

  The present invention uses a vegetable oil in which the linolenic acid component of triglyceride in a carrier liquid is 10% by mass to 60% by mass in a liquid developer for positive charging using vegetable oil as a carrier liquid, and phosphite ester oxidation It has been found that by blending both an antioxidant and a phenolic antioxidant, it is possible to improve the image contrast and solve problems such as an increase in viscosity due to oxidative polymerization during storage. . Furthermore, it has also been found that the fixing characteristics of the transferred image are not deteriorated even by the addition of an antioxidant.

  The detailed reason why the characteristics of the image are improved by combining both phosphite and phenolic antioxidants is unknown, but phosphite and phenolic antioxidants are unknown. By blending both of these agents, it is considered that the charging characteristics of the pigment particles in the vegetable oil become appropriate, and the function of the positive liquid developer is enhanced.

Examples of the vegetable oil that can be used as the carrier liquid of the liquid developer of the present invention include linseed oil, and vegetarian oil blended with linseed oil and other vegetable oils.
The fats and oils are esters of 1 molecule of glycerin and 3 molecules of fatty acid, that is, triglyceride, and an alcohol or fatty acid is reacted therewith to obtain a transesterified oil in which the properties of the starting fats and oils are changed. As vegetable oils, not only vegetable oils but also transesterified oils, mixtures of transesterified oils and non-esterified vegetable oils, or those mixed with fatty acid esters obtained by decomposition of vegetable oils may be used. it can.
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 fatty acid composition of a vegetable oil with a high linolenic acid component content is shown in Table 1 in mass%.

Table 1
Fatty acids Amani oil Rapeseed oil Soybean oil
Palmitic acid 4-9 1-4 5-12
Stearic acid 2-5 0-2 2-7
Oleic acid 20-35 56-64 20-35
Linoleic acid 5-20 15-24 50-57
Linolenic acid 30-61 7-11 3-8

Since the liquid developer of the present invention contains triglyceride containing linolenic acid, a triunsaturated fatty acid, as a constituent component, it tends to cause oxidative polymerization, so that fixing means can be eliminated or simplified.
Moreover, you may enlarge content of the linolenic acid component in vegetable oil by adding linolenic acid ester with respect to vegetable oil with few linolenic acid components. Alternatively, the linolenic acid component may be adjusted to a desired amount by adding an ester having a small amount of linolenic acid component to the linolenic acid component.

For example, it can be easily adjusted by mixing vegetable oils with low linolenic acid components or transesterified oils based on vegetable oils with vegetable oils with high linolenic acid components or transesterified oils based on vegetable oils such as linseed methyl ester. The mixing ratio can be determined in consideration of image contrast and fixability.
In addition, in the case of improving the storage stability, by using oleic acid methyl ester, oleic acid ethyl ester, oleic acid decyl ester rather than using a vegetable oil containing a lot of oleic acid, which is a monovalent fatty acid component of triglyceride, It is preferable to adjust the viscosity, which is also preferable from the viewpoint of the odor of the vegetable oil.
Thus, the characteristics of the carrier of the liquid developer can be adjusted by using the vegetable oil and the fatty acid ester derived from the vegetable oil in combination.
In the liquid developer of the present invention, when the content of the linolenic acid component of the triglyceride in the carrier liquid is less than 10% by mass, the fixability is lowered, and when it is more than 60% by mass, the viscosity is increased. Is not preferable.

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 in a liquid state in the operating temperature range 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 0.01% by mass to 4.0% by mass.
When the amount is less than 0.01% by mass, the effect of improving the image contrast is small.

Moreover, as the phenolic antioxidant to be blended in the liquid developer of the present invention, a phenolic compound that exists stably in vegetable oil is preferable.
Specifically, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-methoxyphenol, 2,6-di-t-butylphenol, 2,6-diphenol -T-butyl-4-ethylphenol, 2,4-dimethyl-6-t-butylphenol, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-bis (2,6 -Di-t-butylphenol), 4,4'-bis (2-methyl-6-t-butylphenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), 4,4′-isopropylidenebis (2,6-di-tert-butylphenol), 2,2'-methyl Bis (4-methyl-6-cyclohexylphenol), 2,2′-methylenebis (4-methyl-6-nonylphenol), 2,2′-isobutylidenebis (4,6-dimethylphenol), 2,6- Mention may be made of bis (2'-hydroxy-3'-t-butyl-5'-methylbenzyl) 4-methylphenol, 3-t-butyl-4-hydroxyanisole, 2-t-butyl-4-hydroxyanisole. it can.

  Further, stearyl 3- (4-hydroxy-3,5-di-t-butylphenyl) propionate, oleyl 3- (4-hydroxy-3,5-di-t-butylphenyl) propionate, 3- (4 -Hydroxy-3,5-di-t-butylphenyl) dodecyl propionate, 3- (4-hydroxy-3,5-di-t-butylphenyl) propionate, 3- (4-hydroxy-3,5 -Octylpropionate-di-t-butylphenyl) tetrakis {3- (4-hydroxy-3,5-di-t-butylphenyl) propionyloxymethyl} methane, 3- (4-hydroxy-3,5-di -T-butylphenyl) propionic acid glycerol monoester, 3- (4-hydroxy-3,5-di-t-butylphenyl) propionic acid and glycerol monooleyl Ester with ether, 3- (4-hydroxy-3,5-di-t-butylphenyl) propionic acid butylene glycol ester, 3- (4-hydroxy-3,5-di-t-butylphenyl) propionic acid thiol A diglycol ester etc. can be mentioned.

In addition, 4,4′-thiobis (3-methyl-6-tert-butylphenol), 4,4′-thiobis (2-methyl-6-tert-butylphenol), 2,2′-thiobis (4-methyl) -6-tert-butylphenol), 2,6-di-tert-butyl-α-dimethylamino-4-methylphenol, 2,6-di-tert-butyl-4- (N, N'-dimethylaminomethylphenol) ), Bis (3,5-di-t-butyl-4-hydroxybenzyl) sulfide, tris {(3,5-di-t-butyl-4-hydroxyphenyl) propionyl-oxyethyl} isocyanurate, tris (3 5-di-t-butyl-4-hydroxyphenyl) isocyanurate, 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, bis {2-methy -4- (3-n-alkylthiopropionyloxy) -5-tert-butylphenyl} sulfide, 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate , Tetraphthaloyl-di (2,6-dimethyl-4-tert-butyl-3-hydroxybenzyl sulfide), 6- (4-hydroxy-3,5-di-tert-butylanilino) -2,4-bis ( Octylthio) -1,3,5-triazine, 2,2-thio- {diethyl-bis-3- (3,5-di-t-butyl-4-hydroxyphenyl)} propionate, N, N'-hexamethylene Bis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamide), 3,5-di-tert-butyl-4-hydroxy-benzyl-phosphate diester, bis (3-methyl- -Hydroxy-5-t-butylbenzyl) sulfide, 3,9-bis [1,1-dimethyl-2- {β- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl] -2,4,8,10-tetraoxaspiro [5,5] undecane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5- Trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, bis {3,3′-bis- (4′-hydroxy-3′-tert-butylphenyl) Butyric acid} glycol ester and the like.
Of these, 2,6-di-t-butyl-4-methylphenol (BHT) and 2,6-di-t-butyl-4-methoxyphenol (BHA) are preferable.
When the content of the phenolic antioxidant is less than 0.05% by mass, the effect of adding the phenolic antioxidant is small, and the content of the phenolic antioxidant is 0.4% by mass. If it exceeds, the image contrast decreases.

  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 linseed oil (manufactured by Nisshin Oilio, the linolenic acid component of fatty acid triglyceride is 56.2%), 0.23 g of dispersant (Ajinomoto Fine Techno's Asper PN411) Pigment Blue 15: 3 which is a positively charged pigment as a cyan pigment, diphenyl mono (2-ethylhexyl) phosphite as a phosphite antioxidant and 2,6-di- as a phenol antioxidant t-Butyl-4-methylphenol (BHT) was sufficiently mixed and dispersed in the amounts shown in Table 2 until the phenolic antioxidant was dissolved. Also, a liquid developer to which no antioxidant was added was prepared and used as a blank.

(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 measured, 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
┌────┬────────────────┬┬─────────┐
│Sample number│ Antioxidant blending amount (mass%) │ Image contrast │
│ ├─────────┬──────┤ │
│ │Phosphoric ester series│Phenol series│ │
├────┼─────────┼──────┼┼─────────┤
│ 1 │ No additive │ No additive │ 0.61 │
│ 2 │ 0.5 │ 0 │ 0.72 │
│ 3 │ 0 │ 0.5 │ 0.54 │
│ 4 │ 0 │ 0.05 │ 0.72 │
│ 5 │ 0.5 │ 0.05 │ 0.77 │
│ 6 │ 0 │ 0.1 │ 0.80 │
│ 7 │ 0.5 │ 0.1 │ 0.83 │
│ 8 │ 0 │ 0.2 │ 0.72 │
│ 9 │ 0.5 │ 0.2 │ 0.89 │
│ 10 │ 0 │ 0.3 │ 0.68 │
│ 11 │ 0.5 │ 0.3 │ 0.77 │
│ 12 │ 0 │ 0.4 │ 0.61 │
│ 13 │ 0.5 │ 0.4 │ 0.62 │
│ 14 │ 0.5 │ 0.5 │ 0.45 │
└────┴─────────┴──────┴┴─────────┘

As shown in the results in Table 2, when the phosphite antioxidant was added, the image contrast was higher than when no additive was added. On the other hand, when only the phenolic antioxidant was added, the image contrast was lowered as compared with the case where no addition was made.
Further, when a phenolic antioxidant was added in addition to the phosphite antioxidant, the image contrast was further increased as compared with the case of using only the phosphite antioxidant.
Further, when the content of the phenol-based antioxidant was larger than 0.4% by mass, the image contrast was lowered.

  Diphenylmono (2-ethylhexyl) phosphite used as a phosphorous acid antioxidant is a transparent liquid, whereas 2,6-di-t-butyl-4-methylphenol (BHT) is a colorless crystal. Although it has a melting point of 65 ° C., it seems that in any case, the image contrast is enhanced by using the colorant particles as an appropriate charged region in the liquid developer.

As vegetable oil, linolenic acid in vegetable oil is mixed with 50 g of linseed oil (manufactured by Nissin Oilio, linolenic acid component of triglyceride is 56.2%) and 50 g of soybean oil (7.0% by mass of linolenic acid component of triglyceride). Using blended oil prepared so that the triglyceride component is 31.6% by mass, the addition amount of the phosphite-based antioxidant shown in Table 3 in each liquid developer is 0.5% by mass, and phenol A liquid developer was prepared in the same manner as in Example 1 except that the addition amount of 2,6-di-t-butyl-4-methylphenol, which is a system antioxidant, was 0.2% by mass. The charging behavior by electrophoresis was evaluated in the same manner as in Example 1, and the results are shown in Table 3.
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 both the phosphite antioxidant and the phenolic antioxidant of the present invention were added, the image contrast was higher than when no additive was added. Further, the phosphite ester having a higher phosphorus content tended to have a higher image contrast value.
In the case of adding both the phosphite antioxidant and the phenolic antioxidant of the present invention, the weighted average is 0.1 or 0.2, and there is substantially no change in odor. It can be said.

Table 3
┌───────────────────┬─────┬─────┬─────┐
│ Phosphite antioxidant │Phosphorus content │Imagecon │Odor │
│ │ (mass%) │ Trust │Test results │
├───────────────────┼─────┼─────┼─────┤
│No addition │ 0 │ 0.57 │1.2 │
│Triphenyl phosphite │ 10.0 │ 0.79 │0.2 │
│Trioleyl phosphite │ 3.7 │ 0.59 │0.2 │
│Dilauryl hydrogen phosphite │ 6.5 │ 0.73 │0.1 │
│Diphenyl hydrogen phosphite │ 13.2 │ 0.73 │0.1 │
│Diphenyl mono (2-ethylhexyl) │ 8.6 │ 0.84 │0.2 │
│phosphite │ │ │ │
│tetra (C12-C15 alkyl) │ 5.3 │ 0.81 │0.2 │
│4-4'-isopropylidenediphenyl │ │ │ │
│phosphite │ │ │ │
│tetraphenyltetra (tridecyl) │ 8.7 │ 0.81 │0.2 │
│Pentaerythritol tetraphosphite│ │ │ │
└───────────────────┴─────┴─────┴─────┘

  According to the results in Table 3, when the phosphite antioxidant of the present invention was added, a higher value was shown rather than no added image contrast. In this case, the image contrast value tended to increase as the phosphorus content increased. A phosphorus content of 5 to 10% by mass gave good results.

As vegetable oil, 50 g of linseed oil (manufactured by Nissin Oilio, the linolenic acid component of triglyceride is 56.2%) and safflower oil (manufactured by Nisshin Oilio, 0.2% of the linolenic acid component of triglyceride)
Using 50 g of the prepared oil prepared by adjusting the linolenic acid component to 28.2% by mass, and using tetra (C12-C15 alkyl) 4-4′-isopropylidene diphenyl diphosphite as an antioxidant, the liquid The blending amount in the developer is changed from 0.01 to 4.0% by mass, and the blending amount of 2,6-di-t-butyl-4-methylphenol is 0.2% by mass for each. Except for this, a liquid developer was prepared in the same manner as in Example 1.
The charging behavior at room temperature at 25 ° C. of each colorant dispersion was measured in the same manner as in Example 1. Table 4 shows the image contrast along with the addition amount (mass%) of the phosphite antioxidant. .
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 solid image was 20 mm × 20 mm in size.
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 0.66 89%
0.01% by mass 0.68 89%
0.1% by mass 0.72 89%
0.3% by mass 0.88 88%
0.5% by mass 0.92 88%
2.0% by mass 0.90 85%
3.0% by mass 0.84 84%
4.0 mass% 0.71 84%
5.0% by mass 0.59 83%

  According to the above results, the image contrast increased as the addition amount of the phosphite antioxidant was increased, and decreased at 5.0% by mass. On the other hand, the fixing rate gradually decreases as the antioxidant is added, but hardly changes up to 0.5% by mass, but at 5% by mass, the fixing rate greatly decreases. Therefore, the addition amount is preferably less than 5% by mass.

320 g of zirconia balls with a diameter of 5 mm in a stainless steel container with a capacity of 500 ml, and a blended oil obtained by mixing oil and various vegetable oils (all manufactured by Nissin Oilio) shown in Table 5 at a predetermined ratio, oil or rapeseed oil 100 g of each single substance, and 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 12 kinds of colorant dispersions were added to 30 g of the same vegetable oil as the vegetable oil used for the preparation of the colored dispersion and mixed well, and tetraphenyltetra ( Tridecyl) pentaerythritol tetraphosphite 0.176 g (corresponding to 0.5% by mass added), 0.07 g 2,6-di-t-butyl-4-methoxyphenol (added 0) as a phenolic antioxidant .. equivalent to 2% by mass) and mixed well to prepare 12 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.
From the above evaluation results, it has been found that the image contrast tends to be relatively higher when the linolenic acid component of the triglyceride is larger. The fixing rate was 88 to 84%, and the higher the linolenic acid component, the higher the fixing rate. However, when the linolenic acid component was 8.8% by mass, the fixing rate decreased to 81%.

Table 5
┌─────────────────┬──────────┬────────┐
│ Other vegetable oils │ Mix ratio │ Formulation oil │
├────────┬────────┼────┬┬─────┼────────┤
│ Type │ Linolenic acid content │ Amani oil │ Other vegetable oils │ Linolenic acid content │
├────────┼────────┼────┼┼─────┼────────┤
│ Amani Oil │ 56.2% │100% │ --- │ --- │
│MO sunflower oil │ 0.3% │ 90% │ 10% │ 50.6% │
Rapeseed oil │ 8.8% │ 80% │ 20% │ 46.7% │
│ Divider oil │ 4.3% │ 70% │ 30% │ 40.6% │
│HOLL Canola │ 3.9% │ 60% │ 40% │ 36.6% │
│Olive oil │ 0.6% │ 50% │ 50% │ 28.4% │
│Peanut oil │ 0.8% │ 55% │ 45% │ 31.3% │
│ Sesame Oil │ 0.3% │ 25% │ 75% │ 14.3% │
│ Corn oil │ 1.0% │ 35% │ 65% │ 20.3% │
│ Cottonseed oil │ 0.8% │ 42% │ 58% │ 24.1% │
│ Saflower oil │ 0.2% │ 30% │ 70% │ 17.0% │
Rapeseed oil │ 8.8% │ −− │100% │ −− │
└────────┴────────┴────┴┴─────┴────────┘
In the table, however,% is mass%.

Table 6
Linolenic acid composition Image contrast Fixing rate
56.2% by mass 0.81 88%
50.6% by mass 0.84 88%
46.7% by mass 0.84 88%
40.6% by mass 0.85 88%
36.6% by mass 0.85 87%
28.4% by mass 0.85 86%
31.3% by mass 0.83 86%
14.3% by mass 0.84 84%
20.3% by mass 0.83 84%
24.1% by mass 0.81 84%
17.0% by mass 0.81 84%
8.8% by mass 0.85 81%

10 parts by weight of oil used in Example 1, 10 parts by weight of linseed fatty acid methyl ester (manufactured by Nisshin Eulio), and 80 parts by weight of oleic acid methyl ester (manufactured by Nippon Oil & Fats) were mixed to prepare a blended oil. The linolenic acid component of the triglyceride of the blended oil was 11% by mass.
To 100 g of the resulting blended oil, P.I. R. 15 g of 185 and 0.23 g of a dispersant (Ajinomoto Fine Techno Ajisper PN411) were mixed, and then the amount of diphenyl mono (2-ethylhexyl) phosphite as a phosphite antioxidant in the liquid developer was 0.5% by mass, phenolic oxidation so that the amount of 2,6-di-t-butyl-4-methoxyphenol (BHA) as a phenolic antioxidant in the liquid developer is 0.2% by mass The mixture was sufficiently mixed and dispersed until the inhibitor was dissolved. Also, a liquid developer to which no antioxidant was added was prepared and used as a blank.

In the same manner as in Example 3, the fixing behavior was evaluated by the charging behavior and the image evaluation test, and the result is shown in Table 7 as the fixing rate.
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.

Table 7
┌──────────┬────────────┬─────────────┐
│ │ 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, in the comparative example in which neither a phosphite ester antioxidant nor a phenol antioxidant was added, solid-liquid separation occurred. 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.

  The liquid developer of the present invention is a liquid developer using a vegetable oil using a positively chargeable pigment as a carrier liquid, and contains a phosphite-based antioxidant and a phenol-based antioxidant. Thus, a liquid developer in which the linolenic acid component of triglyceride is 10% by mass to 60% by mass is used, and there is no increase in viscosity, generation of odor, etc., and both the charging characteristics and the fixability are good. be able to.

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 (5)

In a liquid developer using vegetable oil using a positively charged pigment as a carrier liquid, the liquid developer contains both a phosphite antioxidant and a phenol antioxidant, and the linolenic acid component of triglyceride in the carrier liquid is 10 A liquid developer, characterized in that it is from 60% to 60% by weight. 2. The liquid developer according to claim 1, wherein the vegetable oil contains an oil. The liquid developer contains 0.01 mass% to 4.0 mass% of a phosphite ester antioxidant and 0.05 to 0.4 mass% of a phenolic antioxidant. Item 3. The liquid developer according to Item 1 or 2. 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. The phenolic antioxidant is at least one of 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-methoxyphenol. Item 4. The liquid developer according to any one of Items 1 to 3.

Images