JP4119419B2 - Positively charged black toner for electrophotography - Google Patents

Description

  The present invention is a black toner, particularly a positively charged black toner synthesized by polymerization (for example, suspension polymerization) and preferably used for electrophotography, and maintains good positive charge characteristics even under high temperature and high humidity. The present invention relates to a positively charged black toner for electrophotography.

  In general, in an image forming method such as an electrophotographic method or an electrostatic recording method, the surface of an electrostatic latent image carrier is charged by corona discharge or the like, and then exposed by a laser or the like to form an electrostatic latent image. The electrostatic latent image is developed with toner to form a toner image, and the toner image is transferred to a recording medium to obtain a high quality image.

  In such an image forming method, toner is used, and examples of commonly used toners include pulverized toner and polymerized toner. For example, Patent Document 1 listed below describes a pulverized toner containing a blue colorant such as a phthalocyanine pigment in addition to carbon black as a toner for obtaining a deep black color.

  However, in recent years, there has been a demand for a polymerization toner as a high-quality toner having a smaller particle size and a sharper particle size distribution than pulverized toner.

  However, in the production process of the polymerization toner, it is necessary to disperse carbon black in the liquid monomer. However, it is difficult to disperse the carbon black uniformly, and segregation on the surface is easier than in the case of the pulverized toner. In particular, when a large amount of carbon black is added to increase the blackness of the toner, the conductivity of the toner is increased, resulting in a decrease in charge amount, particularly a significant decrease in charge under high humidity, resulting in toner scattering and image fogging. There is a problem that is likely to occur.

JP-A-1-254968

  An object of the present invention is to provide a positively charged black toner for electrophotography which is a toner synthesized by a polymerization method and maintains good positive charge characteristics even under high temperature and high humidity.

As a result of intensive research to solve the above problems, the present inventor has found that the copper phthalocyanine pigment has a slightly positive charging property, and that the copper phthalocyanine pigment has a toner surface (with an aqueous phase) during suspension polymerization. It has been found that it is relatively easy to migrate and segregate at the interface, and has an effect of suppressing the increase in toner conductivity due to the exposure of carbon black to the toner surface. Furthermore, after extensive research on the total amount of carbon black added and the blending ratio of copper phthalocyanine pigment to carbon, the copper phthalocyanine pigment is contained in an amount of 40 to 60% by weight based on the carbon black, and the carbon black is contained. It has been found that good results can be obtained when the amount is 2 to 8% by weight based on the toner weight, and the present invention has been completed.

The positively charged black toner of the present invention is a positively charged black toner for electrophotography synthesized by a polymerization method, and comprises 2 to 8% by weight of carbon black based on the total amount of toner and the content of the carbon black. 40 to 60% by weight of a copper phthalocyanine pigment.

  Furthermore, in addition to the above configuration, the positively charged black toner of the present invention is characterized in that 40% or more of the copper phthalocyanine pigment contained in the toner is present in the vicinity of the toner surface.

The positively charged black toner of the present invention maintains good positive charging characteristics not only under standard temperature and humidity but also under high temperature and high humidity. Therefore, for example, when an image forming apparatus such as a printer or a copying machine is used under high temperature and high humidity, the positively charged black toner of the present invention is optimal. That is, even when the image forming apparatus is used under such high temperature and high humidity, the positively charged black toner of the present invention can provide high image quality.

<Positively charged black toner>
The positively charged black toner of the present invention contains 2 to 8% by weight of carbon black based on the total amount of toner.

When the content of carbon black is less than 2% by weight based on the total amount of toner, the L ^* value in terms of L ^* a ^* b ^* color coordinates becomes high, and the blackness of the toner is insufficient, resulting in clear black The inconvenience that an image cannot be obtained occurs. On the other hand, when the content of carbon black exceeds 8% by weight with respect to the total amount of toner, the resistance of the toner is lowered, the charge holding ability is lowered, and toner scattering and image fogging due to lowering of the charge amount occur. Occurs.

Further, the positively charged black toner of the present invention contains 40 to 60% by weight of a copper phthalocyanine pigment based on the carbon black content. As a result, the charge amount of the toner can be increased, the decrease of the charge amount can be prevented even under high temperature and high humidity, and toner scattering and image fog can be prevented.

On the other hand, when the content of the copper phthalocyanine pigment is less than 40% by weight with respect to the content of the carbon black, a sufficient effect due to the addition of the copper phthalocyanine pigment cannot be obtained, and the high temperature and high humidity As a result, the charge amount is reduced, and toner scattering and image fog are likely to occur. On the other hand, when the content of the copper phthalocyanine pigment exceeds 60% by weight with respect to the content of carbon black, a decrease in image density due to charge-up occurs. In addition, the b ^* value in the L ^* a ^* b ^* color coordinates increases to the minus side, and the color of the image becomes bluish.

  FIG. 1 shows a graph in which the horizontal axis represents the carbon black content relative to the total toner amount and the vertical axis represents the copper phthalocyanine pigment content relative to the total toner amount. FIG. 1 shows a line segment A indicating a content of 2% by weight and a line segment B indicating a content of 8% by weight as indicating the content of carbon black with respect to the total amount of toner. Furthermore, as the content of the copper phthalocyanine pigment relative to the content of carbon black, a line segment C indicating a content of 60% by weight and a line segment D indicating a content of 20% by weight are shown. Regions surrounded by these line segments A to D indicate regions where the obtained positively charged black toner is good. That is, when the content of the copper phthalocyanine pigment and the content of carbon black are in the region surrounded by the line segments A to D in FIG. 1, the toner has good color and Good positive charging characteristics can be maintained even under high temperature and high humidity.

<Method for producing positively charged black toner>
The positively charged black toner of the present invention can be produced by polymerizing a monomer to which at least a predetermined amount of carbon black and a copper phthalocyanine pigment are added.

  The polymerization method for producing the positively charged black toner of the present invention is preferably suspension polymerization that provides a sharp particle size distribution with a small particle size. In suspension polymerization, first, a colorant (carbon black and copper phthalocyanine pigment), a charge control agent, a release agent and the like are dispersed in a polymerizable composition of a monomer and a crosslinking agent, and a polymerization initiator is added to this dispersion. A polymerizable toner composition is prepared. Thereafter, the polymerizable toner composition is added to purified water containing a suspension stabilizer, stirred with high shear force to form toner-sized droplets, and then heated with gentle stirring to polymerize and polymerize. After completion, the toner is obtained by filtration, washing and drying.

  Examples of copper phthalocyanine pigments that can be used in the present invention include copper phthalocyanine cyan pigments such as CIPigment Blue 15: 3, CIPigment Blue 15: 2, and CIPigment Blue 15: 4. Hostaperm Blue B2G (CIPigment Blue 15: 3 / Clariant), Fastgen Blue GP-100A (CIPigment Blue 15: 2 / Dainippon Ink), Fastgen Blue FGS (CIPigment Blue 15: 4 / Dainippon Ink) Etc.).

  Examples of the monomer that can be used in the present invention include styrene monomers such as styrene, methylstyrene, and ethylstyrene; acrylic acid (acrylic acid ester, acrylic acid such as 2-ethylhexyl methacrylate, methyl acrylate, ethyl acrylate, and butyl methacrylate). Methacrylic acid ester) monomers; ene monomers such as butadiene, isoprene, cyclohexene, acrylonitrile, acrylamide, and the like. These monomers can be used alone or in combination of two or more.

  Examples of the charge control agent that can be used in the present invention include metal compounds such as quaternary ammonium salt compounds, nigrosine compounds, monoazo metal compounds, and acetylacetone metal compounds, aromatic oxycarboxylic acids, and aromatic carboxylic acids. Group compounds, urea derivatives, boron compounds, resin charge control agents, and the like. These can be used alone or in combination of two or more. The addition amount of the charge control agent is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the monomer in consideration of the dispersibility of the carbon black.

  Examples of the crosslinking agent that can be used in the present invention include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, carboxylic acid esters such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate, and divinyl. And divinyl compounds such as aniline, divinyl ether, divinyl sulfide, and divinyl sulfone. These can be used alone or in combination of two or more. The addition amount of the crosslinking agent is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the monomer.

  Examples of the polymerization initiator that can be used in the present invention include 2,2-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis- (2,4-dimethylvaleronitrile), and 2,2 ′. -Azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, azobisisobutyronitrile, etc. Examples thereof include azo- and diazo-based polymerization initiators, peroxide-based polymerization initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, and lauroyl peroxide. The addition amount of the polymerization initiator is preferably 0.5 to 20 parts by weight with respect to 100 parts by weight of the monomer.

  Examples of the suspension stabilizer that can be used in the present invention include inorganic compounds such as tricalcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, calcium carbonate, magnesium carbonate, polyvinyl alcohol, gelatin, methylcellulose, Examples thereof include organic compounds such as methylhydroxypropylcellulose and ethylcellulose, or sodium salts thereof. The addition amount of the suspension stabilizer is preferably 0.2 to 2.0 parts by weight with respect to 100 parts by weight of the monomer. Moreover, in order to refine | miniaturize these suspension stabilizers, you may add 0.001-0.5 weight part of surfactant with respect to 100 weight part of monomers. Examples of the surfactant herein include sodium dodecylbenzenesulfonate, sodium oleate, sodium laurate, potassium stearate, calcium oleate, and the like.

  In addition to the above components, compounds such as low molecular weight polypropylene, low molecular weight polyolefin, Fischer-Tropsch wax, carnauba wax, and ester wax may be added in order to improve toner fixing properties.

  Suspension polymerization is carried out with stirring in an aqueous phase containing a monomer, carbon black, copper phthalocyanine pigment, charge control agent, crosslinking agent and polymerization initiator, and further containing a suspension stabilizer. The amount of water in this aqueous phase is preferably 300 to 1000 parts by weight with respect to 100 parts by weight of the monomer. Further, in this stirring, the stirring speed and the stirring time may be adjusted so that the toner particles have a desired size, for example, 2000 to 10,000 rpm and 5 minutes to 1 hour. Thereafter, polymerization may be carried out at 50 to 90 ° C. for 2 to 20 hours while maintaining the particle state and stirring to such an extent that the particles can be prevented from settling, and the polymerization is preferably carried out in a nitrogen atmosphere.

  In a toner synthesized by a polymerization method (polymerization method toner) like the positively charged black toner of the present invention, the carbon black having a hydrophilic functional group on the surface is the surface of the toner, that is, the water phase. It tends to segregate at the interface between oil and oil phase. When carbon black having high conductivity is present on the toner surface, a decrease in charge is likely to occur. The decrease in the charge becomes remarkable particularly under high humidity. When the decrease in charge occurs, image fog and toner scattering are likely to occur.

  Therefore, the addition of a copper phthalocyanine pigment and the presence of a copper phthalocyanine pigment having a higher insulating property than carbon on the toner surface can suppress charge leakage due to carbon. Specifically, when 40% or more of the copper phthalocyanine pigment contained in the toner is present in the vicinity of the toner surface, charge leakage due to carbon can be suppressed.

  The amount of the copper phthalocyanine pigment contained in the positively charged black toner and the amount of the copper phthalocyanine pigment present in the vicinity of the toner surface can be measured by, for example, fluorescent X-rays. When 40% or more of the copper phthalocyanine pigment contained in the toner is present in the vicinity of the toner surface, the positively charged black toner becomes a good toner. Therefore, in the positively charged black toner of the present invention, it is preferable that 40% or more of the copper phthalocyanine pigment contained in the toner is present in the vicinity of the toner surface.

  Note that if less than 40% of the copper phthalocyanine pigment contained in the toner is present in the vicinity of the toner surface, the effect of suppressing charge leakage under high temperature and high humidity is insufficient. In addition, the charge amount is reduced, and toner scattering and image fogging are likely to occur.

  Of the copper phthalocyanine pigment contained in the toner, the proportion of the copper phthalocyanine pigment present in the vicinity of the toner surface (hereinafter referred to as “surface abundance ratio”) is determined by the following formula (I): Can do. That is, the positively charged black toner of the present invention preferably has a surface abundance ratio of 40% or more. In addition, “Cua” in the following formula (I) is an intensity measured by a fluorescent X-ray measuring apparatus (RIX2100 type: manufactured by Rigaku Corporation), specifically, X-rays due to copper (Cu) in the toner. Irradiation intensity setting: The detected X-ray intensity resulting from copper at 50 KV-80 mA is shown. “Cus” in the following formula (I) is an intensity caused by copper present in the vicinity of the toner surface, specifically, X-ray irradiation intensity setting: 30 KV, measured by a fluorescent X-ray measurement apparatus. The detected X-ray intensity resulting from copper at −30 mA is shown.

  Hereinafter, the positively charged black toner of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

In addition, some of the following Examples 1 to 12 include a comparative example, but such an example is referred to as a “reference example” and is given a serial number together with the example for convenience. It was decided.
[Examples (Reference Examples) 1 to 12 and Comparative Examples 1 to 10]
(Production of toner by suspension polymerization)
First, a predetermined amount of carbon black and a copper phthalocyanine pigment (copper phthalocyanine cyan pigment) were blended with 80 parts by weight of styrene and 20 parts by weight of 2-ethylhexyl methacrylate. The blending amounts of carbon black and copper phthalocyanine cyan pigment are shown in Tables 1 to 3 below.

  Further, 3 parts by weight of low molecular weight polypropylene, 2 parts by weight of a charge control agent (quaternary ammonium compound, P-51, manufactured by Orient Chemical Co.) and 1 part by weight of a crosslinking agent (divinylbenzene) were obtained. The mixed solution was sufficiently dispersed with a ball mill. Thereafter, 2 parts by weight of 2,2-azobis (2,4-dimethylvaleronitrile) is added as a polymerization initiator, added to 400 parts by weight of purified water, and 5 parts by weight of calcium triphosphate and dodecyl as suspension stabilizers. 0.1 part by weight of sodium benzenesulfonate was added, and the mixture was stirred at 7000 rpm for 20 minutes using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). Suspension polymerization). Then, by filtering, washing and drying, a toner raw powder having a volume average particle diameter of 9 μm was obtained.

  Next, 100 parts by weight of the above toner raw powder and 0.8 parts by weight of silica RA200HS (manufactured by Nippon Aerosil Co., Ltd.) were mixed for 2 minutes with a Henschel mixer to obtain a positively charged black toner for electrophotography.

Thereafter, for the obtained positively charged black toner, the surface abundance ratio of the copper phthalocyanine pigment was determined using a fluorescent X-ray measuring device (RIX2100 type: manufactured by Rigaku Corporation). Furthermore, Gretag Macbeth densitometer: using RD-19 type and (Sakata Inx Corp.), was determined and L ^* values and b ^* values of the toner in the L ^* a ^* b ^* coordinates. The results are shown in Tables 1 to 3 below.

  The amount of carbon black is shown in the item “CB amount” in Tables 1 to 3 in terms of a ratio (% by weight) to the total amount of the positively charged black toner finally obtained. Moreover, the amount of the copper phthalocyanine cyan pigment used in the preparation of the above-mentioned chemicals is shown in “Pigment amount” in Tables 1 to 3 in terms of a ratio (% by weight) to the weight of the blended carbon black.

(Preparation of developer for evaluation)
The various toners (35 g) and the carrier (700 g) were put in a 500 ml plastic container and mixed at 100 rpm for 30 minutes to prepare a developer for evaluation. The carrier used is a carrier having a fluororesin coating for FS-8008C manufactured by Kyocera Mita Corporation.

(Print test)
The initial image density and fog density were evaluated using an electrophotographic printer (FS-8008C manufactured by Kyocera Mita Co., Ltd.). The initial image density and fog density were evaluated based on the average value of data from the first to third printed sheets. Further, the toner scattering after continuous printing of 3000 sheets at a printing rate of 5% was also visually evaluated. These evaluations are performed in two types: evaluation under standard temperature and humidity conditions (temperature 20 ° C./relative humidity 60%) and evaluation under high temperature and high humidity conditions (temperature 35 ° C./relative humidity 85%). It was.

  Further, under standard temperature and humidity conditions, the image density at the time when 3000 sheets of a predetermined image evaluation pattern (A4 original having a printing rate of 5%) was printed was also evaluated. The evaluation results are shown in the item “Continuous Print Image Density” in Tables 1 to 3.

  The image density, fog density and toner scattering were evaluated by the following methods.

(Image density evaluation method)
Gretag Macbeth densitometer: RD-19 type (manufactured by Sakata Inx Corporation) was used to measure the density of the solid black portion of the printer image, and this was used as the image density. An image density of 1.20 or more was regarded as no problem, and when it was less than 1.20, it was regarded as problematic (NG).

(Evaluation method of fog density)
First, the density of the non-image forming portion of the printed image and the density of the base paper were measured using a Gretag Macbeth densitometer: RD-19 type. Then, these density differences (density of non-image forming portion-density of pace paper) were calculated, and the calculation result was used as the fog density. The fog density was 0.005 or less with no problem, and when it exceeded 0.005, there was a problem (NG).

(Evaluation method of toner scattering)
Toner scattering was evaluated by visually observing the state of the toner thin layer on the developing sleeve. The evaluation criteria are as follows, and the results are shown in “Toner scattering” in Tables 1 to 3. ○: No contamination in the evaluation machine due to toner scattering. (Triangle | delta): There exists some dirt in the evaluation machine by toner scattering. X: Contamination within the evaluation due to toner scattering is remarkable.

(Measurement of charge amount)
Samples were measured after being conditioned for 8 hours or more under standard temperature and humidity conditions (temperature 20 ° C / relative humidity 60%) or high-temperature and high-humidity conditions (temperature 35 ° C / relative humidity 85%). Was collected from the developing machine of the evaluation machine. The charge amount Qb (μC / g) was measured with a suction-type charge amount measuring device (manufactured by Sankyo Piotech). The results are shown in Tables 1 to 3 below.

(result)
Table 1 shows the results of the above measurements in Examples (Reference Examples) 1 to 6 and Comparative Examples 1 to 6.

In Examples (Reference Examples) 1 to 6 and Comparative Examples 1 to 6 described in Table 1, MA-100 (manufactured by Mitsubishi Kasei Co., Ltd.) as carbon black and Hostaperm Blue B2G (CIPigment Blue 15: 3 / The evaluation results of the toner performance with respect to various addition amounts of both are shown.

From Table 1, it can be seen that good results were obtained for Examples 2, 4 and 6 . That is, the positively charged black toner containing 2 to 8% by weight of carbon black with respect to the total amount of toner and 40 to 60% by weight of copper phthalocyanine pigment with respect to the carbon black can It can be said that the toner can obtain a good image regardless of whether it is used under wet conditions.

On the other hand, in the case of Comparative Example 1 in which the amount of carbon black is less than 2% by weight with respect to the total amount of toner, the L ^* value in terms of L ^* a ^* b ^* color coordinates is high. The image density under standard temperature and humidity conditions is small. Therefore, a clear black image cannot be obtained.

  In Comparative Example 6 in which the amount of carbon black was larger than 8% by weight with respect to the total amount of toner, the fog density value was as high as 0.008 under the standard temperature and humidity conditions, resulting in a severe toner scattering state. This is considered to be due to a decrease in toner resistance and a decrease in charge retention capability.

In Reference Examples 1, 3 and 5 and Comparative Examples 2 and 4 in which less than 40% by weight of copper phthalocyanine pigment was added to carbon black, the charge amount relative to the increase in humidity was high when used under high temperature and high humidity. The degree of reduction was large, image fogging occurred, and sufficient effects could not be obtained. This is probably because a sufficient amount of copper phthalocyanine pigment was not obtained due to a small amount.

In Comparative Examples 3 and 5 in which the amount of the copper phthalocyanine pigment exceeds 60% by weight with respect to the carbon black, a decrease in image density due to charge-up occurred under standard temperature and humidity conditions. Further, in Comparative Example 3 in which the amount of carbon black is as small as 2% by weight with respect to the total amount of toner, the b ^* value in the L ^* a ^* b ^* color coordinates is increased on the minus side, and the color of the image is bluish. I was born.

  In Comparative Example 1, Comparative Example 3, and Comparative Examples 5 to 6, “-” is described in the table, but this is not satisfactory in the initial image under the standard temperature and humidity conditions or in the 3000 sheet printing test. Because it has occurred, it indicates that the evaluation has not been performed.

The results of the above measurements in Examples (Reference Examples) 7 to 9 and Comparative Examples 7 to 8 are shown in Table 2.

In Examples (Reference Examples) 7 to 9 and Comparative Examples 7 to 8 shown in Table 2, Fastgen Blue GP-100A (CIPigment Blue 15: 2 / manufactured by Dainippon Ink Co., Ltd.) was used as a copper phthalocyanine pigment. The evaluation results of the toner performance with respect to the addition amount are shown. In Examples (Reference Examples) 7 to 9 and Comparative Examples 7 to 8, MA-100 was used as the carbon black as in Example 1 and the like.

From Table 2, it can be seen that good results were obtained for all of Examples 8 and 9. That is, even when the copper phthalocyanine pigment type is changed, the positively charged black toner containing 40 to 60% by weight of the copper phthalocyanine pigment with respect to the carbon black can be used under either of the normal temperature and humidity conditions. It can be said that it is a toner capable of obtaining a good image even if it is used. On the other hand, in Reference Example 7 and Comparative Example 7 in which less than 40% by weight of copper phthalocyanine pigment was added to carbon black, image fogging occurred when used under high temperature and high humidity, and a sufficient effect was obtained. There wasn't. Further, in the case of Comparative Example 8 in which the amount of the copper phthalocyanine pigment exceeds 60% by weight with respect to the carbon black, a decrease in image density due to charge-up occurred under standard temperature and humidity conditions.

  The results of the above measurements in Examples 10 to 12 and Comparative Examples 9 to 10 are shown in Table 3.

  In Examples 10 to 12 and Comparative Examples 9 to 10 shown in Table 3, the results of experiments using still another carbon black and copper phthalocyanine pigment were shown. In other words, Printex L (manufactured by Degussa) as carbon black and Fastgen Blue FGS (CIPigment Blue 15: 4 / manufactured by Dainippon Ink) as copper phthalocyanine pigments are used to evaluate the toner performance for various carbon black additions. showed that.

From Table 3, it can be seen that good results were obtained for all of Examples 10-12. In other words, even when the carbon black species is changed, the positively charged black toner containing 40 to 60% by weight of copper phthalocyanine pigment with respect to the carbon black can be used under both normal temperature and humidity conditions. Even so, it can be said that the toner can obtain a good image. On the other hand, in Comparative Example 9 having less than 2% by weight of carbon black with respect to the total amount of toner and Comparative Example 10 having more than 8% by weight of carbon black with respect to the total amount of toner, good results were not obtained.

4 is a graph showing preferred contents of carbon black and copper phthalocyanine pigment in the positively charged black toner of the present invention.

Claims (1)

A positively charged black toner for electrophotography synthesized by a polymerization method,
Containing 2 to 8% by weight of carbon black based on the total amount of toner and 40 to 60% by weight of copper phthalocyanine pigment based on the content of carbon black ;
A positively charged black toner , wherein 40% or more of the copper phthalocyanine pigment contained in the toner is present in the vicinity of the toner surface .

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