Patent Grant
9740122
This application is entitled to and claims the benefit of Japanese Patent Application No. 2016-054075, filed on Mar. 17, 2016, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an electrostatic charge image developing toner.
2. Description of Related Art
An electrostatic charge image developing toner (hereinafter, also simply referred to as “toner”) for use in electrophotographic image forming is demanded to have reduced thermal energy in fixation for the purposes of an increase in printing speed and saving of energy of an image forming apparatus. In response thereto, a toner with a much better low-temperature fixability is demanded.
With respect to such a toner, for example, a toner is known into which an amorphous polyester and a vinyl resin, and a crystalline polyester having so-called sharp meltability that results in a rapid reduction in elasticity in a narrow temperature region are introduced as binder resins (see, e.g., Japanese Patent Application Laid-Open No. 2004-309996). In the toner described in Japanese Patent Application Laid-Open No. 2004-309996, rheological property is regulated and a viscoelastic behavior is controlled to thereby allow excellent low-temperature fixability to be realized.
With respect to such a toner, for example, a capsule toner is also known into which an amorphous polyester and a crystalline polyester are introduced as binder resins and which is capsulated (see, e.g., Japanese Patent Application Laid-Open No. 2008-268353). In the toner described in Japanese Patent Application Laid-Open No. 2008-268353, the resins having a chemical structure similar to each other are used to thereby control compatibility, and the toner is capsulated to thereby achieve excellent low-temperature fixability and heat resistance.
The toner described in Japanese Patent Application Laid-Open No. 2004-309996, however, has the following problem: when crystallization of the crystalline polyester is insufficient, the glass transition temperature of the toner decreases to cause heat resistance to be insufficient. The toner also has the following problem: when melt viscosity of the toner is too low, an image is not properly separated from a fixing member in high-speed printing, namely, so-called separation failure occurs. Furthermore, when the vinyl resin and the crystalline polyester are included in binder resins, these may largely differ in terms of polarities and chemical structures thereof to thereby cause a large crystal domain to be likely formed. If a large crystal domain is formed in an image after fixation, roughness occurs on the surface of the image, also resulting in the problem of deterioration in uniformity of glossiness of the image.
On the other hand, while the toner described in Japanese Patent Application Laid-Open No. 2008-268353 is excellent in both of low-temperature fixability and heat resistance, the toner has the following problem: melt viscosity of the toner is so low that separation failure occurs in high-speed printing.
As described above, there is room for improvement in the prior art from the viewpoint that a toner sufficiently having all of low-temperature fixability, separation property, high-temperature storage property, and uniformity of glossiness of an image fixed is realized.
An object of the present invention is to provide a toner containing a binder resin including a crystalline resin and a vinyl resin, the toner sufficiently having all of low-temperature fixability, separation property, high-temperature storage property, and uniformity of glossiness of an image fixed.
To achieve at least one of the abovementioned objects, an electrostatic latent image developing toner reflecting one aspect of the present invention includes a toner base particle including a binder resin and a release agent, wherein
the binder resin includes a crystalline resin and a vinyl resin, and
the toner satisfies the following expressions (1) to (3):
G′50° C.≧1×108 (1)
TmB−TmA≦8 (2)
Tm<TmB (3)
In the above expressions, the G′50° C. represents a storage elastic modulus G′ (Pa) of the toner at 50° C. in viscoelasticity measurement from 25° C. to 100° C. in conditions of a frequency of 1 Hz and a rate of temperature rise of 3° C./min, the TmA represents a measurement temperature (° C.) at a G′ of 1×106 Pa in the viscoelasticity measurement, the TmB represents a measurement temperature (° C.) at a G′ of 1×105 Pa in the viscoelasticity measurement, and the Tm represents a peak top temperature (° C.) of an endothermic peak in a first temperature rise process at 10° C./min in differential scanning calorimetry of the toner.
The present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein:
A toner using a crystalline resin is commonly known in which a crystalline polyester is used as the crystalline resin and the degree of compatibilization of the crystalline resin in a binder resin is increased from the viewpoint that sharp meltability is imparted to the toner to enhance low-temperature fixability.
In such a case, however, the glass transition temperature of the toner decreases and the crystalline resin tends to be made compatible from the stage of toner production (no crystal domain is formed). Therefore, the toner tends to be deteriorated in high-temperature storage property. In addition, if the degree of compatibilization is too high, elasticity of the crystalline resin is rapidly reduced in fixation, and the attachment force of the toner to a fixing member tends to be stronger. Thus, separation failure of an image tends to occur.
Meanwhile, when the degree of compatibilization of the crystalline resin in the binder resin is reduced in order to enhance high-temperature storage property, a crystal domain tends to be formed. If the degree of compatibilization is excessively reduced, roughness occurs not only in the toner, but also in an image after fixation, and uniformity of glossiness tends to be deteriorated.
An object of the present invention may be to realize a toner excellent in all of low-temperature fixability, separation property, high-temperature storage property, and uniformity of glossiness of an image fixed, by adjustment of the degree of compatibilization of a crystalline resin in a binder resin so that, while a crystal domain is formed in the toner, no crystal domain is formed in an image after fixation.
A toner of one embodiment of the present invention is an electrostatic latent image developing toner including a toner base particle, the toner base particle containing a binder resin and a release agent. The binder resin contains a crystalline resin and a vinyl resin. The toner satisfies the following expressions (1) to (3).
G′50° C.≧1×108 (1)
TmB−TmA≦8 (2)
Tm<TmB (3)
In the expression (1), the G′50° C. represents the storage elastic modulus G′ (Pa) of the toner at 50° C. in viscoelasticity measurement from 25° C. to 100° C. in conditions of a frequency of 1 Hz and a rate of temperature rise of 3° C./min.
In the expression (2), the TmA represents the measurement temperature (° C.) at a G′ of 1×106 Pa in the viscoelasticity measurement. In the expressions (2) and (3), the TmB represents the measurement temperature (° C.) at a G′ of 1×105 Pa in the viscoelasticity measurement.
In the expression (3), the Tm represents the peak top temperature (° C.) of an endothermic peak in a first temperature rise process at 10° C./min in differential scanning calorimetry (DSC measurement) of the toner. When a plurality of endothermic peaks are observed in the DSC measurement, the above endothermic peak represents the endothermic peak positioned at a temperature corresponding to the highest temperature among the plurality of endothermic peaks, and, when only one endothermic peak is observed, the above endothermic peak represents the endothermic peak observed.
When G′ at 50° C. is 1×108 Pa or more, the storage elastic modulus G′ can be kept high even in a relatively high temperature region (for example, a temperature region of 50° C. or higher and lower than the melting point Tm). The variation in hardness of the surface of the toner is considered to be able to be thus suppressed.
The G′ is rapidly reduced from 1×106 Pa to 1×105 Pa in a narrow temperature region of 8° C. or lower. When the G′ is rapidly reduced, the temperature of the toner exceeds the melting points of both of the crystalline resin and the release agent contained in the toner, to thereby liquefy the toner to allow sharp meltability to be exhibited. While a reduction in the melt viscosity of a resin component contained in the toner is considered to cause separation property of the toner from a fixing member in fixation to be insufficient, the crystalline resin and the release agent contained in the toner are liquefied and leaked out on the surface of paper, and as a result, the toner is considered to be excellent in separation property. In addition, neither offset nor a residue of fusion of the crystalline resin is observed in fixation, and therefore uniformity of glossiness of an image is considered to be kept.
While the storage elastic modulus G′ is described in Examples in detail, these can be determined with a known rheometer (for example, “ARES G2” manufactured by TA instruments. Japan) by use of, as a sample, a pellet formed by pressure molding of a toner particle or a toner base particle. The measurement temperature range of the storage elastic moduli may be any range as long as the substantial feature (behavior) of G′ in the toner are sufficiently exhibited, and may be sufficiently, for example, the range from normal temperature to about 100° C. in the case of a usual electrophotographic image forming toner.
The G′ can be adjusted by, for example, the glass transition temperature Tg, the molecular weight and the polarity of the main component (in the present embodiment, vinyl resin) of the binder resin, the amount, the polarity and the melting point of the crystalline resin, and the HB rate (the rate of the amount of an amorphous resin unit (for example, vinyl resin) in the crystalline resin). The G′ can also be adjusted by the amount, the polarity and the melting point of the release agent. The polarity of the main component of the binder resin can be adjusted depending on the type of a monomer. For example, when the monomer is a vinyl resin, the polarity can be adjusted using a monomer having a structure similar to that of the monomer of the crystalline resin, for example, when the crystalline resin is a crystalline polyester, 2-ethylhexyl acrylate (2-EHA) is used. The polarity, the melting point and the HB rate of the crystalline resin can be adjusted depending on the type of the crystalline resin. Similarly, the polarity and the melting point of the release agent can also be adjusted depending on the type of the release agent.
For example, as Tg and the molecular weight of the main component of the binder resin are higher, the G′ value tends to be higher. In addition, as the difference in polarity between the crystalline resin and the vinyl resin is larger, such resin components are made incompatible with each other, and the G′ value tends to be higher. Furthermore, as the amounts of a crystalline material and the release agent relative to the toner base particle are increased, the G′ value tends to be higher.
The Tm is the melting point of the toner base particle, determined depending on the crystalline material in the toner base particle. Examples of the crystalline material include a crystalline resin and a release agent. When the toner base particle includes two or more of the crystalline materials, the Tm is usually a higher melting point among two or more of the melting points of the crystalline materials. The Tm can be adjusted depending on the molecular weight of the crystalline material and a combination of monomers. For example, as the number of carbon atoms in the monomers is larger, the Tm tends to be higher. While the Tm is described in Examples in detail, it can be measured with a known DSC apparatus such as “Diamond DSC” manufactured by PerkinElmer Co., Ltd. by use of, as a sample, the toner particle or the toner base particle.
The Tm is preferably 60° C. or higher, more preferably 65° C. or higher from the viewpoint that sufficient high-temperature storage property is achieved. In addition, the Tm is preferably 90° C. or lower, more preferably 85° C. or lower from the viewpoint that sufficient low-temperature fixability is achieved.
Moreover, the TmA is preferably 60° C. or higher, more preferably 65° C. or higher from the viewpoint that sufficient heat resistance is achieved. In addition, the TmA is preferably 89° C. or lower, more preferably 84° C. or lower from the viewpoint that sufficient low-temperature fixability and sharp meltability are achieved.
Furthermore, the TmB is preferably 61° C. or higher, more preferably 66° C. or higher from the viewpoint that sufficient heat resistance is achieved. In addition, the TmB is preferably 90° C. or lower, more preferably 85° C. or lower from the viewpoint that sufficient low-temperature fixability and sharp meltability are achieved.
The difference value between the TmB and the TmA (TmB−TmA) can be adjusted by the glass transition temperature Tg and the polarity of a main component (in the present embodiment, vinyl resin) of the binder resin, and the amount, the polarity, the melting point and the HB rate of the crystalline resin. The difference value can also be adjusted by, for example, the amount, the polarity and the melting point of the release agent. As Tg of the main component of the binder resin is decreased, the contents of the crystalline resin and the monomer (for example, 2-EHA) are increased, the HB rate is increased, the Tm is decreased and the region of a lamella structure (described later) formed in the toner base particle is increased, the difference value tends to be smaller.
The difference value is preferably 4 or less from the viewpoint that excellent low-temperature fixability is achieved. The G′ is rapidly reduced from 1×106 Pa to 1×105 Pa in a narrow temperature region of 4° C. or lower, and therefore more excellent sharp meltability is considered to be able to be exhibited.
The toner may be a one-component developer or a two-component developer as long as the G′ is satisfied. The one-component developer is configured from only a toner particle, and the two-component developer is configured by a toner particle and a carrier particle. The toner particle is configured by a toner base particle and an external additive attached to the surface thereof. The toner can be prepared by using a known compound as a toner material according to an ordinary method.
The toner base particle contains a binder resin and a release agent. The binder resin includes the crystalline resin, and a vinyl resin as an amorphous resin.
The crystalline resin refers to a resin not exhibiting a stepwise endothermic change but exhibiting a distinct endothermic peak in DSC of the crystalline resin or the toner particle. The distinct endothermic peak specifically means a peak in which the half-value width of the endothermic peak in DSC measured at a rate of temperature rise of 10° C./min is within 15° C.
The crystalline resin may be of one or more. The melting point Tmc of the crystalline resin is preferably 60° C. or higher from the viewpoint that sufficient high-temperature storage property is achieved, and is preferably 85° C. or lower from the viewpoint that sufficient low-temperature fixability is achieved.
The melting point Tmc can be measured by DSC. Specifically, 0.5 mg of a crystalline resin sample is loaded into an aluminum pan “KITNO.B0143013”, the pan is set to a sample holder of a thermal analysis apparatus “Diamond DSC” (manufactured by PerkinElmer Co., Ltd.), and the temperature is varied in the order of heating, cooling and heating. The temperature is raised from room temperature (25° C.) to 150° C. at a rate of temperature rise of 10° C./min and kept at 150° C. for 5 minutes in first and second heatings, and the temperature is dropped from 150° C. to 0° C. at a rate of temperature drop of 10° C./min and kept at 0° C. for 5 minutes in cooling. The temperature at the peak top of the endothermic peak on the endothermic curve obtained in second heating is adopted as the melting point (Tmc).
The content of the crystalline resin relative to the toner base particle is preferably 5 mass % or more and 20 mass % or less, more preferably 7 mass % or more and 15 mass % or less from the viewpoint that sufficient low-temperature fixability is achieved. If the content is less than 5 mass %, a sufficient plasticization effect is not achieved and low-temperature fixability may be insufficient. If the content exceeds 20 mass %, thermal stability as the toner or stability against a physical stress may be insufficient. When the content is within the preferable range or more preferable range, for example, the configuration of the amorphous resin and a proper production method are selected to thereby more facilitate control to a preferable viscoelasticity.
The crystalline resin may be of one or more. Examples of the crystalline resin include a polyolefin resin, a polydiene resin and a polyester resin. The crystalline resin is preferably a crystalline polyester from the viewpoint that sufficient low-temperature fixability and uniformity of glossiness are achieved.
The number average molecular weight (Mn) of the crystalline resin is preferably 8,500 or more and 12,500 or less, more preferably 9,000 or more and 11,000 or less. If the Mw and Mn are too low, the strength of an image fixed may be insufficient, the crystalline resin may be pulverized in stirring of a developing liquid, and/or the glass transition temperature Tg of the toner may be decreased by an excess plasticization effect to cause thermal stability of the toner to be deteriorated. In addition, if Mw and Mn are too high, sharp meltability is difficult to exhibit, and the fixation temperature may be too high. Mw and Mn can be determined from the molecular weight distribution measured by gel permeation chromatography (GPC).
A specimen is added into tetrahydrofuran (THF) so that the concentration is 0.1 mg/mL, and dissolved therein by warming to 40° C., and thereafter the resultant is treated by a membrane filter with a pore size of 0.2 μm to prepare a specimen liquid. A GPC apparatus HLC-8220GPC (manufactured by Tosoh Corporation) and a column “TSKgel SuperH3000” (manufactured by Tosoh Corporation) are used, and THF as a carrier solvent is allowed to flow at a flow rate of 0.6 mL/min with the column temperature being kept at 40° C. The carrier solvent and 100 μL of the specimen liquid prepared are injected into the GPC apparatus, and the specimen is detected with a differential refractive index detector (RI detector). The molecular weight distribution of the specimen is then calculated using a calibration curve obtained by measurement at 10 points with respect to a monodisperse polystyrene standard particle. When a peak due to the filter is observed in data analysis, the region before generation of the peak is set as a baseline.
The crystalline polyester is obtained by a polycondensation reaction of a di- or higher-valent carboxylic acid (polyvalent carboxylic acid) and a di- or higher-hydric alcohol (polyhydric alcohol).
Examples of the polyvalent carboxylic acid include a dicarboxylic acid. The dicarboxylic acid may be of one or more, is preferably an aliphatic dicarboxylic acid, and may further include an aromatic dicarboxylic acid. The aliphatic dicarboxylic acid is preferably straight from the viewpoint that crystallinity of the crystalline polyester is enhanced.
Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid (dodecanedioic acid), 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, and lower alkyl esters and acid anhydrides thereof. Among them, C6 to 16 aliphatic dicarboxylic acids are preferable, and C10 to 14 aliphatic dicarboxylic acids are more preferable from the viewpoint that the effect of simultaneously satisfying low-temperature fixability and transfer property is easily achieved.
Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, t-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4′-biphenyldicarboxylic acid. Among them, terephthalic acid, isophthalic acid or t-butylisophthalic acid is preferable in terms of availability and ease of emulsification.
The content of the structural unit derived from the aliphatic dicarboxylic acid relative to the structural unit derived from the dicarboxylic acid in the crystalline polyester is preferably 50% by mole or more, more preferably 70% by mole or more, further preferably 80% by mole or more, particularly preferably 100% by mole from the viewpoint that crystallinity of the crystalline polyester is sufficiently ensured.
Examples of the polyhydric alcohol component include a diol. The diol may be of one or more, is preferably an aliphatic diol, and may further include other diol. The aliphatic diol is preferably straight from the viewpoint that crystallinity of the crystalline polyester is enhanced.
Examples of the aliphatic diol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol and 1,20-eicosanediol. Among them, C2 to 20 aliphatic diol are preferable, and C4 to 6 aliphatic diols are more preferable from the viewpoint that the effect of simultaneously satisfying low-temperature fixability and transfer property is easily achieved.
Examples of other diol include a diol having a double bond and a diol having a sulfonic acid group. Specifically, examples of the diol having a double bond include 2-butene-1,4-diol, 3-butene-1,6-diol and 4-butene-1,8-diol.
The content of the structural unit derived from the aliphatic diol relative to the structural unit derived from the diol in the crystalline polyester is preferably 50% by mole or more, more preferably 70% by mole or more, further preferably 80% by mole or more, particularly preferably 100% by mole from the viewpoint that low-temperature fixability of the toner and glossiness of an image to be finally formed are enhanced.
The ratio of the diol to the dicarboxylic acid in the monomer of the crystalline polyester is preferably 2.0/1.0 or more and 1.0/2.0 or less, more preferably 1.5/1.0 or more and 1.0/1.5 or less, particularly preferably 1.3/1.0 or more and 1.0/1.3 or less as the equivalent ratio [OH]/[COOH] of the hydroxy group [OH] of the diol to the carboxy group [COOH] of the dicarboxylic acid.
The monomer that constitutes the crystalline polyester preferably contains 50 mass % or more, more preferably 80 mass % or more of a straight aliphatic monomer. When an aromatic monomer is used, the melting point of the crystalline polyester significantly tends to be higher, and when a branched aliphatic monomer is used, crystallinity significantly tends to be lower. Accordingly, the straight aliphatic monomer is preferably used for the monomer. The straight aliphatic monomer in the toner is preferably used in an amount of 50 mass % or more, more preferably 80 mass % or more from the viewpoint that crystallinity of the crystalline polyester is kept.
The crystalline polyester can be synthesized by polycondensation (esterification) of the polyvalent carboxylic acid and the polyhydric alcohol by use of a known esterification catalyst.
The catalyst that can be used for synthesis of the crystalline polyester may be of one or more, and examples thereof include a compound of any alkali metal such as sodium and lithium; a compound containing any Group 2 element such as magnesium and calcium; a compound of any metal such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium and germanium; a phosphorous acid compound; a phosphoric acid compound; and an amine compound.
Specifically, examples of the tin compound include dibutyltin oxide, tin octylate, tin dioctylate, and salts thereof. Examples of the titanium compound include titanium alkoxides such as tetra-n-butyl titanate, tetraisopropyl titanate, tetramethyl titanate and tetrastearyl titanate; titanium acylates such as polyhydroxy titanium stearate; and titanium chelates such as titanium tetraacetylacetonate, titanium lactate and titanium triethanolaminate. Examples of the germanium compound include germanium dioxide, and examples of the aluminum compound include oxides such as aluminum polyhydroxide, and aluminum alkoxide and tributyl aluminate.
The polymerization temperature of the crystalline polyester is preferably 150° C. or higher and 250° C. or lower. The polymerization time is preferably 0.5 hours or more and 10 hours or less. In polymerization, the reaction system may be, if necessary, under reduced pressure.
The amorphous resin is a resin not having the above crystallinity. For example, the amorphous resin is a resin having no melting point and having a relatively high glass transition temperature (Tg) in differential scanning calorimetry (DSC) of the amorphous resin or the toner particle.
The Tg of the amorphous resin is preferably 35° C. or higher and 80° C. or lower, particularly preferably 45° C. or higher and 65° C. or lower.
The glass transition temperatures can be measured according to the method (DSC method) prescribed in ASTM (American Society for Testing and Materials Standard) D3418-82. In the measurement, a DSC-7 differential scanning calorimeter (manufactured by PerkinElmer Co., Ltd.), a TAC7/DX thermal analysis apparatus controller (manufactured by PerkinElmer Co., Ltd.), and the like can be used.
The amorphous resin may be of one or more. Examples of the amorphous resin include a vinyl resin, a urethane resin, a urea resin, and an amorphous polyester such as a styrene-acrylic modified polyester. In the present embodiment, the amorphous resin includes a vinyl resin from the viewpoint that thermoplasticity is easily controlled.
The vinyl resin is, for example, a polymer of a vinyl compound, and examples thereof include an acrylic acid ester resin, a styrene-acrylic acid ester resin and an ethylene-vinyl acetate resin. Among them, a styrene-acrylic acid ester resin (styrene acrylic resin) is preferable in terms of plasticity in thermal fixation.
The styrene acrylic resin is formed by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer. The styrene monomer includes, in addition to styrene represented by a structural formula CH2═CH—C6H5, a styrene derivative having known side chain and functional group in a styrene structure.
The (meth)acrylic acid ester monomer includes, in addition to an acrylic acid ester and a methacrylic acid ester represented by CH(R1)═CHCOOR2 (R1 represents a hydrogen atom or a methyl group, and R2 represents a C1 to 24 alkyl group), an acrylic acid ester derivative and a methacrylic acid ester derivative each having known side chain and functional group in the ester structure.
Examples of the styrene monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene and p-n-dodecylstyrene.
Examples of the (meth)acrylic acid ester monomer include acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate and phenyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate and dimethylaminoethyl methacrylate.
In the present specification, the “(meth)acrylic acid ester monomer” is a collective term of an “acrylic acid ester monomer” and a “methacrylic acid ester monomer”, and means one or both thereof. For example, “methyl (meth)acrylate” means one or both of “methyl acrylate” and “methyl methacrylate”.
The (meth)acrylic acid ester monomer may be of one or more. For example, the styrene monomer and two or more of the acrylic acid ester monomers can be used to form a copolymer, the styrene monomer and two or more of the methacrylic acid ester monomers can be used to form a copolymer, and the styrene monomer, and the acrylic acid ester monomer and the methacrylic acid ester monomer can be used in combination to form a copolymer.
The content of the structural unit derived from the styrene monomer in the amorphous resin is preferably 40 mass % or more and 90 mass % or less from the viewpoint that plasticity of the amorphous resin is controlled. The content of the structural unit derived from the (meth)acrylic acid ester monomer in the amorphous resin is preferably 10 mass % or more and 60 mass % or less.
The amorphous resin may further contain a structural unit derived from a monomer other than the styrene monomer and the (meth)acrylic acid ester monomer. Such other monomer is preferably a compound that can form an ester bond with the hydroxyl group (—OH) derived from the polyhydric alcohol or the carboxy group (—COOH) derived from the polyvalent carboxylic acid. That is, the amorphous resin is preferably a polymer obtained by polymerization of a compound (bifunctional compound) that can be subjected to addition polymerization with the styrene monomer and the (meth)acrylic acid ester monomer and that has a carboxy group or a hydroxy group.
Examples of the bifunctional compound include compounds having a carboxy group, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl ester and itaconic acid monoalkyl ester; and compounds having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and polyethylene glycol mono(meth)acrylate.
The content of the structural unit derived from the bifunctional compound in the amorphous resin is preferably 0.5 mass % or more and 20 mass % or less.
The styrene acrylic resin can be synthesized by a method of polymerizing a monomer by use of a known oil-soluble or water-soluble polymerization initiator. Examples of the oil-soluble polymerization initiator include an azo or diazo polymerization initiator and a peroxide polymerization initiator.
Examples of the azo or diazo polymerization initiator include 2,2′-azobis-(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis(cyclohexane-1-carbonitrile), 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile and azobisisobutyronitrile.
Examples of the peroxide polymerization initiator include benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, 2,2-bis-(4,4-t-butylperoxycyclohexyl)propane and tris-(t-butylperoxy)triazine.
When the resin particle of the styrene acrylic resin is synthesized by an emulsion polymerization, a water-soluble radical polymerization initiator can be used as the polymerization initiator. Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate, an azobisaminodipropane acetic acid salt, azobiscyanovaleric acid and a salt thereof, and hydrogen peroxide.
The weight average molecular weight (Mw) of the amorphous resin is preferably 5,000 or more and 150,000 or less, more preferably 10,000 or more and 70,000 or less from the viewpoint that plasticity of the amorphous resin is easily controlled.
The structure and the constitutional monomer of the crystalline resin have effects on the degree of crystallization and the amount of heat of fusion of the crystalline resin. The crystalline resin is preferably a hybrid crystalline polyester (hereinafter, also simply referred to as “hybrid resin”) from the viewpoint that the degree of crystallization of the crystalline resin is adjusted within a preferable range for fixation. The hybrid resin may be of one or more. The hybrid resin may be replaced with the total amount of the crystalline polyester, or may be replaced with a part of the crystalline polyester (used in combination).
The hybrid resin is a resin in which a crystalline polyester segment (also referred to as “polyester polymerization segment”) and a resin unit other than the crystalline polyester (also referred to as “other polymerization segment”) are chemically bound. In the present embodiment, the hybrid resin is a resin in which a crystalline polyester segment and an amorphous resin segment are chemically bound. The crystalline polyester segment means a portion derived from the crystalline polyester. That is, the segment means a molecular chain having the same chemical structure as the molecular chain forming the crystalline polyester. The amorphous resin segment means a portion derived from the amorphous resin. That is, the segment means a molecular chain having the same chemical structure as the molecular chain forming the amorphous resin.
The Mw of the hybrid resin is preferably 5,000 or more and 100,000 or less, more preferably 7,000 or more and 50,000 or less, particularly preferably 8,000 or more and 20,000 or less from the viewpoint that sufficient low-temperature fixability and excellent long-term storage stability can be simultaneously certainly satisfied. The Mw of the hybrid resin can be 100,000 or less to thereby impart sufficient low-temperature fixability. On the other hand, the Mw of the hybrid resin can be 5,000 or more to thereby inhibit compatibilization of the hybrid resin and the amorphous resin from excessively progressing in toner storage, effectively suppressing an image defect due to toner fusion.
The crystalline polyester segment may be, for example, a resin having a structure in which other component is copolymerized with the main chain of the crystalline polyester segment, or a resin having a structure in which the crystalline polyester segment is copolymerized with the main chain of other component. The crystalline polyester segment can be synthesized from the polyvalent carboxylic acid and the polyhydric alcohol in the same manner as in the crystalline polyester.
The content of the crystalline polyester segment in the hybrid resin is preferably 80 mass % or more and less than 98 mass %, more preferably 90 mass % or more and less than 95 mass %, further preferably 91 mass % or more and less than 93 mass % from the viewpoint that sufficient crystallinity is imparted to the hybrid resin. The constituent components of the respective segments in the hybrid resin (or in the toner), and the contents of the constituent components can be identified with a known analysis method such as nuclear magnetic resonance (NMR) and methylation pyrolysis gas chromatography/mass spectrometry (P-GC/MS).
The crystalline polyester segment preferably further includes, as a monomer, a monomer having an unsaturated bond from the viewpoint that a chemical bond moiety with the amorphous resin segment is introduced into the segment. The monomer having an unsaturated bond is, for example, a polyhydric alcohol having a double bond, and examples thereof include polyvalent carboxylic acids having a double bond, such as methylenesuccinic acid, fumaric acid, maleic acid, 3-hexenedioic acid and 3-octenedioic acid; and 2-butene-1,4-diol, 3-butene-1,6-diol and 4-butene-1,8-diol. The content of the structural unit derived from the monomer having an unsaturated bond in the crystalline polyester segment is preferably 0.5 mass % or more and 20 mass % or less.
The hybrid resin may be a block copolymer or a graft copolymer. The hybrid resin is preferably a graft copolymer from the viewpoints that orientation of the crystalline polyester segment is easily controlled and sufficient crystallinity is imparted to the hybrid resin, preferably a graft copolymer in which the crystalline polyester segment is grafted with a polymerization segment other than polyester serving as a main chain and a polyester resin segment serving as a side chain in a comb manner. That is, the hybrid resin is preferably a graft copolymer having the amorphous resin segment as a main chain and the crystalline polyester segment as a side chain.
A functional group such as a sulfonic acid group, a carboxy group or a urethane group may be further introduced to the hybrid resin. The functional group may be introduced into the crystalline polyester segment or the amorphous resin segment.
The amorphous resin segment enhances the affinity of the amorphous resin forming the binder resin with the hybrid resin. Thus, the hybrid resin is more easily incorporated into the amorphous resin, resulting in a more enhancement in charging uniformity of the toner. The constituent component of the amorphous resin segment in the hybrid resin (or in the toner), and the content of the constituent component can be identified with a known analysis method such as NMR and methylation P-GC/MS.
The glass transition temperature (Tg) of the amorphous resin segment in a first temperature rise process of DSC is preferably 30° C. or higher and 80° C. or lower, more preferably 40° C. or higher and 65° C. or lower, as in the case of the amorphous resin. The glass transition temperature (Tg) can be measured by the above method.
The amorphous resin segment is preferably configured from the same type of the resin as the amorphous resin (in the present embodiment, vinyl resin) included in the binder resin from the viewpoints that the affinity with the binder resin is enhanced and charging uniformity of the toner is enhanced. Such a mode is adopted to thereby more enhance the affinity of the hybrid resin with the amorphous resin, and the “same type” means that each resin has a common characteristic chemical bond in a repeating unit.
The “characteristic chemical bond” is according to “polymer classification” described in the material database (polymer.nims.go.jp/PoLyInfo/guide/jp/term_polymer.html) of National Institute for Materials Science (NIMS). That is, the “characteristic chemical bond” refers to any chemical bond that can form any polymer classified to 22 polymers in total of polyacryl, polyamide, polyacid anhydride, polycarbonate, polydiene, polyester, polyhaloolefin, polyimide, polyimine, polyketone, polyolefin, polyether, polyphenylene, polyphosphazene, polysiloxane, polystyrene, polysulfide, polysulfone, polyurethane, polyurea, polyvinyl and the like.
When the resin is a copolymer, the “same type of the resin” means that, when the monomer having a chemical bond serves as a structural unit in the chemical structure of a plurality of monomers constituting the copolymer, each resin has a common characteristic chemical bond. Accordingly, even when resins per se exhibit mutually different properties and/or have mutually different molar component rates of the monomers constituting the copolymer, these are assumed to be classified to the same type of the resin as long as a common characteristic chemical bond is included therein.
For example, a resin (or a resin segment) to be formed by styrene, butyl acrylate and acrylic acid, and a resin (or a resin segment) to be formed by styrene, butyl acrylate and methacrylic acid have at least a chemical bond that can form polyacryl, and these resins are classified to the same type of the resin. By way of another example, a resin (or a resin segment) to be formed by styrene, butyl acrylate and acrylic acid, and a resin (or a resin segment) to be formed by styrene, butyl acrylate, acrylic acid, terephthalic acid and fumaric acid have at least a chemical bond that can form polyacryl, as a mutually common chemical bond. Accordingly, these resins are classified to the same type of the resin.
Examples of the amorphous resin segment include a styrene-acrylic resin unit, a vinyl resin unit, a urethane resin unit and a urea resin unit. Among them, a vinyl resin unit is preferable from the viewpoint that thermoplasticity is easily controlled. Such a vinyl resin unit can be synthesized in the same manner as in the above vinyl resin.
The content of the structural unit derived from the styrene monomer in the amorphous resin segment is preferably 40 mass % or more and 90 mass % or less from the viewpoint that plasticity of the hybrid resin is easily controlled. From the same viewpoint, the content of the structural unit derived from the (meth)acrylic acid ester monomer in the amorphous resin segment is preferably 10 mass % or more and 60 mass % or less.
The amorphous resin segment preferably further contains, as a monomer, the bifunctional compound from the viewpoint that a chemical bond moiety with the crystalline polyester segment is introduced into the amorphous resin segment. The content of the structural unit derived from the bifunctional compound in the amorphous resin segment is preferably 0.5 mass % or more and 20 mass % or less.
The content of the amorphous resin segment in the hybrid resin is preferably 3 mass % or more and less than 15 mass %, more preferably 5 mass % or more and less than 10 mass %, further preferably 7 mass % or more and less than 9 mass % from the viewpoint that sufficient crystallinity is imparted to the hybrid resin.
The hybrid resin can be produced by, for example, first to third production methods described below.
The first production method is a method in which a polymerization reaction for synthesis of the crystalline polyester segment is performed in the presence of the amorphous resin segment synthesized in advance, to produce the hybrid resin.
In this method, first, the monomer for constituting the amorphous resin segment (preferably vinyl monomer such as styrene monomer and (meth)acrylic acid ester monomer) is subjected to an addition reaction to synthesize the amorphous resin segment. Next, a polymerization reaction of the polyvalent carboxylic acid and the polyhydric alcohol is performed in the presence of the amorphous resin segment, to synthesize the crystalline polyester segment. The polyvalent carboxylic acid and the polyhydric alcohol are here subjected to a condensation reaction, and also the polyvalent carboxylic acid or the polyhydric alcohol is subjected to an addition reaction to the amorphous resin segment, to thereby synthesize the hybrid resin.
In the first production method, a moiety at which the crystalline polyester segment and the amorphous resin segment can react with each other is preferably incorporated in the crystalline polyester segment or the amorphous resin segment. Specifically, the bifunctional compound is also used, in addition to the monomer for constituting the amorphous resin segment, in synthesis of the amorphous resin segment. The bifunctional compound reacts with a carboxy group or a hydroxy group in the crystalline polyester segment, thereby allowing the crystalline polyester segment to be bound to the amorphous resin segment chemically and quantitatively. In synthesis of the crystalline polyester segment, the compound having an unsaturated bond may also be further contained in the monomer.
The first production method can synthesize a hybrid resin having a structure (graft structure) where the crystalline polyester segment is molecularly bound to the amorphous resin segment.
The second production method is a method in which each of the crystalline polyester segment and the amorphous resin segment is formed in advance and these are bound to produce the hybrid resin.
In this method, first, the polyvalent carboxylic acid and the polyhydric alcohol are subjected to a condensation reaction to synthesize the crystalline polyester segment. The monomer for constituting the amorphous resin segment is subjected to an addition polymerization to synthesize the amorphous resin segment in a reaction system other than the reaction system for synthesis of the crystalline polyester segment. A moiety at which the crystalline polyester segment and the amorphous resin segment can react with each other is here preferably incorporated into one or both of the crystalline polyester segment and the amorphous resin segment, as described above.
Next, the crystalline polyester segment and the amorphous resin segment synthesized can react with each other to thereby synthesize a hybrid resin having a structure in which the crystalline polyester segment and the amorphous resin segment are molecularly bound.
When the reactive moiety is not incorporated into either the crystalline polyester segment or the amorphous resin segment, a method can be adopted in which a compound having a moiety that can be bound to both of the crystalline polyester segment and the amorphous resin segment is charged in the coexistence system of the crystalline polyester segment and the amorphous resin segment. Thus, the compound can allow a hybrid resin having a structure, where the crystalline polyester segment and the amorphous resin segment are molecularly bound, to be synthesized.
The third production method is a method in which a polymerization reaction for synthesis of the amorphous resin segment is performed in the presence of the crystalline polyester segment to produce the hybrid resin.
In this method, first, a condensation reaction of the polyvalent carboxylic acid and the polyhydric alcohol is performed for polymerization to synthesize the crystalline polyester segment in advance. Next, the monomer for constituting the amorphous resin segment is subjected to a polymerization reaction in the presence of the crystalline polyester segment to synthesize the amorphous resin segment. A moiety at which the crystalline polyester segment and the amorphous resin segment can react with each other is preferably incorporated to the crystalline polyester segment or the amorphous resin segment as in the first production method.
The method can synthesize a hybrid resin having a structure (graft structure) in which the amorphous resin segment is molecularly bound to the crystalline polyester segment.
Among the first to third production methods, the first production method is preferable because a hybrid resin having a structure in which a crystalline polyester chain is grafted to an amorphous resin chain is easily synthesized and a production process can be simplified. In the first production method, the amorphous resin segment is formed in advance and the crystalline polyester segment is then bound thereto, and therefore orientation of the crystalline polyester segment is easily made uniform. Accordingly, the first production method is preferable from the viewpoint that a hybrid resin suitable for the toner is certainly synthesized.
As the release agent, a known release agent can be used. The release agent may be of one or more. Examples of the release agent include polyolefin waxes such as polyethylene wax and polypropylene wax, branched hydrocarbon waxes such as microcrystalline wax; long chain hydrocarbon waxes such as paraffin wax and Sasolwax; dialkyl ketone waxes such as distearyl ketone, ester waxes such as carnauba wax, montan wax, behenic acid/behenate, trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitate and distearyl maleate, and amide waxes such as ethylenediamine behenylamide and tristearyl trimellitate amide. The release agent is easily made compatible with the vinyl resin. Therefore, the plasticization effect of the release agent can allow sharp meltability of the toner to be enhanced, thereby imparting sufficient low-temperature fixability. The release agent is preferably an ester wax (ester compound) from the viewpoint that sufficient low-temperature fixability is achieved, more preferably a straight ester wax (straight ester compound) from the viewpoint that furthermore heat resistance and low-temperature fixability are simultaneously achieved.
The melting point Tmr of the release agent is preferably 60° C. or higher, more preferably 65° C. or higher from the viewpoint that sufficient high-temperature storage property is achieved. The melting point Tmr of the release agent is preferably 90° C. or lower, more preferably 75° C. or lower from the viewpoint that sufficient low-temperature fixability of the toner is achieved. The content of the release agent in the toner is preferably 1 mass % or more and 30 mass % or less, more preferably 5 mass % or more and 20 mass % or less.
The content of a release agent in a black toner described later is preferably lower than that in a chromatic toner by 5 to 20 mass % from the viewpoint that a good relationship between the exothermic peak temperature of the black toner and the exothermic peak temperature of the chromatic toner, as described above, is achieved.
The toner may further contain any component other than the crystalline resin, the amorphous resin and the release agent as long as at least one of the effects of the present embodiment is exerted. For example, such other component that may be contained in the toner base particle includes a colorant and a charge control agent.
The colorant may be of one or more. Typical examples of the colorant include respective magenta, yellow, cyan and black colorants.
Examples of the magenta colorant include C.I. Pigment Reds 2, 3, 5, 6, 7, 15, 16, 48:1, 53:1, 57:1, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 139, 144, 149, 150, 163, 166, 170, 177, 178, 184, 202, 206, 207, 209, 222, 238 and 269.
Examples of the yellow colorant include C.I. Pigment Oranges 31, 43, C.I. Pigment Yellows 12, 14, 15, 17, 74, 83, 93, 94, 138, 155, 162, 180 and 185.
Examples of the cyan colorant include C.I. Pigment Blues 2, 3, 15, 15:2, 15:3, 15:4, 16, 17, 60, 62 and 66, and C.I. Pigment Green 7.
Examples of the black colorant include carbon black and a magnetic material particle. Examples of carbon black include channel black, furnace black, acetylene black, thermal black and lampblack. Examples of the magnetic material of the magnetic material particle include ferromagnetic metals such as iron, nickel and cobalt; alloys including such metals, ferromagnetic metal compounds such as ferrite and magnetite; chromium dioxide; and alloys not including any ferromagnetic metal but exhibiting ferromagnetic property by a heat treatment. Examples of the alloy exhibiting ferromagnetic property by a heat treatment include Heusler alloys such as manganese-copper-aluminum and manganese-copper-tin.
The content of the colorant in the toner base particle can be appropriately and independently determined, and is, for example, preferably 1 mass % or more and 30 mass % or less, more preferably 2 mass % or more and 20 mass % or less from the viewpoint that color reproducibility of an image is ensured. The size of the particle of the colorant, as a volume average particle size, is, for example, preferably 10 nm or more and 1,000 nm or less, more preferably 50 nm or more and 500 nm or less, further preferably 80 nm or more and 300 nm or less. The volume average particle size may be a catalog value, and the volume average particle size (median size on a volume basis) of the colorant can be measured by “UPA-150” (manufactured by MicrotracBEL Corp.).
As the charge control agent, a known charge control agent can be used, and examples include a nigrosine dye, a metal salt of naphthenic acid or a higher fatty acid, an alkoxylated amine, a quaternary ammonium salt compound, an azo metal complex and a salicylic acid metal salt. The content of the charge control agent in the toner is usually 0.1 parts by mass or more and 10 parts by mass or less, preferably 0.5 mass % or more and 5 mass % or less based on 100 parts by mass of the binder resin. The size of the particle of the charge control agent is, for example, 10 nm or more and 1,000 nm or less, preferably 50 nm or more and 500 nm or less, more preferably 80 nm or more and 300 nm or less as a number average primary particle size.
The external additive may be of one or more. The external additive is attached to the surface of the toner base particle to enhance charging performance, flow ability or cleaning property of the toner. Examples of the external additive include an inorganic fine particle, an organic fine particle and a lubricant.
Examples of the inorganic compound in the inorganic fine particle include silica, titania, alumina and strontium titanate. The inorganic fine particle may be, if necessary, subjected to a hydrophobic treatment with a surface treating agent such as a known silane coupling agent or a silicone oil. The size of the inorganic fine particle is preferably 20 nm or more and 500 nm or less, more preferably 70 nm or more and 300 nm or less as a number average primary particle size.
As the organic fine particle, an organic fine particle of a homopolymer of styrene or methyl methacrylate, or a copolymer thereof can be used. The size of the organic fine particle is about 10 to 2,000 nm as a number average primary particle size, and the shape of the particle is, for example, a spherical shape.
The lubricant is used for the purpose of further enhancing cleaning property and transfer property. Examples of the lubricant include a metal salt of a higher fatty acid, more specifically include zinc, aluminum, copper, magnesium and calcium salts of stearic acid; zinc, manganese, iron, copper and magnesium salts of oleic acid; zinc, copper, magnesium and calcium salt of palmitic acid; zinc and calcium salts of linoleic acid; and zinc and calcium salts of ricinoleic acid. The size of the lubricant is preferably 0.3 μm or more and 20 μm or less, more preferably 0.5 μm or more and 10 μm or less, as a median size on a volume basis (volume average particle size).
The median size on a volume basis of the lubricant can be determined according to JIS Z8825-1 (2013) (ISO 13320) that is specifically as follows.
A laser diffraction/scattering type particle size distribution analyzer “LA-920” (manufactured by Horiba, Ltd.) is used as a measurement apparatus. Dedicated software “HORIBA LA-920 for Windows (registered trademark) WET (LA-920) Ver.2.02” attached to LA-920 is used for setting of measurement conditions and analysis of measurement data. Ion-exchange water from which solid impurities are removed in advance is used as a measurement solvent.
The measurement procedure is according to the following (1) to (11).
(1) A batch type cell holder is mounted on LA-920.
(2) A predetermined amount of ion-exchange water is placed in a batch type cell, and the batch type cell is set in the batch type cell holder.
(3) The content of the batch type cell is stirred with a dedicated stirrer chip.
(4) The “refractive index” button on the “display condition setting” screen is pushed and file “110A000I” (relative refractive index: 1.10) is selected.
(5) The particle size basis is set to “volume basis” on the “display condition setting” screen.
(6) After a warming-up operation is performed for 1 hour or more, adjustment and fine adjustment of the optical axis, and blank measurement are performed.
(7) About 60 mL of ion-exchange water is placed in a 100-mL flat-bottomed glass beaker. About 0.3 mL of a diluted solution obtained by diluting “Contaminon N” (a 10 mass % aqueous solution of a neutral detergent for washing a precision measuring unit, including a non-ionic surfactant, an anionic surfactant and an organic builder and having a pH of 7, produced by Wako Pure Chemical Industries, Ltd.) with ion-exchange water about 3 mass-fold is added thereinto as a dispersant.
(8) An ultrasonic disperser “Ultrasonic Dispension System Tetora 150” (manufactured by Nikkaki Bios Co., Ltd.) is prepared in which two oscillators each having an oscillatory frequency of 50 kHz are built so as to be out of phase by 180° and which has an electrical output of 120 W. About 3.3 L of ion-exchange water is charged into a water tank of the ultrasonic disperser, and about 2 mL of Contaminon N is added into the water tank.
(9) The beaker in (7) is set in the beaker fixing hole of the ultrasonic disperser, and the ultrasonic disperser is operated. The position of the beaker is adjusted so that the liquid level of the aqueous solution in the beaker resonates to the maximum extent.
(10) While the aqueous solution in the beaker in (9) is irradiated with an ultrasonic wave, about 1 mg of lubricant particles are added in small portions into the aqueous solution in the beaker and dispersed. An ultrasonic dispersing treatment is continued for an additional 60 seconds. Here, the lubricant particles may be formed into a mass and the mass may float on the liquid surface, and in such a case, the beaker is vibrated and moved to thereby allow the mass to be settled in water, and ultrasonic dispersion is then performed for 60 seconds. In such ultrasonic dispersion, the temperature of water in the water tank is appropriately adjusted so as to be 10° C. or higher and 40° C. or lower.
(11) The aqueous solution prepared in (10) in which the lubricant particles are dispersed is added immediately in small portions to the batch type cell with careful attention so that no air bubble is incorporated, and the concentration of the dispersion liquid is adjusted so that the transmittance of light from a tungsten lamp is 90% to 95%. The particle size distribution is measured. The 50% cumulative size is determined based on the resulting particle size distribution data on a volume basis, and defined as the median size of the lubricant on a volume basis.
The particle size of the external additive may be a catalog value or a measured value. The volume average particle size of the external additive can be determined by observing 100 primary particles with respect to the external additive on the toner base particle by a scanning electron microscope (SEM) apparatus, measuring the longest size and the shortest size of the external additive by image analysis of the primary particles observed, and determining the equivalent spherical size from the median value of the longest size and the shortest size to provide the size (D50v) at a cumulative frequency of 50% of the equivalent spherical size. The volume average particle size of the external additive can be adjusted by, for example, pulverization and classification of a coarse particle, and mixing of classified particles.
The content of the external additive in the toner particle is preferably 0.1 parts by mass or more and 10.0 parts by mass or less based on 100 parts by mass of the toner particle. The external additive can be added to the toner base particle with known various mixing apparatuses such as a Turbula mixer, a Henschel mixer, a Nauta mixer and a V-type mixing machine.
The carrier particle includes a magnetic particle. Examples of the magnetic material of the magnetic particle include metals such as iron, ferrite and magnetite; alloys of such a metal with any metal such as aluminum and lead; and a conventionally known material. Among them, the magnetic particle is preferably a ferrite particle.
The carrier particle may be a resin-coated carrier particle having the magnetic particle and a resin layer with which the surface of the magnetic particle is coated, or may be a magnetic material-dispersed carrier particle in which a fine particle of the magnetic material is dispersed in a resin particle. Examples of the resin with which the resin-coated carrier particle is coated include an olefin resin, a cyclohexyl methacrylate-methyl methacrylate copolymer, a styrene resin, a styrene acrylic resin, a silicone resin, an ester resin and a fluororesin. Examples of the resin constituting the resin particle of the magnetic material-dispersed carrier particle include an acrylic resin, a styrene acrylic resin, a polyester, a fluororesin and a phenol resin.
The size of the carrier particle is preferably 15 μm or more and 100 μm or less, more preferably 25 μm or more and 60 μm or less as a volume average particle size. The content of the carrier particle in the toner is, for example, an amount that allows the concentration of the toner particle to be 6 to 8 mass %. The volume average particle size of the carrier particle can be measured by, for example, the same method as in the particle size of the external additive.
The average particle size of the toner particle is preferably 3.0 μm or more and 8.0 μm or less, more preferably 4.0 μm or more and 7.5 μm or less as a volume average particle size from the viewpoints that the occurrence of offset in fixation due to flying of the toner to a heating member in fixation is suppressed, transfer efficiency is enhanced and flow ability of the toner is enhanced. The average particle size of the toner particle can be determined by measuring the volume average particle size with “Coulter Multisizer 3” (manufactured by Beckman Coulter, Inc.), and can be controlled by the concentration of an aggregating agent and the amount of a solvent to be added in aggregation and fusion steps in production of the toner, the fusion time in the aggregation and fusion steps, or the composition of the binder resin.
The average circularity of the toner particle is preferably 0.920 or more and 1.000 or less, more preferably 0.940 or more and 0.995 or less from the viewpoint that transfer efficiency is enhanced. The average circularity is represented by the following expression. In the following expression, L0 represents the boundary length of a projection image of the particle (μm), and L1 represents the boundary length of a circle, determined from the equivalent circle size of the particle (μm). The average circularity can be measured by, for example, an average circularity measurement apparatus “FPIA-2100” (manufactured by Sysmex Corporation).
Average circularity=L1/L0
The toner base particle preferably has a lamella structure therein from the viewpoint that recrystallization of the crystalline resin is facilitated and low-temperature fixability and other characteristics above are thus easily simultaneously satisfied. For example, while the crystalline polyester largely contributes to low-temperature fixability, the crystalline polyester cannot sufficiently exert the effect of enhancing low-temperature fixability in some cases depending on the form thereof present in the toner. When the lamella structure of the crystalline polyester is present at desired position and size, melting of the binder resin is thus more effectively promoted and low-temperature fixability is more effectively exerted from there.
The lamella structure corresponds to a lamellar crystal structure, and means a layered structure in which two or more layers made of the molecular chain of the crystalline resin are laminated.
Examples of a structure at a molecular level that can be taken in the crystalline resin, other than the lamella structure, include a thread-like structure. The thread-like structure means a structure in which the molecular chain is not accumulated to such an extent that the layered structure is constructed.
The lamella structure can be achieved depending on, for example, the type of the material (monomer) of the binder resin. For example, use of a monomer having a configuration close to the crystalline material such as 2-EHA, as the monomer of the amorphous resin, in the case of the styrene acrylic resin, or use of dodecenylsuccinic acid as the monomer of the crystalline polyester can be effective for introduction of the lamella structure.
The presence of a lamella structure in the toner base particle can be confirmed by, for example, observation of the cross section of a piece (thickness of the piece: 60 to 100 nm) cut out from the toner base particle stained with ruthenium tetroxide (RuO4) with a transmission electron microscope “JEM-2000FX” (manufactured by JEOL Ltd.).
The toner base particle preferably has a core-shell structure from the viewpoint that heat resistance (for example, high-temperature storage property) and low-temperature fixability are easily simultaneously satisfied.
The method of producing the toner particle is not limited, and examples thereof include known polymerization methods such as a suspension polymerization method, an emulsion polymerization aggregation method and a dispersion polymerization method. The toner particle may be, for example, a particle having a core-shell structure in which the surface of a core particle including a core resin is coated with a shell layer including a shell resin, or a particle having a mono-layer structure not having such a shell layer. In the case of the particle having a core-shell structure, the shell resin forming the shell layer is preferably an amorphous resin.
While a toner base particle dried, obtained by the method of producing the toner particle, may be used for the toner as it is, a known external additive is added to the toner base particle to provide a toner particle by a dry method in which an external additive is added and mixed, and the toner particle may be used for the toner of the present invention. For the mixing apparatus of the external additive, known various mixing apparatuses such as a Turbula mixer, a Henschel mixer, a Nauta mixer and a V-type mixing machine can be used.
Hereinafter, as the method of producing the toner, a method of producing a yellow toner is specifically described in detail. With respect to a method of producing any toner other than a yellow toner, such as a magenta toner, a cyan toner or a black toner, a colorant to be used can be changed and the method of producing a yellow toner can be suitably adopted. The method of producing a toner according to the present invention is not limited to the following.
<Preparation of Aqueous Dispersion Liquid of Colorant Fine Particle>
Sodium dodecyl sulfate is dissolved in ion-exchange water with stirring, and a yellow colorant is added to the resulting aqueous solution and subjected to a dispersing treatment to thereby prepare an aqueous dispersion liquid of a colorant fine particle, in which a yellow colorant fine particle is dispersed.
<Preparation of Aqueous Dispersion Liquid of Release Agent-Containing Amorphous Vinyl Polymer>
(First Polymerization)
Sodium dodecyl sulfate and ion-exchange water are charged in a reaction vessel equipped with a stirring apparatus, a temperature sensor, a condenser and a nitrogen introduction apparatus, and heated with stirring in a nitrogen gas stream, an aqueous initiator solution in which potassium persulfate is dissolved in ion-exchange water is added, and a monomer-mixed liquid including, for example, styrene (St) as a styrene monomer, n-butyl acrylate (BA) as a (meth)acrylic acid ester monomer, methacrylic acid (MAA) as a compound having a carboxy group [—COOH] or a hydroxy group [—OH], and the like is dropped, and thereafter subjected to polymerization with heating and stirring to prepare dispersion liquid (1) of a resin fine particle.
(Second Polymerization)
A solution in which polyoxyethylene (2) dodecyl ether sodium sulfate is dissolved in ion-exchange water is charged in a reaction vessel equipped with a stirring apparatus, a temperature sensor, a condenser and a nitrogen introduction apparatus, and heated. Thereafter, a solution in which monomers and a release agent are dissolved, the solution including dispersion liquid (1) of a resin fine particle, and, for example, styrene (St) as a styrene monomer, n-butyl acrylate as a (meth)acrylic acid ester monomer, methacrylic acid (MAA) and n-octyl-3-mercaptopropionate as compounds having a carboxy group [—COOH] or a hydroxy group [—OH], and a release agent (behenic acid/behenate (melting point: 73° C.)), is added, and mixed and dispersed to prepare a dispersion liquid including an emulsified particle (oil droplet).
Next, to the dispersion liquid is added an aqueous initiator solution in which potassium persulfate is dissolved in ion-exchange water, and the system is subjected to polymerization with heating and stirring, to prepare dispersion liquid (2) of a resin fine particle.
(Third Polymerization)
After ion-exchange water is added to dispersion liquid (2) of a resin fine particle and well stirred, an aqueous initiator solution in which potassium persulfate is dissolved in ion-exchange water is added, and a monomer-mixed liquid including, for example, styrene (St) as a styrene monomer, n-butyl acrylate (BA) as a (meth)acrylic acid ester monomer, methacrylic acid (MAA) as a compound having a carboxy group [—COOH] or a hydroxy group [—OH], n-octyl-3-mercaptopropionate, and the like is dropped. After completion of the dropping, the resultant is subjected to polymerization by heating and stirring, and thereafter cooled to prepare an aqueous dispersion liquid of a release agent-containing amorphous vinyl polymer.
<Preparation of Aqueous Dispersion Liquid of Crystalline Polyester>
(Synthesis of Crystalline Polyester)
For example, styrene, n-butyl acrylate and acrylic acid, and a polymerization initiator (di-t-butyl peroxide), as raw material monomers and a radical polymerization initiator of an addition polymerization resin segment (that is here a styrene acrylic resin segment), are placed in a dropping funnel.
In addition, for example, sebacic acid as an aliphatic dicarboxylic acid and 1,12-dodecanediol as an aliphatic diol, as raw material monomers of a polycondensation resin segment (that is here a crystalline polyester segment), are placed in a four-neck flask equipped with a nitrogen introduction tube, a dehydration tube, a stirrer and a thermocouple, and heated and dissolved.
Next, the raw material monomers and the radical polymerization initiator of an addition polymerization resin segment, placed in the dropping funnel, are dropped with stirring to the solution heated and dissolved of the materials of a polycondensation resin segment, and aged, and the unreacted addition polymerization monomers are removed under reduced pressure. Thereafter, an esterification catalyst is loaded, and the resultant is heated, and subjected to a reaction under normal pressure and an additional reaction under reduced pressure. After cooling, the resultant is subjected to an additional reaction under reduced pressure to provide a crystalline polyester as a hybrid resin.
(Preparation of Aqueous Dispersion Liquid of Crystalline Polyester)
The crystalline polyester obtained in Synthesis Example above is dissolved in a solvent (for example, methyl ethyl ketone) with stirring. Next, to the solution is added an aqueous sodium hydroxide solution. Water is dropped and mixed with stirring of the solution, to thereby prepare an emulsified liquid. Next, the solvent is removed by distillation from the emulsified liquid, to thereby prepare an aqueous dispersion liquid in which the crystalline polyester is dispersed.
<Preparation of Aqueous Dispersion Liquid of Amorphous Polyester>
(Synthesis of Amorphous Polyester)
For example, a bisphenol A propylene oxide 2 mol adduct, terephthalic acid, fumaric acid and an esterification catalyst (for example, tin octylate) are placed in a reaction vessel equipped with a nitrogen introduction tube, a dehydration tube, a stirrer and a thermocouple, subjected to a polycondensation reaction and further a reaction under reduced pressure, and cooled.
Next, for example, a mixture of acrylic acid as a compound having a carboxy group [—COOH] or a hydroxy group [—OH], styrene as a styrene monomer, butyl acrylate as a (meth)acrylic acid ester monomer, and di-t-butyl peroxide as a polymerization initiator is dropped into the reaction vessel. After the dropping, the resultant is subjected to an addition polymerization reaction, thereafter heated, and kept under reduced pressure, and thereafter the compound having a carboxy group [—COOH] or a hydroxy group [—OH], the styrene monomer and the (meth)acrylic acid ester monomer are removed. Thus, an amorphous polyester in which a vinyl resin segment and a crystalline polyester segment are bound is synthesized.
(Preparation of Aqueous Dispersion Liquid of Amorphous Polyester)
The amorphous polyester obtained in Synthesis Example above is dissolved in a solvent (for example, methyl ethyl ketone) with stirring. Next, to the solution is added an aqueous sodium hydroxide solution. Water is dropped and mixed with stirring of the solution, to thereby prepare an emulsified liquid. Next, the solvent is removed by distillation from the emulsified liquid, to thereby prepare an aqueous dispersion liquid in which the amorphous polyester is dispersed.
<Production of Yellow Toner>
After the aqueous dispersion liquid of a release agent-containing amorphous vinyl polymer, and ion-exchange water are loaded into a reaction vessel equipped with a stirring apparatus, a temperature sensor and a condenser, an aqueous sodium hydroxide solution is added thereto to adjust the pH.
Thereafter, the aqueous dispersion liquid of a colorant fine particle is loaded to the reaction vessel, and an aqueous magnesium chloride solution is then added thereto to prepare a mixed liquid. The mixed liquid is heated, and the aqueous dispersion liquid of a crystalline polyester is further added to the mixed liquid to allow aggregation to progress. When the size of an aggregated particle reaches a desired particle size, the aqueous dispersion liquid of an amorphous polyester is loaded, and an aqueous solution in which sodium chloride is dissolved in ion-exchange water is added to stop growth of the particle. Thereafter, the mixed liquid is heated and stirred to thereby allow fusion of the particle to progress, and the resultant is thereafter cooled.
Next, the mixed liquid is subjected to solid-liquid separation, and the resulting solid (toner base particle) is washed and thereafter dried to thereby provide a yellow toner base particle. To the resulting toner base particle is added an external additive, to thereby produce a yellow toner particle.
(Method of Producing Yellow Toner)
A known ferrite carrier is added to and mixed with the yellow toner particle in an amount so that the toner concentration is 6 mass % or more and 8 mass % or less, to thereby produce a yellow toner.
The toner is used for a known electrophotographic image forming method according to an ordinary method. The toner is useful for formation of a high-quality image because of sufficiently having not only low-temperature fixability, but also all of high-temperature storage property, separation property and uniformity of glossiness, and is also useful in terms of toner distribution because of being also excellent in storage stability.
As is clear from the above description, the toner has a toner base particle containing a binder resin including a crystalline resin and a vinyl resin, and a release agent, and satisfies the following expressions (1) to (3). Accordingly, the toner sufficiently has not only low-temperature fixability, but also all of high-temperature storage property, separation property and uniformity of glossiness.
G′50° C.≧1×108 (1)
TmB−TmA≦8 (2)
Tm<TmB (3)
The toner much more effectively satisfies further the following expression (4) in terms of low-temperature fixability.
TmB−TmA≦4 (4)
Tm is much more effectively 60° C. or higher and 90° C. or lower from the viewpoint that low-temperature fixability and high-temperature storage property are simultaneously satisfied.
Tm is much more effectively 65° C. or higher and 85° C. or lower from the viewpoint that low-temperature fixability and high-temperature storage property are simultaneously satisfied.
The crystalline resin is much more effectively a crystalline polyester in terms of low-temperature fixability and uniformity of glossiness.
The crystalline resin is much more effectively a hybrid crystalline polyester in which a polyester polymerization segment and other polymerization segment are bound, from the viewpoint that the degree of crystallization of the crystalline resin, suitable for a fixing process in an image forming apparatus, is realized.
The melting point Tmc of the crystalline resin is much more effectively 60° C. or higher and 85° C. or lower from the viewpoint that low-temperature fixability and high-temperature storage property are simultaneously satisfied.
The content of the crystalline resin relative to the toner base particle is much more preferably 5 mass % or more and 20 mass % or less from the viewpoint that low-temperature fixability and high-temperature storage property are simultaneously satisfied.
The number average molecular weight of the crystalline resin is much more effectively 8,500 or more and 12,500 or less in terms of low-temperature fixability and high-temperature storage property.
The melting point Tmr of the release agent is much more effectively 60° C. or higher and 90° C. or lower from the viewpoint that low-temperature fixability and high-temperature storage property are simultaneously satisfied.
The melting point Tmr of the release agent is much more effectively 65° C. or higher and 75° C. or lower from the viewpoint that low-temperature fixability and high-temperature storage property are simultaneously satisfied.
The release agent is much more effectively an ester compound in terms of low-temperature fixability.
The release agent is much more effectively a straight ester compound from the viewpoint that heat resistance and low-temperature fixability are simultaneously satisfied.
The present embodiment can provide a toner into which a binder resin containing a crystalline resin and a vinyl resin is introduced, the toner sufficiently having all of low-temperature fixability, separation property, high-temperature storage property, and uniformity of glossiness of an image fixed.
(Synthesis of Amorphous Polyester)
The following components were charged in the following amounts into a reaction vessel equipped with a stirring apparatus, a nitrogen introduction tube, a temperature sensor and a rectifying column, and the temperature of the content in the reaction vessel was raised to 190° C. over 1 hour. “Fumaric acid” and “Terephthalic acid” correspond to polyvalent carboxylic acids. In addition, “2,2-BPPO” represents a “2,2-bis(4-hydroxyphenyl)propane propylene oxide 2 mol adduct”, “2,2-BPEO” represents a “2,2-bis(4-hydroxyphenyl)propane ethylene oxide 2 mol adduct”, and these correspond to polyhydric alcohols.
Fumaric acid 1.8 parts by mass
Terephthalic acid 29.2 parts by mass
2,2-BPPO 58.2 parts by mass
2,2-BPEO 6.7 parts by mass
After the content was confirmed to be uniformly stirred, dibutyltin oxide in an amount of 0.006 mass % based on the total amount of the polyvalent carboxylic acids was loaded as a catalyst into the reaction vessel, and the temperature of the content was raised from the temperature to 240° C. over 6 hours while water generated was distilled off. When the temperature reached 240° C., 2.4 parts by mass of trimellitic acid was further added and thereafter a dehydration condensation reaction was continued to perform a polymerization reaction until the acid value of a product reached 21 mgKOH/g at 240° C., thereby providing amorphous polyester.
Amorphous polyester obtained had a number average molecular weight (Mn) of 3,600 and a glass transition temperature (Tg) of 62° C.
(Preparation of Aqueous Dispersion Liquid A of Fine Particle of Amorphous Polyester)
To a reaction vessel having an anchor blade for imparting a stirring power were added 240 parts by mass of methyl ethyl ketone and 60 parts by mass of isopropyl alcohol (IPA), and nitrogen was supplied thereto to replace air in the system. Next, 300 parts by mass of amorphous polyester was slowly added to the mixed solvent with heating of the mixed solvent to 60° C. by an oil bath apparatus, and was dissolved with stirring. Next, to the resulting solution was added 20 parts by mass of 10% ammonia water, and thereafter 1,500 parts by mass of deionized water was loaded through a metering pump with stirring of the solution. It was confirmed that the liquid in the reaction vessel had an opaque white color and the stirring viscosity was reduced, and it was thus confirmed that emulsification was conducted.
Thereafter, the resultant was transferred to a separable flask having a stirring blade, a reflux apparatus and a vacuum pump as a decompression apparatus, the flask allowing an emulsified liquid to be pumped by the differential pressure based on a centrifugal force to form a wetting wall on the wall of a reaction tank. While the emulsified liquid was continuously stirred, the solvent and a dispersion medium were distilled off under reduced pressure at a wall temperature of the reaction tank of 58° C. A time point where the amount of the dispersion liquid in the emulsified liquid reached 1,000 parts by mass was defined as an end point of the concentrating under reduced pressure, the pressure in the reaction tank was turned to normal pressure, and the resultant was cooled to normal temperature with stirring to provide aqueous dispersion liquid A of a fine particle of amorphous polyester, having a solid content of 30 mass %. The median size D50v on a volume basis of the fine particle of amorphous polyester in aqueous dispersion liquid A was 162 nm.
(Synthesis of Crystalline Polyester 1)
The following raw material monomers and radical polymerization initiator (di-t-butyl peroxide) of an addition polymerization resin (styrene acrylic resin: StAc) unit having di-reactive monomers were placed in a dropping funnel in the following amounts to provide monomer liquid 1A.
Styrene 43.5 parts by mass
n-Butyl acrylate 16 parts by mass
Acrylic acid 3.5 parts by mass
Di-t-butyl peroxide 8 parts by mass
In addition, the following raw material monomers of a polycondensation resin (crystalline polyester: CPEs) unit were placed in a four-neck flask equipped with a nitrogen introduction tube, a dehydration tube, a stirring machine and a thermocouple in the following amounts, and heated to 170° C. and dissolved.
Tetradecanedioic acid 358 parts by mass
1,12-dodecanediol 145 parts by mass
Next, monomer liquid 1A was dropped to the monomer liquid in the four-neck flask with stirring over 90 minutes and aged for 60 minutes, and thereafter the unreacted addition polymerization monomers were removed from the four-neck flask under reduced pressure (8 kPa). The amounts of the monomers removed were very small as compared with the amounts in monomer liquid 1A.
Thereafter, 0.8 parts by mass of Ti(OBu)4 as an esterification catalyst was loaded to the mixed liquid in four-neck flask, the mixed liquid was heated to 235° C., and subjected to a reaction under normal pressure (101.3 kPa) for 5 hours and an additional reaction under reduced pressure (8 kPa) for 1 hour. The resulting mixed liquid was cooled to 200° C., and thereafter further subjected to a reaction under reduced pressure (20 kPa) for 1 hour to thereby provide crystalline polyester 1.
Crystalline polyester 1 included 10 mass % of the resin (StAc) unit other than CPEs relative to the total amount thereof, and was a resin in which CPEs was grafted to StAc. Crystalline polyester 1 obtained had a number average molecular weight (Mn) of 9,500 and a melting point (Tmc) of 72° C.
(Synthesis of Crystalline Polyester 2)
The same manner as in Synthesis of crystalline polyester 1 was performed except that the raw material monomers of the CPEs unit were changed as follows, to thereby provide crystalline polyester 2. Crystalline polyester 2 had a Mn of 8,500 and a Tmc of 63° C.
Adipic acid 236 parts by mass
1,10-Decanediol 241 parts by mass
(Synthesis of Crystalline Polyester 3)
The same manner as in Synthesis of crystalline polyester 1 was performed except that the composition of the monomer liquid of the StAc unit was changed as follows, to thereby provide crystalline polyester 3. Crystalline polyester 3 had a Mn of 9,300 and a Tmc of 69° C.
Styrene 87 parts by mass
n-Butyl acrylate 32 parts by mass
Acrylic acid 7 parts by mass
Di-t-butyl peroxide 16 parts by mass
(Synthesis of Crystalline Polyester 4)
The same manner as in Synthesis of crystalline polyester 1 was performed except that dropping and aging of the monomer liquid of the StAc unit, and removal of the unreacted monomers under reduced pressure were not performed, to thereby provide crystalline polyester 4. Crystalline polyester 4 had a Mn of 11,000 and a Tmc of 75° C.
(Synthesis of Crystalline Polyester 5)
The same manner as in Synthesis of crystalline polyester 1 was performed except that dropping and aging of the monomer liquid of the StAc unit, and removal of the unreacted monomers under reduced pressure were not performed and the reaction time under normal pressure (101.3 kPa) was changed to 90 minutes, to thereby provide crystalline polyester 5. Crystalline polyester 5 had a Mn of 14,000 and a Tmc of 79° C.
(Preparation of Aqueous Dispersion Liquid 1C of Fine Particle of Crystalline Polyester 1)
In 82 parts by mass of methyl ethyl ketone was dissolved 82 parts by mass of crystalline polyester 1 with stirring at 70° C. for 30 minutes. Next, to this solution was added 2.5 parts by mass of an aqueous 25 mass % sodium hydroxide solution (degree of neutralization: approximately 50%). The resulting solution was placed in a reaction vessel having a stirring machine, and 236 parts by mass of water warmed to 70° C. was dropped in and mixed with the solution with stirring over 70 minutes. The solution was clouded in the dropping, and a homogenous emulsion was obtained after the total amount of the water was dropped. The volume average particle size of the oil droplet of the emulsion was measured by a laser diffraction type particle size distribution analyzer “LA-750 (manufactured by Horiba, Ltd.)”, and was 123 nm.
Next, the emulsion was stirred with a diaphragm vacuum pump “V-700” (manufactured by BUCHI Labortechnik AG) under a reduced pressure of 15 kPa (150 mbar) for 3 hours with being kept warm at 70° C., to thereby remove methyl ethyl ketone by distillation, producing “aqueous dispersion liquid 1C of fine particle of crystalline polyester 1” (solid content: 25 mass %), in which the fine particle of crystalline polyester 1 was dispersed. The volume average particle size of the fine particle of crystalline polyester 1 in aqueous dispersion liquid 1C was measured by the particle size distribution analyzer, and was 75 nm.
(Preparation of Aqueous Dispersion Liquids 2C to 5C of Fine Particles of Crystalline Polyesters 2 to 5)
The same preparation as in aqueous dispersion liquid 1C described above was performed except that each of crystalline polyesters 2 to 5 was used instead of crystalline polyester 1, to thereby prepare each of aqueous dispersion liquids 2C to 5C of fine particles of crystalline polyesters 2 to 5. The respective volume average particle sizes of fine particles of crystalline polyesters 2 to 5 in aqueous dispersion liquids 2C to 5C were 400 nm.
The composition of each of aqueous dispersion liquids 1C to 5C of fine particles of crystalline polyesters 1 to 5, and the melting point and the number average molecular weight (Mn) of each of crystalline polyesters 1 to 5 are shown in Table 1.
(Preparation of Aqueous Dispersion Liquid 1A of Fine Particle of Amorphous Resin 1)
(First-Stage Polymerization)
Eight parts by mass of sodium dodecyl sulfate and 3 L of ion-exchange water were charged in a 5-L reaction vessel equipped with a stirring apparatus, a temperature sensor, a condenser and a nitrogen introduction apparatus, and the internal temperature was raised to 80° C. in a nitrogen gas stream with stirring at a stirring rate of 230 rpm. After the temperature rise, to the resulting aqueous solution was added an aqueous initiator solution in which 10 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchange water, and the temperature of the solution was again turned to 80° C.
Next, in the resulting mixed liquid were dropped a monomer-mixed liquid containing the following components in the following amounts over 1 hour, and thereafter subjected to polymerization with heating and stirring at 80° C. for 2 hours to thereby prepare dispersion liquid ×1 of a resin fine particle.
Styrene 480 parts by mass
n-Butyl acrylate 250 parts by mass
Methacrylic acid 68.0 parts by mass
(Second-Stage Polymerization)
An aqueous solution in which 7 parts by mass of polyoxyethylene (2) dodecyl ether sodium sulfate was dissolved in 3 L of ion-exchange water was charged in a 5-L reaction vessel equipped with a stirring apparatus, a temperature sensor, a condenser and a nitrogen introduction apparatus, and heated to 80° C. Thereafter, to the aqueous solution were added 260 parts by mass of dispersion liquid ×1 of a resin fine particle, and a raw material solution dissolved at 80° C. containing the following components in the following amounts, and mixed and dispersed by a mechanical dispersing machine “CLEARMIX” having a circulation pathway (manufactured by M Technique Co., Ltd., “CLEARMIX” being the registered trademark of the company) for 1 hour, to thereby prepare a dispersion liquid including an emulsified particle (oil droplet). “Behenyl behenate” corresponded to a release agent, and the melting point thereof Tmr was 73° C.
Styrene 284 parts by mass
2-Ethylhexyl acrylate 87 parts by mass
Methacrylic acid 28 parts by mass
n-Octyl-3-mercaptopropionate 6.4 parts by mass
Behenyl behenate 140 parts by mass
Next, to the dispersion liquid was added an aqueous initiator solution in which 5.6 parts by mass of potassium persulfate was dissolved in 200 mL of ion-exchange water, and the resulting mixed liquid was subjected to polymerization with heating and stirring at 84° C. over 1 hour to prepare dispersion liquid ×2 of a resin fine particle.
(Third-Stage Polymerization)
Furthermore, to dispersion liquid ×2 of a resin fine particle was added 400 mL of ion-exchange water and well mixed, and thereafter an aqueous initiator solution in which 6.6 parts by mass of potassium persulfate was dissolved in 400 mL of ion-exchange water was further added. The resulting dispersion liquid was heated to 82° C., and a monomer-mixed liquid containing the following components in the following amounts was dropped over 1 hour.
Styrene 430 parts by mass
n-Butyl acrylate 155 parts by mass
Methacrylic acid 51 parts by mass
n-Octyl-3-mercaptopropionate 8 parts by mass
After completion of the dropping, the resultant was subjected to polymerization with heating and stirring for 2 hours, and thereafter cooled to 28° C. to provide aqueous dispersion liquid 1A (solid content: 24 mass %) of a fine particle of amorphous resin 1 including a vinyl resin. The median size D50v on a volume basis of the fine particle of amorphous resin 1 in aqueous dispersion liquid 1A was 220 nm, and amorphous resin 1 had a glass transition temperature (Tg) of 55° C. and a weight average molecular weight (Mw) of 32,000.
(Preparation of Aqueous Dispersion Liquids 2A to 6A of Fine Particles of Amorphous Resins 2 to 6)
The same manner as in preparation of aqueous dispersion liquid 1A was performed except that the raw materials in second-stage polymerization and the amounts thereof were changed as shown in Table 2 below, to thereby provide each of aqueous dispersion liquids 2A to 6A with fine particles of amorphous resins 2 to 6 dispersed.
The fine particle of amorphous resin 2 in aqueous dispersion liquid 2A had a D50v of 215 nm, a Tg of 53° C. and a Mw of 28,000. The fine particle of amorphous resin 3 in aqueous dispersion liquid 3A had a D50v of 230 nm, a Tg of 52° C. and a Mw of 30,000. The fine particle of amorphous resin 4 in aqueous dispersion liquid 4A had a D50v of 210 nm, a Tg of 52° C. and a Mw of 25,000. The fine particle of amorphous resin 5 in aqueous dispersion liquid 5A had a D50v of 215 nm, a Tg of 51° C. and a Mw of 30,000. The fine particle of amorphous resin 6 in aqueous dispersion liquid 6A had a D50v of 220 nm, a Tg of 53° C. and a Mw of 2,800.
The compositions of raw materials of amorphous resins 1 to 6 are shown in Table 2. In Table 2, “St” represents styrene, “BA” represents n-butyl acrylate, “MAA” represents methacrylic acid, “KPS” represents potassium persulfate, “2EHA” represents 2-ethylhexyl acrylate, “NOM” represents n-octyl-3-mercaptopropionate, “BB” represents behenic acid/behenate (melting point: Tmr 73° C.), “MC” represents microcrystalline wax (melting point: Tmr 89° C.), and “SS” represents stearyl stearate (melting point: Tmr 67° C.). The numerical values in Table 2 are represented by parts by mass, except for the melting point Tmr of the release agent.
(Preparation of Aqueous Dispersion Liquid Bk of Colorant Fine Particle) Ninety parts by mass of polyoxyethylene-2-dodecyl ether sodium sulfate was added to 1,510 parts by mass of ion-exchange water and dissolved therein. While the resulting aqueous solution was stirred, 400 parts by mass of carbon black “Regal 330” (produced by Cabot Corporation) was gradually added to the aqueous solution, and thereafter subjected to a dispersing treatment with a stirring apparatus “CLEARMIX” (manufactured by M Technique Co., Ltd.) to thereby prepare aqueous dispersion liquid Bk of a colorant fine particle, having a solid content of 20 mass %.
The average particle size (median size on a volume basis) of the colorant fine particle in aqueous dispersion liquid Bk was measured with “Microtrac UPA-150” (manufactured by Nikkiso Co., Ltd.), and was 110 nm.
In a reaction vessel equipped with a stirring apparatus, a temperature sensor, a condenser and a nitrogen introduction apparatus were charged 3,041 parts by mass of aqueous dispersion liquid 5A, 350 parts by mass of aqueous dispersion liquid Bk and 300 parts by mass of ion-exchange water, and an aqueous 5 mol/L sodium hydroxide solution was added with stirring to adjust the pH of the dispersion liquid in the reaction vessel to 10.5 (20° C.). Aqueous dispersion liquid 5A was an aqueous dispersion liquid of a fine particle of amorphous resin 5, and the amount thereof was 730 parts by mass as a solid content. Aqueous dispersion liquid Bk was an aqueous dispersion liquid of a colorant fine particle, and the amount thereof was 70 parts by mass as a solid content.
Next, to the dispersion liquid was added an aqueous solution, in which 160 parts by mass of chloride magnesium was dissolved in 160 parts by mass of ion-exchange water, at a rate of 10 parts by mass/min. After the resultant was left to stand for 5 minutes, temperature rise was initiated to heat the dispersion liquid to 80° C. over 60 minutes, and the fine particle in the dispersion liquid was aggregated at the temperature.
When the average particle size of the aggregated particle in the dispersion liquid reached 2.4 μm, 333 parts by mass of aqueous dispersion liquid 1C was added to the dispersion liquid over 10 minutes and heated to 85° C. to allow an additional aggregation reaction to progress. Aqueous dispersion liquid 1C was an aqueous dispersion liquid of a fine particle of crystalline polyester 1, and the amount thereof was 100 parts by mass as a solid content.
The aggregation reaction was periodically subjected to sampling to measure the median size on a volume basis of the aggregated particle with a particle size distribution analyzer “Coulter Multisizer 3” (manufactured by Beckman Coulter, Inc.). Stirring was continued, with the stirring rate being if necessary reduced, until the D50v of the aggregated particle reached 5.9 μm, to perform the aggregation reaction.
When the D50v of the aggregated particle reached 5.9 μm, the stirring rate was increased and 333 parts by mass of aqueous dispersion liquid A was added to the dispersion liquid over 40 minutes. Aqueous dispersion liquid A was an aqueous dispersion liquid of a fine particle of amorphous polyester, and the amount thereof was 100 parts by mass as a solid content.
Thereafter, the dispersion liquid was sampled and the supernatant was confirmed to be transparent by centrifugation. Thereafter, an aqueous solution in which 300 parts by mass of sodium chloride was dissolved in 1,200 parts by mass of ion-exchange water was added to the dispersion liquid, the temperature of the dispersion liquid was set at 80° C. and stirring was continued. The average circularity of the particle in the dispersion liquid was measured by a flow particle image analyzer “FPIA-2100” (manufactured by Sysmex Corporation), and when the average circularity reached 0.961, the dispersion liquid was cooled to 30° C. at a rate of 6° C./min to stop a granulation reaction, thereby providing a dispersion liquid of colored particle 1. Colored particle 1 after cooling had an average particle size (D50v) of 6.1 μm and an average circularity of 0.961.
The dispersion liquid of colored particle 1 was subjected to solid-liquid separation with a basket centrifuge machine “MARK III Model 60×40” (manufactured by Matsumoto Machine Co., Ltd.), to provide a wet cake. The wet cake was washed and subjected to solid-liquid separation by the basket centrifuge machine repeatedly until the electrical conductivity of a filtrate was 15 μS/cm, and the wet cake after washing was supplied in small portions to “Flash Jet Drier” (manufactured by Seishin Enterprise Co., Ltd.) and dried by blowing of a stream of air at a temperature of 40° C. and a humidity of 20% RH until the amount of water was about 2.0 mass %, and thereafter cooled to 24° C. Thereafter, a powder cake dried and cooled was transferred to a “vibration fluidized-layer apparatus” (manufactured by Chuo Kakouki Co., Ltd.), and the powder cake was dried at 40° C. for 2 hours. Thus, toner base particle 1 having an amount of water of 0.5% or less was obtained.
Toner base particle 1 was subjected to a treatment with an external additive to thereby provide toner particle 1. In the treatment with an external additive, hydrophobic silica was added in an amount of 1 mass % and also hydrophobic titanium oxide was added in an amount of 1.2 mass % to toner base particle 1, and mixed by a “Henschel mixer” (manufactured by Nippon Coke & Engineering. Co., Ltd.) at a peripheral speed of a rotor blade of 24 mm/sec for 20 minutes, and thereafter a coarse particle was removed with a 400-mesh sieve.
A ferrite carrier particle having a volume average particle size of 32 μm, in which toner particle 1 was coated with an acrylic resin, was added and mixed so that the concentration of the toner particle was 6 mass %, to provide toner 1 as a two-component developer for a black color.
The same manner as in production of toner 1 was performed except that the type and the amount of the aqueous dispersion liquid were changed as shown in Table 3, to thereby produce each of toners 2 to 11.
Resin compositions of toners 1 to 11 are shown in Table 3. In Table 3, the content represents the content in the toner base particle. In Table 3, “APEs” represents an amorphous polyester.
(Evaluation)
(1) Measurement of Peak Top Temperature (Tm) of Endothermic Peak of Toner Particle
Into an aluminum pan KITNO.B0143013 was 5 mg of each of toner particles 1 to 11, set in a sample holder of a thermal analysis apparatus “Diamond DSC” (manufactured by PerkinElmer Co., Ltd.) and heated. In first heating, the peak top temperature Tm of the endothermic peak in temperature rise from 0° C. to 100° C. at a rate of temperature rise of 10° C./min was adopted. When a plurality of endothermic peaks are observed, the peak top temperature of the endothermic peak positioned at the highest temperature was defined as Tm.
(2) Measurement of Storage Elastic Moduli G′ and G′50° C., and TmA and TmB
Each of toner particles 1 to 9 was used as a measurement sample and the storage elastic modulus was measured by the above method.
Weighed was 0.2 g of each of toner particles 1 to 11, and pressure molding was performed by a compression molding machine with application of a pressure of 25 MPa, to produce a columnar pellet having a diameter of 10 mm. A rheometer “ARES G2” (manufactured by TA instruments. Japan) was used and a set of upper and lower parallel plates having a diameter of 8 mm was used to perform measurement at a frequency of 1 Hz. The sample was set at 100° C., the gap between the plates was set at 1.6 mm once, thereafter the sample protruded from the gap between the plates was scraped off, the gap was set at 1.4 mm, and the pellet was cooled to 25° C. with an axial force being applied, and left to still stand for 10 minutes. Thereafter, the axial force was released, and the storage elastic modulus (G′) was measured in temperature rise from 25° C. to 100° C. The measurement was performed at a rate of temperature rise of 3° C./min, to provide the curve of temperature variance. The storage elastic modulus G′50° C. at a measurement temperature of 50° C., the measurement temperature TmA at a G′ of 1×106 Pa, and the measurement temperature TmB at a G′ of 1×105 Pa were measured based on the curve of temperature variance.
Specific measurement conditions are shown below.
Frequency: 1 Hz
Rate of temperature rise (Ramp rate): 3° C./min
Axial force: 0 g
Sensitivity: 10 g
Initial strain: 0.01%
Strain adjustment: 30.0%
Minimum strain: 0.01%
Maximum strain: 10.0%
Minimum torque: 1 g·cm
Maximum torque: 80 g·cm
Sampling interval: 1.0° C./pt
Classification and physical properties of each of toners 1 to 11 are shown in Table 4. In Table 4, “TmB−TmA” represents the difference between TmB and TmA, “Tm<TmB” represents the magnitude relationship between Tm and TmB, “A” represents that TmB is higher than Tm, and “B” represents that TmB is equal to or lower than Tm.
(3) Evaluation of Low-Temperature Fixability
Commercially available full-color multifunctional peripherals “bizhub C754” (manufactured by Konica Minolta Japan, Inc., “bizhub” being the registered trademark of the company) altered were used for an image forming apparatus. The peripherals altered served as an image forming apparatus altered so that the surface temperatures of a fixing belt in a fixing apparatus and a pressure roller of the full-color multifunctional peripherals could be adjusted. The evaluation test of the low-temperature fixability was performed by accommodating each of toners 1 to 11 in the peripherals altered, and outputting a solid image with an amount of each of toners 1 to 11 attached of 11.3 g/m2, on A4 (basis weight: 80 g/m2) normal paper in conditions of a nip width of 11.2 mm, a fixation time of 34 msec, a fixation pressure of 133 kPa and a fixation temperature of 100 to 200° C.
In the evaluation test, the fixation temperature was changed within the above range by 5° C., and the solid image was formed at each fixation temperature. The solid image formed was then visually observed, and the minimum fixation temperature, among fixation temperatures at which a solid image without any smear due to offset in fixation observed was formed, was defined as the minimum fixation temperature. The low-temperature fixability was rated according to the following evaluation criteria. A minimum fixation temperature of 150° C. or higher has no problem in practical use.
(Evaluation Criteria)
A: the minimum fixation temperature was less than 135° C.
B: the minimum fixation temperature was 135° C. or higher and less than 150° C.
C: the minimum fixation temperature was 150° C. or higher and less than 155° C.
D: the minimum fixation temperature was 155° C. or higher.
(4) Evaluation of Separation Property
The surface temperature of the fixing belt was set at a temperature higher than the temperature at which low-temperature offset occurred, by 15° C., in the same method as in the low-temperature fixability test, and a belt-shaped solid image of 5 cm in width was conveyed in a direction perpendicular to the conveyance direction of paper in a longitudinal feeding manner. The separation property of the fixing roller and the paper was evaluated according to the following evaluation criteria. Rating “A”, “B” or “C” of the separation property has no problem in practical use.
(Evaluation Criteria)
A: the fixing roller and the paper were separated without any curling of the paper and any contact with a separating claw.
B: the fixing roller and the paper were separated by a separating claw, but no mark of the separating claw remained on the image.
C: the fixing roller and the paper were separated by a separating claw, but almost no mark of the separating claw remained on the image.
D: the fixing roller and the paper were separated by a separating claw, and the mark of the separating claw remained on the image or the paper was wound around the fixing roller not to separate the fixing roller and the paper.
(5) Evaluation of Uniformity of Glossiness
The surface temperature of the fixing belt was set at a temperature higher than the temperature at which low-temperature offset occurred, by 20° C., in the same method as in the low-temperature fixability test, and the solid image was formed. The uniformity of glossiness was evaluated according to the following evaluation criteria. Rating “A”, “B” or “C” of the uniformity of glossiness has no problem in practical use.
(Evaluation Criteria)
A: when the image was observed by a loupe at 20-fold magnification, no variation in gloss was detected.
B: when the image was observed by a loupe at 20-fold magnification, a slight variation in gloss was detected, but, when the image was visually observed, no variation in gloss was detected.
C: when the image was visually observed, a slight variation in gloss was detected without any problem in terms of image quality.
D: when the image was visually observed, a clear variation in gloss was detected.
(6) Evaluation of High-Temperature Storage Property
Into a 10-mL glass bottle having an inner diameter of 21 mm was loaded 0.5 g of each of toners 1 to 11, and the lid was closed. After the glass bottle was shaken 600 times by a shaking machine “Tap Denser KYT-2000” (manufactured by Seishin Enterprise Co., Ltd.) at room temperature, the glass bottle with the lid being opened was placed in an environment of a temperature of 55° C. and a humidity of 35% RH and left to stand for 2 hours. Next, the total amount of the toner in the glass bottle was carefully loaded on a 48-mesh (opening: 350 μm) sieve so that the aggregate of the toner was not broken. Next, the sieve was set to “Powder Tester” (manufactured by Hosokawa Micron Corporation) and secured by a pressing bar and a knobnut, and vibration was applied thereto for 10 seconds with the vibration strength being adjusted so that the feeding width was 1 mm.
The mass of the toner passing through the sieve was measured, and the sieve permeability Rp was calculated by the following expression. In the following expression, “W0” represents the mass (g) of the toner loaded on the sieve, and “W1” represents the mass (g) of the toner remaining on the sieve. The high-temperature storage property of each of toners 1 to 11 was evaluated according to the following evaluation criteria based on the resulting sieve permeability. As the sieve permeability was higher, aggregation in storage at a high temperature less occurred and high-temperature storage property was good. A sieve permeability of 80% or more has no problem in practical use.
Rp(%)={(W0−W1)/W0}×100
(Evaluation Criteria)
A: the sieve permeability was 90% or more.
B: the sieve permeability was 85% or more and less than 90%.
C: the sieve permeability was 80% or more and less than 85%.
D: the sieve permeability was less than 80%.
The classification and evaluation results of toners 1 to 11 in the evaluation test are shown in Table 5.
As shown in Table 4 and Table 5, toners 1 to 7 were sufficiently good in all of low-temperature fixability, separation property, uniformity of glossiness and high-temperature storage property.
On the contrary, toner 8 was insufficient in high-temperature storage property. The reason for this was considered because G′50° C. was less than 1×108 Pa to thereby make it impossible to suppress the variation in hardness of the surface of toner 8 in a relatively high temperature region.
Toner 9 and toner 10 were insufficient in low-temperature fixability. The reason for this was considered because the difference value of TmB and TmA was more than 8 and sharp meltability was insufficient.
Toner 11 was insufficient in both of separation property and uniformity of glossiness. The reason for this was considered because Tm was higher than TmB and the residue of fusion of the crystalline resin or the release agent was confirmed in fixation of the toner.
The present invention is expected to allow a forming technique of an electrophotographic high-quality image to be developed and further widely used.
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