Carrier core and preparation method thereof and use in developer developing electrostatic image carrier
Technical field
The present invention relates to print field, specifically a kind of use in developer developing electrostatic image carrier core and preparation method thereof and use in developer developing electrostatic image carrier.
Background technology
Electrostatic image development technology has now been applied to multiple fields, in this technology, image obtains by the following method: on photoreceptor, form electrostatic latent image by charging and exposure process, use again the toner that contains colorant by latent electrostatic image developing, then be transferred to transferring member, finally make information visualization by heat fixer.Electrostatic charge image developer comprises two large classes: contain the two-component developing agent of toner and carrier and only contain the monocomponent toner of toner.As the carrier of two-component developing agent, now widely used is the carrier that comprises carrier core and be coated on the resin bed on carrier core surface.
Carrier has two basic functions, on the one hand, by with the friction of toner, make toner there is required carried charge; On the other hand, bearing the function that toner is sent to photoreceptor.In developer, carrier is adsorbed on left magnetic roller owing to being subject to magneticaction.And on the surface of carrier particle, be also attached with multiple toner particles, i.e. the catenulate magnetic brush structure of shape.In the time that magnetic roller rotates, magnetic brush contact photoreceptor, transfers to photosensitive surface by toner and develops, and carrier in developing apparatus by Reusability.In the process using, require the various functions of carrier to keep stable.
In order to realize the basic function of carrier, carrier core should have good magnetic.If the magnetization of carrier core is lower than setting, magnetic force is not enough to resist centrifugal force, and carrier will disperse out from magnetic roller, causes image to occur abnormal, i.e. the so-called carrier phenomenon of dispersing.If the magnetization of carrier core higher than setting, can cause again magnetic brush really up to the mark, can not obtain good image.
In recent years, in order to improve the quality of image, have the demand of the particle diameter that reduces toner particle.Corresponding, the particle diameter of carrier particle also requires further to reduce.But along with the small particle diameter of carrier core, there is again new problem to produce.On the one hand, diameter of carrier diminishes, and may cause the magnetization of carrier to decline, and carrier occurs and disperse.On the other hand, the carrier core of small particle diameter has the tendency of the surface differences that increases carrier core.Generally, the step of preparing carrier core comprises the mixing of raw material, and pulp is pulverized, and granulation, calcines subsequently and sintering makes its Ferrite method.The grain size distribution on the carrier core surface of small particle diameter is wider, not of uniform size, easily occurs coarse grain.The carrier core that this surface differences is huge, and bad adhesion between the coating resin covering in coated operation subsequently, cause carrier and the developer prepared to decline serviceable life.
Carrier core also should have suitable resistivity.In the long-term process using, on carrier, part coating resin can be peeled off, and produces charge leakage phenomenon, causes image deflects.If carrier core has good insulativity, this phenomenon will be inhibited, very helpful for the serviceable life that extends carrier.
Before this, existing publication is devoted to the research of carrier core small particle diameter, for example, in raw material, add micro-strontium element (Sr).Because can making ferrite reaction and sintering, strontium element carries out lentamente, therefore the ferrite inner void forming is few, and particle surface crystal grain homogeneous.The carrier core that uses such method to prepare, in realizing small particle diameter, can make the crystallite dimension of particle surface suitable, and can realize high strength.Experimental result shows, strontium element add the effect that really can play slowed down reaction speed, refinement ferrite crystal grains, but in process of production the addition of strontium be difficult to accomplish just right.If the addition of strontium is on the low side, ferritic crystallite dimension cannot be effectively controlled.If strontium element addition is on the high side, in sintering process, will produce many strontium ferrites.Strontium ferrite has higher residual induction, is unfavorable for the formation of magnetic brush.
Summary of the invention
The object of the invention is in order to solve the problems of the technologies described above, when electrophotographic developing is realized small particle diameter with carrier core, the even grain size of particle surface is moderate, and resistivity is high.
The present invention also provides a kind of preparation method of above-mentioned carrier core, and its technique is simple, flow process controllability is high, and the carrier core of production is in having small particle diameter, and the even grain size of particle surface is moderate, and resistivity is high.
The present invention also provides a kind of use in developer developing electrostatic image carrier that can form good image quality that contains above-mentioned carrier core.
The preparation method of use in developer developing electrostatic image carrier core of the present invention, take the potpourri of metal oxide and rare earth oxide as raw material, make through pulverizing, granulation, calcining, sintering, wherein, in metal oxide, at least contain metallic element Fe, rare earth oxide at least contains a kind of rare earth element in La, Ce, Pr, Nd, Gd, and the content of rare earth oxide is no more than 3% of raw material gross mass, preferably 0.25-1%.
Described metal oxide also contains Mn and/or Mg.
After described pulverizing process, the mean grain size of material is within the scope of 0.5-3.0 μ m, and the mean grain size value of the carrier core of preparation is at 20 μ m-30 μ m.
The use in developer developing electrostatic image carrier core of being prepared by said method, with chemical general formula Mn
xmg
yfe
zo
4composition shown in (0≤x≤1,0≤y≤1,2≤z≤3) is as principal ingredient, and at least contains a kind of rare earth element in La, Ce, Pr, Nd, Gd.
The mean grain size value of described carrier core is more than 20 μ m in the scope below 30 μ m.
The specific insulation of described carrier core is 10
7-10
12Ω cm.
Under the magnetic field intensity effect of the 1000Oe of portion outside of described carrier core, saturation magnetization σ
sfor 40-80Am
2/ kg, remanent magnetization σ
rfor 10.0Am
2below/kg, coercive force H
cfor 5Am
2below/kg.
Use in developer developing electrostatic image carrier of the present invention, comprises described carrier core and is coated on the resin bed on described carrier core.
The small particle diameterization of carrier core requires the raw material of preparing carrier core also will realize small particle diameter.This is the growth of crystal while contributing to suppress high temperature due to the raw material of small particle diameter, can play the surface of controlling carrier core, makes the effect that crystallite dimension is suitable.And in the time that the particle diameter of raw material is larger, the filling rate of pelletizing reduces, preparing carrier core is free hole to produce.But the method that merely reduces raw material particle size is also inadvisable.This is that in sintering process, sintering velocity is very fast, is difficult to control the surface state of carrier core because the little raw material reaction activity of particle diameter is high.Therefore must control sintering process with adjuvant simultaneously.Present inventor is by deep research, is chosen in and in raw material, adds rare earth oxide.The ionic radius of rare earth element is larger, is difficult to enter into ferritic lattice dot matrix and goes, and can only be present in crystal boundary position.In the time that ferrite crystal grains is grown, these rare earth element can play the effect that hinders crystal growth, make the ferrite crystal grains size uniform prepared moderate.Meanwhile, the rare earth oxide in crystal boundary position has also increased the scattering of crystal boundary to conduction electron, has improved the resistivity of carrier core.
Require the mean grain size of material after pulverizing process within the scope of 0.5-3.0 μ m.It is pointed out that in crushing process, the mean grain size of material is compared raw material and can be reduced to some extent, that is to say, the mean grain size of raw material is not limited within the scope of this.
In the preparation process of carrier core, also to add as required bonding agent, spreading agent and defoamer (these become branch to remove) in sintering process.Bonding agent can be selected starch, polyvinyl alcohol (PVA), carboxymethyl cellulose etc., preferably polyethylene alcohol; Spreading agent can be selected fat carboxylic acid, fatty acyl amide, polycarboxylic acid's ammonium salt class, ester class etc., preferably polycarboxylic acid's ammonium salt class; Defoamer is selected n-octyl alcohol.With chemical general formula Mn
xmg
yfe
zo
4composition shown in (0≤x≤1,0≤y≤1,2≤z≤3) is as the principal ingredient of carrier core.Mn ferrite has ferromagnetism, and therefore preferably x > 0.7 has higher saturation magnetization to guarantee carrier core.Although magnesium ferrite magnetic a little less than, it has higher resistivity.These two kinds of ferrites are used in conjunction with and the magnetic characteristic of carrier core and resistivity can be adjusted to desirable level.The content of raw material middle rare earth should not exceed 3% of gross mass.This is not only because rare earth element is expensive, and also, because in the time that its content exceedes this scope, the crystal boundary position of the carrier core of preparing can a large amount of enrichment of rare earth elements.Although this is conducive to the lifting of resistivity, the suffered stress in these positions is very concentrated, thereby carrier is while constantly stirring in developing trough, and stress can broken mode occur with carrier core and be discharged, and the life-span of carrier can significantly shorten.Therefore preferably the content of rare earth element is 0.25-1%, is evenly distributed on crystal boundary position to ensure the rare earth element of sufficient amount, reaches the effect of crystal grain thinning.
The specific insulation of carrier core of the present invention is 10
7-10
12Ω cm.The present patent application people notices, adds after rare earth element, and the specific insulation of carrier core obviously rises, and effectively reduces carrier in Reusability process, and the possibility of charge injection carrier has stoped the phenomenon that carrier self is developed to occur.
The mean grain size value of carrier core of the present invention is preferably 20-30 μ m.Within the scope of this, carrier can stably be carried toner, forms the image of fine.Carrier is made up of carrier core and the resin bed being coated on carrier core, and resin bed is thinner, only plays coating function, and therefore the particle diameter of carrier is decided by the particle diameter of carrier core.In the time that the mean grain size of carrier core is less than above-mentioned scope, the magnetic characteristic of single carrier can decline, and easily produces carrier attachment phenomenon.And in the time that the mean grain size of carrier core is excessive, carrier can not meet the requirement of small particle diameter toner.The concrete component that the present invention is coated on the resin bed on carrier core can need choose reasonable according to prior art and specifically, its content is preferably the 0.1-30% of carrier core weight, more preferably 0.5-10%.In resin bed, preferably adding volume average particle size is the electrically conductive microparticle of 0.1-1 μ m, and its addition accounts for the 2-40% of resin bed gross mass, and the interpolation of electrically conductive microparticle can significantly suppress the decline of carrier resistivity.Described electrically conductive microparticle can be the inorganic particles such as carbon black fine particle, titanium oxide microparticle, tin oxide particulate.
Beneficial effect:
Use in developer developing electrostatic image support core material, preparation method of the present invention is take the potpourri of metal oxide and rare earth oxide as raw material, prepare carrier core through operations such as pulverizing, granulation, calcining, sintering, described method is simple and reliable, controllability good, the features such as to have particle diameter little for the carrier core of preparation, the moderate and high resistance of even grain size;
Use in developer developing electrostatic image diameter of carrier of the present invention is little, and the electrostatic charge image developer therefore producing can form high-quality image.
Accompanying drawing explanation
Fig. 1 is the electron scanning micrograph of embodiment 1 carrier core.
Fig. 2 is the electron scanning micrograph of comparative example 1 carrier core.
Fig. 3 is the electron scanning micrograph of comparative example 4 carrier cores.
Embodiment
The preparation of I, carrier core
(embodiment 1)
Pulverizing, granulation
By 704gFe
2o
3, 259gMn
3o
4, 37gMgO, 10gLa
2o
3as the raw material of carrier core, be distributed in water, being then crushed to mean grain size with wet ball mill is 1.1 μ m, obtains the mixed slurry of above-mentioned substance.The solid content of slurry, i.e. the mass percent of solid constituent, be controlled at more than 50%, preferably more than 60%.Such slurry gained pelletizing intensity after mist projection granulating is high, and after sintering, inner void is few, therefore preferably.Add in addition the polyvinyl alcohol (PVA) of 30g as bonding agent, then add the polyacrylic acid of 10g and the n-octyl alcohol of 5g respectively as spreading agent and defoamer.With centrifugal spray dryer, this slurry is carried out in the hot blast of 200 ℃ to granulation, obtain the pelletizing of particle size range at 10-100 μ m.
Calcining
Gained pelletizing is put in electric furnace, be heated to 800-1000 ℃, in air, calcine 2 hours.
Sintering
By calcining after powder again pulverize, granulation (process is the same), gained pelletizing is put in electric furnace, is heated to 1230 ℃, sintering 2 hours in air.Temperature-fall period passes into high pure nitrogen in stove, adjusts the oxygen content in electric furnace by the flow of controlling nitrogen, guarantees that carrier core has good magnetic characteristic.Remove excessive and too small particle subsequently by sinter fragmentation, then by screening and classification operation, the granularity of carrier core is adjusted to 20-30 μ m.
(embodiment 2)
Use 10gCe except in raw material
2o
3replace 10gLa
2o
3in addition, by condition similarly to Example 1, obtain the carrier core of embodiment 2.
(embodiment 3)
Use 10gPr except in raw material
2o
3replace 10gLa
2o
3in addition, by condition similarly to Example 1, obtain the carrier core of embodiment 3.
(embodiment 4)
Use 10gNd except in raw material
2o
3replace 10gLa
2o
3in addition, by condition similarly to Example 1, obtain the carrier core of embodiment 4.
(embodiment 5)
Use 10gGd except in raw material
2o
3replace 10gLa
2o
3in addition, by condition similarly to Example 1, obtain the carrier core of embodiment 5.
(embodiment 6)
After pulverizing process, the mean grain size of material becomes 1.7 μ m, by condition similarly to Example 1, obtains the carrier core of embodiment 6.
(embodiment 7)
After pulverizing process, the mean grain size of material becomes 2.8 μ m, by condition similarly to Example 1, obtains the carrier core of embodiment 7.
(embodiment 8)
Except La
2o
3quantitative change be beyond 5g, by condition similarly to Example 1, obtain the carrier core of embodiment 8.
(embodiment 9)
Except La
2o
3quantitative change be beyond 22g, by condition similarly to Example 1, obtain the carrier core of embodiment 9.
(comparative example 1)
In raw material, do not add rare earth oxide, by condition similarly to Example 1, obtain the carrier core of comparative example 1.
(comparative example 2)
Except replacing 10gLa with 10gSrO in raw material
2o
3, after pulverizing process, the mean grain size of material becomes beyond 1.5 μ m, by condition similarly to Example 1, obtains the carrier core of comparative example 2.
(comparative example 3)
Except La
2o
3quantitative change be beyond 35g, by condition similarly to Example 1, obtain the carrier core of comparative example 3.
(comparative example 4)
After pulverizing process, the mean grain size of material becomes 3.6 μ m, by condition similarly to Example 1, obtains the carrier core of comparative example 4.
The preparation of II, carrier
Styrene-methyl methacrylate resin and carbon black are dissolved respectively and be scattered in toluene, potpourri stirring was obtained to dispersion liquid after 10 minutes.In the time of 50 ℃, with fluidized bed type coating equipment, dispersion liquid is coated to the carrier core surface of embodiment 1-9 and the comparative example 1-4 of 100 weight portions, makes thus the carrier of embodiment 1-9 and comparative example 1-4.
The batching of carrier is as follows: styrene-toluene methyl acrylate resin 3 weight portions; Carbon black (VXC72, Cabot Corporation manufactures) 0.4 weight portion; Toluene 25 weight portions; Carrier core 100 weight portions.
The preparation of III, developer
The carrier that uses mixer that 5 parts of toners and 95 parts of embodiment 1-9 and comparative example 1-4 are obtained stirs 30 minutes, and products therefrom, through screening, obtains the developer of embodiment 1-9 and comparative example 1-4.
IV, every physics value assay method
Provide the assay method of every physics value of embodiment 1-9 and comparative example 1-4 carrier core below:
Specific insulation
Specific insulation uses GEST-121 Instrument Measuring Resistivity of Carbon Products (Beijing hat test is tested Instrument Ltd. and manufactured) to measure.
Magnetic characteristic
Magnetic characteristic is used HH-10 vibrating sample magnetometer (manufacture of Nanjing Nan great instrument plant) to measure.Record the saturation magnetization σ under the 1000Oe of external magnetic field
s, remanent magnetization σ
rwith coercive force H
c.
Volume average particle size
Volume average particle size is used by laser diffraction granularity tester (as COULTER LS230) mensuration.
Intensity
In KER-1/100A sealed type sample pulverizer (manufacture of Ke Rui sample making apparatus company limited of Zhengjiang City), add the carrier core of 100g broken 60 seconds, the particle diameter of carrier core before and after broken is distributed and compared.The present application is using the volume recruitment of the particle below 22 μ m before and after broken as the index of weighing carrier core intensity, and this numerical value is less, shows that the intensity of carrier core is larger.
The preparation condition transitivity value of each embodiment and comparative example carrier core is as shown in table 1.
[table 1]
Fig. 1 is the electron scanning micrograph of embodiment 1 carrier core.Fig. 2 is the electron scanning micrograph of comparative example 1 carrier core.Fig. 3 is the electron scanning micrograph of comparative example 4 carrier cores.
As shown in Figure 1, add the carrier core even grain size of rare earth oxide moderate, illustrate that rare earth element has suppressed the Fast Growth of crystal grain really, played the effect of controlling grain surface state.And do not add the carrier core (as comparative example 1, Fig. 2) of rare earth oxide, and in sintering process, grain growth is not effectively controlled, and size differs, wider distribution.The carrier core that this surface differences is huge, and bad adhesion between coating resin, to there being adverse effect the serviceable life of carrier and developer.
Can find with reference to table 1, the high order of magnitude of resistivity of the resistivity of embodiment 1-9 and comparative example 1, this shows that the rare earth oxide adding has effectively been distributed in crystal boundary position, has increased the scattering of crystal boundary to conduction electron, thereby has improved the resistivity of carrier core.The content (as comparative example 3) that continues to improve rare earth oxide, resistivity also can further rise.
By comparing magnetic characteristic data, can find that each embodiment and comparative example all have suitable saturation magnetization value.But the remanent magnetization of comparative example 2 is high, and coercive force is large, this is because the addition of Sr is higher, has formed the cause of more strontium ferrite in sintering process.The present patent application people is also noted that when the mean grain size when material is excessive (as comparative example 4), remanent magnetization and coercive force also can raise extremely.By scanning electron microscope, rear discovery is observed in carrier core surface, in Fig. 1, the even grain size of carrier core is moderate, and in Fig. 3, carrier core surface exists more emptying aperture.This is because the mean grain size of material before granulation is excessive, and pelletizing can not be realized fine and close filling, has a large amount of spaces, and therefore carrier core surface and the inside after sintering leaves emptying aperture.Emptying aperture has suppressed the normal growth of ferrite crystal grains, and the crystallite dimension after sintering is too small, and therefore the remanent magnetization of carrier core and coercive force raise.
In the time of the too high levels of rare earth oxide (as comparative example 3), because rare earth element is gathered in crystal boundary position in a large number, stress is too concentrated, causes the intensity of carrier core to decline.In addition, in the time that the mean grain size of material is excessive (as comparative example 4), there is emptying aperture in carrier core, and Fragmentation Phenomena easily occurs in whipping process, and intensity also obviously declines.