SURFACE MODIFIED MAGNETIC CARRIERS USING HYDROPHOBIZED TITANIA

Abstract

A developer mix used in a dual component development (DCD) system is a mixture of toner particles and magnetic carrier particles, wherein the magnetic carrier particle is surface treated with a hydrophobized titania particle. The surface treatment with a hydrophobized titania particle may be selected from either a spherical, disk, or spindle shaped. Tribocharge of the toner and the toner charge stability across cartridge life or environments may be suitably modified by selecting a preferred size and shape of the hydrophobized titania.

Claims

1. A developer mix formulation to be used in an electrophotographic imaging device comprising: toner particles; and magnetic carrier particles having a polymer coating on their outer surface, wherein the outer surface of the polymer coated magnetic carrier particles is surface treated with a hydrophobized titania extra particular additives.

2. The developer mix formulation of claim 1, wherein the polymer coating on the outer surface of the magnetic carrier particles is acrylic.

3. The developer mix formulation of claim 1, wherein the polymer coated magnetic carrier particles have a ferrite core.

4. The developer mix formulation of claim 1, wherein the hydrophobized titania extra particular additives have a spherical shape.

5. The developer mix formulation of claim 4, wherein the spherical hydrophobized titania extra particular additives have a primary particle size of 40 nm and an anatase crystal form.

6. The developer mix formulation of claim 4, wherein the spherical shaped hydrophobized titania extra particular additives have a primary particle size of 15 nm and an anatase crystal form.

7. The developer mix formulation of claim 1, wherein the hydrophobized titania extra particular additives have a disk shape.

8. The developer mix formulation of claim 7, wherein the disk shaped hydrophobized titania extra particular additives have a primary particle size of 40 nm and an anatase crystal form.

9. The developer mix formulation of claim 7, wherein the disk shaped hydrophobized titania extra particular additives have a primary particle size of 40 nm and an anatase-rutile crystal form.

10. The developer mix formulation of claim 1, wherein the hydrophobized titania extra particular additives have a spindle shape.

11. The developer mix formulation of claim 10, wherein the spindle shaped hydrophobized titania extra particular additives have a primary particle size of 5 nm60 nm and a rutile crystal form.

12. The developer mix formulation of claim 1, wherein the hydrophobized titania extra particular additives have an acicular shape.

13. The developer mix formulation of claim 12, wherein the acicular shaped hydrophobized titania extra particular additives have a primary particle size of 130 nm1.68 m and a rutile crystal form.

14. The developer mix formulation of claim 1, wherein the hydrophobizing agent is a silane.

Description

EXAMPLES

[0031] Example Cyan Pigment Dispersion

[0032] About 10 g of AKYPO RLM-100 polyoxyethylene(10) lauryl ether carboxylic acid from Kao Corporation, Bunka Sumida-ku, Tokyo, Japan was combined with about 350 g of de-ionized water and the pH was adjusted to 7-9 using sodium hydroxide. About 10 g of Solsperse 27000 from Lubrizol Advanced Materials, Cleveland, Ohio, USA was added and the dispersant and water mixture was blended with an electrical stirrer followed by the relatively slow addition of 100 g of pigment blue 15:3. Once the pigment was completely wetted and dispersed, the mixture was added to a horizontal media mill to reduce the particle size. The solution was processed in the media mill until the particle size was about 200 nm. The final pigment dispersion was set to contain about 20% to about 25% solids by weight.

[0033] Example Wax Emulsion

[0034] About 12g of AKYPO RLM-100 polyoxyethylene(10) lauryl ether carboxylic acid from Kao Corporation, Bunka Sumida-ku, Tokyo, Japan was combined with about 325 g of de-ionized water and the pH was adjusted to 7-9 using sodium hydroxide. The mixture was then processed through a microfluidizer and heated to about 90 C. About 60 g of polyethylene wax from Petrolite, Corp., Westlake, Ohio, USA was slowly added while the temperature was maintained at about 90 C. for about 15 minutes. The emulsion was then removed from the microfluidizer when the particle size was below about 300 nm. The solution was then stirred at room temperature. The wax emulsion was set to contain about 10% to about 18% solids by weight.

[0035] Example Polyester Resin Emulsion

[0036] A polyester resin having a glass transition temperature (Tg) of about 53 C. to about 58 C., a melt temperature (Tm) of about 110 C., and an acid value of about 15 to about 20 was used. The glass transition temperature is measured by differential scanning calorimetry (DSC), wherein, in this case, the onset of the shift in baseline (heat capacity) thereby indicates that the Tg may occur at about 53 C. to about 58 C. at a heating rate of about 5 per minute. The acid value may be due to the presence of one or more free carboxylic acid functionalities (COOH) in the polyester. Acid value refers to the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of the polyester. The acid value is therefore a measure of the amount of carboxylic acid groups in the polyester.

[0037] 150 g of the polyester resin was dissolved in 450 g of methyl ethyl ketone (MEK) in a round bottom flask with stirring. The dissolved resin was then poured into a beaker. The beaker was placed in an ice bath directly under a homogenizer. The homogenizer was turned on at high shear and 10 g of 10% potassium hydroxide (KOH) solution and 500 g of de-ionized water were immediately added to the beaker. The homogenizer was run at high shear for about 2-4 minutes then the homogenized resin solution was placed in a vacuum distillation reactor. The reactor temperature was maintained at about 43 C. and the pressure was maintained between about 22 inHg and about 23 inHg. About 500 mL of additional de-ionized water was added to the reactor and the temperature was gradually increased to about 70 C. to ensure that substantially all of the MEK was distilled out. The heat to the reactor was then turned off and the mixture was stirred until it reached room temperature. Once the reactor reached room temperature, the vacuum was turned off and the resin solution was removed and placed in storage bottles.

[0038] Example Toner A

[0039] The Example Polyester Resin Emulsion A (or, different polyester resin emulsions may be used in the core layer and shell layer) was divided into two batches, split 70:30 by weight to form the core and the shell of the toner, respectively. The total polyester content represented about 87.7% of the total toner solids. Accordingly, the first batch contained 61.4% of the total toner solids and the second batch contained 26.3% of the total toner solids. Components were added to a 2.5 liter reactor in the following percentages: the first batch of the Example Polyester Resin Emulsion A having 61.4 parts (polyester by weight), 6.8 parts (pigment by weight) of the Example Cyan Pigment Dispersion, and 5 parts (release agent by weight) of the Example Wax Emulsion. Deionized water was then added so that the mixture contained about 12% to about 15% solids by weight.

[0040] The mixture was heated in the reactor to 30 C. and a circulation loop was started consisting of a high shear mixer and an acid addition pump. The mixture was sent through the loop and the high shear mixer was set at 10,000 rpm. Acid was slowly added to the high shear mixer to evenly disperse the acid in the toner mixture so that there were no pockets of low pH. Acid addition took about 4 minutes with 200 g of 1% sulfuric acid solution. The flow of the loop was then reversed to return the toner mixture to the reactor and the temperature of the reactor was increased to about 40-45 C. Once the particle size reached 4.0 m (number average), 5% (wt.) borax solution (30 g of solution having 1.5 g of borax) was added. The borax content represented about 0.5% by weight of the total toner solids. After the addition of borax, the second batch of the Example Polyester Resin Emulsion A was added, which contained 26.3 parts (polyester by weight). The mixture was stirred for about 5 minutes and the pH was monitored. Once the particle size reached 5.5 m (number average), 4% NaOH was added to raise the pH to about 5.95 to stop the particle growth. The reaction temperature was held for one hour. The particle size was monitored during this time period. Once particle growth stopped, the temperature was increased to 88 C. to cause the particles to coalesce. This temperature was maintained until the particles reached their desired circularity (about 0.97). The toner was then washed and dried.

[0041] The dried toner had a volume average particle size of 6.65 m and a number average particle size of 5.49 m. Fines (<2 m) were present at 0.11% (by number) and the toner possessed a circularity of 0.978.

[0042] Toner A was placed in a CYCLOMIX along with about 0.5% by weight of small silica such as Aerosil R812 from Evonik Corporation, 1.0% of medium silica RY50 from Evonik Corporation and 2.0% of large silica such as SGSO100CDM8 from Sukgyung AT Inc. The CYCLOMIX was run for about 90 seconds. Subsequently the finished toner was evaluated.

Example Magnetic Carrier Particle

[0043] Illustrative examples of magnetic carrier particles that can be selected for mixing with the toner prepared as outlined above include those carriers that are capable of triboelectrically obtaining a charge of opposite polarity to that of the toner particles. Examples of such carrier particles include iron, iron alloys, steel, nickel, iron ferrites, including iron ferrites that incorporate magnesium, manganese, magnetites, strontium, copper, zinc and the like. The selected carrier particles can be used with or without a coating. The coating is generally made from acrylic and methacrylic polymers such as methyl methacrylate, acrylic and methacrylic copolymers with fluoropolymers or with monoalkyl or dialkylamines, polyolefins, polystyrenes, such as polyvinylidene fluoride resins, terpolymers of styrene, methyl methacrylate, and a silane such as triethoxy silane, tetraflouroethylenes and other known coatings in the art. Useful magnetic carriers to be used in the present invention have a average volume particle size between 25 m and 40 m, a saturation magnetization between 50 and 120 emu/g (A.m.sup.2/kg), apparent bulk density between 2.0-2.7g/cm.sup.3, and true specific gravity between 4.5-5.3. Unless otherwise stated, all developer mixes discussed are formulated and tested herein comprise a mixture of Toner A described above mixed with a magnetic carrier particle using a ferrite carrier with an acrylic coating having an average size particle between 35 m and 40 m and a saturation magnetization between 65 and 72 emu/g (A.m.sup.2 /kg). This particular magnetic carrier particle is hereinafter referred to as Control Magnetic Carrier.

[0044] Preparation of Comparative Developer Mix 1

[0045] 0.8 grams of Toner A was mixed with 9.2 grams of Control Magnetic Carrier (toner concentration 8% by weight and control magnetic carrier concentration 92% by weight) in a Turbula mixer for about 10 minutes at 56 rpm to form Comparative Developer Mix 1. Initial tribocharge of Comparative Developer Mix 1 was measured in a q/m Epping meter based on a known toner mass. The Epping toner charge value reported for all toners tested herein may be determined by combining the toner and magnetic carrier beads which tribocharge each other. Accordingly, a known amount of toner and carrier beads may be mixed and shaken together, and a pre-weighed sample of such toner/bead combination placed in a Faraday cage with screens on both ends. The Epping meter consists of this cage and directs air in one end of the cage. Charged toner passes with the air stream out of the other end of the cage (i.e., the screen retains the carrier beads). Weights before and after toner removal may provide toner mass; an electrometer may measure the toner charge (i.e., carrier charge of equal and opposite sign corresponding to the toner removed). It should therefore be appreciated that toner charge may serve as a basis for evaluating toner conveyance in an electrophotographic system.

[0046] Preparation of Developer Mix 1a

[0047] 400 grams of Control Magnetic Carrier and 0.20 grams of titania T1, identified in table 1, were weighed in a glass jar, and mixed in a Turbula mixer for about 5 minutes at about 56 rpm to form Magnetic Carrier 1a. Magnetic Carrier 1a was sieved through a 75 m screen. Following this pretreatment step, 0.8 grams of Toner A was mixed with 9.2 grams of Magnetic Carrier 1a (toner concentration 8% by weight and magnetic carrier la concentration 92% by weight) in a Turbula mixer for about 10 minutes at 56 rpm to form Developer Mix 1a. Initial tribocharge of the Developer Mix 1a was measured in a q/m Epping meter based on a known toner mass.

[0048] Preparation of Developer Mix 1b

[0049] Developer Mix 1b was prepared in a manner similar to Developer Mix 1a, with the exception that 0.20grams of titania T2 was used to form Magnetic Carrier 1b.

[0050] Preparation of Developer Mix 1c

[0051] Developer Mix 1c was prepared in a manner similar to Developer Mix 1a, with the exception that 0.20 grams of titania T3 was used to form Magnetic Carrier 1c.

[0052] Preparation of Developer Mix 1d

[0053] Developer Mix 1d was prepared in a manner similar to Developer Mix 1a, with the exception that 0.20grams of titania T4 was used to form Magnetic Carrier 1d.

[0054] Preparation of Developer Mix 1e

[0055] Developer Mix 1e was prepared in a manner similar to Developer Mix 1a, with the exception that 0.20 grams of titania T5 was used to form Magnetic Carrier 1e.

[0056] Preparation of Developer Mix 1f

[0057] Developer Mix 1f was prepared in a manner similar to Developer Mix 1a, with the exception that 0.40 grams of titania T5 was used to form Magnetic Carrier 1f.

TABLE-US-00002 TABLE 2 Effect of Pre-Treating Carrier with Titania on Tribocharge of Toner A Titania Tribocharge Toner Surface after mixing Concentration Additive on Initial Toner for 30 min. after mixing Developer Magnetic Charge Tribocharge Concentration @ 96 rpm for 30 min. @ Mix Carrier distribution (C/g) (% Tc) (C/g) 96 rpm (% Tc) Comparative 1 None Bimodal 76.8 3.46% 68.1 5.86% 1a 0.05% T1 Monomodal 60.1 7.64% 49.6 7.85% 1b 0.05% T2 Monomodal 27.4 8.07% 34.9 8.01% 1c 0.05% T3 Monomodal 17.1 8.10% 27.9 8.00% 1d 0.05% T4 Monomodal 11.9 8.04% 23.4 8.05% 1e 0.05% T5 Monomodal 44.1 8.00% 25.3 7.80% 1f 0.10% T5 Monomodal 26.1 8.17% 12.3 7.85%

[0058] Table 2 summarizes the tribocharge of Toner A as measured using an epping instrument and the charge distribution measured using a qd charge spectrometer such as a q test instrument, manufactured by PES Laboratorium. One key metric when making a developer mix is the uniformity of the developer mix. The uniformity of the developer mix is determined by incorporation of toner on to carrier surface, and no free toner, which would be reflected as multiple charge peaks in a charge distribution. The charge distribution curve as observed for Comparative 1 Developer Mix indicates a bi-modal distribution in contrast to the monomodal distribution observed for Developer Mixes 1a to 1f. This monomodal distribution indicates that either the carrier is not uniformly coated with Toner A or there is a sufficient amount of Toner A that is not on the surface of the magnetic carrier. The Toner Concentration (% Tc) reported in Table 2 for Comparative 1 Developer Mix having an untreated magnetic carrier is an undesirable 3.46% Tc following an epping blow-off measurement. Moreover, the high tribocharge of Comparative 1 Developer Mix (76.8 C/g) may be the result of Toner A adhering to the magnetic carrier or the poor mixing of Toner A with the magnetic carrier. This is not a desirable result. However, when the same magnetic carrier is surface treated with titania additives T1, T2, T3, T4, and T5, Developer Mixes 1a, 1b, 1c, 1d, 1e and if show a more efficient removal of toner from the magnetic carrier surface as measured by an epping blow off measurement % Tc between 7.64% and 8.17%. The higher % Tc readings are desirable for a developer mix because in a printing process the toner is developed on to an imaging substrate by a similar process, and if it is difficult to separate the toner from the magnetic carrier surface, the resulting image on a substrate would be relatively light due to insufficient toner. However, if the separation of toner from the magnetic carrier is efficient, the toner mass on a magnetic roller can be adjusted in a way to get the required mass of toner on an imaging substrate, thereby achieving the required print density on the substrate.

[0059] Furthermore, Table 2 also shows the possibility of tailoring the tribocharge of a toner by surface treating the outer surface of the magnetic carrier with particular titania surface additives, for example as listed in Table 1. Toner A used in the various developer mixes listed in Table 2 was not changed. The tribocharge of Toner A varies from about 60C/g to about 11 C/g. The tribocharge was able to be manipulated by simply varying the type of titania surface additive on the surface of the magnetic carrier. Titania T1 and titania T2 have similar properties including primary particle size of about 40 nm, anatase crystal form, and are hydrophobized using a silane, but vary in their shape. Titania T1 is spherical while titania T2 is a disk shaped. Developer Mix 1a using spherical titania T1 as a surface additive to the magnetic carrier exhibits a charge of about 60 C/g in comparison to a tribocharge of about 27C/g for Developer Mix 1b using disk shaped titania T2 as a surface additive to the magnetic carrier. Another comparison for the different types of titania is the initial charge distribution of Developer Mix 1b versus the initial charge distribution of Developer Mix 1c. Titania T3 is based on an anatase and rutile crystal form. Whereas the use of disk shaped titania T2 as a surface additive to the magnetic carrier imparts a tribocharge of about -27K/g for the Developer Mix 1b, the use of titania T3 having an anatase and rutile crystal form lowers the charge of Developer Mix 1c to about -17 C/g. Titania T2 and T3 titania have a similar size of 40 nm and similar silane surface treatment but differ in their crystal form and interestingly impart a different tribocharge to their respective developer mixes. On the other hand, titania T5 is based on a rutile form and its primary particle size for the spindle shaped structure is 5 nm60 nm. As a surface additive on the magnetic carrier surface, titania tends to exhibit a different behavior on the tribocharge without compromising the efficiency to remove the toner from the carrier surface as evidenced by the resulting % Tc reading in Table 2. By increasing the amount of titania T5 on the magnetic carrier surface to 0.10% as used in Developer Mix 1f, the resulting toner tribocharge of 26.1 C/g tends to approach the tribocharge of the developer mixes using of the anatase form of titania. It can also be appreciated that the tendency for charge to be modulated to be more negative or less negative can be altered by using the crystal form of the titania and/or by adjusting the amount of the titania surface additive. Titania T4 has smaller primary particle size of 15 nm with an anatase crystal form and can also be used to lower the tribocharge of the toner.

[0060] The developer mix in a developer cartridge is subjected to constant mixing and churn, which may inherently change the performance of the developer mix. It is preferred that the developer mix is still capable of exhibiting efficient separation of the toner from the carrier surface. In examining the test results from Table 2, Comparative Developer Mix 1 having no surface treatment on its magnetic carrier particle still exhibits a high toner charge and is unable to achieve the required separation of tonerthus resulting in a lower % Tc of about 5.86%. Although the separation of the toner from the magnetic carrier in Comparative Developer Mix 1 is better following the exposure to a hot/humid environment (See Table 3), it is still inferior compared to the % Tc reported for the developer mixes shown in Table 2. An interesting finding is the variation in charge change as a function of titania type. Whereas the toner tribocharge changes from about 17 C/g to about -28 C/g after churning Developer Mix 1c, Developer Mix 1a shows the charge change in the opposite direction from about 60 C/g to about 49.6 C/g after churning. Additionally Developer Mix 1e shows the same charge change in the opposite direction. Hence, depending on the toner and printer developer cartridge, the tribocharge of the toner through cartridge life can be modified by suitably selecting a surface additive, as shown in Table 2. For example, if a system requires darker prints, charge change can be adjusted to be approaching more neutral, as shown in Examples 1e and 1f, or if a system has a tendency to create more wrong sign toner, an example such as 1b or 1c, can mitigate by exhibiting higher charge on churning the system.

TABLE-US-00003 TABLE 3 Charge stability across environments Surface Epping QT Epping QT Additive on (at Lab (at Developer Magnetic Ambient, % Tc (at 78 F./80% RH, % Tc (at Mix Carrier 60 hrs), C/g LabAmbient) 60 hrs), C/g 78 F./80% RH) Comparative 1 None 76.8 3.46% 74.3 4.28% 1a 0.05% T1 60.1 7.64% 66.3 6.56% 1c 0.05% T3 17.1 8.10% 16.9 8.14% 1d 0.05% T5 44.1 8.00% 39.8 8.03% 1e 0.1% T5 26.1 8.17% 23.8 8.08%

[0061] Earlier, the capability of suitably moderating toner tribocharge by manipulating the particular type of titania surface additive on the magnetic carrier was described. Further to the ability of modifying the toner tribocharge, the possibility of achieving uniform tribocharge across lab ambient environment to a hot/wet environment is also seen by the use of magnetic carrier that is surface treated with a titania surface additive. Comparative Developer Mix 1 shows a charge that is relatively stable, however, the charge is based on about 4.28% Tc of the toner that was removed or developed. In comparison, Developer Mixes listed in Table 3 having magnetic carriers that are surface treated with a titania show efficient removal of toner and also a tribocharge that does not change significantly.

[0062] Preparation of Developer Mix 2a

[0063] 500 grams of Control Magnetic Carrier and 0.5 gram of titania T6 , were weighed and added to a glass jar, and mixed for about 5 minutes. The control magnetic carrier mixed with the titania T6 was screened through a 75 m screen to produce Magnetic Carrier 2a. Following this pretreatment step, 0.8 grams of Toner A was mixed with 9.2 grams of Magnetic Carrier 2a (toner concentration 8% by weight and magnetic carrier 2a concentration 92% by weight) in a Turbula mixer for about 10 minutes at 56 rpm to produce Developer Mix 2a. Initial tribocharge of Developer Mix 2a was measured in a q/m Epping meter based on a known toner mass.

[0064] Preparation of Developer Mix 2b

[0065] 500 grams of Control Magnetic Carrier and 1.25 gram of titania T6 were weighed and added to a glass jar, and mixed for about 5 minutes. The control magnetic carrier mixed with the titania T6 was screened through a 75 m screen to produce Magnetic Carrier 2b. Following this pretreatment step, 0.8 grams of Toner A was mixed with 9.2 grams of Magnetic Carrier 2b (toner concentration 8% by weight and magnetic carrier 2b concentration 92% by weight) in a Turbula mixer for about 10 minutes at 56 rpm to form Developer Mix 2b. Initial tribocharge of Developer Mix 2b was measured in a q/m Epping meter based on a known toner mass.

TABLE-US-00004 TABLE 4 Epping Charge for Developer Mixes Using an Acicular Titania as a Surface Additive on the Magnetic Carrier Surface Additive Initial on Magnetic Tribocharge Toner Concentration Developer Mix Carrier (C/g) (% Tc) Comparative 2 None 76.4 3.59% Example 2a 0.1% Titania T6 79.5 5.82% Example 2b 0.25% Titania T6 78.6 5.35%

[0066] Table 4 explores the feasibility of a using a larger acicular titania sized 130 nm1.68 m, such as titania T6 described in Table 1. In contrast to titania T5 which is a spindle shape having a size of about 5 nm60nm, Titania T6 is significantly larger, measuring 130 nm1.68 m. However, irrespective of the amount of titania T6 on the magnetic carrier surface (0.1% and 0.25%), the resulting Epping charge measurement reported in Table 4 shows a poor separation of toner from the magnetic carrier surface. Developer Mixes 2a and 2b both had a comparable % Tc result of 5.82% and 5.35%, respectively. These % Tc results are better than the % Tc result reported for the Comparative Developer Mix having an untreated magnetic carrier. However the % Tc results for Developer Mixes 2a and 2b are significantly lower than the 7.64% Tc to 8.17% Tc reported for Developer Mixes 1a-1f in Table 2. The titania used as a surface additive to the magnetic carrier in Table 2 exhibited an efficient separation.

[0067] The foregoing description of several methods and an embodiment of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the