PROCESS FOR PASSIVATION OF A POLYMERIC MATERIAL ON THE SURFACE OF TONER PARTICLES

Abstract

A process for passivating a polymeric material on the surface of toner particles, comprising: Treating the surface of the polymeric material on the surface of toner particles, wherein the surface treatment comprises: (i) immersing the polymeric material in an aqueous solution of ruthenium tetroxide or osmium tetroxide, (ii) drying the polymeric material to obtain a passivated polymeric material, and (iii) embedding the toner particles comprising the surface-treated, passivated, polymeric material in a resin, wherein the passivated polymeric material does not interact with the embedding resin; wherein the polymeric material is immersed in the aqueous solution for 10 minutes to 4 hours.

Description

The present invention relates to a novel process for passivating polymeric particles to prevent undesirable environmental interaction. According to the invention, the passivation prevents the interaction between binder polymer resin in toner particles and the embedding epoxy resin, which causes artifacts that can be observed in transmission electron microscopic (TEM) imaging of the toner particles. However, the present embodiments may be used to passivated any polymeric surface.The development of high performance marking materials requires an understanding of the morphology and nanostructure of the various components within such materials that include colorants and specific additives. For example, the microstructure of the composite particles, as well as the location and distribution of the constituent materials within the binder polymer resin affect their performance. Transmission electron microscopy is often used to accurately determine the primary particle dimensions as well as the morphology and distribution of the components comprising the internal structure of marking materials such as toners. To obtain an "image" that images the internal composition of marking materials, which typically have a diameter of less than 10 microns, it is necessary that such particles be initially embedded in a curable resin and then cut into thin disks for TEM analysis. Good candidates for an embedding resin must satisfy the following: (1) encapsulating but not permeating particles, (2) curing at room temperature, and (3) being suitable for cross-sectional fabrication and withstanding irradiation with electron beams without significant loss of mass.However, undesirable artifacts can be seen in the TEM imaging process. For example, it is possible (and frequently occurs) that a possible artifact arises from interaction between embedding epoxy and polyester particles being analyzed. It is believed that the specific interaction studied takes place between the epoxy resin and the crystalline polyester present in the particles. This interaction altered the nature of the crystalline polyester in the toner particles that were studied and would often lead to incorrect interpretations of toner morphology. Several potting resins were tested, but epoxy resin was the only one that works satisfactorily as potting resin. Accordingly, passivation of the surface of the particles is required to obtain accurate images when the particles are embedded in epoxy resin.US 2011 / 0021711 A1 relates to crosslinked polymer particles comprising the polymerized product of a low molecular weight substrate, an allylic co-agent having at least two allyl groups and a free radical inducing species.U.S. Pat. No. 5,298,833 A discloses dielectric black latex particles which have a high black coloration by dyeing with a metal oxide.US 5,213,938 A discloses a method of making toners comprising oxidizing and metal chelating a surface of the toners with a metal oxidizing reagent.G. H. Michler, "Elctron Microscopy of Polymers", Berlin: Springer 2008, ISBN 978-3-540-36350-7, relates inter alia to the preparation of polymer samples for transmission electron microscopy.US 2013 / 0011779 A1 discloses a toner comprising a binder resin and a crystalline polyester resin, wherein the crystalline polyester resin is located near a surface of the toner. The toner can be obtained by a method comprising dissolving or dispersing a toner material comprising a binder resin and a dispersion liquid of the crystalline polyester resin in an organic solvent to obtain a solution or dispersion liquid of the toner material, followed by emulsifying or dispersing the solution or dispersion liquid of the toner material in an aqueous medium to obtain an emulsion or dispersion liquid, and removing the organic solvent from the emulsion or dispersion liquid to obtain the toner.Accordingly, there is a need to develop a technique for passivating polymeric surfaces, such as those of the particles, when it is necessary to make these surfaces such that they do not enter into undesirable interactions with the environment. In certain situations, there is a need to develop such techniques for passivating polymeric particles to allow the embedding of particles, such as toner particles containing crystalline polyesters, in epoxy resin while preventing undesirable artifacts.According to the invention there is provided a process for passivating a polymeric material on the surface of toner particles, comprising: treating the surface of the polymeric material on the surface of toner particles, wherein the surface treatment comprises: (i) immersing the polymeric material in an aqueous solution of ruthenium tetroxide or osmium tetroxide, (ii) drying the polymeric material to obtain a passivated polymeric material, and (iii) embedding the toner particles comprising the surface treated passivated polymeric material in a resin, wherein the passivated polymeric material does not interact with the embedding resin. The polymeric material is immersed in the aqueous solution for 10 minutes to 4 hours. FIG. 1 is a TEM micrograph illustrating a cross section of a polyester composite particle comprising crystalline polyethylene wax; FIG. 2 is a TEM micrograph illustrating a cross section of a polyester composite particle comprising crystalline polyester; FIG. 3 is a bright field transmission electron micrograph of a cross section of a polyester particle pretreated (not in accordance with the invention) with a platinum / palladium thin film by sputter coating prior to embedding in epoxy resin; and FIG. 4 is a bright-field transmission electron micrograph of a cross section of a polyester particle which has been pretreated (in accordance with the invention) by stirring in an aqueous solution of ruthenium tetroxide before embedding in epoxy resin.The present embodiments relate to processes for passivating the surface of a polymer to prevent undesirable chemical attacks. Without the passivation, the epoxy resin causes partial dissolution of the polymer binder in the toner and its subsequent recrystallization, which leads to mispredication of the morphology of toner particles from the TEM images.As part of morphological studies, polyester toner particles must first be encapsulated in an epoxy resin to allow cross-sectional fabrication. Recently, it has been discovered that interaction between the epoxy encapsulating medium and the crystalline polyester occurs in the particles and results in undesirable artifacts. This chemical reaction altered the nature of the crystalline polyester in the toner particles that were studied and thus would lead to incorrect interpretations of morphology. Several potting resins were tested to replace epoxy, but no other resin was found to function satisfactorily. Therefore, passivation of the surface of the particles is required when the particles are embedded in epoxy to prevent the undesirable artifacts. Indeed, passivation of the surface of particles would generally be very convenient to prevent unwanted interaction with any embedding resin.The present inventors have discovered a technique for successfully passivating the surface of particles by coating the surface of the particles with heavy metals. The present embodiments may be used to embed a polymeric material selected from the group consisting of a polyester, polyethylene, polypropylene, polystyrene, poly(butyl acrylate), butadiene, polyisoprene, poly(methyl methacrylate), natural rubber, polyacrylate, poly(vinyl chloride), polyamides, ureas, urethanes, phenols, poly(ethylene terephthalate), acrylonitrile, polycarbonates, and mixtures thereof. The present embodiments help to passivated the particles to allow for undesirable interaction with the particle environment. In embodiments, the particles being treated do not interact with a number of resins that contact the surface of the particles or that are used to embed the particles. For example, the resins used with the present embodiments include epoxy resins or polyepoxides and epoxides, methacrylates and glycol methacrylates, melamines, any acrylic resin derived from acrylic acid, methacrylic acid or other related compounds, and mixtures thereof. The embodiments also include certain commercially available resins including Tracer Low Viscosity Kit available from Ted Pella, Inc. (Redding, California) and ERL 4221 (vinylcyclohexene dioxide), DER 736 (diglycidyl ether of propylene glycol), NSA (nonenylsuccinic anhydride), and DMAE (dimethylaminoethanol); An Araldite 502 kit available from Ted Pella, Inc., which Araldite 502 comprises a diglycidyl ether of bisphenol-A (4,4-isopropylidenediphenol), DDSA (dodecenylsuccinic anhydride), and BDMA (benzyldimethylamine), or DMP-30 (2,4,6-tris(dimethylaminomethyl)phenol); Araldite 6005 kit available from Electron Microscopy Sciences (Hatfield, Pennsylvania), which Araldite 6005, DDSA, BDMA, and DBP (dibutylphthalate); Eponate 12TM kit available from Ted Pella, Inc., and Eponate 12TM comprises an aliphatic epoxy resin based on di- and tri-glycidyl ethers of glycerol, DDSA, NMA (Nadic methylanhydride) and BDMA or DMP-30 or Araldit 502; glycol methacrylate (GMA) kit available from Ted Pella, Inc., and comprising GMA, n-butyl methacrylate and benzoyl peroxide; JB-4 ® and JB-4 Plus ® kits available from Ted Pella, Inc., and based on the embedding resin GMA; Lowicryl kits available from SPI Supplies which are acrylate methacrylate mixtures; Poly-Bed ®-812 Kit available from Ted Pella, Inc. and comprising Poly-Bed 812 ®, DDSA, NMA and BDMA; LR Gold Resin Kit available from Ted Pella, Inc. and comprising LR Gold, a polyhydroxy substituted bisphenol A dimethacrylate with C12 methacrylate ester and the accelerator N,N-dimethylparatoluidine, PVP (polyvinylpyrrolidone), BPO benzoyl peroxide and benzil; LR White Resin kit available from Ted Pella, Inc., which LR White comprises a polar monomeric polyhydroxylated aromatic acrylic resin, and BPO (the accelerator N,N-dimethylparatoluidine is optional); NanoplastTM FB101 kit available from SPI Supplies (West Chester, Pennsylvania), which nanoplast comprises (melamine / formaldehyde resin) and catalyst B52; UnicrylTM kit available from Ted Pella, Inc., which comprises UnicrylTM resin, a styrene monomer, methyl methacrylate, and BPO; A durcupan ® kit available from SPI Supplies, comprising the resin durcupan A, an aliphatic polyepoxide, DDSA, DMP-30, and DBP; durcupan ® ACM kit available from SPI Supplies, comprising the resin durcupan A / M, an aromatic polyepoxide, DDSA, DMP-30, and DBP; maraglass 655 kit available from SPI Supplies, comprising the resin maraglass 655, cardolite NC-513, DBP, and BDMA; Maraglass 732 kit available from SPI Supplies and comprising Maraglass 655, D.E.R.TM 732, DBP and BDMA resin; Quetol 651-NSA kit available from SPI Supplies and comprising Quetol 651 (ethylene glycol diglycidyl ether), NMA, NSA and DMP-30 resin; and Epo-Fix kit available from Electron Microscopy Sciences and comprising bisphenol A diglycidyl ether resin and the curing agent triethylenetetramine.In a specific embodiment, particles containing crystalline polyesters were successfully surface treated with an aqueous solution of RuO 4 or OsO 4. The solution may also comprise in other embodiments (not according to the invention) tetrakistritungstophosphoric acid, bromine, iodine, chlorosulfuric acid, silver sulfide, mercury trifluoroacetate, tin chloride, uranyl acetate, lead(II) acetate, lead(II) citrate, lead(II) nitrate, silver iodide and silver nitrate and mixtures thereof. The particles were then embedded in epoxy without producing undesirable artifacts. In embodiments, the aqueous solution may comprise RuO 4 in an amount of from 0.1 wt % to 2.0 wt %, or from 0.2 wt % to 1.0 wt %, or from 0.4 wt % to 0.6 wt %, of a total weight of the solution. In embodiments, the aqueous solution may comprise OsO 4 in an amount of from 1.0% to 10.0% or 2.0% to 8.0% or from 3.0% to 5.0% by weight of a total weight of the solution. The particles are treated by dipping in the solution for 10 minutes to 4 hours, preferably 15 minutes to 3 hours or 30 minutes to 2 hours. The treated particles are rinsed and then dried for 30 minutes to 24 hours, or 1 hour to 16 hours, or 2 hours to 12 hours, at a temperature of 16°C to 30°C, or 18°C to 28°C, or 20°C to 25°C.• Example 1• MaterialsThe marking materials used in the study included an amorphous polyester matrix within which one or more crystalline phases were dispersed. The formulation further comprised a colorant.The first step in sample preparation was the embedding of the polyester particles in an epoxy resin. The embedding medium was a two component epoxy resin consisting of a high viscosity unmodified resin-based bisphenol A, known as ARALDITE GY6020 (available from Huntsman Advanced Materials (The Woodlands, Texas)) and the curing agent tetraethylene pentamine (available from Sigma-Aldrich Corp. (St. Louis, Missouri)) mixed in a ratio of 12:1, respectively.Cross sections were made using a Leica EM UC6 Ultracut Ultramicrotome (available from Leica Microsystems Inc. (Buffalo Grove, Illinois)) with a diatomic ultrasonic cutter (available from Diatoms AG (Biel, Switzerland)). Microscopy was performed using Philips / FEl CM20 transmission electrode microscopes (available from FEI Company (Hillsboro, Oregon)) and JEOL 2200FS (available from JEOL Ltd. (Tokyo, Japan)).The following colorants were used: 4 percent and 0.5 percent aqueous solutions of osmium and ruthenium tetroxide, respectively. Sputter coating was performed with a Cressington Coater, Model 208HR (available from Cressington Scientific Instruments Ltd. (Watford, UK))• Investigation of the interaction between embedding resin and polyester particlesFirst, two preparations of polyester particles each having one of two different crystalline components therein were prepared. The polyester composite particles were embedded in epoxy resin and, after curing, cross sections of the particles were made and collected on 400 mesh copper grids. For a sample containing a crystalline polyethylene wax, domains 1 appeared intact and unchanged upon TEM analysis (Figure 1). The other polyester composite particle containing a crystalline polyester was found by TEM analysis to have needle-like domains 5 appearing near the surface of the particle (FIG. 2 ).The presence of these features on the particle surface was not seen by scanning electron microscopy. These results strongly suggest that the epoxy interacts with the crystalline polyester component in the particles to alter the near surface domains. Alternative embedding materials were tested without success.• Production of passivated particlesTwo approaches have been used to passivation the polyester particles prior to embedding in epoxy resin to inhibit / prevent interaction with the crystalline polyester: (1) coating the particles with a platinum / palladium thin film by sputtering (not in accordance with the invention), and (2) treating the particles in an aqueous solution of ruthenium tetroxide or osmium tetroxide.• Coating of Metal Coating (not according to the invention)Sputter coating was performed as follows: a) toner particles were lightly scattered onto a glass slide, b) the glass slide was attached to a sample holder in the chamber of the Cressington 208HR sputter coating machine, c) the current for the sputter coating machine and the MTM-20 quartz crystal thickness monitor was turned on, d) the chamber was air depleted and "flushed" 3 times with the inert gas argon, e) when the vacuum reached 0.02 to 0.04 mbar, the rotation of the sample holder with the glass slide attached was started, f) the start / stop key was pressed, g) when the thickness monitor was left 4 nm, the start / stop key was pressed, h) the current to the thickness monitor, The sputter coating machine and sample rotation control were turned off, i) after the chamber reached atmospheric pressure, the chamber was opened and the glass slide with the treated toner particles was removed, j) the treated toner particles were mixed with epoxy resin and placed in a conical BEEM capsule. Once the epoxy was fully cured, the sample was ready for cut fabrication.• Aqueous treatmentThe aqueous solution treatment was carried out as follows: a) a small amount (0.02 g) of toner was placed in a 5 ml vial, b) 2 ml of deionized water was added to the vial and stirred for about 15 minutes, c) 2 ml of 0.5% aqueous ruthenium tetroxide was added with continuous stirring for an additional 30 minutes, d) the suspension of treated particles was placed in 50 ml of deionized water and then filtered through a Nuclepore (Whatman) 1 micrometer filter, e) about 250 ml of deionized water was used to thoroughly rinse the toner particles, f) the toner particles were allowed to dry at room temperature in a Digestorium, g) the treated toner particles were mixed with epoxy resin and placed in a conical BEEM capsule. Once the epoxy was fully cured, the sample was ready for cut fabrication.Both formulations have been found to be effective in surface passivation of polyester particles. However, while the sputter coating provided protection only for those surfaces receiving a thin layer of platinum / palladium, the solution treatment using RuO 4 or OsO 4 formed a barrier surrounding the particles and thereby providing protection for the entire particle against interaction with epoxy resin. Cross sections of the treated particles were examined by transmission electron microscopy. Figures 3 and 4 illustrate the protective effect provided by both treatment processes. In Fig. 3, a sputtering coating of platinum / palladium was provided, while in Fig. 4, a surface treatment with an aqueous solution of RuO 4 was applied. As can be seen from these figures, the integrity of the particle is only partially protected 10 by the sputtered layer, while the uncoated region 12 has needle-like artifacts resulting from the interaction between the epoxy and the sample. It is believed that the epoxy encapsulating material partially dissolves the crystalline polyester which slowly recrystallizes and forms the needle-like features over the curing time of the epoxy. Treatment of the polyester particles by dispersing in and mixing with an aqueous solution of ruthenium or osmium tetroxide results in complete protection or passivation of the entire surface 15, as shown in Figure 4. Although the sputter coating of particles using platinum / palladium on the particles has been only partially successful, the process would still work well on flat surfaces requiring passivation.The present embodiments provide processes for passivating polymeric materials to make the surface of such materials non-interact with the environment. In a specific example, it has been found that the interaction between embedding epoxies and certain polymeric materials, which may lead to imaging artifacts, is prevented by the present processes. To address these problems, the present embodiments provide processes for passivating the surface of the particles prior to embedding in epoxy to prevent any undesirable interaction between the particles and the epoxy. In the present embodiments, the protection of the polymer particles is accomplished by using a thin metal layer that is applied to the particles by chemical (wet) methods to encapsulate the particles.According to the embodiments illustrated herein, a novel process for passivating the surfaces of polymeric materials is provided. In particular, the present embodiments provide a means for passivating the surface of polyester toner particles to thereby prevent any chemical interaction between an embedding resin and the components of the composite particle being examined. In further embodiments, a methodology is provided for passivating any polymeric surface to prevent undesired interaction with its environment.Although the processes have been used in the present invention to treat toner particles prior to TEM analysis, the described present processes can be used for a wide variety of polymeric materials in a variety of scientific and industrial applications.

Claims

A process for passivating a polymeric material on the surface of toner particles, comprising: treating the surface of the polymeric material on the surface of toner particles, wherein the surface treatment comprises: (i) immersing the polymeric material in an aqueous solution of ruthenium tetroxide or osmium tetroxide, (ii) drying the polymeric material to obtain a passivated polymeric material, and (iii) embedding the toner particles comprising the surface treated passivated polymeric material in a resin, wherein the passivated polymeric material does not interact with the embedding resin; wherein the polymeric material is immersed in the aqueous solution for 10 minutes to 4 hours.The process of claim 1, wherein the polymeric material is dried at a temperature of 16°C to 30°C.The process of claim 1, wherein the polymeric material is selected from the group consisting of a polyester, polyethylene, polypropylene, polystyrene, poly(butyl acrylate), butadiene, polyisoprene, poly(methyl methacrylate), natural rubber, polyacrylate, poly(vinyl chloride), polyamides, ureas, urethanes, phenols, poly(ethylene terephthalate), acrylonitrile, polycarbonates, and mixtures thereof.

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