Carrier for electrostatic latent image development and coating agent for use therein

Abstract: A coating agent for a carrier for electrostatic latent image development comprised of (A) an organopolysiloxane having the formula (R 3 SiO 1/2 ) a (R 2 SiO 2/2 ) b (RSiO 3/2 ) c , wherein R is a monovalent hydrocarbon group or an epoxy-functional monovalent organic group, provided that the content of epoxy-functional monovalent organic groups relative to total R groups is 0.1 to 100 mole %, a is 0 or a positive number, b is a positive number, c is a positive number and a + b + c is 1; and (B) a curing agent. Also provided is a carrier for electrostatic latent image development comprised of an inorganic powder coated with the aforementioned coating agent.

Description: This invention provides carriers for electrostatic latent image development and coating agents for such carriers. This invention introduces carriers for electrostatic latent image development that are relatively unaffected by humidity, and coating agents for use in such carriers, which cure rapidly upon heating, and upon cure, have electrification properties that are also relatively unaffected by humidity. In electrophotography and electrostatic printing, an electrostatic latent image is formed on a photosensitive material. Then, a two-component dry developer is brought into close proximity to the said image such that the toner in the dry developer becomes attached thereto. Next, the toner is transferred to a transfer sheet, after which the electrostatic latent image is developed by affixing the toner to the transfer sheet and heating. The two-component dry developer contains a toner and a carrier for electrostatic latent image development. The toner is comprised of a thermosetting resin and a colorant. The carrier is typically iron or glass powder. The toner is held onto the surface of the carrier by frictional electrification i.e. electrical charge. The surfaces of the carrier are coated with a film of a peelable coating, such as silicone resin, for preventing film formation (spending) by the toner. The silicone coating agents conventionally used for coating carrier surfaces have included, for example, silicone resin compositions comprised of silanol-containing organopolysiloxanes (JP-A 56-106968), silicone resins containing organopolysiloxanes, comprised of bifunctional siloxane units and trifunctional siloxane units, and organotin compounds (JP-A 61-284775), and methylphenyl silicone resins in which the ratio of silicon-bonded organic groups to silicon atoms is 1.5 and less (JP-A 2-160259). However, because these coating agents are cured by condensation reactions of silanol groups, there has been a problem that cure does not occur sufficiently without heating at a high temperature for a long time, for example 200 to 250°C. Further, because unreacted silanol groups remain locally in the product cured film, there have also been problems with variations in the electrostatic properties of the carrier obtained, depending upon curing conditions and humidity. We first proposed a coating agent for carriers for electrostatic latent image development comprised of organopolysiloxanes that were composed of bifunctional siloxane units, having aminoalkyl groups, and trifunctional siloxane units in combination with organopolysiloxanes, composed of bifunctional siloxane units having monovalent organic groups containing haloalkyl groups or epoxy groups, and trifunctional siloxane units (JP-A 5-88413). However, those coating agents were cured by reactions between the aminoalkyl groups and the monovalent organic groups. For this reason, there are problems that the obtained films are generally brittle and lack durability. In particular, salts remain as by-products in the obtained cured films produced by the reaction between organopolysiloxanes having aminoalkyl groups, and organopolysiloxanes having haloalkyl groups. Because of this, mechanical properties of the cured film are poor and electrification properties vary greatly with changes in humidity. After we conducted intensive research for solving the aforementioned problems, we derived this invention. The objective of this invention is to provide a coating agent for carriers useful in electrostatic latent image development that are rapidly heat-cured and that form a cured film with electrification properties which are relatively unaffected by humidity. Another objective is to provide a carrier for electrostatic latent image development that possesses electrification properties which are relatively unaffected by humidity. Our coating agent for carriers suitable for electrostatic latent image development comprises (A) 100 parts by weight of organopolysiloxane having the average unit formula: (R 3 S i O 1/2 ) a (R 2 S i O 2/2 ) b (RS i O 3/2 ) c , wherein each R is individually selected from monovalent hydrocarbon groups or epoxy-functional monovalent organic groups, provided that the content of epoxy-functional monovalent organic groups relative to total R groups, is from 0.1 to 100 mole %, a ≥ 0, b > 0, c > 0, a + b + c = 1; and (B) 0.01 to 100 parts by weight of a curing agent. Our carrier for electrostatic latent image formation comprises an inorganic powder that is coated by the above coating agent. Component (A) is used for the purpose of enhancing the curing characteristics of our composition, for improving mechanical and electrification properties of the cured film, and for conferring durable heat resistance, peelability and smoothness. Component (A) is an organopolysiloxane having the average unit formula: (R 3 S i O 1/2 ) a (R 2 S i O 2/2 ) b (RS i O 3/2 ) c . Each R is individually selected from monovalent hydrocarbon groups or epoxy-functional monovalent organic groups. The content of epoxy-functional monovalent organic groups present in component (A), relative to total R groups also present in component (A), is 0.1 to 100 mole %; a is 0 or a positive number indicating the content of monofunctional siloxane units (M units); b is a positive number indicating the content of bifunctional siloxane units (D units); and c is a positive number indicating the content of trifunctional siloxane units (T units). The total of a, b and c is 1. Component (A) is a DT type organopolysiloxane, comprised of bifunctional siloxane units (D units) and trifunctional siloxane units (T units), or an MDT type organopolysiloxane comprised of bifunctional siloxane units, trifunctional siloxane units and monofunctional siloxane units (M units). Component (A) does not have tetrafunctional units (Q units). The reason for this is that the mechanical properties of the product cured film are diminished when a DTQ type organopolysiloxane, or an MDTQ organopolysiloxane is used. In the above formula, each R is individually selected from monovalent hydrocarbon groups or epoxy-functional monovalent organic groups. Monovalent hydrocarbon groups typically include, for example, alkyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl; alkenyl groups, such as vinyl, allyl, butenyl, pentenyl and hexenyl; aryl groups, such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups, such as benzyl or phenethyl; and halogenated alkyl groups, such as chloromethyl groups, 3-chloropropyl groups, 3,3,3-trifluoropropyl groups and nonafluorobutylethyl groups. Methyl or phenyl groups are particularly preferred monovalent hydrocarbon groups. Epoxy-functional monovalent organic groups of the present invention include, for example, epoxyalkyl groups, such as 2,3-epoxypropyl, 3,4-epoxybutyl and 4,5-epoxypentyl; glycidoxyalkyl groups such as 2-glycidoxyethyl, 3-glycidoxypropyl and 4-glycidoxybutyl; and (3,4-epoxycyclohexyl) alkyl groups or such as 2-(3,4-epoxycyclohexyl) ethyl or 3-(3,4-epoxycyclohexyl) propyl. Glycidoxyalkyl or (3,4-epoxycyclohexyl) alkyl are particularly preferable. The content of epoxy-functional monovalent organic groups relative to total R groups is from 0.1 to 100 mole %, and preferably from 5 to 100 mole %. When the content of epoxy-functional monovalent organic groups to total R groups is less than 0.1 mole %, the mechanical properties of the obtained cured film are markedly diminished. Component (A) is a liquid at room temperature or a solid that has a softening point above room temperature. When component (A) is a solid, its softening point is preferably 50 to 200°C. In preferred embodiments, component (A) is an organopolysiloxane having a softening point above room temperature. It is preferable that a = 0, 0.05 ≤ b ≤ 0.7, 0.3 ≤ c ≤ 0.95 and b + c =1. When component (A) has a high content of phenyl groups, it is a solid substance having a softening point above room temperature. Therefore, it is desirable that the content of epoxy-functional monovalent organic groups, relative to total R groups, is 0.1 to 20 mole % and the phenyl group content is 60 to 90 mole %. More preferably, the content of epoxy-functional monovalent organic groups is 5 to 20 mole % and the phenyl group content is 60 to 90 mole %. The preferred R groups are epoxy-functional monovalent organics, methyl and phenyl. In addition, small quantities of alkoxy groups such as methoxy, ethoxy, propoxy and butoxy, or hydroxyl groups may also be bonded to the silicon atoms of component (A), as long as the objectives of the invention are not impeded. Methods for manufacturing the organopolysiloxanes comprising component (A) include, for example, a method in which a dialkoxysilane having epoxy-functional monovalent organic groups is subjected to a re-equilibration reaction in the presence of an acid or alkali catalyst with an organopolysiloxane, obtained by hydrolysis and condensation of an organotrichlorosilane; a method in which a dialkoxysilane or trialkoxysilane, having an epoxy-functional monovalent organic group, is subjected to a re-equilibration reaction in the presence of an acid or alkali catalyst with an organopolysiloxane obtained by hydrolysis and condensation of an organotrichlorosiloxane, and a diorganodichlorosilane, and, as required, a triorganopolysiloxane; and a method in which a dialkoxysilane or a trialkoxysilane, having an epoxy-functional monovalent organic group, is subjected to a condensation reaction in the presence of an acid catalyst, an alkali catalyst or an organic metal compound catalyst with an organopolysiloxane, comprised of bifunctional siloxane units and trifunctional siloxane units, and also having hydroxyl groups or alkoxy groups that are bonded to silicon atoms. The curing agent comprising our component (B) reacts with the epoxy-functional monovalent organic group of component (A) for the purpose of curing our composition. Component (B) is either a crosslinking agent or a curing catalyst. When component (B) is a crosslinking agent, it is selected from, for example, a phenolic compound; a carboxylic acid compound; an aliphatic anhydride, such as dodecenylsuccinic, polyadipic, polyazelaic and polysebacic; an alicyclic anhydride such as methyltetrahydrophthalic, methylhexahydrophthalic, methylhimic, hexahydrophthalic, 4-methylhexahydrophthalic and tetrahydrophthalic acid; aromatic anhydrides, such as phthalic, trimellitic, pryromellitic and benzophenonetetracarboxylic; amine compounds; aliphatic diamines, such as ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylenediamine and 2,5-dimethylhexamethylenediamine; aliphatic polyamine compounds, such as diethylenetriamine, iminobispropylamine, bis(hexamethylene)triamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and tri(ethylamino)hexene; compounds containing alkoxy groups; and the partial reaction products of any of the above listed compounds or their mixtures. The curing catalyst of component (B) is, for example, tertiary amine compounds, such as tris(dimethylaminomethyl)phenol, dimethylbenzylamine, 1,8-diazabicyclo (5,4,0) undecane and 1,8-diazabicyclo (5,4,0) undecene; quaternary ammonium salts, such as tetramethylammonium bromide; imidazole compounds, such as 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole; phenol resins; urea resins; melamine resins; isocyanates; block isocyanates; phosphorus compounds, such as triphenylphosphine; aluminum compounds, such as organoaluminums; and zirconium compounds, such as organozirconiums. The crosslinking agents and curing catalysts of component (B) may be used individually or in combination. In compositions of the present invention, component (B) is present in an amount ranging from 0.01 to 100 parts by weight, per 100 parts by weight of component (A). Compositions containing less than 0.01 part by weight of component (B), or more than 100 parts by weight of component (B), do not readily undergo a curing reaction. As long as the objective of the invention is not impeded, other optional components can be compounded with this composition, including, for example, fillers such as aerosol silica, crystalline silica, sintered silica, wet silica, titanium oxide, zinc carbonate, calcium carbonate, iron oxide and carbon black, higher aliphatic acid esters or metal salts, ester waxes or plasticizers such as stearic acid esters and palmitic acid esters, aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane and heptane, ketone solvents such as acetone and methyl ethyl ketone and organic solvents such as tetrahydrofuran and dioxane. When these organic solvents are compounded, carriers for electrostatic latent image development are manufactured by immersion, spray coating or fluidized beds. Our cure mechanism differs from that of conventional coating agents in that there are no localized, residual silanol groups left as a result of the curing reaction. Thus, the electrification properties of our carrier for electrostatic latent image development is coated with a cured film that is not readily affected by humidity. The inorganic powder of our carrier for electrostatic latent image development includes, for example, magnetic powders such as iron, nickel, cobalt, ferrite and magnetite; tin oxide; silver; steel; bronze; carborundum; glass beads; graphite; carbon black; molybdenum sulfide;,aluminum and silicon dioxide. The average particle diameter of these inorganic powders is, for example, 30 to 1,000 µm, and preferably 50 to 500 µm. The carrier of the present invention is manufactured by the following method. The inorganic powder is first heated. The coating agent is then mixed with the inorganic powder as it is being heated. During the mixing process, the coating agent coats the surfaces of the particles of the inorganic powder. Next, the coating agent is cured. The amount of coating agent added is a quantity sufficient to coat the inorganic powder. The quantity of coating agent that is mixed with the inorganic powder is easily calculated by determining the surface area of the inorganic powder and the thickness of the film to be coated on the inorganic powder. The thickness of the coating agent formed on the surface of the inorganic powder is, for example, 0.1 to 50 µm. The conditions under which mixing of inorganic powder and coating agent occurs is such that the coating agent and inorganic powder undergo a sufficient curing reaction to form a cured film exhibiting mechanical strength. For example, when the temperature at which the coating agent and inorganic powder are mixed is greater than 100°C, mixing time is 0.5 to 15 hours. In this case, the equipment for preparing our carrier for electrostatic latent image development is, a Ross™ mixer, a kneader mixer or a henshel™ mixer. EXAMPLES We shall now present detailed descriptions of the coating agents and carriers for electrostatic latent image development of the present invention. Viscosity in the examples is the value determined at 25°C. The softening points of the organopolysiloxanes were determined with a precision melting point device manufactured by the Shibata™ Science (Shibata Kagaku) Company. The electrification quantity of our carriers were determined as follows: 30 g of carrier for electrostatic latent image development and 1 g of carbon black toner were shaken for 10 minutes with a shaker, after which the electrification quantity after 30 seconds of blow-off was determined by a blow-off powder electrification device of the Toshiba™ Chemical Company. This carrier was allowed to stand for 24 hours in an oven at a temperature of 50°C and a relative humidity of 90%. Thereafter, the electrification quantity of the carrier was determined in the same way as described above. Reference Example 1 100 g of water, 100 g of isopropyl alcohol and 400 g of toluene were introduced into a 3 L round-bottom flask equipped with a stirrer, a thermometer and a dropping funnel. A mixed solution of 297 g (approximately 1.4 moles) of phenyltrichlorosilane, 76 g (approximately 0.3 moles) of diphenyldichlorosilane and 39 g (approximately 0.3 moles) of dimethyldichlorosilane was added to the system dropwise over a period of 1 hour with stirring. The system was then subjected to heating and reflux for 2 hours and allowed to cool. The water in the bottom layer of the system was removed. 600 g of an aqueous solution of sodium hydrogen carbonate of a concentration of 10% were introduced into the system and the materials were again stirred for 30 minutes. Again, the water of the bottom layer of the system was removed. The system was then washed 3 times with water, the toluene and water were removed from the obtained toluene solution and organopolysiloxane was prepared at 150°C at approximately 50 wt %. The viscosity of a toluene solution of this organopolysiloxane was 6 mPa.s (25°C) (centipoise). Next, 25 g of 3-glycidoxypropylmethyldimethoxysilane were introduced into 500 g of a toluene solution of this organopolysiloxane. The system was then stirred for 5 hours at toluene reflux temperature, and a toluene solution of organopolysiloxane having 3-glycidoxypropyl groups was prepared. Subsequently, some of this toluene solution was heated under reduced pressure and solid organopolysiloxane having 3-glycidoxypropyl groups was prepared. The softening point of this latter organopolysiloxane was 75°C. This organopolysiloxane was analyzed by nuclear magnetic resonance spectroscopy and it was confirmed that it was an organopolysiloxane indicated by the following average unit formula. Reference Example 2 450 g of water and 900 g of toluene were introduced into a 3 L round-bottom flask equipped with a stirrer, a thermometer and a dropping funnel. 422 g (approximately 2 moles) of phenyltrichlorosilane was added dropwise over a period of 1 hour to the system as the materials were stirred. The system was then stirred for 1 hour at 60 to 70°C, after which the water of the bottom layer of the system was removed. One liter of water was added to the system and it was stirred, after which it was allowed to stand. Next, the water of the bottom layer was removed and most of the hydrochloric acid was removed. 10 g of sodium hydrogen carbonate and 1 liter of water were introduced into the system and it was stirred for 30 minutes, after which the water of the bottom layer of the system was again removed. The system was then washed 3 times with water, the toluene and water were removed from the obtained toluene solution and organopolysiloxane was prepared at 150°C to approximately 30 wt %. Next, 44 g (approximately 0.2 moles) of 3-glycidoxypropylmethyldimethoxysilane, 1 g of a 10% aqueous solution of sodium hydroxide and 15 g of dimethylformamide were introduced into 900 g (approximately 0.2 moles) of a toluene solution of this organopolysiloxane and the materials were heated. Then, the system was heated to remove toluene containing condensed water and organopolysiloxane was prepared at 150°C to approximately 60 wt %, after which the system was stirred for three hours and an equilibration reaction was effected. Acetic acid was then introduced into the system, after which the salt that was produced was filtered. Some of the toluene solution of this organopolysiloxane was heated under reduced pressure, and organopolysiloxane having 3-glycidoxypropyl groups that was in a solid state at room temperature was prepared. The softening point of this organopolysiloxane was 55°C. This organopolysiloxane was analyzed by nuclear magnetic resonance spectroscopy and it was confirmed that it was an organopolysiloxane indicated by the following average unit formula. Example 1 200 g of a 50 wt % toluene solution of the organopolysiloxane having 3-glycidoxypropyl groups that was prepared in Reference Example 1, 11 g of 4-methylhexahydrophthalic anhydride and 0.4 g of 1,8-diazabicyclo (5,4,0) undecene were mixed uniformly, and a coating agent was prepared therefrom. 20 g of coating agent and 1 kg of ferrite powder of an average particle diameter of 100 µm were mixed for 10 minutes at room temperature using a kneader mixer, after which the materials were heated and mixed for 1 hour at 150°C, and a carrier was thus prepared. The fluidity of this carrier was excellent. When the electrification quantity of this carrier was determined after 30 seconds of blow-off, it was determined to be 25 µC/g. Thus, it was confirmed that this carrier was suitable for use in electrostatic latent image development. When the quantity of electrification of this carrier was determined after this carrier was subjected to moisture resistance tests, it was found to be 24 µC/g. Thus, it was also confirmed that the electrification properties of this carrier were not affected by humidity. Example 2 100 g of a 60 wt % toluene solution of the organopolysiloxane having 3-glycidoxypropyl groups that was prepared in Reference Example 2, 16 g of 4-methylhexahydrophthalic anhydride and 0.5 g of 1,8-diazabicyclo (5,4,0) undecene were mixed uniformly and a coating agent was prepared. 10 g of coating agent and 1 kg of ferrite powder of an average particle diameter of 100 µm were mixed for 10 minutes at room temperature using a kneader mixer, after which the materials were heated and mixed for 1 hour at 150°C and a carrier was prepared. The fluidity of this carrier was excellent. When the electrification quantity of this carrier was determined after 30 seconds of blow-off, it was determined to be 22 µC/g. Thus, it was confirmed that this carrier was also suitable for use in electrostatic latent image development. When the quantity of electrification of this carrier was determined after being subjected to moisture resistance tests, it was found to be 21 µC/g. Thus, it was confirmed that the electrification properties of this carrier were not affected by humidity. Comparative Example 1 A silicone composition that cures via a condensation reaction comprised of an organopolysiloxane (silanol group content = 0.5 wt %) indicated by the average unit formula: ((CH 3 ) 2 S i O 2/2 ) 0.15 (CH 3 S i O 3/2 ) 0.85 and dibutyltindiacetate were diluted with toluene and a 50 wt % toluene solution was prepared. This solution was used as a coating agent. 20 g of this coating agent and 1 kg of ferrite powder of an average particle diameter of 100 µm were mixed for 10 minutes at room temperature using a kneader mixer. There-after, the materials were heated and mixed for 1 hour at 150°C and a carrier was prepared. The fluidity of this carrier was excellent. When the electrification quantity of this carrier was determined after 30 seconds of blow-off, it was determined to be 30 µC/g. Thus, it was confirmed that this carrier was suitable for use in electrostatic latent image development. When the electrification quantity of this carrier was determined after being subjected to moisture resistance tests, it was found to be 25 µC/g. Thus, it was confirmed that the electrification properties of this carrier were markedly reduced by humidity. Comparative Example 2 An organopolysiloxane (silanol group content = 1.0 wt %) as indicated by the average unit formula: ((CH 3 ) 2 S i O 2/2 ) 0.19 ((C 6 H 5 ) 2 S i O 2/2 ) 0.19 (CH 3 S i O 3/2 ) 0.25 (C 6 H 5 S i O 3/2 ) 0.37 was diluted with toluene and a 50 wt % toluene solution was prepared. This solution was used as a coating agent. 20 g of this coating agent and 1 kg of ferrite powder of an average particle diameter of 100 µm were mixed for 10 minutes at room temperature using a kneader mixer, after which the materials were heated and mixed for 1 hour at 150°C and a carrier was prepared. The fluidity of this carrier was excellent. When the electrification quantity of this carrier was determined after 30 seconds of blow-off, it was determined to be 26 µC/g. Thus, it was confirmed that this carrier was suitable for use in electrostatic latent image development. When the electrification quantity of this carrier was determined after being subjected to moisture resistance tests, it was found to be 19 µC/g. Thus, it was confirmed that the electrification properties of this carrier were markedly reduced by humidity.

Claims: A coating agent composition, comprising A) 100 parts by weight of an organopolysiloxane having the average unit formula: (R 3 SiO 1/2 ) a (R 2 SiO 2/2 ) b (RSiO 3/2 ) c , wherein each R is individually selected from monovalent hydrocarbon groups or epoxy-functional monovalent organic groups, the content of epoxy-functional monovalent organic groups relative to the total content of R groups is from 0.1 to 100 mole %, a ≥ 0, b > 0, c > 0, and a+b+c = 1; and B) 0.01 to 100 parts by weight of a curing agent. The coating agent composition of claim 1 wherein each monovalent hydrocarbon group is individually selected from alkyl groups, alkenyl groups, aryl groups, and halogenated alkyl groups. The coating agent composition of claim 1 wherein each epoxy-functional monovalent organic group is individually selected from epoxyalkyl groups, glycidoxyalkyl groups, and (3, 4-epoxycyclohexyl) alkyl groups. The coating agent composition of claim 1 wherein component (B) is a crosslinking agent selected from the group consisting of phenolic compounds, carboxylic acid compounds, aliphatic anhydrides, alicyclic anhydrides, aromatic anhydrides, aliphatic diamines, aliphatic polyamine compounds, alkoxy group containing compounds, partial reaction products thereof, and mixtures thereof. The coating agent composition of claim 1 wherein component (B) is a curing catalyst selected from the group consisting of tertiary amine compounds, quaternary ammonium salts, imidazole compounds, phenol resins, urea resins, melamine resins, isocyanates, block isocyanates, phosphorus compounds, aluminum compounds, and zirconium compounds. A carrier for electrostatic latent image development, comprising: 1) an inorganic powder; and 2) the coating agent composition of claim 1. The carrier of claim 6 wherein the inorganic powder is selected from the group consisting of magnetic powders, tin oxide, silver, steel, bronze, carborundum, glass beads, graphite, carbon black, molybdenum sulfide, aluminum and silicon dioxide. The carrier of claim 6 wherein the inorganic powder has an average particle diameter of 30 to 1,000 µm. The carrier of claim 6 wherein the inorganic powder is thoroughly coated with the coating agent to a thickness of from 0.1 to 50 µm.

Inventors: AKAMASTU SHOJI, AMEMIYA TAKAO, AKAMASTU, SHOJI, AMEMIYA, TAKAO, Akamastu, Shoji, c/o Dow Corning Toray Sil Co, Ltd, Amemiya, Takao, c/o Dow Corning Toray Sil Co, Ltd
Applicants: DOW CORNING TORAY SILICONE, DOW CORNING TORAY SILICONE COMPANY LIMITED
Application year: 1996
Main classification: C09D183
IPC codes: C09D183, G03G9, C08L83