FLUORORESIN-CONTAINING COATING COMPOSITION AND FIXING HEATER ROLLER USING THE SAME

Abstract: A fluororesin-containing composition comprising a fluororesin, a fibrous material coated by an electrically conductive oxide, an acrylic resin and a liquid medium wherein a weight ratio of the fluororesin to the fibrous material is from 95:5 to 50:50, and that of the fluororesin to the acrylic resin is from 100:0 to 85:15, a coating formed form which composition has good heat, chemical and weather resistance and non-tackiness.

Description: The present invention relates to a fluororesincontaining coating composition and use thereof. More particularly, it relates to a coating composition comprising a fluororesin, a fibrous material coated by an electrically conductive oxide , an acrylic resin and a liquid medium, which is suitable for forming a non-tacky antistatic coating on a substrate. Since a fluororesin coating has not only various good properties such as heat resistance, chemical resistance and weather resistance which are the inherent properties of the, fluororesin but also peculiar non-tackiness, it finds various applications in which non-tackiness is required. However, since the fluororesin is a good electrical insulant and easily electrostatically charged, the fluororesin coating is also easily electrostatically charged and absorbs dusts in the air, which is not acceptable in some applications. To overcome such defect of the fluororesin coating, it is proposed to add an electrically conductive material such as carbon black and metal powder thereto. When carbon black is used as the electrically conductive material, the coating is colored black, it is impossible to freely color the coating. When the coating containing carbon black is rubbed with other material, other material is blacked. Further, since carbon black easily agglomerates, it is necessary to disperse the coating composition containing carbon black in a suitable mixing machine such as a ball mill for a long time in order to homogeneously disperse carbon black in the coating composition. When the metal powder is used as the electrically conductive material, the conductivity of the coating does not increase in proportion to an amount of the added metal powder. If a large amount of the metal powder is added to the coating composition, stability of the composition is deteriorated and mechanical strength of the coating is decreased. From WPIL, File Supplier, Derwent Public Ltd, London, GB; AN=84-0456308; & JP-A-59 006 235 a white conductive medium for use in coatings, adhesive tape etc. containing fibrous potassium titanate coated with stannic oxide which can be used mixed with plastics like polyethylene polyamide or polyimide resins is known. This material has an excellent conductivity, improved mechanical strength and surface smoothness. Therefore conductive coatings can be made of this material. One object of the present invention is to provide a fluororesin-containing composition which can impart antistatic property to a coating formed on a substrate. Another object of the present invention is to provide a fluororesin-containing composition which does not suffer from the defects which are caused by the addition of the electrically conductive material to the composition, and does not deteriorate the inherent properties of the fluororesin. According to the present invention, there is provided a fluororesin-containing composition comprising a fluororesin, a fibrous material coated by an electrically conductive oxide, an acrylic resin and a liquid medium wherein the weight ratio of the fluororesin to the fibrous material is from 95:5 to 50:50, that of the fluororesin to the acrylic resin is from 100:0 to 85:15 and the amount of the electrically conductive material is from 5 to 50% by weight based on the total weight of the fluoro resin and the electrically conductive material. One of the characteristics of the present invention resides in the use of fibrous material coated by an electrically conductive oxide such as stannic dioxide and diantimony trioxide. Such electrically conductive material can impart electrical conductivity to the fluororesin coating in a smaller amount than the conventional electrically conductive material such as carbon black and the metal powder. Since a small amount of the electrically conductive material is contained in the coating, it can impart antistatic property to the coating without deteriorating the properties of the fluororesin. Since the electrically conductive material of the present invention is white, the coating composition is also white. Therefore, the composition can be colored by any of suitable colorants. Each particle of the fibrous material has a diameter of 0.01 to 10 micrometers and a length of 1 to 100 micrometers. Those having a larger aspect ratio (length/diameter) are preferred. Specific examples of the fibrous material are fibrous potassium titanate, fibrous silicon carbide, fibrous silicon nitride, fibrous α-alumina and fibrous boron carbide. Among them, fibrous potassium titanate is preferred because of its high whiteness and good heat resistance. The amount of the electrically conductive material is from 5 to 50 % by weight, preferably from 10 to 30% by weight based on the total weight of the fluororesin and the electrically conductive material. When the amount of the electrically conductive material is less than 5 % by weight, the fluororesin coating does not have antistatic property. When it is more than 50 % by weight, evenness, non-tackiness and corrosion resistance of the coating are deteriorated. According to the present invention, the addition of the electrically conductive material decreases the volume resistivity of the fluororesin coating and imparts the antistatic property to the coating. It has been found that the addition of an acrylic resin further decreases the volume resistivity of the fluororesin coating and improves its antistatic property. Namely, when the fluororesin-containing coating composition contains 15 % or less, preferably 0.1 to 15 % and more preferably 5 to 15 % by weight of the acrylic resin based on the weight of the fluororesin, it has a further improved antistatic property. The acrylic resin may be any one of known acrylic resins. Examples of the acrylic resin are polymethyl methacrylate, polymethyl acrylate and polyethyl acrylate. The fluororesin to be used according to the present invention includes polytetrafluoroethylene, tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene/hexafluoropropylene copolymer and mixtures thereof. The liquid medium may by any one of liquid mediums which are conventionally used for the preparation of the coating composition containing the fluororesin. Preferred examples of the liquid medium are water and organic solvents (benzene, toluene and xylene.). The coating composition of the present invention may further contain any additives which are added to the conventional fluororesin-containing coating composition such as a pigment, a viscosity modifier and a dispersant. The coating composition of the present invention is generally spray coated on a substrate, although it may be coated by brushing, impregnation and casting. The coating formed from the coating composition of the present invention has various preferred properties such as non-tackiness, heat resistance and chemical resistance which the fluororesin inherently possesses and imparts antistatic property to the substrate. Further, advantageously, the coating composition of the present invention can be coated thick. When the coating composition contains carbon black as the electrically conductive material, the thickness of the coating should be about 30 to 40 micrometers or less to prevent crack of the coating. According to the present invention, the coating composition can be coated in a thickness of about 100 micrometers without causing crack. The coating composition may be used for coating various substrates, for example, a fixing heater roller or a pressure roller of a copying machine or a facsimile machine, a sizing roller for paper or fiber, a roller for food processing, a conveyer for conveying powder, a hopper or a shooter. When the coating composition of the present invention is coated on the peripheral surface of the fixing heater roller, the roller has good heat resistance and non-tackiness and does not suffer from stain. Thus, it has improved durability. PREFERRED EMBODIMENTS OF THE INVENTION The present invention will be hereinafter explained further in detail by following examples, in which % is by weight unless otherwise indicated. Example 1 By a mixing vessel equipped with mixing blades, fibrous potassium titanate covered by stannic dioxide and diantimony trioxide (fiber diameter: 0.3 to 0.6 µm, fiber length: 10 to 20 µm, volume resistivity: 10² Ωcm) (FF-202 manufactured by Sumitomo Chemical) (40 g) as the electrically conductive material and a dispersant (40 g) containing nonionic surfactant (4.8 g) were mixed. To the mixture, an aqueous dispersion of polytetrafluoroethylene (solid content: 60 %) (100 g) was added and mixed to obtain a coating composition. In this example, the content of the electrically conductive material was 40 % [weight of the electrically conductive material x 100/(weight of the fluororesin + weight of the electrically conductive material)]. The obtained coating composition was coated on a glass plate and heated at 380°C for 10 minutes to prepare a coating of about 20 µm in thickness. Its volume resistivity was measured. In the same manner as above but changing the amount of the coated fibrous potassium titanate to 6. 7 g (content of the electrically conductive material: 10 %), 15 g (content of the electrically conductive material: 20 %), 25.7 g (content of the electrically conductive material: 30 %) or 60 g (content of the electrically conductive material: 50 %), the coating was prepared and its volume resistivity was measured. The results are shown in the Figure. When the coating has volume resistivity of not more than 10⁷ Ωcm, its antistatic performance is deemed to be sufficient. Therefore, the coating prepared from the coating composition of the present invention has satisfactory antistatic performance. Example 2 In the same manner as in Example 1 but further using polymethyl acrylate (6 g), a coating was prepared on the glass plate and its volume resistivity was measured. The results are also shown in the Figure. These results shows that the addition of the acrylic resin further improves the antistatic performance of the fluororesin coating. Comparative Example 1 In the same manner as in Example 1 but using, as an electrically conductive material, mica particles having an average particle size of 10 µm which are covered by stannic dioxide and diantimony trioxide having volume resistivity of 10³ Ωcm (MEC-300 manufactured by Teikoku Kako), a coating was prepared on the glass plate and volume resistivity was measured. The results are shown in the Figure. Example 3 A roller base member made of aluminum having an outer diameter of 40 mm and a length of 340 mm was used. After usual surface preparation of the roller base member for fluororesin coating (blast treatment and primer coating), a coating composition prepared in the same manner as in Example 1 was coated to form a coating having a thickness of about 30 µm. Example 4 In the same manner as in Example 3 but using a coating composition which was prepared in the same manner as in Example 1, a coated roller was prepared. Comparative Example 2 In the same manner as in Example 3 but using a coating composition which was prepared in the same manner as in Example 1 but using no electrically conductive material, a coated roller was prepared. Experiments A peripheral surface of each of the roller produced in Examples 3 and 4 and Comparative Example 2 was rubbed with Nylon felt to electrostatically charge the roller. Then the surface electric potential was measured by a surface potentiometer. The results are show in the following Table. The closer to zero the surface electric potential is, the less a toner adheres to the roller surface.

Claims: A fluororesin-containing composition comprising a fluororesin, a fibrous material coated by an electrically conductive oxide, an acrylic resin and a liquid medium wherein the weight ratio of the fluororesin to the fibrous material is from 95:5 to 50:50, that of the fluororesin to the acrylic resin is from 100:0 to 85:15 and the amount of the electrically conductive material is from 5 to 50% by weight based on the total weight of the fluoro resin and the electrically conductive material. A composition according to claim 1 in which the weight ratio of fluororesin to acrylic resin is 100:0.1 to 85:15. The fluorine-containing composition according to claim 1 or 2, wherein the fibrous material is fibrous potassium titanate. The fluorine-containing composition according to claim 1 or 2, wherein the conductive material is stannic dioxide and diantimony trioxide. A fixing heater roller comprising a roller base member coated with a coating composition according to claims 1 to 4.

Inventors: HONDA, NORIMASA, SANO, MASAHIRO
Applicants: DAIKIN INDUSTRIES, LIMITED
Application year: 1987
Main classification: C08L27
IPC codes: C08L33, C09D127, C09D5, C08K9, C08L27