JP2012006803A - Method for modifying surface of carbon sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for modifying a surface of a carbon sintered body which achieves improvement of impregnating properties of a coating material related to development of a coating film adhesive properties obtained by an anchor effect by reducing surface tension based on addition of an additive on coating a surface of a carbon aggregate molded article dielectrically heatable.SOLUTION: The method for modifying the surface of the carbon sintered body includes forming a surface coating layer by: adhering powder of a thermoplastic fluororesin on a half-dried substrate coating film to which drying treatment is applied after coating an IPA (isopropyl alcohol)-added undercoat to an inner surface of the molded article formed by an aggregate mainly containing carbon powder and particle; and heating and melting the article.

Description

  The present invention relates to a method for modifying the surface of a carbon sintered body. More specifically, the present invention relates to a method for improving the adhesive strength of a fluororesin or the like that is coated on the surface of a molded product made of a carbon sintered body obtained by sintering carbon particles.

  Electromagnetic heating cooking uses electromagnetic induction heating configured such that an eddy current generated by an induction heating coil, which is a high-frequency magnetic field generator, generates heat from a magnetic metal, and is achieved using a stove or rice cooker. . However, iron or stainless steel, which is a magnetic metal, has poor thermal conductivity, so there is a disadvantage that food cannot be heated quickly and uniformly. To eliminate this, a clad material laminated with aluminum, copper, etc. is used. I used it.

  The clad material has problems such as peeling of the laminated interface when the surface is coated with a heat-resistant resin such as fluororesin after drawing on a pot or pot, etc. There has been proposed an induction heating cooker in which a fluororesin is applied to an inner surface, which is a cooking surface, through an undercoat paint after obtaining a molded product such as a pot or a pot (for example, see Patent Document 1).

  Similarly, a means for applying a fluororesin coat of a carbon compression body cut and compressed into a rod-and-pillar shape has been introduced and disclosed to be effective as a cookware at high temperatures (for example, Patent Document 2). reference).

  Moreover, since the sintered body of carbon obtained by coagulating high carbon content powder particles such as coke by heating at 1000 to 3000 ° C. in an oxygen-free state has appropriate conductivity and dielectric properties, It has been proposed to be used in an electromagnetic induction heating cooker, such as a rice cooker, instead of iron. After cooking the carbon sintered body into a pan shape by cutting, the cooker easily peels and cleans the cooked food by applying fluororesin on the pan surface or glassy carbon on the pan surface. Various coatings may be applied, for example, to provide a function that facilitates (see, for example, Patent Document 3).

  However, molded products made by agglomerating carbon raw material particles have very few joints between the agglomerated particles and are extremely brittle, so the carbon particles and the surface layer part when the surface layer is coated or adhered to the sheet The exfoliation phenomenon in which the aggregation between particles is broken occurs more frequently than the exfoliation at the interface. As a result, it was difficult to ensure sufficient adhesive strength.

  In other words, the portion where the carbon powder particles constituting the carbon aggregate are in contact with each other and easily aggregated is easily destroyed, and in order to reinforce the contact portion, a chemical solution can enter the minute pores, or the surface layer of the aggregate can be modified. It was necessary to treat the surface layer by covering it with a paint or the like after coating.

  For example, as a means for modifying the surface of an inorganic porous body, a means for densification by impregnating a surface of a sintered body containing SiC as a main component with a melt of Si has been proposed (see, for example, Patent Document 4). ).

  Similarly, means for achieving improvement in hardness and wear resistance by implanting ions into the surface of the ceramic fired body has been proposed (see, for example, Patent Document 5).

  In addition, a cooking utensil has been proposed in which ceramics are sprayed on the surface of an electromagnetic induction heating carbon bottom plate member, and a sticking agent is impregnated into the sprayed layer and carbon to fix each other to increase the surface hardness (for example, patents). Reference 6).

JP-A-9-75211 JP 09-70352 A JP 09-75211 A JP 2003-071555 A JP 2003-212675 A Japanese Patent Laid-Open No. 10-229941

  However, according to these means (the above-mentioned Patent Documents 4 to 6), it is necessary to leave the aggregate in a high temperature atmosphere again. Since the atmosphere is formed and the modification of the extremely thin portion on the outermost surface is stopped, there is a problem that the improvement can be achieved only extremely insufficiently.

  In other words, since carbon aggregates are likely to undergo oxidative decomposition at high temperatures, it is essential to perform reforming treatment at low temperatures, and the inside and outside of a pot-shaped container formed by combining particles included in the aggregates are communicated with each other. Treating the chemical solution that has entered the microscopic pores at a high temperature may cause a defect due to excessive expansion in the aggregate to cause a decrease in strength.

  In addition, even if this means is applied, it is necessary to treat the aggregate in a specific atmosphere such as a high temperature, so that the carbon aggregate is accompanied by the condensation of carbon particles due to thermal decomposition and uneven expansion during heating. There was concern about a decrease in strength, such as destruction of joints. Furthermore, the measure for improving the strength by increasing the composition ratio of the additive has a problem that the resistance value of the carbon aggregate tends to be excessively increased and inhibits efficient heat generation by electromagnetic induction heating.

  The present invention has been made to solve the above-mentioned problems, and in the surface coating of a carbon aggregate molded product capable of dielectric heating, the impregnation of the paint related to the expression of the coating film adhesion due to the anchor effect is improved. A method of modifying the surface of a carbon sintered body is achieved by reducing the surface tension by adding an additive.

  The method for modifying the surface of a carbon sintered body according to the present invention uses an inner surface of a molded product mainly composed of aggregates of carbon particles, with IPA (isopropyl alcohol) added to an undercoat paint, and is dried after application. A thermoplastic fluororesin powder is deposited on a semi-dried base coating film that has been treated, and this is heated and melted to form a surface coating layer.

  The method for modifying the surface of a carbon sintered body according to the present invention is a semi-dried state in which an inner surface of a molded product mainly composed of carbon powder is formed by adding IPA to an undercoat and then drying. Since the surface coating layer is formed by depositing thermoplastic fluororesin powder on the base coating and heating and melting it, the anchor effect provides sufficient coating adhesion to withstand the load during cooking. Can be obtained, and excellent coating film adhesion can be obtained.

It is a figure which shows Embodiment 1, and shows the manufacturing process of the pots made from carbon. The figure which shows Embodiment 1 and is a coating process figure of the fluororesin to the inner surface corresponded to a cooking surface. The figure which shows Embodiment 1, and is a figure which shows the test result of the adhesiveness of the fluororesin coating film in the pot-shaped molded article inner surface.

Embodiment 1 FIG. (Manufacture of pot-shaped cooker)
The present embodiment relates to an improvement in coating adhesion of a carbon aggregate (improvement improvement method of an inner surface coating), and in the surface coating of a carbon aggregate molded product capable of dielectric heating, a coating film due to an anchor effect. Improve the impregnation of paints related to adhesion development by reducing surface tension by adding additives.

  Cooking utensils such as charcoal pots capable of dielectric heating are molds in which a molding material that is a composite of graphite powder and a non-reacted phenol resin of a thermosetting resin containing carbon in a high concentration has an arbitrary shape. It is a carbon agglomerate obtained by baking a molded product obtained by being pressurized and heated in the interior in an oxygen-free high temperature atmosphere.

  A cooking utensil made of a carbon agglomerated body is formed by processing the inner surface to prevent adhesion with ingredients using an aqueous dispersion of a fluororesin, but only with a surfactant that is a dispersant for the aqueous dispersion. There is a problem that sufficient affinity cannot be obtained and it is difficult to ensure the anchor effect by impregnating the pores of the aggregate. As a result, there has been a problem that it is difficult for the fluororesin coating film to withstand the repeated load applied during long-term use, and peeling is likely to occur.

  The present invention impregnates the pores of a molded product made of a composite of a thermosetting resin carbide containing graphite powder at a high concentration by adding a modifier to the thermoplastic fluororesin aqueous dispersion. It is a means to improve the property and improve the coating film adhesion.

  Of the fluorine-based resin paints used on the inner surface of cookers that include magnetic metals and laminated different types of metals, conventional paints are made by uniformly adding 1% or less of a water-soluble alcohol solvent to the paint that forms the base. After applying to the inner surface of the cooker made of carbon agglomerated by the method, after drying in a heating furnace at 100 to 150 ° C. to a semi-dry state, powder coating with a fluororesin powder coating, at a high temperature of 400 ° C. It melts to form a coating film.

  On the inner surface of the molded product, PES (polyether sulfone) in an aqueous dispersion and 20 vol% PFA (perfluoroalkoxyalkane; tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin, the same as the fluororesin used for the outermost coating ) IPA (isopropyl alcohol), which is a small amount (0.5% or less) of a water-soluble alcohol solvent, is added to the base paint in which fine powder is dispersed and sprayed with a uniform mixture. A dried primer layer was formed. Next, after spraying fine powder of PFA, which is a fluororesin that forms the outermost surface, it was gradually melted from the substrate side in a high-temperature atmosphere at 380 ° C. to form a coating film having a uniform thickness.

  That is, for reforming the surface layer portion where the carbon aggregate is not heat-treated at a high temperature, a resin coating obtained by impregnating the liquid resin into the fine pores provided in the aggregate is coated as a base material. As a result, the oxidative decomposition of the carbon aggregates is suppressed, the particles are in contact with each other and penetrate into the pores formed by condensation, and the surface of the particles is covered and protected. It will not peel easily.

  For this reason, in order to adhere the fluororesin that prevents the cooking utensils from adhering to the surface of the aggregate as an electromagnetic induction heater, the resin used as the base material is adhesive to both the carbon aggregate and the fluororesin. In addition, PES having a high heat resistance and excellent fluidity at the time of melting is suitable, and in order to ensure the safety associated with the absence of solvent in the coating drying process, an aqueous dispersion ( It is preferable to use an emulsion.

  However, since the aqueous dispersion in an emulsion state dispersed with a surfactant has a high surface tension, it has poor affinity with the carbon aggregate and it is difficult to ensure sufficient impregnation by coating. is there. For this reason, this embodiment is characterized in that a small amount of IPA is added to improve the affinity by lowering the surface tension.

  In addition, as the base material, PES made into fine particles smaller than fine pores included in the carbon aggregate was dispersed in water, and PFA was mixed therein. As a result, the bonding with the PFA forming the surface can be strengthened.

  By adding a water-soluble alcohol solvent to the aqueous dispersion of the thermoplastic resin, the affinity with the carbon aggregate that cannot be formed only by the surfactant contained in the aqueous dispersion is improved, and the aggregate is provided. Therefore, it is possible to easily infiltrate the base material in which the fluororesin of the thermoplastic resin is dispersed. For the base coating that is joined and integrated with the outermost fluororesin coating, the use of PES that exhibits a low coefficient of expansion in the high temperature range ensures the holding power to the aggregate as an anchor effect, and cooking As a device, a strong coating film having both heat resistance and non-adhesiveness could be secured by the surface layer provided with PFA which melts with high temperature and has excellent resistance to various chemicals.

  The characteristics of PES (polyether sulfone) are that high rigidity in a high temperature range and low dimensional change rate are maintained / stable, HDT is 200 to 210 ° C., and UL temperature index is 180 ° C.

  PFA (perfluoroalkoxyalkane; tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin) is characterized by high non-adhesiveness and low coefficient of friction, and also as a thermoplastic resin that can be melt-molded. is there.

The structure of PFA is perfluoroalkoxyalkane (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin), and refers to a copolymer of tetrafluoroethylene (C ₂ F ₄ ) and perfluoroalkoxyethylene.

  A pan, which is an electromagnetic induction heating cooker that generates heat in response to an induction current from a heating coil of an electromagnetic induction heating cooker, is a molded product of a carbon agglomerate obtained by joining graphite with a carbon material, and is a base material for this. After impregnating the liquid resin, when forming a surface coating film of fluororesin on the inner surface corresponding to the cooking surface, the surface modification method for obtaining excellent coating film adhesion is based on the manufacturing process shown in FIG. It will be described in detail. FIG. 1 is a diagram showing the first embodiment, and is a diagram showing a manufacturing process of a carbon pot.

  Injection molding, transfer molding, etc., a molding material obtained by mixing graphite powder obtained by firing a coke pulverized product in a high-temperature (3000 ° C.) oxygen-free atmosphere and then pulverizing the graphite aggregate to 300 μm or less and a phenol resin. A cooking pot is obtained by heating and pressure forming. The phenol resin used at this time is preferably a novolak type that generates a small amount of water vapor, unreacted low-molecular substances, and the like, which are double products accompanying curing.

  The obtained molded product is left to stand in an oxygen-free atmosphere and the phenol resin is baked and carbonized to obtain a carbon aggregate molded product of a cooking pan. At this time, it is important to increase the temperature stepwise in order to prevent the phenol decomposition product from staying inside the molded product without being diffused and locally expanding, and the phenol resin is actively decomposed. In the vicinity of 350 ° C., 500 ° C., and 800 ° C., which causes a sudden weight loss, a moderate temperature rise or maintenance is performed. Specifically, the temperature was rapidly increased up to 300 ° C. at 0.5 ° C./min, and then maintained at 350 ° C. at a moderate temperature increase of 1 ° C./hr for 5 hours. Furthermore, after reaching 450 ° C at 5 ° C / hr, reaching 500 ° C at 1 ° C / hr, holding for 5 hours, reaching 750 ° C at 5 ° C / hr, reaching 800 ° C at 2 ° C / hr, then 3 After holding the time, the temperature was reached to 1200 ° C. at 0.5 ° C./min and held for 2 hours. Moreover, about cooling, it cooled to room temperature vicinity at 0.5 degree-C / min.

Molded product of arbitrary shape by molding for molding material in which graphite powder is mixed with phenol resin with high carbon content in mold and heating for curing the molding material Could get. By performing this sintering process in an oxygen-free state, the density of the obtained molded product of the carbon aggregate is provided with a dense aspect of 1.7 g / cm ³ .

  Next, since the cooking pan made of the carbon aggregate obtained is inferior in wear resistance, a coating obtained by diluting a silicon resin with excellent heat resistance with a solvent is applied to the outer surface in order to protect the pan surface from abrasion during cooking. Then, this was dried and cured at 150 ° C. to form a coating film of about 20 to 100 μm.

  Next, the fluororesin coating film which suppresses adhesion | attachment of cooking utensils material is formed in the inner surface which is a cooking surface. FIG. 2 is a diagram showing the first embodiment, and is a drawing of a fluororesin coating process on the inner surface corresponding to the cooking surface. The coating process of FIG. 2 will be described in detail below. The base material is 20% by volume of PES (polyethersulfone) fine particles of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), which is the same as the fluororesin coated on the outermost surface. An emulsion aqueous solution in which the fine particles are stably dispersed using any of nonionic, zwitterionic, anionic, and cationic surfactants such as oxyethylene alkyl ether is used.

  After spraying this base material with a spray, a drying treatment was performed at 120 ° C. for 10 minutes to form a coating film having a thickness of about 20 μm. In the drying process, an undercoat layer that facilitates bonding with the outermost fluororesin PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) is formed by maintaining a wet state without completely removing moisture. To do.

  However, in order to obtain the characteristic that the molded product has both strength and electric conductivity required for cooking by dielectric heating, the graphite powder used is a fine powder of 300 μm or less, so the pores on the surface of the molded product are extremely It is fine and has a size of approximately 0.2 to 1.0 μm. Therefore, an aqueous dispersion in which PES and PFA are mixed in the presence of a surfactant lacks the affinity for the carbon aggregate, and the fine pores of the molded product are sufficiently impregnated with only the surfactant used. Insufficient to perform, the coating film can ensure sufficient adhesion, and the necessary anchor effect cannot be obtained.

  For this reason, there are alcohols as a solvent excellent in affinity with the carbon aggregate. It is essential that PES and PFA form an azeotrope with water to maintain water dispersion using a surfactant and to ensure water retention by stable transpiration. In the embodiment, a minute amount of 1 to 5% of IPA (isopropyl alcohol) was added and used.

  A suitable amount of PFA fine powder, which is a fluororesin, is sprayed onto the wet underlayer, preferably in a thickness of 15 to 50 μm, and then held in an atmosphere of 380 ° C. from the outside. Warm up. As a result, the wall surface of the molded product is preferentially melted, and the fine powder is gradually melted, and has a mode in which no bubbles remain inside, and melts to the outermost surface in a time of 10 to 20 minutes. It is formed.

  In addition, the base material, PES, the main component, can withstand most cooking temperature ranges, has excellent heat resistance and can be used continuously at high temperatures, maintaining creep characteristics and elastic modulus and abrupt temperature changes. Excellent resistance to cracking and property changes. Moreover, since it is exposed to the surface by adding 20 vol% of PFA fine powder to this, the effect of improving the adhesion with the coating film comprising the PFA fine powder constituting the outermost layer can be obtained.

  Modification of the surface layer part on the inner surface of the above-mentioned pot-shaped molded product is a state where the base material is sufficiently impregnated into fine pores provided on the surface of the carbon aggregate molded product, and the coating of the fluororesin is difficult to peel off Got. The effectiveness with respect to the addition of IPA was confirmed by the following method.

  In other words, the paint surface is peeled off by fixing the adhesive tape to the surface of the fluororesin coating film with the cut surface having a 1 mm width on the paint surface so that it does not reach the surface of the carbon material, which is the base material, The operation of instantaneously pulling it up 90 degrees and peeling it off is repeated 10 times. At that time, the number of squares remaining without peeling was measured and evaluated as adhesion of the coating film to the substrate.

  FIG. 3 is a diagram showing the first embodiment and is a diagram showing a test result of the adhesion of the fluororesin coating film on the inner surface of the pan-shaped molded product. As shown in FIG. 3, more than half of the coating film using the base material to which IPA was not added was peeled off from the surface of the carbon aggregate, whereas the coating film according to this embodiment confirmed peeling from the molded article substrate. I did not. For coating film peeling, a small amount of IPA is added to an aqueous dispersion in which a mixture of PES and PFA constituting the base material is uniformly dispersed using a surfactant, and the affinity with the carbon aggregate is improved. It was confirmed that the PFA coating used by applying a base material that facilitates entry into the pores provided on the surface has significantly better adhesion than when using a base material that does not mix IPA. .

  Here, the particle diameter of PES dispersed in the base material applied to the inner surface of the pot-shaped molded product was 0.2 μm, which is significantly smaller than the pore diameter (0.5 μm) of the carbon material. FIG. 3 also shows the adhesion of the coating film using a 2 μm fine powder equivalent to that of the base material. As a result, it is important to ensure that the coating film of the comparative example easily peels off from the carbon aggregate and allows the fine powder of PES and PFA used as the base material to enter the pores on the surface of the molded product. confirmed.

  In addition, excessive addition of IPA inhibits the stable dispersion state of the fine powder of PES and PFA and tends to aggregate, forms a colloid, and lacks storage stability. When this water-dispersed base material was applied, the obtained PFA coating film was significantly inferior in adhesion compared to the case of using a normal dispersed base material, and the PES fine powder in the pores It was confirmed to inhibit invasion.

  From the above, PES has excellent dimensional change at high temperature, hot water resistance and oil resistance, so it has suitable characteristics as a cooking utensil, but does not flow at a high temperature in a non-pressurized state without exhibiting a clear melting point. Therefore, when it was not present in the pores in the molten state, the anchor effect was insufficient, resulting in poor coating film adhesion. Therefore, it is necessary to use a base material that is a dispersion liquid using fine particles in which fine powder of PES easily penetrates into pores, and maintains an aspect having a homogeneous dispersion state.

  Here, PES is used as the fine powder of the heat-resistant resin, but it is not necessary to stick to the above-mentioned resin as long as it has a melting point higher than the maximum temperature that the cooking utensil receives. For example, PPS (polyphenylene sulfide), PSU A heat-resistant thermoplastic resin such as (polysulfone) or PEEK (polyetheretherketone) may be used.

On the inner surface of the molded product, PES (polyether sulfone) in an aqueous dispersion and 20 vol% PFA (perfluoroalkoxyalkane; tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin, the same as the fluororesin used for the outermost coating ) IPA (isopropyl alcohol), which is a trace amount ( 5 % or less) of water-soluble alcohol solvent, is added to the base coating in which fine powder is dispersed and sprayed with a uniform mixture, then heated and semi-dried. The primer layer was formed. Next, after spraying fine powder of PFA, which is a fluororesin that forms the outermost surface, it was gradually melted from the substrate side in a high-temperature atmosphere at 380 ° C. to form a coating film having a uniform thickness.

Claims (7)

  On the inner surface of the molded product consisting mainly of aggregates composed of carbon powder particles, an undercoat paint with IPA (isopropyl alcohol) added is applied and then dried. A method for modifying the surface of a carbon sintered body, comprising attaching a powder and heating and melting the powder to form a surface coating layer.   The method for modifying the surface of a carbon sintered body according to claim 1, wherein the amount of IPA added is 0.2% or more.   The surface modification method for a carbon sintered body according to claim 1 or 2, wherein the base paint is an aqueous dispersion of heat-resistant thermoplastic resin fine particles.   4. The method for modifying the surface of a carbon sintered body according to claim 3, wherein the fine powder of the heat-resistant thermoplastic resin is smaller than the pores of the aggregate.   4. The carbon firing according to any one of claims 1 to 3, wherein the base paint comprises fine powder of fluororesin having the same component as that of the thermoplastic fluororesin having a coating film composition forming the outermost surface. A method for modifying the surface of a bonded body.   6. The carbon firing according to claim 3, wherein the heat resistant resin is PES (polyether sulfone) and the fluororesin is PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer). A method for modifying the surface of a bonded body.   The surface of the carbon sintered body according to claim 6, wherein the PES (polyether sulfone) is formed by dispersing 20 vol% fine powder of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer). Modification method.

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