Stock material or miscellaneous articles – Composite – Of fluorinated addition polymer from unsaturated monomers
Reexamination Certificate
1999-09-03
2004-05-18
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
Composite
Of fluorinated addition polymer from unsaturated monomers
C428S422000
Reexamination Certificate
active
06737164
ABSTRACT:
The present invention relates to composite materials for cooking apparatuses which are produced by applying, to a substrate, a fluorine-containing polymer excellent in heat resistance, non-sticking property, transparency (property for exhibiting clear surface pattern), stain-proofing property and water- and oil-repelling property and particularly in adhesive property to the substrate.
PRIOR ART
With respect to cooking apparatuses represented by a griddle and a rice cooker, it is desired that cooking can be done at higher temperature for shortening of cooking time and to pursue good taste of cooked dishes. Also it is desired that stains such as oil and scorch can be easily removed so as to make cleaning of these apparatuses easy after the cooking. Further good property for exhibiting clear surface pattern is also desired from the viewpoint of appearance thereof.
In order to meet such requirements, for the composite materials used for cooking apparatuses (cooking appliances, wares, utensils, tools, etc.), a fluorine-containing resin which is excellent in heat resistance, chemical resistance, weather resistance, surface properties (friction resistance, etc.), electric insulating property and the like is used in the form of coating or film.
However the fluorine-containing resin involves a substantial problem, namely insufficient adhesion to a metal or glass substrate due to its excellent non-sticking property.
Therefore in case where the fluorine-containing resin is used in the form of coating, there is a method of adhering a fluorine-containing resin to a substrate by roughening the surface of metal chemically or physically with expecting anchor effect between them. However this method requires much labor in the surface roughening itself, and though initial adhesion is possible, lowering of the anchor effect arises when a temperature change is made repeatedly and in case of use at high temperature.
Also a method for chemically activating a surface of a fluorine-containing resin by treating the surface with a solution prepared by dissolving metallic sodium in liquid ammonia has been proposed. However in that method, not only there is a fear that the solution itself causes environmental pollution but also there is a problem that its handling is attended with danger.
Further though a method for carrying out physical and chemical treatment such as plasma sputtering on a surface of a fluorine-containing resin has been proposed, there is a problem that much labor is required for the treatment and an increase in cost is resulted.
Also in order to improve adhesion of a fluorine-containing resin coating composition, investigations with respect to addition of various components and use of a primer have been made.
For example, there is a technique of adding an inorganic acid such as chromic acid to a coating composition containing a fluorine-containing resin to form chemical conversion coating film on a surface of metal for enhancing adhesion of the composition (JP-B-63-2675). However since chromic acid contains hexahydric chromium, it cannot be said that such a technique is sufficient in view of safety in food and coating work. Further in case of use of other inorganic acids such as phosphoric acid, there was a problem that safety of a fluorine-containing resin coating composition is damaged.
Use of a coating composition containing a fluorine-containing resin as a primer, in which heat resistant resins such as polyamideimide, polyimide, polyethersulfone and polyether ether ketone and in addition, a metal powder are added instead of the above-mentioned inorganic acid, has been studied (JP-A-6-264000). Inherently there is almost no compatibility between a fluorine-containing resin and a heat resistant resin. Therefore there arises a phase separation in a coating film, thus easily causing intercoat adhesion failure between the primer and the top coat of the fluorine-containing resin. Further film defects such as pin holes and cracks arise easily at the time of processing at high temperature or during use due to a difference in heat shrinkage between the fluorine-containing resin and the heat resistant resin or due to lowering of elongation of the coating film by the addition of the heat resistant resin. Also since those heat resistant resins are colored brown by baking, property for exhibiting clear surface pattern is poor and it is difficult to use them for applications requiring white and vivid colors and transparency. Further when the heat resistant resin is blended, non-sticking property and friction resistance which the fluorine-containing resin possesses inherently are lowered.
Also for adhesion of a fluorine-containing resin coating composition to glass, etc. requiring transparency, an improvement of the adhesion has been tried by treating the substrate with a silane coupling agent or adding a silicone resin to the fluorine-containing resin coating composition (JP-B-54-42366, JP-A-5-177768). However enhancement of adhesion is insufficient, heat resistance is lowered and separation of film, foaming and coloring arise easily at sintering or in use at high temperature.
On the contrary, fluorine-containing resin coating compositions prepared by copolymerizing a hydrocarbon monomer (containing no fluorine) containing functional group such as hydroxyl or carboxyl have been discussed. However those coating compositions were originally studied mainly for a purpose of weather resistance, and it is difficult to use them for application requiring heat resistance at 200° to 350° C. which is directed by the present invention, and for applications requiring non-sticking property, friction resistance, etc.
Namely with respect to a polymer prepared by copolymerizing a hydrocarbon monomer (containing no fluorine) having functional group, thermal decomposition easily occurs on components of the monomer at the time of processing at high temperature or during use, and thus coating film failure, coloring, foaming, separation, etc. arise, which makes it impossible to attain purposes of coating a fluorine-containing resin.
Further fluorine-containing resins are generally insufficient in mechanical strength and dimensional stability, and high in price. In order to make the best use of the above-mentioned merits of the fluorine-containing polymer and minimize its disadvantages, investigations have been made also with respect to its use in the form of film.
However the fluorine-containing resin inherently has low adhesive force, and it is difficult to adhere the fluorine-containing resin directly to other material (substrate). For example, even if the adhering is tried by thermo-processing, adhesive strength of the fluorine-containing resin is not enough, or even if the resin has adhesive force to a certain extent, such an adhesive force is apt to vary depending on kind of the substrate. Thus in many cases, reliability on the adhesive strength of the fluorine-containing resin has been not so enough.
In order to adhere the fluorine-containing resin film to a substrate, mainly the following methods have been studied:
1. a method for physically roughening a surface of substrate by sand blasting, etc.,
2. a method for surface-treating a fluorine-containing resin film by chemical treatment such as sodium etching, plasma treatment, photochemical treatment, etc.,
3. a method for adhering by using an adhesive, and other methods. With respect to the methods 1 and 2 above, surface-treating steps are required, and the steps are complicated and productivity is poor. Also kinds and shapes of substrates are restricted. The fluorine-containing resin film inherently has low adhesive force, and there easily occur problems with appearance such as coloring and color (property for exhibiting clear surface pattern) of the obtained composite material. Also the method of using a chemical such as sodium etching has a problem with safety.
Use of an adhesive in the method 3 above has also been discussed. A usual hydrocarbon type (non-fluorine-containing) adhesive does not have enough adhesive property and its heat resistance is insuffi
Araki Takayuki
Kumegawa Masahiro
Oka Noritoshi
Sanemasa Hisato
Shimizu Tetsuo
Daikin Industries Ltd.
Sughrue & Mion, PLLC
Zacharia Ramsey
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