Heat generating panel

Abstract

 A heat generating panel (4) mainly composed of waxes has a plane core (1), a pair of foil electrodes (5, 6) embedded in the core, and polyester resin webs (2, 3) between which the core is sandwiched. The core (1) is composed of: 10 - 20 % by weight of a microcrystalline wax; 40 - 70 % by weight of a paraffin wax containing a resin and melt-blended with the microcrystalline wax; 10 - 35 % by weight of a first potassium titanate whisker; and 1 - 15 % by weight of a second potassium titanate whisker, both the conductive whiskers blended with and dispersed in the waxes. The first titanate whisker has a formula: K₂O · nTiO₂/SnO₂ · Sb₂O₅, with the second one having another formula: K₂O·nTiO_2-x/C.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a heat generating panel of a novel type that is flat in shape, comprises waxes as main ingredients and adapted for use in various fields such as a floor heating in houses or buildings and a ground or road heating for melting snow and/or ice.

2. Prior Art

[0002] One of the prior art heat generators of this type is disclosed in the Specification of Japanese Patent No. 1647696 entitled: Heat-Sensitive Composition Serving as a Resistor. This composition comprises a polyalkylene glycol as a main ingredient blended with a carbon powder as a conductor.

[0003] Polyalkylene glycols are however water soluble so that moisture contained in the air is likely to affect the electric resistance of such a composition. From a viewpoint of safety, there is a problem that the carbon powder employed as the conductor in the prior art heat generators is so inflammable that the latter may catch fire in some cases.

OBJECTS OF THE INVENTION

[0004] An object of the present invention is therefore to provide a heat generating panel of a novel type that is free from the drawbacks inherent in the prior art ones. Another object is to provide a heat generating panel which contains potassium titanate as a conductor dispersed in a matrix that is not water soluble, whereby water or moisture is prevented from affecting the resistance of said heat generating panel.

SUMMARY OF THE INVENTION

[0005] These objects will be achieved herein by providing a heat generating panel comprising a plane core, a pair of foil electrodes embedded therein ( as seen in Figs. 1 - 4 showing an embodiment ), and polyester resin webs between which the plane core is sandwiched, wherein the plane core is composed of: 10 - 20 % by weight of a microcrystalline wax; 40 - 70 % by weight of a paraffin wax containing a resin and melt-blended with the microcrystalline wax; 10 - 35 % by weight of a first conductive potassium titanate whisker; and 1 - 15 % by weight of a second conductive potassium titanate whisker, both the potassium titanate whiskers being blended with and dispersed throughout the waxes, and wherein the first whisker has a formula: K₂O • nTiO₂/SnO₂• Sb₂O₅, with one having another formula: K₂O•nTiO_2-x/C ( both available from the Otsuka Chemical Products Co., Ltd. ).

[0006] According to the present invention, a matrix for dispersing the whiskers is composed of: the microcrystalline wax having a melting point of 64 - 101 °C and a flash point of 310 - 320 °C ; and the paraffin wax having a melting point of 56 - 64 °C and a flash point of about 262 °C . Since these waxes are neither water-soluble nor hygroscopic, the heat generating panel will not vary its behavior despite any possible variation in moisture content of the air. The waxes are automatically protected from being heated above 80 °C so as not to catch fire in any event ( as will be detailed below ).

[0007] Each of the abovementioned whiskers dispersed in the matrix consists of extremely fine needle-shaped crystals each having a diameter of 0.3 - 0.6 µm and 10 - 20 µm long. Those crystals are previously treated with a suitable agent so as to be conductive and physically and chemically stable. They can serve as a whole as a conductor or resistor to be incorporated in an electric circuit or the like system.

[0008] The needle-shaped crystals of each whisker have a high strength, a high modulus of elasticity and a high aspect ratio. Therefore, the matrix is well reinforced with the whiskers to provide the core which can consequently be formed to be of any desired small and accurate thickness. Further, a less friction resistance and a high abrasion resistance are afforded to the core and the panel. The whiskers have a high melting point of or higher than 1300 °C , and will thus not be burnt at any temperature below this melting point. Even if any creases are produced in the panel, or the latter is deformed otherwise, the panel will spontaneously recover its intrinsic conductivity by virtue of a number of whisker crystals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] 

Fig. 1 is a plan view of a heat generating panel provided in an embodiment;

Fig. 2 is a cross section taken along the line A A in Fig. 1;

Fig. 3 is a graph showing the heat generated by the panel; and

Fig. 4 is a graph showing the relationship found between the electric resistance and the ambient temperature ( viz., temperature of the panel ).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Now, the present invention will be described in more detail, referring to the drawings which show an embodiment.

[0011] Figs. 1 and 2 illustrate the structure of a heat generating panel provided in the embodiment.

[0012] This heat generating panel 4 consists of a plane core 1, a pair of foil electrodes 5 and 6 embedded in the core, and polyester resin webs secured to an upper and lower faces of the core. Each web consists of a polyester resin sheet 2 and a backing 3 which is a nonwoven polyester fabric attached to an inner side of the sheet 2. The core 1 is composed of: 10 - 20 % by weight of a microcrystalline wax; 40 - 70 % by weight of a paraffin wax containing a resin and melt-blended with the microcrystalline wax; 10 - 35 % by weight of a first conductive potassium titanate whisker; and 1 - 15 % by weight of a second conductive potassium titanate whisker, both the whiskers being blended with and dispersed throughout the waxes. The first whisker may have a formula: K₂O • nTiO₂/SnO₂ • Sb₂O₅, with the second one having another formula: K₂O•nTiO_2-x/C. In manufacture, the microcrystalline wax will be added to the paraffin wax to give a wax mixture. This mixture will be heated to a temperature of 90 - 130 °C so as to blend these waxes evenly with each other. Subsequently, the whiskers will be added to and stirred in the molten wax mixture so as to diffuse uniform throughout this mixture. The molten wax mixture containing the whiskers will then be cooled between the abovementioned polyester webs, into a predetermined thickness.

[0013] In a second embodiment, the plane core 1a comprises a small amount of acetylene black powder in addition to the first and second whiskers described above, whose contents are 10 - 35 % and 1 - 15 % by weight, respectively, similarly to the first embodiment. The small amount of actylene black may preferably be about 0.5 - 2 % by weight. The matrix in this case also consists of 10 - 20 % by weight of a microcrystalline wax and 40 - 70 % by weight of a paraffin wax containing a resin and melt-blended with the microcrystalline wax. This core la having likewise a pair of embedded foil electrodes 5 and 6 is also sandwiched between polyester resin webs each consisting of a polyester sheet 3 and a polyester nonwoven fabric 2 bonded to the inside face of the sheet, so as to provide a heat generating panel 4a. The acetylene black in this embodiment is added to adjust the electric resistance and Joule heat generated by the core.

[0014] It will now be apparent that the microcrystalline wax having a melting point of 64 - 101 °C and a flash point of 310 - 320 °C is blended with the paraffin wax having a melting point of 56 - 64 °C and a flash point of about 262 °C , to form the matrix for dispersing the whiskers. Since these waxes are neither water-soluble nor hygroscopic, any variation in moisture content of the air will not affect the characteristics of the heat generating panel. The waxes are protected from being heated above 80 °C so as not to catch fire in any event. Each whisker dispersed in the matrix consists of extremely fine needle-shaped crystals each having a diameter of 0.3 - 0.6 µm and 10 - 20 µm long. Those crystals are previously treated with a suitable agent so as to be conductive and physically and chemically stable. Thus, they can serve as a whole as a conductor or resistor to be incorporated in an electric circuit or the like system.

[0015] The needle-shaped crystals of each whisker have a high strength, a high modulus of elasticity and a high aspect ratio. Therefore, the matrix is well reinforced with the whiskers to provide the core which can consequently be formed to be of any desired small and accurate thickness. Further, a less friction resistance and a high abrasion resistance are afforded to the core and the panel. The whiskers have a high melting point of or higher than 1300 °C , and will thus not be burnt at any temperature below this melting point. Even if any creases are produced in the panel, or the latter is deformed otherwise, the panel will spontaneously recover its intrinsic conductivity by virtue of a number of whisker crystals.

[0016] The heat generating panel may have an extremely small thickness of about 0.4 mm or less, and a width of 20 - 400 mm. Dimension and chemical composition of this panel's core can be designed freely to accurately meet the condition of or requirements in use. The heat generating panel can thus operate at any voltage of 12 - 200 volts and at any power consumption of 200 - 2400 watts/m.

[0017] Fig. 3 shows a typical example of performance of the heat generating panel, in which the right-hand axis of ordinates is graduated to indicate the ambient temperature ( viz., self-heated temperature of the panel ), with the left-hand axis of ordinates indicating the power consumption. The axis of abscissas is graduated to indicate the time lapse from the turning-on of the heat generating panel. Fig. 4 shows the relationship found between the self-heated temperature and electric resistance of the heat generating panel. As seen in Figs. 3 and 4, a self-control mechanism is afforded to the panel such that as the temperature asymptotically rises towards an apparent highest value, the panels's electric resistance rapidly increases to 10³ - 10⁵ Ω . This means that an energy supply will automatically be reduced to compensate only the heat radiated from this panel ( see Fig. 4 ). In other words, the power consumption decreases as the temperature of this panel arises ( see Fig. 3 ).

[0018] The embodiments described above may be modified in any manner within the scope and spirit of the present invention so as to ensure the performance and advantages afforded herein.

[0019] In summary, the matrix employed herein for dispersing the whiskers is composed mainly of waxes which are neither water-soluble nor hygroscopic, the heat generating panel will not vary its behavior due to any variation in moisture content of the air. The waxes are automatically protected from being heated above 80 °C so as not to catch fire.

[0020] Each whisker dispersed in the matrix consists of fine needle-shaped crystals which are electrically conductive so that the panel can serve as a whole as a conductor or resistor to be incorporated in an electric circuit or the like system. The matrix is reinforced with the whiskers to provide the core of any desired small and accurate thickness. Further, a less friction resistance and a high abrasion resistance are afforded to the core and the panel.

[0021] The whiskers have a high melting point of or higher than 1300 °C , and will thus not be burnt at any temperature below this melting point. Even if any creases are produced in the panel, or the latter is deformed otherwise, the panel will spontaneously recover its intrinsic conductivity by virtue of a number of whisker crystals.

[0022] The heat generating panel may have an extremely small thickness of about 0.4 mm or less and any desired width, if chemical composition of this panel's core is designed properly. The panel can be of any desired electric resistance so as to operate at any desired voltage and at any desired level of power consumption.

Claims

1. A heat generating panel (4) comprising a plane core (1), a pair of foil electrodes (5, 6) embedded therein, and polyester resin webs (2, 3) between which the plane core is sandwiched, wherein the plane core (1) is composed of: 10 - 20 % by weight of a microcrystalline wax; 40 - 70 % by weight of a paraffin wax containing a resin and melt-blended with the microcrystalline wax; 10 - 35 % by weight of a first conductive potassium titanate whisker; and 1 - 15 % by weight of a second conductive potassium titanate whisker, both the potassium titanate whiskers being blended with and dispersed throughout the waxes, and wherein the first titanate whisker has a formula: K₂O • nTiO₂/SnO₂ • Sb₂O₅, with the second one having another formula: K₂O•nTiO_2-x/C.

2. A heat generating panel (4) comprising a plane core (1), a pair of foil electrodes (5, 6) embedded therein, and polyester resin webs (2, 3) between which the plane core is sandwiched, wherein the plane core (1) is composed of: 10 - 20 % by weight of a microcrystalline wax; 40 - 70 % by weight of a paraffin wax containing a resin and melt-blended with the microcrystalline wax; 10 - 35 % by weight of a first conductive potassium titanate whisker; 1 - 15 % by weight of a second conductive potassium titanate whisker, both the potassium titanate whiskers being blended with and dispersed throughout the waxes; and a small amount of acetylene black powder added to adjust the highest temperature of the heat generating panel, and wherein the first titanate whisker has a formula: K₂O • nTiO₂/SnO₂• Sb₂O₅, with the second one having another formula: K₂O•nTiO_2-x/C.

Drawing