JPH07142151A - Panel heater - Google Patents

Abstract

PURPOSE:To decrease the change of the output against the change of the temperature and improve durability by molding a panel from a composition made of a thermosetting resin and a conducting material, laminating a heating element provided with a pair of electrodes at both ends on it, and coating the surface with an insulating thermoplastic resin. CONSTITUTION:Melamine formaldehyde resin of 50wt.%, base resin made of alpha-cellulose of 24wt.%, acetylene black of 23wt.% having the volume resistance value of 2X10<-1>OMEGAcm and the average grain size of 40mum, zinc stearate of 2wt.% serving as a mold releasing agent, and phthalic anhydride of 1wt.% serving as a hardening agent are added, crushed, and mixed, and coarse grains are removed by a 48-mesh sieve to form a molding material. It is heated and hardened by a die of 160 deg.C and a compression molding machine of 180kg/cm<2>, a tin-plated copper stranded wire 3 is fitted to the portion provided on the side face in the longitudinal direction, a heating element 1 is provided at the portion surrounded by it, and the upper and lower faces are pinched by polyethylene sheets as coating layers 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a railroad turnout, a roof, a snowmelt and freezing prevention of a road surface, an agricultural soil, a freezing prevention and heating of tank contents, and an output change due to a temperature used for indoor floor heating. Regarding less panel heaters.

[0002]

2. Description of the Related Art Electric heaters coated with nichrome wire have been widely used. This heating element is inexpensive and has a constant output even when the temperature changes. However, since the heating temperature is high, the nichrome wire and the covering material are prone to deterioration due to heat, and the durability is poor. On the other hand, there are also sheet heating elements containing, for example, carbon black as a conductive material in a thermoplastic resin such as polyethylene or polypropylene, but since the linear expansion coefficient of the thermoplastic resin is larger than that of the thermosetting resin, the environmental temperature is high. It has the characteristic that the output changes due to the change, and has the safety that the amount of heat generation decreases as the temperature rises, but it is difficult to always obtain a constant output.

[0003]

As described above, there is a drawback of the nichrome wire, that is, in the case of obtaining a constant amount of heat generation, since the fine wire having a small heat generation area is used to generate heat, the heat generation temperature is inevitably raised. By using a heating element molded in the shape of a panel, the heating area is increased, and by lowering the heating temperature, deterioration due to the heat of the material used is suppressed, and the output fluctuates greatly depending on the temperature seen in the planar heating element. It is to provide a heater with suppressed characteristics.

[0004]

The present invention uses a thermosetting resin as a base resin, contains 5 to 50% by weight of a conductive material having a volume resistance value of 10 ⁰ Ω · cm or less, and has a volume resistance value of 10 ¹ ~ 1
A resin composition having a conductivity of 0 ⁴ Ω · cm is formed into a panel shape, and a heating element having metal twisted wires, metal braided wires or metal rods as electrodes at both ends thereof is made of an insulating thermoplastic resin as a coating material. A panel-shaped heater having a Vicat softening point of 160 ° C. or less, which covers the periphery of a heating element, and an output change rate at a temperature difference of 50 ° C. is 5% or less. The panel heater of the present invention is manufactured by the following steps.

Powdery and granular thermosetting resins are used in a conductive resin composition which is a raw material of a heating element. The reason for this is that the coefficient of linear expansion of thermosetting resin is smaller than that of thermoplastic resin, the resistance change with temperature when used as a heating element is small, and the softening temperature is higher than that of thermoplastic resin, so that it is coated with thermoplastic resin. This is because it can withstand deformation due to temperature and pressure when forming the layer, and because it is powdery and granular, mixing with the conductive material is simple. Carbon volume resistivity as a conductive material is generally used as the conductive material of the plastic as the following 10 ⁰ Ω · cm black, graphite, metal powder, metal fibers,
Carbon fiber or the like may be used.

When the content of the conductive material is less than 5% by weight, the resistance value is too large and a sufficient output cannot be obtained as a heating element. On the other hand, if it exceeds 50% by weight, the physical strength of the heat generating element is significantly lowered, and thus neither is suitable. The base resin and the conductive material are mixed by using a general crushing device and a powder mixing device such as a ball mill, a Henschel mixer, a ribbon blender and a Nauter mixer. The composition in which the conductive material is mixed forms a panel-shaped heating element by injection molding, compression molding, or transfer molding. It should be noted that a twisted metal wire, a metal braided wire, and a metal rod may be previously installed as electrode wires at both ends in the mold during molding, and the electrode wires may be simultaneously adhered during molding.

From the end of the obtained heating element, an electrode wire and a lead wire are connected to connect to a power source. Further, this heating element is insert-molded by a press molding machine or an injection molding machine to provide an insulating coating layer in a sandwich shape. The resin used as the coating layer has a Vicat softening point of 160.
It is necessary that the temperature is not more than 0 ° C. in order to satisfy the insulating property and the moldability at a temperature at which the heating element is not deformed, and low density polyethylene, high density polyethylene, polypropylene and its elastomer, ionomer, acid modified product and the like are preferable.

[0008]

The present invention will be described in more detail based on the following examples. In the examples,% means% by weight.

[0009]

Example 1 Melamine-formaldehyde resin 50%,
As a filler, 24% of α-cellulose was mixed in a kneader and dried (hereinafter referred to as base resin), and 23% of acetylene black having an average particle diameter of 40 mμ and a volume resistance value of 2 × 10 ⁻¹ Ω · cm, Zinc stearate (2%) as a release agent and phthalic anhydride (1%) as a curing agent were added, and the mixture was pulverized and mixed in a ball mill for 8 hours, and coarse particles were removed with a 48-mesh sieve to obtain a molding material. After heating this molding material to 110 ° C with a high-frequency preheater, mold clamping output 37t
Using a compression molding machine, mold temperature 160 ° C, molding pressure 18
Heat cure at 0 kg / cm ^{2 for} 3 minutes, 50 × 170
A 2.5 mm panel-shaped molded product was molded. At this time,
Tin-plated copper stranded wires having a cross-sectional area of 2 mm ² were arranged on both side surfaces of the inner surface of the mold in the longitudinal direction, and electrode wires were attached at the same time.

Next, a Lycal electric wire was connected to one end of the two electrode wires as a lead wire using a crimp sleeve. When the output change rate was measured by the resistance value of the heating element, it was 130Ω at 0 ° C and 136Ω at 50 ° C. Next, the upper and lower surfaces of the heating element were sandwiched by a sheet having a thickness of 1.5 mm of maleic acid-modified high-density polyethylene having a melt flow rate (MFR) of 1 g / min at 190 ° C. and 2.16 kgf, and 160 ° C. After sufficient preheating with the heat press of 10
Heat at a pressure of 0 kg / cm ² for 2 minutes, then 100 kg
After cooling at a pressure of / cm ² for 4 minutes, a panel heater having a coating layer with a thickness of 1 mm was obtained.

[0011]

[Example 2] Phenolic resin molding material (manufactured by Asahi Organic Material Co., Ltd.
AV light 75K-1) 65%, 35% of average particle size 20μ volume resistance value 1.5 × 10 ^-2 Ωcm artificial graphite
Were mixed with a Henschel mixer. Next, this mixture was molded in a screw-type injection molding machine with a mold clamping pressure of 50 tons, with a cylinder temperature of 80 ° C., a mold temperature of 160 ° C., and a curing time of 3 minutes. Was molded. At this time, as in Example 1, tin-plated copper stranded wires having a cross-sectional area of 2 mm ² were arranged on both sides in the longitudinal direction of the inner surface of the mold on the side surfaces of the mold, and the electrode wires were simultaneously attached to the two electrodes. A Lycal wire was connected to one end of the wire as a lead wire using a crimp sleeve to form a heating element.

Next, using a sheet having a thickness of 1.5 mm and made of low-density polyethylene having a melt flow rate of 0.5 g / min at 190 ° C. and 2.16 kgf, the thickness was increased in the same manner as in Example 1. A panel heater having a 1 mm thick coating layer was obtained. When the output change rate was measured by the resistance value of the heating element, it was 245Ω at 0 ° C and 255 at 50 ° C.
It was Ω.

[0013]

EFFECT OF THE INVENTION By using a thermosetting resin, the present invention can provide a panel heater in which the electric resistance value has a small temperature dependency and a constant calorific value is always obtained.

[Brief description of drawings]

FIG. 1 shows a general view of the present invention.

[Explanation of symbols]

 1: Heating element 2: Coating layer 3: Electrode wire 4: Crimping sleeve 5: Lead wire

Claims (2)

[Claims] 1. A thermosetting resin as a base resin, containing 5 to 50% by weight or less of the conductive material 10 ⁰ Ω · cm in volume resistivity, conductivity of volume resistivity 10 ¹ ~10 ⁴ Ω · cm Of a resin composition having heat resistance is formed into a panel, and a heating element having metal twisted wires, metal braids or metal rods as electrodes on both ends thereof is made of insulating thermoplastic as a covering material and has a Vicat softening point of 160 ° C. A panel-shaped heater characterized by covering the periphery of a heating element with the following resin and having an output change rate of 5% or less at a temperature difference of 50 ° C. 2. The panel-shaped heater according to claim 1, wherein the thermosetting resin contains at least one selected from a phenol resin, a melamine resin, a urea resin, an epoxy resin and a benzoguanamine resin.