JP2023028072A - Planar heat generating element - Google Patents

Abstract

[Problem] To provide a sheet heating element that is inexpensive, does not easily break down, and is capable of efficient heating. [Solution] A sheet heating element 1 having first and second insulating layers 21, 22 made of polyethylene and a heating element main body 10 sealed between the first and second insulating layers, the heating element main body comprising a paper substrate 11 and a resistive heating coating layer 12 formed on the paper substrate, the paper substrate comprising a heating region of the resistive heating coating layer and a non-heating region 110 adjacent thereto. [Selected Figure] Figure 1

Description

The present invention relates to a planar heating element.

A planar heating element with a resistance heating layer coated with heat-generating paint containing conductive particles such as carbon black and a binder resin is used in various fields such as floor heating, defrosting, snow melting on stairs, and pipe heaters. It is For example, the present inventors disclosed a planar heating element capable of efficiently performing stable heating with less temperature unevenness during heating in Patent Document 1, and disclosed a planar heating element capable of generating heat at a higher temperature than conventional ones in Patent Document 2. We are proposing a water-based heat-generating paint and a planar heat-generating element using this paint.

Here, a cheaper one is demanded as a planar heating element. For example, culture of microorganisms, human-derived cells, and the like often uses single-use containers in order to prevent contamination (contamination due to contamination and growth of various bacteria). These cultures need to be performed in a specific temperature range (for example, human-derived cells are around 37°C, and cells are destroyed at 42°C or higher), but efficient heating is required as a heating source. There is a demand for a low-cost product that can be used for single use and that is less likely to cause contamination, even though it is a drop-in type that can be used.

JP 2016-110757 A PCT/JP2021/014503

To provide a planar heating element which is inexpensive, resistant to failure, and capable of efficient heating.

The present invention is intended to solve the above problems, and specific means are as follows.
1. first and second insulating layers made of polyethylene;
a heating element body sealed between the first and second insulating layers;
has
The heating element body comprises a paper substrate and a resistance heating coating layer formed on the paper substrate,
A planar heating element, wherein the paper substrate has a non-heating area adjacent to the heating area of the resistance heating coating layer.
2. 1. At least part of the non-heating area is a non-coating area where the resistance heating coating layer is not formed. The planar heating element according to .
3. 1. The non-heat generating area is at least part of the periphery of the paper substrate. or 2. The planar heating element according to .
4. 1. The basis weight of the paper substrate is 40 g/m ² or more and 300 g/m ² or less. ~3. The planar heating element according to any one of .
5. 1. The resistive heating coating layer contains water-swellable synthetic mica. ~ 4. The planar heating element according to any one of .

The planar heating element of the present invention is very inexpensive because it uses paper and polyethylene as main materials. Polyethylene is a material that is difficult to fuse with other materials, but it can be fused with paper. In the planar heating element of the present invention, the insulating layer made of polyethylene and the heating element main body having the paper substrate are firmly fused together, and delamination is unlikely to occur. Polyethylene is a material that easily deforms when heated, but in the planar heating element of the present invention, the paper substrate has a non-heating region adjacent to the heat-generating region of the resistive heat-generating coating layer. By functioning as a support that suppresses deformation of polyethylene, it is possible to suppress cracking of the heating element paint that accompanies deformation of polyethylene. In addition, since the polyethylene can be prevented from being deformed (shrinked) and rounded with the heating surface of the planar heating element inside, the liquid in contact with the heating surface can be sufficiently exchanged and uniformly heated. .
The planar heating element of the present invention can be sterilized by gamma ray irradiation. Therefore, it can be suitably used as an immersion heater for culturing microorganisms or cells.

1 is an exploded view of a planar heating element that is an embodiment of the present invention; FIG. FIG. 4 is a diagram showing a modification of the heating element main body in the planar heating element of the present invention; FIG. 4 is a diagram showing a modification of the heating element main body in the planar heating element of the present invention; FIG. 4 is a diagram showing a modification of the heating element main body in the planar heating element of the present invention; FIG. 4 is a diagram showing a modification of the heating element main body in the planar heating element of the present invention; FIG. 4 is a diagram showing a modification of the heating element main body in the planar heating element of the present invention; FIG. 4 is a diagram showing a modification of the heating element main body in the planar heating element of the present invention; 5 is a graph showing the rate of change in resistance value after heating and the water temperature of the planar heating elements obtained in Example 1 and Comparative Example 1. FIG. FIG. 4 shows the states of the planar heating elements obtained in Example 1 and Comparative Example 1 before and after heating. 4A and 4B are diagrams showing states before and after heating of planar heating elements obtained in Example 2 and Comparative Example 2. FIG.

FIG. 1 shows an exploded view of a planar heating element which is one embodiment of the present invention. The planar heating element shown in FIG. 1 is merely one embodiment, and the planar heating element of the present invention is not limited to this.
A planar heating element 1, which is one embodiment, comprises first and second insulating layers 21 and 22 made of polyethylene, a paper substrate 11, and a resistance heating coating layer 12 formed on the paper substrate 11. and a heating element main body 10 provided. The heating element body 10 is sealed between the heat-sealed first and second insulating layers 21 and 22 .

- First and Second Insulating Layers The first and second insulating layers 21 and 22 are made of polyethylene. As polyethylene, high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and the like can be used without particular limitation. The thickness of the insulating layer is preferably as thin as possible from the viewpoint of heat transfer, but if it is too thin, the strength will decrease and the layer will be easily broken. In addition, if the thickness of the insulating layer is too thin for the step that exists inside, the step may not be followed at the time of heat sealing, and a hole may be formed. It is preferably 0.8 times or more, more preferably 1.0 times or more, and even more preferably 1.2 times or more the step difference existing inside. Also, the insulating layer may have a different thickness for each portion, for example, the insulating layer covering the resistive heating coating layer may be thinner than other portions. Furthermore, the insulating layer can also be integrated with the walls and bottom of the culture vessel, for example made of polyethylene.

· Heating Element Main Body The heating element main body 10 includes a paper substrate 11 and a resistance heating coating layer 12 formed on the paper substrate 11 . Conductive portions 13a and 13b are provided on both ends of the resistive heating coating layer 12, and lead wires 14a and 14b are connected to the conductive portions 13a and 13b. The paper substrate 11 is provided with a non-heat-generating region 110 which is adjacent to the heat-generating region of the resistive heat-generating coating layer 12 and which is a non-coated region where the resistive heat-generating coating layer 12 is not coated.

"Paper substrate"
The paper base material 11 can be used without any particular limitation as long as it can form a uniform resistance heating coating layer 12 by applying a heat generating paint on its surface. , and the insulating layers 21 and 22, uncoated paper is preferable. Moreover, the basis weight of the paper substrate 11 is preferably 40 g/m ² or more and 300 g/m ² or less. If the basis weight of the paper base material 11 is less than 40 g/m ² , the heat-generating paint may show through, and if it exceeds 300 g/m ² , the paper base material 11 becomes too rigid and bends due to the application of force. In some cases, peeling from the insulating layers 21 and 22 and breakage of the insulating layers may easily occur at the edges of the paper substrate 11 .

"Resistive heating coating layer"
The resistive heat-generating coating layer 12 is formed by applying a heat-generating paint containing at least a conductive material and a binder resin onto the paper substrate 11 and drying it. The heat-generating paint may be either water-based or organic solvent-based, but water-based paints are preferable because they are less burdensome for workers and the environment, and have excellent safety with no risk of fire or explosion.

As the conductive material, those conventionally used in the resistive heating coating layer can be used without particular limitation. Metal-based conductive materials such as gold, silver, copper and nickel, ceramic-based conductive materials such as tungsten carbide, titanium nitride, zirconium nitride and titanium carbide can be used. Among these, carbon-based conductive materials are preferable because those having a small particle size can be obtained at a low cost. The conductive material can be used singly or in combination of two or more.
The conductive material is preferably contained at a ratio of 30 parts by weight or more and 70 parts by weight or less with respect to 100 parts by weight of the solid content of the resistance heating coating layer.

Any binder resin can be used without particular limitation as long as it can be dissolved or dispersed in the heat-generating paint. Examples include polyimide resins, silicone resins, polyamide resins, polyurethane resins, polyester resins, and acrylic resins. , vinyl resins, epoxy resins, etc., or a mixture of two or more thereof. Among these resins, one or more of polyimide resin, silicone resin, and polyamide resin are preferable because of their excellent heat resistance.
The binder resin is preferably contained at a ratio of 15 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the solid content of the resistance heating coating layer.

When the heat-generating paint is a water-based paint, it preferably contains water-swellable synthetic mica. Water-swellable synthetic mica takes in water between its layers and swells. A water-based paint containing swollen mica exhibits thixotropic properties in which the viscosity decreases when shear stress is applied and the viscosity increases when stress is no longer applied. Therefore, the water-based heat-generating paint containing water-swellable synthetic mica is easy to apply and does not drip easily after being applied, making it easy to form a uniform resistive heat-generating coating layer.
When the water-swellable synthetic mica is contained, the water-swellable synthetic mica is preferably contained at a ratio of 3 parts by weight or more and 40 parts by weight or less with respect to 100 parts by weight of the solid content of the resistance heating coating layer.

The water-swellable synthetic mica preferably has an average particle size (median size) of 2 μm or more and 20 μm or less derived from a volume distribution measured by a laser diffraction scattering method. When the average particle size is within the above range, the dispersibility in the water-based heat-generating paint and the coatability are excellent, and a uniform coating film (resistive heat-generating coating layer) is easily formed. More preferably, the average particle size is 2 μm or more and 10 μm or less.

Additives such as a dispersant, a leveling agent, an antifoaming agent, and a curing agent may be added to the heat-generating paint as long as they do not impair the effects of the present invention.
The solid content concentration of the exothermic paint is adjusted so that the viscosity is suitable for the coating method and the like. The solid content concentration can be, for example, about 5% by weight or more and 50% by weight or less depending on the viscosity determined by the coating method or the like.

The resistive heating coating layer 12 can be formed by applying a heating paint to the paper substrate 11 and drying it. The resistive heat-generating coating layer 11 may be formed from a single heat-generating paint, or may be formed by separately coating a plurality of types of heat-generating paints having different compositions. Moreover, it may be a single layer or multiple layers that are overcoated. The resistive heat-generating coating layer 11 is patterned with heat-generating paints having different compositions or having different thicknesses to form regions with low resistance values and regions with high resistance values, thereby patterning the heat-generating properties. can be done.

The resistive heat-generating coating layer 12 generates heat when energized, and the region that generates heat when energized is the heat-generating region. The resistance heating coating layer 12 needs to be energized by wire or wirelessly. In the planar heating element 1 of one embodiment, conductive portions 13a and 13b made of conductive ink or the like are provided at both ends of a resistance heating coating layer 12, and lead wires 14a and 14b connected to a power source are provided to the conductive portions 13a and 13b. are connected by conductive paste or the like. As the conductive ink and conductive paste, among those containing conductive particles such as copper and silver, those that satisfy desired properties such as coatability, adhesion, and fixability can be used. As the lead wires 14a and 14b, copper wires, nickel wires, metal wires such as copper-plated nickel stranded wires, copper-plated aramid fibers, and the like can be used without particular limitation. An aggregate of a plurality of fibers is preferable because it can be flattened by being crushed by pressure. The method for energizing the resistance heating coating layer 12 is not limited to this, and a known method can be used. For example, a conductive adhesive tape can be used instead of the conductive paste.
The lead wires 14a and 14b may be led from different places to the outside of the planar heating element 1, or may be led from the same place. Further, when a temperature sensor such as a thermocouple is sealed inside the planar heating element 1, the cord of this sensor can be led to the outside either from a different location or from the same location.

Non-heat-generating region The planar heating element 1, which is one embodiment, is adjacent to the heat-generating region of the resistive heat-generating coating layer 12, and consists of a non-coating region where the resistive heat-generating coating layer 12 is not coated. 110. Polyethylene, which is the material of the insulating layers 21 and 22, is susceptible to deformation such as expansion and contraction due to heat. In the planar heating element 1, the non-heat generating region 110 provided on the paper substrate 11 functions as a support for suppressing deformation of the polyethylene. can be done.
On the other hand, if the paper substrate does not have a non-heat-generating region, the resistive heat-generating coating layer may crack or curl up with the heat-generating surface facing inward, following the deformation of the polyethylene. If a crack occurs in the resistive heat-generating coating layer, electricity cannot pass through that part, so the electricity concentrates in one part, causing abnormal heating and melting of the polyethylene or a short circuit. . In addition, if the heater is rolled with the heat generating surface facing inward, the liquid in contact with the heating surface is not sufficiently exchanged when the heater is thrown into a liquid as an immersion heater, resulting in uneven heating.

In the planar heating element 1, the non-heating region 110 is provided on the side of the resistance heating coating layer 12 connected to the lead wires 14a and 14b. is not limited to this. 2 to 7 show modifications of the heating element body.
The heating element body 210 shown in FIG. 2 also has a non-heating region 110 on the opposite side of the resistance heating coating layer 12 from the lead wires 14a and 14b. A heating element main body 310 shown in FIG. 3 has a resistive heating coating layer 12 divided into non-heating regions 110 between them. In the heating element body 410 shown in FIG. 4, the conductive parts 13a and 13b are provided only in a part of the resistive heating coating layer 12, and the non-heating region 110 (see FIG. right side of the dotted line). In the heating element body 510 shown in FIG. 5, the conductive portions 13a and 13b are provided on the inner side of the resistive heating coating layer 12, and outside the conductive portions 13a and 13b, the resistive heating coating layer does not generate heat. A non-heat generating region 110 is provided. A heating element main body 610 shown in FIG. 6 includes comb-like electrodes 131a and 131b extending from the conductive portions 13a and 13b, and includes a non-heat generating region 110 between the conductive portion 12 and the resistive heating coating layer 12. As shown in FIG. Moreover, the comb-shaped electrode 131a is also a non-heat generating region. A heating element main body 710 shown in FIG. 7 includes an intermediate conductive portion 132 between the conductive portions 13a and 13b, a resistance heating coating layer 12 provided in a square lattice shape, and a non-heating region 110 provided therebetween.
As shown in FIGS. 1 to 7, it is preferable that the non-heat-generating region 110 is at least a part of the periphery of the paper base material 11 because deformation can be further suppressed. Further, as shown in FIGS. 3 and 7, if the non-heat generating regions 110 and the resistive heat generating coating layers 12 are alternately arranged, deformation can be suppressed as a whole.

The planar heating element of the present invention is made by sandwiching the heating element main body between first and second insulating layers made of polyethylene, heating the heating element body while applying pressure, and heat-sealing the heating element main body to the first and second insulating layers. It can be manufactured by sealing between a second insulating layer. Polyethylene is a material that is difficult to fuse with other materials, but it can be thermally fused with paper. By providing the heat generating body with a paper substrate, the insulating layer made of polyethylene and the heat generating body can be brought into close contact with each other by thermal fusion. At this time, as described above, for example, while maintaining the heat conductivity by thinning the insulating layer covering the resistive heating coating layer, increasing the thickness of the insulating layer covering the lead wire causes the polyethylene to break at the place where the step is large. can also be prevented.

The application of the planar heating element of the present invention is not particularly limited, but since the melting point of polyethylene is about 95 to 140° C., it can be used for applications where the heating temperature is lower than that, for example, it is suitable as a liquid immersion heater. there is Furthermore, the planar heater of the present invention is not easily deteriorated by radiation irradiation and can be sterilized by gamma ray irradiation, so it is particularly suitable as an immersion heater for heating a culture solution of cells or microorganisms.

"Example 1"
Water-swelling synthetic mica (average particle size of 5 μm or less) and deionized water are blended in a water-based exothermic paint containing carbon black and polyimide resin, and a planetary stirring/defoaming device (manufactured by Kurashiki Boseki Co., Ltd., Mazerustar KK-1000W) and stirred for 6 minutes with a standard stirring and defoaming program for high-viscosity materials to obtain 37.2% by weight of carbon black, 33.9% by weight of polyimide resin, and water-swellable synthetic mica. A water-based exothermic paint was prepared with 0% by weight and 20.8% by weight water.
The prepared water-based heat-generating paint was applied to a paper substrate (Kent paper (non-coated paper) Be051, Kanko Kogyo Co., Ltd., basis weight 43 g/m ² ) with a doctor blade to a width of 150 mm, a length of 220 mm, and a thickness of 20 μm. , and 200° C. for 1 hour. Then, a silver paste was applied with a width of 5 mm at intervals of 80 mm in the longitudinal direction, and further baked at 130° C. for 1 hour to form a conductive portion. Cut 90 mm in the length direction so that the conductive parts are located at both ends in the length direction, and 90 mm in the width direction so that the non-coated area is located at the end in the width direction with a width of 1 cm. A heating element main body (90 mm×90 mm) having a non-heat-generating region consisting of a heat-generating region of the coating layer and a non-coating region adjacent thereto was obtained.

The heating element main body except for the non-heat-generating region was sandwiched from above and below with polyethylene having a thickness of 200 μm, and heat-sealed at 130° C. for 10 minutes with a cushioning material of silicone rubber sponge sandwiched therebetween.
After heat-sealing, the lead wire was fixed to the exposed conductive portion of the non-heat-generating region with a polyethylene tape, and the tip of the lead wire and the conductive portion were connected with Ag paste. A hole of φ2.5 was made in the non-heat generating region, and the tip of the thermocouple was overlapped with the hole and fixed with a PE tape.
This non-heat-generating region was sandwiched between 700 μm polyethylene layers from above and below, and heat-sealed at 130° C. for 10 minutes with a cushioning material of silicone rubber sponge sandwiched therebetween. The paper substrate was cut at a distance of 5 mm or more from the edge, and the thickness of each of the first and second insulating layers was 1400 μm at the portion including the non-heating area where the lead wires and the like were sealed, and the resistance heating coating was applied. A planar heating element having a thickness of 400 μm including the layer was obtained.

"Comparative Example 1"
A planar heating element was obtained in the same manner as in Example 1, except that the heating element main body was cut so as not to have a non-heating region.

Each of the planar heating elements obtained in Example 1 and Comparative Example 1 was submerged in 300 ml of water at 20° C., 0.2 W/cm ² was applied, and the rate of change in resistance value after 30 minutes compared with immediately after energization, The water temperature was measured after 30 minutes with a thermocouple of the planar heating element. Thereafter, the water was replaced with water at 20° C., and the rate of change in resistance was repeated in the same manner except that the power was applied so that the watt densities were 0.3 W/cm ² , 0.4 W/cm ² and 0.5 W/cm ² . and measured the water temperature. The results are shown in FIG. FIG. 9 shows the state of the planar heating element before and after heating in this experiment.

The planar heating elements obtained in Example 1 and Comparative Example 1 both exhibited good waterproof properties and heat-generating properties.
The planar heating element obtained in Example 1, in which the paper base material of the present invention has a non-heat-generating region, suppressed deformation of the polyethylene, and had almost no change in shape before and after heating.
On the other hand, the planar heating element obtained in Comparative Example 1, in which the paper base material did not have a non-heating region, left a large warp with the heating surface facing inward after heating. In this experiment, the water temperature was only raised to about 50°C by applying a maximum of 0.5 W/ ^cm2 . , it was suggested that the heated surface was curled inside.

"Example 2"
Adhesive tapes with a width of 10 mm were attached to a paper substrate (Kent paper (non-coated paper) Be051, Kanko Kogyo Co., Ltd., basis weight 43 g/m ² ) at intervals of 10 mm. The water-based exothermic paint prepared in Example 1 was applied with a doctor blade to the surface of the paper substrate to which the adhesive tape was attached in a width of 150 mm, length of 220 mm, and thickness of 20 μm. After drying, the adhesive tape was peeled off. It was calcined at 200° C. for 1 hour. Then, a silver paste was applied in a width of 5 mm at intervals of 80 mm in the width direction, and baked at 130° C. for 1 hour to form a conductive portion. The paper substrate is cut to 110 mm in the length direction and 90 mm in the width direction so that the conductive parts are located at both ends in the length direction, and the non-heating area consists of the non-coating area adjacent to the heat generating area of the resistance heating coating layer. was obtained.
A planar heating element was obtained in the same manner as in Example 1, except that this heating element main body was used.

"Comparative Example 2"
A planar heating element was obtained in the same manner as in Example 2, except that the portion of the paper substrate where the resistance heating coating layer was not formed was hollowed out.

The planar heating elements obtained in Example 2 and Comparative Example 2 were each immersed in 1000 ml of water at 20° C., and 0.2 W/cm ² was applied. FIG. 10 shows the state of the planar heating element before and after heating. In the planar heating element obtained in Example 2, in which the paper substrate of the present invention has non-heat-generating regions, deformation of the polyethylene was suppressed, and there was almost no change in shape before and after heating.
On the other hand, the sheet heating element obtained in Comparative Example 2, in which the non-heat-generating region of the paper substrate is hollowed out and does not have a non-heat-generating region, is slightly warped inward before heating, and the first and second The polyethylene, which is the insulating layer of , had already been deformed in the heat-sealing process. Moreover, after heating, the warpage increased.

Claims (5)

first and second insulating layers made of polyethylene;
a heating element body sealed between the first and second insulating layers;
has
The heating element body comprises a paper substrate and a resistance heating coating layer formed on the paper substrate,
A planar heating element, wherein the paper substrate has a non-heating area adjacent to the heating area of the resistance heating coating layer. 2. The planar heating element according to claim 1, wherein at least a part of said non-heat-generating region is a non-coating region in which said resistance heating coating layer is not formed. 3. The planar heating element according to claim 1, wherein the non-heat-generating region is at least part of the periphery of the paper substrate. The planar heating element according to any one of claims 1 to 3, wherein the paper base material has a basis weight of 40 g/m ² or more and 300 g/m ² or less. The planar heating element according to any one of claims 1 to 4, wherein the resistance heating coating layer contains water-swellable synthetic mica.

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