JPH0472376A - Production of chemical heating element - Google Patents

Abstract

PURPOSE:To readily obtain a homogeneously adhered excellent chemical heating element without requiring labor by electrolyzing an alkali electrolytic liquid containing zinc oxide powder mixed therein at a specific current density using an insoluble anode and a heat-resistant metallic substrate as a cathodic plate, draining the liquid and forming the resultant fine powder. CONSTITUTION:The objective chemical heating element is obtained by electrolyzing an alkali electrolytic liquid containing zinc oxide powder as a principal component, mixed and suspended therein at 3-10A/dm<2> current density using an insoluble anodic plate and a heat-resistant metallic substrate as a cathodic plate while being kept at 10-25 deg.C. The aforementioned cathodic plate on which fine powder of metallic zinc containing the above-mentioned alkali electrolytic liquid is deposited is then taken out and compression is applied thereto to drain the liquid. The obtained plate is formed to afford the objective chemical heating element.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a method for producing a chemical heating element that generates heat by reacting with oxygen or air.

(b) Prior Art The present invention relates to an improvement in the method of manufacturing a chemical heating element disclosed in Japanese Patent Application No. 63-38676.

Conventionally, as a heating element that generates heat by contact with oxygen in the atmosphere, the metal to be oxidized is folded back in a zigzag shape in the form of a foil.
In between, there was a heating element in the form of a laminate in which a tζ oxidation aid was sandwiched. (Special Public Interest 124832.24833
(Refer to No.) This type of heating element requires the simultaneous use of a metal foil to be oxidized and an oxidation aid, and the manufacturing method is basically complicated, making it unsuitable for mass production due to the manufacturing time and effort. Yes
Zinc oxide powder is made into a slurry using a binder and filled into the holes of the net-like or lattice-like substrate, and is coagulated and dried to solidify. A possible method is to then use this as a cathode plate in an alkaline electrolyte and electrolytically reduce it to metal to produce a heating element. In this case as well, not only is the process complicated and time-consuming, but the resulting zinc metal crystal particles are large.
An exothermic reaction with good combustion efficiency cannot be expected. Another disadvantage is that the zinc solidified and fixed on the substrate tends to peel off during the process. Particularly, when used as a heating element, it is often necessary to deposit a large amount of zinc thickly, making it unsuitable.

(c) Problems to be Solved by the Invention The present invention aims to solve the problems caused by the above-mentioned conventional manufacturing methods. Namely, the present invention is easy to operate, and moreover, the obtained fine zinc powder has high activity and superior combustion efficiency.

It is possible to thickly solidify and precipitate a large amount of zinc, which is often required as a chemical heating element, into a plate shape.
It's a small thing.

(d) Means for solving the problems The gist of the present invention is that porous fine powder mainly composed of metallic zinc is uniformly adhered and deposited on a heat-resistant metal substrate to form a plate shape. In a method for manufacturing a chemical heating element in which porous fine powder contains an alkaline solution and generates heat by reacting with oxygen or air, zinc oxide powder is mainly mixed and suspended, and 10% of an alkaline electrolyte is mixed and suspended. ~
After electrolyzing the insoluble anode plate and the heat-resistant metal substrate as the cathode plate at a current and degree of 3 to 1 OA/dm2 while maintaining the temperature at 25°C, the alkaline electrolyte containing the above-mentioned metal zinc Take out the cathode plate on which the fine powder has been deposited.

This is a method for producing a chemical heating element by deliquifying and molding by compression.

(E) Effect By using the above-described manufacturing method, the porous fine powder mainly composed of metallic zinc adheres and precipitates uniformly on the metal substrate to form a plate shape. The electrolytic conditions adopted in the present invention for obtaining a heating element containing an alkaline solution are extremely effective in obtaining such a heating element.

First, when zinc oxide is mixed and suspended in an alkaline solution, some of the zinc is dissolved in the solution and zincate ion Zn
ZnO produces O2'-, but its solubility is relatively low (for example, 5 mol/) in a caustic solution of ZnO.
3 mol/I solution) During electrolysis, this Z
No22- is electrolytically reduced to metal zinc, but if the original rate is lower than the above ion supply rate, in other words, if the solubility of ZnO2'- is small and the metal reduction rate is lower than the ion supply rate, then the ion Due to the deficiency effect, the reduced zinc crystal particles become fine and extremely active. Other conditions for obtaining such activity include maintaining the electrolyte temperature at a relatively low temperature and controlling the current density of the cathode plate. However, it is not possible to freely choose each of these desired conditions, because the active fine powder of zinc produced under unsuitable conditions will be oxidized again by air during electrolysis to become zinc oxide, or Fine metallic zinc powder adheres to the cathode plate and is dispersed in the electrolyte without precipitation.

The activity of the metallic zinc fine powder is maintained from 0 or more, which causes it to float and the initial purpose cannot be obtained. It has been found that a range of electrolytic conditions is suitable.

After the electrolysis is finished, when the cathode plate is lifted out of the electrolyte, a sponge-like electrolytically reduced metallic zinc containing a large amount of the electrolyte is deposited in a layer on the metal substrate. Since this metal zinc is extremely active as mentioned above, the adhesion force between the fine particles of zinc is also very strong, and as soon as the liquid is removed by compression, a porous and strong fine powder is produced. Yes
The fine powder here adheres and precipitates uniformly and firmly on the above-mentioned metal substrate, whether thin or thick. This generated
ζ Fine powder can still be used even after compression and deliquification! /' amount of alkaline electrolyte remains. The strength of the compressing pressure is not particularly limited, as long as it maintains a level of porosity that does not hinder the heat generation of the porous body.

Conventionally, zinc plating has been carried out using a TJ oxide solution (Na2Zn○2 solution) in which zinc is dissolved in a caustic soda solution, but the cathode current density in this case is approximately 2 A/d m.
2 is set as the maximum limit, and if the current and degree are higher than this, the plating will become rough and the zinc will fall off, resulting in poor plating performance. A high temperature of 30 to 40° C. is used for matkometsuki.

This is because the solubility of zinc increases and the current efficiency also improves.1 The present invention is completely different from plating, and the porous fine powder of zinc is uniformly adhered and deposited on a heat-resistant metal substrate to form a plate. 3~10A using an electrolytic solution made by mixing and suspending zinc oxide in an alkaline solution.
/dm2 cathode current and electrolyte temperature 10-25℃
It's a little thing. therefore.

The present invention and plating differ in their objectives, electrolytic conditions, effects, and effects.

(v) Example caustic potash] Add zinc oxide (50g/l) to a solution of OOg/l and stir well to prepare an electrolytic solution as a milky lotion. Electrolysis was carried out using a conventional method using a metal zinc plate as an insoluble anode and about 9 g of copper foil with a thickness of 50 μm and a size of 10 cm×20 cm as a cathode. In this case, the current density of the cathode is 5 A/dm2, and the temperature of the electrolyte is 15
After performing electrolysis for 1 hour in this way, the cathode plate was lifted from the electrolyte and a thick sponge-like zinc layer with a thickness of about 10 mm was deposited uniformly on the copper foil. When this was compressed using a roller press, it was compressed uniformly to a thickness of about 1.5 mm and the liquid was removed (a small amount of electrolyte was attached to the porous fine powder of metallic zinc). A flexible plate-shaped chemical heating element was obtained in which the above substrate was adhered to and precipitated. Its weight is about 30g
(contains about 10% water), then quickly place it in a small, breathable resin bag, seal it, and store it.

In the above embodiments, caustic potash is used as the alkali, but any alkali such as caustic soda can be used. The concentration of alkali is not particularly limited, but it is desirable to keep it low considering economic efficiency, etc. Also, although copper foil was used for the cathode, any heat-resistant metal substrate such as brass or zinc may be used as the material. Furthermore, the metal zinc plate used in this example as an insoluble anode is not limited to a foil, but may be a plate, and is slightly soluble in an alkaline electrolyte. Other materials such as iron and stainless steel can also be used as the insoluble anode.

The present invention provides an additive for maintaining the porosity of a fine powder mainly composed of metallic zinc, or an additive for suppressing hydrogen generated by the reaction between active zinc and water during long-term storage of a heating element. Various additives, such as copper, lead, calcium, and mercury, may be mixed with zinc oxide powder and an alkaline electrolyte, and added to the zinc of the cathode plate during electrolysis.

In the above embodiment, after the electrolysis is completed, the cathode plate is compressed by a roller press machine, but no other press machine is used.
This has the advantage of being able to reduce the number of steps by one step by simultaneously performing the operations simultaneously.

(G) Effects of the Invention The porous fine powder mainly composed of zinc metal obtained by the production method of the present invention as shown in the examples is extremely active, and after generating heat for 1 hour, the fine powder was analyzed. However, almost no metallic zinc remains, so the combustion efficiency is approximately 100%.
%Met. Furthermore, since the zinc constituting the fine powder is active, even a large amount of zinc has a strong mutual bonding force (furthermore, it can be uniformly adhered and deposited on a heat-resistant metal substrate, whether thin or thick, to form a plate shape. It is an excellent effect that such a chemical heating element, which does not have any drawbacks such as the fine powder peeling off from the substrate due to straining, can be easily produced by a simple single electrolytic operation of the present invention.

According to the manufacturing capability iJ- of the present invention, since the electrolytic solution used for electrolysis is an alkaline solution, no special operation for impregnating the porous fine powder with the alkaline solution is required, which facilitates production. It contributes to the weight gain.

As described above, according to the manufacturing method of the present invention, an extremely excellent chemical heating element can be easily manufactured without requiring 47 hours.

Claims (1)

[Claims] A porous fine powder mainly composed of metallic zinc adheres and precipitates uniformly on a heat-resistant metal substrate to form a plate shape, and the porous fine powder contains an alkaline solution, so that oxygen or In the manufacturing method of chemical heating elements that generate heat by reacting with air, zinc oxide powder is mainly mixed,
While maintaining the suspended alkaline electrolyte at a temperature of 10 to 25°C, an insoluble anode plate and a heat-resistant metal substrate are used as cathode plates.
After electrolyzing at a current density of ~10 A/dm^2, the cathode plate on which fine powder of metal zinc containing the alkaline electrolyte has been precipitated is taken out, deliquified by compression, and molded. A method for producing a chemical heating element.