CS266501B1 - A method for producing an electrolytic capacitor paper for low impedance capacitors - Google Patents

Abstract

A method of producing paper for low-impedance electrolytic capacitors, based on the fact that in order to achieve the desired structure of the paper, it is necessary to limit the bonding system between the cellulose fibers, thereby ensuring high electrolyte uptake by the paper in the capacitor and reducing the porosity of the paper. Such an effect can be achieved by adding viscose fiber. Viscose fiber must first be freed from adsorbed impurities, especially sulfates, which remained in the fiber during its production. For this purpose, the fiber is preferably washed with phosphoric acid.

Description

The invention relates to a process for the production of papers for low-impedance capacitors. .

The literature describes the use of variously treated native wood pulps, which generally do not allow to intensively suppress the interfiber bonding system, which reduces the porosity of paper and thus reduces the volume of electrolyte (EJ Smoljaninova, RK Jeremenko, S. N. Miročnik, VV Kučekovskaja: Bumažnaja no thought 2, pp. 14-15; USSR Patent No. 249,931). For low impedance electrolytic capacitor papers, it is necessary to achieve high porosity and maintain paper homogeneity. The methods described in the literature using conventional paper pulp raw materials do not allow this. According to the author's certificate No. 265 901, it is possible to partially replace unavailable natural fibers with modified glass fibers. However, glass fibers of a suitable type are expensive and, in addition, even after treatment, it cannot be ruled out that long-term contact with the electrolyte in the capacitor will not result in partial alkali extraction and thus shorten the life of the capacitor.

The above drawbacks are eliminated by the method according to the invention. Its essence is a process for the production of paper for low-impedance capacitors from long-fiber sulphate pulp, bleached or unbleached, which is freed of harmful impurities so as to contain max. 0.01% iron, 0.005% copper, 0.005% chlorides and 0.005% sulphates. This basic raw material is ground. Depending on the required porosity of the paper, it is mixed with 5 to 50% of viscose fibers. The addition of 5% of viscose fibers achieves a porosity below 0.75, the addition of 50% exceeds the porosity of 0.8. By adding viscose fibers, similarly to the addition of glass fibers, we achieve a decrease in the strength of the paper, which, however, is smaller than when using glass fibers. The technical viscose fiber contains sulphate residues and other impurities which prevent the use of this raw material for the production of electrolytic capacitor papers. Washing of residues of these substances is very difficult due to the sorption properties of cellulose. Desorption of salts is performed by washing viscose fibers with phosphoric acid, the residues of which do not interfere with the function or endanger the durability of electrolytic capacitors. The high porosity ensures a sufficient amount of liquid between the layers of metal foil in the capacitor. The limited pore size prevents direct contact with the surfaces of the wound film.

Table

Influence of the addition of viscose fibers on the porosity of electrolytic papers with a basis weight of 30 g / m, prepared in laboratory conditions.

Addition of viscose fiber 0 i 12.5% 25% 50% Porosity 0.773 0.779 0.827 0.879 Mean pore size / μm (hydraulic radius) 2.9 4.85 8.2 10.0 Pore size through which 5% of permeating medium flows (hydraulic radius) 9.5 14.0 19.0 27.5 apparent thickness of the fibrous 3.43 4.95 7.05 6.0

unit yUm

Table No. 1 characterizes the effect of the addition of viscose fiber, which increases the porosity and of course the pore size. The addition of viscose fibers increases the porosity of the paper. Electrolytic capacitor paper absorbs more electrolyte. The pore size does not grow beyond 40 μm (calculated as the size of the boundary pore through which 95% of the fluid medium flows). In this way, we ensure that electrolytic capacitor paper has properties similar to products containing raw materials such as Manila hemp. Viscose fibers exhibit standard properties, independent of harvesting and processing conditions, such as Manila hemp fibers. Their modification in terms of purity, with regard to the needs of the production of electrolytic capacitor papers, is solved by the present invention.

CS 266 501 Bl

Example

The sulphate pulp, free of chlorides, sulphates, iron and copper, was ground to 40 ° SR and viscose fiber, shortened to 2 to 10 mm in length, was added to the suspension. (The viscose fiber was washed in 0.5% phosphoric acid solution). The suspension was processed on a paper machine into paper with a basis weight below 20 g / m 2. The properties of the paper produced are given in Table 2 in comparison with paper produced in the same way, but without the addition of viscose fibers.

Table 2

Addition of viscose fiber 0% 20% porosity 0,7000,799 mean pore size ^x ^ 48 pore size through which the pit flows 2736% of fluid medium market length along km 3,73,1

x) pore size given by their hydraulic radius.

This method enables the production of paper for electrolytic capacitors from domestic raw materials.

Claims (2)

OBJECT OF THE INVENTION A process for the production of electrolytic capacitor paper for low-impedance capacitors from long-fiber, sulphate pulp, bleached or unbleached, free of harmful impurities so as to contain max. 0.01% iron, 0.005% copper, 0.005% chlorides and 0.005% sulphates, characterized in that that the raw material is mixed with 5 to 50% of viscose fibers, adjusted to a length of 2 to 10 mm by grinding with respect to the desired porosity of the paper. 2. The production method according to item 1, characterized in that the desorption of salts from viscose fibers is carried out with phosphoric acid added in an amount of up to 5%.