SU1726616A1 - Composition for making electric-insulation cardboard - Google Patents

Abstract

The invention relates to the pulp and paper industry and allows increasing density and reducing residual deformation and ash content of cardboard. The composition for making paperboard based on sulphate pulp and water-soluble polyvinyl alcohol fiber further comprises boric acid. The composition contains these components in the following amounts, wt.h .: sulphate pulp 96.5-99.5; water-soluble polyvinyl alcohol fiber 0.5-3.5; boric acid 0.1-1.6. 1 tab.

Description

The invention relates to the technology of pulp and paper production, mainly to the manufacture of electrical insulating paperboard used in transformers and machines with oil filling.

A known method of manufacturing electrical insulating paperboard, in which, to improve the dielectric and strength characteristics of cardboard, ground freshly formed (thermo hydroplastic) polyvinyl alcohol (PVA) fibers with a thickness of 10-20 microns, pre-cut 2-6 mm long, are added as 0, 5-1.0% aqueous suspension in the amount of 1.5-2.0 May. %

The disadvantage of this method is reduced density and increased residual deformation and ash content of the resulting paperboard.

A known method of manufacturing electrical insulating cardboard, according to which the density and dielectric strength while reducing the residual deformation of the cardboard, is increased by using Ms 20-40 drainage nets with the corresponding weft and density during pressing and drying.

A significant disadvantage of the method is the lack of this range of meshes and the inability to control residual deformation in their absence.

The closest to the proposed technical essence is the composition for the manufacture of electrical insulating cardboard, obtained by the method according to which sulphate pulp is used, milled in two steps, and thermo-hydro-plastic polyvinyl alcohol (PVA) fibers, introduced in an amount of 0.3-1 May 5 %

WITH

WITH

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in the pulp mass after the 1st stage of grinding.

Significant disadvantages of the method are the low density and increased residual deformation and ash content of the cardboard.

The purpose of the invention is to increase the density and reduce the residual strain and ash content of cardboard.

The goal is achieved by the fact that the composition for the manufacture of electrical insulating cardboard, including sulphate cellulose and water-soluble polyvinyl alcohol fiber, additionally contains boric acid in the following ratio of components, wt.: Sulfate cellulose 96.5-99.5 Water-soluble polyvinyl alcohol 0, 5- 3.5 Boric acid 0.1-1.6 The composition used is boric acid (orthoborne) NZVOZ, manufactured according to GOST 9656-75. It is a white crystalline powder, soluble in water when heated (by weight: 4.8% at 20 ° C; 10.35% at 50 ° C and 28.7% at 100 ° C).

The invention is exemplified. EXAMPLE 1.199 kg (99.5 parts by weight) of sulphate pulp is dissolved in a pulper at a mass concentration of 3.5% and sent to a basin, then passed through a magnetic separator and a high concentration cleaner. Next, the mass is directed to the 1st stage of grinding on a two-disk refiner to the degree of grinding, for example, 17 ° SH. The ground mass is pumped into the pool for swelling, where 1 kg (0.5 parts by weight) of PVA fiber and 0.2 kg (0.1 parts by weight) of boric acid are metered. After the joint grinding on the 2nd stage disk refiner, for example, up to 43 ° SHR accumulate mass in the engine pool. A multi-layered cardboard sheet is cast and molded on a CDM with two vacuum-forming cylinders at a mass concentration of 0.3% to form an elemental layer weighing 60 g / m2.

Examples 2-5. They are made according to example 1 and differ in the ratio of the components of the composition.

PRI me R 6. Performed according to the example of the prototype. In the example of the prototype, the cardboard was manufactured with a thickness of 1.18 mm (according to TU, the thickness was 1.2 ± 0.9 mm). The cardboard samples were tested

according to the requirements of ТУ 13-7308001-742-86 on the D-grade electrical insulating cardboard for transformers and oil filled apparatuses.

The results of the test paperboard made in examples 1-5 and the example of the prototype (6) are shown in the table.

As follows from the table, the insulating cardboard obtained from the proposed composition differs from the prototype

increased density (by 5.2-10.3%), lower residual strain rates (by 52.6-68.4%) and ash (by 28.6-78.6%), which is significant for obtaining cardboard with high quality indicators ensuring reliable operation of the material in transformers and oil filled devices. At the same time indicators of mechanical and electrical strength remain on

level or above similar indicators of the prototype.

Claims (1)

Claims An inventive composition for making electrically insulating cardboard, including sulphate pulp and a water-soluble polyvinyl alcohol fiber, characterized in that, in order to increase the density and decrease the residual deformation and ash of the cardboard, it additionally contains boric acid in the following ratio of components, parts by weight .: Sulphate cellulose 96.5-99.5 Water-soluble polyvinyl alcohol fiber0, 5-3.5 Boric acid, 0.1-1.6.