CS254473B1 - A method for producing waterproof plywood boards for concrete formwork - Google Patents

Abstract

The method of production technology of waterproof plywood boards for concrete formwork consists in improving the surface of the boards in terms of abrasion resistance, facilitating formwork removal and improving the bending strength of the board by using impregnated beech veneers or other suitable wood species as the surface layer. Thermosetting resins, cresol or phenol-formaldehyde resins are used for impregnation, while the surface of the impregnated veneer can be coated with a suitable thermosetting resin before the actual pre-condensation.

Description

SUMMARY OF THE INVENTION The present invention provides a process for the manufacture of water-resistant plywood boards for concrete formwork, in which the surface veneers of plywood boards are modified during manufacture to increase their abrasion resistance and aggressive action of the concrete mixes.

Plywood boards and especially waterproof plywood for concrete shuttering are commonly manufactured in plywood plants from beech or birch veneer so as to achieve the required parameters in particular in bending strengths. Emphasis is also placed on the surface treatment of these slabs, which must be characterized by high abrasion resistance and resistance to aggressive action of liquid concrete mixtures.

At the same time, there is a requirement for reduced adhesion of the concrete to the plywood surface. This is achieved in particular in waterproof plywood for concrete formwork by surface treatment cured with phenolic resin or by pressing a paper film impregnated with phenolformadehyd resin and cured by elevated temperature and increased pressure in the manufacture of plywood.

Such a treated plywood board for concrete shuttering is fully proven, but its disadvantage is that both surface treatments, which are in the thickness of several hundredths of mm, wear out due to their use and the plywood board loses suitable properties in terms of concrete adherence to the plywood board. .

This drawback is overcome by the manufacturing method of the present invention.

Substantial change in the production method of plywood boards for concrete formwork consists in a new treatment of surface veneers used for their production. As the top veneer, scattered porous wood veneer (preferably beech or birch) is used, which is impregnated (by dipping or pressure) with a thermosetting resin, preferably cresol-formaldehyde, phenol-formaldehyde or a mixture thereof in any ratio prior to folding. Prior to precondensation of the resin in the oven, the veneer may be surface-coated with a suitable formaldehyde resin to improve the adhesive ability of the veneer and to impregnate the impregnation. Pre-condensation in the oven will result in a partial cure of the resin and its anchoring throughout the thickness of the veneer.

Such treated veneers are used in the assembly of sets before pressing as surface veneers of plywood boards for concrete formwork.

By curing the resin when pressing the plywood board under the influence of elevated temperature and pressure in the heated hydraulic press, the topsheet is strengthened, its abrasion resistance is increased and the bending strength of the whole board is increased. This new method of plywood production will result in new types of plywood with improved physical and mechanical properties, particularly suitable for concrete formwork.

He did

Beech peeled veneered. 1.2 mm is impregnated by soaking in baskets with a dilute alcohol solution of cresol formaldehyde resin. The impregnated veneer is coated with a continuous application of phenolformladehyd resin F 5250 prior to precondensation in a turnstile drier.

The thus treated veneer with pre-condensed resin is used as the top veneer when assembling sets of water-resistant plywood for a concrete board 15 mm thick. The whole set is pressed in a hydraulic press at a temperature of 140-150 ° C, a pressure of 1.5 MPa for 10 minutes.

Example 2

Prior to pressing, the double-sided coniferous veneer is first applied to the waterproof plywood (plywood or slatted board) made of coniferous wood veneers, before pressing, with double-sided coniferous wood veneer with resin F 5250 or FX 101 and covered with beech impregnated beech veneer. in a hydraulic press.

Example 3

The impregnated beech (birch) veneer according to Example 1 is used in folding sets of waterproof plywood from coniferous woods so that 2 impregnated veneers with wood fibers perpendicular to each other are deposited on each plywood surface. The assembled assemblies are pressed in a hydraulic press in the usual manner at elevated temperature and pressure.

Example 4

The manufactured plywood panels according to the methods described in Examples 1-3 are surface coated with phenol-formaldehyde or cresol-formaldehyde paper foil weighing 50-400 g / m of foil to further increase the board surface resistance and are molded in a conventional manner at elevated temperature and pressure.

SUBJECT OF THE INVENTION

Claims (4)

SUBJECT OF THE INVENTION Process for the production of water-resistant plywood boards for concrete formwork, characterized in that the surface veneers are impregnated with cresolformaldehyde or phenolformaldehyde resin by dipping or by pressure thermosetting resin, which is fixed in the nozzle by pre-condensation prior to condensation in a hydraulic press. 2. A method according to claim 1, characterized in that the surface veneers are impregnated with a mixture of cresol-formaldehyde or phenol-formaldehyde resins. 3. A method according to claim 1 or 2, wherein the surface of the impregnated veneer is coated with a suitable phenol2 or cresol formaldehyde resin or mixtures thereof in the range of 20 to 300 mg per m surface prior to precondensation. 4. A method according to claim 1, characterized in that the surface of the impregnated veneer is further reinforced during the pressing process by a paper press film impregnated with a thermosetting resin.