SK153094A3 - Method of manufacture of fibrous boards - Google Patents

Abstract

A method for the manufacture of fiberboard according to the dry method starting with lignocellulose-containing material which is disintegrated, glued, dried, formed to a web and pressed. Prior to the defibering, the material is treated with an impregnation solution containing fiber surface activating chemicals and preheated.

Description

Method for producing fiber boards

Technical field

The invention relates to a process for the manufacture of boards from lignocellulose-containing material, such as fiber boards.

BACKGROUND OF THE INVENTION

Boards of this type are produced by disintegrating the material but the particles containing fiber bundles and fibers. Adhesive is added to the disintegrated material, the material is dried, formed with a web, and this is finally pressed at elevated temperature to cure the adhesive from the present sheet formation. The fiber plates are calculated from a material that disintegrates by pulping into more or less loose fibers.

The binder used is a urea-formaldehyde adhesive which is added to the disintegrated material. The amount of adhesive may be 6% or more. The glue is relatively expensive, and therefore it is vital to reduce its content to as low a value as possible. However, when the amount of adhesive is reduced, the strength of the manufactured board deteriorates. In this respect, the addition of the adhesive must be optimized. -

When drying the material to be bonded, more or less water-soluble formaldehyde is released from the adhesive.

After the drying gas has been separated from the fibrous material, for example in a cyclone, the liquid present in the gas is condensed. In conventional purification procedures, water-soluble formaldehyde causes difficulties. Also, formaldehyde advancing the material to the final compression stage can cause difficulties when subsequently released from the finished board. When the glue is added to the material after it has been dried, there is a problem with formaldehyde separation, both in the molding and in the finished boards.

Fiber boards, manufactured by so-called. dry process, usually lc is abbreviated MDF / Medium Density Fiberboard / a fiber product made from wood fibers. Extraction is greater than 95% · Wood chips are preferably used as starting material, which are pulped at a relatively low energy input of 100 to 500 kWh / t of loose fiber. The fibrillated fibrous material is stuck, dried, processed into a web, and pressed in a hot press. Alternatively, the material may be dried prior to bonding. Typically, the material is preheated to a temperature of greater than 150 ° C prior to pulping, and the actual pulping, in which the fibers are released, is carried out under pressure at this high temperature. However, at such a high temperature, the material may degrade and its color may deteriorate due to the ongoing hydrolysis. By reducing the heating time, this deficiency is reduced, but deterioration of the color cannot be avoided and energy consumption increases.

The urea-formaldehyde lotion, which is commonly used, can be mixed with the fibrous material on a conveyor line starting from a fiberizing machine or in a separate mixer. The amount of adhesive to be added may be 6% or more.

To <! the fibrous material is then dried in a tubular dryer with a high temperature gas, more or less of the water-soluble formaldehyde is released from the adhesive. As mentioned above, also the formaldehyde, advancing with the fibrous material to the final pressing stage, can cause problems when it is subsequently released from the finished boards. This drawback is particularly evident when the gluing is carried out after drying of the material which can be carried out in the manufacture of fiber boards.

The above problems can be reduced by E with the present invention, which also exhibits additional advantages.

SUMMARY OF THE INVENTION

In the method of the invention, the fibrous material is treated with an impregnating liquid containing chemicals that activate the surface of the fibers and preheated prior to subsequent disintegration.

Examples of suitable chemicals include lignin attacking chemicals such as sodium sulfite and sodium bisulfite. These chemicals may be added in an amount ranging from 1 to 30 kg per tonne of material relative to sodium sulfite. By the method according to the invention, it is possible to increase the ISO lightness of the manufactured product, to reduce the energy consumption during pulping, to reduce the amount of adhesive while maintaining strength or to increase the strength while maintaining the amount of adhesive. In addition, the separation of formaldehyde can be substantially reduced.

The invention is described in more detail below, with several embodiments of the invention being disclosed.

The fiber board is made as follows:

The raw material in the form of chips, for example of softwood, is impregnated with lignin-attacking chemicals such as sodium sulfite or sodium bisulfite in an amount of 1 pred 30, preferably 10 to 20 kg / ton of fibrous material, calculated on the sulfite content sodium, K ₂ SO 4.

The impregnation, which must be carried out quickly, may take several minutes. Thereafter, the temperature is raised to 150 to 200 ° C, preferably 160 to 180 ° C for 2 to 3 minutes. However, preheating may, of course, be performed prior to or simultaneously with the impregnation. The pH is maintained between 2 and 12.

Accordingly, the nonsolvent solution containing sodium sulfite and sodium bisulfite will contain sulfite ions in the form of HSO2 and / or SO2 ions. The pH can be conveniently controlled by the addition of sodium hydroxide. Due to this chemical treatment (sulphonation), the subsequent pulping, in order to achieve the desired pulping degree, can be carried out with a lower energy input than usual. The energy consumption per tonne of fiber material ranges from 50 to 400 kWh. Energy savings of up to 10% can be achieved compared to conventional pulping.

Due to the impregnation, the lightness of the fiber boards produced is also increased.

As regards the properties of the fiber material, it has been found that both the fine particle content and the agglomerate content are reduced, i. the content of quality fibers is increased.

It has also been found that using the impregnation according to the present invention, the strength properties of the manufactured board are substantially improved, as well as the tensile strength, the modulus of elasticity and the bond strength of the fibers are increased by at least 10%. Alternatively, this effect can be used to reduce the amount of adhesive while maintaining strength properties. The 1X increase in fiber bond strength corresponds to a 135-fold reduction in glue addition, and the sulfonation process of the present invention can also reduce formaldehyde separation, since sulfite ions in the impregnation react with formaldehyde so that formaldehyde is bound in the fibrous material and is not released from the finished material. board.

- y -

uukutočnenia. This example is illustrative only and does not limit the scope of the invention in any way.

DETAILED DESCRIPTION OF THE INVENTION

The raw material in the form of chips is processed by various impregnation processes. One batch is treated with 10% sodium sulfite per tonne of chips and the other batch is treated with 10% sodium bisulfite per tonne of chips. The comparative dose is not administered.

The impregnated material (or control impregnated) is preheated to approximately 170 ° C and then spun. However, urea-formaldehyde adhesive type E2 in the amount of 10% of the dry matter of the adhesive, based on the dry matter of the fiber, is added to the material from the fiberising machine. The material is then dried to a dry matter content of approximately 90%. The fibers are dry-treated to a mat which is pre-compressed at a pressure of about 1.5 MPa and then hot pressed at 170 ° C for 5-6 minutes. The board thus prepared is tested for strength, ISO clearance and formaldehyde content (perforator value). The relative energy consumption at different doses is also measured. The results are: _

Property Comparison Batch with Batch with Batch

Na ₂ S0 ₃ Nah'SO ₃ flexural strength / MPa / fiber bond strength / MPa / ISO clearance /%> / formaldehyde content / mg CH ₂ O / 1C0 g /

33.4

1.8

43.8

2.1 relative energy consumption

1.0

2C

0.95

40.0

2.0

0.95

The above results confirm that with the method according to the invention they achieve the claimed effects. The invention is not limited to the specific embodiments described above, but may be modified in various ways, and the following claims are particularly critical for its scope.

Claims (5)

Process for the production of fiber boards by a dry process, wherein the lignocellulose-containing starting material is disintegrated, glued, dried, processed into a web and pressed, characterized in that before the final disintegration the material is treated with an impregnating solution containing fiber surface activating chemicals , in an amount of 1 to 30 kg, expressed as the amount of sodium sulfite relative to 1 tonne of fibrous material, and preheated to 150 to 200 ° C, maintaining the pH in the range of 2 to 12, disintegrating with a power supply of 50 up to 400 kWh per tonne of fibrous material. Method according to claim 1, characterized in that lignin-attacking chemicals are used as the surface-activating chemicals. Method according to claim 2, characterized in that the impregnating solution comprises sodium sulfite and / or sodium bisulfite. Method according to one of Claims 1 to 3, characterized in that the disintegrated material is first adhered and then dried before processing the web. Method according to one of Claims 1 to 3, characterized in that the disintegrated material is first dried and then glued before processing into a web.