FI97032B - Manufacture of fibreboard - 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

97032

This invention relates to the manufacture of paperboard, such as fibreboard, from a raw material containing lignocellulose.

This type of cardboard is made by breaking down the raw material into bundles containing fibers and fibers. Glue is added to the hosted raw material and the material is dried and a thin sheet is formed, which is finally pressed at an elevated temperature to cure the glue to form a fibrous sheet. The fiberboard is made from a raw material that has been broken down into fibers by grinding, i. more or less free fibers.

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The commonly used binder is urea formaldehyde mixed with the decomposed raw material. The amount of glue can be 6% or more. The adhesive is relatively expensive, and it is therefore desirable to minimize the addition of adhesive. However, a smaller amount of glue 20 degrades the strength of the finished fiberboard.

With this in mind, the addition of glue must be optimized.

When the adhesive is dried, a greater or lesser amount of water-soluble formaldehyde is released from the adhesive. After separating the drying gases 25 from the fibrous material, for example in a cyclone, the liquid content is condensed from the gas. In a conventional cleaning procedure, water-soluble formaldehyde then causes problems. The formaldehyde that follows the final compression of the material can also cause problems as it then separates from the finished fiberboard. When the adhesive is mixed with the substance after drying, there is a problem of formaldehyde separation both in the compression and in the finished sheet.

35 Drywall is commonly referred to as MDF (Medium Density Fiberboard) and is a wood fiber board. The yield rises to 95%. The starting material is preferably wood chips, which are decomposed into fibers with relatively low energy consumption, 100-500 kWh / ton of fibers, in order to remove 97032 fibers. The fibrous material disintegrated into fibers is glued, dried, formed into a sheet and pressed in a hot press. Alternatively, the material may be dried prior to gluing. Prior to fiber breakdown, the raw material is usually preheated to above 150 ° C, after which the fiber breakdown is performed at this high temperature under pressure in order to facilitate the release of the fibers. However, at such a high temperature, the raw material may decompose and change color due to hydrolysis. The short heating time reduces this disadvantage, but the color change cannot be avoided, and at the same time the energy consumption increases.

The commonly used urea-formaldehyde adhesive can be mixed with the fibrous material in a conveying line (blowing line) from the fiber dispersing device or in a separate mixing unit. The amount of glue mixed into the mass may be 6% or more.

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When the fibrous material is then dried in a tube dryer at ambient temperature with gas, a greater or lesser amount of water-soluble formaldehyde is released from the adhesive. As mentioned above, the formaldehyde that accompanies the fibrous material into the final compression 25 can cause problems, even when it subsequently separates from the finished fiberboard. This applies in particular to gluing after the material has dried, which can be done in the future.

The above-mentioned problems can be reduced by the present invention, which at the same time offers other advantages. According to the invention, the fibrous material is treated with a impregnation solution containing chemicals that activate the surface of the fiber and is preheated before the final comminution into fibers.

Examples of such chemicals are those that act on lignin, such as NajSCh and NaHSCL. These chemicals can be added at 1-30 kg / ton of raw material, expressed as Na 2 SO 3.

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According to the invention, it is possible to increase the ISO degree of the finished product, to reduce the energy consumption of the fibers in the disintegration, to reduce the amount of adhesive during the preservation of the strength, or to increase the strength during the preservation of the adhesive. Furthermore, the separation of formaldehyde can be substantially reduced.

The invention is mainly described in the following with reference to a few embodiments thereof.

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The fibreboard is made, for example, by impregnating the raw material in the form of softwood chips with chemicals acting on lingin, such as Na3SO3 and NaHSO3, expressed as Na3SO3 in an amount of 1 to 30, preferably 10 to 20 kg / ton of fiber.

Impregnation, which must be done quickly, can take a few minutes. The temperature is then raised to 150-200 ° C for 2-3 minutes. Preheating can, of course, be done before or simultaneously with impregnation. The pH is maintained in the range of 2-12. This means that the impregnation solution containing Na 3 SO 3 and NaHSO 3 contains sulphite in the form of HSO 3 'and / or SO 2'. The pH can best be adjusted with NaOH. As a result of this chemical treatment (sulfonation), the subsequent decomposition into fibers to the desired degree can be performed with less energy than usual. Energy consumption during this period is 50 to 400 kWh / tonne of fiber. The amount of energy saved can be about 10% compared to conventional fiber disintegration. 30

Due to impregnation, the whiteness of the finished fiberboard also increases.

It was found that with respect to the disintegration of the fiber disintegrant into fibers 35, the concentration of both the fines and the Sirpa lids decreased, i. the amount of first-class fiber increased.

97032 4

It was also found that the impregnation according to the invention substantially improved the strength of the finished fibreboard. The tensile strength as well as the modulus of elasticity and also the bonding of the fibers had improved by at least 10%. This effect can alternatively be exploited to reduce the amount of adhesive while maintaining the strength properties. A 10% increase in fiber binding corresponds to a 1% decrease in glue addition. The sulfonation according to the invention also means that the separation of formaldehyde can be reduced due to the fact that the sulphite ions in the impregnation solution react with formaldehyde so that it binds to the fibrous material instead of separating from the finished sheet.

EXAMPLE

15 The raw material in the form of chips was subjected to various digestion treatments. One batch was treated with 10 kg of Na 3 SO 3 per ton of chips and the other batch with 10 kg of NaHSO 3 per ton of chips. The control batch was not saturated.

The various batches were preheated to about 170 ° C and then decomposed into fibers. E2-type formaldehyde glue 10% dry glue based on the weight of the dry fiber was added as fibers to the post-disintegration blow line. The material was then dried to a dry matter content of about 90%.

These fibers were dry-formed into a mat which was pre-pressed at a pressure of about 1.5 MPa and hot-pressed for 5-6 minutes: at 170 ° C. The fibreboard thus prepared was tested for strength, ISO whiteness and formaldehyde content (perforator value). The relative energy consumption 30 for the different inputs was also measured. The results were as follows:

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Property Reference- Na2SOj- NaHSO3- input_ input input

Flexural strength MPa 38.4 43.8 40.0

Internal bond strength MPa 1.8 2.1 2.0 5 ISO whiteness 24 26 26

Formaldehyde content mg CH 2 O / 100 g 27 20 18

Relative energy consumption 1.0 0.95 0.95 10 The results correspond to the technical values stated above.

The invention is, of course, not limited to the embodiments described above, but can be modified within the scope of the idea of the invention.

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Claims (5)

97032 β Patent claims A method for producing a fibreboard according to the dry process, starting from a lignocellulosic raw material which is broken down into fibers, glued, formed into a sheet and pressed, characterized in that the raw material is treated with an impregnating solution containing a fiber surface before final breaking into fibers. chemicals, expressed as 1-30 kg / tonne of fiber, and preheated to 150-200 ° C, the pH of which is maintained in the range of 2-12, and that the fiberization is carried out with an energy input of 50-400 kWh / ton of fiber. . A method as defined in claim 1, characterized in that the fiber surface activating chemicals are of the lignin type. Process as defined in Claim 2, characterized in that the impregnation solution contains Na 2 SO 3 and / or NaHSO 3. Method as defined in one of Claims 1 to 3, characterized in that the fibrous material is first glued and then dried before it is formed into a sheet. 25 A method as defined in any one of claims 1 to 3,; characterized in that the fibrous material is first dried and then glued before being formed into a sheet. 30 II? 5 97032