AU662432B2 - Manufacture of fibre board - 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

's y i 1 1 "OPI DATE 04/01/94 AOJP DATE 24/03/94 APPLN. ID 43633/93 PCT NUMBER PCT/SE93/00388 i 11111 IIll i IIIII AU9343633 (51) International Patent Classification 5 (11) International Publication Number: WO 93/25358 B27N 1/00(43) International Publication Date: 23 December 1993 (23.12.93) (21) International Application Number: PCT/SE93/00388 (74) Agent: SUNDQVIST, Hans; Sunds Defibrator Industries Aktiebolag, Strandbergsgatan 61, S-112 51 Stockholm (22) International Filing Date: 4 May 1993 (04.05,93) (SE).

Priority data: (81) Designated States: AU, BR, CA, CZ, FI, HU, JP, KR, NO, 9201800-1 11 June 1992 (11.06.92) SE NZ, PL, RO, RU, SK, UA, US, European patent (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE).

(71) Applicant (for all designated States except US): SUN DS DE- FIBRATOR INDUSTRIES AKTIEBOLAG [SE/SE]; S-851 94 Sundsvall Published With international search report.

(72) Inventors; and Inventors/Applicants (for US only) SAFSTROM, Christer [SE/SE); Utkiksbacken 26, S-117 47 Stockholm (SE).

MIKAELSSON, Aron [SE/SE]: Korstabergsvigen 7, S- 856 34 Sundsvall LINDSTROM, Lars-Ake [SE/ 6 6 2 4 SE]; Skonertvigen 18, S-865 00 Aln6 OLOFSSON, Thomas [SE/SE]; R6dhakevagen 8, S-861 00 Timrf (SE).

(54)Title: MANUFACTURE OF BOARD (57) 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.

I i i C1 r V WO 93/25358 PCT/SE93/00388 Manufacture of board This invention relates to the manufacture of board of lignocellulose-containing material, such as fiber board.

Board of this kind is manufactured by disintegrating the material to particles containing fiber bundles and fibers. Glue is added to the disintegrated material and the material is dried and a web is formed which finally is pressed at increased temperature for curing the glue so that a board is formed. Fiber board is made of material which is disintegrated by defibering, i.e. of more or less free fibers.

The binding agent normally used is urea formaldehyde glue, which is admixed to the disintegrated material. The amount of glue can be 6% or more. The glue is relatively expensive, and it is therefore desired to minimize the glue addition. A smaller amount of glue, however, deteriorates the strength of the completed board. In view thereof, the glue addition must be optimized.

At the drying or the glued material, a great or small amount of water soluble formaldehyde is given off from the glue.

After the separation of the drying gas from the fiber material, for example in a cyclone, the liquid content is condensed out of tb gas. In conventional cleaning processes the water soluble formaldehyde then causes problems. The formaldehyde following along with the material to the final pressing also can cause problems when it is successively given off from the completed board. When glue is added to the material after its drying, the problem with formaldehyde separation arises at the pressing as well as from the completed board.

Fiber board manufactured according to the dry method normally is called MDF (Medium Density Fiberboard) and is a board product made of wood fiber. The yield exceeds 95%. The starting material preferably is wood chips, which are defibered with relatively low energy input, 100-500 kWh/ton fibers, for freeing the fibers. The defibered fiber material is glued, dried, formed to a web and pressed in a hot press. Alternatively, the material can be dried prior to the gluing. The material normally is preheated prior to the defibering to above 150 0 C whereafter the defibering is carried out under pressure at this high temperature

F

WO 93/25358 PCT/SE93/00388 2 in order to facilitate the freeing of the fibers. At such a high temperature, however, the material can be degradated and miscoloured due to occurring hydrolysis. A short heating time reduces this shortcoming, but miscolouring yet cannot be avoided, and at the same time the energy consumption increases.

The urea formaldehyde glue normally used can be mixed with the fiber material on the conveying line (blow line) from the defibering apparatus or in a separate mixing device. The amount of admixed glue can be 6% or more.

When the fiber material subsequently is dried in a tube drier by means of gas at high temperature, a great or small Samount of water soluble formaldehyde is given off from the glue.

As stated above, the formaldehyde following along with the fiber material to the final pressing also can cause problems when it is Sgiven off successively from the completed board. This applies especially to gluing after the drying of the material, which can be carried out at the manufacture of fiber board.

The aforesaid problems can be reduced by the present invention, which simultaneously offers further advantages.

According to the invention, the fiber material is treated with an impregnation liquid containing fiber surface activating chemicals and preheated before it is finally disintegrated.

Examples of such chemicals are such which affect the lignin, such as Na 2

SO

3 and NaHSO 3 These chemicals can be added in an amount of 1-30 kg/ton material expressed as Na 2

SO

3 According to the invention, it is possible to increase the ISO-brightness of the completed product, to reduce the energy consumption at the i defibering, to reduce the glue amount at maintained strength or to increase the strength at maintained glue amount. Furthermore, also the formaldehyde separation can be rieuced substantially.

The invention is described in greater detail in the following with reference to some embodiments thereof.

Fiberboard is manufactured by impregnating the raw material in the form of chips of, for exampla, softwood with lignin affecting chemicals, such as Na 2

SO

3 and NaHSO 3 in an amount of 1-30, preferably 10-20 kg/ton fiber material expressed as Na 2

SO

3 I_ a WO 93/25358 PCT/SE93/00388 3 The impregnation, which has to be carried out rapidly, can last some minute. Thereafter the temperature is increased to 150-20 0 C, preferably 160-180 0 C, for 2-3 minutes. However, the preheating can of course be performed prior to or at the same time as the impregnation. The pH value is kept within 2-12. This j implies, that an impregnation solution with Na 2

SO

3 and NaHSO, will contain sulphite in the form of HS0 3 and/or SO32. The pH value suitably can be controlled by NaOH. Due to this chemical treatment (sulphonation), the subsequent defibering can be carried out to the desired defibering degree with an energy input lower than normal. The energy consumption is in the interval 400 kWh/ton fiber material. The energy saving can amount to about compared with conventional defibering.

Owing to the impregnation, also the brightness of the completed fiber board increases.

As regards the fiber disintegration in the defibered material, it was found tha- both the fine material content and the shives content were reduced, i.e. the proportion of prima fiber has increased.

It was also found at the impregnation according to the invention that the strength properties of the completed board have improved substantially. The tensile strength as well as the elasticity modules and the fiber bond have increased by at least Alternatively, this effect can be utilized for reducing the amount of glue addition at maintained strength properties. A increase in the fiber bond corresponds to a 1% decrease in glue addition. The sulphonation according to the invention also implies, that the separation of formaldehyde can be reduced, due to the fact, that the sulphite ions in the impregnation solution react with the formaldehyde so that it is bound in the fiber material instead of being given off from the completed board.

a) I d WO 93/25358 PCT/SE93/00388 4

EXAMPLE

Raw material in the form of chips was exposed to different impregnation treatment. One batch was treated with kg Na 2

SO

3 per ton chips, and one batch with 10 kg NaHSO 3 per ton chips. A reference batch was not impregnated.

The different batches were preheated to about 170 0 C and thereafter defibered. In the blow line after the defibering, urea formaldehyde glue of the type E2 was added in an amount of dry glue calculated on dry fiber. The material was thereafter dried to a dry matter content of about 90%. The fibers were dry formed to a mat, which was prepressed with a pressure of about MPa and hot pressed for 5-6 minutes at 170 0 C. The board thus manufactured was tested on strength, ISO-brightness and formaldehyde content (perforator value). The relative energy consumption for the different batches was also measured. The results were as follows: Property Reference Na 2

SO

3 NaHSO 3 batch batch batch Bending strength MPa 38.4 43.8 40.0 Internal bond strength MPa 1.8 2.1 ISO-brightness 24 26 26 Formaldehyde content mg CH 2 O/100 g 27 20 18 Relative energy consumption 1.0 0.95 0.95 The results confirm the technical effects stated above.

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

Claims (2)

1. A method of manufacturing fiberboard according to the dry method starting with lignocellulose-containing material which is disintegrated, glued, dried, formed to a web and pressed, c h a r a c t e r i z e d in that the material, before it is finally disintegrated is treated with an impregnation solution containing fiber surface activating chemicals in an amount of 1-30 kg/ton fiber material, expressed as Na 2 SO 3 and preheated to

150-200 0 C whereby the pH value is kept within 2-12 and that the disintegration is performed with an energy input of 50-400 kWh/ton fiber material. 2. A method as defined in claim 1, c h a r a c t e r i z e d in that the fiber surface activating chemicals are of a type affecting the lignin. 3. A method a- defined in claim 2, c h a r a c t e r i z e d in that the impregnation solution contains Na 2 SO 3 and/or NaHSO 3 4. A method as defined in anyone of claims 1-3, c h a r a c t e r i z ed in that the disintegrated material first is glued and thereafter dried before it is formed to a web. A method as defined in anyone of claims 1-3, c h a r a c t e r i z e d in that the disintegrated material first is dried and thereafter glued before it is formed to a web. 4, 1 INTERNATIONAL SEARCH REPORT International application No. PCT/SE 93/00388 A. CLASSIFICATION OF SUBJECT MATTER IPC5: B27N 1/00 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) B27N Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched SE,DK,FI,NO classes as above Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) PAPERCHEM. CLAIMS/U.S. PATENTS, DERWENT WORLD PATENTS INDEX C. DOCUMENTS CONSIDERED TO BE RELEVANT I Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A DD, A, 205382 (PECINA HEINZ ET AL), 1 28 December 1983 (28.12.83) A DD, Al, 242193 (TECHNISCHE IUNT'ERSITAT DRESDEN), 1 21 January 1987 (21.01.87) E Further documents are listed in the continuation of Box C. See patent family annex. Special categories of cited dcuments T' later document published after the international filing date or priority date and not in conflict with the application but cited to understand document defining the general state of the art which is not considered the principle or theory underiyiu the invention to be of particular relevance crlier document but published on or after the international filing date document of particular relevance: the claimed invention cannot be considered novel or cannot be considered to involve an inventive document which may throw doubts on priority claim(s) or which is step when the document is taken alone cited to establish the publication date of another citation or other special reason (as specified) document of partielar rele'vance: the claimed invention cannot ie "0 document referring to an oral disclosure, use, exhibition or other considered to involve an inventive step when the document is means combined with one or more other such documents, such combination document published prior to the international filing date but later than being obvious to a person skilled in the art the priority date claimed document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report 14 -0s- 1993 Sept 1993 Name and mailing address of the ISA/ Authorized officer Swedish Patent Office Box 5055, S-102 42 STOCKHOLM l0of Jensdn Facsimile No. 46 8 666 02 86 Telephone No. 46 8 782 25 00 Form PCT/ISA/210 (second sheet) (July 1992) U J M~ERNATIONAL SEARCH REPORT Information on patent family members