DE2553459A1 - PROCESS FOR MANUFACTURING WOOD-BASED MATERIALS - Google Patents

Description

As a glue for the production of chipboard and chipboard materials one uses predominantly urea-formaldehyde resins, also melamine-formaldehyde resins, mixtures of urea and Melamine resins, mixed condensates of urea, melamine and formaldehyde or phenolic resins »All these binders can release formaldehyde during processing, so that in factories, the maximum permissible workplace concentration, especially in the vicinity of the hot presses and in the storage rooms for freshly manufactured products (MAK) of formaldehyde is exceeded.

In the processed state, the chipboard materials can also last for many months in closed rooms, in unfavorable cases even for several years release such amounts of formaldehyde that it is unreasonable to live in such rooms or to stay in them for longer to stop.

About the formaldehyde enrichment of the room air during processing of amino resins and the subsequent elimination of formaldehyde There are many publications available from wood-based materials produced with such resins. Reference is made to Petersen, Reuther, Eisele and Wittmann: "On the elimination of formaldehyde in chipboard production with urea-formaldehyde binders", Wood as raw and material, Vol. 30 (1972), Vol. 31 (1973), Vol. (1974), with further references to literature.

To address the problem of formaldehyde elimination, especially with urea resins Resins with a lower formaldehyde content have been developed to counter this. With these low-formaldehyde resins, their molar ratio Urine f / formaldehyde | is around 1: 1.4, the formaldehyde problem could reduced but not resolved. In addition, 326/75

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these resins have poorer adhesive properties than formaldehyde-rich glues. According to current knowledge, it is not possible to use resins with useful adhesive properties below the stated molar ratio to manufacture.

Another way to combat formaldehyde release, is the addition of formaldehyde-binding substances. Urea is not only the cheapest, but also the most effective of these Middle. Other formaldehyde binders include melamine, protein-rich flours and phenol. All formaldehyde-binding additives to the glue liquor and / or the chips have undesirable side effects: For example, they delay further condensation and thus the Hardening of the glue. The quality of the finished chipboard material can also be noticeable due to the formaldehyde-binding additives be worsened. The chipboards produced in this way release very little formaldehyde, their transverse tensile strength and swelling and the water absorption also reach values which severely limit the possible uses of the chipboard. Therefore could the method to which the chips or a part thereof / e.g. Urea, to raise, not to enforce. Such a method in which finely divided wood components are used as a carrier for the urea are used, is described in DT-OS 1 65Ü5 1Ö7.

It has now been found that wood-based materials with reduced elimination of formaldehyde can be obtained by pressing with formaldehyde resins which can be hardened wood components provided as glue, with free or released formaldehyde binding formaldehyde Means are added and pressed with, is obtained, the aforementioned disadvantages not occurring, and that one is also rich in formaldehyde Glues to produce "low-formaldehyde" wood-based materials can, if the wood components before, during or after gluing with cellulose fibers, e.g. wood or paper cellulose fibers, mixes that have been treated with formaldehyde-binding agents and optionally dried.

The formaldehyde-binding agents, e.g. urea, are expediently dissolved in water; in order to bring as much of it as possible into solution,

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this can be heated to 50 to 7O ^{0 C.} The possibly warm to hot solution (a content of up to 60 $ can be achieved with urea) is mixed with the cellulose fiber in suitable machines. For example, 10 to 100, preferably 50 to 100 $ urea, based on the fiber weight, can be applied to the fibers. The loaded pulp is dried back to the normal chip moisture content. The formaldehyde-binding substance is apparently fixed to the fibrils of the torn cellulose fibers by this process in such a way that it becomes sparingly soluble. The poor solubility is brought about to a particular extent by the use of delignified, low-hemicellulose or hemicellulose-free cellulose fibers which are difficult to wet with water and are difficult to swell. Fibers that arise as waste materials in the manufacture of paper, cardboard and cellulose are particularly suitable, even if they also contain other substances.

To explain the effectiveness of the method according to the invention one can imagine that the moisture, which is brought to the chips with the wood glue, is the urea at room temperature does not dissolve on the cellulose fibers Forms material cake, part of the urea fixed on the cellulose fibers is dissolved. This then binds large ones Amounts of formaldehyde released from the already largely hardened glue. The rest of the deposited on the cellulose fibers Urea becomes effective as a formaldehyde binder when the particle board binders are still used in the further course Formaldehyde is released.

To assess the effects of the present invention, the following is applicable to be sent in advance: The amount of formaldehyde escaping during pressing can be determined using the foil bag method described in the above-mentioned series of publications (Part I). According to this, it was found that with glues low in formaldehyde (molar ratio H: F = 1: 1.4) about 25 $ attached to cellulose fibers

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Urea, based on the amount of glue introduced, is sufficient to to reduce the amount of formaldehyde released to a quarter of the original value. When using formaldehyde-rich Glues (molar ratio up to 1: 1.8) require up to a third of urea, based on the amount of resin, in order to split off formaldehyde to push back in the same way.

Other formaldehyde-binding substances, such as melamine or phenol, are less effective than urea, but the above occurs Success with the help of the invention is in principle also a »

The formaldehyde-binding agents attached to cellulose fibers also remain effective in the finished and processed chipboard. So you can, for example, with the so-called FESYP perforator method on chipboard, which were produced with urea attached to cellulose fibers, a subsequent elimination of formaldehyde measure less than $ 0.01. (FESYP = Federation Europeenne des

of the manufacturer

Syndicats / des Panneaux de Particules) The determination of formaldehyde in wood-based material according to the FESYP perforator method is e.g. in a draft of the British Standards Institution dated December 2, 1971 (BS 1811). Then small cuboids are sawn to size from the air-dry material and each extracted to several in a liquid extractor (Soxhlet extractor) with toluene, and the loaded toluene in turn with Water washed. The water is then iodometric for formaldehyde examined.

The procedure described here has two advantages: Once delayed the poor wettability of the fibers the moisture absorption of the chipboard. On the other hand, the cellulose fibers give the Formaldehyde-binding agents are only released when the moisture content of the chipboard increases to such an extent that high amounts of formaldehyde are also released namely, it is known that there is an immediate difference between the subsequent elimination of formaldehyde and the ambient moisture There is a connection »

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.C.

The process according to the invention was investigated using commercially available urea-formaldehyde resins and modified melamine-urea-formaldehyde resins, which release formaldehyde to a particular extent. These resins, insofar as they are urea resins, usually have a molar ratio of urea to formaldehyde of from 1: 1.4 to 1: 1.8. They are generally obtained by condensation of urea and formaldehyde in weakly acidic to weakly alkaline solution and are usually in the form of 50 to 72 strength aqueous solutions or as water-soluble powders. Depending on the process, they are generally processed in a liquor concentration of 35 to 60fo (all data are percentages by weight).

It follows from what has been said above that the beneficial effect of the invention also applies to other resins which release formaldehyde can occur, as it is only the interaction of free formaldehyde and formaldehyde-binding agents that matters.

Examples

Comparative studies on the effectiveness of the invention Additives were made with four different, commercially available-urea-formaldehyde glue resins and employed a melamine-urea-formaldehyde glue resin.

The essential properties of these resins are as follows Overview shown:

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Table 1 I. II III IV 1 65.0 ^ + 1 V Resin no. 1: 1.4 1: 1.55 1: 1.65 1: 1.8 750-1000
mPa »s - Molar ratio
Urea: form
aldehyde - - - 1.29 : 1.8: 5.5 Melamine: urea
formaldehyde 66.5 ^ + 1 66.5 ^ + 1 72.0 ^ + 1 g / cm- ⁵ 63.0 ^ + 1 Dry content 400-600
mPa's 750-1000
mPa »s 2500-5OOO
mPa * s 3 h 45Ο-6ΟΟ
mPa »s Viscosity at
20 ° C 1.29 1.29 1.30 24 sec. 1.27 Density at 20 ° C g / cnr ⁵ g / cm- ⁵ g / cnr ⁵ 6 mo
nate g / cm ^ 19 h 10V2 h 13 h 12 h Gel time at $ 10
a $ 15 Anmionium
chloride solution
at 20 ^° C 35 sec. 35 sec. 35 sec. 40 sec. 100 ⁰ C 2 mo
nate 3 mo
nate 2 mo
nate 1 month Storage time at 20 ^° C

The glue resins described above were mixed with the usual Auxiliary materials according to those contained in Table .2 below Mixing ratios processed to glue liquors.

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Table 2

Approach ABCDE

Glue resin I 100 - - - - Glue resin II - 100 - - - Glue resin III - - 100 - - Glue resin IV - - - 100 100 Glue resin V - - - - 7th Paraffin emulsion
50 $ 5 5 5.5 5 1 water 17.5 17th 27.5 13th 10 Ammonium chloride
Solution 15:85 10 10 10 10 1 Ammonia 25 $ ig 0.5 1 1 2

Total 133 133 144 130 119

Resin content $ 50 $ 50 $ 50 $ 52;

bed ^ lOO ⁰ ^ ⁷ ^ ^sec * ^{? 2f sec} ° ^{71 sec> 9} ^ ^{sparkling wine 58 sec #} resin on atro ^ ^^ § , $ 5 $ 8.5 $ 8.5 $ 12.0

Deligned cellulose fibers, such as those obtained from the defibrillation of wood and other woody plant parts in a defibrator for the manufacture of paper, cardboard and fibreboard, were mixed with urea from $ 16 to $ 100 of their own weight in such a way that 20 to 70 percent of their own weight were added ⁰ C hot solutions of urea in water with a concentration of 40 to 60% applied to the fibers in a mixing machine. These proportions could

^ In wet disc separators, in disc refiners, in the steam explosion process (Masonite process) Fibers obtained from and other similar processes are also suitable

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are also adhered to when using waste fibers to which other substances (e.g. fillers, adhesives, dyes) were attached.

The moisture content of the fibers mixed with urea solution was between 45 and 60 $ of their dry weight. In a drying process customary for wood chips, the moisture was reduced to below 6%. The fibrous material loaded with urea obtained in this way was mixed in the proportions given in Table 3 below with dried chips in a conventional mixer. At the same time or thereafter, chips and loaded fibers were glued with a binder mixture listed in Table 2. The glued mixture was then poured into a chip cake and pressed in a test press under pressure and heat to form a chipboard. For the individual experiments, the press data were varied in the areas of industrial chipboard production.
Press temperature: l40 - 220 ⁰ C

Press time: 0.14 - 0.40 min per millimeter of panel

raw thickness

Compaction pressure: 1.8 - 3 # 5 N / mm

Through heating pressure: 0.5 - 1.8 N / mm

The cooled chipboard was sanded to the same thickness and then subjected to the usual tests. In table 3 some test results are summarized in extracts.

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Table 3

σ co oo

1) 2))

Determination by the foil bag method "" "Fesyp perforator method

Leading Urea- Tempe Laden 1:20 Urea on glue Thickness (ge density Bend 0 Transverse pull _ _ - O.23 Swelling after % 8.5 water Formaldehyde- me ^ s yes approach MANUFACTURING rature Fibers 1:20 Shavings resin grinding) firm N / mnT consolidate - - O.29 2 h / 24 h 14.0 8.1 recording splitting after- ' jiach Conc ° C on 1: 7.4 speed 26.7 speed - _ 0.33 WATER LAUNCH I8.9 8.2 2 h at ¹ ^ bearable !Tab. 2 tration (Forget: Shavings 1:20 * 1. 24.3 V20 IVlOO - - 0.26 I8.9 Press 20th 1:20 % mm g / car 24.7 N / mm ² 0.64 - - O.821 '0.20 ft 21.3 % % 0.04 I.
A. 20th calibration) 1: 7.4 18.8 19.2 O.65I 22.2 0.66 O.47 0.46J - 1.01 0.24 4.9 16.6 15-7 O.54 0.02 A. 50 20th 1:20 1.6 28.2 19.2 0.664 25.7 O.67 0.61 - O.75 O.26 6.3 I8.I 19.I 0.21 <ro.oi ^; ! A. 50 60 1:20 2.4 47.O 19.2 O.661 24.7 O.54 O.36j - O.56! - O.8I 6.0 22.0 19.9 0.I8 0.01; A. 50 60 1: 7.4 4.0 18.8 19.1 0.645 19.9 0.46 O.51 O.51j -
t 7.0 15.5 22.6 O.17 <0.01 ' A. 60 60 1:20 1.6 28.2 19.2 0.648 30.9 0.44 0.55 j - 5.4 I6.2 17.9 0.19 cO.01 A. 60 (Verg] 1:20 2.4 47.O 19.3 0.640 26.4 0.63 0.50J - 6.0 13.5 19.6 0.17 <o.oi 1 A. 60 20th 1: 7.4 4.0 19.2 O.619 27.3 0.63 0.39 7.6 14.7 28.O O.16 0.09 I. ; B. (Forget: .eich) 29.4 19.2 O.671 26.8 0.59 O.89 5.0 l4.8 14.1 0.64 <"o.oi; B. 50 20th 15:85 2.5
¹ 20.0 O.652 26.7 O.92 6.3 17.3 23.5 O.16 0.09 C. 20th ! .eich) 18.8 19.I 0.650 24.6 0.95 4.9 15.I 15.7 0.97 0.02 C. 50 20th 1:20 1.6 28.2 19.2 0.666 26.5 4.9 14.0 16.4 0.35 0.01 50 60 1:20 2.4 47.O 19.2 O.659 28.1 4.7 14.9 16.3 0.22 <Ό.01 C. 50 60 1: 7.4 4.0 18.8 19.2 O.653 24.1 5.4 13.7 19.7 0.19 o.oi! C. 60 60 1:20 1.6 28.2 I9.2 0.664 32.1 4.7 15.6 15.7 0.31 0.02 i C. 60 (Forget: 1:20 2.4 47.O 19.2 0.664 27.7 4.7 22.7 15.2 0.20 <0.01 y C. 60 20th 1: 7.4 4.0 19.2 0.650 25.7 7.3 8.8 16.4 O.I8 0.16 j ,
> D 20th .eich) 29.4 I9.2 O.674 28.2 4.2 8.8 13.4 1.33 0.01 D. 50 15:85 2.5 29.4 j I9.8 O.65I 29.8 4.7 8.0 17.4 O.27 0.01 50 15:85 2.5 I9.6 O.66I 30.7 8.8 3.5 'j 8.7 30.1 0.35 0.09 E. (Comparison) 13.3 19.2 1 O.634 28.7 3.8 3.4 14.1 0.73 0.03 ■ E 50 20th 1.6 20.0 19.2 0.664 31.2 3.5 3.1 13.7 0.30 0.01 E. 50 20th 2.4 33-3 19.2 0.654 30.6 3.0 3.1 13.5 O.27 0.01 E. 50 20th 4.0 I3.3 19.2 y O.662 27.3 15.2 0.21 0.02 E j 60 60 1.6 20.0 19.1 0.654 13.7 0.30 · 0.01 E. 60 60 2.4 j 33.3 19.2 0.648 13.7 O.28 <0.01 E. 60 y 60 4.0 19.2 0.643 15.2 0.20

) yp

3) urea attached to chips (for comparison)

cn cn co

. *> cn co

Claims (3)

Claims 1J Process for the production of wood-based materials with reduced formaldehyde elimination by pressing wood components provided with curable formaldehyde resins as glue, wherein free or released formaldehyde-binding agents are added and pressed together for binding, characterized in that the wood components are added before, during or after gluing with cellulose fibers mixed that have been treated with formaldehyde-binding agents, 2. The method according to claim 1, characterized in that one uses 10 to 40 $ of the glue resin amount of formaldehyde-binding agents » 3. The method according to claim 1, characterized in that urea is used as the formaldehyde-binding agent. BASF Aktiengesellschaft 709825/0369 ORIGINAL INSPECTED