DE1653266C - Process for the production of wood-based materials with high resistance to hot water - Google Patents

Description

It is known the hot water resistance of wood-based materials made with phenolic resins as binders by adding carbonates of the elements of the first three main groups of the periodic table to improve.

Because this resistance to hot water is the result of the transverse strength after boiling in water for 2 hours is often viewed as a measure of the weather resistance of the panels or moldings there is great interest in the production of wood-based materials with even higher hot water resistance, this for reasons of economy after the shortest possible pressing time, accordingly a low compression factor should be achieved.

The object on which the invention is based is therefore to develop a method with whose help it is possible to produce wood-based materials with increased transverse tensile strengths and lower swelling values to be produced in cold water in an even shorter pressing time. In addition, the hardener should crystallize out and the blooming of the alkali salts can be prevented as far as possible.

The invention now relates to a process for the production of wood-based materials with high hot water resistance by gluing wood flour, wood chips, wood veneers or wood papers with alkali-condensed phenol-aldehyde resins with an aldehyde-phenol ratio of at least 1.6: 1, one Viscosity at a solids content of 48 ° / ₀ of over 200 cP, measured in the Höppler viscometer at 20 ⁰ C, an alkali content of 0.05 to 2 mol per mole of phenol and a content of free phenol of less than 6 ° / ₀ , which is characterized in that 0.01 to 1 mol of alkylene carbonate per mol of phenol is added to the phenolic resins before or during the gluing. Propylene carbonate is preferably used.

If the aldehyde-phenol molar ratio of the phenolic resin is less than 1.6: 1, no satisfactory physical-technical properties are obtained Wood-based materials, because the hardening speed is too slow.

A sufficiently high degree of condensation of the phenolic resins is also essential for the properties. At a solids content of 48 ° ^; _O to the phenolic resin solution having a viscosity of at least 20OcP, corresponding to 50 seconds, measured in a 4 mm DIN cup at 20 ^c C.

Larger amounts of free phenol and formaldehyde in the phenolic resin solution are not beneficial. The free phenol content to below 6 ° / _0, as far as possible below 1 ^{0 /} _0th lie.

Particularly advantageous when processing phenolic short binders it is when the alkylene carbonates are only mixed in shortly before gluing or in the form their solutions separated from the binder on the wood.

the pieces of wood or wood chips are sprayed on. This avoids the use of binders Phenolic resin solutions through the addition of alkylene carbonates already age too much during the time up to their processing. In addition, the addition of the

so carbonate just before processing also the great advantage that you have the middle and top layers, z. B. in the manufacture of chipboard panels, Mix in different amounts of hardness and thereby the different hardening times of the individual layers can compensate.

The advantages of adding alkylene carbonates as hardeners to phenolic resins over adding Are carbonates of the elements of the first three groups of the periodic table

1. Shorter gel times, thereby faster hardening and shorter pressing times of the wood-based materials.

2. Increased flexural strength of wood-based materials.

3. Increased transverse tensile strength of the wood-based materials, especially after 2 hours of cooking.

4. The hardener does not crystallize out.

5. Reduced blooming of alkali salts.

6. Good miscibility of the hardener with the phenolic resins.

example 1

94.1 g of phenol (1 mol), 234.6 ml of a 30% formalin solution (2.55 mol CH ₂ O) and 28.9 ml of a 33% sodium hydroxide solution (0.325 mol NaOH) are mixed in a glass flask with stirring and heated within 40 minutes to 90 ⁰ C, then another 28.9 ml of 33 ° / _o aqueous sodium hydroxide solution are added. It is left to 60 minutes at 90 ⁰ C react distilled 70 ml of water and condenses to a viscosity of 60 seconds as measured in a 4 mm DIN cup at 2O ⁰ C. Subsequently, the 48 ° / ₀ resin solution in divided several samples and mixed with the hardeners listed in the table.

Chipboard panels are produced with these phenolic resin solutions. For this purpose, wood chips are dried to a moisture content of 6 ° / _B and sprayed with 9 parts by weight of phenolic resin per 100 parts by weight of wood in a mixer. The glued wood chips are then scattered to form chipboards and pressed in a hydraulic press at a temperature of 165 ° C. and a pressure of 20 kp / cm ² to form chipboard panels with a density of 0.7.
The chipboard panels obtained have the properties listed in the table.

It is clear from this that the propylene carbonate has a shorter gel time compared to the potassium carbonate and thus a shorter hardening or pressing time

works. The phenolic resin-bonded ones hardened with propylene carbonate Chipboard panels are also characterized by particularly high flexural and transverse tensile strengths, Above all, however, through significantly improved transverse tensile strengths after cooking, such as the values of the Table 1 show.

Table i

Addition of hardener to 100 g phenolic resin solution in g

Without
Hardener additive

4 g of 50% K ₂ CO ₃ solution

4 g 50 "/" ige

Propylene carbonate

solution

Solid in% (L g / 2 h / 120 ° C)

Viscosity in 4 mm DIN cup at 20 ^; C.

Weight at 20 ° C

Gel time at 100 ° C

Hardening time at! 10 ° C

Hardening time at 130 ⁰ C

P "temperature in ⁰ C

P iactor in min./mm

Weight about

Flexural strength in kp / cm ²

Transverse tensile strength in kp / cm ²

Transverse tensile strength in kp / cm ² according to V 100 about 48
63 seconds

1.22

27.3 minutes
106 seconds
45 seconds
165 °
0.4
0.70
219
4.6
1.5

about 48
58 seconds
1.25

17.3 minutes 93 seconds
42 seconds
165 °
0.4
0.69
316
7.4
2.1

about 48

117 seconds

1.23

8.1 minutes 78 seconds 35 seconds 165 °

0.4

0.69 347

8.9

3.1

Example 2

In a suitable heated and coolable stirred autoclave in the. Radiator template and the inlets are eiforderlichen 941 g (ent: prechend 10 moles) of phenol, 2550 g of 30 ° / _o sodium Formdin (containing 25.5 mole of formaldehyde) and 578 ml of 33% sodium hydroxide solution (containing 6.5 mol of sodium hydroxide) at 20 mixed together up to 25 ° C. This mixture is then heated 20 minutes at 35 to 40 ⁰ C, held under cooling for 40 minutes at 40 to 50 ° C and heated in 20 minutes to 90 ⁰ C. A further 578 ml of the 33% strength sodium hydroxide solution are then allowed to run in and the mixture is allowed to react at 90 ° C. for 20 minutes. Then enough water or volatile constituents are distilled off in vacuo that the solids content is 48 ± 1 ° / ₀ . The solution is then post-condensed at 70 ° C. until a viscosity of 600 cP is reached.

The resulting chipboard binder has the following properties:

Solid content in percent by weight (determined with 1 g,

2 hours at 120 ^° C) 48 ± 1%

Viscosity at 20 ⁰ C (Höpplei). 600 cP
Hardening time at 110 ° C, measured
on 1 g of resin solution
Stir in the well of a
Durotest plate up to the Resit

formation 58 seconds

Gel time of the mixture

100 ⁰ C 28 minutes.

2 percent by weight of ethylene carbonate and 2 percent by weight of water are then added to the binder obtained in this way. The measured at 100 ⁰ C gel time of the resin composition lowers thereby to 7 minutes. The considerable reduction in gel time from 28 to about 7 minutes corresponds to a strong acceleration of the hardening process, which is also expressed in an improvement in the physical-technical data of the sheets pressed from the resin.

For the preparation of particle board 104 parts by weight of ethylene carbonate mixed with binder with 20 parts by weight with a 40 ° / ₀ sodium liquor is obtained with a viscosity of 65 cps are mixed water. Beech wood chips are also dried to a residual moisture content of 2 to 4 percent by weight and then glued uniformly in a drum with 25 parts by weight of the 40% liquor, corresponding to a gluing factor of 10%, based on dry chips.

The chips glued in this way are then grounded in a laboratory press at 165 ° C. with a pressure of 20 kp / cm ² with press factors of 0.3 and 0.5 minutes per mm to form 8 mm thick chipboard panels with a density of 0.75 g per millimeter cm ³ and checked for their physical-technical properties after one day.

The results are summarized in the following table:

Table 2

Chip moisture 2 to 4 ° / ₀

Gluing factor 10%

Plate thickness 8 mm

Plate density. 0.75 g per cm ³

Pressing temperature 165 ° C

Pressing pressure 20 kg / cm ²

Press factor in minutes

per mm 0.3 0.5

Thickness swelling in% after
2 hours when tested in accordance with DIN draft 52 364

November 1961 13.6 10.5

Flexural strength in kp per

cm ² according to the DIN draft

52 362 from November 1961 289 344

Transverse tensile strength in kp per

cm ² according to the DIN draft

52 365 of November 1962 7.6 9.2

Transverse tensile strength in kp / cm ⁴

according to V100 2.2 3.2

Claims (2)

1 553 266 claims: 1. Process for the production of wood-based materials with high hot water resistance by gluing wood flour, wood chips, wood veneers or wood papers with alkaline condensed phenol-aldehyde resins with an aldehyde-phenol-Mo! Ratio of at least 1.6: 1, a viscosity for a solid content of 48 ⁰ Z ₀ of over 200 cP, measured in the Höppler viscometer at 20 ° C, an alkali hydroxide content of 0.05 to 2 mol per mol of phenol and a content of free phenol of less than 6 ° / ₀ , characterized in that, that 0.01 to 1 mole of alkylene carbonate per mole of phenol is added to the Phenolhai zen before or during the gluing. 2. The method according to claim 1, characterized in that the alkylene carbonate is propylene carbonate is added.