Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Patent
1995-06-29
1997-10-28
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
528129, 528141, 528147, 528163, 528164, 524401, C08G 804
Patent
active
056819161
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/DE93/01236 filed Dec. 20, 1993, publisheed as WO94/15982 Jul. 21, 1994.
Phenolic resins have been used for a long time in the wood materials industry for producing relatively weather-resistant particleboard (V-100 quality, DIN 68763). Said resins are aqueous, alkaline-curing phenol-formaldehyde condensates produced by reacting phenol and formaldehyde in the presence of alkalis at a mole ratio of phenol to formaldehyde of 1:1.5 to 3.5, preferably 1:2 to 2.7. The quality of the products is primarily determined by solids content, viscosity, and alkali content.
The higher the molarity of said resins, the better the bonding strength and the shorter the curing time and, consequently, the shorter the pressing time required for making the particleboard. With predetermined solids and alkali contents, the size of the molecules or the degree of condensation is strongly dependent on the viscosity of the resin solution which, however, can only be increased to a limited extent due to the production techniques employed.
To lower the hygroscopicity of phenolic resin-bound particleboard and to prevent decay under the influence of moisture, efforts have been intensified in recent years to lower the alkali content in particleboard by lowering the alkali content in the resins. For instance, it has become customary in the manufacture of particleboard to replace high-alkaline, 45 to 48% phenolic resins containing about 10 to 12% sodium hydroxide by lower-alkaline resins containing 5 to 8% NaOH. However, said resins naturally have lower degrees of condensation and poor bonding strengths due to a high degree of penetration into the wood fiber, and they are less reactive whereby longer pressing times are required.
The phenolic resins described in DE-PS 29 44 178 have a degree of condensation which is maintained at the same high level as that of high-alkaline bonding agents by lowering the solids content with water to 30 to 41% without changing the viscosity. However, as a result of their low solids content, said resins influence the water balance in the particleboard. It is necessary either to dry the particles to a higher degree than usually required, or to extend the pressing times in order that the water evaporates from the particleboard. Therefore, said resins are only useful, if at all, in the outer layers of particleboard.
According to European Patent Application EP 84 115 270.5, high condensation degrees of phenolic resins are achieved by adding to phenol-formaldehyde resins having viscosities of from >300 to 20,000 mPa.multidot.s at 20.degree. C., preferably up to 10,000 mPa.multidot.s, 2 to 30 wt. % urea, referring to the phenolic resin solution, prior to or after cooling, whereby the viscosity is reduced to a processing viscosity of max. 1,000 mPa.multidot.s. With respect to the solids and alkali contents, the reaction of the phenol-formaldehyde resins is controlled such that the solids content of the urea-modified resins is in the range of from 30 to 65% and the alkali content is from 2 to 12 wt. % alkali (as NaOH).
Phenolic resins produced in conformity with EP 84 115 270.5 which have an alkali content of from 2 to 6% and are useful as binders for outer-layer particles have acquired great economic importance in the manufacture of particleboard because they are outstanding by their high bonding strengths and the absence of formaldehyde and, furthermore, by their more reasonable price in comparison with conventional, unmodified outer-layer phenolic resins.
Said resins in accordance with EP 84 115 270.5 which have alkali contents of 2 to 6 wt. % are unsuitable as bonding agents for center-layer particles because their alkalinity is not high enough to ensure rapid curing with the customary short pressing times and the temperatures of as low as 100 to 110.degree. C. occurring in the center layers of particleboard during pressing.
The modified phenolic resins containing 6 to 12% alkali which can be produced by the process described in European patent EP 84 115 270.5 do have a higher degree
REFERENCES:
patent: 3903041 (1975-09-01), Bornstein
patent: 4048125 (1977-09-01), Ingram, II
patent: 4433120 (1984-02-01), Chiu
patent: 5011886 (1991-04-01), Buschfeld et al.
Buschfeld Adolf
Gramse Manfred
Krezmin Hans-Jurgen
Lattekamp Matthias
Acquah Samuel A.
Mossman David L.
RWE-DEA Aktiengesellschaft fur Mineraloel und Chemie
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