DD139946A3 - METHOD FOR THE PRODUCTION OF UREA FORMALDEHYDE RESIN PAPERS WITH IMPROVED COLD ADHESIVE FORCED FOR SPATCHPLANT PRODUCTION - Google Patents

Description

The invention relates to a process for the preparation of urea-formaldehyde resin glue with improved KaItklebekraft for chipboard production by condensation of urea and formaldehyde at temperatures above 100 ⁰ C.

Urea-formaldehyde resin glues are widely used as binders in the chipboard industry. In conventional manufacturing processes, the chips are provided with resin solution, formed into a chip web and cold pre-pressed. This happens on a supporting pad, z-.B. a press plate. The pre-pressed chipboard blanks are transported to hot pressing and pressed hot on the press plates. Only after the pressing process, the Preßbleche be separated from the finished chipboard. However, before they can be reused, they must be cooled before forming new blanks. This constant extreme temperature change leads to high wear on press plates and also requires a high energy consumption, of which a large part is lost unused. To avoid these high losses, new technologies have been developed - the so-called tape, tape tray or trayless processes. These require glues, in addition to the previously required properties additionally have a high cold tack.

In these new processes, the chipboard blank after forming and cold pre-pressing is removed from the supporting

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Position by rolling or pushing separated and hot pressed in most cases without supporting pad. This procedure requires a high strength of the chipboard blank so that it does not break or deform in this process, which are synonymous with production losses.

It is known to prepare urea-formaldehyde resin glues which are used for particle board production by continuous or discontinuous condensation of urea and formaldehyde in a molar ratio of 1: 1.8 to 1: 2.2 in two stages. In the first stage, temperatures above 100 C are used. The residence time is 10 to 60 minutes. After addition of urea and sodium hydroxide solution is further -kondensiert at temperatures of 40 to 80 ⁰ C ^ and optionally concentrated (DD-PS 88 196).

With these commercial H-F glues the required "high strength of the pre-pressed chipboard blank, as required in particle board plants, which work without supporting documents, not achieved. An increase in the pressure during cold pre-pressing and an increase in the amount of glue in an economically justifiable measure also do not lead to satisfactory results. It has therefore already been tried to achieve better strengths by adding to usual chipboard glues.

Sb is. It is known to improve the cold tack of urea-formaldehyde resin, malamine-formaldehyde condensates and phenol-formaldehyde condensates by adding sulfite liquors to the finished sizes - these are lignosulfonic acid calcium solutions obtained by the sulfite pulping process by the caustic digestion process v / earth, in amounts of up to 10 % solids, based on liquid glue resin, with a concentration of 45 to 70 %, to add, the sulfite liquor can d.abei be used in liquid or powdered form (DT-OS 2,354,928 ). The disadvantage here is that a

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additional process stage for incorporation of the additive is necessary and an additional energy and equipment costs is required.

It is also known, commercial wood glues before processing to V / erkstücke or to be glued workpieces with additives. These additives are solutions of polybasic and / or olefinically unsaturated carboxylic acids in a water-miscible mono- or polyacidic Arain · Der.pH value of these solutions is 6.5 to (DT-OS 2 351 981).

The disadvantage here is that in addition to the additional energy - and equipment costs for the subsequent incorporation of the additives and the properties of the glues are affected · For this reason, it is also proposed in the DT-OS to mix the additives immediately before processing the glues.

It was therefore an object to develop a urea-formaldehyde Harzleira with high Kaitütebekraft that gives cold pre-compressed chipboard blanks such a high strength that they can be transported without breakage or deformation when working without backing in the chipboard press.

This object is achieved by condensing urea and commercial formaldehyde in a molar ratio of 1 to 1.8 to 1 to 2.2 at elevated pressures and temperatures above 100 ° C continuously or discontinuously, alkali and urea to a final molar ratio of 1 to 1.3 to 1.8, further condensed and optionally concentrated simultaneously in the neutral or weakly alkaline range.

According to the invention, the condensation is carried out at temperatures of 100 to 140 ⁰ G in the presence of 0.5 to 5 % organic or inorganic acids, in particular formic acid, based on the amount of urine used, in a time of 10 minutes.

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The concentration of acids used can be between 2 and 15 % .

Surprising here is that obtained by condensation at temperatures above 100 C with the simultaneous addition of acidic urea-formaldehyde resin glues, with which cold pre-pressed chipboard blanks can be prepared,

which have sufficient strength in said particle board plants.

It is of particular advantage that, when using the new chipboard glue in these chipboard plants, the glue content, based on the Spanmasse, depending on the respective technological conditions (wood, Spanfeuchten, etc.) can be reduced up to 5%. Another essential advantage is that when using the chipboard glue according to the invention caused by mechanical disturbances downtime in the chipboard production line bring no production and material losses more. When using the previously used chipboard glues lose the cold pre-pressed chipboard blanks at downtime due to the loss of moisture so much in strength that they can be transported in any case in the hot press, but must be discarded. By contrast, the strength of the chipboard blank is retained by the use of the chipboard glue according to the invention, and the chipboard production line can be put back into operation without delay.

In addition to the increased cold tack, these resins have good reactivity, storage stability and water compatibility. ·

The strength of the cold pre-pressed chipboard is determined by pouring glued chips to a chip mat of 750 χ 300 mm and then cold pressed. The pressed chipboard is placed on 2 supports at a distance of 650 mm and the time between laying and breaking of the chipboard is measured. The measured time is directly proportional to the cold tack force.

Breaking time in sec,

conventional resin 72

Inventive Resin According to Example 1 394 Inventive Resin According to Example 2 515

example 1

Into a reaction vessel equipped with staged control and stirrer was added a urea-formalin solution containing, on 959 parts by weight of solution, 700 parts by weight of 37% neutralized formaldehyde and 259 parts by weight of urea at a rate of 100 Parts by weight / h. At the same time, 0.25 parts by weight of 10% formic acid were continuously added to the mixing vessel. At a temperature of 128 ⁰ C under these conditions, the reaction mixture had a viscosity of 48 cP, measured at 20 ⁰ C. In the course of one hour, 100 parts by weight of this condensate were fed into a second reaction vessel, the 16.2 wt. Parts / h of a 55% aqueous urea solution and 0.35 parts by weight / h of a 10% sodium hydroxide solution were added. In this second reaction vessel, which was equipped with ÜmwäIzvorrichtung, was at a temperature of 40 to 80 ⁰ C under reduced pressure on. condensed and simultaneously concentrated to a solids content of 67%. The continuously discharged urea-formaldehyde glue with a viscosity of 970 cP / 20 ⁰ C had a high cold tack, was storage stable and particularly suitable for the production of chipboard without press plates suitable.

Example 2

In a heating and cooling-cooled reaction vessel equipped with stirrer and temperature gauge, 600 parts by weight of neutralized 37% formaldehyde were added.

sets. In it, 207 parts by weight of urea were dissolved. The resulting urea-formaldehyde solution was heated at 70 ⁰ C for 30 minutes, then 1.3 parts by weight of a 1 molar hydrochloric acid were added and at 12.1 ⁰ C so condensed until a viscosity of 50 cps / 20 ⁰ C was reached has been. After addition of 3.5 parts by weight of 2.5 molar sodium hydroxide solution was cooled to 80 ⁰ C, added 72 parts by weight of urea and further condensed for 30 minutes at this temperature. After concentration at 50 ⁰ C and 300 Torr, a urea-formaldehyde wood glue having a viscosity of 1020 cP / 20 ⁰ C and a solid resin content of 68% was obtained.

Claims (1)

invention claim A process for preparing urea-formaldehyde resin sizing having improved cold tack for chipboard production by continuous or discontinuous condensation of urea and formaldehyde in a molar ratio of 1 to 1.8 to 1 to 2.2 at elevated pressures and temperatures above 100 oc, addition of Alkali and urea to a final molar ratio of 1 to 1.3 to 1.8 »and further condensation and optionally simultaneous concentration in the neutral or weakly alkaline range, characterized in that the condensation at temperatures of 100 to 140 ⁰ C in the presence of 0, 5 to 5 % of organic or inorganic acids, in particular formic acid, based on the amount of urea used, in a time of 10 to 100 minutes is performed.