DD283502A7 - METHOD FOR PRODUCING PF GLUES - Google Patents

Abstract

The invention relates to the production of PF glues for weatherproof wood materials, especially for Sperrhoelzer made of softwood or softwood combinations. According to the invention, in a multi-stage process, PF glues are prepared such that, in a first technological step, the condensation of phenol, formaldehyde and alkali hydroxide in a molar ratio of 1: 1.5 to 2.0: 05 to 1.0 at a temperature of 355 to 363 K and a pressure of 61 to 101 kPa to a content of three and more nucleants of 10 to 20% is performed. After cooling PF condensate in a second technological step, the condensation by further addition of formaldehyde to a Gesamtmolverhaeltnis phenol: formaldehyde: alkali metal hydroxide of 1: 2.3 to * to 1.0 at a temperature of 360 to 368 K up to a Content of single and double core compounds of 55 to 70% continued. The PF glue is concentrated to a solids content of 48%, and then cooled to a temperature of 288 to 305 K. {glue; Phenol; Formaldehyde; alkali hydroxide; Multi-stage process; Molekuargewichtsverteilung; One- and two-core connections; tri- and higher-nuclear compounds; Woody materials; Plywood; Softwood; Softwood combinations; Heiszverpressen}

Description

Ziol of the invention is the cost-effective production of PF adhesives, which have improved Ksltklebefestigkeit and effect in processing as a binder for wood-based materials, in particular for plywood, technological improvements.

Explanation of the essence of the invention

The object of the invention is a technological process in the production of PF glues, which leads to a molecular weight distribution, which has both a sufficiently large proportion of relatively high molecular weight compounds, which prevents a knocking away of the PF glue from the glue joint, as well as a minimum proportion of low molecular weight One- and two-core compounds containing the cold tack strength of the PF glue ensures. These requirements are opposite in the known technologies for the production of PF glue and not simultaneously feasible. According to the invention, in a first technological step, the condensation of phenol: formaldehyde: alkali hydroxide with a molar ratio of 1: 1.5 to 2.0: 0.5 to 1.0 at a temperature of 355 to 363 K and at a pressure of 61 to 101 kPa to a content of trinuclear and higher nuclear compounds of 10 to 20% out. Thereafter, the PF condensate is cooled to a temperature of 348 to 353 K and in a second technological step, the condensation by further addition of formaldehyde, ie by continuous or stepwise addition of further subsets of formaldehyde to a total molar ratio of phenol: formaldehyde: alkali hydroxide of 1 : 2.3 to 3.0: 0.5 to 1.0 at a temperature of 360-368 K and a pressure of 50-81 kPa up to a content of input unc ¹ binuclear compounds of 55 to 70%, preferably 65%, continued and concentrated to a solids content> 48%. Subsequently, the cooling of the PF glue to a temperature of 288 to 305 K.

The process according to the invention for the production of PF glues in the first process step allows both the condensation of a presented mixture of phenol, formaldehyde and alkali hydroxide, and preferably the reaction of phenol and alkali metal hydroxide to alkali phenolate and subsequent addition of formaldehyde and condensation of this reaction mixture according to the indicated molar ratio of phenol : Formaldehyde: alkali hydroxide too. In the case of this named procedure, in the first technological step, the limited excess of formaldehyde can not form a higher proportion of trinuclear and higher-nuclear compounds.

In the second technological step, a temperature of 368K is not exceeded by the reaction cooling controlled addition of the remaining amount of formaldehyde and additional cooling of the reaction process. As a result, the structure of the low molecular weight single and binuclear compounds is preferred.

By means of high performance liquid chromatography (HPLC) PF-glues produced according to the invention were compared with conventional PF-glues. The clearly different results of the tests are shown in Table 1.

Table 1: Proportion of mono- and binuclear compounds and trinuclear and higher-nuclear compounds in PF glues

orfindungsgemäßer been trading PF-Loim acc. Out usual PF glue Guidance 2 low molecular weight and two-core links 65.6% 43.1% triune and higher nuclear links 34.4% 56.9%

It was found that the reduced proportion of trihydric and higher-nucleated PF condensates had no negative effect on the removal of the glue from the glue joint and can be used to produce wood fibers of very good strength and water resistance (Table 2).

Table 2: Strength of the hot-pressed plywood

according to the present invention

PF glue. Standard PF glue

führungsbeispiel2

Pull shear test after

Water storage sequence G

lt.TGL7448 12.8 N / mm ² 11.6 N / mm ²

The cold tack strength of the PF glue according to the invention (Table 3), tested according to TGL 7448, was significantly improved.

-3- 283 ^ 2 Table 3: Cold bond strength of plywood

according to the present invention

PF glue. Standard PF glue

führungsbeispiel2

Shear strength 1.22MPa 0.50MPa

In the reactivity, the PF-glues are compared at the gel time measured at 373 K (Table 4).

Table 4: Reactivity

according to the present invention

PF glue. Standard PF glue

Guidance Example 1

Gel time at 373K

(TGL35077) 25 to 55 minutes 30 to 65 minutes

The PF glue produced according to the invention has an alkali content of 5 to 7% by weight, it is thus storage-stable and weather-resistant. The particular molecular weight distribution of the PF-glues according to the invention show no negative effects on the pressing times of the wood-based panels. With the use of PF-glues according to the invention, it is not necessary that in the production of wood materials by special additives to the glue liquor, consuming and the quality and productivity of production negative impact measures must be realized. The cold tack of the PF adhesives produced according to the invention corresponds to the requirements of the manufacturers of wood-based materials. In addition to the use of plywood, especially softwoods, PF-glues according to the invention are also advantageous for chipboard and fiberboard, to use veneer-coated chipboard and plywood.

embodiments

example 1

In a commercial, suitable for phenol synthesis 5-liter reaction vessel equipped with a condenser and stirrer, phenol (920g, 87% aqueous phenol), formaldehyde (1243g 37% aqueous formaldehyde solution) and alkali hydroxide (605.5 g 45% aqueous sodium hydroxide solution) in a molar ratio of 1: 1.8: 0.8 and mixed at an average temperature of 355 to 360K and an average pressure of 90 to 95 kPa to a content of trinuclear and höherkernigen compounds of 13.2% im Polycondensed PF condensate and then cooled to 350K. Subsequently, the condensation by addition of formaldehyde (483g 37% aqueous formaldehyde solution) at a temperature of 360 to 368K and a pressure of 70 to 8OkPa at a total molar ratio of phenol: formaldehyde: alkali hydroxide 1: 2.5: 0.8 up to a content of one- and two-core compounds in the PF condensate of 58% continued. The formaldehyde addition can take place continuously or stepwise. By switching the reaction plant from reflux conditions to distillation, the solids content of the PF glue is adjusted to 49%. Thereafter, the PF glue is cooled to a temperature of 298K. The PF glue produced according to the invention has the following characteristics:

Viscosity (measured at 293 K): 52OmPa-s Solids content: 49.1% alkalinity: 6.8% dilutability: > 1:10 Gelzsitbei373K: 39.75 min

The analysis of the PF-size by HPLC showed a proportion of 58.7% one- and two-core compounds and 41.3% of trinuclear and higher-nuclear compounds in the PF condensate.

Example 2

In a 5-liter reaction vessel equipped with a condenser and stirrer, 930 g of phenol are mixed as an 82% aqueous solution and 385 g of 45% sodium hydroxide solution and the resulting Alkaliplionolat cooled. To this mixture is added at 323 K the first amount of 990 g of 37% formaldehyde solution. The condensation is carried out at a temperature of 355 to 363 Kund a pressure of 10OkPa to a content of three- and higher-nuclear compounds of 19.1% and the PF condensate is then cooled to 353 K. In the second step, the condensate is continuously added the second amount of 710g 37% formaldehyde solution, without the product temperature rises substantially above 360K, within 50 to 60min and at a pressure of 71 kPa to a content of single and double core compounds of 65 % condenses. At the same time, the product is dewatered by distillation to a solids content of 48% and then immediately cooled to 300K. The PF glue produced according to the invention has the following characteristics:

Viscosity (measured at 293 K): 45OmPa s Solids content: 48.2% alkalinity: 5.9% dilutability: > 1: 100 Stingy at 373K: 37.55 min

The analysis of the PF-glue by HPLC showed a proportion of 65.6% of low molecular weight single and double core compounds and 34.4% of trinuclear and higher nuclear compounds in the PF condensate.

Example 3

According to Example 2 are added to the cooled Alkaliphenolat at 328K1000g 37% formaldehyde solution. After the onset of the exothermic reaction, the condensation is carried out in a first stage at a temperature of 355 to 360 Kund at 8OkPa to a content of trinuclear and höherkernigen compounds of 15.3%. The resulting PF condensate is immediately cooled to 348K with cooling water and / or reduced pressure. In the second stage, 700 g of a 37% formaldehyde solution are added in total within 5 min. Thereafter, it is condensed at 363 to 368 K and a pressure of 65 kPa to a content of one and two-core compounds of 60.3% and with simultaneous distillation of the PF glue is concentrated to a solids content of 48%. Thereafter, the product is cooled to <305K

 The PF glue produced according to the invention has the following characteristics:

Viscosity (measured at 293K): 545 mPa Solids content: 48.4% alkalinity: 5.8% dilutability: 1; oo Gel time at 373K: 34.75 mi

The analysis of the PF-glue by HPLC showed a proportion of 60.3% of low molecular weight single and two-core compounds and 39.7% of trinuclear and higher-nuclear compounds in the PF condensate.

Claims (1)

Process for the preparation of PF-glues, by condensation of phenol with Formdedeyhd in alkaline medium in several stages, wherein optionally an alkali phenolate partially aqueous formaldehyde solution is added and the addition of further subsets of formaldehyde during the condensation takes place, characterized in that in its first step Condensation of Phenol: Formaldehyde: Alkali hydroxide having a molar ratio of 1: 1.5 to 2.0: 0.5 to 1.0 at a temperature of 355 to 363 K and at a pressure of 61 to 101 kPa to a content of three and higher-nuclear compounds of 10 to 20% and then the PF condensate is cooled to a temperature of 348 to 353 K, then in a second step, the condensation by further addition of formaldehyde to a molar ratio of phenol: formaldehyde: alkali hydroxide of 1: 2 ,? ois 3.0: 0.5 to 1.0 at a temperature of 360 to 368 K and at a pressure of 50 to 81 kPa up to a content of one- and two-core compounds of 55 to 70% continued and the PF glue on a solids content of> 48% and then cooled to a temperature of 288 to 305 K. Field of application of the invention The invention relates to the production of phenol-formaldehyde resin sizes for weatherproof wood materials, in particular for the production of plywood made of softwood or softwood combinations. Characteristic of the known state of the art It is known to produce PF glues by condensation of phenol and formaldehyde in the presence of alkalis. The basic method used is once the condensation of an initially introduced mixture of phenol, formaldehyde and alkali metal hydroxide or, secondly, the reaction of phenol and alkali hydroxide to give alkali polyionolate with subsequent addition of formaldehyde and condensation of this reaction mixture, these basic processes being varied in many ways. The above-mentioned processes usually employ a molar ratio of phenol: formaldehyde, alkali metal hydroxide of from 1: 2.5 to 4: 0.8 to 1.5, the highly reactive sizing agents containing an alkali content of from 6 to 15% to preserve their shelf life, which has an adverse effect on the utility properties of the wood-based materials produced. The main objective of this procedure is the production of high molecular weight PF condensates, on the one hand wegklicken in the glue joint in the wood material and allow a sufficiently thick glue layer to achieve a uniform solid compound of the wood material and on the other hand allow high reactivity to achieve short pressing times of the wood material. The adhesion between Leimschirht and dom wood-based material is generally given after the hot pressing by reaction of the Methylolgru, ~ pen of the PF resin with the hydroxyl groups of wood ingredients sufficiently without special measures. If the technological chain of wood-based material production calls for the step of cold-pressing, the cold-bond strength of the PF-glues produced in this way is insufficient. This deficiency becomes more and more apparent with the processing of softer woods or combinations with them. A known method for the preparation of curable, highly reactive PF-Leimsn Is that is reacted in a multi-stage condensation AlkaliphenolB'i with formaldehyde in a proportion of two-thirds of the total amount at temperatures of 45 ° C to 65 ⁰ C with partial vacuum distillation. Thereafter, the condensation is continued for up to 2 hours, with the addition of the remaining men per formaldehyde at boiling temperature a multiple of the final value amounting viscosity is achieved. Finally, the final viscosity is adjusted by addition of alkalis dissolved in solvents (DD-WP 81172). This procedure leads to a further increase in the high molecular weight fractions compared with the conventional PF adhesives and thus to fulfill the objective of increasing the reactivity, but at the same time required storage stability can only be achieved by the additional technological step of adding alkalis dissolved in organic solvents. With these higher molecular weight PF condensates, the cold bond strength deteriorates even more. In addition, the addition of solvents is costly and brings problems in occupational safety. Of the urea-formaldehyde resin sizes, many activities for increasing the cold-tack resistance are known (eg DD-WP 209839), but the technical solutions proposed here are not transferable to phenol-formaldehyde resins because of fundamentally different reactions. PF glues already show better bonding strength than urea and melamine resin glues when cold-pressing wood-based material pallets. Weiteihin is trying to increase the addition of various substances, the cold tack of the condensation resins in general. This is due to the addition of wheat flour, which, however, is added to the glue flea only immediately before processing and is expected to have a negative effect on the stability of the glue liquor and on the water resistance of the glue joint. It has also been proposed to make an addition of a solution of boric acid in a water-miscible amine in an amount of 0.05 to 10%, which solution can be added just before processing the size liquor and in which because of the curing accelerating effect of boric acid Uncontrolled influences on the intermediate storage of cold-pressed Holzvverkstoffe and the hot pressing are to be suspected. An advanced process for the production of PF glues (DD-WP 134363) provides for the replacement of 25 to 50 wt .-% phenol by sulfite liquor, while maintaining the usual condensation guide. These PF glues have no improvement in the cold tack strength, the additional technological expenses resulting from the introduction of a new raw material have a cost-effective effect.