WO1993003086A1

WO1993003086A1 - Phenolic-resin binder

Info

Publication number: WO1993003086A1
Application number: PCT/DE1992/000651
Authority: WO
Inventors: Wolfgang Erb; Harald Rusche; Jutta Meyer; Wolfgang Seelbach
Original assignee: Hüttenes-Albertus Chemische Werke GmbH
Priority date: 1991-08-06
Filing date: 1992-08-06
Publication date: 1993-02-18
Also published as: DE4126059A1; EP0551505A1; ZA925911B

Abstract

The binder described is a novolak which can be cured with an ordinary accelerator and which is liquefied by the addition of a reactive liquefying agent in the form of phenol or alkyl-substituted phenols (having side chains containing up to 10 C-atoms). The liquefying agent does not behave like an ordinary solvent, but takes part in the curing of the novolak and is - at least for the greater part - bound into the molecular structure. The invention thus makes a binder available which, in contrast to liquid resols, has excellent storage stability, can be converted easily to anhydrous form, does not have to contain any alkaline components and can be produced simply and reliably.

Description

Phenolic resin based binder

In wide areas of technology, phenolic resins are used for wood-based materials, in thermal insulation and in sound insulation, in electrolaminates and other laminates, for paper impregnation, in the foundry industry, in the abrasive industry, and for brake and clutch linings just to name a few typical examples.

In many cases, phenol resins of the resole type, that is to say the self-curing condensation products of phenols and aldehydes, are used, which are generally condensed with a molar deficit of phenol. These resoles are usually in the form of aqueous liquid resins. However, these resoles have some disadvantages, one serious disadvantage of which is that they are not stable in storage. All resols can condense even at low temperatures. As a result, the most important characteristics of these resins change continuously, so that their use in a controlled process is problematic. In particular, the viscosity of resols is constantly increasing, which means that water compatibility also decreases, e.g. the dissolving power for novolaks or the wettability for materials to be bound. Another disadvantage is that the residual alkali content leads to a relatively high hygroscopicity of the resols in the hardened state. This can lead to a loss of quality after prolonged storage of the products manufactured using resols.

The water content of the resols depends on the desired viscosity and is usually relatively high. In some areas of application, however, the water content of the resins should be as low as possible, because the escape of water vapor during the curing process can weaken the resin bridges between the materials to be bound. The However, the production of low-water or water-free resols is quite problematic. The resin solution must be dewatered under a very good vacuum and at temperatures up to 90 ° C., whereby the resin naturally condenses further. This can be mitigated if dewatering is carried out in small batches, but then the production becomes almost uneconomical .

Phenolic resins of the novolak type are stable in storage and practically water-free. Novolaks are the acid-catalyzed condensation products from phenols and aldehydes, which are normally condensed with a molar excess of phenol. They are characterized in particular by the fact that they are not self-curing, so that the water formed in the condensation reaction can be removed without undesired post-condensation. Formaldehyde donors, e.g. Hexamethylene tetramine, or compounds containing methylol groups added as hardeners. Novolaks are generally in solid (lumpy or powdery) form, mostly with hardener already incorporated.

Novolaks are mainly used for the production of products that can be referred to in the broadest sense as molding and molding compounds. However, it has not yet been possible to use novolaks where a liquid binder is required. Resoles, which are produced as an aqueous-liquid resin due to the way they are produced, almost offer themselves as liquid binders. Novolaks, on the other hand, must first be in a solvent such as Ethanol or acetone can be dissolved. In order to subsequently remove the solvent, a further work step has to be accepted with additional costs, especially since measures to protect the environment are generally also required. In the case of volatile solvents, the workload is also increased, since the solvent evaporates continuously, especially in processes that require an elevated temperature. Furthermore, it can also happen that the novolak fails prematurely before the end of the work process due to the decreasing solvent concentration, with the result that the novolak may not be sufficiently incorporated at this point in time and products may result which do not have the required quality .

There is therefore still a need for a phenolic resin-based binder which has the advantageous properties of a novolak and can be used instead of aqueous-liquid resols. In practice, such a phenolic resin is made available with the invention.

The phenolic resin-based binder according to the invention is characterized in that the phenolic resin is a novolak curable with a customary hardener, which has been liquefied by adding a reactive plasticizer in the form of a phenol. Suitable phenols here are (unsubstituted) phenol and / or alkyl-substituted phenols, the weight ratio of novolak to reactive plasticizer being able to vary in the range from 4: 1 to 1: 4 and preferably in the range from 1: 1 to 3: 1 lies.

The invention is based on the surprising finding that mixtures of novolaks and phenol or alkyl-substituted phenols (even if the phenols on which they are based are not inherently liquid but must first be melted for the preparation of the mixture) and that the phenols are liquid do not behave like a simple solvent, but participate in the curing of the novolak and - at least predominantly - are incorporated into the molecular structure. Because of this property, which is decisive for the success of the invention, the phenols are also referred to here as reactive plasticizers.

A special novolak is not required for the binder according to the invention. All common novolaks can be used. If alkyl-substituted phenols are used as reactive plasticizers, these can have one or more aliphatic side chains with up to 10 carbon atoms. Longer side chains are not excluded in principle, but are not practical because the viscosity of the binder obtained increases with increasing chain length. In the case of several side chains, it is additionally required that at least two of the three ortho and para positions of the alkylphenol are not occupied. Of course, the reactive plasticizer can also consist of mixtures of phenol and / or alkylphenols.

The preparation of the binder according to the invention is not tied to any regulation. It is possible to subsequently add the reactive liquefier to a finished novolak, but the novolak can also be prepared in the presence of the reactive liquefier. In certain cases, the binder can also be formed in situ. by adding novolak and reactive liquefier separately to the materials to be bound.

The binder according to the invention is cured by adding the customary curing agents which may already be present in the mixture of novolak and reactive plasticizer or may be added subsequently. If the binder according to the invention is used together with ground novolaks (so-called powder resins), the hardener can also be introduced via the powder resin. The reactivity of the binder can be easily controlled by varying the amount of hardener added.

The binder according to the invention has practically the same good storage stability as that of conventional novolaks. In one example it was found that the viscosity of the binder according to the invention had risen from 2,340 to 2,350 mPa.s / 20 ° C. after one year of storage, while conventional liquid resoles are puncture-resistant after this time. In addition, the binder according to the invention has other obvious advantages, namely the problem-free setting of low water contents, the possibility of avoiding alkaline components and the simple and safe production.

In addition, it should also be pointed out that the modifiers customary in phenolic resins, such as curing accelerators, elasticizing and plasticizing components, can also be introduced without problems.

The invention is illustrated below in examples.

MANUFACTURE OF NOVOLAK

Two different novolaks A and B were produced, as follows:

Novolak A

120 kg of phenol and 1.7 kg of 5% strength hydrochloric acid were placed in a stirrer. The mixture was brought to 100 ° C. Then 37.9 kg of 30% strength formalin were metered in over the course of 4 hours, the temperature having to be kept at 100.degree. The mixture was then stirred for a further 2 hours under pressure at 120 ^° C. to complete the reaction. The reaction mixture was worked up by the customary methods, and 60.5 kg of a solid novolak with the following characteristics were obtained:

Novolak B

300 kg of phenol and 1.4 kg of 16% strength hydrochloric acid were placed in a stirrer. The mixture was brought to 100 ° C. Then 247 kg of 50% formalin were metered in within 4 hours, the temperature having to be kept at 100.degree. The mixture was then stirred under pressure at 120 ^° C. for a further two hours. The reaction mixture was worked up by the customary methods, and 287 kg of a solid novolak were obtained with the following characteristics:

Flow distance / 10% Hexa 41 mm

Water content 0.13% free phenol 3.3%

Viscosity in methanol 50:50 45 mPa.s / 20'C

PRODUCTION OF THE BINDING AGENT

Novolaks A and B were mixed with some selected reactive plasticizers and with hexamethylenetetramine ("Hexa") as a hardener. The weight ratio of novolak plus hexa to reactive plasticizer was 1: 1. The reactive liquefiers used in each case and the characteristic values of the binders thus obtained are summarized in the attached Tables 1 and 2.

It can be seen that in any case binders with result in technically usable gelling times and with a yield of solids (based on the original liquid mixture) which is above the "theoretical" value of 50%. This shows that apparently a corresponding part of the reactive plasticizer reacts in situ with the formaldehyde derived from the hexa during the curing process to form a resin which is then cured together with the original resin component (novolak), that is to say a part of the reactive plasticizer in the hardened binder has been installed. The remaining part of the reactive plasticizer is likely to have been lost during the curing process (which takes place at elevated temperatures), in particular due to evaporation; in any case, the hardened binder no longer contains any disruptive amounts of free reactive plasticizer (contents of free reactive plasticizer normally well below 5%) .

The yields of solids and the gelling times depend, as can be seen in Tables 1 and 2, on the novolaks or reactive plasticizers used. These values can also be controlled, as shown in Table 3, by varying the hexa content and thus adapting them to the respective application. A larger amount of hardener leads to increasing solids yields and decreasing gel times due to an increasing supply of formaldehyde. Here ^'the rise of the solid yields and the reduction of gel times but are converging on limits so that an optimum amount of hardener exist, which can be found easily for each composition of the binder of the invention by simple tests. In the example in Table 3, this optimal amount of hexa is about 15% (phenol) or 10% (cresol), although it can generally be said that a slightly larger amount of hardener should be used in the binder according to the invention than it is would only be necessary for the underlying novolak.

As already mentioned at the beginning, the viscosities of the resulting binders increase with the aliphatic chain length of the alkylphenols. If they are too high in individual application cases, it is readily possible to set lower viscosities by dilution with conventional non-reactive solvents (such as methano, ethanol, isopropanol, acetone and the like), although it is preferred, without such Solving solvents. This is limited for reasons of. Practice the aliphatic chain length the alkylphenols.

APPLICATION EXAMPLE

The following example of use may illustrate the advantageous effect of .reactively liquefied novolaks over liquid resols:

When manufacturing grinding wheels, it is common to use liquid resols as wetting agents. They have the function of moistening the abrasive grain (corundum) to such an extent that it can form an intimate bond with the binder. The binder is usually a powder resin (novolak with hexamethylenetetramine). Up to now, one had to accept the disadvantages of the liquid resols described at the outset, which made it particularly difficult that the water had to be expelled from the wetting agent before the curing process. The reactive liquefied novolaks, on the other hand, which are stable in storage and water-free, can also wet the grain very well, and the curing process can be started immediately after pressing the mass. It is also advantageous that there are no longer any boundaries between resol and novolak, since the same novolak that is also used as a binder can be used as the wetting agent. The grinding wheels made with reactive liquefied novolak had a 50% higher power factor than those made with the resols.

The use of the binder according to the invention in the manufacture of grinding wheels is only one example. In principle, the reactive liquefied novolaks can be used as binders wherever liquid resols or dissolved novolaks have been used up to now. Table 1: Novolak A based binder

5.5 GT reactive condenser

5.0 GT Novolak A

0.5 pbw of hexamethylenetetramine

Table 2: Novolak B based binder

5.5 GT reactive condenser

5.0 GT Novolak B

0.5 pbw of hexamethylenetetramine

Table 3: Dependence of the gelling time on the hexa content

5.5 GT reactive condenser 5.0 GT Novolak A

Reactive liquefier

phenol

Cresol

Claims

1.) Binder based on phenolic resin, characterized in that the phenolic resin is a novolak curable with a formaldehyde dispenser as hardener, which has been liquefied by adding a reactive plasticizer in the form of a phenol.

2.) Binder according to claim 1, characterized in that the ratio of novolak to reactive plasticizer is in the range from 4: 1 to 1: 4.

3.) Binder according to claim 2, characterized in that the novolak and the reactive plasticizer are present in approximately equal parts by weight.

4.) Binder according to claim 2, characterized in that the novolak is in excess of the reactive liquefier.

5.) Binder according to one of claims 1 to 4, characterized gekenn¬ characterized in that phenol is used as reactive plasticizer.

6.) Binder according to one of claims 1 to 5, characterized gekenn¬ characterized in that an alkyl-substituted phenol with side chains of up to 10 carbon atoms is used as a reactive plasticizer.