DD222886A1 - LOW-MOLECULAR, CALINATING PHENOL FORMALDEHYDE RESIN - Google Patents

Abstract

Low molecular weight, cold-curing phenol-formaldehyde resins are used in the foundry industry as core and molding sand binders. The aim of the invention is the preparation of phenol-formaldehyde resins using technologies known per se when using domestic raw materials, wherein the resins are characterized by an increased conversion of phenol and formaldehyde. The object of the invention is the preparation of a low molecular weight, kalthaertenden phenol-formaldehyde resin with reduced monomer cleavage during processing. It has been found that the addition of salts of tertiary amines during condensation produces low molecular weight resins which can be processed excellently in the foundry industry. The addition of the salts of tertiary amines is in a range of 5 to 12 wt .-%, wherein the salts have 3 to 12 carbon atoms, and the phenol-formaldehyde resin by addition of acid to a p H value of 7, 0 to 7.2 is set.

Description

Niedermole kulares, kalthärtendes phenol-formaldehyde »resin

Application area of the invention

Low molecular weight, cold-curing phenol-formaldehyde resins are used primarily in the foundry industry as core and molding sand binders.

Characteristics of the known technical solutions

Unmodified phenol-formaldehyde resins, which are cold-cured by the addition of acids, are technologically easy to process. They are used extensively in the DIR foundry industry in particular Phenol> 15 % and also a proportion of residual formaldehyde to 2.5%, split off during processing, during the mixing process, in the core and mold production and casting phenol and formaldehyde shares, which are above the MAK values · HLe production of this kind Resins correspond to the general state of knowledge. They are generally condensed with the condensation agents Ba (OH) ₂ , Ca (OH) ₂ and NaOH which are customary for Resoil resin preparation. Further, furfuryl alcohol or urea or furfuryl alcohol and urea-modified phenol Formaldehyde resins used (see DE-AS 1156941, DE-AS 1159597) are processed particularly advantageously cold-curing F Substances with low-monomer phenol-formaldehyde resins which are stabilized with furfuryl alcohol or furfuryl alcohol resins and optionally contain small amounts of urea for setting the residual formaldehyde content. At present, furfuryl alcohol is not sufficiently available, and when furfuryl alcohol is used.

'are high material costs ·. '· ·'.

Therefore, there is a legitimate demand for foundry resins that better comply with occupational and environmental protection · This requirement is opposed by the theory of cold curing of phenolic resins «According to K · Hultzsch," Chemistry of Phenolic Resins ", the most favorable kaitha curing conditions in the reaction between! Phenolic alcohols and phenol, So at high free phenol contents available. These resins are due to the high proportion of monomers! ' Phenol, which acts as Lösurigs- and stabilizing agent, exceptionally well preserved, their use is, however, for reasons of health protection of concern ·

They are known to be prepared with molar ratios of 1: 1.2 to 1: 1.4 using Ba (OH) ₂ , Ga (OH) ₂ or · NaOH and the formaldehyde content can not be increased so much that the phenol content after condensation reaches a value < 5% . A molar ratio of 1:> 1.5 is given as not possible an-r, since the Resitbildung takes place exclusively via methylene bridges and in the form of methylol groups or their descendants already attached, but surplus formaldehyde during the acid curing in each case cleaved again , In addition, such resins prepared in a molar ratio of 1:> 1.5 have the following disadvantages:

- low solid resin content

- deterioration of storage properties

- low acid activity.

- high molecular structure -

- poor sand envelope and thus. poor strength properties

It is also known (ζ · Β · Knop / Scheib "Chemistry and preparation of PF-resin") that low molecular weight Resolharze for hot curing can be prepared with high Formaldehydanteilen by the condensation with tertiary amines · The known technical solutions have disadvantages can be summarized as follows:

- The phenol-based cold-curing Resolharze produced by traditional methods emit due to insufficient monomer bonding in the mixing process, in the mold and core production and casting phenol and formaldehyde, the

,:.; --- "-. - --- - ·.; 3 are above the MAK values." The removal of monomers by technological means is complicated and expensive by a complicated process control (DE-OS 2702 806) and is therefore not suitable for mass production. V

The urea-modified PF resins lead to pinhole formation in certain types of casting due to the nitrogen originating from the urea and also have an unfavorable hardening behavior with urea contents of> 15 % .

In the case of the urea resins modified with furfuryl alcohol, there is a tendency during synthesis to formaldehyde-releasing by reaction and, during casting, high quantities of pyrolysis gas are released. _f

Object of the invention

It is an object of the invention to produce the phenolic resins currently used in the foundry industry by using mostly indigenous raw materials with better material utilization. At the same time, it must be ensured that the production is carried out using technologies known per se without the use of complicated technological steps. Another goal is to reduce the production costs, which is achieved by the increased conversion of the raw materials phenol and formaldehyde used. At the same time a reduction of the environmental impact in the resin processing and thus an improvement of the working conditions in the foundries is achieved.

Dar le supply of the essence of the invention

The object of the invention is the production of a low molecular weight, cold-curing PF resin with reduced Monomerabspal- tion during processing, without adversely affecting the foundry technical issues, especially the curing and storage behavior and the strength properties. The object of the "invention is in particular, the Improvement of Monome renabbindung to achieve by changing the condensation guide.

Surprisingly, it has been found that resins obtained by using o-o-orienting condensing agents, for example tertiary amines, in contrast to those conventionally used for the

Preparation of acid-hardening PF resoles used condensation agents, at high Formaldehydanteilen properties that are comparable to those of traditional cold-curing molding materials "These resins can be, due to the o. The fact that the proportion of the amine used for the condensation exerts a significant influence on the phenolic bond and on the low molecular structure of the resin in such a way that the higher the proportion of amine, the higher the proportion of amine, was not to be expected from the outset, since the use of conventional condensing agents in this case results in the formation of high molecular weight resins which, moreover, are not cold-curing.

In addition, the resins of the invention are characterized in that they make it possible by the formation of amine salts, which are not stable in the temperature range of 160-200 ⁰ C, a specific influencing the thermal decay of the foundry cores,

For guidance purposes

The resin according to the invention is illustrated by the following example. , .... · 446 ~ g of pure phenol (4 * 75 mol), 687 g of formalin 37 #ig (8.5 mol) MoI ratio. = 1: 1.8 and 53 g of trimethylamine as a 50 succession solution (12 %) are condensed at 80 to 85 ⁰ C until the formaldehyde connection of ca, 2 % . Thereafter, a pH value of 7.0 to 7 »2 is set ₀ After the neutralization, 30 g of urea are trains pass and thereafter under vacuum to the desired final viscosity of 400 to 500 mPa» s distilled · For the neutralization can be other than acid addition Acetic acid use all common inorganic and organic acids. The trimethylamine can also be replaced by triethylamine or tri-n-butylamine, the proportion can be up to 10 % _t based on the phenol content, increase ₀

The resins obtained in this way exhibit the following characteristic parameters in comparison with the conventionally prepared acid-curing binders:

mPa »s erfindungsge conventional % moderate resin resin viscosity % 400 - 500 400 - 500 free phenol % 2-4 15 free formalin lake. 1 2 ^: y Solid resin content sec. 70-75 70-75 endurance test % 180-300 30-60 B time 2'40-300 60-120 Haoh content 0.1-0.2 -

The workability of the resins in the foundries does not differ from the conventional phenol-formaldehyde resins, since the same curing behavior is dependent on the curing time, which can be seen in subsequent values, the room temperature in the curing 28 ⁰ C ·

Conventional custom resin resin ·

Binder content % 2 2 · -; '; Hardener percentage 1.75 1.75 Bending strength mPa * s after 0,5h. 1.2 / 1.3 1.0 / 1.5 1h 2.5 / 2.4 2.0 / 2.2  2 h 3.8 / 3.8 3.0 / 2.9 , 4 h 4.2 / 4.1 4.4 / 4.0 " 24 hours 5.4 / 6.0 4.5 / 5.0

On the Gußoberfläche or, the Gußqüalität is exercised by the modified binder no adverse effect. The proportion of cleaning work is considerably lower due to the improved nuclear decay. The use of the binder according to the invention guarantees compliance with the MAK values during processing. The production costs are below those of traditional resins.

Claims (2)

In accordance with the invention 1. Low molecular weight, cold-curing phenol-pormaldehyde resin containing free phenol in proportions <4% and is composed essentially by oo-linkages, characterized in that the phenol-pormaldehyde resin 5-12 Gew _e -%, preferably 7 Wt% of tertiary amine salts containing from 3 to 12 carbon atoms and the phenol-pormaldehyde resin is adjusted to a pH of 7.0-7.2 by the addition of acid β 2. Low molecular weight, cold-curing phenol-pormaldehyde resin according to item 1, characterized in that the salts of tertiary amines of trimethyl and / or triethyl and / or tri-n-butylamine and are formed from inorganic or organic acids.