WO2008128908A1

WO2008128908A1 - Preparation of a condensation resin and impregnation process

Info

Publication number: WO2008128908A1
Application number: PCT/EP2008/054431
Authority: WO
Inventors: Wilhelmus Jacobus Cramer; Jan Jacob Hendrik Nusselder; Gerard Evert Oosting; Bernd Ohlmeier; Johannes Hendrikus Gerardus Marie Lommen; Lambertus Cornelis Van Buggenum; Leonardus Jozef Hahn
Original assignee: Dsm Ip Assets B.V.
Priority date: 2007-04-20
Filing date: 2008-04-11
Publication date: 2008-10-30
Also published as: BRPI0810479A2; CN101663087A; EA200901428A1; AU2008240821A1; AR069999A1; KR20090128500A; CA2680480A1

Abstract

The present invention relates to a process for the preparation of a condensation resin at elevated temperature and pressure, wherein the monomers of the condensation resinare fed continuously to a tubular reactor provided with static mixer elements.

Description

PREPARATION OF A CONDENSATION RESIN AND IMPREGNATION PROCESS

The present invention relates to a process for the preparation of a condensation resin from its monomers in an aqueous medium at elevated temperature and pressure.

Processes for the preparation of condensation resins are either performed batch wise, or in recent days also (semi-) continuous. Examples of batch wise preparation are those which are performed in a stirred tank reactor, or even a combination of several of stirred tank reactors, all operated in batch mode. A continuous process has also been considered in the art, an example whereof being presented in EP-A-355,760. In this publication a melamine- formaldehyde precondensate is prepared in a single or double screw extruder.

This has as a consequence that in the extruder (in fact a tubular reactor with dynamic elements) a lot of mixing energy is consumed, next to the fact that only viscous streams can be dealt with.

The present invention recognizes that the use of an extruder is not appropriate for processes for a preparation of a condensation resin in which the process stream has a viscosity well below 50 Pa. s. The present invention also acknowledges that preparation at such low viscosities at more elevated pressures than normally attainable in an extruder are desired, as a result of which the process can be performed at a higher temperature. This all being the consequence of the fact that the resin preparation is performed in an aqueous medium.

The present inventions present a solution for the above indicated items, in that the temperature is between 70 and 200⁰C, the pressure is between 0.2 and 20 MPa, and in that the monomers are continuously fed to a tubular reactor which is provided with static mixer elements.

As a result, the process can be performed with process streams that have a significant lower viscosity than those which are suitable for an extruder- operated process. Generally, the present process can cope with viscosities up to 10 Pa. s; more preferred the viscosity of the contents of the reactor is at most 1800 mPa.s; the viscosity being determined at the local conditions in the reactor (i.e. at the local pressure and temperature conditions).

The tubular reactor used in the process is, in the inside of the reactor, provided with one or more static mixer elements. Such a reactor, also named a static mixer, can be described as a pipe with immovable internal elements that achieve continuous multiple splitting and recombination, and/or turbulence of streams of material passing through and improve distributive mixing. A short compilation of various types of static mixer elements can be found for instance at: http://www.best-mixer.de/html/stromungs- mischer.html.

As a result of the presence of static mixer elements in the tubular reactor a better flow profile of the process stream, with a beneficial influence on both mass and heat transfer during the transport of the process stream through the reactor is achieved. This beneficial influence is also present in comparison with the use of an empty, tubular pipe, as is disclosed in WO 2006/1 19982 for the preparation of a melamine-formaldehyde resin.

The process of the present invention is suitable for the preparation of any condensation resin, in which said preparation takes place in an aqueous medium; or in other words: in all preparations where water is either a solvent or a dispersion agent. Other solvents or dispersing liquids may be present, next to water, but they are only present in a minor amount compared to water.

A non-limiting list of condensation resins that can be prepared with the process of the present invention is polyamides, polyacetals, polyesters, and adhesives useful in engineered wood, such as condensation resins based on phenol, melamine (or more generally triazines), urea, and aldehydes (like (paraformaldehyde). In general, here and herein after, a condensation resin is any class of polymer formed through a condensation reaction, releasing (or condensing) a small molecule by-product such as water or methanol, as opposed to an addition polymer which involves the reaction of unsaturated monomers. Condensation polymerization, a form of step-growth polymerization, is a process by which two molecules join together, with the loss of a small molecule which is often water. The type of end product resulting from a condensation polymerization is dependent on the number of functional end groups of the monomer which can react. Monomers with only one reactive group terminate a growing chain, and thus give end products with a lower molecular weight. Linear polymers are created using monomers with two reactive end groups; monomers with more than two reactive end groups give three dimensional polymers (network polymerization).

The process of the present invention is performed at elevated pressure and temperature, which can be selected for the preparation of the desired resin, within the boundaries of the conditions needed for said preparation. The temperature is between 70 and 200⁰C; the pressure is between 0.2 and 20 MPa. Preferably, the temperature is between 100 and 150⁰C, at a pressure which is at least the corresponding vapor pressure. Of course the skilled man can decide to select his own pressure, deviating from the vapor pressure, for instance by using a pressure control. The dimensions of the tubular reactor can be chosen freely, depending on the desired throughput. Preferably the tubular reactor has a circular cross-section. The diameter of the tube will in general be at least 5 mm, and will in general not exceed 500 mm. The length will in general be at least 25 mm, and will in general not exceed 100 m. The skilled man is able to select the material of the tubular reactor wall and of the static mixer elements, based on the materials (like monomers/polymer, other added ingredients) to be processed in the reactor.

In general the process is be applied using an aqueous medium, in which the solids content of the resin is between 20 and 85 wt.%; more preferred this content is between 45 and 75 wt.%. The process of the present invention is very suitable for the preparation of a condensation resin, wherein said resin is prepared from an aldehyde (preferably (para-)formaldehyde), a triazine (preferably melamine), an aromatic alcohol (preferably phenol), or urea. Next to the individual ingredients, also mixtures of said ingredients can be used (like a mixture of melamine, urea and formaldehyde, resulting in a so-called MUF-resin, or a mixture of melamine, urea, phenol, and formaldehyde, resulting in a MUPF-resin). The preparation of the resin according to the present invention can also start with a so-called precondensate, which is a low-molecular precursor of the desired resin, but in which already some degree of condensation between the constituting monomers has taken place. Preferably, the condensation resin to be prepared according to the process of the present invention is an aminoplast (a condensation resin based on a triazine or urea, and an aldehyde) or a phenolic resin (a condensation resin based on an aromatic alcohol, and an aldehyde). The resulting resin is a so-called network polymer, in contrast to a linear or branched polymer.

In the case of an aminoresin, the triazine is preferably melamine; the aldehyde is preferably (para-)formaldehyde. In the case of a phenolic resin, the aromatic alcohol is preferably phenol; the aldehyde is preferably (para-)formaldehyde,.

Even more preferred is a condensation resin, based on formaldehyde, melamine and urea.

In case a condensation resin is prepared having melamine and -A-

(para-)formaldehyde as the at least two constituting ingredients of the final resin, the F/M ratio (being the molar ratio between the formaldehyde (F) and the melamine (M) in the condensation resin) is generally between 0.5 and 4.0; preferably this ratio is between 0.75 and 1.8. In the present process, all the melamine-formaldehyde resins as disclosed in WO 2006/119982 can be prepared.

The ingredients necessary for the preparation of the condensation resin can be metered to the reactor in any desired way: pre-mixed at a low temperature; or at different locations over the length of the reactor. One can also choose to feed one or more of the ingredients at multiple locations along the length of the reactor. All of these possibilities are available to the skilled man in order to fine-tune the preparation process.

The ingredients can also, and preferably, be metered individually to the reactor, in order to better control the dosage of each ingredient.

In case the ingredients are premixed before entering the tubular reactor, this tubular reactor is preceded with equipment in which the ingredients for the preparation of the condensation resin are premixed. This can be done in a stirred tank, or in a tube, coupled at the front end of the reactor. As a result, a well mixed feedstream of the ingredients in water can be achieved, before the reaction takes place in the tubular reactor. The premixer can also be used to (partially) preheat the mixture from room temperature. Premature polymerization in the premixer should be avoided as much as possible.

Of course also a combination of the above can be used. Reference can be given to a situation in which part of one or more of the ingredients needed for the condensation resin is fed as a premix to the tubular reactor, and in which the remaining amount(s) are directly fed to the reactor, possibly at multiple locations along the length of the reactor. All this is within the skills of the man skilled in the art of process technology.

Next to the ingredients necessary for the preparation of the condensation resin, additives can also be present in the final resin. These additives, the nature and function of which are known to the skilled man, are also fed to the reactor, or added to and in the premixing step, and are for instance catalyst, fillers, emulgators, etc. The reader is referred to the literature hereon, including the teachings of the EP-A-355,760.

The product resulting from the process of the present invention is a condensation resin in an aqueous medium, at elevated temperature and pressure. This makes this product very suitable for use in an impregnation process, in which a substrate (like paper, wool, etc.) is impregnated with the resin, especially when the impregnation process is also performed under elevated pressure (in order to improve the degree and/or speed of impregnation). This effect is the more suitable, when the pressure in the impregnation process is essentially the same or lower, than the pressure in the resin preparation. Then the process for the preparation of the condensation resin and the impregnation process can be directly coupled, so as to avoid for instance storage of the resin, and reheating and repressurizing the stored resin to the impregnation conditions. Preferably, also the impregnation process is performed at a temperature essentially the same as the temperature in the resin preparation. As a result, an inline combination of condensation resin preparation and impregnation is created. In the context of the present specification, the term "essentially" is meaning that the pressure or temperature in the impregnation do not differ more than 15 % of the value(s) thereof in the tubular reactor. Before the impregnation process, and at the exit of the tubular reactor, the usual ingredients used in an impregnation process (like hardener, wetting agent, release agent) are added. The skilled man is aware of these impregnation ingredients and how to supply them. Some of them may also be present in the feed to the tubular reactor, in order to achieve an intimate mix of these ingredients with the resin.

The invention will be elucidated with the following Examples and comparative experiment, which are intended to show the benefits of the invention, but not to restrict it.

The Examples and experiment were performed in a heated steel tubular reactor with an internal diameter of 10 mm and a length of 2.0 m. The reactor was provided with 96 SM X L static elements of Sulzer having a diameter of 10 mm. The result of the Examples was determined with respect to the so-called water- tolerance (W.T.) of the obtained resin. This WT. is the amount of resin that can be dissolved in water at room temperature (dimension: gram/gram).

Example I

Formaline (with 30 wt. % formaldehyde (F), melamine (M), di- ethylene glycol (DEG) and caprolactam were mixed with water to obtain a dispersion with an F/M-molar ratio of 1.65. Table 1 gives the used recipe (in wt. %). The ingredients were mixed in a storage tank, provided with a circulation pump. Table 1

The flow through the reactor was varied. The temperature of the mixture entering the reactor was 120 ⁰C. At the exit of the reactor the temperature was 140 ⁰C; thereafter the mixture was cooled via a water bath to room temperature. The pressure in the reactor was set at 1 MPa. Table 2 gives the realized water tolerances (W.T.) of the produced resin, as a function of the flow through the reactor.

Table 2

Example Il

Example I was repeated, but now with an F/M molar ratio of 1.4. Table 3 gives the recipe (in wt. %).

Table 3

The flow was set at 5.6 kg/h; it resulted in a water tolerance of 0.6.

Comparative experiment A Example I was repeated, but now in absence of the static mixer elements in the reactor (i.e. with the use of a non-filled tube). After 4 hours of experimentation, the tube appeared to be plugged internally due to the formation of polymer on the internal wall of the tube.

Claims

1. Process for the preparation of a condensation resin from its monomers in an aqueous medium at elevated temperature and pressure, wherein the temperature is between 70 and 200 ⁰C, the pressure is between 0.2 and 20

MPa, and the monomers are fed continuously to a tubular reactor provided with static mixer elements.

2. Process according to claim 1 , wherein the temperature is between 100 and 150 ⁰C.

3. Process according to anyone of claims 1-2, wherein the solids content of the resin in the aqueous medium is between 45 and 75 wt.%.

4. Process according to anyone of claims 1-3, wherein the condensation resin is prepared from an aldehyde, melamine, urea, phenol, or mixtures or precondensates thereof.

5. Process according to anyone of claims 1-4, wherein the condensation resin is an aminoplast or a phenolic resin.

6. Process according to anyone of claims 1-5, wherein a melamine-formaldehyde resin is prepared, having an F/M-ratio of between 0.75 and 4.0.

7. Process according to claim 6, wherein the F/M-ratio is between 1.0 and 1.8.

8. Process according to anyone of claims 1-7, wherein the monomers are individually metered to the reactor.

9. Process according to anyone of claims 1-8, wherein a resin is prepared, based on formaldehyde, melamine, and urea.

10. Process according to anyone of claims 1-9, wherein the viscosity of the reactor contents is at most 1800 mPa.s.

11. Process according to anyone of claims 1-10, wherein the tubular reactor is preceded with equipment in which the ingredients for the preparation of the condensation resin are premixed.

12. Process for the impregnation of a substrate, wherein the resin/water mixture prepared in a process according to anyone of claims 1-1 1 is used and wherein the preparation of the resin and the impregnation process are directly coupled.

13. Process according to claim 12, wherein the impregnation process is performed at elevated pressure.

14. Process according to anyone of claims 12-13, wherein the pressure in the impregnation process is essentially the same as the pressure in the resin preparation.

15. Process according to anyone of claims 12-14, wherein the impregnation process is performed at a temperature essentially the same as the temperature in the resin preparation.