|Title of Invention||
A PROCESS FOR PREPARING AMINOPLASTICS AND/OR PHENOLICS
|Abstract||ABSTRACT (1726/MAS/98) A process for preparing aminoplastics and/or phenolics The invention relates to a process for preparing aminoplastics and/or phenolics, in which a precondensate solution is prepared in a first extruder (14), the precondensate solution is continuously fed, with addition of additives, to a second extruder (20) with partial filling in the feed section (E) and devolatilization section (G), devolatilized in the second extruder (20) and then formed to give a molding composition or an end product. The process is particularly suitable for preparing melamine resins, in particular melamine-formaldehyde resins, as well as for preparing urea-formaldehyde resins.|
|Full Text||The invention relates to a process for preparing amino plastics and/or photonics. The
process is used for preparing melamine resins and/or phonetic resins, in particular melamine-formaldehyde resins, urea-formaldehyde resins, phonetic resins and blends.
Amino plastics (injection- or compression-moldings cured either directly or during the further shaping of semi finished products) have good mechanical properties, high flame reentrancy, heat resistance and solvent resistance, high scratch resistance and good appearance (surface). The starting materials for preparing amino plastics are low in price, compared with those for polyamides or other engineering plastics.
A conventional process for preparing melamine resin semi finished or finished parts has a series of steps: the starting materials are firstly precedence batch wise in a heat able mixing vessel to give an amine-formaldehyde resin solution of about 50% strength, the resultant solution is spray-dried to give melamine-formaldehyde resin powder, the resultant resin powder is dry-mixed with fillers in, for example, a plowshare mixer in a further step, then continuously plasticized via heat able calendars to give a compound, and, in further steps, firstly comminuted coarsely, then finely ground; batches are mixed to give uniformity of color and the material is recomputed to give a free-flowing molding composition and finally injection- or compression-molded to give finished parts.
A simplified process for preparing a melamine-formaldehyde resin in a "single pass" reactor is described in IN 161047. It is significant here that the starting materials are crystalline melamine and solid formaldehyde and that operations are carried out in the
absence of water or any other solvent. Solid formaldehyde, however, is more expensive than aqueous formaldehyde solutions. In addition, this process gives melamine-formaldehyde resins which have properties significantly different from those of resins prepared in the presence of solvents.
DE-A 24 51 874 describes an improved process for preparing amino plastics, in which an aqueous solution of a precondensate, with addition of pigments if desired, is passed into a fluidized-bed dryer and there sprayed onto fillers, dried, and then palletized and used directly as molding composition.
It is an object of the present invention to provide a continuous process which permits simple and low-cost preparation of amino plastics in a small number of steps. The novel process should moreover allow the processing and product properties of amino plastics to be specifically adjusted within a wide range in a simple manner.
We have found that this object is achieved by means of a process for preparing amino plastics and/or photonics, in which a precondensate solution is prepared in a first extruder , by continuously feeding the precondensate solution, with addition of additives, to a second extruder with partial filling in the feed section (E) and devocalization section (G), devocalizing the precondensate solution in the second extruder and then forming it to give an end product.
It has been found that the addition of appropriately chosen additives in the second extruder makes it possible to adjust the reactivity of the resin
or to make controlled improvements in product properties, such as in particular impact strength or other mechanical properties. The process moreover allows the residual moisture of the product to be adjusted in the second extruder via devolatilization systems.
In the novel process, a precondensate solution is firstly prepared in a manner known from EP-B 0 355 760, by mixing the starting materials, for example melamine and aqueous formaldehyde solution, and, if desired, paraformaldehyde, in a molar ratio melamine:formaldehyde of from 1:1.5 to 1:3, preferably from 1:2 to 1:3, if desired adding known modifiers and additives which do not disturb the condensation reaction, for example monoalcohols, diols, sulfonamides, sugars, basic catalysts, such as amines, aminoalcohols and hydroxyalkylmelamines, and precondensing them in a first extruder at from 120 to 140CC to a degree of condensation corresponding to a viscosity rise to at least 1 Pa - s. The precondensate solution has a solids content of from 60 to 90%, preferably from 75 to 80%.
Urea-formaldehyde precondensate solutions may be prepared correspondingly from urea solutions and formaldehyde solutions, if desired with suitable additives.
A vital element of the process is a second extruder, to which is fed the precondensate solution prepared in the first extruder in a known manner. While the first extruder must be 100% filled, so that the residence time can be precisely adjusted, giving a defined degree of condensation, the second extruder must, according to the invention, be partly filled in the feed section (E) and in the devolatilization section (G). This makes it possible firstly to add directly into the second extruder additives which can be used to adjust the processing and product properties of the
aminoplastics and secondly to carry out, in the second extruder, a devolatilization of the melt, which would not be possible in a completely filled extruder because of the resultant discharge of solids.
The first extruder is preferably operated in a range of rotation rates of from about 12 to 20 rotations per minute, and the second extruder preferably at from 20 to 300 rotations per minute, particularly preferably from 80 to 150 rotations per minute.
The temperature of the second extruder can be controlled section by section via temperature sensors (TIC), the settings being advantageously from 30 to 170°C, preferably from 80 to 120°C.
At the end of the second extruder, acid catalysts are added which bring about the subsequent curing of the products.
Attached to the second extruder there is equipment which hrings about the forming of the end product in a suitable manner:
In a first version, the fully formulated molding composition devolatilized in the second extruder may be extruded via a multi-strand die, pelletized, given a final drying and cooled. The pellets have properties similar to those of commercially available molding compositions and may be further processed, for example by injection molding.
In a second version, a sheet die may be used at the end of the extruder, and through this the raw molding composition may be shaped to give continuous sheet. The process parameters here are adjusted so that the sheet has sufficient dimensional stability but is not yet fully cured. The resultant sheet is then calibrated and cooled. This gives a salable product
which is a semifinished product capable of further processing and which may be reshaped in heatable presses to give the desired cured finished part.
In a third version, the continuous sheet is calibrated and completely cured at from 130 to 190°C, by attaching a heatable belt press downstream of the sheet die. The fully cured molding can be used in various application sectors, in particular in the electrical, building and motor vehicle sectors.
The invention is further illustrated below using the drawing and a working example.
In a first extruder 14, a precondensate solution is prepared in a manner known from EP-B 0 355 760, following the formulation given in Table 1.
Table 1: Formulation of precondensate solution
In this process, melamine from the storage vessel 3 and paraformaldehyde from the storage vessel 1 are fed via continuous weigh feeders 5 and 6 to the mixer 11. Liquid formaldehyde solution from the stirred storage vessel 2, diethylethanolamine from the vessel 9 and aqueous 5-hydroxy-3-
oxapentylmelamine mixture from the vessel 4 are also fed to the mixer 11 via metering pumps 7, 8 and 10. The suspension is devolatilized in a vessel 12 and, via a pump 13, metered into a first heatable continuous extruder 14. Following this, the solid constituents are dissolved and the resin-like precondensate 16 is produced. The precondensate is formed as a highly viscous aqueous solution of about 80% strength.
The precondensate 16 is fed, either directly or via a metering pump 15, to a second extruder 20. Dry-mixed additives from the storage vessel 17 are also fed to the second extruder 20 via a gravimetric metering system 18. Possible additives are those which alter the processing and/or product properties, for example fibrous or pulverulent inorganic reinforcing agents or fillers, such as glass fibers, metal powders, metal salts or silicates, biological reinforcing agents or fillers, such as cellulosic fibers, pulp or wood flour, elasticizers, such as acrylates, rubber, polyglycols, diols, sorbitol, sugars, pigments, UV stabilizers, reaction inhibitors, such as amines, lubricants, buffers or non-stick agents.
Table 2 gives an example of a molding composition formulation with cellulose as filler, diethylene glycol as modifier, in particular for improving crack resistance, a stearate mixture as lubricant, sodium carbonate as buffer and diallyl phthalate as non-stick agent.
The temperature in the second extruder 20 is preferably controlled via temperature sensors (TIC), the settings being advantageously from 30 to 170°C, preferably from 80 to 120°C.
In the second extruder 20, the reaction mixture is devolatilized via a vacuum pump, making it possible to adjust the residual moisture of the molding composition, preferably in a range of from 8 to 15%. The sheet die 21 at the end of the second extruder 20 continuously shapes the molding composition to give raw sheet, which cures in a positive mold at 140°C within from 0.5 to 10 minutes, preferably within from 1 to 3 minutes.
The shaped and cured sheets were tested for flexural strength and impact strength. For comparison, a commercially available melamine-formaldehyde molding composition MF 152 from Raschig is cured within 5 minutes in a positive mold at 140°C and its mechanical properties determined. The material quality standardized in DIN 7708-152 N was achieved.
1. A process for preparing aminoplastics and/or phenolics, in which a precondensate solution is prepared in a first extruder , by continuously feeding the precondensate solution (16), with addition of additives, to a second extruder (20) with partial filling in the feed section (E) and devolatization section (G), devolatizing the precondensate solution in the second extruder (20) and then forming it to give an end product.
2. The process as claimed in claim 1, wherein the first extruder is operated in a range of rotation rates of from 12 to 20 min"1 and the second extruder in a range of rotation rates from 20 to 300 min-1, preferably from 80 to ISO min-1.
3. The process as claimed in claim 1 or 2, wherein the second extruder (20) is heated, in particular at from 30 to 170°C, preferably at from 80 to I20°C.
4. The process as claimed in any one of claims 1 to 3, wherein the residual moisture is adjusted in the second extruder to from of 8 to 15% by weight of water.
5. The process as claimed in any one of claims 1 to 4, wherein the end product is a molding composition.
6. The process as claimed in any one of claims 1 to 4, wherein the end product is a semifinished product capable of further shaping.
7. The process as claimed in any one of claims 1 to 4, wherein the end product is a finished part.
8. A process for preparing aminoplastics and/or phenolics, substantially as herein described and exemplified with reference to the accompanying drawings.
|Indian Patent Application Number||1726/MAS/1998|
|PG Journal Number||30/2009|
|Date of Filing||31-Jul-1998|
|Name of Patentee||BASF AKTIENGESELLSCHAFT|
|Applicant Address||67056 LUDWIGSHAFEN|
|PCT International Classification Number||B29C47/50|
|PCT International Application Number||N/A|
|PCT International Filing date|