DE3543754A1 - Moulding compositions based on polyamides of reduced inherent adhesion - Google Patents

Abstract

Moulding compositions based on polyamides, i.e. homopolyamides or copolyamides, having greatly reduced inherent adhesion, i.e. without the property of particles of the moulding compositions, in particular granules or powders, adhering to one another or forming clumps at elevated temperature, containing hydrophilic silicone compounds which are homogeneously miscible with the polyamides, added before, during or after the polymerisation in the melt-liquid state in amounts of from 0.005 to 5.00 % by weight.

Description

The present invention relates to molding compositions on the basis

of polyamides, which have a reduced inherent adhesion and thus crucial in terms of handling during their manufacture and processing Have advantages.

It is known that polymers are above their glass transition point have a more or less pronounced tendency to self-liability. This means one the property of the particles of the molding compositions, in particular the granules or Powder to adhere to each other. It increases with increasing temperature and can be up to lead to the formation of lumps if this is not prevented by suitable measures will.

The self-liability is directly related to the softening behavior of the polymers. If a polymer softens, it results in tacking, i.e. a Adhesion that increases with increasing temperature. The bigger the difference is between the glass transition temperature and the respective product temperature, the more pronounced is the self-liability and thus the tendency to clump together, for example granules or powder.

The extent of personal liability is also very important Degree of crystallinity of the polymer influenced. While at Polymers in the amorphous state already at temperatures above the glass transition point If tacking can be detected, the corresponding temperatures are crystallized Polmyeren clearly higher. In the case of polymers with a very high degree of crystallization self-adhesion is only observed at the beginning of the melting range.

In the production and processing of polymer molding compounds it is often an advantage, sometimes even unavoidable, to do this at temperatures above to handle their glass transition point.

The particles of the molding compound agglomerate or form clumps as a result of personal liability, this would have an adverse effect on handling. So will for example the drying of polymers often at temperatures above the glass transition point carried out to meet the required drying times with economically justifiable drying times To achieve moisture levels. In the case of molding compounds whose glass transition point is Room temperature or below can already lead to storage becoming a cause unwanted clumping, especially in hot climates, where storage at temperatures of 400C and above is quite common.

About the tendency to self-adhesion and thus to lump formation and the to reduce the resulting difficulties in handling the molding compounds, are different measures known. So is the case of crystallizable Molding compounds, for example, used the already mentioned fact that the inherent adhesion decreases with increasing degree of crystallinity. The degree of crystallinity of the molding compounds is increased by tempering, proceeding according to a specific temperature program is, accordingly, the temperature is raised as a function of time to the extent becomes, as is the decreasing inherent adhesion due to the increasing degree of crystallinity allows. In the case of copolymers, this tempering can be very time-consuming because it a significantly lower crystallization rate and a lower one have the maximum achievable degree of crystallization than the corresponding homopolymers and the temperature may only be raised very slowly during tempering, without clumping.

Another way to reduce personal liability is to to add a substance that acts as a release agent to the molding compound. In addition is applied to the molding compound present in the form of granules, powder and the like The release agent is applied to the surface in a separate work step. These Release agents, however, have the disadvantage that they lose their effect when the molding compound melted and the release agent thus mixed into the molding compound will. If the release agents cannot be mixed homogeneously with the polymer molding compound, the properties of the molding compound can be influenced in an undesirable manner.

The properties described here in general for polymeric molding compounds and relationships also apply in full to molding compounds based on Polyamides in particular.

The object of the invention was to reduce personal liability by means of a suitable measure of molding compositions based on polyamide without reducing the disadvantages described above.

This object is achieved by molding compositions according to claim 1.

The present invention therefore relates to molding compositions on the basis of polyamides, the inherent adhesion of which is and still exists to a decisive extent in that they are preferably 0.005 to 5% by weight, based on the polymer, of a hydrophilic Contains silicone compound.

All homopolyamides can be used as polyamides in the context of the present invention and mixed polyamides in question, as they are in a known manner from aminocarboxylic acids or, since this is possible, the corresponding lactams and / or diamines and dicarboxylic acids or their salts can be produced. The molding compositions according to the invention can Additives such as stabilizers, plasticizers, pigments, optical brighteners, reinforcing agents and fillers.

As the hydrophilic silicone compounds according to the present invention, silicone-based surfactants are preferably used. These are mainly silicone polyalkylene oxide copolymers, a basic distinction being made between hydrolyzable (according to formula 1) and non-hydrolyzable silicone surfactants (according to formula 2): R stands for H or an alkyl group and R 'for an alkyl group, preferably each having 1 to 6 carbon atoms, m and n are preferably integers between 1 and 4 or 2 or 3.

The polyalkylene oxide group - (CnH2nO) -z can be made of polyethylene oxide or a block polymer made of polyethylene oxide and polypropylene oxide blocks.

Products of this type are commercially available, typical representatives include Silwet L720 and Silwet L-7500 from Union Carbide Corp., Danbury, Baysilon OF / OH-OR 603 from Bayer AG, Leverkusen and silicone oil L 050 from the company Wacker Chemie GmbH, Munich.

The addition of the hydrophilic silicone compounds to the polyamides can take place during or after their manufacture. You can either add before, during or after the polymerisation of the polyamide in the molten state be mixed in, or they can be added to the in solid form, preferably in granules or powder form, the present polyamide can be applied to the surface.

The hydrophilic silicone compounds are preferably used in lengths between 0.005 and 5% by weight, in particular between 0.05 and 2% by weight, based on the polymer, were added. The optimal amounts depend on the type of addition. Will the hydrophilic A silicone compound mixed with the polyamide in the molten state is obtained the best results with amounts between 0.5 and 2 wt.%, with superficial application on the polyamide in solid form, amounts between 0.05 and 0.5% by weight are advantageous.

The examples given below illustrate the present invention closer, but without restricting them in any way.

EXAMPLE 1: 40 parts by weight of laurolactam, 50 wt.

Parts of caprolactam, 2 parts by weight of water and 0.5 part by weight of adipic acid filled and after displacing the air with nitrogen with the autoclave closed Heated to 2900C for 5 hours. The pressure is reduced to a maximum as a result of any relaxation 20 bar held. The pressure is then reduced by releasing the pressure within an hour Autoclave at atmospheric pressure and at the same time the temperature of the reaction mixture lowered to 2600C. There are 0.8 parts by weight of the silicone surfactant Silwet L-7500 der Union Carbide Corp. added and the polymerization by passing over Nitrogen continued. After 8 hours, the desired degree of polymerization is accordingly a solution viscosity of 1.83 (measured as a 0.5% solution in m-cresol at 20 "C), * The polymer is discharged from the autoclave in strand form Solidified and granulated by passing through a water bath.

The granulate is fed into a silo and stored there for 24 hours. The granulate temperature drops from initially 350C to 30 "C during storage. The granulate is then placed in a tumble dryer, the heating medium of which is at room temperature had been cooled, introduced with no difficulty due to clumping of the granules occur. After applying a vacuum of 20 Torr, the tumble dryer is used heated up. After about an hour the heating medium reaches a Temperature of 900C, after about 2 hours the product temperature reaches about 86 ° C. After a further 6 hours of drying time, the desired moisture content is of the granulate reached 0.02% H2O. When draining the granulate from the tumble dryer After the drying process, there are no agglomerations of the granules or of them Granules adhering to the wall of the dryer can be determined.

Example 1A (comparative example): A polyamide granulate according to Example 1 produced with the difference that no silicone compound was added will.

As in example 1, the granulate is fed into a silo however, they can be cooled by passing air through them at around 150C to prevent clumping to avoid. After 24 hours of storage, the granules are as in Example 1. one Tumble dryer fed and dried. To stick together the granules or to avoid on the wall of the dryer, the temperature of the heating medium gradually increased, initially to 45 "C, after one hour to 650C and after one another hour at 850C. The product temperature reaches after a further hour 82 "C. To get the required moisture content of the granulate of 0.02% H2O, an additional drying time of 8 hours is necessary.

The comparison of the procedure in Examples 1 and 1A shows clear that by adding the silicone compounds according to the invention and the The resulting anti-pigmentation of polyamides allows for easier storage especially of not yet tempered and thus crystallized granules as well as a faster and thus more efficient mode of operation when drying these granulates ^ was possible is.

Example 2: 40 parts by weight of caprolactam, 20 parts by weight of AH salt, 16 parts by weight of hexamethylenediamine, 14 parts by weight.

Parts of azelaic acid, 15 parts by weight of dodecanedioic acid and 3 parts by weight.

Divide the water into the water and after displacing the air, divide it for an hour 2600C heated. The pressure in the autoclave is kept at a maximum of 20 bar. Thereafter the pressure in the autoclave is reduced to atmospheric pressure within an hour and the polymerization by passing nitrogen over it to a degree of polymerization continued corresponding to a solution viscosity of 1.55. The polymer becomes off the autoclave, as described in Example 1, discharged, granulated and dried.

100 parts by weight of the granules obtained in this way are mixed with 0.1 parts by weight of the silicone oil L 050 from Wacker-Chemie and then mixed in one Pin mill under simultaneous Cooling with liquid nitrogen ground. The fraction with a grain diameter between 80 and 200 µm as sieved and mixed with 0.1 wt.% Mg stearate. A sample of the so The powder obtained is stored at 40 ° C. for three days, followed by the formation of lumps judged. The result is shown in Table 1.

Example 2A (comparative example): The procedure is as in Example 2, with the difference that the granules are not hydrophilic before grinding Silicone compound is added.

Table 1: Example of the addition of lump formation * No. 2 0.1% by weight silicone oil L 050 0 2A | 2 * Assessment of lump formation O = no lump formation 1 = slight lump formation, lumps can be easily crushed by hand 2 = medium lump formation, lumps can only be crushed by hand under strong: -no pressure 3 = strong lump formation, lumps can no longer be crushed by hand crush

Claims (5)

Molding compounds based on polyamides with reduced inherent adhesion Claims 1. Molding compositions based on polyamides with greatly reduced Self-adhesive, characterized in that they contain hydrophilic silicone compounds. 2. Molding compositions according to claim 1, characterized in that the hydrophilic Silicone compound in an amount of 0.005 to 5% by weight, based on the polyamide, is present. 3. Molding compositions according to claim 1, characterized in that the hydrophilic Silicone compound to the polyamide by adding before, during or after the polymerization has been added. 4. Molding compositions according to claim 1, characterized in that the hydrophilic Silicone compound applied to the polyamide present in granulate or powder form has been. 5. Molding compositions according to claim 1, characterized in that the hydrophilic Silicone compounds consist of silicone-based surfactants.