CH661736A5 - MOLDING MATERIALS BASED ON THERMOPLASTIC, SATURATED HOMO OR MIXED POLYESTERS WITH REDUCED PROPERTY. - Google Patents

Description

The present invention relates to molding compositions based on thermoplastic, saturated polyesters, which have a reduced inherent adhesion and thus have decisive advantages with regard to handling during their manufacture and processing.

It is known that polymers have a more or less pronounced tendency towards self-adhesion above their glass transition point. This means the property of the particles of the molding compositions, in particular granules or powder, to adhere to one another. It increases with increasing temperature and can lead to the formation of clumps if this is not prevented by suitable measures.

Self-adhesion is directly related to the softening behavior of the polymers. If a polymer softens, this results in tacking, i.e. an adherence that increases with increasing temperature. Accordingly, the greater the difference between the glass transition temperature and the respective product temperature, the more pronounced is the self-adhesion and thus the tendency to clump together, for example the granules or the powder.

The extent of self-adhesion is also very significantly influenced by the degree of crystallinity of the polymer. While in the case of polymers in the amorphous state, tacking can be detected even at temperatures above the glass transition point, the corresponding temperatures are significantly higher in crystallized polymers. 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 polymeric molding materials, it is often advantageous, sometimes even inevitable, to handle them at temperatures above their glass transition point. A clumping together or a lump formation of the particles of the molding compound due to self-adhesion would have a disadvantageous effect on handling. For example, the drying of polymers is often carried out at temperatures above the glass transition point in order to achieve the required moisture levels with economically justifiable drying times. In the case of molding compositions whose glass transition point is in the region of room temperature or below, storage can lead to undesirable lump formation, especially in countries with a hot climate, where storage at temperatures of 40 ° C. and above is quite common.

Various measures are known in order to reduce the tendency of self-adhesion and thus the formation of lumps and the resulting difficulties in handling the molding compositions. For example, the fact that self-adhesion decreases with increasing degree of crystallinity is used in the case of crystallizable molding compositions. The degree of crystallinity of the molding compositions is increased by tempering, the process being carried out according to a specific temperature program, according to which the temperature is increased as a function of time to the extent permitted by the decreasing self-adhesion due to the increasing degree of crystallinity. In the case of mixed polymers, this tempering can be very time-consuming, since they have a significantly lower crystallization rate and a lower maximum achievable degree of crystallization than the corresponding homopolymers, and the temperature may only be raised very slowly during the tempering process, without the formation of lumps.

Another possibility for reducing the self-adhesion is to add a substance that acts as a release agent to the molding compound. For this purpose, the release agent is superficially applied to the molding compound in the form of granules, powder and the like in a separate working step. However, these release agents have the disadvantage that they lose their effect when the molding composition is melted and the release agents are thus mixed into the molding composition. If the release agents cannot be mixed homogeneously with the polymeric molding compound, the properties of the molding compound can be influenced in an undesirable manner.

The properties and relationships generally described here for polymeric molding compositions also apply fully to molding compositions based on thermoplastic, saturated polyesters in particular.

The aim of the invention was to reduce the inherent adhesion of molding compositions based on polyester by means of a suitable measure without the disadvantages described above.

The present invention relates to molding compositions based on thermoplastic, saturated polyesters, the inherent adhesion of which is significantly reduced, characterized in that 0.005 to 5% by weight, based on the polymer, of a hydrophilic silicone compound is added.

Suitable polyesters for the purposes of the present invention are all thermoplastic, saturated homopolyesters and mixed polyesters, as are produced in a known manner from dicarboxylic acids, diols, diphenols, hydroxycarboxylic acids or their ester-forming derivatives, optionally with the addition of small amounts of more than two-phase acids or alcohols can be. The molding compositions according to the invention can contain additives, such as stabilizers, plasticizers, pigments, optical brighteners, reinforcing agents and fillers.

Surfactants based on silicone are preferably used as the hydrophilic silicone compounds according to the present invention. These are mainly silicone-polyalkylene oxide copolymers, with a basic distinction being made between the hydrolyzable (according to formula 1) and the non-hydrolyzable silicone surfactants (according to formula 2):

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661 736

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(CnK2n0) zR

R represents H or an alkyl group, R 'represents an alkyl group. The polyalkylene oxide group - (CnH2nO) z- can consist of polyethylene oxide or a block polymer of blocks of polyethylene oxide and polypropylene oxide.

Products of this type are commercially available, typical 15 representatives include Silwet L-720 and Silwet L-7500 from Union Carbide Corp., Danbury, Baysilon OF / OH-OR 603 from Bayer AG, Leverkusen, and silicone oil L 050 from Wacker Chemie GmbH, Munich.

The hydrophilic silicone compound can be added to the 20 polyesters during or after their preparation. They can thus either be added to the polyester in the molten state by addition before, during or after the polycondensation, or they can be applied superficially to the polyester present in solid form, preferably in granular or powder form.

The hydrophilic silicone compounds are added in amounts between 0.005 and 5% by weight, preferably between 0.05 and 2% by weight, based on the polymer. The optimal amounts depend on the type of addition.

If the hydrophilic silicone compound is admixed to the polyester in the molten state, the best results are obtained with amounts between 0.5 and 2% by weight, with surface application to the polyester in solid form, amounts are between 0.05 and 0.5% by weight .-% advantageous.

The examples listed below explain the present invention in more detail, but without restricting it in any way.

4 "

example 1

In a reactor equipped with a stirrer,

Column, condenser and receiver are 194 parts by weight of dimethyl terephthalate, 130 parts by weight of ethylene glycol and 0.15 parts by weight of calcium acetate are dissolved while heating and then with methanol being distilled off at temperatures between 195 and transesterified the dimethyl terephthalate at 235 ° C. After the transesterification has ended, 41.5 parts by weight of isophthalic acid are added to the reaction mixture and esterified at a temperature of about 240 ° C. while distilling off water. The resulting prepolymer is transferred to a polycondensation reactor and 0.075 part by weight of antimony trioxide, 0.025 part by weight of phosphoric acid and 1.5 parts by weight of the silicone surfactant Silwet L-7500 from Union Carbide Corp. added. The temperature is then raised to 280 ° C. and the excess glycol is distilled off while applying a vacuum. After the final vacuum of about 1 mbar has been reached, polycondensation is carried out until the desired degree of polycondensation, corresponding to a solution viscosity of 1.61 (measured as a 1% solution in m-cresol at 20 ° C.), is reached.

The polymeric polyester is discharged in strand form from the autoclave, solidified by passing it through a water bath and granulated. For drying, the granules are conveyed in a tumble dryer at room temperature. After applying a vacuum of 10 mbar, the tumble dryer is heated to 140 ° C within two hours. After a further six hours of drying, the desired moisture content is 0.005% H2O

reached. When the granules are discharged from the tumble dryer after drying has ended, no aggregation of the granules or granules adhering to the wall of the dryer can be determined.

Example 1A (comparative example)

A polyester granulate according to Example 1 is produced with the difference that no silicone compound is added. The granulate is conveyed in a tumble dryer and, after applying a vacuum of 10 mbar, the temperature is increased to 110 CC in a first step. The granules are tempered for four hours at this temperature. This tempering is necessary in order to avoid sticking of the granules to one another or to the wall of the dryer. The temperature is then raised to 140 ~ C and dried again for six hours until a moisture content of 0.005 ° 0 H: 0 is reached.

The comparison of the procedure in Examples 1 and 1A clearly shows that the addition of the silicone compound according to the invention and the resultant reduced inherent adhesion of polyesters enables a faster and therefore more efficient procedure when drying these granules.

Example 2

In a stirred autoclave, 83 parts by weight of terephthalic acid, 83 parts by weight of isophthalic acid, 135 parts by weight of 1,4-butiol and 0.2 part by weight of titanium tetrabutylate at 200 to 240 ° C under Passing through nitrogen esterified and the resulting esterification product then polycondensed at 250 CC and a vacuum of about 1 mbar. The polyester is discharged in strand form from the autoclave, solidified by passing it through a water bath and then granulated. The polyester has a solution viscosity (measured as a 1% solution in m-cresol at 20 ° C.) of 1.65, a DSC melting point of 127 CC and a glass transition point of 24 CC.

100 parts by weight of the granules freed from adhesive water are mixed with 0.1 parts by weight of silicone oil L 050 from Wacker-Chemie and then ground in a pin mill with simultaneous cooling with liquid nitrogen. The fraction with a grain diameter between 80 and 200 µm is sieved from the raw material and mixed with 0.1% by weight Mg stearate. A sample of the powder obtained in this way is stored for three days at 40 ° C. and then the formation of lumps is assessed 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 mixed with a hydrophilic silicone compound before grinding.

Table 1

Example No.

additive

Lump formation *

2nd

0.1% by weight silicone oil

0-1

L 050

2A

-

2nd

* Assessment of lump formation

0 no clumping

1 slight lump formation, lumps can be easily crushed by hand

2 medium lump formation, lumps can only be crushed by hand under strong pressure

3 strong lumps, lumps can no longer be crushed by hand c;

Claims (5)

661 736 1. Molding compositions based on thermoplastic, saturated homo- or mixed polyesters with reduced self-adhesion, characterized in that they contain hydrophilic silicone compounds. 2. Molding compositions according to claim 1, characterized in that the hydrophilic silicone compound is contained in an amount of 0.005 to 5 wt .-%, based on the polymer. 2nd PATENT CLAIMS 3. Molding compositions according to claim 1, characterized in that they contain silicone-based surfactants as the hydrophilic silicone compound. 4. A process for the preparation of molding compositions according to claim 1, characterized in that the hydrophilic silicone compound is mixed with the polyester by adding before / during or after the polycondensation. 5. A process for the production of molding compositions according to claim 1, characterized in that the hydrophilic silicone compound is applied to the polyester in granular or powder form.