DE2919629A1 - Thermoplastic polyester polycarbonate block copolymer prepn. - by heating melt mixt. below polyester m.pt. in oxygen-free atmos. - Google Patents

Abstract

Thermoplastic polyester/polycarbonate block copolymers are prepd. by mixing polyesters and polycarbonates in the melt and heating the mixt. between 180 degrees C. and a temp. which is >=5 degrees C. below the polyester melting temp., for 5-50 hrs., under O2-exclusion. Heat treatment of melt mixt. bonds the polycarbonate to the polyester and prevents its extn. by solvents, e.g. the extn. of a flame-retarding brominated polycarbonate with chlorinated solvents.

Description

Process for the production of thermoplastic polyester /

Polycarbonate block copolymers, polymer blends of polyesters, preferably Polybutylene terephthalate, and polycarbonates, especially those based on Bisphenol A and tetrabromobisphenol A are known.

Their production and properties are described, for example in DE-OS 24 14 849, 24 17 002, 27 08 381, 27 31 141, 27 50 733 and 27 51 969.

A disadvantage of these polymer blends is their poor resistance to stress corrosion cracking. It is particularly important that the advantage of the good solvent resistance of the Polyester is lost through mixing with the polycarbonates.

This disadvantage is overcome when the polycarbonate is converted into the polyester is incorporated by chemical bonds.

So when you make polyester / polycarbonate block copolymers. In the DE-OS 26 36 783 is a process for the production of such block copolymers, preferably based on aliphatic polyesters. There are finished polyester blocks reacted with a bisphenol and phosgene in an interfacial condensation.

this process is technically relatively complex, and you must subsequently remove solvent residues from the reaction products and prepare them.

The invention was therefore based on the object of a simple method for the production of polyester / polycarbonate block copolymers.

This object is achieved by using polyester and polycarbonate mixed with one another in the melt and the mixture then subjected to a heat treatment subject.

The invention therefore relates to a method for production of thermoplastic polyester / polycarbonate block copolymers by blending of polyesters and polycarbonates in the melt and subsequent heat treatment the mixture between 1800C and a temperature that is at least 50C below the The melting temperature of the polyester is at a residence time between 5 and 50 Hours, with exclusion of oxygen.

To characterize the polyesters and polycarbonates used is the relative solution viscosity, measured as a 0.5 weight percent solution in a mixture of phenol and ortho-dichlorobenzene in a weight ratio of 3: 2 at 25 cm used. The relative viscosity of the polyester should preferably be 1.2 to 1.7, that of the polycarbonates are 1.05 to 1.6.

Preferred polyesters are polyalkylene terephthalates with crystallite melting points above 2000C, for example polybutylene terephthalate, polyethylene terephthalate, Polypropylene terephthalate, polyethylene naphthalate-1,6. It can also be segmented Copolyether esters are used, preferably those based on polybutylene terephthalate hard segments and polytetrahydrofurna soft polytetrahydrofurna I soft segments.

Suitable polycarbonates are preferably those based on aromatic Alcohols, for example based on bisphenol A, tetrabromobisphenol A or their Mixtures in a molar ratio between 1: 99 and 99: 1. If brominated polycarbonates are used, then one obtains flame-retardant molding compositions. Since doing the flame retardant is chemically bonded to the polyester, chlorinated solvents cannot do it extracted more as it would otherwise.

The weight ratio of the polyester component to the polycarbonate component can be varied within wide limits between 20:80 and 99: 1. With high proportions Polycarbonate must be checked for sticking at temperatures above 1800C of the granulate occurs. If so, such a mixture cannot are subjected to the method according to the invention In the method according to the invention the mixture of polyester and polycarbonate can also contain the usual additives or others Polymers are added. Usual stabilizers, nucleating agents, Plasticizers, color pigments, lubricants and mold release agents or flame retardants be used. If brominated poly carbonates are used, the mixture contains expediently 1 to 10 percent by weight, based on the total mixture, of one Flame retardant synergists, preferably antimony trioxide.

Up to a weight fraction of 30%, other polymers, such as polyolefins, polyamides, polysulfones, styrene copolymers or rubbers on the Base of polyacrylates or polybutadiene can be added. By mixing in 5 to 60 percent by weight, based on the total mixture, of reinforced active fillers, such as glass fibers, glass spheres or mineral fillers, the strength of the molding compounds can be increased.

The components can be mixed on conventional mixing units, E.g. extruding, kneading or rolling advantageously at temperatures between 230 and 30000 can be made.

In the preferred blend from the extruder,} the obtained homogeneous melt cooled in a water bath and the polymer mixture granulated. The polymer mixture is then with a residence time of 5 to 50, preferably Subjected to heat treatment for 10 to 40 hours, the temperature at least 5 ° C., preferably more than 10 ° C. below the melting temperature of the polyester and is at least 1800C; The melting temperature of the polyester is that To understand the temperature when the polyester is melted in the differential scanning calorimeter (DSC) the maximum of the endothermic peak at a heating rate of 20 C / min. is equivalent to. The temperature treatment can be carried out either under reduced pressure as well as under normal pressure, preferably in a nitrogen or other inert gas atmosphere. It must only be ensured that the presence of oxygen is excluded is. Tumble dryers are suitable for carrying out the method according to the invention, Rotary tube dryer or shaft dryer.

The parts and percentages given in the examples relate to the weight.

Examples of polyesters and polycarbonates were made at the temperatures indicated mixed in a twin screw extruder and then for 36 hours in a nitrogen atmosphere one Tumble dryer treated. Before and after this heat treatment, granulate samples were made Extracted for 24 hours with boiling chloroform and the extracted polycarbonates precipitated by pouring into methanol. The proportion of non-extractable polycarbonate is a measure of the formation of the block copolymers.

Example 1 A mixture of 75% polybutylene terephthalate produced at 2500 C with a relative viscosity of 1.45 and 25% bisphenol A polycarbonate with a relative viscosity of 1.37 was treated at 210C.

From the heat treatment, 22.5% polycarbonate was extractable. the relative viscosity of the mixture was 1.43.

After the treatment, only 0.7% poly carbonate could be extracted. The relative viscosity had increased to 1.64. ' Example 2 One made at 2500C Mixture of 60% polybutylene terephthalate with a relative viscosity of 1.40 and 40% bisphenol A polycarbonate having a relative viscosity of 1.37 treated at 21000.

Before the heat treatment, 35% polycarbonate was extractable. Thereafter O%. The relative viscosity had increased from 1.34 to 1.56.

Example 3 A mixture of 50% polyethylene terephthalate produced at 2700C the relative viscosity of 1.36 and 50% Bisphenol A poly carbonate the relative viscosity of 1.37 was treated at 2400C.

Before the heat treatment, 47% polycarbonate was extractable, afterwards 1 %. The relative viscosity had increased from 1.32 to 1.55.

Example 4 At 2500C a mixture of 74% polybutylene terephthalate was made the relative viscosity 1.45, 20% polycarbonate based on tetrabromobisphenol A with a relative viscosity of 1.1 and 6% antimony trioxide.

The granules obtained were treated at 210.degree.

Before the treatment, the tetrabromobisphenol A polycarbonate was allowed to 95% are extracted, then not at all. The relative viscosity was increased from 1.28 to 1.59. In the fire test, the molding compound obtained corresponded Underwriter's Laboratories standard UL 94-VO.

Claims (7)

Claims Process for the production of thermoplastic polycarbonate block copolymers by mixing polyesters and poly carbonates in the melt and then Heat treatment of the mixture, characterized in that the heat treatment between 1800C and a temperature that is at least 5 0C below the melting temperature of the polyester is, with a Vertgeilzeit between 5 and 50 hours, in the absence of oxygen is carried out. 2. The method according to claim 1, characterized in that the relative Viscosity, measured as a 0.5 weight percent solution in a mixture of phenol / ortho - dichlorobenzene in a weight ratio of 3: 2 at 250C, the polyester 1.2 to 1.7 and the poly carbonate Is 1.05 to 1.6. 3. The method according to claim 1, characterized in that as Polyester polyalkylene terephthalate and, as polycarbonate, aromatic polycarbonates begins. 4. The method according to claim 1, characterized in that as Polyester polybutylene terephthalate is used. 5. The method according to claim 1, characterized in that one Polycarbonate based on bisphenol A is used. 6. The method according to claim 1, characterized in that one is a Polycarbonate based on tetrabromium bisphenol A or one Mixture of bisphenol A with tetrabromobisphenol A is used. 7. The method according to claim 1, characterized in that the weight ratio the polyester component to the polycarbonate component is 20:80 to 99: 1.