IE903578A1 - Rapidly crystallizing polyester molding materials - Google Patents

Abstract

Thermoplastic moulding composition essentially consisting of, in each case, at least one (A) polyalkylene terephthalate having a reduced specific viscosity (measured in 1% strength solution in dichloroacetic acid at 25 DEG C) of at least 0.3 dl/g, (B) nucleating agent, (C) crystallisation accelerators and (D) optionally reinforcing agents and other conventional additives, in which (C) is at least one N,N'-disubstituted asymmetric oxalic acid bisamide. When mouldings produced from the moulding composition are heated, the use of such components (C) leads to only slight migration and sublimation, so that satisfactory surface characteristics result. The nucleating agents and accelerators used in the moulding composition ensure that the mould temperature can be reduced to at least 100 to 110 DEG C.

Description

Description Rapidly crystallizing polyester molding materials The invention relates to a thermoplastic molding material consisting of a polyalkylene terephthalate, preferably polyethylene terephthalate (PET), an Ν,Ν'-disubstituted asymmetrical oxalic acid bisamide as plasticizer and a nucleating agent, and, if required, at least one filler or reinforcing agent and further conventional additives.

Polyalkylene terephthalates are of considerable importance as raw materials for the production of fibers, films and moldings. Because of their partly crystalline structure and their relative heat resistance, they are particularly suitable for the production of shaped articles subjected to high mechanical stress and high temperatures . An additional improvement in the mechanical properties can be achieved by incorporating reinforcing materials, such as, for example, glass fibers.

Pure polyethylene terephthalate, as used for the production of fibers and films, is suitable only to a limited extent for the production of moldings by injection molding, since its crystallization properties necessitate mold temperatures of about 140C and relatively long compression times. Attempts have therefore been made, by means of suitable additives, to increase the crystallization rate in such a manner, and to lower the crystallization temperature of the PET to such an extent, that it is possible to use water-heated molds and the cycle times are sufficiently short for practical purposes. In general, the crystallization of the PET begins during the cooling of the melt in the injection mold at as high a temperature as possible and continues during cooling to as low a temperature as possible. The recrystallization temperature TH is the temperature at which the crystallization from the melt begins on cooling. The crystallization temperature Tc denotes the temperature up to which substantial crystallization of the polyester takes place. Both crystallization temperatures can be measured with the aid of a differential scanning calorimeter (DSC).

There are many known additives which can influence the crystallization properties of linear saturated polyesters and in particular of PET. An important class consists of the nucleating agents, which includes many compounds (D. Garcia, J. Polym. Sci., Pol. Phys. Ed., 22, (1984), 2063). Preferably used nucleating agents for PET are sodium salts or potassium salts of organic carboxylic acids, and these carboxylic acids may be low molecular weight or high molecular weight ones (DE-B 29 07 729).

Another important class of additives consists of low molecular weight organic compounds, which are referred to as plasticizers and essentially have an effect on the crystallization temperature Tc and on the glass transition temperature TG of the polymer. Known compounds of this type are those which, in combination with a nucleating agent, result in a lowering of the crystallization temperature Tc in the case of PET (DE-B 29 07 729).

Furthermore, sulfonic esters and imide compounds have been described as additives for rapidly crystallizing polyester materials (DE-B 26 39 428, EP-B 0 214 112 and 0 247 427) .

These organic compounds are said to meet several criteria as additives in slowly crystallizing molding materials, for example in the case of PET, and they must be sufficiently soluble in PET and at the same time lower the crystallization temperature or increase the crystallization rate. Furthermore, during incorporation or processing, they must not undergo any interactions with the polyester in the melt which lead to degradation of the polyester. In addition, they should show as little tendency as possible to migrate in the polyester, so that, when the molding is heated, they do not substantially migrate to its surface and sublime. Sublimation, in particular of the low molecular weight organic com5 pounds, can lead to the formation of deposits on colder parts of the surroundings and have, for example, undesirable surface effects there, including those relating to conductivity and corrosion.

If ester compounds are used as crystallization-accelerat10 ing additives (DE-B 29 07 779 and EP-A 0 257 331), they may lead to interactions with the polyester in the melt during relatively long residence times, i.e. the viscosity of the polyester then decreases as a result of transesterification processes. Sulfonamide compounds (EP-B 0 096 947), which are likewise effective additives, are more resistant in the polyester melt but still exhibit substantial volatility when the polyester is heated. When higher molecular weight or oligomeric compounds are used as plasticizers and crystallization accelerators, they are not as effective because they act in the form of molecules and a much larger amount by weight has to be used for a comparable molar concentration. This may then in turn have an adverse effect on the mechanical properties of the moldings.

It is the object of the present invention to provide a rapidly crystallizing polyester molding material which is based on polyethylene terephthalate and contains a crystallization accelerator which exhibits as little migration and sublimation as possible.

The thermoplastic molding material according to the invention consists substantially of, in each case, at least one (A) polyalkylene terephthalate having a reduced specific viscosity (measured in 1% strength solution in dichloroacetic acid at 25 °C) of at least 0.3 dl/g, (B) nucleating agent, (C) crystallization accelerator, and (D) if required, reinforcing agents and other conventional additives, wherein (C) is at least one Ν,Ν'-disubstituted asymmetric oxalic acid bisamide of the formula (i: x-Ό· nh-co-co-nh-r2 (II) RA-<0)n NH- CO- CO- NH- R3 - NH- CO- CO- NHR -<0)n (III) R2-NH-CO-CO or -NB-^^-X -CO-CO-NH-1 in which R1 is a hydrocarbon radical having 1 to 4 C atoms, R2 is an aliphatic hydrocarbon radical having 10 to 25, preferably 12 to 20, C atoms and R3 is an aliphatic saturated or unsaturated alkylene radical having 4 to 20, preferably 8 to 16, C atoms, n is zero or preferably 1 and X is CH2, C(CH3)2, CO, SO2, 0 or S.

The component (C), the oxalic acid bisamide derivative, is present in the mixture with the polyester in amounts of 0.5 to 20, preferably 1 to 10, in particular 2 to 6, % by weight, based on the mixture of (A) to (C).

In principle all known crystallizable, linear or slightly branched polyesters are suitable for the polyester according to component (A) of the molding material according to the invention, as are described, for example, in R.E. Wilfong, J. Polymer Sci. 54, pages 385-410 (1961) or in Ullmanns Enzyklopadie der technischen Chemie [Ullmanns Encyclopedia of Industrial Chemistry] (4th edition) 19, pages 61-68 (1980). However, polyethylene terephthalate is preferred. Another polyester which can also be used according to the invention is, for example, polycyclohexane 1,4-dimethylolterephthalate.

Other suitable polyesters are those which contain, as acid components in addition to terephthalic acid, up to 20 mol percent, preferably up to 10 mol percent, of other aromatic or aliphatic dicarboxylic acids and/or up to 2 mol percent, preferably up to 1 mol percent, of trifunctional or polyfunctional carboxylic acids and which contain, as the diol component in addition to 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol or cyclohexane-1,4-dimethanol, but preferably ethylene glycol, up to 20 mol percent, preferably up to mol percent, of other aliphatic diols and/or up to 2 mol percent, preferably up to 1 mol percent, of trifunctional or polyfunctional alcohols.

The dicarboxylic acids and the trifunctional or polyfunc15 tional carboxylic acids mentioned here include, for example, isophthalic acid, phthalic acid, alkyl-substituted phthalic, isophthalic or terephthalic acid, and aliphatic dicarboxylic acids, e.g. succinic acid, adipic acid, sebacic acid or trimellitic acid.

The diol components mentioned above or the trifunctional or polyfunctional alcohols include, for example, trimethylene glycol, di- or triethylene glycol, trimethylolpropane or pentaerythritol.

The polyesters used according to the invention have a reduced specific viscosity of at least 0.3 dl/g, preferably 0.5 to 2.0 dl/g, particularly preferably 0.6 to 1.6 dl/g, measured as a 1% strength solution in dichloroacetic acid at 25°C.

Suitable nucleating agents corresponding to component (B) of the molding materials according to the invention are the conventional compounds known for this purpose in the case of polyesters, such as, for example, talc, titanium dioxide, mica, silica, etc. According to the invention, alkali metal compounds are preferably used for this purpose.

In general, all compounds of these metals with H-acidic inorganic or organic compounds are suitable as compounds of the alkali metals, provided that they do not have a disadvantageous effect on the transesterification or polycondensation.

Suitable inorganic compounds of the alkali metals, preferably of sodium but also of potassium, are, for example, the corresponding silicates, phosphates, phosphites, sulfates or, preferably, carbonates, bicarbonates and hydroxides.

The organic compounds of the alkali metals, preferably of sodium but also of potassium, include the corresponding salts of aliphatic, araliphatic or aromatic carboxylic acids having, preferably, up to 30 C atoms and preferably 1 to 4 carboxyl groups. Examples of these are the alkali metal salts of formic acid, acetic acid, propionic acid, stearic acid, cyclohexanecarboxylic acid, succinic acid, adipic acid, terephthalic acid, trimellitic acid, benzoic acid and substituted benzoic acids.

Sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium salts of mono- and polycarboxylie acids, in particular the aliphatic mono- and polycarboxylic acids having preferably 2 to 18 C atoms, in particular 2 to 6 C atoms, and up to four, preferably up to two, carboxyl groups, and sodium alcoholates having preferably 2 to 15 C atoms, in particular 2 to 8 C atoms, are preferably used. Particularly preferred typical examples are: sodium acetate, sodium propionate, sodium butyrate, sodium oxalate, sodium malonate, sodium succinate, sodium methylate, sodium ethylate and sodium glycolate. It is also possible to use mixtures of different alkali metal compounds.

The amount of nucleating agent is in general 2.103 to 0.1 mol, preferably 5.10'3 to 6.102 mol per kg of the polyester.

Component (B) may be added at different times during the synthesis of the polyester or during the incorporation steps of the further additives, depending on the type of salt.

In the molding material according to the invention, at least one Ν,Ν'-disubstituted, asymmetric oxalic acid bisamide of the abovementioned formulae (I) to (III) is used as the crystallization accelerator (component (C)).

The use of the substituted oxalic acid bisamides accord10 ing to the invention in the thermoplastic polyester molding materials has the advantage that these amides do not react with the polyester and have only very little volatility compared with other organic plasticizers of similar molecular weight. Therefore, when the moldings are heated at relatively high temperatures, for example in certain applications, the said amides result in only little migration and sublimation, as can be established by weight measurements .

Compounds of the formula (I) have been disclosed as ultraviolet absorbers for organic materials of all types, including saturated and unsaturated polyesters (German Offenlegungsschrift 1,693,010). Their possible use as crystallization accelerators is not mentioned in the prior publication.

Examples of compounds (C) are: oxalic acid N-(4-methoxyphenyl-N'-dodecyldiamide -N'-octadecyldiamide -N'-stearyldiamide -N'-oleyldiamide oxalic acid N-(4-ethoxyphenyl-N'-stearyldiamide 4,4'-bis-(N’-stearyloxalamido)-diphenylmethane 1,12-bis-[N'-(4-methoxyphenyl)-oxalamido]-dodecane.

Because of their solubility, the asymmetrically substituted oxalic acid bisamides act as plasticizers and crystallization accelerators particularly in polyethylene terephthalate, in that they lower the crystallization temperature Tc and the glass transition temperature TG, and the duration of crystallization, in which the poly5 ester composition cools in the mold, is thus prolonged. The crystallization rate of the PET is increased by nucleating agents (B) and organic plasticizers (C) as additives at relatively low temperatures to such an extent that the mold temperature of the injection mold can be reduced to at least 100 to 110°C, preferably to 80 to 100°C.

The molding materials according to the invention may contain reinforcing agents as component (D) . Metals, silicates, carbon, glass, chiefly in the form of fibers, fabrics or mats, and fibers of high-strength organic filaments having a high modulus, for example of fully aromatic polyamides or of liquid crystalline polyesters, have proven suitable for this purpose. Glass fibers are a preferred reinforcing material.

In addition, inorganic or organic pigments, dyes, lubricants and parting agents, UV absorbers and thermal oxidation stabilizers may be added as conventional fillers. These fillers and reinforcing materials may account for up to about 60% by weight, preferably 10 to 50% by weight, of the molding materials.

The molding materials may furthermore contain known additives, such as flameproofing agents, impact modifiers, stabilizers, mold release agents, antistatic agents or the like. Such additives are described in, for example, German Patent 2,920,246 or in R. Gachter and H. Muller, Runststoff-Additive [Plastics Additives], Carl Hanser Verlag 1983 (Munich, Vienna).

In order to obtain flame retardant molding materials, 2 to about 20% by weight, based on the molding materials, of conventional flameproofing agents are added. These are, for example, halogen-containing compounds, elemental phosphorus or phosphorus compounds, phosphorus/nitrogen compounds, ammonium trioxide or mixtures of these substances . A mixture of a bromine-containing compound with antimony trioxide is preferably used as a flameproofing additive.

Impact modifiers or another polyester, such as polybutylene terephthalate as a co-component for the polyethylene terephthalate, or polycarbonates or poly10 arylates, may be present in the molding material in an amount of up to 25% by weight.

The preparation of the molding materials from components (A) to (D) can be carried out in a conventional manner using commercial mixing apparatuses, at above the melting point of the polyester or of the mixture. The mixture can then be extruded and granulated.

The molding materials according to the invention are starting materials for the production of moldings of all types, the injection molding method being used in par20 ticular .

Examples The examples below were carried out using polyethylene terephthalate having a reduced specific viscosity of 0.82 dl/g, measured for a one percent strength solution in dichloroacetic acid at 25°C.

Anhydrous sodium acetate, which was added at the time of PET preparation (0.21%, based on dimethyl terephthalate), was used as the nucleating agent.

The total mixture for the preparation of the polyester 30 molding materials consisted of: a) 65.0% by weight of polyethylene terephthalate, nucleated with Na acetate, b) 30.0% by weight of 4.5 mm cut glass fibers c) 0.5% by weight of an epoxy resin based on bisphenol A and epichlorohydrin, epoxide equivalent weight 750-830, d) 0.25% by weight of a thermal oxidation stabilizer based on a triaryl phosphite and a sterically hindered phenol (®Irganox B 225, Ciba-Geigy AG, Basle, Switzerland) e) 0.25% by weight of a mold release agent (oxidized polyethylene wax, acid number 18, degree of hydrolysis 32) and f) 4.0% by weight of component (C).

The nucleated PET was premixed with the organic additives and metered into a twin screw extruder having a conven15 tional screw design, while the cut glass fibers were metered into the melt via a second hopper in zone 2 of the extruder. In the downstream zone 3 of the extruder, reduced pressure was employed in order to strip off volatile constituents from the melt. The extruder temper20 atures were about 240°C in the feed zone and 260 to 270eC in the other zones of the extruder up to the die. The polyester extrudate was granulated in a water bath, downstream of the cooling zone.

The crystallization behavior was evaluated by differen25 tial calorimetry with the aid of a DSC-2C apparatus from Perkin-Elmer, Dberlingen, Lake Constance, Federal Republic of Germany. To ensure a standard basis, all samples (milled granules) were melted under a nitrogen atmosphere in the course of 5 minutes at 290 °C prior to the measure30 ment and were then quenched. In the subsequent measuring cycle, the samples were heated from room temperature (20°C) to 290°C at a rate of 10’C/min under a nitrogen atmosphere and then cooled directly at a rate of 20°C/ min. When the quenched samples were heated up, the measuring cycle exhibited an exothermic crystallization peak whose maximum is designated as the crystallization temperature Tc. On cooling from the melt, the samples likewise exhibit a crystallization peak, whose maximum is designated as the recrystallization temperature TR.

The migration resistance and sublimation resistance of the additives in the polyester matrix were monitored over one to three weeks in the course of heating granules and moldings at 150°C in a drying oven. For this purpose, the samples were weighed daily after cooling to room temperature, and the percentage weight decrease was calculated.

Table 1 shows the glass transition temperatures and crystallization temperatures measured for the extruded polyester molding materials, each of which contains the same amounts (see above) of the crystallizationaccelerating component (C). The weight decrease in % on heating 10 g of the granules at 150°C is plotted in Figure 1, and the corresponding results for heating moldings are plotted in Figure 2. The superiority of the oxalic acid bisamide derivatives according to the invention which were used is evident from the diagrams.

Claims (12)

1. Patent Claims: HOE 89/F 329

1. A thermoplastic molding material consisting substantially of, in each case, at least one (A) polyalkylene terephthalate having a reduced specific viscosity (measured in 1% strength solution in dichloroacetic acid at 25°C) of at least 0.3 dl/g, (B) nucleating agent, (C) crystallization accelerator, and (D) if required, reinforcing agents and other conventional additives, wherein (C) is at least one N,Ν'-disubstituted asymmetric oxalic acid bisamide of the formula (I) (II) HH-CO-CO-NH-R 2 (0) Z^yNH-OO-CO-KH-R’-NS-CO-CO-NH-^^ ^To )o -R l (III) R 2 -NH-CO-CO-t«- -X nh-co-co-nh-r 2 in an amount of 0.5 to 20% by weight, based on the mixture (A) to (C), in which R 1 is a hydrocarbon radical having 1 to 4 C atoms, R 2 is a hydrocarbon radical having 10 to 25 C atoms and R 3 is an aliphatic saturated or unsaturated alkylene radical having 4 to 20 C atoms, n is zero or 1 and X is CH 2 , C(CH 3 ) 2 , CO, SO 2 , 0 or S.

2. A molding material as claimed in claim 1, wherein the polyalkylene terephthalate is polyethylene terephthalate and component (C) accounts for 1 to 10, in particular 2 to 6, % by weight of the mixture.

3. A molding material as claimed in claim 1 or 2, wherein component (A) has a viscosity of 0.5 to 2.0 dl/g and the

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12. 12. amount of component (B) is 2.10 3 to 0.1 mol per kg of the polyalkylene terephthalate. A molding material as claimed in one or more of claims 1 to 3, which contains a sodium compound and/or potassium compound as nucleating agent. A molding material as claimed in one or more of claims 1 to 4, which contains, as the nucleating agent, the sodium salt of a carboxylic acid or of a polymeric compound having carboxyl groups . A molding material as claimed in one or more of claims 1 to 5, which consists of up to 60% by weight, based on the components (A) to (D), of a filler and/or a reinforcing agent. A molding material as claimed in one or more of claims 1 to 6, which contains up to 25% by weight, based on the molding material, of an impact modifier or of another polyester, polycarbonate or polyarylate. Use of the molding material as claimed in claim 1 for the production of moldings . A molding as claimed in claim 8, produced by the injection molding method. A thermoplastic molding material according to claim 1, substantially as hereinbefore described and exemplified. A thermoplastic molding material according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings. Use according to claim 8, substantially as hereinbefore described.