Polyester mixture, its preparation and use

Abstract: A polyester mixture is prepared composed of a diol, a dicarboxylic acid and optionally a monofunctional compound as a chain stopper, in which there is less than 3wt% of compounds having a molecular weight of up to 800. The process preferably involves stripping off volatile components from the mixture, for example by molecular distillation. The mixture may be used for forming shaped plastic objects for use in car interiors.

Description: The present invention relates to an improved polyester mixture, as well as to its preparation and use. More specifically, it relates to a certain polyester mixture prepared from approximately equivalent quantities of at least: a) one C₂ - C₇ diol b) one C₄ - C₄₅ dicarboxylic acid, and c) optionally a monofunctional C₄ - C₂₀ compound, acting as a chain stopper, the polyester mixture having an acid value of less than 5 and a hydroxyl value of less than 35. Polyester mixtures of this kind are widely used as polymeric plasticizers in plastics such as polyvinyl chloride. Although such polyester mixtures have a relatively high molecular weight, they are still subject to migration in the plastic, and can also evaporate and exude from it. This evaporation is particularly undesirable, because the evaporating polyesters can entrain other substances with them, which then form a deposit elsewhere. This can happen especially inside cars, where the evaporation of these components occurs mainly when the temperature inside the vehicle rises greatly in the sun, whereas the windscreen and the windows remain relatively cold, so that a layer of greasy blue wax is deposited on these inside surfaces, which is all the worse for being difficult to remove. The attempt to eliminate this undesirable phenomenon has led to the development of special plasticizers such as the trimellitates of e.g. octanol, which have a relatively low volatility. However, these esters still undergo migration in the plastic, and in addition, they are quite expensive. It is known from Soviet Patent Specification SU-A No. 840,056 to take polyesters prepared from glycols and dicarboxylic acids and free them from low-molecular by-products by distilling them from with C₁ - C₆ alcohols at 80 - 140°C under a pressure of 1 - 40 mm Hg. Only by-products with a molecular weight of up to about 400 can be removed in this way. Moreover, there is no suggestion in this document to use polyesters based on dimer fatty acids. German Patent Specification (DE-A) No. 1,593,577 describes a method for the treatment of high-molecular esters with alkali metal or alkali earth metal alkoxides, followed by the thin-film vacuum distillation of the resulting esters. The distillate, which does not suffer any appreciable thermal decomposition during this process, can then be used as a polymeric plasticizer or synthetic lubricant. Again, there is no reference to dimer fatty acids. The polyester mixtures according to the present invention are prepared from approximately equivalent quantities of: a) at least one C₂ - C₇ straight-chain or branched and preferably aliphatic diol, such as ethylene glycol, propylene glycol, neopentyl glycol, butane-1,3-diol, butane-1, 4-diol and hexane-1,6-diol; b) at least one C₄ - C₄₅ straight-chain or branched and preferably aliphatic dicarboxylic acid, such as adipic, sebacic, azelaic, phthalic, isophthalic and terephthalic acid, with the proviso that at least part of component b) is a C₃₆ - C₄₄ dimer acid; and c) optionally a C₄ - C₂₀ monofunctional compound acting as a chain stopper in the form of either a monohydric alcohol such as butanol, pentanol, hexanol, octanol, tridecanol, palmityl alcohol, and stearyl alcohol, or else as a monocarboxylic acid, such as valeric, caproic, pelargonic, myristic or stearic acid. The term "approximately equivalent quantity" covers an up to 5% excess, and it is usually the alcohol that is used in excess. However, a larger excess of up to 35 Eq-% of alcohol is introduced when making up the reaction mixture, but part of it is stripped off during the re-esterification. The final polyester mixture according to the present invention preferably has an acid value of under 3 and a hydroxyl value of under 20. The polyester prepared according to the present invention has the composition specified above but is free of the disadvantages resulting from highly volatile impurities, exhibits little migration, and differs from the formulations known so far by containing less than 3 wt% (and preferably less than 1.5 wt%) of compounds with a molecular weight of up to 800. The polyester mixture according to the present invention has an average molecular weight of at least 1000, such as at least 1500, to less than 10,000, preferably less than 7,000, most preferably less than 4000. This is its number-average molecular weight, determined on the basis of the amount of monofunctional material present per unit weight of polyester, and on the basis of the acid and hydroxyl value. From the point of view of the ease of processing, and especially the viscosity, it is best if the polyester mixtures have a molecular weight of less than 5000, preferably less than 3000, and sometimes even below 2000. In this way, the polyester mixture according to the present invention can also be regarded as a polyester composition from which a 4 - 25 wt% fraction of lower esters with a molecular weight of up to 800 has been eliminated. The present invention also relates to a process for the preparation of a polyester plasticizer comprising the following steps: I.) esterifying and/or reesterifying: a component (a) consisting of at least on C₂-C₇ straight chain or branched diol with a component (b) consisting of at least one C₄ - C₄₅ straight chain or branched dicarboxylic acid, which component (b) at least in part consists of a C₃₆ - C₄₄ dimer of an unsaturated fatty acid, in approximately equivalent amounts, and optionally a component (c) consisting of at least one C₄ - C₂₀ monohydroxy alcohol or one C₄ - C₂₀ monocarboxylic acid acting as a chain stopper, until a polyester mixture has been obtained having an acid value of less than 5 and a hydroxyl value of less than 35, II.) stripping off the volatile components (especially the used mono- and di- alcohols) from the polyester and III.) subjecting the polyester mixture to molecular distillation to remove a fraction consisting of 4-25 wt.% of the polyester mixture that consists of lower ester compounds with a molecular weight up to 800, thereby obtaining a polyester having a number average molecular weight of between 1000 and 10000 The most highly volatile ester constituents are preferably removed by molecular distillation carried out by the thin-film method under a high vacuum of eg. 0.005 mm Hg (0,0067 mbar) at a temperature of eg. 225°C. The most volatile ester constituents can also be removed by supercritical extraction. The invention also relates to a process for the preparation of plastic compositions, particularly those based on polyvinyl chloride, by incorporating in them 10 - 40 wt% of a polyester mixture according to the present invention, this amount being calculated on the final plastic composition. The polyester mixture according to the present invention has a low volatility, good processing characteristics, a light colour and a high thermal stability. The present invention also relates to the resulting plastic compositions, preferably those based on polyvinyl chloride, which contain 10 - 40 wt% of a polyester mixture according to the present invention. These plastic compositions may be made in the form of eg. extrudates, granules or powders. In addition to the polyester plasticizer according to the present invention, the plastic composition can also contain the customary other constituents, such as stabilizers and mould release agents. The present invention also relates to shaped plastic objects that can be used in particular for structural purposes in car interiors and which partly or wholly consist of a plastic comprising 10 - 40 wt% of the polyester mixture according to the present invention. Particularly good results are obtained when the present invention is used to produce shaped plastic objects for use as dashboard panels, parcel shelves behind the back seats, inside door panels, and other interior covering or facing materials. The formation of a blue waxy layer on the inside surface of the windscreen and the windows of cars is considerably reduced in this way. The shaped plastic objects can also be used for food packaging. The following examples are intended to illustrate the present invention. Example 1 A mixture having the following composition was made up, where the amounts are specified in parts by weight: 58 parts of adipic acid 7 parts of a dimer fatty acid (saturated C₃₆ fatty acid having a 98% purity) 38 parts of propylene glycol, and 13 parts of 2-ethylhexanol The mixture was heated at 225°C for 3 h until its acid value had dropped to below 6. This esterification was carried out in such a way that the reaction water distilled off, and the reactants were not entrained into the distillate. 0.03% of tetrabutyl titanate was then added, the sample temperature of 225°C was maintained, and the pressure was reduced to 5 mm Hg (6,67 mbar). A re-esterification step and the distillation of part of the excess alcohol ensued simultaneously here. These conditions were maintained until the viscosity of the resulting polyester had risen to about 4.5 Pa.sec at 25°C. The polyester mixture obtained was found to have an acid value of 0.2 and a hydroxyl value of 19. The polyester mixture obtained here, which still contained some relatively low-molecular ester constituents, was then subjected to molecular distillation at 225°C under vacuum of 0.005 mm Hg (0,0067 mbar). The distillate amounted to 5.6 wt% of the total polyester mixture subjected to distillation and mainly consisted of short-chain polyesters with a molecular weight of up to about 800. The molecular-weight distribution of the polyester mixture was determined by gel-permeation chromatography both before and after the molecular distillation. The curves thus obtained, which are shown in Fig. 1, indicate that the finished polyester mixture (UNI1.RI), which had an acid value of 0.2 and a hydroxyl value of 15, was virtually free of short-chain polyesters, containing at most 2.0% of polyesters with a molecular weight of less than 800. As the data in Table 1 show, this ensured a greatly reduced volatility in the open-cup test. This polyester mixture was used to produce a PVC sheet containing 66 parts (p.h.r.) of polyester per hundred parts of PVC and additives. The volatility, which was determined, indicated that the other additives also play a part here. Example 2 A mixture with the following composition was made up: 85 parts of adipic acid 21 parts of a dimer acid (saturated C₃₆ acid having a 98% purity), and 59 parts of propylene glycol. The mixture was esterified and re-esterified as described in Example 1. The target viscosity for the end of the re-esterification was 40 Pa.sec at 25°C. The resulting polyester mixture had an acid value of 0.3 and a hydroxyl value of 31. The molecular distillation was also carried out as in Example 1, but the temperature was now 245°C. The distillate amounted to about 4 wt% of the starting polyester mixture. The polyester mixture thus obtained had an acid value of 0.3 and a hydroxyl value of 28 and contained at most 2.0 wt% of lower polyesters with a molecular weight of up to 800. The drop in the volatility exhibited by the resulting polyester mixture in the open-cut method is shown in Table 1. Example 3 A mixture with the following composition was made up: 58 parts of adipic acid 7 parts of a dimer fatty acid (saturated C₃₆ fatty acid having a 98% purity) 36 parts of propylene glycol, and 23 parts of 2-ethylhexanol. The mixture was esterified and re-esterified as described in Example 1. The target viscosity for the end of the re-esterification was 1.2 Pa.sec at 25°C. The molecular distillation was also carried out as in Example 1, the distillate amounting to 14.7% of the initial polyester mixture. Fig. 2 shows the curves for the molecular-weight distribution before (UNI4.RI) and after (UNI3.RI) the molecular distillation. The resulting polyester mixture had an acid value of 0.2 and a hydroxyl value of 16 and contained at most 1.5 wt% of low-molecular polyesters having a molecular weight of under 800. The volatility was determined by the open-cup method both for this polyester mixture and for a PVC sheet that comprised 66 p.h.r. parts of it (see Table 1). Weight loss occurring during the volatility test 1 h at 150°C (open-cup) 3 days at 105°C (0.5-mm-thick PVC sheet with a 66 p.h.r. polyester content) Example 1 before mol. dist. 0.21% 1.2% after mol. dist. 0.002 0.6% Example 2 before mol. dist. 0.14% - after mol. dist. 0.00% - Example 3 after mol. dist. 0.02% 0.4% Mol. dist. = molecular distillation

Claims: A polyester mixture useful as plasticizer which is the reaction product of a component a. consisting of at least one C2 - C7 straight chain or branched diol and a component b. consisting of at least one C4 - C45 straight chain or branched dicarboxylic acid in approximately equivalent amounts, and optionally at least one C4 - C20 monohydroxy alcohol or a C4 - C20 monocarboxylic acid acting as chain stopper, said polyester mixture having an acid value of less than 5 and a hydroxyl value of less than 35, characterized in that component b. consists at least in part of a C36 - C44 dimer of an unsaturated fatty acid and that the polyester mixture has a number average molecular weight of between 1000 and 10 000 and contains less than 3 wt% of lower ester compounds with a molecular weight of up to 800. A polyester mixture according to claim 1, characterized in that it contains less than 1.5 wt% of lower ester compounds with a molecular weight of up to 800. A polyester mixture according to claim 1, characterized in that the average molecular weight is between 2000 and 8000. A process for preparing a polyester plasticizer comprising the steps: I. esterifying and/or re-esterifying: a component a. consisting of at least one C2 - C7 straight chain or branched diol with a component b. consisting of at least one C4 - C45 straight chain or branched dicarboxylic acid, which component b. at least in part consists of a C36 - C44 dimer of an unsaturated fatty acid in approximately equivalent amounts and optionally a component c. consisting of at least one C4 - C20 monohydroxy alcohol or one C4 - C20 monocarboxylic acid acting as chain stopper till a polyester mixture has been obtained having an acid value of less than 5 and a hydroxyl value of less than 35, II. stripping volatile compounds, in particular unreacted diol, from the polyester mixture and III. subjecting the polyester mixture to molecular distillation to remove a fraction consisting of 4 - 25 wt% of the polyester mixture that consists of lower ester compounds with a molecular weight up to 800, thereby obtaining a polyester having a number average molecular weight of between 1000 and 10 000. A process according to claim 4, characterized in that the lower ester compounds with a molecular weight up to 800 are removed from the polyester mixture by molecular distillation by the thin film method under a high vacuum . A process for the preparation of a plasticized resin composition, characterized in that 10 to 40 wt% of a polyester mixture as claimed in any one of the preceding claims 1 - 3 or as prepared by a process claimed in any one of the preceding claims 4 and 5 are incorporated in the resin composition. Shaped plastic products that can be used as components of car interiors, characterized in that they partly or wholly consist of a plasticized resin obtained by the process according to claim 6.

Inventors: HARMSEN JOHAN, HARMSEN, JOHAN
Applicants: UNICHEMA CHEMIE BV
Application year: 1990
Main classification: C08G63
IPC codes: C08F6, C08L67, C08G63, C08L101, C08L27