Phosphate ester composition for flame-retardant flexible PVC with high color stability

Abstract

The present invention relates to the general formula (I)(RO) m (PhO) 3-m The present invention relates to a mixture containing at least two substances of P=O(I)[wherein m=1, 2, or 3, R corresponds to a residue (formula II), and Ph corresponds to a phenyl group]. This mixture exhibits a unique combination of high color stability, high flame retardancy, and plasticizing effect, and as a result, they are recommended for use as flame retardants in PVC compounds, as working fluids, as lubricating additives, or as additives for paints, adhesives, sealants, or coatings.

Description

Technical Field

[0001] The present invention relates to a phosphate ester composition for flame - retardant flexible PVC having high color stability.

Background Art

[0002] Phosphate esters can be used in various technical applications, for example, the following applications: lubricants (see Patent Document 1), hydraulic fluids (see Patent Document 2), plasticizers (see Patent Document 3), or flame retardants (see Patent Document 4).

[0003] The flame - retardant effect of phosphate esters has been demonstrated in various plastics, for example, the following: in PVC (see Patent Document 5), in polyolefins (see Patent Document 6), in cellulose esters (see Patent Document 7), in polyurethanes (see Patent Document 4), or in styrene polymers (see Patent Document 8).

[0004] In the prior art, various types of phosphate esters and their use as flame retardants are described. For example, aryl esters of phosphoric acid are used, and they are composed of phenol, cresol, tert - butylated phenol, isopropylated phenol, or mixtures thereof.

[0005] In addition to triaryl phosphates, alkylaryl phosphate mixtures are also known to those skilled in the art. These are used, for example, as flame retardants when high color stability or thermal stability is required (see Patent Document 9). This is particularly required for plastics used outdoors, especially for coatings, cables, waterproofing sheets, awnings, or tents, where the material must not yellow under heat. However, compared to triaryl phosphates, improving color stability comes at the expense of flame retardancy. For this reason, Patent Document 9 uses a mixture of diarylalkyl phosphate and triaryl phosphate. According to Patent Document 9, this drawback can be mitigated by using a mixture of diarylalkyl phosphate and triaryl phosphate, but the poor flame retardancy of alkylaryl phosphates remains a disadvantage. Using preparations of two different flame retardants, as in Patent Document 9, also reveals considerable complexity in synthesis.

[0006] Patent Document 10 discloses a process for mixed alkylated triaryl phosphates, in which the first step involves the reaction of alkylated phenol (including up to 25% dialkylated phenol) with POCl3, resulting in a reaction product containing more than approximately 75 mol% monoalkylphenyl dichlorophosphate. This is then reacted with a further alkyl or aryl alcohol to form a triester (see Claim 1). However, the triesters thus obtained do not show improved color stabilization compared to conventional flame retardants (see Table 23), and the interpretation of the results is further complicated because it is not specifically identified which of the flame retardants of the invention were used in Examples TS-06-9D to TS-06-9F.

[0007] Similarly, (Patent Document 11) describes the use of a mixture of cyclic aryl phosphate and a halogen-containing compound to produce a color-stable flame-retardant PVC material. However, the use of halogen-containing flame retardants often presents regulatory challenges.

[0008] The triaryl ester compositions of phosphoric acid described in the prior art generally exhibit high flame retardancy in PVC. However, flexible PVC materials manufactured using these compositions have poor thermal stability. A further drawback of many of the triaryl ester compositions of phosphoric acid from the prior art is their triphenyl phosphate content. Due to their hazardous properties, there is a demand for even lower levels of these substances in consumer applications.

[0009] Complex formulations, including plasticizers, flame retardants, stabilizers, and possibly further additives, for producing flexible PVC with improved thermal stability are also known to those skilled in the art. For example, (Patent Document 12) describes the production of flame-retardant flexible PVC, which uses a mixture of trioctyl trimellitate (plasticizer), antimony trioxide (flame retardant), calcium-zinc stabilizer, and calcium carbonate (filler). However, the large number of required additives adds considerable technical complexity. In addition, antimony trioxide negatively affects the transparency of the PVC compound, which is undesirable in some demanding applications. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 10,414,964B2 [Patent Document 2] U.S. Patent No. 6,703,355B2 [Patent Document 3] German Patent No. 1 768 076 [Patent Document 4] U.S. Patent No. 8,129,457B2 [Patent Document 5] British Patent No. 2 302 543A [Patent Document 6] U.S. Patent No. 11,008,440B2 [Patent Document 7] U.S. Patent No. 9,000,148B2 [Patent Document 8] U.S. Patent No. 8,026,303B2 [Patent Document 9] U.S. Patent No. 5,087,521 [Patent Document 10] U.S. Patent Application Publication No. 20120004438A1 [Patent Document 11] European Patent No. 0401366A4 [Patent Document 12] International Publication No. 2022 / 121330A1 brochure [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Therefore, the object of the present invention was to provide a flame retardant preparation that, in addition to sufficient flame retardant effect, has a plasticizing effect on plastics, particularly PVC molding compounds, and also has high color stability. Preferably, the flame retardant should be in liquid form at room temperature and should be able to be produced by a simpler process with a low triphenyl phosphate content. [Means for solving the problem]

[0012] The aforementioned objective is expressed by the following general formula (I): (RO) m (PhO) 3-m P=O(I) [In the formula, m = 1, 2, or 3, and R is based on the following: [ka] corresponds to, and Ph corresponds to a phenyl group is achieved by a mixture containing at least two substances of .

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] In a preferred embodiment of the present invention, the mixture according to the present invention contains the following: (RO)3P=O, (RO)2(PhO)P=O, (RO)(PhO)2P=O, and (PhO)3P=O (triphenyl phosphate, "TPP"), and optionally a secondary component, for example, thymol, phenol, a catalyst component, or a by-product.

[0014] The mixture according to the present invention preferably contains 50% by mass or more, particularly preferably 70% by mass or more, extremely particularly preferably 80% by mass or more, and most preferably 90% by mass or more of the following general formula (I): (RO) m (PhO) 3-m P=O (I) [wherein, R, Ph, and m have the definitions shown above] substance is included.

[0015] In a preferred embodiment, the mixture according to the present invention (i) 5% to 90% by mass of (RO)2(PhO)P=O, and<00**********02>(ii) 5% to 90% by mass of (RO)(PhO)2P=O [in each case, the amount is based on the total mass of the compound of formula (I), m = 0, 1, 2, or 3, and R and Ph have the definitions shown above] is included.

[0016] [[ID=**38]] A more preferred embodiment is as follows: (RO)3P=O: 0% to 30% by mass (RO)2(PhO)P=O: 5% to 90% by mass (RO)(PhO)2P=O: 5% to 90% by mass (PhO)3P=O ("TPP"): 0% to 30% by mass [In each case, the total mass of the compound of formula (I) having m=0, 1, 2, or 3 is used as the basis, preferably the total mass of the mixture in each case, and R and Ph have the definitions shown above.] It is a mixture containing [something].

[0017] The mixture in the present invention preferably contains less than 1% by mass, particularly preferably less than 0.5% by mass, even more preferably less than 0.2% by mass, most particularly preferably less than 0.5% by mass, and most preferably 0.1% by mass or less of triphenyl phosphate.

[0018] The mixture according to the present invention is preferably in liquid form at 23°C, because such a state facilitates, and even makes possible, its use as a flame retardant, lubricant, or hydraulic fluid. The mixture according to the present invention preferably has a dynamic viscosity of 20 to 5000 mPa·s, and particularly preferably 50 to 2000 mPa·s (in each case, at 23°C).

[0019] Preferably, the mixture according to the present invention has an acid value of less than 5 mg KOH / g, preferably less than 1 mg KOH / g, particularly preferably less than 0.3 mg KOH / g, and very preferably less than 0.1 mg KOH / g.

[0020] Surprisingly, it was discovered that PVC molding compounds containing the mixture according to the present invention possess high color stability and high flame retardancy. Unexpectedly, the mixture according to the present invention can be easily prepared in a novel process. A preferred embodiment of the process allows the mixture to be prepared in a form that contains no triphenyl phosphate or only a small amount.

[0021] The present invention further provides a process for preparing the mixture according to the present invention, the process comprising the following steps: a) A step of preparing a mixture containing phosphorus oxychloride and thymol, b) A step of reacting at least a portion of the mixture from a) at a temperature between 80°C and 300°C while removing hydrogen chloride. c) Add phenol to the mixture obtained from b) and further react at a temperature of 100°C to 300°C while removing hydrogen chloride.

[0022] In an alternative embodiment, at least a portion of the phosphorus oxychloride is metered and charged only in step b). It is also possible to meter and charge at least a portion of the thymol only in step b).

[0023] Optionally, a catalyst may be added to the mixture prepared in step a) or during step b). Suitable catalysts include NaCl, KCl, LiCl, MgCl2, MgO, CaCl2, AlCl3, FeCl3, ZnCl2, TiCl4, SbCl4, and others. Optionally, one or more catalysts may be added before or during step c).

[0024] The reaction in step b) is usually carried out in the range of 80°C to 300°C, preferably in the range of 100°C to 250°C, and particularly preferably in the range of 100°C to 200°C.

[0025] Optionally, between step b) and step c), distillation may be performed to remove the (unreacted) reactants and / or by-products generated from step a). Distillation may be carried out as a batch process or as a continuous process. The distillation temperature is preferably in the range of 80°C to 250°C. It is particularly preferable to carry out the distillation at the reaction temperature of step b), or at a temperature between 80°C and the reaction temperature of step b). Distillation is carried out at a pressure in the range of 0.01 mbar to 1013 mbar, preferably in the range of 0.01 mbar to 100 mbar, and most particularly preferably in the range of 0.01 mbar to 50 mbar.

[0026] The reaction in step c) is usually carried out in the range of 100°C to 300°C, preferably in the range of 100°C to 250°C, and particularly preferably in the range of 120°C to 250°C.

[0027] In alternative embodiments, at least a portion of the phenol is metered in only during the reaction in step c). Alternatively, at least a portion of the reaction mixture obtained from step b) (which may be directly added, or after the reagents from step a) and / or the by-products generated in step b) have been distilled off) may be metered in during the reaction in step c).

[0028] Optionally, the (unreacted) reagent and / or by-products generated in step b) and / or step c) may be removed by distillation after step c). Distillation can be carried out as a batch process or as a continuous process. The distillation temperature is preferably in the range of 80°C to 250°C. Distillation is carried out at a pressure in the range of 0.01 mbar to 1013 mbar, preferably in the range of 0.01 mbar to 100 mbar, and most preferably in the range of 0.01 mbar to 50 mbar.

[0029] Depending on the application, the mixture according to the present invention may contain further additives. Examples of suitable additives include plasticizers, plasticizing polymers, polymer modifiers, stabilizers (e.g., heat stabilizers, light stabilizers, antioxidants), co-stabilizers (e.g., acid scavengers, free radical scavengers), internal and external lubricants, viscosity modifiers, fillers, coloring pigments, dyes, flame retardants, flame retardant synergists, foaming agents, and further functional additives, such as antistatic agents, nucleating agents, UV protectants, or biocides (see, for example, RDMaier, M.Schiller, Handbuch Kunststoff-Additive [Plastics Additives Handbook], 4th edition, Munich, Carl Hanser Verlag, 2016, p.513ff).

[0030] The mixture according to the present invention is suitable as a flame retardant. Therefore, the present invention further provides the use of the mixture according to the present invention as a flame retardant.

[0031] The mixture according to the present invention can be used as a flame retardant in all applications of flame retardants known to those skilled in the art. The mixture according to the present invention is preferably used as a flame retardant for the following: - Synthetic polymers, such as polyolefins, polyvinyl chloride, polycarbonates, styrene-based (co) polymers, polyamides, polyesters, polyurethanes, elastomers, such as NBR, CR, SBR, or EPDM, and thermosetting resins, such as epoxy resins, unsaturated polyester resins, and phenol-formaldehyde resins. - Plant-derived materials, such as wood, wood-plastic composites, paper, and cardboard, and - Materials derived from animals, such as leather.

[0032] Particularly preferred is the use of the mixture according to the present invention as a flame retardant for compositions containing polyvinyl chloride (PVC), such as PVC molded compounds, i.e., PVC in the form of granules, powders, pastes, or plastisols.

[0033] Accordingly, the present invention also provides compositions comprising the mixture according to the present invention and polyvinyl chloride (PVC), preferably in the form of granules, powders, pastes, or plastisols. The PVC molding compounds in the present invention are preferably flexible PVC. The PVC molding compounds in the present invention can be produced by mixing and compounding PVC with the mixture according to the present invention and optionally, possibly, further auxiliary agents, such as stabilizers, in known ways (see, for example, G. Becker, D. Braun, Kunststoff-Handbuch, Polyvinylchlorid [Plastics Handbook, Polyvinyl Chloride], Vol.2 / 2, Munich, Vienna, Carl Hanser Verlog, 1986, p.829ff), or by dispersing it to form a ready-to-use plastisol or organosol.

[0034] The PVC molding compound according to the present invention contains, based on 100 parts by mass of PVC, preferably 5 to 150 parts by mass, and particularly preferably 30 to 70 parts by mass of the phosphate ester of formula (I). In a preferred embodiment, the PVC molding compound according to the present invention contains, based on 100 parts by mass of PVC, preferably 5 to 150 parts by mass, and particularly preferably 30 to 70 parts by mass of the phosphate ester of formula (I).

[0035] The PVC molding compound according to the present invention can be used for coatings, films, cables, pipelines, hoses, seals, conveyor belts, roof membranes, adhesive tape films, waterproof sheets, sunshades, and tents.

[0036] The present invention further provides the use of the mixture according to the present invention in or for producing a working fluid. The mixture according to the present invention is preferably used in a flame-retardant working fluid.

[0037] The present invention further provides the use of the mixture according to the present invention as a lubricating additive. The mixture according to the present invention is preferably used in a flame-retardant lubricant.

[0038] The present invention further provides the use of the mixture according to the present invention as an additive for paints, adhesives, sealants, and coatings.

[0039] The present invention further provides the use of the mixture according to the present invention as a heat transfer medium or in a preparation used as a heat transfer medium. The mixture according to the present invention is preferably used as a heat transfer medium or in a heat transfer medium preparation for immersion cooling of electrical components. In addition to the mixture according to the present invention, the heat transfer medium preparation further includes, for example, the following: trialkyl phosphates, triaryl phosphates, mineral oils, polyalphaolefins, esters, antioxidants, metal deactivators, flow additives, corrosion inhibitors, anti-foaming agents, anti-emulsifiers, and / or pour point depressants. [Examples]

[0040] Example of synthesis <Synthesis Example 1> In a reactor equipped with a stirrer, internal thermometer, nitrogen inlet, and reflux condenser, phosphorus oxychloride (200 parts by mass), thymol (197 parts by mass), and magnesium chloride (0.1 parts by mass) were initially charged. The reaction mixture was heated with stirring to 120°C and maintained at this temperature until gas generation was almost completely eliminated. The pressure in the apparatus was gradually reduced from atmospheric pressure to 10 mbar and maintained at the final conditions for 1 hour. After adding phenol (307 parts by mass), the temperature of the reaction mixture was gradually increased to a final temperature of 160°C and maintained at this temperature until the conversion was complete. Excess phenol was removed at the final temperature of 160°C and a pressure of 10 mbar. The mixture of reaction products was isolated as a viscous liquid (110 mPa·s at 23°C). Its acid value was less than 0.1 mg KOH / g. The mixture of reaction products contained: 0.6 mass% (thymol O)3P=O, 12.7 mass% (thymol O)2(PhO)P=O, 86.3 mass% (thymol O)-(PhO)2P=O, and 0.4 mass% (PhO)3P=O ("TPP").

[0041] <Synthesis Example 2> In a reactor equipped with a stirrer, internal thermometer, nitrogen inlet, and reflux condenser, phosphorus oxychloride (200 parts by mass), thymol (295 parts by mass), and magnesium chloride (0.1 part by mass) were initially charged. The reaction mixture was gradually heated to 160°C with stirring and maintained at this temperature until gas generation was almost completely eliminated. After adding phenol (307 parts by mass), the temperature of the reaction mixture was gradually increased to a final temperature of 190°C and maintained at this temperature until the conversion was complete. Excess phenol was removed at the final temperature of 190°C and a pressure of 10 mbar. The mixture of reaction products was isolated as a viscous liquid (210 mPa·s at 23°C). Its acid value was less than 0.1 mg KOH / g. The mixture of reaction products contained: 2.4 mass% (thymol O)3P=O, 56.0 mass% (thymol O)2(PhO)P=O, 41.4 mass% (thymol O)-(PhO)2P=O, and 0.2 mass% (PhO)3P=O ("TPP").

[0042] <Synthesis Example 3> In a reactor equipped with a stirrer, internal thermometer, nitrogen inlet, and reflux condenser, phosphorus oxychloride (200 parts by mass), thymol (394 parts by mass), and magnesium chloride (0.1 parts by mass) were initially charged. The reaction mixture was gradually heated to 160°C with stirring and maintained at this temperature until gas generation was almost completely eliminated. After adding phenol (186 parts by mass), the temperature of the reaction mixture was gradually increased to a final temperature of 190°C and maintained at this temperature until the conversion was complete. Excess phenol was removed at the final temperature of 190°C and a pressure of 10 mbar. The mixture of reaction products was isolated as a viscous liquid (390 mPa·s at 23°C). Its acid value was less than 0.1 mg KOH / g. The mixture of reaction products contained: 8.6 mass% (thymol O)3P=O, 81.1 mass% (thymol O)2(PhO)P=O, 10.2 mass% (thymol O)-(PhO)2P=O, and less than 0.1 mass% (PhO)3P=O ("TPP").

[0043] The amounts used in synthesis examples S1 to S3 are summarized in Table 1.

[0044] [Table 1] In the table, (ThymylO) represents the thymol O group derived from thymol.

[0045] <Measurement of the composition of phosphate ester compositions> GC-FID quantitative analysis was performed using an Agilent 7890A GC instrument equipped with a CB-Sil 5 CB quartz capillary (length: 30 m, diameter: 0.32 mm, film thickness: 3.00 μm). Hydrogen was used as the carrier gas. The sample (dissolved in acetone) was injected at a temperature of 300°C in split mode (86:1). The following temperature program was set: starting temperature 60°C, heating rate 10°C / min to 150°C, then heating rate 25°C / min to 280°C, holding time: 10 minutes, then heating rate 25°C / min to a final temperature of 320°C / min, holding time: 10 minutes. Evaluation was performed by integrating the signal separated from the corresponding baseline and converting the peak area to a pre-calibrated content.

[0046] <Measurement of viscosity of phosphate ester composition> The dynamic viscosity of phosphate esters was determined in accordance with DIN 53018 using an Anton Paar MCR102 shear rheometer at a given temperature over 200 seconds. -1 The measurement was taken using the shear rate.

[0047] <Measurement of acid value of phosphate ester compositions> The acid value of the sample was measured according to DIN EN ISO 2114 (Method B, colorimetric titration using phenolphthalein). For this purpose, 10 g of the sample was weighed, dissolved in 200 mL of acetone and 50 mL of water, and mixed with 2-3 drops of phenolphthalein solution (0.1% by mass in ethanol / water (v / v=4 / 1)). From a burette, sodium hydroxide solution (0.1 mol / L) was titrated with stirring until the color changed from colorless to pink (maintained for at least 10 seconds). A blank value was measured in the same manner without the sample.

[0048] Comparative samples of known phosphate ester compositions Table 2 lists known phosphate ester compositions used as comparative samples for the production of flexible PVC. All comparative samples are products of Lanxess Deutschland GmbH.

[0049] [Table 2]

[0050] Manufacturing of flexible PVC The flexible PVC molding compound used for the test was prepared using a laboratory roll mill. A mixture of all the components (see Table 3) was added, and then the mixture was rolled to form a sheet. The compound was then compounded on the roll mill for another 10 minutes after the sheet was formed, and finally, the rolled sheet was removed. The rolling temperature was 165°C.

[0051] Test specimens for measuring LOI were prepared from rolled sheets using a press. The press temperature was 170°C. The press time consisted of 4 minutes at low pressure (less than 10 bar) for preheating, followed by 2 minutes at high pressure (over 100 bar). Test specimens with dimensions of 90 × 13 × 4 mm were cut from a 4 mm thick press sheet.

[0052] The test specimen (50 x 40 x 6 mm) used to measure the hardness of the compound was pressed for a longer period at the same temperature due to its large thickness of 6 mm. The pressing time consisted of 7 minutes for preheating at low pressure and 3 minutes for compression molding at high pressure.

[0053] The test specimens for the color stability test were cut from thin (less than 1 mm) rolled sheets, which were removed from the roll mill after a 10-minute rolling time.

[0054] [Table 3]

[0055] The PVC test specimens were prepared according to this procedure.

[0056] <Measurement of flame retardancy and plasticizing effect> The Limiting Oxygen Index (LOI) was used to evaluate flame retardancy. LOI is a measure of the combustion behavior of plastics and other materials. Under standardized conditions, LOI is the minimum oxygen concentration in a nitrogen / oxygen mixture required to cause combustion of the test specimen. The tests were conducted in accordance with ISO 4589-2. For practical applications, a value of at least 30 should be achieved in the tests.

[0057] The plasticizing effect of phosphate esters was measured using Shore A hardness testing of a soft PVC compound containing phosphate esters. The measurement principle is based on the penetration depth when a metal test pin is inserted into the material sample with a force of 12.5 N for 15 seconds. Shore A hardness was measured on test specimens with dimensions of 50 × 40 × 6 mm. Shore hardness measurements were performed in accordance with DIN ISO 7619-1. A Shore A hardness of less than 95 is considered to indicate a plasticizing effect.

[0058] The measurement results are summarized in Table 4.

[0059] [Table 4]

[0060] These results indicate that the phosphate ester compositions according to the present invention provide comparable flame retardancy in PVC to the comparative products Disflamoll DPK, Disflamoll TKP, Disflamoll 51092, and Reofos 65. As expected, the LOI of the PVC compound with Disflamoll DPO, an alkylaryl ester of phosphate, was significantly lower, accompanied by a lower flame retardant effect. All flame retardants used achieved a Shore A hardness lower than 95 in the above tests, i.e., they exhibited a plasticizing effect.

[0061] <Measurement of color stability> All plastics undergo an undesirable aging process, which manifests as changes in mechanical values ​​and color (usually yellowing). The color stability of flexible PVC compounds under thermal stress was tested using a Mathis oven (Mathis Thermotester LTE T). In this case, material samples were placed in a convection oven at 180°C for 30 minutes. The material samples were removed from the heating oven area at time intervals, thereby obtaining material samples exposed to high temperatures at different times. The yellow value (delta E value) was measured using a Minolta Chroma Meter CR400. Measurements were performed in accordance with DIN-EN-ISO 10545-16.

[0062] [Table 5]

[0063] These results indicate that in PVC compounds containing the phosphate ester compositions S1, S2, and S3 according to the present invention, the increase in yellow value (i.e., discoloration) occurs significantly later than in compounds containing comparative products.

Claims

1. The following general formula (I): (RO) ｍ (PhO) ３－ｍ P=O (I) [In the formula, m = 1, 2, or 3, and R is the basis shown below: 【Chemistry 1】 This corresponds to the phenyl group. A mixture containing at least two of the following substances.

2. (i) 5% to 90% by mass of (RO) ２ (PhO)P=O, and (ii) 5% to 90% by mass of (RO)(PhO) ２ P = O, [In the formula, R and Ph have the definitions set forth in claim 1.] The mixture according to claim 1, comprising:

3. The mixture according to claim 1 or 2, containing only less than 1% by mass, preferably less than 0.5% by mass, particularly preferably less than 0.2% by mass, and most preferably 0.1% by mass or less of triphenyl phosphate.

4. The mixture according to any one of claims 1 to 3, which exists as a liquid at 23°C and 1013 mbar, and preferably has a dynamic viscosity of 20 to 5000 mPa·s, particularly preferably 50 to 1000 mPa·s (in each case at 23°C).

5. (a) at least, - Phosphorus oxychloride - Timor Steps to prepare a mixture containing: (b) a step of reacting at least a portion of the mixture from a) at a temperature between 80°C and 300°C while removing hydrogen chloride, and (c) Add phenol to the mixture obtained from (b) and further react at a temperature of 100°C to 300°C while removing hydrogen chloride. A method for producing the mixture according to any one of claims 1 to 4, including the mixture described in any one of claims 1 to 4.

6. The method according to claim 5, wherein the removal of the reactant and / or by-products from step a) is carried out between step b) and step c).

7. The method according to claim 5 or 6, wherein the removal of the reactants and / or by-products from step b) and / or c) by distillation is carried out after step c).

8. Use of the mixture according to any one of claims 1 to 4, preferably as a flame retardant for synthetic polymers, plant-derived materials, or animal-derived materials, and particularly preferably as a flame retardant for polyvinyl chloride (PVC).

9. A molding compound comprising the mixture according to any one of claims 1 to 4 and polyvinyl chloride (PVC).

10. The molding compound according to claim 9, comprising 5 to 150 parts by mass, preferably 30 to 70 parts by mass, of the phosphate ester of formula (I), based on 100 parts by mass of PVC.

11. Use of the molding compound according to claim 9 or 10 for manufacturing coatings, films, cables, pipelines, hoses, seals, conveyor belts, roof membranes, adhesive tape films, waterproof sheets, awnings, or tents.

12. Use of the mixture according to any one of claims 1 to 4 as a working fluid.

13. Use of the mixture according to any one of claims 1 to 4 as a lubricating additive.

14. Use of the mixture according to any one of claims 1 to 4 as an additive for paints, adhesives, sealants, or coatings.

15. Use of the mixture described in any one of claims 1 to 4 as a heat transfer medium.

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