Phosphoric acid ester compositions for flame-retardant soft PVC with high thermostability

Abstract

The invention relates to mixtures containing at least two substances of the general formula (I) (RO)m(PhO)3-mP=O, where m = 1, 2 or 3, in which R corresponds to the residue (A) and Ph corresponds to the phenyl group. The mixtures exhibit a unique combination of high thermal stability, high flame retardance, and plasticising effect, as a result of which they are recommended for use as flame retardants in PVC compounds, as hydraulic fluids, as lubricant additives, or as additives for paints, adhesives, sealants, or coatings.

Description

[0001] Phosphoric acid ester compositions for flame-retardant soft PVC with high thermal stability

[0002] Phosphoric acid esters can be used in various technical applications, e.g. as plasticizers (cf. DE 1 768 076), as flame retardants (cf. US 8,129,457 B2), in lubricants (cf. US 10,414,964 B2) or in hydraulic fluids (cf. US 6,703,355 B2).

[0003] The flame retardant effect of phosphoric acid esters has already been demonstrated in various plastics, e.g. in PVC (cf. GB 2 302 543 A), in polyolefins (cf. US 11,008,440 B2), in cellulose esters (US 9,000,148 B2), in polyurethanes (cf. US 8,129,457 B2), in styrene polymers (cf. US 8,026,303 B2) or in polycarbonate / acrylonitrile butadiene styrene (PC / ABS; cf. WO 2014171122 A1).

[0004] The prior art describes various types of phosphoric acid esters and their use as flame retardants. For example, aryl phosphoric acid esters derived from phenol, cresol, tert-butylated phenol, isopropylated phenol, or mixtures thereof are used.

[0005] In addition to triaryl phosphoric acid esters, the skilled person is also familiar with mixed alkyl aryl phosphoric acid esters. US Pat. No. 5,087,521 discloses that a mixture of diarylalkyl phosphates and (monoalkylated) triaryl phosphates produces particularly thermally stable PVC compounds. This property is desirable for all applications of soft PVC, since such materials are manufactured at high temperatures. PVC molding compounds with high thermal stability are therefore characterized by easier processing and better recyclability. However, the use of two different flame retardant formulations according to US Pat. No. 5,087,521 represents a considerable additional synthetic effort.

[0006] Similarly, EP 0401366 A4 uses blends of cyclic aryl phosphates with halogen-containing compounds to produce thermally stable, flame-retardant PVC materials. However, the use of halogen-containing flame retardants is often problematic from a regulatory perspective.

[0007] The triaryl phosphoric acid ester compositions described in the prior art generally exhibit high flame retardancy in PVC. However, the soft PVC materials produced with them exhibit low thermal stability. Another disadvantage of many triaryl phosphoric acid ester compositions from the prior art is their triphenyl phosphate content. Its hazardous properties have led to increasingly lower levels of this substance being required in consumer applications.

[0008] For the production of soft PVC with increased thermal stability, complex formulations containing a plasticizer, a flame retardant, a stabilizer, and optionally other additives are also known to those skilled in the art. For example, WO 2022 121330 A1 describes the production of flame-retardant soft PVC using a mixture of trioctyl trimellitate (plasticizer), antimony trioxide (flame retardant), a calcium-zinc stabilizer, and calcium carbonate (filler). However, the large number of additives required results in considerable additional technical effort. In addition, antimony trioxide has a negative effect on the transparency of the PVC compound, which is undesirable for some demanding applications.

[0009] The object of the present invention was therefore to provide a flame retardant preparation which, in addition to sufficient flame retardancy, also exhibits a plasticizing effect for plastics, particularly for PVC molding compounds, and also exhibits high thermal stability. This flame retardant should preferably be in liquid form at room temperature, be obtainable by a relatively inexpensive process, and have a low triphenyl phosphate content.

[0010] The stated object is achieved by mixtures containing at least two substances of the general formula (I)

[0011] (RO) m (PhO)3-mP=O with m = 1 , 2 or 3, where R is the residue and Ph corresponds to the phenyl residue.

[0012] In a preferred embodiment of the invention, R in formula (I) corresponds to the radical

[0013] In a further preferred embodiment of the invention, the mixture according to the invention contains (RO)3P=O, (RO)2(PhO)P=O, (RO)(PhO)2P=O and (PhO)3P=O (triphenyl phosphate, “TPP”) and optionally secondary components, such as guaiacol, phenol, catalyst components, or secondary products.

[0014] The mixtures according to the invention preferably contain 50% by weight or more, particularly preferably 70% by weight or more, very particularly preferably 80% by weight or more and most preferably 90% by weight or more of substances of the general formula (I)

[0015] (RO) m (PhO) 3.m P=O (I), where R, Ph and m have the meanings given above.

[0016] In a preferred embodiment, the mixtures according to the invention contain

[0017] (i) 5 to 90 wt% (RO)2(PhO)P=O, and

[0018] (ii) 5 to 90 wt.% of (RO)(PhO)2P=O, where R and Ph have the meanings given above.

[0019] A further preferred embodiment is mixtures containing:

[0020] (RO)3P=O 0 to 30 wt.%

[0021] (RO)2(PhO)P=O 5 to 90 wt.%

[0022] (RO)(PhO)2P=O 5 to 90 wt.%

[0023] (PhO)3P=O (“TPP”) 0 to 30% by weight, in each case based on the total weight of the compounds of the formula (I) with m = 0, 1, 2 or 3, preferably based on the total weight of the mixture, where R and Ph have the meanings given above. The mixtures according to the invention preferably contain less than 10% by weight, preferably less than 5% by weight, particularly preferably less than 1% by weight, very particularly preferably less than 0.5% by weight and most preferably not more than 0.2% by weight of triphenyl phosphate.

[0024] The mixtures according to the invention are preferably in liquid form at 23°C, since such a state facilitates or even enables their use as flame retardants or in lubricants or hydraulic fluids. The mixtures according to the invention preferably have a dynamic viscosity of 20 to 5000 mPa s, particularly preferably of 50 to 2000 mPa s (each at 23°C).

[0025] The mixtures according to the invention preferably have an acid number of less than 5 mg KOH / g, preferably less than 1 mg KOH / g, particularly preferably less than 0.3 mg KOH / g, very preferably less than 0.1 mg KOH / g.

[0026] Surprisingly, it was found that PVC molding compounds containing the inventive mixture exhibit high thermal stability and high flame retardancy. The inventive mixtures can be produced unexpectedly easily using a novel process. A preferred embodiment of the process allows production in a mold in which the mixture contains no or very little triphenyl phosphate.

[0027] The invention further relates to a process for the preparation of the mixtures according to the invention, comprising the steps: a) providing a mixture containing phosphorus oxychloride and guaiacol, b) reacting at least part of the mixture from a) at temperatures between 80°C to 300°C with elimination of hydrogen chloride, c) adding phenol to the mixture obtained from b) and further reacting between 100°C to 300°C with elimination of hydrogen chloride,

[0028] In an alternative embodiment, at least a portion of the phosphorus oxychloride is only added in step b). It is also possible for at least a portion of the guaiacol to be added in step b). A catalyst can be added for the reaction in step b) and / or c). Suitable catalysts include: NaCl, KCl, LiCl, MgCh, MgO, CaCh, AlCl3, FeCh, ZnCh, TiCl, SbCl. The addition can take place in step a), b) or c) or between steps a) and b) or b) and c).

[0029] The reaction according to step b) is usually carried out in the range from 80°C to 300°C, preferably in the range from 80°C to 250°C, particularly preferably in the range from 80°C to 200°C.

[0030] Optionally, between step b) and step c), a distillative separation of (unreacted) reactants from step a) and / or by-products formed can take place. The distillation can be carried out as a batch process or as a continuous process. The distillation temperature is preferably in the range from 80°C to 250°C. Particular preference is given to carrying out the distillation at the reaction temperature of step b) or at a temperature between 80°C and the reaction temperature of step b). The distillation is carried out in a pressure range from 0.01 mbar to 1013 mbar, preferably in the range from 0.01 mbar to 100 mbar, very particularly preferably in the range from 0.01 mbar to 50 mbar.

[0031] The reaction according to step c) is usually carried out in the range from 100°C to 300°C, preferably in the range from 100°C to 250°C, particularly preferably in the range from 120°C to 250°C.

[0032] In an alternative embodiment, at least a portion of the phenol is added during the reaction in step c). It is also possible for at least a portion of the reaction mixture obtained from step b) (either directly or after distillative separation from the reactants of step a) and / or by-products formed in step b)) to be added during the reaction in step c).

[0033] Optionally, after step c), a distillative separation of (unreacted) reactants and / or by-products formed in steps b) and / or c) can be carried out. The distillation can be carried out as a batch process or as a continuous process. The temperature of the distillation is preferably in the range from 80°C to 250°C. The distillation is carried out in a pressure range from 0.01 mbar to 1013 mbar, preferably in the range from 0.01 mbar to 100 mbar, very particularly preferably in the range from 0.01 mbar to 50 mbar. The mixtures according to the invention can, depending on the application, also contain further auxiliaries. Examples of auxiliaries include plasticizers, plasticizing polymers, polymeric modifiers, stabilizers (e.g., thermal stabilizers, light stabilizers, antioxidants), co-stabilizers (e.g.,Acid scavengers, radical scavengers), internal and external lubricants, viscosity regulators, fillers, color pigments, dyes, flame retardants, flame retardant synergists, blowing agents and other functional additives such as antistatic agents, nucleating agents, UV protectants or biocides (see e.g. RD Maier, M. Schiller, Handbook of Plastics Additives, 4th edition, Munich, Carl Hanser Verlag, 2016, p. 513 ff).

[0034] The mixtures according to the invention are suitable as flame retardants. The present invention therefore further relates to the use of the mixtures according to the invention as flame retardants.

[0035] The mixtures according to the invention can be used as flame retardants in all applications for flame retardants known to the person skilled in the art. The mixtures according to the invention are preferably used as flame retardants for

[0036] - synthetic polymers such as polyolefins, polyvinyl chloride, polycarbonates, styrene-based (co-)polymers, polyamides, polyesters, polyurethanes, elastomers such as NBR, CR, SBR, or EPDM and thermosets such as epoxy resins, unsaturated polyester resins and phenol-formaldehyde resins,

[0037] - Materials of plant origin, such as wood, wood-plastic composites, paper and cardboard, and

[0038] - Materials of animal origin, such as leather, are used.

[0039] The mixtures according to the invention are particularly preferably used as flame retardants for polyvinyl chloride (PVC), for example in PVC molding compounds, ie in compositions containing PVC which are in the form of a granulate, a powder, a paste or a plastisol.

[0040] The invention therefore also relates to compositions, preferably in the form of granules, a powder, a paste, or a plastisol, containing a mixture according to the invention and polyvinyl chloride (PVC). These PVC molding compositions according to the invention are preferably plasticized PVC. The PVC molding compositions according to the invention can be produced by mixing PVC with the mixtures according to the invention and, if appropriate, further auxiliaries, e.g., stabilizers, in a manner known per se (see, for example, G. Becker, D. Braun, Kunststoff-Handbuch, Polyvinylchlorid, Vol. 2 / 2, Munich, Vienna, Carl Hanser Verlag, 1986, p. 829 ff.) and compounding or dispersing the mixture to form a ready-to-process plastisol or organosol.

[0041] The PVC molding composition according to the invention preferably contains 5 to 150 parts by weight, particularly preferably 30 to 70 parts by weight, of phosphoric acid esters of formula (I), based on 100 parts by weight of PVC. In a preferred embodiment, the PVC molding composition according to the invention contains 5 to 150 parts by weight, particularly preferably 30 to 70 parts by weight, of phosphoric acid esters of formula (I), based on 100 parts by weight of PVC.

[0042] The PVC molding compound according to the invention is used in coatings, films, cables, pipelines, hoses, seals, conveyor belts, roofing membranes, adhesive tape films, tarpaulins, awnings and tents.

[0043] The invention further relates to the use of the mixtures according to the invention in hydraulic fluids or for the production of hydraulic fluids. The mixtures according to the invention are preferably used in flame-retardant hydraulic fluids.

[0044] The invention further relates to the use of the mixtures according to the invention as lubricant additives. The mixtures according to the invention are preferably used in flame-retardant lubricants.

[0045] A further object of the invention is the use of the mixtures according to the invention as additives for paints, adhesives, sealants and coatings.

[0046] The invention further relates to the use of the mixtures according to the invention as heat transfer media or in preparations used as heat transfer media. The mixtures according to the invention are preferably used as heat transfer media or in heat transfer media preparations in the immersion cooling of electrical components. In addition to the mixtures according to the invention, the heat transfer media preparations contain, for example, other trialkyl phosphates, triaryl phosphates, mineral oils, polyalphaolefins, esters, antioxidants, metal deactivators, flow additives, corrosion inhibitors, foam inhibitors, demulsifiers, and / or pour point depressants.

[0047]

[0048] Synthesis example 1

[0049] Phosphorus oxychloride (200 parts by weight), guaiacol (162 parts by weight), and magnesium chloride (0.1 part by weight) were placed in a reactor equipped with a stirrer, internal thermometer, nitrogen inlet, and reflux condenser. The reaction mixture was heated to 100°C with stirring and maintained at this temperature until gas evolution was barely observable. The pressure in the apparatus was gradually reduced from atmospheric pressure to 10 mbar and maintained at final conditions for 1 h. After adding phenol (308 parts by weight), the temperature of the reaction mixture was gradually increased to a final temperature of 140°C and maintained at this temperature until complete conversion. Excess phenol was removed at a final temperature of 140°C and a pressure of 10 mbar. The product mixture was isolated as a viscous liquid (180 mPa s at 23°C). The acid number was <0.1 mg KOH / g. The product mixture contained 0.4 wt.% (GuajacylO)3P=O, 8.6 wt.-% (GuiacylO)2(PhO)P=O, 86.5 wt.% (GuiacylO)(PhO)2P=O and 4.5 wt.% (PhO)3P=O (“TPP”).

[0050] Synthesis example 2

[0051] Phosphorus oxychloride (200 parts by weight), guaiacol (243 parts by weight), and magnesium chloride (0.1 part by weight) were placed in a reactor equipped with a stirrer, internal thermometer, nitrogen inlet, and reflux condenser. The reaction mixture was gradually heated to 100°C with stirring and maintained at this temperature until gas evolution was barely observable. After adding phenol (307 parts by weight), the temperature of the reaction mixture was gradually increased to a final temperature of 120°C and maintained at this temperature until complete conversion. Excess phenol was removed at a final temperature of 160°C and a pressure of 10 mbar. The product mixture was isolated as a viscous liquid (430 mPa s at 23°C). The acid number was <0.1 mg KOH / g. The product mixture contained 2.9 wt% (guaiacylO)3P=O, 45.8 wt% (guaiacylO)2(PhO)P=O, 47.8 wt% (guaiacylO)(PhO)2P=O, and 3.5 wt% (PhO)3P=O (“TPP”). Synthesis Example 3

[0052] Phosphorus oxychloride (200 parts by weight), guaiacol (324 parts by weight), and magnesium chloride (0.1 part by weight) were placed in a reactor equipped with a stirrer, internal thermometer, nitrogen inlet, and reflux condenser. The reaction mixture was gradually heated to 120°C with stirring and maintained at this temperature until gas evolution was barely observable. After adding phenol (185 parts by weight), the temperature of the reaction mixture was gradually increased to a final temperature of 140°C and maintained at this temperature until complete conversion. Excess phenol was removed at a final temperature of 160°C and a pressure of 10 mbar. The product mixture was isolated as a viscous liquid (1810 mPa s at 23°C). The acid number was 0.4 mg KOH / g. The product mixture contained 11.4 wt% (GuiacylO)3P=O, 81.5 wt% (GuiacylO)2(PhO)P=O, 6.9 wt% (GuiacylO)(PhO)2P=O and 0.2 wt% (PhO)3P=O (“TPP”).

[0053] The quantities used in synthesis examples S1 to S3 are summarized in Table 1:

[0054] Table 1: Amounts used in synthesis examples S1 to S3. Determination of the composition of phosphoric acid ester compositions

[0055] Quantitative GC-FID analysis was performed using an Agilent 7890A GC equipped with a CB-Sil 5 CB quartz capillary column (length: 30 m, diameter: 0.32 mm, path length: 3.00 μm). Hydrogen was used as the carrier gas. The sample (dissolved in acetone) was injected in split mode (86:1) at a temperature of 300°C. The following temperature program was set: 60°C starting temperature, heating rate 10°C / min up to a temperature of 150°C, then with a heating rate of 25°C / min to 280°C, holding time: 10 min, then with a heating rate of 25°C / min to a final temperature of 320°C / min, holding time: 10 min. The evaluation was performed by integrating the corresponding baseline-separated signal and converting the peak areas into a concentration after prior calibration.

[0056] Determination of the viscosity of phosphoric acid ester compositions

[0057] The dynamic viscosity of phosphoric acid esters was measured using an Anton Paar shear rheometer of type MCR 102 at the specified temperature with a shear rate of 200 s -1 according to DIN 53018.

[0058] Determination of the acid number of phosphoric acid ester compositions

[0059] The acid number of the samples was determined according to DIN EN ISO 2114 (Method B, colorimetric titration with phenolphthalein). For this purpose, the sample (10 g) was weighed, dissolved in acetone (200 mL) and water (50 mL), and 2-3 drops of a phenolphthalein solution (0.1 wt% in ethanol / water (v / v = 4 / 1)) were added. Sodium hydroxide solution (0.1 mol / L) was titrated from a burette until the color change from colorless to pink persisted for at least 10 seconds while stirring. A blank value was measured in the same way but without the sample.

[0060] Table 2 lists known phosphoric acid ester compositions that were used as reference samples for the production of soft PVC. The triguaiacyl phosphate was produced according to WO 2014171122 A1. The other reference samples are commercial products from Lanxess Deutschland GmbH. Table 2: Reference samples used.

[0061] Production of soft PVC

[0062] The soft PVC molding compounds used for testing were produced on a laboratory rolling mill. After adding the mixture of all formulation components (see Table 3), the mixture was left on the mill until a sheet formed. From this point on, the compounds were compounded on the mill for a further 10 minutes and finally removed as a rolled sheet. The rolling temperature was 165°C.

[0063] The test specimens for determining the LOI were produced from the rolled sheets using a press. The press temperature was 170°C, and the press time was 4 minutes for preheating at low pressure (< 10 bar) and 2 minutes at high pressure (> 100 bar). Test specimens measuring 90 x 13 x 4 mm were sawn from the 4 mm thick press sheets.

[0064] The test specimens used to determine the hardness of the compounds (50 x 40 x 6 mm) were pressed for a longer time at the same temperature due to their large thickness of 6 mm. The pressing time was 7 minutes for preheating at low pressure and 3 minutes for compression molding at high pressure.

[0065] The test specimens for thermal stability testing were cut from a thin (< 1 mm) rolled sheet, which was removed from the rolling mill after 10 minutes of rolling time. Table 3: Recipe ingredients for the production of soft PVC.

[0066] PVC samples were produced according to this specification (Table 4).

[0067] Determination of flame retardancy and plasticizer effect

[0068] The Limiting Oxygen Index (LOI) was used to assess flame retardancy. The LOI is a measure of the fire behavior of plastics and other materials. The LOI is the minimum oxygen concentration of a nitrogen / oxygen mixture at which combustion of a test specimen can just occur under standardized conditions. The test was conducted according to ISO 4589-2. For practical application, a value of at least 30 should be achieved.

[0069] The plasticizing effect of the phosphoric acid esters was determined by measuring the Shore A hardness of the phosphoric acid ester-containing soft PVC compounds. The measurement principle is based on the penetration depth of a metal test pin into the material sample for 15 seconds with a force of 12.5 N. The Shore A hardness was determined using test specimens measuring 50 x 40 x 6 mm. The Shore hardness measurement was carried out in accordance with DIN ISO 7619-1. A Shore A hardness of less than 95 is considered an indicator of a plasticizing effect.

[0070] The results of the measurements are summarized in Table 4. Table 4: Determination of the flame retardancy of the produced PVC samples

[0071] The results show that both the comparative products (Examples C1-C5) and the inventive mixtures S1, S2, and S3 (Examples E6-E8) exhibit good flame retardant properties. The plasticizing effect (Shore A hardness) for Comparative Examples C1-C4 and the inventive Examples E6-E8 is below 95. In contrast, the triguaiacyl phosphate (Example C5), known from WO 2014171122 A1, does not exhibit sufficient plasticizing effect. This compound is therefore unsuitable as a plasticizing flame retardant and was not investigated further.

[0072] Determination of thermal stability

[0073] Thermal stability was determined using the Congo Red method based on DIN EN ISO 182-1 3. For this purpose, the material sample was heated to 180°C in a test tube in a temperature-controlled oil bath. At this temperature, the PVC gradually decomposes, releasing hydrochloric acid. This process is strongly influenced by the formulation ingredients, which can accelerate or delay the release of hydrochloric acid. The hydrochloric acid released during the test is detected using a paper strip soaked in a Congo Red solution and placed 3 cm above the PVC sample in the test tube. The time until the color changes from red to blue was measured. The measurement results are summarized in Table 5. Table 5: Determination of the thermal stability of the PVC samples using the Congo Red method.

[0074] The results show that the inventive mixtures S1, S2, and S3 (Examples E6-E8) have a higher thermal stability than the comparative examples (Examples V1-V4).

Claims

Patent claims 1. Mixtures containing at least two substances of the general formula (I) (RO) m (PhO)3-mP=O (I) with m = 1 , 2 or 3, where R is the residue and Ph corresponds to a phenyl residue.

2. Mixtures according to claim 1, wherein R is the radical corresponds.

3. Mixtures according to claim 1 or 2, which (i) 5 to 90 wt% (RO)2(PhO)P=O, and (ii) 5 to 90 wt.% of (RO)(PhO)2P=O, where R and Ph have the meanings given above.

4. Mixtures according to one or more of claims 1 to 3, which contain less than 10% by weight, preferably less than 5% by weight, particularly preferably less than 1% by weight, very particularly preferably less than 0.5% by weight and most preferably not more than 0.2% by weight of triphenyl phosphate.

5. Mixtures according to one or more of claims 1 to 4, which are present as a liquid at 23°C and 1013 mbar, preferably as a liquid with a dynamic viscosity of 20 to 5000 mPa s, particularly preferably of 50 to 2000 mPa s (in each case at 23°C).

6. A process for the preparation of mixtures according to one or more of claims 1 to 5 comprising the steps: (a) Providing a mixture containing at least - phosphorus oxychloride and - Guaiacol, (b) reacting at least part of the mixture from a) at temperatures between 80°C and 300°C with separation of hydrogen chloride, (c) adding phenol to the mixture obtained from b) and further reacting between 100°C and 300°C with removal of hydrogen chloride, 7. The process according to claim 6, wherein between step b) and step c) a distillative separation of reactants of step a) and / or by-products takes place.

8. Process according to claim 6 or 7, wherein after step c) a distillative separation of reactants and / or by-products of steps b) and / or c) takes place.

9. Use of a mixture according to one or more of claims 1 to 5 as a flame retardant, preferably as a flame retardant for synthetic polymers, materials of plant origin or materials of animal origin, and particularly preferably as a flame retardant for polyvinyl chloride (PVC).

10. Molding composition comprising a mixture according to one or more of claims 1 to 5 and polyvinyl chloride (PVC).

11. Moulding composition according to claim 10, which contains from 5 to 150 parts by weight, preferably from 30 to 70 parts by weight, of phosphoric acid ester of formula (I) based on 100 parts by weight of PVC.

12. Use of compositions according to claim 10 or 11 for the production of coatings, films, cables, pipelines, hoses, seals, conveyor belts, roofing membranes, adhesive tape films, tarpaulins, awnings and tents.

13. Use of a mixture according to one or more of claims 1 to 5 as a hydraulic fluid.

14. Use of a mixture according to at least one of claims 1 to 5 as a lubricant additive.

15. Use of a mixture according to one or more of claims 1 to 5 as an additive for paints, adhesives, sealants or coatings.

16. Use of a mixture according to one or more of claims 1 to 5 as a heat transfer medium.

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