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

Abstract

The invention relates to mixtures containing at least two substances of the general formula (I) (RO)m(PhO)3-mP=O (I), where m = 1, 2 or 3, in which R corresponds to the residue (formula II) and Ph corresponds to the phenyl group. The mixtures exhibit a unique combination of high colour 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 color stability

[0002] Phosphoric acid esters can be used in various technical applications, e.g. as lubricants (cf. US 10,414,964 B2), hydraulic fluids (cf. US 6,703,355 B2), plasticizers (cf. DE 1 768 076) or as flame retardants (cf. US 8,129,457 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) or in styrene polymers (cf. US 8,026,303 B2).

[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 esters, those skilled in the art are also familiar with mixed alkyl aryl phosphoric esters. These are used, for example, as flame retardants when increased color or heat stability is required (cf. US Pat. No. 5,087,521). This is necessary, among other things, for plastics used in outdoor applications, particularly for coatings, cables, tarpaulins, awnings, or tents, to prevent the material from yellowing under the influence of heat. However, the increased color stability comes at the cost of lower flame retardancy compared to triaryl phosphates. Therefore, US Pat. No. 5,087,521 uses mixtures of diarylalkyl phosphates and triaryl phosphates. Even if this deficiency can be mitigated according to US Pat. No. 5,087,521 by using mixtures of diarylalkyl phosphates and triaryl phosphates, the poor flame retardancy of alkyl aryl phosphoric esters remains a disadvantage.The use of two different flame retardant preparations according to US 5,087,521 also represents a considerable additional synthetic effort.

[0006] US 20120004438 A1 discloses a process for producing mixed alkylated triaryl phosphates, in which the first step involves reacting an alkylated phenol (containing up to 25% dialkylated phenol) with POC to obtain a product containing more than about 75 mol% monoalkylphenyl dichlorophosphates. This product is then further reacted with other alkyl or aryl alcohols to form the triester (see claim 1). However, the triesters obtained do not exhibit improved color stabilization compared to the prior art flame retardants (see Table 23). Interpretation of the results is further complicated by the fact that it is not specifically stated which of the inventive flame retardants were used in Examples TS-06-9D to TS-06-9F.

[0007] Similarly, EP 0401366 A4 uses mixtures of cyclic aryl phosphates with halogen-containing compounds to produce color-stable, flame-retardant PVC materials. However, the use of halogen-containing flame retardants is often problematic from a regulatory perspective.

[0008] 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.

[0009] 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 leads to considerable additional technical effort. Furthermore, antimony trioxide has a negative effect on the transparency of the PVC compound, which is undesirable for some demanding applications.

[0010] 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, in particular for PVC molding compounds, and also exhibits high color 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. This object is achieved by mixtures comprising at least two substances of the general formula (I)

[0011] (RO) m (PhO)3-mP=O (I) 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, 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 thymol, phenol, catalyst components or by-products.

[0013] 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

[0014] (RO)m(PhO) 3.m P=O (I), where R, Ph and m have the meanings given above.

[0015] In a preferred embodiment, the mixtures according to the invention contain

[0016] (i) 5 to 90 wt% (RO)2(PhO)P=O, and

[0017] (ii) 5 to 90 wt.% (RO)(PhO)2P=O, based in each case on the total amount of compounds of formula (I) with m = 0, 1, 2 or 3, where R and Ph have the meanings given above. A further preferred embodiment is a mixture comprising:

[0018] (RO)3P=O 0 to 30 wt.%

[0019] (RO)2(PhO)P=O 5 to 90 wt.%

[0020] (RO)(PhO)2P=O 5 to 90 wt.%

[0021] (PhO)3P=O (“TPP”) 0 to 30 wt.%, each based on the total weight of the compounds of formula (I) with m = 0, 1, 2 or 3, preferably each based on the total weight of the mixture, where R and Ph have the meanings given above

[0022] The mixtures according to the invention preferably contain less than 1% by weight, particularly preferably less than 0.5% by weight, further preferably less than 0.2% by weight, very particularly preferably less than 0.5% by weight and most preferably not more than 0.1% by weight of triphenyl phosphate.

[0023] 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).

[0024] 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.

[0025] Surprisingly, it was found that PVC molding compounds containing the inventive mixture exhibit high color 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.

[0026] 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 thymol, 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,

[0027] In an alternative embodiment, at least a portion of the phosphorus oxychloride is added only in step b). It is also possible that at least a portion of the thymol is added only in step b).

[0028] A catalyst can optionally be added to the mixture prepared in step a) or during step b). Suitable catalysts include NaCl, KCl, LiCl, MgCl2, MgO, CaCh, AlCl, FeCl, ZnCl, TiCl, SbCl, and others. Optionally, one or more catalysts can also be added before or during step 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 100°C to 250°C, particularly preferably in the range from 100°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 only 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). Optionally, after step c), a distillative separation of (unreacted) reactants and / or by-products formed in steps b) and / or c) 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. 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.

[0033] Depending on the application, the mixtures according to the invention may 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, free 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 stabilizers, or biocides (see, for example, RD Maier, M. Schiller, Handbuch Kunststoff-Additive, 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 thus 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 those skilled in the art. The mixtures according to the invention are preferably used as flame retardants for 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.

[0036] Materials of plant origin, such as wood, wood-plastic composites, paper and cardboard, and

[0037] Materials of animal origin, such as leather, are used. 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 granules, a powder, a paste, or a plastisol.

[0038] 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 and compounding 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.) or by dispersing the mixture to form a ready-to-process plastisol or organosol.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] The invention further relates to the use of the mixtures according to the invention as additives for paints, adhesives, sealants, and coatings. 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 for 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.

[0044]

[0045] Synthesis example 1

[0046] Phosphorus oxychloride (200 parts by weight), thymol (197 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 120°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 (307 parts by weight), the temperature of the reaction mixture was gradually increased to a final temperature of 160°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 (110 mPa s at 23°C). The acid number was <0.1 mg KOH / g. The product mixture contained 0.6 wt% (ThymylO)3P=O, 12.7 wt%.-% (ThymylO)2(PhO)P=O, 86.3 wt.% (ThymylO)-(PhO)2P=O and 0.4 wt.% (PhO)3P=O (“TPP”).

[0047] Synthesis example 2

[0048] Phosphorus oxychloride (200 parts by weight), thymol (295 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 160°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 190°C and maintained at this temperature until complete conversion. Excess phenol was removed at a final temperature of 190°C and a pressure of 10 mbar. The product mixture was isolated as a viscous liquid (210 mPa s at 23°C). The acid number was <0.1 mg KOH / g. The product mixture contained 2.4 wt.% (ThymylO)3P=O, 56.0 wt.% (ThymylO)2(PhO)P=O, 41.4 wt.% (ThymylO)(PhO)2P=O, and 0.2 wt.% (PhO)3P=O (“TPP”). Synthesis Example 3

[0049] Phosphorus oxychloride (200 parts by weight), thymol (394 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 160°C with stirring and maintained at this temperature until gas evolution was barely observable. After adding phenol (186 parts by weight), the temperature of the reaction mixture was gradually increased to a final temperature of 190°C and maintained at this temperature until conversion was complete. Excess phenol was removed at a final temperature of 190°C and a pressure of 10 mbar. The product mixture was isolated as a viscous liquid (390 mPa s at 23°C). The acid number was <0.1 mg KOH / g. The product mixture contained 8.6 wt% (ThymylO)3P=O, 81.1 wt% (ThymylO)2(PhO)P=O, 10.2 wt% (ThymylO)(PhO)2P=O and < 0.1 wt% (PhO)3P=O (“TPP”).

[0050] The amounts used in synthesis examples S1 to S3 are summarized in Table 1.

[0051] Table 1: Amounts used and analytical data of synthesis examples S1 to S3. Determination of the composition of the phosphoric acid ester composition

[0052] 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.

[0053] Determination of the viscosity of the phosphoric acid ester composition

[0054] 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.

[0055] Determination of the acid number of the phosphoric acid ester composition

[0056] 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.

[0057] Table 2 lists known phosphoric acid ester compositions that were used as reference samples for the production of soft PVC. All reference samples are products of Lanxess Deutschland GmbH. Table 2: Reference samples used.

[0058] Production of soft PVC

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The test specimens for the color stability test 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.

[0063] PVC samples were produced according to this regulation.

[0064] Determination of flame retardancy and plasticizer effect

[0065] 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.

[0066] 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.

[0067] The results of the measurements are summarized in Table 4. Table 4: Determination of the flame retardancy of the produced PVC samples

[0068] The results show that the inventive phosphoric acid ester compositions in PVC exhibit similarly good flame retardant properties as the comparative products Disflamoll DPK, Disflamoll TKP, Disflamoll 51092, and Reofos 65. As expected, the LOI of the PVC compound of the phosphoric acid alkyl aryl ester Disflamoll DPO is significantly lower, which is associated with a lower flame retardant effect. All flame retardants used achieved Shore A hardnesses of less than 95 in the test, i.e., they exhibited a plasticizing effect.

[0069] Determination of color stability

[0070] All plastics are subject to an undesirable aging process, which manifests itself in altered mechanical properties and a change in color, usually yellowing. The color stability of the soft PVC compounds under thermal stress was tested using the Mathis oven (Mathis Thermotester LTE T). Material samples were stored at 180°C in a convection oven for 30 minutes. Material samples were removed from the hot oven area at intervals, so that material samples exposed to different temperatures were obtained. The yellowness values ​​(Delta E values) were determined using a Minolta Chroma Meter CR 400. The measurement was carried out in accordance with DIN EN ISO 10545-16. Table 5: Measured yellowness values ​​after storage in an oven at 180°C

[0071] The results show that in the PVC compounds containing the phosphoric acid ester compositions S1, S2 and S3 according to the invention, the increase in

[0072] Yellowness (i.e. discoloration) occurs significantly later than in the compounds containing the comparison products.

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 the phenyl residue.

2. Mixtures according to claim 1, 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.

3. Mixtures according to one or more of claims 1 or 2, which contain less than 1% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.2% by weight and most preferably not more than 0.1% by weight of triphenyl phosphate.

4. Mixtures according to one or more of claims 1 to 3, 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 1000 mPa s (in each case at 23°C).

5. A process for the preparation of mixtures according to one or more of claims 1 to 4 comprising the steps: (a) Providing a mixture containing at least: - Phosphorus oxychloride - Thymol, (b) reacting at least part of the mixture of a) at temperatures between 80°C and 300°C with separation of hydrogen chloride and (c) Addition of phenol to the mixture obtained from b) and further reaction between 100°C and 300°C with removal of hydrogen chloride.

6. The process according to claim 5, wherein between step b) and step c) a distillative separation of reactants of step a) and / or by-products takes place.

7. The process according to claim 5 or 6, wherein after step c) a distillative separation of reactants and / or by-products of steps b) and / or c) takes place.

8. Use of mixtures according to one or more of claims 1 to 4 as flame retardants, preferably as flame retardants for synthetic polymers, materials of plant origin or materials of animal origin, and particularly preferably as flame retardants for polyvinyl chloride (PVC).

9. Molding composition comprising a mixture according to one or more of claims 1 to 4 and polyvinyl chloride (PVC).

10. Moulding composition according to claim 9, 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.

11. Use of molding compositions according to claim 9 or 10 for the production of coatings, films, cables, pipelines, hoses, seals, conveyor belts, roofing membranes, adhesive tape films, tarpaulins, awnings or tents.

12. Use of mixtures according to one or more of claims 1 to 4 as hydraulic fluid.

13. Use of mixtures according to one or more of claims 1 to 4 as lubricant additive.

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

15. Use of a mixture according to one or more of claims 1 to 4 as a heat transfer medium.

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