Triphenyl phosphate-free mixtures for flame-retardant soft PVC

Abstract

The invention relates to mixtures containing at least two substances of the general formula (I) (R1O)n(R2O)o(R3O)pP=O (I), in which n, o and p can each be 0, 1, 2 or 3 and the sum of n, o and p is 3, and R1, R2 and R3 are independently selected from the residues (II), (III), (IV), (V). The mixtures exhibit a unique combination of low phosphorus content combined with 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] Triphenyl phosphate-free compounds for flame-retardant soft PVC

[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. These esters are derived from aromatic and / or aliphatic alcohols. Often, mixtures of different alcohols are used, resulting in mixtures consisting of the various combinations of esters.

[0005] Compositions consisting of triaryl phosphoric esters and / or alkylaryl phosphoric esters have proven effective for use as flame retardants in PVC. For both economic and application-related reasons, the aryl radicals in these products are always derived at least partially from phenol or cresol. In fact, the state of the art even strongly discourages the use of exclusively highly substituted phenols (see, for example, WO 2017140609 A1). This is because the resulting phosphoric esters would exhibit poor flame retardancy due to their comparatively low phosphorus content.

[0006] A disadvantage of phenol-based mixtures is their content of triphenyl phosphate ("TPP"), which is inevitably present at least in small amounts due to the synthesis process. The hazardous properties of this substance have led to a decline in the acceptance of triphenyl phosphate-containing materials in consumer applications. Therefore, various methods have been described in the state of the art to reduce the TPP content in mixtures:

[0007] For example, WO 2017140609 A1 describes a two-step process in which phosphorus oxychloride is pre-reacted with a substoichiometric amount of alkylphenols before the resulting reaction mixture is fully reacted with phenol. However, the resulting products still contained at least 0.1 wt% TPP. Furthermore, the additional process step represents additional expense.

[0008] EP 0 573 082 B1 describes the purification of TPP-containing mixtures by distillation. However, this additional process step leads to increased production costs. Furthermore, the TPP content of the purified products was still above 1 wt%.

[0009] The use of cresol-based mixtures is also problematic from a toxicological and regulatory perspective, as ortho-cresyl phosphates are highly neurotoxic (see, for example, I. van der Veen, J. de Boer Chemosphere 2012, 88, 1119-1153). The cresol fraction used to produce phosphoric acid esters must therefore be virtually free of ortho-cresol, which requires considerable technical effort.

[0010] In order to overcome the disadvantages of the state of the art, phenol- and cresol-free alternatives are desirable.

[0011] Since the production of phosphorus is both cost- and energy-intensive, there is a particular need for flame retardants that require a low phosphorus content.

[0012] The object of the present invention was therefore to provide mixtures as flame retardants for plastics, in particular for PVC molding compounds, which are completely or almost free of triphenyl phosphate and tricresyl phosphates and have a lower phosphorus content with comparable flame retardancy.

[0013] This object is achieved by mixtures containing at least two substances of the general formula (I)

[0014] (R 1 O) n (R 2 O)o(R 3 O)pP=O (I) where n, o and p can each be 0, 1, 2 or 3 and the sum of n, o and p is 3, and R 1 , R 2 and R 3 independently of each other the remains

[0015] In a preferred embodiment, these two substances have at least one of the radicals R 1 , R 2 or R 3 together and at least one of the two substances contains two different residues.

[0016] In a further embodiment, mixtures of phosphoric acid esters are used in which all four of the above radicals for R 1 , R 2 and R 3 are present in the mixture (where, of course, each phosphorus atom is bonded to a maximum of three different radicals). However, mixtures containing a maximum of three of these radicals are preferred, and mixtures containing two of these radicals are more preferred.

[0017] The mixtures according to the invention preferably contain at least two substances of the general formula (I)

[0018] (R 1 O) n (R 2 O)o(R 3O)pP=O (I) where n = 1, 2 or 3, o = 0, 1 or 2 and p = 0, the sum of n and o being 3, where R 1 and R 2 independently of each other the remains In a preferred embodiment, these two substances have at least one of the radicals R 1 or R 2 together and at least one of the two substances has two different residues R 1 or R 2 on.

[0019] In a preferred embodiment, the content of triphenyl phosphate and tricresyl phosphates, based on the total weight of the mixture, is in each case less than 1 wt.%, preferably in each case less than 0.2 wt.%, particularly preferably in each case less than 0.1 wt.% and most preferably in each case less than 0.01 wt.%. In a further preferred embodiment of the invention, the mixtures according to the invention (R 1 O)3P=O, (R 1 O)2(R 2 O)P=O, (R 1 O)(R 2 O)2P=O and (R2 O)3P=O and optionally secondary components such as tert-butylphenol, thymol, guaiacol, phenoxyethanol, catalyst components or by-products.

[0020] In a preferred embodiment, the mixtures according to the invention contain

[0021] (R 1 O)3P=O 0 to 30 wt.%

[0022] (R 1 O)2(R 2 O)P=O 5 to 90 wt.%

[0023] (R 1 O)(R 2 O)2P=O 5 to 90 wt.%

[0024] (R 2 O)3P=O 0 to 30 wt.%, each based on the total weight of the compounds of formula (I), preferably based on the total weight of the mixture, where R 1 and R 2 have the meanings mentioned above.

[0025] The mixture according to the invention preferably has an acid number of less than 5 mg KOH / g, preferably less than 1 mg KOH / g, particularly preferably less than 0.5 mg KOH / g.

[0026] The mixture according to the invention preferably has a phosphorus content based on the total mass of phosphoric acid esters contained of less than 8.0 wt.%, preferably less than 7.5 wt.%, more preferably less than 7.2 wt.%.

[0027] The mixtures according to the invention can be prepared analogously to the known synthesis processes for phosphoric acid esters, as described, for example, in Methods of Organic Chemistry (Houben-Weyl), Thieme-Verlag, Stuttgart 1964, Volume XII / 2, p. 323 f.

[0028] The present invention therefore also relates to a process for the preparation of the mixtures according to the invention, wherein phenols of the formulas R 1 -EAR 2 -OH and possibly R 3 - OH can be reacted with POCI3 to form compounds of formula (I).

[0029] 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, Handbook of Plastics Additives, 4th edition, Munich, Carl Hanser Verlag, 2016, p. 513 ff.).

[0030] Surprisingly, it was found that the mixture according to the invention is well suited for the production of soft PVC and, despite its low phosphorus content, has a high flame retardant effect.

[0031] 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.

[0032] 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

[0033] - 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,

[0034] - Materials of plant origin, such as wood, wood-plastic composites, paper and cardboard, and

[0035] - Materials of animal origin, such as leather, are used.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] A further object of the invention is the use of the mixtures according to the invention as additives for paints, adhesives, sealants and coatings.

[0043] 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, further trialkyl phosphates, triaryl phosphates, mineral oils, polyalphaolefins, esters, antioxidants, metal deactivators, flow additives, corrosion inhibitors, foam inhibitors, demulsifiers, and / or pour point depressants. General procedure for the preparation of the mixtures according to the invention

[0044] The phenolic building blocks are placed in a reactor equipped with a stirrer, nitrogen inlet, internal thermometer, dropping funnel, and intensive condenser and dissolved in dichloromethane. At room temperature, triethylamine is added with stirring in a nitrogen countercurrent. After the addition is complete, the reaction mixture is cooled to 2-8°C and treated with a solution of POCh in dichloromethane over a period of 1-2 hours. An internal temperature of 24°C is not exceeded. After the addition is complete, stirring is continued for a further 1 hour at room temperature. The reaction mixture is filtered off, and the filter cake is washed in several portions with dichloromethane. The filtrate is washed at room temperature with aqueous sodium hydroxide solution (2 wt%) and water. The solvent and excess phenolic building blocks are then removed by distillation.

[0045] Synthesis example 1

[0046] Prepared from POCh (200 parts by weight), thymol (305 parts by weight), p-tert-butylphenol (306 parts by weight), and triethylamine (441 parts by weight) in CH2Cl2 (440 parts by weight). The acid number was 0.4 mg KOH / g. The mixture contained 24.7 wt% (ThymylO)3P=O, 19.5 wt% (ThymylO)2(p-tert-butylphenylO)P=O, 30.8 wt% (ThymylO)(p-tert-butylphenylO)2P=O, and 25.0 wt% (p-tert-butylphenylO)3P=O. The content of triphenyl phosphate and tricresyl phosphates was <0.01 wt% each.

[0047] Synthesis example 2

[0048] Prepared from POCh (201 parts by weight), guaiacol (261 parts by weight), p-tert-butylphenol (314 parts by weight), and triethylamine (442 parts by weight) in CH2Cl2 (412 parts by weight). The acid number was 1.5 mg KOH / g. The mixture contained 11.8 wt% (guaiacylO)3P=O, 37.4 wt% (guaiacylO)2(p-tert-butylphenylO)P=O, 38.0 wt% (guaiacylO)(p-tert-butylphenylO)2P=O, and 12.8 wt% (p-tert-butylphenylO)3P=O. The content of triphenyl phosphate and tricresyl phosphates was each <0.01 wt%. Synthesis Example 3

[0049] Prepared from POCh (200 parts by weight), guaiacol (257 parts by weight), thymol (307 parts by weight), and triethylamine (440 parts by weight) in CH2Cl2 (400 parts by weight). The acid number was 1.0 mg KOH / g. The mixture contained 20.0 wt% (guaiacylO)3P=O, 35.0 wt% (guaiacylO)2(thymylO)P=O, 30.0 wt% (guaiacylO)(thymylO)2P=O, and 15.0 wt% (thymylO)3P=O. The content of triphenyl phosphate and tricresyl phosphates was <0.01 wt% each.

[0050] Synthesis example 4

[0051] Prepared from POC (202 parts by weight), phenoxyethanol (281 parts by weight), p-tert-butylphenol (306 parts by weight), and triethylamine (441 parts by weight) in CH2Cl2 (400 parts by weight). The acid number was 0.4 mg KOH / g. The mixture contained 10.0 wt% (phenoxyethyl)3P=O, 34.2 wt% (phenoxyethyl)2(p-tert-butylphenyl)P=O, 39.6 wt% (phenoxyethyl)2(p-tert-butylphenyl)2P=O, and 16.2 wt% (p-tert-butylphenyl)3P=O. The content of triphenyl phosphate and tricresyl phosphates was <0.01 wt% each.

[0052] Synthesis example 5

[0053] Prepared from POC (201 parts by weight), phenoxyethanol (281 parts by weight), guaiacol (251 parts by weight), and triethylamine (440 parts by weight) in CH2Cl2 (400 parts by weight). The acid number was 0.4 mg KOH / g. The mixture contained 7.7 wt% (phenoxyethylO)3P=O, 37.2 wt% (phenoxyethylO)2(guaiacylO)P=O, 44.4 wt% (phenoxyethylO)2(guaiacylO)2P=O, and 10.7 wt% (guaiacylO)3P=O. The content of triphenyl phosphate and tricresyl phosphates was <0.01 wt% each.

[0054] Synthesis example 6

[0055] Prepared from POCl3 (200 parts by weight), phenoxyethanol (281 parts by weight), thymol (305 parts by weight), and triethylamine (403 parts by weight) in CH2Cl2 (407 parts by weight). The acid number was 0.6 mg KOH / g. The mixture contained 12.6 wt% (phenoxyethylO)3P=O, 41.7 wt% (phenoxyethylO)2(thymylO)P=O, 34.6 wt% (phenoxyethylO)2(thymylO)2P=O, and 11.1 wt% (thymylO)3P=O. The content of triphenyl phosphate and tricresyl phosphates was <0.01 wt% each. Determination of the composition of the mixtures

[0056] 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.

[0057] The analytical data of synthesis examples S1 to S6 are summarized in Table 1.

[0058] Table 1: Amounts used and analytical data of synthesis examples S1 to S6.

[0059] Determination of the acid number of the phosphoric acid ester composition

[0060] 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 with stirring. A blank value was measured in the same way, but without the sample.

[0061] Comparison samples of known phosphoric acid ester compositions

[0062] 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.

[0063] Table 2: Comparison samples used.

[0064] Production of soft PVC

[0065] 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.

[0066] 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.

[0067] Table 3: Recipe ingredients for the production of soft PVC.

[0068] Determination of flame retardancy

[0069] The Limiting Oxygen Index (LOI) was used to assess flame resistance. The LOI is a measure of the fire behavior of plastics and other materials. The LOI is the minimum oxygen concentration of a

[0070] 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. The measurement results are summarized in Tables 4 and 5.

[0071] Table 4: Flame retardancy of PVC containing triaryl phosphoric acid ester The results show that PVC compounds containing the known phosphoric acid triaryl ester compositions Disflamoll® DPK, Disflamoll® 51092, and Reofos® 65 achieve LOI values ​​of 31.4 to 32.9 (Examples 1-3). The inventive phosphoric acid triaryl ester compositions S1, S2, and S3 achieve values ​​in the same range despite their significantly lower phosphorus content (Examples E1 to E3).

[0072] Table 5: Flame retardancy of PVC containing phosphoric acid arylalkyl esters

[0073] The LOI value of the PVC compound containing the mixed phosphoric acid arylalkyl ester composition Disflamoll® DPO is significantly lower (27.4; Example C4) than that of phosphoric acid triaryl ester compositions. However, the mixed phosphoric acid arylalkyl ester compositions S4, S5, or S6 according to the invention achieve higher LOI values ​​(27.8-27.9) than Disflamoll® DPO despite their lower phosphorus content (Examples E4-E6).

[0074] All plasticizers listed in Tables 4 and 5 were suitable for producing soft PVC compounds.

[0075] Since in the prior art a high phosphorus content of a mixture is described as a prerequisite for a high flame retardancy (see e.g. WO 2017140609 A1), it was surprising for the person skilled in the art that with the phosphoric acid triaryl ester compositions according to the invention, despite a significantly lower phosphorus content, a flame retardancy comparable to or even better than the corresponding classes (phosphoric acid triaryl esters or mixed phosphoric acid arylalkyl esters) can be achieved.

Claims

1. Mixtures containing at least two substances of the general formula (I) (R 1 O)n(R 2 O)o(R 3 O) p P=O (I) where n, o and p can each be 0, 1, 2 or 3 and the sum of n, o and p is 3, and R 1 , R 2 and R 3 are independently selected from the residues 2. Mixtures according to claim 1, wherein the two substances contain at least one of the radicals R 1 , R 2 or R 3 in common and at least one of the two substances has two different residues.

3. Mixtures according to claim 1 or 2 containing at least two substances of the general formula (I) (R 1 O) n (R 2 O)o(R 3 O)pP=O (I) where n = 1, 2 or 3, o = 0, 1 or 2 and p = 0, the sum of n and o being 3, where R 1 and R 2have the meaning given above and wherein preferably the two substances contain at least one of the radicals R 1 or R 2 in common and at least one of the two substances has two different residues R 1 or R 2 has.

4. Mixtures according to one or more of claims 1 to 3, wherein the content of triphenyl phosphate and of tricresyl phosphates is in each case less than 1 wt.%, preferably in each case less than 0.2 wt.%, particularly preferably in each case less than 0.1 wt.% and most preferably in each case less than 0.01 wt.%, based on the total weight of the mixture.

5. Mixture according to one or more of claims 1 to 4 containing (i) 0 to 30 wt.% (R 1 O)3P=O, (ii) 5 to 90 wt.% (R 1 O)2(R 2 O)P=O, (iii) 5 to and (iv) 0 to each based on the total weight of compounds (i) to (iv), where R 1and R 2 have the meanings mentioned above.

6. Mixture according to one or more of claims 1 to 5, wherein the phosphorus content, based on the total mass of the phosphoric acid esters contained, is less than 8.0 wt.%, preferably less than 7.5 wt.%, more preferably less than 7.2 wt.%.

7. Mixture according to one or more of claims 1 to 6 containing one or more flame retardants different from the composition and optionally one or more auxiliaries.

8. A process for the preparation of mixtures according to one or more of claims 1 to 7, comprising the reaction of phenols of the formulas R 1 -EAR 2 - OH and possibly R 3 -OH with POCI3 to form compounds of formula (I).

9. Use of a mixture according to one or more of claims 1 to 7 as a flame retardant, preferably as a flame retardant for synthetic polymers, materials of plant origin or materials of animal origin, 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 7 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 esters of formula (I) based on 100 parts by weight of PVC.

12. Use of molding 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 or tents.

13. Use of mixtures according to one or more of claims 1 to 7 as hydraulic fluid.

14. Use of mixtures according to one or more of claims 1 to 7 as lubricant additive.

15. Use of mixtures according to one or more of claims 1 to 7 as an additive for paints, adhesives, sealants or coatings.

16. Use of a mixture according to one or more of claims 1 to 7 as a heat transfer medium.

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