DE102011056368A1 - Halogen-free flame retardant for thermoplastic polyurethane (TPU) - Google Patents

Abstract

Halogen-free flame retardant for flameproofing of thermoplastic polyurethane (TPU), which contains a mixture of melamine polyphosphate and melamine cyanurate, and self-extinguishing thermoplastic polyurethane (TPU) containing this halogen-free flame retardant.

Description

Subject of the invention

The invention relates to a halogen-free flame retardant for flameproofing of thermoplastic polyurethanes (TPU) and self-extinguishing thermoplastic polyurethanes containing the halogen-free flame retardant of the invention.

Background of the invention

One way to make polymers flame retardant, the addition of halogen-containing flame retardants, however, are increasingly replaced by halogen-free flame retardants, as far as possible due to heavy flue gas development and partly the release of toxic substances in case of fire. Among the flame-retardant alternative substances, especially derivatives of phosphoric acid, pyrophosphoric acid and polyphosphoric acids are used in halogen-free flame retardants. Ammonium and melamine derivatives of the abovementioned substances and also piperazine phosphate and ethylenediamine phosphate have the property of inflating themselves embedded in molding compounds to form voluminous protective layers at high temperatures and to act as an insulating layer against a heat source. The swelling, the so-called intumescence, in contrast to the mode of action of halogen-containing flame retardants without the development of larger amounts of flue gases.

A quality feature of a flame retardant is the requisite amount of flame retardant needed to provide sufficient effectiveness in a particular polymeric material. Often, 30 to 60 weight percent or more of flame retardant must be added to a polymer to achieve acceptable potency. However, in many cases this leads to an undesirable change in particular of the mechanical, electrical and / or optical properties of the polymer.

So far, the most effective flame retardants include mixtures of ammonium polyphosphate with amines, such as. B. mixtures with melamine compounds and / or pentaerythritol. Other known intumescent mixtures are based on ammonium polyphosphates in combination with THEIC (1,3,5-tris-hydroxyethyl isocyanuric acid).

The disadvantage of these mixtures, however, is that they have a very high water solubility even after incorporation into a polymer, so that they are partially washed out and therefore can no longer develop their effect. Furthermore, they have a low decomposition temperature, which sometimes already results in the formation of the plastic objects from the polymers to be protected to a decomposition of the flame retardant additive. Furthermore, despite improved efficacy, these blends must be used in high concentrations in a polymer, thereby lowering the processability and flexibility of the polymer.

Thermoplastic polyurethanes (TPU) are used in many areas of technology, for example in the electrical and electronics sector, in the construction sector, in building technology, in automotive construction and in public transport. They have advantageous mechanical properties and have good processability and chemical resistance. The production of thermoplastic polyurethanes (TPU) is known (see, for example, US Pat. Kunststoff-Handbuch, Volume VII, Polyurethane, Carl-Hanser-Verlag, Munich, 1st edition, 1966, edited by dr. R. Vieweg and dr. A. Höchtlen, and 2nd edition, 1983, edited by Dr. med. G. Oertel ).

TPUs are highly flammable, which is why they are used in many applications with halogen-containing or halogen-free flame retardants. However, the addition of halogen-containing flame retardants often has a negative impact on the mechanical properties of the TPU and is associated with the disadvantages previously described, which are generally associated with the use of halogen-containing flame retardants. The use of halogen-free flame retardants in TPU is therefore desirable. TPU with melamine or melamine derivatives as flame retardants are for example in US-A-4,221,875 . US-A-4,258,141 . US-A-4,293,657 . JP-A-79175 629 . DE-A-40 05 373 . EP-A-0 389 768 and EP-A-0 352 528 described. The EP-A-0 617 079 and the JP-A-79/85242 describe the use of melamine cyanurate as a flame retardant also for TPU.

There are a number of parameters pertaining to the suitability of a substance as a flame retardant for polymeric materials and are examined in standardized tests. As a rule, it is only the first All of the parameters that determine whether a substance can be used as a flame retardant in a given application.

The UL94 test measures the time it takes to extinguish the flame or the glow of a specimen and checks whether burning drops drip off the specimen and ignite the cotton below ("burning dripping"). Both are taken alone, but especially in combination, very important criteria for the suitability of a substance as a flame retardant.

Many good halogen-free flame retardants are known from the prior art. However, it has been shown that it is precisely for the flame-retardant finish of TPU that the known flame retardants provide good to excellent results with respect to certain of the test parameters mentioned above, but there is room for improvement in other equally important parameters. For example, it has been found that some of the known flame retardants commonly used individually or in the usual combinations, although very good in the UL94 test, d. H. short times reach until the extinction of the flame, but they drop relatively strong. Gerde the dropping of burning drops is undesirable and dangerous in many applications of flame-retardant plastics, because on the one hand a major risk of injury to persons who are struck by falling burning drops, on the other hand, the falling burning drops ignite other objects, which are just avoided should.

Object of the invention

The present invention has for its object to provide halogen-free flame retardants for flameproofing of thermoplastic polyurethanes (TPU), which reduce the burning dripping in case of fire compared to known flame retardants. The flame retardants should not substantially affect the mechanical properties and the processing properties of the TPU.

Description of the invention

This object is achieved by a halogen-free flame retardant for flameproofing of TPU containing a mixture of melamine polyphosphate and melamine cyanurate.

The use of melamine derivatives in numerous combinations with other components as components of flame retardants has long been known. In many polymer materials, these flame retardants can show quite good properties in terms of burning or non-burning dripping in case of fire. In TPU, however, dripping resistance was lower than desired for flame retardants containing melamine derivatives.

The inventors have now surprisingly found that it is precisely through the combination of melamine polyphosphate and melamine cyanurate that a synergistic effect is achieved in TPU and the burning dripping can be significantly reduced compared with other flame retardants and in particular with respect to the individual substances melamine polyphosphate and melamine cyanurate.

Without wishing to be bound by or limited by any theory, the inventors believe that the synergistic effect is due to the fact that the melamine polyphosphate contributes to the formation of a carbon protective layer and the melamine cyanurate promotes the swelling of this solid protective layer. As a result, the melting and dripping of the material is significantly reduced because the easily deformable TPU is protected by an insulating layer.

In a preferred embodiment of the flame retardant according to the invention, the weight ratio of melamine polyphosphate to melamine cyanurate in the flame retardant is 25:75 to 75:25, preferably 35:65 to 65:35, particularly preferably 45:55 to 55:45.

An optimum weight ratio of melamine polyphosphate to melamine cyanurate depends on the properties of the TPU. In a TPU type, which is easier to form a carbon layer by itself, e.g. B. if proportionately less aliphatic groups are contained in the TPU, a smaller amount of melamine polyphosphate is sufficient to build up an efficient carbon layer in cooperation with the melamine cyanurate. Endothermic effects contribute to the fact that the material does not ignite.

Has a TPU type, however, rather a low tendency to build a carbon layer, eg. B. if many aliphatic groups are present in the polymer, then a larger amount of Melaminpolyphosphat be used because its decomposition can form a protective layer of polyphosphoric acid and carbon, which protects the underlying polymer from further decomposition and ignition and thus prevents burning dripping. The melamine cyanurate helps to form the protective layer by decomposing into inert gases and cooling endothermically. Therefore, outside of the preferred ranges of weight ratio of melamine polyphosphate to melamine cyanurate, the material will be easier to ignite or ignite. The variation of the weight ratio of melamine polyphosphate to melamine cyanurate as a function of the TPU type used does not impair the above-described surprising synergistic effect of the components used according to the invention.

In a further preferred embodiment of the invention, the flame retardant melamine polyphosphate and melamine cyanurate to substantially equal parts by weight, d. H. in a weight ratio of 1: 1 and 50:50 respectively.

In yet another embodiment of the invention, the flame retardant consists essentially only of melamine polyphosphate and melamine cyanurate to substantially equal parts by weight, apart from conventional and / or production-related impurities.

In yet another preferred embodiment of the flame retardant according to the invention, the mixture of melamine polyphosphate and melamine cyanurate makes up 50 to 100% by weight or 60 to 90% by weight or 70 to 80% by weight of the flame retardant.

If in the flame retardant according to the invention the mixture of melamine polyphosphate and melamine cyanurate constitutes 100% by weight, the flame retardant consists essentially only of this mixture, apart from customary and / or production-related impurities.

In addition to melamine polyphosphate and melamine cyanurate, however, the flame retardant may contain further constituents which improve the anti-hamming effect. It can be added in terms of gas formation active (gas-active) substances such. As phosphinates or polymeric DOPO derivatives, or flame retardants that can enhance the protective layer to be formed, such as. B. boron phosphate, melamine phosphate. Furthermore, substances may be included in the flame retardant that reduce the smoke density, z. As zinc phosphate, zinc borate, copper hydroxide, etc. The auxiliaries and / or additives further contained in the flame retardant according to the invention in addition to melamine polyphosphate and melamine cyanurate are preferably themselves flame-retardant and / or intumescent substances, glass formers or the drip-inhibiting additives.

In a preferred embodiment of the invention, the flame retardant contains in addition to melamine polyphosphate and melamine cyanurate 1 to 50 wt .-% or 5 to 40 wt .-% or 15 to 30 wt .-% ammonium polyphosphate (APP). Ammonium polyphosphate supports the formation of a protective layer in the flame retardant according to the invention, since it decomposes at temperatures as low as 250.degree. However, the amount of ammonium polyphosphate should be within the aforementioned limits because too high an amount of ammonium polyphosphate can destabilize the polymer and degrade the mechanical properties, water solubility and processability.

In a further preferred embodiment of the invention, the flame retardant contains in addition to melamine polyphosphate and melamine cyanurate 0.05 to 5 wt .-% or 0.1 to 2 wt .-% or 0.2 to 1 wt .-% polytetrafluoroethylene (PTFE) or tetrafluoroethylene ( TFE) terpolymers, for example those with vinyl acetate (VAc) and polydimethylsiloxane methyl acrylate (PDMSMA), P (TFE-ter-VAc-ter-PDMSMA) and others, the z. B. from the US-A-4,029,868 are known.

It has surprisingly been found that even a small amount of PTFE or TFE terpolymer can be sufficient to considerably improve the dripping behavior of TPU with the flame retardant according to the invention. It is believed that PTFE or TFE terpolymer forms within the polymer linear structures that affect the viscoelastic properties of the polymer in terms of improved dripping behavior without significantly affecting the mechanical properties of the polymer. On the other hand, excessively large amounts of PTFE or TFE terpolymer disadvantageously alter the physical properties of the polymer, in particular the surface properties, giving, depending on the amount used, a strongly to very strongly hydrophobic surface. Too small amounts of PTFE or TFE terpolymer do not have the desired effect described above.

In a further preferred embodiment of the invention, the flame retardant contains in addition to melamine polyphosphate and melamine cyanurate 0.1 to 5 wt .-% or 0.2 to 2.5 wt .-% or 0.5 to 2 wt .-% of a glass former, preferably one Silicates or borates, more preferably melamine borate or boron phosphate. Too small an amount of the glass former has no effect, whereas too much may affect the mechanical properties of the polymer.

In a further preferred embodiment of the invention, in the flame retardant, the melamine polyphosphate has a mean condensation degree n (number average)> 20, a pH of a 10% slurry of the melamine polyphosphate in water at 25 ° C of 5 or higher, a molar ratio of melamine to Phosphorus (M / P) <1.1 and a decomposition temperature> 320 ° C. The molar ratio of melamine to phosphorus (M / P) is determined indirectly by determining the chain length of the melamine polyphosphate by means of phosphorus NMR (31P-NMR).

In another embodiment, the melamine polyphosphate has a molar ratio of melamine to phosphorus (M / P) ≦ 1.0, preferably in the range of 0.8 to 1.0.

In another embodiment, a 10% slurry of the melamine polyphosphate in water at 25 ° C has a pH in the range of 5.1 to 6.9.

In a further embodiment, the decomposition temperature of the melamine polyphosphate is higher than 360 ° C, preferably higher than 380 ° C, particularly preferably higher than 400 ° C.

In a further preferred embodiment of the invention, the melamine polyphosphate in the flame retardant has a solubility in water at 25 ° C. of <0.1 g / 100 ml, preferably <0.01 g / 100 ml.

The invention also relates to a self-extinguishing thermoplastic polyurethane (TPU) with a halogen-free flame retardant according to the invention described herein, wherein the halogen-free flame retardant in an amount of 5 to 40 wt .-% or in an amount of 10 to 30 wt .-% or in an amount from 15 to 25 wt .-% based on the total thermoplastic polymer composition.

Basically, the flame retardant effect increases with increasing amount of flame retardant in the TPU. However, it is an effort to keep the amounts of flame retardant and thus its influence on the properties of the polymer with a good or sufficient flame retardancy as low as possible. Excessive amount of flame retardant in the TPU affects the mechanical properties of the polymer, complicates processing and thus limits the scope of application of the TPU. An advantage of the flame retardant according to the invention is its surprisingly good effectiveness in TPU, which has the advantage that you can manage with smaller amounts of flame retardant to achieve compared to other flame retardants from the prior art, a comparable flame retardant effect.

Examples

In the following examples, both flame retardant compositions according to the invention and non-inventive compositions in thermoplastic polyurethanes are compared with regard to their flame-retardant action and to burning drops in the event of fire.

For the examples, specimens were prepared for various investigations in a Grabender plastic kneader. For this purpose, the polymer material was initially melted with no flame retardant additive with movement. Subsequently, the components of the flame retardant were added in one step as a mixture or successively the melt. After a homogenization phase of 10 to 15 minutes, the polymer material was removed and pressed by means of a heated press into sheets with thicknesses of 3.2 mm. The pressed plates were cut to suitable test specimens using a saw and subjected to the tests described below.

UL94 vertical test

To perform the UL94 vertical test, a set of five 3.2 mm thick specimens each was clamped at one end in a vertical position. A Bunsen burner flame was held twice for 10 seconds at the free end of the test specimen. Thereafter, the time was until the expiration of the Flame or the annealing of the specimen measured. At the same time it was determined whether inflamed drops of the test specimen could ignite underlying cotton ("burning dripping").

"TBT" indicates the sum of the burn times of a total of 5 test specimens in seconds.

The tests were carried out in accordance with the specifications of Underwriter Laboratories, Standard UL 94V. "UL94" means the fire rating of the specimen, where V0 means that the total burn time of 5 specimens tested was less than 50 seconds and cotton was not ignited by dripping glowing or burning components of the specimen. The rating V2 means that the total burning time of 5 test specimens tested was less than 250 seconds in total, but a cotton cloth was inflamed by dripping test specimen constituents. The statement n. C. means that the burning time was more than 250 seconds or the test specimen burned down to a clamp in which it was clamped.

The "burning dripping" was additionally evaluated separately on a scale from 0 to 4, where the numerical values have the following meaning:
0 no burning dripping
1 low burning dripping
2 medium burning drips
3 strong burning drips
4 very strong burning dripping

The compositions of the different test specimens or comparison test specimens and the results of the tests are given in Table 1. Explanation of the terms used: Budit 3141: Melamine polyphosphate (manufacturer: Budenheim Iberica) Budit 315: Melamine cyanurate (manufacturer: Budenheim Iberica) FR CROS C30: melamine-coated ammonium polyphosphate FR CROS 489: melamine-coated and crosslinked ammonium polyphosphate (Manufacturer of all FR CROS products: Budenheim Iberica) MM 5935: PTFE derivative

The results clearly show that the flame retardants according to the invention have a significant improvement in terms of flame retardant properties (eg fire protection class) and / or the burning dripping behavior compared to comparison agents in TPU. Table 1: Compositions, results of flame retardancy tests and weight loss of the flame retardant (without plastic) of 2% Example no. 1 2 3 4 5 6 7 8th 9 Compositions [% by weight] Budit 3141 10 5 5 7.5 10 7.46 Budit 315 10 5 5 5 7.5 10 7.46 FR CROS 489 5 FR CROS C30 20 10 5 4.96 M 5935 0.12 TPU 90 90 90 90 80 80 80 80 80 Flame retardant tests test layer thickness TBT [sec] 3.2 mm 53 69 16 112 > 250 34 12 14 38 UL94 [class] 3.2 mm V-2 V-2 V-2 V-2 nc V-0 V-0 V-2 V-0 Burning dripping 3.2 mm 3 4 2 2 - 1 1 2 0

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4221875 A [0007]
• US 4258141 A [0007]
• US 4293657 A [0007]
• JP 79175629 A [0007]
• DE 4005373 A [0007]
• EP 0389768 A [0007]
• EP 0352528 A [0007]
• EP 0617079A [0007]
• JP 79/85242 A [0007]
• US 4029868A [0025]

Cited non-patent literature

• Kunststoff-Handbuch, Volume VII, Polyurethane, Carl-Hanser-Verlag, Munich, 1st edition, 1966, edited by dr. R. Vieweg and dr. A. Höchtlen, and 2nd edition, 1983, edited by Dr. med. G. Oertel [0006]

Claims (11)

Halogen-free flame retardant for flameproofing of thermoplastic polyurethane (TPU), characterized in that the flame retardant contains a mixture of melamine polyphosphate and melamine cyanurate. Halogen-free flame retardant according to Claim 1, characterized in that the weight ratio of melamine polyphosphate to melamine cyanurate in the flame retardant is 25:75 to 75:25, preferably 35:65 to 65:35, particularly preferably 45:55 to 55:45. Halogen-free flame retardant according to one of the preceding claims, characterized in that the mixture of melamine polyphosphate and melamine cyanurate 50 to 100 wt .-% or 60 to 90 wt .-% or 70 to 80 wt .-% of the flame retardant makes up. Halogen-free flame retardant according to one of the preceding claims, characterized in that it contains, in addition to melamine polyphosphate and melamine cyanurate further auxiliaries and / or additives. Halogen-free flame retardant according to one of the preceding claims, characterized in that it contains, in addition to melamine polyphosphate and melamine cyanurate 1 to 50 wt .-% or 5 to 40 wt .-% or 15 to 30 wt .-% ammonium polyphosphate. Halogen-free flame retardant according to one of the preceding claims, characterized in that it contains, in addition to melamine polyphosphate and melamine cyanurate, 0.05 to 5% by weight or 0.1 to 2% by weight or 0.2 to 1% by weight polytetrafluoroethylene (PTFE) or tetrafluoroethylene (TFE) terpolymer. Halogen-free flame retardant according to one of the preceding claims, characterized in that in addition to melamine polyphosphate and melamine cyanurate 0.1 to 5 wt .-% or 0.2 to 2.5 wt .-% or 0.5 to 2 wt .-% of a glass former , preferably a silicate or borate, particularly preferably melamine borate or boron phosphate. Halogen-free flame retardant according to one of the preceding claims, characterized in that the melamine polyphosphate a mean condensation degree n (number average)> 20, a pH of a 10% slurry of Melaminpolyphosphates in water at 25 ° C of 5 or higher, a molar ratio of melamine to phosphorus (M / P) <1.1 and a decomposition temperature> 320 ° C. Halogen-free flame retardant according to one of the preceding claims, characterized in that the melamine polyphosphate has a solubility in water at 25 ° C of <0.1 g / 100 ml, preferably <0.01 g / 100 ml and / or the molar ratio of melamine to Phosphorus (M / P) <1.0, preferably in the range of 0.8 to 1.0, and / or a 10% slurry of the melamine polyphosphate in water at 25 ° C has a pH in the range of 5.1 to 6.9 and / or the decomposition temperature of the melamine polyphosphate is higher than 360 ° C, preferably higher than 380 ° C, particularly preferably higher than 400 ° C. Halogen-free flame retardant according to one of the preceding claims, characterized in that the flame retardant further gas-active substances, preferably phosphinates or polymeric DOPO derivatives, and / or other flame retardants, preferably boron phosphate or melamine phosphate, and / or the flue gas density lowering substances, preferably zinc phosphate, zinc borate or Contains copper hydroxide phosphate, and / or intumescent substances, glass formers or the dripping inhibiting additives. Self-extinguishing thermoplastic polyurethane (TPU) with a halogen-free flame retardant according to any one of the preceding claims, wherein the halogen-free flame retardant in an amount of 5 to 40 wt .-% or in an amount of 10 to 30 wt .-% or in an amount of 15 to 25 wt .-% based on the total thermoplastic polymer composition.