WO2008071719A1 - Flame-resistant polyamide and process for producing it - Google Patents

Abstract

The invention relates to the field of chemistry and concerns a flame-resistant polyamide which can, for example, be used as component for housings and a process for producing it. It is an object of the present invention to provide a flame-resistant polyamide which has improved properties compared to conventional flame-resistant polyamides. The object is achieved by a flame-resistant polyamide comprising a polyamide matrix, from 0.1 to 30% by mass of a flame retardant and from 0.1 to 20% by mass of a reactive resin hardener component, with the resin hardener component forming a network on the surface and in the regions close to the surface of the polymer matrix. The object is also achieved by a process in which a resin and a hardener are compounded in a proportion of from 0.1 to 20% by mass together with from 0.1 to 30% by mass of a flame retardant in a polymer matrix and processed to produce a shaped part.

Description

 Flame resistant polyamide and process for its preparation

The invention relates to the fields of chemistry and safety technology and relates to a flame-resistant polyamide, which can be used for example in the plastics processing and plastics industry as a component for housing, as fibers or as an electronic component and a method for its preparation.

In addition to good mechanical, thermal and electrical properties, polyamides have a considerable fire potential.

For this reason, it is necessary in many applications to add the materials flame retardants. These substances are applied with the objective of interrupting a set fire cycle at one or more points. The fire cycle consists of thermal decomposition, diffusion of the pyrolysis gases, oxidation and heat release with simultaneous realization of the "Thermal Feedback". To break the fire cycle different mechanisms and groups of flame retardants for plastics are distinguished.

The very effective halogen-containing systems, which may sometimes also contain two halogens in combination [US Pat. No. 4,111,134, US Pat. No. 4,388,429, US Pat. No. 5,358,991] and frequently synergistically reinforced with antimony trioxide, zinc borate, zinc oxide or other compounds [DE 2141036, DE 2114235], suppress combustion in the gas phase by initiating rapid radical reactions by emission of chemical species, which reduce the oxygen content in the immediate vicinity of the burning plastic.

However, in case of fire, an increased density of toxic and corrosive fumes, including halogenated dibenzodioxins and dibenzofurans, must be expected. Furthermore, the recycling of halogenated flame retardant polyamides is problematic.

In order to exclude these environmental and ecotoxicological disadvantages from the outset, the trend of modern flame retardants is towards halogen-free systems.

The commonly used inorganic materials based on magnesium and aluminum hydroxide act on the emitted at the combustion temperatures of them water, which displaces air from the reaction field and the evaporation leads to a strong heat extraction.

Although there is a very environmentally friendly solution, the material properties of the plastics are sustainably adversely affected, since the inorganic additives must be added to the polymeric matrix up to 50% by mass.

Also known are intumescent flame retardants which are multicomponent systems and, besides compounds which tend to char, such as polyalcohols [G. Camino, L. Costa, G. Martinasso, Polym. Degr. Rod. 23 (1989) 359; 28 (1990) 17; US 2106938], from gas-forming blowing agents, such as melamine or melamine compounds [A. Mukherjee, Plast. Eng., (2001) 57, 42-46; SV Levchik, AI Balabanovich, GF Levchik, G. Camino, L. Costa, Polym. Degr. Rod. 1998], and acid donors, which are substances that acidify under heat, such as ammonium polyphosphate, organic phosphates, phosphonates and phosphinates [SA Levchik, GA Levchik, AF Selevich, Al Leshnikovich, Vesti AN Belarusi, Ser. Khim. 3 (1995) 34; EP 245207 B1 (1987); EP 496241 (1992)]). In the event of fire, a carbonization of the polyalcohols initiated by the acids occurs, which, together with the phosphorus compounds under simultaneous foaming initiated by the blowing agent, builds up a voluminous protective layer of carbon and polyphosphoric acid. In addition to the removal of heat by the formation of gas, the inhibition of pyrolysis gas and heat diffusion and the restriction of the access of oxygen cause the extinction of the flame. In this approach, however, the high levels of additive and sublimation or evaporation phenomena of components during processing prove to be detrimental. Furthermore, a partially occurring susceptibility to hydrolysis of the potential acid generator is problematic.

The intumescent systems are closely related to flame retardants which act exclusively on the basis of phosphorus or phosphorus compounds. The most important representatives are red phosphorus, ammonium polyphosphate or ammonium phosphates and organophosphinates [J.R.A. Broadbent, M.M. Hirschler, European Polymer Journal 11 (1987) 1087; J.E. Stevenson, R. Guest, Fire Safety Proceedings, Fire Retardant Chemicals Association, New Orleans 1987, 141; DE 4015490; DE 2646218], which can sometimes be nanoscale (DE 10 2004 035517 A1). Here, too, it comes under fire conditions to acidification and charring. However, not previously compounded polyols carbonise, but the polymeric substrates themselves and the insulating surface layer of carbon and polyphosphoric acid is not foamed by specially added propellant.

Coincidentally, layer-forming systems, whether intumescent or non-intumescent, are pyrolytic processes that, with the participation of anhydride and esterified phosphorus-oxygen compounds and elimination of water, result in relatively branched, highly condensed, carbon-rich organic structures to which the formation of the charred crust decreases significantly.

A disadvantage of these systems is a less effective flame retardancy compared to the halogen-containing materials, which requires high amounts of additive to meet given ratings. This negatively affects the mechanical parameters of the plastics. Furthermore, it is possible that decomposition reactions of flame retardant components occur during processing or in the application phase. As a result, both degradation processes on the polymeric matrix can be initiated and the electrical characteristics (insulation) of the materials can be changed.

Overall, it can be estimated that the previously developed

Flame retardant solutions must always be tailored to specific plastics and optimized for the specific application, qualitatively and quantitatively.

Disadvantages are often occurring toxicological and ecological risks, high

Additive quantities and costs, negative influences on the property profiles of

Materials and problems in plastics recycling.

Object of the present invention is to provide a flame-resistant polyamide, which has improved properties over conventional flame-retardant polyamides due to the low addition of a reactive resin-hardener system, and a simple and inexpensive process for its preparation.

The object is achieved by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims.

The flameproof polyamide according to the invention consists of a polyamide matrix, from 0.1 to 30 Ma. -% of a flame retardant and from 0.1 to 20 Ma. % of a reactive resin-hardener component, wherein the resin-hardener component contains at least one resin and at least one hardener in the ratio of 100: 1 to 1:10, and the resin-hardener component is reactivated under fire conditions and at the Surface and forms a network in the near-surface regions of the polymer matrix. Advantageously, the polyamides PA 6, PA 12, PA 6,6 are present.

Further advantageously, as a flame retardant layer-forming flame retardants are present, which are more advantageously hydroquinone Dehvate of 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide.

Also advantageously, the flame retardants are present in proportions of 0.1 to 30%.

Also advantageously, as the resin of the resin-hardener component, phenol-formaldehyde condensates of the novolak type with phenol or cresol as aromatic structural units or melamine-formaldehyde resins are present.

And it is also advantageous if polyoxymethylene is present as a hardener of the resin-hardener component.

It is furthermore advantageous if the resin to the hardener in the ratio of 10: 1 to 1: 2 is present.

It is also advantageous if known reinforcing or fillers and additives are present.

It is also advantageous if the resin-hardener component, a catalyst or a catalyst mixture are added, which are still advantageously present as catalysts acid and / or base-splitting compounds such as decabromodiphenyl ether, ammonium polyphosphate or melamine cyanurate.

In the process according to the invention for producing a flameproof polyamide matrix material, a resin and a curing agent which form a network as a resin hardener component under fire conditions on the surface and in the near-surface regions of the polymer matrix are mixed and in a proportion of 0.1 until 20 Ma. -% together with 0.1 to 30 Ma. - Compounded% of a flame retardant in a polymer matrix and a molding processed.

Advantageously, the mixture of the resin-hardener component is carried out at temperatures below the melting points of both materials.

Also advantageously, a proportion of 0.1 to 20% of resin-hardener component is added.

Further advantageously, a proportion of 0.1 to 5% of a catalyst or a catalyst mixture is added to the mixture.

With the solution according to the invention, it is possible to specify a flameproof polyamide matrix material which has a high flame resistance. This is realized by the flame-retardant effect of conventional flame retardants or analog-acting additives is enhanced by a novel, reactive system. As a result, a reduction in the combustibility is achieved with significantly lower amounts of flame retardants or analogous additives acting altogether.

The solution according to the invention is based on the compounding of a reactive resin-hardener component of varying composition, which substantially enhances the flame retardant effect of intumescent and non-intumescent layer-forming conventional flame retardants or of analogously acting additives.

The reactive resin-hardener component which is contained in a proportion of 0.1 to 20 Ma. % of the polyamide plastic is added, consists of a resin and a curing agent, wherein the reactive resin-hardener component, and in particular the curing agent, a catalyst or a catalyst mixture may be added. Under fire conditions, the reactive resin-hardener component is activated and crosslinked immediately at the burning phase boundary on the surface and in the near-surface zones of the plastic. As a result, a region of high network density is formed on the surface of the thermoplastic polyamide matrix. Because network building is simultaneous with other superficial processes As a result of their height and density as well as their rate of formation, this hybrid layer acts as a particularly effective barrier to progression or re-flaring the fire process and thus has a pronounced potential for sustainable flame retardance. It is particularly advantageous if the flame retardant present in the polyamide or the analogously acting additive can be reactively integrated into the network formation of the reactive resin hardener component.

Notwithstanding the high reactivity at the combustion temperatures, the chemical and physical stability of the reactive resin-hardener component ensures easy compounding into the thermoplastic polyamide matrix or further processing of the compounds.

As the resin component of the reactive resin hardener component, novolak type phenol-formaldehyde condensates having phenol or cresol as aromatic structural units and melamine-formaldehyde resins are preferably used.

In parallel with the resin component, a hardener or a hardener-catalyst system is compounded, which remains under the processing conditions, however, in a deactivated, passive state and is activated only at the combustion temperatures under fire conditions and then leads to rapid crosslinking of the resin component.

The following substances or mixtures are used as hardeners or hardener catalyst systems.

a) - polyoxymethylene / decabromodiphenyl ether b) - polyoxymethylene / melamine cyanurate c) - polyoxymethylene / ammonium polyphosphate d) - ammonium polyphosphate

The proportions between resin and hardener or hardener mixture vary from 100: 1 to 1:10 and depend on the specific polyamide, the attached compounded flame retardant and the desired classification in the fire behavior.

The crosslinking mechanisms proceed in the cases of use of the curing agents a), b) and c) via hydroxymethylation of the resin component by formaldehyde, the formaldehyde being released in upstream thermal decomposition processes of the polyoxymethylene and followed by condensation reactions between the oligomeric aromatics. In this case, acidic (pyrolysis of the DBDE under HBr formation) and alkaline (thermal decomposition of melamine cyanurate or ammonium polyphosphate with liberation of ammonia) catalysis accelerate the reactions.

When using the hardener according to d) crosslinking of the resin without involvement of formaldehyde occurs.

With the solution according to the invention it is possible to achieve an optimum composition of polyamide matrix with reinforcing components and flame retardants or analogously acting additives, which has a lower overall content of flame retardants and / or leads to extinguishment of the fire in significantly faster times.

Since the reactive resin-hardener component consists of inexpensive basic materials, a significant cost reduction results for the fulfillment of certain specified fire test criteria. Furthermore, a considerable reduction of the ecological and ecotoxicological risks is achieved. The reduction of the required additive concentration makes it possible to better maintain the property profiles of the polyamide plastics or to adjust the mechanical, electrical and thermal characteristics of the materials more independently of the flame retardant content. Since the reactive resin-hardener component is stable under processing conditions, the problems that partially occur during the compounding of the flame retardants or in the phase of the thermal shaping are avoided or weakened in their effect.

The invention will be explained in more detail below with reference to several exemplary embodiments. Comparative Example 1 (according to the prior art)

In 500 g of polyamide 6 75 g of the hydroquinone Dehvates of 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPH, melting point 252 ° C) are compounded as a flame retardant additive. Test specimens made from these materials were extinguished 2.5 seconds after the burner flame was removed.

example 1

In 500 g of polyamide 6, 75 g of the hydroquinone Dehvates of 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPH, mp 252 ° C) as a flame retardant additive and 10 g of a resin-hardener component mixed, wherein the resin-hardener component consists of 66% by weight of phenol novolak having an average molecular weight of 1952 g / mol and 33% by mass of polyoxymethylene and 1% by mass Dekabromdiphenylether. Test specimens made from this material were extinguished immediately after removal of the burner flame.

Comparative Example 2 (according to the prior art)

In 500 g of polyamide 12, 40 g of the terephthalaldehyde Dehvates of 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPT) are compounded as a flame retardant additive. Test specimens made of these materials burned on for 6 seconds after the torch flame was removed.

Example 2

In 500 g of polyamide 12 are mixed 40 g of the terephthalaldehyde Dehvates of 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPT) as a flame retardant additive and 10 g of a resin-hardener component, wherein the resin Hardener component of 67% by mass Kresolnovolak and 33% by mass of melamine cyanurate. Test specimens made from this material were extinguished 1 second after removing the Burner flame.

Comparative Example 3 (according to the prior art)

In 500 g of polyamide 6 10 g of red phosphorus are compounded as a flame retardant. Test specimens made of these materials burned on for 12 seconds after the torch flame was removed.

Example 3

In 500 g of polyamide 6, 10 g of red phosphorus as a flame retardant and 10 g of a resin-hardener component are mixed, wherein the resin-hardener component consists of 67% by weight of cresol novolak and 33% by weight of melamine cyanurate. Test specimens made from this material were extinguished 5 seconds after the burner flame was removed.

Claims

claims 1. Flame-resistant polyamide, consisting of a polyamide matrix, from 0.1 to 30% by mass of a flame retardant and from 0.1 to 20 Ma. % of a reactive resin-hardener component, wherein the resin-hardener component contains at least one resin and at least one hardener in the ratio of 100: 1 to 1:10, and the resin-hardener component is reactivated under fire conditions and at the Surface and forms a network in the near-surface regions of the polymer matrix. 2. Flame-resistant polyamide according to claim 1, wherein the polyamides PA 6, PA 12, PA 6,6 are present. 3. Flame-resistant polyamide according to claim 1, wherein the flame retardant layer-forming flame retardants are present. 4. Flameproof polyamide according to claim 3, in which are present as flame retardants hydroquinone derivatives of 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide. 5. Flame-resistant polyamide according to claim 1, wherein the flame retardants are present in proportions of 0.1 to 30%. A flame-resistant polyamide according to claim 1, wherein as the resin of the resin-hardener component, phenol-formaldehyde condensates of novolak type with phenol or cresol as aromatic structural units or melamine-formaldehyde resins are present. 7. Flame-resistant polyamide according to claim 1, wherein the hardener of the resin-hardener component is polyoxymethylene. A flame-retardant polyamide according to claim 1, wherein the resin to the curing agent is present in a ratio of 10: 1 to 1: 2. 9. Flame-resistant polyamide according to claim 1, in which known reinforcing or fillers and additives are present. 10. Flame-resistant polyamide according to claim 1, wherein the resin-hardener component, a catalyst or a catalyst mixture are added. 11. Flame-resistant polyamide according to claim 10, in which are present as catalysts acid and / or base-splitting compounds, such as decabromodiphenyl ether, ammonium polyphosphate or melamine cyanurate. 12. A process for producing a flame-resistant polyamide, in which a resin and a curing agent, which form a network as a resin-hardener component under fire conditions on the surface and in the near-surface regions of the polymer matrix, mixed and in a proportion of 0.1 to 20 Ma. -% together with 0.1 to 30 Ma. -% of a flame retardant compounded in a polymer matrix and processed into a molded part. 13. The method of claim 12, wherein the mixture of the resin-hardener component is carried out at temperatures below the melting points of both materials. 14. The method of claim 12, wherein a proportion of 0.1 to 20% of resin-hardener component is added. 15. The method of claim 12, wherein the mixture is added to a proportion of 0.1 to 5% of a catalyst or a catalyst mixture.