GB1590802A

GB1590802A - Textile-reinforced rubber articles

Info

Publication number: GB1590802A
Application number: GB30238/77A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-07-21
Filing date: 1977-07-19
Publication date: 1981-06-10
Also published as: BE857046A; DE2632741A1; DE2632741B2; FR2359172A1

Description

(54) TEXTILE-REINFORCED RUBBER ARTICLES (71) We, HOECHST AKTIENGESELLSCHAFT a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to shaped articles, especially conveyor belts for underground working, of a textile fabric reinforced vulcanized polychlorobutadiene.

Rubber mixtures based on polychlorobutadiene which are inflammable only with difficulty are known to be suitable, inter alia, for the manufacture of textile-reinforced rubberized conveyor belts. When such materials are used in underground working they must meet high safety requirements as regards their burning and smoldering behavior. Generally, the known rubber mixtures contain, besides inorganic fillers, a series of substances which ensure that the belt is self-extinguishing in the case of fire.

Textile-reinforced rubberized conveyor belts to be used in underground working must be flame resistant and have favorable smoldering properties, in other words the amount and composition of the volatile products formed by smoldering are of decisive importance as some of the smoldering products have a detrimental effect on the service life of gas masks.

Hence, it must be ensured that the volatile smoldering product formed in the case of fire do not impair the function of gas masks or breathing filters. The breathing filters comprise an outer textile filter of cellulosic material (cotton or viscose) serving to absorb the coarse particles contained in the gases formed by burning and smoldering. Certain volatile smoldering products may have a swelling and clogging effect on the textile filter, whereby the respiratory resistance increases considerably after a short period of time and finally the breathing filter becomes useless.

Hitherto known flame-resistant rubber mixtures based on polychlorobutadiene and textile-reinforced conveyor belts produced therewith have a flame resistance that is adequate in practice, but their smoldering properties are unsatisfactory, i.e. on smoldering, volatile products are formed which clog the breathing filters of gas masks. In addition, their behavior after glowing is not always satisfactory.

The present invention seeks to provide a textile-reinforced shaped rubber article, especially a textile-reinforced conveyor belt for underground mining, which does not have the above disadvantages, that is to say which develops no smoldering products which clog breathing filters, the residue from burning of which does not continue to glow and which, at the same time, is flame resistant and self-extinguishing. In accordance with the invention, this objective can be achieved by a rubber mixture based on polychlorobutadiene which contains, besides the usual additives, such as anti-ageing agents and fillers, a specific combination of flame-proofing substances and hydrogen halide acceptors.

The present invention therefore provides a shaped article, for example a conveyor belt for underground working, comprising a textile fabric-reinforced vulcanized polychlorobutadiene (as hereinafter defined), the polychlorobutadiene containing, per 100 parts by weight thereof: (a) from 4 to 12, preferably from 5 to 10, parts by weight of antimony trioxide; b) from 1 to 10, preferably from 2 to 5, parts by weight of hydrated aluminium oxide; (c) from 1 to 10, preferably from 2 to 5, parts by weight of boric acid and/or zinc borate; (d) from 5 to 25, preferably from 5 to 15 parts by weight of one or more phosphorus-free organic halogen compounds having a halogen content of at least 50 obey weight;; (e) from 5 to 20, preferably from 5 to 14, parts by weight of one or more halogen containing phosphoric acid esters; and (f) from 2 to 35, preferably from 7 to 25, parts by weight of magnesium carbonate and/or calcium carbonate; or of basic magnesium carbonate and/or basic calcium carbonate; or of a mixture of magnesium carbonate and/or calcium carbonate and of basic mag nesium carbonate and/or basic calcium carbonate, the amounts of basic magnesium carbonate and basic calcium carbonate, when present, being such as not to have impaired vulcanization of the polychlorobutadiene.

The term "polychlorobutadiene" is used to include mixtures of major amounts by weight of polychlorobutadiene and other chlorine-containing, vulcanizable polymers, for example chlorinated and chlorosulfonated polyethylenes.

The total amount of component (a), component (b) and component (c) preferably does not exceed 25 parts by weight, and more preferably is from 10 to 15 parts by weight.

If the total amount of components (a), (b) and (c) is above 15 parts by weight, it is recommended to increase the proportion of component (a) at the expense of components (b) and (c).

The total amount of components (d) and (e) preferably does not exceed 30 parts by weight. It is more preferably from 10 to 30 parts by weight per 100 parts by weight of polychlorobutadiene.

The amount of component (f) is preferably greater than the total amount of (d) and (e).

In general, the weight ratio of the total amount of (d) and (e) to (f) should be from 1:1 to The total amount of components (a) to (f) is expediently from 20 to 110, preferably from 30 to 80, parts by weight per 100 parts by weight of polychlorobutadiene.

The solid components of the material of the invention are suitably used in a finely divided form, the particle size preferably being below 20 microns.

The antimony trioxide and the hydrated aluminum oxide used as components (a) and (b), respectively, have a flame-proofing effect, whereas the boric acid and/or zinc borate used as component (c) mainly prevents glowing. In the material of the invention, a synergistic effect is observed between these components.

Zinc borates are described, for example, in P.H. Kemp. The Chemistry of Borates, London, Borax Consolidated, 1957.

The phosphorus-free organic halogen compounds used as component (d), which are known to have a flame-proofing effect in combination with antimony trioxide and/or aluminium oxide, are preferably halogen-containing hydrocarbons having a halogen content of at least 50% by weight, expediently 60 to 80% by weight, which can be sufficiently distributed in the polychlorobutadiene. Their softening point is preferably in the range of from -5 to 100"C. Preferred halogens are chlorine and bromine.

Compounds of this type are, for example chlorinated or brominated aliphatic hydrocarbons (paraffins) which may be branched or unbranched, and chlorinated cycloaliphatic compounds, such as the dimer of hexachlorocyclopentadiene or hexabromocyclodecane.

Other suitable compounds are halogenated aromatic hydrocarbons, especially those having from 6 to 14 carbon atoms which can be fused or linearly bound, optionally via a CH2 bridge or hetero atoms, for example pentachlorobenzene, pentabromotoluene, hexabromobenzene, tetrabromodiphenyl, hexabromodiphenyl, pentabromodiphenyl ether and tribromo-trichlorodiphenyl ether. Halogen-containing mixed aliphatic-aromatic ethers can also be used, for example dibromopropyl-(tribromodichlorophenyl) ether. Further examples of this class of compounds are described, for example in German Auslegeschiften 1,669,811 and 1,911,434. Mixtures of such aliphatic and aromatic compounds may also be used. Other compounds of this class are described in Thater, Brennverhalten von Plastformstoffen, VEB Deutscher Verlag fir Grundstoffindustrie, Leipzig, 1968, pages 124125.

Other suitable components (d) are phosphorus-free halogen-containing polymers having a halogen-content of at least 50 % by weight, preferably from 60 to 70 % by weight, and being sufficiently distributable in polychlorobutadiene, for example polyvinylidene chloride or highly chlorinated polyolefins, especially polyethylene.

Preferred components (e) are neutral, halogen-containing phosphoric acid esters having a halogen-content of at least 45 % by weight, preferably from 60 to 70% by weight, the halogen preferably being bromine and/or chlorine. The organic radical in the ester compo nent can be an aromatic or, preferably, an aliphatic hydrocarbon radical preferably having from 1 to 10 and especially from 1 to 6, carbon atoms. It is also possible to use mixed esters containing different alcohol moieties, as well as mixtures of uniform and/or mixed esters.

Examples of component (e) are tris(2,3-dibromopropyl) phosphate, tris(chloroethyl) phosphate, tris(chloroisopropyl) phosphate, tris(1 ,3-dichloroisopropyl) phosphate, and mixtures of such esters. Further examples of such compounds are described in Thater, Brennverhalten von Plastformstoffen, VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig 1968, pages 125 to 127 and Vogel, Flammfestmachen von Kunststoffen, Alfred Hiittig Verlag, Heidelberg, 1966, pages 106 to 153.

The magnesium carbonate and calcium carbonate which may be used as, or as part of, component (f) are preferably in precipitated form. The corresponding basic carbonates may be used instead of, or together with, these neutral carbonates; however, since the basic carbonates are capable of acting as vulcanization agents, they are used in relatively small amounts only, so that they do not impair the vulcanization properties of the polychlorobutadiene.

Suitable fillers are, in the first place, carbon black and/or active silicic acid (that is silicic acid produced by precipitation having a large surface area) in an amount of from 15 to 50, preferably 20 to 40, parts by weight per 100 parts by weight of polychlorobutadiene. It may prove advantageous to reduce the content of carbon black at the expense of active silicic acid, whereby the tendency to glowing of the rubber mixture is diminished and the smoldering properties may be improved.

The starting mixture used for the manufacture of the shaped articles in accordance with the invention also contains vulcanization agents and, optionally, vulcanization accelerators.

Examples of vulcanization agents are zinc oxide, which is preferably used in an amount of from 5 to 15, more preferably from 5 to 7, parts by weight per 100 parts by weight of polychlorobutadiene, and magnesium oxide which is suitably used in an amount of from 2 to 6, preferably from 2 to 4 parts by weight per 100 parts by weight of polychlorobutadiene.

Examples of vulcanization accelerators are tetramethyl thiuram disulfide (thiuram) and 2-mercapto-imidazoline (accelerator Na-22). The vulcanization accelerators are suitably added in amounts of from 1 to 2.5, preferably from 1 to 1.5 parts by weight per 100 parts by weight of polychlorobutadiene. Under the vulcanization conditions, thiuram splits off sulfur and therefore acts also as vulcanization agent.

Residues of the vulcanization agents and optionally of the vulcanization accelerators are naturally contained in the rubber mixtures prepared from the starting components by vulcanization and in the shaped articles of the invention made from the said rubber mixtures.

The rubber mixture to be used for making the shaped article of the invention also contains conventional rubber additives, for example anti-ageing agents such as phenyl-a a naphthylamine (PAN) and phenyl-P-naphthylamine (PBNl. Other suitable additives are listed in the book by W. Kleemann, Einfuhrung in die Rezepturentwicklung der Gummiindustrie, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1963, page 415.

The textile-reinforced shape articles of the present invention, more especially conveyor belts, have an oxygen index (LOI) of at least 0.4, preferably of from 0.4 to 0.5. The oxygen index is determined as described in ASTM 2863-72, by measuring the limiting oxygen index of an oxygen-nitrogen gas mixture in which a sample is just able to burn.

The shaped articles of the present invention, especially conveyor belts for underground mining, are reinforced by a textile fabric, preferably of synthetic fibers, for example of polyesters such as polyethylene terephthalate, and polyamides, such as poly--caprolactam or polyhexamethylendiamine adipate. Mixed fabrics of polyester and polyamide fibers may also be used. Most preferably the textile fabric is made of polyester fibers.

The proportion of fabric to rubber will vary depending on whether the conveyor belt has a light or a heavy textile insert. In conveyor belts having a strength of up to about 400 decanewtons (daN) per centimeter width, the amount by weight of rubber is from 4 to 10 times the amount by weight of fabric. In conveyor belts having a strength of from 800 to 1,000 daN per centimeter width the fabric should be correspondingly heavier and the amount by weight of rubber should be about from 2 to 5 times the amount by weight of the fabric.

It is surprising that the shaped articles of the invention and especially the textile reinforced conveyor belts are characterized not only by good flame-resisting properties and good anti-glowing properties but also by such a favorable smoldering behavior, that is to say in the case of fire, volatile smoldering products which could clog breathing filters are not formed, although a combination of antimony trioxide, hydrated aluminium oxide and organic halogen compounds together with the textile fabric exhibits a distinct tendency to clog filters in the case of fire.

The following Examples illustrate the invention.

The experiments were carried out with rubber mixtures as defined in the following table.

The tested samples corresponded to a finished conveyor belt and consisted of 2 or 4 layers of fabric with rubber interlayer(s) and an upper and lower covering layer having a thickness of 1 to 3 mm.

The rubber mixtures were rolled into 1 mm thick sheets. The textile insert was a polyester fabric (weight per square meter 650 g, plain weave, 93 warps and 40 filling threads per square centimeter, the warp and filling polyester threads having a titer of 1,100 dtex x 2 with 70 T/m). For improving the adhesion, the fabric was impregnated with a vinyl pyridine latex-resorcinol-formaldehyde resin mixture. The fabric layers were inserted each between two rubber sheets and the whole was vulcanized under conventional conditions. For the test the fully vulcanized sample was used.

The obstructing effect on rescue filters was tested in a smoldering apparatus in which a 3 x 3 cm sample was heated on a heating plate within 20 minutes to 6000C and the generated pyrolysis gases were passed by a defined air current into a chamber into which animals could be placed to examine the toxicity of the flue and combustion gases and in which a rescue filter was inserted by which the smoke mixture was sucked up and blown out at a respiratory rate. The increase in the flow resistance was measured.

Table I (the parts being by weight) Mixture No. 1 2 3 4 5 6 polychlorobutadiene 100 100 100 100 100 100 chloroparaffin 5 10 5 5 15 15 tris(2,3-dibromopropyl) phosphate 5 10 10 5 5 10 antimony trioxide 5 10 5 5 5 10 hydrated aluminium oxide 5 1 5 7 5 5 zinc borate 5 5 5 5 5 1 calcium carbonate 10 10 10 10 10 10 magnesium carbonate 10 15 15 15 15 active silicic acid 10 30 10 10 20 20 carbon black 20 - 10 10 - zinc oxide 5 5 5 5 5 5 magnesium oxide 4 4 4 4 4 4 anti-ageing agent (PAN) 1 1 1 1 1 1 accelerator 1 1 1 1 1 1 burning and glowing behavior (DIN 22118) conditions complied with flow resistance of filter did not increase LOI 0.41 0.45 0.45 0.43 0.46 0.49 WHAT WE CLAIM IS: 1.A shaped article comprising a textile fabric-reinforced vulcanized polychlorobutadiene (as hereinbefore defined), the polychlorobutadiene containing, per 100 parts by weight thereof: (a) from 4 to 12 parts by weight of antimony trioxide; (b) from 1 to 10 parts by weight of hydrated aluminium oxide; (c) from 1 to 10 parts by weight of boric acid and/or zinc borate; (d) from 5 to 5 parts by weight of one or more phosphorus-free organic halogen com pounds having a halogen content of at least 50% by weight; (e) from 5 to 20 parts by weight of one or more halogen-containing phosphoric acid esters; and (f) from 2 to 35 parts by weight of magnesium carbonate and/or calcium carbonate; or of basic magnesium carbonate and/or basic calcium carbonate; or of a mixture of mag nesium carbonate and/or calcium carbonate and of basic magnesium carbonate and/or basic calcium carbonate, the amounts of basic magnesium carbonate and basic calcium carbonate, when present, being such as not to have impaired vulcanization of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The experiments were carried out with rubber mixtures as defined in the following table.

The tested samples corresponded to a finished conveyor belt and consisted of 2 or 4 layers of fabric with rubber interlayer(s) and an upper and lower covering layer having a thickness of 1 to 3 mm.

The rubber mixtures were rolled into 1 mm thick sheets. The textile insert was a polyester fabric (weight per square meter 650 g, plain weave, 93 warps and 40 filling threads per square centimeter, the warp and filling polyester threads having a titer of 1,100 dtex x 2 with 70 T/m). For improving the adhesion, the fabric was impregnated with a vinyl pyridine latex-resorcinol-formaldehyde resin mixture. The fabric layers were inserted each between two rubber sheets and the whole was vulcanized under conventional conditions. For the test the fully vulcanized sample was used.

The obstructing effect on rescue filters was tested in a smoldering apparatus in which a 3 x 3 cm sample was heated on a heating plate within 20 minutes to 6000C and the generated pyrolysis gases were passed by a defined air current into a chamber into which animals could be placed to examine the toxicity of the flue and combustion gases and in which a rescue filter was inserted by which the smoke mixture was sucked up and blown out at a respiratory rate. The increase in the flow resistance was measured.

Table I (the parts being by weight) Mixture No. 1 2 3 4 5 6 polychlorobutadiene 100 100 100 100 100 100 chloroparaffin 5 10 5 5 15 15 tris(2,3-dibromopropyl) phosphate 5 10 10 5 5 10 antimony trioxide 5 10 5 5 5 10 hydrated aluminium oxide 5 1 5 7 5 5 zinc borate 5 5 5 5 5 1 calcium carbonate 10 10 10 10 10 10 magnesium carbonate 10 15 15 15 15 active silicic acid 10 30 10 10 20 20 carbon black 20 - 10 10 - zinc oxide 5 5 5 5 5 5 magnesium oxide 4 4 4 4 4 4 anti-ageing agent (PAN) 1 1 1 1 1 1 accelerator 1 1 1 1 1 1 burning and glowing behavior (DIN 22118) conditions complied with flow resistance of filter did not increase LOI 0.41 0.45 0.45 0.43 0.46 0.49 WHAT WE CLAIM IS: 1.A shaped article comprising a textile fabric-reinforced vulcanized polychlorobutadiene (as hereinbefore defined), the polychlorobutadiene containing, per 100 parts by weight thereof: (a) from 4 to 12 parts by weight of antimony trioxide; (b) from 1 to 10 parts by weight of hydrated aluminium oxide; (c) from 1 to 10 parts by weight of boric acid and/or zinc borate; (d) from 5 to 5 parts by weight of one or more phosphorus-free organic halogen com pounds having a halogen content of at least 50% by weight; (e) from 5 to 20 parts by weight of one or more halogen-containing phosphoric acid esters; and (f) from 2 to 35 parts by weight of magnesium carbonate and/or calcium carbonate; or of basic magnesium carbonate and/or basic calcium carbonate; or of a mixture of mag nesium carbonate and/or calcium carbonate and of basic magnesium carbonate and/or basic calcium carbonate, the amounts of basic magnesium carbonate and basic calcium carbonate, when present, being such as not to have impaired vulcanization of the

polychlorobutadiene.
2. A shaped article as claimed in claim 1, wherein the polychlorobutadiene contains per 100 parts by weight thereof, from 5 to 10 parts by weight of component (a), from 2 to 5 parts by weight of component (b), from 5 to 7 parts by weight of component (c), from 5 to 15 parts by weight of component (d), from 4 to 14 parts by weight of component (e) and as component (f), from 7 to 25 parts by weight of magnesium carbonate and/or calcium carbonate; or of basic magnesium carbonate and/or basic calcium carbonate; or of a mixture of magnesium carbonate and/or calcium carbonate and of basic magnesium carbonate and/or basic calcium carbonate.
3. A shaped article as claimed in claim 1, wherein the total amount of components (a), (b), (c), (d), (e) and (f) in the polychlorobutadiene is from 20 to 110 parts by weight per 100 parts by weight of polychlorobutadiene.
4. A shaped article as claimed in any one of claims 1 to 3, wherein the total amount of components (a), (b) and (c) in the polychlorobutadiene is from 6 to 25 parts by weight per 100 parts by weight of polychlorobutadiene.
5. A shaped article as claimed in any one of claims 1 to 4, wherein the total amount of components (d) and (e) in the polychlorobutadiene is from 10 to 30 parts by weight per 100 parts by weight of polychlorobutadiene.
6. A shaped article as claimed in any one of claims 1 to 5, having an oxygen index of at least 0.4.
7. A shaped article as claimed in any one of claims 1 to 6, wherein component (e) is tris(2,3-dibromopropyl) phosphate, tris(chloromethyl) phosphate, tris(chloroisopropyl) phosphate, tris(1,3-dichloroisopropyl) phosphate, or a mixture of any two or more such phosphates.
8. A shaped article as claimed in any one of claims 1 to 7, which also contains as filler, from 15 to 50 parts by weight of carbon black and/or active silicic acid per 100 parts by weight of polychlorobutadiene.
9. A shaped article as claimed in any one of claims 1 to 8, wherein the textile fabric is a fabric of polyester threads, optionally combined with polyamide threads.
10. A shaped article as claimed in any one of claims 1 to 9, in the form of a conveyor belt.
11. A shaped article as claimed in claim 1 substantially as hereinbefore described.