GB1562835A - Flame-resistant sealing composition - Google Patents

Description

(54) FLAME-RESISTANT SEALING COMPOSITION (71) We, THE FURUKAWA ELECTRIC COMPANY LIMITED. of No. 6-1. Marunouchi 2-chome, Chiyoda-ku, Tokyo, Japan, a Japanese Corporation, 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 a flame-resistant sealing composition which may be crosslinked or uncrosslinked.

A putty-like, non-drying component (hereinafter called putty) is used for many purposes such as for filling and completely sealing gaps or void spaces in walls, and partitions, in the fields of civil engineering, architecture, automobile manufacturing and ship-building for instance. Conventional putty has normally been prepared by using polybutene, silicon or paraffin as the principal constituent with some inorganic filler material or inorganic fibre added thereto in order to obtain a desired consistency.

However, in most of such putty products, an inflammable organic matter is employed for adjustment of the consistency and tackiness. This imparts inflammability to the putty. Since such putty is not sufficiently self-extinguishing in the presence of heat and oxygen, it does not give a sufficient sealing effect because it loses sealing effect when exposed to fire.

Although it is conceivable to solve the above stated problem by decreasing the ratio of the inflammable component while increasing the ratio of the inorganic filler in putty, such arrangement can only delay the speed of combustion of putty to some extent because there is a limit to such arrangement if the functional requirements of putty are to be retained.

In view of this difficulty, therefore, it is also conceivable to add a chlorinated polymer such as chlorinated polyethylene to replace the whole of or a part of the polybutene or other principal component therewith. However, the use of such chlorinated polymers is not desirable, because they produce a poisonous gas when exposed to fire.

Furthermore, addition of a metal oxide such as antimony trioxide, a boron compound, a phosphorus compound or an inorganic hydrated compound, also reduces the inflammability of the putty. However, the quantity of such additive is again limited in order to retain the functional properties required for putty. Thus, there has not been provided any putty compound which has thigh degree of flameresistance while being capable of functioning as putty.

The "Testing Method for Flammability of Polymer Materials Using the Oxygen Index Method" of JIS K 7201-1972 is considered the most effective method for determining the flame resistance of materials. According to the results of a test conducted in accordance with this procedure, a commercially available putty, which is said to excel in flame resistance, consisting of butyl rubber as the principal constituent, a non-drying oil, an inorganic filler and asbestos has an oxygen index of 29. Oxygen indices less than 19 are regarded as readily flammable: 20-27 as slowly flammable and above 28 as self-extinguishing.Therefore, the above stated value of 29 indicates that the putty has a self-extinguished capabilit. However, in case of a fire, the putty does not function sufficiently well as putty and such a drawback is particularly disadvantageous where such putty is used at penetrating parts in floors and walls, for electrical cables.

The sheath of a power cable is generally made of polyvinyl chloride (oxygen index 27) or polyethylene (oxygen index 17) and is relatively quick to ignite.

According to the standard fire temperature curve of JIS A 1301, such sheath catches fire in several minutes to expose the conductor in 15 to 20 minutes. With the wall or floor penetrating part of such power cable being sealed with the commercially available putty, the putty surface begins to burn when fire comes in contact therewith. Then, the cable catches fire and the heat and the fire are propagated to continue the combustion. The sealing function is degraded and this causes smoke or various kinds of gas to leak through a gap in cable penetrations about 25 minutes after ignition. Thus, flames of the fire eventually come to pass through the cable penetrations while further burning the cable.

This invention, therefore, is directed to the elimination of such drawbacks of conventional putty.

Accordingly, we have sought to provide a composition which effectively solves the above stated problems and which is particularly suitable for sealing penetrations of electrical cables installed through walls, ceilings and floors.

Thus, the present invention provides a flame-resistant sealing composition comprising 100 parts by weight of at least one chloroprene rubber having a molecular weight of from 2,500 to 6,000 and a viscosity at room temperature of 10,000 to 120.000 cps, 100 to 450 parts by weight of at least one water-insoluble inorganic filler containing water of hydration and I to 15 parts by weight of at least one inorganic fibrous material with the proviso that up to half the weight of the water-insoluble inorganic filler containing water of hydration may optionally be replaced by an inert inorganic filler.

The sealing composition which may be crosslinked or uncrosslinked, is in a non-drying putty-like state and is particularly suitable for sealing penetrations of electrical cables, including power cables and communication cables, installed through walls, ceilings and floors.

The chloroprene rubber may be with or without an end functional group.

In accordance with this invention, excellent flame resistance can be obtained by virtue of a synergistic effect brought about by the chemical self-extinguishing property of the chloroprene rubber and the physical quenchability resulting from the endothermic discharge of the hydration water contained in the inorganic filler.

Furthermore, the use of an inorganic fibre in addition to these two constituents further ensures an excellent sealing effect against fire.

The chloroprene rubber has a low-molecular weight, i.e. mean values of molecular weight ranging from 2,500 to 6,000, and is in a liquid state at room temperature and atmospheric pressure. In order to cross-link a flame-resistant sealing composition, the chloroprene rubber must be crosslinked having an end functional group. At room temperature, the chloroprene rubber is a highly viscous liquid measuring 10,000 to 120,000 cps in viscosity. When mixed with the inorganic matter described below, therefore, the chloroprene rubber satisfies the sealing requirement over a wide range of mixing ratios. In addition to that, in case of fire, as apparent from its chemical constitution, only a negligible amount of poisonous gas will be produced as compared with the halogenides that have hitherto been used for conventional putty compounds.

In accordance with a particular embodiment of this invention, the chloroprene rubber is crosslinkable. In other words, with a crosslinking agent (a curing agent) mixed beforehand, a hardening reaction can be brought about at room temperature as desired so that the desired function as putty can be continuously performed over a long period of time and the chemical and thermal stability can be further improved.

The water-insoluble, inorganic filler used in accordance with this invention is preferably, aluminium oxide hydrate, Al203 . 3H2O or Al(OH)3, magnesia hydrate, calcium silicate hydrate, and, of these, the use of aluminium oxide hydrate is most preferable.

This inorganic filler endothermically discharges its water of hydration either before or at the beginning of burning or ignition of chloroprene rubber. By virtue of such, the filler is much superior to the conventional inert inorganic fillers such as calcium carbonate, talc, clay and titanium dioxide, in respect of flame resistance.

Yet, with regard to the sealing effect, the filler compares favourably with these conventional fillers. Further, a filler having a small grain size is preferable. The range of the mixing ratio is set as mentioned above because: a sufficient degree of flame resistance cannot be obtained with the filler mixing ratio less than 100 parts while the sealing power and other properties as putty decrease with the filler mixing ratio exceeding 450 parts. Preferably 150 to 400 parts by weight of the filler containing water of hydration are used per 100 parts by weight of the chloroprene rubber. Furthermore, up to half of the filler having water of hydration water can be replaced with a conventional inert inorganic filler such as those previously listed.

The fibre is used for the purpose of imparting pressure resistivity to the flame resistive sealing composition consisting of the liquid chloroprene rubber and the inorganic filler. With the fibre used, the internal bonding strength of the composition can be enhanced by the entanglement of the fibre with the liquid and powder constituents. An attempt to obtain a desired degree of pressure resistance using the liquid chloroprene and the inorganic filler without using the fibre woBld result in excessively increased hardness of the compound, which then would become incapable of functioning as putty.

The inorganic fibre may be selected from fibres such as glass fibre, asbestos, rock wool, stainless steel and carbon, for example. Of these fibres, the use of glass fibre is most advantageous and the glass fibre is preferably shaped to measure less than several tens of microns in diameter and 1 to 5 mm in length.

The inorganic fibre not only possesses a heat resisting property but also forms a fused layer when in contact with flames. Accordingly, the fibre component of the composition synergistically enhances flame resistance in conjunction with the endothermic effect resulting from the discharge of the water of hydration.

As for the blending ratio of the inorganic fibre, I to 15 parts by weight of the fibre is mixed with 100 parts by weight of the liquid chloroprene rubber because: with the ratio of the fibre less than 1 part, the desired internal bonding strength of the composition cannot be obtained and would result in a so-called weak sealing material which is hardly usable; while, with the fibre used in a ratio of more than 15 parts, the composition would become excessively hard thus effecting workability as well as its sealing power.

In practising this invention, other constituents such as pigments, antioxidants, stabilizers against heat or light, and the like of course may be added. It is desired, however, to limit the quantity of such additive to 10 ' of the total quantity of the composition and preferably to less than 5%.

For preparation of the flame-resistant sealing composition according to the invention in crosslinked form, a curing agent is added at the time of mixing the three essential constituents in a ratio of 1--5 parts by weight to 100 of the liquid chloroprene rubber and preferably 1.54 parts by weight to 100 parts by weight of the three components. With the additive quantity of the curing agent less than 1 part by weight, crosslinking cannot be effected even to a minimum degree required. Then, it will be impossible to obtain the desired flame resisting property with increased consistency and bonding strength. On the other hand, with the curing agent added in a ratio exceeding 5 parts by weight, the composition will be cured to an excessive degree and the workability thereof will be lost.Further, for making the composition into a crosslinked composition, the mixing ratio of the inorganic filler is preferably set between 100 and 300 parts by weight. The curing agent is generally selected from the following amine compounds: Aliphatic-series Compounds:

R-N-(R1NH2)2 HzN(C2H4NH)nH wherein R: H or alkyl R': Alkylene n: 14 Aliphatic-series Compounds: Aminoalkyl piperidine and aminoalkyl piperazine Modified Amine: Epoxy amine adduct and (meta acrylate amine adduct Of the above compounds, tetraethylene pentamine, aminoethyl piperazine, mxylene diamine, are preferably employed as the curing agent.

Other curing agents that are usable in accordance with this invention include metal halogenide-series curing agents such as ZnBr2, SnBr2, Zinc12, CoCI2, NiCI2 and Nibs^.

An additive may be used to accelerate the cross-linking of the chloroprene rubber, e.g. a zinc compound such as active zinc powder or basic zinc carbonate brings about a good effect.

The invention is further illustrated by the following Examples in which, the compositions are prepared through a continuous mixing process carried out by means of a kneader mill in the sequence of liquid chloroprene rubber-various kinds of filler-inorganic fibre. All mixing ratios are indicated in parts by weights.

EXAMPLE I Composition 1 (According to the invention) Liquid chloroprene rubber* (mean molecular weight 2,500) 100 parts Al2(oH)3 (mean grain size weight 3--20EL) 300 parts Glass fibre (dia 9 ,*4 length 3 mm) 5 parts Sb2O3 3 parts Total 408 parts Composition 2 (According to the invention) Liquid chloroprene rubber* (mean molecular weight (3,500) 100 parts Al2(OH)3 250 parts Glass fibre 5 parts Sb2O3 3 parts Total 358 parts Composition 3 (According to the invention) Liquid chloroprene rubber* (mean molecular weight 2,500) 100 parts Al2(OH)3 170 parts Glass fibre 5 parts Sb2O3 3 parts Tetraethylene pentamine (TEPA) 3 parts Total 281 parts Composition 4 (Comparison Example) Liquid chloroprene rubber* (mean molecular weight 2,500) 100 parts Talc 300 parts Sb2O3 3 parts Total 403 parts Note: *Denka LCR (Trade name) manufactured by Denki Kagaku Kogyo Co.

Compound 5 (An example of conventional products) This is a commercially available composition manufactured with a synthetic rubber employed as principal constituent and. with a non-drying oil, a filler and asbestos fibre added thereto.

The compositions 1 to 5 indicated in the foregoing were subjected to a combustion test. The results of the test are shown in following Table 1.

For the test, a sample of each composition was applied to a copper wire piece measuring '.0 mm in outer diameter and 100 mm in length to coat the copper wire with the sample in a coating thickness of 1.0 mm. The tip of each test piece thus prepared was also covered with the sample.

TABLE 1 Combustion Test by Oxygen Index Method. JIS K 7201-1972 Matter Oxygen index Composition 1 73 Composition 2 75 Composition 3 75 Composition 4 42 Composition 5 29 Next, a floor penetrating part was arranged in actual size and scale and a simulated penetrating part burning test was conducted on each composition under the following test conditions: 1) Cable Conduit made of steel: 1.5 mm in thickness. 1016 mm inner dia., and 50 mm in length above the floor.

2) Floor: Iron plate measuring 3.0 mm in thickness (welded to the conduit) 3) Cable: Polyethylene insulated and sheath control cable, 2x5.5 mm2x7/1.0, in conductor size and 13.5 mm, in overall diameter.

4) Number of Cables: 10 occupying about 50 n of the inner space of the conduit.

5) Putty filling degree: About 30 mm in depth, filled by hand from the upper part of the conduit tube.

6) Burning method: rags with gasoline were used.* Combustion was allowed to continue until the cable which was in contact with the flame became a conductor; and then combustion was allowed to continue for fifteen minutes further until the effect of the sealed part was confirmed. The combustion time was 30 minutes and the maximum temperature reached 980"C.

7) Compositions: Used to fill and seal spaces between cables and between the cables and the conduit. (The depth of the seal was limited to 50 mm). The test results are as shown in Table 2.

TABLE 2 Matter Results of combustion Composition 1 No leakage of smoke. The sealed part which came into contact with the flame became swollen by foaming and the combustion was thereby completely prevented from spreading further.

Composition 2 The same as composition 1.

Composition 3 The same as composition 1.

Composition 4 Cracks appeared from the parts which contacted the flame. The sheath of the cable at the cracked parts was ignited. However, the combustion was prevented from spreading. No leakage of smoke.

Composition 5 Smoke began to leak from space between cables in 15 minutes after the start of the test. In 25 minutes, a part of the sealed part dropped off and smoke burst out from that part.

According to the results of the above mentioned test, the sample of conventional putty (Composition 5) came off with its organic constituent having been burnt and having been softened to a great extent by heat. In the case of the comparison example (Composition 4), the test results indicated that the speed at which the decomposition of the liquid chloroprene rubber took place could not be delayed by the use of the inert filler alone. The test results also indicated that cracking was allowed to take place with no fibre added to the composition.

Further. with a compression deflection tester used, the plasticity of these compositions was tested by making preparatory heating for 10 minutes; then by subjecting the heated sample to a load of 1 kg; and by measuring a temperature that caused the rate of deformation of the sample to exceed 70". when it was under the 1 kg load for 10 minutes. Table 3 shows the results of the test.

TABLE 3 Compositions 1 2 3 4 5 Temperature, "C 65 70 80 50 35 EXAMPLE 2 In this example, tests were conducted to find the effect brought about by addition of an inert filler on the oxygen index. The test results are as shown in Table 4.

TABLE 4 Compositions 6 7 8 9 10 11 12 Liquid chloroprene rubber (mean molecular weight 2,500) 100 100 100 100 100 100 100 Al(OH)3 300 - 100 200 300 100 300 Glass fibre 5 5 5 5 5 5 5 Talc - 300 100 100 150 - - Calcium carbonate - - - - - 100 150 Oxygen index 75 42 55 59 75 56 74 The same results were also obtained by using clay, barium sulphate, diatomaceous earth, mica and various kinds of balloon (silica and glass), in place of talc and calcium carbonate, as the inert filler.

WHAT WE CLAIM IS: 1. A flame-resistant sealing composition comprising 100 parts by weight of at least one chloroprene rubber having a molecular weight of from 2,500 to 6,000 and a viscosity at room temperature of 10,000 to 120,000 cps, 100 to 450 parts by weight of at least one water-insoluble inorganic filler containing water of hydration and 1 to 15 parts by weight of at least one inorganic fibrous material with the proviso that up to half the weight of the water-insoluble inorganic filler containing water of hydration may optionally be replaced by an inert inorganic filler.

2. A composition as claimed in claim 1, which is cross-linked.

3. A composition as claimed in claim 1, which is uncrosslinked.

4. A composition as claimed in claim 2, which comprises from 1 to 5 parts by weight of a curing agent.

5. A composition as claimed in any of claims 1 to 4, comprising 150 to 400 parts by weight of the filler.

6. A composition as claimed in any of claims 1 to 5, wherein the water insoluble inorganic filler containing water of hydration is at least one of aluminium oxide hydrate [Al203. 3H2O or Al(OH)3], magnesia hydrate and calcium silicate hydrate.

7. A composition as claimed in any of claims 1 to 6, wherein the organic fibrous material is at least one of glass fibre, asbestos, rock wool, stainless steel fibre and carbon fibre.

8. A flame-resistant sealing composition substantially as herein described with reference to Compositions 1, 2 and 3.

9. A method of making a flame-resistant sealing composition which comprises intimately mixing together 100 parts by weight of at least one chloroprene rubber having a molecular weight of from 2,500 to 6,000 and a viscosity at room temperature of 10,000 to 120,000 cps, 100 to 450 parts by weight of at least one water-insoluble inorganic filler containing water of hydration and 1 to 15 parts by weight of at least one inorganic fibrous material with the proviso that up to half the weight of the water-insoluble inorganic filler may optionally be replaced by an inert inorganic filler.

10. A flame-resistant sealing composition when made by a method as claimed

Claims (1)

1. in claim 9.