GB1605293A - Fabrics for protection from thermal radiation - Google Patents

Description

(54) FABRICS FOR PROTECTION FROM THERMAL RADIATION (71) I, THE MINISTER OF NATIONAL DEFENCE OF HER MAJESTY'S CANADIAN GOVERNMENT, OTTAWA. CANADA. do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to fabrics for protection from flashes of intense heat radiation, for example, from thermo-nuclear devices.

The various types of thermo-nuclear weapons, for example, present a thermal hazard within a period many times too short for any conscious action to be of use, so that some type of constant protection is necessary.

The present invention provides a fabric which can be used as a covering for protecting personnel or property of various kinds from intense thermal radiation. The fabric has good flexibility and ventilating properties, is less inflammable than ordinary garment material, and can provide substantially complete protection against flashes of thermal radiation having intensities up to 30 calories per square centimetre delivered in a few seconds.

According to the invention, a fabric for protection from thermal radiation comprises a net having a coating comprising a mixture of neoprene and an initiatory explosive, the explosive igniting when subjected to a flash of intense thermal radiation causing the neoprene to burn and form a protective screen of dense smoke.

For this type of protection to be effective, the smoke must be produced and formed into a screen in front of the article to be protected within about 0.1 second of the arrival of the beginning of the heat flash. The heat energy incident during this 0.1 second must raise the surface layers of the target to a high temperature and produce and eject a smoke of adequate density. It has been found that common initiatory explosives are the most effective, the preferred ones being tetrazene, lead styphnate and silver fulminate.

It is necessary to incorporate a fuel into the protective fabric in order to provide a dense smoke when the fuel is burnt by the initiator.

Neoprene, as the fuel, does produce dense smoke, but is more effective as a neoprene cement. Compounded neoprene cements are surprisingly effective in producing a uniform dense cloud of smoke which effectively absorbs or disperses the incident heat radiation.

A protective covering in the form of a net in accordance with the invention, has several advantages, for example it is light, provides good ventilation and does not seriously obstruct visibility, which enables it to be widely used. To insure good protection the net should be made from a heat resistant material and nylon has been found to be highly satisfactory for this purpose. Other materials have been tested and have also been found to be satisfactory. The hole size of the coated net should preferably not be larger than 5 mm. to insure complete protection against radiation intensities up to 30 cal/cm2. in a few seconds.

To produce a coated net according to the invention a nylon net is preferably first completely coated with a compounded neoprene cement. This makes an ideal backing since it is totally compatible with a neoprene-tetrazene mixture and has the additional qualities of being quite resistant to both heat and wear. One or more coatings of a neoprene-tetrazene mixture are then applied to the surface of the neoprene-coated net facing the incident radiation so that the smoke is emitted in the direction of the incident radiation. The neoprene-tetrazene mixture should contain 6%-10% by weight of tetrazene, and preferably about 8%, based on the solid content.

The actual amount of neoprene-tetrazene mixture to be applied to the net can vary greatly. It has been found that the rate of.

emission of smoke is dependent on the intensity of the radiation so that the actual thickness of the coating will be dependent on the anticipated intensity of radiation and the length of time which the coating is expected to be subjected to the radiation. For protection of inanimate objects which cannot take avoiding action it is probable that thicker coatings would be needed than for protection of personnel.

The sequence of events which occur during the smoke production is that first a small amount of the radiant energy is reflected without any resultant thermal stress, and since the neoprene-tetrazene mixture is nearly black, being from 0.3 to 2.5 microns thick, this reflection is often only a very few percent.

Next all of the remaining radiant energy is absorbed while penetrating a very small distance beneath the surface of the mixture.

The resultant temperature rise explodes the initiatory explosive and burns the fuel. These reactions are exothermic and material is ejected and forms a smoke which scatters and absorbs the incoming radiant energy. During and following this period energy is transferred in all directions (but mostly in the direction opposite to that of the incident radiation) by mass transfer of gases, vapors or small pieces of material. Some mass transfer can, of course, occur back through the holes of the net but this is a relatively minor amount. The heat developed in the material of the net is conducted to the near surface and then transferred by conduction through the air to the target. A small amount of heat may be reradiated at long wave lengths through the net holes or from the surface of the net facing the object being protected.

A series of suitable coating compounds, in which the composition is expressed as parts by weight, are as follows: Compound No. 1 Neoprene 100.00 Zinc Oxide 10.00 Magnesia 10.00 "Nonox SWP"' 2.00 "CalceneTM"2 50.00 "Hi Sil 233"3 20.00 Titanium Dioxide 10.00 Na22 0.50 1 "Nonox WSP" is the trade mark of Imperial Chemical Industries for an alkylated bisphenol.

2 "Calcene TM" is the trade mark of Columbia Southern Chemical Corp. for fine particle, precipitated calcium carbonate pigment.

3 "Hi Sil 233" is the trade mark of Columbia Southern Chemical Corp. for hydrated silica.

Compound No. 2 Compound 1 202.50 "Chlorowax 70" 10.00 AntimonyTrioxide 40.00 "Chlorowax 70" is the trade mark of Diamond Alkali Co. for a chlorinated paraffin wax.

Compound No. 3 Neoprene 100.00 Zinc Oxide 10.00 Magnesia 10.00 Symmetrical di-beta-naphthyl para-phenylene diamine 2.00 Phenyl-B-naphthylamine 2.00 Na22 0.50 Compound No. 4 Compound3 124.50 EPC Black 25.00 Compound No. 5 Compound3 1 124.50 "Mineralite 3X"l 50.00 "Chlorowax 70" 10.00 Antimony Trioxide 40.00 1 "Mineralite 3X" is the trade mark of Mineralite Sales Corp. for a mica-type filler.

These compounds were then used for preparing coating solutions. Nets were coated by being dipped in a xylene solution of one of the above compounds and cured by heating.

The nets were dipped several times in the solution and cured after each dip, the number of dips being determined by the thickness of coating desired. The final coating layer was produced from a xylene solution of one of the above compounds to which was added 8 parts by weight of tetrazene per 100 parts solids.

Details of seven smoke-producing nets PN1 - PN7 produced in this way are as follows: I 1 I Final Base Base Base Layer 1 Layer2 Final Sq. Yd.

Net Net Coat Coat Cure of Wt.

No. Type Cure both Layer 1 (ozs) and Layer 2 PN1 TypeA No. 1 30mins. No.4 No.4+ 17.9 15% at 250"F 20% Tetrazene solids solids 200 -- Dips-4 solids PN2 Type B No. 1 30 mins. No.4 No. 4 + 15% at250"F 20% Tetrazene 20.2 solids solids 20% solids - Dips-4 PN3 Type B No. 2 30 mins. No.4(a) No.4(a) + 15% at250"F 15% Tetrazene -- 18.5 solids solids solids Dips-4 PN4 Type B No. 2 30 mins. No.4(a)+ 15% at 2500F Tetrazene -- -- 11.9 solids 15% Dips-4 solids PN5 Type B No. 5 60 mins. No.4(a)+ 60 mins.

Coloured at 2800F Tetrazene -- at 200"F 12.0 Olive 15% solids Drab 20% solids Dips-4 PN6 Type B No.5 60 mins. No.3(a) 60 mins.

Coloured at 2800F Coloured -- at 200"F 11.1 Olive Olive Drab Drab 20% solids + Tetra Dips4 zene 15% solids PN7 Type B No. 5 60 mins. No.4(a)+ Coloured At 2800F Tetrazene -- 60 mins.

Olive 15% solids at200 F 13.5 Drab 20% solids Dips-4 The designation (a) after the compound number indicates that an accelerator was added to the solution in an amount of 8 parts by weight per 100 parts solids.

Base net type A is a 100% nylon net of 4 oz/ yd2 with a hole size of approximately 4 mm, about 6 holes per inch in warp direction and 4 holes per inch in weft direction.

Base net type B is 100% nylon, 5 oz/yd2, hole size 2 mm, 6 holes warpways and 10 holes weftways.

The following examples show the effectiveness of the protective nets.

Example 1 A sample of 13 oz/yd2 khaki coloured all wool serge was subject without anyprotection to an exposure intensity of 8 callcmL in 1 second in a solar furnace. After the exposure the fabric was visibly charred and it had no appreciable bursting strength.

Example 2 Example 1 was repeated at an exposure intensity of 20 cal/cm2/sec with protective net PN 1, as hereinbefore described in the Table, in front of and in contact with the fabric. Even though the intensity of the radiation was 2 1/2 times the intensity in Example 1, the fabric was only very slightly singed and the bursting strength was reduced by only about 10%.

Example 3 Example 2 was repeated at an exposure intensity of 30 cal/cm2/sec and in this case the fabric was singed in the pattern of the net and the bursting strength was reduced by about 25%.

Example 4 Example 3 was next repeated using a different protective net, the net in this case being PN 2 which had a mesh opening of 2mm. A notable improvement was obtained over Example 3 since the fabric was only very slightly singed and the bursting strength remained unchanged.

Example 5 Example 4 was repeated with protective net PN 3. This was the same basic nylon net as PN 2 but the coating contained an accelerator and was slightly lighter than PN 2. The results with PN 3 were the same as with PN 2.

Example 6 Example 1 was repeated with 9 oz/yd2 cotton drill in place of the wool serge. As with the wool serge, the fabric was severely charred.

Example 7 A sample of 9 oz/yd2 cotton drill was subjected to an exposure intensity of 30 cal/cm2/sec while being protected by protection net PN 5 placed 5 mm in front of the fabric. PN 5 is a relatively light weight protective net. After an exposure of 1 sec the fabric was only slightly discoloured and the bursting strength was unchanged.

Example 8 Example 7 was repeated at an exposure intensity of 20 cal/cm2/sec with the protective net in contact with the fabric. Again the fabric was only slightly discoloured but the bursting strength was reduced by 75%.

Example 9 Example 8 was repeated substituting a 5 oz/ yd2 mixed nylon and cotton fabric for the cotton drill. After exposure the fabric was slightly singed and the bursting strength was reduced by about 2/3.

Example 10 A protective net PN 3, which is heavier than PN 5, was placed in contact with a 8.3 oz/yd2 nylon/cotton cloth and subjected to thermal radiation in a solar furnace. The intensity was 30 caUcm2/sec and after a 1 sec exposure the fabric was slightly singed and the bursting strength was reduced by 25%.

Tests were also conducted to determine the effectiveness of the protective nets as well as the nets together with the above fabrics in protecting bare flesh. These tests were conducted by placing a protective net or net and piece of fabric over the bare skin of the inner forearm and subjecting this to thermal radiation. Such tests are relevant to the problem of protecting normally unclothed areas such as the eyes and hands, for which cases the nets are considered suitable.

Example 11 A layer of protective net PN 1 was spaced 5 mm from the bare skin of an inner forearm and this was subjected to exposures of varying intensities in a solar furnace. After 1 sec exposure at 10 caVcm2/sec and 15 caUcm2/sec the skin was slightly reddened. At a 20 cal/ cm2/sec intensity, after 1 sec the skin was discoloured and several days after the exposure slight blistering was noted.

Example 12 A layer of protective net PN 1 and a layer of serge or cotton drill were placed in contact with the bare skin of an inner forearm and subjected to radiation exposure of intensity of 30 cal/cm2/sec in a solar furnace. The exposure was for 1 second and no immediate effect was noted with either combination. However, if the heated cloth was held in contact with the skin for some time slight erythema occurred.

Example 13 A layer of protective net PN 1 and a layer of cotton-nylon combat cloth were placed on the bare skin of an inner forearm. This was subjected to an exposure intensity of 15 cal/ cm Isec for 1 second and no effect on the skin was apparent.

These experiments have shown that the coated net is extremely effective in protecting against thermal radiation and that very little radiant energy penetrates the holes of the nets used. This would clearly indicate that most of the energy is absorbed or scattered by the smoke.

The coated net is very durable under intense radiation and while the smoke absorbs and scatters the heat waves so that they do not pass between the open spaces in the net, these spaces serve an essential purpose in that they provide ventilation for a person being protected with the result that heat stress i.e.

extreme discomfort and exhaustion from exertions in an unventilated garment due to a water-vapour impermeable layer is avoided.

This is very important in clothing. Also it has been found by field tests that clothing made from the nets of this invention does not have any more tendency to snag than orthodox clothing, nor do the nets cause dizziness when used for several hours to protect the eyes.

It will be appreciated that the protective device of this invention has a wide field of use.

For example, buildings and vehicles represent quite good forms of protection against thermal radiation but most of these have one major hazard which is the entry of radiation through windows. The coated net of this invention could be useful as screens over windows to prevent such entry of radiation.

These nets can also be used for the protection of apparatus and equipment which is stored in the open. Particularly when used for protecting buildings and materials, in which case a thick coating of the neoprene-tetrazene mixture can be used, the protective material has the advantage that the emission of smoke ceases instantaneously with the termination of the thermal radiation and will commence again on being again subjected to radiation. This can be repeated until the fuel supply for the smoke has been exhausted. The nets tend to be selfextinguishing after exposure to radiant energy, and are less likely to catch fire than normal clothing fabrics.

WHAT I CLAIM IS: 1. A fabric for protection from thermal radiation comprising a net having a coating comprising a mixture of neoprene and an initiatory explosive, the explosive igniting when subjected to a flash of intense thermal radiation causing the neoprene to burn and form a protective screen of dense smoke.

2. A fabric according to Claim 1 in which the initiatory explosive is tetrazene, lead styphnate or silver fulminate, or a mixture of these compounds.

3. A fabric according to Claim 1 or Claim 2 wherein the coating consists of a compounded cement containing neoprene, the initiatory explosive and an inert filler.

4. A fabric according to Claim 3 wherein the compounded cement is substantially as any one of the compounds Nos. 1 to 5 hereinbefore described.

5. A fabric according to any preceding claim in which the net is made of nylon.

6. A fabric according to any preceding claim in which only one face of the net is coated.

7. A fabric according to any preceding claim wherein the coating contains about 6-10 per cent by weight of tetrazene.

8. A fabric according to any preceding claim in which the net is provided with a foundation coating comprising neoprene but without any initiatory explosive.

9. A fabric according to any preceding claim in which the net has a mesh size not greater than about 5 millimeters.

10. A process for the preparation of fabric for protection from thermal radiation which comprises immersing a net in a xylene solution of a compounded cement containing neoprene, an initiatory explosive and inert filler, removing the net from the solution, heating the net to cure the coating thus formed, and repeating the immersion and curing cycle a sufficient number of times to produce a coating of the desired thickness.

11. A process according to Claim 10 in which the net is coated with compounded cement containing neoprene before immersion in the xylene solution.

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

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. repeated until the fuel supply for the smoke has been exhausted. The nets tend to be selfextinguishing after exposure to radiant energy, and are less likely to catch fire than normal clothing fabrics. WHAT I CLAIM IS:

1. A fabric for protection from thermal radiation comprising a net having a coating comprising a mixture of neoprene and an initiatory explosive, the explosive igniting when subjected to a flash of intense thermal radiation causing the neoprene to burn and form a protective screen of dense smoke.

2. A fabric according to Claim 1 in which the initiatory explosive is tetrazene, lead styphnate or silver fulminate, or a mixture of these compounds.

3. A fabric according to Claim 1 or Claim 2 wherein the coating consists of a compounded cement containing neoprene, the initiatory explosive and an inert filler.

4. A fabric according to Claim 3 wherein the compounded cement is substantially as any one of the compounds Nos. 1 to 5 hereinbefore described.

5. A fabric according to any preceding claim in which the net is made of nylon.

6. A fabric according to any preceding claim in which only one face of the net is coated.

7. A fabric according to any preceding claim wherein the coating contains about 6-10 per cent by weight of tetrazene.

8. A fabric according to any preceding claim in which the net is provided with a foundation coating comprising neoprene but without any initiatory explosive.

9. A fabric according to any preceding claim in which the net has a mesh size not greater than about 5 millimeters.

10. A process for the preparation of fabric for protection from thermal radiation which comprises immersing a net in a xylene solution of a compounded cement containing neoprene, an initiatory explosive and inert filler, removing the net from the solution, heating the net to cure the coating thus formed, and repeating the immersion and curing cycle a sufficient number of times to produce a coating of the desired thickness.

11. A process according to Claim 10 in which the net is coated with compounded cement containing neoprene before immersion in the xylene solution.