US 3502537 A
Description (OCR text may contain errors)
United States Patent C) 3,502,537 AIR-PERMEABLE PROTECTIVE MATERIALS William M. Pearson, Halifax, and Thomas S. Crosby, Huddersfield, England, assignors to Bondina (B.D.A.) Limited, Halifax, England, a British company No Drawing. Filed Dec. 19, 1966, Ser. No. 602,491 Claims priority, application Great Britain, Jan. 4, 1966, 341/66; Aug. 23, 1966, 37,743/66 Int. Cl. 1332b 5/16 US. Cl. 16187 9 Claims ABSTRACT OF THE DISCLOSURE An air-permeable protective fabric comprising a composite of a woven or knitted fabric and a non-woven fabric impregnated with a binder and having a layer of charcoal bonded to one side of said composite by means of a binder composition comprising an acrylate resin which is capable of forming a soft film.
This invention relates to materials which can be made up into protective garments that will provide protection to the wearer against toxic chemicals and other substances such as might be used, for instance, in agricultural sprays.
The basic requirements for such a material are in many cases contradictory. For example, for the safety of the wearer, the material must not be permeable to harmful vapours and must have a high tensile and tear strength, while, at the same time, for the comfort of the wearer, it must be permeable to air as well as being flexible, thin and light. In practice the aim is to provide a material with a permeability of about 100 linear feet of air per minute at a pressure difference across the material of /2 inch water gauge.
It is known to incorporate activated charcoal into protective materials to absorb liquid or gaseous toxic chemicals coming into contact with it. Woven fabrics are strong and permeable, but droplets of toxic chemicals tend to strike through; if a tightly woven fabric is chosen to reduce this tendency, the incorporation of a charcoal layer may render the fabric impermeable, or reduce its permeability to an unacceptable extent. Non-woven fabrics have the advantage that droplets settling on or coming into contact with them tend to spread on the surface or in the material and do not pass straight through as they would with a woven fabric, but a simple non-woven fabric is too low in tear strength and serious damage can be caused to it, for example, by snagging on barbed wire.
A somewhat stronger fabric which combines the strength of woven fabric with the variable properties of non-woven fabric can be produced by needling one or more layers of a non-woven fibrous web on to a backing of woven or knitted material and impregnating the resulting composite material with a binder. Conventional binders for non-woven fabrics can be used but where flame resistance is required, a polychloroprene binder vulcanised in situ has proved very satisfactory provided that a suitable antioxidant formulation including Zinc oxide as an acid acceptor is present to reduce degradation by light. The resistance to burning may be further improved by the incorporation of antimony trioxide.
According to the invention, a protective material is formed from a composite of a woven or knitted fabric and a non-woven fabric impregnated with a binder and having a layer of charcoal bonded to one side of the material by a binder composition comprising an acrylate resin. Advantageously the composite of woven or knitted fabric and non-woven fabric may be rendered repellent to both oil and water by treatment with a dispersion of a fluoroice carbon resin, such as that sold under the trade mark Scotchgard PC 208. Scotchgard PC 208 is a 28% dispersion of a fluorocarbon polymer of the type described in US. Patent No. 2,803,615. In use, protective materials according to the invention will be made into protective garments so that the charcoal layer is on the inside of the garment; if it were on the outside, it would absorb chemicals. When the layer is on the inside, the majority of the droplets coming into contact with the garment will be shed by the oil and Water repellent finish of the material, or will tend to spread in the non-woven layer of the material, and thus the danger of the charcoal layer becoming saturated is reduced.
Preferably the charcoal layer is applied to the woven surface of the composite material, and the protective garment is subsequently made up so that the non-woven surface of the material is outermost. For certain uses, however, the charcoal layer may be applied to the non-woven surface of the composite material, and the garment then made up so that the woven surface of the material is outermost.
The bonding of the charcoal layer to the composite material must be such that a minimum of charcoal can be rubbed off, for example onto the clothes of the wearer of a protective garment, under wet or dry conditions, while at the same time the capacity of the charcoal to absorb chemicals is not substantially reduced. Furthermore the stiffening effect on the fabric must be kept to a minimum, and this means that the binder must form a soft film.
The charcoal and binder composition are best sprayed on to the material together as an aqueous dispersion which is dried to give a bonded layer of charcoal, and such dispersions require to be stabilised: in extreme cases the dispersion could not be made without a stabiliser being present, or having been made, would then be insuificiently stable to be applied to the material by spraying. At the same time the stabiliser, although only present in very small quantities, can have a pronounced effect on the adhesion of the charcoal and binder to the material and on the gas absorbency of the charcoal layer.
Stabilised natural rubber latex is known as a binder for charcoal giving a charcoal layer with good initial charcoal adhesion and gas absorbency properties. Ammoniated casein serves as an excellent stabiliser for binder compositions incorporating natural rubber. However natural rubber, under these circumstances, is vulnerable to ageing resulting in rapid loss of charcoal adhesion and gas absorbency properties, so that the charcoal can be left virtually unbonded after as little as six months after manufacture.
Our binder composition may comprise an acrylate resin as the sole binder material, or the binder composition may comprise an acrylate resin with a lesser proportion of natural rubber. Preferably the acrylate resin will comprise at least 50% by weight of the binder composition in any case. We have found that if a binder cornposition comprising an acrylate resin with a lesser proportion of natural rubber stabilised with ammoniated casein is used fairly satisfactory ageing properties of the charcoal layer are obtained. Natural rubber is an excellent binder, and the total amount acrylate resin and natural rubber necesary to bond the charcoal layer may be as low as 15% by weight calculated on the dry weight of the charcoal. Good charcoal adhesion, and high initial gas absorbency properties are observed, but the gas absorbency of the charcoal does decrease with time, probably because of the ageing of the rubber. If an acrylate resin is the sole binder material, good adhesion may only be obtained in certain circumstances using amounts of it which somewhat reduce the effectiveness of the charcoal as an absorbent; the ageing characteristics of a composition in which acrylate resin is the sole binder material are so superior to those of compositions containing natural rubber, however, as largely to offset this drawback. On balance we prefer that an acrylate resin should be the sole binder material. In the absence of natural rubber, however, that is to say when an acrylate resin is the sole binder in the binder composition ammoniated casein, although still a good stabiliser, is an undesirable constituent because it reduces the initial capacity of the charcoal to absorb gas when sufficient of the acrylate resin is present to achieve good adhesion of the charcoal. When using an acrylate resin as the sole binder material, therefore, we prefer to stabilise the aqueous dispersion of the binder and charcoal with a water-soluble cellulose ether. The use of suitable proportions of a cellulose ether as stabiliser results in a charcoal layer with excellent gas absorbency when sufiicient acrylate resin is used to ensure good charcoal adhesion. The proportion of cellulose ether in the binder composition should be kept to a minimum since large quantities do tend to impair adhesion especially under wet conditions; we prefer not to incorporate more than about dry weight on the dry weight of charcoal and normally we prefer to use about 0.5% to 1.5%. The amount of acrylate resin required will normally be not less than 30% dry weight on the dry weight of the charcoal and will not normally exceed 130%. We have found about 50% to be satisfactory in many cases.
Suitable water soluble cellulose ethers include methyl celluloses, which are available in various viscosity grades. Particularly suitable materials are those which give a viscosity of about 100 centipoises at C. as a 2% aqueous solution, and which can thus readily be used to form binder compositions of convenient viscosity for spraying. The methyl cellulose sold under the trademark Celacol M100 (methyl cellulose with a degree of methyl substitution of about 1.6 to 1.7) is especially suitable, but cellulose ethers of higher or lower viscosity may also be used.
It is very desirable that the acrylate resin used as the binder or as part of the binder composition should form a soft film, and we prefer to use dispersions of resins which form a film which has an ultimate hardness (TUKON) of not more than 1. Examples of suitable materials include the dispersions of acrylate resin sold under the trademarks Primal B15 (a 46% solid content carboxylated polyacrylate of the type described in British Patent No. 791,767), Acronal KR 2151 (a 40% solid content emulsion of carboxylated polybutyl acrylate) and Texicryl 712B (a 46% solid content carboxylated polyacrylate emulsion).
The activated charcoal used is commonly derived from coconut shells, and contains various metal compounds, for example compounds of iron and copper. We have now found that we can not only improve the ageing characteristics of the binder composition when natural rubber is present, but can also increase the capacity of the charcoal for holding toxic gas whether natural rubber is present in the binder composition or not if we first subject the charcoal to acid washing to remove these metal compounds. Accordingly we prefer to use charcoal which has been washed with hot dilute acid to remove metal compounds, a suitable treatment, for example, involving washing with 5% hydrochloric acid at 95 C., then Washing with water and finally neutralising by rinsing with dilute ammonia solution.
The binder in the composite material may be a polychloroprene as described above or may be a composition comprising an acrylate resin cured in situ. The acrylate composition can include chlorinated polymers and an timony oxide to provide flame resistance if this is required.
Two examples will now be given:
EXAMPLE 1 A composite is formed by needling 60 grams per square metre of an even fibrous fleece consisting of 85% nylon and 15% viscose fibre onto a 26 grams per square metre cotton scrim backing, and then impregnating the product with a dispersion of a formulated binder based on Neoprene 842A (a 50% solid content polychloroprene latex containing sodium rosinate as an emulsifier) so as to deposit 60 grams per square metre of binder solids. The impregnated material is dried, vulcanised and washed. Next it is treated with a solution of aluminum acetate, dried and rewashed and thereafter with a dispersion of Scotchgard PC 208 resin to provide a finish which after curing will repel oil and water. The purpose of immersing the material in the aluminum acetate solution and then drying it is to deposit a chemical which will prevent the fluorocarbon from penetrating deeply into the material, since as far as possible the fluorocarbon should be retained on the surface.
The charcoal is applied as a dispersion of the following compositions.
Parts by weight Acid-washed dry charcoal 170 15% casein solution 30 centrifuged natural rubber latex (60% solids) 24 Acrylate resin dispersion (35% solids) sold under the trademark Primal H A543 Water to make 1000 parts by Weight.
EXAMPLE 2 The process of Example 1 was repeated, using a dispersion of binder and charcoal composed as follows:
Parts by weight Acid-washed dry charcoal 2 /2% solution of Celacol M100 29.2 Primal B15 Water 592 The finished product had good gas absorption and age ing properties.
The concentration of Primal B15 can be reduced somewhat to give the final product a slightly higher gas absorption, at the expense of slightly lower adhesion of the charcoal layer, or vice versa, but the dispersion described gives very satisfactory overall results.
1. An air-permeable protective material consisting essentially of a composite of a woven or knitted fabric and a non-woven fabric impregnated with a binder selected from the group consisting of an acrylate resin capable of forming a soft film having a hardness of not more than 1 (TUKON), olychloroprene and mixtures thereof and a layer of charcoal bonded to one side of said composite, said layer of charcoal being the dried residue of a composition consisting essentially of an aqueous dispersion of charcoal and a member selected from the group consisting of an acrylate resin and a mixture of at least 50% by weight of an acrylate resin and natural rubber, said acrylate resin being one which is capable of forming a soft film having a hardness of not more than 1 (TUKON), said member being present in an amount of at least 30% dry weight based upon the dry weight of the charcoal present when said member is an acrylate resin, and in an amount of at least 15% dry weight based upon the dry weight of the charcoal present when said member is a mixture of an acrylate resin and natural rubber.
2. A. material according to claim 1 in which the layer of charocal is bonded to the woven or knitted side of the material.
3. A material according to claim 2 wherein said membet is a mixture of an acrylate resin with a lesser proportion of natural rubber.
4. A material according claim 3 wherein said composition includes ammoniated casein as a dispersion stabilizer.
5. A material according to claim 1 wherein said member is an acrylate resin.
6. A material according to claim 5 wherein said composition contains a water-soluble cellulose ether as a dispersion stabilizer.
7. A material according to claim 6 wherein said watersoluble cellulose ether is methyl cellulose.
8. A material according to claim 1 in which the composite or woven or knitted fabric and non-woven fabric is an oiland water-repellent fluorocarbon resin-treated fabric.
9. A material according to claim 1 in which the charcoal is an acid-washed charcoal,
References Cited UNITED STATES PATENTS 2,979,157 4/1961 Clark. 2,984,584 5/1961 Glarum et a1. 11776 3,061,473 10/1962 TcSOro 117l35.5 X 3,091,550 5/1963 Doying 11783 X 3,206,351 9/1965 Smith 161154 X 3,326,713 6/1967 Smith et al 117135.5 X 3,377,313 4/1968 Jupa et a1. 260-41 FOREIGN PATENTS 986,686 3/ 1965 Great Britain.
MURRAY KATZ, Primary Examiner RALPH HUSACK, Assistant Examiner US. Cl. X.R.
117-43, 76, so, 83, 135.5, 140; 16l8l, 89; 2 0-41,