Flameproofing Combustible Sheet Materials

Abstract

A flameproofing agent is applied to combustible sheet material in a pattern in which small areas of high concentration of flameproofing agent are distributed substantially uniformly on the sheet material and alternate with areas of low to zero concentration of the flameproofing agent.

Description

The present invention relates to the flameproofing of sheet materials.

Hitherto the flameproofing treatments of sheet material, in particular textile sheet material such as fabrics has been carried out by padding onto such sheet material solutions or dispersions of suitable flameproofing agents, i.e., by impregnating the sheet material with aqueous or non-aqueous solutions or dispersions of such agents followed by squeezing between the rollers of a mangle to remove the excess of thebath. Since rather high amounts of flameproofing agents are necessary to achieve a substantial reduction of the rate of burning or of flame propagation, such flameproofing or flame-retarding treatments tend to affect the handle of treated textile sheet material seriously, i.e., they cause stiffening due to the reduction of fiber to fiber and yarn to yarn mobility. In the case of synthetic thermoplastic material, which has a much lower bath take-up than cellulosic or wool fibers, it is in most cases impossible to apply by padding amounts of flame-retarding agents sufficient to produce improvements in the flame-retardance, and one had to resort to coating, which affects the properties of the sheet material, and in particular the handle to such an extent that such coated fabrics could no longer be used for apparel fabrics and other textile applications.

All these flameproofing or flame-retarding treatments produced a continuous coating or an enclosure of all individual fibers of the entire sheet material, and it was believed that it was important to have the agent distributed as uniformly as possible over the surface of fibers, yarns and fabrics.

According to the present invention an improved and more universally obtainable flame-retardant effect can be achieved if agents having a flame-retarding action are present on sheet material, in particular textile sheet material, in the form of a pattern only locally, i.e., where areas with a high concentration of the agent alternate with areas with low to zero concentration of such agents, and where the average distance between areas of high concentration of flame-retarding agents preferably is at most ten times, preferably less than five times the thickness of the sheet material.

The present invention also includes a process for imparting flame-retardant properties to sheet material by applying agents which have a flame-retarding action to said sheet material in the form of a pattern, in which areas with a high concentration of the agent alternate with areas with low to zero concentration of such an agent.

This local application of flame-retarding agents has been found to produce at the same total concentration of the agent on the weight of the sheet material, flame-retarding effects of at least the same magnitude as with a uniform distribution (all-over distribution) of flame-retarding agents even though there is no or relatively little flame-retarding agent present between the areas of high concentration. The handle, stiffness or drape of sheet material containing flame-retarding agents only locally is much less affected than by a uniform application in the same concentration of the same flameproofing agent. By the term "flame-retarding agent" is to be understood any agent which, when applied to a certain sheet material, is capable of reducing the rate at which a flame propagates itself along this sheet material, or which reduces the ease of ignition of this sheet material, i.e., which for instance increases the time during which the sheet material has to be exposed to a defined source of heat such as a flame until it ignites, or which increases the amount of heat required to ignite the sheet material, or which enhances the ease of extinction of the flame on the burning sheet material.

Many different methods have been proposed for the evaluation of flame-retarding or flameproofing effects, either by determining the rate of propagation of a flame through a sample of sheet material, which may be at any angle between 0.degree. to 90.degree. to the horizontal plane, by measuring the oxygen consumption rate of a flame on the material to be tested, the rate or ease of ignition, ignition temperatures, ease of extinction, length of the charred area and so on. Such methods are for instance described in Textile Chemist and Colorist 2 (1970), p. 123-125. Such flame-retarding agents may act either by giving off gases which do not support combustion and thus displace oxygen in the air present in and around the sheet material exposed to a flame, by forming a virtually non-combustible coating around the components of the sheet material if exposed to ignition temperatures, by catalytic or chemical interaction with the material of the sheet material or components thereof, or with gases developing during burning, by influencing thermal decomposition characteristics (such as for instance by lowering the thermal decomposition temperature of the material to below its ignition temperature), the ignition temperature or the heat of combustion or the heat capacity of the sheet material or components thereof. The mechanism of the action of flame-retarding agents is still not completely understood. Such agents are believed to act by decomposing at temperatures equal to or below the temperature of the flame and-or to have a catalytic effect at these temperatures on gases given off during burning, on the burning material itself, or both. In some cases they may act by dissipating heat or by decomposing into non-combustible gases.

Different types of flame-retarding agents are known which all may be used for products and processes according to the present invention per se or in mixtures. Agents giving off non-combustible gases comprise halogen compounds having a relatively low decomposition temperature, in particularly organic chloro and bromo compounds, compounds containing boron, nitrogen compounds, in particular ammonium salts of acids and nitrogen compounds where nitrogen is bonded to other atoms with preferably only one bond. Most widely used among flame-retarding agents whose active ingredient remains predominantly in the charred product, are inorganic and in particular organic phosphorous compounds, which at least in the case of cellulose are believed to change catalytically the mechanism of thermal decomposition. Other elements present as active ingredients in flame-retarding agents are molybdenum, antimony, silicon, aluminum and other polyvalent atoms. Agents preferred for the present invention are phosphorous compounds and agents at least partly acting in the gas phase, such as nitrogen, halogen and boron compounds, in particular in mixture with phosphorous compounds.

All these agents according to the present invention may be present in or may be applied per se or in mixtures to sheet material, in particular fibrous sheet material, such as paper, woven, knitted or non-woven fabrics, but also in sheets of foam, plastics, and wood. They are present in the form of an irregular or random or a regular pattern, where the areas of high concentrations of those agents may or may not be interconnected, i.e., where the agent may be present for instance in the form of dots (not interconnected) or lines alone or dots interconnected by lines, or in any other pattern where between areas of high concentration on the agent there are areas with relatively low or zero concentration of the flame-retarding agent. The total amount of flame-retarding agents applied to the sheet material is between 2 and 30 percent, usually between 5 and 15 percent of the weight of the sheet material depending on the agents used and flame-retarding requirements. The areas of high concentration may lie within the body of the sheet material, i.e., imbedded in the sheet material without adding to its thickness (this is particularly useful if the sheet material is relatively thick) or they may only partly penetrate in the sheet material or sit virtually only on its surface (thus increasing the thickness of the sheet material) on either or both sides or faces of the sheet material.

Generally speaking the total area of the areas of low or zero concentration of the flame-retarding agent should not exceed the total area of the area of high concentration by a factor of more than 10, preferably 5. The distance between the edges of high concentration areas should not be more than five times, preferably three times or less than the median diameter of the high concentration area, and the distance between high concentration areas should be less than 10 times, preferably five tiems or less the thickness of the sheet material. In the case of thin sheet material (for instance up to the thickness of a poplin fabric or of print cloth) the flame-retarding material may sit on the surface of the sheet material on either or both sides depending on the pattern and the flame-retardancy requirements, without substantially penetrating into the sheet material.

This minimizes stiffness due to blocking of interfiber movement. In the case of thicker sheet material it is advantageous to have more flame-retarding material present within the structure of the sheet material, particularly if a high degree of flame-retardancy is required. More blocking of interfiber mobility will, however, take place which will result in increased stiffness, which stiffness of course will still be lower than if the flame-retarding agent would be distributed evenly throughout the sheet material.

Flame-retarding agents may be present in pure form or together with thermoplastic or non-thermoplastic binders, finishing agents, white or colored pigments, etc. They may be applied in the form of dispersions, emulsions, dry powders or pastes by known methods such as printing, dry powder application (scattering, powder-dot transfer), and spraying. These agents may at the time they are applied already be polymeric or they may be subsequently transformed into polymers, be chemically modified or reacted with other agents present or with the sheet material or components thereof.

The sheet material may consist of cellulose or derivatives thereof, of proteinic material such as present in wool, of synthetic thermoplastic polymers such as polymerisates, co-polymerisates or mixed polymerisates of acrylic, vinylic, olefinic monomers, of lactams or lactones, or they may be polycondensates of poly-hydroxy-compounds and poly-hydroxylic acids, of poly-carboxylic acids and polyamines, of poly-hydroxy compounds and isocyanates or mixtures of such polymers. These polymers may be present as fibers in the form of textile fabrics (woven, knitted or non-woven), as films, sheets containing or consisting of one or more polymeric components, as paper, cardboard or woodlike sheet material, sheets of foam or laminates of two or more of the sheet materials mentioned. Such sheet material, if present in the form of textile fabrics, may be given the flame-retarding treatment according to the present invention at any stage of finishing, but preferably this treatment is applied as one of the last steps in the finishing sequence. Such sheet material, whether present in the form of textile fabrics or otherwise, may be coated with polymeric material and/or be mechanically deformed for instance by embossing or pressing prior or subsequent to being given the flame-retarding treatment according to the present invention. By the term "sheet material" is to be understood a shape that is thin in relation to its length and breadth. It may be sheetlike in the sense of sheets of fabrics of paper or of films, where a thin material is present in lengths exceeding the width by a factor of 10, 20 or more or it may consist of parts cut from such sheets or formed in that way. It has been found possible to apply flame-retarding agents according to the present invention in a discontinuous form on only one side of the face of the sheet material or on both. A one-sided localized application is particularly useful in cases where fabrics in actual use are exposed to the accidental action of an incendiary only from one side and where the flame-retarding agent thus can be located on the invisible side of the material where it cannot unfavorably affect other properties as would the same agent if distributed evenly throughout the sheet material.

The discontinuous, pattern-like application of flame-retarding agents also has the advantage that one may apply agents in the form of pigments, powders, in molten form, in the form of soluble or insoluble polymers, dispersions, emulsions, etc., i.e., one has a much wider choice of formulation and thus may use agents which could not be used by conventional methods leading to a uniform distribution throughout the sheet material or by coating. Even though there are areas where there are high concentrations of the flame-retarding agent than if the same agent is distributed uniformly throughout the sheet material, there always will be areas in between the high concentration areas which are not affected at all by the presence of the flame-retarding agent and thus will bend very easily. Total stiffness thus is much lower than if the same amount of the same agent is uniformly distributed over the sheet material.

Following is a description by way of example only of methods of carrying the invention into effect.

Example I

A cotton broad cloth which had been desized, bleached, mercerized and given a wash and wear finish was treated with a paste containing 2.4 g. Carbopol as a thickening agent and 20 g. diammonium phosphate as the flame-retarding agent in 100 ml of water was printed on one side in a pattern of dots, each dot having a diameter of 0.8 mm. and the dots being disposed in rows so that the distance between the edges of adjacent dots is 1 mm. and the total high concentration area is 20 percent of total cloth area. The amount of flame-retarding agent applied to the fabric was 5 percent of the weight of the fabric.

Example II (Comparison)

The fabric of Example I was padded in an aqueous solution of diammonium phosphate as a flame-retarding agent, the add-on being adjusted in such a way that the fabric also contained 5 percent diammonium phosphate, uniformly distributed thereon. The treated sample of Example I in which the flame-retarding agent was present in a discontinuous form had a softer handle than the sample of Example II in which the agent was distributed uniformly throughout the fabric. The two samples and an untreated control were tested according to AATCC 33-1962 (45.degree. configuration of the fabric).

Sample 1 (dots): Burning time 6.4 sec.

Sample 2 (uniform distribution): Burning time 6.5 sec.

Control (untreated): Burning time 4.0 sec.

Example III

Examples I and II were repeated, the add-on of diammonium phosphate this time being 10 percent on the weight of the fabric. When subjected to the same burning test neither fabric sample burned.

Example IV

The sample treated according to Example I was wrapped around a piece of polyurethane foam. The same was done with an untreated control. A gas flame (length 2 cm) was directed towards the two samples for 7 seconds. The foam wrapped in the control started to burn immediately, while the flame on the foam wrapped in fabric treated according to Example I died after the gas flame had been removed, both when the dots were on the inside or on the outside of the wrapping fabric.

Example V

Example I was repeated for a 50:50 cotton/polyester blend (shirting), the treatment being applied to one side only, and the amount of flame-retardant being present on the fabric in an amount of 5 percent by weight on the weight of the fabric. On conducting burning tests at 45.degree. configuration of fabric and on contact with a gas flame for one second a slight melting of the polyester was noted and the flame died after a second. An identical test on an untreated control resulted in melting and burning of the polyester.

Example VI

Example V was repeated for a polyester blouse material. In the burning tests, the treated material melted slightly and the flame died immediately on removal from the gas flame. The untreated melted and burned.

Example VII

A cotton poplin (desized, bleached, mercerized and vat dyed, weight 120 g/m.sup.2) was padded in an aqueous solution containing 400 g water and 600 g Flammentin AC (a 50 percent solution of an organic compound containing halogen, phosphor and nitrogen atoms, made by Quehl, Speyer, Germany). The solids add-on after squeezing and drying was 25 percent on the weight of the fabric (sample A, treated control).

A second sample was prepared in the same way, but with an add-on of only 20 percent solids (sample B, treated control B).

On two samples (samples C and D) of the same poplin, the same flameproofing agent (Flammentin AC) was screen-printed in the form of a thickened paste (522,5 g Flammentin AC, 50 percent solids; 322,5 g Meyprogum AC 7 as thickening agent. Meyprogum is galactomannane, sold by Meyhall Chemical AG, Kreuzlingen, Switzerland).

Sample C: printing screen with circular holes arranged in a regular pattern, 25 percent of screen area open, add-on in solids (arranged in the form of dots separated by areas of fabric containing no flameproofing agent): 13 percent

Sample D: As sample B, but 34 percent of printing acreen open, solids add-on 19 percent.

After printing, the samples B and C were dried as sample A.

Testing of all samples: Strips 25 by 2 cm in vertical position were ignited by contact (2 seconds) with a gas flame at the lower edge of the strip.

Sample add-on of flame Test Result proofing agent (A) (treated control): 25% does not ignite uniform distribution of flame proofing agent (B) (treated control): 20% ignites, stops uniform distribution burning after 5 seconds (B):discontinuous 13% ignites, flame distribution stops burning after 5 seconds (C):discontinuous 19% does not ignite distribution Untreated control -- ignites, complete- ly burnt after 12 seconds

Example VIII

A cotton/polyester blend (50/50) after desizing and bleaching was padded in a solution of 200 grams/liter of diammonium phosphate, then squeezed and dried. The add-on of solids was 12 percent on the weight of the fabric (sample A, treated control).

To the same fabric (sample B) the same amount of the same flameproofing agent was applied by printing by means of the screen printing method described in Example 7, 34 percent of the screen being open. The flameproofing agent thus was present on the sample in the form of dots separated by areas of fabric not containing any flameproofing agent. The area covered by dots was about one third of the total area.

Flammability tests were carried out as described in Example 7.

Sample Add-on Flammability (A) uniform distribution 12% ignites, stops burn- of flame proofing agent ing after 4 seconds (B) local application of 12% does not ignite flame proofing agent

Claims

What is claimed is:

1. A process for flameproofing combustible sheet material which comprises applying to said sheet material a pattern of a flameproofing agent in which small areas of high concentration of flameproofing agent are distributed substantially uniformly on said sheet material and alternate with areas of low to zero concentration of flameproofing agent, said areas of low to zero concentration not exceeding said areas of high concentration by a factor of about 10, and the distance between said areas of high concentration being less than about 10 times the thickness of said sheet material, the total amount of flameproofing agent applied to said sheet material being from about 2 to about 30 percent, by weight, based on the weight of said sheet material.

2. The process according to claim 1 wherein the total amount of flameproofing agent applied to said sheet material is from about 5 to about 15 percent, by weight, based on the weight of said sheet material.

3. The process according to claim 1 wherein the distance between said small areas of high concentration of flame-proofing agent is less than about five times the thickness of said sheet material.

4. The process according to claim 1 wherein the total area of the areas of low to zero concentration of flameproofing agent does not exceed the total area of the small areas of high concentration of flameproofing agent by a factor of more than about 5.

5. The process according to claim 1 in which the distance between the edges of adjacent small areas of high concentration of flameproofing agent is not more than about five times the mean diameter of said areas of high concentration.

6. The process according to claim 1 in which the distance between the edges of adjacent small areas of high concentration of flameproofing agent is not more than about three times the mean diameter of said areas of high concentration.

7. The process according to claim 1 wherein said sheet material comprises textile sheet material.

8. The process according to claim 1 wherein said small areas of high concentration of flameproofing agent comprise a regular pattern of disconnected dots on the surface of said sheet material.

9. A flameproof sheet material comprising an ordinarily combustible sheet material having a flameproofing agent applied thereto in a pattern in which small areas of high concentration of the flameproofing agent are distributed substantially uniformly on said sheet material and alternate with areas of low to zero concentration of flameproofing agent, said areas of low to zero concentration not exceeding said areas of high concentration by a factor of about 10, and the distance between said areas of high concentration being less than about 10 times the thickness of said sheet material, the total amount of flameproofing agent applied to said sheet material being from about 2 to about 30 percent, by weight, based on the weight of said sheet material.

10. A flameproof sheet material according to claim 9 wherein the total amount of flameproofing agent applied to said sheet material is from about 5 to about 15 percent, by weight, based on the weight of said sheet material.

11. A flameproof sheet material according to claim 9 wherein the distance between said small areas of high concentration of flameproofing agent is less than about five times the thickness of said sheet material.

12. A flameproof sheet material according to claim 9 wherein the total area of the areas of low to zero concentration of flameproofing agent does not exceed the total area of the small areas of high concentration of flameproofing agent by a factor of more than about 5.

13. A flameproof sheet material according to claim 9 wherein the distance between the edges of adjacent small areas of high concentration of flameproofing agent is not more than about five times the mean diameter of said areas of high concentration.

14. A flameproof sheet material according to claim 9 wherein the distance between the edges of adjacent small areas of high concentration of flameproofing agent is not more than about three times the mean diameter of said areas of high concentration.

15. A flameproof sheet material according to claim 9 wherein said sheet material comprises textile sheet material.

16. A flameproof sheet material according to claim 9 wherein said small areas of high concentration of flameproofing agent comprise a regular pattern of disconnected dots on the surface of said sheet material.