Title:
ABRASION RESISTANT GAS GENERATING COMPOSITIONS FOR USE IN INFLATING SAFETY CRASH BAGS
United States Patent 3779823
Abstract:
An abrasion resistant granular gas generating composition comprising a metallic azide, oxidizers for the azide, and a small amount of a novel cured polymeric binder having a relatively high oxygen content and prepared entirely from solid binder ingredients having a melting point in the range of 45° C to 130° C. The compositions are resistant to abrasion during long storage periods and when ignited produce predominately non-toxic gases.
US Patent References:
POLY - BETA - HYDROXYAMINES PROPELLANT COMPOSITIONS PREPARED WITH LITHIUM PERCHLORATE
Bedell - August 1969 - 3454436
Novel pyrotechnics
Kaufman - February 1964 - 3122462
Compound detonators
Bain et al. - February 1947 - 2415806
Solid propellants containing hydrazonium azide and boron compounds
Rausch - March 1967 - 3309248
Gas generator grain
Boyer - April 1961 - 2981616
POLY - BETA - HYDROXYAMINES PROPELLANT COMPOSITIONS PREPARED WITH LITHIUM PERCHLORATE
Bedell - August 1969 - 3454436
Novel pyrotechnics
Kaufman - February 1964 - 3122462
Compound detonators
Bain et al. - February 1947 - 2415806
Solid propellants containing hydrazonium azide and boron compounds
Rausch - March 1967 - 3309248
Gas generator grain
Boyer - April 1961 - 2981616
Inventors:
Price, Raymond M. (Brigham City, UT)
Reed, Russell (Brigham City, UT)
Reed, Russell (Brigham City, UT)
Application Number:
05/200172
Publication Date:
12/18/1973
Filing Date:
11/18/1971
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
423/351, 149/35, 280/741, 149/20
International Classes:
C06B35/00; C06B45/10; C06D5/06; C06B45/00; C06D5/00; C06D5/06
Field of Search:
149/19,20,35 208/15AB
Primary Examiner:
Padgett, Benjamin R.
Claims:
We claim
1. An abrasion resistant granular gas generating composition for inflating safety crash bags consisting essentially of from about 25 percent to about 90 percent by weight of metallic azide, from about 15 percent to about 75 percent by weight of at least one oxidizer for the azide selected from the group consisting of metallic sulfides, metallic oxides, and sulfur, and from 1 percent to 10 percent by weight of a cured polyether based polyurethane binder having a high oxygen content.
2. The composition as in claim 1 wherein the metallic azides are alkali metal azides selected from the group consisting of sodium azide, lithium azide, and potassium azide.
3. The composition as in claim 1 wherein the azide is sodium azide.
4. The composition as in claim 1 wherein the metallic sulfides are selected from the group consisting of molybdenum disulfide, antimony trisulfide, bismuth sulfide, ferrous sulfide, stannous sulfide, and tungsten disulfide.
5. The composition as in claim 4 wherein the metallic sulfide is molybdenum disulfide.
6. The composition as in claim 1 wherein the oxidizers for the azide are a mixture of molybdenum disulfide and sulfur.
7. The composition as in claim 1 wherein the cured binder is the reaction product of a solid organic diisocyanate, a solid polyethylene glycol having a molecular weight of 2,000 to 6,000, and a solid multifunctional hydroxyl curing agent.
8. The composition as in claim 7 wherein the components of the binder are solids with melting points in the range of 45° C to 130° C.
9. The composition as in claim 7 wherein the solid organic diisocyanate is bitolylene diisocyanate.
10. The composition as in claim 7 wherein the solid polyethylene glycol is polyethylene glycol of the molecular weight of 4,000.
11. The composition as in claim 7 wherein the solid polyethylene glycol is a multifunctional hydroxyl-terminated copolymer of propylene oxide and ethylene oxide containing at least 70 percent ethylene oxide with a melting point in the range of 45° C to 130° C.
12. The composition as in claim 7 wherein the solid multifunctional hydroxyl curing agent is trimethylol propane.
13. An abrasion resistant granular gas generating composition for inflating safety crash bags consisting essentially of from 50 to 70 percent by weight of metallic azide, 25 percent to 50 percent by weight of at least one oxidizer for the azide selected from the group consisting of metallic sulfides, metallic oxides, and sulfur, and 3 percent to 5 percent by weight of cured polyether based polyurethane binder having a high oxygen content.
14. The composition as in claim 13 wherein the metallic azides are alkali metal azides selected from the group consisting of sodium azide, lithium azide, and potassium azide.
15. The composition as in claim 13 wherein the azide is sodium azide.
16. The composition as in claim 13 wherein the metallic sulfides are selected from the group consisting of molybdenum disulfide, antimony trisulfide, bismuth sulfide, ferrous sulfide, stannous sulfide, and tungsten disulfide.
17. The composition as in claim 16 wherein the metallic sulfide is molybdenum disulfide.
18. The composition as in claim 13 wherein the oxidizers for the azide are a mixture of molybdenum disulfide and sulfer.
19. The composition as in claim 13 wherein the cured binder is the reaction product of a solid organic diisocyanate, a solid polyethylene glycol having a molecular weight of 2,000 to 6,000, and a solid multifunctional hydroxyl curing agent.
20. The composition as in claim 19 wherein the components of the binder are solids with melting points in the range of 45° C to 130° C.
21. The composition as in claim 19 wherein the solid organic diisocyanante is bitolylene diisocyanate.
22. The composition as in claim 19 wherein the solid polyethylene glycol is polyethylene glycol of the molecular weight of 4,000.
23. The composition as in claim 19 wherein the solid polyethylene glycol is a multifunctional hydroxyl-terminated copolymer of propylene oxide and ethylene oxide containing at least 70 percent ethylene oxide with a melting point in the range of 45° C to 130° C.
24. The composition as in claim 19 wherein the solid multifunctional hydroxyl curing agent is trimethylol propane.
25. The composition as in claim 1 wherein the metallic oxide is selected from the group consisting of molybdenum trioxide, tungsten trioxide, and vanadium pentoxide.
26. A method of making an abrasion resistant granular gas generating composition utilizing all solid ingredients, said composition consisting essentially of a metallic azide; at least one oxidizer for the azide selected from the group consisting of metallic sulfides, metallic oxides, and sulfur; and a cured polymeric binder based upon curable polymer forming solid binder components having melting points in the range of 45° C to 130° C. said method comprising the steps of:
27. The method as in claim 26 wherein the pellets in step (f) are heated for 20 minutes at 220° F.
28. The method as in claim 26 wherein the metallic azide, the oxidizer for the azide, and the curable polymer forming binder components are blended together and ground in a single step prior to the fluid energy milling step of step (d).
29. The method of claim 26 wherein the azide is sodium azide.
30. The method of claim 26 wherein the oxidizers are molybdenum disulfide and sulfur.
31. The method of claim 26 wherein the curable polymer-forming solid ingredients consist of a solid polyethylene glycol, a solid organic diisocyanante, and a solid curing agent, all components having melting points in the range of 45° C to 130° C.
32. The method as in claim 26 wherein the curable polymer-forming solid ingredients consist of polyethylene glycol of the molecular weight of 4,000, bitolylene diisocyanante, trimethylolpropane, and ferric acetylacetonate.
33. The method as in claim 26 wherein the abrasion resistant granular gas generating composition is prepared consisting of an intimate mixture of 50 percent to 70 percent by weight of sodium azide, 25 percent to 50 percent by weight of molybdenum disulfide, 0.5 percent to 5.0 percent by weight of sulfur, and 1 percent to 10 percent by weight of curable polymeric binder.
1. An abrasion resistant granular gas generating composition for inflating safety crash bags consisting essentially of from about 25 percent to about 90 percent by weight of metallic azide, from about 15 percent to about 75 percent by weight of at least one oxidizer for the azide selected from the group consisting of metallic sulfides, metallic oxides, and sulfur, and from 1 percent to 10 percent by weight of a cured polyether based polyurethane binder having a high oxygen content.
2. The composition as in claim 1 wherein the metallic azides are alkali metal azides selected from the group consisting of sodium azide, lithium azide, and potassium azide.
3. The composition as in claim 1 wherein the azide is sodium azide.
4. The composition as in claim 1 wherein the metallic sulfides are selected from the group consisting of molybdenum disulfide, antimony trisulfide, bismuth sulfide, ferrous sulfide, stannous sulfide, and tungsten disulfide.
5. The composition as in claim 4 wherein the metallic sulfide is molybdenum disulfide.
6. The composition as in claim 1 wherein the oxidizers for the azide are a mixture of molybdenum disulfide and sulfur.
7. The composition as in claim 1 wherein the cured binder is the reaction product of a solid organic diisocyanate, a solid polyethylene glycol having a molecular weight of 2,000 to 6,000, and a solid multifunctional hydroxyl curing agent.
8. The composition as in claim 7 wherein the components of the binder are solids with melting points in the range of 45° C to 130° C.
9. The composition as in claim 7 wherein the solid organic diisocyanate is bitolylene diisocyanate.
10. The composition as in claim 7 wherein the solid polyethylene glycol is polyethylene glycol of the molecular weight of 4,000.
11. The composition as in claim 7 wherein the solid polyethylene glycol is a multifunctional hydroxyl-terminated copolymer of propylene oxide and ethylene oxide containing at least 70 percent ethylene oxide with a melting point in the range of 45° C to 130° C.
12. The composition as in claim 7 wherein the solid multifunctional hydroxyl curing agent is trimethylol propane.
13. An abrasion resistant granular gas generating composition for inflating safety crash bags consisting essentially of from 50 to 70 percent by weight of metallic azide, 25 percent to 50 percent by weight of at least one oxidizer for the azide selected from the group consisting of metallic sulfides, metallic oxides, and sulfur, and 3 percent to 5 percent by weight of cured polyether based polyurethane binder having a high oxygen content.
14. The composition as in claim 13 wherein the metallic azides are alkali metal azides selected from the group consisting of sodium azide, lithium azide, and potassium azide.
15. The composition as in claim 13 wherein the azide is sodium azide.
16. The composition as in claim 13 wherein the metallic sulfides are selected from the group consisting of molybdenum disulfide, antimony trisulfide, bismuth sulfide, ferrous sulfide, stannous sulfide, and tungsten disulfide.
17. The composition as in claim 16 wherein the metallic sulfide is molybdenum disulfide.
18. The composition as in claim 13 wherein the oxidizers for the azide are a mixture of molybdenum disulfide and sulfer.
19. The composition as in claim 13 wherein the cured binder is the reaction product of a solid organic diisocyanate, a solid polyethylene glycol having a molecular weight of 2,000 to 6,000, and a solid multifunctional hydroxyl curing agent.
20. The composition as in claim 19 wherein the components of the binder are solids with melting points in the range of 45° C to 130° C.
21. The composition as in claim 19 wherein the solid organic diisocyanante is bitolylene diisocyanate.
22. The composition as in claim 19 wherein the solid polyethylene glycol is polyethylene glycol of the molecular weight of 4,000.
23. The composition as in claim 19 wherein the solid polyethylene glycol is a multifunctional hydroxyl-terminated copolymer of propylene oxide and ethylene oxide containing at least 70 percent ethylene oxide with a melting point in the range of 45° C to 130° C.
24. The composition as in claim 19 wherein the solid multifunctional hydroxyl curing agent is trimethylol propane.
25. The composition as in claim 1 wherein the metallic oxide is selected from the group consisting of molybdenum trioxide, tungsten trioxide, and vanadium pentoxide.
26. A method of making an abrasion resistant granular gas generating composition utilizing all solid ingredients, said composition consisting essentially of a metallic azide; at least one oxidizer for the azide selected from the group consisting of metallic sulfides, metallic oxides, and sulfur; and a cured polymeric binder based upon curable polymer forming solid binder components having melting points in the range of 45° C to 130° C. said method comprising the steps of:
27. The method as in claim 26 wherein the pellets in step (f) are heated for 20 minutes at 220° F.
28. The method as in claim 26 wherein the metallic azide, the oxidizer for the azide, and the curable polymer forming binder components are blended together and ground in a single step prior to the fluid energy milling step of step (d).
29. The method of claim 26 wherein the azide is sodium azide.
30. The method of claim 26 wherein the oxidizers are molybdenum disulfide and sulfur.
31. The method of claim 26 wherein the curable polymer-forming solid ingredients consist of a solid polyethylene glycol, a solid organic diisocyanante, and a solid curing agent, all components having melting points in the range of 45° C to 130° C.
32. The method as in claim 26 wherein the curable polymer-forming solid ingredients consist of polyethylene glycol of the molecular weight of 4,000, bitolylene diisocyanante, trimethylolpropane, and ferric acetylacetonate.
33. The method as in claim 26 wherein the abrasion resistant granular gas generating composition is prepared consisting of an intimate mixture of 50 percent to 70 percent by weight of sodium azide, 25 percent to 50 percent by weight of molybdenum disulfide, 0.5 percent to 5.0 percent by weight of sulfur, and 1 percent to 10 percent by weight of curable polymeric binder.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to abrasion resistant gas generating compositions and a method for their manufacture. More particularly, this invention relates to abrasion resistant gas generating compositions in granular form for inflating passenger vehicle crash bags. While the present compositions are particularly useful in the inflation of passenger protective crash bags in passenger vehicles, it can readily be seen that the compositions may be used in the inflation of other inflatable devices as for example, inflatable boats, rafts, escape ladders etc.
2. Description of the Prior Art
The concept of utilizing an inflatable bag or envelope to protect passengers traveling in vehicles such as automobiles, boats, and aircraft during a collision or crash is generally known in the art. Such crash bags which are known in the art and which may be utilized in the practice of this invention are disclosed in U.S. Pat. Nos. 2,834,609, 3,117,424, 3,336,045, 3,450,414, and 3,573,885.
In the older devices, it was proposed that cylinders containing compressed gas be used to inflate the crash bag. However, the use of compressed gas for this purpose revealed several very serious disadvantages. For example, it was found that the compressed gas devices were bulky and difficult to package compactly in places such as the steering column or dashboard of an automobile. Moreover, the compressed gas devices presented hazard in shipping, handling, and storage. The compressed gas inflation devices were also subject to the additional hazard of increased pressure in the container as a result of high ambient temperatures. Finally, the compressed gas devices generally exhibited response times which are regarded as relatively slow.
Recently, it has been proposed to inflate these crash bags by utilizing gases generated from chemical gas generating compositions. However, such gas generating compositions must meet a number of requirements which have been difficult to entirely satisfy.
Thus, the gas generating composition must generate gases at a relatively high rate in order to inflate the bag within about 0.040 seconds. The temperature of the gas produced by the gas generating composition must be relatively low in order to avoid burning the passenger in the event of bag rupture. The gases produced by the gas generating composition must also be non-toxic in order to prevent injury to the passenger by inhalation during bag rupture. The gas generating composition must also be relatively insensitive to temperature change. Finally, gas generating compositions which are utilized in solid form such as for example, pellets must be able to resist the abrasion caused by lengthy storage periods under conditions of vibration to which they are exposed in passenger vehicles. In general, the previously proposed gas generating compositions have failed to meet one or more of these requirements. More particularly, previously proposed chemical gas generating compositions were difficult in that their response rates were too slow or the temperature of the gas produced was too high.
A major improvement over the prior art gas generating compositions referred to above is disclosed in copending application Ser. No. 158,108 filed June 29, 1971, incorporated herein by reference. The invention described therein disclosed pelleted nitrogen gas generating compositions with rapid response times capable of generating substantial volumes of relatively low temperature, non-toxic gases. However, it has since been found that the pelleted nitrogen gas generating compositions of the type described therein are subject to abrasion as a result of the long storage periods under conditions of vibration to which they are exposed in the passenger vehicle. It has been further found that as the pellets are abraded significant amounts of fine materials are produced. These fine materials produce an erratic and increased burning rate.
This undesired increase in burn rate is objectionable since it leads to increased pressure in the crash bag and the possibility of bag rupture.
SUMMARY OF THE INVENTION
It has been discovered quite unexpectedly that incorporating a small amount of a novel curable solid polymeric binder composition having a high oxygen content and prepared entirely from solid binder ingredients having melting points in the range of 45° C to 130° C into a mixture of gas generator solids and then curing said binder produces a gas generating composition which is abrasion resistant during lengthy storage periods and yet upon ignition burns uniformly and releases gases which are predominately nontoxic.
The use of binders is well known in the propellant art. However, the binders of propellant compositions are used for an entirely different purpose than the binder composition of the present invention. Propellant composition binders in general are used to hold large quantities of oxidizers and normally constitute the fuel component of the composition. Thus, the propellant binder may be regarded as a fuel binder.
The curable solid polymeric binder composition of the present invention is not used as a fuel binder but rather as an adhesive and coating medium to hold the gas generator solid components tightly together and to provide an impact and abrasion resistant barrier. An indication of this difference in purpose is the small amount of solid binder composition used in the gas generator composition of this invention. Thus, the gas generator composition will contain not more than 10% and preferably less than 6% of binder composition.
The novel features of the gas generator compositions of the present invention will become apparent from the objectives of the invention and detailed description which follows.
It is the object of this invention to provide an abrasion resistant gas generating composition. More particularly it is the object of this invention to provide an abrasion resistant gas generating composition in granular form for use as a gas generator in the inflation of passenger protective crash bags. A further object of the invention is to provide a granular abrasion resistant gas generating composition which is low in toxic products. A further object of the invention is to provide a method for manufacturing the granular abrasion resistant gas generating composition. Additional objects will appear from the specification and claims which follow.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The objectives and advantages of the present invention are accomplished by the preparation of a granular composition comprising a metallic azide, oxidizers for the azide, and from about 1 percent to 10 percent by weight of the total composition of a cured solid polymeric binder composition having a high oxygen content and prepared entirely from solid binder ingredients having a melting point in the range of 45° C to 130° C. It has been found that such a composition when formulated as described hereinafter produces a gas generating composition which is resistant to abrasion under conditions of vibration and upon ignition releases gases which are predominately non-toxic.
The improved abrasion resistance is substantially due to inclusion in the composition of the cured polymeric binder which serves a dual function. Thus, the binder composition acts as an internal adhesive holding the gas generating granules tightly together and also produces a solid coating around said granules which acts as a barrier imparting resistance to impact and abrasion.
The polymeric binder composition of the present invention exhibits several novel and unique characteristics. Thus, for example, the solid physical nature of the binder ingredients permit the solid gas generating ingredients to be pressed together into a homogeneous solid mass before curing. Further, the mixed solid ingredients have an almost infinite pot life below the melting point of the binder components. In addition, the binder composition cures rapidly when the temperature is raised above the melting points of the binder ingredients. Moreover, the use of the novel binder composition permits utilization of Wiley mill (i.e., a blade mill) for grinding purposes without producing excessive amounts of extreme fines which has been a problem with previously proposed pelleted gas generating compositions. Finally, the polymeric binder of the present invention is based on a polymer containing a substantial amount of oxygen. The binder will preferably contain a substantial quantity of oxygen because during ignition the binder is oxidized by the gas generator oxidizers. Thus, a binder containing a substantial amount of oxygen will contain less carbon and hydrogen percentages and thereby the amount of flammable and toxic gases produced will be less. Moreover, since the polymeric binder contains a substantial amount of oxygen, its combustion should produce only a relatively minor amount of additional heat. As defined in the context of this specification, the terms "high oxygen content" or "substantial amount of oxygen" refer to a binder composition in which the polymer component of the binder contains at least 26 percent oxygen.
Solid polymeric binders which are useful in the composition of the present invention include polyurethane and polyether polymers. The polyurethane polymers may be made in known manner by reaction of diisocyanates with polyethers and subsequent curing of the isocyanate-terminated polymers with polyols. However, the solid physical nature and processability of the granular gas generating composition which is the subject of this invention makes the selection of the binder ingredients critical. Thus, all binder ingredients must be solids with melting points in the range of 45° C to 130° C.
In accordance with the above requirement, the isocyanates selected for use in the binder composition will be solids with melting points in the range of 45° C to 130° C such as, for example, bitolylene diisocyanate, dianisidine diisocyanate, methylene bis p,p' diphenyl diisocyanate, and 1,5 napthalene diisocyanate. The preferred solid isocyanates useful in the practice of this invention are bitolylene diisocyanate commerically available as Isonate 136 T and dianisidine diisocyanate commerically available as Isonate 148 D. Since the main criticality of the diisocyanate selected for use in the binder is that it be a solid with a melting point in the above specified range and that it be capable of reacting with a polyether to form an isocyanate terminated polymer, it is expected that virtually any diisocyanate meeting these requirements can be used. Thus, it is expected that commerically available solid isocyanates such as polyethylene glycol capped with lysine methyl ester diisocyanate (LDIM), trishydroxyethyl isocyanurate capped with LDIM, or trimethylol propane capped with LDIM can be used.
The solid isocyanates referred to above may be reacted with hydroxyl-terminated polyethers such as the polyethylene glycols. In this regard, multifunctional hydroxyl copolymers of propylene oxide and ethylene oxide containing at least 70 percent ethylene oxide are particularly useful. Again, the only criticality is that said polyethylene glycols are solids with melting points in the range of 45° C to 130° C. Thus, the preferred polyethylene glycols will be solid polyethylene glycols having a molecular weight of about 2,000 to 6,000. The most preferred polyethylene glycol is polyethylene glycol of the molecular weight of 4,000 commerically available under the name Carbowax 4,000.
The isocyanate terminated polymers which result from the reaction of the solid isocyanates and hydroxyl terminated polyethers mentioned above may then be cured and cross linked by solid polyfunctional polyols with melting points in the range of 45° C to 130° C such as for example, trimethylol propane, trimethylol ethane, or 1, 2, 3 hexanetriol. It should be expected that virtually any multifunctional hydroxyl curing agent capable of cross-linking the isocyanate-terminated polymer referred to above can be used so long as it is a solid with a melting point in the range of 45° C to 130° C. The most preferred curing agent useful in the practice of this invention is trimethylol propane.
A preferred solid polymeric binder composition used in the gas generating composition of the present invention has been obtained by reacting bitolylene diisocyanate with polyethylene glycol of the molcular weight of 4,000 and curing the resulting isocyanateterminated polymer with trimethylol propane in the presence of ferric acetylacetonate catalyst.
While the polymeric binder of the present invention is based on the polyether polymers it is expected that a polyester based binder can be used in much the same manner. Thus, one would fully expect that a polyester binder can be prepared by utilizing solid forms of dibasic acids, diols, and polyepoxide curing agents to form a cured polyester binder so long as the binder ingredients are solids with melting points in the range of 45° C to 130° C.
As indicated previously, the granular gas generating composition of the present invention contains metallic azides and oxidizers for the azides in addition to the polymeric binder.
Metallic azides which are useful in the present invention are the alkali metal azides and the alkaline earth metal azides as disclosed in copending applications Ser. No. 158,108 filed June 29, 1971 and incorporated herein by reference. The preferred metallic azides are sodium azide, lithium azide, potassium azide, and aluminum azide. The most preferred azide is sodium azide.
As indicated previously, the gas generating composition of this invention contains oxidizers or a mixture of oxidizers for reaction with the metallic azide. Oxidizers which are useful in the practice of the present invention are the metallic sulfides, metallic oxides, and sulfur. The preferred metallic sulfides are molybdenum disulfide, antimony trisulfide, bismuth sulfide, ferrous sulfide, stannous sulfide and tungsten disulfide. The most preferred metallic sulfide is molybdenum disulfide.
The preferred metallic oxides are molybdenum trioxide, tungsten trioxide, and vanadium pentoxide.
The amounts of the three principal ingredients of the present compositions may vary over a relatively wider range. However, the amount of curable solid polymeric binder utilized in the present composition should be kept at a relatively low value i.e., from 1 percent to 10 percent preferably 3 percent to 5 percent by weight of the total composition. The amount of metallic azide used in the composition of the present invention may vary from about 25 percent to 90 percent by weight of the total composition but will preferably be used in the range of 50 percent to 70 percent by weight of the composition.
The oxidizers or mixture of oxidizers used to react with the azides may also vary widely in amount i.e., from about 15 percent to 75 percent by weight of the composition but will preferably be used in the range of 25 percent to 50 percent by weight of the composition.
In addition to the metallic azide, oxidizer and binder components of the composition, small amounts of special purpose ingredients such as curing catalyst, burning rate modifiers, etc., may be used.
While various procedures may be used in formulating the abrasion resistant gas generating compositions of the present invention, excellent results were obtained by the following procedure in which all of the ingredients used were solids.
The uncured polymer-forming binder composition was prepared by first grinding each solid component of the binder composition separately to a powdered form. The ground components were then combined by blending them homogenously in a dry powder blender. The blended powders were then further ground to obtain an intimate mixture of solid binder components. The gas generator solid components i.e., metallic azide and oxidizer were then combined utilizing the same process to produce an intimate mixture of gas generator solids. The two solid mixtures i.e., the binder solids composition and the gas generator solids composition were then blended together in the dry powder blender. The average particle diameter in the resulting blend was about 12 microns. The resulting blend of gas generator components and binder components was then passed through a fluid energy mill at a temperature below 77° F. in order to produce a blend of granules with an average particle diameter of 1 to 3 microns. The blended product from the fluid energy mill was then pelletized in a standard pressure type pelletizer at 25,000 psi and 25° C. to produce pellets of the gas generator composition. The resulting pellets were then heated on aluminum plates for 20 minutes at 220° F in order to react the binder composition to form polyurethane in situ and to cure the polyurethane, thereby binding the gas generator composition ingredients into an abrasion resistant form. The cured pellets were then fed through a blade mill e.g. a Wiley mill containing a No. 6 U.S. standard mesh screen at 185 rmp to produce granules of gas generator composition. This procedure permits one to prepare granular gas generator compositions of widely varying particle size e.g. from about 3 microns to 3,000 microns.
It will be evident from the process as described above that the procedure may be varied in several ways. Thus, for example, it is possible to mix all solid components of the composition together in the first step and then grind, blend, and pelletize, etc. The process described above produces a granular abrasion resistant gas generating compositions capable of being stored for long periods of time.
Ignition of the present compositions in order to inflate the crash bag may be accomplished by conventional means known in the art. Thus, a hot particle type ignition such as a boron and potassium ignition system or a sodium azide/sulfur ignition system can be used.
The present invention is further illustrated by the following examples in which the parts are by weight based on the total weight of the composition unless otherwise indicated.
In order to determine the effect of the binder on the abrasion resistance of the gas generating composition separate mixtures of granular polymer-forming binder ingredients and granular gas generator ingredients (i.e., metallic azide and oxidizers) of the composition shown below were prepared by the method described previously herein. A portion of the granular gas generator mixture was then passed through the fluid energy mill and pelletized for use as a control composition. The granular polymerforming binder mixture was then blended with the granular gas generator mixture in such proportions to produce a composite blend consisting of 96 percent gas generator ingredients and 4 percent binder ingredients. The resulting composite blend was then passed through the fluid energy mill and pelletized. The pellets were heated for 20 minutes at 220° F to react and cure the binder composition thereby forming the cured polyurethane binder. The pelleted control composition and pelleted composition containing cured binder were then tested for abrasion resistance and upon ignition the gases produced were analyzed for toxic products in the manner and with the results shown below.
The binder composition consisted of the following solid ingredients.
Parts by Weight Components of Binder Polyethylene glycol m.w. 4,000 47.47 Bitolylene diisocyanate (Isonate 136T) 41.18 Trimethylolpropane 11.35 Ferric acetylacetonate 0.20
As indicated previously, the above binder composition was prepared in granular form by grinding each ingredient separately and then combined in a dry powder blender.
The gas generator composition consisted of the following solid ingredients:
Components Parts by Weight Sodium azide 64.00 Molybdenum disulfide 35.00 Sulfur 1.00
The above gas generator composition was prepared in granular form in the same manner as the binder composition. The above gas generator composition was pelleted and used as the control composition. A composite blend consisting of 4 percent of the binder composition and 96 percent of the gas generator composition show above was pelletized and cured for use as the test composition.
In order to measure the comparative abrasion resistance of the control composition and the composition containing 4 percent cured binder, pellets of each composition were passed through a Wiley mill at 185 rpm with a blade clearance of 0.06 in. and screened.
The results as to comparative particle size distribution of the product which served as a comparison of the relative amount of abrasion resistance of the respective compositions were as follows:
U. S. Standard Screen Mesh Control Composition Size (no binder) with 4% binder No. 6 Percent through screen 100.00 100.00 No. 20 Percent through screen 14.50 4.85 No. 45 Percent through screen 5.80 1.30
Thus, it is evident that the gas generating composition granules containing 4% cured binder were more resistant to impact and abrasion as is shown by the relative amount of fines produced. While 100% of both compositions passed through a No. 6 mesh screen only 4.85 percent of the composition containing 4 percent cured binder passed through a No. 20 mesh screen while 14.5 percent of the control containing no binder passed through the same screen.
An analysis of the gaseous products of the control composition and the 4 percent binder composition was made by firing each composition into an evacuated metal chamber with the following results:
Mole Percentages Composition Product Control no Binder with 4% Binder H 2 Trace Trace O 2 1.7 1.6 N 2 96.6 90.4 CO 0.1 0.5 CO 2 Nil Nil CH 4 Nil Nil NH 3 Trace Trace NO 2 Nil Nil N 2 O Nil Nil
From the above description and examples, it should be apparent that the present invention provides a gas generating composition capable of achieving the objects set forth in the specification.
The gas generating composition of the present invention is abrasion resistant and yet upon ignition produces predominately non-toxic gases.
1. Field of the Invention
This invention relates to abrasion resistant gas generating compositions and a method for their manufacture. More particularly, this invention relates to abrasion resistant gas generating compositions in granular form for inflating passenger vehicle crash bags. While the present compositions are particularly useful in the inflation of passenger protective crash bags in passenger vehicles, it can readily be seen that the compositions may be used in the inflation of other inflatable devices as for example, inflatable boats, rafts, escape ladders etc.
2. Description of the Prior Art
The concept of utilizing an inflatable bag or envelope to protect passengers traveling in vehicles such as automobiles, boats, and aircraft during a collision or crash is generally known in the art. Such crash bags which are known in the art and which may be utilized in the practice of this invention are disclosed in U.S. Pat. Nos. 2,834,609, 3,117,424, 3,336,045, 3,450,414, and 3,573,885.
In the older devices, it was proposed that cylinders containing compressed gas be used to inflate the crash bag. However, the use of compressed gas for this purpose revealed several very serious disadvantages. For example, it was found that the compressed gas devices were bulky and difficult to package compactly in places such as the steering column or dashboard of an automobile. Moreover, the compressed gas devices presented hazard in shipping, handling, and storage. The compressed gas inflation devices were also subject to the additional hazard of increased pressure in the container as a result of high ambient temperatures. Finally, the compressed gas devices generally exhibited response times which are regarded as relatively slow.
Recently, it has been proposed to inflate these crash bags by utilizing gases generated from chemical gas generating compositions. However, such gas generating compositions must meet a number of requirements which have been difficult to entirely satisfy.
Thus, the gas generating composition must generate gases at a relatively high rate in order to inflate the bag within about 0.040 seconds. The temperature of the gas produced by the gas generating composition must be relatively low in order to avoid burning the passenger in the event of bag rupture. The gases produced by the gas generating composition must also be non-toxic in order to prevent injury to the passenger by inhalation during bag rupture. The gas generating composition must also be relatively insensitive to temperature change. Finally, gas generating compositions which are utilized in solid form such as for example, pellets must be able to resist the abrasion caused by lengthy storage periods under conditions of vibration to which they are exposed in passenger vehicles. In general, the previously proposed gas generating compositions have failed to meet one or more of these requirements. More particularly, previously proposed chemical gas generating compositions were difficult in that their response rates were too slow or the temperature of the gas produced was too high.
A major improvement over the prior art gas generating compositions referred to above is disclosed in copending application Ser. No. 158,108 filed June 29, 1971, incorporated herein by reference. The invention described therein disclosed pelleted nitrogen gas generating compositions with rapid response times capable of generating substantial volumes of relatively low temperature, non-toxic gases. However, it has since been found that the pelleted nitrogen gas generating compositions of the type described therein are subject to abrasion as a result of the long storage periods under conditions of vibration to which they are exposed in the passenger vehicle. It has been further found that as the pellets are abraded significant amounts of fine materials are produced. These fine materials produce an erratic and increased burning rate.
This undesired increase in burn rate is objectionable since it leads to increased pressure in the crash bag and the possibility of bag rupture.
SUMMARY OF THE INVENTION
It has been discovered quite unexpectedly that incorporating a small amount of a novel curable solid polymeric binder composition having a high oxygen content and prepared entirely from solid binder ingredients having melting points in the range of 45° C to 130° C into a mixture of gas generator solids and then curing said binder produces a gas generating composition which is abrasion resistant during lengthy storage periods and yet upon ignition burns uniformly and releases gases which are predominately nontoxic.
The use of binders is well known in the propellant art. However, the binders of propellant compositions are used for an entirely different purpose than the binder composition of the present invention. Propellant composition binders in general are used to hold large quantities of oxidizers and normally constitute the fuel component of the composition. Thus, the propellant binder may be regarded as a fuel binder.
The curable solid polymeric binder composition of the present invention is not used as a fuel binder but rather as an adhesive and coating medium to hold the gas generator solid components tightly together and to provide an impact and abrasion resistant barrier. An indication of this difference in purpose is the small amount of solid binder composition used in the gas generator composition of this invention. Thus, the gas generator composition will contain not more than 10% and preferably less than 6% of binder composition.
The novel features of the gas generator compositions of the present invention will become apparent from the objectives of the invention and detailed description which follows.
It is the object of this invention to provide an abrasion resistant gas generating composition. More particularly it is the object of this invention to provide an abrasion resistant gas generating composition in granular form for use as a gas generator in the inflation of passenger protective crash bags. A further object of the invention is to provide a granular abrasion resistant gas generating composition which is low in toxic products. A further object of the invention is to provide a method for manufacturing the granular abrasion resistant gas generating composition. Additional objects will appear from the specification and claims which follow.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The objectives and advantages of the present invention are accomplished by the preparation of a granular composition comprising a metallic azide, oxidizers for the azide, and from about 1 percent to 10 percent by weight of the total composition of a cured solid polymeric binder composition having a high oxygen content and prepared entirely from solid binder ingredients having a melting point in the range of 45° C to 130° C. It has been found that such a composition when formulated as described hereinafter produces a gas generating composition which is resistant to abrasion under conditions of vibration and upon ignition releases gases which are predominately non-toxic.
The improved abrasion resistance is substantially due to inclusion in the composition of the cured polymeric binder which serves a dual function. Thus, the binder composition acts as an internal adhesive holding the gas generating granules tightly together and also produces a solid coating around said granules which acts as a barrier imparting resistance to impact and abrasion.
The polymeric binder composition of the present invention exhibits several novel and unique characteristics. Thus, for example, the solid physical nature of the binder ingredients permit the solid gas generating ingredients to be pressed together into a homogeneous solid mass before curing. Further, the mixed solid ingredients have an almost infinite pot life below the melting point of the binder components. In addition, the binder composition cures rapidly when the temperature is raised above the melting points of the binder ingredients. Moreover, the use of the novel binder composition permits utilization of Wiley mill (i.e., a blade mill) for grinding purposes without producing excessive amounts of extreme fines which has been a problem with previously proposed pelleted gas generating compositions. Finally, the polymeric binder of the present invention is based on a polymer containing a substantial amount of oxygen. The binder will preferably contain a substantial quantity of oxygen because during ignition the binder is oxidized by the gas generator oxidizers. Thus, a binder containing a substantial amount of oxygen will contain less carbon and hydrogen percentages and thereby the amount of flammable and toxic gases produced will be less. Moreover, since the polymeric binder contains a substantial amount of oxygen, its combustion should produce only a relatively minor amount of additional heat. As defined in the context of this specification, the terms "high oxygen content" or "substantial amount of oxygen" refer to a binder composition in which the polymer component of the binder contains at least 26 percent oxygen.
Solid polymeric binders which are useful in the composition of the present invention include polyurethane and polyether polymers. The polyurethane polymers may be made in known manner by reaction of diisocyanates with polyethers and subsequent curing of the isocyanate-terminated polymers with polyols. However, the solid physical nature and processability of the granular gas generating composition which is the subject of this invention makes the selection of the binder ingredients critical. Thus, all binder ingredients must be solids with melting points in the range of 45° C to 130° C.
In accordance with the above requirement, the isocyanates selected for use in the binder composition will be solids with melting points in the range of 45° C to 130° C such as, for example, bitolylene diisocyanate, dianisidine diisocyanate, methylene bis p,p' diphenyl diisocyanate, and 1,5 napthalene diisocyanate. The preferred solid isocyanates useful in the practice of this invention are bitolylene diisocyanate commerically available as Isonate 136 T and dianisidine diisocyanate commerically available as Isonate 148 D. Since the main criticality of the diisocyanate selected for use in the binder is that it be a solid with a melting point in the above specified range and that it be capable of reacting with a polyether to form an isocyanate terminated polymer, it is expected that virtually any diisocyanate meeting these requirements can be used. Thus, it is expected that commerically available solid isocyanates such as polyethylene glycol capped with lysine methyl ester diisocyanate (LDIM), trishydroxyethyl isocyanurate capped with LDIM, or trimethylol propane capped with LDIM can be used.
The solid isocyanates referred to above may be reacted with hydroxyl-terminated polyethers such as the polyethylene glycols. In this regard, multifunctional hydroxyl copolymers of propylene oxide and ethylene oxide containing at least 70 percent ethylene oxide are particularly useful. Again, the only criticality is that said polyethylene glycols are solids with melting points in the range of 45° C to 130° C. Thus, the preferred polyethylene glycols will be solid polyethylene glycols having a molecular weight of about 2,000 to 6,000. The most preferred polyethylene glycol is polyethylene glycol of the molecular weight of 4,000 commerically available under the name Carbowax 4,000.
The isocyanate terminated polymers which result from the reaction of the solid isocyanates and hydroxyl terminated polyethers mentioned above may then be cured and cross linked by solid polyfunctional polyols with melting points in the range of 45° C to 130° C such as for example, trimethylol propane, trimethylol ethane, or 1, 2, 3 hexanetriol. It should be expected that virtually any multifunctional hydroxyl curing agent capable of cross-linking the isocyanate-terminated polymer referred to above can be used so long as it is a solid with a melting point in the range of 45° C to 130° C. The most preferred curing agent useful in the practice of this invention is trimethylol propane.
A preferred solid polymeric binder composition used in the gas generating composition of the present invention has been obtained by reacting bitolylene diisocyanate with polyethylene glycol of the molcular weight of 4,000 and curing the resulting isocyanateterminated polymer with trimethylol propane in the presence of ferric acetylacetonate catalyst.
While the polymeric binder of the present invention is based on the polyether polymers it is expected that a polyester based binder can be used in much the same manner. Thus, one would fully expect that a polyester binder can be prepared by utilizing solid forms of dibasic acids, diols, and polyepoxide curing agents to form a cured polyester binder so long as the binder ingredients are solids with melting points in the range of 45° C to 130° C.
As indicated previously, the granular gas generating composition of the present invention contains metallic azides and oxidizers for the azides in addition to the polymeric binder.
Metallic azides which are useful in the present invention are the alkali metal azides and the alkaline earth metal azides as disclosed in copending applications Ser. No. 158,108 filed June 29, 1971 and incorporated herein by reference. The preferred metallic azides are sodium azide, lithium azide, potassium azide, and aluminum azide. The most preferred azide is sodium azide.
As indicated previously, the gas generating composition of this invention contains oxidizers or a mixture of oxidizers for reaction with the metallic azide. Oxidizers which are useful in the practice of the present invention are the metallic sulfides, metallic oxides, and sulfur. The preferred metallic sulfides are molybdenum disulfide, antimony trisulfide, bismuth sulfide, ferrous sulfide, stannous sulfide and tungsten disulfide. The most preferred metallic sulfide is molybdenum disulfide.
The preferred metallic oxides are molybdenum trioxide, tungsten trioxide, and vanadium pentoxide.
The amounts of the three principal ingredients of the present compositions may vary over a relatively wider range. However, the amount of curable solid polymeric binder utilized in the present composition should be kept at a relatively low value i.e., from 1 percent to 10 percent preferably 3 percent to 5 percent by weight of the total composition. The amount of metallic azide used in the composition of the present invention may vary from about 25 percent to 90 percent by weight of the total composition but will preferably be used in the range of 50 percent to 70 percent by weight of the composition.
The oxidizers or mixture of oxidizers used to react with the azides may also vary widely in amount i.e., from about 15 percent to 75 percent by weight of the composition but will preferably be used in the range of 25 percent to 50 percent by weight of the composition.
In addition to the metallic azide, oxidizer and binder components of the composition, small amounts of special purpose ingredients such as curing catalyst, burning rate modifiers, etc., may be used.
While various procedures may be used in formulating the abrasion resistant gas generating compositions of the present invention, excellent results were obtained by the following procedure in which all of the ingredients used were solids.
The uncured polymer-forming binder composition was prepared by first grinding each solid component of the binder composition separately to a powdered form. The ground components were then combined by blending them homogenously in a dry powder blender. The blended powders were then further ground to obtain an intimate mixture of solid binder components. The gas generator solid components i.e., metallic azide and oxidizer were then combined utilizing the same process to produce an intimate mixture of gas generator solids. The two solid mixtures i.e., the binder solids composition and the gas generator solids composition were then blended together in the dry powder blender. The average particle diameter in the resulting blend was about 12 microns. The resulting blend of gas generator components and binder components was then passed through a fluid energy mill at a temperature below 77° F. in order to produce a blend of granules with an average particle diameter of 1 to 3 microns. The blended product from the fluid energy mill was then pelletized in a standard pressure type pelletizer at 25,000 psi and 25° C. to produce pellets of the gas generator composition. The resulting pellets were then heated on aluminum plates for 20 minutes at 220° F in order to react the binder composition to form polyurethane in situ and to cure the polyurethane, thereby binding the gas generator composition ingredients into an abrasion resistant form. The cured pellets were then fed through a blade mill e.g. a Wiley mill containing a No. 6 U.S. standard mesh screen at 185 rmp to produce granules of gas generator composition. This procedure permits one to prepare granular gas generator compositions of widely varying particle size e.g. from about 3 microns to 3,000 microns.
It will be evident from the process as described above that the procedure may be varied in several ways. Thus, for example, it is possible to mix all solid components of the composition together in the first step and then grind, blend, and pelletize, etc. The process described above produces a granular abrasion resistant gas generating compositions capable of being stored for long periods of time.
Ignition of the present compositions in order to inflate the crash bag may be accomplished by conventional means known in the art. Thus, a hot particle type ignition such as a boron and potassium ignition system or a sodium azide/sulfur ignition system can be used.
The present invention is further illustrated by the following examples in which the parts are by weight based on the total weight of the composition unless otherwise indicated.
In order to determine the effect of the binder on the abrasion resistance of the gas generating composition separate mixtures of granular polymer-forming binder ingredients and granular gas generator ingredients (i.e., metallic azide and oxidizers) of the composition shown below were prepared by the method described previously herein. A portion of the granular gas generator mixture was then passed through the fluid energy mill and pelletized for use as a control composition. The granular polymerforming binder mixture was then blended with the granular gas generator mixture in such proportions to produce a composite blend consisting of 96 percent gas generator ingredients and 4 percent binder ingredients. The resulting composite blend was then passed through the fluid energy mill and pelletized. The pellets were heated for 20 minutes at 220° F to react and cure the binder composition thereby forming the cured polyurethane binder. The pelleted control composition and pelleted composition containing cured binder were then tested for abrasion resistance and upon ignition the gases produced were analyzed for toxic products in the manner and with the results shown below.
The binder composition consisted of the following solid ingredients.
Parts by Weight Components of Binder Polyethylene glycol m.w. 4,000 47.47 Bitolylene diisocyanate (Isonate 136T) 41.18 Trimethylolpropane 11.35 Ferric acetylacetonate 0.20
As indicated previously, the above binder composition was prepared in granular form by grinding each ingredient separately and then combined in a dry powder blender.
The gas generator composition consisted of the following solid ingredients:
Components Parts by Weight Sodium azide 64.00 Molybdenum disulfide 35.00 Sulfur 1.00
The above gas generator composition was prepared in granular form in the same manner as the binder composition. The above gas generator composition was pelleted and used as the control composition. A composite blend consisting of 4 percent of the binder composition and 96 percent of the gas generator composition show above was pelletized and cured for use as the test composition.
In order to measure the comparative abrasion resistance of the control composition and the composition containing 4 percent cured binder, pellets of each composition were passed through a Wiley mill at 185 rpm with a blade clearance of 0.06 in. and screened.
The results as to comparative particle size distribution of the product which served as a comparison of the relative amount of abrasion resistance of the respective compositions were as follows:
U. S. Standard Screen Mesh Control Composition Size (no binder) with 4% binder No. 6 Percent through screen 100.00 100.00 No. 20 Percent through screen 14.50 4.85 No. 45 Percent through screen 5.80 1.30
Thus, it is evident that the gas generating composition granules containing 4% cured binder were more resistant to impact and abrasion as is shown by the relative amount of fines produced. While 100% of both compositions passed through a No. 6 mesh screen only 4.85 percent of the composition containing 4 percent cured binder passed through a No. 20 mesh screen while 14.5 percent of the control containing no binder passed through the same screen.
An analysis of the gaseous products of the control composition and the 4 percent binder composition was made by firing each composition into an evacuated metal chamber with the following results:
Mole Percentages Composition Product Control no Binder with 4% Binder H 2 Trace Trace O 2 1.7 1.6 N 2 96.6 90.4 CO 0.1 0.5 CO 2 Nil Nil CH 4 Nil Nil NH 3 Trace Trace NO 2 Nil Nil N 2 O Nil Nil
From the above description and examples, it should be apparent that the present invention provides a gas generating composition capable of achieving the objects set forth in the specification.
The gas generating composition of the present invention is abrasion resistant and yet upon ignition produces predominately non-toxic gases.