Table 111. Comparison of Polyethylene Shipping Containers with Several Frequently Used Returnable Shipping Containers Container Glass carboy in wood box (ICC-1A) Polyethylene carboy in plywood drum (ICC-1F) Polyethylene drum in ICC-GJ steel drum
Stainless steel drum (ICC-5C)
Actual Capacity, Gal. 13
Price $12
T a r e Weight, Lb. 68
13.7 14 3 28 52.7
16 14 20 24
26 22 40
15.3 56
24 75
24 105
64
The 13-gallon polyethylene carboy and the 14-gallon polyethylene drum are slightly higher in price than the 13-gallon glass carboy, but are substantially lower in tare weight. I n many instances the freight savings alone, due to the lower tare weight of the polyethylene container, are sufficient to justify the higher cost. The polyethylene containers, of equivalent capacity, are appreciably less expensive in first cost than stainless steel drums, and thereby permit a substantially lower investment in returnable containers. Polyethylene shipping containers should be included in container evaluations because of their possible economic advantage. In addition, there are commodities for which no other satisfactory container is available. For aqueous hydrofluoric acid up to 60% concentration glais carboys are completely unsatisfactory, as are stainless steel drums. Polyethylene shipping containers are not without limitation. Although polyethylene has excellent chemical resistance, it cannot be used for all commodities. The effect of the specific commodity on the polyethylene actually used in the specific con-
tainer under consideration should be determined carefully. The shipper alone is responsible for seeing that the container material is resistant to the commodity. What may be expected in the future? Development work is well along on fiber drum overpacks for the polyethylene carboy and the polyethylene drum, and fiber drum overpacks probably will be eventually included in the ICC regulations. One manufacturer has approached the Bureau of Explosives with a container consisting of a polyethylene carboy encased in a n open framework of steel rod. The M C S Miscellaneous Packages Committee is currently engaged in test work t o demonstrate the adequacy of this container for the shipment of dangerous commodities. 9 preliminary study recently conducted by the MCA Miscellaneous Packages Committee, to determine the relative puncture resistance of polyethylene compared to that of several other container materials, has yielded some interesting information. A continuation of this work along Tvith development work on the part of plastic container manufacturers may lead to a polyethylene container which can be shipped safely without an overpack. OTHER PLASTICS
Most of the plastic industrial container work to date has been done with polyethylene. Work now under way indicates that modifications of polyethylene with other materials may improve its performance with certain commodities. What of the many other plastics? Will they, too, find application in industrial containers? The future, of course, holds the answer to these questions, but plastic containers will play a n increasingly important part in the future, in the safe and economical transportation of the many products of the chemical industry. RECEIVED for review October 15, 1954.
. ~ C C E P T E D March
25, 1955.
Aerosols in the Smaller Bulk Container Field Although aerosol products appeared on the market only 9 years ago, 1953 production was valued a t $160,000,000, and more than 60 types of products are reaching the consumer. Aerosols are pressurized, self-spraying units that deliver an active ingredient in a spray, a foam, or a dry powder. Behind them all is the convenience of the push-button container, with its liquefied gas that can expand more than 240 times when released from pressure. Research is developing more corrosion-resistant containers, safer containers, and better valves with a wider range of usefulness.
H. W. HAMILTON Chemical Specialties Manufacturers Association. h e . , Xew York 17, S. Y .
LOOK a t aerosol products from the viewpoint of the large scale package producer might be likened to hunting out one particular tree in a huge forest for, volumewise, the aerosol industry’s appetite for containers is small compared with the demand for more common types of containers. I t is an appetite that is increasing, however, and may, not too many years hence, occupy a sizable portion of the packaging platter. ilerosol products are pressurized, self-spraying products that a t the press of a valve button deliver an active ingredient in a fine spray (insecticides and room deodorants), a heavier spray (paints and enamels), a foam (shave creams), and newest among the applications, a dry powder. 1198
Although aerosol products appeared on the consumer market only 9 years ago, with insecticides as the initial application, they have grown steadily in volume from the 1947 production of 5,000,000 units to 140,000,000 units in 1953, with a retail value in the neighborhood of %160,000,000. I n 1954 the industry, spurred on by introduction of ultra-lowpressure glass and plastic containers probably turned out a t least 200,000,000 units of products, at a retail value of about $220,000,000. More than 60 different types of products are now reaching the consumer in self-spraying aerosol containers. I n addition to the product types already mentioned, they include such household
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Handling of Chemicals aids as rug and upholstery cleaners, hand cleaners, dust mop sprays, furniture polish, mothproofers, waterrepellents, lubricants, rust preventives, window cleaners, and artificial Christmas snow. I n the fast-growing personal products and pharmaceutical fields, there are aerosol aids like adhesive tape remover, topical anesthetics, antiperspirants, spray-on plastic bandages, burn preparations, colognes and perfumes, hair net sprays and dressings, hand lotions, shampoos, and sun tan sprays.
the government researchers to a group of nonflammable, nonexplosive, and virtually nontoxic fluorinated hydrocarbon compounds for many years used as refrigerants. Cooled below their boiling points or held under pressure, these fluorinated propellents remain in their liquid state. But, above their boiling point or when released from pressure, they vaporize rapidly. And as they change into a gas a t atmospheric pressure, their volume is increased some 240 times. T h a t rapid expansion, and their ability to exert a constant, uniform pressure so long as one drop of liquid is available for vaporization, are the secret of the areosol principle. The first postwar aerosol containers had heavy steel shells and a turn- or twist-type valve on one end (Figure 1). Their appearance and the fact that they were a wartime development for use against insecticides, dubbed them as “bug bombs.’’ These first “high pressure” aerosols dispensed their active ingredient a t a pressure of about 70 pounds per square inch gageatroomtemperature, as opposed to about half t h a t pressure used in the more common insecticide aerosols today. They were larger, too, than the currently popular 12-ounce container and many of them were refillable. Perhaps more important, from the consumer standpoint, they were costly-three to four times as expensive as today’s low-pressure, throw-away metal container. TWO-PHASE SYSTEM
Figure 1.
c
Early aerosol packages
Industrial applications have not been overlooked. There are antifoam sprays, antistatic solutions, leather belt dressings, design layout inks, dye penetrants and developers, dry graphite lubricants, mold-release compounds for the plastics industry, rust cutters and inhibitors, sanitary lubricants, and textile yarn dressings. Behind all of them is the convenience of the push-button container deriving its dispensing pressure from a liquefied gas that has the ability to expand more than 240 times when it is released from pressure and changes from a liquid to a gas as it leaves the container through the atomizing nozzle. Actually the term “aerosol” is somewhat of a misnomer as used by the pressurized packaging industry. 4 n aerosol is by definition a dispersion of particles so fine t h a t they mill float in the air for a reasonably long time. While the term \Tithin reasonable limits accurately describes aerosol insecticides or room deodorant space sprays, it can hardly be applied properly to the wide variety of residual insecticides, paints and laequers, or powders which can be dispensed from the pressurized container. But the word “aerosol” has been adopted by the industry and the public in general to describe products packaged in push-putton operated cans.
Figure 2 is a cutaway section of a typical 12-ounce aerosol container as used today. The container itself is essentially a gastight package, made up of the outer shell of black iron, tin plate, drawn aluminum, glass, or plastic, with a valve closure. A standpipe extends from the valve t o the bottom of the container. The darker area inside the can and occupying about two thirds of its volume in this illustration represents the liquid phase, or a solution made up of the active ingredient (assume in this case an insecticide) and the liquefied fluorinated hydrocarbon propellent. The light area in the upper one third of the container is the gas phase, or head space, occupied b y the vaporized propellent. The
DEVELOPMENT OF AEROSOL I S D U S T R Y
I n order t o appreciate fully the problems of the aerosol phase of the smaller bulk container field, a few comments are necessary on the aerosol industry’s history. Although the use of liquefied gases as propellents had been investigated as early as the 1920’9, the firEt practical products as we know them today stemmed from U. S. Department of Agriculture research during World War 11, directed toward improved methods of dispensing insecticides to combat disease among overseas troops. Compressed gases such as carbon dioxide or nitrous oxide were possible choices but their high pressures would make containers unusually heavy and costly. Food products, such a s whipped cream, continue t o use nitrous oxide and carbon dioxide. The search for a propellent that would be capable of blasting liquid insecticide into fine air-borne particles, and still permit a light, easily assembled, and relatively inexpensive dibpenser, led June 1955
A B
- Valve
- Standpipe -Metal Container
~
Figure 2.
Typical two-phase aerosol container
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typical propellent used in such an aerosol product is a 50/50 mixture of trichlorompofluoromethane and dichlorodifluoromethane which, in its gaseous phase, exerts a pressure of approximately 38 pounds per square inch gage a t 70 F. on the top of the liquid solution. A maximum pressure of 40 pounds per square inch gage a t 70' F. is permitted by Interstate Commerce Commission regulations, as promulgated by the Bureau of Explosives of the American Association of Railroads. O
tainer is depressed, the pressure of the gaseous propellent forces only active ingredient up through the standpipe and out through the atomizing nozzle. T h e liquid propellent in the bottom of t h e can simply bubbles up through the active ingredient t o vaporize in the head space of the can and maintain a uniform dispensing pressure. FOAM PRODUCTS
Foam products operate a little differently (Figure 4),although basically they are a three-phase system in that the aqueous soap solution and propellent separate into two distinct layers when the product is not in use and stands a while. Foam products must be shaken well before use in order to disperse the propellent through the soap solution and produce an emulsion. Once the container is shaken sufficiently, there is what appears t o be a two-phase system, and as the valve is depressed and some of the soap-propellent emulsion is ejected the rapidly vaporizing propellent expands the soap solution and whips it into a foam.
(pressure approximately 40 psig at 70°F)
I
1.
Figure 3. Typical threephase glass aerosol container
When the valve button on the container is depressed, the pressure in the head space of the can momentarily drops as some of the liquid solution of insecticide and propellent is forced up the standpipe t o the valve. Immediately, enough liquid propellent vaporizes out of the solution t o bring the pressure in the head space of the container back t o its desired 38 pounds per square inch a t 70" F. This pressure forces the liquid propellent and insecticide out through an atomizing nozzle in the valve. As it leaves the valve orifice, the liquid propellent vaporizes, expanding some 240 times as it changes from a liquid to a gas. This rapid expansion blasts the liquid insecticide apart-into particles SO fine that they float for a long time in the air. THREE-PHASE S Y S T E M
This drawing is an example of the two-phase system, as used in about 80% of the modern aerosol products. A variation is the three-phase system (Figure 3), required in products in which the active ingredient is not miscible with the propellent. The outer container and valve are about like that illustrated, but in a true three-phase system there are two distinct liquid layers in addition t o the gas phase. The bottom layer or darkest portion represents the liquefied propellent. The lighter layer, floating on top on the propellent, represents the active ingredient. I n this three-phase system, the standpipe, instead of extending to the bottom of the container, stops just short of the bottom of the active ingredient layer, so t h a t when the valve on the con-
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A
OPERATES BY PRESSING TO ONE SIDE
(Vapor Phase)
yn]
A -Valve B -Container
-
n Containel
__t
Figure 4. Cross section of typical aerosol package for foam-type product
Whipped cream in pressurized containers is another example of a foam product. T h e fluorinated hydrocarbon propellents, however, have not been applied t o food products. T h e propellent commonly used in such applications is nitrous oxide, or nitrous oxide and carbon dioxide, in either case as a compressed gas rather than as a compressed liquefied gas. ICC regulations have set a top pressure limit of 105 pounds per square inch gage a t 70" F., and 140 pounds per square inch gage a t 13O0F., for such products, using a compressed gas rather than a liquefied gas as the propellent. Cream in pressurized metal containers under refrigeration js subject t o special regulations. Aerosol products can be loaded either in a refrigerated or pressure system. T h e decision as to which loading system to use is based primarily on two factors: the composition of the active ingredient, and the loading speed desired. Formulations containing moisture or other ingredients that might freeze out in
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Handling of Chemicals loading a t temperatures of 40" F., and lower, must naturally be loaded by the pressure method. I n either case, the active ingredient is loaded first into the can through the open top. In the refrigerated operation, the propellent, cooled below its boiling point, is then loaded into the can as a liquid and the valve and standpipe are inserted and crimped in place t o give a gas-tight package. All t h a t remains then is t o run the container through the standard 130" F. water bath test, t o assure that the container is safe and does not leak, and insert the decorative valve cover; and the finished product is ready for sale.
Figure 5.
Metal aerosol containers
I n pressure loading, the valve is crimped in place immediately after the active ingredient has been loaded and air evacuated from the can. Then, the propellent is forced into the can under pressure through the fine orifice of the valve, the container is submitted to the water bath test, decorative valve cover is inserted, and it goes on its way t o the customer. Because the propellent is introduced through a larger opening as a free-flowing liquid, the refrigerated system is a much faster loading operation. PROB LEiM S
concave bottom and dome top, offered by Continental Can Co. Both oi these are crimped and soldered side-seam cans formed from flat plate. The two cans with plastic tops in the center foreground are examples of seamless, drawn cans provided by the Crown Can Division of the Crown Cork and Seal Co. Only crimping in this can is on the concave bottom and the valve assembly. And on the far right are two typical drawn aluminum containers offered by Sun Tube Corp. Various lacquers and resins are used as an internal coating on some tin-plate cans and solve the corrosion problems in many cases. Aluminum generally has no internal coating. These types of metal cans are satisfactory from a corrosion standpoint in the packaging of about 80% of the more than 60 different types of aerosol products. But they have not provided an entirely satisfactory solution t o the packaging of products like shampoos which contain synthetic detergents, perfumes and colognes which contain alcohol, or personal deodorants which contain aluminum salts. Incidentally, hair net sprays, which contain alcohol, have been largely packaged up t o this time in metal, with some corrosion difficulties. This particular corrosion difficulty has been somewhat diminished by the use of absolute alcohol. The problems with hair net sprays, however, have not been serious enough t o bar use of the metal container. I n cases where corrosion is a more serious problem, the glass, or the more recently introduced plastic container, appears t o answer many corrosion problems. But glass brings up the additional problem of safe pressures-a phase of the over-all problem about which there are many differing opinions today. Safety. Until introduction of glass aerosol containers early this year, practically all aerosol products were of the low or high pressure types, using dispensing pressures in the range of 30 t o 70 pounds per square inch gage a t 70" F. Among the metal containers, low and high pressure aerosols are by far the most popular, with two basic types of container in use. One is acceptable for packaging products in which the internal pressure does not exceed 40 pounds per square inch gage at 70' F. The other, termed the 2P can and currently offered by only one manufacturer, is required by Interstate Commerce Commission regulations when the dispensing pressure is between 40 and 60 pounds per square inch gage a t 70" F. The Bureau of Explosives of the Association of American Railroads cooperates in the testing and eatablishing of permitted standards for shipping aerosols.
What are some of the problems, other than mechanical ones, involved in turning out reliable, useful aerosol products: From the packager's standpoint, the problems might be narrowed down to these: Compatibility of the propellent with the active ingredient. Spray characteristics, which involve principally valve design and the proper formulation of propellent and active ingredient. Container corrosion, dependent upon the reaction between the active ingredient and the container over the normal life of the product. Safety of t h e container, from a mechanical construction standpoint. This, of course, must take into consideration the internal pressure in t h e container. The first two-compatibility and spray characteristics-are chemical and physical problems t o be solved in the formulation of the product. Normally, those problems will have been solved before the loader or packager enters the picture. Corrosion. Container corrosion and container safety, however, are of prime concern to packagers. T h e answer to corrosion, of course, rests in the packager's ability to find a container which will resist the potential corrosive action of the active ingredients in the formulation. The bulk of today's aerosol pro4ucts are packed in metal containers, principally uncoated or lacquered tin plate or black iron. The major types of metal containers are shown in Figure 5. T h e can at the extreme left, with concave top and bottom, is that provided by the American Can Co. Immediately forward and t o its right is a can with June 1955
Figure 6.
Dispensing valves
Glass containers like these, on the other hand, use an ultralow-pressure propellent like Freon-114 dichlorotetrafluoroethane, in which the dispensing pressure is in the range of 10 t o 18 pounds per square inch gage at 70" F. The big question in the aerosol industry today revolves around the potential hazards in the pressurized glass bottle. Uncoated glass bottles used in the packaging of pressurized cologne and perfume are considered sufficiently safe by many. Others contend that, particularly in the case of personal toiletry items, the glass bottle requires some extra protective coating t o avoid the danger of shattering in case it is dropped. Plastic coatings have been developed for the glass
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bottle, but they add to the cost of the finished package and that brings up the question of economics in the highly competitive toiletry goods market. How far will the manufacturers be willing to go in absorbing the cost of extra protection, or how much extra will the consumer be willing t o pay? There is a question, too, of safety regulations, for if manufacturers do not provide a n absolutely safe package, state or federal agencies, such as the Federal Trade Commission, may step into the picture and set up standards. Plastic Containers. Plastic containers are a n even newer development. Although they have not yet been tested on the consumer market, many think they provide the answer t o some of the fears of breakage in the glass container. Plastic and glass containers find greatest application in packages of 2 to 6 ounces. Polyethylene materials, such as those used in squeeze-type plastic dispenser packages, would be ideal, but present indications are t h a t they are permeable to fluorinated hydrocarbon propellents and, therefore, would not be satisfactory for retaining these under pressure. Valves. Valves constitute another part of the aerosol industry’s problems, and much work remains t o be done on improving the spray pattern and freedom from clogging. A fine spray requires a fine valve orifice and places a limit on particle
size of the active ingredient. The first commercially produced valves cost more than double the present prices. The presentday valve is a more accurately made product and almost any desired spray pattern may be obtained. Some of the many valves available today for use in aerosol containers are pictured in Figure 6. Research is going ahead in both the container and valve fields t o develop more corrosion-resistant containers, safer containers, and better and more efficient valves with a wider range of usefulness. Problems are being solved every day and members of the aerosol industry are confident that, given time, no problem is insurmountable. ACKNOWLEDGMENT
The assistance of Frank Zumbro, Kinetic Chemicals Division, E. I. du Pont de Kemours & Co., Inc., John D . Conner, CSRfA counsel, and many others in the Aerosol Division of the Chemical Specialties Manufacturers Association, who contributed photographs and material for this presentation, is gratefully acknowledged. RECEIVED for review October 15, 1954.
ACCEPTEDMarch 25, 1955.
precautionary Labeling of
Hazardous Chemicals Active work is continuing, with Government and industry cooperating, to develop and make effective and uniform labeling of hazardous chemicals.
R. D. MINTEER Monsanto Chemical Co., St. Louis, M o .
P
OSSIBLY the least understood part of the business of pro-
ducing, transporting, and handling of chemicals is the part played by precautionary labeling. The need for warning labels was recognized many years ago. Introduction in Congress of the Bingham Act, in 1932, caused a vigorous awakening on the part of the chemical industry. As a result, a permanent committee was organized to work out with the Surgeon General of the United States a series of agreements between the manufacturers of some 8 or 10 chemical products and the Surgeon General’s office, whereby the manufacturers voluntarily agreed to affix a warning label on all shipments of these products from the manufacturer’s plant. The texts of the various labels were worked out by the committee and representatives of the Surgeon General’s office. These agreements, entered into early in 1934, were kept until 1952, when they mere discontinued as a result of the introduction of a large number of new, and in many cases hazardous, products not covered by the agreements, and the existence of the Manufacturing Chemists’ Association labeling principles (on which study was begun in 1944 by MCh’s Labeling and Precautionary Information Committee), which were considered to provide for more appropriate warning labels. The U. S. Public Health Service has recently reactivated the Chemical Products Agreement Committee to work with the Manufacturing Chemists’ Association in a continual evaluation of labeling requirements. The objectives of the labeling committee were largely attained with the development of the warning label program and the pub-
1202
lishing of the first manual. The manual has been through three revisions, the latest published in 1953. Industry voluntarily adopted the program to a remarkable degree, and it was felt t h a t this would forestall state and federal ordinances requiring warning labels. However, this has not been the case. STATE REGULATIONS
The California Division of Industrial Safety determined t o publish a regulation setting forth labels which must be placed on every container of hazardous chemicals to be used in t h a t state. A great deal of correspondence was carried on between t h e Manufacturing Chemists’ Association and the state of California in a n endeavor to have this California regulation correspond t o LAPI principles. An agreement was reached, and LAPI labels were accepted by California. Oregon soon followed suit, but, instead of publishing a list of required labels, simply stated t h a t labels as set forth in the M C S manual mould be acceptable. I n 1948 the Federal Insecticide, Fungicide, and Rodenticide Act was passed, which required, among other things, t h a t labels for economic poisons should contain warning statements to protect the users of these substances. The LAPI Committee worked closely with the U. S. Department of Agriculture, with the result that regulations published under the above law required warning labels which correspond closely with LAPI principles. After the Federal Insecticide, Fungicide, and Rodenticide Act was passed, msny states revised old laws or passed new ones which closely followed the federal pattern, with the result
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