The concentric bottle design and pressure bottom of Novapak's 4-liter ultra-clean bottle prevent distortion under pressure and maintain stability for safe shipping of ammonium hydroxide, an ultra-pure chemical with high vapor pressures.

To prevent contamination, 4-liter pressure-bottom bottles are capped prior to shipment to Puritan, and the caps are removed immediately prior to filling.

Ammonium hydroxide solution boils at ambient temperatures around 85°F (29°C), at which point vapor pressure inside the bottle approaches 45 psi (310 kPa), necessitating a robust container able to withstand high pressures swelling. Maintaining proper fill levels and monitoring quality are critical.

Highly filtered nitrogen is used both to blow mold and to leak test the containers (shown).

ALLENTOWN, PA — In semiconductor manufacturing, contaminants in minute amounts can have devastating effects on microcircuits, and on the bottom line. Chemicals are used to remove traces of organics, metals, oxide residues, and other contaminants, but are themselves a potential source of contamination. Therefore, maintaining high purity throughout the filling and packaging of these chemicals is critical. The process must begin with a container that is free of contaminants. "Using an ultra-clean container ensures the purity of our formulations and demonstrates to our customers that we are on the cutting edge when it comes to maintaining the quality of our product," explains Lou DiRenzo, president of Puritan Products, a leading supplier of chemicals for the semiconductor and laboratory industries.

A 4-liter (1-gallon) ultra-clean pressure bottom container from Novapak Corp., Eatontown, NJ, has proven suitable for one such chemical solution-ammonium hydroxide-used in the semiconductor industry to clean and etch integrated circuits. "The 4-liter pressure-bottom container we're using for our ammonium hydroxide product is molded of virgin HDPE in a controlled manufacturing environment," says DiRenzo. "The fact that this container is ultra clean is a key feature that we market to our customers, and the other characteristics of the bottle make it well suited for a chemical like ammonium hydroxide."

HDPE has little branching, giving it stronger intermolecular forces and tensile strength than lower density polyethylene. It is also harder and can withstand somewhat higher temperatures.

"The main challenge of packaging a chemical like ammonium hydroxide is withstanding its high vapor pressure," DiRenzo explains. Ammonium hydroxide solution boils at ambient temperatures around 85°F (29°C), at which point vapor pressure inside the bottle approaches 45 psi (310 kPa). "The container must be robust enough to withstand such pressure and guard against swelling," he adds. "At 210 gm [0.5 lb], the container is robust, and employs a concentric design that eliminates weak points where the bottle might begin to protrude under high pressures. It also has a pressure bottom, which provides stability."

"A pressure vessel such as this cannot have a hollow molded-in handle," explains Alan Wood, VP of Marketing for Novapak's Airopak Division. "The inside of the container must form a bullet or cylinder shape, narrowing at the top, in order to maintain the internal pressure being exerted on the container walls and guard against distortion. Therefore, the design of this container includes an integrated compression-molded handle, which is designed to eliminate the need for a separate snap-on T-type handle," adds Wood.

Combined, these factors work to maintain chemical purity, preserve the aesthetics of the bottle, drive down costs, and ensure safety in transportation and storage.
 

Barefoot HDPE, filtered nitrogen, caps prevent contamination

The HDPE used in the production of the 4-liter ultra-clean container is "barefoot," or free of additive packages and regrind. Unlike conventional blow molded containers, the ultra-clean container uses nitrogen instead of compressed plant air as the blowing gas. The nitrogen used is highly filtered to preclude exposing contaminants to the inside of the container. "By eliminating the air compressor, the possibility of oil blow off or other contaminants entering the inside of the bottle is also eliminated," says Wood.

During the extrusion process, HDPE is extruded through a die as a molten tube or "parison," which is then captured inside a cooled metal mold and inflated by blowing nitrogen through hollow metal "blow pins." Once the formed bottle has cooled sufficiently, it is ejected from the mold.

Cleanliness is maintained throughout the manufacturing process. Even the conveying line transporting parts is blanketed with filtered nitrogen which, being heavier than air, is pumped above the conveyor.

From the extrusion blow molding machine the bottles are conveyed to a leak detection station where they are pressurized with filtered nitrogen and checked for pinholes or defects that would allow for leakage. Immediately thereafter the bottles are capped and packed in cartons to prevent contamination. Caps are removed immediately prior to filling at Puritan Products.

The bottles are produced in Manchester, PA, at the Novapak plant nearest to Puritan's Bethlehem, PA facility. "Having this bottle produced locally is advantageous for us, " explains DiRenzo. "With larger bottles such as these, where each truckload contains only about 6000 bottles, proximity to our supplier helps minimize freight costs."