Process and apparatus for producing blow molded thermoplastic articles having improved weld strength

Claim 2

A process for blow molding an article which comprises the steps of: (1) extruding a thermoplastic material to form a parison closed at one end, (2) introducing an inert gas into the open end of the parison, (3) closing a blow mold around the parison to seal off the open end thereof, and (4) injecting a blowing gas containing an oxidizing agent into the closed parison until the parison conforms to the contour of said mold.

Claim 3

The process of Claim 1 wherein said inert gas of step (2) is a commercially available nitrogen containing at least 99.9% by volume nitrogen.

Claim 4

The process of Claim 1 wherein said oxidizing agent of step (4) is oxygen or fluorine.

Claim 5

The process of Claim 1 wherein said blowing gas of step (4) comprises a mixture of about 0.1% to 10% by volume fluorine and the balance being an inert gas.

Claim 6

The process of Claim 4 wherein step (5) is included and comprises evacuating the blowing gas from the resulting blow molded article after step (4) without contaminating the surrounding atmosphere.

Claim 7

The process of Claim 5 wherein step (6) is included and comprises scrubbing the fluorine from the balance of the evacuated blowing gas from step (5) and recovering the resulting fluorine-free inert gas.

Claim 8

The process of Claim 6 wherein said fluorine-free inert gas from step (6) is recycled for use in step (2) and/or in step (4).

Claim 9

The process of Claim 6 wherein said fluorine-free inert gas from step (6) contains at least 99.9% by volume nitrogen.

Claim 10

A process for blow molding a container which comprises the steps of extruding a thermoplastic material to form a parison closed at one end thereof, introducing an inert gas into said parison as it is extruded to maintain said parison open and free from other gases, closing a mold around said parison so that it is closed at both ends, expanding said parison with a blowing gas containing an oxidizing agent to conform the parison to the interior surface of the mold and to thereby form the container, cooling the container, removing the container having improved weld strength from the mold and repeating the method.

Claim 11

A process for blow molding a container which comprises the steps of extruding a thermoplastic material to form a parison closed at one end thereof, introducing an inert gas into said parison as it is extruded to maintain said parison open and free from other gases, closing a mold around said parison so that it is closed at both ends, expanding said parison with a blowing gas containing an oxidizing agent to conform the parison to the interior surface of the mold and to thereby form the container, cooling the container, removing the container having improved weld strength from the mold and repeating the method.

Claim 12

In an apparatus for blow molding an article comprising in combination an extrusion means for continuously forming an expandable parison of a thermoplastic material which parison is closed at one end, a plurality of blowing molds having internal surfaces corresponding to the contour of the article to be produced and into which each expandable parison is sequentially introduced and the other end of the parison is sealed from the surrounding atmosphere and blow pin means for injection into the interior of the parison enclosed within said blowing mold, the improvement for preventing failure of the weld seam at each end of the parison, which comprises first means for introducing an inert gas into the parison as it is being formed and second means in fluid communication with said blow pin means for supplying said pin with a gaseous blowing gas containing an oxidizing agent to conform the parison to said internal surface of said mold,

Claim 13

In an apparatus for blow molding an article comprising in combination an extrusion means for continuously forming an expandable parison of a thermoplastic material which parison is closed at one end, a plurality of blowing molds having internal surfaces corresponding to the contour of the article to be produced and into which each expandable parison is sequentially introduced and the other end of the parison is sealed from the surrounding atmosphere and blow pin means for injection into the interior of the parison enclosed within said blowing mold, the improvement for preventing failure of the weld seam at each end of the parison, which comprises first means for introducing an inert gas into the parison as it is being formed and second means in fluid communication with said blow pin means for supplying said pin with a gaseous blowing gas containing an oxidizing agent to conform the parison to said internal surface of said mold,

Claim 14

The apparatus of Claim 10 wherein said oxidizing agent is oxygen or fluorine.

Claim 15

The apparatus of Claim 11 wherein blending means is in fluid communication with said second means for blending fluorine or a fluorine-containing gas with an inert gas to serve as the blowing gas.

Claim 16

The apparatus of Claim 12 wherein said blowing gas comprises a mixture of about 0.1 to 10% by volume fluorine and the balance being an inert gas.

Claim 17

The apparatus of Claim 12 wherein evacuating means are provided for evacuating the blowing gas from the resulting blow molded article.

Claim 18

The apparatus of Claim 14 wherein said blow pin means and said evacuating means are combined into a dual device for alternating between injecting and evacuating functions.

Claim 19

The apparatus of Claim 15 wherein absorption means are provided for absorbing the fluorine from the evacuated blowing gas.