Articles such as ``Molders forced into gas-assist legal fray'' [Page 1, Aug. 5] are newsworthy and deserve a more-detailed investigation as to the underlying issue and history involved in the litigation. Your article states [the lawsuits center on] ``... a Melea patent covering `timely injection,' which is defined as injecting the gas `in a timely fashion to prevent the plastic from stopping its movement in the mold cavity.''' This is too vague and will leave the reader confused. The U.S. patent number should be listed.
It is No. 5,110,533 filed Nov. 7, 1990. This patent has one independent claim, which describes a process for solving the problem of ``surface degradation due to hesitation marks.'' According to the invention, this is accomplished by:
Injecting a first amount of molten resin that is in a percentage range of 20-70 percent of the total volume of material to be used.
Injecting a charge of pressurized gas.
ontinue to inject a second amount of molten plastic resin into the cavity simultaneously with the step of injecting gas. Conversely the second plastics amount would be in the range of 80-30 percent.
ontinue to inject gas after the second amount of molten plastic resin.
elieve the gas pressure.
emove the part.
This first and second amounts of material for processing gas- assist hollow parts was not a new method for the inventor, Jim Hendry. In fact, it is described eight years earlier within claim one of U.S. patent No. 4,474,717, filed May 24, 1982 [also Hendry]. It states ``injecting a small amount of plastic material ... into the mold cavity ... thereafter injecting ... gas under pressure through the probe after the initial injection of the small amount of the plastic material into the cavity ... and thereafter injecting more inert gas ... while injecting additional plastic material into the cavity.''
It appears the only difference between the two references is that patent 533 states a first and second amounts of material divided by the injection of gas, while patent 717 states a small or initial amount followed by an additional amount again divided by the injection of gas.
However, no amount of patent attorney wordsmithing can overcome the physical realities that in gas-assist injection molding substantially all of the resin required to form a gas-assist part must be in the cavity prior to injecting the gas pressure, due to the tremendous viscosity difference between molten resin and gas.
A more realistic description of how the process works and how to solve the problem of hesitation lines can be found in the description of U.S. patent No. 5,047,183 [Battenfeld] filed Oct. 7, 1988.
This filing date is two years earlier than patent No. 5,110,533 and patent 183 is not cited as prior art in the prosecution of patent 533. Column 4, lines 15-22 state ``the final phase of the injection of the plastics material and the initial phase of the introduction of the flowable medium (gas) temporarily overlap. In this manner, it is ensured that, thus, the plastic material is transported in a problem-free and uniform manner to the surface of the mold cavity in the injection mold.''
(Note: This description is not a claim.)
I find it both sad and amusing that the issue of ``injecting the gas in a timely fashion'' can be litigated at all. It was originally developed by Jim Hendry at Kmmco Structure Foam in the early 1980s and written about in Plastics Technology in the June 1983 issue.
Let the record show that timing the introduction of gas into the injection molding flow front was well-known to Mr. Hendry, as well as the molding community at large long before patent 533 was filed on Nov. 7, 1990.
The article as written does not reflect the facts and history at issue. Also, it plays right into the hands of those who continue to bully molders with bull instead of focusing on truly innovative improvements to help the molder successfully process gas-assist injection molded parts.
Erikson is president of Epcon Gas Systems Inc. of Troy, Mich.