Methods of and apparatus for coating lightguide fiber

An apparatus for coating an elongated material to provide a substantially bubble-free covering, said apparatus including:

• container means for holding a coating material;
• first die means communicating with said container means and including an exit orifice at one end thereof;
• second die means for sizing coating material about the elongated material, said second die means communicating at one end thereof with said exit orifice at said first die means and having an exit orifice at an opposite end thereof which is aligned with said exit orifice of said first die means;
• a chamber which is interposed between said first and second die means, the coating material being disposed in a continuum which extends from a free surface in said container means, through said first die means and said chamber, and into said second die means;
• moving means for advancing the elongated material through said apparatus at a velocity which is sufficiently high to cause air to become entrained in the coating material, and to cause a pressure gradient to be established between portions of said first die means;
• and
• means for flowing coating material into said chamber at a pressure which sufficiently enhances the pressure gradient between said portions of said first die means and which establishes sufficient volumetric flow from said chamber into said first die means to remove any bubbles adjacent to the elongated material and to cause the coated elongated material to be substantially bubble-free.

An apparatus for applying a liquid coating material to a drawn lightguide fiber which is being advanced to provide a substantially concentrically disposed bubble-free covering, said apparatus including:

• first die means for holding the coating material, said means including a reservoir and a die, said die including a cylindrical passageway, which has a diameter substantially greater than that of the fiber and which has an entrance that communicates with said reservoir and an exit, said die also including an exit orifice, a land, and a tapered portion which connects said exit of said cylindrical passageway with said land;
• second die means which includes a housing having a first portion, and a second portion depending from said first portion, said depending second portion having a chamber which communicates with a tapered lower portion and a die through which the fiber exits, said first die means being supported in said second die means with a portion of said die of said first die means extending through said first portion of said housing and into said chamber, the coating material extending in a continuum from a free surface of said reservoir through said die of said first die means, and into said second die means;
• and
• means for flowing pressurized coating material into said chamber at a pressure which sufficiently enhances a pressure gradient that is established between said exit orifice of said die of said first die means and said exit of said cylindrical passagway during the advance of the fiber through said apparatus and which establishes sufficient net volumetric flow upwardly to cause bubbles to be removed from the lightguide fiber and to cause the coating material in said chamber and on the coated fiber to be substantially bubble-free.