Two material frame having dissimilar properties for thermal ink-jet cartridge

A printer ink cartridge including an ink reservoir, comprising:

• a frame structure comprising an external frame structural member fabricated from a first rigid plastic material and an interior frame member fabricated from a second plastic material;
• means for attaching together said external frame member and said interior frame member;
• first and second impervious membranes formed of a third plastic material, said membranes joined to said interior frame member to form, with said frame structure, said ink reservoir;
• wherein said second plastic material is compatible with said third plastic material to permit a leak-proof joinder of said membranes to said interior frame member;
• wherein a first opening is formed in said external frame structure, said second plastic material of said interior frame structure disposed through said first opening and defining a passageway extending through said interior frame structure and between edges of said first and second impervious membranes, said passageway in direct communication with said ink reservoir and providing a fill port for filling said ink reservoir with ink, said passageway characterized by a circular cross-section of a passageway diameter;
• and
• means for sealing said passageway, comprising a spherical member having a diameter larger than said passageway diameter, said spherical member being press fitted into said passageway to seal said passageway.