Filter and method

A method of making a filter for a respirator, the method comprising:

• providing a layer of flexible plastic netting material having a plurality of openings allowing free passage of air through the plurality of openings of the flexible plastic netting material;
• providing a layer of polymeric filter media for filtering impurities in air passing through the filter;
• positioning the layer of flexible plastic netting material and the layer of polymeric filter media to lie one on top of another to form a multilayer of flexible plastic netting material and polymeric filter media;
• moving the multilayer of flexible plastic netting material and polymeric filter media to a pleater;
• pleating the multilayer of flexible plastic netting material and polymeric filter media to form a pleated composite layer of flexible plastic netting material and polymeric filter media having an overall structure of continuous and adjacent pleated folds;
• moving a length of the pleated composite layer to a forming, assembly and sealing unit;
• at the forming, assembly and sealing unit, combining the length of the pleated composite layer with a preformed filter mounting element, the preformed filter mounting element molded from a plastic material, the preformed filter mounting element comprising:
• a rim flange;
• a filter mounting connector;
• and
• a plenum devoid of the pleated composite layer, the plenum defining a free volume between the filter mounting connector and the pleated composite layer allowing passage of unrestricted inhaled air through the filter mounting connector after the inhaled air has passed through the polymeric filter media of the filter;
• the forming, assembly and sealing unit having a thermoforming tool including a mold configuration conforming generally to contours of the preformed filter mounting element, the mold configuration having an upper and lower elements;
• and by the upper and lower elements:
• melting and pressing together an edge region including plastic material of the pleated composite layer and a plastic material of the rim flange of the preformed filter mounting element,
• thereby to join and bond together, by the melting of the plastic material of the pleated composite layer and the plastic material of the rim flange, the edge region,
• thereby forming an air impermeable seal extending around a periphery of the filter.