L/D Ratio - A term used to define an extrusion screw which denotes the ratio of the screw length to the screw diameter.

Laminar Flow - Laminar flow of thermoplastic resins in a mold is accompanied by solidification of the layer in contact with the mold surface that acts as an insulating tube through which material flows to fill the remainder of the cavity. This type of flow is essential to duplication of the mold surface.

Laminate - A product made by bonding together two or more layers of material or materials.

Land - (1) The horizontal bearing surface of a semipositive or flash mold by which excess material escapes. See Cut-off. (2) The bearing surface along the top of the flights of a screw in a screw extruder. (3) The surface of an extrusion die parallel to the direction of melt flow.

Lattice Pattern - In reinforced plastics, a pattern of filament winding with a fixed arrangement of open voids.

Leach - To extract a soluble component from a mixture by the process of percolation.

Light-resistance - The ability of a plastics material to resist fading after exposure to sunlight or ultra-violet light. Nearly all plastics tend to darken under these conditions.

Limiting Oxygen Index - The concentration of oxygen required to maintain burning. See ASTM Procedure D2863-74.

Linear Molecule - A long chain molecule as contrasted to one having many side chains or branches.

Loss Factor - The product of the power factor and the dielectric constant.

Low Pressure Laminates - In general, laminates molded and cured in the range of pressures from 400 psi. down to and including pressures obtained by the mere contact of the plies.

Luminescent Pigments - Special pigments available to produce striking effects in the dark. Basically there are two types: one is activated by ultra-violet radiation, producing very strong luminescence and, consequently, very eye-catching effects; the other type, known as phosphorescent pigments, does not require any separate source of radiation.

Luminous Transmittance - The ratio of the luminous flux transmitted by a body of the flux incident upon it.