Glossary

Plastics Glossary - D

Daylight opening The maximum distance that can be obtained between the stationary platen and the moving platen in a mold clamping system when the actuating mechanism is fully retracted without a mold or spacers installed.

Daylight The distance between opened mold halves or platens.

Dead Oils Tardistillates that are heavier than water.

Deblooming Bleaching of oils to reduce fluorescence.

Decompression See suck back.

Deep-draw mold A mold having a core which is long in relation to the wall thickness.

Deflection temperature under load (DTUL) The temperature at which a D648 test bar deflects 0.010" in. under a load of 66 or 264 psi. ASTM D648. Test specimens can be 1/2, 1/4, or 1/8 inch thick, compression or injection molded (all of which changes DTUL temperature).

Deflocculate Converse of clumping or clustering of particles.

Defoamer Substance of low intrinsic surface tension that reduces or destroys frothing.

Degassing In injection molding, the momentary opening and closing of a mold during the early stages of the cycle to permit the escape of air or gas from the heated compound.

Degradation Deleterious change in the chemical structure of a plastic reflected in the appearance or physical properties many times caused by excessive time at an elevated temperature or the presence of a substance which causes polymerization. A harmful change in the chemical nature of the plastic.

Degree of polymerization Number of structural units or mers in the average polymer molecule in a sample measure of molecular weight. Generally, the degree of polymerization is in the thousands.

Delamination The surface of the finished part separates or appears to be composed of layers of solidified resins. Strata or fish scale-type appearance where the layers may be separated.

Denaturing Making a product unfit for human consumption, as by the addition of chemicals influencing the taste or toxicity.

Densimeter Instrument for measuring the density or specific gravity of liquids.

Density (Absolute) Mass per unit volume of a substance.

Desiccant bed dehumidifying dryer A type of dryer capable of producing a dew point of –20ºF to –40ºF that is necessary to dry some plastics. Like other types of dryers, it heats the air to the specified drying temperature; however, the air is circulated in a closed-loop system.

Desiccant A component of the desiccant system in the desiccant bed dehumidifying dryer. Molecular pieces of drying agent that absorb enough moisture from the circulating air to achieve a dew point of –20ºF to –40ºF. Air going through the desiccant must be below 130ºF for the desiccant to work. Half-life is 3000 hours.

Design Review A review of a buluprint, of an application, to be molded in a plastic material. Recommendations given for design, material, processing, tooling.

Detergent Surface-active material or combination of surfactants designed for removal of unwanted contamination from the surface of an article.

Dew point The temperature at which moisture in the air begins to condense.

Dialysis Separation of colloids from dissolved substances by selective diffusion through a semipermeable membrane.

Diaphragm gate Used in symmetrical cavity filling to reduce weld-line formation and improve filling rates.

Die swell ratio Ratio of the thickness of the extrudate to the die opening.

Dielectric 1) Any insulating medium that intervenes between two conductors. 2) A material having the property that energy required to establish an electric field is recoverable in whole or in part, as electric energy.

Dielectric constant (Permittivity or specific inductive capacity). That property of a dielectric which determines the electrostatic energy stored per unit volume for unit potential gradient. Note: permittivity is the preferred term.

Dielectric heating The plastic to be heated forms the dielectric of a condenser to which is applied a high frequency (20-80 mc) voltage. Dielectric loss in the material is the basis.

Dieletric Strength A measure of the voltage required to puncture a material, expressed in volts per mil of thickness (ASTM D-149)

Diffusion Mixing of molecules or atoms by random molecular or atomic motion.

Dilatant Increasing instantaneously the apparent viscosity of a fluid with increasing rate of shear.

Diluent Diluting agent

Dilution Act of reducing the proportion of a substance in a solution by addition of more solvent.

Dilution Ratio Volume of solute divided by volume of solvent.

Dimensional stability The ability of a plastic part to retain the precise shape in which it was molded.

Dimer A substance formed from two identical molecules of a monomer.

Dipole Molecule that has an electrical moment (charge separated by a distance).

Direct gate The sprue feeds directly into the mold cavity.

Disc gate Mold gate used in an ID of a molded part generally having the same cross section as the mold runner.

Discoloration A general change in the original color of the plastic material.

Dispersed Phase Dissolved or suspended phase in a colloidal solution or suspension.

Dispersing Agent Surfactant that is used to separate, or keep separated, aggregations of particles by reducing the cohesive attraction between the particles.

Dispersing Medium Continuous phase of a dispersion.

Dispersion aids Devices usually placed in the nozzle of an injection molding machine to aid in the mixing or dispersing of colorant. These devices are not recommended due to the high pressure losses associated with their operation.

Dispersion Finely divided particles of a resin held in suspension in another material.

Dissipation factor (Loss tangent, tan j, approx. power factor). The tangent of the loss angle of the insulating material.

Dissociation Breaking up of molecule or associated species into smaller entities.

Dissolving Formation of a solution by dispersion of one material (solute) at a molecular (or less) level in another material (solvent ).

Distortion A curve or distortion in the part. Also called bowing.

Distribution Ratio Ratio of concentrations of a dissolved substance in two immiscible solvents.

DMA Dynamic mechanical analysis.

Doming Preserving and enhancing the appearance of nameplates, labels or decals by applying a clear "dome" over a preprinted graphic.

Double Layer Potential Electrical potential difference between a substance and a solvent.

Downtime Any time when the machine is not cycling and producing parts.

Draft angle The slight angle given to a vertical wall of a molded part so that the part separates from the mold easily during ejection.

Draft The tapered design of a mold wall which facilitates removal of molded parts. The angle or slope given to part walls to aid in ejection and to give the part greater strength.

Drooling Leakage of resin from a nozzle, sprue, or gate in injection molding. Thin strands of plastic that get caught in the mold.

Dropping Point Temperature at which a grease passes from a semi- solid to a fluid state.

Drying The removal of moisture from the resin pellets by exposure to certain time and temperature. All Hydroscopic Material must be dried prior to molding.

DSC Differential scanning calorimetry. One of several thermal tests used to characterize plastics.

DTA Differential thermal analysis. One of several thermal tests used to characterize plastics.

DTUL Abbreviation for Deflection Temperature Under Load

Dual Emulsion Emulsion in which both the internal and external phase contain portions of the opposite phase instead of being homogeneous. This is also referred to as a mixed emulsion.

Ductility Amount of plastic strain a material can withstand before it fractures.

Durometer An instrument used for measuring the hardness of a material.

Dwell Pause in the mold closing cycle of a compression molding operation to permit gas to escape from the molding material. Sometimes synonymous with holding or second stage in injection molding.

Dwell time The time the screw spends in the back position, waiting for the next shot.

Dwell Pause in the mold closing cycle of a compression molding operation to permit gas to escape from the molding material. Sometimes synonymous with holding or second stage in injection molding.

Dynamic Viscosity An index of molecular friction within a fluid that is proportional to the rate of deformation and the viscosity coefficient of a fluid (absolute viscosity).

Dynamics Behavior of bodies under the action of forces that produce changes of motion in them.