Graphics and Pre-Press Terms
A cross laminated polyethylene film. It is made with two oriented polyethylene films laminated with their orientation directions crossed at roughly 90 degrees (45 degrees from the machine direction). It is used primarily in the explosives and construction industries.
A plastic film produced with minute voids that result in an opaque material. Cavitated materials such as polypropylene are used most often as ice cream bar wrap.
Coefficient of Friction measuresthe slipperiness of a surface determined by observing the force required to pull a known weight over a surface. STATIC COF is the force required to initiate motion while KINETIC COF is the force required to continue the movement of the one surface over the other. Static COF is always greater than Kinetic COF. As a general rule, low coefficient of friction allows for lower power requirements and easier machining where flexible materials are being pulled over stationary machine parts. However too low a COF can also result in telescoping rolls, poor tracking, and packages that will slide when stacked.
An extensible film is one that can be stretched easily. Most stretch wrap, and heat shrink films made of low density polyethylene, linear low density polyethylene and polyvinyl chloride are common examples.
Specular reflection of light from the film surface.
An instrument which is used to measure specular reflection gloss of a surface. Gloss is determined by projecting a beam of light at a fixed intensity and angle onto a surface and measuring the amount of reflected light at an equal but opposite angle. There are a number of different geometries available for gloss measurement, each being dependent on the type of surface to be measured. For materials as coatings and plastics the amount of reflected light increases with a greater angle of illumination, as some of the light penetrates the surface material and is absorbed into it or diffusely scattered from it depending on its color.
A “cloudy” discoloration of a transparent film or coating.
An instrument which is used to measure the transparency; haze, see-through quality, and total transmittance of a material, based on how much visible light is diffused or scattered when passing through a material. Transparency is important because a material needs to be more or less see-through depending on its practical usage, e.g. a grocery bag needs the light to be more diffused so that less can be seen while food packaging film needs the light to be less diffused so that the contents can be seen clearly. For reasons such as these haze meters are necessary to determine which material is needed for which practical purposes. The data gained from the haze meter can be transferred to a PC for further data processing to ensure a consistent product.
A measure of the rate of water or moisture vapor transmission through a material. Expressed as WVTR (water vapor transmission rate), or MVTR (moisture vapor transmission). It is normally measured at 100% relative humidity, expressed in grams/100 square inches/24 hours, (or grams/square meter/24 Hrs.)
A film that is not easily stretched during the converting process. Common films such as polyester, nylon and polypropylene are not typically stretched when winding.
Material that will not transmit light. Materials that Overwraps use include metallized PET, metallized OPP, and white opaque PE.
Normally referred as Oxygen transmission rate (OTR) is the measurement of the amount of oxygen gas that passes through a substance over a given period. Standard conditions of testing are 0, 60 or 100% relative humidity. Units are cc/100 square inches/24 hours (or cc/square meter/24 Hrs.). (cc = cubic centimeters)