A substance used to join two materials together , by chemical or mechanical action. Generally applied as a liquid , or as a solid activated by heat or pressure.

Paper or fabric tape with an adhesive layer applied. The adhesive layer is generally activated by pressure , or by the application of heat or water. Pressure sensitive or 'sticky' tapes should not be used for materials intended for long term , since the adhesive degrades and yellows and the adhesive residues can become impossible to remove.

An additive used in plastic , generally at 1 or 2%, that roughens the film surface and prevents film surfaces from adhering to each other. The most common antiblocks are based on clay by-products.

Organic compounds which are incorporated in plastic resins at low concentrates to inhibit or retard polymer oxidation and its degrading effects.

Application of an additional layer to an item to provide support. Sometimes called lining. backing is a conservation treatment used on weakened sheet paper items.

Blocking is the term given to describe the tendency of some film material to stick to itself, making separation difficult. Many virgin polymer films have a smooth, glossy surface which will readily block or stick together, making openability of packaging items poor, or causing problems with downstream processing equipment. High winder tension , insufficient cooling, and high nip roll pressure are a few of the possible causes of blocking in film process. Additives such as diatomaceous earth can be incorporated to roughen up the surface and reduce blocking.

In blown film extrusion , this is the ratio of the diameter of the bubble to the diameter of the die. 6366 x flat film with/die diameter.

Abbreviation for "bags on a roll." Refers to the process of winding bottom sealed , perforated bags , which are not yet separated from one another , onto a core.

A hole in the seal area of a bag caused by excessive heat. A burn through can also be caused by a light spot in the bag as it goes through the bag machine.

Not easily decomposed or otherwise modified chemically. This is a desirable characteristic for materials used in preservation, since it suggests an ability to resist chemical degradation , such as paper embrittlement , over time and/or exposure to varying conditions during use or storage. Sometimes described as chemically inert.

The process whereby film is produced in layers using two or more extruders feeding one die. Co-extrusion is a complex and special process that permits different resins to be use to produce films of different C.O.F on each side , different seal characteristics , different barrier properties , and other variations not obtainable through single layer extrusion.

A measure of how slippery a film is. Coefficient Of Friction is a number that expresses , for a given surface, the ratio of the force required to slide an object over a frictionless surface to the force required to slide the same object over the actual surface. Kinetic COF relates to the force required to maintain movement once it has started , or the "drag". Static COF relates to the force required to start the slippage , or break the object loose from its resting position. The lower the number, the higher the slip of the film. Polyethylene can range between .10 (high slip) and 1.5 (no slip).

The COF , or slip properties , of film are important in determining how that film will perform on conversion equipment and in final form such as in openability or stacking. This test determines the ability of film to slide over itself and is used to determine the effectiveness of slip additives incorporated into resins. Both static (starting) and kinetic (sliding) friction are measured.

Weight per unit volume of a substance, expressed in grams per cubic centimeter. Also called Specific Gravity. Polyethylene ranges between .9100 - .9650. Water = 1.000, anything less than that floats; greater than that will sink. LDPE is low density polyethylene, HDPE is high density polyethylene.
Density is a basic molecular property that can affect many essential physical properties of a polymer. Density , in part , is a function of the crystalline structure of the polymer. It is an excellent means of identifying a product , following physical changes , and determining uniformity.

A line or series of lines on the film surface that run in the machine direction. If there are numerous die lines , it is generally due to the buildup of oxidized materials on the die. If the die line is a single , deep line it is generally due to a foreign object on the die.

The degree to which a material retains its physical properties while subjected to stress, such as heavy use , or adverse environmental conditions. To say a material is durable suggests that it has high initial strength , and will last a long time under normal conditions of use.

The increase in length produced in the gage length of the test specimen by a tensile load , usually expressed in percentages. The test is performed on the Tensile Tester.

Regions of increased thickness on a roll of film; produced by winding thicker film in the same place on a reel. Eliminated by rotating the die. Also known as Piston Rings.

Gels are hard , unmelted particles randomly distributed throughout the film. Gels are unattractive and, in most cases , will be detrimental to film downgauging. The types of imperfections vary , but four of the most common are pinpoint, arrowhead , fisheyes , and oxidized or discolored gels. As different applications will tolerate varying levels of film purity , a gel count test gives the producer or extrusion shop indications as to end-use expectations. This test is very useful as a quality control tool.

A measure of the reflectivity (shininess) of a film's surface of light from a given angle , in this case - 45 degrees. The higher the number , the shinier the film. Gloss can impact desirability of consumers to purchase the film product or something packaged within it. Gloss in film can be optimized by adjustment of extrusion parameters. Once processing conditions are perfect , changing resins to a higher melt index and higher density at a constant MW and MWD will generally result in better gloss.

A measure of the clarity or transparency of film. It is expressed as the amount of light that is not transmitted through a film sample. The lower the number , the higher the clarity. In certain applications, high clarity and minimal haze or frostiness is desirable. This is the case in many packaging applications where good clarity enhances the sales. Both surface roughness and polymer structure diffuse light as it passes through film and cause the hazy appearance. Extrusion parameters can be optimized to improve haze along with proper resin selection.

An adhesive which is liquid when hot but solid at room temperature. Hot melt adhesives are extensively used in paperback bindings , but are generally inflexible and can become brittle and yellow. Pages become easily detached when this happens.

A measurement of the strength of film and its ability to withstand the shock of a falling "dart" without breaking, in other words, puncture resistance. Expressed as the gram weight of the heaviest dart which doesn't break the film when dropped from a specific height. The impact strength of film can be determined and applied to end-use properties through a number of different impact tests. Knowing these results aids in determining which particular resins are best suited for high-strength applications such as the construction and agriculture market.

A process of reinforcing fragile sheet material, usually using transparent or translucent sheets of plastic or paper. Some forms of lamination such as those using cellulose acetate are considered unacceptable as preservation methods because of high heat and pressure during application, instability of lamination materials or difficulty in removing lamination from the item, especially a long time after the lamination was performed.

A partially crystalline , lightweight thermoplastic , polymerized form ethylene gas at controlled temperature and pressure.

The direction of the film which corresponds to the way it came out of the extruder. On rolled film it is the length of the film. Some film properties vary according to film direction.

Melt index is commonly used to classify polymeric resins. Melt index uniformity is essential in maintaining control of processing parameters , and melt index is inversely proportional to molecular weight or polymeric chain length. Melt index heavily influences physical properties.

Average molecular weight and molecular weight distribution (polydispersity) are properties that reveal much of the test specimen. Elongation is a measure of length a film will stretch before it will yield or break. It is expressed as a percent of the original length.

A set of rollers used to compress the plastic bubble into a sheet , or to feed the film to the winder at the proper tension.

The amount of light that will penetrate through a colored item. Opacity is higher with thicker films or with greater loading of color. It has nothing to do with the particular shade or color of the film.

The common name for the plastic polyethylene terephthalate. Its characteristics include transparency , lack of colour , high tensile strength , and chemical stability (when made with no coatings or additives). Used in sheet or film form to make folders , encapsulations , and book jackets. Trade names include Mylar and Melinex. Used in web form ('Reemay')to support paper during wet treatments , and as a relatively nonstick surface through which moisture can pass during mending, drying etc.

In its pure form , a chemically stable plastic material. Used in film form to make sleeves for photographic materials and other uses. A cheaper alternative to polyester film.

In its pure form , a chemically stable plastic material. Used in film form to make sleeves for photographic materials and other uses. Used in sheet form for boxes, folders and such. A cheaper alternative to polyester film. .

A plastic usually abbreviated as PVA. A colourless , transparent solid, it is used in adhesives which are themselves also referred to as PVA or PVA adhesive. There are many varieties of PVA adhesives. The types referred to as 'internally plasticised' have greater chemical stability , and are preferred for use in preservation. PVA adhesives are often used in an emulsion form or 'white glue'. They have a milk like appearance , but dry clear.

Plastic usually abbreviated as PVC, or sometimes 'vinyl'. Not as chemically stable as some other plastics. It can emit acidic components which damage cellulosic materials. Added chemicals called plasticisers are also used to make PVC more flexible. These also damage library materials.

A buildup of material that resembles a hard knot or bump in the roll, generally at the edge of the roll. This is generally worse with no slip EVA materials and can be minimized by using light layon pressures.

Sometimes called 'sticky' tape. An adhesive tape that attaches to a surface when pressure is applied. The adhesive frequently degrades leaving a brown residue which stains and embrittles paper. Not recommended for materials intended for long term preservation.

A measurement of the percent of film shrinkage under a controlled temperature and time interval. As a result of the manufacturing process, internal stresses may be locked into the film which can be released by heating. The temperature at which shrinkage will occur related to the processing techniques employed to manufacture the film and may also be related to a phase transition in the base resin. The magnitude of the shrinkage will vary with the temperature of the film Shrinkage of a particular material produced by a particular process may be characterized by this test method by making measurements at several temperatures through the shrinkage range of the material. This property is important to consider when handling film in downstream equipment that requires heating.

Substances added to make the sliding action easier. These additives are designed to bloom to the surface and provide an invisible coating on the film , reducing the coefficient of friction. Fatty acid amines are an example which is widely used in film extrusion.

A measurement of the strength of a film and its ability to resist tearing under specific conditions. Tear strength is the force required to continue an initially started slit across a film specimen. This widely used test has some value in quality control of film production, but is not a very useful indicator of the strength of film in service.

A measurement of the strength of a film and its ability to withstand stretching or pulling. Tensile properties which include tensile strength at yield , ultimate tensile (or break tensile strength) , and elongation, are tests used to determine relative strength of different films. Yield strength measures the point at which the film, when , stretched, will not resume its original shape. Ultimate tensile is the measure of a load that will cause the film to rupture. Both yield and ultimate measurements are measured in lb/ in2 of a cross-sectional area of useful information on how polymers process and perform. For example, polyolefins generally tend to process with easier and wider MWD and improved drawdown. Within a given family of resins, many film properties can be correlated with molecular properties.

The process of using high frequency electrical discharge to oxidize the film surface, thereby making the surface more acceptable of printing and other substances.

The ability of polyolefin films to retain inks, coatings, adhesives, etc. is dependant upon the character of the surface and can be improved by surface treating techniques such as corona discharge or flame treatment. Wetting tension is utilized to determine the degree or level of treatment applied by establishing a correlation between surface tension (wetting tension) and treatment level.