Fundamentals of Film Laminates

Type of Adhesive

The single characteristic most often used to define a laminating film is the adhesive. As commonly used, the adhesive type is an indication of the melting temperature of the adhesive. The property in turn determines what kind of laminating equipment can be used to process the film.

The three standard categories of overlaminates are:

• Thermal
• Heat Assist (Heatset or LowTemp)
• Pressure Sensitive (Cold)

Thermal Films 

These films are the least expensive of the three. They require relatively high processing temperatures (185–240F) and relatively low roller pressures for processing. The adhesive used in thermal films is polyethylene. The downside of thermal film is that it is not predictable for all laminating scenarios. Thermal films are not recommended for inkjet jobs with heavy ink deposits or on photogloss paper. Thermal films are also not recommended for use on printable media that expand and contract with temperature changes, such as vinyl.

Heat Assist (HeatSet Films) 

Often described as a middle ground between pressure sensitive and thermal films, heat assist films cost more than thermal films but bond more reliably in most situations, and are generally recommended for inkjet prints. The temperatures required to process heat set films are lower than that of thermal films (185–210 F), while roller pressures are similar (30–60 psi). An advantage of heat assist films is that they cure almost instantly, allowing graphics to be rolled immediately. Heat assist films have a release liner.

Pressure-Sensitive (Cold) Films 

The most expensive of the three categories, pressure-sensitive or cold films are generally high performance products with a wide-range of compatibility. Pressure-sensitive films bond using moderate to high pressure. Because pressure-sensitive films do not require heat, they can be processed with less expensive laminating equipment. These films have a release liner.

Film Types (Base Film or Substrate)

The type of film describes the base polymer or plastic used to make the overlaminate. It is the base film onto which the adhesive is coated. The innate properties of the base film define many of the key performance characteristics of a laminating film.

Common Base Film Polyester

Shiny, transparent, tough thermoplastic polymer used as the substrate in most thermal laminating film. Polyester is dimensionally stable, and resists abrasion and penetration by many chemicals. However, it is not as effective for outdoor jobs or applications requiring flexibility.

Polyvinyl Chloride (Vinyl) 

One of the most popular base materials for pressure-sensitive and heatset overlaminates, vinyl is strong and conformable. It is not as dimensionally stable or heat resistant as polyester, however. There are many grades of vinyl used in the finishing industry. One of the most important distinguishing factors is Monomeric vs Polymeric formulation. In general, polymeric vinyl films are more appropriate for outdoor use, and applications where additional clarity and flexibility are required.

Polypropylene 

Soft, transparent thermoplastic polymer used as a substrate in laminating film. It has excellent chemical resistance but prone to scuffing.

Polycarbonate 

A very strong and durable plastic preferred for applications requiring heat and cold resistant plastic used in injection-molded items such as streetlight lenses, automotive taillights and audio compact discs.

Other Base Films

Acetate 

Cellulose acetate or cellulose triacetate or cellulose acetate butyrate has the appearance, toughness, heat and solvent resistance found in polyesters.

Nylon 

Shiny, transparent, tough, thermoplastic polymer used as a substrate in laminating film. It resists abrasion and has hygrospic properties that impart lay flat properties.

Base Film Thickness and Ratio of Base Film to Adhesive

These related properties are critical to the performance of the film. Along with the nature of the base film polymer, the thickness of the film affects the rigidity of the film. This is turn affects such properties as, how the finished graphic hangs or installs, whether it can be rolled for shipping, etc. The total thickness or gauge of an overlaminate film is made up of two components (or layers), base film or polymer.

Adhesive layer(s)

The thickness of the base film is far more important to the performance of the applied overlaminate than the adhesive layer. A thicker film:

• Provides more protection from moisture and industrial pollution.
• Improves the overall rigidity of the laminated graphic.
• Improves the visual quality of the underlying graphic.
• Reflects light more accurately.
• Enhances the brilliance of printed colors

Greater thickness is not always better. For graphics which will be applied to contoured or dimensional surfaces, especially vehicle sides, a thinner film may be more desirable. When specifying overlaminates, it is not always clear how much of the total thickness of an overlaminate is the film layer and how much is the adhesive layer. Thermal films are reported one way and pressure-sensitive film another.

Thermal Films 

In addition to the total thickness in mils, more detailed information about the film to adhesive ratio is available. The most common way to report this ratio is with a fraction, which is expressed as film thickness/adhesive thickness. A three-millimeter film consisting of one millimeter of base film coated with two millimeters of adhesive would be reported as 1/2. A 10-millimeter film consisting of seven millimeters of base film coated with three millimeters of adhesive would be reported as 7/3.

Pressure-Sensitive Films 

When the gauge is given for a cold film, the number usually represents the base film only. A three-millimeter vinyl overlaminate consists of a three-millimeter base film of vinyl plus the adhesive layer. Therefore, the true total thickness of a three-millimeter overlaminate will be between four and 4.5 millimeters.

Surface Finish and Texture

An overlaminate affects the gloss level of the image beneath it. Most overlaminate films are available in a range of finishes from matte to gloss, with finishes in between described as satin or semi-gloss. The surface finish is an important factor in how well the image can be viewed under specific lighting conditions.

Overlaminate films are also offered in a wide variety of textures, including pebble, embossed, canvas and leather. Specialty textures can simulate an art substrate such as canvas, providing protection and texture simultaneously on inexpensive media such as paper. The texture of an overlaminate may also be critical to its performance in the field. Floor graphics, for example, require textured surfaces to prevent slipping.

Clarity

The clarity of a film is an important factor in the visual quality of the laminated graphic. Films appear equally clear prior to processing, so request further specifications from the manufacturer if this is an important property. Most films look equally clear when viewed alone. The actual optical clarity of two different overlaminates are best compared by overlaminating both of them on white media. Films with less clarity will show a yellow cast.

Other Properties

Opacity 

Usually a factor in backing films, which are used to minimize showthrough of backgrounds, light spill or display hardware.

UV Protection 

This is a property of many overlaminate films. UV-inhibiting agents may be incorporated into either the base film or the adhesive. These agents act as either absorbers or stabilizers. Absorbers protect the underying image and media, while stabilizers act to prevent breakdown of the film itself.