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Question and Answer

Laminating Films

by Staff

November-December, 2010
Choosing the correct laminating films for a particular job is not always as simple as it may first appear. Just using what is on the shelf or thinking any type of film will work can end up causing challenges once the laminating process begins. This Q&A article will cover several of the issues that should be considered closely when laminating printed material.

Is dyne level an important element when utilizing laminating film on a particular job?
The surface tension of the substrate becomes important when working with processes such as UV coatings, overprint varnishes, ink jet applications, adhesives and foil stamping. A low dyne level on the surface (less than 38) will mean a marginal to unsuccessful bond to the substrate. In the case of laminated surfaces, dyne is used as a predictive tool for the degree of adhesion to the product during the process application.

The most common type of dyne measurement tools in the print market today is dyne solutions, which come in pen format or solutions in jars. The pens are easily acquired, simple to use and come in different dyne indication levels.

Most laminating films can be corona-treated to increase the dyne level, which is always recommended due to the gradual decay of the surface charge. Any film roll that has been corona-treated should never be stood up on its end on the floor. This can provide a discharge path for the static charge captured on the film surface.

Typical dyne levels for film is standardized by a minimum of 40 dyne on a wide variety of films. The typical dyne level is usually 42 on the surface and much greater on the adhesive side. Minimum requirements for UV coatings and foil stamping applications are preferred to be at a dyne level of around 40.

Factors Affecting Dyne Levels
Ionized Sprayers. These devices are used to reduce static electricity in stacked paper. They are used primarily in conditions of low humidity at the feeder sections of presses, laminators, folders and coaters. Ionized sprayers spray out ionized air that reduces static and also reduces the dyne level, especially in areas closest to the nozzle. If a localized area of dyne failure exists, this may be the root cause.

Paper. Paper is a variable that, at times, will disguise itself as a film problem. Some papers have a pH difference between the wire side and the felt side (print side). It is not uncommon to find a neutral pH on the felt side and a high alkaline pH on the wire side. This is not a problem for lamination, but for applications such as presentation folders, overlay boxing and case bound book covers, it does create a problem. A high pH has the same effect on adhesive binding applications as it does in many litho-print applications. The ink, as well as the glue, do not dry. Emulsification results with a high alkaline condition where ink or glue absorbency is required. An alkaline condition inhibits ink drying and curing; the same is true for an adhesive that would be used to adhere a laminated surface to the unlaminated surface with water-based glue. The recommendation here is to check both sides of the paper stock and make a note of the findings in the job folder. There are pH pens that indicate neutral, acid or alkaline conditions in paper.

Humidity. High humidity and very low humidity will affect the interpretation of a dyne reading so all readings would be best served at pressroom environment, which should be maintained at roughly 50 percent RH.

Time. Not using the corona-treated film within the manufacturer’s suggested timeframe might cause a less than desirable performance. There is a bleed-off of charge over a period of time known as dark decay – even though the film still may be wrapped and packaged.

Poor Handling. As mentioned earlier, a corona-treated roll never should be stacked on its end, which will provide a discharge path for the corona treatment.

Glue recommendations and additional information about other finishing applications should be obtained from the film supplier.

Additional Resources

  • pH pens (Alkaline paper checker) – Printing Supply USA Inc., 800.516.8443
  • Dyne test markers (available in various dyne levels) – Diversified Enterprises, 800.833.4644

      What is the best type of film for my particular application?
      Several films are available on the market today – each has its own unique set of characteristics for certain applications.

      Oriented Polypropylene (OPP) Films (sometimes referred to as BOPP)

      Description: Oriented Polypropylene (OPP) is a very clear and flexible film used in several applications from dust jackets on case bound books to food wrap applications.

      Clarity: OPP is probably the clearest of laminate films available today. Clarity becomes an issue especially in applications involved in print because the clearer the film the less apparent color shift. All films and other coating applications will shift or enrich the colors on a printed piece, especially in the pastel color renditions of the print.

      Durability: Another key characteristic of OPP is its flexibility. It is used primarily for dust jackets on case bound books and gives the book a “sparkle” for shelf appeal.

      Versatility: OPP has limited versatility because it is difficult to overprint, glue, UV coat and foil stamp. Sometimes you will see dust jackets that include foil stamping on the cover but this is usually done prior to the application of the OPP film. However, OPP does emboss very well.

      Unique Characteristic: OPP is a flexible film that is very soft and scratches easily. Additionally, it is FDA-approved right off the shelf so it is suitable for some food packaging applications. It is the most cost-effective film on the market.

      Typical Application: Due to the cost effectiveness and the extreme flexibility of OPP, it is used for direct mail pieces, advertising magnets, dust jackets and most anything that has a dated life that most likely will be discarded.

      PET or Polyester (PET) Films (sometimes referred to as Mylar® – trade name of DuPont)

      Description: PET has the largest family of thicknesses for laminating films. Thicknesses range from 1.2 mil to 15 mil thick in conventional, day-to-day applications.

      Clarity: The clarity is just a little less than OPP but also is dependent upon the thickness of the PET film. The thicker the PET the less clear a product will appear. This fall-off in clarity is virtually impossible to notice by the human eye and will only render a difference in a side-by-side comparison of OPP and PET laminates.

      Durability: PET is extremely durable and has a hard surface and structure that is more rigid than flexible.

      Versatility: PET is more versatile than OPP and can be glued, foil stamped and UV coated. It has a limited range for embossing due to the rigidity factor, so thickness will be a key issue if embossing is required as a finishing application.

      Unique Characteristics: Since it is highly durable, PET is used for identification applications such as security cards, ID cards and menu applications. The durability factor also ensures the product will be usable over extended periods – especially long timeframe demands requiring years of use.

      Typical Application: Case bound book covers, menus, credit cards, loyalty cards and gift cards. PET with a special coating makes it ideal for write-on/wipe-off dry erase boards as well.

      Nylon Films

      Description: Nylon is the first commercially successful synthesized product and is used on a wide range of products from balloons to books covers to food packaging applications.

      Clarity: Nylon is consistent with the clarity of PET film.

      Durability: Extremely durable, nylon is not susceptible to mildew so it ages very well and continually protects the surface to which it is adhered.

      Versatility: Probably the best and most versatile film available today, nylon typically has a good dyne level so spot UV, gluing, foil stamping, printing and embossing all work well with nylon films.

      Unique Characteristics: There are many misconceptions regarding nylon and the book component industry. Perhaps the most popular is the concept that nylon is porous and allows moisture to pass through the film structure. This is simply not true and is misleading. Nylon, however, is wickable, meaning that it allows moisture to be drawn off. This also means that it can absorb moisture. Hence, it is good for gluing applications such as presentation folders, franking and inkjet addressing. The flexibility aspect of nylon makes it ideal for perfect bound books. Nylon eliminates the curled cover situation in environments of variable humidity. Nylon does allow for the expansion of the book cover caused by humidity and also allows for the cover to return to a flat condition once it has equalized the humidity, provided that the nylon film has been applied correctly.

      Typical Application: Perfect bound book covers, presentation folders and any single-sided application requiring lamination.

      Cellulous Acetate Films (biodegradable films)

      Description: Cellulous acetate films are essentially derived from wood and are a biodegradable film that is a sustainable option. It is being used for book covers, presentation folders and gift cards.

      Clarity: It has excellent clarity, equivalent or better than OPP film.

      Durability: Currently, cellulous acetates are being used in the gift card market and have not come into high demand in the book component industry. However, it would have the durability properties for these applications as well. It is a very durable film for a variety of applications.

      Versatility: Cellulous acetate film has many of the same characteristics as nylon and surpasses nylon in clarity and run-ability.

      Unique Characteristic: Cellulous acetate is a biodegradable film made from wood and wood by-products. There has been much curiosity regarding biodegradable films and as environmental concerns continue, the use of these films is sure to grow. Price is the major obstacle due to the current low volume of production. If volume continues to grow the overall price will come down. Additionally, cellulous acetate is a brittle film, which means that it will snap easier and not have film roll-up on the trailing edge of the sheet.

      Typical Application: Gift cards, presentation folders and book covers.

      What should be considered when gluing to a laminated surface?

      Many applications exist that require a laminated sheet to be glued. Case or hard bound books are a common example of where the laminated sheet is flood coated with glue and the two book boards and spine are set on the glue side and then folded over. Another application is a laminated presentation folder where a laminated tab is folded over onto itself as the glue tab for one or more pockets on the folder. This is a critical application because the glue needs to adhere to the laminated face of the tab and the inside cover all within a suitable amount of time. Typically, for production runs on a folder-gluer, a combination of a hot melt glue to hold the flap and a water-based glue for long-term adherence is used. Compatibility is the key focal point. Glue that works with nylon film may not work with PET or OPP films.

      A recommended test for the glue on a laminated product once it is set and cured is to place the sample in a freezer for 12 hours and then test the bond again. What works and responds at room temperature may fail after it has been exposed and/or stored in a cold warehouse or transported in a truck in the winter.

      Another concern with glue is the compatibility with paper surface pH. Many C1S sheets are neutral pH on the surface and are high alkaline on the wire side. As mentioned earlier, a high pH tends to emulsify when an acidic solution is placed in contact with it, which can result in failing adhesion.

      InsideFinishing would like to thank John Dawson with Protect-all, Inc. for his assistance with this article. Protect-all is a world-class manufacturer of standard and premium clarity laminating films as well as specialty, packaging, decorative and commercial lamination products. For more information, contact Dave Koskinen at 262.724.3292, call 888.HEATLAM or visit www.protect-all.com.