Selecting the right product & technical guidelines
Choosing the right product for the job
Asking the right questions is the key to choosing the right self-adhesive product and the following questions will help you to select the correct product:
- What surface is the label to be applied to? The material, shape and texture are all important factors
- Is the label to be fixed permanently or is it to be removed?
- Under what conditions will the label be applied? Temperature and moisture will affect the adhesive.
- What temperature will the label be exposed to once applied? Extremes of temperature will affect the performance of the adhesive.
- Is the label to be used indoors or outdoors? Avoid using paper labels outdoors.
- What is the printing/conversion process to be used and what sheet size will be required?
- Does the label need to be opaque to obscure information under the label?
- What type of backing is required-solid or split?
- Will the label come into direct or indirect contact with food?
- Will the label need to be child friendly?
- When printing pre-cut labels, select a product that is compatible with the main printing process. For example, if the label is to be litho printed with a small amount of laser printing subsequently, use one of the labels s designed for litho printing (A, B & S ranges) If the predominant printing process is laser/inkjet/copier use a label from the laser range (LBC and LDC). While all ranges are interchangeable the best results will be obtained by following these recommendations.
Once the most suitable product has been selected there is no substitute for running field trials for as long a period as possible to ensure that the label performs as expected. This is very important as even relatively good surfaces such as glass or steel may be coated with agents to prevent scuffing or corrosion. Plastics may be contaminated with release agents used during the manufacturing process or may be prone to gassing. All of these factors will affect the adhesive bonding process.
It is also important to test removable adhesive for as long as possible under service conditions as some coatings and surface finishes may affect the performance of the adhesive.
- The ideal storage conditions for self-adhesive are 20-22°C with a relative humidity of 50-55%
- Materials should be kept in their original packing until required and unpacked sheets should be covered if left overnight.
- Unused labels should always be kept in their polythene bags.
- Self-adhesive materials stored in good conditions will have a shelf life of over 12 months.
- Stack heights should not exceed 25 packs of 200 sheets.
- Store material flat. Do not store on edge.
- Always keep the printing surface upwards
- Move sheets into the printing environment 48 hours before use.
- Check with your ink supplier that the inks to be used are suitable, particularly when printing non-absorbent surfaces such as foils and plastics.
- Care should be taken to insure that static is not introduced into the material, particularly with synthetic materials.
- Sheets and labels should always be separated by fanning apart prior to printing.
- To avoid curl or adhesive bleed use minimum printings pressures and remember that self-adhesive laminates have an overall weight of typically 180 to 200g/m2.
- If solvent inks are used avoid contact with the adhesive.
- Care should be taken to keep material flat between processes.
- When die cutting or perforating sheets take care to avoid ‘cut through’ as this will weaken the sheet and create problems when dispensing or applying the labels.
- When printing sheets of labels ensure that the labels are not pulled from the sheet during printing by using low tack inks.
- Laminate must be protected from direct sunlight, excessive temperature and moisture changes at all times.
- Ensure that all guillotining and drilling equipment is kept clean and sharp. Ideally, silicon spray should be used regularly on the cutting faces to aid clean cutting.
- Do not guillotine more than 100 sheets at a time.
- Cut laminate face down to help achieve a clean cut.
- The finished product should be packed flat and wrapped in polythene to provide protection from moisture.
- Do not use excessive pressure when wrapping or banding material, as this will cause edge marking and possibly damage.
- Date the packaging labels to assist with stock rotation and identification of shelf life.
Application of label
- Ensure that the surface to which the label will be applied is clean and free from dirt and grease.
- Remove the silicon liner from the label (rather than the face material from the liner) as this will keep the label flat and reduce the risk of edge lift at a latter date.
- Position the label and apply gentle pressure to smooth out the label and expel any trapped air and to accelerate bonding.
Self-adhesive (Pressure sensitive adhesive)
The term self-adhesive is actually misleading as the adhesive will not stick by itself but requires the application of an even and overall pressure to optimise adhesion. Self-adhesives are also known, more correctly, as Pressure sensitive adhesives. Put simply, if you don’t apply pressure all over the label it won’t stick properly. This is particularly true with difficult surfaces such as plastic and cardboard packaging which often contain a high proportion of recycled paper and other elements that hampers the adhesion process.
Further information may be obtained on the Finat web site: www.finat.com. (test methods)
Choosing Films for Self Adhesive Labels
HOW SAM (UK) CAN HELP
SAM (UK) can help you with expert advice on the correct film to use. We have in stock a wide range of films including both standard and special vinyls for offset printing as well as BOPP films which are available in a range of finishes including Gloss White, Gloss Clear and Matt White. In addition to our comprehensive range of litho printable films, SAM also stocks an extensive selection of films suitable for all digital printing technologies.
THE FILMS - THEIR ADVANTAGES AND DISADVANTAGES
Polyvinyl Chloride (PVC or Vinyl)
· Soft and conformable
· Manufactured in clear and various colours and thicknesses
· Indoor and outdoor uses (depending upon the grade and adhesive, guaranteed for up to seven years)
· Reasonable resistant to chemicals or oils
· Not stable in warm or hot conditions
· Needs special vinyl inks to print or fully oxidising inks if litho printing.
· Not clear - hazy and can be distorted
· Not environmentally friendly during manufacture or recycling
· Requires special dies to die cut shapes successfully
· Cannot be used in proximity to food packaging due to possible plastizer migration.
PVC has many unique features particularly in outdoor or point of sale applications that require longevity. Typical uses include advertising posters (both indoor and outdoor - depending on the grade), banners produced on plotter or wide format printers, commercial signage, automotive applications such as car and truck body stripes or decals.
Low and High Density Polyethylene (PE, LDPE and HDPE)
Advantages (Low Density Polyethylene)
· Soft and conformable
· Manufactured in clear and white
· Much thinner films available compared with vinyl
· Can be printed with standard fully oxidising water based or UV inks
Disadvantages (Low Density Polyethylene)
· Tears easily in both cross and machine directions
· Low temperature resistance
· Tensile strength low and the film can distort during the printing process
· Not as clear as HDPE
Used more in packaging than labels
Advantages (High Density Polyethylene)
· Reasonable tensile strength medium
· Image quality is good
· Product clarity is good
· Reasonable life span when stored under the recommended conditions both prior to and after printing and converting.
· Reasonable resistance to chemicals or oils
Disadvantages (High Density Polyethylene)
· Tears easily in a cross machine direction if the edges are ‘nicked’ or damaged
· Requires a print receptive coating (normally applied by the manufacturer)
· Requires a specific filmic die to die cut properly (dies used to cut paper, if they work at all, will have their useful life considerably shortened if used to die cut films)
Used where conformability, flexibility or squeezability are required, particulary on plastic bottles or containers and household or personal care products where the container may be of an irregular shape and require squeezing to dispense the contents.
Biaxially orientated polypropylene (PP or BOPP)
· Available in both clear and white
· Good sheet stability
· Reasonable tensile strength
· Reasonable temperature resistance
· No image distortion
· Good print image quality
· “Touch clear” after application - if the material is viewed through the film and adhesive (after the backing sheet has been removed but prior to application) it appears cloudy and not clear; however, once applied, the film becomes fully clear or “touch clear”.
· Reasonable shelf life if stored under the recommended conditions both prior to and after printing and converting.
· Tears in the cross direction if ‘nicked’ or cut
· Non conformable
· Low to medium resistance to chemicals or oils. Testing should take place prior to any printing or application process to ensure that the product inside the container to be labelled has no effect on either the print surface or the stability and adherence of the label itself.
· Requires a print receptive coating prior to printing
· Requires a specific filmic die to die cut properly. Paper dies, if they work at all, will have their useful life considerably shortened if used to die cut films
Food and beverage packaging and labels, medical packaging and labels, personal care product packaging and labels, tamper-proof films - printed or clear
Polyester (common reference for polyethylene terephthalate or PET)
· Does not tear easily even if ‘nicked’ or cut
· Available in clear, white and silver
· Due to its inherent strength, significantly reduced thicknesses of film can be used than with vinyl, PE or BOPP films
· Very high clarity (with the clear versions)
· Excellent print image quality
· No distortion of image
· Very high tensile strength in both cross and machine directions
· Very high resistance to temperature
· Very high resistance to chemicals and oils
· Requires no print receptive coating prior to printing
· Good shelf life if stored under the recommended conditions prior to and after printing and converting.
· Cost high versus PE or BOPP films and vinyl
· Not conformable
· Requires a specific high quality die to die cut shapes due to its high tensile strength. The normal life of the die is also shortened for the same reasons.
Its resistance to heat makes PET the best choice for high temperature printing such as toner machines. PET is regularly used in top end packaging applications such as cosmetic labelling (for small, round cosmetic dispensers that require both high end graphics and clarity). It is also used in pharmaceutical packaging and labelling, tamper-proof packaging and labels, labelling chemical drums and automotive applications - both outside and inside the engine compartment - where longevity is required. Similarly, the labelling of white goods (technical specification labels which replace the original metal labels) and computer technical labels (front and reverse side) that require clear information, graphics and longevity despite the small size are ideal applications for PET.
Non-absorbent materials such as plastic films and metal foils cannot be printed with conventional litho inks as these inks are only designed to work with absorbent or porous printing substrates like paper. If conventional litho inks are used on non-absorbent surfaces, they will not dry.
Printing on films demands inks that dry primarily through oxidisation and are referred to as oxidising inks or fully oxidising inks. Prior to printing, always ask your ink supplier about the selection of the correct inks and best press conditions.
Many films today are printed digitally and it is important to select the correct film for the specific digital printing process. If long print runs are required at high temperatures (typically associated with some digital toner machines), polyester should be used as it is more tolerant to the temperature extremes involved.
Printing self-adhesive films digitally is not the same as printing paper or plastic without adhesive and there may be some initial curling of the sheet which normally settles down after a period of time. It is also important to fan the material prior to loading the feeding unit in order to get as much air as possible into the material. The minimum temperature necessary should be used to avoid subjecting the labels to excessive heat.