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When Things Get Sticky – Tips For Successful Gluing

Successful gluing work needs a scientific approach and an artistic touch.  The four horsemen of gluing – paper, ink, coatings, and glue – are about equal contributors to a job’s success.  Their combinations are nearly infinite and unexpected results do frequently occur.  Sometimes ez release glue tears paper fiber.  Sometimes permanent glues perform like ez release.  The wizard Merlin would even be puzzled.

Graphic arts glues are mainly oil, resin or latex based.  Each type performs as expected most of the time, but there are more exceptions than anyone would like.  Both ez release and permanent oil based glues offer good adhesive properties and are appropriate for physically heavy or varnished pieces.  However, their relative great bulk may result in unattractive product from a marketing viewpoint.  Resin based permanent glues are cold applied and provide a good bond with a relatively small amount of residue.  Latex ez release glues are thin, generally reliable, inexpensive to apply, energy efficient (applied cold), environmentally friendly, and FDA approved for many food packaging applications.  However latex is a natural rubber tree product and coagulates when contacted by steel, iron or plastic.  Coagulation can cause machine applicator problems.  Also, latex glue doesn’t work well in compressed air applicator systems.

EZ Release Glue (a.k.a. Removable or Fugitive)
Ez release glue performs well 19 out of 20 times.  But one tough job will prove there’s no ez release from gluing headaches.

Ez release glue performs best on penetration resistant, highly calendared, dense paper with heavily inked and coated surfaces.  Matte and other lightly calendared enamel stock, offset paper or sheets with a heavy clay fill are susceptible to delamination and fiber tearing when the intention is an ez release effect.

Latex ez release glues require long set up times (3 to 4 minutes) and tend to spread when the opposing sheet is tightly squeezed.  Their curing period is really 24 hours even though they appear to be dry after 10 minutes.  Unfortunately, products that perform properly 10 minutes after manufacturing can change in 24 hours and pull fiber.  Oil based ez release glues have a shorter curing time, but glue bulk remains an issue.

Managing variable adhesion and chemical reactions is important.  Some ez release glue solvents, such as ammonia, dissolve aqueous and other coatings and result in unintentional permanent adhesion.  Occasionally, permanent resin glues can function as ez release on aqueous coatings because when dry they become very brittle and perform better than latex or oil-based ez release glue.

Temperature and humidity conditions can greatly affect glued products’ performance.  One summer my company shipped a trailer load of latex ez release glued product to Texas.  Our client reported that the job was unacceptable because fiber was tearing.  Although our time pull production samples functioned perfectly, we saw their samples and agreed.  We sent an employee to Texas and discovered that the two inch mylar tape used to seal the shipping cartons had blistered.  Our tape manufacturer explained that blistering occurs with their product when exposed to heat greater than 120°.  We next found that our truck remained outside during an intensely hot weekend prior to delivery.  Interestingly, fiber tearing product was only in the cartons on the external layer of the skids, not in the more protected internal cartons.  Clearly extreme heat caused further reaction in the curing of the ez release glue.

Permanent Glue
Permanent gluing problems do occur, but are infrequent.  For best results, select a paper with a porous surface and position the glue away from ink and coatings.  Permanent glue needs to bite into paper, so the harder the surface, the more difficult it is to penetrate the sheet and create good adhesion.  Knock out ink, varnish, UV and aqueous coatings wherever you place permanent glue because glue tends to rest on top of coatings and cannot penetrate and grip fiber.  Permanent resin glue spreads on stocks and coatings with a high barrier to penetration and can result in a poor bond or sloppy glue coverage.  Absorbent and porous paper will allow glue to penetrate paper fibers and produce a strong bond.  If gluing must occur over ink coverage, use wax-free ink.  When stuck with a difficult permanent gluing job with aqueous coating, as a last resort, try using an ammonia based latex ez release glue instead of permanent.  It might just work.

Since water-based resin glues spread, those with critical glue registration require constant monitoring and sample pulls during production.  Take special care when applying resin glue in a trim-out area.  If glue reaches the paper’s edge, sheets will stick together.  Conversely, if glue spreads too far into the piece, it will not be removed in the final trimming process.  If trim-out area is shorter than a 3/8”, consider using ez release instead of permanent glue because negative consequences of excess glue spread are less.

When gluing sheets 8pts or thicker, paper memory can cause puckering at the fold.  Hot melt oil-based permanent glues perform well with thick stock because its open (setting) time is much shorter than that of cold applied resin glue.  Resin (and latex ez release) glue work by evaporation and have three or more minutes of open time.  Hot melt sets as soon as its temperature drops below 250 degrees, which is nearly instantaneous once the fold is made.  When applying permanent glue in conjunction with remoistenable glue, be careful that water based glues don’t come in contact with the backside of the remoistenable glue strip.  Moisture seepage might migrate through the sheet and activate the remoistenable glue strip.

Unfortunately, hot melt can be hard to apply.  Contamination problems occur more frequently in jobs requiring small applicator orifices because any glue pot overheating creates char which causes clogs.  Since a hot melt unit has at a working temperature over 300°, fixing problems while in operating condition is difficult.  Hot melt contamination usually requires a time consuming system flush which wastes a lot of expensive glue.  One method of reducing hot melt glue waste is to clean contaminated applicator heads with hot vegetable oil.

Machinery Issues
Prior to the 1970’s, gluing wasn’t widely viable.  Electronic systems which sense the presence of a sheet, wait a specified period of time and then apply glue have made gluing practical.  Most systems on the market now have pretty good electronics, but the next big advance in gluing technology is almost here.  Today’s air activated non-contact permanent gluing systems are extremely accurate and remarkably trouble free.  The capability to apply permanent glue from the bottom of a sheet is useful.  My company would replace all our gluing machines with air activated units if only they performed well with ez release glue.  Although some ez release glues will work with these machines, we haven’t found them to be reliable on a wide enough range of paper stock and ink combinations … yet.

Develop a Good Relationship with a Glue Supplier
Be in frequent contact with your glue suppliers.  Since most glues have a short shelf life, purchase and use glue biweekly to ensure good adhesive properties.  Often jobs require custom made glues for special situations.  You may need glue to penetrate a tough aqueous coating, work in high humidity, hold in freezing and thawing situations, or bind folded plastic while in a washing machine.  (My company has actually done all of these.)  A responsive supplier can save you hours of fruitless experimentation and help you meet deadlines.  Good suppliers know government regulations.  For example, when uncertain of FDA requirements, call a trusted supplier and have them fax back applicable regulatory code.

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Increase your likelihood of success.  If you aren’t gluing on a daily basis, get expert advice before beginning critical jobs.  Consultant Dick Gorelick recently said, “Knowledge used to mean knowing how to do something.  Now it means knowing where to get something done.”

Jack Rickard is a former President of the Binding Industries of America and President of Rickard Bindery (which has 18 gluing machines).  His company specializes in finding solutions to extremely challenging bindery jobs.  He can be reached at (800) 747-1389.