Ask Vinnie

  • The adhesive will perform best at room temperature or higher.
  • There are several types of adhesives used to manufacture cores. In order to answer this question. The composition of the adhesive has to be known. Is it based on polyvinyl acetate, polyvinyl acohol, dextrin, or sodium silicate? Whatever it is, I am not surprised that it doesn’t work at 40 Degrees F. I suggest the company asking the question go to their supplier and ask for the optimum application temperature.
  • Solution and emulsion adhesives are typically intended to be run around ‘room temperature’. It’s understood that that will not always be the case, but when there are drastic deviations from this, many things can be affected: emulsion stability, set speed, and viscosity are probably the most important. At very low temperature, viscosity will increase dramatically, leading to difficulty controlling application amount; adhesive will not set as fast, since paper surface gets denser and since it takes more energy to flash water off; at very low temperatures, emulsion adhesives will ‘break’, which means the suspended resin will coagulate. This is non-reversible, and means the adhesive has become unusable.Most of these issues can be accommodated by choosing an adhesive whose properties are suited for low-temp use (i.e. thinner, faster set speed). However, 40F is probably approaching the point at which your emulsion will break. It would be good practice to leave more of a buffer. Store adhesive containers in a warmer area, and add some ambient heaters to the area around the gluepots.

An adhesive for light weight paper can be made with polyvinyl alcohol and boric acid. In some cases, users add clay to this type of adhesive to increase solids and speed drying. The clay can also limit the absorption of the adhesive by the paper.

Adhesive without clay:

  • For each gallon of cool water, adjust the pH to about 4.5 with any acid while stirring. Continuing to stir, add 400 grams (0.9 lbs) of Elvanol® 71-30 polyvinyl alcohol and 28 grams (one ounce by weight) of boric acid.
  • When the boric acid is fully dissolved, heat the polyvinyl alcohol slurry with stirring to 90 C (about 195 F) and hold it at that temperature for 30 minutes to make sure all the polyvinyl alcohol has dissolved. The adhesive can be used immediately or allowed to cool. If faster cooling is desired, leave some of the water out of the recipe and add it as cool water at the end.
  • If clay is desired, simply add between one and two pounds of dry clay to the above formula before cooking the polyvinyl alcohol. Allow the clay to completely mix in the slurry before heating.

pVOH can be softened by adding glycerin or propylene glycol after cooking and cooling. Addition rate is typically 5-10% of the dry pVOH weight in the cook. The tradeoff is set speed. Both glycerin and pg act as humectants (materials which hold onto water, and slow set), which can be detrimental to winding operations. Water -resistance of the finished tubes could be adversely affected as well. Another option is to purchase a plasticized resin emulsion from an adhesive supplier. The level of addition to the pVOH adhesive would be determined by the amount of flexibility required. In addition to providing flexibility, the resin base would improve specific adhesion (thus stronger, deeper bonds). Emulsion increases wet-pound cost of the adhesive mixture, but you will usually be able to apply a thinner film of adhesive with higher emulsion content (more active adhesive solids), which will mitigate the increased cost and help further with flexibility. Emulsion should be added to the pVOH cook after it has cooled below 120°F, and thoroughly blended.

I would recommend adding an (EVA) Ethylene-Vinyl Acetate Co-Polymer to the adhesive. Recommend maybe 15-20% on a wet basis. This should soften the glue line and make the dry film more pliable.

Specialty Adhesives, Inc.

My recommendation would be a PVOH (Polyvinyl alcohol/clay mixture. You can purchase a pvoh/clay pre-mix in 50# bags or bulk sacks. This dry material comes pre-mixed and ready for use. You would require a vessel (kettle) to cook the material and a steam generator (boiler). The material is cooked (dissolved) in water with direct steam until it is totally converted from dry to liquid. This finished adhesive performs very well and should reduce overall cost in the long run.

This is a very hard question to answer without more detail on the processing and end-use requirements for the tubes. The properties of the different adhesive types you mention can be vastly different. For example:

  • Poly vinyl acetate (PVA) emulsions typically have very fast set speed and excellent adhesion, but rigidity is generally less than the other types mentioned, and wet-pound cost is usually higher.
  • Poly vinyl alcohol (pVOH)/clay cooks have moderate cost and are fairly versatile, but have more limited specific adhesion (ability to adhere difficult papers) than PVA, and tend to add more moisture into the finished tubes (dimensional stability, drying/staging time, moisture content issues).
  • Dextrins are moderate in cost, have good rigidity, and add moderate moisture to the finished tubes, but they have limited specific adhesion and generally slower set speed (trimmer issues).
  • Silicates have the lowest wet-lb. cost and a very rigid dry film, but have the most limitation in terms of set speed, specific adhesion, and contribution of moisture to the finished tubes. Inner and outer plies often require a different type of adhesive applied to hold the assembly together until silicate can dry.
  • The best starting point may be to prepare a clay/pVOH cook, and post-add some PVA resin emulsion ‘sweetener’. We would be happy to have a representative of our company contact you to help you develop a strategy to fit your and your customers’ needs.

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