From a chemical point of view, film laminating adhesives of the Jowacoll® 764.xx series are dispersion adhesives based on acrylate copolymers. They were specially developed for film laminating applications and provide a wide range of adhesion to the printing inks and films used in print finishing (e.g. OPP, PET, acetate or compostable films).
Jowacoll® film laminating adhesives are self-crosslinking and can be processed as one- or two-component systems (to see whether a product can be processed with a second component, please refer to the technical data sheet). In addition, many adhesives have been assessed and tested for use in packaging with food contact according to the requirements under EU 1935/2004.
Characteristics of Dispersion Adhesives
Dispersion adhesives are a mixture of two phases. Solid plastic particles are evenly dispersed in an aqueous carrier. Depending on the type of dispersion, the size of the plastic particles can vary from 0.03 μm to 5 μm. They are so small that they are not visible to the naked eye. Only very finely dispersed products are used in print finishing applications, with particle diameters between approx. 200 and 800 nm (1 nm = 0.001 μm) that deliver a very clear and transparent adhesive film. The technical data sheets for the individual dispersions of the Jowacoll® series provide further information about the solids content, viscosity, pH value, as well as the adhesive characteristics and processing parameters of the corresponding adhesive.
In order to bond two substrates together, the different adhesive systems must be liquid or in fluid form when applied on the foil. The film-forming and hardening mechanism that takes place when the adhesive dries is mainly a physical process. On drying, the aqueous Dispersion evaporates, the plastic particles move closer
together and eventually come into contact with each other. When all water has evaporated, the particles merge and the polymer chains flow together due to the high capillary pressure between the particles. The result is a strong adhesive film that ensures the bonding of the film and the printed material after lamination.
Directions for Use and Recommendations
In general, dispersion adhesives should be stored at room temperature. Temperatures below 5 °C can lead to a premature coagulation of the plastic particles (clotting of adhesive components) and damage the dispersion. Under certain conditions, the plastic particles may settle on the bottom of the container after extended storage (sedimentation). If that happens, the dispersion can be made homogeneous again by stirring with a mixer. Skin which has formed on an already open container has to be removed before processing. Please observe that skin formation can always be a source of particles and could therefore cause stripes in the application. The containers should be closed hermetically whenever possible. Before processing, the adhesive should have a normal “processing temperature” of around 15 °C – 25 °C. Storage temperatures that are too low can lead to a limited coating flow of the adhesive on the substrates.
Conditions for Good Laminating Results
All printing inks used should meet the requirements of DIN ISO 2836. Printing inks according to the standard have to be resistant against solvents (DIN ISO 2836, 6.2.2, 6.2.3) and alkali (DIN ISO 2836; 5.3). If special inks or Pantone inks are used, the colour pigment may bleed through after laminating. The printing inks must be completely dry before the laminating process is started. If necessary, the printed sheets may be aerated by restacking. Coated, cast-coated or calendered paper and cardboard are ideal for perfect laminating results. The surface tension of the films to be laminated as well as of the printing inks should be at least 38 mN/m. It is recommended to test the surface Tension using test inks.
For a superior appearance, it is preferable to coat the printed sheets with a primer instead of using a print powder. Use a strip of adhesive tape to check whether the adhesion of the primer to the printing ink is strong enough. If the sheets to be laminated are already powdered, the powder should be removed as far as possible using the polishing roller or brush roller of the laminator. If this is not possible, the application amount of the adhesive should be increased to embed the print powder in the adhesive layer and to ensure a higher quality result. This prevents the graining from standing out on the laminated sheet and causing unwanted effects.
Before the Dispersion is Filled into the Laminator
Print finishing is a high-end application that requires an absolutely clean processing unit, inside and outside. The slightest contamination (for instance aerosols from silicone sprays or oily rags used on printing units) can have an extremely detrimental effect on quality due to flawed wetting.
The rollers and cylinders inside the unit (application roller, deflection roller, drying roller, laminating cylinder, counter pressure roller) must be free of impurities. The reservoir, pump, and hoses should be clean and free of adhesive residues. This is absolutely essential to ensure that no components enter the adhesive circuit. The inlet connector of the supply line into the adhesive reservoir should have a filter installed on it (e.g. an 80 μm fine mesh filter).
Recommended Amount of Crosslinking Agent
If the laminated materials are exposed to high mechanical stress in downline processing, the recommended amount of crosslinker to be added is 1.5 – 5 %.
This applies especially if downline processing involves one of the following:
• hot foil embossing
• fold burning
• 3-knife + Plano trimming
The addition of a crosslinking agent is especially advisable if the films to be laminated have a high rigidity or are inelastic (e.g. acetate or PET films). This will make it easier for the laminated composite to compensate for the higher tension forces of the film when deformed (compared to “elastic” OPP films). Using a crosslinking agent is also recommended if the films to be laminated are thicker (e.g. 30 μm Forchheim films), because thicker films also expose the composite to higher tension forces.
Before curing, machines and equipment may be cleaned after use with warm or cold water, using Jowat® Cleaner Concentrate 192.40. Already dried adhesive can be dissolved using Jowat® Thinner 401.30. Please also observe the instructions in the corresponding technical data sheet and the safety data sheet.
Mixing Instructions for 2-C Adhesive System
For a manual mixing of the adhesive and the crosslinking agent, please follow the instructions below:
Fill the crosslinking agent Jowat® 195.70/79 into a feeding container which is used exclusively for Jowat® 195.70/79.
If the crosslinking agent is supplied in a 1.25 kg bottle, the cap has to be cut off.
Canisters or bottles which were opened and have been in use have to be re-closed at all times to prevent any reactions with humidity.
An ideal mixing amount would be 25 to 30 kg of the dispersion Jowacoll® 764.xx, so that it can be used up fast. Leftover amounts can be remixed with new batches, but should be reserved for operations which do not demand such high-quality surfaces.
The homogenisation is done with an electronically adjustable drill with rotor attachment.
Fill the mixing container with Jowacoll® 764.xx, preventing foam formation as far as possible. Any foaming is eliminated by atomiser. The sprayed liquid consists of a water/alcohol (ethanol) mixture. The mixing ratio is 10:1.
Start the mixer in the container filled with Jowacoll® 764.xx. Then add the crosslinking agent Jowat® 195.70/79 slowly and continuously at medium speed of the drill, approx. 1,000 rpm, over 90 seconds directly at the rotor and another 90 seconds, so that the crosslinker and adhesive may mix immediately and homogeneously.
Ensure that the mixing is done with the least possible foaming to prevent the formation of particles due to drying (crystallisation).
The following are to be prevented:
• too high stirring speeds, which allows too much air to be mixed in
• immersion of the rotor not deep enough, which leads to the same effect
Water-emulsifiable, aliphatic isocyanate crosslinking agents like Jowat® 195.70/79 also react with water and humidity. This causes side effects forming polyurea chains and possibly crystals that can cause particles. In order to keep this effect down as far as possible, the crosslinker must be incorporated as finely and homogenously as possible, and finished mixtures are to be processed as soon as possible. This reduces the risk of application failures like blade stripes later in the production process.