Wet Bond Lamination or Dry Bond Lamination- Which is Right for Your Machinery Parts?
Several lamination processes are available on the market for different industries and various products, all of them having different specifications. A commonly used lamination process is called web laminating. Web laminating is mostly dictated by the way the substrate will be used after lamination occurs. It is commonly used in the food industry for their packaging and also the tech world for products like solar energy panels, devices, and insulation panel sectors. The machinery industry also uses a laminating to offer protection and enhancement to industrial products and is integral to numerous types of parts, components, and materials used in industrial manufacturing, production, as well as other industries. Laminating machinery is a complex process and takes two or more flexible packaging webs by joining them together with a bonding agent. The substrates that make up the webs may consist of films, papers, or aluminum foils. Usually an adhesive is applied to a less absorbent substrate web, and then the second web is pressed next to it producing a two-layer laminate. The biggest benefits to laminating machinery parts, components and materials are that it will make the specific piece:
- More durable
- Longer lasting
- More rigid (or flexible)
- Enhanced aesthetically
Depending on the piece that needs laminating, you may have to choose between wet bond, dry bond, solvent-less, or waxy lamination for your machinery parts. Different processes cater to specific industries and even parts, but the central concept remains the same—bonding. Of equal importance to the bonding is the resistance of the created structures ability to attack chemicals in the product to be packaged and adhesives now being modified to provide barrier qualities. All lamination systems will use a lamination nip to combine the webs under controlled pressure (or have a controlled gap between them) and typically use two rolls to press. The rolls are generally two different surfaces, one being a hard surface (e.g.: chrome plated steel) and the other a resilient surface like rubber. The reason behind having two different surfaces is because it allows the rolls to be pressed together to generate the necessary force to combine the webs without damaging the surface of the rolls. Factors like the pressure of the rolls will affect which techniques and the laminating system will be used because each bonding type has unique requirements. Wet and dry bond lamination are two of the most widely used options for machinery part lamination, so we are focusing on the different features that set them apart.
WET BOND LAMINATION
Wet lamination refers to when the bonding agent is a liquid adhesive and then combined with a second ply to create the laminate. Once the wet bonding process is applied to each substrate, the two substrates will be immediately combined prior to going through the oven drying process which will adhere the two substrates together. Waterborne adhesives such as casein or sodium silicate helped provide the process with the name “wet” laminating since drying occurs after the combining of the substrates. And although not wet, solvent-free or 100% solids adhesives will still combine right after the adhesive application when used in this lamination process.
This process generally results in a flexible packaging and is mainly used when one of the substrates is porous, such as paper. For example, you might use wet bond laminating with a light gauge aluminum foil to a tissue paper, either using an adhesive like casein or sodium silicate or using a low-pressure unheated lamination nip. In the case of a solvent-borne adhesive, one of the webs must be permeable to the solvent vapor. Once the webs are combined, it is important that they are dried (if using a water or solvent based adhesive), cured/cross-linked (if using a 100% solid curable or cross-linked coating), or cooled (if using thermoplastic adhesives) immediately because the adhesive won’t develop full holding strength to the webs until that happens.
Wet-bond lamination takes a short time, with a low to medium heat temperature and the lamination tip either running at a low to medium pressure requirement and/or with a gap between the rolls. The pressure specification is a critical requirement because the adhesive between the layers of the web is still in liquid form, so too much pressure can result in the adhesive being squeezed into the porous web or out from between the webs. This would ultimately result in a poor bonding of the layers.
DRY BOND LAMINATION
Contrary to wet bond lamination, dry bond is used to laminate two substrates which are either non-porous or impervious to filtration. Also differing from wet bond laminating, the adhesive used to combine the two substrates will first be applied to either one of the substrates and then put into the drying oven to evaporate the carrier solvent. Then after that process, the adhesive coated web is laminated to the second substrate under strong pressure using heated rollers to improve the bond strength of the laminate. Due to the water or solvent being removed prior to lamination, neither of the webs needs to be porous like with the wet lamination process. An example of when to use the dry bond lamination would be with using film on film or film on foil. The adhesives used to combine the two substrates together will be applied first to one of the substrates, dried in the oven and then combined with the second substrate. Afterward, the two substrates will be combined for maximum efficiency of the dry bond lamination process.
Since the adhesive is already solidified prior to lamination, dry bond lamination uses a medium to high heat temperature and medium to high-pressure requirement. In dry bond lamination, the steel roll used in the laminating nip is typically heated either with internal electric heating or by passing a heating fluid such as steam, water or oil through the roll to combine the webs. Occasionally two steel or two rubber rolls will be used for the lamination tip in dry bond lamination if two thick webs both require preheating or if you are laminating a film to a thick steel or aluminum web, in which case two rubber rolls would be used. Ultimately, dry bond lamination can be used to bond film to film, foil or paper.
WHICH LAMINATION PROCESS IS RIGHT FOR YOUR PART?
Only certain types of industrial products should be put through wet and dry bond lamination. Ultimately your pieces physical properties and material characteristics will determine with lamination system you should use. The type of lamination system that you use to combine your webs will depend on several factors including:
- Pieces physical properties and material characteristics pre-lamination
- The adhesive being used to join the webs
- Desired properties of the final product
When deciding on a partner in lamination, it is important to keep several factors in mind relating to design considerations for your project to ensure proper lamination. These include:
- The machines laminating rolls alignment to each other and the balance of the machine
- Web handling in and out of the laminating section, including proper tension control, especially with wet bond lamination where the bond strength between the layers has not yet formed and can be damaged by incorrect tension.
- Driving the rolls at the laminating nip (how to drive and how to control the drives)
With so many different techniques and technologies available today, it is important to have a lamination expert like Jessup Manufacturing analyze your project and then help you review the available types of lamination processes you can choose from to enhance or improve your products.