Facts & Terms Explained

One way degassing valves for Coffee Bags

Roasted Coffee releases CO2 which means that over time the pressure inside the coffee bag increases “blowing the bag up like a balloon”. To solve this situation one way degassing valves (pictured above) were created. The valves are made of PET. These valves let the CO2 escape without allowing air to re-enter the bag, resulting in a fresher bag of coffee. When the pressure reaches 0.1375psi (9.5 millibar) the valve will release the air from bag automatically until the pressure decreases to 0.0375psi(2.6millibar). Degassing valves are a coffee industry standard and are highly recommended by our Coffee Bags Team. We only provide the best quality valves from Switzerland and Italy.

AL is an abbreviation for aluminium and is used as a light and oxygen barrier in 3 ply materials, due to its excellent insulation against oxygen and light.

PE is an abbreviation for polyethylene. PE is used as a bonding agent in wet lamination.

PP is an abbreviation for polypropylene.

PET is an abbreviation for Polyethylene terephthelate and is a form of polyester often used as the outer substrate on laminates, due to its excellent tear strength, elongation properties and competitive price. Images and artwork are usually printed on the reverse side.

OPP is an abbreviation for oriented polypropylene. OPP is used as a substitute for PET due to being highly price competitive. OPP can also have a matt finish. This laminate substrate can wrinkle easier when heat sealed compared with other products.

VMPET means metalized PET. This material consists of PET which has been metalized with aluminium. It serves as a light and oxygen barrier, and is often used instead of aluminium. It has a slightly smoother appearance than aluminium, however it is slightly less efficient as a light/oxygen barrier. It is however cheaper and more environmentally friendly.

LLDPE Linear low-density polyethylene. A strong, clear or white film ideal for packaging of foods. It is heat sealable, has excellent puncture and tear resistance, and has a high degree of stiffness. It’s used as the inner layer in all laminates and meets FDA regulations.

Vinyl (Polyvinyl chloride), or PVC. This strong clear material is used as the outer substrate on some coffee bags. It presents well, has excellent elongation and tear strength properties, and is used on coffee bags, where appearance is more important than price.

Natural Kraft is a durable and strong form of paper that can be used as the outer substrate on bags and pouches. It gives a more natural feeling to the bag. Natural Kraft can be printed in up to 8 colours.

Laminate is a composite material made of 2 or more dissimilar substrates such as PET and AL bonded together. Laminate for coffee bags and roll stock can be 2-ply or 3-ply, with the outer layer being Natural Kraft, PET, vinyl or MOPP. The optional central barrier substrate can be AL or VMPET, and the inner substrate is usually LLDPE. The generic term for laminate is web.

Laminate production process - after the artwork has been approved, the production process starts with the manufacture of the print cylinders/drums. Once a proof has been produced (extra charges & time delays may occur, depending on what proof is required eg. digital, paper or top layer), the production begins with the image being reverse printed in up to 8 colours on the outer PET substrate. The next step is the lamination, where the substrates or layers are bonded together. After this the laminate is wound, cut, and packaged.

Lamination is a process by which a sandwich of film layers is bound together by adhesives, coatings, or other polymers to form substrates with improved physical and chemical properties. There are two types of lamination processes – dry lamination and wet lamination.

2-ply laminate typically consists of an outer layer of PET or vinyl and an inner layer of LLDPE (linear low-density polyethylene). The LLDPE can be white, in which case the laminate will appear opaque. The LLDPE can also be clear, in which case the laminate will be clear. 2-ply laminate will often have a better look than traditional 3-ply laminate, however the shelf life of coffee products packed in 2 layer laminate will be shorter, as the contents are less shielded against light and oxygen.  

3-ply laminate is a 3-layer laminate, where the middle layer can be AL,  or VMPET. 3-ply laminates protect the bags contents against oxygen and light better than 2 ply laminates.

Dry lamination is a solvent based adhesive lamination process offering the best bond strength. Dry laminate cuts slightly easier than wet laminate, but is less cost effective.

Wet  lamination offers a cost effective alternative to dry lamination and is used when the product does not require the strongest bond strength. The bonding liquid used by our manufacturers is a PE resin.

Pre-made bags are bags already formed at the factory. This is as opposed to roll stock.

Reverse Gravure Printing - this is the transfer of ink from an etched cylinder (normally steel or copper print drums) to the substrate, eg. paper/film/foil. The colors are printed onto the substrate one color at the time. The image is printed onto the reverse side (inner) of the outer substrate. The equipment is a multi-station (up to nine) printing machine to print and/or coat up to eight colours on to a fast-moving web of material. All types of coffee bags and laminates except for aluminum foil and gold foil are printed. Print drums are re-usable and one print drum is required per colour.

Custom print - The reverse gravure printing of logos, descriptions and pictures on bags, pouches, roll stock, or laminate according to designs submitted by the customer.

Substrate - The generic term for the layers that the laminate is composed of. A wide range of materials can be used, such as AL, LLDPE, PE, PET, VMPET, Natural Kraft, Vinyl and MOPP. The choice of material depends on the use of the bag/ pouch.

Retort - The process of cooking food in the package that it is sold in eg. baby food or soups that have meat or vegetables that need to cook at a temperature to kill off the micro-organisms and to avoid botulism. The temperature is generally around 121º C

Retort Pouch - the bag / pouch created to store a food product that will be heated before the food product is consumed

Die lines. Die lines measure the form / shape / outline of the item being made, and is an aid in the artwork design phase for roll (or flat) stock items

Pouch lines are similar to die lines and measure the form / shape / outline of the pouch instead of a flat bag / pouch

Roll Stock is bag /pouch material supplied in a flat form and on a roll.

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