The base paper for paper cups is called "
cup board", and is made on special multi-ply
paper machines. It has a barrier coating for waterproofing. The paper needs high stiffness and strong
wet sizing. The cup board grade has a special design for the cup manufacturing processes. The mouth roll forming process requires good elongation properties of the board and the plastic coating. A well formed mouth roll provides stiffness and handling properties in the cup. The basis weights of the cup boards are 170–350 g/m2. To meet hygiene requirements, paper cups are generally manufactured from virgin (non-recycled) materials. The one exception to this is when the paper cup features an extra insulating layer for heat retention, which never comes into contact with the beverage, such as a corrugated layer wrapped around a single-wall cup.
Waterproofing Originally, paper cups for hot drinks were glued together and made waterproof by dropping a small amount of clay in the bottom of the cup, and then spinning at high speed so that clay would travel up the walls of the cup, making the paper water-resistant. However, this resulted in drinks smelling and tasting of cardboard. Cups for cold drinks could not be treated in the same way, as condensation forms on the outside, then soaks into the board, making the cup unstable. To remedy this, cup manufacturers developed the technique of spraying both the inside and outside of the cup with wax. Clay and wax-coated cups disappeared with the invention of
polyethylene (PE)-coated cups; this process covers the surface of the board with a very thin layer of PE, waterproofing the board and welding the seams together. In 2017, the Finnish board manufacturer Kotkamills launched a new kind of cup (food service) board which uses no wax or plastic for waterproofing, and thus can be recycled as part of the normal paper and board waste stream,
biodegraded, or even
composted in small quantities. In 2017, the Newport Beach, California, company Smart Planet Technologies, launched "reCUP" for the UK market, a recyclable paper cup using a polyethylene and mineral-blended coating branded EarthCoating, that is engineered to be recycled through traditional paper recycling systems. Paper cups with EarthCoating are sold by Detpak, Huhtamaki, Linstol, and Pureco USA. Paper cups and paper bags made from "Pinyapel", paper made from discarded pineapple leaves, were introduced in 2019. The water-resistant
food packaging alternative material was developed by a consortium made up of the Department of Trade and Industry Design Center of the Philippines (DCP), Cagayan de Oro Handmade Paper, Nature's Fresh, and Ideatechs Packaging Corporation. The innovation was a Wood Pencil Awardee in the 2019 edition of the annual D&AD Future Impact Awards. Tests by the DCP show that the 55.32 percent mass loss of Pinyapel in four weeks is much higher than the 21.33 percent mass loss in commercial paper bags, giving evidence that the material decomposes faster than other paper products.
Printing on paper cups Originally paper cups were printed using rubber blocks mounted on cylinders, with a different cylinder for each colour. Registration across different colours was very difficult, but later
flexography plates became available and with the use of mounting systems it became easier to register across the colours, allowing for more complex designs. Printing flexographic has become ideal for long runs and manufacturers generally use this method when producing over a million cups. Machines such as
Comexi are used for this, which have been adapted to take the extra large reels that are required by paper cup manufacturers. Ink technology has also changed and where
solvent-based inks were being used, water-based inks are instead being utilised. One of the side effects of solvent-based inks is that hot drink cups in particular can smell of solvent, whereas water-based inks have eliminated this problem. Other methods of printing have been used for short runs such as
offset printing, which can vary within a range from 10,000 to 100,000 cups. Offset printing inks have also been developed and although in the past these were solvent based, the latest
soya-based inks have reduced the danger of cups smelling. The latest development is
Direct-printing, which allows printing on very small quantities, typically from 1,000 cups, and is used by companies including Brendos Ltd offering small quantities in short lead times.
Rotogravure can also be used, but this is extremely expensive and is normally only utilised for items requiring extremely high quality printing like ice cream containers. ==Environmental impact==