10 декабря, 2015 
Pokraskin Envelopes are manufactured from a wide variety of materials, and in many types and sizes. Not surprisingly, in the manufacture of envelopes production speeds have been ever-increasing, with today’s state of the art reaching 1500 units per minute (Figure 8.43).
Although plastic films are used, paper is still the most important raw material for the production of envelopes. The side joints of envelopes made from paper are commonly bonded with plasticized polyvinyl acetate homopolymer-based adhesives, whereas both plasticized polyvinyl acetate homopolymer or EVA copolymer-based adhesives are used for the bonding of windows made from glassine or transparent polystyrene foils. A special feature of the typical envelope is another adhesive application which is used only by the consumer for the purpose of closing the envelope — the water-reactivated gummed flap. These widely known products are manufactured by applying dextrin-based, dextrin/synthetic resin-based or synthetic resin-based adhesives and force-drying them before packing. A number of requirements must be fulfilled: the consumer wants the gum to be quickly reactivated with water, while the producer wants it to dry quickly and to have anti-blocking properties to prevent premature bonding. The humidity in the air must not reactivate the gum in
|
Figure 8.43 The production of window envelopes. |
such a way that bonding takes place. Envelopes can also be closed by means of latex or PSA coatings. Latex is rubber milk which originates from the Hevea tree; latex closures require a coating to be placed on both sides of the envelope, with bonding taking place when the two sides are pressed against; at this point a diffusion bonding process occurs between both sides. Currently, PSA-coated envelopes are capturing the market, most likely because the PSA film has simply to be pressed onto the paper surface to close the envelope. PSA coatings must be covered with siliconized papers or plastic foil to prevent premature bonding, and are commonly made from acrylate dispersions. Occasionally, acrylate hot melts or thermoplastic rubbers, mixed with resins or oils according to the desired application, are used.
The production of advertising mail is one of the most thriving and prospering sectors of the paper industry. Advertising mail is a short-lived, printed product that frequently contains PSA labels or other adhesive applications, for example for laminating purposes (to reach the thickness required by postcards), or for the resealing (gumming or PSA) of envelopes contained in the advertising mail.
Опубликовано в рубрике 