Paper Carrier Bag Production Explained: Bag Types, Hot-Melt Construction and Design Specifications

Gluing a paper carrier bag together is an ancient handicraft. Yet in post-press finishing, most printers can speak knowledgeably about bookbinding or about carton creasing and gluing — ask them how a paper carrier bag is actually built, and the answer is often far less certain. Paper carrier bags split broadly into two families: ordinary packaging bags and premium shopping bags. Ordinary packaging bags come off a rotary printing bag-making machine in one continuous run. Their strength is output speed; their weakness is a coarse, unrefined finish — which is why they mostly wrap ordinary, everyday merchandise.

Premium shopping bags take a very different route. Sheets are colour printed, then given PP lamination or hot stamping; the bag factory then shapes them by hand or on semi-automatic machines, and the handles are finally threaded and knotted manually before the paper bag is finished. The advantage: any bag format can be produced. The disadvantage: production is slow. Bags like these are mainly used for high-end product packaging, as gift bags, or as advertising bags for every kind of commercial activity — and these refined, attractive paper bags have ended up as the convenient carry-all shoppers reach for on a day out. What characteristics should a shopping bag have?

Eco-friendly and attractive, refined and durable

A shopping bag should first of all be an extension of corporate image and product advertising strategy, so making one means paying attention to eco-friendliness and good looks, refinement and durability. Tight construction that will not drop its bottom or loosen its handle: hot-melt adhesive, run on a fully automatic bag-making machine, bonds each part of the shopping bag into a tightly integrated structure, so the base and the handle will never come away — unlike conventional post-press processing of paper carrier bags, where “white glue” pastes the bag body and the handles are hand-threaded and knotted, a method that regularly fails with dropped bottoms and loose handles. Crease-free surfaces and accurate, attractive bonding: because the shopping bag is made on a fully automatic bag-making machine, its surface carries no creases, and hot-melt adhesive grips strongly and dries fast, so the bonds come out accurate and clean. Conventional bag processing folds and pastes by hand, leaving fold lines on the surface; white glue also dries slowly and, if over-applied, squeezes out and slides, so the bag shape suffers.

Upright cotton-rope handles — no punched holes, no knots

Two sheets of heavy-duty kraft paper hold the cotton rope with hot-melt adhesive, and the kraft is then bonded to the paper bag, so the handle is “upright” and needs neither a punched hole nor a protruding knot. On conventional handmade paper bags the body is punched first and a nylon rope is threaded through and knotted by hand, with the knot catching against the bag — so under load the knot works loose, or the rope hole tears open. Strengthening the overall structure to boost packaging performance: handle, kraft board, paper bag and base are integrally formed with hot-melt adhesive, which reinforces the bag’s whole structure so it can carry items of more than 5 kilograms. On conventionally made bags, the handle relies on a nylon knot caught against the body and the top flap is never bonded to the body, so the load-bearing capacity is weaker.

Design specifications and manufacturing principles for shopping bags: the top edge of the paper bag is always folded inward by 60 mm to reinforce the anchoring of the handle. The base edge of the paper bag is 15 mm wide to strengthen the load-bearing capacity of the bag bottom (the edge width is reduced by 15 mm).

The glued edge of the paper bag is always 30 mm and has to sit on the right side — that is the only way the bag can be glued automatically.

Final artwork for a shopping bag should include folding marks — 2 glued-edge lines, 6 top-edge lines and 6 bottom-edge lines — so the bag forms correctly. Manufacturing dimensions must match the paper’s cutting layout to stay economical. Paper grain direction has to run parallel to the “height” of the bag so the paper folds properly.

Bag-making specifications — paper bag length: 180–350 mm.

Paper bag width: 60–160 mm.

Paper bag height: 270–450 mm.

Paper thickness: around 100–150 lb.

Handle choice: paper rope or cotton rope.

Type S / full-paper quarto bag

Size — 18 cm long × 7 cm wide × 27 cm high.

Paper used — 15″ × 21″.

Grain direction — parallel 31 × 43.

Type M / chrysanthemum-paper folio bag

Size — 22 cm long × 8 cm wide × 30 cm high.

Paper used — 17″ × 25″.

Grain direction — parallel 31 × 43.

Type L / full-paper folio bag

Size — 27 cm long × 10 cm wide × 38 cm high.

Paper used — 21″ × 31″.

Grain direction — parallel 43 × 31.

Type X / chrysanthemum-paper full-sheet bag

Size — 32 cm long × 10 cm wide × 45 cm high.

Paper used — 25″ × 35″.

Grain direction — parallel 25 × 35.

Type T / full-paper third-sheet bag

Size — 24 cm long × 10 cm wide × 24 cm high.

Paper used — 15″ × 28″.

Grain direction — parallel 31 × 43.

Kraft paper — tough in texture, and distinguished by colour as white kraft, yellow kraft, two-tone kraft and other types; by paper quality it further divides into pure kraft and coated kraft. Kraft paper of 80–120 lb is basically suitable for making every kind of shopping bag. Coated paper — suited to high-quality colour printing, which is why art shopping bags are usually made from 120–150 lb coated stock; coated paper has lower toughness, so PP film glazing is normally applied to reinforce it. Art paper — a loose term used to describe paper that has been processed and dyed; it is generally tougher than coated paper and comes in far greater variety, and many 100–150 lb art papers are quite suitable for shopping bags, though the paper cost is higher. Specialty paper — for example Nanya synthetic paper, 3M Tyvek, PP imitation kraft paper, and so on.

— Reprinted from China Packaging Network (pack.cn); original link: http://news.pack.cn/show-362278.html