Industry News

Paper bags can be found everywhere in our daily life. Whether it is cookie bags, sandwich bags, candy bags in the food industry, gift bags, luxury paper bags in the retail industry, or sterilization pouches, paper pill bags in the healthcare industry, all of them can not be separated from the manufacturer's persistent pursuit of quality and the careful polishing of details. So, what are the processes of making an exquisite packaging paper bag? This article will introduce 5 production processes: raw materials selection, flexographic printing, forming, surface treatment, quality control and packaging.

CI Type Flexo Printing Machine for Kraft Paper Bags

Raw Materials Selection

The different uses and designs of paper bags determine their different raw materials. Common raw materials for paper bags are wood pulp paper, straw pulp paper, recycled paper, kraft paper and so on.

Wood Pulp Paper

Wood pulp fiber is longer and has a strong interweaving effect on each other. Therefore, wood pulp paper is able to withstand greater weight and tension. It is very suitable for the production of paper bags with large weight, such as shopping bags, food storage packaging bags, flower bags, etc..

Straw Pulp Paper

Straw pulp paper is made of straw, wheat straw and other grass plants, which is not as strong as wood pulp paper, but the cost is lower. It is more suitable for making bags for some lightweight goods, such as paper document envelope.

Stacking Flexographic Printing Machine for Nuts Snack Chips Pouches

Recycled Paper

Recycled paper is a kind of paper which is made by recycling, processing and remanufacturing of waste paper. It has the advantages of environmental protection and resource saving, and is widely used in some occasions with high requirements for environmental protection, such as reusable shopping bags and courier bags.

Kraft Paper

Kraft paper is tough and strong. Its good waterproof and tear resistance makes it very suitable for making bread bags, chocolate chip cookie bags, hamburger bags, fried chicken paper bags and so on. It protects the food from moisture and prevents the paper bag from being torn in the process of carrying.

Stacked Type Flexo Printing Machinery for Luxury Paper Bags

Flexographic Printing

Flexographic printing is mainly divided into four processes: design and plate making, printing preparation, printing, and drying and curing.

Design and Plate Making

According to the customer's needs, design the information, branding and marketing promotions on the paper bag and make the printing plate for flexo press. Choosing the appropriate thickness and hardness of the plate according to the printing requirements and the characteristics of the flexographic press. At the same time, attention should be paid to the characteristics of flexo printing such as dot gain and screen count.

Printing Preparation

Installing the prepared printing plate on the plate roller of the flexographic printer and paying attention to precise alignment. Each color requires a separate printing plate. Flexography machine mostly use water-based inks or alcohol-soluble inks, which are environmentally friendly and suitable for paper bag printing.

Plate Roller of Central Impression Flexo Printer for Popcorn Paper Bag

Printing

The ink transfer roller pick up ink and pass ink to the anilox roller. The doctor blade removes the excess ink from the smooth non-engraved portions of the anilox roll and the land areas of the cell walls. Anilox roller even spread ink in the surface of the plate roller. Printing roller and plate roller press paper bag and transfer ink to the surface of paper bag.

Printing Unit of Tower Type Flexographic Machine for Perfume Paper Bag

Drying and Curing

After being printed by flexographic printing equipment, paper bags need to go through a drying or curing process to fix the ink. Common drying methods in flexographic printing press include hot air drying, infrared drying, ultraviolet curing, LED UV curing, hot air and infrared combined drying, etc. Manufacturers of takeout paper bag, coffee bean paper bag, dog food paper bag, dental use sterilization pouch, Christmas gift paper bag, fertilizer paper bag, etc. can select according to the material properties of the paper bag substrate and the ink properties.

Drying System of Stacked-Unit Flexo Paper Bag Printing Machine

Forming

Paper bag forming includes cutting, folding and gluing, making handles, die-cutting and other processes.

Cutting

Cut the printed paper according to the size of the paper bag to get the right paper.

Folding and Gluing

Folding: Fold the paper into the shape of a paper bag by machine or by hand.

Gluing: Use glue or heat seal to firmly paste the sides and bottom of the paper bag.

Making Handles

The handles can be made of paper, rope, ribbon, etc., and fixed to the paper bag by pasting, sewing or punching.

Die-Cutting

The die-cutting process is to combine the die-cutting knife and the creasing knife on the same template, and use the die-cutting machine to die-cut and creasing the printed product.

Surface Treatment

Common surface treatment processes include lamination, coating, hot stamping, varnish, etc.

Lamination

Lamination is used to enhance the waterproof, abrasion resistance and glossiness of paper bags by covering the surface of the bag with a layer of transparent plastic film (e.g. PP, PET, etc.).

Lamination Unit of Flexible Printing Machine

Coating

Coating is the process of coating the surface of a paper bag with a liquid functional material, which is dried and cured to form a thin film that gives the paper a specific function. Common types of coating are acrylic coating (for moisture-proof paper bag, such as baking food paper bags, dried cranberries paper bags), PU coating (wear-resistant, flexible, suitable for supermarket shopping bags that need to be used repeatedly), PVDF coating (anti-oil and anti-dirt, used for the inner layer of the fast-food paper bag) and so on.

Hot Stamping

Hot stamping is to transfer metal foil (e.g. aluminum foil) to the surface of paper bag through high temperature and pressure to form metallic luster pattern or text. It can significantly enhance the grade and aesthetics of the paper bag, which is commonly used in jewelry paper bag, cosmetic paper bag and so on.

Hot Stamping Unit of Flexo Graphic Printing Machine

Varnishing

Varnishing is to apply a layer of varnish on the surface of paper bags to increase the gloss and texture of tea and sugar paper bag, T-shirt clothes and shoes paper bag, advertising paper bag, etc. It also plays a certain protective role. It enhances the abrasion resistance and water resistance of the paper bags and is suitable for paper bags that need to be visually enhanced.

Quality Control and Packaging

The factory should carry out a comprehensive quality inspection on the made paper bags to ensure that the appearance, size, printing pattern, printing quality, adhesive firmness, sealing effect and other aspects of the paper bags meet the customer's requirements. After passing the quality inspection, the qualified paper bags will be packaged. Paper bags are generally packaged in cartons or plastic film for easy transportation and storage.

Medical instrument sterile pouches, agriculture feed food paper bags, pet food paper bags and other paper bag products not only carry items, but also convey the value and warmth of the brand. From the strict selection of raw material to the precise control of flexographic printing; from the ingenious design of forming process to the exquisite finishing of surface treatment; and then to the rigorous quality control and proper handling of packaging, each step is indispensable, which jointly creates the practicality and aesthetics of the paper bag.