Common quality issues in packaging bag printing and accurate design ideas

The world is full of complex and confusing things. Appearances often mask the essence of things, causing people to be constantly busy with anomalies and unable to change things fundamentally. For many manufacturing companies, frequent packaging quality problems have become a constraint that restricts the widespread circulation of products in the market. Today, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will explain common problems in gravure printing of flexible packaging with real pictures from three aspects: printing, lamination, and slitting, providing the most valuable reference for companies when designing packaging and encountering packaging quality problems.

 

 

I. Common Printing Problems

1. Misregistration

 

 

In the process of multicolor printing, the colors do not completely overlap and there is a certain deviation. If the deviation exceeds the standard (generally ≤0.2mm for the main picture, ≤0.35mm for the secondary picture), it becomes a defective product.

2. Doctor Blade Marks (Knife Lines)

 

 

Also known as ink knife marks, these refer to linear ink marks or blank lines appearing on the surface of the printed product. The lines vary in shape; some have ink, some do not, some are continuous, and some are intermittent.

Common causes: damaged doctor blade edge, impurities in the ink, poor plate polishing, etc.

3. Missing Print

 

 

The phenomenon of missing parts of the printed pattern or text.

Common causes: ink drying causing plate clogging; aging and hardening of the pressure roller rubber, insufficient elasticity; pits on the pressure roller, etc.

4. Ink Not Scraped Clean (Plate Smudging)

 

 

Because the ink on the non-image area of the printing plate is not scraped clean, it is transferred to the film during printing, resulting in large areas of contamination. This phenomenon is more likely to occur with black ink.

Common causes: insufficient doctor blade pressure; doctor blade wear; damage to the printing plate surface; ink viscosity is too high and difficult to scrape clean.

5. Ink Spatter

 

 

Ink droplets splashing onto the material during printing, contaminating the surface of the printed product, mostly occurring at the edges of the material.

This defect is usually caused by low ink viscosity, high speed, and inadequate protection at both ends of the printing plate.

6. Color Difference

 

 

Color difference between channels, rolls, and batches of the same product. Differences exceeding the upper and lower limits of the standard sample or national standard are considered unqualified.

7. Color Bite (Reverse Printing)

 

 

The ink of the previous color sticks to the printing plate of the next color during overprinting, and the color of the previous color can be clearly seen on the next color.

Reasons: insufficient drying of the previous color ink; excessive pressure of the pressure roller in the next color printing.

II. Common Lamination Problems

1. Bubbles

 

 

Refers to the appearance of bubbles inside the laminated film after curing.

Common causes: insufficient surface tension (corona treatment) of the substrate; insufficient pressure of the laminating roller causing air between the films not to be completely expelled, or low surface temperature of the laminating roller, insufficient activation of the adhesive; good barrier properties of both substrates (PET//VMPET, PET/AL), causing the gas generated by the reaction of the adhesive after curing to be unable to escape.

2. Tunnels

 

 

Refers to the strip-like hollow delamination phenomenon appearing in the laminated film after leaving the machine or curing.

Common causes: mismatch in tension between the two substrates; when the initial adhesive strength is lower than the stress of film deformation rebound, the substrate with larger deformation shrinks; failure to cure promptly after leaving the machine.

3. Wrinkles

 

 

Refers to the uneven surface of the film, folded together. Mostly appears in the core and surface of the film roll.

Common causes: uneven core tube; uneven joints; substrate misalignment during lamination; insufficient winding tension causing offset.

4. Delamination

 

 

Interlayer separation due to unqualified interlayer peel strength, mostly occurring during use (such as retort pouches after retorting).

Common causes for dry lamination or solvent-free lamination: insufficient adhesive application; insufficient corona treatment of the substrate; incomplete curing of the adhesive; improper use of adhesive type, etc.

III. Common Slitting Problems

1. Slitting Deviation

 

 

Slitting position deviation exceeds the standard range. This is manifested as: part of the pattern is cut off.

Common causes: inaccurate installation of the cutting knife; insufficient winding tension, causing lateral offset of the material roll.

2. Roll Skewing

 

 

Refers to the uneven end face caused by the film sliding to both sides during winding.

Common causes: insufficient winding tension; uneven tightness on both sides of the substrate; low coefficient of friction on the film surface.

3. Bulging

 

 

Refers to the protruding phenomenon appearing on the surface of the film roll.

Common causes: uneven thickness; excessive winding tension.

4. Daisy Petals

 

 

Refers to the phenomenon similar to "daisy petals" appearing in the center of the film roll end face.

Common causes: short paper tube length, causing the part of the film roll core that exceeds the two ends of the paper tube to have no support; excessive winding tension.

For designers, it is very important to accumulate knowledge related to printing and later processes and materials. New designers often ask me various questions related to this online. Therefore, a brief introduction to the early process flow of flexible packaging (national unified standard) is provided here.

Many newly employed designers are unaware of the specifics of soft plastic packaging. Some mistakenly believe that the machines used to print plastic bags and paper are the same, and they may not even know how to create print files for plastic bags. I sometimes encounter clients who are just starting out and want to print three to five thousand plastic bags, not realizing that the minimum order quantity for plastic bags is usually 6000 meters of film, and the number of commonly sized plastic bags is at least 30,000.

 

The plate length and width depend on the packaging's plate length and width.

 

Text information engraving on the printing substrate

 

 

 

 

The diameter and length of the cylinder (plate) vary because different printing plants use different printing machine models, requiring different plate sizes. Since each plate has a different size, the plate-making costs also vary, approximately 700-900 yuan per plate.

Generally, if a plastic package uses real photos, the photo portion will have four colors: red, yellow, blue, and black, requiring four plates. Other full-color single-color designs require one plate per color. When designing packaging, designers should try to keep the number of colors below nine, as most printing machines can only print nine colors. Of course, there are now printing machines that can print 12 colors. Files should be created in PS format. If designers send CDR or AI format files to the plate-making factory, the factory will need to convert them to PS files, adding unnecessary trouble.

Shunxingyuan Packaging will use the following example to illustrate the problems with design files. The following packaging was designed for a client and is an aluminum-plated back-sealed bag.

 

 

This is its unfolded diagram. When this PS file is sent to the plate-making factory, the factory will adjust and separate the colors. We don't need to worry about color separation; that's the plate-making factory's job. It's better to spend that energy improving creativity.

 

 

 

 

The document the plate-making factory gives to the client for signature looks like this. This packaging has four colors: black, gold, silver, and white.

HP Indigo electronic inks comply with the following regulations:

Article 3 of the EU Framework Regulation No. 1935/2004 concerning the printing of non-contact surfaces of commonly used polymer food packaging materials. Packaging printed using these materials can be used to store all types of food at temperatures up to 100℃.

EU Good Manufacturing Practices (GMP).

Swiss Ordinance on Food Contact Materials and Articles (RS 817.023.21).

The requirements of the U.S. Federal Food, Drug, and Cosmetic Act 21 U.S.C 201 (FFDCA) concerning the printing of non-contact surfaces of commonly used polymer food packaging materials. Packaging printed using these materials can be used to store all types of food at temperatures up to 100℃.

EUPIA Printing Ink Guidelines for non-food contact surfaces of food packaging materials and articles (November 2011 version).

All pigments used in the HP Indigo electronic ink formulation are listed in List 1 or List 2 of Technical Document 1 of the European Council Resolution (2005/2).

Migration and Smudging

Packaging components can migrate to the food inside the packaging in various ways.

Migration refers to the passage of substances through the packaging material to the food. The concentration unit of transfer ink is milligrams/square decimeter of packaging or milligrams/kilogram of food (packaging components).

Smudging occurs when the packaging is stacked or rolled up after printing. During this stage of the printing process, molecular substances may transfer from the printed side of the substrate to the food-contact side.

Migration Limits

The amount of migrating molecules that migrate from the packaging to the product inside the packaging depends on the initial concentration of the migrating molecules on the printed packaging, the migration rate, and the solubility of the migrating molecules in the packaging or food.

The overall migration limit (OML) is the maximum amount of all non-volatile substances allowed to migrate from the packaging to the product inside the packaging.

The maximum amount of a substance allowed to be released into food is called the specific migration limit (SML).

Testing and Evaluating Migration

HP Indigo has engaged renowned consultants at prominent European and American laboratories to conduct extensive testing, according to recognized standards, to assess whether HP Indigo electronic inks meet the food packaging regulations requirements in the table below.

These tests simulate the contact of the packaging with food under specific conditions. The test conditions are carefully selected to reflect possible conditions of use and to simulate more extreme conditions to ensure compliance with applicable regulations.

HP Indigo Meets US Regulatory Requirements

HP Indigo Electronic Inks Food Packaging and the US Food and Drug Administration (FDA)

Tests show that HP Indigo electronic inks (specifically Indigo cyan, magenta, yellow, black, white, orange, purple, and green inks) comply with the Federal Food, Drug, and Cosmetic Act (FFDCA) and all applicable food additive regulations and can be used for printing on the non-food contact side of the food contact layer of multilayer polymer food packaging.

The food contact layer can be made of one of the following materials:

1. Low-density polyethylene (LDPE) at least 40 microns thick

2. Polypropylene at least 20 microns thick

3. Polyester fiber at least 12 microns thick

4. Polycarbonate (Lexan) at least 20 microns thick

Packaging printed using these materials can be used to store all types of food at temperatures up to 100℃ (also known as FDA Use Condition B "boiling water sterilization", 21CFR176.170). These conclusions are based on the ink formulation, expected conditions of use, results of evaluations in FDA-approved laboratories, and the advice and opinions of independent consultants.