Causes, Effects, and Solutions
Corrugated boxes and sheets are the backbone of global packaging. From e-commerce shipping to food and industrial goods, corrugated packaging ensures safe storage, stacking strength, and ease of handling. However, one of the most common quality issues in this industry is cracking.
Cracking may occur on the surface liner of corrugated sheets, along folds and creases, or on the finished corrugated boxes during conversion and usage. These cracks compromise not only the aesthetic appeal but also the structural strength and durability of packaging. For manufacturers, cracking leads to waste, customer complaints, rejections, and financial loss.
In this blog, we will explore why cracking happens in corrugated boxes and sheets, its impact on packaging performance, and the best practices to prevent it.
Understanding Corrugated Sheets and Boxes:
Corrugated packaging is made from a combination of linerboards (flat paper) and fluting (wavy paper sandwiched between liners). Together, they provide strength, cushioning, and versatility.
During manufacturing and conversion, corrugated board undergoes:
Corrugation – fluting medium is shaped.
Lamination – liners are glued to fluting.
Die-cutting and creasing – board is cut into box blanks.
Folding and gluing – blanks are converted into boxes.
Cracking typically occurs at folding, creasing, or printing stages when the paper’s surface fibers are stressed beyond their flexibility.
What is Cracking in Corrugated Packaging?
Cracking refers to the visible breakage or tearing of surface fibers (usually the outer linerboard) during:
- Folding or creasing of sheets.
- Printing or varnishing processes.
- Handling during converting machines.
- Box assembly under stress.
Forms of cracking include:
- Surface liner cracking: visible splits in the outer paper surface.
- Crease cracking: along fold lines of the box.
- Edge cracking: at cut or perforated areas.
Even small cracks can:
- Expose inner fibers, weakening box integrity.
- Reduce print quality and aesthetics.
- Allow moisture penetration, reducing durability.
Causes of Cracking in Corrugated Boxes and Sheets:
1. Paper Quality Issues
Low fiber flexibility: Recycled fibers are stiffer and less elastic than virgin fibers.
High GSM (grammage) liners: Thick papers tend to crack more on folds.
Low bursting strength: Weak papers cannot withstand folding stress.
Coated or laminated liners: Hard coatings restrict fiber bending, causing cracks.
2. Moisture Content
Too low moisture: Paper becomes brittle, leading to cracking during creasing.
Too high moisture: Weakens bonding, though cracking risk decreases.
Poor moisture control in storage: Seasonal changes in humidity directly affect performance.
3. Improper Creasing and Folding
Incorrect creasing depth or profile damages fibers instead of helping folds.
Excessive pressure during creasing causes cracks at fold lines.
Poorly aligned folding machines create uneven stress.
4. Corrugator Machine Parameters
Incorrect heat and pressure during corrugation reduce paper flexibility.
Uneven glue application causes weak spots.
High production speed increases stress on paper surfaces.
5. Printing & Coating Processes
UV and water-based inks may dry the liner surface excessively.
Varnishes and laminates add rigidity, reducing foldability.
Over-drying in IR or hot-air systems makes the paper brittle.
6. Design-Related Issues
Sharp folds or tight box designs force extreme bending.
Narrow flutes (like E or F flute) increase surface cracking risk compared to B or C flutes.
Impact of Cracking on Packaging Performance
Corrugated packaging is made from a combination of linerboards (flat paper) and fluting (wavy paper sandwiched between liners). Together, they provide strength, cushioning, and versatility.
During manufacturing and conversion, corrugated board undergoes:
Corrugation – fluting medium is shaped.
Lamination – liners are glued to fluting.
Die-cutting and creasing – board is cut into box blanks.
Folding and gluing – blanks are converted into boxes.
Cracking typically occurs at folding, creasing, or printing stages when the paper’s surface fibers are stressed beyond their flexibility.
How to Prevent Cracking in Corrugated Packaging:
1. Optimize Paper Selection
2. Control Moisture Content
3. Improve Creasing & Folding Techniques
Use correct creasing matrix and die profiles.
Calibrate folding machines to avoid excessive pressure.
Regularly maintain rollers and dies for smooth operation.
4. Corrugator Machine Settings
5. Printing & Coating Adjustments
6. Packaging Design Considerations
7. Environmental & Storage Controls
Case Studies:
Case 1: Export Fruit Packaging
A corrugated box manufacturer in Spain faced liner cracking during winter. Investigation revealed moisture content had dropped below 6%. Solution: Humidifiers were installed in the plant, maintaining paper moisture at 9–10%, reducing cracking by 70%.
Case 2: FMCG Printed Cartons
An Indian manufacturer producing printed corrugated boxes for FMCG brands experienced cracking along creases. Cause: Over-drying during IR curing of water-based inks. Solution: Reduced IR intensity and introduced moisture conditioning. Rejections dropped significantly.
Case 3: Heavy-Duty Industrial Boxes
A German producer of triple-wall corrugated boxes observed frequent cracking at fold lines. Switching from recycled-only liners to a blend of virgin kraft improved flexibility, eliminating cracks while maintaining strength.
Case Studies:
Case 1: Export Fruit Packaging
A corrugated box manufacturer in Spain faced liner cracking during winter. Investigation revealed moisture content had dropped below 6%. Solution: Humidifiers were installed in the plant, maintaining paper moisture at 9–10%, reducing cracking by 70%.
Case 2: FMCG Printed Cartons
An Indian manufacturer producing printed corrugated boxes for FMCG brands experienced cracking along creases. Cause: Over-drying during IR curing of water-based inks. Solution: Reduced IR intensity and introduced moisture conditioning. Rejections dropped significantly.
Case 3: Heavy-Duty Industrial Boxes
A German producer of triple-wall corrugated boxes observed frequent cracking at fold lines. Switching from recycled-only liners to a blend of virgin kraft improved flexibility, eliminating cracks while maintaining strength.
Frequently Asked Questions (FAQs)
Q1: Why do corrugated sheets crack during folding?
Because surface liners lose flexibility due to low moisture, poor creasing profiles, or excessive pressure.
Q2: How can cracking be avoided?
Q3: Does flute type affect cracking?
Q4: Can coatings prevent cracking?
Q5: What is the ideal paper moisture for corrugated boxes?
Typically 8–12% for balanced flexibility and strength.
Conclusion:
Cracking in corrugated boxes and sheets is a serious issue that affects performance, aesthetics, and customer satisfaction. The causes range from poor paper quality and moisture imbalance to improper machine settings and harsh environmental conditions.
By optimizing raw materials, controlling moisture, improving creasing and folding processes, and using innovative technologies, manufacturers can drastically reduce cracking issues.
