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If you’re a manufacturer of Corrugated Paperboard, warp as a concept wouldn’t be something you’d be unfamiliar with. Elimination of warp can at times be slightly tricky. This article will give an insight into the causes of warp and possible solutions to eliminate it.

Corrugated Paperboard becomes bent or is twisted out of shape, typically as an aftereffect of improper heat or moisture levels which eventually causes huge losses to businesses. Warp is one of the very common manufacturing issues faced by manufacturers worldwide which leads to excessive scrap generation, something that definitely is very unappealing.

Here’s a list of causes that can lead to warp with solutions that can help in eliminating it.

PROBLEMS THAT ARISE DUE TO INSUFFICIENT HEATING ON MACHINE ROLLS

  • Low Heat on Pre-heater Rolls: Excessive moisture on the paper needs to be eliminated to avoid warp. If the preheating rolls do not function effectively, moisture from the kraft paper cannot be eliminated which can lead to warp.

Solution: Install a pre-heater roll and check if it is functioning properly. It is inevitable to have them functional in places with high humidity levels. Modern machines mostly have pre-heaters installed. So this will be a problem that arises if you have older machines.

  • Low Heat on Pressure and / or Fluting Rolls: Improper heat on the fluting rolls not only affects the flutes of the paperboard but can lead to warp. With low heat on the rolls, the adhesive may not gelatinize properly which can lead to delamination and at the same time excess moisture due to non-gelatinization can lead to warp.

Solution: Maintain at least 180o C – 200o C on the rolls to ensure proper gelatinization. In-case of non-gelatinization, machine speed should be reduced to ensure that paper and glue get more heat. To eliminate warp, machine speed and temperature settings have to be adjusted accordingly to ensure that it gets just enough heat to gelatinize.

MOISTURE RELATED PROBLEMS DUE TO THE ADHESIVE WHICH IS USED

  • Application of excessive adhesive: More adhesive means more moisture, which can cause the problem of warp to arise.

Solution: Adhesive should be consistently applied only to the flute tips. Reduce the glue setting on the machine to apply only the needed amount of adhesive to bind the different layers of paper together. If more adhesive is applied, not only the cost of manufacturing increases, but it can also cause warp.

  • High Gel temperature of adhesive: If the gel temperature of the adhesive used is too high, the adhesive may fail to gelatinize leading to delamination and warp.

Solution: Reduce the machine speed to ensure more heat to the slow drying adhesive or use a fast drying adhesive with low gel temperature.

  • Low viscosity of the adhesive: More water in adhesive means more dampness, which can lead to warp.

Solution: The adhesive should have appropriate solid contents to ensure proper bonding and the viscosity should be adjusted according to the paper used.

MOISTURE RELATED PROBLEMS DUE TO THE PAPER WHICH IS USED

  • High Moisture level in paper: If the paper used has more moisture content, it can lead to warp.

Solution: Install pre-heaters to eliminate moisture from the paper.

  • Absorption of Moisture by paperboard after manufacturing: This particularly is a problem faced in areas with high humidity. Paper being hygroscopic in nature can regain moisture during storage or transit.

Solution:

Two alternatives that can help in eliminating warp are enumerated below.

  1. One possible solution could be to change the top paper to reduce the surface area from which moisture can get absorbed. This alternative can be slightly costlier.
  2. Another possible solution, which is also cost effective and easy to be implemented is the use of low-alkaline and non-alkaline adhesive in the manufacturing process. Kraft Paper attracts moisture from the atmosphere. Similarly, highly alkaline adhesive with higher pH values also attract moisture from the atmosphere. This traditional combination of highly alkaline adhesive with kraft paper causes moisture problems. Low-alkaline and non-alkaline adhesive can help in resisting absorption of atmospheric moisture. Pre-mix Moisture resistant adhesives are available, which can save the hassles of storing and adding different chemicals.

TENSION DUE TO MISALIGNMENT OF MACHINE ROLLS AND COMPONENTS

To avoid paper stresses, tension stresses and wrinkles on the paper

  1. Ensure bearings and rolls are freely moving to avoid tension stress.
  2. Ensure that all bearings and rolls are adjusted to effectively pull the paper without creating any wrinkles or folds or paper stresses.
  3. Ensure all components and rolls are adjusted to function parallel

Warp has always been one of the common problems faced by corrugated carton manufacturers worldwide. Hiring an experienced operator and selecting the right raw materials can help in eliminating warp issues.

http://www.indianadhesive.com  /  www.sanjayadhesives.com


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Impact of Adhesive on overall Performance of Corrugated Cartons

Corrugated boxes are frequently used as packaging and shipping containers. . Boxes are needed to contain the product for transferring it from manufacturer to distributors and other intermediaries for sale and sometimes even for end-use. Even while inner components such as cushioning, bracing and blocking are used to provide extra protection to fragile contents, corrugated boxes themselves too provide some degree of protection to the contained products. In fact, one of the important functions of a corrugated box is to provide crush resistance (product protection) and adequate strength for stacking in warehouses.

Corrugated Carton in itself is a low value item, but it is designed to carry items which may be of very high value. Since the very basic functions of corrugated carton is to contain and protect the products inside, its performance has to meet certain quality parameters. As a result, corrugated box design has gained a lot of importance.

Packaging engineers work to meet the performance requirements of a box while controlling total costs throughout the system. If long-term storage of corrugated boxes in high humidity is expected, extra strength and moisture resistance becomes indispensable. In fact, Fibre Box Association has identified moisture level/humidity as one of the factors having considerable effect on the compression strength.

To obtain better quality, corrugators have always placed deal of emphasis on the quality of paper. Adhesive has been the most neglected raw material in the manufacturing of corrugated cartons. Adhesive constitutes merely 2-3% of total raw materials used in the manufacturing process, but has the ability to affect the overall performance of the board.

Adhesive has the ability to affect a lot of parameters of the final output. Firstly and obviously, corrugated carton is nothing but multiple layers of paper (liners and fluted medium) which is adhered together. If a less tacky adhesive is used in the process, the resulting board will have very little fibre tear which may cause delamination.

Believe it or not the right kind of adhesive can help in resisting the absorption of Moisture. Excessive Moisture makes the flutes softer. When boards with softer flutes are stacked vertically, the flutes get pressed resulting in caliper loss. Again, it is the flutes of the board that imparts Compression Strength (C.S). Also when the flutes become soft, or in other words lose its stiffness, Bursting Strength (B.S) of the board reduces. This results in reduction of the overall strength of the board. Reduced strength means lesser protection to the contained products.

Even though adhesive constitutes merely 2-3% of the total raw materials used in the manufacturing process, the impact it has on overall performance is considerable. Hence it will not be wrong to state that Adhesive is the Heart of Corrugated Carton. The change in adhesive is also economical because of the small amounts in which it is used. Changes in paper is a costlier affair.

(For detailed information about how moisture affects the overall performance and steps to reduce the adverse effects of excessive moisture check the blog https://goo.gl/oaW53L.)

For more details about adhesive feel free to get in touch with us on sales@indianadhesive.com or visit us on www.indianadhesive.com.


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Types of Starch Based Adhesive used in Corrugation Industry

Starch based Adhesive are generally classified based on the process for which it is used as

  1. Corrugation Adhesive
  2. Pasting / Laminating Adhesive

Corrugation Adhesive

Corrugation Adhesive refers to the adhesive used on Single Facer/ Corrugator /Corrugation Machine.

For Semi-Automatic Operations:

Corrugation Adhesive is used for preparing 2 ply liners. This adhesive is applied on the flute tips and it is adhered to the kraft liner.

1

For Automatic Operations:

Corrugation Adhesive is used for preparing the Corrugation Board in fully automatic Corrugation Machines. The adhesive is applied on the exposed flute tips at the single facer and double backer station to form a board.

2

Corrugation adhesive cannot be applied directly with water. This adhesive needs heating in the presence of water to gain its bonding or adhesion property. Corrugation Adhesive is mixed with water (in the ratio provided by your adhesive supplier) and is poured in the gum tray. It gains it adhesion property when it is applied to the flute tip in the presence of heat on the Corrugation and Pressure Rolls.

 

Pasting Adhesive

Pasting Adhesive refers to the adhesive used on Laminating or Pasting Machine. This adhesive is used to stick the top paper to the flutes or to assemble the top paper and liners to form 3ply/ 5ply/ 7ply boards. This adhesive is used only in Semi-Automatic / Manual Operations.

3

Pasting Adhesive, is mixed with water and is used at room temperature. This adhesive, unlike corrugation adhesive, does not require heat for gaining its adhesion property. It is a gelatinized adhesive used for adhering the top paper at room temperature.

So what is Gelatinization? This important concept of Gelatinization will be discussed in the next post.

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Starch based Adhesive v/s Synthetic Adhesive in Corrugated Carton Manufacturing

The two types of adhesive used in the manufacturing of corrugated cartons are

  1. Starch Based Adhesive
  2. Synthetic Adhesive

Starch based adhesive refers to the adhesive derived from starch obtained from sources like maize and tapioca.  While Synthetic adhesive refers to the adhesive that is derived from resin-based emulsions such as a suspension of polyvinyl acetate in water. Fevicol is an example of synthetic adhesive used for the manufacturing of corrugated cartons.

Now let’s understand what impact each of these have on the Corrugated Carton Manufacturing. The adhesive used in the manufacturing process can have impact on two major parameters – QUALITY and COST.

So let’s first understand the adhesive’s IMPACT ON QUALITY.

  1. Impact on Bursting Strength

Starch based Adhesive penetrate into the fibers of the paper. This penetration not only creates a strong green bond, but also strengthens the fibers of the paper.  As a result the Bursting Strength of the Corrugated Cartons is positively impacted.

(Kindly note, if highly alkaline adhesive are used in the manufacturing process, it attracts high levels of atmospheric moisture as a result of which Bursting Strength is negatively impacted. It is always advisable to use low alkali or no alkali / pH neutral adhesive for manufacturing of corrugated cartons.)

On the other hand, synthetic adhesive merely creates a soft film between two layers of papers holding them together. Hence this adhesive does not have any significant impact on the Bursting Strength of the Corrugated Carton.

  1. Impact on Stiffness and Compression Strength

The penetration of starch based adhesive in the paper fiber also adds to the stiffness of paper. This improves the Compression Strength and overall stiffness of the Corrugated Carton.

(Kindly note, highly alkaline adhesive will have adverse impact on the Compression Strength, stiffness as well as caliper of the Corrugated Cartons.)

On the other hand, synthetic adhesive merely creates a soft bonding film which has no impact on the Compression Strength and stiffness of the Corrugated Carton.

  1. Impact on Bonding Strength

Starch based adhesive have higher solid content as against the synthetic adhesive used in the manufacturing of Corrugated Cartons. Solid Content refer to proportion of non-volatile material contained in the adhesive solution. The ideal percentage of solid content should be approx. 25% for excellent bonding.

Synthetic adhesive with higher solid content are available for wood articles. However, they are too expensive to be used in the manufacturing of Corrugated Cartons. On the other hand any good supplier of starch based adhesive will ensure 25% solid contents to avoid any delamination issue. And the starch based adhesive with 25% solid contents is a lot more pocket friendly.

Next let’s move on the adhesive’s IMPACT ON COSTING

  1. Cost of Adhesive

The cost of synthetic adhesive is more than double the cost of starch based adhesive. This affects the profitability.

Starch based adhesive are available in powder form. It is mixed with water, which is available free of cost or at minimal cost, in the factory by its users. Hence the users pay only for the solid content.

While in case of synthetic adhesive, the adhesive is delivered in liquid form. The buyer has to pay for both, the solid and liquid content.

  1. Cost of Transportation

The freight paid hence is also relatively higher, because no freight is paid for water (liquid content) in case of starch based adhesive.

OTHER DIFFERENCES BETWEEN STARCH BASED ADHESIVE AND SYNTHETIC ADHESIVE

  1. Starch based adhesive has little or no odor. While synthetic adhesive has a strong odor.
  2. Starch based adhesive is made from food items and hence is also bio-degradable in nature. While synthetic adhesive is not bio-degradable.

Starch based adhesive has gained a lot of popularity due to the economic cost and the strength that it offers. Presently, it is the widely used adhesive in the Corrugated Carton Manufacturing Industry. While Synthetic adhesive constitutes a meagre share in the Industry.

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Humidity affects Quality of Corrugated Boxes

Humidity has a significant impact on the quality of Corrugated Boxes. It is one of the factor which cannot be controlled. And most importantly you can do nothing to prevent your boxes from getting into a humid environment. After all what can you do to control humidity when in transit? Especially during monsoons?

linkBelieve it or not – Moisture is the Invisible Culprit which affects the quality of Corrugated Boxes in all parts of the World. The quality deterioration is very much visible when you work with lower quality paper, while if you work with very high quality paper, you may always think that your quality is absolutely perfect, given the fact that you get no complaints from your customers. But the fact can be that your quality is far away from what it should have been with the combination of papers used.

Moisture in the atmosphere is one of the major factors which has a tremendous impact on the Quality of Corrugated Boxes. While it is necessary to have some amount of moisture (approx. 6% – 7%) to ensure proper creasing and avoid cracking, high levels of moisture content can have negative impact on the quality of boxes.

It is practically impossible to stack the boxes horizontally, given the space constraints and handling problems. Hence the boxes have to be stacked vertically. When the boxes have more moisture content, some of the moisture obviously gets absorbed by the flutes of the board. This absorption makes the flutes soft. When the boards with these soft flutes are stacked vertically, the flutes get pressed and reduce in height. This leads to caliper loss.

Again, it is the flutes of the board that impart Compression Strength (C.S). Also when the flutes become soft, or in other words lose its stiffness, Bursting Strength (B.S) of the board reduces.

Till the early 90’s very little attention was paid to the “Quality” aspect. But with increase in competition, Quality has become an indispensable element.

So the big Question that arises is how can we stop the penetration of Atmospheric Moisture when we have no control on the humidity and other natural elements?

One possible solution could be to change the top paper to reduce the surface area from which moisture can get absorbed.

Second possible solution could be the use of de-humidifiers.

Both the above alternatives have one thing in common. Both the alternatives are expensive to be incorporated which would eat away the profits, as the customers are never willing to pay more.

Last but not the least; one possibility could be to change the adhesive, since change in paper is an expensive affair. But the question that pops up next is that, Can a change in adhesive help restrict the absorption of atmospheric moisture?

The answer is YES!

Kraft paper which is used in the manufacturing of boards is hygroscopic in nature, i.e. It attracts moisture from the atmosphere. Similarly, Alkaline adhesive with higher pH values is also hygroscopic in nature. This traditional combination of highly alkaline adhesive with kraft paper causes Moisture problems.

The use of Low / Non Alkali Adhesive can solve these moisture Problems. These pre – mix adhesives are readily available in the market. The Boxes made with Low / Non Alkali Adhesive can withstand the harsh conditions in the Deep Freezers without deterioration in Quality.

This change in adhesive is very cost effective because adhesive consumption constitutes not more than 4% of paper consumption.
For more details feel free to write to us on sales@indianadhesive.com or visit us on www.indianadhesive.com.