Counterplates

    Matrix, Phenolic Counterplates & Milled Steel Cutting Plates
 
Some of you may remember a time when doing a press make-ready consisted of “Cutting a Mat” when die cutting folding cartons.  No, it doesn’t have anything to do with framing pictures.  The process was to clean off the steel cutting plate, adhere a sheet of mat material or the stock being die cut, to the cutting plate using double sided tape or spray adhesive. Then the operator would make a full cut press impression, using carbon paper, onto the stock.  This would give a clear indication of the exact location of all the creases and cuts.  The plate would then be removed from the press so that the operator could manually use a sharp knife to carefully cut all the crease channels out of the mat.  The balance of the stock would then have to be cut and skived away leaving a shape very much like today’s phenolic counterplates.  Mind you, this explanation has been rather simplified.  Later, 2 axis manually operated grinding/cutting machines were introduced to reduce make-ready time and improve accuracy of the crease channels.  Regardless of the method you were using, make-ready times would be several hours per job.
 
The added downside of these methods was its lack of longevity.  As the press ran, the edges of the channels would compress and round over, causing the degradation of the crease definition on the cartons.  The only thing that could be done was to strip the plate and start over.  As you can well imagine, on a high volume run the make-ready process would have to be duplicated multiple times throughout the run to ensure a reliable crease definition.  Therefore the downtime costs were excessive.
 
Matrix
 
However there was another option available to a converter which was Matrix.  In the 1950’s in London, England, a Diemaker and Inventor by the name of Mr. Harry Squire founded a company called Channel that introduced to the world for the very first time, a self locating creasing matrix.  This invention proved out to be a great solution for many converters.  Matrix resulted in the reduction of make-ready times since they only had to be cut to length, trim the angles on the ends of the matrix, pushed onto the creases, remove the adhesive tape backer, transfer them onto the steel cutting plate and remove the plastic locator strips.  Once the locator strips have been removed, use a sharp knife or chisel to chamfer the angled ends of the matrix to prevent “bruising” of the cartons.  Wah la, you were ready to go.  If a piece of matrix moves or becomes damaged, it is easy enough for the operator to replace individual pieces and get back up running again.
 
 
Please feel free to watch this short video to see “How to use Creasing Matrix”.
https://youtu.be/TvBnMSr6n7Y?feature=shared
 
Types and Usage of Matrix
 
PVC plastic:
  • Good for abrasive board, plastic, virgin board, corrugated board
  • Recommended for long runs of 100,000 impressions or more.
 
Metal-based PVC plastic:
  • Good for abrasive board, virgin board, corrugated board
  • Recommended for long runs of 100,000 impressions or more.
 
Hybrid material:
  • Good for abrasive board, virgin board, corrugated board
  • Recommended for long runs of 100,000 impressions or more.
 
Fiber material:
  • Easily skived, not good for plastic,
  • Recommended for shorter runs less than 100,000 impressions.
 
PVC corrugated matrix:
  • Good for all corrugated material & thicker and solid fiberboard (wider base)
  • Recommended for any type of run length.
 
Creasing Matrix can easily be purchased through your local die supply company or you can contact us for more supplier information.

Phenolic Counterplates

Then came the 1980’s with the development and implementation of Rillma counterplates.  These counterplates were cut on a CNC milling machine as a unitary plate that incorporated all the necessary crease channels for a single clone and was profiled using 160 or 170 degree Chamfer cutters to ensure that the counterplate wasn’t going to leave bruising in the corners at the ends of the creases. Bruising can also occur when ejection rubber is situated over the chamfered edges of the counterplate and the rubber puts vertical pressure on the substrate being die cut, over the profile.  The material is malleable enough that it can be carefully carved with a chisel or knife to fine tune the counterplate on press for best results.  Or if practical, the ejection rubber can be cut back to eliminate the interference.  The corresponding cutting dies are fabricated with counterplate pin locating holes so that the counterplates can be positioned and transferred precisely to the press cutting plate for a perfect registration of the creasing channels to the die.

In North America, Rillma is better known as Pertinax® or Phenolic.  The term Pertinax® is a registered trademark of the Dr. Dietrich Mueller GmbH company in Germany.  Pertinax® is comprised of a hard paper substrate that has been impregnated with phenolic resin and then several layers are laminated together under high pressure.  The more predominately recognized use of this material is in the electrical industry for circuit boards because of its insulating properties, mechanical strength and chemical resistance.  This also makes it an ideal material for the fabrication of counterplates.
The mechanical strength and chemical resistance of this phenolic resin based material maintains the durability of the creasing channel edges much longer than channel matrixes.  This results in a crease definition that is much more sustainable, making it the better choice for dies with a higher number of clones, repeat jobs and medium to high volume jobs.  Phenolic counterplates are very economical and reduce the amount of make-ready time significantly.  Some additional benefits to using Phenolic Counterplates is the integration of Braille, Embossing/Debossing, Custom Cut/Crease, Custom Cut/Cutscore, Reverse Cutting or Reverse Score plates and Reverse Creasing.
 
Usage of Phenolic Material
 
  • Good for abrasive board, plastic, virgin board, corrugated board
  • Available up to 2.0mm (0.079”) which covers most thicknesses of solid and corrugated materials
  • Recommended for long runs of 100,000 impressions or more.
 Milled Steel Cutting Plates
 
As a result of the great success of the development of Phenolic Counterplates, the 1990’s brought on a whole new thought process of eliminating the phenolic material and milling the channels directly into the steel cutting plate.  This concept was revolutionary since it was discovered that there was less lateral draw across the die cut sheets which resulted in the carton nicks remaining intact during die cutting and sheet transfer through the press.  It eliminated carton bruising, stripping & blanking was more reliable, the cartons stacked much flatter and the overall press speeds were increasing.  Also, the downstream processes such as the Folder/Gluers and product filler machines were experiencing functionality improvements.  The biggest downside in the infancy stages was the exorbitant plate costs.  It didn’t take long before the introduction of using a 1mm thin plate grabbed the industry.  For example, if your press utilized a 5mm cutting plate, all you had to do was get a 4mm precision ground Filler Plate so that you could put the 1mm medium or hard thin plate on top which had all the crease channels milled into it.  It only stands to reason that for the most optimal and precise results, the die being used in conjunction with a milled steel cutting plate must be dimensionally stable.  This technology is still widely used today and caters to converters that have a demand for higher press speeds, repeat jobs and high volume requirements.  It is only limited by the size of the press as to how many clones can be fit on the die and available tonnage capacity.
 
It has come to our knowledge, on some lower to medium volume jobs where there is also a reduced number of clones, converters have been using conventional wood based dies along with a 1mm soft steel cutting plate, usually 304 Stainless Steel, in an attempt to lower their costs further.  This is not necessarily recommended due to the vulnerability of the wood based die and steel cutting plate to climatic changes within the plants.  Of the two, the die is the most susceptible product since the two products do not expand or contract at the same rate.  So in 3 to 6 months or sooner, you will find that they don’t lineup with each other like they had when first purchased.  Our experience has shown that growth as much as 1/32” can occur from side to side on a large format die.  At best the only thing that can be done if the error is small, without purchasing new tooling, is to split the error by lining up the steel plate with the die working outwards from the center in both directions.  Depending on the end customers acceptance of such cartons, be aware that the gamble could be a costly one.  If you can ensure that the die base is dimensionally stable, the use of a 1mm 304 Stainless Steel cutting plate can be quite successful.
 
Usage of Steel Cutting Plates
 
  • Good for abrasive board, plastic, virgin board and corrugated board
  • Limited in thickness from 1 mm (0.039″), 1.15 mm (0.045″)  to  1.5 mm (0.059″)
  • For thicker, solid fiber or corrugated board other types are available but may require a machine modification for different cutting plate thicknesses
  • Recommended for long runs of 500,000 impressions or more.
How to Determine Crease Rule Thickness
 
The thickness of crease rules when using Matrix, Phenolic Counterplates or Milled Steel Cutting Plates
The thickness p of the crease rules depends on the type of substrate that is being die cut and its thickness s.
How to Determine Crease Rule Heights
The heights of crease rules when using Matrix or
Phenolic Counterplates
When using Matrix or Phenolic Counterplates,
the thickness of the material at the bottom of the
channel t and adhesive must be taken into consideration.
Usually, the closest lower crease height z is to be selected.
Note:  For microflute stocks, first measure the thickness of
the crushed flutes to get value s for the formula.
 
                           Example:          z = 0.937 – 0.018 – 0.006
                                                      z = 0.913            Therefore, 0.912” 2pt would be the most readily available
                                                                                  crease in this particular scenario
The heights of crease rules when the creasing channels
are milled into a steel cutting plate or a thin plate
The height of crease rules is typically equal to the height
of the cutting rules.
How to Determine Phenolic Counterplate & Milled Steel Cutting Plate Thickness
 
The process of determining the required thickness
of Phenolic material is the easiest of all the formulas

we have, relative to counterplates.  Add the thickness

of the substrate to be die cut s and the thickness of the
material at the bottom of the channel t together.  If
we use the numbers from our previous formula, it
would look like this:            r = s + t
                                                r = 0.018 + 0.006 = 0.024”
In certain situations there are times, such as with recycled substrates, which the customer may need to push the stock deeper to get a better crease definition to obtain a lower score bend value.  So one method to achieve this is to increase the thickness of phenolic to the next thickness available, which in this case would be 0.026” or even 0.028”.  Typically, the phenolic material is readily available in the following sizes:  0.016” (0.4mm), 0.018” (0.45mm), 0.020” (0.5mm), 0.024” (0.6mm), 0.026” (0.65mm), 0.028” (0.7mm), 0.030” (0.75mm), 0.032” (0.8mm), 0.036” (0.9mm), 0.039” (1.0mm), 0.043” (1.1mm) & 0.050” (1.3)   Additional thicknesses up to 0.078″ (2.0mm) can be custom ordered.
 
The known thicknesses of medium & hard steel thin plates for Milled Steel Cutting Plates are 1.0mm, 1.15mm and 1.5mm with the most widely used being 1mm or 0.039”.  When it comes to the softer 304 Stainless Steel, they are designated based on “gauge”.  For instance, 20 gauge and 16 gauge.  Some die cutting machines utilize a 3mm (0.118”) or 0.125” cutting plates that can also be milled, if so desired.
 
How to Determine Crease Channel Depths
 
How far should we be pushing the substrate into the creasing channel?  The simple answer is that you need to achieve the best crease definition or score bend test value to satisfy the customer’s requirements.  But to do that you must first understand that regardless of substrate type or whether virgin fibers vs recycled or manufacturer or coated vs uncoated or type of ink or ink colour or same thickness or from one day to the next, no substrates will ever crease in the exact same manner and there is a direct relationship between the channel widths vs channel depths to achieve a good crease.
 
The most standard and simplest when talking about paperboard substrates, is that the channel depth D is equal to the substrate thickness s.   However, when dealing with recycled substrate, we recommend increasing the creasing channel depth and crease rule by about 0.004” on a milled steel cutting plate or just increase the phenolic counterplate thickness by 0.004”.How a crease gets “formed” in folding carton substrates
 
When a die goes under impression in the press, there are basically 5 critical steps or stages that take place.
 
  1. The rubber touches the substrate which applies pressure to hold the substrate tightly against the cutting plate so that no lateral movement can take place and maintains registration between the die and the printed substrate.  If matrix or phenolic counters are being used, the substrates’ fibers start to be stretched or laterally compromised over what can be viewed as a mountainess terrain, in the small world of the substrate thickness.
  2. The cutting & creasing rules make contact with the substrate which starts another series of reactions.  The cutting edge starts to compress the substrate and the crease rule starts to pinch the stock against the two upper corners of the crease channel, referred to as the Critical Distance.
  3. During the continued closer of the press, the substrate gets trapped in the CD zone and starts to cause the board fibers to stretch and delaminate as the crease rule pushes the substrate into the crease channel.  This is referred to as a controlled delaminating process.
  4. As the cutting & creasing rules get closer to the cutting plate, an immense amount of back pressure is built up which needs to be released.  If the make ready of the cutting rules has been done properly with the right amount of finesse, the cutting blades will act like an axe head with the sharp edge penetrating the surface of the substrate and the angle of the wedge (54 or 42 degree bevel) causing a “burst” and separation of the substrate.  This results in the cutting edge not getting damaged because it is not getting slammed against the steel cutting plate with too much force.  At this instant, the crease rules have also reached their lowest vertical position and have completed the extent of a Partial Delamination of the substrate fibers.  Full Delamination of the substrate fibers only occurs when the carton panels are folded 180 degrees against each other with the carton panels acting as levers.
  5. The last stage is when the ejection materials are pushing the substrate off of the cutting rule edges and releasing the substrate.
Contrary to what you may think, there are actually two pivot points that a properly formed crease folds on.  This is true as long as the crease is symmetrical and the critical distance CD is equal on both sides of the crease rule.  If the crease is not symmetrical, then this is when you will have biting on one side or the other and the creases will fold on the predominant pivot point causing the carton to fold up incorrectly.  This will result in issues at the folder / gluer and potentially in the product filling machines.
 
How to Determine Crease Channel Widths
 
Since there are such a wide number of variables that come into play, it is impossible to state that there is only one formula that should be used to calculate creasing channel widths for phenolic or milled steel cutting plates.  A formula is a great tool to give you a starting point and should allow you to get through a complete run.  However, based on a comprehensive Crease Testing Program that was completed over the past several years on a Thomson clamshell press, we have been able to observe some consistent results for different types of stock which has helped us to improve our customer’s success.
 
A virgin board like SBS is made from brand new pulp and the fibers are at their longest, which makes the board structure durable but yet flexible because of the fiber weave.  You can see what we mean if you take a piece of SBS substrate and a recycled piece.  Now fold them in half “with the grain” and also “across the grain” without using a proper crease.  You can immediately observe that the SBS has only a small amount of fracturing, but the recycled substrate will have a significantly higher amount of fracturing.  This is because the fibers of the recycled substrate are shorter and not able to handle the same level of stress without being pulled apart.  From this you can see why it is so important to ensure that the crease widths are set correctly so that the crease bead is “formed” to produce the best quality possible, for the substrate being die cut.  As we proceed keep in mind that forming crease beads parallel with the fiber structure or grain takes less effort than perpendicular to the grain.  Therefore the crease bead needs to be a bit wider when perpendicular to the grain so that the fibers don’t become compromised or fail.
 
W = The width of the creasing channel, either parallel or perpendicular to the fiber or grain direction
WG = With Grain – The width of the creasing channel parallel to the fiber or grain direction
XG = Across Grain – The width of the creasing channel perpendicular to the fiber or grain direction
P = Thickness of crease rule based on pointage being used   (1pt = 0.014)
S = Substrate thickness that is to be die cut
Multiplier Factors = 1.3, 1.5, 1.8 or 2.0
 
This first formula is highly recommended and from our testing program, we would have to agree that it does a great job when working with virgin board substrates such as SBS.
 
 
 

Example:     WG = (0.018 x 1.3) + 0.028 = 0.051”                                                   XG = (0.018 x 1.5) + 0.028 = 0.055”

This second formula was a result of our development when performing our Crease Testing Program and is suitable for use with non-SBS & corrugated substrates.  However due to the versatility of SBS, it still worked but was light on the crease bead definition.

Example:     WG = (0.018 x 1.8) + 0.028 = 0.060”                                                    XG = (0.018 x 2.0) + 0.028 = 0.064”

This third scenario is a derivative of a recommended chart for Milled Steel Cutting Plates.

In Summary

Ultimately, the customer always gets the final say about what specs they want to have used.  So if the customer has their own chart for Channel Depths, Widths and Crease Rule Heights, that’s what SRD will use.  There is also times when the paperboard supplier may have a recommended set of specifications that would also be provided to us from the customer.
For additional supplementary information about Folding Carton Creasing, there are two informative articles in the Resource Library on the www.IADD.org website.  They are as follows:

Creasing Dynamics –Anatomy of a Folding Carton Crease   –   by John Dickison, Bobst North America Inc.
How is a Crease Formed in Paperboard?   –   By Kevin Carey, Die-Cutting Works Inc.