The science behind the heart of corrugated MEDIUM

The science behind the heart of corrugated MEDIUM

Tom Staal MQ/OE MEDIUM FROM THE USER PERSPECTIVE

THE SCIENTISTS Institute of Paper Chemistry McKee, Gander, Wachuta 1961 Edge Crush Test developed 1963 Box compression prediction aka McKee Formula 1983 ECT from Ring Crush -W. Whitsitt USDA Forest Products Laboratories Institute of Paper Science and Technology J. J. Batelka Corrugating Medium Reference Many, many others

WHAT DO BUYERS WANT FROM CORRUGATED BOXES? Stack Protect Contain Transport

WHAT DO BOX MAKERS WANT FROM MEDIUM? Machinability Durability

WHAT PROPERTIES RELATE TO MACHINABILITY? Absorptivity T831 Water Absorption of Corrugating Medium: Water Drop Penetration Test T 832 Water Absorption of Corrugating Medium: Float Curl Method T835 Water Absorption of Corrugating Medium: Water Drop Absorption Test Adhesive Penetration/Porosity T 536 Resistance of paper to passage of air (high-pressure Gurley method) T 547 Air permeance of paper and paperboard (Sheffield method) Tensile strength T494 Tensile Breaking Properties of Paper and Paperboard

WHAT PROPERTIES RELATE TO DURABILITY? Flat Crush T809 -Flat Crush of Corrugating Medium (CMT)

WHAT DO BOX DESIGNERS WANT FROM MEDIUM? Structure Cushion Stack

WHAT PROPERTIES RELATE TO STACK? Bending Stiffness T836 Bending Stiffness, Four point method Compression Strength T 822 Ring crush of paperboard (RCT) T826 Short span compressive strength of containerboard (SCT) T 843 Fluted edge crush of corrugating medium (CCT)

Stephan Burnett P. Eng Quality Tests CORRUGATING MEDIUM

WHAT IS MEDIUM PAPER? Containerboard is made of linerboard and corrugating medium paper The liners are used as outer layers whereas the medium is placed between the two. Atlantic Packaging uses 100% recycled paper for both types of paper Both liner and medium paper have different grades (higher grades are heavier and stronger) Medium paper plays a large role in the final properties of the box; therefore, quality control measures must be taken

QUALITY CONTROL TESTS FOR MEDIUM Basis weight Moisture CMT (Corrugated Medium Test) CFC (Fluted Edge Crush of Corrugated Medium) Water Drop Test Air Permeability STFI (Short Span Compression Test) RCT TSI Bending Stiffness

BASIS WEIGHT TAPPI T410 Mass per unit area of the corrugating sheet Procedure: Cut, condition and weigh 5x5 inch paper, divide weight by area Significance to corrugator: Impacts many properties; correlates with strength. Significance to box customer: Depending on the product, higher basis weight may be required to maintain box shape and retention (heavier or more fragile products may require heavier basis weight paper).

MOISTURE TAPPI T550 Moisture is the percent water content of the paper Procedure: Cut any size piece of paper, measure weight, dry for 24 hours, weigh again Significance to corrugator: Compared to liner paper, medium has to be more pliable to be fluted. Too much moisture can cause flute failure when humid. Significance to box customer: Impacts strength of box; low moisture leads to a brittle box and high moisture results in a soft box.

CMT ( CORRUGATED MEDIUM TEST) TAPPI T809 Measures the potential flat crush resistance of a corrugated board Procedure: Cut 15 mm strip of paper in machine direction, put through fluting machine, quickly trap strip in medium fluter, tape on pressure sensitive tape, operate Compression Tester designed to measure CMT Significance to corrugator: Indicates the ease or difficulty raised by the corrugated paper, in order to maintain at a constant distance between both liners. Significance to box customer: Impacts strength of box and ability to withstand crush (vital when boxes are stacked).

CCT ( FLUTED EDGE CRUSH) TAPPI T843 The strength of paper flutes under a vertical compression load (similar to CMT but measures in a different direction) Procedure: Cut 15 mm strip of paper in machine direction, put through fluting machine, mount test piece in holder, operate Compression Tester designed to measure CFC Significance to corrugator: Simulates the load received by the paper inside the carton wall. Significance to box customer: Test simulates the stress when boxes are stacked.

WATER DROP TEST TAPPI T831 Time (in seconds) taken for a drop of water on the surface of the paper to be completely absorbed Procedure: Fill syringe with distilled water, drop water on surface, immediately start stop watch, stop at the first visual indication of water on the lower side of the paper specimen Significance to corrugator: Absorptivity for corrugating medium must be controlled to ensure it has the proper receptivity to the corrugating adhesive. Significance to box customer: Impacts how well box holds together; boxes that fail water drop tests may experience delamination issues (liner paper falling apart from the fluted paper).

AIR PERMEABILITY (POROSITY) TAPPI T536 The time needed, so that a specific air quantity may pass through a certain paper surface Procedure (electronic): Cut 10 5x5 inch pieces of paper, choose air permeability measure option, press measure, repeat for all samples and find mean value Significance to corrugator: Indication of absorptivity, and fiber compaction. A closed sheet is also harder to drain of water, which in turn affects moisture. Significance to box customer: Can help indicate many issues related to moisture; for example, baggy edge, blisters, wrinkles etc.

SHORT SPAN COMPRESSION TEST (STFI) TAPPI T826 Measures the paper s compressive strength unaffected by the paper s other properties Procedure: Cut 15mm inch piece of paper in cross direction, insert in short span compression tester, press measure Significance to corrugator: Although more significant for liner paper, STFI can help to determine overall compression strength of medium paper. Significance to box customer: Can help to determine if medium paper was cause of any box issues or failure.

RCT (RING CRUSH TEST) TAPPI T822 RCT correlates with edgewise compression strength of paperboard Procedure: Cut 15 mm strip of paper in machine direction, place in grade specific specimen holder, operate Compression Tester designed to measure RCT Significance to corrugator: Edgewise compression strength is considered to relate to the eventual compression strength of combined board made from the component. Significance to box customer: Shipping containers are frequently subjected to loads which are resisted by compression strength, making this property an important measure of the performance characteristics of corrugated board.

TENSILE STIFFNESS INDEX (TSI) TAPPI T494 TSI is an elastic property of paper and is indicative of the strength derived from factors such as fiber strength, fiber length, and bonding Procedure: Cut a paper sample across length of reel, calibrate tensile testing machine, start measurement Significance to corrugator: Indicates potential baggy edge issues that may cause runnability issues on the machine. Significance to box customer: Boxes made from liner paper with varying TSI values may fail due to warp and lean issue.

BENDING STIFFNESS TAPPI T489 Measures the force applied perpendicular to the plane of the strip required to bend the paper Procedure: Cut 5x5 test paper, condition, place in clamps of stiffness tester (pressure should not be excessive), operate instrument Significance to corrugator: Relates to the amount of fiber in the paperboard (or its caliper) and hence, its cost Significance to box customer: Can help determine the top to bottom stacking strength of the final box product and its resistance to bulging when filled

MILL COMPARISON Basis Weight Moistur e Mill A Mill B Mill C Mill D Mill E Mill F Mill G Mill H Mill I Mill J 10 10 CMT 10 CFC 3 Water Drop 5 Porosity 3 STFI 2 RCT 2 TSI 3 Sum

CMT VS CCT CMT better indicator for FLAT CRUSH, potentially more important on Mullen grade boxes CCT better indicator of COMPRESSION STRENGTH, potentially more important on ECT grade boxes *Both can be used in conjunction or with a Cross directional strength test for better predictive accuracy (STFI or RC)

SOURCES http://www.fibrelab.ubc.ca/files/2013/01/topic 11 Papermaking Introduction text.pdf http://www.paperonweb.com/paperpro.htm http://l w.com/wp content/uploads/283_en_lw_tsotester.pdf https://www.researchgate.net/publication/293757091_runnability_and_corrugating_medium_properties www.tappi.org/content/sarg/t822.pdf http://www.tappi.org/content/tag/sarg/t826.pdf techlabsystems.com/en/datasheets/corrugated/holders ect rct pat web.pdf

Chris Massie ChE WHAT ARE FACTORS THAT CAN IMPACT THE STRENGTH OF CORRUGATING MEDIUM

STRENGTH Sheet strength is controlled by fiber bonding Wood - individual fibers held together by a organic glue called lignin Pulping wood chips removes the glue and releases the fibers The fibers are treated and formed into a sheet Increase the fiber development Optimize formation Maximize bonding sites

PULP FURNISH Hardwood Oak, Poplar, Maple, Birch, Ash, ect Hardwoods have short fiber length 0.7 1.7 mm length Most often a high yield, semi-chem process NSSC, Green liquor, Carbonate Softwood Pine, Longleaf Pine, Loblolly Pine, Slash Pine Softwoods have 3.5 5.0 mm fiber length Typically a Kraft (Sulfate, Caustic) process, lower yield OCC Old Corrugated Containers: Recycled Fiber A mixture of hardwood and softwood Typically not as strong as virgin fiber, needs further strength development to be comparable

FIBER DEVELOPMENT Refining Wood fibers are passed between metal plates to improve bonding Factors affecting refining: Plate design Gap width, Bar width, bar height, bar angle, alloy of material Rotating speed Applied horsepower Production throughput Consistency ph Temperature

CONTAMINANT REMOVAL Contaminants interfere with fiber to fiber bonding From virgin pulp: Lignin, bark, dirt, shives From OCC pulp: plastics, styrofoam, glass, metal, wax, stickies Removal Equipment Screens Barrier removal of oversize particles Cleaners Separation of either lightweight or heavyweight pieces Floatation/Settling Further separation by density Parameters: Pressure drop, consistency, velocity

STRENGTH ADDITIVES Chemical additives Starch corn starch Polymers phenolics, polyacrylamides Cellulose derivitives carboxymethylcellulose Control factors: Consistency Temperature Retention time Charge Mixing

FORMATION Headbox factors- Fourdrinier Headbox consistency Delivery angle L/b, pressure forming vs velocity forming Velocity Rush/Drag: Affects fiber orientation Slice adjustment or dilution control adjusts cross machine profile Forming fabric (wire) Wire design for flow direction Void volume Draining Activity water removal elements help to evenly disperse fiber Vacuum boxes remove as much water as possible before pressing

PRESSING Number of press nips and types of nips Conventional two roll press nip Roll covers, nip pressure, crowning Wide nip press (shoe press) Hydraulic loading pressure, zones width Press felts Must carry the water out of the sheet Void volume, batting, weight Carries the sheet and controls the path of the sheet travel The press nips densify the sheet and improve fiber bonding Too much intenstity or water in the nip can cause breaks

WHAT ARE FACTORS THAT CAN IMPACT THE RUNNABILITY OF CORRUGATING MEDIUM

RUNNABILITY Accept moisture / steam Glue and hold Uniform weight and moisture MD and CD Target speeds

WATER ABSORPTION Typically medium accepts water easily Can be affected by either wax or pitch carryover from the stock furnish Overrefining to get strength can close up the sheet Densifying the sheet can restrict water penetration Chemical can be added to control water absorption Rewet chemical surfactant to affect water tension to increase absorption Sizing can be added to prevent the medium from absorbing too quickly

WEIGHT AND MOISTURE PROFILE Measurement Online traversing scanner Nuclear source for weight Microwave sensor for moisture As narrow as 0.5 inch increments then compiled for control Control - QCS MD weight by weight valve or motor drive MD moisture by steam pressure in dryers CD weight by headbox actuators CD moisture by a profiling steambox or waterspray

OBJECTIVE Dependable, predictable, uniform product Meets all of the strength requirements for box strength Bonds evenly and stays together Forms into flutes easily and retains the shape

INTERSTED IN LEARNING MORE? Corrugated Box Technical Committee (CORBOTEC) Meets immediately following this session Fiberboard Shipping Container Testing Committee (FISCOTEC) Meets tomorrow 12PM to 1:30