Paper and Paperboard Packaging Midterm 2-Corrugated Manufacturing Overview
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5 basic elements in manufacturing corrugated board
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paper adhesive heat pressure moisture
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two types of paper
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linerboard and medium
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Most important property of linerboard
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moisture content must be controlled on the corrugator. if moisture content is high, the corrugated board may not bond properly
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Bonding problems can occur...
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if the liner board is too dry
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Warping
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may frequently occur if the moisture contents of the 2 liner boards in the corrugated structure differ by more than 2 to 3%
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Elements of the medium that must be controlled
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heat and moisture
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Why must the medium be both hot and moist at the time of flute formation?
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in order for the corrugator rolls to form the medium into flutes at high speed
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Containerboard
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Linerboard-sulfate/Kraft process, softwood trees, uniform color, clean, smooth, water resistant, strength (column) Corrugating medium-chemical/mechanical processes, hardwood trees, rougher, absorbent, strength (arches/columns), formability, 70-85% of total thickness
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Three primary requirements in mind for medium
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1. Strength required to form strong arches and columns 2. Formability 3. Ability to bond to liner board at high rates of speed
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Four primary requirements in mind for linerboard
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1. Strength required to add to the column strength 2. Good print characteristics 3. a degree of water resistance 4. ability to bond quickly to the medium
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Top and Base of linerboard
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Top-Outside layer, 10-30% of total thickness, processed for smoothness, appearance, and water resistance, may be bleached Base-Bonds to medium, 70-90% of total thickness, processed primarily for strength, rougher and slightly more absorptive, typically unbleached
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Adhesive
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used to bond the medium to the liners usually a mixture of starch, caustic soda and borax in water
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Cornstarch
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adhesive due to relatively low cost, good adhesive quality, and ease of availability, this is most commonly used in corrugated manufacture
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Starch
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starch can become an adhesive only after it has been gelled moisture and heat must be present to cause the starch to gel and to form what is called a GREEN BOND between the liner and medium -the final high strength adhesive bond is formed by removing moisture from the green bond after gelling
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Heat
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necessary for moisture control, fluting quality and bond formation
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How is heat supplied?
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1. Single face and double face preheating rolls 2. Preconditioner roll 3. Steam shower and steam chest 4. Corrugating rolls 5. Pressure rolls 6. Hot plates
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Pressure
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required to form the bonds between the medium and liners Required between the two corrugator rolls in order for the medium to be properly formed during fluting
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What happens with too much or too little pressure?
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Too little pressure will result in poorly formed flutes, low caliper and low flat crush Too much pressure will fracture the medium
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Moisture
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necessary for good flute formation as well as for gelling starch is important but is also a source of major problems
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What is the usual moisture content for paper coming into a box plant?
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6 and 9 %
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Moisture and warp
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If the two liner boards have different moistures at the time that the single face web and the double face liner are bonded together, the finished corrugated board may warp Warped sheets can cause productivity problems in down stream printing and package set-up equipment
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Steam
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Moisture is also added to the medium when it is steamed GOAL: to insure that enough moisture gets into the medium to guarantee the fiber flexibility required for good flute formation
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What is a large source of moisture?
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the adhesive. the water must be present so that the starch particles will be uniformly dispersed and will flow uniformly when pumped. the presence of water is also required to allow the starch particles to gel when heat is applied
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Starch and water (moisture)
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when adding a normal amount of starch adhesive to the corrugated board, the amount of water added is equivalent to an additional 10% moisture content If more adhesive than necessary is added or if much more adhesive is added to the single face than to the double face or vice versa, serious warp problems can occur
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How much space does a typical corrugator take up? and the corrugating rolls?
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12' x 200' - corrugator 7'-8' wide - corrugating rolls the most common corrugator roll widths in recent times have been between 87 and 98 inches; however some corrugator rolls are as wide as 110 inches
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Corrugator speed?
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newer corrugators have speed potentials of 1,000 feet per minute (FPM) Corrugators today typically run between 500 and 1000 FPM most of the time
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What does a typical corrugator produce?
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an 8' wide by 800' long web of corrugated board (6400 sq feet) every minute
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Primary functions of the corrugator
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1. Flute the Medium 2. Combine the fluted medium to the single face liner (single face web) 3. Combine the single face web to the double face line (single face board) 4. Slit the web to sheet widths and apply scores to the board 5. Cut the sheets to length 6. Stack individual sheets
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What series of machines are in a corrugator?
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1. Roll stands 2. Single Facer 3. Double Backer 4. Slitter 5. Cut-off Knife and Stacker
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Roll Stands
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Rolls of liner board and medium are shipped from the paper mill to the box plant. The rolls are stored on end in the warehouse. The individual rolls of liner board and medium are delivered to the production floor, and prepared for mounting on the corrugator just before an order of corrugated board is to be manufactured
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What do roll stands do?
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They allow the rolls of paper from the paper mill to be unwound at a uniform tension. Most roll stands hold two rolls
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How do roll stands work?
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One roll is unwinding while the other is mounted and prepared to splice in when the first roll runs out
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How does a single facer work?
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the single facer pulls the medium in from one direction, steams and heats it on the preconditioned and in the steam shower, flutes it in the corrugating rolls, and then applies adhesive to the tips of the flutes. at the same time, the single facer pulls a LINERBOARD in from the other direction, passes it over a preheater, and brings it into contact with the fluted medium
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Why are preheater rolls used?
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(in relation to the single facer) to reduce the moisture content of high moisture liner board as well as to heat the liner board so that it bonds more rapidly
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Why is the pressure roll used?
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(in relation to the single facer) to create good contact between the liner board and the medium and to help form the bond between them
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Adhesive (liners and medium)
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the adhesive used to bond the liners and mediums together is a mixture of approx 25% cornstarch and 75% water mixture must be heated in order to become an adhesive
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two purposes of the steam-heated preheater
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1. to get heat into the liner so that the starch adhesive bond is easier to form 2. to evaporate moisture from the liner board
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Number of single facers
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most corrugators have at least two single facers -only one is used when manufacturing single wall board -both are used when manufacturing double wallboard -corrugators with three single facers are capable of producing triple wall board
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Double Backer
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The SFW is pulled over a preheater and down into the double facer glue machine. The glue machine applies starch adhesive to the flute tips of the SFW and the SFW is pulled into the hot plate section. The second liner board or facing, the double face liner, is pulled into the hot plates where it contacts the adhesive coated flute tips of the SFW
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What is the purpose of the hot plate section of the double backer?
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to provide heat and light pressure so that the starch will gel and bond the flutes to the double face liner
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Unheated cooling/traction section-double backer
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hot plates are followed by an unheated cooling/traction section, which keeps the pressure on just a little longer and helps insure the bond is fully developed also provides the pulling power to pull the corrugated web through the double facer *various kinds of coatings, such as anti-skids or water resistant materials, can be applied to the board after it leaves the cooling/traction section
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Slitter
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fourth step. the board is then pulled into the slitter where it is slit to width and scored
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Scoring-slitter
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scores are placed in corrugated board to allow the board to be easily folded at specific locations. these scores generally become the flap scores in a finished box Initially slitters had three sets of scoring heads and so were called triplex slitters
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Cut-off Knife and Stacker
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fifth step. the board is then pulled into a rotary knife. the knife cuts the sheets to length Most corrugators are equipped with a double knife. Each knife's rotation can be set independently to cut a different length sheet. Some corrugators have triple knives and can cut sheets of three different lengths
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How does the cut-off knife and stacker step work?
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the cut, trimmed and scored sheets are fed on belts to automatic stacking machines which stack the blanks in five to seven foot high stacks. each sheet is a rectangle that has been cut to a specific length and width **the sheets which are manufactured for the most common styles of corrugated packaging will also have two scores running the length of each sheet
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Parts of the converting process
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1. the flexo-folder gluer 2. printer slotter 3. die cutting 4. unitizing and shipping
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Converting process
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in the converting process, stacks of sheets are taken from the corrugator and fed one sheet at a time into machines, which have a succession of operations that convert them into finished corrugated products
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Flexo-folder gluer
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one of the most common pieces of converting equipment is the flexo-folder gluer PRIMARY FUNCTION: to convert each scored sheet from the corrugator into a printed and finish, ready to use box
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Operations necessary to create a finished box are:
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Sheet feeding (printing, scoring, slotting and slitting) Glue tab formation Glue application Folding Glue Tab Bonding Counting (stacking KD boxes) Bundling Unit Load Forming
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Variations of flexo-folder gluer
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there are many variations of flexo-folder gluers some print on top of the sheet while others print on the bottom *must print before scoring and slotting but some score and slot first Some have only one print station, which others have as many as four Some flexes can perform complex die cutting operations Others can perform only simple die cutting functions (access holes used to pull or pick up boxes and vent holes) Some flex machines have no die cutting capability at all
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Printer Slotter - functions
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common machine Primary functions: sheet feeding printing scoring slotting and slitting counting stacking finished blanks
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Printer slotter
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can turn out flat, unglued finished product, such as trays and wrap-arounds, which can be banded and shipped to the customer *in order to create a KD box, blanks from the pinter slitter must be processed on a folder gluer, folder taper, or folder stitcher
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Flexographic Process
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the primary printing process used on corrugated today. their inks are water washable -typically have from one to four printing units (the number of units used on any given order depends on customer specifications)
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What happens in the flexo process?
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ink is picked up by an engraved anilox roll, wiped off to a uniform thickness by a wiper roll or blade, then transferred to the raised surfaces on the flexographic printing plate and then to the board surface
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Die cutting
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die cutter is another popular piece of converting equipment Die cutting allows the manufacture of more complex types of boxes than can be produced on a printer slitter or flexo-folder-gluer. Can add many features to box designs
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Die cutting features
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angular scores and cuts perforated scores and cuts reverse score (platen only) slit scores or low knife (platen only) scores offset to slots hinge scores locking bottoms and tops cut outs, hand holes, vent holes, etc. embossing (dry stamps) zipper cuts (tear tabs)
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Two types of die cutters
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Soft Anvil Rotary Die Cutter Platen Die Cutter
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Soft Anvil Rotary Die Cutter
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may be utilized on flexo-folder-gluers, printer-slotters or may be done on freestanding die cutting units -freestanding units may or may not have printing capability -rotary die cutter uses steel cutting and scoring rule mounted on a curved board, which cuts through the corrugated and into a curved soft urethane backing
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Platen Die Cutter
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Free standing pieces of machinery. May or may not have printing capability Uses a flatbed cutting die. It operates on the basic principle of one flat surface cutting die squarely striking a metal platen
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Unitizing and Shipping
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flat knocked down boxes or stacks of die cut sheets are usually formed into bundles. these bundles may or may not be tied with twine. bundles are stacked to form unit loads for shipment to the customer. units are held securely together by metal or plastic strapping Units may or may not be wrapped in a plastic wrap for protection and they may or may not be placed on pallets. units are typically arranged to fit on a 40-inch by 48 inch common pallet and are anywhere from four to six feet high
