Industrial Paper Bags and Shipping Sacks: Key Terms of Sustainable Packaging

March 4, 2021

Paper Bags and Shipping Sacks come in a range of sizes and styles. Bags can be made from single or multiple layers of paper and plastic film. Bags made for shipping are generally made of multiple plies of paper (multi-wall) and are designed for durability and strength. 

Each year, billions of multi-wall paper shipping sacks are produced and sold. From food ingredients to chemicals, industrial paper bags carry a wide variety of materials across the globe.

shutterstock_132469877 (1)

Common industrial paper bag styles sold by Southern Packaging include:

  • Pasted Valve (PVSE)

  • Pinch Bottom Open Mouth (PBOM)

  • Sewn Open Mouth (SOM)

  • Webb-Pinch Open Mouth (SSWPT)

  • Self Opening Satchel (SOS)

Why should you use industrial multi-wall paper bags?

shutterstock_132469910 (1)Cost Effectiveness

Paper packaging is a highly cost-effective form of bulk packaging. Empty paper bags are easily folded and compressed for efficient transportation to the user. Empty bags are often palletized in quantities of 1,000 to 5,000 or more. The typical price of an industrial multi-wall paper bag ranges from $.20-80 per unit.

Functionality

Paper shipping sacks come in a variety of styles and sizes. In essence, they can be tailored to the exact needs of the customer. Whether it’s for hazardous chemicals or flour, a paper bag can be constructed to package and transport nearly any material.  

Strength

Multi-wall paper bags can easily hold 50 to 100lbs of material. Their multi-layer construction allows the bag to withstand the abuse of filling, handling and transportation.

Sustainability

Paper bags are made from renewable resources and can be easily recycled. Trees are one of mankind’s most important commodities The U.S. now grows more wood than it harvests each year. The paper bag industry is committed to maintaining a sustainable supply of raw material. 

Industrial Paper Bag and Shipping Sack Key Terms:

The following key terms have been identified and defined by the PSSMA (Paper Shipping Sack Manufacturers’ Association). These terms are intended to educate bag purchasers and promote high technical proficiency within the industrial bag industry. For questions or technical advice, we strongly encourage you to reach out to one of our experienced sales staff. 

For more information on the paper shipping sack industry visit https://www.pssma.org/

A

Abrasion
The rubbing or wearing away of a sheet of packaging material through contact with some other material. (also see scuffing, chafing).

 

Absorbency

Pertains to the amount of liquid taken up by paper, or the rate of uptake or time required for a paper to take up a given amount of liquid. Rate or time of absorbency is more commonly used.

 

Acid-Resistant Paper

Paper which has been treated to resist the actions of acids or acid fumes.


Adhesion

The state of sticking together or bonding two or more materials.


Adhesive, hot melt

An adhesive that is solid at room temperature, liquefied by heat, applied in molten state and forms a bond by cooling and solidifying.


Adhesive, palletizing

An adhesive used to unitize loads of bags or cases on a pallet providing low peel strength with high shear strength to prevent sliding.


Adhesives

Bonding agents used in the manufacture of shipping sacks. Most common adhesives are the waterproof-types made from starch or dextrines. Others are polyvinyl acetate resin emulsions, latex and hot melt.

 

Alkali-Resistant Paper

A paper used to wrap materials that have an alkaline reaction, such as soaps or alkaline adhesives. Paper which does not show appreciable discoloration when wet with one percent sodium hydroxide (caustic soda) is considered alkali-resistant.


All Creped Multiwall Sack

A sack in which all walls or paper plies are made from creped paper.


Aluminum Foil Coatings

Aluminum foil coated with polyethylene or other materials.


Aluminum Foil Laminations

A combination of thin aluminum foil with a paper backing used as a barrier. A typical foil lamination is kraft backing with aluminum foil laminated to the kraft paper by means of an adhesive or extruded polyethylene.


Angle of Slide

The height at which a weighted sample placed on another sample of the same material will begin to move or slide down an incline as expressed in degrees of an angle.


Anti-Slip Paper

A sheet of paper chemically or mechanically altered to increase the coefficient of friction (COF).

 

Automatic Sack

An alternative name for a self-opening sack (SOS).

B

Bag

A term frequently used interchangeably with sacks, but more accurately applied to smaller consumer size packages, generally less than 20 lbs net contents.


Bag Paper

Any paper used in making consumer sized bags. The choice of paper depends upon the goods to be packed and the performance expected.


Bale

Assembled, unfilled sacks wrapped and/or tied at the manufacturing plant ready for shipping to customers.


Baler Bag

A large sack, usually made of one to three walls, designed to carry or unitize a quantity of filled smaller bags.


Bar Pasting

Pasting together the walls of a sack with lines (or bars) of paste as contrasted with spot pasting.


Basis Weight

The weight in pounds or grams of a given area of paper. For shipping sack kraft, this is the weight in pounds of 3,000 square feet. Historically, this represents the weight of a 500 sheet ream cut 24 inches by 36 inches.


Beater Drying

A method of coloring paper in which colorants are added to the pulp before it is formed into a sheet.


Beater Sack

Entire sack and contents such as clay or titanium dioxide can be thrown into a beater for repulping. The sack is made of repulpable kraft or bleached kraft and water-soluble adhesives and water-dispersible inks.

 

Bleaching

The process of treating pulp with chemical agents whereby non-cellulose materials are removed or altered to make the pulp a whiter color.


Bleed

A surplus printed area extending into the tucks and/or bottom of a sack to allow for design tolerance while the sack is being formed in manufacturing.

 

Bottom

The end of the sack that usually rests on the floor or holder when being filled.


Bottom Paste

Adhesive used to make the end closure of pasted open mouth and pasted valve sacks.


Bottom Patch

A paper patch pasted over the bottom of a pasted open mouth sack or both ends of a pasted valve sack to prevent sifting.


Bottom Print

The design or lettering of the brand that is printed on the bottom of the bag or sack.


Bottomer

A machine which automatically forms and seals both ends of a valve sack or one end of a pasted open mouth sack.


Bottoming

The complete process of cutting and folding a bottom in a tube for pasted end bags. On certain machines, it also refers to forming the valve end of the pasted end sack.


Bound Over Tape

Plain, extensible or creped paper tape sewn into the closure of a sewn style multiwall sack.

 

Breakaway Adhesive

An adhesive used to bond film to the kraft ends of a sack giving the film the ability to break away at the sack ends without tearing paper fibers.


Brightness

The reflectivity or whiteness of a sheet of paper measured under standard conditions. Not a measure of color.

Bulk Density

The weight of a unit volume of a substance expressed as pounds per cubic foot or kilograms per cubic meter or equivalent units.

 

Bundle

A group of 15, 25, 50, or 100 bags that have been compressed and tied ready for shipment to the customer.


Bursting Strength

The resistance of paper to rupture under pressure. Usually determined on a Mullen tester and expressed in pounds per square inch. Also referred to as Mullen, Mullen strength, or pop test.


Butt

That part of the sack that becomes the top and the bottom when the bag is expanded upon filling.


Butt Printing

Printing on the ends of a pasted sack.

C

Calcium Carbonate Paper

A coating of calcium carbonate pigment and binder on kraft paper to improve acid protection


Calender

A series of rolls, through which paper is passed, to polish the surface and/or increase the density of the paper.


Calender Cuts

Defects in paper caused by wrinkles in the paper as it passes through the calendar rolls. Defects appear as slits or creases along the sheet.


Calendered Kraft Paper

Kraft paper having a smoother surfaced than regular natural kraft paper that was produced by a calender unit.


Caliper

The thickness of a material such as paper or film expressed in thousandths of an inch or mil.

 

Chafing

The abrasion or scuffing caused by materials rubbing against one another or against another surface.

 

Clay-Coated

A coating of clay and binder on paper to improve printing quality and appearance. Generally used for consumer packaging applications.


Closure

The result of sealing the ends of tubes.


Coated Paper

A term applied to paper and paperboard whose surface has been treated with clay or a pigment and adhesive mixture or other materials to improve the surface finish with respect to printing quality, color, smoothness, opacity or other surface properties. The term also is applied to lacquered and varnished papers.

 

Coefficient of Friction (COF)

The ratio of the frictional force to gravity acting perpendicular to the two surfaces in contact. The tangent of the angle of slide. Also see Static COF and Kinetic COF.

 

Cold melt

A pattern of polyvinyl acetate water emulsion coating applied on the printing press or bag machine to provide heat sealable closure on paper bags or roll stock.


Cold seal

A natural latex rubber adhesive applied as a pattern or overall coating to paper or film webs that only seals to itself under pressure without heat. Also called self-sealing coating.


Color Fastness

The resistance of color in paper, or printed inks, to change shades when exposed to light, heat chemicals or other deleterious influences.


Colored Kraft

Natural or bleached kraft paper to which a dye or pigment has been added to produce the desired color.


Conditioning

The exposure of paper to controlled and specified atmospheric conditions, so that moisture content of the paper reaches equilibrium with the controlled atmospheric conditions.

 

Conversion Materials

All materials used in the construction of a bag or sack. Common conversion materials are paper, thread, tape, adhesives, inks, etc.


Converter

A company that converts packaging materials into finished products such as bags, sacks, envelopes, pouches, boxes, tape, etc.

 

Creped Paper

A term describing the effect produced by “crowding” a wet sheet on a roll by means of a doctor blade. In sack manufacture, creped paper is used to add flexibility and anti-slip properties.The degree of crepe is indicated by percentages and usually ranges from 3% to 30%. For example, 20 percent crepe paper will stretch 20% in a direction at right angles to the creping before it breaks.


Creped Sleeves

A tube of creped paper used to from an internal or tuck-in closure in valve sacks.


Creped Tape

Tape used in the end closure of sewn multiwall sacks.


Cross Direction

The direction at right angles to the machine direction, corresponding to the direction of the width of a sheet of paper wound in a roll. Also expressed as “across the machine” and “across the grain”.


Cross Pasting

Spot or bar pasting across the width of a paper bag. Also see bar pasting and spot pasting.


Cubic Capacity

The volume of material that a sack will hold. Cubic capacity cannot accurately be determined from measurements of an empty sack, but must be determined by filling trials, taking into account entrained air in the product.


Curl

Usually applied to labels. An undesirable condition in a stack of paper sheets, labels or wrappers usually caused by uneven rates of absorption or evaporation of moisture on the two sides, or internal stresses in the paper. The axis of the curl is usually parallel to the machine direction of the paper.


Cut-Off

In sack or bag manufacturing, that part of the tubing operations when the individual sack or bag is cut from the tubular web.

D

Density

The weigh per unit of volume, usually stated as pounds per cubic foot or grams per cubic centimeter.


Diamond Fold

A simple method of folding the top and bottom of a pasted sack distinguished by the diamond shape at both ends of the top or bottom folds before sealing.


Die cut

Paper cut with a sharp tool or die into a shape other than square cornered.


Die-Wiping Paper

A kraft sheet used in the printing and engraving trade for wiping the surfaces of printing plates. The significant properties are a high finish, smooth surface, strength and freedom from fuzz or lint.

 

Double Sewer

A sewing machine with two sewing heads on opposite sides for effecting the closure of both ends of a multiwall sack during one pass of the bag through the sewing machine.

 

Drop Test

A method of comparing sack performance by dropping filled sacks from predetermined heights and positions until sack failure occurs.

 

Dryers

A series of steam-heated, rotating metal drums on a paper machine against which the wet paper is held by endless felts for the purpose of drying the paper.

 

Dunnage

Any blocking, lining, strapping, inflatable sacks or similar bracing or supports used to hold a load in position for the purpose of preventing loss or damage in transit.


Duplex Paper

Any paper showing different colors, texture or finish on one side compared to the other side. Such paper may be made by combining two different stocks on a paper machine.


Duplex Sacks

Sacks made with two walls of paper, film or other flexible materials which may or may not be the same grade, type basis weight, etc.

E

Ears

The pointed extensions which appear at the corners of sacks after they are filled and closed. Primarily appears on flat tube sacks.


Edge Printing

The printing along the edge of a flat tube. The printing is visible on the side of the sack when the sack is filled.

 

Edge Protectors

Heavy paper used to protect the ends of paper rolls during shipment


Embossed Paper

Papers with impressed patterns created by special impression cylinders running against a back-up roll. Lines or other designs are created by embossing.


Ending

The operation of finishing a sack by closing the ends of the sack.

 

Extended Lip Valve

A type of diamond fold valve used in pasted multiwall bags wherein a valve extension is cut in one or all plies at the tuber and forms a flap or lip which extends into the bag and increases the length of the paper in the valve.

F

Face

The front of a bag or the side opposite the side of the bag on which the longitudinal seam is located.


Face Length

The length of the finished, empty sack or bag measured from top to bottom


Face Width

The distance from one edge of one gusset or side of a sack or bag to the opposite edge measured across the face of the sack or bag.

 

Fiber

The unit cell of vegetable growth, many times longer than its diameter, which is the basis of paper pulp.


Fiber Tear

A condition of bond or seal strength in paper or other fibrous laminates where separation of components causes rupture or tearing of the fibers.


Filler Cord

A cushioning medium introduced around the thread in needle holes so that the needle holes are sealed and the sack strengthened. The material is usually twisted soft yarn, cotton or twisted paper that is sewn into the needle holes to prevent sifting and to act as a cushion for the sewing stitches.


Fin Seal or Fin Seam

A seam formed by bringing the same sides of a ply together and sealing as opposed to an overlap seam where one side is brought together with the other side.


Finish

The surface property of a sheet of paper determined by its texture and gloss. High finish means smooth, glossy, hard surfaces. Low finish means the absence of a high-gloss surface. Finish is measured by reflected light.


Flat Bag

A bag having no gussets.


Flat Paper

Paper that is relatively smooth, as opposed to a sheet that has been creped. (See Creped Paper)


Flat Sewn Open Mouth

A flat tube, without gussets, with one end sewn closed by the sack manufacturer.


Flat Sewn Valve

A flat tube, without gussets, closed top and bottom by sewing that has a small opening or valve formed in one corner for filling.


Flat Tube

A tube that has no gussets.


Flexographic Printing

A type of printing done while the paper is still in the web and before the paper is formed into bags or sacks. Flexographic printing is generally water based inks, although some solvent based inks are used.


Flush Cut Top

All sack walls are cut off evenly across the top; not stepped-end.


Fold Over Tape

The tape sewn into the closure of a multiwall sack.

 

Fourdrinier Machine

A type of paper machine on which the web is formed by depositing pulp on the surface of a moving endless wire screen, called a wire or machine cloth. When the pulp is fed onto this wire, it is 99% water and 1% fiber. The wire screen permits most of the water to drain out of the sheet and the fibers have become more tightly interlocked. When the paper leaves the Fourdrinier wire, it enters the press section of the paper machine.


Free Film

A plastic film incorporated into a multiwall sack as a separate ply.


Freeboard

The distance between the top of the product and the top of the sack when the sack is placed upright.


Freight Classification Stamp

An imprint bearing the sack manufacturer’s name or symbol that guarantees that the construction of the sack meets or exceeds the requirements of the applicable freight classification.

G

Gauge

Caliper or thickness expressed as 100 times millage. e.g. 1 mil = 100ga.


Glassine Paper

Highly hydrated pulp made into paper and then super-calendered. Used as a grease barrier and can be colored or tinted.


Greaseproof Paper

A descriptive term for any highly refined and dense sheet of paper that has been treated or coated to provide a good barrier to some fats and oils.

 

Gusset Pasting

Small dots or bars of paste applied between the plies of a tube in the gusset area.


Gusset Print

Print design or lettering occurring in the gusset of the bag for product identification when bags are filled and stacked on pallets.


Gussets

The reverse folds in the sides of square, automatic and sewn multiwall sacks. Not found in flat tube sacks.

H

Halftone Printing

A process using printing plates, usually copper or zinc, produced by the photoengraving process. A reproduction of original artwork having a gradation of tones. The surface of the plate consists of dots of various sizes, generally spaced from 40 to 180 per linear inch, which are capable of rendering not only the extreme lights and darks of a picture but all gradations in between.


Hands of Stack

A term used to describe a group of sacks ranging from about 15 to 25 sacks placed in a stacking pattern for palletizing unfilled sacks.

 

Heat Reactivation Closure

A closure constructed of thermoplastic resin allowing it to be sealed with the application of heat. Primarily used with pinch bottom sacks.


Heat Sealable Sack

A term applied widely to a variety of surface-coated papers that can be sealed by the application of heat.


Heavy Duty Plastic Bag

A plastic bag of single or multiple ply construction, designed to serve as the prime shipping container.


Hot Melt Adhesive

A thermoplastic adhesive composed of blends of polymers, resins, and/or waxes. The adhesive is liquefied by heat, applied molten and forms a bond by cooling and solidifying.


Humidity

The amount of moisture present in the air.


Hygroscopic

Having the property of readily absorbing atmospheric moisture.

I

Impact Strength

Resistance of a plastic film to shock impact. It is measured by dropping a weighted round dart onto the film from a given height. Also called Dart Impact.

 

Impression Cylinder

A large cylinder on a printing press over which the paper is threaded. As the inked plate comes around, it strikes the paper at the point where the inked plate passes over the impression cylinder.


Imprint

Identification marks or symbols printed on a multi-wall sack, consisting of code numbers, freight classification stamp, etc. Not part of the brand printing.


Industrial Papers

Papers that are manufactured for industrial uses such as impregnating, insulating, and packaging as opposed to cultural papers or fine papers used for writing and publishing.


Ink coverage

The amount of ink printed on a sack or bag in relation to the total area of the package available for printing.


Ink Receptivity

That property of a sheet of paper, or other material, which causes it to absorb ink.

 

Inverted Bottoms

Pasted sack bottoms folded in the opposite way from bottoms normally produced on the sack machine.

K

Kinetic COF

The resisting frictional force required to keep one object moving over another at a constant speed. The force needed to keep an object moving once it is started in motion.


Kraft Paper

A paper made entirely from wood pulp produced by a modified sulphate pulping process. The paper is coarse and noted for its strength. The name is obtained from the German word “kraft” meaning strength. It is usually manufactured on a Fourdrinier machine. Its natural color is brown, but by using semi-bleached or bleached sulphate pulp it can produce lighter shades including white. Kraft paper used for shipping sacks and bags is most commonly made in basis weights from 25 to 80 lbs.

L

Lacquer

A transparent coating applied on the printing press over the ink to provide gloss, protection from ink scuffing, higher slide angle or, in some cases, lower slide angle.


Laminated Paper

A combination of two or more sheets of paper, film or foil bonded together in order to make a sheet stronger or more resistant to moisture, grease or odor.


Lap

In sack manufacturing, the amount of the web necessary to allow one edge to extend over the other so that they can be joined by an adhesive to form a tube. Also refers to the paper necessary in the ends of pasted bags to allow one side of the tube to be folded over the other to form a pasting area.

 

Length (Finished)

The longest dimension of an unopened sack exclusive of lips or thumb tabs.


Letterpress Printing

The process of printing directly from an inked, raised surface against which the paper is pressed.

 

Liner

A heat-sealed plastic sack inserted inside a paper sack to provide barrier protection for the product packed.


Linerboard

A high basis weight and stiffer natural kraft paper generally intended for rigid applications such as a corrugated box. Linerboard is used for roofing shingle wrap and single-wall baler sacks.

 

Low-Stretch Crepe Paper

Paper with only 3 to 7.5 percent crepe for a rough outer surface to improve handling and stacking.

M

Machine Crepe

Creped paper produced on the paper machine, not as a secondary off-machine operation.


Machine Direction

The direction of paper parallel to its forward movement on the paper machine. Also called “with the grain.”


Machine Finish

The finish obtainable on a particular paper machine without the aid of any added equipment such as water boxes or super calenders.


Machine Glazed

A high finish paper made on a Fourdrinier machine with a Yankee Dryer. The latter gives the paper a smooth, glossy, high finish on one side.


Melting Point

The temperature at which a solid substance begins to melt under standard conditions.


Metallized

A very thin coating of metal, usually aluminum, which is vacuum deposited on film and foil.


Micron

Caliper or thickness in metric system 1.0 mil = 25.4 microns.


Mil

The caliper of thickness expressed in mils. 1 mil = One thousandth (1/1000) of an inch or 0.001 inch.

 

Moisture Barrier Sheet

Paper with an ability to resist transmission of water or water vapor.


Moisture Content

The percentage of water in a material. It is usually determined by completely drying a sample at 100 to 105 o C. (212 to 221o F). The result is expressed as a percentage of the original weight of the sample.

 

Moisture Vapor Transmission Rate

The rate of grams of moisture that will pass through an area of 100 sq in of barrier material in a 24 hour period expressed as gm/100 sq in/24 hr.


Mold Inhibitor

A chemical additive used in paper to prevent or delay the growth of mold.


Mullen

The resistance of paper to rupture under pressure. Usually determined on a Mullen tester and expressed in pounds per square inch. Also referred to as bursting strength.


Multiwall Paper Shipping Sack

A flexible container made from two to six plies of kraft paper, meeting designated specifications. The walls or plies may be made up of 40, 50, 60 or 70 lb paper and one or more plies could be a plastic film, foil, or a laminated sheet.


Mylar

DuPont trade name for polyester film.

N

National Motor Freight Classification

A national tariff published by the American Trucking Association which sets forth container specifications for all commodities being moved by common carrier trucks.


Natural Paper

Paper that is not bleached, dyed or tinted. Paper that is the color of natural kraft, a light tan or brown.


Needle Thread

The thread which is inserted by the needle which passes completely through the sewn sack


Nesting

The manner in which the walls of a sack fit within or nest to one another; with correct nesting each wall will bear its proportionate share of the burden.

 

Notch

The portion of a sewn valve tube that is cut away leaving an extension at one corner to be folded into the sack when the valve is formed. The depth of the notch determines the valve extension depth.


Notch Depth

In multiwall bags, the deepness of the notch cut out of the tube.

O

Offset Gussets

The offsetting of the face and back of gusseted open mouth sacks to allow opening the sack for placement on a filling spout.


Offset Printing

A method of printing in which plates receive the ink and transfer the image to a rubber blanket which in turn prints on the paper. Also referred to as lithography.


Opacity

The resistance of paper to light transmission.


Open Corner Sack

A type of “intermediate” multiwall sack between the basic two styles: valve and open mouth. It usually has a sewn bottom and the top is partially closed by sewing.


Open Mouth Sack

A sewn or pasted sack, factory closed at one end.

 

Overall Perforations

Perforations occurring over the entire surface of the bag.


Overprint Varnish or Lacquer

In the printing operation, a special coating applied over the printed areas of a web on the printing press. This coating can provide gloss, rub resistance, slip requirements and other special properties.

 

Oxygen Transmission Rate

The rate in cubic centimeters that pure oxygen will pass through an area of 100 Sq in of barrier material in 24 hours, expressed as: cc/100sq in/24 hr.

P

Palletizing

The operation of stacking materials on a pallet, manually or mechanically.


Paper

A mat of cellulose fibers which is formed by suspension in water on a wire screen, and which subsequently has had the water removed by
means of a vacuum and heat drying.


Paste

A mixture of starches, dextrines or similar materials with water, used as an adhesive. This type of adhesive is commonly used in multiwall bag and sack manufacturing.


Paste Line

The stripes of adhesive applied to the longitudinal seams of the sack.


Pasted Open Mouth Sack

A non-gusseted or flat tube sack with a pasted bottom closure. Also referred to as a satchel bottom sack.


Pasted Open Mouth Self-Opening Sack

A gusseted sack with a formed pasted bottom. This sack may be opened with a quick snap, forming a rectangular bottom.


Pasted Open Mouth Stepped-End Sack

A flat or gusseted sack with the face, gussets and back stepped at different lengths so that when folded over, the back stepping pattern adheres to the corresponding surface of the opposite face.


Patched Seam

A strip pasted over the longitudinal seam to prevent sifting of the product.


PE Coated Paper

A paper coated with polyethylene.

 

Perforate

The act of making perforations in a tube or bag.


Perforation Knife

A serrated knife used to perforate each wall of paper prior to separation to make stepped-end tubes.


Perforations

Small vent holes punched through the walls of a bag to allow air to escape from the bag rapidly during the filling operation.


Photopolymer Plates

Printing plates made from a polymer material.


Pick Test

A means of measuring the resistance of paper to fiber separation.


Picking

A term for a defect in the printing on a label involving removal of small areas of the coated surface of the paper.

 

Pinch Bottom Sack

A pasted open mouth stepped end sack.

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Pinch Stock

A term used to describe the stepped-end closures of a flat tube or gusseted pasted open mouth sack in which the stepping pattern of the various plies provides for more sift-resistance in the ends of the sack and allows the sack, when filled, to form a more box-like shape.


Pinhole Perforations

Small holes in a sack made by perforation pins to allow the escape of air during packing. Perforations may be under the valve and/or over the entire surface of the sack or in a barrier ply only.


Pinholes

Minute holes in a sheet of paper that may be caused either by spaces between the fibers or by foreign particles, or both.


Plain Bag

An unprinted bag or sack.


Ply

A wall of a sack. A single thickness or fold of paper. Plies are described from the inside ply of the package to the outside ply.

 

Poly

A generic term for polyolefins, including polyethylene and polypropylene.


Polyethylene

A thermoplastic material composed solely of polymers of ethylene abbreviated PE.


Polymer

A compound formed by the linking together of two or more monomers. A homopolymer means that the monomers are the same. A copolymer means that the monomers are different.


Pop Test

A slang term for Mullen or bursting strength.


Porosity

The characteristic of a sheet of paper that permits the passage of air through the sheet. A measure of time in seconds required for the passage of 100 cc of air through one square inch of paper.


Porosity Block

A coating printed on the outer ply of a multiwall bag in an area that will be contacted by vacuum cups of automatic bag placement equipment.


Pouches

A term used to identify small bags holding up to 10 pounds.


Pressure-Sensitive Tape

Kraft tape, coated on one side with a pressure-sensitive material and on the second side with a release agent. Requires only brief pressure at room temperature to use. Some pressure sensitive tapes are supplied with a release backing of paper that is removed at the time of use.

 

Print Copy

A sample bag or plate proof, bearing a print number ink shade and register, the likeness of which is to be reproduced on the printing press.


Print Impression

The pressure required to transfer the ink from the printing press etched roller to the printing plate and from the printing plate to the web being printed. This affects the sharpness of the printed image on the substrate.


Print Roll

A roll of paper or other material that has been printed.

 

Printability

The property of a paper or other material that determines how well the material can be printed.


Proof

A test print or trial impression in the printing process that is taken for examination or correction.


Punch Holes

Holes punched in multiwall sacks to allow product to breath. Distinguished from perforation holes in which a sharp instrument pierces holes in the paper, but removes no material in the process. Punched holes remove material equal to the diameter of the punch.


Puncture

A measure of the force required to push a probe through a packaging material.

Q

Quilon

A DuPont Trade Named special chemical treatment applied internally or to surface of paper to provide water repellency.


R

Ream

A term used to denote 500 sheets of industrial paper 24″ x 36″ or 3000 square feet of paper.

 

Reel

A term applied to the untrimmed roll of paper of full machine width, wound on a large shaft a the dry end of the paper machine.


Register

In printing, the exact placing of successive colors as they are printed by the sequential printing stations over or adjacent to each other on the web.


Regular Finish

The normal finish on multiwall paper, neither smooth or rough.


Relative Humidity

The amount of moisture in the air at a given temperature, expressed as a percentage of the total amount of moisture the air could hold at that temperature.


Repeat Length

In printing, the total circumference of the printing press plate cylinder with a printing plate of correct thickness in place.


Rewinder

A machine to wind paper or other materials from one roll to another. Also called a winder.


Rip Tape

A cord, thread or tape used to open a sewn sack without tearing the sack. Sometimes called a rip cord or tear tape.


Roll Print

Printed paper on a roll.


Roll Width

The width of material wound in a roll.


Rosin Size

A sizing material made from pine resin that is frequently added or applied to paper to render it moisture resistant.


Rotogravure Printing

The process of printing from a cylindrical surface having an etched or recessed, design.


Rough Finish

Multiwall paper have a rough or course textured surface or finish.


Rug resistance

The resistance of ink to smearing or transfer when rubbed against itself or another material.

S

Sack

A non-rigid container made from paper or other flexible material. It is made by forming a tube and closing one or both ends but leaving an opening through which the material to be carried in the container is introduced. Preferably used to describe packages of 20 pounds net weight or above.


Saran

DuPont trade name for PVDC coating.


Satchel Bottom

A pasted bottom which forms a flat base when filled.


Scoring

A crease placed near the top or bottom of the sack for easy forming in opening or closing operations. Also called creased top.


Scrim Paper

Paper sheet reinforced with open mesh, textile or glass fiber threads

 

Scuffing

The raising of the fibers on the surface of a paper or paperboard when one piece is rubber against another or comes in contact with a rough surface.


Seal Strength

The force required to separate a seal. Seals are made under standard conditions of pressure, temperature, and dwell time. Seal strength is usually expressed as the grams of force required to separate a one inch wide seal.


Sealability

The property of a material that renders it capable of being fused or sealed to itself by the application of heat and pressure.


Sealant

The layer of a packaging material that seals to another layer or itself when heat and pressure are applied.


Seam

The overlapping and pasting portion which runs the entire length of the tube from which a sack is formed.


Seam Paste

The adhesive used in forming the seam of a paper tube.

 

Self-Sealing Valve

Valves in multiwall sacks that close automatically from the pressure of the contents.


Serrated End

The “saw-tooth” edge at the end of a paper sack.


Sewing Thread

The thread used to close the ends of sacks in sewn closures.


Sewn Closure

A method of closing filled sacks with a special sewing machine.


Sewn Open Mouth Sack

A gusseted or flat tube sack, factory sewn with thread or tape on one end.


Shear Cut

The cut on bag tubes made by a knife with a straight edge.


Shifted Slits

Slits at the end of a tube to give shingling of walls at pasted ends improved sift resistance as opposed to flush cutting or cutting all walls together.

 

Shipping Sack Kraft

Normally 40 to 60 pound basis weight kraft paper manufactured specifically to meet the requirements of shipping sack packaging.

 

Side Seam

A longitudinal seam placed at or near the edge of the sack to avoid having the seam in the printed area.


Sift Proof Bottom

A bottom formation which prevents loss of contents by sifting,


Size or Sizing

Chemicals that are added to paper to render them resistant to moisture. Size may be added at the size press or internally.


Size Press

Located between dryer sections on a paper machine the size press consists of a tank and a pair of press rolls. The sizing material is applied to the paper as it passes between the rolls. The pressure between the rolls determines the amount of material applied to the sheet.


Sized Paper

A paper that has been treated internally or on the surface to resist the penetration of liquids.


Skid

A low platform on which material is loaded in order to store or transport it. Sometimes referred to as a pallet.


Skid-Resistance

That property of the outer surface of a bag or sack that prevents it from sliding.


Slack Fill

A loosely filled bag.


Sleeve

A separately applied piece of paper and/or plastic film in the valve opening to prevent sifting.


Sleeve Extension

The distance a tuck-in sleeve extends out of the valve, measured from the edge of the valve to the outside or mouth end of the sleeve.


Sleeve, Internal

A single ply insert extending through the valve opening into the multiwall sack to prevent sifting.


Sleeve, Tuck-In

An outer sleeve extension on a valve sack that is folded and tucked in by hand after the sack has been filled.


Slide Angle

The angle at which paper will start sliding when in contact with another piece of the same paper and under standard test conditions.


Slip Sheet

A sheet of material that is inserted between two surfaces to separate or protect them. Can be used in place of a pallet, with proper push-pull attachment to a forklift for loading and unloading.


Slitter Cuts

Small cuts made in the paper parallel to the sack edge to aid in forming the ends.


Slitter Dust

Dust from the slitter that may be caught up in the moving web of paper and may cause trouble in subsequent finishing or printing operations.


Soft End Roll

A roll of paper on which the ends are softer or looser than the rest of the roll.


Soft Ends

Ends of sewn sacks in which the bound over tape is not drawn tightly over the ends of the tube or sewn too close to the tube end.


Softening Point

The temperature at which a plastic film becomes too soft to withstand stress or begins to block. High packing temperatures (filling sacks with hot products) can have an adverse effect on some films.


Splice

The joining together of two lengths of material by their ends. Used to repair a break or to attain greater continuous length in a roll. Splices are made using either glues or adhesive tapes.


Splice Tag

A marker put in the edge of a roll to show the location of a splice. Also called a flag.


Spot Label

A label that covers only a portion of the package. Usually refers to a small supplementary label. Sometimes used for small quantities of a specific product for use with a standard printed sack.


Spot Pasted

The pasting together of the walls of multiwall sacks with small spots of adhesive near the open end. This facilitates opening the bag and prevents product from getting between the plies when filling.


Spray Closure

A pasted closure for a filled sack made by spraying adhesive through an air brush.


Square Bag

A gusseted bag with a machine formed pasted bottom. Sometimes referred to as an SOS or Self Opening Square or Automatic bag. The bag may be opened with a quick snap forming a rectangular bottom.


Square Cut

A label, band or wrapper that is square or rectangular, usually cut on a guillotine cutter.


Staggered Gussets

Gussets formed so that edges are slightly offset with both edges able to be seen from one side.


Static COF

The resisting frictional force required to start an object to move when in contact with another object also at rest. The initial sliding force of an object on another.


Static Electricity

The electrical charge that sometimes collects on paper, film and other materials when in contact with other substances. It is most evident at low relative humidity levels and may cause undesired sparking.


Stepped-End Open Mouth Sack

A flat or gusseted sack with the face, gussets and back stepped at different lengths so that a flap or extension of the front, on one end of the bag tube and a flap on the back surface of the opposite end is produced. In the bag plant, hot melt adhesive is applied to the flap at the bottom of the bag, the flap is folded over the opposite surface and pressure applied to complete the closure. Hot melt adhesive also is applied to the flap on the open end of the bag in the bag plant, but the flap is not folded. After the bag is filled, the bag is closed on a pinch bottom sealer that reactivates the hot melt adhesive, folds the end flap over the opposite face and applies compression to complete the closure.


Stepped-End Tube

A tube in which each ply is cut individually in a stepped pattern rather than all plies cut together and straight across. Successive plies extend, one beyond the other, so that when the bag is pasted shut, each ply is pasted to itself.


Stretch

The amount of extension or elongation of a paper or film when under tension. Usually measured by tensile test equipment and reported as a percentage of elongation before the sheet breaks.


Stretch Wrap

A copolymer film with modifiers that impart a high degree of elasticity. When stretched around a bundle or pallet load under tension less than its elastic limit, its restoring forces will exert tension on the bundle or load it contains.


Substrate

Any material such as paper, film and foil to which adhesives, inks or coating are applied


Super Calendered Paper

A paper with a very smooth finish obtained by running the paper through a special finishing machine. Such a finishing machine consists of alternative hard and soft rolls while a conventional finishing machine or calender stack has only hard rolls.

T

Tack

Stickiness. Adhesives, inks, lacquers, varnish and other coatings that impart a tacky or sticky characteristic to the substrate, especially if not properly applied or dried.


Tagging

The inclusion of a tag in the closure, either at the time of sack manufacture or when the filled sack is closed. Usually done with sewn closures.


Tape

A narrow band of paper, generally creped, folded over the ends of a bag and sewn to the bag to form the closure.


Tape Over Stitching

Tape applied after the bag has been sewn closed in order to cover the stitch line at the bag closure to prevent sifting and improve barrier properties. Wet adhesive, hot melt, or heat sealed thermoplastic coated tape can be used.


Tape Top Closure

The sewn closure of filled sacks incorporating bound over tape.


Tear Tape

A narrow tape pasted along the inside of a bag to provide a quick and easy opening feature.


Tearing Strength

The force, in grams, required to tear a sample of paper under standard conditions.


Tensile Strength

The force, in lbs/inch of width, required to break a paper strip of a specified width and length under specified conditions of loading.


Thumb Notch

A small, semi-circular cut made at the top center of a paper bag to facilitate opening of the bag.


Tolerance

The allowable variation from specified dimensions of a package


Top

The upper end of a bag or sack when viewed with the printing in an upright position. Frequently open mouth bags are closed at the top end in the factory in order to provide special features such as easy-opening.


Trap

The printing of a subsequent color of ink over another in a satisfactory manner that does not show the first color. The first color printed must be lighter than subsequent colors in order to be trapped by the darker color.


Treated Papers

Papers that have functional characteristics added through special treatment. Among the most common are: Insect Resistant, Mold Resistant, Silicone (release) coated, clay coated, flame retardant.


Trim

The widest sheet of paper, after removal of the deckle edges, that can be made on a given paper machine. Also refers to a true cut to an exact size by cutting away edges of paper in a web or sheet.


Tube Length

The length of the tube of paper or other material before the sack is ended.


Tubing

The forming of continuous webs of paper into a cylinder on a bag-making machine and then cutting to length to produce a tube for a given bag size.


Tuck-In Sleeve

A sleeve which extends out of the valve and which may be folded and tucked into the valve after filling the bag.

U

Unbleached

A term applied to paper or pulp that has not been treated with bleaching agents.


Uniform Freight Classification

A national tariff published by the railroad industry that sets forth container specifications for all commodities being moved by rail.


Universal Product Code

A ten to 14 digit code printed on packages that uniquely identifies the product and package size and permits a photocell to read and record the product for automatic inventory control.


Unsized

A term applied to papers which have no sizing added.


UV Resistance

The resistance of a material to degradation from ultra-violet rays in sunlight, usually expressed in terms of hours at which a given percent of tensile strength is retained.

V

Valve

An opening folded into a corner of a sack through which the sack is filled.


Valve Extension

The distance that the valve notch extends beyond the normal valve in-fold.


Valve Insert

A strip of material pasted into the valve opening to make the valve stronger and more sift-resistant.


Valve Perforations

Perforations placed beneath the valve of a multiwall sack to release air pressure during filling.


Valve Position

The identification of location of the valve when facing the front of the bag, the face opposite the longitudinal seam, when the printing is upright. Referred to as upper left hand (ULH), upper right hand (URH), lower left hand (LLH) or lower right hand (LRH).


Valve Sack

A sack whose top and bottom are factory closed, with the exception of a small opening at one corner called a valve.


Valve Size

The internal, lay flat, dimension of the opening in the corner of a valve sack.


Vent Holes

Holes punched in multiwall plies to allow the package to breathe when the product is packed.


Viscosity

The property of a fluid that offers resistance to flow or motion within itself. The higher the viscosity, the thicker or heavier the liquid.

W

Wall

Any one of the sheets of paper or other materials making up the plies of a sack.


Water Repellent

A property imparted to certain papers to shed water. Often recommended for use where the sack is exposed to water droplets or water spray.


Water Resistant Paper

Paper that has been impregnated, coated or laminated to resist the penetration of water.


Water Vapor Transmission Rate

A term used to express the weight of water transmitted per unit of time, per unit area, when the barrier separates a dry atmosphere from an atmosphere of specified relative humidity and temperature. The grams of moisture that will pass through and area of 100 sq in of material in a 24 hour period, expressed as gm/100 sq in/24 hr.


Waterproof Adhesive

An adhesive class of synthetic resin or latex base designed to be used in sack constructions with water resistant or wet strength paper. These adhesives are resistant to failure when soaked in water.


Wax Laminated Kraft

Two sheets of kraft held together with wax.

 

Waxed Kraft

Kraft paper that has been treated with wax to give it resistance to moisture, water, and grease.


Weather Resistant Paper

Highly sized and/or highly finished paper used as an outer wall in sacks to help repel water.

 

Weight Mark

The printed amount of weight of contents which a filled sack or bag will contain.

 

Wet Strength Paper

Paper made from pulp treated with urea formaldehyde or other materials to retain a substantial part of its original dry strength when saturated with water.


Width

For an empty sack, the measurement from edge to edge. Often called the face width.


Wire Side

The side of the paper web that was in contact with the wire on the wet end of the paper machine during manufacture of the paper.


Wire Tie

A wire covered in paper or plastic that is used to close some consumer bags.

Y

Yield

The number of square inches per pound of material or square meters per kilogram of material.