Coating Defect Roller Speed Not Continuous Paper Web Coating Defecets

DEFECTS IN PAPER

DEFECTS IN PAPER

Air  Bells

Tiny circular thin spot in the paper. Also known as bubble marks or steam blisters.

Air  Bubbles

Light spots in a sheet caused by bubbles of air that form in the stock on a Fourdrinier wire (forming fabric) and are entrained in the stock as it cascades in trays and channels. The term also refers to bubbles of air formed in the coating operation and the defective imprint that is caused by the bubble bursting.

Air  Doctor Mottle

A paper coating defect caused by excessively high solid content or high viscosity of coating solution or poor adjustment of doctor.

Air  Knife Mark

A paper coating defect caused during the coating operation with an air-knife coater, producing areas that are more transparent than the rest of the sheet. They are called blade streaks when occurring in narrow areas running in the machine direction.

Alum Spot

Paper sheet having small undissolved alum crystals.

Backing Roll Mark

A paper coating defect caused by the building up of coating in areas along the machine direction where low spots occur in the coating back-up roll.

Backing Roll Mark

A paper coating defect caused by the building up of coating in areas along the machine direction where low spots occur in the coating back-up roll.

Baggy Paper

A paper which is thicker in middle than edges.

Bark Specks

These specks originates from outer bark of wood.

Binder Specks

A variation in ink receptivity caused by non-uniform binder distribution. A coated paper defect that results in a grainy or textured appearance on the coated surface.

Blackening

A paper showing burn marks on the surface.

Lowering of opacity of paper as a result of uneven formation, too much moisture, and crushing caused by too much during calendering. It produces darkening effect on the sheet.

Blade Cut

A blade scratch that cuts deeply into or through the web.

Blade Marks

Paper coating defects caused at the time of coating operation with a blade coater, producing areas which are more transparent than the rest of the sheet. It is also known as air knife marks or blade streaks.

Blade Scratch

A very fine, hair like indentation in a coated surface that runs in the machine direction, caused by a particle of varied origin becoming lodged behind the blade during coating.

Blade Wrinkle

A blade coating defect where the sheet has been folded over on itself when passing under the blade. It is irregular line essentially in machine direction.

Bleach Scale

Used for pearly, light brown, brittle spots in paper.

Blemish

Undesirable marks on the surface of paper sheet.

Blistering (Coated Paper)

Caused when water vapours can not escape fast enough through coating layers in the coating dryer section of the heat-set press.

Bristle Marks (Coated Paper)

Use for indentations in the surface of coated papers in the shape of brush bristles.

Brush Marks (Coated Paper)

Used for streaks in the surface of coated papers made by brushes which spread on the coating in the papermaking process.

Buckles

The edge of a roll, usually only part of the diameter, where the paper along that edge is thinner and longer than the balance of the width of the paper on the roll. To compensate for this extra length, it buckles as it is wound.

Burst

The defect in paper characterized by rapture in the web not extended to edges. It is caused by too high web tension between a hard and soft section of the reel during winding and results in a machine direction shearing force that exceeds the strength of paper.

Calender Blackened or Calender Crushed

A paper whose color has been darkened because of calendering it while it is still wet or with too much pressure. This crushes the fibers and disorients the formation resulting in to darkened color and reduced opacity and surface characteristics.

Calender Cut

A mark or cut occurring in the paper sheet as a result of wrinkles in the web while being calendered.

CourtesySCA

Calender Mark

Paper defects caused by faulty calender roll surfaces or extraneous matter which has entered the nips and stick to its surface.

Calender Streaks

Are relatively high(er) gloss bands in the machine direction, resulting from non-uniform wet pressing, drying, coating, etc, and these bands gloss more in the calender.

Chalking

1. Breaking away of pigment from paper surface during finishing and converting operation.

2. Rubbing off the ink pigment from printed paper surface.

Cloudy Paper

Paper with unevenness in look-through.

Coal Specks

It is a type of dirt. These are black, insoluble particles that are often in a pulverized condition, as a result of the action of calender rolls.

Coating Defects

Coating streaks are continuous defects that may be very clear and long, but they can be short and extremely narrow. Other coating defects are skips and splashes. Skip can be very subtle and detection is the main problem. On the other hand, coating splashes may provide a clear contrast with a specific shape.

Coating Lump

A random piece of dried coating that has been redeposited onto the web of paper.

Coating Mottle

A slight mottle created during the calendaring process due to a non-uniform base sheet or coating process.

Coating Splash

Random spots of excess coating.

Cockling

When the surface of the paper has wave like appearance.

Contraries

Presence of any foreign substance such as sand, dirt etc.

Corrugation

Simply put, corrugations are accordion-like paper folds that form when the web, strained beyond its yield point, cannot return to its original shape.
Corrugations can form on the paper machine, coater, calender stack or winder. They are caused by a combination of an uneven distribution of weight across the web and an uneven nip, which create strain.

Couch Marks

Defects which appear as a regular pattern, always when viewed by transmitted light and sometimes when viewed by direct light. Cause is usually some non-uniform water removal from the sheet of paper at the suction couch roll  and takes the pattern of the drilled hole in suction couch roll.

Crack

1. A defect in coated paper, caused by the separation of the coating layer on the formation of fissures in the surface of the coating due to printing or other converting process.

2. Crack at fold: Fissures in the crease when any paper is folded along a fold line. May be due to separation of coating or separation of fibers. More prevalent when the paper has been over-dried. In boards it may occur along score-folds even though the scoring has been done to minimize cracking at the fold. The term is also applied when coatings crack without fiber failure during a folding operation.

Cracked Edge

A paper web and Fourdrinier wire defect occurring as small breaks on the edges, with very little migration towards the center.

Crater (Coated Paper)

Small pits in coated papers.

Crazing

Defects in paper coating, appearing as short, random, intersecting cracks in the coating surface.

Crease

1. Deformation remaining from a fold over.

2. Cross direction wrinkles( Washboard): Fold over of a web in the cross machine direction, giving a crease running in the machine direction.

3. Blade crease: A crease essentially in the machine direction devoid of coating in the creased area.

4. Calender Crease: Usually a sharp crease caused by passage through the Calender of a crease or of a fold generated at the Calender; often cut through when it is preferable to call it a Calender out.

5. Smoothed crease: A flattened-out crease running mainly in the machine direction. Can occur at the wet press section, dryer (dryer wrinkles), size press, winder or sheeter.

Crepe Wrinkles

Crepe wrinkles are crease-like paper defects that occur mostly in newsprint and LWC papers. Typically an 1/8-inch to a 1/4-inch wide, crepe wrinkles generally form as a result of paper slippage in poorly built-up rolls, and excessive caliper variation of the sheet. Once the excessive and localized layer-to-layer slippage is momentarily blocked or interrupted, the wrinkle is formed. Paper that is severely weakened in creped areas is doomed to break in successive processes.

Crepe wrinkles can be found virtually anywhere in a roll, but primarily in the areas below a splice after a web break. They also form at the outer diameter of the roll during the rewinding process, as well as near the core.

Crush

A rippled paper surface defect that is caused by the use of too high pressure and/ or too high moisture in the press section.

Curl

Papers which curl up when placed on a flat surface.

Damp Streaks

 Streaks caused by uneven pressing or drying during paper manufacturing.

Dandy Marks/ Dandy Pick

 A defect consisting of a small, thin area left on the paper sheet due to the disturbance or picking up of fibers from the web by dandy roll.

Dark Spots

 Dark spots can be any kind of dirt or scrap. These are normally random defects and it is very difficult to find their origin.

Dead Spots

Paper sheet having any dull areas in an otherwise highly glossy surface.

Delamination

Paper peeling apart or separating from within.

Dirt

Any foreign material that is unintentionally embedded into the sheet of paper.

Drag Spots

Irregular streaks or long thin lumpy areas on the paper's surface.

Dust

Small particles of paper, fibers or coating materials that are found in a finished roll of paper or at the edges of a skid.

Edge Cut

Edge tears fold over during the winding operation. It may be caused by dull slitter that nicks the edge after which the stress of winding will cause the tear to open or the reel is bumped on the edge.

Courtesy SCA

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Felt Hair

A paper defect caused by felt filaments coming out of felt and embedded in to paper surface.

Courtesy SCA

Felt Mark

A paper defect caused by dirty or poor surface condition of wet felt in press section. It appears as spot or thin area on the sheet.

Fiber Clumps

Small pieces of fiber bundles loosely adhered to the surface of the sheet.

Fish Eye or Bird Eye

A paper defect appearing as glazed, translucent spot caused by slime, fiber bundles, and/or improperly prepared chemical additives in the stock.

Foam Spots

Holes or weak spots in the finished paper caused by foam in the wet end of the paper machine, or surface defects such as spots occurring in a coated paper surface as a result of foam in the coating.

Fuzz

Fibrous projections on the surface of a sheet of paper, caused by excessive suction, insufficient beating or lack of surface sizing. Lint appears in much the same manner but is not attached to the surface.

Haircuts

Hair-thin cuts in the surface of a sheet where it appears that hairs or long fibers have been pulled out of the surface.

Courtesy SCA

Hickey

An irregularity in the ink coverage of a printed page. Hickeys are caused by paper or pressroom dust, dirt, or pick out on the printing blanket, all of which prevent the ink from adhering to the paper surface.

Courtesy SCA

Holes

Holes may be clean or with some dirt at the edges. Typical clean holes are wire holes, calender cuts and edge cracks. If a hole is caused by foreign material, that has been in the sheet and later fallen off, there still may be some dirt left at the edge.

Reasons to slime holes are wet end slime, splashes of sizing material, or even wet fiber lumps.  The appearance of spot varies.

Iron Specks

It is a type of dirt. Iron specks can be determined by treating the speck with 10% HCl acid solution and potassium ferrocyanide solution. If speck is iron, it will turn intense blue. Rust specks are reddish brown to black in color.

Lint

Lint originates from loosely bonded surface fibers. This is also called fuzz or fluff also. Lint can cause fiber build up in the printed image areas when the lint mixes with ink.

Courtesy SCA

Missing Coating (Coated Paper)

Coating is missing at spots or in machine direction due to some problem at coater.

Orange Peel

A granular or pebble-like textured appearance (like an orange peel) that appears as a defect on the surface of a coated or printed paper.

Paper Dust

Cut or Broken fibers, fines, fillers depositing on paper during cutting or slitting.

Pin Holes

Imperfections in paper which appear as minute holes upon looking through the sheet. They originate from foreign particles, which are pressed through the sheet.

Piping

Defect in reels, consisting of ridges running around the circumference, due to moisture take-up by the surface layers or uneven binding or hard and soft spots.

Courtesy SCA

Pitch Specks

These are usually translucent specks which varies from amber to black in color. These comes from pitch.

Poor Joint

1. The joint tape is not properly placed and therefore sticks to the paper underneath.

2. The two webs are not put in line with each other  and therefore paper protrude at the end of the reel.

3. The joint tape is not covered by the paper or the backing. The tape stick to other paper layer and may cause a break.

Courtesy SCA

Poor Slitter Cut

Caused by dull or chipped off slitter. The cut appear irregular or rough. It gives the reel end a wavy or shaggy appearance.

Profile/Slack Edges

This results from non-uniform thickness and moisture content across the web. It may cause mis-register problems and web breaks in severe cases.

Courtesy SCA

Resin Specks

These are usually translucent specks which varies from amber to black in color. These comes from undissolved resin.

Ridge

A ring around the circumference of a roll or an area in a skid of paper in the machine direction that is harder or higher than an adjacent area; also called hard spot.

Roping

Paper defect appearing as a machine direction wrinkle in the sheet.

Longitudinal wrinkles in a coated paper.

Seam Marks

Is a defect in the web, normally running at approximate right angles to the machine direction and is seen as a light streak when viewed by transmitted light. Point of origin is usually an article of machine clothing, a wire or a felt, that is seamed. The distance from one defect to the other is a clue as to the origin of the mark.

Shadow Mark

A defect in paper appearance which looks like the drilling pattern in a suction roll. It is due to opacity effects caused by areas of vacuum and pressure as the wet web passes over a suction roll.

Shiners

Transparent spots in a sheet of paper caused by squeezing partly cooked fiber bundles and splinters during calendering.

Slaps

Ruptured spots at the edges of machine-made papers.

Slime Holes

A hole in paper, characterized by brownish translucent material around the edges. Caused by a lump of slime which has formed in stock system from the growth microorganisms, then becoming detached and flowing onto the paper machine wire with the fiber to form a non-fibrous area.

Slitter Dust

The accumulation of dust, primarily filler, fibers, or coating thrown off during the slitting operation, and remaining on or in the roll.

Slivers and Shives

Shives are small pieces of wood that have been cooked but whose fibers are not separated.

Slivers are small splinters of wood in a sheet of paper that have not been cooked.

Snailing

Streaks or snake like marks on the surface of a sheet.

Soft Start

The foundation of any roll is the first few layers of paper on the roll's core. If those first few layers carry a low-level wound-in tension, a soft start condition exists. Problems associated with soft starts include:

• The bond between the paper and the core breaks causing a loss of coupling with the unwind break.
• Starring develops.
• The roll tightens during unwinding, taking up loose paper at the core. This layer-to-layer slippage causes crepe wrinkles and breaks over the unwind core chucks

Spongy Papers

Paper that is too compressible or ink absorbent for its intended purpose.

Spots by Liquid Droplets

Liquid droplets cause spots, which have more regular shape than other spots. Oil spots are so translucent that they may be mixed with holes.

Starring

Starring is a common structural defect that appears as a collapse near the core of the roll. Caused by uneven stress distribution inside the roll, the starring or collapse of paper is initiated once a portion of the roll, which is wound with a low wound-in tension, increases and a ring or hoop of tightly wound paper causes a collapse of the softer wound interior. A highly unstable situation, virtually any outside blow can collapse the highly stressed ring into its softer foundation.

While most collapses are usually local and involve only two or three lines, more severe collapses can damage the paper in the fault area and require the roll be unwound. A starred roll is very difficult to unwind because it loses its concentricity. Because of severe tension fluctuations, the operator has to reduce the speed of the secondary process. If the roll is too damaged to rewind, recycling it is the only alternative.

Stickies

Stickies are tacky substances contained in the paper pulp and process water systems of paper machines. Stickies have a large tendency to make deposits on the processing equipment in certain stages of the papermaking process. Contaminations of paper that that are classified as tacky are also called stickies. The main sources for stickies are recycled paper, waxes, and soft adhesives.

Table Rolls Mark

Basis weight variations of web caused by waves on the wire created by table rolls.

Tacky Speckles

Types of contaminants found in de-inked pulp caused by plastic adhesive -like particles originating from heat seal coating, backing adhesive etc.

Telescoped Roll

A misaligned roll with one edge concave and another convex.

Trash in Roll

Any foreign material such as loose piece of paper, dust, dirt etc. caught up or blown in to a roll of paper during manufacturing or rewinding.

Trim in Roll

A paper roll defect caused by the rewinder slitter trim shaving inadvertently being wound up in the roll.

Uneven Caliper or Thickness (Not due to basis weight variation)

Variation in thickness on spot or in cross direction. May be caused by defective or improper crowning of press/calender  rolls.

Uneven Winding

A random edge formed at the end of a paper roll during rewinding caused by the lateral movement of the sheet and/or core.

Wild Formation

Paper sheet with uneven, random distribution of fibers, yielding a mottled appearance on look-through.

Winder Welts

Long grain-direction ridges in the surface of the sheet.

Wire Marks

Marks left on the paper web from the formation wire.

Wrinkle

Wrinkles are narrow folds in the paper caused by uneven paper tension profile. The wrinkles have a typical visual appearance, but often very subtle.

Wrinkle can happen in press, dryer or calender section or on winder and rewinder.

Yellowing

The deterioration and discoloration of a sheet of paper due to exposure to air, light or heat.

A Great source of Newsprint and Reel Defect Check List by WAN-IFRA (World Association of Newspapers and News Publishers.

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Source: https://www.paperonweb.com/PaperDefects.htm

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