Print Paper Overview - Common Paper Diseases

The appearance quality of printed paper and common paper diseases

Paper defects that are not included in the paper quality technical requirements can be referred to as paper diseases. Paper sickness includes not only invisible, but only certain performance defects known through experiment or printing, such as brittle, print-through, lint-free, powder-fat, etc., as well as those that can be seen or felt directly. Various defects and defects on the surface of the paper, such as dust, dirt, etc. Here the latter is called paper appearance disease.

The appearance of paper is a lot of diseases, including dust, spots, net marks, wool marks, "cloud flowers", seersucker, wrinkles, creases, dirt, turf, clear spots, temperature spots, holes, embossing, scars, pulp, Hard blocks, uneven quantification, poor uniformity, etc. Some of these appearances of paper diseases are caused by paper materials before papermaking, some are caused by poor technical operation or poor technology in the papermaking process, and some are caused by poor environmental hygiene in the factory. Once it appears, it is relatively continuous, such as felt marks and “cloud flowers”. Once it appears, it will always exist if no measures are taken; some appearance paper diseases have some kind of accidentality or occur only after a relatively long time, such as dirty spots. , holes and so on. The presence of some paper diseases will deteriorate the quality of the paper, such as dust, felt, etc. Some paper diseases will make the paper waste, such as offset printing paper with hard blocks or copper plates with large dirty spots. Paper can only be disposed of as waste.

According to different types of common paper diseases can be divided into:

※ fluctuations in paper ration and uneven web quantification

The first kind of fluctuation is generally caused by periodic vibration of the feed system of the paper feed headbox, vibration of the rotor screen in front of the headbox or vibration of the pulp pump, and sometimes due to the uniformity of the headbox. The squeegee is bent or the hole is unreasonable.

The second kind of fluctuation is generally caused by reasons such as unreasonable production process or improper operation management.

※ Poor formation. The phenomenon is:

1) Tufty structure: refers to the state where the fibers are mixed together into a mass.

2) "Cloud Flower": Also called cloud organization, it means that the fibers in the paper are distributed like clouds on the paper sheet.

3) Fibrous tissue disjoint: refers to poor fiber interweaving in the running direction of the paper machine.

4) Wave-like fibrous structure: It refers to a wavy thickening layer that curves along the width of the paper.

5) Puddle: Refers to some of the visible longitudinal strip marks on the web.

※ Dust, spots, sand and hard blocks

1) Dust: It can be classified into three types: "fibrous dust," "non-metallic dust," and "metal dust."

2) Spots: Can be divided into "moist spots and vapor spots", "cylinder spots", "calender spots", "spots", "bubble spots", "filler spots and paint spots", "bright spots and white spots ".

3) Sand: refers to the sand, lime residue, carbon residue and other hard mineral sands present on the surface of the paper.

4) Hard block: Refers to the occasional hard texture on the surface of the paper, and the blocky material or coarse material that is higher than the paper surface, such as knots, grass knots, pulp blocks, etc., is the most damaging to the printing.

※ hole and curtain

1) Hole: It refers to the complete penetration of the surface of the paper, no holes in the fiber. Holes can be divided into pinholes, holes, and holes by size.

2) Curtain: It means that the fiber layer on the paper sheet is thin but not completely penetrated, and its light transmittance is larger than other parts of the paper sheet. The little ones are called light spots, and the big ones are called curtains.

※ Embossing and various prints

1) Embossing: In the pressing process, the fibrous tissue forming the wet paper breaks down under strong pressure, leaving a scattered distribution on the paper surface, irregular shape, high transparency and many gaps. The small pinholes, the phenomenon that the wet paper is pressed by the press roll, are called embossing. Severe embossing can easily cause the wet paper to break in the press section.

2) Streaks: refers to strip marks that are different from paper gloss or color under light irradiation.

3) Gross cloth mark: refers to the imprint of the latitude and longitude lines of the papermaking felt on the paper.

4) Other impressions: Net marks, watermark roll marks, and vacuum roller marks.

※folds and creases

1) Crease: refers to the folds or overlaps of the paper sheets that form the folds or creases. Can be divided into dead and sub-folding.

2) Warping and arching: Warpage refers to the state where the paper is curled on both sides or corners, and the middle is concave; the arching refers to a state in which a large area in the middle or in the middle of a paper is arched, and two sides or four corners are concave.

3) Bubbling and bubble sands: Partial shrinkage of blisters refers to paper sheets, resulting in protruding foams on the paper surface, and fine wrinkles on the paper surface around the bubbles; bubble sand refers to the paper surface A dense, fine bubble point.

4) Various wrinkles: According to the size and shape of the wrinkles, fine oblique wrinkles, curly wrinkles and so on.

※Other paper diseases

1) Rift: A crack or break in the middle or edge of a sheet.

2) The edges of the paper are not neat and unclean: The edge of the paper is not neat. On the other hand, it means that the edges of the paper cannot be parallel or rectangular after the paper sheet is cut or the edges of the paper are burrs, bends, and twists. On the other hand, it means cutting. After the paper size is uneven or the back-end surface of the rewinder has a phenomenon of "in and out". Unclean paper edges refer to burrs, zigzag edges, incomplete edges, and dirty edges on cut sheets.

3) Hue inconsistency: refers to the inconsistency of the whiteness and color of the same batch of products even with the ream.

4) "Load lace": It means that the edge of the paper, especially the longitudinal edge, has lost its flat state and it is in a curved state that is not in the same plane as the paper surface.

5) Obvious two-sidedness: The gross difference between the two sides of the paper can be seen with the naked eye (except for single-sided offset paper and single-sided coated paper).

6) Incomplete, broken and shredded paper: Incomplete and broken sheets refer to papers with incomplete pages, which have missing corners, lack of edges, broken or only half, etc.; shredded paper refers to the size of paper that is not included in the paper. A small piece of paper.

Source: Graphic Arts Perspective