Paper defects that are not included in the technical requirements of paper quality can be called paper diseases. Paper diseases include not only invisible and intangible, but also certain performance defects that can be known only through experiments or printing, such as brittleness, through-printing, hair loss, powder loss, etc., as well as those that can be directly seen or felt. Various defects and defects on the surface of the paper, such as dust and dirty spots. The latter is referred to here as the appearance of paper.
The appearance of the paper is a lot of diseases, such as dust, spots, net marks, woolen marks, "cloud flowers", seersucker, wrinkles, folds, dirty spots, turf, transparent spots, warm spots, holes, embossing, scars, pimples, Hard blocks, uneven quantitative, poor uniformity, etc. Some of these appearance paper diseases are caused by the paper material 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 woolen marks and "cloud flowers", etc. Once it appears, it will persist if no measures are taken; some appearance paper diseases have a certain chance or appear only once at a long interval, such as dirty spots. , Holes, etc. Some paper diseases will deteriorate the quality of the paper, such as dust, woolen cloth marks, etc .; some paper diseases will make the paper waste, such as offset printing paper with hard blocks or copperplate with large dirty spots Paper can only be treated as waste.
According to different types of common paper diseases can be divided into:
Paper quantitative fluctuation and paper web quantitative unevenness
The first kind of fluctuation is generally caused by the periodic vibration of the paper feed system to the headbox, the shaking of the rotor screen in front of the headbox or the vibration of the pulp pump, and sometimes due to the uniform Caused by unreasonable bending or opening of the pulp roller. The second type of fluctuation is generally caused by reasons such as unreasonable production processes or improper operation management.
Poor uniformity. The phenomena are:
1) Tufted structure: refers to the state in which fibers are clumped together to form a mass.
2) "Cloud Flower": It is also called cloud-shaped organization, which means that the fibers in the paper are distributed in the paper like clouds.
3) Fibrous tissue disjoint: refers to poor interweaving of fibers in the running direction of the paper machine.
4) Wavy fibrous structure: refers to a thick layer of wavy waves that appear tortuous along the width of the paper.
5) Pulp path: refers to some longitudinal stripe-shaped pulp marks on the paper web that are visible to the light.
Dust, spots, sand and hard blocks
1) Dust: It can be divided into three types: "fibrous dust", "non-metallic dust", and "metallic dust".
2) Spots: can be divided into "wet spots and vapor spots", "cylinder spots", "calender dark spots", "paste spots", "bubble spots", "filler spots and paint spots", "bright spots and white spots" ".
3) Sand: refers to the hard mineral sand grains such as silt, lime product residue, carbon residue and so on existing on the paper surface.
4) Rigid block: refers to the blocky material or coarse-grained materials that occur on the paper surface by chance and have a hard texture that is higher than the paper surface, such as wood knots, grass knots, and pulp blocks, etc., which are the most harmful to printing.
Holes and blinds
1) Holes: Refers to the holes on the paper that are completely penetrated and have no fibers. Holes can be divided into pinholes, holes and holes according to size.
2) Penetrating curtain: refers to the idea that the fiber layer on the paper sheet is thin but not fully penetrated, and its light transmittance is larger than other parts of the paper sheet. The small ones are called light-transmitting points, and the big ones are called transparent curtains.
Embossing and various marks
1) Embossing: refers to that the fibrous tissue forming wet paper collapses under the strong pressure during the pressing process, leaving scattered distribution on the paper surface, irregular shape, high transparency and many gaps The small pinholes, this phenomenon of wet paper crushed by the press roll is called embossing. Severe embossing can easily cause the wet paper to break at the press section.
2) Strip marks: refers to strip marks with different gloss or color from the paper surface under the irradiation of light.
3) Felt marks: refers to the marks on the paper of the warp and weft of papermaking felt.
4) Other marks: there are net marks, watermark roller marks and vacuum roller marks.
Folds and creases
1) Fold: refers to the folding or overlapping of paper sheets to form folds or creases. Can be divided into two kinds of dead fold and live fold.
2) Warping and arching: Warping refers to the state where the paper is curled on both sides or four corners, and the middle is concave; arching refers to the state where a large area is arched in the middle or middle of the paper, and the sides or four corners are concave.
3) Bubbling and bubble sand: Bubbling refers to the local contraction of the paper sheet, resulting in protruding bubbles on the paper surface, and there are fine wrinkles on the paper surface around the bubble; bubble sand refers to the arrangement of the paper surface Denser small bubble point
4) Various wrinkles: Divided into curved wrinkles, fine diagonal wrinkles, curly wrinkles, etc. according to size and shape.
Other paper diseases
1) Crack: refers to a crack or tear in the middle or edge of the paper.
2) Uneven and unclean paper edges: Uneven paper edges mean that the paper edges cannot be parallel lines or rectangles after the paper is cut, or that the paper edges have burrs, bends, and twists. The rear paper code is unevenly placed or there is a phenomenon of "in and out" in the rear end of the rewinding. Unclean paper edge means that the paper sheet has burrs, jagged edges, torn edges and dirty edges after cutting.
3) Inconsistent color tone: refers to the inconsistency between the same batch of products and even the whiteness and color of the paper.
4) "Loose lace": refers to the edge of the paper, especially the longitudinal edge, loses its straight state, and forms a curved state that is not in the same plane as the paper.
5) Obvious difference between the two sides: a rough observation with the naked eye can see the obvious difference between the two sides of the paper (except single-sided offset paper and single-sided coated paper).
6) Torn, torn and torn pieces of paper: torn and torn pieces of paper refer to incomplete sheets of paper, with missing corners, missing edges, torn or only half pieces, etc .; shredded paper refers to the size of the paper that is mixed in One small piece of paper.
The appearance quality of paper refers to the paper quality condition that can be distinguished only by human senses without using instruments and equipment. It can be divided into the appearance quality of the paper sheet itself and the appearance quality of the piece of paper formed by one sheet of paper or a long strip of paper sheet.
No matter what kind of appearance quality affects the use of paper to varying degrees. Poor appearance quality will not only reduce the use value and printing yield of paper, but also make the paper a waste product in severe cases. In addition, some serious appearance paper diseases such as hard paper blocks, etc. in the paper will also damage the printing plate and rubber roller during printing, causing damage to the printing equipment. The appearance quality and physical properties of paper are also closely related. For example, the smoothness and opacity of paper with obvious seersucker appearance will also be affected.
The appearance quality inspection of paper should achieve the following three purposes:
Check the quality of the paper. Mainly include: whether the shape of the piece of paper is good, whether the size is qualified, the packaging quality and the degree of damage, etc.
Master the basic paper quality of the paper. Including color, uniformity and smoothness, flexibility and tensile strength, smoothness and cleanliness.
Randomly check the approximate miss rate of lithographic paper (the percentage of paper with obvious paper diseases).
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