Detect paper basics
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Paper packaging acceptance
At present, lithographic paper packaging mainly uses wood splint packaging and wooden box packaging.
Two basic forms. For qualified lithographic paper, the appearance of the package generally has two or more layers of wrapping paper, and then the wooden board is wrapped with a metal strip. The wrapping paper used mainly includes wax paper, tar paper, kraft paper, snake paper, and the like. On the wooden plywood or on the wooden box, indicate the words “moisture-proof” and “do not throw”, and some also indicate the direction of the silk of the paper. The product certificate should also be affixed on the wood splint or on the wooden box, and the product name, specifications, weight, each order, paper grade, execution standard, production date, and manufacturer name should be indicated. The outer packaging should be intact and should not be deformed or damaged. If the outer packaging is severely damaged and the paper is exposed to the packaging, you should not hesitate to reject it or take other measures to avoid unnecessary damage. Acceptance of paper packaging is a basic acceptance, and this level must be strictly controlled.
Appearance acceptance after removal of the outer packaging
After removing the outer packaging of the paper, first check to see if there is a quality checklist, then check the paper phase and color of the paper.
The normal paper phase, the basic feature is that it has a good flatness, that is, the paper is flat and the end surface is flat. As for a piece of paper, whether the paper phase is normal or not is relatively difficult to judge unless the paper has been severely deformed.
The usual method is to unpack the paper and stack it to a height of 1 m to see if the paper phase is normal. When the paper phase is abnormal, it has a variety of shapes, and the common ones are wavy and dish-shaped. Other shapes such as a mountain shape, a valley shape, an angular warping shape, a bag shape, a slope shape, a valley shape, a curl shape, a saddle shape, and the like.
There are many reasons for the production of these poor paper phases. In summary, there are mainly the following aspects: (1) the uneven water content on the entire surface of the paper, resulting in uneven local shrinkage; 2 the thickness of the paper formed during the papermaking process. Uneven; 3 paper has inconsistent expansion and contraction on the front and back sides, especially single-sided coated paper is more obvious.
In addition, it can be seen from the side of the paper stack whether the color of the paper is uniform. In any case, the same batch of paper must be uniform in whiteness, uniform in color, and small in color. Otherwise, after the printed matter is bound into a book, the parts of the sky, the feet, the incisions and the like will have obvious gradation of color tone.
How to detect paper size
The paper size shall be measured according to the national standard using a steel tape with a length of 2 m and an accuracy of 1 mm. When measuring, three samples should be taken in the same package. The measurement results are expressed in all measured values, accurate to 1mm. Paper length dimensions allow an error of ±3mm. Paper skewing can cause the paper to be undersized or excessive, causing the angle between the long side and the short side of the paper not to be at right angles. Therefore, in addition to measuring the length of the paper, the skew of the paper should be measured. Paper skew tolerance is 3mm~5mm.
In addition, the size stability of the paper can also be expressed by the expansion ratio of the paper. The elongation of the paper in the water can be measured by the acceptance of the paper. Cut a horizontal paper strip with a size of 2cm×20cm and put it in water for 1h~2h, so that it expands fully until the size remains unchanged. Take it out and lay it on the glass plate, measure the size with a transparent ruler, and calculate the extension. Long rate and compare with the standard.
If the paper is already in poor paper phase after unpacking and the elongation of the paper in the water is too large, it is best to reject such paper to avoid future troubles.
How to detect the surface strength of paper
Paper surface strength is a very important property of paper. Each type of printing paper has certain requirements for it.
Therefore, the state has clearly defined the surface strength of each type of printing paper.
If the surface strength of the paper fails to meet the printing requirements, the paper will be detached, powdered, and even delaminated during printing. Therefore, the inspection of the surface strength of the paper is also an important part of the acceptance of the paper, but often many printing companies ignore it, so a variety of printing failures occur during printing.
There are some simple ways to judge the surface strength of the paper when accepting the paper. Such as the Danny raw wax stick method test. Although this method has some shortcomings, it is still a relatively simple method to determine the anti-glare ability of a particular paper.
During the measurement, the end of the wax rod of a certain grade is melted and pressed against the surface of the paper to be tested, and after 15 minutes, it is quickly pulled up, and the peeled paper or paper powder is inspected on the end surface. Another easy way is to use a slightly damp finger (usually a thumb) to rub it on the surface of the paper and quickly separate it after a little tilting to see if the finger surface is stained with short fibers or powder.