Coating detection and control technology in the pr

Coating detection and control technology in the process of processing paper production

Abstract: This paper expounds the research status of the detection and control technology of coating amount and paper tension in the process of processing paper coating

key words: coating amount tension detection and control

coating processing is a processing process in which one or more layers of covering layers are coated on the surface of base paper or paperboard to make it have some special properties. Coating paper has various purposes: it can improve the surface properties of base paper and improve its printing adaptability; It can improve the strength of base paper; It can improve the moisture-proof, oil-proof and other protective properties of base paper; It can enhance the beauty of the base paper; It can enhance the photosensitivity of the base paper. Therefore, the scope of coating processing is quite wide, and the coating processing equipment also has its own characteristics. The coating quality is closely related not only to the level of papermaking technology, but also to the detection and control technology in the coating process. Among them, the detection and control of coating amount and paper tension is an important aspect of coating process control. The control of coating amount is related to the uniform distribution of coating and the economical use of coating; The control of paper tension affects the efficiency of coating and the use of machines. This paper mainly introduces the detection and control of coating amount and paper tension in the coating process of processing paper

1 detection and control of coating amount

for the production of coated paper, both in-machine coating and out of machine coating require uniform and fast coating. The measurement of coating amount is extremely important for identifying product quality; The correct control of the coating amount can make the production reach the best state. Therefore, we should choose a better way to measure and control the coating amount

1.1 determination of coating amount

the coating amount measurement method used can be divided into offline measurement method and measurement method. Off line measurement often requires manual calculation, indirect measurement, and the measurement cycle is relatively long, which affects the efficiency of measurement and is not conducive to the real-time control of coating amount. Optical measurement can be divided into indirect measurement and direct measurement

(1) offline measurement method of coating amount

① ash method in production practice, ash method is a more accurate method of measuring coating amount. During the measurement, the ash content, moisture content and the quantity of the base paper and the finished paper can be measured at the same time, and the coating amount can be calculated. Of course, we also need to know the type and proportion of pigments in the paint formula and the amount of adhesive, because pigments and adhesives may be burned or lose their crystal water at high temperature. It can be calculated by the following formula:

where: bt - coating amount, g/m2

bc -- paper weight, g/m2

ac -- ash content of finished paper,%

ay -- ash content of base paper,%

mc -- moisture content of the finished paper,%

my -- moisture content of base paper,%

h -- conversion coefficient of coating amount

h=hythpf

where: hy - conversion coefficient of pigment. Calcium carbonate is 1.786, kaolin is 1.16

hpf -- conversion coefficient of coating formula. Its value is equal to the total solid content divided by the pigment content in the formula

when sampling, it should be noted that the base paper and the finished paper should be taken from the paper machine at the same time as far as possible. Generally speaking, at the same time, the ash content in the base paper on the paper machine is basically stable and the error is small

② in the actual production process of on-board banner quantitative method, it is generally necessary to quickly measure the value of the coating amount in order to adjust the coating amount in time. The on-board banner quantitative method is a simple and fast approximate measurement method. During the measurement, the whole base paper and finished paper can be obtained on the paper machine at the same time when the paper is broken or introduced, and the coating amount can be determined according to the quantitative difference of multiple points measured on the whole. In order to minimize errors, first of all, the time interval between taking the base paper and the finished paper sample should be as short as possible; Secondly, it should also be noted that the moisture content of the two should be close. When cutting quantitative samples, it is best to fold the base paper and finished paper samples in half, and cut samples at the same position of the banner. Generally, there should be no less than 5 samples cut on the banner

③ wet coating film weight method for general contact cloth applicators, the coating amount can be determined by measuring the weight of the layer film on the back roll that will pose a threat to ecological safety after wet coating, or the measuring pressure required for coating, such as the pressure of the scraper, can be determined according to the coating amount. A 1 is required for determination Preparation and technology of new functional high molecular materials use a scraper with a known width to collect the measured pigment from the back roll, and calculate the coating amount by measuring the weight of the wet paint collected within a certain period of time. Generally speaking, the coating amount is not equal to the no-load height weight of the collected paint wheel and nut screw adjustable experimental machine, but has an equipment coefficient, which is provided by the equipment manufacturer. For example, for the expected transfer roll coating, only part of the coating on the transfer roll is transferred to the paper, and this coefficient is the transfer rate

(2) measurement method of coating amount

optical measurement method can be divided into indirect measurement method and direct measurement method according to different measurement principles

① indirect determination method this method is the most commonly used method on the coater at present. The basic principle is to determine the quantitative moisture and other parameters of the base paper and the finished paper according to the different absorption and reflection abilities of the base paper and the finished paper to a certain wavelength of light before and after coating, and to determine the coating amount by calculating the quantitative difference between the finished paper and the base paper, and referring to the sensor with angular force of the bearing plate device to test the changes of moisture and ash. It uses a data processing software package to convert the measured optical signal change into the coating amount change

② direct determination method this method adopts infrared sensor for direct determination. Its working principle is to selectively absorb some infrared wavelengths according to the coating composition. When the sensor is placed on the scanner in front of and behind the coater, the sensor can measure the component ratio in the test coating, and then determine the coating amount. At present, sensors with unique detection infrared wavelength bands for clay, latex, moisture, fiber, etc. have been applied to measure the coating amount of paper. These sensors using infrared technology are usually measured on one side. As the light source of this sensor, it is blackbody radiation from high-temperature objects. Different measured objects have their own unique absorption wavelength band, and the narrow wavelength band with selectivity is detected. The measurement accuracy of infrared sensor is mainly affected by the performance of the sensor and process parameters, which affects the measurement of coating amount