FI75199B - BELAGT PAPPER, KARTONG ELLER DYLIKT SAMT FOERFARANDE OCH ANLAEGGNING FOER TILLVERKNING AV DETSAMMA. - Google Patents

Description

751 99 Coated paper, paperboard or the like and method and apparatus for its production - Paper, paperboard or paperboard for the manufacture and sale of paperboard

The invention relates to a coated paper, board or the like, which is coated on one or both sides so that at least two steps are coated on at least one side, wherein the size distribution of the coating paste of the first step 5 is such that at least seventy percent of all particles less than 5 μιη.

The printing paper used for more demanding printing purposes is generally coated with a thin layer of coating paste during the papermaking process. This can take place either as a separate work step in the so-called as an off-machine coating or as a so-called work step combined with the manufacture of base paper. on-machine coating. In either case, a simple layer of coating paste is applied to each side of the paper separately or sometimes simultaneously.

Numerous different types and variations of unit devices suitable for coating a coating paste layer are known. The coating paste can be applied to the surface of the paper, for example by means of a roller or extrusion. Leveling and scraping the layer thinly, on the other hand, can be done, for example, with the help of a blade or rod scraper or a roller nip.

The blade coating gives a very even coating layer after the blade. The blade is used to fill the unevenness of the paper and scrape off the excess. However, due to dewatering of the blade, the coating layer shrinks and follows the irregularities of pin-25 nan when tapered. At the same time, the uncoated fiber surfaces left by the scraper are exposed. Thus, although such a single-coated paper is perfectly good for many uses, its quality, in particular its suitability for the most demanding printing jobs, can be improved by measures which increase in particular the smoothness, gloss and uniformity of ink absorption.

2 75199

In the coating of certain subtypes of so-called fine paper, the paper has been coated in two stages for a long time, i.e. the so-called kak-soispäällystetty. First, for example, the paper is coated with an adhesive press or similar device, often also with a blade coating or some intermediate form of these (so-called pigmentation), which is sometimes done as an on-machine work step. The same side is then coated repeatedly with a blade coating. The latter is done in practice as a separate off-machine work step. After surface gluing, the highest quality products are coated twice 10 on each side.

The advantages of double coating also in some subtypes of thin printing papers, the so-called There is information on LWC grades. In LWC quality, the amount of a simple coating layer is e.g. 10 g / mJ. Thicker so-called mechanical pulp containing MWC grades are made in 15 double coatings already commercially. In this case, the coating amounts are higher than could be considered for LWC grades.

However, even with coating amounts of 10-12 g / m1, double coating gives a better result than single coating with the same coating-20. The superiority of the double coating is already visible in the smoothness measurements and clearly in the print as a smoother and glosier, more photographic image. At present, carbonate with an L / h ratio (explained later) of about 25 2 is generally used as the pigment wave in the coating paste of the first coating step. In this case, the coverage in the first step is poor, which results in a large total coating requirement.

Current double coating methods do not take into account the importance of the coating steps, and in particular the first coating step, for the coated product, nor for the manufacturing method and equipment structure. The most important consideration in coating is, of course, the properties of the final product, i.e. coated paper, board or the like, such as smoothness, gloss and absorption of inks. It has now surprisingly been found that the properties of the coated product

II

3 75199 can be obtained with lower total coating amounts if at least 85% of the particles of the coating paste of the first stage of the coated product (paper, board or similar) are such that they meet the condition L / h 5 is greater than 10- L / h ratio means maximum and the ratio of the smallest dimension. In addition, the particle size distribution must be such that at least 7 to 10 per cent of all particles have an equivalent diameter of less than 5 μπι. Equivalent diameter means the diameter of a sphere having similar sedimentation properties as a particle of a particular shape. As a test for determining the equivalent diameter of the masking agent, for example, the Sedigraph 5000 test, which is performed with a Micromeritics device, can be used. The use of such a coating material provides a highly opaque coating paste, whereby it is possible to obtain paper, board or the like having certain surface and printing properties with a smaller total amount of coating. This effect is due to the fact that the size distribution of the particles of the covering substance is small and the particles are plate-shaped, as shown by the ratio L / h. In addition, such a masking agent can in most cases be hydrophobic, so that its dewatering is rapid. This fact offers considerable methodological advantages. Auxiliary pigments with a very low L / h ratio can also be added to the coating paste. Thus, these auxiliary pigments do not provide opacity but achieve other properties.

The amount of coating paste in the first coating step is less than half of the total coating. The total amount of coating is up to 18 g / m2. Paper with good properties can be obtained with a coating amount of even less than 15 g / m 2 by using the first stage coating paste according to the invention. Typically, the amount of coating paste in the first coating step is about 44% of the total amount of coating and at least 2 g / m 2. The masking agent may preferably be, for example, kaolin or talc, 4,751,99 with an L / h ratio of typically 20-40, or a mixture thereof. The water retention (dehydration) of the coating paste of the first coating step is of the order of 10s to 80s, preferably 20s to 40s. Water retention is then determined by the "S.D. Warren" test, 5 TAPPI, Feb. 1958, vol. 41, N ° 2.

The invention also relates to a method for coating paper, board or the like in at least two stages on at least the same surface of the web, whereby the web to be coated is guided supported from one coating stage to another.

10 From a methodological point of view, double coating with current technology on both sides of the track requires the construction of four coating stations with one coating unit, either in connection with a paper machine or in a separate coating machine or partly in both. The current equipment is designed in such a way that the track to be paved is guided between the paving stations through stationary rotating rollers and other auxiliary devices. This use of rollers requires strength from the track, so track moisture is essential to the operation of the method and equipment. Thus, after each application unit, the entire web must be dried to 96-20 97% dry matter. This means that intermediate drying significantly increases operating costs. In addition, e.g., coating at four coating stations (two-stage coating on both sides of the track) significantly reduces the efficiency of the production line, requires more supervisors, and results in a higher number of rejects as a result of increasing the susceptibility to interference.

In addition, the current coating methods are characterized in that the water retention capacity of the pigment paste, i.e. water retention, is as high as possible.

The object of the method according to the invention is to provide an improvement in the drawbacks of the present coating technique.

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The method allows considerable freedom of choice for the properties of the pigment paste of the first coating step, since the strength properties of the web to be coated are not decisive for the operation of the method. Thus, the opacity and waterproofing properties of the pigment paste can always be optimally selected. In addition, the method enables an apparatus construction in which a single coating station can perform all coating steps because it can be equipped with at least two coating units.

To achieve this object, the method according to the invention is mainly characterized in that the support is performed by a member moving along the track. In this case, the humidity of the track can be high between the coating steps, because the track is not subjected to high stresses. In this case, for example, the coating paste of the first coating step can be selected so that it is rapidly dewatered. In this way, the web can absorb the moisture of the coating paste and thus speed up the reaching of the pour point of the first stage coating paste. By pour point is meant the dry content of the coating paste at which the individual pigment particles can no longer move relative to each other, but movement can still occur in the binder portion. That is, the method allows conditions to be arranged after the first coating step so that the dry matter content of the coating paste on the web surface quickly reaches a certain level, which is typically 78-85%, while it is typically 55-60% in the coating paste application stage. At least a portion of the dehumidification of this coating paste can be accomplished by selecting the coating paste as having a low water retention, whereby the coating paste is rapidly absorbed by moisture into the web to be coated. This is made possible by the track support implemented in accordance with the invention, as a result of which there are no steps requiring dry strength of paper, board or the like between the coating steps. It is clear that according to the method, the dry matter content of the web can also be increased between the coating steps by removing the liquid by evaporating it to the outside space. This is useful, for example, if the machine speed is high or a small hardware size is desired.

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As can be seen from the above, an essential aspect of the invention is the selection of the properties of the coating paste of the first coating step so that the properties of the final product, i.e. coated paper, board or the like, are desired with a smaller total amount of coating. Thus, the first coating step is essential for the properties of the product as well as the implementation of the method. With the next, at least one coating unit, the conditions can be freely selected within the framework of what properties are set for the final product.

10 The measurement and adjustment of the thickness of the coating layers is now also possible in such a method. For example, an X-ray fluorescence measurement technique known per se can be used in the measurement.

The invention further relates to an apparatus with which paper, board or the like according to the invention can be produced using a method. The apparatus comprises two or more lubrication units for coating at least the first surface of the track and at least in two stages. The paper web, paperboard web or the like to be coated is supported from one coating step 20 to another.

As stated above, in the current equipment, the track to be coated is guided between the coating stations equipped with one coating unit via stationary rotating rollers and other auxiliary devices.

The apparatus according to the invention is mainly characterized in that the track supporting member in the apparatus is arranged to move with the track.

As some preferred constructive alternatives to implement the above-mentioned member can be mentioned around its longitudinal axis

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7 75199 a rotatably arranged cylinder, the outer circumference of which is adjacent to at least two circumferentially spaced lubrication units, or an endless conveyor in connection with which at least two coating units are arranged at a distance from one another in the longitudinal direction of the conveyor.

The invention is further illustrated in the following description with reference to the accompanying drawing. In the drawings, Figures 1 and 2 schematically show alternative preferred embodiments of the apparatus according to the invention.

Figure 1 shows a hardware application in which the supporting and movable member is a single cylinder 2 rotatable about its longitudinal axis. The cylinder 2 together with the coating units 3 and 4 form a coating station, by means of which a paper web, a paperboard web or the like 1 can be coated. 15 on the first surface in two stages. The diameter of the cylinder 2 as well as the distance between the coating units 3 and 4 placed on the circumference of the cylinder 2 are chosen so that the distance between the coating steps and the web speed from the first coating step to the second coating step are particularly suitable for realizing suitable.

Between the strip units 3 and 4, a heating device 5 promoting dehumidification can be placed on the outer surface of the cylinder 2, which can be, for example, a radiator operating in the infrared range. The shape of the heat dissipating surface of such a heating device can be shaped to correspond to the shape of the surface of the cylinder 2. The heater can be equipped with ventilation soles that enhance drying. Furthermore, the surface of the cylinder 2 can be formed to strongly reflect thermal radiation. This can be done, for example, in the case of a metal cylinder by polishing the surface of the cylinder. In addition, the cylinder can be heated or cooled, for example by liquid circulation or air blowing from the inside or from the top, in order to achieve the preferred temperature balance.

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Figure 2 shows another preferred embodiment of the apparatus according to the invention with corresponding reference numerals, in which the web supporting member is one endless conveyor 2 'arranged on the rollers or the like 6 and 7 to move at the speed of the paper web. The sleeve units 3 'and 4' are spaced apart in the longitudinal direction of the conveyor. In addition, the conveyor 2 'may be supported on the side opposite to the track by support plates 8 or the like.

As slip units 3, 4 and 3 ', 4', 10 ns can preferably be used. short residence units in which the blade device transfers the coating paste to the surface of the web through a nozzle formed by the brush blade of the front wall. The advantage of the short residence unit is that the paper is less wet before scraping, thus reducing breaks. The blade pressures acting on the track are relatively low. In addition, washing during breaks is easier and faster.

Such short residence units are known per se as a brush device. The invention can advantageously take advantage of the fact that the tendency to cause interference is low even at high driving speeds, which makes them particularly well-suited for the purpose of the invention. This does not preclude other types of brush units, but in this case equal driving speeds cannot be achieved. One area of application of the invention is the replacement of old paper machines. In this case, there is little available structural space, so that the application of the invention is advantageous. For other reasons, the speed of old paper machines is often limited to a maximum of 700-800 m / min. In this case, a device other than a short-stay device may just as well be considered.

In addition to papers and paperboards, the invention also includes 30 e.g. different types of laminate structures, the top layer of which is a wood pulp-based material.

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Table 1 below shows some coating pastes that are particularly suitable as pastes for the first coating step. The proportions are by weight and coating pastes 1 and 2 are offset pastes and 3 are gravure pastes.

TABLE 1 1_2_3

Kaolin 100

Talc - 100 100

Latex (eg styrene butadiene) 10.5 11 4

Water-soluble binder (eg carboxymethylcellulose) 11-

Lubricant

Dispersant 0.3 0.3 0.3 pH adjuster 0.02 0.02 0.02

Hardener 0.1 0.1

Wetting agent - 0 ... 1 0 ... 1 5 The following Table 2 shows suitable second stage pastes (proportions by weight) TABLE 2

Offset_Syväpaino

Kaolin 100

Talc - 100

Latex A 11 -

Latex B 4

Water - soluble binder 1

Dispersant 0.03 0.03

Lubricant 0.5

Hardener 0.1

Wetting agent - 0 ... 1 pH adjusting agent 0.02 0.1 10 751 99

The following Table 3 shows the properties of offset paper when using LWC base paper and the amount of first-stage coating paste is 5 g / m2.

TABLE 3

Total amount of coatings g / m2_10_12_

Gloss, Hunter 75 °% 60-70 63 - 73

Brightness ISO% 65-76 68 - 77 IGT surface strength m / s 0.6-1.0 0.75-1.1 K&N color absorption% 7-12 8-14

Roughness PPS slO μπι 0.6 - 1.2 0.4 - 0.8

Roughness PPS s20 μπι 0.3 - 0.6 0.3 - 0.5

Further, Table 4 shows an example of the quality values of gravure paper 5 and the amount of coating paste in the first stage is 5 g / m2. TABLE 4 Number of coatings__g / m2_10_12_

Roughness PPS slO μπι 0.6 - 1.2 0.4 - 0.8

Roughness PPS s20 μπι 0.3 - 0.6 0.3 - 0.5

Sileys Fogra, 4.9 mPa% 40-65 45 - 75

Heliotest mm 60 -90 70 -105

Kiilto, Hunter 75% 50 70 55 - 80 il 11 751 99

Also attached is an example curve of the cumulative percentage distribution in terms of L / h for two different talc grades (Finnminerals Oy, Talc C10 (l) and M15 (2)) - O / / o ioo ---,

cl / X

60 / H / / i u / / 5? //

Il 0 L ^ I I-1-1-1 — I — I — I — I— O 10 20 HO 60 QO 100 fauoio coefficient (L / h ratio.)

Claims (10)

1. Coated paper, cardboard or the like, which is coated on one or both sides thereof, such that at least one side is provided with at least a double coating, the size distribution in the coating material of a first step coating smith being such that: at least 70% of all particles have an equivalent diameter less than 5 µm, characterized in that at least 85% of the particles in the coating material of a first stage coating smith are such that they meet the condition L / h greater than 10 , wherein the ratio L / h refers to the ratio between the largest and the smallest dimension of the particles. Paper, paperboard or the like according to claim 1, characterized in that the amount of coating smear in the first step is not more than half of the total amount of coating material and that the total amount of coating material is not more than 18 g / m. Paper, paperboard or the like according to claim 1, characterized in that the coating material comprises kaolin and / or taik, whose L / h ratio is typically between 20 - 40. Paper, paperboard or the like according to claim 1, characterized in that the water retention of a coating smith for the first step is 10s ... l60s, preferably 20s ... 40s. 25 A method for coating paper, paperboard or the like in at least two steps on the same surface of a paper web, the paper web being moved supported from one coating step to the other, characterized in that the support is performed with an element (2, 2 '). ) moving with the paper web (1, 1 ').