JPH0478546B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to coated paper rolls, and in particular to gloss calender rolls and machine calender rolls used in white paperboard coating lines, and various rolls and rolls used in other equipment in the lines. This is a proposal for a surface-treated roll that is suitable for application to rolls used in production lines for various types of coated paper other than white paperboard, as well as uncoated printing paper and wrapping paper. (Prior Art) Cardboard used for cardboard boxes, gift boxes, etc. is preferably hard and durable, and is generally called paperboard. Among these, the paper used for high-quality paper containers for cosmetics, pharmaceuticals, etc. is called white paperboard, and is printed in color. The most important quality characteristic of such white paperboard is the surface printing characteristic, and to obtain this characteristic, kaolin (clay: main component Al ₂ Si ₂ O ₅ (OH) ₄ ) or calcium carbonate is usually used as the main component. coating paint,
The paper is subjected to a so-called coating treatment, which improves the smoothness, gloss, and printing characteristics of the paper surface. This coating process is also called a coating part and is located on the downstream side of the papermaking line. FIG. 1 shows an outline of the coating line. The coating process will be explained below according to the drawings. First, the paperboard 1 that has been made and dried enters a calender coating part B from a part A called a dryer part, and is transferred to a machine calender roll 2, a coating agent tank 3,
A smoothing coating of pulp fibers is applied via a coating agent 4, a drying roll 5, and a machine calender 6, and then a gloss calender roll 7 makes the thickness uniform and gives gloss. Conventionally, the surface of gloss calender rolls has been plated with hard chrome (hereinafter simply referred to as "chrome plating") in order to provide uniformity and gloss. (Problem to be solved by the invention) However, the gloss calender roll coated with a chrome plating film does not provide sufficient gloss to the coated paper base paper, and it is essential to add a super calender roll treatment in the post-process. There was a problem with this. In addition, coated paper rolls with a chromium plating film are coated with fine hard particles (e.g., clay whose main component is Al ₂ Si ₂ O ₅ (OH) ₄ ) in the coating agent supplied to the paperboard coating surface. Since the roll loses its luster in a short period of time, it has the disadvantage that it lacks the ability to maintain a mirror surface, which is necessary for a gloss calender roll. Furthermore, in the coating process, a hard metal doctor blade such as knife steel is used to clean the surface in order to remove excess coating agent that adheres to the surface during roll operation. Adopting the doctor blade method on the plating surface had the disadvantage that the plating surface was easily damaged and its function was lost in a short period of time. For the reasons mentioned above, conventional chrome-plated coated paper rolls have to be replaced every 2 to 6 months, and chilled steel rolls have to be replaced every 2 weeks to 1 year, which increases maintenance and management costs. This also caused a drop in productivity due to line stoppages. In response to this, in the past, aiming to improve productivity and quality by simplifying the coating process, it was considered to raise the surface temperature of the gloss roll from the current around 150℃ to around 300℃, but of
It was found that heating to 300°C led to a decrease in hardness and significantly deteriorated wear resistance, and this method did not provide an effective solution. SUMMARY OF THE INVENTION An object of the present invention is to develop and propose a roll having a highly functional coating that can overcome the above-mentioned various problems that need to be solved in the prior art. (Means for Solving the Problems) The present invention provides high hardness, high density tungsten carbide (hereinafter abbreviated as "WC") and Co on the surface of the gloss calender roll or machine calender roll.
Alternatively, a cermet sprayed coating is formed using a material mixed with a Ni-Cr alloy, and then the sprayed coating is polished to a smooth surface, thereby providing a roll having a good mirror surface. The above-mentioned WC cermet sprayed coating in the present invention has a Vickers hardness of Hv: 1100 to 1300 (hardness of the chrome plating film Hv: 800 to 900), and has a hardness due to the abrasion effect of the coating material and the use of a hard doctor blade. It will not damage the surface. In addition, this thermal spray coating does not lose its hardness like chrome-plated coatings even when heated to 300°C, making it possible to use a hard doctor blade for a long period of time, maintaining the mirror surface of the roll, and improving the quality of the paper. Since the gloss-imparting function can be maintained indefinitely, high-quality products can be produced at low cost. The present invention relates to rolls for coated paper, such as gloss calender rolls and machine calender rolls, which are thermally sprayed with a carbide cermet made of WC as a main component mixed with cobalt or a nickel-chromium alloy. Thermal spraying is done so that the porosity in the sprayed coating is 1.2% or less, and
The present invention provides a gloss calender roll obtained by polishing the obtained thermal sprayed coating so that the surface roughness Rmax is 1.8 μm or less, and machine calender rolls surrounding the same. (Function) In the present invention, the cermet spray coating of WC sprayed onto the roll surface has a chromium plating layer (Hv:
800~900), with a Bitkers hardness Hv of 1100
~1300, and has excellent wear resistance. Microscopic observation of the surface reveals that WC has an acute angle.
It appears like a forest of fine particles. For this reason,
In this state, the coated paper is likely to be scratched or indented, and paper scraps and coating sludge are likely to adhere to the coated paper. In addition, such cermet thermal spray materials are a mixture of highly hard WC particles and metal,
The film obtained by spraying this with plasma is WC
It has a structure in which metal particles are arranged around particles. However, since WC particles are hard and do not deform plastically, collisions during thermal spraying can cause the WC itself to break and part of it falls off, and the energy of the collision can cause cracks in the already formed film. , there is a tendency for pores to occur in thermal spray coatings.
When pores are present in the sprayed coating, the pores are exposed when the sprayed coating is polished and appear as pits on the mirror-polished surface. As a result, the mirror surface becomes unsuitable for gloss calender rolls and other rolls. In this sense, the gloss calender roll of the present invention ultimately needs to have a mirror finish, so even if the thermal spray coating has a high density (low porosity) and contains pores, It is also necessary that the pores be so fine that they do not affect the specular gloss finish. On the other hand, since the WC grains are extremely hard, a great deal of labor and expense is required to achieve the mirror finish required for the surface of a thermal spray coating roll. Therefore, for gloss calender rolls, it is important to form a thermal spray coating that fully takes these problems into account, and to select an appropriate polishing finish. Therefore, the present inventors first investigated the thermal spraying conditions for obtaining a dense thermal sprayed coating, and found that (1) the thermal spray particles become softer due to an increase in the ambient temperature, and (2) the impact energy on the surface of the object to be thermally sprayed increases. We focused on However, the above (1)
In this method, the high temperature causes WC to transform into an oxide, making it impossible to utilize its high hardness as a carbide. Therefore, the present inventors further investigated method (2). Specifically, by using an oxygen-hydrogen gas combustion flame as a heat source and increasing the gas supply pressure to the thermal spray gun, the combustion gas injection speed (the higher the fuel gas supply pressure, the higher the combustion gas injection speed). The aim was to reduce the porosity of the sprayed coating by increasing the collision energy of the sprayed particles.
FIG. 2 shows the relationship between the supply pressure of oxygen-hydrogen gas to the thermal spray gun and the porosity of the obtained thermal spray coating. As is clear from this figure, it can be seen that the higher the fuel gas supply pressure is, the more a sprayed coating with a lower porosity can be obtained. Next, using rolls on which WC cermet thermal spray coatings with various porosities were formed, coating was performed experimentally using the gloss calender roll shown in Figure 1 and the attached machine calender roll. The mechanism of action was observed. As a result, it was found that the following characteristics were found. (1) The machine calendar roll 2 installed before the coating process usually has a large nip pressure (30~
80 kg/cm), and an operation is performed to add some moisture to the passing paper in order to smoothen the fibers of the passing paper, give it directionality, and adjust the thickness of the paper. It was found to be able to withstand mechanical pressure and corrosion caused by moisture. (2) By using a mirror-finished roll with a very hard WC cermet thermal spray coating, there will be no scratches on the coated paper or on the coated surface, resulting in extremely beautiful coated paper. (3) Since the WC cermet spray coating is very hard,
It is highly resistant to abrasion caused by the clay contained in the coating agent, and does not cause any damage to the thermally sprayed coating (roll surface). (4) Even when using a hard doctor blade made of high-speed steel, the WC cermet thermal spray coating is not damaged and foreign substances such as coating agents and paper scraps can be completely removed, keeping the roll surface in a healthy state at all times. This greatly contributes to cost reduction as it eliminates the need for maintenance and management over a long period of time. (5) The above functions do not change at all even when the roll surface temperature reaches 300℃, and the use of heated rolls further improves the gloss of the coated surface, making it suitable for producing high-quality coated paper. It has been found. (6) However, even if a WC cermet film has a high porosity, many pits caused by pores will appear on the surface even if a mirror finish is applied, making it impossible to obtain a mirror finish. As a result, excess paint and coating scum remain in the recesses, resulting in poor gloss on the coated surface, uneven coating film thickness, and reducing the effectiveness of the doctor blade, resulting in its function not being fully demonstrated. Its value as a finished product has declined. (7) Furthermore, in the machine calender roll (number 2 in the first figure) on which a film with high porosity was formed, red rust was observed due to moisture intruding into the interior through the pores. (Especially when the line is stopped) From the above findings, it was concluded that for the gloss calender roll of the present invention, it is important to determine the balance between the porosity of the WC cermet spray coating and its surface finish. Ta. Figure 3 shows the relationship between the porosity of the WC cermet sprayed coating and the roughness Rmax of the polished surface. As is clear from this result, a film with low porosity can be polished to a so-called mirror finish, and the surface roughness can be improved.
Rmax of 1.0 μm or less is also possible. On the other hand, with a thermally sprayed coating having a high porosity, the inherent pores become visible as pits on the polished surface, making it impossible to achieve a mirror finish. The WC cermet sprayed coating was polished using a synthetic diamond grindstone or paste, and the surface roughness was measured using a stylus surface roughness meter. The porosity of a thermal sprayed coating is a value obtained by taking a photograph of the cross section of the thermal spraying coating magnified 500 times using an optical microscope, then coloring the pores, and determining the area using an image analysis device. moreover,
The surface roughness of the sprayed coating was all standardized to Rmax. The reason is that there are generally three symbols that represent surface roughness: Ra, Rz, and Rmax.
Even if Ra, which indicates the center line average roughness of the roughness curve, and Rz, which indicates the 10-point average roughness, are small, if there is even one rough spot, this will cause scratches on the coated surface, poor gloss, uneven gloss, and damage to the doctor blade. Therefore, in the present invention, emphasis is placed on Rmax, and this is adopted. Next, examples will be given to explain why the porosity of the WC cermet film is limited to 1.2% or less and the reason why the film surface roughness Rmax is limited to 1.8 μm or less in the gross calender roll and machine calender roll of the present invention. This will be explained in conjunction with. (Examples) Example 1 Figure 1 shows the white paperboard coating line used in this example. In the figure, white paperboard 1 that has undergone predetermined papermaking processes such as papermaking and drying is sent from the right side. This white paperboard passes through eight stages of machine calender rolls 2 to smoothen the pulp fibers, that is, smoothen the board surface, and then is led to the coating agent tank 3. Coating agent 4 is in coating agent tank 3.
(Main components: kaolin, calcium carbonate, acrylic resin, wax emulsion), and the white paperboard that has passed through this coating agent is dried by a dryer 5 and then transferred to a four-stage machine calender roll again. 6
and reaches the gross calendar roll 7. The gloss calender roll 7 is paired with a synthetic rubber-wrapped roll 8, and when the white paperboard passes through the contact surfaces of both rolls, the coated part is strongly pressed against the gloss calender roll surface, creating an excellent glossy surface. The system is such that it is granted. The tip of a doctor blade 9 made of high-speed steel is brought into contact with the gloss calender roll 7, and the coating sludge and paper waste adhering to the surface of the gloss calender roll 7 are removed by the doctor blade 9. The white paperboard that has been given gloss through the steps described above is passed through a cooling roll 10 and wound up, or sometimes sent to a printing process. In this example, WC cermet thermal spray coatings 1 to 9 (88% WC-12% Co, 73%WC−20%Cr−
7% Ni was formed. The operating temperature of the gross calendar roll 7 is as follows:
280-310℃, material of doctor blade 9 is JIS
G4401 carbon tool steel SK7 with hardness HRC57. In addition, the chrome-plated rolls (plating thickness 100 μm, surface roughness Rmax 0.1, 0.3 μm hardness Hv820-890) used as comparative examples (Nos. 10 and 11) were also used under the same conditions as above. . As evaluation items, the gloss of the white paperboard coated surface after passing through the gloss calender roll 7, the state of contamination and damage on the surface of the gloss calender roll 7, the state of damage to the doctor blade 9, and changes in the hardness of the film were observed and investigated. Table 1 shows the results obtained when each gloss calender roll was operated continuously for about 3 months. As is clear from this table, the chrome-plated roll used as a comparative example has an extremely smooth mirror-like surface, which gives it an excellent gloss on white paperboard (especially at the beginning of use). However, the following drawbacks were also observed. That is, as the operating period progresses, the roll surface gradually becomes contaminated; that is, the adhesion of coating sludge and paper waste gradually increases, and as a result, when these are removed using the doctor blade 9, the softened plating film is removed. It was found that they were becoming more susceptible to pickpockets.
Once scratches occur on the plating film,
Paint scum and paper waste are more likely to adhere to that area, and as a result, the doctor blade 9 will be used more frequently, damaging not only the plating film but also the doctor blade itself. Both had no choice but to switch. On the other hand, the gloss calender roll of the present invention has less adhesion of coating sludge and paper waste, and the roll surface is always maintained in a clean state, so that the doctor blade 9 itself is less damaged. In addition, the hardness of the WC cermet film does not change at all even when exposed to high temperatures (280°C to 310°C) during operation, maintaining excellent hardness, and the film is not damaged by the doctor blade 9. It was not recognized at all. However, only the gloss calender rolls on which the film was formed in Test Nos. 6 to 9 did not provide sufficient gloss to the white paperboard, and it was seen that the market value as coated paper was somewhat lowered. From the above results, the porosity and surface roughness of the WC cermet film for gloss calender rolls that meet the purpose of the present invention fall within the shaded area in FIG. In other words, it was confirmed that a WC cermet film with a porosity of 1.2% or less and a surface roughness Rmax of 1.8 μm or less can be applied. In addition, the type of thermal spray material
WC (88%) - Co (12%) and WC (73%) - Cr (20%)
-Ni (7%) showed no difference, and both exhibited excellent performance.

[Table] Example 2 This example (Test Nos. 12 to 16) uses machine calender rolls (roll dimensions: diameter 400 mm x length 2000 mm) 2 and 6 and drying roll ( Roll dimensions: diameter 1000mm x length 2000mm)
The WC cermet film tests Nos. 1 to 5 of the present invention were applied as they were to No. 5. Comparative example (No.17,
18) The current chrome plated roll (same as Specification Example 1) and chilled steel polishing roll (No. 19)
was used under the same conditions for about 6 months. Table 2 shows that even on machine calender rolls and drying rolls, the surface of the WC cermet film of the present invention is not contaminated by coating sludge or paper waste, and is completely scratch-free, without stopping the coating line (no need for cleaning). (Because there is no On the other hand, the chrome-plated roll in the comparative example required cleaning approximately every month due to adhesion of coating sludge and paper waste, so the line had to be stopped each time to clean the plating surface. Ta. 6
Looking at the roll surface after a month of operation, we found that the chrome-plated surface had been abraded by the kaolin particles contained in the coating agent, causing small scratches.
It was estimated that the lifespan of the roll coating would be extremely short. Yet another comparative chilled steel polishing roll had to be replaced every two weeks to one month due to surface wear and scratches. In this example as well, there was no difference between the two types of thermal spray materials, and the excellent performance as described above was exhibited. In addition, the film of the present invention was applied to the machine calender 2 before coating (this machine calender smooths, directs, and adjusts the paper thickness of white paperboard fibers that have not been coated with a coating agent). As a result of 10 months of operation, we were able to maintain a good surface condition for a long period of time, despite the fact that the passing paper contains some moisture, which creates corrosive effects due to moisture as well as nip pressure during operation. . As can be seen from the above results, it was found that the machine calender rolls 2 and 6 coated with the film of the present invention exhibited excellent performance regardless of the presence or absence of the coating agent on the passing paper.

[Table] 〓Remarks〓 Although cleaning of the roll of the present invention is not particularly necessary, we took advantage of the opportunity when the line was stopped to clean the chrome-plated roll and chilled steel polishing roll of the comparative example and cleaned it just in case. be.
(Effects of the Invention) As explained above, the gloss calender roll for white paperboard coated paper according to the present invention has an Rmax of 1.8 μm on the surface of the WC cermet roll with a porosity of 1.2% or less.
Since it is finished to the following mirror surface, excellent gloss can be imparted to the coated paper during the coating process, and a hard doctor blade can be used. As a result, the adhesion of paint foil and paper waste to the surface of the coating is reduced, and the roll function can be maintained for a long period of time, which is effective in improving the productivity of coated paper and reducing costs. Furthermore, since the gloss calender roll according to the present invention does not change the hardness of the WC cermet film even if the operating temperature is increased, the gloss of the coated paper can be further improved, making it possible to manufacture high-quality coated paper. It is. Furthermore, in machine calender rolls, the coating of the present invention withstood large nip pressures and the corrosive effects of moisture, and exhibited excellent performance over a long period of time. This eliminates the increase in work costs due to roll regrinding and replacement, which frequently occurred with conventional rolls, and the decrease in productivity due to line stoppages.

[Brief explanation of the drawing]

Figure 1 is a flow diagram of a white paperboard coating line, and Figure 2 shows the relationship between the supply pressure of the fuel gas for thermal spray heat source to the thermal spray gun and the porosity in the thermal spray coating formed by the combustion gas. The graph showing the relationship, Figure 3, is
1 is a graph showing the relationship between the porosity of a WC cermet thermal spray coating and the surface finish roughness of the coating (the symbols ˜ in the figure indicate the properties of the thermal spray coating tested in Example 1). 1...White paperboard, 2...Machine calendar roll,
3... Coating agent tank, 4... Coating agent, 5... Drying roll, 6... Machine calendar roll, 7... Gloss calendar roll, 8... Synthetic rubber roll, 9...
Doctor blade, 10...cooling roll.

Claims (1)

[Claims] 1. In a coated paper roll having a cermet sprayed coating on the surface, the porosity of the sprayed coating is
1.2% or less and film surface roughness Rmax
A roll for coated paper characterized by a thickness of 1.8μm or less. 2. The coated paper roll according to claim 1, wherein the cermet thermal spray coating is obtained by thermally spraying a carbide cermet made of a mixture of tungsten carbide and cobalt or a nickel-chromium alloy.