JPS6331264B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous coating method using a reverse roll coater that provides a uniform and smooth coating film and a beautiful finish.

Furthermore, the present invention relates to a continuous coating method that can easily apply highly viscous paints, thixotropic paints, or paints containing large particles, which have conventionally been difficult to roll coat.

Conventionally, substrates (hereinafter simply referred to as substrates) such as metal plates such as steel plates and aluminum plates, flat plates such as gypsum board and wooden plywood, paperboard, and plastic plates,
As shown in Figure 1, 2 is a method of continuously applying paint made of synthetic resin, etc. for the purpose of improving corrosion resistance, weather resistance, imparting strength, and improving appearance.
The reverse coating method using this roll was common. That is, the paint R is pumped up from the paint pan 1 with the pick-up roll 2, and the paint roll 3 which is rotating naturally with the pick-up roll 2 is pumped up.
Then, the paint on the paint roll 3 is reversed onto the substrate P, which is supported by the back-up roll 4 and is traveling in the opposite direction to the rotation direction of the paint roll 3. This is a method of painting.

This method has the advantages of being able to produce a large quantity of coated plates in a short period of time, providing a stable and uniform coating amount, and providing a beautiful coating finish compared to conventional paints. However, when using a paint that lacks roll coating suitability, a so-called roping pattern occurs, making it impossible to obtain a uniform and stable coating film, impairing the beauty of the surface, and reducing corrosion resistance. It was hot. Paints that are unsuitable for roll coating are those that lack fluidity, such as vinyl chloride-based sol paints, synthetic rubber-based paints, and other extremely viscous paints, as well as paints that contain large amounts of extender pigments such as calcium carbonate. These include low-gloss paints, highly thixotropic paints such as water-based acrylic emulsion paints, and paints containing inorganic pigments such as aluminum powder with large particle diameters of 30μ or more, and organic pigments such as urethane beads. The roping pattern is a pattern in which the painted surface is uneven in the form of water spots, which occurs on the surface of the coating roll 3, and this is directly transferred to the painted surface, making it impossible to finish the painted surface smoothly. As a result, not only the beauty of the surface is impaired, but also foaming occurs during drying in thick areas of the paint film, and the protection ability such as corrosion resistance for substrates decreases in thin areas of the paint film, resulting in extremely poor product quality. to degrade.

As a method for coating these paints with poor fluidity and unsuitable rollability, a reverse coating method using three rolls as shown in FIG. 2 was considered. That is, the amount of paint on the surface of the pick-up roll 2 is adjusted by scraping off a portion of the paint R pumped up by the pick-up roll 2 with the metering roll 5 rotating in reverse, and the amount of paint R drawn up by the pick-up roll 2 is adjusted. R is removed from the metering roll 5 with a doctor knife 6. The paint R left on the surface of the pick-up roll 2 is transferred to the paint roll 3, which is rotating in reverse relative to the pick-up roll 2, and is further transferred by the paint roll 3 onto the substrate P, which is moving in the opposite direction. Reverse painted.
In this method, all rolls are rotated in reverse, based on the consideration that the occurrence of roping patterns is caused by the tearing phenomenon of the paint, and no roping patterns occur.

However, since the metering roll 5 is mainly relied on to adjust the coating thickness, another problem arises in that the coating thickness cannot be adjusted sufficiently and becomes non-uniform. In other words, the cause of uneven coating film thickness is mainly due to the mechanical precision of the coater, but in the case of this method, due to the necessity of adjusting the coating film thickness, the metering roll 5
cannot be pressed against the pick-up roll 2, and it is extremely difficult to make the horizontal mechanical precision between the metering roll 5 and the pick-up roll 2 less than 50μ. Generally, the wet film thickness when continuously coated in roll coating is in the range of 40 to 300μ, and for a given film thickness,
It is necessary to control the upper and lower limits within 20μ. Therefore, the reverse coating method using three rolls as shown in Fig. 2, in which it is difficult to achieve a mechanical precision of 50 μm or less, has been difficult to put into practical use because of large variations in the coating thickness of the object to be coated.

The present invention is a coating method developed for the purpose of applying these paints that are not suitable for roll coating, that is, so-called poor fluidity, accurately, with a uniform coating thickness, smoothly, and with a beautiful finish. That is,
The present invention is a continuous coating method using a reverse roll coater, in which a paint film is formed on the pick-up roll by passing the paint through a gap formed by a doctor bar placed on the pick-up roll and the pick-up roll. Then, some or almost all of the paint on the pick-up roll is transferred onto the surface of the paint roll that is rotating in reverse relative to the pick-up roll, and then onto the surface of the substrate that is moving in the opposite direction to the rotational direction of the paint roll. It is characterized by transferring part or almost all of the paint on the paint roll.

Hereinafter, the present invention will be explained in detail based on FIGS. 3 to 5 showing embodiments of the present invention.

FIG. 3 is a cross-sectional explanatory diagram for explaining one embodiment of the method of the present invention. In FIG. 3, the paint R is drawn up from the paint pan 7 as the pick-up roll 8 rotates. This paint R then passes through a gap formed between the pick-up roll 8 and the doctor bar 9, and its amount is adjusted. Therefore, it is necessary that the amount of gap formed between the pick-up roll 8 and the doctor bar 9 is always stable. Therefore, it is desirable to use a material with high rigidity.

In addition, especially in the case of paint with poor fluidity, when the paint passes through, a force that expands the gap acts, causing the doctor bar 9 to be lifted up, or depending on the type of pigment in the paint, to damage the doctor bar 9. This may occur, and the amount of gaps may increase only in the center. In order to prevent this, the doctor bar 9 is held firmly by using an appropriate fixture, if necessary, so that the relative distance with the pick-up roll 8 does not change, and the rigidity of the doctor bar 9 itself is It is desirable to prevent deformation of the doctor bar 9 by increasing the thickness of the doctor bar 9 or by using a backup mechanism with high rigidity.

From this point of view, the pick-up roll 8 and the doctor bar 9 are preferably made of, for example, steel or stainless steel.

The amount of gap formed between the pick-up roll 8 and the doctor bar 9 in the present invention is determined by the type of paint, the amount of coating, the rotational speed of the pick-up roll, etc. For example, when the board passing speed is slow or when the amount of coating is small, the gap amount is narrowed, and when the board passing speed is fast or the amount of coating is large, the gap is widened. The gap amount is generally adjusted between 20 and 750μ. If the particle size is less than 20μ, the mechanical precision of rolls and bearings will have a significant effect, and if the particle size of the pigment is large, it may not be able to pass through the gap. Moreover, if the gap is 750 μm or more, the paint on the surface of the pick-up roll will develop a flow pattern, which is undesirable because it will cause problems such as uneven coating.

In the case of the present invention, the coating film thickness is adjusted using the doctor bar 9 as described above, and the pick-up roll 8 is pressed downward against the bearing, and unlike the conventional system, the metering roll 5 is not used, so that the thickness is adjusted horizontally. Mechanical accuracy is significantly improved.

Next, part or almost all of the paint R that has passed through the gap is transferred from the pick-up roll 8 onto the coating roll 10 that is rotating in reverse with the pick-up roll 8. Next, the paint R is applied in reverse by the paint roll 10 onto the surface of the substrate P, which is traveling in a direction opposite to the rotational direction of the paint roll 10.
The substrate P is supported by a backup roll 11. Here, the coating roll 10 is used to ensure smooth transfer between the pick-up roll 8 and the substrate P, and also to maintain a uniform coating thickness even when the substrate P has a shape defect such as an ear wave or a variation in thickness. It is preferable to coat the surface with rubber or the like to give it elasticity, and also to prevent damage to the painted surface even when small lumps are contained in the paint.

The rotation speed of the pick-up roll 8 is determined by the gap amount,
Determined by coating amount, substrate threading speed, etc.
When the amount of coating is to be reduced or when the board passing speed is slow, the rotation speed is set to be low, and when the amount of coating is to be increased or the board passing speed is fast, the rotation speed is set to be high. However, in the case of paint with low viscosity, if the rotation speed is extremely slow, the paint may not be picked up sufficiently.
Furthermore, if the rotation speed is extremely high, there are problems such as the paint pan 7 being agitated by the rotation of the pick-up roll 8 and foaming. The ratio is preferably in the range of 0.1 to 2.0. That is,
If it is lower than 0.1, the amount of pick-up may not be sufficient and the desired film thickness may not be obtained.
With ultra-high speeds, the agitation of the paint pan becomes more intense, causing problems such as foaming and paint spilling out of the paint pan.

To adjust the amount of paint adhering to the board, first take into consideration the type and viscosity of the paint to be applied, set the amount of gap formed between the pick-up roll and the doctor bar, and then adjust the speed of board passing during painting. A preferred method is to change the rotational speed of the pick-up roll depending on the amount of time. Furthermore, similar to the conventional reverse roll coating method, a method of adjusting the pressing pressure between the pick-up roll and the coating roll is also used to finely adjust the coating amount.

Figures 4 and 5 are explanatory diagrams of how to install the doctor bar and how to adjust the gap, respectively.
is a side view, and B is a front view.

In FIG. 4, the doctor bar 9 is installed on the surface of the pick-up roll 8 via a shoe 12 for adjusting the gap. At this time, the doctor bar 9 is held down by fixtures 20, 20' to prevent it from moving back and forth on the pick-up roll 8.

The gap is adjusted by rotating the adjustment screw 13 and changing the relative height between the shoe 12 and the doctor bar 9. Since the lower end of the shoe 12 is on the surface of the pick-up roll 8, the gap between the pick-up roll 8 and the doctor bar 9 can be adjusted by changing the relative height between the shoe 12 and the doctor bar 9. . In this method, the accuracy of the cylindricity and roundness of the pick-up roll 8 is poor, and even if there is roll eccentricity, the relative position between the surface of the pick-up roll 8 and the lower surface of the doctor bar 9 does not change, so fluctuations in the amount of gap are prevented. The coating thickness is extremely small, making it easy to adjust the coating thickness and improving uniformity.

In FIG. 5, height adjustment shoes 16 are fixed to both ends of the doctor bar 9 with bolts 17. This shoe 16 rests on the wedge 15, and the wedge 15 is further mounted on the adjustment screw 1.
It has a mechanism that allows it to move forward and backward by rotating 8. These devices are fixed on the bearings 14 of the pick-up roll 8. doctor bar 9
To adjust the gap between the pick-up roll 8 and the pick-up roll 8, rotate the adjustment screw 18 and move the wedge 15 back and forth to move the shoe 16 up and down, changing the relative distance between the pick-up roll 8 and the doctor bar 9. Do it by letting it happen.

A feature of this method is that, unlike the method shown in FIG. 4, the shoe 16 is not in direct contact with the pick-up roll 8, so there is no wear on the shoe 16. Note that the doctor bar 9 is held down by a fixture (not shown) similar to that shown in FIG. 4 so as not to move back and forth.

Examples are shown below.

Example 1 An NBR synthetic rubber solution with a viscosity of 10,000 to 20,000 cps was used as a paint. This paint could not be coated by the conventional reverse coating method shown in FIG. 1 due to the severe roping phenomenon.

When this paint was applied under the following conditions using the equipment shown in FIG. 3 with the doctor bar shown in FIG. 5 installed, a very smooth coating film with a wet film thickness of 90 to 100 μm was obtained.

Conditions: Gap between doctor bar: 150μ Rotation speed of pick-up roll: 25m/min Rotation speed of coating roll: 30m/min Passing speed of substrate: 20m/min Transfer amount to coating roll: Approx. 100% Type of substrate and Size: cold rolled steel plate, 0.4mm thickness, 914
mm width.

Example 2 As a paint, a low gloss paint obtained by mixing 10 parts by weight of calcium carbonate powder with 100 parts by weight of a polyester resin paint was used. The surface gloss of the dry coating surface of this paint is 5 to 10 in 60 degree specular reflectance, the viscosity is 120 seconds at #4FC (foad cup), and the thixotropic index (TI value) is higher than that of normal paint. It was 3.2 to 3.4, which is more than double.

When painting with this paint in the method shown in Figure 2, even when we tried to adjust the film thickness to 35-40μ with wet paint, it actually varied greatly from 15-70μ, making it difficult to achieve stable color tone. Moreover, it was not possible to put it into practical use because of the problem of foaming on the surface. Using this paint, the doctor bar shown in FIG. 4 was installed in the equipment shown in FIG. 3, and coating was carried out under the following conditions. A very smooth coating film with a wet film thickness of 38 to 42 μm was obtained.

Conditions: Gap between doctor bar: 300μ Rotation speed of pick-up roll: 20m/min Rotation speed of coating roll: 80m/min Passing speed of board: 60m/min Amount transferred to coating roll: Approximately 2/3 has been transferred Adjust the pressing pressure so that the board type and size: Galvanized steel plate, 0.8mm
Thickness, 914mm width.

Example 3 Polyester resin clear paint as paint
A mixture of 100 parts by weight and 25 parts by weight of colored urethane beads having a diameter of 20 to 60 μm was used. This paint had a viscosity of #4FC of 150 seconds and a very high TI value of 2.2-2.6. When this paint was reverse coated using the three rolls shown in Figure 2, even though we tried to adjust the film thickness to 120-130μ wet, it actually varied greatly from 60-300μ, and the color tone was not stable. Nakatsuta. In addition, when painting was performed using the conventional two-roll reverse coating shown in Figure 1 to suppress variations in film thickness, the coating surface was severely roped due to the tearing phenomenon between the pick-up roll and the coating roll, making it impossible to put it into practical use. Ta.

When this paint was applied to the equipment shown in FIG. 3 with the doctor bar shown in FIG. 4 installed under the following conditions, a very smooth and beautiful coating film with a wet film thickness of 110 to 120 μm was obtained.

Conditions: Gap between doctor bar: 500μ Rotation speed of pick-up roll: 30m/min Rotation speed of coating roll: 140m/min Passing speed of substrate: 120m/min Transfer amount to coating roll: Approx. 100% Type of substrate and Size: Galvanized steel plate, 0.4mm
Thickness, 1000mm width.

As detailed above, the coating method according to the present invention can coat paints that are difficult to apply using conventional two-roll or three-roll reverse coating methods, etc., in a uniform, smooth, and beautiful coating over a wide range of thickness. This invention is considered to be extremely useful.

Note that the method of the present invention can be applied not only to strip-shaped substrates but also to sheet-shaped substrates with flat surfaces such as gypsum boards and wooden plywood by installing appropriate guides before and after the back-up roll 11. Needless to say.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional reverse coating method using two rolls. FIG. 2 is an explanatory diagram of a conventional reverse coating method using three rolls. FIG. 3 is an explanatory diagram of the method of the present invention. Fourth
5 and 5 are explanatory diagrams showing a method of attaching a doctor bar according to the method of the present invention, where A is a side view and B is a front view, respectively. 1...Paint pan, 2...Pick-a-sprowl,
3...Paint roll, 4...Back-up roll,
5... Metering roll, 6... Doctor knife, 7... Paint pan, 8... Pick-up roll, 9... Doctor bar, 10... Paint roll,
11...Backup Prowl, 12...Show,
13... Adjustment screw, 14... Bearing, 15... Wedge, 16... Shoe, 17... Bolt, 18...
...adjustment screw, 20, 20'...fixing tool, P...board, R...paint.

Claims (1)

[Claims] 1. In a continuous coating method using a reverse roll coater, paint is passed through a gap formed by a doctor bar placed on the pick-up roll and the pick-up roll to form a coating film on the pick-up roll. is formed, and then part or almost all of the paint on the pick-up roll is transferred onto the surface of the paint roll that is rotating in reverse relative to the pick-up roll, and then moved in the opposite direction to the rotational direction of the paint roll. A continuous coating method characterized by transferring part or almost all of the paint on a paint roll onto the surface of a substrate. 2. The doctor bar is installed on the pick-up roll via a shoe in contact with the pick-up roll, and the gap between the doctor bar and the pick-up roll is adjusted by changing the relative height of the doctor bar and the show. 2. The continuous coating method according to claim 1, which has a mechanism for 3 A doctor bar is installed on a wedge that is fixed on a bearing and can be moved back and forth via a shoe, and the gap between the doctor bar and the pick-up roll is adjusted by moving the wedge back and forth. A continuous coating method according to claim 1, which comprises: