JP4506450B2 - Roll coating method and apparatus - Google Patents

Description

  The present invention relates to a roll coating method and apparatus suitable for roll coating of a band-shaped metal used particularly for the production of a coated metal plate such as a pre-coated steel plate.

  Conventionally, a roll coating device called a roll coater has been used for continuous coating of a belt-like substrate. In particular, as a roll coating device for strip metal substrates such as plated steel plates and aluminum plates, in addition to a backup roll, a pick-up roll (usually a hard chrome-plated metal roll) and an applicator roll (usually a rubber lining roll) are provided. Two-roll type roll coaters are the mainstream.

  An outline of this type of roll coater is shown in FIG. The coating liquid in the paint pan 5 is captured by the pick-up roll 3, then transferred to the applicator roll 2, and further transferred to the band-shaped metal substrate 4 conveyed by the backup roll 1, so that the coating on the substrate 4 is performed. Done.

  When the rotation direction of the backup roll 1 and the applicator roll 2 that conveys the base material 4 is reverse rotation as shown in the figure, reverse coating is performed, and the rotation direction of the pickup roll 3 and applicator roll 2 is opposite to the illustration. The case where the rotation direction of the backup roll 1 and the applicator roll 2 is natural rotation is called a natural coat. Also in the reverse coating, since the rotation direction between the pickup roll 3 and the applicator roll 2 is natural rotation, it can be said that the two-roll reverse coating is more strictly a natural / reverse rotation system.

  In general, natural coats tend to have vertical streak patterns called "roll eyes" or "ribs", so reverse coating is used in the production of painted metal sheets such as pre-coated steel sheets that require a uniform appearance. It is normal. However, even with reverse coating, it is difficult to prevent the occurrence of roll eyes, and there is a problem that the appearance in the vertical direction (L direction) is different from that in the horizontal direction (T direction).

  As a countermeasure, add a metering roll 6 with a blade 7 for scraping the coating liquid and use three rolls (2, 3, 6) in addition to the backup roll 1 as shown in FIG. In addition, the three-roll full reverse coater where the rotation between the three rolls in total is a reverse rotation, and although not shown, the paint drops from the roller like a curtain onto a strip-shaped metal substrate that is conveyed in the horizontal direction. A method using a roller curtain (also called a curtain flow coater) has been put into practical use.

  The three-roll full reverse coater requires a new metering roll, which increases the number of rolls to be washed, increases the size of the paint pan, and increases the amount of waste paint.

The roller curtain has a problem that it is difficult to perform thin film coating in terms of ensuring the stability of the coating curtain that freely falls.
As another coating defect in roll coating, it is also known that there is a defect caused by air entrainment of the pickup roll and applicator roll. Due to air entrainment of the pick-up roll, pick-up failure occurs, and a thin portion of the coating film is locally generated. In addition, when the applicator roll is entrained with air, it causes unevenness of the entire painted surface called ripples.

As a method for suppressing such air entrainment, in roll coating in a field different from the production of a coated metal plate,
1) The air entrainment limit can be improved by reducing the upstream side from the atmospheric pressure, and
2) By substituting the upstream atmosphere with carbon dioxide, the entrained gas is dissolved in the water-based paint and the air entrainment is suppressed.
Has been proposed.

However, in order to decompress the upstream side, a large facility cost is required. Also, the method of filling the upstream side with carbon dioxide requires a large equipment cost and is not effective for solvent-based paints that are common as paints.
Technical Information Association "Coating Technology" pp. 339-347

  The present invention is a roll coating method capable of effectively suppressing coating defects caused by roll eyes and air entrainment and forming a coating film having a good appearance in a simple and inexpensive manner in roll coating. Another object is to provide a device.

  The reason why rolls (rib patterns) are generated in reverse-coating two-roll coating is that the rotation direction between the pickup roll and the applicator roll is natural. That is, a roll is generated at a portion A (between the pickup roll 3 and the applicator roll 2) in FIG. The generation of the roll is an inevitable phenomenon as long as the roll is rotated at an industrial speed to distribute the liquid.

  The present inventors have previously found that when the resin film is brought into contact with the coating liquid on the applicator roll, the rib pattern can be smoothed to eliminate the rolls. However, it was found that when the rotation speed of the applicator roll is increased, a large number of short (several centimeters) linear streaks are generated.

  As a result of examining the cause, air entrained from the upstream side along the applicator roll is randomly mixed in the coating liquid from the contact portion where the resin film and the coating liquid are in contact, and it is pulled. It turned out to be short linear streaks.

  It has been found that the air entrainment can be remarkably suppressed and the occurrence of short linear streaks can be prevented by slightly pressurizing the contact portion between the coating liquid and the resin film with a roll or the like from above the film, and the present invention. It came to.

Here, the present invention provides a roll coating, the coating liquid on the applicator roll, the resin film having a thickness of 50μm or more 500 [mu] m or less flexible, the applicator roll so as to deflect along the periphery of the applicator roll the coating liquid and the circumferential direction is contacted with a length of at least 5mm Rutotomoni, and the contact portion between the coating liquid and the resin film pressed by the following pressure 10 g / cm or more 2500 g / cm through the resin film The air entrained from the upstream side along the applicator roll from the contact portion where the resin film and the coating liquid come into contact with the applicator roll while suppressing random mixing in the coating liquid. The roll coating method is characterized in that the formed rolls are smoothed .

The present invention also provides a flexible resin film having a thickness of 50 μm or more and 500 μm or less arranged so as to be in contact with the coating liquid on the applicator roll, and a contact portion between the coating liquid and the resin film via the resin film. The resin film is bent along the outer periphery of the applicator roll, contacts the coating liquid on the applicator roll with a length of at least 5 mm in the circumferential direction, and pressurizes the resin film. It means the contact portion between the coating liquid and the resin film, characterized in Rukoto pressurized by the following pressure 10 g / cm or more 2500 g / cm by the, also relates to a roll coating apparatus.

  According to the present invention, it is possible to stably and industrially produce a coated metal plate having a uniform coating thickness with no rolls or linear streaks by two-roll reverse coating.

  Hereinafter, the present invention will be described in more detail. The roll coating method and apparatus of the present invention is characterized in that a resin film is brought into contact with a coating liquid on an applicator roll, and this contact portion is slightly pressed from above the film.

The present invention is suitable for a two-roll reverse coating, whereby rolls that have been unavoidable in the past can be eliminated.
However, even when the present invention is applied to a two-roll natural coat, the effect of reducing roll eyes can be obtained. In addition, the present invention can be applied to other roll coatings such as three-roll coating by bringing a resin film into contact with an applicator roll and pressurizing it, and rolls and / or entrained air are also applied. There are cases in which the effect of eliminating the line-drawing due to is obtained. Accordingly, the roll coating method of the present invention is not particularly limited. Hereinafter, the present invention will be described with respect to the two-roll reverse method.

  As shown in FIG. 3, the roll coating apparatus of the present invention has a resin film 8 disposed so as to be in contact with the coating liquid on the applicator roll 2, and contact between the resin film 8 and the coating liquid on the applicator roll. A pressing roll 9 is provided as means for pressing the part. Other components of the roll coating apparatus, that is, the backup roll 1, the applicator roll 2, the pickup roll 3, the driving means thereof, the paint pan 5 and the like may be the same as those of the conventional roll coating apparatus.

  Although the resin film 8 is not shown, one end is supported by an appropriate jig, and the other end is a free end as shown in the drawing, and the applicator roll and the coating liquid are passed through at or near the tip. Contact. The contact between the resin film and the coating liquid on the applicator roll preferably occurs, for example, over a length of at least about 5 mm, preferably 20 mm or more in the circumferential direction. Accordingly, it is preferable that the resin film bends slightly along the shape of the applicator roll.

  If the thickness of the resin film 8 is too large, a new roll will be formed. On the other hand, if the film is too thick, high flatness is required without being well adapted to the roll. Furthermore, a “cut-back” occurs on the film cut surface on the downstream side of the roll, and this also becomes a factor that makes a beautiful coating impossible. Therefore, the thickness of the resin film is 500 μm or less, preferably 300 μm or less. However, since wrinkles are generated when the film is too thin, the film thickness is preferably 50 μm or more.

  The material of the resin film is selected so that it does not dissolve or swell even when immersed in the coating solution for a long time. Moreover, what has a certain amount of flexibility which bends along the outer periphery of an applicator roll is preferable. Although it varies depending on the paint system, generally preferred resin film materials include PET (polyethylene terephthalate), PP (polypropylene), PE (polyethylene), PTFE (polytetrafluoroethylene) and the like.

  The surface roughness of the resin film (surface roughness on the surface in contact with the coating liquid) is preferably 1 μm or less in terms of Ra. If the surface irregularities are too large, a good paint appearance cannot be obtained. Moreover, it becomes easy to entrain air and tends to generate the short streaks described above.

  The pressure applied through the resin film to suppress air entrainment from the upstream side along the applicator roll is 10 g / cm 3 or more. When the applied pressure is less than 10 g / cm 3, there is not much difference between the case where the resin film is not pressurized and the result, and it is difficult to suppress short striation due to air entrainment. If the applied pressure is too large, the coating liquid may be squeezed, or streaking may occur when a foreign matter such as an agglomerated pigment is involved. In that sense, the applied pressure is preferably 2500 g / cm or less, more preferably 2000 g / cm or less.

  The applied pressure may be determined so as to prevent the occurrence of linear streaks, and may be varied according to factors such as the thickness of the resin film and the viscosity of the coating liquid. In general, it is necessary to increase the pressure as the thickness of the resin film increases and the viscosity of the coating liquid increases.

  Any pressurizing method can be adopted as the pressurizing method as long as the resin film can be uniformly pressed over the entire width of the roll. A preferred method is to place a pressure roll 9 as shown in FIG. This pressure roll is not rotated and is supported by an appropriate jig so that a predetermined pressure can be applied. The pressure roll may be made of various materials such as metal, plastic and ceramics.

  Pressurization of the resin film is performed so as to pressurize the portion (contact portion) where the coating liquid and the film come into contact. However, the pressurizing means (the pressurizing roll 9 in the illustrated example) does not necessarily have to be disposed immediately above the contact portion. If a pressing force can be applied to the contact portion, it is possible to arrange a pressurizing means in the vicinity of the contact portion. However, if the pressurization location is too downstream from the contact portion, the air entrained once flows into the downstream side even if a little pressure is applied, so that the linear streak remains without disappearing.

  If only one film cannot smooth the coating film by contact with the pressurized film (formation of a uniform coating film without defects such as rolls), use a plurality of films. Smoothing of the coating film may be achieved.

  The coated substrate is not particularly limited, but is generally a strip metal substrate. For example, a cold-rolled steel strip, a stainless steel strip, an aluminum strip, those obtained by chemical conversion treatment thereof, those obtained by plating them, those obtained by plating and chemical treatment thereof, and the like can be mentioned. A primer (undercoat) is generally applied to the substrate before roll coating. The roll coating of the present invention can also be applied to this undercoat.

  The type of paint (coating liquid) to be painted is not particularly limited. In general, a thermosetting baking paint is used, but a dry paint that forms a film at room temperature or by heat drying may be used. The paint may be water-based or solvent-based. The coating thickness may be the same as in conventional roll coating, and is usually in the range of 1 to 300 μm.

  Using a conventional 2-roll / reverse coat coating apparatus as shown in FIG. 1 and a 2-roll / reverse coat coating apparatus according to the present invention as shown in FIG. The pick-up roll was a chrome-plated metal roll, and the applicator roll was a urethane rubber lining roll.

The coated base material is a molten 55% Al-Zn alloy-plated steel strip (thickness 0.3 mm), ground treatment (coating-type chromate 30 mg / m ² as Cr adhesion amount) and Nippon Fine Coating Primer (NP250). The thickness was 5 μm.

  The top coat used for roll coating is a metallic paint (CF501) made by Nippon Fine Coat. The roll gap between the pick-up roll and the applicator roll and the dilution ratio of the paint so that the dry film thickness is 15 to 20 μm. Adjusted. Baking after painting was performed by hot air drying under the condition that the maximum plate temperature reached 230 ° C.

In all cases, the sheet steel belt passing speed was 100 m / min, the pick-up roll rotating speed was 120 m / min, and the applicator roll rotating speed was 40 m / min.
The resin film used in the apparatus shown in FIG. 3 is a PET film having a different thickness, and a pressure roll (made of a metal having a diameter of 50 mm) disposed immediately above the contact portion between the film and the coating liquid on the applicator roll. The pressure applied from the round bar was also changed. The PET film had a surface roughness Ra of 0.5 μm on both sides. The contact length in the circumferential direction between the resin film and the coating liquid on the applicator roll was in the range of 5 to 150 mm.

  The results of visual observation of the coating appearance of the roll-coated steel strip are shown in Table 1 together with the presence or absence of the PET film, its thickness, and the applied pressure. In the appearances in Table 1, those where roll eyes (ribs) were observed were indicated as x, those where short linear streaks were observed as Δ, and those where roll eyes and streaks were not observed and appearance was good. (Good).

  As shown in Table 1, rolls are generated in the conventional two-roll reverse coat in which no PET film is provided. When the PET film is placed in contact with the coating liquid on the applicator roll, the occurrence of roll eyes can be prevented, but if the pressure is not applied to the contact area or the pressure is below 10 g / cm 2, it is short. Linear line drawing occurs.

  By applying a pressing force of 10 g / cm 3 or more to the contact portion according to the present invention, it is possible to perform coating with a good appearance with no streaking and no rolls. However, if the applied pressure is too high, streaking due to foreign matter will occur. When the thickness of the PET film is larger than 500 μm, roll eyes due to the resin film itself are generated.

It is explanatory drawing of the roll coating apparatus of the conventional 2 roll reverse coat system. It is explanatory drawing of the roll coating apparatus of the conventional 3 roll full reverse coat system. It is explanatory drawing of the roll coating apparatus of the 2 roll reverse coat type which concerns on this invention.

Explanation of symbols

  1: Backup roll, 2: Applicator roll, 3: Pickup roll, 4: Band-shaped metal substrate, 5: Paint pan, 6: Metering roll, 7: Blade, 8: Resin film, 9: Press roll

Claims (8)

A flexible resin film having a thickness of 50 μm or more and 500 μm or less is applied to the coating liquid on the applicator roll, and the length is at least 5 mm in the circumferential direction with the coating liquid on the applicator roll while bending along the outer periphery of the applicator roll. contact portion Rutotomoni contacting, in the contact portion between the coating liquid and the resin film pressed at 10 g / cm or more 2500 g / cm or less of pressure through a resin film, resin film and the coating solution is in contact with is To smooth the rolls formed in the coating liquid on the applicator roll while suppressing random entrainment of air entrained from the upstream side along the applicator roll. roll coating method characterized by causing.   The roll coating method according to claim 1, wherein the surface roughness of the resin film on the side in contact with the coating liquid is 1 μm or less in terms of Ra.   The roll coating method according to claim 1, wherein the contact part is pressurized by a roll.   The roll coating method according to any one of claims 1 to 3, wherein the substrate to be coated is a band-shaped metal and the applicator roll is rubber-lined. For pressing a contact portion between a flexible resin film having a thickness of 50 μm or more and 500 μm or less disposed so as to contact the coating liquid on the applicator roll and the coating liquid and the resin film through the resin film and means,
The resin film contacts the coating liquid on the applicator roll with a length of at least 5 mm in the circumferential direction while bending along the outer circumference of the applicator roll, and the means for pressurizing the coating liquid and the resin film. the contact portion is pressurized by the following pressure 10 g / cm or more 2500 g / cm and wherein the Rukoto, roll coating apparatus.   The roll coating apparatus according to claim 5, wherein the surface roughness Ra of the contact surface with the coating liquid of the resin film is 1 µm or less.   The roll coating apparatus according to claim 5 or 6, wherein the pressurizing means is a roll.   The roll coating apparatus in any one of Claims 5-7 for coating the strip | belt-shaped metal base material with which the applicator roll is rubber-lined.

Images