JPS61146369A - Coating method - Google Patents

Abstract

PURPOSE:To coat a coating liq. in beads on a supporting body having a rugged surface at high speed and to prevent crawling trouble by giving an electric potential higher than a specified value to a bead-forming part or to the surface of the supporting body immediately before the bead-forming part. CONSTITUTION:In a coating method wherein a supporting body 8 having aq rugged surface is continuously traveled at high speed, a DC electrode 10 is brought into contact with the surface of the supporting body 8 immediately before a bead 9, or a DC electrode is formed on a backup roller 7 to impress a DC voltage on the surface. Accordingly, a 0.1kv potential is given to the bead 9 forming part or the surface of the supporting body 8 immediately before the bead 9 forming part. Consequently, a coating liq. is attracted to the surface of the supporting body 8 by the generated electrostatic field, the coated liq. can be completely intruded into the rugged surface of the supporting body 8, and the generation of the so-called crawling trouble can be effectively prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a method of coating a coating liquid by forming beads on the surface of a support that is continuously running at high speed.

[Conventional technology]

In addition to those with a glossy surface, photographic paper is available in various types with textured or uneven patterns to meet market needs. The latter type of photographic paper is produced by placing molten polyolefin on a pulp-based base paper and pressing it with a roller with an uneven surface, or by colliding fine particles such as sand with a roller to create an uneven surface. A support is prepared and a predetermined coating liquid is applied to the surface of the support.

If this coating solution is applied at high speed by a bead coating method using a slide hopper or the like, there is a risk that the coating solution will not penetrate sufficiently into the irregularities on the surface of the support, resulting in a so-called repelling failure. This repelling failure is more likely to occur as the coating speed is faster, and the irregularities on the surface of the support are formed randomly rather than regularly.

In other words, the lower the specular gloss, the more likely it is to occur.Therefore, in the past, when bead-coating a coating solution onto a support with an uneven surface, the coating speed was extremely slow; No increase could be expected, and it was inevitable that running costs would rise.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and aims to provide a coating method that does not cause repellency failure by bead coating a coating liquid at high speed on a support having an uneven surface.

[Structure of the invention]

In order to achieve the above object, the present invention provides a method in which a support having an uneven surface is continuously run at high speed and a coating liquid is applied to the surface of the support by forming a bead. Or 0 on the support surface just before reaching it.
The gist of the invention is to apply a potential of 1 KV or more.Next, an apparatus for carrying out this invention will be explained based on the accompanying drawings.

In the figure, l is a slide hopper, and the slide hopper 1 has an inclined slide surface 2.

A liquid reservoir 4 communicates with the slide surface 2 through a slit 3.
It is equipped with Several types of coating liquids 5 are continuously fed into the liquid reservoir 4 at a constant flow rate by a pump (not shown), rise through the slit 3, protrude in a film form on the slide surface 2, and move along the slope thereof. descend. The coating liquid 5 descending down this slide surface 2 flows down in a layered manner with the upstream side riding on the upper surface of the downstream side, and is supported by a backup roller 7 running in the direction of the arrow so that it approaches the lip end 6 of the slide surface 2. The coating is applied by forming beads 9 on the surface of the body 8. In this case, the support 8 used is a material having a low specular gloss obtained by placing a polyolefin film on the surface of a base paper and processing the film into irregularities. Here, the term "low specular gloss" refers to one whose surface gloss is 20% or less when measured with a specular gloss meter at an incident angle of 75 degrees.

Reference numeral 10 denotes a DC electrode that is in contact (or may be non-contact) with the surface of the support 8 immediately before reaching the bead 9, and the DC electrode 10 includes a positive electrode and a negative electrode on the surface that contacts the support 8. A group of electrodes is provided. When a voltage from a DC power supply (approximately 500 to 3000 V) is applied to the DC electrode 10, a dielectric polarization phenomenon occurs on the surface of the support 8, and a charge of the opposite sign to that on the electrode is induced. Therefore, an electrostatic field is generated at the bead forming portion or in front of the bead stand, and the coating liquid 5 is attracted to the surface of the support 8.

Even if there are irregularities on the surface of the support 8, the coating liquid completely enters the recesses, thereby preventing the so-called repelling failure from occurring. The larger this electrostatic field is, the better the effect of preventing repellency failure is.For this purpose, if the potential of the support surface at the bead forming part or in front of the rod is set to 0.1 KV or more, the specular gloss of the two surfaces can be improved. Even when high-speed coating is performed at a coating speed of 50 m/min or more on a support having a coating composition of 20% or less, the above-mentioned repelling failure can be effectively prevented. In addition.

Any potential may be applied as long as the effects of the present invention can be obtained, but for practical purposes, up to about 2 KV is sufficient.

In addition to the above-mentioned method, the potential may be applied to the support 8 by forming a DC electrode on the back amplifier roller 7 and applying the voltage thereto, or by other methods.
It should be noted that recently, the back side of the support is coated with an antistatic agent, or the surface is coated with an undercoat layer to strengthen the adhesion with the coating composition after drying. In some cases, it becomes difficult to charge the surface of the support, but even if the support itself is not charged, it is possible to apply an electrostatic field to the bead forming portion.

It is preferable to apply a potential to the support 8 not at the start of coating, but after the start of coating, that is, after bead formation. This may lead to uneven adhesion, which may lead to bubbles being drawn into the bead and streak-like failures.

This is to prevent this.

In addition, although the above explanation shows the case where a slide hopper type coating device is used as the coating method, it goes without saying that the same effect can be obtained when using a device that coats while forming a bead, such as an extrusion coating device. It can be easily inferred that the above effects can be obtained also in a coating method using other coating devices such as a coating device.

The above explanation assumes that the photosensitive material is applied to the support of photographic paper, but this is not limited to this, and as long as the liquid material is applied to a substantially continuous support, photographic film, It can also be widely applied to adhesive tapes, magnetic recording tapes, and other products.

〔Example〕

◎Example-(11) Using a slide hopper type coating device, multilayer coating of coating liquids having the wet coverage and viscosity shown in Table 2 was carried out.

As supports, polyethylene-coated papers for photographic printing paper having three different degrees of specular gloss, A, B, and C below, were used.

A: Flat surface Specular gloss 90.6% B: Regularly uneven surface 18.2% C: Random uneven surface 〃8.6% Coating conditions are coating speed: 16 strokes/min Bead back pressure -20 m/Ag Bead gap: 200 μm.

Coating was carried out under the above conditions while changing the potential of the surface of the support immediately before coating, and the presence or absence of repellency failure was observed. The results are shown in Table 2.

Table 2 Symbol O - No repelling failure〃 Δ→Minor repelling failure occurred〃 × - Repelling failure occurred As is clear from the above results, when the support surface is flat (specular gloss 90.6%), apply It is related to the presence or absence of potential on the surface of the support immediately before it (repellent failure does not occur, but if the support surface has unevenness, the specular gloss level 1
Even in the case of 8.2% or 8.6%, as long as the potential on the surface of the support is 0.5 KV or more, there will be no repelling failure, or even if there is, it will be slight and can be ignored.

■Example-(2) Coating was carried out under the same conditions as in Example-(1) above, using Support C with a surface specular gloss of 8.6%, and varying the surface potential and coating speed of the support. The presence or absence of cissing failure was then observed. The results are shown in Table 3.

Table 3 Symbol Q - No repelling failure〃 Δ - Slight occurrence of repelling failure〃 ×→ Repelling failure occurred From the above results, when the coating speed is 40+++/min for the support surface with extremely low specular gloss, there is no potential. No repelling failure occurs regardless of the coating speed, but as the coating speed increases to 100.160.220 m/min, the influence of the potential on the surface of the support becomes apparent. That is, the potential of the support surface is O.1K when the coating speed is 100+w/min or less.
V or more, 160III/min or less, 0.5KV or more,
It can be seen that at 220 m/min or less, if the voltage is 1 KV or more, no cissing failure will occur.

〔Effect of the invention〕

As explained above, the present invention provides a method in which a support having an uneven surface is continuously run at high speed, and a coating liquid is applied to the surface of the support by forming a bead. Since the feature is that a potential of a certain level or higher is applied to the surface of the support immediately before the support, the support is
Even when coating at high speeds of m/min or more, by applying a potential of 0.1 KV or more to the bead forming area or before stirring, the coating liquid is attracted to the surface of the support by the action of the electrostatic field generated thereby. The coating liquid can completely penetrate into the uneven surface of the support, and the occurrence of so-called repelling failure can be effectively prevented. Furthermore, it has excellent effects in that an increase in production volume and a reduction in running costs can be expected by increasing the coating speed.

Furthermore, in the present invention, the application of a potential above a certain level to the surface of the support at the bead forming portion or immediately before it is performed by applying a high voltage to a DC electrode that is in contact with or not in contact with the support, or by When a high voltage is applied to a DC electrode formed on a backup roller, it is easy to form an electrostatic field, and there is an advantage that the equipment cost is low.

[Brief explanation of drawings]

The figure is a sectional view of a slide hopper type coating device that implements the present invention. 1- Slide hopper 2--slide surface 5-Coating liquid 7--Backup roller 8-Support 9-Bead IO--DC electrode

Claims (3)

[Claims] (1) In a method in which a support having an uneven surface is continuously run at high speed and a coating liquid is applied to the surface of the support by forming a bead, the support surface at the bead forming part or immediately before reaching the bead formation part. A coating method characterized by applying a potential of 0.1 KV or more to. (2) The coating method according to claim 1, wherein the potential is applied by applying a high voltage to a DC electrode that is in contact with or not in contact with the support. (3) The coating method according to claim 1, wherein the potential is applied by applying a high voltage to a DC electrode formed on a backup roller of the support.