JP2006341532A - Coated steel sheet for writing board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel sheet for a writing board which improves simultaneously visibility and marker wiping properties. <P>SOLUTION: When the parallel direction and the right-angled direction to the rolling direction of a steel sheet are respectively made the direction L and the direction C, the coated steel sheet for the writing board has a surface coating film layer with Ra of 0.5-5 μm both in the direction L and in the direction C, and with Sm of 0.7-5 mm on average in the direction L and in the direction C. The surface coating film layer that has such a special surface state as this can be realized by coating the steel sheet with a coating constituting a surface coating film layer through an undercoat coating film layer having, for example, an uneven surface with the Ra of ≥1.5 μm both in the direction L and in the direction C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coated steel sheet used for a writing board in which characters written with ink or the like can be easily wiped off.

The material used for the writing board is required to be excellent in “visibility” so that characters or the like written on the surface can be clearly distinguished by the correct color. For that purpose, it is important that an image of a bright light source such as illumination is not reflected depending on the viewing angle. It is also important that the white board has a high brightness.
On the other hand, letters and the like are written on the writing board surface with a water-based or oil-based marker, but it is necessary that the ink can be easily wiped off, that is, the “marker wiping property” is excellent.

  At present, enamel is often used as a whiteboard material, and recently, coated steel sheets have been used mainly for relatively low grade applications such as home use.

  The haze can give sufficient brightness, and by forming moderate irregularities on the surface, incident light can be scattered and the sharpness can be lowered. For this reason, it is a material having excellent “visibility” as a writing board. In addition, it exhibits excellent “marker wiping properties” for inks developed for writing boards. However, since cocoons are produced by applying glaze on the surface of the steel sheet and firing at a high temperature of 800 to 900 ° C., it has a drawback that the production cost is higher than that of the coated steel sheet.

  On the other hand, a coated steel plate can be manufactured in the state of a steel strip in a continuous line (so-called precoated steel plate). For this reason, it becomes very advantageous in terms of cost. However, the present condition is that the precoat steel plate which provided the high performance for writing boards has not yet appeared. The main cause is that it is difficult to achieve both “visibility” and “marker wiping performance”. In other words, the pre-coated steel sheet is generally produced continuously by applying the paint to the surface of the steel strip with a roll coater and then baking it. In this case, the surface of the paint film must be treated without adding a matting agent to the paint. Becomes highly smooth, and an image such as illumination is reflected and visibility is lowered. On the other hand, when a matting agent is added, the reflection can be reduced, but since the surface becomes rough, the marker wiping property is not ensured.

  Patent Document 1 describes a projection / writing board having a 60 ° specular reflectance of 40% or less by incorporating a fine reflecting material made of an inorganic or metallic material into a ceramic coating layer. However, this material is also considerably more expensive than the precoated steel sheet.

  Patent Documents 2 and 3 disclose a technique of performing base coating with a paint that forms a splash pattern when applied to the surface of a steel plate substrate. This coating material contains organic particles having a surface tension different from that of the resin and the crosslinking agent and having a melting point lower than the reaction temperature of the resin and the crosslinking agent, and a repelling pattern is formed in the state after coating and baking. It is said that by forming a top coat film on the base coat film on which this repellency pattern is formed, a coated steel sheet exhibiting a yuzu skin appearance with a feeling of flesh is obtained. However, a designable steel sheet having such an uneven surface does not exhibit visibility and marker wiping properties suitable for a writing board.

  Patent Documents 4 and 5 also describe a designable steel sheet having a concavo-convex coating surface composed of a base coating film and a top coating film. However, these are intended to form a glossy surface with high reflectivity (Patent Document 4, paragraph 0001, Patent Document 5, paragraph 0060), and no pre-coated steel sheet that can be applied to a writing board is disclosed.

  Patent Documents 6 and 7 describe a coated steel sheet in which the coating film hardness is increased by incorporating an aggregate in the coating film, and durability against brush washing or the like in a tunnel interior material on a highway is improved. In this case, surface irregularities are formed due to the aggregate, but visibility and marker wiping properties suitable for a writing board are not obtained.

JP-A-6-27532 JP 62-53775 A JP-A-7-275787 JP 2003-236981 A JP 2004-66519 A Japanese Patent Laid-Open No. 7-256821 Japanese Patent Laid-Open No. 11-42735

  The present invention aims to develop and provide a coated steel sheet that is less expensive than cocoons and that has both “visibility” and “marker wiping performance” at a high level and exhibits a highly uniform appearance. .

  As a result of detailed studies, the inventors have found that the above object can be achieved by controlling the surface morphology of the coating film. It was found that the form can be specified by Ra and Sm.

That is, the present invention provides a coated steel sheet for a writing board having a surface coating layer satisfying the following (1) and (2) when the parallel direction to the rolling direction of the steel sheet is L direction and the perpendicular direction is C direction.
(1) Ra is 0.5 to 5 μm in both the L direction and the C direction.
(2) Sm is 0.7 to 5 mm on average in the L direction and the C direction.
Further, those satisfying the following (3) are suitable targets as whiteboards.
(3) The lightness L ^* value is 83 or more.

Here, Ra and Sm are the arithmetic mean roughness and the average interval of irregularities defined in JIS B0601 (1994), respectively. The lightness L ^* value is defined in JIS K5600-4-4.

  The surface coating layer having a special surface form as described in the above (1) and (2) can be realized by forming it on a ground surface to which irregularities are imparted. Examples of the ground treatment surface include a ground coating layer formed on a steel sheet substrate, and Ra has a concavo-convex surface with Ra of 1.5 μm or more in both the L direction and the C direction. Such unevenness of the undercoat film layer can be realized by using a paint that forms an uneven surface by surface tension by itself, and also by a paint containing an aggregate. The coating composition constituting the surface coating layer may be applied directly on the surface of the base coating layer provided with irregularities, and another base coating layer is formed on the base coating layer. The above may be interposed.

However, in order to give a highly uniform appearance, it is preferable that the base coating layer is formed so as to cover the steel plate surface without any gap and to have an average coating thickness of 3 μm or more.
Here, “covering the surface of the steel plate without a gap” means creating a state in which the steel plate substrate is not exposed by the base coating layer. That is, the surface coating layer is not in direct contact with the steel sheet substrate. As the average coating thickness, the value of the coating thickness after drying calculated from the coating amount per unit area of the steel sheet can be adopted. In addition, the steel plate substrate here is the surface of the coated raw plate. For example, when a galvanized steel plate is used as the coated original plate, the plated surface (the coated surface subjected to the surface treatment if the surface is treated) is the steel plate substrate. It hits.

  ADVANTAGE OF THE INVENTION According to this invention, it became possible to provide the coated steel plate which comprises "visibility" and "marker wiping off" equivalent or better than the conventional smoked writing board. This coated steel sheet can be mass-produced as a so-called pre-coated steel sheet and is less expensive than cocoons. In addition, it is possible to provide coated steel sheets of various colors with improved visibility and marker wiping, so not only for whiteboards, but also for writing boards that display colors similar to those of traditional blackboards. It can be suitably used. In this case, a blackboard that does not use chalk can be realized by using ink with high lightness and high concealment, which can contribute to indoor beautification. Thus, the present invention contributes to the provision of a highly practical and inexpensive writing board.

  In FIG. 17, one example of the cross-sectional structure of the coated steel plate of this invention is typically shown. This is an example of a type using a base coating layer having an uneven surface as a base processing surface. A base coating layer 2 having an uneven surface is provided on a steel plate substrate 1. The base coating film layer 2 has such a property that the surface tension is adjusted by adding a component such as silicone oil, and the coating film itself has a large uneven surface. A paint based on a so-called “Yuzu skin primer” or a paint to which a Yuzu skin forming agent (for example, a main component of polyethylene wax) is added can be used. In addition to the yuzu skin forming agent, a matting agent (for example, a material mainly composed of silica) may be added. Moreover, unevenness | corrugation can also be provided to a base coating film layer with the coating material which added aggregate (for example, polyacrylonitrile bead). A surface coating layer 3 is formed on the base coating layer 2. The surface coating layer 3 can be a general paint used for a pre-coated steel sheet for whiteboard. For example, acrylic resin-based paints and polyester resin-based paints can be used. The large irregularities formed in the base coating layer 2 are alleviated by applying a paint having a general surface tension thereon, and as a result, the surface coating layer 3 having a desired surface form is formed. It is.

The base coating film layer 2 can form a coating film in an island shape when the coating amount is reduced. That is, it is possible to make a base surface that leaves a portion where the steel plate substrate is exposed. Even in this way, it is possible to make the surface of the surface coating layer 3 into a predetermined uneven shape. In this case, since it was possible to save the paint for the base, it was expected as a method with a high cost reduction effect. However, when put to practical use as a whiteboard, it was found that the steel plate substrate was transparent from the surface coating layer 3 at the exposed portion of the steel plate substrate on the underlying surface, and it was difficult to sufficiently conceal it. This is not preferable because a good appearance with high uniformity cannot be obtained.
As a result of various studies, it is desirable that the undercoat film layer 2 be formed so as to cover the steel sheet surface without any gap and to have an average coat film thickness of 3 μm or more. For whiteboards, it is desirable that the lightness L ^* value be 93 or more.

  Increasing the surface Ra is effective for providing “visibility” in which light sources such as lighting and window lights are not reflected on the writing board. For example, a large Ra can be obtained with a paint to which a matting agent is added, and reflection of a light source can be remarkably prevented. On the other hand, “marker wiping” is sacrificed. This is because a surface property that is as smooth as possible is advantageous for improving the marker wiping property. As a result of various studies, it has been found that these conflicting characteristics can be achieved by maintaining a large Ra and increasing Sm. And such a desired surface unevenness | corrugation was realizable by the method of forming a surface coating layer on the base-treatment surface with a large unevenness | corrugation formed as mentioned above, for example.

  In general, it is relatively easy to increase Ra on the coating surface. For example, Ra increases by adding a matting agent, and the coating surface of the above-mentioned “Yuzu skin primer” also exhibits a large Ra. However, Sm becomes small on these coating surfaces. That is, the uneven pitch becomes too fine, and the marker wiping property is deteriorated. Therefore, in the present invention, by utilizing the properties of a general paint that is intended to relieve the irregularities on the surface, the large Ra and small Sm of the base are relaxed, so that the Ra can be increased while maintaining Ra to some extent. Is intended. In addition, in FIG. 17, since the cross section is typically shown on the assumption that the convex part of the base coating film layer 2 was located in a line, Sm of the base coating film layer 2 and the surface coating film layer 3 Although the change is not expressed, the convex part of the undercoat layer 2 is actually distributed randomly in a plane, so apply a paint with the property to alleviate the surface irregularities on it. Thus, both Ra and Sm are relaxed, Ra is smaller and Sm is larger.

  As a result of detailed investigations by the inventors, Ra of the surface coating layer needs to be in the range of 0.5 to 5 μm in both the L direction and the C direction of the steel sheet. If Ra is smaller than this, the reflection of the light source increases and the visibility is impaired. Moreover, when Ra exceeds 5 micrometers, it will become difficult to improve marker wiping property. More preferable Ra is 0.7 to 3 μm in both the L direction and the C direction.

  Sm of the surface coating layer is set to 0.7 to 5 mm on the average in the L direction and the C direction. When the Sm is smaller than this, the marker wiping property is deteriorated, and when the Sm is large, the reflection of the light source is increased and the visibility is impaired. More preferable Sm is 0.9 to 3.5 mm on average in the L direction and the C direction.

  In order to control Ra and Sm of the surface coating layer within the above range, the uneven form of the ground surface is important. Since the surface Ra is relaxed (decreased) by the surface coating layer, the surface Ra should be set to 0.5 μm or more stably in both the L direction and the C direction as described above. It is preferable that both the L direction and the C direction be 1.5 μm or more. However, if the Ra of the ground surface is too large, it is difficult to satisfy the desired Ra value unless the surface coating layer is made very thick, which is uneconomical. For this reason, it is preferable that Ra of the ground surface is suppressed to a range of 10 μm or less. The Sm of the ground surface is preferably 1.5 mm or less, and more preferably 1 mm or less.

  Using a hot-dip galvanized steel sheet having a thickness of 0.5 mm as a coating original sheet, various undercoat coating layers and surface coating layers were formed, and visibility and marker wiping properties were examined. The coating method employs a method in which a base coat layer is applied using a roll coater and then baked at 200 ° C., and a surface coat layer is applied using a roll coater and then baked at 215 ° C. The method to do was adopted. The coating amount was set such that the average coating thickness was 1 to 5 μm for the base coating layer and 14 to 20 μm for the surface coating layer.

For the base coating layer, use a commercially available epoxy resin-based smooth primer as it is, or based on a polyester resin-based yuzu skin primer, or a commercially available yuzu skin-forming agent based on polyethylene wax as an epoxy resin-based paint. What was added was used. In some samples, a matting agent based on silica was added. Moreover, what added the aggregate which has a polyacrylonitrile bead as a main component was also prepared.
The surface coating layer was formed using a polyester-based white paint. As a result of the measurement, the lightness L ^* values were all 83 or more. For comparison, commercially available smoked whiteboards and whiteboards made of painted steel sheets were obtained and used for investigation. Each sample was examined for visibility and marker wiping.

For visibility, a sample steel plate cut to a size of 300 x 500 mm is affixed to the surface of a commercially available smoked whiteboard, and the reflection of lighting and window lights is visually compared with the surrounding smoked whiteboard. Was evaluated as ○ evaluation, a slightly inferior one was evaluated as △ evaluation, and a considerably inferior one was evaluated as × evaluation.
In addition, as an index that quantitatively represents the reflection of the light source, the sharpness (of-image) was examined by a method based on ASTM E430 using a Murakami color image clarity gloss meter DGM-30.

  Marker wiping is achieved by wiping off characters and filled figures written with commercially available markers for writing boards (each color of ethanol-based ink and ketone-based ink) using a commercially available marker eraser. The presence or absence was examined by a method of judging visually. In this case, the evaluation was also made by comparison with a commercially available smoked white board. In other words, all the markers used had less wiping residue than or equal to the smoked whiteboard evaluated as ○, and at least one type of marker left uncleaned from the smoked whiteboard △ evaluated and wiped The remaining was considerably more than the smoked whiteboard, and those that were clearly inferior to wiping were rated as x.

Ra and Sm were measured by a stylus type surface roughness measuring instrument based on JIS B0601 (1994).
These results are shown in Table 1. Examples of roughness curves for some samples shown in Table 1 for reference are shown in FIGS.
In the examples of the invention, the base coating layer is formed so as to cover the steel sheet surface without any gap and the average coating thickness is 3 μm or more, and is not described in the table. The Ra of the coating layer satisfied 1.5 μm or more in both the L direction and the C direction.

  As can be seen from Table 1, the coated steel sheet having the surface coating layer defined in the present invention has excellent “visibility” and “marker wiping property” equal to or better than commercially available smoked whiteboards that have been widely used conventionally. Is provided.

The figure which illustrated the roughness curve in sample No. 3 of Table 1. The figure which illustrated the roughness curve in sample No. 4 of Table 1. The figure which illustrated the roughness curve in sample No. 5 of Table 1. The figure which illustrated the roughness curve in sample No. 6 of Table 1. The figure which illustrated the roughness curve of the base coating-film layer surface in sample No. 6 of Table 1. FIG. The figure which illustrated the roughness curve in sample No. 7 of Table 1. The figure which illustrated the roughness curve in sample No. 8 of Table 1. The figure which illustrated the roughness curve in sample No. 9 of Table 1. The figure which illustrated the roughness curve in sample No. 10 of Table 1. The figure which illustrated the roughness curve in sample No. 11 of Table 1. The figure which illustrated the roughness curve in sample No. 13 of Table 1. The figure which illustrated the roughness curve of the base coating-film layer surface in sample No. 13 of Table 1. FIG. The figure which illustrated the roughness curve in sample No. 14 of Table 1. The figure which illustrated the roughness curve of the base coating-film layer surface in sample No. 14 of Table 1. FIG. The figure which illustrated the roughness curve in sample No. 14 of Table 1. The figure which illustrated the roughness curve of the base coating-film layer surface in sample No. 14 of Table 1. FIG. The figure which illustrated typically the section structure of the coated steel plate of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate base 2 Base coating layer 3 Surface coating layer

Claims (6)

  When the parallel direction to the rolling direction of the steel sheet is the L direction and the perpendicular direction is the C direction, Ra is 0.5 to 5 μm in both the L direction and C direction, and Sm is 0.5 to 5 mm on average in the L direction and C direction. A coated steel sheet for a writing board having a surface coating film layer. When the parallel direction to the rolling direction of the steel sheet is the L direction and the perpendicular direction is the C direction, Ra is 0.5 to 5 μm in both the L direction and C direction, and Sm is 0.5 to 5 mm on average in the L direction and C direction. A coated steel sheet for a writing board having a surface coating layer having a lightness L ^* value of 83 or more.   The coated steel sheet for a writing board according to claim 1 or 2, wherein the surface coating layer is formed on a ground-treated surface provided with irregularities.   The coated steel sheet for a writing board according to claim 1 or 2, wherein the surface coating layer is formed through a base coating layer having an uneven surface with Ra of 1.5 µm or more in both the L direction and the C direction. .   The coated steel sheet for a writing board according to claim 4, wherein the base coating film layer is formed so as to cover the steel sheet surface without any gap and to have an average coating film thickness of 3 μm or more.   The coated steel sheet for a writing board according to claim 4 or 5, wherein the base coating layer contains an aggregate.

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