JP4771880B2 - Projection blackboard and manufacturing method thereof - Google Patents

Description

  The present invention relates to a blackboard (also referred to as a chalk board) formed with a straw layer on the surface, and particularly to a smoked blackboard that has both an excellent blackboard function and an excellent screen function. The “excellent blackboard function” as used in the present invention means that it has a function that makes it easy to write and view characters, images, etc. with chalk, and to easily erase written characters, images, etc. Further, the “excellent screen function” means having a function that allows an image such as a character to be clearly projected when an image such as a character is projected by a projector, an OHP, or the like.

  Conventionally, a blackboard (chalk board) has a function of drawing characters, images, and the like on the surface so as to be erasable with chalk, and has been used as an aid for various explanations, lectures, lectures, and the like. For this reason, as specified in JIS S 6007, the conventional blackboard (chalk board) has a surface that is appropriately roughened to make it easier to write and erase characters and images with chalk. In addition, dark-colored materials have been used to make it easier to see letters and images written in chalk.

  However, in recent years, it has become common to use various projectors such as slides and OHPs to project a prepared material on a screen and give explanations while pointing with a pointing stick or the like. When using various projectors to provide explanations, it is necessary to prepare both a projection screen and a blackboard that can draw and erase characters with chalk for supplementary explanation.・ It took a lot of work to clean up. This is because when the image is projected onto a conventional blackboard with various projectors, the image quality becomes dark and unclear, so the conventional blackboard was not used as a screen.

  On the other hand, a reflective screen whose main purpose is to project an image with various projectors uses a white or high brightness color material in order to improve reflection characteristics. For this reason, when drawing with chalk (white ink) on the screen, the contrast will be low and the recognition characteristics of characters, images, etc. will be lowered, and general screens such as beads and white mats will have low surface hardness, When drawing or erasing with chalk, there was a problem that the screen was worn. For this reason, as shown in Patent Document 1 and Patent Document 2, for example, the screen is not used as a chalk board even if it is used as a marker board for drawing and erasing with a marker.

For such a problem, for example, Patent Document 3 proposes a projection-screen enamel blackboard in which a blue dye is mixed into a glaze to form a rough enamel layer having a brightness of 8 to 4 on a steel plate. Has been.
Japanese Patent Laid-Open No. 02-153080 Japanese Unexamined Patent Publication No. 04-229299 Japanese Utility Model Publication No.57-183190

  However, the blackboard manufactured by the technique described in Patent Document 3 has a low reflection luminance and a strong tendency to make the image unclear, and it is difficult to obtain a clear image particularly when a projector having a low luminance is used. However, there is a problem that the recent required characteristics as a screen cannot be sufficiently satisfied. The present invention advantageously solves the above-described problems of the prior art, makes it easy to draw characters, images, etc. with chalk (white ink), is easy to see, has excellent recognition of chalk characters, and characters, images written with chalk (white ink). Etc. can be easily erased, with excellent chalk character recognition, chalk drawing and erasing characteristics, and projected images can be projected vividly and with excellent image recognition. The purpose of the present invention is to provide a projection blackboard and a method for manufacturing the same. Note that the projection blackboard targeted by the present invention is a smoked blackboard having at least one straw layer on the outer surface of the metal substrate.

  In order to achieve the above-mentioned problems, the present inventors diligently studied factors that affect the chalk character recognition property, chalk drawing / erasure property, and video recognition property of smoked blackboards. As a result, the blackboard surface has a predetermined range of lightness and a predetermined range of surface roughness in order to ensure the same or better chalk character recognition and chalk character drawing / erasability than conventional blackboards. At the same time, in order to further improve the image recognition, it has been thought that it is important to adjust the surface ridge layer so as to have a reflection characteristic having a peak gain of a predetermined value or more.

  In such a surface glaze layer, the glaze to be used is a glaze in which at least an appropriate amount of titanium oxide-coated particles or further a titanium oxide glaze is blended with a transparent mat glaze which is a normal chalk board glaze, and firing conditions. It was newly found that it can be generated by adjusting the range to an appropriate range, and it has been found that a blackboard can have both an excellent blackboard function and an excellent screen function.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) A blackboard having at least one glazing layer on a metal substrate, wherein the outermost surface glazing layer among the glazing layers has a brightness V of 3.0 to 7.0 as defined in JIS Z 8721-1993. A projection blackboard characterized by having a certain color tone, a surface characteristic having a surface roughness Rz defined by JIS B 0601-2001 of 5 to 25 μm, and a reflection characteristic having a peak gain of 0.28 or more.

(2) In (1), the surface glaze layer is a glaze layer formed using at least a titanium oxide-coated particle in a transparent mat glaze, or a glaze that further contains a titanium oxide glaze. Projection blackboard.
(3) The projection blackboard according to (1) or (2), wherein the surface glaze layer has any one of black, gray, green, brown, and amber.

(4) In any one of (1) to (3), the surface wrinkle layer has a 75-degree specular gloss Gs (75 °) defined by JIS Z 8741-1997 of 1 to 30%. Projection blackboard.
(5) Oite (2), projection blackboard which the titanium oxide coated particles, characterized in that it is a particle formed by coating titanium oxide on the surface of mica particles.
(6) After applying a laxative glaze to the surface of the metal substrate and firing to form a base glaze layer, or without forming the base glaze layer, at least titanium oxide coated particles on the transparent mat glaze, or In addition, a titanium oxide glaze is blended , and a black pigment, gray pigment, green pigment, brown pigment, yellow pigment, or amber pigment is used alone or in combination, depending on the color tone of the blackboard. Apply the glaze added and fired at 400-800 ° C, excellent chalk character recognition and chalk character erasability with chalk (black ink), excellent blackboard function and image recognition, A method for producing a projection blackboard, comprising forming a surface glazing layer having an excellent screen function .

(7) The method of manufacturing a projection blackboard according to (6), wherein the metal substrate is a cold-rolled steel plate, an aluminum-plated steel plate, or a Zn-Al alloy-plated steel plate.
(8) A method for producing a projection blackboard according to (6) or (7), wherein the titanium oxide-coated particles are particles formed by coating titanium oxide on the surfaces of mica particles.

  According to the present invention, a projection blackboard that is excellent in chalk character recognition and chalk character erasability, excellent in image recognition, easy to handle, and excellent in workability can be manufactured at low cost, and is remarkably industrially superior. The effect of.

  The projection blackboard according to the present invention is a blackboard having at least one eaves layer on a metal substrate. In the present invention, the type of the metal substrate to be used is not particularly limited, but is preferably a cold-rolled steel plate. The cold-rolled steel sheet used as the metal substrate is preferably subjected to Ni plating in order to improve the adhesion between the metal substrate and the glaze. Examples of the cold rolled steel sheet include a low carbon steel sheet and a stainless steel sheet. The C content of the low-carbon steel plate is preferably 0.0200% or less in mass%, more preferably 0.0100% or less, and still more preferably 0.0050% or less.

Moreover, as a metal substrate, it is good also as an aluminum plating steel plate or a Zn-Al alloy plating steel plate. Examples of the Zn-Al alloy-plated steel sheet include a plated steel sheet having a plating layer comprising an Al content of 4 to 70 mass%, the balance Zn and inevitable impurities. Needless to say, the plating layer may contain an additive for improving the properties of the plating film.
Among the above-mentioned glazing layers formed on the metal substrate, the outermost surface glazing layer is defined by the color tone specified by JIS Z 8721-1993 with a lightness V of 3.0 to 7.0 and JIS B 601-2001. Surface roughness Rz of 5 to 25 μm and reflection characteristics of a peak gain of 0.28 or more. The lightness V in the present invention is measured according to the color measurement method defined in JIS Z 8722-2000, and is displayed according to the color display method defined in JIS Z 8721-1993. Value shall be used. When displayed in the Hunter Lab color system, the lightness L of the outermost surface layer of the projection blackboard according to the present invention has a color tone of about 30-70.

The projection blackboard of the present invention first needs to maintain chalk character recognition and chalk character erasability equal to or higher than those of conventional blackboards, and maintain excellent blackboard functions.
For this purpose, first, characters, images and the like drawn with chalk become easy to see, that is, in order to ensure the recognition of chalk characters, in the present invention, the surface wrinkle layer has a brightness V defined in JIS Z 8721-1993. Is from 3.0 to 7.0, preferably any one of black, gray, green, brown, and amber, and more preferably a dark color tone of black, green, or brown And If the brightness V deviates from the above range, it will be too dark and the image recognition will be reduced when the image is projected. On the other hand, if the brightness V deviates from the above range, it will become too bright and chalk character recognition will occur. Sex is reduced. In addition, the color tone and brightness of the soot layer can be adjusted by the type and amount of the additive pigment. In order to adjust the brightness V to 3.0 to 7.0, it is preferable to add Co, Cr, Ti metals or their oxides alone or in combination as pigments. The lightness V is preferably 4.0 to 6.0. When displayed in the Hunter Lab color system, the lightness L is preferably 40-60. More preferably, the lightness V is 4.0 or more and less than 5.0, and when displayed in the Hunter Lab color system, the lightness L is 40 or more and less than 50.

Further, in the projection blackboard of the present invention, the surface characteristics of the surface glazing layer are defined in accordance with JIS B 0601-2001 in order to ensure the drawing and erasing of chalk characters, which makes it easy to write and erase characters, images, etc. with chalk. Is adjusted so that the surface roughness Rz specified in 5 is 25 to 25 μm. In addition, Preferably it is 10-22 micrometers, More preferably, it is 14-20 micrometers.
When the surface roughness Rz of the surface ridge layer is out of the above range and approaches flat, the chalk slips, the chalk drawing performance deteriorates, and the image recognition performance also deteriorates. On the other hand, if the above-mentioned range is exceeded and the unevenness is too large, the chalk character erasability is lowered and the image recognizability is lowered. The surface properties of the surface glaze layer described above can be achieved by setting the combination of the composition of the glaze applied to the metal substrate and the firing conditions after the glaze application within an appropriate range, as will be described later.

In the projection blackboard of the present invention, the surface glazing layer has the above-described color tone and surface characteristics, maintains an excellent blackboard function, and further has a peak gain of 0.28 or higher, preferably a half gain of 13 or higher. Have
For example, as shown in FIG. 2, the reflection characteristics of the plate to be measured are as follows: the incident light 1 is irradiated from the light source 10 in the direction perpendicular to the center of the plate S to be measured; The magnitude of the reflected light 2 (reflection luminance) at a point shifted by 5 ° in the range is obtained from a reflection characteristic curve (see FIG. 1) obtained by measuring with the luminance meter 11. The “peak gain” in the present invention is the ratio of the reflected luminance of the blackboard to be measured measured under the same conditions to the reflected luminance when light is applied to a standard white plate (complete diffuser plate: pure white plate baked with magnesium sulfate). In this case, however, the reflected luminance at a viewing angle of 5 ° is usually used. Further, the “half gain” in the present invention refers to a viewing angle width (degrees) when the reflection luminance in the reflection characteristic curve becomes 1/2 of the peak.

  If the peak gain is less than 0.28, the projected image is dark and inferior in image recognizability and cannot satisfy the requirements for a projection blackboard. Therefore, 0.28 is set as the lower limit of the peak gain. The peak gain is preferably 0.35 to 1.0, more preferably 0.35 to 0.60. In order to obtain a wide viewing angle, the half gain is preferably set to 13 or more. For this reason, in the present invention, the surface ridge layer has a reflection characteristic having a peak gain of 0.28 or more and preferably a half gain of 13 or more.

As described later, the reflection characteristics of the above-described surface wrinkle layer are added to the glaze applied to the metal substrate with an appropriate amount of titanium oxide-coated particles having an appropriate particle size distribution, preferably mica particles coated with titanium oxide, This can be achieved by adjusting the firing temperature to an appropriate range.
The surface wrinkle layer having the above-described characteristics preferably has a surface gloss of 1 to 30% as specified in JIS Z 8741-1997 with a 75 ° specular gloss Gs (75 °). If Gs (75 °) is less than 1%, the choke character erasability deteriorates, the reflection luminance decreases, and the image becomes unclear. On the other hand, if Gs (75 °) exceeds 30%, the writing performance of chalk characters deteriorates, and halation is likely to occur, resulting in a narrow viewing angle. More preferably, Gs (75 °) is 15 to 25%, more preferably more than 20% and 25% or less.

  The surface soot layer contains titanium oxide-coated particles. By including titanium oxide-coated particles in the surface glazing layer, sharpness is improved, irregularities are formed on the surface, diffuse reflectance is improved, halation is suppressed, and reflection characteristics are improved. In the present invention, the surface soot layer preferably contains 2 to 40%, more preferably 3 to 20%, of titanium oxide-coated particles in mass% based on the total amount of the surface soot layer. When the titanium oxide-coated particles are less than 2% by mass, the effect of improving reflection characteristics is small. If the titanium oxide-coated particles are contained in an amount exceeding 40% by mass, the surface roughness Rz becomes excessively large, the choke character erasability deteriorates, the lightness becomes excessive, and the choke character is recognized. Sex is reduced.

  The titanium oxide-coated particles preferably have an average particle size of 100 μm or less. More preferably, it is 5-80 micrometers. If the average particle size of the titanium oxide-coated particles is less than 5 μm, the diffuse reflectivity decreases. On the other hand, if the average particle size of the titanium oxide-coated particles exceeds 100 μm, the surface roughness of the surface wrinkle layer becomes excessively large, and the choke character Eraseability is reduced. In addition, the average particle diameter of a particle | grain here shall mean the 50% cumulative particle diameter measured using the laser diffraction type particle size distribution measuring apparatus. The titanium oxide-coated particles are preferably particles in which the surface of mica particles is coated with titanium oxide, and the mica particles are more preferably lamellar mica particles.

  The surface glaze layer having the above-mentioned characteristics is a glaze layer formed using a glaze glaze containing at least a titanium oxide coated particle, or further a titanium oxide glaze, or even a transparent gloss glaze, in a transparent mat glaze. It is preferable to do. Note that the thickness of the surface ridge layer is preferably 200 μm or less from the viewpoint of peelability. More preferably, it is 150 μm or less.

The surface glaze layer formed by using the above glaze glaze is in mass%, and the total amount of titanium oxide containing titanium oxide in the titanium oxide-coated particles is TiO ₂ , TiO ₂ : 0.5 to 15%, more preferably 0.5 to less than 10%, more preferably 2 to 5%, and further selected from SiO ₂ : 15 to 45%, Al ₂ O ₃ : 5 to 30%, Na ₂ O, K ₂ O, Li ₂ O In addition, it is preferable to form a soot layer containing one or two or more kinds in total: 2 to 20% and B ₂ O ₃ : 2 to 20%. In the present invention, a blackboard surface gray layer is selected from black pigments, gray pigments, green pigments, brown pigments, yellow pigments, and amber pigments in order to obtain a desired color. Needless to say, the total amount of pigments is 40% by mass or less.

Next, a preferred method for manufacturing the projection blackboard of the present invention will be described.
The projection blackboard of the present invention is obtained by applying a glaze glaze to the surface of a metal substrate and baking to form a base glaze layer, or without forming a ground glaze layer, and then coating the transparent mat glaze with at least titanium oxide It is preferable to manufacture the particles by using a manufacturing method in which a surface glaze layer is formed by applying particles, or further titanium oxide glaze, or further transparent glaze glaze, and baking at 400 to 850 ° C. The metal substrate is preferably a cold-rolled steel plate, an aluminum-plated steel plate, or a Zn-Al alloy-plated steel plate.

  When a cold-rolled steel sheet is used as the metal substrate, it is preferable to apply Ni plating to the surface of the cold-rolled steel sheet (metal substrate) after applying Ni plating to the cold-rolled steel sheet, and baked to form an undercoat layer . The agate glaze is not particularly limited, and any of the agate glazes used in conventional smoked blackboards is suitable. Any known coating method such as spray or roll coater can be applied to apply the laxative glaze.

As the laxative glaze, for example, it is contained by mass% with respect to the total solid content, SiO ₂ : 20 to 80%, and the balance is TiO ₂ : 0 to 15%, ZrO ₂ : 0 to 20%, B _{2 O 3: 0~25%, Al 2} O 3: 0~25%, Na 2 O: 0~20%, Li 2 O: 0~20%, K 2 O: 0~20%, PbO: 0~40 %, ZnO: 0~50%, BaO : 0~15%, CaO: 0~15%, CaF 2: 0~10%, CoO: 0~20%, NiO: 0~20%, MnO: 0~20 It is preferable to use a SiO ₂ -based glaze containing%.

A surface glaze is applied to the surface of the obtained base glaze layer, and then fired at 600 to 850 ° C. to form a surface glaze layer. For the application of the glaze glaze, any known application method such as spray or roll coater can be applied.
Glaze glaze is 100 to 20 parts by weight of titanium oxide glaze (frit), or 20 parts by weight of transparent gloss glaze (frit), or 100 parts by weight of transparent mat glaze (frit). It is preferable to use a glaze in which an appropriate amount of titanium oxide-coated particles is added to the glaze to which no more than a part is added. Moreover, it is preferable that the addition amount of a titanium oxide coating particle shall be 1-25 weight part with respect to transparent mat glaze or mixed glaze (slip): 100 weight part (weight conversion after baking).

  Glaze glaze is obtained by grinding a transparent mat glaze frit, or a transparent mat glaze, titanium oxide glaze, or even a transparent gloss glaze frit and, if necessary, a mixture of various additives and pigments and water. An appropriate amount of titanium oxide-coated particle powder is added to and mixed with the resulting mud (slip). As the pigment, it is necessary to add any one of black pigment, gray pigment, green pigment, brown pigment, yellow pigment, and amber pigment according to the desired color tone of the blackboard. . The added amount of the pigment is preferably 20 parts by weight or less in total with respect to 100 parts by weight of slip (in terms of weight after firing). If the amount added exceeds 20 parts by weight, the fluidity of the slip will decrease.

As the transparent mat glaze (frit), by mass% with respect to total _{solids, SiO 2: 30~45%, Al} 2 O 3: 20~35%, B 2 O 3: 5~15%, K 2 O _{: 5~15%, Na 2 O:} 10~25%, hints, the balance, BaO: 0~15%, CaO: 0~15%, F 2: 0~10%, TiO 2: 0~10% It is preferable to use a glaze containing the above.
As a titanium oxide glaze (frit), it contains 10 to 30% of TiO _{2 by} mass% with respect to the total solid content, and the balance is SiO ₂ : 0 to 80%, Al ₂ O ₃ : 0 to 20%, B ₂ O ₃ : 0 to 25%, Na ₂ O: 0 to 20%, K ₂ O: 0 to 20%, Li ₂ O: 0 to 20%, P ₂ O ₅ : 0 to 10%, ZrO ₂ : 0 20%, BaO: 0~15%, CaO: 0~15%, MgO: 0~5%, PbO: 0~40%, ZnO: 0~50%, CaF 2: the glaze, including 0 to 10% It is preferable to do. In addition, it may replace with the titanium oxide which is a pigment of a titanium oxide glaze, and it is good also as 1 type, or 2 or more types of pigments among a zirconium oxide, an antimony oxide, and a zinc oxide.

As the transparent gloss glaze (frit), by mass% with respect to total solids, SiO _2: comprises 40 to 65%, the _{balance, B 2 O 3: 5~20%} , Na 2 O, K 2 O, Li 2 5-40% in total of one or more one of _{O, F 2: 0~10%,} Al 2 O 3: 0~10%, CaO: 0~10%, TiO 2: 0~10%, ZnO: It is preferable to use a glaze containing 0 to 10%, MgO: 0 to 5%, and the like. In addition, it may replace with the titanium oxide which is a pigment of a titanium oxide glaze, and it is good also as 1 type, or 2 or more types of pigments among a zirconium oxide, an antimony oxide, and a zinc oxide.

When the firing temperature is less than 600 ° C., the surface roughness becomes too rough and the reflection characteristics deteriorate. On the other hand, when the temperature exceeds 850 ° C., the surface becomes too smooth, and the chalk character recognizability and the chalk character drawing / erasing property deteriorate.
Moreover, when using an aluminum plating steel plate or a Zn-Al alloy plating steel plate as a metal substrate, it is preferable to apply a glaze on the surface of the metal substrate and to fire at 400 to 600 ° C. to form a surface glaze layer.

  In this case, it is necessary to use a low melting point glaze from the viewpoint of preventing melting of the plating layer. For this reason, it is preferable to use a glaze obtained by blending a glaze in which phosphoric acid is blended in place of the above-described transparent matte glaze with titanium oxide-coated particles or further with a titanium oxide glaze. The content of phosphoric acid in the glaze containing phosphoric acid is 40% by mass or more, preferably 80% by mass or less, and more preferably 70% by mass or less.

As the glaze (frit) containing phosphoric acid, it contains P ₂ O ₅ : 40 to 80% by mass% with respect to the total solid content, and the balance is SiO ₂ : 0 to 40%, Al ₂ O ₃ : 0 _{~50%, B 2 O 3:} 0~25%, Na 2 O: 0~20%, K 2 O: 0~20%, Li 2 O: 0~20%, TiO 2: 0~30%, Sb _{2 O 3: 0~25%, ZnO} : 0~20%, BaO: 0~15%, CaO: 0~15%, MgO: 0~5%, PbO: 0~10%, SrO: 0~20% It is preferable to use a glaze containing the above.

In addition, when using an aluminum-plated steel sheet or a Zn-Al alloy-plated steel sheet as a metal substrate, from the viewpoint of preventing melting of the plating layer, a low melting point glaze is used, so that adhesion is improved, and Application is not always necessary.
Moreover, when using an aluminum plating steel plate or a Zn-Al alloy plating steel plate as a metal substrate, if the firing temperature is less than 400 ° C., the adhesion of the soot layer decreases. On the other hand, when it exceeds 600 degreeC, the problem that a plating layer will fuse | melt will arise.

Example 1
A cold-rolled steel plate (C: 0.0050 mass% ultra-low carbon steel plate) was used as the metal substrate. A nickel plating layer was formed on the surface of the cold rolled steel sheet in a nickel sulfate bath. Next, a glaze glaze was applied to both surfaces of the nickel-plated cold-rolled steel sheet by a roll coater method, and then fired at 800 ° C. to form a 30 μm-thick undercoat layer. The glaze is composed of SiO ₂ glaze (frit): 100 parts by weight, clay: 6 parts by weight, magnesium carbonate: 0.15 parts by weight, borax: 0.4 parts by weight, silica: 1 part by weight, water: 70 parts by weight The blended raw material to which was added was put into a ball mill, mixed and pulverized to form a slip.

Next, a glaze was applied to one surface of the obtained base soot layer by a spray method, and then fired at 750 ° C. to form a 70 μm surface soot layer as a sample blackboard. In some blackboards, the firing temperature was varied in the range of 700-780 ° C.
In addition, transparent mat glaze (frit) having the composition shown in Table 1 was added to 100 parts by weight of clay: 5.5 parts by weight, sodium nitrite: 0.15 parts by weight, silica: 0.5 parts by weight, water: 70 parts by weight, As pigments, TiO ₂ , Sb ₂ O ₅ , NiO total: 1 part by weight, Cr ₂ O ₃ : 8.2 parts by weight, Co, Cr total: 10.0 parts by weight, Fe ₂ O ₃ , CuO, CoO, MnO, etc. Total: 0.1 part by weight was added, and a slip A obtained by mixing and pulverizing with a ball mill was prepared. Titanium oxide glaze shown in Table 2: 100 parts by weight, clay: 5.5 parts by weight, chloride Potassium: 0.2 parts by weight, sodium aluminate: 0.3 parts by weight, water: 54 parts by weight were added, mixed and pulverized by a ball mill to obtain slip B, and then slip B: 100 parts by weight (weight after firing) Conversion), 20 parts by weight of titanium oxide-coated particle powder is added together with 45 parts by weight of water, and mixed to prepare slip C. And-up A and slip C, 3: blended 1 ratio, was enamel on glaze used in admixture invention. In some cases, the mixing ratio of slip A and slip C was changed. The titanium oxide-coated particle powder used was a particle obtained by coating the surface of a thin plate-like mica particle with titanium oxide. The average particle size was 20 μm and the titanium oxide coating rate was 30%. The average particle size is indicated by a 50% cumulative particle size measured using a laser diffraction particle size distribution measuring device.

As a conventional example, transparent mat glaze (frit) having the composition shown in Table 1 is added to 100 parts by weight of clay: 5.5 parts by weight, sodium nitrite: 0.15 parts by weight, silica: 0.5 parts by weight, and water: 70 parts by weight. Furthermore, as a pigment, TiO ₂ , Sb ₂ O ₅ and NiO are combined: 0.5 parts by weight, Cr ₂ O ₃ : 4.1 parts by weight, Co and Cr are combined: 5.0 parts by weight, Fe ₂ O ₃ , CuO, CoO, MnO A total of 0.05 parts by weight, etc. were added, and the slip D obtained by mixing and pulverizing with a ball mill was used as a glaze for glaze, and calcined at a firing temperature of 700 ° C.

About the surface glazing layer of the obtained sample blackboard, the composition, surface roughness, color tone, glossiness, and reflection characteristics were investigated.
(1) Surface roughness The surface roughness was measured using a contact-type surface roughness meter, and the arithmetic average roughness Ra and the maximum height Rz were determined in accordance with the provisions of JIS B 0601-2001.

(2) Color tone The color tone was measured in accordance with the provisions of JIS Z 8722-2000, and the color tone of each sample blackboard was displayed in accordance with the provisions of JIS Z 8721-1993.
(3) Glossiness As for the glossiness, 75 ° specular glossiness Gs (75 °) was determined in accordance with JIS Z 8741-1997.

(4) Reflection characteristics As shown in FIG. 2, the reflection characteristics are as follows. The incident light 1 is irradiated from the light source 10 in the direction perpendicular to the center of the plate S to be measured, and the same arc from the center point is in the range of 75 ° left and right. The magnitude of the reflected light 2 (reflected luminance) at a point shifted by 5 ° was measured with a luminance meter 11, and peak gain and half gain were obtained. The peak gain is defined as the ratio of the reflection luminance of the sample blackboard measured under the same conditions to the reflection luminance when light is applied to a standard white plate (complete diffusion plate: pure white plate baked with magnesium sulfate). The reflection luminance was the reflection luminance at a viewing angle of 5 °.

An example of the reflection characteristics of the blackboard of the present invention (the product of the present invention) and the conventional blackboard (conventional product) is shown in FIG. The vertical axis represents the ratio of the reflection luminance of the blackboard to be measured when the reflection luminance (peak) of the standard white board is 100%.
(5) Blackboard function Furthermore, in accordance with the provisions of JIS B 6007, letters were drawn on the obtained sample blackboard with chalk (white ink), and the ease of wearing of white ink and the ease of dropping were determined. The ease of wearing the black ink was determined by checking whether the line was uneven when viewed from a position 1 m away from the blackboard surface and whether the line was clear when viewed at a position 8 m away. Choke character recognizability was evaluated with ◎ when there was no line unevenness and clearness, ◯ when the sharpness slightly decreased, and x when there was line unevenness or not clear. Also, the ease of white ink removal is when the characters drawn on the blackboard are rubbed with an eraser (made of felt) and then viewed at a distance of 1 m from the blackboard, and there are no handwriting marks or erase irregularities on the blackboard surface. The erasability of chalk characters was evaluated with ◯ when the handwriting was left slightly and x when it was not.

  The obtained results are shown in Tables 3 and 4.

  All of the examples of the present invention maintain chalk character recognition and chalk character erasability equivalent to those of conventional blackboards, maintain an excellent blackboard function, obtain a peak gain of 0.28 or more, and have excellent reflection characteristics. When a video is projected, the blackboard is excellent in video recognition and suitable for projection. In the comparative example that is out of the scope of the present invention, the blackboard function of chalk character recognition and chalk character erasability is degraded, or the reflection characteristics are inferior, and the image recognition is degraded.

(Example 2)
A cold-rolled steel sheet (C: 0.0050 mass% ultra-low carbon steel sheet) was used as the metal substrate. A nickel plating layer was formed on the surface of the cold rolled steel sheet in a nickel sulfate bath. Next, a glaze glaze was applied to both surfaces of the nickel-plated cold-rolled steel sheet by a roll coater method, and then fired at 750 ° C. to form an undercoat layer of 30 μm. The same armpit glaze used was the same as in Example 1.

Next, a glaze was applied to one surface of the obtained base soot layer by a spray method, followed by baking at 765 to 785 ° C. to form a 70 μm surface soot layer as a sample blackboard.
In addition, transparent matte glaze (frit) having the composition shown in Table 1: 90 parts by weight, transparent gloss glaze (frit) shown in Table 5: 10 parts by weight, clay: 5.5 parts by weight, sodium nitrite: 0.15 parts by weight, silica : 0.5 parts by weight, water: 70 parts by weight, and as a pigment, TiO ₂ , Sb ₂ O ₅ and NiO are added in total: 1.0 part by weight, Cr ₂ O ₃ : 8.2 parts by weight, Co and Cr are added in total: 7.5 A total of 0.1 parts by weight of Fe ₂ O ₃ , CuO, CoO, MnO, etc. is added, and a slip D obtained by mixing and pulverizing with a ball mill is prepared, and the titanium oxide glazes shown in Table 2 ( Frit): 100 parts by weight, clay: 7.5 parts by weight, potassium chloride: 0.2 parts by weight, sodium aluminate: 0.3 parts by weight, water: 54 parts by weight, and as a pigment, Co and Cr total: 1.2 parts by weight Parts were added and mixed and pulverized with a ball mill to obtain slip E, and then the slip E was added to 100 parts by weight (in terms of weight after firing). Titanium-coated particle powder: 20 parts by weight and water: 45 parts by weight are added and mixed to produce slip F. These slip D and slip F are blended at a ratio of 3: 1 and mixed to produce the present invention. The glaze used in the examples was used. The titanium oxide-coated particle powder used was a particle obtained by coating the surface of a thin plate-like mica particle with titanium oxide, the average particle size was 20 μm, and the titanium oxide coating rate was 30%. The average particle size is indicated by a 50% cumulative particle size measured using a laser diffraction particle size distribution measuring device.

About the surface glazing layer of the obtained sample blackboard, the composition, surface roughness, color tone, glossiness, and reflection characteristics were investigated. The investigation method was the same as in Example 1. The color tone was also measured using the Hunter Lab color system.
Table 7 shows the obtained results.

  All of the examples of the present invention maintain chalk character recognition and chalk character erasability equivalent to those of a conventional blackboard, maintain an excellent blackboard function, and have a glossiness Gs (75 °) of 21% or more and 0.40 or more. The blackboard has a peak gain and has excellent reflection characteristics. When a video is projected, the blackboard has excellent video recognition and is suitable for projection.

It is a graph which shows an example of a reflection characteristic curve. It is a schematic explanatory drawing which shows the measuring method of reflected luminance.

Explanation of symbols

1 Incident light 2 Reflected light 3s Blackboard to be measured (sample)
10 Light source
11 Luminance meter

Claims (7)

  A blackboard having at least one glazing layer on a metal substrate, wherein the outermost surface glazing layer among the glazing layers has a color tone having a lightness V of 3.0 to 7.0 as defined in JIS Z 8721-1993; A projection blackboard characterized by having surface characteristics with a surface roughness Rz of 5 to 25 μm as defined in JIS B 0601-2001 and reflection characteristics with a peak gain of 0.28 or more.   The projection blackboard according to claim 1, wherein the surface glaze layer is a glaze layer formed by using glaze with at least titanium oxide-coated particles blended with a transparent mat glaze.   The projection blackboard according to claim 1 or 2, wherein the surface glazing layer has any one of black, gray, green, brown, and amber.   The projection blackboard according to any one of claims 1 to 3, wherein the surface glazing layer has a 75-degree specular gloss Gs (75 °) defined by JIS Z 8741-1997 of 1 to 30%. . The projection blackboard according to claim 2, wherein the titanium oxide-coated particles are particles formed by coating titanium oxide on the surfaces of mica particles. After applying the laxative glaze to the surface of the metal substrate and baking to form a base glaze layer, or without forming the base glaze layer, then blend at least titanium oxide coated particles into the transparent mat glaze, and further add pigment Apply black glaze , gray pigment, green pigment, brown pigment, yellow pigment, amber pigment, or a mixture of glazes added alone or in combination according to the color tone of the blackboard. , Baked at 400-850 ° C, surface chalk that has excellent blackboard function with excellent chalk character recognition and chalk character erasability by chalk and excellent screen function with excellent image recognition A method for producing a projection blackboard, comprising forming a layer.   The method for producing a projection blackboard according to claim 6, wherein the titanium oxide-coated particles are particles formed by coating titanium oxide on the surfaces of mica particles.

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