JP6738784B2 - Coated white board for laser marking and method for producing the same - Google Patents

Description

The present invention relates to a coated white paperboard for laser marking and a method for manufacturing the same.

The coated white paperboard has a basis weight of 150 g/m ² or more, and the base paper generally has a multilayer structure of 3 to 9 layers. For example, it is manufactured by combining multiple layers called a white layer, a white lower layer, and a middle layer. Specifically, the outermost layer is a layer using bleached pulp with high whiteness called white layer, then a layer using waste paper with relatively high whiteness called white bottom layer inside the white layer, and further inside It is composed of layers of recycled paper called middle layer. On the white layer, a coating layer is provided for the purpose of improving the whiteness of the white paper surface, the appearance of white unevenness, and imparting printability.

As such a coated white paperboard, for example, Patent Document 1 discloses a coated white paperboard in which two or more coating layers containing heavy calcium carbonate as a pigment in an amount of 45 mass% or more of all pigments are provided. There is. Further, in Patent Document 2, the white layer of a white paperboard having a multi-layer papermaking structure having at least a white layer, a white lower layer, a middle layer and a back layer, contains 3% by mass or more of heavy calcium carbonate based on the amount of pulp of the white layer, Disclosed is a coated white paperboard in which a pigment coating layer containing wet heavy calcium carbonate as a main raw material is provided on at least one surface of a white paperboard configured by internally adding less than 10% by mass.

By the way, although such a coated white paperboard is printed and used for packaging, it may be laser-marked when it is used for packaging of medicines and the like. The laser marking mentioned here is to provide a black solid printing portion by offset printing or the like on the pigment coating layer of coated white paperboard, irradiate the solid printing portion with laser light, and remove the ink of the solid printing portion. The marking is performed by partially removing it. Variable information such as expiration date and lot number is recorded by laser marking. As such laser marking, in addition to using a CO ₂ laser, there is a method using a YVO ₄ laser or a YAG laser.

However, when the coated white paperboard disclosed in Patent Documents 1 and 2 is subjected to laser marking, the printed portion is discolored as if it is scorched, and the contrast between the printed portion and the black ink layer is lowered, and the printed portion becomes unclear. There was a problem. This becomes remarkable especially when a carbon dioxide laser is used. Carbon dioxide laser has a longer wavelength than YVO ₄ laser and YAG laser, and due to its properties, it not only scrapes the black ink layer but also the pigment coating layer of coated white paperboard, and even up to the paper layer. It is assumed that the cause is that the paper layer is burnt.

JP, 2008-231586, A JP, 2014-19975, A

An object of the present invention has been made in view of such a problem, and an object of the present invention is to provide a coated white paperboard for laser marking in which the discoloration of a printed portion due to laser marking is small.

The coated white paperboard for laser marking of the present invention comprises an undercoating coating layer containing a pigment and a binder and a topcoating coating on the surface of the white layer of the base paper having at least three layers in the order of white layer, white lower layer and middle layer. A coated white paperboard in which layers are sequentially provided, and the content of calcium carbonate contained as a filler in the white layer is 1 part by mass or less based on 100 parts by mass of pulp in the white layer, The working layer is characterized by containing 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment contained in the undercoating layer. With such a configuration, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, in the coated white paperboard for laser marking of the present invention, it is preferable that the topcoat coating layer contains 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment contained in the topcoat coating layer. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, in the coated white paperboard for laser marking of the present invention, it is preferable that the white layer does not contain calcium carbonate as a filler. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, in the coated white paperboard for laser marking of the present invention, it is preferable that 50% by mass or more of the pulp contained in the white layer is fresh pulp. Discoloration of the printed portion due to laser marking can be easily reduced as compared with the case where a large amount of waste paper is contained in the white layer.

Further, in the coated white paperboard for laser marking of the present invention, it is preferable that the white layer contains aluminum sulfate. It is possible to easily reduce discoloration of the printed portion due to laser marking.

Further, in the coated white paperboard for laser marking of the present invention, it is preferable that the undercoating layer and/or the overcoating layer contains kaolin as a pigment. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, the method for producing a coated white paperboard for laser marking of the present invention comprises a step of making a base paper having at least three layers in the order of a white layer, a white lower layer and a middle layer by a paper machine using raw materials adjusted for each layer. And, the undercoat coating layer coating material containing a pigment and a binder is applied to the surface of the white layer to form an undercoat coating layer, and then an overcoat containing a pigment and a binder on the undercoat coating layer. A method for producing a coated white paperboard comprising a step of forming a topcoat coating layer by applying a coating layer coating material, the addition amount of calcium carbonate to be added as a filler in the raw material of the white layer, 1 part by mass or less with respect to 100 parts by mass of pulp contained in the raw material of the white layer, and 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment is contained in the undercoat coating layer coating material. And

Further, in the method for producing a coated white paperboard for laser marking of the present invention, it is preferable that the coating material for the overcoat coating layer contains 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, in the method for producing a coated white paperboard for laser marking of the present invention, it is preferable not to add calcium carbonate as a filler in the raw material of the white layer. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, in the method for producing a coated white paperboard for laser marking of the present invention, it is preferable to add aluminum sulfate to the raw material of the white layer. It is relatively easy to reduce discoloration of the printed portion due to laser marking.

In addition, in the method for producing a coated white paperboard for laser marking of the present invention, it is preferable to add aluminum sulfate to the raw material of the white lower layer. It is relatively easy to reduce discoloration of the printed portion due to laser marking.

In addition, in the method for producing a coated white paperboard for laser marking of the present invention, it is preferable that the undercoating layer coating material and/or the overcoating layer coating material contain kaolin as a pigment. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

Further, in the method for producing a coated white paperboard for laser marking of the present invention, it is preferable that the Canadian standard freeness (CSF) of the pulp contained in the raw material for the white layer is 300 ml or less. Further, it is possible to reduce discoloration of the printed portion due to laser marking.

According to the present invention, it is possible to provide a coated white paperboard for laser marking in which the discoloration of the printed portion due to laser marking is small.

Hereinafter, embodiments of the present invention will be described in detail.

(1) Base Paper The base paper of the coated white paperboard for laser marking of the present invention has at least three layers: a white layer, a white lower layer and a middle layer. The outermost layer is a white layer, and then a white lower layer and an intermediate layer are laminated. The middle layer may be a multilayer having two or more layers. Further, it may be composed of a multi-layered composite in which one or more back layers are laminated next to the middle layer. The basis weight of each layer, for example, white layer is composed of ^{20g / m 2 ~60g / m 2} , white lower layer ^{50g / m 2 ~80g / m 2} , middle layer ^{50g / m 2 ~110g / m 2} . The constitution of the back layer may be changed depending on the use of the coated white paperboard, and may be the same as that of the lower white layer or the white layer, for example. For coated white board paper for laser marking which are mainly used in packaging applications, the basis weight extensive and ^{150g / m 2 ~600g / m 2} . To change the basis weight of coated white paperboard, the number of middle layers and the basis weight of the rice may be varied. Depending on the application, there is a demand for coated white paper for laser marking that has no difference in whiteness between the front and back, coated white paper for laser marking that has high whiteness on the front side but low whiteness on the back side, etc. It is adjusted by making a difference in the basis weight of the layer and the basis weight of the back layer, or by changing the coating amount of the pigment coating layer on the surface of the front layer and the surface of the back layer. For example, the basis weight of the white layer can be 25 to 45 g/m ² , and the basis weight of the back layer having the same structure as the white layer can be ²⁰ to 30 g/m ² . Further, the back layer has a whiteness of the same level as or lower than the whiteness of the middle layer, and there are cases where coating is performed and cases where coating is not performed.

In the present invention, the base paper is mainly composed of pulp, but the type of pulp used for each layer is not particularly limited. For example, a hardwood bleached chemical pulp (L-BKP) mainly composed of natural pulp composed of wood fiber, bast fiber, bast fiber and the like may be used as a main component. Specific examples of other wood pulps include bleached softwood pulp (N-BKP), bleached softwood pulp (N-BSP) and bleached hardwood pulp (L-BSP). In addition, waste paper pulp such as mechanical pulp (GP), chemithermo-mechanical pulp (CTMP), and deinking pulp (DIP) can be blended in any proportion depending on the application. Among these, it is preferable to use a pulp having a relatively high whiteness for the white layer, it is preferable to use a fresh pulp such as L-BKP, N-BKP, and a high-quality pulp is used when a waste paper pulp is used to reduce the environmental load. It is preferable to use waste paper pulp. In the present invention, the used paper pulp used in the white layer is preferably less than 50% by mass, and more preferably less than 30% by mass, because it is necessary to suppress discoloration of the printed portion due to laser marking. Further, waste paper pulp (for example, DIP) having a lower whiteness than the pulp of the white layer can be used for the lower white layer. It is possible to use waste paper pulp having a lower whiteness (for example, DIP or undeinked waste paper pulp) in the middle layer.

Further, a filler can be added to the pulp slurry. As the filler, it is possible to use a conventionally known filler, for example, calcium carbonate, talc, kaolin, calcined kaolin, titanium dioxide, aluminum hydroxide, white carbon and the like, these may be used alone or in combination. Can be used. Among these, kaolin, calcined kaolin, titanium dioxide, aluminum hydroxide and talc are preferable. Moreover, since calcium carbonate as a filler is highly effective in improving the whiteness of the base paper and suppressing the black ground feeling, it is generally widely used as a filler and is highly mixed. However, the coated white paperboard for laser marking of the present invention is solid-printed with black ink or the like on the surface of the coating layer containing a pigment and a binder, and laser marking is applied to the solid-printed portion by irradiating a laser beam. As described above, the irradiated laser light (especially carbon dioxide laser light) scrapes not only the black ink layer but also the pigment coating layer of coated white paperboard, and even reaches the paper layer. Therefore, the paper layer may be burnt. That is, in order to reduce the discoloration of the printed portion due to the laser marking which is the object of the present invention, it is necessary that the paper layer is not easily scorched (hard to discolor), but in the conventional white paperboard containing a certain amount of calcium carbonate, It was found that the more calcium carbonate contained in the paper layer, the more easily the paper layer burned. Therefore, in the present invention, the content of calcium carbonate contained as a filler in the white layer is set to 1 part by mass or less based on 100 parts of pulp in the white layer. Furthermore, it is preferable not to add calcium carbonate as a filler to the white layer. When the content of calcium carbonate contained as a filler in the white layer exceeds 1 part by mass, the paper layer is burnt and discolored during laser marking, and the contrast between the printed part with laser marking and the solid printed part with black ink etc. Becomes low and the print becomes unclear.

Further, in the present invention, the filler may or may not be added to the white layer. The filler other than calcium carbonate that can be used in the white layer is not particularly limited as long as it does not easily tarnish the paper layer during laser marking, and examples thereof include talc, kaolin, calcined kaolin, and dioxide. There are titanium, aluminum hydroxide and the like, and they can be blended in any proportion depending on the application. The filler content in the base paper is preferably 20 parts by mass or less based on 100 parts by mass of the dry mass of pulp. It is more preferably 15 parts by mass or less. More preferably, it is 10 parts by mass or less. If it exceeds 20 parts by mass, the strength of the base paper itself is insufficient and it cannot withstand printing and processing, and it is difficult to practically use it. Further, among these fillers, it is preferable to use kaolin or talc because the discoloration of the printed portion due to laser marking can be further suppressed.

In the present invention, as described above, it is important not to include a certain amount or more of calcium carbonate in the white layer, but when used paper pulp is used as the pulp for the white layer, calcium carbonate is not used as a filler. However, calcium carbonate contained in waste paper pulp may be brought into the white layer, and the effect of suppressing discoloration of the printed portion due to laser marking may be diminished. Therefore, in the present invention, 50% by mass or more of the pulp used for the white layer is preferably fresh pulp. It is more preferably 70% by mass or more, further preferably 80% by mass or more, and most preferably 100% by mass (that is, all pulp is fresh pulp). Here, the fresh pulp is also called virgin pulp, and is a pulp produced directly from wood or non-wood rather than recycled paper. Since the fresh pulp basically contains no inorganic filler, it is possible to prevent calcium carbonate from being brought into the white layer.

Further, in the present invention, it is preferable that the white layer contains aluminum sulfate. As mentioned above, when used paper pulp is used in the white layer, calcium carbonate contained in the used paper pulp may be brought into the white layer. In addition, industrial water added to the raw material of the white layer and papermaking. Calcium carbonate contained in the white water circulated in the process may be brought into the white layer. Therefore, in the present invention, mixing of calcium carbonate in the white layer may be suppressed in some cases by adding aluminum sulfate to the raw material of the white layer to make it acidic and facilitate the dissolution of calcium carbonate. Here, for the purpose of only dissolving calcium carbonate, other acids such as dilute hydrochloric acid and dilute sulfuric acid may be used. However, when aluminum sulfate is used, the printing portion by laser marking is more effective than when other acids are used. It was found that the effect of suppressing the discoloration of was high. The reason for this is not clear, but it is believed that the addition of calcium carbonate to a raw material containing no calcium carbonate will have an effect, and therefore aluminum sulfate itself will be effective in suppressing discoloration of the printed portion due to laser marking. The amount of aluminum sulfate added is preferably 0.5 to 3.5 parts by mass, more preferably 1 to 3 parts by mass, and still more preferably 1.5 to 100 parts by mass with respect to 100 parts by mass of pulp in the raw material for the white layer. 2.5 parts by mass. When the amount of aluminum sulfate added is less than 0.5 parts by mass, the effect of suppressing discoloration of the printed portion due to laser marking is poor, and when it exceeds 3.5 parts by mass, the effect is not reached and the pH of the raw material becomes low. If it is too much, the balance of the papermaking system may be lost, and stains may be generated in the papermaking process.

Further, like the white layer, the lower white layer preferably contains aluminum sulfate. By including aluminum sulfate in the lower white layer, it is possible to further suppress discoloration of the printed portion due to laser marking. The amount of aluminum sulfate added is preferably 0.1 to 3.5 parts by mass, more preferably 0.3 to 2.0 parts by mass, and still more preferably 100 parts by mass of pulp in the raw material of the lower white layer. It is 0.5 to 1.5 parts by mass. Although the addition of aluminum sulfate is effective even in a small amount, if it is less than 0.1 parts by mass, the effect is poor, and if it exceeds 3.5 parts by mass, the effect is not reached and the pH of the raw material is too low. There is a risk that the balance of the papermaking system may be lost and stains may be generated in the papermaking process.

In the present invention, the Canadian Standard Freeness (CSF) of the pulp in the raw material of each layer is not particularly limited, but the CSF of the pulp in the raw material of the white layer is preferably 400 ml or less. It is preferably 100 to 350 ml, more preferably 150 to 330 ml, for example 150 to 300 ml. Although the reason is not clear, discoloration of the printed portion due to laser marking can be further suppressed by setting the CSF of the pulp in the raw material of the white layer in such a range. For example, as the pulp in the raw material for the white layer, pulp adjusted to 200 to 280 ml of CSF consisting of 40 to 60% of high-quality waste paper pulp and 40 to 60% of hardwood pulp (L-BKP) can be used.

In the present invention, in the raw material of each layer, various known paper-making materials can be added within a range that does not impair the effects of the present invention. For example, a paper-strengthening agent, a coloring agent such as a dye or a pigment, and the like. , A sizing agent, a retention improving agent, a drainage improving agent, an antifoaming agent and the like can be appropriately used.

The white layer, the lower white layer, the middle layer and, if necessary, the back layer are paper-made using the raw materials adjusted for the respective layers, and then combined to produce a base paper for coated white paperboard. The papermaking method is not particularly limited, and a known papermaking method such as a Fourdrinier method or a round net method can be used.

(2) Coating layer In the present invention, an undercoating coating layer containing a pigment and a binder and an overcoating coating layer are sequentially provided on the surface of the white layer of the base paper. Pigments used for each coating layer include calcium carbonate, kaolin, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth. Inorganic pigments such as aluminum hydroxide and magnesium hydroxide and organic pigments such as acrylic, styrene, vinyl chloride and nylon are preferred, and calcium carbonate, kaolin and titanium dioxide are preferred.

Further, the binder used in each coating layer is not particularly limited, and a conjugated diene polymer resin such as styrene/butadiene copolymer resin (SBR) or methyl methacrylate/butadiene copolymer, oxidized starch , Starches such as enzyme-modified starch, esterified starch, etherified starch, cationic starch, amphoteric starch, water-soluble polymers such as gelatin, casein, soybean protein, polyvinyl alcohol, vinyl acetate, ethylene vinyl acetate, polyurethane resin Examples thereof include synthetic resins such as acrylic resin, polyester resin, and polyamide resin. From these, one kind or two or more kinds are appropriately selected and used according to the purpose. In particular, starch generally used in coated paper for printing is preferable from the viewpoint of strength of the coating layer and cost reduction.

The content ratio of the pigment and the binder in each coating layer is not particularly limited, but in each layer, the binder is preferably 3 to 50 parts by mass per 100 parts by mass of the pigment, and 5 to 40 parts by mass, For example, it is more preferably 8 to 20 parts by mass. If the compounding amount of the binder is less than 3 parts by mass, the coating layer may fall off, and if it exceeds 50 parts by mass, it is not preferable from the viewpoint of cost reduction. The proportion of the butadiene copolymer resin in the binder is preferably 3 to 30 parts by mass with respect to 100 parts by mass of the pigment. If it is less than 3 parts by mass, the coating layer may fall off, and if it exceeds 30 parts by mass, it is not preferable from the viewpoint of cost reduction.

As described above, it is preferable that the white layer of the base paper does not contain calcium carbonate, but considering only suppression of discoloration of the printed portion due to laser marking, calcium carbonate is further contained in the undercoat coating layer in contact with the white layer. It is also considered preferable that it is not included. However, if the undercoating layer does not contain calcium carbonate at all, the ink absorbency of the coating layer cannot be satisfied, and it becomes difficult to increase the whiteness. Further, as a result, the contrast of the printed portion due to the laser marking may be impaired. Therefore, in the present invention, 1 to 40 parts by mass of calcium carbonate is contained per 100 parts by mass of the pigment contained in the undercoat layer. It is preferably 5 to 35 parts by mass, and more preferably 10 to 30 parts by mass. If the content of calcium carbonate exceeds 40 parts by mass, the printed part by laser marking is discolored, and if it is less than 1 part by mass, the contrast of the printed part by laser marking is impaired.

Further, in the present invention, it is preferable to contain 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment contained in the overcoat layer. The amount is more preferably 5 to 35 parts by mass, further preferably 10 to 30 parts by mass. With such a configuration, it is possible to further suppress the discoloration of the printed portion due to laser marking, and since it is easy to satisfy the ink absorbency and the whiteness, it is possible to increase the contrast of the printed portion. .. When the content of calcium carbonate exceeds 40 parts by mass, discoloration of the printed part due to laser marking may not be suppressed, and when it is less than 1 part by mass, the effect of improving the contrast of the printed part by laser marking is poor.

Further, in the present invention, it is preferable to add kaolin as a pigment to either or both of the top coating layer and the under coating layer. The reason is not clear, but when kaolin is contained as a pigment in the coating layer, it is possible to further suppress discoloration of the printed portion due to laser marking. The content of kaolin is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and further preferably 100 parts by mass of the pigment in the coating layer in both the overcoating layer and the undercoating layer. Is 60 parts by mass or more. However, if kaolin is excessively blended in the coating layer, the whiteness is likely to decrease and the absorbability of the ink may be impaired. Therefore, the upper limit is 100 parts by weight of the pigment in the coating layer. It is preferable to use 75 parts by mass or less in the coating layer and 90 parts by mass or less in the undercoating layer.

As an example of the content ratio of the pigment in each coating layer in the present invention, in the top coating layer, 50-80 parts by mass of kaolin, 10-20 parts by mass of calcium carbonate in 100 parts by mass of the pigment in the coating layer. , Titanium dioxide 10 to 20 parts by mass, and in another embodiment, kaolin 45 to 65 parts by mass, calcium carbonate 35 to 50 parts by mass, and titanium dioxide 15 to 25 parts by mass. .. .. Further, in the undercoat coating layer, it is possible to use 60 to 90 parts by mass of kaolin and 10 to 40 parts by mass of calcium carbonate in 100 parts by mass of the pigment in the coating layer.

Further, each coating layer, as long as the effect of the present invention is not impaired, various auxiliaries as necessary, for example, a viscosity modifier, a softening agent, a gloss imparting agent, a water resistance agent, a dispersant, a flow modifier, An ultraviolet absorber, a stabilizer, an antistatic agent, a cross-linking agent, a sizing agent, an optical brightening agent, a coloring agent, a pH adjusting agent, a defoaming agent, a plasticizer, and a preservative can be appropriately added.

(3) Coating method In the present invention, first, the undercoat coating layer coating material is applied to the surface of the white layer of the base paper to form an undercoat coating layer, and then the topcoat coating layer is overcoated. A coating material for a working layer is applied to form a top coating layer. The method of applying the coating layer is not particularly limited, and a commonly used coating device can be used. For example, air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, sprayer Various known coating devices such as a coater, a gate roll coater and a lip coater can be used.

The coating amount of each coating layer is not particularly limited as long as it does not impair the effects of the present invention, the undercoat layer may be in the range of 5g / m ² ~15g / m ² in both the top coat layer. In the present invention, it is possible to provide a coating layer on the surface of the back layer of the base paper, that is, to provide a coating layer on both sides of the base paper. In this case, the coating layer provided on the surface of the back layer is not particularly limited and can be appropriately configured according to the purpose.

(4) Calender treatment In the present invention, a calender treatment can be performed after the base paper is provided with a coating layer. As the calender processing device, a normal super calender, a gross calender, a shoe nip calender, a soft calender, or the like can be used. At this time, the processing conditions such as the pressurizing device form, the number of pressing nips, and the temperature conditions can be appropriately adjusted for processing.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the following examples and comparative examples, parts and% mean solid content parts by mass and solid content mass%, respectively.

(Example 1)
As the raw material for the white layer, pulp adjusted to 250 ml of CSF consisting of 50% high-quality waste paper pulp and 50% hardwood pulp (L-BKP) is used, and as the raw material for the lower white layer, deinked bleached pulp from newspaper waste paper is not beaten. Use the recycled magazine pulp as the raw material for the middle layer, and use the newspaper waste paper pulp as the raw material for the back layer to make a white layer/lower white layer/middle layer/back layer. (Manufactured by Seiki Seisakusho Co., Ltd.) was used to make a base paper of 290 g/m ² in tsubo. The white layer had a weight of 35 g/m ² , the white lower layer had a weight of 50 g/m ² , the middle layer had a weight of 170 g/m ² , and the back side had a weight of 35 g/m ² . No filler was added to the raw material for the white layer. On the surface of the white layer of this base paper, as a paint for the undercoat layer, 60 parts of kaolin (Hydrasperth manufactured by Keimin Co.), 40 parts of calcium carbonate (Carbital 90 manufactured by Imeryth Mineramez Japan), styrene-butadiene copolymer latex 15 Part and 4 parts of phosphoric acid esterified starch are dispersed in water to adjust the solid content concentration to 60% by mass, and the resulting coating composition is coated with a bar coater to a solid content of 10 g/m ² and dried to form an undercoat layer. Formed. Then, 50 parts of kaolin (Amazon SB manufactured by Kadam Co., Ltd.), 50 parts of calcium carbonate (Carbital 90 manufactured by Imeryth Mineramez Japan Co., Ltd.), and 15 parts of styrene/butadiene copolymer latex were dispersed in water as a coating material for the top coating layer. A coating material adjusted to a solid content concentration of 60% is applied to the surface of the undercoating layer with a bar coater so that the solid content is 10 g/m ^2, and dried to form an overcoating layer, which is used for laser marking. A white paperboard was obtained.

(Example 2)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that calcium carbonate as a filler was added to the raw material for the white layer in an amount of 1 part by mass per 100 parts by mass of the pulp.

(Example 3)
Example except that the addition amount of kaolin (hydra sparse manufactured by Keimin Co., Ltd.) and the addition amount of calcium carbonate (Carbital 90 manufactured by Imeryth Mineramez Japan Co., Ltd.) were 20 parts, which were added to the coating material for the undercoat layer. A coated white board for laser marking was obtained in the same manner as in 1.

(Example 4)
To the raw material for the white layer, 1 part by mass of calcium carbonate was added as a filler per 100 parts by mass of pulp, and the addition amount of kaolin (hydrapersperm manufactured by Caymin Co., Ltd.) was added to the coating material for the undercoat layer to be 80 parts by weight. A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that the addition amount of calcium (Carbital 90 manufactured by Imeryth Mineramez Japan KK) was changed to 20 parts.

(Example 5)
Example except that the amount of kaolin (Amazon Kabama Co., Ltd. SB) added to the coating material for the overcoat layer was 60 parts and the amount of calcium carbonate (Imeris Mineramez Japan Carbital 90) was 40 parts. A coated white board for laser marking was obtained in the same manner as in 1.

(Example 6)
The amount of kaolin (hydra sparse manufactured by Keimin Co., Ltd.) added to the coating material for the undercoat layer was 80 parts, and the amount of calcium carbonate (Carbital 90 manufactured by Imeryth Mineramez Japan Co., Ltd.) was 20 parts, and the top coating layer The amount of kaolin (Kamadam's Amazon SB) added to the paint is 60 parts, the amount of calcium carbonate (Imeris Mineramez Japan Carbital 90) is 20 parts, and titanium dioxide (Ishihara Sangyo Co., Ltd.) is added. A coated white board for laser marking was obtained in the same manner as in Example 1 except that 20 parts of PFC-503) was added.

(Example 7)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that the pulp used as the raw material for the white layer was 100% high-quality waste paper pulp.

(Example 8)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that 2 parts by weight of aluminum sulfate was added to 100% by weight of pulp as the raw material for the white layer.

(Example 9)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that 3.5 parts by weight of aluminum sulfate was further added to the raw material for the white layer per 100 parts by weight of pulp.

(Example 10)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that 0.5 part by weight of aluminum sulfate was further added to the raw material for the white layer per 100 parts by weight of pulp.

(Example 11)
To the raw material for the white layer, 2 parts by weight of aluminum sulfate was added per 100 parts by mass of the pulp, and to the raw material for the white lower layer, 1 part of aluminum sulfate was added per 100 parts by mass of the pulp, and added to the coating material for the undercoat layer The addition amount of kaolin (hydra sparse manufactured by Keimin Co., Ltd.) is 80 parts, and the addition amount of calcium carbonate (carbital 90 manufactured by Imeryth Mineramez Japan Co., Ltd.) is 20 parts, which is added to the coating material for the top coating layer. The addition amount of Kadam Amazon SB) was 60 parts, the addition amount of calcium carbonate (Imeris Mineramez Japan Carbital 90) was 20 parts, and titanium dioxide (Ishihara Sangyo PFC-503) was added 20 parts. A coated white board for laser marking was obtained in the same manner as in Example 1 except for the above.

(Example 12)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that 5 parts by mass of talc (T-light 83 manufactured by Taihei Talc Co., Ltd.) as a filler was added to the raw material for the white layer per 100 parts by mass of pulp.

(Example 13)
To the raw material for the white layer, talc (T-light 83 manufactured by Taihei Talc Co., Ltd.) was added as a filler in an amount of 5 parts by mass per 100 parts by mass of pulp, and aluminum sulfate was further added in an amount of 2 parts per 100 parts by mass of the pulp. In addition, 1 part of aluminum sulfate per 100 parts by mass of pulp is added to the coating material for the undercoat layer, the amount of kaolin (hydrapersper made by Caymin Co.) is set to 80 parts, and calcium carbonate (Imeris Minera Mez Japan Co., Ltd.) is added. Carbital 90) made in 20 parts, kaolin (Amazon SB made by Kadam Co., Ltd.) added in the coating material for the overcoat layer is made 60 parts, and calcium carbonate (Carbital 90 made by Imeryth Minerames Japan Co., Ltd.) Was added to 20 parts, and 20 parts of titanium dioxide (PFC-503 manufactured by Ishihara Sangyo Co., Ltd.) was further added to obtain a coated white paperboard for laser marking in the same manner as in Example 1.

(Example 14)
As a raw material for the white layer, a pulp adjusted to 350 ml of CSF consisting of 50% high-quality waste paper pulp and 50% hardwood pulp (L-BKP) was used, and 2 parts aluminum pulp was added per 100 parts by mass of pulp. A coated white paperboard for laser marking was obtained in the same manner as in Example 1.

(Example 15)
As a raw material for the white layer, a pulp adjusted to 350 ml of CSF consisting of 50% high-quality waste paper pulp and 50% hardwood pulp (L-BKP) is used, and 1 part by mass of calcium carbonate is added as a filler per 100 parts by mass of pulp. A coated white board for laser marking was obtained in the same manner as in Example 1 except for the above.

(Comparative Example 1)
A coated white paperboard for laser marking was obtained in the same manner as in Example 1 except that calcium carbonate as a filler was added to the raw material for the white layer in an amount of 3 parts by mass per 100 parts by mass of the pulp.

(Comparative example 2)
Example except that the addition amount of kaolin (hydrapersper manufactured by Keimin Co., Ltd.) and the amount of calcium carbonate (Carbital 90 manufactured by Imeryth Mineramezu Japan Co., Ltd.), which were added to the coating material for the undercoat layer, were 50 parts and 50 parts, respectively. A coated white board for laser marking was obtained in the same manner as in 1.

Table 1 shows the constitution and evaluation of the coated white board for laser marking obtained in each Example and Comparative Example. The evaluation was carried out by the following method.

<Burning evaluation>
Solid coating with black ink is performed on the surface of the coating layer of coated white paperboard for laser marking, and a carbon dioxide laser marker (LP-430U/Panasonic Device SUNX Co., Ltd.) with a wavelength of 10600 nm and an output of 30 W is applied to this solid printing portion. Manufactured by CO2 gas laser) was used to print a barcode pattern at an output of 100% (30 W) and a scanning speed of 4000 mm/sec. After that, the bar code pattern portion (the portion where the black ink was removed by the laser) was visually observed, and the degree of discoloration of the paper was evaluated on a 7-point scale. The sample with the least discoloration was rated as 7, the sample with the most discoloration was 1, and 2 to 7 were passed. The bar code pattern portion is the one with the least discoloration, and the bar code pattern with the most discolored color is brown. Therefore, the more the color change is not seen, the higher the contrast between the black ink portion and the barcode portion.

As is clear from Table 1, the coated white paperboards for laser marking obtained in Examples 1 to 15 were excellent in burn evaluation. On the other hand, the coated white paperboard for laser marking obtained in Comparative Example 1 was inferior in burnt evaluation because the amount of calcium carbonate contained as a filler in the white layer was too large. Further, the coated white paperboard for laser marking obtained in Comparative Example 2 was inferior in burnt evaluation because the amount of calcium carbonate contained in the undercoat layer was too large.

Claims (14)

On the surface of the white layer of the base paper having at least three layers of the white layer, the white lower layer and the middle layer in this order, there is further provided an undercoat coating layer containing a pigment and a binder, and further an overcoat coating layer on the surface. It is a coated white paperboard having sequentially,
The content of calcium carbonate contained as a filler in the white layer is 1 part by mass or less with respect to 100 parts by mass of pulp in the white layer,
The undercoat layer contains 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment contained in the undercoat layer, the coated white board for laser marking. The coated white paperboard for laser marking according to claim 1, wherein the overcoat coating layer contains 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment contained in the overcoat coating layer. The coated white paperboard for laser marking according to claim 1 or 2, wherein the white layer does not contain calcium carbonate as a filler. The coated white paperboard for laser marking according to claim 1, wherein 50% by mass or more of the pulp contained in the white layer is fresh pulp. The coated white paperboard for laser marking according to claim 1, wherein the white layer contains aluminum sulfate. The coated white paperboard for laser marking according to any one of claims 1 to 5, wherein the lower white layer contains aluminum sulfate. The coated white paperboard for laser marking according to any one of claims 1 to 6, wherein the undercoat coating layer and/or the topcoat coating layer contains kaolin as a pigment. A step of making a base paper having at least three layers of a white layer, a white lower layer and a middle layer in this order by a paper machine using raw materials adjusted for each layer, and an undercoat containing a pigment and a binder on the surface of the white layer The coating material for coating layer is applied to form an undercoating layer, and then the coating material for topcoating layer containing a pigment and a binder is applied on the undercoating layer to form a topcoating layer. A method of manufacturing a coated white paperboard, the method including:
The amount of calcium carbonate added as a filler in the raw material of the white layer is 1 part by mass or less with respect to 100 parts by mass of pulp contained in the raw material of the white layer,
The method for producing a coated white paperboard for laser marking, wherein the undercoat coating layer coating contains 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment. The method for producing a coated white paperboard for laser marking according to claim 8, wherein the coating material for the overcoat layer contains 1 to 40 parts by mass of calcium carbonate per 100 parts by mass of the pigment. The method for producing a coated white paperboard for laser marking according to claim 8 or 9, wherein calcium carbonate is not added as a filler to the raw material of the white layer. Aluminum sulfate is added to the raw material of the said white layer, The manufacturing method of the coated white paperboard for laser markings as described in any one of Claims 8-10 characterized by the above-mentioned. Aluminum sulfate is added to the raw material of the said white lower layer, The manufacturing method of the coated white board for laser marking as described in any one of Claims 8-11. The coated white paperboard for laser marking according to any one of claims 8 to 12, wherein kaolin is contained as a pigment in the undercoat coating layer coating material and/or the topcoat coating layer coating material. Manufacturing method. The method for producing a coated white paperboard for laser marking according to any one of claims 8 to 13, wherein the pulp contained in the raw material for the white layer has a Canadian standard freeness (CSF) of 300 ml or less. ..