JP7544451B2 - Coated white paperboard - Google Patents
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- JP7544451B2 JP7544451B2 JP2021552373A JP2021552373A JP7544451B2 JP 7544451 B2 JP7544451 B2 JP 7544451B2 JP 2021552373 A JP2021552373 A JP 2021552373A JP 2021552373 A JP2021552373 A JP 2021552373A JP 7544451 B2 JP7544451 B2 JP 7544451B2
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/36—Coatings with pigments
- D21H19/38—Coatings with pigments characterised by the pigments
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/80—Paper comprising more than one coating
- D21H19/82—Paper comprising more than one coating superposed
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Description
本発明は、塗工白板紙に関する。特に、本発明は、塗工層割れに強いオフセット・グラビア共用塗工白板紙に関する。The present invention relates to a coated white paperboard. In particular, the present invention relates to a coated white paperboard for both offset and gravure printing that is resistant to coating layer cracking.
白板紙は、通常２～９層の多層基紙構造からなる厚紙で、環境に対する取組みやコストダウンに対する要求が高まっていることから、古紙パルプが多く使用されている。例えば、表層には、晒パルプまたは脱墨パルプあるいは漂白された白色度の高い古紙パルプが、また中層、裏層にはより白色度が低く、安価な脱墨パルプおよび脱墨しない古紙パルプが使用されている。年々古紙パルプの配合比率は上昇し、グレードの低い白板紙では古紙パルプはほぼ１００％配合されるほどになっている。こうした状況の中、古紙配合率増加に伴う基紙の問題として、チリ、黒点等の欠陥、および白色ムラの発現の増加がある。チリ等の異物を除去するために、脱墨工程や除塵工程を強化する対策がなされ、脱墨技術や除塵装置の進歩によりチリの問題は大幅に改善されてきているが、まだ完全に除去できるまでには至っていない。脱墨処理や除塵処理を強化するほど、歩留が悪化し、経済的に不利になることから、現状では、一定のレベル以上には脱墨、除塵処理は施されない。 Whiteboard is a thick paperboard with a multi-layered base paper structure, usually 2 to 9 layers, and recycled paper pulp is often used due to the increasing demand for environmental initiatives and cost reduction. For example, bleached pulp, deinked pulp, or bleached recycled paper pulp with high whiteness is used for the surface layer, while deinked pulp or non-deinked recycled paper pulp with lower whiteness and cheaper is used for the middle and back layers. The ratio of recycled paper pulp is increasing year by year, and low-grade whiteboard contains almost 100% recycled paper pulp. In this situation, problems with the base paper caused by the increase in the recycled paper content include an increase in defects such as dust and black spots, and the occurrence of white unevenness. Measures have been taken to strengthen the deinking and dust removal processes in order to remove foreign matter such as dust, and the problem of dust has been greatly improved due to advances in deinking technology and dust removal equipment, but it is not yet possible to completely remove it. The more intensive the deinking and dust removal processes are, the worse the yield becomes and the more economically disadvantageous it becomes, so currently deinking and dust removal processes are not carried out beyond a certain level.
塗工白板紙は、多層抄きされた基紙に顔料と接着剤を主成分とする塗工液を塗工した顔料塗工層を有する白板紙であり、主として、化粧品、医薬品、石鹸、ギフト品等の包装箱に使用されている。内包した商品をアピールするため各種印刷方式により塗工白板紙表面に印刷が施された後に、各種の後加工を施されて紙器に加工される。この塗工白板紙は、基紙構成および塗工層形成状態の違いから、高級白板紙、特殊白板紙、塗工白ボールに分類される。高級白板紙は全層に化学パルプが使用され、両面に塗工層が設けられた白板紙であり、特殊白板紙は、表層および裏層には化学パルプが、それらより内側の層には古紙が利用され、両面あるいは片面に塗工層が設けられた白板紙であり、これら高級白板紙と特殊白板紙とをマニラボールと称している。また、塗工白ボールは、表層には化学パルプが、裏層およびそれらより内側の層には古紙が用いられ、片面に塗工層が設けられた白板紙である。
塗工白板紙は、印刷作業、打ち抜きなどの工程を経て、多くは箱などに加工される。箱に組立てる時は折り曲げる必要があるが、折り曲げる際に塗工白板紙の表側は伸びの力を受けるため、この力に塗工白板紙の表層部の強度が負けると破壊が起こり裂けてしまう。この破断を「罫割れ」や「塗工層割れ」といい、軽度のものは表層がひび割れ状となるが、ひどいものは基紙部分も含め大きく割れが生じる。塗工層割れを生じたものは、外観上見苦しいだけではなく、組立てた箱の強度が低下し、包装構造体として致命的な欠陥となる。
このような塗工層割れの対策として、基紙の表層にパルプとして、針葉樹晒クラフトパルプを５重量％以上含有させる塗工ライナーに関する技術や、塗工板紙の密度、プリントサーフラフネス、透気度を特定の範囲のものとする技術が開示されている（例えば、特許文献１、２を参照。）。しかしながら、これらの従来技術は、未だ十分な効果が得られるものではなく、塗工層割れを防止する新たな技術が求められている。
Coated whiteboard is a whiteboard with a pigment coating layer formed by coating a multi-layered base paper with a coating liquid mainly composed of pigments and adhesives, and is mainly used for packaging boxes for cosmetics, medicines, soaps, gifts, etc. After printing is applied to the surface of the coated whiteboard using various printing methods to appeal to the enclosed product, it is processed into paper containers by various post-processing. This coated whiteboard is classified into high-grade whiteboard, special whiteboard, and coated whiteboard based on the difference in the base paper composition and the coating layer formation state. High-grade whiteboard is a whiteboard with chemical pulp used in all layers and coated layers on both sides, while special whiteboard is a whiteboard with chemical pulp used in the front and back layers and recycled paper used in the inner layers, and coated layers on both sides or one side. These high-grade whiteboard and special whiteboard are called manilaboard. Coated white board is a white paperboard with a surface layer made of chemical pulp, a back layer and layers further inward made of recycled paper, and a coating layer on one side.
Coated white paperboard is often processed into boxes after being printed, punched, and other processes. When it is folded to be assembled into a box, the surface of the coated white paperboard is subjected to a stretching force, and if the strength of the surface layer of the coated white paperboard cannot withstand this force, it will break and tear. This break is called "crease cracks" or "coating layer cracks", and in mild cases the surface layer will crack, but in severe cases large cracks will form including in the base paper. Coated layer cracks are not only unsightly in appearance, but they also reduce the strength of the assembled box, making them a fatal defect in the packaging structure.
As a countermeasure against such coating layer cracking, a technology relating to a coated liner in which 5% by weight or more of bleached softwood kraft pulp is contained as pulp in the surface layer of a base paper, and a technology for setting the density, print surface roughness, and air permeability of a coated paperboard within specific ranges have been disclosed (see, for example, Patent Documents 1 and 2). However, these conventional technologies have not yet achieved a sufficient effect, and new technologies for preventing coating layer cracking are desired.
本発明は、上記のような状況を鑑みてなされたものであり、折り曲げの負荷に耐え得る、顔料塗工層割れに強い塗工白板紙の提供を課題としている。The present invention was made in consideration of the above-mentioned situation, and its objective is to provide a coated white paperboard that can withstand the load of bending and is resistant to cracking of the pigment coating layer.
本発明者は、上記課題を解決するために鋭意研究を重ねた結果、顔料塗工層のいずれもが、顔料として粒度分布曲線の７５累積重量％の粒子径（Ｄ７５）と２５累積重量％の粒子径（Ｄ２５）との比（Ｄ７５／Ｄ２５）が３．３以上４．０以下の重質炭酸カルシウムを含有し、最外となる上塗り顔料塗工層における前記重質炭酸カルシウムの含有割合を、前記上塗り顔料塗工層に含まれる全顔料の５重量％を超え、３０重量％以下とすることにより、折り曲げの負荷に耐え得る強度を有する塗工白板紙が得られることを見出し、本発明を完成するに至ったものである。As a result of extensive research into solving the above problems, the inventors have discovered that a coated white paperboard having strength sufficient to withstand bending loads can be obtained by having all of the pigment coating layers contain heavy calcium carbonate as a pigment, with the ratio (D75/D25) of the particle diameter at 75 cumulative weight % (D75) to the particle diameter at 25 cumulative weight % (D25) on the particle size distribution curve being 3.3 to 4.0, and by setting the content of said heavy calcium carbonate in the outermost topcoat pigment coating layer to more than 5% and not more than 30% by weight of the total pigment contained in said topcoat pigment coating layer, and thus completing the present invention.
本発明は、具体的には次の事項を要旨とする。
１．基紙の表面に２層以上の顔料塗工層を備えた塗工白板紙であって、
前記顔料塗工層のいずれもが、顔料として粒度分布曲線の７５累積重量％の粒子径（Ｄ７５）と２５累積重量％の粒子径（Ｄ２５）との比（Ｄ７５／Ｄ２５）が３．３以上４．０以下の重質炭酸カルシウムを含有し、
最外となる上塗り顔料塗工層における前記重質炭酸カルシウムの含有割合は、前記上塗り顔料塗工層に含まれる全顔料の５重量％を超え、３０重量％以下であることを特徴とする塗工白板紙。
２．前記上塗り顔料塗工層における前記重質炭酸カルシウムの含有割合は、前記上塗り顔料塗工層に含まれる全顔料の１８重量％以上、２３重量％以下であることを特徴とする１．に記載の塗工白板紙。
３．前記上塗り顔料塗工層は前記重質炭酸カルシウムを含む炭酸カルシウムを含有し、前記上塗り顔料塗工層における炭酸カルシウムの含有割合は、前記上塗り顔料塗工層に含まれる全顔料の１５重量％以上５０重量％以下の範囲であることを特徴とする、１．または２．に記載の塗工白板紙。
４．前記上塗り顔料塗工層における前記炭酸カルシウムの含有割合は、前記上塗り顔料塗工層に含まれる全顔料の１９重量％以上４０重量％未満の範囲であることを特徴とする、３．に記載の塗工白板紙。
５．前記上塗り顔料塗工層より基紙に近い下塗り顔料塗工層は、顔料としてカオリンを、前記下塗り顔料塗工層に含まれる全顔料の５重量％以上２５重量％以下含有することを特徴とする、１．～４．のいずれかに記載の塗工白板紙。
６．前記下塗り顔料塗工層は、カオリンとして平均アスペクト比が３０以上６０以下のデラミネーテッドカオリンを含有することを特徴とする、５．に記載の塗工白板紙。
７．前記上塗り顔料塗工層より基紙に近い下塗り顔料塗工層における前記重質炭酸カルシウムの含有割合は、前記下塗り顔料塗工層に含まれる全顔料の６０重量％以上であることを特徴とする、１．～６．のいずれかに記載の塗工白板紙。
８．前記上塗り顔料塗工層は、顔料としてカオリンを、前記上塗り顔料塗工層に含まれる全顔料の５重量％以上８０重量％以下含有することを特徴とする、１．～７．のいずれかに記載の塗工白板紙。
９．前記上塗り顔料塗工層は、接着剤として０℃以上３０℃以下の単一のガラス転移温度を有するスチレン－ブタジエン系ラテックスを含有することを特徴とする、１．～８．のいずれかに記載の塗工白板紙。
１０．前記上塗り顔料塗工層より基紙に近い下塗り顔料塗工層は、接着剤として－５０℃以上０℃未満の単一のガラス転移温度を有するスチレン－ブタジエン系ラテックスを含有することを特徴とする、１．～９．のいずれかに記載の塗工白板紙。
１１．前記顔料塗工層のいずれもが、顔料と接着剤を、顔料１００重量部に対し、接着剤５重量部以上３０重量部以下の範囲で含有することを特徴とする、１．～１０．のいずれかに記載の塗工白板紙。
１２．前記上塗り顔料塗工層の塗工量は、乾燥重量で片面あたり、合計で３～１５ｇ／ｍ２であることを特徴とする、１．～１１．のいずれかに記載の塗工白板紙。
１３．前記上塗り顔料塗工層より基紙に近い下塗り顔料塗工層の塗工量は、乾燥重量で片面あたり、合計で５～３０ｇ／ｍ２であることを特徴とする、１．～１２．のいずれかに記載の塗工白板紙。
１４．前記基紙は、少なくとも３層のパルプ層を有することを特徴とする、１．～１３．のいずれかに記載の塗工白板紙。
Specifically, the present invention relates to the following items.
1. A coated white paperboard having two or more pigment coating layers on the surface of a base paper,
each of the pigment coating layers contains ground calcium carbonate as a pigment, the ratio (D75/D25) of the particle size distribution curve of the 75th cumulative weight % particle size (D75) to the 25th cumulative weight % particle size (D25) being 3.3 or more and 4.0 or less;
A coated white paperboard, characterized in that the content of said ground calcium carbonate in the outermost topcoat pigment coating layer is more than 5% by weight and not more than 30% by weight of all pigments contained in said topcoat pigment coating layer.
2. The coated white paperboard according to 1., characterized in that the content of the ground calcium carbonate in the top-coat pigment coating layer is 18% by weight or more and 23% by weight or less of the total pigment contained in the top-coat pigment coating layer.
3. The coated white paperboard according to 1. or 2., characterized in that the topcoat pigment coating layer contains calcium carbonate including the heavy calcium carbonate, and the content of calcium carbonate in the topcoat pigment coating layer is in the range of 15% by weight to 50% by weight of the total pigment contained in the topcoat pigment coating layer.
4. The coated white paperboard according to 3., characterized in that the content of the calcium carbonate in the top-coat pigment coating layer is in the range of 19% by weight or more and less than 40% by weight of the total pigment contained in the top-coat pigment coating layer.
5. The coated white paperboard according to any one of 1. to 4., characterized in that the undercoat pigment coating layer, which is closer to the base paper than the topcoat pigment coating layer, contains kaolin as a pigment in an amount of 5% by weight to 25% by weight of the total pigment contained in the undercoat pigment coating layer.
6. The coated white paperboard according to 5., characterized in that the undercoat pigment coating layer contains delaminated kaolin having an average aspect ratio of 30 or more and 60 or less as the kaolin.
7. The coated white paperboard according to any one of 1. to 6., characterized in that the content of the ground calcium carbonate in the undercoat pigment coating layer, which is closer to the base paper than the topcoat pigment coating layer, is 60% by weight or more of the total pigment contained in the undercoat pigment coating layer.
8. The coated white paperboard according to any one of 1. to 7., characterized in that the top-coat pigment coating layer contains kaolin as a pigment in an amount of 5% by weight to 80% by weight of the total pigments contained in the top-coat pigment coating layer.
9. The coated white paperboard according to any one of 1. to 8., characterized in that the top pigment coating layer contains, as an adhesive, a styrene-butadiene-based latex having a single glass transition temperature of 0°C or higher and 30°C or lower.
10. The coated white paperboard according to any one of 1. to 9., characterized in that the undercoat pigment coating layer, which is closer to the base paper than the topcoat pigment coating layer, contains a styrene-butadiene-based latex having a single glass transition temperature of -50°C or more and less than 0°C as an adhesive.
11. The coated white paperboard according to any one of 1. to 10., characterized in that each of the pigment coating layers contains a pigment and an adhesive in a range of 5 parts by weight to 30 parts by weight of the adhesive per 100 parts by weight of the pigment.
12. The coated white paperboard according to any one of 1. to 11., characterized in that the coating amount of the top pigment coating layer is 3 to 15 g/ m2 in total per side in terms of dry weight.
13. The coated white paperboard according to any one of 1. to 12., characterized in that the coating amount of the undercoat pigment coating layer, which is closer to the base paper than the topcoat pigment coating layer, is 5 to 30 g/ m2 in total per side in terms of dry weight.
14. The coated white paperboard according to any one of 1. to 13., characterized in that the base paper has at least three pulp layers.
本発明によれば、２層以上の顔料塗工層のいずれもが、粒度分布がある程度広い重質炭酸カルシウムを含有しているため、顔料塗工層中の空隙が減少し、密度の高い強固な顔料塗工層となるため、ギフト品などの包装箱の使用に好適な、顔料塗工層割れに強い塗工白板紙を提供することができる。According to the present invention, since each of the two or more pigment coating layers contains heavy calcium carbonate with a relatively wide particle size distribution, the voids in the pigment coating layer are reduced, resulting in a dense and strong pigment coating layer, making it possible to provide a coated white paperboard that is resistant to cracking of the pigment coating layer and is suitable for use in packaging boxes for gifts and the like.
以下、本発明の塗工白板紙について詳細に説明する。
＜顔料塗工層について＞
本発明の塗工白板紙は、基紙の表面に、重質炭酸カルシウムを含む顔料および接着剤を含有する顔料塗工層を２層以上備えるものである。本発明の顔料塗工層においては、最外塗工層を上塗り顔料塗工層、当該上塗り顔料塗工層を形成する塗工液を上塗り顔料塗工液ともいう。また、上記最外塗工層より基紙に近い層を下塗り顔料塗工層、当該下塗り顔料塗工層を形成する塗工液を下塗り顔料塗工液ともいう。
The coated white paperboard of the present invention will be described in detail below.
<About the pigment coating layer>
The coated white paperboard of the present invention has two or more pigment coating layers containing a pigment containing heavy calcium carbonate and an adhesive on the surface of a base paper. In the pigment coating layers of the present invention, the outermost coating layer is also called the topcoat pigment coating layer, and the coating liquid that forms the topcoat pigment coating layer is also called the topcoat pigment coating liquid. In addition, the layer that is closer to the base paper than the outermost coating layer is also called the undercoat pigment coating layer, and the coating liquid that forms the undercoat pigment coating layer is also called the undercoat pigment coating liquid.
（重質炭酸カルシウムについて）
本発明の顔料塗工層のいずれもが、顔料として、Ｘ線透過式沈降法粒度分布測定法（Ｘ線透過式重力沈降法）により測定した７５累積重量％の粒子径（Ｄ７５（μｍ））と２５累積重量％の粒子径（Ｄ２５（μｍ））との比（Ｄ７５／Ｄ２５）が３．３以上であり４．０以下の範囲の重質炭酸カルシウムを含有するものである。本発明において、Ｄ７５／Ｄ２５の下限値は、３．３より大きいことが好ましく、３．４以上であることがより好ましく、３．５以上であることが特に好ましい。
このＤ７５／Ｄ２５の値は、小さいほど粒度分布が狭い、すなわち粒度分布のピークがシャープな重質炭酸カルシウムであることを意味する。したがって、本発明の顔料塗工層中に使用する重質炭酸カルシウムは、粒度分布がある程度広いものである。本発明では、重質炭酸カルシウムの粒度分布をある程度広いものとし、均一な粒子径のものとしないことにより、顔料塗工層中の空隙を減少することができ、密度の高い強固な顔料塗工層とすることができる。また、顔料塗工層の空隙が減ることで、少ないバインダー量で顔料間を結着することができ、接着効率が良好な顔料塗工層とすることができる。
Ｘ線透過式沈降法粒度分布測定法による粒度分布の測定は、液相沈降法を採用し、ストークスの法則に基づいて粒子径を測定する。また、沈降中の懸濁液にＸ線を照射し、そのＸ線透過量からランベルト・ベールの法則に従い粒度分布を測定する。本発明においては、Ｘ線透過式沈降法粒度分布測定装置（マイクロメリティックス社製セディグラフ５１００）によって測定した値を使用する。
(About ground calcium carbonate)
All of the pigment coating layers of the present invention contain heavy calcium carbonate as a pigment, in which the ratio (D75/D25) of the particle size of 75 cumulative weight % (D75 (μm)) to the particle size of 25 cumulative weight % (D25 (μm)) measured by X-ray transmission sedimentation particle size distribution measurement method (X-ray transmission gravity sedimentation method) is in the range of 3.3 or more and 4.0 or less. In the present invention, the lower limit of D75/D25 is preferably larger than 3.3, more preferably 3.4 or more, and particularly preferably 3.5 or more.
The smaller the D75/D25 value, the narrower the particle size distribution, i.e., the sharper the peak of the particle size distribution of the heavy calcium carbonate. Therefore, the heavy calcium carbonate used in the pigment coating layer of the present invention has a relatively broad particle size distribution. In the present invention, the particle size distribution of the heavy calcium carbonate is made relatively broad and not uniform in particle size, thereby reducing the voids in the pigment coating layer and making it possible to obtain a pigment coating layer with high density and strength. Furthermore, by reducing the voids in the pigment coating layer, the pigments can be bonded with a small amount of binder, making it possible to obtain a pigment coating layer with good adhesion efficiency.
The measurement of particle size distribution by the X-ray transmission sedimentation particle size distribution measurement method employs a liquid phase sedimentation method, and measures the particle size based on Stokes' law. In addition, X-rays are irradiated onto the suspension during settling, and the particle size distribution is measured from the amount of X-ray transmission according to the Beer-Lambert law. In the present invention, values measured using an X-ray transmission sedimentation particle size distribution measurement device (Sedigraph 5100 manufactured by Micromeritics) are used.
本発明の顔料塗工層における最外となる上塗り顔料塗工層は、上記重質炭酸カルシウムを、上塗り顔料塗工層に含まれる全顔料の５重量％を超え、３０重量％以下の範囲で含有する。含有量がこの範囲であれば、塗工層割れ抑制効果を顕著なものとすることができる。５重量％以下であると、配合量が少ないため、十分な塗工層割れ抑制効果を得ることができず、３０重量％より多いと、白色顔料粒子間の空隙が減ることで、顔料塗工層の光散乱性が低下するため、不透明度が劣る可能性がある。
上記重質炭酸カルシウムを、上塗り顔料塗工層に含まれる全顔料の１０重量％以上含有することが好ましく、１５重量％以上含有することがより好ましく、１８重量％以上含有することが特に好ましい。また、２８重量％以下含有することが好ましく、２５重量％以下含有することがより好ましく、２３重量％以下含有することが特に好ましい。
また、本発明の顔料塗工層における基紙に近い下塗り顔料塗工層は、上記重質炭酸カルシウムを、下塗り顔料塗工層に含まれる全顔料の６０重量％以上含有することが塗工層割れ抑制効果を得るうえで好ましく、７０重量％以上含有することがより好ましく、８０重量％以上含有することが特に好ましい。
The topcoat pigment coating layer, which is the outermost layer in the pigment coating layer of the present invention, contains the above-mentioned heavy calcium carbonate in a range of more than 5% by weight and not more than 30% by weight of the total pigment contained in the topcoat pigment coating layer. If the content is within this range, the effect of suppressing coating layer cracking can be remarkable. If it is 5% by weight or less, the amount is too small to obtain a sufficient effect of suppressing coating layer cracking, and if it is more than 30% by weight, the gaps between the white pigment particles are reduced, reducing the light scattering properties of the pigment coating layer, which may result in poor opacity.
The ground calcium carbonate is contained in an amount of preferably 10% by weight or more, more preferably 15% by weight or more, and particularly preferably 18% by weight or more, based on the total weight of the pigment contained in the topcoat pigment coating layer, and is contained in an amount of preferably 28% by weight or less, more preferably 25% by weight or less, and particularly preferably 23% by weight or less.
In addition, in the pigment coating layer of the present invention, the undercoat pigment coating layer close to the base paper preferably contains the above-mentioned heavy calcium carbonate in an amount of 60% by weight or more of the total pigment contained in the undercoat pigment coating layer in order to obtain the effect of suppressing coating layer cracking, more preferably 70% by weight or more, and particularly preferably 80% by weight or more.
本発明の下塗り顔料塗工層は、さらに顔料としてカオリンを含有してもよい。下塗り顔料塗工層に含まれる全顔料の０重量％以上３０重量％以下の範囲で含有するとよく、５重量％以上２５重量％以下の範囲がより好ましい。下塗り顔料塗工層がカオリンを含有する場合は、デラミネーテッドカオリンが好ましい。デラミネーテッドカオリンは、六角板状結晶が積層した通常のカオリンを単層に剥がすことにより得られ、比較的粒子径が大きく、アスペクト比が高いために、塗工層に配合すると、基紙の被覆性が良好になり、平滑性が向上する。中でも、平均アスペクト比が３０以上６０以下のデラミネーテッドカオリンが好適である。平均アスペクト比が３０以上６０以下のデラミネーテッドカオリンは、白色ムラを改善し、保水性をさらに向上させる。これは、顔料の隙間を扁平な顔料が埋めることにより脱水が抑制され保水性が良好になることによると推測される。しかし一方で、アスペクト比の高いデラミネーテッドカオリンなどの扁平顔料は、酸性基の主面を持つため、ラテックス等の酸性基を多く含む接着剤との親和性が悪く、接着効率が低い。そのため、顔料塗工層中のデラミネーテッドカオリンの含有量は３０重量％以下が好ましく、２５重量％以下がより好ましい。
また、本発明の上塗り顔料塗工層は、高い隠蔽性、平滑性、箱加工時の高い滑り性を得るために、さらに顔料としてカオリンを含有していることが好ましい。その含有量は、上塗り顔料塗工層に含まれる全顔料の５重量％以上８０重量％以下の範囲が好ましく、３０重量％以上８０重量％以下の範囲がより好ましい。
The undercoat pigment coating layer of the present invention may further contain kaolin as a pigment. The content of kaolin in the undercoat pigment coating layer is preferably in the range of 0% by weight to 30% by weight, more preferably in the range of 5% by weight to 25% by weight. When the undercoat pigment coating layer contains kaolin, delaminated kaolin is preferred. Delaminated kaolin is obtained by peeling off ordinary kaolin, which is a laminate of hexagonal plate-shaped crystals, into a single layer. Since it has a relatively large particle size and a high aspect ratio, when it is added to the coating layer, the coverage of the base paper is improved and the smoothness is improved. Among them, delaminated kaolin with an average aspect ratio of 30 to 60 is preferred. Delaminated kaolin with an average aspect ratio of 30 to 60 improves white unevenness and further improves water retention. It is presumed that this is because the flat pigment fills the gaps between the pigments, suppressing dehydration and improving water retention. On the other hand, flat pigments such as delaminated kaolin with a high aspect ratio have a main surface with acidic groups, and therefore have poor affinity with adhesives containing many acidic groups such as latex, resulting in low adhesion efficiency. Therefore, the content of delaminated kaolin in the pigment coating layer is preferably 30% by weight or less, more preferably 25% by weight or less.
In order to obtain high hiding power, smoothness, and high slipperiness during box processing, the top-coat pigment coating layer of the present invention preferably further contains kaolin as a pigment, the content of which is preferably in the range of 5% by weight to 80% by weight, more preferably 30% by weight to 80% by weight, of the total pigments contained in the top-coat pigment coating layer.
本発明の顔料塗工層は、上記以外に従来の公知の顔料をさらに含有することができる。具体的には、例えば、クレー、焼成クレー、ケイソウ土、タルク、焼成カオリン、軽質炭酸カルシウム、炭酸マグネシウム、炭酸バリウム、二酸化チタン、酸化亜鉛、酸化ケイ素、非晶質シリカ、亜硫酸カルシウム、石膏、ホワイトカーボン、水酸化アルミニウム、水酸化カルシウム、水酸化マグネシウム、水酸化亜鉛、製紙スラッジ、脱墨フロスからの再生無機粒子等の無機填料、尿素－ホルマリン樹脂、ポリスチレン樹脂、塩化ビニル樹脂、メラミン樹脂、フェノール樹脂、プラスチック微小中空粒子などの有機填料等が挙げられる。
中でも、高い白色度を維持しつつ隠蔽性を得るためには顔料塗工層のいずれか一層に軽質炭酸カルシウムを含有することが好ましく、特に、隠蔽性、高い白色度が求められる上塗り顔料塗工層に含有することがより好ましい。上塗り顔料塗工層が軽質炭酸カルシウムを含有する場合は、軽質炭酸カルシウムおよび重質炭酸カルシウムの炭酸カルシウムの割合は、上塗り顔料塗工層に含まれる全顔料に対し、その下限値は１５重量％以上が好ましく、１８重量％以上がさらに好ましく、１９重量％以上が特に好ましく、その上限値は５０重量％以下が好ましく、４５重量％以下がさらに好ましく、４０重量％未満が特に好ましく、３５重量％以下が最も好ましい。
The pigment coating layer of the present invention may further contain conventionally known pigments in addition to the above.Specific examples of the pigments include inorganic fillers such as clay, calcined clay, diatomaceous earth, talc, calcined kaolin, light calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, calcium sulfite, gypsum, white carbon, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, papermaking sludge, and recycled inorganic particles from deinking floss, and organic fillers such as urea-formalin resin, polystyrene resin, vinyl chloride resin, melamine resin, phenol resin, and plastic hollow microparticles.
In particular, in order to obtain hiding power while maintaining high whiteness, it is preferable to contain light calcium carbonate in any one of the pigment coating layers, and it is more preferable to contain it in the topcoat pigment coating layer, which is particularly required for hiding power and high whiteness. When the topcoat pigment coating layer contains light calcium carbonate, the lower limit of the proportion of light calcium carbonate and heavy calcium carbonate relative to the total pigment contained in the topcoat pigment coating layer is preferably 15% by weight or more, more preferably 18% by weight or more, and particularly preferably 19% by weight or more, and the upper limit is preferably 50% by weight or less, more preferably 45% by weight or less, particularly preferably less than 40% by weight, and most preferably 35% by weight or less.
本発明における顔料塗工液に含有する接着剤（バインダー）は特に制限されず、塗工紙に従来から用いられている接着剤を使用できる。具体的には、例えば、スチレン－ブタジエン系、スチレン－アクリル系、エチレン－酢酸ビニル系、ブタジエン－メチルメタクリレート系、アクリル酸－メチルメタクリレート系、酢酸ビニル－ブチルアクリレート系、スチレン－無水マレイン酸系、エチレン－無水マレイン酸系等の各種共重合またはラテックス、完全ケン化ポリビニルアルコール、部分ケン化ポリビニルアルコール、アセトアセチル化ポリビニルアルコール、カルボキシ変性ポリビニルアルコール等のポリビニルアルコール類、カゼイン、大豆蛋白、合成蛋白等の蛋白質類、酸化澱粉、カチオン化澱粉、尿素燐酸エステル化澱粉、ヒドロキシエチルエーテル化澱粉等のエーテル化澱粉、デキストリン等の澱粉類、カルボキシメチルセルロース、ヒドロキシエチルセルロース、ヒドロキシメチルセルロース、ナノセルロース等のセルロース誘導体等が挙げられ、これらの接着剤１種類以上を適宜選択して使用することができる。
中でも、本発明の顔料塗工液に使用する接着剤は、ラテックスおよび澱粉を含有することが好ましい。使用するラテックスとしては単一のガラス転移温度（以下、「Ｔｇ」ということがある。）を有するスチレン－ブタジエン系ラテックス（以下、「ＳＢＲ」ということがある。）を使用することが好ましい。本発明では、下塗り顔料塗工層にはＴｇが低いＳＢＲを含有することが好ましく、上塗り顔料塗工層にはＴｇが高いＳＢＲを含有することが好ましい。具体的には、下塗り顔料塗工層に使用するＳＢＲのＴｇは－５０℃以上０℃未満が好ましく、上塗り顔料塗工層に使用するＳＢＲのＴｇは０℃以上３０℃以下が好ましい。ＳＢＲは、一般的にＴｇが低い方が柔らかいため、各顔料塗工層に上述のＴｇを有するＳＢＲを使用することで、下塗り顔料塗工層にはクッション性を付与し、上塗り顔料塗工層には強度を付与することができる。
また、顔料塗工液に澱粉を使用することで、顔料塗工液の保水性を高めることができる。保水性の高い顔料塗工液を使用すると、塗工時の接着剤成分の紙への浸透が抑制され、顔料塗工層中に接着剤を多く保持することができるため、顔料塗工層中の接着剤成分の効果が高く発現され、顔料塗工層強度、表面強度、クッション性に優れた顔料塗工層を得ることができる。
The adhesive (binder) contained in the pigment coating liquid in the present invention is not particularly limited, and adhesives conventionally used for coated paper can be used.Specific examples include various copolymers or latexes such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, butadiene-methyl methacrylate, acrylic acid-methyl methacrylate, vinyl acetate-butyl acrylate, styrene-maleic anhydride, and ethylene-maleic anhydride, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, and carboxy-modified polyvinyl alcohol, proteins such as casein, soy protein, and synthetic protein, starches such as oxidized starch, cationic starch, urea phosphate esterified starch, etherified starch such as hydroxyethyl etherified starch, starches such as dextrin, and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, and nanocellulose, and one or more of these adhesives can be appropriately selected and used.
Among them, the adhesive used in the pigment coating liquid of the present invention preferably contains latex and starch. The latex used is preferably a styrene-butadiene-based latex (hereinafter sometimes referred to as "SBR") having a single glass transition temperature (hereinafter sometimes referred to as "Tg"). In the present invention, the undercoat pigment coating layer preferably contains an SBR having a low Tg, and the topcoat pigment coating layer preferably contains an SBR having a high Tg. Specifically, the Tg of the SBR used in the undercoat pigment coating layer is preferably -50°C or more and less than 0°C, and the Tg of the SBR used in the topcoat pigment coating layer is preferably 0°C or more and 30°C or less. Since SBR is generally softer when its Tg is lower, by using an SBR having the above-mentioned Tg in each pigment coating layer, it is possible to impart cushioning properties to the undercoat pigment coating layer and strength to the topcoat pigment coating layer.
Furthermore, the use of starch in the pigment coating liquid can increase the water retention of the pigment coating liquid. When a pigment coating liquid with high water retention is used, the penetration of the adhesive components into the paper during coating is suppressed, and a large amount of adhesive can be retained in the pigment coating layer, so that the effectiveness of the adhesive components in the pigment coating layer is highly expressed, resulting in a pigment coating layer with excellent pigment coating layer strength, surface strength, and cushioning properties.
本発明の各顔料塗工層を形成する顔料塗工液の顔料と接着剤の配合比率は、所望の顔料塗工液が得られる範囲で適宜調整される。通常は、固形分比率で、顔料１００重量部に対し、接着剤５重量部以上３０重量部以下の範囲で含有することが好ましく、さらに好ましくは８重量部以上２０重量部以下の範囲である。５重量部より少ないと、顔料塗工層強度が弱くなってしまい、紙粉が発生する、印刷強度が劣るなどの問題が発生しやすい。また、３０重量部より多いと、塗工層中の白色顔料粒子間の空隙が減ることで、接着効率は上がるものの、顔料塗工層の光散乱性が低下するため、不透明度が劣る、コストが高くなるなどの問題が発生しやすい。The blending ratio of the pigment and adhesive in the pigment coating liquid forming each pigment coating layer of the present invention is appropriately adjusted within a range in which the desired pigment coating liquid can be obtained. Usually, it is preferable to contain 5 to 30 parts by weight of adhesive per 100 parts by weight of pigment in terms of solid content ratio, and more preferably 8 to 20 parts by weight. If it is less than 5 parts by weight, the strength of the pigment coating layer is weakened, and problems such as the generation of paper powder and poor printing strength are likely to occur. Also, if it is more than 30 parts by weight, the gaps between the white pigment particles in the coating layer are reduced, and although the adhesion efficiency is increased, the light scattering property of the pigment coating layer is reduced, and problems such as poor opacity and high costs are likely to occur.
本発明の顔料塗工層を形成する顔料塗工液には、顔料と接着剤の他に、必要に応じて、分散剤、粘性改良剤、保水剤、消泡剤、耐水化剤、蛍光染料、着色染料、界面活性剤、ｐＨ調整剤、カチオン性樹脂、アニオン性樹脂、紫外線吸収剤、金属塩など、通常の塗工紙用顔料塗工液に配合される各種助剤を適宜使用できる。
顔料塗工液の固形分濃度は、５８重量％以上が好ましく、６２重量％以上がより好ましい。固形分が５８重量％より低いと、保水性が低下するため、顔料塗工液の基紙への過剰な浸透により塗工白板紙の品質が低下することがある。一方、固形分濃度の上限は特に制限されないが、送液性等を考慮すると、７５重量％以下が好ましく、７０重量％以下がより好ましい。
In addition to the pigment and adhesive, the pigment coating liquid that forms the pigment coating layer of the present invention may contain, as necessary, various auxiliary agents that are typically blended into pigment coating liquids for coated paper, such as dispersants, viscosity improvers, water retention agents, defoamers, water resistance agents, fluorescent dyes, coloring dyes, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, and metal salts.
The solids concentration of the pigment coating liquid is preferably 58% by weight or more, and more preferably 62% by weight or more. If the solids concentration is lower than 58% by weight, the water retention decreases, and the quality of the coated white paperboard may decrease due to excessive penetration of the pigment coating liquid into the base paper. On the other hand, there is no particular upper limit to the solids concentration, but taking into consideration the liquid transportability, etc., it is preferably 75% by weight or less, and more preferably 70% by weight or less.
＜基紙について＞
本発明の塗工白板紙における基紙は、２層以上のパルプ層（紙層）を多層抄きしたものであることが好ましい。基紙の層数は、好ましくは３層以上であり、より好ましくは５層以上である。基紙の最も外側の紙層を表層および裏層といい、表層および裏層に挟まれる内側の層を中層という。また、表層に接し中層側に向って２層目を表下層という。中層は１層でもよく２層以上の多層でもよい。また本発明の基紙の各層は、顔料塗工層を設けた側から数えて、１層目、２層目、３層目と呼ぶこともある。
本発明の基紙は、一般に塗工白板紙の基紙に使用されるものを例外なく使用できるが、多層抄きの基紙の少なくとも一層の紙層に古紙パルプが配合されていることが好ましい。古紙パルプを多く含む基紙を用いることはコスト面でも有利であり、また、環境負荷も低くなる。古紙パルプとしては脱墨パルプ（ＤＩＰ）でも、脱墨していないパルプでもよく、古紙パルプの原料としては、上質紙、中質紙、下級紙、新聞紙、チラシ、雑誌などの選別古紙やこれらが混合している無選別古紙を使用できる。また、古紙パルプ以外のパルプは特に制限されず、広葉樹や針葉樹を原料とするクラフトパルプ、亜硫酸パルプなどの化学パルプ；サーモメカニカルパルプ、加圧砕木パルプなどの機械パルプ；ケミカルサーモメカニカルパルプなどの半化学パルプが使用できる。使用するパルプは、これら各種パルプを混合したものでもよいし、同一のパルプを用いたものでもよい。また、異なるパルプを含有する紙層を１層以上重ねてもよい。
本発明の基紙は、例えば、中層に白色度の低いパルプを用いて、表層、裏層にそれより白色度の高いパルプを用いることもできるし、すべての層のパルプを同じにして重ねることもできる。本発明において、基紙の層数を３層以上とした場合、表層および裏層には白色度が高く夾雑物の少ない、広葉樹晒クラフトパルプ（以下、「ＬＢＫＰ」ということがある。）を、表層若しくは裏層のパルプ１００重量％に対し３０重量％以上含有することが好ましく、５０重量％以上含有することがより好ましい。また、中層には、白色度が低く比較的夾雑物の多い古紙パルプを、中層のパルプ１００重量％に対し１０重量％以上含有することが好ましく、３０重量％以上含有することがより好ましい。
<About the base paper>
The base paper in the coated white paperboard of the present invention is preferably a multi-layered paper having two or more pulp layers (paper layers). The number of layers of the base paper is preferably three or more, and more preferably five or more. The outermost paper layers of the base paper are called the front layer and back layer, and the inner layer sandwiched between the front layer and back layer is called the middle layer. The second layer in contact with the front layer toward the middle layer is called the lower surface layer. The middle layer may be one layer or two or more layers. The layers of the base paper of the present invention may be called the first layer, second layer, third layer, etc., counting from the side where the pigment coating layer is provided.
The base paper of the present invention can be any paper generally used for coated white paperboard, but it is preferable that recycled paper pulp is blended in at least one layer of the multi-layered base paper. Using a base paper containing a large amount of recycled paper pulp is advantageous in terms of cost and also reduces the environmental load. The recycled paper pulp may be deinked pulp (DIP) or non-deinked pulp, and the raw material for the recycled paper pulp may be selected recycled paper such as fine paper, medium-quality paper, low-grade paper, newspaper, flyers, magazines, etc., or unselected recycled paper in which these are mixed. Pulps other than the recycled paper pulp are not particularly limited, and chemical pulps such as kraft pulp and sulfite pulp made from broadleaf or softwood trees; mechanical pulps such as thermomechanical pulp and pressurized groundwood pulp; and semi-chemical pulps such as chemical thermomechanical pulp can be used. The pulp used may be a mixture of these various pulps, or the same pulp may be used. Also, one or more paper layers containing different pulps may be superimposed.
The base paper of the present invention may, for example, use a pulp with low whiteness in the middle layer and a pulp with higher whiteness in the front and back layers, or may use the same pulp in all layers. In the present invention, when the number of layers of the base paper is three or more, the front and back layers preferably contain 30% by weight or more, more preferably 50% by weight or more of hardwood bleached kraft pulp (hereinafter sometimes referred to as "LBKP"), which has high whiteness and little impurities, relative to 100% by weight of the pulp of the front or back layer. The middle layer preferably contains 10% by weight or more, more preferably 30% by weight or more of waste paper pulp, which has low whiteness and relatively high impurities, relative to 100% by weight of the pulp of the middle layer.
本発明における基紙は、通常填料が内添される。填料としては特に限定されないが、例えば、クレー、焼成クレー、ケイソウ土、タルク、カオリン、焼成カオリン、デラミネーテッドカオリン、重質炭酸カルシウム、軽質炭酸カルシウム、炭酸マグネシウム、炭酸バリウム、二酸化チタン、酸化亜鉛、酸化ケイ素、非晶質シリカ、亜硫酸カルシウム、石膏、ホワイトカーボン、水酸化アルミニウム、水酸化カルシウム、水酸化マグネシウム、水酸化亜鉛、製紙スラッジ、脱墨フロスからの再生無機粒子等の無機填料、尿素－ホルマリン樹脂、ポリスチレン樹脂、塩化ビニル樹脂、メラミン樹脂、フェノール樹脂、プラスチック微小中空粒子などの有機填料、さらには古紙やブローク等に含まれている填料を、単独もしくは適宜２種類以上を組み合わせて使用できる。基紙への填料配合は、中層に存在するチリ、色むらを覆い隠すため、裏層には上記填料を、裏層のパルプ１００重量％に対し２重量％以上配合することが好ましい。表層、中層への填料配合は特に制限はないが、填料の配合割合が多くなると、基紙の層間強度が低くなるので、目的とする品質に合わせて適宜調整することが必要である。The base paper in the present invention is usually internally added with a filler. There are no particular limitations on the filler, but examples include inorganic fillers such as clay, calcined clay, diatomaceous earth, talc, kaolin, calcined kaolin, delaminated kaolin, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, calcium sulfite, gypsum, white carbon, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, papermaking sludge, and inorganic particles recycled from deinking floss, organic fillers such as urea-formaldehyde resin, polystyrene resin, vinyl chloride resin, melamine resin, phenolic resin, and plastic micro-hollow particles, and fillers contained in waste paper and broken paper, etc., can be used alone or in combination of two or more types as appropriate. In blending fillers into the base paper, in order to cover up dust and color unevenness present in the middle layer, it is preferable to blend the above fillers in the back layer in an amount of 2% by weight or more per 100% by weight of the pulp in the back layer. There are no particular restrictions on the amount of filler contained in the surface and middle layers, but as the filler content increases, the interlaminar strength of the base paper decreases, so it is necessary to adjust the amount appropriately according to the desired quality.
本発明における基紙の抄紙方法は特に限定されず、トップワイヤー等を含む長網抄紙機、オントップフォーマー、ギャップフォーマー、丸網抄紙機、長網抄紙機と丸網抄紙機を併用した板紙抄紙機、ヤンキードライヤーマシン、これらを組み合わせたハイブリッド型抄紙機等を用いて行なうことができる。抄紙時のｐＨは、酸性、中性、アルカリ性のいずれでもよい。また、多層抄きの基紙の場合、各層の抄紙時のｐＨは、同一でもよいし、各層で異なってもよい。抄紙速度は、特に限定されない。なお、本発明の塗工白板紙における基紙の坪量は、通常１５０～６５０ｇ／ｍ２程度である。
また本発明により塗工白板紙を製造する場合は、顔料塗工層の形成前に、基紙をオンラインソフトカレンダ、オンラインチルドカレンダなどにより、予め平滑化しておいてもよい。
The method for making the base paper in the present invention is not particularly limited, and may be carried out using a Fourdrinier papermaking machine including a top wire, an on-top former, a gap former, a cylinder papermaking machine, a board papermaking machine using a combination of a Fourdrinier papermaking machine and a cylinder papermaking machine, a Yankee dryer machine, or a hybrid papermaking machine combining these. The pH during papermaking may be acidic, neutral, or alkaline. In the case of a multi-layered base paper, the pH during papermaking may be the same for each layer or may be different for each layer. The papermaking speed is not particularly limited. The basis weight of the base paper in the coated white paperboard of the present invention is usually about 150 to 650 g/ m2 .
When producing a coated white paperboard according to the present invention, the base paper may be previously smoothed with an online soft calender, online chilled calender or the like before the pigment coating layer is formed.
本発明において、基紙を乾燥させる方法は制限されない。例えば蒸気加熱シリンダ、加熱熱風エアドライヤ、ガスヒータードライヤ、電気ヒータードライヤ、赤外線ヒータードライヤ等各種の方法が単独もしくは併用して用いられる。In the present invention, there is no limitation on the method for drying the base paper. For example, various methods such as a steam heating cylinder, a heated hot air dryer, a gas heater dryer, an electric heater dryer, and an infrared heater dryer can be used alone or in combination.
また、本発明においては、平滑性の低い基紙を用いてもよいが、顔料塗工層の形成時のパドリングと呼ばれる塗工液溜まりが発生しない範囲で、平滑性の高い基紙を使用できる。基紙の平滑性を高めるために、前述のとおり、顔料塗工層の形成前にプレカレンダ等の処理を行なってもよい。
さらに、基紙の平滑性を改善する手段として、顔料塗工層の形成前に、澱粉を主成分としたクリア塗工液または顔料を含んだ顔料塗工液を基紙にプレ塗工することができる。このプレ塗工された基紙は、乾燥工程を経ないまま、すなわち基紙上の塗工液が濡れた状態で、顔料塗工層の形成に供してもよい。このように、顔料塗工層の形成に供される前のプレ塗工後の基紙の状態は制限されない。
In the present invention, a base paper having low smoothness may be used, but a base paper having high smoothness may be used as long as the accumulation of the coating liquid, called puddling, during the formation of the pigment coating layer does not occur. In order to increase the smoothness of the base paper, as described above, a treatment such as pre-calendering may be performed before the formation of the pigment coating layer.
Furthermore, as a means for improving the smoothness of the base paper, a clear coating liquid mainly composed of starch or a pigment coating liquid containing a pigment can be pre-coated on the base paper before the formation of the pigment coating layer. This pre-coated base paper may be used for the formation of the pigment coating layer without undergoing a drying process, i.e., while the coating liquid on the base paper is wet. In this way, there are no restrictions on the state of the base paper after pre-coating before being used for the formation of the pigment coating layer.
本発明の顔料塗工層は、重質炭酸カルシウムを含む顔料や接着剤などの必要な成分と水
とを、ミキサー等の通常の混合手段を用いて混合して調製した顔料塗工液を、基紙の表面に塗工することにより形成する。
＜塗工方法について＞
本発明の顔料塗工層を形成する塗工方法について特に制限はなく、ブレードコーター、ロッドコーター、エアナイフコーター、ロールコーター、カーテンコーターなどの通常の各種塗工装置が用いられる。
中でも、ブレードコーターやロッドコーターを使用する塗工方法は、顔料塗工層の密度を高め、顔料塗工層割れが発現し難い顔料塗工層を得ることが出来るため、本発明の塗工方法として好適である。ロッドコーターは、バーコーターまたはバーブレードコーターと呼ばれることもある。
The pigment coating layer of the present invention is formed by coating the surface of the base paper with a pigment coating liquid prepared by mixing necessary ingredients such as a pigment containing heavy calcium carbonate and an adhesive with water using a conventional mixing means such as a mixer.
<Coating method>
There is no particular limitation on the coating method for forming the pigment coating layer of the present invention, and various common coating devices such as a blade coater, a rod coater, an air knife coater, a roll coater, and a curtain coater can be used.
Among these, the coating method using a blade coater or a rod coater is suitable as the coating method of the present invention because it can increase the density of the pigment coating layer and obtain a pigment coating layer that is less likely to crack. A rod coater is also called a bar coater or a bar blade coater.
本発明において顔料塗工層の塗工量は、乾燥重量で片面あたり、各層の合計で８～５０ｇ／ｍ２が好ましく、４５ｇ／ｍ２以下とすることがより好ましい。１０～４０ｇ／ｍ２がさらに好ましく、１１～３５ｇ／ｍ２が特に好ましい。塗工量が各層の合計で８ｇ／ｍ２未満では、顔料塗工層が薄くなり塗工白板紙の白色度、白色ムラの改善効果が十分に得られない場合がある。一方、塗工量が各層の合計で５０ｇ／ｍ２を超えると、乾燥工程での乾燥性が低下するなど操業性が低下したり、バインダーマイグレーションによる印刷ムラの原因になったりすることがある。
本発明において、下塗り顔料塗工層の塗工量と上塗り顔料塗工層の塗工量は、特に制限されないが、隠蔽性と白色度を両立させるということから、乾燥重量で片面あたり、下塗り顔料塗工層が合計で５～３０ｇ／ｍ２、上塗り顔料塗工層が３～１５ｇ／ｍ２の範囲であることが好ましい。下塗り顔料塗工層および上塗り顔料塗工層の塗工量がそれぞれ５ｇ／ｍ２、３ｇ／ｍ２未満では、塗工白板紙の白色度、白色ムラの改善効果が十分に得られない場合がある。一方、塗工量が多すぎると、乾燥工程での乾燥性が低下するなど操業性が低下する他、顔料塗工層割れが発生しやすくなる傾向が見られる。
In the present invention, the coating amount of the pigment coating layer is preferably 8 to 50 g/ m2 , more preferably 45 g/ m2 or less, in total for each layer, in terms of dry weight per side. It is further preferably 10 to 40 g/ m2 , and particularly preferably 11 to 35 g/ m2 . If the coating amount is less than 8 g/ m2 in total for each layer, the pigment coating layer becomes thin and the effect of improving the whiteness and whiteness unevenness of the coated white paperboard may not be sufficiently obtained. On the other hand, if the coating amount is more than 50 g/ m2 in total for each layer, the drying process may be impaired, resulting in impaired operability, or binder migration may cause printing unevenness.
In the present invention, the coating weight of the undercoat pigment coating layer and the coating weight of the topcoat pigment coating layer are not particularly limited, but in order to achieve both hiding power and whiteness, it is preferable that the undercoat pigment coating layer has a total dry weight of 5 to 30 g/m 2 and the topcoat pigment coating layer has a dry weight of 3 to 15 g/m 2 per side. If the coating weights of the undercoat pigment coating layer and the topcoat pigment coating layer are less than 5 g/m 2 and 3 g/m 2 , respectively, the effect of improving the whiteness and whiteness unevenness of the coated white paperboard may not be sufficient. On the other hand, if the coating weight is too high, the drying process will be impaired, and operability will decrease, and the pigment coating layer will tend to be more susceptible to cracking.
本発明の塗工白板紙は、基紙上に顔料塗工層を設けた後、通常の乾燥工程を経て製造されるが、必要に応じて表面処理工程等で平滑化処理してもよい。好ましい態様において、製造後の塗工白板紙の水分量が３～１０重量％、より好ましくは４～８重量％程度となるように調整して仕上げられる。平滑化処理には、通常のスーパーカレンダ、グロスカレンダ、ソフトカレンダ、熱カレンダ、シューカレンダ等の平滑化処理装置を用いることができる。平滑化処理装置は、オンマシンやオフマシンで適宜用いられ、加圧装置の形態、加圧ニップの数、加温等も適宜調整される。
本発明の好ましい態様において、製造後の塗工白板紙のクランプ圧２０００ｋＰａの条件におけるＰＰＳラフネスが、０．５μｍ以上１．６μｍ以下となるように平滑性を調整して仕上げられる。ＰＰＳラフネスは０．８μｍ以上であることが好ましい。ＰＰＳラフネスが０．５μｍ未満であると、平滑化処理に伴う顔料塗工層の高密度化が著しく、顔料塗工層の不透明度が低下し、基紙のチリ、色むらの隠蔽効果が低下する傾向が見られる。一方、ＰＰＳラフネスが１．６μｍを超えると、平滑性が低く、白紙面感や印刷面感が低下する傾向が見られる。
The coated white paperboard of the present invention is produced by providing a pigment coating layer on a base paper and then undergoing a normal drying process, but may be smoothed by a surface treatment process or the like, if necessary. In a preferred embodiment, the moisture content of the coated white paperboard after production is adjusted to about 3 to 10% by weight, more preferably about 4 to 8% by weight. For the smoothing treatment, normal smoothing treatment devices such as a supercalender, gloss calender, soft calender, thermal calender, shoe calender, etc. can be used. The smoothing treatment device is used on-machine or off-machine as appropriate, and the type of the pressure device, the number of pressure nips, heating, etc. are also adjusted as appropriate.
In a preferred embodiment of the present invention, the smoothness is adjusted so that the PPS roughness of the coated white paperboard after production is 0.5 μm or more and 1.6 μm or less under a clamp pressure of 2000 kPa. The PPS roughness is preferably 0.8 μm or more. If the PPS roughness is less than 0.5 μm, the pigment coating layer becomes significantly densified due to the smoothing treatment, the opacity of the pigment coating layer decreases, and the effect of hiding dust and color unevenness of the base paper tends to decrease. On the other hand, if the PPS roughness exceeds 1.6 μm, the smoothness is low and the feeling of the blank paper surface and the feeling of the printed surface tend to decrease.
本発明においては、剛度付与およびカール抑制のために裏層表面にクリア塗工層を設けてもよい。裏層表面にクリア塗工層を形成するクリア塗工液には、必要に応じて、従来から公知公用のバインダーおよび、分散剤、粘性改良剤、保水剤、消泡剤、耐水化剤、界面活性剤、ｐＨ調整剤、カチオン性樹脂、アニオン性樹脂、紫外線吸収剤、金属塩など、通常の塗工液に配合される各種助剤を適宜使用できる。In the present invention, a clear coating layer may be provided on the surface of the back layer to impart stiffness and suppress curling. The clear coating liquid that forms the clear coating layer on the surface of the back layer may contain, as necessary, various auxiliary agents that are conventionally known and used, such as binders, dispersants, viscosity improvers, water retention agents, defoamers, water resistance agents, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, and metal salts, which are typically blended into coating liquids.
以下、実施例にて本発明を詳細に説明するが、本発明は、これらの例に限定されるものではない。なお、各実施例及び比較例中、特にことわらない限り「部」は「重量部」、「％」は「重量％」を示す。The present invention will be described in detail below with reference to the following examples, but the present invention is not limited to these examples. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified.
［実施例１］
＜基紙＞
ＬＢＫＰ１００重量％のパルプを使用して坪量３３ｇ／ｍ２の表層（１層目）、脱墨古紙パルプ１００％のパルプを使用して坪量３６ｇ／ｍ２の表下層（２層目）、脱墨しない雑誌古紙パルプ１００重量％のパルプを使用して４５ｇ／ｍ２の中層及び裏層（３～７層目）をそれぞれ抄紙して抄き合わせ、プレス、乾燥処理を行い、７層の紙層を有する坪量２９４ｇ／ｍ２の基紙を得た。各層のパルプスラリーには、パルプ１００重量％に対し紙力剤０．６重量％、硫酸バンド１．５重量％を添加した。
[Example 1]
<Base paper>
A surface layer (1st layer) with a basis weight of 33 g/ m2 was made using 100% LBKP pulp, a subsurface layer (2nd layer) with a basis weight of 36 g/ m2 was made using 100% deinked waste paper pulp, and a middle layer and a back layer (3rd to 7th layers) with a basis weight of 45 g/ m2 were made using 100% non-deinked magazine waste paper pulp. These were then combined, pressed and dried to obtain a base paper with a basis weight of 294 g/m2 and 7 paper layers. 0.6% by weight of a paper strength agent and 1.5% by weight of aluminum sulfate were added to the pulp slurry of each layer based on 100% by weight of pulp.
＜上塗り顔料塗工液１＞
微粒カオリン（Ｔｈｉｅｌｅ社製、カオファイン）６０重量部、重質炭酸カルシウム（イメリス社製、カービタル９７、Ｄ７５／Ｄ２５＝３．８７）２０重量部、紡錘状軽質炭酸カルシウム（奥多摩工業社製、ＴＰ－２２１Ｆ、Ｄ７５／Ｄ２５＝２．５）１５重量部、二酸化チタン５重量部からなる顔料スラリーを調製した後、顔料１００重量部に対して、接着剤としてスチレン・ブタジエン共重合ラテックスＡ（旭化成社製、ＡＬＢ１４４３：Ｔｇ＝１７℃）１４．５重量部、尿素燐酸エステル化澱粉２重量部を添加し、さらに水を添加して、固形分濃度６０％の上塗り顔料塗工液を得た。
＜下塗り顔料塗工液１＞
重質炭酸カルシウム（イメリス社製、カービタル９０、Ｄ７５／Ｄ２５＝３．８２）８０重量部、デラミネーテッドカオリン（イメリス社製、Ｃｏｎｔｏｕｒ１５００、平均アスペクト比６０）２０重量部からなる顔料スラリーを調製した後、顔料１００重量部に対して、接着剤としてスチレン・ブタジエン共重合ラテックスＢ（旭化成社製、ＡＬＢ１７３５：Ｔｇ＝－８℃）１２重量部、尿素燐酸エステル化澱粉３重量部を添加し、さらに水を添加して、固形分濃度６０％の下塗り顔料塗工液を得た。
<Topcoat pigment coating liquid 1>
A pigment slurry consisting of 60 parts by weight of fine kaolin (Kaofine, manufactured by Thiele), 20 parts by weight of heavy calcium carbonate (Carbital 97, manufactured by Imerys, D75/D25=3.87), 15 parts by weight of spindle-shaped precipitated calcium carbonate (TP-221F, manufactured by Okutama Kogyo Co., Ltd., D75/D25=2.5), and 5 parts by weight of titanium dioxide was prepared, and then 14.5 parts by weight of styrene-butadiene copolymer latex A (ALB1443, manufactured by Asahi Kasei Corporation: Tg=17° C.) as an adhesive and 2 parts by weight of urea phosphate esterified starch were added per 100 parts by weight of the pigment, and water was further added to obtain a topcoat pigment coating liquid with a solids concentration of 60%.
<Undercoat pigment coating liquid 1>
A pigment slurry consisting of 80 parts by weight of heavy calcium carbonate (Imerys, Carbital 90, D75/D25 = 3.82) and 20 parts by weight of delaminated kaolin (Imerys, Contour 1500, average aspect ratio 60) was prepared, and then 12 parts by weight of styrene-butadiene copolymer latex B (Asahi Kasei, ALB1735: Tg = -8°C) as an adhesive and 3 parts by weight of urea phosphate esterified starch were added per 100 parts by weight of the pigment, and water was further added to obtain an undercoat pigment coating liquid with a solids concentration of 60%.
＜塗工＞
基紙の表層の表面に、下塗り顔料塗工液１をロッドコーターにより、乾燥重量で片面あたり塗工量が８ｇ／ｍ２となるように塗工した後に、乾燥工程を経ることなく、上塗り顔料塗工層１をブレードコーターにより、乾燥重量で片面あたり塗工量が１２ｇ／ｍ２となるように塗工、乾燥した。その後、カレンダで平滑化処理を行い、坪量が３１４ｇ／ｍ２の塗工白板紙１を製造した。得られた塗工白板紙１の紙厚は３７５μｍであった。
<Coating>
Undercoat pigment coating solution 1 was applied to the surface of the base paper using a rod coater so that the coating amount per side was 8 g/ m2 in dry weight, and then, without a drying process, topcoat pigment coating layer 1 was applied using a blade coater so that the coating amount per side was 12 g/ m2 in dry weight, and dried. After that, a smoothing treatment was performed using a calendar, and coated white paperboard 1 with a basis weight of 314 g/ m2 was produced. The paper thickness of the obtained coated white paperboard 1 was 375 μm.
［実施例２］
上記「上塗り顔料塗工液１」中の重質炭酸カルシウムを２５重量部とし、軽質炭酸カルシウムを２０重量部とした以外は、実施例１と同様にして塗工白板紙２を製造した。得られた塗工白板紙２の坪量は３１４ｇ／ｍ２、紙厚は３８７μｍであった。
[Example 2]
Except for changing the amount of heavy calcium carbonate and light calcium carbonate in the "topcoat pigment coating solution 1" to 25 parts by weight and 20 parts by weight, respectively, coated white paperboard 2 was produced in the same manner as in Example 1. The basis weight of the obtained coated white paperboard 2 was 314 g/ m2 and the paper thickness was 387 μm.
［実施例３］
上記「上塗り顔料塗工液１」中の重質炭酸カルシウムを１５重量部とし、軽質炭酸カルシウムを３０重量部とした以外は、実施例１と同様にして塗工白板紙３を製造した。得られた塗工白板紙３の坪量は３１４ｇ／ｍ２、紙厚は３７５μｍであった。
[Example 3]
Coated white paperboard 3 was produced in the same manner as in Example 1, except that the heavy calcium carbonate and light calcium carbonate in the "topcoat pigment coating liquid 1" were changed to 15 parts by weight and 30 parts by weight, respectively. The basis weight of the obtained coated white paperboard 3 was 314 g/ m2 , and the paper thickness was 375 μm.
［実施例４］
上記「上塗り顔料塗工液１」中の重質炭酸カルシウムを３０重量部とし、軽質炭酸カルシウムを１５重量部とした以外は、実施例１と同様にして塗工白板紙４を製造した。得られた塗工白板紙４の坪量は３１４ｇ／ｍ２、紙厚は３７５μｍであった。
[Example 4]
Except for changing the amount of heavy calcium carbonate and light calcium carbonate in the "topcoat pigment coating solution 1" to 30 parts by weight and 15 parts by weight, respectively, coated white paperboard 4 was produced in the same manner as in Example 1. The basis weight of the obtained coated white paperboard 4 was 314 g/ m2 and the paper thickness was 375 μm.
［実施例５］
上記「上塗り顔料塗工液１」中の微粒カオリンを８６重量部とし、重質炭酸カルシウムを９重量部とし、軽質炭酸カルシウムを５重量部とした以外は、実施例１と同様にして塗工白板紙５を製造した。得られた塗工白板紙５の坪量は３１４ｇ／ｍ２、紙厚は３７５μｍであった。
[Example 5]
Coated white paperboard 5 was produced in the same manner as in Example 1, except that the amount of fine kaolin, heavy calcium carbonate, and light calcium carbonate in the "topcoat pigment coating liquid 1" was 86 parts by weight, 9 parts by weight, and 5 parts by weight, respectively. The basis weight of the obtained coated white paperboard 5 was 314 g/ m2 , and the paper thickness was 375 μm.
［実施例６］
上記「下塗り顔料塗工液１」中の重質炭酸カルシウムを７０重量部とし、カオリンを３０重量部とした以外は、実施例１と同様にして塗工白板紙６を製造した。得られた塗工白板紙６の坪量は３１４ｇ／ｍ２、紙厚は３７５μｍであった。
[Example 6]
Except for changing the amount of heavy calcium carbonate in the "undercoat pigment coating liquid 1" to 70 parts by weight and the amount of kaolin to 30 parts by weight, coated white paperboard 6 was produced in the same manner as in Example 1. The basis weight of the obtained coated white paperboard 6 was 314 g/ m2 and the paper thickness was 375 μm.
［比較例１］
上記「上塗り顔料塗工液１」中の重質炭酸カルシウム（イメリス社製、カービタル９７、Ｄ７５／Ｄ２５＝３．８７）を、重質炭酸カルシウム（ファイマテック社製、ＦＭＴ－ＯＰ、Ｄ７５／Ｄ２５＝３．０）に変更した以外は、実施例１と同様にして塗工白板紙ａを製造した。得られた塗工白板紙ａの坪量は３１４ｇ／ｍ２、紙厚は３８６μｍであった。
[Comparative Example 1]
Coated white paperboard a was produced in the same manner as in Example 1, except that the heavy calcium carbonate in the "topcoat pigment coating solution 1" (Imerys, Carbital 97, D75/D25 = 3.87) was replaced with heavy calcium carbonate (Fimatec, FMT-OP, D75/D25 = 3.0). The basis weight of the resulting coated white paperboard a was 314 g/ m2 , and the thickness was 386 μm.
［比較例２］
上記「上塗り顔料塗工液１」中の重質炭酸カルシウム（イメリス社製、カービタル９７、Ｄ７５／Ｄ２５＝３．８７）を４重量部とし、重質炭酸カルシウム（ファイマテック社製、ＦＭＴ－ＯＰ、Ｄ７５／Ｄ２５＝３．０）を１６重量部配合した以外は、実施例１と同様にして塗工白板紙ｂを製造した。得られた塗工白板紙ｂの坪量は３１４ｇ／ｍ２、紙厚は３７５μｍであった。
[Comparative Example 2]
Coated white paperboard b was produced in the same manner as in Example 1, except that the amount of heavy calcium carbonate (Imerys, Carbital 97, D75/D25 = 3.87) in the "topcoat pigment coating solution 1" was 4 parts by weight, and 16 parts by weight of heavy calcium carbonate (Fimatec, FMT-OP, D75/D25 = 3.0) was added. The basis weight of the obtained coated white paperboard b was 314 g/m 2 , and the paper thickness was 375 μm.
＜顔料塗工層割れ評価方法＞
上記実施例１～６と比較例１、２において製造した塗工白板紙１～６およびａ、ｂの顔料塗工層上に、枚葉印刷機で藍１００％のベタ印刷をした後、印刷面にラボ用クリーサーで罫線処理を施した。その後、罫線部を折り曲げて、折り曲げ箇所の顔料塗工層割れを以下の評価基準により、目視で評価した。なお、評価結果の「◎」と「〇」のみを実用性がある塗工白板紙と判断した。評価結果を下記表１に示す。
［評価基準］
◎：顔料塗工層割れが見られない
○：顔料塗工層割れがほとんど見られない
△：顔料塗工層割れがやや見られる
×：顕著な顔料塗工層割れが認められる
<Method for evaluating cracks in pigment coating layer>
The pigment coating layers of the coated white paperboards 1 to 6 and a, b produced in Examples 1 to 6 and Comparative Examples 1 and 2 above were printed with 100% indigo solid ink using a sheet-fed printing press, and the printed surface was then creasing processed using a laboratory creaser. The creasing was then folded and the pigment coating layer cracks at the folded area were visually evaluated according to the following evaluation criteria. Only the evaluation results of "◎" and "◯" were judged to be practical coated white paperboards. The evaluation results are shown in Table 1 below.
[Evaluation Criteria]
◎: No cracks in the pigment coating layer are observed. ○: Almost no cracks in the pigment coating layer are observed. △: Some cracks in the pigment coating layer are observed. ×: Significant cracks in the pigment coating layer are observed.
本発明の塗工白板紙は、２層以上の顔料塗工層のいずれもが、粒度分布がある程度広い重質炭酸カルシウムを含有しているため、顔料塗工層中の空隙を抑制し、密度の高い強固な顔料塗工層となるため、ギフト品などの包装箱の使用に好適で、顔料塗工層割れに強く有用である。
The coated white paperboard of the present invention has two or more pigment coating layers, each of which contains heavy calcium carbonate with a relatively wide particle size distribution, which suppresses voids in the pigment coating layer and results in a dense, strong pigment coating layer, making it suitable for use in packaging boxes for gifts, etc., and useful as it is resistant to cracking of the pigment coating layer.
Claims (13)
前記顔料塗工層のいずれもが、顔料として粒度分布曲線の７５累積重量％の粒子径（Ｄ７５）と２５累積重量％の粒子径（Ｄ２５）との比（Ｄ７５／Ｄ２５）が３．３以上４．０以下の重質炭酸カルシウムを含有し、
最外となる上塗り顔料塗工層における前記重質炭酸カルシウムの含有割合は、前記上塗り顔料塗工層に含まれる全顔料の５重量％を超え、３０重量％以下であり、
前記上塗り顔料塗工層より基紙に近い下塗り顔料塗工層における前記重質炭酸カルシウムの含有割合は、前記下塗り顔料塗工層に含まれる全顔料の６０重量％以上であることを特徴とする塗工白板紙。 A coated white paperboard having two or more pigment coating layers on the surface of a base paper (excluding base paper made only of recycled paper pulp) ,
each of the pigment coating layers contains ground calcium carbonate as a pigment, the ratio (D75/D25) of the particle size distribution curve of the 75th cumulative weight % particle size (D75) to the 25th cumulative weight % particle size (D25) being 3.3 or more and 4.0 or less;
the content of the ground calcium carbonate in the outermost topcoat pigment coating layer is more than 5% by weight and not more than 30% by weight of the total pigment contained in the topcoat pigment coating layer;
A coated white paperboard, characterized in that the content of said ground calcium carbonate in the undercoat pigment coating layer, which is closer to the base paper than said topcoat pigment coating layer, is 60% by weight or more of the total pigment contained in said undercoat pigment coating layer .
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| JP3222221B2 (en) * | 1992-11-09 | 2001-10-22 | 三菱製紙株式会社 | Pigment coated paper for printing and method for producing the same |
| JP3552007B2 (en) * | 1996-11-29 | 2004-08-11 | 王子製紙株式会社 | Coated paper for web offset printing |
| WO2012133092A1 (en) | 2011-03-30 | 2012-10-04 | 日本製紙株式会社 | Coated white board and manufacturing method thereof |
| JP2014208940A (en) | 2013-03-29 | 2014-11-06 | 日本製紙株式会社 | Coated white paperboard and method for producing the same |
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| JP2002363887A (en) | 2001-06-04 | 2002-12-18 | Oji Paper Co Ltd | Offset and gravure printing |
| JP2003166199A (en) | 2001-11-28 | 2003-06-13 | San Nopco Ltd | Surface-reforming composition for manufacturing paper- coating agent and method of producing the same |
| JP2012062580A (en) | 2010-09-14 | 2012-03-29 | Oji Paper Co Ltd | Coated white paperboard |
| JP2015074858A (en) | 2013-10-11 | 2015-04-20 | 王子ホールディングス株式会社 | Coated white paperboard |
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| JP2019056193A (en) | 2017-09-22 | 2019-04-11 | 北越コーポレーション株式会社 | Coating white paperboard for laser marking and method for producing the same |
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