JP4371826B2 - Water resistant paperboard and manufacturing method thereof - Google Patents

Description

  The present invention relates to a water-resistant paperboard that maintains a water-repellent effect even after being wetted and has excellent dimensional stability and printability, and a method for producing the same.

  Paperboard is thick paper used for paper containers, packaging, building materials, etc., and most of it is consumed as corrugated cardboard. In recent years, since paperboard can be recycled relatively easily, paperboard has come to be used in various fields as a substitute for plastics, wood, etc. in response to a demand for resource saving.

  Paper exhibits the unique properties of paper that are weak against water due to the high affinity of cellulose fibers as a raw material for water, but paperboard is no exception, for example, it has properties such as high hygroscopicity or low water repellency. Yes. When paperboard is used as a substitute for plastic or the like, the following problems arise due to this property.

  Paperboard is manufactured by laminating paper layers by combining multiple paper stocks, but if the degree of moisture absorption differs between each paper layer, especially the front and back layers, the degree of expansion differs depending on the paper layer. Will be warped.

  Conventionally, resins such as formalin-based resins, melamine-based resins, polyamide-epichlorohydrin-based resins have been used to prevent dimensional changes of paper due to moisture absorption. However, the warping of the paperboard cannot be completely prevented only by blending these resins.

  On the other hand, high water repellency is required depending on the use of the paperboard. As a method for imparting water repellency to paperboard, a method of applying a wax to the surface or a method of impregnating with wax is known. However, if an amount of wax that can provide a sufficient water repellent effect is used, there is a problem that the amount of wax is too large to recycle the paperboard.

Japanese Patent Application Laid-Open No. 2000-28156 proposes a corrugated cardboard sheet in which a water repellent agent is applied to both front and back surfaces and a cross section (Patent Document 1). It is described that this corrugated cardboard sheet is recyclable because the amount of wax used is small, and is excellent in water repellency because it can prevent moisture from entering from the cross section in addition to the front and back surfaces. However, once this corrugated cardboard sheet gets wet, water penetrates into the inner surface of the liner and the cardboard and the water repellency of the corrugated cardboard sheet decreases.
JP 2000-281066 A (paragraph numbers (0014) and (0015))

  An object of the present invention is to provide a water-resistant paperboard and a method for producing the water-resistant paperboard that can maintain a water-repellent effect, have excellent dimensional stability and printability, and can be recycled.

  As a result of diligent research, the present inventors have found that a paperboard in which a predetermined amount of a water repellent agent is internally added to at least one of a surface layer and a back layer is excellent in water repellent effect durability, dimensional stability, and printability. It was. Furthermore, the present invention has been completed by finding that this paperboard can be easily recycled because the amount of wax or the like that becomes a problem during recycling can be reduced.

  The present invention for solving the above problems is described below.

  [1] A water-resistant paperboard in which a water-repellent agent is internally added to the surface layer and / or the back layer in an amount of 0.5 to 1.8% by weight with respect to the pulp solid content in a paperboard having an intermediate layer between the surface layer and the back layer.

  [2] The water-resistant paperboard according to [1], wherein the water repellency after immersing in at least one side of water for 5 minutes is R6 or more.

  [3] The water-resistant paperboard according to [1] or [2], wherein a water repellent is applied to the outer surface of the surface layer and / or the back layer.

  [4] The water-resistant paperboard according to any one of [1] to [3], wherein the underwater elongation in a direction perpendicular to the papermaking direction (horizontal direction) is 2% or less.

  [5] The water-resistant paperboard according to any one of [1] to [4], wherein the wax content is 1.5% by mass or less.

  [6] The method for producing water-resistant paperboard according to any one of [1] to [5], wherein a paper is made by adding a water repellent to the surface layer paper and / or the back layer paper.

  The paperboard of the present invention has excellent water repellent effect and printability, and is suitable as a corrugated cardboard case for fresh products. For example, when a cardboard case for seedlings is manufactured using the paperboard of the present invention and seedlings are used, the water repellent effect is maintained even when water spraying is repeated, and the case is not broken. Moreover, since the underwater elongation is low and the dimensional stability is excellent, warpage due to moisture absorption does not occur, which is suitable for a bulletin board or the like. Furthermore, the paperboard of the present invention can be recycled by setting the amount of wax used within a predetermined range. Therefore, the paperboard of the present invention is useful as a substitute for wood such as plastic products and plywood.

  The water-resistant paperboard of the present invention comprises at least three layers, and an intermediate layer is provided between a first surface layer (hereinafter simply referred to as “surface layer”) and a second surface layer (hereinafter simply referred to as “back layer”). The layer constituting the water-resistant paperboard may be three layers having one middle layer between the surface layer and the back layer, but for applications where strength and thickness are required, a total of two to seven middle layers are provided. 4-9 layers are preferred.

  The raw pulp constituting the water-resistant paperboard of the present invention includes corrugated used paper, old paper, used newspaper, used magazine, used colored paper, Kent used paper, coated used paper, high quality used paper, bleached kraft pulp, unbleached Virgin pulp such as kraft pulp and mechanical pulp can be used according to the strength and appearance required of the paperboard.

  The water-resistant paperboard of the present invention only needs to have a water repellent added internally to either the surface layer or the back layer. When only one sheet of water-resistant paperboard is used depending on the application, it is preferable that both the surface layer and the back layer contain a water repellent.

  As water repellents, wax emulsion obtained by emulsifying wax such as paraffin wax and natural wax; synthetic resin such as polyamide resin and polyamine resin; fluororesin such as polytetrafluoroethylene and polychlorotrifluoroethylene; polymethyl Mention may be made of silicone resins such as hydrogen siloxane and polydimethylsiloxane.

  The content of the water-repellent agent internally added to the surface layer or the back layer is 0.5 to 1.8% by mass with respect to the pulp solid content of the surface layer or the back layer, and 0.7 to 1.5% by mass. More preferably. If the content of the water repellent is less than 0.5% by mass, the water repellency of the paperboard becomes insufficient, and if it exceeds 1.8% by mass, the printability of the paperboard decreases.

  As described above, the water-resistant paperboard of the present invention can use wax as a water repellent, but it is preferable to reduce the wax content in the paperboard as much as possible from the viewpoint of recycling. When wax is used as the water repellent, the content of wax in the paperboard is preferably 1.5% by mass or less based on the dry mass.

A water repellent may be applied (externally added) to the outer surface of the surface layer or the back layer of the water-resistant paperboard of the present invention. By applying a water repellent to the surface of the paperboard, the water repellency of the paperboard can be further increased. The water repellent applied to the surface of the paperboard can be the same as the water repellent internally added to the surface layer or the back layer. The coating amount (solid content) of the water repellent is preferably 0.1 to 1 g / m ² .

  The water-resistant paperboard of the present invention preferably contains a wet paper strength agent in order to maintain strength when wet. Examples of the wet paper strength agent include amphoteric polyacrylamide type paper strength agents and polyamide epichlorohydrin type paper strength agents.

  Amphoteric polyacrylamide is a polymer in which a cationic group is introduced into polyacrylamide. For example, a copolymer of acrylamide and a cationic monomer such as acrylamide-vinyl monomer copolymer, acrylamide-dimethylaminoethyl methacrylate copolymer, , Mannich modified polyacrylamide, Hoffmann-degraded polyacrylamide, and the like.

  Examples of the polyamide epichlorohydrin-based paper strengthening agent include polyamidoamine and epichlorohydrin.

  The content of the wet paper strength agent in the water-resistant paperboard of the present invention is preferably 0.1 to 0.8% by mass with respect to the pulp solid content of each paper layer containing the strength agent. If the content of the wet paper strength agent is less than 0.1% by mass, a sufficient paper strength enhancing effect cannot be obtained, and if it exceeds 0.8% by mass, it is difficult to obtain an effect commensurate with the added amount.

  In the water-resistant paperboard of the present invention, the wet paper strength agent may be contained in any one of the surface layer, the middle layer and the back layer, but is preferably contained in at least one of the middle layers. It is more preferable that it is contained in.

  When glyoxal is added together with the paper strength agent, the wet paper strength of the paperboard of the present invention can be further increased. As content of a glioxal, it is preferable to carry out 0.2-1 mass% with respect to pulp solid content.

  The water-resistant paperboard of the present invention may contain a paper strength agent other than the wet paper strength agent and other additives. Examples of other paper strength agents include starches such as starch, oxidized starch, and carboxymethylated starch; plant gums; polyvinyl alcohol; carboxymethylcellulose and the like. Examples of the additive include a sizing agent, a pigment, a fixing agent, an antifoaming agent, and a release agent.

The rice paper weight of the water-resistant paperboard of the present invention is preferably 150 to 450 g / m ² and more preferably 200 to 400 g / m ² on a dry mass basis.

  Although there is no restriction | limiting in particular as thickness of a water-resistant paperboard, It is preferable to set it as 170-650 micrometers, and it is more preferable to set it as 250-600 micrometers.

  The water-resistant paperboard of the present invention has a JAPAN TAPPI No. after at least one side immersed in water for 5 minutes. The water repellency according to 68 is preferably R6 or more. The water repellency can be set to such a range by adjusting the amount of the water repellent contained in the surface layer or the back layer.

  Furthermore, the water-resistant paperboard of the present invention has a JAPAN TAPPI No. in the direction perpendicular to the papermaking direction (transverse direction). It is preferable that the underwater elongation according to No. 27 is 2% or less. The elongation in water can be within the above range by adjusting the content of the water repellent in the surface layer or the back layer.

The water-resistant paperboard of the present invention can be produced using a known multilayer paper machine by the following steps.
(1) If necessary, a water repellent and other components are added to and mixed with the slurry obtained by dispersing pulp in water to produce a stock for the surface layer, middle layer and back layer.
(2) Each paper stock is made on a wire and put together.
(3) Press with a pressure roll to remove moisture.
(4) Dry with a dryer cylinder and if necessary apply a water repellent with a calendar.
(5) Wind up on a reel to obtain water-resistant paperboard.

Examples 1 to 4 and Comparative Examples 1 to 6
A stock containing 20% by weight of softwood bleached kraft pulp (freeness 500 ml CSF) and 80% by weight of hardwood bleached kraft pulp (freeness 400 ml CSF) was prepared for the first layer. Furthermore, the paper for the second to fifth layers was adjusted by disaggregating the used corrugated paper. A water repellent (Daiwa Chemical Co., Ltd., Coat Sizer MN-2L) is added to the first layer or the fifth layer as necessary, and wet paper strength is added to the second to fourth layer materials. An agent (polyamide-epichlorohydrin resin: manufactured by Seiko PMC, WS547) was added. These stocks were supplied to a circular multi-layer paper machine, and a five-layer paperboard was made at a papermaking speed of 130 m / min.

After the paperboard was pressed and dried, a water-repellent agent (Paratex NS-6, manufactured by Seiko PMC Co., Ltd.) dissolved in water was applied only to the surface on the first layer side by a calendar and wound on a reel. Tables 1 and 2 show the contents of the water repellent and the wet paper strength agent and the surface coating amount of the water repellent in each layer of the obtained paperboard. Paperboard basis weight 220 g / m ² both the (basis weight 44 g / m ² in each layer), and a thickness of 265μm.

  The water repellency, elongation in water, interlayer strength, and printability of the paperboard were evaluated by the following methods. The results are shown in Tables 1 and 2.

<Water repellency>
The water repellency of the surface on the first layer side of the paperboard is determined by JAPAN TAPPI No. Measured according to 68 regulations.

<Water repellency after immersion in water>
After immersing the test piece in water at 23 ° C. for 5 minutes, the water repellency of the surface on the first layer side was determined by JAPAN TAPPI No. Measured according to 68 regulations.

<Underwater elongation>
JAPAN TAPPI No. According to 27, the elongation of the paperboard in the direction perpendicular to the papermaking direction was measured.

<Interlayer strength>
JAPAN TAPPI No. It was measured according to the provision of 18-2.

<Printability>
Using a 110-line anilox roll, flexographic ink (FK-99, manufactured by Sakata Inx) was solid-printed on the surface of the first layer side of the paperboard, and the presence or absence of ink bleeding or flipping was evaluated according to the following evaluation criteria.
Evaluation criteria ○: No ink bleeding or repelling.
X: There is ink bleeding and repelling.

* 1) Coating amount per wax solid content * 2) Content relative to pulp solid content in each layer

Claims (6)

In the paperboard having a middle layer between the surface layer and the back layer,
A wet paper strength agent is contained in any one of the surface layer, the middle layer, and the back layer ,
Table layer, water repellent is within 0.7 to 1.8 wt% added with respect to the surface of the pulp solids, further at least a surface layer of the outer surface, water repellent 0.1 to 1 g / m ^{2. A} water-resistant paperboard that is coated and has a water repellency of R6 or more on the outer surface of the surface layer after being immersed in water for 5 minutes. The wet paper strength agent is contained in any one of the surface layer, the middle layer, and the back layer in an amount of 0.1 to 0.8% by mass with respect to the pulp solid content, and stretched in water in the direction perpendicular to the paper making direction (lateral direction). The water-resistant paperboard according to claim 1, wherein the degree is 2% or less. The water-resistant paperboard according to claim 1 or 2, wherein the wax content is 1.5% by mass or less. (1) Using a slurry obtained by dispersing pulp in water, a process for producing a stock for a surface layer, a middle layer and a back layer, wherein the stock is produced in any one of the surface layer, the middle layer and the back layer A process for producing a paper material for the surface layer, the middle layer, and the back layer, wherein a wet paper strength agent is added to the slurry for use, and a water repellent is added to and mixed with the slurry for producing the surface material stock.
(2) A process of making paper for each layer on a wire and making them together,
(3) A step of pressing with a pressure roll to remove moisture,
(4) A step of applying a water repellent to at least the outer surface of the surface layer after drying with a dryer cylinder;
(5) It is manufactured by a process of winding on a reel and obtaining water-resistant paperboard,
In the paperboard having a middle layer between the surface layer and the back layer,
A wet paper strength agent is contained in any one of the surface layer, the middle layer, and the back layer ,
Table layer, water repellent is within 0.7 to 1.8 wt% added with respect to the surface of the pulp solids, further at least a surface layer of the outer surface, water repellent 0.1 to 1 g / m ^{2. A} method for producing a water-resistant paperboard, which is a coated paper-resistant paperboard, wherein the water repellency of the outer surface of the surface layer after being immersed in water for 5 minutes is R6 or more. The wet paper strength agent is contained in any one of the surface layer, the middle layer, and the back layer in an amount of 0.1 to 0.8% by mass with respect to the pulp solid content, and stretched in water in the direction perpendicular to the paper making direction (lateral direction). The method for producing water-resistant paperboard according to claim 4, wherein the degree is 2% or less. The method for producing a water-resistant paperboard according to claim 4 or 5, wherein the wax content is 1.5 mass% or less.