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JP-7857106-B2 - Waterproof paper and method for manufacturing the same

JP7857106B2JP 7857106 B2JP7857106 B2JP 7857106B2JP-7857106-B2

Inventors

  • 川▲崎▼ 賢太郎
  • 川真田 友紀
  • 松野 祐也

Assignees

  • 日本製紙株式会社

Dates

Publication Date
20260512
Application Date
20220131

Claims (8)

  1. (a) Paper substrate and (b) A primer layer provided on at least one side of a paper substrate, comprising a synthetic resin having a glass transition temperature of 65 to 260°C, (c) A waterproof layer containing styrene-acrylic resin and wax, which is provided as the outermost layer on top of the undercoat layer, A waterproof paper having a 30-minute Cobb water absorption of 7 g/m² or less , The waterproof paper described above, wherein the water repellency at the stage when the undercoat layer is applied, before the waterproof layer is applied, is R7 or less when measured by the method specified in Paper Pulp Test Method No. 68, and the waterproof layer does not contain pigment .
  2. The waterproof paper according to claim 1, wherein the undercoat layer does not contain wax, the coated surface with the waterproof layer has a Wanggan smoothness of 15 seconds or more, and the coated surface with the waterproof layer has a gloss .
  3. The waterproof paper according to claim 1 or 2, wherein the synthetic resin used in the undercoat layer comprises polyvinyl alcohol and/or a styrene-acrylic resin.
  4. The waterproof paper according to any one of claims 1 to 3, wherein the synthetic resin used in the undercoat layer includes a styrene-acrylic resin.
  5. The waterproof paper according to any one of claims 1 to 4, wherein the water repellency at the stage when the undercoat layer is applied, before the waterproof layer is applied, is R3 or less.
  6. The waterproof paper according to any one of claims 1 to 5 , wherein the paper base material is multi-layered cardboard.
  7. A method for manufacturing waterproof paper according to any one of claims 1 to 6, The process involves applying a primer layer containing a synthetic resin with a glass transition temperature of 65 to 260°C to at least one side of a paper substrate so that the water repellency, as specified in Paper Pulp Test Method No. 68, is R7 or less, and A step of applying a waterproof layer containing styrene-acrylic resin and wax on top of the undercoat layer, The above method, including.
  8. The method according to claim 7, further comprising the step of drying the coating layer under conditions that the temperature of the coating layer is 60°C or higher and less than 120°C.

Description

This invention relates to waterproof paper and a method for manufacturing the same. Traditionally, various forms of paper-based containers and packaging materials have been used to package a wide range of goods. Generally, because paper containers and packaging materials use paper as their base material, they are extremely permeable to water vapor, which can lead to a decrease in strength due to moisture generated from the packaged goods. Furthermore, some goods being packaged are highly sensitive to water vapor entering from the outside. Additionally, when transporting chilled products, such as those containing ice, paper containers and packaging materials must be waterproof. For this reason, methods have been proposed for forming a wax layer by coating the surface of a paper substrate with a water-repellent wax composition, and for forming a resin coating by laminating polyethylene film, polypropylene film, etc. For example, Patent Document 1 describes moisture-proof paper in which a mixture of a wax emulsion and a water-insoluble synthetic resin emulsion, along with a surfactant, is applied to at least one side of the paper, and then heat-treated to form a surfactant layer on the outermost layer. Patent Document 2 describes a moisture-proof liner having at least two coating layers on at least one side of the base paper, wherein the outermost coating layer contains microcapsules encapsulating wax, the coating amount is 0.5 g/ m² to 2.5 g/ m² in terms of solid content, and the coating layer located between this outermost coating layer and the base paper contains an acrylic copolymer and/or a styrene copolymer. Furthermore, Patent Document 3 proposes producing paper with a high level of moisture resistance and waterproofing by drying the waterproof coating layer under specific drying conditions. Japanese Patent Application Publication No. 10-266096Japanese Patent Publication No. 2011-162899Japanese Patent Publication No. 2020-165039 This figure shows the carrier used for evaluating waterproofing (assembly diagram).This figure shows the carrier used for evaluating waterproofing (unfolded view).This figure shows the carrier used for evaluating waterproofing (folded diagram). This invention relates to waterproof paper. In this invention, waterproof paper means paper that does not absorb water even when exposed to water for a long time. Specifically, waterproof paper refers to paper whose Cobb water absorption rate, as described later, is 40 g/ m² or less after 30 minutes. In a preferred embodiment, the waterproof paper according to the present invention prevents water from seeping out of a paper container and leaves it for a week, and the container does not deform, or only slight deformation is observed, maintaining the container's shape. In a more preferred embodiment, the waterproof paper according to the present invention prevents water from seeping out of a paper container and leaves it for three weeks, and the container does not deform, or only slight deformation is observed, maintaining the container's shape. There are no particular restrictions on the uses of the waterproof paper according to the present invention. For example, it can be used as a corrugated cardboard box or individual packaging box, and can be used to contain food products such as fresh fish and vegetables, or to contain hygroscopic substances such as detergents. The basis weight of the waterproof paper according to the present invention is not particularly limited, but can be, for example, 30 to 800 g/ m² . When the paper substrate is single-layer paper, the basis weight of the waterproof paper can be, for example, 30 to 350 g/ m² or 50 to 300 g/ m² . Furthermore, when the paper substrate is multilayer paperboard having two or more paper layers, the basis weight of the waterproof paper can be 75 to 800 g/ m² , 100 to 700 g/ m² , or even 200 to 600 g/ m² . In a preferred embodiment, the waterproof paper of the present invention has a 30-minute Cobb water absorption of 40 g/ m² or less on its surface, more preferably 25 g/ m² or less, and may be 15 g/ m² or less or 7 g/ m² or less. In the present invention, the Cobb water absorption is measured in accordance with the Cobb method specified in JIS P 8140, by contacting 100 ml of distilled water with the coating layer and measuring the weight of water absorbed per unit area after a specified time. The lower the Cobb water absorption even under conditions of extended measurement time, the lower the water absorption of the coating layer. The waterproof paper of the present invention also has excellent moisture resistance, and in a preferred embodiment, the moisture permeability is 100 g/ m² ·24h or less, more preferably 75 g/ m² ·24h or less, and even more preferably 50 g/ m² ·24h or less. Here, the moisture permeability of the paper can be measured from the coated layer side of the waterproof paper in accordance with JIS Z 0208, and a smaller value indicates higher moisture resistance. The