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JP-2026075725-A - Coated paper

JP2026075725AJP 2026075725 AJP2026075725 AJP 2026075725AJP-2026075725-A

Abstract

[Problem] To provide coated paper that is less prone to cracking of the coating layer even when subjected to bending load during the bag-making process for flexible packaging. [Solution] A paper substrate with a basis weight of less than 100 g/ m² and a coating layer containing PHBH and EVA on at least one surface, The coating amount (dry mass) of the aforementioned coating layer is 5 g/ m² or more per side. The coating layer contains 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH, The aforementioned EVA is a coated paper having a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%. [Selection Diagram] None

Inventors

  • 増野 由圭莉
  • 堀越 達也
  • 角田 浩佑

Assignees

  • 日本製紙株式会社

Dates

Publication Date
20260511
Application Date
20241023

Claims (4)

  1. A paper substrate with a basis weight of less than 100 g/ m² and a coating layer containing PHBH and EVA on at least one surface, The coating amount (dry mass) of the aforementioned coating layer is 5 g/ m² or more per side. The coating layer contains 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH, Coated paper characterized in that the EVA has a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%.
  2. The coated paper according to claim 1, characterized in that the molar ratio of ethylene to vinyl acetate in the EVA (ethylene:vinyl acetate, total 100) is 5:95 to 35:65.
  3. The coated paper according to claim 1, characterized in that the glass transition temperature (Tg) of the EVA is -25°C or higher and 10°C or lower.
  4. A flexible packaging body having coated paper as described in any one of claims 1 to 3.

Description

This invention relates to coated paper having a coating layer containing PHBH. In recent years, efforts have begun to prevent environmental damage caused by plastic waste, and there is a growing demand to replace single-use plastic products with materials that have a smaller environmental impact. Examples of alternative materials to plastic include biodegradable plastics, wood, and paper. Aliphatic polyesters such as polylactic acid and polycaprolactone are known as biodegradable plastics. However, aliphatic polyesters have the problem that they take a long time to biodegrade at low temperatures, and their decomposition rate in natural environments such as the ocean is slow. Poly(3-hydroxybutyrate) resins are microbially produced thermoplastics with excellent biodegradability under both aerobic and anaerobic conditions, and possess the remarkable property of being rapidly decomposed by microorganisms even in water such as oceans. Furthermore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter also referred to as PHBH), a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, is attracting attention due to its biodegradability and resin properties. Patent Document 1 proposes a coated paper with few coating defects, having a coating layer containing PHBH and an adhesive on at least one surface of a paper substrate, where the solid content mass ratio of PHBH to adhesive in the coating layer is 99.9/0.1 to 60.0/40.0, and it is stated that this can be used as heat-sealable paper, water-resistant paper, oil-resistant paper, etc. Here, a flexible packaging material using heat-sealable paper has been proposed (see Patent Documents 2 and 3, etc.). These flexible packaging materials are used as wrapping sheets and pillow packaging materials. When used as wrapping sheets, the flexible packaging material is used to cover a cardboard box with its glossy side (coated side) facing outwards, and is folded along the edges of the cardboard box. In the case of pillow packaging, when forming vertical pillow packaging bags, horizontal pillow packaging bags, etc., from a long sheet, the coated side is facing inwards and the material is folded in the CD direction via folds along the direction of travel (MD direction) to form a cylindrical shape. Thus, flexible packaging materials require at least folding in order to enclose their contents. While evaluating the suitability of heat-sealable paper having a coating layer made of PHBH as a flexible packaging material, the inventors discovered that the coating layer is weak against bending and prone to cracking at the bent portion of the coating layer. When cracks occur at the bent portion of a flexible packaging material, water adhering to the outer surface of the packaging material can reach the interior through the cracks, and microorganisms such as mold and E. coli, as well as fine particles such as PM2.5 adhering to the outer surface of the flexible packaging material, may penetrate the interior through the cracks. International Publication No. 2021/256381Japanese Patent Publication No. 2023-011579Japanese Patent Publication No. 2023-081594 The coated paper of the present invention has a paper substrate with a basis weight of less than 100 g/ m² and a coating layer containing PHBH and EVA on at least one surface. The coating amount (dry mass) of the coating layer is 5 g/ m² or more per side. The coating layer contains 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH. EVA has a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%. In this specification, tensile strength and elongation are values evaluated according to JIS-K-6251:2017, sections 3.4 and 3.5, respectively. Furthermore, in this specification, "A to B" (where A and B are numerical values or ratios) refers to a numerical range including A and B. The coated paper of the present invention may have a coating layer on one of its outermost surfaces, or it may have coating layers on both outermost surfaces. Furthermore, other layers such as an anchor layer, a water vapor barrier layer, a gas barrier layer, or an ink-receiving layer may be present between the paper substrate and the coating layer. (Paper base material) The paper substrate is a sheet mainly made of pulp, and is obtained by papermaking a pulp containing fillers, various auxiliary agents, etc. Examples of pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood pulp (NUKP), and sulfite pulp; mechanical pulps such as stone-ground pulp and thermomechanical pulp; wood fibers such as deinked pulp and recycled paper pulp; and non-wood fibers obtained from kenaf, bamboo, hemp, etc. One or more of these can be used in appropriate blends. Among these, chemical pulps made from wood fibers and mechanical pulps made from wood fibers are preferred, and more preferably, chemical pulps made from wood fibers, because they are less lik