Moisture-proof paper and method for manufacturing moisture-proof paper

Abstract

To provide moisture-proof paper having a paper layer provided with a polyethylene resin layer, wherein the moisture-proof paper achieves improved moisture proofness without increasing the thickness of the polyethylene resin layer.SOLUTION: The inventive moisture-proof paper has a paper layer provided with, on one side of it, a polyethylene resin layer; or the moisture-proof paper has a paper layer (A) and a paper layer (B) provided with, between them, a polyethylene resin layer. The polyethylene resin layer has, from the paper layer side, at least three layers of: a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to moisture-proof paper having a polyethylene resin layer with excellent moisture-proof properties, and a method for producing the same. [Background technology]

[0002] Moisture-proof paper, which is made by laminating a moisture-proof polyethylene resin layer onto paper, is used as a packaging material for, for example, foods that should not absorb moisture, powdered detergent, etc. Conventionally, moisture-proof paper having a laminated structure of a resin layer made of low-density to medium-density polyethylene resin and paper has been used, but when high moisture-proof properties are required, it has been proposed to use high-density polyethylene resin as the resin layer (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 3-13360 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, in consideration of the global environment, the use of moisture-proof paper has been considered as an alternative to plastic film or plastic packaging. For example, moisture-proof paper is expected to be used in a variety of bags and boxes for detergents, confectioneries, dried foods, tableware, and other products. Therefore, further improving the moisture-proof properties of moisture-proof paper has become an issue. Patent Document 1 improves moisture-proof properties by switching from low-density polyethylene resin to high-density polyethylene resin, but further improvement is necessary. Increasing the thickness of the polyethylene resin layer improves moisture-proof properties, but this reduces processability and impairs the texture of the moisture-proof paper. The issue of the present invention is to improve moisture-proof properties without increasing the thickness of the polyethylene resin layer. [Means for solving the problem]

[0005] As described in Patent Document 1, it is known that using a high-density polyethylene resin for the polyethylene layer improves moisture resistance. However, it has been difficult to further improve moisture resistance without changing the thickness of the polyethylene resin layer. As a result of intensive research into the polyethylene resin layer to solve the above-mentioned problem, the present inventors discovered that moisture resistance can be further improved by laminating a high-density polyethylene resin and a low-density polyethylene resin, which have different densities, and arrived at the present invention. Specifically, the present invention is as follows.

[0006] (1) Moisture-proof paper with a polyethylene resin layer on one side of the paper layer, The moisture-proof paper has at least three polyethylene resin layers, from the paper layer side, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c). (2) A moisture-proof paper having a polyethylene resin layer between paper layers (A) and (B), The moisture-proof paper has at least three polyethylene resin layers, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c) from the paper layer (A) side. (3) The moisture-proof paper according to (1) or (2), wherein the polyethylene resin layer is a layer obtained by coextrusion lamination of at least three layers: a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c). (4) The moisture-proof paper according to any one of (1) to (3), wherein the polyethylene resin layer has a thickness of 20 to 40 μm. (5) The moisture-proof paper according to any one of (1) to (4), wherein the thickness of the low-density polyethylene resin layer is 20% or more and 40% or less of the total thickness of the polyethylene resin layer. (6) The moisture-proof paper according to any one of (1) to (5), wherein the polyethylene resin layer contains a polyethylene resin derived from plants. (7) Moisture permeability measured based on the cup method B specified in JIS Z-0208 is 13 g / m 2 The moisture-proof paper according to any one of (1) to (6), which lasts for 24 hours or less. (8) A method for producing moisture-proof paper in which at least three layers of polyethylene resin layers, namely a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c), are co-extrusion laminated onto one side of a paper layer from the paper layer side. (9) A method for manufacturing moisture-proof paper in which at least three layers of polyethylene resin layers, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c), are co-extrusion laminated between the paper layer (A) and the paper layer (B) from the paper layer (A) side to join the paper layer (A) and the paper layer (B). [Effects of the Invention]

[0007] According to the present invention, it is possible to provide moisture-proof paper that has excellent moisture-proof properties and can be used for a variety of purposes. DETAILED DESCRIPTION OF THE INVENTION

[0008] <Polyethylene resin layer> The present invention is a moisture-proof paper having a polyethylene resin layer provided on one side of a paper layer or between paper layers (A) and (B). The polyethylene resin layer has at least three layers, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c) from the paper layer side or the paper layer (A) side, and these layers are laminated by coextrusion lamination.

[0009] The density of polyethylene resin is 0.942 g / cm 3 High density polyethylene resin and 0.942g / cm 3 They can be broadly classified into low-density polyethylene resins and low-density polyethylene resins. It is known that the use of high-density polyethylene resin in the polyethylene resin layer improves moisture resistance. It has been difficult to further improve moisture resistance without changing the thickness of the polyethylene resin layer, but by incorporating a low-density polyethylene resin layer with a different density within the high-density polyethylene resin layer, moisture resistance is significantly improved. The reason why a structure with a low-density polyethylene resin layer inside has better moisture resistance than a single high-density polyethylene resin layer is probably because the laminated structure of polyethylene resin layers with different moisture crystallinity provides a moisture-proof effect. Note that a layer made of a mixture of high-density polyethylene resin and low-density polyethylene resin has a lower moisture resistance.

[0010] The resin forming the low-density polyethylene resin layer (b) is a polyethylene having a density of 942 kg / m 3 Polyethylene resins with a density of less than 0.930 g / cm are used. 3 The resin forming the high-density polyethylene resin layers (a) and (c) is preferably a polyethylene resin having a density of 0.942 g / cm or less, since it has excellent moisture resistance. 3 The above polyethylene resin is used. It is preferable that the high-density polyethylene resin layers (a) and (c) are made of the same resin component, since the resins can be prepared simultaneously.

[0011] The polyethylene resin may be either fossil fuel-derived or biomass-derived, as long as it satisfies the density of each layer. In consideration of building a recycling-oriented society, it is preferable to blend biomass-derived polyethylene resin. Biomass-derived polyethylene resin is a resin containing polyethylene obtained by polymerizing a monomer containing ethylene derived from biomass. The method for producing biomass-derived ethylene is not particularly limited, and it can be obtained by a conventionally known method. For example, biomass-derived fermented ethanol can be obtained from plant raw materials such as wood, corn, sugarcane, and beet, and ethylene can be obtained from this fermented ethanol. The polyethylene resin layer may contain other components as long as the effects of the present invention are not impaired.

[0012] The polyethylene resin layer must have three or more layers: high-density polyethylene resin layer (a), low-density polyethylene resin layer (b), and high-density polyethylene resin layer (c). For example, a five-layer structure, such as high-density polyethylene resin layer (a), low-density polyethylene resin layer (b), high-density polyethylene resin layer (c), low-density polyethylene resin layer (b), and high-density polyethylene resin layer (c), is also included. Furthermore, it is preferable to laminate the polyethylene resin layer to the paper layer by coextrusion lamination, as this provides excellent adhesion between the paper layer and the high-density polyethylene resin layer and excellent adhesion at the interfaces between the individual polyethylene resin layers.

[0013] The thickness of the polyethylene resin layer is not particularly limited, but is preferably 20 μm or more, more preferably 25 μm or more, to obtain moisture resistance. The thicker the layer, the better the moisture resistance. However, considering the suitability for molding into bags, boxes, etc., the upper limit is preferably 40 μm or less, more preferably 38 μm or less. Among these, it is preferable for the thickness of the low-density polyethylene resin layer to be 20% or more and 40% or less of the total thickness of the polyethylene resin layer, as this provides excellent moisture resistance.

[0014] <Paper layer> Known paper substrates can be used for the paper layer. For example, papers such as unbleached kraft paper, semi-bleached kraft paper, bleached kraft paper, single-gloss kraft paper, fine paper, art paper, coated paper, and paperboard such as white paperboard, colored paperboard, yellow paperboard, and chipboard can be used as appropriate. When paper layer (A) and paper layer (B) are joined with a polyethylene resin layer, paper layer (A) and paper layer (B) may be made of the same paper substrate or different paper substrates. It is advisable to combine paper thicknesses according to the application. In addition, the surface of the paper layer that comes into contact with the polyethylene resin can be corona-treated in advance to enhance the adhesion of the polyethylene resin.

[0015] <Moisture-proof paper> The moisture-proof paper of the present invention has at least three polyethylene resin layers on one side of a paper layer, consisting of, from the paper layer side, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c). There are no particular limitations on the uses, but the paper can be used, for example, as a packaging bag with the polyethylene resin layers on the inside. The high-density polyethylene layer (c), which is furthest from the paper layer, may have a sealant function. Alternatively, a sealant resin layer may be further provided on the surface of the high-density polyethylene layer (c). Having a sealant function makes the moisture-proof paper highly suitable for processing into bags. The moisture-proof paper of the present invention has a polyethylene resin layer consisting of at least three layers, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c), on one side of the paper layer (A), and a paper layer (B). There are no particular limitations on the use of the paper, but the paper can be thick enough to be used as a packaging box, etc. A pigment coating layer may be applied to the side of the paper layer (A) or paper layer (B) that is not in contact with the polyethylene resin layer. A pigment coating layer may also be applied to the side in contact with the polyethylene resin layer. It should be noted that the polyethylene resin layer is what contributes greatly to the moisture-proof properties of the moisture-proof paper of the present invention, and the adoption of the above-mentioned at least three-layer structure provides a remarkable moisture-proof effect.

[0016] <Moisture permeability> The moisture permeability of the moisture-proof paper of the present invention measured according to the cup method B specified in JIS Z-0208 is 13 g / m 2 24 hours or less is preferable, and 12 g / m 2 It is more preferable that it be 24 hours or less. [Example]

[0017] The present invention will be explained in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

[0018] "Preparing ingredients" Paper base material (A) White court ball (Oji Materia, basis weight 450 g / m 2 ) was prepared. Paper base material (B) Unbleached kraft paper (Oji Materia, basis weight 100g / m 2 ) was prepared. High-density polyethylene resin Petroleum-derived high-density polyethylene (product name: LW13D, manufactured by Tosoh Corporation, density: 0.956 g / cm 3 , MFR: 14g / 10min) was prepared. Low-density polyethylene resin Biomass-derived linear low-density polyethylene (product name: SBC818, manufactured by Braskem, biomass content: 95% or more, density: 0.918 g / cm 3 , MFR: 8.3 g / 10 min) was prepared.

[0019] Example 1 The back side of paper substrate (A) (the side with the least amount of pigment coating) was bonded to paper substrate (B) by coextrusion lamination of three polyethylene resin layers: high-density polyethylene resin, low-density polyethylene resin, and high-density polyethylene resin. The polyethylene resin layers were high-density polyethylene resin (11 μm), low-density polyethylene resin (6.5 μm), and high-density polyethylene resin (11 μm). The surface of the paper layer that would be bonded to the polyethylene resin layer was previously subjected to corona treatment.

[0020] Comparative Example 1 The back side (the side with the least amount of pigment coating) of the paper substrate (A) was bonded to the paper substrate (B) by extrusion lamination with a high-density polyethylene resin as a polyethylene resin layer to obtain moisture-proof paper. The polyethylene resin layer was 28.5 μm thick. In addition, the surface of the paper layer that would be bonded to the polyethylene resin layer was previously subjected to corona treatment.

[0021] Comparative Example 2 The back side of paper substrate (A) (the side with the least amount of pigment coating) was extrusion laminated to paper substrate (B) using a polyethylene resin layer made of a mixed resin of 80% high-density polyethylene resin and 20% low-density polyethylene resin to obtain moisture-proof paper. The polyethylene resin layer was 28.5 μm thick. In addition, the surface of the paper layer that would be bonded to the polyethylene resin layer was previously subjected to corona treatment.

[0022] The moisture permeability of the obtained moisture-proof paper was measured by the following measurement method, and the results are shown in Table 1. <Measurement method> Moisture permeability: Measured according to JIS Z-0208 (cup method) B method at 40°C and 90% (RH) with the paper substrate (B) facing outward. The smaller the value, the better the moisture resistance.

[0023] [Table 1]

[0024] The moisture-proof paper of Example 1, in which the polyethylene resin layer was composed of a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c), exhibited excellent moisture-proof properties, whereas Comparative Example 1, which had only a high-density polyethylene resin layer, and Comparative Example 2, in which high-density polyethylene resin was mixed with low-density polyethylene resin, were moisture-proof papers of the same thickness as Example 1 but had inferior moisture-proof properties. Note that in the above examples, the polyethylene resin layer was configured with paper layers on both sides, but the polyethylene resin layer contributed greatly to the moisture-proof properties, so the same effect was achieved even if the paper layer was on only one side.

Claims

1. Moisture-proof paper (excluding those for liquid paper containers) with a polyethylene resin layer formed by extrusion lamination on one side of the paper layer, The moisture-proof paper is a layer in which the polyethylene resin layer is a layer in which at least three layers, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c), are laminated by co-extrusion lamination from the paper layer side (however, this does not include the case where a nylon layer is present between the paper layer and the polyethylene resin layer).

2. 2. The moisture-proof paper according to claim 1, wherein the polyethylene resin layer has a thickness of 20 to 40 μm.

3. 3. The moisture-proof paper according to claim 1, wherein the thickness of the low-density polyethylene resin layer is 20% or more and 40% or less of the total thickness of the polyethylene resin layer.

4. The moisture-proof paper according to any one of claims 1 to 3, wherein the polyethylene resin layer contains a plant-derived polyethylene resin.

5. The moisture permeability measured based on the cup method B specified in JIS Z-0208 is 13 g / m ２ The moisture-proof paper according to any one of claims 1 to 4, wherein the durability is 24 hours or less.

6. A method for manufacturing moisture-proof paper (excluding those for liquid paper containers) in which at least three layers of polyethylene resin layers, namely, a high-density polyethylene resin layer (a), a low-density polyethylene resin layer (b), and a high-density polyethylene resin layer (c), are co-extrusion laminated onto one side of a paper layer from the paper layer side (excluding cases in which a nylon layer is present between the paper layer and the polyethylene resin layer).

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